Environmental Engineering Reference
In-Depth Information
promising adsorbents with higher adsorption capacity and better regen-
eration ability is still in progress.
In recent years, nanotechnology has introduced a myriad of novel nano-
materials that can have promising outcomes in environmental clean-up
and remediation [20]. Particularly, carbon-based nanomaterials such as
carbon nanotubes and graphene are being intensively studied as new types
of adsorbents for removal of toxic pollutants from aquatic systems. This
extraordinary interest stems from their unique morphology, nanosized
scale and novel physicochemical properties [21-24]. Both carbon nano-
tubes and graphene offer chemically inert surfaces for physical adsorption,
and their high specific surface areas stand comparison with those of acti-
vated carbon. They also have far more well-defined and uniform structure
than activated carbon and most other adsorbent materials reported till
date. In addition, these nanoadsorbents are not only capable of sequester-
ing contaminants with varying molecular size, but also have considerably
high adsorption capacities and can be easily regenerated for repeated use.
With the aforementioned, this chapter reviews the potential of carbon-
based nanoadsorbents (CBNAs), viz., carbon nanotubes and graphene,
in treating colored effluents. The advantages and limitations of CBNAs in
adsorptive treatment of dye wastewaters are evaluated. To highlight their
treatment performance, selected information such as optimum pH, reac-
tion time and temperature, the initial concentration of dye pollutant, and
adsorption capacity is also presented. We further emphasize the role of
surface modification of these nanosystems, and discuss its effects on the
adsorption properties of CBNAs. Finally, the chapter concludes by high-
lighting the key challenges involved in the development of these novel
nanoadsorbents to help identify future research directions for this emerg-
ing field to continue to grow.
2.2
Basic Properties of Carbon Nanoadsorbents
2.2.1 Carbon Nanotubes
Ever since their discovery in 1991 by Ijima, carbon nanotubes (CNTs) have
been the focus of considerable research because of their unprecedented
physical and chemical properties [25]. CNTs are cylinder-shaped macro-
molecules made up of a hexagonal lattice of carbon atoms analogous to
the atomic planes of graphite (i.e., graphene), normally capped at their
ends by one half of a fullerene-like molecule [26]. They can be either single
walled (SWCNTs) with diameters as small as 0.4 nm and length of up to
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