Chloride adsorption on aminobenzoate intercalated layered double hydroxides: Kinetic, thermodynamic and equilibrium studies

Abstract

MgAl layered double hydroxides (MgAl-LDHs) directly intercalated with aminobenzoate ions were synthesized by conventional calcination-rehydration method. The kinetic, thermodynamic and equilibrium studies on the chloride adsorption of the as-fabricated LDHs were performed by batch experiment technique. Besides, the microstructures of as-obtained MgAl-LDHs were observed by X-ray diffraction and FT-IR spectra. The results indicate that the chloride adsorption on the MgAl-LDHs is significantly affected by the initial pH value, LDHs dosage and contact time. Langmuir isotherm can provide a better fit for the experimental data of Cl− adsorption on the MgAl-LDHs than Freundich isotherm. The negative values of Gibbs free energy change (ΔG0) and standard enthalpy change (ΔH0) for the process calculated using Langmuir constants are obtained, confirming the spontaneous and exothermic nature of the chloride adsorption process. In addition, the quasi-second order kinetic model is well suitable to describe the chloride adsorption process. The anion exchange in the interlayer of MgAl-LDHs is contributed to the Cl− adsorption, which has been demonstrated by the microstructure observation.