Fe(III)-Doped g-C3N4 Mediated Peroxymonosulfate Activation for Selective Degradation of Phenolic Compounds via High-Valent Iron-Oxo Species

Herein, we proposed a new peroxymonosulfate (PMS) activation system employing the Fe(III) doped g-C₃N₄ (CNF) as catalyst. Quite different from traditional sulfate radical-based advanced oxidation processes (SR-AOPs), the PMS/CNF system was capable of selectively degrading phenolic compounds (e.g., p-chlorophenol, 4-CP) in a wide pH range (3-9) via nonradical pathway. The generated singlet oxygen (¹O₂) in the PMS/CNF3 (3.46 wt % Fe) system played negligible role in removing 4-CP, and high-valent iron-oxo species fixated in the nitrogen pots of g-C₃N₄ (≡Fe^V═O) was proposed as the dominant reactive species by using dimethyl sulfoxide as a probe compound. The mechanism was hypothesized that PMS was first bound to the Fe(III)-N moieties to generate ≡Fe^V═O, which effectively reacted with 4-CP via electron transfer. GC-MS analysis indicated that 4-chlorocatechol and 1,4-benzoquinone were the major intermediates, which could be further degraded to carboxylates. The kinetic results suggested that the formation of ≡Fe^V═O was proportional to the dosages of PMS and CNF3 under the experimental conditions. Also, the PMS/CNF3 system exhibited satisfactory removal of 4-CP in the presence of inorganic anions and natural organic matters. We believe that this study will provide a new routine for effective PMS activation by heterogeneous iron-complexed catalysts to efficiently degrade organic contaminants via nonradical pathway.