Elaboration and properties of a new SDS/CTAB@Montmorillonite organoclay composite as a superb adsorbent for the removal of malachite green from aqueous solutions

In this study, the SDS/CTAB@Mt composite as a novel adsorbent has been prepared via a facile synergistic effect of cationic surfactant (CTAB) and anionic surfactant (SDS) for the modification of montmorillonite, and it was utilized to remove malachite green (MG) from aqueous solutions. The structure and the morphology of the SDS/CTAB@Mt composite were characterized by X-ray diffraction (XRD), Fourier Transform Infra-Red (FT-IR) spectroscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive Analysis of X-rays (EDAX), and N-2 adsorption/desorption isotherms (BET method). The SDS/CTAB@Mt composite was found to be highly negatively surface charged, and showed good adsorption properties for MG molecules, reaching a maximum dye adsorbed amount of 1021.45 mg/g. Further, at the equilibrium, the experimental adsorption isotherms were in good agreement with the theoretical predicted data by the Langmuir model (R-2 = 0.99), indicating that the MG molecules were homogenously adsorbed and formed a monolayer on the SDS/CTAB@Mt surface. Moreover, the adsorption kinetics data were well fitted with pseudo-second-order model (R-2 = 0.99). From the adsorption temperature effect study, the thermodynamic parameters, such as G, Delta H and Delta S were assessed, and their values revealed that the adsorption reaction was spontaneous, exothermic and resulted in a decrease of the MG adsorbed molecules randomness on the adsorbent surface. Finally, a new adsorption mechanism was proposed and confirmed that the MG molecules adsorption from water onto the SDS/CTAB@Mt adsorbent resulted from synergistic effect of the hydrophobic and the hydrophilic interactions.

Automated summary

The SDS/CTAB@Mt composite, prepared through the synergistic effect of CTAB and SDS, showed a highly negatively charged surface and good adsorption properties for malachite green. The adsorption process followed the Langmuir model and pseudo-second-order kinetics, with a maximum adsorbed amount of 1021.45 mg/g. Thermodynamic parameters indicated that the adsorption of malachite green onto the composite was spontaneous, exothermic, and led to a decrease in randomness of adsorbed molecules.