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A novel lanthanum hydroxide nanostructure prepared by cathodic electrodeposition
Materials Letters 65 (2011) 1466–1468
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
A novel lanthanum hydroxide nanostructure prepared by cathodic electrodeposition Mustafa Aghazadeh a,b, Ahmad Nozad Golikand b,⁎, Mehdi Ghaemi c, Taher Yousefi b a b c
Department of Chemistry, Tarbiat Modares University, P.O. Box: 13145-185, Tehran, Iran Material Research School, NSTRI, P.O. Box: 14395-836, Tehran, Iran Department of Chemistry, Science Faculty, Golestan University, P.O. Box: 49138-15739, Gorgan, Iran
a r t i c l e
i n f o
Article history: Received 27 December 2010 Accepted 10 February 2011 Available online 15 February 2011 Keywords: Nanocrystalline materials Electrodeposition La(OH)3 FTIR
a b s t r a c t A novel and interesting nanostructure of La(OH)3 was prepared by electrochemical method under mild conditions without any hard templates and surfactants. In this method, La(OH)3 was galvanostatically deposited from low-temperature nitrate bath on the steel substrate by electrogeneration of base. X-ray results showed that the obtained deposit has single crystalline hexagonal phase of La(OH)3. Morphological characterization revealed that the product has compact morphology with capsule-like structures having approximately an average diameter of 15 nm and the length of up to 50 nm. The results showed that lowtemperature cathodic electrodeposition can be recognized as an easy and facile method for the synthesis of La (OH)3 nanocapsules. © 2011 Elsevier B.V. All rights reserved.
1. Introduction There has been growing interest in the study of nanomaterials in recent years due to their potential applications in many different areas of science and technology. Particular attention has been given to the design of methods for preparation of one or two-dimensional (1D or 2D) metal oxide and hydroxide structures at nanoscale. Nanostructures of these materials are essential in the design of catalysts, sensors and others devices [1–3]. Lanthanum hydroxide, La(OH)3, is of great research interest for being used in many fields such as high potential oxide ceramics, superconductive materials, hydrogen storage materials, electrode materials, etc. Furthermore, La(OH)3 has long been used as a catalyst and sorbent material [4,5]. In the recent years, a variety of La(OH)3 nanostructures such as nanotubes [6,7], nanorods [7–12], nanowires [13] and nanospheres [14] have been reported by electrochemical, hydrothermal, sol–gel and solvothermal methods. Electrochemical synthesis, i.e. cathodic electrodeposition, can be considered as an easy, clean and effective method for preparation of La(OH)3 nanostructures. For example, high quality arrays of La(OH)3 nanotubes have been successfully fabricated by cathodic electrodeposition process using anodic alumina membrane templates [6]. Also, Zheng et al. [7] have recently reported that large-scale La(OH)3 nanorod/nanotube arrays have been grown directly on Cu substrates via a template-free electrodeposition and selective etching process. Furthermore, very recently, hexagonal and vertically aligned La(OH)3 nanorod arrays have been fabricated in a large scale via electrodeposition method without using any hard
⁎ Corresponding author. Tel./fax: +98 21 82063112. E-mail address: [email protected] (A.N. Golikand). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.02.039
templates and surfactants [12]. Previously, we reported the preparation of Y2O3 nanospheres by cathodic electrodeposition from chloride bath at room temperature [15]. In the present work, we report a novel and new-type nanostructure of lanthanum hydroxide prepared by an easy, one-step, template-free and versatile electrochemical method. In this method, La(OH)3 nanostructures are galvanostatically electrodeposited from lowtemperature nitrate bath by cathodic electrodeposition, i.e. electrogeneration of base (OH−) at the cathode surface. Morphological analysis revealed that the prepared hydroxide has capsule-like structure at nanoscale. It is noteworthy that to our knowledge, there are no reports for the synthesis of this type of nanostructures of metal hydroxides or oxides in the literature. In fact, to our knowledge, this is the first report on the synthesis of nanocapsules as a new type of La(OH)3 nanostructures. 2. Experimental procedure La(OH)3 was obtained by cathodic electrodeposition from an additive free aqueous 0.005 M La(NO3)3 bath. The bath temperature was fixed at 10 °C. The electrochemical cell included a cathodic steel substrate (316 L, 100 × 50 × 0.5 mm) centered between the two parallel graphite anodes. Deposition experiments were carried out in galvanostatic mode at a current density of 1 mA cm− 2 and without stirring. After drying in air for 48 h, the deposit was scraped from the steel electrodes. Crystal structure of obtained deposit was determined by X-ray diffraction (XRD, Phillips, PW-1800). Morphological characterization was investigated by scanning electron microscopy (SEM, Philips 515) and transmission electron microscopy (TEM, Phillips EM 2085) with an accelerating voltage of 100 kV. IR spectrum was obtained with a Bruker Vector 22 FT-IR spectrometer.
M. Aghazadeh et al. / Materials Letters 65 (2011) 1466–1468
1467
3. Results and discussion -0.6
Cathodic electrodeposition of La(OH)3 is achieved at the cathode through a mechanism of base (OH−) electrogeneration in nitrate solution, according to the possible cathodic reactions [16]. These reactions include the nitrate ions, dissolved oxygen and water reduction (Eqs. (1)–(4)):
Potential / V
-0.7
-0.8
-0.9
−
−
−
−
NO3 þ H2 O þ 2e →NO2 þ 2OH
ð1Þ
-1.0 −
−
þ
NO3 þ 7H2 O þ 8e →NH4 þ 10OH
−
ð2Þ
-1.1 0
100
200
300
400
500
600
−
O2 þ 2H2 O þ 4e →4OH
Time / S Fig. 1. Variations of the potential as a function of time during the electrodeposition of La (OH)3 at 1 mA cm− 2.
−
−
−
2H2 O þ 2e →H2 þ 2OH
ð3Þ ð4Þ
The above reactions result in an increase of the pH near the steel electrode surface. By increasing OH− concentration, La(OH)3 will form and deposit on the cathode electrode:
211
101
Intensity (a.u.)
3þ
110
La
201
−
þ 3OH →LaðOHÞ3 ðsÞ
ð5Þ
321
100
200
311
112
210
302 202
10
20
30
40
50
60
70
80
2θ (deg.) Fig. 2. X-ray diffraction pattern of the as-prepared La(OH)3.
In this work, the electrodeposition experiments were performed in the galvanostatic regime, applying current density of 1 mA cm− 2. Fig. 1 shows the variation of the potential during this process. Considering the potential value (− 1.03 V), it seems that the reduction of water (Eq. (4)) has a major role in the production of OH− at the applied current density. The XRD pattern of the deposit is shown in Fig. 2. All diffraction peaks can be indexed as the hexagonal La(OH)3 with the lattice constants of a = 6.528 Å and c = 3.858 Å, which are very consistent with the values in the standard card (JCPDS 41-4019). The broadening of these diffraction peaks indicated that the crystal size of La(OH)3
Fig. 3. SEM (a, b) and TEM (c, d) images of the as-prepared La(OH)3.
M. Aghazadeh et al. / Materials Letters 65 (2011) 1466–1468
Transmittance (a.u.)
1468
850 1635
1048 560 647
3605 3440
1476
during the electrodeposition process. The peaks at about 1476 cm− 1 and 1048 cm− 1 can be attributed to the carbonate group, which originate from the reaction of La(OH)3 with CO2 from air during the analysis. It is worth noting that further works are underway on the synthesis of ordered and oriented nanocapsules with uniformity in diameter and length. Furthermore, the nano-capsules of the other metal oxides and hydroxides such as Y(OH)3, ZrO2 and NiO have been synthesized by our method and their manuscripts are being developed.
1377
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1) Fig. 4. FTIR spectrum of the as-prepared La(OH)3.
particles is very fine. Morphological characteristics of as-prepared La (OH)3 are shown in Fig. 3. The SEM images of La(OH)3 only represented a compact morphology. Further magnifications by TEM (Fig. 3c and d) disclosed that the underlying morphologies are composed exclusively of disoriented bundles of capsules. It is observable from this sub-micrometer scale that the compact structure is an aggregate of the particles arranged in different orientations. The roughly oriented capsule-like particles tend to grow in groups, parallel to the surface (Fig. 3b and c). The size of capsules is not uniform. This lack of uniformity is completely evident in the capsules' length (Fig. 3d). The diameter and length of the nanocapsules range from 10 to 20 nm and 20 to 50 nm, respectively, as shown in the TEM image (Fig. 3d). FTIR spectrum of the as-prepared La(OH)3 is shown in Fig. 4. FTIR spectrum has the typical peaks of physically adsorbed H2O and the structural O\H of La(OH)3. The band that appears at 3605 cm− 1 could be attributed to the tension of the hydroxyl groups of lanthanum hydroxide [7]. The two bands at 3440 cm− 1 and 1635 cm− 1 are associated with the hydroxyl groups of molecular H2O. Other two distinct bands, observed at 674 and 560 cm− 1, are characteristic of the La\OH bond vibrations in La(OH)3. A sharp and strong absorption peak at 1377 cm− 1 is assigned to the vibration modes of NO3− anions intercalated in the structure of the deposit
4. Conclusion A facile low-temperature electrochemical method was developed to prepare La(OH)3 capsule-like nanostructures. In this method, the La (OH)3 deposit was obtained by galvanostatic cathodic electrodeposition from nitrate bath at 10 °C. Crystal structure and spectral analysis confirmed that the obtained product is a pure hexagonal phase of La (OH)3. Morphological studies revealed that the prepared La(OH)3 has the capsule-like nanostructure, with the average particle diameter of 15 nm and the length of up to 50 nm.
References [1] Shen G. Recent Pat Nanotechnol 2008;2:160–8. [2] Jayakumar OD, Salunke HG, Kadam RM, Mohapatra M, Yaswat G, Kulshreshtha SK. Nanotechnology 2006;17:1278–85. [3] Kriha O, Zhao L, Pippel E, Gosele U, Wehrspohn RB, et al. Adv Funct Mater 2007;17: 1327–32. [4] Zhu JL, Zhou YH, Yang HX. J Power Sources 1997;69:169–73. [5] Rosynek MP, Magnuson DT. J Catal 1977;46:402–13. [6] Rovira LG, Sanchez-Amaya JM, Lopez-Haro M, et al. Nanotechnology 2008;19: 495305–14. [7] Zheng D, Shi J, Lu X, Wang C, et al. Cryst Eng Comm 2010;10:1039–42. [8] Zhu J, Gui Z, Ding Y. Mater Lett 2008;62:2373–6. [9] Deng J, Zhang L, Au CT, Dai H. Mater Lett 2009;63:632–4. [10] Ma X, Zhang H, Xu J, Yang D. Mater Lett 2004;58:1180–2. [11] Qian L, Gui Y, Guo S, Gong Q, Qian X. J Phys Chem Solids 2009;70:688–93. [12] Yao CZ, Weia BH, Ma HX, et al. Mater Lett 2011;65:490–2. [13] Bocchetta P, Santamaria M, Quarto FD. Electrochem Commun 2007;9:683–8. [14] Tang B, Ge J, Zhuo L. Nanotechnology 2004;15:1749–51. [15] Aghazadeh M, Nozad A, Adelkhani H, Ghaemi M. J Electrochem Soc 2010;157: D519-22. [16] Zhitomirsky I. Adv Colloid Interface Sci 2002;97:279–317.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
A novel lanthanum hydroxide nanostructure prepared by cathodic electrodeposition Mustafa Aghazadeh a,b, Ahmad Nozad Golikand b,⁎, Mehdi Ghaemi c, Taher Yousefi b a b c
Department of Chemistry, Tarbiat Modares University, P.O. Box: 13145-185, Tehran, Iran Material Research School, NSTRI, P.O. Box: 14395-836, Tehran, Iran Department of Chemistry, Science Faculty, Golestan University, P.O. Box: 49138-15739, Gorgan, Iran
a r t i c l e
i n f o
Article history: Received 27 December 2010 Accepted 10 February 2011 Available online 15 February 2011 Keywords: Nanocrystalline materials Electrodeposition La(OH)3 FTIR
a b s t r a c t A novel and interesting nanostructure of La(OH)3 was prepared by electrochemical method under mild conditions without any hard templates and surfactants. In this method, La(OH)3 was galvanostatically deposited from low-temperature nitrate bath on the steel substrate by electrogeneration of base. X-ray results showed that the obtained deposit has single crystalline hexagonal phase of La(OH)3. Morphological characterization revealed that the product has compact morphology with capsule-like structures having approximately an average diameter of 15 nm and the length of up to 50 nm. The results showed that lowtemperature cathodic electrodeposition can be recognized as an easy and facile method for the synthesis of La (OH)3 nanocapsules. © 2011 Elsevier B.V. All rights reserved.
1. Introduction There has been growing interest in the study of nanomaterials in recent years due to their potential applications in many different areas of science and technology. Particular attention has been given to the design of methods for preparation of one or two-dimensional (1D or 2D) metal oxide and hydroxide structures at nanoscale. Nanostructures of these materials are essential in the design of catalysts, sensors and others devices [1–3]. Lanthanum hydroxide, La(OH)3, is of great research interest for being used in many fields such as high potential oxide ceramics, superconductive materials, hydrogen storage materials, electrode materials, etc. Furthermore, La(OH)3 has long been used as a catalyst and sorbent material [4,5]. In the recent years, a variety of La(OH)3 nanostructures such as nanotubes [6,7], nanorods [7–12], nanowires [13] and nanospheres [14] have been reported by electrochemical, hydrothermal, sol–gel and solvothermal methods. Electrochemical synthesis, i.e. cathodic electrodeposition, can be considered as an easy, clean and effective method for preparation of La(OH)3 nanostructures. For example, high quality arrays of La(OH)3 nanotubes have been successfully fabricated by cathodic electrodeposition process using anodic alumina membrane templates [6]. Also, Zheng et al. [7] have recently reported that large-scale La(OH)3 nanorod/nanotube arrays have been grown directly on Cu substrates via a template-free electrodeposition and selective etching process. Furthermore, very recently, hexagonal and vertically aligned La(OH)3 nanorod arrays have been fabricated in a large scale via electrodeposition method without using any hard
⁎ Corresponding author. Tel./fax: +98 21 82063112. E-mail address: [email protected] (A.N. Golikand). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.02.039
templates and surfactants [12]. Previously, we reported the preparation of Y2O3 nanospheres by cathodic electrodeposition from chloride bath at room temperature [15]. In the present work, we report a novel and new-type nanostructure of lanthanum hydroxide prepared by an easy, one-step, template-free and versatile electrochemical method. In this method, La(OH)3 nanostructures are galvanostatically electrodeposited from lowtemperature nitrate bath by cathodic electrodeposition, i.e. electrogeneration of base (OH−) at the cathode surface. Morphological analysis revealed that the prepared hydroxide has capsule-like structure at nanoscale. It is noteworthy that to our knowledge, there are no reports for the synthesis of this type of nanostructures of metal hydroxides or oxides in the literature. In fact, to our knowledge, this is the first report on the synthesis of nanocapsules as a new type of La(OH)3 nanostructures. 2. Experimental procedure La(OH)3 was obtained by cathodic electrodeposition from an additive free aqueous 0.005 M La(NO3)3 bath. The bath temperature was fixed at 10 °C. The electrochemical cell included a cathodic steel substrate (316 L, 100 × 50 × 0.5 mm) centered between the two parallel graphite anodes. Deposition experiments were carried out in galvanostatic mode at a current density of 1 mA cm− 2 and without stirring. After drying in air for 48 h, the deposit was scraped from the steel electrodes. Crystal structure of obtained deposit was determined by X-ray diffraction (XRD, Phillips, PW-1800). Morphological characterization was investigated by scanning electron microscopy (SEM, Philips 515) and transmission electron microscopy (TEM, Phillips EM 2085) with an accelerating voltage of 100 kV. IR spectrum was obtained with a Bruker Vector 22 FT-IR spectrometer.
M. Aghazadeh et al. / Materials Letters 65 (2011) 1466–1468
1467
3. Results and discussion -0.6
Cathodic electrodeposition of La(OH)3 is achieved at the cathode through a mechanism of base (OH−) electrogeneration in nitrate solution, according to the possible cathodic reactions [16]. These reactions include the nitrate ions, dissolved oxygen and water reduction (Eqs. (1)–(4)):
Potential / V
-0.7
-0.8
-0.9
−
−
−
−
NO3 þ H2 O þ 2e →NO2 þ 2OH
ð1Þ
-1.0 −
−
þ
NO3 þ 7H2 O þ 8e →NH4 þ 10OH
−
ð2Þ
-1.1 0
100
200
300
400
500
600
−
O2 þ 2H2 O þ 4e →4OH
Time / S Fig. 1. Variations of the potential as a function of time during the electrodeposition of La (OH)3 at 1 mA cm− 2.
−
−
−
2H2 O þ 2e →H2 þ 2OH
ð3Þ ð4Þ
The above reactions result in an increase of the pH near the steel electrode surface. By increasing OH− concentration, La(OH)3 will form and deposit on the cathode electrode:
211
101
Intensity (a.u.)
3þ
110
La
201
−
þ 3OH →LaðOHÞ3 ðsÞ
ð5Þ
321
100
200
311
112
210
302 202
10
20
30
40
50
60
70
80
2θ (deg.) Fig. 2. X-ray diffraction pattern of the as-prepared La(OH)3.
In this work, the electrodeposition experiments were performed in the galvanostatic regime, applying current density of 1 mA cm− 2. Fig. 1 shows the variation of the potential during this process. Considering the potential value (− 1.03 V), it seems that the reduction of water (Eq. (4)) has a major role in the production of OH− at the applied current density. The XRD pattern of the deposit is shown in Fig. 2. All diffraction peaks can be indexed as the hexagonal La(OH)3 with the lattice constants of a = 6.528 Å and c = 3.858 Å, which are very consistent with the values in the standard card (JCPDS 41-4019). The broadening of these diffraction peaks indicated that the crystal size of La(OH)3
Fig. 3. SEM (a, b) and TEM (c, d) images of the as-prepared La(OH)3.
M. Aghazadeh et al. / Materials Letters 65 (2011) 1466–1468
Transmittance (a.u.)
1468
850 1635
1048 560 647
3605 3440
1476
during the electrodeposition process. The peaks at about 1476 cm− 1 and 1048 cm− 1 can be attributed to the carbonate group, which originate from the reaction of La(OH)3 with CO2 from air during the analysis. It is worth noting that further works are underway on the synthesis of ordered and oriented nanocapsules with uniformity in diameter and length. Furthermore, the nano-capsules of the other metal oxides and hydroxides such as Y(OH)3, ZrO2 and NiO have been synthesized by our method and their manuscripts are being developed.
1377
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1) Fig. 4. FTIR spectrum of the as-prepared La(OH)3.
particles is very fine. Morphological characteristics of as-prepared La (OH)3 are shown in Fig. 3. The SEM images of La(OH)3 only represented a compact morphology. Further magnifications by TEM (Fig. 3c and d) disclosed that the underlying morphologies are composed exclusively of disoriented bundles of capsules. It is observable from this sub-micrometer scale that the compact structure is an aggregate of the particles arranged in different orientations. The roughly oriented capsule-like particles tend to grow in groups, parallel to the surface (Fig. 3b and c). The size of capsules is not uniform. This lack of uniformity is completely evident in the capsules' length (Fig. 3d). The diameter and length of the nanocapsules range from 10 to 20 nm and 20 to 50 nm, respectively, as shown in the TEM image (Fig. 3d). FTIR spectrum of the as-prepared La(OH)3 is shown in Fig. 4. FTIR spectrum has the typical peaks of physically adsorbed H2O and the structural O\H of La(OH)3. The band that appears at 3605 cm− 1 could be attributed to the tension of the hydroxyl groups of lanthanum hydroxide [7]. The two bands at 3440 cm− 1 and 1635 cm− 1 are associated with the hydroxyl groups of molecular H2O. Other two distinct bands, observed at 674 and 560 cm− 1, are characteristic of the La\OH bond vibrations in La(OH)3. A sharp and strong absorption peak at 1377 cm− 1 is assigned to the vibration modes of NO3− anions intercalated in the structure of the deposit
4. Conclusion A facile low-temperature electrochemical method was developed to prepare La(OH)3 capsule-like nanostructures. In this method, the La (OH)3 deposit was obtained by galvanostatic cathodic electrodeposition from nitrate bath at 10 °C. Crystal structure and spectral analysis confirmed that the obtained product is a pure hexagonal phase of La (OH)3. Morphological studies revealed that the prepared La(OH)3 has the capsule-like nanostructure, with the average particle diameter of 15 nm and the length of up to 50 nm.
References [1] Shen G. Recent Pat Nanotechnol 2008;2:160–8. [2] Jayakumar OD, Salunke HG, Kadam RM, Mohapatra M, Yaswat G, Kulshreshtha SK. Nanotechnology 2006;17:1278–85. [3] Kriha O, Zhao L, Pippel E, Gosele U, Wehrspohn RB, et al. Adv Funct Mater 2007;17: 1327–32. [4] Zhu JL, Zhou YH, Yang HX. J Power Sources 1997;69:169–73. [5] Rosynek MP, Magnuson DT. J Catal 1977;46:402–13. [6] Rovira LG, Sanchez-Amaya JM, Lopez-Haro M, et al. Nanotechnology 2008;19: 495305–14. [7] Zheng D, Shi J, Lu X, Wang C, et al. Cryst Eng Comm 2010;10:1039–42. [8] Zhu J, Gui Z, Ding Y. Mater Lett 2008;62:2373–6. [9] Deng J, Zhang L, Au CT, Dai H. Mater Lett 2009;63:632–4. [10] Ma X, Zhang H, Xu J, Yang D. Mater Lett 2004;58:1180–2. [11] Qian L, Gui Y, Guo S, Gong Q, Qian X. J Phys Chem Solids 2009;70:688–93. [12] Yao CZ, Weia BH, Ma HX, et al. Mater Lett 2011;65:490–2. [13] Bocchetta P, Santamaria M, Quarto FD. Electrochem Commun 2007;9:683–8. [14] Tang B, Ge J, Zhuo L. Nanotechnology 2004;15:1749–51. [15] Aghazadeh M, Nozad A, Adelkhani H, Ghaemi M. J Electrochem Soc 2010;157: D519-22. [16] Zhitomirsky I. Adv Colloid Interface Sci 2002;97:279–317.