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

Abstract

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.