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

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 NP 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 (O-1(2)) is the key active specie and the surface-bound sulfate radical (SO4 center dot-) 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 O-1(2) and surface-bound SO4 center dot- 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.