Abstract
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 () 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 (NM). 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.
Highlights
Pollution of aquatic systems due to the industrial wastes associated with the creation and consumption of varied products such as paper, cotton, silk, wool, and leather, represents a global challenge [1,2]
Stock solutions (1 g L−1) of Crystal violet (CV) were prepared and the desired concentrations for adsorption experiments were obtained by diluting the stock solution with deionized water
5.93 to 7.85 kJ mol−1 by increasing the adsorption temperature from 25 to 55 ◦C and these results suggested that the interaction between CV and magnetic Fe3O4 nanoparticles (MNP)/CTAB and exfoliated Fayum clay (CTAB-EC) involved physical adsorption forces
Summary
Pollution of aquatic systems due to the industrial wastes associated with the creation and consumption of varied products such as paper, cotton, silk, wool, and leather, represents a global challenge [1,2]. The incessant release of toxic pollutants, including hazardous organic dyes, even at small concentrations, into water bodies is greatly harmful for human beings [3,4]. Coagulation, precipitation, biological treatment and adsorption have been reported as alternative methods to reduce the concentrations of organic dyes in water [4]. The use of adsorbents based on available and low-cost materials such as clays and zeolites is reported to be a favorable method in water purification processes. Those raw materials can be further modified through varied strategies to produce new composites with improved surface chemistry where several function groups (i.e., active adsorption sites) are available to interact with the water pollutants
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