The adsorptive removal of cationic dye from aqueous solution using Poly (methacrylic acid) Hydrogels:Part-I. equlibrium studies

Abstract

In this work poly(methacrylic acid) hydrogels were prepared by free radical aqueous polymerization of methacrylic acid(MAc) using N,N’ -methylene bisacrylamide (MB) as crosslinker and potassium persulfate (KPS) as initiator. The hydrogels were characterized by FTIR and TG analysis. The gels exhibited pH-dependent swelling behavior, with equilibrium percent mass swellings of about 110 and 403 at pH 1.0 and 7.4 respectively. The swelling exponent, n, was found to be 0.31 and 0.59 respectively, thus indicating a diffusion controlled and chain relaxation controlled swelling at these pH values respectively. The equilibrium adsorption of a cationic dye Methylene Blue (MB) was studied at 25°C using the Langmuir and the Freundlich adsorption isotherm models. The maximum sorption capacity Q0 was found to be 169.43 mg/g. The equilibrium dye uptake was found to increase with the pH of the adsorbate medium and attained an optimum value of 77.8 mg/g for the initial dye concentration of 200 mg/L at 25°C at pH 5.2. The adsorption showed negative temperature dependency thus suggesting exothermic nature of the adsorption process. Finally, the various thermodynamic parameters were also evaluated.