Photocatalytic properties of TiO2-SiO2 sandwich multilayer films prepared by sol-gel dip-coating

Abstract

TiO2–SiO2 sandwich multilayer films on sapphire substrates were prepared via the sol–gel method and their structural and photocatalytic properties were investigated. The samples were characterized using X-ray diffraction, scanning electron microscopy, and ultraviolet–visible light spectrophotometry. The photocatalytic activities of the samples were evaluated based on their photodegradation of methylene blue in an aqueous solution. The presence of SiO2 in the sandwich structure generated more trap levels and improved photocatalytic activity. In particular, the presence of SiO2 in the second layer from the surface resulted in superior photocatalytic activity owing to the thinner TiO2 layer at the surface, which allowed holes to reach the surface easily to react with methylene blue.