Journal
CHEMISTRY OF MATERIALS
Volume 25, Issue 10, Pages 2184-2191Publisher
AMER CHEMICAL SOC
DOI: 10.1021/cm401294j
Keywords
silica mesoporous crystals; surfactant; costructure directing agent; hexagonal close-packing; electron microscopy
Funding
- VR
- Knut and Alice Wallenberg Foundation
- Berzelii EXSELENT (Sweden)
- WCU, Korea [R-31-2008-000-10055-0]
- National Natural Science Foundation of China [21201120]
- 973 project of China [2009CB930403, 2013CB934101]
- Evonik industry
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Close-packed spheres can be stacked into two crystalline structures: cubic close-packed (ccp) and hexagonal close-packed (hcp). Both of these structures were found in silica mesoporous crystals (SMCs). Herein, pure hcp mesostructure with P6(3)/mmc symmetry of silica mesoporous crystals (SMCs) has been obtained in the synthetic system of cationic gemini surfactant as template and the N-[(3-trimethoxysilyl)propyl]ethylenediamine triacetix acid trisodium salt (EDTA-silyl) as the costructure directing agent (CSDA), which gives rise to the three-dimensional (3D) hexagonal structure and hexagonal plate morphology. The formation of the pure hcp structure was controlled by organic/inorganic interface curvature induced by charge matching between carboxylate groups of the CSDA and quaternary ammonium head groups of surfactant. Electrostatic potential distribution 3D map was reconstructed using Fourier analysis of HRTEM images based on electron crystallography, which showed characteristic features of the shape and connectivity of mesopores in the hcp structure. Small windows for connecting cages can be found only between layers, which determine the symmetry and local curvature of structures. As a result, the point group symmetry of mesopores becomes (6) over bar m2, instead of the m (3) over barm symmetry observed for perfect spheres in the ccp. The mechanism of stabilization and favorable growth of the pure hcp structure in mesoscale has been proposed based on synthesis strategy and symmetry support. This work provides people a better understanding of the priority of two sphere close-packed forms by comparing hcp and ccp structures.
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