- Email: [email protected]
Room temperature preparation of cuprous oxide hollow microspheres by a facile wet-chemical approach
Applied Surface Science 256 (2010) 7335–7338
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Short communication
Room temperature preparation of cuprous oxide hollow microspheres by a facile wet-chemical approach Ning Wang ∗ , Hongcai He, Li Han State Key Lab of Electronic Thin Films & Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
a r t i c l e
i n f o
Article history: Received 17 March 2010 Received in revised form 8 May 2010 Accepted 9 May 2010 Available online 31 May 2010 Keywords: Cuprous oxide Hollow microsphere Nanomaterials Crystal growth
a b s t r a c t Cuprous oxide hollow spheres have potential applications in drug-delivery carriers, biomedical diagnosis agents, and cell imaging. From a commercial point of view, the low-temperature, template-free, facile method is widely popular synthetic method for the synthesis of cuprous oxide hollow spheres. In this letter, we describe a novel facile template-free wet-chemical route to prepare crystallized cuprous oxide microspheres at room temperature. XRD patterns and SEM images revealed that pure crystallized cuprous oxide hollow microspheres were successfully obtained at room temperature. The diameter of cuprous oxide hollow sphere can be adjusted (0.7–7 m) by concentration control of hydrazine hydrate. Generated N2 gas bubbles in the aqueous solution, serving as “soft” templates, play a key role in the formation of hollow microspheres. © 2010 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Cuprous oxide, an important p-type semiconductor with the band gap in the range of 1.8–2.5 eV [1], has obtained increasing interest, because it has many potential applications in solar energy conversion [2], magnetic storage [3], lithium ion batteries [4], photocatalytic degradation of organic pollutants [5], and gas sensors for methane [6], carbon dioxide [7]. With specific morphologies, hollow nanostructures are more desirable because of their numerous potential applications in drugdelivery carriers [8], biomedical diagnosis agents [9], and cell imaging [10]. Recently, some methods have been reported for the preparation of cuprous oxide with hollow structures [11–15]. However, these methods require either hard or soft templates, or a high synthesis temperature above 80 ◦ C. From a commercial point of view, the low-temperature, template-free, facile method for synthesis of nanostructured materials is the widely popular synthetic method. Here, we describe a novel facile template-free wet-chemical route to prepare crystallized cuprous oxide microspheres at room temperature. This method has many advantages, such as one-step, rapid, low cost, easy to large-scale, without using any organic template etc. Furthermore, the possible formation mechanism of cuprous oxide hollow microspheres was proposed.
All chemicals were analytically pure and were used without further purification. First, CuSO4 ·5H2 O powder was completely solved into the de-ionized water and formed a 0.02 mol/L light blue aqueous solution. Second, hydrazine hydrate was solved in de-ionized water and formed the solutions with the various concentrations of 0.001 mol/L, 0.01 mol/L and 0.1 mol/L. Under the condition of strongly stirring, the hydrazine hydrate aqueous solutions were titrated slowly into the CuSO4 aqueous solution at room temperature. After about 5 min, the light red precipitation began to form, accompanied by a great number of bubbles emerging from the aqueous solution. In order to prevent the reaction to continue, after about 10 min, these turbid solutions were rapidly put into the beakers with 100 mL high-purity ethanol, respectively. The final products were obtained by centrifugation, washing several times with ethanol and drying at about 30 ◦ C. The crystalline phases of specimens were determined by powder X-ray diffraction (XRD, Rigaku RINT-2100, Japan). The morphologies of specimens were observed by using a field-emission scanning electron microscope (FESEM, JEOL JSM-6330F, Japan).
3. Results and discussion 3.1. Crystal phase of as-prepared cuprous oxide
∗ Corresponding author. Tel.: +86 28 83203807; fax: +86 28 83202569. E-mail address: [email protected] (N. Wang). 0169-4332/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2010.05.029
Fig. 1 displays a typical XRD pattern of the product prepared with 0.02 mol/L CuSO4 and 0.01 mol/L hydrazine hydrate. The as-
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N. Wang et al. / Applied Surface Science 256 (2010) 7335–7338
Fig. 1. XRD pattern of product prepared with 0.02 mol/L CuSO4 and 0.01 mol/L hydrazine hydrate.
prepared product shows clear X-ray diffractions at 2 = 29.7◦ , 36.6◦ , 42.5◦ , 61.7◦ and 73.9◦ . All the peaks of the pattern can be assigned to diffractions from the (1 1 0), (1 1 1), (2 0 0), (2 2 0) and (3 1 1) crystal planes of cubic Cu2 O with lattice constant a = 0.425 nm (ICSD No. 26963, JCPDS No. 74-1230), which indicates that room temperature crystallization of Cu2 O is realized successfully. No impurity peak is observed, which indicates that high-purity cuprous oxide crystalline is successfully synthesized at room temperature by our simple wet-chemical approach.
3.2. Morphology of as-prepared cuprous oxide Fig. 2(a) shows field-emission scanning electron microscopy (FESEM) photographs of cuprous oxide prepared with 0.02 mol/L CuSO4 and 0.01 mol/L hydrazine hydrate. It can be clearly seen that as-prepared cuprous oxide is spherical, with the diameter of 2–3 m. When the micrograph of microsphere is further enlarged to high magnification (Fig. 2(b)), it is found the microsphere is composed of abundant nanoparticles. From Fig. 2(a), it can be clearly seen that some spheres are broken. Enlarged micrograph shows that as-prepared cuprous oxide microspheres are hollowstructured (Fig. 2(c)). The hollow microspheres are composed of 2–3 layers nanoparticles with the wall thickness of 200–300 nm and the crystal size of 50–100 nm. When the concentration of hydrazine hydrate was increased to 0.1 mol/L, much larger cuprous oxide microspheres were obtained (Fig. 3(a)). The diameter of microspheres is increased from 2–3 m to 6–7 m. Shape of nanoparticles on the surface of cuprous oxide hollow microspheres changes from spherical into rod-like. When the concentration of hydrazine hydrate was decreased to 0.001 mol/L, much smaller cuprous oxide hollow microspheres was synthesized (Fig. 3(b)). The diameter of hollow microspheres is decreased from 2–3 m to 700–800 nm. Shape of nanoparticles on the surface of cuprous oxide hollow microspheres still keeps spherical. Above-mentioned phenomena strongly indicate that the diameter of cuprous oxide hollow microspheres is very sensitive to the concentration of hydrazine hydrate. Moreover, the diameter of hollow microspheres has similar change trend to the concentration of hydrazine hydrate.
Fig. 2. FESEM micrographs of cuprous oxide hollow micropheres prepared with 0.02 mol/L CuSO4 and 0.01 mol/L hydrazine hydrate: (a) low magnification; (b) magnified hollow spheres marked with a white rectangle in (a); (c) magnified hollow spheres marked with a white circle in (a).
3.3. Formation mechanism of cuprous oxide hollow microspheres In our experiment, the chemical reactions to form cuprous oxide hollow microspheres are formulated as follows: N2 H4 + H2 O → N2 H5 + + OH−
(1)
Cu2+ + 2OH− → Cu(OH)2
(2)
Cu(OH)2 + 2OH− → (CuO2 )2− + 2H2 O
(3)
(CuO2 )2− + 1/4N2 H4 + 1/2H2 O → 1/2Cu2 O + 1/4N2 + 2OH− (4)
N. Wang et al. / Applied Surface Science 256 (2010) 7335–7338
7337
Fig. 3. FESEM micrographs of cuprous oxide hollow micropheres with various hydrazine hydrate concentrations: (a) 0.10 mol/L; (b) 0.001 mol/L.
The formation of cuprous oxide can divide into two main stages. In the initial stage, (CuO2 )2− complex was formed in the aqueous solution, shown in reaction (1)–(3). In aqueous solution, hydrazine hydrate decomposed into (OH)− , which could react with Cu2+ to form Cu(OH)2 . Cu(OH)2 further reacted with (OH)− to generate (CuO2 )2− complex [16]. In the subsequent stage, the reduction reaction of (CuO2 )2− complex by hydrazine took place, shown in reaction (4). Thus, cuprous oxide was generated. From XRD patterns (Fig. 1), it can be found that room temperature crystallization of cuprous oxide is realized. The energy for the crystallization of cuprous oxide possibly comes from the heat generated by the reduction reaction. Our experimental evidence has led us to believe that generated N2 gas plays a key role in the formation of cuprous oxide hollow microspheres. Generally, hollow spheres are prepared by template-assisted methods, in which used templates are either hard [17–18] or soft ones [19–20]. In our case, the fresh produced N2 gaseous bubbles can serve as “soft” template to prepare the hollow spheres. The fresh produced N2 gaseous bubbles have high surface energy due to their small diameter and provide the heterogeneous nucleation center for newly formed nanoparticles to aggregate around the gas–liquid interface. Driven by the minimization of the interfacial energy, the spherical aggregates are then formed by aggregation of original nanocrystallites nucleated on the gas–liquid interface [21]. Meanwhile, N2 gaseous bubbles are remaining in the interior of the aggregates. Thus, hollow spherical structure is formed. The schematic illustration for the formation process of cuprous oxide hollow microspheres is shown in Fig. 4. First, original nanocrystallites nuclei and gas bubbles are gener-
ated at the same time (Fig. 4(a)). Second, original cuprous oxide nanocrystallites nuclei aggregate on the interface of freshly generated N2 gaseous bubbles (Fig. 4(b)), because of minimization of the interfacial energy. Nanocrystallites aggregated on the surface of the bubble have a role as nucleation seeds. Thus, the subsequent crystallization process can carry out, and finally the hollow microspheres are formed by layer-by-layer stacking of nanocrystallites (Fig. 4(c)). The size of hollow structures strongly depends on the sizes of bubble templates [22,23] According to the classical theory of bubble nucleation, the formation of bubbles in solutions includes the nucleation stage and the growth process [24]. During the growth process of bubbles, two small bubbles can merge to form a larger bubble [25]. In our case, higher concentration of hydrazine hydrate can generate more N2 bubbles in the nucleation stage, further form larger bubbles in the growth process, and thus lead to the formation of cuprous oxide hollow spheres with larger size. 4. Conclusion A simple wet-chemical approach without any template and additive was developed to synthesize crystallized cuprous oxide hollow microspheres at room temperature. Hydrazine hydrate was selected as an alkali source and reluctant. As-prepared product is cubic cuprous oxide with a hollow spherical structure. The diameter of hollow sphere can be adjusted (0.7–7 m) by concentration control of hydrazine hydrate. Generated N2 gas bubbles, serving as “soft” templates, play a key role in the formation of hollow microspheres. Driven by the minimization of the interfacial energy, original cuprous oxide nanocrystallites nuclei aggregate on the gas–liquid interface of N2 gas bubbles. Continuing aggregates of cuprous oxide nanocrystallites lead to the formation of hollow microspheres. Higher concentration of hydrazine hydrate can generate larger N2 bubbles, and thus form cuprous oxide hollow spheres with larger size. Acknowledgments
Fig. 4. Schematic illustration for the formation process of cuprous oxide hollow microspheres.
The authors are grateful to International Cooperation MOSTJST Program Fund (No. 2010DFA61410), National Natural Science Foundation of China (No. 50802013), Research Fund for Doctoral Program of Higher Education (No. 200806141019), Open Fund of State Key Lab of New Ceramics & Fine Processing and UESTC Youth Fund (No. JX0722).
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N. Wang et al. / Applied Surface Science 256 (2010) 7335–7338
References [1] M. Nolan, S.D. Elliott, Thin Solid Films 516 (2008) 1468. [2] R.N. Briskman, Sol. Energy Mater. Sol. Cells 27 (1992) 361. [3] H. Zhang, D. Zhou, L. Zhang, D.F. Zhang, L. Guo, L. He, C.P. Chen, J. Nanosci. Nanotechnol. 9 (2009) 1321. [4] P. Poizot, S. Laruelle, S. Grugeon, L. Dupont, J.M. Taracon, Nature 407 (2000) 496. [5] P.E. de Jongh, D. Vanmaekelbergh, J.J. Kelly, Chem. Commun. (1999) 1069. [6] A.H. Jayatissa, P. Samarasekara, G. Kun, Phys. Status Solidi A 206 (2009) 332. [7] P. Samarasekara, N.U.S. Yapa, N.T.R.N. Kumara, M.V.K. Perera, Bull. Mater. Sci. 30 (2007) 113. [8] A.H. Pei, Z.W. Shen, G.S. Yang, Mater. Lett. 61 (2007) 2757. [9] J. Chen, F. Saeki, B. Wiley, H. Cang, M.J. Cobb, Z. Li, L. Au, H. Zhang, M.J. Kimmey, X. Li, Y. Xia, Nano Lett. 5 (2005) 473. [10] J. Chen, D. Wang, J. Xi, L. Au, A. Siekkinen, A. Warsen, Z.Y. Li, H. Zhang, Y. Xia, X. Li, Nano Lett. 7 (2007) 1318. [11] J.T. Zhang, J.F. Liu, Q. Peng, X. Wang, Y.D. Li, Chem. Mater. 18 (2006) 867.
[12] L.S. Xu, X.H. Chen, Y.R. Wu, C.S. Chen, W.H. Li, W.Y. Pan, Y.G. Wang, Nanotechnology 17 (2006) 1501. [13] H.R. Zhang, C.M. Shen, S.T. Chen, Z.C. Xu, F.S. Liu, J.Q. Li, H.J. Gao, Nanotechnology 16 (2005) 267. [14] J.J. Teo, Y. Chang, H.C. Zeng, Langmuir 22 (2006) 7369. [15] M.Q. Yang, Y.W. Zhang, G.S. Pang, S.H. Feng, Eur. J. Inorg. Chem. 24 (2007) 3841. [16] H.H. Strehblow, V. Maurice, P. Marcus, Electrochim. Acta 46 (2001) 3755. [17] F. Caruso, X. Shi, R.A. Caruso, A. Susha, Adv. Mater. 13 (2001) 740. [18] V.S. Maceira, M. Spasova, M. Farle, Adv. Funct. Mater. 15 (2005) 1036. [19] X.L. Yu, C.B. Cao, H.S. Zhu, Q.S. Li, C.L. Liu, Q.H. Gong, Adv. Funct. Mater. 17 (2007) 1397. [20] Y.R. Ma, J.M. Ma, H.M. Cheng, Langmuir 19 (2003) 4040. [21] P. Hu, L.J. Yu, A.H. Zou, C.Y. Guo, F.L. Yuan, J. Phys. Chem. C 113 (2009) 900. [22] L. Guo, F. Liang, X. Wen, S. Yang, L. He, W. Zheng, C. Chen, Adv. Funct. Mater. 17 (2007) 425. [23] M. Agrawal, A. Pich, S. Gupta, N.E. Zafeiropoulos, P. Simon, M. Stamm, Langmuir 24 (2008) 1013. [24] C.F. Delale, J. Hruby, F. Marˇsík, J. Chem. Phys. 118 (2003) 792. [25] Z.J. Wang, C. Valeriani, D. Frenkel, J. Phys. Chem. B 113 (2009) 3776.
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Short communication
Room temperature preparation of cuprous oxide hollow microspheres by a facile wet-chemical approach Ning Wang ∗ , Hongcai He, Li Han State Key Lab of Electronic Thin Films & Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
a r t i c l e
i n f o
Article history: Received 17 March 2010 Received in revised form 8 May 2010 Accepted 9 May 2010 Available online 31 May 2010 Keywords: Cuprous oxide Hollow microsphere Nanomaterials Crystal growth
a b s t r a c t Cuprous oxide hollow spheres have potential applications in drug-delivery carriers, biomedical diagnosis agents, and cell imaging. From a commercial point of view, the low-temperature, template-free, facile method is widely popular synthetic method for the synthesis of cuprous oxide hollow spheres. In this letter, we describe a novel facile template-free wet-chemical route to prepare crystallized cuprous oxide microspheres at room temperature. XRD patterns and SEM images revealed that pure crystallized cuprous oxide hollow microspheres were successfully obtained at room temperature. The diameter of cuprous oxide hollow sphere can be adjusted (0.7–7 m) by concentration control of hydrazine hydrate. Generated N2 gas bubbles in the aqueous solution, serving as “soft” templates, play a key role in the formation of hollow microspheres. © 2010 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Cuprous oxide, an important p-type semiconductor with the band gap in the range of 1.8–2.5 eV [1], has obtained increasing interest, because it has many potential applications in solar energy conversion [2], magnetic storage [3], lithium ion batteries [4], photocatalytic degradation of organic pollutants [5], and gas sensors for methane [6], carbon dioxide [7]. With specific morphologies, hollow nanostructures are more desirable because of their numerous potential applications in drugdelivery carriers [8], biomedical diagnosis agents [9], and cell imaging [10]. Recently, some methods have been reported for the preparation of cuprous oxide with hollow structures [11–15]. However, these methods require either hard or soft templates, or a high synthesis temperature above 80 ◦ C. From a commercial point of view, the low-temperature, template-free, facile method for synthesis of nanostructured materials is the widely popular synthetic method. Here, we describe a novel facile template-free wet-chemical route to prepare crystallized cuprous oxide microspheres at room temperature. This method has many advantages, such as one-step, rapid, low cost, easy to large-scale, without using any organic template etc. Furthermore, the possible formation mechanism of cuprous oxide hollow microspheres was proposed.
All chemicals were analytically pure and were used without further purification. First, CuSO4 ·5H2 O powder was completely solved into the de-ionized water and formed a 0.02 mol/L light blue aqueous solution. Second, hydrazine hydrate was solved in de-ionized water and formed the solutions with the various concentrations of 0.001 mol/L, 0.01 mol/L and 0.1 mol/L. Under the condition of strongly stirring, the hydrazine hydrate aqueous solutions were titrated slowly into the CuSO4 aqueous solution at room temperature. After about 5 min, the light red precipitation began to form, accompanied by a great number of bubbles emerging from the aqueous solution. In order to prevent the reaction to continue, after about 10 min, these turbid solutions were rapidly put into the beakers with 100 mL high-purity ethanol, respectively. The final products were obtained by centrifugation, washing several times with ethanol and drying at about 30 ◦ C. The crystalline phases of specimens were determined by powder X-ray diffraction (XRD, Rigaku RINT-2100, Japan). The morphologies of specimens were observed by using a field-emission scanning electron microscope (FESEM, JEOL JSM-6330F, Japan).
3. Results and discussion 3.1. Crystal phase of as-prepared cuprous oxide
∗ Corresponding author. Tel.: +86 28 83203807; fax: +86 28 83202569. E-mail address: [email protected] (N. Wang). 0169-4332/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2010.05.029
Fig. 1 displays a typical XRD pattern of the product prepared with 0.02 mol/L CuSO4 and 0.01 mol/L hydrazine hydrate. The as-
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N. Wang et al. / Applied Surface Science 256 (2010) 7335–7338
Fig. 1. XRD pattern of product prepared with 0.02 mol/L CuSO4 and 0.01 mol/L hydrazine hydrate.
prepared product shows clear X-ray diffractions at 2 = 29.7◦ , 36.6◦ , 42.5◦ , 61.7◦ and 73.9◦ . All the peaks of the pattern can be assigned to diffractions from the (1 1 0), (1 1 1), (2 0 0), (2 2 0) and (3 1 1) crystal planes of cubic Cu2 O with lattice constant a = 0.425 nm (ICSD No. 26963, JCPDS No. 74-1230), which indicates that room temperature crystallization of Cu2 O is realized successfully. No impurity peak is observed, which indicates that high-purity cuprous oxide crystalline is successfully synthesized at room temperature by our simple wet-chemical approach.
3.2. Morphology of as-prepared cuprous oxide Fig. 2(a) shows field-emission scanning electron microscopy (FESEM) photographs of cuprous oxide prepared with 0.02 mol/L CuSO4 and 0.01 mol/L hydrazine hydrate. It can be clearly seen that as-prepared cuprous oxide is spherical, with the diameter of 2–3 m. When the micrograph of microsphere is further enlarged to high magnification (Fig. 2(b)), it is found the microsphere is composed of abundant nanoparticles. From Fig. 2(a), it can be clearly seen that some spheres are broken. Enlarged micrograph shows that as-prepared cuprous oxide microspheres are hollowstructured (Fig. 2(c)). The hollow microspheres are composed of 2–3 layers nanoparticles with the wall thickness of 200–300 nm and the crystal size of 50–100 nm. When the concentration of hydrazine hydrate was increased to 0.1 mol/L, much larger cuprous oxide microspheres were obtained (Fig. 3(a)). The diameter of microspheres is increased from 2–3 m to 6–7 m. Shape of nanoparticles on the surface of cuprous oxide hollow microspheres changes from spherical into rod-like. When the concentration of hydrazine hydrate was decreased to 0.001 mol/L, much smaller cuprous oxide hollow microspheres was synthesized (Fig. 3(b)). The diameter of hollow microspheres is decreased from 2–3 m to 700–800 nm. Shape of nanoparticles on the surface of cuprous oxide hollow microspheres still keeps spherical. Above-mentioned phenomena strongly indicate that the diameter of cuprous oxide hollow microspheres is very sensitive to the concentration of hydrazine hydrate. Moreover, the diameter of hollow microspheres has similar change trend to the concentration of hydrazine hydrate.
Fig. 2. FESEM micrographs of cuprous oxide hollow micropheres prepared with 0.02 mol/L CuSO4 and 0.01 mol/L hydrazine hydrate: (a) low magnification; (b) magnified hollow spheres marked with a white rectangle in (a); (c) magnified hollow spheres marked with a white circle in (a).
3.3. Formation mechanism of cuprous oxide hollow microspheres In our experiment, the chemical reactions to form cuprous oxide hollow microspheres are formulated as follows: N2 H4 + H2 O → N2 H5 + + OH−
(1)
Cu2+ + 2OH− → Cu(OH)2
(2)
Cu(OH)2 + 2OH− → (CuO2 )2− + 2H2 O
(3)
(CuO2 )2− + 1/4N2 H4 + 1/2H2 O → 1/2Cu2 O + 1/4N2 + 2OH− (4)
N. Wang et al. / Applied Surface Science 256 (2010) 7335–7338
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Fig. 3. FESEM micrographs of cuprous oxide hollow micropheres with various hydrazine hydrate concentrations: (a) 0.10 mol/L; (b) 0.001 mol/L.
The formation of cuprous oxide can divide into two main stages. In the initial stage, (CuO2 )2− complex was formed in the aqueous solution, shown in reaction (1)–(3). In aqueous solution, hydrazine hydrate decomposed into (OH)− , which could react with Cu2+ to form Cu(OH)2 . Cu(OH)2 further reacted with (OH)− to generate (CuO2 )2− complex [16]. In the subsequent stage, the reduction reaction of (CuO2 )2− complex by hydrazine took place, shown in reaction (4). Thus, cuprous oxide was generated. From XRD patterns (Fig. 1), it can be found that room temperature crystallization of cuprous oxide is realized. The energy for the crystallization of cuprous oxide possibly comes from the heat generated by the reduction reaction. Our experimental evidence has led us to believe that generated N2 gas plays a key role in the formation of cuprous oxide hollow microspheres. Generally, hollow spheres are prepared by template-assisted methods, in which used templates are either hard [17–18] or soft ones [19–20]. In our case, the fresh produced N2 gaseous bubbles can serve as “soft” template to prepare the hollow spheres. The fresh produced N2 gaseous bubbles have high surface energy due to their small diameter and provide the heterogeneous nucleation center for newly formed nanoparticles to aggregate around the gas–liquid interface. Driven by the minimization of the interfacial energy, the spherical aggregates are then formed by aggregation of original nanocrystallites nucleated on the gas–liquid interface [21]. Meanwhile, N2 gaseous bubbles are remaining in the interior of the aggregates. Thus, hollow spherical structure is formed. The schematic illustration for the formation process of cuprous oxide hollow microspheres is shown in Fig. 4. First, original nanocrystallites nuclei and gas bubbles are gener-
ated at the same time (Fig. 4(a)). Second, original cuprous oxide nanocrystallites nuclei aggregate on the interface of freshly generated N2 gaseous bubbles (Fig. 4(b)), because of minimization of the interfacial energy. Nanocrystallites aggregated on the surface of the bubble have a role as nucleation seeds. Thus, the subsequent crystallization process can carry out, and finally the hollow microspheres are formed by layer-by-layer stacking of nanocrystallites (Fig. 4(c)). The size of hollow structures strongly depends on the sizes of bubble templates [22,23] According to the classical theory of bubble nucleation, the formation of bubbles in solutions includes the nucleation stage and the growth process [24]. During the growth process of bubbles, two small bubbles can merge to form a larger bubble [25]. In our case, higher concentration of hydrazine hydrate can generate more N2 bubbles in the nucleation stage, further form larger bubbles in the growth process, and thus lead to the formation of cuprous oxide hollow spheres with larger size. 4. Conclusion A simple wet-chemical approach without any template and additive was developed to synthesize crystallized cuprous oxide hollow microspheres at room temperature. Hydrazine hydrate was selected as an alkali source and reluctant. As-prepared product is cubic cuprous oxide with a hollow spherical structure. The diameter of hollow sphere can be adjusted (0.7–7 m) by concentration control of hydrazine hydrate. Generated N2 gas bubbles, serving as “soft” templates, play a key role in the formation of hollow microspheres. Driven by the minimization of the interfacial energy, original cuprous oxide nanocrystallites nuclei aggregate on the gas–liquid interface of N2 gas bubbles. Continuing aggregates of cuprous oxide nanocrystallites lead to the formation of hollow microspheres. Higher concentration of hydrazine hydrate can generate larger N2 bubbles, and thus form cuprous oxide hollow spheres with larger size. Acknowledgments
Fig. 4. Schematic illustration for the formation process of cuprous oxide hollow microspheres.
The authors are grateful to International Cooperation MOSTJST Program Fund (No. 2010DFA61410), National Natural Science Foundation of China (No. 50802013), Research Fund for Doctoral Program of Higher Education (No. 200806141019), Open Fund of State Key Lab of New Ceramics & Fine Processing and UESTC Youth Fund (No. JX0722).
7338
N. Wang et al. / Applied Surface Science 256 (2010) 7335–7338
References [1] M. Nolan, S.D. Elliott, Thin Solid Films 516 (2008) 1468. [2] R.N. Briskman, Sol. Energy Mater. Sol. Cells 27 (1992) 361. [3] H. Zhang, D. Zhou, L. Zhang, D.F. Zhang, L. Guo, L. He, C.P. Chen, J. Nanosci. Nanotechnol. 9 (2009) 1321. [4] P. Poizot, S. Laruelle, S. Grugeon, L. Dupont, J.M. Taracon, Nature 407 (2000) 496. [5] P.E. de Jongh, D. Vanmaekelbergh, J.J. Kelly, Chem. Commun. (1999) 1069. [6] A.H. Jayatissa, P. Samarasekara, G. Kun, Phys. Status Solidi A 206 (2009) 332. [7] P. Samarasekara, N.U.S. Yapa, N.T.R.N. Kumara, M.V.K. Perera, Bull. Mater. Sci. 30 (2007) 113. [8] A.H. Pei, Z.W. Shen, G.S. Yang, Mater. Lett. 61 (2007) 2757. [9] J. Chen, F. Saeki, B. Wiley, H. Cang, M.J. Cobb, Z. Li, L. Au, H. Zhang, M.J. Kimmey, X. Li, Y. Xia, Nano Lett. 5 (2005) 473. [10] J. Chen, D. Wang, J. Xi, L. Au, A. Siekkinen, A. Warsen, Z.Y. Li, H. Zhang, Y. Xia, X. Li, Nano Lett. 7 (2007) 1318. [11] J.T. Zhang, J.F. Liu, Q. Peng, X. Wang, Y.D. Li, Chem. Mater. 18 (2006) 867.
[12] L.S. Xu, X.H. Chen, Y.R. Wu, C.S. Chen, W.H. Li, W.Y. Pan, Y.G. Wang, Nanotechnology 17 (2006) 1501. [13] H.R. Zhang, C.M. Shen, S.T. Chen, Z.C. Xu, F.S. Liu, J.Q. Li, H.J. Gao, Nanotechnology 16 (2005) 267. [14] J.J. Teo, Y. Chang, H.C. Zeng, Langmuir 22 (2006) 7369. [15] M.Q. Yang, Y.W. Zhang, G.S. Pang, S.H. Feng, Eur. J. Inorg. Chem. 24 (2007) 3841. [16] H.H. Strehblow, V. Maurice, P. Marcus, Electrochim. Acta 46 (2001) 3755. [17] F. Caruso, X. Shi, R.A. Caruso, A. Susha, Adv. Mater. 13 (2001) 740. [18] V.S. Maceira, M. Spasova, M. Farle, Adv. Funct. Mater. 15 (2005) 1036. [19] X.L. Yu, C.B. Cao, H.S. Zhu, Q.S. Li, C.L. Liu, Q.H. Gong, Adv. Funct. Mater. 17 (2007) 1397. [20] Y.R. Ma, J.M. Ma, H.M. Cheng, Langmuir 19 (2003) 4040. [21] P. Hu, L.J. Yu, A.H. Zou, C.Y. Guo, F.L. Yuan, J. Phys. Chem. C 113 (2009) 900. [22] L. Guo, F. Liang, X. Wen, S. Yang, L. He, W. Zheng, C. Chen, Adv. Funct. Mater. 17 (2007) 425. [23] M. Agrawal, A. Pich, S. Gupta, N.E. Zafeiropoulos, P. Simon, M. Stamm, Langmuir 24 (2008) 1013. [24] C.F. Delale, J. Hruby, F. Marˇsík, J. Chem. Phys. 118 (2003) 792. [25] Z.J. Wang, C. Valeriani, D. Frenkel, J. Phys. Chem. B 113 (2009) 3776.