Synthesis and characterization of novel chitosan-clay coated iron oxide nanoparticles for optimized adsorption and mechanistic study of methyl orange in industrial wastewater.

Eliminating toxic chemicals is a major environmental concern for countries such as Morocco, whose economies rely significantly on the textile and dyeing industries. Thus, a novel biocomposite have been synthesized using chitosan, clay, and iron oxide nanoparticles (crosslinked by precipitation) to remove methyl orange from aqueous media. The new composite's structural and chemical properties were deeply investigated using XRD, FTIR, TGA, BET, SEM-EDX, and XPS techniques. The purpose of this research was to assess the adsorption efficiency of the composite in removing methyl orange from aqueous solutions. For that, adsorption was examined at different dosages (0-100 mg), concentrations (10-100 mg/L) and pH values (1-12). In adsorption tests, this biocomposite revealed remarkable efficiency, with a maximum removal efficiency of 98.5% at pH 6.5. In addition, the maximum adsorption capacity was 125 mg g-1, and the adsorption equilibrium was attained within in 120 min. According to the thermodynamic study, adsorption process is solely entropy-driven, and the isosteric heat of adsorption ranges from -25.3 to -10.5k J mol-1. On the other hand, The XPS analyses showed that methyl orange adsorption mostly involves the amine groups of chitosan and Fe/clay complex and is achieved by a mixture of surface complexation, hydrogen bonding, and electrostatic interactions. The experimental results were confirmed and supplemented by theoretical calculations. Indeed, based on single-layer statistical physical modeling, the adsorption process was endothermic and entropy-driven, with adsorption energies varying between 12.31 and 16.66 kJ mol-1 at temperatures between 25 and 45 °C. Finally, where resources are limited, the obtained results indicate that the chitosan/clay/iron oxide biocomposite is an effective and enduring adsorbent for removing methyl orange and possibly other azo dyes from industrial wastewater.