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One-Dimensional Hierarchical Layered KxMnO2 (x < 0.3) Nanoarchitectures: Synthesis, Characterization, and Their Magnetic Properties Jiechao Ge,† Linhai Zhuo,† Fei Yang,† Bo Tang,*,† Lizhu Wu,‡ and Chenho Tung‡ College of Chemistry, Chemical Engineering and Materials Science, Shandong Normal UniVersity, Jinan 250014, People’s Republic of China, and Technical Institute of Physics and Chemistry, Chinese Academy of Sciences (CAS), Beijing, 100101, People’s Republic of China ReceiVed: May 22, 2006; In Final Form: July 22, 2006
One-dimensional (1D) hierarchical nanostructures of ultralong layered KxMnO2 (x < 0.3) bundles with diameters 50-100 nm and lengths up to 50-100 µm have been successfully prepared by a PEG-assisted hydrothermal method based on the reaction of KMnO4 with 2-ethylhexanol. The obtained samples ascribe to the monoclinic phase and exhibit ferromagnetic behaviors below 32 K and paramagnetic behaviors above 32 K, which may make this system a promising base material for magnetic devices. A series of contrastive experiments have illustrated that 2-ethylhexanol, PEG 400, KOH, and reaction time play an important role in the synthesis of the nanobundles. A possible growth mechanism has been proposed.
Introduction Over the past few years, one-dimensional (1D) nanostructured materials, such as nanotubes, nanowires, and nanobelts have been intensively studied due to their fundamental importance and wide range of potential applications in nanoelectronics, ultrasmall optical devices, and biosensors.1 Currently, the fabrication of nanomaterials with well-defined structures and novel properties is playing an important role in the development of nanotechnology. 2-10 Therefore, for novel technologies based on nanoscale machines and devices, we not only need to prepare 1D nanomaterials but also to try to organize them into wellaligned patterns of nanocrystals. Recently, much effort has been made to integrate nanorods or nanowires as building blocks into 1D complex superstructures, such as mesoporous silica fibers;3 Cd(OH)2 nanostrands;4 WO3,5 ZnS, and ZnSe nanowire bundles;6 hierarchically ordered CdS nanowires;7 oriented arrays of singlecrystal TiO2 nanofibers;8 Ag nanowire bundles;9 and aligned [Mo3Se3-]∞ nanowires.10 These results not only provide feasible ways to assemble 1D nanostructures for future microscale functional devices but also offer opportunities to explore their novel collective properties. However, it is still a challenge to build 1D hierarchical nanoarchitectures from wire-like building blocks in solution. As an important functional oxide, MnO2 has been attracting intensive attention due to its distinctive properties and potential applications in the fields such as catalysts, electrode materials, and soft magnetic materials.11 A lot of investigations on the synthesis of tunnel-like 1D MnO2 nanostructures have been reported.12,13 For example, helical R-MnO2 fibers have been fabricated by spontaneous formation.12a 1D single-crystal nanowires of R-MnO2 and β-MnO2 have been synthesized via a hydrothermal procedure employing MnSO4 with oxidizing reagents such as (NH4)2S2O8 or KMnO4.12c,12d Well-aligned γ-MnO2 nanowires were also obtained through a coordinationpolymer-precursor route.12f However, few reports have focused
on the formation of 1D layered MnO2 (δ-MnO2 or naturally occurring birnessite-related MnO2, which is characterized to be a layered structure comprised of edge-sharing MnO6 octahedra with a basal spacing of about 7 Å) nanostructures.14 To the best of our knowledge, the synthesis of the hierarchical layered K-birnessite MnO2 nanowire bundles has not been reported to date. In addition, until now the investigation of the application of 1D hierarchical layered K-birnessite MnO2 nanostructures as magnetic materials still remains vacant, although the ion doping, shape, size, and surface layers of manganese oxide is generally believed to influence their magnetic properties.15-18 Herein, we report the synthesis of ultralong layered K-birnessite MnO2 nanowire bundles and their magnetic properties. Although organic molecules, such as formic acid, glycol, glycerol, toluene, and sugar have been used to reduce KMnO4 to fabricate manganese compounds with an oxidation state of +4, +3, and +2,19 1D nanostructures were seldom obtained. In our work, the ultralong layered K-birnessite MnO2 nanowire bundles were synthesized by a novel reduction route with a surfactant-assisted hydrothermal method. The reducing agent in this synthetic process is 2-ethylhexanol, which is used to fabricate 1D MnO2 nanostructures for the first time, though it has been used to react with KMnO4 to produce MnO2.20 The obtained hierarchical nanostructures are assembled by nanowires with diameters of 50-100 nm and lengths ranging between 50 and 100 µm. The effects of 2-ethylhexanol, PEG 400, KOH, and reaction time on the morphology of the final layered K-birnessite MnO2 nanowire bundles are studied in detail, and the formation mechanisms of the hierarchical nanoarchitectures are also discussed. Experimental Section Synthesis of Layered MnO2 Nanowire Bundles. The basic reaction employed for the synthesis of the layered MnO2 nanowire bundles is formulated in the equation below.
* Corresponding author. E-mail:
[email protected]. † Shandong Normal University. ‡ Chinese Academy of Sciences.
10.1021/jp0631127 CCC: $33.50 © 2006 American Chemical Society Published on Web 08/23/2006
1D Hierarchical Layered KxMnO2 Nanoarchitectures
Figure 1. XRD patterns of the synthesized products after hydrothermal treatment at 180 °C for 24 h.
All chemicals were of analytical grade and were purchased from Beijing Chemical Reagents Co. Utralong layered MnO2 nanowire bundles were synthesized by the typical synthesis route as follows: 316 mg of KMnO4, 5 mL of 2-ethylhexanol, 5 mL of poly(ethylene glycol) (average molecular weight 400, abbreviated as PEG 400), and 5 mL of distilled water were introduced into a 50-mL flask to give an amaranth solution. Then, 5 mL of 3 M KOH was added dropwise to the above mixture solution under constant stirring at room temperature. Gray precipitation of MnO2 was soon produced. After stirring for 15 min, the mixture solution was transferred to a Teflonlined autoclave of 25 mL capacity. The autoclave was maintained at 180 °C for 24 h and then cooled to room temperature naturally. The resulting black solid product was filtered and washed repeatedly with ethanol and distilled water and then dried at 60 °C for 4 h. Methods. The powder XRD analysis was performed using an X′Pert PRO (Philips) X-ray diffractometer with graphitemonochromatized Cu K radiation (k ) 0.154 18 nm). XPS measurements were taken with an ESCALab220i-XL electron spectrometer (VG Scientific) using 300-W Al KR radiation. TEM images and HRTEM images were obtained with an accelerating voltage of 200 kV on a JEOL-200 CX transmission electron microscope and a JEOL-2010 electron microscope, respectively. Scanning electron microscopy (SEM) was carried out on a HITACAI S-4300 at an accelerating voltage of 100 kV. The amount of K in the products was determined by atomic absorption spectrometry (Z-8000) after dissolving the products in a 12 mol‚dm-3 HCl solution. Magnetic properties of the samples were investigated from 5 to 293 K with a superconducting quantum interference device (SQUID) magnetometer (MPMS-7) in a field of up to 2 T. In each experiment, about 80 mg of sample was loaded in a plastic sample holder. Results and Discussion Morphology and Structure. Figure 1 shows the X-ray diffraction (XRD) patterns of the as-prepared products. It could be obviously found that the sample is composed of two phases of manganese oxides, which are the monoclinic phase of K-birnessite (a ) 5.14 Å, b ) 2.84 Å, c ) 7.18 Å) for the most part and a very small fraction of the γ-Mn2O3 phase. The diffraction peaks at 2θ values of 12.54°, 25.25°, 36.22°, 37.31°, 40.02°, 42.60°, 51.83°, 56.32°, 58.33°, 63.31°, and 65.63° are assigned to monoclinic phase of K-birnessite (JCPDS80-1098) and 28.8° and 32.4° to the tetragonal phase of γ-Mn2O3 (JCPDS18-803). Further evidence for the quality and composition was also obtained by X-ray photoelectron spectroscopy (XPS) (Figure 2). The C1s peak at 284.8 eV was used as an
J. Phys. Chem. B, Vol. 110, No. 36, 2006 17855
Figure 2. XPS analysis of synthesized products after hydrothermal treatment at 180 °C for 24 h.
Figure 3. (a) TEM images of samples collected after hydrothermal treating at 180 °C for 24 h. (b) The high-magnification TEM images of a single nanowire bundle originated from a single knot (indicated by the black pane in part a). (c) SEM images of samples collected after hydrothermal treatment at 180 °C for 24 h. (d) The highmagnification SEM images of several nanowire bundles originated from a single knot (indicated by the white pane in part c).
inner standard calibration to eliminate the effect of charging up by emission of photoelectrons. The spectrum of the sample shows main peaks in the regions of Mn (3s, 3p, 2s, 2p), O (1s, 2s), and K (2p, 2s). The Mn2p region consists of a spin-orbit doublet with binding energy of 654.4 eV (Mn2p1/2) and 642.7 eV (Mn2p3/2), which are characteristic of a mixed-valence manganese system (Mn4+ and Mn3+).21 All these characterizations revealed that the layered K-birnessite with γ-Mn2O3 as tiny impurities could be obtained under the current synthesis conditions. The morphologies of the samples were studied by TEM and SEM. Figure 3a,b shows the TEM images of samples prepared by the typical synthesis route, revealing that the as-synthesized products are dominated by the very long bundle-like nanostructures assembled with several or tens of nanowires. The widths of these nanowire bundles are about 50-100 nm and the lengths are up to 50-100 µm, leading to the aspect ratio of these nanowire bundles as high as nearly 1000. The SEM images (Figure 3c) show that the products could be obtained at high yield. The high-magnification images of several nanowire bundles originated from a single knot (Figure 3d) also reveal
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Figure 4. TEM (a), SAED (b), and HRTEM (c, d) images of layered MnO2 bundle nanowires obtained by the typical synthesis route.
that the single bundle is assembled by several nanowires, indicating that such 1D hierarchical nanoarchitecture is a novel nanostructure among layered MnO2 family. More experiments were carried out to reveal the structure of as-synthesized nanowire bundles. Figure 4a is a TEM image of an individual bundle, clearly exhibiting that the bundle with diameter of 80 nm is assembled by several wires (each wire with diameter of about 20-30 nm). A selected-area electron diffraction pattern (Figure 4b) taken from the individual nanobundle is shown in Figure 4a, which reveals its single crystal nature. Figure 4c is a high-resolution transmission electron microscopy (HRTEM) image of a single bundle obtained from Figure 4a (indicated by the white pane). The crystalline growth in different nanowires of each bundle is along the [100] direction, and the interplanar spacing is about 0.70 nm, which corresponds to the interlayer distance of (001) planes in layered K-birnessite. The connectors with discrete diameter are disorderedly located between the nanowires (indicated by black circles). It is remarkable that the crystallinity is maintained through the connectors between the wires. Figure 4d is an amplificatory high-resolution transmission electron microscopy (HRTEM) image from Figure 4c (indicated by the white pane). The result reveals that the interplanar spacing is about 0.28 nm, which should ascribe to the interlayer distance of (103) planes in γ-Mn2O3. These structural characterizations revealed the existence of tiny γ-Mn2O3 doped in the layered K-birnessite nanowire bundle, which coincided well with the XRD results. Time-Dependent Experiments. The evolution of layered MnO2 nanowire bundles was studied by TEM at various stages of the hydrothermal process. When KOH was added to the mixture of KMnO4, 2-ethylhexanol, and PEG, the solution changed color from amaranth to gray and produced a large amount of precipitate, indicating that the reducing ability of 2-ethylhexanol works only with the presence of KOH. Figure 5a shows a TEM image of the product obtained at this stage. This image reveals that the products mainly consist of particles from 50 to 150 nm in size; the XRD patterns of the samples show a great similarity to that of amorphous manganese oxide (Figure 6a). After heating for 1 h, these particles change into
Ge et al.
Figure 5. TEM images of four samples collected after hydrothermal treating at 180 °C for (a) 0 h, (b) 1 h, (c) 6 h, and (d) 9 h.
flakes (Figure 5b) several micrometers in size and several nanometers in thickness. However, upon further prolonged reaction time (6 h), the sample displays a lamellae shape, as shown in Figure 5c, which has shown the tendency to curl, and bundles of folds appear on these lamellas. The characteristic diffraction peaks of layered K-birnessite corresponding to 0.70 and 0.35 nm appeared in the patterns. Meanwhile, two diffraction peaks at about 0.31 and 0.28 nm appeared in the patterns, indicating that the mesophase was formed22 (Figure 6b). When the reaction time is prolonged to 9 h, TEM images (Figure 5d) reveal that the number of folds increases and that these folds spontaneously agglomerate together. It seems that the curl of the lamellae leads to both the folds and the agglomeration of the folds. During this process, there are interesting changes in the morphology of the sample: the previously lamellae structure breaks into wire-like fragments and assembles into bundle-like wires, which is very critical in the formation process of MnO2 nanowire bundles. The crystallinity of the layered K-birnessite was improved by extending the heating time to 12 h, since the peak intensities of layered K-birnessite were increased (Figure 6c). Further extending the heating time to 24 h can make the layered K-birnessite nanowire bundles even longer. Effects of PEG 400 and the Concentration of KOH. To learn more about the formation of K-birnessite nanowire bundles, various synthetic conditions were tested. When the experiment was carried out in the absence of PEG 400 following the typical route, only short nanorod bundles with low aspect ratio (∼100) could be formed (Figure 7a). Compared with other synthetic routes of MnO2 nanowires or nanorods mentioned above, 2-ethylhexanol and PEG 400 are essential to the largescale formation of the ultralong K-birnessite nanowire bundles. That is, 2-ethylhexanol may act as not only a reducing agent for the reduction of KMnO4 but also a structure-directing agent for the bundle-like structure of MnO2, whereas PEG 400 acts as an accelerating agent for the growth of the MnO2 crystals along a certain direction by absorbing on the surfaces of MnO2 colloids, which is similar to the action of polyacrylamide on the formation of CdS nanowires.23 K-birnessite is a layered manganese oxide with exchangeable K ions between layers.24 It is apparent that the concentration of K+ ions should also have a great influence on the growth of nanowire bundles. In our
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Figure 6. XRD patterns of the synthesized products after hydrothermal treatment with different reaction times: (a) 0 h, (b) 6 h, and (c) 12 h.
Figure 7. TEM and SEM images of the products obtained at 180 °C for 24 h with various conditions: (a) without using PEG 400, (b) 2 M of KOH, and (d) 4 M of KOH. (c) XRD patterns of the product b.
experiment, an increase of the amounts of KOH leads to an increase in the concentration of K+. If the concentration of KOH solutions is 2 M, rodlike or blocklike products could be obtained (Figure 7b). All the X-ray diffraction peaks in Figure 7c can be perfectly indexed to a pure tetragonal phase of γ-Mn2O3 (JCPDS18-803), indicating that the low concentration of K+ is not suitable for the formation of layered K-birnessite nanowire bundles. Layered structures may need more cations or H3O+ to be stable.12e Therefore, when the concentration of KOH increased to the range of 2.5-3.5 M, layered K-birnessite nanowire bundle was produced at a higher K+ concentration. As the concentration of KOH was increased beyond 4 M, only lamellar K-birnessite structures were obtained (Figure 7d). This result indicated that a high enough K+ concentration could restrain the lamellar structure from curling, and the bundle-like structure could not be obtained under this condition. According to these results, the formation of the obtained nanowire bundles can be divided into several steps. First, KMnO4 reacted with 2-ethylhexanol at an appropriate KOH concentration to produce amorphous manganese oxide nanoparticles with a relatively wide range of sizes. After that, the amorphous manganese oxide nanoparticles evolved into flake structures at an elevated temperature and pressure under hydrothermal conditions, in which the smaller flakes may redissolve into the solution phase and the bigger ones grow into lamellae. As the reaction proceeded, the lamellae structures broke into wire-like structures and exhibited the tendency to curl. Finally, these wires assembled together and grew into wellcrystallized ultralong nanowire bundles. This interesting transition process is very similar to the rolling mechanism, which
has been widely used to explain the growth of 1D structures such as 1D MnO2 nanostructures, CdS nanorods, and aluminumbased nanorods or nanotubes.12e,25 Magnetic Properties. The magnetic properties of layered MnO2 nanowire bundles were characterized by recording both magnetization curves as a function of temperature (Figure 8a) and hysteresis loops at various temperatures (Figure 8b). The zero-field-cooled (ZFC)/field-cooling (FC) magnetization curves at an applied field (H) of 1000 as well as the ZFC magnetization curves at applied fields of 1000 and 20 Oe clearly show that there exists a phase transition from ferromagnetic to paramagnetic phase at the corresponding low temperatures (Tc) of 32 and 40 K, respectively,26 indicating that the increase of applied fields will result in the decrease of phase transition temperature of 1D layered MnO2 nanostructures. In Figure 8b, the field dependence of the magnetization for the layered MnO2 nanowire bundles is shown at 293 and 5 K, respectively. At 293 K, the magnetization does not show any hysteresis at all, revealing that a paramagnetic state exists in this temperature range. Whereas at 5 K, below the lower transition temperature, it exhibits a much larger hysteresis curve and shows a ferromagnetic behavior with saturation magnetization (Ms), remanent magnetization (Mr), and coercivity (Hc) values of ca. 14 emu/ g, 9 emu/g, and 4100 Oe, respectively, indicating that 1D layered MnO2 has larger coercivity than other MnO2 nanostructures.16 To explore the reason of the larger coercivity of the final products, the magnetic properties of samples with different aspect ratios and different K+ concentrations were determined. Figure 9a exhibits the hysteresis loops of sample with a low aspect ratio as shown in Figure 7a. According to literature,27 the interlayer K ions were almost completely exchanged with H+ during the acid washing procedures. The interlayer H+ (more probably H3O+) species are expected to maintain the chargeneutrality in the MnO2 nanowire bundles. Therefore, we used dilute HCl solution (0.1 mol‚dm-3) instead of ethanol and distilled water to wash the final product to decrease the K concentration. Figure 9b shows the hysteresis loops of sample after washing with dilute HCl in the typical synthesis route. The K+ contents of these two samples and as-synthesized product were measured by atomic absorption spectrometry. The detailed morphologic features, K+ content, and magnetic properties of these samples were extracted, as reported in Table 1, from which we can conclude that the magnetic properties of the samples vary with the aspect ratios and K+ contents, and the samples with higher aspect ratio and higher K+ concentration would have larger coercivity (Hc), saturation magnetization (Ms), and remanent magnetization (Mr). Therefore, the typical ferromagnetic behaviors may be attributed to the following reasons: First, the bundle-like structures with higher aspect ratios (∼1000) may inevitably lead to there being a new stable magnetic state with ferromagnetic components for the 1D layered MnO2 samples. Second, birnessite-related manganese oxide layers usually contain many oxygen vacancies, 14 which
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Figure 8. (a) The temperature dependence of the magnetization curves under zero-field cooling (ZFC) and field cooling (FC) with an applied field of 1000 Oe for layered MnO2 nanowire bundles prepared by a typical synthesis route. (b) Magnetization hysteresis loops of layered MnO2 nanowire bundles prepared by a typical synthesis route at different temperatures.
Figure 9. Magnetization hysteresis loops of layered MnO2 bundles at 5 K. (a) Without using PEG 400 in the typical synthesis route. (b) Washed with HCl solution instead of ethanol and distilled water in the typical synthesis route.
TABLE 1: Morphologic Features, K+ Content, and Magnetic Properties of 1D Layered MnO2 Nanostructures by Different Treatments in the Typical Synthesis Route treatment
morphology
aspect ratios
K (wt %)
Ms (emu/g) at 5 K
Mr (emu/g) at 5 K
Hc (Oe) at 5 K
washed with water washed with HCl without PEG 400
nanowire bundles nanowire bundles nanorod bundles
∼1000 ∼1000 ∼100
3.20 0.27 3.45
14.0 4.4 5.2
9.0 2.5 1.8
4100 3490 3478
are contributive to a ferromagnetic moment. 16a Third, the relatively large coercivity also benefits from the doping of tiny K+ and γ-Mn2O3 nanophase. On one hand, K+- or Na+-containing manganese oxides samples have been known to exhibit a higher magnetic susceptibility. 18 On the other hand, γ-Mn2O3 nanophase has been proved to be ferromagnetic at a low temperature similar to MnO nanoclusters. The latter with γ-Mn2O3 nanoclusters as tiny impurities exhibited an anomalous magnetic property with large coereivities up to 9500 Oe at 2 K.15b Conclusion Novel one-dimensional (1D) hierarchical nanostructures of layered MnO2 bundles with γ-Mn2O3 as tiny impurities have been synthesized by a hydrothermal procedure employing 2-ethylhexanol as reducing reagent. The XRD, TEM, SEM, XPS, HRTEM, and SQUID magnetometer have been provided for the characterizations of the 1D hierarchical nanostructures. The experiment results exhibit that 2-ethylhexanol, PEG 400, the concentration of KOH, and the reaction time are the key points for the preparation of K-birnessite nanowire bundles in aqueous solution. The possible formation mechanism of the assynthesized nanowire bundles was proposed. The obtained samples show ferromagnetic behaviors below 32 K and paramagnetic behaviors above 32 K, which may make this system a promising base material for magnetic devices. Since the formation of a relatively stable complex is universal for various metal oxides, we confirm that such a simple aqueous solution synthetic route can be extended to the synthesis of other metal oxides or noble metals with 1D nanostructures.
Acknowledgment. This work was supported by Program for New Century Excellent Talents in University (NCET-040651), the National Natural Science Foundation of China (Nos. 90401019 and 20335030), the State Key Laboratory Foundation of Electroanalytical Chemistry, and the Shandong Excellent Young and Middle Aged Scientist Foundation (No.2004BS04002). References and Notes (1) (a) Hu, J.; Ouyang, M.; Yang, P. D.; Lieber, C. M. Nature 1999, 399, 48. (b) Pan, Z. W.; Dai, Z. R.; Wang, Z. L. Science 2001, 291, 1947. (c) Xia, Y. N.; Yang, P. D.; Sun, Y.; Wu, Y.; Mayers, B.; Gates, B.; Yin, Y.; Kim, F.; Yan, H. AdV. Mater. 2003, 15, 353. (d) Peng, X. G.; Manna, L.; Yang, W. Y.; Wickham, J.; Scher, E.; Kadavanich, A.; Alivisatos, A. P. Nature 2000, 404, 59.(e) Shi, W. S.; Peng, H. Y.; Wang, N.; Li, C. P.; Xu, L.; Lee, C. S.; Kalish, R.; Lee, S. T. J. Am. Chem. Soc. 2001, 123, 11095. (f) Liu, J. F.; Li, Q. H.; Wang, T. H.; Yu, D. P.; Li, Y. D. Angew. Chem., Int. Ed. 2004, 43, 5048. (2) (a) Park, S.; Lim, J. H.; Chung, S. W.; Mirkin, C. A. Science 2004, 303, 348. (b) Grzybowski, B. A.; Stone, H. A.; Whitesides, G. M. Nature 2000, 405, 1033. (c) Cao, A. M.; Hu, J. S.; Liang, H. P.; Wan, L. J. Angew. Chem., Int. Ed. 2005, 44, 4391. (d) Hu, J. S.; Guo, Y. G.; Liang, H. P.; Wan, L. J.; Jiang, L. J. Am. Chem. Soc. 2005, 127, 17090. (3) Yang, Y. G.; Suzuki, M.; Fukui, H.; Shirai, H.; Hanabusa, K. Chem. Mater. 2006, 18, 1324. (4) (a) Luo, Y. H.; Huang, J. G.; Ichinose, I. J. Am. Chem. Soc. 2005, 127, 8296. (b) Ichinose, I.; Huang, J. G.; Luo, Y. H. Nano. Lett. 2005, 5, 97. (c) Ichinose, I.; Kurashima, K.; Kunitake, T. J. Am. Chem. Soc. 2004, 126, 7162. (5) (a) Gu, Z. J.; Ma, Y.; Yang, W. S.; Zhang, G. J.; Yao, J. N. Chem. Commun. 2005, 3597. (b) Polleux, J.; Gurlo, A.; Barsan, N.; Weimar, U.; Antonietti, M.; Niederberger, M. Angew. Chem., Int. Ed. 2006, 45, 261. (6) (a) Moore, D. F.; Ding, Y.; Wang, Z. L. J. Am. Chem. Soc. 2004, 126, 14372. (b) Xiong, S. L.; Shen, J. M.; Xie, Q.; Gao, Y. Q.; Tang, Q.; Qian, Y. T. AdV. Funct. Mater. 2006, 18, 1787.
1D Hierarchical Layered KxMnO2 Nanoarchitectures (7) Thiruvengadathan, R.; Regev, O. Chem. Mater. 2005, 17, 3281. (8) Yoo, S.; Akbar, S. A.; Sandhage, K. H. Adv. Mater. 2004, 16, 260. (9) Lee, S. J.; Morrill, A. R.; Moskovits, M. J. Am. Chem. Soc. 2006, 128, 1200. (10) (a) Messer, B.; Song, J. H.; Yang, P. J. Am. Chem. Soc. 2000, 122, 10232. (b) Xia, Y. N.; Whitesides, G. M. Angew. Chem., Int. Ed. 1998, 37, 550. (c) Messer, B.; Song, J. H.; Huang, M.; Wu, Y.; Kim, F.; Yang, P. Adv. Mater. 2000, 12, 1526. (11) (a) Morales, A. M.; Lieber, C. M. Science 1998, 279, 208. (b) Shen, Y. F.; Zerger, R. P.; DeGuzman, R. N.; Suib, S. L.; McCurdy, L.; Potter, D. I.; O′Young, C. L. Science 1993, 260, 511. (c) Yamamoto, N.; Endo, T.; Shimada, M.; Takada, T. Jpn. J. Appl. Phys. 1974, 13, 723. (12) (a) Giraldo, O.; Brock, S. L.; Marques, M.; Suib, S. L.; Hillhouse, H.; Tsapatsis, M.; Nature 2000, 405, 38. (b) Benaissa, M.; Yacaman, M. J.; Xiao, T. D.; Strutt, P. R. Appl. Phys. Lett. 1997, 70, 2120. (c) Wang, X.; Li, Y. D. J. Am. Chem. Soc. 2002, 124, 2880. (d) Wang, X. Li, Y. D. Chem. Commun. 2002, 764. (e) Wang, X.; Li, Y. D. Chem. Eur. J. 2003, 9, 300. (f) Xiong, Y. J.; Xie, Y.; Li, Z. Q.; Wu, C. Z. Chem. Eur. J. 2003, 9, 1645. (13) (a) Li, Q. G.; Olson, J. B.; Penner, R. M. Chem. Mater. 2004, 16, 3402. (b) Gao, Y. Q.; Wang, Z. H.; Wan, J. X.; Zou, G. F.; Qian, Y. T. J. Cryst. Growth 2005, 279, 415. (c) Zhang, Y. C.; Qiao, T.; Hu, X. Y.; Zhou, W. D. J. Cryst. Growth 2005, 280, 652. (d) Chen, Y.; Liu, C.; Li, F.; Cheng, H. M. J. Alloys Compd. 2005, 397, 282. (e) Zheng, D. S.; Sun, S. X.; Fan, W. L.; Yu, H. Y.; Fan, C. H.; Cao, G. X.; Yin, Z. L.; Song, X. Y. J. Phys. Chem. B 2005, 109, 16439. (14) Ma, R. Z.; Bando, Y.; Zhang, L. Q.; Sasaki, T. AdV. Mater. 2004, 16, 918. (15) (a) Seo, W. S.; Jo, H. H.; Lee, K.; Kim, B.; Oh, S. J.; Park, J. T. Angew. Chem., Int. Ed. 2004, 43, 1115. (b) Lee, G. H.; Huh, S. H.; Jeong, J. W.; Choi, B. J.; Kim, S. H.; Ri, H. C.; J. Am. Chem. Soc. 2002, 124, 12094. (16) (a) Yang, J. B.; Zhou, X. D.; James, W. J. Appl. Phys. Lett. 2004, 85, 3160. (b) Ding, Y. S.; Shen, X. F.; Gomez, S.; Luo, H.; Aindow, M.; Suib, S. L. AdV. Funct. Mater. 2006, 16, 549. (17) (a) Duan, P.; Dai, S. Y.; Tan, G. T.; Lu, H. B.; Zhou, Y. L.; Cheng, B. L.; Chen, Z. H. J. Appl. Phys. 2004, 95, 5666. (b) Haghiri-Gosnet, A.
J. Phys. Chem. B, Vol. 110, No. 36, 2006 17859 M.; Renard, J. P. J. Phys. D 2003, 36, R127. (c) Sarma, S. D. Nat. Mater. 2003, 2, 292. (d) Park, J.; Kang, E.; Bae, C. J.; Park, J. G.; Noh, H. J.; Kim, J. Y.; Park, J. H.; Park, H. M.; Hyeon, T. J. Phys. Chem. B 2004, 108, 13594. (18) (a) Ananth, M. V.; Venkatesan, V.; Dakshinamurthi, K. J. Power Sources 1998, 72, 99. (b) Akimoto, J.; Takahashi, Y.; Gotoh, Y.; Kawaguchi, K. Chem. Mater. 2003, 15, 2984. (19) (a) Ching, S.; Roark, J. L.; Duan, N. G.; Suib, S. L. Chem. Mater. 1997, 9, 750. (b) Wang, X.; Li, Y. D. Mater. Chem. Phys. 2003, 82, 419. (c) Zhang, Y. C.; Qiao, T.; Hu, X. Y.; Zhou, W. D. J. Cryst. Growth 2005, 280, 652. (20) (a) House, O. H. Modern Synthetic Reaction; W. A. Benjamin Inc.: New York, 1965; p 78. (b) Stewart, R. Oxidation in Organic Chemistry; Wiberg, K. B., Ed.; Academic Press: New York, 1965; Part A. p 1. (c) Ladbury, J. W.; Cullis, C. F. Chem. ReV. 1958, 58, 403. (d) Xing, Q. Y.; Xu, R. Q.; Zhou, Z.; Pei, W. W. Basic Organic Chemistry; Higher Education Press: Beijing, 1993; p 386. (21) (a) Yang, X. J.; Makita, Y.; Liu, Z. H.; Sakane, K.; Ooi, K. Chem. Mater. 2004, 16, 5581. (b) Banerjee, D.; Nesbitt, H. W. Geochim. Cosmochim. Acta 2001, 65, 1703. (22) (a) Ching, S.; Petrovay, D. J.; Jorgensen, M. L.; Suib, S. L. Inorg. Chem. 1997, 36, 883. (b) Wang, W. L.; Jiang, H.; Liu, Z. Q.; Liu, X. M. J. Mater. Chem. 2005, 15, 1002. (23) Zhan, J. H.; Yang, X. G.; Wang, D. W.; Li, S. D.; Xie, Y.; Xia, Y. N.; Qian, Y. T. AdV. Mater. 2000, 12, 1348. (24) Silvester, E.; Manceau, A.; Drits, V. A. Am. Mineral. 1997, 82, 962. (25) (a) Yang, J.; Zeng, J. H.; Yu, S. H.; Yang, L.; Zhou, G. E.; Qian, Y. T. Chem Mater. 2000, 12, 3259. (b) Yada, M.; Hiyoshi, H.; Ohe, K.; Machida, M.; Kijima, T. Inorg. Chem. 1997, 36, 5565. (26) Dwight, K.; Menyuk, N. Phys. ReV. 1960, 119, 1470. (27) Omomo, Y.; Sasaki, T.; Watanabe, M. Solid State Ionics 2002, 151, 243. Komaba, S.; Kumagai, N.; Chiba, S. Electrochim. Acta 2000, 46, 31.
