Morphology Development of Mesoporous Materials: a Colloidal Phase Separation Mechanism
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- 作者：Chengzhong Yu ; Jie Fan ; Bozhi Tian ; and Dongyuan Zhao
- 刊名：Chemistry of Materials
- 出版年：2004
- 出版时间：March 9, 2004
- 年：2004
- 卷：16
- 期：5
- 页码：889 - 898
- 全文大小：551K
- 年卷期：v.16,no.5(March 9, 2004)
- ISSN：1520-5002
文摘
Synthetic conditions such as temperature, stirring rate, ionic strength, acidity, and reactantratios that affect the mesostructures and macrostructures of mesoporous materials havebeen extensively studied in the nonionic block copolymer templating system. Highly orderedSBA-15 materials with ~100% rodlike morphologies (~1-2 
m long) have been obtained inthe presence of inorganic salts. Synthesis conditions such as low temperature, low acidity,and low ionic strength that increase the induction time give rise to the morphologies ofmesoporous silica with increased curvatures. The particle growth process of rodlike SBA-15materials from solutions has been examined by directly observing the morphologies ofparticles as a function of time. A colloidal phase separation mechanism (CPSM) for theformation of mesoporous materials is proposed. It is suggested that the formation processof mesoporous materials involves three stages: (1) cooperative self-assembly of inorganic/organic composites; (2) formation of a new crystal-like phase rich in aggregates of blockcopolymer/silica species; and (3) phase separation of this liquid crystal-like phase from thesolution and further growth of solid mesostructures driven by further condensation of silicaspecies. The morphologies of mesoporous materials are developed after the phase separationstage and influenced by the competition mainly between the free energy of mesostructureself-assembly (
G) and the colloidal surface free energy (F), as well as other interactionssuch as the shearing force. When the phase separation stage occurs early, G is dominantand the macrostructure of mesoporous materials is developed together with the formationof mesostructure; therefore, mesoporous materials with crystal-like morphologies can begenerated. The role of inorganic salts is well explained based on the CPSM by taking intoaccount the colloidal interaction enhanced by inorganic salts. Cubic (Im
m) mesoporous singlecrystals have been obtained with exclusively rhombdodecahedron shapes (1-2 m in size).Ultrathin microtoming TEM measurements confirm that such polyhedral particles are perfectsingle crystals. The different influences of hydrothermal treatments upon the mesostructuresand macrostructures have been discussed in the hexagonal and cubic synthesis systems. Byemploying the CPSM, hexagonal mesoporous single crystals have been obtained in theabsence of inorganic salts; the size limitation (~1-2 m) of mesoporous single crystals hasalso been discussed. Such understandings may be useful in the fabrication of mesoporousmaterials with well-defined, crystal-like morphologies.
m long) have been obtained inthe presence of inorganic salts. Synthesis conditions such as low temperature, low acidity,and low ionic strength that increase the induction time give rise to the morphologies ofmesoporous silica with increased curvatures. The particle growth process of rodlike SBA-15materials from solutions has been examined by directly observing the morphologies ofparticles as a function of time. A colloidal phase separation mechanism (CPSM) for theformation of mesoporous materials is proposed. It is suggested that the formation processof mesoporous materials involves three stages: (1) cooperative self-assembly of inorganic/organic composites; (2) formation of a new crystal-like phase rich in aggregates of blockcopolymer/silica species; and (3) phase separation of this liquid crystal-like phase from thesolution and further growth of solid mesostructures driven by further condensation of silicaspecies. The morphologies of mesoporous materials are developed after the phase separationstage and influenced by the competition mainly between the free energy of mesostructureself-assembly (G) and the colloidal surface free energy (F), as well as other interactionssuch as the shearing force. When the phase separation stage occurs early, G is dominantand the macrostructure of mesoporous materials is developed together with the formationof mesostructure; therefore, mesoporous materials with crystal-like morphologies can begenerated. The role of inorganic salts is well explained based on the CPSM by taking intoaccount the colloidal interaction enhanced by inorganic salts. Cubic (Imm) mesoporous singlecrystals have been obtained with exclusively rhombdodecahedron shapes (1-2 m in size).Ultrathin microtoming TEM measurements confirm that such polyhedral particles are perfectsingle crystals. The different influences of hydrothermal treatments upon the mesostructuresand macrostructures have been discussed in the hexagonal and cubic synthesis systems. Byemploying the CPSM, hexagonal mesoporous single crystals have been obtained in theabsence of inorganic salts; the size limitation (~1-2 m) of mesoporous single crystals hasalso been discussed. Such understandings may be useful in the fabrication of mesoporousmaterials with well-defined, crystal-like morphologies.