Exfoliated Clay Decorated with Magnetic Iron Nanoparticles for Crystal Violet Adsorption: Modeling and...

Surfactant-modified exfoliated Fayum clay (CTAB-EC) obtained after chemical treatment with a CTAB/H₂O₂ solution was further decorated with magnetic Fe₃O₄ nanoparticles (MNP). The final nanocomposite (MNP/CTAB-EC) was characterized by XRD, SEM, FTIR, TEM and its adsorptive capability against a model cationic dye, crystal violet (CV), was evaluated. A comparison of the adsorption performance of the raw clay and its modified counterparts using H₂O₂, CTAB, CTAB/H₂O₂ or MNP indicated that the adsorption capacity of MNP/CTAB-EC was the highest for CV removal at pH 8.0. The pseudo‒second order for the kinetics and Freundlich model for adsorption equilibrium fitted well the CV removal experimental data at all tested temperatures (25, 40 and 55 °C). The enhancement of the Langmuir adsorption capacity from 447.1 to 499.4 mg g^-1 with increasing the temperature from 25 to 55 °C revealed an endothermic nature of the removal process. The interactions between CV and MNP/CTAB-EC were interpreted using advanced statistical physics models (ASPM) in order to elucidate the adsorption mechanism. Multilayer model fitted the adsorption process and therefore, the steric and energetic factors that impacted the CV adsorption were also interpreted using this model. The aggregated number of CV molecules per MNP/CTAB-EC active site ( n ) was more than unity at all temperatures, representing thus a vertical adsorption orientation and a multi‒interactions mechanism. It was determined that the increase of CV uptake with temperature was mainly controlled by the increase of the number of active sites (N_M). Calculated adsorption energies (ΔE) revealed that CV removal was an endothermic and a physisorption process (ΔE < 40 kJ mol ^-1). MNP/CTAB-EC was magnetically separated, regenerated by NaOH, and reused without significant decrease in its adsorption efficiency, supporting a prosperity of its utilization as an effective adsorbent against hazardous dyes from wastewaters.