Poly(AA-co-VPA) hydrogel cross-linked with N-maleyl chitosan as dye adsorbent: Isotherms, kinetics and thermodynamic investigation.

In this study, hydrogel polymer was synthesized by incorporation of acrylic acid (AA), vinylphosphonic acid (VPA) and N-maleyl chitosan which was prepared through the acylation reaction between maleic anhydride and chitosan. N-maleyl chitosan crosslinked P(AA-co-VPA) hydrogel was utilized for the effective adsorption of crystal violet (CV) and methylene blue (MB) dyes from aqueous solutions. The synthesized hydrogel was characterized by using FTIR, SEM, EDS, TGA-DTA, and DSC methods. The effecting parameters on adsorption of dyes such as initial concentration of dyes, temperature, pH and adsorbent polymer dose were studied. The adsorption isotherm was analyzed in different temperature using Langmuir, Freundlich, Temkin and Redlich-Peterson models and the adsorption data were well described by Redlich-Peterson isotherm model. The adsorption kinetics was analyzed using pseudo first-order, pseudo second-order, intraparticle and film diffusion models in 20, 30, 40 and 50 mg/L of dye solutions and the adsorption data were well described by pseudo-second-order model. The maximum adsorption capacity of the hydrogel polymer for removal of CV and MB in 50 mg/L of dye solutions was 64.56 mg/g and 66.89 mg/g, respectively. Thermodynamic studies recommended that the adsorption process was endothermic and spontaneous. Furthermore, the adsorbent was successfully employed for successive four cycles of adsorption-desorption.