Environmental Engineering Reference
In-Depth Information
Meanwhile, the applications of pseudo-kinetic models, particularly the
pseudo-second-order kinetic model, have provided a good description of
the batch adsorption kinetic data. However, these models require a pseudo-
rate constant that is concentration dependent and also do not account for
pH variations. It is thus suggested to apply the well-established surface
ionization/complexation model or the double-layer retention model to
investigate the effect of pH or ionic strength on the adsorption capacity of
CBNAs.
Thirdly, it is necessary to conduct regeneration studies as they help deter-
mine the reusability of an adsorbent, which in turn contributes in evaluat-
ing the effectiveness and economic feasibility of the adsorbent. Based on
the literature, not many adsorbent regeneration studies have been reported
and should therefore be performed in detail.
Fourthly, it is extremely essential to investigate the simultaneous
removal of many coexisting dye pollutants from multicomponent solu-
tions. Unlike laboratory tests using pure aqueous solutions, real textile
effluents contain different types of dye pollutants and other undesirable
substances. However, most of the studies reported so far are based on
single-solute systems. There is absolutely little or no effort in investigating
the competitive adsorption of dyes. Such studies are essential for accurate
designing of adsorption systems as the effect of competitive interactions
may cause deterioration in the adsorption capacity. Therefore, some future
research in this respect should be pursued to provide insights into com-
petitive adsorption and possible interference from other contaminants to
target species removed by CBNAs.
Fifthly, although several processes, including ion exchange, electrostatic
interactions, π-π electron donor-acceptor interactions, surface adsorp-
tion, and complexation, have been suggested to explain the mechanisms
involved in the adsorption between water pollutants and CBNAs, mech-
anistic studies need to be conducted in detail to validate the proposed
binding mechanism of aquatic pollutants with CBNAs. Finally, very little
information is currently available on the toxicity and biocompatibility of
graphene and related materials. Future investigations should, therefore,
focus on
in vitro
and
in vivo
interactions between CBNAs and different
living systems to effectively evaluate the utilization of CBNAs in dye waste-
water remediation.
Undoubtedly, CBNAs hold great potential for being robust materi-
als to address the environmental problems posed by synthetic colorants.
However, it is only when we overcome the above-mentioned challenges
that the commercial application of CBNAs in dye-wastewater treatment
can be successfully realized.
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