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RU ET AL.
(
(
2 0 0) and (2 2 0) planes of the typical face‐centered cubic
f c c) Pd lattices, respectively for 3D IL‐rGO/Pd were
which is located between the interplanar spacing of the
single metal palladium catalyst and the single metal cop-
per catalyst, indicating that the lattice of the palladium
o
o
o
seen at 40 , 46 and 68 .(JCPDS no. 05–0681) And the
peak corresponding to the (1 1 1), (2 0 0) and (2 2 0)
planes of the typical face‐centered cubic (f c c) Cu lattices
[
19]
copper alloying shrinks.
X‐ray photoelectron spectroscopy (XPS) measurements
were used on 3D IL‐rGO/Pd Cu catalysts to study their
o
o
o
for 3D IL‐rGO/Cu were seen at 43.3 , 50.5 and 74.2 .
JCPDS no. 04–0836) (Figure 1 (a) and(g)) The series of
D IL‐rGO/Pd‐Cu composites has only a single diffraction
2.5
2.5
(
3
surface elemental composition and to investigate the
chemical state of the Pd and Cu metals (Figure 4). In the
wide energy spectrum of catalysts, three peaks at
286.7 eV, 401.6 eV and 542.3 eV are found obviously,
which were attributed to C1s, N1 s and O1s, respectively.
Other two peaks at 335.8 eV and 933.3 eV corresponded
to Pd 3d and Cu 2p. From Figure 4(b), it can be seen that
the C‐C bonding of C1s peak (284.6 eV) was dominant,
while the peak value of C(C=O, C (epoxy/ether)) was sig-
nificantly reduced. The new peak at 285.9 eV is newly pro-
duced corresponded to C‐N bonding. Moreover, the N1 s
band is centered at 401.7 eV and the lower binding energy
is 399.9 eV from Figure 4(c). These results were caused by
peak, located between the face centered cubic Pd (1 1 1)
crystal plane. It presented that the 3D IL‐rGO/Pd‐Cu cat-
alyst forms a solid‐solution (alloy) structure.
worth mentioning that the diffraction angles are observed
to be shifted toward the peak of the Cu (1 1 1) crystal
plane of Cu gradually with the increase of Cu. (Figure 1
[15]
It is
(b)‐(f)) Moreover, the XRD data also clearly reflected the
nanoparticle size increased with the addition of copper
since Pd NPs had smaller dimensions of crystal than
Cu.
average crystallite sizes of nanoparticles supported on
each catalyst can be calculated. From (a) to (g), the sizes
were about 2.5 nm, 3.22 nm, 3.45 nm, 3.58 nm, 3.64 nm,
[16]
According to the Debye–Scherrer formula the
[
20]
the success of NH ‐IL grafted graphene sheets.
From
2
Figure 4(d), it was concluded by the detailed examination
of the deconvoluted XPS spectra that Pd was found all in
the metallic state ((336.2 eV, Pd 3d5/2) and (341.5 eV, Pd
3d3/2)). It is believed that the bimetallic catalyst had a
stronger antioxidant capacity than the monometallic cata-
lyst compared to the reference data (more than one chem-
4
.49 nm and 5.53 nm, which were consistent with the
TEM results.
A transmission electron microscopy (TEM) image of
the as‐prepared 3D IL‐rGO/Pd and 3D IL‐rGO/Pd‐Cu
with different mass ratio is shown in Figure 2. It is easily
discerned that graphene modified by ionic liquids can
form a transparent layer structure with very few curling
and agglomeration. From Figure 2(a)‐(f), TEM with dif-
ferent magnification with different Pd Cu ratio all showed
that metals can be evenly dispersed on the surface of the
carrier with no significant difference. It indicated that the
introduction of Cu did not lead to the agglomeration of
metal particles. Meanwhile, the interaction of metal ions
with defect points on IL‐functionalized graphene pro-
vided favorable conditions for nucleation of metal nano-
particles, and this effect also effectively reduces the
surface mobility of metal particles, enabling the metal to
[
21]
ical state of Pd).
From Figure 4(e), Cu is mainly in the
zero valent state ((952.2 eV, Cu 2p1/2) and (932.1 eV, Cu
2p3/2)). But there were also a small amount of CuO
detected in the sample, which were corresponded with
peaks ((953.2 eV, CuO 2p1/2) and (933.2 eV, CuO 2p3/
[
22]
2)).
Meanwhile, a negative shift of the Pd 3d5/2 peak
(336.2 eV) and a positive shift of Cu 2p3/2 peak
(932.1 eV) was observed compared to the reference data
0
0
[23]
(Pd 336.9 eV Cu 932.5 eV).
As Cu has a lower reduc-
tion potential than the Pd, the synergistic effect of the Pd
and Cu via alloying can transfer electrons from Cu to
Pd. The such electron transfer essentially changed the
electronic states of Pd or Cu atoms, leading Pd to zero oxi-
dation state (electron rich state), which are beneficial to
the oxidative addition of aryl halides in the Suzuki
[17]
be uniformly supported on the carrier.
According to
particle size analysis, average particle diameter from (a)
to (f) were 2.56 nm, 2.67 nm, 2.78 nm, 3.0 nm, 3.57 nm
and 4.16 nm. It was found that metal particles gradually
increased respectively, which was due to the gradual
introduction of Cu. The HRTEM image of 3D IL‐rGO/
Pd, 3D IL‐rGO/Pd Cu . and 3D IL‐rGO/Cu were
shown in Figure 3. The interplanar spacing of the single
metal palladium catalyst 3D IL‐rGO/Pd was 0.224 nm,
which was consistent with the (1 1 1) crystal plane of
the face centered cubic Pd. The interplanar spacing of
the single metal copper catalyst 3D IL‐rGO/Cu is
[
24]
coupling process.
While The Cu/Pd atomic ratio at
the catalyst surface was measured to be 1/0.86, which
was consistent with the alloy composition determined by
ICP‐AES (Table 1). In addition, it can be seen from the
Table 1 that the actual loading of Pd‐Cu in this series of
3D IL‐rGO/Pd‐Cu is almost the same as the theoretical
load. This indicated that Pd‐Cu bimetal alloy can also be
well loaded on ionic liquid functionalized graphene.
In order to determine the distribution of Pd and Cu in
IL‐RGO catalyst, we collected the HAADF‐STEM images
and elemental mappings and EDS line scanning profiles
(Figure 5). Noticeably, Pd and Cu were uniformly
2.5
2.5
0
.208 nm, which was corresponded to the (1 1 1) crystal
[18]
plane of face‐centered cubic Cu.
ing of the alloy catalyst rGO/Pd Cu
The interplanar spac-
is 0.218 nm,
2.5
2.5
Ru, Yu
