CONICET | Buscador de Institutos y Recursos Humanos

The adsorption process of crystal violet (CV) on montmorillonite (MMT) was studied through kinetic analysis, microstructural characterization, surface charge and contact angle determination. Adsorption kinetic was studied in situ by attenuated total reflectance Fourier-transform infrared analysis (ATR-FTIR); MMT microstructural changes were determined by small angle X-Ray scattering (SAXS) and N2 adsorption/desorption analysis; wettability and surface charge were determined by contact angle and a particle charge detection technique, respectively. Pseudo-second order kinetic and intraparticle diffusion models fitted well the experimental results in all the studied concentration. The contribution of surface adsorption and intraparticle diffusion processes at different CV initial concentrations on the global adsorption rate was determined. Different molecular arrangements were postulated, depending on the amount of adsorbed CV. For low CV content, the dye molecules enter in the MMT interlaminar space as a parallel monolayer. At medium CV content, the molecules enter the MMT interlaminar space in a paraffin-like monomolecular with tilt angle arrangement or with CV molecules in a bilayer configuration, parallel to the interlayer surface. In both cases, increment of the basal spacing, reduction of wettability, diminution of negative surface charge and the interaction of CV molecule with surface through its quaternary amine group were determined. At higher CV content, the wettability decreases and surface charge shifted to positive values. This behavior indicates the presence of CV bilayer arrangements, with the polar region of the molecules facing away from the surface. Results of this work help in the development of efficient adsorbents and in the understanding on the fate of CV (and similar compounds) in water and sediments.

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