Adsorption of copper(II) ions by zeolite modified with organosilicon thiosemicarbazide

Abstract

The article is devoted to the calculation of the kinetics and thermodynamics of adsorption of copper(II) ions by zeolite activated with hydrochloric acid and modified 1-(3-triethoxysilylpropyl)thiosemicarbazide. For the calculation of the kinetic parameters, we used the Lagergren, Ho, and Mackay equation. The activation energy was found using the Arrhenius equation. For the calculation of thermodynamic parameters, the linearized Van't Hoff equation and the Gibbs-Helmholtz equation were used. A comparison of the determination coefficients of the pseudo-first (from 0.815 to 0.892) and pseudo-second (from 0.995 to 0.999) order models allowed choosing the latter as the leading model for the adsorption of Cu(II) ions. Pseudo-second order rate constants depending on temperature were in the range 0.201-3.915 g⋅mmol-1⋅min.-1. The determined value of the activation energy 42.3 kJ mol-1 was in the range of 40-120 kJ, which is typical for chemisorption of ions Cu(II). Adsorption isotherms were well described by the Langmuir model. Adsorption proceeded with the formation of sorbate monolayer on the outer surface. Adsorption limit values ranged from 0.0016 to 0.0039 mol g-1 depending on temperature from 238 to 309 K. The processes of adsorption of Cu(II) ions on the surface of the modified zeolite occurred spontaneously. A decrease in the Gibbs energy ΔG0 was observed (from -14.20 to -16.29 kJ mol-1) with increasing temperature. Positive enthalpy value Δ𝐻0 (3.6 kJ mol-1) indicated that the adsorption of Cu(II) ions occurred endothermically. Positive entropy value Δ𝑆0 (58.15 J mol-1) indicated an increase in randomness at the interface due to the destruction of the solvation shells surrounding the transition metal ions in solution. Thus, the ratios of kinetic and thermodynamic quantities indicated that a significant contribution to the process of adsorption of Cu(II) ions by a modified zeolite was made by processes associated with the chemical interaction of adsorbate molecules and functional nitrogen and sulphur containing groups of thiosemicarbazide.