Synthesis of oxygen vacancy-enriched N/P co-doped CoFe2O4 for high-efficient degradation of organic pollutant: Mechanistic insight into radical and nonradical evolution

Oxygen vacancy-enriched N/P co-doped cobalt ferrite (NPCFO) was synthesized using ionic liquid as N and P sources, and then the catalytic performance and mechanism of NPCFO upon peroxymonosulfate (PMS) activation for the degradation of organic pollutants were investigated. The as-synthesized NPCFO-700 exhibited excellent catalytic performance in activating PMS, and the degradation rate constant of 4-chlorophenol (4-CP) increased with the increase of OV concentration in NPCFO-x. EPR analysis confirmed the existence of ·OH, SO4·-, and 1O2 in the NPCFO-700/PMS system, in which OV could induce the generation of 1O2 by PMS adsorption and successive capture, and also served as electronic transfer medium to accelerate the redox cycle of M2+/M3+ (M denotes Co or Fe) for the generation of radical to synergistically degrade organic pollutants. In addition, the contribution of free radical and nonradical to 4-CP degradation was observed to be strongly dependent on solution pH, and SO4·- was the major ROS in 4-CP degradation under acid and alkaline condition, while 1O2 was involved in the degradation of 4-CP under neutral condition due its selective oxidation capacity, as evidenced by the fact that such organic pollutants with ionization potential (IP) below 9.0 eV were more easily attacked by 1O2. The present study provided a novel insight into the development of transition metal-based heterogeneous catalyst containing massive OV for high-efficient PMS activation and degradation of organic pollutants.