Applicability of diclofenac-montmorillonite as a selective sorbent for adsorption of palladium(II); kinetic and thermodynamic studies

A novel organo-nanoclay, i. e., diclofenac modified montmorillonite was used as a green and selective support for the adsorption of Pd(II) ions from aqueous solution. The diclofenac-montmorillonite composite was prepared and characterized by Fourier transform infrared (FT-IR) spectroscopy, elemental analysis, scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. Batch experiments were carried out with an equilibrium time of 30 min and the kinetics models of the interaction were studied. The selectivity of the sorbent towards Pd(II) was extremely good at a pH of 6.0-7.0, while the adsorption of other cations was low. The adsorption data were measured at room temperature and the yielded Langmuir monolayer capacity was 20.0 mg g(-1). The adsorption reaction was exothermic and the thermodynamic parameters, Delta H, Delta S and Delta G, at room temperature were -34.37 kJ mol(-1), -116.56 J K-1 mol(-1), and + 0.96 kJ mol(-1), respectively. The specific surface area increased from 35.8 m(2) g(-1) to 80.6 m (2)g(-1) for the modified clay, suggesting that intercalation creates a porous framework thereby increasing the surface area and increasing the selectivity of this sorbent for the adsorption of Pd(II) ions. In order to evaluate the applicability of this support for the uptake of palladium from complex matrices, different real samples such as: road dust, rice, urine and water samples were analyzed.