Enhancing Corn Starch Hydrogels for Effective Sorption of Potentially Toxic Metals: The Role of Amylose and Amylopectin Content

Abstract

This study evaluated the effect of corn starch's amylose/amylopectin content on the development of crosslinked hydrogels with trisodium citrate for the sorption of potentially toxic metals (PTMs). The results, obtained through a robust methodology, indicated a clear relation between the amylose content and crosslinking degree, thereby impacting the properties of the hydrogels. The hydrogel with high amylose (70 wt.%) and low amylopectin (30 wt.%) content (Hylon VII®) demonstrated a high crosslinking degree (0.297) and good thermal stability and water absorption (72.71%), with a semicrystalline structure. The hydrogel with low amylose (1.8 wt.%) and high amylopectin (98.2 wt.%) content (Amisol 4000®), on the other hand, showed the lowest degree of crosslinking (0.109), water absorption (49.77%), and high solubility (46%), which makes its applicability difficult due to its low stability in aqueous media. The influence of amylose (28 wt.%) and amylopectin (72 wt.%) content indicated that the Amisol 3408® hydrogel showed valuable properties, presenting a higher potential for PTMs sorption with the following affinity order: Cu²⁺ (68.62%) > Cd²⁺ (63.13%) > Mn²⁺ (37.36%) > Zn²⁺ (26.61%) > Cr⁶⁺ (16.80%). Besides, the possible sorption mechanism was ion exchange between Cu²⁺/Cd²⁺/Mn²⁺/Zn²⁺ and H⁺ in the hydrogels. Thus, starch-based hydrogel is an alternative sorbent to remove and recover PTMs from wastewater.