Mechanisms and kinetics of chelating reaction between chitosan and Pd(II) in chemical plating pretreatment

Abstract

The adsorption capability and kinetics of the adsorption of Pd(II) on polyester fabric treated with chitosan have been studied. Batch adsorption experiments were carried out in which the experimental parameters such as the initial metal ion concentration, contact time and temperature were varied. Langmuir and Freundlich isotherm models were employed to analyze the experimental data. The best approximation to the experimental data was given by the Langmuir isotherm and the maximum adsorption capacity was found to be 1.241 mg·g-1 for Pd(II) on chitosan. The kinetic data were analyzed using pseudo-first-order and pseudo-second-order kinetic models. The data correlated well with the pseudo-second-order kinetic model, indicating that the chemical sorption was the rate-limiting step. The thermodynamic parameters like Gibbs free energy (ΔG° ), enthalpy (ΔH°) and entropy (ΔS° ) were also evaluated by applying the Van’t Hoff equation. The results indicated the exothermic nature of the adsorption process. This study offers a general model for the study of the kinetics of reactions between chitosan and metal ions on a polyester fabric base. It could be confirmed that the Pd-chitosan layer was deposited on polyester fabric when observed by scanning electron microscopy (SEM) and scanning probe microscopy (SPM).