Abstract
We report a new approach to tuning the properties of metal-organic framework nanosheets (MONs) by blending functionalised ligands to produce multivariate MONs (MTV-MONs). This approach enabled not only fine tuning of the MONs properties, but also resulted in MTV-MONs that show enhanced performance compared to their single-ligand counterparts. Layered copper paddle-wheel based MOFs were synthesised incorporating two or more 2,5-difunctionalised-benzene-1,4-dicarboxylate (fu-BDC) ligands. Liquid ultrasonic exfoliation resulted in the formation of nanosheets down to monolayer thickness presenting multiple functional moieties. Blending of ligands with relatively hydrophilic (methoxy-propoxy) and hydrophobic (pentoxy) moieties resulted in MTV-MONs that showed enhanced dispersion in both polar and apolar solvents compared to either single-ligand parent MON as well as intermediary binding properties. Blending of different fu-BDC ligands with different length alkoxy chains (methoxy-pentoxy) allowed incorporation of up to five different ligands within a single MTV-MON, including ligands which do not form this structure individually. This study demonstrates the potential of blending multiple ligands within an MTV-MON to enable fine-tuning of their structure and properties but also create new nanosheets which are more than the sum of their parts.
Highlights
Two-dimensional (2D) materials have received considerable attention thanks to their high surface area, anisotropic structures and nanoscopic dimensions.[1,2,3,4] the simple inorganic composition of most of these materials means it is difficult to systematically alter the surface properties of these nanosheets without disrupting their structure or other properties.[5]
We report a new approach to tuning the properties of metal–organic framework nanosheets (MONs) by blending functionalised ligands to produce multivariate MONs (MTV-MONs)
DFT modelling demonstrated H2O could coordinate to the axial PW sites,[53] and Pawley and Rietveld refinement of high-resolution Synchrotron powder X-ray diffraction (PXRD) data enabled structural modelling of the frameworks both pre- and postexfoliation in acetonitrile (MeCN).[54]
Summary
One strategy that has been extensively used to modify the properties of other molecular materials, but to our knowledge. Paper has yet to be applied to MONs, is blending multiple different ligands non-stoichiometrically within a single framework. Blending ligands with different functional groups has the potential to aid the exfoliation of layered MOFs to form MONs by weakening interlayer interactions and enhancing interaction with solvent molecules to aid dispersion. We synthesise a new series of layered MTV-MOFs using combinations of these linkers and exfoliate them to investigate the effect of different ligand combinations on the structure and properties of the resulting nanosheets. We speculated that random inclusion of the ligands[57] within the 2D net could reduce interlayer interactions and so lead to higher yields and thinner nanosheets than seen in any of the parent compounds
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