Hydrothermal Synthesis of Anatase Nanocrystals - IEEE Xplore

XIII INTERNATIONAL CONFERENCE AND SEMINAR ON MICRO/NANOTECHNOLOGIES AND ELECTRON DEVICES EDM 2012

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Hydrothermal Synthesis of Anatase Nanocrystals Natalia F. Karpovich1,2, Ilya V. Korolkov3, Konstantin S. Makarevich1,2, Maxim A. Pugachevsky1,2, Dmitry S. Shtarev1, Alexander V. Syuy1, Victor V. Atuchin4, Member, IEEE Department of Physics, Far Eastern State Transport University, Khabarovsk, Russia Institute for Materials Science of FEB of Russian Academy of Science, Khabarovsk, Russia 3 Laboratory of Crystal Chemistry, Institute of Inorganic Chemistry, SB RAS, Novosibirsk, Russia 4 Laboratory of Optical Materials and Structures, Institute of Semiconductor Physics, SB RAS, Novosibirsk, Russia 1

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Abstract – The hydrothermal synthesis of TiO2 (anatase) nanocrystals has been produced. The conditions of reproducible synthesis of anatase nanocrystals by thermal treatment of water solution of titanium isopropoxide and triethanolamine at T = 80-100°С by 48 h have been found. Phase composition of final product has been verified by TEM and XRD analysis. As it has been obtained, the dimensions of TiO2 particles varied in the range 10-100 nm with mean value of 45 nm. Index Terms – Nanotechnology, synthesis, anatase, TEM, XRD.

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I. INTRODUCTION

ITANIUM dioxide, TiO2, is widely used in modern catalytic, optical and electronic technologies that is governed by unique combination of its physical and chemical characteristics [1-7]. This material possesses high chemical stability, wide optical transmittance spectrum covering nearly all visible and near-IR spectra, high dielectric susceptibility and top-rank refractive indices Chemical bond Ti-O shows high electronic polarizability and titanium oxide is appropriately used in synthesis of effective ceramic materials, integrated optics and creation of nonlinear optical crystals [6-16]. During recent years, the photocatalytic properties of TiO2 polymorph modifications are studied in reaction of water decomposition to hydrogen and oxygen under solar illumination [1,5,12]. As it is well-known, the properties of oxide materials containing transition metals are not infrequently dependent on the synthesis conditions [17-22]. In particular, this is a property of simple oxides, when the existence of several polymorph modifications with close formation energies is typical. For such oxide crystals, the phase transitions between different modifications are usually kinetically controlled. In this case, the micromorphology and phase composition of micro- and nanocrystalline products are specifically sensitive to starting reagent selection and synthesis route [1,4,16,22]. Titanium dioxide, TiO2, besides amorphous state, can exist in several crystalline modifications and rutile, space group P42/mnm, anatase, space group I41/amd, and brukite, space group Pbca, are among most known. Crystal structure of anatase is shown in Fig.1 [23,24].It is known that anatase nanocrystals possess increased photocatalytic properties in

reference to those of other modifications. TiO2 nanomaterials of different morphology can be synthesized by sol-gel method under hydrolysis of titanium-bearing precursors [25]. Then, the top-surface properties and phase-transition parameters of TiO2 nanotubes, nanowires, nanorods and nanodisks under pressure and heating become size-sensitive and are dependent on the variation of geometry and crystal structure of the nanocrystals. Presently, TiO2 nanocrystals of different shape and phase composition can be fabricated. Nevertheless, key factors governing size and shape of the particles during synthesis are not known in details that limits the preparation of TiO2 powder products with controlled crystal geometry. Thus, present study is aimed at synthesis of TiO2 nanocrystals with homogeneous size and micromorphology. II. EXPERIMENTAL Hydrothermal synthesis of the nanocrystals is produced in steel autoclave equipped with teflon insert. The pressure in autoclave is significantly defined by temperature and solution volume. The growth of TiO2 particles proceeds preferably under low water content, low hydrolysis rate and an excess of titanium alcoholate in reaction solution. Triethanolamine is used as a reagent controlling the shape of TiO2 nanocrystals. This substance is used for regulation рН and as the stabilizer of a colloid system. It is known, that diethyl amine, trimethylamine and triethylamine operate as complexing agents of ions Ti (IV) for magnification of elliptic particles with a low relation of legs. Making of particles of the various shapes usually is carried out by speed control of propagation of various crystal planes of crystals TiO2. Such process is possible due to pH variation which results in a various degree of adsorption of those substances - governors of the shape of particles on the different planes of a crystal. The long-term heating of the prepared gel above 100°С is used for prevention of agglomerations of TiO2 particles during crystallization. Titanium isopropoxide (Ti[OCH(CH3)2]4) (98%, Acros, USA) immixed with triethanolamine (98.6 %, Merck, Germany) in the ratio 1:2 and lead up distilled water to concentration 0.5 мole/litre3. The solution gained thus

ISBN 978-1-4673-2520-2 © IEEE, 2012

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withstood in a vulcanizer at temperature 100°С by 24

Fig. 2. TEM image of TiO2 nanocrystals.

Fig. 1. Crystal structure of anatase. Unit cell is outlined. Lone atoms are omitted for clarity.

hours and at 80°С by 24 more hours. Further the precipitate filtered off and inciderated on air at temperature 250°С. The synthesized powder was washed out with 100 % ethanol, and then treated at 600°С. Values of a specific surface area of all exemplars, defined on thermal adsorption of nitrogen on Sorbi 4.1, the error in definition did not exceed 4 %. Micromorphology and phase composition of TiO2 nanocrystals were evaluated by TEM using Zeiss Libra-120 device (electron energy 120 keV) with HAADF detector and Ω-filter. Calibration of diffraction patterns in TEM mode was produced by polycrystalline Au films. ASTM data collection was used for the phase analysis. Phase composition was evaluated with X-ray diffraction (XRD) analysis. XRD patterns were recorded using Shimadzu XRD-7000 (Cu Ka radiation, Ni – filter, 5 – 70° 2q range, 1 s per step) device.

anatase crystal phase is detected. Nanocrystal diameter estimated by Sherer relation in reference to Si etalon is as low as 22(1) nm. This value is noticeably lower than mean nanoparticle diameter obtained by TEM analysis. As it appears, TiO2 particles are of complex layered structure and crystalline grain with diameter of ~ 20 nm is covered by amorphous oxide shell with thickness of 20-40 nm. It is known that oxide products can be activated by doping or special treatments [26-31]. Now, these methods can be applied to TiO2 nanocrystals formed by hydrothermal process developed in present study. For example, doping agents can be added directly into reaction solution.

VI. CONCLUSION The hydrothermal synthesis at 80-100°C during 48 h provides reproducible fabrication of TiO2 nanoparticles with diameter 10-100 nm. The oxide product has complex structure and the particles are formed by crystalline (anatase) and amorphous components. The diameter of crystalline grain is ~ 20 nm.

REFERENCES III. RESULTS AND DISCUSSION In Figure 2 the TEM images of TiO2 nanocrystals are shown. It is evident, that final product contains spherical particles of close dimensions. As estimated by TEM analysis, the particle diameter varies over the range 10-100 nm. Granulometric measurements yield the mean particle diameter 45 nm. Specific surface area of TiO2 powder is as high as 64.4±1.2 m2/g. TEM patterns show a combination of hallo and diffraction sports related to anatase crystalline component [22]. Phase composition of final powder product is also verified by XRD analysis and the presence of only

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V.V., Vemuri R.S., Ramana C.V. Growth and structural properties of a-MoO3 (010) microplates with atomically flat surface // Mater. Sci. Eng. B 2010. V. 174. No. 1-3. pp. 159-163. Makarevich K.S., Lebukhova N.V., Chigrin P.G., Karpovich N.F. Catalytic properties of CuMoO4 doped with Co, Ni, and Ag // Inorg. Mater. 2010. V. 46. No. 12. pp. 1359-1364. Ramana C.V., Carbajal-Franco G., Vemuri R.S., Troitskaia I.B., Gromilov S.A., Atuchin V.V. Optical properties and thermal stability of germanium oxide (GeO2) nanocrystals with a-quartz structure // Mater. Sci. Eng. B 2010. V. 174. No. 1-3. pp. 279-284. Karmali R., Borker V.P., Rane K.S., Deshpande S.K. Citrate gel route for synthesis of dense pyrochlores // Mater. Chem. Phys. 2011. V. 129. pp. 1116-1120. Pugachevskii M.A. Morphology and phase changes in laser ablated TiO2 particles during thermal annealing // Techn. Phys. Lett. 2012. V. 38. No. 4. pp. 328–331. Natalia F. Karpovich was born in Gorodez / Russia on May, 1969. She received the diploma degree in Chemistry from the Khabarovsk Pedagogical university, Russia in 1991 and the Ph.D. degree in physical and inorganic chemistry from the Siberian State Technological University , Krasnoyarsk, Russia, in 2005.In 2000, she joined the Institute of Materials, FEB RAS, Khabarovsk/ Russia as an staff scientist. Its main interests are in the field of kinetics of heterogeneous processes, synthesis of metal and oksidny nanocrystals. She is the author or coauthor of 51 publications in refereed journals. Ilya V. Korolkov was born in Novosibirsk/ Russia on September, 1981, graduated from the Novosibirsk State University, Novosibirsk/Russia in 2003 and defended Ph.D. thesis in physical chemistry in 2008. Staff scientist in the lab. of Crystal Chemistry, Institute of Inorganic Chemistry of SB of RAS since 2008. Research interests: crystal chemistry of inorganic materials, crystal and powder X-ray analysis, full profile analysis. He is the coauthor of 30 publications in refereed journals. E-mail: korolkov@@niic.nsc.ru. Konstantin S. Makarevich was born in Khabarovsk / Russia on November, 1978. He received the diploma degree in Chemistry from the Khabarovsk Pedagogical university, Russia in 2000 and the Ph.D. degree in materials science from the Komsomolsk-on-Amur State Technical University, Russia, in 2005.In 2005, he joined the Institute of Materials, FEB RAS, Khabarovsk/Russia as an staff scientist. Its main interests are in the field of kinetics of heterogeneous processes, synthesis of metal and oksidny nanocrystals. He is the author or coauthor of 48 publications in refereed journals. Maxim A. Pugachevsky was born in Khabarovsk / Russia on July, 1982. graduated from the Far Eastern State Transport University, Khabarovsk/ Russia in 2003 and defended Ph.D. thesis in condensed matter physical from in 2006. In 2003, he joined the Institute of Materials, FEB RAS, Khabarovsk/Russia as an staff scientist. Its main interests are in the field of electron microscopy, atomic force microscopy, laser ablation. He is the author or coauthor of 85 publications in refereed journals. Dmitry S. Shtarev was born in Khabarovsk/ Russia on October, 1983, graduated from the Far Eastern State Transport University, Khabarovsk/ Russia in 2006 and defended Ph.D. thesis in condensed matter physical from in 2011. In 2006, he joined the Far Eastern State Transport University as senior Lecturer. Research interests: crystal chemistry of inorganic materials, optics. He is the coauthor of 9 publi-cations in refereed journals.

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Alexander V. Syuy was born in Komsomolskon-Amur / Russia on October, 1975. He received the diploma degree in engineer from the Komsomolskon-Amur State Technical University, Komsomolskon-Amur /Russia in 1997 and the Ph.D. degree in optics from the Far Eastern State Transport University, Khabarovsk/Russia, in 2000. In 1997, he joined the Far Eastern State Transport University as graduate student, and as Head of research in september 2009. Since 1997, his principal research interests have been in the fields of optics, and solid state physics, and materials science. His interests include fabrication and characterization of ferroelectrics. He is the author or coauthor of 35 publications in refereed journals. A.V. Syuy is a member of OSA. Victor V. Atuchin was born in Prokopievsk / Russia on August, 1957. He received the diploma degree in radiophysics from the Tomsk State University, Tomsk/Russia in 1979 and the Ph.D. degree in solid state physics from the Institute of Semiconductor Physics of SB of RAS, Novosibirsk/Russia, in 1993. In 1980, he joined the Institute of Semiconductor Physics as an Engineer of Electronics, and as Head of Laboratory of Optical Materials and Structures in July 2002. Since 1980, his principal research interests have been in the fields of solid state physics and materials science. His interests include fabrication and characterization of thin films, surface science and chemistry of oxide crystals. He is the author or coauthor of 218 publications in refereed journals. V.V. Atuchin is a member of IEEE and IUCr.