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Characterizing cavity containing materials using electron microscopy: A study of metal oxides, mesoporous crystals and porous material containing nanosized metal-particles
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
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 [en]
Electron microscopy
National Category
Inorganic Chemistry Materials Chemistry
Research subject
Structural Chemistry
Identifiers
URN: urn:nbn:se:su:diva-64164ISBN: 978-91-7447-247-9 (print)OAI: oai:DiVA.org:su-64164DiVA: diva2:461531
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
List of papers
1. Ordered Mesoporous Pd/Silica-Carbon as a Highly Active Heterogeneous Catalyst for Coupling Reaction of Chlorobenzene in Aqueous Media
Open this publication in new window or tab >>Ordered Mesoporous Pd/Silica-Carbon as a Highly Active Heterogeneous Catalyst for Coupling Reaction of Chlorobenzene in Aqueous Media
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2009 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 12, 4541-4550 p.Article in journal (Refereed) Published
Abstract [en]

Heterogeneous palladium catalysts, which are supported on ordered mesoporous silica-carbon nanocomposites, have been applied in water-mediated coupling reactions of chlorobenzene without assistance of any phase-transfer catalysts. Characterization by XRD, TEM, N2 sorption, FT-IR, TG, XPS, and H2 chemisorption techniques reveals the highly ordered mesostructure, high surface areas (?345 m2/ g), large pore volumes (?0.46 cm3/g), uniform mesopore sizes (?6.3 nm), hybrid silicate and carbonaceous compositions, and a high dispersion of palladium nanoparticles (about 3 nm) in the mesopores. The catalyst exhibits a high yield for trans-stilbene (?60%) in the Heck coupling reaction of chlorobenzene and styrene at 100 ‹C and for biphenyl (46%) in the Ullmann coupling reaction of chlorobenzene at 30 ‹C, using water as a solvent. When substituted aryl chlorides (hydroxyl, methoxyl, and methyl) are involved in the Ullmann reaction, the yields of symmetrical substituted biphenyl are also higher than 44% (this value reaches 86% for the coupling reaction of 4-chlorophenol) at a low temperature of 30 ‹C. This heterogeneous catalyst is stable, which shows negligible metal leaching, and can be reused more than 20 times. For comparison, the catalytic activities for Pd catalysts supported on pure mesoporous polymeric, carbonaceous, and silicate frameworks are also investigated. The results clearly indicate that the pore wall nature shows great influence on the dispersion of metallic Pd species and, in turn, the catalytic performance.

 

National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-36709 (URN)10.1021/ja808481g (DOI)000264792900067 ()
Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2011-12-09Bibliographically approved
2. An Appraisal of High Resolution Scanning Electron Microscopy Applied To Porous Materials
Open this publication in new window or tab >>An Appraisal of High Resolution Scanning Electron Microscopy Applied To Porous Materials
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2009 (English)In: JEOL News, Vol. 44, no 1, 17-22 p.Article in journal (Refereed) Published
Abstract [en]

Nanoporous materials such as zeolites and mesoporous silica crystals have attracted a lot of attention in recent years. In particular, the incorporation of various materials such as organic molecules, or metal nanoparticles and other inorganic compounds within their pores which give rise to fascinating new functions. For such materials, it is essential to determine their structure, composition and mechanisms of growth in order to maximize their utility in future applications.

Recent progress in the performance of SEM is enormous, especially in low energy imaging where we can now directly observe fine surface structures of porous materials even those that are electrical insulators. Furthermore, by precise filtration and detection of emitted electrons by their energy, we can selectively obtain different types of information such as material composition, location of particles inside or outside the pores etc. The physical processes and technologies behind this precise tuning of landing and detection energies for both impact and emitted electrons, respectively, are explained and illustrated using a number of porous materials including zeolite LTA, SBA-15, SBA-16, zeolite LTL, FDU-16 and Au@TiO2 ' rattle spheres,' along with comparisons with other techniques such as atomic force microscopy (AFM) and transmission electron microscopy (TEM). We conclude that, by using extremely low landing energies, advanced sample preparation techniques and through a thorough understanding of the physical processes involved, HRSEM is providing new and unique information and perspectives on these industrially important materials.

National Category
Chemical Sciences
Research subject
Inorganic Chemistry; Structural Chemistry
Identifiers
urn:nbn:se:su:diva-36800 (URN)
Note

Totalt antal författare 17 st.

Available from: 2010-01-27 Created: 2010-01-26 Last updated: 2012-11-20Bibliographically approved
3. Mesopore generation by organosilane surfactant during LTA zeolite crystallization investigated by high-resolution SEM and Monte Carlo simulation
Open this publication in new window or tab >>Mesopore generation by organosilane surfactant during LTA zeolite crystallization investigated by high-resolution SEM and Monte Carlo simulation
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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.

Keyword
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:nbn:se:su:diva-55035 (URN)10.1016/j.solidstatesciences.2010.04.022 (DOI)000289965900011 ()
Available from: 2011-02-25 Created: 2011-02-25 Last updated: 2017-12-11Bibliographically approved
4. A new HRSEM approach to observe fine structures of novel nanostructured materials
Open this publication in new window or tab >>A new HRSEM approach to observe fine structures of novel nanostructured materials
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2011 (English)In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 146, no 1-3, 11-17 p.Article in journal (Refereed) Published
Abstract [en]

A new approach for observing fine structures of novel thin, nanostructured materials called through the employed to observe interesting features on a variety of new, catalyticallyimportant hierarchically porous rattlespheres.

Keyword
HRSEM, Crystal growth, Rattlespheres
National Category
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-65177 (URN)10.1016/j.micromeso.2011.06.010 (DOI)000295769400003 ()
Available from: 2011-12-04 Created: 2011-12-04 Last updated: 2017-12-08Bibliographically approved
5. Advanced electron microscopy characterization for pore structure of mesoporous materials; a study of FDU-16 and FDU-18
Open this publication in new window or tab >>Advanced electron microscopy characterization for pore structure of mesoporous materials; a study of FDU-16 and FDU-18
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2011 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 21, no 35, 13664-13671 p.Article in journal (Refereed) Published
Abstract [en]

We present a comprehensive analysis for pore structures of cage-type ordered mesoporous carbons (OMCs) using various electron microscopy techniques in addition to conventional nitrogen adsorption isotherm studies. The benefits and drawbacks of these techniques are evaluated, and it is shown that they are complementary to each other. Knowledge of the structural properties, pore sizes, and connectivity gives insight into the synthesis strategies and how they are affecting the material properties that are useful within the possible applications. Herein, focus is put on the two OMCs with Im (3) over barm and Fm (3) over barm symmetries specified by FDU-16 and FDU-18. The central techniques used in this study are high resolution scanning electron microscopy combined with cross-section polisher and three-dimensional reconstruction methods (electron tomography and electron crystallography) based on transmission electron microscopy observations.

National Category
Materials Chemistry Physical Chemistry
Research subject
Structural Chemistry
Identifiers
urn:nbn:se:su:diva-66876 (URN)10.1039/c1jm11789k (DOI)000294176600072 ()
Note
7Available from: 2011-12-22 Created: 2011-12-21 Last updated: 2017-12-08Bibliographically approved
6. Exit wave reconstruction from focal series of HRTEM images, single crystal XRD and total energy studies on SbxWO3+y (x~0.11)
Open this publication in new window or tab >>Exit wave reconstruction from focal series of HRTEM images, single crystal XRD and total energy studies on SbxWO3+y (x~0.11)
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(English)Article in journal (Refereed) Submitted
National Category
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-65179 (URN)
Available from: 2011-12-04 Created: 2011-12-04 Last updated: 2011-12-09Bibliographically approved

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