Journal of Porous Materials 12: 95–105, 2005 c  2005 Springer Science + Business Media, Inc. Manufactured in The Netherlands. Preparation of Spherical Hexagonal Mesoporous Silica HSIN-YU LIN AND YU-WEN CHEN ∗ Department of Chemical Engineering, Nanocatalysis Research Center, National Central University, Chung-Li 32054, Taiwan ywchen@cc.ncu.edu.tw Received April 30, 2004; Revised October 26, 2004 Abstract. A series of hexagonal mesoporous silica (HMS) have been synthesized by the neutral assemble pathway in water-alcohol cosolvent systems, using dodecylamine (DDA) and tetraethyl orthosilicate (TEOS) as the starting materials. These materials were characterized with powder X-ray diffraction, nitrogen sorption measurement, dif- ferential thermal analysis, and transmission electron microscopy. The XRD patterns of these samples exhibited a strong intense reflection at low angle, suggesting the excellent mesostructures of the samples. The particle size of HMS decreased and the morphology of HMS exhibited high textural porosity as the HMS was prepared with high addition rate of TEOS. The particle size of HMS prepared without aging was smaller than that aged for 18 h, due to the reaction time of TEOS was not enough to form complete particles. Addition of NaCl and HCl hindered the formation of HMS mesoporous structure. In contrast, addition of 1-butanol did not affect the formation of HMS mesoporous structure. The sphereical HMS silica with uniform size has been synthesized by adjusting DDA and TEOS concentrations. The shape of HMS became larger and more spherical as the concentrate on of DDA decreased. The stirring rate of the reaction mixture had no effect on either the shape or the size of the spheroid HMS silicas. However, the particles started to crack at higher stirring rates. Keywords: hexagonal mesoporous silica, nanoparticles, neutral assemble pathway, neutral surfactant 1. Introduction Following the announcement of the novel class of mesoporous M41S molecular sieved by Mobil re- searchers [1, 2], diverse and burgeoning interest has occurred in the use of structure-directing surfactant molecules to organize a variety of metal oxide net- works into mesoscopically ordered composite materi- als. The M41S family, consisted of MCM-41 (hexag- onal phase), MCM-48 (cubic phase) and MCM-L (lamellar phase) [3, 4], can be achieved through the self-assembly process involving electrostatic interac- tions between charged surfactant micelles and in- organic precursors. The electrostatic assembly path- ways to the synthesis of the mesoporous molecular ∗ To whom correspondence should be addressed. sieves, including: (i) the direct pathways, so-called S + I − and S − I + pathways, which involves the direct co- condensation of anionic inorganic species with cationic surfactant (S + I − ), or cationic inorganic species co- condense with anionic surfactant (I + S − ) and (i) the counter-ion mediated pathways, S + X − I + (X − = Cl − or Br − ), and S − M + I − (M + = Na| + or K + ), where sur- factant and inorganic reagents are brought together at the micelles interface through triple ion interactions [3]. The neutral assembly pathway to the mesoporous molecular sieves has been reported by Pinnavaia et al. [5, 6]. Based on the hydrogen bonding interactions and self-assembly between neutral amine surfactants (S ◦ ) or nonionic PEO-based surfactant (N o ) with neutral inorganic precursors (I ◦ ), the hexagonal meso- porous silica (HMS) with wormhole-like framework