Vol.11 no.3 2019
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Research paper : Challenge towards synthesis of non-silica-based hybrid mesoporous materials (T. KIMURA)−113−Synthesiology - English edition Vol.11 No.3 (2018) 2 Summary of extension of compositional control range for mesoporous materials and technological issuesIn this study, I discuss raising the level of control technology for framework composition of mesoporous materials. From the viewpoint of the synthesis chemistry, I summarize the difficulty of achieving mesoporosity in non-silica-based materials, the technological issues that prevent inorganic-organic compounding, while comparing with hybridization (inorganic-organic compounding) of the silica materials. The main elemental technologies of synthetic research for mesoporous materials are as follows:(1)Selection of appropriate inorganic starting material, andreaction control of inorganic species in solution,(2)Design of interaction between inorganic species andamphiphilic organic molecules in solution,(3)Understanding the self-assembly behaviors of amphiphilicmolecules that are newly produced by interaction,(4)Adjustment of the process of liquid-crystal-like structureformation and the following polymerization of inorganicspecies,(5)Development of removal method of amphiphilic organicmolecules, and(6)Process design assuming application development inthin lms, powders, and others.Figure 3 shows these elemental technologies in conjunction with each stage of formation of mesoporous silica precursors. The most important point here is to understand all elemental technologies comprehensively. That is, this research result, or the composition design technology of advanced mesoporous materials, could not have been made unless these elemental technologies were integrated.The formation mechanism of mesoporous silica precursors that was shown immediately after the discovery of mesoporous silica drew controversy. If one understood that the precursors were formed by the liquid crystal template route as shown in Fig. 3 (top), it was sufficient to believe that space design at nanometer level could be done easily inside oxide materials. However, as a result of follow-up investigation, it was found that in most cases, the precursors (composite of liquid-crystal-like structured silica and amphiphilic organic molecules) are produced by concerted organization, as shown in Fig. 3 (bottom), rather than the liquid crystal template route. First, the hydrophilic regions of amphiphilic organic molecules interact with the dissolved silicate species in oligomer form. At this point, if the molecular size of inorganic species is too big, precursors with structural order cannot be obtained, or precipitates are formed beforehand. If interaction with inorganic species goes well, it can be considered that new inorganic-organic composite molecules with amphiphilic properties have been formed. If self-assembly of this composite molecule and the bonding of inorganic species occur simultaneously (concertedly), precursors with high structural order containing liquid crystal structures are obtained. Finally, when organic molecules are removed by firing or other methods so the structural order is not broken, an orderly mesospace is formed inside the material.Fig. 2 Comparison between molecule size and range of pore size control of mesoporous silica50 nmMicroporous material (less than 2 nm)Macroporous material (more than 50 nm)[Size of molecule]Hydrogen(H2)Water(H2O)Methane(CH4)Benzene(C6H6)Mesoporous material(2~50 nm)※Active range as synthesis vessel(eective for liquid-phase reaction)※Helpful range for smoothdiusion of molecule(eective for gas-phasereaction)2 nm1.5~4 nm~10 nm5~10 nm~30 nm~100 nm※Alkylammonium type surfactant+Solubilizing agent+Solubilizing agent※Triblock copolymer (Symmetric type)※Block copolymer (Asymmetric type)DNAFine chemical~15 nm 1 nm [Technology to control pore size of mesoporous silica]Protein

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