The thermally-induced structural transformations are studied of three imogolite-type nanotube (NT) materials: i) proper imogolite (IMO, (OH)3Al2O3SiOH) with outer surface covered by Al-OH-Al groups and inner one lined by silanols; ii) methyl-imogolite (Me-IMO, (OH)3Al2O3SiCH3), in which at the inner surface silanols have been replaced by methyl groups, while the outer surface is unchanged, and iii) the material Me-IMO-NH2, obtained by grafting the outer surface of Me-IMO with 3-aminopropylsilane (3-APS). TG-MS analysis on the parent IMO only shows loss of water (up to ca. 700 K), while XRD indicates the formation of a lamellar phase, because of the mutual reaction of inner silanols. With both Me-IMO and Me-IMO-NH2, Mass spectrometry and NMR analysis reveals the occurrence of a more complex collapsing mechanism, basically due to the reaction of outer Al-OH groups and inner Si-CH3, following the cleavage of the NTs structure, yielding methane and transient Al-O-CH2-Si species. All three materials show a limited decrease in the interlayer distance caused by collapse, as well as a substantial residual porosity. It is concluded that the layered structure can be conceived as consisting in an overall buckled structure, the strong strain within the silico-alumina layer of the single-walled nanotube providing the driving force against a complete flattening. As a minor feature, decomposition of perchlorate species to chloride anions with release of molecular oxygen is observed with IMO, species which are trapped during the synthesis at the narrow interpores cavities.
Thermal collapse of sigle-walled aluminosilicate nanotubes: transformation mechanisms and morphology of the resulting lamellar phases / C. Zanzottera; A. Vicente; M. Armandi; C. Fernandez; E. Garrone; B. Bonelli. - In: JOURNAL OF PHYSICAL CHEMISTRY. C. - ISSN 1932-7447. - STAMPA. - 116:44(2012), pp. 23577-23584. [10.1021/jp3090638]
|Titolo:||Thermal collapse of sigle-walled aluminosilicate nanotubes: transformation mechanisms and morphology of the resulting lamellar phases|
|Data di pubblicazione:||2012|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1021/jp3090638|
|Appare nelle tipologie:||1.1 Articolo in rivista|
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