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Fabrication of polycrystalline lanthanum manganite (LaMnO3) nanofibers by electrospinning
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Materials Letters 62 (2008) 470 – 472 www.elsevier.com/locate/matlet
Fabrication of polycrystalline lanthanum manganite (LaMnO3) nanofibers by electrospinning Xianfeng Zhou a,b , Yong Zhao b , Xinyu Cao b , Yanfeng Xue a , Dapeng Xu a , Lei Jiang b , Wenhui Su a,c,⁎ a College of Physics, Jilin University, Changchun 130023, PR China Center for Molecular Sciences, Institute of Chemistry Chinese Academy of Sciences, Beijing 100080, PR China Center for the Condensed Matter Science and Technology, Harbin Institute of Technology, Harbin,150001, PR China b
c
Received 10 March 2007; accepted 27 May 2007 Available online 2 June 2007
Abstract Lanthanum manganite (LaMnO3) nanofibers were successfully fabricated by electrospinning utilizing sol–gel precursors. Polycrystalline cubic-perovskite structure LaMnO3 fibers of 50–100 nm were obtained by calcination of the inorganic/organic hybrid fibers at 600 °C for 1 h. The XRD results showed that the grain size of the fibers increased significantly with the increase of calcinations temperature. The average diameter of crystal grains was 17 nm after calcined at 400 °C for 2 h, then grew to 20 nm after heated up to 600 °C for 1 h. The morphology, microstructure, crystal structure and thermal analysis were investigated by SEM, TEM, XRD and TG-DSC, respectively. © 2007 Elsevier B.V. All rights reserved. Keywords: Perovskites; Sol–gel preparation; Nanofibers; Electrospinning; Calcinations
1. Introduction Perovskite-type complex oxides are well known as functional inorganic materials for application as electrode materials in solid oxide fuel cells (SOFCs) [1], gas sensors, membranes for separation processes and catalysts etc. [2,3]. Especially, Lanthanum manganate (LaMnO3) and related compounds have attracted much attention due to their excellent electrical, magnetic and catalytic properties. It is well known that nanosized materials exhibit unique physical and chemical properties compared with those of conventional bulk materials because of its smaller size and large specific surface areas [4,5]. In particular, the preparation of one-dimensional (1D) ceramic nanostructures such as fibers, wires, and rods has received great interest owing to their potential applications in many technologically important areas such as electronics, photonics, mechanics and magnetics [6–8]. Recently, there has been an intense research on electrospinning of ceramics
since it is a straightforward and versatile way to synthesize 1D nanostructure. This technique has been fabricated for a large number of ultrafine fibers or nanofibers from a variety of materials, such as polymers, composites, and ceramics [9]. The ceramic nanofibers synthesized via electrospinning were reported first in 2002 [10]. Since then, this technique has been used to prepare more than 20 varieties of ceramic nanofibers or ultrafine fibers that include, for example, TiO2, ZnO, Al2O3, BaTiO3 and YBa2Cu3O7 − δ etc. [11–15]. A typical electrospinning procedure consists of three major steps: (1) preparation of an inorganic sol or a solution containing a polymer together with an alkoxide or salt; (2) electrospinning of the solution to prepare nanofibers of polymer/inorganic composite; (3) calcination of the composite fibers to obtain the desired ceramic nanofibers. In this paper, we describe the preparation and characterization of LaMnO3 nanofibers produced by electrospinning of La, Mn acetates/PVA sol solution and following heat treatments. 2. Experimental
⁎ Corresponding author. College of Physics, Jilin University, Changchun 130023, PR China. Tel.: +86 431 88499048; fax: +86 431 88499039. E-mail address: [email protected] (W. Su). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.05.063
Based on conventional sol–gel process, lanthanum acetate and manganese acetate with 1:1 molar ratio of La: Mn was
X. Zhou et al. / Materials Letters 62 (2008) 470–472
471
Fig. 1. SEM images of LaMnO3 nanofibers. (a) as-prepared; (b) after calcination at 400 °C for 2 h; (c) after calcination at 600 °C for 1 h.
used as starting materials. In a typical procedure, 1.715 g of La(CH3COO)3·1.5H2O (Alfa Aesar) and 1.225 g of Mn (CH3COO)2·4H2O (Beijing Chemical Co. Ltd.) were dissolved in 10 mL of deionized water. The precursor solution was stirring for 2 h, then put it into the 10 mL aqueous PVA (ACROS ORGANICS, Mw ≈ 88,000) solution of 10 wt.% and was stirring for 24 h. The mixture was loaded into a plastic syringe. A piece of flat aluminum foil was placed ∼ 15 cm below the tip of the needle to collect the nanofibers, which was held at 30° horizontal angle. Non-woven mat structure of LaMnO3 nanofibers was fabricated by applied electric voltage of 15 kV between the collector and the needle tip. The electrospinning was conducted in air. Finally, the electrospinning nanofibers were calcined at 400 °C for 2 h in order to remove PVA and volatile components, and then calcined the fibers film in air at 600 °C for 1 h to obtain LaMnO3 nanofibers. The heating rate is 2 °C/min in the above two processes. The SEM images were recorded by JEOL JSM-6700F field emission electron microscope. Powder X-ray diffraction patterns were obtained from Rigaku D/max-2500 X-ray diffractometer using Cu Kα radiation. The TEM measurement was performed using a JEM-2000EX ELECTRON MICROSCOPE instrument. TG-DSC was attained on a NETZSCH STA 409PC thermo-analyzer in air.
Fig. 2. XRD patterns of LaMnO3 nanofibers. (a) as-prepared; (b) after calcinated at 400 °C for 2 h; (c) after calcinated at 600 °C for 1 h.
3. Results and discussion SEM photographs of the hybrid fibers and the fibers obtained after calcinated at 400 °C and 600 °C were presented in Fig. 1(a, b, and c) respectively. The results show that the as-prepared hybrid fibers are smooth and their diameters range from 100 to 200 nm (Fig. 1a). After calcinated at 400 °C, the hybrid fibers surface shrinked and became porous due to the decomposition of PVA and crystallization of lanthanum manganate (Fig. 1b). When calcination temperature was increased to 600 °C, the diameters of nanofibers ranged from 50 to 100 nm, which is smaller than the hybrid fibers due to complete removal of PVA from the hybrid fibers (Fig. 1c). The XRD patterns of the hybrid fibers and the fibers obtained after calcinated at 400 °C and 600 °C are shown in Fig. 2(a, b, and c),
Fig. 3. TEM image with corresponding ED of LaMnO3 nanofibers after calcinated at 400 °C for 2 h (a) and 600 °C for 1 h (b).
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X. Zhou et al. / Materials Letters 62 (2008) 470–472
sition of lanthanum acetate and manganese acetate and the combustion of PVA [16], which was in agreement with the weight loss of ∼ 20% in the TG curve. This combustion accompanied the formation of LaMnO3 with perovskite-type structure. After 550 °C, there was no change in weight loss, which indicated the formation of pure LaMnO3.
4. Conclusion
Fig. 4. TG-DSC curves of hybrid fibers of LaMnO3/PVA.
respectively. The results manifested that there is no LaMnO3 phase in the as-prepared hybrid fibers (Fig. 2a), and LaMnO3 emerge in the fibers after calcinated at 400 °C for 2 h (Fig. 2b), the sample completely crystallized after calcinated at 600 °C for 1 h (Fig. 2c). The peaks in Fig. 2c can be indexed to the cubic structure of LaMnO3, and the calculated lattice constant is a = 0.3875 nm and Volume = 0.05817 nm3, matching well the literature values of a = 0.3880 nm and Volume = 0.05841 nm3 (JCPDS card No. 75-0440). The grain size was calculated by Scherrer formula. The calculated results showed that the grain size of the fibers increased significantly with the increase of calcinations temperature. The average diameter of crystal grains was 17 nm after calcined at 400 °C for 2 h, then grew to 20 nm after heated up to 600 °C for 1 h. The TEM images with corresponding electron diffractions (ED) of the LaMnO3 nanofibers after calcinated in air at 400 °C for 2 h and 600 °C for 1 h were shown in Fig. 3a and b respectively. The results verified that the nanofibers are porous and the average size of LaMnO3 grains grew approximately from 15 nm (Fig. 3a) to 20 nm (Fig. 3b) in diameter, which agrees well with XRD results. The ED of LaMnO3 nanofibers showed the central halo and faint diffused rings, which revealed that it is essentially polycrystalline structure. The simultaneous TG/DSC recording, performed at a heating rate of 5 °C/min, showed that thermal decomposition of hybrid nanofibers could be largely divided into three degradation steps and a perovskitetype structure finally formed (Fig. 4). The first weight loss of ∼ 7%, started at 122 °C, mainly involved dehydration of the hybrid fibers. The second weight loss of ∼ 38%, started at 260 °C, was predominantly due to decomposition of the acetate ligands [16]. The following weight loss of ∼ 20% from 360 °C to 413 °C corresponded to further degradation of unsaturated backbone residues and the burn of organic composites. As observed in the DSC curve, the prominent exothermic peak at about 393 °C was associated with the continuous decompo-
Polycrystalline lanthanum manganite nanofibers with cubicperovskite structure were successfully fabricated at low temperatures by the electrospinning technique in combination with sol–gel method. The surface morphology and the average diameters of the ceramic nanofibers depended on the calcinations temperature. We demonstrated here that the electrospinning technique provided a simple and versatile method for synthesizing nanofibers of Perovskite-type complex oxides. Acknowledgements This work was supported by grants from the National Science Foundation of China (No. 30374046). References [1] E.P. Vyshatko, V. Kharton, A.L. Shaula, E.N. Naumovich, F.M.B. Marqnes, J. Mater. Res. Bull. 38 (2003) 185. [2] M. Alifanti, J. Kirchnerova, B. Delmon, J. Appl. Catal. A, Gen. 245 (2003) 231. [3] R. Spinicci, A. Tofanari, A. Delmastro, D. Mazza, S. Ronchetti, J. Mater. Chem. Phys. 78 (2002) 393. [4] G.H. Lee, S.H. Hoh, J.W. Jeong, B.J. Choi, S.H. Kim, H.C. Ri, J. Am. Chem. Soc. 124 (2002) 12094. [5] E.F. HiLinski, P.A. Lucas, Y. Wang, J. Chem. Phys. 89 (1998) 3435. [6] Y.N. Xia, P. Yang, Y. Sun, Y. Wu, B. Mayers, B. Gates, Y. Yin, F. Kim, H. Yan, Adv. Mater. 15 (2003) 353. [7] M. Law, J. Goldberger, P. Yang, Annu. Rev. Mater. Res. 34 (2004) 83. [8] Z.L. Wang, Annu. Rev. Phys. Chem. 55 (2004) 159. [9] D. Li, Y.N. Xia, Adv. Mater. 16 (2004) 1151. [10] C.L. Shao, H.Y. Kim, J. Gong, D.K. Lee, Nanotechnology 13 (2002) 635. [11] S. Madhugiri, B. Sun, P.G. smirniotis, J.P. Ferraris, K.J. Balkus, Micropor. Mesopor. Mater. 69 (2004) 77. [12] X.H. Yang, C.L. Shao, H.Y. Guan, X.L. Li, J. Gong, Inorg. Chem. Commun. 7 (2004) 176. [13] G. Larsen, R. Velarde-Ortiz, K. Minchow, A. Barrero, I.G. Loscertales, J. Am. Chem. Soc. 125 (2003) 1154. [14] J. Yuh, J.C. Nino, W.M. Sigmund, Mater. Lett. 59 (2005) 3645. [15] X.M. Cui, W.S. Lyoo, W.K. Son, D.H. Park, J.H. Choy, T.S. Lee, W.H. Park, Supercond. Sci. Technol. 19 (2006) 1264. [16] S. Bilger, E. Syskakis, A. Naoumidis, H. Nickel, J. Am. Ceram. Soc. 75 (1992) 964.
Materials Letters 62 (2008) 470 – 472 www.elsevier.com/locate/matlet
Fabrication of polycrystalline lanthanum manganite (LaMnO3) nanofibers by electrospinning Xianfeng Zhou a,b , Yong Zhao b , Xinyu Cao b , Yanfeng Xue a , Dapeng Xu a , Lei Jiang b , Wenhui Su a,c,⁎ a College of Physics, Jilin University, Changchun 130023, PR China Center for Molecular Sciences, Institute of Chemistry Chinese Academy of Sciences, Beijing 100080, PR China Center for the Condensed Matter Science and Technology, Harbin Institute of Technology, Harbin,150001, PR China b
c
Received 10 March 2007; accepted 27 May 2007 Available online 2 June 2007
Abstract Lanthanum manganite (LaMnO3) nanofibers were successfully fabricated by electrospinning utilizing sol–gel precursors. Polycrystalline cubic-perovskite structure LaMnO3 fibers of 50–100 nm were obtained by calcination of the inorganic/organic hybrid fibers at 600 °C for 1 h. The XRD results showed that the grain size of the fibers increased significantly with the increase of calcinations temperature. The average diameter of crystal grains was 17 nm after calcined at 400 °C for 2 h, then grew to 20 nm after heated up to 600 °C for 1 h. The morphology, microstructure, crystal structure and thermal analysis were investigated by SEM, TEM, XRD and TG-DSC, respectively. © 2007 Elsevier B.V. All rights reserved. Keywords: Perovskites; Sol–gel preparation; Nanofibers; Electrospinning; Calcinations
1. Introduction Perovskite-type complex oxides are well known as functional inorganic materials for application as electrode materials in solid oxide fuel cells (SOFCs) [1], gas sensors, membranes for separation processes and catalysts etc. [2,3]. Especially, Lanthanum manganate (LaMnO3) and related compounds have attracted much attention due to their excellent electrical, magnetic and catalytic properties. It is well known that nanosized materials exhibit unique physical and chemical properties compared with those of conventional bulk materials because of its smaller size and large specific surface areas [4,5]. In particular, the preparation of one-dimensional (1D) ceramic nanostructures such as fibers, wires, and rods has received great interest owing to their potential applications in many technologically important areas such as electronics, photonics, mechanics and magnetics [6–8]. Recently, there has been an intense research on electrospinning of ceramics
since it is a straightforward and versatile way to synthesize 1D nanostructure. This technique has been fabricated for a large number of ultrafine fibers or nanofibers from a variety of materials, such as polymers, composites, and ceramics [9]. The ceramic nanofibers synthesized via electrospinning were reported first in 2002 [10]. Since then, this technique has been used to prepare more than 20 varieties of ceramic nanofibers or ultrafine fibers that include, for example, TiO2, ZnO, Al2O3, BaTiO3 and YBa2Cu3O7 − δ etc. [11–15]. A typical electrospinning procedure consists of three major steps: (1) preparation of an inorganic sol or a solution containing a polymer together with an alkoxide or salt; (2) electrospinning of the solution to prepare nanofibers of polymer/inorganic composite; (3) calcination of the composite fibers to obtain the desired ceramic nanofibers. In this paper, we describe the preparation and characterization of LaMnO3 nanofibers produced by electrospinning of La, Mn acetates/PVA sol solution and following heat treatments. 2. Experimental
⁎ Corresponding author. College of Physics, Jilin University, Changchun 130023, PR China. Tel.: +86 431 88499048; fax: +86 431 88499039. E-mail address: [email protected] (W. Su). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.05.063
Based on conventional sol–gel process, lanthanum acetate and manganese acetate with 1:1 molar ratio of La: Mn was
X. Zhou et al. / Materials Letters 62 (2008) 470–472
471
Fig. 1. SEM images of LaMnO3 nanofibers. (a) as-prepared; (b) after calcination at 400 °C for 2 h; (c) after calcination at 600 °C for 1 h.
used as starting materials. In a typical procedure, 1.715 g of La(CH3COO)3·1.5H2O (Alfa Aesar) and 1.225 g of Mn (CH3COO)2·4H2O (Beijing Chemical Co. Ltd.) were dissolved in 10 mL of deionized water. The precursor solution was stirring for 2 h, then put it into the 10 mL aqueous PVA (ACROS ORGANICS, Mw ≈ 88,000) solution of 10 wt.% and was stirring for 24 h. The mixture was loaded into a plastic syringe. A piece of flat aluminum foil was placed ∼ 15 cm below the tip of the needle to collect the nanofibers, which was held at 30° horizontal angle. Non-woven mat structure of LaMnO3 nanofibers was fabricated by applied electric voltage of 15 kV between the collector and the needle tip. The electrospinning was conducted in air. Finally, the electrospinning nanofibers were calcined at 400 °C for 2 h in order to remove PVA and volatile components, and then calcined the fibers film in air at 600 °C for 1 h to obtain LaMnO3 nanofibers. The heating rate is 2 °C/min in the above two processes. The SEM images were recorded by JEOL JSM-6700F field emission electron microscope. Powder X-ray diffraction patterns were obtained from Rigaku D/max-2500 X-ray diffractometer using Cu Kα radiation. The TEM measurement was performed using a JEM-2000EX ELECTRON MICROSCOPE instrument. TG-DSC was attained on a NETZSCH STA 409PC thermo-analyzer in air.
Fig. 2. XRD patterns of LaMnO3 nanofibers. (a) as-prepared; (b) after calcinated at 400 °C for 2 h; (c) after calcinated at 600 °C for 1 h.
3. Results and discussion SEM photographs of the hybrid fibers and the fibers obtained after calcinated at 400 °C and 600 °C were presented in Fig. 1(a, b, and c) respectively. The results show that the as-prepared hybrid fibers are smooth and their diameters range from 100 to 200 nm (Fig. 1a). After calcinated at 400 °C, the hybrid fibers surface shrinked and became porous due to the decomposition of PVA and crystallization of lanthanum manganate (Fig. 1b). When calcination temperature was increased to 600 °C, the diameters of nanofibers ranged from 50 to 100 nm, which is smaller than the hybrid fibers due to complete removal of PVA from the hybrid fibers (Fig. 1c). The XRD patterns of the hybrid fibers and the fibers obtained after calcinated at 400 °C and 600 °C are shown in Fig. 2(a, b, and c),
Fig. 3. TEM image with corresponding ED of LaMnO3 nanofibers after calcinated at 400 °C for 2 h (a) and 600 °C for 1 h (b).
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X. Zhou et al. / Materials Letters 62 (2008) 470–472
sition of lanthanum acetate and manganese acetate and the combustion of PVA [16], which was in agreement with the weight loss of ∼ 20% in the TG curve. This combustion accompanied the formation of LaMnO3 with perovskite-type structure. After 550 °C, there was no change in weight loss, which indicated the formation of pure LaMnO3.
4. Conclusion
Fig. 4. TG-DSC curves of hybrid fibers of LaMnO3/PVA.
respectively. The results manifested that there is no LaMnO3 phase in the as-prepared hybrid fibers (Fig. 2a), and LaMnO3 emerge in the fibers after calcinated at 400 °C for 2 h (Fig. 2b), the sample completely crystallized after calcinated at 600 °C for 1 h (Fig. 2c). The peaks in Fig. 2c can be indexed to the cubic structure of LaMnO3, and the calculated lattice constant is a = 0.3875 nm and Volume = 0.05817 nm3, matching well the literature values of a = 0.3880 nm and Volume = 0.05841 nm3 (JCPDS card No. 75-0440). The grain size was calculated by Scherrer formula. The calculated results showed that the grain size of the fibers increased significantly with the increase of calcinations temperature. The average diameter of crystal grains was 17 nm after calcined at 400 °C for 2 h, then grew to 20 nm after heated up to 600 °C for 1 h. The TEM images with corresponding electron diffractions (ED) of the LaMnO3 nanofibers after calcinated in air at 400 °C for 2 h and 600 °C for 1 h were shown in Fig. 3a and b respectively. The results verified that the nanofibers are porous and the average size of LaMnO3 grains grew approximately from 15 nm (Fig. 3a) to 20 nm (Fig. 3b) in diameter, which agrees well with XRD results. The ED of LaMnO3 nanofibers showed the central halo and faint diffused rings, which revealed that it is essentially polycrystalline structure. The simultaneous TG/DSC recording, performed at a heating rate of 5 °C/min, showed that thermal decomposition of hybrid nanofibers could be largely divided into three degradation steps and a perovskitetype structure finally formed (Fig. 4). The first weight loss of ∼ 7%, started at 122 °C, mainly involved dehydration of the hybrid fibers. The second weight loss of ∼ 38%, started at 260 °C, was predominantly due to decomposition of the acetate ligands [16]. The following weight loss of ∼ 20% from 360 °C to 413 °C corresponded to further degradation of unsaturated backbone residues and the burn of organic composites. As observed in the DSC curve, the prominent exothermic peak at about 393 °C was associated with the continuous decompo-
Polycrystalline lanthanum manganite nanofibers with cubicperovskite structure were successfully fabricated at low temperatures by the electrospinning technique in combination with sol–gel method. The surface morphology and the average diameters of the ceramic nanofibers depended on the calcinations temperature. We demonstrated here that the electrospinning technique provided a simple and versatile method for synthesizing nanofibers of Perovskite-type complex oxides. Acknowledgements This work was supported by grants from the National Science Foundation of China (No. 30374046). References [1] E.P. Vyshatko, V. Kharton, A.L. Shaula, E.N. Naumovich, F.M.B. Marqnes, J. Mater. Res. Bull. 38 (2003) 185. [2] M. Alifanti, J. Kirchnerova, B. Delmon, J. Appl. Catal. A, Gen. 245 (2003) 231. [3] R. Spinicci, A. Tofanari, A. Delmastro, D. Mazza, S. Ronchetti, J. Mater. Chem. Phys. 78 (2002) 393. [4] G.H. Lee, S.H. Hoh, J.W. Jeong, B.J. Choi, S.H. Kim, H.C. Ri, J. Am. Chem. Soc. 124 (2002) 12094. [5] E.F. HiLinski, P.A. Lucas, Y. Wang, J. Chem. Phys. 89 (1998) 3435. [6] Y.N. Xia, P. Yang, Y. Sun, Y. Wu, B. Mayers, B. Gates, Y. Yin, F. Kim, H. Yan, Adv. Mater. 15 (2003) 353. [7] M. Law, J. Goldberger, P. Yang, Annu. Rev. Mater. Res. 34 (2004) 83. [8] Z.L. Wang, Annu. Rev. Phys. Chem. 55 (2004) 159. [9] D. Li, Y.N. Xia, Adv. Mater. 16 (2004) 1151. [10] C.L. Shao, H.Y. Kim, J. Gong, D.K. Lee, Nanotechnology 13 (2002) 635. [11] S. Madhugiri, B. Sun, P.G. smirniotis, J.P. Ferraris, K.J. Balkus, Micropor. Mesopor. Mater. 69 (2004) 77. [12] X.H. Yang, C.L. Shao, H.Y. Guan, X.L. Li, J. Gong, Inorg. Chem. Commun. 7 (2004) 176. [13] G. Larsen, R. Velarde-Ortiz, K. Minchow, A. Barrero, I.G. Loscertales, J. Am. Chem. Soc. 125 (2003) 1154. [14] J. Yuh, J.C. Nino, W.M. Sigmund, Mater. Lett. 59 (2005) 3645. [15] X.M. Cui, W.S. Lyoo, W.K. Son, D.H. Park, J.H. Choy, T.S. Lee, W.H. Park, Supercond. Sci. Technol. 19 (2006) 1264. [16] S. Bilger, E. Syskakis, A. Naoumidis, H. Nickel, J. Am. Ceram. Soc. 75 (1992) 964.