An

ZSa

b

a

ARRAA

KEHNEH

1

fabcsfftbmad

m

g

0h

Sensors and Actuators B 171– 172 (2012) 1073– 1080

Contents lists available at SciVerse ScienceDirect

Sensors and Actuators B: Chemical

journa l h o mepage: www.elsev ier .com/ locate /snb

facile electrosynthesis method for the controllable preparation of electroactiveickel hexacyanoferrate/polyaniline hybrid films for H2O2 detection

hongde Wanga, Shoubin Suna, Xiaogang Haoa,∗, Xuli Maa, Guoqing Guanb,∗∗, Zhonglin Zhanga,hibin Liua

Department of Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, ChinaNorth Japan Research Institute for Sustainable Energy (NJRISE), Hirosaki University, 2-1-3, Matsubara, Aomori 030-0813, Japan

r t i c l e i n f o

rticle history:eceived 15 February 2012eceived in revised form 12 June 2012ccepted 18 June 2012vailable online 26 June 2012

eywords:lectrosynthesisybrid film

a b s t r a c t

Electroactive hybrid films with cubic nickel hexacyanoferrate/polyaniline (NiHCF/PANI) were synthe-sized on carbon nanotubes (CNTs) modified platinum electrodes by a facile one-step electrosynthesismethod using cyclic voltammetry (CV). The morphologies and structures of the as-preparedNiHCF/PANI/CNTs films were characterized using scanning electron microscopy (SEM) and Fourier trans-form infrared spectroscopy (FT-IR), respectively. Due to the introduction of CNTs with carboxyl groups,an acidic micro-environment was provided for the nitrogen atoms in the PANI chains, which could main-tain its electroactivity in neutral aqueous solutions. The hybrid films were applied for hydrogen peroxide(H2O2) detection and showed synergy and higher electrocatalytic activity with a higher sensitivity, a faster

ickel hexacyanoferrate/polyanilineletrocatalysisydrogen peroxide

response time and a lower detection limit. It was found that detection sensitivity could be regulated bycontrolling the time of CV of electrosynthesis during the preparation of the hybrid film. A catalytic rateconstant of 1.29 × 108 cm3 mol−1 s−1 was obtained from an investigation of the kinetics of the catalyticreaction. SEM images showed that the cubic composite nano-particles of PANI and NiHCF were formedand distributed uniformly on the CNTs. The hybrid film prepared had good stability and reproducibility

and s

in the detection of H2O2,

. Introduction

Hydrogen peroxide (H2O2) is widely used as an oxidizing agentor minerals and food processing, treatment of municipal sewagend industrial waste, and a bleach for textiles, pulp and variousiological materials [1,2]. The excessive concentration of H2O2 dis-harged with wastes from chemical industries and nuclear powertations could dramatically affect the environment [3–5]. There-ore, the detection of hydrogen peroxide is of great importanceor environmental monitoring and waste handling in these indus-ries. Although various kinds of sensors for H2O2 detection haveeen developed based on electrocatalytic reduction of H2O2 [6–10],aterials with high electrocatalytic activity, long-term stability

nd excellent selectivity for H2O2 electroreduction are still muchesired.

Prussian blue (PB) and its analogous forms, prototypes ofixed-valence transition metal hexacyanoferrates such as nickel

∗ Corresponding author. Tel.: +86 351 6018193; fax: +86 351 6018554.∗∗ Corresponding author. Tel.: +81 17 762 7756; fax: +81 17 735 5411.

E-mail addresses: xghao@tyut.edu.cn (X. Hao),uan@cc.hirosaki-u.ac.jp (G. Guan).

925-4005/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.snb.2012.06.036

hould be useful in practical H2O2 sensors.© 2012 Elsevier B.V. All rights reserved.

hexacyanoferrate (NiHCF) and cobalt hexacyanoferrate, haveproven to be an excellent catalyst for H2O2 reduction at lowpotentials [4,5,11–15]. Although NiHCF is a much more stable elec-trocatalyst compared to PB and enzymes such as peroxidase, NiHCFfilms prepared are usually mechanically unstable and their long-term operational stability is easily affected by OH− ions generatedfrom the electrochemical reduction of H2O2 [16–19], particularly inneutral solution [5] or in electrolytes containing Na+ [14]. In orderto improve stability, hybrid organic/inorganic films such as con-ducting polymer/MHCF or carbon nanotubes (CNTs) compositeshave been developed and applied for H2O2 detection [14,16,20,21].Liu et al. [22] prepared PANI/PB double-layer films based on PBnanoparticle-coated PANI nanowires by several steps for H2O2detection. In this kind of film, the sensitivity of the sensor waslimited because the two materials were not hybridized and theelectroactivity of PANI was poor in neutral solution. In our previ-ous work [15], nickel hexacyanoferrate/chitosan/carbon nanotubesfilm has been successfully electrodeposited onto nickel net sub-strate and applied for H2O2 detection. An excellent stability wasachieved. However, the sensitivity was not sufficiently high to

detect low concentrations of H2O2 due to the poor electrical con-ductivity of chitosan. It is thus necessary to explore other polymericmaterials with a view toward enhancing the performance of H2O2sensors.

1 tuator

htmearamrtptcaikertmPmcAtdttwtsemwt

uneecnpesdcd

2

2

p1nwCwsfEs

074 Z. Wang et al. / Sensors and Ac

Among the various conducting polymers, polyaniline (PANI)as been considered most attractive because of its high conduc-ivity, good redox reversibility, environmental stability and facile

ethod of preparation. However, the electroactivity of PANI gen-rally decreases with increase in pH value, and shows almost noctivity when pH > 4 [23]. In various MHCFs, nickel hexacyanofer-ate (NiHCF) shows high electro-catalytic activity and capacity withn excellent stability when it is used as a sensor and ion exchangeaterial. In particular, it has been identified to exhibit well-defined,

eversible and reproducible responses even in supporting elec-rolytes containing alkali-metal cations [24–30]. Kulesza et al. [31]repared PANI/NiHCF hybrid films by alternative electrodeposi-ion of NiHCF and PANI layers. In this kind of film, two materialsould interact electrostatically with each other, where PANI servess an electronic conductor in the potential range where NiHCFs electroactivated. The experimental results indicated that thisind of hybrid film had fast dynamics for charge transport. How-ver, no electroactivity appeared at pH = 7. This was due to theedox reactions of PANI requiring the involvement of protons inhe electrolyte. In order to solve this problem, acidic groups (nor-

ally sulfo or carboxyl groups) have been introduced into theANI chains, resulting in a “self-doped” PANI and a change of theicro-environment around it, so that its electrochemical activity

ould be maintained even in neutral or basic solutions [32–34].lso, incorporation of CNTs with the carboxyl groups in PANI made

he as-prepared film have a higher electrocatalytic activity for theetection of H2O2 in the neutral aqueous solution due to a synergis-ic effect between PANI and CNTs [20]. Therefore, it was expectedhat a hybrid film could be formed by incorporating PANI and CNTsith MHCF for H2O2 sensor or ion exchange processes. However,

o date, this kind of hybrid film is generally prepared by a two-tep method or step-by step method [16,17,35]. For example, Lint al. [35] deposited NiHCF nanoparticles on a porous PANI-CNTatrix by the two-step electrodeposition method, but the NiHCFas not really combined with PANI at molecular scale. Moreover,

he preparation procedures were too complicated.In the present study, a facile one-step electrosynthesis method

sing cyclic voltammetry (CV), in which cubic NiHCF/PANI hybridano-particles can be easily deposited on CNTs-modified platinumlectrode, was proposed. In order to provide an acidic micro-nvironment for the nitrogen atoms in the PANI chains, whichould maintain the electroactivity of cubic NiHCF/PANI hybridano-particles in neutral solution, acid-functionalized CNTs wererepared and used for the fabrication of a hybrid film. It wasxpected that the NiHCF/PANI/CNTs hybrid composites will showynergistic augmentation for the response current with loweretection limit, higher sensitivity, more outstanding catalytic rateonstant, better stability and reproducibility for practical H2O2etections in neutral aqueous solutions.

. Experimental

.1. Instruments and reagents

All reagents were analytical grade and all solutions were pre-ared using deionized water. CNTs (purity > 95%, average diameter:0–20 nm) were supplied by Institute of Process Engineering, Chi-ese Academy of Sciences [36]. CNTs with carboxylic acid groupsere prepared by refluxing HNO3 (1.0 mol L−1) solution containingNTs powders for 4–5 h [21]. The acid-functionalized CNTs wereashed with double-distilled deionized water until the pH of the

uspension was nearly 7.0. Electrochemical experiments were per-ormed using a VMP3 Potentiostat (Princeton, USA) controlled withC-Lab software at room temperature. Infrared (IR) spectra of theamples in KBr pellets were recorded on Fourier transform infrared

s B 171– 172 (2012) 1073– 1080

spectrometer (Shimadzu FTIR-8400) workstation. Morphologies ofthe samples were characterized by scanning electron microscopy(SEM, American KEVEX SIGAMA unit).

2.2. Electrode pretreatment

A 1 cm × 1 cm piece of platinum sheet was first polished intoa mirror with fine-grade aqueous alumina slurries (grain size,5–0.5 �m) on a piece of cloth, followed by rinsing with deion-ized water and finally drying in air. A 4.5 mm2 effective surfacearea was created using a PVC tape mask adhered to one side ofthe electrode and another PVC tape to cover the other side. Priorto the one-step electrosynthesis, the platinum electrode was elec-trochemically cleaned in 1.0 mol L−1 H2SO4 solution by cycling thepotential from −0.675 V to 1.675 V at a scan rate of 100 mV s−1 for50 times, and then rinsed with water and dried.

2.3. Preparation of film electrode

25 mg of CNTs was dispersed in 5 mL of dimethylformamide(DMF) with the aid of ultrasonic agitation for 15 min. The obtainedsuspension was dropped onto the pretreated platinum sheet andthen dried at room temperature for 48 h. In this way, a CNTs-modified platinum sheet was obtained.

The CNTs-modified platinum sheet, a saturated calomel elec-trode (SCE), and platinum wire served as a working electrode,a reference electrode and a counter electrode in a three-electrode cell, respectively. Various hybrid films used in thisstudy were electrochemically prepared in this three-electrodecell containing an aqueous solution of 0.002 M NiSO4 + 0.25 MNa2SO4 + 0.002 M K3Fe(CN)6 + 0.02 M Aniline monomer + 0.5 MH2SO4 using cyclic voltammetry between −0.2 and 0.85 V at asweep rate of 50 mV s−1 for 5, 10, 15 and 20 cycles, respectively.Simplex NiHCF and simplex PANI films used in this study were alsoelectrochemically prepared using cyclic voltammetry between−0.2 and 0.85 V at a sweep rate of 50 mV s−1 for 10 cycles, in thethree-electrode cell containing an aqueous solution of 0.002 MNiSO4 + 0.25 M Na2SO4 + 0.002 M K3Fe(CN)6 and 0.02 M anilinemonomer + 0.5 M H2SO4, respectively. All films obtained wererinsed with deionized water and dried before use.

2.4. Hybrid film performance test

An as-prepared hybrid film was first immersed in a 0.05 M ofphosphate buffer solution (PBS, pH 6.5) containing 0.05 M of KCl,and the performance test was then carried out using cyclic voltam-metry between −0.2 and 0.9 V with a scan rate of 50 mV s−1. Thesample was rinsed with deionized water for several times and driedin the desiccator before characterizing its surface morphology andstructure using SEM and FT-IR.

Amperometric responses of the hybrid film electrode to vari-ous concentrations of H2O2 by successive injection of H2O2 intoa conventional three-electrode electrochemical cell (40 mL) con-taining electrolytes with stirring were measured. The responses at0 V versus SCE and typically stable responses to successive injec-tion of H2O2 during the measurement were recorded. Before thesuccessive addition of H2O2, electrodes were first polarized at theoperating potential until the background current became stable.

3. Results and discussion

3.1. One-step electrosynthesis for the fabrication of

NiHCF/PANI/CNTs hybrid films

Fig. 1 shows CV curves during the electrochemical electrosyn-thesis of NiHCF/PANI hybrid film on the CNTs-modified Pt substrate

Z. Wang et al. / Sensors and Actuator

Fig. 1. (A) Cycle voltammograms recorded during one-step electrosynthesis ofNiHCF/PANI film on CNTs-modified Pt electrode in the solution containing 0.002 MNiSO4, 0.25 M Na2SO4, 0.002 M K3Fe(CN)6, 0.02 M aniline and 0.5 M H2SO4 at a scanrts

i0stosIPovfiit

Se

ate of 50 mV s−1. (B) The tenth cyclic voltammetric behavior of the simplex NiHCF,he simplex PANI and NiHCF/PANI films were grown on the CNTs-modified Pt sub-trate.

n the solution containing 0.002 M of NiSO4, 0.25 M of Na2SO4,.002 M of K3Fe(CN)6, 0.02 M of aniline and 0.5 M of H2SO4 at acan rate of 50 mV s−1. One can see that the voltammogram ofhe hybrid film exhibited comprehensive electrochemical featuresf the NiHCF and PANI components. The peak currents increasedystematically in the course of voltammetric potential cycling.ncreases in the peaks at ca. 0/0.2 V and 0.85 V (corresponding toANI) and at ca. 0.42/0.45 V (related to NiHCF redox pair) werebserved. To further characterize the composite system, cyclic

oltammetric behaviors of the simplex NiHCF and the simplex PANIlms formed on the CNTs-modified Pt substrate (Fig. 1(B)) were

nvestigated. This provided clear evidence of redox reactions ofhe NiHCF and PANI in hybrid film. The regular increases of all

cheme 1. Schematic illustration of the process and reactions involved in the preparatilectrosynthesis method (outside the circle) and electrocatalytic reduction mechanism in

s B 171– 172 (2012) 1073– 1080 1075

voltammetric peak currents (corresponding to both components)in Fig. 1, indicated that PANI and NiHCF could be deposited homo-geneously on the electrode. As stated above, it should be noted thatthe polymerization of PANI was an oxidative process that took placeduring the positive potential scans, whereas NiHCF was electrode-posited during negative potentials scans [31], where ferricyanidewas reduced to ferrocyanide followed by reaction of ferrocyanidewith Ni2+ on the electrode [23,24,27]. On the other hand, the alter-natively produced and deposited PANI and NiHCF with oppositecharges should interact electrostatically with each other, resultingin the hybrid film obtained being adhesive and stable.

Schematic representations for the fabrication of the cubicNiHCF/PANI/CNTs nanocomposite film modified electrode by one-step electrosynthesis and related reactions (outside the circle) aswell as electrocatalytic reduction mechanism on the hydrogenperoxide sensor (inside the circle) are illustrated in Scheme 1.As stated in the experimental section, CNTs functionalized withcarboxylic acid groups were first prepared by refluxing HNO3solution containing CNTs powders, and then the DMF solution ofthe acid-functionalized CNTs were dropped onto the pretreatedplatinum sheet. Finally, a hybrid film was prepared by a one-step electrosynthesis method using cyclic voltammetry in theconventional three-electrode electrochemical cell. Electrostaticinteraction between ANI–CNTs which were covalently grafted toform the composite material from the acid functionalized CNTsand aniline [37], [Fe(CN)6]3− and aniline in the base solution forelectrosynthesis is shown in the dashed panel of Scheme 1. In theone-step electrosynthesis process, PANI should be precipitated onthe CNTs surface during positive potential scans in which the acidfunctionalized CNTs bound with the PANI by forming CO NH

bond between its COOH group and free NH2 group of PANI (at theend of its chain), whereas NiHCF with a polynuclear microstructurewas electrodeposited on the PANI layer during negative poten-tial scans [31]. As shown in Scheme 1 (inner solid panel), in the

on of cubic NiHCF/PANI/CNTs nanocomposite film modified electrode by one-step the hydrogen peroxide sensor (inside the circle).

1 tuators B 171– 172 (2012) 1073– 1080

owrrctp

Npt

2

2

3N

aaNfn

FN

076 Z. Wang et al. / Sensors and Ac

ne-step electrosynthesis process, the PANI formed was first dopedith oxidative-state Fe(CN)6

3−, and then, Ni2+ was doped into theeductive-state PANI, where ferricyanide was also reduced to fer-ocyanide. The polymer PANI and the inorganic polynuclear NiHCFompound in the cubic hybrid microstructure should interact elec-rostatically with each other since the partially oxidized PANI wasositively charged while NiHCF was anionic.

Electrocatalytic reduction of hydrogen peroxide in the cubiciHCF/PANI/CNTs nanocomposite film modified electrode shouldroceed via the oxidation of Fe(CN)6

4− by hydrogen peroxide andhe electrochemical reduction of Fe(CN)6

3− as follows:

FeII(CN)64− + H2O2 + 2H+ = 2FeIII(CN)6

3− + 2H2O (1)

FeIII(CN)63− + 2e− = 2FeII(CN)6

4− (2)

.2. Morphologies and microstructure analysis ofiHCF/PANI/CNTs hybrid film

Fig. 2 shows SEM images of typical surfaces of CNTs (A)nd NiHCF/PANI/CNTs film (B) modified Pt electrode with 30,000

nd 50,000 magnifications, respectively. One can see that cubiciHCF/PANI nanoparticles were tightly formed on the smooth sur-

ace (A) of the purified CNTs. The diameter of the NiHCF/PANIanoparticle in the dispersed granular form was about 30–50 nm.

ig. 2. Typical SEM images obtained for the surface of CNTs (A) andiHCF/PANI/CNTs (B) film on Pt electrode.

Fig. 3. FT-IR spectra of NiHCF/PANI/CNTs film.

It should be noted that the CNTs layer on the electrode had athree-dimensional porous network-like structure, which providedan ideal matrix for the uniform deposition of the cubic PANI/NiHCFcomposite nanoparticles along the CNTs surface. Moreover, thiskind of network-like structure could reduce the polarization andimprove the electron transport rate of the hybrid film.

Fig. 3 shows a typical infrared spectrum of the NiHCF/PANI/CNTshybrid film. The absorption band at 2086 cm−1 was assigned tothe stretching vibration of the CN group in the cyanometallate lat-tice of NiHCF [15,25]. The peak at 3423 cm−1 corresponded to theaniline N H stretching vibration [38], vibrational peak centered at1566 cm−1 was attributed to the stretching frequencies of quinoidrings of PANI and the stretching frequencies at 1058 cm−1 was dueto SO4

2− doped in PANI [39]. These bands were in good agreementwith the spectrum of PANI when it was in the form of an emeral-dine salt. In addition, a peak at 1419 cm−1, which was assigned tothe symmetric stretching vibration of the COO− group [40], wasalso observed. Such a structure should be attributed to the acidicmicro-environment provided for the conductivity of PANI chainsby CNTs in the neutral solution.

3.3. Electrochemical performance of NiHCF/PANI/CNTs hybridfilm for H2O2 detection

Voltammetric behavior of the hybrid film was measured in a

solution of 0.05 M KCl + 0.05 M PBS (pH 6.5) containing various con-centrations of H2O2. Fig. 4 shows the cyclic voltammetry curveswhen different concentrations of H2O2 were used. One can see thata turning point of the reduction peak current appeared at 0 V during

Fig. 4. Voltammetric responses of NiHCF/PANI/CNTs film in the solution with dif-ferent concentrations of H2O2 in the solution of 0.05 M KCl + 0.05 M PBS (pH 6.5) ata scan rate of 50 mV s−1.

Z. Wang et al. / Sensors and Actuators B 171– 172 (2012) 1073– 1080 1077

Fig. 5. Dependences of sensitivity (A) and molar percent of NiCHF and( C6H4 NH )4 in the PANI (B) on the number of deposition cycles. The sensitiv-isa

tgif

tfssroaofoifriettrcbaawtdrtcftcbTi

ecosoA

fied by about 90 times compared to the PANI/CNTs film withoutNiHCF. The rapid response property and ultra-high sensitivity of thepresent film should be attributed to the homogeneously dispersed

ty was obtained by amperometric responses of the NiHCF/PANI/CNTs film duringuccessive addition of H2O2 to the solution of 0.05 M KCl + 0.05 M PBS (pH 6.5) at anpplied potential of 0 V (vs. SCE).

he negative potential scans. It is notable that the reduction currentradually increased with an increase in H2O2 concentration. Thisndicated that the hybrid film electrode had good catalytic activityor the reduction of H2O2.

In general, the amount of the hybrid film could be regulated byuning the deposition or electrosynthesis cycles. Hence, the per-ormance of the NiHCF/PANI/CNTs-based H2O2 sensor should betrongly correlated with the number of deposition cycles. Fig. 5hows that the sensitivity, which was obtained by amperometricesponses of the NiHCF/PANI/CNTs film when successive additionsf H2O2 to the solution of 0.05 M KCl + 0.05 M PBS (pH = 6.5) atn applied potential of 0 V (vs. SCE), depended on the numberf deposition cycles for the fabrication of the hybrid film. It wasound that the sensitivity of the H2O2 sensor strongly dependedn the number of deposition cycles. One can see that the sensitiv-ty increased with an increase in the number of deposition cyclesrom Fig. 5(A), corresponding to the enhancement of the molaratio of NiHCF to ( C6H4 NH )4 in the PANI. With an increasen the number of deposition cycles, more NiHCFs which served aslectron-mediator was formed in the film, which was beneficial forhe sensor. Moreover, the molar ratio of NiHCF to ( C6H4 NH )4 inhe PANI increased due to the growing of PANI chains at a very lowate during the initial stage, where the charges allowed the PANIhains to nucleate over the substrate surface. However, it shoulde noted that the sensitivity and the molar ratio began to decreasefter 10 deposition cycles. The growing of PANI chains was acceler-ted after 10 deposition cycles because the polymerization reactionas an autocatalytic process, and this resulted in the decrease of

he molar ratio. In general, the film could have become thicker andenser with the increase in the number of deposition cycles, whichesulted in the blocking of H2O2 diffusion in the NiHCF lattice ofhe hybrid film. Furthermore, in this case, the electron transfer rateould have decreased while the penetration of the counterion (K+)rom the solution to the film, which was generally required in theransition between oxidized and reduced NiHCF for preservation ofharge neutrality, could have also become difficult as the distanceetween the film outer layer and the electrode surface increased.hus, a maximum sensitivity to H2O2 should be observed whilencreasing the number of deposition cycles from a low value.

Fig. 6 shows the amperometric responses of the hybrid filmlectrode to successive additions of H2O2 into the stirred solutionontaining 0.05 M KCl + 0.05 M PBS (pH 6.5) at an applied potential

f 0 V. The corresponding calibration curve for H2O2 detection ishown in Fig. 7. When the electrode was held at a zero potential, thexidized form of hybrid films was converted to the reduced form.t the same time, the hybrid film electrode showed a characteristic

Fig. 6. Amperometric responses of the NiHCF/PANI/CNTs film when successive addi-tion of H2O2 to the solution of 0.05 M KCl + 0.05 M PBS (pH 6.5) at an applied potentialof 0 V (vs. SCE). Inset: amplified part of the amperometric response curve.

cathodic response. This cathodic response (current) was directlyrelated to the H2O2 concentration. One can see that there weregood linear relationships between reduction current and H2O2concentration. In this study, a linear response range of 1 × 10−6

to 3 × 10−3 M with a correlation coefficient of 0.9988 had beenachieved, and the detection limit was as low as 1.24 × 10−7 M ona signal-to-noise ratio of 3. Furthermore, a very high sensitivity of2288 mA M−1 cm−2 with a rapid response had been demonstratedfor the hybrid film prepared. It was found that the current couldreach steady state within 2 s after dropping H2O2 into the solution.To the best of our knowledge, these are the lowest response timeand highest sensitivity achieved to date comparing with the H2O2detection sensors reported [4,5,11–15,20]. As shown in Table 1,the sensitivity of the present NiHCF/PANI/CNTs film prepared byone-step electrosynthesis was about 4–5 times higher than thoseof other metal hexacyanoferrate-based composite films [15,16]. InFig. 7, the calibration curve for H2O2 detection using the PANI/CNTsand the NiHCF/PANI/CNTs nanocomposite film synthesized by two-step electrodeposition [35] is also shown. It can be seen that thesensitivity and linear response range of the present film were sig-nificantly higher than those of the film prepared by step-by-stepelectrodeposition method. The H2O2 reduced current was ampli-

Fig. 7. Calibration curves for H2O2 detection using PANI (�) and NiHCF/PANI filmprepared by one-step electrosynthesis method (�) and two-step deposition method(�) on Pt electrode modified with CNTs in the solution of 0.05 M KCl + 0.05 M PBS(pH 6.5) at 0 V (vs. SCE). Inset: amplified part of calibration curves.

1078 Z. Wang et al. / Sensors and Actuators B 171– 172 (2012) 1073– 1080

Table 1Metal hexacyanoferrate-based film modified electrodes for H2O2 detection in the literatures.

Electrode Range of linearity (M) Sensitivity (mA M−1 cm−2) Detection limit (M) Response time (s) Reference

PB 1 × 10−8–1 × 10−2 60 10−8 – [4]PB–NiHCF 1 × 10−7–1 × 10−3 350 1 × 10−7 – [5]Nano-PB 1 × 10−8–1 × 10−2 200 10−8 – [11]PB 1 × 10−6–4 × 10−4 625 1 × 10−6 4 [12]NiHCF/PPY* 1 × 10−4–9 × 10−4 88.33 10−4 – [14]PB/PANI/CNTs** 8 × 10−9–5 × 10−6 526.43 5 × 10−9 5 [16]PANI/PB/CNTs*** 8 × 10−8–1 × 10−5 508.18 10−8 15 [17]NiHCF/PANI/CNTs 1 × 10−6–3 × 10−3 2288 1.24 × 10−7 2 This paper

NtteNi

3

hitiFdsbu

wlceE

o

FtKd

electrode was considerably stable.

* One-step copolymerization on GCE.** Step-by-step electrodeposition on GCE.

*** Multi-step chemical synthesis on GCE.

iHCF/PANI hybrid nanoparticles on the 3D porous CNTs struc-ure with high surface area, and the superior transducing ability ofhe homogeneously-deposited PANI in the hybrid film by one-steplectrosynthesis. Also, the synergistic effect among CNTs, PANI andiHCF in the hybrid film should have also contributed toward the

mprovement in electrocatalytic performance in H2O2 detection.

.4. Chronoamperometric measurements

The electrocatalytic process of H2O2 at the NiHCF/PANI/CNTsybrid film electrode was investigated using chronoamperometry

n quiescent solution. Fig. 8(A) shows the current–time curves inhe detection of a blank sample (a) and 0.125 mM H2O2 (b) at 0 Vn the solution containing 0.1 M PBS + 0.1 M KCl. The I–t curve inig. 8(A) indicates that the current observed was controlled by H2O2iffusion rate in the solution. One can see that the current reachedteady state in 10 s. Catalytic reaction rate constant for the reactionetween H2O2 and redox sites in the hybrid film could be evaluatedsing Galus method [41]:

Icat

IL= �1/2

[�1/2erf (�1/2) + exp(−�)

�1/2

](3)

here Icat is the catalytic current of H2O2 in the hybrid film, IL theimiting current in the absence of H2O2, and � = kC0t (C0 is the bulkoncentration of H2O2, t the time elapsed (s)) the argument of therror function. When � exceeds 2, the error function is about 1 andq. (3) can be rewritten as:

I

cat

IL= �1/2�1/2 = �1/2(kC0t)1/2 (4)

Based on the slope of the Icat/IL versus t1/2 plot, k could bebtained for a given H2O2 concentration. Fig. 8(B) shows the

ig. 8. (A) Chronoamperograms when NiHCF/PANI/CNTs film modified electrode inhe absence (a) and presence of 0.125 mM H2O2 (b). Supporting electrolyte: 0.05 MCL + 0.05 M PBS (pH 6.5). Insert: (B) Dependence of Icat/IL on t1/2 derived from theata of chronoamperograms of (a) and (b) in (A).

dependence of Icat/IL on t1/2 derived from the chronoamperogramsdata of the hybrid film electrode in the absence and presenceof 0.125 mM of H2O2. Thus, the value of k was calculated as1.29 × 108 cm3 mol−1 s−1, which was about 100 times higher thanthat of PANI modified electrodes used for electro-oxidation ofascorbic acid (5.6–7.5 × 105 cm3 mol−1 s−1) [32,42]. Therefore, inthe present study, the high sensitivity and fast response time for thedetection of H2O2 using the NiHCF/PANI/CNTs hybrid film shouldhave resulted from the high rate constant.

3.5. Stability and reproducibility of the sensor

The main drawback of hexacyanometallates-based modifiedelectrodes is their gradual dissolution during continuous potentialscanning, hindering their practical performances [43,44]. To assessthe long-term stability of the hybrid film electrode produced by theone-step electrosynthesis method, we monitored the change in thecapacity as measured from the integrated charge passed under theCV redox peaks over 400 cyclic scans (800 segments). Fig. 9 showsthe stability of the hybrid film electrode. It was found that 94.4% ofits initial capacity was retained after 400 consecutive cycles usingan applied potential between −0.2 and 0.85 V at a sweep rate of50 mV s−1 by cyclic voltammetry in a solution of 0.05 M KCl + 0.05 MPBS (pH 6.5). The storage stability of the hybrid film was also inves-tigated by storing it in PBS (pH 6.5) when it was not used for H2O2detection. It was found that the response current at steady statedecreased by 11.3% after 40 days, indicating that the hybrid film

Furthermore, when the hybrid film sensor was repetitively usedto measure a solution containing 0.1 mM of H2O2, excellent repro-ducibility was also observed. In this case, the relative standard

Fig. 9. Electrochemical stability of the NiHCF/PANI/CNTs film fabricated by one-step electrosynthesis method (10 cycles electrodeposition). The data were obtainedfrom the cyclic voltammograms of the electrode in a 0.05 M KCl + 0.05 M PBS (pH6.5) solution at a scan rate of 50 mV s−1 and the capacity values were normalized bytheir corresponding initial capacity.

tuator

dTlCptct

4

Ntmtidetf

A

eo1

R

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

Z. Wang et al. / Sensors and Ac

eviation (RSD) was only 2.07% after five successive measurements.he long-term stability should also be attributed to the excel-ent structure of the hybrid film prepared, in which the porousNTs matrix provided a high surface area for loading PANI–NiHCFarticles while the PANI further stabilized the NiHCF. Moreover,he existence of electrostatic attraction between the negativelyharged NiHCF and the positively charge PANI could also improvehe long-term stability [31].

. Conclusions

In this paper, an organic/inorganic hybrid film composed ofiHCF/PANI cubic nano-particles was prepared on platinum elec-

rode modified with CNTs by a facile one-step electrosynthesisethod. Compared with known amperometric detection of H2O2,

he fabricated hybrid film showed excellent electro-catalytic abil-ty with a higher sensitivity, a faster response time and a loweretection limit in neutral aqueous solutions due to the synergisticffect of NiHCF, PANI and CNTs. This simple one-step electrosyn-hesis method for the fabrication of hybrid films could be beneficialor the mass production of H2O2 sensors at low costs.

cknowledgements

This work was financially supported by the National Natural Sci-nce Foundation of China (No. 20676089), Shanxi Scholar Councilf China (No. 2008-32), Science Star Foundation of Taiyuan (No.0011611)

eferences

[1] Y.J. Lee, J.Y. Park, Y. Kim, J.W. Ko, Amperometric sensing of hydrogen perox-ide via highly roughened macroporous Gold-/Platinum nanoparticles electrode,Current Applied Physics 11 (2011) 211–216.

[2] C. Tsiafoulis, P. Trikalitis, M. Prodromidis, Synthesis, characterization andperformance of vanadium hexacyanoferrate as electrocatalyst of H2O2, Elec-trochemistry Communications 7 (2005) 1398–1404.

[3] Y. Wang, J. Huang, C. Zhang, B. Wei, X. Zhou, Determination of hydrogen perox-ide in rainwater by using a polyaniline film and platinum particles co-modifiedcarbon fiber microelectrode, Electroanalysis 10 (1998) 776–778.

[4] A.A. Karyakin, E.A. Puganova, I.A. Budashov, I.N. Kurochkin, E.E. Karyakina, V.A.Levchenko, V.N. Matveyenko, S.D. Varfolomeyev, Prussian blue based nano-electrode arrays for H2O2 detection, Analytical Chemistry 76 (2004) 474–478.

[5] N.A. Sitnikova, A.V. Borisova, M.A. Komkova, A.A. Karyakin, Superstableadvanced hydrogen peroxide transducer based on transition metal hexacyano-ferrates, Analytical Chemistry 83 (2011) 2359–2363.

[6] Y. Shi, Z.L. Liu, B. Zhao, Y.J. Sun, F.G. Xu, Y. Zhang, Z.W. Wen, H.B. Yang, Z. Li,Carbon nanotube decorated with silver nanoparticles via noncovalent interac-tion for a novel nonenzymatic sensor towards hydrogen peroxide reduction,Journal of Electroanalytical Chemistry 15 (2011) 29–33.

[7] M.S.M. Quintino, H. Winnischofer, K. Araki, H.E. Toma, L. Angnes, Cobaltoxide/tetraruthenated cobalt–porphyrin composite for hydrogen peroxideamperometric sensors, Analyst 130 (2005) 221–226.

[8] T.A. Ivandini, R. Sato, Y. Makide, A. Fujishima, Y. Einaga, Pt-implanted boron-doped diamond electrodes and the application for electrochemical detectionof hydrogen peroxide, Diamond and Related Materials 14 (2005) 2133–2138.

[9] P. Santhosh, K.M. Manesh, A. Gopalan, K. Lee, Fabrication of a new polyanilinegrafted multi-wall carbon nanotube modified electrode and its application forelectrochemical detection of hydrogen peroxide, Analytica Chimica Acta 575(2006) 32–38.

10] Y. Shen, M. Trauble, G. Wittstock, Detection of hydrogen peroxide producedduring electrochemical oxygen reduction using scanning electrochemicalmicroscopy, Analytical Chemistry 80 (2008) 750–759.

11] E.A. Puganova, A.A. Karyakin, New materials based on nanostructured Prussianblue for development of hydrogen peroxide sensors, Sensors and Actuators B109 (2005) 167–170.

12] Y. Liu, Z.Y. Chu, W.Q. Jin, A sensitivity-controlled hydrogen peroxide sensorbased on self-assembled Prussian blue modified electrode, ElectrochemistryCommunications 11 (2009) 484–487.

13] M.H. Yang, J.H. Jiang, Y.H. Yang, X.H. Chen, G.L. Shen, R.Q. Yu, Carbonnanotube/cobalt hexacyanoferrate nanoparticle-biopolymer system for the

fabrication of biosensors, Biosensors and Bioelectronics 21 (2006) 1791–1797.

14] P.A. Fiorito, S.I. Cordoba de Torresi, Hybrid nickel hexacyanoferrate/polypyrrolecomposite as mediator for hydrogen peroxide detection and its application inoxidase-based biosensors, Journal of Electroanalytical Chemistry 581 (2005)31–37.

[

[

s B 171– 172 (2012) 1073– 1080 1079

15] Z.D. Wang, X.G. Hao, Z.L. Zhang, S.B. Liu, Z.H. Liang, G.Q. Guan, One-step unipolarpulse electrodeposition of nickel hexacyanoferrate/chitosan/carbon nanotubesfilm and its application in hydrogen peroxide sensor, Sensors and Actuators B162 (2012) 353–360.

16] Y.J. Zou, L.X. Sun, F. Xu, Prussian blue electrodeposited on MWNTs–PANI hybridcomposites for H2O2 detection, Talanta 72 (2007) 437–442.

17] Y.J. Zhou, L.X. Sun, F. Xu, Biosensor based on polyaniline–Prussian blue/multi-walled carbon nanotubes hybrid composites, Biosensors and Bioelectronics 22(2007) 2669–2674.

18] G.L. de Lara Gonzalez, H. Kahlert, F. Scholz, Catalytic reduction of hydrogenperoxide at metal hexacyanoferrate composite electrodes and applications inenzymatic analysis, Electrochimica Acta 52 (2007) 1968–1974.

19] A.A. Karyakin, E.E. Karyakina, Prussian blue-based artificial peroxidase as atransducer for hydrogen peroxide detection: Application to biosensors, Sensorsand Actuators B 57 (1999) 268–273.

20] F.L. Qu, M.H. Yang, J.H. Jiang, G.L. Shen, R.Q. Yu, Amperometric biosensorfor choline based on layer-by-layer assembled functionalized carbon nan-otube and polyaniline multilayer film, Analytical Biochemistry 344 (2005)108–114.

21] J.X. Wen, L. Zhou, L.T. Jin, X.N. Cao, B.C. Ye, Overoxidized polypyrrole/multi-walled carbon nanotubes composite modified electrode for in vivo liquidchromatography–electrochemical detection of dopamine, Journal of Chro-matography B 877 (2009) 1793–1798.

22] J. Liu, Y. Lin, L. Liang, J.A. Voigt, D.L. Huber, Z. Tian, E. Coker, B. Mckenzie, M.J.Mcdermott, Templateless assembly of molecularly aligned conductive poly-mer nanowires: a new approach for oriented nanostructures, Chemistry: AEuropean Journal 9 (2003) 604–611.

23] W.S. Huang, B.D. Humphrey, A.G. MacDiarmid, Polyaniline, a novel conductingpolymer. Morphology and chemistry of its oxidation and reduction in aque-ous electrolytes, Journal of Chemical Society, Faraday Transactions 1 82 (1986)2385–2400.

24] X.G. Hao, D.T. Schwartz, Tuning intercalation sites in nickel hexacyanoferrateusing lattice nonstoichiometry, Chemistry of Materials 17 (2005) 5831–5836.

25] W. Chen, X.H. Xia, Highly stable nickel hexacyanoferrate nanotubes for elec-trically switched ion exchange, Advanced Functional Materials 17 (2007)2943–2948.

26] X.Y. Wang, Y. Zhang, C.E. Banks, Q.Y. Chen, X.B. Ji, Non-enzymatic amperometricglucose biosensor based on nickel hexacyanoferrate nanoparticle film modifiedelectrodes, Journal of Colloids and Surfaces B 78 (2010) 363–366.

27] X.G. Hao, Y.G. Li, M. Pritzker, Pulse delectrodeposition of nickel hexacyano-ferrate films for electrochemically switched ion exchange, Separation andPurification Technology 63 (2008) 407–414.

28] W. Chen, J. Tang, H.J. Cheng, X.H. Xia, A simple method for fabrication of solecomposition nickel hexacyanoferrate modified electrode and its application,Talanta 80 (2009) 539–543.

29] W. Chen, J. Tang, X.H. Xia, Composition and shape control in the construc-tion of functional nickel hexacyanoferrate nanointerfaces, Journal of PhysicalChemistry C 113 (2009) 21577–21581.

30] X.G. Hao, T. Yan, Z.D. Wang, S.B. Liu, Z.H. Liang, Y.H. Shen, M. Pritzker,Unipolar pulse electrodeposition of nickel hexacyanoferrate thin films withcontrollable structure on platinum substrates, Thin Solid Films 520 (2012)2438–2448.

31] P.J. Kulesza, K. Miecznikowski, M.A. Malik, M. Galkowski, M. Chojak, K. Caban,A. Wieckowski, Electrochemical preparation and characterization of hybridfilms composed of Prussian blue type metal hexacyanoferrate and conductingpolymer, Electrochimica Acta 46 (2001) 4065–4073.

32] L. Zhang, S.J. Dong, The electrocatalytic oxidation of ascorbic acid on polyanilinefilm synthesized in the presence of camphorsulfonic acid, Journal of Electroan-alytical Chemistry 568 (2004) 189–194.

33] S. Mu, J. Kan, The electrocatalytic oxidation of ascorbic acid on polyaniline filmsynthesized in the presence of ferrocenesulfonic acid, Synthetic Metals 132(2002) 29–33.

34] H.K. Lin, S.A. Chen, Synthesis of new water-soluble self-doped polyaniline,Macromolecules 33 (2000) 8117–8118.

35] Y.H. Lin, X.L. Cui, Electrosynthesis, characterization, and application of novelhybrid materials based on carbon nanotube–polyaniline–nickel hexacyanofer-rate nanocomposites, Journal of Materials Chemistry 16 (2006) 585–592.

36] S.L. Zhan, Y.J. Tian, Y.B. Cui, H. Wu, Y.G. Wang, S.F. Ye, Y.F. Chen, Effect of processconditions on the synthesis of carbon nanotubes by catalytic decomposition ofmethane, China Particuology 5 (2007) 213–219.

37] J. Narang, N. Chauhan, C.S. Pundir, A non-enzymatic sensor for hydrogen perox-ide based on polyaniline, multiwalled carbon nanotubes and gold nanoparticlesmodified Au electrode, Analyst 136 (2011) 4460–4466.

38] H.Y. Mi, X.G. Zhang, S.D. Yang, X.G. Ye, J.M. Luo, Polyaniline nanofibers as theelectrode material for supercapacitors, Materials Chemistry and Physics 112(2008) 127–131.

39] H.F. Jiang, X.X. Liu, One-dimensional growth and electrochemical properties ofpolyaniline deposited by a pulse potentiostatic method, Electrochimica Acta55 (2010) 7175–7181.

40] F. Quiles, A. Burneau, Infrared and Raman spectra of alkaline-earth and copper(II) acetates in aqueous solutions, Vibrational Spectroscopy 16 (1998) 105–117.

41] Z. Galus, Fundamentals of Electrochemical Analysis, Ellis Horwood Press, NewYork, 1976, pp. 313–320.

42] J. Zhang, C.H. Zhang, L. Zhang, Polymerization of aniline on orthanilic acid func-tionalized glassy carbon electrode and its application for electro-oxidation ofascorbic acid, Chinese Journal of Analytical Chemistry 9 (2009) 1281–1285.

1 tuator

[

[

B

ZatTa

STa

Xwvh

080 Z. Wang et al. / Sensors and Ac

43] T.R.I. Cataldi, G.E.D. Benedetto, On the ability of ruthenium to stabilizepolynuclear hexacyanometallate film electrodes, Journal of ElectroanalyticalChemistry 458 (1998) 149–154.

44] P. Prabhu, R.S. Babu, S.S. Narayanan, Amperometric determination of l-dopa bynickel hexacyanoferrate film modified gold nanoparticle graphite compositeelectrode, Sensors and Actuators B 156 (2011) 606–614.

iographies

hongde Wang received his BS degree from Northeast Petroleum University in 2003nd received his MS degree at Sichan University in 2007. He is currently pursuinghe PhD degree in Chemical Engineering and Technology at Taiyuan University ofechnology. His research is focused on the development of electroactive materialsnd its application for sensor and electrochemical switched ion exchange.

houbin Sun is currently a Master student majoring in Chemical Engineering andechnology at Taiyuan University of Technology in China. He researched in electro-nalytical chemistry.

iaogang Hao began his college education at Sichuan University in 1983, and thenas successively granted the degrees of BS, MS and PhD (D.E.). He worked as a

isiting scholar at University of Washington, University of Waterloo and Yoko-ama National University, respectively. Presently, he is serving as a professor at

s B 171– 172 (2012) 1073– 1080

Department of Chemical Engineering of Taiyuan University of Technology. His mainresearch interests include electrochemical switched ion exchange technology andapplication of electroactive functional materials.

Xuli Ma received the PhD degree at Taiyuan University of Technology in 2010.Her current research interests include electrochemical sensors and electrochemicalswitched ion exchange technology.

Guoqing Guan received his first PhD in Chemical Engineering from Sichuan Uni-versity (China) in 1995 and second PhD in Materials Physics and Engineering fromKyushu University in 2004 (Japan). He is currently an associate professor at NorthJapan Research Institute for Sustainable Energy (NJRISE), Hirosaki University, Japan.His research interests include energy materials, coal/biomass gasification, electro-chemical sensors and gas separation membranes.

Zhonglin Zhang received the PhD degree at Taiyuan University of Technology in2011. His current research interests include the fabrication of nanocomposite mate-rials for DMFC and sensor application.

Shibin Liu received BS, MS and PhD degrees in Chemical Engineering from TaiyuanUniversity of Technology in 1985, 1988 and 2007, respectively. Since 2009, he hasalso served as a Competency Leader for Chemical Engineering at Taiyuan Universityof Technology. His research interests include the use of nanocomposite functionalmaterials for Li-ion Batteries, sensors and DMFC.