Aerosol assisted chemical vapour deposition of hydrophobic TiO2-SnO2 composite film with novel microstructure and enhanced photocatalytic activity

Aerosol assisted chemical vapour deposition (AACVD) was used to synthesise a TiO2-SnO2 composite film onto a glass substrate. For comparison a TiO2 film and a SnO2 film were also prepared. All films were characterised by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and wavelength dispersive X-ray spectroscopy (WDX). XPS and WDX of the composite film revealed a TiO2 rich film with a high level of SnO2 segregation at the surface. Highly structured pyramid-like features gave rise to hydrophobic films with static water contact angles of 134 degrees. Photocatalytic activities were determined by monitoring the degradation of intelligent ink (containing Resazurin redox dye) via UV-visible spectroscopy. Under UVA irradiation, the TiO2 film only began to degrade the dye after being irradiated in excess of 100 minutes, whereas the composite TiO2-SnO2 film required only 6 minutes of irradiation before degradation was observed. The formal quantum efficiency (FQE) for the TiO2-SnO2 composite was determined to be 1.01 x 10(-2) molecules per incident photon and the formal quantum yield (FQY) was 1.17 x 10(-2) molecules per absorbed photon. This is an order of magnitude superior to Pilkington Activ (TM) self-cleaning glass a commercial self-cleaning TiO2 coating on glass. This improved photocatalytic activity is attributed to the presence of electron scavenging SnO2 sites that increase charge separation and the increased surface area due to the highly structured morphology.