Plasmonic metal decorated titanium dioxide thin films for enhanced photodegradation of organic contaminants

Abstract

Photocatalysis using titanium dioxide as photocatalyst is an efficient way for the removal of organic contaminants in water using solar energy. In this study, thin films of copper and silver were deposited on fused silica using the thermal evaporation technique. A 100 nm film of titanium dioxide (TiO2) was then deposited on the plasmonic metal films using a sputter coating technique. The opposite order of deposition of the film was also explored. The prepared thin films were fully characterized using high resolution scanning electron microscopy (HRSEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS). The effect of plasmonic metal film thickness, order of deposition and the use of bimetallic layers on the photocatalytic activity of the TiO2 photocatalyst was evaluated using methyl orange as a model pollutant. It was shown that, the increase in Ag film thickness underneath the TiO2 film increased the photocatalytic activity of the TiO2 photocatalyst until an optimum film thickness of 20 nm was attained. In the case of copper, the increase in film thickness above 5 nm led to reduced photocatalytic activity. Silver was found to be a better plasmonic metal than copper in enhancing the photocatalytic activity of TiO2 under UV light illumination. Cu was found to perform better when deposited underneath the TiO2 film whereas Ag performed better when deposited on top of the TiO2 photocatalyst film. The use of bimetallic layers was found to enhance TiO2 photocatalytic activity more than monometallic layers.