Environmental Engineering Reference
In-Depth Information
organic solvents from the surface of water. A versatile strategy to fabricate graphene-based
macroscale hydrogels and aerogels via a metal ion-induced self-assembly process was
reported recently.
39
The adsorption capacity increased about 31% in the presence of 5 wt%
GO in the composite. However, the maximum capacity was reported to be only 99 mg/g.
A reduction of GO sheets by Fe
2+
leading to the simultaneous formation of α-FeOOH
nanorods and magnetic Fe
3
O
4
nanoparticle (NP)-embedded hydrogels and aerogels was
reported recently. These materials demonstrated exceptional adsorption capacities for oil
and metal ions such as Cr(VI) and Pb (II).
40
The use of functionalized graphene coupled
with polypyrrole (graphene-Ppy composite) as an electrically switched ion exchanger
for perchlorate removal from wastewater was reported by Zhang et al.
41
Compared with
Ppy ilms, the 3-D nanostructured graphene-Ppy nanocomposite displayed signiicantly
improved uptake capacity for ClO
4−
.
Nanoadsorbents anchored on substrates have the added advantage that they can be eas-
ily removed from the reaction mixture after the adsorption process. This simpliies the
posttreatment handling. Recently, Liu et al.
42
devised a method to synthesize GO/RGO-
immobilized silica composite through covalent binding of GO and used these composite
material for solid-phase extraction (SPE). The carboxy groups on the surface of GO/RGO
were covalently anchored to the amino groups of an amino-terminated silica adsorbent.
Taking chlorophenols as the model system, the utility of the material in SPE was demon-
strated. Figure 34.1d through k show the scanning electron microscopy (SEM) images and
the eficiency of the adsorption of chlorophenols on the prepared material. Gao et al.
43
also
anchored GO on a silica surface. Thiol-modiied GO was anchored onto silica and was
termed as “super sand” because of the 5-fold increase in adsorption capacity of the com-
posite for removing heavy metal and dyes compared with pure sand. Generally top-down
approaches (or most chemical synthesis processes) for synthesis of graphene utilize graphite
as the precursor. However, recent studies indicated that graphene could be prepared from
other resources as well. An
in situ
strategy to synthesize immobilized graphenic material
on sand, termed graphene-sand composite (GSC) (Figure 34.1l and m), from high molecu-
lar petroleum fractions was reported recently.
44
The synthesized material was found to be
highly eficient in removing pesticides and dyes from water (Figure 34.1n). The compos-
ite was able to decolorize Coca cola by removing the colored fraction from the mixture,
pointing to the high activity of the material for water remediation applications. Compared
with the reported adsorption eficacy of super sand, the prepared composite exhibited 12×
enhanced eficacy. A similar strategy was reported for creating graphene from sugar and
its immobilization on sand.
45
This composite also exhibited high capacity for removing
dyes and pesticides from water. Liu et al.
46
reported a similar silica-immobilized graphene
adsorbent for the removal of pesticides. The composite as expected demonstrated high
adsorption capacity compared with common adsorbents such as graphite carbons, AC,
pure graphene, C18 silica, and silica for the removal of 11 pesticides tested. The adsorption
mechanism was also proposed, and the electron-donating abilities of the S, P, and N atoms
and the strong π-bonding network of the benzene rings was understood to be the reason for
the high adsorption eficacy. Synthesis of various metal/metal oxide graphene composites
at room temperature through a versatile
in situ
strategy where the formed composite can be
bound on solid substrates was reported by Sreeprasad et al.
47
Here, the composite is formed
via a redox process without the use of any hazardous chemical reducing agents. A green
strategy to anchor these composites on solid substrates such as silica or sand particles was
also demonstrated. Chitosan, an abundant eco-friendly biopolymer, was used for this and
the immobilization facilitated easy posttreatment handling. The immobilized composites
were used for the removal of heavy metals from drinking water and compared with some
