Sustainable Fabrication of Chitosan–Starch–Mucilage/ZnO Nanocomposites for Efficient Carmoisine Dye Removal: Adsorption Performance and Ecotoxicity Evaluation

The removal of food‐grade carmoisine dye (E122) using a zinc oxide nanoparticle‐doped polymeric nanocomposite (starch–chitosan–mucilage–ZnO nanocomposites (S–C–M–ZnO)) was investigated. Experimental parameters, including adsorbent dosage, dye concentration, pH, temperature, and contact time, were optimized. Adsorption kinetics, isotherms, and thermodynamic behavior were systematically evaluated, along with environmental safety using a seed germination assay. Under optimal conditions—adsorbent dosage of 0.003 g, pH 7, temperature of 50°C, and contact time of 90 min—the adsorption efficiency reached 91.34%. Kinetic analysis showed that the adsorption process was best described by the pseudo‐second‐order model ( R 2 = 0.99), indicating that this model adequately represented the adsorption kinetics under the investigated conditions. Among isotherm models, the Freundlich model ( R 2 = 0.93841) best described the system, suggesting adsorption on a heterogeneous surface with the possibility of multilayer adsorption. Thermodynamic parameters revealed the process to be spontaneous and exothermic, with negative values of enthalpy (Δ H ° = −24.586 kJ mol − 1 ), entropy (Δ S ° = −50.096 J mol − 1 K − 1 ), and Gibbs free energy (Δ G °), indicating decreased randomness at the solid–liquid interface. Furthermore, the adsorption‐treated solution exhibited a 94% seed germination rate, indicating reduced phytotoxicity and providing a preliminary ecotoxicity assessment of the developed nanocomposite under the investigated conditions.