Pseudomorphic transformation of amorphous silica microtubes into mesoporous MCM-41 type silica tubes. Synthesis, characterization and surface functionalization with titania, vanadia and zirconia

Abstract

Silica tubes with MCM-41 type mesostructures were successfully synthesized by a combination of the Stoeber process and a pseudomorphic transformation using electrospun macrosized polystyrene fibres as structure directing templates. Two different morphologies of mesoporous silica tubes are accessible with this method: a hollow morphology with tunable silica wall thickness and with a mesoporous silica shell structure and a core containing amorphous silica. All one dimensional tube like porous silica materials have a high specific surface area of approximately 1000 m² g⁻¹ with well-ordered hexagonal mesopores. Grafting of Ti, V and Zr metallocene dichloride molecular complexes has been employed resulting in the deposition of titanium-, vanadium-, zirconium-oxide in the interior of the silica tubes after ceramisation of the green body composites. The respective oxides were coated on top of the inner mesoporous silica surface of the tubes. Such silica based hybrids might be potential support materials in heterogeneous catalysis (e.g. vanadia) as well as interesting catalysts for photocatalysis (for TiO₂, ZrO₂). All materials were characterised by X-ray diffraction (SAXS and XRD), nitrogen adsorption at 77 K, UV/VIS diffuse reflectance spectroscopy (UV-DRS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM).