Journal
MICROPOROUS AND MESOPOROUS MATERIALS
Volume 88, Issue 1-3, Pages 63-71Publisher
ELSEVIER
DOI: 10.1016/j.micromeso.2005.08.033
Keywords
mesoporous SiO2 gel; silylation; hydrophilic/hydrophobic modification; hydrothermal stability; dimethyldichlorosilane; trimethylchlorosilane
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Mesoporous silica gels with various pore sizes are hydrophobised by liquid-phase silylation with mono- and difunctional methylchlorosilanes. Changes in the pore structure as a result of the silylation reactions are monitored in order to assess the distribution of the hydrophobic groups. Extensive polymerisation of dirnethyldichlorosilane (DMDCS) causes blocking of the micropore fraction. For silica with pore sizes in the supermicroporous range (2 nm pore diameter), this leads to hydrophobisation of almost exclusively the outer surface. While for trimethylchlorosilane (TMCS) a smaller number of molecules react with the surface, modification is more homogeneous and an open structure is optimally preserved. Both silanes lead to lower surface polarity and increased hydrothermal stability, i.e., preservation of the porous structure during exposure to water. As DMDCS reacts more extensively, this agent would be recommended for ceramics with pore diameters larger than about 6 nm. TMCS is the most suitable agent for pore diameters smaller than 4 nm and in case preservation of micropores is required. (c) 2005 Elsevier Inc. All rights reserved.
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