Biochar co-doped with nitrogen and boron switching the free radical based peroxydisulfate activation into the electron-transfer dominated nonradical process

Abstract In this study, N/B co-doped biochars were employed as metal-free activators of peroxydisulfate (PDS) for tetracycline degradation, more importantly, the roles of dopants and the relative contribution of radical vs nonradical oxidations were comprehensively investigated. Integrating with electron paramagnetic resonance and kinetics calculations, we showed that co-doping N and B into biochars not only boosted the catalytic activity but also switched the radical PDS-activated process into the electron transfer-dominated nonradical process. Compared with pristine biochar/PDS systems (22%), the nonradical contribution of N/B co-doped biochar/PDS systems increased to 59%, exhibiting outstanding stability and selectivity. Galvanic oxidation tests and theoretical simulations unveiled that doped biochars as conductive tunnels accelerate the potential difference-driven electron transfer from the highest occupied molecular orbital of pollutants to the lowest unoccupied molecular orbital of PDS due to the lower energy gap. This study provided new insights into the critical role of heteroatom-doped carbocatalysts in PDS nonradical activation.