Nanocomposite Cryogels Based on Chitosan for Efficient Removal of a Triphenylmethane Dye from Aqueous Systems

This work addresses the environmental challenge represented by persistent triphenylmethane dyes in aquatic systems through the development of chitosan (CS)–zeolite nanocomposite cryogels for the adsorption of chrome azurol S (CAS), as model dye. Nanocomposite cryogels were prepared via cryogelation at −20 °C with systematic variation in cross-linker concentration and zeolite content to modulate the network architecture and sorption performance. Comprehensive physicochemical characterization (SEM, EDX, FTIR) demonstrated that an intermediate cross-linker content (7.5 wt.% GA) combined with moderate zeolite loading (20 wt.%) yielded cryogels with the highest gel fraction yield and a homogeneous, highly interconnected macroporous structure. Swelling experiments at pH 1.2 revealed rapid water uptake equilibrium within 10 min, whereas adsorption isotherm analysis indicated that CAS sorption followed the Freundlich model, consistent with multilayer physical adsorption. The highest CAS adsorption capacity was achieved by CSGA5Z40 (250.81 mg g−1), indicating that low cross-linking combined with high zeolite loading maximizes uptake. These findings demonstrate that chitosan–zeolite nanocomposite cryogels are promising, reusable, and tunable adsorbents for sustainable removal of persistent dyes from wastewater.