Thiol-modified ZIF-8 composite materials: Lead ion adsorption performance and synergistic action mechanism

The development of high-efficiency adsorbents for addressing Pb(II) contamination in aquatic environments remains an urgent challenge in environmental remediation. This study presents a novel thiol-functionalized ZIF-8-based adsorbent (ZIF-8-TMT) with a stable 3D framework and abundant thiol groups, designed to overcome the limitations of conventional adsorption materials. The synthesized ZIF-8-TMT demonstrated a substantial BET surface area (456.58 m 2 /g) and numerous active adsorption sites, exhibiting exceptional Pb(II) adsorption capacity (494.9 mg/g) that surpassed most previously reported adsorbents. Systematic characterization revealed that the composite achieved rapid adsorption kinetics, with approximately 80 % removal efficiency within 30 min, and maintained excellent regenerability - showing negligible capacity reduction after three adsorption-desorption cycles and retaining over 60 % removal efficiency after five cycles. The adsorption mechanism was comprehensively investigated through Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and computational simulations including density functional theory (DFT), bond order density (BOD), and natural adaptive orbital (NAdO) analyses. Results indicated that the superior adsorption performance originated from synergistic effects between electrostatic interactions and dual coordination involving the N3 atoms in 2-methylimidazole ligands and thiol (-SH) groups from TMT. This study not only provides fundamental insights into the coordination chemistry of Pb(II) adsorption but also demonstrates the practical potential of ZIF-8-TMT for wastewater treatment applications, offering a promising solution for heavy metal pollution control with its combination of high capacity, rapid kinetics, and excellent reusability.