Iron(V)/Iron(IV) species in graphitic carbon nitride-ferrate(VI)-visible light system: Enhanced oxidation of micropollutants

Abstract This paper investigated for the first time the visible light-induced oxidation of micropollutants using graphitic carbon nitride (g-C3N4) photocatalyst in the presence of ferrate(VI) (FeVIO42-) under mild alkaline conditions. The studied micropollutants have different molecular structures (i.e., carbamazepine (CBZ), sulfamethoxazole (SMX), sulfadimethoxine (SDM), trimethoprim (TMP), diclofenac (DCF), flumequine (FLU), atenolol (ATL), and caffeine (CAF)). Enhanced oxidation of all investigated micropollutants by the combined g-C3N4-FeVIO42- system was observed compared to g-C3N4 or FeVIO42- alone under visible light irradiation. For example, 5.0 µM CBZ could be almost completely degraded in 5.0 min by the g-C3N4-FeVIO42- system. Comparatively, only ∼40% degradation of CBZ occurred by g-C3N4 or FeVIO42- alone in 5.0 min under the same condition. Similar observations were found with other micropollutants, and the magnitude of enhancement varied with the structure of the micropollutants. The degradation experiments with and without oxygen in solution suggested the generation of O2●- and 1O2 in g-C3N4-visible light system. However, with the presence of FeVIO42- in solution, the g-C3N4-visible light system generated high-valent iron-oxo intermediates (FeV/FeIV) as the oxidizing species, evidenced by the selective conversion of methyl phenol oxide (PMSO) to PMSO2, to cause increased oxidation of micropollutants. A plausible mechanism involving reactive species to oxidize micropollutants by the g-C3N4-FeVIO42- system under visible light irradiation was discussed. Oxidized products of CBZ were identified to reveal possible reaction pathways. The results of the g-C3N4-FeVIO42--visible light system provided a new advanced oxidation process to synergistically degrade micropollutants in water efficiently.