JP2016137463A - Photocatalytic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tungsten-oxide-based photocatalytic material of a visible light responsive type having a high photocatalytic activity.SOLUTION: A photocatalytic material 1 comprises a core particle 2 containing a metal oxide composed of a tungsten oxide particle or composed of a composite of a tungsten oxide particle and a metal oxide other than tungsten oxide, and a promoter 3 containing at least one kind of metal such as platinum, palladium, iron, silver, gold, and nickel carried on the surface of the core particle 2. The photocatalytic material is doped with a halogen such as chlorine, and further includes a shell layer of titanium oxide that covers the whole surface of the core particle 2 and the promoter 3.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a photocatalytic material, and more particularly to a visible light responsive photocatalytic material.

  The photocatalytic material has semiconductor physical properties, and an electron-hole pair is generated in a conduction band and a valence band by irradiating light with a band gap or more. As a result, active oxygen species such as hydroxyl radicals and superoxide ions are generated on and around the surface of the photocatalytic material by the redox action of electron-hole pairs. The photocatalytic material is a substance that has an organic substance decomposing action and a self-cleaning action by oxidizing power and hydrophilization of these active oxygen species.

  Among photocatalytic materials, titanium oxide has a high photocatalytic effect and has been widely studied. However, titanium oxide has a large band gap and absorbs ultraviolet light but does not absorb visible light. Therefore, titanium oxide exhibits photocatalytic activity under ultraviolet light, but does not exhibit visible light activity, and therefore cannot exhibit a photocatalytic effect in an indoor environment with a very small amount of ultraviolet light.

  On the other hand, tungsten oxide is known as a visible light responsive photocatalytic material. However, since tungsten oxide has a lower potential at the lower end of the conduction band than the redox potential of oxygen, it is difficult to reduce oxygen with electrons excited in the conduction band. Therefore, on the contrary, electrons cause recombination with holes, and tungsten oxide alone does not show high photocatalytic activity.

  Therefore, it is known that an electron-withdrawing substance (co-catalyst) is formed on the surface of tungsten oxide particles and can be used as a visible light responsive photocatalyst. In this visible light responsive photocatalyst, recombination between electrons excited in the conduction band by light irradiation and holes generated in the valence band is suppressed, so that the photocatalytic activity of the tungsten oxide particles is enhanced.

  For example, Patent Document 1 discloses a photocatalyst in which platinum particles having a primary particle diameter of 3 nm to 20 nm are supported on the surface of tungsten oxide particles by 0.03 to 5 parts by weight per 100 parts by weight of tungsten oxide particles. Furthermore, this photocatalyst has high photocatalytic activity by being supported on the surface of each of the platinum oxide particles in a state of being in contact with each other (in a bead shape) on at least a part of the surface of the tungsten oxide particles.

  In addition, since tungsten oxide is easily dissolved in an alkaline solution, the photocatalytic activity may be reduced by a basic gas such as ammonia generated in a smoking room or a toilet. In addition, for example, when the wall surface coated with tungsten oxide is cleaned by wiping with a household basic detergent, the photocatalytic activity may similarly decrease.

  Therefore, in Patent Document 2, since tungsten oxide and a promoter supported on the surface of tungsten oxide are partially coated with titanium oxide, the photocatalytic activity is higher than that of uncoated tungsten oxide. It is disclosed to rapidly decompose volatile aromatic compounds therein.

JP 2009-160566 A (released on July 23, 2009) JP 2012-110831 A (released on June 14, 2012)

  However, the photocatalytic activity of the conventional tungsten oxide photocatalyst is still low, and improvement of the photocatalytic activity is demanded.

  Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a photocatalytic material having a higher photocatalytic activity than a conventional tungsten oxide photocatalyst.

In order to solve the above problems, a photocatalyst material according to an aspect of the present invention is a photocatalyst material including core particles containing tungsten oxide and a promoter supported on the surface of the core particles.
It is characterized by being doped with halogen.

  According to one embodiment of the present invention, there is an effect that the photocatalytic activity of a tungsten oxide photocatalytic material can be increased.

It is sectional drawing which shows typically the photocatalyst material which concerns on Embodiment 1 of this invention. It is sectional drawing which shows typically the photocatalyst material which concerns on Embodiment 2 of this invention. It is sectional drawing which shows typically the photocatalyst material which concerns on Embodiment 3 of this invention. It is sectional drawing which shows typically the photocatalyst material which concerns on Embodiment 4 of this invention. It is a graph which shows the relationship between the addition amount of hydrochloric acid and the decomposition rate constant in the photocatalyst material which concerns on this invention. It is the figure which showed the relationship between hydrochloric acid addition amount and the relative chlorine concentration contained in tungsten oxide in the photocatalyst material which concerns on this invention.

  Tungsten oxide exhibits a photocatalytic effect while having low photocatalytic activity. Electrons excited in the conduction band generate an active oxidizing species through a two-electron reduction reaction or a four-electron reduction reaction of oxygen, and an oxidative decomposition reaction of the active oxidizing species. It is thought that it is caused by.

  However, in order to efficiently proceed the multi-electron reduction reaction of oxygen, it is necessary to transport the electrons excited in the conduction band to the surface of the photocatalyst particle and a promoter (noble metal or the like) supported on the surface.

  As a result of intensive studies by the present inventors, the present inventors have found that the photocatalytic activity is improved by adding halogen as an n-type impurity to the tungsten oxide photocatalyst material, thereby completing the present invention.

Embodiment 1
An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view schematically showing a photocatalytic material 1A according to the present embodiment.

  As shown in FIG. 1, the photocatalytic material 1 </ b> A includes core particles 2 and a promoter 3 supported on the surface of the core particles 2. Furthermore, although not shown, the photocatalytic material 1A contains halogen as an impurity.

(Core particle 2)
In the photocatalytic material 1A, the core particle 2 is composed of tungsten oxide particles. Therefore, the photocatalytic material 1A is a visible light responsive photocatalytic material that exhibits photocatalytic activity when irradiated with visible light. In addition, although the core particle 2 of this Embodiment 1 is comprised from a tungsten oxide, this invention is not limited to this, The core particle 2 should just contain a tungsten oxide at least.

  The particle diameter of the core particle 2 is not particularly limited, but is preferably 5 nm or more and 100 nm or less. When the particle size is smaller than 5 nm, the particles tend to aggregate, and when the particle size is larger than 100 nm, the photocatalytic activity decreases. In addition, the particle size of the core particle 2 here is an average particle size calculated based on the BET specific surface area. The core particle 2 may be composed of particles having a uniform particle size or may be composed of a mixture of particles having a non-uniform particle size. That is, the spread (size) and distribution shape of the particle size distribution of the core particle 2 are not particularly limited, and a plurality of particle size distribution peaks may exist.

  The manufacturing method of tungsten oxide constituting the core particle 2 may be a general method, for example, a method of thermally decomposing ammonium paratungstate (APT), a method of heating metallic tungsten powder in an oxygen atmosphere, or the like. When the particle size distribution of tungsten oxide obtained by the above method is large, it is used after removing the tungsten oxide having a large particle size through an appropriate filter. Commercially available tungsten oxide may also be used.

Further, the tungsten oxide constituting the core particles 2, as long as it has a photocatalytic activity by irradiation of visible light, for _example, like _{WO 3, W 25 O 73,} W 20 O 58, W 24 O 68 .

(Cocatalyst 3)
The cocatalyst 3 is supported on the surface of the core particle 2. The cocatalyst 3 enhances the photocatalytic activity of the photocatalytic material 1A. The cocatalyst 3 is composed of a metal or a metal compound having an electron withdrawing property. Examples of the metal constituting the promoter 3 include copper, platinum, palladium, iron, silver, gold, nickel, ruthenium, iridium, niobium, and molybdenum. Examples of the metal compound constituting the promoter 3 include chloride, bromide, iodide, oxide, hydroxide, sulfate, nitrate, carbonate, phosphate, organic acid salt of the metal constituting the promoter 3. Etc.

  As a method for forming the promoter 3 on the surface of the core particle 2, (1) a method of kneading the tungsten oxide particles constituting the core particle 2 and the metal particles or metal compound particles constituting the promoter 3, (2 ) After adding the tungsten oxide particles constituting the core particle 2 to the solution containing the metal or the metal compound constituting the promoter 3, the obtained solution is heated or the obtained solution is irradiated with light to core particle 2 And a method of depositing a metal or a metal compound constituting the promoter 3 on the surface of the catalyst.

  The addition amount of the metal or metal compound constituting the promoter 3 (that is, the loading amount of the promoter 3 supported on the surface of the core particle 2) is 0. It is preferable that it is 01 to 3 weight%. When the promoter 3 is a metal compound, the amount of the metal compound added (the amount of the promoter 3 supported) indicates the amount of metal in the metal compound. When the amount of the metal or metal compound added is less than 0.01% by weight, the effect as the cocatalyst 3 is reduced, and high photocatalytic activity cannot be obtained. Further, when the amount of the metal or metal compound added is more than 3% by weight, the amount of the promoter 3 that covers the surface of the core particle 2 increases. As a result, the amount of light reaching the core particle 2 is reduced, so that high photocatalytic activity cannot be obtained.

(Impurity halogen)
The photocatalytic material 1A is doped with halogen. That is, the photocatalytic material 1A contains a halogen added as an n-type impurity. The halogen added as an n-type impurity may be contained in at least one of the core particle 2 or the cocatalyst 3 of the photocatalytic material 1 </ b> A, and is preferably contained in the core particle 2. The photocatalytic material 1A is preferably doped with at least one of chlorine, fluorine, bromine, and iodine, and more preferably doped with chlorine from the viewpoint of easy acquisition and handling of raw materials. .

  The method of doping the photocatalyst material 1A with halogen is not particularly limited, and examples thereof include a method of treating the core particle 2 or the core particle 2 supporting the promoter 3 with a nonmetallic halide. For example, the n-type impurity is added to the photocatalyst material 1A by a method in which the nonmetal halide is dissolved alone or in a suitable solvent, and the core particle 2 or the core particle 2 supporting the promoter 3 is immersed in the solution. Halogen can be added as

  In the present specification, the “non-metal halide” refers to a compound containing no metal element and containing at least one halogen element. In addition, the category of “non-metal halide” includes halogen alone (chlorine, fluorine, bromine, iodine, etc.).

  Examples of the nonmetal halide include hydrogen halide, hydrohalic acid, and ammonium halide. Examples of the hydrogen halide include hydrogen chloride, hydrogen fluoride, hydrogen bromide, and hydrogen iodide. Hydrohalic acid is an aqueous solution of hydrogen halide, and examples thereof include hydrochloric acid (hydrochloric acid), hydrogen fluoride (hydrofluoric acid), hydrogen bromide (odoric acid), and hydrogen iodide (iodic acid). It is done. Examples of the ammonium halide include ammonium chloride, ammonium fluoride, ammonium bromide, and ammonium iodide.

  As described above, the photocatalytic material 1A of the present embodiment contains halogen added as an n-type impurity. Thereby, the photocatalytic activity of the tungsten oxide photocatalytic material 1A can be enhanced. The principle of improving the photocatalytic activity of the photocatalytic material 1A is unknown. However, it is considered that the photocatalytic activity is improved by doping the halogen and improving the electrical conductivity of the photocatalytic material 1A. That is, the photocatalytic material 1A is an n-type semiconductor by being doped with halogen, which is an n-type impurity. Usually, in an n-type semiconductor, electrons from a donor are excited to a conduction band at about room temperature. For this reason, also in the photocatalytic material 1A doped with halogen, electrons from the doped halogen (donor) are excited to the conduction band of tungsten oxide (core particle 2). For this reason, in the photocatalyst material 1A, excited electrons exist before light irradiation (visible light irradiation). As a result, the presence of the electrons facilitates the electrons excited in the conduction band after light irradiation to the photocatalyst material 1A to flow to the promoter 3. Thereby, it is thought that the electrical conductivity of 1 A of photocatalyst materials improves, and photocatalytic activity improves. Therefore, the tungsten oxide photocatalyst material 1A having excellent photocatalytic activity under irradiation with visible light can be provided.

[Embodiment 2]
The following will describe another embodiment of the present invention with reference to FIG. FIG. 2 is a cross-sectional view schematically showing the photocatalytic material 1B according to the present embodiment. For convenience of explanation, members having the same functions as those described in the first embodiment are given the same reference numerals, and descriptions thereof are omitted.

  As shown in FIG. 2, the photocatalyst material 1B according to this embodiment is different from the photocatalyst material 1A of Embodiment 1 only in that the entire surfaces of the core particles 2 and the promoter 3 are covered with the shell layer 4. Is different.

  Also in the photocatalytic material 1B of the present embodiment, halogen is doped in the same manner as the photocatalytic material 1A of the first embodiment. The halogen added as an n-type impurity to the photocatalytic material 1B may be contained in at least one of the core particle 2, the promoter 3, and the shell layer 4, and is preferably contained in the core particle 2.

  The shell layer 4 completely covers the entire surface of the core particle 2 and the cocatalyst 3. The shell layer 4 is preferably composed of titanium oxide.

  If the thickness of the shell layer 4 is less than 1 nm, the surface of the core particle 2 and the surface of the cocatalyst 3 cannot be completely covered. On the other hand, when the thickness of the shell layer 4 is larger than 50 nm, the photocatalytic activity of the core particle 2 is lowered. Therefore, the thickness of the shell layer 4 is preferably 1 nm or more and 50 nm or less.

  The weight ratio of the shell layer 4 to the core particles 2 is preferably 1.0 or less, and more preferably 0.01 or more and 1.0 or less. Thereby, it becomes possible to provide photocatalyst material 1B which has alkali resistance and was excellent in photocatalytic activity. In addition, alkali resistance shows the residual rate of the photocatalyst material 1B after implementing an alkali-proof process. Specifically, when the weight of the photocatalyst material 1B before the alkali resistance treatment is Wa and the weight of the photocatalyst material 1A after the alkali resistance treatment is Wb, the alkali resistance is calculated by (Wa−Wb) / Wa × 100. Value. The alkali resistance treatment can be performed, for example, by immersing the photocatalytic material 1B in a 1 mol / L sodium hydroxide aqueous solution for 24 hours.

  When the shell layer 4 is a titanium oxide layer, the core particle 2 on which the promoter 3 is formed is coated with the shell layer 4 by oxidizing the core particle 2 on which the promoter 3 is formed in a solution in which the core particle 2 is dispersed. A method of growing a titanium oxide layer on the surface of the tungsten oxide particles that are the core particles 2 and the surface of the promoter 3 formed on the surface of the tungsten oxide particles by adding a solution containing a titanium precursor (so-called solution) Law). In such a solution method, the titanium oxide precursor is uniformly formed while gradually growing as a titanium oxide layer on the surfaces of the core particles 2 and the promoter 3 in the solution after the addition of the solution containing the titanium oxide precursor. To go. At this time, the formed titanium oxide layer may be amorphous.

  As the titanium oxide precursor, an alkoxide such as titanium tetraisopropoxide, a complex such as titanium acetylacetonate or titanium lactate, or an aqueous titanium solution such as an aqueous titanium chloride solution or an aqueous titanium sulfate solution is used.

  In Patent Document 1, a method of depositing a titanium oxide layer on the surface of tungsten oxide particles by adding tungsten oxide particles to a solution containing a titanium oxide precursor and volatilizing a solvent in the solution (so-called impregnation method). Is described. However, in the impregnation method, a titanium oxide precursor is attached to the surface of the core particle and then heated to form a titanium oxide layer. Therefore, the titanium oxide layer is not uniformly formed, and the surface of the core particle and the core particle are not formed. The surface of the supported promoter cannot be completely covered by the titanium oxide layer.

  When the shell layer 4 is a titanium oxide layer, it is preferably made of crystalline titanium oxide obtained by heat treatment after formation. This is because crystalline titanium oxide densifies shell layer 4 than non-crystalline titanium oxide. Thereby, the photocatalyst material 1B having the shell layer 4 made of crystalline titanium oxide has higher alkali resistance than the photocatalyst material having the shell layer 4 made of amorphous titanium oxide.

  As the crystalline titanium oxide constituting the shell layer 4, one of anatase type, rutile type, or a mixture thereof is suitable. Anatase-type titanium oxide is obtained by heating in the atmosphere at a temperature of 400 ° C. or higher. On the other hand, rutile-type titanium oxide is obtained by heating at a temperature of 900 ° C. or higher. However, even below the above temperature, anatase type and rutile type titanium oxide may be partially formed depending on the production conditions.

  As described above, the photocatalytic material 1B of the present embodiment includes the shell layer 4 that covers the surface of the core particle 2 and the entire surface of the promoter 3 in addition to the configuration of the photocatalytic material 1A. Thus, in addition to the effect exhibited by the photocatalytic material 1A, it is possible to provide a tungsten oxide-based photocatalytic material 1B having higher alkali resistance than the conventional photocatalytic material in which a portion of the tungsten oxide surface not covered with titanium oxide is present. It becomes possible.

  Further, when the shell layer 4 is a titanium oxide layer, it is possible to provide the photocatalytic material 1B that exhibits photocatalytic activity even by irradiation with ultraviolet light.

[Embodiment 3]
Next, still another embodiment of the present invention will be described with reference to FIG. FIG. 3 is a cross-sectional view schematically showing the photocatalytic material 1C according to the present embodiment. As in the case of the second embodiment, for the sake of convenience of explanation, members having the same functions as those described in the first and second embodiments are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 3, the photocatalytic material 1 </ b> C according to the present embodiment is different from the photocatalytic material 1 </ b> A according to the first embodiment in that the core particle 2 a is provided instead of the core particle 2. In the photocatalyst material 1C of the present embodiment, halogen is doped as in the photocatalyst materials 1A and 1B of the first and second embodiments. The halogen added to the photocatalyst material 1C as an n-type impurity may be contained in at least one of the core particle 2a or the cocatalyst 3, and is preferably contained in the core particle 2a.

  The core particle 2a is composed of a composite of tungsten oxide and metal oxide. Metal oxides constituting the composite are titanium oxide, iron oxide, zinc oxide, copper oxide, platinum oxide, palladium oxide, silver oxide, gold oxide, nickel oxide, ruthenium oxide, iridium oxide, niobium oxide, and molybdenum oxide. Mention may be made of one or more oxides selected from the group consisting of: The metal oxide preferably absorbs light in a wavelength region different from that of tungsten oxide, and is one or more oxides selected from the group consisting of titanium oxide, iron oxide, and zinc oxide. Is more preferable. That is, the core particle 2a may contain one type of metal oxide or a plurality of types of metal oxides in addition to tungsten oxide.

  The particle diameter of the core particle 2a is preferably 5 nm or more and 100 nm or less, similarly to the particle diameter of the core particle 2 in the photocatalytic material 1A of Embodiment 1. When the particle size is smaller than 5 nm, the particles tend to aggregate, and when the particle size is larger than 100 nm, the photocatalytic activity decreases.

  The metal oxide constituting the core particle 2a of the composite is preferably larger than 0.01% by weight and smaller than 100% by weight with respect to tungsten oxide. When the content is less than 0.01% by weight, the mixing effect of the metal oxide does not appear, and when the content is more than 100% by weight, the mixing effect of the tungsten oxide does not appear.

  In the mixture of tungsten oxide and metal oxide constituting the core particle 2a, the metal oxide can absorb a wavelength of light different from that of tungsten oxide. Specifically, the absorption edge of tungsten oxide is around 460 nm. For this reason, when the metal oxide is titanium oxide or the like, it is possible to provide a photocatalytic material 1C that exhibits photocatalytic activity even when irradiated with ultraviolet light. On the other hand, when the metal oxide is copper oxide or the like, the absorption edge is around 620 nm, which extends to a longer wavelength region than tungsten oxide. Therefore, the core particle 2a can absorb light in a longer wavelength region than the core particle 2 made of tungsten oxide alone. For this reason, it becomes possible to improve the photocatalytic activity of the photocatalyst material 1C during visible light irradiation.

  As a method for producing a composite of tungsten oxide and a metal oxide other than tungsten oxide, a method of kneading tungsten oxide particles and metal oxide particles, or adding tungsten oxide particles to a metal oxide precursor solution, Examples include a method of volatilizing the solvent in the solution.

  A photocatalyst material 1C is obtained by forming the cocatalyst 3 on the produced core particle 2a by the method described in the first embodiment.

  As described above, the photocatalytic material 1C of the present embodiment includes the core particles 2a different from the photocatalytic material 1A, and the core particles 2a are made of a metal oxide other than tungsten oxide in addition to tungsten oxide. Thereby, in addition to the effect which 1A of photocatalyst materials show | play, the light of a wavelength of a wider range can be absorbed. Therefore, it is possible to provide the photocatalyst material 1C having a wavelength different from that of the photocatalyst materials 1A and 1B of Embodiments 1 and 2 and exhibiting photocatalytic activity.

[Embodiment 4]
The following will describe another embodiment of the present invention with reference to FIG. FIG. 4 is a cross-sectional view schematically showing the photocatalytic material 1D according to the present embodiment. For convenience of explanation, members having the same functions as those described in the first to third embodiments are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 4, the photocatalyst material 1D according to this embodiment is different from the photocatalyst material 1C of Embodiment 3 only in that the entire surfaces of the core particles 2a and the promoter 3 are covered with the shell layer 4. Is different.

  Also in the photocatalyst material 1D of the present embodiment, halogen is doped in the same manner as the photocatalyst materials 1A, 1B, and 1C of the first to third embodiments. The halogen added to the photocatalyst material 1D as an n-type impurity may be contained in at least one of the core particle 2a, the promoter 3 and the shell layer 4, and is preferably contained in the core particle 2.

  The shell layer 4 completely covers the entire surfaces of the core particles 2a and the cocatalyst 3 as in the photocatalytic material 1B of the second embodiment. The shell layer 4 is preferably composed of titanium oxide.

  As described above, the photocatalytic material 1D of the present embodiment includes the shell layer 4 that covers the surface of the core particle 2a and the entire surface of the promoter 3 in addition to the configuration of the photocatalytic material 1C. Thus, in addition to the effect exhibited by the photocatalytic material 1C, it is possible to provide a tungsten oxide-based photocatalytic material 1D having higher alkali resistance than the conventional photocatalytic material in which a portion of the tungsten oxide surface not covered with titanium oxide is present. It becomes possible.

  Further, when the shell layer 4 is a titanium oxide layer, it is possible to provide a photocatalytic material 1D that exhibits photocatalytic activity even when irradiated with ultraviolet light.

[Summary]
Photocatalyst materials 1A to 1D according to aspect 1 of the present invention are photocatalyst materials 1A to 1D including core particles 2 and 2a containing tungsten oxide and promoter 3 supported on the surfaces of the core particles 2 and 2a. It is characterized by being doped with halogen.

  According to said invention, the halogen added as an n-type impurity is contained. Thereby, the photocatalytic activity of the tungsten oxide photocatalytic material 1A can be enhanced.

  In the photocatalyst materials 1A to 1D according to aspect 2 of the present invention, in the above aspect 1, the core particles 2 and 2a are composed of tungsten oxide particles, or tungsten oxide particles and a metal oxide other than tungsten oxide. And a complex.

  According to said invention, when the core particle 2 consists of a tungsten oxide particle, the composition of a photocatalyst material can be simplified. On the other hand, when the core particle is formed of a composite of tungsten oxide and metal oxide, the metal oxide absorbs light having a wavelength different from that of tungsten oxide. Accordingly, it is possible to absorb light in a wider range of wavelengths and exhibit a photocatalytic action.

  In the photocatalyst materials 1B and 1D according to the aspect 3 of the present invention, it is preferable that the aspect 1 or 2 includes the shell layer 4 that covers the entire surface of the core particles 2 and 2a and the promoter 3.

  According to the above invention, it becomes possible to provide tungsten oxide photocatalyst materials 1B and 1D having higher alkali resistance than conventional photocatalyst materials in which a portion of the tungsten oxide surface not coated with titanium oxide is present.

  In the photocatalyst materials 1B and 1D according to the fourth aspect of the present invention, in the third aspect, the shell layer 4 is preferably made of titanium oxide.

  According to said invention, since the shell layer 4 is a titanium oxide layer, it becomes possible to provide photocatalyst material 1B, 1D which shows photocatalytic activity also by irradiation of an ultraviolet light.

  In the photocatalyst materials 1A to 1D according to the fifth aspect of the present invention, in the first to fourth aspects, the doped halogen may be chlorine.

  According to the above invention, since the doped halogen is chlorine, it is possible to provide a photocatalytic material that is easily available and easy to handle.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention. Furthermore, a new technical feature can be formed by combining the technical means disclosed in each embodiment.

(Experimental example 1)
Disperse tungsten oxide particles by dispersing 135 g of commercially available tungsten oxide (Kishida Chemical, 99.9%) in 1215 g of ion-exchanged water, followed by pulverization and dispersion using a bead mill (Nihon Coke Industries, MSC50). A liquid was obtained. The operation conditions of the bead mill apparatus were a bead diameter of 0.1 mm (Nikkato), a peripheral speed of 10 m / s, and a processing time of 360 minutes.

  Subsequently, hexachloroplatinum (VI) hexahydrate was added to the obtained dispersion of tungsten oxide particles so that the weight ratio of platinum alone to the weight of tungsten oxide particles was 0.025 wt%. The product (Kishida chemistry, 98.5%) was dissolved. Thereafter, the dispersion is heated at 100 ° C. to evaporate water, and then calcined at 400 ° C. for 30 minutes, whereby tungsten oxide particles (core) supporting 0.025 wt% platinum (promoter) are supported. Particles).

  An aqueous solution (hydrochloric acid) obtained by diluting the obtained tungsten oxide particles supporting platinum with a ratio of 2.5 mL of hydrochloric acid (Kishida Chemical, 35.0%) and 5 mL of ion-exchanged water per 1 g of tungsten oxide particles supporting platinum. : Volume ratio of ion-exchanged water = 1: 2), and then water was evaporated by heating to 100 ° C. As a result, a photocatalytic material in which tungsten oxide particles carrying platinum were doped with chlorine as a halogen was obtained.

Next, the photocatalytic activity (decomposition rate constant) was measured using the following method in order to evaluate the photocatalytic activity of the obtained photocatalytic material due to visible light irradiation of environmental pollutants. First, 1.3 g of the obtained photocatalytic material was put in a petri dish, the petri dish was put in a 5 L gas bag, and acetaldehyde was further introduced into the gas bag so as to have a concentration of 500 ppm. Thereafter, the gas bag was irradiated with a blue LED (wavelength: 450 nm, irradiation intensity of the photocatalyst material: 7 mW / cm ² ), and the change over time in the residual amount of acetaldehyde was measured with a gas detector tube. The logarithmic display of the measured residual amount of acetaldehyde was taken on the vertical axis, the elapsed time on the horizontal axis, the magnitude of the gradient of the graph was calculated, and the value was defined as the decomposition rate constant. Based on the value of the decomposition rate constant, the gas decomposition performance, that is, the photocatalytic activity of the photocatalytic material was evaluated.

  The decomposition rate constant of the photocatalyst material obtained in Experimental Example 1 was 3.84 [/ h].

(Experimental example 2)
Except for immersing 1 g of tungsten oxide particles carrying platinum in an aqueous solution (hydrochloric acid: ion exchanged water volume ratio = 1: 20) diluted with 0.25 mL of hydrochloric acid and 5 mL of ion exchanged water, In the same manner as in Experimental Example 1, a photocatalytic material in which platinum as a tungsten oxide particle on which chlorine was doped as a halogen was obtained.

  Next, the measurement and evaluation of the photocatalytic activity (decomposition rate constant) of the obtained photocatalytic material by the visible light irradiation of the environmental pollutant were also performed in the same manner as in Experimental Example 1. As a result, the obtained decomposition rate constant was 3.07 [/ h].

(Experimental example 3)
Except for immersing 1 g of tungsten oxide particles supporting platinum in an aqueous solution (hydrochloric acid: ion-exchanged water volume ratio = 1: 4) diluted with 1.25 mL of hydrochloric acid and 5 mL of ion-exchanged water, In the same manner as in Experimental Example 1, a photocatalytic material in which platinum as a tungsten oxide particle on which chlorine was doped as a halogen was obtained.

  Next, the measurement and evaluation of the photocatalytic activity (decomposition rate constant) of the obtained photocatalytic material by the visible light irradiation of the environmental pollutant were carried out in the same manner as in Experimental Example 1. As a result, the obtained decomposition rate constant was 3.33 [/ h].

(Experimental example 4)
Experiments were conducted except that 1 g of tungsten oxide particles carrying platinum was immersed in an aqueous solution (hydrochloric acid: ion-exchanged water volume ratio = 1: 1) diluted with 5 mL of hydrochloric acid and 5 mL of ion-exchanged water. In the same manner as in Example 1, a photocatalytic material in which platinum as a tungsten oxide particle doped with chlorine as a halogen was obtained.

  Next, the measurement and evaluation of the photocatalytic activity (decomposition rate constant) of the obtained photocatalytic material by the visible light irradiation of the environmental pollutant were also performed in the same manner as in Experimental Example 1. As a result, the obtained decomposition rate constant was 3.59 [/ h].

(Comparative Example 1)
A photocatalytic material was prepared using the same method as in Experimental Example 1 except that immersion using hydrochloric acid was not performed, and a photocatalytic material composed of tungsten oxide particles carrying platinum not doped with chlorine was obtained. As a result of analyzing the composition of the obtained photocatalytic material, chlorine was not detected.

  Next, the measurement and evaluation of the photocatalytic activity (decomposition rate constant) of the obtained photocatalytic material by the visible light irradiation of the environmental pollutant were carried out in the same manner as in Experimental Example 1. As a result, the obtained decomposition rate constant was 3.24 [/ h].

  The measurement results in the above Experimental Examples 1 to 4 and Comparative Example 1 are summarized in the graph shown in FIG. FIG. 5 plots the vertical axis as the decomposition rate constant and the horizontal axis as the amount of hydrochloric acid added during the immersion of tungsten oxide. Moreover, the chlorine concentration of the photocatalyst material obtained in Experimental Example 1, Experimental Example 4 and Comparative Example 1 was relatively measured using TOF-SIMS. The measurement results are summarized in FIG. Although the absolute concentration of chlorine contained in each photocatalytic material is unknown, the amount of hydrochloric acid added is 5 mL of photocatalytic material (Experimental Example 4) than that of 2.5 mL of photocatalytic material (Experimental Example 1). On the other hand, the relative concentration of hydrochloric acid contained in the photocatalytic material is increased. It is considered that the intensity indicating the relative concentration of hydrochloric acid was detected even in the photocatalyst material with 0 mL of hydrochloric acid added because of the background.

  5 and 6, the photocatalytic activity (decomposition rate constant) of the photocatalyst material doped with chlorine (Experimental Examples 1 to 4) is higher than that of the photocatalyst material not doped with chlorine (Comparative Example 1). You can see that As for the amount of hydrochloric acid added, it was found that a photocatalytic material in which the amount of hydrochloric acid added was 1.5 mL or more with respect to 1 g of tungsten oxide particles showed particularly excellent photocatalytic activity. In addition, although the decomposition rate constant of the photocatalyst material (experimental example 2) whose hydrochloric acid addition amount is 0.25 mL is a little lower value than the photocatalyst material (comparative example 1) to which hydrochloric acid is not added, This is thought to be due to variations in measurement. That is, when the addition amount of hydrochloric acid is a small amount (less than 1.25 mL), the effect of the present invention that the photocatalytic activity of the photocatalytic material is improved by doping with halogen (chlorine) appears so remarkably. However, if the addition amount of hydrochloric acid is 1.25 mL or more, it is considered that the effect of the present invention is remarkably exhibited.

(Experimental example 5)
A dispersion containing tungsten oxide particles was obtained in the same manner as in Experimental Example 1. Subsequently, hexachloroplatinum (VI) hexahydrate was added to the obtained dispersion of tungsten oxide particles so that the weight ratio of platinum alone to the weight of tungsten oxide particles was 0.025 wt%. The product (Kishida chemistry, 98.5%) was dissolved. Thereafter, the dispersion was heated at 100 ° C. to evaporate water, and then baked at 400 ° C. for 30 minutes. As a result, tungsten oxide particles carrying 0.025% by weight of platinum with respect to the weight of the tungsten oxide particles were obtained.

  6 g of the obtained tungsten oxide particles carrying platinum were added to 24 g of ion-exchanged water, and the above-mentioned tungsten oxide particles carrying platinum were dispersed using a stirrer (Primix Co., Ltd., Filmix 40-40 type). Went. The operating conditions of the agitator were a peripheral speed: 40 m / s and a processing time of 10 minutes.

  Next, in order to form a shell layer composed of titanium oxide, 9 mL of the above dispersion, 7 mL of titanium tetrachloride aqueous solution having a titanium concentration of 16% by weight (Toho Titanium), and 100 mL of ion-exchanged water are round-bottomed. After mixing in a flask to obtain a mixed solution, the obtained mixed solution was heated for 5 hours at a temperature of 95 ° C. using a mantle heater for a round bottom flask.

  Then, after separating the powder by centrifuging at 9000 rpm for 5 minutes with respect to the heated mixed liquid, the pH of the separated liquid part was measured. As a result, it was larger than -1 and smaller than 0. . Thereafter, the mixed liquid was heated at 100 ° C. for 1 h to evaporate the separated liquid, and the separated powder was dried. As a result, a powder of tungsten oxide particles carrying platinum supported by a shell layer made of titanium oxide was obtained.

  The obtained powder was baked at 400 ° C. for 30 minutes in the atmosphere to obtain a photocatalytic material composed of tungsten oxide particles carrying platinum and covered with a shell layer made of titanium oxide.

  As a result of the composition analysis of the photocatalyst material obtained in Experimental Example 5, tungsten was 5.8 atomic%, titanium was 24.5 atomic%, oxygen was 68.8 atomic%, and chlorine was 0.9 atomic%. there were.

  Further, the measurement and evaluation of the photocatalytic activity (decomposition rate constant) of the obtained photocatalytic material by the visible light irradiation of the environmental pollutant were performed in the same manner as in Experimental Example 1. As a result, the obtained decomposition rate constant was 3.8 [/ h].

(Experimental example 6)
After separating the powder using centrifugation, the supernatant was discarded, ion-exchanged water was added, and the powder was separated again using centrifugation, whereby the process of washing the powder was repeated three times. Except for the above, a photocatalytic material composed of tungsten oxide particles carrying platinum and coated with a titanium oxide shell was obtained in the same manner as in Experimental Example 5. Further, as a result of measuring the pH of the dispersion after the final washing, the pH of the dispersion after the final washing was 3.

  Since the pH value of the dispersion liquid measured in Experimental Example 6 is larger than the pH value of the dispersion liquid after the final washing measured in Experimental Example 5, the photocatalyst material of Experimental Example 6 is used. It can be seen that the amount of doped halogen (chlorine) is less than that of the photocatalytic material obtained in Experimental Example 5 by repeating the above washing step.

  The measurement and evaluation of the photocatalytic activity (decomposition rate constant) of the obtained photocatalytic material by the visible light irradiation of the environmental pollutant were performed in the same manner as in Experimental Example 1. As a result, the obtained decomposition rate constant was 3.4 [/ h].

(Comparative Example 2)
After separating the powder using centrifugation, discarding the supernatant, adding ion-exchanged water, and again separating the powder using centrifugation, the process of washing the powder is repeated 9 times. Except for the above, a photocatalytic material composed of tungsten oxide particles carrying platinum and coated with a titanium oxide shell was obtained using the same method as in Experimental Example 5. Further, as a result of measuring the pH of the dispersion after the final washing, the pH of the dispersion after the final washing was 7.

  As a result of analyzing the composition of the obtained photocatalyst material, chlorine was not detected.

  Further, the measurement and evaluation of the photocatalytic activity (decomposition rate constant) of the obtained photocatalytic material by the visible light irradiation of the environmental pollutant were performed in the same manner as in Experimental Example 1. As a result, the obtained decomposition rate constant was 2.8 [/ h].

  As described above, from the results of Experimental Examples 5 and 6 and Comparative Example 2, the tungsten oxide particles carrying platinum particles are used as core particles, and the surface is composed of the core particle surface and the titanium oxide shell layer covering the entire surface of the platinum particles. In addition, it was confirmed that the photocatalytic material in which the shell layer or the shell layer and the core particle are doped with chlorine exhibits high photocatalytic activity when the photocatalytic material is doped with chlorine.

  Since the present invention shows high catalytic activity for visible light, it can be used for visible light responsive photocatalytic functional products. The photocatalytic functional product includes a photocatalyst layer formed of the photocatalytic material of the present invention on the surface of a base material, and has a function of adsorbing environmental pollutants and decomposing and removing them with visible light. Specifically, building materials such as ceiling materials, tiles, glass, wallpaper, wall materials, floors, and interior materials for automobiles, home appliances such as refrigerators and air conditioners, and textile products such as clothes and curtains can be used.

1A, 1B, 1C, 1D Photocatalytic material 2, 2a Core particle 3 Promoter catalyst 4 Shell layer

Claims (5)

In a photocatalytic material comprising core particles containing tungsten oxide and a promoter supported on the surface of the core particles,
A photocatalytic material, which is doped with halogen.   2. The photocatalytic material according to claim 1, wherein the core particles are composed of tungsten oxide particles, or are composed of a composite of tungsten oxide particles and a metal oxide other than tungsten oxide. .   The photocatalyst material according to claim 1 or 2, further comprising a shell layer that covers the entire surface of the core particles and the promoter.   The photocatalytic material according to claim 3, wherein the shell layer is made of titanium oxide.   The photocatalytic material according to any one of claims 1 to 4, wherein the doped halogen is chlorine.

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