Adsorption Properties of Poly(N‐vinylpyrrolidone‐co‐methacrylic acid) Hydrogels

In this study, N‐vinylpyrrolidone (VP)/methacrylic acid (MAA) copolymers have been prepared at three different mole percents for which the methacrylic acid composition is around 5, 10, and 15%. MAA and VP monomer mixtures have been irradiated in a 60Co‐γ source at different irradiation doses and percent conversions have been determined gravimetrically. ∼80% conversion of monomers into hydrogels were performed at 3.4 kGy irradiation dose. Poly(N‐vinylpyrrolidone‐co‐methacrylic acid) P(VP/MAA) hydrogels have been used for the adsorption of some dyes such as Safranine‐O, Methylene Blue from aqueous solutions. These hydrogels were swollen in distilled water and in aqueous solutions of dyes at pH 4.0, 7.0, and 9.0. P(VP/MAA)1 hydrogel which contains the higher methacrylic acid content showed the maximum % swelling at pH 9.0 in water and swelling increased in the order of Safranine‐O>Methylene Blue. Diffusion of water and aqueous solution of dyes within hydrogels was found to be of non‐Fickian character. Diffusion coefficients of water and aqueous dye solution in P(VP/MAA) hydrogels were calculated. In the dye adsorption experiments, the effects of pH, concentration of aqueous dye solution and the composition of hydrogels on adsorption process were investigated. When the pH and concentration of aqueous solutions of dyes and the MAA content in hydrogels increased, the adsorption increased as well. From the adsorption studies, the cationic dyes could be repeatedly adsorbed and desorbed with P(VP/MAA) hydrogel without significant loss in their adsorption capacity.