Environmental Engineering Reference
In-Depth Information
common adsorbents, the composite showed highly enhanced removal eficiency. This com-
posite was also tested in real water and found to be highly suitable for ield application
with appropriate modiications (Figure 34.1o through r).
Sometimes, the anchoring of other materials on graphene can result in the composites
having special attributes that can improve their utility or can simplify the application pro-
cess. For example, by making a graphene-based composite involving a magnetic material
can result in a highly adsorbent magnetic composite. This can help in the postadsorption
treatment where the adsorbent can be magnetically removed easily, simplifying the post-
treatment process. Various graphene-based magnetic composites have been reported for
adsorption-based remediation of polluted water. Chandra et al.
48
did the pioneering work
in this direction where a water-dispersible magnetite-RGO composite was prepared and
used for arsenic removal. Compared with bare magnetite particles, the composite showed
high binding capacity for As(III) and As(V). Also, as proposed earlier, the composite being
superparamagnetic can be separated by an external magnetic ield after the removal pro-
cess. A graphene-based multifunctional iron oxide sheet consisting of needle-like iron
oxide NPs grown on the surface of the graphene sheets with tunable properties was
reported by Koo et al.
49
recently. A paper-like material was fabricated using the compos-
ite here, which exhibited maximum adsorption capacities of 218 and 190 mg/g for As(V)
and Cr(VI), respectively. A highly eficient composite for the removal of arsenate from
drinking water was developed by Zhang et al.
50
This composite consisted of GO and ferric
hydroxide where GO was cross linked with ferric hydroxide. At arsenate concentration of
51.14 ppm, 95% removal with an absorption capacity of 23.78 mg arsenate/g was reported
over a wide range of pH from 4 to 9. Sheng et al.
51
investigated the As(V) adsorption by
graphene-Fe
3
O
4
(MGO) composite. They observed that the adsorption of As(V) on MGO
decreased with increasing pH due to the electrostatic interaction, and the adsorption is
greatly affected by the presence of coexisting ions. The presence of anions had an inhibit-
ing effect on As(V) adsorption (more eficient at low pH), and the presence of coexisting
cations had an enhancing effect (more eficient at high pH).
51
Composite-comprising graphene sheets decorated with
Cyanobacterium metallothionein
(SmtA, a cysteine-rich metal-binding protein) was used for the ultrahigh selective adsorp-
tion of cadmium in the presence of other anionic species by Yang et al.
52
The hybrid was
prepared by assembling this SmtA-GO composite on a cytopore, which showed an enrich-
ment factor of 14.6. This hybrid was also used for selective detection of cadmium with a
detection limit of 1.2 ng/L. A polymer containing graphene-based composite (polypyrrole-
RGO) was used for the highly selective adsorption of Hg
2+
recently.
53
A composite with
15 wt% GO loading showed highly selective absorption of Hg
2+
with an enhanced adsorp-
tion eficacy up to 980 mg/g and an extremely high desorption eficiency up to 92.3%, indi-
cating the reusability of the composite. Bhunia et al.
54
recently devised a high-temperature
strategy to prepare an iron-iron oxide graphene matrix for the removal of heavy metals
from water. Heating iron oxide NPs in the presence of graphene in an H
2
/Ar atmosphere
at elevated temperatures resulted in the formation of a highly porous matrix of iron-iron
oxide on the graphene surface. A magnetic composite of graphene and magnetic cyclo-
dextrins was reported by Fan et al.
55
for the removal of chromium from wastewater. A
maximum adsorption capacity of 120 mg/g was reported in this study. Zhang et al.
56
dem-
onstrated that modiication of graphene-Fe
3
O
4
composite with polyacrylic acid can make
the hybrid composite a highly recyclable adsorbent for different heavy metal ions such as
Cu
2+
, Cd
2+
, and Pb
2+
. An interesting example reported by Zhao et al.
57
demonstrated the
selective adsorption of heavy metal ions on graphene-Ppy composite leading to its selec-
tive electrochemical detection.
