Adsorption of cationic dyes onto mesoporous silica

Highly-ordered mesoporous SBA-15 molecular sieves were successfully synthesized through direct-synthesis using non-ionic surfactants as structure directing agent under strong acidic conditions. The textual and structural properties of the prepared materials were characterized by powder X-ray diffraction patterns (XRD), nitrogen physisorption isotherms, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). In terms of adsorption properties, the performance was examined by adsorption of dyes on prepared materials. It was observed that SBA-15 exhibited an excellent adsorptive capability of cationic molecules but almost no adsorption to anionic and neutral molecules. The isotherm models, kinetic models, and thermodynamic properties were analyzed to describe the adsorption behavior of prepared materials. Langmuir model, Freundlich model, and pseudo-second-order kinetics were well-fitted in the simulation of the adsorption behavior of dyes on prepared materials. The synthesized mesoporous SBA-15 materials were found to be effective adsorbents for MB and JGB from aqueous solutions.

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► The mesoporous SBA-15 materials are effective adsorbents for cationic dyes removal from aqueous solutions.
► The SBA-15 exhibits the ability of selective adsorption for cationic molecules, which is due to the electrochemical interaction between cationic molecules and the negative charges on the SBA-15 surfaces.
► The adsorption isotherms can be well fitted with Langmuir and Freundlich models.
► The adsorption kinetics follows the pseudo-second-order model.
► Thermodynamics calculations indicate that the adsorption of cationic molecules on SBA-15 is an exothermic and spontaneous reaction.