Kapok fiber derived biochar as an efficient electro-catalyst for H2O2 in-situ generation in an electro-Fenton system for sulfamethoxazole degradation

Developing highly efficient, low-cost, and environmental-friendly catalysts to generate hydrogen peroxide (H 2 O 2 ) through two-electron oxygen reduction reaction (2e − –ORR) is very important for the electro-Fenton systems. In this work, nitrogen (N) self-doped biochar were synthesized through the carbonization of natural Kapok fiber (KF), and they were used as 2e − –ORR catalysts to generate H 2 O 2 in electro-Fenton systems. The KF-derived biochar that carbonized at 700 °C (named as KFBC-700) exhibited the optimal 2e − –ORR catalytic performance. The pyridinic-N and COOH played key roles on O 2 adsorption and reduction. The maximum H 2 O 2 accumulated concentration of the KFBC-700 electro-Fenton system was as high as 108.5 mg/L. Sulfamethoxazole (SMX) can be completely removed through both the Fe 2+ catalyzed homogeneous and the FeOCl mediated heterogeneous electron-Fenton reactions within 60 min. Moreover, the electro-Fenton systems showed an excellent stability and reusability for SMX degradation. Additionally, SMX was possibly degraded through three pathways according to the detected degradation intermediates. This paper for the first time used KF-derived biochar as 2e − -ORR catalysts of the electro-Fenton system, and obtained a prominent H 2 O 2 in-situ generation efficiency and a high efficient SMX removal. • Kapok fiber derived biochar (KFBC) was an excellent 2e − –ORR catalyst. • The maximum H 2 O 2 accumulated concentration within 30 min is up to 108.5 mg/L. • The removal of SMX is up to 100 % in Fe 2+ /FeOCl catalyzed electro-Fenton systems. • The pyridinic-N and COOH played a key role on O 2 adsorption and reduction.