Roles of alkali metal dopants and surface defects on polymeric carbon nitride in photocatalytic peroxymonosulfate activation towards water decontamination

Polymeric carbon nitride (PCN) has been extensively employed in peroxymonosulfate (PMS) activation for water decontamination. However, limited photocatalytic efficiency can be achieved by pristine PCN due to its intrinsic deficiencies like high electron-hole recombination rate and resistance to charge transfer. Herein, in a two-stage thermal treatment process, the nontoxic and stable Na and K were successfully anchored among the PCN skeleton with surface defects created, leading to an elevated photocatalytic activity for PMS activation. The SO4.- and 1O2 were identified as the dominant reactive oxygen species, which were generated from electron transfer processes between PMS and catalyst. Experimental and theoretical analyses suggested that the defective structures and metal dopants improved the optical properties of catalyst, endowing it a wider light absorption range and a lower energy barrier for electron transitions. The modified structures were also beneficial to electron transfer processes due to the weaker electron confinement effect, accelerating the production of SO4- on the defective sites and 1O2 on the metal sites. The synergy of radical and non-radical species weakened the influence of side reactions between radicals from PMS and coexisting inorganic anions in practical water, hence to promote the resistance of modified catalysts in complex water matrices.