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Preparation and characterization of hollow Co3O4 spheres
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Materials Letters 62 (2008) 772 – 774 www.elsevier.com/locate/matlet
Preparation and characterization of hollow Co3O4 spheres Weiwei Zhao, Yang Liu, Hulin Li ⁎, Xiaogang Zhang Department of Chemistry, Nanjing University of Aeronautics and Astronautics Nanjing 210016, People's Republic of China Received 12 June 2007; accepted 22 June 2007 Available online 28 June 2007
Abstract Co3O4 hollow spheres were successfully prepared using hydrothermal synthesis in conjunction with the templating approach at 180 °C, with the addition of glucose and CoSO4·7H2O in sequence, followed by heating to 550 °C in air. The synthesized products were characterized by X-ray diffraction technique (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM results indicated that these Co3O4 hollow spheres had average diameters of ca. 1000 nm, and the wall thickness around the shell was approximately 200 nm. The Brunauer– Emmett–Teller (BET) surface area of these spheres was about 49.1 m2/g. The possible formation mechanism of Co3O4 hollow spheres has also been proposed. © 2007 Elsevier B.V. All rights reserved. Keywords: Co3O4; Hollow spheres; Hydrothermal; Microstructure; Nanomaterials
1. Introduction The fabrication of transition metal oxides has been the target of scientific interests in recent years because of their various properties [1,2]. Among these oxides, Co3O4 belongs to the spinel crystal structure based on a cubic closely-packed structure of oxide ions [3,4] and has attracted extra attention due to their broad range of applications such as solid-state sensors, ceramic pigments, catalysts and intercalation compounds for energy storage [5–12]. Meanwhile, hollow spherical structure materials have received considerable interests because of their potential applications in a large variety of fields including the controlled release of drugs, confined-space catalysis [13,14]. Up to now, various synthesis routes have been proposed to prepare metal oxide hollow spheres [15–19] and spinel oxide Co3O4 [20–22]. However, the methods about simple fabrication of Co3O4 hollow spheres are still scarce. Herein we reported a facile and novel method for the preparation of Co3O4 hollow spheres. This was accomplished easily by templating against colloidal particles under hydrothermal conditions. Besides, it involved non-use of initiators, surfactant or other toxic reagents that are commonly used for
production of hollow spheres, so it's also an environmentally friendly process. 2. Experimental All chemicals of analytical grade were used as received without further purification in the synthesis process and all aqueous solutions were prepared using high purity water (18 MΩ cm). 2.1. Preparation of Co3O4 hollow spheres Glucose was dissolved in distilled water (80 mL, 0.5 M) to form a clear solution. Subsequently, the obtained solution was placed in 100-mL Teflon-lined stainless steel autoclave and maintained at 180 °C for 16 h. Some of the obtained products were added with 1.5 g glucose and 1 g CoSO4·7H2O and then kept still under hydrothermal conditions at 180 °C for another 24 h. The products were centrifuged, washed several times, with water and then alcohol, and oven-dried at 80 °C for 5 h. Finally, the products were heated to 550 °C at 1 °C min− 1 for 3 h using a tube furnace in air. 2.2. Characterization
⁎ Corresponding author. Tel.: +86 13951021276; fax: +86 25 52112626. E-mail address: [email protected] (H. Li). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.06.057
X-ray diffraction technique (XRD) patterns of all the samples were conducted on a Bruker D8-ADVANCE diffractometer with
W. Zhao et al. / Materials Letters 62 (2008) 772–774
773
3. Results and discussion
Fig. 1. XRD patterns of the as prepared Co3O4 hollow spheres.
CuKα radiation of wavelength λ = 0.15418 nm. The Brunauer– Emmett–Teller (BET) surface area was measured on a Micromeritics ASAP 2010 instrument. The microscopic features of the samples were observed with a field-emission scanning electron microscope (FESEM) (LEO1530VP), and transmission electron microscopy (TEM) (FEI Tecnai G2 20 S-TWIN) operated at 200 kV.
Fig. 2. FESEM images of the as prepared Co3O4 hollow spheres.
The crystalline structure of the sample was characterized using an X-ray diffractometer and shown in Fig. 1. All these diffraction peaks, including not only the peak positions but also their relative intensities, can be perfectly indexed into the cubic phase of Co3O4. The result is in good agreement with the standard spectrum (JCPDS, No. 42-1467). No characteristic peaks of other impurity phases have been detected, indicating that the final product is of high purity. FESEM and TEM images of the final product are shown in Figs. 2 and 3, respectively. Both intact and broken hollow spheres were obtained (Fig. 2a). Breakage of the spheres may be due to the escaping of CO2 during calcinations. As was seen in the SEM picture of an individual sphere (Fig. 2b), the surface roughness was due to the aggregation of Co3O4 nanospheres, leading to an inherent porosity and a high surface area could be expected. TEM (Fig. 3a and b) shows the spherical hollow structures of the product. A wall thickness of approximately 200 nm was estimated from the minimum separation between the hollow core and the exterior surface of the shell. The BET surface area of the sample was about 49.1 m2/g. The hollow structure and high surface area of Co3O4 should be of interest to material scientists, since many properties (including the electronic and catalytic) are size-dependent, and this would greatly widen its range of applications in various fields. The formation mechanism on Co3O4 hollow spheres is also proposed, which can be attributed to the templating against colloidal particles under hydrothermal conditions. When aqueous glucose solution was maintained under hydrothermal conditions at 180 °C, carbon spheres with hydrophilic and reactive surface could be formed [23], which involved the aromatization and carbonization steps and then appeared to comply with the LaMer model [24–26]. After the addition of CoSO4·7H2O and glucose as new carbon source, under
Fig. 3. TEM images of the as prepared Co3O4 hollow spheres.
774
W. Zhao et al. / Materials Letters 62 (2008) 772–774
hydrothermal conditions again, the hydrophilic and reactive surface surrounding these spheres was reactivated and dehydration and carbonization steps recontinued, the cobalt ions were then embedded into the new-formed carbon layer during this process. Filtration and calcinations of the solid content led to Co3O4 hollow spheres.
4. Conclusions Co3O4 hollow spheres were successfully prepared by a simple and environmentally friendly synthesis route. The XRD analysis demonstrated that the product was a cubic structure Co3O4. FESEM and TEM revealed the hollow spherical structures. Nitrogen adsorption displayed the surface area of the product. The possible formation mechanism on Co3O4 hollow spheres is also proposed. This approach may be extended to the preparation of various metal oxide hollow spheres. Acknowledgement The authors acknowledge support from the Foundation of Nanjing University of Aeronautics and Astronautics (grants S0427-062). References [1] W.F.S. Spear, D.S. Tamhuser, Phys. Rev., B 7 (1993) 831. [2] W.C. Hagel, J. Appl. Phys. 36 (1965) 2586.
[3] C. Mocuta, A. Barbier, G. Renaud, Appl. Surf. Sci. 56 (2002) 162. [4] A.F. Wells, Structural Inorganic Chemistry, vol. 4, Clarendon Press, Oxford, U.K., 1975 [5] S. Weichel, P. Møller, J. Surf. Sci. Technol. 399 (1998) 219. [6] E. Matijevic, Chem. Mater. 5 (1993) 412. [7] P. Poizot, S. Laruelle, S. Grugeon, L. Dupont, J.M. Tarascon, Nature 407 (2000) 496. [8] T. Sugimoto, E. Matijevic, J. Inorg. Nucl. Chem. 41 (1979) 165. [9] R. Xu, H.C. Zeng, J. Phys. Chem., B 107 (2003) 926. [10] J. Feng, H.C. Zeng, Chem. Mater. 15 (2003) 2829. [11] W.-Y. Li, L.-N. Xu, J. Chen, Adv. Funct. Mater. 15 (2005) 851. [12] T. Maruyama, S. Arai, J. Electrochem. Soc. 143 (1996) 1383. [13] K. Kamata, Y. Lu, Y. Xia, J. Am. Chem. Soc. 125 (2003) 2384. [14] Y. Wang, L. Cai, Y. Xia, Adv. Mater. 17 (2005) 473. [15] Y. Lu, et al., Nature 398 (1999) 223. [16] B.M. Discher, et al., Science 284 (1999) 1143. [17] A. Imhof, Langmuir 17 (2001) 3579. [18] T. von Werne, T.E. Patten, J. Am. Chem. Soc. 123 (2001) 7497. [19] R.K. Rana, Y. Mastai, A. Gedanken, Adv. Mater. 14 (2002) 1414. [20] R.N. Singh, J.F. Koenig, G. Poillerat, P. Chartier, J. Electrochem. Soc. 137 (1990) 1480. [21] C.S. Cheng, M. Serizawa, H. Sakata, T. Hirayama, Mater. Chem. Phys. 53 (1998) 255. [22] M.E. Baydi, G. Poillerat, J.L. Rehspringer, J.L. Gautier, J.F. Koenig, P. Chartier, J. Solid State Chem. 109 (1994) 281. [23] X. Sun, Y. Li, Angew. Chem., Int. Ed. Engl. 43 (2004) 597. [24] T. Sakaka, M. Shibata, T. Miki, H. Hirosue, N. Hayashi, Bioresour. Technol. 58 (1996) 197. [25] G.C.A. Luijkx, F. van Rantwijk, H. van Bekkum, M.J. Antal Jr., Carbohydr. Res. 272 (1995) 191. [26] V.K. LaMer, Ind. Eng. Chem. 44 (1952) 1270.
Materials Letters 62 (2008) 772 – 774 www.elsevier.com/locate/matlet
Preparation and characterization of hollow Co3O4 spheres Weiwei Zhao, Yang Liu, Hulin Li ⁎, Xiaogang Zhang Department of Chemistry, Nanjing University of Aeronautics and Astronautics Nanjing 210016, People's Republic of China Received 12 June 2007; accepted 22 June 2007 Available online 28 June 2007
Abstract Co3O4 hollow spheres were successfully prepared using hydrothermal synthesis in conjunction with the templating approach at 180 °C, with the addition of glucose and CoSO4·7H2O in sequence, followed by heating to 550 °C in air. The synthesized products were characterized by X-ray diffraction technique (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM results indicated that these Co3O4 hollow spheres had average diameters of ca. 1000 nm, and the wall thickness around the shell was approximately 200 nm. The Brunauer– Emmett–Teller (BET) surface area of these spheres was about 49.1 m2/g. The possible formation mechanism of Co3O4 hollow spheres has also been proposed. © 2007 Elsevier B.V. All rights reserved. Keywords: Co3O4; Hollow spheres; Hydrothermal; Microstructure; Nanomaterials
1. Introduction The fabrication of transition metal oxides has been the target of scientific interests in recent years because of their various properties [1,2]. Among these oxides, Co3O4 belongs to the spinel crystal structure based on a cubic closely-packed structure of oxide ions [3,4] and has attracted extra attention due to their broad range of applications such as solid-state sensors, ceramic pigments, catalysts and intercalation compounds for energy storage [5–12]. Meanwhile, hollow spherical structure materials have received considerable interests because of their potential applications in a large variety of fields including the controlled release of drugs, confined-space catalysis [13,14]. Up to now, various synthesis routes have been proposed to prepare metal oxide hollow spheres [15–19] and spinel oxide Co3O4 [20–22]. However, the methods about simple fabrication of Co3O4 hollow spheres are still scarce. Herein we reported a facile and novel method for the preparation of Co3O4 hollow spheres. This was accomplished easily by templating against colloidal particles under hydrothermal conditions. Besides, it involved non-use of initiators, surfactant or other toxic reagents that are commonly used for
production of hollow spheres, so it's also an environmentally friendly process. 2. Experimental All chemicals of analytical grade were used as received without further purification in the synthesis process and all aqueous solutions were prepared using high purity water (18 MΩ cm). 2.1. Preparation of Co3O4 hollow spheres Glucose was dissolved in distilled water (80 mL, 0.5 M) to form a clear solution. Subsequently, the obtained solution was placed in 100-mL Teflon-lined stainless steel autoclave and maintained at 180 °C for 16 h. Some of the obtained products were added with 1.5 g glucose and 1 g CoSO4·7H2O and then kept still under hydrothermal conditions at 180 °C for another 24 h. The products were centrifuged, washed several times, with water and then alcohol, and oven-dried at 80 °C for 5 h. Finally, the products were heated to 550 °C at 1 °C min− 1 for 3 h using a tube furnace in air. 2.2. Characterization
⁎ Corresponding author. Tel.: +86 13951021276; fax: +86 25 52112626. E-mail address: [email protected] (H. Li). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.06.057
X-ray diffraction technique (XRD) patterns of all the samples were conducted on a Bruker D8-ADVANCE diffractometer with
W. Zhao et al. / Materials Letters 62 (2008) 772–774
773
3. Results and discussion
Fig. 1. XRD patterns of the as prepared Co3O4 hollow spheres.
CuKα radiation of wavelength λ = 0.15418 nm. The Brunauer– Emmett–Teller (BET) surface area was measured on a Micromeritics ASAP 2010 instrument. The microscopic features of the samples were observed with a field-emission scanning electron microscope (FESEM) (LEO1530VP), and transmission electron microscopy (TEM) (FEI Tecnai G2 20 S-TWIN) operated at 200 kV.
Fig. 2. FESEM images of the as prepared Co3O4 hollow spheres.
The crystalline structure of the sample was characterized using an X-ray diffractometer and shown in Fig. 1. All these diffraction peaks, including not only the peak positions but also their relative intensities, can be perfectly indexed into the cubic phase of Co3O4. The result is in good agreement with the standard spectrum (JCPDS, No. 42-1467). No characteristic peaks of other impurity phases have been detected, indicating that the final product is of high purity. FESEM and TEM images of the final product are shown in Figs. 2 and 3, respectively. Both intact and broken hollow spheres were obtained (Fig. 2a). Breakage of the spheres may be due to the escaping of CO2 during calcinations. As was seen in the SEM picture of an individual sphere (Fig. 2b), the surface roughness was due to the aggregation of Co3O4 nanospheres, leading to an inherent porosity and a high surface area could be expected. TEM (Fig. 3a and b) shows the spherical hollow structures of the product. A wall thickness of approximately 200 nm was estimated from the minimum separation between the hollow core and the exterior surface of the shell. The BET surface area of the sample was about 49.1 m2/g. The hollow structure and high surface area of Co3O4 should be of interest to material scientists, since many properties (including the electronic and catalytic) are size-dependent, and this would greatly widen its range of applications in various fields. The formation mechanism on Co3O4 hollow spheres is also proposed, which can be attributed to the templating against colloidal particles under hydrothermal conditions. When aqueous glucose solution was maintained under hydrothermal conditions at 180 °C, carbon spheres with hydrophilic and reactive surface could be formed [23], which involved the aromatization and carbonization steps and then appeared to comply with the LaMer model [24–26]. After the addition of CoSO4·7H2O and glucose as new carbon source, under
Fig. 3. TEM images of the as prepared Co3O4 hollow spheres.
774
W. Zhao et al. / Materials Letters 62 (2008) 772–774
hydrothermal conditions again, the hydrophilic and reactive surface surrounding these spheres was reactivated and dehydration and carbonization steps recontinued, the cobalt ions were then embedded into the new-formed carbon layer during this process. Filtration and calcinations of the solid content led to Co3O4 hollow spheres.
4. Conclusions Co3O4 hollow spheres were successfully prepared by a simple and environmentally friendly synthesis route. The XRD analysis demonstrated that the product was a cubic structure Co3O4. FESEM and TEM revealed the hollow spherical structures. Nitrogen adsorption displayed the surface area of the product. The possible formation mechanism on Co3O4 hollow spheres is also proposed. This approach may be extended to the preparation of various metal oxide hollow spheres. Acknowledgement The authors acknowledge support from the Foundation of Nanjing University of Aeronautics and Astronautics (grants S0427-062). References [1] W.F.S. Spear, D.S. Tamhuser, Phys. Rev., B 7 (1993) 831. [2] W.C. Hagel, J. Appl. Phys. 36 (1965) 2586.
[3] C. Mocuta, A. Barbier, G. Renaud, Appl. Surf. Sci. 56 (2002) 162. [4] A.F. Wells, Structural Inorganic Chemistry, vol. 4, Clarendon Press, Oxford, U.K., 1975 [5] S. Weichel, P. Møller, J. Surf. Sci. Technol. 399 (1998) 219. [6] E. Matijevic, Chem. Mater. 5 (1993) 412. [7] P. Poizot, S. Laruelle, S. Grugeon, L. Dupont, J.M. Tarascon, Nature 407 (2000) 496. [8] T. Sugimoto, E. Matijevic, J. Inorg. Nucl. Chem. 41 (1979) 165. [9] R. Xu, H.C. Zeng, J. Phys. Chem., B 107 (2003) 926. [10] J. Feng, H.C. Zeng, Chem. Mater. 15 (2003) 2829. [11] W.-Y. Li, L.-N. Xu, J. Chen, Adv. Funct. Mater. 15 (2005) 851. [12] T. Maruyama, S. Arai, J. Electrochem. Soc. 143 (1996) 1383. [13] K. Kamata, Y. Lu, Y. Xia, J. Am. Chem. Soc. 125 (2003) 2384. [14] Y. Wang, L. Cai, Y. Xia, Adv. Mater. 17 (2005) 473. [15] Y. Lu, et al., Nature 398 (1999) 223. [16] B.M. Discher, et al., Science 284 (1999) 1143. [17] A. Imhof, Langmuir 17 (2001) 3579. [18] T. von Werne, T.E. Patten, J. Am. Chem. Soc. 123 (2001) 7497. [19] R.K. Rana, Y. Mastai, A. Gedanken, Adv. Mater. 14 (2002) 1414. [20] R.N. Singh, J.F. Koenig, G. Poillerat, P. Chartier, J. Electrochem. Soc. 137 (1990) 1480. [21] C.S. Cheng, M. Serizawa, H. Sakata, T. Hirayama, Mater. Chem. Phys. 53 (1998) 255. [22] M.E. Baydi, G. Poillerat, J.L. Rehspringer, J.L. Gautier, J.F. Koenig, P. Chartier, J. Solid State Chem. 109 (1994) 281. [23] X. Sun, Y. Li, Angew. Chem., Int. Ed. Engl. 43 (2004) 597. [24] T. Sakaka, M. Shibata, T. Miki, H. Hirosue, N. Hayashi, Bioresour. Technol. 58 (1996) 197. [25] G.C.A. Luijkx, F. van Rantwijk, H. van Bekkum, M.J. Antal Jr., Carbohydr. Res. 272 (1995) 191. [26] V.K. LaMer, Ind. Eng. Chem. 44 (1952) 1270.