KR20120008929A - Preparation of hollow-type metal oxide particle - Google Patents

Abstract

PURPOSE: A method for manufacturing hollow metal oxide particles is provided to reduce the particle size distribution of metal oxide hollow nanoparticles and obtain fine average particle sizes of the nanoparticles. CONSTITUTION: A method for manufacturing hollow metal oxide particles includes the following: iron oxide particles are obtained as core particles. The iron oxide particles are dispersed in a water solvent or an organic solvent. Oxide is coated on the surface of the iron oxide particles to obtain core-shell type complex particles. The iron oxide particles are eliminated through an acid-based washing process. The iron oxide particles are Fe_2O_3, FeOOH, or Fe_3O_4. The iron oxide particles are formed into spherical, cubical, ellipsoidal, peanut, platelet, and circular shapes.

Description

Preparation method of hollow-type metal oxide particles

The present invention relates to a method for producing hollow oxide particles that can be usefully used in the production method of metal oxide hollow microspheres. It provides a method for producing hollow particles by selectively removing the cargo through pickling.

Hollow particles are special particulate materials in the form of hollow particles. They are very low in density, light, and have high surface area and pore volume. Inorganic delivery carriers, porous adsorbents, catalytic supports, light weight fillers, optical coating agents, and other useful materials in a variety of industries, including electronic materials, optical materials and lightweight construction materials. It is actively used for the purpose of (optical coating agent) and low k-dielectrics.

Color mermaid: Hollow particles, core-shell, silica, porous body, optical coating

Looking at the results of prior studies on the manufacturing of the conventional hollow particles are as follows. In US Pat. No. 3,030,215, glass is melted at a high temperature of 1050 ° C. or higher and blown to report a hollow glass manufacturing method of 40 μm or more. In Japanese Patent JP 2007-230794, 60 nm to 30 μm of an emulsion is used. A method for producing hollow silica having a wide particle size distribution has been introduced. In addition, US Pat. No. 6,103,379 reported a method for preparing silica hollow spheres obtained by coating silica on a surface of a polymer microsphere using a surfactant and then removing the polymer through pyrolysis. Korean patent KR 2003-0092441 also discloses about 450 nm hollow silica obtained by heat treatment after coating silica on the surface of a polymer as a core. In addition, WO 2007-021508 introduces a method for producing hollow silica having a uniform particle size by coating with alkoxysilane on the surface of the polymer particles and pyrolysis. In JP2006-0342023, the preparation of hollow silica with a copolymer as a template and the low refractive index characteristics were introduced. US 6,221,326 describes the preparation of hollow silica using soluble CaCO ₃ as a core and its application to lightweight fillers for insulators, polymers, building materials, rubber, paper, absorbents, toothpaste abrasives, active material carriers, and sunscreen carriers. KR 2005-0083489 introduces a method for controlling the thickness of the silica coating layer in the synthesis of hollow silica by removing the polymer particles after coating the polymer particles as core particles and coating the surface with silica.

Representative methods of preparing hollow particles include spray-drying process, emulsion-polymerization process, self-assembly process, and polymers or organic materials, or CaCO ₃ or ZnS, CdSe and The same inorganic template technology is known. The most common method for the production of hollow particles is a polymer material such as PC, PMMA, etc. as a core material and coated on the surface of the particle with an inorganic material (mainly SiO ₂ ), which is a desired shell material. There is a method of obtaining hollow particles by synthesizing the core-shell composite particles of an inorganic material and then removing the polymer material as a core material by using a heat treatment or a special solvent. In this case, however, the structure of the wall material is destroyed during the removal of the polymer, and thus it is difficult to synthesize the hollow particles having a uniform shape.In addition, since the polymer is burned and removed through heat treatment, serious side effects of environmental pollution occur. It is pointed out. As another method, an emulsion using an organic material in a solution is formed, and then a surface of the micelle is coated with a desired inorganic material, and similarly to the above method, a method of removing an organic material, which is a mouselle forming material, through combustion is known. This method can form hollow particles of relatively small size, sub-micro, but has similar problems as the polymer template method, and the yield is very low in mass production, and the actual industrialization is difficult. A simple method is to prepare hollow particles by spray-drying an aqueous solution or a water-dispersible inorganic material. This method can be produced only for large particles of several micros to several tens of micrometers. The distribution is very wide. Although attempts have been made to produce hollow oxide particles through the introduction of various synthetic methods, there has been little mass production of hollow particles having a uniform particle size distribution.

The present invention provides a method for synthesizing new hollow particles with high reliability and economical efficiency by using nano-sized iron oxide or iron hydroxide particles (Fe ₂ O ₃ , FeOOH, Fe ₃ O _4, etc.) as sacrificial core materials. . In the case of using an inorganic sacrificial material, especially iron oxide as in the present invention, several features that are difficult to achieve by the conventional method can be expected. First, in the case of iron oxide, as one of the metal oxides, which are easy to manufacture particles of various shapes as well as various sizes, there is a feature that can be selected very widely according to the size and shape of the desired hollow. Second, iron oxide has an advantage that can be easily removed using a simple method of pickling in removing the core particles because the solubility in the acid solution is very large. Third, in the case of removing the core particles through pickling, high quality hollow particles are significantly reduced because cracking or breaking of hollow particles in the silica shell is significantly reduced compared to the method of removing the core material by the combustion method. Fourth, the solution containing iron ions (Fe ^{3 +} or Fe ^{2 +} ) ions, which is a wastewater resulting from pickling, can be recycled since it is used for the synthesis of core materials. There is a feature that can be removed at its source. Fifthly, in the case of iron oxide, especially r-Fe ₂ O ₃ or Fe ₃ O ₄ when using a magnetic field as a ferromagnetic material (ferromagnetic materials) very simple to separate and wash the particulate matter from the solution. In particular, in the case of handling nano-level particles, it is difficult to apply a solid-liquid separation method using centrifugal separation or a filter-bag in the field, and in this case, there is a feature that can be utilized as a very effective solid-liquid separation method. Sixth, the Fe ion has a unique brown color in aqueous solution, so the removal of core particles can be easily monitored with the naked eye without using a special spectroscopic method.

The present invention relates to a method for producing a hollow metal oxide using the iron oxide as an inorganic material, which is easy to control the size and shape of the particles, and is simple by using iron oxide having high solubility in acid as the core material. Hollow hollow particles are manufactured by easily removing the core particles through an pickling process to form a cavity in the particles.

More specifically, the present invention synthesizes Fe ₂ O ₃ , FeOOH, or Fe ₃ O ₄ and iron oxide having various shapes and sizes by using a precursor of an appropriate iron oxide, and the iron oxide is used as a solvent or Dispersing through stirring or ultrasonic pulverization in an organic solvent, and adding a wall material or a precursor to coat the wall material on the surface of the iron oxide core particles, thereby preparing core-shell composite particles of iron oxide-metal oxide. And selectively removing iron oxide as a core material through an acid treatment.

The following describes the production method of the present invention in more detail.

As the iron oxide, which is a core material used in the present invention, an iron compound, such as FeOOH, Fe ₂ O ₃ and Fe ₃ O ₄ , may be preferably used as an iron compound which can be easily removed by pickling as an oxide or hydroxide type compound. . Known methods such as coprecipitation method, sol-gel method, hydrothermal synthesis method can be used for the synthesis of iron oxide without limitation, and the shape of the particles may be spherical, cubic, ellipsoidal, Peanut, platelet, acicular, etc. can be applied in various ways. In addition, the size of the particles can be arbitrarily selected and applied according to the size of the desired hollow. Therefore, the size of the particles of iron oxide can be applied without limitation from several nanometers to several tens of micrometers, the present invention is particularly effective in synthesizing hollow particles having a particle size of several micrometers or less and showing a uniform particle size distribution There are features that can be applied. On the other hand, if necessary when using ferromagnetic materials (γ-Fe ₂ O ₃ and Fe ₃ O ₄ ) of the iron oxide it can be easily performed to recover the separation of the material using a magnetic field (magnet).

A step of uniformly dispersing the iron oxide particles in a solution for producing a core-shell-type composite particles of iron oxide-metal oxide using iron oxide as a core particle. The dispersion may be used without limitation, known oxide particle dispersion methods such as stirring or ultrasonic grinding. In the case of ferromagnetic iron oxides (γ-Fe ₂ O ₃ and Fe ₃ O ₄ ), it is necessary to disperse the inorganic or organic dispersant if necessary to minimize the aggregation due to the magnetic dipole moment between the particles. It may be desirable. At this time, as the inorganic dispersant, polysilicic acid made by prehydrolysis of TEOS (tetraethoxysilicate) may be preferably used, and as the organic dispersant, cationic, anionic and nonionic surfactants may be preferably used. . Typically oleic acid, cetyltrimethylammonium salt and the like can be used. As a dispersion solvent, an organic solvent such as an aqueous solution, alcohol, or a mixed solvent of an aqueous solvent and an organic solvent may be used without limitation.

As a method of coating the metal oxide on the surface of the dispersed iron oxide core particles, the sol-gel method may be preferably used. As a precursor of the metal oxide, any compound that can be coated by hydrolysis on the surface of the metal oxide particles, such as metal nitrate, metal chloride salt, metal sulfate, and metal alkoxide, may be used regardless of the type, and metal alkoxide is most preferred. Can be used. At this time, the size, shell thickness, wall porosity, etc. of the composite particles are controlled according to the type of metal oxide precursor, amount of addition, concentration, and reaction conditions (time, temperature, pH, etc.).

Selective dissolution method using pickling is applied to remove iron oxide as core material from core-shell composite particles of iron oxide-metal oxide. This method of selective removal through acid solution can remove core particles without destroying wall material, which is very effective in providing high quality hollow particles. Also, if necessary, the core-shell composite particles may include heating the composite particles prior to pickling. Through the heating process, the organic matter present in the composite particles can be decomposed and decomposed, and depending on the material, there is an advantage that the mechanical properties of the hollow particles can be improved by strengthening the three-dimensional network of the wall material through the heating process. The heat treatment temperature is preferably 300 to 600 ℃. When the temperature is less than 300 ° C., the heating temperature may not be low enough to cause combustion of the organic material. If the temperature is higher than 600 ° C., particle aggregation may occur due to sintering of the composite particles, and the density of the shell material may be dense, making it difficult to remove the core particles. As the acid solution used in the pickling process, any solution having a pH of <3 or less may be preferably used. Typically, hydrochloric acid, nitric acid and sulfuric acid solutions may be preferably used. In addition, the temperature at the time of acid washing is preferably 30 ~ 100 ℃, more preferably 60 ~ 80 ℃. If it is less than 30 ℃ elution time of the core particles by pickling is too long, there is a problem in economic efficiency, and if it is above 100 ℃ volatilization of the solvent is not preferable because it is sudden. In addition, it is preferable to wash repeatedly within 1 to 6 hours of pickling. The process of removing the core material by pickling has an advantage that it can be easily determined by the naked eye because of the unique color of the iron ions. When the pickling is completed, washed thoroughly with distilled water or an organic solvent or a mixed solvent and then dried to complete the preparation of hollow particles.

As described above, the present invention provides a method for more effectively synthesizing hollow particles having various shapes and sizes according to the size and shape of the core particles. It is suitable for the synthesis of high quality hollow particles by removing the core particles by a simple method through pickling. In addition, according to the present invention, metal oxide hollow nanoparticles having a fine average particle size of 5 micrometers or less and a particle size distribution in a very narrow range can be prepared. In addition, the hollow nanoparticles of the present invention can impart electronic and chemical properties in addition to the specific surface area and optical properties of the hollow nanoparticles of the present invention, compared to the conventional hollow particles, which are mainly used in transport or catalyst fields based on low density and wide specific surface area. Therefore, it is more suitable for the application to the high-tech field using so-called nanotechnology.

The representative figure is a transmission electron micrograph of the hollow particles obtained after pickling the Fe ₂ O ₃ -SiO ₂ core-shell composite particles synthesized through a two-step coating process using spherical Fe ₂ O ₃ as a core particle.
1 is a transmission electron microscope photograph of a hollow particle obtained after pickling a Fe ₂ O ₃ -SiO ₂ core-shell composite particle synthesized through a two-step coating process using cubic Fe ₂ O ₃ as a core particle.
2 is a hollow particle obtained after pickling a Fe ₂ O ₃ -SiO ₂ core-shell composite particle synthesized by silica coating using Fe ₃ O ₄ , which is a magnetic fluid, as a core particle, and CTA as an organic template. Electron micrograph.

Hereinafter, the present invention will be described in detail with reference to preferred examples of the present invention. However, the present invention is not limited to the following examples.

Example 1

Spherical α-Fe ₂ O ₃ core particles were synthesized by hydrothermal synthesis using FeCl ₃ and Fe (NO ₃ ) ₃ as starting materials. [Fe ^{3 +} ] and [H ⁺ ] in the reaction were 3.12 x 10 ^-2 and 3.20 x 10 ^-3 mol, respectively ^. dm ^-3 and FeCl ₃ , FeCl ₃ / [FeCl ₃ + Fe (NO ₃ ) ₃ ] (xFeCl ₃ ) were varied from 0.0 to 1.0 to synthesize α-Fe2O3 particles of different sizes. Hydrolysis and crystallization reaction was carried out at 100 ° C for 7 days under hydrothermal conditions. After the reaction was completed, washed three times with distilled water and dried for 12 hours in an electric oven at 60 ℃ was used as core particles. In this case, spherical α-Fe ₂ O ₃ core particles having a size of 20 to 300 nm were obtained.

[Example 2]

Peanut, pseudocubic and ellipsoidal α-Fe ₂ O ₃ core particles were also synthesized using hydrolysis and crystallization of FeCl ₃ . Peanut-like α-Fe ₂ O ₃ core particles were synthesized using a hydrolysis-hydrothermal synthesis method. First of all, 0.4 mol ^. FeCl _{3 in} dm ^{-3 .} 6H ₂ O was dissolved in 100 mL of distilled water to prepare 0.4M ferric chloride solution. The 5.4 N NaOH solution is slowly titrated with vigorous stirring of the iron chloride aqueous solution to form a viscous iron hydroxide gel. The amorphous Fe (OH) ₃ formed was transferred to 800 mL of Teflon vessel and the reaction was performed at 160 ° C. for 24 hours. After the reaction was completed, washed three times with distilled water and dried for 12 hours in an electric oven at 60 ℃ was used as core particles. Synthesis of pseudocubical particles was similar to that of peanut-type particles, and more specifically T.Sugimoto et al. J. Colloid Inter. Sci. 159, 1993, 372. In the case of pseudocubic particles, 2.0 M aqueous FeCl ₃ solution was used as a starting material, and hydrolysis and crystallization reaction was performed at 100 ° C. for 48 hours. Ellipsoidal core particles were synthesized using Na ₂ SO ₄ as an additive to control the shape of the particles (T. Sugimoto et al. Colloids & Surface A: 134, 1998, 265). The hydrothermal reaction was carried out at 100 ° C. for 48 hours.

Example 3

Ferromagnetic Fe ₃ O ₄ was synthesized by coprecipitation using chlorides of ferrous (Fe ^{2 +} ) / ferric (Fe ^{3 +} ). That is, FeCl ₂ (1 mol) / FeCl ₃ (2 mol) = 1/2 and a base solution was added to synthesize Fe ₃ O ₄ particles. First, the distilled water used to make the metal salt solution is heated before use to remove dissolved oxygen while flowing nitrogen. Ferric chloride as a raw material of FeCl ₂ ^. 4H ₂ O and FeCl ₃ were used, respectively. 0.85 mL of 12.1 N HCl is added to 25 mL of deoxygenated distilled water. 3.18 g of FeCl ₂ ^. Dissolve cleanly by adding 4H ₂ O and 5.41 g FeCl ₃ . The ferric chloride solution thus prepared is titrated with vigorous stirring with 250 mL of 1.5N NaOH. It can be observed that if a certain amount of NaOH is added, a sharp black precipitate is formed in the reactor. After the titration was completed, the mixture was further stirred for 30 minutes to complete the reaction, and washed three times with distilled water. At this time, the obtained Fe ₃ O _{4 It} could be easily separated using a magnet. After washing with water, 500 mL of 0.01 N HCl solution is added and neutralized to synthesize a ferrofluid hydrosol having colloidal stability. At this time, the synthesized Fe ₃ O _{4 It} was about 8 ~ 10 nm.

Example 4

The α-Fe ₂ O ₃ core particle surfaces having various sizes and shapes synthesized through Examples 1 and 2 were coated with silica using a two-step process. First, 46 g of tetraethylorthosilicate (TEOS) was mixed with 354 g of distilled water, and then the pH of the solution was adjusted to 4 by the addition of 1N-HCl solution, followed by stirring at room temperature for 12 hours for clear polysilic acid. A polysilicic solution was synthesized. In the first step, 1 g of α-Fe ₂ O ₃ core particles were added to 40 mL of distilled water and ultrasonically dispersed for 20 minutes. Then, 1 mL of a polysilic acid solution prepared in advance was added and mixed with vigorous stirring for 30 minutes. To this was added 1 mL NH 4 OH and stirred at room temperature for 3 hours to induce hydrolysis of silica on the core particle surface. In the two-stage coating, the surface-treated core particles were added to 40 mL ethanol solution and stirred and redispersed. 0.19 g of TEOS was titrated thereto, followed by the addition of 6 mL of NH 4 OH to induce the hydrolysis-condensation reaction of TEOS. After coating reaction for 3 hours at room temperature, separated and washed sufficiently with ethanol solution and dried for 12 hours at 60 ℃ SiO ₂ Coated Fe ₂ O ₃ core-shell composite particles were prepared.

Example 5

Silica coating reaction using the two-step process was also performed using the magnetic fluid synthesized as in Example 3 as a core particle. 1 g of Fe ₃ O ₄ core particles were added to 50 mL of distilled water and ultrasonically dispersed for 30 minutes. 2 mL of polysilic acid solution was added thereto, followed by stirring for 10 minutes. 2 mL of NH ₄ OH was then added and stirred for 12 hours to modify the surface of the Fe ₃ O ₄ core particles with silica. 0.6 mL of TEOS was added thereto, stirred for 10 minutes, and 10 mL of NH ₄ OH was added to induce hydrolysis of silica. After the reaction for 2 hours was washed three times with a mixed solvent of ethanol and distilled water and dried for 12 hours at 60 ℃ to prepare a SiO ₂ -coated Fe ₃ O ₄ core-shell composite particles.

Example 6

In the same manner as in Example 3, a method of using a bulk organic material as a template in a process of coating a magnetic fluid synthesized as a core particle with silica was attempted. 1 g of Fe ₃ O ₄ core particles were added to a mixture of 100 mL distilled water and 100 mL ethanol, and ultrasonically dispersed for 30 minutes. Cetyltrimethylammonium bromide (CTA) was added 1.0 g and stirred for 10 minutes. Next, 100 mL of NH ₄ OH was added, followed by 5.2 g of TEOS, followed by stirring for 12 hours, thereby modifying the Fe ₃ O ₄ core particle surface with silica. After completion of the reaction, the mixture was washed 5 times with distilled water and ethanol mixed solvent and dried at 120 ° C. for 12 hours to prepare organic-modified SiO 2 -coated Fe 3 O 4 core-shell composite particles. This was heat treated at 550 ° C. for 4 hours to decompose the organics.

Example 7

The magnetic fluid synthesized in the same manner as in Example 6 was used as core particles and coated with silica. However, oleic acid was used as an organic template instead of CTA. Likewise, Fe ₃ O ₄ core-shell composite particles having a porous silica shell were synthesized by heat treatment at 550 ° C. for 4 hours.

Example 8

Core-shell composite particles synthesized in Examples 4, 5, 6, and 7 were subjected to acid treatment to remove iron oxide, a core material, to synthesize hollow particles. In the core particle removal method, 1 g of each composite particle was added to 100 mL of 2N hydrochloric acid solution, and then stirred at 80 ° C. for 2 hours to dissolve and remove iron oxide. Pickling was repeated three times. 1 is a transmission electron microscope (TEM) observation result of the hollow silica particles synthesized through Example 1, Example 4 and Example 8. It was confirmed that the hollow particles having a size of about 150 nm and a thickness of about 10 nm were synthesized. 2 is a transmission electron microscope (TEM) observation result of the hollow silica particles synthesized through Examples 2, 4 and 8. It could be confirmed that the hollow particles having a size of about 200 nm and a thickness of about 10 nm were synthesized. 3 is a transmission electron microscope (TEM) observation result of the hollow silica particles synthesized through Examples 3, 6 and 8. It was confirmed that the hollow particles having a size of about 30 nm and a thickness of about 10 nm were synthesized.

Claims (8)

The present invention relates to a method for producing hollow metal oxide particles, comprising the steps of (1) preparing iron oxide particles as core particles, (2) dispersing iron oxide particles in an aqueous solvent or an organic solvent, and (3) on the surface of iron oxide particles. Coating the oxide to produce a core-shell (core-shell) type composite particles, (4) The manufacturing method characterized in that the core particles of iron oxide particles are removed by pickling.
The method of claim 1, wherein the iron oxide particles, which are the core particles, are Fe ₂ O ₃ , FeOOH or Fe ₃ O ₄ in spherical, cubic, plate-shaped, elliptical, peanut-shaped, needle-like form.
The method according to claim 1, wherein the iron oxide particles are dispersed in water or an alcohol mixed alone or in a mixed solvent.
The method of claim 1, wherein the surface is coated with silica, titania, alumina, titania, cerima, zirconia.
The method of claim 4, wherein the surface coating method is a metal alkoxide, metal chloride, nitrate as a starting material, the coating method using a hydrolysis method, hydrothermal synthesis method, sol-gel method.
The method according to claim 5, wherein the surface coating process uses a two-step coating method or an organic template.
The method of claim 1, wherein the iron oxide metal core particles are removed by pickling.
The pickling acid solution according to claim 7, characterized in that the aqueous solution of hydrochloric acid, nitric acid, sulfuric acid, acetic acid and removed while stirring at a temperature of 30 ~ 100 ^° C.

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