Comparative study of photoinduced wettability conversion between [PW12O40]3−/brookite and [SiW12O40]4−/brookite hybrid films

Abstract

Two tungsten-based Keggin-type heteropolyacids (PW12: ([PW12O40]3−) and SiW12: ([SiW12O40]4−)) were hybridized with brookite-type TiO2. Then photocatalytic decomposition activity, photoinduced hydrophilicity, and sustainability of the hydrophilicity in the dark were evaluated using gaseous 2-propanol (IPA) decomposition and sessile drop method. The obtained films were transparent in the visible wavelength range. Both hybrid films exhibited higher photocatalytic decomposition activity and had higher photoinduced hydrophilicizing rates than pure brookite films under UV illumination. The PW12/TiO2 film exhibited better photocatalytic performance than the SiW12/TiO2 film did. Atmosphere dependence, XPS analysis, and electrochemical experiments indicated the cause of these two films' different levels of sustainability of hydrophilicity to be differences in their electron storage capability. Results show that the electron scavenger capability and reoxidation efficiency of the heteropolyacid are key factors affecting the overall performance of wettability conversion of this hybrid film system before and after UV illumination.