Removal of cationic methylene blue dye using magnetic and anionic-cationic modified montmorillonite: kinetic, isotherm and thermodynamic studies

Abstract

In this study, the synthesis of new class of the modified montmorillonite with magnetic nanoparticles and surfactants was studied. The synthesis was carried out via intercalation of a mixture of sodium eicosenoate (SEIA, anionic surfactant) and cetyltrimethylammonium chloride (CTMAC, cationic surfactant) on the surface or within interlamellar spaces of montmorillonite (Mt) and thereafter the immobilization of Fe3O4 MNPs (magnetic nanoparticles) to afford Fe3O4-CTMAC/SEIA-Mt system. Next, the nanocomposite of CTMAC-Mt, SEIA-Mt, CTMAC/SEIA-Mt and CTMAC/SEIA-Fe3O4-Mt (In this case, magnetic montmorillonite was primarily prepared and then modified with a mixture of CTMAC/SEIA surfactants) were also synthesized. The prepared nanocomposite systems were characterized using FT-IR, XRD, SEM, EDX, TGA and VSM analyses and then utilized for the removal of cationic methylene blue (MB) dye from aqueous solutions. Among the examined composite systems, Fe3O4-CTMAC/SEIA-Mt showed a superior adsorption capacity. In this area, the influence of adsorbent dosage, contact time, initial concentration of MB and temperature towards the adsorption of MB on Fe3O4-CTMAC/SEIA-Mt system was also investigated. The obtained results exhibited that the kinetic of adsorption and the model of isotherm obeyed from the pseudo-second order and Langmuir model, respectively. Moreover, Fe3O4-CTMAC/SEIA-Mt system showed an extraordinary adsorption capacity for MB (246 mg g–1). Because of superparamagnetic characteristic of magnetite, the adsorbent of Fe3O4-CTMAC/SEIA-Mt can be easily separated from the reaction mixture by an external magnetic field. Thermodynamic studies also represented that the adsorption of MB on Fe3O4-CTMAC/SEIA-Mt was endothermic and it was carried out as a spontaneous process.