Thiourea-assisted one-step fabrication of a novel nitrogen and sulfur co-doped biochar from nanocellulose as metal-free catalyst for efficient activation of peroxymonosulfate

The N, S co-doped biochar (N, S-BC) with multistage pore structure was successfully synthesized from nanocellulose and thiourea by one-step pyrolysis, which could effectively activate peroxymonosulfate (PMS) to degrade sulfamethoxazole (SMX) in water. Moreover, the removal efficiency of SMX by this oxidation system was 2.3–3.1 times than that of other systems activated by common metal oxides (such as Fe3O4、Fe2O3, and MnO2). More importantly, the mechanism of the N, S-BC/PMS process was deduced by reactive oxygen species (ROS) quenching experiment and electron paramagnetic resonance (EPR) test, which exhibited that surface-bound free radicals and singlet oxygen (1O2) played an essential role in the SMX degradation. Surprisingly, the sulfate radical (SO4•-) and hydroxyl radical (•OH) produced in this system existed in a bound state on the surface of the carbon catalyst to react with SMX, rather than dispersed in the aqueous solution. This particular form of free radicals could resist the influence of background substances and pH changes in water, and maintain excellent SMX degradation efficiency under different water matrices and pH. This study provides a new insight into the application of carbon catalyst in actual water pollution control.