Synthesis of urea-formaldehyde resin@chitosan composite for the removal of Congo red from an aqueous solution via adsorption: Box-Behnken design optimization.

The removal of the toxic dye Congo red (CR) from aqueous solutions is crucial for water purification and environmental protection. In this work, a urea-formaldehyde@chitosan (UF@Ch) composite was prepared using a simple process, and its adsorption performance for CR removal was evaluated. The structural and morphological properties of the composite material were determined by XRD, FTIR, and SEM-EDX analysis. Adsorption kinetics fitted well to the PSO model, while the Langmuir isotherm model fitted well with the equilibrium data, confirming monolayer adsorption with a maximum capacity of 34.95 mg g-1 at 50 °C. Thermodynamically, the process was found to be spontaneous and endothermic. Besides, the UF@Ch composite was highly reusable, as substantial adsorption efficiency was retained after multiple cycles. In this paper, RSM-BBD was applied to optimize the adsorption performance of UF@Ch by considering X1: UF@Ch dose, X2: dye concentration, and X3: pH. Under the obtained optimal conditions of 0.5 g L-1 UF@Ch dose, pH 2.0, and 60 mg L-1 dye concentration, the maximum CR removal was found to be 99.68 %. Hence, these observations show great potential for using this composite material as a nontoxic adsorbent in efficient CR removal from wastewater and searching for a sustainable solution against dye-laden industrial effluents.