Peroxymonosulfate conversion to singlet oxygen over π-electron delocalized carbon nitride for selective degradation of emerging contaminants

Graphitic carbon nitride is a promising catalyst for peroxymonosulfate (PMS) activation towards removal of emerging contaminants in water environment. However, the dependence on light and the non-selectivity of PMS activation pathway limit its practical applications. In this work, a two-step thermal treatment process was developed to modulate the π-electron delocalization degree of carbon nitride. The obtained modified carbon nitride (TCN) showed excellent capability on PMS activation without light, and simultaneously achieved high selectivity on the generation of non-radical species 1O2. Based on the results of quenching and probe experiments, isotopic solvent effect, as well as in-situ capture technique, the dominant contribution of 1O2 to the degradation of pollutants was clarified. The TCN/PMS system showed highly selective degradation of electron-donating pollutants, further demonstrating the dominant role of 1O2. Combining the control experimental results, PMS was speculated to be catalytically activated mainly through the spontaneous decomposition pathway. Further, according to the characterizations results and density functional theoretical calculations, it was the delocalized π-electrons at modified C-N heterocycles that accelerated the self-decomposition reactions of PMS. The high selectivity towards 1O2 endowed good resistance of TCN/PMS system in complex water matrices, achieving efficient removal of a number of emerging contaminants.