Overestimation of 1O2 role in N-doped carbon materials/peroxymonosulfate system: The misleading of furfuryl alcohol quenching effect

Singlet oxygen (1O2) is frequently observed in persulfate-based advanced oxidation processes (PS-AOPs), however its significance in the removal of organic compounds is debatable. To evaluate the role of 1O2, some organic pollutants that have been proven to be successfully degraded by 1O2 in earlier research were selected as the targeted pollutants of this study. In the activation of peroxymonosulfate (PMS) using Co-BTC (a type of metal-organic framework)/melamine derived nitrogen-doped carbon material (Co-BTC/10MNC) as the catalyst, 1O2 and surface-bound SO4•- are discovered, however only surface-bound SO4•- was the dominant species. The degree of inhibition of furfuryl alcohol (FFA) on the removal of organics is reliant on the reaction rates of SO4•- and organics, rather than on the quenching impact of FFA on 1O2. The lower kSO4•- organics have, the easier it is for FFA to inhibit their removal. In short, the quenching effect of FFA is not solid evidence to identify 1O2. Besides, it is found that the influence of HCO3− is related to the second order reaction rate constant (kHCO3•) between HCO3• and organics, implying that the selective removal of some organics is due to that corresponding inorganic radicals (Cl•, NO3•, HCO3• or HPO4•-) have good ability to degrade these organics, rather than 1O2 as the key reactive oxygen species.