Significant enhancement of photocatalytic activity over bifunctional ZnO-TiO₂ catalysts for 4-chlorophenol degradation.

In this study, ZnO-TiO₂ binary oxide catalysts were successfully prepared by a solid-state dispersion. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, diffuse reflectance spectroscopy, transmission electron microscopy, Brunauer-Emmett-Teller and photoluminescence techniques. It was observed that the interaction between ZnO and TiO₂ affected the photocatalytic efficiency of binary oxide catalysts. 20 wt% ZnO-TiO₂ photocatalyst exhibited much higher photocatalytic activity than pure TiO₂, ZnO and P-25 in the degradation of 4-chlorophenol under low UV irradiation. The chemical interaction between ZnO and TiO₂ in the form of the Zn-O-Ti- bond may affect the photoefficiency of binary oxide catalysts. The profound effect of binary oxide catalyst for 4-chlorophenol degradation was generally considered due to small particle size, lower band gap energy and the presence of more surface OH groups than that of the pure TiO₂ and ZnO photocatalyst. It was concluded that in the case of 20 wt% ZnO-TiO₂ catalyst, the main intermediates of degradation were phenol, 2-chlorophenol, hydroquinone and catechol, while with P-25 the main intermediates were ring-opening products, suggesting that different reaction mechanisms may have taken place depending on the nature of the catalyst.