Hello!
I would like to measure a N2 Physisorption Isotherm for ZIF-8 (zeolitic imidazolate framework) material. Degassing temperature in literature are about 150-200 °C. How about the tolerance and equilibration time? I am using an Autosorb 6 from Quantachrome. Any recommendations about how long the samples need to equilibrate and which pressure region I should cover? It seems that the pores are below 2 nm.
I am happy for your suggestions. Many thanks in advance.
If you're doing BET surface area cover the pressure region (P/P0): 0.05-0.25. If you're doing PSD, cover the entire isotherm (P/P0: 0-1.0). Make sure your instrument is sensitive enough to measure pores below 2nm.
Hi Jack Oneill ,
Microporous materials will display adsorption at relative pressures below 0.05 in the N2 sorption Isotherm . To be able to obtain a meaningful pore size distribution, your equipment need to have a 1 Torr transducer. Try to use 10 or 15 cm3/g of incremental doses, and use DFT to generate your PSD curve. The BET surface area is calculated using points of your N2 sorption Isotherm data. The IUPAC recommends to use data in the range of 0.05-0.3 P/Po. To obtain this data, a 1000 Torr transducer is sufficient. For microporous materials, I usually use a shorter ranges like that Zaid Assaf mentioned or shorter. Regards the degas step, 200 oC for 2 hours was enough for me. Here is some references:
(1) Article Importance of surface modification of γ-alumina in creating ...
(2) Article Effect of metal–ligand ratio on the CO 2 adsorption properti...
Best Regards,
Alexandre Goncalves
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