Brunauer, Emmett, and Teller BET Surface Area

The surface area of porous nanofiber mats determined using the Brunauer, Emmett, and Teller (BET) gas adsorption model has been reported for a limited number of electrospun polymers (Ding et al. 2003 Gong et al. 2004 Ryu et al. 2003 Zhang, Y. Z., et al. 2006c). Determinations that rely on gas adsorption involve several key assumptions  

Gas interaction with the polymer occurs with a constant heat of adsorption and exclusively due to van der Waals interactions between the gas and nanofiber surface (i.e., there is no significant sorption of the gas by the nanofibers). 

Adsorbed molecules on the surface do not interact with each other. 

Additional layers of gas molecules can be deposited on the surface of a complete or incomplete monolayer with the heat of adsorption being equal to heat of liquefaction of the gas. 

The classical Langmuir model for sorption of a monolayer of gas molecules on a solid surface is described by the following simple expression  

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When the anode is first charged, it slowly approaches the lithium potential and begins to react with the electrolyte to form a film on the surface of the electrode. This film is composed of products resulting from the reduction reactions of the anode with the electrolyte. This film is called the solid electrolyte interphase (SEI) layer [30], Proper formation of the SEI layer is essential to good performance [31-34], A low surface area is desirable for all anode materials to minimize the first charge related to the formation of SEI layer. Since the lithium in the cell comes from the lithium in the active cathode materials, any loss by formation of the SEI layer lowers the cell capacity. As a result, preferred anode materials are those with a low Brunauer, Emmett, and Teller (BET) surface area... 

Sorption capacities of granular activated carbons and activated carbon fibers were measured, but they were relatively low, e.g., 1 g/g for activated carbon granules with llOOm /g surface area and 19g/g for those with 1220m /g, and no relation to the Brunauer, Emmett, and Teller (BET) surface area was observed. Therefore, the experimental results on different carbon materials showed that macropores, which make bulk density lower, are mainly responsible for their large sorption capacity. Fibrous particles of carbon may be advantageous for easy deformation of macropores to be suitable for sorption of heavy oils. 

Wheeler [16] proposed that the mean radius, r, and length, L, of pores in a catalyst pellet (of, for that matter, a porous solid reactant) are determined in such a way that the sum of the surface areas of all the pores constituting the honeycomb of pores is equal to the BET (Brunauer, Emmett and Teller [17]) surface area and that the sum of the pore volume is equed to the experimental pore volume. If represents the external surface area of the porous particle (e.g. as determined for cracking catalysts be sedimentation [18]) and there are n pores per unit external area, the pore volume contained by nSx cylindrically shaped pores is nSx nr L. The total extent of the experimentally measured pore volume will be equal to the product of the pellet volume, Vp, the pellet density, Pp, and the specific pore volume, v. Equating the experimental pore volume to the pore volume of the model... 

Another example of a DMC-catalyzed esterification reaction is the esterification of free fatty acids with glycerol [32]. This reaction again used Zn-Fe(II)-DMC as a catalyst yet the activity of the material could be tuned by varying the synthesis temperature. As such, DMCs with different acidities (as evidenced by NHj-TPD), crystallite sizes (calculated from the Debye-Scherrer equation), particle sizes (studied with scanning electron microscopy (SEM)), and BET (Brunauer, Emmett and Teller) specific surface areas were obtained. The highest catalytic conversions were observed for the catalysts synthesized at elevated temperatures these materials featured both the highest specific surface area and the largest number of acid sites. 

Surface Areas by the Brunauer, Emmett and Teller BET Method... 

The intrinsic dissolution rates of pharmaceutical solids may be calculated from the dissolution rate and wetted surface area using Eq. (36) or (37). For powdered solids, two common methods are available the powder intrinsic dissolution rate method, and the disc intrinsic dissolution rate method. In the former method, the initial dissolution rate of one gram of powder is determined by a batch-type procedure as illustrated in Fig. 13A. The initial wetted surface area of one gram of powder is assumed to equal the specific surface area determined by an established dry procedure, such as monolayer gas adsorption by the Brunauer, Emmett, and Teller (BET) procedure [110]. 

The number of gas molecules can be measured either directly with a balance (gravimetric method) or calculated from the pressure difference of the gas in a fixed volume upon adsorption (manometric method). The most frequently apphed method to derive the monolayer capacity is a method developed by Brunauer, Emmett, and Teller (BET) [1], Starting from the Langmuir equation (monolayer adsorption) they developed a multilayer adsorption model that allows the calculation of the specific surface area of a sohd. The BET equation is typically expressed in its linear form as... 

The most definitive surface area measurements are probably those made by nitrogen adsorption using the BET theory. Neither the Brunauer, Emmett and Teller (BET) theory nor equation (11.5), used to calculate surface area from mercury intrusion data makes any assumptions regarding pore shape for surface area determinations. When these two methods are compared there is often surprisingly good agreement. When... 

Gas Adsorption by the Brunauer, Emmett, and Teller (BET) Method. The specific surface area of porous or finely divided solids is measured. The method is limited to solids that do not react with the gas used (e.g., while the gas is adsorbed), and nonmicroporous materials. For standards, see Table 1 ( Specific Surface, BET Method and N2 Adsorption ). 

The most well-known method for determining the specific surface area of powders is based on a theory of multimolecular adsorption of gases developed by Brunauer, Emmett, and Teller (BET) (1). The BET method involves the determination of the quantity of a gas which, when adsorbed on the surface of the solid, would completely cover the solid with a monolayer of the gas. 

British Standard 4359 Part 1 1969. Nitrogen adsorption (BET method). Deutsche Normen DIN 66131, 1973. Bes-timmung der spezifischen Oberflache von Feststoffen durch Gasadsorption nach Brunauer, Emmett and Teller (BET). Norme Franpaise 11-612, 1975. Determination de l aire mas-sique (surface specifique) des poudres par adsorption de gaz. American National Standard, ASTM D 3663-78. Standard test method for surface area of catalysts. 

It is important to realize that useful zeolites have large internal surfaces, that is, a reminder of the sponge analogy, and it is these surfaces that control their observable surface properties. Normally, surface areas of inorganic materials are quantified by standard gas sorption techniques, for example, N2 uptake analyzed by Brunauer, Emmett, and Teller (BET) isotherm plots, and zeolites have nitrogen surface areas in the approximate region 100-1000m g. These estimates should be considered with caution because ... 

Details of several different methods for determining the specific surface area of carbon black are described in ASTM D 3037. The different types of equipment used and procedures are included in separate sections. Another standard gives full details of procedure of conventional Brunauer, Emmett, and Teller (BET) method based on multilayer gas adsorption. The results of determination are in both cases given in the surface area in square meters per gram of substance. 

SA is surface area by nitrogen adsorption using, the Brunauer. Emmett, and Teller (BET) method 121. 

Methods for micro-measurement of surface areas include the Brunauer, Emmett, and Teller (BET) method (2), which relies on the adsorption of monolayers of gas, commonly nitrogen or argon, the adsorption of organic molecules such as ethylene glycol and ethylene glycol monoethyl ether (EGME) (10). and the use of infrared internal reflectance spectroscopy (11) which characterizes bonding of sorbed water. These last two techniques have been confined principally to surface areas of clay minerals. 

The theory of physical adsorption of gas molecules on solid surfaces was derived by Brunauer, Emmett, and Teller (BET). The theory serves as the basis for the most widely used technique to assess specific surface area of powders and solids. It extends the Langmuir isotherm concept. 

The method developed by Brunauer, Emmett, and Teller (BET) to estimate the particle size relies on determining the surface area of the powder, which is calculated from the N2-isotherm observed at the boiling point of N2. The BET equation is... 

Physical adsorption is the basis for the various techniques to measure surface area of ceramic powders. The surface area is determined in terms of the amount of the gas adsorbed by a given mass of solid powder at a given temperature, under different gas pressures p. In practice, gases with a fixed volume are used for the powder, so that the amount of gas adsorbed can be identified according to the decrease in pressure of the gas. The amount of gas adsorbed versus p, or p/po, when the gas is at pressures below its saturation vapor pressure po, can be plotted as a graph, which is known as the adsorption isotherm. Figure 4.3 shows the types of these isotherms, according to Brunauer, Emmett and Teller (BET) classification [35-38]. The Type VI isotherm is called stepped isotherm, which is relatively rarely observed, but has special theoretical interest. This isotherm offers the possibility to determine the monolayer capacity of a solid, which is defined as the amount of gas that is required to cover the surface of the unit mass of the solid with a monolayer, so as to calculate the specific surface area of the solid. 

It is evident that if the physical adsorption capacity were limited to a close-packed monolayer, determination of the saturation limit from an experimental isotherm with a molecule of known size would provide a simple and straightforward method of estimating the specific area. The main difficulty is that in chemisorption the sites are usually widely spaced so that the saturation limit bears no obvious relationship to specific surface area while physical adsorption generally involves multilayer adsorption. The formation of the second and subsequent molecular layers commences at pressures well below that required for completion of the monolayer so it is not immediately obvious how to extract the monolayer capacity from the experimental isotherm. This problem was first solved by Brunauer, Emmett, and Teller (BET) who developed a simple model isotherm to account for multilayer adsorption and used this model to extract the monolayer capacity and hence the specific surface area. A number of refinements to the BET model and to the experimental method have been developed more recently but the basic BET method remains the most widely used technique for measurement of specific surface... 

Nitrogen adsorption at low temperature is a routine characterization technique of nanoporous materials. For instance, the specific surface of porous materials is usually assessed from adsorption experiments (prior to capillary condensation of the fluid) on the basis of the Brunauer, Emmett, and Teller (BET) method. The BET model corresponding to the N2 adsorption isotherm at 77 K in the atomistic model of MCM-41 materials fits very well the simulated data with a correlation coefficient = 0.999 (see [39] for the comparison). We found Sbet 1000 m /g (the latter value is obtained by considering as the surface area occupied by an adsorbed N2 molecule, A 2 = 0.162 nm ) and C = 100. The value obtained for C... 

The surface area of a solid material is important in that it provides information on the available void spaces on the surfaces of a powdered solid. In addition, the dissolution rate of a solid is partially determined by its surface area. The most reproducible measurements of the sruface area of a solid are obtained by adsorbing a monolayer of inert gas onto the solid surface at reduced temperature, and subsequently, desorbing this gas at room temperatme. The sorption isotherms obtained in this technique are interpreted using the equations developed by Brunauer, Emmett, and Teller (BET), and therefore, the technique is referred to as the BET method. The surface area is obtained in units of square meters of sruface per gram of material. 

NPs are generally believed to exert toxic effects via a number of mechanisms, all of which are related to OS [6, 7]. The extent of the effects noted has been well correlated with Brunauer, Emmett, and Teller (BET) [8] surface areas of the NPs in a number of studies [9, 10]. BET surface areas are widely used to evaluate catalytic activity in promoting chemical reactions and it is well known that the quantity of surface and not the mass of a heterogeneous catalyst is what determines the degree of chemical reaction [11]. It is currently believed that insoluble NPs act in an analogous manner. 

Brunauer, Emmett, and Teller (BET method) measures surface area of material based on the adsorption of gaseons nitrogen at the temperature of liquid nitrogea For a full information how this method is carried out, one may refer to ISO 5794/1 Annex D or ASTM C1274-12. 

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