BJH pore-size distribution curve

Figure 1 presents the nitrogen adsorption and desorption isotherms with BJH pore size distribution curves for MCM-48. The isotherms are type IV according to the lUPAC... 

Fig. 3. Niteogen adsorption isotherms (A) and the corresponding BJH pore size distribution curves (B) of the mesoporous titania as-prepared (MTi02 80), modified by ceria mesoporous titania support as-prepared (CeMTi 80) and calcined at 400 °C (CeMTi 400), and gold-based catalysts calcined at 400 °C with different gold content (2 Au/CeMTi 400 and 5 Au/CeMTi 400).

The BJH pore size distribution curves of the studied samples are shown in Fig. 2. The volumes of larger pores (the radii about 15 nm) after polymer treatment are similar. It suggests that the greater part of OV-17 phase is adsorbed inside the mesopores. 

Fig. 2 left) XRD patterns and right) N2 adsorption-desorption isotherms and the corresponding BJH pore size distribution curves of the synthesized samples. 

Figure 3. Pore size distribution curve for S3 sample, calculated from the desorption branch of the nitrogen adsorption isotherm using the BJH method.

FIGURE 2.68 (a) Relative NMR spin-eeho intensities versus temperature for cyclohexane confined within the pores of titania spherical particles (b) pore size distribution curves of the MTx samples determined by H NMR cryoporometry and BJH method (dashed fines) (c) insert with field-emission (FE) SEM image of MT400. (Adapted with permission from Ryu, S.-Y., Kim, D.S., Jeon, J.-D., and Kwak, S.-Y., Pore size distribution analysis of mesoporous TiOj spheres by H nuclear magnetic resonance (NMR) cryoporometry, J. Phys. Chem. C 114,17440-17445, 2010, Copyright 2010 American Chemical Society.)... 

The nitrogen adsorption isotherms for the onion-like Fe-modified MLV-0.75 materials are of type IV, although their hysteresis loops are of complex types, HI, H2, and H3. The H2-type hysteresis loop indicates the presence of bottle-shaped pores. The pore sizes obtained with the BJH method can be assigned to entry windows of mesopores. For pure MLV-0.75 and Fe-modified MLV-0.75 (x = 1.25), the pore size distributions exhibit two peaks (Fig. Id). The first peak appears at 9.0 and ca. 6 nm for MLV-0.75 and Fe-MLV-0.75, respectively. The shift of the broad peak maximum of the distribution curve... 

Nevertheless, bearing in mind the above-mentioned reservations, it is possible to interpret the pore size distributions obtained using the BJH method with the Harkins and Jura t-curve (Fig. 2). Firstly, it would seem obvious that the peaks centred on 4 nm relate to the closing of the hysteresis at around p/p° = 0.42. One should ignore these, as they are artefacts due to the non-stability of the nitrogen meniscus under these conditions. However, the peaks observed in the case of mlO and mVT4, centered on 40 nm and 100 nm respectively, are significant. It is these peaks that can be confidently used for further comparison. 

Figure 1.7 shows the physisorption isotherm, obtained using the non continuous volumetric technique, of a mesoporous alumina (type IV isotherm) and the results of analysis procedures (BET transform, /-curve, BJH porous distribution). This solid presents a specific surface area of approximately 200 m /g with the narrow pore size distribution at around 10 nm. The shape of the /-curve shows that it does not contain any micropores. 

Fig. 5. Normalized pore size distributions and stnicture-factor lengths for all four pore models. In each graph, the solid curve is the geometrically-obtained pore size distribution, the dot-dashed curve is obtained from the adsorption isotherm with the BJH method, the solid vertical line conesponds to the structure factor peak at low coverages, and the dashed vertical line corresponds to the structure factor peak at high coverages.

An important issue in the classical methods of pore size analysis is the selection of the t-ctirve, i.e., the statistical film thickness on the carbon surface. In the original method [136], it was assumed that the film thickness on the pore walls does not depend on the pore radius but only on the relative pressure. Thus, this BJH method required two relations for the evaluation of the pore-size distribution from adsorption isotherms. The first, represented by the Kelvin Eq. (70), is the relation between the pore radius and the relative pressure at which capillary condensation occurs in the pores. The second represents the functional dependence of the statistical film thickness on the relative pressure. It should be noted that existing relationships for t-curves reported some time ago do not represent low-pressure adsorption behavior because the relevant low-pressure data were not available at that time [13], The corresponding low-pressure adsorption isotherms on carbon surfaces are now available and can be used to evaluate the t-curve for the entire pressure range. 

Adsorption isotherms on ordered mesoporous silicas such as MCM-41, which exhibits hexagonally ordered cylindrical pores [148], were used to verify and correct fundamental relations required for pore size analysis. For example, a series of high-quality MCM-41 materials was used to elaborate an accurate method for the determination of the pore-size distribution based on the BJH algorithm [67, 149]. Based on the nitrogen adsorption isotherms for the aforementioned series of MCM-41 materials, it was possible to obtain the t-curve for the silica surface from the nitrogen adsorption isotherm at 77 K on macroporous (virtually non-porous) LiChrospher Si-1000 silica. This standard adsorption isotherm was reported in tabular form by Jaroniec et al. [26]. It should be noted that the aforementioned... 

It was shown [150] that the applicability of the BEurett, Joyner and Halenda (BJH) computational method based on the Kelvin equation could be extended significantly towards small mesopores and large micropores when a proper t-curve was used to represent the fihn thickness of nitrogen adsorbed on the carbon surface. The t-curve proposed in the work [150] gave the pore-size distribution functions for the carbons studied that reproduce the total pore volume and show realistic behavior in the range at the borderline between micropores and mesopores. 

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