A novel mercapto-functionalized bimetallic Zn/Ni-MOF adsorbents for efficient removal of Hg(II) in wastewater

Abstract

Heavy metals, especially mercury ions, pose extreme hazards to human health and environmental sustainability. Receiving significant interest lately, metal-organic frameworks with mercapto-functionalization (SH-MOFs) have shown impressive efficacy in effectively eliminating highly hazardous Hg(II) from wastewater. In this investigation, a novel mercapto-functionalized Zn/Ni bimetallic MOF (ZNM-2) was synthesized utilizing a simple solvothermal technique employing zinc and nickel as metal sources and 2-mercaptobenzimidazole (MBI) as the organic ligand. The Hg(II) adsorption capacity by ZNM-2 reached 744.4 mg/g, surpassing that of a single-nickel MOF (NM) 328.8 mg/g. More impressively, ZNM-2 successfully eliminated 99.99 % of Hg(II) from actual water samples, achieving a concentration level for Hg(II) that is lower than the threshold of 1.0 μg/L specified in the GB 5749–2022 drinking water standard. When the pH of Hg(II) solution ranged from 2.0 to 6.0, it exhibited exceptional adsorption capacity and sustained high removal efficiency throughout four consecutive regeneration cycles. The adsorption mechanisms observed in this study were found to conformity with the Langmuir model and PSO kinetic model, suggesting that the predominant mode of Hg(II) adsorption is through a chemisorption process occurring at a monolayer level. The superior Hg(II) removal rate of ZNM-2 can be attributed to the predominant coordination of Hg(II) to the thiol (-SH) groups, as revealed by a combination of FT-IR, XPS analysis, and DFT calculations. Therefore, ZNM-2 is an efficacious Hg(II) absorbent that provides a novel approach to alleviate mercury contamination in wastewater.