Synthesis of graphene quantum dots stabilized bimetallic AgRh nanoparticles and their applications

Article abstract of DOI:10.1016/j.ica.2019.119031

The design and synthesis of highly efficient and ultrafine bimetallic nanoparticles catalysts is challenging. Here we report the synthesis of AgRh bimetallic nanoparticles (AgRh BNPs) stabilized by graphene quantum dots (GQDs) and their exceptional catalytic activities in the reduction of 4-nitrophenol, 2,4-dinitrophenol and 4-nitrobenzene diazonium tetrafluoroborate and generation of hydroxyl radicals. Construction of AgRh BNPs nanocomposites is accomplished by mixing of GQDs and sodium borohydride, followed by the addition of simple commercial Ag and Rh salt at 0 °C in water. Among them, AgRh BNPs 4 exhibits excellent catalytic performance owing to a positive synergistic effects between the Ag and Rh atoms on GQDs, and its catalytic activity is better than those of both monometallic counterparts.

Full text of DOI:10.1016/j.ica.2019.119031

Accepted Manuscript
Synthesis of Graphene Quantum Dots Stabilized Bimetallic AgRh Nanoparti-
cles and Their Applications
Ning Li, Weifeng Chen, Jialu Shen, Shaona Chen, Xiang Liu
PII:
S0020-1693(19)30761-3
https://doi.org/10.1016/j.ica.2019.119031
119031
DOI:
Article Number:
Reference:
ICA 119031
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
24 May 2019
12 July 2019
20 July 2019
Please cite this article as: N. Li, W. Chen, J. Shen, S. Chen, X. Liu, Synthesis of Graphene Quantum Dots Stabilized
Bimetallic AgRh Nanoparticles and Their Applications, Inorganica Chimica Acta (2019), doi: https://doi.org/
10.1016/j.ica.2019.119031
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Synthesis of Graphene Quantum Dots Stabilized Bimetallic AgRh Nanoparticles
and Their Applications
Ning Li,a# Weifeng Chen,a# Jialu Shen,a Shaona Chen,a and Xiang Liua,b*
aCollege of Materials and Chemical Engineering, Key Laboratory of Inorganic Nonmetallic Crystalline and Energy
Conversion Materials, China Three Gorges University, Yichang, Hubei 443002, China. Email:
xiang.liu@ctgu.edu.cn
bMaterial Analysis and Testing Center, China Three Gorges University, Yichang, Hubei 443002, China.
#These authors are contributed equally to this work and should be considered as co-first authors
Abstract
The design and synthesis of highly efficient and ultrafine bimetallic nanoparticles catalysts is
challenging. Here we report the synthesis of AgRh bimetallic nanoparticles (AgRh BNPs)
stabilized by graphene quantum dots (GQDs) and their exceptional catalytic activities in the
reduction of 4-nitrophenol, 2,4-dinitrophenol and 4-nitrobenzene diazonium tetrafluoroborate and
generation of hydroxyl radicals. Construction of AgRh BNPs nanocomposites is accomplished by
mixing of GQDs and sodium borohydride, followed by the addition of simple commercial Ag and
Rh salt at 0oC in water. Among them, AgRh BNPs 4 exhibits excellent catalytic performance
owing to a positive synergistic effects between the Ag and Rh atoms on GQDs, and its catalytic
activity is better than those of both monometallic counterparts.

Introduction
In the last few decades, bimetallic nanoparticle (BNPs) with novel compositions and well-defined
structures are of particular current interest due to their composition-dependent electronic, optical
and catalytic properties.[1] They have been widely used as efficient heterogeneous or homogeneous
catalysts for a broad range of inorganic and organic reactions,[2] owing to the synergistic effects
between different metal atoms of BNPs often result in remarkable enhancement of the overall
catalytic activity and selectivity by restructuring the average binding energy of the surface of
BNPs, compared with monometallic nanoparticles.[3] As a result, plenty of cost-effective BNPs
catalysts have been developed by dilution of scarce and noble metals using comparatively earth-
abundant metals. AgRh bimetallic nanoparticles has generated enormous excitement because of its
wide applications in the hydrogen absorption,[4] catalysis[5] and oxynitride decomposition.[6] The
AgRh BNPs system has thus been utilized as an effective method to further improve catalytic
activity and selectivity and to reduce the required amount of Rh by alloying with much cheaper
and more abundant Ag, since Rh is extremely scarce and expensive. Although Ag and Rh are
o
immiscible even at 2000 C in bulk form, this problem has been recently solved by reducing the
NPs size to a very few nm.[7] However, the physical and chemical behavior of AgRh BNPs have
been less investigated than other BNPs, therefore, an efficient and simple way to construct AgRh
BNPs is still necessary.
Graphene quantum dots (GQDs) have attracted considerable attention from researchers due to
their low toxicity, biocompatibility and chemical inertness.[8] GQDs, consisting of ultrasmall
fragments of graphene nanosheets, have the excellent chemical and physical properties of
graphene, including high surface area, surface groups and better surface grafting using π-π
conjugation. Therefore, they have been successfully used as efficient catalyst supports for
stabilizing transition metal nanoparticles (TMNPs). For example, AuNPs on GQDs for
electrochemical detection of H2O2 in biological environments,[9] for S. aureus specific gene
detection[10] and for Pb2+ detection.[11] Our laboratory has long term interest in the synthesis of
TMNPs and their application.[12] Hence, in this work, we first report the synthesis of various
graphene quantum dots stabilized AgRh bimetallic nanoparticles and their exceptional catalytic
activity in the reduction of 4-nitrophenol, 2,4-dinitrophenol and 4-nitrobenzene diazonium
Starch + water
A
A
A
A
A
NaBH4
Rh(NO3)3
AgNO3
+
AgRh
A
A
H2O, r.t.
A
A
A
A
A
GQDs A
Figure 1. The synthesis of AgRh BNPs

tetrafluoroborate and generation of hydroxyl radicals. In our study, we used our previously
reported GQDs A (Figure 1) with a narrow size distribution range from 2.25 to 3.50 nm as the
model system for the AgRh BNPs supports.[13] GQDs A were made from only natural polymer
starch and water, and have uniform structure. In addition, A is highly soluble in water, allowing
for stabilizing AgRh BNPs to be conducted in water with great stability. GQDs plays a decisive
role on stabilizing the nanoparticles in a controlled fashion to prevent the aggregation.
Construction of the AgRh BNPs has been conducted here by direct coordination of Ag(I) and
Rh(III) ions onto GQDs followed by NaBH4 reduction in water. The alloyed nano-structure with
optimized ratio 1:1 of Rh : Ag compositions is significantly more active as catalysts than Rh and
Ag itself in the reduction of 4-nitrophenol, 2,4-dinitrophenol and 4-nitrobenzene diazonium
tetrafluoroborate and generation of hydroxyl radicals.
Experimental
Chemicals and reagents
All commercial materials were used without further purification, unless indicated. The deionized
water was prepared in the laboratory. The starch, AgNO3, Rh(NO3)3, 4-nitrophenol, 2,4-
diaminophenol, 4-aminobenzene diazonium nium tetrafluoroborate, H2O2 (w%, 30%), methylene
blue and NaBH4 were purchased from Aladdin Reagent Co., Ltd. (Shanghai, China,
http://www.aladdin-e. com/).
Instruments
UV-Vis absorption spectra were recorded on a UV1900 spectrophotometer (Shimadzu, China)
with a 1 cm quartz cell. Transmission electron microscopy (TEM) measurements were performed
on a TECNAI F-20 electron microscope (JEOL 2100F, Netherlands) at an accelerating voltage of
200 kV. Surface analysis by XPS was performed in a Thermo SCIENTIFIC ESCALAB 250Xi
(ThermoFischer, USA) system spectrometer in an ultra-high vacuum (UHV) chamber.
Preparation of the GQDs
GQDs were synthesized from only commercial natural polymer starch and water using our
previously reported method.[13] The starch of 0.3g was firstly dispersed in 25 mL deionized water
and stirred at 60℃ for 15 min. After it is dissolved, the solution was immediately poured into a
100 mL Teflon lined stainless autoclave, which was then heated in an oven at 180 ℃ for 8 h. Then,
the autoclave was taken out to be cooled freely. The final brown product was transferred into
centrifugal tubes, and centrifuged at 10000 r/min for 30 min to separate out the precipitate. The
pale yellow liquid which was obtained finally was the solution of graphene quantum dots (GQDs)：

0.31 g/L.
The preparation of AgRh BNPs 4 as a general procedure
First, 1 mL(0.31 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 oC. Then a colorless solution of NaBH4 (5 x10-3 mmol in 1 mL
water is added to the solution of GQDs. And the solution is stirred for 30 mins. A 1-mL aqueous
solution containing 1.25×10-4 mmol AgNO3 and 1.25×10-4 mmol RhNO3 is added dropwise,
provoking a color change to brownish yellow (Figure S4) due to the reduction of the cation to the
zero-valent metal and formation of AgRh BNPs 4. The 4 were kept in aqueous solution for
characterization and their used as the catalysts. AgRh BNPs 3 (Figure S3) and 5 (Figure S5) were
synthesized in the same method.
Catalysis of 4-nitrophenol reduction
An aqueous solution (2.5 mL) containing 4-nitrophenol (0.09 mmol) and NaBH4 (9 mmol) is
prepared in a standard quartz cuvette (3 mL, path length: 1 cm). The TMNPs catalyst (5 mol%) is
injected into this solution, and the reaction progress is detected by UV-vis. spectroscopic analysis
every min at 22 oC. (Figure S6-S19)
Generation of Hydroxyl Radicals
An aqueous solution containing 3 mL of AgNPs (1.5x10-4 mmol) and methylene blue (3.375x10-5
mmol) is prepared in a standard quartz cuvette (3 mL, path length: 1 cm). The H2O2 (0.1 eq -10 eq)
is injected into this solution, and the reaction progress is detected by UV-vis. spectroscopic
analysis every min at 22 oC. (Figure S20-S27)
Results and Discussion
Synthesis of the AgNPs, RhNPs and AgRh BNPs
First, as a comparative experiment, Ag and Rh monometallic nanoparticles (1 and 2) were
conducted by adding simple commercial silver nitrate and rhodium nitrate into a solution of as-
o
synthesized GQDs and sodium borohydride at 0 C, respectively. A color change to orange
(AgNPs) due to the reduction of the cation to the zero-valent metal and formation of the AgNPs
(Figure 1). The characteristic peak at 400 nm of AgNP, with a size of 14.65 nm, has also been
observed in UV-vis spectra (Table 1 and Figure 2a), while RhNPs (2.14 nm) appear by TEM
(vide infra) to be too small to be plasmonic (Figure 2b). Then, we further synthesized AgRh
BNPs 3-5 by dilution of Rh with Ag that altered the Ag to Rh molar ratios, for further increasing
the catalytic efficiency and selectivity and to reduce the required amount of Rh.

(a)
(b)
(c)
(d)
Figure 2. TEM images of AgNPs (a), Rh NPs(b), AgRh2 NPs (c) and Ag2Rh NPs (d)
(a)
(b)
Figure 3. (a) TEM image of AgRh NPs; (b) HRTEM image of AgRh NPs.
The synthesis of GQDs-stabilized AgRh NPs 3-5 were conducted by using as-synthesized GQDs
and sodium borohydride dissolved in water, and followed by the addition of different molar ratios
of Ag and Rh salts(1:2, 1:1 and 2:1), respectively. Typically, the total amounts of AgNO3 and
Rh(NO3)3 is fixed at 2.5×10-4 mmol. Ag (I) and Rh (III) ions were bonded to -COOH and -OH
groups of the GQDs, and the corresponding nanoparticles have a small size and are good catalysts.
However, the characteristic peaks of AgNPs do not appear in the UV-vis spectra of all the AgRh
BNPs 3-5, due to the interference of RhNPs. Figures 2 and 3 exhibit the representative TEM
images of as-obtained AgRh BNPs with different Rh to Ag molar ratios. The monodispersed
RhAg BNPs are homogeneously surrounded and stabilized by GQDs A. As the results of the NP

size distribution histogram, the sizes of AgRh BNPs 4 (4.52 nm) is much bigger than those of
AgRh2 BNPs 3 (2.10 nm) and Ag2Rh BNPs 5 (3.20 nm). Moreover, a representative HRTEM
image of alloyed AgRh BNPs 4 also exhibits the (111) lattice fringe distance of 0.274 nm (Figure
3b), indicating an increase of the interatomic separation distance for alloyed AgRh BNPs.
The X-ray photoelectron spectroscopy (XPS) spectrum of 4 has also been recorded, for further
verifying the exact oxidation states of the constituent metals in BNPs. The Rh 3d core level XPS
spectrum of 4 is shown in Figure 4a. Rh 3d is fitted with two pair of peaks for the 3d5/2 and 3d3/2
doublets, the Rh 3d5/2 and 3d3/2 peak positions at 309.0 and 314.2 eV are assigned to Rh(0),
respectively, whereas peaks at 310.3 and 315.3 eV correspond to 3d5/2 and 3d3/2 of Rh-O,
respectively. It is clear that Rh has been partially oxidized to Rh2O3, due to the small size (4.52
nm) and the free molar energy of formation of Rh2O3 (-39 kcal/mol). In fact, the excellent
catalytic activity of Rh is crucially attributed to Rh2O3 surface of RhNPs.[14] On the other hand, the
Ag 3d5/2 and Ag 3d3/2 peaks at 368.2 and 374.1 eV, with a difference of 5.9 eV, is due to the Ag(0)
in the 4 in Figure 4b, respectively. Thus, Rh has been partially oxidized to Rh2O3 in the 4,
whereas the oxidation of Ag has not been observed.
Rh-O
Rh (0)
(a)
(b)
Figure 4. XPS spectra of (a) Rh 3d, and (b) Ag 3d over AgRh NPs.

Compared catalytic performance of 1-5 in the 4-nitrophenol reduction by NaBH4
The catalytic performance of these AgRh BNPs have been investigated here in the reduction of 4-
nitrophenol, a highly hazardous and poisonous pollutants, by sodium borohydride. The 4-
nitrophenol reduction (eq. 1), which is a classic reaction for the assessment of the metal
nanoparticles’ catalytic properties, is easily monitored by UV-vis spectra due to the absorption
band of 4-nitrophenol at 400 nm and that of 4-aminophenol at 300 nm, respectively.[15] The
reduction of 4-nitrophenol has been carried out in the presence of 5.0 mol% NPs with 100 equiv of
NaBH4 in water at room temperature (Table 1 and Figure S6-S15 in the ESI). The results show
all the reduction reaction did not need induction time (Table 1, entry 1-6). First, pure AgNPs 1 and
RhNPs 2 are used in 5% mmol only providing kapp=2.0× 10-3 and 2.8× 10-3 s-1, respectively
(Table 1, entry 1 and 2). The reaction rate kapp of 4 (3.2×10-3 s-1) is much higher than these of 3
(2.5×10-3 s-1) and 5 (2.9×10-3 s-1) (Table 1, entry 3-5). It is obvious that 4 with molar ratio of
1:1 of Ag and Rh, shows the highest reaction rate among these BNPs (Table 1, entry 4), this is
due to the positive synergistic effect of Ag and Rh atoms. In addition, to study the scope and
generality of the present system, the reduction of 2,4-dinitrophenol (Eq. 2) and 4-nitrobenzene
diazonium tetrafluoroborate (Eq. 3) have also been studied in the presence of 4 under the same
condition as 4-nitrophenol reduction. The results exhibit that 2,4-dinitrophenol (the characteristic
peaks at 360 nm and 440 nm decreases) and 4-nitrobenzene diazonium tetrafluoroborate (the
characteristic peak at 400 nm decreases) have been successfully reduced to 2,4-diaminophenol and
4-aminobenzene diazonium nium tetrafluoroborate with the reaction rate kapp=2.0 × 10-3 and 1.4 ×
10-3 s-1 (Figure S16- S19 in the ESI).
Table 1. 4-Nitrophenol reduction catalyzed by AgRh BNPs in water.a
5% NPs
HO
NO2
HO
NH2
100 eq NaBH4, H2O, r.t.
Eq. 1
TM (2.5×10-
4mmol)
Ag
SPBd(nm
b
Entry
T0 (s)
Kappc×10-3 s-1
De(nm)
NPs
)
1
2
3
4
1
2
3
4
0
0
0
0
2
400
14.65
2.14
2.10
4.52
Rh
2.8
2.5
3.2
/
/
AgRh2
AgRh
/
5
Ag2Rh
5
0
2.9
/
3.20
a5.0 mol % NPs were used in the catalyzed 4-nitrophenol reduction NaBH4 is in excess (100/1). bInduction time.cRate constant.
dSurface plasmon band. eCore size ( TEM) of the NPs.

5% AgRh BNPs
HO
O2N
NO2
HO
NH2
100 eq NaBH4, H2O, r.t.
H2N
Eq. 2
Eq. 3
5% AgRh BNPs
100 eq NaBH4, H2O, r.t.
O2N
N2BF4
H2N
N2BF4
Effect of AgRh BNPs 4-Generated Hydroxyl Radicals.
It is well-known that AgNPs have been demonstrated to catalyze conversion of H2O2 into highy
reactive oxidizing species such as hydroxyl radicals (Figure 5), via the Fenton-like reaction
between AgNPs and H2O2.[16] The generation of hydroxyl radicals can be monitored by the system
of •OH oxidized reaction from methylene blue (MB) to MB-OH in the decrease of absorption of
MB at 666 nm in the UV-vis spectrum. The time dependent UV-vis spectrum of MB during 0.05
mmol/L 4 and 0.25 mmol/L (5 eq) H2O2 is shown in Figure 6a. After 25 mins, the peak of MB
(666 nm) intensity decreases 0.170 is much higher than those of pure AgNPs (0.102) and pure
RhNPs (0.032). It is expected that a drastic absorption change has been observed, verifying that
generation of hydroxyl radicals induced by 4, which is more efficient than pure AgNPs, and
further oxidized MB to MB-OH. Then 4 induced •OH generation has been studied with different
concentration of hydrogen peroxide in Figure 6b (Figure S31-S36 in ESI). From 0.1 to 1.0 eq of
H2O2 (compared to the amount of 4), the generation of hydroxyl radicals presents a linear
relationship. While above 1 eq of H2O2, the production of hydroxyl radicals no longer increased,
indicating the saturation of the reactivity of 4. In addition, MB peak intensity remains unchanged
without 4 or H2O2. It is completely consistent with the proposed Fenton-like reaction between
AgNPs and H2O2 for generating •OH.
Ag+ + OH + H2O
A
A
A
A
A
A
AgRh
A
A
A
A
MB-OH
MB
A
A
H2O2 + H+
Figure 5. Schematic illustration of 4-generated hydroxyl radicals.

(a)
(b)
Figure 6. (a) UV–Visible absorption spectra for the oxidization of methylene blue by 4 and 5 eq
H2O2; (b) Effect of H2O2 on the generation of hydroxyl radicals from samples containing 3 mL of
1.5x10-4 mmol 4, 3.375x10-5 mmol methylene blue and H2O2 at different concentrations.
Conclusion
A green and facile method of synthesis of graphene quantum dots stabilized AgRh bimetallic
nanoparticles has been developed in this work. Construction of pure AgNPs, pure RhNPs and
AgRh BNPs 3-5 nanocomposites are accomplished by mixing GQDs and sodium borohydride,
followed by the addition of simple commercial Ag or Rh salt at 0oC in water. Among them, 4
exhibits excellent catalytic performance in reduction of 4-nitrophenol by NaBH4 and generation of
hydroxyl radicals and further oxidized MB to MB-OH, via a positive synergistic effects between
the Ag and Rh atoms on GQDs, than those of other BNPs and pure Ag or RhNPs. The present
work provides a green and facile method for synthesis of high performance bimetallic NPs.
Acknowledgment
Financial support from the National Natural Science Foundation of China (Grant No. 21805166),

the 111 Project of Hubei Province (Grant No. 2018-19-1) and China Three Gorges University is
gratefully acknowledged.
Reference
[1] (a) Stamenkovic VR, Fowler B, Mun BS, Wang G, Ross PN, Lucas CA, Markovic NM (2007) Improved
oxygen reduction activity on Pt3Ni(111) via increased surface site availability. Science 315(5811):493-497; (b)
Tao F, Grass ME, Zhang Y, Butcher DR, Renzas JR, Liu Z, Chung JY, Mun BS, Salmeron M, Somorjai GA
(2008) Reaction-driven restructuring of Rh-Pd and Pt-Pd core-shell nanoparticles. Science 322(5903):932-934;(c)
Lim B, Jiang M, Camargo PHC, Cho EC, Tao J, Lu X, Zhu Y, Xia Y (2009) Pd-Pt bimetallic nanodendrites with
high activity for oxygen reduction. Science 324(5932):1302-1305; (d) Omori T, Ando K, Okano M, Xu X, Tanaka
Y, Ohnuma I, Kainuma R, Ishida K (2011) Superelastic effect in polycrystalline ferrous alloys. Science 333(6038):
68-71; (e) González E, Arbiol J, Puntes VF (2011) Carving at the nanoscale: sequential galvanic exchange and
kirkendall growth at room temperature. Science 334(6061): 1377-1380.
[2] (a) Liu X, Wang D, Li Y (2012) Synthesis and catalytic properties of bimetallic nanomaterials with various
architectures. Nano Today 7(5):448–466; (b) Peng X, Pan Q, Rempel GL (2008) Bimetallic dendrimer-
encapsulated nanoparticles as catalysts: a review of the research advances. Chem Soc Rev 37:1619–1628; (c)
Gawande MB, Goswami A, Asefa T, Guo H, Biradar AV, Peng D, Zboril R, Varma RS (2015) Core–shell
nanoparticles: synthesis and applications in catalysis and electrocatalysis. Chem Soc Rev 44:7540–7559; (d)
Zhang L, Xie Z, Gong J (2016) Shape-controlled synthesis of Au-Pd bimetallic nanocrystals for catalytic
applications. Chem Soc Rev 45:3916-3934; (e) Astruc D, Lu F, Ruiz J (2005) Nanoparticles as recyclable catalysts:
the frontier between homogeneous and heterogeneous catalysis. Angew Chem Int Ed 44:7852-7872; (f) Liu X,
Hamon JR, (2019) Recent developments in penta-, hexa- and heptadentate Schiff base ligands and their metal
complexes. Coord. Chem. Rev, 389: 94-118; (g) Zhang HJ, Watanabe T, Okumura M, Haruta M, Toshima N
(2012) Catalytically highly active top gold atom on palladium nanocluster. Nat Mater 11:49-52.
[3] (a) Liu JH, Wang AQ, Chi YS, Lin HP, Mou CY (2005) Synergistic effect in an Au-Ag alloy nanocatalyst: CO
Oxidation. J Phys Chem B 109(1):40–43; (b) Wang D, Villa A, Porta F, Prati L, Su D (2008) Bimetallic
gold/palladium catalysts: Correlation between nanostructure and synergistic effects. J Phys Chem C 112(23):8617–
8622; (c) Mott D, Luo J, Njoki PN, Lin Y, Wang L, Zhong CJ (2007) Synergistic activity of gold-platinum alloy
nanoparticle catalysts. Catal Today 122(3-4):378–385; (d) Zhang L, Iyyamperumal R, Yancey DF, Crooks RM,
Henkelman G (2013) Design of Pt-shell nanoparticles with alloy cores for the oxygen reduction reaction. ACS
Nano 7(10):9168–9172.
[4] Yayama T, Ishimoto T, Koyama M (2016) Theoretical investigation of hydrogen absorption properties of
rhodium–silver alloys. J. Alloy. Compd. 662:404-408.
[5] (a) Garcıa S, Zhang L, Piburn GW, Henkelman G, Humphrey SM. (2014) Microwave synthesis of classically
immiscible rhodium–silver and rhodium–gold alloy nanoparticles: Highly active hydrogenation catalysts. ACS
Nano 8(11):11512-11521; (b) Wang C, Ciganda R, Yate L, Moya S, Salmon L, Ruiz J, Astruc D (2017)
RhAg/rGO nanocatalyst: ligand-controlled synthesis and superior catalytic performances for the reduction of 4-
nitrophenol. J Mater Sci 52（16）：9465-9476. (c) Roy A, Debnath B, Sahoo R, Chandrakumar KRS, Ray C,
Jana J, Pal T (2016) Enhanced catalytic activity of Ag/Rh bimetallic nanomaterial: evidence of an ensemble effect.
J Phys Chem C 120(10):5457-5467.
[6] Inderwildi OR, Jenkins SJ, King DA (2007) When adding an unreactive metal enhances catalytic activity: NOx
decomposition over silver–rhodium bimetallic surfaces. Surface Science 601 (17): L103-L108.

[7] (a) Hirakawa K, Toshima N (2003) Ag/Rh bimetallic nanoparticles formed by self-assembly from Ag and Rh
monometallic nanoparticles in solution. Chem Lett 32(1):78–79; (b) Toshima N, Kanemaru M, Shiraishi Y, Koga
Y (2005) Spontaneous formation of core/shell bimetallic nanoparticles: a calorimetric study. J Phys Chem B
109(34):16326–16331; (c) Yang A, Sakata O, Kusada K, Yayama T, Yoshikawa H, Ishimoto T, Koyama M,
Kobayashi H, Kitagawa H (2014) The valence band structure of AgxRh1-x alloy nanoparticles. Appl Phys Lett
105(15):153109; (d) Kusada K, Yamauchi M, Kobayashi H, Kitagawa H, Kubota Y (2010) Hydrogen-storage
properties of solid-solution alloys of immiscible neighboring elements with Pd. J Am Chem Soc 132(45):15896–
15898; (e) Dai Y, Wang Y, Liu B, Yang Y (2015) Metallic nanocatalysis: an accelerating seamless integration
with nanotechnology. Small 11(3):268-289.
[8] (a) Li XM, Rui MC, Song JZ (2015) Carbon and graphene quantum dots for optoelectronic and energy devices:
a review. Adv Funct Mater 25(31): 4929-4947. (b) Bacon M, Bradley SJ, Nann T (2014) Graphene quantum dots.
Part Part Syst Charact 31(4): 415-428; (c) Li LS, Yan X (2010) Colloidal graphene quantum dots. J Phys Chem
Lett 1(17): 2572-2576; (d) Tetsuka H, Asahi R, Nagoya A, Okamoto K, Tajima I, Ohta R, Okamoto A (2012)
Optically tunable amino-functionalized graphene quantum dots. Adv Mater 24(39):5333-5338; (e) Suzuki N,
Wang Y, Elvati P, Qu ZB, Kim K, Jiang S, Baumeister E, .Lee J, Yeom B, Bahng JH, Lee J, Violi A, Kotov NA (
2016) Chiral graphene quantum dots. ACS Nano 10(2)1744−1755; (f) Peng J, Gao W, Gupta BK, Liu Z, R-Aburto
R, Ge L, Song L, Alemany LB, Zhan X, .Gao G, Vithayathil SA, Kaipparettu BA, Marti AA, Hayashi T, Zhu JJ,
Ajayan PM (2012) Graphene quantum dots derived from carbon fibers. Nano Lett 12(2):844-849; (g) Guo CX,
Yang HB, Sheng ZM, Lu ZS, Song QL, Li CM (2010) Layered graphene/quantum dots for photovoltaic devices.
Angew Chem Int Ed 49(17):3014-3017; (h) Ponomarenko LA, Schedin F, Katsnelson MI, Yang R, Hill EW,
Novoselov KS, Geim AK (2008) Chaotic dirac billiard in graphene quantum dots. Science 320(5874): 356-358; (i)
Liu F, Jang MH, Ha HD, Kim JH, Cho YH, Seo TS (2013) Facile synthetic method for pristine graphene quantum
dots and graphene oxide quantum dots: origin of blue and green luminescence. Adv Mater 25(27):3657-3662; (j)
Shen J, ZhuY, Yang X, Li C (2012) Graphene quantum dots: emergent nanolights for bioimaging, sensors,
catalysis and photovoltaic devices. Chem Commun 48: 3686-3699; (k) Yan X, Li Q, Li LS (2012) Formation and
stabilization of palladium nanoparticles on colloidal graphene quantum dots. J Am Chem Soc 134(39):16095−
16098.
[9] Ju J, Chen W (2015) In situ growth of surfactant-free gold nanoparticles on nitrogendoped graphene quantum
dots for electrochemical detection of hydrogen peroxide in biological environments. Anal Chem 87(3):1903−1910.
[10] Shi J, Chan C, Pang Y, Ye W, Tian F, Lyu J, Zhang Y, Yang M, (2015) A fluorescence resonance energy
transfer (FRET) biosensor based on graphene quantum dots (GQDs) and gold nanoparticles (AuNPs) for the
detection of meca gene sequence of staphylococcus aureus. Biosens. Bioelectron. 67:595-600.
[11] Niu X, Zhong Y, Chen R, Wang F, Liu Y, Luo D (2018) A “ turn-on” fluorescence sensor for Pb2+
detection based on graphene quantum dots and gold nanoparticles. Sensor. Actuat. B-Chem 255 (2): 1577-1581
[12] (a) Liu X, Astruc D (2018) Atomically precise copper nanoclusters and their applications. Coord. Chem Rev
359:112-126; (b) Liu X, Astruc D (2017) From galvanic to anti-galvanic synthesis of bimetallic nanoparticles and
applications in catalysis, sensing, and materials science. Adv Mater 29(16):1605305; (c) Liu X, Ruiz J, Astruc D
(2017) Prevention of aerobic oxidation of copper nanoparticles by anti-galvanic alloying: gold versus silver. Chem
Commun 53:11134-11137; (d) Liu X, Gregurec D, Irigoyen J, Martinez A, Moya S, Ciganda R, Hermange P, Ruiz
J, Astruc D (2016) Precise localization of metal nanoparticles in dendrimer nanosnakes or inner periphery and
consequences in catalysis. Nat Commun 7:13152; (e) Liu X, Ruiz J, Astruc D (2018) Compared catalytic
efficiency of click-dendrimer-stabilized late transition metal nanoparticles in 4-nitrophenol reduction. J Inorg
Organomet Polym Mater 28(2):399-406; (f) Astruc D, Deraedt C, Djeda R, Ornelas C, Liu X, Rapakousiou A,
Ruiz J, Wang Y, Wang Q (2018) Dentromers, a family of super dendrimers with specific properties and

applications. Molecules 23(4):966;(g) Chen W, Shen J, Lv G, Li D, Hu Y, Zhou C, Liu X, Dai Z (2019) Green
synthesis of graphene quantum dots from cotton cellulose. ChemistrySelect 4(10):2898-2902; (h) Yan J, Liu G, Li
N, Zhang N, Liu X, (2019) Porphyrin-stabilized Transition Metal Nanoparticles and Their Applications in the
Reduction of 4-Nitrophenol and Generation of Hydroxyl Radicals. Eur. J. Inorg. Chem. 23: 2806-2810; (i) Chen W,
Shen J, Chen S, Yan J, Zhang N, Zheng K., Liu X, (2019) Synthesis of Graphene Quantum Dots Stabilized Gold
Nanoparticles and Its Application, RSC Adv. 9:21215-21219.
[13] Chen W, Li D, Tian L, Xiang W, Wang T, Hu W, Hu Y, Chen S, Chen J, Dai Z (2018) Synthesis of graphene
quantum dots from natural polymer starch for cell imaging. Green Chem 20:4438-4442.
[14] (a) Kim SM, Qadir K, Seo B, Jeong HY, Joo SH, Terasaki O, Park JY (2013) Nature of Rh oxide on Rh
nanoparticles and its effect on the catalytic activity of CO oxidation. Catal Lett 143:1153–1161; (b) Kim S, Qadir
K, Jin S, Reddy AS, Seo B, Mun BS, Joo SH, Park JY (2012) Trend of catalytic activity of CO oxidation on Rh
and Ru nanoparticles: role of surface oxide. Catal Today 185:131–137
[15] (a) Kuroda K, Ishida T, Haruta M (2009) Reduction of 4-nitrophenol to 4-aminophenol over Au nanoparticles
deposited on PMMA. J Mol Catal A: Chem 298(1-2):7–11; (b) Wunder S, Polzer F, Lu Y, Ballauff M (2010)
Kinetic analysis of catalytic reduction of 4-nitrophenol by metallic nanoparticles immobilized in spherical
polyelectrolyte brushes. J Phys Chem C 114(19):8814–8820; (c) Saha S, Pal A, Kundu S, Basu S, Pal T (2010)
Photochemical green synthesis of calcium-alginate-stabilized Ag and Au nanoparticles and their catalytic
application to 4-nitrophenol reduction. Langmuir 26(4):2885–2893; (d) Wang SN, Zhang MC, Zhang WQ (2011)
Yolk-shell catalyst of single Au nanoparticle encapsulated within hollow mesoporous silica microspheres. ACS
Catal. 1(3):207–211; (e) Wunder S, Lu Y, Albrecht M, Ballauff M (2011) Catalytic activity of faceted gold
nanoparticles studied by a model reaction: evidence for substrate-induced surface restructuring. ACS Catal
1(8):908-916; (f) Li J, Liu CY, Liu Y (2012) Au/graphene hydrogel: synthesis, characterization and its use for
catalytic reduction of 4-nitrophenol. J Mater Chem 22:8426–8430; (g) Liu FF, Liu X, Astruc D, Gu HB, (2019)
Dendronized triazolyl-containing ferrocenyl polymers as stabilizers of gold nanoparticles for recyclable two-phase
reduction of 4-nitrophenol. J. Colloid. Interf. Sci. 533:161-170; (h) Liu X, Mu SD, Long YR, Qiu, GR, Ling, Q
J, Gu HB, Lin W, (2019) Gold Nanoparticles Stabilized by 1,2,3-Triazolyl Dendronized Polymers as Highly
Eicient Nanoreactors for the Reduction of 4-Nitrophenol. Catalysis Letters,, 149 (2):544-551; (i) Liu Y, Mu SD,
Liu X, Ling QJ, Hang, CD, Ruiz J, Astruc D, Gu HB, (2018) Ferrocenyl Janus mixed-dendron stars and their
stabilization of Au and Ag nanoparticles. Tetrahedron, 74(37):4777-4789; (j) Zhao L, Ling Q, Liu X, Hang C,
Zhao Q, Liu F, Gu HB, (2018) Multifunctional triazolylferrocenyl Janus dendron: Nanoparticle stabilizer, smart
drug carrier and supramolecular nanoreactor. Appl. Organomet. Chem., 32(2): e4000.
[16] (a) Wang L, Zheng J, Li Y, Yang S, Liu C, Xiao Y, Li J, Cao Z and Yang R (2014) AgNP-DNA@GQDs
hybrid: new approach for sensitive detection of H2O2 and glucose via simultaneous AgNP etching and DNA
cleavage. Anal Chem 86(24):12348-12354. (b) He W, Zhou YT, Wamer WG, Boudreau MD, YinJJ (2012)
Mechanisms of the pH dependent generation of hydroxyl radicals and oxygen induced by Ag nanoparticles.
Biomaterials 33(30):7547-7555; (c) Mohamed RM, Aazam ES (2014) Novel Ag/YVO4 nanoparticles prepared by
a hydrothermal method for photocatalytic degradation of methylene-blue dye. J Ind Eng Chem 20(6): 4377-4381.
1. The design and synthesis of highly efficient and ultrafine bimetallic nanoparticles catalysts is
challenging.
2.
Here we report the synthesis of AgRh bimetallic nanoparticles stabilized by graphene
quantum dots (GQDs)
3. Their exceptional catalytic activities in the reduction of 4-nitrophenol, 2,4-dinitrophenol and 4-
nitrobenzene diazonium tetrafluoroborate and generation of hydroxyl radicals.

OH
OH
Starch + water
NH2
NO2
A
A
A
A
A
A
NaBH4
H2O, r.t.
Rh(NO3)3
AgNO3
+
AgRh
A
A
Ag+ + OH + H2O
A
A
A
A
GQDs A
H2O2 + H+
The design and synthesis of highly efficient and ultrafine bimetallic nanoparticles catalysts is
challenging. Here we report synthesis of graphene quantum dots-stabilized bimetallic AgRh
nanoparticles and their exceptional catalytic activity in the reduction of 4-nitrophenol, 2,4-
dinitrophenol and 4-nitrobenzene diazonium tetrafluoroborate and generation of hydroxyl radicals.