Chitosan@Fe₂O₃/Ag/Cu nanocomposites: Multifunctional catalysts for accelerated reduction and oxidative reactions

The present work reports the fabrication and evaluation of chitosan-derived hydrogel matrices decorated with trimetallic Fe₂O₃/Ag/Cu nanoparticles for rapid removal of toxic organic dyes in aqueous media. Chitosan-based hydrogels (CDNH) were synthesized using 2-dimethylaminoethyl acrylate (DMAEA), methyl methacrylate (MMA), and N-hydroxymethyl acrylamide (NHMA) via free radical solution polymerization initiated by potassium persulfate. NHMA, containing both vinyl and hydroxyl functionalities, played a crucial role in tailoring the hydrogel crosslinked network structure. To optimize crosslinking density, three hydrogel grades were prepared by varying NHMA content. Trimetallic Fe₂O₃/Ag/Cu nanoparticles were synthesized through a co-precipitation route, while the CDNH@ Fe₂O₃/Ag/Cu nanocomposites were synthesized through a hydrothermal process, fabricating three composite grades (CDNH@Fe₂O₃/Ag/Cu NC-1 to NC-3). The hydrogels and nanocomposites were characterized using EDX, FTIR, SEM, TEM, TGA, UV-visible spectroscopy and XRD, to analyse the chemical and physical properties. Methylene blue (MB) dye used as a model pollutant to assess catalytic activity. The hydrogels exhibited excellent swelling-deswelling behaviour, with CDNH 1 demonstrating the highest swelling ratio and water-retention capacity at pH 4. Catalytic tests revealed that CDNH@Fe₂O₃/Ag/Cu NC-2 showed superior performance in the presence of NaBH₄ (96.99% MB removal), whereas CDNH@Fe₂O₃/Ag/Cu NC-3 achieved efficiency with H₂O₂ (98.56% MB removal) under basic conditions. The methylene blue (MB) dye degradation followed pseudo-first-order kinetics. The NaBH₄ assisted pathway showed a higher K_app (=10^-1 s^-1), whereas the H₂O₂ mediated pathway exhibited a lower K_app value (=10^-3 s^-1). The synthesized CDNH@Fe₂O₃/Ag/Cu nanocomposites remarkable catalytic efficacy indicating a promising future for their use in the remediation of toxic wastewater effluents.