Mechanochemical synthesis of biochar encapsulated FeMn nanoparticles with strong metal–carbon interactions for efficient degradation of tetracycline via activating peroxymonosulfate

Transition metal and carbon nanomaterials are well-known for their peroxymonosulfate (PMS) activation capabilities. However, metal-based materials often suffer from ion leakage and poor reusability, while carbon-based materials have limited catalytic efficiency. To overcome these challenges and leverage the strengths of both, we introduce carbon-coated Fe/Mn composites (FeMn@BC), that establish strong interactions between metal components and the carbon substrate. FeMn@BC exhibited exceptional selectivity for 1O2 generation via PMS activation. In practical applications, FeMn@BC efficiently degraded tetracycline by activating PMS, achieving 99.1% removal in just 30 min. Importantly, FeMn@BC demonstrated remarkable stability, especially under visible light exposure. XPS analyses revealed strong interactions between FeMn components and the biochar shell, enhancing the electron transfer capacity of FeMn@BC through Fe(III)/Fe(II) and Mn(III)/Mn(II) redox pairs. In-situ attenuated total reflection Fourier-transform infrared (ATR-FTIR) analysis highlighted abundant hydroxyl groups in FeMn@BC as crucial active sites for electron transfer. Quenching experiments and electron paramagnetic resonance (EPR) measurements unveiled that FeMn@BC catalyzed 1O2 generation primarily through the disproportionation of O2− and energy transfer from oxygen vacancy to O2. Our work demonstrates the possibility of simple ball milling of biomass in the presence of iron salts for iron-catalyzed mechanochemical synthesis of biochar-based catalysts. This study not only presents a novel strategy for large-scale biochar-encapsulated transition metal catalyst synthesis but also explores the potential use of agricultural waste for value-added applications.