Synthesis of graphene quantum dots stabilized CuNPs and their applications in CuAAC reaction and 4-nitrophenol reduction

Article abstract of DOI:10.1016/j.inoche.2019.107588

Here we report the synthesis of graphene quantum dots (GQDs) stabilized copper nanoparticles in neat water. Construction of six CuNPs 1–6 nanocomposites are accomplished by mixing GQDs and NaBH₄, and followed by the addition of different amount

Full text of DOI:10.1016/j.inoche.2019.107588

Journal Pre-proofs
Synthesis of Graphene Quantum Dots Stabilized CuNPs and Their Applica-
tions in CuAAC Reaction and 4-Nitrophenol Reduction
Yu Huang, Weifeng Chen, Jialu Shen, Yanlan Wang, Xiang Liu
PII:
S1387-7003(19)30880-9
DOI:
https://doi.org/10.1016/j.inoche.2019.107588
INOCHE 107588
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Inorganic Chemistry Communications
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Revised Date:
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27 August 2019
17 September 2019
17 September 2019
Please cite this article as: Y. Huang, W. Chen, J. Shen, Y. Wang, X. Liu, Synthesis of Graphene Quantum Dots
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Chemistry Communications (2019), doi: https://doi.org/10.1016/j.inoche.2019.107588
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Synthesis of Graphene Quantum Dots Stabilized CuNPs and Their
Applications in CuAAC Reaction and 4-Nitrophenol Reduction
[a]
[a]
[a]
[b]
[a]
Yu Huang, Weifeng Chen, Jialu Shen, Yanlan Wang, and Xiang Liu *
Abstract: Here we report the synthesis of graphene quantum dots (GQDs)
stabilized copper nanoparticles in neat water. Construction of six CuNPs 1-
nanocomposites are accomplished by mixing GQDs and NaBH , and
nanoparticles (CuNPs) and their applications in CuAAC reaction and
4-nitrophenol reduction. In this work, GQDs A with the size from 2.25
to 3.50 nm has been synthesized from only commercial starch and
water by our previously reported method (Fig. 1).[6a] Construction of
the CuNPs have been carried out by here direct coordination of
different amounts of Cu(II) ions into GQDs A solution followed by
6
4
followed by the addition of different amounts of copper sulfate at 0 ℃ in
water, respectively. Among them, CuNP-3, with the size of 2.6 nm,
exhibits excellent catalytic performance in the CuAAC reaction over than
other CuNPs. Moreover, the CuNP-3 has also been successfully applied
for the reduction of 4-nitrophenol with excellent catalytic activity.
4
NaBH reduction in neat water (Table 1). GQDs A is very stable and
soluble in water, allowing for stabilizing the CuNPs in a controlled
fashion to avoid the aggregation. Then these six CuNPs are
investigated in the CuAAC reaction in neat water. Among them,
CuNPs-3 exhibits excellent catalytic activity over than other CuNPs.
The
3 has also been characterized by UV-vis spectroscopy,
1
. Introduction
transmission electron microscopy (TEM) and X-ray photoelectron
spectroscopy (XPS). In addition, CuNPs-3 has also been measured for
the reduction of 4-nitrophenol with high activity.
Click chemistry was first reported by Sharpless, Kolb and Finn in 2001,
as a general concept for the high-efficiency assembly of organic
molecules.[1] Among the various click reactions, the copper catalyzed
azide-alkyne cycloaddition (CuAAC) reaction has attracted wide
attention, because its selectively corresponding product 1,4-
disubstituted 1,2,3-triazole, one kind of important N-containing
heterocycles,[2] has been widely used in medicinal chemistry,
fluorescent materials, corrosion-retarding agents, agricultural products,
dyes and chem-sensing.[3] In general, the CuAAC reaction requires
Starch + water
CuSO4.5H2O
CuNPs
NaBH4
GQDs A
I
stoichiometric quantities of Sharpless-Fokin Cu catalyst for obtaining
Figure 1. The synthesis of CuNPs.
high yield and avoiding the byproduct of 1,5-disubstituted 1,2,3-
triazoleis.[4] However, this “click” chemistry is always restricted in the
field of electronics and biomedicine due to the difficult removal of the
large quantity of copper ions.[5]
2
. Results and Discussion
Graphene quantum dots (GQDs), a new kind of graphene fragments
nanomaterial, have been extensively investigated in biomedical,
optoelectronic, fluorescent sensor, catalysis and energy related fields
because of their high intrinsic fluorescence, high biocompatibility, high
photostability, low toxicity, chemical inertness, large surface area and
surface functional groups (including carbonyl, carboxyl, epoxy and
hydroxyl groups).[6] In addition, GQDs have also been successfully
developed as a novel stabilizer for transition metal nanoparticles. For
2
.1. Synthesis of the CuNPs 1-6
First, GQDs A with the size of from 2.25 to 3.50 nm has been
synthesized from only commercial starch and water.[6a] The synthesis
of GQDs-stabilized CuNPs 1-6 was conducted by using GQDs A and
sodium borohydride dissolved in water, and followed by the addition
-3
-3
-3
4 2
of different amounts of CuSO ·5H O (5.0 × 10 , 2.0 × 10 , 1.0 ×10 ,
-4
-4
-4
5.0 × 10 , 2.5 × 10 , 1.0 × 10 mmol) at 0 ℃, respectively, provoking
the formation of yellow color (CuNPs), corresponding to the reduction
example, GQDs stabilized AuNPs for DNA damage detection,[7]
2 2
H O
electrochemical detection,[8] and Pb2+ detection.[9] In fact, our group
has long term interest in the synthesis of transition metal nanoparticles
and their applications.[10] In the present work, we first developed a
facile and novel approach for graphene quantum dots stabilized copper
of the Cu2+ ions to the Cu(0) metal and CuNPs 1-6 formation (Table
). Cu2+ ions are first bonded by -OH and -COOH groups of the GQDs,
1
then reduced by NaBH , further as-synthesized CuNPs has been
4
stabilized by these -OH and -COOH groups. As a comparative
experiment, the commercial starch has also been used as a substitute
for GQDs A in the same above condition. The result shows that starch
is insoluble in water at 0 ℃ and does not stabilize CuNPs.
[
a]
Mr. Y. Huang, Dr. W. Chen, Mr. J. Shen, Prof. X. Liu. College of
Materials and Chemical Engineering, Key Laboratory of Inorganic
Nonmetallic Crystalline and Energy Conversion Materials, Material
Analysis and Testing Center,China Three Gorges University, Yichang,
Hubei 443002, China. Email: xiang.liu@ctgu.edu.cn
2
.2. Compared catalytic activities of CuNPs in the click reaction
[b]
Prof. Y. Wang. College of Chemistry and Chemical Engineering,
Liaocheng University, Liaocheng, Shandong, 252059, China
These six CuNPs compared catalytic performance in click reaction of
phenylacetylene and benzyl azide has been scrutinized. As shown in
Table 1, the reactions were carried out with phenylacetylenes (0.5
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))

corresponding 1,4-disubstituted 1,2,3-triazoles. As shown in Table 2, a
Table 1. Optimization of the reaction condition.[a]
variety of alkynes and organic azides are well suited for this “click”
Ph
CuNPs
Ph
+ Ph
N3
N
o
N
H O, 30 C. 24 h
2
N
Ph
1a
2a
3a
Yield[b] (%)
11.7
Entry
Cu (Ⅱ) ions (mmol)
CuNPs
CuNPs (mol)
1
2
3
4
5
6
7
8
9
5.0×10-3
2.0×10-3
1.0×10-3
1.0×10-3
1.0×10-3
1.0×10-3
5.0×10-4
2.5×10-4
1.0×10-4
1
2
3
3
3
3
4
5
6
0.01%
0.01%
0.01%
0.02%
0.05%
0.10%
0.01%
0.01%
0.01%
(a)
(b)
26.1
86.0
90.2
95.1
92.4
83.5
(d)
(c)
5.5
Figure 2. (a) TEM image of CuNP-3;(b) Diameter histogram distribution of CuNP-3;
c) UV-vis. Spectrum of CuNP-3. (d) HRTEM of CuNP-3.
(
28.0
[
a]
Reaction conditions: 1a (0.5 mmol),2a (0.6 mmol), H
Isolated yield.
2
O (2 ml), 30 ℃, 24 h.
[b]
mmol) and benzyl azide (0.6 mmol) in the presence of CuNPs 1-6
0.01 mol%) in H O (2 mL) at 30℃ for 24 h, respectively (Table 1,
(
2
entry 1-3 and 7-9). Among them, CuNP-3 provides the highest yield of
the desired product 3a (86.0 %). Next, we investigated the different
loadings of CuNP-3, we found the amount of 0.02 mol %, 0.05 mol%
and 0.10 mol % obtained 90.2, 95.1 and 92.4 % yields, respectively
2
(Table 1, entries 4-6). Thus, 0.05 mmol % CuNP-3 in H O is chosen
as the optimal conditions for this click reaction. Then TEM and UV-vis.
spectrum have been measured to confirm the morphology and size of
the CuNP-3. As shown in Fig. 2a and 2b, we found the size of CuNP-
3
is 2.6 nm. However, the characteristic peaks of CuNP-3 did not
appear in the UV-vis spectrum, due to its small size (Fig. 2c). The
representative high-resolution transmission electron microscopy
Figure 3. XPS of CuNP-3.
(HRTEM) image of CuNP-3 exhibits the Cu (111) lattice fringe
distance of 0.209 nm in the inner region (Fig. 2d). Furthermore, the
crystalline nature of the CuNP-3 was determined using X-ray
diffraction (XRD), only graphene (002) was observed in Fig. S1, due
to too little of CuNPs. To further verify the formation of CuNP-3, the
XPS of CuNP-3 has been recorded. Cu 2p is fitted with two pair of
peaks for the Cu 2p3/2 and 2p1/2 doublets in the XPS. The Cu 2p3/2 peak
positions are around 932.5 and 934.0 eV. These positions are assigned
to Cu(0) at 932.5 eV and to Cu(II) at 934.0 eV, respectively.[11]
Obviously, CuNP-3 has been partly oxidized to Cu(I) and Cu(II). All
reaction with the CuNP-3 as the catalyst. For instance, either the
electron donating substituted or withdrawing substituted acetylenes
6 4 6 4
including Ph-C≡CH, 4-Br-C H C≡CH, 3-F-C H C≡CH, 4-Cl-
C
6
H
4
C≡CH and 4-MeO- C C≡CH with benzyl azide obtaining the
6 4
H
corresponding 1,4-disubstituted 1,2,3-triazole derivatives 3a-e in good
to excellent yields (72 to 95 %). Similar excellent isolated yields (71 to
8
8 %) of 1,4-disubstituted 1,2,3-triazoles 3f-h are afforded when
ethynylbenzene is reacted with variously electronically substituted R2-
organic azides (such as 4-F-C CH , 4-CN-C CH and 4-
Me-C CH ). However, the lowest yield of 3i (47 %) is obtained,
N
3
6
H
4
2
N
3
6
H
4
2 3
N
I
of these results showed that the CuNP-3 was in its classic Cu state for
6
H
4
2 3
N
click reaction.
when the azide contains the 4-Cl group.
Under the optimized reaction conditions, we extended the study with
different acetylenes and benzyl azides for the synthesis of the
In addition, the CuNP-3 has also been successfully applied for
preparing some key functional materials. Such as“click”-triazole
functionalized moxestrol (Eq. 1) and “click”-triazole functionalized 7-

(propargyloxy)-coumarin (Eq. 2). Estradiol, as the predominant sex
presence of 5% CuNP-3 and 100 eq NaBH
4
in water at room
hormone present in female, has been mainly used in hormone
temperature (Fig. 4a). The result shows the reduction reaction does not
[
a]
Table 2. CuAAC reactions between various azides and alkynes
1
R
CuNP-3
R1
R2
+
N3
N
NO2
OH
NH2
OH
o
N
H O, 30 C. 24 h
N
R2
1
2
2
3
5 % CuNP-3
1
00 eq NaBH4, H2O
F
Br
N
N
N
N
N
N
N
N
N
3a 95%
3b 88%
3c 87%
Cl
MeO
N
N
N
N
N
N
N
N
N
3d 84%
3e 72%
3f 85%
F
N
N
N
N
N
N
N
(a)
N
N
3g 88%
3h71%
3i 47%
CN
Cl
2
[a] Reaction conditions: Azide 0.6 mmol, alkyne 0.5 mmol, H O 2 mL, 30 °C, 24 h.
replacement therapy and menopausal hormone therapy in women,
reproduction, nervous system, the skeletal system and pharmaceuticals.
Here the CuAAC click reaction of benzyl azide and ethynyl estradiol,
in the presence of 0.05% CuNP-3 in H
2
O at 30 ℃ for 24 h, provided
“
click”-triazole functionalized moxestrol 3j in 83% isolated yield (Eq
1
). On the other hand, coumarin and its derivatives are widely used in
fluorescent probes and the perfume industry.[12] Thus, click-triazole-
(
b)
functionalized 7-(propargyloxy)-coumarin 3k was obtained from 7-
Figure 4. (a) UV-vis spectrum in which 4-nitrophenol reaction is monitored 25 ℃; (b)
Consumption rate of 4-nitrophenol -ln(C/C ) versus reaction time
(prop-2-yn-1-yloxy)-2H-chromen-2-one and benzyl azide in water in
0
8
8 % isolated yield in the presence of CuNP-3 (0.05 %) .
need any induction time and is completed in 1 h. The apparent rate
constant kapp is 8 × 10-4 s-1 (Fig. 4b).
OH
H
N
N
OH
H
N
H
0.05% CuNP-3
H2O, 30 oC, 24h
N3
H
Eq. 1
Eq. 2
H
H
HO
H
H
HO
3j 83%
3. Conclusion
O
O
O
N
O
O
O
N3 0.05% CuNP-3
N
A green and facile method of synthesis of graphene quantum dots
stabilized CuNPs has been developed in this present work.
Construction of six CuNPs 1-6 nanocomposites are accomplished by
mixing GQDs and sodium borohydride, and followed by the addition
N
o
H2O, 30 C, 24h
3k 88%
2
.3. Catalytic activities of CuNP-3 in the 4-nitrophenol reduction
4 2
of different amounts of CuSO ·5H O at 0 ℃ in water, respectively.
The CuNP-3 has also been successfully applied for the reduction of 4-
Among them, CuNP-3 exhibits excellent catalytic performance in the
CuAAC reaction over than other CuNPs. The CuNP-3 has also been
characterized by UV-vis spectroscopy, TEM, XRD and XPS. Then a
variety of alkynes and organic azides are well suited for this “click”
reaction with the CuNP-3 as the catalyst, leading to the regioselective
formation of various 1,4-disubstituted 1,2,3-triazoles (including
“click”-triazole functionalized moxestrol and “click”-triazole
functionalized 7-(propargyloxy)-coumarin) in high isolated yields. The
CuNP-3 has also been successfully applied in the reduction of 4-
nitrophenol with excellent catalytic activity. In addition, we are trying
to immobilize our CuNPs on magnetic Fe O for the recyclability of
nitrophenol, a highly hazardous and poisonous industrial pollutants, to
4
-aminophenol. As a industrial intermediate, 4-aminophenol has been
widely used in hair dying agents, anticorrosion lubricants and
antipyretic and analgesic medicine. thus efficient CuNP-3 catalysis of
4
-nitrophenol reduction is of great significance. Besides, it is very
convenient to monitor the progress of 4-nitrophenol reduction by UV-
vis. spectra, due to the distinct peak of 4-nitrophenol and 4-
aminophenol are at 400 and 300 nm, respectively.[13] The other key
sign of the reaction progress is the disappearance of the yellow color of
the solution. The 4-nitrophenol reduction has been carried out in the
3
4
graphene quantum dots stabilized CuNPs. Such work will be published

in the future. The graphene quantum dots stabilized CuNPs show wide
potential applications in cell image, sensor, and catalysis fields.
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. Preparation of CuNPs
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First, 1 mL(0.29 g/L) GQDs are dissolved in 2 mL of deionized water
in a Schlenk flask, and the solution is stirred for 10 mins at 0 ℃. Then
(1 x10-2 mmol in 1 mL water is added to
a colorless solution of NaBH
the solution of GQDs. And the solution is stirred for 30 mins. A 1-mL
aqueous solution containing 1.0 ×10-3 mmol CuSO
is added dropwise,
4
4
provoking the formation of yellow color, corresponding to the
reduction of the cation to the zero-valent metal and CuNP-3 formation.
The CuNP-3 were kept in aqueous solution for characterization and
used as the catalysts. Other CuNPs were synthesized in the same
method.
3
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2
. The general procedure of the click reaction
All reactions were performed on a 0.50 mmol scale of triazole. The
phenylacetylene (0.5 mmol), benzyl azide (0.6 mmol), CuNPs-3
(
0.05% mmol) and 2 mL of H
equipped with stirrer. The resulting mixture was stirred for 24 h at
0 ℃. After cooling to room temperature, and extracted with acetic
ether (3 × 10 mL). The combined organic phases were washed with
brine (2 × 5mL), dried over anhydrous MgSO and concentrated under
2
O were taken into a round bottom flask
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desired 3a as light yellow solid (95.1% yield).
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3
. Catalysis of 4-nitrophenol reduction
An aqueous solution (2.5 mL) containing 4-nitrophenol (2.5 × 10-4
mmol) and NaBH
(2.5 × 10-2 mmol) is prepared in a standard quartz
4
[6] (a) W. Chen, D. Li, L.Tian, W. Xiang, T. Wang, W. Hu, Y. Hu, S. Chen, J. Chen,
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Acknowledgment
[
2
Financial support from the National Natural Science Foundation of
China (No. 21805166), the 111 Project of Hubei Province (No. 2018-
[
[
(
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1
9-1), China Three Gorges University is gratefully acknowledged.
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Appendix A. Supplementary data
Supplementary data to this article can be found online
at
2
1215-21219; (i) N. Li, W. Chen, J. Shen, S. Chen, X. Liu, Inorg. Chim. Acta. 496
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1
2
3
. Graphene quantum dots stabilized copper nanoparticles has been synthesized in water
. The as-synthesized CuNPs shows high catalytic activity in the “click” reaction
. The as-synthesized CuNPs show high catalytic activity in the reduction of 4-nitrophenol
Here we report the synthesis of
graphene quantum dots (GQDs)
stabilized copper nanoparticles in
Copper Nanoparticles
OH
OH
Yu Huang, Weifeng Chen,Jialu
Shen, You Wu, Yanlan Wang, and
Xiang Liu*
Starch + water
water.
The
as-synthesized
NH2
NO2
nanoparticles show high catalytic
activity in the “click” reaction and
reduction of 4-nitrophenol
A
A
A
A
A
A
R1
NaBH4
H2O
+
CuSO4.5H2O
CuNPs
A
R2
N
Page No. 1– Page No.5
A
N
N
A
A
A
A
GQDs A
Synthesis of Graphene Quantum
Dots Stabilized CuNPs and Their
Applications in CuAAC Reaction
and 4-Nitrophenol Reduction
R1
+
R2 N3
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Conflicts of interest
All the authors confirm that there are no conflicts to declare
Yu Huang, 1468206916@qq.com
Weifeng Chen, 504901529@qq.com
Jialu Shen, 1005620815@qq.com
Yanlan Wang, wangyanlan@lcu.edu.cn
Xiang Liu, xiang.liu@ctgu.edu.cn