Activated carbon pore structure

Williams PT, Reed AR (2006) Development of activated carbon pore structure via physical and chemical activation of biomass fibre waste. Biomass Bioenergy 30(2) 144-152... 

Ahmadpour et al. prepared MSC from a naturally occurring substrate (Iranian walnut shell) and a commercial activated carbon (Silcarbon), using four different methods based on the adjustment of pore openings in the activated carbon pore structure. In the first two methods, activated carbons were heated in a tubular furnace in... 

Similarly, the selectivity ratios of O2/N2, as obtained from their respective uptake curves (Figures 14 - 17), are shown in Table 3. The adsorption capacity for O2 and N2 is lower than for the carbon dioxide equilibrium capacity, with low selectivity ratios of 1.0 to 2.2. Selectivity improved slightly at low burn-off values but still the results indicated poor kinetic separation effects. The kinetic diameters of CO2, CH4, O2 and N2 are 3.3, 3.8, 3.46 and 3.64 A respectively. Hence, the CO2 molecule, being the smallest of all, could be quickly and preferentially adsorbed in the activated carbon pore structure, over the largest methane molecule. However the kinetic diameters of O2 and N2 differ only slightly, which makes their separation difficult in the existing activated carbons from raw lignite. Such separation would require the preparation of a product... 

Maruyama J, K-i S, Kawaguchi M, Abe 1 (2004) Influence of activated carbon pore structure on oxygen reduction at catalyst layers supported on rotating disk electrodes. Carbon 42 3115-3121... 

Activated carbon surface structure (pore sizes and shapes) and surface... 

Zeolite templated carbons exhibit high performance without extensive activation due to the high surface areas and long range orders of their porous structures. Wang et al. [37] used zeolite X (670 m. gr, 1.4 nm pore size) and 8 hr of chemical vapor deposition (CVD) to introduce carbon into the template. The resulting template CNX-2 (2700 m2.g i) had capacitance of 158 Rgy (at 0.25 A.gyi) and energy density of 25 Wh.gyi, respectively, in aqueous electrolyte. Due to the ordered nature of the pore structure, over 97% of the capacitance was retained at rates of 2 A.gyi. The zeolite could produce dense carbon pore structure (1.07 cm. g-i) and improved volumetric capacitance versus most activated carbon materials [37]. 

Endo, M., Takeuchi, K., Sasuda, Y., Matsubayashi, K., Oshida, K. and Drcsselhaus, M. S., Fractal analysis on pore structure for activated carbon fibers. Electron. Commun. Jpn., Part II Electron., 1994, 77(6), 98 107. 

Economy, J., Daley, M., Hippo, E. J. and Tandon, D., Elucidating the pore structure of activated carbon fibers through direct imaging using scanning tunneling microscopy (STM), Carbon, 1995, 33(3), 344 345... 

Alcaniz-Monge, J., Cazorla-Amoros, D., Linares-Solano, A., Yoshida, S. and Oya, A., Effect of the activating gas on tensile strength and pore structure of pitch-based carbon fibers. Carbon, 1994, 32(7), 1277 1283. 

The activated carbon materials are produced by either thermal or chemical activation as granular, powdered, or shaped products. In addition to the form of the activated carbon, the final product can differ in both particle size and pore structure. The properties of the activated carbon will determine the type of application for which the carbon will be used. 

Liquid phase applications account for nearly 80% of the total use of activated carbon. Activated carbon used in liquid phase applications typically have a high fraction of pores in the macropore (>50nm) range. This is to permit the liquid phase molecules to diffuse more rapidly into the rest of the pore structure [15]. 

Adsorbents, and activated carbon in particular, are typically characterized by a highly porous structure. Adsorbents with the highest adsorption capacity for gasoline or fuel vapors have a large pore volume associated with pore diameters on the order of 50 Angstroms or less. When adsorption occurs in these pores, the process is comparable to condensation in which the pores become filled with hquid adsorbate. Fig. 5 depicts the adsorption process, including transfer of adsorbate molecules through the bulk gas phase to the surface of the solid, and diffusion onto internal surfaces of the adsorbent and into the pores. 

Pores of the activated carbon exist throughout the particle in a manner illustrated in Figure 2. The pore structure of activated carbon affects the large surface-to-size ratio. The macropores do not add appreciably to the surface area of the carbon but provide a passageway to the particle interior and the micropores. The micropores are developed primarily during carbon activation and result in the large surface areas for adsorption to occur. 

Carbons may have closed and open pores with a large variety of dimensions from a few Angstroms to several microns. In terms of structure, the pores in active carbons are divided into three basic classes [66, 69] macropores, transitional pores, and micropores. Pores are formed during the production of carbon (pyrolysis of its precursors), or can be formed by other means such as oxidation by 02, air, C02, or H20 [66]. According to Dubinin s... 

Effectiveness of selective adsorption of phenanthrene in Triton X-100 solution depends on surface area, pore size distribution, and surface chemical properties of adsorbents. Since the micellar structure is not rigid, the monomer enters the pores and is adsorbed on the internal surfaces. The size of a monomer of Triton X-100 (27 A) is larger than phenanthrene (11.8 A) [4]. Therefore, only phenanthrene enters micropores with width between 11.8 A and 27 A. Table 1 shows that the area only for phenanthrene adsorption is the highest for 20 40 mesh. From XPS results, the carbon content on the surfaces was increased with decreasing particle size. Thus, 20 40 mesh activated carbon is more beneficial for selective adsorption of phenanthrene compared to Triton X-100. 

Mesoporous carbon materials were prepared using ordered silica templates. The Pt catalysts supported on mesoporous carbons were prepared by an impregnation method for use in the methanol electro-oxidation. The Pt/MC catalysts retained highly dispersed Pt particles on the supports. In the methanol electro-oxidation, the Pt/MC catalysts exhibited better catalytic performance than the Pt/Vulcan catalyst. The enhanced catalytic performance of Pt/MC catalysts resulted from large active metal surface areas. The catalytic performance was in the following order Pt/CMK-1 > Pt/CMK-3 > Pt/Vulcan. It was also revealed that CMK-1 with 3-dimensional pore structure was more favorable for metal dispersion than CMK-3 with 2-dimensional pore arrangement. It is eoncluded that the metal dispersion was a critical factor determining the catalytic performance in the methanol electro-oxidation. 

The adsorption process, in principle, is an anion-exchange process which is restricted only to the surface of the activated charcoal. This fact makes the loading or the exchange capacity of activated charcoal to be relatively smaller in comparison with ion-exchange resins, and it is for this reason that charcoals are quite often treated suitably to improve their loading capacities. The surface and the pore structure characteristics of activated carbon are the important factors upon which its industrial applications depend. 

The absorption property exhibited by active carbon certainly depends on the large specific surface area of the material, though an interpretation that it is based solely on this is incomplete. This is borne out by the fact that equal amounts of two activated carbon specimens, prepared from different raw materials or by different processes and having the same total surface area, may behave differently with regard to adsorption. Such differences can be partly explained in terms of the respective surface properties of the carbon samples and partly in terms of their relative pore structure and pore distribution. Every activated carbon particle is associated with at least two types of pores of distinctly different sizes. They are the macropores and the micropores. The macropores completely permeate each particle and act as wide pathways for the diffusion of material in and out of carbon, but they contribute very little to the total surface area. The micropores are more important since they... 

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