Insight into the defects of cage-type silica mesoporous crystals with Fd3̄m symmetry: TEM observations and a new proposal of "Polyhedron Packing" for the crystals

Lu Han, Yasuhiro Sakamoto, Shunai Che, Osamu Terasaki

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)

Abstract

Silica mesoporous crystals were synthesized by using a gemini cationic surfactant (C18-3-1) as the directing agent, carboxyethylsilanetriol sodium salt as the co-structure directing agent (CSDA), and varying amounts of HCl. By using transmission electron microscopy (TEM) we observed 1) a structural change from the close-packed structures of spherical micelles-face-centered cubic (Fmi3̄m) and hexagonal close-packed (P63/mmc)-to Fd3̄m structures with an increase of HCl and 2) a few structural defects in the crystals with Fc3̄m symmetry. The structure of a crystal with Fd3̄m symmetry is described as one of the tetrahedrally close-packed (tcp) structures consisting of 512 and 51264 polyhedra. The observed TEM images of the structural defects were explained well through use of simulated TEM images by introducing new 13-15 polyhedra comprising 51262, 51263 4 151062, 42586 5, and 4151064, which have been observed in bubbles by Matzke. The mesostructural changes and defect formation are discussed in terms of the hardness of micelles composed of surfactant/CSDA/ silica species that have formed through a change of the interaction between the surfactant and CSDA, which causes the micelles to change from a regime of close-packing to one of minimum-area packing.

Original languageEnglish
Pages (from-to)2818-2825
Number of pages8
JournalChemistry - A European Journal
Volume15
Issue number12
DOIs
Publication statusPublished - 2009 Mar 9

Keywords

  • Crystal growth
  • Defects
  • Electron microscopy
  • Mesoporous materials
  • Template synthesis

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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