Application of Large Pore MCM-41 Molecular Sieves To Improve Pore Size Analysis Using Nitrogen Adsorption Measurements

Abstract

MCM-41 siliceous molecular sieves were used to test the applicability of the Kelvin equation for nitrogen adsorption in cylindrical pores of the size from 2 to 6.5 nm. It was shown that the Kelvin equation for the hemispherical meniscus, corrected for the statistical film thickness, is in quite good agreement with an experimental relation between the pore size and the capillary condensation pressure. The agreement can be made quantitative in the pore size range from ca. 2 to 6.5 nm, if a simple correction to the Kelvin equation is introduced. The required statistical film thickness curve (t-curve) was calculated using nitrogen adsorption data for large pore MCM-41 samples and the obtained results were extrapolated using an adsorption isotherm for a macroporous silica gel. Moreover, an accurate analytical representation of the t-curve was found. Since both the corrected Kelvin equation for cylindrical pores and the t-curve have simple analytical forms, they can conveniently be used in a variety of methods to evaluate porosity. It was shown that the BJH method with the corrected Kelvin equation accurately reproduces pore sizes of MCM-41 materials. A comparison was made between the specific surface areas for the MCM-41 samples calculated on the basis of the BET equation and those obtained using other independent methods. The results strongly suggest that when nitrogen adsorption data are used, the BET method overestimates the specific surface area of siliceous materials. The latter conclusion was supported by the examination of the obtained statistical film thickness curve.

Melting and freezing of water in cylindrical silica nanopores

“…This is illustrated by the fact that the value of t derived with the present set of MCM-41 samples is greater than that reported in our earlier study (t = 0.38 nm); 3 but this difference can be traced back to the fact that in the earlier work the pore size was determined by an empirical method which yields values of the pore diameter D about 0.6 nm smaller than those obtained by the KJS prescription. 35 As mentioned in section 3.2, changing the values of the pore radii of the set of MCM-41 materials by a certain increment causes a shift in t by a similar amount, such that the values of the core radius R s = R À t remain nearly unchanged. Although the pore size determination of the present materials is more reliable than in previous studies, the remaining uncertainty in R is about AE0.10 nm, which translates into an uncertainty in t of similar magnitude.…”

Growth of Gd2O3 nanoparticles inside mesoporous silica frameworks

“…The samples were degassed at 473 K for 9 h before measurement. The specific surface area was determined by the Brunauer-Emmett-Teller (BET) model [15] over the relative pressure (P/P 0 ) range of 0.08 -0.2, the pore size distribution was derived from the adsorption isotherm branch using the Kruk-Jaroniec-Sayari (KJS) method [16]. Finally, the total pore volume was calculated from the amount of adsorbed N 2 at P/P 0 = 0.975, and the micropore volume was determined using the t-plot method at a fitted thickness range of 0.35 -0.50 nm.…”

Hierarchical porous carbon templated with silica spheres of a diameter of 14 nm from pure chitosan or a chitosan/ZnCl2 solution

“…The micropore and mesopore volumes were calculated by the α s -plot with non-graphitized soot as a standard. The mesopore size distributions were obtained by BJH-KJS method [34], whereas the distributions of the size of pores within the diameter up to 3.2 nm were calculated by Do's method optimized by ASA algorithm [35][36][37].…”

“…However, the distributions of the size of primary mesopores resulted from templating, were determined using the BJH-KJS model Table 2 Elemental bulk and surface composition and some textural parameters of chitosan-derived carbons V t single point pore volume (measured at the partial pressure indicated italics), V mi volume of micropores, V mes volume of mesopores, d p pore diameters derived from the adsorption branch by the BJH-KJS method, a obtained from α s -plot analysis using N 2 adsorption data of BP280 carbon black as reference [39] results presented in the reference [39]. [34]. This approach does not impose the need to cut the peak, which extends up to about 3.2 nm, in the proximity of its maximum at 2 nm and allows to estimate a contribution of effective pores created as the concentration of the ZnCl 2 modifier increases.…”