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

• ZnO–TiO2 mixed oxide nanoparticles as a photocatalyst for enhancing of the activity.
• The solid-state dispersion for photocatalysis.
• The catalytic performance depends on the ZnO/TiO2 loading.
• The form of the Zn–O–Ti– bond may affect the photoefficiency of binary oxide catalysts.
• Higher activity is associated with the structural and optical properties of the catalyst.

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.

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