Environmental Engineering Reference
In-Depth Information
Li et al. (2001) reported that CNT supported amorphous alumina had a fluoride
adsorption capacity ~13.5 times higher than that of AC-300 carbon and 4 times higher
than that of -Al
2
O
3
(Li et al., 2001). After oxidation with nitric acid, CNTs also showed
exceptional adsorption capability and high adsorption efficiency for lead removal from
water (Li et al., 2002). Li et al. (2003) have investigated the sorption of Pb(II), Cu(II)
and Cd(II) onto MWNTs. They reported maximum sorption capacities of 97.08 mg/g for
Pb(II), 24.49 mg/g for Cu(II) and 10.86 mg/g for Cd(II) at room temperature, pH 5.0 and
metal ion equilibrium concentration of 10 mg/l. It was also found that the metal-ion
sorption capacities of the MWNTs were 3-4 times larger than those of powder activated
carbon and granular activated carbon (Li et al., 2003b). Qi and Su (2004) have evaluated
the sorption of Pb(II) onto chitosan nanoparticles (40-100 nm) prepared by ionic
gelation of chitosan and tripolyphosphate. The phosphate-functionalized chitosan
nanoparticles have a maximum Pb(II) sorption capacity of 398 mg/g (Qi and Xu, 2004).
Li et al. (2003b) studied individual and competitive adsorption capacities of Pb
2+
,
Cu
2+
and Cd
2+
by nitric acid treated MWNTs. The maximum sorption capacities
calculated by applying the Langmuir equation to single ion adsorption isotherms were
97.08 mg/g for Pb
2+
, 24.49 mg/g for Cu
2+
and 10.86 mg/g for Cd
2+
at an equilibrium
concentration of 10 mg/l. The competitive adsorption studies showed that the affinity
order of the three metal ions adsorbed by CNTs is Pb
2+
> Cu
2+
> Cd
2+
. The Langmuir
adsorption model can represent experimental data of Pb
2+
and Cu
2+
well, but does not
provide a good fit for Cd
2+
adsorption data. The effects of solution pH, ionic strength and
CNT dosage on the competitive adsorption of Pb
2+
, Cu
2+
and Cd
2+
ions were investigated.
The comparison of CNTs with other adsorbents suggests that CNTs have great
application potential in environmental protection regardless of their higher cost at
present (Li et al., 2003b).
Peng et al. (2003) used as-grown CNTs and graphitized CNTs as adsorbents to
remove 1,2-dichlorobenzene from water. It was confirmed that it takes only 40 min for
CNTs to attain equilibrium; the adsorption capacity of the as-grown and graphitized
CNTs is 30.8 and 28.7 mg/g, respectively, from a 20 mg/l solution. CNTs can be used as
adsorbents in a wide pH range of 3-10. Thermodynamic calculations indicate that the
adsorption reaction is spontaneous with a high affinity and the adsorption is an
endothermic reaction (Peng et al., 2003). Similarly, Chen and Wang (2006) studied the
adsorption of Ni(II) onto oxidized MWNTs as a function of contact time, pH, ionic
strength, MWNT concentration, and temperature. The results showed that the Ni
adsorption onto MWNTs is strongly dependent on pH and oxidized MWNT
concentration and, to a lesser extent, ionic strength. Kinetic data indicated that the
adsorption process achieved equilibrium within 40 min and follows a pseudo-second-
order rate equation. The thermodynamic data indicated the spontaneous and endothermic
nature of the process. Results of a desorption study showed that Ni(II) adsorbed onto
oxidized MWNTs could be easily desorbed at pH < 2.0. Ion exchange was predicted to
be the predominant mechanism of Ni adsorption on oxidized MWNTs. This study
Search WWH ::
Custom Search