Degradation of Tetracycline Hydrochloride via Activation of Peroxymonosulfate by Magnetic Nickel–Cobalt Ferrite: Role of High-Valent Metal Species as Primary Reactive Agents

Non-radical-based advanced oxidation processes, particularly those dominated by high-valent metals, have caught a great deal of attention because of their exceptional degradation selectivity and robust interference resistance. This study reports the synthesis of a novel ferrite, designated as Co0.5Ni0.5Fe2O4, through a solvothermal reaction, aimed at activating PMS for the removal of TCH from water. It was observed that calcination time played an important role in adjusting the particle size of the catalyst, which subsequently increased its surface area. This enlargement, in turn, led to an increase in active sites, ultimately enhancing the catalytic efficiency. Within the Co0.5Ni0.5Fe2O4/PMS system, high-valent metals Fe(IV) and Co(IV) became prominent as the primary active species, with O21 serving as a secondary contributor. The activation mechanism of PMS was thoroughly analyzed and discussed. Co0.5Ni0.5Fe2O4 exhibited remarkable stability in complex reaction environments and during multiple recycling tests, maintaining a TCH removal efficiency exceeding 98%. This study not only increases awareness of the interaction between catalyst structure and performance but also provides a viable platform for high-valent metal-dominated ferrite catalysts.