Plasmon–exciton co-driven surface catalyticreaction in
electrochemical G-SERSPeijie Wang,a,b Wen Liu,a,b Weihua Linb and
Mengtao Sunb*
We report the plasmon–exciton co-driven surface catalytic
reactions in the electrochemical G-SERS in the liquid
environments,where the graphene–Ag hybrid nanostructure forms the
substrate for G-SERS. Compared with the traditional
plasmon-drivenchemical reaction in the electrochemical SERS in the
liquid environments, we can see that great advantages of it on
G-SERS canbe clearly demonstrated. G-SERS can be potentially
applied in the surface spectral analysis in electrochemical
environments.Copyright © 2017 John Wiley & Sons, Ltd.
Introduction
Plasmon-driven chemical reaction has been first reported
onsurface-enhanced Raman spectroscopy (SERS) scattering
in2010.[1,2] Since then, it has been attracting a lot of attentions
onthat, which is due to its special advantages.
Plasmon-drivenchemical reactions have been revealed by
surface-enhancedRaman scattering (SERS) spectroscopy, tip-enhanced
Ramanspectroscopy (TERS) in atmosphere, high-vacuum TERS
(HV-TERS),and electrochemical SERS in liquid environment.[3–7]
Furthermore,silver can be the source of the Raman enhancement. For
example,microprobe study of enhanced Raman scattering effect on
WO3/Ag thin films was also reported.[8]
Colomban reviewed the Raman spectroscopy of nanomaterials,in
which the Raman spectra related to disorder, particle size,
andmechanical properties have been discussed in detail.[9]
Recently, plasmon–exciton coupling for co-driven
chemicalreactions has also been reported on the graphene-mediated
SERS,and the advantage of surface-catalytic reaction-co-driven
byplasmon-graphene hybrid has been also revealed, [10–16]
especiallyrevealed by ultrafast transition absorption spectroscopy,
whichdirectly demonstrated ultrafast dynamics of charge
transferbetween exciton and plasmon for the system of exciton
andplasmon hybrid.[10] The plasmon–exciton coupling of
monolayerMoS2–Ag nanoparticles with different sizes for co-driven
chemicalreactions also has been reported, in which advantages of
theplasmon–exciton coupling the for co-driven chemical reactions
isalso physically interpreted.[17]
p-Nitroaniline (PNA), with both nitro (�NO2) and amine
(�NH2)groups, is the best candidate for studying the selectivity
forplasmon-driven chemical reactions under different
environments.Recently, it has been reported that PNA (see Fig.
1(a)) canbe selectively converted to 4,40-diaminoazobenzene (DAAB,
seeFig. 1(b)) on a roughed Ag electrode in an aqueous
environment.[18]
Ding also reported the selective surface catalytic reaction of
PNA toDAAB on the graphene mediated SERS (G-SERS).[14] All of
themdemonstrated that PNA was reduced to DAAB via –NO2 group,not
oxidized to 4,40-dinitroazobenzene (DNAB, see Fig. 1(c)) via�NH2
group, both in the atmosphere and liquid environments.In this
letter, we report the plasmon–exciton co-driven surface
catalytic reactions in the electrochemical G-SERS in the
liquid
environments, where the graphene–Ag hybrid nanostructure
formsthe substrate for G-SERS. Compared with the traditional
plasmon-driven chemical reaction in the electrochemical SERS in the
liquidenvironments, we can see that great advantages of it on
G-SERScan be clearly demonstrated.
Experimental details
The p-nitroaniline (PNA) and DAAB were purchased from
AldrichChemical Co. The powder of graphene quantum dot (GQD)
waspurchased from Nanjing Yoshikura Nano Technology Co. Thediameter
and the thickness are distributed from 0.8–3 μm, and0.8–1.2 nm,
respectively.
The Ag electrode (a single-crystal silver rod of 99.99% purity)
waspolished with emery paper and then was carefully cleaned with
the
* Correspondence to: Mengtao Sun, Beijing Key Laboratory for
Magneto-Photoelectrical Composite and Interface Science, School of
Mathematics andPhysics, University of Science and Technology
Beijing, Beijing 100083, China.E-mail: [email protected]
a The Beijing Key Laboratory for Nano-Photonics and
Nano-Structure, Center forCondensed Matter Physics, Department of
Physics, Capital Normal University,Beijing 100048, China
b Beijing Key Laboratory for Magneto-Photoelectrical Composite
and InterfaceScience, School of Mathematics and Physics, University
of Science andTechnology Beijing, Beijing 100083, China
Figure 1. Molecular structures of PNA (a), DAAB (b), and DNAB
(c).
J. Raman Spectrosc. 2017, 48, 1144–1147 Copyright © 2017 John
Wiley & Sons, Ltd.
Rapid communication
Received: 4 April 2017 Revised: 3 June 2017 Accepted: 5 June
2017 Published online in Wiley Online Library: 18 July 2017
(wileyonlinelibrary.com) DOI 10.1002/jrs.5199
1144
http://orcid.org/0000-0002-8153-2679
Milli-Q water in the ultrasonic bath. Next, the Ag electrode was
putinto the electrochemical cell, in which the solution of 3 M KCl
wasused for roughening the Ag electrode. The double potential
stepswere used to roughen the surface of Ag electrode, by
applyingthe voltage of +0.25 V for 8 s, and then applying the
voltage of�0.35 V. The GQD powder is dissolved in water (0.02
mg/ml), anddrop on the roughened Ag substrate. Last, the electrode
was putinto the electrochemical cell containing the solution of 0.1
MNa2SO4 with 0.02 M PNA.The SERS spectra were measured using the
microprobe Raman
system RH13325 spectrophotometer. The voltages of
workingelectrode were controlled by the electrochemical
instrument
(CHI619B). The samples were excited with 532-nm lasers with
aneffective powder of 0.077 mW, where the 50× objective was
used.
Results and discussion
The SEM images of the roughened Ag substrate without and withGQD
were obtained using a Hitachi S-4800 microscope, see Fig. 2(a)and
(b). In Fig. 1(b), the parts marked with red color
clearlydemonstrate that the roughened Ag electrode is covered
byGQD. Figure 2(c) is the Raman spectrum of GQD, where the 2Dpeak
of GQD cannot be clearly observed, due to the opticalproperties of
GQD.[19]
The Raman spectrum of PNA powder and electrochemicalSERS
spectrum of PNA without potential can be seen fromFig. 3(a); it is
found that profiles of them are the same. Thepotential dependent
electrochemical SERS of PNA can be seenfrom Fig. 3(b). It is found
that from 0 to �0.4 V, the SERS spectraof PNA is the same as the
Raman spectrum of PNA powder,where the vibrational mode at 1282
cm�1 is the –NO2 vibration;while with the further increase of
potential, the SERS spectra ofPNA are significantly different from
the Raman spectrum ofPNA powder, where the vibrational mode of –NO2
is disappearedwhen potentials are from �0.5 to �1.2 V, see Fig.
3(b).Comparing the SERS spectra of PNA at �1.2 V in Fig. 3(b)
withRaman spectrum of DAAB powder, we can clearly see that theSERS
of PNA at �1.2 V were catalyzed to DAAB by plasmon,see Fig. 3(c).
Using the roughened Ag substrate covered withGQD in Fig. 2(b), we
also measured the potential dependentelectrochemical G-SERS of PNA,
see Fig. 3(d), which are the casesof potentials from 0 to �1.2 V.
The advantages of G-SERS for thesurface catalytic reaction is the
PNA can be reduced to DAABeven when the potential is at 0 V, which
is much easier thanthe reduced reaction of PNA to DAAB on SERS
substrate withoutgraphene, by comparing Fig. 3(b) and (d). To study
the influenceof graphene on the SERS measurement using G-SERS
substrate,we also studied the potential dependent SERS of graphene,
seeFig. S1 in Supporting Information, where potentials are from 0to
�1.2 V. We can see that GQD is stable with the changing
ofpotentials. The potential dependent SERS peaks of GQD do
notinfluence the electrochemical G-SERS spectra, which can be
seenfrom Fig. 4, where the Raman peaks of graphene, as
thebackground, is too weak to be observed in the G-SERS spectrumof
PNA.
Figure 4. Compared Raman spectra among DAAB powder, PNA on
G-SERSat �1.2 V, and SERS of graphene at �1.2 V. [Colour figure can
be viewed atwileyonlinelibrary.com]
Figure 5. (a) Cyclic voltammograms of PNA adsorbed on the Ag
substrate without and with modified GQD, and (b) the physical
mechanism of plasmon–exciton co-driven chemical reactions. [Colour
figure can be viewed at wileyonlinelibrary.com]
P. Wang et al.
wileyonlinelibrary.com/journal/jrs Copyright © 2017 John Wiley
& Sons, Ltd. J. Raman Spectrosc. 2017, 48, 1144–1147
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To confirm the advantages of the G-substrate for surface
catalyticreaction, we measured the reduction potential in the
absence ofPNA adsorbed on these two kinds of substrates in Fig.
2(a) and(b). The reduction potential in the absence of PNA adsorbed
onthese two kinds of substrates can be seen from Fig. 5(a), and it
isfound that reduction peak for the roughened Ag substrate is
at�0.45 V; while the reduction peak of GQD covered on theroughened
Ag substrate is shifted to 0 V, see the green dash linewith arrow.
It reveals that the coupling interaction between excitonof GQD and
plasmon of Ag can significantly decrease the reductionpotential in
electrochemical system. Physically, the Fermi level ofGQD-Ag hybrid
can be increased, due to the electron transfer fromGQD to Ag
substrate, comparedwith that of Ag substrate alone, seeFig. 5(b).
By laser radiation, the plasmonic hot electrons can transferto
holes of exciton of graphene, with this way, the kinetic energy
ofhot electrons can be absorbed by graphene, and more
additionaltransferred electrons on the graphene can be carriers.
So, thetransferred hot electrons on graphene are of larger density
of stateand longer lifetime,[10] which can significantly improve
theprobability and efficiency of surface catalytic reactions.
Conclusion
The plasmon–exciton co-driven surface catalytic reactions
inelectrochemical G-SERS were reported, which demonstrate
greatadvantages for plasmon–exciton co-driven chemical reactions
onG-SERS in liquid environments, and which can be
potentiallyapplied in the surface spectral analysis in
electrochemicalenvironments.
Acknowledgements
This work was supported by the National Natural
ScienceFoundation of China (Grant Nos. 11374353, 91436102
and21473115), and Beijing Municipal Science and Technology
Project(No. Z17111000220000).
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Supporting information
Additional Supporting Information may be found online in
thesupporting information tab for this article.
Electrochemical G-SERS
J. Raman Spectrosc. 2017, 48, 1144–1147 Copyright © 2017 John
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