Nitrogen doping sludge-derived biochar to activate peroxymonosulfate for degradation of sulfamethoxazole: Modulation of degradation mechanism by calcination temperature

The surface property of biochar can be modulated through nitrogen doping and calcination temperature. In this study, nitrogen-doped sludge-derived biochar (NSDB) was prepared and applied to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) degradation, focusing on the effect of calcination temperature on the degradation mechanism. The results showed that the contribution of free radicals to SMX degradation decreased gradually when calcination temperature increased from 300 to 800 °C. In contrast, the contribution of surface-bound reactive species increased gradually. However, the contribution of surface-bound reactive species to SMX degradation decreased for NSDB prepared at 900 °C. The change of physiochemical properties such as contact angle caused by calcination temperature was responsible for the shift of SMX degradation mechanism. NSDB prepared at 800 °C showed higher catalytic activity to PMS compared to NSDB prepared at other temperatures. Compared to sludge-derived biochar (SDB), NSDB had much higher catalytic activity, indicating that nitrogen doping could improve the catalytic activity of SDB. This study provided a way to modulate the degradation mechanism of SMX by calcination temperature of biochar to activate PMS for degradation of organic pollutants.