JP2005041766A - Method of manufacturing metallic oxide fine structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems that cesium being an expensive alkali metal is used, it is necessary to fire at 800-1,000°C for several ten hours or the like to induce the increase in costs and an impurity (cesium) remains in a method using a layered titanate, specifically cesium titanate for a raw material in the conventional method of manufacturing a metallic oxide fine structure. <P>SOLUTION: The method of manufacturing the metallic oxide fine structure has a process for enlarging a distance between layers by inserting protons between the layers of metallic oxide hollow fibers having a scroll type layered structure. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a novel method for producing a metal oxide microstructure.

  In recent years, metal oxides such as titanium oxide have been widely applied as functional materials such as photocatalyst materials, cosmetic pigments, catalysts, catalyst carriers, and insulating materials because of their physical and chemical stability and excellent optical properties. Has been. For these metal oxides, isotropic spherical particles are usually used. For example, as a method for producing titanium oxide, a gas phase method in which titanium chloride is oxidized at high temperature in a gas phase, or titanium chloride / titanium sulfate is used as a raw material. And a sol / gel method for hydrolyzing alkoxytitanium and the like. However, metal oxide fine particles that have undergone such a high-temperature process usually become secondary particles in which primary particles are aggregated, which may cause appearance defects such as white turbidity at the time of thin film formation or cause problems in adhesion to the substrate. It has become. As a technique for solving the problem in such metal oxide fine particles, a proposal has been made to make the structure of the metal oxide into a flaky microstructure (see, for example, Non-Patent Documents 1 and 2).

In Non-Patent Document 2, when cesium titanate is converted to titanic acid by acid treatment, cesium in titanate is 0.04 in terms of atomic ratio (Cs / Ti) to titanium, and about 4% cesium is It has been reported to remain. Non-Patent Document 1 does not describe the amount of cesium, but the production method is almost the same as that of Non-Patent Document 2, and it is considered that cesium remains in the same manner.
“Journal of the American Chemical Society”, Vol.118, P8329 (1996) “Journal of Physical Chemistry B”, Vol.105, P10893 (2001)

In the method for producing a flaky metal oxide microstructure, when producing a layered titanate as a raw material, specifically, cesium titanate, cesium that is an expensive alkali metal is used, There is a problem that the cost is high, for example, it is necessary to perform baking at 1000 ° C. for several tens of hours.
Moreover, the cesium which is an impurity remains, and there existed a subject that it might have a bad influence depending on a use. For example, when used as a charge transfer device such as a photocatalyst or a photo semiconductor electrode, it may cause scattering of carriers (electrons and holes) that move in the metal oxide. There is a possibility.

  The above problem can be solved by the following configuration and manufacturing method of the present invention. That is, the present invention has a step of expanding a layer by inserting protons between layers of a metal oxide hollow fiber having a scroll-like layered structure, and a method for producing a metal oxide microstructure Is to provide.

  The basic idea of the present invention is to expand the interlayer by inserting protons between the layers of the metal oxide hollow fiber having a scroll-like structure. At this time, protons are inserted between the layers, and the adsorption to the metal oxide layer occurs, thereby stabilizing the surface of the metal oxide layer and reducing the interaction between the metal oxide layers one after another. Interlayer swelling of the hollow fiber is possible, and as a result, conversion to a fine structure is possible.

  In one aspect of the present invention, the metal oxide microstructure is flaky. By making it into a flaky shape, for example, a fine structure having excellent adhesion to a substrate can be obtained. The metal oxide microstructure of the present invention may have a shape in which flakes are assembled.

  In another aspect of the present invention, the metal oxide microstructure has a hollow fiber shape having a diameter of 15 nm or more and 30 nm or less. Such a hollow fiber is a novel structure which has not been known so far. Applications such as selective separation media and optical semiconductor electrodes are conceivable.

  In a preferred aspect of the present invention, the step of expanding the interlayer is a step of bringing the metal oxide hollow fiber into contact with an acid aqueous solution. As a method of inserting protons between the layers of the hollow fiber, the method of contacting with an acid is the simplest.

  In a preferred embodiment of the present invention, the method includes a step of contacting the metal oxide hollow fiber with an aqueous amine solution after the step of bringing the metal oxide hollow fiber into contact with an aqueous acid solution. By contacting with an aqueous amine solution, dispersibility can be improved and interlayer swelling can be further promoted.

  In a preferred embodiment of the present invention, the metal oxide hollow fiber is made of titanium oxide or titanium hydroxide. Titanium oxide or titanium hydroxide is more preferably used because the hollow fiber can be easily produced and can be produced at low cost.

  In a preferred embodiment of the present invention, the ratio of the molar amount (B) of the alkali metal to the molar amount (A) of the main component metal of the metal oxide microstructure contained in the metal oxide microstructure (B / A) is 0.03 or less. If the value of B / A is 0.03 or less, the influence of impurities is extremely small. In the present invention, a microstructure having a very low B / A of about 0.001 is also obtained.

  In another aspect of the present invention, the metal oxide microstructure is plate-shaped rutile-type titanium oxide particles. Such plate-like rutile-type titanium oxide particles have a novel structure that has not been known so far. Applications to photocatalysts and photo semiconductor electrodes are conceivable.

It is possible to provide a novel method for producing a metal oxide microstructure in which problems such as formation of aggregates and specific surface area of conventional metal oxide fine particles are solved. The manufacturing method of the metal oxide microstructure of the present invention is simpler than the conventional manufacturing method, and a product with less impurities can be obtained.
In addition, since the metal oxide microstructure of the present invention can be improved in dispersibility in solution, adhesion to a substrate, and anisotropy compared to conventional spherical particles, the catalyst, catalyst carrier, Photocatalyst material, photo semiconductor electrode, chemical sensor electrode, biosensor electrode, dielectric material, conductive material, insulating material, paint, filler, UV shielding material, optical material, pigment, cosmetic pigment, proton conductor, hydrogen storage Application as a body is expected.

  Hereinafter, terms used in the present invention will be described. The “roll-like” used in the present invention has a rod-like form and has a spiral shape whose cross section is schematically shown in FIG. The “flaky shape” in the present invention is a strip shape or a sheet shape having a thickness of 10 nm or less. Moreover, the form which the flakes gathered may be sufficient. The “ratio (B / A) of the molar amount (B) of the alkali metal to the molar amount (A) of the main component metal of the flaky metal oxide contained in the flaky metal oxide” in the present invention is the induction plasma. Confirmed by luminescence analysis (ICP-AES) or atomic absorption spectrophotometry, specifically, an ICP-AES measurement apparatus (for example, “ICPS-1000W” manufactured by Shimadzu Corporation) or an atomic absorption spectrophotometry apparatus (for example, , "SAS-7500" manufactured by Seiko Electronics Co., Ltd.).

  “Plate” in the present invention has a thickness (D) of 2 to 30 nm, and an aspect ratio (D / Ls) defined by the thickness (D) and the length (Ls) in the short direction of the plate shape. It is a form that is 1 or less. In addition, about thickness, it is the value measured by (circle).

  In the present invention, “orientated in the (110) direction” means that the (110) plane may be arranged in parallel to the thickness direction of the plate-like particles. That is, even if all the (110) planes are not arranged in parallel to the thickness direction of the plate-like particles, the (110) planes may be preferentially arranged. The orientation here is confirmed by, for example, electron beam diffraction measurement using a transmission electron microscope, and specifically measured by H-9000UHR III manufactured by Hitachi, Ltd.

  As the “metal oxide” in the present invention, Zn, As, Al, Sb, Yb, Y, In, U, Er, Cd, Gd, K, Ga, Ca, Cr, Si, Ge, Co, Sm, Dy , Zr, Hg, Sc, Sn, Sr, Cs, Ce, Ti, Ta, W, Ti, Tm, Fe, Tb, Te, Cu, Th, Na, Ni, Nb, Nd, V, Hf, Pd, Ba Metal oxides or hydroxides such as Bi, Pu, Pr, Be, B, Ho, Po, Mg, Mn, Mo, Eu, La, Li, Rb, and Re are preferably used, and more preferably titanium oxide Alternatively, titanium hydroxide is used. Here, titanium oxide or titanium hydroxide is more preferably used because the hollow fiber can be easily produced and can be produced at low cost.

  The size of the metal oxide hollow fiber having a scroll-like layered structure used in the present invention is preferably 6 nm to 10 nm in diameter and 2 nm to 6 nm in diameter in the hollow portion. Here, it is difficult to produce a metal oxide hollow fiber having a diameter of less than 6 nm or greater than 10 nm, and it is also difficult to produce a metal oxide hollow fiber having a hollow diameter of less than 2 nm or greater than 6 nm. is there.

 In the present invention, as a method for producing a metal oxide hollow fiber having a scroll-like layered structure, for example, a method of hydrothermally treating titanium oxide particles in an aqueous sodium hydroxide solution is preferably used. The average primary particle diameter of the titanium oxide powder is preferably 3 nm or more and 200 nm or less, more preferably 10 nm or more and 100 nm or less. Here, when the particle diameter is less than 3 nm, it is difficult to form a hollow fiber due to rapid dissolution of the raw material titanium oxide particles, and when the particle diameter is larger than 200 nm, a large amount of residual titanium oxide particles may remain. There is. When the particle diameter is less than 10 nm, the hollow fiber can be produced, but an amorphous fine particle residue may be generated. When the particle diameter is larger than 100 nm, the titanium oxide particle residue may remain. . Moreover, as a density | concentration of sodium hydroxide, 1M or more and 20M or less are preferable, More preferably, they are 3M or more and 15M or less. Here, at 1M or less, the raw material titanium oxide particles hardly dissolve, and at 20M or more, there is a possibility of becoming amorphous titanium oxide particles. If it is less than 3M, dissolution of the raw material titanium oxide particles occurs, but a residue of titanium oxide particles may remain. If it is greater than 15M, amorphous titanium oxide particles may remain as a residue.

  The hydrothermal treatment temperature is preferably 20 ° C. or higher and 150 ° C. or lower, more preferably 60 ° C. or higher and 140 ° C. or lower. Here, if it is less than 20 degreeC, melt | dissolution of a raw material titanium oxide particle will not occur easily, and if it is higher than 150 degreeC, it may become an amorphous titanium oxide particle. When the temperature is lower than 60 ° C., the raw material titanium oxide particles dissolve, but there is a possibility that the titanium oxide particle residue may remain. When the temperature is higher than 140 ° C., the raw material titanium oxide particles dissolve, but the amorphous titanium oxide particles. Alternatively, the raw material titanium oxide particles may remain as a residue.

  In the present invention, a method of bringing the metal oxide hollow fiber into contact with an acid aqueous solution is preferable as the step of expanding the interlayer by inserting protons between the layers of the metal oxide hollow fiber having a scroll-like layered structure. Used for. Examples of the acid used here include nitric acid, hydrochloric acid, sulfuric acid, perchloric acid, hydrofluoric acid, bromic acid, iodic acid, nitrous acid, acetic acid, and oxalic acid. The acid aqueous solution and the metal oxide hollow fiber can be brought into contact with each other by adding the metal oxide hollow fiber to the acid aqueous solution to prepare a suspension, and then allowing the suspension to stand, stirring and shaking. The method of making it, etc. is used preferably.

  As temperature conditions at the time of making it contact, 0 degreeC or more and less than 100 degreeC are preferable, More preferably, they are 10 degreeC or more and 50 degrees C or less. Here, under the temperature condition of less than 0 ° C., water as the solvent may freeze, and insertion of protons between layers may be hindered, and under the temperature condition of 100 ° C. or more, it exceeds the boiling point of water. Therefore, there is a possibility that the volatilization of the solvent becomes remarkable and the dissolution / decomposition reaction of the metal oxide hollow fiber is promoted. When the temperature is lower than 10 ° C., the diffusion reaction of protons into the metal oxide hollow fiber is slowed by a decrease in diffusion in the solution, and when the temperature is higher than 50 ° C., the dissolution / decomposition reaction of the metal oxide hollow fiber may occur. There is sex.

The acid concentration of the acid aqueous solution is preferably from 0.1 M to 10 M, and more preferably from 0.2 M to 5 M. Here, when the concentration is less than 0.1M, protonation may be insufficient, and when the concentration is more than 10M, the dissolution / decomposition reaction of the metal oxide hollow fiber may proceed. And when it is less than 0.2M, the proton insertion reaction may be slow, and when it is more than 5M, the dissolution / decomposition reaction of the metal oxide hollow fiber may occur. Here, when the metal oxide hollow fiber is allowed to stand in an acid aqueous solution for 2 days or longer under an acid concentration condition of 1 M or more and 5 M or less, the conversion from the metal oxide hollow fiber to the plate-shaped rutile type particles easily occurs. .

  The concentration of the metal oxide hollow fiber with respect to the acid aqueous solution is preferably 0.01 mg / ml or more and 500 mg / ml or less, and more preferably 1 mg / ml or more and 50 mg / ml or less. Here, when the concentration is less than 0.01 mg / ml, the amount of the acid aqueous solution used is increased, leading to an increase in cost. When the concentration is more than 500 mg / ml, the protonation of the metal oxide hollow fiber is not achieved. It may be enough. Furthermore, if the concentration is less than 1 mg / ml, the proton excess condition may occur, so the dissolution / decomposition reaction of the metal oxide hollow fiber may occur. If the concentration is greater than 50 mg / ml, the metal oxide in the acid aqueous solution Since diffusion into the hollow fiber is hindered, the protonation of the metal oxide hollow fiber may not be performed efficiently.

  Furthermore, in the present invention, in order to improve the dispersibility of the microstructure and further promote the interlayer swelling, the metal oxide hollow fiber may be brought into contact with an aqueous acid solution and then brought into contact with an aqueous amine solution. Specifically, the amines include alkylamines such as ammonia, methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, tert-butylamine, n-pentylamine, n-hexylamine, and halogens thereof. Acid salts or diamines such as ethylenediamine and propanediamine, and quaternary ammonium hydroxides such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide are preferably used.

  As a method of bringing the aqueous amine solution into contact with the metal oxide hollow fiber, a method of adding the metal oxide hollow fiber to the aqueous amine solution and preparing a suspension, and then allowing the suspension to stand, or stirring and shaking. Etc. are preferably used.

  As temperature conditions at the time of making it contact, 0 degreeC or more and less than 100 degreeC are preferable, More preferably, they are 10 degreeC or more and 50 degrees C or less. Here, under the temperature condition of less than 0 ° C., water as a solvent is frozen, so that the insertion of amine between layers is hindered, and under the temperature condition of 100 ° C. or more, the boiling point of water is exceeded. In addition, the volatilization of the solvent may become significant, and the dissolution / decomposition reaction of the metal oxide microstructure may be accelerated. If the temperature is lower than 10 ° C., the amine insertion reaction between layers is delayed due to a decrease in diffusion in the solution. If the temperature is higher than 50 ° C., the dissolution / decomposition reaction of the metal oxide microstructure may occur. .

  The amine concentration of the aqueous amine solution is preferably 0.001M or more and 10M or less, more preferably 0.01M or more and 2M or less. Here, if the concentration is less than 0.001M, the amine may be insufficiently adsorbed on the metal oxide layer. If the concentration is more than 10M, the dissolution / decomposition reaction of the metal oxide microstructure may occur. There is a possibility to go forward. If it is less than 0.01M, the amine insertion reaction may be slow, and if it is greater than 2M, the dissolution / decomposition reaction of the metal oxide microstructure may occur.

  The concentration of the metal oxide microstructure with respect to the aqueous amine solution is preferably 0.01 mg / ml or more and 500 mg / ml or less, and more preferably 0.1 mg / ml or more and 20 mg / ml or less. Here, if the concentration is less than 0.01 mg / ml, the amount of the aqueous amine solution used increases, resulting in high costs. If the concentration is greater than 500 mg / ml, the amine is not sufficiently adsorbed on the metal oxide layer. There is a possibility. Also, when the concentration is less than 0.1 mg / ml, when an aqueous amine solution containing a metal oxide microstructure is used as a coating agent, there is a possibility that it is difficult to make a thin film or a thick film because the substantial content is small. If the concentration is higher than 20 mg / ml, the metal oxide content is large, so that long-term stability may be deteriorated.

  The metal oxide microstructure of the present invention and the manufacturing method thereof have been described above. Thereby, the novel manufacturing method of the metal oxide fine structure which solved the problems, such as formation of the aggregate of the conventional metal oxide fine particle, a specific surface area, can be provided.

EXAMPLES Next, although an Example demonstrates this invention concretely, it is not restrict | limited to these Examples at all.
1. Preparation of Titanium Oxide Hollow Fiber 0.64 g of titanium oxide powder (trade name P25, manufactured by Nippon Aerosil Co., Ltd., average primary particle size of about 25 nm, specific surface area of about 55 m ^{2 /} g) was put into 80 ml of 10M aqueous sodium hydroxide solution, A white suspension was obtained by stirring for 1 minute with a glass rod. This white suspension was put in a 100 ml fluororesin container, and further this fluororesin container was put in a stainless steel container, and this stainless steel container was put in a drier and kept at 110 ° C. for 20 hours. After completion of the reaction, the stainless steel container was allowed to cool naturally to room temperature, and a solution containing a white precipitate was collected. As a washing step, the supernatant was first removed from the solution containing the white precipitate with a dropper. To the remaining white precipitate, 100 ml of 0.1 M hydrochloric acid aqueous solution was added little by little. After the entire amount of aqueous hydrochloric acid was added, the mixture was allowed to stand at room temperature (20 ° C.) for 3 hours. After standing, the supernatant was removed. This washing step was performed three times in total, and it was confirmed that the supernatant liquid had a pH of 7 or less. After these neutralization operations, the remaining white precipitate was washed twice with distilled water to obtain a white powder. When the fine structure of this white powder was observed with a scanning electron microscope (SEM S-800, manufactured by Hitachi, Ltd.), a rod-like structure having a diameter of 5 to 15 nm and a length of 0.1 to 2 μm was produced ( Figure 2). Moreover, when this white powder was observed with a scanning transmission electron microscope (STEM S-5200, manufactured by Hitachi, Ltd.), the white powder obtained by this method was an aggregate of titanium oxide hollow fibers at a magnification of 150,000 times. It was confirmed that the center of each fiber had a hollow structure with a diameter of 3 to 5 nm.

2. Production of Flaky Titanium Oxide The white powder produced by the above method was added to 64 ml of 2M aqueous nitric acid solution and stirred with a magnetic stirrer at room temperature for 15 hours. After stirring, the obtained translucent solution was centrifuged at 5000 rpm for 30 minutes by a centrifuge (M200-IVD manufactured by Sakuma Seisakusho Co., Ltd.) to obtain a white gel. Furthermore, white powder was obtained by drying this white gel at room temperature. When the fine structure of the white powder was observed with a scanning electron microscope (S-800, manufactured by Hitachi, Ltd.), a flaky structure having a side length of 0.05 to 2 μm and a thickness of 10 nm or less was obtained. It was generated (FIGS. 3 and 4). Moreover, when observed with a scanning electron microscope (SEM S-800, manufactured by Hitachi, Ltd.), a hollow fiber-like structure having a diameter of 15 nm to 30 nm was similarly generated (FIG. 5). Furthermore, when the molar ratio (Na / Ti) of sodium to titanium in this white powder was measured by an atomic absorption spectrophotometer SAS-7500 manufactured by Seiko Electronics Co., Ltd., it was 0.0013.

3. Preparation of plate-like rutile type titanium oxide particles A white powder prepared in the same manner as above was added to 64 ml of a 2M aqueous nitric acid solution and allowed to stand at room temperature in the dark for 1 week. After leaving still, the obtained translucent solution was centrifuged at 5000 rpm for 30 minutes with a centrifuge (M200-IVD, manufactured by Sakuma Seisakusho Co., Ltd.) to obtain a white gel with added protons. Further, this white gel was added to an aqueous solution of 0.1M tetraethylammonium hydroxide and shaken with a shaker at room temperature for 3 days to obtain a white transparent coating agent. The translucent coating agent dispersed in an aqueous solution of tetraethylammonium hydroxide did not precipitate even after 60 days at room temperature. When the particles in the white transparent coating solution were observed with a transmission electron microscope (H-9000UHR III, manufactured by Hitachi, Ltd.), the particles had an elliptical shape at a magnification of 250,000 times, and the short length was about Particles having a length of 25 nm and a long length of 120 nm were observed. From the electron diffraction pattern of a single particle, this elliptical particle coincides with the spot of rutile titanium oxide, and further, a spot attributed to the (110) plane from the electron diffraction pattern from the (1-10) direction. As a result, it was clarified that the elliptical rutile particles have a crystal structure in which the thickness direction is oriented in the (110) direction. Further, when the surface of the borosilicate glass substrate on which the white transparent coating solution was dropped and dried was observed with an atomic force microscope (Nanoscope 3a manufactured by Digital Instruments Inc.), the thickness of the elliptical particles was about 20 nm. all right. From these results, the particles contained in the white coating liquid have an elliptical shape, a thickness of about 20 nm, a length in the short direction of about 25 nm, and a length in the long direction of about 120 nm. And a single crystal fine particle of plate-like rutile type titanium oxide having a thickness direction oriented in the (110) direction.

Since the metal oxide microstructure of the present invention can be improved in dispersibility in solution, adhesion to a substrate, and anisotropy compared to conventional spherical particles, it can be used as a catalyst, a catalyst carrier, and a photocatalytic material. , Optical semiconductor electrodes, chemical sensor electrodes, biosensor electrodes, dielectric materials, conductive materials, insulating materials, paints, fillers, UV shielding materials, optical materials, pigments, cosmetic pigments, proton conductors, hydrogen storage materials, etc. Application as is expected.

It is a figure which shows typically the cross section of the metal oxide hollow fiber used for the method of this invention. It is a scanning electron micrograph of the titanium oxide hollow fiber used for the method of this invention. It is a scanning electron micrograph of the flaky titanium oxide microstructure produced by the method of the present invention. It is the scanning electron micrograph which expanded the fine structure of the titanium oxide fine structure produced by the method of this invention. It is a scanning electron micrograph of the hollow fiber-like titanium oxide microstructure produced by the method of the present invention. It is a figure which shows the transmission electron micrograph and electron beam diffraction image of the plate-shaped rutile type titanium oxide particle which concern on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Hollow part, 2 ... Metal oxide layer, 3 ... Interlayer

Claims (8)

A method for producing a metal oxide microstructure, comprising a step of expanding a layer by inserting protons between layers of a metal oxide hollow fiber having a scroll-like layered structure. The manufacturing method according to claim 1, wherein the metal oxide microstructure is in a flaky shape. The manufacturing method according to claim 1, wherein the metal oxide microstructure has a hollow fiber shape having a diameter of 15 nm or more and 30 nm or less. 4. The method according to claim 1, wherein the step of enlarging the interlayer is a step of bringing the metal oxide hollow fiber into contact with an acid aqueous solution. The method according to claim 4, further comprising a step of contacting the metal oxide hollow fiber with an aqueous amine solution after the step of bringing the metal oxide hollow fiber into contact with an aqueous acid solution. The manufacturing method according to claim 1, wherein the metal oxide hollow fiber is made of titanium oxide or titanium hydroxide. The ratio (B / A) of the molar amount (B) of the alkali metal to the molar amount (A) of the main component metal of the metal oxide microstructure contained in the metal oxide microstructure is 0.03 or less. The manufacturing method according to claim 1, wherein: The manufacturing method according to claim 1, wherein the metal oxide microstructure is a plate-like rutile-type titanium oxide particle, and a thickness direction of the plate-like particle is oriented in a (110) direction.

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