Hierarchically Structured Millimeter-Sized (Organo) Silica Spheres with a Macroporous Shell and a Meso/Microporous Core

Abstract

Tailored hierarchically structured (organo) silica beads with particle diameters between 0.3 and 2.5 mm have been prepared using an emulsion based sol−gel approach. Poly(propylene oxide)-poly(ethylene oxide) triblock copolymers as surfactants, aniline or 1-butanol as solvent and different silanes such as tetraethyl silicate, [3-(2-aminoethylamino)propyl]trimethoxysilane and phenyltrimethoxysilane are used to direct morphology and porosity. The silica spheres provide specific surface areas up to 900 m2/g and adjustable porosity in the meso- and macroporous region. The texture includes particulate structures with controllable size between 80 nm and 2.5 μm of the silica particles on the inside of the spheres and a macroporous foam-like shell with macropores in the range between 0.2 and 4.0 μm and a thickness of the shell between 0.6 and 44 μm. The high variability of this preparation method and the simultaneous control of the nano- to millimeter scale structure including the porosity as well as the morphology allows one to design tailor-made adsorbents and catalysts.