Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34−xFexO6−δ
(BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2
reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar
energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ (BCNFCo),
exhibited an optical absorption edge at ∼800 nm, p-type conduction and a distinct photoresponse
up to 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo
and g-C3N4 (CN) was prepared via a facile solvent-assisted exfoliation/blending approach using
dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by
wrapping on perovskite established an effective heterojunction between the materials for charge
separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased
photoelectrochemical performance. A blend composed of 40 wt% perovskites and CN performed
optimally, whilst achieving a photocurrent density as high as 1.5 mA cm−2 for sunlight-driven
water-splitting with a Faradaic efficiency as high as ∼88%.
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Pawan Kumar
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34-xFexO6-δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6-δ (BCNFCo), exhibited an optical absorption edge at ~ 800 nm, p-type conduction and a distinct photoresponse upto 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskite and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm-2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ~ 88%.
Vapor Deposition of Semiconducting Phosphorus Allotropes into TiO2 Nanotube A...Pawan Kumar
Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward exploiting alternative energy resources such as solar energy. Here, we report the successful low-cost and easily accessible synthesis of hybrid semiconductor@TiO2 nanotube photocatalysts. In order to realize its maximum potential in harvesting photons in the visible-light range, TiO2 nanotubes have been loaded with earth-abundant, low-band-gap fibrous red and black phosphorus (P). Scanning electron microscopy– and scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron microscopy, and UV–vis measurements have been performed, substantiating the deposition of fibrous red and black P on top and inside the cavities of 100-μm-long electrochemically fabricated nanotubes. The nanotubular …
Heterojunctions of halogen-doped carbon nitride nanosheets and BiOI for sunli...Pawan Kumar
A fluorine-doped, chlorine-intercalated carbon nitride (CNF-Cl) photocatalyst has been synthesized for simultaneous improvements in light harvesting capability along with suppression
of charge recombination in bulk g-C3N4. The formation of heterojunctions of these CNF-Cl nanosheets with low bandgap, earth abundant bismuth oxyiodide (BiOI) was achieved, and the
synthesized heterojunctions were tested as active photoanodes in photoelectrochemical water splitting experiments. BiOI/CNF-Cl heterojunctions exhibited extended light harvesting with a
band-edge of 680 nm and generated photocurrent densities approaching 1.3 mA cm−2 under AM1.5 G one sun illumination. Scanning Kelvin probe force microscopy under optical bias
showed a surface potential of 207 mV for the 50% BiOI/CNF-Cl nanocomposite, while pristine CNF-Cl and BiOI had surface photopotential values of 83 mV and 98 mV, respectively, which in turn, provided direct evidence of superior charge separation in the heterojunction blends. Enhanced charge carrier separation and improved light harvesting capability in BiOI/CNF-Cl hybrids were found to be the dominant factors in increased photocurrent, compared to the pristine constituent materials.
Heterojunctions of halogen-doped carbon nitride nanosheets and BiOI for sunli...Pawan Kumar
A fluorine-doped, chlorine-intercalated carbon nitride (CNF-Cl) photocatalyst has been synthesized for simultaneous improvements in light harvesting capability along with suppression of charge recombination in bulk gC 3 N 4. The formation of heterojunctions of these CNF-Cl nanosheets with low bandgap, earth abundant bismuth oxyiodide (BiOI) was achieved, and the synthesized heterojunctions were tested as active photoanodes in photoelectrochemical water splitting experiments. BiOI/CNF-Cl heterojunctions exhibited extended light harvesting with a band-edge of 680 nm and generated photocurrent densities approaching 1.3 mA cm− 2 under AM1. 5 G one sun illumination. Scanning Kelvin probe force microscopy under optical bias showed a surface potential of 207 mV for the 50% BiOI/CNF-Cl nanocomposite, while pristine CNF-Cl and BiOI had surface photopotential values of 83 mV and 98 mV …
Vapor Deposition of Semiconducting Phosphorus Allotropes into TiO2 Nanotube A...Pawan Kumar
Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward
exploiting alternative energy resources such as solar energy. Here, we
report the successful low-cost and easily accessible synthesis of hybrid
semiconductor@TiO2 nanotube photocatalysts. In order to realize its
maximum potential in harvesting photons in the visible-light range, TiO2
nanotubes have been loaded with earth-abundant, low-band-gap fibrous
red and black phosphorus (P). Scanning electron microscopy− and
scanning transmission electron microscopy−energy-dispersive X-ray
spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron microscopy, and UV−vis measurements have been performed,
substantiating the deposition of fibrous red and black P on top and
inside the cavities of 100-μm-long electrochemically fabricated nanotubes. The nanotubular morphology of titania and a vapor-transport technique are utilized to form heterojunctions of P and
TiO2. Compared to pristine anatase 3.2 eV TiO2 nanotubes, the creation of heterojunctions in the hybrid material resulted in
1.5−2.1 eV photoelectrocatalysts. An enhanced photoelectrochemical water-splitting performance under visible light compared
with the individual components resulted for the P@TiO2 hybrids. This feature is due to synergistically improved charge
separation in the heterojunction and more effective visible-light absorption. The electronic band structure and charge-carrier
dynamics are investigated in detail using ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy to elucidate
the charge-separation mechanism. A Fermi-level alignment in P@TiO2 heterojunctions leads to a more reductive flat-band
potential and a deeper valence band compared to pristine P and thus facilitates a better water-splitting performance. Our results
demonstrate effective conversion efficiencies for the nanostructured hybrids, which may enable future applications in
optoelectronic applications such as photodetectors, photovoltaics, photoelectrochemical catalysts, and sensors.
Air- and water-stable halide perovskite nanocrystals protected with nearly-mo...Pawan Kumar
Halide perovskites are exciting candidates for broad-spectrum photocatalysts but have the problem of ambient stability. Protective shells of oxides and polymers around halide perovskite nano- and micro-crystals provide a measure of chemical and photochemical resilience but the photocatalytic performance of perovskites is compromised due to low electron mobility in amorphous oxide or polymer shells and rapid charge carrier recombination on the surface. Herein an in situ surface passivation and stabilization of CsPbBr3 nanocrystals was achieved using monolayered graphenic carbon nitride (CNM). Extensive characterization of carbon nitride protected CsPbBr3 nanocrystals (CNMBr) indicated spherical CsPbBr3 nanoparticles encased in a few nm thick g-C3N4 sheets facilitating better charge separation via percolation/tunneling of charges on conductive 2D nanosheets. The CNMBr core-shell nanocrystals demonstrated enhanced photoelectrochemical water splitting performance and photocurrent reaching up to 1.55 mA cm−2. The CNMBr catalyst was successfully deployed for CO2 photoreduction giving carbon monoxide and methane as the reaction products.
tA highly efficient, recyclable and magnetically separable core-shell structured CuZnO@Fe3O4microspherewrapped with reduced graphene oxide (rGO@CuZnO@Fe3O4) photocatalyst has been developed and usedfor the photoreduction of carbon dioxide with water to produce methanol under visible light irradiation.Owing to the synergistic effect of the components and to the presence of a thin Fe2O3layer on Fe3O4,rGO@CuZnO@Fe3O44 exhibited higher catalytic activity as compared to the other possible combinationssuch as CuZnO@Fe3O42 and GO@CuZnO@Fe3O43 microspheres. The yield of methanol in case of using2 and 3 as photocatalyst was found to be 858 and 1749 mol g−1cat, respectively. However, the yieldwas increased to 2656 mol g−1cat when rGO@CuZnO@Fe3O44 was used as photocatalyst under sim-ilar experimental conditions. This superior photocatalytic activity of 4 was assumed to be due to therestoration of the sp2hybridized aromatic system in rGO, which facilitated the movement of electronsand resulted in better charge separation. The synthesized heterogeneous photocatalyst could readily berecovered by external magnet and successfully reused for six subsequent cycles without significant loss in the product yield.
Effect of morphology on the photoelectrochemical performance of nanostructure...Pawan Kumar
Cu2O is a promising earth-abundant semiconductor photocathode for sunlight-driven water splitting. Characterization results are presented to show how the photocurrent density (Jph), onset potential (Eonset), band edges, carrier density (NA), and interfacial charge transfer resistance (Rct) are affected by the morphology and method used to deposit Cu2O on a copper foil. Mesoscopic and planar morphologies exhibit large differences in the values of NA and Rct. However, these differences are not observed to translate to other photocatalytic properties of Cu2O. Mesoscopic and planar morphologies exhibit similar bandgap (e.g.) and flat band potential (Efb) values of 1.93 ± 0.04 eV and 0.48 ± 0.06 eV respectively. Eonset of 0.48 ± 0.04 eV obtained for these systems is close to the Efb indicating negligible water reduction overpotential. Electrochemically deposited planar Cu2O provides the highest photocurrent density of 5.0 mA cm−2 at 0 V vs reversible hydrogen electrode (RHE) of all the morphologies studied. The photocurrent densities observed in this study are among the highest reported values for bare Cu2O photocathodes.
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Pawan Kumar
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34-xFexO6-δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6-δ (BCNFCo), exhibited an optical absorption edge at ~ 800 nm, p-type conduction and a distinct photoresponse upto 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskite and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm-2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ~ 88%.
Vapor Deposition of Semiconducting Phosphorus Allotropes into TiO2 Nanotube A...Pawan Kumar
Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward exploiting alternative energy resources such as solar energy. Here, we report the successful low-cost and easily accessible synthesis of hybrid semiconductor@TiO2 nanotube photocatalysts. In order to realize its maximum potential in harvesting photons in the visible-light range, TiO2 nanotubes have been loaded with earth-abundant, low-band-gap fibrous red and black phosphorus (P). Scanning electron microscopy– and scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron microscopy, and UV–vis measurements have been performed, substantiating the deposition of fibrous red and black P on top and inside the cavities of 100-μm-long electrochemically fabricated nanotubes. The nanotubular …
Heterojunctions of halogen-doped carbon nitride nanosheets and BiOI for sunli...Pawan Kumar
A fluorine-doped, chlorine-intercalated carbon nitride (CNF-Cl) photocatalyst has been synthesized for simultaneous improvements in light harvesting capability along with suppression
of charge recombination in bulk g-C3N4. The formation of heterojunctions of these CNF-Cl nanosheets with low bandgap, earth abundant bismuth oxyiodide (BiOI) was achieved, and the
synthesized heterojunctions were tested as active photoanodes in photoelectrochemical water splitting experiments. BiOI/CNF-Cl heterojunctions exhibited extended light harvesting with a
band-edge of 680 nm and generated photocurrent densities approaching 1.3 mA cm−2 under AM1.5 G one sun illumination. Scanning Kelvin probe force microscopy under optical bias
showed a surface potential of 207 mV for the 50% BiOI/CNF-Cl nanocomposite, while pristine CNF-Cl and BiOI had surface photopotential values of 83 mV and 98 mV, respectively, which in turn, provided direct evidence of superior charge separation in the heterojunction blends. Enhanced charge carrier separation and improved light harvesting capability in BiOI/CNF-Cl hybrids were found to be the dominant factors in increased photocurrent, compared to the pristine constituent materials.
Heterojunctions of halogen-doped carbon nitride nanosheets and BiOI for sunli...Pawan Kumar
A fluorine-doped, chlorine-intercalated carbon nitride (CNF-Cl) photocatalyst has been synthesized for simultaneous improvements in light harvesting capability along with suppression of charge recombination in bulk gC 3 N 4. The formation of heterojunctions of these CNF-Cl nanosheets with low bandgap, earth abundant bismuth oxyiodide (BiOI) was achieved, and the synthesized heterojunctions were tested as active photoanodes in photoelectrochemical water splitting experiments. BiOI/CNF-Cl heterojunctions exhibited extended light harvesting with a band-edge of 680 nm and generated photocurrent densities approaching 1.3 mA cm− 2 under AM1. 5 G one sun illumination. Scanning Kelvin probe force microscopy under optical bias showed a surface potential of 207 mV for the 50% BiOI/CNF-Cl nanocomposite, while pristine CNF-Cl and BiOI had surface photopotential values of 83 mV and 98 mV …
Vapor Deposition of Semiconducting Phosphorus Allotropes into TiO2 Nanotube A...Pawan Kumar
Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward
exploiting alternative energy resources such as solar energy. Here, we
report the successful low-cost and easily accessible synthesis of hybrid
semiconductor@TiO2 nanotube photocatalysts. In order to realize its
maximum potential in harvesting photons in the visible-light range, TiO2
nanotubes have been loaded with earth-abundant, low-band-gap fibrous
red and black phosphorus (P). Scanning electron microscopy− and
scanning transmission electron microscopy−energy-dispersive X-ray
spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron microscopy, and UV−vis measurements have been performed,
substantiating the deposition of fibrous red and black P on top and
inside the cavities of 100-μm-long electrochemically fabricated nanotubes. The nanotubular morphology of titania and a vapor-transport technique are utilized to form heterojunctions of P and
TiO2. Compared to pristine anatase 3.2 eV TiO2 nanotubes, the creation of heterojunctions in the hybrid material resulted in
1.5−2.1 eV photoelectrocatalysts. An enhanced photoelectrochemical water-splitting performance under visible light compared
with the individual components resulted for the P@TiO2 hybrids. This feature is due to synergistically improved charge
separation in the heterojunction and more effective visible-light absorption. The electronic band structure and charge-carrier
dynamics are investigated in detail using ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy to elucidate
the charge-separation mechanism. A Fermi-level alignment in P@TiO2 heterojunctions leads to a more reductive flat-band
potential and a deeper valence band compared to pristine P and thus facilitates a better water-splitting performance. Our results
demonstrate effective conversion efficiencies for the nanostructured hybrids, which may enable future applications in
optoelectronic applications such as photodetectors, photovoltaics, photoelectrochemical catalysts, and sensors.
Air- and water-stable halide perovskite nanocrystals protected with nearly-mo...Pawan Kumar
Halide perovskites are exciting candidates for broad-spectrum photocatalysts but have the problem of ambient stability. Protective shells of oxides and polymers around halide perovskite nano- and micro-crystals provide a measure of chemical and photochemical resilience but the photocatalytic performance of perovskites is compromised due to low electron mobility in amorphous oxide or polymer shells and rapid charge carrier recombination on the surface. Herein an in situ surface passivation and stabilization of CsPbBr3 nanocrystals was achieved using monolayered graphenic carbon nitride (CNM). Extensive characterization of carbon nitride protected CsPbBr3 nanocrystals (CNMBr) indicated spherical CsPbBr3 nanoparticles encased in a few nm thick g-C3N4 sheets facilitating better charge separation via percolation/tunneling of charges on conductive 2D nanosheets. The CNMBr core-shell nanocrystals demonstrated enhanced photoelectrochemical water splitting performance and photocurrent reaching up to 1.55 mA cm−2. The CNMBr catalyst was successfully deployed for CO2 photoreduction giving carbon monoxide and methane as the reaction products.
tA highly efficient, recyclable and magnetically separable core-shell structured CuZnO@Fe3O4microspherewrapped with reduced graphene oxide (rGO@CuZnO@Fe3O4) photocatalyst has been developed and usedfor the photoreduction of carbon dioxide with water to produce methanol under visible light irradiation.Owing to the synergistic effect of the components and to the presence of a thin Fe2O3layer on Fe3O4,rGO@CuZnO@Fe3O44 exhibited higher catalytic activity as compared to the other possible combinationssuch as CuZnO@Fe3O42 and GO@CuZnO@Fe3O43 microspheres. The yield of methanol in case of using2 and 3 as photocatalyst was found to be 858 and 1749 mol g−1cat, respectively. However, the yieldwas increased to 2656 mol g−1cat when rGO@CuZnO@Fe3O44 was used as photocatalyst under sim-ilar experimental conditions. This superior photocatalytic activity of 4 was assumed to be due to therestoration of the sp2hybridized aromatic system in rGO, which facilitated the movement of electronsand resulted in better charge separation. The synthesized heterogeneous photocatalyst could readily berecovered by external magnet and successfully reused for six subsequent cycles without significant loss in the product yield.
Effect of morphology on the photoelectrochemical performance of nanostructure...Pawan Kumar
Cu2O is a promising earth-abundant semiconductor photocathode for sunlight-driven water splitting. Characterization results are presented to show how the photocurrent density (Jph), onset potential (Eonset), band edges, carrier density (NA), and interfacial charge transfer resistance (Rct) are affected by the morphology and method used to deposit Cu2O on a copper foil. Mesoscopic and planar morphologies exhibit large differences in the values of NA and Rct. However, these differences are not observed to translate to other photocatalytic properties of Cu2O. Mesoscopic and planar morphologies exhibit similar bandgap (e.g.) and flat band potential (Efb) values of 1.93 ± 0.04 eV and 0.48 ± 0.06 eV respectively. Eonset of 0.48 ± 0.04 eV obtained for these systems is close to the Efb indicating negligible water reduction overpotential. Electrochemically deposited planar Cu2O provides the highest photocurrent density of 5.0 mA cm−2 at 0 V vs reversible hydrogen electrode (RHE) of all the morphologies studied. The photocurrent densities observed in this study are among the highest reported values for bare Cu2O photocathodes.
Radial Nano-Heterojunctions Consisting of CdS Nanorods Wrapped by 2D CN:PDI P...Pawan Kumar
Solar energy harvesting using semiconductor photocatalysis offers an enticing solution to two of the biggest societal challenges, energy scarcity and environmental pollution. After decades of effort, no photocatalyst exists which can simultaneously meet the demand for excellent absorption, high quantum efficiency and photochemical resilience/durability. While CdS is an excellent photocatalyst for hydrogen evolution, pollutant degradation and organic synthesis, photocorrosion of CdS leads to the deactivation of the catalyst. Surface passivation of CdS with 2D graphitic carbon nitrides (CN) such as g-C3N4 and C3N5 has been shown to mitigate the photocorrosion problem but the poor oxidizing power of photogenerated holes in CN limits the utility of this approach for photooxidation reactions. We report the synthesis of exfoliated 2D nanosheets of a modified carbon nitride constituted of tris-s-triazine (C6N7) linked pyromellitic dianhydride polydiimide (CN:PDI) with a deep oxidative highest occupied molecular orbital (HOMO) position, which ensures sufficient oxidizing power for photogenerated holes in CN. The heterojunction formed by the wrapping of mono-/few layered CN:PDI on CdS nanorods (CdS/CN:PDI) was determined to be an excellent photocatalyst for oxidation reactions including photoelectrochemical water splitting, dye decolorization and the photocatalytic conversion of benzyl alcohol to benzaldehyde. Extensive structural characterization using HR-TEM, Raman, XPS, etc., confirmed wrapping of few-layered CN:PDI on CdS nanorods. The increased photoactivity in CdS/CN:PDI catalyst was ascribed to facile electron transfer from CdS to CN:PDI in comparison to CdS/g-C3N4, leading to an increased electron density on the surface of the photocatalyst to drive chemical reactions.
Metal-organic hybrid: Photoreduction of CO2 using graphitic carbon nitride su...Pawan Kumar
A novel heteroleptic iridium complex supported on graphitic carbon nitride was synthesized and used for photoreduction of carbon dioxide under visible light irradiation. The methanol yield obtained after 24 h irradiation was 9934 μmol g−1cat (TON 1241 with respect to Ir) by using triethylamine (TEA) as a sacrificial donor, which was significantly higher as compared to the semiconductor carbon nitride 145 μmol g−1cat under identical conditions. The presence of triethylamine was found to be vital for the higher methanol yield. After the reaction, the photocatalyst could easily be recovered and reused for subsequent six runs without significant loss in photo activity.
Metal-organic hybrid: Photoreduction of CO2 using graphitic carbon nitride su...Pawan Kumar
A novel heteroleptic iridium complex supported on graphitic carbon nitride was synthesized and used
for photoreduction of carbon dioxide under visible light irradiation. The methanol yield obtained after
24 h irradiation was 9934 mmol g1cat (TON 1241 with respect to Ir) by using triethylamine (TEA) as a
sacrificial donor, which was significantly higher as compared to the semiconductor carbon nitride
145 mmol g1cat under identical conditions. The presence of triethylamine was found to be vital for the
higher methanol yield. After the reaction, the photocatalyst could easily be recovered and reused for
subsequent six runs without significant loss in photo activity.
Metal-organic hybrid: Photoreduction of CO2 using graphitic carbon nitride su...Pawan Kumar
A novel heteroleptic iridium complex supported on graphitic carbon nitride was synthesized and used
for photoreduction of carbon dioxide under visible light irradiation. The methanol yield obtained after
24 h irradiation was 9934 mmol g1cat (TON 1241 with respect to Ir) by using triethylamine (TEA) as a
sacrificial donor, which was significantly higher as compared to the semiconductor carbon nitride
145 mmol g1cat under identical conditions. The presence of triethylamine was found to be vital for the
higher methanol yield. After the reaction, the photocatalyst could easily be recovered and reused for
subsequent six runs without significant loss in photo activity.
Reduced graphene oxide–CuO nanocomposites for photocatalyticconversion of CO2...Pawan Kumar
Reduced graphene oxide (rGO)–copper oxide nanocomposites are prepared by covalent grafting of CuOnanorods on the rGO skeleton. Chemical and structural features of rGO–CuO nanocomposites are probedby FTIR, XPS, XRD and HRTEM analyses. Photocatalytic potential of rGO–CuO nanocomposites is exploredfor reduction of CO2into the methanol under the visible light irradiation. The breadth of CuO nanorods andthe oxidation state of Cu in the rGO–CuO/Cu2O nanocomposites are systematically varied to investigatetheir photocatalytic activities. The pristine CuO nanorods exhibited very low photocatalytic activity owingto fast recombination of charge carriers and yielded 175 mol g−1methanol, whereas rGO–Cu2O andrGO–CuO exhibited significantly improved photocatalytic activities and yielded five (862 mol g−1) andseven (1228 mol g−1) folds methanol, respectively. The superior photocatalytic activity of CuO in therGO–CuO nanocomposites was attributed to slow recombination of charge carriers and efficient transferof photo-generated electrons through the rGO skeleton. This study further excludes the use of scavengingdonor.
Reduced graphene oxide–CuO nanocomposites for photocatalyticconversion of CO2...Pawan Kumar
tReduced graphene oxide (rGO)–copper oxide nanocomposites are prepared by covalent grafting of CuOnanorods on the rGO skeleton. Chemical and structural features of rGO–CuO nanocomposites are probedby FTIR, XPS, XRD and HRTEM analyses. Photocatalytic potential of rGO–CuO nanocomposites is exploredfor reduction of CO2into the methanol under the visible light irradiation. The breadth of CuO nanorods andthe oxidation state of Cu in the rGO–CuO/Cu2O nanocomposites are systematically varied to investigatetheir photocatalytic activities. The pristine CuO nanorods exhibited very low photocatalytic activity owingto fast recombination of charge carriers and yielded 175 mol g−1methanol, whereas rGO–Cu2O andrGO–CuO exhibited significantly improved photocatalytic activities and yielded five (862 mol g−1) andseven (1228 mol g−1) folds methanol, respectively. The superior photocatalytic activity of CuO in therGO–CuO nanocomposites was attributed to slow recombination of charge carriers and efficient transferof photo-generated electrons through the rGO skeleton. This study further excludes the use of scavengingdonor.
Enhanced charge separation in g-C3N4–BiOI heterostructures for visible light ...Pawan Kumar
Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered
graphitic carbon nitride (g-C3N4) and few layered graphitic carbon nitride sheets (g-C3N4-S) are
synthesized and investigated as an active photoanode material for sunlight driven water splitting. HRTEM and elemental mapping reveals formation of a unique heterostructure between BiOI platelets and
the carbon nitride (g-C3N4 and g-C3N4-S) network that consisted of dendritic BiOI nanoplates
surrounded by g-C3N4 sheets. The presence of BiOI in g-C3N4-S/BiOI and g-C3N4-S/BiOI
nanocomposites extends the visible light absorption profile from 500 nm up to 650 nm. Due to excellent
charge separation in g-C3N4/BiOI and g-C3N4-S/BiOI, evident from quenching of the carbon nitride
photoluminescence (PL) and a decrease in the PL lifetime, a significant increase in photoelectrochemical
performance is observed for both types of g-C3N4–BiOI heterojunctions. In comparison to
heterojunctions of bulk g-C3N4 with BiOI, the nanocomposite consisting of few layered sheets of gC3N4 and BiOI exhibits higher photocurrent density due to lower recombination in few layered sheets. A
synergistic trap passivation and charge separation is found to occur in the g-C3N4-S/BiOI
nanocomposite heterostructure which results in a higher photocurrent and a lower charge transfer
resistance.
C3N5: A Low Bandgap Semiconductor Containing an Azo-Linked Carbon Nitride Fra...Pawan Kumar
Modification of carbon nitride based polymeric 2D materials for tailoring their optical, electronic and chemical properties for various applications has gained significant interest. The present report demonstrates the synthesis of a novel modified carbon nitride framework with a remarkable 3:5 C:N stoichiometry (C3N5) and an electronic bandgap of 1.76 eV, by thermal deammoniation of the melem hydrazine precursor. Characterization revealed that in the C3N5 polymer, two s-heptazine units are bridged together with azo linkage, which constitutes an entirely new and different bonding fashion from g-C3N4 where three heptazine units are linked together with tertiary nitrogen. Extended conjugation due to overlap of azo nitrogens and increased electron density on heptazine nucleus due to the aromatic π network of heptazine units lead to an upward shift of the valence band maximum resulting in bandgap reduction
C3N5: A Low Bandgap Semiconductor Containing an Azo-Linked Carbon Nitride Fra...Pawan Kumar
Modification of carbon nitride based polymeric
2D materials for tailoring their optical, electronic and
chemical properties for various applications has gained
significant interest. The present report demonstrates the
synthesis of a novel modified carbon nitride framework with a
remarkable 3:5 C:N stoichiometry (C3N5) and an electronic
bandgap of 1.76 eV, by thermal deammoniation of the melem
hydrazine precursor. Characterization revealed that in the
C3N5 polymer, two s-heptazine units are bridged together with
azo linkage, which constitutes an entirely new and different
bonding fashion from g-C3N4 where three heptazine units are
linked together with tertiary nitrogen. Extended conjugation
due to overlap of azo nitrogens and increased electron density
on heptazine nucleus due to the aromatic π network of heptazine units lead to an upward shift of the valence band maximum
resulting in bandgap reduction down to 1.76 eV. XRD, He-ion imaging, HR-TEM, EELS, PL, fluorescence lifetime imaging,
Raman, FTIR, TGA, KPFM, XPS, NMR and EPR clearly show that the properties of C3N5 are distinct from pristine carbon
nitride (g-C3N4). When used as an electron transport layer (ETL) in MAPbBr3 based halide perovskite solar cells, C3N5
outperformed g-C3N4, in particular generating an open circuit photovoltage as high as 1.3 V, while C3N5 blended with
MAxFA1−xPb(I0.85Br0.15)3 perovskite active layer achieved a photoconversion efficiency (PCE) up to 16.7%. C3N5 was also
shown to be an effective visible light sensitizer for TiO2 photoanodes in photoelectrochemical water splitting. Because of its
electron-rich character, the C3N5 material displayed instantaneous adsorption of methylene blue from aqueous solution reaching
complete equilibrium within 10 min, which is significantly faster than pristine g-C3N4 and other carbon based materials. C3N5
coupled with plasmonic silver nanocubes promotes plasmon-exciton coinduced surface catalytic reactions reaching completion
at much low laser intensity (1.0 mW) than g-C3N4, which showed sluggish performance even at high laser power (10.0 mW).
The relatively narrow bandgap and 2D structure of C3N5 make it an interesting air-stable and temperature-resistant
semiconductor for optoelectronic applications while its electron-rich character and intrasheet cavity make it an attractive
supramolecular adsorbent for environmental applications.
Nitrogen-Enriched Carbon Nanobubbles and Nanospheres for Applications in Ener...Devika Laishram
Multifunctional carbon nanomaterials have attracted remarkable consideration for use in various energy
conversion and storage devices because of their ultrahigh specific
surface area, unique morphology, and excellent electrochemical
properties. Herein, we report the synthesis of highly uniform and
ordered nitrogen-enriched carbon nanospheres (CS) and nanobubbles (CNB) by a modified Stöber reaction using resorcinol and
formaldehyde in the presence of ethylenediamine as a nitrogen
source. A comparative study of the prepared CS and CNB
nanomaterials is presented here with potential use in a wide variety
of applications involving large surface area and electrical
conductivity. As counter electrode materials in solar cells, CNB and CS showed enhanced photoelectrochemical activity for
catalytically reducing I3
− to I− and improved capacitive behavior with a low charge transfer resistance and remarkable power
conversion efficiency (PCE) of 10.40% with improved Jsc (20.20 mA/cm2
) and Voc (0.73 V). The enhanced performance of the
fabricated photoelectrochemical cell is due to the excellent point contact and good conductivity that offered better charge
transportation of electrons with minimum recombination. The enhanced adsorption upon increasing the pressure without an
apparent saturation level signified the large CO2 adsorption with 2 mmol/g for the CS. Additionally, the rectangular-shaped CV
curve indicated the double-layer capacitive behavior, good electrochemical reversibility, and high-power characteristics, prerequisites
for supercapacitor application. This study probes the practical possibility of nitrogen-enriched carbon nanostructures as a
multifunctional material for prospective applications.
Arrays of TiO2 nanorods embedded with fluorine doped carbon nitride quantum d...Pawan Kumar
Graphenic semiconductors such as carbon nitride are attracting increasing attention as photocatalysts due to their chemical stability, visible light absorption and excellent electronic properties. The photocatalytic activity of nanostructured TiO2 catalysts is constrained by the wide bandgap and concomitant low visible light responsivity of TiO2. In this context we present the formation of new fluorine doped carbon nitride quantum dots (CNFQDs) by solid state reaction and the subsequent examination of their heterojunctions with TiO2 for photoelectrochemical water splitting. Arrays of rutile phase TiO2 nanorods embedded with CNFQDs were synthesized by a simple in situ hydrothermal approach and the resulting nanomaterials were found to exhibit strong visible light absorption. The energetics at the heterojunction were favorable for efficient electron transfer from CNFQDs to TiO2 under visible light irradiation and …
Arrays of TiO2 nanorods embedded with fluorine doped carbon nitride quantum d...Pawan Kumar
Graphenic semiconductors such as carbon nitride are attracting increasing attention as photocatalysts due to their chemical stability, visible light absorption and excellent electronic properties. The photocatalytic activity of nanostructured TiO2 catalysts is constrained by the wide bandgap and concomitant low visible light responsivity of TiO2. In this context we present the formation of new fluorine doped carbon nitride quantum dots (CNFQDs) by solid state reaction and the subsequent examination of their heterojunctions with TiO2 for photoelectrochemical water splitting. Arrays of rutile phase TiO2 nanorods embedded with CNFQDs were synthesized by a simple in situ hydrothermal approach and the resulting nanomaterials were found to exhibit strong visible light absorption. The energetics at the heterojunction were favorable for efficient electron transfer from CNFQDs to TiO2 under visible light irradiation and transfer of holes to the aqueous electrolyte. CNFQD-sensitized TiO2 nanorods exhibited a strong photoelectrochemical response up to 500 nm. Reuse experiments confirmed robustness and long term stability of the sample without exhausting the catalytic performance. The present work demonstrates a new pathway to sensitize TiO2 to visible photons by the in situ formation of embedded heterojunctions with fluorine doped carbon nitride quantum dots
Noble Metal Free, Visible Light Driven Photocatalysis Using TiO2 Nanotube Arr...Pawan Kumar
Bulk g‐C3N4 is an earth‐abundant, easily synthesizable, and exceptionally stable photocatalyst with an electronic bandgap of 2.7 eV. Herein, the concepts of P‐doping and size quantization are combined to synthesize highly fluorescent P‐doped carbon nitride quantum dots (CNPQDs) with a bandgap of 2.1 eV. CNPQDs are hosted on anatase‐phase and rutile‐phase TiO2 nanotube array scaffolds, and examined as photoanodes for sunlight‐driven water‐splitting and as photocatalysts for surface catalytic reactions. Square‐shaped rutile phase TiO2 nanotube arrays (STNAs) decorated with CNPQDs (CNPQD‐STNA) generate 2.54 mA cm−2 photocurrent under AM1.5 G simulated sunlight. A champion hydrogen evolution rate of 22 µmol h−1 corresponds to a Faradaic efficiency of 93.2%. In conjunction with Ag nanoparticles (NPs), the CNPQD‐STNA hybrid is also found to be an excellent plexcitonic photocatalyst for the visible light‐driven transformation of 4‐nitrobenzenethiol (4‐NBT) to dimercaptoazobenzene (DMAB), producing reaction completion at a laser power of 1 mW (532 nm) while Ag NP/TNA and Ag NP/STNA photocatalysts cannot complete this transformation even at 10 mW laser power. The results point the way forward for photochemically robust, noble metal free, visible light harvesting photoacatalysts based on nanostructured heterojunctions of graphenic frameworks with TiO2.
Enhanced charge separation in gC 3 N 4–BiOI heterostructures for visible ligh...Pawan Kumar
Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered graphitic carbon nitride (g-C3N4) and few layered graphitic carbon nitride sheets (g-C3N4-S) are synthesized and investigated as an active photoanode material for sunlight driven water splitting. HR-TEM and elemental mapping reveals formation of a unique heterostructure between BiOI platelets and the carbon nitride (g-C3N4 and g-C3N4-S) network that consisted of dendritic BiOI nanoplates surrounded by g-C3N4 sheets. The presence of BiOI in g-C3N4-S/BiOI and g-C3N4-S/BiOI nanocomposites extends the visible light absorption profile from 500 nm up to 650 nm. Due to excellent charge separation in g-C3N4/BiOI and g-C3N4-S/BiOI, evident from quenching of the carbon nitride photoluminescence (PL) and a decrease in the PL lifetime, a significant increase in photoelectrochemical performance is observed …
Enhanced charge separation in g-C3N4–BiOI heterostructures for visible light ...Pawan Kumar
Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered
graphitic carbon nitride (g-C3N4) and few layered graphitic carbon nitride sheets (g-C3N4-S) are
synthesized and investigated as an active photoanode material for sunlight driven water splitting. HRTEM
and elemental mapping reveals formation of a unique heterostructure between BiOI platelets and
the carbon nitride (g-C3N4 and g-C3N4-S) network that consisted of dendritic BiOI nanoplates
surrounded by g-C3N4 sheets. The presence of BiOI in g-C3N4-S/BiOI and g-C3N4-S/BiOI
nanocomposites extends the visible light absorption profile from 500 nm up to 650 nm. Due to excellent
charge separation in g-C3N4/BiOI and g-C3N4-S/BiOI, evident from quenching of the carbon nitride
photoluminescence (PL) and a decrease in the PL lifetime, a significant increase in photoelectrochemical
performance is observed for both types of g-C3N4–BiOI heterojunctions. In comparison to
heterojunctions of bulk g-C3N4 with BiOI, the nanocomposite consisting of few layered sheets of g-
C3N4 and BiOI exhibits higher photocurrent density due to lower recombination in few layered sheets. A
synergistic trap passivation and charge separation is found to occur in the g-C3N4-S/BiOI
nanocomposite heterostructure which results in a higher photocurrent and a lower charge transfer
resistance.
Nickel Decorated on Phosphorous-Doped Carbon Nitride as an Efficient Photocat...Pawan Kumar
Nickel nanoparticle-decorated phosphorous-doped graphitic carbon nitride (Ni@g-PC3N4)
was synthesized and used as an efficient photoactive catalyst for the reduction of various
nitrobenzenes under visible light irradiation. Hydrazine monohydrate was used as the source
of protons and electrons for the intended reaction. The developed photocatalyst was found to be
highly active and afforded excellent product yields under mild experimental conditions. In addition,
the photocatalyst could easily be recovered and reused for several runs without any detectable
leaching during the reaction.
Noble Metal Free, Visible Light Driven Photocatalysis Using TiO2 Nanotube Arr...Pawan Kumar
Bulk g‐C3N4 is an earth‐abundant, easily synthesizable, and exceptionally stable photocatalyst with an electronic bandgap of 2.7 eV. Herein, the concepts of P‐doping and size quantization are combined to synthesize highly fluorescent P‐doped carbon nitride quantum dots (CNPQDs) with a bandgap of 2.1 eV. CNPQDs are hosted on anatase‐phase and rutile‐phase TiO2 nanotube array scaffolds, and examined as photoanodes for sunlight‐driven water‐splitting and as photocatalysts for surface catalytic reactions. Square‐shaped rutile phase TiO2 nanotube arrays (STNAs) decorated with CNPQDs (CNPQD‐STNA) generate 2.54 mA cm−2 photocurrent under AM1.5 G simulated sunlight. A champion hydrogen evolution rate of 22 µmol h−1 corresponds to a Faradaic efficiency of 93.2%. In conjunction with Ag nanoparticles (NPs), the CNPQD‐STNA hybrid is also found to be an excellent plexcitonic photocatalyst …
Heterostructured nanocomposite tin phthalocyanine@mesoporous ceria (SnPc@CeO2...Pawan Kumar
Heterostructured tin phthalocyanine supported to mesoporous ceria was synthesized and used a
photocatalyst for CO2 reduction under visible light. The photoreduction CO2 activities of the
heterostructures were investigated in the presence of triethylamine as sacrificial agent. The developed
photocatalyst exhibited high catalytic activity for photoreduction of CO2 and after 24 hours of visible
light irradiation 2342 mmol g1 cat of methanol (fMeOH ¼ 0.0223 or 2.23%) and 840 mmol g1 cat of CO
(fCO ¼ 0.0026 or 0.26%) were obtained as the major reaction products. The methanol formation rate
(RMeOH) and CO formation rate (RCO) was found to be 97.5 mmol h1 g1 cat and 35.0 mmol h1 g1 cat
respectively. While under the identical experimental conditions mesoporous ceria (meso-CeO2) gave
only 316 mmol g1 cat of methanol (fMeOH ¼ 0.003 or 0.30%) and 126 mmol g1 cat CO (fCO ¼ 0.0004
or 0.04%) with product formation rate RMeOH ¼ 13.2 mmol h1 g1 cat and RCO ¼ 5.3 mmol h1 g1 cat.
Furthermore, the recovered catalyst showed consistent catalytic activity for at least five runs without any
significant loss in product yields
Zinc Oxide–Titania Heterojunction-based Solid Nanospheres as Photoanodes for ...Devika Laishram
Agile nanostructure architectures and smart combinations of
semiconducting metal oxide materials are key features of
high-performing dye-sensitized solar cells (DSSCs). Herein,
we synthesize mesoporous solid nanospheres of ZnO–TiO2
with type-II heterojunction and use these as an efficient photoanode material for excellent photoconversion. These polydisperse aggregates doped with 1%, 5%, and 10% of ZnO
exhibit improved solar cell performance with respect to pristine TiO2 under AM 1.5 G. The 1% ZnO doped TiO2 nanosphere possess high specific surface area (84.23 m2
g
@1
) as
a photoanode and shows high photoconversion efficiency of
about 8.07% with ca. 18% improvement in the photocurrent
density (Jsc) compare to TiO2 nanosphere. The improved
solar cell performance (Dh=40%) of ZnO decorated TiO2
nanospheres is ascribed to type-II heterojunction of ZnO–
TiO2
, that reduces the electron recombination and synergistically enhances the electron mobility and charge collection
capability
More Related Content
Similar to Water-splitting photoelectrodes consisting of heterojunctions of carbon nitride with a p-type low bandgap double perovskite oxide
Radial Nano-Heterojunctions Consisting of CdS Nanorods Wrapped by 2D CN:PDI P...Pawan Kumar
Solar energy harvesting using semiconductor photocatalysis offers an enticing solution to two of the biggest societal challenges, energy scarcity and environmental pollution. After decades of effort, no photocatalyst exists which can simultaneously meet the demand for excellent absorption, high quantum efficiency and photochemical resilience/durability. While CdS is an excellent photocatalyst for hydrogen evolution, pollutant degradation and organic synthesis, photocorrosion of CdS leads to the deactivation of the catalyst. Surface passivation of CdS with 2D graphitic carbon nitrides (CN) such as g-C3N4 and C3N5 has been shown to mitigate the photocorrosion problem but the poor oxidizing power of photogenerated holes in CN limits the utility of this approach for photooxidation reactions. We report the synthesis of exfoliated 2D nanosheets of a modified carbon nitride constituted of tris-s-triazine (C6N7) linked pyromellitic dianhydride polydiimide (CN:PDI) with a deep oxidative highest occupied molecular orbital (HOMO) position, which ensures sufficient oxidizing power for photogenerated holes in CN. The heterojunction formed by the wrapping of mono-/few layered CN:PDI on CdS nanorods (CdS/CN:PDI) was determined to be an excellent photocatalyst for oxidation reactions including photoelectrochemical water splitting, dye decolorization and the photocatalytic conversion of benzyl alcohol to benzaldehyde. Extensive structural characterization using HR-TEM, Raman, XPS, etc., confirmed wrapping of few-layered CN:PDI on CdS nanorods. The increased photoactivity in CdS/CN:PDI catalyst was ascribed to facile electron transfer from CdS to CN:PDI in comparison to CdS/g-C3N4, leading to an increased electron density on the surface of the photocatalyst to drive chemical reactions.
Metal-organic hybrid: Photoreduction of CO2 using graphitic carbon nitride su...Pawan Kumar
A novel heteroleptic iridium complex supported on graphitic carbon nitride was synthesized and used for photoreduction of carbon dioxide under visible light irradiation. The methanol yield obtained after 24 h irradiation was 9934 μmol g−1cat (TON 1241 with respect to Ir) by using triethylamine (TEA) as a sacrificial donor, which was significantly higher as compared to the semiconductor carbon nitride 145 μmol g−1cat under identical conditions. The presence of triethylamine was found to be vital for the higher methanol yield. After the reaction, the photocatalyst could easily be recovered and reused for subsequent six runs without significant loss in photo activity.
Metal-organic hybrid: Photoreduction of CO2 using graphitic carbon nitride su...Pawan Kumar
A novel heteroleptic iridium complex supported on graphitic carbon nitride was synthesized and used
for photoreduction of carbon dioxide under visible light irradiation. The methanol yield obtained after
24 h irradiation was 9934 mmol g1cat (TON 1241 with respect to Ir) by using triethylamine (TEA) as a
sacrificial donor, which was significantly higher as compared to the semiconductor carbon nitride
145 mmol g1cat under identical conditions. The presence of triethylamine was found to be vital for the
higher methanol yield. After the reaction, the photocatalyst could easily be recovered and reused for
subsequent six runs without significant loss in photo activity.
Metal-organic hybrid: Photoreduction of CO2 using graphitic carbon nitride su...Pawan Kumar
A novel heteroleptic iridium complex supported on graphitic carbon nitride was synthesized and used
for photoreduction of carbon dioxide under visible light irradiation. The methanol yield obtained after
24 h irradiation was 9934 mmol g1cat (TON 1241 with respect to Ir) by using triethylamine (TEA) as a
sacrificial donor, which was significantly higher as compared to the semiconductor carbon nitride
145 mmol g1cat under identical conditions. The presence of triethylamine was found to be vital for the
higher methanol yield. After the reaction, the photocatalyst could easily be recovered and reused for
subsequent six runs without significant loss in photo activity.
Reduced graphene oxide–CuO nanocomposites for photocatalyticconversion of CO2...Pawan Kumar
Reduced graphene oxide (rGO)–copper oxide nanocomposites are prepared by covalent grafting of CuOnanorods on the rGO skeleton. Chemical and structural features of rGO–CuO nanocomposites are probedby FTIR, XPS, XRD and HRTEM analyses. Photocatalytic potential of rGO–CuO nanocomposites is exploredfor reduction of CO2into the methanol under the visible light irradiation. The breadth of CuO nanorods andthe oxidation state of Cu in the rGO–CuO/Cu2O nanocomposites are systematically varied to investigatetheir photocatalytic activities. The pristine CuO nanorods exhibited very low photocatalytic activity owingto fast recombination of charge carriers and yielded 175 mol g−1methanol, whereas rGO–Cu2O andrGO–CuO exhibited significantly improved photocatalytic activities and yielded five (862 mol g−1) andseven (1228 mol g−1) folds methanol, respectively. The superior photocatalytic activity of CuO in therGO–CuO nanocomposites was attributed to slow recombination of charge carriers and efficient transferof photo-generated electrons through the rGO skeleton. This study further excludes the use of scavengingdonor.
Reduced graphene oxide–CuO nanocomposites for photocatalyticconversion of CO2...Pawan Kumar
tReduced graphene oxide (rGO)–copper oxide nanocomposites are prepared by covalent grafting of CuOnanorods on the rGO skeleton. Chemical and structural features of rGO–CuO nanocomposites are probedby FTIR, XPS, XRD and HRTEM analyses. Photocatalytic potential of rGO–CuO nanocomposites is exploredfor reduction of CO2into the methanol under the visible light irradiation. The breadth of CuO nanorods andthe oxidation state of Cu in the rGO–CuO/Cu2O nanocomposites are systematically varied to investigatetheir photocatalytic activities. The pristine CuO nanorods exhibited very low photocatalytic activity owingto fast recombination of charge carriers and yielded 175 mol g−1methanol, whereas rGO–Cu2O andrGO–CuO exhibited significantly improved photocatalytic activities and yielded five (862 mol g−1) andseven (1228 mol g−1) folds methanol, respectively. The superior photocatalytic activity of CuO in therGO–CuO nanocomposites was attributed to slow recombination of charge carriers and efficient transferof photo-generated electrons through the rGO skeleton. This study further excludes the use of scavengingdonor.
Enhanced charge separation in g-C3N4–BiOI heterostructures for visible light ...Pawan Kumar
Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered
graphitic carbon nitride (g-C3N4) and few layered graphitic carbon nitride sheets (g-C3N4-S) are
synthesized and investigated as an active photoanode material for sunlight driven water splitting. HRTEM and elemental mapping reveals formation of a unique heterostructure between BiOI platelets and
the carbon nitride (g-C3N4 and g-C3N4-S) network that consisted of dendritic BiOI nanoplates
surrounded by g-C3N4 sheets. The presence of BiOI in g-C3N4-S/BiOI and g-C3N4-S/BiOI
nanocomposites extends the visible light absorption profile from 500 nm up to 650 nm. Due to excellent
charge separation in g-C3N4/BiOI and g-C3N4-S/BiOI, evident from quenching of the carbon nitride
photoluminescence (PL) and a decrease in the PL lifetime, a significant increase in photoelectrochemical
performance is observed for both types of g-C3N4–BiOI heterojunctions. In comparison to
heterojunctions of bulk g-C3N4 with BiOI, the nanocomposite consisting of few layered sheets of gC3N4 and BiOI exhibits higher photocurrent density due to lower recombination in few layered sheets. A
synergistic trap passivation and charge separation is found to occur in the g-C3N4-S/BiOI
nanocomposite heterostructure which results in a higher photocurrent and a lower charge transfer
resistance.
C3N5: A Low Bandgap Semiconductor Containing an Azo-Linked Carbon Nitride Fra...Pawan Kumar
Modification of carbon nitride based polymeric 2D materials for tailoring their optical, electronic and chemical properties for various applications has gained significant interest. The present report demonstrates the synthesis of a novel modified carbon nitride framework with a remarkable 3:5 C:N stoichiometry (C3N5) and an electronic bandgap of 1.76 eV, by thermal deammoniation of the melem hydrazine precursor. Characterization revealed that in the C3N5 polymer, two s-heptazine units are bridged together with azo linkage, which constitutes an entirely new and different bonding fashion from g-C3N4 where three heptazine units are linked together with tertiary nitrogen. Extended conjugation due to overlap of azo nitrogens and increased electron density on heptazine nucleus due to the aromatic π network of heptazine units lead to an upward shift of the valence band maximum resulting in bandgap reduction
C3N5: A Low Bandgap Semiconductor Containing an Azo-Linked Carbon Nitride Fra...Pawan Kumar
Modification of carbon nitride based polymeric
2D materials for tailoring their optical, electronic and
chemical properties for various applications has gained
significant interest. The present report demonstrates the
synthesis of a novel modified carbon nitride framework with a
remarkable 3:5 C:N stoichiometry (C3N5) and an electronic
bandgap of 1.76 eV, by thermal deammoniation of the melem
hydrazine precursor. Characterization revealed that in the
C3N5 polymer, two s-heptazine units are bridged together with
azo linkage, which constitutes an entirely new and different
bonding fashion from g-C3N4 where three heptazine units are
linked together with tertiary nitrogen. Extended conjugation
due to overlap of azo nitrogens and increased electron density
on heptazine nucleus due to the aromatic π network of heptazine units lead to an upward shift of the valence band maximum
resulting in bandgap reduction down to 1.76 eV. XRD, He-ion imaging, HR-TEM, EELS, PL, fluorescence lifetime imaging,
Raman, FTIR, TGA, KPFM, XPS, NMR and EPR clearly show that the properties of C3N5 are distinct from pristine carbon
nitride (g-C3N4). When used as an electron transport layer (ETL) in MAPbBr3 based halide perovskite solar cells, C3N5
outperformed g-C3N4, in particular generating an open circuit photovoltage as high as 1.3 V, while C3N5 blended with
MAxFA1−xPb(I0.85Br0.15)3 perovskite active layer achieved a photoconversion efficiency (PCE) up to 16.7%. C3N5 was also
shown to be an effective visible light sensitizer for TiO2 photoanodes in photoelectrochemical water splitting. Because of its
electron-rich character, the C3N5 material displayed instantaneous adsorption of methylene blue from aqueous solution reaching
complete equilibrium within 10 min, which is significantly faster than pristine g-C3N4 and other carbon based materials. C3N5
coupled with plasmonic silver nanocubes promotes plasmon-exciton coinduced surface catalytic reactions reaching completion
at much low laser intensity (1.0 mW) than g-C3N4, which showed sluggish performance even at high laser power (10.0 mW).
The relatively narrow bandgap and 2D structure of C3N5 make it an interesting air-stable and temperature-resistant
semiconductor for optoelectronic applications while its electron-rich character and intrasheet cavity make it an attractive
supramolecular adsorbent for environmental applications.
Nitrogen-Enriched Carbon Nanobubbles and Nanospheres for Applications in Ener...Devika Laishram
Multifunctional carbon nanomaterials have attracted remarkable consideration for use in various energy
conversion and storage devices because of their ultrahigh specific
surface area, unique morphology, and excellent electrochemical
properties. Herein, we report the synthesis of highly uniform and
ordered nitrogen-enriched carbon nanospheres (CS) and nanobubbles (CNB) by a modified Stöber reaction using resorcinol and
formaldehyde in the presence of ethylenediamine as a nitrogen
source. A comparative study of the prepared CS and CNB
nanomaterials is presented here with potential use in a wide variety
of applications involving large surface area and electrical
conductivity. As counter electrode materials in solar cells, CNB and CS showed enhanced photoelectrochemical activity for
catalytically reducing I3
− to I− and improved capacitive behavior with a low charge transfer resistance and remarkable power
conversion efficiency (PCE) of 10.40% with improved Jsc (20.20 mA/cm2
) and Voc (0.73 V). The enhanced performance of the
fabricated photoelectrochemical cell is due to the excellent point contact and good conductivity that offered better charge
transportation of electrons with minimum recombination. The enhanced adsorption upon increasing the pressure without an
apparent saturation level signified the large CO2 adsorption with 2 mmol/g for the CS. Additionally, the rectangular-shaped CV
curve indicated the double-layer capacitive behavior, good electrochemical reversibility, and high-power characteristics, prerequisites
for supercapacitor application. This study probes the practical possibility of nitrogen-enriched carbon nanostructures as a
multifunctional material for prospective applications.
Arrays of TiO2 nanorods embedded with fluorine doped carbon nitride quantum d...Pawan Kumar
Graphenic semiconductors such as carbon nitride are attracting increasing attention as photocatalysts due to their chemical stability, visible light absorption and excellent electronic properties. The photocatalytic activity of nanostructured TiO2 catalysts is constrained by the wide bandgap and concomitant low visible light responsivity of TiO2. In this context we present the formation of new fluorine doped carbon nitride quantum dots (CNFQDs) by solid state reaction and the subsequent examination of their heterojunctions with TiO2 for photoelectrochemical water splitting. Arrays of rutile phase TiO2 nanorods embedded with CNFQDs were synthesized by a simple in situ hydrothermal approach and the resulting nanomaterials were found to exhibit strong visible light absorption. The energetics at the heterojunction were favorable for efficient electron transfer from CNFQDs to TiO2 under visible light irradiation and …
Arrays of TiO2 nanorods embedded with fluorine doped carbon nitride quantum d...Pawan Kumar
Graphenic semiconductors such as carbon nitride are attracting increasing attention as photocatalysts due to their chemical stability, visible light absorption and excellent electronic properties. The photocatalytic activity of nanostructured TiO2 catalysts is constrained by the wide bandgap and concomitant low visible light responsivity of TiO2. In this context we present the formation of new fluorine doped carbon nitride quantum dots (CNFQDs) by solid state reaction and the subsequent examination of their heterojunctions with TiO2 for photoelectrochemical water splitting. Arrays of rutile phase TiO2 nanorods embedded with CNFQDs were synthesized by a simple in situ hydrothermal approach and the resulting nanomaterials were found to exhibit strong visible light absorption. The energetics at the heterojunction were favorable for efficient electron transfer from CNFQDs to TiO2 under visible light irradiation and transfer of holes to the aqueous electrolyte. CNFQD-sensitized TiO2 nanorods exhibited a strong photoelectrochemical response up to 500 nm. Reuse experiments confirmed robustness and long term stability of the sample without exhausting the catalytic performance. The present work demonstrates a new pathway to sensitize TiO2 to visible photons by the in situ formation of embedded heterojunctions with fluorine doped carbon nitride quantum dots
Noble Metal Free, Visible Light Driven Photocatalysis Using TiO2 Nanotube Arr...Pawan Kumar
Bulk g‐C3N4 is an earth‐abundant, easily synthesizable, and exceptionally stable photocatalyst with an electronic bandgap of 2.7 eV. Herein, the concepts of P‐doping and size quantization are combined to synthesize highly fluorescent P‐doped carbon nitride quantum dots (CNPQDs) with a bandgap of 2.1 eV. CNPQDs are hosted on anatase‐phase and rutile‐phase TiO2 nanotube array scaffolds, and examined as photoanodes for sunlight‐driven water‐splitting and as photocatalysts for surface catalytic reactions. Square‐shaped rutile phase TiO2 nanotube arrays (STNAs) decorated with CNPQDs (CNPQD‐STNA) generate 2.54 mA cm−2 photocurrent under AM1.5 G simulated sunlight. A champion hydrogen evolution rate of 22 µmol h−1 corresponds to a Faradaic efficiency of 93.2%. In conjunction with Ag nanoparticles (NPs), the CNPQD‐STNA hybrid is also found to be an excellent plexcitonic photocatalyst for the visible light‐driven transformation of 4‐nitrobenzenethiol (4‐NBT) to dimercaptoazobenzene (DMAB), producing reaction completion at a laser power of 1 mW (532 nm) while Ag NP/TNA and Ag NP/STNA photocatalysts cannot complete this transformation even at 10 mW laser power. The results point the way forward for photochemically robust, noble metal free, visible light harvesting photoacatalysts based on nanostructured heterojunctions of graphenic frameworks with TiO2.
Enhanced charge separation in gC 3 N 4–BiOI heterostructures for visible ligh...Pawan Kumar
Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered graphitic carbon nitride (g-C3N4) and few layered graphitic carbon nitride sheets (g-C3N4-S) are synthesized and investigated as an active photoanode material for sunlight driven water splitting. HR-TEM and elemental mapping reveals formation of a unique heterostructure between BiOI platelets and the carbon nitride (g-C3N4 and g-C3N4-S) network that consisted of dendritic BiOI nanoplates surrounded by g-C3N4 sheets. The presence of BiOI in g-C3N4-S/BiOI and g-C3N4-S/BiOI nanocomposites extends the visible light absorption profile from 500 nm up to 650 nm. Due to excellent charge separation in g-C3N4/BiOI and g-C3N4-S/BiOI, evident from quenching of the carbon nitride photoluminescence (PL) and a decrease in the PL lifetime, a significant increase in photoelectrochemical performance is observed …
Enhanced charge separation in g-C3N4–BiOI heterostructures for visible light ...Pawan Kumar
Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered
graphitic carbon nitride (g-C3N4) and few layered graphitic carbon nitride sheets (g-C3N4-S) are
synthesized and investigated as an active photoanode material for sunlight driven water splitting. HRTEM
and elemental mapping reveals formation of a unique heterostructure between BiOI platelets and
the carbon nitride (g-C3N4 and g-C3N4-S) network that consisted of dendritic BiOI nanoplates
surrounded by g-C3N4 sheets. The presence of BiOI in g-C3N4-S/BiOI and g-C3N4-S/BiOI
nanocomposites extends the visible light absorption profile from 500 nm up to 650 nm. Due to excellent
charge separation in g-C3N4/BiOI and g-C3N4-S/BiOI, evident from quenching of the carbon nitride
photoluminescence (PL) and a decrease in the PL lifetime, a significant increase in photoelectrochemical
performance is observed for both types of g-C3N4–BiOI heterojunctions. In comparison to
heterojunctions of bulk g-C3N4 with BiOI, the nanocomposite consisting of few layered sheets of g-
C3N4 and BiOI exhibits higher photocurrent density due to lower recombination in few layered sheets. A
synergistic trap passivation and charge separation is found to occur in the g-C3N4-S/BiOI
nanocomposite heterostructure which results in a higher photocurrent and a lower charge transfer
resistance.
Nickel Decorated on Phosphorous-Doped Carbon Nitride as an Efficient Photocat...Pawan Kumar
Nickel nanoparticle-decorated phosphorous-doped graphitic carbon nitride (Ni@g-PC3N4)
was synthesized and used as an efficient photoactive catalyst for the reduction of various
nitrobenzenes under visible light irradiation. Hydrazine monohydrate was used as the source
of protons and electrons for the intended reaction. The developed photocatalyst was found to be
highly active and afforded excellent product yields under mild experimental conditions. In addition,
the photocatalyst could easily be recovered and reused for several runs without any detectable
leaching during the reaction.
Noble Metal Free, Visible Light Driven Photocatalysis Using TiO2 Nanotube Arr...Pawan Kumar
Bulk g‐C3N4 is an earth‐abundant, easily synthesizable, and exceptionally stable photocatalyst with an electronic bandgap of 2.7 eV. Herein, the concepts of P‐doping and size quantization are combined to synthesize highly fluorescent P‐doped carbon nitride quantum dots (CNPQDs) with a bandgap of 2.1 eV. CNPQDs are hosted on anatase‐phase and rutile‐phase TiO2 nanotube array scaffolds, and examined as photoanodes for sunlight‐driven water‐splitting and as photocatalysts for surface catalytic reactions. Square‐shaped rutile phase TiO2 nanotube arrays (STNAs) decorated with CNPQDs (CNPQD‐STNA) generate 2.54 mA cm−2 photocurrent under AM1.5 G simulated sunlight. A champion hydrogen evolution rate of 22 µmol h−1 corresponds to a Faradaic efficiency of 93.2%. In conjunction with Ag nanoparticles (NPs), the CNPQD‐STNA hybrid is also found to be an excellent plexcitonic photocatalyst …
Heterostructured nanocomposite tin phthalocyanine@mesoporous ceria (SnPc@CeO2...Pawan Kumar
Heterostructured tin phthalocyanine supported to mesoporous ceria was synthesized and used a
photocatalyst for CO2 reduction under visible light. The photoreduction CO2 activities of the
heterostructures were investigated in the presence of triethylamine as sacrificial agent. The developed
photocatalyst exhibited high catalytic activity for photoreduction of CO2 and after 24 hours of visible
light irradiation 2342 mmol g1 cat of methanol (fMeOH ¼ 0.0223 or 2.23%) and 840 mmol g1 cat of CO
(fCO ¼ 0.0026 or 0.26%) were obtained as the major reaction products. The methanol formation rate
(RMeOH) and CO formation rate (RCO) was found to be 97.5 mmol h1 g1 cat and 35.0 mmol h1 g1 cat
respectively. While under the identical experimental conditions mesoporous ceria (meso-CeO2) gave
only 316 mmol g1 cat of methanol (fMeOH ¼ 0.003 or 0.30%) and 126 mmol g1 cat CO (fCO ¼ 0.0004
or 0.04%) with product formation rate RMeOH ¼ 13.2 mmol h1 g1 cat and RCO ¼ 5.3 mmol h1 g1 cat.
Furthermore, the recovered catalyst showed consistent catalytic activity for at least five runs without any
significant loss in product yields
Similar to Water-splitting photoelectrodes consisting of heterojunctions of carbon nitride with a p-type low bandgap double perovskite oxide (20)
Zinc Oxide–Titania Heterojunction-based Solid Nanospheres as Photoanodes for ...Devika Laishram
Agile nanostructure architectures and smart combinations of
semiconducting metal oxide materials are key features of
high-performing dye-sensitized solar cells (DSSCs). Herein,
we synthesize mesoporous solid nanospheres of ZnO–TiO2
with type-II heterojunction and use these as an efficient photoanode material for excellent photoconversion. These polydisperse aggregates doped with 1%, 5%, and 10% of ZnO
exhibit improved solar cell performance with respect to pristine TiO2 under AM 1.5 G. The 1% ZnO doped TiO2 nanosphere possess high specific surface area (84.23 m2
g
@1
) as
a photoanode and shows high photoconversion efficiency of
about 8.07% with ca. 18% improvement in the photocurrent
density (Jsc) compare to TiO2 nanosphere. The improved
solar cell performance (Dh=40%) of ZnO decorated TiO2
nanospheres is ascribed to type-II heterojunction of ZnO–
TiO2
, that reduces the electron recombination and synergistically enhances the electron mobility and charge collection
capability
Nickel and cobalt transfigured natural clay: a green catalyst for low-tempera...Devika Laishram
Soot particulates in engine exhausts pose a severe threat to the environment and human health – causing cancer, affecting the heart and lungs and drives metal processes. This study proposes a practical,
real-world application of transition metal modified natural clay as an environmentally benign, low-cost,
green catalyst for soot oxidation. Ni and Co (NC-Clay) incorporated natural clay catalysts were prepared
by a simple wet impregnation method and meticulously characterized by different characterization
techniques. The catalyst exhibited higher H2 absorption at a lower temperature with similar trends as
observed in O2 TPD that indicated a remarkable redox property, which is useful for applications as a
catalyst in soot oxidation. Excellent catalytic activity with a very low T50 of 358 1C was observed and can
be accredited to the improved surface oxygen vacancies and thermal stability by the metal modification
of clay
Recent advances in ultra-low temperature (sub-zero to 100 8C) synthesis, mech...Devika Laishram
The development of titania (TiO2) nanomaterials for next-generation photonic, optoelectronic, and
catalytic applications necessitates a facile and cost-effective synthetic methodology for precisely tuning
the composition, phase, and morphology at nanometer scales. In this review, an attempt has been made
to comprehend the progress of the emerging and rapidly developing synthesis methods evolved for the
low-temperature synthesis of titania with a particular emphasis on sub-zero temperature. Insights and
understandings of how the temperature affects the characteristic surface properties and morphology of
titania, along with a detailed discussion on the material characteristics for various technological device
applications are dealt with various methods of analysis. Furthermore, the temperature-dependent
morphological (0D–3D) and structural changes and their impact on different energy-harvesting and
storage and water remediation applications are elucidated. Thus, this review specifically opens the
understanding of different TiO2 polymorph syntheses and their physiochemical comprehension for
advanced technological device performance enhancements
Engineered ZnO-TiO2 Nanospheres for High Performing Membrane Assimilated Phot...Devika Laishram
This paper is a study of ZnO doped TiO2 in various percentages
ranging from 0% (undoped) up to 10%. The effect of doping
was observed via the change in morphological, optical,
electrical and physical properties of ZnO-TiO2 nanospheres.
Hydrothermally grown nanospheres are used for removing
contaminants photo-catalytically from waste water and also as
photoanodes in dye-sensitized solar cells (DSSCs) with graphene as counter electrode. Of the many approaches that have
been explored for purification of contaminated water, this work
presents designing of an environmental friendly solution, based
on easily available filter paper membrane and incorporating it
with the synthesized catalyst for photodegradation of the
harmful toxic substances. These reusable membranes assist in
the photodegradation process by creating room for better
light-catalyst-dye interaction via large surface sites. The spherically structured heterojunction of ZnO-TiO2 generates excitons
that oxidize methyl orange (MO) and reduce harmful Cr(VI) to
non-toxic Cr(III) with high efficacy. Additionally, the agile
nanostructures were employed as efficient photoanode material by fabricating dye sensitized solar cells with graphene as
counter electrode.
HfO2 nanodots incorporated in TiO2 and its hydrogenation for high performance...Devika Laishram
Black titania (H-TiO2) as a photoanode material has attracted huge attention due to its extremely high
optical absorption in the visible region. Herein, black TiO2 doped with HfO2 shows 45.7% higher photoconversion efficiency than H-TiO2 under identically similar conditions. The incorporation of HfO2
nanodots increased the optical scattering in H-TiO2 only when it underwent hydrogenation along with
TiO2. Hafnia-doped TiO2 (HfO2/TiO2) is synthesized by a combination of simple sol–gel and
hydrothermal method followed by thermal annealing under controlled hydrogen atmosphere. The
hydrogenated H-(TiO2/HfO2) exhibited very high optical absorption but slightly lower than H-TiO2 due
to light scattering by HfO2 nanodots. We observed a sharp decrease in optical band gap of TiO2/HfO2
from 3.2 to 2.4 eV up on hydrogen annealing, which is important in solar applications as demonstrated
by the fabrication of high efficiency dye sensitized solar cells (DSSC)
High-performance dye-sensitized solar cell using dimensionally controlled tit...Devika Laishram
The subject of the current study is a concoct of anatase and rutile mixed phase titania synthesized at 40 C and
10 C. At these sub-zero temperatures, highly crystalline, phase-oriented nanostructured titania were formed.
At 40 C, nanocrystals of TiO2 consist of the anatase phase while nanorods dominated by the rutile phase form
at 10 C. These samples are remarkable photoanode materials with excellent photon scattering ability in dyesensitized solar cells (DSSCs). On performance optimization of DSSCs, a composition of 0.5 wt% TiO2 (prepared
at 40 C) and P25 improved the photon harvesting by providing a large number of sites for interaction, resulting
in a high photocurrent of 18.46 mA cm2 and 8.6% photoconversion efficiency.
Recent Progress in Synthesis of Nano- and Atomic-Sized CatalystsDevika Laishram
Well-defined nano-and atomic-sized heterogeneous catalysts with extremely high
catalytic activities and unique selectivities show promise in addressing the critical
energy- and environment-related challenges of this century. The exceptional
properties of these catalysts, such as their electronic and geometric structures and
the effective interactions between metals and supports, give rise to unprecedented
catalytic efficiency over that of conventional catalysts. The facile prospects for
tuning the active sites of these catalysts pave the way to optimizing their activities,
selectivities, and stabilities, thus offering extensive application possibilities in
significant industry-related catalytic reactions. A prerequisite for synthesizing
nano- and atomic-sized catalyst is to prepare extremely disperse nano- and
subnanoscale atoms on suitable supports. This book chapter summarizes various
synthesis methods employed to synthesize nano- and atomic-scale catalysts.
State of the Art in the Characterization of Nano- and Atomic-Scale CatalystsDevika Laishram
Nanometer and subnanometer particles and films are becoming an essential and
integral part of new technologies and inventions in different areas. Some of the
most common areas include the microelectronic industry, magnetic recordings,
photovoltaic applications, and optical coatings. Because of the ultrasmall size at
atomic levels, the effect of quantum size becomes prominent, and the sensitivity
of size is defined even by a difference of a single atom. Additionally, the effect
is of utmost importance as the single-atom catalysts are far more advantageous
than conventional catalysts as they tend to anchor easily because of their low
coordination. Also, the presence of a single-atom catalyst in reactions creates
efficient charge transfer as it forms a strong interaction with the support.
Furthermore, catalysts in the subnanometer regime exhibit different electronic
states and adsorption capabilities compared to traditional catalysts. Therefore, to
fully appreciate the subnanometer catalysis reactions, it is essential to study the
means of characterizing the prepared subnano catalysts,
Solution Processed Hafnia Nanoaggregates: Influence of Surface Oxygen on Cata...Devika Laishram
Hafnium dioxide (HfO2) nanoaggregates are
synthesized by sol−gel and hydrothermal routes followed by
hydrogen annealing at different time durations. The proposed
study aims to explore the effect of hydrogen annealing time on
the properties of HfO2 and also envisage the catalytic soot
oxidation using HfO2 nanoaggregates. It is observed that
annealing under a hydrogen atmosphere brought about
substantial changes in certain attributes such as chemical and
textural properties with marginal changes in some other
properties like optical activity and band gap. The pristine
HfO2 without hydrogen annealing showed a lower ignition
temperature, whereas hydrogen annealed HfO2 for 2 h showed
the best catalytic performance characterized by the soot
combustion temperature (T50) in contrast to samples prepared at longer duration because of the higher surface adsorbed
oxygen species in its widely distributed pores.
Boosting Photocatalytic Activity Using Carbon Nitride Based 2D/2D van der Waa...Devika Laishram
The surging demand for energy and staggering pollutants in the
environment have geared the scientific community to explore sustainable
pathways that are economically feasible and environmentally compelling. In this
context, harnessing solar energy using semiconductor materials to generate
charge pairs to drive photoredox reactions has been envisioned as a futuristic
approach. Numerous inorganic crystals with promising nanoregime properties
investigated in the past decade have yet to demonstrate practical application due
to limited photon absorption and sluggish charge separation kinetics. Twodimensional semiconductors with tunable optical and electronic properties and
quasi-resistance-free lateral charge transfer mechanisms have shown great
promise in photocatalysis. Polymeric graphitic carbon nitride (g-C3N4) is
among the most promising candidates due to fine-tuned band edges and the
feasibility of optimizing the optical properties via materials genomics.
Constructing a two-dimensional (2D)/2D van der Waals (vdW) heterojunction
by allies of 2D carbon nitride sheets and other 2D semiconductors has demonstrated enhanced charge separation with improved
visible photon absorption, and the performance is not restricted by the lattice matching of constituting materials. With the advent of
new 2D semiconductors over the recent past, the 2D/2D heterojunction assemblies are gaining momentum to design high
performance photocatalysts for numerous applications. This review aims to highlight recent advancements and key understanding in
carbon nitride based 2D/2D heterojunctions and their applications in photocatalysis, including small molecules activation,
conversion, and degradations. We conclude with a forward-looking perspective discussing the key challenges and opportunity areas
Multifunctional materials for clean energy conversionDevika Laishram
With the rapid depletion of fossil fuels, rising environmental concerns,
and population growth, it is inevitable to develop clean energy technologies
to power our future society [1e4]. These energy conversion and storage
technologies are anticipated to be sustainable and also capable of meeting
our long-term energy needs. During the past few years, extensive research
interests have been devoted to the advancement of energy conversion devices, as they play a crucial role in the prosperity and economic growth of
a country. Particularly, the energy conversion technologies such as solar
and fuel cells have proved to be highly reliable and can offer clean and sustainable energy at affordable rate [5e8]. However, the performance potential of these devices, such as output voltage, conversion efficiency, and
stability, are greatly relied on the materials used. The energy conversion process comprises physical and/or chemical reactions at th
Surface fluorination of α-Fe2O3 using selectfluor for enhancement in photoele...Devika Laishram
Fluorinated α-Fe2O3 nanostructures are synthesized via a facile hydrothermal route using Selectfluor™ (F-TEDA)
as a fluorinating as well as growth directing agent. The addition of incrementally increasing amount of F-TEDA
to Fe precursor under hydrothermal conditions resulted in preferential growth of α-Fe2O3 along (110) orientation with respect to (104) direction by ~ 35%, the former being important for enhanced charge transport.
On increasing fluorination, the heirarchical dendritic-type α-Fe2O3 changes to a snow-flake type structure (FTEDA-20%) anisotropically growing along the six directions however, at higher F-TEDA concentrations (≥
30%), loosely held particulate aggregates are seen to be formed. The X-Ray Photoelectron Spectroscopy (XPS)
suggest the maximum fluorinarion of α-Fe2O3 at 1.21 at% in 30% F-TEDA. Further, optical absorption studies
reveal reduction in optical band gap from 2.10 eV in case of pristine to 1.95 eV for fluorinated α-Fe2O3. A
photoanode made by taking 20% fluorinated α-Fe2O3 in a ratio of 10:90 with respect to TiO2 (P-25) showed
improved performance in dye sensitized solar cells with an increase in efficiency by ~16% in comparision to that
of pristine Fe2O3 and TiO2. Furthermore, anode consisting of thin films of fluorinated α-Fe2O3 on FTO also
exhibit enhanced current density on illumination of ~100 W/m2
. The increase in photoelectrochemical activity
seems to be due to the combination of two factors namely preferential growth of α-Fe2O3 along (110) direction
resulting in an improved charge transfer efficiency and reduced recombination losses due to the presence of
fluorine.
On the study of phase and dimensionally controlled titania nanostructures syn...Devika Laishram
The present studies are about surfactant free simple synthesis for titania (TiO2) nanostructures, by which morphology and phase can be tuned through temperature variation. The formation of oval shaped nanocrystals
and nanorods at different temperatures are attributed to the phase transformation between anatase and rutile
by one-step chemical reaction involving titanium tetraisopropoxide and aqueous ethyl alcohol. Categorically,
two different morphologies of TiO2 were observed with respect to variation in temperature with nanorods
formation at −20 °C and −10 °C and oval shape formation at −40 °C and −30 °C with higher surface area.
Crystalline nature and size of nano-TiO2 were determined by transmission electron microscopy (TEM) and
X-ray diffraction (XRD). The energy gap of TiO2 nanoparticles were determined by optical absorption measurement and found to be in the range of ~2.92 to 3.02 eV with an indirect band nature.
Air- and water-stable halide perovskite nanocrystals protected with nearly-m...Devika Laishram
Halide perovskites are exciting candidates for broad-spectrum photocatalysts but have the problem of ambient
stability. Protective shells of oxides and polymers around halide perovskite nano- and micro-crystals provide a
measure of chemical and photochemical resilience but the photocatalytic performance of perovskites is
compromised due to low electron mobility in amorphous oxide or polymer shells and rapid charge carrier
recombination on the surface. Herein an in situ surface passivation and stabilization of CsPbBr3 nanocrystals was
achieved using monolayered graphenic carbon nitride (CNM). Extensive characterization of carbon nitride
protected CsPbBr3 nanocrystals (CNMBr) indicated spherical CsPbBr3 nanoparticles encased in a few nm thick gC3N4 sheets facilitating better charge separation via percolation/tunneling of charges on conductive 2D nanosheets. The CNMBr core-shell nanocrystals demonstrated enhanced photoelectrochemical water splitting performance and photocurrent reaching up to 1.55 mA cm− 2
. The CNMBr catalyst was successfully deployed for CO2
photoreduction giving carbon monoxide and methane as the reaction products.
Heterostructured HfO2/TiO2 spherical nanoparticles for visible photocatalytic...Devika Laishram
Photocatalytic activity of low band gap hydrogenated HfO2 doped TiO2 (H-HfO2/TiO2), HfO2 doped TiO2
(HfO2/TiO2) and TiO2 (pristine) were investigated by photocatalytic degradation of five different industrial dyes. The current study envisages the effect of doping hydrogen and HfO2 up on TiO2 for photocatalytic degradation of different chemically structured dyes. Methylene Blue attains fast degradation
efficiency of 90%, within 10 min of the reaction due to high photocatalytic adsorption and degradation
over the rough TiO2 surface. Effect of pH on dye degradation is observed, leading to disintegration and
mineralization.
The ability to recreate computational results with minimal effort and actionable metrics provides a solid foundation for scientific research and software development. When people can replicate an analysis at the touch of a button using open-source software, open data, and methods to assess and compare proposals, it significantly eases verification of results, engagement with a diverse range of contributors, and progress. However, we have yet to fully achieve this; there are still many sociotechnical frictions.
Inspired by David Donoho's vision, this talk aims to revisit the three crucial pillars of frictionless reproducibility (data sharing, code sharing, and competitive challenges) with the perspective of deep software variability.
Our observation is that multiple layers — hardware, operating systems, third-party libraries, software versions, input data, compile-time options, and parameters — are subject to variability that exacerbates frictions but is also essential for achieving robust, generalizable results and fostering innovation. I will first review the literature, providing evidence of how the complex variability interactions across these layers affect qualitative and quantitative software properties, thereby complicating the reproduction and replication of scientific studies in various fields.
I will then present some software engineering and AI techniques that can support the strategic exploration of variability spaces. These include the use of abstractions and models (e.g., feature models), sampling strategies (e.g., uniform, random), cost-effective measurements (e.g., incremental build of software configurations), and dimensionality reduction methods (e.g., transfer learning, feature selection, software debloating).
I will finally argue that deep variability is both the problem and solution of frictionless reproducibility, calling the software science community to develop new methods and tools to manage variability and foster reproducibility in software systems.
Exposé invité Journées Nationales du GDR GPL 2024
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Salas, V. (2024) "John of St. Thomas (Poinsot) on the Science of Sacred Theol...Studia Poinsotiana
I Introduction
II Subalternation and Theology
III Theology and Dogmatic Declarations
IV The Mixed Principles of Theology
V Virtual Revelation: The Unity of Theology
VI Theology as a Natural Science
VII Theology’s Certitude
VIII Conclusion
Notes
Bibliography
All the contents are fully attributable to the author, Doctor Victor Salas. Should you wish to get this text republished, get in touch with the author or the editorial committee of the Studia Poinsotiana. Insofar as possible, we will be happy to broker your contact.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Comparative structure of adrenal gland in vertebrates
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitride with a p-type low bandgap double perovskite oxide
1. Nanotechnology
PAPER
Water-splitting photoelectrodes consisting of
heterojunctions of carbon nitride with a p-type low
bandgap double perovskite oxide
To cite this article: Pawan Kumar et al 2021 Nanotechnology 32 485407
View the article online for updates and enhancements.
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3. nano-spikes etc), surface area enhancement, light trapping and
heterojunction formation [13]. Unfortunately, none of the sys-
tems can consistently approach desirable photoconversion effi-
ciencies in excess of 10% in conjunction with durability and low
cost. The key impediments to high performance are limited
visible light absorption, charge carrier recombination losses and
high overpotentials for redox reaction steps.
Recently, halide perovskites have gained attention for
solar energy harvesting due to their intense optical absorption
and long carrier diffusion lengths (lower recombination).
Halide perovskites, which constitute a topic of intense sci-
entific and commercial interest for photovoltaic devices,
suffer the problem of severe ambient instability due to air and
moisture. Recently, many efforts have been paid to make
perovskite stable i.e. some halide-based perovskites encap-
sulated/passivated with inorganic, organic and graphenic
materials have been reported to exhibit excellent photo-
catalytic performance in photovoltaics, CO2 reduction, dye
degradation and water splitting [14–21]. However, for long-
term usage, stability still remains a significant consideration.
Further, the usage of toxic lead-based perovskites is highly
undesirable from environmental and health viewpoints.
The family of oxide perovskites (ABO3) has received
significant research attention as highly stable and durable
potential substitutes for halide perovskite. However, the vast
majority of oxide perovskites studied for photocatalytic appli-
cations, such as SrTiO3, CaxTiyO3, CoTiO3, LaMnO3,
LaCoO3, LaNiO3, PbZrO3, NaNbO3, KNbO3, SrNbO3,
NaTaO3, CaSnO3, CaVO3, SrVO3, etc have wide band gaps
exceeding 3.0 eV due to which they harvest a small portion of
the solar spectrum [22]. BiFeO3 has a moderate bandgap of
2.2 eV. There has been far less work on low bandgap oxide
perovskites (Eg<2 eV) for photocatalysis. Members of a
subclass of the oxide perovskite family called double per-
ovskites with a general formula A2B′B″O6 are intriguing can-
didate materials due to their earth abundance, structural, optical
(small direct bandgap), thermal stability and magnetic proper-
ties [23]. Double perovskite materials have just begun to be
explored for photovoltaics, CO2 reforming, fuel cells and
electrocatalysis [22, 24–31]. Barium and niobium-based double
perovskite oxides are found to work as a bifunctional catalyst
for overall water splitting in acidic and basic media [31–34].
Ba2Bi1.4Nb0.6O6 [35, 36], SrNb0.1Co0.7Fe0.2O3–δ perovskite
nanorods (SNCF‐NRs) [37] and layered NdBaMn2O5.5 [38]
showed excellent hydrogen evolution reaction and oxygen
evolution reaction performance under visible light.
Only a handful of reports are available on the use of
double perovskite oxides in photocatalytic/photoelec-
trocatalytic applications due to high polaron binding energies
(which limits the open circuit voltage that can be generated
under solar illumination) and short carrier diffusion length/
low mobility which reduces the recombination lifetime and
fill-factor of photoelectrochemical devices [39]. Substitution
with different metal/nonmetal atoms can significantly influ-
ence the electronic and optoelectronic properties to optimize
photocatalytic performance [40, 41].
Another approach to lower the charge carrier recombi-
nation is to form heterojunctions with other semiconductors
or high mobility materials, for instance, graphenic networks.
Recently, graphitic carbon nitride (g-C3N4, CN), a polymeric
semiconductor composed of tri-s-triazine (heptazine, C6N7)
units linked together with tertiary N atoms forming 2D sheets
structure has shown great promise for various applications
including catalysis (base free oxidation, reduction and cou-
pling reactions etc) and photocatalysis (water splitting, CO2
reduction, photo-organic transformation) due to its remark-
able physical, chemical and optoelectronic properties [42–44].
In contrast with graphene which is a zero bandgap semi-
conductor, the conjugated network of alternative aromatic
carbons and nitrogen gives rise to a bandgap of 2.7 eV (ECB, –
1.1 eV and EVB, +1.6 eV) in g-C3N4 [45]. Additionally,
graphitic carbon nitride can be synthesized with cheap
nitrogenous precursors such as urea, dicyandiamide, mela-
mine and thiourea constituting an additional advantage over
graphene which requires chemical vapor deposition or harsh
chemical synthesis from graphite and therefore difficult to
scale up in synthesis to the industrial scale [46]. Due to the
presence of a finite bandgap and a conjugated network, car-
bon nitride (CN) performs a dual function via assisting in
charge separation by forming a heterojunction and enabling
fast percolation of charge carriers in the CN sheets. The
bandgap of 2.7 eV is associated with blue light absorption and
CN’s band structure can be manipulated to harvest more
visible light through doping (P, F, S etc) [47, 48], chemical
structure modification [49–51] and heterojunction formation
[48, 52–54]. Even though carbon nitride is a promising
photocatalyst, its activity in bulk form is limited due to
intersheet recombination of photogenerated charge carriers in
stacked sheets. On the other hand, the transformation of bulk
CN into one or two atom-thick sheets increases its bandgap
due to the quantum confinement effect restricting its absorp-
tion to the UV region [55–57]. Additionally, the transfor-
mation of CN into monolayer sheets enables intersheets
hydrogen bonding which promotes charge localization and
acts as trap sites, quenching photogenerated charge. Previous
experimental and theoretical studies on graphenic 2D mate-
rials suggest a profound quantum confinement effect, which is
observed only if the number of CN sheets becomes lower than
4. Hence the best way to preserve crystallinity (ordered
stacking) to maintain a low bandgap and lower the intersheets
charge recombination is to keep the numbers of sheets higher
than 4–6 [58–63]. Solvent-assisted exfoliation using a polar
solvent is a facile route to get few-layered carbon nitride
sheets while maintaining crystallinity [64]. Interestingly,
carbon nitride (due to the 2D structure and flexibility of
sheets) can form a heterojunction with most of the semi-
conductor materials via weak van der Waals (vdW) interac-
tion thus removing the constraint of epitaxial lattice matching
in conventional inorganic semiconductor heterojunctions.
Indeed, numerous carbon nitride-based 1D/2D and 2D/2D
van der Waals heterojunctions such as BiOI/CN, MoS2/CN,
LDHs/CN, phosphorene/CN, etc have been synthesized
recently for various applications including photocatalysis
[65–67]. Further, our previous studies demonstrated that
heterojunctions of inorganic semiconductor materials (SnIP as
1D semiconductor [68] and BiOI as layered semiconductor
2
Nanotechnology 32 (2021) 485407 P Kumar et al
4. [69]) with few-layered CN show improved charge
separation. Perovskite oxides and CN-based vdW hetero-
junction has shown great promise due to their excellent
photophysical properties, photocorrosion resistance and better
interfacial charge separation [70, 71]. Inspired by these
observations, we report a nanocomposite of double per-
ovskite, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ (BCNFCo), and
few-layered CN synthesized via a simple solvent assisted
exfoliation accompanied by mild heating. The CN sheets
wrapped around the Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ in the
composite which facilitated better charge separation resulting
in improved performance in photoelectrochemical water
splitting reaching a maximum current density of 1.5 mA cm−2
in 40% BCNFCo/CN composite.
2. Results and discussion
2.1. Structure and composition of BCNFCo-CN hybrids
The condensation polymerization of dicyandiamide at high
temperature (550 °C) forms a tertiary nitrogen-linked tris-s-
triazine network leading to the formation of graphitic car-
bon nitride (CN). Solvent-mediated exfoliation of graphitic
materials is a simple and powerful technique to prepare few-
layered CN sheets. We chose o-dichlorobenzene (ODCB) as
the exfoliating agent given its nearly optimal interfacial
tension (∼37 mJ m−2
) as well as its aromaticity and
resulting π–π stacking interactions with CN sheets [72]. We
further note that ODCB is effective in exfoliating unfunc-
tionalized graphene to yield stable, non-aggregating dis-
persions [73]. Furthermore, binary solvent mixtures
containing glycerol have been shown to stabilize aggregates
and assist in exfoliating graphitic materials [74, 75]. The
Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ (BCNFCo) double per-
ovskite oxide was prepared using a conventional solid-state
method by physically mixing and sintering (1350 °C/24 h)
stoichiometric amount of BaCO3, CaCO3, Nb2O5, Fe2O3,
and Co3O4 [76]. The sonication and stirring of BCNFCo
with CN at 80 °C in o-dichlorobenzene/glycerol facilitated
exfoliation and improved the dispersion of CN affording
BCNFCo/CN nanocomposite (figure 1). The carbon nitride
interacts with BCNFCo via weak van der Waals (vdW)
interaction leading to the formation of CN wrapped
BCNFCo core–shell type structure.
The fine morphological attributes of CN and BCNFCo/CN
samples were investigated with high-resolution transmission
electron microscopy (HR-TEM) (figure 2). The HR-TEM ima-
ges of CN at low magnification show a nanoporous, crumpled
sheets morphology (figure 2(a)). The HR-TEM at high magni-
fication (50 nm scale bar) clearly shows graphene-like carbon
nitride sheets (figure 2(b)). The nanoporous structure of syn-
thesized heptazine-based carbon nitride was clearly visible in the
HR-TEM image of CN samples at a 5 nm scale bar (figure 2(c)).
The FFT of the TEM image in figure 2(c) shows a broad dif-
fraction ring corroborating the amorphous nature of carbon
nitride complying with the reported literature [77]. Additionally,
electron energy loss spectroscopy (EELS) which provides
information on the nature of C and N bonding was performed
on CN samples to examine the C K-edge and N K-edge (figure
S1 (available online at stacks.iop.org/NANO/32/485407/
mmedia)). Two major peaks due to the contribution of C
K-edge and N K-edge loss were observed in the EELS spectrum
of CN. The C K-edge was composed of two peak components
located at 283.4 and 293.8 eV assigned to 1s-π*
and 1s-σ*
electronic transition of sp2
hybridized carbons trigonally coor-
dinated with nitrogens in heptazine motif (figure S1) [78–80].
The intense π*
C K-edge signal demonstrates conjugated π
orbital overlap in the heptazine ring system. Similarly, the two
peak components in the N K-edge’s energy loss located at 393.6
and 401.6 eV, were attributed 1s-π*
and 1s-σ*
electronic trans-
ition of sp2
hybridized nitrogens in heptazine ring and tertiary
bridging N verifying successful synthesis of N-rich carbon
nitride framework (figure S1) [81]. The HR-TEM images of
BCNFCo/CN demonstrate dense BCNFCo wrapped and
sandwiched between carbon nitride sheets in the solid-state
matrix (figure 2(d)). The high magnification image at the 5 nm
scale bar shows the amorphous CN containing crystalline
BCNFCo (figure 2(e)). To confirm that the dense region was
composed of BCNFCo, we performed FFT on the selected area
demonstrating sharp spots indicating crystalline structure
while the less dense region did not display any diffraction
spots suggesting these regions were constituted of amorphous
CN (inset of figure 2(e)). Further, iFFT on the selected
area shows a d-spacing of 0.27 nm ascribed to BCNFCo
(figure 2(f)). Another high magnification HR-TEM image at
5 nm scale bar also shows crystalline BCNFCo surrounded
with a zone of amorphous carbon nitride revealing wrapping of
CN sheets around crystalline BCNFCo (figure 2(g)). The
magnified region of crystalline lattice and iFFT of the image
Figure 1. Synthesis protocol for formation of Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ/g-C3N4 (BCNFCo/CN) nanocomposite.
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Nanotechnology 32 (2021) 485407 P Kumar et al
5. shows lattice fringes with 0.27 nm interplanar d-spacing
assigned to Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ double perovskite
(figure 2(h)).
To discern the presence of CN around the BCNFCo
perovskite in BCNFCo/CN nanocomposite, EDX elemental
mapping was performed in STEM mode (figures 3 and S2).
The bright-field image of BCNFCo/CN shows dense
BCNFCo perovskite surrounded with less dense CN sheets
(figures 3(a) and S2(a)). The EDX elemental maps of
BCNFCo/CN show the presence of all the perovskite con-
stituent elements Ba, Ca, Co, Fe, Nb and O concentrated in
the dense region, while carbon and nitrogen constituting CN
were distributed all around the composite, which confirms the
presence of BCNFCo cemented in CN sheets (figures 3(b)–(i)
and S2(b)–(k)). Further, the composite images prepared by
the permutation of different elemental combinations of
BCNFCo and CN show that the elements present in BCNFCo
were centered in the dense region while C and N were
overlapped with the dense region and also present in the less
dense region suggesting CN was wrapped around BCNFCo
(figures 3(j)–(l) and S2(j)–(o)). The observance of relatively
low intensities of C and N in the dense region was because of
the low atomic weight of C and N compared to heavy Ba and
Ca resulting in low electron counts in the STEM detector.
Additionally, the RGB composite of the images made by
selecting Ba and Ca as representative elements of BCNFCo
while C and N as representative of CN followed by line scan
show homogeneous distribution of C and N element all
around the heterostructure validating the presence of CN
enwrapped BCNFCo (figure S3).
The surface/sub-surface chemical composition and
binding energies of CN, BCNFCo and BCNFCo/CN were
determined using XPS (figures S4–S6). The XPS elemental
survey scan of CN, BCNFCo and BCNFCo/CN exhibited
featured peaks (CN: C1s, N1s and O1s; W6: Ba3d, Ca2p,
Nb3d, Fe2p and O1s and BCNFCo/CN: Ba3d, Ca2p, Nb3d,
Fe2p, C1s, N1s and O1s) along with sub-core level peaks (i.e.
OKLL, CKLL, BaMNN, Ba2p etc) confirming the presence
of all constituent elements in pristine and composite materials
(figures S4–6(a)). The core level high-resolution XPS spec-
trum of CN in the C1s region can be deconvoluted into three
peak components centered at BE≈284.8, 286.2 and
288.1 eV (figure S4(b)). The XPS peak located at 284.8 eV
originated from sp3
hybridized adventitious and turbostratic
carbons, while the peaks at 286.2 and 288.1 eV were assigned
to sp2
hybridized C–(N)3 and N=C–N aromatic carbons of
heptazine unit in carbon nitride, respectively [82–84]. The
deconvoluted HR-XPS of CN in the N1s region exhibits four
peaks located at 398.6, 399.7, 400.9 and 404.4 eV (figure
S4(c)). The XPS peaks at 398.6 and 399.7 eV were assigned
to secondary C=N–C and tertiary N–(C)3 nitrogens present in
the heptazine unit of carbon nitride ring systems while
another peak at 400.9 eV appeared due to the contribution of
terminal primary nitrogens (–NH2) [82, 85–87]. Additionally,
a small peak at 404.4 eV originated due to π–π*
transition in
the conjugated aromatic system. HR-XPS in the O1s region of
Figure 2. TEM images of CN (a) low magnification image at 0.5 μm scale bar and (b) moderate magnification image at 100 nm scale bar
showing nanosheets structure (c) HR-TEM image at 10 nm scale bar showing nanoporous structure; inset showing corresponding FFT image
(d) HR-TEM of BCNFCo/CN nanohybrid at 5 nm scale bar 50 nm scale bar showing CN wrapped around BCNFCo. (e) HR-TEM images of
BCNFCo/CN at 5 nm scale bar demonstrating BCNFCo entrapped in CN matrix, Inset 1 and 2 are FFT of the selected region showing
amorphous CN and crystalline BCNFCo domains (f) enlarged region showing close contact between CN and BCNFCo and iFFT showing
lattice fringes overlapping with crystal plane of BCNFCo and corresponding d-spacing (g) high magnification image at 5 nm scale bar
showing lattice fringes of double perovskite oxide and wrapping of CN around the lattice; inset FFT of entire images and (f) magnified view
of the selected area showing interplanar d-spacing and corresponding overlapped iFFT showing 0.27 nm d-spacing.
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Nanotechnology 32 (2021) 485407 P Kumar et al
6. CN was deconvoluted into three peaks component centered at
531.7, 533.5 and 534.8 eV corresponding to C=O, N=C–O
and –OH oxygens of adventitious oxygen and oxidized
terminal carbons (figure S4(d)) [88].
The HR-XPS spectra of Ba2Ca0.66Nb0.68Fe0.33
Co0.33O6−δ (BCNFCo) in Ba3d region displayed two main
peak components located at 779.4 and 794.8 eV originating
from Ba3d5/2 and Ba3d3/2 orbital splitting of Ba2+
in
BCNFCo lattice (figure S5(b)) [89, 90]. The Co2p peak could
not be observed due to the coinciding binding energy of Ba3d
and the lower concentration of Co. The two peak components
in HR-XPS of BCNFCo in the Ca2p region at BE≈346.8
and 350.2 eV were assigned to Ca2p3/2 and Ca2p1/2 peak
components of Ca2+
state (figure S5(c)) [29]. The two intense
peak components in Nb3d region at 205.9 and 208.7 eV were
assigned to Nb3d5/2 and Nb3d3/2 components of Nb present
in 5+oxidation state (figure S5(d)) [91, 92]. Fe2p region of
BCNFCo displayed two main peaks due to Fe2p3/2 and
Fe2p1/2 orbital splitting (figure S5(e)). The Fe2p3/2 peak was
deconvoluted into two components at BE value 710.5 and
713.4 eV assigned to Fe present in Fe3+
and Fe2+
state
[85, 93–95]. Further, observance of satellite peak at BE value
718.0 eV confirmed the presence of iron in the mixed-valence
state. The deconvoluted HR-XPS spectra of BCNFCo in the
O1s region displayed three peaks at 528.4, 529.2 and
530.9 eV assigned to oxygen atoms present in the lattice
structure, C=O and –OH of adsorbed oxygens respectively
[38, 96]. The relatively intense C=O peak might be due to the
residual solvent used for the film formation. In BCNFCo/CN
composite, all the peaks corresponding to CN and BCNFCo
were observed at almost identical binding energy values
suggesting weak van der Waals interaction between CN and
BCNFCo and undermining the presence of any strong che-
mical interactions (figure S6).
The nature of chemical functional groups present in the
materials was determined using Fourier transform infrared
(FTIR) spectroscopy (figure 4(a)). The FTIR spectrum of
BCNFCo showed intense IR absorption bands at 533, 1035,
1568, 2840 and 3219 cm−1
. The absorption band at ca.
533 cm−1
was assigned to the characteristic metal-oxygen
stretch (M-O) while another peak at 3219 cm−1
originated
due to O–H stretching (νO–H) vibration. Other IR peaks at
1035, 1568 and 2840 cm−1
appeared due to the presence of
the residual solvent used for the formation of the film. The
Figure 3. STEM EDX elemental mapping of 40% BCNFCo/CN nanocomposite (a) bright field (BF) image of mapped area, and EDX
elemental mapping for (b) Ba (red), (c) Ca (blue), (d) Co (green), (e) Fe (cyan), (f) Nb (magenta), (g) O (pink), (h) C (yellow), (i) N (violet);
(j) composite image for Ba, Ca, Co, Fe, Nb, O (k) composite of C, N and (l) composite of Ba, Ca, Co, Fe, Nb, O, C and N.
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Nanotechnology 32 (2021) 485407 P Kumar et al
7. FTIR spectrum of CN exhibited an IR absorption band at
3127 cm−1
due to residual –NH2 and –OH (νN–H, νO–H)
stretch [97]. Characteristic IR absorption bands at 1126–1522
cm−2
and 799 cm−1
were arisen due to triazine (C3N3) ring
stretch and bending vibration (figure 4(a)) [98–100]. In the
40% BCNFCo/CN composite all characteristic peaks of CN
were observed and no shift in the peak position was found,
verifying that the intact CN sheets interacted with BNCFCo
through weak vdW interactions.
Figure 4(b) displays the Raman spectra of CN, BCNFCo
and 40% BCNFCo/CN collected using a 632 nm laser as the
excitation source. The Raman spectrum of BCNFCo exhib-
ited an intense peak at 780 cm−1
. The Raman spectrum of CN
shows an intense peak at 1453 cm−1
that originated due to the
cumulative D+G bands of the graphitic carbon nitride
structure [69, 101–103]. The D band arises due to out-of-
plane vibration of sp3
hybridized C and N in graphitic carbon
nitride sheets while the G band appears due to the in-plane
vibration of sp2
hybridized C–N’s [104–106]. Due to exten-
sive stacking in bulk carbon nitride, some vibrations were
restricted and a merged D+G band was observed. In the
Raman spectrum of 40% BCNFCo/CN nanocomposite, two
Raman peaks at 1353 and 1570 cm−1
assigned to D and G
bands of the graphitic structure were clearly observed
[105, 107]. Usually, in the carbon nitride, E2g modes (G band)
arise from the sp2
bonded C–N are Raman active and
observed at 1581 cm−1
. Another Raman-active D band cen-
tered at ∼1360 cm−1
originates from defects state in carbon
nitride structures. The sp2
linked heptazine units of carbon
nitride structure are not completely planar due to variation of
the bond angle in N rich structure [108, 109]. The non-
coherent out-of-plane vibration of these C=N’s in N-linked
heptazine units gives rise to the D band. The relative inten-
sities of the D band in carbon nitride-based structure is highly
dependent on the amount of nitrogen which influences the
number of out-of-plane vibrations in the CN network [110].
As CN is composed of alternate C and N’s present in 3:4
stoichiometry, the equal intensity of the D and G band can be
expected. Compared to bulk CN, the well-separated D and G
band in BCNFCo/CN composite can be explained as follows:
the synthesis of BCNFCo/CN composite proceeds via exfo-
liation of bulk carbon nitride in glycerol/dichlorobenzene
under continuous heat and stirring resulting in the formation
of few-layered sheets. Due to the breaking of stacked struc-
ture and the formation of few-layered structures on the surface
of BCNFCo, the restricted out-of-plane vibration becomes
free to show well-separated D and G bands [111, 112].
The crystallinity of CN, BCNFCo and their composites
was determined using x-ray diffraction (XRD) (figure 4(c)).
The crystal structure of the investigated phase Ba2
Ca0.67Nb0.67Fe0.33Co0.33O6−δ exhibited a 1:1 ordered cubic
double perovskite structure (JCPDS# 49-0425). For refine-
ment, an ideal phase double-perovskite (figure S8),
Ba3CaNb2O9, with space group Fm-3m (No. 225) was used.
Table S1 lists the atomic position and occupancy values
obtained from Rietveld refinement analysis. Furthermore, the
lattice constant of BCNFCo was determined to be a=8.3739
(9) Å; where the absence of any secondary phases was also
confirmed by reliability factors (χ2
=1.21; Rp =12.71%). In
an ideal Fm-3m space group, cubic double-perovskite
involves an octahedral arrangement (figure S8) of alternative
layers of oxygens around Ca(Nb) and Nb atoms, which shares
the crystallographic positions 4a and 4b, respectively. The Ba
atoms are located in spaces between these octahedra. For each
Ba atom, there are twelve oxygens at close distances—so that,
the Ba–O sublattice involves BaO12 units with dodecahedral
geometry. In the case of BCNFCo, the transition metal (Fe,
Co) doping seems like a (proper) replacement of Nb cations at
Figure 4. (a) FTIR spectra of BCNFCo, CN and 40% BCNFCo/CN, (b) Raman spectra of BCNFCo, CN and 40% BCNFCo/CN (c) powder
XRD (P-XRD) diffraction pattern of CN, BCNFCo and their composites with different wt%; Color: CN (black), 10% BCNFCo/CN (pink),
20% BCNFCo/CN (green), 30% BCNFCo/CN (blue), 40% BCNFCo/CN (red), 50% BCNFCo/CN (yellow), BCNFCo (violet).
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Nanotechnology 32 (2021) 485407 P Kumar et al
8. the B-site of the double perovskite—subsequently forming
oxygen vacancies. The B-site substitution on similar per-
ovskite-type oxides has previously been reported by Than-
gadurai et al group—showcasing the materials for solid oxide
fuel cells [113] and CO2 gas sensor [114] applications.
Likewise, co-authors of this work have previously demon-
strated BCNF to be a p-type semiconductor in the bulk using
ambient-dependent AC and DC impedance measure-
ments [114].
As shown in figure 4(c), the XRD pattern of bulk g-C3N4
displayed two distinct peaks at 2θ values 27.1° and 13.0°
indexed to the 002 and 100 planes of graphitic carbon nitride
[15, 115]. The 002 reflection with a 0.32 nm interplanar d-
spacing originated due to interplanar stacking of carbon
nitride sheets while in-plane packing of heptazine units in
carbon nitride sheets was responsible for the 100 reflection
with 0.68 nm spacing [116]. The characteristic 002 and 100
peaks of carbon nitride were present in all the BCNFCo/CN
composites indicating the preservation of the stacked structure
of CN in the composite. Furthermore, specific peaks of
BCNFCo were also observed in the BCNFCo/CN composite
materials demonstrating the intact crystalline structure of
BCNFCo.
Thermogravimetric analysis (TGA) of CN and best per-
forming 40% BCNFCo/CN was performed to elucidate the
thermal stability of materials (figure S10). The TGA ther-
mogram of CN demonstrated a very small weight loss (∼5%)
in the 50 °C–550 °C temperature range due to loss of surface
adsorbed water/organic molecules and polymerization of
residual uncondensed moieties in CN framework releasing
NH3. Another sharp weight loss (∼92%–95%) in the temp-
erature range of 600 °C–750 °C was ascribed to degradation
of heptazine (C6N7) moieties. The 40% BCNFCo/CN het-
erostructure composite demonstrated three weight loss
regions in the TGA thermogram. The first less prominent
weight loss (∼3%–4%) in the region of 50 °C–190 °C was
observed due to the removal of adsorbed water and o-
dichlorobenzene. The second minor weight loss (∼4%–5%)
in the temperature range of 250 °C–425 °C was assigned to
the degradation of intercalated glycerol and loss of NH3
during condensation of unreacted heptazine units. The third
major weight loss of approximately ∼38% was observed in
the temperature range of 550 °C–700 °C due to the degrada-
tion of carbon nitride tris-s-triazine moieties. Subsequently,
no weight loss was observed which suggests high-temperature
stability of remaining BCNFCo perovskite oxide crystals.
2.2. Optical and photoluminescence spectra of BCNFCo-CN
hybrids
The optical absorption of materials was evaluated from dif-
fuse reflectance UV–vis (DR-UV–vis) spectra (figure 5(a)).
The DR-UV–vis spectrum of CN exhibited the characteristic
absorption band in the 200–420 region and an extended band
tail up to 460 nm arising from the band-to-band transition
between the valence band composed of nitrogen 2p orbitals
and conduction band composed of the carbon atom 2p orbi-
tals. The weak peak at 330 nm in the UV–vis spectrum of CN
was assigned to π→π*
transition while another sharp peak
around 390 nm was assigned to n→π*
transition in carbon
nitride framework [117–120]. The UV–vis spectrum of
BCNFCo perovskite oxide shows a broad absorption range
extending all the way down to the near-infrared region. After
the formation of heterojunction, the absorption profile of the
composite was extended toward longer wavelengths as per the
percentage of blended perovskite due to contribution from
perovskite absorption. Additionally, the effective optical
bandgaps of CN, BCNFCo and BCNFCo/CN composites
were calculated using a Tauc plot. A plot between (αhν)1/2
versus hν followed by extrapolation of the linear tangent to
abscissa provide band gap value of material; where α is
absorption coefficient, h is plank constant and ν is the light
frequency (figure S7). The values of optical bandgap obtained
from the Tauc plot for CN and as-prepared BCNFCo were
found to be 2.58 and 0.69; whereas the bandgap values for
BCNFCo/CN composites with BCNFCo content varying
from 10%, 20%, 30%, 40% and 50% were 1.02, 1.00, 0.88,
0.88 and 0.70 eV, respectively. The obtained bandgap for CN
was in good agreement with previously reported literature
[121, 122].
Photoluminescence (PL) spectra were acquired at an
excitation wavelength of 365 nm (figure 5(b)). CN displayed
a broad intense PL peak centered at 451 nm suggesting a
populated charge recombination process [123–125]. Bulk
carbon nitride composed of 2D tris-s-triazine units’ network
possesses several uncondensed NH/NH2 moieties leading to
intersheets and intrasheets hydrogen bonding. These moieties
also work as radiative recombination centers giving rise to an
intense PL peak. In multilayer carbon nitride, intersheets
charge recombination remains prevalent resulting in a
decrease in photocatalytic performance. After the formation
of composite with BCNFCo, the PL peak intensity of
BCNFCo/CN composite was not quenched. Interestingly, the
observed small gradual decrease in the emission intensity of
CN as wt% of BCNFCo was increased, is attributable to the
lower mass fraction of CN in the composites and interfacial
radiative recombination in the vdW heterostructure. dis-
sociated at the CN/BCNFCo heterojunction. This inference
has the major implication that the photoelectrochemical per-
formance of CN/BCNFCo heterojunction nanocomposite
photoanodes (discussed in the next section) derives mostly
from the separation of photogenerated charge carriers in the
BCNFCo.
2.3. Photoelectrochemical water splitting performance of
BCNFCo-CN hybrids
The pristine and composite materials were tested as photo-
anodes for photoelectrochemical (PEC) water splitting
(figure 6). The PEC water splitting experiments were carried
out in a three-electrode configuration with FTO deposited
bare/hybrid materials as photoanode (working electrode)
while Pt and Ag/AgCl electrode were used as photocathode
(counter electrode) and reference electrodes respectively. For
the measurement, all three electrodes were immersed in a
0.1 M Na2SO4 electrolyte followed by irradiation of the
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Nanotechnology 32 (2021) 485407 P Kumar et al
9. photoanode by AM1.5 G simulated sunlight (one sun inten-
sity). The photoresponse of materials was measured using
linear sweep voltammetry by sweeping the applied bias from
−1.0 to +1.0 V versus Ag/AgCl. All the samples demon-
strated a negligible current density under dark conditions
(figure 6(a)). However, under AM1.5 G irradiation all the
samples displayed a photoresponse. Pristine CN and
BCNFCo exhibited low photocurrent densities of 0.45 and
0.40 mA cm−2
at +0.6 V versus Ag/AgCl. After the forma-
tion of heterojunction between BCNFCo and CN, the pho-
tocurrent density was remarkably improved. The 40%
BCNFCo/CN sample displayed the highest photocurrent
density (1.51 mA cm−2
) under AM1.5 G irradiation—a nearly
four-fold increase in performance over the pristine material
photoanodes (figures 6 and 7). Under identical conditions, the
photocurrent densities for 10% BCNFCo /CN, 20%
BCNFCo /CN, 30% BCNFCo/CN and 50% BCNFCo/CN
were measured to be 0.61, 0.67, 0.99 and 0.73 mA cm−2
respectively. A similar pattern ensued when a 420 nm
cut-off filter was used to exclude short wavelength photons
(figures S13–18).
The photocurrent response of material during light On–
Off cycles was measured as the function of time (i–t curve) at
0.6 V applied bias to clearly show that the current originated
from illumination rather than a redox effect (figures 6(b),
7(a)–(c)). The test duration of 180 s for the On–Off cycling is
long enough to show the effects (if any) of short-term che-
mical or photochemical degradation. No such degradation
was observed which demonstrates the photochemical stability
of the heterojunction nanocomposite. As in the LSV mea-
surement, the photocurrent response of 40% BCNFCo/CN
sample increased linearly as a function of voltage, which
seems like the ohmic current. To verify the originated current
was not ohmic in nature LSV during the On–Off cycle was
collected. As clear from figure 7(a), the photocurrent reaches
almost zero during dark suggesting superimposing with dark
current suggests the observed current was purely originated
from photoelectrochemical water splitting. The steady pho-
tocurrent response of all the samples throughout measurement
and presence of peak and trough in photocurrent response
during light On–Off validates the photoresponse of the
materials. The observance of spikes in the transient photo-
current measurement followed by the attainment of constant
current during the light-on cycle was due to the generation of
a large number of electron–hole pairs during light illumina-
tion which are accumulated at the surface on opposite sides of
the semiconductor-electrolyte interface. Photogenerated
electrons in BCNFCo are injected into CN while photo-
generated holes in BCNFCo are supplied to hydroxyl ions at
the interface. Due to the slow transport of electrons in the CN,
interfacial recombination of a portion of accumulated elec-
trons and holes occurs, reducing the photocurrent to a steady-
state value given by the flat portion of the pulses in the linear
sweep voltammograms. Note that the recombination process
has a time constant of several seconds. In contrast, the initial
charge separation process directed by the space charge
capacitance has a time-constant of ∼1 μs as shown in table
S11. Figures 7(c) and (d) show appreciable visible light
harvesting by the 40% BCNFCo/CN nanocomposite with a
distinguishable photoresponse even at 640 nm. This shows
the potential of optimized double perovskite oxide systems
based on BCNFCo to overcome the issue of poor visible light
Figure 5. (a) DR-UV–vis spectra and (b) steady-state PL (ssPL) spectra of CN, 10% BCNFCo/CN, 20% BCNFCo/CN, 30% BCNFCo/CN,
40% BCNFCo/CN, 50% BCNFCo/CN, BCNFCo acquired at 360 nm excitation; Color: CN (black), 10% BCNFCo/CN (pink), 20%
BCNFCo/CN (green), 30% BCNFCo/CN (blue), 40% BCNFCo/CN (red), 50% BCNFCo/CN (yellow), BCNFCo (violet).
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Nanotechnology 32 (2021) 485407 P Kumar et al
10. harvesting by conventional photochemically and thermally
stable photoanodes such as TiO2, SrTiO3, NaNbO3, etc.
To discern the true origin of photocurrent from photo-
electrochemical water splitting and overrule the possibility of
any side reactions/photocorrosion or electrolysis, the evolved
gaseous reaction product was collected on Pt cathode in H-cell
(Please ESI for experimental detail). The gaseous product was
analyzed in a gas chromatograph equipped with a pulse dis-
charge detector (GC-PDD). The rates of hydrogen evolution
for BCNFCo, CN and 40% BCNFCo/CN under AM1.5 G one
sun illumination were found to be 0.57, 0.84 and 1.15 μmol
h−1
respectively which was consistent with the observed trend
in photocurrent (figures 6, 7 and S13–S18). The increased
hydrogen evolution rate for 40% BCNFCo/CN indicates the
synergistic enhancement in photoactivity. Furthermore, the
Faradaic efficiency, which is a true measure of efficiency in
actual operating conditions was calculated for the photoelec-
trochemical water splitting using BCNFCo, CN and 40%
BCNFCo/CN. Faradaic efficiency (FE%) is a ratio of observed
hydrogen in experimental condition to theoretically evolved H2
Figure 6. (a) Linear sweep voltammograms of CN, 10% BCNFCo/CN, 20% BCNFCo/CN, 30% BCNFCo/CN, 40% BCNFCo/CN, 50%
BCNFCo/CN, BCNFCo samples showing change in photocurrent density versus applied potential (J–V ), under dark and simulated solar
AM1.5 G light irradiation (100 mW cm−2
) (b) photocurrent versus time (i–t) plot showing response during light On–Off cycles at +0.6 V
applied bias, under AM1.5 G light irradiation (100 mW cm−2
); all the measurements were performed in 0.1 M Na2SO4 solution at a scan rate
of 0.1 mV s−1
and (c) calculated Faradaic efficiencies for hydrogen evolution using BCNFCo, CN and 40% BCNFCo/CN photocatalyst.
9
Nanotechnology 32 (2021) 485407 P Kumar et al
11. was calculated using the following expression.
⎡
⎣
⎢
⎤
⎦
⎥
( )
( )
( )
·
=
Faradaic efficiency %
Experimental gas evolution measured H
Theoretical H gas evolution based on photocurrent
100.
2
2
The calculated Faradaic efficiencies for the BCNFCo,
CN and BCNFCo/CN photoanode-based photoelec-
trochemical H-cells were found to be 64.32%, 83.38% and
87.72% respectively (figure 6(c)). In comparison to the pris-
tine materials, the increased FE% for the BCNFCo/CN
demonstrates better charge separation in the heterojunction.
Additionally, the high stability of the material toward pho-
tocorrosion was inferred from the excellent FE for the
BCNFCo. It is well-established that in photoelectrochemical
oxidation/reduction, the additional current generated from the
non-photophysical processes derives from the material’s
corrosion and side reaction. These reactions promote the
oxidation of photoanode which compromises the photo-
stability of the materials. The high Faradaic efficiency sug-
gests only a tiny fraction of BCNFCo photoanode is
potentially corroded during the measurement which suggests
the hybridization of BCNFCo not only improves the photo-
electrochemical performance but also increases its resilience.
Figure 7. (a) Linear sweep voltammogram of 40% BCNFCo/CN showing photocurrent density versus applied potential (J–V ),
photoresponse during light On–Off cycle under dark, solar simulated AM1.5 G light irradiation without filter (100 mW cm−2
) and AM1.5 G
light irradiation with 420 nm cut-off filter, (b) photocurrent versus time (i–t) plot of 40% BCNFCo/CN showing response during light On–
Off cycle at +0.6 V applied bias, under solar simulated AM1.5 G light irradiation without filter (100 mW cm−2
) and AM1.5 G light
irradiation with 420 nm cut-off filter, (c) photocurrent response versus time of 40% BCNFCo/CN during light On–Off cycle at +0.6 V
applied bias, under 420, 460, 520, 580, 640 and 840 nm LEDs (100 mW cm−2
) (d) enlarged photocurrent versus time graph showing
photoresponse of 40% BCNFCo/CN under 580, 640 and 840 nm LEDs (100 mW cm−2
) all the measurement were performed in 0.1 M
Na2SO4 solution at a scan rate of 0.1 mV s−1
.
10
Nanotechnology 32 (2021) 485407 P Kumar et al
12. The band alignment at the heterojunction was determined
using XPS valence band (XPS-VB) spectra (figure 8). All
energy band positions in the ensuing discussion are listed
versus the vacuum level (Evac). From the XPS VB spectra, the
valence band positions for CN, BCNFCo and BCNFCo/CN
were found to be 2.04, 0.68 and 0.80 eV respectively below
the Fermi level [126]. The shifting of valence band position in
BCNFCo/CN indicating the establishment of a type-II het-
erojunction. Interestingly, the calculated valence band posi-
tions for CN, BCNFCo and 40% BCNFCo/CN were found to
be close to the optical band gap value of materials calculated
from the Tauc plot and demonstrate that the Fermi level was
close to the conduction band thus displaying the n-type
character. Further, the Mott–Schottky plot obtained from
impedance potential measurement also demonstrate n-type
characteristics of materials and calculated flat band positions
(Vfb) of CN, 10% BCNFCo/CN, 20% BCNFCo/CN, 30%
BCNFCo/CN, 40% BCNFCo/CN, 50% BCNFCo/CN were
found to be −0.37, −0.45, −0.33, −0.32, −0.48 and
−0.54 V versus Ag/AgCl respectively. The n-type conduc-
tion of BCNFCo/CN hybrids determined from the Mott–
Schottky plot (figure 8(d)) indicates the Fermi level to be
close to the conduction band. Hence the obtained flat band
potential (Vfb) can be assigned to the conduction band posi-
tion. As the BCNFCo content in the composite is increased,
the conduction band minimum (ECB) gets upshifted versus the
vacuum level (Evac). The upshifting of ECB in the composite
can be explained based on the formation of a p–n type
Figure 8. XPS valence band (XPS-VB) spectra showing valence band position with respect to Fermi level of (a) CN, (b) BCNFCo and (c)
40% BCNFCo/CN and (d) Mott–Schottky plots showing flat and potential of CN (black), 10% BCNFCo/CN (pink), 20% BCNFCo/CN
(green), 30% BCNFCo/CN (blue), 40% BCNFCo/CN (red), 50% BCNFCo/CN (yellow).
11
Nanotechnology 32 (2021) 485407 P Kumar et al
13. heterojunction between p-type BCNFCo and n-type CN. As
we know the formation of heterojunction involves Fermi level
alignment. Before contact with CN, the p-type BCNFCo was
electron-deficient; however, after contact with CN, the elec-
trons from the CN were transferred to the BCNFCo com-
pensating the positive hole leading to Fermi level
equilibration. During Fermi level alignment, the CB of
BCNFCo gets upshifted due to the accumulation of excessive
electrons from CN and a built-in electric field is generated
which facilitates the transfer of electrons from BCNFCo to
CN in the depletion layer (figure 9). The translation of the flat
band potential to the RHE (NHE) scale which is usually used
for the expression of redox potential gives the following
values of Vfb for the various BCNFCo/CN composites:
−0.17, −0.253, −0.13, −0.12, −0.28 and −0.34 V versus
NHE at pH-0. The more negative CB compared to the
reduction potential of hydrogen (H+
/H2; 0.00 V versus NHE
at pH-0) suggests all the composites can catalyze the process
of hydrogen evolution.
PL spectra (figure 5(b)) show that the bound exciton in
CN is not dissociated at the BCNFCo/CN interface. There-
fore, the dramatic improvement of photoelectrochemical
performance in the 40% BCNFCo/CN photoanodes does not
derive from improved separation and collection of photo-
generated excitons in CN. Instead, the increased photocurrent
density (Jph) derives from better separation and utilization of
electron–hole pairs generated in BCNFCo. Individually, bare
CN and bare BCNFCo photoanodes generated maximum Jph
values of 0.4 and 0.55 mA cm−2
respectively under AM1.5 G
illumination at an applied bias of 0.6 V versus Ag/AgCl
(figures 6(a) and (b)). Under identical conditions, the 40%
BCNFCo/CN photoanode generates ∼1.5 mA cm−2
, which
is higher than the sum of the maximum photocurrent densities
generated by the bare CN and bare BCNFCo photoanodes. In
figures 7(c) and (d), it is clear that the 40% BCNFCo/CN
hybrids show a photoresponse all the way down to 640 nm,
where the CN does not even absorb. Therefore, the increased
photoelectrochemical performance derives from better
separation of carrier-pairs generated in BCNFCo.
The better charge separation and migration in BCNFCo/
CN nanocomposite were further confirmed by EIS measure-
ment which demonstrates a smaller arc of the semicircle in the
Nyquist plot for composite materials (lower charge transfer
resistance) (figure S12). The pristine BCNFCo and CN
samples exhibit rather a high charge transfer resistance (RCT)
values of 219.5 Ω and 264.7 Ω respectively (table S2) due to
the absence of a heterojunction to facilitate charge separation.
The 10% BCNFCo/CN sample exhibits the highest RCT
value (pink curve in figure S12(a)) due to an inadequate
amount of the p-type component of the heterojunction
resulting in more dead-ends for holes. As the amount of
BCNFCo is increased in the nanocomposites, there exists a
sufficient amount of both the n- and p-type components of the
heterojunction to ensure charge separation and also deliver
holes to the electrolyte species. Therefore, we see the RCT
value dropping sharply for the 20% BCNFCo/CN, 30%
BCNFCo/CN and 40% BCNFCo/CN samples with the
lowest charge transfer resistance of 39.84 Ω seen for the 30%
BCNFCo/CN sample. However, charge transport limitations
become increasingly important as the amount of BCNFCo is
further increased. The poor carrier transport in the BCNFCo
phase increases the series resistance (RS) of the sample and
concomitantly increases the charge transfer resistance. Thus
we see the 40% BCNFCo/CN and 50% BCNFCo/CN
samples exhibiting both a higher RS and RCT than the 20%
BCNFCo/CN and 20% BCNFCo/CN samples. At the same
time, BCNFCo is the primary photon absorber with a band-
edge that extends to well beyond 700 nm as shown in
figure 5(a). As the amount of BCNFCo is increased, the
number of generated electron–hole pairs is also increased
albeit with a higher fraction recombining due to charge
transport limitations (also accounting for the larger arc for the
40% BCNFCo/CN sample in figure S12(b)). As a con-
sequence of the trade-off between light absorption and charge
separation, the 40% BCNFCo/CN blend exhibits the best
photoelectrochemical performance as shown in figure 6.
To explain the improved photocatalytic performance, a
plausible mechanism was proposed based on optical band
Figure 9. A plausible mechanism of Fermi level alignment and formation of p–n heterojunction between BCNFCo and CN.
12
Nanotechnology 32 (2021) 485407 P Kumar et al
14. gap/electronic band positions and existing literature. For self-
sustained water splitting under solar light, the bandgap of
materials should be higher than 1.23 eV with a conduction
band position more negative than 0.00 V versus NHE at pH-0
(water reduction potential, H+
/H2) while the position of the
valence band should be more positive than +1.23 V versus
NHE at pH-0 (water oxidation potential, H2O/O2) [127]. The
calculated optical band gap value of BCNFCo was found to
be 0.69 eV, demonstrating its inability to perform water
splitting by itself. Further, the poorly oxidative valence band
(0.68 eV below the Fermi level) also prevents BCNFCo to
work as a stand-alone photocatalyst for water splitting which
explains the observation of a small photocurrent in PEC. On
the other hand, CN has a bandgap of 2.58 eV with CB and VB
positions of −0.37 and +2.27 V respectively, calculated from
Mott–Schottky measurement and optical band gap, suggest-
ing CN has the potential to facilitate water splitting reaction.
However, the absorption of CN is limited to the blue region of
the solar spectrum and prevalent inter-sheet charge recombi-
nation decrease the PEC performance. The formation of a
nanocomposite between BCNFCo and CN significantly
increased the photocatalytic performance for 40% BCNFCo/
CN materials. The boosted photocatalytic performance can be
explained due to the formation of p–n type heterojunction and
better charge separation in BCNFCo/CN nanocomposite as
evident from the lower RCT of 40%BCNFCo/CN than pris-
tine CN and BCNFCo (figure S12) [128–131]. The p-type
BCNFCo interacts with n-type CN leading to charge transfer
from CN to BCNFCo during the Fermi level alignment and
forms p–n heterojunctions shown in figure 9. This Fermi level
alignment upraised the CB position of BCNFCo. In
BCNFCo/CN heterojunction, due to the presence of charge
gradient originated from the accumulation of negative charge
on BCNFCo and the positive charge on CN interface, an in-
built electric field is generated across the depletion layer. Due
to the establishment of p–n heterojunction and the presence of
an in-built electric field the photogenerated electrons are
transferred to the conduction band of CN while holes move in
the opposite direction. In photoelectrochemical conditions,
BCNFCo after absorption of visible light transfers photo-
generated electrons to the conduction band of CN from where
the electrons are transported to the Pt cathode through the
external circuit to reduce protons in the electrolyte to
hydrogen while holes left in the VB of BCNFCo are sca-
venged by Na2SO4.
3. Conclusion
This is the first report on the use of double perovskites as
narrow bandgap semiconductors for light harvesting appli-
cations. A nanocomposite of double perovskite oxide with
Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ composition and g-C3N4
was prepared by a facile mixing/sonication approach in
DCB/glycerol solution. The extensive mixing leads to inter-
calation of solvents in between the sheets which afford few-
layered carbon nitride sheets wrapped around the perovskite
material. The materials characterization with various tools
confirms the formation of nanocomposite between two
materials. HR-TEM and Raman validate the presence of
carbon nitride in a few-layered sheet structure which provides
a charge transport pathway to facilitate better charge separa-
tion in the composite materials. Among various wt% com-
positions of composite 40%BCNFCo/CN nanocomposite
displayed the highest photocurrent density (1.5 mA cm−2
)
under solar simulated AM1.5 G irradiation. A particularly
promising result is the observation of a distinct photoresponse
at 640 nm in most of the blends, which is attributable only to
absorption by the double perovskite since CN does not absorb
at this wavelength. This result indicates electron–hole pairs
generated in the double perovskite are separated and perform
useful work.
Acknowledgments
We would like to thank the Natural Sciences and Engineering
Research Council of Canada (NSERC), the National Research
Council Canada (NRC), Future Energy Systems (FES) for
direct and indirect (equipment use) financial support. DL
thanks DST-SERB/UoA for providing research fellowship.
National Research Council—National Institute for Nano-
technology (NRC-NINT) and the University of Alberta
Nanofab facilities are acknowledged for support in the ana-
lysis of samples. Dr Kai Cui is kindly acknowledged for HR-
TEM and EDX elemental mapping of the samples. The
authors are thankful to Sheng Zeng and Ehsan Vahidzadeh for
helping with GC and TGA analysis respectively.
Data availability statement
The data generated and/or analyzed during the current study
are not publicly available for legal/ethical reasons but are
available from the corresponding author on reasonable
request.
ORCID iDs
Pawan Kumar https:/
/orcid.org/0000-0003-2804-9298
Karthik Shankar https:/
/orcid.org/0000-0001-7347-3333
References
[1] Roger I, Shipman M A and Symes M D 2017 Earth-abundant
catalysts for electrochemical and photoelectrochemical water
splitting Nat. Rev. Chem. 1 0003
[2] Yan Y, Xia B Y, Zhao B and Wang X 2016 A review on
noble-metal-free bifunctional heterogeneous catalysts for
overall electrochemical water splitting J. Mater. Chem. A 4
17587–603
[3] Maeda K and Domen K 2010 Photocatalytic water splitting:
recent progress and future challenges J. Phys. Chem. Lett. 1
2655–61
13
Nanotechnology 32 (2021) 485407 P Kumar et al
15. [4] Joya K S, Joya Y F, Ocakoglu K and van de Krol R 2013
Water‐splitting catalysis and solar fuel devices: artificial
leaves on the move Angew. Chem. Int. Ed. 52 10426–37
[5] Kannan N and Vakeesan D 2016 Solar energy for future
world:—a review Renew. Sustain. Energy Rev. 62 1092–105
[6] Tachibana Y, Vayssieres L and Durrant J R 2012 Artificial
photosynthesis for solar water-splitting Nat. Photon. 6 511
[7] Ardo S, Rivas D F, Modestino M A, Greiving V S, Abdi F F,
Llado E A, Artero V, Ayers K, Battaglia C and Becker J-P
2018 Pathways to electrochemical solar-hydrogen
technologies Energy Environ. Sci. 11 2768–83
[8] Lewerenz H-J and Peter L 2013 Photoelectrochemical Water
Splitting: Materials, Processes and Architectures
(Cambridge UK: Royal Society of Chemistry)
[9] Zong X and Li C 2018 Metal Oxides in Heterogeneous
Catalysis (Amsterdam: Elsevier) pp 355–99
[10] Hisatomi T, Kubota J and Domen K 2014 Recent advances in
semiconductors for photocatalytic and photoelectrochemical
water splitting Chem. Soc. Rev. 43 7520–35
[11] Kar P et al 2019 High rate CO2 photoreduction using flame
annealed TiO2 nanotubes Appl. Catal. B 243 522–36
[12] Kudo A and Miseki Y 2009 Heterogeneous photocatalyst
materials for water splitting Chem. Soc. Rev. 38 253–78
[13] Moniz S J, Shevlin S A, Martin D J, Guo Z-X and Tang J
2015 Visible-light driven heterojunction photocatalysts for
water splitting—a critical review Energy Environ. Sci. 8
731–59
[14] Liao J-F, Xu Y-F, Wang X-D, Chen H-Y and Kuang D-B
2018 CsPbBr3 nanocrystal/MO2 (M = Si, Ti, Sn)
composites: insight into charge-carrier dynamics and
photoelectrochemical applications ACS Appl. Mater.
Interfaces 10 42301–9
[15] Shen L, Lei G, Fang Y, Cao Y, Wang X and Jiang L 2018
Polymeric carbon nitride nanomesh as an efficient and
durable metal-free catalyst for oxidative desulfurization
Chem. Commun. 54 2475–8
[16] Wu H, Lin S, Wang R, You X and Chi Y 2019 Water-stable
and ion exchange-free inorganic perovskite quantum dots
encapsulated in solid paraffin and their application in light
emitting diodes Nanoscale 11 5557–63
[17] Wu L Y, Mu Y F, Guo X X, Zhang W, Zhang Z M,
Zhang M and Lu T B 2019 Encapsulating perovskite
quantum dots in iron‐based metal-organic frameworks
(MOFs) for efficient photocatalytic CO2 reduction Angew.
Chem. Int. Ed. 58 9491–5
[18] Lv W, Li L, Xu M, Hong J, Tang X, Xu L, Wu Y, Zhu R,
Chen R and Huang W 2019 Improving the stability of metal
halide perovskite quantum dots by encapsulation Adv.
Mater. 31 1900682
[19] Xu Y-F, Yang M-Z, Chen B-X, Wang X-D, Chen H-Y,
Kuang D-B and Su C-Y 2017 A CsPbBr3 perovskite
quantum dot/graphene oxide composite for photocatalytic
CO2 reduction J. Am. Chem. Soc. 139 5660–3
[20] Wei Y, Cheng Z and Lin J 2019 An overview on enhancing
the stability of lead halide perovskite quantum dots and their
applications in phosphor-converted LEDs Chem. Soc. Rev.
48 310–50
[21] Wang Q, Tao L, Jiang X, Wang M and Shen Y 2019
Graphene oxide wrapped CH3NH3PbBr3 perovskite
quantum dots hybrid for photoelectrochemical CO2
reduction in organic solvents Appl. Surf. Sci. 465 607–13
[22] Zeng S, Kar P, Thakur U K and Shankar K 2018 A review on
photocatalytic CO2 reduction using perovskite oxide
nanomaterials Nanotechnology 29 052001
[23] Kan W H, Samson A J and Thangadurai V 2016 Trends in
electrode development for next generation solid oxide fuel
cells J. Mater. Chem. A 4 17913–32
[24] Yin W-J, Weng B, Ge J, Sun Q, Li Z and Yan Y 2019 Oxide
perovskites, double perovskites and derivatives for
electrocatalysis, photocatalysis, and photovoltaics Energ.
Environ. Sci. 12 442–62
[25] Sheikh M S, Ghosh D, Dutta A, Bhattacharyya S and Sinha T
2017 Lead free double perovskite oxides Ln2NiMnO6
(Ln = La, Eu, Dy, Lu), a new promising material for
photovoltaic application Mater. Sci. Eng. B 226 10–7
[26] Li C, Wang W, Xu C, Liu Y, He B and Chen C 2011 Double
perovskite oxides Sr2Mg1−xFexMoO6−δ for catalytic
oxidation of methane J. Nat. Gas Chem. 20 345–9
[27] Xu X, Chen Y, Zhou W, Zhu Z, Su C, Liu M and Shao Z
2016 A perovskite electrocatalyst for efficient hydrogen
evolution reaction Adv. Mater. 28 6442–8
[28] Zhu Y, Zhou W, Yu J, Chen Y, Liu M and Shao Z 2016
Enhancing electrocatalytic activity of perovskite oxides by
tuning cation deficiency for oxygen reduction and evolution
reactions Chem. Mater. 28 1691–7
[29] Zhang L, Zhou Q, He Q and He T 2010 Double-perovskites
A2FeMoO6−δ (A=Ca, Sr, Ba) as anodes for solid oxide
fuel cells J. Power Sources 195 6356–66
[30] Kan W H and Thangadurai V 2015 Challenges and prospects
of anodes for solid oxide fuel cells (SOFCs) Ionics 21
301–18
[31] Kim N-I, Afzal R A, Choi S R, Lee S W, Ahn D,
Bhattacharjee S, Lee S-C, Kim J H and Park J-Y 2017
Highly active and durable nitrogen doped-reduced graphene
oxide/double perovskite bifunctional hybrid catalysts
J. Mater. Chem. A 5 13019–31
[32] Jung J I, Jeong H Y, Lee J S, Kim M G and Cho J 2014 A
bifunctional perovskite catalyst for oxygen reduction and
evolution Angew. Chem. Int. Ed. 53 4582–6
[33] Xu X, Su C, Zhou W, Zhu Y, Chen Y and Shao Z 2016 Co‐
doping strategy for developing perovskite oxides as highly
efficient electrocatalysts for oxygen evolution reaction
advanced Science 3 1500187
[34] Zhao B, Zhang L, Zhen D, Yoo S, Ding Y, Chen D, Chen Y,
Zhang Q, Doyle B and Xiong X 2017 A tailored double
perovskite nanofiber catalyst enables ultrafast oxygen
evolution Nat. Commun. 8 14586
[35] Weng B, Grice C R, Ge J, Poudel T, Deng X and Yan Y 2018
Barium bismuth niobate double perovskite/tungsten oxide
nanosheet photoanode for high‐performance
photoelectrochemical water splitting Adv. Energy Mater. 8
1701655
[36] Weng B, Xiao Z, Meng W, Grice C R, Poudel T, Deng X and
Yan Y 2017 Bandgap engineering of barium bismuth
niobate double perovskite for photoelectrochemical water
oxidation Adv. Energy Mater. 7 1602260
[37] Zhu Y, Zhou W, Zhong Y, Bu Y, Chen X, Zhong Q,
Liu M and Shao Z 2017 A perovskite nanorod as
bifunctional electrocatalyst for overall water splitting Adv.
Energy Mater. 7 1602122
[38] Wang J, Gao Y, Chen D, Liu J, Zhang Z, Shao Z and Ciucci F
2017 Water splitting with an enhanced bifunctional double
perovskite ACS Catal. 8 364–71
[39] Wang W, Xu M, Xu X, Zhou W and Shao Z 2019 Perovskite
oxide‐based electrodes for high‐performance
photoelectrochemical water splitting: a review Angew.
Chem. Int. Ed. 59 136–52
[40] Zhu Y, Zhou W, Sunarso J, Zhong Y and Shao Z 2016
Phosphorus‐doped perovskite oxide as highly efficient water
oxidation electrocatalyst in alkaline solution Adv. Funct.
Mater. 26 5862–72
[41] Fujito H, Kunioku H, Kato D, Suzuki H, Higashi M,
Kageyama H and Abe R 2016 Layered perovskite
oxychloride Bi4NbO8Cl: a stable visible light responsive
14
Nanotechnology 32 (2021) 485407 P Kumar et al
16. photocatalyst for water splitting J. Am. Chem. Soc. 138
2082–5
[42] Kumar P, Boukherroub R and Shankar K 2018 sunlight-
driven water-splitting using two-dimensional carbon based
semiconductors J. Mater. Chem. A 6 12876–931
[43] Ong W-J, Tan L-L, Ng Y H, Yong S-T and Chai S-P 2016
Graphitic carbon nitride (g-C3N4)-based photocatalysts for
artificial photosynthesis and environmental remediation: are
we a step closer to achieving sustainability? Chem. Rev. 116
7159–329
[44] Ye S, Wang R, Wu M-Z and Yuan Y-P 2015 A review on
g-C3N4 for photocatalytic water splitting and CO2 reduction
Appl. Surf. Sci. 358 15–27
[45] Martin D J, Reardon P J T, Moniz S J and Tang J 2014
Visible light-driven pure water splitting by a nature-inspired
organic semiconductor-based system J. Am. Chem. Soc. 136
12568–71
[46] Zhang Y, Liu J, Wu G and Chen W 2012 Porous graphitic
carbon nitride synthesized via direct polymerization of urea
for efficient sunlight-driven photocatalytic hydrogen
production Nanoscale 4 5300–3
[47] Zhang Y, Mori T, Ye J and Antonietti M 2010 Phosphorus-
doped carbon nitride solid: enhanced electrical conductivity
and photocurrent generation J. Am. Chem. Soc. 132 6294–5
[48] Jiang L, Yuan X, Pan Y, Liang J, Zeng G, Wu Z and Wang H
2017 Doping of graphitic carbon nitride for photocatalysis: a
reveiw Appl. Catal. B 217 388–406
[49] Kumar P et al 2019 C3N5: a low bandgap semiconductor
containing an azo-linked carbon nitride framework for
photocatalytic, photovoltaic and adsorbent applications
J. Am. Chem. Soc. 141 5415–36
[50] Chauhan D K, Jain S, Battula V R and Kailasam K 2019
Organic motif’s functionalization via covalent linkage in
carbon nitride: an exemplification in photocatalysis Carbon
152 40–58
[51] Shiraishi Y, Kanazawa S, Kofuji Y, Sakamoto H, Ichikawa S,
Tanaka S and Hirai T 2014 Sunlight‐driven hydrogen
peroxide production from water and molecular oxygen by
metal‐free photocatalysts Angew. Chem. Int. Ed. 53 13454–9
[52] Kumar P, Thakur U K, Alam K, Kar P, Kisslinger R, Zeng S,
Patel S and Shankar K 2018 Arrays of TiO2 nanorods
embedded with fluorine doped carbon nitride quantum dots
(CNFQDs) for visible light driven water splitting Carbon
137 174–87
[53] Zhao Z, Sun Y and Dong F 2015 Graphitic carbon nitride
based nanocomposites: a review Nanoscale 7 15–37
[54] Zhou L, Zhang H, Sun H, Liu S, Tade M O, Wang S and
Jin W 2016 Recent advances in non-metal modification of
graphitic carbon nitride for photocatalysis: a historic review
Catal. Sci. Technol. 6 7002–23
[55] Zhang J, Zhang M, Lin L and Wang X 2015 Sol processing of
conjugated carbon nitride powders for thin‐film fabrication
Angew. Chem. Int. Ed. 54 6297–301
[56] Yang S, Gong Y, Zhang J, Zhan L, Ma L, Fang Z, Vajtai R,
Wang X and Ajayan P M 2013 Exfoliated graphitic carbon
nitride nanosheets as efficient catalysts for hydrogen
evolution under visible light Adv. Mater. 25 2452–6
[57] Niu P, Zhang L, Liu G and Cheng H M 2012 Graphene‐like
carbon nitride nanosheets for improved photocatalytic
activities Adv. Funct. Mater. 22 4763–70
[58] Schwinghammer K, Mesch M B, Duppel V, Ziegler C,
Senker J R and Lotsch B V 2014 Crystalline carbon nitride
nanosheets for improved visible-light hydrogen evolution
J. Am. Chem. Soc. 136 1730–3
[59] Kang Y, Yang Y, Yin L C, Kang X, Wang L, Liu G and
Cheng H M 2016 Selective breaking of hydrogen bonds of
layered carbon nitride for visible light photocatalysis Adv.
Mater. 28 6471–7
[60] Ou H, Lin L, Zheng Y, Yang P, Fang Y and Wang X 2017
Tri‐s‐triazine‐based crystalline carbon nitride nanosheets for
an improved hydrogen evolution Adv. Mater. 29 1700008
[61] Jiang J, Ou-yang L, Zhu L, Zheng A, Zou J, Yi X and Tang H
2014 Dependence of electronic structure of g-C3N4 on the
layer number of its nanosheets: a study by Raman
spectroscopy coupled with first-principles calculations
Carbon 80 213–21
[62] Zhang R and Yang J 2015 Few-layer C2N: a promising
metal-free photocatalyst for water splitting arXiv:1505.
02768
[63] Zhang R, Li B and Yang J 2015 Effects of stacking order,
layer number and external electric field on electronic
structures of few-layer C 2 N-h 2D Nanoscale 7 14062–70
[64] Dong X and Cheng F 2015 Recent development in exfoliated
two-dimensional gC3N4 nanosheets for photocatalytic
applications J. Mater. Chem. A 3 23642–52
[65] Ran J, Guo W, Wang H, Zhu B, Yu J and Qiao S-Z 2018
Metal-free 2D/2D phosphorene/g-C3N4 Van der Waals
heterojunction for highly enhanced visible-light
photocatalytic H2 production Adv. Mater. 30 1800128
[66] Dong G, Qiu P, Meng F, Wang Y, He B, Yu Y, Liu X and
Li Z 2020 Facile synthesis of sulfur-doped polymeric carbon
nitride/MoS2 face-to-face heterojunction for highly efficient
photocatalytic interfacial charge separation Chem. Eng. J.
384 123330
[67] Alam K M, Kumar P, Kar P, Goswami A, Thakur U K,
Zeng S, Vahidzadeh E, Cui K and Shankar K 2019
Heterojunctions of halogen-doped carbon nitride nanosheets
and BiOI for sunlight-driven water-splitting Nanotechnology
31 084001
[68] Ott C et al 2019 Flexible and ultrasoft inorganic 1D
semiconductor and heterostructure systems based on SnIP
Adv. Funct. Mater. 29 1900233
[69] Alam K M, Kumar P, Kar P, Thakur U K, Zeng S, Cui K and
Shankar K 2019 Enhanced charge separation in
g-C3N4–BiOI heterostructures for visible light driven
photoelectrochemical water splitting Nanoscale Adv. 1
1460–71
[70] Jiang D, Wang T, Xu Q, Li D, Meng S and Chen M 2017
Perovskite oxide ultrathin nanosheets/g-C3N4 2D-2D
heterojunction photocatalysts with significantly enhanced
photocatalytic activity towards the photodegradation of
tetracycline Appl. Catal. B 201 617–28
[71] Shi J, Mao L, Cai C, Li G, Cheng C, Zheng B, Hu Y,
Huang Z, Hu X and Żyła G 2020 One-pot fabrication of 2D/
2D HCa2Nb3O10/g-C3N4 type II heterojunctions towards
enhanced photocatalytic H2 evolution under visible-light
irradiation Catal. Sci. Technol. 10 5896–902
[72] Xu Y, Cao H, Xue Y, Li B and Cai W 2018 Liquid-phase
exfoliation of graphene: an overview on exfoliation media,
techniques, and challenges Nanomaterials 8 942
[73] Hamilton C E, Lomeda J R, Sun Z, Tour J M and Barron A R
2009 High-yield organic dispersions of unfunctionalized
graphene Nano Lett. 9 3460–2
[74] Li B, Hong S, Zhang X, Xiong C, Zhao G, Yang Q and Liu H
2019 Understanding interfacial mechanics and mechanisms
of exfoliation and stabilization of graphene using urea/
glycerol solvents Adv. Theory Simul. 2 1900155
[75] Chen J et al 2015 A binary solvent system for improved
liquid phase exfoliation of pristine graphene materials
Carbon 94 405–11
[76] Mulmi S, Chen H, Hassan A, Marco J F, Berry F J, Sharif F,
Slater P R, Roberts E P, Adams S and Thangadurai V 2017
Thermochemical CO2 splitting using double perovskite-type
Ba2Ca0.66Nb1.34−xFexO6−δ J. Mater. Chem. A 5 6874–83
[77] He F, Chen G, Yu Y, Zhou Y, Zheng Y and Hao S 2015 The
synthesis of condensed C-PDA–g-C3N4 composites with
15
Nanotechnology 32 (2021) 485407 P Kumar et al
17. superior photocatalytic performance Chem. Commun. 51
6824–7
[78] Axen N, Botton G, Somekh R and Hutchings I 1996 Effect of
deposition conditions on the chemical bonding in sputtered
carbon nitride films Diam. Relat. Mater. 5 163–8
[79] Talapaneni S N, Mane G P, Park D-H, Lakhi K S,
Ramadass K, Joseph S, Skinner W M, Ravon U,
Al-Bahily K and Vinu A 2017 Diaminotetrazine based
mesoporous C3N6 with a well-ordered 3D cubic structure
and its excellent photocatalytic performance for hydrogen
evolution J. Mater. Chem. A 5 18183–92
[80] Mane G P, Dhawale D S, Anand C, Ariga K, Ji Q,
Wahab M A, Mori T and Vinu A 2013 Selective sensing
performance of mesoporous carbon nitride with a highly
ordered porous structure prepared from 3-amino-1, 2,
4-triazine J. Mater. Chem. A 1 2913–20
[81] Mane G P, Talapaneni S N, Lakhi K S, Ilbeygi H, Ravon U,
Al‐Bahily K, Mori T, Park D H and Vinu A 2017 Highly
ordered nitrogen‐rich mesoporous carbon nitrides and their
superior performance for sensing and photocatalytic
hydrogen generation Angew. Chem. Int. Ed. 56 8481–5
[82] Yi S-S, Yan J-M, Wulan B-R, Li S-J, Liu K-H and Jiang Q
2017 Noble-metal-free cobalt phosphide modified carbon
nitride: an efficient photocatalyst for hydrogen generation
Appl. Catal. B 200 477–83
[83] Kumar A, Kumar P, Borkar R, Bansiwal A,
Labhsetwar N and Jain S L 2017 Metal-organic hybrid:
photoreduction of CO2 using graphitic carbon nitride
supported heteroleptic iridium complex under visible light
irradiation Carbon 123 371–9
[84] Xia P, Zhu B, Yu J, Cao S and Jaroniec M 2017 Ultra-thin
nanosheet assemblies of graphitic carbon nitride for
enhanced photocatalytic CO2 reduction J. Mater. Chem. A 5
3230–8
[85] Xu X, Chen Y, Zhou W, Zhong Y, Guan D and Shao Z 2018
Earth‐abundant silicon for facilitating water oxidation over
iron‐based perovskite electrocatalyst Adv. Mater. Interfaces
5 1701693
[86] Yu S, Li J, Zhang Y, Li M, Dong F, Zhang T and Huang H
2018 Local spatial charge separation and proton activation
induced by surface hydroxylation promoting photocatalytic
hydrogen evolution of polymeric carbon nitride Nano
Energy 50 383–92
[87] Du X, Zou G, Wang Z and Wang X 2015 A scalable chemical
route to soluble acidified graphitic carbon nitride: an ideal
precursor for isolated ultrathin gC3N4 nanosheets Nanoscale
7 8701–6
[88] Guo S, Zhu Y, Yan Y, Min Y, Fan J and Xu Q 2016 Holey
structured graphitic carbon nitride thin sheets with edge
oxygen doping via photo-Fenton reaction with enhanced
photocatalytic activity Appl. Catal. B 185 315–21
[89] Ananyev M, Eremin V, Tsvetkov D, Porotnikova N,
Farlenkov A, Zuev A Y, Fetisov A and Kurumchin E K
2017 Oxygen isotope exchange and diffusion in
LnBaCo2O6−δ (Ln=Pr, Sm, Gd) with double perovskite
structure Solid State Ion. 304 96–106
[90] Guo D, Hua H, Hu C and Xi Y 2013 Defect-induced and UV-
irradiation-enhanced ferromagnetism in cubic barium
niobate J. Phys. Chem. C 117 14281–8
[91] Roy P, Waghmare V, Tanwar K and Maiti T 2017 Large
change in thermopower with temperature driven p–n type
conduction switching in environment friendly
BaxSr2−xTi0.8Fe0.8Nb0.4O6 double perovskites Phys. Chem.
Chem. Phys. 19 5818–29
[92] Srisombat L, Ananta S, Singhana B, Lee T R and Yimnirun R
2013 Chemical investigation of Fe3+
/Nb5+
-doped barium
titanate ceramics Ceram. Int. 39 S591–4
[93] Jin F, Shen Y, Wang R and He T 2013 Double-perovskite
PrBaCo2/3Fe2/3Cu2/3O5+δ as cathode material for
intermediate-temperature solid-oxide fuel cells J. Power
Sources 234 244–51
[94] Kan W H, Chen M, Bae J-S, Kim B-H and Thangadurai V
2014 Determination of Fe oxidation states in the B-site
ordered perovskite-type Ba2Ca0.67Fe0.33NbO6−δ at the
surface (nano-scale) and bulk by variable temperature XPS
and TGA and their impact on electrochemical catalysis
J. Mater. Chem. A 2 8736–41
[95] Zhao K, Li L, Zheng A, Huang Z, He F, Shen Y, Wei G,
Li H and Zhao Z 2017 Synergistic improvements in stability
and performance of the double perovskite-type oxides
La2−xSrxFeCoO6 for chemical looping steam methane
reforming Appl. Energy 197 393–404
[96] Sun H, Chen G, Zhu Y, Liu B, Zhou W and Shao Z 2017 B‐
site cation ordered double perovskites as efficient and stable
electrocatalysts for oxygen evolution reaction Chem.–Eur. J.
23 5722–8
[97] Peng G, Xing L, Barrio J, Volokh M and Shalom M 2018 A
general synthesis of porous carbon nitride films with tunable
surface area and photophysical properties Angew. Chem. Int.
Ed. 57 1186–92
[98] Xue Z, Liu F, Jiang J, Wang J and Mu T 2017 Scalable and
super-stable exfoliation of graphitic carbon nitride in
biomass-derived γ-valerolactone: enhanced catalytic activity
for the alcoholysis and cycloaddition of epoxides with CO2
Green Chem. 19 5041–5
[99] Jian X, Liu X, Yang H-M, Li J-G, Song X-L, Dai H-Y and
Liang Z-H 2016 Construction of carbon quantum dots/
proton-functionalized graphitic carbon nitride
nanocomposite via electrostatic self-assembly strategy and
its application Appl. Surf. Sci. 370 514–21
[100] Tian H, Liu M and Zheng W 2018 Constructing 2D graphitic
carbon nitride nanosheets/layered MoS2/graphene ternary
nanojunction with enhanced photocatalytic activity Appl.
Catal. B 225 468–76
[101] Niu P, Yin L C, Yang Y Q, Liu G and Cheng H M 2014
Increasing the visible light absorption of graphitic carbon
nitride (Melon) photocatalysts by homogeneous self‐
modification with nitrogen vacancies Adv. Mater. 26
8046–52
[102] Li Q, Yang J, Feng D, Wu Z, Wu Q, Park S S, Ha C-S and
Zhao D 2010 Facile synthesis of porous carbon nitride
spheres with hierarchical three-dimensional mesostructures
for CO2 capture Nano Res. 3 632–42
[103] Fu Y, Zhu J, Hu C, Wu X and Wang X 2014 Covalently
coupled hybrid of graphitic carbon nitride with reduced
graphene oxide as a superior performance lithium-ion
battery anode Nanoscale 6 12555–64
[104] Kumar S, Kumar P and Jain S L 2014 Graphene oxide
immobilized copper phthalocyanine tetrasulphonamide: the
first heterogenized homogeneous catalyst for
dimethylcarbonate synthesis from CO2 and methanol
J. Mater. Chem. A 2 18861–6
[105] Xu C, Han Q, Zhao Y, Wang L, Li Y and Qu L 2015 Sulfur-
doped graphitic carbon nitride decorated with graphene
quantum dots for an efficient metal-free electrocatalyst
J. Mater. Chem. A 3 1841–6
[106] Mou Z, Dong Y, Li S, Du Y, Wang X, Yang P and Wang S
2011 Eosin Y functionalized graphene for photocatalytic
hydrogen production from water Int. J. Hydrog. Energy 36
8885–93
[107] Li C, Li X, Sun X, Zhang X, Duan L, Yang X, Wang L and
Lü W 2019 Porous carbon networks derived from graphitic
carbon nitride for efficient oxygen reduction reaction
Nanoscale Res. Lett. 14 249
16
Nanotechnology 32 (2021) 485407 P Kumar et al
18. [108] Chowdhury A K M S, Cameron D C and Hashmi M S J 1998
Vibrational properties of carbon nitride films by Raman
spectroscopy Thin Solid Films 332 62–8
[109] Suter T et al 2018 Synthesis, structure and electronic
properties of graphitic carbon nitride films J. Phys. Chem. C
122 25183–94
[110] Kaufman J, Metin S and Saperstein D 1989 Symmetry
breaking in nitrogen-doped amorphous carbon: infrared
observation of the Raman-active G and D bands Phys. Rev.
B 39 13053
[111] Gonçalves R, Lima T M, Paixão M W and Pereira E C 2018
Pristine carbon nitride as active material for high-
performance metal-free supercapacitors: simple, easy and
cheap RSC Adv. 8 35327–36
[112] Hernández-Torres J, Gutierrez-Franco A, González P,
García-González L, Hernandez-Quiroz T, Zamora-Peredo L,
Méndez-García V and Cisneros-de la Rosa A 2016
Photoluminescence and Raman spectroscopy studies of
carbon nitride films J. Spectrosc. 2016 5810592
[113] Kan W H, Roushanafshar M, Vincent A, Fürstenhaupt T,
Parvez M, Luo J and Thangadurai V 2013 Effect of
substitution of B-sites by Mn, Fe and Co in double
perovskite-type Ba3CaNb2O9 on structure and electrical
properties RSC Adv. 3 23824–32
[114] Mulmi S and Thangadurai V 2013 Preparation, structure and
CO2 sensor studies of BaCa0.33Nb0.67−xFexO3−δ
J. Electrochem. Soc. 160 B95–101
[115] Yang P, Zhao J, Qiao W, Li L and Zhu Z 2015 Ammonia-
induced robust photocatalytic hydrogen evolution of
graphitic carbon nitride Nanoscale 7 18887–90
[116] Song X, Yang Q, Jiang X, Yin M and Zhou L 2017 Porous
graphitic carbon nitride nanosheets prepared under self-
producing atmosphere for highly improved photocatalytic
activity Appl. Catal. B 217 322–30
[117] Kumar A, Kumar P, Joshi C, Ponnada S, Pathak A K, Ali A,
Sreedhar B and Jain S L 2016 A [Fe (bpy) 3] 2+grafted
graphitic carbon nitride hybrid for visible light assisted
oxidative coupling of benzylamines under mild reaction
conditions Green Chem. 18 2514–21
[118] Cui Y, Zhang J, Zhang G, Huang J, Liu P, Antonietti M and
Wang X 2011 Synthesis of bulk and nanoporous carbon nitride
polymers from ammonium thiocyanate for photocatalytic
hydrogen evolution J. Mater. Chem. 21 13032–9
[119] Tonda S, Kumar S, Kandula S and Shanker V 2014 Fe-doped
and-mediated graphitic carbon nitride nanosheets for
enhanced photocatalytic performance under natural sunlight
J. Mater. Chem. A 2 6772–80
[120] Jiang J, Ou-yang L, Zhu L, Zheng A, Zou J, Yi X and Tang H
2014 Dependence of electronic structure of gC3N4 on the
layer number of its nanosheets: a study by Raman
spectroscopy coupled with first-principles calculations
Carbon 80 213–21
[121] Zhang M, Duan Y, Jia H, Wang F, Wang L, Su Z and
Wang C 2017 Defective graphitic carbon nitride synthesized
by controllable co-polymerization with enhanced visible
light photocatalytic hydrogen evolution Catal. Sci. Technol.
7 452–8
[122] Jiang Z, Zhu C, Wan W, Qian K and Xie J 2016 Constructing
graphite-like carbon nitride modified hierarchical yolk–shell
TiO2 spheres for water pollution treatment and hydrogen
production J. Mater. Chem. A 4 1806–18
[123] Liu S, Ke J, Sun H, Liu J, Tade M O and Wang S 2017 Size
dependence of uniformed carbon spheres in promoting
graphitic carbon nitride toward enhanced photocatalysis
Appl. Catal. B 204 358–64
[124] Jing L, Ong W-J, Zhang R, Pickwell-MacPherson E and
Jimmy C Y 2018 Graphitic carbon nitride nanosheet
wrapped mesoporous titanium dioxide for enhanced
photoelectrocatalytic water splitting Catal. Today 315 103–9
[125] Zhang Y, Pan Q, Chai G, Liang M, Dong G, Zhang Q and
Qiu J 2013 Synthesis and luminescence mechanism of
multicolor-emitting gC3N4 nanopowders by low temperature
thermal condensation of melamine Sci. Rep. 3 1943
[126] Zhang M, Bai X, Liu D, Wang J and Zhu Y 2015 Enhanced
catalytic activity of potassium-doped graphitic carbon nitride
induced by lower valence position Appl. Catal. B 164 77–81
[127] Ahmad H, Kamarudin S, Minggu L and Kassim M 2015
Hydrogen from photo-catalytic water splitting process: a
review Renew. Sustain. Energy Rev. 43 599–610
[128] Zheng D, Cao X N and Wang X 2016 Precise formation of a
hollow carbon nitride structure with a janus surface to
promote water splitting by photoredox catalysis Angew.
Chem. Int. Ed. 55 11512–6
[129] Pan Z, Zheng Y, Guo F, Niu P and Wang X 2017 Decorating
CoP and Pt nanoparticles on graphitic carbon nitride
nanosheets to promote overall water splitting by conjugated
polymers ChemSusChem 10 87–90
[130] Wang X, Blechert S and Antonietti M 2012 Polymeric
graphitic carbon nitride for heterogeneous photocatalysis
ACS Catal. 2 1596–606
[131] Kessler F K, Zheng Y, Schwarz D, Merschjann C,
Schnick W, Wang X and Bojdys M J 2017 Functional
carbon nitride materials—design strategies for
electrochemical devices Nat. Rev. Mater. 2 17030
17
Nanotechnology 32 (2021) 485407 P Kumar et al