Oxytetracycline Degradation by Heterogeneous Photo-Fenton-Like Process Using h@MIL-100(Fe) with LED Visible Light

Abstract

MIL-100(Fe) is water-stable, mainly consists of Fe(III), and exhibits photocatalytic activity owing to its narrow low bandgap. Owing to these advantages, MIL-100(Fe) was explored as a heterogeneous Fenton-like photocatalyst for degrading oxytetracycline (OTC), which is a popular antibiotic used worldwide. To improve the reaction, Fe(II) species (h@MIL-100(Fe)) were introduced by modifying MIL-100(Fe). The physicochemical properties of both materials were examined using FESEM, XRD, FT-IR, XPS, and UV-Vis spectroscopy. The data showed that MIL-100(Fe) was synthesized adequately without hydrofluoric acid as a mineralizing agent and had a band gap of 1.76 eV. h@MIL-100(Fe) had a higher Fe content (11.95%) than did MIL-100(Fe) (7.32%). Moreover, Fe(II) species (peaks at 723.0 eV and 709.4 eV) were only observed in h@MIL-100(Fe). The embedded Fe(II) species did not hamper the original photocatalytic activity of MIL-100(Fe). OTC was steadily, but not efficiently, degraded by the photocatalytic activity of MIL-100(Fe) (k = 4.1 x 10(-3)/min) or h@MIL-100(Fe) (k = 2.8 x 10(-3)/min) under visible-light irradiation using a conventional LED lamp. When H2O2 was added, h@MIL-100(Fe) showed a higher Fenton-like catalytic ability (k = 3.1 x 10(-2)/min) than did MIL-100(Fe) (k = 2.1 x 10(-2)/min), owing to the synergistic catalytic effects between Fe(II) and Fe(III) species, which generate more hydroxyl radicals for OTC degradation. During the degradation process, 12 types of transformation products were observed, and their transformation mechanisms included decarbonylation of C1, hydroxylation of the aromatic ring and C11a, demethylation at low N-C bonds, and secondary alcohol oxidation of C5.