Successful preparation of tercopolymer hydrogel for the removal of toluidine dye from contaminated water: Experimental and DFT study

Polymeric hydrogel with pH-sensitive surface was prepared in this study. The surface morphologies of the synthesized materials were examined using scanning electron microscopy. Surface area and pore sizes of the hydrogels were determined using Brunauer-Emmett-Teller. Fourier transform infra-red spectroscopy was used for the identification of various functional groups on the surface of these adsorbents. These hydrogels were extremely efficient in removing toxic toluidine dye from contaminated water. Kinetics and isothermal models were used for the calculations of adsorption parameters of the synthesized materials. The adsorption data were impeccably explained with pseudo-second order and the Langmuir model as compared to other models. The spontaneity of the reaction was confirmed by thermodynamic study. In this study the value of enthalpy ( increment H degrees) was 7322.6 kJ/mol. The values of Gibbs energy ( increment G degrees) were -453.9, -984.4 and -1515.2 kJ/mol, at 293K, 313K and 333K, respectively, for toluidine dye, which showed that the process is endothermic and spontaneous in nature. Moreover, the value for entropy ( increment S degrees) was calculated as 26.54 Jmol/K for toluidine dye. The interactions of various functional groups on the surface of adsorbent and toluidine dye molecules were studied with density functional theory simulations. The large binding energies (-5.73 to -25/74 kcal/mol) of different complexes showed that the hydrogels had strong affinity for the adsorption of toluidine dye molecules while the negative values revealed that the process is spontaneous and endothermic. These results were consistent with the experimental results. This study revealed that the synthesized hydrogel is efficient adsorbent material for toluidine dye removal from contaminated water. The adsorption capacity of the prepared hydrogel was 526 mg/g for toluidine dye.