Journal of Nanoparticle Research

, Volume 11, Issue 3, pp 731–736

Copper sulfide nanotubes: facile, large-scale synthesis, and application in photodegradation

Authors

  • Xue-ying Wang
    • Anhui Key Laboratory of Functional Molecular Solids, College of Chemistry and Materials ScienceAnhui Normal University
    • Anhui Key Laboratory of Functional Molecular Solids, College of Chemistry and Materials ScienceAnhui Normal University
  • Xiu Lin
    • Anhui Key Laboratory of Functional Molecular Solids, College of Chemistry and Materials ScienceAnhui Normal University
Brief Communication

DOI: 10.1007/s11051-008-9480-2

Cite this article as:
Wang, X., Fang, Z. & Lin, X. J Nanopart Res (2009) 11: 731. doi:10.1007/s11051-008-9480-2

Abstract

Large-scale synthesis of copper sulfide (CuS) nanotubes with uniform size could be achieved via a facile hydrothermal method. The whole process could be adjusted to prepare CuS with different nanostructures by simply changing the concentration of NaOH or reaction temperature while keeping other conditions unchanged. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Photoluminescence (PL) spectroscopy were used to characterize the products. The as-prepared CuS nanotubes showed good photocatalytic activity of degrading eosin Y under UV-vis light irradiation, which indicated the potential application of the CuS nanotubes in eliminating pollution and environmental protection.

Keywords

Hydrothermal methodSemiconductorNanotubesPhotocatalysisColloids

Introduction

Soon after the discovery of carbon nanotubes (Iijima 1991), inorganic nanotubes attracted considerable attention due to their novel electrical, optical, magnetic, and catalytic (Peralta-Inga et al. 2003; Kempa et al. 2003; Shen et al. 2006) properties and their potential applications in numerous areas. Various tube-like inorganic nanomaterials were fabricated, including metal oxides (Yan and Xue 2008; Dobley et al. 2001; Zhan et al. 2004; Muhr et al. 2000), metal sulfides (Hu et al. 2004; Yin et al. 2005; Zhou et al. 2007), metals (Cao et al. 2003; Sun and Xia 2004; Sander and Gao 2005; Yu et al. 2005), other metal salts (Souza Filho et al. 2004; Liang et al. 2004; Park et al. 2004), nonmetals (Journet et al. 1997; Schlittler et al. 2001), hydroxides (Fang et al. 2003; Zang et al. 2003), and heterostructures (Gu et al. 2007; Zhou et al. 2007a, b).

As an important semiconductor with unusual electrical, optical, and catalytic prosperities (Crespo et al. 2007), CuS was a promising material with potential applications in many fields such as cathode material, nanocrystallites, semiconductor, solar cells, light-emitting diodes, and biological labeling (Dobson et al. 2001). Many methods of synthesis of copper sulfide nanotubes had been explored, such as templating method (Wu et al. 2006; Yao et al. 2007; Zhang et al. 2007; Zhu et al. 2007), aqueous phase reaction (Ni et al. 2004), hydrogel synthesis (Kalyanikutty et al. 2006; Tan et al. 2005), and hydrothermal process (Lu et al. 2002). However, facile and large scale synthesis of CuS nanotubes was scarcely reported as far as we know. In this article, a facile hydrothermal route to synthesize copper sulfide nanotubes in large scale without any structure-directing surfactants was described. The shape of CuS nanotubes was controlled by adjusting the concentration of NaOH and the reaction temperature.

Experimental section

All reagents (analytical-grade purity) used in this work were gained from commercial market, and were used without any further purification. In a typical experimental procedure, 2.4 mmol CuCl2·2H2O and 2.4 mmol CH3CSNH2 (TAA) were dissolved in 20 mL distilled water, respectively, and sonicated for 5 min to give a clear solution. The two solutions were mixed and stirred vigorously for 5 min. A total of 10 mL of 0.4 M NaOH aqueous solution was added to the above mixture and stirred for 5 min at room temperature to yield an opaque (final concentration of NaOH is 0.08 M). The opaque was transferred into a Teflon-lined stainless steel autoclave with a capacity of 60 mL. The autoclave was heated to 160 °C and maintained at this temperature for 6 h. After the autoclave was cooled to room temperature, the flocculent black green precipitate was collected, and then washed with absolute ethanol and distilled water several times to remove any possible residual impurities. The as-obtained samples were dried in a vacuum-drying oven at 60 °C for 6 h before further characterization.

The X-ray powder diffraction patterns (XRD) of the samples were measured using a Shimadzu X-ray diffractometer (XRD-6000). The morphology, structure, and size of the samples were characterized by scanning electron microscopy (SEM, Hitachi, and Model S-4800) and transmission electron microscopy (TEM, Hitachi, Model H-800). The excitation and photoluminescence (PL) spectrum of the as-obtained samples was measured on an Edinburgh 920 fluorescence spectrophotometer with a Xe lamp at room temperature. The photocatalytic performance of CuS nanotubes was evaluated by the degradation of eosin Y under UV irradiation; an aqueous suspension of CuS was prepared by adding 100 mg CuS nanotubes to an aqueous solution of eosin Y (100 mL, 10−4 M). The solution was protected from light and stirred for 6 h to reach adsorption equilibrium and uniform dispersion before irradiation. Then, the solution was irradiated by UV lamp with wavelengths centered at 365 nm, which was placed 10 cm high over the solution for 60 min. At 10 min intervals after irradiation, the dispersion was centrifuged, and the eosin Y concentration was determined by using a UV–vis absorption spectroscopy (Shimadzu, Model UV-3010).

Results and discussions

Figure 1 showed the XRD pattern of the as-obtained CuS nanotubes. All observed diffraction peaks could be perfectly indexed to the hexagonal phase CuS with cell parameters a = 3.791 Å and c = 16.433 Å in accordance with the literature (JCPDS Card No. 78–0876). No crystalline impurity peaks were observed, indicating the high purity of the products.
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Fig. 1

XRD pattern of as-prepared copper sulfide nanotubes

The morphology of the products was checked by SEM. Figure 2a is a low magnification SEM image of the obtained sample, which revealed that the products consisted of a large quantity of nanotubes with lengths up to several microns. Typical nanotubes were not all straight as indexed by arrows, which were different from other inorganic nanotubes except carbon nanotubes. Careful inspection of nanotubes in high magnification (Fig. 2b) showed that the inner diameters of nanotubes were 235 ± 15 nm, and the outer diameters were approximately 300 nm. The tube walls were constructed by nanoparticles with diameters of several tens of nanometers. The detailed structure of CuS nanotubes was also characterized by TEM, as shown in Fig. 2c. The clear contrast between the fringe and the interior of the sample also indicated that the products were nanotubes.
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Fig. 2

(a) and (b) SEM image of copper sulfide (CuS) nanotubes (10 mL of 4 M NaOH, at 160 °C 6 h). (c) TEM images of as-abstained CuS nanotubes

In our former works, NaOH acted as an important miner in the synthesis of oriented attachment La2MnO5 nanorods and ZnO with 3D nanostructures (Fang et al. 2006a; Fang et al. 2006b). In the current experiment, NaOH also acted as an important morphology controlling reactant. If no NaOH was added, the morphologies of as-obtained samples were rods with flowers, as shown in Fig. 3a. When NaOH was added with a concentration of 10−4 M, the products changed into short tubes with flowers (Fig. 3b). Increasing the concentration of NaOH further to 2 M made the flowers disappeared, while short tubes dominated (Fig. 3c). The various morphologies of CuS under different alkali concentration indicated that NaOH acted as a vital morphology controlling reactant. The accurate function of alkali in determining the final morphology of CuS needs further study and the process is under way. Besides NaOH, the reaction temperature can also affect the morphology of the as-obtained sample. Plenty of nanoparticles appeared in the products when the reaction temperature decreased to 140 °C (Fig. 3d); no nanotubes were obtained when the reaction temperature was 180 °C. The whole process can be easily adjusted to prepare CuS nanomaterials with different nanostructures by simply changing the concentration of NaOH or reaction temperature while keeping other conditions unchanged.
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Fig. 3

SEM images of copper sulfide (CuS) nanomaterials prepared from different concentrations of NaOH or temperatures: (a) (10 mL distilled water, at 160 °C 6 h), (b) (10 mL of 10−4 M NaOH at 160 °C 6 h), (c) (10 mL of 2 M NaOH at 160 °C 6 h), (d) (10 mL of 4 M NaOH, at 140 °C 6 h)

In order to study the optical properties and crystal defects of CuS nanotubes, room temperature PL spectra were measured using a 321-nm Xe laser as the excitation source. Figure 4 shows the PL spectrum of the CuS nanotubes; a strong emission band centered at 467 nm was observed. This green luminescence of CuS nanotubes was consistent with the color of the final products. The result was different from other reported results for CuS, which gave fluorescence emission spectra (Yu et al. 2007); it may be due to the structures of nanotubes, which were different from former reports.
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Fig. 4

PL spectrum of the CuS nanotubes

Figure 5 shows the decrease in UV/Vis absorption intensity of the solution of eosin Y with time, recorded at 10-min intervals. As illustrated in Fig. 5, the absorption peak intensity weakened and the peak almost disappeared with time extension. The decrease of peak intensity indicated that CuS nanotubes exhibited photocatalytic abilities and a fine photodegradation efficiency. The outstanding photodegradation efficiency of CuS nanotubes lays on two facts. One is the UV light absorption of CuS nanotubes, which generate the electron hole pair; the electron hole pair on the surface of CuS nanotubes oxidizes or reduces eosin subsequently. The other is the excellent suspending property of CuS nanotubes. The flocculent products are steady-suspended in water for about 15 days, which makes a sufficient contact between CuS nanotubes and eosin Y, and improves the photodegradation efficiency of CuS nanotubes finally. The photodegradation property of CuS nanotubes indicated its application in eliminating pollution and environmental protection.
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Fig. 5

UV/Vis absorption intensity of the solution for various times

Conclusion

In conclusion, uniform and well-defined CuS nanotubes in pure hexagonal phase was easily synthesized via a facile hydrothermal method and the product was obtained in high-yield. Experiments revealed that a successful morphological transformation of copper sulfide nanomaterials can be achieved at different concentrations of NaOH or various reaction temperatures. The PL and photodegradation results indicated that CuS nanotubes have an outstanding optical property.

Acknowledgements

Financial supports from the National Natural Science Foundation of China (20701002), the Special Project Grants of Anhui Normal University (2007xzx12), Science and Technological Fund of Anhui Province for Outstanding Youth (08040106834), and the Education Department of Anhui Province (No. 2006KJ006TD) are gratefully acknowledged.

Copyright information

© Springer Science+Business Media B.V. 2008