We got 0.2 m2/g-1 as the pore size in a BET study for Nitrogen adsorption.
Is this data is reliable enough for include in a research paper or are there any conclusions can be made why we got this value?
Dear researcher, 0.2 m2/g is the specific surface area of your sample (not pore volume). It means your sample has not any porous structure. however, I suggest repeat the test.
This question does not have a reliable answer. One is a correctly performed experiment and the other is its correct description using the equation. Both must be reliable. Regards,
Generally for the BET Values, there are two basic requirements
1. C value has to be positive.
2. Correlation coefficient has to be greater than 0.9975 with atleast three to five points.
3. In general, the BET equation will be a straight line from 0 to (0.3 p/p0), for some material it will be linear only till 0.2 (ex carbon black).
4. If you measure a full isotherm, you will come to know about the nature (Porous, non porous) of the material
BET and BJH methods are widely accepted and popular. However, degassing of sample is highly required.
The researcher should repeat the experiment. Consider whether your consideration is for mono-layer or multi-layer adsorption. Bear in mind the amount adsorbed in relation to the relative pressure, (P/Po) which brings about classifications of isotherms to types (I, II, III, IV, V).
High precision equipment is required for adsorption processes and the fundamental principles should be applied. Please check out for these and you will get a reliable results. Apply the principles that involve BET theory.
0.2 m2/g is a very small surface area to measure with N2 at 77 K, because the error in the free volume measured is higher to the precision to you need. I recommend use Kr. If you haven’t this gas, use Ar at the same temperature, 77 K. Obviously use 1 ó 2 g of solid, calibrate very carefully the free volume, and applied the BET equation very carefully.
Dear Yasashri, The reliability of your determination depends on the amount of sample that you were using. Recently, I carried out nitrogen and krypton adsorption on a sample with a very low specific surface. With nitrogen, I obtained 0.33, 0.34 and 0.35 m2/g in three consecutive measurements. With krypton, I obtained 0.32, 0.33 and 0.32 m2/g in three consecutive measurements. If I agree with Dr Parra that krypton is more precise than nitrogen, I was agreeably surprised by the precision obtained with nitrogen adsorption. The key of this precision was the amount of sample that I used, nearly 10g. I measured the cold and warm volumes with helium after the measurements although given the very low surface area you could do that before, no helium entrapment is foreseen because I do not think that your sample has very narrow porosity.
I hope this helped you, best wishes, Vanessa
Hi,
I agree with Vanessa Fierro if you can´t switch gas to Kr just go up with sample mass. If you normally pour 200mg of sample try with 1g or more (if it fits in the sampler). It depends on the instrument type and model but generally this is enough to compensate the low accuracy of N2 adsorption with very low SSA material.
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