I have obtained nitrogen adsorption desorption isotherms for a mesoporous sample. From these isotherms and BJH size distribution, I have calculated surface area, pore volume and average pore diameter. But, when I am asked "what is the pore volume fraction of meso and micropores?", what do I need to calculate and how?
First of all, BJH is not the best model for micropores, use the DFT calculation instead. From the graphs, take total pore volume (PV), micropore volumes (
This might help. However, note that if you get the user guide of the Nova 2200e or whichever model you are using, it is well explained and easy to calculate.
https://www.researchgate.net/post/How_can_I_measure_mesopore_volume_and_micropore_volume_from_BET_isotherm
For the Micromeritics instruments all models are built in in the software or can be downloaded from their homepage (registered users only).
You can make a t-plot for estimating the microporous volume of the sample: https://pubs.acs.org/doi/abs/10.1021/la5026679.
Be aware of the following:
1. N2 is not the best probe for ultra-micropores:
https://www.degruyter.com/downloadpdf/j/pac.2015.87.issue-9-10/pac-2014-1117/pac-2014-1117.pdf
2. DFT calculations are not universal, they are valid either for particular materials or, in special cases, for families of solids.
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