| 1. |
|
|
| 2. |
- Kapaca, Elina, 1987-
(författare)
-
A journey towards complete structure determination of zeolites by electron crystallography methods
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electron crystallography has recently become very successful for structural studies of materials with sub-micrometer sized crystals. In this thesis two major techniques have been applied for structure elucidation – 3-dimensional electron diffraction (3D ED) and high-resolution transmission electron microscopy (HRTEM) imaging. Both can provide information about the structure at the atomic level and have been used for structure determination. During the last decade, two 3D ED methods have been used in our group; the stepwise rotation electron diffraction (RED) method developed in our lab and continuous rotation electron diffraction (cRED) where improvements on the already existing RED method were implemented. Both 3D ED methods can be used for fast structure determination of ordered crystalline materials. HRTEM imaging is very useful for structure determination of more complex and severely disordered materials. For complex structures it is often necessary to combine several methods including powder X-ray diffraction (PXRD). Zeolites are microporous crystalline materials. They have complex structures and often synthesized as polycrystalline powders. The aforementioned electron crystallography methods have unique advantages in elucidation of atomic structures of such zeolites. In this thesis, the development of 3D ED methods, especially from RED to cRED, is described through the journey of structure determination of four zeolites; a known pure silicate silicalite-1 for testing the RED method, and three new zeolites. The new zeolites include two extra-large pore germanosilicates ITQ-56 and SYSU-3 and one small-pore aluminosilicate EMM-37. The thesis shows the limitations and advantages of the RED and cRED methods and how different challenges in the structure determination of zeolites are tackled by the advances of 3D ED methods. Finally the thesis presents a detailed structural study of disorders in an aluminosilicate zeolite ITQ-39 by combining HRTEM, RED with sample preparation by ultramicrotomy. The structure of ITQ-39 was determined in 2012 by our group. Here three new zeolite polytypes of ITQ-39 were identified from the HRTEM images and their structure models are proposed. A complete structure determination of zeolites includes elucidation of the framework structure, guest species such as structure directing agent (SDA) molecules and ions in the pores, and any structural disorder in the crystal. This thesis reflects to all of these structural characteristics of zeolites, presenting the power of electron crystallography.
|
|
| 3. |
- Kapaca, Elina, et al.
(författare)
-
Detailed Structural Survey of the Zeolite ITQ-39 by Electron Crystallography
- 2017
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 17:4, s. 1910-1917
-
Tidskriftsartikel (refereegranskat)abstract
- The structure of the highly faulted zeolite ITQ-39 was previously determined by electron crystallography, revealing the presence of stacking disorders and twinning. Structural models of three polytypes were proposed, providing a basic description of the ITQ-39 material. Here, a more comprehensive description of the complex structure of the ITQ-39 zeolite is presented based on a onedimensional periodic building unit. The study includes a detailed description of the structural defects in the material based on the analysis of high resolution transmission electron microscopy images and information on how the defects influence the pore system. A new structure arrangement with alternating twinning was found in the material, and structural models of three twinned end-members are presented. The geometry of the different structural models is evaluated to understand the formation of the crystals.
|
|
| 4. |
- Kapaca, Elina, et al.
(författare)
-
Small Pore Aluminosilicate EMM-37 : Synthesis and Structure Determination Using Continuous Rotation Electron Diffraction
- 2019
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 58:19, s. 12854-12858
-
Tidskriftsartikel (refereegranskat)abstract
- A new aluminosilicate zeolite, denoted EMM-37, with a 3D small pore channel system, has been synthesized using a diquaternary ammonium molecule as the structure directing agent (SDA) and metakaolin as the aluminum source. The structures of both as-made and calcined forms of EMM-37 were solved and refined using continuous rotation electron diffraction (cRED) data. cRED is a powerful method for the collection of 3D electron diffraction data from submicron- and nanosized crystals, which allows for successful solution and refinement of complex structures in symmetry as low as P (1) over bar.
|
|
| 5. |
|
|
| 6. |
- Kapaca, Elina, et al.
(författare)
-
Synthesis and Structure of a 22 x 12 x 12 Extra-Large Pore Zeolite ITQ-56 Determined by 3D Electron Diffraction
- 2021
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:23, s. 8713-8719
-
Tidskriftsartikel (refereegranskat)abstract
- A multidimensional extra-large pore germanosilicate, denoted ITQ-56, has been synthesized by using modified memantine as an organic structure-directing agent. ITQ-56 crystallizes as plate-like nanocrystals. Its structure was determined by 3D electron diffraction/MicroED. The structure of ITQ-56 contains extra-large 22-ring channels intersecting with straight 12-ring channels. ITQ-56 is the first zeolite with 22-ring pores, which is a result of ordered vacancies of double 4-ring (d4r) units in a fully connected zeolite framework. The framework density is as low as 12.4 T atoms/1000 angstrom(3). The discovery of the ITQ-56 structure not only fills the missing member of extra-large pore zeolite with 22-ring channels but also creates a new approach of making extra-large pore zeolites by introducing ordered vacancies in zeolite frameworks.
|
|
| 7. |
- Korde, Akshay, et al.
(författare)
-
Single-walled zeolitic nanotubes
- 2022
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 375:6576, s. 62-66
-
Tidskriftsartikel (refereegranskat)abstract
- We report the synthesis and structure of single-walled aluminosilicate nanotubes with microporous zeolitic walls. This quasi-one-dimensional zeolite is assembled by a bolaform structure-directing agent (SDA) containing a central biphenyl group connected by C10 alkyl chains to quinuclidinium end groups. High-resolution electron microscopy and diffraction, along with other supporting methods, revealed a unique wall structure that is a hybrid of characteristic building layers from two zeolite structure types, beta and MFI. This hybrid structure arises from minimization of strain energy during the formation of a curved nanotube wall. Nanotube formation involves the early appearance of a mesostructure due to self-assembly of the SDA molecules. The biphenyl core groups of the SDA molecules show evidence of π stacking, whereas the peripheral quinuclidinium groups direct the microporous wall structure.
|
|
| 8. |
- Su, Jie, et al.
(författare)
-
Structure analysis of zeolites by rotation electron diffraction (RED)
- 2014
-
Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 189, s. 115-125
-
Tidskriftsartikel (refereegranskat)abstract
- Single crystal X-ray diffraction and powder X-ray diffraction (PXRD) are powerful methods for determination of unknown crystal structures including zeolites. However, these techniques have some limitations. For instance, single crystal X-ray diffraction requires large enough crystals which are often difficult to synthesize. For powder X-ray diffraction, peak indexing and intensity extraction become difficult if there exist peak broadening caused by small crystal sizes and peak overlap due to large unit cell and high symmetry. This becomes even more complicated for samples that contain more than one phase. We developed a new rotation electron diffraction (RED) method that can overcome these limitations. Almost complete three-dimensional electron diffraction datasets can be collected from micron- or nano-sized single crystals in a transmission electron microscope by combining electron beam tilt and goniometer tilt. Here, we demonstrate the power and limitations of the RED method for ab initio structure determination of four sub-micron sized zeolites, including a calcined silicalite-1, an EUO-type germanosilicate, an FER-type aluminogermanosilicate and an AST-type aluminogermanosilicate. The latter three zeolites were found in multiphasic samples. We show how the tilt range, tilt step and resolution affect the unit cell determination, structure solution and structure refinement. The EUO-, FER- and AST-type zeolites were found in two multiphasic samples in the Al-Ge-Si system, which were also characterized by PXRD and N-2 sorption.
|
|
| 9. |
- Zhang, Chuanqi, et al.
(författare)
-
An Extra-Large-Pore Zeolite with 24 x 8 x 8-Ring Channels Using a Structure-Directing Agent Derived from Traditional Chinese Medicine
- 2018
-
Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 57:22, s. 6486-6490
-
Tidskriftsartikel (refereegranskat)abstract
- Extra-large-pore zeolites have attracted much interest because of their important applications for processing larger molecules. Although great progress has been made in academic science and industry, it is challenging to synthesize these materials. A new extra-large-pore zeolite SYSU-3 (Sun Yat-sen University no?) has been synthesized by using a novel sophoridine derivative as an organic structure-directing agent (OSDA). The framework structure was solved and refined using continuous rotation electron diffraction (cRED) data from nanosized crystals. SYSU-3 exhibits a new zeolite framework topology, which has the first 24 x 8 x 8-ring extra-large pore system and a framework density (FD) as low as 11.4 T/1000 angstrom(3). The unique skeleton of the OSDA plays an essential role in the formation of the distinctive zeolite structure. This work provides a new perspective for developing new zeolilic materials by using alkaloids as cost-effective OSDAs.
|
|
| 10. |
- Åhlén, Michelle, et al.
(författare)
-
Gas sorption properties and kinetics of porous bismuth-based metal-organic frameworks and the selective CO2 and SF6 sorption on a new bismuth trimesate-based structure UU-200
- 2022
-
Ingår i: Microporous and Mesoporous Materials. - : Elsevier. - 1387-1811 .- 1873-3093. ; 329
-
Tidskriftsartikel (refereegranskat)abstract
- Bismuth-based metal-organic frameworks (Bi-MOFs) such as bismuth subgallate are important for applications ranging from medicine to gas separation and catalysis. Due to the porous nature of such Bi-MOFs, it would be valuable to understand their gas sorption and separation properties. Here, we present the gas sorption properties of three microporous Bi-MOFs, namely, CAU-17, CAU-33, and SU-101, along with a new trimesate-based structure, UU-200. We perform a detailed analysis of the sorption properties and kinetics of these Bi-MOFs. UU-200 shows good uptake capacities for CO2 (45.81 cm3 g-1 STP) and SF6 (24.69 cm3 g-1 STP) with CO2/N2 and SF6/N2 selectivities over 35 and 44, respectively at 293 K, 100 kPa. The structure of UU-200 is investigated using continuous rotation electron diffraction, and is found to be constructed with a 3D porous framework containing pores with diameters of 3.4-3.5 Å. Bi-MOFs as a group of relatively under-investigated type of MOFs, have interesting sorption properties that render them promising for greenhouse gas adsorbents with good gas uptake capacities and high selectivities.
|
|
