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Argon adsorption on MCM-41 mesoporous crystal studied by in situ synchrotron powder X-ray diffraction
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
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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.

Place, publisher, year, edition, pages
2008. Vol. 112, no 29, 10803-10813 p.
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:su:diva-24696DOI: 10.1021/jp800385tISI: 000257724100035OAI: oai:DiVA.org:su-24696DiVA: diva2:198130
Available from: 2008-02-25 Created: 2008-02-12 Last updated: 2017-12-13Bibliographically approved
In thesis
1. 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
Open this publication in new window or tab >>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
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
XRD, Mesoporous, Gas adsorption, Laves Phase, MEM
Research subject
Structural Chemistry
Identifiers
urn:nbn:se:su:diva-7367 (URN)978-91-7155-588-5 (ISBN)
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
2. A structural study into the boundary surface and associated curvature of three-dimensional mesoporous silica crystals
Open this publication in new window or tab >>A structural study into the boundary surface and associated curvature of three-dimensional mesoporous silica crystals
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
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:nbn:se:su:diva-7651 (URN)978-91-7155-672-1 (ISBN)
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

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