Structured carbon adsorbents from clay, zeolite and mesoporous aluminosilicate templates

The lithium form of taeniolite, intercalated with hydroxyaluminum and hydroxyaluminum−zirconium cations, served as the molecular template for carbon−mineral nanocomposites and derived carbons. The ...

Pore Structure of Carbon−Mineral Nanocomposites and Derived Carbons Obtained by Template Carbonization

The lithium form of taeniolite served as the molecular template for carbon nanocomposites. It was intercalated with hydroxy aluminum and hydroxy aluminum-zirconium cations. Aliquots of the inorganic matrices were saturated by furfuryl alcohol followed by its interlayer polymerization. The structures were heated at 973 K in nitrogen to carbonize the polymeric precursor. Additional materials were mixed with polypropylene glycol which was then carbonized within the mineral layers. The surface properties of the nanocomposites were studied by X-ray diffraction (XRD), DTA, SEM and sorption experiments (sorption of nitrogen). The results showed that structural properties of the derived materials depend on the inorganic matrix and organic precursor. The carbon-taeniolite nanocomposites derived from polyfurfuryl alcohol as a precursor were characterized by high carbon content and a high percentage of its surface area in micropores. A broad spectrum of surface characteristics of the final products were found, depending on the history of the sample.

Study of Nanocomposites Obtained by Carbonization of Different Organic Precursors within Taeniolite Matrices

Structural changes accompanying thermal transformation in Na-montmorillonite samples up to a temperature of 500°C have been investigated by X-ray line profile analysis. The method of Fourier initial slope and variance analysis of X-ray line profiles have been used to calculate the different microstructural parameters like crystallite size, r.m.s. strain ( 1/2 ), variation of inter layer spacing (g), fraction of planes affected by such defects (γ), etc. at different stages of the dehydration process. The dehydration mechanism also has been explained based on thermogravimetric analysis (TGA).

Microstructural parameters and layer disorder accompanying dehydration transformation in Na-montmorillonite

Nanocomposites and carbons obtained from carbonization of Indoine Blue cations at different temperatures (from 673 to 1473 K) within inorganic taeniolite matrices have been studied by a series of physicochemical methods including transmission electron microscopy (TEM), FTIR and sorption measurements. Carbonaceous materials separated from the mineral host have varying microtexture which is related to the degree of carbonization and subsequent orientation of the so-called basic structural units (BSUs). Low pyrolysis temperatures (673 K) lead to the creation of an amorphous carbon with well pronounced features characteristic of the organic precursor. Higher pyrolysis temperatures (1073 K) result in significant constrained chemistry and, consequently, structure of the materials. The microtexture of the carbons obtained is governed by the effects of temperature and properties of the matrix and consequently the orientation of BSUs within the interlayer space. They influence the graphitizability of these carbons: disoriented BSUs result in turbostratic carbon; BSUs with parallel orientation result in polycrystalline graphite.

Structural and adsorption properties of carbons synthesized within taeniolite matrices

Carbon/oxide nanocomposites were formed by thermal treatment of montmorillonite/ammonium complexes, in the range 500–1000 °C. Although montmorillonite is decomposed above 700 °C, the lamellar structure is maintained up to 1000 °C by the presence of “intercalated” carbon. The amount of carbon in the composites can be adjusted by varying the nature of the organic ammonium cations so as to reach the computed value given by the theoretical equation for the formation of β′-SiAlON (19%). Starting from the montmorillonite/safraninium complex, the carbon content in the nanocomposite was 17.3%. β′-SiAlON was synthesized by heat treatment of this composite to 1350 °C under nitrogen. Since the oxide and the carbon source are intimately mixed on the nanoscale, β′-SiAlON is even obtained at temperatures as low as 1100 °C. Compared with other processes, the temperature for β′-SiAlON formation can be lower by approximately 300 °C.

M. Crespin

Papers

Production of β′-SiAlONs through carbon/oxide nanocomposites obtained from montmorillonite/aromatic-ammonium complexes