Influence of the OH groups on the photocatalytic activity and photoinduced hydrophilicity of microwave assisted sol-gel TiO2 film

In the present work the influence of the OH groups on the photocatalytic activity and the photoinduced hydrophilicity of microwave assisted sol-gel TiO2 films was investigated. The prepared TiO2 films were characterized using XRD and AFM. Furthermore, the surface of the TiO2 films was examined by help of XPS in order to determine the amount of OH groups before and after UV irradiation at different humidities. The activity of the TiO2 films was determined using stearic acid as a model compound and the photoinduced superhydrophilicity was investigated through contact angle measurements. The results of this investigation showed that the microwave assisted sol-gel technique produces highly homogeneous and efficient TiO2 films without the need for heat treatment for crystallization. Based on the conducted experiments it is suggested that the amount of OH groups on the TiO2 surface highly influence the photocatalytic activity and the photoinduced superhydrophilicity and that the two mechanisms may be closely related. It is suggested that the superhydrophilicity is obtained through a combination of photocatalytic degradation of organic contaminants and surface structural changes in form of an increased amount of OH-groups. (C) 2009 Elsevier B.V. All rights reserved.