Simulation of Pb²⁺ Adsorption Process by Metal-Organic Framework UiO-66-NH₂: A Density Functional Theory Study

Abstract

Background: Lead contamination in aqueous environments poses significant health risks, necessitating effective remediation strategies. Metal-organic frameworks (MOFs) have emerged as promising adsorbents due to their high surface area and tunable properties.

Objective: This study aims to simulate and evaluate the adsorption capability of Pb²⁺ ions from aqueous solutions using the amino-functionalized metal-organic framework UiO-66-NH₂ through density functional theory (DFT) calculations.

Methods: Gaussian 16 software with B3LYP functional and 6-31G(d,p) basis set was employed for structure optimization and adsorption energy calculations. The UiO-66-NH₂ model was constructed using Zr₆O₄(OH)₄ clusters as metal nodes and 2-aminoterephthalic acid as organic linkers. Solvent effects were investigated using the polarizable continuum model (PCM) for water, methanol, ethanol, and chloroform.

Results: The calculated adsorption energy was -186.4 kJ/mol in aqueous medium, indicating favorable adsorption. Pb²⁺ ions primarily interact with amino groups (-NH₂) and carboxylate oxygen atoms with bond distances of 2.48 Å and 2.52 Å, respectively. The theoretical adsorption capacity reached 285.7 mg/g. Solvent effects showed decreasing adsorption efficiency in the order: water > methanol > ethanol > chloroform.

Conclusion: UiO-66-NH₂ demonstrates high potential for Pb²⁺ removal from aqueous solutions due to its porous structure and specific binding sites. The study provides valuable insights into the molecular-level adsorption mechanism and solvent effects.