Equilibrium, thermodynamic, and kinetic modeling studies for the adsorptive removal of oxyanions from water

Abstract

Water is being contaminated by different oxyanions which have many negative effects on the human body. This study deals with the adsorptive removal of Cr₂O₇⁻², AsO₄⁻³, and ClO₄⁻¹ oxyanions from water using diethanolaminomethylcalix[4]arene bonded silica (DBS) resin. The capacity of DBS resin for the removal of oxyanions was checked through batch method under the optimized parameters such as pH, adsorbent dosage, concentration of oxyanions, and effect of temperature. The experimental data were analyzed through Langmuir, Freundlich, and Dubinin–Radushkevitch (D–R) adsorption isotherm models and the Langmuir model was the best fit model with a good correlation coefficient (R² 0.998). The thermodynamic and kinetic studies were performed to check the mechanism and adsorption pathway of oxyanions onto DBS resin. The thermodynamic parameters such as (ΔH°, ΔS°, and ΔG°) describes that the adsorption of oxyanions was spontaneous and endothermic and followed by pseudo second order kinetic models very well. The reusability of resin was also checked and it has been observed that after 27 cycles only 2% loss in adsorption capacity. Moreover, the oxyanions were optimized at the B3LYP/LANL2DZ/6-311++G (d,p) level using G09W software to analyze the oxyanions-DBS interactions phenomenon. Graphical abstract