Activation of peroxymonosulfate by distillers' grains biochar for the degradation of ciprofloxacin: critical roles of singlet oxygen and electron transfer

Abstract

The distillers' grains biochar was prepared by a simple ball-milled process, followed by pyrolysis at different temperatures. The as-prepared biochars were then utilized to degrade ciprofloxacin (CIP) via peroxymonosulfate (PMS) activation. At the optimal pyrolysis temperature of 900 °C, a biochar with a high density of surface defects and a large surface area was generated. Therefore, 100% CIP degradation was attained within 40 min using the DBC900/PMS system. This system also showed good stability across five reuse cycles as well as good performance over a wide range of pH values. The water matrix showed a negligible effect on CIP degradation in this system. Electron paramagnetic resonance (EPR), quenching experiments and electrochemical analysis demonstrated that CIP degradation involved non-radical and electron transfer pathways. The production of ¹O₂ and electron transfer mediated by the metastable complex DBC900-PMS* were crucially involved in this degradation reaction. Moreover, a possible degradation pathway of CIP was proposed based on the analysis of the intermediate products. Overall, this study provided an enhanced understanding of the biochar-activated PMS mechanism and offered a compelling strategy for the resourceful utilization of waste distillers' grains.