日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

Sheet-like nanomaterials with thicknesses ranging from a few nanometers to a dozen nanometers are called nanosheets. Since they are the ultimate thin functional materials, they contribute to miniaturize various devices/products and resource conservation. Many nanosheets reported so far are produced by exfoliating macro-scale materials. This requires many processes such as synthesis of macro-scale crystals under high temperature and high pressure, exfoliation, preparation of dispersion solutions for exfoliated materials (nanosheets), and film formation of exfoliated nanosheets. In addition, the exfoliation process requires chemical or physical stimulations such as sonication under existence of solvents or grinding which causes degradation and re-agglomeration of the nanosheets. We have developed a simple method by utilizing air/water interfaces for creating molecular nanosheets. The major process is dropping a solution containing organic molecules, which are the building blocks of nanosheets, onto a water surface at room temperature. With the air/water interfacial synthesis, we have succeeded in creating nanosheets of crystalline and porous coordination polymers (MOFs: metal-organic frameworks) and hydrogen-bonded organic frameworks (HOFs: hydrogen-bonded organic frameworks). Organic molecules spread at the air/liquid interface connect each other in a two-dimensional direction and align regularly, resulting in formation of crystalline nanosheets with uniform nanopores. These nanosheets are stable without aggregation at the air/water interface and can be transferred to various substrates depending on the required application while retaining their porous structure. Such nanosheets with regularly arranged molecules and nanopores of uniform shape and size can be used diverse applications including high-performance separation membranes, thin film solar cells, molecular sensors and electrodes of batteries. In this article, detailed synthetic procedures of MOF and HOF nanosheets using the air/water interface are explained together with their characterization methods and potential applications.