In-situ growing of metal-organic frameworks on iron mesh as a recyclable remediation material for removing hexavalent chromium from groundwater

The recovery and reuse of adsorbents is crucial for the effectiveness and sustainability of mitigation methods for groundwater pollution. Considering the difficulty in recovering powder materials and the low mechanical strength of membrane materials, we developed a sheet material with good recyclability and certain mechanical strength. In this study, an in situ synthesized MIL-100(Fe) film sample was produced by hydrothermal reaction using a commercially available iron mesh as the substrate. The MIL-100(Fe) samples were characterized by SEM, XRD, XPS, and FT-IR. The experiments showed that the material presented excellent removal ability toward Cr (VI) and good recovery performance. In the fourth cycle test, the Cr(VI) removal rate reached more than 95%. The material characterization and adsorption kinetics indicated that the removal mechanism was oxidationreduction reaction and electrostatic adsorption. The removal experiments at different pH values and with different co-existing ions demonstrated that the material can maintain good removal capacity at pH values between 2 and 8, and common ions in groundwater can promote the removal of Cr(VI) under neutral conditions. The recycling test demonstrated that the sample can be reused. After the sample was recovered and calcined in an inert environment, a network sample containing zero-valent iron was obtained, and it removed Cr(VI) from water at a low pH in 20 min. This study provides a new alternative for the practical removal of Cr(VI) from groundwater.