Brunauer-Emmett-Teller analysis

The observed roughness factors (ratio of true to geometric surface) of the surfaces employed in this study varied from 1.2 to 1.4 (Table IV). This checked with electron microscope pictures of alumina and silica replicas from electropolished single crystal copper surfaces. It is unlikely that the surface areas determined by the Brunauer-Emmett-Teller analysis are too high by 50% or even by 25%, because in several cases this would lead to a roughness factor of less than unity. 

Films with a density ranging from 1 to 1.4g/cm can be grown depending on the precursor clusters. Brunauer-Emmett-Teller analysis shows a surface specific area of 665 m /g [32]. 

The structural properties of carbon aerogels have been investigated by scanning electron microscopy (SEM), nitrogen adsorption, and X-ray diffraction methods. Specific surface areas are determined by the standard BET (Brunauer-Emmett-Teller) analysis. X-ray diffraction (XRD) of the carbon aerogel is performed in a diffraction with CuKa radiation [54]. 

Gelb LV, Gubbins KE. Characterization of porous glasses simulation studies, adsorption isotherms, and the Brunauer-Emmett-Teller analysis method. Langmuir 1998 14 ... 

PCNTs are marketed commercially by Hyperion Catalyst International Inc. (Cambridge, Mass. USA), based on a patent [22] Graphite Fibrils. The method of production appears to be essentially the same as that used for Endo PCNTs. The material consists of MWCNTs, 10-20 nm in diameter and 10-12 j,m long, with ca. 10 coaxial layers within each tube. The tubes have hollow cores of ca., 2 nm diameter. The Brunauer-Emmett-Teller (BET) analysis characteristically shows a surface area of 250 m /g, true density 2.0 g/cm- and bulk density of less than 0.1 g/cm (95% void vol). 

Nitrogen adsorption was performed at -196 °C in a Micromeritics ASAP 2010 volumetric instrument. The samples were outgassed at 80 °C prior to the adsorption measurement until a 3.10 3 Torr static vacuum was reached. The surface area was calculated by the Brunauer-Emmett-Teller (BET) method. Micropore volume and external surface area were evaluated by the alpha-S method using a standard isotherm measured on Aerosil 200 fumed silica [8]. Powder X-ray diffraction (XRD) patterns of samples dried at 80 °C were collected at room temperature on a Broker AXS D-8 diffractometer with Cu Ka radiation. Thermogravimetric analysis was carried out in air flow with heating rate 10 °C min"1 up to 900 °C in a Netzsch TG 209 C thermal balance. SEM micrographs were recorded on a Hitachi S4500 microscope. 

EA = elemental analysis IR = infrared spectroscopy PXRD = powder X-ray diffraction BET = Brunauer-Emmett-Teller method (specific BET surface area) and BJH = Barrett-)oyner-Halenda method (determination of pore volume and diameter), both determined by nitrogen physisorption ... 

Multilayer adsorption and the popular Brunauer-Emmett-Teller (BET) method of analysis are described in Section 9.5. This section also describes the determination of specific areas by gas adsorption. Low-temperature N2 adsorption and the BET method of analysis are so widely used for this purpose that these topics will receive special attention. 

EXAMPLE 9.5 Calculating the Adsorption Energy from the Brunauer-Emmett-Teller Isotherm. The BET analysis uses p/p0 rather than p as a variable just as we used this pressure ratio to compare Langmuir adsorption at different temperatures in Example 9.3. What corrections, if any, are needed in the apparent adsorption energy of about 14 kJ mole-1 as calculated in Example 9.3 ... 

Brunauer-Emmett-Teller (BET) analysis was carried out on the ceramic aggregate with both nitrogen and krypton as adsorbates. The sample was crushed and dry sieved, and the fraction between 74 and 589 micrometer was retained for analysis. Results were repeatable, and consistent for the two gases. Over the range of firing and proportioning conditions studied, specific surface area of the ceramic aggregate was between 0.3 and 6 m Vg, which can be compared, for example, to a non-porous... 

The most common method used for the determination of surface area and pore size distribution is physical gas adsorption (also see 1.4.1). Nitrogen, krypton, and argon are some of the typically used adsorptives. The amount of gas adsorbed is generally determined by a volumetric technique. A gravimetric technique may be used if changes in the mass of the adsorbent itself need to be measured at the same time. The nature of the adsorption process and the shape of the equilibrium adsorption isotherm depend on the nature of the solid and its internal structure. The Brunauer-Emmett-Teller (BET) method is generally used for the analysis of the surface area based on monolayer coverage, and the Kelvin equation is used for calculation of pore size distribution. 

In the analysis of isotherm data in the literature the so-called BET (Brunauer. Emmett. Teller) isotherm equation is frequently used ... 

Evidence for a specific inclusion process promoted by molecular imprinting is directly given through sensor effects in comparison to non-imprinted layers of equivalent height. Detailed interpretation of specific inclusion or non-specific adsorption phenomena is accessible with the Brunauer-Emmett-Teller (BET) isotherm adsorption analysis [18] a typical BET-isotherm is shown in Fig. 21.2. 

We now cite the types of experimental data in the literature, by which an analysis of surface adsorption effects is carried out. One common experiment involves measuring adsorption isotherms. By weighing or by volumetric techniques one determines as a function of equilibrium gas pressure the amount of gas held on a given surface at a specified temperature. Usually this quantity varies sigmoidally with rising pressure P, as sketched in Fig. 5.2.1 for a variety of temperatures 7). By standard methods that rely on the Brunauer, Emmett, Teller isotherm equa-tion one can determine the point on the isotherms at which monolayer coverage of the surface is complete it is usually is located fairly close to the knee of the isotherm. From the cross sectional area of the adsorbate molecules and from the amount needed for monolayer coverage one may then ascertain more or less quantitatively the surface area of the adsorbent. As-... 

Gas adsorption is a suitable method for a fractal analysis because it is sensitive to the fine structure of the pores and has negligible adverse affects on the pore system. The results are usually analyzed by using fractal generalizations of the Brunauer-Emmett-Teller (BET) isotherm (30) or of the Frenkel-nalsey-TfiU (FHH) isotherm (31). The latter may also be seen as a fractal generalization of the Kelvin equation and is therefore also applicable in the capillary condensation regime (32). It has been claimed that the fractal BET theory is more appropriate for mass fractals (see sect. Fractals ), whereas surface fractals are to be analyzed using the fractal FHH theory (33). These methods have been applied to cellulose powders (34) and tablets (35). 

The Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-deBoer (GAB) sorption isotherm models were used to obtain experimental steady-state moisture contents in dry basis by linear regression analysis according to Kouassi and Roos (2002). These equations provide the value of monolayer water content, which is an important parameter in food deterioration studies. 

The surface areas were measured by multipoint Brunauer-Emmett-Teller (BET) techniques. In NH3-catalyzed materials, the fraction of micropores is extremely low (<1 vol %). In acid catalysis, the micropore content increased with decreasing surface area. The CH3 content was determined by IR spectroscopic analysis of CH3 groups only in NH3-catalyzed composites could a loss of CH3-containing units be observed. 

A electronic nose based on an array of eight quartz microbalance-based (QCM) sensors coated with modified MPPs (5,10,15,20-tetraphenylporphyrin) was used for apple aroma measurements [13], The response of each QCM sensor was modeled with Brunauer-Emmett-Teller (BET) adsorption isotherms. By means of multivariate analysis on all sensor responses, the different compounds could be discriminated well and quantified accurately. This calibration protocol can be used to characterize the sensors for the vapors of complex mixtures. 

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