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 m(2) 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 TiO(2), ZrO(2)). 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).

Hierarchically structured nanoporous carbon tubes for high pressure carbon dioxide adsorption

“…PS fibres ( 1 ) prepared by the electrospinning technique were subjected to a plasma treatment for effective tethering of the silica precursors. The silica@polystyrene green body composite ( 2 ) is obtained by the addition of silica particles [38] via the Stoeber process. The sample is subsequently heat treated to obtain the silica@carbon composite ( 3 ).…”

“…A homogeneous coverage of silica spheres of 200 nm diameter obtained from the Stoeber process is observed on the fibre surface of 1 (Fig. 2) [38]. After heat treatment, a silica@carbon material 3 with a hollow tube structure results (Fig.…”

“…In a similar manner as described in [38], electrospinning was performed in a homebuilt apparatus. Polystyrene (PS) fibres were electrospun from a 16 wt % PS THF/DMF 3:2 solution.…”

“…Analogous to our previous work [38], a modified Stoeber method was used to coat the plasma-treated, and thus oxo-functionalized, PS fibres with a silica shell. In a typical reaction, the oxo-functionalized PS fibres were suspended in EtOH and a TEOS/H 2 O/NH 3 mixture (molar ratio of 1:4.4:24.9) was added under stirring.…”

The Mechanism of Pseudomorphic Transformation of Spherical Silica Gel into MCM-41 Studied by PFG NMR Diffusometry

“…This strategy was shown to be suitable for the transformation of pre-shaped pellets of a commercial zeolite Y to MCM-41 [20]. Recently, our approach was also applied by Patzsch and Schneider [21] for the transformation of amorphous silica microtubes into an MCM-41-based material. As the presence of sodium cations is known to disturb the formation of MCM-41-type materials [22], it was one aim of this study to compare the products of pseudomorphic transformation with CTAOH solution to those obtained with CTABr/NaOH solution as widely reported in the literature (vide supra).…”