Fabrication of Metal-organic Framework (MOF) thin films from copper hydroxide nano-assemblies

Thin films of metal-organic frameworks (MOFs) have attracted huge interests for various applications (e.g., sensing, catalysts and opto-electronics) due to their large porosity and tunable chemical property. Controlling the position and orientation of MOF crystals on device-scale substrates (over the centimeter scale) is required for the practical use of these sophisticated applications. Cu(OH)2 is a good precursor of the Cu-based MOF thin film due to their high reactivity with organic linkers, which allows for the growth of MOFs under mild conditions. In addition, lattice matching allows for the epitaxial growth of MOFs on Cu(OH)2. This article describes our recent progress on the fabrication of MOF thin films grown on assemblies of nanostructured Cu(OH)2. The approach enables us to control both position and orientation of MOF crystals on a substrate. The present approach for oriented MOF thin film growth is expanded for the oriented MOF-on-MOF thin films where different types of MOF layers possess epitaxial interfaces. A unique anisotropic plasmon resonance is found in the oriented MOFon- MOF films accommodating Ag nanoparticles. These materials demonstrated here are considered as good candidates for functional porous coatings for solid catalysts, bio-sensors, electrical/optical devises and others. © 2020 Japan Society of Powder and Powder Metallurgy.