Photocatalytic activity of cadmium doped TiO2 films for photocatalytic degradation of dyes

The TiO2 thin films have encouraging photocatalytic activity in dyes degradation and can be used in wastewater advanced treatment. Thin films were obtained by doctor blade, for avoiding the problems raised by powder–TiO2 leaching and separation. Hence, this technique may be viable for large volumes of low dye concentration wastewater, resulted in the textile finishing industry. Usually, these wastewaters have also a low heavy metal content (e.g. from phtalocyanine pigments) that interferes with the photodegradation. Cadmium is one often participant in the process and, in a real situation, it can adsorb on the photocatalyst surface, modifying the photocatalytic activity. The modification can be beneficial, if it results in doping. Therefore this study investigates the cadmium doping effect on TiO2 photocatalyst. Degussa P25 TiO2 powder and cadmium precursors were used as materials for doped TiO2 thin films obtained using the doctor blade deposition method. Effects of TiO2 doping with cadmium were analysed, considering the morphology, visible light response, and photocatalytic performance. The phase structure, microstructure and surface properties of the coatings were characterized by using X-ray diffraction and atomic force microscopy (AFM). The spectroscopic analysis was investigated by UV–vis techniques. The photocatalytic reactivity was evaluated by the Methyl Orange (MO) and Methylene Blue (MB) degradation on cadmium doped TiO2. The effect of the initial dyes concentration, of the illumination time, the dopant concentration and the cadmium precursors were investigated. In this study, highest catalytic activity was found to be strongly dependent both on catalyst structure and on the dyes concentration. There is a linear correlation between the band gap energy of the cadmium doped TiO2 films and dyes photodegradation efficiency, which allows the materials optimization for the best photocatalytic efficiencies.