Perborate accelerated copper-immobilized carbon nanofibers activating peroxymonosulfate process for sulfadiazine degradation: Performance and mechanisms understanding

•Copper-immobilized carbon nanofibers (Cu-CNF-x) was firstly synthesized from PAN and Copper phthalocyanine.•The addition of BO3− successfully mitigated the issue of water acidification resulting from PMS usage.•BO3− significantly enhanced the adsorption energy (Ead) of PMS onto Cu-CNF-x, raising it from 0.43 eV to 4.75 eV.•BO3− greatly augmented the utilization efficiency of PMS and facilitated the generation of H2O2 in the Cu-CNF-x/PMS system.•The mechanism involved in BO3−/Cu-CNF-x/PMS system was proposed.