Selective and Rapid Pb (II) Adsorption by Core–Shell Zinc-Glutamate-MOF @Bth-TFPOT-COF: Thermodynamic and Kinetic Insights

Abstract

Effectively reclaiming Pb (II) adsorbents is crucial for tackling environmental pollution. Metal–organic framework (MOF) and covalent organic framework (COF) composites, with their multiple functional groups, are anticipated to show outstanding Pb (II) adsorption capabilities. Nevertheless, creating and developing COF and MOF composite adsorbents for highly efficient Pb (II) removal remains a challenge. In this study, we synthesized a core–shell ZnGlu@Bth-TFPOT-COF (referred to as M@C) adsorbent via Schiff base reaction. Adsorbent demonstrated remarkable properties, including excellent durability, specificity, and straightforward solid–liquid separation. Under 298 K and pH 6.0 conditions, M@C effectively adsorbed Pb (II) and achieved 49.40 mg/g adsorption capacity within 15 min. Remarkably, it effectively eliminated Pb (II) from a solution containing multiple ions, demonstrating an adsorption efficiency of 99.80% and a K_d (partition coefficient) of 4.99 × 10⁶ mL/g in the presence of 10 other ions. The adsorption process was controlled by the Freundlich isotherm model, and the pseudo-second-order kinetic model validated that multilayer chemisorption was the mechanism for removing Pb (II). A thermodynamic study showed that the removal process was both spontaneous and exothermic. M@C exhibited outstanding adsorption performance, achieving a capacity of 476.19 mg/g, and demonstrated exceptional selectivity. This makes it an excellent material for the efficient and selective removal of Pb (II).