Synthesis of highly crystalline photocatalysts based on TiO₂ and ZnO for the degradation of organic impurities under visible-light irradiation

A TiO₂–ZnO binary oxide system (with molar ratio TiO₂:ZnO = 8:2) was synthesized by a hydrothermal method, assisted by calcination at temperatures of 500, 600 and 700 °C, using zinc citrate as the precursor of ZnO. The morphology (SEM, TEM), crystalline structure (XRD, Raman spectroscopy), diffuse reflectance spectra (DRS), chemical surface composition (EDXRF), porous structure parameters (low-temperature N₂ sorption) and characteristic functional groups (FT-IR) of the TiO₂–ZnO oxide materials were comprehensively analyzed. The novelty of this work is the observation of the coexistence of the crystalline structures of anatase and ZnTiO₃ in TiO₂–ZnO oxide materials. Moreover, it is shown that the obtained materials absorb visible radiation. The key stage of the study was the evaluation of the photocatalytic activity of the TiO₂–ZnO binary oxide systems in the degradation of model organic pollutants: C.I. Basic Red 1, C.I. Basic Violet 10, C.I. Basic Blue 3 and 4-nitrophenol. For all synthesized materials, a high efficiency of degradation of the model organic impurities was demonstrated. The results show that the synthesized products may be materials of interest for use in the degradation of organic pollutants. Moreover, the kinetics of the photocatalytic degradation of selected organic compounds were determined based on the Langmuir–Hinshelwood equation, assuming a pseudo-first-order (PFO) reaction.

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