One-step synthesis of mixed-valence NH2-MIL-101(Fe2+/Fe3+) with controllable morphology for photocatalytic removal of tetracycline and Cr(Ⅵ)

With the development of industrialization, tetracycline hydrochloride (TCH) and hexavalent chromium (Cr(Ⅵ)) wastewater are discharged in large quantities which poses a serious hazard to aquatic environments and human health. Herein, a stable MOF-based mixed-valence NH2-MIL-101(Fe2+/Fe3+) photocatalyst was designed to degrade TCH and remove Cr(Ⅵ). In this MOF, Fe2+ and Fe3+ formed mixed-valence clusters, the performance of which was similar to that of biological enzymes, with Fe2+ as the active centre and Fe3+ as the high-valence metal ion. The Fe2+/Fe3+ redox-active centre can improve the migration and separation of photogenerated electron-hole pairs, which is the main factor for improving catalytic activity under sunlight irradiation. Hence, NH2-MIL-101(Fe2+/Fe3+) provided a higher photocatalytic degradation of TCH (94% removal within 2 h) than NH2-MIL-101(Fe) (50% removal within 2 h). And 99.32% of Cr(Ⅵ) can be removed with NH2-MIL-101(Fe2+/Fe3+) within two hours. Quenching experiments indicated that·O2–,·OH, and H+ participated in the degradation of TCH. The intermediates were identified using LC-MS, and possible pathways of antibiotics degradation were identified. We used the ECOSAR software to simulate the environmental toxicity of the degradation intermediates. This study broadens the application of building a single-semiconductor photocatalyst with high performance and good stability in the field of environmental remediation.