From BJH plot (pore diameter vs dV/dD pore volume), how to estimate the range of pore size distribution accurately if there is not sharp peak? Is there any thumb rule for this method?
You mean that there is NOT a sharp peak in the dV/dD - D plot? That would be clarified into two cases:
1. No nano-pores exist in the sample, where I mean less than around 100 nm for "nano".
2. All the pores would be less than 2 nm which are micropores. BJH method (when N2 is applied for the experiment as the adsorbate) fails for micropores.
A distinct difference for the two cases mentioned above is the BET surface area. The former would have a typical data of less than a few m2/g, while the latter more than several hundred m2/g.
Hi Vaibhav,
If you would share your BJH graph then it will be easier to understand the reason. One more thing, you have not mentioned that in BJH pore-size distribution method which branch(adsorption/desorption) you are using. Generally its desorption branch is used for PSD calculation. Please mention all the details along with N2 isotherm if possible.
If you need help, please fell free to contact
best
raeesh
Hello Vaibhav!
I will like to know the type of material that your are working with, may be you need to make shure that the pores are free to adsorbe N2.
Thanks for reply Raeesh Muhammad !
Here I have attached BJH plots for all my observed samples. I wanted to know that can I accurately say that for 0.8 M sample the pore size distribution is 5-30 nm range, for 0.9 M sample it is 5-40 nm and for others it is 5-50 or 5-60 nm range like this?
Hi Vaibhav,
Did you calculated you poresize distribution using desorption branch? Can you do PSD using DFT model also. If yes please send those file also. Your observation about the poresize of the sample for 0.6 M, 0.8 M and 0.9 M seems correct to me but for 0.5 M, 0.7 M and 1.0 M the PSD graph is very wide so you need to cross check it with the PSD result obtained from DFT model. Generally DFT is used for microporous materials but you can use it for mesopoorus materials for cross checking your data obtained from BJH model.
regards
raeesh
Hi ALi,
The technical answer to this question is that the desorption isotherm is thermodynamically more stable. This means that at any given relative pressure ,in regions of hysteresis, (usually > 0.35 relative pressures) the volume that remains adsorbed on the sample is more on the desorption isotherm than on the adsorption isotherm. In regions of no hysteresis (usually < 0.35 relative pressures) , it is equal.
regards
raeesh
Vaibhav, can you plz send me the origin file or excell file of BJH plots that you attached? i would like to see how you got the graph.
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