Publication details

Mesoporous hybrid inorganic-organic phosphosilicates by non-hydrolytic sol-gel reactions



Year of publication 2014
Type Conference abstract
MU Faculty or unit

Central European Institute of Technology

Description Non-hydrolytic sol-gel reactions based on condensation of two functional groups are studied as an alternative to aqueous techniques for the synthesis of multimetallic oxides and inorganic-organic hybrid materials in the form of xerogels, nanoparticles, and thin films. We developed a non-hydrolytic sol-gel route based on acetic acid ester elimination providing parent phosphosilicate and its hybrid inorganic-organic derivatives. The polycondensation reactions between Si(OAc)4 and OP(OSiMe3)3 provides microporous phosphosilicate xerogels with surface areas up to 570 m2 g-1. Substitution reactions of residual acetoxy and trimethylsiloxy groups on the surface with a variety of reagents, such as SiCl4, RSiCl3, POCl3, AlX3, ROH, and Me3SiOSiMe3, show versatility of the synthesized phosphosilicate xerogels in tuning their properties, such as Bronsted and Lewis acidity. The consecutive substitution of Si and P precursors by acetoxysilanes 1RxSi(OC(O)CH3)4-x (1R = Me, Ph; x = 1-2) and trimethylsilylesters of phosphonic acid 2RP(O)(OSiMe3)2 (2R = c-Hex, Ph) caused the decrease of surface areas and increase of average pore sizes because of the lower cross-linking ability of the substituted precursors. To avoid a significant decrease of surface areas of hybrid xerogels we used as precursors acetoxysilanes and phosphonic acid esters with bridging alkyl or aryl groups, such as (AcO)3Si-(CH2)x-Si(OAc)3 (x = 1-3, 6) and (Me3SiO)2P(O)-3R-P(O)(OSiMe3)2 (3R = C2H4, C6H4). We were able to tune the pore size of resulting xerogels to the mesoporous range. The prepared xerogels were characterized by elemental analyses, solid-state 13C, 29Si, 31P NMR spectroscopy, IR spectroscopy, surface area analysis, thermal analysis TG/DSC, and XRD measurements.
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