Vol.11 no.3 2019
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Research paper : Challenge towards synthesis of non-silica-based hybrid mesoporous materials (T. KIMURA)−116−Synthesiology - English edition Vol.11 No.3 (2018) or compounding with functions derived from inorganic species. As mentioned earlier, the progress from silica to organosilica went relatively smoothly. On the other hand, why did not the research for non-silica oxides lead to synthesis research for inorganic-organic compounding? It was probably because rather than the difculty in controlling the reaction of a starting material, there was no such starting material. Other than silica, alkoxide materials or similar compounds that include bridged organic groups in the structure are not available commercially. In reality their synthesis methods are not reported. I found three types of tin compounds that were bridged by organic groups.[14] If I had to develop synthesis methods of such compounds for each metal species, I would have to spend an enormous amount of energy on preparing raw materials for mesoporous materials, and I thought this was not a realistic approach.3.1 Proposal of synthesis method: Limit of organically bridged phosphonic acidFrom the above background, I have searched for compounds that are capable of bond formation with various metal species and included bridged organic groups within the molecular structure. As a result, I proposed the use of bisphosphonate compounds (similar to phosphoric acid that are bridged with organic groups). The synthesis technology for phosphonic acid was almost established. Moreover, in the synthesis of metal phosphates, for example, if the mol of phosphoric acid in solution was the same as the metal species, the reaction of the metal species would be inhibited, and I thought this advantage could be utilized. The mesoporous material was synthesized using commercially available phosphonates bridged with organic groups. Since I set the design of a “hydrophilic surface structure” as the first research goal, initially I spent my efforts on the synthesis of mesoporous aluminum phosphonates in which aluminum was the metal species. As a result, I was able to propose a synthesis route of a non-silica-based hybrid mesoporous material, as shown in Fig. 5 for the rst time.[15] For verication, I selected the simplest reaction of methylene bridged phosphonates and aluminium isopropoxide that is the aluminum source, and conducted the synthesis using an alkyltrimethylammonium (CnTMA) surfactant under alkaline conditions. The facts that the structural order could not be obtained sufciently when achieving mesoporosity and that low-temperature ring had to be used since the surfactant could not be extracted (the bond between phosphorus atoms and bridged organic groups is partially disconnected) were seen as new issues.The rst issue, to improve the orderliness of the mesoporous structure, was not too difficult.[16] The structural order improved greatly just by using methylene bridged phosphonates and aluminum chloride (AlCl3) with suitable reactivity as the aluminum source, and by changing the synthetic condition to an acid condition. As a surfactant, Fig. 5 Proposal of the synthesis route from organically bridged phosphonate compound, and progress in composition control technology (with the number of signicant technologies shown in Fig. 3)POHOOHPOHOOHMOOOOOO(HO)2OPPO(OH)2(HO)2OPPO(OH)2(HO)2OPPO(OH)2PPS3HOPPPPPPNH2PPSO3HH2NPP⑤ Removal of amphiphilic organic molecules (low-temperature calcination, extraction, etc.)① Formation of P-O-M bond② Interaction with soluble inorganic species③④ Self-assembling + condensation reaction of inorganic speciesAlAlTi& VOrganically bridged phosphonateMetal speciesVariation of inorganic species and organic groups(Early stage of development)(This development)

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