Abstract
The research in this thesis is focused on the application of metal-organic frameworks (MOFs) for the uptake and release of semiochemicals to be utilised in pest lure traps. In addition, phase changes in MOF induced on exposure to volatile molecules at room temperature have been studied as is the usage of flow NMR as a screening method for semiochemical uptake in MOFs.Chapter one introduces metal-organic frameworks, outlining definitions, structural features, synthetic routes, and typical characterisation methods. In addition, an outline of molecular simulation is given focusing on classical methods. An overview of prevalent applications of MOFs is presented including, gas storage, molecular separations, catalysis, drug delivery and uses in agriculture. Finally, semiochemicals are introduced with a focus on 3-octanone, isobutyl acetate, and 1-hexanol.
Chapter two studies the effect of changing the alkyl chain size in IRMOF materials [ZnO4(bdc-NHR)3] (R = Pr, Bu, Pent, Hex, Hep, Oct) and [ZnO4(bdc-OR’)3] (R’ = Pr, Bu, Pent) for the uptake and release of the semiochemicals 3-octanone, isobutyl acetate, and 1-hexanol. It was found that increasing the alkyl chain length resulted in a decrease in uptake and a slower release rate of semiochemicals. In the case of 1-hexanol, degradation of the IRMOF materials was observed highlighting that the suitability of each MOF series must be tested for each semiochemical. Computational studies showed that dispersion interactions were the most significant between the MOF and semiochemical, as well as a gating effect observed with the alkyl chains.
Chapter three investigates several functionalised DMOF materials of general formula [Zn2(bdc-x)2(DABCO)] (x = H, Br, Br2, NO2, C4H4, NHR’, OR’) for the uptake and release of semiochemicals. It was found with the addition of bulkier functional groups that the uptake of semiochemicals was generally reduced, and the release rate was slower. It was also found that by changing the topology to a system containing larger central pore, seen with DMOF-1-kgm, results in a significant increase in the uptake and faster release rate of semiochemicals. As with the IRMOF materials in chapter two, computational studies showed that the most significant MOF-semiochemical interactions were dispersion interactions.
Chapter four is an investigation into phase changes occurring to MOFs on exposure to guest molecules. In the first section a return of crystallinity is studied in IRMOF materials upon exposure to 3-octanone or isobutyl acetate vapour. The second section studies the post-synthetic transformation of DMOF-1-kgm to DMOF-1 on exposure to alcohols. It was found that bulkier alcohols cause a slower rate of transformation.
Chapter five investigates experimentally the semiochemical uptake and release from a range of zeolitic imidzolate frameworks (ZIFs) and the open-metal site MOFs HKUST-1 [Cu3(TMA)] and Cu-MOF-74 [Cu2(dobdc)]. The ZIF materials showed that with an increase in pore window size the uptake and release rate of semiochemicals was increased. In the case of ZIF-4 pore expansion was observed when exposed to isobutyl acetate and 1-hexanol, which enhanced the uptake, and upon release the pores contract resulting in a faster release rate. This highlights that this pore breathing could be a useful feature for the uptake and release of guest molecules.
Chapter six explores the potential to use flow 1H NMR spectroscopy as a screening tool to assess the uptake of semiochemicals in MOFs. Two approaches were taken to introduce the semiochemical (3-octanone or isobutyl acetate). These involved either, an injection method where the semiochemical was added to the system before the MOF packed column or a method where the MOF was preloaded with semiochemical. A range of different MOFs were assessed using both methods and it was found that slow flow rates were critical to obtain information on the retention of guest molecules.
Chapter seven gives some overall conclusions and presents ideas for further work from the results of this thesis. Finally, Chapter eight outlines the methods used to conduct this thesis.
| Date of Award | 4 Dec 2023 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Andrew Burrows (Supervisor), Tina Düren (Supervisor) & Catherine Lyall (Supervisor) |