Parameters to be considered for the development of highly photoactive TiO2 layers on aluminium substrates by RF magnetron sputtering for treating polluted air

Abstract

In this study, photoactive titanium dioxide films deposited on aluminium substrates using Radio-Frecquency (RF) magnetron sputtering have been developed, with the goal of advancing this technology for indoor air treatment. With this goal in mind, the influence of deposition parameters, namely post annealed heat treatment, working pressure and deposition time, on the physico-chemical properties of the layers has been studied. Photocatalytic efficiency for trichloroethylene degradation in gas phase, and self-cleaning performance of the developed materials have been evaluated. Samples have been thoroughly examined using different techniques (SAXRD, UV-Vis, SEM-EDX, contact angle, profilometry, hardness, among others) in order to determine the structural-photocatalytic relationship. The findings indicate that high-temperature annealing promotes the diffusion of alumina, copper and iron ions towards the surface of the samples resulting in the formation of aluminium alloys. These alloyed species can act as recombination centres adversely affecting the photocatalytic activity. The sputtering pressure also affects the nature of the titanium phases formed during the sputtering. Increasing the thickness of the TiO2 layer leads to rougher surfaces with TiO2-anatase as the predominant crystal phase. Annealing temperatures of 350 °C, argon pressures between 0.8 and 1.0 Pa, and TiO2 layer thickness of ca. 110 nm are the optimal conditions to prepare well-adhered TiO2 layers with high photocatalytic performance. UV-A photoinduced superhydrophilicity phenomena was observed for all TiO2/Al materials.