Chemistry Reference
In-Depth Information
Fig. 3 Lerf-Klinowski model for graphene oxide structure. Reproduced from Ref. 38 page
4482 with permission of the American Chemical Society.
While un-functionalised graphene may not be a suitable catalyst be-
cause of the low amount of active sites, graphene oxide (GO) exhibits high
reactivity under mild conditions. GO is obtained as a intermediate
product in graphene synthesis, which is typically prepared using the
Hummers method. This method involves adding KMnO
4
to graphite
dispersed in concentrated H
2
SO
4
followed by quenching with aqueous
H
2
O
2
.
37
Under this strongly oxidizing conditions, a variety of oxygen-
containing functional groups (e.g. phenol, aldehydes, and carboxylic
acids) are introduced on carbon surface. Figure 3 shows the most com-
monly accepted model for graphene oxide, known as the Lerf-Klinowski
model.
38
GO is both highly acidic and strong oxidizer, and exhibits
propensity to undergo reduction when exposed to various chemical re-
agents.
39
Liu et al.
40
studied the catalytic oxidation of SO
2
to SO
3
over
porous graphene oxide foams. GO acts not only as a catalyst for the re-
action but also supplies oxygen for the reaction. GO is reduced during the
course of reaction turning from hydrophilic (brown colour) to hydro-
phobic (black colour). In this process, some oxygen-containing groups of
GO were consumed to oxidize SO
2
. This can be a green and inexpensive
method for the treatment of SO
2
gas because occurs at room temperature
and does not need noble metal catalyst.
The Bielawski group reported recently that GO is able to hetero-
geneously catalyze a broad range of synthetic transformation in liquid
phase including alcohol,
41,42
olefin,
42,43
and C-H oxidations,
43
alkyne
hydrations,
42
and combinations thereof.
44
Graphene oxide has also
showed activity in coupling reaction such as the aza-Michael addition of
amines
45
and as photocatalyst for H
2
generation from water,
46
providing
an interesting alternative to metal-containing photocatalysts.
2.1.3 Complete oxidation: Advanced oxidation processes. Some
studies have shown that carbon materials are ecient catalyst for the
