pH-responsive poly(gellan gum-co-acrylamide-co-acrylic acid) hydrogel: Synthesis, and its application for organic dye removal

A poly(gellan gum-co-acrylamide-co-acrylic acid) (GGDA) hydrogel was synthesized by modifying gellan gum (GG) with partly neutralized acrylic acid (AAc) and acrylamide (AAm) under the crosslinking agent trimethyloipropane triglycidyl ether. With the introduction of carboxyl and amino groups by the AAc and AAm, the GGDA showed better regularity than GG, leading to a more porous structure and higher thermal stability. Methylene blue (MB) was used as a model organic dye to evaluate the adsorption capacity of the GGDA. The GGDA exhibited excellent MB adsorption abilities and pH sensitivity. The pseudo-second-order and Freundlich isotherm models produced the best fits for the adsorption kinetics and adsorption equilibrium, respectively. The Gibbs free energy, enthalpy, and entropy of adsorption indicated that the adsorption was a spontaneous, exo-thermic, and entropy-decreasing process. The maximum equilibrium adsorption capacity of MB was 423.46 +/- 13.60 mg/g. This pH-sensitive hydrogel is a potential alternative absorbent for organic dye removal in aqueous solutions. (C) 2020 Elsevier B.V. All rights reserved.