High-Resolution Adsorption Isotherms of Microporous Solids

Abstract

High-resolution static adsorption of nitrogen and argon at 77 K was determined on six microporous carbons and two synthetic zeolites. The adsorption behavior at very low relative pressures such as 10-6 was examined in close detail. An S-shaped feature was observed in the low-pressure region of most of the nitrogen and argon isotherms on microporous carbons. A novel mechanism for the physical processes involved in the filling of micropores designated as monolayer-induced micropore filling is proposed to account for this behavior. Examination of the low-pressure region of these high-resolution adsorption isotherms also revealed that the ultramicropores are filled in the region of 10-5 relative pressure.

Constrained Equilibrium as a Tool for Characterization of Deformable Porous Media

“…In other words, an increase of the mean pore size h(ρ) may result from a pore blocking effect. This interpretation is coherent with the one proposed by the authors of 10 , who claimed that the S-shaped feature (the loop) signals a switching from the ultramicropore to micropore filling. Nevertheless, this qualitative analogy between the matrix swelling and heterogeneity requires further analysis, including a competition of the repulsive and attractive interactions.…”

“…It should be emphasized that, since we deal with a constrained equilibrium, the loop does not violate the thermodynamic stability 11 . Therefore, this feature can be readily found under suitable experimental conditions, similar to those realized in the low-pressure adsorption into microporous matrices 10 . In this respect it is worth noting that quite similar loop features have been detected 10 for nitrogen and argon adsorption in microporous carbons and synthetic zeolites.…”

“…Nevertheless, in contrast to our assumption, there is no evidence for an insertioninduced dilatation of these slit-shaped materials. The loops have been interpreted as a signature of a monolayer-induced micropore filling 10 . In this context we can propose an alternative interpretation of our results, making a link to the experimental observations.…”

Negative linear compressibility in confined dilatating systems

“…spherical pores) as well as that of a non-zero distribution width (f (h|ρ)) and the potential softness k could also be discussed. Another interesting point is to describe the sorption behavior, that is, changing ρ by varying N at fixed S. In this way we can mimic a "dosen" adsorption 29 or the equilibrium with an infinite bulk reservoir.…”

Asymmetric Profiles and Prewetting Lines in the Filling of Planar Slits with Ne

“…The CE scheme provides Δμ( T ) for all values of n . When in this frame the data exhibit S-shaped van der Waals isotherms, − the two coexisting stable states (thin and thick films) located at n thin and n thick (i.e., at normalΓ scriptl , thin and normalΓ scriptl , thick , respectively) satisfying μ ( n thin ) = μ ( n thick ) = μ eq ( Ω eq / A ) are determined by applying the Maxwell rule of equal areas as in refs , , and ∫ n thin n thick false[ μ ( T ) − μ 0 ( T ) false] ⁡ d n = Δ μ pw false( T false) false[ n thick − n thin false] This Maxwell construction is depicted in Figure , where the points M S1 and M S2 stand for symmetric states which films formed at both walls coincide, respectively, with the...…”