I only have the BET surface report and I want to find the size and volume of the pores using these data. is there any way to find itt
Dear G.A. Khan,
It can be calculated from nitrogen absorption branch using the BJH method.
It could be more understood by following link.
https://www.iitk.ac.in/che/pdf/resources/BET-TPX-Chemi-reading-material.pdf
Beware of misusing theories. That are some assumptions for each theory on gas adsorption, and to use those theories your isotherm MUST allow you to do those assumptions! For example, If your isotherm is a type III, it doesn't make sense for you to apply BJH method as suggested.
Answering specifically for your question, the Gurvich rule is one of the most used methods for finding total pore volume (micro and mesopores, as macropores are not determined by gas adsorption), this rule assumes that your pores are filled with liquid nitrogen, and the pore volume will be equal to the volume adsorbed, at a plateau. However, it also has its limitations, I recommend you to read the IUPAC report (2015) before doing calculations!
No doubt BJH method is also valuable tool but the suggestion from Luiz Fernando de Sousa Lima is pretty good.
If the data is limited to a p/p0 range only data sufficient to calculate a BET area, then no, it is not possible to calculate total pore volume or pore size (and certainly not from just a BET result).
To know pore volume from gas adsorption, the isotherm must represent pore filling. Micropores fill at p/p0 below the BET range so one could infer something about micropore volume, but it would be quite unreliable without corroborating data. Data points that overlap the BET range up to usually about p/p0 = 0.5 can be employed in the t-plot calculation which can yield a reasonable estimate of micropore volume and in combination with BET area an estimate of micropore area and meso/macro pore area. To know the meso/macropore volume, the isotherm must reach a plateau at which point a total volume approximation can be calculated (so-called Gurvich volume). Then if you really want to stretch the math, you can employ the relationship between area and volume of a cylinder to calculate a pore size (d = 4V/A). But is it real? Usually not. Luiz Fernando de Sousa Lima made a great suggestion to read the IUPAC 2015 Technical Report.
These videos can be helpful: https://www.youtube.com/watch?v=_7OZrokDY3c&list=PLxbTf96DhNSQ2NNF1nsX1RcdFAhrVx9Fz
Unfortunately, you can not calculate neither pore volume, nor pore size from BET data. You must have the adsorption isotherm of your sample to define these parameters
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