Novel Carbon-Based Nanoadsorbents for Removal of Synthetic Textile Dyes from Wastewaters - Green Chemistry for Dyes Removal from Wastewater - page 56

another study by Mishra et al. [96], f f-MWCNTs developed by an acid treat-
ment method have been used as an efficient adsorbent material for three
different azo dyes: Congo Red, Reactive Green HE4BD and Golden Yellow
MR. An extremely fast dye uptake rate was observed with the experimental
kinetic data conforming to the pseudo-first-order model. Adsorption iso-
therms for all the three dyes followed Langmuir, Freundlich and Temkin
models. The maximum dye adsorption capacity of f f-MWCNTs was found
to be 148.08, 151.88 and 141.61 mg g -1 for Congo Red, Reactive Green
HE4BD and Golden Yellow MR, respectively. Similarly, f -MWCNTs have
also been found effective to remove Bromothymol Blue [94], Methyl Red
[95], and Malachite Green [97] from aqueous solutions.
2.3.1.2 CNT-BasedNanocomposites
From a series of discussions we had in the previous section of this chapter,
it is evident that CNTs have an extremely high affinity for many classes of
dyes. Compared to activated carbon, CNTs offer a number of advantages
including fast adsorption rate and small adsorbent dose, which make them
attractive alternatives for the selective removal of toxic dyes from indus-
trial wastewaters. However, the separation of CNTs from aqueous medium
after treatment is very difficult because of their smaller size and high aggre-
gation property. This problem can be overcome by making composites
of CNTs with different materials such as polymers, metal oxide, carbon,
etc., which act as a stable matrix to the CNTs, thereby facilitating the easy
separation of CNTs from the aqueous environment. These materials also
provide additional active sites to CNTs, which in turn makes them bet-
ter adsorbents compared to their parent nanomaterial. As such, a number
of CNT-based composites have been developed and used as a promising
adsorbent for the treatment of colored wastewaters in recent years. The
adsorption characteristics of these nanocomposites will be discussed in
this section.
Chatterjee et al. [98] impregnated MWCNTs with chitosan hydro-
gel beads and used it as adsorbent to remove Congo Red from aqueous
solution by batch adsorption process. The kinetic data conformed to the
pseudo-second-order kinetic model with intraparticle diffusion playing a
significant role during the initial stage of adsorption. The equilibrium data
fitted well to the Langmuir isotherm model. The composite exhibited a
remarkably high adsorption capacity of 450.4 mg g -1 . Zhu et al. [99] inves-
tigated the adsorption of Methyl Orange onto calcium alginate/MWCNTs
composites with respect to MWCNT content, initial dye concentration and
pH. The adsorption uptake increased with increasing MWCNT content