The present study shows how electronic parameters (e.g. band gap energy, band edge positions) on semiconductors affect photoelectrochemical activity in simulated solar light using WO 3 , TiO 2 and WO 3 / TiO 2 as model systems. Hydrothermal synthesis was conducted to study heterostructure (HE) formation, which the loading of WO 3 in TiO 2 structure were varied to 20, 40 and 80 wt%. Scanning electron microscopy images show that WO 3 and TiO 2 particles are in contact with each other and the synthesis method as well as the deposition method are appropriate for the formation of WO 3 /TiO 2 HE film. Important findings were obtained with a hole scavenger during photoelectrochemical characterization of WO 3 /TiO 2 -40 wt% film. This strategy was effective to clearly distinguish charge transport from charge separation, the essential mechanisms that affect water splitting which are often misinterpreted experimentally for HE. The hole scavenger experiment depicts the increase by 17.5% in photocurrent density for the WO 3 /TiO 2 -40 wt% film as compared to WO 3 film, corresponding to 210 and 12 mA cm À2 vs Ag/AgCl respectively. Additionally, this HE film showed water oxidation initiated at lower applied potentials and indicating that coupling of the materials resulted in optimization of band edge properties for water splitting with the increase on light absorption at the visible range. Flat band potential was determined by the Mott-Schottky plot and it indicated the difference of 1.08 V vs Ag/AgCl between TiO 2 and WO 3 potentials, which makes the charge injection from one structure to another effective and thermodynamically stable for charge separation. A charge carrier density of 1.59 Â 10 20 was observed for the WO 3 /TiO 2 -40 wt% and it supports the best photoelectrochemical performance for water oxidation.

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Anatase TiO2 is a promising photocatalyst due to its chemical stability, non-toxic characteristics, notable UV light absorption as well as photo-corrosion resistance and oxidative properties. Surface area and TiO2 dispersion quality are important factors that affect photoactivity of TiO2:SiO2 nanocomposites. In order to improve these factors, TiO2 nanoparticles were immobilized on mesoporous silica substrate through the polymeric precursors method, obtaining the nanocomposites in a simple routine. The TiO2 resin was synthesized by the polymeric precursors method and different resin thickness (0.5; 1.0; 2.0; 3.5; 5.0 nm) on silica were synthesized by calcination during 4 hours at 450 degrees C in pH 1.5. The selected pH for immobilization ensured adhesion of TiO2 nanoparticles onto the silica substrate surface. X-Ray Diffraction patterns indicate that all samples were predominantly anatase phase and immobilization improved surface area. Ametryn kinetic evaluation presents better results for SAM 3.5 and SAM 0.5. The results show that difference in TiO2 loading, surface area and crystallinity of samples are factors that influence photocatalytic efficiency.