- Email: [email protected]
Electrochemical synthesis of nanostructured nickel oxide powder using nickel as anode
Materials Letters 106 (2013) 175–177
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Electrochemical synthesis of nanostructured nickel oxide powder using nickel as anode Zh. Boroun a,n, M.R. Vaezi a, G. Kavei b, A.A. Youzbashi b, I. Kazeminezhad c a
Division of Nanotechnology and Advanced Materials, Materials and Energy Research Center, Karaj, Iran Division of Semiconductors, Materials and Energy Research Center, Karaj, Iran c Department of Physics, Shahid Chamran University, Ahvaz, Iran b
art ic l e i nf o
a b s t r a c t
Article history: Received 9 April 2013 Accepted 2 May 2013 Available online 13 May 2013
In this research, nanostructured nickel oxide powder has been obtained by electrolysis of Ni in aqueous solution of CTAB and subsequent calcination. AAS, FT-IR, XRD and TEM analysis were used for characterization of the resulting powder. XRD result showed that the product is FCC nickel oxide. Also XRD and AAS results proved good purity of the powder. TEM image showed that the final product is aggregated structure of NiO nanoparticles and FT-IR graphs indicated the calcinaton reaction. Finally based on observations and analysis results, mechanism of the synthesis process was proposed in which Br− ions of the solution form complex with nickel oxide transpassive layer of the anode and the nickel complex forms the subsequent compounds. & 2013 Elsevier B.V. All rights reserved.
Keywords: Nickel oxide Nanostructure Electrochemical synthesis FT-IR XRD TEM
1. Introduction
2. Material and methods
Nickel oxide (NiO) has many applications such as gas sensors [1], chemical catalysts [2] and electrochromic devices [3]. Nanostructures give superior properties to those applications particularly to the gas sensors [4]. In recent years, a new electrochemical synthesis method has begun to emerge as an option among conventional wet chemical methods like coprecipitation to generate metal oxide nanoparticles such as Fe3O4 [5], Cu2O [6] and ZnO [7]. The framework of this electrochemical synthesis method is to submerge two electrode of the same metal as a sacrificial anode and as a cathode in an aqueous electrolyte consisting particle stabilizer (surfactant) and then performing electrolysis to generate oxide (or other compounds such as hydroxide) nanoparticles of that metal. One major advantage of this method compared to coprecipitation is to control mass input of reactants by electrical parameters such as applied voltage and current intensity and therefore there is more room to modify the average particle size and the particle size distribution. The other major advantage is high purity (been free of excessive precursor salts) of final products. In this research, nanostructured nickel oxide powder was fabricated indirectly by this electrochemical method in the aqueous solution of cetyltrimethyl ammonium bromide (CTAB) and subsequent calcination.
Two electrodes consisting of a consuming nickel anode (1 1 cm2 dimensions and 2 mm thick) purchased from “Alfa” and a nickel cathode (1 4 cm2) were used for the synthesis. The exposing faces of both anode and cathode were polished and washed by water and then cleaned by acetone. The distance between electrodes was 1.5 cm for all experiments. Prior to synthesis the electrodes were submerged into a 0.1 M solution of NaOH and then electrolysis was performed by means of JPS-302D power supply with current intensity of 0.25 A at 25 1C for 30 min to passivate the anode. After the passivation process, the electrodes were washed only with water. Electrolyte used for the synthesis was 0.0034 M aqueous solution (80 ml) of CTAB. The process of synthesis was performed by means of JPS-302D with current intensity of 0.01 A for 180 min at 25 1C under mechanical stirring conditions. The result of the process was a black suspension which was centrifuged and washed with distilled water (only one time) and dried at 80 1C for 24 h to yield a black powder and subsequently heated at 400 1C for 90 min. Elemental chemical analysis of the final product was performed by means of “GBC 932 AAS” instrument. For its study the powder sample was dissolved in 63% HNO3 (Merck) and qualitative analysis for detection of typical impurities of metallic Ni and NiO nanoparticles was carried out. Chemical bondings of the resulting powder were investigated by infrared spectroscopy in a “Perkin Spectrum 400”. X-Ray diffractogram of the powder between 2θ ¼101 and 801 was recorded by means of a “UNISUNTIS-XMD 300”. Finally images of the product before and after the calcination were analyzed by a “Philips
n
Corresponding author. Tel.: +98 263 6204131; fax: +98 263 6201888. E-mail address: [email protected] (Zh. Boroun).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.05.022
176
Zh. Boroun et al. / Materials Letters 106 (2013) 175–177
CM200” TEM and a “Philips CM200” FETEM (both operated at 200 KeV) respectively.
Analysis results: Electrolyte at the beginning of the synthesis was colorless and became ultimately black. It is obvious that the resulting suspension was not Ni(OH)2 because of its black color. Qualitative AAS results of final product in Table 1 shows that it is a nickel compound with no typical impurity. Fig. 1 represents FT-IR spectrums of the resulted powder before and after the calcination, in both mid and far modes. For powder before calcination the broad bands around 3400 cm−1 and 1600 cm−1 correspond to stretching and bending vibrations of absorbed water molecules respectively. The intense and broad peak at 1383 cm−1 is assigned to bending vibration of CH3 group, δ (CH3) [8] probably from CTAB. An intense and narrow peak at 3640 cm−1 is similar to O–H stretching vibrations in structural water and the peaks at 560, 460 and 350 cm-1 are apparently corresponding to vibrations of different chemical bondings of nickel (Ni–O and Ni–O–H) in NiO(OH) [9]. For calcinated powder, the peak at 420 cm−1 is corresponding to vibrations of Ni–O in NiO [10]. Also peaks at 3640 cm−1 and 1383 cm−1 disappear after the calcination. From the FT-IR results we deduce that the resulting powder before calcination is probably a nickel oxyhydroxide which transforms to nickel oxide after the calcination (associated with simultaneous surfactant removal). Fig. 2 shows XRD diffractograms of the resulting powder before and after the calcination. The diffractogram of the powder before calcination appears to be amorphous-like with an intense and broad peak at 17.521 and 3 minor peaks at 33.451, 38.241 and 59.601 respectively. It should be mentioned that we were not able to find any standard XRD data that match this diffractogram. However from diffractogram of the calcinated powder it can be deduced that it is NiO (FCC) according to standard spectrum (JCPDS, No. 04-0835) with a high purity because unlike other wet chemical methods, after washing only one time before calcination unwanted peaks of precursor salts are not present.
100000 80000 60000 40000 20000 0
10
20
30
40
50
60
70
Element
Detection state
Wavelength of lamp (nm)
Li Na K Mg Fe Co Ni
N.D N.D N.D N.D N.D N.D D
670.8 589.6 766.5 285.5 248.3 240.7 351.5
N.D¼Not detected, D ¼Detected
80
90
2θ (deg)
Fig. 2. XRD diffractograms of the the powder before and after calcination.
Fig. 3 represents TEM images of the resulting powder before and after the calcination plus corresponding SAEDs. The left image indicates that the uncalcinated powder is nanoparticulate and the right image indicates that the calcinated powder is nanostructured in which nanoparticles are locally aggregated together. Mechanism of formation: Based on our observations during the synthesis process and analysis results we propose the following mechanisms for the formation of NiO nanostructure: First a nickel oxide layer is formed on the nickel anode during the pretreatment process Ni(electrode)+H2O-NiO(electrode)+2H+ (aq)+2e
(3-1)
In presence of Br− ions of solved CTAB during the synthesis process, the transpassive nickel oxide layer dissolves to a high valent nickel complex [11] probably positively charged, because ejection of some yellow species from the anode were observed NiO(electrode)+Br−(aq)-NiComplex(aq)
(3-2)
The above reaction causes destruction of oxide layer, however repassivation reaction similar to Eq. (3-1) occurs at the anode [11]. Simultaneously hydrogen evolution reaction occurs at the cathode 2H2O+2e−-2OH−(aq)+H2(g)
(3-3) −
At the electrolyte, the nickel complex reacts with OH ions and forms a nickel oxyhydroxide NiComplex(aq)+OH−(aq)-HxNiO2(suspension)
Table 1 Results of qualitative AAS of the final productn.
n
After calcination
120000 XRD Intensity
3. Results and discussion
Before calcination
140000
(3-4)
HxNiO2 is the general formula of nickel oxyhydroxide structures as reported by Van der Ven et al. [12]. Due to steric stabilization of surfactant (CTAB) and low mass input, diffusion limited growth of the particles is ensured so that the resulting nickel oxyhydroxide is nanoparticulate [13]. It should be mentioned that exact chemical composition of the nickel complex and nickel oxyhydroxide are beyond the purpose of this research. During the calcination process, the nanoparticulate nickel oxyhydroxide transforms to aggregated nickel oxide nanoparticles: x 1−ðx=2Þ Hx NiO2ðpowderÞ -NiOðpowderÞ þ H2 OðgÞ þ O2ðgÞ 2 2
ð3 5Þ
4. Conclusions
Fig. 1. FT-IR spectrums of the resulted powder before and after the calcination.
Nanostructured nickel oxide powder was indirectly obtained by an electrochemical method using nickel as anode. According to analysis results, the resulting material may be a good candidate for future applications because of its high purity and nanostructured form. The surfactant (CTAB) had two distinctive roles in the synthesis process: complex former and particle stabilaizer. Although our main objective was to synthesize nanostructured NiO powder, the precursor of the NiO before calcination was a compound similar to NiO (OH) in terms of appearance and chemical bondings.
Zh. Boroun et al. / Materials Letters 106 (2013) 175–177
177
Fig. 3. TEM images of the powder with corresponding SAEDs: (a) before calcination and (b) after calcination.
Acknowledgments Authors want to thank all of Materials and Energy Research Center's personals who helped us in our research. References [1] Gyu Cho N, Hwang IS, Kim HG, Lee JH, Kim ID. Gas sensing properties of p-type hollow NiO hemispheres prepared by polymeric colloidal templating method. Sensors Actuators B 2011;155:366–71. [2] Kumar P, Sun Y, Idem RO. Comparative study of Ni-based mixed oxide catalyst for carbon dioxide reforming of methane. Energy Fuels 2008;22:3575–82. [3] Cerc Korošec R, Bukovec P. Sol–gel prepared nio thin films for electrochromic applications. Acta Chim Slov 2006;53:136–47. [4] Miller TA, Bakrania SD, Perez C, Wooldridge MS. Functional Nanomaterials. USA: American Scientific Publishers; 1–24. [5] Cabrera L, Gutierrez S, Menendez N, Morales MP, Herrasti P. Magnetite nanoparticles: electrochemical synthesis and characterization. Electrochim Acta 2008;53:3436–41.
[6] Yang H, Ouyang J, Tang A, Xiao Y, Li X, Dong X, et al. Electrochemical synthesis and photocatalytic property of cuprous nanoparticles. Mater Res Bull 2006;41:1310–8. [7] Kazeminezhad I, Sadollahkhani A, Farbod M. Synthesis of ZnO nanoparticles and flower-like nanostructures using nonsono- and sono-electrooxidation methods. Mater lett 2013;92:29–32. [8] Silva BL, Freire PTC, Melo FEA, Guedes I, Araujo Silva MA, Mendes F, et al. Polarized Raman spectra and infrared analysis of vibrational modes in L-threomine crystals. Braz J Phys 1998;28:19–24. [9] Tu PC, Lampert CM. In-situ spectroscopic studies of electrochromic hydrated nickel oxide films. In: Proceedings of the Society of Photo-Optical Instrumentation; 1987. 823, p. 113–123. [10] Salavati Niasari M, Mohandes F, Davar F, Mazaheri M, Monemzadeh M, Yavarinia N. Preparation of NiO nanoparticles from metal-organic frameworks via a solid-state decomposition route. Inorg Chim Acta 2009;362:3691–7. [11] Abd El Aal EE. Breakdown of passive film on nickel in borate solutions containing halide anions. Corros Sci 2003;45:759–75. [12] Van der Ven A, Morgan D, Meng YS, Ceder G. Phase stability of nickel hydroxides and oxyhydroxides. J Electrochem Soc 2006;153(2):A210–5. [13] Cao G. Nanostructures & Nanomaterials. London: Imperial College Press; 2004.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Electrochemical synthesis of nanostructured nickel oxide powder using nickel as anode Zh. Boroun a,n, M.R. Vaezi a, G. Kavei b, A.A. Youzbashi b, I. Kazeminezhad c a
Division of Nanotechnology and Advanced Materials, Materials and Energy Research Center, Karaj, Iran Division of Semiconductors, Materials and Energy Research Center, Karaj, Iran c Department of Physics, Shahid Chamran University, Ahvaz, Iran b
art ic l e i nf o
a b s t r a c t
Article history: Received 9 April 2013 Accepted 2 May 2013 Available online 13 May 2013
In this research, nanostructured nickel oxide powder has been obtained by electrolysis of Ni in aqueous solution of CTAB and subsequent calcination. AAS, FT-IR, XRD and TEM analysis were used for characterization of the resulting powder. XRD result showed that the product is FCC nickel oxide. Also XRD and AAS results proved good purity of the powder. TEM image showed that the final product is aggregated structure of NiO nanoparticles and FT-IR graphs indicated the calcinaton reaction. Finally based on observations and analysis results, mechanism of the synthesis process was proposed in which Br− ions of the solution form complex with nickel oxide transpassive layer of the anode and the nickel complex forms the subsequent compounds. & 2013 Elsevier B.V. All rights reserved.
Keywords: Nickel oxide Nanostructure Electrochemical synthesis FT-IR XRD TEM
1. Introduction
2. Material and methods
Nickel oxide (NiO) has many applications such as gas sensors [1], chemical catalysts [2] and electrochromic devices [3]. Nanostructures give superior properties to those applications particularly to the gas sensors [4]. In recent years, a new electrochemical synthesis method has begun to emerge as an option among conventional wet chemical methods like coprecipitation to generate metal oxide nanoparticles such as Fe3O4 [5], Cu2O [6] and ZnO [7]. The framework of this electrochemical synthesis method is to submerge two electrode of the same metal as a sacrificial anode and as a cathode in an aqueous electrolyte consisting particle stabilizer (surfactant) and then performing electrolysis to generate oxide (or other compounds such as hydroxide) nanoparticles of that metal. One major advantage of this method compared to coprecipitation is to control mass input of reactants by electrical parameters such as applied voltage and current intensity and therefore there is more room to modify the average particle size and the particle size distribution. The other major advantage is high purity (been free of excessive precursor salts) of final products. In this research, nanostructured nickel oxide powder was fabricated indirectly by this electrochemical method in the aqueous solution of cetyltrimethyl ammonium bromide (CTAB) and subsequent calcination.
Two electrodes consisting of a consuming nickel anode (1 1 cm2 dimensions and 2 mm thick) purchased from “Alfa” and a nickel cathode (1 4 cm2) were used for the synthesis. The exposing faces of both anode and cathode were polished and washed by water and then cleaned by acetone. The distance between electrodes was 1.5 cm for all experiments. Prior to synthesis the electrodes were submerged into a 0.1 M solution of NaOH and then electrolysis was performed by means of JPS-302D power supply with current intensity of 0.25 A at 25 1C for 30 min to passivate the anode. After the passivation process, the electrodes were washed only with water. Electrolyte used for the synthesis was 0.0034 M aqueous solution (80 ml) of CTAB. The process of synthesis was performed by means of JPS-302D with current intensity of 0.01 A for 180 min at 25 1C under mechanical stirring conditions. The result of the process was a black suspension which was centrifuged and washed with distilled water (only one time) and dried at 80 1C for 24 h to yield a black powder and subsequently heated at 400 1C for 90 min. Elemental chemical analysis of the final product was performed by means of “GBC 932 AAS” instrument. For its study the powder sample was dissolved in 63% HNO3 (Merck) and qualitative analysis for detection of typical impurities of metallic Ni and NiO nanoparticles was carried out. Chemical bondings of the resulting powder were investigated by infrared spectroscopy in a “Perkin Spectrum 400”. X-Ray diffractogram of the powder between 2θ ¼101 and 801 was recorded by means of a “UNISUNTIS-XMD 300”. Finally images of the product before and after the calcination were analyzed by a “Philips
n
Corresponding author. Tel.: +98 263 6204131; fax: +98 263 6201888. E-mail address: [email protected] (Zh. Boroun).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.05.022
176
Zh. Boroun et al. / Materials Letters 106 (2013) 175–177
CM200” TEM and a “Philips CM200” FETEM (both operated at 200 KeV) respectively.
Analysis results: Electrolyte at the beginning of the synthesis was colorless and became ultimately black. It is obvious that the resulting suspension was not Ni(OH)2 because of its black color. Qualitative AAS results of final product in Table 1 shows that it is a nickel compound with no typical impurity. Fig. 1 represents FT-IR spectrums of the resulted powder before and after the calcination, in both mid and far modes. For powder before calcination the broad bands around 3400 cm−1 and 1600 cm−1 correspond to stretching and bending vibrations of absorbed water molecules respectively. The intense and broad peak at 1383 cm−1 is assigned to bending vibration of CH3 group, δ (CH3) [8] probably from CTAB. An intense and narrow peak at 3640 cm−1 is similar to O–H stretching vibrations in structural water and the peaks at 560, 460 and 350 cm-1 are apparently corresponding to vibrations of different chemical bondings of nickel (Ni–O and Ni–O–H) in NiO(OH) [9]. For calcinated powder, the peak at 420 cm−1 is corresponding to vibrations of Ni–O in NiO [10]. Also peaks at 3640 cm−1 and 1383 cm−1 disappear after the calcination. From the FT-IR results we deduce that the resulting powder before calcination is probably a nickel oxyhydroxide which transforms to nickel oxide after the calcination (associated with simultaneous surfactant removal). Fig. 2 shows XRD diffractograms of the resulting powder before and after the calcination. The diffractogram of the powder before calcination appears to be amorphous-like with an intense and broad peak at 17.521 and 3 minor peaks at 33.451, 38.241 and 59.601 respectively. It should be mentioned that we were not able to find any standard XRD data that match this diffractogram. However from diffractogram of the calcinated powder it can be deduced that it is NiO (FCC) according to standard spectrum (JCPDS, No. 04-0835) with a high purity because unlike other wet chemical methods, after washing only one time before calcination unwanted peaks of precursor salts are not present.
100000 80000 60000 40000 20000 0
10
20
30
40
50
60
70
Element
Detection state
Wavelength of lamp (nm)
Li Na K Mg Fe Co Ni
N.D N.D N.D N.D N.D N.D D
670.8 589.6 766.5 285.5 248.3 240.7 351.5
N.D¼Not detected, D ¼Detected
80
90
2θ (deg)
Fig. 2. XRD diffractograms of the the powder before and after calcination.
Fig. 3 represents TEM images of the resulting powder before and after the calcination plus corresponding SAEDs. The left image indicates that the uncalcinated powder is nanoparticulate and the right image indicates that the calcinated powder is nanostructured in which nanoparticles are locally aggregated together. Mechanism of formation: Based on our observations during the synthesis process and analysis results we propose the following mechanisms for the formation of NiO nanostructure: First a nickel oxide layer is formed on the nickel anode during the pretreatment process Ni(electrode)+H2O-NiO(electrode)+2H+ (aq)+2e
(3-1)
In presence of Br− ions of solved CTAB during the synthesis process, the transpassive nickel oxide layer dissolves to a high valent nickel complex [11] probably positively charged, because ejection of some yellow species from the anode were observed NiO(electrode)+Br−(aq)-NiComplex(aq)
(3-2)
The above reaction causes destruction of oxide layer, however repassivation reaction similar to Eq. (3-1) occurs at the anode [11]. Simultaneously hydrogen evolution reaction occurs at the cathode 2H2O+2e−-2OH−(aq)+H2(g)
(3-3) −
At the electrolyte, the nickel complex reacts with OH ions and forms a nickel oxyhydroxide NiComplex(aq)+OH−(aq)-HxNiO2(suspension)
Table 1 Results of qualitative AAS of the final productn.
n
After calcination
120000 XRD Intensity
3. Results and discussion
Before calcination
140000
(3-4)
HxNiO2 is the general formula of nickel oxyhydroxide structures as reported by Van der Ven et al. [12]. Due to steric stabilization of surfactant (CTAB) and low mass input, diffusion limited growth of the particles is ensured so that the resulting nickel oxyhydroxide is nanoparticulate [13]. It should be mentioned that exact chemical composition of the nickel complex and nickel oxyhydroxide are beyond the purpose of this research. During the calcination process, the nanoparticulate nickel oxyhydroxide transforms to aggregated nickel oxide nanoparticles: x 1−ðx=2Þ Hx NiO2ðpowderÞ -NiOðpowderÞ þ H2 OðgÞ þ O2ðgÞ 2 2
ð3 5Þ
4. Conclusions
Fig. 1. FT-IR spectrums of the resulted powder before and after the calcination.
Nanostructured nickel oxide powder was indirectly obtained by an electrochemical method using nickel as anode. According to analysis results, the resulting material may be a good candidate for future applications because of its high purity and nanostructured form. The surfactant (CTAB) had two distinctive roles in the synthesis process: complex former and particle stabilaizer. Although our main objective was to synthesize nanostructured NiO powder, the precursor of the NiO before calcination was a compound similar to NiO (OH) in terms of appearance and chemical bondings.
Zh. Boroun et al. / Materials Letters 106 (2013) 175–177
177
Fig. 3. TEM images of the powder with corresponding SAEDs: (a) before calcination and (b) after calcination.
Acknowledgments Authors want to thank all of Materials and Energy Research Center's personals who helped us in our research. References [1] Gyu Cho N, Hwang IS, Kim HG, Lee JH, Kim ID. Gas sensing properties of p-type hollow NiO hemispheres prepared by polymeric colloidal templating method. Sensors Actuators B 2011;155:366–71. [2] Kumar P, Sun Y, Idem RO. Comparative study of Ni-based mixed oxide catalyst for carbon dioxide reforming of methane. Energy Fuels 2008;22:3575–82. [3] Cerc Korošec R, Bukovec P. Sol–gel prepared nio thin films for electrochromic applications. Acta Chim Slov 2006;53:136–47. [4] Miller TA, Bakrania SD, Perez C, Wooldridge MS. Functional Nanomaterials. USA: American Scientific Publishers; 1–24. [5] Cabrera L, Gutierrez S, Menendez N, Morales MP, Herrasti P. Magnetite nanoparticles: electrochemical synthesis and characterization. Electrochim Acta 2008;53:3436–41.
[6] Yang H, Ouyang J, Tang A, Xiao Y, Li X, Dong X, et al. Electrochemical synthesis and photocatalytic property of cuprous nanoparticles. Mater Res Bull 2006;41:1310–8. [7] Kazeminezhad I, Sadollahkhani A, Farbod M. Synthesis of ZnO nanoparticles and flower-like nanostructures using nonsono- and sono-electrooxidation methods. Mater lett 2013;92:29–32. [8] Silva BL, Freire PTC, Melo FEA, Guedes I, Araujo Silva MA, Mendes F, et al. Polarized Raman spectra and infrared analysis of vibrational modes in L-threomine crystals. Braz J Phys 1998;28:19–24. [9] Tu PC, Lampert CM. In-situ spectroscopic studies of electrochromic hydrated nickel oxide films. In: Proceedings of the Society of Photo-Optical Instrumentation; 1987. 823, p. 113–123. [10] Salavati Niasari M, Mohandes F, Davar F, Mazaheri M, Monemzadeh M, Yavarinia N. Preparation of NiO nanoparticles from metal-organic frameworks via a solid-state decomposition route. Inorg Chim Acta 2009;362:3691–7. [11] Abd El Aal EE. Breakdown of passive film on nickel in borate solutions containing halide anions. Corros Sci 2003;45:759–75. [12] Van der Ven A, Morgan D, Meng YS, Ceder G. Phase stability of nickel hydroxides and oxyhydroxides. J Electrochem Soc 2006;153(2):A210–5. [13] Cao G. Nanostructures & Nanomaterials. London: Imperial College Press; 2004.