Nitrogen self-doped Chlorella biochar as a peroxydisulfate activator for sulfamethazine degradation: The dominant role of electron transfer

Nitrogen-doped biochar has been proven to be an advantageous peroxodisulfate (PDS) activator. However, few studies on PDS activation by biochar prepared from biomass containing intrinsic nitrogen have been reported, and the performance and mechanism are still unclear. In this study, nitrogen self-doped Chlorella biochar (NCB) was prepared by pyrolysis. The results showed that the increase of pyrolysis temperature promoted the formation of graphitic structure in NCB, and the biochar prepared at 900 °C (NCB-900) had the best performance in activating PDS for sulfamethazine (SMZ) degradation. The NCB-900/PDS system had a wide pH applicability and excellent resistance to anion interference, as well as excellent performance in applications such as groundwater remediation. It was suggested that the graphitic nitrogen structures were the main active sites, and the sp2-hybridized graphitic carbon network was favorable for surface electron transfer in the redox reactions on the NCB-900 surface. The degradation mechanism was thoroughly investigated by electron paramagnetic resonance (EPR) test, quenching experiments, chemical probes, electrochemical measurements, and in situ Raman analysis. Rather than free radicals and singlet oxygen (1O2), surface electron transfer mediated by the NCB-900–PDS* complex dominated SMZ degradation in the NCB-900/PDS system.