Metal-Organic Frameworks and Carbon Nanotubes – Imparting Electrical Conductivity to MOF Composites

Abstract

Metal-organic frameworks (MOFs) and carbon nanotubes (CNTs) have emerged as two of the most promising material classes in the last few years. Both material classes have been thoroughly investigated regarding their structures, production methods, as well as physical and chemical properties. However, despite the versatility of MOFs, nearly all members are electrically insulating. Hence, these materials have not been the first choice in the field of electronic devices. On the contrary, CNTs show high electrical and thermal conductivities, combined with low densities and high mechanical robustness. Up to now, only a few MOF–CNT-composites have been described with the focus on hydrogen storage, the use in supercapacitors or as humidity sensors.[1-3] In this work, we describe MOF–CNT-composites that combine the electrical conductivity of CNTs with the high porosity of MOFs and, furthermore, coagulate the CNTs to minimize unfavourable health effects. We present the results of the crystallization of the MOFs on CNTs by using the stable Zr-based MOFs of the UiO-66 group[4] with different linker molecules to create different chemical properties and electronic effects. The MOF particles sizes and morphologies are controlled be using modulated syntheses.[5] The composites can be provided in different forms. On the one hand, strongly intergrown composites of MOF particles that have crystallized around carbon nanotubes, application as electrode materials in batteries or in thermoelectric can be envisaged. On the other hand, thin films of the composites can be anchored on different substrates. Furthermore, we also can create nanoobjects consisting of individual CNT bearing MOF nanoparticles (Fig. 1).