Synthesis and Characterization of Chitosan-Grafted-Poly(Acrylic Acid)/Kaolin Nanocomposite for Adsorption of Malachite Green from Aqueous Solutions: Application of Thermodynamic and Isotherm Models

In an in-depth study of Malachite Green (MG) dye adsorption on a chitosan-graft-poly(acrylic acid)/Kaolin (CS-g-P(AA)/Kaolin) nanocomposite, FTIR, FE-SEM, and adsorption isotherm analysis revealed significant findings. A pronounced decrease in absorption bands associated with amino and hydroxyl groups suggested their active involvement in dye sorption through hydrogen bonding. Post-adsorption FE-SEM images showed a roughened surface, indicating dye adsorption. The study carefully examined the effect of adsorbent weight on MG adsorption and found that surface saturation reduced adsorption efficiency beyond 0.05 gm. To maximise dye removal efficiency, adsorbent weight must be balanced. The Freundlich isotherm model favoured multilayer adsorption on heterogeneous surfaces, as demonstrated by a stronger correlation coefficient (R²= 0.9448) compared to Langmuir and Temkin models. Enhanced kinetic energy and entropy caused increased adsorption at higher temperatures, suggesting a largely physical adsorption process. Positive enthalpy (ΔH) and entropy (ΔS) changes in thermodynamic analysis support physical bonding, while positive Gibbs free energy (ΔG) indicates non-spontaneous adsorption. Conclusions show that CS-g-P(AA)/Kaolin can remove MG dye, and that adsorbent weight, surface contacts, and temperature are crucial. The findings help optimise adsorption techniques for environmental remediation, notably dye pollution management, demonstrating a scientific approach to dealing with environmental issues.