Santa Barbara Amorphous-15

Typical SBA-15 powder sample

SBA-15, an acronym for Santa Barbara Amorphous-15, is a silica-based ordered mesoporous material that was first synthesized by researchers at the university of California Santa Barbra in 1998. This material proved important for scientists in various fields such as material sciences, drug delivery, catalysis, fuel cells and many other due to its desirable properties and ease of production.

Synthesis procedure

The procedure is a typical Liquid-Crystal templating that consists of three steps:

The gel obtained in the second synthesis phase.

1. Solution preparation — Pluronic P123 is dissolved in an acidic solution of water at specific molar ratios and the silica precursor typically TEOS or TMOS (sometimes EGMS) is added and mixed in for some time.
2. Hydrothermal treatment — The solution is sealed in a container and subjected to a temperature T1 for about 24 hours and then a higher temp T2 for 48 hours.
3. Washing and calcination — The gel obtained from the previous step is washed with water and ethanol under centrifuging, and finally calcinated at about 550 °C for 6 hours.

Structure

The interest in SBA-15 comes from the fact that its mostly mesoporous – meaning the pores are in the range of 2 nm to 50 nm according to the IUPAC definition and the fact that these pores have a well defined structure that is cylindrical shape in hexagonal ordering with their relatively thick pore walls which gives thermal stability.

The sorption isotherms of these materials, demonstrate typical hysteric behavior, which is still under discussion for its causes.

TEM

The transmission electron microscopy of the sample shows the cylindrical pores but also highlights then fact that the pores of this material exhibit geometric deformations.

SAXS

The small-angle X-ray scattering pattern shows typical Bragg peaks to the hexagonal structure of the material. The peak positions, is directly related to the lattice parameter.

$q_{hk}=\frac{4\pi }{a\sqrt{3}}\sqrt{h^2+k^2+hk}$

where h and k are the miller indices.

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  TEM of a typical SBA-15 sample
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  Demonstration of the hexagonal structure of SBA-15.
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  Small angle x-ray scattering pattern of a SBA-15 sample(data from Haidar et al.)
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  Typical isotherm SBA-15 sample, data from Haidar et al.