Combined experimental and theoretical investigation on selective removal of mercury ions by metal organic frameworks modified with thiol groups

Highly efficient and selective extraction of mercury from wastewater is still a challenging issue for public health and ecosystem protection. Herein, defective UiO-66 modified with thiol groups (denoted as UiO-66-SH) was achieved through a facile method under mild conditions and applied for the selective extraction of mercury from aqueous solutions. UiO-66-SH displayed a fast adsorption rate for Hg(II) ions with a high pseudo-second-order rate constant of 3.4 × 10⁻² g/(mg·min) and a high adsorption amount of 3.91 mmol/g. In addition, UiO-66-SH showed high adsorption performance over a broad pH range (2.3–8.0) and retained high effectiveness (>90%) after being regenerated seven times. Moreover, it displayed selective adsorption towards Hg(II) ions under the inteference of divalent metal ions (i.e., Co²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Ba²⁺ and Mn²⁺). However, it's adsorption rate decreased by an average of 30 and 40% under interfering Zn(II) and Pb(II), respectively. Experimental data and density function theory (DFT) calculations disclosed that the excellent extraction effectiveness could stem from the strong interaction between Hg(II) ions and the thiol groups in the surface of UiO-66-SH. The results of DFT calculations carried out for the capture of Ba²⁺, Zn²⁺, Pb²⁺, and different Hg(II) species (Hg²⁺ and Hg(OH)⁺) provided a reasonable explanation for the selectivity and the slight decrease of the adsorption rate with the increase of solution pH. UiO-66-SH also provided a high affinity for organic mercury forms (MeHg⁺, EtHg⁺ and PhHg⁺). Therefore, our approach to functionalize the defective UiO-66 by thiol groups would provide a new insight for mercury decontamination in the cleanup of environmental pollution.