Saeidi Bidokhti, Naghmeh; (2018) Synthesis, characterisation and application of carbonised metal-organic frameworks. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The main purpose of this project was to synthesise, characterise and evaluate metal organic frameworks (MOFs) and MOF-derived carbons for different applications. Carbon is widely used in the structure of electrodes of electrochemical energy conversion/storage devices. In order to control the pore size distribution of such carbons, the pyrolysis of MFOs under inert atmosphere was considered. MOFs are highly porous crystalline materials constructed from metal ions linked together by different organic ligands. When MOFs are pyrolysed, the resulting carbon material inherits the pore structure of the precursor MOF. By combining different metal ions and organic linkers, it is possible to create MOFs with different pore sizes. In this research, we aimed to take advantage of this property and derive carbons from MOFs to produce porous carbons with controlled pore size distributions and evaluate their behaviour in electrochemical energy conversion/storage devices to improve the performance of the latter. Three different MOFs were selected in terms of their pore sizes (ZIF-8, MOF-5 and MIL-100(Fe)) and were hydrothermally synthesised and characterised with Brunauer–Emmet–Teller (BET) and powder X-ray diffraction. These MOFs were then carbonised under an argon atmosphere and characterised with BET and energy dispersive spectroscopy analysis. The electrocatalyst was made by loading platinum on the carbonised ZIF-8 and characterised with EDS to measure the amount of platinum loaded and assess the homogeneity of the platinisation process for fuel cell application. The Pt/CZIF-8 was electrochemically characterised by cyclic voltammetry, oxygen reduction reaction and durability tests to evaluate its electrochemical behaviour. For the supercapacitor applications, all MOF-derived carbons were characterised by cyclic voltammetry and the cyclic charge–discharge curve. The separation ability of the MOFs was also assessed by immersion calorimetry, and when any unexpected behaviour was observed, the assessment was applied to the replica MOF (carbonised MOFs), and their behaviour was observed. After evaluating the results, the best MOF/carbonised MOF for each application was introduced. Four different MOFs, ZIF-8, HKUST, UiO-66 and UiO-67, were synthesised and characterised with BET and X-ray diffraction, and their separation ability was investigated using immersion calorimetry in xylene isomers. Since HKUST and UiO-66 had unexpected adsorption behaviour, the replicas of these MOFs were also produced under argon, and their separation ability was evaluated in m-xylene.

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