Metal-free carbocatalysis for persulfate activation toward nonradical oxidation: Enhanced singlet oxygen generation based on active sites and electronic property

In recent years, metal-free carbocatalysis and persulfate-based advanced oxidation processes have appealed much attention due to the high efficiency and environmental sustainability. This study aimed to investigate catalytic performance of carbon nanofibers (CNFs) on persulfate for removal of 2,4-dichlorophenol and elucidate the intrinsic mechanism of PS activation. Singlet oxygen (1O2) generation was hypothesized to be the dominant pathway for the nonradical organic oxidation. Carbonyl groups and structural defects were determined as the primary active sites via CNFs modification. Density functional theory (DFT) calculations further unearthed that armchair and zigzag edges were favorable to electron transfer and vacancy sites enhanced PS adsorption on CNFs. A higher density of states (DOS) with lower π and σ electronic binding energies would make CNFs more active, and a lower work function (Ф) would lead to a lower inner electron excitation energy barrier to enhance the electron transfer. The degradation pathways were finally determined by combining mass spectrum analysis and DFT calculations (Fukui function), where 1O2 molecules were likely to attack the Cl and O atoms.