Catalytic Ozonation for the Degradation of 5-Sulfosalicylic Acid with Spinel-Type ZnAl2O4 Prepared by Hydrothermal, Sol-Gel, and Coprecipitation Methods: A Comparison Study

This study presents a novel spinel-type zinc aluminate nanometer catalyst and is applied in catalytic ozonation for wastewater treatment. The zinc aluminate (ZnAl₂O₄) catalysts were synthesized by hydrothermal, sol-gel, and coprecipitation methods, and their characteristics were analyzed by X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectrum, Fourier transform infrared, and X-ray photoelectron spectroscopy (XPS) techniques. 5-Sulfosalicylic acid (SSal) was selected as the typical pharmaceutical and personal care product and used to evaluate the catalytic activity of ZnAl₂O₄. Compared to ozonation, an obviously higher removal efficiency for the SSal degradation was achieved with the nanocatalyst addition in catalytic ozonation. The removal of SSal and chemical oxygen demand reached 64.8 and 46.2%, respectively, after 60 min in the presence of ZnAl₂O₄, whereas it was only 49.4 and 33.2%, respectively, in ozonation. The comparison of catalysts showed that the ZnAl₂O₄ prepared by the hydrothermal method presented a better catalytic activity in ozonation. The effect of radical scavenger experiment results and the characterization of XPS implied that ^•OH was the main active oxidative species in catalytic ozonation. The reusability results showed that the ZnAl₂O₄ catalyst possessed a high stability and could be widely used in catalytic ozonation for wastewater treatment.