I did a BET test and pore size distribution (PSD) was calculated from BJH method the during the test. And now I want to calculate PSD according to DFT method.
How can I do that?
The NLDFT model is recommended for the characterization of nanoporous materials. The desorption branches of Ar isotherms reflect the peculiarities of nonuniform pore structures in more detail than the N isotherms. Therefore, the 2 employment of the desorption Ar isotherms is preferable for pore size distribution calculations.
Dear Dr. Al-Noor,
Thanks for your answer. Unfortunately, I do not have the possibility of repeating the test. And I am searching for a software to calculate pore size distribution according to DFT method using the existing data.
You need to use some software for DFT. Both large manufacturers of adsorption apparatus have the DFT methods included in their software. Quantachrome as ASiQ and Micromeritics has SAIEUS.
Programming the methods yourself is quite hard.
Dear Fernando Vallejos-Burgos
Thank you for your answer. according to my knowledge, using the micromeritics software needs to repeat the BET test. But, because of the current situation, I could not do it again. I used Demo version of SAIEUS, but it doesn't provide the pore size distribution in the range >30 nm. I am searching for a way to have the pore distribution in the range of 0.3 - 100 nm.
All modern apparatus that measure the adsorption-desorption isotherms have the program of BET, DFT and others theory included. No need for hard mathematical calculations manually.
Good luck
@Bita Karami
The pores larger than 30 nm cannot be easily measured by gas adsorption, since the pore is so large as compared to the molecules that the behavior of the molecules is just as if it was a non-porous surface (the molecule cannot "feel" both pore walls).
Fernando Vallejos-Burgos Mounir Daoud Laksaci Hamza T. H. Al-Noor Thanks alot
Bita Karami,
If the adsorbent is a porous carbon, you are looking for the Tikhonov regularization method. This is a system of equations, AX=B, where, B is your nitrogen isotherm, X is the PSD (unknown) and A is a matrix with theoretical N2 isotherms of DFT simulations (or NLDFT or GCMC), performed on single pore carbon models of variable widths. Most sorption instruments can solve the Tikhonov with a click of the mouse. Thereby, send the isotherm to a colleague having access in such an instrument, to compute the PSD for you. Depending on which database is available, I would recommend the NLDFT or the GCMC.
By the way, if the adsorbent is not a carbon but a crystalline framework (MOF) you don't need DFT to compute the PSD. You can make a computational pore size analysis on the basis of the crystal information file (CIF) of the solid. I would recommend the poreblazer code, it is in Fortran. Recently, I used the module to compute the PSDs in carbon nanotube bundles. I describe this briefly in an open access paper: Article Pulling Simulations and Hydrogen Sorption Modelling on Carbo...
Fernando Vallejos-Burgos Gas adsorption can in fact measure pores to many hundreds of nm diameter. The confinement effect on the gas phase does decrease as the pore wall are further apart (larger pores) but it is still significant in modifying the capillary condensation behavior.
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