Thermodynamics, Equilibrium and Kinetic Evaluation of Lead Ion Interactions on Zinc Salt of Trimesic Acid MOF in Aqueous Solution

Abstract

Adsorptive interactions between adsorbents and toxic contaminants are significantly exploited to the advantage of water treatment goals. In this study, adsorptive interactions in aqueous solution between Pb (II) ions and a lowly toxic and structurally robust metal–organic framework, zinc-trimesate framework (Zn-H3btc), were evaluated using thermodynamic, equilibrium and kinetic models to establish the capacity of the material to adsorb Pb (II) ions from water. Zn-H3btc was synthesized by refluxing mixtures of zinc nitrate and trimesic acid in DMF solvent and characterized using FTIR, SEM, EDS, PXRD, TGA and DTG methods. Adsorption experiments were carried out on the basis of variation in initial concentration, contact time, pH, adsorbent dosage, and temperature. Langmuir isotherm was the best-fitting isotherm. The maximum monolayer adsorption capacity of Zn-H3btc was 54.05 mg/g. Kinetic studies revealed a pseudo-second-order controlled adsorption process, and hence a chemisorption mechanism. The thermodynamic parameters, Gibbs free energy, ΔG, activation energy, Ea, sticking probability, S*, and isosteric heat of adsorption ΔHx, indicated that the adsorption process was spontaneous and required a minimal energy barrier; however, it had a fairly large amount of isosteric heat (133.39 kJ/mol) released. The findings confirm the applicability of Zn-H3btc as an adsorbent of Pb (II) ions in aqueous solution.