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

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.