Effect of Iminodiacetic Acid on the Temporal Dependence of Chromium Sorption in Poly(ethylene glycol)-Based Hydrogels

Abstract Chromium remains a persistent concern because of its industrial use and its risks to ecosystems and human health. Its behavior and toxicity depend on its chemical speciation, mainly on its oxidation states Cr(III) and Cr(VI). Speciation analysis remains a challenge, and the proposal of innovative materials as substitutes for solid-phase extractors or preconcentrators is relevant. However, the sorption pathways and ligand-induced changes in hydrogel matrices remain less understood. In this work, poly(ethylene glycol)-based hydrogels were prepared by modification with glycidyl methacrylate and cross-linked with N,N′-methylenebis(acrylamide). The hydrogel properties were characterized by swelling, scanning electron microscopy, Brunauer–Emmett–Teller surface area, and point of zero charge determination. We found that after incorporation of iminodiacetic acid, the internal structure of the hydrogel changed, increasing pore size from mostly below 5 μm to approximately 100 μm and decreasing the surface area from 566 to 229 m2 g–1. In addition, the point of zero charge remained close to pH 7.0 for both materials. Chromium sorption assays revealed higher affinity for Cr(III) than for Cr(VI). Compared to the control hydrogel, the presence of iminodiacetic acid in the hydrogels delayed Cr(VI) sorption; uptake began only after approximately 300 min, achieving about 40% after 1440 min. Cr(III) sorption followed pseudo-second-order behavior combined with intraparticle diffusion after iminodiacetic acid incorporation, whereas Cr(VI) sorption was better described by the Avrami model, indicating a complex multistep process. Adsorption isotherm data showed that the Freundlich model best described chromium sorption by both hydrogels. Acid desorption assays demonstrated a virtually quantitative release of Cr(III) from the control hydrogel but only about 72% from the hydrogel containing iminodiacetic acid, corroborating stronger retention of Cr(III) via chelation. These results show that iminodiacetic acid incorporation modulates not only chromium affinity but also the sorption kinetics in poly(ethylene glycol)-based hydrogels.