Study on the nonradical pathways of nitrogen-doped biochar activating persulfate for tetracycline degradation

• Nitrogen-doped biochar was prepared and showed great performance for TC degradation. • The formation of a graphitized structure enhanced the catalytic performance of biochar materials. • Nitrogen doping and high pyrolysis temperature promoted the formation of the graphitized structure of biochar. • The degradation of TC mainly depended on the electron transfer process between PS and pollutants. Tetracycline (TC) is a kind of refractory pollutant and widely exists in environment, and it is urgent to develop effective methods for TC treatment. In this study, nitrogen-doped biochar (N-BCX) was successfully synthesized and was used to activate persulfate (PS) to degrade TC. The materials were characterized by XPS, Raman spectrum, SEM, BET and FT-IR. SEM and BET results showed that the catalyst had an obvious pore structure and large specific surface area, which increased with increasing pyrolysis temperature. Nitrogen doping could increase the content of graphite-N in biochar; the defect edge of the material increased, further formed the graphitization structure, and enhanced the catalytic performance of the material. TC (20 mg/L) could be completely removed within 120 min under the optimal conditions of 200 mg/L of catalyst dosage, 2 mM of PS dosage and initial pH of 7. The results of EPR, quenching experiments and electrochemical experiments showed that the degradation of TC in the system did not depend on the action of radicals, the electron transfer between TC and PS on the surface of biochar maybe the main pathway. Efficient and environmentally friendly nitrogen-doped biochar can provide a reference for the related antibiotic wastewater treatment.