Journal of Colloid and Interface Science 326 (2008) 138–142 Contents lists available at ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis Size-controllable synthesis of monodispersed colloidal silica nanoparticles via hydrolysis of elemental silicon Jianjun Guo ∗ , Xuehui Liu, Yuchuan Cheng, Yong Li, Gaojie Xu, Ping Cui Department of Functional Materials and Nano-Devices, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China article info abstract Article history: Received 7 May 2008 Accepted 11 July 2008 Available online 17 July 2008 Keywords: Colloidal silica Nanoparticles Silicon powder A new method is presented for preparing monodisperse and uniform-size silica nanoparticles using a two-stage hydrolysis of silicon powder in aqueous medium. The influence of synthesis conditions includ- ing solution composition and temperature on the formation of silica nanoparticles were systematically investigated. The structure and morphology of the silica particles were characterized via transmission electron microscopy (TEM) and dynamic light scattering (DLS). Various-sized particles in the range 10– 100 nm were synthesized. The size of the nanoparticles can be precisely controlled by using a facile regrowth procedure in the same reaction media.  2008 Elsevier Inc. All rights reserved. 1. Introduction Uniform nanosized colloids are one of the cornerstones of nanoscience and nanotechnology due to their well-defined dimen- sions and functional properties and have fascinated scientists for a long time [1,2]. Monodisperse silica materials are one of the most attractive issues in colloidal science. Despite the fact that col- loidal silica as investigation object was studied for many years, the interest towards this system does not only weaken but on the con- trary becomes stronger. Particularly in recent years with appearing of the nanotechnology during the preparation of materials on the base of silica, the role of the colloidal silica as well as the problems of its stabilization increases. Many researchers were dedicated to silica materials with a narrow size distribution, controlled size and shape, and various surface properties because they are ideal candi- dates for applications in several fields from formation of synthetic opals and their inverse [3], stabilizing agent for organic compounds subject to temperature–humidity degradation conditions [4] to col- loidal template [2] and vehicle for gene and drug delivery [5]. Notably, spherical and monodisperse silica was first prepared in solution and systematically characterized in 1968 by Stöber et al. [6]. This synthesis is based on ammonium-catalyzed hydrolysis– condensation reactions of tetraethylorthosilicate (TEOS) with water in low molecular weight alcohols, and different sizes of silica par- ticles were prepared ranging from 50 nm to 1 μm with a narrow size distribution. The size of particles depends on the type of sili- con alkoxide and alcohol. Particles prepared in methanol solutions are the smallest, while the particle size increases with increasing * Corresponding author. Fax: +86 574 8668 5163. E-mail address: jjguo@nimte.ac.cn (J. Guo). chain length of the alcohol. The particle size distribution also be- comes broader when longer-chain alcohols are used as solvents. This method was later improved by many others, and now seems to be the simplest and most effective route to monodispersed sil- ica spheres. While the main limitation of the Stöber-based pro- cess remains in the preparation of smaller particles. It’s hard to achieve silica nanoparticles with monodispersity better than 4–5% when the size is below ca. 120 nm. Furthermore, the Stöber pro- cess needs large quantities of alcohol to generate the homogeneous phase for producing a monodisperse shape. Recently, a facile method was developed for preparation of monodisperse silica particles with the sizes ranging form 12 to 200 nm and a monodispersity better than 2% [7,8]. This approach utilizes amino acid (i.e. lysine or arginine) as a base catalyst, while TEOS is delivered heterogeneously using a top organic layer, such as cyclohexane. Here, we reported the production of monodisperse small silica particles of controllable sizes by a straightforward scalable method using one of the most affordable silica precursors—elemental sili- con. This method was first documented by Balthis et al. [9]. They hydrolyzed finely-divided elemental silicon with water using am- monia as catalyst at a temperature range of 20–90 ◦ C. Before re- action, the elemental silicon must be activated by washing with aqueous hydrofluoric acid, pure water, alcohol and ether consecu- tively to remove a film of silicon dioxide from the surface of the particles and expose a clean silicon surface. Zhang et al. [10] im- proved the preactivation process by high-temperature reaction. The obtained silica colloids from these methods have a relatively broad distribution ranging from 8 to 20 nm. In this process, two main types of reactions are involved: (i) silanol groups are formed by hydrolysis and (ii) siloxane bridges are formed by a condensation polymerization reaction. This reac- 0021-9797/$ – see front matter  2008 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2008.07.020