Preparation and photocatalytic activity of Keggin-ion tungstate and TiO₂ hybrid layer-by-layer film composites

Keggin ions (PW₁₂O₄₀^3- (PW₁₂), SiW₁₂O₄₀^4- (SiW₁₂), H₂W₁₂O₄₀^6- (H₂W₁₂)) and TiO₂ hybrid thin films were prepared using the layer-by-layer method. Their photocatalytic activities were investigated using gaseous 2-propanol decomposition. All films were transparent in the visible wavelength range. For 2-propanol decomposition, H₂W₁₂ was the most effective for the combination with TiO₂ despite having the smallest TiO₂ deposition amount. The photocatalytic activity of the PW₁₂-TiO₂ hybrid film was increased 2.3 times by visible light with UV illumination. This increase was less remarkable for hybrid films of other Keggin ions, suggesting that the visible light excitation of reduced PW₁₂ plays an important role in the enhancement of 2-propanol decomposition.