Nonradical-dominated peroxymonosulfate activation through bimetallic Fe/Mn-loaded hydroxyl-rich biochar for efficient degradation of tetracycline

Biochar-based transition metal catalysts have been identified as excellent peroxymonosulfate (PMS) activators for producing radicals used to degrade organic pollutants. However, the radical-dominated pathways for PMS activation severely limit their practical applications in the degradation of organic pollutants from wastewater due to side reactions between radicals and the coexisting anions. Herein, bimetallic Fe/Mn-loaded hydroxyl-rich biochar (FeMn-OH-BC) is synthesized to activate PMS through nonradical-dominated pathways. The as-prepared FeMn-OH-BC exhibits excellent catalytic activity for degrading tetracycline at broad pH conditions ranging from 5 to 9, and about 85.0% of tetracycline is removed in 40 min. Experiments on studying the influences of various anions (HCO₃⁻, NO₃⁻, and H₂PO₄⁻) show that the inhibiting effect is negligible, suggesting that the FeMn-OH-BC based PMS activation is dominated by nonradical pathways. Electron paramagnetic resonance measurements and quenching tests provide direct evidence to confirm that ¹O₂ is the major reactive oxygen species generated from FeMn-OH-BC based PMS activation. Theoretical calculations further reveal that the FeMn-OH sites in FeMn-OH-BC are dominant active sites for PMS activation, which have higher adsorption energy and stronger oxidative activity towards PMS than OH-BC sites. This work provides a new route for driving PMS activation by biochar-based transition metal catalysts through nonradical pathways.