Vol.11 no.3 2019

Research paper : Challenge towards synthesis of non-silica-based hybrid mesoporous materials (T. KIMURA)−115−Synthesiology - English edition Vol.11 No.3 (2018) the difficulty of obtaining mesoporous material from non-silica-based materials. To prevent formation of precipitation while controlling bond formation of inorganic species, first, a transparent precursor solution is prepared. Next, a solvent evaporation method[11][12] is used to rapidly form a mesoporous structure to obtain a highly ordered mesoporous lm. Preparation of a precursor solution is done mainly with an ethanol solvent. However, an alkoxide starting material cannot interact with the hydrophobic region of amphiphilic organic molecules. To slowly promote progression of hydrolysis and condensation reactions of alkoxide materials, a small amount of hydrochloric acid is added. Even then, when amphiphilic organic molecules and dissolved inorganic species interact, solvent evaporation is immediately promoted by processes such as spin coat and spray-dry, to bring them to a quick nish as precursors of mesoporous materials.[13] Even more troublesome is the fact that polymerization reaction of oxide materials progresses even after film formation. As a desperate measure to forcibly delay this reaction, sometimes, the product may be placed in a freezer (about -20 °C).In the actual follow-up test, it has been confirmed that the structural order greatly decreases if it is not placed in a freezer. This is fine for goal-oriented basic research of performance evaluation of materials or for studying structure correlation. However, this cannot lead to process design for mass synthesis or mass production for practical use. Moreover, surprisingly, a majority of non-silica-based mesoporous materials presented as powder samples in published papers are actually synthesized by a solvent evaporation method. I have heard that there are cases in which the precursor solution is spread thinly as possible and then samples are collected by lm formation. As a result of the difficulty of synthesizing non-silica-based mesoporous materials, such heavy-handed synthesis methods are used worldwide. Synthesis research mindful of process design suitable for practical application cannot be done unless understanding is deepened for the reactivity of inorganic materials and composition control technology is advanced in a true sense. In addition, there are expectations for the material to be used as a catalyst carrier by only using the effect of increased surface area like alumina. In most cases, sufcient function expression cannot be expected unless the crystalline property of the oxide framework is increased. For those that realized the synthesis of mesoporous film using oxides of transition metal, proposals were made for new application technologies as device parts such as sensor materials or electrode materials. Therefore, I did see effects of increasing adsorption volume of photo-responsive molecules or adsorption sites of sensing target components. However, since it was not possible to increase the crystalline property sufficiently while maintaining porosity derived from the mesoporous structure, it seemed that the effect of achieving mesoporosity was limited.3 Non-silica-based hybrid mesoporous material: Toward building of substance groupAs discussed above, functional design derived from silica cannot be expected. In starting this research, it was necessary to simultaneously realize inorganic-organic compounding of the framework, in addition to achieving mesoporosity in non-silica-based materials. I set opening the way to this advanced material design as the ultimate goal of synthesis study. When I started, in reality, there was not even a way of synthesizing non-silica-based hybrid mesoporous materials. If I could develop a universal synthesis technology for a mesoporous material that was non-silica-based and was composed of an inorganic-organic framework, I could clear the way toward advanced material design, such as arbitrarily changing the environment inside the nanospace from hydrophobic to hydrophilic using properties of non-silica material surfaces, Fig. 4 Synthesis of mesoporous organosilica: Variation of organic groups (with the number of significant technologies shown in Fig. 3)Mesoporous organosilica③④ Self-assembling + condensation reaction of inorganic species⑤ Extraction of amphiphilic organic molecules① Formation of Si-O-Si bond② Interaction with soluble inorganic speciesOrganically bridged silane

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