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Defect engineering of UiO-66 metal-organic framework (MOF) for improved hydrogen storage applications
Thesis (PhD)--Stellebosch University, 2021.
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| Format: | Thesis |
| Language: | en_ZA |
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Stellenbosch : Stellenbosch University
2021
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| _version_ | 1867613902393573376 |
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| access_status_str | Open Access |
| author | Ledwaba, Mpho Violet |
| author2 | Barbour, Leonard J. |
| author_browse | Barbour, Leonard J. Ledwaba, Mpho Violet |
| author_facet | Barbour, Leonard J. Ledwaba, Mpho Violet |
| author_sort | Ledwaba, Mpho Violet |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (PhD)--Stellebosch University, 2021. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/109943 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:43:31.605Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2021 |
| publishDateRange | 2021 |
| publishDateSort | 2021 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/109943 Defect engineering of UiO-66 metal-organic framework (MOF) for improved hydrogen storage applications Ledwaba, Mpho Violet Barbour, Leonard J. Ren, Jianwei Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. Metal Organic Frameworks Hydrogen -- Adsorption UiO-66 Defects in manufactures UCTD Thesis (PhD)--Stellebosch University, 2021. ENGLISH ABSTRACT: Metal–organic frameworks (MOFs) as a relatively new class of porous crystalline materia ls have attracted much interest in many applications due to their high porosity, diverse structures, and controllable chemical structures. However, the specific geometrical morphologies, limited functions and unsatisfactory performances of pure MOFs hinder their further applicatio ns . Several modifying strategies for engineering MOF crystals have been developed based on their desired features and applications. In nature there are no "ideal crystals" with an infinite periodic repetition or ordering of the same groups of atoms in space. The structure of "real crystals" often deviates from the ideal arrangement and includes a significant density of structural irregularities or deficiencies. Crystal irregularities may arise from compositio na l inhomogeneities, and this term is often used interchangeably. By using defective technology strategies during their synthesis, crystal imperfections may be introduced into the MOF framework, thereby enhancing their performance in the envisioned applications. Defect engineering is one of the most effective approaches that one can use to change their physical and chemical features such as thermal stability, textural properties, mechanical properties and gas adsorption abilities. In order to achieve the desired changes, it is essential to control the defects, otherwise these defects may have an adverse effect on the MOFs. Therefore, it is vitally important to apply synthetic control over defects; the exact nature and concentration of the defects may be controlled by modifying the synthetic conditions and post-synthet ic modifications. Structurally characterising inherent or engineered defects is very challenging and this challenge has not been addressed substantially. This thesis explores the experimental creation of structural defects via post-synthetic modification, the role of structural defects and their relationship to gas adsorption, with emphasis on hydrogen adsorption. Through a combination of techniques, including powder X- ray diffraction (PXRD), thermogravimetric analysis (TGA), acid-base titration and Brunauer– Emmett–Teller (BET) surface area and pore size measurements, missing linkers and missing cluster defects have been identified and analysed. In Chapter 4, we seek to understand the relationship between some of the major synthetic parameters and the physicochem ic a l characteristics of UiO-66 (Universitetet i Oslo) MOF and discover a "non-defective" sampling technique for this material. The technique produces non-defective UiO-66 MOFs at a specific temperature (493 K), with the linker ratio being greater than that of the salt previously reported by Shearer et al. As described in Chapter 5, by varying the concentrations of modulator and the linker, we demonstrate that the linker vacancies can be systematically tuned, leading to significantly increased surface areas. The defects are caused by partial terephthalic acid eplacement with smaller formate groups from the formic acid modulator. The BET surface areas of the obtained samples range from 1200 to 1600 m2.g-1, and the best sample has a surface area that is about 30% higher than the theoretical value of the surface area of defect-free UiO- 66. Additionally, linker vacancies are proven to have profound effects on the gas adsorption behaviour of UiO-66 by improving the hydrogen uptake from 1.51 wt. % to 2.0 wt. % at 77 K and 1 bar. Chapters 5 and 6 include detailed studies of two conventional methods for generating defects (i.e., de novo defect technology and post-synthetic modification (PSM)) discussed in each chapter respectively. Still in chapter 5, experimental investigations are discussed that show the impact of modulator and linker concentration on H2 adsorption and thermal stability. Chapter 6 provides insight into the impact on thermal stability and adsorption properties brought about by the post-synthetic modification methods. The resultant materials typically have high surface areas, large pore volumes and structures with hierarchical pores, which makes them more practical for hydrogen storage applications. AFRIKAANSE OPSOMMING: Raadpleeg teks vir opsomming Doctoral 2021-03-04T01:21:51Z 2021-04-21T14:33:09Z 2021-03-04T01:21:51Z 2021-04-21T14:33:09Z 2021-03 Thesis http://hdl.handle.net/10019.1/109943 en_ZA Stellenbosch University 165 pages application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Metal Organic Frameworks Hydrogen -- Adsorption UiO-66 Defects in manufactures UCTD Ledwaba, Mpho Violet Defect engineering of UiO-66 metal-organic framework (MOF) for improved hydrogen storage applications |
| title | Defect engineering of UiO-66 metal-organic framework (MOF) for improved hydrogen storage applications |
| title_full | Defect engineering of UiO-66 metal-organic framework (MOF) for improved hydrogen storage applications |
| title_fullStr | Defect engineering of UiO-66 metal-organic framework (MOF) for improved hydrogen storage applications |
| title_full_unstemmed | Defect engineering of UiO-66 metal-organic framework (MOF) for improved hydrogen storage applications |
| title_short | Defect engineering of UiO-66 metal-organic framework (MOF) for improved hydrogen storage applications |
| title_sort | defect engineering of uio 66 metal organic framework mof for improved hydrogen storage applications |
| topic | Metal Organic Frameworks Hydrogen -- Adsorption UiO-66 Defects in manufactures UCTD |
| url | http://hdl.handle.net/10019.1/109943 |
| work_keys_str_mv | AT ledwabamphoviolet defectengineeringofuio66metalorganicframeworkmofforimprovedhydrogenstorageapplications |