Water is contaminated by different toxicants such as anions, cations, and organic waste products. In this regard, this study reveals the removal of Cr 2 O 7 ions from water using calix[4]arene modified silica (CMS) resin under the optimized conditions of concentration, pH, resin dosage, and effects of temperature. During the experiments, it was noticed that the adsorption of Cr 2 O 7 ions onto CMS resin is highly pH-dependent and has high adsorption capacity using only 25 mg of resin. The adsorption equilibrium data have been subjected to different isotherm models such as Langmuir, Freundlich, and Dubinin−Radushkevich (D-R). From the results, it has been observed that the Freundlich model is the best fit for an adsorption phenomenon as compared to the Langmuir model, while the D-R model demonstrates that the adsorption is an ion exchange type according to the values of E (kJ/mol). The thermodynamic study reveals that the values of ΔH, ΔG, and ΔS show that the adsorption process is endothermic and spontaneous. Dichromic acid (H 2 Cr 2 O 7 ) and its conjugated base (Cr 2 O 7 2− anion) were optimized at the B3LYP/LANL2DZ/6-311++G(d,p) level by using G09W software to analyze the adsorbate-adsorbent interaction mechanism. The efficiency and adsorption capacity of CMS resin have also been checked on real wastewater collected samples.
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