IUPAC recommendation consequences for micropore adsorption studies
The IUPAC-report “Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution” contains essential guidelines for obtaining and interpreting experimental data by means of gas adsorption [1]. This includes an extended classification of physisorption isotherms and hysteresis types. Furthermore, it takes account of scientific and technological progress made in the characterization of porous materials during the last 30 years. A key topic within that report is the recommendation to employ argon at the boiling point temperature of liquid argon (87 K) for micropore analysis. Argon atoms provide distinct advantages over nitrogen molecules for gas sorption analyses, including the following:
- Unlike nitrogen, argon has no quadrupole moment. Thus, using argon as adsorbate eliminates specific chemical interactions with polar/ionic surface sites.
- As a result, argon physisorption isotherms provide much more reliable fingerprints of the interactions modeled by today’s most advanced DFT-techniques for pore size characterization.
- Argon sorption analyses at its boiling point 87 K can be significantly faster than conventional N2 77 K experiments, because the filling of a pore size can occur much more readily at higher relative pressures.
