Water adsorption properties of alumina pillared clay

Oxide and Metal Intercalated Clay Nanocomposites

Truly nanocomposite materials that are stable to about 400 to 700°C can be prepared by intercalating oxides or metal clusters of about 0.4 to 2.0 nm in between ∼1.0 nm layers of smectite clays. Both the chemistry and size of intercalates (pillars) can be varied to introduce unique catalytic, molecular sieving, dehumidifying and adsorption properties in these materials. The intercalated clays also provide opportunities to prepare compositionally and stoichiometrically diverse nanocomposite precursors to high temperature structural and electronic ceramics. Although montmorillonite is the most widely used host, further designing in properties can be achieved by using other members of smectite family having subtle crystal chemical and compositional variations, such as beidellite, nontronite, saponite or hectorite. The sol-gel chemistry involving the preparation of positively charged mono- or multiphasic solution-sol or colloidal-sol particles is a viable approach to introduce chemically diverse oxide particles in the interlayers of smectite. Reduction of transition metal ions or complexes in the interlayers of smectite to zerovalent metal clusters/particles using polar liquids is another novel approach to develop catalytically active, high surface area materials.

Study on Microstructure Variation Laws of Al-Pillared Montmorillonite

Al3+/clay ratio is one of the important factors influencing microstructure of Al-pillared montmorillonite. Microstructure variation laws of Al-pillared montmorillonite prepared under the condition of different Al3+/clay ratio are systematically studied by XRD, FTIR, specific surface area and pore size analysis. The results show that the interlayer spacing and BET specific surface area of Al-pillared montmorillonite are remarkably affected by the Al3+/clay ratio. The interlayer spacing d(001) value and BET specific surface area of Al-pillared montmorillonite increase firstly and then decrease with the increases of the Al3+/clay ratio, and they reach to maximum when the Al3+/clay ratio is 10mmol/g. Besides, the BJH porous volume distribution of Al-pillared montmorillonite is the most probable distribution, and the most probable pore size is about 2 nm, which is attributed to mesopore. The porous structure of hydroxy-Al pillared montmorillonite is characterized as parallel plate slit or “house-of-cards” wedge-shaped pore which is formed by novel meso-microporous delaminated structure and fragments. With the increase of the Al3+/clay ratio, BJH total porous volume and mesoporous volume of hydroxy-Al pillared montmorillonite decreases, while the proportion of microporous volume in the total porous volume increases. The proportion of microporous specific surface area of all the hydroxy-Al pillared montmorillonite samples is about 62% and is much larger than that of Na-M and those of mesopore and macropore, indicating the main action of intercalation of hydroxy-Al pillaring solution into montmorillonite interlayer is to increase the micropore amount.

Investigation on Pore Structure Formed in a Pillared Montmorillonite Interlayer Using Adsorption Methods and a Carbonization Technique

The structure of pores formed in the alumina- or chromia-pillared montmorillonite (PMT) interlayer was investigated by analyzing the porous solid itself and the negative carbon replica formed in the pores of the parent material. The nitrogen adsorption on these materials allowed us to estimate the pillar structure and the density of pillar sites in the montmorillonite interlayers. The amount of Al(13) polycation in an exchanging solution governed the interpillar distance in the pillared clay gallery without changing the diameters of the pillar (ca. 0.6 nm). The aperture size of Al-PMT was 0.8 nm in height and 0.5-0.9 nm in width depending on Al content. On the other hand, the aperture size of Cr-PMT was 0.5 nm in height and 0.8 nm in width, and the diameter of a pillar was estimated to be ca. 0.4 nm. Copyright 2001 Academic Press.