Electrochimica Acta 85 (2012) 42 48

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Electrochimica Acta

jou rn al h om epa ge: www.elsev ier .com

Green ell-nanoco e resorci

Li Zaijun juna School of Cheb School of Fooc National Univd Zhejiang Zany

a r t i c l

Article history:Received 18 February 2012Received in revised form 24 July 2012Accepted 22 August 2012Available online 30 August 2012

Keywords:GrapheneGoldNanocompositSensing materElectrodeposit

The paper described a green and controllable strategy to fabricate well-dispersed graphenegoldnanocomposite lm. To prepare graphenegold nanocomposite lm, graphene and gold nanoparticleswere alternately electrodeposited on the surface of glassy carbon electrode. Since electrochemical tech-nique offers control over reaction parameters and excellent repeatability, the amounts of graphene andgold nanoparticles for the each layer can be pre-determined by controlling concentrations of graphene

1. Introdu

Graphentopic in meffective stthe integratially pavesand electronanocompomicrowavetures of grause of highlposites, maapplied to tFor exampl

CorresponE-mail add

0013-4686/$ http://dx.doi.oe lmialsion

oxide and chlorauric acid. The as-prepared graphenegold nanocomposite lm was characterized byinfrared spectrum, scanning electron microscope, Raman spectrum and X-ray diffraction, and its elec-trocatalytic activity was estimated by Lavirons model. The apparent heterogeneous electron transferrate constant of 37.67 0.19 cm s1 was obtained, indicating fast electron transfer of Fe(CN)64 to theelectrode. Further, the lm was investiaged as sensing materials for synchronously detection of hydro-quinone and resorcinol. When the cencentrations are in the ranges of 1.6 108 to 1.2 104 mol l1for hydroquinone and 1.0 108 to 2 106 mol l1 for resorcinol, differential pulse voltammetric peakcurrent of the sensor linearly increases. The sensitivities of differential pulse voltammetric response are30.5 A M1 cm2 for hydroquinone and 117.83 A M1 cm2 for resorcinol. The detection limits werefound to be 5.2 109 mol l1 for hydroquinone and 2.2 109 mol l1 for resorcinol (S/N = 3). Proposedmethod is simple, sensitive and selective, it has been applied to the determination of hydroquinone andresorcinol in real water samples with a spiked recovery in the range of 96.0103.4%.

2012 Published by Elsevier Ltd.

ction

emetal nanocomposite has become a hot researchaterial science because the hybridization can be anrategy to enhance the functionality of materials, andtion of nanomaterials on graphene nanosheets poten-

a new way to enhance their electronic, chemical,chemical properties [14]. Typically, graphenemetalsite was prepared by chemical [5,6], thermal [7,8],

[9,10] or solvothermal [11,12] reduction of the mix-pheme oxide (GO) and metallic precursor. To avoid they toxic chemicals and improve dispersivity of the com-ny environmentally friendly reducing agents have beenhe fabrication of graphenemetal nanocomposites [13].e, Tian and co-workers reported that -cyclodextrin

ding author. Tel.: +86 5105811863; fax: +86 5105811863.ress: zaijunli@263.net (L. Zaijun).

was empolyed for in situ thermal reduction of graphene oxide andchlorauric acid. In essence, GO, -cyclodextrin and chlorauric acidwere mixed and heated for 2 h in an alkaline solution at 60 C. Theinvestigation demonstrated that -cyclodextrin could reduce chlo-rauric acid to gold nanoparticles in strong alkaline condition [14].To further improve electrochemical performance, some functionalreagents were also introduced into graphenemetal nanocompos-ites. The chemical functionalization of graphene offers the means ofmodifying its already existing fascinating electronic properties. Itcan also result in the formation of covalent and ionic bonds as wellas non-covalent van der Waals interactions, which would improvethe immobilizations of metal particles on the graphene nanosheetsas well as the composites on electrode surface. For example, Sidorovand co-workers developed a method that deposits graphene elec-trostatically from highly-oriented pyrolytic graphite onto Si/SiO2surfaces functionalized with (aminopropyl)trimethoxysilane [15].The method for decorating graphene with noble metal nano-structures may have interesting optical, electronic, and chemicalproperties for the applications in nanoelectronics, sensing, and

see front matter 2012 Published by Elsevier Ltd.rg/10.1016/j.electacta.2012.08.094and controllable strategy to fabricate wmposite lm as sensing materials for thnol with electrodepositiona,, Sun Xiulanb, Xia Qianfanga, Li Ruiyi c, Fang Yinmical and Material Engineering, Jiangnan University, Wuxi 214122, Chinad Science and Technology, Jiangnan University, Wuxi 214122, Chinaersity of Ireland, Maynooth, Co., Kildare, Irelandu Technology Co., Ltd., Hangzhou 310009, China

e i n f o a b s t r a c t/ locate /e lec tac ta

dispersed graphenegolddetection of hydroquinone and

d, Yang Shupinga, Liu Junkanga

L. Zaijun et al. / Electrochimica Acta 85 (2012) 42 48 43

Fig. 1. Photoe n for 1nanocomposit

catalysis. Mfor fabricatgold nanopslide. Becauhybrid lm the lm serysis [16]. Hotime or labo

In recenfor synthesiple, fast, anto GO aqeopotential toimportant ito fabricateHere, GO wwas then imone-step elthat graphethey are moresolve the prepare gragraphene laresult, the cites were relm [2426eration andthe redox reobtained grvery poor d

In the scontrollablenanocompoquinone anallows singwere alternbon electrodoffers excel

2. Experim

2.1. Chemic

Graphitenol (RC) w(Mainland, phate buffe

ol l1

yed wre p, andation

para

trocchemmica

micrde soltag/Agm wcarbBefor5 mubly. Thscann0.1 Vgednde

cryssed fer anarea sed id wa

10 ms of the solution after 0.5 mg ml1 GO mixed with 0.5 m mol l1 chlorauric acid solutioes (c).

oreover, Kim and co-workers reported another methoding the hybrid lm of gold and GO by directly growingarticles on supported thin layers of GO lms on a glassse of the high desorption efciency of analytes from thewithout inducing signicant fragmentation of analytes,ves as successful LDI platform for small-molecule anal-wever, above methods required multiple steps that arer consuming.t years, electrochemical reduction of GO is attractives of the graphenemetal nanocomposite due to its sim-d green nature. Often, metal nanoparticles were addedus solution. The mixture is then reduced at a negative

yield a graphenemetal nanocomposites [17]. Mores the electrochemical method can be directly applied

graphenemetal nanoparticle on the electrode surface.as coated on the electrode surface, and the electrodemersed in a metallic precursor solution to perform

ectrochemical reduction [1821]. The study showedne sheets are not separated by metal particles sincestly located on the surface of graphene lm [22,23]. Toproblem, Luo and co-workers reported a new strategy tophenegold composite lm by cyclic voltammetry. Theyers were spaced by layer of gold nanoparticles. As aonductivity and surface area of graphenegold compos-markably enchanced compared to the pure graphene]. However, the method cannot avoid obvious agglom-

precipitation of GO nanosheets in the electrolyte due toaction between chlorauric acid and GO. This results theaphenegold nanocomposite lm is very coarse withispersion (Fig. 1).tudy, we focus on the development of green and

strategy to fabricate well-dispersed graphenegold

0.01 memploand weChina)puric

2.2. Ap

Elecelectrotrochecrystalelectrocyclic vwith Aplatinuglassy trode. and 0.0acid/do20 mincyclic from unchandried uquartzwere udiametin the immerdistilleHCl forsite lm as sensing materials for the detection of hydro-d resorcinol in real water samples. The techniquele-layer graphene nanosheet and gold nanoparticlesately electrodeposited on surface of the glassy car-e. The as-prepared graphenegold nanocomposite lmlent electrocatalytic activity.

ental

als

, chlorauric acid, hydroquinone (HQ) and resorci-ere obtained from SigmaAldrich Chemical CompanyChina) and used without further purication. A phos-red saline (PBS, pH 7.0, Na2HPO4KH2PO4NaClKCl,

The upper ascrews andside of the experimentimental solua nitrogen ameasureme

2.3. Electro

GraphiteHummers mwas exfoliaform homoreduced an min (a) and 24 h (b) and the electrode surface modied graphene/gold

) was prepared in the laboratory. All other reagentsere of analytical reagent grade or with highest quality

urchased from Shanghai Chemical Company (Shanghai, ultra pure water (18.2 M cm) puried from a Milli-Q

system was used throughout the experiment.

tus

hemical experiments were performed with an IM6eical system (ZAHNER Elektrik, German), CHI660B elec-

l workstation (Shanghai, China) and CHI400B quartzobalance (QCM) (Shanghai, China). Conventional three-ystem was used for chronopotentiometric deposition,mmetry (CV) and differential pulse voltammetry (DPV)Cl (saturated KCl) electrode as the reference electrode,ire as the counter electrode, and bare or modied

on electrode (GCE, 2 mm in diameter) as working elec-e use, the GCE was polished successively with 1.0, 0.3,

alumina powder, and sonicated in a 6.0 mol l1 nitric distilled water and ethanol/doubly distilled water foren, the GCE as working electrode was subjected toing in 0.5 mol l1 H2SO4 solution in a potential range

to 1.0 V. When the cyclic voltammogram was almost, the electrode was taken out, cleaned with water andr a stream of nitrogen. The circular AT-cut 7.995 MHztals coated with polished gold electrodes on both sidesor QCM analysis. The quartz crystals were 14 mm in thed 0.2 mm thick and the gold electrodes were 0.196 cm2

and 100 nm thickness. For cleaning purpose, they weren 1 mol l1 NaOH for 20 min. After being washed withter and nitrogen-dried, they were immersed in 1 mol l1

in and rinsed with distilled water, followed by ethanol.

nd lower pieces of the cell were held together by two

sealed between two O-rings. The QCM crystal had oneelectrode exposed to the solution. All electrochemical

was carried out under room temperature, and all exper-tion was degassed by nitrogen for at least 15 min. Then,tmosphere was maintained during the electrochemicalnts.

deposition of graphene

oxide was prepared from natural graphite by modiedethod [27,28]. The synthesized graphite oxide powder

ted in ultra pure water by ultrasonication for 30 min togeneous GO dispersion. Then, GO was electrochemicallyd deposited on the surface of glassy carbon electrode

44 L. Zaijun et al. / Electrochimica Acta 85 (2012) 42 48

Fig. 2. Typical c) andSection 2.3.

with constapersion undelectrode wdry at room

2.4. Electro

Gold nanprepared grin 0.01 mmH2SO4 undtrode was tunder room

2.5. Materi

Infraredimage, Ramobtained useter attenuS4800 eldmicroprobe2200vpc (Rand 20 mA a

3. Results

3.1. Synthe

The userauric acid SEM images of the GCE surface after electrodeposited in 0.005 (a), 0.01 (b), 0.05 (nt potential at 1.2 V for 50 s in a 0.01 mg ml1 GO dis-er temperature of 10 C. After the electrodeposition, theas thoroughly rinsed with ultra water and allowed to

temperature for further modication.

deposition of gold nanoparticles

oparticles were electrochemically deposited on the as-aphene/GCE with constant potential at 0.25 V for 50 sol l1 of chlorauric acid solution containing 0.5 mol l1

er temperature of 10 C. After the deposition, the elec-horoughly rinsed with ultra water and allowed to dry

temperature for further modication.

als characterizations

spectrum (IR), scanning electron microscope (SEM)an spectrum and X-ray diffraction (XRD) patterns wereing a AVATAR 360 Fourier transform infrared spectrom-ated total reection infrared spectroscopy, HITACHI

emission scanning electron microscope, HR800 Raman with a 514 nm laser excitation and X-ray D/max-igaku Corporation, Japan) instrument operated at 40 kVnd using Cu K radiation (k = 0.15406 nm), respectively.

and discussion

sis

of an appropriate concentration of GO and chlo- was strongly required to fabricate well-dispersed

graphenegcontains lapart of GO dissociationmoved to tthe electroequilibriumtrolyte willand reducetively low obtain smasingle stepprecipitate ronment duin GO sheetrolyte wasadding anygated the eduring the concentratithe electroemployed fcovered wiconcentratiincrease rapthe electrodsheets. Howgraphene snicantly dThus, a 0.01electrodepo 0.1 (d) mg ml1 of GO dispersion. Other conditions are described inold nanocomposite lm. Since GO is weak acid whichrge numbers of carboxyl and hydroxyl groups, onlywill be dissociated into GO anion due to existing the

equilibrium of weak acid, which GO anions may behe electrode surface, reduced and nally deposited onde surface under electrical stress. Based on acidbase

theory, the concentration of the GO anion in the elec- rapidly increase with increasing pH of the solution

with decreasing pH value. On the one hand, a rela-and constant GO anion concentration is benecial toll amounts of graphene on the electrode surface for

electrodeposition. On the other hand, GO is easy tofrom aqueous phase in relatively strong acidic envi-e to the protonation of carboxyl and hydroxyl groupsts. Thus, a pH 7.0 of the GO dispersion as the elec-

employed for the graphene electrodeposition without base and supporting electrolyte. Further, we investi-ffect of precursor GO concentration in the electrolytegraphene electrodeposition. As shown in Fig. 2, the GOon obviously inuence on amounts of the graphene onde surface. When a very low concentration of GO wasor the deposition, the electrode surface cannot be wellth the graphene nanosheets. With increase of the GOon number and density of the graphene sheets willidly. When GO concentration is about to 0.01 mg ml1,e surface is almost covered with single-layer grapheneever, with increasing GO obvious agglomeration of theheets was clearly observed, which would lead to sig-ecreased surface area of the modied graphene layer.

mg ml1 of GO dispersion was selected for the graphenesition. After one-step graphene electrodeposition was

L. Zaijun et al. / Electrochimica Acta 85 (2012) 42 48 45

Fig. 3. Typical SEM images of the graphene/GCE surface after electrodeposited in 0.005 (a), 0.01 (b), 0.were described in Section 2.4.

completed, chlorauric acid was electrochemically reduced and thendeposited on the electrode modied graphene with constant poten-tial at 0.25 V for 50 s in different concentration of chlorauricacid solution containing 0.5 mol l1 H2SO4. Fig. 3 presents typicalSEM images of the electrode surface modied in different con-centration of chlorauric acid solution. We clearly see from Fig. 3chlorauric acid concentration in the electrolyte remarkably effectson the size and densities of gold nanoparticles. When a low chlo-rauric acid concentration was employed for the gold deposition,the gold nanoparticles are very rare with a small size on the elec-trode surface. With the increasing chlorauric acid concentrationthe size and densities of gold nanoparticles increased obviously,which leads to signicantly decrease of the surface area of thegold-layer. age particlesurface whto 0.01 mmthe each elemployed foa well-dispeby alternatnanoparticlrepeatabilitmeasured bFig. 4 exhibduces almothat the eleity.

0

50

100

150

200

0

F (

Hz)

Fig. 4. Decreagraphene or gditions were d

3.2. Structu

Fig. 5 prgraphenegregular andwith an avtern there a38.28, 44.4Au (1 1 1), centered cuThe (0 0 1) peak of grapgraphene m

educocesstal

vely g sone n

6 pro pring D

the an of ed nphites.A

in t redemovstabs sm

an iphitere ively0 cm

Thedefoespe

C Oeak,However, the single-layer gold particles with an aver- size of 10 nm were well dispersed on the electrodeen precursor chlorauric acid concentration is aboutol l1. To obtain single-layer gold nanoparticles forectrodeposition, a 0.01 mmol l1 chlorauric acid wasr the gold electrodeposition. Under optimal conditions,rsed graphenegold nanocomposite lm was preparedely electrodepositing single-layer graphene and goldes on the electrode surface for 20 cycles. To evaluatey of the strategy, the amounts of modied layer werey QCM after the each step electrodeposition completed.its the each step deposition of graphene or gold pro-st same decrease value of QCM frequency, indicatingctrochemical technique has an excellent repeatabil-

(graphene)

(gold)

been rtion prlow cryeffectishowingraphe

Fig.are twincludresentphonoincreasent graincreasto 1.31ing thewere rbe re-ework ilead toent gralm wa relatat 162water.to the C O, ring andvery w4 8 12 16 20

Cycle number

se value of QCM frequency resulted by single step deposition ofold. GO: 0.01 mg ml1, chlorauric acid: 0.01 mmol l1, and other con-escribed in Sections 2.22.4.

groups. Aftecontaining of the mostand IR havgrapheneg

3.3. Electro

To undenanocompo05 (c) and 0.1 (d) mmol l1 chlorauric acid solution. Other conditions

re characterization

esents typical SEM and XRD images of the as-preparedold nanocomposite lm. The gold particles are very

these are separated on the wrinkled graphene sheetserage particle size of about 10 nm. On the XRD pat-re four sharp diffraction peaks at scattering angles of8, 64.6 and 77.64, corresponding to crystal planesAu (2 0 0), Au (2 2 0) and Au (3 1 1) of the gold face-bic crystallographic structure (JCPDS card No. 65-2870).peak of graphene oxide almost disappear and (0 0 2)hene nanosheets is wider and weaker than that of pureaterials. The results suggest that graphene oxide has

ed into graphene nanosheets during the electrodeposi-s. The obtained graphenegold nanocomposite shows alinity, and the restacking of the graphene nanosheets isprevented, corresponding to the SEM image in Fig. 5a,me gold nanoparticles located on the surfaces of theanosheets.esents typical Raman and IR spectrum of the lm. Thereominent peaks on the Raman spectrum of graphene,

band (1355 cm1) and G band (1600 cm1), which rep-mount of sp3 carbons in the surroundings and the E2gsp2 C atoms. Because a higher level of disorder and anumber of defects in the graphene. Compared with par-e, the ratio of intensities of the D and G bands (ID/IG)fter electrochemical reduction, the ID/IG ratio increaseshe as-prepared graphene-gold nanoparticle lm. Dur-uction process, most of the oxygen-containing groupsed, and the conjugated G network (sp2 carbon) wouldlished. However, the size of the re-established G net-aller than the original one, which would consequentlyncrease in the ID/IG ratio [29]. IR spectrum of the par-e GO and as-prepared graphenegold nanocompositeshown in Fig. 6b. We clearly observed from Fig. 6b

broad peak at 3414 cm1 and relatively sharp peak1 demonstrated that the samples contain adsorbed

peaks at 1397 cm1 and 1081 cm1 can be assignedrmation vibration of O H and stretching vibration ofctively. Characteristic bands of C O carbonyl stretch-

C vibration located at 1720 cm1 and 1250 cm1 are indicating the small amount of these two functional

r the electrochemical reduction, the removal of oxygen-groups is clearly indicated by the gradual disappearance

absorption bands. Above results of SEM, XRD, Ramane demonstrated that we have obtained successfully aold nanocomposite lm with electrodeposition.

catalytic activity

rstand electrocatalytic activity of the graphenegoldsite lm, we investigated the effect of varying the scan

46 L. Zaijun et al. / Electrochimica Acta 85 (2012) 42 48

Fig. 5. SEM image (a) and XRD patterns (b) of the as-prepared graphenegold nanocomposite lm.

A B

ty (

a.u

.)

D

G

itta

nce /%

GO

rate on thecontaining 1that all scanpeaks withtials with rpeak currenroot as shotion corres

Fig. 7. (A) Cyc(from a to ax) 8.0, 8.2, 8.4, 8.Inte

nsi

Tra

nsm0 500 1000 1500 2000 2500

Raman shift/cm-1

360

Fig. 6. Raman (a) and IR spectra (b) of the as-prepared graphen

performance of the modied electrode in pH 7.0 PBS m mol l1 K4Fe(CN)6 in 0.1 mol l1 of KCl. Fig. 7A shows

rates resulted in well-dened reduction and oxidation little shift in both cathodic and anodic peak poten-espect to scan rate. Further, both cathodic and anodicts are linearly proportional with the scan rate squarewn in Fig. 7B, which indicates that electrode reac-ponds to the solution phase quasi-reversible process.

The small pelectron traapparent e37.67 0.19

ks = mnFvRT

-120

-90

-60

-30

0

30

60

90

120

-0. 200.20.40.6

I/A

E vs(Ag/AgCl/V)

a

ax

-120

-80

-40

0

40

80

120A B

0.4

I p/

A

lic voltammograms of the graphenegold nanocomposite modied GCE in pH 7.0 PBS coof 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.4, 6, 8.8, 9.0, 9.2, 9.4, 9.6, 9.8 and 10 V/s. (B) Plot of the Ip vs. v1/2.Grapite

The film60012001800240030000

Wavenumber/cm-1

egold nanocomposite lm.

eak-to-peak separation value (Ep) illustrates a fastnsfer rate. When the nEp is less than 200 mV, thelectron transfer rate constant (ks) is estimated to be

cm s1 by using the following equation [30]:

(1)

1 1.6 2.2 2.8

Scan ra te1/2/V1/2 s-1/2

ntaining 1 mmol l1 K4Fe(CN)6 in 0.1 mol l1 KCl at various scan rates4.6, 4.8, 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, 6.2, 6.4, 6.6, 6.8, 7.0, 7.2, 7.4, 7.6, 7.8,

L. Zaijun et al. / Electrochimica Acta 85 (2012) 42 48 47

100

200A B

G/GCE

G-Au/GCE

-125

-95

-0. 4-0.3-0. 2-0.10

E vs (Ag/AgCl)/V

(RC)(HQ)

GCE

G/GCE

G-Au/GCE

Fig. 8. CVs (a) BS containing 1 104 mol l1 of HQ and 1 104 mol l1 of RC. The DPVparameters we v initial potential.

where m is temperaturThe value ofand bare GC

To furthegraphenegrials to syntypical CVsGCE (G/GCGCE (GAuHQ and 1 very weak G/GCE and ously with for their siGAu/GCE RC than G/Gtiles imprographene n

3.4. Analyti

Fig. 9 diand RC. Wicurrent (Ip1.2 104 mThe linear signicant RC, with stwhich Ip issitivities of117.83 A be 5.2 10were obtain(S/N = 3). ElHQ and RC adeviation (Rreproducibiconditions aof the sensolong term ssamples. Thviously rep[31,32].

terference of coexisting substances

evaluate selectivity of the sensor, the inuence of variousnces on the determination of 1.0 106 mol l1 of HQ and RCdied by DPV. It was found that 1500-fold Ca(II), Mg(II), Na(I),

H4(I), Cu(II), Zn(II), Al(III), F, Cl, Br, NO3, SO42, CO32,0-fold glucose, ascorbic acid, uric acid do not interfere withermination. The tolerance limit was estimated to be less thanhe relative error. This indicates the proposed method has annt an

plicanol in

feasvestis weater, he cament-200

-100

0

-0.4 -0.2 0 0.2 0.4 0.6

I/A

E vs (Ag/AgCl)/V

GCE -65

-35

-5

I p/

A

at scan rate of 100 mV/s and DPVs (b) of GCE, G/GCE and GAu/GCE in pH 7.0 Pre set to a scan rate of 4 mV/s, 50 mV pulse amplitude, 20 ms pulse width and 0.4

a parameter related to peak-to-peak separation; T is thee; n is the number of electrons; and v is the scan rate.

ks is higher than graphene modied GCE (11.02 cm s1)E (4.47 0.13 cm s1).r evaluate the electrocatalytic activity, the as-preparedold nanocomposite lm was applied as sensing mate-chronously detection of HQ and RC. Fig. 8 presents

(a) and DPVs (b) of bare GCE, graphene modiedE) and graphenegold nanocomposite lm modied/GCE) in pH 7.0 PBS containing 1 104 mol l1 of

104 mol l1 of RC. As expected, bare GCE showscurrent response to HQ and RC. In comparison, bothGAu/GCE can well distinguish HQ and RC, simultane-increased oxidation currents, showing great potentialmultaneous determinations. Moreover, we observedexhibits more sensitive current response to HQ andCE. This is because the introduction of gold nanopar-

ves the conductivity and avoids the agglomeration ofanosheets.

cal characteristics of the sensor

splays DPV curves for different concentration of HQth the increasing HQ and RC concentration the peak) increased linearly in the ranges of 1.6 108 tool l1 for HQ and 1.0 108 to 2 106 mol l1 for RC.

equations were Ip = 0.9547 C for HQ, with statisticallycorrelation coefcient of 0.9996, and I = 3.6997 C for

3.5. In

To substawas stuK(I), Nand 20the det5% of texcelle

3.6. Apresorci

Thewas insampleTap wfrom texperip

atistically signicant correlation coefcient of 0.9998, in A and concentration (C) in mol l1. The sen-

DPV response are 30.5 A M1 cm2 for HQ andM1 cm2 for RC. The detection limits were found to

9 mol l1 for HQ and 2.2 109 mol l1 for RC thated from the signal-to-noise characteristics of these dataeven successive determinations of 1 106 mol l1 oft one modied electrode resulted in a relative standardSD) of 1.22% for HQ and 1.81% for RC, suggesting a highlity. The proposed sensor was stored in air at ambientnd its sensitivity was checked every day. The responser was 95% of its initial value after 180 days which showstability and very good sensitivity for the analysis of realese analytical parameters are better than results pre-orted for electrochemical determination of HQ and RC

Fig. 9. (a) DPVwere set to a 0.4 v initial ppeak current (ti-interference ability.

tion to the determination of hydroquinone and water samples

ibility of the developed method for possible applicationsgated by analyzing real water samples. Waste waterre collected from the factory for producing HQ and RC.ground water and lake water samples were collectedmpus at Jiangnan University. The spike and recoverys were performed by measuring the DPV responses to curves of different concentration HQ and RC. The DPV parametersscan rate of 4 mV/s, 50 mV pulse amplitude, 20 ms pulse width andotential. Insets: calibration plots of concentration of HQ and RC vs.Ip).

48 L. Zaijun et al. / Electrochimica Acta 85 (2012) 42 48

Table 1The results for the determination of HQ and RC in real water samples (N = 5).

Sample Tap water Lake water Ground water Waste water

HQ RC HQ RC HQ RC HQ RC

Added (mol l1) 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00Determined (mol l1) 0.99 0.98 1.01 1.02 0.96 0.99 1.16 1.09RSD (%) 1.7 1.1 2.3 1.5 1.0 1.9 1.8 1.4Recovery (%) 99.0 98.0 98.8 101.2 96.0 99.7 101.2 103.4

the sample in which the known concentrations of HQ and RC wereadded. The mean of each sample and recovery of each spiked sam-ple were calculated and the values are reported in Table 1. Table 1shows the recovery of HQ and RC for spiked samples analysis is inthe range of 96.0103.4%, indicating good accuracy and precision.

4. Conclusions

Green and controllable strategy was developed for the fabri-cation of well-dispersed graphenegold nanocomposite lm. Theinvestigation demonstrated that the amounts of graphene andgold nanoparticles for each layer can be well pre-determined bycontrolling concentrations of GO and metallic precursor. Due togood dispersivity, the as-prepared lm shows better electrocat-alytic activity towards hydroquinone and resorcinol than that ofother technologies in literatures. The method for the preparationof grapheneable, it can composite tion such as

Acknowled

The autNational N20771045 ajiang Provinsupport scisponsored b

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gements

hors acknowledge the nancial support from theatural Science Foundation of China (Nos. 21176101,nd 20676052), the Natural Science Foundation of Zhe-ce (Y4080404), the country 12th Five-Year Plan to

ence and technology project (No. 2011BAK10B03) andy Qing Lan Project.

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Green and controllable strategy to fabricate well-dispersed graphenegold nanocomposite film as sensing materials for the ...1 Introduction2 Experimental2.1 Chemicals2.2 Apparatus2.3 Electrodeposition of graphene2.4 Electrodeposition of gold nanoparticles2.5 Materials characterizations

3 Results and discussion3.1 Synthesis3.2 Structure characterization3.3 Electrocatalytic activity3.4 Analytical characteristics of the sensor3.5 Interference of coexisting substances3.6 Application to the determination of hydroquinone and resorcinol in water samples

4 ConclusionsAcknowledgementsReferences