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

Abstract

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°. 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 × 10⁻² molecules per incident photon and the formal quantum yield (FQY) was 1.17 × 10⁻² molecules per absorbed photon. This is an order of magnitude superior to Pilkington Activ™ 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.