Boosting Degradation of C4mim Cation by Metal Alkoxide-Derived Co4S3-activated Oxone: Yolk-Shell-Engineered Enhancement and DFT-assisted Toxic Evaluation

The low bio-degradability of room-temperature ionic liquids (RTILs) makes RTILs a new class of persistent contaminants. It is urgent to develop useful technology to eliminate RTILs to prevent their presence in the environment. Sulfate-radical advanced oxidation processes (SR-AOPs) are particularly suitable for degrading such low-biodegradability pollutants. This study introduces a novel SR-AOP aimed at eliminating the representative RTIL, 1-butyl-3-methylimidazolium chloride (C4M), using an enhanced catalyst to activate Oxone. Traditionally, cobalt (Co) has been used for Oxone activation, but homogeneous catalysis with Co ions poses recovery challenges and secondary pollution risks. Recent studies suggest that cobalt sulfides (CSs) are more promising due to their superior redox properties, which are critical for effective Oxone activation. In this work, we developed a catalyst composed of cobalt sulfide (CS) with a unique yolk-shell (YS) structure, termed YSCS, to maximize catalytic activity. YSCS was easily fabricated from Co-Glycerate (CoG) precursors through a selfdestruction/reconstruction process during sulfidization, resulting in a YS structure covered by self-assembled Co4S3 nanoplates. This morphology provides a highly mesoporous structure, enhanced electrochemical properties, and expanded active sites. Consequently, YSCS demonstrated significantly higher catalytic activity for Oxone activation compared to its precursor CoG and the benchmark Co3O4, with a reaction rate constant (k) of 0.108 min-1, surpassing those of Co3O4 NP + Oxone (0.007 min-1) and CoG + Oxone (0.023 min-1). Additionally, YSCS + Oxone exhibited a lower activation energy (Ea) of 17.8 kJ/mol for C4M degradation. The degradation pathway of C4M by YSCS + Oxone was thoroughly investigated using Fukui indices and analyzing the degradation by-products. Toxicity assessments showed that YSCS + Oxone significantly reduces the acute toxicity and bioconcentration factor of C4M, as well as potential mutagenicity and developmental toxicity risks. These findings confirm that YSCS is a highly effective catalyst for Oxone activation and RTIL degradation in water.