One of the first indicators to determine if a material contains nanoparticles—and may qualify as a nanomaterial—is its specific surface area. Because nanoparticles are very small, their surface-to-volume ratio is significantly high. As a result, nanoparticles exhibit a relatively high surface area per unit mass compared to micrometer-sized particles. This characteristic is crucial for assessing the properties and potential applications of nanomaterials.
The European Commission has issued guidelines for identifying nanomaterials. These guidelines emphasize the importance of specific surface area in the classification process. According to the guidelines, a material is classified as a nanomaterial if 50% or more of its particles fall within the size range of 1 to 100 nanometers.
To measure specific surface area accurately, researchers often use the BET (Brunauer-Emmett-Teller) analysis method. This technique involves adsorbing gas molecules onto the material’s surface and measuring the amount of gas that can be adsorbed. The resulting data provides valuable insights into the material’s surface characteristics. It also helps researchers determine whether the material meets the criteria for nanomaterial classification.
Understanding the nuances of BET analysis is essential for researchers and manufacturers working with nanomaterials. Accurate identification and classification are critical for compliance with regulatory guidelines. This ensures that products are developed and marketed responsibly. As the demand for nanomaterials continues to grow, effective BET analysis will play a key role in advancing research and innovation in this exciting field.
Porous Nanomaterial BET Analysis
We can effectively measure the specific surface area of porous, non-porous, and nanoparticle materials using BET analysis. This method employs physical gas adsorption of nitrogen at 77 K. The resulting specific surface area is known as BET surface area and is expressed in m²/g.
To reflect density differences among nanomaterials and nanoparticles, we incorporate true density into our calculations. This adjustment leads to the concept of Volume Specific Surface Area (VSSA), expressed in m²/m³. We measure the true density of each material, including nanomaterials, using helium or nitrogen pycnometry.
The European Commission has established guidelines for identifying nanomaterials based on particle shape and VSSA values. According to these guidelines, a material qualifies as a nanomaterial if its VSSA is greater than 20 m²/m³ but less than 60 m²/m³. Conversely, low cut-off values below 6 m²/m³ to 24 m²/m³ indicate that a material is not a nanomaterial.
If we find high VSSA values, we follow up with confirmatory techniques. These techniques may include electron microscopy, differential centrifugal sedimentation, and dynamic light scattering.
It is essential to note that porous materials can show high VSSA values without containing nanoparticles. Thus, they do not qualify as nanomaterials. Therefore, specific surface area primarily serves as a screening parameter for identifying nanomaterials. This distinction is crucial for ensuring accurate classification and compliance with regulatory guidelines in nanomaterial research and applications.
