Accelerating radical generation from peroxymonosulfate by confined variable Co species toward ciprofloxacin mineralization: ROS quantification and mechanisms elucidation

Abstract

Cobalt and oxides are the most recognized catalysts for peroxymonosulfate (PMS)-based advanced oxidation processes. However, the valence states – catalysis relations remain ambiguous. Herein, Co0/CoO/Co3O4 @K, N, O-doped carbons (Co-K-N-O-C) were synthesized via low-temperature pyrolysis. The cobalt species resulted in defective and doped carbons, and KOH facilitated the formation of low-valent Co species and carbon porosity. The synergy between Co and K facilitated peroxymonosulfate (PMS) activation and ciprofloxacin (CIP) mineralization due to enhanced electron transfer. Kinetics analysis was coupled with quenching experiments, electron paramagnetic resonance (EPR) detection and chemical probe identification to elucidate the contributions of each reactive oxygen species. As a result, hydroxyl radical (HO•) dominated the degradation (~64.8 ± 1.2%), followed by sulfate radicals (SO4•−, ~34.2 ± 1.1%) and singlet oxygen (1O2, <2.0%). The low-valent Co species, especially Co0, greatly promoted radical generation. This study dedicates to in-depth elucidation of PMS activation mechanisms over metal/oxides@carbon composites for purifying recalcitrant contaminants in wastewater.