JPH10146531A - Metal superfine particle carrying photocatayst and of its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a photocatalytic substance composed of titanium dioxide wherein a particle size of supported metal superfine particles is a nano-scale and increased in photocatalytic efficiency. SOLUTION: A particle size of metal superfine particles is set to a range capable of markedly developing quantum size effect and an average particle size of metal superfine particles is numerically set to a range of 1-10nm. Hydrophobic colloid of an organometal complex and photocatalyst particles are mixed in a hydrophilic solvent to bond hydrophobic colloid on the surfaces of a photocatalyst particles and, after this mixed soln. is dried, the residue is baked to prepare a metal ultrafine particle supported photocatalyst. A colloid soln. of an organometal compd. and a photocatalyst powder are sprayed in a mutually opposed state to bond a large number of organometal compd. colloid on the surfaces of photocatalyst powdery particles and these colloid bonded particles are heat-treated on the way of falling to strongly support metal superfine particles on the surfaces of photocatalyst particles to continuously produce a metal superfine particle supported photocatalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal-supported photocatalyst in which metal particles are supported on the surface of a photocatalyst.
The present invention relates to an ultrafine metal particle-supported photocatalyst in which a metal particle is minimized to ultrafine metal particles of a nano-scale, whereby a quantum size effect of the metal is remarkably exhibited, and the photocatalytic efficiency is remarkably improved, and a method for producing the same.

[0002]

2. Description of the Related Art The photocatalytic reaction of titanium dioxide was announced to Nature in 1972 and became known worldwide as the Honda-Fujishima effect. Since then, research has been actively conducted to realize photosynthesis, which was performed only by plants, with titanium dioxide under light irradiation. In the meantime, the oil problem in the Middle East caused an economic panic in Japan, triggered by the global environmental problem of global warming, and the decomposition reaction of obtaining hydrogen from water using titanium dioxide and the decomposition of organic matter aqueous solution etc. Research on reactions has been conducted worldwide.

[0003] The mechanism of this photocatalyst depends on the photocatalytic properties of titanium dioxide as a semiconductor. When titanium dioxide is irradiated with light having an energy greater than its band gap energy, for example, ultraviolet light, electrons in the valence band are excited and transition to the conduction band, leaving positively charged holes in the valence band. An electron-hole pair is generated. The electrons and holes move through the titanium dioxide and reach the catalyst surface. The electrons not only directly reduce external substances, but also form O ₂ ⁻ (superoxide anion) from oxygen in the air. It is also said to act strongly on substances. The holes not only directly oxidize and decompose external organic substances, but also oxidize water molecules adhering to the surface to form strong oxides called hydroxyl radicals, and oxidize external substances by the oxidizing power of the hydroxyl radicals. Although it is said that O ₂ ⁻ is deeply involved in this oxidation process, its detailed reaction circuit is still being studied. The organic matter is decomposed into carbon dioxide and water by the electron-hole pairs generated by the light.

In this research, it has been pointed out that the photocatalytic efficiency of titanium dioxide alone is limited because electrons and holes may be recombined and eliminated before redoxing an external substance. . Specifically, titanium dioxide is a powder in a normal state, and when one particle is considered, lattice defects such as countless point defects and plane defects are present on the surface and inside thereof. When electrons and holes induced in titanium dioxide by ultraviolet rays encounter a lattice defect in the course of their movement, they are captured by the lattice defect and recombined. Even if the electrons can move to the surface, recombination may occur when electrons and holes approach. To improve this, a technique for producing titanium dioxide free from lattice defects and a technique for separating electrons and holes at the surface must be developed. Regarding the former, the improvement of the crystal growth technique has been successively made, and since it is not directly related to the present invention, the details are omitted here.

Regarding the technique of separating electrons and holes at the surface, an electrode for collecting excited electrons is formed on titanium dioxide, and holes are separated on the surface of titanium dioxide and electrons are separated on the surface of the metal electrode. Photocatalysts have been proposed. It was considered that this would allow electrons to be efficiently collected on the metal electrode, and that holes and electrons could be separated, reducing the probability of recombination. This type of photocatalyst is called a metal-supported photocatalyst, and Pt (platinum) conventionally used as a catalyst has been used.
And Cu (copper) were formed on titanium dioxide. The idea is that if a metal alone has a catalytic action, it will have a synergistic effect with the catalytic action of titanium dioxide.

As a method of supporting a metal on a semiconductor such as titanium dioxide, a light deposition method, a mixing method, an impregnation method, a chemical deposition method, a simultaneous precipitation method and the like have been developed. The metal particles remained on the order of microns. Further, in these methods, the number of metal fine particles carried per titanium dioxide particle usually stays in the range of several tens. The limitation of the loading density is due to the problem of the production method and the large size of the loaded metal fine particles. In other words, one of the causes is that so many metal fine particles do not adhere to one titanium dioxide particle because the particle size of the metal fine particles is large. Regarding the metal loading effect, for example, it is reported that Pt-supported titanium dioxide is more effective than titanium dioxide alone in a hydrogen generation reaction,
It has also been found that the reaction activity and reaction selectivity can be changed by changing the type of metal or semiconductor. However, the catalytic efficiency of these conventional metal-supported photocatalysts was only enhanced about 2 to 4 times as compared with titanium dioxide alone. This means that this efficiency is only about the sum of the efficiency of titanium dioxide and the efficiency of metal fine particles.

[0007]

SUMMARY OF THE INVENTION The present inventors have theoretically examined why the catalytic efficiency is not so enhanced with micron-sized metal fine particles. In order to efficiently incorporate electrons generated in titanium dioxide into the metal electrode, it is desirable to minimize the barrier of electron transition at the interface between titanium dioxide and the metal. However, when the particle size of the metal fine particles is a micron size (about 0.1 μm or more), the electronic state has the same band structure as that of a large solid crystal (bulk crystal). In other words, the valence band and the conduction band are clearly formed with a certain band gap, and the conduction band has a structure in which free electrons are densely packed in order from the bottom to the uppermost Fermi level. On the other hand, since titanium dioxide is a bulk crystal, its electronic state naturally takes a band structure. In the band structure, the energy levels constituting the band are arranged almost continuously and densely, and the wave function corresponding to each level is sharply localized in the substance. In other words, since the wave function does not protrude out of the material, the probability that electrons staying at the level are emitted out of the material is considerably reduced.

In this state, as shown in FIG. 12, suppose that titanium dioxide is irradiated with ultraviolet rays to excite electrons into the conduction band and generate electron-hole pairs. In order for these electrons to reduce an external substance or generate a superoxide anion, it is necessary for the electrons to move quickly from titanium dioxide into the metal and further from the metal to an external substance outside the metal. However, as described above, since the metal fine particles have a micron size, not only do they have a band structure similar to that of a crystal having a large electronic state, but also have a structure in which the wave function is sharply localized in the metal fine particles. Therefore, it is not easy for electrons that have risen to the conduction band of titanium dioxide to ride on the wave function of the metal, and it is not easy to move to the conduction band of the metal. Also, even if the electrons can somehow move to the metal, it is also not easy to move from the metal to the external substance, so it quickly falls on the Fermi level in the conduction band of the metal before leaving the metal. And the chance of reacting with external substances is further reduced. In other words, when the conduction band level density is large as in a band structure, the time for the electron to fall above the Fermi level (relaxation time) becomes extremely short, and the localization of the wave function and the electron It blocks outbound movement. In other words, since electrons are difficult to escape to the outside at the micron size, electrons are excessively accumulated in the metal, and the anti-power generation field prevents electrons in the titanium dioxide from moving into the metal. I will. After all,
It can be concluded that in the region where the particle diameter of the metal fine particles is in the micron size, the probability that electrons remain in the titanium dioxide or the metal fine particles due to the energy band structure and the localization of the wave function and are emitted to the outside of the metal is reduced. At the same time, in the case of micron-sized metal fine particles, the number of metal fine particles supported on one titanium dioxide particle is limited to several tens, and these limit the catalytic efficiency of the metal-supported photocatalyst. That's why.

Next, the present inventors have sequentially confirmed the conventional method for producing a metal-supported photocatalyst. First, a light precipitation method in which a semiconductor is suspended in an aqueous solution of a supported metal salt and a reducing agent is added thereto to irradiate light. Second, an impregnation method in which a semiconductor is immersed in an aqueous solution of a supported metal salt, dried and reduced, and thirdly, A chemical precipitation method in which a semiconductor was vigorously stirred in an aqueous solution of a supported metal salt to add a reducing agent thereto, and a fourth method in which an aqueous solution of a supported metal salt was added to a semiconductor raw material to cause simultaneous precipitation, followed by firing, were tested. What is common to these is that an aqueous solution of a supported metal salt is used, and these methods can only form micron-sized metal fine particles having a particle size of 0.1 μm or more on titanium dioxide. Also, as other methods, a kneading method of kneading the semiconductor and the supporting metal powder well in a mortar, a shaking method of shaking the semiconductor and the supporting metal powder in a container and shaking with a shaker or the like,
A method of adding a metal powder in which a semiconductor and a supported metal powder were separately added to a reaction solution and suspended and mixed was tested. However, similarly, micron-sized metal fine particles could only be formed on titanium dioxide, and only tens of metal fine particles could be supported on one titanium dioxide particle. Therefore, it is difficult to remarkably improve the catalytic efficiency of the metal-supported photocatalyst by these conventional production methods.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks, and a photocatalyst carrying ultrafine metal particles according to the present invention is based on the fact that ultrafine metal particles are supported on a photocatalytic substance. It has a configuration. In particular, the particle size of the metal ultrafine particles is set in a range where the quantum size effect can be remarkably exhibited, and numerically, the average particle size of the metal ultrafine particles is 1 to 10
nm. Further, the average number of ultrafine metal particles supported per photocatalyst fine particle is 10
It is characterized in that the number is zero or more.

As a method for producing a photocatalyst supporting metal ultrafine particles, a mixed solution of an organic metal compound reducible by heating and a photocatalytic substance is dried, and the residue is calcined to strongly support the metal ultrafine particles on the surface of the photocatalytic substance. Provide a way.
More specifically, a colloid preparation method, that is, a hydrophobic colloid of an organometallic complex and a metal oxide semiconductor powder particle that is a photocatalytic substance are mixed in a hydrophilic solvent to adhere the hydrophobic colloid to the metal oxide semiconductor powder particle surface, After the mixture is dried, the residue is calcined to provide a method for producing a photocatalyst supporting metal ultrafine particles. In addition, a colloidal solution of an organometallic compound and a photocatalyst powder are sprayed in opposition to each other so that a large number of organometallic compound colloids adhere to the surface of the photocatalyst powder particles. Provided is a method for producing a photocatalyst carrying metal ultrafine particles, in which ultrafine particles are firmly supported on the surface of photocatalyst powder particles and the photocatalyst supporting metal ultrafine particles is continuously produced.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted intensive studies to enhance the photocatalytic function of metal-supported titanium dioxide. It was found that the photocatalytic function can be enhanced about 10 times, and more preferably about 100 times or more under favorable conditions. Therefore, even when compared with titanium dioxide supporting micron-scale metal fine particles,
The catalyst efficiency can be increased to about 3 to 25 times. This is to convert metal from fine particles to ultra fine particles,
In other words, it can be achieved by minimizing the particle size from the micron scale to the nanoscale, in other words, the particle size to about 1/10 to 1/100 of the micron scale (about 0.1 μm or more). The average particle diameter of the ultrafine metal particles used in the present invention is 1 to 10 nm, more preferably 1 to 5 n.
m. If it is larger than this, the expression of the quantum size effect, which will be described later, will be reduced, and the enhancement of the photocatalytic efficiency will not be remarkable. It becomes extremely expensive.

When a fine powder of titanium dioxide or the like is used as the photocatalytic substance, the number of ultrafine metal particles that can be carried by one photocatalyst fine particle, that is, the loading density of the ultrafine metal particles is an important factor together with the particle diameter. Become. In the present invention, it is possible to support a large number of ultrafine metal particles on one photocatalyst fine particle by using ultrafine metal particles reduced to the nanoscale. In other words, the reduction in particle size from micron-scale metal fine particles to nanoscale metal ultrafine particles has achieved a dramatic improvement in the carrying density. According to the study of the present inventors, it is desired that the average number of ultrafine metal particles supported per photocatalyst fine particle is set to 100 or more, preferably 200 or more. If the loading density is 100 or more, the photocatalytic efficiency can be significantly increased due to a synergistic effect with the quantum size effect. If the number is 200 or more, a remarkable increase in photocatalytic efficiency can be achieved. Of course, if the loading density can be further increased, the photocatalytic efficiency can be further increased.

The quantum size effect first manifested by ultrafine metal particles will be discussed below. For example, when ultrafine particles having a diameter of 1 nm are considered, only about 10 to 100 metal atoms are present therein, depending on the size of the atoms. Also, when it comes to ultrafine metal particles having a diameter of 10 nm, about 10,000 to 1
It is believed to contain 00000 atoms. In such ultrafine metal particles having a small number of atoms, the electron energy state of the metal starts to be gradually discrete from the band structure, and the energy levels are distributed over a wide range. For example, when considering a conduction band, a large number of energy levels constituting the conduction band are distributed over a wide range up and down while being dispersed from a state of being densely packed. This level discretization has the effect of increasing the relaxation time of the electrons, that is, the time required for the electron to fall from that level to the Fermi level. In other words, the time that electrons stay at the level becomes longer. At the same time, the wave function corresponding to the energy level protrudes to the outside of the metal while extending the tail to the left and right, and has the effect of reducing the peak at the same time. .
That is, the electrons on the wave function can easily move to the outside due to the quantum tunnel effect. In the present invention, the term “quantum size effect” means the occurrence of the quantum tunnel effect due to the discretization of the energy level and the delocalization of the wave function as described above.

FIG. 1 shows an energy state when ultrafine metal particles are supported on titanium dioxide. When titanium dioxide is irradiated with ultraviolet rays, electron-hole pairs are formed, and electrons are excited in the conduction band while leaving holes in the valence band. When excited by ultraviolet rays having high energy, electrons transition to a higher position in the conduction band, but gradually fall to the bottom of the conduction band while losing energy. Since the energy levels of the metal are discretely dense to some extent, there is always an energy level corresponding to the bottom of the conduction band of titanium dioxide. In addition, the wave function of the level has long tails to the left and right, and the left end extends into titanium dioxide and the right end extends to the outside of the metal. That is, the energy levels of titanium dioxide and the metal are resonantly continuous via the wave function of the metal. Excited electrons in the conduction band of titanium dioxide are emitted at once by the quantum tunnel effect via the metal on the wave function of the metal. Since the titanium dioxide and the metal are in a resonance state, this quantum tunnel effect is called resonance tunneling. At this time, since the levels in the metal are discretized, the relaxation time of the electrons is long, so that the electrons are easily emitted out of the metal before falling on the Fermi level of the metal.

The holes in the valence band of titanium dioxide move to the surface of titanium dioxide and oxidize the external substance D. It is also believed that not only is the external substance oxidized, but also the water adhering to the surface is oxidized to form a strong oxide called a hydroxyl radical, and the hydroxyl radical oxidizes and decomposes the external substance. Meanwhile, electrons emitted by the resonant tunneling outside metal not only reducing the external substance A directly, by reducing oxygen in the air with the O ₂ ^- generated superoxide anion that, the anion is the external substance D It is also thought to be involved in the decomposition of. In particular, in the present invention, the excited electrons transferred from the titanium dioxide to the metal are immediately discharged to the outside without being accumulated in the metal, so that an anti-power generation field is not formed outside, and it is possible to successively attract the excited electrons by ultraviolet irradiation. It has excellent reducing power in that it can be used.

The type of photocatalyst used in the present invention is not limited to titanium dioxide, but depends on the substance to be decomposed to be reduced. When the decomposition target substance is a substance to be reduced, a reduction potential exists, and when the decomposition target substance is a substance to be oxidized, an oxidation potential exists. These reduction potentials and oxidation potentials must be located in the energy gap between the valence band and the conduction band of the photocatalytic substance. Specifically, as shown in FIG. 1, it is desired to select a photocatalytic substance in which the reduction potential is located on the upper side in the gap and the oxidation potential is located on the lower side in the gap. In this case, the excited electrons fall to the reduction potential from the bottom of the conduction band to reduce the target substance, and the holes rise to the oxidation potential from the top of the valence band to oxidize the target substance. However, in the present invention, since the resonance tunneling of the ultrafine metal particles is effective, the reduction potential may be at the bottom of the conduction band. In recent studies, electrons reduce O ₂ to a superoxide anion O ₂ ⁻ , and holes oxidize water to form hydroxyl radicals. These O ₂ ⁻ and hydroxyl radicals are used as target substances. Is thought to break down. Therefore, the photocatalytic substance can be selected by selecting the O ₂ potential as the reduction potential and the OH potential as the oxidation potential. That is, electron-hole pairs are generated by irradiation of ultraviolet rays, electrons reduce oxygen in the air or water to generate superoxide anions, and holes oxidize water attached to the surface to generate hydroxyl radicals. Any photocatalytic substance may be used.

Semiconductors are suitable as photocatalytic substances.
If insulators have too large a gap energy, it is difficult to generate electron-hole pairs with ordinary ultraviolet light, and if a substance with a small gap energy has difficulty in locating oxidation and reduction potentials within the forbidden band. Both are unsuitable because they are easily dissolved in an aqueous solution. Among the semiconductors, metal oxide semiconductors are suitable for the present invention. Metal oxide is a substance that is extremely stable as compared with a simple substance of metal, and thus has low reactivity with other substances, is safe, and can sufficiently transfer and receive electrons. Therefore, a metal oxide semiconductor satisfying these properties can be used as the photocatalyst substance of the present invention, for example, WO ₃ , CdO ₃ , In
₂ O ₃ , Ag ₂ O, MnO ₂ , Cu ₂ O ₃ , Fe
₂ O ₃ , V ₂ O ₅ , TiO ₂ , ZrO ₂ , RuO ₂ , C
r ₂ O ₃ , CoO ₃ , NiO, SnO ₂ , CeO ₂ , N
b ₂ O ₃ , KTaO ₃ , SrTiO ₃ , K ₄ NbO ₁₇
And the like can be selected from known substances including, for example, the substance to be decomposed. Among them, from the viewpoints of the density of generated electrons and holes, the density of superoxide anions and hydroxyl radicals, and the corrosion resistance and safety of the material, Ti
O ₂ , SrTiO ₃ , and K ₄ NbO ₁₇ are preferred, and TiO _2, which is titanium dioxide, is most preferred.

It is preferable that the photocatalytic substance is fine particles rather than a large solid substance. The reason is that the fine particles have an extremely large surface area, so that the probability of contact with environmental pollutants increases and, at the same time, a large number of metal ultrafine particles can be carried on the surface. Further, the fine particles have a larger effective light receiving area for ultraviolet rays and the like, and the photocatalytic efficiency is much higher than that of the bulk material. Since the metal oxide is usually a powder, a metal oxide semiconductor such as titanium dioxide is suitable for the present invention. The particle size is 30 nm to 1000 nm, more preferably 50 nm to 500 nm. If the particle size is smaller than this, the particles approach the ultrafine particles, so that a special technique and cost are required for the production. If the particle size is larger than this, the specific surface area is reduced, and the reactivity with environmental pollutants, human toxic substances, malodorous substances and the like is deteriorated. For example, it is possible to make titanium dioxide into ultrafine particles of about 10 nm, but it does not exist as independent particles, and the titanium dioxide ultrafine particles are aggregated to form a dumpling,
Eventually, it becomes a large titanium dioxide lump as described above. In this case, the reactivity is higher because the surface area is larger than that of a single solid due to the ruggedness. The present invention also includes such photocatalyst fine particles. The form of the photocatalyst fine particles is not particularly limited as long as the ultrafine metal particles can be supported.

The supported ultrafine metal particles may be transition metals. The transition metal element is an element having an incomplete d-shell and having atomic numbers 21 (Sc) to 29 (Cu) and 39 (Y) to 4
7 (Ag), 57 (La) -79 (Au) and 89
It is a metal element consisting of four groups (Ac) to 111 in theory. The outer shell is d due to the imperfect d shell
The electrons have directionality, and as a result, excited electrons coming from the photocatalytic substance are easily captured on the surface of the metal ultrafine particles, and a superoxide anion is easily generated. A metal that can be used alone as a catalyst is desirable, and from the viewpoint of safety, Au, Pt, Ag, and Pd are preferable, and Au, Pt, and Pd are more preferable from the viewpoint of stability as a metal.

A feature of the present invention is to establish a method of carrying and forming ultrafine metal particles on the surface of a photocatalytic substance composed of fine particles or large crystals. The conventional manufacturing method was able to support micron-sized metal fine particles, but it was impossible to form and support nanoscale ultrafine metal particles. This limitation of the conventional production method was also a factor that hindered the improvement of the photocatalytic efficiency. As described above, the conventional production method uses a metal salt or metal powder as a raw material, whereas the present invention achieves a dramatic improvement in photocatalytic efficiency by using an organic metal compound that can be reduced by heating. It is. Reducible by heating means that only metal can be isolated from the organometallic compound by heating, in other words, other organic substances are separated. Among the organometallic compounds, organometallic complexes are particularly suitable for the purpose of the present invention.
However, it goes without saying that there is no particular limitation as long as the organic metal compound can be reduced by heating.

For example, Li-based compounds such as ethyllithium and p-dimethylaminophenyllithium; Na thread compounds such as n-propyl sodium and 2-methylfuryl sodium; K-based compounds such as ethyl potassium and phenyl potassium; ethyl rubidium; Rb compounds such as triphenylmethyl rubidium; Cs compounds such as ethyl cesium and benzyl cesium; Be compounds such as dimethyl beryllium and isopropyl beryllium methoxide; Mg compounds such as methyl magnesium iodide and dimethyl magnesium; dimethyl calcium; Ca thread compounds such as phenyl calcium iodide; Sr-based compounds such as ethyl strontium iodide and dimethyl strontium; Ba-based compounds such as dimethyl barium and phenyl barium iodide; dimethyl zinc and diethyl Zn-based compounds such as lead isoquinolinate; Cd-based compounds such as diisobutylcadmium and diphenylcadmium; Hg-based compounds such as methylmercury bromide, methylmercury iodide and bis (trifluoromethyl); As-based compounds such as dimethylarsenic and phenyldichloroarsenic Compound;
Sb-based compounds such as dimethylbromoantimony and trimethylantimony; Bi-based compounds such as dimethylbismuth and trimethylbismuth; Se-based compounds such as methylselenocyanate and dimethylselenide; Te-based compounds such as dimethyltelluride and β-dimethyltelluride dichloride Compounds; Po-based compounds such as polonium carbonyl and dimethyl polonium;
B-based compounds such as tricyclooctylborane and 2,4-dimethylborazine; Al-based compounds such as trimethylaluminum and dimethylaminodimethylaluminum; Ga-based compounds such as trimethylgallium and phenyldibromogallium; trimethylindium and diphenylbromoindium In-based compounds; Tl-based compounds such as dimethylbromothallium and dimethylmethoxythallium; Cu such as copper tricarbonyl, phenylcopper and bis (chlorocopper) acetylene
Ag compounds such as isobutenyl silver and phenyl silver; Au compounds such as methyldibromogold, trimethylgold and diisopropylcyanogold; dichloro- (cyclooctadiene-1,5) -palladium and π-cyclopentadienyl- Pd-based compounds such as π-cyclopentenyl palladium; Pt-based compounds such as π-cyclopentadienyl-π-allyl-platinum and dichloro- (cycloocta-1,5-diene) -platinum; methyl-penta (carbonyl) -rhenium; Re-based compounds such as chloro-bis (phenylacetylene) -rhenium; Rh-based compounds such as π-cyclopentadienyl-di (ethylene) -rhodium and octa (carbonyl) -dirhodium; penta (carbonyl) -ruthenium, π- R such as cyclopentadienyl-methyl-di (carbonyl) -ruthenium Tc-based compounds such as cyclopentadienyl-tri (carbonyl) technetium; Ti-based compounds such as methyl-trichloro-titanium, di-cyclopentadienyl-titanium, triisopropoxy-phenyl-titanium; hexa (carbonyl) ) -Vanadium, di-π-cyclopentadienyl-
V-based compounds such as dichloro-vanadium; W-based compounds such as hexa (carbonyl) tungsten and tri (carbonyl)-(benzene) -tungsten; Zr-based compounds such as cyclopentadienyltrichlorozirconium; π-allyl-tri (carbonyl) ) Co-based compounds such as cobalt and di-π-cyclopentadienyl cobalt; Cr-based compounds such as π-cyclopentadienyl-chlorodi (nitroosyl) chromium, tri (carbonyl)-(thiophene) chromium and dibenzenechromium; dibromo Tetra (carbonyl) iron, tetra (carbonyl)-(acrylonitrile)
Fe compounds such as iron; Ir compounds such as tri (carbonyl) -iridium; Mn compounds such as bromopenta (carbonyl) manganese; Mo compounds such as tri (carbonyl)-(benzene) -molybdenum; tetratri (carbonyl) N such as nickel and diacrylonitrile nickel
i-based compound; (benzene)-(cyclohexadiene-
1,3) Os-based compounds such as osmium; Si-based compounds such as methyltrichlorosilane and methyldifluorosilane;
Ge-based compounds such as hexaethyldigermanium and allylgermanium trichloride; ethyltin trichloride;
Sn-based compounds such as (2-cyano-1-methylethyl) triphenyltin; and Pb-based compounds such as triethyl-n-propyl lead and triethyl lead methoxide.

As described above, from the viewpoints of stability and safety, metals such as Au compounds, Ag compounds,
It is preferable to use at least one of a Pd-based compound, Rh-based compound and Pt-based compound. More preferably A
It is a compound of u, Ag, Pd, Rh or Pt and a sulfur-containing organic substance, and most preferably a compound of Au, Pd, Rh or Pt and a sulfur-containing organic substance. For example, methyl mercaptan, ethyl mercaptan, propyl mercaptan, butyl mercaptan, octyl mercaptan,
Alkyl mercaptans such as dodecyl mercaptan, hexadecyl mercaptan and octadecyl mercaptan; thioglycolic acids such as butyl thioglycolate; and trimethylolpropane tris thioglycolate, thioglycerol, thioacetic acid, thiobenzoic acid, thioglycol, thiodipropionic acid Thiourea, t-butylphenylmercaptan, t-butylbenzylmercaptan and the like. In addition, balsam gold (C ₁₀ H ₁₈
SAuCl _1-3 ), Balsam platinum (C ₁₀ H ₁₈ SP)
tCl _1-3 ), balsam palladium (C ₁₀ H ₁₈ S)
PdCl _1-3 ), balsam rhodium (C ₁₀ H ₁₈ S)
RhCl _1-3 ) and the like can be used.

By dispersing the above-mentioned organometallic compound and a powder of a photocatalytic substance such as titanium dioxide in an appropriate known hydrophilic solvent, a hydrophobic colloid or the like of the organometallic compound can be formed. Many adhere to the surface of. When this mixture is dried and the remaining solid residue is calcined, the organic matter among the organometallic compounds escapes, and only the metal is converted into nanoscale ultrafine particles and carried on the surface of the photocatalytic fine particles. Drying and firing may be a series of steps, such as heating the mixed solution itself to evaporate the solvent and further firing the solid residue by heating.
When the photocatalytic substance is a large solid substance, only the organometallic compound is dispersed in a solvent to form an organometallic compound colloid, and the photocatalytic substance is immersed in the mixed solution, or the mixed solution is coated on the surface of the photocatalytic substance. When sprayed or coated on the substrate, and then taken out and fired, the metal ultrafine particles can be supported and formed on the surface of the photocatalytic substance. As another manufacturing method, when the above-mentioned colloidal solution of the organometallic compound and the photocatalyst powder are sprayed to face each other, a large number of colloids adhere to the surface of the photocatalyst powder particles, and the colloid-adhered photocatalyst powder particles are subjected to heat treatment while falling. Then, the ultrafine metal particle-supported photocatalyst fine particles can be continuously deposited on the bottom of the container.

The solution concentration of the organometallic compound can be appropriately set according to the final product or the like, but is usually 0.1% by weight or more, preferably 0.5 to 50% by weight. The solvent can be appropriately selected depending on the type of the organometallic compound, and alcohols,
Known organic solvents such as esters and aromatics can be used.

Known additives such as a co-catalyst may be contained in the mixed solution as long as the effects of the present invention are not impaired.
As the co-catalyst, for example, V, Mo, W, Nb, Cr, T
a or the like or an oxide thereof, an alkali metal (Li, Na,
K, Rb, Cs, Fr), alkaline earth metals (Be, M
g, Ca, Sr, Ba, Ra) and other heavy alkali metals.

The firing temperature in the present invention can be appropriately changed within a temperature range which is usually higher than the reduction precipitation temperature of the organometallic compound and lower than the melting point of the metal to be reduced and deposited. More specifically, in order to isolate a metal from an organometallic compound such as an organometallic complex, it is necessary to completely decompose the organometallic compound and leave only metal atoms to escape other organic atoms. No. This temperature is defined as the reduction precipitation temperature of the metal. Next, the isolated metal atoms must be assembled and rearranged into ultrafine metal particles. The upper limit temperature is not more than the melting point of the bulk metal, and is preferably 80% or less, particularly 70% or less of the melting point of the deposited metal. The firing atmosphere may be an oxidizing atmosphere or diluted air, and may be appropriately selected according to the final product.

As described above, the photocatalyst used in the present invention is a metal oxide semiconductor, and among them, titanium dioxide is most preferable at present. Rutile type and anatase type are known as crystal structures of titanium dioxide. When heated to about 600 ° C. or higher, all of the anatase type undergoes a phase transition to the rutile type, and becomes a rutile type at a low temperature after cooling. 600 ° C
Even below, a part of the anatase type undergoes a phase transition to the rutile type.
Industrially, the rutile type can be manufactured at lower cost, but the anatase type is overwhelmingly the titanium dioxide conventionally used as a photocatalyst that does not carry a metal.

The reason why the expensive anatase type is used is that the O ₂ potential which is the reduction potential is 3.13 eV.
On the other hand, the band gap energy of the rutile type is as small as 3.05 eV and that of the anatase type is 3.2 eV.
The reason is that it is rather large. FIG. 2 shows a rutile band structure. Electrons excited in the conduction band by ultraviolet light try to reduce oxygen while falling to the bottom of the conduction band. However, since the reduction potential is slightly above the bottom of the conduction band, it cannot be reduced without receiving any external energy. Therefore, the rutile-type simple substance has an extremely low oxygen reduction efficiency. On the other hand, in the case of the anatase type shown in FIG. 3, even when electrons are excited to the conduction band by ultraviolet rays and then fall to the bottom of the conduction band, the reduction potential is lower than the bottom of the conduction band. Because it is located, oxygen can be reduced.

The present invention makes it possible to realize the same oxidation-reduction function as the anatase type even when inexpensive rutile type titanium dioxide is used as a photocatalyst. FIG. 1 has described the case where, when electrons are excited into the conduction band by ultraviolet rays, the electrons fall to the bottom of the conduction band while relaxing, and move horizontally to the metal level and the reduction potential. However, in the case of reducing the oxygen at the reduction potential, electrons are immediately carried out by resonance tunneling to the outside of the metal on the wave function of the metal level at the horizontal position while relaxing from the excitation level in the conduction band. Included in the invention. Since resonance tunneling by metal ultrafine particles functions more effectively than relaxation, electrons can be emitted to the outside in a wide range from the excitation level corresponding to the ultraviolet energy to the bottom of the conduction band. That is, before the excited electrons fall to the bottom of the conduction band, the energy of the electrons is transferred to the reduction level without wasting the energy of the electrons. The remarkable expression of the quantum size effect by the ultrafine metal particles has opened the way for the rutile type to be used as a photocatalyst like the anatase type.

The light source that can be used in the present invention may be any light source having energy equal to or higher than the band gap energy of the photocatalyst, and usually an ultraviolet lamp is used. In particular, when titanium dioxide is used, there are a rutile type and an anatase type. When each gap energy is converted into a wavelength, the rutile type is 407 nm and the anatase type is 388 nm.
m. Therefore, it is desirable that the wavelength distribution of the light source for titanium dioxide has 400 nm near the peak.
The attractant lamp having the wavelength distribution of FIG. 4 is effective for both rutile and anatase types, and is very preferable because 400 nm is near the peak.

The natural sunlight having the wavelength distribution shown in FIG.
Visible light is the center, but is fully available because it contains 400 nm. 388nm especially for natural sunlight
Since the light intensity is higher at 407 nm, the rutile type is more effective than the anatase type. Therefore, the fact that rutile-type titanium dioxide can be used as a photocatalyst according to the present invention opens a great way to utilize natural sunlight. This is in contrast to the conventional anatase type, in which an ultraviolet lamp can be used, but in the case of natural sunlight, the catalytic efficiency is extremely low. In addition, in the conventional photocatalyst, the use of sunlight outdoors was possible because of the high light intensity, but the indoor use was a weak point because the light intensity was low. However, in the present invention, since the photocatalytic efficiency is remarkably enhanced, it is possible to expand the use of the photocatalyst indoors using sunlight as a light source.

[0033]

EXAMPLES Examples of the photocatalyst supporting ultrafine metal particles and the method for producing the same according to the present invention will be described below to further clarify the features of the present invention.

Example 1 [Preparation of Two Kinds of Pt Ultrafine Particle-Supported Photocatalyst] An organometallic complex colloid having a concentration of 2.5% by weight was prepared by dispersing a hydrophobic colloid of balsam Pt as an organometallic complex in hydrophilic acetone. A solution was prepared. Titanium dioxide powder having a rutile crystal structure and an average particle diameter of 300 nm was mixed with the colloid solution as photocatalyst fine particles, and the colloid was attached to the titanium dioxide fine particles. This colloid solution was applied to a Pyrex glass plate, dried, baked at 500 ° C. for 30 minutes, and peeled from the glass plate to obtain a photocatalyst A carrying ultrafine metal particles. Similarly, a photocatalyst B supporting ultrafine metal particles was obtained using titanium dioxide powder having a rutile crystal structure and an average particle size of 70 nm. FIG. 6 is a transmission electron micrograph of A and FIG. 7 is a transmission electron micrograph of B, showing the state of Pt ultrafine particles being supported on titanium dioxide fine particles. FIG. 8 shows a lattice image of A by a high-resolution transmission electron microscope, and it is proved from the lattice spacing that Pt is supported on rutile-type titanium dioxide. FIG. 9 shows the particle size distribution of the ultrafine Pt particles of A and B, wherein the average particle size of A is 3 nm and the average particle size of B is 1.5 n.
m. According to the colloid firing method, ultrafine metal particles having a small average particle diameter can be supported on titanium dioxide, and the quantum size effect, which is the core of the present invention, can be most effectively exerted.

Example 2 [Measurement of the supported density of the Pt ultrafine particle-supported photocatalyst of Example 1] The Pt of samples A and B obtained in Example 1
The carrying density of the ultrafine particles was measured. At this time, the titanium dioxide fine particles and the Pt ultrafine particles approximated to a spherical shape. A in FIG.
According to the electron micrograph of the above, about 120 Pt ultrafine particles were present on the surface of one titanium dioxide fine particle having a diameter of 200 nm, and the carrying density per 1 cm ² was 2 × 10 ¹¹ . Similarly, from the electron micrograph of FIG.
Approximately 300 Pt ultrafine particles were present on the surface of one nm of titanium dioxide, and the loading density was 4 × 10 ¹² particles / cm ² . From the viewpoint of easy understanding, in the present invention, the loading density is expressed by the number of ultrafine metal particles per photocatalyst fine particle.

Example 3 [Comparison of Photocatalytic Efficiency of Photocatalysts Supporting Six Kinds of Ultrafine Metal Particles] A method similar to that of Example 1 except that balsam Pt was replaced with Pt butyl mercaptan, and the average particle diameter was 300 nm.
Ultrafine metal particles were supported on the titanium dioxide of Example 1 to produce six types of ultrafine metal particle-supported photocatalysts. Specifically, it is rutile, anatase, rutile / Pt, rutile / Au, anatase / Au, or anatase / Pd. Rutile and anatase are metal-free titanium dioxide simple substances. These photocatalyst powders are called C, D, E, F, G, and H in this order. After the photocatalyst powders C to H were placed in a sealed container, the ethanol was sealed, and the amount of acetaldehyde and acetic acid produced after 1 hour under exposure to an ultraviolet lamp was measured. The results are shown in Table 1. Since ethanol is decomposed into acetaldehyde and then to acetic acid, the total amount of acetaldehyde and acetic acid produced serves as an indicator of decomposition power. Anatase D is rutile C
Since it is about 1.8 times that of anatase, it was demonstrated that anatase was effective alone. E, F, G and H are each about 5 of C
About 8 times, about 9 times, about 7 times, and about 3 times D,
It can be seen that the decomposition power is as high as about four times, about five times, and about four times.
Therefore, it was found that the decomposition power of the photocatalyst supporting ultrafine metal particles was remarkably excellent.

[0037]

[Table 1]

Example 4 [Continuous production apparatus of photocatalyst fine particles carrying ultrafine metal particles] FIG.
Reference numeral 0 is a schematic sectional view of an apparatus for continuously producing photocatalytic fine particles carrying ultrafine metal particles. A spray mechanism 2 for spraying an organometallic complex colloid solution and a fine particle nozzle 6 for spraying photocatalytic fine particles are arranged in a spray section 2 at the top of the apparatus. For example, when the titanium dioxide fine particles and the Pt butyl mercaptan colloid solution are sprayed to face each other, many colloid particles adhere to the titanium dioxide fine particles. The colloid-adhered fine particles fall under their own weight into the first heating tank, where they are dried at about 100 ° C. Below the first flange portion 10 is a second heating tank 12, in which the colloid-adhered fine particles are forcibly passed between the baffle plates 13 by the flow fan 11 and heated to about 500 ° C. The organic matter is completely decomposed by this heating, and rearranges into ultrafine metal particles while the metal atoms assemble with each other. Below the second flange portion 14 are perforated buffer plates 16 and 20, between which a fan 18 is installed. The photocatalyst particles carrying the ultrafine metal particles pass through the porous buffer plates 16 and 20 due to the suction force of the fan 18. The photocatalyst particles that have joined together and become larger in a dumpling shape are blocked here. Is prepared. The photocatalyst fine particles are stored in the container 2 via the buffer 22.
4 is continuously deposited. The airflow is sucked and exhausted to the outside via the porous buffer plate 26.

Example 5 [Comparison of Pt loading by continuous production apparatus and conventional photocatalyst fine particles] Rutile-type titanium dioxide having an average particle diameter of 70 nm was converted to an average particle diameter of 1.5 n by the continuous production apparatus shown in Example 4.
m Pt ultrafine particles were supported to produce photocatalyst fine particles supporting metal ultrafine particles. The loading density of Pt ultrafine particles was 600 per titanium dioxide fine particle. The photocatalytic efficiency of the Pt ultrafine particle-supported photocatalyst fine particles was determined to be an average particle size of 70 nm.
Was compared with a simple substance of anatase type titanium dioxide and a simple substance of rutile type titanium dioxide having an average particle diameter of 70 nm. Oxygen and argon gas were prepared as reaction atmospheres, and the effect of superoxide anion was also confirmed. Pt ultrafine particle-supported photocatalyst fine particles / O ₂ are I, anatase / O ₂ is J, anatase / Ar is K, and rutile / O ₂ is L. In all four types, the catalyst weighed 0.5 g. In order to check the decomposition efficiency of acetaldehyde to acetic acid, the measurement was started from a concentration of acetaldehyde in the sealed container of 100 ppm, and the measurement was continued until the concentration became 1 ppm. The results are shown semi-logarithmically in FIG. From the comparison of I and J at the same time from the start of measurement, Pt
It can be seen that the supported catalyst has a catalytic efficiency about 100 times or more higher than that of anatase alone, and is much higher than that of Example 3.
The reason for this is that the metal loading density is rather large and Pt
The reason is that the particle diameter of the ultrafine particles is uniform and quite small. From the comparison between J and K, it was proved that decomposition was not promoted with argon gas and the presence of oxygen was effective. That is, the presence of the superoxide anion effectively acts on the oxidation-reduction process. Further, in the case of rutile alone, the catalytic efficiency is the worst even in oxygen, which demonstrates that the explanation has been made with reference to FIGS.

The present invention is not limited to the above embodiment, but includes various modifications and design changes within the technical scope of the present invention without departing from the technical concept of the present invention.

[0041]

As described in detail above, the present invention remarkably enhances the photocatalytic function by minimizing the amount of metal supported on photocatalyst fine particles to ultrafine metal particles.
When the metal is reduced to a nanoscale region of 1 to 10 nm, excited electrons can be immediately emitted to the outside due to the development of the quantum size effect. Moreover, the average number (supporting density) of ultrafine metal particles supported per photocatalyst fine particle can be set to 100 or more, so that the photocatalytic reaction efficiency can be remarkably enhanced. As a result, the redox power to external substances can be remarkably enhanced, and a photocatalyst having organic substance decomposing power far superior to the photocatalyst fine particles alone or the photocatalyst fine particles carrying a micron-sized metal has been realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a band structure for explaining a quantum size effect of ultrafine metal particles.

FIG. 2 is a schematic diagram of a band structure for explaining that rutile-type titanium dioxide hardly reduces oxygen.

FIG. 3 is a schematic diagram of a band structure explaining that anatase type titanium dioxide can easily reduce oxygen.

FIG. 4 is a wavelength distribution diagram of the ultraviolet light of the attracting lamp that can efficiently excite both rutile type and anatase type of titanium dioxide.

FIG. 5 is a wavelength distribution diagram of natural sunlight.

FIG. 6 is a transmission electron micrograph showing a state in which ultrafine Pt particles are supported on titanium dioxide having an average particle diameter of 300 μm.

FIG. 7 is a transmission electron micrograph of a state in which ultrafine Pt particles are supported on titanium dioxide having an average particle diameter of 70 μm.

8 is a lattice image of the state shown in FIG. 6 using a high-resolution transmission electron microscope.

FIG. 9 is a particle size distribution diagram of the Pt ultrafine particles of FIGS. 6 and 7.

FIG. 10 is a schematic sectional view of an apparatus for continuously producing photocatalyst fine particles carrying ultrafine metal particles.

FIG. 11 is a time course of acetaldehyde decomposition by Pt-supported titanium dioxide and titanium dioxide alone.

FIG. 12 is an explanatory diagram of a band structure of a conventional metal-supported photocatalyst.

[Explanation of symbols]

 2. Spraying unit 4. Spray mechanism 6. Fine particle nozzle 8. First heating tank 10. First flange part 11. Sending fan 12. Second heating tank 13. Baffle plate 14. 2nd flange part 16 perforated buffer plate 18 fan 20 perforated buffer plate 22 buffer 24 container 26 perforated buffer plate

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01J 37/16 B01J 37/16 C07C 45/29 C07C 45/29 47/06 47/06 51/245 51/245 // C07B 61 / 00 300 C07B 61/00 300

Claims (10)

[Claims] 1. A photocatalyst carrying ultrafine metal particles, wherein ultrafine metal particles are supported on a photocatalytic substance. 2. The photocatalyst supporting ultrafine metal particles according to claim 1, wherein the photocatalyst substance is photocatalyst fine particles. 3. The photocatalyst supporting ultrafine metal particles according to claim 1, wherein the ultrafine metal particles have a particle size exhibiting a quantum size effect. 4. The ultrafine metal particles have an average particle size of 1 to 10 nm.
The metal ultrafine particle-supported photocatalyst according to claim 3, wherein the photocatalyst is within the range. 5. The average number of ultrafine metal particles supported per photocatalyst fine particle is 100 or more.
5. The photocatalyst supported by ultrafine metal particles according to any one of items 4 to 4. 6. Ultrafine metal particles are composed of a transition metal,
The photocatalyst carrying ultrafine metal particles according to claim 1, wherein the photocatalytic substance is a metal oxide semiconductor having an ability to generate hydroxyl radicals and / or superoxide anions by ultraviolet irradiation. 7. Ultrafine metal particles are Pt, Au, Pd, Ag.
7. The photocatalyst carrying ultrafine metal particles according to claim 6, wherein the photocatalyst substance comprises at least one of the following: 8. A method for drying a mixture of an organometallic compound and a photocatalytic substance which can be reduced by heating, followed by baking the residue to strongly support the ultrafine metal particles on the surface of the photocatalytic substance. A method for producing a supported photocatalyst. 9. The organic metal compound is a hydrophobic colloid of an organometallic complex, the photocatalytic substance is metal oxide semiconductor powder particles, and both substances are mixed in a hydrophilic solvent to form a hydrophobic colloid on the surface of the metal oxide semiconductor powder particles. Claim 8
3. The method for producing a photocatalyst supported by ultrafine metal particles according to item 1. 10. A colloid solution of an organometallic compound and a photocatalyst powder are sprayed in opposition to each other to deposit a large number of organometallic compound colloids on the surface of the photocatalyst powder particles, and a heat treatment is performed on the colloid-adhered photocatalyst powder particles while falling. The method for producing a photocatalyst carrying ultrafine metal particles, comprising: strongly supporting the ultrafine metal particles on the surface of the photocatalyst powder particles to continuously produce the photocatalyst carrying ultrafine metal particles.