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Solvent-Dependent Stability of Highly Defective UiO-66 to Acids and Bases
preprintrevised on 21.01.2021, 18:07 and posted on 22.01.2021, 07:32 by Daniele Cartagenova, Fabio A. Peixoto Esteves, Nathan T. Fischer, Jeroen A. van Bokhoven, Marco Ranocchiari
UiO-66 is one of the most chemically stable Metal-organic frameworks (MOFs) available. However, little is known about its stability in organic solvents. In this study, we synthesized a highly defective UiO-66 (HD-UiO-66) and explored how its textural properties change when exposed to weak and strong acids, both organic and inorganic in nature, and dissolved in different solvents, water, dichloromethane (DCM), and tetrahydrofuran (THF). Exposing defective UiO-66 to weak acids and bases, such as acetic acid and triethylamine, maintains its crystalline structure and porosity, irrespective of the solvent. Sulphuric acid decomposes HD-UiO-66 in organic solvents but not in water, trifluoroacetic acid decomposes the framework only in DCM. Tetramethylguanidine decomposes HD-UiO-66 in organic solvents but mantains some of the MOFs porosity and crystalline structure in water, whereas potassium carbonate damages the MOF to a greater extent in water than in organic solvents. Our results show that the acid/base properties of the solvent modulate the strength of acids and bases and its polarity determines the extent of their solvation, thus playing a crucial role in altering the MOF’s textural properties. This systematic investigation highlights the central role played by the solvent in tuning the stability of MOFs, which is relevant for liquid-phase applications in acidic and basic environments, such as catalysis and adsorption.