Specific Surface Area of Metal-Organic Frameworks
III International School-Conference «Applied Nanotechnology and Nanotoxicology»
10-13 Oct 2019
|| Melgunov Maksim Sergeevich
Boreskov Institute of Catalysis SB RAS
Porous metal-organic frameworks (MOFs) are the nanomaterials with ordered structure of mutually arranged inorganic connectors, organic linkers, and the within pores with apertures in the range of 0.5 – 3 nm, usually. Significant part of MOFs have a so-called impermanent porosity, which forms as the response of their structure to the external
conditions: depending on the latter the material can be totally nonporous, or microporous. Such transitions can be reversible or irreversible, even under cryogenic conditions typical to, e.g. nitrogen porometry. All this introduces ambiguity in interpretation of porosity studies, and makes the problem of characterization of MOFs’ porous structure significant.
In this talk we discuss the possibilities of the BET method for the specific surface area measurement for MOFs. Application of the BET method to microporous materials is traditionally not recommended due to special mechanism of micropore filling different from adsorption on a flat surface. However, starting with 2000-xx the significant advance on testing of MOFs with the BET method coupled with theoretical calculation of the specific surface area accessible for spherical probes of known size have been performed by Dr. Snurr’s group [1–3]. As it was shown, both values coincide within 10% or better for the considerable number of structures. That have become possible due to application of the special restriction criteria to the BET method regarding the range of pressures [4,5]. Only a part of MOFs with intermediate pores in a range 2-3 nm fell out from a general trend . According to our knowledge, even if the applied restriction criteria is fulfilled, this is not sufficient for proper application of the BET method. We elaborated the more suitable technique to apply the BET method , which returns the falling-out group of MOFs into the range of the 10% deviation between BET results and theoretical calculations. Thus, one can conclude that despite on serious distinctions between the mechanisms of micropore filling and adsorption on a flat surface, the BET method can be applied with a known accuracy as a testing technique for the majority of MOFs.
Acknowledgement. This work is supported by Ministry of Science and Higher Education of the Russian
Federation (project АААА-А17-117041710079-8).