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siderable potential as excellent supporting material for various
heterogeneous catalysts since it affords high theoretical specific
surface area of about 2600 m2 g−1, has attracted increasing atten-
have being investigated with equal interest [25]. Notably, the high
surface area of graphene materials does not depend on the distribu-
tion of pores in solid state, but comes from the interconnected open
channels between graphene layers distributed in a 2D architecture
[26]. In addition, due to the inevitable carbon vacancy defects and
functional groups presented in chemically derived graphene, metal
ions can be adsorbed and intercalated into graphene sheets to form
thermally stable composite materials. More importantly, usage of
the support can increase the stability of the catalyst, optimize the
dispersion of the active components of the catalyst and provide
important chemical, mechanical, thermal and morphological prop-
erties. Fu et al. [27] reported that interfaces between graphitic
overlayers and metal surfaces act as 2D confined nanoreactors,
in which catalytic reactions are promoted. This finding contrasts
with the conventional knowledge that graphitic carbon poisons a
catalyst surface but opens up an avenue to enhance catalytic per-
formance through the coating of metal catalysts with controlled
graphitic covers.
Tremendous progress has so far been achieved in compos-
ite materials. CB, which has a large specific surface area, cheap
price and can form an open space network channel, is recognized
CB contents have been prepared by a simple vacuum filtration
method. The CB particles between the graphene layers act as spac-
ers that prevent the restacking of graphene layers and inhibit the
agglomeration of graphene sheets [28]. Fan et al. [26] prepared rGO-
CB pulverous composites by ultrasonication and in-situ reduction
methods. The as-fabricated rGO-CB powder-composite electrode
shows enhanced capacitance and rate capability. Currently, the
reported rGOCB material has only been used in electrochemistry.
It is desirable to develop a new-type of supported-catalysts for
the synthesis of DMC to take full advantage of rGO-CB. Therefore,
work.
between Cu NPs and graphene, as well as CB, has been investigated,
which is also useful for understanding the interaction between Cu
NPs and the support. The properties of the Cu/rGO-CB catalyst were
evaluated by liquid-phase oxidative carbonylation of methanol,
with excellent cycling stability exhibited.
2. Experimental
2.1. Materials
GO was obtained from Jinneng Co., Ltd. of Institute of the
Coal Chemistry, Chinese Academy of Sciences (Taiyuan, China). CB
was obtained as a commercial product from the Xinhua chemi-
cal plant (Taiyuan, China). Copper nitrate (Cu(NO3)2·3H2O) was
purchased from Sinopharm Chemical Reagent Co., Ltd. Methanol,
ethanol, hydrazine and N,N-dimethylformamide (DMF) were pur-
chased from Sinopharm Chemical Reagent Co. Ltd. (Beijing, China).
Hexadecyltrimethyl-ammonium Bromide (CTAB) was obtained
from Shanghai Nuotai Chemical Co., Ltd. All chemicals were of ana-
lytical grade and were used without any further purification.
2.2. Cu/rGO-CB and Cu/rGO nanocomposite synthesis
For the preparation of the Cu/rGO-CB catalyst, GO (200 mg)
was first mixed with 200 mL of absolute ethanol under ultrasonic
sonication at room temperature for 2 h. Meanwhile, 50 mg of CB
(>200 mesh) was dispersed into 200 mL of absolute DMF under
ultrasonic sonication for 1 h. Subsequently, the as-prepared CB dis-
persions with a volume of 5 mL were diluted with 50 mL of DMF.
Then, the two suspensions were mixed and kept under ultrasonic
sonication for another 2 h. Next, the mixture was magnetically
stirred to form a homogeneous mixture using a water bath at room
temperature. In the subsequent step, 80 mg of Cu(NO3)2·3H2O and
a small quantity of CTAB, acting as a dispersing agent, were added
to the mixture, while maintaining a vigorous agitation for 3 h at
90 ◦C. Ultimately, 0.5 mL of hydrazine (50 wt.% in water) was added
to the mixture dropwise. The solution turned from deep orange to
black within minutes, followed by the appearance of a black precip-
itate to yield Cu/rGO-CB composites. Finally, the solid was filtered
and washed several times with distilled water and alcohol, then
dried at 100 ◦C for 12 h in a vacuum oven. Hitherto, the resulting
sample labeled as Cu/rGO-CB was prepared. Similarly, as a com-
parison, Cu/rGO was synthesized without CB. Scheme 1 shows the
fabrication scheme for the Cu/rGO-CB nanocomposite.
It is well known that metal oxide (or metal hydroxide) NPs can
aggregation, thereby increasing the interplanar spacing and contact
area with the reactant [29,30]. Various strategies have been devel-
and microwave-assisted synthesis [33,34]. Several studies have
addressed the applications of graphene for various catalytic reac-
activity and stability [35]. Some studies [36] have demonstrated
that the catalytic activity can be influenced by the metal active site
supported on graphene. Meanwhile, the oxygen functional groups
on the surface of the support also have an effect on the catalyst
structure and catalytic activity [37].
2.3. Catalyst characterization techniques
The analysis of the crystal structure and phase composition
of the catalyst was completed using X-ray diffraction (XRD) on a
Rigaku D/Max 2500 system with a Cu K␣ radiation ( = 1.54056 Å)
and a graphite monochromator. The voltage and current of the mea-
surements were operated at 40 kV and 100 mA, and the scanning
speed was 8◦/min at a scanning region of 5–85◦. The crystallite
size of Cu metal for the catalysts was calculated using the Scherrer
equation.
In our work, an innovative and economical approach has been
employed for synthesizing a Cu/rGO-CB catalyst by a simple ultra-
sonication and vacuum filtration process. The synthetic effects of
rGO sheets and CB lead to a large accessible surface area for the
Cu NPs. As spacers, CB particles can not only increase the dis-
tance between the graphene sheets, but also provide rapid diffusion
paths for reactants in double-layer films. Furthermore, CB can also
provide adsorption sites for Cu NPs. As a result, the CB spacers
ensure high specific surface utilization of graphene layers, as well
as the open nanochannels provided by the three-dimensional rGO-
CB hybrid material. Using catalyst characterization, the interaction
The Cu K-edge X-ray absorption fine structure (XAFS) analysis
of the catalysts was performed by the Soft X-ray Micro-
characterization Beamline (SXRMB) of the Canadian Light Source.
SXRMB is a medium energy beamline with a range of 1.7–10 keV.
The monochromator of the beamline consists of two pairs of crys-
tals, InSbC (111) and Si (111).
A Fourier transform infrared (FT-IR) spectroscopy analysis was
conducted to explore the change of oxygen-containing functional
groups on GO after reduction by hydrazine using a FT-IR spectrom-
eter (Nicolet Nexus 470, Thermo Nicolet, Madison, WL USA) in the
range of 500–4000 cm−1
.