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Journal of Nanomaterials
Volume 2013 (2013), Article ID 130514, 7 pages
http://dx.doi.org/10.1155/2013/130514
Research Article

Hydrothermal Synthesis of Ln(OH)3 Nanorods and the Conversion to Ln2O3 (Ln = Eu, Nd, Dy) Nanorods via Annealing Process

School of Physics and Microelectronics, Hunan University, Changsha 410082, China

Received 11 September 2013; Accepted 13 November 2013

Academic Editor: Anukorn Phuruangrat

Copyright © 2013 Yanhua Zhu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

One-dimensional rare earth oxides and hydroxides are of importance in many applications due to their rich physicochemical properties. In this work, we synthesized Ln(OH)3 (Ln = Eu, Nd, Dy) nanorods by a hydrothermal method with the assistance of n-butylamine as an alkaline resource. The porous Ln2O3 nanorods were produced through annealing the corresponding Ln(OH)3 nanorods. XRD and TEM techniques were employed to characterize the products. The annealing process and the optical properties of as-synthesized Ln2O3 are also investigated by TG and PL test. We expected that these nanomaterials could find potential applications in the future.

1. Introduction

Over the past decades, one-dimensional (1D) nanostructures, such as nanowires, nanorods, nanotubes, and nanoribbons, have attained increasing attention due to unique properties in mesoscopic physics and applications for nanoscale devices [16]. In particular, the corresponding porous nanomaterials are of interest in a broad range of applications, relying on the incorporation of specific guests into pores of different sizes and on the transport of such guests through the pores [79]. Moreover, chemical composition also plays an important role in determining physicochemical properties of the materials and interfacial interactions [1013]. Therefore, it is meaningful to synthesize the 1D mesoporous nanostructures with varied chemical components and investigate the relations between chemical components and properties.

Rare earth compounds have been extensively investigated in many fields including high performance magnets, luminescent devices, catalysts, and other technical applications based on the electronic, optical, and chemical characteristics arising from their 4f electrons [1420]. So much effort has focused on the synthesis of rare earth oxides [2022]. Hydrothermal method is proved to be an effective route to synthesize materials with various nanostructures [23, 24]. Therefore, it is meaningful to develop an alternative hydrothermal method for preparing rare earth compounds.

In this work, we developed a facile hydrothermal method for synthesizing Ln(OH)3 (Ln = Eu, Nd, Dy) nanorods. Moreover, the porous Ln2O3 nanorods with the same shape have been obtained through annealing the Ln(OH)3 nanorods. Various techniques were employed to characterize the products, and the results showed that the hydroxide and oxide nanorods displayed the same shape and high crystallinity. It is expected that these nanomaterials could find potential applications in the future.

2. Experimental Section

2.1. Chemicals

All of the chemicals were purchased without further purification.

2.2. Synthesis

In a typical synthesis, 0.5 mmol of Ln(NO3)3·6H2O (Ln = Eu, Nd, Dy) was dissolved in 12 mL of distilled water, and then 3 mL of n-butylamine was added under constant stirring. Subsequently, the resulting solution was transferred into a 20 mL Teflon-lined autoclave. The autoclave was sealed, heated, and maintained at 180°C for 16 h. After the autoclaves were completed, the resulting product was centrifuged, followed by washing with distilled water and ethanol several times. The as-synthesized precursor nanorods were finally dried in a vacuum oven at 60°C for 4 h and used for further characterization. Porous Ln2O3 (Ln = Eu, Nd, Dy) nanorods were obtained by calcining the as-prepared precursor nanowires at 700°C for 2 h.

2.3. Characterization

The X-ray diffraction (XRD) patterns of the products were recorded with a Rigaku D/max Diffraction System, using a Cu Kα source (λ = 0.15406 nm). The high-resolution transmission electron microscopy (HRTEM) images were taken on a JEOL 2010 high-resolution transmission electron microscope performed at 200 kV. The specimen of HR-TEM measurement was prepared via spreading a droplet of ethanol suspension onto a copper grid, coated with a thin layer of amorphous carbon film, and allowed to dry in air. The thermogravimetric analysis (TGA) was investigated on continuous measurement of weight on a thermobalance as sample temperature is increased. The room temperature photoluminescence (PL) spectra of samples were recorded on a Hitachi F-4500 FL spectrophotometer with a Xe lamp as the excitation light source.

3. Results and Discussion

3.1. Characterizations of Structure and Morphology

The purity and crystallinity of as-prepared samples were examined by XRD technique (Figure 1). Figures 1(a)–1(c) show the XRD patterns of the as-prepared Eu(OH)3, Nd(OH)3, and Dy(OH)3 nanorods, respectively. The diffraction patterns of the as-prepared three products can be indexed to the pure hexagonal phase (space group P63/m), which are consistent with the values in the standard cards (JCPDS no. 85-2203 for Eu(OH)3, 17-0781 for Nd(OH)3, and 19-0430 for Dy(OH)3). The narrow sharp peaks suggest that the Ln(OH)3 (Ln = Eu, Nd, Dy) samples are highly crystalline. No other peaks are observed, indicating high purity of the as-prepared samples. Interestingly, we found that as Ln atom increases, the diffraction patterns shift to small angles. This is attributed to the fact that crystal lattice of Ln(OH)3 is increased as the atomic number is increased.

130514.fig.001
Figure 1: XRD patterns of the as-synthesized Ln(OH)3: (a) Eu(OH)3, (b) Nd(OH)3, and (c) Dy(OH)3.

The morphology and structure of as-synthesized Ln(OH)3 nanorods were characterized by transmission electron microscope (TEM), as shown in Figure 2. Figures 2(a) and 2(b) show the low- and high-magnification TEM images of Eu(OH)3 nanorods, respectively. In Figure 2(a), one can find that the length of Eu(OH)3 nanorods ranges from 60 to 150 nm, and their diameter is about 15 nm. In Figure 2(b), one can find that not all the surface of the nanorods is well crystalline. Figures 2(c) and 2(e) show the TEM images of Nd(OH)3 and Dy(OH)3 nanorods, respectively. The length of Nd(OH)3 nanorods is about 120 nm, and their diameter ranges from 20 to 30 nm, as shown in Figure 2(c). For Dy(OH)3 nanorods, they have not a uniform length ranging from 200 nm to several micrometers, and diameter is about 20 nm. Similarly, the high-magnification TEM images of Nd(OH)3 and Dy(OH)3 nanorods (Figures 2(d) and 2(f)) display that their surface is not well crystalline. However, there are clear crystalline lattices for some places of their surfaces, as shown in the inset of Figures 2(b), 2(d), and 2(f). The growth of Ln(OH)3 nanorods can be explained by the 1D growth habit and assistance of n-butylamine [25].

fig2
Figure 2: TEM images of the as-synthesized Ln(OH)3: ((a) and (b)) Eu(OH)3, ((c) and (d)) Nd(OH)3, and ((e) and (f)) Dy(OH)3.
3.2. Conversion of Ln(OH)3 to Ln2O3 (Ln = Eu, Nd, Dy)

The decomposition process was studied by TGA test. As shown in Figure 3, the TGA results indicate the experimental mass losses of ~13.9% (for Eu(OH)3), ~14.1% (for Nd(OH)3), and ~13.3% (for Dy(OH)3), which are corresponding to the theoretical values (13.3% for Eu(OH)3, 13.9% for Nd(OH)3 and 12.7% for Dy(OH)3, resp.). The good agreement with theoretical values implies that the as-prepared precursor nanorods have been completely decomposed during the calcination process, which lays an excellent foundation for the crystallization of the Ln2O3 nanostructures. Moreover, TGA curves also exhibit a multiple dehydration process during the decomposition, which can generally be described by the two equations [26]: Figure 4 shows the XRD patterns of the as-decomposed products of the Ln(OH)3 (Ln = Eu, Nd, Dy) nanorods obtained after 2 h treatment at 700°C. The XRD peaks of Ln(OH)3 (Ln = Eu, Nd, Dy) completely disappeared and only the peaks of Ln2O3 (Ln = Eu, Nd, Dy) were observed. All of the peaks in this pattern can be indexed as the pure cubic phase, which are consistent with the values in the standard cards (JCPDS no. 86-2476 for Eu2O3, 12-0393 for Nd2O3, and 10-0059 for Dy2O3). After complete decomposition at 700°C, the well-faceted Ln(OH)3 (Ln = Eu, Nd, Dy) nanorods were fully transformed into nanoporous Ln2O3 (Ln = Eu, Nd, Dy) nanorods with no significant changes in the overall morphology, as shown in Figures 5(a)5(f). The detailed structures of the as-synthesized Ln2O3 (Ln = Eu, Nd, Dy) samples were further investigated by TEM (Figures 5(b), 5(d), and 5(f)). One could see that there exist some defects on the surface of Eu2O3 nanorods (the insets of Figure 5(b)). In addition, the pores on the Ln2O3 (Ln = Eu, Nd, Dy) nanorods could also be clearly detected, as shown in Figures 5(b), 5(d), and 5(f). The formation of porous structures is originated from the release of water molecular [27].

fig3
Figure 3: TGA curves of decomposition processes: (a) Eu(OH)3, (b) Nd(OH)3, and (c) Dy(OH)3.
130514.fig.004
Figure 4: XRD patterns of the as-synthesized Ln2O3: (a) Eu2O3, (b) Nd2O3, and (c) Dy2O3.
fig5
Figure 5: TEM images of the as-synthesized Ln2O3: ((a) and (b)) Eu2O3, ((c) and (d)) Nd2O3, and ((e) and (f)) Dy2O3.

Figure 6 shows the PL spectrum of Eu2O3 nanorods that were selected as a representative to study the optical property of the as-synthesized Ln2O3 nanorods. One can find from the figure that the Eu2O3 nanorods exhibit a strong emission peak around 618 nm, which is caused by the forced electric dipole transition (5D07F2) [28]. This indicates that the pure cubic phase Eu2O3 has been produced, which is consistent with the XRD result.

130514.fig.006
Figure 6: Luminescence spectrum (excitation at 254 nm) of as-synthesized Eu2O3 nanorods at room temperature.

4. Conclusion

In summary, we have successfully synthesized the Ln(OH)3 (Ln = Eu, Nd, Dy) nanorods via a facile hydrothermal route assisted by n-butylamine and obtained the corresponding porous Ln2O3 nanorods through annealing the Ln(OH)3 nanorods. The XRD and TEM techniques have been employed to characterize the hydroxide and oxide nanorods. Moreover, the possible formation mechanism of Ln(OH)3 nanorods has been proposed. The as-synthesized Ln(OH)3 and Ln2O3 nanorods are expected to be used in catalysis, gas sensors, and other fields in the future.

Conflict of Interests

The authors would like to declare that they do not have any commercial or associative interests that represents a conflict of interest in connection with the submitted paper.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (Grant nos. 11074069 and 61176116), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant no. 20120161130003), the Hunan Provincial Science and Technology Project of China (Grant no. 2013FJ4043), and Aid program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province.

References

  1. J. T. Robinson, G. S. Hong, Y. Y. Liang, B. Zhang, O. K. Yaghi, and H. Y. Dai, “In vivo fluorescence imaging in the second near-infrared window with long circulating carbon nanotubes capable of ultrahigh tumor uptake,” Journal of the American Chemical Society, vol. 134, no. 25, pp. 10664–10669, 2012.
  2. J. M. Ma, Y. P. Wang, Y. J. Wang, Q. Chen, J. B. Lian, and W. J. Zheng, “Controlled synthesis of one-dimensional Sb2Se3 nanostructures and their Electrochemical properties,” Journal of Physical Chemistry C, vol. 113, no. 31, pp. 13588–13592, 2009. View at Publisher · View at Google Scholar · View at Scopus
  3. L. F. Hu, J. Yan, M. Y. Liao et al., “An optimized ultraviolet-a light photodetector with wide-range photoresponse based on zns/zno biaxial nanobelt,” Advanced Materials, vol. 24, no. 17, pp. 2305–2309, 2012. View at Publisher · View at Google Scholar · View at Scopus
  4. J. M. Ma, Y. P. Wang, Y. J. Wang et al., “One-dimensional Sb2Se3 nanostructures: solvothermal synthesis, growth mechanism, optical and electrochemical properties,” CrystEngComm, vol. 13, no. 7, pp. 2369–2374, 2011. View at Publisher · View at Google Scholar · View at Scopus
  5. J. M. Ma, L. Mei, Y. J. Chen, et al., “α-Fe2O3 nanochains: ammonium acetate-based ionothermal synthesis and ultrasensitive sensors for low-ppm-level H2S gas,” Nanoscale, vol. 5, no. 3, pp. 895–898, 2013.
  6. S. La, J. H. Hafner, N. J. Halas, S. Link, and P. Nordlander, “Noble metal nanowires: from plasmon waveguides to passive and active devices,” Accounts of Chemical Research, vol. 45, no. 11, pp. 1887–1895, 2012.
  7. X. J. Xu, X. S. Fang, T. Y. Zhai et al., “Tube-in-tube TiO2 nanotubes with porous walls: fabrication, formation mechanism, and photocatalytic properties,” Small, vol. 7, no. 4, pp. 445–449, 2011. View at Publisher · View at Google Scholar · View at Scopus
  8. Y. Q. Qu, H. L. Zhou, and X. F. Duan, “Porous silicon nanowires,” Nanoscale, vol. 3, no. 10, pp. 4060–4068, 2011. View at Publisher · View at Google Scholar · View at Scopus
  9. X. L. Zhang, F. Y. Cheng, J. G. Yang, and J. Chen, “LiNi0.5Mn1.5O4 Porous nanorods as high-rate and long-life cathodes for Li-ion batteries,” Nano Letters, vol. 13, no. 6, pp. 2822–2825, 2013.
  10. J. M. Ma, J. Teo, L. Mei Z, et al., “Porous platelike hematite mesocrystals: synthesis, catalytic and gas-sensing applications,” Journal of Materials Chemistry, vol. 22, no. 23, pp. 11694–11700, 2012.
  11. J. M. Ma, J. Zhang, S. R. Wang et al., “Topochemical preparation of WO3 nanoplates through precursor H2WO4 and their gas-sensing performances,” Journal of Physical Chemistry C, vol. 115, no. 37, pp. 18157–18163, 2011. View at Publisher · View at Google Scholar · View at Scopus
  12. J. M. Ma, J. Zhang, S. R. Wang et al., “Superior gas-sensing and lithium-storage performance SnO2 nanocrystals synthesized by hydrothermal method,” CrystEngComm, vol. 13, no. 20, pp. 6077–6081, 2011. View at Publisher · View at Google Scholar · View at Scopus
  13. J. M. Ma, X. C. Duan, J. B. Lian et al., “Sb2S3 with various nanostructures: controllable synthesis, formation mechanism, and electrochemical performance toward lithium storage,” Chemistry, vol. 16, no. 44, pp. 13210–13217, 2010. View at Publisher · View at Google Scholar · View at Scopus
  14. G. S. Wu, L. D. Zhang, B. C. Cheng, T. Xie, and X. Y. Yuan, “Synthesis of Eu2O3 nanotube arrays through a facile Sol-Gel template approach,” Journal of the American Chemical Society, vol. 126, no. 19, pp. 5976–5977, 2004. View at Publisher · View at Google Scholar · View at Scopus
  15. F. Cui, J. Zhang, T. Cui et al., “A facile solution-phase approach to the synthesis of luminescent europium methacrylate nanowires and their thermal conversion into europium oxide nanotubes,” Nanotechnology, vol. 19, no. 6, Article ID 065607, 2008. View at Publisher · View at Google Scholar · View at Scopus
  16. J. M. Li, X. L. Zeng, Y. H. Dong, and Z. A. Xu, “White-light emission and weak antiferromagnetism from cubic rare-earth oxide Eu2O3 electrospun nanostructures,” CrystEngComm, vol. 15, no. 13, pp. 2372–2377, 2013.
  17. C. R. Michel, A. H. Martinez-Preciado, and N. L. L. Contreras, “Gas sensing properties of Nd2O3 nanostructured microspheres,” Sensor, vol. 184, pp. 8–14, 2013.
  18. B. Umesh, B. Eraiah, H. Nagabhushana et al., “Synthesis and characterization of spherical and rod like nanocrystalline Nd2O3 phosphors,” Journal of Alloys and Compounds, vol. 509, no. 4, pp. 1146–1151, 2011. View at Publisher · View at Google Scholar · View at Scopus
  19. M. Chandrasekhar, D. V. Sunitha, N. Dhananjaya et al., “Thermoluminescence response in gamma and UV irradiated Dy2O3 nanophosphor,” Journal of Luminescence, vol. 132, no. 7, pp. 1798–1806, 2013. View at Publisher · View at Google Scholar · View at Scopus
  20. M. Norek, E. Kampert, U. Zeitler, and J. A. Peters, “Tuning of the size of Dy2O3 nanoparticles for optimal performance as an MRI contrast agent,” Journal of the American Chemical Society, vol. 130, no. 15, pp. 5335–5340, 2008. View at Publisher · View at Google Scholar · View at Scopus
  21. L. X. Zhang, Y. X. Sun, H. F. Jiu, Y. H. Fu, Y. Z. Wang, and J. Y. Zhang, “Solvothermal synthesis of hollow Eu2O3 microspheres using carbon template-assisted method,” Chemical Papers, vol. 66, no. 8, pp. 741–747, 2012.
  22. P. Zhang, Y. Zhao, T. Zhai et al., “Preparation and magnetic properties of polycrystalline Eu2O3 microwires,” Journal of the Electrochemical Society, vol. 159, no. 4, pp. D204–D207, 2012. View at Publisher · View at Google Scholar · View at Scopus
  23. J. M. Ma, D. N. Lei, X. C. Duan, et al., “Designable fabrication of flower-like SnS2 aggregates with excellent performance in lithium-ion batteries,” RSC Advances, vol. 2, no. 9, pp. 3615–3617, 2012.
  24. J. M. Ma, D. N. Lei, L. Mei et al., “Plate-like SnS2 nanostructures: hydrothermal preparation, growth mechanism and excellent electrochemical properties,” CrystEngComm, vol. 14, no. 3, pp. 832–836, 2012. View at Publisher · View at Google Scholar · View at Scopus
  25. S. Y. Liu, Y. Cai, X. Y. Cai, et al., “Catalytic photodegradation of Congo red in aqueous solution by Ln(OH)3 (Ln = Nd, Sm, Eu, Gd, Tb, and Dy) nanorods,” Applied Catalysis A, vol. 453, pp. 45–53, 2013.
  26. M. P. Rosynek and D. T. Magnuson, “Preparation and characterization of catalytic lanthanum oxide,” Journal of Catalysis, vol. 46, no. 3, pp. 402–413, 1977. View at Scopus
  27. J. M. Ma, J. Q. Yang, L. F. Jiao et al., “NiO nanomaterials: controlled fabrication, formation mechanism and the application in lithium-ion battery,” CrystEngComm, vol. 14, no. 2, pp. 453–459, 2012. View at Publisher · View at Google Scholar · View at Scopus
  28. N. Du, H. Zhang, B. Chen, J. Wu, D. Li, and D. Yang, “Low temperature chemical reaction synthesis of single-crystalline Eu(OH)3 nanorods and their thermal conversion to Eu2O3 nanorods,” Nanotechnology, vol. 18, no. 6, Article ID 065605, 2007. View at Publisher · View at Google Scholar · View at Scopus