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Electrochemical synthesis of copper frameworks from trimesic acid and sodium dicyanamide

par Nguyen, Thu Phuong
Président du jury Visart de Bocarmé, Thierry
Promoteur Buess Herman, Claudine
Co-Promoteur Doneux, Thomas
Publication Non publié, 2018-11-12

Thèse de doctorat

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Résumé :

Cu-BTC (Copper(II) benzene-1,3,5-tricarboxylate also known as HKUST-1 or MOF-199) is one of the most widely studied metal organic framework (MOF) structures for potential use in industrial applications. In this work, Cu-BTC metal organic frameworks were synthesized by a direct electrochemical method that consists in oxidizing a copper surface to copper ions in a solution containing the dissolved linker. The electrochemical delivery of copper ions has been performed by three different methods: potentiodynamically, galvanostatically and potentiostatically. The characterization of the samples was performed by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS) and specific surface determination using the BET method.Distinct Cu-BTC structures can be obtained according to the experimental conditions. The 3D Cu-BTC or Cu3(BTC)2 is obtained when a low current (100 mA) or a low positive potential (0 to 1 V) is used to synthesize the MOF from a methanol solution containing 0.05 M H3BTC and 0.05 M NaNO3. To validate the recently proposed reaction mechanism that implies the formation of Cu+, dicyanamide anions (dca) have been added to the solution since we have shown that a thin film of Cu(I)dca can be formed by the reduction of dissolved Cu2+ and the oxidation of a Cu surface in the presence of dca ions in aqueous and methanol solutions.The potentiostatically synthesized material is present as a film on the surface and as a powder in solution. Irrespective of the potential and dca concentration used in this work, FTIR and XRD data reveal that the powder recovered from the solution is not composed of dca and corresponds to Cu3(BTC)2. In contrast, the FTIR, XRD, TGA and XPS analyses of the film deposited at the electrode indicate that both dca and BTC are present in the film. All these data demonstrate that dca reacts with Cu(I) formed at the electrode before formation of Cu(II) ions and facilitates instead of inhibiting the growth of the Cu-BTC MOF. Specific surface area and adsorption capacities for gases (CO2, CO) and dyes (methylene blue, Congo red and methyl orange) are similar when the Cu-BTC MOF is formed in the presence and absence of Nadca and compare well to earlier reported data for Cu-BTC prepared by solvothermal methods.