Photocatalytic ozonation-based degradation of phenol by ZnO–TiO₂ nanocomposites in spinning disk reactor

Spinning disk reactor (SDR) has emerged as a novel process intensification photocatalytic reactor, and it has higher mass transfer efficiency and photon utilization for the degradation of toxic organic pollutants by advanced oxidation processes (AOPs). In this study, ZnO–TiO₂ nanocomposites were prepared by sol-gel method, and coated on the disk of SDR by impregnation-pull-drying-calcination method. The performance of catalyst was characterized by X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, photoluminescence and ultraviolet–visible diffuse reflectance spectroscopy. Photocatalytic ozonation in SDR was used to remove phenol, and various factors on degradation effect were studied in detail. The results showed that the rate of degradation and mineralization reached 100% and 83.4% under UV light irradiation after 50 min, compared with photocatalysis and ozonation, the removal rate increased by 69.3% and 34.7%, and mineralization rate increased by 56.7% and 62.9%, which indicated that the coupling of photocatalysis and ozonation had a synergistic effect. The radical capture experiments demonstrated that the active species such as photogenerated holes (h⁺), hydroxyl radicals (·OH), superoxide radical (·O₂⁻) were responsible for phenol degradation, and ·OH played a leading role in the degradation process, while h⁺ and ·O₂⁻ played a non-leading role.