Effective removal of divalent metal ions: synthesis and characterization of pH-sensitive guar gum based hydrogels

The present paper reports the modification of Guar gum network through grafting of acrylamide by free radical polymerization. The amide groups in the grafted network have been subsequently hydrolyzed by saponification. The hydrogels have been characterized by FTIR, Elemental Analysis, DSC, and TGA techniques. The nature and extent of swelling of these hydrogels is observed to be dependent on gel structure and pH. The pH dependence of uptake capacity of the hydrogels for metal ions Cu, Ni, Pb, and Zn2+ has been studied. The results reveal a very high metal uptake capacity of modified hydrogel attributed to the presence of carboxylic acid functionality. The metal adsorption is found to follow pseudo-first-order kinetics under pH 1.2 and pseudo-second-order kinetics under pH 7.0.