Structural, textural and adsorption characteristics of bentonite-based composite

• Structure of the composite is a proven cause of its micro- and mesoporosity.
• Montmorillonite undergoes a change of d001 distance during composite synthesis.
• There is a relationship among composite structure, texture and adsorption properties.
• Methylene blue can be adsorbed onto composite in more than one layer.
• High adsorption capacity for methylene blue even at low pH was observed.

An application of coatings composed of mixed (hydr)oxides over bentonite particles in aqueous suspension, in narrow range of pH, has been proven as a useful method for obtaining bentonite based composite with a developed, specific surface area and pronounced adsorption features toward cationic pollutants. This paper deals with detailed characterization of structure as well as textural and adsorption properties of bentonite based composite. The structure of the composite was examined by using XRD technique providing results that confirm changes in orientation of layered quasi-crystalline particles of montmorillonite, which is the most common component of bentonite clay. Surface area and pore volumes were determined by N2 adsorption at −196 °C using BET, t-plot, αs-plot, Dubinin Radushkevich and Dollimore–Heal method. The results have revealed that the specific surface area for composite is about two times higher than for starting bentonite. Moreover, modification of bentonite leads to significant changes in the meso- and microporosity. Adsorption properties of the composite were studied by analyzing the adsorption of dye methylene blue which was used in this study as a model of cationic pollutant in water. The most prominent role in the mechanism of dye molecules retention on the surface, interlayers and in the pores of the adsorbent is ascribed to establishing of electrostatic, van der Waals and hydrogen bonds. The shape of adsorption isotherm indicates that methylene blue can be adsorbed onto composite in more than one layer.

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