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Structural study of nano-structured materials: electron crystallography approaches
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). (Peter Oleynikov)ORCID iD: 0000-0003-4814-3740
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The structural analysis serves as a bridge to link the structure of materials to their properties. Revealing the structure details allows a better understanding on the growth mechanisms and properties of materials, and a further designed synthesis of functional materials. The widely used methods based on X-ray diffraction have certain limitations for the structural analysis when crystals are small, poorly crystallized or contain many defects. As electrons interact strongly with matter and can be focused by electromagnetic lenses to form an image, electron crystallography (EC) approaches become prime candidates for the structural analysis of a wide range of materials that cannot be done using X-rays, particularly nanomaterials with poor crystallinity.

Three-dimensional electron diffraction tomography (3D EDT) is a recently developed method to automatically collect 3D electron diffraction data. By combining mechanical specimen tilt and electronic e-beam tilt, a large volume of reciprocal space can be swept at a fine step size to ensure the completeness and accuracy of the diffraction data with respect to both position and intensity. Effects of the dynamical scattering are enormously reduced as most of the patterns are collected at conditions off the zone axes. In this thesis, 3D EDT has been used for unit cell determination (COF-505), phase identifications and structure solutions (ZnO, Ba-Ta3N5, Zn-Sc, and V4O9), and the study of layer stacking faults (ETS-10 and SAPO-34 nanosheets).

High-resolution transmission electron microscope (HRTEM) imaging shows its particular advantages over diffraction by allowing observations of crystal structure projections and the 3D potential map reconstruction. HRTEM imaging has been used to visualize fine structures of different materials (hierarchical zeolites, ETS-10, and SAPO-34). Reconstructed 3D potential maps have been used to locate the positions of metal ions in a woven framework (COF-505) and elucidate the pore shape and connectivity in a silica mesoporous crystal.

The last part of this thesis explores the combination with X-ray crystallography to obtain more structure details.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry (MMK), Stockholm University , 2016. , 101 p.
Keyword [en]
structural analysis, electron crystallography, 3D EDT, HRTEM imaging, defects
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-129233ISBN: 978-91-7649-425-7 (print)OAI: oai:DiVA.org:su-129233DiVA: diva2:920230
Public defence
2016-06-08, Magnéli Hall, Arrhenius Laboratory, Svante arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 1486801
Available from: 2016-05-16 Created: 2016-04-18 Last updated: 2017-02-23Bibliographically approved
List of papers
1. Cobalt phosphate-modified barium-doped tantalum nitride nanorod photoanode with 1.5% solar energy conversion efficiency
Open this publication in new window or tab >>Cobalt phosphate-modified barium-doped tantalum nitride nanorod photoanode with 1.5% solar energy conversion efficiency
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2013 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 4, 2566Article in journal (Refereed) Published
Abstract [en]

Spurred by the decreased availability of fossil fuels and global warming, the idea of converting solar energy into clean fuels has been widely recognized. Hydrogen produced by photoelectrochemical water splitting using sunlight could provide a carbon dioxide lean fuel as an alternative to fossil fuels. A major challenge in photoelectrochemical water splitting is to develop an efficient photoanode that can stably oxidize water into oxygen. Here we report an efficient and stable photoanode that couples an active barium-doped tantalum nitride nanostructure with a stable cobalt phosphate co-catalyst. The effect of barium doping on the photoelectrochemical activity of the photoanode is investigated. The photoanode yields a maximum solar energy conversion efficiency of 1.5%, which is more than three times higher than that of state-of-the-art single-photon photoanodes. Further, stoichiometric oxygen and hydrogen are stably produced on the photoanode and the counter electrode with Faraday efficiency of almost unity for 100 min.

National Category
Chemical Sciences
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-97043 (URN)10.1038/ncomms3566 (DOI)000326470400010 ()
Note

AuthorCount:14;

Available from: 2013-12-02 Created: 2013-12-02 Last updated: 2017-12-06Bibliographically approved
2. A conductive ZnO-ZnGaON nanowire-array-on-a film photoanode for stable and efficient sunlight water splitting
Open this publication in new window or tab >>A conductive ZnO-ZnGaON nanowire-array-on-a film photoanode for stable and efficient sunlight water splitting
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2014 (English)In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 7, no 5, 1693-1699 p.Article in journal (Refereed) Published
Abstract [en]

We report highly stable and efficient sunlight water splitting on a ZnO-ZnGaON nanowire-array-on-a-film photoanode without the assistance of any co-catalyst. The single crystalline ZnO-ZnGaON nanowirearray- on-a-film photoanode was synthesized via a high-temperature vapor-phase diffusion reaction of gallium (Ga) and nitrogen (N) on a single crystal domain ZnO nanowire-array-on-a-film structure. The synthesized ZnO-ZnGaON photoanode offers visible light absorption through N incorporation, improved electrical conductivity via Ga incorporation, and structural advantages with the high-aspect-ratio nanowire array. Compared to the chemically unstable ZnO nanowire photoanode, the ZnO-ZnGaON nanowire photoanode significantly improves the anti-photocorrosive ability for water splitting. A highly stable photocurrent density of similar to 1.5 mA cm(-2) is obtained with the ZnO-ZnGaON nanowire photoanode at an applied bias of 0.8 V-RHE under continuous sunlight illumination over five hours without noticeable degradation.

National Category
Chemical Sciences
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-104130 (URN)10.1039/c3ee43806f (DOI)000335013700018 ()
Note

AuthorCount:5;

Available from: 2014-06-03 Created: 2014-06-03 Last updated: 2017-12-05Bibliographically approved
3. High performance nanosheet-like silicoaluminophosphate molecular sieves: synthesis, 3D EDT structural analysis and MTO catalytic studies
Open this publication in new window or tab >>High performance nanosheet-like silicoaluminophosphate molecular sieves: synthesis, 3D EDT structural analysis and MTO catalytic studies
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2014 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 2, no 42, 17828-17839 p.Article in journal (Refereed) Published
Abstract [en]

Nanosheet-like silicoaluminophosphate (SAPO) molecular sieves SAPO-34 (CHA-type) and SAPO-18 (AEI-type) with different silicon contents were synthesized under hydrothermal conditions by using tetraethylammonium hydroxide as the template. Three-dimensional electron diffraction tomography (3D EDT) technique was applied for ab initio structure solutions. Electron microscopy observations confirmed the existence of defects, i.e., intergrowth of CHA- and AEI-type frameworks caused by the different stacking manners of double 6-ring layers, but the layers were highly coherent along c direction. Compositions, acidities, chemical environments, and texture properties of all the samples were characterized by ICP, EDS, NH3-TPD, MAS NMR, and N-2 adsorption-desorption measurements. The catalytic performances of methanol-to-olefin (MTO) reactions over nano SAPO catalysts with different silicon contents were systematically studied. All of these catalysts showed excellent catalytic activity, among which SAPO-34 showed superior catalytic performance compared to SAPO-18. DFT calculations were utilized to study the different catalytic performance of CHA and AEI. Significantly to date, SAPO-34 with the lowest silicon content exhibited the longest catalyst lifetime and the lowest coking rate in the MTO reaction than any of the reported catalysts, tested under similar conditions. The straight 8-ring pore channel along the c direction provided the optimum diffusion pathway as well as the shortest diffusion length for reactant and generated olefins, thus significantly reduced the coking rate. This work demonstrates that a 3D EDT approach combined with TEM and EDS analysis from a single nanocrystal can provide a clear crystal structure, crystal orientation and compositional information of nanocrystals, which are useful for the better understanding of the catalytic performance of nanosized crystalline catalysts.

National Category
Chemical Sciences
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-110173 (URN)10.1039/c4ta03419h (DOI)000343961300017 ()
Note

AuthorCount:11;

Available from: 2015-02-09 Created: 2014-12-08 Last updated: 2017-12-04Bibliographically approved
4. pi-pi interaction of aromatic groups in amphiphilic molecules directing for single-crystalline mesostructured zeolite nanosheets
Open this publication in new window or tab >>pi-pi interaction of aromatic groups in amphiphilic molecules directing for single-crystalline mesostructured zeolite nanosheets
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2014 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 5, 4262Article in journal (Refereed) Published
Abstract [en]

One of the challenges in material science has been to prepare macro-or mesoporous zeolite. Although examples of their synthesis exist, there is a need for a facile yet versatile approach to such hierarchical structures. Here we report a concept for designing a single quaternary ammonium head amphiphilic template with strong ordered self-assembling ability through pi-pi stacking in hydrophobic side, which stabilizes the mesostructure to form single-crystalline mesostructured zeolite nanosheets. The concept is demonstrated for the formation of a new type of MFI (zeolite framework code by International Zeolite Association) nanosheets joined with a 90 degrees rotational boundary, which results in a mesoporous zeolite with highly specific surface area even after calcination. Low binding energies for this self-assembling system are supported by a theoretical analysis. A geometrical matching between the arrangement of aromatic groups and the zeolitic framework is speculated for the formation of single-crystalline MFI nanosheets.

National Category
Chemical Sciences
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-106605 (URN)10.1038/ncomms5262 (DOI)000338840800001 ()
Note

AuthorCount:12;

Available from: 2014-08-13 Created: 2014-08-12 Last updated: 2017-12-05Bibliographically approved
5. Structural Study of Hexagonal Close-Packed Silica Mesoporous Crystal
Open this publication in new window or tab >>Structural Study of Hexagonal Close-Packed Silica Mesoporous Crystal
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2013 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 25, no 10, 2184-2191 p.Article in journal (Refereed) Published
Abstract [en]

Close-packed spheres can be stacked into two crystalline structures: cubic close-packed (ccp) and hexagonal close-packed (hcp). Both of these structures were found in silica mesoporous crystals (SMCs). Herein, pure hcp mesostructure with P6(3)/mmc symmetry of silica mesoporous crystals (SMCs) has been obtained in the synthetic system of cationic gemini surfactant as template and the N-[(3-trimethoxysilyl)propyl]ethylenediamine triacetix acid trisodium salt (EDTA-silyl) as the costructure directing agent (CSDA), which gives rise to the three-dimensional (3D) hexagonal structure and hexagonal plate morphology. The formation of the pure hcp structure was controlled by organic/inorganic interface curvature induced by charge matching between carboxylate groups of the CSDA and quaternary ammonium head groups of surfactant. Electrostatic potential distribution 3D map was reconstructed using Fourier analysis of HRTEM images based on electron crystallography, which showed characteristic features of the shape and connectivity of mesopores in the hcp structure. Small windows for connecting cages can be found only between layers, which determine the symmetry and local curvature of structures. As a result, the point group symmetry of mesopores becomes (6) over bar m2, instead of the m (3) over barm symmetry observed for perfect spheres in the ccp. The mechanism of stabilization and favorable growth of the pure hcp structure in mesoscale has been proposed based on synthesis strategy and symmetry support. This work provides people a better understanding of the priority of two sphere close-packed forms by comparing hcp and ccp structures.

Keyword
silica mesoporous crystals, surfactant, costructure directing agent, hexagonal close-packing, electron microscopy
National Category
Chemical Sciences
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-92019 (URN)10.1021/cm401294j (DOI)000319856000023 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

AuthorCount:6;

Available from: 2013-07-17 Created: 2013-07-15 Last updated: 2017-12-06Bibliographically approved
6. Weaving of organic threads into a crystalline covalent organic framework
Open this publication in new window or tab >>Weaving of organic threads into a crystalline covalent organic framework
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2016 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 351, 365-369 p.Article in journal (Refereed) Published
Abstract [en]

A three-dimensional covalent organic framework (COF-505) constructed from helical organic threads, designed to be mutually weaving at regular intervals, has been synthesized by imine condensation reactions of aldehyde functionalized copper(I)-bisphenanthroline tetrafluoroborate, Cu(PDB)2(BF4), and benzidine (BZ). The copper centers are topologically independent of the weaving within the COF structure and serve as templates for bringing the threads into a woven pattern rather than the more commonly observed parallel arrangement. The copper(I) ions can be reversibly removed and added without loss of the COF structure, for which a tenfold increase in elasticity accompanies its demetalation. The threads in COF-505 have many degrees of freedom for enormous deviations to take place between them, throughout the material, without undoing the weaving of the overall structure.

National Category
Chemical Sciences
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-129172 (URN)10.1126/science.aad4011 (DOI)
Available from: 2016-04-17 Created: 2016-04-17 Last updated: 2017-11-30Bibliographically approved

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