Metal-organic frameworks (MOFs) are of significant interest because they can be loaded with a broad array of materials, ranging from liquid hydrogen to drug molecules. They are also of interest for heterogeneous catalysis. However, one problem in the synthesis of MOFs concerns a phenomenon called interpenetration, which results in a reduction in the size of the voids within the frameworks, hence reducing their carrying capacity.
Now scientists at the Departments of Physical Chemistry and Inorganic Chemistry at the Ruhr-University in Bochum (RUB) have developed a new method of synthesising MOFs called liquid phase epitaxy, which bypasses this interpenetration problem. The method depends on so-called ‘intelligent surfaces’ which are alternately dipped into MOF structural elements. This makes it possible to produce materials with significantly larger pores than had been the case to date.
The intelligent surfaces are produced by dipping metal substrates into solutions of organothiols (sulphurous organic molecules). The sulphur atoms bind tightly to the metal substrate, thus acting as anchors for the organic molecules, yielding self-assembled monolayers (SAMs). The growth of the frameworks on the surface of the SAMs can then be controlled by the particular choice of the organothiol. It is even possible dictate their orientation by using tailor-made SAMs