Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.800565
Title: The design, synthesis and applications of copper paddle-wheel based metal-organic framework nanosheets
Author: Ashworth, David J.
ISNI:       0000 0004 8509 2839
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2019
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Abstract:
Metal-organic framework nanosheets (MONs) are an exciting new class of modular two-dimensional (2D) nanomaterial. They are formed from organic linker ligands that link metal ions or clusters in two dimensions. These 2D materials combine the tunability of metal-organic structures with properties of other 2D materials, such as large external surface area, nanoscopic dimensions and high aspect ratio. This has led to increasingly widespread utilisation of MONs in applications as diverse as catalysis, sensing, gas separation, water purification, optoelectronics and energy conversion. Top-down exfoliative methods can be used to produce MONs from layered metal-organic frameworks (MOFs). Factors that govern this process are poorly understood. MON design remains in its infancy, with most current MONs utilising well-known, relatively simple building blocks, such as benzene-1,4- dicarboxylate (BDC). In this thesis, new isoreticular series of layered MOFs were synthesised utilising different functionalised BDC (fu-BDC) ligands to link copper paddle-wheel (PW) secondary building units in two dimensions. These were exfoliated using liquid ultrasonic exfoliation to form MONs and characterised using a diverse range of techniques in order to understand the effect of different functional groups on the structure, dimensions and properties of the MONs formed. In Chapter 3, functionalisation with relatively hydrophilic or hydrophobic moieties influenced the concentration, morphology and size of MONs when exfoliated in a wide range of solvents. Generally, MONs formed using the relatively hydrophilic ligand were observed in higher concentration in polar solvents. Clear differences in the binding properties of small aromatic heterocycles were observed, and DFT calculations indicated potential intramolecular coordination of the relatively hydrophilic moiety upon removal of DMF from axial coordination sites of the PW. Functionalisation with a series of different length alkoxy chains enabled synthesis of an isoreticular MOF series in Chapter 4. Pawley and Rietveld refinements of PXRD data allowed structure determination, which indicated that increasing the chain length increased the interlayer spacing. This corresponded to an increase in CO2 adsorption. Statistical particle size analyses showed that increasing the chain length resulted in MONs of decreasing height but larger lateral dimensions. Chapter 5 and Chapter 6 demonstrated that multiple different fu-BDC ligands could be blended within the layered MOF structure to form mixed-ligand multivariate-(MTV-)MOFs. Liquid ultrasonic exfoliation resulted in mixed-ligand MTV-MONs for the first time. Blending of relatively hydrophilic and hydrophobic fu-BDC resulted in MONs with which had intermediary properties compared to the single-ligand parent MONs. Blending different fu-BDC ligands with different length alkoxy chains demonstrated tuneable MON composition. In Chapter 6, a different series of fu-BDC ligands (fu= (H)2, NH2, (Cl)2, (Br)2 and NO2) was used to synthesise a series of isoreticular layered MOFs and exfoliation formed MONs down to monolayer thickness. Eleven MTV-MOFs were then synthesised using combinations of fu-BDC, in which generally a larger number of different ligands produced nanosheets with a decreased average height. Overall, this thesis demonstrates the utility of liquid ultrasonic exfoliation as a top-down exfoliative method for the production of MONs from layered, PW-based MOFs. MONs are a modular class of nanomaterial that fall at the interface of 2D and metal-organic chemistry. The isoreticular approach to their design demonstrates tunability of the materials' chemistry. MONs therefore have significant potential as 2D nanomaterials with controllable, tuneable surface chemistry.
Supervisor: Foster, Jonathan A. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.800565  DOI: Not available
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