Scanning studies on capillary condensation and evaporation of nitrogen. Part 2.—Analysis of ascending and descending scanning curves within B-type hysteresis loops

Abstract

The mechanism of emptying and filling of pore domains along the adsorption as well as the desorption boundary curve of the hysteresis loop was studied by the determination of a V-S curve derived from the tangents to primary scanning curves immediately after a pressure reversal at the boundaries of the hysteresis region. In all three cases studied, the V-S curve for the desorption process exhibits a discontinuity aroundp,/po = 0.5, pointing to a sudden breakdown of the capillarycondensed state, which is not directly related to the detailed domain properties of the system. This breakdown of the capillary-condensed state invalidates in a number of cases the usual procedures for obtaining pore size distributions. The filling of slit-shaped pores was found to proceed most probably by additional sorption of one to two nitrogen molecules between adjacent adsorbed layers.

Rapid Access to Ordered Mesoporous Carbons for Chemical Hydrogen Storage

“…Them esoporous properties of CFC@XA structures were investigated with Brunauer-Emmett-Teller (BET) N 2 isotherms and pore size distributions were obtained using both Barrett, Joyner and Halenda (BJH) and nonlocal density functional theory (NLDFT) methods (Figure 1e,fand S18). In particular, the N 2 adsorption-desorption isotherms of CFC@500A demonstrates IUPAC type IV BET curve with aH 2h ysteresis loop, [19] indicating the uniform microporous and mesoporous structure with bottle type of pore geometries.T he BET surface areas,t otal pore volumes,a verage pore sizes of all the synthesized structures are summarized in Table 1. Thes mall portion of micropore volume originates from the COP-122 structure,a nd the large amount of increased total pore volume is ascribed by the uniform mesoporous structure from the ordered Fe 3 O 4 nanoparticle templated voids.B oth BET surface area and total pore volume substantially increased for CFC@500A, compared to the initial CF structure (32 vs.4 78 m 2 g À1 and 0.1311 vs. 0.6845 cm 3 g À1 ,r espectively).…”

Hysteresis Loop and Scanning Curves of Argon Adsorption in Closed-End Wedge Pores

“…In arrays of connected pores with different degrees of connectivity, a number of other forms of scanning curves have been observed, for example, (i) crossing between boundaries, (ii) converging to its closure point, and (iii) returning back to the boundary. − ,,,− Most theoretical studies have used parallel-sided pore models; however, this exact geometry is unlikely to be found in real materials. Here, we show, by carrying out computer simulations for an argon adsorbate at a range of temperatures in wedge-shaped pores, that domains of commensurate and incommensurate packing can significantly affect adsorption and scanning behavior.…”

A Macrothermodynamic Approach to the Limit of Reversible Capillary Condensation

“…Any desorption loop begun at higher pressure is terminated by a sudden evaporation when this threshold of relative pressure is reached (see curve b of Figure ). This effect, suggestively defined as catastrophic desorption, is at the basis of a frequent artifact in the evaluation of pore size: the sudden desorption is attributed to a narrow distribution of pores around 4 nm in diameter, albeit the actual porosity has smaller size and is more broadly distributed. , …”