Physisorption

Physisorption

Characterization of pore size distributions and pore network structures of a sample

Physisorption analysis is an important method for determining the pore size distribution and characterising pore network structures of microporous samples. The analysis is based on the sorption of gases, which fill pores of different diameters at distinct partial pressures. From a complete adsorption and desorption isotherm, a complete pore size distribution in the micro, meso and macro pore range can be determined. In addition, statements can also be made about the pore network of a sample. Our laboratory has a range of different gases (N2, Ar, Kr and CO2) which can be used for physisorption measurements depending on the general application.

Figure 1: Comparison of two sorption isotherms of a claystone measured with nitrogen (N2) and argon (Ar). The sorbed quantity of the gas used (mmol/g) is shown as a function of the partial pressure (p/p0). However, one can see the sorbent-dependent deviation at the kink point of the desorption branch (N2 = 0.55 and Ar = 0.47 p/p0). For nanoporous materials argon is the better choices as sorbent due to its smaller atomic diameter compared to nitrogen. The relevant partial pressure range (approx. 0.05 to 0.35 p/p0) for determining the specific surface area of a sample is highlighted in yellow.

Applications

Physisorption analyses are primarily carried out by universities and research institutions, but can also be a powerful tool for material characterisation in industry. Some applications are listed below:
  • Characterisation of the porosity of rocks, e.g. for relevant lithologies of nuclear waste storage
  • Determination of pore size distributions and pore network structure of membranes or filters
  • Structure analysis of nanoporous materials for gas storage applications, e.g. metal-organic frameworks (MOFs)
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