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Mesopore generation by organosilane surfactant during LTA zeolite crystallization investigated by high-resolution SEM and Monte Carlo simulation
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
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2011 (English)In: Solid State Sciences, ISSN 1293-2558, E-ISSN 1873-3085, Vol. 13, no 4, 750-756 p.Article in journal (Refereed) Published
Abstract [en]

The crystallization of LTA zeolite under a hydrothermal synthesis condition that contained a quaternary ammonium-type organosilane surfactant was studied with X-ray powder diffraction (XRD), high-resolution scanning electron microscopy (HRSEM) and Monte Carlo simulation of the crystal growth. The hydrothermal reaction products were collected at various crystallization times, and investigated with XRD and HRSEM. The HRSEM images of the final zeolite products were taken as synthesized and also after cross-sectioning with an argon ion beam. The HRSEM investigation revealed presence of a disordered network of mesoporous channels that penetrated the microporous zeolite crystal. Unless the loading of the surfactant was exceedingly high, the microporous zeolite particles exhibited truncated cubic morphologies that were almost like single crystals, despite penetration by the mesopores. The outline of the zeolite particle became progressively rounded as the mesoporosity was increased according to the surfactant loading. The mesoporosity in the zeolite crystals was well maintained against crystal-ripening processes for 6 d. This result supports the fact that the organosilane surfactant micelles became incorporated inside the zeolite crystal as a mesopore generator during the crystallization process. Data from Monte Carlo simulation agreed with these experimental results.

Place, publisher, year, edition, pages
2011. Vol. 13, no 4, 750-756 p.
Keyword [en]
Mesoporous zeolite, Hierarchical zeolite, Zeolite LTA, Organosilane surfactant, Mesopore-generating agent, High resolution SEM, Cross-section polishing technique
National Category
Chemical Sciences
Research subject
Materials Chemistry; Structural Chemistry
Identifiers
URN: urn:nbn:se:su:diva-55035DOI: 10.1016/j.solidstatesciences.2010.04.022ISI: 000289965900011OAI: oai:DiVA.org:su-55035DiVA: diva2:400405
Available from: 2011-02-25 Created: 2011-02-25 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Characterizing cavity containing materials using electron microscopy: A study of metal oxides, mesoporous crystals and porous material containing nanosized metal-particles
Open this publication in new window or tab >>Characterizing cavity containing materials using electron microscopy: A study of metal oxides, mesoporous crystals and porous material containing nanosized metal-particles
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis concerns the characterization of novel materials by utilizing electron microscopy techniques. The examined materials contain cavities with certain attributes that enables desired properties for applications such as gas separation, catalysis and fuel cells. The specimens concerned herein belong to the following groups of materials: Metal oxides in the Sb-W-Mo-O system; ordered mesoporous silicas and carbons; hollow spheres containing Au-nanoparticles; zeolite LTA incorporated with mesopores; metal organic frameworks doped with nickel.

With scanning electron microscopy (SEM) and transmission electron microscopy (TEM) you get vast possibilities within the field of characterization. This thesis utilizes conventional electron microscopy techniques such as imaging, energy-dispersive spectroscopy and electron diffraction as well as reconstruction techniques, such as exit-wave reconstruction, electron tomography and electron crystallography. Furthermore, the sample preparation technique cross-section polishing has been used in conjunction with low voltage SEM studies.

The scientific approach is to gain knowledge of nano-sized cavities in materials, in particular their shape, size and content. The cavities often have irregularities that originates from the synthesis procedure. In order to refine the synthesis and to understand the properties of the material it is required to carefully examine the local variations. Therefore average characterization techniques such as crystallography needs to be combined with local examination techniques such as tomography. However, some of the materials are troublesome to investigate since they to some extent bring limitations to or gets easily damaged by the applied characterization technique. For the development of novel materials it is essential to find means of overcoming also these obstacles.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry (MMK), Stockholm University, 2011. 84 p.
Keyword
Electron microscopy
National Category
Inorganic Chemistry Materials Chemistry
Research subject
Structural Chemistry
Identifiers
urn:nbn:se:su:diva-64164 (URN)978-91-7447-247-9 (ISBN)
Public defence
2012-01-20, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:15 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 6: Submitted.Available from: 2011-12-15 Created: 2011-11-11 Last updated: 2012-03-26Bibliographically approved
2. A structural investigation into the complexity of mesoporous silica crystals: From a view of curvature and micellar interaction to quasicrystallinity
Open this publication in new window or tab >>A structural investigation into the complexity of mesoporous silica crystals: From a view of curvature and micellar interaction to quasicrystallinity
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mesoporous silica crystals have a large variety of structures mainly due to the versatility of their structure template. The configuration and the chemical state of the templating micellar surfactants, together with the kinetic process of silica will determine the final outcome of the synthesis. Increasing the understanding of the complex formation processes involved will enable a possibilityto fine tune the material for specific uses, today focused into the fields of photoniccrystals, drug delivery, catalysis and separation technology.

In this thesis emphasis is put on (1) increasing the understanding the formation mechanism yielding the different species of mesoporous silica crystals through an in depth study of quasicrystallinity (2) Characterization and description of the structural complexity through various characterization techniquesand also by studying the kinetic structural transformation phenomenon related to the minimal G- and D-surfaces. (3) The structural studies of the versatile surfactant liquid crystals for establishing a thermodynamically stable basis to evaluate the kinetic mesoporous silica growth processes. Furthermorethe thesis both enlightens the possibilities of and contributes to the developmentof electron microscopy characterization techniques.

In these studies, electron microscopy is largely employed in the characterization to give a thorough picture of the mesoporous structures. This is combined with the sample preparation techniques cross-section polishing and ionslicing. Low voltage scanning electron microscopy is utilized for studying the surfaces and cross-sections of various materials at the limit of the resolution. Here, a deep understanding of the electron beam-material interaction is used for a better interpretation of the detected signals. Transmission electron microscopyis combined with electron crystallographic reconstruction to yield a three dimensional structural model. For determination of the quasicrystallinity level for a structure of dodecagonal tiling, revealed in the scope of this study,a phason strain analysis was made.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry (MMK), Stockholm University, 2012. 110 p.
Keyword
electron microscopy, mesoporous silica, quasicrystal, minimal surface
National Category
Chemical Sciences
Research subject
Structural Chemistry
Identifiers
urn:nbn:se:su:diva-82382 (URN)978-91-7447-602-6 (ISBN)
Public defence
2012-12-21, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:30 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 7: Manuscript.

Available from: 2012-11-29 Created: 2012-11-13 Last updated: 2012-11-20Bibliographically approved

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