Investigation of dye adsorption onto poly(vinyl imidazole) hydrogel and its quaternized derivatives

In this study, poly(vinyl imidazole) (p-VIm) hydrogel cross-linked with the ratio of 1.2% was synthesized by using free radical polymerization and then this hydrogel was quaternized partially by straight-chained alkyl halides including different numbers of carbon atoms. The functional groups of the synthesized p-VIm and its partially quaternized derivatives were analyzed by using Fourier Transform Infrared Spectroscopy (FT-IR); the surface morphologies were investigated by Scanning Electron Microscope (SEM). The partially quaternization of P-VIm hydrogel was supported by elemental analysis, Energy Dispersive X-ray Spectroscopy (EDS) and zeta potential measurements. The surface areas of hydrogels were measured by Brunauer-Emmett-Teller (BET) method and the equilibrium swelling ratio was determined in pure water at room temperature by gravimetric method. p-VIm hydrogel and its partially quaternized derivatives were used as an adsorbent to remove of Orange II (OII) from aqueous solutions. The effects of pH, the initial OII concentration and the temperature on the adsorption process of OII onto hydrogels were studied and by using obtained data; the isotherm, kinetic and thermodynamic parameters of adsorption were calculated. Kinetic evaluations were performed by Lagergren-first-order, pseudo-second-order kinetic and intraparticular diffusion models and adsorption equilibrium was studied by Langmuir and Freundlich isotherm models. Changes of enthalpy, free energy and entropy and activation energy of the adsorption process were also calculated by using kinetic parameters.