Environmental Engineering Reference
In-Depth Information
nanocomposites like CNT/alumina, CNT/titania and CNT/ZnO has also been re-
ported [60-62].
Chitosan (CS) is one of the best adsorbents for the removal of dyes due to its
multiple functional groups, biocompatibility and biodegradability, but its low me-
chanical strength limits its commercial applications. Impregnation of CS hydrogel
beads with CNTs (CS/CNT beads) resulted in significant improved mechanical
strength. In CS/CNT composite, CNTs and CS are like a symbiosis, CNTs help
to improve the mechanical strength of CS while CS help to reduce the cost of
CNTs for adsorption, while the resulted composite solves the problem of separat-
ing CNTs from aqueous medium. To resolve the aggregation and dispersion prob-
lem of CNTs, prepared the CNTs/activated carbon fabric (CNTs/ACF) composite
and its application was investigated for the removal of phenol and basic violet
10 (BV10). CNTs/ACF was prepared via directly growing nanoscaled CNTs on
microscaled carbon matrix. Polyacrylo nitrile was used as a source of carbon.
From the results, it was observed that dye adsorption equilibrium time for CNTs/
ACF is shorter as compared to ACF and monolayer adsorption capacity does not
display a linear increase with increasing the BET surface area. The decoration of
CNTs tends to lower the porosity of the ACF from 1065 to 565 m
2
/g. This finding
indicates that the total microporosity of ACF cannot be fully accessed by the dye
molecules. Therefore, the appearance of CNTs plays a positive role in (i) facilitat-
ing the pore accessibility to adsorbates and (ii) providing more adsorptive sites for
the liquid-phase adsorption. This reflects that CNTs/ACF contains a large number
of mesopore channels, thus preventing the pore blockage from the diffusion path
of micropores for adsorbates to penetrate [72, 73].
Incorporation of magnetic property in CNTs is another good technique to
separate CNTs from solution. The magnetic adsorbent can be well dispersed in
the water and easily separated magnetically. Magnetic-modified MWCNTs were
used for removal of cationic dye crystal violet (CV), thionine (Th), janus green B
(JG), and methylene blue (MB). To find the optimum adsorption, effect of vari-
ous parameters including initial pH, dosages of adsorbent and contact time have
been investigated. The optimum adsorption was found to be at pH 7.0 for all
dyes. The removal efficiency of cationic dyes using GG/MWCNT/Fe
3
O
4
is higher
as compared with other adsorbents such as MWCNTs and MWCNT/Fe
3
O
4
. The
magnetic GG/MWCNT/Fe
3
O
4
possesses the high adsorption properties and mag-
netic separation and can therefore be used as magnetic adsorbents to remove the
contaminants from aqueous solutions. A novel magnetic composite bio adsorbent
composed of chitosan wrapping magnetic nanosized γ-Fe
2
O
3
and multi-walled
carbon nanotubes (m-CS/γ-Fe
2
O
3
/MWCNTs) was prepared for the removal of
methyl orange. The adsorption capacity of MO onto m-CS/γ-Fe
2
O
3
/MWCNTs
was 2.2 times higher than m-CS/γ-Fe
2
O
3
. The adsorption capacity of MO onto
m-CS/γ-Fe
2
O
3
/MWCNTs was also higher than MWCNTs. Kinetics data and
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