Synergistic Oxygen Vacancy and Dual-Electron Centers for Enhancing Peroxymonosulfate Activation by Fe─Mn─Mg LDH/BC: Insights into the Key Roles of Magnesium.

Enhancing singlet oxygen (O)-dominated nonradical oxidation with higher selectivity and longer lifetime is crucial for efficient antibiotic degradation. Herein, Fe/Mn/Mg layered double hydroxides (FeMnMg-LDH) modified rice husk biochar composites (BC/FeMMg-LDH, x = 1, 2, and 3) are prepared to activate peroxymonosulfate (PMS) for sulfamethazine (SMT) removal. Increasing Mg content in FeMnMg-LDH enhances catalytic efficiency, achieving 99.2% SMT removal (50 mg L) within 30 min with BC/FeMMg-LDH/PMS. O is identified as the primary active species, with its dominance increasing as Mg content rises. High Mg content induces lattice strain and structural disorder in LDH by atom intercalation in the octahedron, creating abundant oxygen vacancies (Vo) and surface M─OH groups. These Vo amplify the Fe─Mg polarization effect and promote the formation of electron-rich Fe centers. Simultaneously, the elevated d-band center at the Mn site develops electron-donating centers, facilitating short-range electron transfer to Vo and the electron-rich Fe center, boosting high local electron density. This process enhances PMS activation and O regulation. Moreover, the neutral pH microenvironment constructed by Mg, hydroxyl and interlayer carbonates supports stable O generation and broad pH applicability. This study offers new insights into the Mg-induced structural effects in BC/FeMMg-LDH and the development of efficient O-dominated PMS catalysts.