Adsorption-desorption isotherm

N2 adsorption-desorption isotherms revealed that MCs had hi surface area (>1200 m /g) and large pore volume (>1.0 cm /g). From SAXS patterns of the prepared materials, it was confirmed that pores of SBA-15 and CMK-3 retained highly ordered 2-dimensional hexagonal type arrangement [5], while MCM-48 had 3-dimensional cubic type pore structure. It should be noted that a new scattering peak of (110) appeared in the CMK-1 after the removal of MCM-48 template. Furthermore, the pore size of CMK-1 and the wall thickness of MCM-48 were found to be 2.4 nm and 1.3 nm, respectively. This result demonstrates that a systematic transformation of pore structure occurred during the replication process from MCM-48 to CMK-1 [6]. 

In order to elucidate the pore structure of Csx, the adsorption-desorption isotherm of N2 was first measured. Tsrical results are given in Figure 4. H3PW12O40 exhibited a Type II isotherm (according to the lUPAC classification... 

Figure 3.42. Nitrogen adsorption/desorption isotherm for a commercial y-alumina. The arrows denote the mode of changing the pressure, viz. increasing or decreasing pressure.

Catalysts Characterization Catalysts were characterized by nitrogen adsorption-desorption isotherms, XRD, XPS, TEM, and FT-IR. The concentration and the strength of the acid sites were determined using a combination of NHs-chemisorption and FTIR. Detailed procedures are given elsewhere [18, 19]. 

Fig.3.1.9 (a) The adsorption-desorption isotherm (circles, right axis) and the self-diffusion coefficients D (triangles, left axis) for cyclohexane in porous silicon with 3.6-nm pore diameter as a function of the relative vapor pressure z = P/PS1 where Ps is the saturated vapor pressure, (b) The self-diffusion coefficients D for acetone (squares) and cyclohexane (triangles) as a function of the concentration 0 of molecules in pores measured on the adsorption (open symbols) and the desorption (filled symbols) branches. 

Fig. 3.5.9 NMR measured local adsorption/desorption isotherms extracted from ROIs within the (a) Al203 and (b) ZnO ceramics shown in Figure 3.5.8. Adapted from Ref [21].

The adsorption/desorption isotherms measured by NMR (equivalent to conventionally measured isotherms), extracted from two different regions of the imaging field of view corresponding to the two ceramics, are shown in Figure 3.5.9. Once these local isotherms are extracted, they are simply the local adsorption for that point in space contained within the material, measured non-invasively and non-destructively. Conventional analysis techniques for adsorption isotherms (such as BET theory) can therefore be applied to the data, to determine the microstructural properties corresponding to that isotherm curve. 

Nitrogen adsorption/desorption isotherms of all the activated carbons are of Type I, i.e. characteristic of basically microporous solids. There is a lack of adsorption/desorption hysteresis. More careful analysis permits to notice significant differences in the porous texture parameters depending on precursor origin. 

Specific surface area (SSA), total pore volume and average pore diameter were measured by N2 adsorption-desorption isotherms at 77K using Micromeritics ASAP 2020. The pore size was calculated on the adsorption branch of the isotherms using Barrett-Joyner-Helenda (BJH) method and the SSA was calculated using the Brunauer-Emmett-Teller (BET) method. 

Nitrogen adsorption/desorption isotherms on Zeolite and V-Mo-zeolite are very similar and close to a type I characteristic of microporous materials, although the V-Mo-catalysts show small hysterisis loop at higher partial pressures, which reveals some intergranular mesoporosity. Table 1 shows that BET surface area, microporous and porous volumes, decrease after the introduction of Molybdenum and vanadium in zeolite indicating a textural alteration probably because of pore blocking by vanadium or molybdenum species either dispersed in the channels or deposited at the outer surface of the zeolite. The effect is far less important for the catalysts issued from ZSM-5. 

Figure 2 shows us the N2 adsorption-desorption isotherm of Beta/montmorillonite composite. At low relative pressure a sharp adsorption of nitrogen indicates the existence of large amount of micropore. The hysteresis shown in figure 2 is ascribed to type H4 which usually can be observed on layered clay and other materials [2], It is obvious that part of the pore structure in montmorillonite is still preserved after calcination under high temperature and the following hydrothermal crystallization. 

Figure 2. N2 adsorption-desorption isotherm of Beta/montmorillonite composite...

Figure 1. Nitrogen adsorption-desorption isotherms at 77 K on (void squares) SBA-15 synthesized at 403 K, (void lozenges) SBA-15 synthesized at 343 K, (filled triangles) MCM-41.

The X-ray diffraction pattern of the spheres before the immersion in SBF shows the typical diffraction peak ascribable to the (100) reflection of the ordered mesophase with a dioo of 3.45 nm. Nitrogen adsorption-desorption isotherms are of type IV and pore size from DFT model results 2.4 nm (data not reported). 

Nitrogen adsorption-desorption isotherms of MCM-41-IBU after 2 hours of immersion in SBF show the characteristic mesopore filling at p/p° below 0.25 (type IV isotherm). 

N2 adsorption-desorption isotherms show instead occlusion of mesopores between 2 and 9 hours of immersion, possibly due to reaction of silica with SBF. This seems to vanish between 24 and 27 hours, only in the case of ibuprofen-loaded spheres. We suggest that in this latter case the entrapped molecules play a role in the temporary reopening of the pores. 

The N2 adsorption-desorption isotherms of dried chitosan gel and chitosan-zeolite composites are reported in Figure 4 (a). Dried chitosan gels present a surface area lower than 5 m2 g"1 and virtually no porosity, the evaporation of water having brought about the coalescence of the polymer fibrils. The composites with a small amount of zeolites (less than 8 % for the zeolite X composite) present a type 4 isotherm leaning towards... 

Figure 4. (a) Adsorption-desorption isotherms of N2 at -196°C of 80°C-outgassed (empty squares) chitosan, (filled trangles) zeolite X-chitosan composite from in-situ zeolite synthesis and (empty triangles) zeolite Y-chitosan composite from encapsulation of the zeolite in the gelling chitosan. (b) Scanning electron micrographs of a calcined zeolite-chitosan bead prepared by zeolitisation of a silica-chitosan composite. 

The parent zeolites, MOR and BEA, show reversible type-I adsorption/desorption isotherm with a steep rise at pipe, < 0.01, typical for microporous solid while the recrystallized exhibit rather sharp steps at pipe, 0.35, corresponding to the existence of uniform mesopores (typical for MCM-41 phase). According to BJH calculation, the size of the mesopores was about 3.0 nm. The contribution of micro- and mesopores in recrystallized materials was adjusted by variation of alkalinity during recrystallization procedure [2] (Table 1). The formation of mesopores resulted in significant increase of pore volumes of the samples upon recrystallization. 

To determine any structure modification to the Degussa C-aluminoxide support during wet impregnation and calcinations, adsorption/desorption isotherms obtained before and after modifications were compared. The results as presented in Figure 14.1 are in agreement with our previous results.39 It is found that the... 

Surface Acoustic Waves (SA Ws). The basic idea of this technique is to use the dependence of the frequency and propagation of surface acoustic waves on mass loading in a film. The porous film has to be deposited on a piezoelectric substrate (quartz), which is then placed into a physisorption setup to condense nitrogen at 77 K. Adsorption and condensation of N2 result in a shift of the oscillation frequency, and thus measurements of the oscillation frequency as a function of N2 partial pressure provide an adsorption-desorption isotherm.30 Although the technique has proven to provide a concise characterization of porous films,29,30 the requirement for the deposition directly onto the SAW piezoelectric substrate represents a certain restriction. 

Figure 4.24 TEM image (left), XRD pattern (middle), and nitrogen adsorption-desorption isotherm (right) of a typical MCM-41 material. (Courtesy of F. Kleitz.)...

Adsorption of water by cellulose displays hysteresis. The adsorption isotherm is not identical to the desorption isotherm and the amount of adsorbed water in equilibrium with the atmosphere at a particular relative humidity is higher during desorption from a higher humidity than during adsorption from a lower humidity. A plot of the adsorption/desorption isotherm is shown in Figure 5.4. 

DiToro DM, Horzempa LM (1982) Reversible and resistant components of PCB adsorption-desorption isotherms. Environ Sci Technol 16 594... 

Characterization. The high resolution TEM images were obtained on a JEOL 2010 electron microscope with an acceleration voltage of 200 kV. Measurement of nitrogen adsorption-desorption isotherms was performed on a Micromeritics ASAP... 

Bolt GH, De Boodt MF, Hayes ME, McBride MB (eds) (1991) Interactions at the soil coUoid-solution interface. NATO ASI Series—Applied Science—Series E vol 190, Kluwer, Dordrecht Bowman BT (1979) Method of repeated additions for generating pesticide adsorption-desorption isotherm data. Can J Soil Sci 59 435-437... 

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