MOF-templated hollow cobalt sulfide as an enhanced Oxone activator for degradation of UV Absorber: Key role of sulfur Vacancy-Induced highly active CoII sites

This study aimed to design hollow rhombic cobalt sulfide (HRCS) via a single-step sulfidation of cobaltic metal organic framework (CoMOF) as a template. The obtained HRCS with abundance of defects and sulfur vacancy (SV) was then employed for degradation of Novantisol (NVT), a sunscreen agent, through Oxone activation. The superior catalytic performance of HRCS was attributed to its more electroactive sites and low charge transfer resistance that were enhanced by highly active CoII due to the existence of SV for increased generation of SO4•− as a predominant species. Although •OH and 1O2 were proved to be generated obviously from activation of Oxone over HRCS, their contribution to NVT degradation was marginal. While •OH and SO4•− were generated mainly by CoII-activated Oxone, the formation of SO4•− was accelerated by sulfur species and the disproportionation of SO5•−. The limited conversion of SO4•− by reacting with −OH and undirect self-hydrolysis of Oxone, on the other hand, contributed to enhanced •OH generation. Further experiments on furfuryl alcohol (FFA) consumption showed that 1O2 generated from O2•− as an intermediate species did not account for the NVT degradation but rather from self-decomposition of Oxone, dissociation and self-combination of SO5•−, and disproportionation of •OH. The degradation pathway was also investigated and unveiled in details via DFT calculation, which further validated that HRCS appeared to be a superior catalyst for NVT degradation through Oxone activation.