Stable ZnO@TiO2 core/shell nanorod arrays with exposed high energy facets for self-cleaning coatings with anti-reflective properties

Abstract

Nanostructured metal oxides such as ZnO and TiO₂ have been extensively employed as self-cleaning coatings due to their large band gaps as well as their hydrophilic and photocatalytic properties. We have developed a simple hydrothermal method to coat thin TiO₂ nanosheets with exposed (001) facets onto a ZnO nanorod array. The chemical stability of the ZnO nanorods was great improved due to the existence of the TiO₂ layer. Owing to the porous structure of the ZnO@TiO₂ nanorod arrays, this thin coating layer possesses anti-reflective properties. A transmittance improvement of ∼5% was observed for one-side coated FTO glass. This coating also exhibits good hydrophilic properties, after addition of the TiO₂ nanosheets. More importantly, these ZnO@TiO₂ nanorod arrays display excellent photocatalytic properties for the degradation of dye molecules, due to the heterojunction between the ZnO nanorods and TiO₂ nanosheets. This heterojunction facilitates the charge separation of photo generated carriers. Based on the above features, the ZnO@TiO₂ core/shell nanorod array film has many advantages as a self-cleaning coating.