Catalytic performance of Cu(II)-supported graphene quantum dots modified NiFe2O4 as a proficient nano-catalyst in the synthesis of 1,2,3-triazoles

Article abstract of DOI:10.1007/s00706-020-02652-z

Abstract: NiFe₂O₄ nanoparticles are modified by graphene quantum dots (GQDs) and utilized to stabilize the Cu(II) nanoparticles as a novel magnetically retrievable catalytic system (Cu(II)/GQDs/NiFe₂O₄) for gree

Full text of DOI:10.1007/s00706-020-02652-z

Monatshefte für Chemie - Chemical Monthly
https://doi.org/10.1007/s00706-020-02652-z
ORIGINAL PAPER
Catalytic performance of Cu(II)‑supported graphene quantum dots
modifed NiFe2O4 as a profcient nano‑catalyst in the synthesis
of 1,2,3‑triazoles
Razieh Deilam1 · Farid Moeinpour1 · Fatemeh S. Mohseni‑Shahri1
Received: 14 February 2020 / Accepted: 18 June 2020
© Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract
NiFe2O4 nanoparticles are modifed by graphene quantum dots (GQDs) and utilized to stabilize the Cu(II) nanoparticles as a
novel magnetically retrievable catalytic system (Cu(II)/GQDs/NiFe2O4) for green formation of 1,4-disubstituted 1,2,3-tria-
zoles by means of alkyne–aryl azide cycloaddition. The prepared catalyst can be isolated assisted by an outer magnet and
recovered for fve courses without signifcant reduction in its efciency. The as-prepared magnetic heterogeneous nanocom-
posite was characterized by UV–Vis, FT-IR, XRD, EDS, VSM, TEM, and ICP. Performing the reactions in environmentally
friendly and afordable conditions (water), the low catalyst percentage, high yield of products, short reaction times, and easy
workup are the merits of this protocol.
Graphic abstract
N
N
Cu(II)/GQDs/NiFe2O4
H2O, 60 °C
1
1
+
R
R
N
R
3
N
R
Keywords NiFe2O4 · Graphene quantum dots · 1,2,3-Triazole · Nano-catalyst
Introduction
remain a major challenging task. To achieve greater spe-
cifc area and more efective sites, nano-catalysts should be
functionalized by activated moieties [7–9]. It is proved that
the modifcation of the nano-catalyst with GQDs avoids
the aggregation of fne particles and, therefore, enhances
the active specifc area for an efective catalytically reac-
tion [8, 9]. Magnetic nanoparticles have been the focus
of attention to researchers for consecutive years [10].
Many works have been published and also indicated the
importance of magnetic catalysts [11–14]. Among them,
NiFe2O4 has been getting more consideration, owing to
its strong coercive power, appropriate magnetic induc-
tion, and high permanence [15]. Several researches verify
the outlooks of using NiFe2O4 as an efective nano-cat-
alyst [16–19]. The immobilization of nano-NiFe2O4 on
GQDs will lead to a multi-purpose nano-scafold for ef-
cient catalytic activity [20]. The cycloaddition reaction
between alkynes and azides presented by Huisgen [21].
Graphene quantum dots (GQDs) are the zero-dimension
nano-graphenes with special characteristics like small
size, chemical inertness, photoluminescence, ease to be
functionalized with biomolecules, and biocompatibility
have received a lot of attention in the nanotechnology
researches [1–3]. Nevertheless, the diverse uses of GQD,
little consideration has been given for applying GQD as
solid support or catalyst in the reactions [4–6]. Preparation
of high-performing nano-catalysts for organic reactions is
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s00706-020-02652-z) contains
supplementary material, which is available to authorized users.
* Farid Moeinpour
fmoeinpour@iauba.ac.ir
1
Department of Chemistry, Bandar Abbas Branch, Islamic
Azad University, 7915893144 Bandar Abbas, Iran
Vol.:(0123456789)
1 3

R. Deilam et al.
This reaction without catalyst usually generates two iso-
meric triazoles (1,4- and 1,5-), making it unsuitable for
organic preparations. In 2002, the application of copper to
the reaction under mild conditions was described [22–24].
Lately, this procedure has been developed as a prevalent
way for preparation of triazoles by diverse catalysts such
as copper(II) acetate [25], nano-CuO [26], silica/nano-Cu
[27], nanomagnetic/Cu [28], Cu nanoparticles immobi-
lized on modifed magnetic zeolite [14], and copper(II)
porphyrin graphene oxide [29]. Nevertheless, a large
number of these procedures have impediments that must
be considered. Therefore, the application of newer and
greener approaches is remaining necessary. Herein, the
preparation of Cu(II)/GQDs/NiFe2O4 by way of an easy
co-sedimentation of NiFe2O4 nanoparticles on GQDs and
its identifcation by diverse methods are discussed. The
catalyst synthesis process is illustrated in Scheme 1. Upon
full identifcation, the catalyst performance was investi-
gated in preparation of 1,4-disubstituted 1,2,3-triazole
derivatives. The overall reaction is shown in Scheme 2.
Scheme 1
Scheme 2
1 3

Catalytic performance of Cu(II)‑supported graphene quantum dots modifed NiFe2O4 as…
the proper fuorescence emission peaks were found at 454,
Result and discussion
463, and 469 nm respectively. The emission peaks indicate
a gentle red shift with a raising in the excitation wavelengths
(360–400 nm). It has been observed that the color of the
GQDs aqueous solution is weak yellow under visible light,
but when excited by UV light at 365 nm, it seems blue, as
indicated in the Fig. 1b. Changes in fuorescence intensity
after the synthesis of GQDs/NiFe2O4 were also examined.
The fluorescence spectra of GQDs/NiFe2O4, excited at
360, 380, and 400 nm is indicated in Fig. 2. The fuores-
cence emission peaks were found at 486, 483, and 480 nm,
respectively. It has been found that with increasing excita-
tion wavelengths, a slight blue shift is observed in emission
peaks. This diferentiation in the fuorescence properties
in comparison to the graphene quantum dots demonstrate
the change in the chemical surface of the GQDs/NiFe2O4
implying a probable linkage of graphene quantum dots on
the nickel ferrite nanoparticles, leading to a change in the
surface characteristics of graphene quantum dots.
The catalyst (Cu(II)/GQDs/NiFe2O4) was synthesized as
specifed by the procedure outlined in Scheme 1, by means
of GQDs and NiFe2O4 nanoparticles produced in accord
with literature [6, 15, 20, 30]. To verify synthesis of the
nano-catalyst, it was completely identifed using diverse
methods comprising UV–Vis and fuorescence spectros-
copy, FT-IR spectroscopy, XRD, EDS, TEM, VSM, and
ICP spectroscopy.
The light-conducting characteristics of the prepared
graphene quantum dots were examined by UV–Vis and
fuorescence spectroscopy. The absorbing spectrum of gra-
phene quantum dots does not give any peak as illustrated in
Fig. 1a. The fuorescence spectra of graphene quantum dots
could be observed in Fig. 1b. The graphene quantum dots
were excited at wavelengths of 360, 380, and 400 nm and
FT-IR spectroscopy was accomplished to validate the
exterior framework of the nano-catalyst. The FT-IR spectra
of NiFe2O4 and Cu(II)/GQDs/NiFe2O4 have been displayed
in Fig. 3. The wide peak at 3362.97 cm−1 is assigned to the
hydroxyl (O–H) groups on the basal plane of GQDs and
also showing the absorption of water by the Cu(II)/GQDs/
NiFe2O4. The bands located at 2981 cm−1 and 1450 cm−1
are related to the C–H bond vibrational stretching from C–H
bonds on the basal plan of GQDs and remaining citric acid,
implying the partial citric acid carbonization [31]. The peak
located at 1001.35 cm−1 is related to the vibrational stretch-
ing of the C–O–C bond. The peaks located at 1415.34 and
1594.81 cm−1 would be the result of skeletal vibrations of
aromatic rings in graphene quantum dots [32]. The pres-
ence of NiFe2O4 is validated by absorption bands located
at 550.64 and 685.24 cm−1, which are correlated to Ni–O
and Fe–O bonds vibrations, respectively [33]. The outcomes
Fig. 1 a UV–Vis absorbance spectrum of GQDs. b Fluorescence
spectra of GQDs. Inset indicates images of GQDs solution taken
under visible light (weak yellow) and 365 nm excitation (blue) (color
fgure online)
Fig. 2 Fluorescence spectra of Cu(II)/GQDs/NiFe2O4
1 3

R. Deilam et al.
and low crystallization degree of graphene quantum dots in
GQDs/NiFe2O4 [15, 34].
The EDS was employed as an infuential method to iden-
tify the chemical constitution of the produced nano-catalyst.
The EDS analysis verifes the existence of envisaged ele-
ments comprising nickel, iron, oxygen, carbon, and copper
in the catalyst structure (Fig. 5).
The morphology and structural characteristics of the syn-
thesized nano-catalyst were observed under TEM technique
(Fig. 6). It is revealed that the darker region in Cu(II)/GQDs/
NiFe2O4 image, is related to agglomeration of NiFe2O4
nanoparticles on GQDs. Also, the TEM micrograph of
the nano-catalyst indicates that the mean sizes of Cu(II)/
GQDs/NiFe2O4 nanoparticles are approximately not more
than 40 nm. The specifed area of the Cu(II)/GQDs/NiFe2O4
catalyst been tested by BET and was 421.2 m2/g.
The magnetic characteristic of Cu(II)/GQDs/NiFe2O4 was
studied by VSM. As evidenced in Fig. 7, the value of the sat-
uration magnetization of Cu(II)/GQDs/NiFe2O4 (60.82 emu
g−1), almost equal to Fe3O4 nanoparticles (61.60 emu g−1)
which indicates that the nano-catalyst has magnetic proper-
ties and their magnetic characteristics are so high that they
could be isolated by a typical magnet.
Fig. 3 FT-IR spectra of a NiFe2O4 and b Cu(II)/GQDs/NiFe2O4
of this analysis confrm successful synthesis of magnetic
nano-catalyst.
The quantity of Cu loading onto the nano-catalyst was
determined by the ICP technique which was obtained to be
0.94 mmol g−1.
X-ray diffraction technique was employed to acquire
information about the crystallinity of the nano-catalyst.
XRD pattern of GQDs/NiFe2O4 was displayed in Fig. 4.
The GQDs/NiFe2O4 difraction pattern was agreed well
with the standard NiFe2O4 (JCPDS 10-0325) exhibits the
important difraction lines at 2θ = 17.15°, 30.59°, 35.76°,
37.30°, 43.43°, 53.84°, 57.34°, and 63.01°, which may be
attributed the (220), (311), (222), (400), (422), (511), and
(440) planes of NiFe2O4, respectively. The difraction peak
of graphene quantum dots (004) (JCPDS 26-1080) is not
recognizable, may have been due to their high dispersals
After validating the successful synthesis of nano-catalyst
by various techniques, its catalytic capability was examined
in the synthesis of 1,2,3-triazoles. To achieve this goal,
4-nitrophenyl azide and phenylacetylene were used as model
substrates for optimizing the reaction elements including
solvent, nano-catalyst amount, and temperature. At the
beginning, the above reaction was also conducted without
and in the presence of various quantities of the nano-catalyst
(Table 1). The outcomes revealed that the reaction did not
progress in the absence of nano-catalyst in some polar and
Fig. 4 XRD pattern of Cu(II)/
GQDs/NiFe2O4
1 3

Catalytic performance of Cu(II)‑supported graphene quantum dots modifed NiFe2O4 as…
Fig. 5 EDS pattern of Cu(II)/GQDs/NiFe2O4
Fig. 7 Magnetization curve of Cu(II)/GQDs/NiFe2O4
Fig. 6 TEM image of Cu(II)/GQDs/NiFe2O4
progress was detected in the model reaction when apply-
ing the other components of nano-catalyst in the absence
of copper, verifying that the existence of copper is vital
for catalyzing the reaction. Also, the model reaction was
carried out using copper(II) acetate (Cu(OAc)2) for 1 h at
60 °C, 1-(4-nitrophenyl)-4-phenyl-1H-1,2,3-triazole was
obtained in 21% isolated yield (entry 20). The result shows
that Cu(OAc)2 displayed poor activity under optimal condi-
tions, in contrast to those with Cu(II)/GQDs/NiFe2O4.
After creating optimal reaction conditions, Cu(II)/GQDs/
NiFe2O4 the range of the reaction was expanded to diverse
azides and various terminal alkynes. In accord with the out-
comes presented in Table 2, the electronic efects did not
have extraordinary afection on outcome of the reaction, thus
non‐polar solvents and solvent-free state, even after 24 h
(entries 1–6). Enhancing the nano-catalyst dosage to 10 mg
raised the reaction efficiency (entries 7–14). Moreover,
the reaction yield in polar solvents was better than those
of non-polar solvents. Lastly, the greatest efciency was
achieved when the model reaction was performed in a H2O
in the presence of 10 mg of nano-catalyst at 60 °C (entry
15). To illustrate the role of copper in the reaction progress,
the function of other components of the nano-catalyst like
NiFe2O4, GQDs, and GQDs/NiFe2O4 was also examined
in the reaction under optimal conditions. The outcomes
are displayed in Table 1 (entries 17–19). As illustrated, no
1 3

R. Deilam et al.
Table 1 Optimization of solvent, temperature, and nano-catalyst dosage
Entry
Condition
Catalyst /mg, mol%
Temp. /°C
Time /h
Yield /%a
TONb
TOFc
1
2
3
4
5
6
7
8
9
H2O
MeOH
EtOH
–
–
–
–
–
–
rt
rt
rt
rt
rt
rt
rt
rt
rt
24
24
24
24
24
24
5
Trace
Trace
Trace
Trace
Trace
Trace
12
–
–
–
–
–
–
–
–
–
–
–
–
5.11
6.38
–
n-Hexane
Solvent-free
H2O/EtOH
MeOH (Cu(II)/GQDs/NiFe2O4) 5.00, 0.47
EtOH (Cu(II)/GQDs/NiFe2O4)
25.53
31.91
–
5.00, 0.47
5.00, 0.47
5
5
15
Trace
n-Hexane (Cu(II)/GQDs/
NiFe2O4)
10
11
Solvent-free (Cu(II)/GQDs/
5.00, 0.47
5.00, 0.47
rt
rt
5
5
Trace
18
–
–
NiFe2O4)
H2O/EtOH (Cu(II)/GQDs/
38.30
7.66
NiFe2O4)
12
13
14
15
16
17
18
19
20
H2O (Cu(II)/GQDs/NiFe2O4)
H2O (Cu(II)/GQDs/NiFe2O4)
H2O (Cu(II)/GQDs/NiFe2O4)
H2O (Cu(II)/GQDs/NiFe2O4)
H2O (Cu(II)/GQDs/NiFe2O4)
H2O (NiFe2O4)
H2O (GQDs)
H2O (GQDs/NiFe2O4)
Cu(OAc)2
5.00, 0.47
rt
5
30
40
60
98
63.83
42.55
63.83
104.26
104.26
–
12.77
17.02
25.53
417.02
417.02
–
10.00, 0.94
10.00, 0.94
10.00, 0.94
10.00, 0.94
10.00, 0.94
10.00, 0.94
10.00, 0.94
10.00, 0.94
40
50
60
80
60
60
60
60
2.5
2.5
0.25
0.25
1.0
1.0
1.0
1.0
98
None
None
None
21
–
–
–
–
22.34
22.34
aOn the basis of isolated yield
bTurnover number
cTurnover frequency=TON/time
all aryl azides with electron-withdrawing or electron-releas-
ing groups provided similar yields (7–28 min). Benzyl azide
in comparison to phenyl azides needed shorter time for the
reaction (entries 13–15). It seems that the greater electron‐
releasing efects of the benzyl group (Ph-CH2), compared
to the phenyl group, increase the electron density on nitro-
gen atoms in benzyl azides and enhance their tendency to
attack phenyl acetylene. Each of the aromatic and aliphatic
terminal acetylenes produced the related 1,2,3-triazoles in
excellent efciencies.
to eliminate remained product, dried and reapplied in subse-
quent reactions. The outcomes revealed that the nano-cata-
lyst could be successively retrieved without any considerable
reduction in its performance (Fig. 8).
To explore the leaking of copper, ICP study of the
retrieved catalyst was additionally performed. In accord
with the acquired outcomes, no considerable reduction
was monitored in the Cu quantity. The Cu amount in the
new nano-catalyst and the recovered one was 0.94 and
0.91 mmol g−1, respectively, which revealed the amount of
leached Cu for this nano-catalyst is very slight. Transmission
electron microscopy of the recovered Cu(II)/GQDs/NiFe2O4
catalyst indicated in Fig. 9. From the obtained TEM micro-
graph obviously exhibited the fresh and used form of catalyst
structure approximately similar. Thus, emphasizing no con-
siderable changes happened during the course of reaction.
To investigate the heterogeneous character of the catalytic
process, the hot fltration examination for the model reac-
tion in attending Cu(II)/GQDs/NiFe2O4 was studied. The
model reaction was ceased after half the required reaction
time and the nano-catalyst was fully isolated with the aid of
a magnet and allowed the reaction to progress for further
time (30 min). The product generation was not detected as
In accord with literature [35, 36], a plausible catalytic
mechanism for the preparation of 1,2,3-triazoles by Cu(II)/
GQDs/NiFe2O4 is shown in Scheme 3. At frst, alkyne is
coordinated to Cu of the nano-catalyst. This interaction
speeds up activation of the C–H bond and thereby facilitates
the copper–alkylidine complex formation. Next step includes
reaction of aryl azide with the Cu–alkylidine intermediate,
accompanied by intramolecular cyclization to generate the
fve-membered triazole ring.
The reusability of the catalyst (Cu(II)/GQDs/NiFe2O4)
was examined in the sample reaction. For this goal, upon
termination of the reaction, the nano-catalyst was separated
with the aid of a magnet and washed with acetone and water
1 3

Catalytic performance of Cu(II)‑supported graphene quantum dots modifed NiFe2O4 as…
Table 2 Synthesis of
1,2,3-triazoles 3a–3o using
Cu(II)/GQDs/NiFe2O4 as
catalysta
Entry
R
R1
Productb
Time /min
Yield /%c
Melting point /°C
Found
Reported
1
2
3
4
5
6
7
8
Ph
Ph
Ph
Ph
Ph
Ph
Ph
CH2OH
CH2OH
CH2OH
CH2OH
CH2OH
CH2Br
Ph
3a
3b
3c
3d
3e
3f
3 g
3 h
3i
3j
3k
3l
3m
3n
3o
20
15
20
16
23
15
15
25
15
25
20
28
8
98
98
92
95
95
98
91
93
89
88
94
90
96
92
97
96–97
97–98 [37]
254 [37]
232 [37]
174–176 [37]
228 [37]
168 [37]
4-NO2Ph
4-BrPh
4-CH3Ph
4-ClPh
4-CH3OPh
Ph
4-NO2Ph
4-BrPh
4-CH3Ph
4-ClPh
4-NO2Ph
PhCH2
PhCH2
PhCH2
254–255
232–233
174–176
227–229
168
116–117
200–202
134–135
124–125
144–145
151–153
129–131
75–76
116–118 [38]
201–202 [38]
135–137 [39]
124–125 [40]
144–145 [41]
152–154 [42]
129–131 [40]
75–77 [41]
124–126 [42]
9
10
11
12
13
14
15
CH2OH
CH2Br
7
12
123–125
aReaction conditions: azides 1a–1 g (1.1 mmol), terminal alkynes 2a–2c (1 mmol), 0.01 g Cu(II)/GQDs/
NiFe2O4 at 60 °C in H2O
bKnown products identifed by comparison of their melting points; some selected compounds identifed by
1H NMR and 13C NMR
cIsolated yields
Scheme 2
1 3

R. Deilam et al.
adequate catalytic performance quickly under environmen-
tally friendly and afordable conditions (water).
Conclusions
We have successfully synthesized a copper heterogeneous
catalyst on graphene quantum dots/NiFe2O4 nanomagnetic
particles as a very stable and recoverable nano-catalyst for
the green production of 1,2,3-triazoles derivatives rapidly
in aqueous media. The proposed reaction, in which the
designed Cu(II)/GQDs/NiFe2O4 as a recoverable catalyst,
consistent with the principles of green chemistry owing to
the following properties: no toxicity, great durability, recov-
ery capability, shorter times of reaction, aqueous medium,
and excellent products yields. Above all others, the nano-
catalyst could be recovered fve runs without any failure in
its productivity. So, the nanomagnetic heterogeneous cata-
lyst is might be useful in related industries.
Fig. 8 Reusability of Cu(II)/GQDs/NiFe2O4 in the model reaction
Experimental
Citric acid, sodium hydroxide, nickel nitrate, Fe(III) nitrate,
and Cu(II) acetate were purchased from Sigma. UV–Vis
absorption investigations were conducted by Hach DR
6000 UV–visible spectrophotometer. Fluorescence exami-
nations were done on Jasco FP-6200 spectrofuorophotom-
eter (Hitachi Japan). The phase crystallinity of the prepared
nano-catalyst was studied by a difractometer at wavelength
of 1.540 Å (Philips Company). Transmission electron
microscopy (TEM) picture was captured by means of Zeiss
electron microscope, LEO 912AB (120 kV), Germany. Fou-
rier transform infrared (FT-IR) spectra were recorded on
a Bruker model 470 spectrophotometer. Magnetic charac-
teristics were registered on a vibrating sample magnetom-
eter apparatus (VSM, LDJ9600) at environment tempera-
ture. EDS spectroscopy study was conducted with 133 eV
resolution (model 7353, Oxford Instruments, UK). Copper
determination was carried out by inductively coupled plasma
(ICP) technique on a Varian VISTA‐PRO. NMR spectra
were registered in CDCl3 on a Bruker Advance 300 MHz
Fig. 9 Used Cu(II)/GQDs/NiFe2O4 TEM image
monitored by TLC which proves the nano-catalyst is hetero-
geneous in character.
To validate the advantage of the present research, appli-
cation of Cu(II)/GQDs/NiFe2O4 in producing of 1,2,3-tria-
zoles derivatives in comparison with other formerly reported
heterogeneous catalysts is presented in Table 3. In accord-
ance with the results, the introduced catalyst indicates more
Table 3 Comparison of Cu(II)/
GQDs/NiFe2O4 nano-catalyst
with other heterogeneous
catalysts in synthesis of
1,2,3-triazole 3a
Entry
Catalyst
Solvent
Temp. /°C
Time /min
Yield /%a
Ref
1
2
3
4
5
6
Cu(II)/hydrotalcite
AgN(CN)2
Cu(PPh3)2NO3
Nano-Cu/SiO2
Cu/magnetic zeolite
Cu(II)/GQDs/NiFe2O4
CH3CN
H2O/EG
Solvent-free
DMSO
EtOH:H2O
H2O
Rt
Rt
Rt
Rt
50
60
360
120
40
25
120
20
86
95
96
97
91
98
[43]
[44]
[45]
[46]
[14]
This study
aIsolated yield
1 3

Catalytic performance of Cu(II)‑supported graphene quantum dots modifed NiFe2O4 as…
instrument. The melting points were measured on an Elec-
trothermal Type 9100 device.
reaction was controlled using TLC (thin layer chromatog-
raphy), whenever the reaction was completed, the reaction
mixture was diluted with ethyl acetate and the nano-catalyst
was isolated with the aid of a magnet, washed with acetone
and then dried on a night to be ready to react again. The
organic layer was dried over anhydrate sodium sulfate and
after that, evaporated to separate the solvent. The remaining
part was recrystallized in ethanol to provide corresponding
triazole derivatives. The products were recognized by their
melting points, 13C NMR and 1H NMR spectroscopy. The
selected spectral data of some synthesized products have
been included in Supplementary Material.
Synthesis of NiFe2O4 nanoparticles
Egg white (60 cm3) was added to 40 cm3 distilled water and
was shaken hard to perfectly mix. Subsequently, 2.9081 g of
nickel nitrate hexahydrate (10 mmol) and 8.0800 g of Fe(III)
nitrate nonahydrate (20 mmol) were dissolved in the above
solution and was stirred hard at ordinary temperature for
2 h. Then, whilst the mixture was agitated, it was warmed to
80 °C until dried. The consequent powder was grinded and
then heated at 700 °C for 3 h [15].
Acknowledgements This work is fnancially assisted by the Islamic
Azad University-Bandar Abbas Branch. The authors are grateful for
that.
Synthesis of graphene quantum dots (GQDs)
GQDs were made from thermally decomposed citric acid
[30]. Concisely, 0.2 g citric acid (1.0 mmol) was melted and
heated at 200° C for 5 min. Then, the subsequent yellowish
liquid was added progressively into 20 cm3 of 0.25 M NaOH
solution. Thereafter, the GQDs solution was dialyzed in a
1 kDa dialysis bag for 24 h (dialysate was exchanged every
8 h) to eliminate the unreacted chemicals. The produced
graphene quantum dot solution was maintained in 4 °C.
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Synthesis of Cu(II)/GQDs/NiFe2O4
GQDs/NiFe2O4 (0.5 g) was dispersed in 25 cm3 acetone
at ordinary temperature for 30 min. Afterwards, 0.018 g
copper(II) acetate (0.1 mmol) was added gently to the fask
comprising GQDs/NiFe2O4 nanocomposite. The consequent
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was added to a solution comprising aryl azide (1.1 mmol),
terminal alkyne (1.0 mmol) in 3 cm3 water under continu-
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