Modification of titanium surface species of titania by attachment of silica nanoparticles

Abstract

Silica nanoparticles-attached titania (TiO2@SiO2) was prepared by modification of the surface of titania (TiO2) with octadecyltrichlosilane (OTS) as a source of silica. The attachment of silica was achieved through repeated deposition-hydrolysis-calcination of OTS on the surface of titania particles. For comparison, the silica-titania composite (TiO2-SiO2) containing titania and silica agglomerated particles was also prepared. The physicochemical characteristics of TiO2@SiO2 and TiO2-SiO2 particles are experimentally studied by X-ray diffraction (XRD), UV-vis diffuse reflectance (UV-vis DR), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and 29Si solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) techniques. The effect of silica attaching on activity of titanium surface species has been tested in the liquid phase epoxidation of 1-octene to 1,2-epoxyoctane with aqueous hydrogen peroxide. It is demonstrated that the surface attachment of titania with silica nanoparticles enhances the epoxidation activity of titania. UV-vis DR spectra of the solid particles showed the increase in intensity of the tetrahedral titanium in TiO2@SiO2. This indicates the occurrence of the transformation of some of the octahedral titanium to the tetrahedral structure during silica attaching of TiO2@SiO2 in which titanium tends to bond with -Si(OH)2(OSi)2 to make it stable in tetrahedral form. Considering that the tetrahedral titanium was considered the most active species in epoxidation of alkene, it can be concluded that a high epoxidation activity of TiO2@SiO2 particle was related to the modification of the local environment of titanium surface species by attachment of silica nanoparticles.