Bisphenol S degradation via persulfate activation under UV-LED using mixed catalysts: Synergistic effect of Cu–TiO₂ and Zn–TiO₂ for catalysis

A photocatalyst composed of Zn–TiO₂ and Cu–TiO₂ through simple physical mixing was used to activate persulfate(PS) for Bisphenol S (BPS) degradation. Zn–TiO₂ and Cu–TiO₂ were prepared with a sol gel method and were characterized by X-ray diffraction (XRD), Raman, Transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The two catalysts have shown an obvious synergistic effect in the photocatalytic degradation process. When 5 mM persulfate and 0.3 g/L catalyst were used, the removal rate of mixed catalyst (0.2 g/L Zn–TiO₂ and 0.1 g/L Cu–TiO₂) is 100 % in 18 min, which is significantly better than that of 0.3 g/L Zn–TiO₂(58 %) and 0.3 g/L Cu–TiO₂(90 %). Typically, the effects of various operation parameters, including the ratio of Cu–TiO₂/Zn–TiO₂, catalyst dosage, persulfate dosage, initial concentration of BPS, and initial solution pH, were examined. Reactive oxygen species (ROS) in the UV/mixed catalyst/PS process was identified by scavenger and electron paramagnetic resonance (EPR) tests. The superoxide radicals generated by both Zn–TiO₂ and the hydrolysis of persulfate in the system could accelerate the Cu (II)/Cu(I) redox cycles and results in the synergistic effect. This study proposed a new and effective way to improve the reaction by simply combining two catalysts, and unraveled the mechanism behind the synergistic effect, which could provide new ideas to use the catalyst more effectively for wastewater treatment or other areas.