Biochar-regulated LDH-derived Co–Mn spinel for non-radical peroxymonosulfate activation: high-efficiency imidacloprid degradation dominated by high-valent metal–oxo species and singlet oxygen

Neonicotinoid insecticides (NNIs), notably imidacloprid (IMI), are widely detected in aquatic ecosystems, presenting substantial ecological threats due to their persistence and detrimental effects on non-target organisms. Current remediation strategies are frequently constrained by inefficiencies or excessive energy consumption. Here, we engineered a suite of cobalt–manganese spinel/biochar composites (CoMn_x/BC) through the controlled calcination of CoMn-layered double hydroxide intercalated with BC. The optimized CoMn_0.75/BC composite demonstrated exceptional efficacy in activating peroxymonosulfate (PMS), achieving a 96.9% removal of 5 mg L⁻¹ IMI within 40 min and a degradation rate constant of 0.209 min⁻¹. Mechanistic investigations unveiled that while CoMn₂O₄ primarily activates PMS via radical pathways involving hydroxyl radicals (·OH), the CoMn_x/BC composites shift the activation mechanism towards non-radical routes, dominated by high-valent metal–oxo species and singlet oxygen (¹O₂). Our findings elucidate the pivotal synergistic role of BC in modulating both the structural attributes and catalytic mechanisms of spinel-based composites. These insights offer a rational design blueprint for advanced BC-hybrid catalysts tailored for the efficient treatment of high-strength industrial wastewater contaminated with NNIs.