Environmental Engineering Reference
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adsorption capacity towards cationic dyes compared to anionic dyes. More
than 93% of the cationic dyes were removed during the first 10 min of dye-
adsorbent contact. The maximum adsorption capacity of G-SO
3
H/Fe
3
O
4
for cationic dyes, calculated from the Langmuir isotherm, increased in the
following order: Safranine T < Victoria Blue < Neutral Red. Furthermore,
the nanocomposite could be easily regenerated using ethanol (adjusted to
pH 2.0 with 0.1 mol L
−1
HCl) as eluent and reused for at least six adsorption-
desorption cycles without any significant loss in adsorption capacity.
Magnetic CoFe
2
O
4
-functionalized graphene sheet (CoFe
2
O
4
-FGS)
nanocomposites were prepared by Li
et al.
[130] to remove Methyl Orange.
The adsorption process followed pseudo-second-order kinetics and the
adsorption capacity was found to be as high as 71.54 mg g
-1
. Recently,
Farghali
et al.
[131] have also synthesized CoFe
2
O
4
-FGS nanocomposites
for the removal of Methyl Green from aqueous solution. The adsorption
isotherm was well described by the Langmuir model, whereas the adsorp-
tion kinetics corresponded to the pseudo-second-order kinetic model.
Although intraparticle diffusion was involved in the adsorption process, it
was not the rate-controlling step. Also, thermodynamic analyses indicated
that adsorption of Methyl Green was a spontaneous, endothermic and a
physisorption process.
In another study conducted by Sen Gupta
et al.
[132], graphene immobi-
lized on sand was used as an adsorbent for the removal of Rhodamine 6G.
Graphene was prepared
in situ
from cane sugar and anchored onto the
surface of river sand without the need of any additional binder, result-
ing in a composite, referred to as graphene-sand composite (GSC). The
ability of GSC to remove Rhodamine 6G from its aqueous solution was
tested through batch and continuous column experiments. The adsorp-
tion process followed pseudo-second-order kinetics and equilibrium was
attained in 8 h. The equilibrium adsorption capacity of Rhodamine 6G was
55 mg g
-1
at 303 ± 2 K. Fixed-bed column experiments were performed to
study the practical applicability of the adsorbent and breakthrough curves
at different bed depths were obtained. The bed depth service time (BDST)
model showed good agreement with the dynamic flow experimental data.
Desorption studies revealed that GSC could be regenerated using acetone
for multiple uses. In general, the results suggested that GSC should be
considered for dye wastewater treatment with appropriate engineering. In
another study by the same research group [133], GSC was prepared using
asphalt as the carbon source and tested as an adsorbent for removal of
Rhodamine 6G. Both batch and continuous column experiments were car-
ried out. Similar to their previous work, the experimental data correlated
well with the pseudo-second-order model and an adsorption capacity of
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