An efficient pH sensitive hydrogel, with biocompatibility and high reusability for removal of methylene blue dye from aqueous solution

An efficient method for the removal of methylene blue dye (MB) (cationic-dye) from aqueous solution under alkaline conditions was explored, by synthesizing and utilizing suitable pH sensitive poly (acrylic acid-co-vinylsulfonic acid) hydrogel (PAAVSA). The hydrogel was synthesized by free radical polymerization reaction using optimum ratio of the acrylic acid and vinylsulfonic acid monomers. The functional groups present in PAAVSA (i.e. COO− and SO3− groups) have strong affinity with positively charged (cationic) dye molecule, enabling absorption and trapping of cationic dyes from aqueous solution. Synthesized PAAVSA was characterized by Raman and Fourier-transform-infrared-spectroscopy techniques, while significant pH response of PAAVSA, was evident through swelling studies, indicating large swelling ratio, ~250, at higher pH values. Field-emission-scanning-electron-microscopy (FESEM) images of the respective freeze-dried PAAVSA samples swelled at different pH, exhibit distinct pH-responsive change in surface morphology of the hydrogel. PAAVSA shows significant efficiency as an adsorbent for the removal of cationic dyes (MB-dye) from aqueous solution at higher pH values (pH 7 and above), along with biocompatibility and excellent reusability, leading to potential application in waste-water treatment. The adsorption kinetics and isotherm analysis indicate that the overall adsorption process was governed by chemisorption through heterogeneous surfaces having different activation energies for adsorption of MB-dye.