Effective Removal of the Direct Black-38 Dye from Wastewater Using a New Silica-Modified Resin: Equilibrium and Thermodynamics Modeling Studies

In this study, the synthesis of p-diethanolaminomethylcalix[4]arene and its immobilization on a silica surface have been performed for the removal of the direct black (DB-38) dye from wastewater samples. The newly synthesized p-diethanolaminomethylcalix[4]arene-immobilized silica (DIS) resin has been analyzed and characterized by FTIR spectroscopy and SEM techniques. To check the efficiency of the DIS resin, batch and column adsorption procedures have been applied under the optimized parameters, i.e., resin dosage, pH, and temperature. To validate the experimental data, Langmuir, Freundlich, and D-R models have been applied. The results show that adsorption follows the Freundlich model well with a good correlation coefficient (R-2 = 0.999). Moreover, the energy E (kJ/mol) was calculated with the help of the D-R model, which suggested that the adsorption has an ion exchange nature. The DIS resin was also applied to real industrial samples of DB-38 dye wastewater. The results show that the DIS resin removes 99% of the dye successfully. Thermodynamics studies were conducted to know the feasibility and the mechanism of the adsorption reaction. The thermodynamic parameters show that the adsorption is spontaneous and exothermic. The theoretical calculation was performed at the B3LYP/DZP calculation level of the ADF program, and the power of the interaction between adsorbent and dye molecules can be determined in the light of chemical reactivity analysis.