Abstract: New graphene oxide (GO)-tethered–CoII phthalocyanine
complex [CoPc–GO] was synthesized by a stepwise
procedure and demonstrated to be an efficient, cost-effective
and recyclable photocatalyst for the reduction of carbon
dioxide to produce methanol as the main product. The developed
GO-immobilized CoPc was characterized by X-ray
diffraction (XRD), FTIR, XPS, Raman, diffusion reflection UV/
Vis spectroscopy, inductively coupled plasma atomic emission
spectroscopy (ICP-AES), thermogravimetric analysis
(TGA), Brunauer–Emmett–Teller (BET), scanning electron microscopy
(SEM), and transmission electron microscopy (TEM).
FTIR, XPS, Raman, UV/Vis and ICP-AES along with elemental
analysis data showed that CoII–Pc complex was successfully
grafted on GO. The prepared catalyst was used for the photocatalytic
reduction of carbon dioxide by using water as
a solvent and triethylamine as the sacrificial donor. Methanol
was obtained as the major reaction product along with the
formation of minor amount of CO (0.82 %). It was found that
GO-grafted CoPc exhibited higher photocatalytic activity
than homogeneous CoPc, as well as GO, and showed good
recoverability without significant leaching during the reaction.
Quantitative determination of methanol was done by
GC flame-ionization detector (FID), and verification of product
was done by NMR spectroscopy. The yield of methanol
after 48 h of reaction by using GO–CoPc catalyst in the presence
of sacrificial donor triethylamine was found to be
3781.8881 mmolg1 cat., and the conversion rate was found
to be 78.7893 mmolg1cat.h1. After the photoreduction experiment,
the catalyst was easily recovered by filtration and
reused for the subsequent recycling experiment without significant
change in the catalytic efficiency.
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
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
Reduced graphene oxide–CuO nanocomposites for photocatalyticconversion of CO2...Pawan Kumar
tReduced graphene oxide (rGO)–copper oxide nanocomposites are prepared by covalent grafting of CuOnanorods on the rGO skeleton. Chemical and structural features of rGO–CuO nanocomposites are probedby FTIR, XPS, XRD and HRTEM analyses. Photocatalytic potential of rGO–CuO nanocomposites is exploredfor reduction of CO2into the methanol under the visible light irradiation. The breadth of CuO nanorods andthe oxidation state of Cu in the rGO–CuO/Cu2O nanocomposites are systematically varied to investigatetheir photocatalytic activities. The pristine CuO nanorods exhibited very low photocatalytic activity owingto fast recombination of charge carriers and yielded 175 mol g−1methanol, whereas rGO–Cu2O andrGO–CuO exhibited significantly improved photocatalytic activities and yielded five (862 mol g−1) andseven (1228 mol g−1) folds methanol, respectively. The superior photocatalytic activity of CuO in therGO–CuO nanocomposites was attributed to slow recombination of charge carriers and efficient transferof photo-generated electrons through the rGO skeleton. This study further excludes the use of scavengingdonor.
tA highly efficient, recyclable and magnetically separable core-shell structured CuZnO@Fe3O4microspherewrapped with reduced graphene oxide (rGO@CuZnO@Fe3O4) photocatalyst has been developed and usedfor the photoreduction of carbon dioxide with water to produce methanol under visible light irradiation.Owing to the synergistic effect of the components and to the presence of a thin Fe2O3layer on Fe3O4,rGO@CuZnO@Fe3O44 exhibited higher catalytic activity as compared to the other possible combinationssuch as CuZnO@Fe3O42 and GO@CuZnO@Fe3O43 microspheres. The yield of methanol in case of using2 and 3 as photocatalyst was found to be 858 and 1749 mol g−1cat, respectively. However, the yieldwas increased to 2656 mol g−1cat when rGO@CuZnO@Fe3O44 was used as photocatalyst under sim-ilar experimental conditions. This superior photocatalytic activity of 4 was assumed to be due to therestoration of the sp2hybridized aromatic system in rGO, which facilitated the movement of electronsand resulted in better charge separation. The synthesized heterogeneous photocatalyst could readily berecovered by external magnet and successfully reused for six subsequent cycles without significant loss in the product yield.
Photocatalytic reduction of carbon dioxide to methanol using a ruthenium trin...Pawan Kumar
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
A highly efficient, recyclable and magnetically separable core-shell structured CuZnO@Fe3O4 microsphere
wrapped with reduced graphene oxide (rGO@CuZnO@Fe3O4) photocatalyst has been developed and used
for the photoreduction of carbon dioxide with water to produce methanol under visible light irradiation.
Owing to the synergistic effect of the components and to the presence of a thin Fe2O3 layer on Fe3O4,
rGO@CuZnO@Fe3O4 4 exhibited higher catalytic activity as compared to the other possible combinations
such as CuZnO@Fe3O4 2 and GO@CuZnO@Fe3O4 3 microspheres. The yield of methanol in case of using
2 and 3 as photocatalyst was found to be 858 and 1749 mol g−1 cat, respectively. However, the yield
was increased to 2656 mol g−1 cat when rGO@CuZnO@Fe3O4 4 was used as photocatalyst under similar
experimental conditions. This superior photocatalytic activity of 4 was assumed to be due to the
restoration of the sp2 hybridized aromatic system in rGO, which facilitated the movement of electrons
and resulted in better charge separation. The synthesized heterogeneous photocatalyst could readily be
recovered by external magnet and successfully reused for six subsequent cycles without significant loss
in the product yield
Visible light driven photocatalytic oxidation of thiols to disulfides using i...Pawan Kumar
The present paper describes the synthesis of graphene oxide immobilized iron phthalocyanine (FePc) for
the photocatalytic oxidation of thiols to disulfides under alkaline free conditions. Iron phthalocyanine
tetrasulfonamide was immobilized on carboxylated graphene oxide supports via covalent attachment.
The loading of FePc on GO nanosheets was confirmed by FTIR, Raman, ICP-AES, UV-Vis and elemental
analyses. The synthesized catalyst was found to be highly efficient for the photo-oxidation of thiols to
disulfides in aqueous medium using molecular oxygen as oxidant under visible light irradiation. The
identification of photo-oxidation products and their quantitative determination was done using GC-MS.
After completion of the reaction, the catalyst was easily recovered by filtration and reused for several
runs without loss in activity and no leaching was observed during the reaction
Carbon Nitride Grafted Cobalt Complex (Co@npg-C3N4) for Visible LightAssiste...Pawan Kumar
Azide containing bipyridine complex of cobalt was grafted to
the propargylated nanoporous graphitic carbon nitride (npg-C3
N4) via click reaction to obtain heterogenized photocatalyst
which could efficiently provide direct esterification of aldehydes
under visible light irradiation at room temperature. The use of
click reaction as grafting strategy provided covalent attachment
of the cobalt complex to support which not only provided
higher loading but also precluded the leaching. Furthermore,
the presence of carbon nitride support exhibited synergistic
effect to enhance the reaction rate. In addition, the milder basic
nature of nitrogen containing graphitic support provided
efficient ester synthesis without the need for an external base.
The synthesized photocatalyst was found to be quite robust
which could easily be recovered and reused several times
without significantly losing activity.
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
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
Reduced graphene oxide–CuO nanocomposites for photocatalyticconversion of CO2...Pawan Kumar
tReduced graphene oxide (rGO)–copper oxide nanocomposites are prepared by covalent grafting of CuOnanorods on the rGO skeleton. Chemical and structural features of rGO–CuO nanocomposites are probedby FTIR, XPS, XRD and HRTEM analyses. Photocatalytic potential of rGO–CuO nanocomposites is exploredfor reduction of CO2into the methanol under the visible light irradiation. The breadth of CuO nanorods andthe oxidation state of Cu in the rGO–CuO/Cu2O nanocomposites are systematically varied to investigatetheir photocatalytic activities. The pristine CuO nanorods exhibited very low photocatalytic activity owingto fast recombination of charge carriers and yielded 175 mol g−1methanol, whereas rGO–Cu2O andrGO–CuO exhibited significantly improved photocatalytic activities and yielded five (862 mol g−1) andseven (1228 mol g−1) folds methanol, respectively. The superior photocatalytic activity of CuO in therGO–CuO nanocomposites was attributed to slow recombination of charge carriers and efficient transferof photo-generated electrons through the rGO skeleton. This study further excludes the use of scavengingdonor.
tA highly efficient, recyclable and magnetically separable core-shell structured CuZnO@Fe3O4microspherewrapped with reduced graphene oxide (rGO@CuZnO@Fe3O4) photocatalyst has been developed and usedfor the photoreduction of carbon dioxide with water to produce methanol under visible light irradiation.Owing to the synergistic effect of the components and to the presence of a thin Fe2O3layer on Fe3O4,rGO@CuZnO@Fe3O44 exhibited higher catalytic activity as compared to the other possible combinationssuch as CuZnO@Fe3O42 and GO@CuZnO@Fe3O43 microspheres. The yield of methanol in case of using2 and 3 as photocatalyst was found to be 858 and 1749 mol g−1cat, respectively. However, the yieldwas increased to 2656 mol g−1cat when rGO@CuZnO@Fe3O44 was used as photocatalyst under sim-ilar experimental conditions. This superior photocatalytic activity of 4 was assumed to be due to therestoration of the sp2hybridized aromatic system in rGO, which facilitated the movement of electronsand resulted in better charge separation. The synthesized heterogeneous photocatalyst could readily berecovered by external magnet and successfully reused for six subsequent cycles without significant loss in the product yield.
Photocatalytic reduction of carbon dioxide to methanol using a ruthenium trin...Pawan Kumar
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
A highly efficient, recyclable and magnetically separable core-shell structured CuZnO@Fe3O4 microsphere
wrapped with reduced graphene oxide (rGO@CuZnO@Fe3O4) photocatalyst has been developed and used
for the photoreduction of carbon dioxide with water to produce methanol under visible light irradiation.
Owing to the synergistic effect of the components and to the presence of a thin Fe2O3 layer on Fe3O4,
rGO@CuZnO@Fe3O4 4 exhibited higher catalytic activity as compared to the other possible combinations
such as CuZnO@Fe3O4 2 and GO@CuZnO@Fe3O4 3 microspheres. The yield of methanol in case of using
2 and 3 as photocatalyst was found to be 858 and 1749 mol g−1 cat, respectively. However, the yield
was increased to 2656 mol g−1 cat when rGO@CuZnO@Fe3O4 4 was used as photocatalyst under similar
experimental conditions. This superior photocatalytic activity of 4 was assumed to be due to the
restoration of the sp2 hybridized aromatic system in rGO, which facilitated the movement of electrons
and resulted in better charge separation. The synthesized heterogeneous photocatalyst could readily be
recovered by external magnet and successfully reused for six subsequent cycles without significant loss
in the product yield
Visible light driven photocatalytic oxidation of thiols to disulfides using i...Pawan Kumar
The present paper describes the synthesis of graphene oxide immobilized iron phthalocyanine (FePc) for
the photocatalytic oxidation of thiols to disulfides under alkaline free conditions. Iron phthalocyanine
tetrasulfonamide was immobilized on carboxylated graphene oxide supports via covalent attachment.
The loading of FePc on GO nanosheets was confirmed by FTIR, Raman, ICP-AES, UV-Vis and elemental
analyses. The synthesized catalyst was found to be highly efficient for the photo-oxidation of thiols to
disulfides in aqueous medium using molecular oxygen as oxidant under visible light irradiation. The
identification of photo-oxidation products and their quantitative determination was done using GC-MS.
After completion of the reaction, the catalyst was easily recovered by filtration and reused for several
runs without loss in activity and no leaching was observed during the reaction
Carbon Nitride Grafted Cobalt Complex (Co@npg-C3N4) for Visible LightAssiste...Pawan Kumar
Azide containing bipyridine complex of cobalt was grafted to
the propargylated nanoporous graphitic carbon nitride (npg-C3
N4) via click reaction to obtain heterogenized photocatalyst
which could efficiently provide direct esterification of aldehydes
under visible light irradiation at room temperature. The use of
click reaction as grafting strategy provided covalent attachment
of the cobalt complex to support which not only provided
higher loading but also precluded the leaching. Furthermore,
the presence of carbon nitride support exhibited synergistic
effect to enhance the reaction rate. In addition, the milder basic
nature of nitrogen containing graphitic support provided
efficient ester synthesis without the need for an external base.
The synthesized photocatalyst was found to be quite robust
which could easily be recovered and reused several times
without significantly losing activity.
Graphene oxide immobilized copper phthalocyanine tetrasulphonamide: the first...Pawan Kumar
The first successful synthesis of DMC directly from methanol and carbon dioxide using a heterogenized
homogeneous graphene oxide immobilized copper phthalocyanine tetrasulphonamide catalyst in the
presence of N,N0-dicyclohexylcarbodiimide (DCC) as a dehydrating agent is described. The presence of a
dehydrating agent was found to be vital and in its absence the yield of DMC was found to be decreased
significantly. Under the optimized reaction conditions, the maximum yield of DMC reaches up to 13.3%.
Although the homogeneous copper phthalocyanine tetrasulphonamide catalyst provided a little higher
yield of DMC (14.2%), the facile recovery and recycling ability of the heterogeneous catalyst make the
developed method more attractive from environmental and economical viewpoints.
Hexamolybdenum clusters supported on graphene oxide: Visible-light induced ph...Pawan Kumar
Hexamolybdenum (Mo6) cluster-based compounds namely Cs2Mo6Bri
8Bra6
and
(TBA)2Mo6Bri
8Bra
6 (TBA = tetrabutylammonium) were immobilized on graphene oxide (GO)
nanosheets by taking advantage of the high lability of the apical bromide ions with
oxygen-functionalities of GO nanosheets. The loading of Mo6 clusters on GO nanosheets
was probed by Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron
spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and elemental
mapping analyses. The developed GO-Cs2Mo6Bri
8Bra
x and GO-(TBA)2Mo6Bri
8Bra
x
composites were then used as heterogeneous photocatalysts for the reduction of CO2 under
visible light irradiation. After 24 h visible light illumination, the yield of methanol was
found to be 1644 and 1294 lmol g1 cat for GO-Cs2Mo6Bri
8Bra
x and GO-(TBA)2Mo6Bri
8Bra
x,
respectively. The quantum yields of methanol by using GO-Cs2Mo6Bri
8Bra
x and
GO-(TBA)2Mo6Bri
8Bra
x as catalysts with reference to Mo6 cluster units presented in 0.1 g
amount of catalyst were found to be 0.015 and 0.011, respectively. The role of immobilized
Mo6 clusters-based compounds on GO nanosheets is discussed to understand the
photocatalytic mechanism of CO2 reduction into methanol.
Hexamolybdenum clusters supported on graphene oxide: Visible-light induced ph...Pawan Kumar
Hexamolybdenum (Mo6) cluster-based compounds namely Cs2Mo6Bri
8Bra6
and
(TBA)2Mo6Bri
8Bra
6 (TBA = tetrabutylammonium) were immobilized on graphene oxide (GO)
nanosheets by taking advantage of the high lability of the apical bromide ions with
oxygen-functionalities of GO nanosheets. The loading of Mo6 clusters on GO nanosheets
was probed by Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron
spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and elemental
mapping analyses. The developed GO-Cs2Mo6Bri
8Bra
x and GO-(TBA)2Mo6Bri
8Bra
x
composites were then used as heterogeneous photocatalysts for the reduction of CO2 under
visible light irradiation. After 24 h visible light illumination, the yield of methanol was
found to be 1644 and 1294 lmol g1 cat for GO-Cs2Mo6Bri
8Bra
x and GO-(TBA)2Mo6Bri
8Bra
x,
respectively. The quantum yields of methanol by using GO-Cs2Mo6Bri
8Bra
x and
GO-(TBA)2Mo6Bri
8Bra
x as catalysts with reference to Mo6 cluster units presented in 0.1 g
amount of catalyst were found to be 0.015 and 0.011, respectively. The role of immobilized
Mo6 clusters-based compounds on GO nanosheets is discussed to understand the
photocatalytic mechanism of CO2 reduction into methanol.
Abstract: Novel graphene oxide (GO) tethered Co(II) phthalocyanine complex [CoPc–GO] was synthesized via a stepwise procedure and demonstrated to be an efficient, cost effective and recyclable photocatalyst for the reduction of carbon dioxide to produce methanol as the main product. The developed GO-immobilized CoPc was characterized by X-ray diffraction (XRD), FT-IR, XPS, Raman, diffusion reflection UV-Vis spectroscopy, inductively coupled plasma atomic emission spectroscopy (ICP-AES), TGA, BET, SEM and TEM. FT-IR, XPS, Raman, UV-Vis and ICP-AES along with elemental analysis results showed that Co(II) Pc complex was successfully grafted on GO. The prepared catalyst was used for the photocatalytic reduction of carbon dioxide by using water as a solvent and triethylamine as the sacrificial donor. Methanol was obtained as the major reaction product along with the formation of minor amount of CO (0.82 %). It was found that GO-grafted CoPc exhibited higher photocatalytic activity than homogeneous CoPc as well as graphene oxide and showed good recoverability without significant leaching during the reaction. Quantitative determination of methanol was done by GC-FID and confirmation of product was done by NMR. The yield of methanol after 48 hours of reaction by using GO-CoPc catalyst in the presence of sacrificial donor triethylamine was found to be 3781.8881μmol.g-1-cat and the conversion rate was found to be 78.7893 μmol.g-1cat.h-1. After the photoreduction experiment, the catalyst was easily recovered by filtration and reused for the subsequent recycling experiment without significant change in the catalytic efficiency
A bridged ruthenium dimer (Ru–Ru) for photoreduction of CO2 under visible li...Pawan Kumar
A bridged binuclear complex consisting of two ruthenium units (Ru–Ru) connected through a bridging ligand was synthesized, in which one unit serves as a photosensitizer, while another unit works as a catalyst. The synthesized Ru–Ru photocatalyst was tested for photoreduction of CO2 to give CO and HCOOH under visible light irradiation in the presence of triethanolamine as a sacrificial donor. The yield of CO and HCOOH was found to be 54 ppm and 28 ppm respectively after 12 h of irradiation. Due to the binding of photosensitizer and catalyst units in a single molecule via bridging ligand provides faster and efficient electron transfer from sensitizer to catalyst unit which resulted in the higher activity and better product yields.
Metal-organic hybrid: Photoreduction of CO2 using graphitic carbon nitride su...Pawan Kumar
A novel heteroleptic iridium complex supported on graphitic carbon nitride was synthesized and used
for photoreduction of carbon dioxide under visible light irradiation. The methanol yield obtained after
24 h irradiation was 9934 mmol g1cat (TON 1241 with respect to Ir) by using triethylamine (TEA) as a
sacrificial donor, which was significantly higher as compared to the semiconductor carbon nitride
145 mmol g1cat under identical conditions. The presence of triethylamine was found to be vital for the
higher methanol yield. After the reaction, the photocatalyst could easily be recovered and reused for
subsequent six runs without significant loss in photo activity.
Metal-organic hybrid: Photoreduction of CO2 using graphitic carbon nitride su...Pawan Kumar
A novel heteroleptic iridium complex supported on graphitic carbon nitride was synthesized and used
for photoreduction of carbon dioxide under visible light irradiation. The methanol yield obtained after
24 h irradiation was 9934 mmol g1cat (TON 1241 with respect to Ir) by using triethylamine (TEA) as a
sacrificial donor, which was significantly higher as compared to the semiconductor carbon nitride
145 mmol g1cat under identical conditions. The presence of triethylamine was found to be vital for the
higher methanol yield. After the reaction, the photocatalyst could easily be recovered and reused for
subsequent six runs without significant loss in photo activity.
Metal-organic hybrid: Photoreduction of CO2 using graphitic carbon nitride su...Pawan Kumar
A novel heteroleptic iridium complex supported on graphitic carbon nitride was synthesized and used for photoreduction of carbon dioxide under visible light irradiation. The methanol yield obtained after 24 h irradiation was 9934 μmol g−1cat (TON 1241 with respect to Ir) by using triethylamine (TEA) as a sacrificial donor, which was significantly higher as compared to the semiconductor carbon nitride 145 μmol g−1cat under identical conditions. The presence of triethylamine was found to be vital for the higher methanol yield. After the reaction, the photocatalyst could easily be recovered and reused for subsequent six runs without significant loss in photo activity.
Nickel Decorated on Phosphorous-Doped Carbon Nitride as an Efficient Photocat...Pawan Kumar
Nickel nanoparticle-decorated phosphorous-doped graphitic carbon nitride (Ni@g-PC3N4)
was synthesized and used as an efficient photoactive catalyst for the reduction of various
nitrobenzenes under visible light irradiation. Hydrazine monohydrate was used as the source
of protons and electrons for the intended reaction. The developed photocatalyst was found to be
highly active and afforded excellent product yields under mild experimental conditions. In addition,
the photocatalyst could easily be recovered and reused for several runs without any detectable
leaching during the reaction.
A bridged ruthenium dimer (ru–ru) for photoreduction of co2 under visible lig...Pawan Kumar
A bridged binuclear complex consisting of two ruthenium units (Ru–Ru) connected through a bridging
ligand was synthesized, in which one unit serves as a photosensitizer, while another unit works as a
catalyst. The synthesized Ru–Ru photocatalyst was tested for photoreduction of CO2 to give CO and
HCOOH under visible light irradiation in the presence of triethanolamine as a sacrificial donor. The yield
of CO and HCOOH was found to be 54 ppm and 28 ppm respectively after 12 h of irradiation. Due to the
binding of photosensitizer and catalyst units in a single molecule via bridging ligand provides faster and
efficient electron transfer from sensitizer to catalyst unit which resulted in the higher activity and better
product yields
Visible light assisted reduction of nitrobenzenes using Fe(bpy)3+2/rGOnanocom...Pawan Kumar
Visible-light-induced photocatalytic reduction of aromatic nitrobenzenes to the corresponding anilinesat room temperature using reduced graphene oxide (rGO) immobilized iron(II) bipyridine complex asphotocatalyst is described. The rGO-immobilized iron catalyst exhibited superior catalytic activity thanhomogeneous iron(II) bipyridine complex and much higher than metal free rGO photocatalysts. Theheterogeneous photocatalyst was found to be robust and could easily be recovered and reused for severalruns without any significant loss in photocatalytic activity.
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.
A novel Ru/TiO2 hybrid nanocomposite catalyzed photoreduction of CO2 to metha...Pawan Kumar
A novel in situ synthesized Ru(bpy)3/TiO2 hybrid nanocomposite is developed for the photoreduction of
CO2 into methanol under visible light irradiation. The prepared composite was characterized by means of
SEM, TEM, XRD, DT–TGA, XPS, UV–Vis and FT-IR techniques. The photocatalytic activity of the synthesized
hybrid catalyst was tested for the photoreduction of CO2 under visible light using triethylamine
as a sacrificial donor. The methanol yield for the Ru(bpy)3/TiO2 hybrid nanocomposite was found to be
1876 μmol g−1 cat (MeOH 0.024 mol Einstein−1) that was much higher in comparison with the in situ synthesized
TiO2, 828 μmol g−1 cat (MeOH 0.010 mol Einstein−1) and the homogeneous Ru(bpy)3Cl2
complex, 385 μmol g−1 cat (MeOH 0.005 mol Einstein−1).
Since the Nobel prize for Physics was awarded to Andre Geim and Konstantin Novoselov “for groundbreaking experiments regarding the two-dimensional material graphene”, the eyes of the scientific world have been focused on this so-called miracle material.
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Pawan Kumar
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34-xFexO6-δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6-δ (BCNFCo), exhibited an optical absorption edge at ~ 800 nm, p-type conduction and a distinct photoresponse upto 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskite and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm-2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ~ 88%.
Reduced graphene oxide–CuO nanocomposites for photocatalyticconversion of CO2...Pawan Kumar
Reduced graphene oxide (rGO)–copper oxide nanocomposites are prepared by covalent grafting of CuOnanorods on the rGO skeleton. Chemical and structural features of rGO–CuO nanocomposites are probedby FTIR, XPS, XRD and HRTEM analyses. Photocatalytic potential of rGO–CuO nanocomposites is exploredfor reduction of CO2into the methanol under the visible light irradiation. The breadth of CuO nanorods andthe oxidation state of Cu in the rGO–CuO/Cu2O nanocomposites are systematically varied to investigatetheir photocatalytic activities. The pristine CuO nanorods exhibited very low photocatalytic activity owingto fast recombination of charge carriers and yielded 175 mol g−1methanol, whereas rGO–Cu2O andrGO–CuO exhibited significantly improved photocatalytic activities and yielded five (862 mol g−1) andseven (1228 mol g−1) folds methanol, respectively. The superior photocatalytic activity of CuO in therGO–CuO nanocomposites was attributed to slow recombination of charge carriers and efficient transferof photo-generated electrons through the rGO skeleton. This study further excludes the use of scavengingdonor.
Heterostructured nanocomposite tin phthalocyanine@mesoporous ceria (SnPc@CeO2...Pawan Kumar
Heterostructured tin phthalocyanine supported to mesoporous ceria was synthesized and used a
photocatalyst for CO2 reduction under visible light. The photoreduction CO2 activities of the
heterostructures were investigated in the presence of triethylamine as sacrificial agent. The developed
photocatalyst exhibited high catalytic activity for photoreduction of CO2 and after 24 hours of visible
light irradiation 2342 mmol g1 cat of methanol (fMeOH ¼ 0.0223 or 2.23%) and 840 mmol g1 cat of CO
(fCO ¼ 0.0026 or 0.26%) were obtained as the major reaction products. The methanol formation rate
(RMeOH) and CO formation rate (RCO) was found to be 97.5 mmol h1 g1 cat and 35.0 mmol h1 g1 cat
respectively. While under the identical experimental conditions mesoporous ceria (meso-CeO2) gave
only 316 mmol g1 cat of methanol (fMeOH ¼ 0.003 or 0.30%) and 126 mmol g1 cat CO (fCO ¼ 0.0004
or 0.04%) with product formation rate RMeOH ¼ 13.2 mmol h1 g1 cat and RCO ¼ 5.3 mmol h1 g1 cat.
Furthermore, the recovered catalyst showed consistent catalytic activity for at least five runs without any
significant loss in product yields
Visible light driven photocatalytic oxidation of thiols to disulfides using i...Pawan Kumar
The present paper describes the synthesis of graphene oxide immobilized iron phthalocyanine (FePc) for the photocatalytic oxidation of thiols to disulfides under alkaline free conditions. Iron phthalocyanine tetrasulfonamide was immobilized on carboxylated graphene oxide supports via covalent attachment.
The loading of FePc on GO nanosheets was confirmed by FTIR, Raman, ICP-AES, UV-Vis and elemental analyses. The synthesized catalyst was found to be highly efficient for the photo-oxidation of thiols to
disulfides in aqueous medium using molecular oxygen as oxidant under visible light irradiation. The identification of photo-oxidation products and their quantitative determination was done using GC-MS. After completion of the reaction, the catalyst was easily recovered by filtration and reused for several runs without loss in activity and no leaching was observed during the reaction.
Graphene oxide immobilized copper phthalocyanine tetrasulphonamide: the first...Pawan Kumar
The first successful synthesis of DMC directly from methanol and carbon dioxide using a heterogenized
homogeneous graphene oxide immobilized copper phthalocyanine tetrasulphonamide catalyst in the
presence of N,N0-dicyclohexylcarbodiimide (DCC) as a dehydrating agent is described. The presence of a
dehydrating agent was found to be vital and in its absence the yield of DMC was found to be decreased
significantly. Under the optimized reaction conditions, the maximum yield of DMC reaches up to 13.3%.
Although the homogeneous copper phthalocyanine tetrasulphonamide catalyst provided a little higher
yield of DMC (14.2%), the facile recovery and recycling ability of the heterogeneous catalyst make the
developed method more attractive from environmental and economical viewpoints.
Hexamolybdenum clusters supported on graphene oxide: Visible-light induced ph...Pawan Kumar
Hexamolybdenum (Mo6) cluster-based compounds namely Cs2Mo6Bri
8Bra6
and
(TBA)2Mo6Bri
8Bra
6 (TBA = tetrabutylammonium) were immobilized on graphene oxide (GO)
nanosheets by taking advantage of the high lability of the apical bromide ions with
oxygen-functionalities of GO nanosheets. The loading of Mo6 clusters on GO nanosheets
was probed by Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron
spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and elemental
mapping analyses. The developed GO-Cs2Mo6Bri
8Bra
x and GO-(TBA)2Mo6Bri
8Bra
x
composites were then used as heterogeneous photocatalysts for the reduction of CO2 under
visible light irradiation. After 24 h visible light illumination, the yield of methanol was
found to be 1644 and 1294 lmol g1 cat for GO-Cs2Mo6Bri
8Bra
x and GO-(TBA)2Mo6Bri
8Bra
x,
respectively. The quantum yields of methanol by using GO-Cs2Mo6Bri
8Bra
x and
GO-(TBA)2Mo6Bri
8Bra
x as catalysts with reference to Mo6 cluster units presented in 0.1 g
amount of catalyst were found to be 0.015 and 0.011, respectively. The role of immobilized
Mo6 clusters-based compounds on GO nanosheets is discussed to understand the
photocatalytic mechanism of CO2 reduction into methanol.
Hexamolybdenum clusters supported on graphene oxide: Visible-light induced ph...Pawan Kumar
Hexamolybdenum (Mo6) cluster-based compounds namely Cs2Mo6Bri
8Bra6
and
(TBA)2Mo6Bri
8Bra
6 (TBA = tetrabutylammonium) were immobilized on graphene oxide (GO)
nanosheets by taking advantage of the high lability of the apical bromide ions with
oxygen-functionalities of GO nanosheets. The loading of Mo6 clusters on GO nanosheets
was probed by Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron
spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and elemental
mapping analyses. The developed GO-Cs2Mo6Bri
8Bra
x and GO-(TBA)2Mo6Bri
8Bra
x
composites were then used as heterogeneous photocatalysts for the reduction of CO2 under
visible light irradiation. After 24 h visible light illumination, the yield of methanol was
found to be 1644 and 1294 lmol g1 cat for GO-Cs2Mo6Bri
8Bra
x and GO-(TBA)2Mo6Bri
8Bra
x,
respectively. The quantum yields of methanol by using GO-Cs2Mo6Bri
8Bra
x and
GO-(TBA)2Mo6Bri
8Bra
x as catalysts with reference to Mo6 cluster units presented in 0.1 g
amount of catalyst were found to be 0.015 and 0.011, respectively. The role of immobilized
Mo6 clusters-based compounds on GO nanosheets is discussed to understand the
photocatalytic mechanism of CO2 reduction into methanol.
Abstract: Novel graphene oxide (GO) tethered Co(II) phthalocyanine complex [CoPc–GO] was synthesized via a stepwise procedure and demonstrated to be an efficient, cost effective and recyclable photocatalyst for the reduction of carbon dioxide to produce methanol as the main product. The developed GO-immobilized CoPc was characterized by X-ray diffraction (XRD), FT-IR, XPS, Raman, diffusion reflection UV-Vis spectroscopy, inductively coupled plasma atomic emission spectroscopy (ICP-AES), TGA, BET, SEM and TEM. FT-IR, XPS, Raman, UV-Vis and ICP-AES along with elemental analysis results showed that Co(II) Pc complex was successfully grafted on GO. The prepared catalyst was used for the photocatalytic reduction of carbon dioxide by using water as a solvent and triethylamine as the sacrificial donor. Methanol was obtained as the major reaction product along with the formation of minor amount of CO (0.82 %). It was found that GO-grafted CoPc exhibited higher photocatalytic activity than homogeneous CoPc as well as graphene oxide and showed good recoverability without significant leaching during the reaction. Quantitative determination of methanol was done by GC-FID and confirmation of product was done by NMR. The yield of methanol after 48 hours of reaction by using GO-CoPc catalyst in the presence of sacrificial donor triethylamine was found to be 3781.8881μmol.g-1-cat and the conversion rate was found to be 78.7893 μmol.g-1cat.h-1. After the photoreduction experiment, the catalyst was easily recovered by filtration and reused for the subsequent recycling experiment without significant change in the catalytic efficiency
A bridged ruthenium dimer (Ru–Ru) for photoreduction of CO2 under visible li...Pawan Kumar
A bridged binuclear complex consisting of two ruthenium units (Ru–Ru) connected through a bridging ligand was synthesized, in which one unit serves as a photosensitizer, while another unit works as a catalyst. The synthesized Ru–Ru photocatalyst was tested for photoreduction of CO2 to give CO and HCOOH under visible light irradiation in the presence of triethanolamine as a sacrificial donor. The yield of CO and HCOOH was found to be 54 ppm and 28 ppm respectively after 12 h of irradiation. Due to the binding of photosensitizer and catalyst units in a single molecule via bridging ligand provides faster and efficient electron transfer from sensitizer to catalyst unit which resulted in the higher activity and better product yields.
Metal-organic hybrid: Photoreduction of CO2 using graphitic carbon nitride su...Pawan Kumar
A novel heteroleptic iridium complex supported on graphitic carbon nitride was synthesized and used
for photoreduction of carbon dioxide under visible light irradiation. The methanol yield obtained after
24 h irradiation was 9934 mmol g1cat (TON 1241 with respect to Ir) by using triethylamine (TEA) as a
sacrificial donor, which was significantly higher as compared to the semiconductor carbon nitride
145 mmol g1cat under identical conditions. The presence of triethylamine was found to be vital for the
higher methanol yield. After the reaction, the photocatalyst could easily be recovered and reused for
subsequent six runs without significant loss in photo activity.
Metal-organic hybrid: Photoreduction of CO2 using graphitic carbon nitride su...Pawan Kumar
A novel heteroleptic iridium complex supported on graphitic carbon nitride was synthesized and used
for photoreduction of carbon dioxide under visible light irradiation. The methanol yield obtained after
24 h irradiation was 9934 mmol g1cat (TON 1241 with respect to Ir) by using triethylamine (TEA) as a
sacrificial donor, which was significantly higher as compared to the semiconductor carbon nitride
145 mmol g1cat under identical conditions. The presence of triethylamine was found to be vital for the
higher methanol yield. After the reaction, the photocatalyst could easily be recovered and reused for
subsequent six runs without significant loss in photo activity.
Metal-organic hybrid: Photoreduction of CO2 using graphitic carbon nitride su...Pawan Kumar
A novel heteroleptic iridium complex supported on graphitic carbon nitride was synthesized and used for photoreduction of carbon dioxide under visible light irradiation. The methanol yield obtained after 24 h irradiation was 9934 μmol g−1cat (TON 1241 with respect to Ir) by using triethylamine (TEA) as a sacrificial donor, which was significantly higher as compared to the semiconductor carbon nitride 145 μmol g−1cat under identical conditions. The presence of triethylamine was found to be vital for the higher methanol yield. After the reaction, the photocatalyst could easily be recovered and reused for subsequent six runs without significant loss in photo activity.
Nickel Decorated on Phosphorous-Doped Carbon Nitride as an Efficient Photocat...Pawan Kumar
Nickel nanoparticle-decorated phosphorous-doped graphitic carbon nitride (Ni@g-PC3N4)
was synthesized and used as an efficient photoactive catalyst for the reduction of various
nitrobenzenes under visible light irradiation. Hydrazine monohydrate was used as the source
of protons and electrons for the intended reaction. The developed photocatalyst was found to be
highly active and afforded excellent product yields under mild experimental conditions. In addition,
the photocatalyst could easily be recovered and reused for several runs without any detectable
leaching during the reaction.
A bridged ruthenium dimer (ru–ru) for photoreduction of co2 under visible lig...Pawan Kumar
A bridged binuclear complex consisting of two ruthenium units (Ru–Ru) connected through a bridging
ligand was synthesized, in which one unit serves as a photosensitizer, while another unit works as a
catalyst. The synthesized Ru–Ru photocatalyst was tested for photoreduction of CO2 to give CO and
HCOOH under visible light irradiation in the presence of triethanolamine as a sacrificial donor. The yield
of CO and HCOOH was found to be 54 ppm and 28 ppm respectively after 12 h of irradiation. Due to the
binding of photosensitizer and catalyst units in a single molecule via bridging ligand provides faster and
efficient electron transfer from sensitizer to catalyst unit which resulted in the higher activity and better
product yields
Visible light assisted reduction of nitrobenzenes using Fe(bpy)3+2/rGOnanocom...Pawan Kumar
Visible-light-induced photocatalytic reduction of aromatic nitrobenzenes to the corresponding anilinesat room temperature using reduced graphene oxide (rGO) immobilized iron(II) bipyridine complex asphotocatalyst is described. The rGO-immobilized iron catalyst exhibited superior catalytic activity thanhomogeneous iron(II) bipyridine complex and much higher than metal free rGO photocatalysts. Theheterogeneous photocatalyst was found to be robust and could easily be recovered and reused for severalruns without any significant loss in photocatalytic activity.
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.
A novel Ru/TiO2 hybrid nanocomposite catalyzed photoreduction of CO2 to metha...Pawan Kumar
A novel in situ synthesized Ru(bpy)3/TiO2 hybrid nanocomposite is developed for the photoreduction of
CO2 into methanol under visible light irradiation. The prepared composite was characterized by means of
SEM, TEM, XRD, DT–TGA, XPS, UV–Vis and FT-IR techniques. The photocatalytic activity of the synthesized
hybrid catalyst was tested for the photoreduction of CO2 under visible light using triethylamine
as a sacrificial donor. The methanol yield for the Ru(bpy)3/TiO2 hybrid nanocomposite was found to be
1876 μmol g−1 cat (MeOH 0.024 mol Einstein−1) that was much higher in comparison with the in situ synthesized
TiO2, 828 μmol g−1 cat (MeOH 0.010 mol Einstein−1) and the homogeneous Ru(bpy)3Cl2
complex, 385 μmol g−1 cat (MeOH 0.005 mol Einstein−1).
Since the Nobel prize for Physics was awarded to Andre Geim and Konstantin Novoselov “for groundbreaking experiments regarding the two-dimensional material graphene”, the eyes of the scientific world have been focused on this so-called miracle material.
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Pawan Kumar
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34-xFexO6-δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6-δ (BCNFCo), exhibited an optical absorption edge at ~ 800 nm, p-type conduction and a distinct photoresponse upto 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskite and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm-2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ~ 88%.
Reduced graphene oxide–CuO nanocomposites for photocatalyticconversion of CO2...Pawan Kumar
Reduced graphene oxide (rGO)–copper oxide nanocomposites are prepared by covalent grafting of CuOnanorods on the rGO skeleton. Chemical and structural features of rGO–CuO nanocomposites are probedby FTIR, XPS, XRD and HRTEM analyses. Photocatalytic potential of rGO–CuO nanocomposites is exploredfor reduction of CO2into the methanol under the visible light irradiation. The breadth of CuO nanorods andthe oxidation state of Cu in the rGO–CuO/Cu2O nanocomposites are systematically varied to investigatetheir photocatalytic activities. The pristine CuO nanorods exhibited very low photocatalytic activity owingto fast recombination of charge carriers and yielded 175 mol g−1methanol, whereas rGO–Cu2O andrGO–CuO exhibited significantly improved photocatalytic activities and yielded five (862 mol g−1) andseven (1228 mol g−1) folds methanol, respectively. The superior photocatalytic activity of CuO in therGO–CuO nanocomposites was attributed to slow recombination of charge carriers and efficient transferof photo-generated electrons through the rGO skeleton. This study further excludes the use of scavengingdonor.
Heterostructured nanocomposite tin phthalocyanine@mesoporous ceria (SnPc@CeO2...Pawan Kumar
Heterostructured tin phthalocyanine supported to mesoporous ceria was synthesized and used a
photocatalyst for CO2 reduction under visible light. The photoreduction CO2 activities of the
heterostructures were investigated in the presence of triethylamine as sacrificial agent. The developed
photocatalyst exhibited high catalytic activity for photoreduction of CO2 and after 24 hours of visible
light irradiation 2342 mmol g1 cat of methanol (fMeOH ¼ 0.0223 or 2.23%) and 840 mmol g1 cat of CO
(fCO ¼ 0.0026 or 0.26%) were obtained as the major reaction products. The methanol formation rate
(RMeOH) and CO formation rate (RCO) was found to be 97.5 mmol h1 g1 cat and 35.0 mmol h1 g1 cat
respectively. While under the identical experimental conditions mesoporous ceria (meso-CeO2) gave
only 316 mmol g1 cat of methanol (fMeOH ¼ 0.003 or 0.30%) and 126 mmol g1 cat CO (fCO ¼ 0.0004
or 0.04%) with product formation rate RMeOH ¼ 13.2 mmol h1 g1 cat and RCO ¼ 5.3 mmol h1 g1 cat.
Furthermore, the recovered catalyst showed consistent catalytic activity for at least five runs without any
significant loss in product yields
Visible light driven photocatalytic oxidation of thiols to disulfides using i...Pawan Kumar
The present paper describes the synthesis of graphene oxide immobilized iron phthalocyanine (FePc) for the photocatalytic oxidation of thiols to disulfides under alkaline free conditions. Iron phthalocyanine tetrasulfonamide was immobilized on carboxylated graphene oxide supports via covalent attachment.
The loading of FePc on GO nanosheets was confirmed by FTIR, Raman, ICP-AES, UV-Vis and elemental analyses. The synthesized catalyst was found to be highly efficient for the photo-oxidation of thiols to
disulfides in aqueous medium using molecular oxygen as oxidant under visible light irradiation. The identification of photo-oxidation products and their quantitative determination was done using GC-MS. After completion of the reaction, the catalyst was easily recovered by filtration and reused for several runs without loss in activity and no leaching was observed during the reaction.
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.
Optical Control of Selectivity of High Rate CO2 Photoreduction Via Interband-...Pawan Kumar
Photonic crystals consisting of TiO2 nanotube arrays (PMTiNTs) with periodically modulated diameters were fabricated using a precise charge-controlled pulsed anodization technique. The PMTiNTs were decorated with gold nanoparticles (Au NPs) to form plasmonic photonic crystal photocatalysts (Au-PMTiNTs). A systematic study of CO2 photoreduction performance on as-prepared samples was conducted using different wavelengths and illumination sequences. A remarkable selectivity of the mechanism of CO2 photoreduction could be engineered by merely varying the spectral composition of the illumination sequence. Under AM1.5 G simulated sunlight (pathway#1), the Au-PMTiNTs produced methane (302 µmol h-1) from CO2 with high selectivity (89.3%). When also illuminated by a UV-poor white lamp (pathway#2), the Au-PMTiNTs produced formaldehyde (420 µmol h-1) and carbon monoxide (323 µmol h-1) with almost no methane evolved. We confirmed the photoreduction results by 13C isotope labeling experiments using GC-MS. These results point to optical control of the selectivity of high-rate CO2 photoreduction through selection of one of two different mechanistic pathways. Pathway#1 implicates electron-hole pairs generated through interband transitions in TiO2 and Au as the primary active species responsible for reducing CO2 to methane. Pathway#2 involves excitation of both TiO2 and surface plasmons in Au. Hot electrons produced by plasmon damping and photogenerated holes in TiO2 proceed to reduce CO2 to HCHO and CO through a plasmonic Z-scheme.
Photo-assisted oxidation of thiols to disulfides using cobalt ‘‘Nanorust’’ un...Pawan Kumar
Heterogeneous ‘‘Nanorust’’ containing cobalt oxide has been developed for the visible light assisted
oxidation of thiols to disulfides using molecular oxygen as an oxidant under alkaline free conditions and
therefore more environmentally friendly. Pyrolysis of heterogenized tetrasulfonated cobalt(II) phthalocyanine
(CoPcS) supported on mesoporous ceria (CeO2) transforms it into a novel heterogeneous ‘‘Nanorust’’
containing CoOx-C,N@CeO2 which exhibited higher catalytic activity than the homogeneous CoPcS as well
as the ceria immobilized CoPcS catalyst. Importantly, these catalysts could easily be recovered and recycled
for several runs, which makes the process greener and cost-effective.
Photo-induced reduction of CO2 using a magnetically separable Ru-CoPc@TiO2@Si...Pawan Kumar
An efficient photo-induced reduction of CO2 using magnetically separable Ru-CoPc@TiO2@SiO2@Fe3O4
as a heterogeneous catalyst in which CoPc and Ru(bpy)2phene complexes were attached to a solid
support via covalent attachment under visible light is described. The as-synthesized catalyst was characterized
by a series of techniques including FTIR, UV-Vis, XRD, SEM, TEM, etc. and subsequently tested for
the photocatalytic reduction of carbon dioxide using triethylamine as a sacrificial donor and water as a
reaction medium. The developed photocatalyst exhibited a significantly higher catalytic activity to give a
methanol yield of 2570.78 μmol per g cat after 48 h.
Photo-assisted oxidation of thiols to disulfides using cobalt ‘‘Nanorust’’ un...Pawan Kumar
Heterogeneous ‘‘Nanorust’’ containing cobalt oxide has been developed for the visible light assisted
oxidation of thiols to disulfides using molecular oxygen as an oxidant under alkaline free conditions and
therefore more environmentally friendly. Pyrolysis of heterogenized tetrasulfonated cobalt(II) phthalocyanine
(CoPcS) supported on mesoporous ceria (CeO2) transforms it into a novel heterogeneous ‘‘Nanorust’’
containing CoOx-C,N@CeO2 which exhibited higher catalytic activity than the homogeneous CoPcS as well
as the ceria immobilized CoPcS catalyst. Importantly, these catalysts could easily be recovered and recycled
for several runs, which makes the process greener and cost-effective
Graphene oxide grafted with iridium complex as a superior heterogeneous catal...Pawan Kumar
A novel graphene oxide (GO)-immobilized heteroleptic iridium complex was synthesized and demonstrated
as a first heterogenized homogeneous catalyst for the production of dimethylformamide (DMF)
from carbon dioxide, hydrogen, and dimethylamine. The synthesized hybrid catalyst showed comparable
activity as homogeneous heteroleptic iridium complex with additional benefits such as facile recovery
and recycling of the catalyst. After completion of the reaction, the heterogeneous catalyst was easily
recovered by filtration, and reused for subsequent recycling processes without any significant change in
the catalytic efficiency
Graphene oxide grafted with iridium complex as a superior heterogeneous catal...Pawan Kumar
A novel graphene oxide (GO)-immobilized heteroleptic iridium complex was synthesized and demonstrated
as a first heterogenized homogeneous catalyst for the production of dimethylformamide (DMF)
from carbon dioxide, hydrogen, and dimethylamine. The synthesized hybrid catalyst showed comparable
activity as homogeneous heteroleptic iridium complex with additional benefits such as facile recovery
and recycling of the catalyst. After completion of the reaction, the heterogeneous catalyst was easily
recovered by filtration, and reused for subsequent recycling processes without any significant change in
the catalytic efficiency.
Graphene oxide grafted with iridium complex as a superior heterogeneous catal...Pawan Kumar
A novel graphene oxide (GO)-immobilized heteroleptic iridium complex was synthesized and demonstrated
as a first heterogenized homogeneous catalyst for the production of dimethylformamide (DMF)
from carbon dioxide, hydrogen, and dimethylamine. The synthesized hybrid catalyst showed comparable
activity as homogeneous heteroleptic iridium complex with additional benefits such as facile recovery
and recycling of the catalyst. After completion of the reaction, the heterogeneous catalyst was easily
recovered by filtration, and reused for subsequent recycling processes without any significant change in
the catalytic efficiency.
Photo-induced reduction of CO2 using a magnetically separable Ru-CoPc@TiO2@Si...Pawan Kumar
An efficient photo-induced reduction of CO2 using magnetically separable Ru-CoPc@TiO2@SiO2@Fe3O4
as a heterogeneous catalyst in which CoPc and Ru(bpy)2phene complexes were attached to a solid
support via covalent attachment under visible light is described. The as-synthesized catalyst was characterized
by a series of techniques including FTIR, UV-Vis, XRD, SEM, TEM, etc. and subsequently tested for
the photocatalytic reduction of carbon dioxide using triethylamine as a sacrificial donor and water as a
reaction medium. The developed photocatalyst exhibited a significantly higher catalytic activity to give a
methanol yield of 2570.78 μmol per g cat after 48 h.
Similar to Cobalt Phthalocyanine Immobilized on Graphene Oxide: An Efficient Visible-Active Catalyst for the Photoreduction of Carbon Dioxide (20)
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.
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.
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.
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The increased availability of biomedical data, particularly in the public domain, offers the opportunity to better understand human health and to develop effective therapeutics for a wide range of unmet medical needs. However, data scientists remain stymied by the fact that data remain hard to find and to productively reuse because data and their metadata i) are wholly inaccessible, ii) are in non-standard or incompatible representations, iii) do not conform to community standards, and iv) have unclear or highly restricted terms and conditions that preclude legitimate reuse. These limitations require a rethink on data can be made machine and AI-ready - the key motivation behind the FAIR Guiding Principles. Concurrently, while recent efforts have explored the use of deep learning to fuse disparate data into predictive models for a wide range of biomedical applications, these models often fail even when the correct answer is already known, and fail to explain individual predictions in terms that data scientists can appreciate. These limitations suggest that new methods to produce practical artificial intelligence are still needed.
In this talk, I will discuss our work in (1) building an integrative knowledge infrastructure to prepare FAIR and "AI-ready" data and services along with (2) neurosymbolic AI methods to improve the quality of predictions and to generate plausible explanations. Attention is given to standards, platforms, and methods to wrangle knowledge into simple, but effective semantic and latent representations, and to make these available into standards-compliant and discoverable interfaces that can be used in model building, validation, and explanation. Our work, and those of others in the field, creates a baseline for building trustworthy and easy to deploy AI models in biomedicine.
Bio
Dr. Michel Dumontier is the Distinguished Professor of Data Science at Maastricht University, founder and executive director of the Institute of Data Science, and co-founder of the FAIR (Findable, Accessible, Interoperable and Reusable) data principles. His research explores socio-technological approaches for responsible discovery science, which includes collaborative multi-modal knowledge graphs, privacy-preserving distributed data mining, and AI methods for drug discovery and personalized medicine. His work is supported through the Dutch National Research Agenda, the Netherlands Organisation for Scientific Research, Horizon Europe, the European Open Science Cloud, the US National Institutes of Health, and a Marie-Curie Innovative Training Network. He is the editor-in-chief for the journal Data Science and is internationally recognized for his contributions in bioinformatics, biomedical informatics, and semantic technologies including ontologies and linked data.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
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.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.
Cobalt Phthalocyanine Immobilized on Graphene Oxide: An Efficient Visible-Active Catalyst for the Photoreduction of Carbon Dioxide
1. & Heterogeneous Catalysis
Cobalt Phthalocyanine Immobilized on Graphene Oxide: An
Efficient Visible-Active Catalyst for the Photoreduction of Carbon
Dioxide
Pawan Kumar,[a]
Arvind Kumar,[b]
Bojja Sreedhar,[c]
Bir Sain,[a]
Siddharth S. Ray,[b]
and
Suman L. Jain*[a]
Abstract: New graphene oxide (GO)-tethered–CoII
phthalo-
cyanine complex [CoPc–GO] was synthesized by a stepwise
procedure and demonstrated to be an efficient, cost-effec-
tive and recyclable photocatalyst for the reduction of carbon
dioxide to produce methanol as the main product. The de-
veloped GO-immobilized CoPc was characterized by X-ray
diffraction (XRD), FTIR, XPS, Raman, diffusion reflection UV/
Vis spectroscopy, inductively coupled plasma atomic emis-
sion spectroscopy (ICP-AES), thermogravimetric analysis
(TGA), Brunauer–Emmett–Teller (BET), scanning electron mi-
croscopy (SEM), and transmission electron microscopy (TEM).
FTIR, XPS, Raman, UV/Vis and ICP-AES along with elemental
analysis data showed that CoII
–Pc complex was successfully
grafted on GO. The prepared catalyst was used for the pho-
tocatalytic reduction of carbon dioxide by using water as
a solvent and triethylamine as the sacrificial donor. Methanol
was obtained as the major reaction product along with the
formation of minor amount of CO (0.82%). It was found that
GO-grafted CoPc exhibited higher photocatalytic activity
than homogeneous CoPc, as well as GO, and showed good
recoverability without significant leaching during the reac-
tion. Quantitative determination of methanol was done by
GC flame-ionization detector (FID), and verification of prod-
uct was done by NMR spectroscopy. The yield of methanol
after 48 h of reaction by using GO–CoPc catalyst in the pres-
ence of sacrificial donor triethylamine was found to be
3781.8881 mmolgÀ1
cat., and the conversion rate was found
to be 78.7893 mmolgÀ1
cat.hÀ1
. After the photoreduction ex-
periment, the catalyst was easily recovered by filtration and
reused for the subsequent recycling experiment without sig-
nificant change in the catalytic efficiency.
Utilization of carbon dioxide as a sustainable C1 building block
has emerged as an important area of research in last two dec-
ades mainly due to the concurrently problems of global warm-
ing, as well as depletion of fossil fuels.[1]
The effective use of
clean and abundant solar energy might provide a viable ap-
proach to solve the problems of energy and environmental
crisis by a photocatalytic reduction of carbon dioxide to valu-
able chemicals. Although a number of improved catalytic sys-
tems, such as nanosized titanium oxide, titanium oxide doped
with transition metals, noble metals, and mixed with another
metal oxide have been emerged as potent catalysts for the
photoreduction of CO2, but their quantum yields and selectivi-
ties of products are low.[2–3]
In the recent years, photocatalytic
systems, including transition-metal complexes, such as ruthe-
nium(II) polypyridine carbonyl complex, cobalt(II) trisbipyridine,
cobalt(III) macrocycles, rhenium and iridium complex with
a photosensitizer have emerged to be efficient catalytic sys-
tems to reduce CO2 with relatively high quantum yield and
high selectivity of products.[4]
However, the difficult recovery
and non-recycling ability of a homogeneous complex make
these systems less attractive. To overcome these problems, im-
mobilization of homogeneous metal complexes to solid sup-
port is an obvious way to combine the advantages of homoge-
neous catalysts, for example, high reactivity, selectivity, and
heterogeneous catalysts, such as facile recovery and recycling
of the catalyst.[5]
In this context, a number of homogeneous
photoredox complexes have been supported to various sup-
ports, such as TiO2, organic polymers, ion-exchange resins.
However, in most of the cases, noncovalent attachment of the
metal complex to support materials renders to the leaching of
the active species during the reaction.[6]
Metallophthalocyanines and their derivatives have been
widely used as photosensitizers for various applications in a va-
riety of fields due to their unique properties, such as excellent
semiconductivity, photoconductivity, thermal, and chemical
[a] P. Kumar, Dr. B. Sain, Dr. S. L. Jain
Chemical Sciences Division, CSIR-Indian Institute of Petroleum
Mohkampur, Dehradun 248005 (India)
Fax: (+91)135-2660202
E-mail: suman@iip.res.in
[b] A. Kumar, Dr. S. S. Ray
Analytical Sciences Division, CSIR-Indian Institute of Petroleum
Mohkampur, Dehradun 248005 (India)
[c] Dr. B. Sreedhar
Inorganic and Physical Chemistry Division
CSIR-Indian Institute of Chemical Technology
Hyderabad, 500607, Andhra Pradesh (India)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201304189.
Chem. Eur. J. 2014, 20, 6154 – 6161 2014 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim6154
Full PaperDOI: 10.1002/chem.201304189
2. stability. Most of the studies conducted to date on metal
phthalocyanines for photocatalytic reduction of CO2 were per-
formed either in homogeneous solution or by supporting
them to other semiconductor materials, such as TiO2.[7]
In this
context, Zhou et al.[8]
reported the use of in situ synthesized
TiO2/CoPc nanocomposite for the photocatalytic reduction of
carbon dioxide to formic acid, formaldehyde, and methanol.
Graphene oxide (GO), an oxidized form of grapheme, has
emerged to be a promising material, particularly as a precursor
to prepare reduced GO (rGO), chemically functionalized gra-
phene, and grapheme-based composite materials.[9,10]
Very re-
cently, Hsu et al.[11]
have reported GO as a promising photocat-
alyst for the conversion of CO2 to methanol with the conver-
sion rate of 0.172 mmolgÀ1
cat.À1
hÀ1
under visible light.
Herein, we describe the successful synthesis of covalently
anchored cobalt phthalocyanine to the GO, its characterization,
and use for the photocatalytic reduction of the carbon dioxide
to methanol with improved product yield and selectivity. The
oxygen functionalities on GO are targeted for stable and effi-
cient anchoring of CoPc catalyst on nanosheets of GO through
covalent attachment. The prepared catalyst exhibited higher
photocatalytic activity under visible-light irradiation and gave
methanol with improved yield and selectivity. The quantitative
and qualitative determination of the methanol formation was
performed by GC and 1
H NMR spectroscopy.
Synthesis and characterization of catalyst
GO was obtained from the oxidation of graphite with KMnO4
and H2SO4 following the literature procedure.[12]
High specific
surface area of GO along with easily accessible ample oxygen
functionalities decorated on both side of GO nanosheets pro-
vide great potential as a support material for various cata-
lysts.[13]
Prior to the immobilization, the GO was treated with
chloroacetic acid to convert the epoxy groups into carboxy
(COOH) groups, which were subsequently used for the grafting
of CoPc to the GO surface. The schematic representation of
the synthesis of CoPc immobilized on GO (GO–CoPc) is shown
in Scheme 1.
The morphology and structure of as-prepared GO and GO–
CoPc catalyst was investigated by scanning electron microsco-
py (SEM) and transmission electron microscopy (TEM). As pre-
sented in Figure 1b, the SEM image of GO–CoPc shows twisted
and crumpled nanosheets in an agglomerated phase with lot
of wrinkled features of GO–CoPc catalyst. The TEM images
shown in Figure 2a and b also reveal the nanoscopic features
with layered structure of GO–CoPc catalyst (Figure S1 in the
Supporting Information). The TEM image of carboxylic group
(COOH) containing GO before immobilization of CoPc is shown
in Figure 2c. The dark spots in the TEM image (Figure 2c) are
probably due to the COOH functionalities located on the sur-
Scheme 1. Synthesis of GO-grafted CoPc.
Figure 1. SEM image of a) GO and b) GO-CoPc.
Chem. Eur. J. 2014, 20, 6154 – 6161 www.chemeurj.org 2014 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim6155
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3. face of GO. Selected area electron diffraction pattern of GO–
CoPc shows that material was amorphous in nature (Fig-
ure 2d).
XRD patterns were used to study the changes in structure
(Figure 3). The XRD spectrum of GO shown in Figure 3a gives
characteristic diffraction peak at 10.88 (001), corresponding to
a GO interlayer spacing of approximately 0.74 nm.[14]
After im-
mobilization of CoPc, this peak disappeared, and another
broad diffraction of graphite (002) at 2q value of approximately
268 appeared, indicating that exfoliation of the layered CoPc–
GO was obtained.[15]
The porosity characteristics of the samples were investigated
by measuring the N2 adsorption/desorption isotherms at 77 K
(Figure 4). Total pore volume and surface area of synthesized
GO was found to be 0.1212 cm3
gÀ1
and 87.247 m2
gÀ1
, respec-
tively. Total pore diameter of GO was found to be 5.5566 nm
that was in agreement to mesoporous nature.[16]
The adsorp-
tion/desorption isotherm was of type IV (Figure 4). The negligi-
ble N2 adsorption in GO and GO–CoPc suggested the filled in-
terlayer galleries and the restacked graphitic structure in GO.
Obtained value of SBET 12.34 m2
gÀ1
for GO–CoPc suggested
successful attachment of CoPc at the surface of GO. Total pore
volume and mean pore diameter of GO–CoPc was measured
Figure 2. TEM image of a) GO; b) GO-CoPc; c) GO-COOH; and d) SAED pat-
tern of GO-CoPc.
Figure 3. XRD spectra of a) GO and b) GO-CoPc.
Figure 4. Adsorption/desorption curve of a) GO and b) GO-CoPc.
Chem. Eur. J. 2014, 20, 6154 – 6161 www.chemeurj.org 2014 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim6156
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4. to be 0.09 cm3
gÀ1
and 30.158 nm, respectively (Figure S2 in
the Supporting Information).
The UV/Vis spectra of GO and GO–CoPc are shown in
Figure 5. The UV/Vis spectra of CoPc reveals two main bands,
that is, Soret band at l=300 nm and a Q band at 660 nm (Fig-
ure 5a).[16]
The UV/Vis spectra of GO shows a characteristics
peak at nearly 230 nm, which suggests that the synthesized
GO possess an ordered graphitic structure due to the p–p*
transition of C=C(Figure 5b). Solid UV/Vis spectra of GO-at-
tached CoPc indicates the significant shifting of the absorption
band of GO to a longer wavelength at 300 nm, which clearly
indicates that CoPc was successfully attached to GO (Fig-
ure 5c).
Figure 6 shows the FTIR spectra of as-prepared GO and GO–
CoPc catalysts. The FTIR spectrum of GO shows vibrational
bands at approximately 3410 cmÀ1
due to hydroxyl stretching
vibrations in COOH and/or intercalated water (Figure 6b). The
strong band at 1720 cmÀ1
(n˜C=O) belongs to carboxylic acid
groups, 1630 cmÀ1
—to aromatic C=C, and the bands at
1227 cmÀ1
and 1058 cmÀ1
are attributed to the CÀOH and
alkoxy CÀO stretching vibrations, respectively. After the immo-
bilization reaction, several new peaks appeared in the FTIR
spectrum of GO–CoPc. The characteristic peak of C=O at
1720 cmÀ1
disappeared, and a new peak corresponding to
amide (C(O)NH) stretching vibration at n˜ =1654 cmÀ1
revealed
the formation of amide bond between CoPc and GO.
Further XPS and Raman analyses provided essential and
useful information for the covalent attachment of the CoPc to
GO. The N1s XPS spectrum of CoPc clearly indicated that the
peaks of nitrogen functionalities appeared at 398.95 (CÀN
bonds), 400.43 (NH2), and 401.58 eV (C=N bonds; Figure 7a). In
contrast, CoPc-immobilized GO showed the shifting of bands
and a considerable intensity enhancement of the peak at
400.69 eV due to the electron-withdrawing effect of GO (Fig-
ure 7b).
Furthermore, in the Raman spectrum of GO, there are two
prominent bands at about 1363 (D band) and 1608 (G band)
cmÀ1
(532 nm excitation; Figure 8a). In contrast, both the D
and G bands of GO–CoPc were found to be slightly shifted to
the lower-wave numbers, and a new band at 1512 cmÀ1
was
assigned to pyrrole C=C stretching mode of CoPc (Figure 8b).
Figure 9 shows the TGA curves of the as-prepared GO and
GO–CoPc catalysts. The GO showed initial weight loss near
1088C, evidently owing to evaporation of water molecules,
which are held in the material (Figure 9a). The second signifi-
cant weight loss was observed in the range of 180–2408C, and
is due to thermal decomposition of oxygen-carrying functional-
ities. The thermogram of the GO–CoPc catalyst illustrates an
exothermic major weight loss over a wide range of tempera-
ture (300–5008C) on account of the slow decomposition of the
phthalocyanine moieties: this indicates that the catalyst is suffi-
ciently thermally stable.
The photocatalytic reduction of CO2
First, the reactivity of the GO, physical 1:1 mixture of GO+
CoPc and GO–CoPc, was tested for the photocatalytic reduc-
tion of the CO2 by using triethylamine as sacrificial donor and
water as a solvent (Figure 10). After the photoreduction, 1 mL
liquid sample was withdrawn and analyzed in a GC-FID appara-
tus equipped with a 30 m long Stabilwax w/Integra-Guard
column. Methanol yield was used to evaluate the performance
of the catalysts, because it was obtained as the major reduc-
Figure 5. UV/Vis spectra of a) CoPc; b) GO; and c) GO-CoPc.
Figure 6. IR spectrum of a) CoPc; b) GO; and c) GO-CoPc.
Chem. Eur. J. 2014, 20, 6154 – 6161 www.chemeurj.org 2014 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim6157
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5. tion product. The methanol-formation rate, RMeOH (mmolgÀ1
cat.)
as a function of reaction time was calculated and plotted as
shown in Figure 11. The results clearly indicate that the GO–
CoPc exhibited higher catalytic activity compared to the GO
and the physical 1:1 mixture of GO–CoPc. After illumination for
48 h in visible light by using GO–CoPc as catalyst in the pres-
ence of triethylamine as sacrificial donor, the yield of methanol
was found to be 3781.8881 mmolgÀ1
cat. or production rate
78.7893 mmolgÀ1
cat.hÀ1
. The analysis of gaseous phase by GC
showed 99.17% CO2 and 0.82% CO after 48 h of the reaction.
In the GC analysis of gaseous phase, we did not observe the
presence of methane and other possible products from reduc-
tion of carbon dioxide. Formic acid, formaldehyde, and formate
were not detected in liquid-phase analysis. Blank experiments,
in the absence of GO–CoPc, as well as in the dark reaction,
showed that there was no organic product found for long peri-
ods of CO2 photoreduction.
Further, we tested the recycling of the GO–CoPc catalyst for
the photoreduction of the CO2. After completion of the reac-
Figure 7. N1s XPS spectra of a) CoPc and b) GO-CoPc.
Figure 9. TGA pattern of a) GO and b) GO-CoPc.
Figure 8. Raman spectra of a) GO and b) GO-CoPc.
Figure 10. Reaction illumination conditions.
Chem. Eur. J. 2014, 20, 6154 – 6161 www.chemeurj.org 2014 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim6158
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6. tion, the catalyst was separated by centrifugation and reused
for the subsequent run. ICP analysis of recovered catalyst after
one cycle showed cobalt content 1.05 wt%, indicating that
small leaching had occurred during the reaction.
Moreover, the possible photocatalytic mechanism of the
GO–CoPc has been demonstrated for the better understanding
of the CO2 photoreduction process (Scheme 2). It is reported in
the literature that presence of various oxy functionalites in GO
creates a 2D network of infintite sp2
and sp3
domains.[18,11]
Due
to presence of these domains on GO sheet it behaves as it has
enormous semiconductor devices on its surface.[19]
These sp2
carbon atoms in sheets domain have properties similar to gra-
phene, and electron can flow in this region with minimum re-
sistance: it works like a conduction band. Because the nature
of sp3
carbon atoms is such that the associated electrons are
not mobile, these domains serve as a valance band. GO works
like a semiconductor with valance and conduction bands.[20–22]
Because CoPc absorbs strongly in visible region, Pc got excited
after absorbing photons and formed S0 to S1 state.[23]
CoPc rap-
idly transferred excited electrons to conduction band (CB) of
GO, and then CO2 adsorbed on GO surface can accept elec-
trons that are to be reduced. We assumed that the covalent at-
tachment of CoPc to the functional groups of GO provides the
reduced band gap between valence and conduction bands of
GO. This significantly promoted the reaction and greatly en-
hanced the photoefficiency of CO2 with H2O to produce
CH3OH.[24]
Main advantage of attachment of CoPc to central
plane of GO was better charge injection to conduction band of
GO. Further, the use of sacrificial donor (triethylamine, TEA)
that provides electrons to phthalocyanine also increased yield
of methanol.[25]
CoPc þ visible light ¼ CoPc*ðexcited singlet stateÞ ð1Þ
CoPc* ¼ CoPcþ
þ eÀ
GO ðelectron transfer in CBÞ ð2Þ
CoPcþ
þ TEA ¼ CoPc þ TEAþ
ð3Þ
eÀ
GO ðelectron in CBÞ þ CO2 þ Hþ
¼ CH3OH ð4Þ
In conclusion, we have demonstrated that GO-immobilized
cobalt phthalocyanine is an effective, recyclable, and cost-ef-
fective photocatalyst for the photoreduction of CO2 to metha-
nol. Our studies showed that the presence of CoPc to the GO
surface play an important role, the methanol conversion rate
can be achieved up to 3781.8881 mmolgÀ1
cat. under visible-
light irradiation for 48 h. These conversion rates are much
higher than that of GO. The chemical attachment of CoPc on
GO surface provides the higher yield of the desired methanol
compared to the physical mixing of the GO and CoPc in 1:1
ratio. CoPc can be promoted by visible light to produce elec-
tron–hole pairs. Attachment of CoPc to GO prohibits the re-
combination of hole and electron. In addition, CoPc rapidly
transfers excited electrons to the conduction bands of the GO,
which provides the efficient photoreduction of the CO2 with
water to produce methanol.
Experimental Section
Materials
Graphite flakes, cobalt(II) phthalocyanine (97%), and triethylamine
(99%) were purchased from Sigma–Aldrich. Potassium permanga-
nate 99.0%, sodium nitrate 99.0%, concentrated sulfuric acid, hy-
drogen peroxide (30%), hydrochloric acid, chloroacetic acid, NaOH,
thionyl chloride, chlorosulfonic acid (99%), acetonitrile, and HPLC-
grade water were purchased from Merck (India). All chemicals and
solvents were of analytical grade and used as received. Cobalt–
phthalocyaninetetrasulfonamide complex was synthesized by fol-
lowing the literature procedure.[26]
Techniques used
UV/Vis absorption spectra for GO and GO–CoPc dispersions were
recorded with a Perkin–Elmer lambda-19 UV/Vis-NIR spectropho-
tometer by using a 10 mm quartz cell. Solid-state spectra were re-
corded by using BaSO4 as a reference. FTIR analysis was conducted
by Perkin–Elmer Spectrum RX-1 IR spectrophotometer. HR-TEM of
the GO and GO–CoPc was executed by using FEI-TecnaiG2
TwinTEM
operating at an acceleration voltage of 200 kV. SEM analysis was
performed by Jeol Model JSM-6340F. For FE-SEM analysis, aqueous
dispersions of GO and GO–CoPc were deposited on the glass
slides, whereas very dilute aqueous suspensions were deposited
on carbon-coated copper grids for HR-TEM analysis. X-ray powder
diffraction (XRD) analyses were carried out by using a Bruker D8
Figure 11. Methanol-conversion rate for a) GO; b) GO:Co-Pc (1:1); and c) GO-
CoPc.
Scheme 2. Possible mechanistic pathway of CO2 reduction.
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7. Advance diffractometer at 40 kV and 40 mA with CuKa radiation
(l=0.15418 nm). Sample for XRD was prepared by the deposition
of well-dispersed graphene–CoPc on glass slide followed by
drying; the analysis was performed by using cobalt as the target
material. Thermogravimetric analyses (TGA) of these samples were
carried out by using a thermal analyzer TA-SDT Q-600. All samples
were analyzed in the temperature range of 40 to 9008C at a heat-
ing rate of 108CminÀ1
under the nitrogen flow. The porous proper-
ties of GO and GO–CoPc catalysts were examined by N2 adsorp-
tion/desorption isotherms at 77 K and the related data (surface
area, SBET; pore volume, PV; Micromeritics ASAP 2010) were calcu-
lated. XPS measurements were obtained on a KRATOS-AXIS 165 in-
strument equipped with dual aluminum–magnesium anodes by
using MgKa radiation (hn=1253.6 eV) operated at 5 kV and 15 mA
with pass energy 80 eV and an increment of 0.1 eV. To overcome
the charging problem, a charge neutralizer of 2 eV was applied
and the binding energy of C1s core level (BEffi84.6 eV) of adventi-
tious hydrocarbon was used as a standard. The XPS spectra were
fitted by using a nonlinear square method with the convolution of
Lorentzian and Gaussian functions, after a polynomial background
was subtracted from the raw spectra. The conversions and selectiv-
ity of the products were determined by high-resolution GC-FID
(Varian CP-3800). 1
H NMR spectra of the products were recorded
on 500 MHz by using Bruker Avance-II 500 MHz instrument. ICP-
AES analysis was carried out by inductively coupled plasma atomic
emission spectrometer (ICP-AES, DRE, PS-3000UV, Leeman Labs
Inc., USA). Samples for ICP-AES were prepared by leaching out
0.01 g of sample with HNO3 (conc.), and then heated for 30 min
and volume to 10 mL.
After the photoreduction, the mixture was analyzed by GC. The
gaseous phase was analyzed by GC-thermal conductivity detector
(TCD) and GC-FID (Agilent 7890 A GC system) by using a column
(RGA, refinery gas analyzer) at the flow rate (H2 35, air 350, make-
up flow 27 mLminÀ1
, for TCD reference flow-45 mLminÀ1
, helium
flow 2 mLminÀ1
), injector temperature 2208C, TCD detector tem-
perature and FID detector temperature(2208C). Liquid samples
were analyzed with GC-FID model Varian CP3800 (column specifica-
tion: Stabilwax w/Integra-Guard, length 30 m, 0.25 ID) at the flow
rate 0.5 mLminÀ1
, injector temp 2508C, FID detector temperature
2758C. Autosampler (model no. Varian CP 8410) was used for in-
jecting the same amount of sample (1 mL). Calibration curve was
plotted with the help of auto sampler by injecting one microliter
sample (Figure S3 in the Supporting Information).
Synthesis of graphene oxide (GO)
Graphene oxide (GO) was synthesized from graphite flakes by
using modified Hummers methods.[11]
In a typical synthesis, con-
centrated H2SO4 (34 mL) was added into a flask containing graphite
flakes (1 gm) and sodium nitrate (0.75 gm) under stirring at 08C
(ice bath). Approximately 4.5 gm of KMnO4 was added gently over
20 min to the mixture and kept under stirring at RT for five days.
After that, diluted H2SO4 (50 mL, 5 wt%) was added into the mix-
ture and heated to 908C under continuous stirring for 2 h. Then,
H2O2 (30 wt%; 2.7 mL) was added into the solution and stirred for
another 2 h under ambient conditions. After completion of the re-
action, the mixture was centrifuged (6000 rpm, 15 min) and
washed with H2SO4 (3 wt%), H2O2 (0.5 wt%), and HCl (3 wt%), and
then repeatedly washed with distilled water, until the pH of the fil-
trate became neutral. Finally, the prepared GO was dispersed in
distilled water and the homogeneous GO dispersion was then cen-
trifuged and filtered.
Synthesis of carboxylated GO[27]
In a typical experiment, GO (200 mg) was dispersed in deionized
water (100 mL) by using ultrasonicator to give a concentration of
2 mgmLÀ1
. The obtained suspension was treated with NaOH
(1.2 g) and chloroacetic acid (1.0 g) for 3 h over ultrasonicator bath
to convert the OH groups into COOH groups. The resulting GOÀ
COOH product was neutralized by using a dilute HCl solution and
purified by repeated washing with deionized water and dried
under vacuum.
Immobilization of CoPc–tetrasulfonamide to carboxylated
GO[28,29]
Carboxylated GO (GOÀCOOH; 200 mg) was added in DMF (1 mL)
and treated with excess thionyl chloride at 658C for 12 h to obtain
its acyl chloride derivative. Unreacted thionyl chloride was re-
moved by vacuum distillation. The product was washed with THF
(three times) and vacuum dried. The obtained GO-Cl (100 mg) was
heated at reflux with cobalt phthalocyanine tetrasulfonamide [Co-
Pc-(SO2NH2)4 complex (100 mg) in DMF under nitrogen atmos-
phere. The GO-immobilized CoPc complex was separated from the
mixture by filtration, washed with ethanol (3–4 times) by using
centrifugation and membrane filtration. The GO immobilized CoPc
complex was dried in an oven. The analytical values for the GO-
supported CoPc were found to be C 59.67, H 3.073, N 5.468, and S
4.75 %. The cobalt content in synthesized GO–CoPc was estimated
by ICP-AES analysis, and the value was found to be 1.13 wt% Co.
Based on the value of cobalt, the loading of the CoPc in GO–CoPc
was found to be 2.3 mmolgÀ1
.
Photocatalytic CO2-reduction experiment
Photocatalytic experiment was performed in borosil cylindrical
vessel (100 mL) of 5 cm diameter (Figure 1). Photoirradiation was
carried out under visible light by using 20 W white cold LED flood
light (model no. HP-FL-20W-F-Hope LED Opto-Electric Co., Ltd.). In-
tensity of the light at vessel was measured by intensity meter and
was found to be 75 WmÀ2
. The vessel was charged initially with
water (40 mL) and triethylamine (10 mL), and then the solution
was degassed by continuous purging of nitrogen for 15 min. CO2
was bubbled through the solution for at least 30 min to saturate
the solution, then catalyst (100 mg) was added to the above-de-
scribed solution. The vessel was tightly closed during the reaction
and stirred continuously by a magnetic stirring bar to prevent sedi-
mentation of the catalyst. Samples were collected after every 2 h
by using a long needle, and the catalyst was removed with syringe
filter (2 nm PTFE, 13 mm diameter). Quantitative determination
was done by using GC-FID (flow rate 0.5 mLminÀ1
, injector temper-
ature 2508C, FID detector temperature 2758C). A calibration curve
was prepared for quantification and for confirmation of linear re-
sponse of GC-FID system.
Blank reactions were conducted to ensure that methanol produc-
tion was due to the photoreduction of CO2 and to eliminate sur-
rounding interference. One blank was Vis-illuminated without the
catalyst, and another one was kept in the dark with the catalyst
and CO2 under the same experimental conditions. An additional
blank test was Vis-illuminated with the catalyst filling N2 rather
than CO2. No product was detected in the above-described three
blank tests.
Chem. Eur. J. 2014, 20, 6154 – 6161 www.chemeurj.org 2014 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim6160
Full Paper
8. Acknowledgements
We kindly acknowledge Director, CSIR-IIP for his permission to
publish these results. P.K. and A.K. are thankful to CSIR, New
Delhi for their research fellowships. Analytical department of
the Institute is kindly acknowledged for providing support in
analysis.
Keywords: carbon dioxide reduction · cobalt · heterogeneous
catalysis · photochemistry
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Received: October 28, 2013
Revised: February 17, 2014
Published online on April 2, 2014
Chem. Eur. J. 2014, 20, 6154 – 6161 www.chemeurj.org 2014 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim6161
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