Co/rGO synthesized: Via the alcohol-thermal method as a heterogeneous catalyst for the highly efficient oxidation of ethylbenzene with oxygen

Article abstract of DOI:10.1039/c9nj00470j

Co₃O₄ nanoparticles uniformly dispersed on reduced graphene oxide (Co/rGO) were synthesized by the alcohol-thermal method as a highly efficient catalyst with initiator NHPI for the selective oxidation of ethylbenzene to acetophenone using O₂ as a green oxidant. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were carried out for chemical, morphological, and size analyses of the nanocomposite. The ensuing catalyst was evaluated for the oxidation of ethylbenzene with a high conversion of 84.1% and an acetophenone selectivity of 96.2% within only 2 h. Moreover, the Co/rGO catalyst showed good recyclability and activity towards the selective oxidation of ethylbenzene. It was revealed that the enhanced catalytic activity of Co/rGO was derived from the interaction of the active Co₃O₄ center and the graphene support material.

Full text of DOI:10.1039/c9nj00470j

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Co/rGO Synthesized via Alcohol Thermal Methods as
Heterogeneous Catalyst for Highly Efficient Oxidation of
Ethylbenzene with Oxygen
Received 00th January 20xx,
Accepted 00th January 20xx
Lingfeng Gao*[a] WenYun Zhuge, Xue Feng,[a] Wei Sun,[a] Xu Sun,*[a] Gengxiu Zheng[a]
DOI: 10.1039/x0xx00000x
Co3O4 nanoparticles uniformly dispersed on reduced graphene oxide (Co/rGO) were synthesized by alcohol thermal
method as highly efficient catalyst with initiator NHPI for the selective oxidation of ethylbenzene to acetophenone using
O2 as green oxidant. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM),
and X-ray photoelectron spectroscopy (XPS) were carried out for the chemical, morphological, and size analyses of the
nanocomposite. The ensuing catalyst was evaluated for the oxidation of ethylbenzene with high conversion of 84.1% and
acetophenone selectivity of 96.2% within only 2 h. Moreover, Co/rGO catalyst showed good recyclability and activity
toward the selective oxidation of ethylbenzene. It is revealed that the enhanced catalytic activity of Co/rGO is derived
from
the
interaction
of
the
active
center
Co3O4
and
the
support
material
graphene.
coupling reactions.[21-23] In these cases, graphene oxide (GO) is
frequently used as a precursor for graphene and plays a significant
role as support material, since it may contribute to the dispersion of
metal particles on the surface of graphene because of the oxygen
functional groups (hydroxyl group, epoxy group, carboxyl group)[24-
28] and accelerate the transfer of electrons due to the large number
of carbon-carbon double bonds.[25-29] In addition, GO can be easily
reduced to graphene by chemical reduction, hydrothermal
reduction or thermal annealing.[26,27-29] Based on above, it is widely
believed that graphene is a very promising carbon material applied
in catalytic reactions, combined with the unique advantages of
metal nanoparticles via improving particle dispersion, reducing
particle size, exposing more active sites and enhancing stability.
In consideration of the fact that the alcohol solvet is often
adopted as the solvent for the fabrication of metal oxides with
uniform size ang morphology, here in our work, nano-sized
Co3O4 particles supported on reduced graphene oxide
(Co/rGO) were prepared via the simple alcohol thermal
reaction, during which the glycol adopted as the solvent.
Across the alcohol thermal reaction process, all of precursors
became active until reaching the supercritical conditions, thus
finally leading to the homogeneous reaction solution for the
synthesis of the nano-materials. The as synthesized Co/rGO
exhibited advanced catalytic activity and reusability for the
selective oxidation of ethylbenzene to acetophenone using O2
as green oxidant in the presence of radical initiator.
Introduction
Selective oxidation of ethylbenzene to useful acetophenone is a
significant reaction in the research of organic chemistry and
chemical industry, because acetophenone is an important
intermediate in the production process of resins, alcohols,
aldehydes, esters and pharmaceuticals, and can also be used as
solvent for esters, dyestuff and preservatives.[1-3] Works relating to
liquid-phase oxidation of ethylbenzene to acetophenone have been
reported using transition-metal (Co, Cu, Fe, etc.) compounds as
homogeneous catalysts.[4,5] However, these catalysts not only are
difficult to separate for recovery after oxidation but also encounter
decreased catalytic activity due to self-aggregation of active sites,[6]
thus leading to complicated post-processing and a lot of pollution of
metal. In order to avoid these problems concerning homogeneous
catalysts, it is of great significance to develop more easily-separated,
reusable and environmental friendly heterogeneous catalysts for
ethylbenzene oxidation, such as MnFeSi,[7] MnO2/MgAl-LDH,[8] Co-
N-C/SiO2,[9] Au/rGO,[10] CoZnAl-MMO/Al2O3,[11] and MnOx/HTS.[6]
Among these supported catalysts, graphene-based catalyst has
attracted more and more attention of researchers and has been
widely used in catalysis field.
Graphene, as a novel two-dimensional carbon material with
excellent physical and chemical properties, has been widely
researched in catalytic reactions by combining with metal. aromatic
alcohols oxidation,[12,13] C=C bond selective hydrogenation,[14]
nitroarenes hydrogenation,[15-17] H2O2 decomposition[18-20] and cross
Results and Discussion
Dr. L. Gao W. Y. Zhuge, X. Feng, W. Sun, Dr. X. Sun, Prof. G. Zheng.
School of Chemistry and Chemical Engineering, University of Jinan, No. 336 West
Road of Nan Xinzhuang, Jinan 250022, P.R. China.
E-mail: chm_sunx@ujn.edu.cn, gaolf108@mail.ustc.edu.cn.
‡These authors contributed equally to this work.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See DOI:
10.1039/x0xx00000x
Characterizations
Fig. 1. showed the power X-ray diffraction patterns of GO, rGO
and Co/rGO. The typical diffraction peak (002) was observed at
2θ = 11° from GO,[
33]
attributed to the oxygen functionalities
generated in the interlayer spacing of graphite after oxidation.
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Alone with the reduction, the characteristic peak decreased
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DOI: 10.1039/C9NJ00470J
rapidly in rGO and Co/rGO and appeared around 2θ = 23.1o The XPS spectrum is shown in Fig. 3 to further analyze the
instead, demonstrating that the surface oxygen groups of GO surface elemental composition of the Co/rGO nanocomposite.
were removed partially in the process of alcohol-heating reducing The full survey spectra (Fig. 3, (a)) displays the existence of C,
and conjugated graphene network sp2 was reestablished. In O, Co elements without other impurities. The peak of O 1s
addition, Co/rGO catalyst exhibited new diffraction peaks at 2θ = might stem from the residual oxygen of rGO and the peak of
18.4o, 36.9o, 44.2o and 59.8o, which correspond to the Co (111), Co 2p appeared in 800.1 eV. The surface Co amount in the XPS
(311), (400) and (511) crystal planes of cubic Co3O4.[34] These data is 36.5 wt.% and the total Co loading is 35.8 wt.%
results suggest that the Co3O4 nanoparticles was successfully detected by ICP-OES analysis (Table S1). The tiny variation of
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modified on the surface of rGO.
cobalt concentration between XPS and ICP-OES is due to the
principle differences between the two testing methods, in that
the XPS is a surface analysis method, which provide the
surface element concentration and the surface chemical state.
While, as for ICP-OES, it is a more accurate testing method
from which the overall composition was obtained. The XPS
spectrum of Co 2p shown in Fig. 3 (b) shows two peaks at
binding energies of 781.5 eV and 783.2 eV for Co3+ 2p3/2 and
Co2+ 2p3/2, respectively. The other two peaks assigned to Co
2p1/2 are detected at 797.2 eV for Co3+ cations and 798.5 eV
for Co2+ cations.[35] Additionally, the Co2+ shakeup satellites of
Co3O4 are also observed at 787.1 eV and 803.4 eV.[36]
Figure 1. XRD patterns of GO, rGO and Co/rGO.
TEM and SEM images of Co/rGO are presented in Fig. 2. It can
be seen that Co3O4 nanoparticles with a size distribution in the
11-34 nm range (average diameter 23 nm) are uniformly
deposited on the transparent rGO sheets with crumpling
(Fig.2, (b)), and it is well consistent with SEM observations (Fig. Figure 3. XPS spectrum of (a) Co/rGO catalyst and (b) Co2p.
2, (d)). Moreover, we found that particles are mainly
distributed on the edge of rGO without obvious agglomeration Catalytic activity for the selective oxidation of ethylbenzene
and the thin sheet structure and wrinkles of GO (Fig. 2, (a) and
(c)) are retained after reduction treatment.
The activities of Co/rGO catalyst for the selective oxidation of
ethylbenzene using O2 were summarized in Table 1. It was
clear that the reaction process was difficult to carry out
without any catalyst, giving only 2.6% conversion of
ethylbenzene and 89.1% acetophenone selectivity,
respectively (Table 1, entry 1). Under the same conditions, the
Co/rGO exhibited high catalytic performance with 84.1%
conversion and 96.2% selectivity (Table 1, entry 3) in the
presence of NHPI (hydroxyphthalimide). And GC-MS, HPLC
were also use to check the molecular weight of the product,
There are only benzoic acid and CO2 side-product, wothout
acetophenone acid and other side product. To further explore
the effect of support material in the catalytic reaction, a Co-
free rGO material reduced by the same method was used to
catalyze this reaction and no obvious substrate consumption
(only 3.8% conversion) was observed (Table 1, entry 2), which
indicated rGO had no catalytic activity for this reaction.
Futhermore, different cobalt-based catalysts were investigated
for the selective oxidaton reaction. Co/AC (Active carbon) and
Co/GP (graphite powder) gave relatively low ethylbenzene
conversion (65.5% and 58.3%, respectively) with about 90%
acetophenone selectivity (Table 1, entries 4 and 5). The results
suggested that the catalytic activity of Co/rGO composites
Figure 2. (a) TEM images of rGO. (b) TEM images of Co/rGO
and the particle size of the Co3O4 nanoparticles on rGO. (c)
SEM images of rGO. (d) SEM images of Co/rGO.
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originates from Co3O4 and rGO as a support can contribute to time was extended to 10 h, the selectivity decreased slightly
improve the activity of Co3O4-loaded catalyst. Additionally, but the conversion kept at a preferable level without
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DOI: 10.1039/C9NJ00470J
different amounts of Co/rGO catalysts (0.5 wt%, 1.0 wt%, 1.5 significantly change at the same time.
wt%, 2.0 wt%, 2.5 wt%) for ethylbenzene amount, were
applied for the reaction in order to detect the optimum
amount for ethylbenzene oxidation. The results revealed that
2.0 wt% of Co/rGO showed higher catalytic activity with
increases in catalyst from 0.5 wt% to 2.0 wt% (Table 1, entries
7-10), resulting from the increasement of active sites. Notably,
excessive heterogeneous catalysts may cause conversion
reduction due to the blocks between the substrate and the
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Figure
4 Oxidation of ethylbenzene at different (a)
oxidant (Table 1, entry 11). It could be also found that only
46.8% ethylbenzene conversion was obtained in the absence
of NHPI (Table 1, entry 6), indicating that NHPI plays an
important role as a trigger for oxidation of ethylbenzene.
temperature and (b) time intervals.
For the free radical NHPI initator was introduced in the
reaction system, to explore the effect of the solvent in this
catalytic reaction, various organic solvents were used in the
oxidation of ethylbenzene, such as CH3COOH, CH3COOC2H5,
CH2Cl2, DMF, CH3COCH3, ClCH2CH2Cl, CH3CN and PhCN, and the
results were summarized in Table 2. A series of experiments
showed that CH3CN was the best solvent in this oxidation
system with 84.1% conversion and 96.2% selectivity (Table 2,
entry 2), but CH3COOH and DMF are the opposite, affording
lower ethylbenzene conversion of 34.3% and 35.7%,
respectively (Table 2, entries 3 and 4). When the reaction was
carried out without solvent, the conversion of ethylbenzene
was only 29.5% (Table 2, entry 1). Therefore, CH3CN as a
solvent plays an effective role for the transition of free radical
in the oxidation reaction. The above results revealed that
these solvents have obvious influences on the activity of
Co/rGO for the selective oxidation of ethylbenzene.
Table 1. Oxidation of ethylbenzene to acetophenone catalyzed by
different catalysts. a
Entry
1b
2
Catalyst
Conv./%
2.6
Select./%
89.1
87.0
96.2
89.7
90.4
88.5
89.3
91.2
90.5
96.2
89.7
absence
rGO
3.8
3
Co/rGO
84.1
65.5
58.3
46.8
43.4
67.5
79.4
84.1
86.0
4
Co/AC
5
Co/GP
6c
7
Co/rGO
0.5 wt.% Co/rGO
1.0 wt.% Co/rGO
1.5 wt.% Co/rGO
2.0 wt.% Co/rGO
2.5 wt.% Co/rGO
Table 2. Oxidation of ethylbenzene in different solvents.a
8
Entry
Solvent
Conv./%
29.5
84.1
34.3
35.7
57.9
55.2
70.1
61.5
59.8
Select./%
91.5
9
1
2
3
4
5
6
7
8
--
10
11
CH3CN
96.2
CH3COOH
DMF
84.7
aReaction conditions: 1 mL ethylbenzene, 2 mL CH3CN, 6 mol% NHPI
(hydroxyphthalimide), 2.0 wt% catalyst, 0.3 MPa O2, 120 oC, 2 h.
bCatalyst-free. cNHPI-free.
80.8
Inspired by these intriguing results, we optimized the reaction
conditions in order to further understand the catalytic
performance of Co/rGO, such as the effects of the reaction
temperature and reaction time on the conversion of
ethylbenzene and the selectivity of acetophenone. The
ethylbenzene conversion increased markedly from only 10.4%
CH3COOC2H5
CH3COCH3
CH2Cl2
80.1
92.0
93.3
ClCH2CH2Cl
PhCN
79.8
o
o
at 60 C to 84.1% with the elevated temperature to 120 C,
and the acetophenone selectivity improved by 21.0% from the
original 75.2% (Fig. 4, (a)). However, as reaction temperature
continued to rise, acetophenone selectivity changed to
decrease with slightly increased conversion, indicating that the
overoxidized side-product benzoic acid could generate easily
at excessive temperature.
9
89.1
a
Reaction conditions: 1 mL ethylbenzene, 2 mL solvent, 6 mol% NHPI
(hydroxyphthalimide), 2.0 wt% catalyst, 0.3 MPa O2, 120oC, 2 h.
The effect of different initiators on the oxidation of
ethylbenzene has been also studied (Table 3). In the absence
of any initiator, 46.8% conversion of ethylbenzene and 88.5%
selectivity of acetophenone was obtained over Co/rGO at the
catalyzed by Co/rGO (Table 3, entry 1). When the reaction was
initiated by dibenzoyl peroxide (BPO) and 2,2,6,6-
tetramethylpiperidine-1-oxyl (TEMPO), the conversion is
Fig. 4 (b) illustrated the relationship between the catalytic
activity of Co/rGO and reaction time. Remarkably, the
ethylbenzene conversion and acetophenone selectivity
increased greatly as reaction time was 2 h. When the reaction
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Figure 5. Schematic illustration for the catalytic oxidation ethylbenzene to
dropped sharply to 9.2% and 7.4% respectively, but the former
gave very low selectivity only 66.2% (Table 3, entries 2 and 3).
Azobisisobutyronitrile (AIBN) was use as initiator and showed a
mild effect with 51.5% conversion and 91.4% selectivity (Table
3, entry 4). After several contrast experiments, NHPI proved to
be the best initiator with 84.1% conversion of ethylbenzene
(Table 3, entry 4). The results showed that Co/rGO/NHPI
catalytic system could give much higher conversion of
ethylbenzene and selectivity for acetophenone compared with
the single Co/rGO (Table 3, entry 5).
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DOI: 10.1039/C9NJ00470J
acetophenone by the Co/rGO nanocomposite.
The reusability of the heterogeneous catalyst is a definite
advantage compared with homogeneous catalyst. The Co/rGO
catalyst was reused additional five times under the optimal
reaction conditions after separation from the reaction system
by filtration, washing and lyophilization and the results were
shown in Fig. 6. Only slight decrease was observed in catalytic
activity including conversion and selectivity for oxidation of
ethylbenzene after several cycles, showing that the catalyst
had no overmuch mass loss or deactivation. The X-ray
diffraction analysis of the Co/rGO catalyst after used for five
consecutive times revealed that the crystal structure of Co
nanoparticles anchored on the surface of graphene was not
changed. Furthermore, SEM and EDS images (Fig. S2) exhibited
that the recycled catalyst maintained the original morphology
compared with the catalyst being used before. The results may
be associated with the large specific surface area of graphene
in favor of the dispersion of metal particles and preventing
aggregation.
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Table 3. Oxidation of ethylbenzene catalyzed by Co/rGO using different
initiators.a
Entry
Initiator
--
Conv./%
Select./%
1
2
3
4
5
46.8
9.2
88.5
66.2
BPO
TEMPO
AIBN
7.4
93.0
91.4
96.2
51.5
84.1
NHPI
aReaction conditions: 1 mL ethylbenzene, 2 mL CH3CN, 6 mol% initiator, 2.0
wt% catalyst, 0.3 MPa O2, 120oC, 2 h.
The selective aerobic oxidation ethylbenzene to acetophenone
has been generally accepted as a radical reaction[37,38]. Based on
the above experimential studies carried out in the absence and
presence of Co/rGO catalyst or NHPI, the possible reason may be
accounted for the high activity of Co/rGO/NHPI catalysis system.
The most important intermediate Ⅲ, which is originated from
ethylbenzene combined with O2, can be accelerated to
decompose into to acetophenone by the Co/rGO catalyst in the
absence of any initiator and the result is consistent with Table 3
(Entry 1). Besides, NHPI can be converted to reactive
phthalimide N-oxyl radical (PINO) in the reaction with O2, which
is able to abstract the hydrogen atom from a saturated carbon of
ethylbenzene, forming the corresponding benzylic radical Ⅰ.
Under the oxygen atmosphere, these radicals subsequently react
with O2 to form Ⅱ , that is further translated into Ⅲ and
ultimately acetophenone, as shown in Fig. 5. In order to facilitate
this pathway, Co/rGO catalyst have been utilized and afford
desirable results.
Figure 6. Recycling of Co/rGO catalyst for the selective oxidation of
ethylbenzene.
Table 4. Comparision merit of the Co/rGO catalysts with other similar catalysts
reported.
Catalyst
T /oC
t /h
12
Conv. /%
93
Select. /%
89
Ref.
[39]
Al2O3@CoCuAl-MMO
120
[40]
[41]
[42]
[43]
[44]
[37]
[45]
[46]
[47]
Ag/SiO2
120
80
12
12
24
38
99
98
88
92
91
69
78
66
76
60
93
96
N-rGO
LC-N
80
Ti-Zr-Co
170
120
120
120
155
120
120
4.5 62
Co-N-C/g-C3N4
Car-NHPI/NHQI
Co-N-C-S
Fe@CNTS
Co@GCNs
Co/rGO/NHPI
5
28
70
17
37
68
84
15
5
3
5
2
This
work
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by ultrasound and stirring. Then, the pH value of the system
Reported catalysis come from the references. This work reaction conditions: 1
mL ethylbenzene, 2 mL CH3CN, 6 mol% initiator, 2.0 wt% catalyst, 0.3 MPa O2,
120oC, 2 h.
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DOI: 10.1039/C9NJ00470J
was adjusted to 11-12 by the dropwise addition of KOH
solution (2 mol·L-1) under vigorous stirring. Above suspension
was then transferred into a 50 mL Teflon-lined stainless-steel
o
The Co/rGO catalyst presented in this work exhibits advantages in
terms of short reaction time, high conversion and selectivity for the
selective oxidation of ethylbenzene and the catalytic effects are
compared with other similar catalysts reported in literatures [Table
4]. Firstly, graphene (rGO), as a novel two-dimensional carbon
material with excellent physical, electrical conductivity and
chemical properties, is frequently used as a supporter for transition
metal catalysts, which contribute to the dispersion of metal
particles via the oxygen functional groups (hydroxyl group, epoxy
group, carboxyl group) on the surface of graphene. Secondly,
synergistic catalysis from the π-π stacking of the rGO and
ethylbenzene plays efficiently bonding role.
autoclave followed by thermal treatment at 150 C for 8 h.
After being cooled down to room temperature, the obtained
catalyst was collected by centrifugation and throughly washed
with 0.1 M KOH and distilled water, and lyophilization was
applied to prevent the aggregation of graphene sheets during
the drying process. The Co3O4 nanoparticles supported on
activated carbon (Co/AC) and graphitized carbon (Co/GC) were
synthesized by the same method.
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Selective oxidation of ethylbenzene
The selective oxidation of ethylbenzene to acetophenone over
the synthesized nanocomposite was conducted in a Teflon-
lined stainless-steel autoclave using O2 as oxidant. Typically,
NHPI (N-hydroxyphthalimide) and Co/rGO catalyst were
dispersed in acetonitrile (2 mL) and then the etylbenzene (1
mL) was added. After the reactor was sealed, removed air and
Conclusions
In summary, the Co/rGO nanocomposite was synthesized by
one-step alcohol thermal method. The obtained Co/rGO
catalyst exhibited excellent catalytic activity (84.1%
conversion, 96.2% selectivity) in a short time (2 h) for selective
oxidation of ethylbenzene to acetophenone. Especially, O2 as
cheaper and cleaner oxidant in the catalytic oxidation reaction
makes the catalytic system more practical. The satisfactory
catalytic effect is the result of the combined action of highly
active graphene-supported Co3O4 and free-radical initiator
NHPI. Hence, due to their simple preparation, good
recyclability, low cost and environmental friendliness of the
Co/rGO composites catalysts, it is expected that this work may
offer effect catalyst to practical selective oxidation of
ethylbenzene to produce acetophenone.
o
pressurized with O2, the mixture was heated to 120 C for 2 h
under magnetic stirring. Upon reaction completion, the
heterogeneous catalyst was recycled from reaction mixture by
filtration and the reaction solution was quantitatively analyzed
by an Agilent 7890 series gas chromatograph (GC). And all
products were confirmed by GC-MS (Shimadzu GCMS-QP2020)
as well as by comparing the retention times to respective
standards in GC traces. Agilenft Hypersil ODS column (4.6 ×
250 mm) and UV detector (at 256 nm), was used to analyze
the non-gasifiable products (benzoic acid). The eluent was 0.01
mol L-1 KH2PO4 in an acetonitrile-water mixture.
The recovery of the used catalysts
When the oxidation reaction was finished, the flask was cooled
down to room temperature and the heterogeneous catalyst
Co/rGO was recycled from the reaction mixture by filtration
and washed with ethyl acetate which was combined with the
reaction filtrate for the next gas chromatograph (GC) analysis.
On the other hand, the recycled Co/rGO was purified by
lyophilization.
Experimental Section
Synthesis of GO
GO was prepared from graphite powders by the modified
Hummers method. Graphite powers (1.0 g), NaNO3 (1.0 g) and
H2SO4 (20 mL) were put into a 250 mL flask, and then KMnO4
(3.0 g) was added slowly under stirring in an ice bath. The
reaction system was transferred to a 40 °C water bath and
vigorously stirred for about 30 min. Then ultrapure deionized
water (50 mL) was slowly added to the solution and stirred for
another 30 min at 80 °C. The mixture was poured into 200 mL
water and followed by addition of 10 mL H2O2 (30%), yielding a
yellow suspension of GO. The mixture was filtered and washed
with HCl (10%) aqueous solution and the resulting solid was
dispersed in 300 mL water. Finally, it was purified by dialysis
for one week using a dialysis membrane to remove the
remaining acid and metal species. The generated GO aqueous
dispersion was stirred for 10 h and sonicated for 30 min to
exfoliate it.
Characterization
The crystal structure was studied by X-ray diffractometer (D8
Focus, Bruker) with a Cu Kα irradiation source (λ=1.54 Å).
Transmission electron microscopy (TEM) image was observed
by JEOL JEM-1200EX electron microscope performed at an
accelerating voltage of 100 kV. X-ray photoelectron spectra
(XPS) was recorded on a ThermoFisher K-Alpha System.
Inductively coupled plasma-optical emission spectroscopy (ICP-
OES) analysis was performed on a PerkinElmer 8300 analyzer.
Field-emission scanning electron microscope (FE-SEM) image
and energy dispersive spectroscopy (EDS) data of the sample
were carried out on JSM-7001F SEM unit.
Conflicts of interest
There are no conflicts to declare.
Synthesis of Catalysts
The aqueous solutions of GO (8.2 mg·mL-1, 5.0 mL), 120 mg of
Co(OAc)2·H2O and 60 mg of L-glutamic acid were mixed
together in 35 mL of glycol to form a homogeneous suspension
Acknowledgements
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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35. Y. Sun, S. Gao, F. Lei, J. Liu, L. Liang, Y. Xie, Chem. Sci. 2014, 5, 3976-82.
This work was financially supported by the Natural Science
Foundation of Shandong Province (ZR2017PB005), the
National Natural Science Foundation of China (Nos. 21402064,
Nos. 21601064), General Financial Grant from the China
Postdoctoral Science Foundation (2016M602089). We thank
our colleagues for the characterization studies and their
contributions to the project.
View Article Online
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DOI: 10.1039/C9NJ00470J
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