Facet-Dependent Activation of Oxalic Acid over Magnetic Recyclable Fe3S4 for Efficient Pollutant Removal under Visible Light Irradiation: Enhanced Catalytic Activity, DFT Calculations, and Mechanism Insight

Photo-Fenton-like reaction based on oxalic acid (OA) activation is a promising method for the fast degradation of pollutants due to the low cost and safety. Hence, the magnetic recyclable greigite (Fe3S4) with the exposed {011} facet (FS-011) was prepared using a facile one-pot hydrothermal method and activated OA under visible light irradiation for pollutant removal, in which the removal efficiency values of FS-011 for metronidazole (MNZ) and hexavalent chromium were 2.02 and 1.88 times higher than that of Fe3S4 with the exposed {112} facet, respectively. Density functional theory calculations revealed that OA was more easily adsorbed by the {011} facet of Fe3S4 than by the {112} facet, and the in situ-generated H2O2 preferred to diffuse away from the active sites of the {011} facet of Fe3S4 than from that of the {112} facet, which was conducive to the continuous adsorption and efficient activation of OA. Moreover, the analyses of Fukui index and dual descriptor confirmed the degradation mechanism that the imidazole ring of MNZ was easy to be attacked by electrophilic species, while the amino group of MNZ was easy to be attacked by nucleophilic species. These findings deeply analyzed the mechanism of enhanced OA activation by facet engineering and consolidated the theoretical basis for practical application of Fenton-like reactions.