Water caltrop-based carbon catalysts for cooperative adsorption and heterogeneous activation of peroxymonosulfate for tetracycline oxidation via electron transfer and non-radical pathway

In this study, a water caltrop-based metal-free carbon catalyst for peroxymonosulfate activation was prepared and modified using KOH. The carbonization process improved the crystallinity and porosity of the material, which was beneficial for the efficient modification of KOH. The modification results in higher specific surface area, high porosity, more functional groups, and a highly graphitized structure. BC-OH-700 exhibited excellent adsorption and degradation performance through the synergistic action of surface electrostatic adsorption, non-free radical pathway catalysis, and electron transport. The complete removal of tetracycline could be achieved within 60 min in the BC-OH-700/peroxymonosulfate system. The active sites altered the electrostatic potential distribution and caused the electrostatic adsorption of the reactive components. The surface functional groups could activate peroxymonosulfate to generate reactive oxygen species. The electrical conductivity of the materials could accelerate electron transfer and increase the catalytic degradation rate. The catalytic system was dominated by the ¹O₂ non-free radical pathway. Rapid electron transport could promote the formation of ¹O₂ in the non-radical pathway, thus maintaining the continuity and efficiency of the degradation reaction. The collaborative catalytic system greatly enhanced its adaptability to reaction conditions and provided more possibilities for advanced oxidation via catalytic degradation mechanisms.