pH-responsive poly (xanthan gum-g-acrylamide-g-acrylic acid) hydrogel: Preparation, characterization, and application.

Poly (xanthan gum-g-acrylamide-g-acrylic acid) (XGDA) hydrogel was prepared by grafting acrylamide (AM) and partly neutralized acrylic acid (AA) onto xanthan gum (XG) with trimethylolpropane triglycidyl ether as a cross-linking agent. With the introduction of amino and carboxyl groups by AM and AA, the XG molecules were rearranged with better regularity, leading to higher thermal stability and a more porous structure. The resulting hydrogel exhibited excellent performance in Cu (II)-adsorption and possessed sensitivity to external pH stimuli. The adsorption kinetics and adsorption equilibrium were best described by a pseudo-second-order model and Freundlich isotherms, respectively. The thermodynamic parameters indicated that the adsorption is a spontaneous, endothermic, and a process that increases entropy. The maximum equilibrium adsorption capacity of Cu (II) was 130.31 ± 2.97 mg/g. The XGDA can be regenerated and reused in the following adsorption process. This pH-sensitive hydrogel has potential to be used for the uptake of heavy metal ions from aqueous solution.