Post-functionalized metal−organic framework for effective and selective removal of Hg(II) in aqueous media

For the serious hazards to human and natural environment caused by the toxic Hg(II), a new MOF-based adsorption material, UiO-66-AHMT, was designed and synthesized by incorporating the 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole molecule into the UiO-66-NH2 matrix and used for the removal of Hg(II) from aqueous media. As expected, UiO-66-AHMT exhibits rapid removal ability toward Hg(II) and maximum uptake capacity of 327.88 mg/g at 298 K and pH = 5, the adsorption capacity is improved significantly compared to the unmodified UiO-66-NH2 and comparable in the excellent UiO-66 based adsorbents reported so far. The adsorption behaviors of UiO-66-AHMT conform well to the pseudo-second-order and Langmuir models, respectively, which indicate that the adsorption process is mainly monolayer chemisorption. Meanwhile, UiO-66-AHMT shows strong selectivity to Hg(II) in the coexistence of varieties of metal ions and outstanding recyclability characteristics. To investigate the adsorption mechanism, the Hg(II) loaded UiO-66-AHMT mainly analyzed by XPS suggests that the nitrogen- and sulfur-containing groups in grafted molecule have the synergistic complexation to Hg(II). Furthermore, the binding strength between different function sites and Hg(II) are quantified and the stable complexation patterns are obtained based on the DFT calculation. These results strongly confirm that UiO-66-AHMT is a potential adsorbent in the practical treatment of wastewater containing Hg(II).