Multi-walled carbon nanotubes/TiO2/Chitosan nanocomposite for efficient removal of malachite green dye from aqueous system: A comprehensive experimental and theoretical investigation

This study presents the preparation, characterization, and application of a novel Multi-walled carbon nanotubes/ TiO2/chitosan (MWCNT/TiO2/CS) nanocomposite, prepared using a hydrothermal method, for the removal of malachite green (MG) dye from aqueous solutions. Adsorption studies revealed optimal dye removal within 15 min of adsorption equilibrium time, with maximum removal efficiency of 98.53 % at pH 7.0, dose 0.4 g/L and 298 K. Isotherm studies showed the Langmuir model best described the adsorption equilibrium data with maximum monolayer adsorption (qm) value was found to be 269.98 mg/g at 298 K. Kinetic analyses favored the pseudo-second-order model with qcal value was found to be 201.6 mg/g at Co = 100 mg/L. Thermodynamic investigations indicated an exothermic, spontaneous adsorption process. Seven successful adsorption-desorption cycles were achieved using HCl as an eluent (97.65 % desorption). Theoretical reactivity parameters derived from DFT calculations corroborated experimental findings, elucidating the molecular-level mechanisms underlying the efficient adsorption of MG onto the MWCNT/TiO2/CS surface. The strong electrophilic nature and electron-accepting character of the MG molecule, along with its ability to form electronic interactions, explain its high adsorption affinity. These findings demonstrate the potential of MWCNT/TiO2/CS nanocomposite as an effective and sustainable solution for MG dye removal from aqueous environments.