Micron to Sub-Micron Sized Highly Ordered Mesoporous Silica Particles Prepared Using a High Energy Ball Milling Process
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Micron to Sub-Micron Sized Highly Ordered Mesoporous Silica Particles Prepared Using a High Energy Ball Milling Process J. Eric Hampsey, Claudio L. De Castro, Byron F. McCaughey, Donghai Wang, Brian S. Mitchell and Yunfeng Lu* Tulane University, Department of Chemical Engineering, New Orleans, LA 70118 ABSTRACT Highly ordered mesoporous silica particles with sizes in the micron to sub-micron range are of great interest due to their applications as catalysts and filler materials. Currently, mesoporous silica particles are synthesized using large amounts of solvent, which is impractical for large scale-up in industry. This paper reports on a high-energy ball milling process that has been employed to create micron to sub-micron sized mesoporous silica particles starting from a silica xerogel prepared by a surfactant self-assembly sol-gel process. We have studied the effect of parameters such as milling media (e.g., zirconia, stainless steel, and steel centered nylon balls), milling time, the presence of surfactants during milling, particle size, and pore structure. Results from transmission electron microscopy (TEM), scanning electron microscopy (SEM), Xray diffraction (XRD), and nitrogen adsorption demonstrate the feasibility of producing large quantities of mesostructured particles by a simple milling process. INTRODUCTION 1,2
Since its discovery by Mobile researchers in 1992, MCM-41 and other ordered mesoporous materials have attracted great interest. These mesoporous materials are usually prepared by the cooperative self-assembly of surfactants and inorganic species such as silicates. Removal of the surfactant through either calcination or solvent extraction results in mesoporous materials with hexagonal, cubic, lamellar, disordered, and other pore channels. The size and structure of these pores can be controlled by careful choice of the surfactant system and reaction 3 conditions. Among these materials, mesoporous silica synthesized in the form of thin films, 4 aerogels, and particles are the most cited materials. Synthesis of mesoporous silica particles is of particular interest due to its possible use in catalysts, fillers, chromatographic materials, and other applications. Mesoporous silica particles are typically synthesized in dilute solutions, and 5 6 depending on the reaction conditions such as pH, stirring rate, choice of surfactant, or presence 7 of co-solvents, various particle shapes and morphologies can be achieved. Mesoporous silica 8 9,10 11,12 and other curved shapes such as toroidal, hollow rods, hard spheres, hollow spheres, 13-15 have been reported in the literature. disklike, spiral, and gyroid morphologies Mesostructured spherical particles have also been produced using an aerosol evaporation16,17 induced self assembly process. However, these processes usually require large amounts of solvent and produce relatively small amounts of material. High energy milling is a common physical technique used to produce sub-micron sized 18 particles. During the high energy milling process, the gri
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