For magnetic nanoparticles, I generally found that the Langmuir specific surface area is greater than the BET surface area. I would like to know if it common for any type of materials not just the magnetic nanoparticles and the reason for this?
This is not surprising, since the Langmuir model is simpler than the BET model. This last, in particular, takes into account the adsorbent-adsorbent interaction, i.e. multilayer adsorption.
Strictly speaking, the results of the calculations strongly depend on the range of relative pressures of the gas taken into account. It is believed that it should be in the range of 0.05-0.35.
Dear Ravindra,
Yes, I agree with Vadim S. Gorshkov. BET supposes multi layer adsorption. Langmuir supposes only one layer adsorption. That is why you obtained larger specific surface area with Langmuir in contrast to BET.
If you want to know the the real surface area, the exact and accurate result will be provided by SAXS measurement, without any presumption.
Adam Juhasz There are lots of ways of deciding what the surface area is. SAXS will measure the gaps between particles and there are plenty of assumptions. Depends what you want the SSA for - different gases, different molecules, and different techniques provide different measured SSA's.
I am also agree with Vadim S. Gorshkov and Roman fiala sir.
I am attaching here by a document, may be it will help you in your queries.
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