Eco-Friendly Nanocomposite Hydrogel Beads Filled with Organobentonite as Potential Multicomponent Adsorbents for Water Remediation

Abstract

This research work is focused on the synthesis of environmentally friendly hydrogel beads based on alginate (Alg) and alginate/carboxymethylcellulose (CMC) blends by simultaneous ionic cross-linking with Ca²⁺ and Fe³⁺ ions, designed as potential multifunctional adsorbents for water remediation treatments. To further enhance their performance, an organomodified bentonite with known adsorption capacity was incorporated, yielding bionanocomposite hydrogels. All the systems were characterized in terms of morphology, chemical structure, thermal stability, and mechanical behavior. Adsorption performance of neat and optimal bionanocomposite hydrogel beads was evaluated using an ethylhexyl ester derivative of 2,4-dichlorophenoxyacetic acid (2,4-D), a widely used herbicide and representative emerging contaminant. Morphological analyses of the beads revealed robust core–shell architectures with smooth external surfaces and heterogeneous internal porosities, especially in biopolymeric blends. Thermal analysis confirmed enhanced stability with increasing cross-linking ions concentration and with the presence of CMC. Incorporation of organobentonite improved surface roughness and porosity, while significantly increasing the removal efficiency and adsorption capacity of 2,4-D. Taking into account all the results, a synergistic effect among the polymer matrix composition, Ca²⁺/Fe³⁺ cross-linking and the organomodified bentonite addition was demonstrated, with the optimal formulation (Alg/CMC blend; 0.5 wt % Ca/Fe cross-linking concentration and 30 wt % organobentonite) achieving 73% removal within the first 2 h and an equilibrium removal efficiency of nearly 90% within 24 h. These findings highlight the combined advantages of dual-ion cross-linking and organoclay reinforcement in Alg/CMC matrices, opening opportunities for the design of sustainable nanocomposite hydrogels with high efficiency and versatility for water remediation treatments.