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Hydrogen bonding of water confined in mesoporous silica MCM-41 and SBA-15 studied by H-1 solid-state NMR

Grünberg, B. and Emmler, T. and Gedat, E. and Shenderovich, I. and Findenegg, G. H. and Limbach, H. H. and Buntkowsky, G. (2004):
Hydrogen bonding of water confined in mesoporous silica MCM-41 and SBA-15 studied by H-1 solid-state NMR.
In: Chemistry-a European Journal, 10 (22), pp. 5689-5696, [Online-Edition: http://apps.webofknowledge.com/full_record.do?product=WOS&se...],
[Article]

Abstract

The adsorption of water in two mesoporous silica materials with cylindrical pores of uniform diameter, MCM-41 and SBA-15, was studied by H-1 MAS (MAS = magic angle spinning) and static solid-state NMR spectroscopy. All observed hydrogen atoms are either surface -SiOH groups or hydrogen-bonded water molecules. Unlike MCM-41, some strongly bound water molecules exist at the inner surfaces of SBA-15 that are assigned to surface defects. At higher filling levels, a further difference between MCM-41 and SBA-15 is observed. Water molecules in MCM-41 exhibit a bimodal line distribution of chemical shifts, with one peak at the position of inner-bulk water, and the second peak at the position of water molecules in fast exchange with surface -SiOH groups. In SBA-15, a single line is observed that shifts continuously as the pore filling is increased. This result is attributed to a different pore-filling mechanism for the two silica materials. In MCM-41, due to its small pore diameter (3.3 nm), pore filling by pore condensation (axial-pore-filling mode) occurs at a low relative pressure, corresponding roughly to a single adsorbed monolayer. For SBA-15, owing to its larger pore diameter (8 nm), a gradual increase in the thickness of the adsorbed layer (radial-pore-filling mode) prevails until pore condensation takes place at a higher level of pore filling.

Item Type: Article
Erschienen: 2004
Creators: Grünberg, B. and Emmler, T. and Gedat, E. and Shenderovich, I. and Findenegg, G. H. and Limbach, H. H. and Buntkowsky, G.
Title: Hydrogen bonding of water confined in mesoporous silica MCM-41 and SBA-15 studied by H-1 solid-state NMR
Language: English
Abstract:

The adsorption of water in two mesoporous silica materials with cylindrical pores of uniform diameter, MCM-41 and SBA-15, was studied by H-1 MAS (MAS = magic angle spinning) and static solid-state NMR spectroscopy. All observed hydrogen atoms are either surface -SiOH groups or hydrogen-bonded water molecules. Unlike MCM-41, some strongly bound water molecules exist at the inner surfaces of SBA-15 that are assigned to surface defects. At higher filling levels, a further difference between MCM-41 and SBA-15 is observed. Water molecules in MCM-41 exhibit a bimodal line distribution of chemical shifts, with one peak at the position of inner-bulk water, and the second peak at the position of water molecules in fast exchange with surface -SiOH groups. In SBA-15, a single line is observed that shifts continuously as the pore filling is increased. This result is attributed to a different pore-filling mechanism for the two silica materials. In MCM-41, due to its small pore diameter (3.3 nm), pore filling by pore condensation (axial-pore-filling mode) occurs at a low relative pressure, corresponding roughly to a single adsorbed monolayer. For SBA-15, owing to its larger pore diameter (8 nm), a gradual increase in the thickness of the adsorbed layer (radial-pore-filling mode) prevails until pore condensation takes place at a higher level of pore filling.

Journal or Publication Title: Chemistry-a European Journal
Volume: 10
Number: 22
Uncontrolled Keywords: monolayers nmr spectroscopy pore condensation water chemistry zeolite analogues pore-size distribution neutron-scattering porous silica rabbit lens x-ray diffusion surface h-1-nmr dynamics ice
Divisions: 07 Department of Chemistry
07 Department of Chemistry > Physical Chemistry
Date Deposited: 27 Oct 2014 20:40
Official URL: http://apps.webofknowledge.com/full_record.do?product=WOS&se...
Additional Information:

871OA Times Cited:141 Cited References Count:37

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