КОЛЛОИДНЫЙ ЖУРНАЛ, 2007, том 69, № 3, с. 364-367
УДК 541.13+541.18
ELECTROCHEMICAL CHARACTERIZATION OF PRUSSIAN
BLUE NANOPARTICLES © 2007 Yuqing Miao, Jianrong Chen, Xiaohua Wu
Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces, Zhejiang Normal University, Jinhua 321004, China Поступила в редакцию 29.08.2006 г.
Mixing of FeCl3 solution with excess of K4Fe(CN)6 solution results in well-dispersed Prussian Blue (PB) nano-particles stable during at least one month. Polyaniline was deposited onto the PB nanoparticles modified electrode to provide its stability. The promising results for enhanced detection of H2O2 with these PB nanoparticles are described.
1. INTRODUCTION
2. MATERIALS AND METHODS
The Prussian Blue (PB) is well known due to its interesting electrochemical, electrochromic, photo-physical and magnetic properties. It is a classical mixed valence compound with two forms known as insoluble and soluble PB with the respective chemi-
and
cal formulae as [Fe(3+)]4[Fe(2+)(CN)6]3
K[Fe(3+)]4IFe(2+)(CN)6, distinguished by presence or absence of potassium [1].
the
PB can be oxidized to Berlin Green (BG) or reduced to Prussian White (PW). It has been also shown that the reduced form of PB (PW) has a catalytic activity for the reduction of O2 and of H2O2 [2]. The deposition of PB on an electrode surface, accomplished by a simple chemical or electrochemical synthesis, makes it possible to detect H2O2 amperometrically at a low applied potential, and so it is possible to eliminate the effect of interfering species [3, 4]. PB also acts as an artificial peroxidase and its use in the preparation of oxidase-based biosensors has been extremely studied.
Nanoparticles are very important and interesting materials. They exhibit unique optical, electronic and catalytic properties. Although synthesis of PB and study of its properties are extensively explored, the preparation of PB nanoparticles and the study of its application to elec-troanalysis or biosensing are relatively less reported [5]. Only a few reports were given on fabricating surfactant or polymer protected PB nanoparticles [6-9].
Here, we outline a simple method to prepare surfactant-free water dispersion of negatively charged PB nanoparticles. Mixing of FeCl3 solution with excess of K4Fe(CN)6 solution results in well-dispersed PB nanopar-ticles stable during at least one month. Our method is convenient and fast. In addition, we describe the promising results for enhanced detection of H2O2 with these PB nano-particles.
All chemicals were at least analytical reagent grade and all solutions were prepared by ultra-pure water from Milli-Q water.
PB nanoparticles were prepared by mixing equimolar amount of FeCl3 and K^[Fe(CN)6] aqueous solutions. 2 ml FeCl3 (2mM) solution was slowly dropped into 2 ml K4[Fe(CN)6] (2mM) solution under vigorous stirring. A blue solution was gradually formed.
5 |l PB dispersion was cast onto the surface of platinum electrode and the electrode was allowed to dry at room temperature. Then the electrode was dipped into 10 mM aniline solution in PBS (pH 7). The polyaniline film was deposited onto the surface of PB nanoparticles modified electrode by applying the sweep potential between -0.2 and 1 V vs SCE at a sweep rate of 100 mV/s. The number of sweeps was 5.
Cyclic voltammetry experiments were performed with an Autolab PGSTA30 electrochemical instrument. A platinum net auxiliary electrode and a standard SCE reference electrode were employed. A platinum disk electrode (2mm in diameter) was used as working electrodes. Prior to use, the platinum working electrode was mechanically polished with alumina powder (Al2O3, 0.03 |m), and then was electrochemically cleaned in 1 M H2SO4 by applying a cyclic potential between 0.2 and 2 V until the obtained cyclic voltammograms are identical. Unless otherwise indicated, the potential scan rate in cyclic voltammetry experiments was 100 mV / s. The supporting electrolyte was 0.01 M PBS (pH 7) prepared with KH2PO4 and Na2HPO4, unless stated otherwise.
The physical characteristics of the PB nanoparticles were studied by transmission electron microcopy (TEM, JEM-100C-II).
PffH
** 4 ^
r * ' "^t
Mr _ «
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' 4 »VI- - M ^ik v .. -t. ••
Current, A 1.5E - 05
5.0E - 06
-5.0E - 06
-1.5E - 05
0.2
0.4
0.6
Fig. 1. TEM images of PB nanoparticles.
3. RESULT AND DISCUSSION
PB can be synthesized chemically by mixing solutions containing either Fe3+ and [Fe(2+)(CN)6]4- or Fe2+ and [Fe(3+)(CN)6]3- ions, for example:
3K4Fe(CN)6 + 4FeCl3 = Fe4[Fe(CN)6]3 + 12KCl.
Mixing of stoichiometric amounts of K4Fe(CN)6 and FeCl3 leads to the formation of PB nanoparticles. Usually, surfactants or polymers were used to suppress the PB nanoparticles agglomeration.
Here, PB nanoparticles were prepared by mixing equimolar amount of FeCl3 and K4[Fe(CN)6] aqueous solutions. 2 ml FeCl3 (2 mM) solution was slowly dropped into 2 ml K4[Fe(CN)6] (2 mM) solution under vigorous stirring. Figure 1 is the TEM images of PB nanoparticles. As it shows, the formed PB nanoparticles are well dispersed. The PB nanoparticles are unimodal and their diameter is about 10 nm. This means that excess of K4[Fe(CN)6] leads to the formation of negatively charged PB nanoparticles. Moreover the surfactant-free negatively charged PB nanoparticles are stable during at least one month. Our method is convenient and fast.
As shown in Fig. 2, the oxidation peak of [Fe(2+)(CN)6]4-, the redox peaks of Fe3+ are observed clearly before the mixing of solutions. However, the obtained PB nanoparticles dispersion doesn't give any fa-radic current, which means the reaction is nearly complete. Here, PB nanoparticles were prepared by mixing equimolar amount of FeCl3 and K4[Fe(CN)6] aqueous solutions. It means the existence of excess of K4[Fe(CN)6] since the stoichiometric ratio between K4Fe(CN)6 and FeCl3 is 3 : 4. Since the obtained PB nanoparticles dispersion doesn't give any faradic current, the excess of K4[Fe(CN)6] is rather low.
5 |l PB dispersion was cast onto the surface of platinum electrode and the electrode was allowed to dry at
0.8 1.0 Voltage, V
Fig. 2. Cyclic voltammograms of (1): 2 ml 2 mM K4[Fe(CN)6], (2) 2 ml FeCl3 (2 mM) solution and (3) the obtained PB nanoparticles dispersion prepared from above solutions.
room temperature. The obtained PB modified electrode was studied by cyclic voltammograms. Figure 3 shows the cyclic voltammograms of PB modified electrode registered between -0.4 and +1.3 V. Two pairs of redox peaks are observed in the vicinity 0.06 V and 0.86 V, respectively. The peak I and peak I' are attributed to the redox interconversion of PB and PW. The peak II and peak II' are consistent with the redox interconversion of PB and PG [10].
Current, A 4.0E - 05 r
2.0E - 05
0.0E + 00
-2.0E - 05
-4.0E - 05
PW o PB I
PB o BG
II'
BG o PB
PB o PW
-0.5
0.5
1.0 1.5
Voltage, V
Fig. 3. Cyclic voltammograms of PB modified electrode.
0
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Current, A
Current, A
Fig. 4. Voltammograms of polyaniline electrodeposition onto the surface of PB nanoparticles modified platinum electrode (a), and unmodified platinum electrode (b). 10 mM aniline in PBS solution (pH 7) was used for electrochemical deposition.
The PB nanoparticles directly deposited on the surface of electrode form the modified electrode which is not stable enough. The faradic current due to PB nanoparticles decreases with the increase of sweep scan. In order to obtain the stable PB nanoparticles modified electrode, poly-aniline was deposited onto the PB nanoparticles modified electrode. As shown in Fig. 4, the cyclic voltammograms of aniline polymerization with PB nanoparticles are different to that of the single PB nanoparticles modified electrode or that of aniline polymerization without PB nano-particles.
The PB on the electrode can be oxidized to PG as well as reduced to PW. The latter has a catalytic activity for the reduction of O2 and of H2O2. As shown in Fig. 5, the reduction current of PB decreases after the PBS solution is deoxygenated by bubbling highly pure nitrogen for 15 min. Similarly, the reduction increases with the increase of H2O2 content.
H2O2 emerges in many biological reactions as the main product of several oxidases, and is an important element for the monitoring of underground and rainwater, food industry or bioprocesses. The PB nanoparticles modified
Current, A 3.0E - 05
0.0E + 00
-3.0E - 05
-6.0E - 05
-0.6
-0.3
0.3
0.6 0.9 Voltage, V
Fig. 5. Cyclic voltammograms of PB modified electrode covered by polyaniline in (1) PBS deoxygenated by bubbling highly pure nitrogen for at least 15 min, (2) PBS, (J) PBS with 1 mM H2O2, and (4) PBS with 10 mM H2O2. PBS has pH 7 in all cases.
electrode can act as an electrocatalyst for H2O2 reduction present in sample solution or formed in the course of an enzyme-catalyzed reaction. Therefore, it is possible to develop oxidases based biosensors to eliminate the effect of interfering species since the electrocatalytic process proceeds at a low potential.
ACKNOWLEDGMENTS
This material is based upon work funded by the National Natural Science Foundation of China (Grant No. 90406016), State Key Laboratory of Electroanalytical Chemistry of Chinese Academy of Sciences, Science and Technology Department of Zhejiang Province, and Zhe-jiang Province Natural Science Foundation of China (Grant No. Y404012).
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