Simultaneous determination of catechol and hydroquinone by c(3)

JSolidStateElectrochem(2012)16:3747–37523749

wasobtained.Atotalof5μLGODsolution(10mgmL 1)wasthencoatedontheNiO/TiO2–Gr/GCE(GOD/NiO/TiO2–Gr/GCE)anddriedat4°C.ThemodifiedGCEwasimmersedinPBStoremovethelooselyabsorbedGODandwasstoredat4°Cinarefrigeratorwhennotinuse.

thanthatofTiO2,whichresultsintheshieldingofthegraphenepeaksbythoseofTiO2[21].

Electrochemicalbehaviorsofmodifiedelectrodes

Theelectrochemicalbehaviorsofdifferentmodifiedelectro-deswereinvestigated.TheresultsshowedthatanodicandcathodicpeaksdonotappearatGCE,TiO2–Gr/GCE,NiO/GCE,andNiO/TiO2–Gr/GCEin0.1MPBS(pH7.0).AftercombiningwithGOD,apairofwell-defined,quasireversi-bleredoxpeakscanbeobservedatGOD/NiO/TiO2–Gr/GCEat 0.46and 0.41V,withapeak-to-peakseparationofabout50mV,revealingafastelectrontransferontheelectrode.

Figure2showsthecyclicvoltammetricresponsesobtainedatGOD/GCE,GOD/NiO/GCE,GOD/TiO2–Gr/GCE,andGOD/NiO/TiO2–Gr/GCE,respectively.Apairofbadlydefined,weakredoxpeakscanbeobservedatGOD/GCE.TheredoxpeaksobservedatGOD/NiO/GCEandGOD/TiO2–Gr/GCEobviouslyincreasedwhencom-paredtothatatGOD/GCE,revealingafastelectrontransferatbothmodifiedelectrodes.ThepeakcurrentofredoxpeaksofGOD/NiO/TiO2–Gr/GCEwasthehighestintheaformen-tionedelectrodes,whichwasduetothesynergisticeffectofNiOandTiO2–Gr.

ResultsanddiscussionCharacteristics

TheSEMimageofGr(Fig.1a)revealsthetypicalcrumpledandwrinkledGrsheetstructure.TheintegrationbetweenTiO2andGrcanbevisualizedinFig.1b,inwhichTiO2nanoparticleswithsizeofca.20–30nmareuniformlyandcompactlyembeddedontheGrsubstrate.Figure1cshowsthatNiOnanoparticlesareelectrodepositedonTiO2–Gr.TheXRDpatternsofTiO2–GraregiveninFig.1d.ThepeaksinthisdiffractionpatternscorrespondtotheanatasephaseofTiO2(JCPDSfileno.21–1272),suggestingthecompleteformationofanataseTiO2duringthehydrother-malprocess.However,thediffractionpeaksofGrarenotdistinguishableinXRDpatternsofTiO2–Gr.Thisphenom-enahasalsobeenobservedinotherrelevantworks,anditcanbeascribedtothemuchlowercrystallineextentofGr

Fig.1SEMimagesofGR(a),TiO2–Gr(b),andNiO/TiO2–Gr(c);XRDpatternsofTiO2–Gr(d)

cd

Intensity / a.u.

2500200015001000

004

200105211

204

101

20

40

60

80

2θ/ degree

116220215

500