Sulfur and nitrogen co-doped biochar activated persulfate to degrade phenolic wastewater: Changes in impedance

•The effects of different co-pyrolysis temperature, time and doping ratios on the catalytic degradation of phenol by S,NBC were investigated.•The removal rate of phenol was 98.5% within 90 min by sulfur and nitrogen co-doped biochar.•Sulfur and nitrogen co-doped changed the charge distribution of biochar and improved its electrical conductivity.•Sulfur and nitrogen co-doped biochar successfully lead the reaction to a non-radical pathway.•In addition, the phenol content in simulated coal gasification wastewater decreases from 254 mg/L to 35.4 mg/L after 180 min of reaction, and the TOC removal rate is up to 53.79%, indicating a good purification effect on simulated industrial phenol-containing wastewater. In this research, sulfur and nitrogen co-doped biochar was prepared by co-pyrolysis method. The degradation law of phenol in simulated wastewater by activated potassium persulfate(PDS) was studied, and the effects of preparation conditions on the purification performance of phenol were also discussed. The results show that the phenol degradation rate by biochar with a doping ratio of 20% to activate PDS is up to 98.5%. In addition, the cycle performance of the doped biochar can still maintain 76% at the fifth cycle, indicating a good recycling performance. The results of density functional theory(DFT) calculations and various characterization techniques show that the sulfur and nitrogen exist in the form of thiophene sulfur and graphite nitrogen in the biochar, respectively. The electron density distribution of doped biochar become uneven, and the electrochemical impedance decreases from 32.88 to 10.53, prompting the reaction to proceed via non-radical path. Finally, the purification experiment results reveal that the S,NBC/PDS system possesses an excellent purification effect on simulated coal gasification wastewater, providing a reference for the industrial phenolic wastewater treatment.