Double-network carboxymethyl chitosan/chondroitin sulfate hydrogel microspheres prepared by green-LED-triggered droplet photopolymerization for malachite green adsorption

To overcome the inherent mechanical limitations of polysaccharide hydrogels for dye adsorption, we developed dual-network hydrogel microspheres via efficient one-step droplet photopolymerization initiated by green LED. The primary network was photopolymerized from sodium acrylate monomers and ethylene glycol dimethacrylate cross-linker, while the secondary network formed through Schiff base conjugation between oxidized chondroitin sulfate and carboxymethyl chitosan. Systematic characterization (FTIR, TGA, SEM, XPS) confirmed the hydrogels' structural and thermal properties. Key operational parameters including contact time, temperature, initial MG concentration, pH, and ionic strength were optimized. At room temperature, adsorption equilibrium was achieved within 3 h, following pseudo-second-order kinetics. The adsorption capacity is 806.51 mg/g and fitted the Langmuir isotherm model. Electrostatic interactions dominated the adsorption mechanism, as verified by pH and ionic strength experiments. After five adsorption-desorption cycles, MG removal efficiency remained more than 80 %.