Preparation and characterization of Poly(Acrylamide/N-vinyl imidazole) copolymers by gamma irradiation and their usability in anionic dye adsorption

In this study, Poly[(Acrylamide/N-vinyl imidazole) (P(AAm/VIm)) hydrogels were prepared by γ-irradiation of ternary mixtures of Acrylamide (AAm)-N-vinyl imidazole (VIm)–water with gamma-irradiation using a 60Co γ-source. Solutions of AAm and VIm monomers were prepared using a fixed amount of water in five different compositions (AAm/VIm mole percent ratios: 100/0, 80/20, 72/28, 61/39, 0/100). The prepared monomer mixtures were irradiated at a 60Co-gamma source (1-144 kGy) with a dose rate of 0.938 kGyh-1. Gelation of 100% was reached at around 25 kGy irradiation dose at the end of irradiation. The synthesized hydrogels was characterized by FTIR and TGA methods. Swelling and diffusion properties were determined in water and aqueous GY dye solution. Dynamic swelling experiments were carried out at various pH values and 25°C for different composition of P(AAm/VIm) hydrogels and some important parameters such as swelling ratio at equlibrium (Smax), initial swelling ratio (ro), and diffusion coeficients (D) were calculeted from obtained data. The water and aqueous Golden Yellow (GY) dye solution transport mechanism into copolymeric hydrogels which have high containing VIm was evaluated whether it is Fickian type (diffusion-controlled) and/or non-Fickian type (non-diffusion-controlled) mechanism for copolymeric hydrogels containing higher amount of VIm and those of partially quaternized. The removal of anionic dye, GY (Reactive Yellow 145) from the aqueous solution by using the newly synthesized P(AAm/VIm) hydrogel in the batch system was investigated by adsorption. The effects of the initial concentration of dye solution, initial pH value of solution, hydrogel dosage, contact time and stirring speed on the adsorption process were studied. It was determined that the amount of the adsorbed dye from aqueous and aqueous dye solutions increased at pH 3,0 and hydrogel which containing high VIm content. The maximum percent adsorption was observed to occur at pH 3.0 while the initial dye solution concentration, initial pH value, contact time, stirring speed, and hydrogel dosage were 12.5 mgL-1, 3.0, 150 minute, 400 rpm, and 0.5 g 20mL-1, respectively, the efficiency of dye adsorption on hydrogels was 100.0%. Dimethylsulfate was used as a methylation reagent to partially quaternize the P(AAm/VIm) hydrogel, abbreviated as P(AAm/VIm)3, which is one of the P(AAm/VIm) hydrogels with the highest VIm content, in order to adsorb a higher amount of anionic dye. Spectroscopic and thermal analyses of these hydrogels as a function of quaternization showed that the results are consistent with the existence of quaternized groups when the imidazole rings are partially quaternized. The presence of quaternized monomers in the copolymers were approved spectrophotometrically. P(AAm/VIm)3 hydrogel with the highest VIm content and partially quaternized P(AAm/VIm)3Q hydrogel were used as adsorbents in the removal of GY dye from aqueous solutions. The effects of pH, the initial GY concentration on the adsorption process of GY onto hydrogels were studied and from the obtained data; the isotherm and kinetic parameters of adsorption were calculated. In kinetic evaluations, pseudo-second-order kinetic model was performed, and the suitability of the adsorption equilibrium with Langmuir and Freundlich, Dubinin-Radushkevich isotherm models was investigated. Langmuir, Freundlich, Temkin and Dubinin-Radushkevich adsorption isotherms were used to express the relationship of GY dye with P(AAm/VIm) and partially quaternized copolymeric hydrogel and kinetic analyzes were performed. The correlation coefficient (R2) was used as an indicator of the best model fit of the different models and it was determined that the equilibrium data fit the Langmuir isotherm model and the pseudo second order kinetic model which have large R2 values.The results showed that P(AAm/VIm) hydrogels could be used as a suitable adsorbent to remove anionic dyes from contaminated water.