Equilibrium, Thermodynamic, and Density Functional Theory Modeling Studies for the Removal of Dichromate Ions from Wastewater Using Calix[4]arene Modified Silica Resin

Abstract

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.

Removal of Uranium-238, Thorium-232, and Potassium-40 from Wastewater via Adsorption on Multiwalled Carbon Nanotubes

“…The adsorption of the mean free energy in uranium-238 is 100 kJ/mol and in thorium-232 is 235 kJ/mol, which corresponds to a physical process. 32 Finally, when the R 2 values in Table 3 are compared, all of the isotherm models fit quite well.…”

“…The constant K ad gives an idea about the mean free energy E (kJ/mol) for adsorption per molecule of the adsorbate when it is transferred to the surface of the solid from infinity in the solution and can be calculated using the relationship given in eq 14 . 32 …”

Preparation of Two Calix[4]arene-Functionalized Biopolymers and Evaluations of Their Extraction Abilities Against Cr(VI)/As(V) Anions

“…It is well known that the pH values of the solution affect the formation of arsenate species. For instance, the H2AsO4form from the arsenate species occurs in the solution at a pH range of 3 and 6, while a higher pH value (8)(9)(10)(11) in the solution leads the divalent HAsO4 2form. The H2AsO4and HAsO4 2forms among the arsenate species are potential to construct the hydrogen bonding along with their electrostatic attraction features to the host molecules.…”

“…Therefore, the U.S. Environmental Protection Agency (EPA) listed dichromate compounds, which are extensively used in various industries such as electroplating, leather tanning, metal finishing, steels fabrication, pigments, textile etc., in as "Group A" human carcinogen [9,10]. Excessive or long-term dichromate exposure can bring out chronic chromium poisoning, and cause severe damage to human health [10][11][12]. Hereby, the World Health Organization (WHO) have recommended the allowable limit contaminant level of dichromate in natural water as 0.05 mg/L [13,14].…”

Synthesis of new functionalized Calix[4]arene modified silica resin for the adsorption of metal ions: Equilibrium, thermodynamic and kinetic modeling studies

“…Both upper and lower rims can be functionalized to bind with neutral molecules, anions, and cations. The calixarenes functionalized by different moieties such as amines, amides, carbonyls, nitriles, and other suitable moieties that can bind to metal ions, anions, and neutral molecules [35,36]. Therefore, the chemical immobilization of calix [4] arene-based frameworks onto silica enhances the reusability, selectivity, loading, or adsorption capacity of an adsorbent [37].…”