Activated carbon fibers adsorption properties

We have an excellent activated carbon of fiber morphology, so called activated carbon fiber ACF[3]. This ACF has considerably uniform slit-shaped micropores without mesopores, showing characteristic adsorption properties. The pore size distribution of ACF is very narrow compared with that of traditional granular activated carbon. Then, ACF has an aspect similar to the regular mesoporous silica in particular in carbon science. Consequently, we can understand more an unresolved problem such as adsorption of supercritical gas using ACF as an microporous adsorbent. 

Yang, C.M. and Kaneko, K. Adsorption properties of nitrogen-alloyed activated carbon fiber. Carbon 39, 2001 1075-1082. 

Tamai, H., Kojima, S., Ikeuchi, M., Mondori, J., Kaneda, T. and Yasuda, H., Preparation of mesoporous activated carbon fibers and their adsorption properties. Carbon (Japanese) 175 (1996) pp.243-248. 

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]. 

A fixed bed adsorption unit was examined to study adsorption dynamics in column packed with activated carbon fiber. The packing characteristics of adsorption column and properties of packed adsorbent are given in Table 1. Details of the equipment and operating procedures were described in the previous publication of Yun and Choi [4]. 

In this study, activated carbon fibers (ACFs) deposited by copper metal were prepared by electroplating technique to remove nitric oxide (NO). The surface properties of ACFs were determined by FT-IR and XPS analyses. N2/77K adsorption isotherm characteristics, including the specific surface area, micropore volume were investigated by BET and t-plot methods respectively. And, NO removal efficiency was confirmed by gas chromatographic technique. From the experimental results, the copper metal supported on ACFs appeared to be an increase of the NO removal and a decrease of the NO adsorption efficiency reduction rate, in spite of decreasing the BET S specific surface area, micropore volume, and micro-porosity of the ACFs. Consequently, the Cu content in ACFs played an important role in improving the NO removal, which was probably due to the catalytic reactions of C-NO-Cu. 

A. Matsumoto, K. Kaneko and J.D.F. Ramsay, Neutron scattering investigations of the structure and adsorption properties of activated carbon fibers, in M. Suzuki (Ed.), Fundamentals of Adsorption, Studies in Surface Science and Catalysis Vol. 80, Elsevier, Amsterdam, 1993, pp. 405-412. 

Mangun, C.L., Benak, K.R., Economy, J., and Foster, K.L. (2001). Surface chemistry, pore sizes and adsorption properties of activated carbon fibers and precursors treated with ammonia. Carbon, 39, 1809-20. 

Kobayashi, N., Enoki, T., Ishii, C., et al. (1998). Gas adsorption effects on structural and electrical properties of activated carbon fibers. J. Chem. Phys., 109, 1983-90. 

The extent of competition may also be a function of the adsorbate molecular size, correlated with the activated carbon pore size distribution. Activated carbon fibers tliat are exclusively microporous (more than 96 % of micropore volume) present a selectivity property for pesticides or phenol in the presence of higher molecidar weight compounds like humic substances, due to the direct connection of micropores to their external surface [41]. Using granular activated carbon, which does not have this molKUilar sieve property, a 20 to 70 % reduction in adsorption is obtained for atrazine in raw water compared with equilibria in distilled water [42]. 

For applications that do not require exceptional mechanical properties, carbon fibers made from high performance aramid polymers show considerable potential. These aramid fibers do not require stabilization prior to carbonization, which substantially simplifies the production process. Rayon-based carbon fibers continue to appear in some composite applications, but have become key substrates for the development of activated carbon fibers. These ACFs develop a microp-orous surface structure that is ideal for adsorption of low levels of volatile organic compounds. 

The past two decades have shown an explosion in the developments of new nanoporons materials. Tremendons advances have been made in our capabilities to tailor the porosity and snrface chemistry of oxide molecular sieves and new forms of carbon (carbon molecnlar sieves, super-activated carbon, activated carbon fibers, carbon nanombes, and graphite nanofibers). However, the potential nse of the adsorption properties of these new materials remains largely unexplored. 

ACF and its characterization. Some of physical and chemical properties of two commercial pitch based active carbon fibers (ACF-1 and 2) used in the present study are listed in Table 1. After outgassing at 150°C for 4h, BET surface areas were measured by N2 adsorption at -196°C, using a Simazu ASAP 2000 apparatus. 

Activated carbons or carbon fibers are the most common materials nsed as adsorbents and catalysts. They are employed widely in both liquid and gaseous phases. This universality is due not only to their high surface area and high volume of pores, but also to the variety of chemical properties of their surfaces. Although for physical adsorption the porous structure is the most important feature, for reactive adsorption and catalysis the chemical environment plays an important role, provided that the structure is developed sufficiently for dispersion of active chemical species and for accommodation of molecules to be adsorbed or to undergo a targeted chemical reaction. 

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