Eco-Friendly Synthesis of Hydrogels from Starch, Citric Acid, and Itaconic Acid: Swelling Capacity and Metal Chelation Properties

In this study, eco-friendly superabsorbent hydrogels are prepared by the grafting and crosslinking reactions of itaconic acid and citric acid with starch, using potassium persulfate as the free radical initiator. The structure and morphology of the hydrogels are studied using Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The effect of the citric acid to starch ratio on the swelling properties is evaluated, and it is found that equal parts of citric acid and starch produced the highest swelling ratio of 188 g distilled water per g hydrogel. The hydrogels also exhibit pH-dependent behavior, such that the maximum swelling ratio of 232 g/g is obtained at pH 8. Finally, the metal chelation properties of the hydrogel are tested in solutions of copper, nickel, and zinc, and the adsorption capacity followed the trend Cu > Ni > Zn based on the Freundlich parameter K_F.