Removal of Cr(VI) from aqueous solutions via simultaneous reduction and adsorption by modified bimetallic MOF-derived carbon material Cu@MIL-53(Fe): Performance, kinetics, and mechanism.

Cr(VI) has drawn growing concern because of its acute toxicity and strong carcinogenic properties to most organisms. Metal-organic frameworks (MOFs) have attracted broad interest in removing Cr(VI) as a novel porous adsorbent. In this work, a novel modified Cu@MIL-53(Fe) material and its derivatives have been successfully synthesized via solvothermal and calcination methods and applied for Cr(VI) removal. Experimental parameters, such as the amount of the added Cu, the calcination temperature, the pollutant concentrations, the pH value of solution, etc. were optimized. The Cu@MIL-53(Fe) optimized synthesis parameters were determined as a 0.5 M ratio of Cu/Fe and 800 °C of calcination temperature. The Cr(VI) removal capacities were 20.65 mg/g at 180 min and 13.35 mg/g in 15 min, and 45.55% of total chromium and 99.05% of Cr(VI) were removed at a dose of 0.5 g/L, pH = 3, 25 °C. Batch experiments revealed that the reaction process applied for Langmuir adsorption isotherm and pseudo-second-order models most suitable with q = 724.6 mg/g. Additionally, Cr (VI) could be reduced to less toxic Cr(III) by Fe and Cu during redox reactions. According to further mechanism analysis, the process was primarily monolayer chemical adsorption, followed by electrostatic interaction, redox reaction co-precipitation and coordination effect, etc. A novel promising method of Cr(VI) removal from acidic water by MOFs adsorption is presented in this study.