Langmuir 2008, 24, 11089-11095
11089
A New Route to Self-Assembled Tin Dioxide Nanospheres: Fabrication and Characterization Zhengtao Deng,†,‡,§,# Bo Peng,†,‡ Dong Chen,† Fangqiong Tang,*,† and Anthony J. Muscat§ Laboratory of Controllable Preparation and Application of Nanomaterials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, and Graduate UniVersity of the Chinese Academy of Sciences, Beijing 100080, People’s Republic of China, and Department of Chemical and EnVironmental Engineering and College of Optical Science, The UniVersity of Arizona, Tucson, Arizona 85721 ReceiVed March 29, 2008. ReVised Manuscript ReceiVed July 13, 2008 Nearly monodispersed self-assembled tin dioxide (SnO2) nanospheres with intense photoluminescence (PL) were synthesized using a new wet chemistry technique. Instead of coprecipitating stannous salts, bulk tin (Sn) metal was oxidized at room temperature in a solution of hydrogen peroxide and deionized water containing polyvinylpyrrolidone (PVP) and ethylenediamine (EDA). SnO2 nanocrystals were produced with diameters of ∼3.8 nm that spontaneously self-assembled into uniform SnO2 nanospheres with diameters of ∼30 nm. Analysis was performed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV-vis absorption spectroscopy, PL spectroscopy, and fluorescence lifetime measurements. The SnO2 nanospheres displayed room-temperature purple luminescence with an intense band at 394 nm (∼3.15 eV) and a high quantum yield of ∼15%, likely as a result of emission from the surface states of SnO2/PVP complexes. The present study could open a new avenue to large-scale synthesis of self-assembled functional oxide nanostructures with technological applications as purple emitters, biological labels, gas sensors, lithium batteries, and dye-sensitized solar cells.
Introduction Chemical self-assembly of nanoscale building blocks, such as nanocrystals and nanowires, is a key step toward controlling the collective properties of nanostructures and is important for applications such as micro- and nanoelectronic devices, optics, catalysts, and sensors.1-3 The past few years have been witness to a revolution in understanding the preparation of monodispersed inorganic nanocrystals with controllable sizes and narrow size distributions that show remarkable optical and electronic properties.4-6 Despite these developments, the controllable generation of well-defined nanocrystal-based higher order nanostructures remains a challenge in chemistry. * To whom correspondence should be addressed. E-mail: tangfq@ mail.ipc.ac.cn. † Technical Institute of Physics and Chemistry, Chinese Academy of Sciences. ‡ Graduate University of Chinese Academy of Sciences. § Department of Chemical and Environmental Engineering, The University of Arizona. # College of Optical Science, The University of Arizona. (1) (a) Mirkin, C. A.; Lestinger, R. L.; Mucic, R. C.; Storhoff, J. J. Nature 1996, 382, 607. (b) Caruso, F.; Caruso, R. A.; Mohwald, H. Science 1998, 282, 1111. (2) (a) Tang, Z.; Kotov, N. A.; Giersig, M. Science 2002, 297, 237. (b) Tang, Z.; Kotov, N. A. AdV. Mater. 2005, 17, 951. (c) Tang, Z. Y.; Zhang, Z. L.; Wang, Y.; Glotzer, S. C.; Kotov, N. A. Science 2006, 314, 274. (3) Deng, Z. T.; Chen, D.; Tang, F. Q.; Meng, X. W.; Ren, J.; Zhang, L. J. Phys. Chem. C 2007, 111, 5325. (4) Burda, C.; Chen, X.; Narayanan, R.; El-Sayed, M. A. Chem. ReV. 2005, 105, 1025. (5) Wang, X.; Zhuang, J.; Peng, Q.; Li, Y. D. Nature 2005, 437, 121. (6) Deng, Z. T.; Cao, L.; Tang, F. Q.; Zou, B. S. J. Phys. Chem. B 2005, 109, 16671. (7) (a) Cabot, A.; Arbiol, J.; Morante, J. R.; Weimar, U.; Barsan, N.; Gopel, W. Sens. Actuators, B 2000, 70, 87. (b) Cabot, A.; Vila, A.; Morante, J. R. Sens. Actuators, B 2002, 84, 12. (c) Idota, Y.; Kubota, T.; Matsufuji, A.; Maekawa, Y.; Miyasaka, T. Science 1997, 276, 1395. (d) Scott, R. W. J.; Yang, S. M.; Chabanis, G.; Coombs, N.; Williams, D. E.; Ozin, G. A. AdV. Mater. 2001, 13, 1468. (8) (a) Winter, M.; Besenhard, O. J.; Spahr, M. E.; Novak, P. AdV. Mater. 1998, 10, 725. (b) Han, S.; Jang, B.; Kim, T.; Oh, S. M.; Hyeon, T. AdV. Funct. Mater. 2005, 15, 1845. (c) Chiu, H. C.; Yeh, C. S. J. Phys. Chem. C 2007, 111, 7256.
Tin dioxide (SnO2) is an n-type functional semiconducting oxide that is well-known for its potential applications in photocatalysis, gas sensing, transparent conducting electrodes, dye-sensitized solar cells (DSCs), as well as in lithium batteries.7,8 During the past few years, a wide variety of SnO2 nanostructures, such as nanocrystals,9 nanorods,10 nanobelts,11 nanotubes,12 and hollow spheres,13 have been synthesized. Nevertheless, most of these reported synthesis routes are based on the coprecipitation of stannous salts or require high temperature and special tools such as hydrothermal autoclaves.9-13 Thus, new methods are needed to synthesize uniform SnO2 nanostructures that have desirable properties. Similar to the other well-studied metal-oxide semiconductors, SnO2 (Eg ) 3.6 eV at 300 K) is also expected to be a direct band gap semiconductor exhibiting unique optical properties.14 Bulk SnO2 crystals or deposited SnO2 thin films have no luminescence or have very low emission efficiency at room temperature.15 In the past few years, several studies on the room-temperature (9) (a) Pang, G.; Chen, S.; Koltypin, Y.; Zaban, A.; Feng, S.; Gedanken, A. Nano Lett. 2001, 1, 723. (b) Juttukonda, V.; Paddock, R. L.; Raymond, J. E.; Denomme, D.; Richardson, A. E.; Slusher, L. E.; Fahlman, B. D. J. Am. Chem. Soc. 2006, 128, 420. (c) Subramanian, V.; Burke, W. W.; Zhu, H.; Wei, B. J. Phys. Chem. C 2008, 112, 4550. (10) (a) Cheng, B.; Russell, J. M.; Shi, W. S.; Zhang, L.; Samulski, E. T. J. Am. Chem. Soc. 2004, 126, 5972. (b) Park, M. S.; Wang, G. X.; Kang, Y. M.; Wexler, D.; Dou, S. X.; Liu, H. K. Angew. Chem., Int. Ed. 2007, 46, 750. (11) Pan, Z. W.; Dai, Z. R.; Wang, Z. L. Science 2001, 291, 1947. (12) (a) Zhao, L.; Yosef, M.; Steinhart, M.; Goring, P.; Hofmeister, H.; Gosele, U.; Schlecht, S. Angew. Chem., Int. Ed. 2005, 44, 311. (b) Wang, Y.; Zeng, H. C.; Lee, J. Y. AdV. Mater. 2006, 18, 645. (c) Dong, Q.; Su, H.; Zhang, D.; Cao, W.; Wang, N. Langmuir 2007, 23, 8108. (13) (a) Yang, H. X.; Qian, J. F.; Chen, Z. X.; Ai, X. P.; Cao, Y. L. J. Phys. Chem. C 2007, 111, 14067. (b) Lou, X. W.; Wang, Y.; Yuan, C.; Lee, J. Y.; Archer, L. A. AdV. Mater. 2006, 18, 2325. (14) (a) Batzill, M.; Diebold, U. Prog. Surf. Sci. 2005, 79, 47. (b) Pan, S. S.; Ye, C.; Teng, X. M.; Li, L.; Li, G. H. Appl. Phys. Lett. 2006, 89, 251911. (15) Pinna, N.; Neri, G.; Antonietti, M.; Niederberger, M. Angew. Chem., Int. Ed. 2004, 43, 4345. (16) (a) Hu, J. Q.; Bando, Y.; Liu, Q. L.; Golberg, D AdV. Funct. Mater. 2003, 13, 493. (b) He, J. H.; Wu, T. H.; Hsin, C. L.; Li, K. M.; Chen, L. J.; Chueh, Y. L.; Chou, L. J.; Wang, Z. L. Small 2006, 2, 116.
10.1021/la800984g CCC: $40.75 2008 American Chemical Society Published on Web 09/03/2008
11090 Langmuir, Vol. 24, No. 19, 2008
photoluminescence (PL) of SnO2 nanostructures have been reported. Room-temperature red light emission with a peak at ∼605 nm (2.05 eV) due to oxygen vacancies was observed in SnO2 nanoribbons and beaklike SnO2 nanorods.16a,b Recently, room-temperature blue light emission with a peak at ∼445 nm (2.8 eV) due to a triplet-to-ground-state transition at a neutral oxygen vacancy defect has been reported in SnO2 nanoblades synthesized by a low temperature hydrothermal process. This represents the first report of the room temperature strong blue luminescence from SnO2 nanostructures.17 Moreover, reports have been made of a weak emission peak at ∼398 nm together with a broad red emission from SnO2 nanowhiskers,18a as well as emission peaks at ∼400 nm for 2.8-nm-size SnO2,18b 392 and 439 nm for SnO2 nanoribbons,18c and 399 and 470 nm for SnO2/ Sn nanocables.18d This study reports a simple wet chemistry route for the largescale synthesis of nearly monodispersed self-assembled SnO2 nanospheres by direct hydrogen peroxide oxidation of bulk tin (Sn) metal in deionized water (DIW) with the assistance of polyvinylpyrrolidone (PVP) and ethylenediamine (EDA) at room temperature. The SnO2 nanospheres were grown under mild reaction conditions (room temperature, atmospheric pressure) and did not require subsequent thermal annealing. The nanospheres displayed a strong room-temperature purple luminescence with an emission band at 394 nm (∼3.15 eV) and a high quantum yield (∼15%), which represents the first report of strong PL in this energy range in SnO2 nanostructures.
Deng et al.
Figure 1. XRD profile of (a) the source material of bulk tin and (b) the self-assembled SnO2 nanospheres.
Experimental Section All of the chemical reagents used in the experiments were purchased from Beijing Chemical Reagents Company. In a typical synthesis, 118.7 mg of tin (Sn) powder (
