Synthesis of (Fe0.2Co0.2Ni0.2Cu0.2Mn0.2)Fe2O4 High Entropy Spinel Oxide for Photo-Fenton Degradation of Oxytetracycline Hydrochloride Over a Wide pH Range

Iron-based spinel oxides, with excellent catalytic activity and stability, hold promising potential in the photo-Fenton degradation of organic pollutants. In this study, (Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 Mn 0.2 )Fe 2 O 4 was prepared via the solution combustion method. Multiple characterization techniques confirmed the good stability and morphology of (Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 Mn 0.2 )Fe 2 O 4 . It exhibited high-entropy oxide properties, making it suitable as a photo-Fenton catalyst for the efficient degradation of oxytetracycline hydrochloride (OTC-HCl). Under visible light (Vis) with 10 mM H 2 O 2 , 0.06 g/L OTC-HCl, and pH 4.0, the catalyst achieved a degradation efficiency of 92.9%. In the photo-Fenton system, the utilization rate of H 2 O 2 (calculated as the ratio of the degradation amount of OTC-HCl to the consumption amount of H 2 O 2 ) was 34.5, which is 8.3 times higher than that of pure H 2 O 2 (4.2). The catalyst showed good acid–base adaptability, achieving OTC-HCl removal rates exceeding 92.0% across a pH range of 3–11, with a reaction rate constant of 0.08 min −1 at pH 11. Free-radical capture experiments showed that (Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 Mn 0.2 )Fe 2 O 4 catalyzed H 2 O 2 to generate · OH, · O 2 − , and e − , which are the main free radicals involved in the degradation of OTC-HCl. In summary, (Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 Mn 0.2 )Fe 2 O 4 not only addresses the issue of low H 2 O 2 utilization in traditional photo-Fenton systems but also catalyzes the generation of H 2 O 2 under light conditions. Thus, it can serve as an excellent photo-Fenton catalyst for OTC-HCl degradation. Graphical