Smart dual responsive alginate grafted copolymeric hydrogel for sorption of recalcitrant methylene green from water

The sorptive removal of recalcitrant dyes from aquatic media holds paramount significance in the contemporary research. The pressing problem has been addressed by facile fabrication and subsequent sorption studies on sodium alginate grafted poly (N-isopropyl acrylamide-co-acrylic acid) [Na-Alg-g-p(NIPAm-co-AAc)] hydrogel for sorption of methylene green (MG). The sorbent achieved equilibrium in 30 minutes, whereas highest sorption capacity was noted at optimum pH 5. At 25°C, the sorbed quantity of the adsorbate enhanced with the rise in initial concentration. The data of isothermal studies fitted well into the Langmuir isotherm as suggested by relatively higher R2 of ≈ 0.98. The sorption obeyed pseudo-second-order kinetics as evidenced by exceptionally higher R2 (0.999) and substantial agreement in experimentally obtained and theoretically calculated second-order rate constant. The validity of Langmuir isotherm and pseudo-second-order kinetic models imply the occurrence of chemisorption between anionic [Na-Alg-g-p(NIPAm-co-AAc)] sorbent and cationic MG. Moreover, the material exhibits dual (pH and temperature) responsive nature because the amount sorbed undergoes variation with change in temperature and pH. The results signify potential candidature of the fabricated sorbent for the reclamation of dye contaminated water and related applications.