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Synthesis of single crystal BaMoO4 nanofibers in CTAB reverse microemulsions
Materials Letters 59 (2005) 64 – 68 www.elsevier.com/locate/matlet
Synthesis of single crystal BaMoO4 nanofibers in CTAB reverse microemulsions Zhonghao Li, Jimin Du, Jianling Zhang, Tiancheng Mu, Yanan Gao, Buxing Han*, Jing Chen, Jiawei Chen Center for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, PR China Available online 12 October 2004
Abstract High-aspect-ratio, single crystal BaMoO4 nanofibers with diameters of about 30 nm and lengths up to 30 Am were synthesized in cationic cetyltrimethylammonium bromide (CTAB) reverse microemulsions. The effects of different conditions such as the aging time, the molar ratio of water to surfactant (w), the reactant and CTAB concentration on the evolution of single crystal BaMoO4 nanofibers were discussed. Transmission electron microscope (TEM) and electron diffraction were used to characterize the morphology and the crystal structure of the prepared nanostructured BaMoO4 obtained at different conditions. D 2004 Elsevier B.V. All rights reserved. Keywords: BaMoO4; Nanofibers; CTAB; Microemulsions
1. Introduction In recent years, 1D nanostructures have attracted considerable attention due to their size-dependent properties and potential wide-ranging applications [1–4]. The preparation of high-aspect-ratio nanofibers is of great interest because these nanofibers are very promising in a myriad applications, such as the nanodevices and interconnects for molecular computing, scanning probe microscopy tips, and the polymer filler materials for the alteration of a material’s mechanical and rheological properties [5,6]. Various methods have been used to the preparation of different kind of inorganic nanorods and nanofibers [7–12]. Of these methods, the reverse micelles and microemulsions have been shown to be powerful in the synthesis of colloidal inorganic or organic nanoparticles [13–16]. The principal reason for using microemulsions is that particle shape and corresponding size distributions can be readily controlled by adjusting the molar ratio of water:oil:surfactant. In some * Corresponding author. Tel.: +86 10 62562821; fax: +86 10 62562821. E-mail address: [email protected] (B. Han). 0167-577X/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2004.09.017
cases, further growth and aggregation of the initially formed nanoparticles in microemulsions can result in the formation of nanowires. For example, A variety of 1D nanoscale materials such as CaCO3, BaCO3, BaSO4, CaSO4, BaCrO4, BaWO4, CdS, and Cu nanorods or nanowires have been successfully synthesized in the reverse micelle media [7,17– 24]. The reverse microemulsions used in synthesis of inorganic nanowires with larger lengths are usually formed by anionic surfactant AOT or nonionic surfactants. Cetyltrimethylammonium bromide (CTAB) is a typical cationic surfactant used to form reverse microemulsions. According to the literatures, many inorganic nanoparticle materials have been synthesized in CTAB reverse microemulsions [25–28]. Molybdates such as CaMoO4, SrMoO4, and BaMoO4 belong to the scheelite group, and the corresponding films of these materials have been prepared by the researchers [29–32]. Single crystals of these materials have been studied as hosts for lanthanide activated lasers [33]. Therefore, the preparation of nanoshaped BaMoO4 especially in 1 D dimension will broaden the application of BaMoO4 in the optical and ceramic fields in view of the size and shape dependent properties of the nanomaterials.
Z. Li et al. / Materials Letters 59 (2005) 64–68
In this paper, we report the fabrication of high-aspectratio single crystal BaMoO4 nanofibers with diameter of about 30 nm and length up to 30 Am in the reverse microemulsions formed by cationic surfactant CTAB.
2. Experimental 2.1. Materials CTAB, isooctane, n -pentanol, BaCl 2 d 2H 2 O and NaMoO4d 2H2O were all purchased from Beijing Chemical Reagent Factory. Sodium bis (2-ethylhexyl) sulfosuccinate (AOT) was obtained from Sigma. Double-distilled water was used in all the experiments. 2.2. Synthesis of BaMoO4 nanofibers in reverse microemulsion A quaternary microemulsion, CTAB/water/isooctane/npentanol, was selected for this study. A typical procedure for the formation of BaMoO4 nanofibers with larger length in the CTAB reverse microemulsions is as follows: The reverse microemulsions were prepared by solubilizing a suitable amount of aqueous solution containing Ba2+ or MoO42 ions into 0.1 M CTAB solution in 10 ml isooctane with 0.6 ml npentanol. Then equal volumes of the above two microemulsions were mixed quickly. The resulting solutions were aged without stirring at room temperature. Following the similar procedure, BaMoO4 nanofibers were also prepared at other conditions. 2.3. Characterization A Jeol-2010 transmission electron microscope (TEM) was used to characterize the morphology and structure of the products at an operating voltage of 200 kV. Samples for TEM analysis were prepared at different conditions by dropping a drop of the reverse microemulsions containing the products onto a Formvar-covered copper grid and drying in air at room temperature. Then the sample was washed for 5 s by immersing the grid in pure ethanol in order to obtain grids that were sufficiently thinly coated to allow penetration by the electron beam. Finally, the grid was removed and air-dried.
3. Results and discussion 3.1. Effect of aging time on the evolution of BaMoO4 nanofibers The effect of the aging time on the evolution of the obtained nanoparticles was investigated by using aging times of 5, 30 min, 4 and 48 h, TEM micrographs are shown in Fig. 1a–d. The concentration of Ba2+ or MoO42
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in the droplet of reverse microemulsions (w =20, [CTAB]=0.1M) is 0.1 M. As shown in Fig. 1a, for the samples aged for a short time of 5 min, short BaMoO4 nanorods of very irregular morphologies are formed. As the aging time is increased to 30 min, the regular twodimensional nanorod of BaMoO4 with the diameter about 20 nm and length about 200 nm are formed (shown in Fig. 1b). When the samples are aged for the longer time of 4 h, the long nanofibers of BaMoO4 are obtained (shown in Fig. 1c). The bright spots and diffraction rings in the corresponding electron diffraction pattern suggest the presence of BaMoO4 polycrystals together with individual monocrystal for the nanofibers obtained (Fig. 1c). After aging for 48 h, the length of BaMoO4 nanofibers is increased up to 30 Am, with the diameter of 26–35 nm (Fig. 1d). From the figure it is also found that several nanofibers stick together to form a bundle in some areas. The electron diffraction patterns were recorded from different positions along the nanofibers. All the electron diffraction patterns indicate that the nanofiber formed is a single crystal with a tetragonal scheelite structure (Fig. 1d). These TEM observations of the crystal growth of the BaMoO4 nanowires in reverse microemulsions suggest that the nanowires could be formed by a directional aggregation process. The evolution of BaMoO4 nanofibers can be expressed as the following steps: First small nanoparticles of BaMoO4 formed in reverse microemulsions after mixing the reactant solutions and then the nanoparticles aggregated and grew to short nanorod and longer nanofibers through a directional aggregation process. The formation process of BaMoO4 nanofibres is similar to that of BaCO3 nanowires formed in C12E4 (tetraethylene glycol monododecyl ether) reverse microemulsions by Qi et al. [7]. 3.2. Effect of w value on the morphologies of BaMoO4 nanofibers The molar ratio of water to surfactant (w) is an important parameter which determines the property of the reverse microemulsions. In some cases the value of w can strongly influence the morphology of nanostructured materials synthesized in microemulsions. Fig. 2a and b shows the TEM photographs of the samples prepared respectively from microemulsions of w=5 and w=10 after aging for 48 h. From the figures, it is seen that when the w is as low as 5, only BaMoO4 nanoparticles with the diameter of 10F2 nm were obtained. By increasing the w value to 10, BaMoO4 nanofibers with the diameter of 25–32 nm were obtained. In contrast to the nanofibers shown in Fig. 1d, which were obtained from the microemulsion with the larger w value of 20, it is found that the diameter of the nanofibers is slightly increased with the increasing w value of microemulsions, while the change of the length of the nanofibers is no obvious. This is related to the different size of water droplet in microemulsions with various w values; that is, the larger of the w value is, the larger of the water droplet is.
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Fig. 1. TEM micrographs of BaMoO4 obtained in the microemulsion (w=20, [CTAB]=0.1 M, [BaCl2]=[Na2MoO4]=0.1 M) after aging for different time (t). The inset in panels c and d show the corresponding electron diffraction pattern. (a) t=5 min, (b) t=30 min, (c) t=4 h, (d) t=48 h.
Fig. 2. TEM micrographs of BaMoO4 obtained in w=5 (a) and w=10 (b) microemulsion ([CTAB]=0.1 M, [BaCl2]=[Na2MoO4]=0.1 M) after aging for 48 h.
Z. Li et al. / Materials Letters 59 (2005) 64–68
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Fig. 3. TEM micrographs of BaMoO4 obtained in microemulsion (w=20) after aging for 48 h (a) [CTAB]=0.1 M, [BaCl2]=[Na2MoO4]=0.05 M (b) [CTAB]=0.05 M, [BaCl2]=[Na2MoO4]=0.1 M.
Consequently, the BaMoO4 nanofibers with larger diameter can be obtained at larger w. 3.3. Effect of reactant and CTAB concentration on the morphologies of BaMoO4 We also studied the effect of other experimental conditions, such as the reactant concentration and CTAB concentration, on the evolution of BaMoO4 nanofibers. Fig. 3a shows TEM photographs of the sample obtained at 0.05 M reactant concentration after aging for 48 h, while the other experimental conditions are the same with those shown in Fig. 1d. As we can see, by decreasing the reactant concentration to 0.05 M, only the BaMoO4 nanoparticles with the diameter of 35F6 nm are formed. The aggregation of nanoparticles to form nanofibers depends on the availability of reactant or on the amount of formed nanoparticles. When the reactant concentration is reduced, the number of nanoparticles decreases. Consequently, the amount of nanoparticles cannot afford the aggregation of the nanoparticles to form nanofibers. Fig. 3b shows the TEM photograph of the sample obtained with the lower CTAB concentration of 0.05 M. The concentration of reactants in the droplet in reverse microemulsions (w=20) is 0.1 M. As shown in the figure, the samples obtained at this condition are all in the spherical shape with the diameter of 40F5 nm. This maybe mainly attributed to the decreased overall concentration of the reactants in the reverse microemulsions, which cannot result in the aggregation of BaMoO4 nanoparticles to form nanofibers.
4. Conclusion In this work, high-aspect-ratio, single crystal BaMoO4 nanofibers with diameters of about 30 nm and lengths up to 30 Am were successfully prepared in the reverse microemulsions formed by cationic surfactant CTAB. The crystal
growth of BaMoO4 nanofibers is followed by a directional aggregation process. The diameter and length of the nanofibers can be tuned by the aging time and the molar ratio of the water to surfactant. High reactant or CTAB concentration is favorable to produce BaMoO4 nanofibers, whereas only nanoparticles were obtained as their concentration is low.
Acknowledgement This work was supported by National Natural Science Foundation of China (20133030) and Ministry of Science and Technology (G2000078103).
References [1] G.R. Patzke, F.K. Krumeich, R. Nesper, Angew. Chem., Int. Ed. 41 (2002) 2446. [2] Y. Xia, P. Yang, Y. Sun, Y. Wu, B. Mayers, B. Gates, Y. Yin, F. Kim, H. Yan, Adv. Mater. 15 (2003) 353. [3] O. Harnack, C. Pacholski, H. Weller, A. Yasuda, J.M. Wessels, Nano Lett. 3 (2003) 1097. [4] J. Lee, W. Koh, W. Chae, Y. Kim, Chem. Commun. (2002) 138. [5] S. Yu, H. Cflfen, M. Antonietti, Adv. Mater. 15 (2003) 133. [6] J.Z. Liang, J. Appl. Polym. Sci. 83 (2002) 1547. [7] L. Qi, J. Ma, H. Cheng, Z. Zhao, J. Phys. Chem., B 101 (1997) 3460. [8] A.L. Prieto, M.S. Sander, M.S. Martin-Gonzalez, R. Gronsky, T. Sands, A.M. Stacy, J. Am. Chem. Soc. 1237 (2001) 160. [9] N.R.B. Coleman, N. O’Sullivan, K.M. Ryan, T.A. Crowley, M.A. Morris, T.R. Spalding, D.C Steytler, J.D. Holmes, J. Am. Chem. Soc. 123 (2001) 7010. [10] D. Kuang, A. Xu, Y. Fang, H. Ou, H. Liu, J. Cryst. Growth 244 (2002) 379. [11] C.S. Yang, D.D. Awschalom, G.D. Stucky, Chem. Mater. 14 (2002) 1277. [12] M. Cao, C. Hu, E. Wang, J. Am. Chem. Soc. 125 (2003) 11196. [13] F. Debuigne, L. Jeunieau, M. Wiame, J.B. Nagy, Langmuir 16 (2000) 7605. [14] M. Schwuger, K. Stickdom, R. Schomacker, Chem. Rev. 95 (1995) 849.
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[15] L.M. Gan, B. Liu, C.H. Chew, S.J. Xu, S.J. Chua, G.L. Loy, G.Q. Xu, Langmuir 13 (1997) 6427. [16] P. Feng, X. Bu, G.D. Stucky, D.J. Pine, J. Am. Chem. Soc. 122 (2000) 994. [17] J.D. Hopwood, S. Mann, Chem. Mater. 9 (1997) 1819. [18] M. Li, H. Schnablegger, S. Mann, Nature 402 (1999) 393. [19] G.D. Rees, R. Evans-Gowing, S.J. Hammond, B.H. Robinson, Langmuir 15 (1999) 1993. [20] M. Li, S. Mann, Langmuir 16 (2000) 7088. [21] H. Shi, L. Qi, J. Ma, H. Cheng, Chem. Commun. (2002) 1704. [22] S. Kwan, F. Kim, J. Akana, P. Yang, Chem. Commun. (2001) 447. [23] M.P. Pileni, Langmuir 17 (2001) 7476. [24] B.A. Simmons, S. Li, V.T. John, G.L. Mcpherson, A. Bose, W. Zhou, J. He, Nano Lett. 2 (2002) 263.
[25] C. Wang, D. Chen, T. Huang, Colloids Surf., A 189 (2001) 145. [26] M. Curri, A. Agostiano, L. Manna, M. Della Monica, M. Catalano, L. Chiavarone, V. Spagnolo, M. Lugara, J. Phys. Chem., B 104 (2000) 8391. [27] D. Chen, S. Wu, Chem. Mater. 12 (2000) 1354. [28] X. Fang, C. Yang, Colloid Interface Sci. 212 (1999) 242. [29] W.S. Cho, M. Yoshimura, Solid State Ionics 100 (1997) 143. [30] W.S. Cho, M. Yoshimura, Jpn. J. Appl. Phys., Part 2 35 (1996) L1521. [31] W.S. Cho, M. Yashima, M. Kakihana, A. Kudo, T. Sakata, M. Yoshimura, J. Am. Ceram. Soc. 80 (1997) 765. [32] C.T. Xia, V.M. Fuenzalida, J. Eur. Ceram. Soc. 23 (2003) 519. [33] A.M. Lejus, R. Collongues, in: E. Kaldis (Ed.), Current Topics in Materials Science, vol. 4, North-Holland Publishing, Amsterdam, 1980, p. 481.
Synthesis of single crystal BaMoO4 nanofibers in CTAB reverse microemulsions Zhonghao Li, Jimin Du, Jianling Zhang, Tiancheng Mu, Yanan Gao, Buxing Han*, Jing Chen, Jiawei Chen Center for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, PR China Available online 12 October 2004
Abstract High-aspect-ratio, single crystal BaMoO4 nanofibers with diameters of about 30 nm and lengths up to 30 Am were synthesized in cationic cetyltrimethylammonium bromide (CTAB) reverse microemulsions. The effects of different conditions such as the aging time, the molar ratio of water to surfactant (w), the reactant and CTAB concentration on the evolution of single crystal BaMoO4 nanofibers were discussed. Transmission electron microscope (TEM) and electron diffraction were used to characterize the morphology and the crystal structure of the prepared nanostructured BaMoO4 obtained at different conditions. D 2004 Elsevier B.V. All rights reserved. Keywords: BaMoO4; Nanofibers; CTAB; Microemulsions
1. Introduction In recent years, 1D nanostructures have attracted considerable attention due to their size-dependent properties and potential wide-ranging applications [1–4]. The preparation of high-aspect-ratio nanofibers is of great interest because these nanofibers are very promising in a myriad applications, such as the nanodevices and interconnects for molecular computing, scanning probe microscopy tips, and the polymer filler materials for the alteration of a material’s mechanical and rheological properties [5,6]. Various methods have been used to the preparation of different kind of inorganic nanorods and nanofibers [7–12]. Of these methods, the reverse micelles and microemulsions have been shown to be powerful in the synthesis of colloidal inorganic or organic nanoparticles [13–16]. The principal reason for using microemulsions is that particle shape and corresponding size distributions can be readily controlled by adjusting the molar ratio of water:oil:surfactant. In some * Corresponding author. Tel.: +86 10 62562821; fax: +86 10 62562821. E-mail address: [email protected] (B. Han). 0167-577X/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2004.09.017
cases, further growth and aggregation of the initially formed nanoparticles in microemulsions can result in the formation of nanowires. For example, A variety of 1D nanoscale materials such as CaCO3, BaCO3, BaSO4, CaSO4, BaCrO4, BaWO4, CdS, and Cu nanorods or nanowires have been successfully synthesized in the reverse micelle media [7,17– 24]. The reverse microemulsions used in synthesis of inorganic nanowires with larger lengths are usually formed by anionic surfactant AOT or nonionic surfactants. Cetyltrimethylammonium bromide (CTAB) is a typical cationic surfactant used to form reverse microemulsions. According to the literatures, many inorganic nanoparticle materials have been synthesized in CTAB reverse microemulsions [25–28]. Molybdates such as CaMoO4, SrMoO4, and BaMoO4 belong to the scheelite group, and the corresponding films of these materials have been prepared by the researchers [29–32]. Single crystals of these materials have been studied as hosts for lanthanide activated lasers [33]. Therefore, the preparation of nanoshaped BaMoO4 especially in 1 D dimension will broaden the application of BaMoO4 in the optical and ceramic fields in view of the size and shape dependent properties of the nanomaterials.
Z. Li et al. / Materials Letters 59 (2005) 64–68
In this paper, we report the fabrication of high-aspectratio single crystal BaMoO4 nanofibers with diameter of about 30 nm and length up to 30 Am in the reverse microemulsions formed by cationic surfactant CTAB.
2. Experimental 2.1. Materials CTAB, isooctane, n -pentanol, BaCl 2 d 2H 2 O and NaMoO4d 2H2O were all purchased from Beijing Chemical Reagent Factory. Sodium bis (2-ethylhexyl) sulfosuccinate (AOT) was obtained from Sigma. Double-distilled water was used in all the experiments. 2.2. Synthesis of BaMoO4 nanofibers in reverse microemulsion A quaternary microemulsion, CTAB/water/isooctane/npentanol, was selected for this study. A typical procedure for the formation of BaMoO4 nanofibers with larger length in the CTAB reverse microemulsions is as follows: The reverse microemulsions were prepared by solubilizing a suitable amount of aqueous solution containing Ba2+ or MoO42 ions into 0.1 M CTAB solution in 10 ml isooctane with 0.6 ml npentanol. Then equal volumes of the above two microemulsions were mixed quickly. The resulting solutions were aged without stirring at room temperature. Following the similar procedure, BaMoO4 nanofibers were also prepared at other conditions. 2.3. Characterization A Jeol-2010 transmission electron microscope (TEM) was used to characterize the morphology and structure of the products at an operating voltage of 200 kV. Samples for TEM analysis were prepared at different conditions by dropping a drop of the reverse microemulsions containing the products onto a Formvar-covered copper grid and drying in air at room temperature. Then the sample was washed for 5 s by immersing the grid in pure ethanol in order to obtain grids that were sufficiently thinly coated to allow penetration by the electron beam. Finally, the grid was removed and air-dried.
3. Results and discussion 3.1. Effect of aging time on the evolution of BaMoO4 nanofibers The effect of the aging time on the evolution of the obtained nanoparticles was investigated by using aging times of 5, 30 min, 4 and 48 h, TEM micrographs are shown in Fig. 1a–d. The concentration of Ba2+ or MoO42
65
in the droplet of reverse microemulsions (w =20, [CTAB]=0.1M) is 0.1 M. As shown in Fig. 1a, for the samples aged for a short time of 5 min, short BaMoO4 nanorods of very irregular morphologies are formed. As the aging time is increased to 30 min, the regular twodimensional nanorod of BaMoO4 with the diameter about 20 nm and length about 200 nm are formed (shown in Fig. 1b). When the samples are aged for the longer time of 4 h, the long nanofibers of BaMoO4 are obtained (shown in Fig. 1c). The bright spots and diffraction rings in the corresponding electron diffraction pattern suggest the presence of BaMoO4 polycrystals together with individual monocrystal for the nanofibers obtained (Fig. 1c). After aging for 48 h, the length of BaMoO4 nanofibers is increased up to 30 Am, with the diameter of 26–35 nm (Fig. 1d). From the figure it is also found that several nanofibers stick together to form a bundle in some areas. The electron diffraction patterns were recorded from different positions along the nanofibers. All the electron diffraction patterns indicate that the nanofiber formed is a single crystal with a tetragonal scheelite structure (Fig. 1d). These TEM observations of the crystal growth of the BaMoO4 nanowires in reverse microemulsions suggest that the nanowires could be formed by a directional aggregation process. The evolution of BaMoO4 nanofibers can be expressed as the following steps: First small nanoparticles of BaMoO4 formed in reverse microemulsions after mixing the reactant solutions and then the nanoparticles aggregated and grew to short nanorod and longer nanofibers through a directional aggregation process. The formation process of BaMoO4 nanofibres is similar to that of BaCO3 nanowires formed in C12E4 (tetraethylene glycol monododecyl ether) reverse microemulsions by Qi et al. [7]. 3.2. Effect of w value on the morphologies of BaMoO4 nanofibers The molar ratio of water to surfactant (w) is an important parameter which determines the property of the reverse microemulsions. In some cases the value of w can strongly influence the morphology of nanostructured materials synthesized in microemulsions. Fig. 2a and b shows the TEM photographs of the samples prepared respectively from microemulsions of w=5 and w=10 after aging for 48 h. From the figures, it is seen that when the w is as low as 5, only BaMoO4 nanoparticles with the diameter of 10F2 nm were obtained. By increasing the w value to 10, BaMoO4 nanofibers with the diameter of 25–32 nm were obtained. In contrast to the nanofibers shown in Fig. 1d, which were obtained from the microemulsion with the larger w value of 20, it is found that the diameter of the nanofibers is slightly increased with the increasing w value of microemulsions, while the change of the length of the nanofibers is no obvious. This is related to the different size of water droplet in microemulsions with various w values; that is, the larger of the w value is, the larger of the water droplet is.
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Fig. 1. TEM micrographs of BaMoO4 obtained in the microemulsion (w=20, [CTAB]=0.1 M, [BaCl2]=[Na2MoO4]=0.1 M) after aging for different time (t). The inset in panels c and d show the corresponding electron diffraction pattern. (a) t=5 min, (b) t=30 min, (c) t=4 h, (d) t=48 h.
Fig. 2. TEM micrographs of BaMoO4 obtained in w=5 (a) and w=10 (b) microemulsion ([CTAB]=0.1 M, [BaCl2]=[Na2MoO4]=0.1 M) after aging for 48 h.
Z. Li et al. / Materials Letters 59 (2005) 64–68
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Fig. 3. TEM micrographs of BaMoO4 obtained in microemulsion (w=20) after aging for 48 h (a) [CTAB]=0.1 M, [BaCl2]=[Na2MoO4]=0.05 M (b) [CTAB]=0.05 M, [BaCl2]=[Na2MoO4]=0.1 M.
Consequently, the BaMoO4 nanofibers with larger diameter can be obtained at larger w. 3.3. Effect of reactant and CTAB concentration on the morphologies of BaMoO4 We also studied the effect of other experimental conditions, such as the reactant concentration and CTAB concentration, on the evolution of BaMoO4 nanofibers. Fig. 3a shows TEM photographs of the sample obtained at 0.05 M reactant concentration after aging for 48 h, while the other experimental conditions are the same with those shown in Fig. 1d. As we can see, by decreasing the reactant concentration to 0.05 M, only the BaMoO4 nanoparticles with the diameter of 35F6 nm are formed. The aggregation of nanoparticles to form nanofibers depends on the availability of reactant or on the amount of formed nanoparticles. When the reactant concentration is reduced, the number of nanoparticles decreases. Consequently, the amount of nanoparticles cannot afford the aggregation of the nanoparticles to form nanofibers. Fig. 3b shows the TEM photograph of the sample obtained with the lower CTAB concentration of 0.05 M. The concentration of reactants in the droplet in reverse microemulsions (w=20) is 0.1 M. As shown in the figure, the samples obtained at this condition are all in the spherical shape with the diameter of 40F5 nm. This maybe mainly attributed to the decreased overall concentration of the reactants in the reverse microemulsions, which cannot result in the aggregation of BaMoO4 nanoparticles to form nanofibers.
4. Conclusion In this work, high-aspect-ratio, single crystal BaMoO4 nanofibers with diameters of about 30 nm and lengths up to 30 Am were successfully prepared in the reverse microemulsions formed by cationic surfactant CTAB. The crystal
growth of BaMoO4 nanofibers is followed by a directional aggregation process. The diameter and length of the nanofibers can be tuned by the aging time and the molar ratio of the water to surfactant. High reactant or CTAB concentration is favorable to produce BaMoO4 nanofibers, whereas only nanoparticles were obtained as their concentration is low.
Acknowledgement This work was supported by National Natural Science Foundation of China (20133030) and Ministry of Science and Technology (G2000078103).
References [1] G.R. Patzke, F.K. Krumeich, R. Nesper, Angew. Chem., Int. Ed. 41 (2002) 2446. [2] Y. Xia, P. Yang, Y. Sun, Y. Wu, B. Mayers, B. Gates, Y. Yin, F. Kim, H. Yan, Adv. Mater. 15 (2003) 353. [3] O. Harnack, C. Pacholski, H. Weller, A. Yasuda, J.M. Wessels, Nano Lett. 3 (2003) 1097. [4] J. Lee, W. Koh, W. Chae, Y. Kim, Chem. Commun. (2002) 138. [5] S. Yu, H. Cflfen, M. Antonietti, Adv. Mater. 15 (2003) 133. [6] J.Z. Liang, J. Appl. Polym. Sci. 83 (2002) 1547. [7] L. Qi, J. Ma, H. Cheng, Z. Zhao, J. Phys. Chem., B 101 (1997) 3460. [8] A.L. Prieto, M.S. Sander, M.S. Martin-Gonzalez, R. Gronsky, T. Sands, A.M. Stacy, J. Am. Chem. Soc. 1237 (2001) 160. [9] N.R.B. Coleman, N. O’Sullivan, K.M. Ryan, T.A. Crowley, M.A. Morris, T.R. Spalding, D.C Steytler, J.D. Holmes, J. Am. Chem. Soc. 123 (2001) 7010. [10] D. Kuang, A. Xu, Y. Fang, H. Ou, H. Liu, J. Cryst. Growth 244 (2002) 379. [11] C.S. Yang, D.D. Awschalom, G.D. Stucky, Chem. Mater. 14 (2002) 1277. [12] M. Cao, C. Hu, E. Wang, J. Am. Chem. Soc. 125 (2003) 11196. [13] F. Debuigne, L. Jeunieau, M. Wiame, J.B. Nagy, Langmuir 16 (2000) 7605. [14] M. Schwuger, K. Stickdom, R. Schomacker, Chem. Rev. 95 (1995) 849.
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