NANO LETTERS
One-Step Synthesis and Assembly of Copper Sulfide Nanoparticles to Nanowires, Nanotubes, and Nanovesicles by a Simple Organic Amine-Assisted Hydrothermal Process
2002 Vol. 2, No. 7 725-728
Qingyi Lu, Feng Gao, and Dongyuan Zhao* Molecular Catalysis and InnoVatiVe Materials Lab, Department of Chemistry, Fudan UniVersity, Shanghai 200433, P. R. China Received March 12, 2002; Revised Manuscript Received May 23, 2002
ABSTRACT A simple organic amine-assisted hydrothermal process has been proposed to simultaneously realize the synthesis and assembly of copper sulfide nanoparticles at low temperature (90 ∼ 110 °C). Nanowire-like aggregates (average diameter of 120 nm and length of 2 µm) assembled by digenite phase copper sulfide nanoparticles have been synthesized with triethylenediamine (TEDA) as a linking agent. Nanotube-like aggregates (diameter ranging from 40 to 200 nm and length from 400 nm to 4 µm) and nanovesicle-like aggregates (size ranging from 50 to 180 nm), assembled by djurleite phase copper sulfide nanoparticles, have also been obtained by substituting tramethylethylenediamine (TMEA) and di-n-butylamine (DBA) for TEDA, respectively.
The study of semiconductor nanoparticles is one of the most active areas due to their interesting properties which are far from those of bulk substances.1 Because of their distinguished optical and electronic properties, the control of the size and morphology of chalcogenide nanocrystals has been a primary focus.2 However, the realization of technologically useful nanoparticle-based materials depends not only on the quality of the nanoparticles (e.g., size and shape) but also on their spatial orientation and arrangement.3 The development of practical strategies for the assembly of inorganic nanoparticles into well-defined arrays is thus an area of considerable current interest, because it offers opportunities to exploit their unique optical and electronic properties and possibilities to probe new, potentially collective phenomena.3,4 Nevertheless, compared with the synthesis of discrete nanoparticles, the assembly of nanoparticles into well-defined superstructures remains a challenge and usually requires the initial synthesis of spherical nanoparticles, followed by further processing such as evaporation of hydrophobic colloids,5 molecular cross-linking in colloidal aggregates,6 or template-directed synthesis using porous protein crystals of bacterial superstructures.7 Many efforts focus on the formation of organized two-dimensional (2-D) and 3-D arrays of nanoparticles,8 and just a few reports have appeared regarding the synthesis of 1-D nanoparticle systems or hollow structures including 1-D strands of iron oxide and CdS nanoparticles with biomol10.1021/nl025551x CCC: $22.00 Published on Web 06/05/2002
© 2002 American Chemical Society
ecules as linking agents,9 1-D Au- or Ag-polymer nanochains with pores of Al2O3 or polymer membranes as templates,10 and inorganic-organic nanotube composites with tobacco mosaic virus as guide.11 Herein, we propose a simple organic amine-assisted hydrothermal process for the one-step synthesis and assembly of copper sulfide nanoparticles with CuCl and thiourea as the reactants at low temperature (90 ∼ 110 °C). With triethylenediamine (TEDA) as a linking agent, nanowirelike aggregates (average diameter of 120 nm and length of 2 µm) assembled by digenite phase copper sulfide nanocrystals have been synthesized. By using tramethylethylenediamine (TMEA) and di-n-butylamine (DBA) as the linking agents instead of TEDA, respectively, nanotube-like aggregates (diameter ranging from 40 to 200 nm and length from 400 nm to 4 µm) and nanovesicle-like aggregates (size ranging from 50 to 180 nm) assembled by djurleite phase copper sulfide nanocrystals have also been obtained. The synthesis and assembly of copper sulfide nanoparticles were carried out under hydrothermal conditions at low temperature. In a typical preparation, 1.4 mmol TEDA was dissolved into 50 g of 0.055 M (2.8 mmol) thiourea solution and then the TEDA-thiourea solution was transferred into a Telfon bottle, then 5.0 mmol CuCl was added into the bottle. After the bottle was heated at 90 ∼ 110 °C for 40 h, a black precipitate with yield higher than 90% was collected,
Figure 1. XRD patterns of the semiconductor copper sulfide samples prepared under low-temperature hydrothermal conditions with (a) TEDA (1.4 mmol), (b) (1,12)-dodecyl-diamine, (c) TEDA (14 mmol), (d) TMEA, (e) DBA.
filtered, washed with distilled water and absolute alcohol several times, and dried at room temperature. Figure 1a shows the X-ray diffraction (XRD) pattern of the sample prepared with TEDA as linking agent (1.4 mmol) under low temperature (90 ∼ 110 °C) hydrothermal conditions, recorded on a Rigaku D/Max-IIA using filtered Cu KR radiation. All diffraction peaks can be indexed as digenite phase copper sulfide with lattice parameters comparable to that of JCPDS card (23-962). No XRD peaks arising from impurities can be detected. The relatively broad XRD peaks reveal the small size of copper sulfide crystals, and according to the Scherrer diffraction formula the average particle size is approximately 12 nm. Transmission electron microscopy (TEM) images (Figure 2a,b) of this sample were obtained using Japan JEOL JEM2011 high-resolution transmission electron microscopy, revealing that fibrous aggregates with average width of 120 nm and length of 2 µm have been obtained. The diffraction rings in the selected area electron diffraction (SAED) pattern (inset in Figure 2b) can be indexed as (555), (10100), and (5515) reflections, respectively, associated with pseudo cubic structure, indicating that these copper sulfide nanowires are composed of polycrystals of digenite phase copper sulfide. The sample has also been embedded in resin and then sliced up for TEM observation. A TEM image of the embedded sample (Figure 2c) can reveal the section morphology of the nanowires, clearly showing that these nanowires are assembled by dozens of nanoparticles with average size of 15 × 25 nm. The highresolution TEM image (inset in Figure 2c) shows that these nanoparticles are single crystals with interplanar distance of 3.21 Å, corresponding to the (555) direction of digenite phase copper sulfide. In our experiments, almost all of the copper salt reactants can be transformed into copper sulfides under the hydrothermal conditions, and the yield for the copper sulfide solids is very high (>90%). It should be noted that based on TEM observation, the fraction of the nanowirelike aggregates is calculated to be about 60% and the remnant 726
Figure 2. TEM images and the selected area electron diffraction (SAED) patterns of the copper sulfide samples prepared with different concentration TEDA under low-temperature hydrothermal conditions with (a) (b) (c) 1.4 mmol TEDA and (d) 14 mmol TEDA (inset b,d, showing the SAED pattern). For TEM image (c), the sample was embedded in the resin and sliced up for TEM observation (inset c showing TEM image with large magnification).
consists of discrete nanoparticles that compose the nanowirelike aggregates. To the contrary, without the addition of organic amine, copper sulfide nanocrystals cannot be formed under our experimental conditions because the interaction between CuCl and thiourea is too strong to decompose, confirmed by an XRD pattern (not shown). The sample prepared with (1,12)-dodecyl-diamine as a linking agent is also digenite phase copper sulfide (Figure 1b). TEM images (not shown) reveal that this sample consists of discrete digenite phase copper sulfide nanocrystals with average size about 15 nm. Figure 3 shows the UV-vis absorption spectra of the samples prepared with different organic amines, recorded with an Agilent 8453 spectrophotometer. Copper sulfide nanoparticles prepared with (1,12)-dodecyl-diamine display an absorption maximum at 515 nm (Figure 3a), which might be assigned to the optical transition of the first excitonic state.12 With TEDA (1.4 mmol) as linking agent, the product has an absorption peak at 555 nm (Figure 4b). The red shift of the maximum is associated with the formation of aggregated nanowire-like structures with TEDA as linking agent.13 The interaction between a metal ion and an organic amine molecule is an important factor to the structure and morNano Lett., Vol. 2, No. 7, 2002
Figure 3. UV-vis absorption spectra of the copper sulfide samples prepared under low-temperature hydrothermal conditions with (a) (1,12)-dodecyl-diamine, (b) TEDA (1.4 mmol).
Figure 4. TEM images and the SAED patterns of the samples prepared under low-temperature hydrothermal conditions with (a) (b) TMEA and (c) (d) DBA. (inset a,d showing the SAED pattern). For TEM image (b), the sample was embedded in the resin and sliced up for TEM observation (inset c showing TEM image with large magnification).
phological controls of the product.14 In our experiment, TEDA is of importance not only in the synthesis and assembly of copper sulfide nanoparticles but also in the morphological control of copper sulfide nanocrystals. To optimize the reaction conditions to get maximum fraction of nanowire-like aggregates, we adjusted the used amount of TEDA. We found that with proper concentration of TEDA, the nanowire-like aggregates are the dominating product and the maximum fraction is about 60%. At low concentration of TEDA (such as 0.5 mmol) just a few Nano Lett., Vol. 2, No. 7, 2002
nanoparticles can assemble to form copper sulfide nanowires, and many discrete copper sulfide nanoparticles are observed in the product. On the other hand, high concentration of TEDA also does not increase the fraction of nanowire-like aggregates and especially, 14 mmol TEDA leads to the formation of copper sulfide single-crystal nanorods. The XRD pattern (Figure 1c) shows that the sample prepared with high concentration TEDA (14 mmol) is also digenite phase copper sulfide, but the diffraction peaks are relatively sharp, indicating large crystal size of the sample. TEM image (Figure 2d) shows that the product is copper sulfide nanorods with nonuniform diameter in the range from 40 to 180 nm and length in the range from 500 nm to 3 µm, and the inserted SAED pattern confirms that these copper sulfide nanorods are single crystals with (111) growth direction. For comparison, other organic amines have also been used as linking agents for the synthesis and assembly of copper sulfide nanocrystals. Figure 1d,e shows the XRD patterns of the samples prepared with TMEA and DBA as linking agent. All diffraction peaks can be indexed as djurleite phase copper sulfide with lattice constants comparable to those of JCPDS card (34-660). These results indicate that with TMEA and DBA as linking agent, djurleite phase instead of digenite phase copper sulfides are formed, which may be due to different interactions between copper ions and different amines.14 By the Scherrer diffraction formula, the average crystal sizes of the samples prepared with TMEA and DBA as linking agent are both calculated to be about 10 nm. Like the sample prepared with TEDA as linking agent, the yields of copper sulfides prepared with TMEA and DBA as linking agent are also very high (>90%). TEM image (Figure 4a) shows that the sample prepared with TMEA has a special tube-like morphology. These nanotubes with diameters in the range from 40 to 200 nm and lengths from 400 nm to 4 µm are open-ended and not very uniform. The diffraction rings in the SAED pattern (inserted in Figure 4a) can be indexed as (811), (333), (433), (821), (802), (424), (514), (1312), (835) and (1242) reflections, respectively, associated with orthorhombic phase copper sulfide, indicating that these nanotubes are assembled by polycrystals of djurleite phase copper sulfides. The sample has also been embedded in resin and then sliced up for TEM observation. TEM image of the embedded sample (Figure 4b) shows the cross sections and vertical sections of nanotubes, confirming that these nanotubes are assembled by nanoparticles with average size of 8 × 20 nm. The thickness of nanotube wall is about 10 ∼ 50 nm and the inner diameter is about 20 ∼ 100 nm. Its highresolution TEM image (inset in Figure 4b) displays that these nanoparticles are single crystals with interplanar distance of 2.82 Å, corresponding to the (424) (or (514)) direction of djurleite phase copper sulfide. On the other hand, by using DBA as a linking agent, copper sulfide nanovesicles with size ranging from 50 to 180 nm are formed (Figure 4c,d). The SAED pattern (inset in Figure 4d) indicates that these nanovesicles are also assembled by polycrystals of djurleite phase copper sulfide, in agreement with the results from XRD measurement. The fractions of both nanotube-like and nanovesicle-like aggregates are about 40% from the TEM 727
observation. In the sample prepared with DBA as linking agent, the remnant consists of discrete nanoparticles. In contrast, in addition to discrete nanoparticles, there are also some nanowire-like and nanovesicle-like aggregates observed in the sample obtained with TMEA as linking agent, but the fractions of those nanowire-like and nanovesicle-like aggregates are both lower than 10%. The organic amines such as ethylenediamine, diethylenediamine, (1,3)-propyl-diamine, and (1,4)-dodecyl-diamine can also be used as linking agents. In the case of ethylenediamine, the interaction between CuCl and ethylenediamine is very strong and the complex of ethylenediamine with copper is formed, instead of copper sulfide, under lowtemperature hydrothermal conditions.15 For diethylenediamine, (1,3)-propyl-diamine, and (1,4)-dodecyl-diamine, only discrete copper sulfide nanoparticles or short nanochains (∼400 nm in length) can be obtained. The assembly functions of different organic amines may be related to their coordination abilities and molecular structures.16,17 The reaction temperature is also a key factor to the formation and assembly of the copper sulfide nanoparticles. When hydrothermal temperature is lower than 70 °C, copper sulfide nanocrystals cannot be formed, since the copper-amine complex may be stable enough at this temperature that it does not decompose to copper sulfide nanoparticles. High hydrothermal temperatures such as 170 °C lead to the further growth of the nanoparticles and are unfavorable to the assembly of nanoparticles, resulting in the formation of discrete copper sulfide nanoparticles. In summary, we have demonstrated that a simple organic amine-assisted hydrothermal process can be employed to achieve the synthesis and assembly of copper sulfide nanoparticles in one step. Nanowire-like aggregates with average diameter of 120 nm and length of 2 µm, nanotubelike aggregates with diameters ranging from 40 to 200 nm and lengths from 400 nm to 4 µm, and nanovesicle-like aggregates with sizes ranging from 50 to 180 nm have been synthesized at 90 ∼ 110 °C with TEDA, TMEA, and DBA as the linking agents, respectively. This method is very simple and can be easily extended to the synthesis and assembly of other inorganic nanocrystals. Acknowledgment. The work was supported by the National Natural Science Foundation of China, (Grant
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29925309 and 20101002), Education Ministry of China, Shanghai Science Foundation (00JC14014), State Key Basic Research Program of PRC (2001CB610505), and Chinese Post-Doctor Foundation. References (1) (a) Peng, X.; Manna, L.; Yang, W.; Wickham, J.; Scher, E.; Kadavanich, A.; Alivisatos, A. P. Nature 2000, 404, 59. (b) Petit, C.; Taleb, A.; Pileni, M. P. AdV. Mater. 1998, 10, 259. (c) Taleb, A.; Petit, C.; Pileni, M. P. J. Phys. Chem. B 1998, 102, 2214. (2) (a) Manna, L.; Scher, E. C.; Alivisatos, A. P. J. Am. Chem. Soc. 2000, 122, 12700. (b) Jun, Y. W.; Lee, S. M.; Kang, N. J.; Cheon, J. J. Am. Chem. Soc. 2001, 123, 5150. (c) Mohamed, M. B.; Wang, Z. L.; El-Sayed, M. A. J. Phys. Chem. A 1999, 103, 10255. (3) Firestone, M. A.; Williams, D. E.; Seifert, S.; Csencsits, R. Nano Lett. 2001, 1, 129. (4) Li, M.; Schnablegger, H.; Mann, S. Nature 1999, 402, 393. (5) (a) Murray, C. B.; Kagan, C. R.; Bawendi, M. G. Science 1995, 270, 1335. (b) Wang, Z. L. AdV. Mater. 1998, 10, 13. (6) (a) Brust, M.; Bethell, D.; Schiffrin, D. J.; Kiely, C. J. AdV. Mater. 1995, 7, 795. (b) Mirkin, C. A.; Letsinger, R. L.; Mucic, R. C.; Storhoff, J. J. Nature 1996, 382, 607. (c) Li, M.; Wong, K. K. W.; Mann, S. Chem. Mater. 1999, 11, 23. (7) (a) Shenton, W.; Pum, D.; Sleytr, U. B.; Mann, S. Nature 1998, 389, 585. (b) Dieluweit, S.; Pum, D.; Sleytr, U. B. Supramol. Sci. 1998, 5, 15. (8) (a) Marinakos, S. M.; Brousseau, L. C.; Jones, A.; Feldheim, D. L. Chem. Mater. 1998, 10, 1214. (b) Korgel, B. A.; Fullam, S.; Connolly, S.; Fitzmaurice, D. J. Phys. Chem. B 1998, 102, 8379. (c) Maoz, R.; Frydman, E.; Cohen, S. R.; Sagiv, J. AdV. Mater. 2000, 12, 424. (d) Andres, R. P.; Bielefeld, J. D.; Henderson, J. I.; Janes, D. B.; Kolagunta, V. R.; Kubiak, C. P.; Mahoney, W. J.; Osifchin, R. G. Science 1996, 273, 1690. (9) (a) Mann, S. J. Chem. Soc., Dalton Trans. 1993, 1. (b) Lee, T. A. T.; Cooper, A.; Apkarian, R. P.; Conticello, V. P. AdV. Mater. 2000, 12, 1105. (10) Chung, S.-W.; Markovich, G.; Hearth, J. R. J. Phys. Chem. B 1998, 102, 6685. (11) Shenton, W.; Douglas, T.; Young, M.; Stubbs, G.; Mann, S. AdV. Mater. 1999, 11, 253. (12) Weller, H. Angew. Chem, Int. Ed. Engl. 1993, 32, 41. (13) Yanezawa, T.; Onoue, S.; Kimizuka, N. AdV. Mater. 2001, 13, 140. (14) Jiang, X.; Xie, Y.; Lu, J.; He, W.; Zhu, L.; Qian, Y. J. Mater. Chem. 2000, 10, 2193. (15) Yang, J.; Zeng, J. H.; Yu, S. H.; Yang, L.; Zhou, G. E.; Qian, Y. T. Chem. Mater. 2000, 12, 3259. (16) Zhu, S.; Zhou, Y.; Shen, B. Coordinating Chemistry; Tianjin kexue jishu press: Tianjin, 1990. (17) Ozin, G. A. Chem. Commun. 2000, 419.
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