Adsorption Congo Red Dye on SnZnFeO Nanocomposite: Statistical Modeling and Interpretation

This study investigates the removal of Congo red (CR) dye from aqueous solutions using synthetically prepared SnO 2 /ZnO/Fe 2 O 3 nanocomposite (SnZnFeONPs). The structural properties of the nanocomposites were characterized using SEM, EDX, FTIR, and XRD techniques. The effects of key parameters, including initial CR dye concentration, pH, ultrasound duration, and adsorbent dosage, on dye removal efficiency were systematically evaluated. Under optimized conditions, an adsorption efficiency exceeding 97% was achieved. Equilibrium data fitted the Langmuir model best ( R 2 = 0.996) with a Q max of 344.82 mg g − 1 , indicating monolayer adsorption of CR molecules. However, the Freundlich model ( R 2 = 0.968) also suggested some degree of surface heterogeneity and possible multilayer interactions. Kinetic studies indicated that the adsorption process followed a pseudo‐second‐order (PSO) model. Computational simulations revealed that CR molecules adsorbed in a parallel orientation on the nanocomposite surface. Thermodynamic analysis indicated that the adsorption process is exothermic and primarily governed by physical interactions. The adsorption intensity values (n) at 25°C, 35°C, and 45°C were 0.599, 0.593, and 0.563, respectively, all less than 1, confirming favorable adsorption. Furthermore, the saturation adsorption capacity (Q s a t ) decreased from 438.465 mg g − 1 at 298 K to 34.633 mg g − 1 at 318 K, indicating reduced interaction at higher temperatures. These findings suggest that SnZnFeONPs exhibit excellent potential for efficient CR dye removal from industrial effluents through adsorption.