Enhanced Hg0 removal via α-MnO2 anchored to MIL-96(Al)

Metal-organic frameworks (MOFs) are porous materials with highly ordered structures, and find application in various fields such as gas transportation and catalysis. In the present study, Al-based MOFs (MIL-96(Al)) were chosen as supports for α-MnO2 because of their large specific surface area, excellent thermal stability, and environmental friendliness. Different loadings of α-MnO2 (5%, 10%, and 15%) were anchored to MIL-96(Al) via a one-step process of hydrothermal synthesis, and all the samples were characterized by XRD, ICP-AES, SEM, TEM, and XPS. The results show positive synergistic effects between the reactants and the support. Structurally, α-MnO2 is evenly dispersed on the surface of MIL-96(Al). Unlike common supports such as Al2O3 and SiO2, MIL-96(Al) is not static during the process of loading. The reactant KMnO4 modifies the surface of the support by destroying its organic ligands and forming erosion-induced holes, which help improve the dispersion of α-MnO2. In terms of mercury removal, MIL-96(Al) exposes more active sites of α-MnO2 by even dispersion of the latter, further enhancing the chemical adsorption and catalytic oxidation of α-MnO2. The mercury removal efficiency of the sample MM-15 is 1.55 times that of pure α-MnO2. XPS analysis was performed to determine the mechanism of Hg0 removal by α-MnO2-MIL-96(Al), and the capture agent was determined to be a combination of chemical adsorbent and catalyst. The Hg0 is oxidized to HgO by α-MnO2-MIL-96(Al), while Mn4+ is reduced to Mn3+, and α-MnO2 can also catalyze the reaction between O2 and Hg0. We believe that our research can introduce new avenues for effective understanding of the removal of heavy metals that threaten human health.