In situ synthesis of Fe3O4 nanocatalyst in chitosan-agarose hydrogel membranes for the sustainable and efficient degradation of organic compounds.

The efficient degradation of organic pollutants is critical for environmental sustainability, driving the search for eco-friendly catalytic materials. Biopolymer-based magnetic hydrogels are promising candidates, though current systems often face challenges such as poor mechanical stability, uneven nanocatalyst distribution, and complex synthesis. Here, we present a green, simple, and scalable method for fabricating chitosan-agarose dual-network hydrogels incorporating Fe₃O₄ nanoparticles (NPs) synthesized in situ from two iron salts. This strategy ensures uniform NPs dispersion within a mechanically robust and biocompatible matrix, enabling multifunctional hydrogels that combine catalytic efficiency, magnetic responsiveness, and reusability. The Fe₃O₄ content was systematically varied to tune the hydrogel's physicochemical, mechanical, and magnetic properties. Structural characterization by X-ray diffraction and transmission electron microscopy confirmed successful in situ Fe₃O₄ NPs formation, with differences in size and morphology depending on the iron precursor. Rheological analysis showed increased stiffness with higher Fe₃O₄ content, while swelling tests revealed reduced water uptake due to pore filling. Catalytic performance was evaluated using model pollutants achieving up to 94 % degradation within 90 min under mild conditions. These nanocomposite hydrogels offer a sustainable, magnetically recoverable, and reusable platform for efficient pollutant removal, highlighting the synergistic advantages of dual-biopolymer matrices and in situ nanocatalyst formation for water remediation.