Non-aqueous template-assisted synthesis of mesoporous nanocrystalline silicon orthophosphate

Abstract

The first synthesis of mesoporous nanocrystalline silicon orthophosphate Si₅P₆O₂₅ is presented. The synthetic procedure is based on the non-hydrolytic sol–gel reaction in the presence of Pluronic P123 template and subsequent calcination in air. The condensation of silicon acetate, Si(OAc)₄, and tris(trimethylsilyl)phosphate, OP(OSiMe₃)₃ (TTP), in non-aqueous solvents driven by elimination of trimethylsilyl acetate provides a homogeneous network with a high content of Si–O–P bonds and SiO₆ moieties. After burning out the template, mesoporous silicon orthophosphate was obtained with surface areas up to 128 m² g⁻¹ and pore sizes around 20 nm. The nanocrystalline Si₅P₆O₂₅ phase forms relatively easily (500 °C, 4 h) in comparison with other synthetic routes. All samples were characterized by SEM, TEM, elemental analysis, TGA, nitrogen adsorption, SAXS, ¹H, ¹³C, ²⁹Si, and ³¹P solid-state NMR spectroscopy, and powder XRD. These xerogels showed superior catalytic activity and selectivity in methylstyrene dimerization.