Materials Science and Engineering B 133 (2006) 49–54 Modification of titanium surface species of titania by attachment of silica nanoparticles Hadi Nur ∗ Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia Received 4 April 2006; received in revised form 22 April 2006; accepted 6 May 2006 Abstract Silica nanoparticles-attached titania (TiO 2 @SiO 2 ) was prepared by modification of the surface of titania (TiO 2 ) 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 (TiO 2 –SiO 2 ) containing titania and silica agglomerated particles was also prepared. The physicochemical characteristics of TiO 2 @SiO 2 and TiO 2 –SiO 2 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 29 Si 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 TiO 2 @SiO 2 . This indicates the occurrence of the transformation of some of the octahedral titanium to the tetrahedral structure during silica attaching of TiO 2 @SiO 2 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 TiO 2 @SiO 2 particle was related to the modification of the local environment of titanium surface species by attachment of silica nanoparticles. © 2006 Elsevier B.V. All rights reserved. Keywords: Silica nanoparticles-attached titania; Titanium surface species; Surface modification 1. Introduction Titanium dioxide or titania is one of the most utilized partic- ulate materials in the world. Although it was discovered more than 200 years ago and has been commercially processed for 85 years, it is still being actively researched. Titania is the most widely used as pigment in cosmetic and paint products, and photocatalyst. The photochemical activity of titania is modified by promoting or suppressing the recombination of electron and hole pairs which are formed by UV light excitation [1]. High photochemical activity is required when titania is used as pho- tocatalyst, whereas low photochemical activity is preferred for paint or cosmetics application. One of methods to improve the photocatalytic activity of titania is by attachment of silica. It ∗ Tel.: +60 7 5536077; fax: +60 7 5536080. E-mail address: hadi@kimia.fs.utm.my. URL: http://www.ibnusina.utm.my/∼hadi. has been reported that the photoactivity of silica-incorporated titania was three times higher than that of the Degussa P25 [2]. However, the reason why the photoactivity of silica-incorporated titania gave a higher activity compared to that of bare titania have not yet been clearly understood. Recently room temperature sol–gel attachments of silica have been successfully adopted in order to coat titania with silica [3]. The attachment of titania with stable oxide layers has been also done by spraying of a metal oxide precursor solution on the sur- face of titania nanoparticles [4–6], acid hydrolysis of polysilicate [7] and hydrolysis of tetraethylorthosilicate (TEOS) using chlo- roform catalyst [8]. However, attachment of silica on the surface of titania by using octadecytrichlorosilane (OTS) as a source of silica had not been investigated yet. OTS was selected because it is well-known compound used in surface-modification reactions with surface hydroxyl groups. Recently, Park and Kang [9] also successfully prepared silica-coated titanium dioxide by using TEOS as a source of silica. In such system, silica is evenly coated on the surface of 0921-5107/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2006.05.003