KR20030042569A - A method for producing semiconductor oxide particles coated with titanium oxide - Google Patents

Abstract

PURPOSE: A method for producing semiconductor oxide particles coated with titanium oxide is provided to produce photocatalysts in which extra ultraviolet rays are not required to be irradiated by preparing semiconductor oxide in small particles and coating the surface of the particles with titanium oxide as irradiating sunlight with a certain wavelength. CONSTITUTION: In a method for producing photocatalyst comprising titanium oxide, the method for producing semiconductor oxide particles coated with titanium oxide comprises a step (a) of preparing semiconductor oxide particles having band-gap energy less than 3.0 electron volt by passing the metal salt solution through an electric furnace of 100 to 1,200 deg.C constructed in multistage after dispersing a metal salt solution in a solution carrier gas using ultrasonic waves; a step (b) of coating the surface of the semiconductor oxide particles with titanium oxide by agitating the solution as irradiating light onto the solution after dispersing the semiconductor oxide particles prepared in the step (a) into a solution into which titanium compound is dissolved; and a step (c) of sintering the collected coated semiconductor oxide particles in the gas or vacuum state after collecting the centrifuged semiconductor oxide particles by centrifuging the titanium oxide coated particles prepared in the step (b).

Description

A method for producing semiconductor oxide particles coated with titanium oxide}

The present invention relates to a method for producing oxide semiconductor particles coated with titanium oxide, and more particularly, to irradiate light having a specific wavelength while dispersing the particles formed in the first step and the first step of forming the oxide semiconductor particles in the titanium compound solution Unlike the photocatalyst, which exhibits photocatalytic ability as UV irradiation, the particles are prepared in two steps of coating the titanium oxide thin film on the surface of the particles and three steps of stabilizing the coated particles in the second step. The present invention relates to a method for producing oxide semiconductor particles coated with titanium oxide, which exhibits excellent photocatalytic properties even with visible light having a larger wavelength (the main component of sunlight).

When the semiconductor is irradiated with light with energy above band-gap energy, electrons in the valence band are excited as the conduction band, and positive holes (h ⁺ ) are in the valence band. increasing the concentration of the conduction band and the ^{electron-increasing} the concentration of the (electron, e).

Holes or electrons increased by light irradiation can be recombined directly after recombination or transfer to the semiconductor surface for thermal equilibrium.

When holes and electrons that migrate to the semiconductor surface are combined with ions or molecules adsorbed on the semiconductor surface, other products are obtained when light is not irradiated. This process is called photocatalysis and the semiconductor in which the photocatalysis occurs is called photocatalysis.

Titanium oxide (TiO ₂ ), zinc oxide (ZnO), iron oxide (Fe ₂ O ₃ ) and so on exhibit photocatalytic properties. In particular, titanium oxide has properties such as antibacterial, antifouling, self-purifying and hydrophilic properties. It is widely used in various industries such as manufacturing antimicrobial products, water quality and soil purification.

Titanium oxide is an n-type semiconductor whose primary carrier showing electrical conductivity is electrons. In general, the photocatalytic ability of titanium oxide increases as the reaction between the holes or electrons generated by light and the species on the surface increases.

However, since the band gap energy of titanium oxide is 3.0 (λ = 410 nm) or anatase 3.2 (λ = 380 nm) electron volts of rutile, photocatalytic activity is achieved by UV light having a wavelength of 410 nm or less having an energy greater than the band gap energy. Therefore, the efficiency of photocatalytic ability is very low by the sunlight which mainly consists of visible region which has a wavelength longer than an ultraviolet-ray.

When the titanium oxide is applied to an industrial field, a separate ultraviolet irradiation is necessary to enhance the photocatalytic ability, and thus, various equipment and techniques required for ultraviolet irradiation in addition to titanium oxide are required.

In addition, ultraviolet rays cause various side effects on the human body and cause skin cancer, and may cause a harmful effect on the person handling the ultraviolet irradiation device, it is pointed out that the trouble of separately preparing ultraviolet protection equipment.

Therefore, researches for improving the photocatalytic ability of titanium oxide with solar rays mainly containing visible rays, which are harmless to the human body having a wavelength longer than ultraviolet rays, continue to be conducted.

As an example, a doping method is applied, in which a small amount of metal cations are added to titanium oxide to create a separate energy level within the titanium oxide ban band, and to excite electrons by irradiating visible light from the energy level. There was an attempt.

However, the concentration of electrons and holes, which must be moved to the surface of the semiconductor to promote chemical reactions by doping into the titanium oxide ban and being used as a recombination site of photogenerated electrons and holes, is used again. Therefore, there is a problem that the photocatalytic ability is not significantly improved (M. Anpo, Cata. Surv. Jpn. 1. 169. (1997)).

Recently, studies have been conducted to dope anions of nitrogen or oxygen in place of metal cations, and titanium oxides having photocatalytic activity in light having a wavelength of 400 nm or more have been reported (R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki, Y. Tage, SCIENCE Vol 293, 13 (269-271) July 2001 .; T. Ihara, M. Miyoshi, M. Ando, S. Sugiharaand Y. Iriyama, J. Mater.Sci. 36 (2001), 4201-4207).

However, since the method partially heats the titanium oxide using a laser or the like in a nitrogen or oxygen atmosphere, the homogeneity of the doping is poor and the doped nitrogen or oxygen is discharged over time.

In addition to the above methods, research has been made to make titanium oxide into small grains to increase the concentration of electrons and holes that move to the surface by increasing the surface area of titanium oxide and inhibiting recombination of electrons and holes in titanium oxide (Korean patent) Application No. 2000-0067090) and a method of adhering it onto a substrate (Korean Patent Application No. 2000-006570, Korean Patent Application No. 1999-0046492) have been reported.

However, this method does not reduce the band gap energy of titanium oxide, so that the photocatalytic ability in the visible light region does not improve.

Therefore, the development of a photocatalyst that has a longer wavelength than ultraviolet rays and exhibits high photocatalyst characteristics even by irradiation of sunlight that is not harmful to the human body and can solve problems in use due to troublesome equipment and the like.

Accordingly, the inventors of the present invention can prepare a semiconductor having a constant energy after dispersing a semiconductor other than titanium oxide, that is, an oxide semiconductor having a band gap energy lower than the band gap energy of titanium oxide into small particles and dispersing it in a titanium compound solution. The light of the wavelength was irradiated to coat titanium oxide on the surface of the oxide semiconductor. When the titanium oxide coated oxide semiconductor was irradiated with light in the visible region, holes and electrons generated in the oxide semiconductor were transferred to the coated titanium oxide, thereby performing a chemical reaction on the surface of the titanium oxide. The invention has been completed.

Accordingly, the present invention provides a method for manufacturing an oxide semiconductor having a band gap energy lower than that of titanium oxide, using small particles, and irradiating light with a specific wavelength to generate holes and electrons to coat the particles with titanium oxide. Sintering the coated particles to provide stability, and provides a method for producing oxide semiconductor particles coated with titanium oxide having a longer wavelength than ultraviolet rays and exhibiting high photocatalytic properties even in sunlight harmless to the human body Its purpose is to.

1 is a surface electron micrograph of nickel oxide particles prepared according to Example 1. FIG.

FIG. 2 is a surface electron micrograph of the iron oxide particles prepared in Example 2. FIG.

3 is a surface electron micrograph of the tungsten oxide particles prepared in Example 3.

4 is a surface electron micrograph of tungsten oxide particles shown in an enlarged view of FIG. 3.

5 shows a schematic structure of a photoacoustic spectroscopy.

6 is a UV-VIS spectrum obtained after coating titanium oxide on a quartz plate.

7 is a photoacoustic spectrum of nickel oxide particles and titanium oxide coated nickel oxide particles prepared in Example 1. FIG.

8 shows nickel oxide particles coated with titanium oxide prepared in Example 1

It is the UV-VIS spectrum obtained after coating on a quartz plate.

9 is a photoacoustic spectrum of iron oxide particles and titanium oxide coated iron oxide particles prepared by Example 2.

10 is a UV-VIS spectrum obtained after coating titanium oxide coated iron oxide particles prepared in Example 2 on a quartz plate.

11 is a photoacoustic spectrum of tungsten oxide particles and titanium oxide coated tungsten oxide particles prepared in Example 3.

12 is a UV-VIS spectrum obtained after coating the titanium oxide coated tungsten oxide particles prepared in Example 3 on a quartz plate.

FIG. 13 is a photoacoustic spectrum of cuprous oxide and titanium oxide coated copper oxide prepared in Example 4. FIG.

FIG. 14 compares phase shifts of photoacoustic signals of cuprous oxide and titanium oxide coated copper oxide prepared in Example 4. FIG.

15 is a cuprous oxide coated with titanium oxide prepared in Example 4

It is the UV-VIS spectrum obtained after coating the particles on the quartz plate.

FIG. 16 is a diagram comparing the decomposition photocatalytic ability of relative methylene blue when irradiated with a sample of the sample prepared in Example was irradiated with the ultraviolet light of the xenon lamp.

17 is a diagram comparing the decomposition photocatalyst ability of the relative methylene blue when the light of the xenon lamp blocking the ultraviolet rays is irradiated on the quartz plate coated with the sample prepared in Example.

The present invention provides a method for producing a photocatalyst comprising titanium oxide, comprising: 1) multistage dispersing a metal salt solution capable of forming an oxide semiconductor having a bandgap energy of less than 3.0 electron volts in a transport gas and ultrasonically. Making small particles through an electric furnace at 100-1200 ° C .; 2) coating the surface of the particle with titanium oxide by dispersing the oxide semiconductor particles prepared in step 1 in a titanium compound solution and stirring while irradiating light; And 3) collecting the titanium oxide coated particles prepared in step 2 by centrifuging the particles, and then sintering in a gas or in a vacuum state. do.

Hereinafter, the present invention will be described in more detail.

The present invention is a step of coating the titanium oxide thin film on the surface of the particle by irradiating light having a specific wavelength to the particles formed in the first step and the step of forming the oxide semiconductor particles in a step and a method It relates to a method for producing oxide semiconductor particles coated with titanium oxide comprising three steps to give stability by sintering.

The manufacturing method of the oxide semiconductor particles coated with titanium oxide according to the present invention will be described in detail for each step as follows.

The first step is to prepare the oxide semiconductor into small particles.

First, an oxide semiconductor exhibiting the characteristics of a semiconductor in a metal oxide is made of particles having a diameter of 10 μm or less, preferably, for example, 10 nm to 10 μm in diameter, so that a large amount of holes and electrons Should be generated.

At this time, since the oxide semiconductor used is required to form electrons and holes in visible light, the band gap energy of the used oxide semiconductor should be less than 3.0 electron volts lower than titanium oxide.

Specific examples of the oxide semiconductor produced in the present invention include nickel oxide (NiO, about 3.0 electron volts of band gap energy), iron oxide (Fe ₂ O _3, about 2.2 electron volts of band gap energy), tungsten oxide (WO _3, Band gap energy of about 2.5 electron volts) or cuprous oxide (Cu ₂ O, band gap energy of about 2.0 electron volts) may be made of particles. The metal compounds used to produce these oxide semiconductors are complex compounds of metals having nitrates, ammonium salts, acetates of metals selected from nickel, iron, tungsten and copper and ligands containing one or more nitrogen or oxygen atoms. There is this.

Oxide semiconductor particles may be prepared by spraying a 0.001 to 5 M solution in which a metal compound selected from the metal compounds in a solvent is ultrasonically passed through a multi-stage electric furnace heated to 100 to 1200 ° C. At this time, if the concentration of the solution used is less than 0.001 M, the particle size is small, but the productivity is lowered, if it exceeds 5 M there is a manufacturing problem difficult to spray by ultrasonic.

The multi-stage electric furnace is preferably one that is divided into at least three parts, such as a large portion of the evaporation of the solvent, an intermediate portion of the compound decomposition, and a sintering of the resulting oxide particles.

In the solvent evaporation part, water is evaporated from the droplets of ultrasonically sprayed metal compounds, and nitrates, ammonium salts, acetates or complexes of various metals having the shape of spherical particles are formed under the influence of surface tension, and the temperature is 100 to 150 ° C. to be.

In the compound decomposition portion, nitrates, ammonium salts, acetates or complex compounds are pyrolyzed to produce oxide particles, with temperatures of 200 to 600 ° C.

In the particle sintered portion, the produced particles are heated to a high temperature, so that the particles are agglomerated as they are sintered so that an oxide is made of particles having a diameter of 10 μm or less, preferably 10 nm to 10 μm, and the temperature is 600 to 1200 ° C.

A solution transport gas having a constant flow rate is passed through the electric furnace for movement of the sprayed solution particles. At this time, the gas used may be a gas selected from one or two or more selected from air, nitrogen, oxygen, carbon monoxide, hydrogen, helium and argon, the average flow rate of the gas passing through the electric furnace is 1 ~ 10 L / min Let this be maintained.

The second step of the present invention is a step of coating titanium oxide on the surface of the oxide semiconductor particles prepared in step 1.

First, after preparing a solution having a concentration of the titanium compound of 0.001 to 10 M, the appropriate amount of the oxide semiconductor particles prepared in step 1 is continuously stirred and irradiated with light having a specific wavelength.

The light irradiated here depends on the type of oxide semiconductor used, the concentration of the titanium compound, and the thickness of the titanium oxide thin film to be coated.

First, when the light energy to be irradiated is smaller than the band gap energy of the oxide semiconductor, a thin film of titanium oxide is not formed in principle.

Therefore, the light energy to be irradiated should be larger than the band gap energy of the oxide semiconductor used. That is, when the light energy irradiated exceeds the band gap energy of the oxide semiconductor and is less than the band gap energy of the titanium oxide (rutile 3.0 electron volts, anatase 3.2 electron volts), titanium oxide is formed on the surface of the oxide semiconductor produced by the above process. Once coated, the surface of the titanium oxide-coated particles no longer generates electrons or holes, so the rate at which titanium oxide is coated is significantly lowered to obtain an oxide semiconductor coated with titanium oxide having a predetermined thickness.

In addition, when the light energy to be irradiated is larger than the band gap energy of the titanium oxide (rutile 3.0 electron volt, anatase 3.2 electron volt), the titanium oxide is coated on the oxide semiconductor, but is generated by electrons or holes generated from the coated titanium oxide. As the titanium compound in the titanium compound solution continues to decompose, a thick titanium oxide film is formed on the surface of the oxide semiconductor. If the coating thickness of the titanium oxide is too thick on the surface of the oxide semiconductor, electrons or holes generated in the oxide semiconductor are formed of titanium oxide. Since it is difficult to reach the surface, the photocatalytic ability by the irradiation of visible light is significantly reduced.

In addition, in the above case, it is possible to control the thickness of the titanium oxide to be coated by controlling the amount of the titanium compound, but since the thickness of the titanium oxide on the particle surface becomes uneven, there is a problem that the photocatalytic ability is remarkably decreased.

After the light irradiation process is finished, the oxide semiconductor particles coated with titanium oxide may be obtained by washing and separating the particles with a solvent to remove titanium compounds other than titanium oxide.

At this time, the titanium compound is an alkoxide of titanium (Ti (OR) _4, R = C _n H _{2n + 1} , n = 1, 2, 3 ...), halogenated titanium (TiF ₄ , TiCl ₄ , TiBr ₄ ) and one selected from materials capable of forming a titanium oxide thin film from reaction of holes and electrons generated on the surface of the oxide semiconductor, such as titanium nitrate, may be used.

The solvent for dissolving the titanium compound is alcohol (ROH), water, ether (ROR), halogenated carbon (C _n H _{2n + 2-m} X _m , n = 1, 2, 3, .. m = 1, 2, 2n + 2, X = Cl, F, Br), a liquid hydrocarbon and a nitrile-based organic compound can be used.

According to the present invention, the irradiation amount of light and the total amount of the titanium compound may be determined by the thickness of the titanium film to be prepared and the size of the particles of the oxide semiconductor, and the thickness of the titanium oxide film coated by the method according to the present invention is 10 μm or less. It is the range of 10 nm-10 micrometers.

The third step is to stabilize the particles of the oxide semiconductor coated with titanium oxide prepared in the second step by sintering.

The particles separated from the solution are allowed to stand for 5 minutes to 24 hours in a gas mixed with one or two or more selected from air, nitrogen, oxygen, carbon monoxide, hydrogen, helium and argon or in a vacuum at a temperature of 25 to 1200 ° C. . In this process, the structure and composition of the oxide semiconductor inside the particles and the coated titanium oxide can be stabilized.

As shown in the accompanying drawings of the electron micrograph of the oxide semiconductor particle of this invention, FIGS. 1-4, the diameter of a particle | grain is 100 nm-1 micrometer.

Unlike conventional photocatalysts containing titanium oxide, which are prepared by doping cations on the surface of titanium oxide, the photocatalyst prepared according to the method of the present invention has a lower band gap energy than titanium oxide and acts as a semiconductor. The semiconductor is located inside the photocatalyst in the form of particles, and titanium oxide is coated on the surface of the oxide semiconductor.

The photocatalyst having the above form is preferably manufactured in the smallest size as the contact surface with the chemical substance requiring the catalytic action increases the catalytic performance.

The photocatalyst prepared according to the method of the present invention is prepared by dispersing ultrasonically a solution in which a metal compound of an oxide semiconductor located therein is ultrasonically dispersed. Thus, the particle size of the photocatalyst is 100 nm to 1 μm in diameter, and the oxide semiconductor is small. Is coated with titanium oxide and then sintered to provide stability. Therefore, if the coating is not performed, the oxide semiconductor is deformed due to continuous oxidation to prevent the loss of photocatalytic properties. have.

Oxide semiconductor particles coated with titanium oxide prepared by the above process can be used as a photocatalyst, a surface treatment agent, a paint material, etc. and can be used as a raw material for solar cells, light emitters, etc. together with other materials, in particular, photocatalytic efficiency in sunlight There is a high characteristic.

In addition, the solids of the solution prepared in the two steps can be used to apply industrially to the liquid phase in a state that is not separated, there is an advantage to broaden the field of application.

Hereinafter, the present invention will be described in more detail with reference to the following examples, which are not intended to limit the scope of the present invention.

Example 1: Preparation of nickel oxide (NiO) particles coated with titanium oxide

0.25M amine nickel complex (Hexammine nickel (II) nitrate, [Ni (NH ₃ ) ₆ ] (NO ₃ ) ₂ ) solution into the air at 6L / min flow rate by ultrasonic wave The temperature of each part was passed through 150 ° C./600° C./800° C.) to obtain nickel oxide powder.

0.1 g of the nickel oxide particles were mixed with 40 ml of isopropyl alcohol, 0.04 M solution of 0.5 ml of titanium isopropoxide, and stirred for 1 hour while stirring (Xe Lamp, 1000 W). After completion of the reaction, the solution was centrifuged at 2500 RPM to collect only solids. The collected solid was heat-treated for 1 hour in an air furnace at 500 ℃ in air.

Surface electron micrographs of the nickel oxide particles obtained by pyrolysis of the amine nickel complex are shown in FIG. 1, and the average size of the nickel oxide particles was about 500 nm except for some of the large particles.

Example 2: Iron oxide coated with titanium oxide (Fe ₂ O ₃ Particle manufacturing

0.25M nitrate [Fe (NO ₃ ) ₃ · 9H ₂ O, Iron (III) Nitrate Enneahydrate] solution is sprayed into the air at a rate of 6 L / min by ultrasonic wave, and the inside of the heating furnace (heating furnace 150 ° C./600° C./800° C.) to obtain an iron oxide powder.

0.1 g of the prepared iron oxide particles were mixed with a 0.04 M solution prepared by dissolving 0.5 ml of titanium isopropoxide in 40 ml of isopropyl alcohol and irradiated with light (Xe Lamp, 1000W) for 1 hour while stirring. After completion of the reaction, the solution was centrifuged at 2500 RPM to collect only solids. The collected solid was heat-treated for 1 hour in an air furnace at 500 ℃.

Surface image micrographs of iron oxide particles obtained by pyrolysis of the nitrate solution are shown in FIG. 2 and the particle size is about 600 nm.

Example 3 Tungsten Oxide (WO) Coated with Titanium Oxide ₃ Particle Manufacturing

20 g of tungsten oxide powder was dissolved in 350 ml of ammonia water, and then ultrasonically sprayed into air at a flow rate of 6 L / min, and the inside of the furnace made of granules (the temperature of each part of the furnace was 150 ° C / 600 ° C / 800 ° C). The tungsten oxide powder was obtained by passing.

0.1 g of the prepared tungsten oxide was dissolved in 40 ml of isopropyl alcohol and dissolved in 0.04 M solution of 0.5 ml of titanium isopropoxide (titanium isopropoxide), followed by irradiation with light (Xe Lamp, 1000 W) for 1 hour. After completion of the reaction, the solution was centrifuged at 2500 RPM to collect only solids. The solid collected above was subjected to heat treatment for 1 hour in an electric furnace at 500 ° C. in the atmosphere.

Surface electron micrographs of the tungsten oxide particles obtained by pyrolysis of tungsten oxide dissolved in ammonia water are shown in FIG. 3, and the size of the particles is distributed around 1000 nm. 4 is an enlarged photograph of FIG. 3.

Example 4: Cuprous oxide (Cu) coated with titanium oxide ₂ O) Particle Manufacturing

0.1 g of cuprous oxide powder (Aldrich Chem. Co.) and 40 ml of isopropyl alcohol were dissolved in 0.5 ml of titanium isopropoxide, and then mixed with a 0.04 M solution. 1000W). After completion of the reaction, the solution was heat treated for 1 hour in an air furnace at 500 ° C.

Test Example 1 Measurement of Optical Properties by Photoacoustic Spectroscopy

Optical properties of the oxide semiconductor particles coated with titanium oxide prepared in Examples 1 to 4 were analyzed by photoacoustic spectroscopy (PAS), and are shown in the accompanying drawings of FIGS. 7, 9, 11, 13, and 14. .

Photoacoustic spectroscopy uses a microphone to sense the vibrations (sound) generated by light absorbed by the sample, heating the sample, and moving the heat into the gas around the sample to change the pressure of the gas. The thermal wave generated by the energy absorbed by the surface is abruptly reduced as if it is reduced in the medium that absorbs the light, so the resulting photoacoustic signal provides information from the surface to a certain depth.

The sampling depth is related to the modulation frequency of the light, and if the frequency is kept constant, the depth will be about the same, and the optoacoustic signal will increase as the sample absorbs light well.

In addition, since the signal generation of the optoacoustic spectrum is performed by heating the sample by absorbing light and heating the gas around the sample, the generated photoacoustic signal shows the phase and the light to be irradiated. Can be.

If the light is absorbed on the surface of the sample and the surrounding gas is heated, the phase is shifted by 45 °, but as light is not absorbed from the surface and penetrates into the inside of the sample, the phase is gradually increased.

Also, when a thin film is coated over the light absorbing material, the phase shift is greater than otherwise.

In other words, the result of the photoacoustic spectrum shows the degree of light absorption at that wavelength in the magnitude of the photoacoustic signal, and the depth of the surface or the existence of another thin film from the phase shift of the photoacoustic signal.

7, 9, and 11 illustrate the photoacoustic intensities of nickel oxide, iron oxide, and tungsten oxide coated with titanium oxide, respectively, before and after titanium oxide was coated. Since the magnitude of the photoacoustic signal is shown, the result indicates that titanium oxide is present on the surface of the oxide semiconductor.

The nickel oxide shown in FIG. 7 is a P-type oxide semiconductor, and the intensity of the photoacoustic signal is reduced, unlike iron oxide and tungsten oxide, which are the n-type oxide semiconductors shown in FIGS. 9 and 11, respectively. It is thought to be due to the nature of the oxide semiconductor in contact with titanium, but no clear theory has been established, but it is possible to derive the fact that titanium oxide is coated on the surface of nickel oxide.

13 and 14 show the intensity and phase shift spectra of the photoacoustic spectrum when titanium oxide is coated on a commercially available cuprous oxide (Aldrich Chem. Co.) surface. It can be seen that there is a phase shift. That is, it can be said that the result shows that titanium oxide is coated on the first copper oxide surface by the method of the present invention.

Test Example 2 UV-VIS Spectrum Measurement

0.1 g of the oxide semiconductor particles coated with titanium oxide prepared in Examples 1 to 4 and 10 ml of isopropyl alcohol were mixed and coated on a quartz plate by a deep drawing (Dip-Drawing, 10 mm / min) method. After the heat treatment of the quartz plate at 450 ° C. for 1 hour, the results of UV-VIS spectra were shown in FIGS. 6, 8, 10, 12, and 15, respectively.

In the light absorption method by UV-VIS spectrum measurement, the photoacoustic analysis method shown in Test Example 1 directly measures the amount of light absorbed by the sample. After spectroscopy is measured to estimate the luminous intensity of the sample.

Therefore, since the UV-VIS spectrum cannot be directly obtained from an oxide semiconductor coated with titanium oxide, a thin film was formed and tested.

FIG. 6 shows the absorption of light at a wavelength of 340 nm or less, that is, 3.2 electron volts or more, in the UV-VIS spectrum of titanium oxide.

Alternatively, the nickel oxide of Example 1 coated with titanium oxide shown in FIG. 8, the iron oxide of Example 2 shown in FIG. 10, the tungsten oxide of Example 3 shown in FIG. 12, and the first oxide of Example 4 shown in FIG. 15. In the spectrum obtained from copper, the absorption spectrum by the oxide semiconductor can be observed in the wavelength region longer than 340 nm in addition to the peak of 340 nm or less due to the absorbance of titanium oxide.

According to the above results, the shoulder-shaped absorption observed at a wavelength of 340 nm or less may be attributed to titanium oxide coated on the oxide semiconductor, indicating that titanium oxide is coated on the oxide semiconductor surface.

Test Example 3 Measurement of Photocatalytic Activity by Decomposition of Methylene Blue

The quartz plate was coated with nickel oxide, iron oxide, tungsten oxide and cuprous oxide coated with titanium oxide prepared in Examples 1 to 4, and then 0.001 M methylene blue (3,9-bisdimethylaminophenzanothionium Chloride, C ₁₆ H ₁₈ ClN ₃ S, F.wt.374: methylene blue) was coated by dip-drawing method at 10mm / min and then adjusted so that the absorbance was in the range of 0.02 to 0.2 at a wavelength of 570 to 590 nm. It was.

Quartz plate coated with titanium oxide (A: titanium oxide) and four (B: nickel oxide coated with titanium oxide, C: iron oxide coated with titanium oxide, D: coated with titanium oxide The degree of decomposition of methylene blue was confirmed by UV-VIS spectra by irradiating light of a constant intensity on a quartz plate coated with a tungsten oxide and an E: copper oxide coated with titanium oxide solution.

As a light source of irradiated light, a xenon lamp (Xe Lamp (ORIEL Co., Ltd., 1000W)) generating the light closest to natural light was used. In this case, the intensity of the light was 8.9 mW / ㎠ when including ultraviolet light. It was. In addition, when the light of 310 nm which is the wavelength of an ultraviolet range was cut off using the general glass filter, the light intensity was 8.0 mW / cm <2>.

Light intensity was measured by a light quantity measuring device (IL 390B Light Bug, INTERNATIONAL Light Inc.) measured at a specific wavelength (390 nm), and the results are shown in FIGS. 16 and 17, respectively.

That is, the results of comparing the decomposition photocatalytic ability of the methylene blue while irradiating A, B, C, D and E with the light not blocking the ultraviolet rays of the xenon lamp are shown in FIG. 16. In this case, all samples showed high methylene blue resolution. The values of A were 0.0017, B of 0.0044, C of 0.0046, D of 0.0032 and E of 0.0030.

In particular, the titanium oxide coated oxide semiconductor particles prepared according to the present invention B, C, D, E showed a much higher resolution of 0.0013 ~ 0.0030 than the titanium oxide (A) itself, according to the present invention It is a result indicating that the resolution of organic matter of the prepared photocatalyst is superior to conventional titanium oxide.

In addition, the photocatalytic activity of the decomposition of the relative methylene blue according to the sample was compared while irradiating A, B, C, D, and E with the light of the xenon lamp that blocked light having a wavelength of less than 310 nm while passing through a common glass filter. One result is shown in FIG. 17.

In the above case, we want to examine the degree of decomposition of organic material by sunlight, which partially removes ultraviolet rays from the light of xenon lamp. The quartz plate A coated with titanium oxide only has a resolution of 0.0017 compared to FIG. Significantly reduced to 0.0004, samples B, C, D coated with a titanium oxide-coated oxide semiconductor prepared according to the method of the present invention showed a resolution similar to that of FIG. 16 using light including ultraviolet rays, respectively, 0.0018, 0.0026 , 0.0030.

It was found that Sample E coated with titanium oxide coated cuprous oxide showed higher resolution than copper oxide (A) because the oxidation of copper oxide proceeded further, resulting in lower resolution than titanium oxide (A). Can be.

Therefore, according to the method of the present invention, even when irradiating sunlight without irradiating ultraviolet rays, a photocatalyst exhibiting a high resolution similar to when irradiating ultraviolet rays can be produced.

As described above, according to the present invention, the oxide semiconductor having semiconductor characteristics is made into small particles to increase the surface area, and the surface of the particles is coated with titanium oxide while irradiating a specific wavelength, thereby irradiating sunlight having a wavelength larger than ultraviolet rays. Since it can produce a photocatalyst which does not require separate ultraviolet irradiation by exhibiting excellent photocatalytic ability, it is possible to expand the industrial area in which the photocatalyst is used, and it is possible to create a new economic photocatalyst without the need for a separate device and protective equipment for ultraviolet irradiation. There is an effect that can be produced.

Claims (8)

In the photocatalyst manufacturing method containing titanium oxide, 1) dispersing the metal salt solution ultrasonically in the solution transport gas and passing through an electric furnace of 100-1200 ° C. composed of multiple steps to form oxide semiconductor particles having a band gap energy of less than 3.0 electron volts; 2) coating the surface with titanium oxide by dispersing the oxide semiconductor particles prepared in step 1 in a solution in which the titanium compound is dissolved and stirring while irradiating light; And 3) collecting the particles coated with the titanium oxide prepared in step 2 by centrifugation and then sintering in gas or vacuum Method for producing an oxide semiconductor particle coated with titanium oxide, characterized in that comprises a. The oxide coated with titanium oxide according to claim 1, wherein the metal salt solution is a complex solution of metal nitrates, ammonium salts, acetates and metals containing at least one ligand containing at least one nitrogen or oxygen atom. Method for producing semiconductor particles. The method of claim 1, wherein the oxide semiconductor particles are made of particles selected from nickel oxide, iron oxide, tungsten oxide, and copper oxide. The method of claim 1, wherein the titanium compound is coated with titanium oxide, characterized in that selected from a material capable of forming titanium oxide by reaction of holes and electrons generated on the surface of the oxide semiconductor particles prepared in the first step Method for producing oxide semiconductor particles. The titanium compound according to claim 4, wherein the titanium compound is an alkoxide of titanium (Ti (OR) _4, R = C _n H _{2n + 1} , n = 1, 2, 3 ...), halogenated titanium (TiF ₄ , TiCl ₄ , TiBr ₄ ) and a method for producing oxide semiconductor particles coated with titanium oxide, characterized in that selected from titanium nitrate. The method of claim 1, wherein the light irradiated in the second step has an energy greater than the band gap energy of the oxide semiconductor and less than the band gap energy of the titanium oxide. The method of claim 6, wherein the light irradiated in the second step has an energy greater than the band gap energy of the oxide semiconductor and the band gap energy of titanium oxide. Oxide semiconductor particles coated with titanium oxide, characterized in that prepared by the method of claim 1.