碳纳米管-二氧化锰复合材料.pdf

《碳纳米管-二氧化锰复合材料.pdf》由会员分享，可在线阅读，更多相关《碳纳米管-二氧化锰复合材料.pdf（7页珍藏版）》请在得力文库 - 分享文档赚钱的网站上搜索。

1、Analytica Chimica Acta 674(2010)2026Contents lists available at ScienceDirectAnalytica Chimica Actajournal homepage: highly sensitive hydrogen peroxide amperometric sensor based onMnO2-modified vertically aligned multiwalled carbon nanotubesBin Xu,Min-Ling Ye,Yu-Xiang Yu,Wei-De ZhangNano Science Res

2、earch Center,School of Chemistry and Chemical Engineering,South China University of Technology,381 Wushan Road,Guangzhou 510640,Guangdong,Peoples Republic of Chinaa r t i c l ei n f oArticle history:Received 13 April 2010Received in revised form 2 June 2010Accepted 3 June 2010Available online 12 Jun

3、e 2010Keywords:Carbon nanotubesHydrogen peroxideSensorManganese dioxideAmperometrya b s t r a c tIn this report,a highly sensitive amperometric sensor based on MnO2-modified vertically aligned multi-walledcarbonnanotubes(MnO2/VACNTs)fordeterminationofhydrogenperoxide(H2O2)wasfabricatedby electrodepo

4、sition.The morphology of the nanocomposite was characterized by scanning electronmicroscopy,energy-dispersiveX-rayspectrometerandX-raydiffraction.Cyclicvoltammetry,chronoam-perometryandelectrochemicalimpedancespectroscopywereappliedtoinvestigatetheelectrochemicalproperties of the MnO2/VACNTs nanocom

5、posite electrode.The mechanism for the electrochemical reac-tion of H2O2at the MnO2/VACNTs nanocomposite electrode was also discussed.In borate buffer(pH 7.8,0.20M),theMnO2/VACNTsnanocompositeelectrodeexhibitsalineardependence(R=0.998)onthecon-centration of H2O2from 1.2106M to 1.8103M,a high sensiti

6、vity of 1.08106?AM1cm2and adetectionlimitof8.0107M(signal/noise=3).Meanwhile,theMnO2/VACNTsnanocompositeelectrodeis also highly resistant towards typical inorganic salts and some biomolecules such as acetic acid,citricacid,uric acid and d-(+)-glucose,etc.In addition,the sensor based on the MnO2/VACN

7、Ts nanocompositeelectrode was applied for the determination of trace of H2O2in milk with high accuracy,demonstratingits potential for practical application.2010 Elsevier B.V.All rights reserved.1.IntroductionHydrogenperoxideisaveryimportantintermediateinenviron-mental and biological reactions.It als

8、o has been used as a universaloxidant in industrial processes 1.So,the determination of H2O2isof great importance in many different fields,such as food,clinical,pharmaceutical,industrial and environmental analysis.Especiallyin food industry,it is often used as an antibacterial reagent and hastoberem

9、ovedbycatalase2.Uptonow,manyselectiveandsensi-tive methods have been developed for determination of hydrogenperoxide,such as titrimetry and spectrophotometry 35.How-ever,the existing methods usually cannot offer high sensitivity,reliability and operational simplicity at the same time,and oftensuffer

10、 from interferences,time-cost and use of expensive reagents6.Electroanalysis is suitable for the determination of H2O2sinceit can achieve low detection limit and rapid response time onthe basis of direct reduction or oxidation of H2O27.Among theelectrochemical hydrogen peroxide sensors,the enzyme-mo

11、difiedelectrodes are frequently used to detect relatively low concen-tration of H2O2with satisfactory sensitivity 8,9.Nevertheless,the enzyme-modified electrodes have some disadvantages,suchCorresponding author.Tel.:+86 20 8711 4099;fax:+86 20 8711 2053.E-mail address:(W.-D.Zhang).as complicated imm

12、obilization procedure,critical operating situa-tion,instability and high-cost of the enzymes.Recently,a numberof studies have been carried out to improve the electrochemicalresponse of H2O2by modification of the electrode surface 10,11.Immobilization of transition metals,their oxides or complexes on

13、the electrode surface is widely applied 12,13.Manganese oxide has been widely used as the catalysts 1416and electrode materials for supercapacitors 17,18,owing to itseconomicalandenvironmentaladvantages19,20inadditiontoitscatalytic activity for oxygen reduction 21,22.Furthermore,it alsoexhibits high

14、 efficiency towards the catalytic disproportionation ofhydrogenperoxidegeneratedatthesurfaceofaPtelectrode(albeitthehydrogenperoxideformationisveryslight)23.So,someH2O2sensors based on MnO2were fabricated 1,7,2428.For example,TahaandWangeverreportedaglassycarbonelectrode(GCE)modi-fiedbyafilmofMnO2in

15、MnCl2/NaOHsolution,whichshowedalowdetection limit of 80pg(about 1.5107M)but the detection wasconducted in strong alkaline solution 7.Yao et al.24 reported ahydrogen peroxide amperometric sensor based on MnO2nanopar-ticles and dihexadecyl hydrogen phosphate composite film.Linet al.25 synthesized nano

16、structured cryptomelane-type man-ganese oxide for chemical sensing H2O2with a lower detectionpotential(+0.3V vs.SCE).All these studies are based on the strongcatalytic oxidation property of MnO2nanoparticles-modifiedelectrodes.0003-2670/$see front matter 2010 Elsevier B.V.All rights reserved.doi:10.

17、1016/j.aca.2010.06.004B.Xu et al./Analytica Chimica Acta 674(2010)202621Fig.1.Scanning electron microscopy images of(A)VACNTs,(B)MnO2/VACNTs nanocomposite,and(C)EDS spectrum of the MnO2/VACNTs nanocomposite.Meanwhile,carbonnanotubes(CNTs)haveattractedgreatinter-est since they were discovered in 1991

18、 by Iijima 29.Due to theirhigh surface area,unique structures,excellent electrical conduc-tivity,ultra-strong mechanical strength and high stability 30,CNTshavebeenconsideredtobeexcellentcandidatesforelectrodematerialswithelectrochemicalcatalysis3134andsupercapacity16,18,35,36.Recently,effortshaveal

19、sobeenfocusedontheprepa-rationofCNTs-basednanocompositesbymodificationofCNTswithmetals such as Cu,Ag,Au and Pt 3740;or metal oxides such asRuO2,WO3,TiO2and ZnO 4144.Combination of metals or metaloxides with CNTs will lead to new composite materials possess-ing the properties of each component,or eve

20、n with a synergisticeffect 44,which would be useful in the fields of electroanalysisandphotoelectrochemistry.Asanoxidewithmultifunctions,MnO2has also been used to modified CNTs for electroanalysis of glucosewithhighsensitivity45,andforsupercapacitor46,47withwon-derful chargingdischarging properties,

21、high specific capacitanceeven at high discharge current density of 100mAcm2,and excel-lent cycle stability.On the base of our previous study 45,a novelH2O2sensor was developed by modification of MnO2on verticallyalignedmultiwalledcarbonnanotubes(VACNTs).Thesensorshowshigh sensitivity,reproducibility

22、,stability and selectivity,which ispromising for the development of nonenzymatic H2O2sensor.2.Experimental2.1.Reagents and apparatusHydrogen peroxide(30%)and manganese sulfate(MnSO4)werepurchased from Beijing Chemical Reagent Company and ShanghaiChemical Reagent Company,respectively.A borate saline

23、buffersolution was prepared by adjusting 0.20M boric acid with 0.050Mboraxsolution.Allotherreagentswereofanalyticalgradeandusedwithout further purification.All aqueous solutions were preparedwith doubly distilled water(18.4M?cm1).Electrochemical experiments were performed on a CHI 660Celectrochemica

24、l workstation(Shanghai Chenhua,China).A three-electrode configuration was employed with the MnO2/VACNTsnanocompositeelectrodeasaworkingelectrode,anAg/AgCl(3.0MKCl)electrode and a platinum wire as the reference and counterelectrodes,respectively.All potentials werereferredtotheAg/AgCl(3.0M KCl)electr

25、ode.Magnetic stirring was used before CV mea-surementsandthroughoutamperometricmeasurementstoensurethe homogeneity of the solutions.SEM image analysis was carriedoutonaPhilipsXL30FEGmicroscope.ThestructureofMnO2nano-materials was characterized by X-ray diffraction(XRD)(BrukerGADDS diffractometer)wit

26、h an area detector operating under avoltage of 40kV and a current of 40mA using Cu K?radiation(?=0.15418nm).2.2.Preparation of the MnO2/VACNTs nanocomposite electrodeVertically aligned CNTs(VACNTs)were grown on Ta substrates48,49,which are convenient for the fabrication of a VACNTs elec-trode 34,50

27、or for further modification of composite electrodes33,35,51.In this study,the MnO2-modified VACNTs were con-nected to a Cu electrode using conductive silver paint(Structureprobe,Inc.,USA).TheedgeoftheTaplateandCuelectrodewasinsu-lated by pasting with nail enamel.In this work,electrodepositionof MnO2

28、on the VACNTs was carried out in a quiescent ammo-niumbuffersolution(pH9.2)containing10mMMnSO4,whichwaspurged with pure nitrogen for 10min prior to modification,and aconstant potential of+0.60V was applied for different time.Theobtained electrode was washed with deionized water to removethe remainin

29、g ions,and then dried at 60C for 12h.22B.Xu et al./Analytica Chimica Acta 674(2010)2026Fig.2.(A)CVs of VACNTs and MnO2/VACNTs nanocomposite electrodes in 5.0mMK3Fe(CN)6 solution with 1.0M KCl.Scan rate:100mVs1.(B)Impedance spec-tra of VACNTs and MnO2/VACNTs nanocomposite electrodes in 0.10M KCl solu

30、tioncontaining equimolar Fe(CN)63/4(0.01M/0.01M).3.Results and discussion3.1.Morphological characterization of the VACNTs andMnO2/VACNTs nanocomposite electrodesFig.1 shows the overall morphology of the VACNTs and theMnO2/VACNTs composite.The VACNTs have an average diameterof 150nm and a length of 5

31、?m(Fig.1A).After being coated byMnO2,as shown in Fig.1B,the VACNTs become thicker,especiallyat the tips.EDX pattern(Fig.1C)of the composite demonstratesthe existence of MnO2.The crystal structure of the MnO2onthe VACNTs was further characterized by X-ray diffraction.Thereare no apparent sharp and st

32、rong peaks in XRD pattern(datanot shown),indicating an amorphous structure of manganate isobtained.3.2.Electrochemical characterization of the VACNTs andMnO2/VACNTs nanocomposite electrodesTheelectrochemicalpropertiesoftheVACNTsandMnO2/VACNTs nanocomposite electrodes were evaluated bypotential cycli

33、ng in 1.0M KCl containing 5.0mM K3Fe(CN)6.The cyclic voltammetry(CV)response is shown in Fig.2A.TheMnO2/VACNTs nanocomposite electrode encircled larger area andexhibited larger capacitance than the VACNTs electrode,whichdemonstrated the MnO2is an ideal material for supercapacitors46.Apart from this,

34、the difference between the anodic andcathodic peak potentials(?Ep)is 59mV at a bare VACNTs elec-trode and 65mV at the MnO2/VACNTs nanocomposite electrode,suggesting the modification of carbon nanotubes with MnO2inhibits fast electron-transfer kinetics to some extent 35.To estimate the effective surf

35、ace area of the VACNTs andMnO2/VACNTsnanocompositeelectrodes,K3Fe(CN)6wasusedasa probe.CVs on bare VACNTs and MnO2/VACNTs nanocompositeelectrodes in a solution containing 5.0mM K3Fe(CN)6 and 1.0MKClwereperformed.Forareversibleprocess,RandlesSevcikequa-tion(1)is applicable.According to this equation

36、and the knownparameters(n=1,D=0.76105cm2s1),the effective surfaceareas of the VACNTs and MnO2/VACNTs nanocomposite electrodesare estimated to be 0.084cm2and 0.097cm2,respectively.Ip=(2.69 105)n3AD1/20v1/2C0(1)Electrochemical impedance spectroscopy(EIS)is an effectiveapproach for probing the conducti

37、vity of the electrodes.Fig.2Bshows the impedance spectroscopy on the bare VACNTs andMnO2/VACNTs nanocomposite electrodes in 0.10M KCl solutioncontaining equimolar Fe(CN)63/4at an ac frequency varyingfrom 0.10Hz to 100kHz.The Nyquist complex plane plots ofboth bare VACNTs and MnO2/VACNTs nanocomposit

38、e electrodesexhibitanalmoststraightline,whichshowsthattheMnO2/VACNTsnanocomposite electrode still keeps fast electron transfer prop-erty.However,due to the presence of semiconductive MnO2,theinternal resistance of the MnO2/VACNTs nanocomposite electrodeis about 11?higher than that of the bare VACNTs

39、 electrode,which also shows the modification of carbon nanotubes withMnO2inhibits fast electron-transfer kinetics to some extent 43.This further confirmed the successful deposition of MnO2onthe VACNTs.3.3.Voltammetric behavior of H2O2at the MnO2/VACNTselectrodeFig.3A shows the cyclic voltammetric be

40、havior of the VACNTsand MnO2/VACNTs nanocomposite electrodes in the presence andabsence of 0.40mM H2O2in borate buffer(pH 7.8,0.20M)at a scanrate of 10.0mVs1.At the VACNTs electrode,the oxidation of H2O2onlybeginsat0.40V.However,noobviousoxidationandreductionpeak of H2O2was obtained in the potential

41、 range of 01.0V(curveb),compared with curve a without H2O2.At the MnO2/VACNTsnanocompositeelectrode,acoupleofsmalloxidativeandreductivepeaks are observed(curve c),which are assignable to the oxida-tion and reduction of Mn species in the absence of H2O2.WhenH2O2wasaddedinboratebuffer(pH7.8,0.20M),the

42、oxidationcur-rent greatly increased,while the reduction current only increasedslightly.Thewholecyclicvoltammogramdisplaysfourpeaks(curved,from 1 to 4),including two oxidative peaks and two reductivepeaks.Itisknownthat,thesolidMn(III)intermediatesisthermody-namically stable 14 in neutral or alkaline

43、solution.Therefore,thepolyvalent manganese oxide results in this complex voltammet-ric curve.As shown in Fig.3B,the peak current increased upon theincreaseofthescanrate,andagoodlinearitybetweenscanrateandpeak current could be obtained within the range of 10.0100mV/s,which indicates that the electroc

44、hemical kinetics is controlled bythe adsorption of H2O2.The possible reaction mechanism is proposed as follows.Firstly,H2O2was adsorbed at the active sites on the surface of MnO2.Sec-ondly,MnO2is reduced to lower states by the absorbed H2O2(Eqs.(2)and(3),and then lower states of Mn are electro-oxidi

45、zed backto MnO2or Mn2O3(Eqs.(4)and(5)at the electrode surface.It mayresult from the simultaneous coexistence of one-electron and two-electron processes 52.According to the potential diagram of Mnspecies,the oxidation of Mn(III)to Mn(IV)species may contributeB.Xu et al./Analytica Chimica Acta 674(201

46、0)202623Fig.3.(A)CVsofVACNTs(aandb)andMnO2/VACNTsnanocomposite(candd)elec-trodes in the absence(a and c)and presence(b and d)of 0.40mM H2O2in boratebuffer(pH 7.8,0.20M).Scan rate:10mVs1.(B)CVs of MnO2/VACNTs nanocom-posite electrode at different scan rates(10100mVs1)in borate buffer(pH 7.8,0.20M).In

47、set is the plot of oxidation peak current with scan rate.to peak 1,and the oxidation of Mn(II)to Mn(IV)may contribute topeak 2.MnO2+H2O2 Mn2O3+O2+H2O(2)MnO2+H2O2 Mn(OH)2+O2(3)Mn2O3+2OH 2MnO2+H2O+2e(4)Mn(OH)2+2OH MnO2+2H2O+2e(5)At the same time,some lower states of Mn can be chemicallyoxidized back t

48、o MnO2by H2O2(Eqs.(6)and(7),then MnO2and Mn2O3are electro-reduced to lower states(Eqs.(8)and(9).Accordingly,in the reverse sweep,reduction of Mn(III)and Mn(IV)may contribute to peak 3 and 4,respectively.As a result,with theadditionofH2O2,theoxidationcurrentgreatlyincreased,whilethereduction current

49、only increased slightly.These results are consis-tent with some previous reports 14,53.Mn2O3+H2O2 2MnO2+H2O(6)Mn(OH)2+H2O2 MnO2+2H2O(7)Mn2O3+3H2O+2e 2Mn(OH)2+2OH(8)2MnO2+H2O+2e Mn2O3+2OH(9)Fig.4.Effect of work potential and deposition time on the amperometric responsefor 0.10mM H2O2in borate buffer(

50、pH 7.8,0.20M).3.4.Optimization of experimental parameters3.4.1.Operating potentialThe applied constant potential for amperometry at the workingelectrode was chosen on the basis of the electrochemical behaviorof MnO2/VACNTs nanocomposite presented in Fig.4A,where thesignalstrengthfor0.10mMH2O2wasplot