A Novel Vacancy-Containing Sea Urchin-Like Co-Mn Spinel Oxide Catalyst with Efficient Peroxymonosulfate-Activation for Phenol Degradation and its Enhanced Anti-Interference to Anion Poisoning

Heterogeneous peroxymonosulfate (PMS)-activation-based advanced oxidation process (PMS-AOP) using spinel catalysts is an effective way to degrade organic pollutants in water. However, the PMS activation performance for spinel catalysts is always unsatisfactory due to the interference of co-existing anions in waters. In this study, we used a sulfate-modification strategy to prepare a sea urchin-like Co-Mn spinel catalyst (CoMn2O4-S) with abundant oxygen vacancies for counteracting the interference of anions in pollutant degradation. Compared with the conventional Co-Mn spinel catalyst without the sulfate modification (CoMn2O4), CoMn2O4-S exhibited a decreased inhibitory rate of phenol degradation efficiency. For a typical CoMn2O4-S/PMS system, the inhibition of phenol removal rate constants by 5 mM NO3−, Cl−, and SO42− were 24.3%, 13.4%, and 1.7%, which were significantly lower than those for a CoMn2O4/PMS system with 5mM NO3− (46.8%), Cl− (43.2%), and SO42− (21.7%). The decreased inhibitory rate of PE removal was demonstrated to be ascribed to that the sea urchin-like structure could alleviate the agglomeration of catalyst particles of CoMn2O4-S and the resulting decrease of reaction sites. Particularly, H2PO4− inhibited the PE removal by 24.3% in the CoMn2O4/PMS system, whereas it promoted the PE removal by 100.1% in the CoMn2O4-S/PMS system. Electronic paramagnetic resonance (EPR) and quenching experiments showed that the active species in both CoMn2O4/PMS and CoMn2O4-S/PMS systems were mainly sulfate radical. LSV measurements demonstrated that oxygen vacancy and H2PO4− synergistically promoted SO4●− diffusion into bulk water where pollutants could be easily be in a collision with and consequently reacted with, thereby enhancing pollutant degradation. Additionally, CoMn2O4-S presented outstanding applicability and reusability in tap and river waters even in five-cycle reactions. This work provides a facile strategy for overcoming the negative effects of co-existing anions on heterogeneous PMS-activation based water treatment.