Mild synthesis of mercapto zeolitic imidazolate frameworks for selective removal of mercury ion from aqueous solution

Mercury is a biotoxic water pollutant. Zeolitic imidazolate frameworks (ZIFs) are potential adsorbents for heavy metal ion due to their high specific surface area, tunable pore structure and designable surface chemistry. To address challenges such as tedious and high-energy consumption in synthesis processes. In this work, two novel mercapto ZIFs (zinc-2-mercaptobenzimidazole ZIF, Zn-2-SH-Bim; zinc-2-mercaptoimidazole ZIF, Zn-2-SH-Im), were successfully synthesized by a mild solvent-assisted evaporation synthesis strategy. The results show that in the presence of coexisting metals, the adsorption capacity of Zn-2-SH-Bim for Hg²⁺ is 12.86 times that of the Zn-2-SH-Im, indicating that the introduction of benzene ring on the ligand significantly increases the adsorption capacity. The maximum adsorption capability of Zn-2-SH-Bim for Hg²⁺ is 483.03 mg·g⁻¹, consistent with the Langmuir and pseudo-second-order kinetic model. The Zn-2-SH-Bim displays a partition coefficient of 190,596 mL·g⁻¹ for Hg²⁺, Hg²⁺/Ni²⁺ separation factor of 23,766, removal rate of 99.17 % and excellent reusability. Experiments and DFT calculations confirm the stability and good coordination of Zn-2-SH-Bim with Hg²⁺, demonstrating excellent performance for eliminating Hg²⁺ from wastewater and offers valuable insights into the synthesis of mercapto ZIFs using mild syntheses strategies.