Designing of biosafe, multifunctional alginate-nanoclay hydrogels for environmental applications: structure, swelling...

Composite hydrogels (HGs) based on sodium alginate (Alg), with nanoclay montmorillonite (MMT) and LaponiteRD (Lap) fillers, were synthesized using ionic cross-linking with calcium ions (Ca²⁺). The HGs structure was investigated by SEM-EDX, XRD, and FTIR, whereas сation exchange capacity (CEC) and variable surface charge were determined using potentiometric titration. The influence of filler content, cross-linking agent concentration, and pH on the swelling and sorption capacity towards cadmium ions (Cd²⁺) of HGs was analyzed in detail. The cross-linking agent concentration influenced the swelling mechanism of the alginate-based composites with clays as well as their specific type of water diffusion based on the Fick equation. The CaCl₂ concentration (C_CaCl2) of 0.3-0.5 wt% was found as optimal for synthesizing mechanically stable HGs with a large swelling degree and sorption ability for Cd²⁺ ions. The sorption capacities calculated based on the Langmuir model were 1.36, 1.19, and 1.33 mmol/g for Alg, Alg/20%MMT, and Alg/20%Lap synthesized using 0.3 wt% CaCl₂, respectively. The in vitro tests on genotoxicity and cytotoxicity of HGs, performed using the mouse fibroblast cell culture L-929, proved the biosafety of the developed composites for the environment.