Equilibrium, kinetics, and thermodynamics of Pd(II) adsorption onto poly(m-aminobenzoic acid) chelating polymer

Abstract

This study describes the equilibrium, kinetics, and thermodynamics of the palladium(II) (Pd(II)) adsorption onto poly(m-aminobenzoic acid) (p-mABA) chelating polymer. The p-mABA was synthesized by the oxidation reaction of m-aminobenzoic acid monomer with ammonium peroxydisulfate (APS). The synthesized p-mABA chelating polymer was characterized by FTIR spectroscopy, gel permeation chromatography (GPC), thermal analysis, potentiometric titration, and scanning electron microscopy (SEM) analysis methods. The effects of the acidity, temperature, and initial Pd(II) concentration on the adsorption were examined by using batch adsorption technique. The optimum acidity for the Pd(II) adsorption was determined as pH 2. In the equilibrium studies, it was found that the Pd(II) adsorption capacity of the polymer was to be 24.21 mg/g and the adsorption data fitted better to the Langmuir isotherm than the Freundlich isotherm. The kinetics of the adsorption fitted to pseudo-second-order kinetic model. In the thermodynamic evaluation of the adsorption, the ΔG° values were calculated as -16.98 and -22.26 kJ/mol at 25-55°C temperatures. The enthalpy (ΔH°), entropy (ΔS°), and the activation energy (Ea) were found as 35.40 kJ/mol, 176.05 J/mol K, and 61.71 kJ/mol, respectively. The adsorption of Pd(II) ions onto p-mABA was a spontaneous, endothermic, and chemical adsorption process which is governed by both ionic interaction and chelating mechanisms.