Sorption of Pt(IV) ions on poly(m-aminobenzoic acid) chelating polymer: Equilibrium, kinetic and thermodynamic studies

Abstract

In this work, poly(m-aminobenzoic acid) (PABA) chelating polymer was synthesized and its sorption behaviors for Pt(IV) ions have been investigated. The PABA polymer was prepared by the reaction of m-aminobenzoic acid with ammonium peroxydisulfate. Fourier transform-infrared spectroscopy (FT-IR), thermal analysis (TG and DTA), field emission-scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and surface porosity analytical methods were used in the characterization of the polymer. The FE-SEM images showed that the particles of the synthesized PABA polymer were about 2-10 μm. The PABA polymer is thermally stable up to 320 °C. The zero charge point of the polymer was found at pH 3.50. Batch adsorption experiments were used to examine the effects of pH, initial Pt(IV) concentration, contact time and temperature. The best adsorption values were obtained at pH 4, in which is above the zero charge point of the polymer. The equilibrium, kinetics and thermodynamics of Pt(IV) adsorption on the PABA polymer were examined. The Pt(IV) maximum adsorption capacity of the polymer is 2362 μg/g. The adsorption kinetic data fitted best to pseudo-second order kinetic model. The calculations with intra-particle diffusion and the Elovich models showed that the adsorption was controlled by intra-particle diffusion and chemisorption. The adsorption data fitted well to the Langmuir isotherm. It was found that the adsorption followed the pseudo-second-order kinetic model. In the thermodynamic calculations, the Gibbs free energies (ΔG°: (−10.98)-(−17.38) kJ/mol), the enthalpy (ΔH°:70.07 kJ/ mol) and the entropy (ΔS°: 215.3 kJ/mol) change values of the adsorption were calculated. The column adsorption-desorption and reusability studies of the PABA polymer were also performed. The results showed that Pt(IV) sorption on the PABA polymer is endothermic and chemical adsorption process which is governed by both ionic interaction and chelating mechanisms.

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“…The decomposition of the polymer backbone in PABA/AV displays the exothermic decomposition at 550°C. 34 Thus, the results of the threestage decomposition from TGA are substantiated in DTA proving the material to be thermally stable.…”