Periodic mesoporous hydridosilica-synthesis of an "impossible" material and its thermal transformation into brightly photoluminescent periodic mesoporous nanocrystal silicon-silica composite

Date
2011
Authors
Xie, Z.
Henderson, E. J.
Dag, Ö.
Wang, W.
Lofgreen, J. E.
Kübel, C.
Scherer, T.
Brodersen, P. M.
Gu, Zhong-Ze
Ozin, G. A.
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Source Title
Journal of the American Chemical Society
Print ISSN
0002-7863
Electronic ISSN
1520-5126
Publisher
Volume
133
Issue
13
Pages
5094 - 5102
Language
English
Type
Article
Journal Title
Journal ISSN
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Abstract

There has always been a fascination with "impossible" compounds, ones that do not break any rules of chemical bonding or valence but whose structures are unstable and do not exist. This instability can usually be rationalized in terms of chemical or physical restrictions associated with valence electron shells, multiple bonding, oxidation states, catenation, and the inert pair effect. In the pursuit of these "impossible" materials, appropriate conditions have sometimes been found to overcome these instabilities and synthesize missing compounds, yet for others these tricks have yet to be uncovered and the materials remain elusive. In the scientifically and technologically important field of periodic mesoporous silicas (PMS), one such "impossible" material is periodic mesoporous hydridosilica (meso-HSiO1.5). It is the archetype of a completely interrupted silica open framework material: its pore walls are comprised of a three-connected three-dimensional network that should be so thermodynamically unstable that any mesopores present would immediately collapse upon removal of the mesopore template. In this study we show that meso-HSiO1.5 can be synthesized by template-directed self-assembly of HSi(OEt)3 under aqueous acid-catalyzed conditions and after template extraction remains stable to 300 °C. Above this temperature, bond redistribution reactions initiate a metamorphic transformation which eventually yields periodic mesoporous nanocrystalline silicon-silica, meso-ncSi/SiO2, a nanocomposite material in which brightly photoluminescent silicon nanocrystallites are embedded within a silica matrix throughout the mesostructure. The integration of the properties of silicon nanocrystallinity with silica mesoporosity provides a wealth of new opportunities for emerging nanotechnologies.

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Keywords
Aqueous acids, Chemical bondings, Directed self-assembly, Meso-pores, Mesopore, Mesoporosity, Mesoporous, Mesoporous Silica, Mesostructures, Metamorphic transformations, Multiple bonding, Nanocomposite materials, Nanocrystallinity, New opportunities, Open-framework materials, Oxidation state, Physical restriction, Pore wall, Redistribution reactions, Silica composites, Silica matrix, Silicon nanocrystallites, Template extraction, Thermal transformations, Three-dimensional networks, Valence electron
Citation
Published Version (Please cite this version)