Post-modification of Uio-66-NH2 based on Schiff-base reaction for removal of Hg2+ from aqueous solution: Synthesis, adsorption performance and mechanism

A novel composite adsorbent, Uio-66-NH2/AHMP, was successfully synthesized by post-modifying Uio-66-NH2 with 6-amino-4-hydroxy-2-mercaptopyrimidine based on the Schiff-base reaction and applied to remove Hg2+ from aqueous solution. The Uio-66-NH2/AHMP was characterized by Field emission scanning electron microscopy (FE-SEM), X-ray diffractometer (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and Brunner Emmet Teller (BET). The characterization results shown that sulfur/nitrogen/oxygen-containing groups were successfully introduced on the zirconium-based MOF, and that the pore structure of Uio-66-NH2/AHMP mainly contains mesopores. Subsequently, the adsorption and regeneration performance of composite Uio-66-NH2/AHMP were investigated by batch experiments, the effect of solution pH, sorbent dose, reaction time, initial Hg2+ concentration, and coexisting metal ions on the removal performance of Hg2+ were evaluated. The pH value of solution determined the charge distribution on the adsorbent surface and the form of Hg2+ in aqueous solution based on experimental results and zeta potential analysis. The obtained equilibrium time and maximum adsorption capacity were 60 min and 232.5 mg/g at pH 6, 298 K, respectively. The adsorption process of Hg2+ was consistent with the pseudo-second-order kinetic and the Langmuir model. The results of regeneration studies shown that the removal efficiency of 79.2 % could be obtained after four adsorption–desorption cycles. Besides, Uio-66-NH2/AHMP exhibited excellent adsorption selectivity for Hg2+. XPS analysis indicated that the removal process was dominated by chelation between Hg2+ and nitrogen/sulfur/oxygen-containing groups. This work indicates that the Uio-66-NH2/AHMP has a good application prospect in the removal of Hg2+ from aqueous solution.