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Studies of inorganic crystal structures and gas adsorption process in mesoporous crystals: New approach through analysis of electron charge distribution by synchrotron powder X-ray diffraction
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Using synchrotron powder XRD experiments, I studied (i) structures of silica mesoporous MCM-41 and MCM-48 crystals, (ii) gas adsorption processes of Ar and N2 in the mesopores of the mesoporous crystals, and (iii) bonding features of CaAl2-xZnx crystals through the analysis of electron charge density distributions.

In the case of mesoporous crystals, the following two different approaches were taken depending on the number of observed X-ray reflections

1. The analytical expression was chosen and further developed to study the size and shape of the mesopores with the plane group of p6mm by powder XRD experiments. For MCM-41, following the determination of the mesopores’ size and shape, and the thickness of the adsorbed gas layer as a function of the gas pressure were successfully observed. In addition, for carbon pipe mesoporous crystals CMK-5, the carbon pipe thickness was determined and the diffraction pattern was discussed quantitatively focusing on the “accidental extinction.”

2. Maximum entropy method (MEM) was used for the structural study of MCM-48 (3D bicontinuous Ia-3d ) and for the gas adsorption process within the mesopores.

By adopting the MEM approach, the study of “bonding electrons” and associated atomic displacements from the ideal Kagome net in the Laves phase CaAl2-xZnx were observed. In particular, the two Kagome nets in the C36 structure showed different feature in the electron density distributions between each other.

Place, publisher, year, edition, pages
Stockholm: Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi , 2008. , 55 p.
Keyword [en]
XRD, Mesoporous, Gas adsorption, Laves Phase, MEM
Research subject
Structural Chemistry
Identifiers
URN: urn:nbn:se:su:diva-7367ISBN: 978-91-7155-588-5 (print)OAI: oai:DiVA.org:su-7367DiVA: diva2:198133
Public defence
2008-03-17, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 13:30
Opponent
Supervisors
Available from: 2008-02-25 Created: 2008-02-12Bibliographically approved
List of papers
1. An Analytical Approach to Determine the Pore Shape and Size of MCM-41 Materials from X-ray Diffraction Data
Open this publication in new window or tab >>An Analytical Approach to Determine the Pore Shape and Size of MCM-41 Materials from X-ray Diffraction Data
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2006 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 22, 10630-10635 p.Article in journal (Refereed) Published
National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-24694 (URN)
Available from: 2008-02-25 Created: 2008-02-12 Last updated: 2013-11-18Bibliographically approved
2. Powder XRD intensity of mesoporous carbon crystal with two-dimensional symmetry: Accidental extinction in CMK-5
Open this publication in new window or tab >>Powder XRD intensity of mesoporous carbon crystal with two-dimensional symmetry: Accidental extinction in CMK-5
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-24695 (URN)
Note
Part of urn:nbn:se:su:diva-7367Available from: 2008-02-25 Created: 2008-02-12 Last updated: 2010-01-13Bibliographically approved
3. 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: 2011-03-01Bibliographically approved
4. Argon adsorption on MCM-48 mesoporous crystal studied by in situ synchrotron powder X-ray diffraction
Open this publication in new window or tab >>Argon adsorption on MCM-48 mesoporous crystal studied by in situ synchrotron powder X-ray diffraction
Show others...
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-24697 (URN)
Note
Part of urn:nbn:se:su:diva-7367Available from: 2008-02-25 Created: 2008-02-12 Last updated: 2010-01-13Bibliographically approved
5. Electron charge distribution of CaAl2−xZnx: Maximum Entropy Method combined with Rietveld analysis of High-resolution-synchrotron X-ray powder diffraction data
Open this publication in new window or tab >>Electron charge distribution of CaAl2−xZnx: Maximum Entropy Method combined with Rietveld analysis of High-resolution-synchrotron X-ray powder diffraction data
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2008 (English)In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 181, no 8, 1998-2005 p.Article in journal (Refereed) Published
Abstract [en]

Using short wavelength X-rays from synchrotron radiation (SPring-8), high-resolution powder diffraction patterns were collected. In order to study both the structural relationship and the mechanism of stability in the CaAl2−xZnx system, among the Laves phases (MgCu2 and MgNi2 type) and KHg2-type structures, the charge density distribution of CaAl2−xZnx as a function of x was obtained from the diffraction data by Rietveld analysis combined with the maximum entropy method (MEM). In the MEM charge density maps overlapping electron densities were clearly observed, especially in the Kagomé nets of the Laves phases. In order to clarify the charge redistribution in the system, the deformation charge densities from the densities formed by the constituent free atoms are discussed. In the ternary MgNi2-type phase, partial ordering of Al and Zn atoms is observed, a finding that is supported by ab-initio total energy calculations.

Keyword
Intermetallic compounds, Laves phases, Charge density, Maximum entropy method
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-24698 (URN)10.1016/j.jssc.2008.04.034 (DOI)000259098000041 ()
Available from: 2008-02-25 Created: 2008-02-12 Last updated: 2011-03-10Bibliographically approved

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