BASIC CONCEPTS AND AN OVERVIEW - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 6

1.1.2 ACTIVATED CARBON FIBERS (ACFS): PROPERTIES AND
APPLICATION
Activated carbons fibers have been prepared recently and developed a new field
of applications. They have a number of advantages over granular activated car-
bons. The principal merit to prepare activated carbon in fibrous morphology is
its particular pore structure and a large physical surface area. Granular activated
carbons have different sizes of pores (macropores, mesopores and micropores),
whereas ACFs have mostly micropores on their surfaces. In granular activated
carbons, adsorbates always have to reach micropores by passing through macro-
pores and mesopores, whereas in ACFs they can directly reach most micropores
because micropores are open to the outer surface and hence, exposed directly to
adsorbates. Therefore, the adsorption rate, as well as the amount of adsorption, of
gases into ACFs is much higher than those into granular activated carbons [1-3].
In recent work, the amount of adsorption of toluene molecules is much higher,
and desorption proceeds faster in ACFs than granular activated carbons, effective
elimination of SO• from exhausted gases by using ACFs was too. A very high
specific surface area up to 2500 m 2 g -1 and a high micropore volume up to 1.6 cm 3
g -1 can be obtained in isotropic-pitch-based carbon fibers. For the preparation of
these carbon fibers with a very high surface area such as 2500 m 2 g -1 , precursors
which give a carbon with poor crystallinity are recommended; thus, mesophase-
pitch-based carbon fibers did not give a high surface area, whereas isotropic pitch
based carbon fibers did. Other advantage of ACFs is the possibility to prepare
woven clothes and non-woven mats, which developed new applications in small
purification systems for water treatment and also as a deodorant in refrigerators in
houses, recently reported. In order to give the fibers an antibacterial function and
to increase their deodorant function, some trials on supporting minute particles of
different metals, such as Ag, Cu and Mn, were performed. Table 1.2 presents the-
comparison between properties of activated carbon fibers and granular activated
carbons [13-46].

TABLE 1.2 Comparison Between Some Properties of ACF and GAC.

Activated Carbon Fibers Granular Activated Carbons

S BET ( m 2 g -1 ) 700-2500 900-1200

Surface area ( m 2 g -1 ) 0.2-2.0 ~0.001

Mean diameter of pores
(nm)

<40 Frommicro to macropores

Activated carbon fibers (ACFs), due to their microporosity, are an excellent
material for a fundamental study of H 2 adsorption capacity and enthalpy. Synthe-