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graphite felt modified electrode
Electrochimica Acta 171 (2015) 121–127
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Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta
Amperometric detection of hydrazine utilizing synergistic action of prussian blue @ silver nanoparticles / graphite felt modified electrode Jihua Zhao a, * , Jianxin Liu a , Simon Tricard c, Lei Wang a , Yanling Liang a , Linghua Cao a , Jian Fang a , Weiguo Shen a,b a Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, School of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, PR China b School of Chemistry and Chemical Engineering, East China University of Science and Technology, Shanghai 200237, PR China c Laboratoire de Physique et Chimie de Nano-Objets, INSA, CNRS, Université de Toulouse, 135 avenue de Rangueil, 31077 Toulouse, France
A R T I C L E I N F O
A B S T R A C T
Article history: Received 28 November 2014 Received in revised form 19 March 2015 Accepted 6 May 2015 Available online 7 May 2015
In this study, a triple-component hydrazine sensor (PB@Ag/GF) was fabricated with freestanding graphite felt (GF), silver nanoparticles (Ag) and prussian blue (PB). The Ag nanoparticles were electrodeposited on GF ultrasonically (Ag/GF), and acted as a catalyst of the chemical deposition of PB. The electrode was characterized by scanning election microscopy (SEM), infrared spectroscopy (IR), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS). The electrochemical behavior of PB@Ag/GF was measured by cyclic voltammetry and amperometric measurements. The sensor displayed a prominent electrocatalytic activity toward hydrazine oxidation, with a fast response time of 2 s, a low detection limit of 4.9 107 mol L1 and very high detection sensitivity of 26.06 A mol1 L. ã 2015 Elsevier Ltd. All rights reserved.
Keywords: Prussian Blue Silver nanoparticles Graphite Felt Hydrazine
1. Introduction Hydrazine (N2H4H2O) and its derivatives have wide applications in industry, agriculture, and can be used as explosives, antioxidants, photographic developer, oxygen scavengers and propellants [1], but they have also been recognized as carcinogenic and hepatotoxic substances, which could cause liver and kidney diseases, even cancer or genetic damages [2]. All these traits make their detection and quantization problems of considerable importance, notably in agriculture and pharmaceutical industry. The traditional methods reported for the detection of hydrazine are potentiometric [3], chemiluminescence [4], coulometric [5], and spectrophotometric methods [6], which are all expensive and require high demands on devices. Therefore, developing more convenient and cheaper methods for hydrazine detection is important. Based on these considerations, we have chosen to study carbon-based chemically modified electrodes with excellent electron transfer performance between the electrode and the electrolyte [7], to find a new way for hydrazine detection which is both convenient and less cost.
* Corresponding author. Tel.: +869318912541; Fax: +869318912582. E-mail address: [email protected] (J. Zhao). http://dx.doi.org/10.1016/j.electacta.2015.05.027 0013-4686/ ã 2015 Elsevier Ltd. All rights reserved.
Prussian Blue (PB) and its analogues, which belong to a family of cyanide-based coordination network, have been used as electrontransfer mediators thanks to their outstanding electrocatalytic properties, with applications in many fields, such as ion selective electrodes [8], charge storage devices [9], catalysis [10], and biosensors [11]. The traditional synthetic methodology of Prussian Blue is to mix aqueous solutions of ferric (Fe3+) and ferricyanide ([Fe(CN)6]3) ions [12]. However the rate of the reaction is very low and the yield of PB nanoparticles is limited. In order to increase the reaction speed, Au and Pt nanoparticles were found to actively promote the process of PB growth [13,14], while the catalytic effect of Ag nanoparticles has not been examined yet. In this study, graphite felt (GF) was selected as a support because of its cost-effectiveness, its high conductivity, its reasonable chemical stability, and its 3D structure with a high porosity, and thus a high surface area for its functionalization by PB growth [14,15]. To our knowledge, studies reporting GF as working electrode for application in hydrazine sensing has not been reported. Here, we report a novel and original sensor (PB@Ag/GF) for direct electroanalytical determination of hydrazine. The sensor electrode was built in two steps. Firstly, the Ag nanoparticles were deposited on the surface of GF using a simple potentiostatic method under ultrasons. Secondly, Prussian Blue was catalytically deposited on the nanoparticles from a mixture of K3[Fe(CN)6],
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Fig. 1. SEM images of Ag/GF (A) and PB@Ag/GF (B). Inset: SEM image of PB/GF; EDS spectrum of PB@Ag/GF (C); FT-IR spectrum of PB@Ag/GF (D); XRD pattern of Ag/GF (E) and PB@Ag/GF (F).
FeCl3, KCl and HCl, resulting in the formation of the PB@Ag/GF electrode. This electrode was characterized by various techniques and a complete electrochemical characterization was performed, using cyclic voltammetry (CV) and amperometry. Electrochemical studies showed that the sensor has a good performance for the determination of hydrazine, in terms of anodic current increment, regarding the oxidation of N2H4H2O.
2. Experimental 2.1. Chemicals and Apparatus Polyacrylonitrile-based graphite was obtained from Haoshi carbon fiber Institute, without any further treatment. All other chemicals were obtained from Tianjin Guangfu Fine Chemical
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Fig. 2. (A): CV of PB@Ag/GF (trace a) and PB/GF (trace b) electrodes at 50 mV/s. (B): CV of PB@Ag/GF at scan rates from 3 to 300 mV/s. Insets: Plot of the oxidation peak current versus the scan rates from 3 to 300 mV/s (bottom) and to the square root of scan rates from 20 to 300 mV/s (top). (C): CV of PB@Ag/GF during the first 100 cycles at the scan rate of 50 mV/s. Each CV was conducted in a 0.5 mol L1 KCl aqueous solution. CVs of PB@Ag/GF (D), PB/GF (E), GF (F) at 20 mV/s, 30 mV/s, 50 mV/s, 70 mV/s, 100 mV/s, 150 mV/s and 200 mV/s in 0.1 mmol L1 K3[Fe(CN)6] containing 0.1 mol L1 KCl. Insets: Plots of the oxidation peak current of PB@Ag/GF (D), PB/GF (E) and GF (F) versus the scan rates.
Research Institute. All the aqueous solutions were prepared with double distilled water. CV and amperometric measurements were performed with a CHI 618C Electrochemical Workstation (CH Instruments, Shanghai, China) in a standard three electrode cell, with the freestanding GF as working electrode, an Ag/AgCl electrode as reference electrode and a platinum wire electrode as auxiliary electrode. The electrochemical cell volume was 20 mL, and all measurements were performed at room temperature. Powder X-ray diffraction (XRD) data were collected on a Rigaku D/MAX-2400 X-ray diffractometer with graphite monochromatized Cu Ka radiation
(l = 0.15406 nm). Scanning electron microscopy (SEM) experiments and Energy Dispersive Spectroscopy (EDS) experiments were performed with a JEOL JSM-6701F. Infrared spectra (IR) of dried particles pressed into KBr pellets were obtained on a NICOLET NEXUS-670-FTIR spectrometer. 2.2. Ultrasonic-electrodeposition of Ag nanoparticles on the GF ribbons Polyacrylonitrile-based graphite was treated according to a previous procedure [14]. Firstly, the 1.5 mm-thick GF sheets was
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cut into small ribbons with areas of 1 2 cm2. Then, the GF pieces were cleaned by water and methanol alternately, and each for six times. Secondly, after drying completely in a vacuum oven, the GF pieces were refluxed at 100 C for 3 h in concentrated nitric acid. After reaction, the GF pieces were washed by double-distilled water until the filtrate became neutral. The oxidized GF ribbons were soaked into a 5 103 mol L1 AgNO3 solution containing 0.1 mol L1 KNO3 and then treated under ultrasound for 10 min. Then, we applied a potential of 0.4 V [16] for 20 s under ultrasound to form Ag nanoparticles, electrolytically deposited on the surface of GF. The deposition area of each GF ribbon was 1 1 cm2. After deposition, the GF ribbons were taken out and washed by double distilled water to remove the electrolyte. Then the GF pieces were dried at 60 C for 3 h in a vacuum oven. The as prepared GFs were named Ag/GF. 2.3. Synthesis of PB@Ag/GF The Ag/GF electrodes were put into 20 mL of a mixed aqueous solution of 1.0 103 mol L1 K3[Fe(CN)6], 1.0 103 mol L1 FeCl3, 0.1 mol L1 KCl and 0.025 mol L1 HCl [13] for 1 h. The soaked area of each electrode was equal to 1 1 cm2. After deposition of PB, the electrodes were carefully washed by double distilled water and dried at 90 C for 2 h in a vacuum oven. The as prepared electrodes were named PB@Ag/GF. For comparison, PB/GF electrodes (without Ag nanoparticles) were prepared in the same conditions from free standing GF ribbons.
nanoparticles. Fig. 1(C) shows the EDS spectrum of PB@Ag/GF, where the presence of Ag, K and Fe can be verified. The chemical composition of the PB@Ag/GF electrode was confirmed by FT-IR spectroscopy (Fig. 1D). The absorption band at 2088 cm1 is the main characteristics of Prussian Blue and its analogues, corresponding to the stretching vibration of the CRN group, and the absorption band at 504 cm1 is due to the formation of M-CN-M’, indicating the presence of PB. The absorption bands at 1197 cm1 is due to the stretching vibration of C-O for GF [17]. In addition, the absorption bands at 1617 cm1 and 3433 cm1 refer to the H-O-H bending mode and O-H stretching mode, respectively, which indicates that interstitial water was present in the sample [13,18]. The Ag/GF and PB@Ag/GF electrodes were also examined by powder X-ray diffraction (Fig. 1E and F). In Fig. 1(E), a strong absorption at 2u = 25.84 refers to the (002) reflection of the hexagonal structure of GF. The sharp intense peaks at 2u values equal to 38.14 and 44.38 correspond to the (111) and (200) reflections of the face-centered-cubic structure of Ag, respectively, which demonstrates the existence of Ag nanoparticles. In Fig. 1(F), the (002) reflection of GF at 2u = 25.84 was still observed. The peak at 2u = 42.92 , corresponds to the (422) reflections of the facecentered-cubic phase of PB (space group: Fm3m(no. 225)) [19,20], in accordance with the standard values for the bulk cubic Prussian Blue (JCPDS card No 73-0687). By the way, we could not see the peak of Ag in In Fig. 1 (F), because the Ag nanoparticles are wrapped by PB. Additionally, according to the Scherrer formula [21], as shown below:
3. Result and discussion
L = 0.9l/Bcosu,
3.1. Characterization of PB@Ag/GF
Where L is the average particle size, l the X-ray wavelength (1.54056 Å for Cu-Ka radiation), B the half-peak broadening and u the angle corresponding to the peak maximum. From the XRD pattern of Ag/GF (Fig. 1(E)) and PB@Ag/GF (Fig. 1(F)), the average particle size of Ag and PB are calculated to be equal to 24 and 33 nm, which are in line with the result of the SEM pictures (Fig. 1A and B). Fig. 2(A) shows CV curves of PB@Ag/GF (trace a) and PB/GF (trace b) electrodes in 0.5 mol L1 KCl aqueous solution. Two pairs of sharp redox peaks both appeared on the CV of PB@Ag/GF and PB/ GF; they are related to the Prussian White/Prussian Blue (0.2 V) and Prussian Blue/Berlin Green (0.9 V) redox couples. The peak current of PB@Ag/GF was nonetheless much larger than that of PB/GF for two reasons: 1) the amount of PB on PB/GF was lower than on
GF is known as a highly porous structure and a good medium for fast transmission of electrons [14,15]. After pretreatment, as is shown in the SEM image (Fig. 1A), the GF sheet surfaces have many gaps and cracks, which could provide rich active sites and high specific surface areas for the deposition of Ag nanoparticles. The gaps and cracks also provide convenience for transmission of electron and ion in the electrolyte. SEM images of Ag/GF (Fig. 1A) and PB@Ag/GF (Fig. 1B) reflected that Ag and PB nanoparticles have been successfully deposited on the GF, and that the diameters of Ag and PB nanoparticles are about 20–30 and 30–40 nm, respectively. As we can see in the inset of Fig. 1(B), a small amount of PB deposited on GF in the absence of Ag
Fig. 3. (A): CV of PB@Ag/GF electrode in the absence (solid curve) and presence (dashed curve) of 5 104 mol L1 N2H4H2O at the scan rate of 50 mV/s. (B): Chronoamperometric responses of PB@Ag/GF (trace a), PB/GF (trace b) and Ag/GF (trace c) after 17 successive additions of 5 107 mol L1 N2H4H2O. Inset: calibration curve obtained from the chronoamperogram at the PB@Ag/GF modified electrode (R2 = 0.9919).
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Fig. 5. Long-term stability study of the PB@Ag/GF sensor. Each data represents the current response of the sensor to addition of 1 104 mol L1 N2H4H2O (E = 0.3 V). The response is normalized with respect to the response on the first day. Fig. 4. Chronoamperometric responses of PB@Ag/GF-20 (trace a), PB@Ag/GF-10 (trace b) and PB@Ag/GF-30 (trace c) after 17 successive additions of 5 107 mol L1 N2H4H2O.
PB@Ag/GF (see SEM pictures on Fig. 1(B); 2) the presence of the Ag nanoparticles deposited on GF improved the electrical conductivity and the electron transfer rate of the PB electrode. As shown in Fig. 2(B), the intensity of the oxidation peak increased and the separation between the oxidation and the reduction peaks widened with the scan rate in the range of 3300 mV/s. The current was found to be proportional to the scan rates between 3 to 20 mV/s and to the square root of the scan rate between 20 and 300 mV/s (Fig. 2B insets), which suggested that the reaction kinetics was a surface-controlled process at low scan rates and involved a diffusion-controlled process at high scan rates [18]. The stability of PB@Ag/GF presented on Fig. 2(D) was satisfactory, as no significant modification of the CV was observed after 100 cycles. It is noteworthy that the stability the electrode obtained was observed over the entire potential window (-0.1– 1.1 V). This observation suggests that the present electrochemical system demonstrates high stability for the transition between the redox couples of Prussian white / Prussian Blue and Prussian Blue / Berlin Green. This excellent stability also indicates that the permeation of K+ does not damage the structure of Prussian Blue during the process of cyclic voltammetric scanning, for the channel radius of Prussian Blue is about 1.6 Å which is easily accommodate K+ whose hydrated molecules has radii of 1.25 Å [14,22].
The plots of CVs and I-v1/2 at PB@Ag/GF, PB/GF and bare GF electrodes in 0.1 mmol L1 K3[Fe(CN)6] containing 0.1 mol L1 KCl were shown in Fig. 2(E–G). from the slope of the plot of I versus v1/2, the electroactive area for PB@Ag/GF, PB/GF and bare GF electrodes can be calculated based on Eq (1) given by the literature [23]. ip ¼ 269An3=2 DR CR V1=2 1=2
(1)
Where n is electron transfer number, A is the electroactive surface area of the working electrode, CR is the bulk concentration of the redox species (0.1 mmol L1), DR is the diffusion coefficient of the redox species ([Fe(CN)6]4, 6.5 106 cm2 s1). The linear relationship between I and v1/2 could be explained as follows: I = 8.4 103 v1/2 (A, (V s1), R2 = 0.999, PB@Ag/GF), I = 2.2 104 v1/2 (A, (V s1), R2 = 0.990, PB/GF) and I = 1.9 104 v1/2 (A, (V s1), R2 = 0.997, GF). A was calculated to be 122.6 cm2, 4.1 cm2 and 2.8 cm2 for PB@Ag/GF, PB/GF and GF, respectively. The results indicated that the electroactive surface area increased obviously after modified with PB on Ag/GF and GF, which would enhance the current response of hydrazine on the electrode. 3.2. Amperometric response of the modified electrodes to hydrazine As presented in Fig. 3(A), an enhancement of anodic peak current was observed after the addition of N2H4H2O. This behavior reveals that the PB@Ag/GF electrode has a strong electrocatalytic
Table 1 Comparative data for hydrazine sensors based on different modified electrodes Electrode PB/SWNTs/GCE MnHCF/GWCE EPPGE/SWCNT/PB Crhf/SWNTs HMWCNT/GCE o-AP/GCE NiHCF/GWCE Mn(II)-complex/ MWNTs/GCE Pd/CILE MPc-SAMs/Au Au/PPy/GCE PCV/GCE PB@Ag/GF a
Limit of detection.
Potential (V)
LODa (mol L1)
/
5.0 107 6.65 106 6.1 106 4.5 107 6.8 107 5.0 107 1.0 106 5.0 107
0.02 0.35 0.12 0.24 0.30
8.2 107 / 2.0 107 4.2 106 4.9 107
0.20 0.45 / / 0.22 / 0.45
Sensitivity (A mol1 L) 5.4 0.00047 0.16 5.16 0.0208 0.016 / 0.038 / 0.0094 0.0356 / 26.06
Reference [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] Present
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effect for the oxidation of N2H4H2O. The catalytic mechanism is described as the following reaction process [24]: K2Fe2+[Fe2+(CN)6] $ KFe3+[Fe2+(CN)6] + e + K+ (2)
4KFe3+[Fe2+(CN)6] + N2H4 + 4K+ ! 4K2Fe2+[Fe2+(CN)6]+ N2" + 4H+ (3) Based on the result of Fig. 3(A), we chose the working potential equal to 0.3 V for the amperometric sensor. Fig. 3(B) presents the chronoamperogram of the electrode of PB@Ag/GF (trace a) upon 17 consecutive additions of N2H4H2O to 0.5 mol L1 KCl aqueous solution under stirring. We observed a significant increase of the current toward the negative values upon the addition of N2H4H2O, suggesting that the electrode of PB@Ag/GF can be used as a hydrazine sensor. It took less than 2 s for the PB@Ag/GF electrode to reach 90% of the maximum current, which demonstrated that the sensor had a fast amperometric response to the oxidation of hydrazine. The limit of detection (LOD) of the sensor with a signalto-noise ratio of 3 was determined to be 4.9 107 mol L1, limit of quantification (LOQ) was 1.47 106 mol L1 and its sensitivity was determined to be 26.06 A mol1 L. By the way, the detection limit and quantification limit of the sensor are calculated by the formula as is shown below: LOD = 3.3s/k LOQ = 10s/k Where s is the stand deviation of blank test sample, and k is the slope of calibration curve obtained from the chronoamperogram. In order to discern the contribution of individual components and the possible synergistic effect among them, control experiments with PB/GF (trace b) and Ag/GF (trace c) under the same conditions were carried out, as shown in Fig. 3(B). The result highlights a synergistic effect among PB, Ag and GF as the current response of the PB@Ag/GF electrode is significantly greater than the sum of PB/GF and Ag/GF. This phenomenon may be caused by the good conductor of Ag and GF, and 3-D structure of porous GF also create a better communication between electrode and analyte, thus a great current response appear for PB@Ag/GF to determine N2H4H2O. In order to study the influence of electrodeposition time of Ag particles on PB@Ag/GF and its effect on the detection of hydrazine, we prepared PB@Ag/GF-10, PB@Ag/GF-20, and PB@Ag/GF-30, whose electrodeposition time is 10 s, 20 s, and 30 s, respectively, and used them to detect hydrazine at the same condition. As is shown in Fig. 4,IPB@Ag/GF-20>IPB@Ag/GF-30>IPB@Ag/GF-10, where IPB@Pt/GF is the current due to the oxidation of N2H4H2O at the PB@Pt/GF-10, PB@Ag/GF-20 and PB@Ag/GF-30 electrode, respectively. The current order is maybe due to two reasons: 1) the quantity of PB on the electrodes is increased along with the increment of electrodeposition time; 2) Transmission of electron and ion in the electrolyte is blocked when the quantity of PB achieves a certain level. The noise current produced by some common inorganic ions is an important problem with hydrazine sensor. For this reason, an interference study was performed on the PB@Ag/GF sensor in the amperometric response of 1 104 mol L1 N2H4H2O in 0.5 mol L1 KCl aqueous solution. We found that 1 104 mol L1 of Li+, Na+, K+, NH4+, Mg2+, F, Cl, NO2, NO3, SO42 have no noticeable effect on the detection of N2H4H2O, with changes of current response lower than 3% and a standard deviation lower than 1%. Our method thus shows an excellent anti-interference ability.
The long-term stability of the PB@Ag/GF sensor has been evaluated by measuring the electrode responses at intervals of three days. About 90% of the original responses (Fig. 5) can still be detected after 24 days. Our sensor thus has a good stability in time for hydrazine detection. For assessing the analytical performance of our hydrazine sensor, we have listed the characteristics of hydrazine sensors based on different modified electrodes, to compare them with the PB@Ag/GF sensor prepared in this work (Table 1). The survey of the performances displayed in Table 1 reveals that the PB@Ag/GF sensor shows excellent performances on detecting hydrazine, thanks to its high sensitivity and its low detection limit. 4. Conclusions In this article, a PB@Ag/GF hydrazine sensor was synthesized and characterized by various techniques including XRD, FT-IR, and SEM. The electrochemical properties of the electrode were investigated by cyclic voltammetry in 0.5 mol L1 KCl which as supporting electrolyte. The PB@Ag/GF electrode shows excellent performance on detecting hydrazine with a low detection limit and a high sensitivity. The sensor also displays high selectivity and stability toward the detection of N2H4H2O. The strategy of integrating electrochemically active inorganic compound in three dimensional macroporous materials will provide insight into the design of new electrodes for a wide range of applications in the detection of hydrazine. Acknowledgements Financial support was provided by the National Natural Science Foundation of China (Projects 20603014, 20673059, 20973061 and 20903051), the Chinese Ministry of Education (Key Project 105074), the Committee of Science and Technology of Shanghai (Projects 0652nm010 and 08JC1408100) and the Fundamental Research Funds for the Central Universities (Project lzujbky-2011116). References [1] S.S. Narayanan, F. Scholz, A Comparative Study of the Electrocatalytic Activities of Some Metal Hexacyanoferrates for the Oxidation of Hydrazine, Electroanal. 11 (1999) 465. [2] C.A. Reilly, S.D. Aust, Peroxidase Substrates Stimulate the Oxidation of Hydralazine to Metabolites Which Cause Single-Strand Breaks in DNA, Chem. Res. Toxicol. 10 (1997) 328. [3] J.W. Mo, B. Ogorevc, X.J. Zhang, B. Pihlar, Cobalt and Copper Hexacyanoferrate Modified Carbon Fiber Microelectrode as an All-Solid Potentiometric Microsensor for Hydrazine, Electroanal. 12 (2000) 48. [4] Z.K. He, X.L. Liu, Q.Y. Luo, H.W. Tang, X.M. Yu, C. Hui, Y.E. Zeng, Automatic Injection Analysis with Chemiluminescence Detection: Determination of Hydrazine, Microchem. J. 53 (1996) 356. [5] T.J. Pastor, V.J. Vajgand, V.V. Antonijevi c, Coulometric Determination of Thiols and Hydrazines with Electrogenerated Iodine in Methanol in the Presence of Potassium Acetate, Mikrochimica. Acta 3 (1983) 203. [6] A. Afkhami, A.R. Zarei, Simultaneous spectrophotometric determination of hydrazine and phenylhydrazine based on their condensation reactions with different aromatic aldehydes in micellar media using H-point standard addition method, Talanta 62 (2004) 559. [7] S.A. Wring, J.P. Hart, Chemically modified, carbon-based electrodes and their application as electrochemical sensors for the analysis of biologically important compounds, Analyst 117 (1992) 1215. [8] V. Krishnan, A.L. Xidis, V.D. Neff, Prussian blue solid-state films and membranes as potassium ion-selective electrodes, Analytica. Chimica. Acta 239 (1990) 7. [9] P.J. Kulesza, K. Miecznikowski, M.A. Malik, M. Galkowski, M. Chojak, K. Caban, A. Wieckowski, Electrochemical preparation and characterization of hybrid films composed of Prussian blue type metal hexacyanoferrate and conducting polymer, Electrochimica. Acta 46 (2001) 4065. [10] K. Itaya, N. Shoji, I. Uchida, Catalysis of the Reduction of Molecular Oxygen to Water at Prussian Blue Modified Electrodes, J. Am. Chem. Soc. 106 (1984) 3423. [11] A.A. Kayakin, O.V. Gitelmacher, E.E. Kayakina, Prussian Blue-Based FirstGeneration Biosensor. A Sensitive Amperometric Electrode for Glucose, Anal. Chem 67 (1995) 2419.
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Amperometric detection of hydrazine utilizing synergistic action of prussian blue @ silver nanoparticles / graphite felt modified electrode Jihua Zhao a, * , Jianxin Liu a , Simon Tricard c, Lei Wang a , Yanling Liang a , Linghua Cao a , Jian Fang a , Weiguo Shen a,b a Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, School of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, PR China b School of Chemistry and Chemical Engineering, East China University of Science and Technology, Shanghai 200237, PR China c Laboratoire de Physique et Chimie de Nano-Objets, INSA, CNRS, Université de Toulouse, 135 avenue de Rangueil, 31077 Toulouse, France
A R T I C L E I N F O
A B S T R A C T
Article history: Received 28 November 2014 Received in revised form 19 March 2015 Accepted 6 May 2015 Available online 7 May 2015
In this study, a triple-component hydrazine sensor (PB@Ag/GF) was fabricated with freestanding graphite felt (GF), silver nanoparticles (Ag) and prussian blue (PB). The Ag nanoparticles were electrodeposited on GF ultrasonically (Ag/GF), and acted as a catalyst of the chemical deposition of PB. The electrode was characterized by scanning election microscopy (SEM), infrared spectroscopy (IR), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS). The electrochemical behavior of PB@Ag/GF was measured by cyclic voltammetry and amperometric measurements. The sensor displayed a prominent electrocatalytic activity toward hydrazine oxidation, with a fast response time of 2 s, a low detection limit of 4.9 107 mol L1 and very high detection sensitivity of 26.06 A mol1 L. ã 2015 Elsevier Ltd. All rights reserved.
Keywords: Prussian Blue Silver nanoparticles Graphite Felt Hydrazine
1. Introduction Hydrazine (N2H4H2O) and its derivatives have wide applications in industry, agriculture, and can be used as explosives, antioxidants, photographic developer, oxygen scavengers and propellants [1], but they have also been recognized as carcinogenic and hepatotoxic substances, which could cause liver and kidney diseases, even cancer or genetic damages [2]. All these traits make their detection and quantization problems of considerable importance, notably in agriculture and pharmaceutical industry. The traditional methods reported for the detection of hydrazine are potentiometric [3], chemiluminescence [4], coulometric [5], and spectrophotometric methods [6], which are all expensive and require high demands on devices. Therefore, developing more convenient and cheaper methods for hydrazine detection is important. Based on these considerations, we have chosen to study carbon-based chemically modified electrodes with excellent electron transfer performance between the electrode and the electrolyte [7], to find a new way for hydrazine detection which is both convenient and less cost.
* Corresponding author. Tel.: +869318912541; Fax: +869318912582. E-mail address: [email protected] (J. Zhao). http://dx.doi.org/10.1016/j.electacta.2015.05.027 0013-4686/ ã 2015 Elsevier Ltd. All rights reserved.
Prussian Blue (PB) and its analogues, which belong to a family of cyanide-based coordination network, have been used as electrontransfer mediators thanks to their outstanding electrocatalytic properties, with applications in many fields, such as ion selective electrodes [8], charge storage devices [9], catalysis [10], and biosensors [11]. The traditional synthetic methodology of Prussian Blue is to mix aqueous solutions of ferric (Fe3+) and ferricyanide ([Fe(CN)6]3) ions [12]. However the rate of the reaction is very low and the yield of PB nanoparticles is limited. In order to increase the reaction speed, Au and Pt nanoparticles were found to actively promote the process of PB growth [13,14], while the catalytic effect of Ag nanoparticles has not been examined yet. In this study, graphite felt (GF) was selected as a support because of its cost-effectiveness, its high conductivity, its reasonable chemical stability, and its 3D structure with a high porosity, and thus a high surface area for its functionalization by PB growth [14,15]. To our knowledge, studies reporting GF as working electrode for application in hydrazine sensing has not been reported. Here, we report a novel and original sensor (PB@Ag/GF) for direct electroanalytical determination of hydrazine. The sensor electrode was built in two steps. Firstly, the Ag nanoparticles were deposited on the surface of GF using a simple potentiostatic method under ultrasons. Secondly, Prussian Blue was catalytically deposited on the nanoparticles from a mixture of K3[Fe(CN)6],
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Fig. 1. SEM images of Ag/GF (A) and PB@Ag/GF (B). Inset: SEM image of PB/GF; EDS spectrum of PB@Ag/GF (C); FT-IR spectrum of PB@Ag/GF (D); XRD pattern of Ag/GF (E) and PB@Ag/GF (F).
FeCl3, KCl and HCl, resulting in the formation of the PB@Ag/GF electrode. This electrode was characterized by various techniques and a complete electrochemical characterization was performed, using cyclic voltammetry (CV) and amperometry. Electrochemical studies showed that the sensor has a good performance for the determination of hydrazine, in terms of anodic current increment, regarding the oxidation of N2H4H2O.
2. Experimental 2.1. Chemicals and Apparatus Polyacrylonitrile-based graphite was obtained from Haoshi carbon fiber Institute, without any further treatment. All other chemicals were obtained from Tianjin Guangfu Fine Chemical
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Fig. 2. (A): CV of PB@Ag/GF (trace a) and PB/GF (trace b) electrodes at 50 mV/s. (B): CV of PB@Ag/GF at scan rates from 3 to 300 mV/s. Insets: Plot of the oxidation peak current versus the scan rates from 3 to 300 mV/s (bottom) and to the square root of scan rates from 20 to 300 mV/s (top). (C): CV of PB@Ag/GF during the first 100 cycles at the scan rate of 50 mV/s. Each CV was conducted in a 0.5 mol L1 KCl aqueous solution. CVs of PB@Ag/GF (D), PB/GF (E), GF (F) at 20 mV/s, 30 mV/s, 50 mV/s, 70 mV/s, 100 mV/s, 150 mV/s and 200 mV/s in 0.1 mmol L1 K3[Fe(CN)6] containing 0.1 mol L1 KCl. Insets: Plots of the oxidation peak current of PB@Ag/GF (D), PB/GF (E) and GF (F) versus the scan rates.
Research Institute. All the aqueous solutions were prepared with double distilled water. CV and amperometric measurements were performed with a CHI 618C Electrochemical Workstation (CH Instruments, Shanghai, China) in a standard three electrode cell, with the freestanding GF as working electrode, an Ag/AgCl electrode as reference electrode and a platinum wire electrode as auxiliary electrode. The electrochemical cell volume was 20 mL, and all measurements were performed at room temperature. Powder X-ray diffraction (XRD) data were collected on a Rigaku D/MAX-2400 X-ray diffractometer with graphite monochromatized Cu Ka radiation
(l = 0.15406 nm). Scanning electron microscopy (SEM) experiments and Energy Dispersive Spectroscopy (EDS) experiments were performed with a JEOL JSM-6701F. Infrared spectra (IR) of dried particles pressed into KBr pellets were obtained on a NICOLET NEXUS-670-FTIR spectrometer. 2.2. Ultrasonic-electrodeposition of Ag nanoparticles on the GF ribbons Polyacrylonitrile-based graphite was treated according to a previous procedure [14]. Firstly, the 1.5 mm-thick GF sheets was
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cut into small ribbons with areas of 1 2 cm2. Then, the GF pieces were cleaned by water and methanol alternately, and each for six times. Secondly, after drying completely in a vacuum oven, the GF pieces were refluxed at 100 C for 3 h in concentrated nitric acid. After reaction, the GF pieces were washed by double-distilled water until the filtrate became neutral. The oxidized GF ribbons were soaked into a 5 103 mol L1 AgNO3 solution containing 0.1 mol L1 KNO3 and then treated under ultrasound for 10 min. Then, we applied a potential of 0.4 V [16] for 20 s under ultrasound to form Ag nanoparticles, electrolytically deposited on the surface of GF. The deposition area of each GF ribbon was 1 1 cm2. After deposition, the GF ribbons were taken out and washed by double distilled water to remove the electrolyte. Then the GF pieces were dried at 60 C for 3 h in a vacuum oven. The as prepared GFs were named Ag/GF. 2.3. Synthesis of PB@Ag/GF The Ag/GF electrodes were put into 20 mL of a mixed aqueous solution of 1.0 103 mol L1 K3[Fe(CN)6], 1.0 103 mol L1 FeCl3, 0.1 mol L1 KCl and 0.025 mol L1 HCl [13] for 1 h. The soaked area of each electrode was equal to 1 1 cm2. After deposition of PB, the electrodes were carefully washed by double distilled water and dried at 90 C for 2 h in a vacuum oven. The as prepared electrodes were named PB@Ag/GF. For comparison, PB/GF electrodes (without Ag nanoparticles) were prepared in the same conditions from free standing GF ribbons.
nanoparticles. Fig. 1(C) shows the EDS spectrum of PB@Ag/GF, where the presence of Ag, K and Fe can be verified. The chemical composition of the PB@Ag/GF electrode was confirmed by FT-IR spectroscopy (Fig. 1D). The absorption band at 2088 cm1 is the main characteristics of Prussian Blue and its analogues, corresponding to the stretching vibration of the CRN group, and the absorption band at 504 cm1 is due to the formation of M-CN-M’, indicating the presence of PB. The absorption bands at 1197 cm1 is due to the stretching vibration of C-O for GF [17]. In addition, the absorption bands at 1617 cm1 and 3433 cm1 refer to the H-O-H bending mode and O-H stretching mode, respectively, which indicates that interstitial water was present in the sample [13,18]. The Ag/GF and PB@Ag/GF electrodes were also examined by powder X-ray diffraction (Fig. 1E and F). In Fig. 1(E), a strong absorption at 2u = 25.84 refers to the (002) reflection of the hexagonal structure of GF. The sharp intense peaks at 2u values equal to 38.14 and 44.38 correspond to the (111) and (200) reflections of the face-centered-cubic structure of Ag, respectively, which demonstrates the existence of Ag nanoparticles. In Fig. 1(F), the (002) reflection of GF at 2u = 25.84 was still observed. The peak at 2u = 42.92 , corresponds to the (422) reflections of the facecentered-cubic phase of PB (space group: Fm3m(no. 225)) [19,20], in accordance with the standard values for the bulk cubic Prussian Blue (JCPDS card No 73-0687). By the way, we could not see the peak of Ag in In Fig. 1 (F), because the Ag nanoparticles are wrapped by PB. Additionally, according to the Scherrer formula [21], as shown below:
3. Result and discussion
L = 0.9l/Bcosu,
3.1. Characterization of PB@Ag/GF
Where L is the average particle size, l the X-ray wavelength (1.54056 Å for Cu-Ka radiation), B the half-peak broadening and u the angle corresponding to the peak maximum. From the XRD pattern of Ag/GF (Fig. 1(E)) and PB@Ag/GF (Fig. 1(F)), the average particle size of Ag and PB are calculated to be equal to 24 and 33 nm, which are in line with the result of the SEM pictures (Fig. 1A and B). Fig. 2(A) shows CV curves of PB@Ag/GF (trace a) and PB/GF (trace b) electrodes in 0.5 mol L1 KCl aqueous solution. Two pairs of sharp redox peaks both appeared on the CV of PB@Ag/GF and PB/ GF; they are related to the Prussian White/Prussian Blue (0.2 V) and Prussian Blue/Berlin Green (0.9 V) redox couples. The peak current of PB@Ag/GF was nonetheless much larger than that of PB/GF for two reasons: 1) the amount of PB on PB/GF was lower than on
GF is known as a highly porous structure and a good medium for fast transmission of electrons [14,15]. After pretreatment, as is shown in the SEM image (Fig. 1A), the GF sheet surfaces have many gaps and cracks, which could provide rich active sites and high specific surface areas for the deposition of Ag nanoparticles. The gaps and cracks also provide convenience for transmission of electron and ion in the electrolyte. SEM images of Ag/GF (Fig. 1A) and PB@Ag/GF (Fig. 1B) reflected that Ag and PB nanoparticles have been successfully deposited on the GF, and that the diameters of Ag and PB nanoparticles are about 20–30 and 30–40 nm, respectively. As we can see in the inset of Fig. 1(B), a small amount of PB deposited on GF in the absence of Ag
Fig. 3. (A): CV of PB@Ag/GF electrode in the absence (solid curve) and presence (dashed curve) of 5 104 mol L1 N2H4H2O at the scan rate of 50 mV/s. (B): Chronoamperometric responses of PB@Ag/GF (trace a), PB/GF (trace b) and Ag/GF (trace c) after 17 successive additions of 5 107 mol L1 N2H4H2O. Inset: calibration curve obtained from the chronoamperogram at the PB@Ag/GF modified electrode (R2 = 0.9919).
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Fig. 5. Long-term stability study of the PB@Ag/GF sensor. Each data represents the current response of the sensor to addition of 1 104 mol L1 N2H4H2O (E = 0.3 V). The response is normalized with respect to the response on the first day. Fig. 4. Chronoamperometric responses of PB@Ag/GF-20 (trace a), PB@Ag/GF-10 (trace b) and PB@Ag/GF-30 (trace c) after 17 successive additions of 5 107 mol L1 N2H4H2O.
PB@Ag/GF (see SEM pictures on Fig. 1(B); 2) the presence of the Ag nanoparticles deposited on GF improved the electrical conductivity and the electron transfer rate of the PB electrode. As shown in Fig. 2(B), the intensity of the oxidation peak increased and the separation between the oxidation and the reduction peaks widened with the scan rate in the range of 3300 mV/s. The current was found to be proportional to the scan rates between 3 to 20 mV/s and to the square root of the scan rate between 20 and 300 mV/s (Fig. 2B insets), which suggested that the reaction kinetics was a surface-controlled process at low scan rates and involved a diffusion-controlled process at high scan rates [18]. The stability of PB@Ag/GF presented on Fig. 2(D) was satisfactory, as no significant modification of the CV was observed after 100 cycles. It is noteworthy that the stability the electrode obtained was observed over the entire potential window (-0.1– 1.1 V). This observation suggests that the present electrochemical system demonstrates high stability for the transition between the redox couples of Prussian white / Prussian Blue and Prussian Blue / Berlin Green. This excellent stability also indicates that the permeation of K+ does not damage the structure of Prussian Blue during the process of cyclic voltammetric scanning, for the channel radius of Prussian Blue is about 1.6 Å which is easily accommodate K+ whose hydrated molecules has radii of 1.25 Å [14,22].
The plots of CVs and I-v1/2 at PB@Ag/GF, PB/GF and bare GF electrodes in 0.1 mmol L1 K3[Fe(CN)6] containing 0.1 mol L1 KCl were shown in Fig. 2(E–G). from the slope of the plot of I versus v1/2, the electroactive area for PB@Ag/GF, PB/GF and bare GF electrodes can be calculated based on Eq (1) given by the literature [23]. ip ¼ 269An3=2 DR CR V1=2 1=2
(1)
Where n is electron transfer number, A is the electroactive surface area of the working electrode, CR is the bulk concentration of the redox species (0.1 mmol L1), DR is the diffusion coefficient of the redox species ([Fe(CN)6]4, 6.5 106 cm2 s1). The linear relationship between I and v1/2 could be explained as follows: I = 8.4 103 v1/2 (A, (V s1), R2 = 0.999, PB@Ag/GF), I = 2.2 104 v1/2 (A, (V s1), R2 = 0.990, PB/GF) and I = 1.9 104 v1/2 (A, (V s1), R2 = 0.997, GF). A was calculated to be 122.6 cm2, 4.1 cm2 and 2.8 cm2 for PB@Ag/GF, PB/GF and GF, respectively. The results indicated that the electroactive surface area increased obviously after modified with PB on Ag/GF and GF, which would enhance the current response of hydrazine on the electrode. 3.2. Amperometric response of the modified electrodes to hydrazine As presented in Fig. 3(A), an enhancement of anodic peak current was observed after the addition of N2H4H2O. This behavior reveals that the PB@Ag/GF electrode has a strong electrocatalytic
Table 1 Comparative data for hydrazine sensors based on different modified electrodes Electrode PB/SWNTs/GCE MnHCF/GWCE EPPGE/SWCNT/PB Crhf/SWNTs HMWCNT/GCE o-AP/GCE NiHCF/GWCE Mn(II)-complex/ MWNTs/GCE Pd/CILE MPc-SAMs/Au Au/PPy/GCE PCV/GCE PB@Ag/GF a
Limit of detection.
Potential (V)
LODa (mol L1)
/
5.0 107 6.65 106 6.1 106 4.5 107 6.8 107 5.0 107 1.0 106 5.0 107
0.02 0.35 0.12 0.24 0.30
8.2 107 / 2.0 107 4.2 106 4.9 107
0.20 0.45 / / 0.22 / 0.45
Sensitivity (A mol1 L) 5.4 0.00047 0.16 5.16 0.0208 0.016 / 0.038 / 0.0094 0.0356 / 26.06
Reference [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] Present
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effect for the oxidation of N2H4H2O. The catalytic mechanism is described as the following reaction process [24]: K2Fe2+[Fe2+(CN)6] $ KFe3+[Fe2+(CN)6] + e + K+ (2)
4KFe3+[Fe2+(CN)6] + N2H4 + 4K+ ! 4K2Fe2+[Fe2+(CN)6]+ N2" + 4H+ (3) Based on the result of Fig. 3(A), we chose the working potential equal to 0.3 V for the amperometric sensor. Fig. 3(B) presents the chronoamperogram of the electrode of PB@Ag/GF (trace a) upon 17 consecutive additions of N2H4H2O to 0.5 mol L1 KCl aqueous solution under stirring. We observed a significant increase of the current toward the negative values upon the addition of N2H4H2O, suggesting that the electrode of PB@Ag/GF can be used as a hydrazine sensor. It took less than 2 s for the PB@Ag/GF electrode to reach 90% of the maximum current, which demonstrated that the sensor had a fast amperometric response to the oxidation of hydrazine. The limit of detection (LOD) of the sensor with a signalto-noise ratio of 3 was determined to be 4.9 107 mol L1, limit of quantification (LOQ) was 1.47 106 mol L1 and its sensitivity was determined to be 26.06 A mol1 L. By the way, the detection limit and quantification limit of the sensor are calculated by the formula as is shown below: LOD = 3.3s/k LOQ = 10s/k Where s is the stand deviation of blank test sample, and k is the slope of calibration curve obtained from the chronoamperogram. In order to discern the contribution of individual components and the possible synergistic effect among them, control experiments with PB/GF (trace b) and Ag/GF (trace c) under the same conditions were carried out, as shown in Fig. 3(B). The result highlights a synergistic effect among PB, Ag and GF as the current response of the PB@Ag/GF electrode is significantly greater than the sum of PB/GF and Ag/GF. This phenomenon may be caused by the good conductor of Ag and GF, and 3-D structure of porous GF also create a better communication between electrode and analyte, thus a great current response appear for PB@Ag/GF to determine N2H4H2O. In order to study the influence of electrodeposition time of Ag particles on PB@Ag/GF and its effect on the detection of hydrazine, we prepared PB@Ag/GF-10, PB@Ag/GF-20, and PB@Ag/GF-30, whose electrodeposition time is 10 s, 20 s, and 30 s, respectively, and used them to detect hydrazine at the same condition. As is shown in Fig. 4,IPB@Ag/GF-20>IPB@Ag/GF-30>IPB@Ag/GF-10, where IPB@Pt/GF is the current due to the oxidation of N2H4H2O at the PB@Pt/GF-10, PB@Ag/GF-20 and PB@Ag/GF-30 electrode, respectively. The current order is maybe due to two reasons: 1) the quantity of PB on the electrodes is increased along with the increment of electrodeposition time; 2) Transmission of electron and ion in the electrolyte is blocked when the quantity of PB achieves a certain level. The noise current produced by some common inorganic ions is an important problem with hydrazine sensor. For this reason, an interference study was performed on the PB@Ag/GF sensor in the amperometric response of 1 104 mol L1 N2H4H2O in 0.5 mol L1 KCl aqueous solution. We found that 1 104 mol L1 of Li+, Na+, K+, NH4+, Mg2+, F, Cl, NO2, NO3, SO42 have no noticeable effect on the detection of N2H4H2O, with changes of current response lower than 3% and a standard deviation lower than 1%. Our method thus shows an excellent anti-interference ability.
The long-term stability of the PB@Ag/GF sensor has been evaluated by measuring the electrode responses at intervals of three days. About 90% of the original responses (Fig. 5) can still be detected after 24 days. Our sensor thus has a good stability in time for hydrazine detection. For assessing the analytical performance of our hydrazine sensor, we have listed the characteristics of hydrazine sensors based on different modified electrodes, to compare them with the PB@Ag/GF sensor prepared in this work (Table 1). The survey of the performances displayed in Table 1 reveals that the PB@Ag/GF sensor shows excellent performances on detecting hydrazine, thanks to its high sensitivity and its low detection limit. 4. Conclusions In this article, a PB@Ag/GF hydrazine sensor was synthesized and characterized by various techniques including XRD, FT-IR, and SEM. The electrochemical properties of the electrode were investigated by cyclic voltammetry in 0.5 mol L1 KCl which as supporting electrolyte. The PB@Ag/GF electrode shows excellent performance on detecting hydrazine with a low detection limit and a high sensitivity. The sensor also displays high selectivity and stability toward the detection of N2H4H2O. The strategy of integrating electrochemically active inorganic compound in three dimensional macroporous materials will provide insight into the design of new electrodes for a wide range of applications in the detection of hydrazine. Acknowledgements Financial support was provided by the National Natural Science Foundation of China (Projects 20603014, 20673059, 20973061 and 20903051), the Chinese Ministry of Education (Key Project 105074), the Committee of Science and Technology of Shanghai (Projects 0652nm010 and 08JC1408100) and the Fundamental Research Funds for the Central Universities (Project lzujbky-2011116). References [1] S.S. Narayanan, F. Scholz, A Comparative Study of the Electrocatalytic Activities of Some Metal Hexacyanoferrates for the Oxidation of Hydrazine, Electroanal. 11 (1999) 465. [2] C.A. Reilly, S.D. Aust, Peroxidase Substrates Stimulate the Oxidation of Hydralazine to Metabolites Which Cause Single-Strand Breaks in DNA, Chem. Res. Toxicol. 10 (1997) 328. [3] J.W. Mo, B. Ogorevc, X.J. Zhang, B. Pihlar, Cobalt and Copper Hexacyanoferrate Modified Carbon Fiber Microelectrode as an All-Solid Potentiometric Microsensor for Hydrazine, Electroanal. 12 (2000) 48. [4] Z.K. He, X.L. Liu, Q.Y. Luo, H.W. Tang, X.M. Yu, C. Hui, Y.E. Zeng, Automatic Injection Analysis with Chemiluminescence Detection: Determination of Hydrazine, Microchem. J. 53 (1996) 356. [5] T.J. Pastor, V.J. Vajgand, V.V. Antonijevi c, Coulometric Determination of Thiols and Hydrazines with Electrogenerated Iodine in Methanol in the Presence of Potassium Acetate, Mikrochimica. Acta 3 (1983) 203. [6] A. Afkhami, A.R. Zarei, Simultaneous spectrophotometric determination of hydrazine and phenylhydrazine based on their condensation reactions with different aromatic aldehydes in micellar media using H-point standard addition method, Talanta 62 (2004) 559. [7] S.A. Wring, J.P. Hart, Chemically modified, carbon-based electrodes and their application as electrochemical sensors for the analysis of biologically important compounds, Analyst 117 (1992) 1215. [8] V. Krishnan, A.L. Xidis, V.D. Neff, Prussian blue solid-state films and membranes as potassium ion-selective electrodes, Analytica. Chimica. Acta 239 (1990) 7. [9] P.J. Kulesza, K. Miecznikowski, M.A. Malik, M. Galkowski, M. Chojak, K. Caban, A. Wieckowski, Electrochemical preparation and characterization of hybrid films composed of Prussian blue type metal hexacyanoferrate and conducting polymer, Electrochimica. Acta 46 (2001) 4065. [10] K. Itaya, N. Shoji, I. Uchida, Catalysis of the Reduction of Molecular Oxygen to Water at Prussian Blue Modified Electrodes, J. Am. Chem. Soc. 106 (1984) 3423. [11] A.A. Kayakin, O.V. Gitelmacher, E.E. Kayakina, Prussian Blue-Based FirstGeneration Biosensor. A Sensitive Amperometric Electrode for Glucose, Anal. Chem 67 (1995) 2419.
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