Environmental Engineering Reference
In-Depth Information
Magnetic graphene composites have been used for removal of organic dyes as well.
Wang et al.
58
proposed the removal of fuchsine from aqueous solution using RGO-Fe
3
O
4
composites prepared by chemical coprecipitation of Fe
2+
and Fe
3+
in an alkaline solution
of RGO. Adsorption kinetics, capacity of the adsorbent, and the effect of the adsorbent
dosage and solution pH on the removal eficiency of fuchsine were also investigated. A
novel bioadsorbent composed of magnetic chitosan and GO was proposed by Fan et al.
59
for MB removal via a spontaneous and exothermic process. The substrate was found to be
reusable with >90% adsorption eficacy even after four cycles of operation. A mesoporous
RGO -Mg(OH)
2
composite prepared through a chemical deposition method was used for
the removal of MB by Li et al.
60
A highly eficient magnetic graphene composite prepared
via a solvothermal process for the removal of MB was reported by Ai and coworkers
61
as
well. A hybrid graphene-Fe
3
O
4
@carbon (GFC) heterostructure nanomaterial was prepared
by Fan et al.
62
recently. As-synthesized GFC showed good adsorption eficiency for MB
from water in near-neutral as well as in acidic environments (about 86% and 77%, respec-
tively).
62
A Cu
2
O-RGO composite (CGC) was also prepared by the same group through a
similar method for the removal of dye from water, which can be used in supercapacitors.
63
The high adsorption capacity of CGC for RhB and MB was used to fabricate a reactive il-
tration ilm using this composite and was applied to remove dye from wastewater. Sun et
al.
64
also used a similar strategy to fabricate RGO-Fe
3
O
4
and reported an excellent removal
eficiency for RhB (91%) and malachite green (>94%) from real water samples (industrial
wastewater and lake water). An excellent adsorbent for the removal of organic pollutants
from water was synthesized by coating RGO with ZnO NPs (RGO@ZnO).
65
The compos-
ite showed enhanced RhB adsorption capacity and an improved photocatalytic activity
(described in Section 34.1.4) for degrading RhB compared with pure ZnO NPs. The adsor-
bent was found to be highly reusable as well. A graphene-Fe
3
O
4
composite was used for
the adsorption of aniline and
p
-chloroaniline as well.
66
A nickel-RGO composite for the
removal of organic dye from water was reported recently.
67
Sui et al.
68
reported the fabrica-
tion of graphene-CNT aerosols with high adsorption eficiency for the removal organic
dyes and for enrichment of heavy metal ions. Using different dye molecules such as MB,
fuchsine, RhB, and acid fuchsine, as well as heavy metals such as Pb
2+
, Hg
2+
, Ag
+
, and Cu
2+
,
the utility of the composite in water remediation was demonstrated.
34.1.2 Graphene-Based Membranes
Membranes and/or ilters are important parts of the water puriication industry. The pos-
sibility of creating subnanometer pores in a controllable fashion on graphene by methods
such as electron beam irradiation,
69
ion bombardment,
70
or by doping
71
has been explored
both theoretically and experimentally. Molecular dynamics studies about the transport of
ions through 0.5-nm pores in graphene terminated with nitrogen or hydrogen was carried
out by Sint et al.
72
A difference in permeation was observed between N-terminated pores
and H-terminated pores. The former allow the passage of metal ions such as Li
+
, Na
+
, and
K
+
, while the latter allowed Cl
−
and Br
−
to pass through, but not F
−
. The strongly bound
hydration shell in the case of smaller ions was the reason for the low passage rates observed.
Water transport through ultrathin graphene and the rate of transport across 0.75-2.75-nm-
diameter pores in graphene membranes was probed by Suk and Aluru.
73
The transport val-
ues were compared with 2-10-nm-long CNTs with similar diameters. A higher lux (about
two times) through graphene compared with CNTs was reported in the study.
Nanoporous materials in general are advantageous compared with traditional reverse
osmosis (RO) membranes. In an RO membrane, water passage is slow and driven by
