Environmental Engineering Reference
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temperature and pH of the aqueous medium and so forth. Therefore,
the prediction of the actual adsorption mechanism is neither simple
nor straightforward. The mechanisms by which adsorption of dyes
onto CBNAs occur have been a matter of considerable debate. Different
studies have reached different conclusions. It is believed that different
kinds of interactions such as hydrophobic interactions, π-π electron
donor-acceptor interactions, electrostatic attraction, precipitation and
hydrogen bonds act simultaneously during adsorption of dye ions onto
CBNAs, the predominant mechanism being different for different types
of dyes [22,23]. For example, π-π interactions depend on the size and
shape of the aromatic system and the substitution unit of molecules,
and increases with the increasing number of aromatic rings in the dye
molecule [22].
2.5
Conclusion and Future Perspectives
In this chapter, the latest research work on the use of CBNAs as advanced
adsorbent materials for removal of various synthetic dyes from aqueous
solutions has been compiled and summarized. It is evident that CBNAs are
a promising alternative to activated carbon and other adsorbent materials
that are currently being considered for treatment of industrial wastewaters.
Their simplicity, flexibility, fast kinetics, and high adsorption capacities
make them attractive for the selective removal of dye pollutants. However,
research in this area is still in its infancy. There are a number of challenges
that have to be overcome before we can realize the full potential of CBNAs
for practical applications. Here, we would like to highlight some of those
important issues that might help future research.
Firstly, study on the adsorption characteristics of CBNAs is mostly
restricted to batch adsorption studies. There are hardly any reports on
the adsorption of dyes using fixed-bed dynamic adsorption techniques.
Continuous column study is therefore highly recommended since it allows
a more efficient utilization of CBNAs and provides a better quality efflu-
ent. In addition, future research works should also focus on verifying the
performance of CBNAs at the pilot plant scale in order to ascertain their
commercial applications.
Secondly, the equilibrium adsorption data, without exception, have
been empirically correlated with the conventional isotherm models, viz.
Langmuir, Freundlich and a few others. Although a few researchers have
proposed adsorption mechanisms, no further attempts have been made to
interpret the adsorption equilibrium data using the proposed mechanisms.
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