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Hydrothermal synthesis of Co3O4 nanorods on nickel foil
Materials Letters 123 (2014) 187–190
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Hydrothermal synthesis of Co3O4 nanorods on nickel foil Chengjun Dong, Xuechun Xiao, Gang Chen, Hongtao Guan, Yude Wang n Department of Materials Science and Engineering, Yunnan University, 650091 Kunming, People's Republic of China
art ic l e i nf o
a b s t r a c t
Article history: Received 8 January 2014 Accepted 23 February 2014 Available online 12 March 2014
Co3O4 nanorods (NRs) were successfully synthesized on nickel foil by a facile hydrothermal reaction. The X-ray diffraction (XRD) investigation confirms the formation of spinel Co3O4 phase. Owing to the mismatch between Co3O4 and substrate, the Co3O4 NRs initially grouped into bundle structure and then formed dispersed NRs. The length of Co3O4 NRs varies from several micrometers up to tens of micrometers with uniform diameter of about 1 μm. Transmission electron microscopy (TEM) characterization demonstrated that the NRs are stacked layer-by-layer from single grains in 50–200 nm. This facile hydrothermal method for preparation of Co3O4 NRs is significant in the synthesis and future applications of one-dimensional (1D) nanostructures. & 2014 Elsevier B.V. All rights reserved.
Keywords: Oxidation Co3O4 Nanorods Microstructure
1. Introduction Over the past decades, one-dimensional (1D) nanostructures, such as nanotubes, nanowires, NRs, nanofibers and nanobelts have been extensively synthesized and investigated by academia and industry [1,2]. Owing to physical dimension limits, such nanostructures exhibit dramatically novel electronic, optical and mechanical properties. As a consequence, worldwide efforts in both theory and experimental studies have been devoted to understand the novel physical properties and realize the nanoscale electronic and optoelectronic applications on the basis of 1D nanostructures. Co3O4 is an important p-type semiconductor material in applications of lithium ion batteries [3], supercapacitors [4], catalysts [5], gas sensors [6,7] and so forth. In order to improve its electrochemical performances, 1D based on Co3O4 systems including NRs, nanotubes and nanowires, have been synthesized and studied to date, and more novel applications are expected to happen. Shen and co-workers demonstrated that (110) planes of Co3O4 NRs in length of 200–300 nm favor the low temperature CO oxidations [8]. Wang et al. reported that the nanorod-assembled Co3O4 hexapods on copper foil using the hydrothermal method can enhance electrochemical performance for lithium-ion batteries [3]. Also, Co3O4 NRs with length of about 10 μm were prepared by improving traditional molten salt synthesis [9]. Nevertheless, most of these NRs are either powder materials or short on substrate restricting the applicability, which is a kind of motivation for further exploration. Recently, self-supported Co3O4
n
Corresponding author. Tel.: þ 86 87165031124; fax: þ 86 8 716515 3832. E-mail address: [email protected] (Y. Wang).
http://dx.doi.org/10.1016/j.matlet.2014.02.111 0167-577X/& 2014 Elsevier B.V. All rights reserved.
nanowire arrays have been successfully prepared on various conductive substrates including nickel foil, nickel foam and silicon wafer via a facile template-free hydrothermal synthesis method by Xia et al. [4]. In this experiment, the oxygen is indispensable for preparing vertically aligned Co3O4 nanowire arrays. In this present work, we amazedly obtained a mass of uniform Co3O4 NRs with a length up to tens of micrometers on nickel foil substrate modified from their recipe by ten times of NaNO3 without Co3O4 seed layer and oxygen injection. Then the growth mechanism is subsequently of detailed discussion. This work can render a deeper understanding of Co3O4 NRs and widen its applications.
2. Experimental All the reagents used in the experiments were purchased from commercial sources of analytical grade and used without any further purification. A grounded nickel foil with 5 cm 2 cm in size was cleaned by acetone and deionized water sequentially before placing at an angle against the wall of 80 mL Teflon. In a typical synthesis, 10 mmol Co(NO3)2 was firstly dissolved in 30 mL of H2O under stirring for 10 min to obtain a pink color solution, followed by adding 20 mL of 28 wt% ammonia solution till the color gradually turned into black in 30 min. Then 10 mmol NaNO3 was dissolved into the above solution. Lastly, the solution was transferred to the Teflon with nickel foil and the hydrothermal reaction was conducted at 120 1C for respective 6 and 12 h. After the reaction, the autoclave was cooled down to room temperature naturally and then the foil was collected from the solution, rinsed repeatedly with deionized water and annealed at 250 1C for 1 h in air.
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The crystal structure of Co3O4 NRs was characterized by X-ray diffraction (XRD, Rigaku TTRIII) with an incident X-ray wavelength of 1.540 ̊ (Cu Kα line). Scanning electron microscopy (SEM) analysis was taken on FEI QUANTA200 with a microscope operating at 30 kV. Detailed studies of the microstructure were also carried out by transmission electron microscopy (TEM) (JEOL JEM-2100) at an acceleration voltage of 200 kV.
3. Results and discussion The Co3O4 NRs have been successfully deposited on nickel foil. After hydrothermal reaction at 120 1C for 6 h, the foil is randomly covered with red and black products by eye, whereas the foil is uniformly covered for another 6 h. The phases of the precursors and Co3O4 NRs by heat treatment were investigated using XRD.
Fig. 1. (a) JCPDS for Co(OH)2 and (b) Co3O4, respectively. (c) and (d) are the XRD patterns of products after reaction for 6 h and 12 h before annealing on nickel foil. (e) and (f) are the XRD patterns of Co3O4 NRs for reaction time of 6 h and 12 h after annealing on nickel foil, respectively.
As-prepared precursors for reaction time of 6 h and 12 h were the mixture of crystalline Co(OH)2 and Co3O4 phase as illustrated by Fig. 1(c) and (d), which is in good agreement with other reports [4,5 and 10]. Fig. 1(e) and (f) shows the XRD patterns of the Co3O4 NRs after annealing at 250 1C for 1 h in air. All the identical peaks of the thermal treatment samples can be perfectly indexed to a cubic spinel phase of Co3O4 (JCPDS Card no. 42-1467 in Fig. 1(b)) except for the peaks originating from the nickel foil substrate. Besides, two diffraction peaks located at 51.81 and 76.41 from nickel foil are obviously observed in all products. The overview morphologies and microstructures of prepared Co3O4 NRs were viewed using SEM. Fig. 2 shows the top-surface images of typical Co3O4 NRs at low and high magnification, respectively. From the low magnification SEM image in Fig. 2 (a), it can be observed that highly uniform and highly dense Co3O4 NRs covered the whole surface of the substrate on a large scale. It is apparent that the products consist of big straight NRs bundles randomly laying down on the nickel foil. In Fig. 2(b), the featured bundle NRs are grouped from several individual NRs to even around 30 NRs with a slight difference in length. Meanwhile, some dispersed NRs are standing on the surface of NRs bundles as seen in Fig. 2 (c). By careful comparison, the length for dispersed NRs is of the order of micrometers on average, which is several times less than bundle NRs. However, the diameter is uniform about 1 μm in size regardless of bundle NRs or dispersed NRs. From the magnified images, we can see that all NRs are constructed through a great quantity of single uniform grains in both bundle NRs and dispersed NRs. We propose that the difference of both lattice and thermal coefficient between nickel foil and Co3O4 is possibly attributed to the different growth mechanisms, which will be discussed in following sections in more detail. To gain further insight into the detailed structure of Co3O4 NRs, the product was examined under TEM. The TEM images in Fig. 3 (a) clearly show the long isolated rod of about 1 μm in diameter with smooth but rough side walls and a circular solid end. Additionally, the TEM image indicates that the NRs in this sample are composed of subunits with more prominent grain-like structure. After magnification, in Fig. 3 (b), the isolated rod is apparently stacked layer-by-layer from single small grains. It is confirmed that the diameter of grains is of 50–200 nm from the
Fig. 2. (a) The overview SEM morphology of as-prepared Co3O4 NRs at low magnification. (b) and (c) are featured bundle NRs and dispersed NRs, respectively.
C. Dong et al. / Materials Letters 123 (2014) 187–190
189
Fig. 3. (a) is the low-magnification TEM images of isolated Co3O4 NRs. (b) High-magnification TEM image of a Co3O4 NR. (c) The grains from broken Co3O4 NRs.
Fig. 4. (a) The SEM images of bare grounded nickel foil. (b) and (c) are typical Co3O4 NRs after the hydrothermal reaction at 120 1C for 6 h after anneal. (d) The SEM images of Co3O4 NRs when the hydrothermal reaction totally goes on 12 h at 120 1C after anneal.
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broken rod during ultrasonic disperse as depicted in Fig. 3 (c), which of course makes the side walls rough. Time-dependent experiments are carried out to understand the formation process of such interesting Co3O4 NRs. Fig. 4 (a) gives the surface image of the bare nickel foil with obvious grounded trace. As can be seen in Fig.4 (b), the substrate is covered by a dark layer with dispersed grains and white rods in different lengths at the early stage of the reaction (6 h), which consisted of Co(OH)2 and Co3O4 revealed by previous XRD characterization. In Fig.4 (c), it is a typical evidence of the nucleation center for Co3O4 NR growth on the nickel foil. When the reaction duration increasingly goes up to 12 h, the product contains a large number of NRs evolved into bundle Co3O4 NRs at first and then dispersed Co3O4 NRs as shown in Fig.4 (d). It is easy to understand that the Co3O4 NRs incline to agglomerate together to form bundle NRs at the very beginning of growth due to the existence of large difference between nickel foil and Co3O4 in terms of both lattice and thermal coefficient. After prolonged hydrothermal treatment, the dispersed Co3O4 NRs grew on the surface of bundle Co3O4 NRs because of an accommodation mismatch between the Co3O4 and the substrate. The bundle Co3O4 NRs, as matter of fact, play as a buffer for the subsequent growth of the dispersed Co3O4 NRs. 4. Conclusions In summary, Co3O4 NRs, having size as large as up to several tens of micrometers with about 1 μm in diameter have been formed into bundle and dispersed structures on the surface of nickel foil substrate using the simple hydrothermal method. A
plausible formation reason of bundle and dispersed structures is on account of different lattices and thermal coefficients between nickel foil and Co3O4 NRs. By taking a close look at the Co3O4 NRs, it is found that the rod is structured layer-by-layer from individual Co3O4 grain subunit in range of 50–200 nm in size.
Acknowledgments This work was supported by the Department of Science and Technology of Yunnan Province via the Key Project for the Science and Technology (Grant no.2011FA001), National Natural Science Foundation of China (Grant no.51262029), the Key Project of the Department of Education of Yunnan Province (ZD2013006).
References [1] Zhai TY, Yao JN. One-Dimensional Nanostructures: Principles and Applications. Hoboker, New Jersey: John Wiley & Sons, Inc.; 2012. [2] Xia YN, Yang PD, Sun YG, Wu YY, Mayers B, et al. Adv Mater 2003;15:353–89. [3] Wang Lm, Liu B, Ran SH, Huang HT, Wang XF, Liang B, et al. J Mater Chem 2012;22:23541–6. [4] Xia XH, Tu JP, Mai YJ, Wang XL, Gu CD, Zhao XB. J Mater Chem 2011;21:9319–25. [5] Hu LH, Peng Q, Li YD. J Am Chem Soc 2008;130:16136–7. [6] Wen Z, Zhu LP, Mei WM, Hu L, Li YG, Sun LW, et al. Sens Actuators B 2013;186:172–9. [7] Hoa ND, El-Safty SA. J Phys Chem C 2011;115:8466–74. [8] Xie XW, Li Y, Liu ZQ, Haruta M, Shen WJ. Nature 2009;458:746–9. [9] Liu YK, Wang GH, Xu CK, Wang WZ. Chem Commun 2002:1486–7. [10] Li YG, Wu YY. Chem Mater 2010;22:5537–42.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Hydrothermal synthesis of Co3O4 nanorods on nickel foil Chengjun Dong, Xuechun Xiao, Gang Chen, Hongtao Guan, Yude Wang n Department of Materials Science and Engineering, Yunnan University, 650091 Kunming, People's Republic of China
art ic l e i nf o
a b s t r a c t
Article history: Received 8 January 2014 Accepted 23 February 2014 Available online 12 March 2014
Co3O4 nanorods (NRs) were successfully synthesized on nickel foil by a facile hydrothermal reaction. The X-ray diffraction (XRD) investigation confirms the formation of spinel Co3O4 phase. Owing to the mismatch between Co3O4 and substrate, the Co3O4 NRs initially grouped into bundle structure and then formed dispersed NRs. The length of Co3O4 NRs varies from several micrometers up to tens of micrometers with uniform diameter of about 1 μm. Transmission electron microscopy (TEM) characterization demonstrated that the NRs are stacked layer-by-layer from single grains in 50–200 nm. This facile hydrothermal method for preparation of Co3O4 NRs is significant in the synthesis and future applications of one-dimensional (1D) nanostructures. & 2014 Elsevier B.V. All rights reserved.
Keywords: Oxidation Co3O4 Nanorods Microstructure
1. Introduction Over the past decades, one-dimensional (1D) nanostructures, such as nanotubes, nanowires, NRs, nanofibers and nanobelts have been extensively synthesized and investigated by academia and industry [1,2]. Owing to physical dimension limits, such nanostructures exhibit dramatically novel electronic, optical and mechanical properties. As a consequence, worldwide efforts in both theory and experimental studies have been devoted to understand the novel physical properties and realize the nanoscale electronic and optoelectronic applications on the basis of 1D nanostructures. Co3O4 is an important p-type semiconductor material in applications of lithium ion batteries [3], supercapacitors [4], catalysts [5], gas sensors [6,7] and so forth. In order to improve its electrochemical performances, 1D based on Co3O4 systems including NRs, nanotubes and nanowires, have been synthesized and studied to date, and more novel applications are expected to happen. Shen and co-workers demonstrated that (110) planes of Co3O4 NRs in length of 200–300 nm favor the low temperature CO oxidations [8]. Wang et al. reported that the nanorod-assembled Co3O4 hexapods on copper foil using the hydrothermal method can enhance electrochemical performance for lithium-ion batteries [3]. Also, Co3O4 NRs with length of about 10 μm were prepared by improving traditional molten salt synthesis [9]. Nevertheless, most of these NRs are either powder materials or short on substrate restricting the applicability, which is a kind of motivation for further exploration. Recently, self-supported Co3O4
n
Corresponding author. Tel.: þ 86 87165031124; fax: þ 86 8 716515 3832. E-mail address: [email protected] (Y. Wang).
http://dx.doi.org/10.1016/j.matlet.2014.02.111 0167-577X/& 2014 Elsevier B.V. All rights reserved.
nanowire arrays have been successfully prepared on various conductive substrates including nickel foil, nickel foam and silicon wafer via a facile template-free hydrothermal synthesis method by Xia et al. [4]. In this experiment, the oxygen is indispensable for preparing vertically aligned Co3O4 nanowire arrays. In this present work, we amazedly obtained a mass of uniform Co3O4 NRs with a length up to tens of micrometers on nickel foil substrate modified from their recipe by ten times of NaNO3 without Co3O4 seed layer and oxygen injection. Then the growth mechanism is subsequently of detailed discussion. This work can render a deeper understanding of Co3O4 NRs and widen its applications.
2. Experimental All the reagents used in the experiments were purchased from commercial sources of analytical grade and used without any further purification. A grounded nickel foil with 5 cm 2 cm in size was cleaned by acetone and deionized water sequentially before placing at an angle against the wall of 80 mL Teflon. In a typical synthesis, 10 mmol Co(NO3)2 was firstly dissolved in 30 mL of H2O under stirring for 10 min to obtain a pink color solution, followed by adding 20 mL of 28 wt% ammonia solution till the color gradually turned into black in 30 min. Then 10 mmol NaNO3 was dissolved into the above solution. Lastly, the solution was transferred to the Teflon with nickel foil and the hydrothermal reaction was conducted at 120 1C for respective 6 and 12 h. After the reaction, the autoclave was cooled down to room temperature naturally and then the foil was collected from the solution, rinsed repeatedly with deionized water and annealed at 250 1C for 1 h in air.
188
C. Dong et al. / Materials Letters 123 (2014) 187–190
The crystal structure of Co3O4 NRs was characterized by X-ray diffraction (XRD, Rigaku TTRIII) with an incident X-ray wavelength of 1.540 ̊ (Cu Kα line). Scanning electron microscopy (SEM) analysis was taken on FEI QUANTA200 with a microscope operating at 30 kV. Detailed studies of the microstructure were also carried out by transmission electron microscopy (TEM) (JEOL JEM-2100) at an acceleration voltage of 200 kV.
3. Results and discussion The Co3O4 NRs have been successfully deposited on nickel foil. After hydrothermal reaction at 120 1C for 6 h, the foil is randomly covered with red and black products by eye, whereas the foil is uniformly covered for another 6 h. The phases of the precursors and Co3O4 NRs by heat treatment were investigated using XRD.
Fig. 1. (a) JCPDS for Co(OH)2 and (b) Co3O4, respectively. (c) and (d) are the XRD patterns of products after reaction for 6 h and 12 h before annealing on nickel foil. (e) and (f) are the XRD patterns of Co3O4 NRs for reaction time of 6 h and 12 h after annealing on nickel foil, respectively.
As-prepared precursors for reaction time of 6 h and 12 h were the mixture of crystalline Co(OH)2 and Co3O4 phase as illustrated by Fig. 1(c) and (d), which is in good agreement with other reports [4,5 and 10]. Fig. 1(e) and (f) shows the XRD patterns of the Co3O4 NRs after annealing at 250 1C for 1 h in air. All the identical peaks of the thermal treatment samples can be perfectly indexed to a cubic spinel phase of Co3O4 (JCPDS Card no. 42-1467 in Fig. 1(b)) except for the peaks originating from the nickel foil substrate. Besides, two diffraction peaks located at 51.81 and 76.41 from nickel foil are obviously observed in all products. The overview morphologies and microstructures of prepared Co3O4 NRs were viewed using SEM. Fig. 2 shows the top-surface images of typical Co3O4 NRs at low and high magnification, respectively. From the low magnification SEM image in Fig. 2 (a), it can be observed that highly uniform and highly dense Co3O4 NRs covered the whole surface of the substrate on a large scale. It is apparent that the products consist of big straight NRs bundles randomly laying down on the nickel foil. In Fig. 2(b), the featured bundle NRs are grouped from several individual NRs to even around 30 NRs with a slight difference in length. Meanwhile, some dispersed NRs are standing on the surface of NRs bundles as seen in Fig. 2 (c). By careful comparison, the length for dispersed NRs is of the order of micrometers on average, which is several times less than bundle NRs. However, the diameter is uniform about 1 μm in size regardless of bundle NRs or dispersed NRs. From the magnified images, we can see that all NRs are constructed through a great quantity of single uniform grains in both bundle NRs and dispersed NRs. We propose that the difference of both lattice and thermal coefficient between nickel foil and Co3O4 is possibly attributed to the different growth mechanisms, which will be discussed in following sections in more detail. To gain further insight into the detailed structure of Co3O4 NRs, the product was examined under TEM. The TEM images in Fig. 3 (a) clearly show the long isolated rod of about 1 μm in diameter with smooth but rough side walls and a circular solid end. Additionally, the TEM image indicates that the NRs in this sample are composed of subunits with more prominent grain-like structure. After magnification, in Fig. 3 (b), the isolated rod is apparently stacked layer-by-layer from single small grains. It is confirmed that the diameter of grains is of 50–200 nm from the
Fig. 2. (a) The overview SEM morphology of as-prepared Co3O4 NRs at low magnification. (b) and (c) are featured bundle NRs and dispersed NRs, respectively.
C. Dong et al. / Materials Letters 123 (2014) 187–190
189
Fig. 3. (a) is the low-magnification TEM images of isolated Co3O4 NRs. (b) High-magnification TEM image of a Co3O4 NR. (c) The grains from broken Co3O4 NRs.
Fig. 4. (a) The SEM images of bare grounded nickel foil. (b) and (c) are typical Co3O4 NRs after the hydrothermal reaction at 120 1C for 6 h after anneal. (d) The SEM images of Co3O4 NRs when the hydrothermal reaction totally goes on 12 h at 120 1C after anneal.
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C. Dong et al. / Materials Letters 123 (2014) 187–190
broken rod during ultrasonic disperse as depicted in Fig. 3 (c), which of course makes the side walls rough. Time-dependent experiments are carried out to understand the formation process of such interesting Co3O4 NRs. Fig. 4 (a) gives the surface image of the bare nickel foil with obvious grounded trace. As can be seen in Fig.4 (b), the substrate is covered by a dark layer with dispersed grains and white rods in different lengths at the early stage of the reaction (6 h), which consisted of Co(OH)2 and Co3O4 revealed by previous XRD characterization. In Fig.4 (c), it is a typical evidence of the nucleation center for Co3O4 NR growth on the nickel foil. When the reaction duration increasingly goes up to 12 h, the product contains a large number of NRs evolved into bundle Co3O4 NRs at first and then dispersed Co3O4 NRs as shown in Fig.4 (d). It is easy to understand that the Co3O4 NRs incline to agglomerate together to form bundle NRs at the very beginning of growth due to the existence of large difference between nickel foil and Co3O4 in terms of both lattice and thermal coefficient. After prolonged hydrothermal treatment, the dispersed Co3O4 NRs grew on the surface of bundle Co3O4 NRs because of an accommodation mismatch between the Co3O4 and the substrate. The bundle Co3O4 NRs, as matter of fact, play as a buffer for the subsequent growth of the dispersed Co3O4 NRs. 4. Conclusions In summary, Co3O4 NRs, having size as large as up to several tens of micrometers with about 1 μm in diameter have been formed into bundle and dispersed structures on the surface of nickel foil substrate using the simple hydrothermal method. A
plausible formation reason of bundle and dispersed structures is on account of different lattices and thermal coefficients between nickel foil and Co3O4 NRs. By taking a close look at the Co3O4 NRs, it is found that the rod is structured layer-by-layer from individual Co3O4 grain subunit in range of 50–200 nm in size.
Acknowledgments This work was supported by the Department of Science and Technology of Yunnan Province via the Key Project for the Science and Technology (Grant no.2011FA001), National Natural Science Foundation of China (Grant no.51262029), the Key Project of the Department of Education of Yunnan Province (ZD2013006).
References [1] Zhai TY, Yao JN. One-Dimensional Nanostructures: Principles and Applications. Hoboker, New Jersey: John Wiley & Sons, Inc.; 2012. [2] Xia YN, Yang PD, Sun YG, Wu YY, Mayers B, et al. Adv Mater 2003;15:353–89. [3] Wang Lm, Liu B, Ran SH, Huang HT, Wang XF, Liang B, et al. J Mater Chem 2012;22:23541–6. [4] Xia XH, Tu JP, Mai YJ, Wang XL, Gu CD, Zhao XB. J Mater Chem 2011;21:9319–25. [5] Hu LH, Peng Q, Li YD. J Am Chem Soc 2008;130:16136–7. [6] Wen Z, Zhu LP, Mei WM, Hu L, Li YG, Sun LW, et al. Sens Actuators B 2013;186:172–9. [7] Hoa ND, El-Safty SA. J Phys Chem C 2011;115:8466–74. [8] Xie XW, Li Y, Liu ZQ, Haruta M, Shen WJ. Nature 2009;458:746–9. [9] Liu YK, Wang GH, Xu CK, Wang WZ. Chem Commun 2002:1486–7. [10] Li YG, Wu YY. Chem Mater 2010;22:5537–42.