Enhanced activation of persulfate by bimetal and nitrogen co-doped biochar for efficient degradation of refractory organic contaminants: The role of the second metal

The leaching of metal ions limits the application of Fe-biochar catalyst in activating persulfate (PS). In this work, Fe-M (M = Co, Cu) and nitrogen co-doped biochar (Fe-M@N-BC) were synthesized through impregnating bio-waste soybean straw to activate PS for the removal of various refractory organic contaminants (tetracycline (TC), oxytetracycline (OTC), methyl orange (MO) and rhodamine B (RhB)). The catalysts were characterized by XRD, XPS, Raman, BET, TEM, SEM, and the degradation mechanism was investigated through quenching experiments and EPR. The results indicated that the doping of second metal (Co, Cu) has a strong promoting effect on catalytic activity with the order of Co > Cu. Surprisingly, the removal rates of TC, OTC, RhB, MO by Fe–Co@N-BC reached 84.7 %, 90.3 %, 89.4 %, and 91 %, respectively. The excellent catalytic performance of Fe–Co@N-BC was mainly attributed to abundant pyridinic-N, larger specific surface area (270 m2 g−1) and the Co(II)/Co(III) redox cycle promoting the regeneration of Fe(II). Notably, the formation of Co7Fe3 alloy could inhibit the leaching of iron ions and Fe–Co@N-BC possessed excellent reusability. Additionally, non-radical (1O2) was the main active species in the Fe–Co@N-BC/PS system. Finally, the degradation pathway of MO was proposed by HPLC-MS analysis. This research work provided an insight into how to reasonably utilize biological waste to construct highly efficient and stable catalysts for pollutants degradation.