Novel Carbon-Based Nanoadsorbents for Water Purification - Aquananotechnology: Global Prospects - page 749

to be 2.55, indicating the presence of a relatively large amount of disordered graphite com-
ponents in ACF. This disorder increases during nickel impregnation. As also observed,
CNF grown on ACF retains short-range graphitic characteristics with an I D / I G ratio of 2.89.

36.8 ACF/CNF as Adsorbents
The adsorption capacity of an adsorbent may be tested under batch and/or low conditions.
In a typical batch experiment, a ixed amount of adsorbent is mixed with a ixed volume of
water containing an initially predetermined concentration of the solute and is allowed to
come to equilibrium at a constant temperature. The concentration of the solute in the adsor-

= ( 0 , where C 0 and C
are the aqueous-phase solute concentrations before and after equilibrium is attained. V is
the volume of the solution in contact with the adsorbent of weight w . Figure 36.9 presents
the equilibrium concentrations of the luoride ions in the solid phase as a function of the
aqueous-phase concentration for ive types of samples: the ACF substrate, Al-ACF (ACF
impregnated with Al), CNF, and Al-CNF with and without sonication (acid treatment).
The lines regressed through the data are essentially the equilibrium isotherms of luoride
ions vs. Al-impregnated carbon ibers at 35°C. As observed, the solid-phase concentrations
are between 0.10 and 15 mg/g, corresponding to the liquid-phase concentrations between
0.1 and 50 mg/l. For each sample, the data are best explained by the Freundlich isotherm,
q = K × C n , where q is the amount of adsorbed luoride ions in milligrams per gram of ACF,
K is the Freundlich constant, and n is the power of isotherm. The values of the constant n
less than unity indicate a favorable adsorption for the systems reported here.

VC C

bent phase is theoretically determined by the mass balance, q

w

100

Al-CNF (with sonication)
Al-CNF (without sonication)
Al-ACF
CNF
ACF
Freundlich equation
q = K × C n

10

1

0.1

0.0 0.01

0.1
Aqueous-phase fluoride concentration (mg/l)

1 10 100

FIGURE 36.9
Comparative performance of Al-CNF (with and without sonication), Al-ACF, CNF, and ACF for luoride
removal. Solid lines show Freundlich isotherms, q = K × C n ; where K = 1.30, 0.85, 0.59, 0.17, 0.06 and n = 0.61, 0.69,
0.75, 0.59, 0.41 for Al-CNF (with and without sonication), Al-ACF, CNF, and ACF, respectively. (From A. Gupta
et al., I&EC Res ., 48, 9697, 2009.)