Low temperature preparation and visible light photocatalytic activity of mesoporous carbon-doped crystalline TiO2

A visible-light-active TiO₂ photocatalyst was prepared through carbon doping by using glucose as carbon source. Different from the previous carbon-doped TiO₂ prepared at high temperature, our preparation was performed by a hydrothermal method at temperature as low as 160 °C. The resulting photocatalyst was characterized by XRD, XPS, TEM, nitrogen adsorption, and UV–vis diffuse reflectance spectroscopy. The characterizations found that the photocatalyst possessed a homogeneous pore diameter about 8 nm and a high surface area of 126 m²/g. Comparing to undoped TiO₂, the carbon-doped TiO₂ showed obvious absorption in the 400–450 nm range with a red shift in the band gap transition. It was found that the resulting carbon-doped TiO₂ exhibits significantly higher photocatalytic activity than the undoped counterpart and Degussa P25 on the degradation of rhodamine B (RhB) in water under visible light irradiation (λ > 420 nm). This method can be easily scaled up for industrial production of visible-light driven photocatalyst for pollutants removal because of its convenience and energy-saving.     

Influence of operating parameters on photocatalytic degradation of phenol in UV/TiO2 process

The use of hydrogen peroxide (H₂O₂) for improved photocatalytic degradation of phenol in aqueous suspension of commercial TiO₂ powders (Degussa P-25) was investigated. Photodegradation was compared using direct photolysis (UV alone), H₂O₂/UV, TiO₂/UV, and H₂O₂/TiO₂/UV processes in a batch reactor with high-pressure mercury lamp irradiation. The effects of operating parameters such as catalyst dosage, light intensity, pH of the solution, the initial phenol, and H₂O₂ concentrations on photodegradation process were examined. It was shown that photodegradation using H₂O₂/TiO₂/UV process was much more effective than using either H₂O₂/UV or TiO₂/UV process. The effect of the initial phenol concentration on TOC removal was also studied, demonstrating that more than 8 h was required to completely mineralize phenol into water and carbon dioxide. For all the four oxidation processes studied, photodegradation followed the first-order kinetics. The apparent rate constants with 400-W UV ranged from 5.0 × 10⁻⁴ min⁻¹ by direct photolysis to 1.4 × 10⁻² min⁻¹ using H₂O₂/TiO₂/UV process. The role of H₂O₂ on such enhanced photodegradation of phenol in aqueous solution was finally discussed.     

Comparison of photocatalytic efficiencies of TiO2 in suspended and immobilised form for the photocatalytic degradation of nitrobenzenesulfonic acids

The photocatalytic efficiency of TiO₂ immobilised on various supports (glass, cement, red brick and inorganic fibres), using different techniques (sputtering, sol–gel dip-coating, patented method for inorganic fibres), are compared with the photocatalytic efficiency of TiO₂ Degussa P25 in suspension 2 g l⁻¹, for the degradation of 3-nitrobenzenesulfonic acid (3-NBSA) and 4-nitrotoluenesulfonic acid (4-NTSA). In all cases, the fixation of TiO₂ on solid supports appreciably reduces the photocatalytic efficiency. The best results were obtained with TiO₂ on inorganic fibres.     

Photocatalytic oxidation of CO with various oxidants by Mo oxide species highly dispersed on SiO2 at 293 K

The photocatalytic oxidation of CO into CO₂ with oxidants such as NO, N₂O and O₂ proceeded efficiently on a Mo/SiO₂ with high Mo dispersion under UV light irradiation. It was found that the reaction rate greatly depended on the kind and concentration of the oxidant. Photoluminescence investigations reveal the close relationship between the reaction rate and the relative concentration of the photo-excited Mo⁶⁺-oxide species, i.e. charge transfer–excited–triplet state (Mo⁵⁺–O⁻)^*, under steady-state reaction conditions. Moreover, the photocatalytic oxidation of CO with O₂ in excess H₂ was carried out to test suitability for applications to supplying pure H₂. This reaction was seen to proceed efficiently on Mo/SiO₂ with a high CO conversion of 100% and CO selectivity of 99% after 180 min under UV light irradiation, showing higher photocatalytic performance than TiO₂ (P-25) photocatalyst. UV–vis, XAFS, photoluminescence and FT-IR investigations revealed that the high reactivity of the charge transfer–excited–triplet state (Mo⁵⁺–O⁻)^*, with CO as well as the high reactivity of the photoreduced Mo-oxide species (Mo⁴⁺-species) with O₂ to produce the original Mo-oxide species (Mo⁶⁺O²⁻), played a crucial role in the reactions.     

Degradation of neonicotinoid insecticides by different advanced oxidation processes and studying the effect of ozone on TiO2 photocatalysis

Although some studies concerning the effect of pH and ozone dosage on TiO₂ photocatalysis (O₂/TiO₂/UV) have already been published, no complete investigation and explanation of the effects of both parameters on photocatalytic ozonation (O₃/TiO₂/UV) have been carried out. Aqueous solutions of neonicotinoid insecticides (thiacloprid and imidacloprid) were chosen as a degradation medium, since they exhibit a high threat for aquatic systems and it is of great importance to find an effective method for their elimination from the environment. In preliminary stability tests, thiacloprid showed higher photo- and chemical stability compared to imidacloprid, therefore its degradation was studied in detail. To assess the suitability of various treatments for degradation and mineralization of thiacloprid in water at different pH values and ozone dosages, we applied ozonation (O₃) and three different photochemical advanced oxidation processes, namely ozonation, coupled with UV radiation (O₃/UV), O₃/TiO₂/UV and O₂/TiO₂/UV. Light source emitting mainly in UVA range was applied in all three processes. The photocatalytic ozonation (O₃/TiO₂/UV) was found to be the most efficient process irrespective of pH. The synergistic effect of ozone and TiO₂ photocatalysis was noticed at acidic and neutral pH, but the synergism was lost at basic pH, probably due to faster self-decompositon of ozone under alkaline conditions. At acidic pH, also the oxidation of chloride anions to chlorate(V) was noticed in O₃/TiO₂/UV and in O₃/UV processes. By plotting the disappearance rate constants of thiacloprid degradation in O₃/TiO₂/UV and O₃/UV systems as a function of the flow rate of ozone, the synergistic effect of ozone was undoubtedly proven. The slope of the linear fit in case of O₃/TiO₂/UV process was considerably steeper than in case of O₃/UV, which would not happen in absence of synergistic effect. The linearity in O₃/TiO₂/UV system was lost only at very high flow rates of ozone.     

Effect of silver on the photocatalytic degradation of humic acid

In this study, humic acid was mineralized and degraded photocatalytically in presence of bare TiO₂ and silver loaded TiO₂ (0.5–5.0 at.% Ag). X-ray diffraction (XRD) and inductive coupled plasma (ICP) analysis confirm the complete photodeposition of silver over TiO₂ by photodeposition method. X-ray photoemission spectroscopy (XPS) studies confirmed the presence of Ag⁰ in all Ag–TiO₂ samples and the absence of Ag⁺ ions. Silver loading over TiO₂ improved the rate of mineralization and degradation of humic acid with a maximum loading of 1.0 at.% Ag. Ninety percent carbon from humic acid was mineralized to CO₂ only after 60 min by using bare TiO₂ as a photocatalyst. However, this conversion was possible within 40 min by using 1.0 at.% Ag-loaded TiO₂. This observation verifies that coating of metals like silver over TiO₂ acts as an electron sink and can improve the redox reaction by preventing electron–hole recombination reaction. The optimum 1.0 at.% Ag loading in the current work is indicative that the blocking of the TiO₂ surface active sites by silver also plays an important role in the photocatalytic mineralization and degradation of humic acid. As the silver loading is increased, less number of active site are available over the surface of photocatalyst TiO₂ for redox reaction. This finding was supported by the TEM analysis of the photocatalyst samples.     

New industrial titania photocatalysts for the solar detoxification of water containing various pollutants

A new series of titania industrial photocatalysts have been elaborated by Millennium Inorganic Chemicals and were denoted Millennium-PC/10, PC/25 and PC/50 with respective specific surface areas equal to 11, 23 and 43 m² g⁻¹. Their photocatalytic activities have been determined and compared in the solar pilot CPC-photoreactor at the Plataforma Solar de Almeria (PSA) (Spain) in the photocatalytic degradation of four different representative pollutants (4-chlorophenol, nitrobenzene, 2-chlorobenzoic acid and hydrobutanedioic (malic) acid), whose degradation pathways had previously been elucidated in laboratory experiments with artificial light, using titania Degussa P-25 as a reference photocatalyst. The study concerned the influence of (i) the nature of organic pollutants, (ii) the surface area and (iii) the concentration of suspended TiO₂. The affinity of the pollutants for TiO₂ and the presence of heteroatoms in the reactant molecules intervened on the activities of Millennium-PCs when compared to Degussa P-25. The higher the affinity of the organic pollutants for titania, the higher the efficiency of Millennium-PC/10 photocatalyst calibrated on the initial rate of pollutant disappearance. The degradation pathways were found similar for both photocatalysts and the primary steps of the degradation for the different types of molecules were discussed.

4-Chlorophenol (4-CP), a model pollutant for waste waters, was then chosen for the study of the influence of the surface areas and of the concentration of Millennium-PC photocatalysts. The initial apparent rate constants of 4-CP degradation in presence of all Millennium-PC catalysts were all higher than that obtained with Degussa P-25. When choosing the total organic carbon (TOC) disappearance rate as an overall kinetic parameter, Millennium-PC/10 and PC/25 appeared as less active than Degussa P-25, with longer solar exposures (by about 10%) necessary to obtain a total mineralisation. However, Millennium-PC/50 resulted as the best catalyst in all cases. The optimal slurry concentration (g l⁻¹) has been determined for each Millennium TiO₂ sample.

While the optimum of Degussa P-25 had previously been found equal to 0.2 g l⁻¹, higher amounts of Millennium-PC samples were required. A twice higher concentration (0.4 g l⁻¹) increased the activities by factors equal to 1.2 and 1.5 for Millennium-PC/50 and PC/10, respectively. The rate constants of disappearance of intermediates and of TOC were quantitatively affected by factors in agreement with a multiple consecutive reactions model. In any case, titania Millennium-PC/50 appeared as the best catalyst among all those tested, including Degussa P-25.     

Mechanistic approach of the combined (iron–TiO2) photocatalytic system for the degradation of pollutants in aqueous solution: an attempt of rationalisation

Kinetics of oxidative photodegradation of Monuron (3-(4-chlorophenyl)-1,1-dimethylurea) in different photocatalytic systems (iron, TiO₂ and combined system iron + TiO₂) were investigated and compared. The influence of iron addition on TiO₂ photocatalyst and of TiO₂ on the photocatalytic cycle Fe(III)/Fe(II) were carefully studied. A very positive effect of iron addition was observed. This phenomenon was more and more pronounced when TiO₂ concentration was lower. In a suspension of TiO₂ (24 mg L⁻¹) with addition of Fe(III) (3 × 10⁻⁴ mol L⁻¹) the measured rate constant was similar to that obtained in a suspension of TiO₂ with a concentration more than 20 times higher (500 mg L⁻¹). The mechanistic approach carried out in this study allows us to identify the main reactions governing the combined system and a photochemical cycle was proposed. The optimisation of the photocatalytic systems was obtained when each photocatalyst plays a specific role: Fe(III) as a main OH radicals source and TiO₂ as an oxidizing agent of Fe(II).     

稀土元素Ce掺杂TiO_2光催化剂制备及微波强化光催化活性

在[Bmim]PF6离子液体介质中微波辅助制备稀土元素Ce掺杂改性的TiO_2光催化剂TiO_2-Ce,以甲基橙溶液和苯酚溶液为模拟污染物,在紫外光照和微波辐射-紫外光照降解条件下考察TiO_2-Ce催化剂的光催化活性。利用荧光技术以对苯二甲酸作为荧光探针检测TiO_2-Ce催化剂表面产生的羟基自由基,并对光催化降解反应进行动力学分析,以了解光催化降解反应机理。结果表明,通过优化反应条件制得的TiO_2-Ce催化剂具有较高光催化降解活性和热稳定性,在紫外光照和微波辐射-紫外光照条件下降解60 min后,甲基橙降解率分别为98.6%和99.3%,苯酚降解率分别为96.6%和97.2%。荧光光谱分析表明,TiO_2-Ce在微波辐射-紫外光照条件下产生的羟基自由基比紫外光照多,因而微波辐射-紫外光照具有强化TiO_2-Ce降解模拟污染物作用的效果。反应动力学数据表明,TiO_2-Ce光催化降解甲基橙溶液反应呈一级反应动力学规律,其表观速率常数k最大值为0.056 2 min-1。     

光催化辅助高浓度臭氧循环工艺降解对氯苯酚及协同机理

针对臭氧(O3)降解对氯苯酚(4-CP)中效率有限且尾气排放高的问题,采用光催化辅助高浓度臭氧循环工艺并对TiO2浓度、循环气量以及pH值等因素进行研究,结合对苯醌变化及猝灭剂试验分析其协同机理.循环气量为2.0 L·min-1,TiO2投加量为250 mg·L-1时,O3/TiO2/UV体系的降解动力学系数为0.29...     

Visible-light photocatalytic activity of TiO2/ZnS nanocomposites prepared by homogeneous hydrolysis

Photocatalytic active TiO₂/ZnS composites were prepared by homogeneous hydrolysis of mixture of titanium oxo-sulphate and zinc sulphate in aqueous solutions with thioacetamide. The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission microscopy (HRTEM) and electron diffraction (ED). The nitrogen adsorption–desorption was used for surface area (BET) and porosity determination. Diffuse reflectance UV/VIS spectra for evaluation of photophysical properties were recorded in the diffuse reflectance mode (R100) and transformed to an absorption spectra through the Kubelka–Munk function. The method of UV/VIS diffuse reflectance spectroscopy was employed to estimate band-gap energies of the prepared TiO₂/ZnS nanocomposites. The photoactivity of the prepared TiO₂/ZnS nanocomposites was assessed by the photocatalytic decomposition of Orange II dye in an aqueous slurry under irradiation of 255 nm, 365 nm and 400 nm wavelength. Under the same conditions, the photocatalytic activity of the commercially available photocatalyst (Degussa P25), the pure anatase TiO₂ and sphalerite ZnS were also examined. The composite sample having the highest catalytic activity was obtained by hydrolysis of mixture solutions 0.63 M TiOSO₄ and 0.08 M ZnSO₄ · 7H₂O.     

Photocatalytic degradation of organic compounds diluted in water using visible light-responsive metal ion-implanted TiO2 catalysts: Fe ion-implanted TiO2

The application of metal ion-implantation method has been made to improve the electronic properties of the TiO₂ photocatalyst to realize the utilization of visible light. The photocatalytic properties of these unique TiO₂ photocatalysts for the purification of water have been investigated. By the metal ion-implantation method, metal ions (Fe⁺, Mn⁺, V⁺, etc.) are accelerated enough to have the high kinetic energy (150 keV) and can be implanted into the bulk of TiO₂. TiO₂ photocatalysts which can absorb visible light and work as a photocatalyst efficiently under visible light irradiation were successfully prepared using this advanced technique. The UV-Vis absorption spectra of these metal ion-implanted TiO₂ photocatalysts were found to shift toward visible light regions depending on the amount and the kind of metal ions implanted. They were found to exhibit an effective photocatalytic reactivity for the liquid-phase degradation of 2-propanol diluted in water at 295 K under visible light (λ>450 nm) irradiation. The investigation using XAFS analysis suggested that the substitution of Ti ions in TiO₂ lattice with implanted metal ions is important to modify TiO₂ to be able to adsorb visible light.     

Photocatalytic oxidation of multicomponent systems of herbicides: Scale-up of laboratory kinetics rate data to plant scale

The reaction kinetics of the photocatalytic oxidation (PCO) of the herbicides isoproturon, simazine and propazine over irradiated TiO₂ (Degussa P25) suspensions were studied in multicomponent systems in a laboratory-scale annular photoreactor operated in recirculation batch mode. The multicomponent kinetic model established was then extended to take into account the direct effect of radiation absorbed by the TiO₂ photocatalyst in order to obtain intrinsic kinetic parameters independent of the radiation field in the photoreactor. An analysis of the radiation field in the photoreaction space was accomplished using a recently published Six-Flux Radiation Absorption-Scattering model (SFM) to decouple the values of the apparent reaction kinetic constants from the local volumetric rate of photon absorption (LVRPA) in the rate law of PCO of herbicide. The resulting rate laws with explicit dependence on the LVRPA were then used to predict, through accurate reactor modeling, the degradation of the herbicides in an optimal configuration of a flow-through, pilot-scale, falling film photoreactor. In a plant treatment scenario the total operating costs of the PCO of herbicides were calculated to be 3.75 Euro m⁻³.     

Phototransformation of metobromuron in the presence of TiO2

The photocatalytic degradation of the herbicide metobromuron was studied, using TiO₂ photocatalysts (Degussa P25 and Millennium PC50, PC100, PC105 and PC500). Intermediate products were identified by means of liquid chromatography–mass spectrometry (LC–MS–MS) using electrospray (ES) interfacing technique. In order of importance, the main reaction pathways were demethoxylation of the urea chain, ring oxidation leading to ortho hydroxylation with respect to the N atom, substitution of Br by OH, ring oxidation with formation of the meta hydroxylated compound. Demethylation of the demethoxylated product occurred as a secondary reaction. Formation of bromide ions was observed too. In the presence of 2-propanol used as a hydroxyl radical scavenger, demethoxylation was drastically inhibited while the other reactions were only partly inhibited. It suggests that demethoxylation was exclusively due to the oxidation by hydroxyl radicals, whereas the other reactions involved positive holes too. The degradation rate of metobromuron varied in the order: PC50 < PC100 < PC105 < PC500 < Degussa P25. TiO₂ Degussa P25 was therefore the most efficient photocatalyst although its surface area was lower than that of most of Millennium TiO₂.     

Solvothermal syntheses of semiconductor photocatalysts of ultra-high activities

Thermal treatment of titanium(IV) butoxide dissolved in 2-butanol at 573 K under autogenous pressure (alcohothermal treatment) yielded microcrystalline anatase-type titanium(IV) oxide (TiO₂). Thermal treatment of oxobis(2,4-pentanedionato-O,O′)titanium (TiO(acac)₂) in ethylene glycol (EG) in the presence of sodium acetate and a small amount of water at 573 K yielded microcrystalline brookite-type TiO₂. Tungsten(VI) oxide (WO₃) powders of monoclinic crystal structure with high crystallinity were synthesized by hydrothermal treatment (HTT), at 523 or 573 K, of aqueous tungstic acid (H₂WO₄) solutions prepared from sodium tungstate by ion-exchange (IE) with a proton-type resin. Anatase and brookite TiO₂ products were calcined at various temperatures and then used for photocatalytic mineralization of acetic acid in aqueous solutions under aerated conditions and dehydrogenation of 2-propanol under deaerated conditions. Almost all the anatase-type TiO₂ samples showed the activities more than twice higher than those of representative active photocatalysts, Degussa P-25 and Ishihara ST-01 in both reactions. A brookite sample with improved crystallinity and sufficient surface area obtained by calcination at 973 K exhibited the hydrogen evolution rate almost equal to P-25. HTT WO₃ powders with various physical properties were used as photocatalyst for evolution of oxygen (O₂) from an aqueous silver sulfate solution. WO₃ powder of high crystallinity, e.g., IE-HTT-WO₃ synthesized at 573 K, gave much higher O₂ yield than commercially available WO₃ samples.     

Preparations and photocatalytic properties of magnetically separable nitrogen-doped TiO2 supported on nickel ferrite

A magnetically separable nitrogen-doped photocatalyst TiO_2−xN_x/SiO₂/NiFe₂O₄ (TSN) with a typical ferromagnetic hysteresis was prepared by a simple process: the magnetic SiO₂/NiFe₂O₄ (SN) dispersion prepared by a liquid catalytic phase transformation method and the visible-light-active photocatalyst TiO_2−xN_x were mixed, sonificated, dried, and calcined at 400 °C. The prepared photocatalyst is photoactive under visible light irradiation and easy to be separated from a slurry-type photoreactor under the application of an external magnetic field, being one of promising photocatalysts for wastewater treatment. Transmission electron microscope (TEM) and X-ray diffractometer (XRD) were used to characterize the structure of the TSN photocatalyst. The results indicate that the magnetic SiO₂/NiFe₂O₄ (SN) nanoparticles adhere to the surface of TiO_2−xN_x congeries. The magnetic photocatalyst TSN shows high catalytic activity for the degradation of methyl orange in water under UV and visible light irradiation (λ > 400 nm). SiO₂ coating round the surface of NiFe₂O₄ nanoparticles prevents effectively the injection of charges from TiO₂ particles to NiFe₂O₄, which gives rise to the increase in photocatalytic activity. Moreover, the recycled TSN exhibits a good repeatability of the photocatalytic activity.     

Preparation and performances of mesoporous TiO2 film photocatalyst supported on stainless steel

Mesoporous TiO₂ film photocatalysts supported on stainless steel substrates were prepared using the sol–gel method with Ti(OC₄H₉)₄ as a precursor and poly ethylene glycol (PEG) as a structure-directing agent. Mesoporous TiO₂ film with a pore diameter of about 15 nm was obtained with the addition of PEG (molecular WEIGHT =400). The pore diameter of TiO₂film was varied with molecular weight of PEG additive. The structure-directing process was also discussed. Mesoscopically ordered inorganic/polymer composites were believed to form during the process. Compared to conventional TiO₂ film photocatalyst, the mesoporous TiO₂ film showed a good performance for the photo degradation of rhodamine B (RB) solution irradiated with UV light of 365 nm. The photo degradation constant of rhodamine B for mesoporous TiO₂ film photocatalyst can arrive at 22 times of that for conventional TiO₂ film photocatalyst. Also an excellent performance for the degradation of gaseous formaldehyde with mesoporous film photocatalyst was obtained. The photo degradation rate of gaseous formaldehyde for mesoporous TiO₂ film photocatalyst can arrive at six times of that for conventional TiO₂ film photocatalyst.     

Preparation of rough anatase films and the evaluation of their photocatalytic efficiencies

Sol–gel derived rough anatase films without controlled particle sizes were prepared by surfactant templating. The coating sol–gel was obtained by hydrolysis of Ti(OC₃H₇)₄ in ethanol/HNO₃ solution. The gel films, prepared by dipping glass substrates in surfactant solutions, were dried after immersion under an atmospheric pressure. The rough films of TiO₂ anatase were obtained after calcining at 500 °C. The resultant films were transparent, semitransparent or opaque and 136–402 nm thick. It was found that the TiO₂ films prepared from the sol–gel with surfactant showed a granular nanostructure, and they were composed of regular particles, for example; between 50 and 70 nm. The roughness of the films was found to depend on the surfactant concentration in the sol–gel solution and can show a roughness between 0.82 and near of 17 nm. The photocatalytic activity of the films for the degradation and mineralization of phenol, an industrial pollutant, in water and under 365 nm irradiation was improved by the surfactant modification. Kinetic analysis of degradation and mineralization of phenol in water were employed to evaluate the different TiO₂ films under the same experimental conditions. The global photonic efficiency for degradation and mineralization of phenol ξ_g, was calculated to facilitate comparison with a TiO₂ standard photocatalyst named Degussa P-25.     

Kinetics of dye decolorization in an air–solid system

The photocatalytic decolorization of adsorbed organic dyes (Acid Blue 9, Acid Orange 7, Reactive Black 5 and Reactive Blue 19) in air was examined, applicable to self-cleaning surfaces and catalyst characterization. Dye-coated Degussa P25 titanium dioxide (TiO₂) and dye-coated photo-inert aluminum oxide (Al₂O₃) particles, both of sub-monolayer initial dye coverage, were illuminated with 1.3 mW cm⁻² of near-UV light. Visual evidence of color removal is reported with photographic images. Two methods, Indirect and Direct Analysis, were employed to quantitatively examine the decolorization kinetics of dyes using UV–visible transmission and diffuse reflectance spectroscopy, respectively. A decrease in dye concentration with time was observed with near-UV illumination of dye-coated TiO₂ powders for all dyes. Dyes did not photodegrade significantly on photo-inert Al₂O₃.

UV–visible spectroscopy data was used to model the kinetics of the photocatalytic degradation. Two first-order reactions in series provided the most convincing rate form for the photodegradation of dyes adsorbed to TiO₂, with a first step the conversion of colored dye to colored intermediate, and the second the conversion to colorless product(s). The first rate constant was of similar magnitude for all dyes, averaging k₁ = 0.13 min⁻¹. Similarly, for the second, k₂ = 0.0014 min⁻¹.     

Hydrogen evolution by water splitting using novel composite zeolite-based photocatalyst

Novel zeolite-based material showing photocatalytic properties in the visible light have been synthesized by incorporating TiO₂, heteropolyacid (HPA) and transition metal, namely cobalt. This material shows high efficiency for water splitting under visible light irradiation. Hydrogen generation to the tune of 2171 μmol/h/g of TiO₂ has been achieved for the composite photocatalyst synthesized as compared to H₂ evolution rate to the tune of 131.6 μmol/h/g of TiO₂ for Degussa P25. This suggests that the TiO₂ which gets effectively dispersed and stabilized on the surface of zeolite works synergistically with cobalt and heteropolyacid to make the material active in visible light for evolution of hydrogen from water. TiO₂ is the photocatalyst, HPA functions as the dye sensitiser as well as redox system; zeolite functions as support matrix and as electron acceptor in synergy with cobalt. The probable mechanism for improved hydrogen evolution rate using such composite photocatalyst has been discussed.