Determining the Specific Surface Area of Porous Materials by Small-angle X-ray Scattering
The specific surface area is a key parameter for many different applications of porous materi-als, therefore its fast and reliable determination is important for both developing such materials as well as controlling their quality during production. Here we show how small-angle X-ray scattering (SAXS) is applied as a fast and reliable method for determining the specific surface area of a mesoporous controlled pore glass (CPG) sample. The obtained SAXS results are in good agreement with specific surface areas obtained with physical gas (Ar 87 K) adsorption.
Porous materials can be found in a very wide range of applications. Due to their unique properties, these materials are used in energy storage, construction materials, catalysts and many other applications. Among these properties, the specific surface area is probably the most important parameter and therefore its fast, precise and reliable determination is of great importance. According to IUPAC,1 there are three classes of porous materials: macroporous (pore width DP < 50 nm), mesoporous 2 nm < DP < 50 nm) and microporous materials (pore width DP < 2 nm).
The widely used standard method for assessing the surface area of porous materials is based on gas (e.g. nitrogen or argon) adsorption analysis using the Brunauer-Emmett-Teller (BET) method. However, this method implies several challenges and limitations:2
- a time-consuming sample preparation,
- typically long measurement times,
- reliable surface area results are only obtained for non-porous and meso-/macro-porous materials,
- accuracy of surface area results depends on using the proper adsorptive.
Small-angle X-ray scattering (SAXS) is a widely used technique for characterizing the size, shape and further structural properties of nanosized materials. SAXS offers several advantages: it requires i) no sample preparation, i.e. the sample is measured as it is and no preparation artefacts occur, ii) it is a non-destructive method and iii) the overall measurement time is typically short.
SAXS is an ideal complementary analytical technique to gas adsorption for determining the specific area of nanomaterials. Furthermore – since SAXS can generally be applied to any hetero-phase system, in which the phases have a different electron density – the method can also be applied for determining the specific area of nanoparticulate systems such as nanoparticles in dispersion.
1. K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou, R. A. Pieroti, J. Rouquerol, T. Siemieniewska. Pure Appl. Chem.57, (1985).
2. Schlumberger, C., Scherdel, C., Reichenauer, G. Thommes, M. et al., Reliable surface area determination of porous materials: Small-angle X-ray Scattering and Gas Physisorption, Microporous and Mesoporous Materials 329 (2022) 111554
Get the document
To receive this document please enter your email below.