PL221520B1 - Process for the preparation of modified alumina nanoparticles - Google Patents

Description

Description of the invention

The subject of the invention is a method of obtaining modified alumina nanoparticles that can be widely used in many fields of technology, such as optics, electronics or computer science.

Modified alumina nanoparticles can be used alone or added as an intermediate at various stages of the production of optical fibers, luminescent paints, scintillation counters or as an additive to other types of luminescent materials.

The last few years have been a period of intensive research into the use of nanopowders in many industries. Extremely high hopes are associated with the introduction of systems containing nanometric particles of metal, mainly due to their highly developed specific surface. Particles with nanometric dimensions are used primarily for the production of new, technologically advanced products. The addition of nanoparticles to these materials makes it possible to effectively modify their properties and / or obtain materials with completely new, previously unknown properties.

Lanthanide ions occur in the third, less frequently in the second and fourth oxidation states and are known for their specific optical properties. These properties are the result of an incompletely filled 4f shell, strongly shielded with two 5s and six 5p electrons. 4f electrons interact poorly with the environment and do not take part in the formation of chemical bonds. As a result, the influence of external factors, such as the lattice area of the matrix on the spectroscopic properties of rare earth ions is relatively small. As a result, the spectra of lanthanides embedded in dielectric structures retain the nature of the spectra of free ions and only to a small extent depend on the matrix in which they are placed, which makes them an excellent material for use, among others. in optical amplifiers and solid state lasers.

Lanthanide ions show a very long duration of luminescence (on the order of milliseconds), which is especially important when using them as a luminescence active dopant. Unfortunately, these metals also show an unfavorably weak absorption band, which is a major disadvantage when used as luminescent materials. Published by W. De, W. Horrocks, Jr., Gregory F. Schmidt, D.R. Sudnicki, C. Kittreil and R.A. Bernheim, Journal of the American Chemical Society 99, 2378 (1977) reports that most of the rare earths in the form of chelated complexes exhibit good photoluminescent properties. Therefore, in order to break this barrier, lanthanide ions are often coordinated with substituents containing organic chromophores, which, when excited by energy transfer, increase their luminescence (the so-called "antenna effect").

A simpler solution to this problem, however, may be to place the lanthanide ions in the inert ceramic material in the form of a dopant. The first information about optically active composite materials doped with rare earth ions comes from the early 70's in the publication of C.F. Rapp, J. Chrysochoos, Journal of Materials Science 7 (1972), 1090-1092. In 1975 F. Auzel in the publication of F. Auzel, D. Pecile, D. Morin, Journal of Electrochemical Society 122 (1975), 101-107 described ceramics doped with rare earth ions with an oxygen glass phase and a fluoride crystalline phase with excellent properties. spectroscopic.

The addition of rare earth ions to the glass or crystal allows to obtain an active medium for compact solid-state lasers, which is a reasonable alternative to semiconductor materials. They offer better thermomechanical parameters, higher powers and a much better quality of generated radiation than semiconductor lasers. In addition, they allow you to work in the spectral ranges unattainable for modern semiconductor lasers.

The specific properties of lanthanide ions are also used in the production of optical fibers. The first Nd ³⁺ doped fiber made of a composite consisting of an oxide glass phase SiO ₂ -AI ₂ O ₃ with a fluoride crystalline phase is described in BN Samson, PA Tick, NF Borelli, Optics Letters 26 (2001), 145-147. The literature on the subject also reports on fiber-optic structures resulting from the doping of the polymethyl methacrylate (PMMA) matrix with rare earth ions in the form of neodymium octane (NdOA) in the publication of Q. Zhang, H. Ming, Y. Zhai, Journal of Applied Polymer Science 62 (1996 ), 887-891, as well as halate compounds of europium, samarium, terbium and neodymium ions (in the form of hexafluoroacetylacetone HFAA) in T. Kobayashi, S. Nakatsunka. T. Iwafuji, K. Kuriki, N. Imai, T. Nakamoto, Ch.D. Claude, K. Sasaki, Y. Koike, Y. Okamoto, Applied Physics Letters 71 (1997) 2421-2423.

PL 221 520 B1

Rare earth ions such as Tm ³⁺ , Nd ³⁺ , Pr ³⁺ , Sm ³⁺ , Dy ³⁺ , Ho ³⁺ and Tb ³⁺ are the main activators considered in the publications of G. Lakshminarayan, Y. Hucheng, Y. teng, J. Qiu, Journal of Luminescence 129 (2009) 59-68 and AS Gouveia-Neto, LA Bueno, ACM Afonso, JF Nascimento, EB Costa, Y.Messaddeq, SJL Ribeiro, Journal of Non-Crystalline Solids 354 (2008) 509 -514 in the context of the production of materials allowing for efficient emission in the visible and near-UV range.

In the literature on the subject, we can also find many reports on the production of materials based on Al ₂ O ₃ alumina doped with ions of rare earth metals from the lanthanide group.

One technique for producing catalytically active Ln / Al ₂ O ₃ powders is the relatively simple impregnation method presented in T. Konishi, E. Suda, H. Imamura, Journal of Alloys and Compounds 225 (1995) 629-632. It consists in depositing metallic lanthanide particles on porous alumina. In the first step of this process, the finished Al ₂ O ₃ powder was suspended in an aqueous ammonia solution at 198 K. Then metallic ytterbium or europium was added to the stirred suspension. After the metal was deposited on the alumina surface, the excess ammonia was removed under vacuum at 198 K, and the obtained alumina with deposited lanthanide particles was calcined. The material thus obtained showed good catalytic properties in the hydrogenation of alkenes and alkynes to dienes.

Another group of methods for the preparation of metal oxide nanopowders doped with rare earth ions are the techniques of precipitation and co-precipitation followed by the calcination process. J. Mouzon, P. Nordell, A. Thomas, M. Oden, Journal of the European Ceramic Society 27 (2007) 1991-1998 describes a co-precipitation method to obtain the Yb-Y ₂ O ₃ precursor, which was then calcined to obtaining nanopowder. Yttrium nitrate was used as the yttrium compound in this method, while ytterbium nitrate pentahydrate was used as the source of ytterbium ions. The precipitating reagent for the nanopowder was an aqueous ammonia solution or, alternatively, ammonium bicarbonate (AHC) solution.

Another method for preparing modified alumina is presented in B. Dong, ZQ Feng, JF Zu, L. Bai, Journal of Sol-Gel Science and Technology 48 (2008) 303-307. It is a sol-gel method in which the alkoxy aluminum compound [Al (OC ₃ H7) ₃ ] is used as the alkoxy aluminum oxide precursor and the salts of these metals are used as the source of rare earth metal ions. It consists in hydrolyzing the aluminum alkoxy compound with water and then removing the resulting isopropyl alcohol. _{FINO 3} is then added to the reaction system. After 16 hours, ytterbium nitrate was added to the obtained sol (γ-AlOOH). The obtained modified alumina precursor is then calcined to obtain ytterbium-doped alumina.

Also using the sol-gel method in T. Ishizaka and Y. Kurokawa, Journal of Luminescence 92 (2001) 57-63, alumina doped with lanthanum was obtained. However, in the method described there, other reagents were used. The compound that was hydrolyzed with aqueous ammonia was aluminum chloride. The obtained aluminum hydroxide was then aged for 12 hours, filtered and washed with distilled water. The next step was acetic acid to carry out the peptization process. Lanthanide chloride was then added to the obtained sol to obtain an Ln / Al ₂ O _{3 system} , which was then calcined.

Apart from the sol-gel method, the literature on the subject also reports on the existence of many modifications. In the publication of N. Al-Yassir, R. Le Van Mao, Applied Catalysis A: General 317 (2007) 275-283 as a modification of the sol-gel method, for example, the so-called the supercritical drying technique.

Yttria nanopowder doped with rare earth ions can also be obtained using the so-called the single-step gas-phase flame synthesis method as described in X. Quin, T. Yokomori, Y. Ju, Applied Physics Letters, 90, 073104 (2007) 1-3. Y (C11H19O2) 3 and Y (TMHD) 3 were used interchangeably as the yttrium oxide precursor. _{Yb (TMHD) 3} , Er (TMHD) ₃ , Ho (TMHD) ₃ and Tm (TMHD) ₃ were used as the precursors of ytterbium, erbium, holmium and thulium, respectively. The equipment for the synthesis of nanoparticles consisted of an evaporation chamber, a burner, a combustion chamber in which thermal decomposition of the organic precursor took place, an electrostatic filter system collecting nanoparticles, and a vacuum pump.

One of the disadvantages of the above-described methods of obtaining lanthanide ions on e.g. Alumina is the preparation of products with a very poorly developed specific surface. These processes mainly relate to the so-called wet methods, carried out unfavorably in water as the process solvent. These methods are also characterized by a high degree of technology complexity.

The disadvantage of the above-mentioned wet methods is the formation of a large amount of products no4

They are desirable, burden the environment and adversely affect the quality of manufactured products. The obtained final products, powders with nanometric sizes, remain contaminated with reagents and by-products of the process.

_{The method of obtaining modified alumina nanoparticles doped with lanthanide ions according to the invention is characterized in that an organic aluminum compound with the general formula AIR 3} is introduced into an organic solvent selected from the group of hydrocarbons containing from 5 to 20 carbon atoms or aliphatic alcohols containing from 1 to 10 carbon atoms, in which R is an alkyl substituent containing from 1 to 9 carbon atoms, then a lanthanide compound, the whole is mixed in the presence of dry or moist air, the solvent is removed, and the residue after drying is thermally decomposed in the presence of air at a temperature of 300 to 1200 ° C C.

An alkoxy aluminum compound of the general formula Al (OR) ₃ in which R is an alkyl substituent having 1 to 15 carbon atoms can be added to the reaction mixture.

The concentration of the organoaluminum compound in the organic solvent is preferably in the range from 0.001 to 10 mol / l.

Preferably, a lanthanide salt which is soluble in the reaction medium is used as the lanthanide compound.

By carrying out the process according to the invention, alumina nanoparticles doped with rare earth ions are obtained. The average size of the alumina particles doped with lanthanide ions is within the range of 10-100 nm and depends on the process conditions (Fig. 1). The obtained aluminum oxide nanoparticles doped with rare earth ions are characterized by a highly developed specific surface area of over 200 m / g.

Fig. 1. Sample SEM photo of alumina nanopowder doped with lanthanide ions

Lanthanide ions, depending on the process conditions, are built into the crystal structure of aluminum oxide or appear in the form of "flakes" with a diameter of approx. 5 nm and a thickness of 2 nm (Fig. 2).

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Fig. 2. Exemplary TEM photo obtained with the high-resolution method for ytterbium-doped alumina nanopowder b) and the corresponding inverse Fourier transform a). Below, electron diffractions corresponding to the areas marked in the photos, confirming the presence of the ytterbium.

The method according to the invention is not a wet method, which solves the problem of process waste. Additionally, the only undesirable product of the process is carbon dioxide.

The essence of the invention is explained in the following examples:

P r z k ł a d 1

To a 1000 mL reactor equipped with a stirrer, 500 mL of dried hexane was added, followed by the addition of 2.8 mL of triethylaluminum and triisopropoxy aluminum at a triisopropoxy aluminum / triethylaluminum molar ratio of 2: 1, and stirred until the alkoxy aluminum compound was completely dissolved. Then triisopropoxide was added so that the percentage of lanthanide with respect to alumina was 3% by weight. The solvent was then evaporated and the evaporation residue, a white powder, was heated under air at 700 ° C for 24 hours. The obtained was white alumina nanopowder doped with lanthanide ions with a grain size in the range of 30-80 nm.

P r z k ł a d 2

To a 1000 ml reactor equipped with an agitator was added 500 ml of dried hexane followed by yttrium acetylacetonate such that the percentage of lanthanide to alumina was 2% by weight. Then 2.8 ml of triethylaluminum and triisopropoxy aluminum were added such that the triisopropoxy aluminum / triethylaluminum molar ratio was 1: 1. The solvent was then evaporated and the evaporation residue, white powder, was heated in air at 800 ° C for 24 hours. The obtained was white alumina nanopowder doped with lanthanide ions with a grain size in the range of 30-100 nm.

P r z k ł a d 3

To a 1000 mL reactor equipped with a stirrer, 500 mL of dried hexane was added, followed by the addition of triethylaluminum at a weight concentration of 3% triethylaluminum in the hexane. The ytterbium chloride was then added so that the percentage of lanthanide with respect to alumina was 4% by weight. The solvent was then evaporated and the evaporation residue, a white powder, was heated in air at 600 ° C for 24 hours. The obtained was white alumina nanopowder doped with lanthanide ions with a grain size in the range of 30-100 nm.

Claims (3)

Patent claims A method for the preparation of modified alumina nanoparticles, which uses the process of thermal decomposition of the aluminum nanoparticles precursor made of aluminum compounds and lanthanide compounds, characterized in that the organic solvent selected from the group of hydrocarbons containing from 5 to 20 carbon atoms or aliphatic alcohols containing from 1 to 10 carbon atoms are introduced an organoaluminum compound of general formula AIR ₃ in which R represents an alkyl substituent having 1 to 15 carbon atoms and a lanthanide compound and optionally an alkoxy aluminum compound of general formula Al (OR) ₃ in which R is an alkyl substituent containing from 1 to 15 carbon atoms, the whole is mixed in the presence of dry or moist air, then the solvent is removed, and the residue after drying is subjected to thermal decomposition in the presence of air at a temperature of 300-1200 ° C. 2. The method according to p. The process of claim 1, wherein the concentration of the organoaluminum compound in the organic solvent is 0.001 to 10 mol / l. 3. The method according to p. A process as claimed in claim 1 or 2, characterized in that the lanthanide compound is a lanthanide salt which is soluble in the reaction medium.