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A structural study into the boundary surface and associated curvature of three-dimensional mesoporous silica crystals
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Since their first discovery in the early 1990s, mesoporous crystals (MCs) have fascinated researchers in various fields because of their interesting structures and their potential uses. Electron crystallography (EC) gives the direct three-dimensional (3D) realization of a crystal as a reconstructed electrostatic potential map (EPM). Various 3D-EPMs of silica MCs with cubic symmetry have been previously obtained by EC.

The main task in this thesis is the development of structural analyses focusing on MCs and thus to evaluate the properties of periodic mesopores within EC data. How MC structures can be described and solved by EC is discussed in terms of the interpretation of the reconstructed 3D-EPM. Assuming a regime of an equi-potential surface (EPS), a structural description for MCs is suggested as a surface that optimizes the curvature elasticity evaluated on every EPS. The geometric properties of cubic MCs so far already reconstructed by EC, are then analyzed on the basis of the optimized EPSs. The analysis provides the property of the mesopores independently from gas adsorption measurements. A large cage-like MC is further studied by in-situ synchrotron powder X-ray diffraction to help understand the nitrogen adsorption process onto the mesopore wall.

As an additional study, a silica MC showing its crystal morphologies of icosahedron, decahedron, etc. is studied. Results by EC suggest that the spherical uni-modal cages form the cubic close packing. The morphologies observed are explained in terms of the multiple twinning, which is analogous to metal nanoparticles. The occurrence of multiple twinning in MCs is discussed in light of the synthesis condition and the shape of micelles.

Place, publisher, year, edition, pages
Stockholm: Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi , 2008. , 109 p.
Keyword [en]
mesoporous crystal, electron crystallography, electrostatic potential map, equi-potential surface, curvature, multiplly-twinned particle
National Category
Other Basic Medicine
Research subject
Structural Chemistry
Identifiers
URN: urn:nbn:se:su:diva-7651ISBN: 978-91-7155-672-1 (print)OAI: oai:DiVA.org:su-7651DiVA: diva2:198762
Public defence
2008-06-02, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 13:30
Opponent
Supervisors
Available from: 2008-05-12 Created: 2008-05-09 Last updated: 2011-03-01Bibliographically approved
List of papers
1. Structural solution of mesocaged material AMS-8
Open this publication in new window or tab >>Structural solution of mesocaged material AMS-8
2004 In: Chemistry of Materials, ISSN 0897-4756, Vol. 16, 3597-3605 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-25026 (URN)
Note
Part of urn:nbn:se:su:diva-7651Available from: 2008-05-12 Created: 2008-05-09Bibliographically approved
2. Studies of anionic surfactant templated mesoporous structures by electron microscopy
Open this publication in new window or tab >>Studies of anionic surfactant templated mesoporous structures by electron microscopy
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2005 In: Studies in Surface Science and Catalysis, ISSN 0167-2991, Vol. 156, 11-18 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-25027 (URN)
Note
Part of urn:nbn:se:su:diva-7651Available from: 2008-05-12 Created: 2008-05-09Bibliographically approved
3. A lesson from the unusual morphology of silica mesoporous crystals: Growth and close packing of spherical micelles with multiple twinning
Open this publication in new window or tab >>A lesson from the unusual morphology of silica mesoporous crystals: Growth and close packing of spherical micelles with multiple twinning
2006 (English)In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 45, no 39, 6516-6519 p.Article in journal (Refereed) Published
Keyword
crystal growth, electron microscopy, mesoporous materials, silica, surfactants
Identifiers
urn:nbn:se:su:diva-25028 (URN)10.1002/anie.200601451 (DOI)
Note
Part of urn:nbn:se:su:diva-7651Available from: 2008-05-12 Created: 2008-05-09 Last updated: 2017-12-13Bibliographically approved
4. Argon adsorption on MCM-41 mesoporous crystal studied by in situ synchrotron powder X-ray diffraction
Open this publication in new window or tab >>Argon adsorption on MCM-41 mesoporous crystal studied by in situ synchrotron powder X-ray diffraction
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2008 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 29, 10803-10813 p.Article in journal (Refereed) Published
Abstract [en]

Equilibrium argon adsorption from the gas phase on mesoporous MCM-41 silica of hexagonal structure is directly studied by in situ synchrotron powder X-ray diffraction (XRD) measurements at SPring-8. The diffraction intensity data is analyzed by extending the previously developed analytical formula for the crystal structure factors of MCM-41 to account for argon adsorbed in the pores. It is clearly observed that argon adsorbs in layers on the pore walls at low gas pressures and exhibits sudden capillary condensation as the gas pressure increased. The proposed method of interpretation of XRD data allows one to calculate the density ratio between the silica wall and condensed argon, the pore size, and the pore wall fluctuation/roughness, together with the thickness of the adsorbed layer as a function of the gas pressure. The results of in situ XRD experiments are compared with the results of argon adsorption volumetric experiments. The adsorption data are interpreted with the quench solid density functional theory (QSDFT), which takes into account the pore wall roughness. The perfect agreement of the QSDFT isotherm predicted from the adsorption data and the XRD recalculated isotherm suggests that the adsorption porosimetry and XRD measurements can be reconciled provided a proper interpretation of the experimental data.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:su:diva-24696 (URN)10.1021/jp800385t (DOI)000257724100035 ()
Available from: 2008-02-25 Created: 2008-02-12 Last updated: 2017-12-13Bibliographically approved
5. A study of gas adsorption process of mesoporous silica SBA-16 crystal with large cage-like pores
Open this publication in new window or tab >>A study of gas adsorption process of mesoporous silica SBA-16 crystal with large cage-like pores
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Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-25030 (URN)
Note
Part of urn:nbn:se:su:diva-7651Available from: 2008-05-12 Created: 2008-05-09 Last updated: 2010-01-13Bibliographically approved

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