Environmental Engineering Reference
In-Depth Information
reported for deluoridation. In one such study, the adsorptive removal of luoride has been
carried out using carbon derived from zirconium ion-impregnated coconut iber (ZICFC)
[33]. In another study, deluoridation of water has been performed using aluminum (Al)-
impregnated AC [34].
As mentioned earlier, the afinity of iron (Fe(III)) toward inorganic arsenic has been
well established by many researchers. Consequently, several studies have been carried
out, mostly in the last decade, to develop Fe-based adsorbents to increase their adsorption
capacity for arsenic. Conceptually, impregnating iron/iron oxide onto AC produces an
adsorbent with a large surface area and increased afinity for arsenic.
36.4 Novel Carbon Nanoadsorbents
The use of GAC or powdered AC (PAC) in water puriication has been in commercial prac-
tice for a long time. In the last decade, the fabric form of carbon, namely, AC iber (ACF),
has been developed and effectively used for several adsorption applications, including air
and water pollution control, because of its relatively large BET surface area [35,36]. ACFs
are primarily microporous materials possessing a large surface area (~1200-1800 m
2
/g ),
which is a key attribute for an adsorbent. In ACFs, micropores, responsible for adsorption,
are directly connected to the external surface with a small diffusion length because of
the narrow diameter of the iber (usually 1-10 μm). Therefore, the mass transfer diffusion
resistance to the solute is negligible, and the removal rate is adsorption controlled. Figure
36.1 schematically describes the PSD in a carbon iber. ACFs also exhibit catalytic activi-
ties attributed to different surface functional groups, such as hydroxyl, carboxylic, and
quinone. Depending on the type of adsorbate (basic or acidic, anionic or cationic) to be
removed, the surface of an ACF may be functionalized with suitable reagents. ACFs can
also be impregnated with metal catalysts in certain applications.
With the recent success of nanotechnology in the development of several nanomate-
rials, nanostructured carbons, such as carbon nanotubes and carbon nanoibers (CNFs),
have been developed and applied as adsorbents in several environmental remediation
Solutes in bulk phase
External surface of ACF
Macropores
Pore diffusion
Mesopores
≈ 1 µm
Micropores
FIGURE 36.1
Schematic representation of PSD in an ACF. (Reprinted from
Activated Carbon Surfaces in Environmental
Remediation
, 1st ed., T.J. Bandosz, Copyright 2006, with permission from Elsevier.)