Removal of malachite green dye by adsorption onto chitosan-montmorillonite nanocomposite: Kinetic, thermodynamic and equilibrium studies

Abstract

In this study, the efficiencies of chitosan, montmorillonite, and chitosan/montmorillonite composites in various ratios for the removal of malachite green dye from aqueous solutions were investigated, and their maximum adsorption capacities were compared, and the effects of factors such as composite concentration, pH, contact time, dye concentration, and temperature were examined. Recovery attempts using different chemicals were also performed. Adsorption was analyzed using Langmuir and Freundlich isotherm models, and thermodynamic analyses were conducted. Fourier-transform infrared (FTIR) and scanning electron microscopy (SEM) analyses were used to investigate surface changes. The highest adsorption capacity was found for the 20% chitosan/montmorillonite composite (400 mg g⁻¹). Temperature studies indicated a decrease in adsorption capacity with increasing temperature. Kinetic studies observed that the data fit the pseudo-second-order kinetic model better. In recovery attempts, more than 95% recovery was achieved with HNO₃ and HCl. FTIR results showed that chitosan–montmorillonite interactions involved -NH, -OH, C=O, and C-O bonds, while dye binding was mainly through OH bonds. SEM analysis revealed that montmorillonite reduced surface cracks and roughness, creating a more homogeneous structure, and more rough areas appeared after dye binding. As a result, the chitosan/montmorillonite composite significantly enhanced dye adsorption capacity.