Langmuir adsorption model considers that only a monolayer of adsorbate can be formed on top the surface.
In contrast, BET model considers multilayer formation.
Then, if (as generally occurs) multilayers are formed, BET is able to consider that they are not being formed by directly covering the surface, but by covering extra layers. Langmuir will consider that multilayers can only form as the first adsorbed layer, thus resulting in an exaggerate (unrealistic) surface area.
Langmuir adsorption model considers that only a monolayer of adsorbate can be formed on top the surface.In contrast, BET model considers multilayer formation.
Then, if (as generally occurs) multilayers are formed, BET is able to consider that they are not being formed by directly covering the surface, but by covering extra layers. Langmuir will consider that multilayers can only form as the first adsorbed layer, thus resulting in an exaggerate (unrealistic) surface area.
As correctly identified, the Langmuir model assumes a monolayer of adsorbed molecules. The adsorption cross section of an adsorbate depends on numerous factors, not just the molecular size. Furthermore, the observed specific surface area is scale variant, similar to the length of a coastline. A phenomenon known as fractality. That mean that the measured surface area depends on the size of the adsorbate molecule.
As correctly identified, the Langmuir model assumes a monolayer of adsorbed molecules. The adsorption cross section of an adsorbate depends on numerous factors, not just the molecular size. Furthermore, the observed specific surface area is scale variant, similar to the length of a coastline. A phenomenon known as fractality. That mean that the measured surface area depends on the size of the adsorbate molecule.
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Langmuir adsorption model considers that only a monolayer of adsorbate can be formed on top the surface. In contrast, BET model considers multilayer formation.
Then, if (as generally occurs) multilayers are formed, BET is able to consider that they are not being formed by directly covering the surface, but by covering extra layers. Langmuir will consider that multilayers can only form as the first adsorbed layer, thus resulting in an exaggerate (unrealistic) surface area.
You can clearly see the differences in the Wikipedia page for Langmuir adsorption.
Langmuir adsorption model considers that only a monolayer of adsorbate can be formed on top the surface.In contrast, BET model considers multilayer formation.
Then, if (as generally occurs) multilayers are formed, BET is able to consider that they are not being formed by directly covering the surface, but by covering extra layers. Langmuir will consider that multilayers can only form as the first adsorbed layer, thus resulting in an exaggerate (unrealistic) surface area.
You can clearly see the differences in the Wikipedia page for Langmuir adsorption.
More
VOTE