Different mechanisms between biochar and activated carbon for the persulfate catalytic degradation of sulfamethoxazole: Roles of radicals in solution or solid phase

Biochar as a carbonaceous material alternative to activated carbon (AC) has received increasing application in the catalytic degradation of organic pollutants. However, the different underlying mechanism between biochar and AC for the catalytic degradation is still unclear. In this study, two biochar produced from the pyrolysis of peanut shell at 400 degrees C (BC400) and 700 degrees C (BC700) were used to assist persulfate (PS) catalytic degradation of sulfamethoxazole (SMX), a commercial AC was included as a comparison. Results showed that BC700 had a comparable high catalytic degradation performance to AC (88.7% vs 91.2%) but less effective degradation was observed for BC400 (30.4%). Strong sulfate radicals and hydroxyl radials contributed to the higher catalytic abilities of BC700 and AC, as evidenced by Electron Paramagnetic Resonance analysis. Degradation of SMX by BC700 + PS system mainly happened in solution (53.1%) with the relatively complete degradation. High sorption and dominance of radicals in solid phase of AC (84.3%) was responsible for the faster catalytic performance of AC, but incomplete degradation was observed. Density functional theory calculations confirmed that S-N bond adjacent to the S atom in SMX was the susceptible site for radical's attack. Our findings provide new insight into the different catalytic mechanisms for different carbon materials, which is helpful for the specific carbon materials designed for antibiotics wastewater treatment.