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Materials Letters 62 (2008) 2593 – 2595 www.elsevier.com/locate/matlet
Synthesis and characterization of Al2O3 hollow spheres Runjing Liu, Yanjv Li, Hua Zhao, Fengyun Zhao, Yongqi Hu ⁎ College of Chemical and Pharmaceutical Engineering, Hebei University of science and technology, Shijiazhuang 050018, China Received 23 July 2007; accepted 25 December 2007 Available online 16 January 2008
Abstract This paper presents a novel technique to create Al2O3 hollow spherical nanoparticles. It used Al(OH)3 which was synthesized with Al2(SO4)3 and NaOH, and the C-Al(OH)3 core-shell nanoparticle as intermediate phases. The Al2O3 hollow spheres were achieved by the calcination of the carbon cores and the dehydration of Al(OH)3. The chemical composition, morphology, size and superficial crystal structure of the nanoparticles were characterized with TEM, XRD, TGA, FTIR and BET. The result shows that the average diameter of the C-Al(OH)3 core-shell nanoparticles is about 25 nm, the thickness of the Al2O3 shell is about 5 nm and the surface area is 215.2 m2/g. The procedure for the formation of Al2O3 hollow nanoparticles is discussed in details. © 2008 Elsevier B.V. All rights reserved. Keywords: Al2O3 hollow spheres; Synthesis; Characterization; Sol–gel preparation; Microstructure
1. Introduction In recently years, hollow nanoparticles are attracting more and more interests due to their importance in various fields of science and technology, such as biological labels, optical resonances, catalysis, magnetics, ceramics, and pigments. By building up shells on the suitable medium, the core-shell nanoparticles can be generated to meet some special requirements. Furthermore, an important extension of core-shell particles is the subsequent removal of the core by dissolution, decomposition and other method to produce hollow shells . Various methods of producing core-shell nanoparticles have been reported in the literatures, such as electroless plating, precipitation, sonochemical deposition, reverse micelles, sol–gel, and layer-bylayer technique. Generally, these methods can be divided into four categories: surface reaction, surface precipitation, precipitation hetero-coagulation and the layer-by-layer technique [1–3]. Al2O3 was one of the materials studied very early for its potential application as a radiation dose-meter owing to its superior thermal and chemical stability and low effective atomic number [4–6]. Since then, a great deal of efforts has been directed towards the improvement of its sensitivity [7–9]. In this ⁎ Corresponding author. Tel./fax: +86 311 88632175. E-mail addresses: liya[email protected]
(Y. Li), [email protected]
, [email protected]
(Y. Hu). 0167-577X/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.12.069
paper, the core-shell C-Al(OH)3 nanoparticles were produced by using sol–gel preparation of Al(OH)3 on the surface of carbon cores. Subsequently, the Al2O3 shells were created by the removal of the carbon cores and the decomposition of Al(OH)3. The obtained Al2O3 was 20 wt.% of the carbon black, the detailed structures of the hollow Al2O3 shell nanoparticles were investigated [10,11]. 2. Experimental 2.1. Details of sample preparation procedure Both NaOH and Al2(SO4)3·18H2O were of analytical purity and were purchased from Tianjin chemical Factory(china). Carbon black was taken from Beijing university of chemical technology, Ethanol absolute was of chemical purity and was purchased from Tianjin Alcohol Factory(china). Distilled water was used in all the experiments. The detailed experimental procedure is as follows: The carbon black was treated by being heated up to 300 °C for 5 h, this because burning the water can took hydrophilic point on the surface of carbon black, in order to enhance the hydrophilicity of carbon black. The mixture of 2.000 g the treated carbon black particles and 150 mL distilled water was sonicated for 1 h to get stable emulsion. 0.940 g NaOH and 2.600 g Al2(SO4)3·18H2O were dissolved in 100 ml distilled water respectively to acquire NaOH and Al2(SO4)3
R. Liu et al. / Materials Letters 62 (2008) 2593–2595
Fig. 1. Morphologies of (a) C nanoparticles, (b) C-Al(OH)3 core-shell nanoparticles, and (c) Al2O3 hollow spherical nanoparticles.
solution, then, NaOH and Al2(SO4)3 solution were added synchronously into the slurry of carbon black nanoparticles with the flow rate ratio of 1:1 and the mixture was heated up to 70 °C in a water bath. The addition of NaOH and Al2(SO4)3 solution finished after 4.5 h. The pH value of the slurry was about 5–6 and the slurry was aged for 2 h. The C-Al(OH)3 core-shell nanoparticles were obtained after the slurry was washed and filtered with distilled water and Ethanol absolute to remove impurities, and then, the particles were vacuum dried at 80 °C for 5 h. Al2O3 hollow spherical nanoparticles were produced after the calcinations of the carbon core and the dehydration of Al (OH)3. In the process of calcination, the temperature was controlled at about 300 °C for 3 h and then, the temperature was isobarically increased to 600 °C . After 6 h under this condition, the sample was cooled down to room temperature and the Al2O3 hollow spheres were achieved. 2.2. Sample characterization The structure and morphology of the samples were investigated using transmission electron microscopy (H-7500 TEM, Hitachi) and X-ray powder diffraction (D8 advance-XRD, Germany Bruker AXS). The interfacial structure was checked with a fourier transform infrared spectrophotometer (FTIRFTS135, Bio-Rad). Thermogravimetric analysis (SDT2960 Simultaneous DTA-TGA, TA Instrument) and surface area analyzer (Nova 2000 series-BET, Quantachrome Instruments) were also used to characterize the Al2O3 hollow spheres.
using sol–gel preparation. The sol–gel reaction took place as NaOH and Al2(SO4)3 solution were added synchronously which was shown in Eq. (1): Al3þ þ 3OH− ¼ AlðOHÞ3
The coating of Al(OH)3 on the surface of carbon black cores is actually a heterogeneous precipitation process. According to the nucleation theory, the free energy of heterogeneous nucleation is less than that of homogeneous nucleation. When NaOH and Al2(SO4)3 solution were added into the slurry of carbon black nanoparticles, the Al (OH)3 nucleation produced easily and grew to form coating layer on the surface of carbon black nanoparticles. But there was also part of isolated precipitates Al(OH)3 particles synthesized, because there were many influencing factors of temperature, pH and rate of stirring which can lead to the inhomogeneity of distribution of concentration in the reactor and the synthesis of Al(OH)3 sol-granules possibly occured. In the aging process, the isolated Al(OH)3 sol-granules gradually coated on the surface of carbon black cores eventually the C-Al(OH)3 core-shell nanoparticles were obtained. So in the synthesized process of Al2O3 hollow spheres, the intermediate phase obtained consists of C-Al(OH)3 and isolated Al(OH)3 particles. Fig. 1 shows the TEM images of the carbon black nanoparticles, the C-Al(OH)3 nanoparticles and the Al2O3 hollow spheres. From the image of the C-Al(OH)3 core-shell nanoparticles as shown in Fig. 1b, it can be seen that the Al(OH)3 layer is continuously coated on the core particle surface. The shape and size of the Al2O3 hollow spheres as shown in Fig. 1c are similar to that of the carbon nanoparticles as shown in Fig. 1a, which also confirms that the Al(OH)3 layer is continuously coated on the surface of the core carbon nanoparticles. Fig. 1 shows that the size of carbon core is about 15 nm, the C-Al(OH)3 core-shell
3. Results and discussions In the process of the preparation of Al2O3 hollow spheres, the Al (OH)3 layer firstly coated on the surface of carbon black nanoparticles
Fig. 2. XRD spectra of Al2O3 hollow spheres.
Fig. 3. Thermogravimetric analysis of C-Al(OH)3 nanoparticles.
R. Liu et al. / Materials Letters 62 (2008) 2593–2595
was calcinated and the Al(OH)3 was dehydrated to Al2O3 later on, there was a strong interaction between the surface of the carbon core and the Al(OH)3 shell, which made the absorption band shift occur. Moreover, the change of crystal structure may be another reason for the differences. According to BET results, the average pore diameter of the Al2O3 hollow spheres is13.13 nm, the total pore volume is 0.7063 cm3/g and the surface area is 215.2 m2/g. From the TEM image of the C-Al(OH)3 core-shell nanoparticles(Fig. 1b), the size of carbon core is about 15 nm, which is pretty close to the average pore diameter from BET. The results also show that there are some nanopores on the Al2O3 hollow spheres. The nanopore is another important result of the experiment, which will be studied further in the near future.
4. Conclusion Fig. 4. FTIR analysis of (a) pure Al2O3 sample and (b) Al2O3 hollow spherical nanoparticles.
nanoparticle is about 25 nm and therefore, the thickness of Al2O3 shell is estimated at about 5 nm. The XRD pattern of the products as shown in Fig. 2 indicates the presence of the reflection characteristics of the products. The result shows that the synthesized Al2O3 hollow sphere is amorphous. Fig. 3 shows the TGA measurement of the C-Al(OH)3 nanoparticles. The C-Al(OH)3 sample was determined through the weight loss up to 900 °C. The TGA curves reveal that the weight loss occurred in two temperature ranges: 30–150 °C and 150–700 °C. The first zone occurs around 82.77 °C and the weight decrease is 10.69%, which is caused by the desorption of water, which was possibly absorbed onto the particle surface in the cooling process. The second weight loss is caused by the calcination of the carbon core and the following reaction of Al(OH)3 as shown in Eq. (2). The decomposition temperature of Al (OH)3 is about 220 °C and the burning point of the carbon core is about 600 °C. In the zone of 150–700 °C the loss value is 73.32%. So, the weight of the Al2O3 shell account for the 16% of total weight left after the calcination process. 2AlðOHÞ3 ¼ Al2 O3 þ 3H2 O
Fig. 4 show the FT-IR spectra of the analytical pure grade Al2O3 sample and the Al2O3 hollow spherical nanoparticles respectively. In the spectrum of Al2O3 hollow spherical nanoparticle, the peak at 3450 cm− 1(Fig. 4b) indicates the presence of –OH, which is resulted from a small quantity of H2O contained in the sample of Al2O3 hollow sphere. The absorption peaks in the region of 700−400 cm− 1(Fig. 4a,b) correspond to the existence of Al2O3. The result shows that the IR absorption of the Al2O3 hollow spherical nanoparticle is similar to the absorption of analytical pure grade Al2O3 sample, indicating that Al2O3 nanoparticles can be created with this method. However, there still exist some differences, which might be ascribed to the preparation procedure of the Al2O3 particles. In this technique, the C-Al(OH)3 core-shell nanoparticle was first generated. Although the carbon core
Al2O3 hollow spherical nanoparticles can be successfully prepared by coating Al(OH)3 on the surface of carbon black, followed by the calcinations of the carbon core and the dehydration of Al(OH)3. The Al2O3 hollow spheres thus obtained have a specific surface area about 215.2 m2/g and a pore diameter of 13.13 nm. Compared with other methods reported in the literatures, this method provides a much easier way to synthesize hollow shell nanoparticles of Al2O3 as well as many other materials. Acknowledgements The authors are grateful to the support from Hebei Analytical and Testing Center and College of Chemical and Pharmaceutical Engineering at Hebei University of science and technology. References  J.L. Yin, X.F. Qian, J. Yin, M.W. Shi, G.T. Zhou, Mater. Lett. 57 (2003) 3859–3863.  H.Q. Wu, M.W. Shao, J.S. Gu, X.W. Wei, Mater. Lett. 58 (2004) 2166–2169.  S.C. Zhang, X.G. Li, Powder Technol. 141 (2004) 75–79.  Ranjan K. Pati, Jagadish C. Ray, Panchanan Pramanik, Mater. Lett. 44 (2000) 299–303.  M.S. Kulkarni, D.R. Mishra, K.P. Muthe, Ajay Singh, M. Roy, S.K. Gupta, et al., Radiat. Meas. 39 (2005) 277–282.  Burkhard C. Schmidt, Fabrice Gaillard, Mark E. Smith, Solid State Nucl. Magn. Reson. 26 (2004) 197–202.  S.K. Mehta, S. Sengupta, Phys. Med. Biol. 21 (1976) 955–964.  M. Osvay, T. Biro, Nucl. Instrum. Methods 175 (1980) 60–61.  D. Lapraz, P. Iacconi, D. Daviller, et al., Phys. Status Solidi, A Appl. Res. 126 (1991) 521–531.  J.Y. Li, Y.M. Wang, J. Xiamen University (Nat. Sci.). 42 (2003) 626–628.  Q.W. Zhou, Y. Shen, Y.G. Li, Acta Scientiarum Naturalium Universitatis Sunyatseni 41 (2002) 121–122.  Y.C. Luo, Inorg. Chem. Ind. 33 (2001) 3–5.