Photocatalytic Activity For Hydrogen Generation Research Articles

Graphene supported Co–Mo–P catalyst for efficient photocatalyzed hydrogen generation

In this work, graphene(GP) supported Co–Mo–P catalysts for H2 generation were prepared via an in-situ synthesis strategy with the help of photogenerated electrons. The transmission electron microscopy images (TEM) of the catalysts indicated that the elements of Co, Mo and P were distributed in a relatively homogeneous manner in the catalysts. The Co–Mo–P/GP catalyst exhibited high photocatalytic activity for hydrogen generation sensitized by Eosin Y (EY) under visible light. The Mo/(Co + Mo) molar ratio (χMo) was varied in the catalyst to study the effect of Mo doping on the catalytic efficiency. The highest rate of the H2 generation was found to be as high as 33.3 mmol·h−1·gCo−1 when the χMo was 10%. The apparent quantum efficiency (AQE) of the reaction over the Mo doped catalyst under 430 nm irradiation was 52.6%, which was six times higher than that using the un-doped Co–P/GO catalyst.

Photocatalytic and photo electrochemical properties of cadmium zinc sulfide solid solution in the presence of Pt and RuS2 dual co-catalysts

A new combination of co-catalysts and photocatalyst, Pt-RuS2-Cd0.5Zn0.5S, is found to exhibit enhanced photocatalytic activity for hydrogen generation from water. The presence of dual co-catalysts not only improves the photocatalytic activity but also increases the stability of the CdZnS photocatalyst. Increased visible light absorption and a decrease in bandgap occur for Cd0.5Zn0.5S in the presence of the co-catalysts. All samples exist as nanocrystalline materials with a particle size in the range of 20–50nm. In this system, Ru is in 4+ oxidation state and Pt is in metallic state. Photoluminescence studies suggest the presence of a number of defect levels/surface states in these catalysts, whose energy vary with the composition of the catalyst. The enhanced photocatalytic activity of Pt-RuS2-Cd0.5Zn0.5S is attributed to the better separation of photogenerated charge carriers assisted by the dual co-catalysts. Another remarkable property exhibited by this system is the increased stability for repeated use, which can be attributed to the effective transfer of photogenerated holes from Cd0.5Zn0.5S to RuS2, which minimizes the photo corrosion of the catalyst. Photoelectrochemical results show a significant increase in the photocurrent with applied voltage and excellent switching characteristics for both Pt-RuS2-Cd0.5Zn0.5S and Cd0.5Zn0.5S. No discernible improvement in photocurrent is seen for Pt-RuS2-Cd0.5Zn0.5S compared to Cd0.5Zn0.5S. The difference in the photocatalytic and photo electrochemical property is explained based on the inherent differences of the two phenomena.

Ceria Supported Pt/PtO-Nanostructures: Efficient Photocatalyst for Sacrificial Donor Assisted Hydrogen Generation under Visible-NIR Light Irradiation

In photocatalysis, imperative photoredox behavior and narrow band gap are important properties to exploit solar light for water splitting reaction. Nanostructured ceria (cerium dioxide/CeO2) with Ce3+/Ce4+ (photoredox couple) shows significant enhancement in photocatalytic activity, however, no significant activity for water splitting reaction. The present study mainly focuses on incorporation of Pt on nanostructured mesoporous ceria by wet-impregnation method and its evaluation for donor assisted photocatalytic water splitting reaction. The BET analysis shows much higher surface area (119–131 m2 g–1) for unmodified as well as Pt modified mesoceria samples as compared to commercial ceria (24.4 m2 g–1), although structure was not ordered. The incorporation of Pt on mesoceria shows remarkable influence on photocatalytic hydrogen generation activity, and 1 wt % Pt was found to be optimized content, with broader light absorption. This photocatalyst was optimized with respect to photocatalyst dose, use of diff...

The enhancement of electron transportation and photo-catalytic activity for hydrogen generation by introducing spin-polarized current into dye-sensitized photo-catalyst

Implanting polyiodides into graphene not only realized spin-polarization of photo electrons, but induced an optimum Rashba spin–orbit coupling to promote the spin electrons tunneling through the honeycomb sub-lattices of graphene, thus the HER and TOF was highly improved.

A dye-like ligand-based metal–organic framework for efficient photocatalytic hydrogen production from aqueous solution

A dye-like based Gd-MOF exhibits efficient photocatalytic activity for hydrogen generation without a co-catalyst. Depositing Ag further enhances its activity.

Photocatalytic degradation of organic compounds by PbMoO4 synthesized by a microwave-assisted solvothermal method

The microwave-assisted solvothermal (PbMH) and conventional solvothermal (PbH) synthesis were successfully used to prepare PbMoO4 particles with different morphologies, crystallinity degree and particle size. The material was structurally characterized by X-ray diffraction (XRD), their morphologies were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The textural and optical properties were analyzed by adsorption–desorption N2 isotherms (BET), diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) measurements, respectively. The photocatalytic activity of PbMoO4 particles was evaluated by degradation of indigo carmine (IC), orange G (OG), tetracycline (TC), salicylic acid (SA) and ciprofloxacin (CIP) compounds in aqueous solution under UV–vis light irradiation. The PbMH sample showed the highest photocatalytic activity reaching half-life times (t1/2) of 6, 7, 18, 75 and 125min for TC, CIP, IC, SA and OG. Moreover, PbMoO4 samples were evaluated in the H2 production from aqueous solutions using ethanol as sacrificial agent. The results showed that the PbH sample has the highest photocatalytic activity for hydrogen generation probably attributed to its high crystallinity degree.

Tuning Phase Composition of TiO2 by Sn(4+) Doping for Efficient Photocatalytic Hydrogen Generation.

The anatase-rutile mixed-phase photocatalysts have attracted extensive research interest because of the superior activity compared to their single phase counterparts. In this study, doping of Sn(4+) ions into the lattice of TiO2 facilitates the phase transformation from anatase to rutile at a lower temperature while maintaining the same crystal sizes compared to the conventional annealling approach. The mass ratios between anatase and rutile phases can be easily manipulated by varying the Sn-dopant content. Characterization results reveal that the Sn(4+) ions entered into the lattice of TiO2 by substituting some of the Ti(4+) ions and distributed evenly in the matrix of TiO2. The substitution induced the distortion of the lattice structure, which realized the phase transformation from anatase to rutile at a lower temperature and the close-contact phase junctions were consequently formed between anatase and rutile, accounting for the efficient charge separations. The mixed-phase catalysts prepared by doping Sn(4+) ions into the TiO2 exhibit superior activity for photocatalytic hydrogen generation in the presence of Au nanoparticles, relatively to their counterparts prepared by the conventional annealling at higher temperatures. The band allignment between anatase and rutile phases is established based on the valence band X-ray photoelectron spectra and diffuse reflectance spectra to understand the spatial charge separation process at the heterojunction between the two phases. The study provides a new route for the synthesis of mixed-phase TiO2 catalysts for photocatalytic applications and advances the understanding on the enhanced photocatalytic properties of anatase-rutile mixtures.

Realization of high photocatalytic hydrogen generation activity by nanostructured Ga1−xZnxO1−zNz solid-solution without co-catalyst

Photocatalysis requires light absorption as well as efficient extraction of the photogenerated electron–hole pairs to chemically active sites. To avoid electron–hole recombination, we need tailored nanostructures which can demonstrate novel light absorption and thermodynamic properties. This work shows that band gap modification/narrowing due to the formation of solid solution along with an increased surface area of the nanostructures are ideal for solar harvesting and is a self sufficient photocatalytic agent even in absence of a co-catalyst. The present study suggests that the rate of H2 production for GaN was negligible and it increased to 32.43 μmol/g/h for the solid solution under visible light irradiation (>400 nm) even in the absence of a co-catalyst. The apparent quantum yield (AQY) efficiency of H2 evolution was found to be 0.8%. This highly desirable increased H2 generation activity is attributed to the additional linewidth broadening in the photoluminescence spectra of nanostructured wurtzite Ga1−xZnxO1−zNz solid-solution due to Ga/Zn and N/O interdiffusion giving rise to a modified bandgap and N2p-O2p interaction in the lattice. These inferences are also corroborated by diffuse reflectance spectra of the samples. For the first time, origin of hitherto unreported weak features appearing in the low energy Raman spectrum is also discussed. A series of characterization tools including structural, microstructural, optical, spectroscopic and Photocatalytic hydrogen production studies were employed to support our claim.

Bifunctional Modification of Graphitic Carbon Nitride with MgFe2O4 for Enhanced Photocatalytic Hydrogen Generation.

To gain high photocatalytic activity for hydrogen evolution, both charge separation efficiency and surface reaction kinetics must be improved, and together would be even better. In this study, the visible light photocatalytic hydrogen production activity of graphitic carbon nitride (g-C3N4) was greatly enhanced with MgFe2O4 modification. It was demonstrated that MgFe2O4 could not only extract photoinduced holes from g-C3N4, leading to efficient charge carrier separation at the g-C3N4/MgFe2O4 interface, but also act as an oxidative catalyst accelerating the oxidation reaction kinetics at g-C3N4 surface. This dual function of MgFe2O4 thus contributed to the great improvement (up to three-fold) in photocatalytic activity for hydrogen generation over g-C3N4/MgFe2O4 as compared to pristine g-C3N4, after loading Pt by photoreduction method. It was revealed that in the Pt/g-C3N4/MgFe2O4 system, the photoinduced electrons and holes were entrapped by Pt and MgFe2O4, respectively, giving rise to the promoted charge separation; moreover, as evidenced by electrochemical analysis, the electrocatalysis effect of MgFe2O4 benefited the oxidation reaction at g-C3N4 surface.

Visible light photocatalytic H2-production activity of wide band gap ZnS nanoparticles based on the photosensitization of graphene

Visible light photocatalytic H2 production from water splitting is considered an attractive way to solve the increasing global energy crisis in modern life. In this study, a series of zinc sulfide nanoparticles and graphene (GR) sheet composites were synthesized by a two-step hydrothermal method, which used zinc chloride, sodium sulfide, and graphite oxide (GO) as the starting materials. The as-prepared ZnS-GR showed highly efficient visible light photocatalytic activity in hydrogen generation. The morphology and structure of the composites obtained by transmission electron microscope and x-ray diffraction exhibited a small crystallite size and a good interfacial contact between the ZnS nanoparticles and the two-dimensional (2D) GR sheet, which were beneficial for the photocatalysis. When the content of the GR in the catalyst was 0.1%, the ZG0.1 sample exhibited the highest H2-production rate of 7.42 μmol h−1 g−1, eight times more than the pure ZnS sample. This high visible-light photocatalytic H2 production activity is attributed to the photosensitization of GR. Irradiated by visible light, the electrons photogenerated from GR transfer to the conduction band of ZnS to participate in the photocatalytic process. This study presents the visible-light photocatalytic activity of wide bandgap ZnS and its application in H2 evolution.

Nanohybrid MoS2-PANI-CdS photocatalyst for hydrogen evolution from water

A ternary nanohybrid material, MoS2-PANI(polyaniline)-CdS, exhibits enhanced photocatalytic activity for hydrogen generation from water compared to single phase CdS, MoS2-CdS and PANI-CdS composites. The photocatalytic activity increases further when palladium is used as co-catalyst. The modified CdS composite catalyst is found to be stable for repeated cycles of photocatalytic experiments. Increased visible light absorption is seen when CdS is modified with PANI and MoS2 having a layered structure. Detailed characterization suggests that CdS, PANI and MoS2 exist as an intimate blend in the composite. Time resolved fluorescence studies show an increased lifetime for the photogenerated charge carriers in MoS2-PANI-CdS composite. Photocurrent measurements show relatively higher current output for the MoS2-PANI-CdS sample compared to CdS and other binary composites. The increased photocatalytic activity of the modified CdS catalyst is attributed to the increased visible light absorption, increased photoresponse and increased lifetime of the photogenerated charge carriers promoted by both PANI and MoS2. In the presence of Pd co-catalyst, interfacial transfer of electrons from the catalyst to Pd occurs, which enhances the separation of charge carriers and provides active sites for hydrogen evolution. Present study provides insights for improving the photocatalytic activity of CdS photocatalyst.

Enhanced photocatalytic generation of hydrogen by Pt-deposited nitrogen-doped TiO2 hierarchical nanostructures

We report the photocatalytic activity of hydrogen generation on Pt nanoparticles deposited on hierarchically porous N-doped TiO2 nanostructures (Pt-NHPT). The photocatalysts are composed of Pt nanoparticles well dispersed throughout hierarchical macroporous TiO2 fibrous channels. The interstitial N doping extends light absorption toward the visible region. We found that the porosity of N-doped TiO2 nanostructures can be tuned using different annealing temperatures. While Pt-NHPT catalysts calcined at 300°C (Pt-NHPT-300) have both macro- and mesoporosity, Pt-NHPT catalysts calcined at 800°C (Pt-NHPT-800) exhibit only macroporosity. We found that Pt-NHPT-300 shows a two-fold higher H2 evolution activity than that of Pt-NHPT-800, and 30% higher activity than undoped hierarchical catalysts (Pt-HPT-300). The enhanced photoactivity is attributed to the synergistic effects of N doping, hierarchical porosity, and charge transfer between the TiO2 nanostructures and the Pt co-catalyst.

Synergistic effect of double-shelled and sandwiched TiO₂@Au@C hollow spheres with enhanced visible-light-driven photocatalytic activity.

A novel approach for the fabrication of double-shelled, sandwiched, and nanostructured hollow spheres was proposed, using hydrotherm reaction and calcination. The negatively charged nanoparticles (e.g., Au, Ag, and Pt) could be adsorbed successively onto the positively charged hollow spheres (e.g., TiO2, ZnO, and ZrO2). The resulted nanocomposites (TiO2@Au, as a proof-of-concept) were dispersed in glucose solution under hydrothermal conditions. After calcination, uniform double-shelled and sandwiched TiO2@Au@C hollow spheres were obtained and Au nanoparticles were sandwiched between the shell wall of TiO2 and C. The samples were characterized by SEM, TEM, XRD, XPS, BET, and UV-vis DRS. The photocatalytic activity for the degradation of 4-nitroaniline was in the order of TiO2@Au@C > TiO2@C > TiO2/Au > P25. The visible-light photodegradation rate of 92.65% for 4-nitroaniline was achieved by TiO2@Au@C, which exhibited an increase of 75% compared to Degussa P25 TiO2. Furthermore, no deactivation occurred during catalytic reaction for three times, i.e., the TiO2@Au@C microspheres exhibited superior photocatalytic stability. TiO2@Au@C microspheres could also enhance the photocatalytic activity for hydrogen generation from methanol/water solutions. The synergistic effect of coupling TiO2 hollow spheres with Au nanoparticles and C shell on photocatalytic performance was proved by us. The photoexcited electrons from Au nanoparticles could be captured by the conduction band of TiO2 and then the electron-hole separation was improved. Moreover, both the visible light absorption and the affinity between TiO2 and pollutants could be improved by the coexistence of carbonaceous materials, which could facilitate the photocatalytic interface reaction.

Nitrogen-doped CeOxnanoparticles modified graphitic carbon nitride for enhanced photocatalytic hydrogen production

Nitrogen-doped CeOxnanoparticles modified g-C3N4was successfully preparedviaa one-pot method, which showed significantly enhanced photocatalytic activity for hydrogen generation under visible light compared to the pure g-C3N4photocatalyst.

Understanding the Influence of Lattice Composition on the Photocatalytic Activity of Defect‐Pyrochlore‐Structured Semiconductor Mixed Oxides

The defect‐pyrochlore‐structured photocatalyst CsTaWO6 is an ideal starting material for anion doping from the gas phase, and is known to be highly active for solar hydrogen generation under simulated sunlight without co‐catalysts. To investigate the active site of CsTaWO6 for hydrogen generation and to understand the effects of the two d0 elements in the compound, systematic and successive element substitution of tantalum and tungsten on the crystallographic 16c sites of the starting material has been performed. Substituting lattice tantalum with niobium hardly changes the band gap of the resulting compounds CsTa(1 −x)Nb x WO6, but the photocatalytic activity for hydrogen generation and oxidation reactions is strongly influenced. By investigating the surface reactivity toward adsorption, surface effects altering the activity are identified. In contrast, substituting lattice tungsten with molybdenum reduces the band gap of CsTaWO6 into the visible‐light range. Materials containing Mo are however not able to generate hydrogen anymore, due to the altered conduction band positions proven by density functional theory calculations. CsTaMoO6 exhibits a band gap of 2.9 eV and evolves oxygen efficiently under UV light irradiation after CoPi co‐catalyst deposition, and even under visible light small amounts of oxygen.

Alcohol solvents evaporation-induced self-assembly synthesis of mesoporous TiO2−x−y C x N y nanoparticles toward visible-light driven photocatalytic activity

A one-step solvent evaporation-induced self-assembly (SEISA) process was demonstrated to prepare carbon and nitrogen co-doping mesoporous TiO2 nanoparticles (MesoTiO2−x−yCxNy-S) using an ionic liquid as carbon and nitrogen sources as well as mesoporous template. After the evaporation of different solvents (methanol, ethanol, and isopropanol) and subsequent calcinations at 773 K, the obtained MesoTiO2−x−yCxNy-S samples were systematically characterized by a variety of spectroscopic and analytical techniques, including small- and large-angle X-ray diffraction (XRD), Raman, transmission electron microscopy (TEM), N2 adsorption–desorption isotherms, Fourier transform infrared (FTIR), and X-ray photoelectron (XPS) spectroscopies. The results indicate that the solvents play an essential role on the chemical microstructure, doping elemental states, and photocatalytic performance of catalysts. The MesoTiO2−x−yCxNy-I samples have the lowest band gap of ca. 2.75 eV and strongest absorbance of visible light in the range of 400–600 nm. Among the MesoTiO2−x−yCxNy-S photocatalysts, the MesoTiO2−x−yCxNy-M catalysts show superior photocatalytic activity of hydrogen generation in methanol aqueous solution under visible light irradiation as compared to MesoTiO2−x−yCxNy-E, MesoTiO2−x−yCxNy-I, and commercial Degussa TiO2. This result could be attributed to the moderate C,N co-doping amounts on their developed mesoporous texture (pore size = 8.0 nm) and high surface area (107 m2 g−1) of TiO2 (crystallite size = 9.9 nm) in the MesoTiO2−x−yCxNy-M catalysts.

Photocatalytic hydrogen production from methanol aqueous solution under visible-light using Cu/S–TiO2 prepared by electroless plating method

Cu was loaded on the S-doped TiO2 by electroless plating method. The prepared Cu/S–TiO2 exhibited high photocatalytic activity for hydrogen generation, and the yield is up to 7.5mmolh−1g−1cat in methanol solution. Their physical structure and chemical properties were characterized by UV–Vis, XRD, XPS and EXAFS. The copper species were CuO and Cu2O, and the sample showed excellent visible light absorption ability. Comparing with the sample prepared by chemical reducing method, the electroless plated copper on S–TiO2 was highly dispersed, which could facilitate photo-generated charges capture, transfer and separation.

Pd–TiO2–SrIn2O4heterojunction photocatalyst: enhanced photocatalytic activity for hydrogen generation and degradation of methylene blue

A novel heterojunction photocatalyst of TiO2–SrIn2O4 is found to be active for hydrogen generation from water as well as for the degradation of methylene blue under sunlight type radiation. Photocatalytic activity for hydrogen generation increases with increase in SrIn2O4 concentration and the optimum concentration is found to be 40% (by weight). The presence of a Pd co-catalyst enhances the photocatalytic activity and the catalyst is found to be stable after repeated cycles of photocatalysis experiments. A higher rate of degradation of methylene blue is observed when the composite is used as photocatalyst compared to pure TiO2 and SrIn2O4. Detailed characterization of the composite revealed that TiO2 exists as a dispersed phase on SrIn2O4 and the particle size of TiO2 and TiO2–SrIn2O4 is around 20 nm and 15 nm, respectively. Photocurrent experiments show a relatively higher current output for the composite compared to pure TiO2. The enhanced photocatalytic activity of the composite is attributed to a synergistic effect of the increased lifetime of the charge carriers in the composite and increased surface area of the sample. The dispersion of TiO2 nanoparticles on SrIn2O4 results in the formation of hetero-junctions between TiO2 and SrIn2O4 leading to efficient interfacial transfer of photogenerated electrons from TiO2 to SrIn2O4 and enhancing the lifetime of the charge carriers. The Pd co-catalyst enhances the activity of the composite further by increasing the availability of electrons in it and providing active sites for hydrogen evolution.

Tin-grafted TiO2 with enhanced activity for photocatalytic hydrogen generation from aqueous methanol solutions

A series of Sn-modified TiO2 samples was prepared by an anhydrous grafting route and applied in the photocatalytic H2 evolution from aqueous methanol solutions. The synthesized samples were characterized by N2 physisorption, X-ray diffraction, Raman, UV–Vis reflectance and photoluminescence spectroscopy. The results revealed that the tin species were highly dispersed on the TiO2 surface and did not alter its crystalline structure. Photocatalytic results showed that Sn-grafting led to a significant improvement in the activity compared to bare TiO2 owing to the improved charge separation. The photocatalytic performance of samples was found to depend highly on the Sn content. Additionally, the influence of Rh co-modification on the photocatalytic activity of Sn-grafted TiO2 was investigated, and a synergetic effect between Sn and Rh was identified, which is attributed to the assumed electron relay among TiO2, tin species and photodeposited Rh nanoparticles.

Loading of CdS nanoparticles on the (101) surface of elongated TiO2 nanocrystals for efficient visible-light photocatalytic hydrogen evolution from water splitting

Abstract The production of hydrogen gas through photocatalytic water splitting has attracted extensive attention owing to the increasing global energy crisis. In this work, elongated TiO 2 nanocrystals along [0 0 1] orientation with stepped (1 0 1) surface were successfully synthesized via a facile solvothermal method and subsequently sensitized by CdS nanoparticles for efficient visible-light photocatalytic hydrogen evolution from water splitting. The diameter and length of the elongated nanocrystals can be controlled by the Cd(CH 3 COO) 2 ·2H 2 O additive, which serves as not only reactant but also structure directing agent. The morphology, microstructure, crystal phase, chemical composition and photoelectrochemical performance of the as-obtained TiO 2 nanocrystals and CdS nanoparticles sensitized TiO 2 nanocrystals have been carefully investigated via various characterizations. Transmission electron microscopy (TEM) revealed that the CdS nanoparticles were contacted with the (1 0 1) surface of the elongated TiO 2 nanocrystals, which is significant for the accelerated separation of photoinduced charge carriers. The synthesized CdS sensitized TiO 2 nanostructures exhibit strong visible-light absorption capability and enhanced photocatalytic activity for hydrogen generation from water splitting under visible light irradiation ( λ > 400 nm). The hydrogen production rate of CdS sensitized TiO 2 nanocrystals can reach 3.85 mmol h −1 g −1 when the optimal Cd/Ti molar ratio is 0.17. A feasible mechanism is proposed for the photoexcited electrons transfer from CdS nanoparticles to the stepped (1 0 1) surface of anatase TiO 2 nanocrystals. This work offers an efficient way to synthesize composite photocatalysts in nanoscale for improved separation efficiency of photoexcited charge carriers.