Metallic nanoparticles loaded Al–SrTiO3 supported with RhCr2O3 and CoOOH cocatalysts for overall water splitting

Developing new renewable, carbon-neutral fuels to diminish the amount of released CO₂ in the atmosphere and to solve global challenges such as global warming and climate change is significant. Among them, hydrogen (H₂) is attracting much attention due to its high energy density, ease of transportation, and multiple means of production. To meet the global demand of H_2, photocatalytic water splitting is one of the most promising methods for large scale production. Herein, Al-doped SrTiO₃ photocatalyst (Al–SrTiO₃) was prepared by a molten flux method. Then, plasmonic metal nanoparticles (Au, Cu, Pt), and cocatalysts Rh/Cr₂O₃ and CoOOH were selectively deposited onto the reductive and oxidative active sites of Al–SrTiO₃ using multi-step photodeposition-impregnation methods for water splitting and H₂ production under UV-rays, UV–Vis. Light, and visible light (λ ≥ 400 nm). Our results showed that, compared with Pt and Cu loaded Al–SrTiO₃ photocatalyst supported with Rh/Cr₂O₃ and CoOOH cocatalysts, Au-loaded samples showed the highest H₂ production efficiency under both UV (920 μmol/h - EQE = 41% at 365 nm) and UV–Vis (100.5 μmol/h) rays. In addition, the amount of evolved H₂ decreased by increasing the weight ratio of Au nanoparticles (NPs) due to the overlap between Au NPs and Rh/Cr₂O₃ cocatalyst. Although Au 0.3 wt%-loaded sample showed high activity under both UV and UV–Vis. Rays, it exhibited almost no efficiency under visible light because of the large bandgap of Al–SrTiO₃ (3.1 eV) and the poor absorption in the visible region. Visible light absorption was then enhanced by increasing the loaded amount of Au NPs and by separating Au NPs and Rh/Cr₂O₃ cocatalyst responsible for H₂ evolution by combining both photodeposition and impregnation methods. Under visible light, Rh/Cr₂O₃-loaded Al–SrTiO₃ with 4 wt % Au NPs showed the highest H₂ evolution efficiency (41 μmol/3 h). This was attributed to the efficient hot electron transfer from Au NPs to Al–SrTiO₃ then to RhCr₂O₃, resulting in charge separation needed for efficient H₂ generation.     

Hydrogen production performance of active Ce/N co-doped SrTiO3 for photocatalytic water splitting

An efficient visible light responsive photocatalyst Ce/N co-doped SrTiO₃ was prepared via a hydrothermal method for hydrogen production. The phase structure, morphology, contents and valence states of the dopant elements, specific surface area, optical properties, and photocatalytic activity of the samples were characterized. The transient photocurrent response and electrochemical impedance spectra under visible light illumination indicated that Ce/N co-doped SrTiO₃ possessed a more intense photo-current response and lower surface resistance than N–SrTiO₃ and Ce–SrTiO₃. The water splitting rate of Ce/N-co-doped SrTiO₃ is 4.28 mmol/g/h, which is 84.49 times higher than that of pure SrTiO₃. The enhanced photocatalytic performance is due to the narrowing of the band gap of SrTiO₃ by Ce ion and N ion impurities.     

Enhancing hydrogen evolution of water splitting under solar spectra using Au/TiO2 heterojunction photocatalysts

An effective improvement of hydrogen evolution from water splitting under solar light irradiation was investigated using quantum dots (QDs) compounds loaded onto a Au/TiO₂ photocatalyst. First, Au/TiO₂ was prepared by the deposition-precipitation method, and then sulfide QDs were loaded onto the as-prepared Au/TiO₂ by a hydrothermal method. QDs were loaded onto Au/TiO₂ to enhance the energy capture of visible light and near-infrared light of the solar spectrum. The results indicated that the as-prepared heterojunction photocatalysts absorbed the energy from the range of ultraviolet light to the near-infrared light region and effectively reduced the electron-hole pair recombination during the photocatalytic reaction. Using a hydrothermal temperature of 120 °C, the as-prepared (ZnS–PbS)/Au/TiO₂ photocatalyst had a PbS QDs particle size of 5 nm, exhibited an energy gap of 0.92 eV, and demonstrated the best hydrogen production rate. Additionally, after adding 20 wt % methanol as a sacrificial reagent to photocatalyze for 5 h, the hydrogen production rate reached 5011 μmol g⁻¹ h⁻¹.     

Photocatalytic water splitting into hydrogen and research on synergistic of Bi/Sm with solid solution of Bi–Sm–V photocatalyst

Photocatalyst Bi_1−xSm_xVO₄ were prepared by solid phase reaction and characterized by XRD, UV–visible DRS, BET, and SEM. Bi_1−xSm_xVO₄ showed two structures with the component content. When the composition was above x = 0.3, Bi_1−xSm_xVO₄ were of single phase with tetragonal type and can be regarded as solid solutions of was BiVO₄ and SmVO₄. When Bi_1−xSm_xVO₄ was loaded with 0.3 wt% Pt, the samples showed photocatalytic activities for water decomposition to hydrogen under UV light. Among these catalysts, Bi_0.5Sm_0.5VO₄ showed the best photocatalytic activity for water splitting, which indicated synergistic of Bi/Sm enhanced the photocatalysis efficiency. What's more, Bi_0.5Sm_0.5VO₄ loaded with other co-catalysts was found to act as a photocatalyst for water decomposition to hydrogen and oxygen under UV light irradiation, and the photocatalyst loaded with Pt/Cr₂O₃ had the best photocatalytic property. The amounts of the produced hydrogen and oxygen, respectively, were about 188.25 μmol h⁻¹ g⁻¹ and 95.90 μmol h⁻¹ g⁻¹. This study indicated that the formation of solid solution was the feasible method to adjust energy band and synergistic of Bi/Sm can enhance the photocatalytic activities of water decomposition.     

Organic-inorganic composite of g-C3N4–SrTiO3:Rh photocatalyst for improved H2 evolution under visible light irradiation

The organic-inorganic composite g-C₃N₄–SrTiO₃:Rh was prepared for the first time as a photocatalyst for hydrogen production and the resulting hydrogen evolution rate under visible light irradiation from aqueous methanol solution was measured. A high hydrogen evolution rate of 223.3 μmol h⁻¹ was achieved by using 0.1 g of as-prepared photocatalyst powder comprised of 20 wt.% g-C₃N₄ 80 wt.% SrTiO₃:Rh (0.3 mol%). The hydrogen evolution rate was greater than that obtained by SrTiO₃:Rh (0.3 mol%) by a factor of 3.24. The quantum efficiency of as-prepared composite photocatalyst was 5.5% at 410 nm for hydrogen evolution. The high activity of the composite photocatalyst for hydrogen evolution stemmed from its electron–hole separation and transportation capabilities due to the hetero-junctions of the organic-inorganic composite materials. The proposed mechanism for the electron–hole separation and hydrogen evolution of the g-C₃N₄–SrTiO₃:Rh composite under visible light irradiation featured the reduced recombination of the photo-generated charge carriers. The doping of Rh ions into the SrTiO₃ has contributed to the high photocatalytic activity by forming a donor level from the valance band to the conduction band.     

Enhanced photocatalytic hydrogen production from aqueous methanol solution using ZnO with simultaneous photodeposition of Cu

The enhanced photocatalytic hydrogen production from aqueous methanol solution using ZnO was investigated with aid of simultaneous metal deposition. The simultaneous deposition for such metals as Ag, Au, Cu, Ni, Pd, Pt, and Rh was evaluated for the H₂ production from aqueous methanol solution. As a result, the addition of Cu ion was effective improvement in photocatalytic hydrogen evolution. The photocatalytic hydrogen production using ZnO photocatalyst with aid of simultaneous deposition of Cu was approximately 130 times better than those obtained with bare ZnO. The Cu-deposited ZnO had the response to the visible light for the hydrogen formation. After the photocatalytic hydrogen production, the in-situ Cu-photodeposited ZnO sample was characterized by X-ray diffraction (XRD), UV–visible diffuse reflectance spectrometry (UV-DRS), and photoluminescence (PL) spectroscopy.     

Promoting hydrogen production by loading PdO and Pt on N–TiO2 under visible light

Nitrogen/titanium dioxide (N/TiO₂) visible light photocatalysts were prepared using the sol–gel method. The catalysts were characterized using transmission electron microscopy, reflective UV–visible spectroscopy, specific surface area measurements, and X-ray diffraction. The prepared catalysts were used to generate hydrogen gas through the water-splitting reaction under visible light (wavelengths greater than 400 nm). Various N/Ti addition ratios were tested, and the hydrogen generation rates were compared to determine the optimal ratio. The maximal hydrogen production rate (approximately 55 μmol h⁻¹ g⁻¹) was attained when the N/Ti ratio of N–TiO₂ was 10. When PdO and Pt were loaded onto the N–TiO₂ catalyst, the hydrogen generation rates increased to 544 and 772 μmol h⁻¹ g⁻¹, respectively. The highest hydrogen production rate (2460 μmol h⁻¹ g⁻¹) was obtained when bimetallic 0.05 wt% PdO-0.10 wt% Pt/N–TiO₂ was used. After three times use the hydrogen yield of the catalyst was maintained as 83%. A possible mechanism of water splitting catalyzed by this visible light photocatalyst is proposed.     

Photocatalytic hydrogen generation through water splitting on nano-crystalline LaFeO3 perovskite

Visible light active ABO₃ type photocatalyst with LaFeO₃ composition was synthesized by sol-gel method. The photocatalyst was characterized by different techniques such as X-ray diffraction, BET surface area analysis, particle size analysis, scanning electron microscopy, UV–visible diffuse reflectance spectroscopy (UV–Visible DRS), and photoluminescence spectroscopy. LaFeO₃ photocatalyst exhibited an optical band gap of 2.07 eV with the absorption spectrum predominantly in visible region of the spectrum. The BET surface area of photocatalyst LaFeO₃ was observed as 9.5 m²/g, with the crystallite size of 38.8 nm as calculated by the Debye-Scherer equation. The photocatalytic activity of LaFeO₃ was investigated for hydrogen generation through sacrificial donor assisted photocatalytic water splitting reaction by varying conditions in feasible parametric changes using visible light source, ethanol as a sacrificial donor and Pt solution of H₂PtCl₆ as a co-catalyst. The rate of photocatalytic hydrogen evolution was observed to be 3315 μmol g⁻¹ h⁻¹ under optimized conditions and using 1 mg dose of photocatalyst with reaction time of 4 h and illumination of 400 W.     

Effect of polystyrene characteristic on photocatalytic hydrogen production by porous polystyrene photocatalyst film under simulated solar light irradiation

In this study, we developed a polystyrene-platinum/nitrogen-doped titanium dioxide/strontium titanate composite-polyvinylpyrrolidone (PS-PNS-PVP) photocatalyst film, which is applied in the process of photocatalytic hydrolysis under simulated sunlight to produce hydrogen, is developed. PS, which is cheap, non-toxic, with high UV resistance, and chemical inertness, is used as a carrier, and a highly effective hydrogen production of Pt/N–TiO₂/SrTiO₃ as a photocatalyst. The influence of the PS concentration on the stability, optical, and electrical properties of the photocatalyst film is discussed. In addition, the influence of the photocatalyst dispersion in the film on the activity under various photocatalyst concentrations was investigated. A polyvinylpyrrolidone pore-forming agent was then used to examine the effect on the photocatalyst film structure and optical properties, and the subsequent influence on photocatalytic hydrogen energy activity. Adjusting the PS concentration to 20 wt% produced good film-forming stability, and the photocatalyst dispersibility in the film under different photocatalyst concentrations. A photocatalyst concentration of 2.5 wt% resulted in good film dispersibility and the realization of added pore-forming agent. The modified photocatalyst film changed the film from a blind pore structure to a connecting void structure, increasing the film's porosity and hydrophilicity. This increased the number of photocatalytic sites, and the optimal hydrogen production of the photocatalyst film reached 21,333 μmol h^?1 g^?1.     

Photocatalytic water splitting for hydrogen production on Au/KTiNbO5

Gold nanoparticles were deposited on potassium titanoniobate, KTiNbO₅ using deposition-precipitation (DP), conventional impregnation (IMP) and photodeposition method in order to improve photocatalytic hydrogen production from water splitting. The effect of synthesis pH value of a HAuCl₄ aqueous solution used in the DP process on the morphology of gold nanoparticles, optical property and photocatalytic activity of water splitting under UV light irradiation was investigated. These catalysts were characterized by powder X-ray diffraction patterns (XRD), inductively coupled plasma mass spectrometry (ICP-MS), UV–visible spectroscopy (UV–vis), and Transmission Electron Microscopy (TEM). The Au/KTiNbO₅ catalysts prepared by the DP method consisted of a good metal–semiconductor interface which allowed for a much higher efficient electron-hole separation. The 0.63 wt% Au/KTiNbO₅ catalyst prepared by the DP method at pH = 10 showed a uniform dispersion of gold nanoparticles with an average gold particle size of 4.2 nm and exhibited an ultra-high photocatalytic water splitting activity (3522 μmol g⁻¹ h⁻¹), about 47 times higher than that exhibited by the KTiNbO₅ photocatalyst.     

A nanoreactor based on SrTiO3 coupled TiO2 nanotubes confined Au nanoparticles for photocatalytic hydrogen evolution

A TiO₂ nanotube-based nanoreactor was designed and fabricated by facile two steps synthesis: firstly, hydrothermal synthesized SrTiO₃ was deposited on TiO₂ nanotubes (TiO₂NTs). Secondly, the Au nanoparticles (NPs) were encapsulated inside the TiO₂NTs followed by vacuum-assisted impregnation. The as-synthesized composites were characterized using Transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Photoluminescence spectra (PL) and Ultraviolet–visible absorption spectroscopy (UV–vis). The photocatalytic performance was evaluated by the hydrogen evolution reaction. The results revealed that the SrTiO₃ modified TiO₂NTs confined Au NPs (STO-TiO₂NTs@Au) achieved an enhanced hydrogen evolution rate at 7200 μmol h⁻¹ g⁻¹, which was 2.2 times higher than that of bald TiO₂NTs@Au at 3300 μmol h⁻¹ g⁻¹. The improved photocatalytic activity could be attributed to the synergistic effect of the electron-donating of SrTiO₃ and TiO₂NTs confinement. The as-designed nanoreactor structure provides an example of efficient carriers' separation photocatalyst.     

Effects of Pt3Ni alloy polyhedral and its de-alloying on CdS's performance in hydrogen evolution from water-splitting under visible light

In this paper, Pt₃Ni alloy polyhedral was synthesized through solvothermal method and loaded on the surface of CdS by photo-induced electrons. Under visible light irradiation, the photocatalytic activity for hydrogen evolution from solar water splitting was performed, Pt₃Ni/CdS showed the hydrogen evolution rate about 40.0 mmol/h/g (QE = 44.90%, λ = 420 nm), which was 1.8 times higher than that of Pt/CdS, indicating that Pt₃Ni NPs could effectively improve the hydrogen production activity of CdS. Next, the influence of de-alloyed Pt₃Ni NPs on the activity of CdS for water-splitting under visible light was investigated, the hydrogen evolution rate of de-alloyed Pt₃Ni NPs modified CdS was 46.1 mmol/h/g (QE = 52.70%, λ = 420 nm), which was 1.2 times as much as that of Pt₃Ni/CdS and 2.1 times as much as that of Pt/CdS, suggesting that de-alloyed Pt₃Ni NPs could further enhance the hydrogen production activity of CdS. In addition, the improved photocatalytic activity was mainly due to the surface unsaturation of Pt atoms in a metastable structure after de-alloying, which will expose more surface active sites of Pt, thus the fast electron hole charge transfer at the interface of CdS and de-alloyed Pt₃Ni NPs.     

Effects of cocatalysts on photocatalytic properties of La doped Cd2TaGaO6 photocatalysts for hydrogen evolution from ethanol aqueous solution

La doped Cd₂TaGaO₆ photocatalyst was successfully synthesized for the first time by a sol–gel method. Several metal oxides and noble metals involving NiO, CuO, Cr₂O₃, Pt, and Ru were respectively loaded onto La doped Cd₂TaGaO₆ as cocatalyst. NiO and noble metal co-loaded photocatalyst was also prepared. The obtained products were characterized by X-ray diffraction (XRD), ultraviolet–visible spectra (UV–Vis), scanning electron microscope (SEM), etc. The results showed that most of cocatalyst loaded photocatalysts exhibited much higher activities for hydrogen evolution from ethanol aqueous solution than single La doped Cd₂TaGaO₆. Compared with sole NiO or noble metal loaded photocatalyst, NiO and noble metal co-loaded La doped Cd₂TaGaO₆ showed superior activity. It is revealed that the loaded NiO and noble metal can interact with each other and cooperate on improving the photocatalytic activity. The effect of the cocatalyst loading amount on photocatalytic properties was discussed. Especially, 0.5 wt% NiO and 0.5 wt% Pt co-loaded La doped Cd₂TaGaO₆ displayed the highest hydrogen production rate of 2.93 mmol h⁻¹, which was ca. 33 times that of single La doped Cd₂TaGaO₆.     

Photocatalytic H2 production from water splitting under visible light irradiation using Eosin Y-sensitized mesoporous-assembled Pt/TiO2 nanocrystal photocatalyst

Sensitized photocatalytic production of hydrogen from water splitting is investigated under visible light irradiation over mesoporous-assembled titanium dioxide (TiO₂) nanocrystal photocatalysts, without and with Pt loading. The photocatalysts are synthesized by a sol–gel process with the aid of a structure-directing surfactant and are characterized by N₂ adsorption–desorption analysis, X-ray diffraction, UV–vis spectroscopy, scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray analysis. The dependence of hydrogen production on the type of TiO₂ photocatalyst (synthesized mesoporous-assembled and commercial non-mesoporous-assembled TiO₂ without and with Pt loading), the calcination temperature of the synthesized photocatalyst, the sensitizer (Eosin Y) concentration, the electron donor (diethanolamine) concentration, the photocatalyst dosage and the initial solution pH is systematically studied. The results show that in the presence of the Eosin Y sensitizer, the Pt-loaded mesoporous-assembled TiO₂ synthesized by a single-step sol–gel process and calcined at 500 °C exhibits the highest photocatalytic activity for hydrogen production from a 30 vol.% diethanolamine aqueous solution with dissolved 2 mM Eosin Y. Moreover, the optimum photocatalyst dosage and initial solution pH for the maximum photocatalytic activity for hydrogen production are 3.33 g dm⁻³ and 11.5, respectively.     

Eosin Y functionalized graphene for photocatalytic hydrogen production from water

Chemically reduced graphene oxide (RGO) can be functionalized by eosin Y (EY). The formation of the stable aqueous EY functionalized graphene (EY-RGO) suspension is due to the non-covalent interaction between EY and RGO surface via hydrogen bonding and π-π stacking. EY-RGO was characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Spectral and photoelectrochemical studies indicate that photoinduced electron transfer occurs from EY to RGO. The EY-RGO is photocatalytic active for water reduction to produce hydrogen. The average production rate of H₂ for the photocatalyst (w_EY/w_RGO = 1) in a 10 vol% triethanolamine aqueous solution can reach 3.35 mmol g⁻¹ h⁻¹ and 0.40 mmol g⁻¹ h⁻¹ under 30 h UV-vis and 10 h visible light irradiation, respectively. The photocatalytic activity of EY-RGO is superior to that of RGO, graphene oxide (GO), and EY-GO. Modification EY-RGO with Pt nanoparticles can further improve photocatalytic activity. All these features demonstrated that organic sensitizers functionalized graphene provided a nice candidate as a photocatalyst for H₂ generation from water under solar light irradiation.     

Effect of tri-doping on H2 evolution under visible light irradiation on SrTiO3:Ni/Ta/La prepared by spray pyrolysis from polymeric precursor

Tri-doped photocatalyst, SrTiO₃:Ni/Ta/La, was prepared by spray pyrolysis from aqueous and polymeric precursor solutions. The third dopant, La³⁺, contributed to the BET surface area and porous morphology by preventing crystal growth, and increased the Ni²⁺/Ni³⁺ ratio by affecting the electron configuration in the lattice structure, which is closely related to the hydrogen evolution rate. The hydrogen evolution rate of the tri-doped photocatalyst, SrTiO₃:Ni(0.2 mol%)/Ta(0.4 mol%)/La(0.3 mol%), was increased by about 60%–895.2 μmol g⁻¹ h⁻¹ from the value of 561.2 μmol g⁻¹ h⁻¹ for the co-doped photocatalyst, SrTiO₃:Ni(0.2 mol%)/Ta(0.4 mol%), and was further enhanced to 2305.7 μmol g⁻¹ h⁻¹ when a polymeric precursor was used instead of an aqueous precursor in spray pyrolysis. The optimum additive content for polymeric precursor solution was 300 mol%.     

Visible-light-driven photocatalytic H2 evolution from water splitting with band structure tunable solid solution (AgNbO3)1−x(SrTiO3)x

(AgNbO₃)_1−x(SrTiO₃)_x samples were successfully employed as photocatalysts for photocatalytic hydrogen evolution under visible light. The samples were characterized by a series of techniques, including X-ray diffractometry, scanning electron microscopy, UV–Vis spectrophotometry, and electrochemistry technology. The band gaps of (AgNbO₃)_1−x(SrTiO₃)_x solid solutions can be tuned continuously from 3.21 to 2.65 eV and the flat-band potentials (V_fb) can be shifted positively from −0.79 to −0.31 V vs. SHE when x decreased from 1 to 0. Band positions of (AgNbO₃)_1−x(SrTiO₃)_x samples were further testified by density functional theory, suggesting that the band gap narrowing of the solid solutions derived from the hybridization of (Ti 3d and Nb 4d) and (O 2p and Ag 4d) orbital. The photocatalytic activities of samples for H₂ evolution with Pt cocatalyst were evaluated in aqueous methanol solution under visible light irradiation. The highest photocatalytic activity was obtained at (AgNbO₃)_0.25(SrTiO₃)_0.75. Photocatalytic activity in hydrogen evolution of these solid solutions proved to be closely dependent on band structures.     

Enhanced photocatalytic hydrogen evolution from reduced graphene oxide-defect rich TiO2-x nanocomposites

Solar-driven photocatalytic hydrogen generation by splitting water molecules requires an efficient visible light active photocatalyst. This work reports an improved hydrogen evolution activity of visible light active TiO_2-x photocatalyst by introducing reduced graphene oxide via an eco-friendly and cost-effective hydrothermal method. This process facilitates graphene oxide reduction and incorporates intrinsic defects in TiO₂ lattice at a one-pot reaction process. The characteristic studies reveal that RGO/TiO_2-x nanocomposites were sufficiently durable and efficient for photocatalytic hydrogen generation under the visible light spectrum. The altered band gap of TiO_2-x rationally promotes the visible light absorption, and the RGO sheets present in the composites suppresses the electron-hole recombination, which accelerates the charge transfer. Hence, the noble metal-free RGO/TiO_2-x photocatalyst exhibited hydrogen production with a rate of 13.6 mmol h^?1g^?1_cat. under solar illumination. The appreciable photocatalytic hydrogen generation activity of 947.2 μmol h^?1g^?1_cat with 117 μAcm^?2 photocurrent density was observed under visible light (>450 nm).     

TiO2 nanosheets loaded with Cu: A low-cost efficient photocatalytic system for hydrogen evolution from water

Rutile TiO₂ nanosheets were prepared by a simple solvothermal process, and Cu was loaded on the surface of TiO₂ nanosheets using the in situ photo-deposition method. Meanwhile, photocatalytic H₂ evolution from water over the as-prepared TiO₂ nanosheets loaded with Cu was explored using methanol as a sacrificial reagent. The results indicate that the TiO₂ nanosheets loaded with Cu is an efficient photocatalyst under UV irradiation. During the first 5 h, a rate of H₂ evolution of approximately 22.1 mmol g⁻¹ h⁻¹ was achieved under optimal conditions. Furthermore, for practical purposes, the photocatalytic hydrogen evolution was studied as a function of content of Cu, pH of solution, concentration of methanol and dosage of photocatalyst, respectively. At last, the photocatalytic mechanism was preliminarily discussed.     

Photodeposition of AuNPs on metal oxides: Study of SPR effect and photocatalytic activity

Effect of photodeposition of AuNPs (gold nanoparticles) on TiO₂, CeO₂, Cu₂O and Fe₃O₄ supports has been illustrated on sacrificial donor based hydrogen evolution. The synthesized samples were characterized by diffuse reflectance spectroscopy (DRS), and transmission electron microscopy (TEM). Highest photocatalytic activity was exhibited by Au/TiO₂ followed by Au/Fe₃O₄, Au/CeO₂ and Au/Cu₂O. Au/TiO₂ under optimized conditions has shown significantly high photocatalytic activity under both UV–visible and visible radiation. Au/TiO₂ shows hydrogen evolution rate of 920 μmol h⁻¹ and 32.4 μmol h⁻¹ under UV–visible and visible radiation, respectively. Significant enhancement in hydrogen evolution rate under visible light is very encouraging and may be attributed to polydispersed nature of AuNPs wherein larger particles facilitate light absorption and the smaller function as catalytic sites. Further studies are in progress to study the influence of various parameters on photocatalytic activity of Au/TiO_2.