Enhanced activation of peroxymonosulfate with metal-substituted hollow MxCo3-xS4 polyhedrons for superfast degradation of sulfamethazine

Developing catalysts with high efficiency is a long-term goal of the sulfate radical-based advanced oxidation processes (SR-AOPs) for emerging contaminant degradations. In this work, a series of transition metal (Mn, Ni, Cu, Zn)-substituted hollow cobalt-based bimetallic sulfide polyhedrons (MxCo3-xS4) were fabricated using MOF-templated sulfuration strategy. The hollow structure supplied a highly reactive shell containing abundant exposed active sites while density functional theory (DFT) calculation revealed that metal substitution increased positive charge density of Co atoms and facilitated PMS adsorption on catalyst surface. The as-synthesized polyhedrons exhibited superior catalytic activities for sulfamethazine (SMT) degradation over a broad pH range (pH = 2-11). Mn0.3Co2.7S4 polyhedrons were selected as the target catalysts for the best performance with nearly 97% SMT was removed within 8 min with the apparent rate constant of 0.363 min(-1) , which was higher than those of reported researches by 3-4 times. Multiple reactive oxygen species including sulfate radical (SO4-center dot), superoxide radical (O-2(center dot-)) and singlet oxygen (O-1(2)) were determined to work by quenching test and electron paramagnetic resonance (EPR). Furthermore, the catalysts showed good reusability for SMT degradation in the presence of PMS over five runs. This work shed new light on the feasibility and superiority of metal substitution in synergistically improving the catalytic activity of cobalt sulfides, and provided a novel class of Co-based catalysts for recalcitrant contaminants degradation by SR-AOPs.