Effective adsorption of Congo red azo dye from different water and wastewater by using porous Fe3O4-bentonite@chitosan nanocomposite: A multivariate optimization

Abstract

In this study, a novel Fe₃O₄-Chitosan@Bentonite (Fe₃O₄-CS/Bent) nanocomposite was synthesized via a green and scalable co-precipitation method for the efficient adsorption of toxic azo dye Congo Red (CR) from wastewater. To analyze the physicochemical changes in nanocomposite before and after CR adsorption SEM-EDS, FTIR, XRD, BET, and VSM were employed. The results revealed that Fe₃O₄-CS/Bent nanocomposite shows significantly enhanced surface area, pore volume, and adsorption capacity compared to pure Fe₃O₄ NPs, making it highly effective for environmental remediation. Despite its lower magnetization due to non-magnetic additives, it retains superparamagnetic properties that facilitate efficient magnetic separation in water treatment. Furthermore, the mesoporous Fe₃O₄-CS/Bent nanocomposite can adsorb CR through electrostatic interactions, hydrogen bondings, and surface interaction under carefully optimized adsorption conditions (pH 5, adsorbent amount of 9 mg, and contact time of 25 min) via multivariate analyses. Subsequently, the adsorption process followed a pseudo-2nd order and Langmuir model, yielding a maximum adsorption capacity of 169 mg/g with 96 % removal efficiency, suggesting a monolayer chemisorption process on a relatively heterogeneous surface. The rate constant was determined to be 0.02 g/g-min suggesting a moderate adsorption rate. Thermodynamic analysis indicated adsorption of CR is spontaneous, exothermic, and feasible at moderate temperatures. Furthermore, Fe₃O₄-CS/Bent exhibits outstanding removal efficiencies in recovery experiments, with 98.6–101.4 % recovery across drinking, tap, canal, and wastewater samples. The adsorbent demonstrated excellent reusability, maintaining over 70 % efficiency after 8th regeneration cycle. These findings establish that Fe₃O₄-CS/Bent nanocomposite is found to be cost-effective environmentally friendly adsorbent for water treatment methods.