KR20030017201A - Mesoporous transition metal oxide thin film and powder and preparation thereof - Google Patents

Abstract

PURPOSE: A method for preparing a thin film or powder of mesoporous transition metal oxide is provided by using a transition metal oxide sol with uniform nanoparticles. Also, a thin film and powder prepared by the method are provided. CONSTITUTION: The method for preparing a thin film or powder of mesoporous transition metal oxide includes (a) adding a structure-inducer such as surfactants or organic polymer to a transition metal oxide sol of the uniform nanoparticles under stirring; (b) coating the resultant mixture on a substrate to form a thin film, or evaporating a solvent under reduced pressure to form a gel; (c) aging the thin film or gel at the constant temperature and relative humidity, for example at a substantially uniform temperature of 0 to 30 deg.C and at a substantially uniform relative humidity of 30 to 80 % to form meso-structure thin film or powders having hexagonal or cubic structure; and (d) optionally, eliminating the structure-inducer such as surfactants or organic polymer from the obtained meso-structure thin film or powder by sintering or ultraviolet-irradiating.

Description

Mesoporous transition metal oxide thin film and powder, and manufacturing method thereof {MESOPOROUS TRANSITION METAL OXIDE THIN FILM AND POWDER AND PREPARATION THEREOF}

The present invention provides a transition metal oxide sol made of uniform nanoparticles, a mesoporous transition metal oxide thin film and powder using the same, and a method of manufacturing the same. More particularly, the present invention provides a transition metal oxide sol composed of uniform nanoparticles of 1 to 10 nm, and a method for preparing the same, using a mesoporous transition metal oxide having a hexagonal or cubic structure in the form of a thin film or powder. It provides a method of preparation and a mesoporous transition metal oxide thin film and powder thus prepared.

The International Union of Pure and Applied Chemistry (IUPAC) classifies porosity based on pore diameter d _p . According to the standards of IUPAC, mesoporous materials refer to materials having 2 nm <d _p <50 nm, and some other documents sometimes classify materials having pore diameters of 1 nm or less as mesoporous. Mesoporous materials are used in applications such as the separation or detection of relatively large organic molecules. Representative examples of mesoporous materials are amorphous or polycrystalline solids such as columnar clays and silicates. The pores of these materials are often irregular and wide in shape and size, and thus have poor selectivity in application to molecular sieves.

On the other hand, the recently spotlighted mesoporous molecular sieve (abbreviated as MMS) is an amorphous solid with a high surface area (up to a surface area of 1400 m 2 / g) and a single diameter of about 1.2-10 nm. It is characterized by having a cylindrical void structure of size. Silica MMS, called MCM-41, has attracted a lot of interest because its large, uniform pore size, organic molecules and the like can be easily and quickly diffused into internal active sites. However, since the MCM-41 family of molecular sieves is a silicate and aluminosilicate material and aluminum and silicon have little activity and utility as catalyst metals, their use is very limited. Thus, after the development of a series of mesoporous molecular sieves (MMS) having a uniform mesoporous hexagonal arrangement based on silica (USP 5,098,684, issued to Kresge et al .; USP 5,057,296 issued to JS Beck), other transitions Much attention and research has been focused on the production of MMS based on metals.

Over the last few years, much research has been made on the synthesis of MMS having a non-silica backbone and a hybrid structure of silica and other metals. Silica-based multicomponent MMS or non-silica MMS have been claimed to be useful as catalysts due to their higher surface area and easier access to active sites compared to microporous zeolites. See GD Stucky et al. Chem. Mater. , 1994, 6: 1176-1191; Antonelli and Ying, Angew. Chem. Int. Ed. Engl. , 1996, 35: 426-430; Chem. Mater. , 1996, 8: 874-881; Antonelli et al., Angew Chem Int. Ed. Engl. , 1996, 35: 541-543; Burkett et al., Chem. Comm. , 1996, 1367-1368; Yang et al., Nature , 1996, 381: 589-592; And Balkus and Kinsel, USP 6,120,891],

However, significant advances have been made over the past few years in the synthesis of MMS using supramolecular molds, which can form non-silica MMS and develop new synthetic methods, extend the composition range beyond the silica range, and process non-silica MMS into film form. Compared with silica, mesoporous transition metal oxides were not easily synthesized due to the difficulty in controlling fast hydrolysis and condensation reactions in aqueous solutions of transition metal ions.

The Stucky group of the United States has solved this problem by producing a powder of transition metal oxide using metal chloride in non-aqueous ethanol (eg Peidong, et al., Nature, 396, 6707, (1999); Peidong , et al., Chem. Mater. , 11. 2813, (1999)). However, these methods have a very low reproducibility because the reaction of the metal chloride is very complicated and influenced by various factors, and it is difficult to synthesize a thin film having high utility because it is mainly synthesized as a powder.

On the other hand, since MMS synthesized from transition metals may exhibit physical and electronic properties such as transition metal oxides, it is important to manufacture them as thin films. A thin film of porous material is available only if there is a pupil accessible from the surface of the thin film. However, all known transition metal oxide MMS materials have hexagonal symmetry, so that the cylindrical pupils grow only in one direction parallel to each other, and when they are made into thin films, the cylinders of the pupils appear parallel to the surface of the substrate. Therefore, there is a problem that can not access to these pores from the surface of the thin film. As a method for solving such a problem, (1) a method of generating a pupil cylinder having a hexagonal structure in a direction perpendicular to the substrate surface and (2) a method using an isotropic cubic symmetric MMS is proposed. There are no examples of these yet.

When the hexagonal MMS is formed into a thin film, the reason why the pupil cylinder grows parallel to the substrate surface is because the interfacial energy between the organic molecules constituting the supramolecular template and inorganic materials such as silica is minimized through this arrangement. Therefore, in order to arrange these pupil cylinders in a direction perpendicular to the substrate, a process such as applying a strong electric field or a magnetic field is required, but this method is unrealistic because it is difficult to apply to a system in which organic molecules and inorganic materials coexist. do.

On the other hand, MMS having a symmetrical symmetry of the cubic system develops the cylinder of the pupil in all directions due to the characteristics of the symmetry, so that even if a thin film is manufactured, the pupil can be accessed from the substrate surface. However, in the case of silica MMS, some cubic materials are synthesized, but in the case of MMS of transition metal oxides, the synthesis is limited and only very few are known.

To date, the preparation of mesoporous MMS has been carried out in the presence of structure-derived materials such as surfactants, in which the precursor sol is prepared from a soluble inorganic precursor into a spherical micelle or liquid crystal phase, which is then periodically arranged crystals, that is, ( 1) hexagonal; (2) cubic; And (3) three mesoporous crystal structures, such as lamellar, from which pyrolysis or extraction of the surfactant results in the production of MMS. Synthesis of such MMS typically requires four reagents: water, structure-derived materials such as surfactants, soluble inorganic precursors, and catalysts, and MMS can range from minutes to days depending on the type of inorganic precursor (as a precipitate). It is formed at 180 to -14 ℃. Thus, the research so far focused mainly on the types of these reagents, their concentrations and ratios, and the reaction and ripening conditions.

On the other hand, many literatures are known about the production of microparticles having a uniform particle size or distribution or a sol thereof by using the sol-gel method, but to prepare a "transition metal oxide sol of uniform nanoparticles" Not much is known about.

Generally, in sol-gel chemistry, when silica sol is prepared from a silicon alkoxide precursor, the solubility of silica is low under acidic conditions, so if the pH of the polymerization / condensation step is 2 or less, the particles are difficult to grow to 2 nm or more in diameter. In addition, it is known that the polymerization process is stopped at a diameter of 2 to 4 nm even when the pH is 2 to 6, and the particle size is also increased because the solubility of the silica is increased to pH 7 or more. However, in the case of the transition metal, it is not easy to control the particle size.

For example, USP 5,238,625 discloses a process for preparing a hydrolyzate by treating zirconium alkoxide with aqueous hydrogen peroxide in the presence of an acid at room temperature, and evaporating the solvent followed by redispersion in an organic solvent. . In this patent, zirconia exhibits tetragonal crystals of size 0.5 μm or less, and hydrogen peroxide is a strong oxidizing agent that oxidizes alkyl groups that may remain during sol preparation, and serves to prevent the formation of residual carbon in the sintering step. It is described that it does not cause a problem in subsequent steps such as gelation because it is redispersed after removing the solvent.

USP 5,911,965 discloses a solution of tungsten oxide precursor acidified to pH 2 or less with aqueous hydrogen peroxide to be converted into a peroxypolytungstate sol or solution, which is dried and refluxed in anhydrous ethanol to contain about 17% tungsten oxide. It is described to obtain a stable oxide polytungstate solution or sol. This patent document does not describe the size or particle size distribution of the sol particles.

In addition, USP 6,107,241 discloses a method for preparing amorphous titanium peroxide sol by adding an alkali hydroxide to an aqueous titanium tetrachloride solution to form amorphous titanium hydroxide (Ti (OH) ₄ ), separating it, and then treating it with an aqueous hydrogen peroxide solution. Doing. According to this patent document, the resulting amorphous titanium peroxide sol appears as a yellow transparent liquid with a pH of 6.0-7.0, a particle size of 8-20 nm and a sol concentration of 1.40-1.60%, which can be stored for a long time at room temperature. It is. The amorphous titanium peroxide sol thus formed is converted to titanium oxide sol at a temperature of 100 ° C. or higher, for example, when heated at 100 ° C. for 6 hours, anatase titanium oxide in the form of a yellow suspension having a pH of 7.5-9.5 and a particle size of 8-20 nm. It is described that a sol is formed. However, when titanium hydroxide is reacted with hydrogen peroxide, it is reacted at low temperature because metatitanic acid is formed unless heat generation is suppressed.

US Pat. No. 6,183,658 discloses a process for producing non-aggregated nano-sized iron-containing oxide particles having a uniform particle size distribution, but modifying the particle surface with a silane compound to prevent aggregation.

When preparing the transition metal oxide sol from the transition metal precursor through the sol-gel method, the present inventors have prepared the above-described transition metal precursor into a uniform nanoparticle by heating and refluxing the solvent in a water-alcohol in the presence of an acid catalyst and hydrogen peroxide. It has been found that a transition metal oxide sol can be prepared, in particular a transition metal oxide sol of nanoparticles having a uniform size of 1-10 nm. In addition, it has been found that a powder or film of the transition metal MMS can be reproducibly produced by using a uniform nanoparticle prepared as a transition metal oxide sol mixed with a structure-inducing substance such as a surfactant in a conventional liquid crystal forming method. It was.

1A and 1B show TEM and EDX analysis diagrams of nanoparticles synthesized by the present invention, respectively.

2A and 2B show XRD and TEM images of cubic symmetric thin films synthesized by the present invention, respectively.

3A and 3B show XRD and TEM images of hexagonal symmetric thin films synthesized by the present invention, respectively.

Figure 4 shows a flow chart of the synthesis of the mesoporous material of the present invention.

A first object of the present invention is to provide a method for producing a thin film or powder of mesoporous transition metal oxide by using a transition metal oxide sol of uniform nanoparticles, and a thin film or powder prepared according to the method. The manufacturing method includes the following steps:

a) adding a structure-derived material such as a surfactant or organic polymer to a transition metal oxide sol of uniform nanoparticles under stirring;

b) coating the resulting mixture onto a substrate to form a thin film or evaporating the solvent under reduced pressure to form a gel;

c) the hexagonal or cubic structure of the above-described thin film or gel by aging at a constant temperature and relative humidity, for example at a substantially constant temperature selected between 0 to 30 ° C. and a substantially constant relative humidity selected from 30 to 80%. Forming a meso structure thin film or a powder having a; And

d) optionally removing structure-derived material such as surfactant or organic polymer from the mesostructured thin film or powder obtained by sintering or ultraviolet irradiation.

Other objects, features and details of the present invention are described in detail below with reference to the accompanying drawings. Particular embodiments of the invention are given for the purpose of description and are not intended to limit the invention. The principal features of the invention can be used in various embodiments without departing from the scope of the invention.

One of the features of the present invention is the use of "transition metal oxide sols of uniform nanoparticles", more preferably "transition metal oxide sols of uniform nanoparticles of 1-10 nm".

In the present specification, "1-10 nm uniform nanoparticles" means 70% or more, preferably 80% or more, more preferably 90% or more of the total nanoparticles are 1-10 nm It means to indicate the size.

"Nanoparticle transition metal oxide sol" means that the nanoparticles constituting the sol consist essentially of the transition metal oxide.

According to a preferred embodiment of the present invention, "transition metal oxide sol of uniform nanoparticles" can be prepared by heating and refluxing the transition metal precursor in an aqueous solvent such as a water-lower alcohol in the presence of an acid catalyst and hydrogen peroxide. More specifically, the transition metal halide may be prepared by refluxing at a temperature of 80-90 ° C. for 2-5 hours in a solvent of water-alcohol in the presence of an acid catalyst and hydrogen peroxide. In another variant, it is also possible to use transition metal alkoxides.

Reflux is carried out at a temperature of 60 to 100 ° C, preferably 80 to 90 ° C. Generally, nanoparticle sol may be formed within 5 hours at a temperature of 60 ° C. or higher in a 1: 1 solvent mixture of water-ethanol, but a precipitate may be formed at 100 ° C. or higher. However, although theoretically, nanoparticles may be formed even at a temperature of 60 ° C. or lower, reaction time is required for a long time and there may be a change in uniformity of the formed nanoparticles.

The transition metal nanoparticle sol prepared according to the reflux method has a particle size of 1 to 10 nm and a uniform particle size distribution, as well as excellent stability and durability, even after long-term storage at room temperature, for example, for one week or more. It has the advantage that it can be used for the manufacturing method of the thin film or powder of the mesoporous transition metal oxide of this invention.

Examples of transition metal precursors usable in the reflux method include halides, sulfates or alkoxides of transition metals, preferably transition metal halides such as chloride, bromide, or iodide, or mixtures thereof Include.

In the preparation of the "transition metal oxide sol of homogeneous nanoparticles" according to the invention, there are several important points, one of which is pH control. In the case of using a titanium alkoxide as a precursor, the pH of the solution is too high than in the case of using a chloride precursor, so that the hydrolysis and condensation reaction of titanium is too fast to control, making it difficult to synthesize uniform nanoparticles. When using titanium alkoxides as precursors, this problem may be solved by using higher amounts of hydrochloric acid.

Acid catalysts may refer to inorganic or organic acid catalysts used in sol-gel synthesis, preferably inorganic acid catalysts such as hydrochloric acid, sulfuric acid, nitric acid and the like, more preferably hydrochloric acid. Although the use of an inorganic or organic base catalyst is not excluded as necessary, it is not preferable because the pH of the above-described high pH is not easy to control the hydrolysis and condensation of the transition metal compound. The amount of the catalyst to be used is not particularly limited, but may be used in an amount sufficient to control the desired pH in the conventional sol-gel method.

In the above production method, hydrogen peroxide is thought to play a role in controlling the condensation reaction rate of the transition metal element while binding with the transition metal, and may be referred to those described in the prior art (USP 6,107,241 and USP 5,238,625). have. The amount of hydrogen peroxide used is not particularly limited, but is generally used in an amount of about 0.5 to 3 moles, preferably about 0.8 to 2 moles, based on the transition metal.

According to a preferred embodiment of the present invention, when hydrochloric acid is used as a catalyst, the volume ratio of hydrochloric acid and hydrogen peroxide (H ₂ O ₂ ) is preferably 2/1 to 6/1, preferably about 4/1.

Although the kind of the aqueous solvent used in the method of the present invention is not particularly limited, preferably a mixed solvent of water-lower alcohol is used, and may be used in a volume ratio of 1: 9 to 9: 1. If necessary, other organic solvents which are inert to the reaction conditions may be used.

Nanoparticles of the transition metal oxide prepared according to the method may be composed of a compound represented by the following formula (1):

MO _{n- (x + y + z) / 2} X _x (OH) _y (OEt) _z

Wherein x, y and z are positive numbers satisfying the condition of 0 <x + y + z <6, X represents a halogen atom, specifically Cl, I, Br or F, and M is Ti, Transition metals such as Zr, Ta, Nb, Sn, Fe, and W or combinations thereof, where n is a number of 2 ≦ n ≦ 3.

It is also possible to use "transition metal oxide sols of homogeneous nanoparticles" prepared by methods different from those described above, for example "transition metal oxide sols of uniform nanoparticles" prepared in the prior art mentioned above. Without departing from the scope of the invention. In this case, the transition metal oxide sol may be pretreated with hydrogen peroxide.

According to the present invention, a mesoporous transition metal oxide thin film or powder is prepared using the "transition metal oxide sol of uniform nanoparticles" obtained as described above according to a method consisting of the following steps:

a) to a "transition metal oxide sol of homogeneous nanoparticles" is added a structure-inducing substance such as a surfactant or an organic polymer with stirring;

b) coating the resulting mixture onto a substrate to form a thin film or evaporating the solvent under reduced pressure to form a gel;

c) aging the above-described thin film or gel to form a meso structured thin film or powder having a hexagonal or cubic structure; And

d) optionally removing structure-derived material such as surfactant or organic polymer from the mesostructured thin film or powder obtained by sintering or ultraviolet irradiation.

According to one preferred embodiment of the present invention, the aging is a constant temperature and a constant humidity (error range, respectively) determined at a temperature of 0 to 30 ° C. and a relative humidity of 30 to 80% depending on the composition and the desired structure of the mixture. Preferably at ± 3 ° C and 10%).

In the present invention, the transition metal to be used is not particularly limited, but may be particularly selected from the group consisting of Ti, Zr, Ta, Nb, Sn, Fe, W, and combinations thereof.

According to one preferred variant of the invention, a silicon compound, such as tetraethoxysilane (TEOS), is added to any of the steps a) to d) to produce a thin film or powder of SiO ₂ -modified mesoporous transition metal oxide. It may also be prepared. The amount of the silicon compound added may be up to 1: 1 in an atomic ratio with respect to the transition metal, preferably 0.1 to 1: 1.

According to the present invention, the structure-inducing material is not particularly limited, but is specifically selected from the group consisting of surfactants or amphoteric polymer materials disclosed in the prior art (USP 5,858,457, USP 5,958,367, USP 6,120,891 and USP 6,203,925). Can be. These prior arts are incorporated herein by reference. Preferred examples of such surfactants or amphoteric polymeric materials are C _n H _{2n + 1} N (CH ₃ ) ₃ X, C _n H _{2n + 1} N (C ₂ H ₅ ) ₃ X (where X = F, Cl , Br, I, 8 ≦ _n ≦ 18), C _n H _{2n + 1} (OCH ₂ CH ₂ ) _x OH (= C _n EO _x ) (wherein 12 ≦ _n ≦ 18, 4 ≦ _x ≦ 100) It includes.

In the present invention, although the correlation between the structure-derived material used and the particle size of the "transition metal oxide sol of uniform nanoparticles" is not clear, the appropriate structure-derived material is determined according to the particle size. It is desirable to select, and the transition metal oxide thin film or powder may be prepared from a sol having a particle size of 1 nm or less, or 10 nm or more, depending on the type and / or type of structure-derived material.

The support used in the present invention is not particularly limited and may be selected from the group consisting of silicon wafers, ITO, synthetic resins, metal plates, glass, and the like. Preferably, a silicon wafer and glass are used.

In the present invention, the mesostructured thin film or powder comprising the transition metal oxide and the structure-derived material aged in step c) usually exhibits a hexagonal or cubic structure. These are sintered by heating to 300-400 ° C. or irradiating with UV light for 3 to 24 hours to remove the above-described structure-derived material to yield a transition metal oxide MMS of hexagonal or cubic structure. Such sintering conditions are known in the art and can be easily changed by those skilled in the art.

In the present invention, the resulting hexagonal or cubic mesoporous transition metal oxide thin film or powder may exhibit a pore size of 1 to 15 nm and a surface area of 100 to 600 m 2 / g. The aforementioned thin film or powder may be composed of a compound represented by the following Chemical Formula 2 or 3:

MO _n (1)

(Wherein M represents a transition metal such as Ti, Zr, Ta, Nb, Sn, Fe, and W or a combination thereof, and n is 2 ≦ n ≦ 3)

M _1-x N _x O _n (2)

(wherein, x is 0 <x <1, M has the meaning as defined above, N stands for Si, n is 2 ≦ n ≦ 3)

According to the present invention, by using nanoparticles synthesized in an aqueous solution as an inorganic precursor and using an organic polymer such as a cation or a neutral surfactant as a structure-inducing substance, it is generally difficult to control polymerization and hydrolysis reactions. Oxides were synthesized into mesoporous materials of various pore sizes and structures.

The reason why the mesoporous transition metal oxide thin film or powder can be reproducibly produced using nanoparticle sol having a uniform particle size of 1 to 10 nm in the present invention is not the theoretical aspect thereof and thereby the present invention. This is not limited, but can be described as follows. That is, when the structure-inducing substance forms a liquid crystal-like mesostructure with the sol particles of the transition metal oxide, many process parameters such as, for example, temperature, pressure, humidity, type and structure of the structure-inducing substance, composition ratio, etc. However, control of their optimum conditions is still not established. In the conventional method, transition metal precursors are formed of sol particles while forming a liquid crystal-like structure together with the structure-inducing material in the presence of the structure-inducing material, and it is difficult to form a uniform particle size in the process. However, when the uniform transition metal oxide nanoparticles of 1 to 10 nm in the sol state are added as in the present invention, the liquid crystal-like meso structure is more easily facilitated with the structure-derived material because the nanoparticles are already formed in an appropriate meso size. It is thought that this is because it can be formed uniformly. Therefore, when the size of the nanoparticles is uniform, even when the size of the nanoparticles is 1 nm or less or 10 nm or more, it is possible to reproducibly produce a mesoporous transition metal oxide thin film or powder by appropriately selecting the structure-inducing material. It is anticipated that this also does not depart from the scope of the invention.

By using nanoparticles with uniform size, the method of synthesizing the transition metal compound of mesoporous structure has been greatly improved, and the reproducibility of the synthesis is remarkably improved. In particular, in the case of a thin film, it is possible to synthesize a meso pupil material having a cubic structure so as to have a pupil accessible from the surface of the thin film by controlling the composition of the solution and the maturing conditions.

One of the structural features of the mesoporous thin film according to the present invention is that the material formed on the thin film has an isotropic cubic structure, so that an inlet that can enter the mesopores at the surface of the thin film or the support is necessarily created. Hexagonal crystals formed from the mesostructured thin film of the transition metal oxide prepared according to the above-mentioned prior art are known that their axes are generally parallel to the surface of the thin film or the support.

All of these thin film samples are optically transparent, and in addition to the electrical properties of the transition metal oxide and the broad surface area of the meso-pore structure, a very high functional material that combines optical functional properties using electrons and holes by light is combined. It can have

Uniform pores in the nanometer range of mesoporous transition metal oxides can be used as carriers for catalytic activators such as transition metal compounds, amines, oxides, etc., and can also be used as catalysts for direct acid, base and oxidation / reduction reactions. .

Titanium dioxide and the like containing silica in an amount of 10% or less is known to have good photocatalytic properties. The uniform and regular nanometer-sized mesoporous structure can be used as a carrier for making metal nanorods, etc. which are recently spotlighted. In addition, it can be used as a separator and an adsorbent.

In addition, the thin film having a mesoporous structure of titanium dioxide having semiconductor characteristics may be utilized as an electrode material such as an electrode catalyst, a photocatalyst, and a solar cell due to a pore structure that can penetrate into the sample from the surface of the thin film.

Example

The invention is illustrated in more detail by the following examples, but is not limited to these. In the present invention, the particle size of the transition metal oxide sol is measured by the absorption threshold wavelength value at the absorption of UV-Vis. It is difficult to measure the particle size of the transition metal oxide sol by TEM, since the nanoparticles are further processed in the process of making a TEM sample, and the particle size may be changed in this process. It is not accurate to calculate the particle size as. On the other hand, according to the TEM photograph of the synthesized mesoporous material, it is clear that the thickness of the wall made of TiO ₂ is uniform at 2-3 nm, so that the particle size is quite uniform.

Preparation Example 1

30 g of C ₂ H ₅ OH, 20 g of TiCl ₄ and 50 g of conc-HCl / 35% H ₂ O ₂ (v / v = 4/1) were mixed under stirring and at a temperature of 80-90 ° C. for about 2 hours To reflux to prepare a TiO ₂ nanoparticle sol. Their particle size was 1-2 nm in diameter.

TEM photographs and EDX analysis graphs of the nanoparticles thus obtained are shown in FIGS. 1A and 1B, respectively.

The obtained sol was very thermally and chemically stable and durable, so after 2 weeks storage at ambient temperature, the sol retained its physical properties and could be used reproducibly in the MMS synthesis according to the present invention.

Preparation Example 2

24 g of C ₂ H ₅ OH, 16 g of TiCl ₄ and 40 g of conc-HCl / 35% H ₂ O ₂ (v / v = 2/1) were mixed under stirring and at a temperature of 60-70 ° C. for about 24 hours. To reflux to prepare a TiO ₂ nanoparticle sol. Its particle size was 2-3 nm in diameter.

Preparation Example 3

The TiO ₂ nanoparticle sol was prepared by repeating the procedure of Preparation Example 1, except using a solution of conc-HCl / 35% H ₂ O _{2 at} a volume ratio of 6/1 or 1/1. These particle sizes were 1 nm or less in diameter and 10 nm or more, respectively.

Example 1

To 10 g of the sol solution obtained in Preparation Example 1, 1.0-2.0 g of C ₁₆ EO ₂₀ was added and stirred at room temperature for 10 hours. The resulting solution was dip-coated on a silicon wafer to form a thin film, which was aged for 4 days in a vessel at 10 ° C. and a relative humidity of about 80% to prepare a thin film of meso structure.

The thin film thus obtained was sintered at a temperature of about 300 ° C. for 3 hours to obtain a TiO ₂ thin film having a cubic meso structure. The XRD and TEM images of the cubic meso structure thin film thus obtained are shown in FIGS. 2A and 2B, respectively.

Example 2

The deep coated thin film obtained in Example 1 was maintained at a temperature of about 18 ° C. and a relative humidity of about 80% for 4 days, and sintered at 350 to 450 ° C. for 3 hours to form a hexagonal meso structured TiO ₂ thin film. Obtained.

Example 3

The dip-coated thin film obtained in Example 1 was kept at a temperature of about 18 ° C. and a relative humidity of about 80% for 4 days, and sintered by irradiating it with UV light of 180 to 254 nm for 3 to 24 hours, thus being cubic. A meso structured TiO ₂ thin film was obtained.

Example 4

Similar to Example 1, however, the amount of C ₁₆ EO ₂₀ used and aging conditions were changed to obtain a hexagonal meso structured TiO ₂ thin film.

That is, to 10 g of the sol solution obtained in Preparation Example 1, 0.5-1.0 g of C ₁₆ EO ₂₀ was added and stirred at room temperature for 10 hours. The resulting solution was dip-coated on a silicon wafer to form a thin film, which was kept at a temperature of about 18 ° C. and a relative humidity of about 80% for 4 days, and sintered at 350 to 450 ° C. for 3 hours, to form hexagonal meso A TiO ₂ thin film of structure was obtained.

Example 5

Except for sintering by ultraviolet irradiation, the procedure of Example 4 was repeated to obtain a hexagonal mesostructured TiO ₂ thin film.

Example 6

Similar to Example 1, but the aging conditions were changed to obtain a hexagonal mesostructured TiO ₂ thin film.

To 10 g of the sol solution obtained in Example 1, 1.0-2.0 g of C ₁₆ EO ₂₀ was added and stirred at room temperature for 10 hours. The resulting solution was dip-coated on a silicon wafer to form a thin film, which was maintained at a temperature of about 25 ° C. and a relative humidity of about 30% for 4 days, which was then subjected to UV light at 180 to 254 nm for 3 to 24 hours. Sintering was performed to obtain a TiO ₂ thin film having a hexagonal meso structure.

Example 7

Except for using C ₁₆ EO ₁₀ instead of C ₁₆ EO ₂₀ , the procedure of Example 1 was repeated to obtain a hexagonal mesostructured TiO ₂ thin film.

Example 8

Except for using C ₁₆ EO ₁₀ instead of C ₁₆ EO ₂₀ , the procedure of Example 3 or 6 was repeated to obtain a hexagonal mesostructured TiO ₂ thin film.

Example 9

To 10 g of the sol solution obtained in Preparation Example 1, 1.5-2.0 g of C ₁₄ H ₃₃ N (CH ₃ ) ₃ Br was added and stirred at room temperature for about 10 hours. The resulting solution was dip-coated on a silicon wafer to form a thin film, which was aged for 4 days in a container at a temperature of about 25 ° C. and a relative humidity of about 30% to prepare a thin film of meso structure.

The thin film thus obtained was sintered at a temperature of about 350 ° C. for 3 hours to obtain a TiO ₂ thin film having a cubic meso structure.

Example 10

Except for using C ₁₄ H ₃₃ N (CH ₃ ) ₃ Br in an amount of 1.0 ~ 1.5g, the procedure of Example 9 was repeated to obtain a hexagonal mesostructured TiO ₂ thin film.

Example 11

Repeating the procedure of Example 9 or 10, except that C ₁₆ H ₃₅ N (CH ₃ ) ₃ Br is used instead of C ₁₄ H ₃₃ N (CH ₃ ) ₃ Br, the TiO ₂ of cubic or hexagonal mesostructures. A thin film was obtained. Example 12

A TiO ₂ thin film was prepared by repeating the same procedure as in Examples 1 to 11 except for using C ₁₂ EO ₂₃ or C ₁₂ EO ₄ as a surfactant. The thin film thus obtained did not have any mesostructure.

Example 13

The TiO ₂ thin film was prepared by repeating the procedure of Examples 1 to 6 except that the sol obtained in Preparation Example 3 was used. The thin film thus obtained did not have any mesostructure.

Example 14

According to the procedure of Example 1, 4 or 7, a solution containing TiO ₂ nanoparticle sol and surfactant was prepared and vacuum evaporated at 60 ° C. to obtain a gel.

The obtained gel was sintered at about 350 ° C. for 3 hours to obtain a TiO ₂ powder having a meso structure.

Example 15

Solutions containing TiO ₂ nanoparticle sol and surfactant were prepared according to the procedures of Examples 1-6, and tetraethoxysilane (TEOS) was added in an amount such that the molar ratio TiCl ₄ / TEOS = 10 / 1-3. .

The resulting solution was dip-coated on the silicon wafer to form a thin film, which was aged for 4 days in a container at a temperature of about 18 ° C. and a relative humidity of about 80% to prepare a thin film of meso structure.

The thin film thus obtained was sintered at a temperature of about 300 ° C. for 3 hours to obtain a TiO ₂ -SiO ₂ composite thin film having a cubic meso structure.

According to the present invention, it is possible to prepare a sol of transition metal oxide nanoparticles having a uniform particle size, and by using this, it is easy to use a hexagonal or cubic structure of mesoporous transition metal oxide thin film and powder difficult to synthesize by the conventional method. And reproducible production.

According to the present invention, the mesoporous transition metal oxide thin film may be optionally prepared in a cubic or hexagonal structure according to the composition and / or aging conditions of the starting material.

Such thin films are highly functional in a wide variety of fields due to their optical transparency, electrical properties of transition metal oxides, excellent properties such as high surface area due to mesoporous structure, and optical functional properties that utilize the functions of electrons and holes by light. It can be used as a substance.

Claims (9)

Method for producing a mesoporous transition metal oxide in the form of a thin film or powder comprising the following steps: a) to a "transition metal oxide sol of homogeneous nanoparticles" is added a structure-inducing substance such as a surfactant or an organic polymer with stirring; b) coating the resulting mixture onto a substrate to form a thin film or evaporating the solvent under reduced pressure to form a gel; c) aging the above-described thin film or gel to form a meso structured thin film or powder having a hexagonal or cubic structure; And d) optionally removing structure-derived material such as surfactant or organic polymer from the mesostructured thin film or powder obtained by sintering or ultraviolet irradiation. The method of claim 1, wherein the aforementioned transition metal is selected from the group consisting of Ti, Zr, Ta, Nb, Sn, Fe, W, and combinations thereof. The method of claim 1, wherein a silicon compound such as tetraethoxysilane is added to form a SiO ₂ -modified porous transition metal oxide composite. The method of claim 1, wherein the structure-derived material described above is C _n H _{2n + 1} N (CH ₃ ) ₃ X, C _n H _{2n + 1} N (C ₂ H ₅ ) ₃ X (wherein, X = F, Cl, Br, I, 8 ≦ _n ≦ 18), C _n H _{2n + 1} (OCH ₂ CH ₂ ) _x OH (= C _n EO _x ) (wherein 12 ≦ _n ≦ 18, 4 ≦ _x ≦ 100 ) Is selected from the group consisting of. The method according to claim 1, wherein the aging of step c) is carried out at a constant temperature and a constant humidity (error range, ± 3 respectively), which is determined at a temperature of 0 to 30 ° C and a relative humidity range of 30 to 80% depending on the composition of the mixture and the desired structure. And at 10%). The transition metal oxide nanoparticle sol according to claim 1, wherein the transition metal halide sol is prepared at 12 to 36 at a temperature of 80 to 90 ° C. in the presence of an acid catalyst and hydrogen peroxide (H ₂ O ₂ ) in an aqueous solvent such as water-lower alcohol. Characterized in that it is obtained by reflux for a time: 7. The process according to claim 6, wherein the acid catalyst is hydrochloric acid and the volume ratio of hydrochloric acid / hydrogen peroxide is 2: 1 to 6: 1. A hexagonal or cubic structured thin film or powder of mesoporous transition metal oxide, consisting of a compound represented by Formula 2 or 3 and having a pore size of 1 to 15 nm and a surface area of 100 to 600 m 2 / g: [Formula 2] MO _n (2) (Wherein M represents a transition metal such as Ti, Zr, Ta, Nb, Sn, Fe, and W or a combination thereof, and n is 2 ≦ n ≦ 3) [Formula 3] M _1-x N _x O _n (3) (Wherein x is 0 <x <1, M has the meaning as defined above, N represents Si and n is 2 ≦ n ≦ 3) The nanoparticles have a homogeneous particle size of 1 to 10 nm and consist of a compound represented by the formula (1) and are transition metal oxide nanoparticle sol: [Formula 1] MO _{n- (x + y + z) / 2} X _x (OH) _y (OEt) _z Wherein x, y and z are positive numbers satisfying the condition of 0 <x + y + z <6, X represents a halogen atom, specifically Cl, I, Br or F, and M is Ti, Transition metals such as Zr, Ta, Nb, Sn, Fe, and W or combinations thereof, where n is a number of 2 ≦ n ≦ 3.