PVA-Assisted Hydrothermal Synthesis of Copper@Carbonaceous

Ultralong Cu@carbonaceous submicrocables with diameters of 0.4−0.6 μm and lengths up to and exceeding 100 μm have been fabricated successfully by ...
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J. Phys. Chem. C 2007, 111, 2490-2496

PVA-Assisted Hydrothermal Synthesis of Copper@Carbonaceous Submicrocables: Thermal Stability, and Their Conversion into Amorphous Carbonaceous Submicrotubes Jun-Yan Gong, Shu-Hong Yu,* Hai-Sheng Qian, Lin-Bao Luo, and Tan-Wei Li DiVision of Nanomaterials & Chemistry, Hefei National Laboratory for Physical Sciences at the Microscale, School of Chemistry & Materials, Department of Chemistry, UniVersity of Science and Technology of China, Heifei 230026, China ReceiVed: NoVember 5, 2006; In Final Form: December 17, 2006

Ultralong Cu@carbonaceous submicrocables with diameters of 0.4-0.6 µm and lengths up to and exceeding 100 µm have been fabricated successfully by a poly(vinyl alcohol)- (PVA-) assisted hydrothermal carbonization process using copper chloride and maltose as materials. In this one-pot synthesis, poly(vinyl alcohol) (PVA) played an important role in the formation of these submicrocables as a structure-directing agent to effectively restrain the formation of carbonaceous spheres that are normally nucleated from bulk solutions. In addition, the combined synergistic effects of both the carbohydrates and the PVA enable the formation of elegant Cu@carbonaceous submicrocables. Furthermore, control of the initial pH value (∼7-8) and reaction temperature (∼180 °C) is also essential for the formation of cablelike structures. The effects of other saccharides such as glucose, β-cyclodextrin, and starch on the formation of Cu@carbonaceous submicrocables were also examined under similar conditions. The thermal stability of as-prepared Cu@carbonaceous submicrocables was studied. In addition, removal of the copper cores of Cu@carbonaceous submicrocables at ambient temperature in a mixed solution of hydrochloric acid and H2O2 can form well-defined amorphous carbonaceous submicrotubes.

1. Introduction As a kind of new nanostructure, core-shell nanostructures are undergoing increasing investigation because these composite nanoparticles are constructed of cores and shells of different chemical compositions, which allows the possibility of combining the advantages or distinctive properties of varied materials together.1 More recently 1-D core-shell nanostructures, i.e., nanocables, have begun to receive intense attention because their functionalities can be further enhanced by fabricating coresheath heterostructures, and thus many efforts have been made to synthesize such special core-shell nanostructures.2 Ag@SiO2 nanocables can be formed using a sol-gel method to coat Ag nanowires with amorphous silica.3 Ag@C hybrid nanocables4 and Ag nanowires5 have been obtained by a mild hydrothermal carbonization process in the presence of a carbohydrate. It is well-known that copper is one of the most important metals in modern technologies, given that it is malleable, ductile, and a good conductor of heat and electricity (second only to silver in electrical conductivity), and the fabrication of one-dimensional (1-D) nanomaterials of copper (wires/cables/rods) has been received considerable attention in recent years.6 The availability of copper nanocables with well-defined dimensions should be able to allow new types of applications or enhance the performance of currently existing electric devices.7 Recently, we developed a synergistic soft-hard template strategy for the synthesis of silver@cross-linked PVA nanocables,8 Cu@cross-linked PVA,9 and Te@cross-linked PVA core-shell nanostructures,10 and ultrathin Te@carbon rich composite nanocables.11 Normally, the polymerization and carbonization of the glucose dispersed in solution by a hydro* Corresponding author. E-mail: [email protected]. Fax: + 86 551 3603040.

thermal process results in the formation of uniform carbonaceous colloid spheres,12 the formation of various types of hollow metal oxide spheres,13 the poly(vinyl pyrrolidone)-assisted synthesis of Ag@C core-shell spheres,14 and the coupled synthesis of metal oxides@C nanostrutures.15 In addition, one-step hydrothermal carbonization of starch or glucose in the presence of silver ions can result in the formation of Ag@carbonaceous nanocables, accompanying the formation of massive carbonaceous spheres.4 A modified hydrothermal approach combining the syngerstic effects of both poly(vinyl alcohol) (PVA) and glucose during the carbonization and formation of silver nanowires can effectively restrain the formation of carbonaceous spheres that are nucleated from the bulk solutions,16 which can produce well-defined silver@carbon riched composite submicrocables. Copper nanowires of Cu@cross-linked PVA exhibit better chemical stability than single copper nanowires because of the existence of shell layers;17 this is of importance to potential applications in nanoscale electronic, optoelectronic, and sensing devices. Recently, a hydrothermal approach assisted by cetyltrimethylammonium bromide (CTAB) for the synthesis of Cu@C submicrocables has been demonstrated in which an aqueous hexamethylenetetramine (HMT) solution was used both as a reducing agent and as a carbonaceous source.18 However, to the best of our knowledge, the synthesis of core-shell nanostructures with Cu as the core component and an amorphous carbonaceous material as the shell has rarely been reported. In this article, we present an efficient one-pot poly(vinyl alcohol)- (PVA-) assisted hydrothermal carbonization process to synthesize Cu@carbonaceous coaxial submicrocables at a large scale using copper chloride and maltose as raw materials. In this system, copper chloride and maltose act as the oxidizing and reducing agents, respectively, and poly(vinyl alcohol) (PVA)

10.1021/jp067284f CCC: $37.00 © 2007 American Chemical Society Published on Web 01/25/2007

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is used as a structure-directing agent to form Cu@carbonaceous submicrocables. The pH value, temperature, reaction time, and different carbon sources play important roles in the formation of such nanostructures, and the formation mechanism has been investigated systematically. 2. Experimental Section Synthesis of Cu@Carbonaceous Submicrocables. The copper@carbonaceous submicrocables were synthesized hydrothermally by the reduction of Cu2+ in a maltose solution and the carbonization of maltose. In a typical procedure, CuCl2‚ 2H2O (0.5 mmol), maltose (0.3 g), and 3 mL of a poly(vinyl alcohol) (PVA, 3 wt %) solution were dissolved in 5, 10, and 5 mL of water, respectively, and then the maltose solution and the CuCl2 solution were dropwise added to the PVA solution. The pH value of the reaction solution was adjusted to 7.0 with 1 M NaOH and then stirred for 30 min. Finally, the entire solution was transferred into a Teflon-lined autoclave with a volume of 30 mL. After the autoclave had been sealed, it was heated and maintained in an oven at 180 °C for 48 h. After the reaction, brown-black products were obtained. The products were collected and washed several times with doubly distilled water and ethanol to remove ions and possible remnants in the final product. Purification Process for Cu@Carbonaceous Submicrocables. The purification process for the Cu@carbonaceous submicrocables included adding water and then, under sonication for about 1 min, removing the upper floating material and keeping the deep brown-black sediment. This purification process was repeated 3 or 4 times. After that, the sediment was washed with water and then ethanol and finally dried at 60 °C for further characterization. By applying this simple purification process, uniform Cu@carbonaceous submicrocables can be obtained. The upper black matter was also collected for characterization after the same washing and drying procedures. Synthesis of Amorphous Carbonaceous Submicrotubes. Amorphous carbonaceous submicrotubes were achieved by etching the core of the Cu@carbonaceous coaxial submicrocables in a mixed solution of hydrochloric acid (36.5 wt %)/ H2O2 (30 wt %)/H2O (1:5:10, v/v/v) at room temperature for 6 h. Characterization. The final products were characterized by various techniques. X-ray powder diffraction (XRD) was carried out on a Rigaku D/max-rA X-ray diffractometer with Cu KR radiation (λ ) 1.54178 Å). A scan rate of 0.05°/s was applied to record the pattern in the 2θ range of 10-90°. The morphology and size of the as-prepared products were observed by fieldemission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), on a JSM-6700F fieldemission scanning electron microscope and a Hitachi model H-800 transmission electron microscope, respectively. Highresolution TEM images (HRTEM) and the corresponding selected-area electron diffraction (SAED) patterns were recorded on a JEOL-2010 high-resolution transmission electron microscope at an acceleration voltage of 200 kV. To obtain further evidence for the purities and compositions of the as-prepared products, X-ray photoelectron spectra (XPS) were obtained on an ESCALab MKII X-ray photoelectron spectrometer, using Mg KR radiation as the exciting source. IR spectra were measured on a Bruker Vector-22 FT-IR spectrometer at room temperature. Raman spectra were excited by radiation of 514.5 nm from a Jobin Yvon (France) LABRAM-HR Confocal Laser MicroRaman Spectrometer. Thermogravimetric analysis (TGA) was

Figure 1. XRD pattern of the as-prepared product obtained at 180 °C for 48 h.

carried out on a TGA-50 thermal analyzer (Shimadzu Corporation) at a heating rate of 10 °C min-1 in flowing nitrogen or air. 3. Results and Discussion 3.1. Synthesis of Cu@Carbonaceous Submicrocables under Suitable Conditions. After carbonization, there are two kinds of products, i.e., the floating material and the sediment. After the separation and washing treatment, the products were each examined by X-ray diffraction (XRD). The XRD pattern confirmed that the brown-black sediment after the washing treatment was a composite material (Figure 1). All of the reflections can be indexed to the face-centered cubic (fcc) phase of Cu and are in good agreement with the reported data (JCPDS card no. 4-836, a ) 3.615 Å). Additionally, there is an obvious broadening peak at about 20° that corresponds to amorphous carbon, considering the carbonization of carbohydrates under the present reaction conditions. The XRD pattern for the floating material showed only a broadening peak around 20°, corresponding to a pure carbonaceous material. Figure 2a shows a photograph of the as-prepared product after the washing treatment, clearly indicating that the presence of the black floating material and brown-black sediment. The morphologies and microstructures of the as-prepared product were further investigated by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). A general overview FESEM image (Figure 2b) shows that the floating product consists of a large number of spheres with diameters of 3-5 µm. However, the brown-black sediment is composed of well-defined ultralong fibers with an average diameter of about 500 nm and lengths longer than 100 µm as shown in Figure 2c,d. Figure 3a,b shows bright-field TEM images of the fibers shown in Figure 2c,d. Dark/light contrast can clearly be observed along the radial direction, showing the core-shell cable structure with a core wire about 200 nm in diameter and a shell thickness of about 150 nm (Figure 3a,b). Each submicrocable is straight and has a uniform diameter throughout its length. The typical HRTEM image in Figure 3c was recorded from the core section of the cable. The clear lattice spacing of 2.1 Å corresponds to the interplanar distance of {111}. The angle between {111} and {110} is 35.3°, which is consistent with the value calculated for the face-centered cubic structure. The corresponding selectedarea electron diffraction (SEAD) pattern (Figure 3d) taken along the [1h10] zone axis confirmed that the core Cu wire is singlecrystalline. The results confirmed that the wire axis is along

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Figure 2. (a) Photograph of the product obtained by a hydrothermal carbonization reaction at 180 °C for 48 h, showing the upper floating material and the sediment. (b) SEM image of the upper part of the product shown in part a. (c,d) coaxial Cu@carbonaceous submicrocables precipitated shown in part a.

[110], which is consistent with the results reported previously for Cu@PVA nanocables,9 as well as the observations of Xu et al.18 As-prepared Cu@carbonaceous submicrocables are uniform in diameter and are well separated, such that they are not entangled with each other as in the case of Cu@cross-linked PVA cables prepared in the absence of a carbon source via a hydrothermal approach.9 The XPS spectrum in Figure 4 indicated that the C 1s and O 1s binding energies of the obtained sample are 284.67 and 532.40 eV, respectively. However, the binding energy at 933.90 eV for Cu 2p3/2 cannot be detected, implying that all Cu nanowires are coated by carbonaceous material. The quantitative analysis of the sample gives C, O, and Cu molar contents of 75.14%, 23.83%, and 1.03%, respectively. Therefore, the XPS results confirm that almost all of the copper nanowires are completely confined within shells of carbonaceous matter. Obviously, the molar ratio of C to O (about 3:1 based on elemental analysis) in the product increased markedly, compared to the value for pure maltose (about 1:1). It can be inferred that the change in C/O molar ratio is due to the carbonization of maltose. Previous studies have indicated that carbonization of glucose and starch4 can take place under similar conditions without using PVA; thus, the uniform shell of the Cu submicrocables obtained should be composed of carbonaceous matter. The Raman spectra shown in Figure 5 show two major peaks located at 1385 and 1595 cm-1 that correspond to the in-plane vibration of disordered amorphous carbon (D band) and crystalline graphic carbon (G band), respectively.19 These results also coincide with those obtained by XRD. As revealed by the weak reflections, the material actually contains a quantity of carbonaceous substance. In addition, the corresponding FTIR spectra show essentially that there exists a large amount of functional groups

such as sOH or CdO covalently bonded onto the carbon framework in the carbonaceous matter (see Supporting Information, Figure S1), which is consistent with the formation of colloidal carbon spheres.12 3.2. Influence of Reaction Time, Temperature, pH Value, and PVA Concentration on the Formation of Cu@Carbonaceous Submicrocables. The influence of reaction temperature and reaction time on the formation of Cu@carbonaceous submicrotubes was investigated. The XRD pattern in Figure 6a shows that the product obtained at 160 °C for 48 h can also be indexed as the face-centered cubic (fcc) phase of Cu (JCPDS card no. 4-836, a ) 3.615 Å). Increasing the reaction temperature can effectively improve the carbonization speed and efficiency. Figure 6b shows that the product obtained at 180 °C for 24 h contains some CuCl phase in addition to the Cu phase. Further prolonging the reaction time to 48 h produces the Cu@carbonaceous submicrocables, indicating that the CuCl phase is only an intermediate product and can ultimately be converted to Cu. This finding is similar to that observed previously in the preparation of Cu@cross-linked PVA nanocables.9 Furthermore, short and straight Cu nanowires were obtained in a low yield at 160 °C for 48 h (Figure 7). These results confirm that reaction time that is too short or temperature that is too low are not favorable for carbonization, resulting in lower yields. Furthermore, suitable pH values of the reaction solution are essential for the formation of cables. The pH dropped dramatically from its initial value of ∼7.0-8.0 to ∼3.0-4.0 for the residual solution after the reaction for 48 h, implying that the solution after the reaction becomes more acidic. It was found that nanocables can be obtained only when the initial pH of the reaction solution is controlled within the range from 7 to 8. When the initial pH value was kept at 4.5 without adjustment

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Figure 3. (a,b) TEM images of typical Cu@carbonaceous submicrocables prepared at 180 °C for 48 h. (c) HRTEM image and electron diffraction pattern taken from a typical cable shown in part b. (d) SAED pattern taken from the [1h10] zone axis.

Figure 4. XPS spectrum of the Cu@carbonaceous submicrocables obtained at 180 oC for 48 h.

Figure 5. Raman spectra of Cu@carbonaceous submicrocables prepared after hydrothermal carbonization for different reaction times: (a) 180 °C, 24 h; (b) 180 °C, 48 h.

by dilute NaOH solution, no Cu@carbonaceous submicrocables were obtained; instead, only massive aggregated carbon microspheres with a size of 2.5-5.5 µm were obtained (Figure 8). It can be inferred that an acidic solution can improve the carbonization speed so that many carbon microspheres can be produced. When the initial pH value is kept in a more alkaline range, maltose cannot be carbonized, even if other conditions are kept the same. Therefore, both a suitable pH value and a suitable reaction time are essential for the synthesis of Cu@carbonaceous submicrocables.

To verify the important influence of PVA on the formation of Cu@carbonaceous cables in this system, more careful investigation was conducted. In the absence of PVA, only a small fraction of wirelike particles appeared, even under otherwise identical conditions, as shown in Figure 9, indicating that PVA indeed plays a key role in inducing the formation of Cu@carbonaceous submicrocables, as in the formation of Ag@carbon rich composite submicrocables.16 In the absence of carbohydrates, cross-linking of PVA can happen when only the temperature increases to 200 °C and the initial pH value is

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Figure 9. SEM and TEM images of the as-prepared products obtained at 180 °C for 48 h without addition of PVA.

Figure 6. XRD patterns of the as-prepared products obtained under different conditions: (a) 160 °C, 48 h; (b) 180 °C, 24 h. The asterisk (*) indicates the CuCl phase.

Figure 10. SEM images of nanocables synthesized using different carbon sources: (a) starch, (b) β-cyclodextrin.

Figure 7. (a) SEM image and (b) TEM image of the product synthesized at 160 °C for 48 h.

Figure 8. SEM image of the as-prepared products obtained at 180 °C for 48 h. The initial pH value of the solution was 4.5.

10-13, as reported previously.9 Thus, the PVA will not be crosslinked at lower temperature (180 °C) under the present conditions, which also corresponds to the experimental observation that most of the PVA still remains in the bulk solution after the carbonization reaction. This phenomenon is different from that in the synthesis of Ag@carbon rich composite cables (carbon and cross-linked PVA) under similar conditions where the PVA is cross-linked.16 This evidence emphasizes that it is the combined synergistic effects of both the carbohydrates and the PVA that enable the formation of elegant Cu@carbonaceous submicrocables here. In fact, we have proposed that the formation of Ag@cross-linked PVA nanocables is controlled by a synergistic growth mecha-

nism, which we called a synergistic soft-hard template mechanism (SSHM).8 Herein, a similar synergistic process controls the formation of hybrid cables, which include the reduction speed of copper ions, the interactions among the copper nanoparticles, the carbonization of maltose to form the shell, and the mutual interactions between the gel-like matrix and the copper nanoparticles. In the present system, PVA is again responsible for the one-dimensional (1-D) oriented growth of cables. With the help of PVA, copper nanoparticles grows into nanowires when they are reduced by maltose. At the same time, maltose is carbonized in situ on the surface of the copper nanowires, and the copper wires act as a backbone on which the carbon shell forms. Remarkably, in this route, the formation of nanowires and the carbonization process of the carbohydrates occur simultaneously. 3.3. Influence of Other Carbohydrates on the Synthesis of Cu@Carbonaceous Submicrocables. To understand whether other saccharides such as glucose, β-cyclodextrin, and starch can influence the formation of Cu@carbonaceous submicrocables, similar experiments were performed under the same conditions. However, it is interesting to note that the samples from glucose were quite different from those synthesized using starch and β-cyclodextrin. The product obtained from the carbonization of glucose was composed of some isolated wires/ rods and massive carbon microspheres (see Supporting Information, Figure S2), whereas products similar to submicrocables can be synthesized in the presence of starch and β-cyclodextrin (Figure 10). According to the above results, it is supposed that formation of a cablelike structure is more difficult through the carbonization of glucose, compared to use of maltose, β-cyclodextrin, and starch. It is well-known that maltose, β-cyclodextrin, and starch are glucose-based saccharides that can all be gradually converted into glucose, catalyzed by hydrogen ions or metal ions. Therefore, the formation of Cu@carbonaceous cables could be related to the molecular weight of the saccharide, even though they are composed of similar functional units. Throughout the reaction process, these two glucose-based saccharides first hydrolyze into glucose and then carbonize to transform into carbonaceous matter including graphitic carbon. The carbonization rate and co-redox reaction rates have some

Copper@Carbonaceous Submicrocables

Figure 11. Thermogravimetric (TG) curves of the Cu@carbonaceous submicrocables under different flowing atmospheres: (a) nitrogen, (b) air.

Figure 12. XRD pattern of the sample obtained by calcination of the Cu@carbonaceous submicrocables at 550 °C for 1 h.

differences in the presence of different saccharide with different molecular weights, which determine the uniformity of the product as well as the quality of the cablelike core-shell structures. 3.4. Stablity of Cu@Carbonaceous Submicrocables. The Cu@carbonaceous submicrocables obtained by the present hydrothermal carbonization are relatively stable under ambient conditions in their dry state. The thermal stability of the samples was examined by thermogravimetric analysis (TGA) in a flowing nitrogen atmosphere. Figure 11a shows that the Cu@carbonaceous submicrocables began to slightly lose weight in the temperature range from 100 to 150 °C, which is due to the loss of water in the sample. This was followed by a marked weight loss starting at about 260 °C that can be attributed to further carbonization and decomposition of the carbon shell, as reported for other carbohydrates.20,21 The total weight-loss percentages for the Cu@carbonaceous submicrocables are 50 wt %. It can be concluded that the obvious weight loss occurs in the temperature range from 260 to 550 °C. Above 550 °C, the weight remained unchanged. In contrast, the thermal stability of the produced Cu@carbonaceous submicrocables was also examined in a flowing air atmosphere, which is similar to that in inert atmosphere but with two differences (Figure 11b): (i) The product underwent a quick mass loss between 200 and 290 °C (37 wt %) that still

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Figure 13. SEM image of amorphous carbonaceous submicrotubes obtained by etching the core Cu nanowires in Cu@carbonaceous submicrocables at room temperature for 6 h in a mixed solution of hydrochloric acid (36.5 wt %)/H2O2 (30 wt %)/H2O (1:5:10, v/v/v).

Figure 14. TEM images of amorphous carbonaceous submicrotubes obtained by etching the core Cu nanowires in Cu@carbonaceous submicrocables at room temperature in a mixed solution of hydrochloric acid (36.5 wt %)/H2O2 (30 wt %)/H2O (1:5:10, v/v/v) at room temperature for 6 h: (a,b) typical amorphous carbonaceous submicrotubes with obvious hollow channels, (c) magnified TEM image of an individual tube.

corresponds to further carbonization and decomposition of carbon shell. (ii) There was also a marked loss between 290 and 500 °C (41 wt %) that could be due to the oxidation of carbon in the samples. The value might be caused mainly by the conversion from Cu@carbonaceous submicrocables to CuO17b and CO2. To confirm this possibility, the XRD pattern of the product obtained by calcining the Cu@carbonaceous submicrocables at 550 °C for 1 h was obtained and showed that the product is well-crystalline monoclinic CuO (JCPDS card no. 48-1548; Figure 12). Although the conversion of Cu to CuO can lead to a slight increase in weight, the weight loss of carbon is still relatively significant and greater than the increase in weight. Above 500 °C, the weight remained unchanged, and the last product had a mass percentage of 12 wt %, which was near the theoretical value (14.5 wt %). 3.5. Synthesis of Amorphous Carbonaceous Submicrotubes. The copper core in Cu@carbonaceous submicrocables can be etched away using a mixture of hydrochloric acid and H2O2, and then well-defined amorphous carbonaceous submicrotubes can be easily obtained. During this procedure, the copper core could be easily etched completely after about 6 h at ambient temperature. The general SEM image in Figure 13 demonstrates that the wirelike morphology was still kept. A typical TEM image shows that the copper core can be completely removed from its interior and that the thickness of the channel in the amorphous carbonaceous submicrotubes is about 100 nm (Figure 14). Furthermore, during this etching

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Gong et al. applications in encapsulating or acting as a carrier for metal catalyst, among other areas. Acknowledgment. S.-H.Y. acknowledges the special funding support from the Centurial Program of the Chinese Academy of Sciences and the Natural Science Foundation of China (Grants 20325104, 20321101, 20671085), the 973 project (2005CB623601), the Anhui Development Fund for Talent Personnel (2006Z027), and the Scientific Research Foundation for the Returned Overseas Chinese Scholars supported by the State Education Ministry, the Specialized Research Fund for the Doctoral Program (SRFDP) of Higher Education State Education Ministry, and the Partner-Group of the Chinese Academy of Sciences-Max Planck Society.

Figure 15. TEM images of partially etched Cu@carbonaceous submicrocables after etching at room temperature in a solution of hydrochloric acid (36.5 wt %) and water (1:10, v/v) without H2O2.

process, the H2O2 plays an important role. In this mixed aqueous solution, H2O2 in the solution generates oxygen slowly, which is helpful in dissolving copper as evidenced by the fact that partially etched submicrocables were observed when H2O2 was not added (Figure 15). The main reactions can be expressed as follows:

2H2O2 ) 2H2O + O2 2Cu + 4HCl + O2 ) 2CuCl2 + 2H2O 4. Conclusions In summary, ultralong Cu@carbonaceous coaxial submicrocables can be synthesized from solutions of different glucosebased saccharides by a one-step poly(vinyl alcohol)- (PVA-) assisted hydrothermal carbonization process in the presence of Cu2+. In this one-pot synthesis, PVA plays an important role in the formation of the submicrocables as a structure-directing agent, and an appropriate pH value (∼7-8) and reaction temperature (∼180 °C) are also essential for the production of this type of structure. The choice of different saccharides can determine the uniformity of the product as well as the quality of the cablelike core-shell structures. The thermal stability of the as-prepared Cu@carbonaceous submicrocables was studied. Well-defined amorphous carbonaceous submicrotubes can also be produced by removal of the copper cores of such submicrocables using a chemical method at ambient temperature. Cables with copper (a good conductor of heat and electricity) as the core and an insulating carbonaceous sheath are expected to find applications as conducting submicrowires for the connection of minitype devices and in other fields. The study of the conducting behavior of an individual Cu@carbonaceous submicrocable is underway and will be reported in due course. In addition, the available amorphous carbonaceous submicrotubes with high aspect ratio obtained here might find potential

Supporting Information Available: FTIR spectrum of the CU@carbonaceous submicrocables (Figure S1). SEM and TEM images of the as-prepared product (Figure S2). This material is available free of charge via the Internet at http://pubs.acs.org. References and Notes (1) (a) Caruso, F. AdV. Mater. 2001, 13, 11. (b) Daniel, M. C.; Astruc, D. Chem. ReV. 2004, 104, 293. (c) Van Bommel, K. J. C.; Friggeri, A.; Shinkai, S. Angew. Chem., Int. Ed. 2003, 42, 3027. (2) (a) Wong, Y. H.; Li, Q. J. Mater. Chem. 2004, 14, 1413. (b) Lauhon, L. J.; Gudiksen, M. S.; Wang, D. L.; Lieber, C. M. Nature 2002, 420, 57. (c) Li, Q.; Wang, C. R. J. Am. Chem. Soc. 2003, 125, 9892. (d) Wu, Y. Y.; Yang, P. D. Appl. Phys. Lett. 2000, 77, 43. (e) Zhang, Y.; Suenaga, K.; Colliex, C.; Iijima, S. Science 1998, 281, 973. (f) Jang, J.; Lim, B.; Lee, J.; Hyeon, T. Chem. Commun. 2001, 83. (g) Obare, S. O.; Jana, N. R.; Murphy, C. J. Nano Lett. 2001, 1, 727. (3) Yin, Y. D.; Lu, Y.; Sun, Y.G.; Xia, Y. N. Nano. Lett. 2002, 2, 427. (4) Yu, S. H.; Cui, X. J.; Li, L.; Li, K., Yu, B.; Antonietti, M.; Co¨lfen, H. AdV. Mater. 2004, 16, 1636. (5) Sun, X. M.; Li. Y. D. AdV. Mater. 2005, 17, 2626. (6) (a) Molares, M. E. T.; Buschmann, V.; Dobrev, D.; Neumann, R.; Scholz, R.; Schuchert, I. U.; Vetter, J. AdV. Mater. 2001, 13, 62. (b) Choi, H. Park, S. H. J. Am. Chem. Soc. 2004, 126, 6248. (c) Monson, C. F.; Woolley, A. T. Nano Lett. 2003, 3, 359. (d) Yen, M. Y.; Chiu, C. W.; Hsia, C. H.; Chen, F. R.; Kai, J. J.; Lee, C. Y.; Chiu, H. T. AdV. Mater. 2003, 15, 235. (7) Monson, C. F.; Woolley, A. T. Nano. Lett. 2003, 3, 359. (8) Luo, L. B.; Yu, S. H.; Qian, H. S.; Zhou, T. J. Am. Chem. Soc. 2005, 127, 2822. (9) Gong, J. Y.; Luo, L. B.; Yu, S. H.; Qian, H. S. J. Mater. Chem. 2006, 1, 101. (10) Qian, H. S.; Luo, L. B.; Gong, J. Y.; Yu, S. H.; Li, T. W.; Fei, L. F. Cryst. Growth Des. 2006, 6, 607. (11) Qian, H. S.; Yu, S. H.; Luo, L. B.; Gong, J. Y.; Fei, L. F.; Liu, X. M. Chem. Mater. 2006, 18, 2102. (12) (a) Sun, X. M.; Li, Y. D. AdV. Mater. 2005, 17, 2626. (b) Sun, X. M.; Li, Y. D. Angew. Chem., Int. Ed. 2004, 43, 597. (c) Wang, Q.; Li, H.; Chen, L. Q.; Huang, X. J. Carbon 2001, 39, 2211. (13) Titirici, M.-M.; Antonietti, M.; Thomas, A. Chem. Mater. 2006, 18, 3808. (14) Sun, X. M.; Li, Y. D. Langmuir 2005, 21, 6019. (15) Sun, X. M.; Liu, J. F.; Li, Y. D. Chem. Mater. 2006, 18, 3486. (16) Luo, L. B.; Yu, S. H.; Qian, H. S.; Gong, J. Y. Chem. Commun. 2006, 7, 793. (17) (a) Liu, Z. P.; Yang, Y.; Liang, J. B.; Hu, Z. K.; Li, S.; Peng, S.; Qian, Y. T. J. Phys. Chem. B 2003, 107, 12658. (b) Chang, Y.; Lye, M. L.; Zeng, H. C. Langmuir 2005, 21, 3746. (18) Deng, B.; Xu, A.W.; Chen, G. Y.; Song, R. Q.; Chen, L. P. J. Phys. Chem. B 2006, 110, 11711. (19) Ilie, A.; Durkan, C.; Milne, W. I.; Welland, M. E. Phys. ReV. B 2002, 66, 045412. (20) Aggarwal, P.; Dollimore, D. A. Thermochim. Acta 1998, 319, 17. (21) Aggarwal, P.; Dollimore, D. A. Thermochim. Acta 1998, 324, 1.