Synthesis of Nanoscale Mesoporous Silica Spheres with Controlled Particle Size

A simple one-step procedure is described for the synthesis of spherical mesoporous silica, in which the size of the particles is controlled over a range of diameters from 65 to 740 nm by varying the initial silicate/surfactant concentration under dilute conditions. The particles were characterized using X-ray diffraction, transmission electron microscopy, and liquid nitrogen adsorption. Synthesis using a charged template, cetyltrimethylammonium bromide, under aqueous conditions yielded particles of irregular spherical shape with highly ordered mesoporous channels. Synthesis under ethanol/water cosolvent conditions yielded smooth spheres with a starburst mesopore structure extending from the center of the particle to the circumference. All materials were thermally stable and exhibited two steps in their liquid nitrogen isotherms corresponding to reversible channel filling and non-reversible adsorption between particles. Mesopore volumes varied from 0.64 to 0.93 cm3 g-1 and surface areas varied from 917 to 1373 m2 g-1. From analysis of mesopore geometry and overall particle shape a three-stage mechanism for synthesis is proposed.