Modification of MCM-41 by surface silylation with trimethylchlorosilane and adsorption study

Zhao, XS and Lu, GQ (1998) Modification of MCM-41 by surface silylation with trimethylchlorosilane and adsorption study. Journal of Physical Chemistry B, 102 9: 1556-1561. doi:10.1021/jp972788m


Author Zhao, XS
Lu, GQ
Title Modification of MCM-41 by surface silylation with trimethylchlorosilane and adsorption study
Journal name Journal of Physical Chemistry B
ISSN 1089-5647
Publication date 1998-01-01
Year available 1998
Sub-type Article (original research)
DOI 10.1021/jp972788m
Open Access Status Not Open Access
Volume 102
Issue 9
Start page 1556
End page 1561
Total pages 6
Publisher AMER CHEMICAL SOC
Language eng
Abstract Siliceous MCM-41 samples were modified by silylation using trimethylchlorosilane (TMCS). The surface coverage of functional groups was studied systematically in this work. The role of surface silanol groups during modification was evaluated using techniques of FTIR and Si-29 CP/MAS NMR. Adsorption of water and benzene on samples of various hydrophobicities was measured and compared. It was found that the maximum degree of surface attachments of trimethylsilyl (TMS) groups was about 85%, corresponding to the density of TMS groups of 1.9 per nm(2). The degree of silylation is found to linearly increase with increasing pre-outgassing temperature prior to silylation. A few types of silanol groups exist on MCM-41 surfaces, among which both free and geminal ones are responsible for active silylation. Results of water adsorption show that aluminosilicate MCM-41 materials are more or less hydrophilic, giving a type IV isotherm, similar to that of nitrogen adsorption, whereas siliceous MCM-41 are hydrophobic, exhibiting a type V adsorption isotherm. The fully silylated Si-MCM-41 samples are more hydrophobic giving a type III adsorption isotherm. Benzene adsorption on all MCM-41 samples shows type IV isotherms regardless of the surface chemistry. Capillary condensation occurs at a higher relative pressure for the silylated MCM-41 than that for the unsilylated sample, though the pore diameter was found reduced markedly by silylation. This is thought attributed to the diffusion constriction posed by the attached TMS groups. The results show that the surface chemistry plays an important role in water adsorption, whereas benzene adsorption is predominantly determined by the pore geometry of MCM-41.
Keyword Chemistry, Physical
Mesoporous Molecular-sieves
Silica
Water
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
Collection: Australian Institute for Bioengineering and Nanotechnology Publications
 
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Created: Mon, 13 Aug 2007, 20:21:58 EST