Structure and composition regulation of MgCoFe-LDO: Efficient activation of peroxymonosulfate with suppressed cobalt leaching

Despite extensive studies on Co-based layered double hydroxide (LDH) catalysts for peroxymonosulfate (PMS) activation, systematic investigations on metal-ion leaching behavior through compositional and structural regulation of LDHs remain scarce. In this work, MgCoFe-LDHs with various cation ratios were synthesized and calcined at different temperatures to obtain MgCoFe-LDOs. While exploring the optimal catalytic performance toward PMS activation, the leaching behaviors of Co and Fe ions were simultaneously evaluated. The results showed that both calcination temperature and the proportion of Co incorporated into the divalent-metal sites significantly affected PMS activation performance and metal-ion release. When 16% of the divalent-metal sites were substituted with Co, the Co-ion concentration after reaction decreased by approximately 57.70% (from 0.3865 mg·L −1 to 0.1635 mg·L −1 ) for the sample calcined at 300 °C compared with the uncalcined precursor. The improved Co leaching levels are significantly lower than the Co emission limit (< 1.0 mg/L) stipulated in The Emission Standard of Pollutants for Copper, Nickel, and Cobalt Industry (GB 25467–2010). Moreover, both the catalytic performance and the leaching control capability are superior to those of representative Co-based catalysts reported under comparable conditions. Additionally, the effects of inorganic anions on MB degradation in the MgCoFe-LDO/PMS system and the catalyst's applicability toward different dye contaminants were examined. Radical-quenching tests and electron paramagnetic resonance (EPR) analyses confirmed that singlet oxygen ( 1 O 2 ) was the dominant reactive species. Based on XPS results and other characterizations, a possible degradation mechanism of MB in the MgCoFe-LDO/PMS system is proposed.