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Prussian blue micro-composites in a low-temperature hydrothermal process
Applied Surface Science 253 (2007) 9030–9034 www.elsevier.com/locate/apsusc
Preparation, characterization, and property of polyaniline/Prussian blue micro-composites in a low-temperature hydrothermal process Xiaoli Zhang, Chunhong Sui, Jian Gong *, Rui Yang, Yunqing Luo, Lunyu Qu Key Laboratory of Polyoxometalates Science of Ministry of Education, Northeast Normal University, Changchun 130024, PR China Received 25 December 2006; received in revised form 8 May 2007; accepted 11 May 2007 Available online 18 May 2007
Abstract Polyaniline/Prussian blue micro-composites have been synthesized by a low-temperature hydrothermal process. Prussian blue is obtained using the single iron-source precursor K3[Fe(CN)6] in acidic aqueous solution. The composite was characterized by field-emission scanning electron microscopy (FE-SEM), Fourier transmission infrared spectroscopy (FT-IR), and X-ray diffractometer (XRD). The magnetic behavior of polyaniline/Prussian blue composites and the effect of the concentration of K3[Fe(CN)6] on the morphology of polyaniline/Prussian blue micro-composites have been investigated. # 2007 Elsevier B.V. All rights reserved. Keywords: Polyaniline; Prussian blue; Magnetic properties
1. Introduction In recent years, conducting polymers have received much attention in modern technology as they have potential applications in optical and microelectronic devices, chemical sensors, catalysis, drug delivery and energy storage systems [1–3]. Recently, the combination of conducting polyaniline (PANI) with different inorganic materials has become a new direction because the hybrid materials frequently exhibit synergetic and complementary properties derived from both components [4,5]. And more and more multifunctional PANI nano-structures have been prepared by blending PANI with inorganic electrical, optical and magnetic nano-particles to form nano-composites, such as PANI/nano-ZnO fibers [5], PANI/vanadium oxide nano-sheets [6], PANI/CdS microwires [7], PANI/Fe3O4 nano-particles [8], PANI/Au nanofibers [9], and PANI/TiO2 nano-composites [10], etc. Among the inorganic nano-materials, magnetic nano-materials have been the subject of increasing interest due to their physical and technological applications [11,12]. Prussian blue is a mixedvalence iron(III) hexacyanoferrate(II) compound of composition Fe4[Fe(CN)6]3XH2O with as face-centered-cubic struc-
* Corresponding author. Tel.: +86 431 5099765. E-mail address: [email protected] (J. Gong). 0169-4332/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2007.05.022
ture, in which Fe3+ in the N-coordinated sites is in the high-spin state and Fe2+ in the C-coordinated sites is in the low-spin sate [13]. As a pigment in various dyes, Prussian blue is a first choice substrate for modification of conducting polymers [14], due to its potential molecular magnets [15–17], optomagnets [18], and molecular sensors [19] and so on. Hammond group has synthesized multiple-color electrochromism PANI/Prussian blue electrode using layer-by-layer-assembled method [20] to date. Shilpa N. Sawant et al. has also prepared PANI/ Prussian blue hybrid using chemical synthesis and electrochemical synthesis [21]. Meanwhile, cyclic voltammetry and X-ray photoelectron spectroscopy investigations confirmed the formation of a network typical of Prussian blue inside the polyaniline matrix. To our best knowledge, however, there has been never report on the true morphology of PANI/Prussian blue micro-composite, especially Prussian blue micro-composite enveloped by typical PANI membranous, by hydrothermal process. In this present work, we report a very simple approach for the preparation of PANI/Prussian blue micro-composite. In this approach, Prussian blue capped with PANI membrane is obtained using the single iron-source precursor K3[Fe(CN)6] in acidic aqueous solution by hydrothermal process. The effect of the concentration of K3[Fe(CN)6] on the morphology of PANI/Prussian blue micro-composite has been investigated.
X. Zhang et al. / Applied Surface Science 253 (2007) 9030–9034
2. Experimental All chemical used in this study were analytical reagent grade and used as received. The commercial aniline was distilled twice under vacuum before used. In a typical synthesis, K3[Fe(CN)6] was dissolved in 8 mL distilled water to form a clear solution of a certain concentration. 0.11 g (NH4)2S2O8 (APS) and 0.5 g H4SiW12O40 was added into the K3[Fe(CN)6] solution, respectively with stirring until the solution became clear. The clear solution was transferred into 12 mL Teflonsealed autoclave. Then 0.02 g of aniline was dripped into the autoclave. The autoclave was maintained at 140 8C for 24 h and then air-cool to room temperature. The dark green precipitate was collected and filtrated. The precipitates were washed with distilled water and anhydrous alcohol several times, and then dried in vacuum at 50 8C for 12 h. In this work, different concentration of K3[Fe(CN)6] (0.050, 0.055, and 0.060 mol/L, respectively) was used. IR spectrum of the PANI/Prussian blue micro-composites was carried out on Impact 410 FT-IR spectrophotometer. X-ray powder diffraction pattern of the PANI/Prussian blue microcomposites was collected on a Japan Rigaku Dmax 2000 X-ray diffractometer with Cu Ka radiation. Scanning electron microscopy (SEM) images and EDAX spectrum of the morphologies and sizes were obtained by using a XL-30 ESEM FEG scanning electron microscope operated at 20 kV with gold sputtered on samples. For variable-temperature, solid-state magnetic susceptibility data were collected on powdered samples in 1 T applied a Quantum Design MPMS-5 SQUID magnetometer in the temperature range 2–300 K.
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observed by SEM image. Usually, the conclusion of the nanoparticles capped with PANI membrane can only be presumed from the transmission electron micrograph (TEM) of the PANI/ nano-particles composites because of the nano-size of the inorganic particles. With increasing the size of the inorganic particles, the SEM image of the PANI/inorganic particles prepared with ordinary method cannot reflect the actually enveloped image due to the demolishment of the PANI membrane. This SEM image of the PANI/Prussian blue microcomposites prepared by the low-temperature hydrothermal process supports, for the first time, the conclusion that the Prussian blue crystal particles are rather encapsulated by the PANI membrane. At the same time, we give TEM images in Fig. 2a and b. It can be seen clear that many Prussian blue particles were incorporated in a flake of PANI. The diameter of the Prussian blue particles capped with PANI is about 300 nm. In fact, some bigger cubical particles of Prussian blue, which unthread from PANI membrane, can be found also when the concentration of [Fe(CN)6]3 is increased. As shown in Fig. 1b, with increasing the concentration of [Fe(CN)6]3, the morphology of the PANI/Prussian blue micro-composites changed obviously. It is interesting that there is no membranous structure, while a lot of micro-cubes with diameters in several hundred of nanometers can be seen. A closer look at the particles reveals that the micro-cubes have a rough surface, which is actually aggregates of nano-particles with diameters around 30–40 nm (as shown in Fig. 1b, inset). This result shows that PANI membrane will be torn apart by the bigger Prussian blue particles with the increase of the concentration of [Fe(CN)6]3 and the growth of the Prussian blue particles.
3. Results and discussion 3.2. Energy-dispersive X-ray analysis (EDAX) 3.1. SEM and TEM morphology Fig. 1a shows the SEM image of the PANI/Prussian blue micro-composites synthesized with 0.050 mol/L K3[Fe(CN)6] at 140 8C for 24 h. The SEM observations reveal that the PANI/ Prussian blue micro-composites show a membranous structure (as shown in Fig. 1a, inset). That is Prussian blue crystal particles are capped with PANI membrane. The slippery and compact configuration of the PANI membrane has never been
The compositions of above two micro-composites are also confirmed by an energy-dispersive X-ray analysis (EDAX), which reveals the presence of carbon, nitrogen, oxygen, iron, and tungsten (Fig. 3a and b). Two testing results are accordant and the amounts of C and N are considerably large by counting. This result proves that the substances with two different morphologies above mentioned are PANI/Prussian blue microcomposites.
Fig. 1. SEM images of the PANI/Prussian blue micro-composites prepared with 0.050 mol/L (a) and 0.060 mol/L (b) K3[Fe(CN)6] at 140 8C for 24 h.
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Fig. 2. TEM images of the PANI/Prussian blue micro-composites prepared with 0.050 mol/L K3[Fe(CN)6] at 140 8C for 24 h.
Fig. 3. EDAX spectrum of the PANI/Prussian blue micro-composites prepared with 0.050 mol/L (a) and 0.060 mol/L (b) K3[Fe(CN)6] at 140 8C for 24 h.
In the reaction process, the generation of Prussian blue is simultaneous with the polymerization of aniline. A typical slow decomposition and hydrolysis of K3[Fe(CN)6] to produce Fe3+ in the presence of H+ ions (Eq. (1)). Subsequently the Fe3+ reacts with undissociated [Fe(CN)6]3 to form Fe(III)[Fe(III)(CN)6] (Eq. (2)). Finally, Fe(III)[Fe(III)(CN)6] can react with Fe3+ again, and obtain electron from the mixing solution to form Prussian blue (Eq. (3)). The chemical steps can be shown as follows: ½FeðCNÞ6 3 þ 6Hþ ! Fe3þ þ 6HCN
(1)
Fe3þ þ ½FeðCNÞ6 3 ! FeðIIIÞ ½FeðIIIÞ ðCNÞ6
(2)
composites [23]. The band at 1414 cm1 is related to the C– H and C–N bending vibration in the spectrum of the PANI/ Prussian blue micro-composites [24,25]. The bands at 1302 and 1247 cm1 are the C–N and N Q N stretching mode, respectively. The band at 1152 cm1 is due to the bending modes for the benzeniod units [26]. The band at 2072 cm1 is corresponds to the Fe–CN stretching mode in the cyanometallate lattice [27]. All these bands indicate that PANI/Prussian blue micro-composites are prepared with the low-temperature hydrothermal process.
3FeðIIIÞ ½FeðIIIÞ ðCNÞ6 þ Fe3þ þ 3e ! Fe4 ðIIIÞ ½FeðIIÞ ðCNÞ6 3 (3) 3.3. FT-IR spectra Fig. 4 shows the IR spectrum of PANI/Prussian blue microcomposites. The characteristic bands of emeraldine salt form of the PANI at 1577 cm1 (C C stretching mode of the quinoid rings), 1498 cm1 (C C stretching mode of benzenoid rings) appear, indicating the formation of PANI [22]. In the range of 700–1100 cm1, the appearance of the four characteristic bands of H4SiW12O40 indicates that the doped H4SiW12O40 still keeps the Keggin structure in the PANI/Prussian blue micro-
Fig. 4. IR spectrum of the PANI/Prussian blue micro-composites prepared at 140 8C for 24 h with low-temperature hydrothermal process.
X. Zhang et al. / Applied Surface Science 253 (2007) 9030–9034
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3.5. Magnetic behavior of PANI/Prussian blue microcomposites
Fig. 5. XRD pattern of the PANI/Prussian blue micro-composites prepared at 140 8C for 24 h with low-temperature hydrothermal process.
3.4. X-ray diffraction The structure of PANI/Prussian blue micro-composites can also be confirmed by the XRD pattern. As shown in Fig. 5, the intense peaks corresponding to 2u = 17.48 (2 0 0), 2u = 24.68 (2 2 0), 2u = 35.28 (4 0 0), 2u = 39.48 (4 2 0) and 2u = 43.48 (4 2 2), Bragg reflections of Fe4[Fe(CN)6]3 are in agreement with those reported for Fe4[Fe(CN)6]3 crystal particles [13]. The broad peak at 2u = 7.028 can be assigned as the periodic distance with relatively distinct Bragg reflections [28]. This result indicates that the PANI/Prussian blue micro-composites contain Prussian blue crystal particles. An estimation of mean size of Prussian blue particles is performed from the width of the (2 2 0) Bragg reflection using the Debye–Scherrer equation. The mean size of the Prussian blue particles is about 400 nm. Although it is difficult to obtain the size distribution of the capped Prussian blue particles from the SEM image because of the illegibility of Prussian blue particles capped with PANI membrane, this result basically accord with the size of the Prussian blue particles, which is viewed from the SEM image of the PANI/Prussian blue micro-composites.
The magnetic behavior of Prussian blue composite, which is of importance for practical applications, is investigated for the PANI/Prussian blue micro-composites obtained with the lowtemperature hydrothermal process. The curve of the variabletemperature (5–300 K) magnetic susceptibility is shown in Fig. 6. The magnetic behavior of the Prussian blue particles capped with PANI membrane was determined by measurement of dcmagnetic as a function of temperature (Fig. 6). The magnetic susceptibility obeys the Curie–Weiss law above 80 K. The determined Weiss constant is u = 24 K (Fig. 6, inset). The positive Weiss constant indicates ferromagnetic exchange interactions between Fe3+ ions [16]. It is worthy to note that the measured magnetic susceptibility and Weiss constant of Prussian blue particles capped with PANI membrane are different from the common bulk [29]. This interesting feature is also observed in other polymers composites with magnetic particles [30,31]. When the Prussian blue capped with PANI, the magnetic susceptibility and Weiss constant changed. It is mostly due to that the Prussian blue capped with PANI is more freely aligned with the external field than the uncapped particles [31,32]. Therefore, the arrangement of Prussian blue particles within the PANI membrane has a significant effect on the magnetic properties of Prussian blue particles. 4. Conclusion In summary, we have introduced herein a novel and direct low-temperature hydrothermal method for preparing PANI/ Prussian blue micro-composites. The morphology of Prussian blue capped with PANI membrane is viewed for the first time by SEM image. The Prussian blue particles with small size (ca. < 500 nm) can be capped by PANI membrane. However, with increasing the size of the Prussian blue particles, the Prussian blue particles will unthread from PANI membrane. The presence of the PANI membrane takes an important role in the change of the magnetic property of Prussian blue particles. Acknowledgments We greatly appreciated the financial supports from the Science Foundation of Jilin province and the project-sponsored by SRF for ROCS, SEM. References
Fig. 6. Temperature dependence of magnetic susceptibility for the PANI/ Prussian blue micro-composites prepared at 140 8C for 24 h with low-temperature hydrothermal process in a field of 1000 Oe. The inset shows the corresponding inverse susceptibility.
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Preparation, characterization, and property of polyaniline/Prussian blue micro-composites in a low-temperature hydrothermal process Xiaoli Zhang, Chunhong Sui, Jian Gong *, Rui Yang, Yunqing Luo, Lunyu Qu Key Laboratory of Polyoxometalates Science of Ministry of Education, Northeast Normal University, Changchun 130024, PR China Received 25 December 2006; received in revised form 8 May 2007; accepted 11 May 2007 Available online 18 May 2007
Abstract Polyaniline/Prussian blue micro-composites have been synthesized by a low-temperature hydrothermal process. Prussian blue is obtained using the single iron-source precursor K3[Fe(CN)6] in acidic aqueous solution. The composite was characterized by field-emission scanning electron microscopy (FE-SEM), Fourier transmission infrared spectroscopy (FT-IR), and X-ray diffractometer (XRD). The magnetic behavior of polyaniline/Prussian blue composites and the effect of the concentration of K3[Fe(CN)6] on the morphology of polyaniline/Prussian blue micro-composites have been investigated. # 2007 Elsevier B.V. All rights reserved. Keywords: Polyaniline; Prussian blue; Magnetic properties
1. Introduction In recent years, conducting polymers have received much attention in modern technology as they have potential applications in optical and microelectronic devices, chemical sensors, catalysis, drug delivery and energy storage systems [1–3]. Recently, the combination of conducting polyaniline (PANI) with different inorganic materials has become a new direction because the hybrid materials frequently exhibit synergetic and complementary properties derived from both components [4,5]. And more and more multifunctional PANI nano-structures have been prepared by blending PANI with inorganic electrical, optical and magnetic nano-particles to form nano-composites, such as PANI/nano-ZnO fibers [5], PANI/vanadium oxide nano-sheets [6], PANI/CdS microwires [7], PANI/Fe3O4 nano-particles [8], PANI/Au nanofibers [9], and PANI/TiO2 nano-composites [10], etc. Among the inorganic nano-materials, magnetic nano-materials have been the subject of increasing interest due to their physical and technological applications [11,12]. Prussian blue is a mixedvalence iron(III) hexacyanoferrate(II) compound of composition Fe4[Fe(CN)6]3XH2O with as face-centered-cubic struc-
* Corresponding author. Tel.: +86 431 5099765. E-mail address: [email protected] (J. Gong). 0169-4332/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2007.05.022
ture, in which Fe3+ in the N-coordinated sites is in the high-spin state and Fe2+ in the C-coordinated sites is in the low-spin sate [13]. As a pigment in various dyes, Prussian blue is a first choice substrate for modification of conducting polymers [14], due to its potential molecular magnets [15–17], optomagnets [18], and molecular sensors [19] and so on. Hammond group has synthesized multiple-color electrochromism PANI/Prussian blue electrode using layer-by-layer-assembled method [20] to date. Shilpa N. Sawant et al. has also prepared PANI/ Prussian blue hybrid using chemical synthesis and electrochemical synthesis [21]. Meanwhile, cyclic voltammetry and X-ray photoelectron spectroscopy investigations confirmed the formation of a network typical of Prussian blue inside the polyaniline matrix. To our best knowledge, however, there has been never report on the true morphology of PANI/Prussian blue micro-composite, especially Prussian blue micro-composite enveloped by typical PANI membranous, by hydrothermal process. In this present work, we report a very simple approach for the preparation of PANI/Prussian blue micro-composite. In this approach, Prussian blue capped with PANI membrane is obtained using the single iron-source precursor K3[Fe(CN)6] in acidic aqueous solution by hydrothermal process. The effect of the concentration of K3[Fe(CN)6] on the morphology of PANI/Prussian blue micro-composite has been investigated.
X. Zhang et al. / Applied Surface Science 253 (2007) 9030–9034
2. Experimental All chemical used in this study were analytical reagent grade and used as received. The commercial aniline was distilled twice under vacuum before used. In a typical synthesis, K3[Fe(CN)6] was dissolved in 8 mL distilled water to form a clear solution of a certain concentration. 0.11 g (NH4)2S2O8 (APS) and 0.5 g H4SiW12O40 was added into the K3[Fe(CN)6] solution, respectively with stirring until the solution became clear. The clear solution was transferred into 12 mL Teflonsealed autoclave. Then 0.02 g of aniline was dripped into the autoclave. The autoclave was maintained at 140 8C for 24 h and then air-cool to room temperature. The dark green precipitate was collected and filtrated. The precipitates were washed with distilled water and anhydrous alcohol several times, and then dried in vacuum at 50 8C for 12 h. In this work, different concentration of K3[Fe(CN)6] (0.050, 0.055, and 0.060 mol/L, respectively) was used. IR spectrum of the PANI/Prussian blue micro-composites was carried out on Impact 410 FT-IR spectrophotometer. X-ray powder diffraction pattern of the PANI/Prussian blue microcomposites was collected on a Japan Rigaku Dmax 2000 X-ray diffractometer with Cu Ka radiation. Scanning electron microscopy (SEM) images and EDAX spectrum of the morphologies and sizes were obtained by using a XL-30 ESEM FEG scanning electron microscope operated at 20 kV with gold sputtered on samples. For variable-temperature, solid-state magnetic susceptibility data were collected on powdered samples in 1 T applied a Quantum Design MPMS-5 SQUID magnetometer in the temperature range 2–300 K.
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observed by SEM image. Usually, the conclusion of the nanoparticles capped with PANI membrane can only be presumed from the transmission electron micrograph (TEM) of the PANI/ nano-particles composites because of the nano-size of the inorganic particles. With increasing the size of the inorganic particles, the SEM image of the PANI/inorganic particles prepared with ordinary method cannot reflect the actually enveloped image due to the demolishment of the PANI membrane. This SEM image of the PANI/Prussian blue microcomposites prepared by the low-temperature hydrothermal process supports, for the first time, the conclusion that the Prussian blue crystal particles are rather encapsulated by the PANI membrane. At the same time, we give TEM images in Fig. 2a and b. It can be seen clear that many Prussian blue particles were incorporated in a flake of PANI. The diameter of the Prussian blue particles capped with PANI is about 300 nm. In fact, some bigger cubical particles of Prussian blue, which unthread from PANI membrane, can be found also when the concentration of [Fe(CN)6]3 is increased. As shown in Fig. 1b, with increasing the concentration of [Fe(CN)6]3, the morphology of the PANI/Prussian blue micro-composites changed obviously. It is interesting that there is no membranous structure, while a lot of micro-cubes with diameters in several hundred of nanometers can be seen. A closer look at the particles reveals that the micro-cubes have a rough surface, which is actually aggregates of nano-particles with diameters around 30–40 nm (as shown in Fig. 1b, inset). This result shows that PANI membrane will be torn apart by the bigger Prussian blue particles with the increase of the concentration of [Fe(CN)6]3 and the growth of the Prussian blue particles.
3. Results and discussion 3.2. Energy-dispersive X-ray analysis (EDAX) 3.1. SEM and TEM morphology Fig. 1a shows the SEM image of the PANI/Prussian blue micro-composites synthesized with 0.050 mol/L K3[Fe(CN)6] at 140 8C for 24 h. The SEM observations reveal that the PANI/ Prussian blue micro-composites show a membranous structure (as shown in Fig. 1a, inset). That is Prussian blue crystal particles are capped with PANI membrane. The slippery and compact configuration of the PANI membrane has never been
The compositions of above two micro-composites are also confirmed by an energy-dispersive X-ray analysis (EDAX), which reveals the presence of carbon, nitrogen, oxygen, iron, and tungsten (Fig. 3a and b). Two testing results are accordant and the amounts of C and N are considerably large by counting. This result proves that the substances with two different morphologies above mentioned are PANI/Prussian blue microcomposites.
Fig. 1. SEM images of the PANI/Prussian blue micro-composites prepared with 0.050 mol/L (a) and 0.060 mol/L (b) K3[Fe(CN)6] at 140 8C for 24 h.
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Fig. 2. TEM images of the PANI/Prussian blue micro-composites prepared with 0.050 mol/L K3[Fe(CN)6] at 140 8C for 24 h.
Fig. 3. EDAX spectrum of the PANI/Prussian blue micro-composites prepared with 0.050 mol/L (a) and 0.060 mol/L (b) K3[Fe(CN)6] at 140 8C for 24 h.
In the reaction process, the generation of Prussian blue is simultaneous with the polymerization of aniline. A typical slow decomposition and hydrolysis of K3[Fe(CN)6] to produce Fe3+ in the presence of H+ ions (Eq. (1)). Subsequently the Fe3+ reacts with undissociated [Fe(CN)6]3 to form Fe(III)[Fe(III)(CN)6] (Eq. (2)). Finally, Fe(III)[Fe(III)(CN)6] can react with Fe3+ again, and obtain electron from the mixing solution to form Prussian blue (Eq. (3)). The chemical steps can be shown as follows: ½FeðCNÞ6 3 þ 6Hþ ! Fe3þ þ 6HCN
(1)
Fe3þ þ ½FeðCNÞ6 3 ! FeðIIIÞ ½FeðIIIÞ ðCNÞ6
(2)
composites [23]. The band at 1414 cm1 is related to the C– H and C–N bending vibration in the spectrum of the PANI/ Prussian blue micro-composites [24,25]. The bands at 1302 and 1247 cm1 are the C–N and N Q N stretching mode, respectively. The band at 1152 cm1 is due to the bending modes for the benzeniod units [26]. The band at 2072 cm1 is corresponds to the Fe–CN stretching mode in the cyanometallate lattice [27]. All these bands indicate that PANI/Prussian blue micro-composites are prepared with the low-temperature hydrothermal process.
3FeðIIIÞ ½FeðIIIÞ ðCNÞ6 þ Fe3þ þ 3e ! Fe4 ðIIIÞ ½FeðIIÞ ðCNÞ6 3 (3) 3.3. FT-IR spectra Fig. 4 shows the IR spectrum of PANI/Prussian blue microcomposites. The characteristic bands of emeraldine salt form of the PANI at 1577 cm1 (C C stretching mode of the quinoid rings), 1498 cm1 (C C stretching mode of benzenoid rings) appear, indicating the formation of PANI [22]. In the range of 700–1100 cm1, the appearance of the four characteristic bands of H4SiW12O40 indicates that the doped H4SiW12O40 still keeps the Keggin structure in the PANI/Prussian blue micro-
Fig. 4. IR spectrum of the PANI/Prussian blue micro-composites prepared at 140 8C for 24 h with low-temperature hydrothermal process.
X. Zhang et al. / Applied Surface Science 253 (2007) 9030–9034
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3.5. Magnetic behavior of PANI/Prussian blue microcomposites
Fig. 5. XRD pattern of the PANI/Prussian blue micro-composites prepared at 140 8C for 24 h with low-temperature hydrothermal process.
3.4. X-ray diffraction The structure of PANI/Prussian blue micro-composites can also be confirmed by the XRD pattern. As shown in Fig. 5, the intense peaks corresponding to 2u = 17.48 (2 0 0), 2u = 24.68 (2 2 0), 2u = 35.28 (4 0 0), 2u = 39.48 (4 2 0) and 2u = 43.48 (4 2 2), Bragg reflections of Fe4[Fe(CN)6]3 are in agreement with those reported for Fe4[Fe(CN)6]3 crystal particles [13]. The broad peak at 2u = 7.028 can be assigned as the periodic distance with relatively distinct Bragg reflections [28]. This result indicates that the PANI/Prussian blue micro-composites contain Prussian blue crystal particles. An estimation of mean size of Prussian blue particles is performed from the width of the (2 2 0) Bragg reflection using the Debye–Scherrer equation. The mean size of the Prussian blue particles is about 400 nm. Although it is difficult to obtain the size distribution of the capped Prussian blue particles from the SEM image because of the illegibility of Prussian blue particles capped with PANI membrane, this result basically accord with the size of the Prussian blue particles, which is viewed from the SEM image of the PANI/Prussian blue micro-composites.
The magnetic behavior of Prussian blue composite, which is of importance for practical applications, is investigated for the PANI/Prussian blue micro-composites obtained with the lowtemperature hydrothermal process. The curve of the variabletemperature (5–300 K) magnetic susceptibility is shown in Fig. 6. The magnetic behavior of the Prussian blue particles capped with PANI membrane was determined by measurement of dcmagnetic as a function of temperature (Fig. 6). The magnetic susceptibility obeys the Curie–Weiss law above 80 K. The determined Weiss constant is u = 24 K (Fig. 6, inset). The positive Weiss constant indicates ferromagnetic exchange interactions between Fe3+ ions [16]. It is worthy to note that the measured magnetic susceptibility and Weiss constant of Prussian blue particles capped with PANI membrane are different from the common bulk [29]. This interesting feature is also observed in other polymers composites with magnetic particles [30,31]. When the Prussian blue capped with PANI, the magnetic susceptibility and Weiss constant changed. It is mostly due to that the Prussian blue capped with PANI is more freely aligned with the external field than the uncapped particles [31,32]. Therefore, the arrangement of Prussian blue particles within the PANI membrane has a significant effect on the magnetic properties of Prussian blue particles. 4. Conclusion In summary, we have introduced herein a novel and direct low-temperature hydrothermal method for preparing PANI/ Prussian blue micro-composites. The morphology of Prussian blue capped with PANI membrane is viewed for the first time by SEM image. The Prussian blue particles with small size (ca. < 500 nm) can be capped by PANI membrane. However, with increasing the size of the Prussian blue particles, the Prussian blue particles will unthread from PANI membrane. The presence of the PANI membrane takes an important role in the change of the magnetic property of Prussian blue particles. Acknowledgments We greatly appreciated the financial supports from the Science Foundation of Jilin province and the project-sponsored by SRF for ROCS, SEM. References
Fig. 6. Temperature dependence of magnetic susceptibility for the PANI/ Prussian blue micro-composites prepared at 140 8C for 24 h with low-temperature hydrothermal process in a field of 1000 Oe. The inset shows the corresponding inverse susceptibility.
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