Carbon adsorbents surface area/pore volume

Active carbon (AC), carbon nanotubes, carbon fibers, and other carbonaceous adsorbents, owing to their low atomic weight, high surface area, pore volume, and suitable mechanical properties, are excellent options as adsorbents for hydrogen storage [81,147,165-184],... 

Abstract. Structural and adsorption characteristics of various adsorbents such as fumed silicas, silica gels, activated carbons and carbon/silicas were analyzed. The adsorption of a variety of compounds reveals the effects of adsorbent grain size, specific surface area, pore volume, pore size distribution, surface chemistry, conditions of adsorbent synthesis and pre-treatment. Both dynamic (nonequilibrium) and static (equilibrium) adsorption conditions are addressed. 

Pendleton and coworkers [46] showed (Fig. 25.5) that the adsorption of dodecanoic acid on different activated carbons linearly decreased when the oxygen content of the carbonaceous adsorbent increased and that the adsorption was not related to the micropore volume of the adsorbent. They concluded that the surface chemistry more accurately predicted the adsorption of dodecanoic acid in aqueous phase compared with the surface area or micropore volume. In addition, carbon surface chemistry also had a significant influence on dodecanoic acid adsorption kinetics. Thus, the adsorption rate was reduced by the high surface oxygen content of the carbon adsorbent, whereas its pore volume made a smaller contribution [47],... 

The high-pressure, low-temperature adsorbed density of hydrogen on activated carbon seems to correlate linearly with the micropore volume and the specific surface area of the adsorbent. The density of hydrogen inside the micropores can be estimated from the ratio of the excess density adsorbed to the micropore volume, to which must be added the contribution of the bulk phase in the micropores. This yields a value of 62mg/cm, suggesting that at 77 K and 35 bar, the density of hydrogen inside the micropore is already close to that of liquid hydrogen. Similar values (from 61 to 71 mg/ cm ) are obtained for other activated carbon adsorbents with different pore volumes and specific surfaces. ... 

The gas adsorption-desorption technique relates to the adsorption of nitrogen (or, less commonly, carbon dioxide, argon, xenon, and krypton), at cryogenic temperatures, via adsorption and capillary condensation from the gas phase, with subsequent desorption occurring after complete pore filling. An adsorption-desorption isotherm is constructed based upon the relationship between the pressure of the adsorbate gas and the volume of gas adsorbed/desorbed. Computational analysis of the isotherms based on the BET (Brunauer-Emmett-Teller) (Brunauer et al. 1938) and/or BJH (Barrett-Joyner-Halenda) (Barrett et al. 1951) methods, underpinned by the classical Kelvin equation, facilitates the calculation of surface area, pore volume, average pore size, and pore size distribution. 

In recent years, activated carbons fibers (ACFs) because of their high surface area, microporous character, and the chemical nature of their surface have been considered potential adsorbents for the removal of heavy metals from industrial wastewater [1 3]. The properties of ACFs are determined by their microstructure, it is therefore important to investigate the microstructure of ACFs in terms of specific surface area, micropore volume, pore size distributions, surface chemistry and so on. Also, the adsorption properties of carbonaceous adsorbents are dependent on not only the porous structure but also the surface chemistry [3,4]. 

Although differences in the adsorption capacities are apparent, no correlation between them and the surface areas of the carbons can be established. We can therefore conclude that the extent of the adsorption at the zero surface coverage should be more directly related to the adsorbate and pore size and shape than to the total surface area (or volume of pores) of the adsorbent. In connection with this, the adsorption of CO2 on activated carbons from diluted ambient environments, measured in a conventional gravimetric system, has recently been shown to be more closely related with micropore size distribution rather than with the surface area or volume of micropores [17]. 

The H2O adsorption on superhigh surface area carbon was studied by the in situ X-ray diffraction technique [36]. The surface area, micropore volume, and pore width of superhigh surface area carbon were 2670 m /g, 0.97 ml/g, and 1.3 nm, respectively. The H2O adsorption isotherm determined at 303 K was of typical type V. The H2O molecules were not adsorbed below P/Po = 0.6 and then they were abundantly adsorbed above P/Pq = 0.6. Fig. 8 shows the X-ray diffraction patterns of adsorbed H2O as a function of... 

Several techniques for VOC removal have been investigated such as thermal incineration, catalytic oxidation, condensation, absorption, bio-filtration, adsorption, and membrane separation. VOCs are present in many types of waste gases and are often removed by adsorption [1]. Activated carbon (AC) is commonly used as an adsorbent of gases and vapors because of its developed surface area and large pore volumes [2]. Modification techniques for AC have been used to increase surface adsorption and hence removal capacity, as well as to improve selectivity to organic compounds [3]. 

Materials. Methyltrioxorhenium, NH4Re04 and Re207 were purchased from Aldrich and used as received. The silica-alumina was Davicat 3113 (7.6 wt.% Al, BET surface area 573 mVg, pore volume 0.76 cmVg), provided by Grace-Davison (Columbia, MD). For reactions involving MeReOs, silica-alumina was pretreated by calcination for 12 h under 350 Torr O2 at 450°C to remove adsorbed water, hydrocarbons, and carbonates, then allowed to cool to room temperature under dynamic vacuum. The silica was Aerosil 200 (BET surface area 180 mVg, with no significant microporosity) from Degussa (Piscataway, NY). 

Most of the adsorbents used in the adsorption process are also useful to catalysis, because they can act as solid catalysts or their supports. The basic function of catalyst supports, usually porous adsorbents, is to keep the catalytically active phase in a highly dispersed state. It is obvious that the methods of preparation and characterization of adsorbents and catalysts are very similar or identical. The physical structure of catalysts is investigated by means of both adsorption methods and various instrumental techniques derived for estimating their porosity and surface area. Factors such as surface area, distribution of pore volumes, pore sizes, stability, and mechanical properties of materials used are also very important in both processes—adsorption and catalysis. Activated carbons, silica, and alumina species as well as natural amorphous aluminosilicates and zeolites are widely used as either catalyst supports or heterogeneous catalysts. From the above, the following conclusions can be easily drawn (Dabrowski, 2001) ... 

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