Magnetic nickel ferrite for efficient persulfate activation to remove aqueous refractory organics: Synthesis, advantages, mechanism, and environmental implications

Magnetic spinel ferrites are promising catalysts for activating persulfate for aqueous organics removal. Herein, a high-efficiency ferrite NiFe2O4 was synthesized and comprehensively investigated for persulfate activation. The optimal preparation conditions and their interactions were successfully determined by response surface methodology. The resultant catalyst was characterized with favorable properties for persulfate activation, e.g., porous morphology, excellent magnetism, and good redox activity. The study of operating parameters showed good adaptability of the NiFe2O4 +PS system to pH variation (3-9), and 100 % diclofenac removal was achieved. Mineralization and PS consumption tests showed high TOC removal (65.6 %) and a low PS demand (PS:diclofenac = 6.7:1), which were clear advantages of NiFe2O4, indicating its excellent activity towards PS decomposition. Additionally, the catalyst could be recovered quickly and completely during reuse (> 90 % recovery within 10 s). In addition, persulfate was considered to bind to the catalyst via electrostatic and chemical bonding, followed by the generation of surface-bound SO4 center dot-. A potential mechanism of persulfate activation by NiFe2O4 and three possible degradation routes of diclofenac were proposed. Finally, the environmental implications of the NiFe2O4 +persulfate system for treating actual waters and multiple pollutants were revealed. This work supplemented ferrite for persulfate activation and provided an effective oxidative system for decontamination.