Silicophosphate Gels by Nonhydrolytic Condensation Reactions
| Authors | |
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| Year of publication | 2011 |
| Type | Conference abstract |
| MU Faculty or unit | |
| Citation | |
| Description | Phosphosilicate gel materials are usually synthesized from aqueous phosphoric acid and silicon alkoxides by hydrolysis. A high hydrolytic instability of the Si-O-P bonds leads to the products that are actually silicagels impregnated by aqueous H3PO4. Their calcination then provides crystalline silicophosphate phases. We prepared phosphosilicate gels by an elimination of acetic acid esters in heterocondensation reactions between Si(OC(O)CH3)4 and OP(OSiMe3)3 in nonaqueous organic solvents. 3 Si(OC(O)CH3)4 + 4 OP(OSiMe3)3 = 12 CH3C(O)OSiMe3 + Si3P4O16 While the ester elimination from metal alkoxides and silicon tetraacetate was reported previously, its application to phosphoric acid esters is new. The nonhydrolytic ester elimination provides clear amorphous phosphosilicate gels at room temperature with a high surface area up to 450 m2 g-1. Trimethylsilylester of acetic acid was identified by NMR and GC/MS as the elimination byproduct. 29Si CPMAS NMR evidenced the presence of octahedral SiO6 groups that must be connected to phosphorus atoms and thus attest to the presence of the Si-O-P bonds in the green gel. The condensation degree was 75-82% as established by gravimetric method. Infrared spectroscopy shows that the surface of the prepared gel is covered with residual acetate and trimethylsiloxy reactive groups. We can selectively replace acetates by the reaction with substituted phenols. That can be used for further modification of the surface properties. Crystallization of the gels upon calcination was studied by thermal analysis TG/DSC/FT-IR and powder XRD methods. |
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