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Preparation of crystalline manganese oxides hollow spheres
Powder Technology 145 (2004) 172 – 175 www.elsevier.com/locate/powtec
Short communication
Preparation of crystalline manganese oxides hollow spheres Jisen Wang*, Jinkai Yang, Ying Bao, Jinquan Sun The School of Power and Control Engineering, Shandong University of Science and Technology, Jinan 250031, P.R. China Received 9 December 2003; received in revised form 26 June 2004; accepted 8 July 2004 Available online 25 August 2004
Abstract Manganese oxides hollow spheres were synthesized by heating manganese carbonate precursors prepared by a one-step, solid-state method. Addition of sodium chloride (NaCl) and surfactant nonylphenyl ether (NP9), heating time and heating temperature played important roles in the synthesis process. The crystals were characterized by X-ray powder diffraction (XRD) and transmission electronic microscopy (TEM). It was shown that the product was pure and crystallized very well. D 2004 Elsevier B.V. All rights reserved. Keywords: Hollow spheres; NaCl and NP9; Heating time; Heating temperature; XRD
1. Introduction Morphologically well-defined hollow particles are materials of interest both from academic and technological points of view. Compared with bulk materials, hollow particles show lower density, higher surface area and distinct optical properties [1]. Such properties have been proved in a number of applications such as fillers, coatings, pigments and capsule agents for drug delivery. Procedures for the preparation of hollow polymer spheres have been reported and such materials have been used as pigments and paper whiteners [1–3]. Manganese oxides give rise to a rather complex oxides system with the most usual stiochiometries MnO, Mn3O4, Mn2O3 and MnO2 [4]. Considerable research has recently focused on manganese oxides due to their ion-exchange, molecular adsorption, catalytic, electrochemical, and magnetic properties [5–8]. Mn3O4 is known to be an active catalyst for several processes, such as the oxidation of methane and carbon monoxide or the selective reduction of nitrobenzene. Moreover, in recent studies, different polymorps of Mn3O4 (hausmannite) have been found to be active and stable catalysts for the combustion of organic * Corresponding author. Tel./fax: +86 5315903432. E-mail address: [email protected] (J. Wang). 0032-5910/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2004.07.001
compounds at temperatures of 373–773 K [9]. Many methods have been applied to synthesize Mn3O4 crystalline with different morphologies [4,9,10]. To our knowledge, this work is the first achievement of synthesizing Mn3O4 hollow spheres by heating MnCO3 precursors. In this work, we established a novel and simple approach to the synthesis of crystal Mn3O4 hollow spheres that exploits a one-step, solid-state reaction to prepare MnCO3 precursors at ambient temperature subsequently depositing Mn3O4 hollow spheres in NaCl and nonylphenyl ether (NP9). Our approach requires neither complex apparatus and sophisticated techniques nor metal catalysts and template.
2. Experimental procedure All of the chemical reagents used in this experiment were analytical grade. In a typical synthesis, MnCl2d 4H2O (1.98 g) and Na2CO3 (1.06 g) were mixed and ground with NaCl (6 g) for about 30 min. Then the product was washed with distilled water and ethanol three times, respectively, and vacuum-dried at 60 8C for 3 h. The obtained product was collected for the preparation of Mn3O4 hollow spheres. The as-prepared precursor (1 g) was mixed with NaCl (4 g) and NP9 (10 ml) in an agate mortar and the mixture was
J. Wang et al. / Powder Technology 145 (2004) 172–175
ground for 5 min. The mixed sample was heated at 350 8C for different times. The heat-treated sample was cooled gradually to room temperature in air, washed several times with distilled water, filtered, and dried in an oven at 70 8C to get the final product. The phase purity of the product was examined by X-ray powder diffraction using a Japan Rigaku D/max gA X-ray diffractometer equipped with graphite monochromatized Cu-Ka radiation (k=1.5418 2). Transmission electron microscopy investigation was made on a Hitachi H-800 transmission electron microscope with an accelerating voltage of 200 kV.
3. Results and discussion Fig. 1 shows the XRD pattern of final product after the precursors had been heated for 2.5 h. All the peaks can be indexed to the pure hausmannite (g-Mn3O4) with the lattice constants a=5.762 2 and c=9.469 2, which agree well with the values reported in the literature (JCPDS Card. No. 24-0734). Thus it can be determined that the crystals are of tetragonal structure and the average diameter is about 20 nm estimated by the Scherrer equation. No significant orientation can be seen from the XRD patterns due to the random arrangement of different small crystals. Fig. 2 shows the TEM images of the final product that had been heated for different times. It is clear that the result is different from previous reports [4,9] and our prior results [10]. Fig. 2a indicates that quarter hollow spheres are obtained after heating treatment for about 1.0 h; Fig. 2b is a three-quarter hollow sphere. We can see that the spheres of the two images are all composed of small particles for about 20 nm in diameter and it agrees well with the XRD result.
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Fig. 2c is the typical TEM image of the prepared Mn3O4 hollow spheres with the specific surface area about 0.13 m2/ g. It was gotten after the precursors had been heated for 2.5 h; Fig. 2(d) is the corresponding EDP of it, from which the diffraction rings with the d-values of 2.7678, 1.9960, 1.8290, 1.5767, 1.4259, 1.3485, 1.3056, 1.2307 and 1.1314 2 can be attributed to the planes of (103), (213), (204), (321), (323), (305), (332), (404) and (424) of Mn3O4 crystals, respectively. The result indicates that the product is nanocrystalline Mn3O4. It is obvious that the spheres are no longer hollow with the prolonging of heating time (as shown in Fig. 2e and f) and this may result from the aggregating of the hollow spheres. So, we can conclude that heating time is a key factor for the synthesis of hollow spheres. Solid spheres will be prepared when the time is too long. The change of the diameter is due to the aggregation of the spheres. Fig. 3 is the thermogravity and differential thermal analysis (TG/DTA) curves of the MnCO3 precursor. It shows one big and broad endothermic peak at ca. 100 8C, which is the result of the evaporation of surface water. There is an endothermic peak at ca. 320 8C, which is attributed to the weight loss during the formation of Mn3O4 from the decomposition of MnCO3 precursor. In the reaction temperature of 350 8C, manganese carbonate decomposed into nanosized manganese oxide particles. Then the particles are supposed to have assembled into hollow spheres. The reaction may be described as follows: Na2 CO3 þ MnCl2 YMnCO3 þ 2NaCl 3MnCO3 YMn3 O4 þ 2CO2 þ CO In the first step of our experiment, NaCl can disperse the obtained MnCO3 precursor powder and prevent unnecessary
Fig. 1. XRD image of Mn3O4 crystals with the heat treatment for 2.5 h.
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J. Wang et al. / Powder Technology 145 (2004) 172–175
Fig. 2. TEM images of Mn3O4 hollow spheres prepared by heating the precursor at 350 8C at different times: (a) 1 h, (b) 2 h, (c) 2.5 h, (e) 3 h, and (f) 4 h. The corresponding electron diffraction pattern of (c) is shown in (d).
aggregating of the powder, which may be helpful to the synthesis of MnCO3 precursors with small diameter as we have formerly pointed out [10]. In order to reveal the effect of NaCl and NP9, we have studied the fabrication of the Mn3O4 hollow spheres by following comparative experiments under the same synthesis conditions (the same heating temperature, quantity of starting materials, and grinding time). ! addition of only NaCl, " addition of only NP9, and # no addition of NaCl and NP9. However, the experiments produced only particles, instead of hollow spheres. The result indicated that only when NaCl and NP9 all existed could Mn3O4 hollow spheres be obtained. They together formed a circumstance favorable to the growth of Mn3O4 hollow spheres. The detailed context is under investigation. Marcia et al. [1] have synthesized hollow zinc oxide microparticles using polystyrene (PS)/inorganic composite precursors. In their synthesis process, PS was used as template and zinc oxide particles coated on PS to synthesize hollow morphology. The distribution of zinc oxide particles on PS was uniform.
It was obvious that the forming process of theirs is different from that of ours. We also investigated the influence of temperature on the growth of Mn3O4 hollow spheres. In these studies, MnCO3
Fig. 3. TG/DTA curves of MnCO3 precursor.
J. Wang et al. / Powder Technology 145 (2004) 172–175
were heated for 2.5 h at different temperatures in the range of 300–400 8C. We found that Mn3O4 hollow spheres were formed only in a temperature window between 320 and 380 8C. When the temperature was lower than 320 8C, welldispersed nanoparticles were formed. As the heating temperature was increased beyond 400 8C, Mn3O4 nanoparticles that were heavily aggregated were prepared.
4. Conclusions In this work, Mn3O4 hollow spheres were successfully synthesized at 350 8C by decomposing MnCO3 precursor in NaCl and NP9 atmosphere. Both XRD and TEM results verified that the product was pure and crystallized very well. Synthetic studies showed that the precursor which was heated at 350 8C for about 2.5 h with the addition of NaCl and NP9 was the optimum condition. The advantages of this route are the simplicity of apparatus and the procedure.
Acknowledgements The authors would like to acknowledge support from the Program of Science and Technology Bureau of Qingdao under grant no. 03-2-IR-18.
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References [1] Marcia C. Neves, Tito Trindade, Ana M.B. Timmons, Julio D. Pedrosa de Jesus, Materials Research Bulletin 36 (2001) 1099 – 1108. [2] Jianwei Liu, Mingwang Shao, Qun Tang, Xiangyang Chen, Zhaoping Liu, Yitai Qian, Carbon 411 (2002) 1645 – 1687. [3] Guozhen Shen, Di Chen, Kaibin Tang, Yitai Qian, Shuyuan Zhang, Chemical Physics Letters 375 (2003) 177 – 184. [4] J. Boyero Macstre, E. Fernandez Lopez, J.M. Gallardo-Amores, R. Ruano Casero, V. Sanchez Escribano, E. Perez Bernal, International Journal of Inorganic Materials 3 (2001) 889 – 899. [5] Xiaodan Sun, Chunlai Ma, Li Zeng, Yude Wang, Hengde Li, Materials Research Bulletin 37 (2002) 331 – 341. [6] C. Tsang, J. Kim, A. Manthiram, Journal of Solid State Chemistry 137 (1998) 28 – 32. [7] G.J. Moore, R. Portal, A. Le Gal La Salle, D. Guyomard, Journal of Power Sources 97–98 (2001) 393 – 397. [8] Zhong-Yong Yuan, Zaoli Zhang, Gaohui du, Tie-Zhen Ren, Bao-Lian Su, Chemical Physics Letters 378 (2003) 349 – 353. [9] Wenzhong Wang, Congkang Xu, Guangzhou Wang, Yingkai Liu, Changlin Zheng, Advanced Materials 14 (2002) 837 – 840. [10] Jisen Wang, Jinquan Sun, Ying Bao, Xiufang Bian, Journal of Materials Science and Technology 19 (2003) 489 – 491.
Short communication
Preparation of crystalline manganese oxides hollow spheres Jisen Wang*, Jinkai Yang, Ying Bao, Jinquan Sun The School of Power and Control Engineering, Shandong University of Science and Technology, Jinan 250031, P.R. China Received 9 December 2003; received in revised form 26 June 2004; accepted 8 July 2004 Available online 25 August 2004
Abstract Manganese oxides hollow spheres were synthesized by heating manganese carbonate precursors prepared by a one-step, solid-state method. Addition of sodium chloride (NaCl) and surfactant nonylphenyl ether (NP9), heating time and heating temperature played important roles in the synthesis process. The crystals were characterized by X-ray powder diffraction (XRD) and transmission electronic microscopy (TEM). It was shown that the product was pure and crystallized very well. D 2004 Elsevier B.V. All rights reserved. Keywords: Hollow spheres; NaCl and NP9; Heating time; Heating temperature; XRD
1. Introduction Morphologically well-defined hollow particles are materials of interest both from academic and technological points of view. Compared with bulk materials, hollow particles show lower density, higher surface area and distinct optical properties [1]. Such properties have been proved in a number of applications such as fillers, coatings, pigments and capsule agents for drug delivery. Procedures for the preparation of hollow polymer spheres have been reported and such materials have been used as pigments and paper whiteners [1–3]. Manganese oxides give rise to a rather complex oxides system with the most usual stiochiometries MnO, Mn3O4, Mn2O3 and MnO2 [4]. Considerable research has recently focused on manganese oxides due to their ion-exchange, molecular adsorption, catalytic, electrochemical, and magnetic properties [5–8]. Mn3O4 is known to be an active catalyst for several processes, such as the oxidation of methane and carbon monoxide or the selective reduction of nitrobenzene. Moreover, in recent studies, different polymorps of Mn3O4 (hausmannite) have been found to be active and stable catalysts for the combustion of organic * Corresponding author. Tel./fax: +86 5315903432. E-mail address: [email protected] (J. Wang). 0032-5910/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2004.07.001
compounds at temperatures of 373–773 K [9]. Many methods have been applied to synthesize Mn3O4 crystalline with different morphologies [4,9,10]. To our knowledge, this work is the first achievement of synthesizing Mn3O4 hollow spheres by heating MnCO3 precursors. In this work, we established a novel and simple approach to the synthesis of crystal Mn3O4 hollow spheres that exploits a one-step, solid-state reaction to prepare MnCO3 precursors at ambient temperature subsequently depositing Mn3O4 hollow spheres in NaCl and nonylphenyl ether (NP9). Our approach requires neither complex apparatus and sophisticated techniques nor metal catalysts and template.
2. Experimental procedure All of the chemical reagents used in this experiment were analytical grade. In a typical synthesis, MnCl2d 4H2O (1.98 g) and Na2CO3 (1.06 g) were mixed and ground with NaCl (6 g) for about 30 min. Then the product was washed with distilled water and ethanol three times, respectively, and vacuum-dried at 60 8C for 3 h. The obtained product was collected for the preparation of Mn3O4 hollow spheres. The as-prepared precursor (1 g) was mixed with NaCl (4 g) and NP9 (10 ml) in an agate mortar and the mixture was
J. Wang et al. / Powder Technology 145 (2004) 172–175
ground for 5 min. The mixed sample was heated at 350 8C for different times. The heat-treated sample was cooled gradually to room temperature in air, washed several times with distilled water, filtered, and dried in an oven at 70 8C to get the final product. The phase purity of the product was examined by X-ray powder diffraction using a Japan Rigaku D/max gA X-ray diffractometer equipped with graphite monochromatized Cu-Ka radiation (k=1.5418 2). Transmission electron microscopy investigation was made on a Hitachi H-800 transmission electron microscope with an accelerating voltage of 200 kV.
3. Results and discussion Fig. 1 shows the XRD pattern of final product after the precursors had been heated for 2.5 h. All the peaks can be indexed to the pure hausmannite (g-Mn3O4) with the lattice constants a=5.762 2 and c=9.469 2, which agree well with the values reported in the literature (JCPDS Card. No. 24-0734). Thus it can be determined that the crystals are of tetragonal structure and the average diameter is about 20 nm estimated by the Scherrer equation. No significant orientation can be seen from the XRD patterns due to the random arrangement of different small crystals. Fig. 2 shows the TEM images of the final product that had been heated for different times. It is clear that the result is different from previous reports [4,9] and our prior results [10]. Fig. 2a indicates that quarter hollow spheres are obtained after heating treatment for about 1.0 h; Fig. 2b is a three-quarter hollow sphere. We can see that the spheres of the two images are all composed of small particles for about 20 nm in diameter and it agrees well with the XRD result.
173
Fig. 2c is the typical TEM image of the prepared Mn3O4 hollow spheres with the specific surface area about 0.13 m2/ g. It was gotten after the precursors had been heated for 2.5 h; Fig. 2(d) is the corresponding EDP of it, from which the diffraction rings with the d-values of 2.7678, 1.9960, 1.8290, 1.5767, 1.4259, 1.3485, 1.3056, 1.2307 and 1.1314 2 can be attributed to the planes of (103), (213), (204), (321), (323), (305), (332), (404) and (424) of Mn3O4 crystals, respectively. The result indicates that the product is nanocrystalline Mn3O4. It is obvious that the spheres are no longer hollow with the prolonging of heating time (as shown in Fig. 2e and f) and this may result from the aggregating of the hollow spheres. So, we can conclude that heating time is a key factor for the synthesis of hollow spheres. Solid spheres will be prepared when the time is too long. The change of the diameter is due to the aggregation of the spheres. Fig. 3 is the thermogravity and differential thermal analysis (TG/DTA) curves of the MnCO3 precursor. It shows one big and broad endothermic peak at ca. 100 8C, which is the result of the evaporation of surface water. There is an endothermic peak at ca. 320 8C, which is attributed to the weight loss during the formation of Mn3O4 from the decomposition of MnCO3 precursor. In the reaction temperature of 350 8C, manganese carbonate decomposed into nanosized manganese oxide particles. Then the particles are supposed to have assembled into hollow spheres. The reaction may be described as follows: Na2 CO3 þ MnCl2 YMnCO3 þ 2NaCl 3MnCO3 YMn3 O4 þ 2CO2 þ CO In the first step of our experiment, NaCl can disperse the obtained MnCO3 precursor powder and prevent unnecessary
Fig. 1. XRD image of Mn3O4 crystals with the heat treatment for 2.5 h.
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J. Wang et al. / Powder Technology 145 (2004) 172–175
Fig. 2. TEM images of Mn3O4 hollow spheres prepared by heating the precursor at 350 8C at different times: (a) 1 h, (b) 2 h, (c) 2.5 h, (e) 3 h, and (f) 4 h. The corresponding electron diffraction pattern of (c) is shown in (d).
aggregating of the powder, which may be helpful to the synthesis of MnCO3 precursors with small diameter as we have formerly pointed out [10]. In order to reveal the effect of NaCl and NP9, we have studied the fabrication of the Mn3O4 hollow spheres by following comparative experiments under the same synthesis conditions (the same heating temperature, quantity of starting materials, and grinding time). ! addition of only NaCl, " addition of only NP9, and # no addition of NaCl and NP9. However, the experiments produced only particles, instead of hollow spheres. The result indicated that only when NaCl and NP9 all existed could Mn3O4 hollow spheres be obtained. They together formed a circumstance favorable to the growth of Mn3O4 hollow spheres. The detailed context is under investigation. Marcia et al. [1] have synthesized hollow zinc oxide microparticles using polystyrene (PS)/inorganic composite precursors. In their synthesis process, PS was used as template and zinc oxide particles coated on PS to synthesize hollow morphology. The distribution of zinc oxide particles on PS was uniform.
It was obvious that the forming process of theirs is different from that of ours. We also investigated the influence of temperature on the growth of Mn3O4 hollow spheres. In these studies, MnCO3
Fig. 3. TG/DTA curves of MnCO3 precursor.
J. Wang et al. / Powder Technology 145 (2004) 172–175
were heated for 2.5 h at different temperatures in the range of 300–400 8C. We found that Mn3O4 hollow spheres were formed only in a temperature window between 320 and 380 8C. When the temperature was lower than 320 8C, welldispersed nanoparticles were formed. As the heating temperature was increased beyond 400 8C, Mn3O4 nanoparticles that were heavily aggregated were prepared.
4. Conclusions In this work, Mn3O4 hollow spheres were successfully synthesized at 350 8C by decomposing MnCO3 precursor in NaCl and NP9 atmosphere. Both XRD and TEM results verified that the product was pure and crystallized very well. Synthetic studies showed that the precursor which was heated at 350 8C for about 2.5 h with the addition of NaCl and NP9 was the optimum condition. The advantages of this route are the simplicity of apparatus and the procedure.
Acknowledgements The authors would like to acknowledge support from the Program of Science and Technology Bureau of Qingdao under grant no. 03-2-IR-18.
175
References [1] Marcia C. Neves, Tito Trindade, Ana M.B. Timmons, Julio D. Pedrosa de Jesus, Materials Research Bulletin 36 (2001) 1099 – 1108. [2] Jianwei Liu, Mingwang Shao, Qun Tang, Xiangyang Chen, Zhaoping Liu, Yitai Qian, Carbon 411 (2002) 1645 – 1687. [3] Guozhen Shen, Di Chen, Kaibin Tang, Yitai Qian, Shuyuan Zhang, Chemical Physics Letters 375 (2003) 177 – 184. [4] J. Boyero Macstre, E. Fernandez Lopez, J.M. Gallardo-Amores, R. Ruano Casero, V. Sanchez Escribano, E. Perez Bernal, International Journal of Inorganic Materials 3 (2001) 889 – 899. [5] Xiaodan Sun, Chunlai Ma, Li Zeng, Yude Wang, Hengde Li, Materials Research Bulletin 37 (2002) 331 – 341. [6] C. Tsang, J. Kim, A. Manthiram, Journal of Solid State Chemistry 137 (1998) 28 – 32. [7] G.J. Moore, R. Portal, A. Le Gal La Salle, D. Guyomard, Journal of Power Sources 97–98 (2001) 393 – 397. [8] Zhong-Yong Yuan, Zaoli Zhang, Gaohui du, Tie-Zhen Ren, Bao-Lian Su, Chemical Physics Letters 378 (2003) 349 – 353. [9] Wenzhong Wang, Congkang Xu, Guangzhou Wang, Yingkai Liu, Changlin Zheng, Advanced Materials 14 (2002) 837 – 840. [10] Jisen Wang, Jinquan Sun, Ying Bao, Xiufang Bian, Journal of Materials Science and Technology 19 (2003) 489 – 491.