Multifunctional Chitosan@TiO₂/PPy nanocomposite for high-performance adsorption of malachite green: Kinetics, isotherms, and thermodynamics

Industrial discharge of synthetic dyes poses serious threats to aquatic ecosystems and human health. In this study, a novel ternary nanocomposite, Chitosan@TiO₂/Polypyrrole (PPy) nanocomposite was fabricated through a green in situ oxidative polymerization approach for Malachite Green (MG) removal, utilizing the synergistic adsorption capabilities of TiO₂, PPy, and chitosan via electrostatic, hydrogen bonding, and π–π interactions. Characterization confirmed the formation of a thermally stable, mesoporous structure with a surface area of 52.11 m 2 /g and pHₚzc of 6.56. The synthesized composite exhibited excellent adsorption capacity, reaching 304.45 mg/g under optimal conditions (25°C, 50 ppm MG concentration). The kinetic behavior followed a pseudo-second-order model (R 2 = 99.2), indicating that the adsorption mechanism likely involved chemical interactions. Equilibrium analysis showed strong agreement with the Langmuir isotherm (R 2 = 98.6–99.2), reflecting monolayer coverage of MG molecules on a homogeneous surface. Thermodynamic parameters confirmed the process as energetically favorable and exothermic in nature (ΔH° = –44.15 kJ/mol; ΔG° = –25.73 kJ/mol at 298 K), underscoring the material’s efficiency and suitability for sustainable dye remediation applications.