Comparison of different S-doped biochar materials to activate peroxymonosulfate for efficient degradation of antibiotics

The goal of this work was to elucidate the ability of biochar materials prepared by different methods to degrade antibiotics by activating peroxymonosulfate (PMS). S atom was doped into biochar using diphenyl disulfide (DD), sodium thiosulfate (ST), and thiourea (TU) as S precursors. The different doped materials were used to activate PMS and tested for the ability to degrade tetracycline hydrochloride, sulfadiazine sodium salt, and levofloxacin hydrochloride. The average degradation efficiencies of DD-doped hydrothermal + pyrocarbon (DD-HPBC), TU-doped hydrothermal + pyrocarbon (TU-HPBC), and ST-doped hydrothermal + pyrocarbon (ST-HPBC) were 83.76%, 86.74%, and 93.60%, respectively, all higher than the degradation efficiency of the undoped material. When sodium thiosulfate-doped pyrocarbon (ST-PBC), hydrochar (ST-HBC), and hydrothermal + pyrocarbon (ST-HPBC) were used to activate PMS, the highest degradation efficiencies were achieved, with average rates of 71.59%, 78.22% and 97.20%, respectively. ST-HPBC exhibited the highest concentration of environmentally persistent free radicals (EPFRs), 9.47 × 1018 spin/g, among all biochar materials. Given this high concentration of EPFRs, use of ST-HPBC to activate PMS resulted in a very high rate of antibiotic degradation, and the concentration of EPFRs was positively correlated with the degradation efficiency. Increase of specific surface area, the thiophene S (-C-S-C-) ratio, and concentration of EPFRs in S-doped biochars promoted the degradation of antibiotics. For PMS activated by biochar, reactive oxygen species (ROS) degraded antibiotics in the order of sulfate radical (SO4•-) > singlet oxygen (1O2) > hydroxyl radical (•OH) > superoxide radical (•O2-). This work provides new insight into the application of S-doped sludge biochar materials.