N, P co-doped core/shell porous carbon as a highly efficient peroxymonosulfate activator for phenol degradation

Abstract A nitrogen and phosphorus co-doped metal-free porous carbon (NPC) with core/shell structure was successfully synthesized by pyrolysis of ZIF-8@phytic acid (PA) and demonstrated outstanding catalytic performance on PMS activation for the degradation of phenol (98.0% within 30 min at pH = 7.0). Results suggested that optimized N-P co-doping strategy played a synergistic effect in promoting the catalytic activity of NPC. In addition, NPC displayed excellent acid-base tolerance (pH = 3.0–10.0) and insensitive to anions (Cl−, HCO3– and H2PO4−) and humic acid when employed as PMS activator for phenol degradation. Based on quenching tests, electron paramagnetic resonance (EPR) measurements and electrochemical analysis, singlet oxygen (1O2) is the key active specie and the surface-bound sulfate radical (SO4 −) plays an auxiliary role in the removal of phenol in NPC/PMS system while surface electron transfer is also a non-radical pathway. Large BET specific surface areas (SSA), total pore volumes (TPV) and hierarchical porous structure are beneficial to expose more active sites (essentially graphite N and C O) for generating 1O2 and surface-bound SO4 − to enhance catalytic performance of NPC. This work opens up a new way for the synthesis of highly efficient N-P co-doped metal-free PMS activators and provides novel insights into the mechanism of PMS activation by NPC.