Environmental Engineering Reference
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using graphene nanolakes (GNFs) as electrodes is also reported. 81 A maximum equilib-
rium electrosorption capacity of 0.88 mg/g (higher than AC) was attained at a low rate
and electrical voltage of 25 mL/min and 2.0 V, respectively. The electrosorption capacities
of cations on the GNFs followed the order Fe 3+ > Ca 2+ > Mg 2+ > Na + . The same group also
evaluated the electrosorptive performance of GNF electrodes with different bias poten-
tials, low rates, and ionic strengths, 82 and conducted a comparative study of electrosorp-
tive capacities of single-walled CNTs and graphene. 83
Graphene-based composites have also been tried to get better performance from gra-
phene as the electrode material for CDI. Wang et al. 84 recently tried a graphene-resol nano-
composite (RGO-RF) as the electrode for the removal of ferric iron. GO was aggregated due
to the addition of resol, and upon calcination the structure collapsed with high pore size.
A high electrosorptive capacity of 3.47 mg/g was demonstrated by RGO-RF at optimum
conditions. A graphene-CNT composite also was reported to show enhanced CDI perfor-
mance. 85 The insertion of CNTs helped avoid the aggregation of graphene, thereby increas-
ing the conductivity in the vertical direction resulting in increased eficiency. Similar
composites of RGO with AC 86 and mesoporous carbon (MC) 87 have also been reported.
RGO-AC composite with 20% RGO content showed enhanced capacity compared with
pure AC for the capacitive removal of salt ions from brackish water. 86 The graphene-MC
electrode showed an enhanced adsorption capacity (731 mg/g) compared with MC alone
(590 mg/g). 87 Wang et al. 88 reported a novel pyridine-based thermal strategy for preparing
graphite oxide, where pyridine was used as the intercalating agent and dispersant, which
used the resultant material for a CDI application. These studies indicated the utility of
graphenic materials in CDI-based water remediation.
34.1.4 Photocatalytic Removal
Pioneering work in photocatalysis was done during the seventies, and since then the
interest in this area has grown. A large number of catalysts have been reported, and sev-
eral reviews are available on this topic. 89-91 Water remediation by nanomaterials-based
photocatalysts have also been a hot area of research. 91 Here a material (the photocata-
lyst) catalyzes the degradation of a contaminant via light-induced reaction. Recently,
graphene-based composites were also used for this purpose. Numerous reports are
available in the literature where different combinations of graphenic materials and TiO 2
(one of the most eficient photocatalyst) were used for the decontamination of water.
Photocatalytic degradation of MB using a composite prepared by self-assembling TiO 2
nanorods on large-area GO sheets at a water/toluene interface under ultraviolet (UV)
light irradiation was reported recently. 92 The effective charge antirecombination and
the effective absorption of MB on GO was proposed to be the reason for the enhanced
activity. They also observed that the degradation rate of MB in the second cycle is faster
than that in the irst cycle. This might be due to the reduction of GO under UV light
irradiation, leading to more eficient charge antirecombination by RGO. Nguyen-Phan
et al. 93 probed the role of GO/RGO content on the photocatalytic eficiency of graphene-
based photocatalysts by taking TiO 2 -GO (prepared through a simple colloidal blending
method) as the model system. They found that compared with pure TiO 2 , the composites
have superior adsorption and photocatalysis performance under both UV and visible
radiation. It was also observed that increasing the GO content to 10 wt% resulted in the
increased removal eficiency and the photodegradation rate of MB. This was explained
to be due to the synergy effects, including the increase in speciic surface area with GO
amount as well as the formation of both π-π conjugates between dye molecules and
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