You can use another graph p/p0. Or Langmuir graph value

You are using 2 different methods, adsorption and desorption. They give slightly different results. Use one of them, just mention which one is used. Most likely the desorption values are better?

Henrik Romar Sir,

it would be great if you give a reference too. because I am unable to find this in literature.

Thanks and Regards

Khaled A Abd El-Rahem Sir,

Please give a reference too.

Thanks and Regards

I really like a paper by Freek Kapteijn on adsorption characterization. It includes extensive discussions, etc, of the use of the BJH method and errors and uncertainties.

For the BJH method, they say:

"Thus starting from saturation, the distribution of pore sizes can be recursively calculated following the desorption branch, for which it was derived. It is also feasible to apply this approach to the adsorption branch, although this is not advised based on the underlying assumptions of the model."

This is the paper:

https://www.sciencedirect.com/science/article/abs/pii/S138718111400482X

That would suggest you should ideally use the desorption branch. You do need to be a bit careful about the size of the pores you are trying to analyse using the BJH method (see Fig. 8 in the above paper). I was going to comment that yours look a bit small, but I see that is radius (i.e. a diameter of over 4 nm using the desorption branch), so that might be okay; although the surface area and pore size look quite low. So I'm not sure how accurate these values are. It's important to really look at the data, to make sure the analysis is likely to be reliable.

Best regards,

Darren

Darren Paul Broom Thanks for such an explanation.

Thanks and Regards

The size of the pores i close to the limit of BJH, it is not suitable for micropores. Try DFT or t-plot and compare results. And remember, whatever method you use, they are all calculated values, not mesured. All calculations are based on the isotherms.

Henrik Romar that's what I meant when I said that Ayushi Mishra needs to be a bit careful about the size of the pores she is trying to analyse using the BJH method. If the pore diameter is over 4 nm, though, that is well outside the microporous regime. Micropores are < 2 nm in diameter or width, which would give a radius of < 10 Angstroms, rather than 21.5 Angstroms, as Ayushi has obtained from the desorption branch.

Isotherms from a microporous material would also be unlikely to give different answers from the adsorption and desorption isotherm data because they would not exhibit hysteresis, i.e. the adsorption/desorption isotherms would be pretty much identical.

I think we would probably need to see the data to comment any further.

Best regards,

Darren

@Darren Paul Broom. I fully agree regarding the pore sizes. Made a mistake with nm and Å.