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. Copyright © 2022 Published by Elsevier B.V.