Photocatalysis and photoinduced hydrophilicity of WO3 thin films with underlying Pt nanoparticles

The photocatalytic oxidation and photoinduced hydrophilicity of thin tungsten trioxide (WO3) films coupled with platinum (Pt) nanoparticles were investigated. WO3 films with underlying Pt nanoparticles (WO3/Pt/substrate) and those with overlying Pt nanoparticles (Pt/WO3/substrate) were synthesized by sputtering and sol-gel methods. Between these films, underlying Pt nanopaticles greatly enhanced the photocatalytic oxidation activity of WO3 without decreasing the photoinduced hydrophilic conversion. However, overlying Pt nanoparticles deteriorated the hydrophilicity of WO3 because the Pt nanoparticle surface was hydrophobic. The enhanced photocatalytic reaction by the Pt nanoparticles was attributed to the multi-electron reduction in Pt, which is caused by the injected electrons from the conduction band of WO3. The relationship between photocatalytic activity and thin film structure, including the size of Pt nanoparticles, the thickness and porosity of the WO3 layer, were investigated. Consequently, the optimum structure for high performance in both photocatalysis and photoinduced hydrophilicity was WO3 (50 nm)/Pt(1.5 nm)/substrate, and this film exhibited a significant self-cleaning property even under visible light irradiation.