Control of micro/mesoporosity in silicophosphate xerogels
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| Year of publication | 2015 |
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| Description | Silicophosphates are widely used as advanced technology materials. Because of their high proton conductivity, special optical and electrical properties and biocompatibility they can be applied as heterogeneous catalysts, proton conducting electrolytes, optical glasses and biomaterials. The synthesis of these compounds by hydrolytic sol-gel methods poses considerable obstacles, the reason being that Si–O–P bonds are unstable under hydrolytic conditions and therefore phase separation to silica and phosphoric acid occurs. As a solution, we have recently developed a non-hydrolytic sol-gel method based on ester elimination starting from silicon(IV) acetate and tris(trimethylsilyl)phosphate. This reaction principle was further developed for the synthesis of hybrid organic-inorganic materials based on silicophosphate skeleton.2 The reactions of bridged acetoxysilanes (AcO)3Si-X-Si(OAc)3 and phosphoryl reagents (Me3SiO)2P(O)-X-P(O)(OSiMe3)2 have also been investigated and found to produce gels that exhibit large surface areas (up to 700 m2 g-1). The presence of SiO6 structural units in bridged-phosphoryl xerogels is related to their microporosity while the absence of such moieties in bridged acetoxysilane networks is congruent with significant mesoporosity. Several important parameters are identified which can be used to tailor the properties of these hybrid matrices such that gels with specific polarity, porosity and surface area can be targeted at the time of synthesis. The condensation reaction, structure of resulting materials, effects on porosity and use of prepared silicophosphates in catalytic test reaction will be described in detail. |
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