Rational design and synthesis of metal-organic frameworks and their composite materials with tunable structural properties and enhanced chemical stability
Creators: name: Wei, Xiuming
Publisher: name: The University of Edinburgh
Year: 2024
Subjects: metal-organic frameworks
MOFs
ZIF-8
ZOmAF-OA
stability
oleic acid

description: Metal-organic frameworks (MOFs), a novel class of organic-inorganic hybrid porous materials, are formed through the self-assembly of central metal ions or clusters and organic ligands, resulting in a periodic network structure. MOFs have garnered considerable interest due to their unique features. A distinctive property of MOFs that sets them apart from other porous materials, like zeolites and carbons, is their tunability. The structure of MOFs is governed by the geometry of the secondary building units (SBUs) and the dimensions and form of the organic ligands. This allows for a considerable degree of customization. By carefully choosing the appropriate SBUs and linkers, it is possible to fine-tune MOFs to achieve the exact pore size, structure, and functionality required for specific applications. The flexibility and great compatibility of MOFs promote the fabrication of MOF composite materials to achieve specific functionalities. This adaptability has led to extensive research on MOFs for various applications, including gas storage and separation, energy storage, catalysis, sensing, and drug delivery. However, the fabrication of MOF coating structure requires further research, and the practical feasibility of MOF and its composite material is often restricted by limited chemical stability. Therefore, the systemic control of MOF and its composite structure with enhanced chemical stability is urgently needed. To achieve a fundamental understanding of the control of MOF coating on the substrate, a facile subclass of MOF zeolitic imidazolate framework-8 (ZIF-8) was studied. The manipulation of ZIF coating on membrane support including ZIF morphology and coating density was achieved by varying the synthesis conditions such as cosolvent and synthesis time. Desired ZIF coating morphology could be obtained by simply controlling the ratio of ethanol, the coating density and permeability could be controlled by varying synthesis time. The optimized ZIF-8 formation was further explored on other organic (polyamide, ABS, PLA, HIPS, melamine, and polypropylene) and metal (stainless steel) substrates. In addition, the assynthesized ZIF-coated materials were invested for oil/water separation and antibacterial performance. Although the ZIF composite materials exhibited great performance in water remediation and antibacterial tests, the stability of ZIF coating greatly limited their practical application. Therefore, the hydrolysis of ZIF-L and its composite material was systematically studied in aqueous media under different pHs, and a facile post-synthetic modification of silk fibroin (SF) protein was proposed to enhance the chemical stability of ZIF composite material without altering the surface wettability of the ZIF-L composite mesh. SF protein coating was proved effective for the stability enhancement of both ZIF-L coatings and powder samples in aqueous media. The SF-ZIF-L-SS meshes preserved their switchable wetting properties with superior separation performance for oil/water mixture. However, the SF protein coating ZIF-L mesh exhibited limited enhancement in the hydro stability, to further tackle this issue, an organic linker with a long alkane chain (oleic acid-OA) was utilized to increase the wettability, and eventually enhance the stability in aqueous media. The superhydrophobic Zinc Organic Monoacid Framework-Oleic Acid (ZOmAF-OA) composite meshes were fabricated by a facile one-step synthesis. The coating morphology and coverage of ZOmAF-OA on the mesh skeleton were systematically studied by varying the mesh number, oleic acid concentration, and synthesis temperature. The chemical stability of the ZOmAF-OA-SS composite mesh was studied in detail under various conditions and exhibited excellent stability in aqueous media. The surface superhydrophobic wettability and oil/water performance were well retained after the stability experiments. The superhydrophobic ZOmAF-OA demonstrated exceptional chemical stability and opened a new area in the world of 2D coordinated materials. A series of ZOmAFs with tuneable nanostructures were fabricated through the solution synthesis at ambient conditions. The structural tunability was successfully achieved by the manipulation of organic monoacid geometry. The physical properties and chemical composition of ZOmAFs were investigated. Furthermore, a layered 2D coordinated structure was established to describe ZOmAFs. In summary, the results in this thesis demonstrate the facile fabrication of MOF and MOmAF and their composite materials with controllable coating properties, including coating morphology, density, and wettability. In addition, this thesis presents a remarkable contribution towards the stability enhancement of MOFs and MOmAFs and their composite materials.