Efficient degradation of emerging contaminant by newly-constructed Ni-CoO yolk-shell hollow sphere in the presence of peroxymonosulfate: Performance and mechanism

Constructing hollow structure is an effective strategy to boost the activity of heterogeneous catalysts in peroxymonosulfate (PMS) activation. Herein, a newly-designed Ni-CoO yolk-shell hollow sphere was first synthesized by a step-by-step method. Interestingly, the etching treatment of NH3·H2O endowed Ni-CoO sphere with hollow yolk-shelled structure, which was beneficial for the increase of specific surface area and the full exposure of active sites. The calcination treatment reduced the charge transfer resistance and enhanced the redox ability of Ni-CoO, further improving its catalytic activity. As expected, 93.1% of diclofenac sodium (DCF) could be rapidly degraded within 5 min over developed Ni-CoO-3/PMS system, and removal efficiency of TOC was as high as 73.3%. Significantly, redox couples of Co3+/Co2+ and Ni3+/Ni2+ were responsible for PMS activation based on radical pathways (namely SO4•−, OH• and O2•−). As the typical radical pathway, 1O2 was also involved in DCF degradation. More importantly, Ni-CoO-3-PMS* complexes mediated the direct electron transfer between DCF and PMS. Furthermore, Ni-CoO-3/PMS system with great stability had excellent practical application prospect in actual wastewater treatment. In short, current work not only offered a high-efficiency catalyst for PMS activation, but also shared some insights into the research on advanced oxidation processes.