Pore-size distribution in typical adsorbent systems
01 Aug 1970-Vol. 33, Iss: 4, pp 508-519
TL;DR: In this paper, the effect of changing the method for the calculation of the thickness of an adsorbed layer has been examined and the results of the analysis of the results are shown.
Abstract: Pore-size distribution data are calculated from nitrogen desorption isotherms on 36 samples of silica and alumina. Several methods for calculating t, the thickness of an adsorbed layer, have been proposed, but all suffer from uncertainties and no one method can be taken to be universally applicable to all adsorbents. This paper shows the effect upon the distribution results produced by changing the method for the calculation of t. It is convenient, but not necessarily theoretically correct, to take a comparison of cumulative area and BET area as a basis for the choice of the best values for t. From this comparison and an examination of the smoothness of the distribution curve, the expression for t in picometers (pm) given by de Boer: t = 354 − 5 ln P Po 1 3 is recommended.
Citations
More filters
TL;DR: In this paper, the melting and freezing of water in a series of mesoporous silica materials with a hexagonal arrangement of unidimensional cylindrical pores and narrow pore-size distribution was studied by differential scanning calorimetry (DSC).
Abstract: The melting and freezing of water in a series of mesoporous
silica materials with a hexagonal arrangement of unidimensional cylindrical
pores and narrow pore-size distribution (MCM-41 with pore diameters
from 2.9 to 3.7 nm, and SBA-15 with pore diameters from 4.4 to 11.7
nm) was studied by differential scanning calorimetry (DSC). A lowering of
the melting temperature ΔTm
=
Tmb
−
Tm(R) up to 50 K was found for
water in pores of decreasing radius R. The melting point data can
be represented by a modified Gibbs–Thomson equation, ΔTm(R) =
K/(R-t), with K
=
52 K nm and t
= 0.4 nm, in agreement with an earlier study
of water in MCM-41 materials of pore width 2 to 4 nm. The value of K
agrees with an estimate of the Gibbs–Thomson constant based on thermodynamic
data for the normal melting point of ice, and the parameter t can
be taken as the thickness of a surface layer of non-frozen water at
the pore wall. DSC scans of the freezing of H2O and D2O
in partially filled pores of SBA-15 reveal a peak pattern depending
on the degree of pore filling ϕ. The different peaks are attributed
to different states of the liquid in the pore space, iz.
pore water in completely filled regions, and water as an adsorbed film at
the pore wall. These two states coexist in a pore filling range ϕmin<ϕ<1,
but only the film state exists at ϕ<ϕmin.
The freezing peak of pore water appears to be nucleated by external bulk
ice (at ϕ>1) but exhibits substantial supercooling at ϕ<1.
On the other hand, the peak attributed to the freezing of film water exhibits
no significant supercooling and is found at temperatures near 237 K, almost
independent of ϕ and the pore width of the SBA-15 sample.
The nature of a further (small) peak near 233 K is not yet understood. Contrary
to cooling scans, only one DSC peak is observed in heating scans, independent
of the pore filling. This finding indicates that the adsorbed liquid film
is metastable relative to the frozen pore liquid.
415 citations
TL;DR: In this paper, it was shown that although the total porosity and inherent moisture of coals are determined primarily by rank effects, systematic differences in pore size distribution between inertinite and vitrinite-rich coals exist.
185 citations
TL;DR: A review of the pore characterization of carbonaceous materials, including activated carbon, carbon fibres, carbon nanotubes, etc., using adsorption techniques is given in this paper.
Abstract: A review is given of the pore characterization of carbonaceous materials, including activated carbon, carbon fibres, carbon nanotubes, etc., using adsorption techniques. Since the pores of carbon media are mostly of molecular dimensions, the appropriate modern tools for the analysis of adsorption isotherms are grand canonical Monte Carlo (GCMC) simulations and density functional theory (DFT). These techniques are presented and applications of such tools in the derivation of pore-size distribution highlighted.
156 citations
Cites methods from "Pore-size distribution in typical a..."
...Before discussing the two advanced methods for pore characterization, it should be noted that the classical methods presented in the literature are only applicable to mesoporous solids (Barrett et al. 1951; Innes 1957; Cranston and Inkley 1957; Dollimore and Heal 1964, 1970)....
[...]
01 Aug 1981
Abstract: Adsorption of water vapor at 293°K was investigated on nonporous calcium silicate, cement raw material, and porous hardened cement paste (hcp). Two parameters are sufficient to fit the entire set of data from 1 to 95% relative humidity (r.h.) for the nonporous samples. The statistical thickness of the adsorbed water film ( t curve) is given for a hydrophilic adsorbent, using the BET C constant as parameter. For the case of water adsorbed on hcp, surface areas calculated by V-t plots using this t curve agree well with BET surface areas. As capillary condensation cannot be distinguished from adsorption above 95% r.h., our data are completed by ellipsometric measurements of H 2 O on fused silica surfaces in the high-humidity range. For the chemical potential μ of the adsorbate a simple mathematical expression is given and discussed. Frequently, the Frenkel-Halsey-Hill (F.H.H.) theory is used to describe adsorption phenomena, assuming dispersion forces as the dominant factor. The predictions according to the F.H.H. theory lie more than one order of magnitude below the experimental values. It is shown that hydrogen-oxygen bonding is more suitable to characterize adsorption phenomena of water on hydrophilic surfaces. For porous materials the influence of the opposite pore wall on the chemical potential is discussed.
141 citations
TL;DR: In this paper, the Borden solids were applied to aquifer material acquired at a site in Borden, Ontario, where numerous transport studies have been conducted, and the properties of the aquifer were evaluated.
140 citations
References
More filters
11,414 citations
TL;DR: In this article, a quasi-chemical theory of interaction (BET) was used to analyze adsorption on a uniform surface and showed that the hypotheses of the BET theory lead to substantially no adorption beyond the first layer if E2 = EL, and stepwise isotherms if E1>E2>E3>···>EL.
Abstract: Analysis of adsorption on a uniform surface using the quasi‐chemical theory of interaction shows that the hypotheses of the BET theory lead to substantially no adsorption beyond the first layer if E2 = EL, and stepwise isotherms if E1>E2>E3>···>EL. For the monolayer adsorption of gases on silver, platinum, and steel, the heterogeneous nature of the adsorbing surface is clearly indicated. Cooperative adsorption on the non‐uniform surface is treated, and the cooperative analog of the Freundlich equation derived. The typical multi‐layer isotherm is shown to be composed of three regions: non‐cooperative adsorption on a strongly heterogeneous surface; cooperative adsorption on a still heterogeneous surface; and cooperative multi‐layer adsorption induced by small van der Waals perturbations some distance from the surface.The isotherm p/p0=exp{—a/θr} is derived and shown to be a good representation of adsorption data that conform to the BET Type I, II, or III shapes.
1,233 citations
TL;DR: In this paper, a method for calculating the pore size distribution from adsorption isotherms on porous solids is described, which is more exact and less tedious to use than some previously described methods.
Abstract: A method for calculating the pore size distribution from adsorption isotherms on porous solids is described, which is more exact and less tedious to use than some previously described methods. The method of compiling tables for calculation is shown and an example of such a calculation is given.
809 citations
TL;DR: In this paper, an identical multimolecular adsorption curve of nitrogen at liquid nitrogen temperature was found for a wide variety of adsorbents, provided no capillary condensation occurs and no narrow pores are put out of action in the course of progressing adorption.
736 citations