Hello,
I was thinking to use the BJH model to measure the pore size distribution of low porosity (mostly meso and macropores)-containing materials.
In this regard, I have got the following questions:
1) Which relative pressure range should I consider? P/P0 >0.35?
2) Which isotherm branch should I apply the BJH model to? Ads or Des? How does this choice relate to the Hysteresis type?
3) Would DFT model be more suitable?
Thanks,
Antonio
DFT (NLDFT and QSDFT) methods are much more suitable than BJH for micro and mesopores.
For BJH you need the desorption branch (have a look at the original paper, I think I uploaded it in RG somewhere...).
You cannot measures macropores by adsorption (macropores behave like non-porous surface towards gas molecules)... you need something like mercury porosimetry.
Fernando Vallejos-Burgos , thanks for your reply. As concerns DFT, which relative pressure range should I cover? I am expecting a nearly non-porous material with possibly no micropores at all so I was thinking to acquire points at P/P0 >= 0.01 or something like that. Also, which isotherm branch should I consider?
Dear Dr. Antonio Salituro, determining if a such material is porous or non- porous by adsorption studies is simple. After carrying out the adsorption study for the entire range of P/Po, compare the obtained isotherm with the IUPAC isotherm classification. For this you can consult:
Rouquerol, F., Rouquerol, J., Sing, KSW., Llewellyn, P. and Maurin, G. Adsorption by powders and porous solids: Principles, methodology and applications, Academic Press, 2012.
If the obtained isotherm is type II according to the IUPAC classification, then the material is non-porous or macropore material.
As suggested, the dear colleague Dr. Burgos:
You can not measure macropores by adsorption (macropores behave like non-porous surface towards gas molecules) ... you need something like mercury porosimetry.
To be even today, the best method to meassurement the porosity is the mercury porosimetry technique.
Best Regards
DFT is the most suitable model which gives reliable information about both micro and mesopore distribution.
Antonio Salituro
DFT methods will automatically consider all the adsorption range where you measured the isotherm. The best practice is always to have a continuous range of adsorbed volumes starting from near negligible adsorption, that is, adsorption isotherms are unreliable if in the first point, already a considerable amount was adsorbed.
Regarding your second question, most DFT methods have both branches programmed, so you just need to choose the branch corresponding to your experimental data. This is usually adsorption branch for microporous samples and desorption for mesoporous.
Artur Braun , how would you work out porosity information from small angle X-ray diffraction? Could you please provide some references?
Thanks,
Antonio
The best method to measurement the porosity is the mercury porosity technique. DFT is the most suitable model which gives reliable information about both micro and meso pore distribution
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