芳基重氮化修饰玻碳电极和金电极

The modi?cation of glassy carbon and gold electrodes with aryl diazonium salt:The impact of the electrode materials

on the rate of heterogeneous electron transfer

Guozhen Liu,Jingquan Liu,Till Bo ¨cking,Paul K.Eggers,J.Justin Gooding

*

School of Chemistry,The University of New South Wales,Sydney,NSW 2052,Australia

Received 1December 2004;accepted 23March 2005

Available online 23May 2005

Abstract

The heterogeneous electron-transfer properties of ferrocenemethylamine coupled to a series of mixed 4-carboxyphenyl/phenyl monolayers on glassy carbon (GC)and gold electrodes were investigated,by cyclic voltammetry,in aqueous bu?er solutions.The electrodes were derivatized in a step-wise process.Electrochemical reduction of mixtures of 4-carboxyphenyl and phenyl dia-zonium salts on the electrode surfaces yielded stable monolayers.The introduction of carboxylic acid moieties onto the surfaces was veri?ed by X-ray photoelectron spectroscopy.Subsequently the 4-carboxyphenyl moieties were activated using water-soluble carbo-diimide and N -hydroxysuccinimide and reacted with ferrocenemethylamine.The rate constants of electron transfer through the monolayer systems were determined from cyclic voltammograms using the Marcus theory for electron transfer and were found to be an order of magnitude higher for the ferrocene-modi?ed monolayer systems on gold than those on GC electrodes.The results suggest the electrode material has an important in?uence on the rate of electron transfer.ó2005Elsevier B.V.All rights reserved.

Keywords:Self-assembled monolayers;Electron transfer;Carbon;Gold;Diazonium salts

1.Introduction

The modi?cation of conducting surfaces with mono-layers has received extensive research interest of late be-cause of their utility as model systems for understanding electron transfer [1,2],molecular electronics [3,4],bio-electronics [5,6]and sensors [7]amongst other applica-tions.The most popular chemistry for forming monolayers on electrode surfaces is alkanethiol self-assembly onto coinage metals,in particular gold [8],although other systems have also attracted interest such as silanes on metal oxide electrodes [9]and alkenes on highly doped silicon [10].The attractiveness of gold–

thiol chemistry is that well ordered monolayers can be formed relatively easily,with a reasonably strong bond formed between the organic molecule and the electrode,and that a diverse range of molecules can be synthesized with which to modify an electrode.The advantages of gold–thiol chemistry are somewhat o?set by a number of disadvantages,including alkanethiols being oxida-tively or reductively desorbed at potentials typically out-side the window de?ned by à800to +800mV versus Ag/AgCl.Other disadvantages include:alkanethiols being desorbed at temperatures over 100°C,gold being a highly mobile surface which results in the monolayers moving across the electrode surface,the gold–thiolate bond being prone to oxidation and the gold/thiol junc-tion creating a rather large tunneling barrier ($2eV)[11].The last point regarding a large tunneling barrier

0301-0104/$-see front matter ó2005Elsevier B.V.All rights reserved.doi:10.1016/j.chemphys.2005.03.033

*

Corresponding author.

E-mail address:justin.gooding@https://www.wendangku.net/doc/1c1563791.html,.au (J.J.Gooding).

https://www.wendangku.net/doc/1c1563791.html,/locate/chemphys

Chemical Physics 319(2005)

136–146

has implications for the rate of electron transfer from the organic monolayer to the electrode which is impor-tant for all molecular scale devices where communica-tion with the macroscopic world is achieved through electron transport.

We are interested in alternative monolayer systems to gold–thiol chemistry which overcome some of the disad-vantages but do not severely compromise the advanta-ges of gold/thiol chemistry.The electrochemical reduction of aryl diazonium salts is one possible alterna-tive which has most frequently been used as a method for the covalent derivatization of glassy carbon(GC) surfaces[12–14].The reduction reaction results in the loss of the N2and the formation of a carbon–carbon covalent bond which is strong,stable over both time and temperature,non-polar and conjugated[11].Thus, the conjugated carbon network in the GC electrode can be thought of as continuing into the monolayer sys-tem rather than the abrupt change from electrons being in a metallic environment to an organic environment. The continuity of the electrode material into the mono-layer has resulted in the suggestion that GC electrodes modi?ed by aryl diazonium salts have the potential to reduce the barrier towards electron transfer from the carbon electrode into the monolayer[11].McCreery and coworkers[15–18]have extensively studied the elec-tron transfer kinetics of GC surfaces in di?erent redox probe solutions.However,to the best of our knowledge heterogeneous electron transfer between redox active molecules and GC electrodes through aryl diazonium salt derived monolayers has yet to be investigated.Nor has the notion that the C–C bond will allow e?cient electron transfer.

The attractiveness of aryl diazonium salts are en-hanced further by recent studies showing they can also be grafted to a variety of metal[19,20]and semicon-ductor[21]surfaces as well as carbon nanotubes[22]. This feature raises the exciting possibility of one monolayer forming system being suitable for a large range of electrode materials for a diverse range of applications.This possibility is helped by a rich array of di?erent diazonium salts which have now been pre-pared including molecular wires[23]and polyethylene glycol terminated molecules designed to resist protein adsorption[24,25].The purpose of this study is to modify GC and gold substrates using mixtures of aryl diazonium salt molecules(introducing phenyl and4-carboxyphenyl groups onto the surface)and to com-pare the kinetics of electron transfer to GC and gold surfaces from the same ferrocene-based monolayer sys-tem.A similar ferrocene-based system prepared by a mixed self-assembled monolayers(SAMs)of4-merca-ptobenzoic acid(MBA)and1-propanethiol(PT)has also been prepared on gold surfaces and the rates of electron transfer have been studied for further comparison.2.Experimental

2.1.Reagents and materials

Tetrabutylammonium tetra?uoroborate(NBu4BF4), sodium tetra?uoroborate(NaBF4),p-aminobenzoic acid,aniline,4-mercaptobenzoic acid(MBA),1-propa-nethiol(PT),ferricyanide(K4Fe(CN)6),1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC),N-hydroxysuccinimide(NHS),N-[2-hydroxy-ethyl]piperazine-N0-[2-ethanesulfonic acid](HEPES), ferrocenecarboxaldehyde,sodium cyanoborohydride and acetonitrile(CH3CN,HPLC grade)were obtained from Sigma(Sydney,Australia).Benzoic acid diazo-nium tetra?uoroborate and benzene diazonium tetra-?uoroborate were synthesized according to the method by Saby et al.[26].Ferrocenemethylamine was synthe-sized using the procedure from Kraatz[27].Reagent grade dipotassium orthophosphate,potassium dihydro-gen orthophosphate,potassium chloride,sodium hydroxide,sodium chloride,sodium nitrite,ammonium acetate,sulphuric acid,hydrochloric acid,methanol and diethyl ether were purchased from Ajax Chemicals Pty. Ltd.(Sydney,Australia).All reagents were used as re-ceived,and aqueous solutions were prepared with puri-?ed water(18M X cmà1,Millipore,Sydney,Australia). Phosphate bu?er solutions used in this work contained 0.05M KCl and0.05M K2HPO4/KH2PO4and were ad-justed with NaOH or HCl solution.

2.2.Modi?cation of electrodes

The GC and gold electrodes were modi?ed with dia-zonium salts followed by attachment of ferrocenemeth-ylamine as depicted in Scheme1.The GC electrodes were purchased commercially(Bioanalytical System Inc.,USA)as3-mm-diameter rods.The electrodes were polished successively in1.0,0.3,and0.05l m alumina slurries made from dry Buehler alumina and Milli-Q water on microcloth pads(Buehler,Lake Blu?,IL, USA).The electrodes were thoroughly rinsed with Milli-Q water and sonicated in Milli-Q water for 5min between polishing steps.Before derivatization, the electrodes were dried with an argon gas stream. The bare GC electrodes had an electrochemical rough-ness factor(the ratio of the electrochemical area to geo-metric area)of 1.43.Surface derivatization of GC electrodes was performed in a solution of1mM aryl diazonium salt and0.1M NaBu4BF4in acetonitrile using cyclic voltammetry(CV)with a scan rate of 100mV sà1for two cycles between+1.0andà1.0V. The diazonium salt solution was deaerated with argon for at least15min prior to derivatization.The elec-trodes were rinsed with copious amounts of acetonitrile and then water and dried under a stream of argon prior to the next step.

G.Liu et al./Chemical Physics319(2005)136–146137

Poly-crystalline gold electrodes,prepared as de-scribed previously[28],were polished to a mirror-like ?nish with 1.0l m alumina,followed by0.3and 0.05l m alumina slurry on microcloth pad.After re-moval of trace alumina from the surface,by rinsing with water and brief cleaning in an ultrasonic bath with eth-anol and then water,electrochemical cleaning in0.05M H2SO4by cycling the electrodes betweenà0.3and1.5V was carried out until a reproducible CV was obtained. Before derivatization,the cleaned electrodes were rinsed with water and dried under a stream of argon.The derivatization of gold electrodes with a mixture of dia-zonium salts was conducted in exactly the same manner as described for the carbon electrodes.The alkanethiol modi?ed gold electrodes were prepared by immersing the gold electrodes in a1mM mixed thiol solution(mer-captobenzoic acid and propanethiol with di?erent dilu-tion ratios)in ethanol overnight(see Scheme2).The electrode was rinsed with copious amounts of ethanol, then water and?nally dried under a stream of argon prior to the next step.

Covalent attachment of ferrocenemethylamine to car-boxylic acid terminated monolayers followed the proce-dures described by Liu et al.[29].The modi?ed surfaces were incubated in an aqueous solution of10mM N-hydroxysuccinimide(NHS)and40mM1-ethyl-3-(3-di-methyl aminopropyl)carbodiimide hydrochloride (EDC)for1h.After the activation,the electrodes were rinsed with water and incubated in a5mM ferrocenem-ethylamine solution in HEPES bu?er pH7.3for24h.

2.3.Electrochemical measurements

All electrochemical measurements were performed with a BAS-100B electrochemical analyser(Bioanalyti-cal System https://www.wendangku.net/doc/1c1563791.html,fayette,IL)and a conventional three-electrode system,comprising a GC or a gold work-ing electrode,a platinum foil as the auxiliary electrode, and a Ag/AgCl3.0M NaCl electrode(from BAS)as ref-erence.All potentials were reported versus the Ag/AgCl reference electrode at room temperature.All CV mea-surements were conducted in pH7.0phosphate bu?er. The area under the Faradaic peaks in the CVs of the fer-rocene modi?ed electrodes were used to determine the surface coverage of ferrocene.The rate constants for electron transfer were calculated from the variation in peak potential over a wide range of scan rates.For elec-trodes with prominent redox peaks the rate constants were determined by?tting the variation in peak poten-tial with scan rate using the Marcus theory for electron transfer as described previously[30–32]whilst at low surface coverages of ferrocene the rates of electron

Scheme2.Schematic of ferrocenemethylamine immobilized covalently on mixed monolayers of MBA and PT on gold surfaces. 138G.Liu et al./Chemical Physics319(2005)136–146

transfer were determined using the Laviron[33]formal-ism.This was because peak shape and position was very sensitive background subtraction at with small redox peaks and therefore?tting the entire background sub-tracted CV peak as required for our Marcus simulation became unreliable.When both methods were employed on the same data very similar rate constants for electron transfer were obtained.

2.4.XPS measurements

XP spectra were obtained using an EscaLab220-IXL spectrometer with a monochromated Al K a source (1486.6eV),hemispherical analyzer and multichannel detector.The spectra were accumulated at a take-o?an-gle of90°with a0.79mm2spot size at a pressure of less than10à8mbar.

3.Results

3.1.Aryl diazonium salt modi?ed glassy carbon electrodes

Glassy carbon electrodes were modi?ed with diazo-nium salts via electrochemical reduction of an aryl dia-zonium salt(1mM in acetonitrile)with0.1M tetrabutylammonium tetra?uoroborate as background electrolyte.The?rst sweep showed the characteristic reduction peak atà0.16V versus Ag/AgCl with no associated oxidation peak indicative of the loss of N2 and the formation of a4-carboxyphenyl radical fol-lowed by covalent binding to the carbon surface[34]. Subsequent scans showed no electrochemistry indicative of a passivated electrode.The passivation of the GC sur-faces after the modi?cation with aryl diazonium salts was con?rmed using potassium ferricyanide as a redox probe.Fig.1shows a cyclic voltammogram before and after modi?cation with(4-carboxyphenyl)diazonium tetra?uoroborate in1mM ferricyanide in a0.05M phosphate bu?er(0.05M KCl,pH7.0)at a scan rate of100mV sà1.After the modi?cation of the surface with the aryl diazonium salts,the redox peaks of ferricy-anide observed with bare GC electrodes were almost completely suppressed.This gave strong evidence that a uniform monolayer which blocked access of ferricya-nide to the electrode had formed on the GC surfaces. Based on the area of the reduction peak during the mod-i?cation of the GC electrode surface with the aryl diazo-nium salt,the coverage of the4-carboxyphenyl moieties was calculated to be7.4·10à10mol cmà2.The reported surface coverage on GC substrates varies in the range of 4–30·10à10mol cmà2[35]with the theoretical maxi-mum surface coverage[29]for a monolayer on GC sur-faces being12·10à10mol cmà2.The surface coverage of7.4·10à10mol cmà2indicates the GC electrode was modi?ed with a monolayer rather than multilayers of aryl groups as has been reported by some workers[36–38].

The modi?cation of the GC electrode by electro-chemical reduction of(4-carboxyphenyl)diazonium tet-ra?uoroborate was con?rmed by X-ray photoelectron spectroscopy(XPS).Survey spectra showed the expected carbon1s and oxygen1s peaks at$284and$532eV, respectively,and also a small nitrogen1s peak at $400eV(Fig.2).The level of oxygen was increased in comparison to the bare GC surface as expected for the introduction of4-carboxyphenyl groups onto the sur-face.The presence of the small nitrogen1s peak in the survey spectra was partially due to nitrogen containing species already detectable on the unmodi?ed GC elec-trodes,which has been observed previously[13,34].Fur-thermore,nitrogen species with a binding energy of $400eV can be introduced onto the surface during the modi?cation reaction.It has been proposed that these are due to a hydrazine generated by reaction of the dia-zonium salt with phenol groups on the GC surface[26]

.

Fig.2.XP survey spectrum and carbon1s narrow scan(inset)of a GC

electrode modi?ed by electrochemical reduction of(4-carboxyphenyl)

diazonium tetra?uoroborate.

G.Liu et al./Chemical Physics319(2005)136–146139

Nitrogen1s narrow scans(not shown)were consistent with the formation of low levels of the hydrazine,which exhibited a slightly di?erent binding energy to that of the nitrogen species already present on the bare GC electrode.

The carbon1s narrow scan(Fig.2,inset)showed a peak centred at288.8eV,which was typical of the car-bon of the carboxylic acid group[13].This peak was ab-sent from the carbon1s narrow scan of unmodi?ed GC surfaces.The carbon1s peak at284.4eV was slightly broadened compared to the graphitic peak of an unmodi?ed GC surface and was assigned to the gra-phitic carbon of the underlying GC electrode and the aromatic carbons of the monolayer.The pronounced asymmetry of this peak with a broad shoulder on the high binding energy side($286.2eV)was attributed to an oxidized species present on the GC surface and or-ganic contaminants adsorbed on the monolayer.

After modi?cation of the GC electrode surface with the aryl diazonium salt the next step in the fabrication of the modi?ed electrodes was the attachment of ferro-cene.CVs measured in an aqueous solution of0.05M phosphate bu?er(0.05M KCl,pH7.0)at a scan rate of100mV sà1before and after the immobilization of ferrocene on the4-carboxyphenyl modi?ed GC elec-trode are shown in Fig.3.The strong redox peaks after the attachment of ferrocene showed linear variation in peak current with scan rate indicating that the ferrocene was surface bound.In the absence of EDC and NHS such that no covalent coupling of the ferrocene could occur,only very weak redox peaks due to physisorption were observed.The CVs of the ferrocene coupled to the 4-carboxyphenyl monolayers show non-ideal behaviour

[1]with regards to peak separation at slow scan rates

(D E p=79mV rather than the ideal D E p=0mV)and the full width half maximum(greater than200mV rather than the ideal E FWHM=90.6mV/n where in this case n=1).With regards to both peak separation and the E FWHM the non-ideal behaviour has been attributed to the ferrocene molecules being located in a range of environments with a range of formal electrode potentials (E0)[39,40].We[29,41]and others[42]have noted pre-viously that fabricating redox active SAMs by assem-bling the SAM and then attaching the redox molecule, results in broader FWHM than observed with electrodes where a redox active alkanethiol was attached directly to the electrode.The reason for modifying electrodes in this step-wise manner,where the monolayer is formed and then the redox active molecule attached,rather than synthesizing a pure redox active self-assembling mole-cule followed by assembly on the electrode,is because in applications of our interest,bioelectronics,the step-wise strategy is the only viable approach.

With a monolayer containing only4-carboxyphenyl moieties the number of redox active molecules attached to the surface,as determined from the charge passed under the Faradaic peaks in the ferrocene modi?ed electrode,is approximately(0.073±0.012)·10à10 mol cmà2with a close to unity ratio of anodic to cathodic peak areas(see Table1).Comparing the surface coverage of4-carboxyphenyl groups of7.4·10à10mol cmà2,to that of the number of redox centres attached indicates that only approximately10%of the 4-carboxyphenyl monolayers had a ferrocene attached. At this surface coverage the average area per ferrocene molecule,assuming homogeneous distribution,is 2.2nm2which suggests there is a high possibility of interaction between redox active centres[29,42].

Interaction between redox active centres has been re-ported to decrease the reorganization energy and in-crease the electron transmission e?ciency[4,43,44], hence providing an anomalously high measure of the rate constant for electron transfer.As a consequence, the number of coupling points within the monolayer that the ferrocene could couple was reduced by forming mixed monolayers composed of the4-carboxyphenyl diazonium salt and the phenyl diazonium salt(Table 1).Table1shows that the surface coverage initially in-creased with the spacing of the coupling points followed by the more expected decrease as the number of cou-pling points decreased.The reason for the initial in-crease in surface coverage of ferrocene as the solution composition from which the monolayer forms changes from entirely4-carboxyphenyl diazonium salt to a1:1 ratio of4-carboxyphenyl to phenyl diazonium salt is un-clear.The percentage of carboxyl groups to be activated using EDC/NHS,as used here,in a SAM composed of entirely carboxylic acids has been shown to be approxi-mately50%[45]which is equivalent to all the4-carboxy-phenyl groups being activated in a1:1monolayer. Furthermore,the relative surface coverages of the

4-

carboxyphenyl to ferrocene is10:1in the entirely4-carb-oxyphenyl monolayer so there should be excess coupling points for the ferrocene to attach.Therefore,it is sug-gested that the introduction of a second component into the monolayer(the phenyl diluent)in e?ect introduces a hydrophobic component into the monolayer.As ferro-cene has been shown previously to adsorb onto the sur-face of hydrophobic self-assembled monolayers[41,46]. Therefore,it is proposed that more ferrocene is attached when the phenyl component is introduced into the monolayer because the surface is more energetically favourable location for the ferrocene compared with an entirely carboxyphenyl monolayer.

The rate constant for electron transfer was deter-mined from the variation in peak position between the anodic and cathodic scans as a function of scan rate. In this study,the variation in peak potential over a wide range of scan rates was?tted using the Marcus theory for electron transfer as described previously[30–32] rather than the Laviron[33]formalism which relies on simple Butler–Volmer kinetics and gives rate constants for electron transfer which are sensitive to the choice of sweep rates investigated.Table1shows that across the spectrum of dilution ratios investigated the rate con-stant for electron transfer(k app)is approximately15–20sà1.

3.2.Aryl diazonium salt modi?ed gold electrodes

Gold electrodes were modi?ed with aryl diazonium salts via electrochemical reduction in exactly the same manner to the GC electrodes.The reduction peak for the attachment of the aryl diazonium salt onto the gold electrode,observed in the?rst sweep,was shifted anod-ically230mV relative to carbon being at+70mV versus Ag/AgCl.Subsequent sweeps showed no electrochemis-try indicating a monolayer coverage of4-carboxyphenyl moieties on the electrode surface.The4-carboxyphenyl monolayer blocked access of potassium ferricyanide to the electrode in a similar manner to that depicted in Fig.1for the carbon electrode but to a lesser extent. The coverage of the4-carboxyphenyl moieties on the electrode surface was6.4·10à10mol cmà2which was lower than the7.4·10à10mol cmà2observed on GC electrodes and hence lower than the theoretical maxi-mum surface coverage[34]for a monolayer of 12·10à10mol cmà2.The lower surface coverage could be a re?ection of the aryl diazonium salt not being nor-mal to the surface of the gold,as suggested by infra-red spectroscopy[20].Again,the presence of a monolayer or submonolayer of aryl diazonium salt on the gold elec-trode is important due to the possibilities of obtaining multilayers with aryl diazonium salts as shown for both carbon[36–38]and metal surfaces[20].

An XP survey spectrum of gold modi?ed with(4-carboxyphenyl)diazonium tetra?uoroborate showed the expected1s peaks of carbon and oxygen at$285 and$532eV,respectively,but no signi?cant evidence of a nitrogen1s peak(Fig.4).The carbon1s envelope (Fig.4,inset)was?tted with four peaks at288.7, 286.2,284.6and283.9eV assigned to the carboxylic acid moieties,C–O species,the aromatic carbons of the monolayer and the metal-bonded carbon,respectively. The binding energy observed for the carboxylic acid group on gold was consistent with that observed on the GC surface.The inclusion of the metal carbide peak is exceedingly tentative as a good?t to the spectra could be obtained without the presence of this peak.The assignment of the metal carbide peak is based on the

Table1

Some parameters of ferrocenemethylamine immobilized on GC electrodes modi?ed with mixed monolayers of4-carboxyphenyl and phenyl moieties.

D E p is recorded at a scan rate of100mV sà1

[Benzyl]/[benzoic acid]E0(mV)D E(mV)E FWHM(mV)C(pmol cmà2)C a/C c k app(sà1) 0264±1579±10241±1072.8±11.60.89±0.0717±10 1279±1378±14213±19100.3±10.4 1.03±0.0428±10 5292±989±25227±2567.4±10.70.94±0.0515±5 10298±793±10262±3848.1±6.90.88±0.1116±2 20304±17101±21220±2929.4±3.40.71±0.1615±10 40317±19107±10289±1413.3±2.00.77±0.1310±

2

Fig.4.XP survey spectrum and carbon1s narrow scan(inset)of a

gold electrode modi?ed by electrochemical reduction of(4-carboxy-

phenyl)diazonium tetra?uoroborate.

G.Liu et al./Chemical Physics319(2005)136–146141

precedence of Pinson and co-workers[19,20,47]who have previously proposed the existence of such a peak for the electroreduction of diazonium salts onto metal surfaces.On iron surfaces the case for a metal–carbide peak is compelling with a very pronounced shoulder when a high resolution instrument is used[47]with the intensity of this shoulder sensitive to take-o?angle indi-cating it is a surface bound species.However,on copper electrodes[20]and other examples on iron[19]the shoulder on the carbon1s spectra is less pronounced similar to the observations on gold here.

The electrochemical parameters after the attachment of ferrocene to the4-carboxyphenyl modi?ed gold elec-trodes are shown in Table2.The trends were very sim-ilar to the GC modi?ed electrodes with broader than ideal E FWHM and non-ideal D E p at slow scan rates. The surface coverage of ferrocene with di?erent ratios of diluent to4-carboxyphenyl were slightly lower than those on GC in common with the lower coverage in gen-eral of the aryl diazonium salts on gold compared with GC.Most importantly,the rates of electron transfer measured on the gold modi?ed surface were signi?cantly greater than that observed on carbon.Typically rates of more than a100sà1were observed,which was approx-imately one order of magnitude higher than for the same monolayer system on GC electrodes.The values of the rate constants at the low surface coverage of ferrocene (last three entries in the table)were particularly di?cult to determine because with small redox peaks back-ground subtraction can have a large impact on the peak positions.As a consequence the rate constants quoted represent the lower limits and therefore we expect the true rate constant is closer to that observed at the1:5 monolayer.

3.3.Aryl thiol modi?ed gold electrodes

For comparison with the monolayers formed by elec-trochemical reduction of aryl diazonium salts we also prepared mixed monolayers of aryl thiol self-assembled monolayers on gold electrodes with attached ferrocene moieties as shown in Scheme2.The rate constants deter-mined for this equivalent aryl thiol system were in the order of103sà1(at the limits of what can be measured electrochemically)which was approximately5–10times the values observed for the aryl diazonium salt–gold sys-tem but two orders of magnitude higher than those ob-served for the aryl diazonium salt–GC system.These observations indicate that the metal surface has a signif-icant e?ect on the rate of electron transfer.

4.Discussion

The rate constants for electron transfer are remark-ably slower for the carbon electrodes relative to the gold electrodes.This is contrary to the suggestion that with diazonium salt modi?ed carbon electrodes the continu-ity of conjugated carbon network from the electrode into the monolayer will result in a lower barrier for elec-tron transfer than with organic monolayers on metallic electrodes[11].The question that arises is why there is a di?erence in rate constants of around one order of magnitude for the same redox active molecule connected to electrodes by the same bridge molecule?

The Marcus–Hush expression for electron transfer between a donor and acceptor through an organic bridge in solution includes terms for electronic coupling between the donor and acceptor,the Gibbs free energy for electron transfer(the driving force,D G ET)and the nuclear reorganization energy(k)of the redox molecule as a consequence of its change in oxidation state[48]. For a given donor and acceptor pair the rate of electron transfer decays exponentially with distance according to a proportionality constant,the b value,sometimes called a damping factor.When the organic bridge is anchored to an electrode such that it can act as the donor and/or acceptor the situation is complicated somewhat as the electronic properties of the electrode can also play a role in the rate of electron transfer[2].Equations describing the rate constant for electron transfer now incorporate terms related to the Fermi levels of the electrode and the e?ective density of electronic states near the Fermi level.In this study,the only changes between the mono-layer systems studied relate to the electrode material and the bond to the electrode.Hence,the reorganization en-ergy and the driving force will remain unchanged.The electronic coupling may be in?uenced by the electrode

Table2

Some parameters of ferrocenemethylamine immobilized on gold electrodes modi?ed with mixed monolayers of4-carboxyphenyl and phenyl moieties.

D E p is recorded at a scan rate of100mV sà1

[Benzyl]/[benzoic acid]E0(mV)D E(mV)E FWHM(mV)C(pmol cmà2)C a/C c k app(sà1) 0268±1281±14209±1149.3±7.60.87±0.13257±41 1277±2585±9191±1780.6±5.90.86±0.09530±42 5280±1875±10227±853.7±5.40.72±0.14211±23 10282±1492±12260±1525.8±4.00.92±0.0783±50 20292±1989±8272±1413.3±2.40.76±0.0369±50 40317±2181±16308±107.1±1.00.93±0.0268±50 142G.Liu et al./Chemical Physics319(2005)136–146

material,as changes in electrodes may alter the extent of wave function mixing between the organic molecules and the substrates,especially when conjugated mole-cules are involved as in this case.A detailed discussion of the theory of electron transfer and how di?erent elec-trode materials will in?uence the electron transfer is clearly not within the scope of our expertize.However, some comments on the large di?erence in the rate of electron transfer within the limited knowledge of the experimental systems investigated is worthwhile and may stimulate useful debate.

The?rst possibility is that there are multilayers on the carbon electrode rather than monolayers of the bridge molecule as the rate of electron transfer decays exponentially with distance.However,the surface cov-erage of the reduced aryl diazonium salts on the elec-trode,as determined from the charge passed,was below the maximum theoretical coverage for a mono-layer of reduced aryl diazonium salts.This suggests a monolayer or submonolayer modi?cation of the carbon electrode.Hence,any signi?cant multilayering can be ruled out and the di?erence in electron transfer rate must,in someway,be related to the di?erent electrode surfaces.

The di?erent electrode surfaces could in?uence the rate of electron transfer due to the di?erent electronic properties of the surfaces or the nature of the linkage made to each electrode or both.Our results support both of these possibilities playing a role.We draw this conclusion from the di?erences in rate constant calcu-lated on the gold surface for the aryl diazonium salt rel-ative to aryl thiol monolayers and the large di?erence the aryl diazonium salt derived monolayers on gold ver-sus the carbon electrodes.The investigation of the aryl thiol monolayer systems on gold was necessary to draw this conclusion because of the uncertainty in the nature of the bond formed between the monolayer and the gold surface during the electroreduction of the aryl diazo-nium salt.On carbon electrodes a carbon–carbon cova-lent bond with little charge transfer is well established but the existence of a metal–carbon bond much less so.As indicated in the results section,the?tting of the C1s spectrum with a metal carbide bond is tentative, as a good?t could also be achieved without including this bond.The suggestion of a metal–carbon bond is based on the precedence of Pinson and coworkers [19,20,47]who have provided good evidence for a metal carbon bond on iron and copper surfaces with very lim-ited charge transfer[20].That is a similar bond to that formed on a carbon electrode.The gold–thiol bond however,although also the subject of some controversy, is generally accepted as being a pseudocovalent bond with signi?cant ionic character[49].In our hands the rate constant for the gold–thiol system is at least?ve times that for the aryl diazonium derived monolayer on gold,despite the extra bond between the phenyl ring and the electrode,which is the reason for the assertion that the bond to the electrode is playing some role.1 If the bond between the organic monolayer and the electrode is only of minor importance when considering the large di?erence in rate constants between the gold and carbon electrodes,what is it about the electrode materials which cause such a large di?erence?For satu-rated bridge molecules in metal–molecule–metal junc-tions fabricated by assembling a monolayer on an electrode surface and contacting the top with a conduct-ing probe atomic force microscope,Beebe et al.[50]have shown that the contact resistance is increased with increasing work function of the metals in the junction. Although GC is a heterogeneous material,the work function for carbon is approximately5.0eV whilst for polycrystalline gold it is5.1eV[51].The similarity in the work-functions suggests this is not a dominant fac-tor in the large di?erence in the rate constant for elec-tron transfer.As a consequence,we propose the di?erence in rate constant is due to a di?erence in the electronic coupling between the electrode and the redox molecule,perhaps as a consequence of wave function mixing between the molecule and the electrode[52]. Stokbro et al.[53]have calculated for dithiol benzene assembled on a gold molecular break junction that when a gold–thiolate bond is formed the energies of the HOMO and LUMO of the dithiol benzene fall below the Fermi level of the organic molecule.Therefore,the electron density of the metal spills over into the organic molecule and both the HOMO and LUMO are occu-pied.A similar type of conclusion is arrived at by Hall et al.[54]for a molecular break junction with the same chemical system.Thus,we propose that spill over of electron density into the resultant monolayer derived from the aryl diazonium salts occurs on gold surfaces to a far greater extent than carbon surfaces and hence the rate of electron transfer is signi?cantly greater.

The proposed chemical functionalities at the surface of polished GC electrodes include quinones,lactones, ketones,alcohols and carboxylic acids[16]as shown in Fig.5A.The inference of Fig.5A is that the delocaliza-tion of electrons throughout the carbon network is a consequence of an aromatic network of fused benzene rings.Radical attack by reduced aryl diazonium salts is expected to occur at electron rich centres such as car-bons in the benzene rings and the carbons ortho to the 1Note we are not suggesting here that the carbon–carbon bond and the carbon–gold bond are identical,just that they are more similar than the gold–thiol bond.With the electroreduction of the aryl diazonium salt on either electrode material it appears that a covalent bond with limited charge transfer is formed between a phenyl ring and the electrode.In contrast,with the gold–thiol case a pseudocovalent bond is formed with an ionic character and a sulphur atom,which can provide a signi?cant barrier to electron transfer[11],resides between the phenyl ring and the electrode.

G.Liu et al./Chemical Physics319(2005)136–146143

alcohols.Therefore,after attack by the aryl radicals the modi?ed surface is expected to look like Fig.5B.The hydrazine species proposed are observed in the XPS of the aryl diazonium salt modi?ed carbon surfaces whilst no hydrazine species were observed after modi?cation of the gold electrodes with the aryl diazonium salts as ex-pected.Ignoring the hydrazine,which the XPS suggests is only a minor component of the surface,the carbon–carbon single bond between the bulk GC and the aryl rings from the diazonium salt suggests rather than a continuation of the aromaticity of the carbon surface,the coupling of the monolayer to this aromatic network by a single bond actually forms a barrier to the aromatic network.Biphenyl serves as an analogy to a phenyl dia-zonium salt coupled to a GC electrode,as it is one ben-zene ring connected to another benzene ring by a carbon–carbon single bond.Although aromatic biphe-nyl represents two e?ectively isolated aromatic rings with little or no delocalization of electrons between the rings.We propose therefore that with the carbon sur-faces the mixing of delocalized electrons between the GC and the monolayer on the surface is unlikely to oc-cur to a signi?cant extent and hence there is a greater barrier to electron transfer than with the gold electrodes where electron density can spill over into the organic monolayer.

Evidence to support the notion that there is little mix-ing of delocalized electrons between a GC electrode and an aryl diazonium salt derived monolayer comes from Solak et al.[55].Solak et al.[55]showed that a biphenyl diazonium salt modi?ed GC electrode was e?ectively passivating to outer sphere redox active molecules in solution,a similar observation to Fig.1.However,upon poising the electrode at à0.2V,in which an electron is injected into the biphenyl ring,the organic layer depos-ited onto the GC electrode became conducting.Further layers of diazonium salts could be deposited and good electron transfer could occur to redox species in solu-tion.Thus,the situation changed from the monolayer being a layer over the electrode to part of the electrode.It was proposed that the injection of an electron resulted in a change in the organization of p -bonds with a double bond connecting the GC electrode to the monolayer.Thus,the injection of the electron caused a signi?cant decrease in the HOMO–LUMO gap,a reduction in the barrier to electron transfer and a higher electronic conductance.Thus,with the data presented in this pa-per,if on gold there is mixing of delocalized electrons between the gold electrode and the organic monolayer but little or no mixing of delocalized electrons on the GC electrodes there should be a di?erence in the amount of electron transfer that can be achieved with a redox ac-tive molecule in solution rather than attached to the monolayer.

The electrochemistry of the monolayer modi?ed GC and gold electrodes with redox active molecule in solu-tion are shown in Fig.6.In both cases the electrode is modi?ed with a 1:1ratio of the carboxyphenyl to phenyl component.The two redox active molecules are ferricy-anide in aqueous solution and ferrocene recorded in ace-tonitrile.These were chosen as they are both redox molecules which undergo outer sphere electron transfer rather than adsorbing onto an electrode surface prior to electron transfer occurring.Ferricyanide is negatively charged and may be repelled from the electrode surface by the carboxylate species at the electrode surface whilst ferrocene is neutral.Fig.6clearly shows di?usion con-trolled CVs where there is signi?cantly more electron transfer through the monolayer on gold as distinct from carbon.This is particularly dramatic with the ferrocene redox couple where on gold the redox chemistry is iden-tical to when the monolayer is absent.It is important to emphasize the ferricyanide electrochemistry was per-formed after the ferrocene measurements,verifying the monolayer is present.Thus assuming the packing of the diazonium salt derived monolayer is not dramati-cally di?erent,and the similarity in surface coverage during deposition suggests the coverage of monolayer is similar on each electrode material,these results pro-vide good evidence that the order of magnitude di?er-ence in electron transfer ability between aryl diazonium salt derived monolayer on gold and the

same

Fig.5.Schematic of (A)a GC electrode showing the functional groups typically found on the electrode surface and (B)after modi?cation with an aryl diazonium salt.

144G.Liu et al./Chemical Physics 319(2005)136–146

monolayer on GC is due to better mixing of delocalized electrons on the gold surface.

5.Conclusions

Electrochemical reduction of mixtures of 4-carboxy-phenyl and phenyl diazonium salts on GC and gold surfaces yielded stable monolayers to which ferrocenem-ethylamine could be covalently attached via activation of the surface bound 4-carboxyphenyl moieties.The rates of the heterogeneous electron transfer for immobi-lized ferrocene through the mixed monolayers were an order of magnitude higher for the gold electrodes in comparison to the GC electrodes.Furthermore,mixed diazonium salt derived monolayers on GC showed stronger blocking of electron transfer from redox-cou-ples in solution than the equivalent monolayers on gold.These results suggest that the mixing of delocalized elec-trons between the electrode material and the monolayer occurs to a greater extent for gold than for GC allowing more rapid electron transfer for the system on gold than that on GC.

Acknowledgements

Aspects of this work were supported ?nancially by the Australian Research Council and the CASS Foun-dation.Guozhen Liu thanks the Australian Government for an International Postgraduate Research Scholarship.We thank Associate Professor Mike Ford and Dr.Jason Harper for useful discussions.

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碳糊修饰电极的应用研究进展

课程论文

碳糊修饰电极的应用研究进展 姓名：王添璞学院：材料科学与工程学院 班级：2007级应用化学学号：0714431027 摘要：本文主要是对使用碳糊修饰电极对Pb2+、I-、痕量银、痕量铜、痕量钪及水中镉离子的电化学测定方法的研究进展做一简单综述。 关键词：碳糊修饰电极痕量测定 1.引言 电化学分析具有快速、简便、灵敏的特点，其中固体电极特别是碳糊电极的优点尤其突出，主要表现在:无毒，残余电流小，制作简单，表面易更新，电位使用范围宽，价格便宜。因而碳糊电极广泛应用于测定无机离子、有机物。 2.碳糊电极简介 碳糊电极，即利用导电性的石墨粉与憎水性的粘合剂混制成糊状物，然后将其涂在电极棒上或填充入电极管中而制成的一类电极。由于CPE具有制作方便、无毒、应用范围广、使用寿命长、重现性好等特点，因而自从Adams于二十世纪五十年代制备出第一根碳糊电极起，特别是七十年代“化学修饰”概念的出现，以及八十年代“直接混合”技术的引入以来，碳糊电极倍受广大电分析化学工作者的青睐。碳糊电极(CPE)的性能取决于其所用的材料(碳粉和粘合刑)、制备方法、电极表面状态以及使用时间等。碳粉为多晶粉末，由于其吸附性能很大程度上取决于它的表面结构，因此它的不同来源及颗粒度的粗细对CPE 的性能影响较大，一般来说，碳粉的平均直径应在0.01-0.02mm之间，粉末越细的碳粉越易混匀，因而也就越易制得重现性好、残余电流小的碳糊电极。粘合剂的作用是使碳粉粘合成糊状，有时还起着选择性萃取以提高分析选择性的作用。与其它种类的电极相比，CPE 具有许多优点，突出表现在:残余电流小，制作简单，表面易更新，电位使用范围宽特别是正电位可适用+1.7V(vs.SCE)，价格便宜，因而碳糊电极广泛应用于测定无机离子、有机物，还可以应用于电化学反应机理研究、化学物相分析等。【1】 3.碳糊修饰电极简介 在碳糊中加入一定量的修饰剂便制得了均匀的化学修饰碳糊电极（CMCPE）。一般的固体修饰电极，在电极表面接着或涂敷了具有选择化学基团的一层薄膜，虽然达到了对电极表面进行人工修饰的目的，但制备手续繁琐，又不易控制电极表面的修饰，存在性能不够稳定的问题。在电分析化学中，一般所用的电极都只有电子授受的单一作用，溶液中大多数离子在电极上电子转移的速度较慢，如何使电极性能成为预定地、有选择地进行反应，并提供更快的电子转移速度已成为电极的一个重要方向，于是提出了化学修饰电极。CMCPE 是化学修饰电极的一种，它继承了CPE的全部优点，同时，由于特效性修饰剂的引入，使其灵敏度、选择性进一步提高，而且还具有了修饰电极的特征，如易于制成各种功能的电

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A highly sensitive hydrogen peroxide amperometric sensor based onMnO2-modi?ed vertically aligned multiwalled carbon nanotubes，Analytica Chimica Acta，2010 MnO2-多臂碳纳米管 Cu电极 Gold nanoparticles mediate the assembly of manganese dioxide nanoparticles for H2O2 amperometric sensing，Electrochimica Acta，2010 MnO2–AuNP/ GCE H2O2电流传感 器 A novel nonenzymatic hydrogen peroxide sensor based on MnO2/graphene oxide Nanocomposite，Talanta，2010 GO/MnO2/ GCE（氧化 石墨烯） H2O2电流传感 器 Electrochemical investigation of MnO2 electrode material for supercapacitors，ScienceDirect，2011 MnO2泡沫镍电极MnO2电活性物 质作为超级电容 材料 Facile synthesis of novel MnO2 hierarchical nanostructures and their application to nitrite sensing，Sensors and Actuators B: Chemical，2009 MnO2/QPVP-Os/GCE (联吡啶锇取代的聚乙 烯吡啶) 亚硝酸盐传感器 Preparation of MnO2/graphene composite as electrode material for supercapacitors，J Mater Sci ，2011 MnO2/grapheme(石墨 烯) 超级电容器 Hydrogen peroxide sensor based on glassy carbon electrode modified with β-manganese dioxide nanorods，Microchim Acta (2011) β-MnO nanorods/GCE 。 H2O2电化学传 感器 Mn3O4 Graphene Hybrid as a High-Capacity Anode Material for Lithium Ion Batteries，American Chemical Societ，2010 Mn3O4/RGO（还原石墨 电极） 锂离子电池阳极 材料 Non-enzymatic electrochemical CuO nano?owers sensor for hydrogen peroxide detection，Talanta，2010 CuO/Cu箔H2O2电流传感 器（无酶） Synthesis of CuO nanostructures and their application for nonenzymatic glucose sensing，Sensors and Actuators B: Chemical，2010 CuO以碳为基底做成电 极 葡萄糖传感器 （无酶） A highly sensitive nonenzymatic glucose sensor based on CuO nanoparticles-modi?ed carbon nanotube electrode，Biosensors and Bioelectronics，2010 CuO/MWCNTs/Cu电极葡萄糖传感器 （无酶） An improved sensitivity nonenzymatic glucose biosensor based on a CuxO modi?ed electrode，Biosensors and Bioelectronics，2010 CuxO/Cu箔葡萄糖传感器 （无酶） Synthesis of CuO nanoflower and its application as a H2O2 sensor，Bull. Mater. Sci，2010 CuO NFS/Nafion-Au电 极 H2O2电流传感 器（无酶）

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碳糊电极和化学修饰碳糊电极的制备及应用综述摘要：碳糊电极和化学修饰碳糊电极在电化学研究中起着非常重要的作用.从电极材料选用和修饰剂选择方面综述了碳糊电极和化学修饰碳糊电极制备的几种方法，概括了近年来化学修饰电极的应用.关键词：碳糊电极；修饰剂；制备；应用；CPE；CMCPE 所谓碳糊电极（carbon paste electrode，简称CPE）是利用导电性的石墨粉（颗粒度0.02 mm~0.01mm）与憎水性的粘合剂（如石蜡、硅油等）混合制成糊状物，再将其涂在电极棒表面或填充入电极管中而制成的一类电极.由于碳糊电极无毒、电位窗口（依实验条件电位范围为-1.4~+1.3V，最高至+1.7 V）制作简单、成本低廉、表面容易更新，备受电化学分析工作者的青睐.然而，单纯的CPE 作用有限，后来通过电极修饰的方法使其具有一定功能，即化学修饰碳糊电极（CMCPE）.CMCPE 是在CPE 基础上发展起来的，由碳糊表面接着化学修饰剂构成，通过对电极表面的分子剪裁，可按意图给电极修饰预定的功能.CMCPE的出现提高了CPE 的选择性和灵敏度，使分离、富集和选择性测定三者合而为一. 迄今为止，CPE 及CMCPE 已在无机物分析、有机物分析及药物分析、电化学和生物传感器等研究中得到广泛应用. 1. 碳糊电极（CPE）的制备方法 将石墨粉和粘合剂按适当比例充分混匀至糊状，将该糊状物压入适当直径的绝缘槽内（如玻璃管等），另一端与导线相连，紧密

填实，抛光即可.从CPE 的制备方法可知，其原料除石墨粉外，还有粘合剂，这里粘合剂的作用仅使电极成型而不参与导电.石墨粉与粘合剂混合的比例是CPE 制备的关键因素之一.通常因粘合剂种类不同，混合比例也不同.制备CPE 的粘合剂主要有两大类. 1.1 非导体粘合剂 （1）有机液体粘合剂，如石蜡、硅油、矿物油、环氧树脂等.在这类电极上，电化学反应在电极与试液界面上进行. （2）固体粘合剂，如固体石蜡、PVC（Polyvinyl chlorid）等.固体石蜡作粘合剂的CPE 比普通CPE 具有更多的优越性，如电极表面光洁稳定、重现性好、背景噪音低、灵敏度高、选择性好等，并且能够在流动体系中应用. 1.2 电解质溶液粘合剂 NaOH 即是一种电解质溶液粘合剂，使用这类粘合剂制备的CPE，电化学反应可在电极本体内进行，从而扩大了CPE 的应用范围，电极表面易于更新，正电位残余电流低.但由于该电极坚固性较差，在负电位区背景电流大，导致以该种粘合剂制备的CPE 在电化学研究中鲜于使用. 2. 化学修饰碳糊电极（CMCPE）的制备方法 CMCPE 与普通CPE 不同的是决定电极性能的关键因素是修饰剂. 修饰剂的种类和用量直接关系到电极的灵敏度和选择性. 修

线性扫描伏安法测定废水中的镉离子含量

线性扫描伏安法测定废水中的镉 摘要：本实验利用线性扫描伏安法扫描废水中镉离子浓度，使用铋膜碳电极为工作电极，Ag/AgCl 电极为参比电极，Pt为辅助电极的三电极系统，在CHI660A电化学工作站采用常规峰电流对镉离子浓度作回归方程，结果测得：对常规峰进行处理后得方程y = 356.44x + 0.0348，相关系数R2达0.9997，测得含量为50.40 mg.L-1。此法精度高、迅速、灵敏，结果令人满意。 关键词：线性扫描伏安法镉离子常规峰电流半微分峰电流 1.引言 镉（Cadmium）是一种重金属，与氧、氯、硫等化学元素形成无机化合物分布于自然界中。人体健康的危害主要来源于工农业生产所造成的环境污染。镉在工业中有广泛应用，如电池、电镀合金、油漆和塑料等的生产和使用。镉对肾、肺、肝、睾丸、脑、骨骼及血液系统均可产生毒性，且环境中的镉不能生物降解，所以现今镉的污染已经处于较为严重的状况[1]。 目前国家对于镉离子分析的标准测定方法有：无火焰原子吸收分光光度法、火焰原子吸收分光光度法、双硫脉分光光度法[2]。 伏安法和极谱法是一种特殊的电解方法。以小面积、易极化的电极为工作电极，以大面积、不易极化的电极为参比电极组成电解池，电解被分析物质的稀溶液，由所测得的电流－电压特性曲线来进行定性和定量分析的方法。使用滴汞电极或其他表面能够周期性更新的液体电极者称极谱法,使用表面静止的液体或固体电极者称伏安法。伏安法由极谱法发展而来，后者是伏安法的特例。极谱法的使用涉及到汞，毒性问题较为严重；且若采用极谱法，则需要消除氧波（加入Na2SO3、抗坏血酸、通惰性气体或N2保护）和极谱极大（加入一些表面活性物质如明胶、PVA、Triton X-100等）的干扰，过程较为繁琐。由于线性扫描伏安法扫描的速度比较快，氧波和前波的干扰很小，可不除氧，前放电物质存在也不干扰测定[3]。 伏安法作为一种非分析方法，主要用于研究各种介质中的氧化还原过程、表面吸附过程以及化学修饰电极表面电子转移机制。伏安法选择性和灵敏度较高，而且随着低成本的电子放大装置出现，伏安法开始大量用于医药、生物和环境分析中[4]。相对于其他测定痕量镉的方法包括 ICP-AES[5]，火焰原子光谱法[2]等，这些方法同样需要绘制回归方程，相对误差较大（在1%-5%左右），相关系数R一般比较低。而采用线性伏安法仪器造价低廉、灵敏度高、有一定精确度、测试速度快、维护成本较低、携带方便。 综上所述，本实验中将采用线性扫描伏安法对废水样品中镉离子浓度进行测量。 2.实验部分

电沉积纳米金的读书笔记

[1]吉玉兰, 王广凤, 方宾. 纳米金/单壁碳管修饰玻碳电极对黄芩苷的电催化作用及快速检 测[J].2010, 6(6): 11-12. NG/GCE电极的制备 将l mg酸化的SWNT分散在5 mL DMF中，超声振荡至溶液均一。玻碳电极先在0.05 μm A2O3上抛光，然后分别在无水乙醇和二次蒸馏水中各超声清洗l min，晾干后，用微量进样器取10.0μL上述SWNT分散液滴加在玻碳电极表面，晾干，即得SWNT/GCE。将SWNT/GCE用二次水冲净置于0.1 mg/mL HAuCl4中，以扫速50 mV/s，于1.2～-0.6 V范围连续扫描5圈，取出用水反复冲净，晾干得NG／SWNT／GCE。 [2]张英，袁若，柴雅琴等. 纳米金修饰玻碳电极测定对苯二酚[J]. 西南师范大学学报, 2002, 6(31):87-90. NG/GCE电极的制备 将玻碳电极分别用0.1 μm和0.03 μm A12O3。粉末抛光成镜面，二次水冲洗，依次用(1+1) HNO3，无水乙醇和二次水超声清洗5 min，取出后用二次水冲净置于1 mg/mL HAuCl4中，以饱和甘汞电极(SCE)为参比，铂丝为对电极，于-0.2 V下保持60 s，取出后用二次水反复冲洗，得NG／GCE修饰电极，悬在pH为7.0的PBS上方保存备用。 NG/GCE修饰电极的性能 图1(a)是裸GCE和NG/GCE修饰电极在 5.0 mmol/L Fe(CN)63-/4- + 0.1 mol/L PBS(pH=7.0)中的循环伏安图．从图中可以看出，Fe(CN)63-/4-在NG/GCE修饰电极上峰电流明显增加，并且氧化还原峰电位差值减小，这主要是因为：NG使GCE电极的表面粗糙度和有效面积增加以及带正电荷的NG叫同带负电荷Fe(CN)63-/4-有较强的静电作用，使氧化还原发应更容易发生．图l(b)是裸GCE和NG/GCE修饰电极在5.0 mmol/L Fe(CN)63-/4-+0.1 mol/L PBS(pH=7.0)中的交流阻抗图，由图可知，NG/GCE电极膜的阻抗比裸GCE小很多，这说明NG能很好地增强电子的传输． [3]朱强，袁若，柴雅琴等.以纳米金为介质的无标记电流型甲胎蛋白免疫传感器的研 究[J]. 西南师范大学学报, 2002, 2(32):82-90.

碳糊电极的制备、处理及表征

实验二碳糊电极的制备、处理与表征（CV 法） 一、实验目的 1. 学习和掌握碳糊电极的制作方法； 2. 了解碳糊电极的性质。 二、实验原理 CHI 660电化学工作站（上海辰华公司）。实验采用三电极系统，以碳糊电极（φ= 2.4 mm）作为工作电极，对电极为铂丝电极，参比电极为银/氯化银电极（Ag/AgCl Sat. KCl）。 碳粉，石墨粉，糊碳(Electrodag 423SS, Acheson Colloids, Plymouth, UK ) ，银糊(silver ink，Electrodag 427，SS Acheson Colloids, Plymouth, UK) 氯化银糊(sliver chloride ink ，DB 2275, Acheson Colloids, Plymouth, UK)，液体石蜡油。二硫化钼，玻璃研钵，环氧树脂版（0.5 mm），自制不绣钢电极摸版，玻璃管（φ= 2.4 mm），铜导线。所用试剂均为分析纯，所有溶液均为二次去离子超纯水（Milli-Q公司超纯水(18. 0 MΩ)。0.10 mol·L-1K4 [Fe(CN)6]；0 10 mol·L-1 KCl。 三、实验步骤 1. 碳糊电极的制备与性能评价 将100 μL 液体石蜡油加入到盛有800 mg碳粉或石墨粉的玻璃研钵中，充分研磨得到颗粒细小、均匀的碳糊，再将其装填到玻璃管（φ= 2.4 mm）中，插入铜导线，即制成碳糊电极。

将100 μL 液体石蜡油加入到盛有800 mg碳粉或石墨粉及一定量二硫化钼混合的（这个条件要选择）玻璃研钵中，充分研磨得到颗粒细小、均匀的碳糊，再将其装填到玻璃管（φ= 2.4 mm）中，插入铜导线，即制成碳糊电极。 将所制碳糊电极在滤纸上磨檫处理，使其表面至平整。每次实验前碳糊电极均在0.10 mol/L 磷酸盐缓冲溶液（pH=7.4）中以100 mV/s扫速在0 ~ 1.2 V之间循环扫描，直至得到稳定的循环伏安曲线为止。 1. 考察不同量的二硫化钼对碳糊电极电化学行为性能的影响， 在0.04 mol·L-1 K4[Fe(CN)6] （含支持电解质KCl浓度为0.1 mol·L-1）溶液中，插入处理好的碳糊电极，以此更新处理的碳糊电极为指示电极，铂丝电极为辅助电极，饱和甘汞电极为参比电极，进行循环伏安仪测定。以5 mV/s、25 mV/s、50 mV/s、80 mV/s、100 mV/s、150 mV/s、200 mV/s的扫描速度，在-0.2至+0.6 V电位范围内扫描，分别记录循环伏安图，考察峰电流与扫速的关系。计算电极面积。 更新电极表面5次，测量某已确定（如50 mV/s）扫速下5次电极所得电流的相对标准偏差。说明电极制作的重复性。 2. 考察不同量的二硫化钼对碳糊电极上钌联吡啶电化学发光行为的影响 发光试验同第二次试验的过程，电极换为不同的碳糊电极。

葡萄糖氧化酶-金纳米粒子修饰电极灵敏检测葡萄糖浓度

葡萄糖氧化酶-金纳米粒子修饰电极灵敏检测葡萄糖浓度2016-06-19 12:24来源：内江洛伯尔材料科技有限公司作者：研发部 自组装法制备GOD/AuNPs/Chit-GP/GC 修饰电极过程示意图 近年来, 氧化还原酶与电极间的直接电子传输的相关研究引起了越来越多研究者的关注. 该领域的研究不但可以为深入探究生物体系复杂的电子传输机理提供良好的模型, 还可为新型的电化学生物传感器,生物燃料电池以及酶反应器等诸多方面的研究奠定基础. 然而, 由于酶的氧化还原中心往往深埋于其结构内部, 而且酶在裸电极表面容易因吸附而失活, 因此酶的活性中心与电极表面间的直接电子转移难以实现. 近期的研究发现, 选择合适的生物相容性材料和适宜的酶固载方法不仅可以有效保持酶的生物活性,还可较好地实现酶与电极间的直接电子传输. 由于其独特的结构和性质, 纳米材料尤其是碳基的纳米材料, 已被广泛应用到了酶的固载及新型生物传感器的构筑等方面. 例如, Sun等利用壳聚糖功能化石墨烯与葡萄糖氧化酶(GOD)间的自组装制备了GP-GOD玻碳(GC)修饰电极, 并利用其实现了对葡萄糖高效、灵敏的检测. Jiang等利用非共价修饰方法将壳聚糖修饰于单壁碳纳米管(SWNT)表面, 并进一步在复合物表面原位生长Au纳米粒子(GNPs), 从而制备了 SWNT-GNPs复合物. 利用该复合物与微过氧化物酶-11(MP-11)所构筑的 MP-11/SWNT-GNPs/Au修饰电极, 不仅可有效促进固载酶在电极表面的直接电子传输, 还可实现其对氧气的有效电催化. 作为一种新型碳基二维纳米材料,石墨烯由于具有较大的比表面积和良好的电子传输性等优点在电化学领域受到了广泛的关注. 研究表明, 利用石墨烯作为电极材料不仅可以促进氧化还原酶与电极间的直接电子转移, 还可以使所构筑的电化学生物传感器具有较好的性能. 例如, Zhao等将细胞色素c吸附到壳聚糖-石墨烯膜修饰的GC电极上成功构建了化学修饰电极. 该修饰电极不仅可实现细胞色素c与电极间的直接电子转移, 还可对NO表现出较好的电催化能力.然而, 由于石墨烯纳米片间存在强烈的范德华力及π-π相互作用, 致使其易发生团聚, 甚至堆叠成石墨, 从而使石墨烯丧失其特有的单片结构具有的独特性质, 也减少了其比表面积. 此外, 石墨烯表面的疏水性还阻碍了石墨烯与水溶性的氧化还原酶的进一步作用, 限制了石墨烯在生物传感器方面的应用. 因此, 制备兼具水溶性和生物相容性的石墨烯复合材料, 对其在氧化还原酶的固载及在第三代生物传感器构筑中的应用甚为重要.

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芦丁在纳米金修饰玻碳电极上的电化学行为及其测定一、实验目的 1．初步掌握电化学工作站的使用方法，掌握循环伏安法和差分脉冲伏安法的基本原理和测量技术 2. 通过对体系的测量，了解如何根据峰电流、峰电势及峰电势差和扫描速度之间的函数关系来判断电极反应过程的可逆性，以及求算有关的热力学参数和动力学参数。 3. 学习固体电极表面的处理方法 二、实验原理 芦丁(Rutin）是一种多羟基黄酮类化合物，存在于多种植物的茎和叶中，是一些中草药的有效成分。在临床上它可用于治疗过敏性紫瘫及各种因毛细管脆性增加而引起的出血性疾病和冠状动脉高血压病等。 循环伏安法是用途最广泛的研究电活性物质的电化学分析方法，在电化学、无机化学、有机化学、生物化学等领域得到了广泛的应用。由于它能在很宽的电位范围内迅速观察研究对象的氧化还原行为，因此电化学研究中常常首先进行的是循环伏安行为研究，如电极过程的可逆性、电极反应机理、计算电极面积和扩散系数等电化学参数。

循环伏安是在工作电极上施加一个线性变化的扫描电压，以恒定的变化速度扫描，当达到某设定的终止电位时，再反向回归至某一设定的起始电位，记录工作电极上得到的电流与施加电压的关系曲线，对溶液中的电活性物质进行分析。 典型的循环伏安图如图所示： 选择施加在a 点的起始电位E i ，然后沿负的电位即正向扫描，当电位负到能够将Ox 还原时，在工作电极上发生还原反应：Ox + Ze = Red ，阴极电流迅速增加（b-d ），电流在d 点达到最高峰，此后由于电极附近溶液中的Ox 转变为Red 而耗尽，电流迅速衰减（d-e ）；在f 点电压沿正的方向扫描，当电位正到能够将Red 氧化时，在工作电极表面聚集的Red 将发生氧化反应：Red = Ox + Ze ，阳极电流迅速增加（i-j ），电流在j 点达到最高峰，此后由于电极附近溶液中的Red 转变为Ox 而耗尽，电流迅速衰减（j-k ）；当电压达到a 点的起始电位E i 时便完成了一个循环。 循环伏安图的几个重要参数为：阳极峰电流（i pa ）、阴极峰电流（i pc ）、阳i E 还原峰 E pc i pc E pa 氧化峰 a b g h i j I 0.8V I –0.2V k i pa f c d e

对苯二酚在金_银纳米粒子修饰的玻碳电极上电化学响应的比较

Vol.27No.1安徽工业大学学报第27卷第1期January2010J.of Anhui University of Technology2010年1月 文章编号：1671-7872（2010）01-0027-03 对苯二酚在金、银纳米粒子修饰的玻碳 电极上电化学响应的比较 张超，董永平，俞飞，方林,张千峰 （安徽工业大学化学与化工学院分子工程与应用化学研究所，安徽马鞍山243002） 摘要：制备了柠檬酸钠保护的金和银纳米粒子，并用自组装法制备了金和银纳米粒子修饰的玻碳电极，在近中性的磷酸缓冲溶液中，比较研究对苯二酚在金和银纳米粒子修饰玻碳电极上的电化学响应情况。结果表明金和银纳米粒子均对对苯二酚的电氧化过程具有优越的电催化效果；与银纳米粒子修饰电极相比，金纳米粒子修饰电极表现出了良好的稳定性；对苯二酚在金纳米粒子修饰玻碳电极上的电化学反应是受扩散控制的。 关键词：金纳米粒子；银纳米粒子；纳米修饰电极；对苯二酚 中图分类号：O657.32文献标识码：A doi:10.3969/j.issn.1671-7872.2010.01.006 Comparison of Electrochemical Signals of Hydroquinone on Modified Glassy Carbon Electrodes with Gold and Silver Nanoparticles ZHANG Chao,DONG Yong-ping,YU Fei,FANG Lin,ZHANG Qian-feng (Institution of Molecular Engineering and Applied Chemistry,School of Chemistry and Chemical Engineering, Anhui University of Technology,Ma′anshan243002,China) Abstract:Gold and silver nanoparticles stabilized by citrate were prepared and self-assembled on a glassy carbon electrode.The electrochemical signals of hydroquinone on gold and silver nanoparticles modified glassy carbon electrodes were studied in neutral PBS solutions respectively.The results show that gold and silver nanoparticles exhibit excellent catalytic effects on electrochemical reactions of https://www.wendangku.net/doc/1c1563791.html,pared with silver nanoparticles modified electrode,gold nanoparticles modified electrode show good stability.The electrochemical reactions of hydroquinone on gold nanoparticles modified glassy carbon electrode are controlled by diffusion process. Key words:gold nanoparticles;silver nanoparticles;nanoparticles modified electrode;hydroquinone 酚类物质的测定在生理学、医学和环境保护中都具有重要的意义，人们对此进行了大量的研究。对苯二酚可用作照相显影剂、阻聚剂、橡胶防老剂和食品抗氧化剂等，对环境造成一定污染，从其应用和防止污染两方面考虑，建立快速、方便且能准确测定其含量的方法十分必要[1-4]。近年来，以碳纳米管为材料制备的纳米修饰电极被广泛应用于灵敏检测酚类物质，但对苯二酚在以金、银、铂等贵金属纳米粒子为主体制备的纳米修饰电极上的电化学性质的研究工作开展得比较少[5]。因此，比较研究对苯二酚在金和银纳米粒子修饰的玻碳电极上的电化学行为，研究结果表明金和银纳米粒子对对苯二酚的电化学氧化还原过程具有良好的电催化效果，其中金纳米粒子修饰电极的稳定性和灵敏度都高于银纳米粒子修饰电极，这样的结论可望能用于对环境污染物中对苯二酚含量的检测。 收稿日期：2009-08-20 基金项目：教育部“新世纪优秀人才”支持计划(NCET-06-0556) 作者简介:张超(1983-),男，山东潍坊人，硕士生。