Single-atom catalysts (SACs) aim at bridging the gap between homogeneous and heterogeneous catalysis. The challenge is the development of materials with ligands enabling coordination of metal atoms in different valence states, and preventing leaching or nanoparticle formation. Graphene functionalized with nitrile groups (cyanographene) is herein employed for the robust coordination of Cu(II) ions, which are partially reduced to Cu(I) due to graphene-induced charge transfer. Inspired by nature's selection of Cu(I) in enzymes for oxygen activation, this 2D mixed-valence SAC performs flawlessly in two O2-mediated reactions: the oxidative coupling of amines and the oxidation of benzylic CH bonds toward high-value pharmaceutical synthons. High conversions (up to 98%), selectivities (up to 99%), and recyclability are attained with very low metal loadings in the reaction. The synergistic effect of Cu(II) and Cu(I) is the essential part in the reaction mechanism. The developed strategy opens the door to a broad portfolio of other SACs via their coordination to various functional groups of graphene, as demonstrated by successful entrapment of FeIII/FeII single atoms to carboxy-graphene.
Vapor growth of binary and ternary phosphorus-based semiconductors into TiO2 ...Pawan Kumar
We report successful synthesis of low band gap inorganic polyphosphide and TiO2 heterostructures with the aid of short-way transport reactions. Binary and ternary polyphosphides (NaP7, SnIP, and (CuI)3P12) were successfully reacted and deposited into electrochemically fabricated TiO2 nanotubes. Employing vapor phase reaction deposition, the cavities of 100 μm long TiO2 nanotubes were infiltrated; approximately 50% of the nanotube arrays were estimated to be infiltrated in the case of NaP7. Intensive characterization of the hybrid materials with techniques including SEM, FIB, HR-TEM, Raman spectroscopy, XRD, and XPS proved the successful vapor phase deposition and synthesis of the substances on and inside the nanotubes. The polyphosphide@TiO2 hybrids exhibited superior water splitting performance compared to pristine materials and were found to be more active at higher wavelengths. SnIP@TiO2 emerged to be the most active among the polyphosphide@TiO2 materials. The improved photocatalytic performance might be due to Fermi level re-alignment and a lower charge transfer resistance which facilitated better charge separation from inorganic phosphides to TiO2.
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 intra sheet cavity make it an attractive supramolecular adsorbent for environmental applications.
Asymmetric Multipole Plasmon-Mediated Catalysis Shifts the Product Selectivit...Pawan Kumar
Cu/TiO2 is a well-known photocatalyst for the photocatalytic transformation of CO2 into methane. The formation of C2+ products such as ethane and ethanol rather than methane is more interesting due to their higher energy density and economic value, but the formation of C–C bonds is currently a major challenge in CO2 photoreduction. In this context, we report the dominant formation of a C2 product, namely, ethane, from the gas-phase photoreduction of CO2 using TiO2 nanotube arrays (TNTAs) decorated with large-sized (80–200 nm) Ag and Cu nanoparticles without the use of a sacrificial agent or hole scavenger. Isotope-labeled mass spectrometry was used to verify the origin and identity of the reaction products. Under 2 h AM1.5G 1-sun illumination, the total rate of hydrocarbon production (methane + ethane) was highest for AgCu-TNTA with a total CxH2x+2 rate of 23.88 μmol g–1 h–1. Under identical conditions, the CxH2x+2 production rates for Ag-TNTA and Cu-TNTA were 6.54 and 1.39 μmol g–1 h–1, respectively. The ethane selectivity was the highest for AgCu-TNTA with 60.7%, while the ethane selectivity was found to be 15.9 and 10% for the Ag-TNTA and Cu-TNTA, respectively. Adjacent adsorption sites in our photocatalyst develop an asymmetric charge distribution due to quadrupole resonances in large metal nanoparticles and multipole resonances in Ag–Cu heterodimers. Such an asymmetric charge distribution decreases adsorbate–adsorbate repulsion and facilitates C–C coupling of reaction intermediates, which otherwise occurs poorly in TNTAs decorated with small metal nanoparticles.
Visible light assisted photocatalytic reduction of CO2 using a graphene oxide...Pawan Kumar
A new heteroleptic ruthenium complex containing 2-thiophenyl benzimidazole ligands was synthesized using a microwave technique and was immobilized to graphene oxide via covalent attachment. The synthesized catalyst was used for the photoreduction of carbon dioxide under visible light irradiation without using a sacrificial agent, which gave 2050 μmol g−1 cat methanol after 24 h of irradiation
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.
Consistently High Voc Values in p-i-n Type Perovskite Solar Cells Using Ni3+-...Pawan Kumar
Leading edge p-i-n type halide perovskite solar cells (PSCs) severely underperform n-i-p PSCs. p-i-n type PSCs that use PEDOT:PSS hole transport layers (HTLs) struggle to generate open-circuit photovoltage values higher than 1 V. NiO HTLs have shown greater promise in achieving high Voc values albeit inconsistently. In this report, a NiO nanomesh with Ni3+ defect grown by the hydrothermal method was used to obtain PSCs with Voc values that consistently exceeded 1.10 V (champion Voc = 1.14 V). A champion device photoconversion efficiency of 17.75% was observed. Density functional theory modeling was used to understand the interfacial properties of the NiO/perovskite interface. The PCE of PSCs constructed using the Ni3+-doped NiO nanomesh HTL was ∼34% higher than that of conventional compact NiO-based perovskite solar cells. A suite of characterization techniques such as transmission electron microscopy, field emission scanning electron microscopy, intensity-modulated photocurrent spectroscopy, intensity-modulated photovoltage spectroscopy, time-resolved photoluminescence, steady-state photoluminescence, and Kelvin probe force microscopy provided evidence of better film quality, enhanced charge transfer, and suppressed charge recombination in PSCs based on hydrothermally grown NiO nanostructures.
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.
Harvesting Hot Holes in Plasmon-Coupled Ultrathin Photoanodes for High-Perfor...Pawan Kumar
The harvesting of hot carriers produced by plasmon decay to generate electricity or drive a chemical reaction enables the reduction of the thermalization losses associated with supra-band gap photons in semiconductor photoelectrochemical (PEC) cells. Through the broadband harvesting of light, hot-carrier PEC devices also produce a sensitizing effect in heterojunctions with wide-band gap metal oxide semiconductors possessing good photostability and catalytic activity but poor absorption of visible wavelength photons. There are several reports of hot electrons in Au injected over the Schottky barrier into crystalline TiO2 and subsequently utilized to drive a chemical reaction but very few reports of hot hole harvesting. In this work, we demonstrate the efficient harvesting of hot holes in Au nanoparticles (Au NPs) covered with a thin layer of amorphous TiO2 (a-TiO2). Under AM1.5G 1 sun illumination, photoanodes consisting of a single layer of ∼50 nm diameter Au NPs coated with a 10 nm shell of a-TiO2 (Au@a-TiO2) generated 2.5 mA cm–2 of photocurrent in 1 M KOH under 0.6 V external bias, rising to 3.7 mA cm–2 in the presence of a hole scavenger (methanol). The quantum yield for hot-carrier-mediated photocurrent generation was estimated to be close to unity for high-energy photons (λ < 420 nm). Au@a-TiO2 photoelectrodes produced a small positive photocurrent of 0.1 mA cm–2 even at a bias of −0.6 V indicating extraction of hot holes even at a strong negative bias. These results together with density functional theory modeling and scanning Kelvin probe force microscope data indicate fast injection of hot holes from Au NPs into a-TiO2 and light harvesting performed near-exclusively by Au NPs. For comparison, Au NPs coated with a 10 nm shell of Al2O3 (Au@Al2O3) generated 0.02 mA cm–2 of photocurrent in 1 M KOH under 0.6 V external bias. These results underscore the critical role played by a-TiO2 in the extraction of holes in Au@a-TiO2 photoanodes, which is not replicated by an ordinary dielectric shell. It is also demonstrated here that an ultrathin photoanode (<100 nm in maximum thickness) can efficiently drive sunlight-driven water splitting.
Vapor growth of binary and ternary phosphorus-based semiconductors into TiO2 ...Pawan Kumar
We report successful synthesis of low band gap inorganic polyphosphide and TiO2 heterostructures with the aid of short-way transport reactions. Binary and ternary polyphosphides (NaP7, SnIP, and (CuI)3P12) were successfully reacted and deposited into electrochemically fabricated TiO2 nanotubes. Employing vapor phase reaction deposition, the cavities of 100 μm long TiO2 nanotubes were infiltrated; approximately 50% of the nanotube arrays were estimated to be infiltrated in the case of NaP7. Intensive characterization of the hybrid materials with techniques including SEM, FIB, HR-TEM, Raman spectroscopy, XRD, and XPS proved the successful vapor phase deposition and synthesis of the substances on and inside the nanotubes. The polyphosphide@TiO2 hybrids exhibited superior water splitting performance compared to pristine materials and were found to be more active at higher wavelengths. SnIP@TiO2 emerged to be the most active among the polyphosphide@TiO2 materials. The improved photocatalytic performance might be due to Fermi level re-alignment and a lower charge transfer resistance which facilitated better charge separation from inorganic phosphides to TiO2.
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 intra sheet cavity make it an attractive supramolecular adsorbent for environmental applications.
Asymmetric Multipole Plasmon-Mediated Catalysis Shifts the Product Selectivit...Pawan Kumar
Cu/TiO2 is a well-known photocatalyst for the photocatalytic transformation of CO2 into methane. The formation of C2+ products such as ethane and ethanol rather than methane is more interesting due to their higher energy density and economic value, but the formation of C–C bonds is currently a major challenge in CO2 photoreduction. In this context, we report the dominant formation of a C2 product, namely, ethane, from the gas-phase photoreduction of CO2 using TiO2 nanotube arrays (TNTAs) decorated with large-sized (80–200 nm) Ag and Cu nanoparticles without the use of a sacrificial agent or hole scavenger. Isotope-labeled mass spectrometry was used to verify the origin and identity of the reaction products. Under 2 h AM1.5G 1-sun illumination, the total rate of hydrocarbon production (methane + ethane) was highest for AgCu-TNTA with a total CxH2x+2 rate of 23.88 μmol g–1 h–1. Under identical conditions, the CxH2x+2 production rates for Ag-TNTA and Cu-TNTA were 6.54 and 1.39 μmol g–1 h–1, respectively. The ethane selectivity was the highest for AgCu-TNTA with 60.7%, while the ethane selectivity was found to be 15.9 and 10% for the Ag-TNTA and Cu-TNTA, respectively. Adjacent adsorption sites in our photocatalyst develop an asymmetric charge distribution due to quadrupole resonances in large metal nanoparticles and multipole resonances in Ag–Cu heterodimers. Such an asymmetric charge distribution decreases adsorbate–adsorbate repulsion and facilitates C–C coupling of reaction intermediates, which otherwise occurs poorly in TNTAs decorated with small metal nanoparticles.
Visible light assisted photocatalytic reduction of CO2 using a graphene oxide...Pawan Kumar
A new heteroleptic ruthenium complex containing 2-thiophenyl benzimidazole ligands was synthesized using a microwave technique and was immobilized to graphene oxide via covalent attachment. The synthesized catalyst was used for the photoreduction of carbon dioxide under visible light irradiation without using a sacrificial agent, which gave 2050 μmol g−1 cat methanol after 24 h of irradiation
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.
Consistently High Voc Values in p-i-n Type Perovskite Solar Cells Using Ni3+-...Pawan Kumar
Leading edge p-i-n type halide perovskite solar cells (PSCs) severely underperform n-i-p PSCs. p-i-n type PSCs that use PEDOT:PSS hole transport layers (HTLs) struggle to generate open-circuit photovoltage values higher than 1 V. NiO HTLs have shown greater promise in achieving high Voc values albeit inconsistently. In this report, a NiO nanomesh with Ni3+ defect grown by the hydrothermal method was used to obtain PSCs with Voc values that consistently exceeded 1.10 V (champion Voc = 1.14 V). A champion device photoconversion efficiency of 17.75% was observed. Density functional theory modeling was used to understand the interfacial properties of the NiO/perovskite interface. The PCE of PSCs constructed using the Ni3+-doped NiO nanomesh HTL was ∼34% higher than that of conventional compact NiO-based perovskite solar cells. A suite of characterization techniques such as transmission electron microscopy, field emission scanning electron microscopy, intensity-modulated photocurrent spectroscopy, intensity-modulated photovoltage spectroscopy, time-resolved photoluminescence, steady-state photoluminescence, and Kelvin probe force microscopy provided evidence of better film quality, enhanced charge transfer, and suppressed charge recombination in PSCs based on hydrothermally grown NiO nanostructures.
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.
Harvesting Hot Holes in Plasmon-Coupled Ultrathin Photoanodes for High-Perfor...Pawan Kumar
The harvesting of hot carriers produced by plasmon decay to generate electricity or drive a chemical reaction enables the reduction of the thermalization losses associated with supra-band gap photons in semiconductor photoelectrochemical (PEC) cells. Through the broadband harvesting of light, hot-carrier PEC devices also produce a sensitizing effect in heterojunctions with wide-band gap metal oxide semiconductors possessing good photostability and catalytic activity but poor absorption of visible wavelength photons. There are several reports of hot electrons in Au injected over the Schottky barrier into crystalline TiO2 and subsequently utilized to drive a chemical reaction but very few reports of hot hole harvesting. In this work, we demonstrate the efficient harvesting of hot holes in Au nanoparticles (Au NPs) covered with a thin layer of amorphous TiO2 (a-TiO2). Under AM1.5G 1 sun illumination, photoanodes consisting of a single layer of ∼50 nm diameter Au NPs coated with a 10 nm shell of a-TiO2 (Au@a-TiO2) generated 2.5 mA cm–2 of photocurrent in 1 M KOH under 0.6 V external bias, rising to 3.7 mA cm–2 in the presence of a hole scavenger (methanol). The quantum yield for hot-carrier-mediated photocurrent generation was estimated to be close to unity for high-energy photons (λ < 420 nm). Au@a-TiO2 photoelectrodes produced a small positive photocurrent of 0.1 mA cm–2 even at a bias of −0.6 V indicating extraction of hot holes even at a strong negative bias. These results together with density functional theory modeling and scanning Kelvin probe force microscope data indicate fast injection of hot holes from Au NPs into a-TiO2 and light harvesting performed near-exclusively by Au NPs. For comparison, Au NPs coated with a 10 nm shell of Al2O3 (Au@Al2O3) generated 0.02 mA cm–2 of photocurrent in 1 M KOH under 0.6 V external bias. These results underscore the critical role played by a-TiO2 in the extraction of holes in Au@a-TiO2 photoanodes, which is not replicated by an ordinary dielectric shell. It is also demonstrated here that an ultrathin photoanode (<100 nm in maximum thickness) can efficiently drive sunlight-driven water splitting.
Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems...Pawan Kumar
Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic-scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer-like atomic-scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III-V, or II-VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.
Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C3N5 Co...Pawan Kumar
We present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C3N5 is a low-band-gap (Eg = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C3N5 nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged, while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C3N5 heterojunctions using density functional theory (DFT) simulations, finite difference time domain (FDTD) simulations, time-resolved terahertz spectroscopy (TRTS), and photoconductivity measurements. TRTS indicated high carrier mobilities >450 cm2 V–1 s–1 and carrier relaxation times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower mobilities <150 cm2 V–1 s–1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J–V characteristics of CdS NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C3N5 in CdS-MHP. C3N5, with its extended π-conjugation and low band gap, can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core–shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis.
TiO2-HfN Radial Nano-Heterojunction: A Hot Carrier Photoanode for Sunlight-Dr...Pawan Kumar
The lack of active, stable, earth-abundant, and visible-light absorbing materials to replace
plasmonic noble metals is a critical obstacle for researchers in developing highly efficient and costeffective photocatalytic systems. Herein, a core–shell nanotube catalyst was fabricated consisting of
atomic layer deposited HfN shell and anodic TiO2 support layer with full-visible regime photoactivity
for photoelectrochemical water splitting. The HfN active layer has two unique characteristics: (1) a
large bandgap between optical and acoustic phonon modes (2) and no electronic bandgap, which
allows a large population of long life-time hot carriers, which are used to enhance the photoelectrochemical performance. The photocurrent density (≈2.5 mA·cm−2 at 1 V vs. Ag/AgCl) obtained in
this study under AM 1.5G 1 Sun illumination is unprecedented, as it is superior to most existing
plasmonic noble metal-decorated catalysts and surprisingly indicates a photocurrent response that
extends to 730 nm. The result demonstrates the far-reaching application potential of replacing active
HER/HOR noble metals such as Au, Ag, Pt, Pd, etc. with low-cost plasmonic ceramics.
Synthesis of flower-like magnetite nanoassembly: Application in the efficient...Pawan Kumar
A facile approach for the synthesis of magnetite microspheres with flower-like morphology is reported that proceeds via the reduction of iron (III) oxide under hydrogen atmosphere. The ensuing magnetic catalyst is well characterized by XRD, FE-SEM, TEM, N2 adsorption-desorption isotherm and Mössbauer spectroscopy and explored for a simple yetbut efficient transfer hydrogenation reduction of a variety of nitroarenes to respective anilines in good to excellent yields (up to 98%) employing hydrazine hydrate. . The catalyst could be easily separated at the end of reaction using an external magnet and can be recycled up to 10 times without any loss in catalytic activity.
A ruthenium trinuclear polyazine complex was synthesized and subsequently immobilized through
complexation to a graphene oxide support containing phenanthroline ligands (GO-phen). The developed
photocatalyst was used for the photocatalytic reduction of CO2 to methanol, using a 20 watt white cold
LED flood light, in a dimethyl formamide–water mixture containing triethylamine as a reductive
quencher. After 48 h illumination, the yield of methanol was found to be 3977.57 5.60 mmol gcat
1.
The developed photocatalyst exhibited a higher photocatalytic activity than graphene oxide, which
provided a yield of 2201.40 8.76 mmol gcat
1. After the reaction, the catalyst was easily recovered and
reused for four subsequent runs without a significant loss of catalytic activity and no leaching of the
metal/ligand was detected during the reaction.
This work studied the effect of applying pulse current
(ton=off=1s) on the electrodeposition of silver nanoparticles on
carbon sphere surface as a substrate. The electrolyte is made of 0.1
M KNO3, 0.1 M KCN and 0.01M AgNO3. The pH value has been
adjusted in the alkaline region of 9.1 with the help of K(NO3)
addition. Experiments were carried out at room temperature for
periods up to 12 minutes. The cell is fitted with a mechanical stirrer
to keep the electrolyte in a dynamic state. Product(s) was
characterized with the help of SEM and EDX and field emission.
Results obtained show that silver nanoparticles has successfully
electrodeposited under pulse current conditions with a particle size
of 100–400 nm after 2 minutes. Deposition takes place on certain
accessible sites of the carbon surface of the substrate forming a
monolayer of scattered silver nanoparticles. Formation of macro
particles with larger diameter and multilayer in thickness takes
place with continuous deposition of silver nanoparticles on the
formerly deposited silver. Pulse current helps management of the
monolayer deposition as compared to the steady DC application
with respect to particle diameter and number of layers.
Electron transfer between methyl viologen radicals and graphene oxidekamatlab
Methyl viologen radicals are capable of transferring electrons to graphene oxide and partially restore the sp2 network. The reduced graphene oxide serves as a scaffold to anchor Ag nanoparticles. The growth of these silver nanoparticles is dictated by the ability of RGO to store and shuttle electrons. The RGO/Ag nanocomposites discussed in the present work offer new opportunities to design next generation photocatalysts.
Visit our website, KamatLab.com, for the latest news, publications, and research from our group.
Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems...Pawan Kumar
Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic-scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer-like atomic-scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III-V, or II-VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.
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-Free Sulfonate/Sulfate-Functionalized Carbon Nitride for Direct Convers...Pawan Kumar
Metal-free heteroatom-doped carbonaceous materials such as carbon nitride (CN) with secondary/tertiary nitrogen-rich catalytic centers as well as chemical and thermal resilience can potentially serve as catalysts for many organic reactions. However, because of the stable alternate Csp2–Nsp2 configuration of N-linked heptazine units (C6N7), the chemical modification of CN via doping and functionalization has been a critical challenge. Herein, we report an exceptional 9.2% sulfur content in CN with sulfonate/sulfate functional groups (CNS) via a one-step in situ synthesis approach. When used as a catalyst for the dehydration/hydration of glucose, CNS catalysts demonstrate a relatively high yield and selectivity toward levulinic acid, LLA, (≈48% yield with 57% selectivity) production. CNS’s high activity of direct conversion of glucose to LLA can be attributed to the synergistic catalytic effects of multiple sulfur functionalities, better dispersibility, and microstructural porosity. The synthesized CNS catalysts offer an energy efficient direct LLA production route to bypass the multistep process of sugar to LLA conversion.
Unusual Electronic Properties of Cellulose Nanocrystals Conjugated to Cobalt ...Pawan Kumar
Octacarboxylated cobalt phthalocyanine (CoPc) was covalently conjugated to cellulose nanocrystals (CNCs) by employing an esterification protocol. Solid-state NMR, X-ray photoelectron spectroscopy (XPS), Raman, and infrared spectra were used to verify and study the nature of covalent attachment responsible for the immobilization of CoPc on the CNC surface. The covalent attachment was investigated from a theoretical simulation perspective using dispersion-corrected density functional theory (DFT) calculations, which verified the stable bond formation between CNC and CoPc. CoPc is an organic semiconductor with a high exciton binding energy, and CNCs are known to be insulating. Yet, Kelvin probe force microscopy (KPFM) indicated charge carrier generation and long-lived charge separation in the CNC–CoPc conjugate compared to pristine CoPc under visible light illumination. Such behavior is more typical of a semiconductor nanocomposite. The CNC–CoPc conjugate exhibited superior performance in the visible-light-driven surface photocatalytic reduction of 4-nitrobenzenethiol (4-NBT) to p,p′-dimercaptoazobenzene (DMAB) and photodegradation of rhodamine B.
Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems...Pawan Kumar
Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic-scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer-like atomic-scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III-V, or II-VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.
Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C3N5 Co...Pawan Kumar
We present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C3N5 is a low-band-gap (Eg = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C3N5 nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged, while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C3N5 heterojunctions using density functional theory (DFT) simulations, finite difference time domain (FDTD) simulations, time-resolved terahertz spectroscopy (TRTS), and photoconductivity measurements. TRTS indicated high carrier mobilities >450 cm2 V–1 s–1 and carrier relaxation times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower mobilities <150 cm2 V–1 s–1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J–V characteristics of CdS NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C3N5 in CdS-MHP. C3N5, with its extended π-conjugation and low band gap, can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core–shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis.
TiO2-HfN Radial Nano-Heterojunction: A Hot Carrier Photoanode for Sunlight-Dr...Pawan Kumar
The lack of active, stable, earth-abundant, and visible-light absorbing materials to replace
plasmonic noble metals is a critical obstacle for researchers in developing highly efficient and costeffective photocatalytic systems. Herein, a core–shell nanotube catalyst was fabricated consisting of
atomic layer deposited HfN shell and anodic TiO2 support layer with full-visible regime photoactivity
for photoelectrochemical water splitting. The HfN active layer has two unique characteristics: (1) a
large bandgap between optical and acoustic phonon modes (2) and no electronic bandgap, which
allows a large population of long life-time hot carriers, which are used to enhance the photoelectrochemical performance. The photocurrent density (≈2.5 mA·cm−2 at 1 V vs. Ag/AgCl) obtained in
this study under AM 1.5G 1 Sun illumination is unprecedented, as it is superior to most existing
plasmonic noble metal-decorated catalysts and surprisingly indicates a photocurrent response that
extends to 730 nm. The result demonstrates the far-reaching application potential of replacing active
HER/HOR noble metals such as Au, Ag, Pt, Pd, etc. with low-cost plasmonic ceramics.
Synthesis of flower-like magnetite nanoassembly: Application in the efficient...Pawan Kumar
A facile approach for the synthesis of magnetite microspheres with flower-like morphology is reported that proceeds via the reduction of iron (III) oxide under hydrogen atmosphere. The ensuing magnetic catalyst is well characterized by XRD, FE-SEM, TEM, N2 adsorption-desorption isotherm and Mössbauer spectroscopy and explored for a simple yetbut efficient transfer hydrogenation reduction of a variety of nitroarenes to respective anilines in good to excellent yields (up to 98%) employing hydrazine hydrate. . The catalyst could be easily separated at the end of reaction using an external magnet and can be recycled up to 10 times without any loss in catalytic activity.
A ruthenium trinuclear polyazine complex was synthesized and subsequently immobilized through
complexation to a graphene oxide support containing phenanthroline ligands (GO-phen). The developed
photocatalyst was used for the photocatalytic reduction of CO2 to methanol, using a 20 watt white cold
LED flood light, in a dimethyl formamide–water mixture containing triethylamine as a reductive
quencher. After 48 h illumination, the yield of methanol was found to be 3977.57 5.60 mmol gcat
1.
The developed photocatalyst exhibited a higher photocatalytic activity than graphene oxide, which
provided a yield of 2201.40 8.76 mmol gcat
1. After the reaction, the catalyst was easily recovered and
reused for four subsequent runs without a significant loss of catalytic activity and no leaching of the
metal/ligand was detected during the reaction.
This work studied the effect of applying pulse current
(ton=off=1s) on the electrodeposition of silver nanoparticles on
carbon sphere surface as a substrate. The electrolyte is made of 0.1
M KNO3, 0.1 M KCN and 0.01M AgNO3. The pH value has been
adjusted in the alkaline region of 9.1 with the help of K(NO3)
addition. Experiments were carried out at room temperature for
periods up to 12 minutes. The cell is fitted with a mechanical stirrer
to keep the electrolyte in a dynamic state. Product(s) was
characterized with the help of SEM and EDX and field emission.
Results obtained show that silver nanoparticles has successfully
electrodeposited under pulse current conditions with a particle size
of 100–400 nm after 2 minutes. Deposition takes place on certain
accessible sites of the carbon surface of the substrate forming a
monolayer of scattered silver nanoparticles. Formation of macro
particles with larger diameter and multilayer in thickness takes
place with continuous deposition of silver nanoparticles on the
formerly deposited silver. Pulse current helps management of the
monolayer deposition as compared to the steady DC application
with respect to particle diameter and number of layers.
Electron transfer between methyl viologen radicals and graphene oxidekamatlab
Methyl viologen radicals are capable of transferring electrons to graphene oxide and partially restore the sp2 network. The reduced graphene oxide serves as a scaffold to anchor Ag nanoparticles. The growth of these silver nanoparticles is dictated by the ability of RGO to store and shuttle electrons. The RGO/Ag nanocomposites discussed in the present work offer new opportunities to design next generation photocatalysts.
Visit our website, KamatLab.com, for the latest news, publications, and research from our group.
Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems...Pawan Kumar
Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic-scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer-like atomic-scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III-V, or II-VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.
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-Free Sulfonate/Sulfate-Functionalized Carbon Nitride for Direct Convers...Pawan Kumar
Metal-free heteroatom-doped carbonaceous materials such as carbon nitride (CN) with secondary/tertiary nitrogen-rich catalytic centers as well as chemical and thermal resilience can potentially serve as catalysts for many organic reactions. However, because of the stable alternate Csp2–Nsp2 configuration of N-linked heptazine units (C6N7), the chemical modification of CN via doping and functionalization has been a critical challenge. Herein, we report an exceptional 9.2% sulfur content in CN with sulfonate/sulfate functional groups (CNS) via a one-step in situ synthesis approach. When used as a catalyst for the dehydration/hydration of glucose, CNS catalysts demonstrate a relatively high yield and selectivity toward levulinic acid, LLA, (≈48% yield with 57% selectivity) production. CNS’s high activity of direct conversion of glucose to LLA can be attributed to the synergistic catalytic effects of multiple sulfur functionalities, better dispersibility, and microstructural porosity. The synthesized CNS catalysts offer an energy efficient direct LLA production route to bypass the multistep process of sugar to LLA conversion.
Unusual Electronic Properties of Cellulose Nanocrystals Conjugated to Cobalt ...Pawan Kumar
Octacarboxylated cobalt phthalocyanine (CoPc) was covalently conjugated to cellulose nanocrystals (CNCs) by employing an esterification protocol. Solid-state NMR, X-ray photoelectron spectroscopy (XPS), Raman, and infrared spectra were used to verify and study the nature of covalent attachment responsible for the immobilization of CoPc on the CNC surface. The covalent attachment was investigated from a theoretical simulation perspective using dispersion-corrected density functional theory (DFT) calculations, which verified the stable bond formation between CNC and CoPc. CoPc is an organic semiconductor with a high exciton binding energy, and CNCs are known to be insulating. Yet, Kelvin probe force microscopy (KPFM) indicated charge carrier generation and long-lived charge separation in the CNC–CoPc conjugate compared to pristine CoPc under visible light illumination. Such behavior is more typical of a semiconductor nanocomposite. The CNC–CoPc conjugate exhibited superior performance in the visible-light-driven surface photocatalytic reduction of 4-nitrobenzenethiol (4-NBT) to p,p′-dimercaptoazobenzene (DMAB) and photodegradation of rhodamine B.
Partial Thermal Condensation Mediated Synthesis of High-Density Nickel Single...Pawan Kumar
Direct selective transformation of greenhouse methane (CH4) to liquid oxygenates (methanol) can substitute energy-intensive two-step (reforming/Fischer–Tropsch) synthesis while creating environmental benefits. The development of inexpensive, selective, and robust catalysts that enable room temperature conversion will decide the future of this technology. Single-atom catalysts (SACs) with isolated active centers embedded in support have displayed significant promises in catalysis to drive challenging reactions. Herein, high-density Ni single atoms are developed and stabilized on carbon nitride (NiCN) via thermal condensation of preorganized Ni-coordinated melem units. The physicochemical characterization of NiCN with various analytical techniques including HAADF-STEM and X-ray absorption fine structure (XAFS) validate the successful formation of Ni single atoms coordinated to the heptazine-constituted CN network. The presence of uniform catalytic sites improved visible absorption and carrier separation in densely populated NiCN SAC resulting in 100% selective photoconversion of (CH4) to methanol using H2O2 as an oxidant. The superior catalytic activity can be attributed to the generation of high oxidation (NiIII═O) sites and selective C─H bond cleavage to generate •CH3 radicals on Ni centers, which can combine with •OH radicals to generate CH3OH.
Synthesis & Characterization of Fluorescent Silver Nanoparticles stabilized b...IJERA Editor
Synthesis of silver nanoparticles (Ag-NPs) was achieved by a simple green procedure using Tinospora Cordifolia leaf extract as stabilizer/reducing agents. Ag-NPs in the size range of 2–19 nm is obtained by the treatment of aqueous silver ions with leaf extracts of Tinospora Cordifolia. This eco-friendly approach is simple, amenable for large scale commercial production and technical applications. Further, photoluminiscence studies of these Ag-NPs were recorded & suggested that the present particles were suitable for fluorescence emitting probes. These red emitting Ag-NPs exhibited distinct fluorescence properties (both emission and stokeshift).
Synthesis, spectroscopic, magnetic properties and superoxide dismutase (SOD) ...IOSR Journals
Three new ternary copper(II) complexes formulated as [Cu(HIda)(bipy)] 1; [Cu(HIda)(phen)] 2; [Cu(HIda)(dmp)] 3; where HIda =N-(2-hydroxyethyl)-2- iminodiacetic acid ; bipy = 2, 2’- bipyridine; phen = 1,10- phenanthroline; dmp = 2,9-dimethyl 1,10-phenanthroline, have been synthesized and characterized by partial elemental analysis, FAB-mass (m/z), EPR, UV-visible and CV measurements. The magnetic and spectroscopic data of all these complexes 1-3 indicate distorted octahedral geometry. The EPR spectra of these complexes in frozen DMSO solutions showed a single at g ca. 2. The trend in g-value (g||>g>2.0023) suggests that the unpaired electron on copper (II) has dx2–y2 character. The SOD activities of the complexes have been investigated. Antibacterial and antifungal activity of these complexes were also measured and discussed.
One Pot Hydrothermal Synthesis Characterizations Of Silver Nanoparticles On R...IOSRJAC
Graphene-based nanocomposite have significant applicability in catalysis, electronics, medicine, and energy. In this report silver nanoparticles (AgNPs) with Reduced Graphene Oxide (RGO) - nanocomposite was prepared by a one-pot hydrothermal process using silver nitrate as a precursor. Under hydrothermal process Graphene oxide (GO) was reduced to reduced graphene oxide (RGO), without using chemical reagents. As synthesized (Ag-RGO) nanocomposite was characterized by XRD, UV Vis-spectroscopy, Scanning electron microscope, and Raman spectroscopy. Antimicrobial activities of the composite were investigated against both Gram-positive and Gram-negative bacteria. The results demonstrate that Ag-RGO nanocomposite was a strong bactericide against Gram-negative bacteria. Antioxidant activity was evaluated for bare GO, Ag and Ag-RGO nanocomposite by DPPH radical scavenging assay. It was observed that Ag/RGO nanocomposite has enhanced antioxidant activity than bare GO and Ag.
Nitrogen-doped graphene-supported copper complex: a novel photocatalyst for C...Pawan Kumar
A copper(II) complex grafted to nitrogen-doped graphene (GrN700–CuC) was synthesized and then
demonstrated as an efficient photocatalyst for CO2 reduction into methanol under visible light irradiation
using a DMF/water mixture. The chemical and microstructural features of GrN700–CuC nanosheets were
studied by FTIR, XPS, XRD and HRTEM analyses. Owing to its truly heterogeneous nature, GrN700–CuC
could be easily recovered after the photocatalytic reaction and showed efficient recyclability for
subsequent runs.
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.
Synthesis of 2-aminocyclopent-1-ene-1-carbodithioic acid (ACA) Capped Silver ...IJERA Editor
The present work deals with the formation, morphology and photophysical activity of the 2-aminocyclopent-1-ene-1-carbodithioic acid (ACA) Capped Silver nanoparticles via chemical reduction method. The method utilizes a simple chemical reaction of silver idodide and sodium borohydride. The advantages of this method are ease of preparation, convenience in use and especially, that the obtained silver nano particles are uniform in their shapes and sizes. This is important for fluorescence & bio-evolution measurements. Furthermore, UV-visible (UV-vis) spectroscopy is employed to monitor the formation process of the nano particles and to determine the optimum conditions for the preparation of stable and highly fluorescence-active silver colloids. Specifically, we observed changes in the shapes of the silver nano particles during the formation. This may be helpful in understanding the growth of the nano particles and creates a new dimension in controlling the shapes of the nano particles.SEM, TEM and XRD studies are carried out. The suitability of ACA capped Ag-NPs as Biomarkers is also Tested by Fluorescence study.
Si-Imidazole-HSO4 Functionalized Magnetic Fe3O4 Nanoparticles as an Efficient...Iranian Chemical Society
An efficient and simple method for the preparation of Si-Imidazole-HSO4 functionalized magnetic Fe3O4 nanoparticles (Si-Im-HSO4 MNPs) and used as an efficient and reusable magnetic catalysts for the regioselective ring opening of epoxides under green conditions in water. This catalyst was used for the ring opening of epoxide corresponding to the thiocyanohydrins and azidohydrines. Compared to the classical ring opening of epoxides, this new method consistently has the advantage of excellent yields, short reaction times, and methodological simplicity.
Design, Synthesis and Structural Inspection of Some Novel Di- And Tri-Azometh...CrimsonPublishersACSR
In this study, NBA imine compound was synthesized via an easy one-pot condensation of 3-nitro-benzaldyhide with 2-amino benzoic acid in 1:1 ratio and DAPH imine compound derived from 2,6-diacetyl pyridine and phenyl hydrazine hydrochloride. Consequences of the newly synthesized compounds
hooked up with the aid of FT-IR, elemental analyses, 13C-NMR ,1H-NMR and digital spectral research.
Experiments had been consistent with their chemical structures. Theoretical DFT calculations had been
implemented to confirm the molecular geometry of the investigated chemo-sensors. The sensor property
of all organized imines had been tested upon addition of the metal ions, consisting of Cr(III) ,Fe(II) ,Co(II) ,
Ni(II) ,Cu(II) ,Zn(II) ,Mn(II), VO(II) and Pd(II) .The interactions among receptors and ions are effortlessly
monitored with the aid of UV-visible spectroscopy. DAPH receptor confirmed color modification from
blood red to excessive deep green color to Co(II) ,a yellow color to Cu(II) and different colors to different
ions. Where the NBA receptor showed color modification from light yellow to excessive deep orange color
to Fe(II), pale orange to Pd(II) and different colors for other ions.
Cost Effective Experimental Setup for Gas Sensing Applicationsiosrjce
IOSR Journal of Applied Chemistry (IOSR-JAC) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of applied chemistry and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in Chemical Science. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
Study of the Influence of Nickel Content and Reaction Temperature on Glycerol...IJRESJOURNAL
ABSTRACT: La2O3-SiO2-supported nickel catalysts were evaluated in glycerol steam reforming. The samples (30wt% La and 5, 10 and 15wt% of Ni on 70wt% commercial SiO2), prepared by the simultaneous impregnation method, were characterized by EDX, nitrogen physisorption, XRD, in-situ XRD, XANES and TPR. The analyses revealed NiO species weakly interact with the support and the different metallic surface areas of the catalysts. Catalytic tests were performed in a fixed bed reactor at 600oC and 15Ni catalyst, which showed the best performance, was also evaluated at 500oC and 700oC. According to the results, the Ni content on the catalyst surface interferes in the distribution of gaseous products H2, CO, CO2 and CH4. The increase in the Ni content increases the carbon formation during reaction. The reaction temperature affected the catalytic performance and the best results were obtained with the 15Ni catalyst at 600oC, which was also tested for 20 hours for the analysis of its stability.
Nitrogen-doped graphene-supported copper complex: a novel photocatalyst for C...Pawan Kumar
A copper(II) complex grafted to nitrogen-doped graphene (GrN700–CuC) was synthesized and then
demonstrated as an efficient photocatalyst for CO2 reduction into methanol under visible light irradiation
using a DMF/water mixture. The chemical and microstructural features of GrN700–CuC nanosheets were
studied by FTIR, XPS, XRD and HRTEM analyses. Owing to its truly heterogeneous nature, GrN700–CuC
could be easily recovered after the photocatalytic reaction and showed efficient recyclability for
subsequent runs.
Mixed Ligand, Palladium(II) and Platinum(II) Complexes of Tertiary Diphosphin...Karwan Omer
Palladium(II) and platinum(II) complexes containing the mixed ligands tertiary
diphosphinesdppm. dppp and dppf with Thioester ligand S-1H benzo[d] imidazole-2-yl benzothioate
(HSBIBT) have been prepared by the reaction of PdCl2 and PtCl2 with one equiv of tertiary
diphosphines ligands to form [Pd(k2-dppf)Cl2], [Pd(k2-dppp)Cl2] and [Pt(k2-dppmCl)Cl2] complexes
and then add the ligand HSBIBT to these complexes to form mixed ligand complexes. The prepared
complexes have been characterized by single-crystal X-ray diffraction, elemental analysis, magnetic
susceptibility, molar conductance, IR spectral data and UV-Visible. The results suggested that the
ligand HSBIBT bonded to the metal through N atom and square planner geometries were assigned
for the complexes.
Isolated Iridium Sites on Potassium-Doped Carbon-nitride wrapped Tellurium Na...Pawan Kumar
Many industrial processes such transesterification of fatty acid for biodiesel production, soap manufacturing and biosynthesis of ethanol generate glycerol as a major by-product that can be used to produce commodity chemicals. Photocatalytic transformation of glycerol is an enticing approach that can exclude the need of harsh oxidants and extraneous thermal energy. However, the product yield and selectivity remain poor due to low absorption and unsymmetrical site distribution on the catalyst surface. Herein, tellurium (Te) nanorods/nanosheets (TeNRs/NSs) wrapped potassium-doped carbon nitride (KCN) van der Waal (vdW) heterojunction (TeKCN) is designed to enhance charge separation and visible-NIR absorption. The iridium (Ir) single atom sites decoration on the TeKCN core-shell structure (TeKCNIr) promotes selective oxidation of glycerol to glyceraldehyde with a conversion of 45.6% and selectivity of 61.6% under AM1.5G irradiation. The catalytic selectivity can reach up to 88% under 450 nm monochromatic light. X-ray absorption spectroscopy (XAS) demonstrates the presence of undercoordinated IrN2O2 sites which improved catalytic selectivity for glycol oxidation. Band energies and computational calculations reveal faile charge transfer in the TeKCNIr heterostructure. EPR and scavenger tests discern that superoxide (O2•−) and hydroxyl (•OH) radicals are prime components driving glycerol oxidation.
Isolated Iridium Sites on Potassium-Doped Carbon-nitride wrapped Tellurium Na...Pawan Kumar
Many industrial processes such transesterification of fatty acid for biodiesel production, soap manufacturing and biosynthesis of ethanol generate glycerol as a major by-product that can be used to produce commodity chemicals. Photocatalytic transformation of glycerol is an enticing approach that can exclude the need of harsh oxidants and extraneous thermal energy. However, the product yield and selectivity remain poor due to low absorption and unsymmetrical site distribution on the catalyst surface. Herein, tellurium (Te) nanorods/nanosheets (TeNRs/NSs) wrapped potassium-doped carbon nitride (KCN) van der Waal (vdW) heterojunction (TeKCN) is designed to enhance charge separation and visible-NIR absorption. The iridium (Ir) single atom sites decoration on the TeKCN core-shell structure (TeKCNIr) promotes selective oxidation of glycerol to glyceraldehyde with a conversion of 45.6% and selectivity of 61.6% under AM1.5G irradiation. The catalytic selectivity can reach up to 88% under 450 nm monochromatic light. X-ray absorption spectroscopy (XAS) demonstrates the presence of undercoordinated IrN2O2 sites which improved catalytic selectivity for glycol oxidation. Band energies and computational calculations reveal faile charge transfer in the TeKCNIr heterostructure. EPR and scavenger tests discern that superoxide (O2•−) and hydroxyl (•OH) radicals are prime components driving glycerol oxidation.
Isolated Iridium Sites on Potassium-Doped Carbon-nitride wrapped Tellurium Na...Pawan Kumar
Many industrial processes such transesterification of fatty acid for biodiesel production, soap manufacturing and biosynthesis of ethanol generate glycerol as a major by-product that can be used to produce commodity chemicals. Photocatalytic transformation of glycerol is an enticing approach that can exclude the need of harsh oxidants and extraneous thermal energy. However, the product yield and selectivity remain poor due to low absorption and unsymmetrical site distribution on the catalyst surface. Herein, tellurium (Te) nanorods/nanosheets (TeNRs/NSs) wrapped potassium-doped carbon nitride (KCN) van der Waal (vdW) heterojunction (TeKCN) is designed to enhance charge separation and visible-NIR absorption. The iridium (Ir) single atom sites decoration on the TeKCN core-shell structure (TeKCNIr) promotes selective oxidation of glycerol to glyceraldehyde with a conversion of 45.6% and selectivity of 61.6% under AM1.5G irradiation. The catalytic selectivity can reach up to 88% under 450 nm monochromatic light. X-ray absorption spectroscopy (XAS) demonstrates the presence of undercoordinated IrN2O2 sites which improved catalytic selectivity for glycol oxidation. Band energies and computational calculations reveal faile charge transfer in the TeKCNIr heterostructure. EPR and scavenger tests discern that superoxide (O2•−) and hydroxyl (•OH) radicals are prime components driving glycerol oxidation.
Solar-Driven Cellulose Photorefining into Arabinose over Oxygen-Doped Carbon ...Pawan Kumar
Biomass photorefining is a promising strategy to address the energy crisis and transition toward carbon carbon-neutral society. Here, we demonstrate the feasibility of direct cellulose photorefining into arabinose by a rationally designed oxygen-doped polymeric carbon nitride, which generates favorable oxidative species (e.g., O2–, •OH) for selective oxidative reactions at neutral conditions. In addition, we also illustrate the mechanism of the photocatalytic cellulose to arabinose conversion by density functional theory calculations. The oxygen insertion derived from oxidative radicals at the C1 position of glucose within cellulose leads to oxidative cleavage of β-1,4 glycosidic linkages, resulting in the subsequent gluconic acid formation. The following decarboxylation process of gluconic acid via C1–C2 α-scissions, triggered by surface oxygen-doped active sites, generates arabinose and formic acid, respectively. This work not only offers a mechanistic understanding of cellulose photorefining to arabinose but also sets up an example for illuminating the path toward direct cellulose photorefining into value-added bioproducts under mild conditions.
Solar-Driven Cellulose Photorefining into Arabinose over Oxygen-Doped Carbon ...Pawan Kumar
Biomass photorefining is a promising strategy to address the energy crisis and transition toward carbon carbon-neutral society. Here, we demonstrate the feasibility of direct cellulose photorefining into arabinose by a rationally designed oxygen-doped polymeric carbon nitride, which generates favorable oxidative species (e.g., O2–, •OH) for selective oxidative reactions at neutral conditions. In addition, we also illustrate the mechanism of the photocatalytic cellulose to arabinose conversion by density functional theory calculations. The oxygen insertion derived from oxidative radicals at the C1 position of glucose within cellulose leads to oxidative cleavage of β-1,4 glycosidic linkages, resulting in the subsequent gluconic acid formation. The following decarboxylation process of gluconic acid via C1–C2 α-scissions, triggered by surface oxygen-doped active sites, generates arabinose and formic acid, respectively. This work not only offers a mechanistic understanding of cellulose photorefining to arabinose but also sets up an example for illuminating the path toward direct cellulose photorefining into value-added bioproducts under mild conditions.
Solar-Driven Cellulose Photorefining into Arabinose over Oxygen-Doped Carbon ...Pawan Kumar
Biomass photorefining is a promising strategy to address the energy crisis and transition toward carbon carbon-neutral society. Here, we demonstrate the feasibility of direct cellulose photorefining into arabinose by a rationally designed oxygen-doped polymeric carbon nitride, which generates favorable oxidative species (e.g., O2–, •OH) for selective oxidative reactions at neutral conditions. In addition, we also illustrate the mechanism of the photocatalytic cellulose to arabinose conversion by density functional theory calculations. The oxygen insertion derived from oxidative radicals at the C1 position of glucose within cellulose leads to oxidative cleavage of β-1,4 glycosidic linkages, resulting in the subsequent gluconic acid formation. The following decarboxylation process of gluconic acid via C1–C2 α-scissions, triggered by surface oxygen-doped active sites, generates arabinose and formic acid, respectively. This work not only offers a mechanistic understanding of cellulose photorefining to arabinose but also sets up an example for illuminating the path toward direct cellulose photorefining into value-added bioproducts under mild conditions.
Partial Thermal Condensation Mediated Synthesis of High-Density Nickel Single...Pawan Kumar
Direct selective transformation of greenhouse methane (CH4) to liquid oxygenates (methanol) can substitute energy-intensive two-step (reforming/Fischer–Tropsch) synthesis while creating environmental benefits. The development of inexpensive, selective, and robust catalysts that enable room temperature conversion will decide the future of this technology. Single-atom catalysts (SACs) with isolated active centers embedded in support have displayed significant promises in catalysis to drive challenging reactions. Herein, high-density Ni single atoms are developed and stabilized on carbon nitride (NiCN) via thermal condensation of preorganized Ni-coordinated melem units. The physicochemical characterization of NiCN with various analytical techniques including HAADF-STEM and X-ray absorption fine structure (XAFS) validate the successful formation of Ni single atoms coordinated to the heptazine-constituted CN network. The presence of uniform catalytic sites improved visible absorption and carrier separation in densely populated NiCN SAC resulting in 100% selective photoconversion of (CH4) to methanol using H2O2 as an oxidant. The superior catalytic activity can be attributed to the generation of high oxidation (NiIII═O) sites and selective C─H bond cleavage to generate •CH3 radicals on Ni centers, which can combine with •OH radicals to generate CH3OH.
Selective Cellobiose Photoreforming for Simultaneous Gluconic Acid and Syngas...Pawan Kumar
Here, we demonstrate the selective cellobiose (building block of cellulose) photoreforming for gluconic acid and syngas co-production in acidic conditions by rationally designing a bifunctional polymeric carbon nitride (CN) with potassium/sulfur co-dopant. This heteroatomic doped CN photocatalyst possesses enhanced visible light absorption, higher charge separation efficiency than pristine CN. Under acidic conditions, cellobiose is not only more efficiently hydrolyzed into glucose but also promotes the syngas and gluconic acid production. Density functional theory (DFT) calculations reveal the favorable generation of •O2− during the photocatalytic reaction, which is essential for gluconic acid production. Consequently, the fine-designed photocatalyst presents excellent cellobiose conversion (>80%) and gluconic acid selectivity (>70%) together with the co-production of syngas (~56 μmol g-1 h-1) under light illumination. The current work demonstrates the feasibility of biomass photoreforming with value-added chemicals and syngas co-production under mild condition.
Selective Cellobiose Photoreforming for Simultaneous Gluconic Acid and Syngas...Pawan Kumar
Here, we demonstrate the selective cellobiose (building block of cellulose) photoreforming for gluconic acid and syngas co-production in acidic conditions by rationally designing a bifunctional polymeric carbon nitride (CN) with potassium/sulfur co-dopant. This heteroatomic doped CN photocatalyst possesses enhanced visible light absorption, higher charge separation efficiency than pristine CN. Under acidic conditions, cellobiose is not only more efficiently hydrolyzed into glucose but also promotes the syngas and gluconic acid production. Density functional theory (DFT) calculations reveal the favorable generation of •O2− during the photocatalytic reaction, which is essential for gluconic acid production. Consequently, the fine-designed photocatalyst presents excellent cellobiose conversion (>80%) and gluconic acid selectivity (>70%) together with the co-production of syngas (~56 μmol g-1 h-1) under light illumination. The current work demonstrates the feasibility of biomass photoreforming with value-added chemicals and syngas co-production under mild condition.
Selective Cellobiose Photoreforming for Simultaneous Gluconic Acid and Syngas...Pawan Kumar
Here, we demonstrate the selective cellobiose (building block of cellulose) photoreforming for gluconic acid and syngas co-production in acidic conditions by rationally designing a bifunctional polymeric carbon nitride (CN) with potassium/sulfur co-dopant. This heteroatomic doped CN photocatalyst possesses enhanced visible light absorption, higher charge separation efficiency than pristine CN. Under acidic conditions, cellobiose is not only more efficiently hydrolyzed into glucose but also promotes the syngas and gluconic acid production. Density functional theory (DFT) calculations reveal the favorable generation of •O2− during the photocatalytic reaction, which is essential for gluconic acid production. Consequently, the fine-designed photocatalyst presents excellent cellobiose conversion (>80%) and gluconic acid selectivity (>70%) together with the co-production of syngas (~56 μmol g-1 h-1) under light illumination. The current work demonstrates the feasibility of biomass photoreforming with value-added chemicals and syngas co-production under mild condition.
Partial Thermal Condensation Mediated Synthesis of High-Density Nickel Single...Pawan Kumar
Direct selective transformation of greenhouse methane (CH4) to liquid oxygenates (methanol) can substitute energy-intensive two-step (reforming/Fischer–Tropsch) synthesis while creating environmental benefits. The development of inexpensive, selective, and robust catalysts that enable room temperature conversion will decide the future of this technology. Single-atom catalysts (SACs) with isolated active centers embedded in support have displayed significant promises in catalysis to drive challenging reactions. Herein, high-density Ni single atoms are developed and stabilized on carbon nitride (NiCN) via thermal condensation of preorganized Ni-coordinated melem units. The physicochemical characterization of NiCN with various analytical techniques including HAADF-STEM and X-ray absorption fine structure (XAFS) validate the successful formation of Ni single atoms coordinated to the heptazine-constituted CN network. The presence of uniform catalytic sites improved visible absorption and carrier separation in densely populated NiCN SAC resulting in 100% selective photoconversion of (CH4) to methanol using H2O2 as an oxidant. The superior catalytic activity can be attributed to the generation of high oxidation (NiIII═O) sites and selective C─H bond cleavage to generate •CH3 radicals on Ni centers, which can combine with •OH radicals to generate CH3OH.
Recent advancements in tuning the electronic structures of transitional metal...Pawan Kumar
The smooth transition from finite non-renewables to renewable energy conversion technologies will require efficient electrocatalysts which can harness intermittent energies to store in the form of chemical bonds. The oxygen evolution reaction (OER) impedes the widespread usage of water electrolyzers to convert H2O into H2 and persists as a bottleneck, including other energy conversion devices with sluggish four H+/e− kinetics. In this context, designing highly active and stable catalysts capable of driving a lower overpotential in the OER to produce continuous hydrogen (H2) is a primary demanded. This chapter discussed the mechanism of the OER in conventional adsorbate oxygen and lattice oxygen participation in transition metal oxides (TMOs). Further, the influences of surface engineering, doping, and defects in the TMOs and understanding the electronic structure to screen electrodes towards the structure–activity relationship are highlighted. Specifically, the adsorption strength of O 2p is understood in detail as its binding ability over the surface of TMOs can be correlated directly to the OER activity. The iterative development of TMOs in terms of understanding electronic structural attributes is essential for the commercial deployment of energy conversion technologies. The comprehensive outlook of this chapter investigates thoroughly how TMOs can be used as significant materials for the OER in the near future.
Hole transport materials (HTMs) have a significant impact on the effectiveness of organic electronic devices; therefore, we present a molecular architecture of pyrazino[2,3-g]quinoxaline (PQ10)-based room-temperature organic liquid crystalline semiconductor (OLCS) as an alternative HTM. The PQ10 compound exhibits three different rectangular columnar (Colr) phases offering an impressive hole mobility of 8.8 × 10−3 cm2V−1s−1 which is found to be dexterous than most of existing polymeric hole transport materials. The charge transport mechanism is governed by the hole polarons hopping through H-aggregates of the PQ10 molecules and the hole mobility remains nearly constant throughout the mesophase range, but it decreases with increasing applied electric field. The current-voltage characteristics of the PQ10 have also been investigated in all three Colr phases and explained via the Poole-Frenkel conduction mechanism. The dielectric spectroscopy has been eventually carried out to understand the nature of dielectric permittivity and conductivity as a function of temperature and a correlation is established between the molecular architecture of the Colr phases and aforementioned physical properties. Solar cell simulation has been additionally performed to demonstrate that the PQ10 material can be a better choice as HTM for organic electronics and photovoltaic applications.
Multifunctional carbon nitride nanoarchitectures for catalysisPawan Kumar
Catalysis is at the heart of modern-day chemical and pharmaceutical industries, and there is an urgent demand to develop metal-free, high surface area, and efficient catalysts in a scalable, reproducible and economic manner. Amongst the ever-expanding two-dimensional materials family, carbon nitride (CN) has emerged as the most researched material for catalytic applications due to its unique molecular structure with tunable visible range band gap, surface defects, basic sites, and nitrogen functionalities. These properties also endow it with anchoring capability with a large number of catalytically active sites and provide opportunities for doping, hybridization, sensitization, etc. To make considerable progress in the use of CN as a highly effective catalyst for various applications, it is critical to have an in-depth understanding of its synthesis, structure and surface sites. The present review provides an overview of the recent advances in synthetic approaches of CN, its physicochemical properties, and band gap engineering, with a focus on its exclusive usage in a variety of catalytic reactions, including hydrogen evolution reactions, overall water splitting, water oxidation, CO2 reduction, nitrogen reduction reactions, pollutant degradation, and organocatalysis. While the structural design and band gap engineering of catalysts are elaborated, the surface chemistry is dealt with in detail to demonstrate efficient catalytic performances. Burning challenges in catalytic design and future outlook are elucidated.
Production of Renewable Fuels by the Photocatalytic Reduction of CO2 using Ma...Pawan Kumar
The photo-reductive performance of natural ilmenite was boosted and the production of renewable fuels from the reduction of CO2 was enhanced by doping the natural mineral with magnesium. The doping was achieved by high energy ball milling in the presence of MgO and Mg(NO3)2. The photo-reduction of CO2 in aqueous solution led to the evolution of H2, CH4, C2H4, and C2H6, and the insertion of Mg in the structure of ilmenite enabled increases of up to 1245% in the fuel production yield, reaching total production of 210.9 µmol h-1 gcat-1. Displacements of the conduction band to more negative potentials were evidenced for the samples doped with magnesium. Indirect effects such as increases in the valence band maximum, and the introduction of intermediate energy levels were also evidenced through the measurement of the crystallite size and the determination of the band structure of the materials. Mott-Schottky analyses of the samples showed the n-type nature of the semiconductor materials and enabled the estimation of the density of charge carriers, which strongly influenced the photocatalytic performance. The strong potential of the application of natural ilmenite in gas phase artificial photosynthesis was proved by the evaluation of CO2 reduction in gas conditions, which allowed the enhancement in the selectivity and significantly increased the production of CH4 as compared to aqueous solution, reaching an important yield of CH4 of 16.1 µmol h-1 gcat-1.
Nanoengineered Au-Carbon Nitride Interfaces Enhance PhotoCatalytic Pure Water...Pawan Kumar
Photocatalytic pure water splitting using solar energy is one of the promising routes to produce sustainable green hydrogen (H2). Tuning the interfacial active site density at catalytic heterojunctions and better light management are imperative to steer the structure-activity correlations to enhance the photo-efficiency of nanocomposite photocatalysts. Herein, we report the decoration of nitrogen defects-rich carbon nitride CN(T) with metallic Au nanostructures of different morphologies and sizes to investigate their influence on the photocatalytic hydrogen evolution reactions (HER). The CN(T)-7-NP nano-heterostructure comprises Au nanoparticles (NPs) of ~7 nm and thiourea-derived defective CN exhibits an excellent H2 production rate of 76.8 µmol g–1 h–1 from pure water under simulated AM 1.5 solar irradiation. In contrast to large-size Au nanorods, the high activity of CN(T)-7-NP was attributed to their strong localized surface plasmon resonance (LSPR) mediated visible absorption and interfacial charge separation. The surface ligands used to control Au nanostructures morphology were found to play a major role in the stabilization of NPs and improve interfacial charge transport between Au NPs and CN(T). First-principles calculations revealed that defects in CN and Au-CN interfacial sites in these nanocomposites facilitate the separation of e-/h+ pairs after light excitation and provide lower energy barrier pathways for H2 production by photocatalytic water splitting.
Nanoengineered Au-Carbon Nitride Interfaces Enhance Photo-Catalytic Pure Wate...Pawan Kumar
Photocatalytic pure water splitting using solar energy is one of the promising routes to produce sustainable green hydrogen (H2). Tuning the interfacial active site density at catalytic heterojunctions and better light management are imperative to steer the structure-activity correlations to enhance the photo-efficiency of nanocomposite photocatalysts. Herein, we report the decoration of nitrogen defects-rich carbon nitride CN(T) with metallic Au nanostructures of different morphologies and sizes to investigate their influence on the photocatalytic hydrogen evolution reactions (HER). The CN(T)-7-NP nano-heterostructure comprises Au nanoparticles (NPs) of ~7 nm and thiourea-derived defective CN exhibits an excellent H2 production rate of 76.8 µmol g–1 h–1 from pure water under simulated AM 1.5 solar irradiation. In contrast to large-size Au nanorods, the high activity of CN(T)-7-NP was attributed to their strong localized surface plasmon resonance (LSPR) mediated visible absorption and interfacial charge separation. The surface ligands used to control Au nanostructures morphology were found to play a major role in the stabilization of NPs and improve interfacial charge transport between Au NPs and CN(T). First-principles calculations revealed that defects in CN and Au-CN interfacial sites in these nanocomposites facilitate the separation of e-/h+ pairs after light excitation and provide lower energy barrier pathways for H2 production by photocatalytic water splitting.
Cooperative Copper Single Atom Catalyst in Two-dimensional Carbon Nitride for...Pawan Kumar
Renewable electricity powered carbon dioxide (CO2) reduction (eCO2R) to high-value fuels like methane (CH4) holds the potential to close the carbon cycle at meaningful scales. However, this kinetically staggered 8-electron multistep reduction still suffers from inadequate catalytic efficiency and current density. Atomic Cu-structures can boost eCO2R-to-CH4 selectivity due to enhanced intermediate binding energies (BEs) resulting from favorably shifted d-band centers. Herein, we exploit two-dimensional carbon nitride (CN) matrices, viz. Na-polyheptazine (PHI) and Li-polytriazine imides (PTI), to host Cu-N2 type single atom sites with high density (∼1.5 at%), via a facile metal ion exchange process. Optimized Cu loading in nanocrystalline Cu-PTI maximizes eCO2R-to-CH4 performance with Faradaic efficiency (FECH4) of ≈68% and a high partial current density of 348 mA cm−2 at a low potential of -0.84 V versus RHE, surpassing the state-of-the-art catalysts. Multi-Cu substituted N-appended nanopores in the CN frameworks yield thermodynamically stable quasi-dual/triple sites with large interatomic distances dictated by the pore dimensions. First-principles calculations elucidate the relative Cu-CN cooperative effects between the two matrices and how the Cu-Cu distance and local environment dictate the adsorbate BEs, density of states, and CO2-to-CH4 energy profile landscape. The 9N pores in Cu-PTI yield cooperative Cu-Cu sites that synergistically enhance the kinetics of the rate-limiting steps in the eCO2R-to-CH4 pathway.
Bioinspired multimetal electrocatalyst for selective methane oxidationPawan Kumar
Selective partial electrooxidation of methane (CH4) to liquid oxygenates has been a long-sought goal. However, the high activation energy of C–H bonds and competing oxygen evolution reaction limit product selectivity and reaction rates. Inspired by iron (IV)-oxo containing metalloenzymes’ functionality to activate the C–H bond, here we report on the design of a copper-iron-nickel catalyst for selective oxidation of CH4 to formate via a peroxide-assisted pathway. Each catalyst serves a specific role which is confirmed via electrochemical, in situ, and theoretical studies. A combination of electrochemical and in situ spectroelectrochemical studies revealed that H2O2 oxidation on nickel led to the formation of active oxygen species which trigger the formation of iron (IV) at low voltages. Density functional theory analysis helped reveal the role of iron (IV)-oxo species in reducing the activation energy barrier for CH4 deprotonation and the critical role of copper to suppress overoxidation. Our multimetal catalyst exhibits a formate faradaic efficiency of 42% at an applied potential of 0.9 V versus a reversible hydrogen electrode.
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.
Remote Sensing and Computational, Evolutionary, Supercomputing, and Intellige...University of Maribor
Slides from talk:
Aleš Zamuda: Remote Sensing and Computational, Evolutionary, Supercomputing, and Intelligent Systems.
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Inter-Society Networking Panel GRSS/MTT-S/CIS Panel Session: Promoting Connection and Cooperation
https://www.etran.rs/2024/en/home-english/
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
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.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
DERIVATION OF MODIFIED BERNOULLI EQUATION WITH VISCOUS EFFECTS AND TERMINAL V...Wasswaderrick3
In this book, we use conservation of energy techniques on a fluid element to derive the Modified Bernoulli equation of flow with viscous or friction effects. We derive the general equation of flow/ velocity and then from this we derive the Pouiselle flow equation, the transition flow equation and the turbulent flow equation. In the situations where there are no viscous effects , the equation reduces to the Bernoulli equation. From experimental results, we are able to include other terms in the Bernoulli equation. We also look at cases where pressure gradients exist. We use the Modified Bernoulli equation to derive equations of flow rate for pipes of different cross sectional areas connected together. We also extend our techniques of energy conservation to a sphere falling in a viscous medium under the effect of gravity. We demonstrate Stokes equation of terminal velocity and turbulent flow equation. We look at a way of calculating the time taken for a body to fall in a viscous medium. We also look at the general equation of terminal velocity.
Phenomics assisted breeding in crop improvementIshaGoswami9
As the population is increasing and will reach about 9 billion upto 2050. Also due to climate change, it is difficult to meet the food requirement of such a large population. Facing the challenges presented by resource shortages, climate
change, and increasing global population, crop yield and quality need to be improved in a sustainable way over the coming decades. Genetic improvement by breeding is the best way to increase crop productivity. With the rapid progression of functional
genomics, an increasing number of crop genomes have been sequenced and dozens of genes influencing key agronomic traits have been identified. However, current genome sequence information has not been adequately exploited for understanding
the complex characteristics of multiple gene, owing to a lack of crop phenotypic data. Efficient, automatic, and accurate technologies and platforms that can capture phenotypic data that can
be linked to genomics information for crop improvement at all growth stages have become as important as genotyping. Thus,
high-throughput phenotyping has become the major bottleneck restricting crop breeding. Plant phenomics has been defined as the high-throughput, accurate acquisition and analysis of multi-dimensional phenotypes
during crop growing stages at the organism level, including the cell, tissue, organ, individual plant, plot, and field levels. With the rapid development of novel sensors, imaging technology,
and analysis methods, numerous infrastructure platforms have been developed for phenotyping.
Comparing Evolved Extractive Text Summary Scores of Bidirectional Encoder Rep...University of Maribor
Slides from:
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Track: Artificial Intelligence
https://www.etran.rs/2024/en/home-english/
Comparing Evolved Extractive Text Summary Scores of Bidirectional Encoder Rep...
Mixed-Valence Single-Atom Catalyst Derived from Functionalized Graphene
1. Copyright WILEY-VCH Verlag GmbH & Co. KGaA, 69469 Weinheim, Germany, 2019.
Supporting Information
for Adv. Mater., DOI: 10.1002/adma.201900323
Mixed-Valence Single-Atom Catalyst Derived from
Functionalized Graphene
Aristides Bakandritsos, Ravishankar G. Kadam, Pawan
Kumar, Giorgio Zoppellaro, Miroslav Medved’, Jiří Tuček,
Tiziano Montini, Ondřej Tomanec, Pavlína Andrýsková,
Bohuslav Drahoš, Rajender S. Varma, Michal Otyepka, Manoj
B. Gawande,* Paolo Fornasiero,* and Radek Zbořil*
2. 0
Copyright WILEY-VCH Verlag GmbH & Co. KGaA, 69469 Weinheim, Germany, 2019.
Supporting Information
Mixed-Valence Single-Atom Catalyst Derived from Functionalized Graphene
Aristides Bakandritsos, Ravishankar G. Kadam, Pawan Kumar, Giorgio Zoppellaro, Miroslav
Medveď, Jiří Tuček, Tiziano Montini,Ondřej Tomanec, Pavlína Andrýsková, Bohuslav Drahoš,
Rajender S. Varma, Michal Otyepka, Manoj B. Gawande,* Paolo Fornasiero,* and Radek Zbořil*
Dr. A. Bakandritsos, Dr. R. G. Kadam, Dr. P. Kumar, Dr. G. Zoppellaro, Dr. M. Medveď, Dr. J.
Tuček, O. Tomanec, P. Andrýsková, Dr. R. S. Varma, Prof. M. Otyepka, Dr. M. B. Gawande, Prof.
R. Zbořil
Regional Centre of Advanced Technologies and Materials
Department of Physical Chemistry, Faculty of Science, Palacký University Olomouc
Šlechtitelů 27, 783 71 Olomouc, Czech Republic
E-mail: manoj.gawande@upol.cz; radek.zboril@upol.cz
Dr. B. Drahoš
Regional Centre of Advanced Technologies and Materials
Department of Inorganic Chemistry, Faculty of Science, Palacký University Olomouc
17. listopadu 12, 771 46 Olomouc, Czech Republic
Prof. P. Fornasiero, Prof. Tiziano Montini
Department of Chemical and Pharmaceutical Sciences, INSTM Trieste Research Unit and ICCOM-
CNR Trieste Research Unit, University of Trieste
via L. Giorgieri 1, I-34127 Trieste, Italy
E-mail: pfornasiero@units.it
Keywords: cyanographene, single-atom catalysis, cooperative catalysis, amine coupling, C-H
oxidation
This PDF file includes:
Materials and Methods
Figures M1–M5
Results - Supplementary Figures and Tables
Tables S1–S11
Figures S1–S15
Supplementary references S1-S29
3. 1
Materials and Methods
Reagents and materials. Graphite fluoride (>61 wt.% F, C1F1.1), NaCN (p.a. ≥97%), N,N-
Dimethylformamide (≥99.8%), CuCl2∙2H2O (99.99%), Na2SO4 anhydrous (≥99%), ethyl acetate
anhydrous (99.8%), 1,4-Dioxane anhydrous (99.8%), triethylamine (≥99%), Fe(NO3)3·9H2O (ACS
reagent, ≥98%), graphene oxide nanocolloids (product No 795534), all aromatic benzyl amines,
secondary cyclic amines and anilines were purchased from Sigma Aldrich and used as received
without further purification. All solvents were HPLC grade. All aqueous solutions were prepared
with ultrapure water (18 MΩ cm–1
).
Synthesis of G-CN, G-COOH, and metal immobilization. Cyanographene and graphene-acid
nanosheets were synthesized by following our previous method.30
Briefly, fluorinated graphite (120
mg, ∼4 mmol of C-F units) was added to 15 mL of DMF and stirred for 2 days. Then sonicated
(Bandelin Sonorex, DT 255H type, frequency 35 kHz, power 640 W, effective power 160 W) for 4
h under nitrogen atmosphere. Then 800 mg of NaCN (∼16 mmol) was added and the mixture was
heated at 403 K with a condenser under stirring (500 rpm). After 2 days, the mixture was left to
cool to room temperature. After washing and isolation of the pure product, the material was
suspended in distilled water. Hydrolysis of the nitrile groups on G-CN to carboxyl groups was
performed with 20% HNO3, according to the published procedure,30
in order to synthesize the
graphene acid derivative (G-COOH). Copper loading was performed by mixing an aqueous
suspension of G-CN (20 mL containing 120 mg of G-CN) with CuCl2∙2H2O (2 mL containing 60
mg of Cu ions). After 24 h of stirring, the mixture was separated with centrifugation. H2O was
added in the pellet, mixed and finally centrifuged in order to isolate the final copper-loaded G-CN.
The catalyst (the copper-loaded G-CN) was finally freeze-dried and stored for further use. The
determination of the copper content in the solid catalyst was performed with ICP-MS. The BET
surface area of G(CN)-Cu catalyst was found to be 153 m2
g–1
.
G-COOH loaded with Fe was performed following the same procedure, using
Fe(NO3)3·9H2O. ICP-MS indicated Fe content in the G(COOH)-Fe hybrid of 4.3 wt.%.
The reduced graphene oxide (rGO) copper loaded material was prepared starting with
commercial GO (PlasmaChem, Germany) and mixing with CuCl2∙2H2O following an identical
procedure as with G-CN. After isolation of the final solid, hydrazine was added to reduce GO and
solid was washed well with water and freeze-dried for further use.
Structural and physicochemical characterization techniques. The surface chemical properties of
materials were determined with X-ray photoelectron spectroscopy (XPS) performed on a PHI
VersaProbe II (Physical Electronics) spectrometer using an Al Kα source (15 kV, 50 W). The fine
morphological characteristics of catalyst were determined with transmission electron microscopy
(TEM) at 80 kV accelerating voltage on FEI Titan G2 60-300 transmission electron microscope
equipped with X-FEG electron gun, objective-lens image spherical aberration corrector and
ChemiSTEM EDS detector. While the ultrafine structure of catalysts was obtained on TEM JEOL
2010 with LaB6 type emission gun, operating at 160 kV with a resolution of 0.19 nm. For the
sample preparation, a very dilute dispersion of catalyst (~0.1 mg mL–1
) was prepared by sonication
and deposited on a carbon-coated copper grid and analyzed after drying for 24 h at room
temperature. STEM-elemental mapping for determining EDS pattern and distribution of elements
with the help of STEM-HAADF (high-angle annular dark-field imaging) analyses was recorded on
a FEI Titan HRTEM microscope operating at 80 kV. The nitrogen adsorption–desorption was
carried out using Micromeritics Flex 3 surface area and porosity analyzer. Before the measurements,
the sample was degassed under vacuum at 373 K for 24 hours in a degasser.
EPR spectra were recorded on JEOL JES-X-320 operating at X-band frequency (~9.1 GHz),
equipped with a variable temperature control ES 13060DVT5 apparatus. The cavity (Q) quality
factor was kept above 7000 in all measurements, microwave power was kept under non-saturating
conditions and highly pure quartz tubes were employed in the measurements (Suprasil, Wilmad,
4. 2
<0.5 OD). Experimental parameters in the spin trap experiments in Figure 4B of the main text were
as follows: mod. frequency 100 kHz, mod. amplitude of 0.35 mT, time const. of 30 ms, applied
microwave power of 0.6 mW, sweep time of 240 s, phase 0°, T = 248 K. Simulation of the EPR
envelope (Sim) using third-order perturbation theory (spin-Hamiltonian parameters: giso= 2.0053,
AN = 1.51 mT, AH (-proton) = 1.49 mT, tumbling effects included in the line-width function
(a+bm+cm2
) with coefficients a = 8.6, b = –0.1, c = –0.6 and Lorentzian/Gaussian ratio of 0.5.
Cu K-edge EXAFS and XANES data were measured on the SAMBA beamline at the
Synchrotron SOLEIL (Gif sur Yvette, France).[S1]
Spectra were collected by measuring the Kα
fluorescence line with a 36 pixels Germanium detector (Canberra), while transmission data was
simultaneously recorded with ionization chambers (IC-SPEC, FMB-Oxford) for the sample and a
Cu foil. Harmonic rejection has been accomplished by using two Pd coated mirrors. Data analysis
has been performed with the DEMETER software package.[S2]
ATHENA software has been used to
extract EXAFS signals, by background subtraction (Autobk algorithm) and normalization with the
edge height. Fourier transforms to R space of the k3
-weighted EXAFS data was performed in a k
range of 1–12 Å-1
using the Hanning window function, where ‘‘k’’ indicates a photoelectron wave
number and ‘‘R’’ represents the distance between the absorber atom and a scatterer atom. The
EXAFS signals were analyzed using Artemis software over a k range of 1–12 Å-1
and a R range of
0.8–3 Å. The maximum number of independent points can be estimated from the expression IP =
[(2kR/) + 1], where k is the extent of the data in k-space and R the R range to be modelled.
The number of variables used for the analysis (9 at most) remained well below the number of
independent points (IP = 16). The values of Fj(k), j(k) and j(k) for Cu-O and Cu-Cu were
generated by the Atoms 2.5 and FEFF 8.0 codes using the crystallographic data of Cu2O and Cu
metal. The fits were performed in the R-space. The passive electron reduction factor S0
2
was
determined experimentally on the Cu2O and Cu foil as standard materials. During the fit procedure
of the samples the coordination number (N), bond distance (R) and Debye–Waller factor (2
) were
allowed to adjust freely. The passive electron reduction factor (S0
2
) was held constant at the value
of reference sample.
The metal content of fresh and reused catalyst was determined with ICP-MS (Agilent 7700x,
Agilent, Japan). A weighted amount of sample from the catalyst (on a 0.01 mg read-out balance,
Kern ABT 220-5DNM) was digested with nitric acid in microwave digester followed by dilution
with water. The mixture was centrifuged to precipitate solid residues, and the upper half of the
supernatant was used for Cu determination. 1
H and 13
C NMR spectra of imines produced from the
catalytic reactions were recorded on 400 MHz NMR Varian spectrometer (Varian, Santa Clara, CA,
USA) and on an JNM-ECA600II NMR spectrometer (JEOL, Japan) at 298 K, using CDCl3/DMSO-
d6 as a solvent and TMS as an internal standard. The raw data were processed with Masternova®
6.1 software. The chemical shifts were expressed in parts per million relative to TMS. The reaction
products were analyzed by gas chromatography (Model: Agilent 6820) equipped with an Agilent
DB-5 capillary column (30 m × 0.32 mm, 0.5 m) under the operation parameters: inlet temperature
473 K, flame ionization detector (FID) temperature 523 K, oven temperature 523 K with a ramp
rate 10° min–1
from 373 K.
Transmission 57
Fe Mössbauer spectrum of the G(COOH)Fe sample was recorded employing
a Mössbauer spectrometer operating in a transmission geometry and constant acceleration mode and
equipped with a 50 mCi 57
Co(Rh) radioactive source of γ-rays radiation. For the Mössbauer
spectroscopy measurement at 5 K, the sample was placed inside a cryomagnetic system (Oxford
Instruments, U.K.), to which a Mössbauer spectrometer is mounted. The collected 57
Fe Mössbauer
spectrum was analyzed with mathematical fitting algorithms and routines in the MossWinn software
package;[S3]
prior to fitting, the signal-to-noise ratio was adjusted by the filtering algorithms built in
the MossWinn software program and by statistically-based approach developed by Prochazka et
al.[S4]
The values of the isomer shift are referred to metallic α-Fe at room temperature.
Computational details. The structural features, stabilities, spin and charge distributions, and other
characteristics associated with the binding of benzylic amines to copper atoms, which are bound to
5. 3
the G-CN surface, were analyzed. To this end, we selected two representative amines, namely
benzylamine (BAM) and 2-picolylamine (PAM), for our computational studies. The former exhibits
high conversion rates and selectivity in the studied G(CN)-Cu catalyzed cross-oxidative coupling
reactions, but the conversion and selectivity associated with the latter are noticeably lower. In
addition to the formation of G(CN)-Cu-BAM/PAM complexes, we have also explored the binding
of Cu(II)/Cu(I) cations to the G-CN surface. The reaction sites (copper atoms) are positively
charged. Therefore, we applied the finite cluster approach, where the size of the G(CN)-Cu model
systems was carefully chosen to obtain converged values of the relevant binding characteristics (see
below).
The ground state (GS) structures of all the investigated species were optimized via the B3LYP
method[S5,S6]
using the 6-31+G(d) basis set.[S7]
The spin-unrestricted formalism was applied for the
open-shell system. Furthermore, the suitability of this approach was verified by comparing the
results for selected structures with those obtained by the spin-restricted open-shell formalism. The
solvent effects were included by using the universal continuum solvation model based on solute
electron density (SMD).[S8]
The structures of ligands (H2O, BAM, PAM, O2, OH) were fully relaxed in the geometry
optimizations, to mimic the semi-local rigidity of graphene sheets. However, the G(CN)-Cu-
BAM/PAM structures were obtained via geometry optimizations of the local region containing the
copper atom(s) with ligands, cyano groups, and the two closest carbon atoms at the reaction site.
During these optimizations, the rest of the structure was frozen (see Figure M1a). The structure of
corronene-2CN (cor-2CN) was generated through a fully unconstrained optimization in a given
solvent. In contrast, the cyc14-2CN structure was pre-optimized in the gas phase and then re-
optimized in a given solvent with fixed positions of edge carbon atoms (see Figure M1b). All
calculations were performed with the Gaussian09 program.[S6,S9]
Figure M1. The structure of a) cor-2CN-Cu model. The red arrows indicate the carbon atoms that
are included (in addition to both cyano groups and the copper atom) in constrained optimizations in
our analysis, b) cyc14-2CN model, and c) cyc10-4CN-2Cu model.
Representative procedure for homo-oxidative coupling. In the typical experimental procedure, a
10 mL vial was charged with benzyl amines (1.83 mmol) and G(CN)-Cu catalyst (20 mg, 10.7 µmol
Cu, or 0.58% mol loading in reaction) and the resulting reaction mixture was sonicated for 5 min.
The ensuing reaction mixture was stirred at 358 K for 12 h under an air balloon, thereby yielding
the desired N-Benzyl-1-phenylmethanimine product. The progress of the reaction was monitored
via thin layer chromatography (TLC). After completion of the reaction, 5 mL of ethyl acetate was
added to the reaction mixture and the catalyst was removed by centrifugation. A crude product was
obtained by vacuum-drying the resulting supernatant. The conversion (94%) and selectivity (99%)
were determined via gas chromatography (GC) with flame-ionization detection (GC-FID).
Moreover, the imine product was further purified by column chromatography, thereby yielding 2a
in 91%. 1
H NMR (400 MHz, CDCl3): δ = 8.36 (t, J = 1.4 Hz, 1H), 7.78–7.76 (m, 2H), 7.41–7.37 (m,
3H), 7.33 (d, J = 4.4 Hz, 4H), 7.27–7.21 (m, 1H) 4.80 (d, J = 1.4 Hz 2H) ppm; 13
C NMR (100.5
MHz, CDCl3): δ = 162.05, 139.30, 136.14, 130.81, 128.64, 128.53, 128.31, 128.01, 127.03, 65.08
ppm. Further corresponding imines are synthesized following the above procedure. The compounds
are all reported in the literature.[S10–S17]
6. 4
Figure M2. 1
H NMR of N-Benzyl-1-phenylmethanimine in CDCl3 using TMS as internal standard.
Figure M3. 13
C NMR of N-Benzyl-1-phenylmethanimine in CDCl3 using TMS as internal standard.
7. 5
Representative procedure for oxidative cross-coupling. In the typical experimental procedure, a
10 mL vial was charged with benzyl amine (1.83 mmol) and aniline (5.49 mmol) in a 1:3 mol ratio,
and G(CN)-Cu catalyst (20 mg, 10.7 µmol Cu) was subsequently added to the vial. The resulting
reaction mixture was sonicated for 5 min and stirred at 358 K for 24-30 h under an air balloon, to
obtain the desired cross-coupled imine product. The progress of the reaction was monitored via
TLC. After completion of the reaction, 5 mL of ethyl acetate was added to the reaction mixture and
the catalyst was removed by centrifugation. The resulting supernatant was vacuum-dried, thereby
yielding (N-(4-Fluorophenyl)-1-(4-methoxyphenyl)methanimine (99% conversion and 98%
selectivity, by GC-FID). Further purification of the imine product was performed by column
chromatography that yielded 5a in 94%. 1
H NMR (400 MHz, CDCl3): δ = 8.35 (s, 1H), 7.84–7.81
(m, 2H), 7.18–7.13 (m, 2H), 7.08–7.03 (m, 2H), 6.99–6.95 (m, 2H), 3.85 (s, 3H) ppm; 13
C NMR
(100.5 MHz, CDCl3): δ = 162.24, 162.17, 159.50, 148.23, 130.46, 129.04, 122.17, 115.90, 114.18,
55.40 ppm. Other corresponding imines are synthesized following the above procedure. The
compounds are all reported in the literature.[S10–S17]
Figure M4. 1
H NMR of N-(4-Fluorophenyl)-1-(4-methoxyphenyl)methanimine in CDCl3 using
TMS as internal standard.
8. 6
Figure M5. 13
C NMR of N-(4-Fluorophenyl)-1-(4-methoxyphenyl)methanimine in CDCl3 using
TMS as internal standard.
Representative procedure for benzylic C-H oxidation. The oxidation reaction was carried out in
a 10 mL Schlenk tube. In a typical experimental procedure, tube was charged with ethyl benzene
(0.5 mmol), N-hydroxyphthalimide (NHPI) 15 mol%, 10 mg of G(CN)-Cu in 3 mL of acetonitrile
under O2 1 atm. This reaction mixture was heated at 60 °C for 24 h. Aliquots of the mixture were
extracted and checked by means of GC-FID (97% conversion and 99% selectivity). The
aforementioned synthesis procedure was followed for other benzylic C-H oxidation of hydrocarbon
derivatives.
9. 7
Results - Supplementary Figures and Tables
Table S1. Oxidative coupling of amines, a comparison of performance: mixed-valence G(CN)-Cu
catalyst vs. state-of-the-art catalysts.
Entry
Catalyst
(Qty)
Substrates
Time
(h)
Temp
. (K)
Amine
(mmol
)
Conv./
Yield
(%)
Select.
(%)
Conv./Select.
after
recycling
1
CuO
nano-
flakes
(20 mg)
12 373 1.83 98 98
~42/- after
five cycles
ref. 34
Comments: Poor reusability, relatively high temperature, oxygen balloon, high
metal loadings.
2
Cu(0)
(0.05
mol)
20 363 9.3 88 100
N/A
ref. [S18]
Comments: Non-reusable (due to oxidative corrosion), relatively high temperature,
poor conversions/selectivity, relatively long reaction time, poor conversion for
cross-coupling products.
3
Graphite
oxide
(50
wt.%)
4 373 5 99 98
92/- after five
cycles
ref. 39
4 373 5 - -
Comments: High catalyst loading, high O2 pressure (5 atm), high temperature, poor
conversion and selectivity for aliphatic amines, scalable production of GO is tedious
and requires hazardous oxidizing agents and chemicals.
4
(ba-GO)
(5 wt.%)
12 363 9.3 98 - 93/- after six
cycles
ref. 37
Comments: Scalable production of GO is tedious and requires hazardous oxidizing
agents and chemicals, non-active for alkylamines, applicability of catalyst to cross
coupling of amines is unknown.
10. 8
Entry
Catalyst
(Qty)
Substrates
Time
(h)
Temp
. (K)
Amine
(mmol
)
Conv./
Yield
(%)
Select.
(%)
Conv./Select.
after
recycling
Ref.
5
P-doped
graphene
(10
wt.%)
12 373 0.4 82 -
73/- after 6
cycles
ref. [S19]
12 373 0.4 <10 -
Comments: High reaction temperature, poor selectivity, poor conversion for
aliphatic amines, inapplicable to cross couplings, catalyst synthesis requires a
template, high temperature, and acid washing.
6
Au/graph
ite
(5 mol%
Au)
17 383 0.4 69 -
80/- after 10
cycles
ref. [S20]
Comments: Long reaction time, high temperature, high amount of noble metal
required resulting in expensive protocol, very low conversion, solvent was used.
Only with O2 the performance could be improved.
7
NHPI/Fe
(BTC)
MOFs
(75 mg)
24 373
4.57
(0.5
mL)
98 90 96/91 after 2
cycles
ref. [S21]
10 373
4.57
(0.5
mL)
- -
Comments: Increased reaction time, high temperature, relatively large amount of
catalyst for small amount of amine, O2 balloon, tedious synthesis, narrow range of
substrates, relatively low selectivity, catalyst ineffective for coupling of alkyl
amines, and cross-coupling reactions.
8
MOF-
253
(0.15
mmol)
6 373 10 >99 -
98/- after 6
cycles
ref. [S14]
Comments: High reaction temperature, O2 balloon, tedious synthetic procedure for
MOF by using various expensive organic ligands.
9
CoTPP(C
F3)4
(5 × 10−4
mmol)
3 403 5 87 -
N/A
ref. 36
Comments: High reaction temperature, homogeneous catalyst, low conversion,
high pressure of O2 (6 atm), catalyst explored for self-coupling only.
11. 9
Entry
Catalyst
(Qty)
Substrates
Time
(h)
Temp
. (K)
Amine
(mmol
)
Conv./
Yield
(%)
Select.
(%)
Conv./Select.
after
recycling
Ref.
10
PdCu
NPs
(10 mg)
3 383 1.83 87 87.5
85.2/86.3
after 4 cycles
ref. [S22]
Comments: High reaction temperature, low conversion, precious metal and O2
balloon.
11
meso
Cs/MnOx
(25 mg)
3 383 0.5 99 93 2.2 (TON)
after four
recycling
ref. 35
+
(1:3)
3 383
0.5:1.5
(1:3)
15 70
Comments: High reaction temperature, relatively high catalyst loading, toluene
solvent.
12
Au-
Pd@CN
T
(0.10 g)
(Au:Pd,
1:1 mol
ratio)
4 393 1.0 95 98
N/A
ref. [S23]
Comments: High reaction temperature, use of noble metal, scalable synthesis of
CNTs is difficult, O2 balloon, p-xylene solvent.
13
MnOx/Ce
O2
(100 mg)
5 393 3.5 98.4 95.4
82.3/97.2
after 3 cycles
ref. 33
Comments: Increased reaction temperature, relatively large amount of catalyst,
poor conversion and selectivity, was explored for self-coupling only, O2 balloon.
14
G(CN)-
Cu
(20 mg,
0.58%
molCu)
12 358 1.83 94 >99
89/98 after 5
cycles
this work
12 358 1.83 30 -
+
(1:3)
12 358
1.8:5.5
(1:3)
99 92
Comments: Low reaction temperature and time, high conversion and selectivity for
self- and cross-coupling reactions, low catalyst loading, improved reusability, and
catalytic performance after reuse; scalable production of catalyst, no need for an
oxygen-rich atmosphere.
12. 10
Figure S1. X-ray diffraction diagrams from i) pristine fluorographene (FG, the precursor of G-CN),
ii) cyanographene (G-CN) and iii) the copper-loaded cyanographene (G(CN)-Cu). X-Ray radiation
used: Co K-alpha (1.789 Å). Comments: The catalyst powder (as well as the rest of the solids)
lacks completely reflections from any inorganic nanoparticles. Only the very broad reflection at
30.4 degrees is present, typical of non-restacked graphene powders and present in carbon materials.
The extent of the parallel stacking of graphenes (thickness of the crystallites, Lc) can be estimated
from the Scherrer formula.[S24, S25]
In the case of the G(CN)-Cu is 1.8 nm, which confirms that the
catalyst is composed of few layer graphene stacks, which are in a disordered state between each
other.
Figure S2. High-angle annular dark field scanning transmission electron microscopy images
showing heavier (and thus brighter) single metal atoms embedded in the G˗CN support.
13. 11
Figure S3. a) First derivative of the normalized X-ray absorption edge structure (XANES)
spectra of a G(CN)-Cu sample and relevant standard materials. Inset: the associated linear
combination analysis of the G(CN)-Cu spectrum, based on the spectra of Cu(H2O)6
2+
and Cu2O
standards (i.e. Cu(I) and Cu(II) species), confirming the copresence of Cu(I) and Cu(II). The
quality of the fit was compromized becasue aquaeous solutions of CuCl undergo spontaneous
oxidation to Cu(II), making it impossible to prepare a suitable atomically diapsersed Cu(I)
standrad. b) Fourier-Transformed k3
-weighted extended X-ray absorption fine structure
(EXAFS) spectra of G(CN)-Cu sample and relevant standard materials. Comments: The
XANES spectrum of G(CN)-Cu (panel a) resembles that of Cu(H2O)6
2+
more closely than those
of Cu2O and CuO, indicating that the Cu species in G(CN)-Cu are atomically dispersed. The
EXAFS spectra in panel b further confirm the presence of atomically dispersed Cu species in
the catalyst: peaks at the Cu-Cu distance corresponding to the 2nd coordination shell are visible
in the Fourier-transformed EXAFS signals of Cu2O and CuO, but not in those of G(CN)-Cu and
Cu(H2O)6.
14. 12
Figure S4. HR-XPS analysis of a) the Cu 2p3/2 core-level spectra of the two copper/graphene
systems (G-CN and reduced GO after interaction with CuCl2) b) the C 1s core level spectra of the
same graphene/copper systems. Reduced GO/Cu was prepared using the same procedure as G(CN)-
Cu, but with reduced graphene oxide (rGO) instead of G-CN. HR-XPS analysis revealed that Cu in
rGO occurs mainly in the Cu(II) valence state, as indicated by the intense satellite peaks, which are
characteristic of divalent copper ions. This experiment also demonstrates that (i) the cyano group of
the G(CN)-Cu catalyst is crucial for the charge transfer and stabilization of the mixed valence
Cu(I)/Cu(II) system, and (ii) the presence of an electron-rich 2D graphene skeleton alone is
insufficient for Cu(II) reduction (the very high content of sp2
carbon centers in the rGO is
demonstrated by the strong peak at 284.7 eV,shown in Figure S4b). This control sample (rGO-Cu)
confirms that the presence of Cu(I) ions should be attributed to specific interactions with the G-CN
support rather than reduction by the XPS electron beam.[S26]
Figure S5. EPR spectra of the G(CN)-Cu catalyst dispersed in hexane before (blue line) and after
(red line) adding hydrogen peroxide (30 %, 30 μL) directly into the EPR tube. An increase in the
Cu(II)-induced spectral signal was observed. We thus conclude that Cu(I) cations were indeed
present in the as-prepard catalyst, and they became EPR detectable after oxidation. Therefore, their
15. 13
presence was not a product of interaction with the XPS beam. Experimental parameters: Frequency
9.168 GHz, mod. Freq. 100 KHz, mod. amplitude of 0.8 mT, time const. of 30 ms, applied
microwave power of 0.6 mW, sweep time of 240 s, phase 0 deg, T = 143 K.
Comments on the analysis of the HR-XPS N1s envelope. Two different batches of the
starting G˗CN and of the catalyst (G(CN)-Cu) were evaluated, with identical results (Figure S6a).
Deconvolution clearly showed that after the binding of Cu ions, the ratio of the areas of the two
main N1/N2 components of G-CN changed significantly, from 1.3 to 1.7. That is, the lower binding
energy N1 component was enriched after coordination of the Cu(II) ions. This was surprising
because the Cu dication should attract electron density from its ligands. For instance, both
experimental and computational studies have shown that nitrogen atoms in N-doped graphene shift
to higher binding energies upon complexation with Co2+
. [S27]
The increased area of the lower
binding energy component after coordination was thus a clear indication of charge-transfer toward
the -C≡N groups in this case. The shift in the binding energy also confirms the interactions (i.e. the
formation of coordinative bonds) between the nitrile groups and Cu cations.
The two main components in the N1s XPS spectra can be ascribed to the attachment of
nitrile groups in different local environments (i.e. environments with and without nearby defects in
the graphene skeleton). This is also clearly reflected in the IR band of the nitrile groups, which is
asymmetric and was fitted with two major C≡N components (Figure S6b). The observation of
nitrile groups in multiple local environments is also consistent with the fact that not all copper
atoms are reduced upon interaction with cyanographene.
Figure S6. a) Deconvoluted HR-XPS N1s spectra for two different batches of G-CN and G(CN)˗Cu
samples. Circles represent experimental data and solid lines the fitting results. b) IR spectrum of
G˗CN showing the asymmetric nitrile band at 2200 cm-1
. The inset shows this asymmetric band
after deconvolution into three components, supporting the hypothesis that the material contains
nitrile groups in distinct local environments.
16. 14
Table S2. The binding of Cu(II) cations to G-CN in various solvents. The structures, selected bond
lengths (Å), binding energies (kcal mol–1
), spin density plots (contour value: 0.001), atomic spin,
and natural charge densities (a.u.) on the copper atom of model R-CN-Cu(II) systems were
computed at the U-B3LYP/6-31+G(d)/SMD level of theory. The structures were obtained via
constrained geometry optimizations at the same level of theory (see text for details on the
constraints).
Model ACN-Cu(II) Corronene-2CN-Cu(II) Cyc14-2CN-Cu(II)
Structure
RC-N/RN-Cu
Water 1.157/2.108 1.159/1.867 1.159/1.863
PAM 1.156/2.090 1.157/1.871 1.158/1.872
BAM 1.157/2.071 1.157/1.873 1.158/1.875
Binding energy
Water –8.1 –29.7 (–28.7)a
–28.0
PAM –17.7 –56.5 (–55.7) –59.5
BAM –28.7 –87.6 (–86.8) –92.8
Spin density
Spin density on Cu
Water 1.00 0.01 0.00
PAM 0.72 0.00 0.00
BAM 0.68 0.00 0.00
Charge density on Cu
Water 1.96 (1.68)b
1.04 (0.74) 1.03 (0.77)
PAM 1.67 (1.31) 1.02 (0.72) 1.01 (0.78)
BAM 1.63 (1.28) 1.01 (0.71) 1.00 (0.74)
a
The values in parentheses were obtained from the RO-B3LYP calculations.
b
The values in parentheses were determined via Mulliken population analysis.
Comments:
1. The similarity of the main structural characteristics, binding energies as well as spin and charge
densities of the two model G(CN)-Cu(II) systems justifies the use of a smaller model
(corronene-2CN-Cu(II)) for further analysis.
2. The spin unrestricted (U-B3LYP) and restricted-open shell (RO-B3LYP) formalisms yielded
similar binding energies for corronene-CN-Cu(II). This similarity and the low spin
contamination of the U-B3LYP ground state density (S2
< 0.751) confirmed that the U-B3LYP
approach is suitable for studying the open-shell states of G(CN)-Cu species.
3. Owing to the possibility of charge transfer, the binding of Cu(II) ions to the CN group in
G(CN)-Cu(II) systems differed considerably from and was significantly stronger than the
binding in ACN-Cu(II). This significantly stronger binding was accompanied by a significant
17. 15
decrease in the charge and spin densities on the copper atom. The charge transfer from
cyanographene to Cu(II) can thus facilitate the reduction of the copper oxidation state.
4. The solvent polarity had a significant effect on the stability of the G(CN)-Cu(II) systems.
Namely, less polar solvents were more effective in stabilizing the complex compared with more
polar solvents, where the solvation energy of Cu(II) ions is larger.
Similar C≡N bond lengths occurred in all R-CN-Cu(II) species and the bond lengths were
practically independent of the solvent polarity. The RCN of R-CN-Cu(II) species was only slightly
smaller than the C≡N bond in ACN (1.165 Å) indicating that the triple bond character was
preserved in R-CN-Cu(II). We collected the FT-IR spectra of the G(CN)-Cu catalyst focusing on
the very characteristic band of the nitrile (cyano) groups (occurring at 2200 cm–1
, as previously
reported30
), and no shift of the band frequency was observed. This concurred with the DFT
calculations, where no changes in the C≡N bond length were observed, since the charge transfer
originated from the aromatic graphene lattice (rather than from the electrons of the nitrile bond).
Table S3. Optimization studies and the effect of various reaction parameters on amine to imine
conversion using the G(CN)-Cu catalyst.a
Entry Catalyst Time (h) Temp (K) Conv. (%)b
Select. (%) TOF (h–1
)
1
2
3
4
5
6
7
8
9
10
11
-
G(CN)-Cu
G(CN)-Cu
G(CN)-Cu
G(CN)-Cu
G(CN)-Cu
G(CN)-Cu
G(CN)-Cu
CuO
rGO-Cu
GO
24
12
12
12
12
12
12
18
18
12
18
358
358
358
358
RT
348
373
358
358
358
358
-
96c
94
-d
-
78
99
97
64h
48h
13
-
99
>99
-
-
99
98
>99
97
94
92
-
14
14
-/-
-/-
11
14
9
6
6
1
a
Reaction conditions: 20 mg catalyst (10.7 µmol Cu), benzylamine 0.2 mL (1.83 mmol), air balloon (1 atm);
b
determined via GC; c
under O2 atmosphere (1 atm); d
nitrogen balloon-20 mg; RT: room temperature.
Comments:
1. No reaction occurred in the absence of the catalyst (entry 1). However, a 96% conversion (12 h
at 358 K under O2, >99% selectivity) was achieved for the imine (entry 2) when the G(CN)-Cu
catalyst was included. Approximately the same conversion (i.e., 94%) was attained, when the
reaction was conducted under air (entry 3, highlighted). This indicated the effectiveness of the
catalyst under low-oxygen conditions and its value for increased safety and cost-effectiveness
of the process. No reaction product was observed under nitrogen, thereby confirming that the
reaction requires O2 as an oxidant for the oxidative dehydrogenation of the amines (entry 4).
2. The robustness of the G(CN)-Cu catalyst was verified by examining various catalysts under the
same conditions. Pristine G˗CN and CuO yielded 25% and 64% conversions, respectively
18. 16
(entry 9). Furthermore, the importance of the nitrile groups of G-CN and the mixed valence
character was revealed by testing rGO-Cu that contained Cu(II) ions mainly (rGO-Cu used
previously for XPS comparisons with G(CN)-Cu). The results revealed a conversion of only
48% for rGO-Cu (entry 10). Pure GO was subsequently tested with conversion of 13% (entry
11).
3. TON = moles of desired product (Nz)/(moles of catalyst (Nc) or moles of active sites)
Conversion (C%) = moles of all product (Np × 100)/moles of reactant (Nr), or Np = (C%) × Nr/100
Selectivity (S%) = [moles of desired product (Nz) × 100/moles of all product (Np)]
or Nz = (S%) × Np/100, or Nz = (S%) × [(C%) × Nr/100]/100 = (S%) × (C%) × Nr/104
Turnover number (TON) = Nz/Nc = [(S%) × (C%) × Nr/104
]/Nc
Turnover frequency (TOF) = rate of product formation over catalyst = TON/time
Example: Table S3, entry 11:
TON = [92 × 13 × 1.83 (mmol)/104
]/10.7 × 10–3
(mmol) = 20.4
TOF = 20.4518 = 1.1 h–1
Table S4. Optimization of benzylamine and aniline molar ratio for the generation of asymmetrical
imine products using the G(CN)-Cu catalyst.a
Entry Benzylamine:Aniline
(mole ratio)
Conv. (%)b
Product 1a Select.
(%)
Product 2a Select. (%)
1
2
3
4
5
3:1
2:1
1:1
1:2
1:3
97
>99
>99
>99
>99
83
72
44
12
8
17
28
56
88
92
a
Reaction conditions: Catalyst 10.7 µmol Cu, benzylamine 1.83 mmol, and aniline 5.49 mmol (for 1:3 ratio), air balloon
(1 atm); 24–30 h; b
determined via GC.
Table S5. Elemental chemical composition (at.%) as determined from HR-XPS of the fresh and the
recycled G(CN)-Cu catalyst.
Times used C 1s N 1s O 1s Cu 2p
Fresh
G(CN)-Cu
77.7 14.1 7.6 0.7
After 5th
recycle
76.8 15.5 6.8 0.9a
a
The higher content of Cu in the fifth cycle is due to the measurement uncesrtainty of XPS.
19. 17
Figure S7. HR-XPS analysis. G(CN)-Cu catalyst after the 1st (left panels) and the 5th recycling
(right panels) steps. Deconvolution in the a),b) Cu 2p region, c,d) C 1s region, and e),f) N 1s region.
20. 18
Table S6. The stability of G(CN)-Cu2+
aqua complexes in various solvents. The structures, selected
bond lengths (Å), and complex formation energies (kcal mol–1
) of model G(CN)-Cu2+
aqua
complexes in selected solvents were computed at the B3LYP/6-31+G(d)/SMD level of theory. The
structures were obtained via constrained geometry optimizations at the same level of theory (see
text for details on the constraints).
Model cor-2CN-Cu
2+
/1w cor-2CN-Cu
2+
/2w-Y cor-2CN-Cu
2+
/3w-Tg
Structure
Description
One water molecule bound
at the axial position
Two water molecules in a Y
position
Three water molecules
at the Tg coordination
RN-Cu/RCu-O
Water 1.851/1.961 unstable 2.008/2.002 (2.004, 2.004)
PAM 1.864/1.956 unstable unstable
BAM 1.866/1.965 1.860/2.004 (2.358) unstable
Binding energy
Water -15.1 NA -27.1
PAM -13.4 NA NA
BAM -17.5 -23.3 NA
Model cor-2CN-Cu
2+
/3w-Th cor-2CN-Cu
2+
/4w-tbpy cor-2CN-Cu
2+
/5w-Oh
Structure
Description
Three water molecules
at the Th coordination
Four water molecules at the
tbpy coordination
Five water molecules
at the Oh coordination (non-
equivalent equatorial bonds)
RN-Cu/RCu-O
Water unstable unstable 2.045/2.040 (2.04, 2.50)
PAM
1.873/2.191 (2.197,
2.179)
unstable 1.965/2.027 (2.11, 2.34)
BAM
1.873/2.218 (2.204,
2.185)
unstable unstable
Binding energy
water NA NA -27.6
PAM -19.4 NA -26.8
BAM -28.6 NA NA
Comments:
1. The relative stability of G(CN)-Cu2+
aqua complexes with a given coordination number largely
depends on the solvent. In a water environment, the mono- and three-aqua (Tg) have been
identified as the stable structures. The Oh structure exhibits two types of equatorial bonds (in
trans position), which correspond possibly to the Tg structure.
21. 19
2. In BAM and PAM environments, the three-aqua (Th) complex occurs as a stable structure (in
addition to the 1w-axial structure).
Table S7. The binding of benzylic amines to G(CN)-Cu(II) with the amine also acting as a solvent.
The structures, selected bond lengths (Å), complex formation energies (kcal mol–1
), spin density
plots (contour value: 0.001), atomic spin, and charge densities (a.u.) on the copper atom of model
G(CN)-Cu(II)/amine complexes in the corresponding amine solvent were computed at the
B3LYP/6-31+G(d)/SMD level of theory. The structures were obtained via constrained geometry
optimizations at the same level of theory (see text for details on the constraints).
Model
cor-2CN-Cu(II)/
BAM/bare-axial
cor-2CN-Cu(II)/
PAM/bare-Y
cor-2CN-Cu(II)/
PAM/bare-axial
Structure
Description
One BAM molecule
bound
at the axial position
One PAM molecule
bound
at the Y position
One PAM molecule bound
at the axial position
RN-Cu/RCu-N(am)
BAM/PAM 1.861/1.949 1.860/2.032 (2.084) 1.848/1.932
RC-
N(Am)/RN(am)-H
BAM/PAM 1.504/1.024 1.482/1.021 1.494/1.022
Binding energy
BAM/PAM –36.7 (–36.9)a
3.1 11.6
Spin density
plot
Spin density on the copper atom
BAM/PAM 0.00 0.22 0.01
Charge density on the copper atom
BAM/PAM 0.39 0.38 0.36
a
The value obtained when the cyc14-2CN-Cu(II) model is applied.
Comments:
1. Although a PAM molecule can form two bonds with the copper atom (in the Y-like
configuration), its binding is considerably weaker than that of BAM.
22. 20
2. The binding of BAM on G(CN)-Cu(II) leads to the prolongation (i.e., weakening) of C—N and
N—H bonds compared to non-bound BAM (RC-N(am) = 1.475 Å and RN(am)-H = 1.020 Å). This
prolongation increases the bond susceptibility to other reactive agents.
3. The spin and charge density analysis results concur with the findings obtained for the G(CN)-
Cu(II) systems, i.e., the charge of the copper atom decreases significantly and an unpaired
electron is delocalized over the G-CN surface.
23. 21
Table S8. Structures, selected bond lengths (Å), and complex formation energies (kcal mol–1
) of
model G(CN)-Cu(I)/amine complexes in the corresponding amine solvent were computed at the
B3LYP/6-31+G(d)/SMD level of theory. The structures were obtained via constrained geometry
optimizations at the same level of theory (see text for details on the constraints).
Model
cor-2CN-Cu(I)/
BAM/bare-axial
cor-2CN-Cu(I)/
PAM/bare-Y
Structure
Description
One BAM molecule
bound
at the axial position
One PAM molecule
bound
at the Y position
RN-Cu/RCu-N(am)
BAM/PAM 1.858/1.949 1.860/2.055 (2.086)
Binding energy
BAM/PAM –35.8 –2.3
Comments:
1. As in the case of G(CN)-Cu(II), a benzylamine molecule attacks the axial position of the
copper atom bound to the G˗CN surface in a bare fashion, i.e., the simultaneous binding of
water molecules from a side is unfavorable. The binding parameters (relevant bond lengths and
the complexation energy) are almost identical to those of the G(CN)-Cu(II)/BAM complex.
This indicates that the Cu…BAM binding is mainly determined by the positive charge on the
copper atom, which is similar in both cases.
2. The binding of a PAM molecule is considerably weaker than that of BAM.
Catalytic mechanism governing the oxidative dehydrogenation of amines
A theoretical study of the catalytic mechanism governing the oxidative dehydrogenation of amines
was performed at the B3LYP/6-31+G(d)/SMD level using two model systems representing single-
center (Figure M1a) and double-center (Figure M1c) sites on the G(CN)-Cu catalyst. The former
was used for modeling reaction steps involving a single Cu(I)/Cu(II) center (e.g., oxygen activation
and formation of hydroperoxyl radical and release of water, see step 1-I, 2I-2II, in Figure S8).
However, the latter was applied for processes involving two neighboring Cu centers (e.g., formation
of a cyclic intermediate and subsequent hydrogen abstraction, see step 3˗I in Figure S8).
Benzylamine (BAM) was selected as a representative amine, participating in the reaction, as well as
the solvent. The structures playing key roles in the mechanism elaborated in Figures S8–S11 are
displayed in Figure S12.
24. 22
Figure S8. Initial steps of the catalytic mechanism. In step 1-I oxygen binding and activation takes
place. Calculations suggest that this configuration requires a small amount of energy (ca. 20 kcal
mol–1
), in close agreement to the findings on oxygen binding in copper enzymes.17
Calculations also
indicated partial charge-transfer from the G-CN-Cu(I)-amine system (ca. 0.34 e, Figure S12,
structure 1-I) and increase of the nucleophilic character of O-O, thus promoting the first homolytic
hydrogen abstraction from the co-coordinated amine. In step 2-I, the formed hydroperoxo-copper
complex can mediate a second homolytic hydrogen atom abstraction, leading to formation and
release of a water molecule (step 2-II), of the imine and a copper-oxyl complex (step 3-I). The oxyl-
intermediate withdraws one electron from the Cu(I) center, and then facilitates a proton abstraction,
which leaves behind two electrons, one of them reducing the Cu(II) center. The reaction energies
are given in kcal mol–1
; the estimated activation energies are reported in brackets.
25. 23
Figure S9. Oxidation steps involving the cyclic intermediate (3-II) that interacts with a hydrogen
atom on the BAM molecule, which is coordinated to the neighboring Cu center. After abstraction of
the proton, the reaction can proceed either through a single-step or a two-step release of a water
molecule. The former appears to be more favorable (than the latter) due to lower reaction energy
(kcal mol–1
); the estimated activation energies are reported in brackets.
26. 24
Figure S10. Exchange of ligands (amine and imine) on the a) Cu(II) and b) Cu(I) centers. The
reaction energies are given in kcal mol–1
; no activation energy is required for the processes. The low
magnitude of the binding and releasing energies (independent of copper oxidation state) suggests
easy ligand exchange. Nevertheless, the most stable structure (5-III) enables formation of the final
product (see Figure S11).
27. 25
Figure S11. Final steps of the mechanism. a) Reaction of an amine with imine in a concerted
fashion is thermodynamically favorable; although the activation barrier can be rather high (the
reported value represents an upper limit). b) Alternatively, an intermediate state from step (4) can
act as an active site for the reaction leading to a product isomer that transforms to an energetically
more stable product (E = –18.6 kcal mol–1
). In the last step, ammonia can be readily formed via
abstraction of hydrogen from the environment (not shown).
28. 26
Figure S12. The key structures occurring in the catalytic mechanism, as described in Figure S8–
S11. The NBO charges are displayed in selected structures.
29. 27
Table S9. Calculations for the estimation of the copper ions surface density.
Number of atoms in G(CN)-Cua
Cin graphene
b
Cin CN Nin CN
c
Cu
76.3 11.5 11.5 0.7
100 atoms in total
Mass of atoms (g)
Cin graphene Cin CN Nin CN Cu
1.52×10–21
2.29×10–22
2.68×10–22
7.1×10–23d
Total mass of atoms in G(CN)-Cu: 2.09×10–21
g
Surface area calculations
1 g of G(CN)-Cu occupies 153 m2
(the experimental value)
2.09×10–21
g of G(CN)-Cu occupies 3.19×10–19
m2
or 32 Å2
0.7 Cu atoms occupies 32 Å2
or 1 Cu atom occupies ~48 Å2
a
The ratio of the number of atoms was based on the present XPS results, which are in full agreement with the previously
reported findings in ref 28. 100 atoms were considered in total.
b
According to these XPS results, 15% of the carbon atoms in graphene lattice are functionalized with CN groups (i.e.,
15% functionalization degree).
c
The N-content used here is 11.5 (lower than the nominal N-content in the XPS results in Table S5), because, as we
have analyzed in detail in our previous work on the synthesis of G-CN,30
there is a small amount of background N,
coming from the solvent (DMF) during the synthesis of G-CN.
d
This amount equals 3.4 wt.% of Cu atoms in the catalyst, according to the ICP results.
Table S10. Control experiments on the oxidative cross-coupling of benzylamine with aniline.a
Entry Copper–based Catalysts Conv. (%)b
Product 1a
Select. (%) (homo)
Product 2a
Select. (%) (hetero)
1
2
3
4
5
CuCl
CuCl2
CuCl + CuCl2
GCN-Cu (0.5wt%)c
GCN-Cu (3.4wt%)
47
60
56
93
>99
93
100
92
62
8
7
0
8
38
92
a
Reaction conditions: Catalyst (10.7 µmol Cu), 1.83 mmol benzylamine, and 5.49 mmol aniline (giving a 1:3 ratio), air
balloon (1 atm); 24–30 h; b
determined via GC. c
The amount of catalyst used was adjusted to ensure that the total copper
content of the reaction mixture remained constant (3.4 wt%).
6.9Å
6.9Å
30. 28
Figure S13. Two-center amine coupling reaction mechanism: a comparison of benzylamine and
aniline focused on step 2 of the simplified mechanism presented in Fig. 4a. The numbers beneath
the arrows illustrate the energetics of cooperative proton abstraction from an amine by the
neighboring G-(CN)-Cu(II)-O–
complex. a) Proton abstraction from the α˗carbon of benzylamine
(BAM); b) Proton abstraction from the amino group of BAM; and c) Proton abstraction from the
amino group of aniline (AN). In the case of BAM, the C-H bond cleavage is energetically
preferable. For aniline, which lacks α-hydrogens, proton abstraction from N-H is also
thermodynamically accesible through the cyclic intermediate; this can be attributed to the
comparative weaker N-H bond in AN resulting from the mesomeric effect and the stabilization of
resulting radical by the neighboring aromatic ring. The energies (reported in kcal mol-1
) were
obtained at the B3LYP/6-31+G(d) level of theory using the SMD implicit solvent model (solvent =
benzylamine) with the ovalene platform kept frozen during geometry optimizations.
Comments on the importance of Cu(I)/Cu(II) cooperativity for high selectivity toward
crosscoupling. As reported previously (Table S1), BAM undergoes self˗coupling without requiring
cooperativity because the intermediate imine can be formed at a single Cu center (Figure S8, steps
1-I to 2-II). Imine formation is required for the coupling reaction with a second BAM molecule
(Figure S11, step 6-IV). However, AN cannot undergo hydrogen abstraction and activation as BAM
does. Although the first H-abstraction would be possible (Figure S8, step 1˗I), forming a more
nucleophilic N-centered radical anion (Figure S8 step 2-I), this step is energetically demanding
(+21.9 kcal mol-1
) and thus improbable for both BAM and AN. The following step is energetically
very favorable (-32.2 kcal mol-1
), rendering the overall process viable. However, AN, completely
lacking α˗hydrogens, cannot undergo this second step, making its activation improbable.
Consequently, the only possible pathway in a single metal-center reaction is the nucleophilic attack
of AN on the BAM-derived imine, as widely accepted.[S14,S28,S29]
This process gives low yields and
poor selectivity for the cross-coupled product[S21,35]
becasue of AN’s low nucleophilicity.
Nevertheless, the activation of AN through the cyclic two-center mechanism is energetically much
more favorable (Figure S13c). Selectivities comparable to those achieved with G(CN)-Cu have
31. 29
previously only been attained by combining high reaction temperatures with pure O2 atmosphere
and high catalyst reaction loadings.[S14,39]
Figure S14. Electron microscopy on G(COOH)-Fe. a) representative HR˗TEM of a graphene flake
from the G(COOH)-Fe verifying the absence of any nanoparticles. b) HR-TEM image of
G(COOH)-Fe showing several high-contrast isolated spots originating from single Fe atoms
entrapped on the G-COOH flake. c),d) EDS chemical maps on G(COOH)˗Fe for c) Fe and d)
combined C and Fe.
32. 30
Figure S15. 57
Fe Mössbauer spectrum of the G(COOH)-Fe sample, recorded at a temperature of 5
K in absence of external magnetic field. The asymmetric line-shape of the spectrum denotes the
presence of two different Fe components. Deconvolution of the spectrum suggested the presence of
Fe ions in different valence states (Fe(III) and Fe(II)), according to the isomer shift of the
components (see Table S10), which was ascribed to a partial charge transfer from graphene to Fe
centers, as in the case of the G(CN)˗Cu catalyst. In addition, the quadrupole splitting of the two Fe
species underlined the change of the their coordination environment in the G(COOH)-Fe sample, in
comparison to the starting Fe source (Fe(NO3)3·9H2O).
33. 31
Table S11. Values of the Mössbauer hyperfine parameters, derived from the least-square
fitting of the 57
Fe Mössbauer spectrum of the G(COOH)-Fe sample, collected at a temperature
of 5 K, where δ is the isomer shift, ΔEQ is the quadrupole splitting, and RA is the spectral area
of individual spectral components, identified upon spectrum fitting.
Component δ ± 0.01
(mm s–1
)
ΔEQ ± 0.01
(mm s–1
)
RA ± 1
(%)
Assignment
Doublet –0.02 0.43 12 Fe(II)
Doublet 0.56 0.77 88 Fe(III)
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