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Hydrothermal synthesis of γ -MnOOH nanowires and α - MnO2 sea urchin-like clusters
Solid State Communications 141 (2007) 427–430 www.elsevier.com/locate/ssc
Hydrothermal synthesis of γ -MnOOH nanowires and α-MnO2 sea urchin-like clusters Zhiqing Zhang, Jin Mu ∗ Department of Chemistry, Key Laboratory for Ultrafine Materials of Ministry of Education, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China Received 13 April 2006; received in revised form 3 December 2006; accepted 12 December 2006 by G. Abstreiter Available online 28 December 2006
Abstract γ -MnOOH nanowires and α-MnO2 sea urchin-like clusters have been selectively synthesized in two oxidation systems via a facile hydrothermal route. The γ -MnOOH nanowires were obtained from MnSO4 in the presence of H2 O2 as an oxidizer in an alkaline solution, while the α-MnO2 sea urchin-like clusters were formed from MnSO4 in the presence of K2 Cr2 O7 as an oxidizer in an acid solution. c 2006 Elsevier Ltd. All rights reserved.
PACS: 68.65.-k; 68.70.+w; 81.10.Dn Keywords: A. α-MnO2 ; A. γ -MnOOH; B. Nanowires; C. Hydrothermal
1. Introduction Nanostructures are of great interest not only for their fundamental scientific significance but also for many applications that derive from their peculiar and fascinating properties, superior to the corresponding bulk counterparts [1,2]. In recent years, 1-D nanostructures have been demonstrated to be of superior electrical, optical, mechanical and thermal properties, showing their potential applications as building units and interconnections in microelectronic and optoelectronic devices [3–7]. Various convenient synthetic strategies for preparing new nanostructures with novel shapes have been developed. Hydrothermal synthesis is an interesting technique for preparing large quantities of inorganic materials including metals, chalcogenides and metal oxides/hydroxides with different nanoarchitectures such as nanowires, nanorods, nanobelts, nanourchins and so forth [8–13]. Among the metal oxides, manganese dioxide is one of the most attractive inorganic materials because of its excellent physical and chemical properties and wide applications in catalysis, ion exchange, molecular adsorption, biosensors and energy storage, and especially as an
electrode material in Li/MnO2 batteries [14–20]. It is wellknown that manganese dioxide can exist in different structural forms, α-, β-, γ - and λ-types, etc. The α- and γ -MnO2 are promising candidates as cathodes in lithium ion batteries. Manganese oxyhydroxide (MnOOH) is an important metal hydroxide with considerable interest in many applications, e.g. electrochemical reactions, batteries, electrochromics [21]. Much effort has been directed toward the preparation of low-dimensional manganese oxides/hydroxide nanostructures with various polymorphs. However, few reports are focused on the reaction conditions, such as the pH of the system, the reaction time, the kind of oxidizer, and so on. We therefore report on the effect of pH and oxidizer on the morphology and composition of the manganese oxides. In our work, α-MnO2 and γ -MnOOH were synthesized by simple oxidation of MnSO4 solution with two kinds of oxidizer, i.e., K2 Cr2 O7 in H2 SO4 and H2 O2 in NaOH under hydrothermal conditions, respectively. These synthetic routes require no templates, catalysts or organic reagents nor any special post-synthesis treatment for purification. 2. Experimental details
∗ Corresponding author. Tel.: +86 21 64252214; fax: +86 21 64252485.
E-mail address: [email protected] (J. Mu). c 2006 Elsevier Ltd. All rights reserved. 0038-1098/$ - see front matter doi:10.1016/j.ssc.2006.12.009
All chemicals were of analytical grade and used without further purification. Deionized water was used throughout. Two
428
Z. Zhang, J. Mu / Solid State Communications 141 (2007) 427–430
into a salmon pink solution. The following process was similar to the former one. The powder X-ray diffraction (XRD) patterns were measured on a Rigaku D/max 2550 VB/PC X-ray diffractometer ˚ and graphite monochro(Cu Kα radiation, λ = 1.54178 A, mator) at ambient temperature. Scanning electron microscope (SEM, JEOL JSM-6360LV) images were taken at an accelerating voltage of 15 kV. Transmission electron microscopy (TEM, JEM100-CXII) was used to observe the morphology and size of products. 3. Results and discussion 3.1. Composition of the products Fig. 1. XRD patterns of two samples: (a) H2 O2 as the oxidizer in NaOH solution and (b) K2 Cr2 O7 as the oxidizer in H2 SO4 solution.
parallel experiments were carried out by altering the oxidizers and pH of the reaction solution, so that the influence of the two parameters on the composition and morphology of the products can be discovered. In brief, the synthesis process can be described as follows: 10 mmol MnSO4 ·H2 O was added into 0.1 mol/L NaOH solution, then 6 mmol H2 O2 was added, the total volume was adjusted to 18 mL (brown, pH = 8). The brown solution was loaded and sealed into a 24 mL Teflon-lined stainless steel autoclave and heated at 150 ◦ C for 15 h. The autoclave was allowed to cool to room temperature naturally. Then the precipitates were collected and washed repeatedly with deionized water, and finally dried in a vacuum drying oven at 50 ◦ C for 4 h. In another experiment, 4 mmol K2 Cr2 O7 and 10 mmol MnSO4 ·H2 O were added to 1 mol/L H2 SO4 solution (the total volume was 18 mL), in which the reactants turned
Fig. 1 shows the XRD patterns of two products obtained from the two different reaction systems. All the diffraction peaks in Fig. 1(a) can be assigned to γ -MnOOH (JCPDS 411379). Thus, the obtained γ -MnOOH is of high purity and good crystallinity. The extremely narrow and strong diffraction peak positioned at 2θ = 26.2◦ suggests (111) preferential growth of γ -MnOOH under hydrothermal conditions. The XRD pattern in Fig. 1b corresponds to α-MnO2 (JCPDS 44-0141). The chemical reactions involved in the two hydrothermal syntheses are briefly described below: MnSO4 + H2 O2 + 2NaOH → γ -MnOOH + 2H2 O + Na2 SO4 (1) 3MnSO4 + K2 Cr2 O7 + H2 SO4 → 3α-MnO2 + Cr2 (SO4 )3 + K2 SO4 + H2 O(2). (2) In these experiments, no organic template or additional catalyst are used. It is known from the above equations that all
Fig. 2. Typical SEM (a) and TEM (b, c and d) images of the synthesized γ -MnOOH.
Z. Zhang, J. Mu / Solid State Communications 141 (2007) 427–430
429
Fig. 3. Typical SEM (a and b) and TEM (c and d) images of the synthesized α-MnO2 .
of the reactants are soluble in water, and only the target products are in the form of precipitate. Since the reaction needs no posttreatment for purification, this method has potential for largescale production.
second step the growth of the nanowires around these nuclei. The overall size and arm lengths are probably controlled by the precipitation of the α-MnO2 particles. But there are only nanowires in the γ -MnOOH system because of the rapid reaction rate.
3.2. Morphology of the products 4. Conclusions The morphologies of the two products obtained were examined by SEM and TEM. Fig. 2 shows the SEM and TEM images of the nanowires of γ -MnOOH obtained from H2 O2 as the oxidizer in alkaline solution. The nanostructures shown in Fig. 2a and b are composed of thinner and shorter nanowires, as exhibited in Fig. 2c and d. These slim nanowires are several tens of nanometres in diameter, but the length is not uniform, ranging from 400 nm to 2 µm. Fig. 3 shows the SEM and TEM images of 3-D α-MnO2 nanostructures obtained from K2 Cr2 O7 as the oxidizer in acid solution. The low-magnification images in Fig. 3a and c display a lot of sea urchin-like clusters. The higher magnification images in Fig. 3b and d clearly show the hierarchical structures. The clusters are composed of nanowires of 50–60 nm in diameter. The results indicate that the composition and morphology of manganese oxides are dependent on the oxidizer and the pH of the reaction system. In acid solution, the redox potential 3+ (1.33 V) is slightly higher than that of of Cr2 O2− 7 /Cr 2+ MnO2 /Mn (1.23 V), so that the reaction of Mn2+ with 2− Cr2 O7 is mild and slow. However, the reaction of Mn2+ with H2 O2 is relatively rapid in alkaline solution due to the distinguishing redox potential. Hence, we deduce that the sea urchin-like shape of α-MnO2 results from a two-step mechanism. It seems to involve the nucleation first, and in a
The γ -MnOOH nanowires and α-MnO2 sea urchin-like clusters were obtained with simple hydrothermal processes. The oxidizer and pH dominate the composition and morphology of manganese oxides. Acknowledgements This work was supported by Excellent Young Teacher Program of the Ministry of Education and Crystal International (Group) Inc. We thank the Shanghai Education Committee for support. References [1] H.S. Nalwa, Handbook of Nanostructured Materials and Nanotechnology, Academic Press, New York, 2000. [2] C. Burda, X.B. Chen, R. Narayanan, M.A. El-Sayed, Chem. Rev. 105 (2005) 1025. [3] J.T. Hu, T.W. Odom, C.M. Lieber, Acc. Chem. Res. 32 (1999) 435. [4] P.M. Forster, A.K. Cheetham, Angew. Chem. Int. Ed. 41 (2002) 457. [5] (a) X. Wang, J. Zhuang, Q. Peng, Y.D. Li, Nature 437 (2005) 121; (b) J.W. Wang, X. Wang, Y.D. Li, Inorg. Chem. 43 (2004) 7552. [6] K.A. Dick, K. Deooert, M.W. Larsson, T. Martensson, W. Seifert, L.R. Wallenberg, L. Samuelson, Nat. Mater. 3 (2004) 380. [7] Z.L. Wang, Adv. Mater. 15 (2003) 432. [8] G.H. Du, Z.Y. Yuan, G. Van Tendeloo, Appl. Phys. Lett. 86 (2005) 063113.
430 [9] [10] [11] [12]
Z. Zhang, J. Mu / Solid State Communications 141 (2007) 427–430
X. Wang, Y. Li, Chem. Commun. 764 (2002) 435. S. Wei, J. Lu, W. Yu, H. Zhang, Y. Qian, Inorg. Chem. 44 (2005) 3844. L. Qiu, Y. Wei, V.G. Pol, A. Gedanken, Inorg. Chem. 43 (2004) 6061. J.C. Yu, A. Xu, L. Zhang, R. Song, L. Wu, J. Phys. Chem. B 108 (2004) 64. [13] Y. Ding, G. Zhang, H. Wu, B. Hai, L. Wang, Y. Qian, Chem. Mater. 13 (2001) 435. [14] (a) Y. Chabre, J. Pannetier, Prog. Solid State Chem. 23 (1995) 1; (b) M.M. Thackeray, Prog. Solid State Chem. 25 (1997) 1.
[15] L. Espinal, S.L. Suib, J.F. Rusling, J. Am. Chem. Soc. 126 (2004) 7676. [16] R. Chitrakar, H. Kanoh, Y.S. Kim, Y. Miyai, K. Ooi, J. Solid State Chem. 160 (2001) 69. [17] A.R. Armstrong, P.G. Bruce, Nature 381 (1996) 499. [18] B. Ammundsen, J. Paulsen, Adv. Mater. 13 (2001) 943. [19] M. Winter, R.J. Brodd, Chem. Rev. 104 (2004) 4245. [20] X. Chen, X. Li, Y. Jiang, C. Shi, X. Li, Solid State Commun. 136 (2005) 94. [21] S. Ardizzone, C.L. Bianchi, D. Tirelli, Colloids Surf. A 134 (1998) 305.
Hydrothermal synthesis of γ -MnOOH nanowires and α-MnO2 sea urchin-like clusters Zhiqing Zhang, Jin Mu ∗ Department of Chemistry, Key Laboratory for Ultrafine Materials of Ministry of Education, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China Received 13 April 2006; received in revised form 3 December 2006; accepted 12 December 2006 by G. Abstreiter Available online 28 December 2006
Abstract γ -MnOOH nanowires and α-MnO2 sea urchin-like clusters have been selectively synthesized in two oxidation systems via a facile hydrothermal route. The γ -MnOOH nanowires were obtained from MnSO4 in the presence of H2 O2 as an oxidizer in an alkaline solution, while the α-MnO2 sea urchin-like clusters were formed from MnSO4 in the presence of K2 Cr2 O7 as an oxidizer in an acid solution. c 2006 Elsevier Ltd. All rights reserved.
PACS: 68.65.-k; 68.70.+w; 81.10.Dn Keywords: A. α-MnO2 ; A. γ -MnOOH; B. Nanowires; C. Hydrothermal
1. Introduction Nanostructures are of great interest not only for their fundamental scientific significance but also for many applications that derive from their peculiar and fascinating properties, superior to the corresponding bulk counterparts [1,2]. In recent years, 1-D nanostructures have been demonstrated to be of superior electrical, optical, mechanical and thermal properties, showing their potential applications as building units and interconnections in microelectronic and optoelectronic devices [3–7]. Various convenient synthetic strategies for preparing new nanostructures with novel shapes have been developed. Hydrothermal synthesis is an interesting technique for preparing large quantities of inorganic materials including metals, chalcogenides and metal oxides/hydroxides with different nanoarchitectures such as nanowires, nanorods, nanobelts, nanourchins and so forth [8–13]. Among the metal oxides, manganese dioxide is one of the most attractive inorganic materials because of its excellent physical and chemical properties and wide applications in catalysis, ion exchange, molecular adsorption, biosensors and energy storage, and especially as an
electrode material in Li/MnO2 batteries [14–20]. It is wellknown that manganese dioxide can exist in different structural forms, α-, β-, γ - and λ-types, etc. The α- and γ -MnO2 are promising candidates as cathodes in lithium ion batteries. Manganese oxyhydroxide (MnOOH) is an important metal hydroxide with considerable interest in many applications, e.g. electrochemical reactions, batteries, electrochromics [21]. Much effort has been directed toward the preparation of low-dimensional manganese oxides/hydroxide nanostructures with various polymorphs. However, few reports are focused on the reaction conditions, such as the pH of the system, the reaction time, the kind of oxidizer, and so on. We therefore report on the effect of pH and oxidizer on the morphology and composition of the manganese oxides. In our work, α-MnO2 and γ -MnOOH were synthesized by simple oxidation of MnSO4 solution with two kinds of oxidizer, i.e., K2 Cr2 O7 in H2 SO4 and H2 O2 in NaOH under hydrothermal conditions, respectively. These synthetic routes require no templates, catalysts or organic reagents nor any special post-synthesis treatment for purification. 2. Experimental details
∗ Corresponding author. Tel.: +86 21 64252214; fax: +86 21 64252485.
E-mail address: [email protected] (J. Mu). c 2006 Elsevier Ltd. All rights reserved. 0038-1098/$ - see front matter doi:10.1016/j.ssc.2006.12.009
All chemicals were of analytical grade and used without further purification. Deionized water was used throughout. Two
428
Z. Zhang, J. Mu / Solid State Communications 141 (2007) 427–430
into a salmon pink solution. The following process was similar to the former one. The powder X-ray diffraction (XRD) patterns were measured on a Rigaku D/max 2550 VB/PC X-ray diffractometer ˚ and graphite monochro(Cu Kα radiation, λ = 1.54178 A, mator) at ambient temperature. Scanning electron microscope (SEM, JEOL JSM-6360LV) images were taken at an accelerating voltage of 15 kV. Transmission electron microscopy (TEM, JEM100-CXII) was used to observe the morphology and size of products. 3. Results and discussion 3.1. Composition of the products Fig. 1. XRD patterns of two samples: (a) H2 O2 as the oxidizer in NaOH solution and (b) K2 Cr2 O7 as the oxidizer in H2 SO4 solution.
parallel experiments were carried out by altering the oxidizers and pH of the reaction solution, so that the influence of the two parameters on the composition and morphology of the products can be discovered. In brief, the synthesis process can be described as follows: 10 mmol MnSO4 ·H2 O was added into 0.1 mol/L NaOH solution, then 6 mmol H2 O2 was added, the total volume was adjusted to 18 mL (brown, pH = 8). The brown solution was loaded and sealed into a 24 mL Teflon-lined stainless steel autoclave and heated at 150 ◦ C for 15 h. The autoclave was allowed to cool to room temperature naturally. Then the precipitates were collected and washed repeatedly with deionized water, and finally dried in a vacuum drying oven at 50 ◦ C for 4 h. In another experiment, 4 mmol K2 Cr2 O7 and 10 mmol MnSO4 ·H2 O were added to 1 mol/L H2 SO4 solution (the total volume was 18 mL), in which the reactants turned
Fig. 1 shows the XRD patterns of two products obtained from the two different reaction systems. All the diffraction peaks in Fig. 1(a) can be assigned to γ -MnOOH (JCPDS 411379). Thus, the obtained γ -MnOOH is of high purity and good crystallinity. The extremely narrow and strong diffraction peak positioned at 2θ = 26.2◦ suggests (111) preferential growth of γ -MnOOH under hydrothermal conditions. The XRD pattern in Fig. 1b corresponds to α-MnO2 (JCPDS 44-0141). The chemical reactions involved in the two hydrothermal syntheses are briefly described below: MnSO4 + H2 O2 + 2NaOH → γ -MnOOH + 2H2 O + Na2 SO4 (1) 3MnSO4 + K2 Cr2 O7 + H2 SO4 → 3α-MnO2 + Cr2 (SO4 )3 + K2 SO4 + H2 O(2). (2) In these experiments, no organic template or additional catalyst are used. It is known from the above equations that all
Fig. 2. Typical SEM (a) and TEM (b, c and d) images of the synthesized γ -MnOOH.
Z. Zhang, J. Mu / Solid State Communications 141 (2007) 427–430
429
Fig. 3. Typical SEM (a and b) and TEM (c and d) images of the synthesized α-MnO2 .
of the reactants are soluble in water, and only the target products are in the form of precipitate. Since the reaction needs no posttreatment for purification, this method has potential for largescale production.
second step the growth of the nanowires around these nuclei. The overall size and arm lengths are probably controlled by the precipitation of the α-MnO2 particles. But there are only nanowires in the γ -MnOOH system because of the rapid reaction rate.
3.2. Morphology of the products 4. Conclusions The morphologies of the two products obtained were examined by SEM and TEM. Fig. 2 shows the SEM and TEM images of the nanowires of γ -MnOOH obtained from H2 O2 as the oxidizer in alkaline solution. The nanostructures shown in Fig. 2a and b are composed of thinner and shorter nanowires, as exhibited in Fig. 2c and d. These slim nanowires are several tens of nanometres in diameter, but the length is not uniform, ranging from 400 nm to 2 µm. Fig. 3 shows the SEM and TEM images of 3-D α-MnO2 nanostructures obtained from K2 Cr2 O7 as the oxidizer in acid solution. The low-magnification images in Fig. 3a and c display a lot of sea urchin-like clusters. The higher magnification images in Fig. 3b and d clearly show the hierarchical structures. The clusters are composed of nanowires of 50–60 nm in diameter. The results indicate that the composition and morphology of manganese oxides are dependent on the oxidizer and the pH of the reaction system. In acid solution, the redox potential 3+ (1.33 V) is slightly higher than that of of Cr2 O2− 7 /Cr 2+ MnO2 /Mn (1.23 V), so that the reaction of Mn2+ with 2− Cr2 O7 is mild and slow. However, the reaction of Mn2+ with H2 O2 is relatively rapid in alkaline solution due to the distinguishing redox potential. Hence, we deduce that the sea urchin-like shape of α-MnO2 results from a two-step mechanism. It seems to involve the nucleation first, and in a
The γ -MnOOH nanowires and α-MnO2 sea urchin-like clusters were obtained with simple hydrothermal processes. The oxidizer and pH dominate the composition and morphology of manganese oxides. Acknowledgements This work was supported by Excellent Young Teacher Program of the Ministry of Education and Crystal International (Group) Inc. We thank the Shanghai Education Committee for support. References [1] H.S. Nalwa, Handbook of Nanostructured Materials and Nanotechnology, Academic Press, New York, 2000. [2] C. Burda, X.B. Chen, R. Narayanan, M.A. El-Sayed, Chem. Rev. 105 (2005) 1025. [3] J.T. Hu, T.W. Odom, C.M. Lieber, Acc. Chem. Res. 32 (1999) 435. [4] P.M. Forster, A.K. Cheetham, Angew. Chem. Int. Ed. 41 (2002) 457. [5] (a) X. Wang, J. Zhuang, Q. Peng, Y.D. Li, Nature 437 (2005) 121; (b) J.W. Wang, X. Wang, Y.D. Li, Inorg. Chem. 43 (2004) 7552. [6] K.A. Dick, K. Deooert, M.W. Larsson, T. Martensson, W. Seifert, L.R. Wallenberg, L. Samuelson, Nat. Mater. 3 (2004) 380. [7] Z.L. Wang, Adv. Mater. 15 (2003) 432. [8] G.H. Du, Z.Y. Yuan, G. Van Tendeloo, Appl. Phys. Lett. 86 (2005) 063113.
430 [9] [10] [11] [12]
Z. Zhang, J. Mu / Solid State Communications 141 (2007) 427–430
X. Wang, Y. Li, Chem. Commun. 764 (2002) 435. S. Wei, J. Lu, W. Yu, H. Zhang, Y. Qian, Inorg. Chem. 44 (2005) 3844. L. Qiu, Y. Wei, V.G. Pol, A. Gedanken, Inorg. Chem. 43 (2004) 6061. J.C. Yu, A. Xu, L. Zhang, R. Song, L. Wu, J. Phys. Chem. B 108 (2004) 64. [13] Y. Ding, G. Zhang, H. Wu, B. Hai, L. Wang, Y. Qian, Chem. Mater. 13 (2001) 435. [14] (a) Y. Chabre, J. Pannetier, Prog. Solid State Chem. 23 (1995) 1; (b) M.M. Thackeray, Prog. Solid State Chem. 25 (1997) 1.
[15] L. Espinal, S.L. Suib, J.F. Rusling, J. Am. Chem. Soc. 126 (2004) 7676. [16] R. Chitrakar, H. Kanoh, Y.S. Kim, Y. Miyai, K. Ooi, J. Solid State Chem. 160 (2001) 69. [17] A.R. Armstrong, P.G. Bruce, Nature 381 (1996) 499. [18] B. Ammundsen, J. Paulsen, Adv. Mater. 13 (2001) 943. [19] M. Winter, R.J. Brodd, Chem. Rev. 104 (2004) 4245. [20] X. Chen, X. Li, Y. Jiang, C. Shi, X. Li, Solid State Commun. 136 (2005) 94. [21] S. Ardizzone, C.L. Bianchi, D. Tirelli, Colloids Surf. A 134 (1998) 305.