Efficient and convenient strategy for recovering hexavalent chromium ions from wastewater using a novel photocatalytic iron-based metal-organic framework mesh

Considering the difficulty in recovering powder materials and the low photocatalytic efficiency, we have developed a series of Fe-MOFs (MIL-53(Fe), NH2-MIL-53(Fe), MIL-101(Fe), NH2-MIL-101(Fe) and MIL-100(Fe)) on pure iron mesh. In this study, the growth of Fe@MILs on the iron mesh was confirmed through SEM, XRD, and FT-IR characterizations. Among the photocatalytic experiments, Fe@NH2-MIL-53(Fe) and Fe@NH2-MIL-101(Fe), which are amine-functionalized, showed improved photocatalytic activity. This improvement is believed to be due to the combination of NH2 functionality and electron transfer to the Fe-O cluster centre, resulting in dual excitation pathways. Furthermore, Fe@MIL-100(Fe) showed the highest performance for the removal of Cr(vi), with over 92% of Cr(vi) being removed in the fifth photocatalytic cycle. The mechanism indicated the close connection between the compact structure of Fe-MOFs and effective electron migration. Additionally, sacrificial reagent experiments identified two important species for Cr(vi) reduction: electrons (e-) and superoxide radicals (O2-). The photocatalytic recovery tests showed a 97% recovery rate of Cr(vi). This work offers a novel solution for the treatment of water sources contaminated with Cr(vi). A series of Fe@MIL mesh photocatalysts reduced and recovered Cr(vi) under visible light.