The specific surface area value is not measured and is calculated.
We measure the adsorption isotherm of the sample, and then select the appropriate theoretical model to calculate the specific surface area of ​​the sample based on the characteristics of the sample. Therefore, the specific surface measurement process is actually an analysis process. Because different people may have different knowledge of the sample, experimental data analysis of the same set of adsorption isotherms may report different specific surface area results. Therefore, when "measuring" the surface, keep in mind that this is an "analysis" process.
Is BET more specific than surface? How many methods are there to calculate the specific surface area?
The BET method is only one theory in the surface analysis method. Langmuir revealed for the first time the nature of adsorption, which is based on the theory of monolayer adsorption and is suitable for sample analysis with only micropores. ?
The BET theory was published in 1938 and its official name is the theory of multi-layer adsorption, which is a modification of the Langmuir theory. BET is the acronym for the three surrogate names of the theory. Since the BET method is suitable for most samples, it is currently the most popular surface analysis method. However, the BET method is not applicable to all samples, so when the microporous material is analyzed by the analysis method of the mesoporous material, the BET specific surface value automatically generated by the physical adsorption analyzer is wrong. Both ISO9277-2010? and IUPAC? specify the BET surface analysis method for microporous materials and the method for determining BET results. The calculation results given by different theoretical models are different, so the theoretical model most suitable for the nature of the sample should be selected according to the assumptions of the theoretical model. Most theoretical models are named according to the inventor's name or abbreviation and can be used to calculate the theoretical model of the specific surface.
Includes Langmuir, BET, BJH, DR and NLDFT. ?? NLDFT is a non-local density functional theory. Studies have shown that NLDFT calculates the closest surface value to the true value, and the theory is applicable to microporous and mesoporous materials.
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