Photocatalytic and photoelectrocatalytic degradation of aqueous Rhodamine B by low-temperature deposited anatase thin films

Well-crystallized anatase thin films with controlled thickness of 0.4–0.8 μm were deposited on conductive titanium substrates through hydrolysis of titanium tetrafluoride aqueous solution at a low temperature of 60 °C for various durations. A comparative study was carried out on their abilities to assist photocatalytic (PC) and photoelectrocatalytic (PEC) degradation of rhodamine B (RhB) in water. The efficiency of the anatase thin film to assist photodegradation of RhB improved significantly with an applied potential of 0.4 V versus SCE, independence of the film thickness and the calcination temperature. The PC degradation rate increased linearly with increasing film thickness to ca. 0.54 μm, which remained stable with further increasing film thickness. The PEC degradation rate increased dramatically with slightly increasing film thickness from 0.41 to 0.46 μm, which then decreased with further increasing film thickness. After a subsequent calcination at 500 °C, the PC degradation rate reached the optimum value because of the bargaining effect between the increasing crystallinity and increasing grain size with increasing calcination temperatures. The appearance of rutile phase after calcination at temperatures beyond 600 °C due to the direct oxidation of the Ti substrate deteriorated additionally the photocatalytic activity. The optimum calcination temperature for the PEC degradation rate was 500–600 °C due to the additional effect of increasing conductivity of the anatase film with the increasing calcination temperature.