BET Physisorption (BET)
Introduction:
BET (Brunauer–Emmett–Teller) analysis is a physical technique used to study the adsorption of gas molecules on solid surfaces. It is considered a fundamental tool in the field of surface chemistry, providing valuable information about the surface properties of materials, including surface area, particle size, and porosity characteristics.
Nowadays, due to the widespread use of porous materials—especially nanostructured porous materials—in fields such as physics, chemistry, engineering, environmental science, and life sciences, BET analysis has become an essential and widely used tool. Based on gas adsorption and desorption (e.g., nitrogen), this method allows for the statistical estimation of surface area, degree of porosity, pore shape, and the size of micro-, meso-, and macropores in materials. BET analysis works by measuring the volume of nitrogen gas adsorbed and desorbed by the material’s surface at a constant liquid nitrogen temperature (77 K).
It is considered a powerful tool for studying material properties, particularly in surface chemistry and nanomaterials. This technique helps in understanding the behavior of materials in terms of surface gas adsorption and interaction, contributing to the development of effective catalysts and applications in energy and environmental fields.
Working Principle:
The BET technique is based on measuring the amount of gas adsorbed on the surface of a material at specific temperatures. Gases like nitrogen or argon are commonly used.
In BET analysis, the amount of gas absorbed on the surface is directly related to the available surface area. The principle is that the larger the surface area, the greater the amount of gas adsorbed. The volume of gas adsorbed is measured using gases like nitrogen, where the gas is stored in a vacuum chamber, and pressure is recorded at specific temperatures.
The adsorbed gas can be separated from the surface by altering conditions such as lowering the pressure, allowing the dynamic behavior of gases on the solid surface to be studied.
Benefits:
The BET instrument is capable of measuring the amount of gas adsorbed or released from the solid surface under various pressures. By analyzing the shape of adsorption and desorption curves, several important properties can be determined, including:
1. Pore size: Determining the size and shape of open pores in the sample.
2. Surface properties: Estimating the specific surface area of the sample.
3. Porosity: Understanding total and distributed porosity.
Applications and Advantages:
The BET method is considered a relatively fast and efficient way to analyze the physical properties of materials and is used in a variety of applications, including:
Measuring surface area of nanomaterials: Such as nanoparticles, nanorods, nanofibers, and nanosheets, which typically have specific surface areas greater than 1 m²/g.
Catalyst analysis: Measuring the surface area of catalysts and nano-adsorbents, contributing to improved efficiency.
Open pore ratio determination: Measuring the shape and ratio of open pores in porous materials to assess performance in different applications.
Pore size determination: Measuring the shape and size of pores ranging from 0.5 to 200 nanometers, useful for designing advanced applications in storage and adsorption.
Particle size analysis: Measuring average particle size, which is crucial in material development and performance optimization.
Interpreting Results:
BET analysis is mainly used to determine the specific surface area of materials, especially porous ones. This includes several key aspects:
1. Adsorption Curve:
The data from BET analysis typically show a curve representing the relationship between the amount of gas adsorbed (by weight) and the gas pressure. This curve includes several stages:
Initial stage: Rapid gas adsorption indicates many available adsorption sites.
Middle stage: As pressure increases, the adsorption rate slows down, indicating the surface is nearing saturation.
Final stage: At a certain pressure, the curve stabilizes, meaning most adsorption sites are occupied.
2. Surface Area Calculation:
The specific surface area can be calculated by measuring the amount of gas adsorbed at a specific pressure.
3. Interpretation of Results:
Surface area: The specific surface area is the primary value obtained from BET analysis. The higher this value, the greater the material’s ability to adsorb and react with chemicals.
Pore size: BET results can estimate pore size and distribution, providing insight into the material’s internal structure.
Applications: The results indicate the material’s suitability for specific uses such as catalysts, adsorbents, and batteries.
It is important for the analyst to be familiar with how to interpret results and deal with any discrepancies or deviations that may appear. Additional valuable information that advances research and development can be obtained through consultation with experts at Photon Center