Mn-Doped Biochar Derived from Sewage Sludge for Ciprofloxacin Degradation

Three different MnO2 polymorphs, alpha-MnO2, beta-MnO2, and delta-MnO2, with K+-tuned tunnel structures were loaded on sludge-based biochar (BC). Then MnO2-loaded BCs served as the catalyst for ciprofloxacin (CIP) removal. Results showed that as-prepared materials exhibited better catalytic activity than raw BC, among which BC-alpha-MnO2 achieved superior CIP removal than BC-beta-MnO2 and BC-delta-MnO2. CIP removal increased when pH increased from 3 to 5, then slightly decreased with further increase of pH. Desorption experiments confirmed that both adsorption and degradation contributed to the CIP removal by MnO2-loaded BCs. Compared with the raw BC, the contribution of degradation increased 27.87%, 19.87%, and 14.19%, respectively, for BC-alpha-MnO2, BC-beta-MnO2, and BC-delta-MnO2. The radical quenching experiments and electron paramagnetic resonance tests demonstrated the existence of reactive oxidation species (ROS) including O-2(-)center dot, center dot OH, and O-1(2). The O-2(-)center dot and center dot OH were the main ROS during CIP degradation by BC, while O-1(2) was the main ROS for MnO2-loaded BCs. BC-alpha-MnO2 featured the most abundant ROS, followed by BC-beta-MnO2 and BC-delta-MnO2. The persistent free radicals and Mn in MnO2-loaded BCs may serve as the active site for electron transfer during the degradation process, thus leading to the generation of O-2(-)center dot, center dot OH, and O-1(2). (C) 2022 American Society of Civil Engineers.

Automated summary

This study investigated the catalytic activity of MnO2-loaded biochar (BC) with different MnO2 polymorphs for ciprofloxacin (CIP) removal. The results showed that BC-alpha-MnO2 exhibited superior CIP removal compared to BC-beta-MnO2 and BC-delta-MnO2. The pH value and desorption experiments confirmed the contributions of both adsorption and degradation to CIP removal. Radical quenching experiments and electron paramagnetic resonance tests demonstrated the existence of reactive oxidation species (ROS) in BC and MnO2-loaded BCs.