Mercury capture using functionalized metal-organic framework encapsulated in dual hydrogel layers of β-cyclodextrin and polyethylenimine: Synthesis, characterization, adsorption, thermodynamics, and Box–Behnken design analysis

An increasing number of scientists are concentrating on creating methods to eliminate Hg(II) ions from industrial wastewater. Traditional approaches often inadvertently eliminate other valuable metal elements, leading to economic loss. Therefore, it's critical to create materials that can effectively and selectively target Hg(II) ions while preserving other metal supply. The main aim of this study is to develop a new functionalized lanthanum-based metal-organic framework adsorbent, which is modified with glutamic acid and then encapsulated with β-Cyclodextrin (β-CD) and Polyethylenimine (PEI). This process is enhanced by cross-linking with Epichlorohydrin (ECH) to create FLMCP hydrogel beads. The resulting adsorbent is designed for effective and selective capture of Hg(II), utilizing an increased number of practical groups on its surface. The synthesis and characterization of the material showed a surface area of 434.42 m²/g, a pore volume of 0.526 cc/g, and an average pore radius of 1.88 nm. Batch experiments analyzed key adsorption parameters: temperature, Hg(II) concentration, adsorbent amount, and contact duration. The data fit the Langmuir isotherm model, with kinetics following pseudo-second-order. The main adsorption mechanism is chemisorption, as indicated by the computed adsorption energy of 32.14 kJ/mol. The investigation into the impact of temperature on adsorption processes demonstrates an endothermic characteristic. The calculated enthalpy change (ΔHo) is 116.86 kJ/mol.K, signifying that the process requires the absorption of heat. Furthermore, the observed entropy change (ΔSo) of 399.3 J/mol indicates a heightened level of disorder as temperature escalates, which contributes to improved removal efficiency. In addition, the Gibbs free energy change (ΔGo) becomes increasingly negative with rising temperatures, ranging from -0.13 to -10.11 kJ/mol as the temperature varies from 293 to 318 K. This trend suggests a promising condition for the adsorption and removal of Hg(II) ions. This research explores the mechanisms of Hg(II) ions interaction with FLMCP hydrogel beads, which demonstrate excellent reusability across five cycles without notable efficacy loss. Adsorbent stability is evaluated using FT-IR and XRD. Adsorption optimization and analysis utilize Box–Behnken design and Response Surface Methodology.