Effective adsorption of mercury by Zr(IV)-based metal-organic frameworks of UiO-66-NH2 from aqueous solution

In this study, Zr-based metal-organic frameworks (MOFs) of UiO-66 and UiO-66-NH2 were synthesized and applied to removal of mercury from aqueous solution. The characterizations of UiO-66 and UiO-66-NH2 were examined by X-ray diffraction (XRD), scanning electron microscope (SEM), and thermogravimetric analysis (TGA). To investigate the adsorption properties of UiO-66-NH2 for mercury, the experiments of kinetics, isotherm, pH, temperature, and salt concentration were conducted, and the results were compared with those by UiO-66. The result showed that UiO-66-NH2 has a higher adsorption capacity for mercury than UiO-66. The maximum adsorption capacity of UiO-66-NH2 was 223.8 ± 17.8 mg g−1 at 313 K. The salt concentration of NaCl has a significant effect on the adsorption of mercury on UiO-66, while UiO-66-NH2 can maintain the stable adsorption capacity for mercury in the concentration range of 0.1–0.5 M NaCl. Adsorption thermodynamics result indicated that the adsorption process of mercury on UiO-66-NH2 was spontaneous and endothermic. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses showed that the mercury was successfully adsorbed on the surface of UiO-66-NH2 and amino functional group as a soft base played a major role to react with mercury during the adsorption process.