Hollow nanospheres, allophanes ‘All-organic’ synthesis and characterization

Autor: Gottlieb.-G. Lindner, Shigenobu Hayashi, Hiromoto Nakazawa
Rok vydání: 1998
Předmět:
Zdroj: Microporous and Mesoporous Materials. 21:381-386
ISSN: 1387-1811
DOI: 10.1016/s1387-1811(98)00002-x
Popis: Allophanes, hollow spherical aluminosilicates with diameters of 3–4 nm, have been synthesized by the ‘all-organic’ synthesis method. The main wall of these spheres consists of a tetrahedral silicon oxide/hydroxide sheet with partial replacement of Si by Al. Octahedrally coordinated aluminium species (Al-hydroxide) act as counter-ions on the inner surface of the spheres. Pore openings of about 0.35 nm allow description as isolated zeolite-like supercages capable of an exchange of water and small hydrocarbons. The novel synthesis method uses both organic educts (aluminium trialkylates and tetraalkyl orthosilicates) as well as dry organic solvents (alkanes). Slow addition of water as a reactant through diffusion via the gaseous phase, followed by hydrolysis and polycondensation reactions, leads to the formation of the allophanes. Hereby the educts and solvents may be varied and differently combined without significant change in the final allophane product, displaying the universality of the method. The reaction takes place at room temperature and is completed after one to two days. The formation of these allophanes can be explained by means of hydrophilic/hydrophobic interactions of the polar hydrolysis products and the non-polar reaction environment caused by the organic solvent. The products were characterized by XRD, TG/DTA, transmission electron microscopy, IR and 27Al/29Si solid state NMR, the latter two allowing for the modelling of the structure as well as of the reaction mechanism. Structural analogy to the so-called type II allophanes (stream deposited allophanes) is confirmed.
Databáze: OpenAIRE
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