Alkaline water electrolysis driven by renewable energy is a promising technology for green hydrog... more Alkaline water electrolysis driven by renewable energy is a promising technology for green hydrogen generation. The cathode half-cell reaction i.e., the hydrogen evolution reaction (HER) in alkaline water electrolysis suffers from slow kinetics. Ni-P-based alloys have shown to be an e cient and cost-effective electrocatalyst to accelerate the HER rate. In this study, three Ni-P alloy coatings are prepared via electrodeposition by varying the deposition currents viz. 10 mA cm - 2 direct, 10 mAcm - 2 and 100 mAcm - 2 pulsed currents. The XRD patterns of all the Ni-P coatings exhibited the formation of crystalline deposits and con rmed the alloying of P in Ni. The SEM images suggested that the microstructures of the Ni-P alloy deposits are highly dependent on the magnitude and waveform of the applied current employed during preparation of the alloy coatings. The composition of the alloy surface is Ni-rich in all three cases but exhibited local variations as evaluated by EDX. The surface distributions of Ni and P in the pulsed deposited samples are more uniform and homogeneous. The cyclic voltammetry patterns of the Ni-P coatings in KOH media exhibit characteristic peaks due to Ni/Ni 3+ redox phenomenon. The Ni 2+ /Ni 3+ oxidation peak area is lowest for the direct deposited sample and highest for the pulsed deposited one (100 mAcm - 2 ). The Ni-P alloy electrocatalyst deposited under pulsed mode at 100 mAcm - 2 exhibits a current density of -10 mAcm - 2 at 0.09 V overpotential and is most active among all samples. The remarkable electrocatalytic activity of this sample is attributed to its smaller crystallite size, better morphological characteristics and lesser resistances to charge transfer and porosity.
The development of recyclable H2O2-producing photocatalysts with in situ Fenton-like organic poll... more The development of recyclable H2O2-producing photocatalysts with in situ Fenton-like organic pollutant degradation is currently a topical area of research.
Recently, we reported detailed investigations on a hydrolysis step of Cu–Cl thermochemical cycle ... more Recently, we reported detailed investigations on a hydrolysis step of Cu–Cl thermochemical cycle (Singh et al. in Int J Energy Res 44:2845–2863, 2020) where we demonstrated CuCl2 hydrolysis using a fixed-bed reactor under optimized conditions. Thermolysis of CuCl2 and oxide formation are associated hindrances in achieving 100% phase-pure hydrolysis product, Cu2OCl2. With an objective to understand the thermolysis and hydrolysis processes at molecular level, both these reactions were investigated independently in the present study using in situ XAS as a probe. The progress of both the reactions was recorded from RT to 400 °C by monitoring temperature-dependent evolution of Cu species using Cu K-edge XAS measurements at BL-09, Indus-2 SRS, RRCAT, Indore, India. XAS results are also corroborated with ex situ analysis by XRD and TG of samples containing various compositions of CuCl2 mixed with boron nitride (pellets employed for XAS). Besides LCF, hydrolysis product Cu2OCl2 yield was further supported by chemical titrations. EXAFS revealed that with increasing temperature, coordination of Cu atoms in reactant CuCl2 progressively decreased during thermolysis. For hydrolysis process, coordination of Cu atoms in Cu–Cu, Cu–O and Cu–Cl linkages approached towards that of Cu2OCl2 and CuO. CuCl2 diminished and transformed into CuCl (88 mass%) at 350 °C during thermolysis and ~ 60 mass% of Cu2OCl2 and 40 mass% of CuO during hydrolysis reaction. Based on in situ investigations in the present study, the most probable reactions taking place during CuCl2 hydrolysis at different temperatures are proposed for S/Cu of 14.6.
tuning the water oxidation is investigated. Decrease in Ni average oxidation showed stabilization... more tuning the water oxidation is investigated. Decrease in Ni average oxidation showed stabilization of lower Ni oxidation state. Surface intermediate relaxation process is rate limiting step in OER reaction. Fe-O-Ni linkages in FeOx-NiFe-LDH exert a partial charge transfer activation effect. Prototype demonstration of a photovoltaic-electrolyser assembly was done.
Considering the low temperature demand (550 C maximum) and high efficiency (43%), Cu-Cl thermoche... more Considering the low temperature demand (550 C maximum) and high efficiency (43%), Cu-Cl thermochemical water splitting cycle has immense potential as a futuristic scalable hydrogen generation process. CuCl/HCl electrolysis is the crucial hydrogen generation step in the Cu-Cl thermochemical cycle. The efficiency of this electrolysis process is highly dependent on the performance of the membrane electrode assembly (MEA) employed. To explore the suitability of the platinized membrane for this step, in this study, we have investigated a Pt/Nafion-117 MEA prepared by in-situ impregnation-reduction method for CuCl/HCl electrolysis. A single-cell PEM-type electrolyser (4 cm 2 active area) consisting of serpentine channels (2 cm × 2 cm) grooved in graphite flow field plates was designed and fabricated to carry out the CuCl/HCl electrolysis. Platinum electrocatalyst was deposited on Nafion-117 membrane on the cathodic side by reduction of hexachloroplatinic acid (H 2 PtCl 6) with sodium borohydride (NaBH 4) by the impregnation-reduction method which served as the MEA. Monodispersed nanocrystalline Pt particles formed a 30 μm thick electrocatalyst layer on the membrane. Pt/Nafion-117 MEA was found to be effective for CuCl /HCl electrolysis. In a PEM-type electrolyser with Ar-purged 0.2 M CuCl in 2 M HCl solution as anolyte flowing at 8.8 mLmin −1 , a current density of 100 mA cm −2 was achieved at a cell voltage of 1 V. However, undesired Cu-crossover could be noticed from anode to cathode side during operation.
h i g h l i g h t s g r a p h i c a l a b s t r a c t Dispersed Mo 2 C on vulcan carbon (b-Mo 2 C... more h i g h l i g h t s g r a p h i c a l a b s t r a c t Dispersed Mo 2 C on vulcan carbon (b-Mo 2 C phase): an effective electrocatalyst for HER. Excess carbon required in starting material to prepare Mo 2 C/C by carburization. 20 wt % Mo content is best electrocatalyst composition for HER. Electrochemical active surface area follows the order in Mo wt.% as: 20 > 15 > 28~9. EIS studies reveal fastest charge transfer kinetics in 20 wt % Mo sample.
Abstract Visible light driven photocatalysis by Cu and Ag incorporated mesoporous titania nanocub... more Abstract Visible light driven photocatalysis by Cu and Ag incorporated mesoporous titania nanocuboids is monitored in this work. The mesoprous titania is obtained by using non-ionic triblock copolymer P123 as the structure-directing agent, which yields self-organized meso structured titania nanocuboids. The catalysts are well characterized using XRD, SEM, TEM, N2 adsorption study, DR-UV, FTIR, photoluminescence, Raman and X-ray Photoelectron Spectral analysis. The co-exposed 101 and 001 planes of cuboids are observed to be favourable for the photo catalytic activity of anatase titania. Both CuO and Cu2O are identified in Cu doped titania, while silver in zero oxidation state is observed in Ag modified system. The absorbance of the parent titania is extended to visible region by the incorporation of these co-catalysts, and the visible light driven photocatalytic efficiency of the system is commendably improved, as confirmed by methylene blue and phenol degradations and hydrogen production through water splitting. The copper doped mesoporous assembled titania nanostructures promised itself to be the best candidate among the series, which excelled almost all other TiO2 based systems that operated under identical conditions.
Detailed investigations of CuCl 2 hydrolysis step of Cu-Cl thermochemical cycle were carried out ... more Detailed investigations of CuCl 2 hydrolysis step of Cu-Cl thermochemical cycle were carried out on various aspects: (a) characterization and thermal properties of reactants/products using X-ray diffraction (XRD), thermogravimetry-mass spectrometry (TG-MS), scanning electron microscopy (SEM), temperature-programmed desorption (TPD), and extended X-ray absorption fine structure (EXAFS); (b) performance evaluation of fixed bed hydrolysis; (c) parametric optimization with respect to S/Cu, flow rate (gas hourly space velocity, GHSV), reaction duration, temperature, and particle size; and (d) monitored hydrolysis using isothermal TG experiments at 360 C, 370 C, 380 C, 390 C, and 400 C to derive kinetic parameters rate constant (k) and activation energy (E a) on the basis of the shrinking-core model. 97% conversion to Cu 2 OCl 2 at 17 630 h −1 of GHSV, 400 C was achieved using ballmilled CuCl 2 (BM6), as compared with that of 55% over commercial un-ballmilled reactant, CuCl 2 (UBM). Correspondingly, higher k value of 2.84 h −1 over BM6 as compared with 0.97 h −1 over UBM reactant at 400 C was achieved. E a for hydrolysis of BM6 was 93 kJ/mol, while it was 106 kJ/mol for UBM as derived from the Arrhenius plot. A probable pathway for CuCl 2 hydrolysis is proposed here. It was found to be diffusion controlled, and the particle size of reactant molecules affects the packing and diffusion length. Based on our investigations, it is very unlikely to get >99% phase pure product (Cu 2 OCl 2). Cu 2 OCl 2 is labile in nature and tends to transform into structurally similar and stable compounds CuO and CuCl 2. K E Y W O R D S activation energy, Cu 2 OCl 2 , Cu-Cl cycle, CuCl 2 hydrolysis, EXAFS, hydrogen, isothermal TG, rate constant, thermochemical 1 | INTRODUCTION Hydrogen with calorific value of 141.8 MJ/kg (approximately three times that of gasoline) has potential to meet the world's increasing energy demands and replace fossil fuels. 1 For
Zn 1−x Fe x O y nanocomposites have been investigated for bi-functional performance towards photo... more Zn 1−x Fe x O y nanocomposites have been investigated for bi-functional performance towards photoelectrochemical (PEC) and photocatalytic (PC) splitting of water to produce hydrogen. Prepared at varying Zn/Fe atomic ratio via co-precipitation through controlled addition of NH 4 OH to the aqueous solution of iron (III) nitrate nonahydrate [Fe(NO 3) 3 •9H 2 O] and zinc acetate dihydrate [(CH 3 •COO) 2 Zn•2H 2 O], followed by sintering in air at 800 °C, the nanocomposites were characterized by XRD, SEM, TEM, UV-Visible optical absorption, XPS, and Mössbauer spectral analysis. Shift in bandgap energy (E g) and alterations in microstructural characteristics and electrical properties, observed with change in sample-composition, significantly influenced hydrogen generation. Plausible reasons have been offered. The optimum conditions for hydrogen generation via PEC and PC routes, not being similar, have also been worked out.
would be useful to perform sunlight driven scaled eup photocatalytic process using low cost visib... more would be useful to perform sunlight driven scaled eup photocatalytic process using low cost visible light efficient photocatalyst, Cu 0.02 Ti 0.98 O 2-d .
To accentuate the role of pn heterojunctions in composites, the photocatalytic properties of two ... more To accentuate the role of pn heterojunctions in composites, the photocatalytic properties of two composites NTC11 (NiO and TiO2 in 1:1 molar ratio) and NTC36 (0.35:0.65) were investigated in detail for H2 evolution reaction and compared with the component pure oxides, NiO, TiO2 and NiTiO3 prepared by sol-gel route. Among all CB VB VB CB n-type TiO 2 p-type NiO samples, NTC11 was distinctly most active (greater than pure TiO2 by ~22 times, NiO has negligible activity) and yielded reproducible H2 yields for 60 h under repetititive cycles in sunlight confirming its photostability. Maximum photocatalytic Hydrogen yield @ 0.6 L/h/m 2 with apparent quantum efficiency (AQE) of 5.4 % and solar fuel efficiency (SFE) of 0.8 % under sunlight and 1.4 L/h/m 2 with AQE of 7.8 % under UV-visible irradiation along with evolution of bubbles was observed over Pt(1wt%)/NTC11. Synthesis conditions, calcination temperature and phase compositions were very critical and played an essential role in determining the overall hydrogen yield. Presence of NiTiO3 was found to be derogatory for the photocatalytic activity of NTC36. The key factors responsible for enhanced rate of sunlight assisted hydrogen generation over NTC11 were 1. Formation of pn nanojunctions in NTC11 evident by enhanced life times of charge carriers monitored by time resolved photoluminescence, uniform distribution of NiO and TiO2 nanoparticles with Ni/Ti in ratio of 0.99 and 0.95 at bulk and surface, respectively. 2. Favourable morphological characteristics: monodisperse, nanosized faceted particles, higher surface area, better porosity and pore volume. 3. Coformation of minimal NiTiO3 phase. 4. First principles calculations by density functional theory (DFT) over pure NiO revealed it's electronic and band structure that helped in understanding its behavior as PL quencher and its contribution in visible light absorption of composites, 5. Valence band offset (DEv) and conduction band offset (DEc) at NiO and TiO2 heterojunction was calculated to be 0.53 eV and 0.93 eV, respectively. 6. Type-II band alignment was derived at the interface and mechanism was proposed, 7. The effective forbidden gap was deduced to be 3.2(Eg, TiO2)-DEv = 3.6(Eg, NiO)-DEc = 2.67 eV. Thus, a composite of pn oxides offers lower band gap energy of 2.67 eV as compared to both pure oxides TiO2 and NiO with effectiveness in charge separation across the pn junction leading to efficient improved photocatalyst.
A series of Cu doped titania, Cu x Ti 1 À x O 2 À δ (x¼0.0, 0.02, 0.06) and copper oxide-titanium... more A series of Cu doped titania, Cu x Ti 1 À x O 2 À δ (x¼0.0, 0.02, 0.06) and copper oxide-titanium oxide nanocomposites, xCuO-yTiO 2 (x:y¼ 1:9, 2:8, 5:5) were synthesized by sol-gel method and characterized by relevant techniques. The role of Cu ions in enhancement of photocatalytic evolution of H 2 from H 2 Omethanol/glycerol mixtures in both sunlight and UV-visible irradiation over Cu/Ti oxides was investigated. X-ray absorption fine structure (XAFS), supported by X-ray diffraction and Raman studies, revealed that Cu substitution in TiO 2 stabilized anatase lattice, lengthened Ti-O bonds, decreased the coordination number around Cu ions, and induced oxygen ion vacancies and distortion (σ) in lattice. Distorted structures are more open and flexible with improved charge carrier dynamics and favourable photocatalytic properties. Nanosized Cu-Ti-O powders with enhanced N 2-BET surface area and microporosity exhibited improved photocatalytic properties. Reduction of CuO to photocatalytically more active Cu 2 O by photo-generated eon the surface of composites was evident by the absence of Cu 2 þ peak in the XPS spectra of the composite sample after exposure to light. The most active formulations for sunlight assisted photocatalytic H 2 generation were Cu 0.02 Ti 0.98 O 2 for the doped samples, referred to as CuTi(2), and xCuO-yTiO 2 (x:y ¼2:8) for the composite samples. Performance of the most active, CuTi(2), was monitored in a up-scaled photoreactor in order to investigate the influence of illumination area, catalyst concentration, form of catalyst (powder/films) and different sacrificial agents on H 2 yield. With an aim to identify practical materials for pilot plants, 6 mg of CuTi(2) was dispersed on (30 cm  0.7 cm) ITO/PET films that exhibited enhanced efficiency (3.06%) as compared to same amount of CuTi(2) powder (1.41%). The results showed that the utilization of the CuTi(2) photocatalyst (without costly cocatalysts) with the proper selection of optimum operational conditions under sunlight in a up-scaled photoreactor, generated H 2 yield of 1.167 L/h/m 2 with apparent quantum efficiency, AQE, of 7.5% and solar to fuel efficiency, SFE, of 3.9% for the photocatalytic hydrogen evolution reaction (HER). Our results suggest that with this efficiency, H 2 at 1 L/h would be evolved photocatalytically over 0.9 m 2 of CuTi(2) photocatalyst, exposed to sunlight. Inputs obtained from the present study will be useful for further scale up of sunlight driven photocatalytic hydrogen production over low cost and efficient Cu modified TiO 2 .
Comparative evaluation of photodegradation of COD reduction using Ti02 catalyst and citric acid u... more Comparative evaluation of photodegradation of COD reduction using Ti02 catalyst and citric acid under UV radiation on the industrial wastewater, Rajendra Singh Thakur, Silver %Jubilee Young Scientist Congress, M.P.
Pure TiO2 , Ti 0.75 Fe0.25 O2, Ti0.75 Ni0.25 O2, Ti0.75 Co0.25 O2 nanocrystals were prepared by l... more Pure TiO2 , Ti 0.75 Fe0.25 O2, Ti0.75 Ni0.25 O2, Ti0.75 Co0.25 O2 nanocrystals were prepared by low temperature sol-gel method. The samples were characterized by using transmission electron microscope, X-ray diffractometer and ultraviolet-visible spectrophotometer to study the effect of transition metal ions on the photocatalytic properties of TiO2 nanocrystals. The results show that the pure TiO2 and Ti0.75 Fe0.25 O2, Ti0.75 Ni0.25 O2, Ti0.75 Co0.25 O2 nanocrystals were granular and the size of which is 3.5, 2.9, 3.6, 3.9 nm, respectively. The titania anatase phases appear in the pure TiO2 , the Ti0.75 Fe0.25 O2, Ti0.75 Ni0.25 O2, Ti0.75 Co0.25 O2. The absorption edge of Ti0.75 Fe0.25 O2occur red shift comparing with that of pure TiO2 and the absorption edge of Ti0.75 Fe0.25 O2and Ti0.75 Fe0.25 O2occur blue shift comparing with that of pure TiO2. The photocatalytic properties of pure TiO2, Ti0.75 Fe0.25 O2, Ti0.75 Fe0.25 O2, Ti0.75 Fe0.25 O2nanocrystals synthesized at low temperatu...
Fe3O4–TiO2 nanocomposites have been synthesized by hydrothermal method using sonochemically activ... more Fe3O4–TiO2 nanocomposites have been synthesized by hydrothermal method using sonochemically activated precursors. X-ray diffraction analysis of the samples reveals the formation of pure phase composites. The optical properties of the composites are superior to TiO2 as noted from the red shift in the diffused reflectance spectra of the composites. The presence of nanocubes of Fe3O4, nanospheres of TiO2 and heterojunctions of the two in the composite samples have been observed in transmission electron micrographs. The magnetic properties of the samples were determined with the help of vibrating sample magnetometry (VSM) and magnetic force microscopy (MFM). The photocatalytic activity of the samples was investigated in terms of degradation of methyl orange (MO) dye. The composites could be easily separated from the reaction mixture after photocatalysis due to their magnetic behaviour. However, the photocatalytic activity of the composites was observed to be lower compared to bare TiO2. The composite (15% Fe3O4–TiO2) when modified by coating it with Ag showed enhanced photocatalytic activity. Further, the antibacterial activities of the samples were also examined using E. coli as a model organism. Positive results were obtained only for the Ag coated composite with lower MIC (minimum inhibition concentration) values.
Alkaline water electrolysis driven by renewable energy is a promising technology for green hydrog... more Alkaline water electrolysis driven by renewable energy is a promising technology for green hydrogen generation. The cathode half-cell reaction i.e., the hydrogen evolution reaction (HER) in alkaline water electrolysis suffers from slow kinetics. Ni-P-based alloys have shown to be an e cient and cost-effective electrocatalyst to accelerate the HER rate. In this study, three Ni-P alloy coatings are prepared via electrodeposition by varying the deposition currents viz. 10 mA cm - 2 direct, 10 mAcm - 2 and 100 mAcm - 2 pulsed currents. The XRD patterns of all the Ni-P coatings exhibited the formation of crystalline deposits and con rmed the alloying of P in Ni. The SEM images suggested that the microstructures of the Ni-P alloy deposits are highly dependent on the magnitude and waveform of the applied current employed during preparation of the alloy coatings. The composition of the alloy surface is Ni-rich in all three cases but exhibited local variations as evaluated by EDX. The surface distributions of Ni and P in the pulsed deposited samples are more uniform and homogeneous. The cyclic voltammetry patterns of the Ni-P coatings in KOH media exhibit characteristic peaks due to Ni/Ni 3+ redox phenomenon. The Ni 2+ /Ni 3+ oxidation peak area is lowest for the direct deposited sample and highest for the pulsed deposited one (100 mAcm - 2 ). The Ni-P alloy electrocatalyst deposited under pulsed mode at 100 mAcm - 2 exhibits a current density of -10 mAcm - 2 at 0.09 V overpotential and is most active among all samples. The remarkable electrocatalytic activity of this sample is attributed to its smaller crystallite size, better morphological characteristics and lesser resistances to charge transfer and porosity.
The development of recyclable H2O2-producing photocatalysts with in situ Fenton-like organic poll... more The development of recyclable H2O2-producing photocatalysts with in situ Fenton-like organic pollutant degradation is currently a topical area of research.
Recently, we reported detailed investigations on a hydrolysis step of Cu–Cl thermochemical cycle ... more Recently, we reported detailed investigations on a hydrolysis step of Cu–Cl thermochemical cycle (Singh et al. in Int J Energy Res 44:2845–2863, 2020) where we demonstrated CuCl2 hydrolysis using a fixed-bed reactor under optimized conditions. Thermolysis of CuCl2 and oxide formation are associated hindrances in achieving 100% phase-pure hydrolysis product, Cu2OCl2. With an objective to understand the thermolysis and hydrolysis processes at molecular level, both these reactions were investigated independently in the present study using in situ XAS as a probe. The progress of both the reactions was recorded from RT to 400 °C by monitoring temperature-dependent evolution of Cu species using Cu K-edge XAS measurements at BL-09, Indus-2 SRS, RRCAT, Indore, India. XAS results are also corroborated with ex situ analysis by XRD and TG of samples containing various compositions of CuCl2 mixed with boron nitride (pellets employed for XAS). Besides LCF, hydrolysis product Cu2OCl2 yield was further supported by chemical titrations. EXAFS revealed that with increasing temperature, coordination of Cu atoms in reactant CuCl2 progressively decreased during thermolysis. For hydrolysis process, coordination of Cu atoms in Cu–Cu, Cu–O and Cu–Cl linkages approached towards that of Cu2OCl2 and CuO. CuCl2 diminished and transformed into CuCl (88 mass%) at 350 °C during thermolysis and ~ 60 mass% of Cu2OCl2 and 40 mass% of CuO during hydrolysis reaction. Based on in situ investigations in the present study, the most probable reactions taking place during CuCl2 hydrolysis at different temperatures are proposed for S/Cu of 14.6.
tuning the water oxidation is investigated. Decrease in Ni average oxidation showed stabilization... more tuning the water oxidation is investigated. Decrease in Ni average oxidation showed stabilization of lower Ni oxidation state. Surface intermediate relaxation process is rate limiting step in OER reaction. Fe-O-Ni linkages in FeOx-NiFe-LDH exert a partial charge transfer activation effect. Prototype demonstration of a photovoltaic-electrolyser assembly was done.
Considering the low temperature demand (550 C maximum) and high efficiency (43%), Cu-Cl thermoche... more Considering the low temperature demand (550 C maximum) and high efficiency (43%), Cu-Cl thermochemical water splitting cycle has immense potential as a futuristic scalable hydrogen generation process. CuCl/HCl electrolysis is the crucial hydrogen generation step in the Cu-Cl thermochemical cycle. The efficiency of this electrolysis process is highly dependent on the performance of the membrane electrode assembly (MEA) employed. To explore the suitability of the platinized membrane for this step, in this study, we have investigated a Pt/Nafion-117 MEA prepared by in-situ impregnation-reduction method for CuCl/HCl electrolysis. A single-cell PEM-type electrolyser (4 cm 2 active area) consisting of serpentine channels (2 cm × 2 cm) grooved in graphite flow field plates was designed and fabricated to carry out the CuCl/HCl electrolysis. Platinum electrocatalyst was deposited on Nafion-117 membrane on the cathodic side by reduction of hexachloroplatinic acid (H 2 PtCl 6) with sodium borohydride (NaBH 4) by the impregnation-reduction method which served as the MEA. Monodispersed nanocrystalline Pt particles formed a 30 μm thick electrocatalyst layer on the membrane. Pt/Nafion-117 MEA was found to be effective for CuCl /HCl electrolysis. In a PEM-type electrolyser with Ar-purged 0.2 M CuCl in 2 M HCl solution as anolyte flowing at 8.8 mLmin −1 , a current density of 100 mA cm −2 was achieved at a cell voltage of 1 V. However, undesired Cu-crossover could be noticed from anode to cathode side during operation.
h i g h l i g h t s g r a p h i c a l a b s t r a c t Dispersed Mo 2 C on vulcan carbon (b-Mo 2 C... more h i g h l i g h t s g r a p h i c a l a b s t r a c t Dispersed Mo 2 C on vulcan carbon (b-Mo 2 C phase): an effective electrocatalyst for HER. Excess carbon required in starting material to prepare Mo 2 C/C by carburization. 20 wt % Mo content is best electrocatalyst composition for HER. Electrochemical active surface area follows the order in Mo wt.% as: 20 > 15 > 28~9. EIS studies reveal fastest charge transfer kinetics in 20 wt % Mo sample.
Abstract Visible light driven photocatalysis by Cu and Ag incorporated mesoporous titania nanocub... more Abstract Visible light driven photocatalysis by Cu and Ag incorporated mesoporous titania nanocuboids is monitored in this work. The mesoprous titania is obtained by using non-ionic triblock copolymer P123 as the structure-directing agent, which yields self-organized meso structured titania nanocuboids. The catalysts are well characterized using XRD, SEM, TEM, N2 adsorption study, DR-UV, FTIR, photoluminescence, Raman and X-ray Photoelectron Spectral analysis. The co-exposed 101 and 001 planes of cuboids are observed to be favourable for the photo catalytic activity of anatase titania. Both CuO and Cu2O are identified in Cu doped titania, while silver in zero oxidation state is observed in Ag modified system. The absorbance of the parent titania is extended to visible region by the incorporation of these co-catalysts, and the visible light driven photocatalytic efficiency of the system is commendably improved, as confirmed by methylene blue and phenol degradations and hydrogen production through water splitting. The copper doped mesoporous assembled titania nanostructures promised itself to be the best candidate among the series, which excelled almost all other TiO2 based systems that operated under identical conditions.
Detailed investigations of CuCl 2 hydrolysis step of Cu-Cl thermochemical cycle were carried out ... more Detailed investigations of CuCl 2 hydrolysis step of Cu-Cl thermochemical cycle were carried out on various aspects: (a) characterization and thermal properties of reactants/products using X-ray diffraction (XRD), thermogravimetry-mass spectrometry (TG-MS), scanning electron microscopy (SEM), temperature-programmed desorption (TPD), and extended X-ray absorption fine structure (EXAFS); (b) performance evaluation of fixed bed hydrolysis; (c) parametric optimization with respect to S/Cu, flow rate (gas hourly space velocity, GHSV), reaction duration, temperature, and particle size; and (d) monitored hydrolysis using isothermal TG experiments at 360 C, 370 C, 380 C, 390 C, and 400 C to derive kinetic parameters rate constant (k) and activation energy (E a) on the basis of the shrinking-core model. 97% conversion to Cu 2 OCl 2 at 17 630 h −1 of GHSV, 400 C was achieved using ballmilled CuCl 2 (BM6), as compared with that of 55% over commercial un-ballmilled reactant, CuCl 2 (UBM). Correspondingly, higher k value of 2.84 h −1 over BM6 as compared with 0.97 h −1 over UBM reactant at 400 C was achieved. E a for hydrolysis of BM6 was 93 kJ/mol, while it was 106 kJ/mol for UBM as derived from the Arrhenius plot. A probable pathway for CuCl 2 hydrolysis is proposed here. It was found to be diffusion controlled, and the particle size of reactant molecules affects the packing and diffusion length. Based on our investigations, it is very unlikely to get >99% phase pure product (Cu 2 OCl 2). Cu 2 OCl 2 is labile in nature and tends to transform into structurally similar and stable compounds CuO and CuCl 2. K E Y W O R D S activation energy, Cu 2 OCl 2 , Cu-Cl cycle, CuCl 2 hydrolysis, EXAFS, hydrogen, isothermal TG, rate constant, thermochemical 1 | INTRODUCTION Hydrogen with calorific value of 141.8 MJ/kg (approximately three times that of gasoline) has potential to meet the world's increasing energy demands and replace fossil fuels. 1 For
Zn 1−x Fe x O y nanocomposites have been investigated for bi-functional performance towards photo... more Zn 1−x Fe x O y nanocomposites have been investigated for bi-functional performance towards photoelectrochemical (PEC) and photocatalytic (PC) splitting of water to produce hydrogen. Prepared at varying Zn/Fe atomic ratio via co-precipitation through controlled addition of NH 4 OH to the aqueous solution of iron (III) nitrate nonahydrate [Fe(NO 3) 3 •9H 2 O] and zinc acetate dihydrate [(CH 3 •COO) 2 Zn•2H 2 O], followed by sintering in air at 800 °C, the nanocomposites were characterized by XRD, SEM, TEM, UV-Visible optical absorption, XPS, and Mössbauer spectral analysis. Shift in bandgap energy (E g) and alterations in microstructural characteristics and electrical properties, observed with change in sample-composition, significantly influenced hydrogen generation. Plausible reasons have been offered. The optimum conditions for hydrogen generation via PEC and PC routes, not being similar, have also been worked out.
would be useful to perform sunlight driven scaled eup photocatalytic process using low cost visib... more would be useful to perform sunlight driven scaled eup photocatalytic process using low cost visible light efficient photocatalyst, Cu 0.02 Ti 0.98 O 2-d .
To accentuate the role of pn heterojunctions in composites, the photocatalytic properties of two ... more To accentuate the role of pn heterojunctions in composites, the photocatalytic properties of two composites NTC11 (NiO and TiO2 in 1:1 molar ratio) and NTC36 (0.35:0.65) were investigated in detail for H2 evolution reaction and compared with the component pure oxides, NiO, TiO2 and NiTiO3 prepared by sol-gel route. Among all CB VB VB CB n-type TiO 2 p-type NiO samples, NTC11 was distinctly most active (greater than pure TiO2 by ~22 times, NiO has negligible activity) and yielded reproducible H2 yields for 60 h under repetititive cycles in sunlight confirming its photostability. Maximum photocatalytic Hydrogen yield @ 0.6 L/h/m 2 with apparent quantum efficiency (AQE) of 5.4 % and solar fuel efficiency (SFE) of 0.8 % under sunlight and 1.4 L/h/m 2 with AQE of 7.8 % under UV-visible irradiation along with evolution of bubbles was observed over Pt(1wt%)/NTC11. Synthesis conditions, calcination temperature and phase compositions were very critical and played an essential role in determining the overall hydrogen yield. Presence of NiTiO3 was found to be derogatory for the photocatalytic activity of NTC36. The key factors responsible for enhanced rate of sunlight assisted hydrogen generation over NTC11 were 1. Formation of pn nanojunctions in NTC11 evident by enhanced life times of charge carriers monitored by time resolved photoluminescence, uniform distribution of NiO and TiO2 nanoparticles with Ni/Ti in ratio of 0.99 and 0.95 at bulk and surface, respectively. 2. Favourable morphological characteristics: monodisperse, nanosized faceted particles, higher surface area, better porosity and pore volume. 3. Coformation of minimal NiTiO3 phase. 4. First principles calculations by density functional theory (DFT) over pure NiO revealed it's electronic and band structure that helped in understanding its behavior as PL quencher and its contribution in visible light absorption of composites, 5. Valence band offset (DEv) and conduction band offset (DEc) at NiO and TiO2 heterojunction was calculated to be 0.53 eV and 0.93 eV, respectively. 6. Type-II band alignment was derived at the interface and mechanism was proposed, 7. The effective forbidden gap was deduced to be 3.2(Eg, TiO2)-DEv = 3.6(Eg, NiO)-DEc = 2.67 eV. Thus, a composite of pn oxides offers lower band gap energy of 2.67 eV as compared to both pure oxides TiO2 and NiO with effectiveness in charge separation across the pn junction leading to efficient improved photocatalyst.
A series of Cu doped titania, Cu x Ti 1 À x O 2 À δ (x¼0.0, 0.02, 0.06) and copper oxide-titanium... more A series of Cu doped titania, Cu x Ti 1 À x O 2 À δ (x¼0.0, 0.02, 0.06) and copper oxide-titanium oxide nanocomposites, xCuO-yTiO 2 (x:y¼ 1:9, 2:8, 5:5) were synthesized by sol-gel method and characterized by relevant techniques. The role of Cu ions in enhancement of photocatalytic evolution of H 2 from H 2 Omethanol/glycerol mixtures in both sunlight and UV-visible irradiation over Cu/Ti oxides was investigated. X-ray absorption fine structure (XAFS), supported by X-ray diffraction and Raman studies, revealed that Cu substitution in TiO 2 stabilized anatase lattice, lengthened Ti-O bonds, decreased the coordination number around Cu ions, and induced oxygen ion vacancies and distortion (σ) in lattice. Distorted structures are more open and flexible with improved charge carrier dynamics and favourable photocatalytic properties. Nanosized Cu-Ti-O powders with enhanced N 2-BET surface area and microporosity exhibited improved photocatalytic properties. Reduction of CuO to photocatalytically more active Cu 2 O by photo-generated eon the surface of composites was evident by the absence of Cu 2 þ peak in the XPS spectra of the composite sample after exposure to light. The most active formulations for sunlight assisted photocatalytic H 2 generation were Cu 0.02 Ti 0.98 O 2 for the doped samples, referred to as CuTi(2), and xCuO-yTiO 2 (x:y ¼2:8) for the composite samples. Performance of the most active, CuTi(2), was monitored in a up-scaled photoreactor in order to investigate the influence of illumination area, catalyst concentration, form of catalyst (powder/films) and different sacrificial agents on H 2 yield. With an aim to identify practical materials for pilot plants, 6 mg of CuTi(2) was dispersed on (30 cm  0.7 cm) ITO/PET films that exhibited enhanced efficiency (3.06%) as compared to same amount of CuTi(2) powder (1.41%). The results showed that the utilization of the CuTi(2) photocatalyst (without costly cocatalysts) with the proper selection of optimum operational conditions under sunlight in a up-scaled photoreactor, generated H 2 yield of 1.167 L/h/m 2 with apparent quantum efficiency, AQE, of 7.5% and solar to fuel efficiency, SFE, of 3.9% for the photocatalytic hydrogen evolution reaction (HER). Our results suggest that with this efficiency, H 2 at 1 L/h would be evolved photocatalytically over 0.9 m 2 of CuTi(2) photocatalyst, exposed to sunlight. Inputs obtained from the present study will be useful for further scale up of sunlight driven photocatalytic hydrogen production over low cost and efficient Cu modified TiO 2 .
Comparative evaluation of photodegradation of COD reduction using Ti02 catalyst and citric acid u... more Comparative evaluation of photodegradation of COD reduction using Ti02 catalyst and citric acid under UV radiation on the industrial wastewater, Rajendra Singh Thakur, Silver %Jubilee Young Scientist Congress, M.P.
Pure TiO2 , Ti 0.75 Fe0.25 O2, Ti0.75 Ni0.25 O2, Ti0.75 Co0.25 O2 nanocrystals were prepared by l... more Pure TiO2 , Ti 0.75 Fe0.25 O2, Ti0.75 Ni0.25 O2, Ti0.75 Co0.25 O2 nanocrystals were prepared by low temperature sol-gel method. The samples were characterized by using transmission electron microscope, X-ray diffractometer and ultraviolet-visible spectrophotometer to study the effect of transition metal ions on the photocatalytic properties of TiO2 nanocrystals. The results show that the pure TiO2 and Ti0.75 Fe0.25 O2, Ti0.75 Ni0.25 O2, Ti0.75 Co0.25 O2 nanocrystals were granular and the size of which is 3.5, 2.9, 3.6, 3.9 nm, respectively. The titania anatase phases appear in the pure TiO2 , the Ti0.75 Fe0.25 O2, Ti0.75 Ni0.25 O2, Ti0.75 Co0.25 O2. The absorption edge of Ti0.75 Fe0.25 O2occur red shift comparing with that of pure TiO2 and the absorption edge of Ti0.75 Fe0.25 O2and Ti0.75 Fe0.25 O2occur blue shift comparing with that of pure TiO2. The photocatalytic properties of pure TiO2, Ti0.75 Fe0.25 O2, Ti0.75 Fe0.25 O2, Ti0.75 Fe0.25 O2nanocrystals synthesized at low temperatu...
Fe3O4–TiO2 nanocomposites have been synthesized by hydrothermal method using sonochemically activ... more Fe3O4–TiO2 nanocomposites have been synthesized by hydrothermal method using sonochemically activated precursors. X-ray diffraction analysis of the samples reveals the formation of pure phase composites. The optical properties of the composites are superior to TiO2 as noted from the red shift in the diffused reflectance spectra of the composites. The presence of nanocubes of Fe3O4, nanospheres of TiO2 and heterojunctions of the two in the composite samples have been observed in transmission electron micrographs. The magnetic properties of the samples were determined with the help of vibrating sample magnetometry (VSM) and magnetic force microscopy (MFM). The photocatalytic activity of the samples was investigated in terms of degradation of methyl orange (MO) dye. The composites could be easily separated from the reaction mixture after photocatalysis due to their magnetic behaviour. However, the photocatalytic activity of the composites was observed to be lower compared to bare TiO2. The composite (15% Fe3O4–TiO2) when modified by coating it with Ag showed enhanced photocatalytic activity. Further, the antibacterial activities of the samples were also examined using E. coli as a model organism. Positive results were obtained only for the Ag coated composite with lower MIC (minimum inhibition concentration) values.
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