JP2018140358A - Photocatalysis functional member and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photocatalysis functional member capable of improving visible light responsivity.SOLUTION: A photocatalysis functional member 10 comprises: a base material 11; and a surface layer 12 formed on the surface of the base material, and has a rutile type titanium oxide crystal as a main phase, or has a rutile type titanium oxide crystal and a brookite type titanium oxide crystal as main phases, and includes a noble metal. The noble metal included in the surface layer 12 preferably forms nanoparticles 12A. The photocatalysis functional member 10 may further comprise an intermediate layer 13 between the base material 11 and the surface layer 12. The noble metal is at least one kind selected from Au, Ag, Pt and Pd. An amount of the noble metal included in the surface layer 12 is 0.007 at% or more of a total amount of the titanium and the noble metal included in the surface layer 12, an average particle diameter of the nanoparticles 12A is preferably 100 nm or less, in the photocatalysis functional member 10.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a photocatalytic functional member and a method for producing the same.

TiO ₂ (titania), which is an oxide of Ti, exhibits photocatalytic activity, that is, photoinduced organic matter resolution and photoinduced hydrophilicity. Although elements added to the photocatalytic activity increase of the TiO ₂ is effective, when the Au is noble metal element was supported metal nanoparticles also can improve the visible light responsive properties of the TiO ₂ by surface plasmon resonance (SPR) Is known (see, for example, Non-Patent Document 1).

X.Z. Li and F.B.Li: Environ. Sci. Technol. 35 (2001) 2381-2387.

  The objective of this invention is providing the photocatalyst functional member which can improve visible light responsiveness, and its manufacturing method.

  In order to solve the above-mentioned problems, the first invention is a base material and formed on the surface of the base material, and has a rutile type titanium oxide crystal as a main phase, or a rutile type titanium oxide crystal and brookite. It is a photocatalytic functional member comprising a surface layer containing a noble metal as a main phase with a titanium oxide crystal of a type.

  2nd invention is a manufacturing method of the photocatalyst functional member including the process of thermally oxidizing the base material containing titanium and a noble metal in the atmosphere containing oxygen.

  According to the present invention, the visible light response of the photocatalytic functional member can be improved.

FIG. 1 is a cross-sectional view showing an example of the configuration of a photocatalytic functional member according to an embodiment of the present invention. FIG. 2 is a diagram showing α-2θ XRD patterns of atmospheric oxidized TiO ₂ films of Examples 1 to 4 and Comparative Examples 1 and ₂ . 3A is a cross-sectional STEM image of the atmospheric oxidized TiO ₂ film of Example 4. FIG. FIG. 3B is a cross-sectional STEM image of the atmospheric oxidized TiO ₂ film of Example 3. FIG. 4 is a table summarizing the analysis results by α-2θ XRD and the cross-sectional observation results by STEM of the atmospheric oxidized TiO ₂ films of Examples 1 to 4 and Comparative Examples 2 and 3. FIG. 5 is a diagram showing α-2θ XRD patterns of the two-stage thermally oxidized TiO ₂ films of Comparative Examples 6-8. 6A is a cross-sectional TEM image of the two-stage thermally oxidized TiO ₂ film of Comparative Example 8. FIG. 6B is a diagram showing an Au4fXPS spectrum of the two-stage thermally oxidized TiO ₂ film of Comparative Example 8. FIG. FIG. 7 is a chart collectively showing the analysis results by α-2θ XRD and the cross-sectional observation results by TEM of the two-stage thermally oxidized TiO ₂ films of Comparative Examples 6, 7, 9, and 10. FIG. 8 is a graph showing changes in the water contact angle of the atmospheric oxidized TiO ₂ films of Examples 1 and 2, Comparative Examples 2 and 3, and the pure Ti substrate of Comparative Example 4. FIG. 9 is a graph showing changes in water contact angles of the atmospheric oxidized TiO ₂ films of Examples 1, 3, and 4 and the pure Ti substrate of Comparative Example 4. FIG. 10 is a graph showing changes in the water contact angle of the atmospheric oxidized TiO ₂ films of Examples 5 and 6 and Comparative Example 11. FIG. 11 is a graph showing changes in water contact angles of the two-stage thermally oxidized TiO ₂ films of Comparative Examples 6 and 8, the pure Ti substrate of Comparative Example 4, and the Ti—Au alloy substrate of Comparative Example 5. FIG. 12 is a graph showing changes in the water contact angle of the two-stage thermally oxidized TiO ₂ films of Comparative Examples 6, 7, 9, and 10 and the pure Ti substrate of Comparative Example 4. FIG. 13A is a graph for explaining how to obtain the initial contact angle half-life time t _1/2 . FIG. 13B shows the measurement results of the initial contact angle half-time t _1/2 of the TiO ₂ films of Examples 1 to 4, Comparative Examples 2, 3, 6, 7, 9, and 10 and the pure Ti substrate of Comparative Example 4. It is a graph to show. FIG. 14A is a graph showing the relationship between the Au content in the vicinity of the surface of the atmospheric oxidized TiO ₂ film of Examples 1 to 4 and Comparative Example 3 and the initial contact angle half-time t _1/2 . FIG. 14B is a graph showing the relationship between the total amount of Au and C in the vicinity of the surface of the two-stage thermally oxidized TiO ₂ film of Comparative Examples 6, 7, 9, and 10 and the initial contact angle half time t _1/2 . FIG. 15A is a graph showing the relationship between the average particle diameter of Au nanoparticles in the atmospheric oxidized TiO ₂ film of Examples 3 and 4 and the initial contact angle half time t _1/2 . FIG. 15B shows the average particle diameter and initial contact angle half-time t ₁ of Au nanoparticles on the surfaces of the atmospheric oxidized TiO ₂ films of Examples 1, ₂ , and 4 and the two-stage thermally oxidized TiO ₂ films of Comparative Examples 9 and 10. It is a graph which shows the relationship with _{/ 2} . FIG. 16 is a graph showing the antibacterial test results of the atmospheric oxidation TiO ₂ film of Example 1, the two-stage thermal oxidation TiO ₂ film of Comparative Examples 6 and 9, the pure Ti substrate of Comparative Example 4, and the SiO ₂ substrate. It is.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Configuration of photocatalytic functional member]
As shown in FIG. 1, the photocatalytic functional member 10 according to an embodiment of the present invention is formed on a base material 11 and the surface of the base material 11, and has a rutile type titanium oxide crystal as a main phase. Or a surface layer 12 containing a rutile-type titanium oxide crystal and a brookite-type titanium oxide crystal as a main phase and containing a noble metal. The photocatalytic functional member 10 may further include an intermediate layer 13 provided between the base material 11 and the surface layer 12.

(Base material)
Examples of the shape of the base material 11 include a polyhedron shape such as a plate shape and a cubic shape, a columnar shape such as a spherical shape and a columnar shape, and an indefinite shape, but are not particularly limited to these shapes. Further, examples of the shape of the surface of the substrate 11 on which the surface layer 12 is provided include a planar shape, a curved surface shape, an uneven surface shape, or an indefinite shape, but are not particularly limited to these shapes. .

  The base material 11 contains titanium and a noble metal. The noble metal is preferably at least one of gold, silver, platinum and palladium. The content of the noble metal contained in the substrate 11 is preferably 2 atomic% (hereinafter referred to as “at%”) or more, more preferably 3 at%, even more preferably 4 at% or more, and particularly preferably 5 at% or more. When the content of the noble metal is 2 at% or more, the surface layer 12 having excellent visible light responsiveness can be formed on the substrate 11 by the atmospheric oxidation treatment described later. The upper limit of the content of the noble metal contained in the substrate 11 is not particularly limited, but from the viewpoint of reducing the cost of the photocatalytic functional member 10, it is preferably 20 at% or less, more preferably 15 at% or less, Even more preferably, it is 12 at% or less, and particularly preferably 10 at% or less.

  The content of the noble metal contained in the substrate 11 is a value measured by ICP mass spectrometry (ICP-MS).

(Surface layer)
The noble metal contained in the surface layer 12 is preferably at least one of gold, silver, platinum and palladium. The at% (Mb / (Mb + Ma) × 100) of the amount Mb of the noble metal contained in the surface layer 12 with respect to the total amount Ma of the noble metal and titanium contained in the surface layer 12 is preferably 0.007, more preferably 0.098. That's it. When the at% (Mb / (Mb + Ma) × 100) is 0.007 or more, the surface layer 12 having excellent visible light response can be obtained. The upper limit value of the above at% (Mb / (Mb + Ma) × 100) is not particularly limited, but is, for example, 1 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, or 0 .5 or less.

  The content of the noble metal contained in the surface layer 12 is a value measured by XPS (X-ray Photoelectron Spectroscopy).

  The noble metal contained in the surface layer 12 preferably constitutes the nanoparticles 12A. When the surface layer 12 includes the nanoparticles 12A, the nanoparticles exhibit surface plasmon resonance by the visible light irradiation on the surface layer 12, and electrons are excited in the nanoparticles 12A. The excited electrons move into the titanium oxide and cause the photocatalytic reaction to proceed. Therefore, excellent visible light responsiveness can be realized.

  The nanoparticles 12A may exist on the entire surface layer 12, may be localized on the surface of the surface layer 12, or may be localized on the surface of the surface layer 12 and in the vicinity thereof. The nanoparticles 12 </ b> A may have a concentration distribution in the thickness direction of the surface layer 12. When the nanoparticles 12A have a concentration distribution, the concentration of the nanoparticles 12A on or near the surface of the surface layer 12 is preferably higher than the concentration of the nanoparticles 12A inside the surface layer 12. Specifically, it is preferable that the concentration of the nanoparticles 12 </ b> A is highest at the surface of the surface layer 12 or in the vicinity thereof, and decreases from the surface of the surface layer 12 in the thickness direction. When the surface of the surface layer 12 is irradiated with light, the nanoparticles 12A included in or near the surface of the surface layer 12 are more likely to exhibit surface plasmon resonance than the nanoparticles 12A included in the surface layer 12. For this reason, when the density | concentration of the nanoparticle 12A of the surface of the surface layer 12 or its vicinity is high as mentioned above, the further outstanding visible light responsiveness will be acquired. Here, the vicinity of the surface layer 12 refers to a range of a depth of 500 nm from the surface of the surface layer 12.

The noble metal contained in the surface layer 12 is preferably dissolved in the surface layer 12. In this way, the precious metal is in a solid solution, so that excitation of electrons becomes easy and excellent visible light response can be realized. For example, gold, silver, platinum, and palladium are dissolved in the surface layer 12 as Au ³⁺ ions, Ag ⁺ ions, Pt ²⁺ ions, and Pd ²⁺ ions, respectively. From the viewpoint of improving the visible light responsiveness, it is preferable that the surface layer 12 includes the noble metal nanoparticles 12 </ b> A and includes a solid solution noble metal.

  The average particle diameter of the nanoparticles 12A is preferably 100 nm or less, more preferably 60 nm or less, still more preferably 50 nm or less, and particularly preferably 40 nm or less. When the particle diameter of the nanoparticles 12A exceeds 100 nm, the absorption spectrum intensity decreases, and there is a possibility that it becomes difficult to make visible light response by surface plasmon resonance.

  The average particle diameter of the nanoparticles 12A is obtained as follows. First, a cross-sectional thin piece of the photocatalytic functional member 10 is prepared by ion milling or the like, and a cross-sectional STEM (Scanning Transmission Electron Microscope) image is acquired. Next, 20 nanoparticles 12A are randomly selected from the acquired cross-sectional STEM image, and the particle size (diameter) of these nanoparticles 12A is obtained from the STEM image. Further, the particle diameter (diameter) of the nanoparticles 12A existing on the surface is obtained from an SEM (Scanning Electron Microscope) image. Here, when the nanoparticles 12A are not spherical, the largest one (the so-called maximum ferret diameter) of the distances between two parallel lines drawn from all angles so as to contact the contour of the nanoparticles 12A is selected. The particle size is 12A. Subsequently, the average particle diameter of the 20 nanoparticles 12A is simply averaged (arithmetic average) to determine the average particle diameter of the nanoparticles 12A.

(Middle layer)
The intermediate layer 13 is a noble metal rich layer containing a noble metal as a main component or an intermetallic compound layer with Ti.

[Method for producing photocatalytic functional member]
Next, an example of a method for producing a photocatalytic functional member according to an embodiment of the present invention will be described.

  First, the base material 11 containing titanium and a noble metal is produced. Next, this base material 11 is conveyed to a heating furnace, and the base material 11 is thermally oxidized in an atmosphere containing oxygen. Thereby, the surface layer 12 is formed on the base material 11. At this time, the nanoparticles 12A may be generated on the surface layer 12, the noble metal may be dissolved in the surface layer 12, the nanoparticles 12A may be generated on the surface layer 12, and the noble metal may be dissolved. May be.

  The temperature of the thermal oxidation treatment is, for example, 673K or more and 1073K or less. Here, the temperature of the thermal oxidation treatment is the surface temperature of the substrate 11. The time for the thermal oxidation treatment is, for example, 86.4 ks or less. The lower limit value of the time for the thermal oxidation treatment is not particularly limited as long as it is larger than 0 ks. However, for example, it is 0.1 ks or more or 0.3 ks or more. The thermal oxidation treatment may be performed by holding the base material 11 in the heating furnace for a certain period of time, or may be performed by passing the base material 11 through the heating furnace.

  The atmosphere containing oxygen may be an air atmosphere, an oxygen atmosphere (an atmosphere having an oxygen concentration of 100%), or a mixed gas atmosphere containing oxygen and a gas other than oxygen. The gas other than oxygen preferably contains at least one of inert gases such as argon. The mixing ratio of oxygen and a gas other than oxygen (oxygen: gas other than oxygen) is, for example, 0.1 vol%: 99.9 vol% to 100 vol%: 0 vol%, or 1 vol%: 99 vol% to 100 vol%: 0 vol% is there.

[effect]
In the photocatalytic functional member 10 according to one embodiment of the present invention, the surface layer 12 is mainly composed of a rutile type titanium oxide crystal or a rutile type titanium oxide crystal and a brookite type titanium oxide crystal. Since the phase contains a noble metal, the visible light responsiveness of the photocatalytic functional member can be improved. Moreover, the antibacterial property under visible light irradiation can also be expressed.

  In the method for producing a photocatalytic functional member according to an embodiment of the present invention, a rutile-type titanium oxide crystal is used as a main phase by thermally oxidizing the substrate 11 containing titanium and a noble metal in an atmosphere containing oxygen. Alternatively, the surface layer 12 having a rutile type titanium oxide crystal and a brookite type titanium oxide crystal as a main phase can be formed on the substrate 11. Therefore, a photocatalytic functional member having visible light responsiveness can be provided by a simple and inexpensive process.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited only to these Examples.

  In this example, the Au content in the Ti—Au alloy substrate and the Ag content in the Ti—Ag alloy substrate are values measured by ICP-MS.

  In this example, the samples of Examples 1 to 6 and Comparative Examples 1 to 11 may be indicated by the sample names shown in the remarks column of Tables 1 and 2.

[Example 1]
First, pure Ti (CP Ti (Commercially Pure Titanium)) and Au were prepared as raw materials, and a Ti-5 at% Au alloy ingot was produced by arc melting. Next, this ingot was hot-rolled, cut into a square shape or a circular shape, and then one side was mirror-polished to obtain a Ti-Au alloy substrate having a thickness of 1 mm.

Subsequently, a Ti-5 at% Au alloy substrate is placed on a SiO ₂ board, and the surface of the Ti-5 at% Au alloy substrate is air-oxidized in a muffle furnace, whereby a TiO ₂ film (hereinafter referred to as TiO ₂ formed by air oxidation). _Two films were referred to as “atmospheric oxidized TiO ₂ films”. At this time, the temperature of the oxidation treatment was set to 873 K and the time was set to 1.8 ks. Here, the temperature of the oxidation treatment is the temperature at the surface of the Au alloy substrate. As a result, the intended photocatalytic functional member was obtained.

[Example 2]
A photocatalytic functional member was obtained in the same manner as in Example 1 except that an ingot of a Ti-10 at% Au alloy was produced by arc melting.

[Example 3]
A photocatalytic functional member was obtained in the same manner as in Example 1 except that the temperature of the atmospheric oxidation treatment was 673 K and the time was 86.4 ks.

[Example 4]
A photocatalytic functional member was obtained in the same manner as in Example 1 except that the temperature of the atmospheric oxidation treatment was 1073 K and the time was 0.3 ks.

[Example 5]
A photocatalytic functional member was obtained in the same manner as in Example 1 except that an ingot of a Ti-4 at% Au alloy was produced by arc melting, and that the temperature of the atmospheric oxidation treatment was 873 K and the time was 10.8 ks.

[Example 6]
A photocatalytic functional member was obtained in the same manner as in Example 1 except that an ingot of a Ti-3 at% Ag alloy was produced by arc melting and that the temperature of the atmospheric oxidation treatment was set to 873 K and the time was set to 10.8 ks.

[Comparative Example 1]
Pure Ti is prepared as a raw material, a pure Ti ingot is prepared by arc melting, this ingot is hot-rolled, cut into a square shape, and then one side is mirror-polished to obtain a pure Ti substrate having a thickness of 1 mm. It was. The temperature of the atmospheric oxidation treatment was set to 873 K and the time was set to 0.3 ks. Except for the above, a photocatalytic functional member was obtained in the same manner as in Example 1.

[Comparative Example 2]
A photocatalytic functional member was obtained in the same manner as in Example 1 except that an ingot of a Ti-1 at% Au alloy was produced by arc melting and that the temperature of the atmospheric oxidation treatment was set to 873 K and the time was set to 21.6 ks.

[Comparative Example 3]
A photocatalytic functional member was obtained in the same manner as in Comparative Example 1 except that the temperature of the atmospheric oxidation treatment was 873 K and the time was 43.2 ks.

[Comparative Example 4]
A pure Ti substrate was produced in the same manner as in Comparative Example 1, and this was used as a sample without being subjected to atmospheric oxidation treatment.

[Comparative Example 5]
A Ti-4 at% Au alloy substrate was produced in the same manner as in Example 5, and this was used as a sample without being subjected to atmospheric oxidation treatment.

[Comparative Example 6]
First, a pure Ti substrate was produced in the same manner as in Comparative Example 4. Next, the target photocatalytic functional member was obtained by performing the following first and second steps.

In the first step, a pure Ti substrate is held in a reaction tube made of SiO ₂ placed in an electric resistance furnace, and heat treatment for 3.6 ks is performed in an environment of a temperature of 1073 K while introducing 1% CO gas. By carrying out on a pure Ti substrate, a Ti (C, O) film was formed on the surface of the pure Ti substrate.

In the second step, a pure Ti substrate on which a Ti (C, O) film is formed is placed on an SiO ₂ board, and the Ti (C, O) film is oxidized in the air in a muffle furnace, whereby a TiO ₂ film (hereinafter referred to as “TiO ₂ film”) The TiO ₂ film formed by two-stage thermal oxidation was referred to as “two-stage thermal oxidation TiO ₂ film”). At this time, the temperature of the oxidation treatment was 673 K, and the time was 10.8 ks. Here, the temperature of the oxidation treatment is the temperature on the surface of the Ti alloy substrate.

[Comparative Examples 7 to 10]
A photocatalytic functional member was prepared in the same manner as in Comparative Example 6 except that ingots of Ti-1 at% Au alloy, Ti-4 at% Au alloy, Ti-5 at% Au alloy, and Ti-10 at% Au alloy were prepared by arc melting. Obtained.

[Comparative Example 11]
A photocatalytic functional member was obtained in the same manner as in Example 1 except that an ingot of a Ti-0.3 at% Ag alloy was produced by arc melting and that the temperature of the atmospheric oxidation treatment was set to 873 K and the time was set to 10.8 ks. It was.

(Evaluation of structure and chemical state of TiO ₂ film)
The structures of the atmospheric oxidized TiO ₂ film and the two-stage thermally oxidized TiO ₂ film were analyzed by α-2θ XRD (X-Ray Diffraction) using CuKα rays.
Atmospheric oxidation TiO ₂ film cross-section by STEM, and observing the surface of the atmospheric oxidation TiO ₂ film and the two-stage thermal oxide TiO ₂ film by SEM. And when Au nanoparticle was observed, the average particle diameter was calculated | required.
The cross section of the two-stage thermally oxidized TiO ₂ film was observed with a TEM (Transmission Electron Microscope). And when Au nanoparticle was observed by the cross-sectional TEM image, the average particle diameter was calculated | required from the cross-sectional TEM image.
The chemical state of the noble metal present in the atmospheric oxidized TiO ₂ film and the two-stage thermally oxidized TiO ₂ film was analyzed by XPS.

<Atmospheric oxidation TiO ₂ film>
FIG. 2 shows the α-2θ XRD patterns of the atmospheric oxidized TiO ₂ films of Examples 1 to 4 and Comparative Examples 1 and ₂ . 3A and 3B show cross-sectional STEM images of the atmospheric oxidized TiO ₂ films of Examples 4 and 3, respectively. FIG. 4 collectively shows the analysis results of the atmospheric oxidized TiO ₂ films of Examples 1 to 4 and Comparative Examples 2 and 3 by α-2θ XRD and the cross-sectional observation results by STEM.

The following can be seen from FIG.
The atmospheric oxidation TiO ₂ films (Examples 1, 2, 4 and Comparative Examples 2 and 3) formed by the high temperatures 873K and 1073K include rutile type titanium oxide crystals, whereas the atmospheric oxidation TiO ₂ films formed by the low temperature 673K. The oxide TiO ₂ film (Example 3) includes a mixture of a rutile type titanium oxide crystal and a brookite type titanium oxide crystal.
In an atmospheric oxidation TiO ₂ film (Examples 1 to 4 and Comparative Example 2) formed using a Ti—Au alloy substrate as a base material, Au nanoparticles are introduced into the atmospheric oxidation TiO ₂ film, and solute Au ³⁺ Ions are doped. Moreover, the average particle diameter of Au nanoparticles shows a tendency to increase as the content of Au contained in the Ti—Au alloy substrate increases or the temperature of atmospheric oxidation treatment increases.
The distribution of Au nanoparticles in the atmospheric oxidation TiO ₂ film varies depending on the temperature of the atmospheric oxidation treatment. Specifically, in the atmospheric oxidation TiO ₂ films (Examples 1, 2, 4, and Comparative Example 2) formed at high temperatures of 873K and 1073K, Au nanoparticles are present on the outermost surface or in the vicinity of the outermost surface. On the other hand, in the atmospheric oxidation TiO ₂ film (Example 3) formed at a low temperature of 673 K, Au nanoparticles are present in almost the entire atmospheric oxidation TiO ₂ film.

<Two-stage thermal oxide TiO ₂ film>
FIG. 5 shows α-2θ XRD patterns of the two-stage thermally oxidized TiO ₂ films of Comparative Examples 6-8. 6A shows a cross-sectional TEM image of the two-stage thermally oxidized TiO ₂ film of Comparative Example 8. FIG. FIG. 6B shows an Au4fXPS spectrum of the two-stage thermally oxidized TiO ₂ film of Comparative Example 8. FIG. 7 collectively shows the analysis results by α-2θ XRD and the cross-sectional observation results by TEM of the two-stage thermally oxidized TiO ₂ films of Comparative Examples 6, 7, 9, and 10.

The following can be seen from FIG.
The two-stage thermally oxidized TiO ₂ film (Comparative Examples 6, 7, 9, and 10) contains a mixture of anatase type titanium oxide crystals and rutile type titanium oxide crystals.
In the two-stage thermally oxidized TiO ₂ film (Comparative Examples 7, 9, and 10) formed using a Ti—Au alloy substrate as a base material, Au nanoparticles are introduced into the two-stage thermally oxidized TiO ₂ film, and solid solution Au ³⁺ ions and solute C are doped. Moreover, it turns out that the average particle diameter of Au nanoparticle shows the tendency which increases with the increase in content of Au contained in a Ti-Au alloy substrate.

(Visible light response evaluation (1))
A stearic acid decomposition test was used for evaluation of the visible light response. This test is a test method based on JIS R 1753: 2013, and evaluates photocatalytic activity from the decrease in water contact angle accompanying the decomposition of the stearic acid coating film under visible light irradiation. A stearic acid-heptane solution was used for the application of stearic acid. A Xe lamp was used as the light source, and the sample was irradiated with visible light from which ultraviolet light components were removed using a filter. The irradiance was 10 mW · cm ^{−2 on the} sample surface.

<Atmospheric oxidation TiO ₂ film>
FIG. 8 shows changes in the water contact angle of the atmospheric oxidized TiO ₂ films of Examples 1 and 2, Comparative Examples 2 and 3, and the pure Ti substrate of Comparative Example 4. The following can be seen from FIG. In the atmospheric oxidation TiO ₂ film (Examples 1 and 2) formed using a Ti—Au alloy substrate containing 5 at% and 10 at% of Au as the substrate, an improvement in visible light response is recognized. On the other hand, an atmospheric oxidation TiO ₂ film (Comparative Example 3) formed using a pure Ti substrate as a base material, and an atmospheric oxidation TiO ₂ film formed using a Ti—Au alloy substrate containing 1 at% Au as a base material ( In Comparative Example 2), no improvement in visible light responsiveness is observed.

FIG. 9 shows changes in the water contact angle of the atmospheric oxidized TiO ₂ films of Examples 1, 3, and 4 and the pure Ti substrate of Comparative Example 4. Examples 1, 3, and 4 are samples in which the Au content in the Ti—Au alloy substrate is 5 at%, whereas the conditions (temperature, time) of atmospheric oxidation treatment are different. is there. FIG. 9 shows that the visible light responsiveness changes depending on the atmospheric oxidation treatment conditions.

FIG. 10 shows changes in the water contact angle of the atmospheric oxidized TiO ₂ films of Examples 5 and 6 and Comparative Example 11. In the atmospheric oxidation TiO ₂ film (Example 6) formed using a Ti—Ag alloy substrate containing 3 at% of Ag as a substrate, an improvement in visible light responsiveness is recognized. On the other hand, in the atmospheric oxidation TiO ₂ film (Comparative Example 11) formed using a Ti—Ag alloy substrate containing 0.3 at% of Ag as a base material, an improvement in visible light response is not recognized.

<Two-stage thermal oxide TiO ₂ film>
FIG. 11 shows changes in water contact angles of the two-stage thermally oxidized TiO ₂ films of Comparative Examples 6 and 8, the pure Ti substrate of Comparative Example 4, and the Ti-4 at% Au alloy substrate of Comparative Example 5. The following can be seen from FIG. In the two-stage thermally oxidized TiO ₂ film (Comparative Example 8) formed using a Ti—Au alloy substrate containing 4 at% Au as a base material, an improvement in visible light response is recognized. Even in a two-stage thermally oxidized TiO ₂ film (Comparative Example 6) formed using a pure Ti substrate as a base material, an improvement in visible light response is recognized. However, the two-stage thermally oxidized TiO ₂ film (Comparative Example 8) formed using a Ti-4 at% Au alloy substrate is more two-stage thermally oxidized TiO ₂ film (Comparative Example 6) formed using a pure Ti substrate. Compared with the above, the improvement in the visible light response remarkably appears.

FIG. 12 shows changes in the water contact angle of the two-stage thermally oxidized TiO ₂ films of Comparative Examples 6, 7, 9, and 10 and the pure Ti substrate of Comparative Example 4. Comparative Examples 6, 7, 9, and 10 are samples in which the Au content contained in the Ti—Au alloy substrate was changed in the range of 0 to 10 at%. The following can be understood from FIG. In the two-stage thermally oxidized TiO ₂ film (Comparative Examples 6, 7, 9, 10) formed using a Ti—Au alloy substrate containing Au in the range of 1 to 10 at% as a base material, the visible light response is improved. Is recognized.

(Visible light response evaluation (2))
As shown in FIG. 13A, the time t _1/2 at which the initial contact angle is halved was determined using the water contact angle measured in the above “visible light response evaluation (1)”. In the case of the curves A and B shown as examples in FIG. 13A, the half time t _1/2 of the water contact angle of the curve A is smaller than the half time t _1/2 ′ of the water contact angle of the curve B. It can be said that the photocatalytic activity of this sample is superior to the photocatalytic activity of the curve B sample.

FIG. 13B shows the measurement results of the initial contact angle half-time t _1/2 of the TiO ₂ films of Examples 1 to 4, Comparative Examples 2, 3, 6, 7, 9, and 10 and the pure Ti substrate of Comparative Example 4. Show. From FIG. 13B, the atmospheric oxidation TiO ₂ film obtained by atmospheric oxidation of a Ti—Au alloy substrate containing 5, 10 at% Au is obtained by subjecting a pure Ti substrate and a Ti—Au alloy substrate to two-step thermal oxidation. It can be seen that a visible light responsive photocatalytic activity almost equivalent to that of the obtained two-stage thermally oxidized TiO ₂ film can be obtained.

(Visible light response evaluation (3))
The at% of Au in the vicinity of the surface of the atmospheric oxidized TiO ₂ film was determined as follows. First, the contents of Au and Ti in the vicinity of the surface of the atmospheric oxidized TiO ₂ film were measured by XPS. Next, at% of Au in the vicinity of the surface of the atmospheric oxidation TiO ₂ film was obtained from the following formula (1) using the measured contents of Au and Ti.
At% of _Au = C _Au / (C _Au + C _Ti ) × 100 (1)
(In the formula (1), C _Au is the Au content near the surface of the atmospheric oxidized TiO ₂ film, and C _Ti is the Ti content near the surface of the atmospheric oxidized TiO ₂ film.)

At% of the total amount of Au and C in the vicinity of the surface of the two-step thermally oxidized TiO ₂ film was determined as follows. First, the contents of Au, C and Ti in the vicinity of the surface of the atmospheric oxidized TiO ₂ film were measured by XPS. Next, using the measured contents of Au, C and Ti, at% of the total amount of Au and C in the vicinity of the surface of the two-stage thermally oxidized TiO ₂ film was obtained from the following formula (2).
At% of the total amount of Au and C = (C _Au + C _C ) / (C _Au + C _C + C _Ti ) × 100 (2)
(In the formula (2), C _Au is the content of Au in the vicinity of the surface of the two-stage thermally oxidized TiO ₂ film, and C _C is the content of C in the vicinity of the surface of the two-stage thermally oxidized TiO ₂ film. C _Ti is the Ti content in the vicinity of the surface of the two-stage thermally oxidized TiO ₂ film.)

A graph was prepared in which the at% of Au determined as described above is the horizontal axis, and the initial contact angle half-time t _1/2 determined in the above-mentioned “Visible light response evaluation (2)” is the vertical axis ( 14A). Further, the horizontal axis represents at% of the total amount of Au and C determined as described above, and the vertical axis represents the initial contact angle half time t _1/2 determined in the above-mentioned “Visible light response evaluation (2)”. A graph was created (see FIG. 14B).

FIG. 14A shows the relationship between the at% of Au in the vicinity of the surface of the atmospheric oxidized TiO ₂ film of Examples 1 to 4 and Comparative Example 3 and the initial contact angle half time t _1/2 . From FIG. 14A, in the atmospheric oxidation TiO ₂ film, as the Au content (introduction amount) in the vicinity of the surface increases, the initial contact angle half-time t _1/2 decreases, that is, the visible light response improves. Recognize. It can be seen that when the at% of Au in the vicinity of the surface is 0.098 or more, the initial contact angle half-life time t _1/2 is remarkably shortened, that is, the visible light response is remarkably improved.

FIG. 14B shows the relationship between the at% of Au in the vicinity of the surface of the two-stage thermally oxidized TiO ₂ film of Comparative Examples 6, 7, 9, and 10 and the initial contact angle half time t _1/2 . From FIG. 14B, in the two-stage thermally oxidized TiO ₂ film, the initial contact angle half-time t _1/2 becomes shorter as the contents of Au and C (introduced amounts) in the vicinity of the surface increase, that is, the visible light response is improved. It turns out that it improves.

(Visible light response evaluation (4))
Using the average particle diameter of Au nanoparticles determined in the above-mentioned “Evaluation of the structure and chemical state of the TiO ₂ film” as the horizontal axis, the initial contact angle half-time t determined in the above-mentioned “Visible light response evaluation (2)” Graphs having _1/2 as the vertical axis were created (see FIGS. 15A and 15B).

FIG. 15A shows the relationship between the average particle diameter of Au nanoparticles in the atmospheric oxidized TiO ₂ film of Examples 3 and 4 and the initial contact angle half time t _1/2 . FIG. 15B shows the average particle diameter and initial contact angle half-time t ₁ of Au nanoparticles on the surfaces of the atmospheric oxidized TiO ₂ films of Examples 1, ₂ , and 4 and the two-stage thermally oxidized TiO ₂ films of Comparative Examples 9 and 10. Indicates the relationship with _{/ 2} .

15A and 15B show the following.
As the average particle diameter of Au nanoparticles introduced into the atmospheric oxidized TiO ₂ film and the two-stage thermally oxidized TiO ₂ film becomes smaller, the initial contact angle half-time t _1/2 becomes shorter, that is, the visible light responsiveness improves. I understand that.
The particle diameter of the Au nanoparticles introduced into the atmospheric oxidized TiO ₂ film and the two-stage thermally oxidized TiO ₂ film is 100 nm or less. When the particle size of the Au nanoparticles exceeds 100 nm, the absorption spectrum intensity decreases, and there is a possibility that it becomes difficult to make visible light response by surface plasmon resonance.
The following can be understood from the comparison between FIGS. 14A and 15A.
Towards the content of Au in the atmospheric oxidation TiO ₂ film is, than the average particle diameter of the Au nanoparticles contained in the atmospheric oxidation TiO ₂ film, a large influence on visible light responsive properties.

(Antimicrobial evaluation)
The antibacterial properties of the atmospheric oxidized TiO ₂ film of Example 1, the two-stage thermally oxidized TiO ₂ film of Comparative Examples 6 and 9, the pure Ti substrate of Comparative Example 4, and the SiO ₂ substrate were evaluated as follows. That is, based on the glass adhesion method (ISO 27447: 2009), the number of viable bacteria before and after irradiation with visible light (before irradiation: N ₀ , after irradiation: N) is measured, and the viable cell rate (N / N ₀ ) is calculated. did. The test bacterial solution and visible light irradiation conditions are shown below.
Test Bacteria Bacteria: Escherichia coli (E. coli) DH5α
Bacterial concentration: 10 ⁸ CFU mL ⁻¹ in 1/500 NB medium Visible light Light source: Xe lamp (using UV filter)
Irradiance: 1mW · cm ^-2

FIG. 16 shows the evaluation results of the antibacterial test of the atmospheric oxidized TiO ₂ film of Example 1, the two-stage thermally oxidized TiO ₂ film of Comparative Examples 6 and 9, the pure Ti substrate of Comparative Example 4, and the SiO ₂ substrate. FIG. 16 shows that an atmospheric oxidation TiO ₂ film formed using a Ti—Au alloy substrate containing 5 at% Au and a two-stage thermally oxidized TiO ₂ film formed using a Ti—Au alloy substrate containing 5 at% Au. Then, it turns out that antibacterial property develops. On the other hand, it can be seen that antibacterial properties are not exhibited in the SiO ₂ substrate and the mirror-polished pure Ti substrate. In addition, although the two-stage thermally oxidized TiO ₂ film formed using a pure Ti substrate exhibits antibacterial properties, it can be seen that the effect is lower than that of Example 1 and Comparative Example 9.

Table 1 shows the configurations of the photocatalytic functional members of Examples 1 to 6 and Comparative Examples 1 to 5 and 11, and the conditions for the atmospheric oxidation treatment.

Table 2 shows the structures of the photocatalytic functional members of Comparative Examples 6 to 10 and the conditions for the two-stage oxidation treatment.

Summarizing the above evaluation results, in the atmospheric oxidation treatment, it is possible to obtain a TiO ₂ film having visible light responsive photocatalytic activity substantially equivalent to the two-stage thermal oxidation treatment. Note that the atmospheric oxidation treatment has an advantage that it is simpler and less expensive than the two-stage thermal oxidation treatment.

  Although the embodiments and examples of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments and examples, and various modifications based on the technical idea of the present invention are possible. It is.

  For example, the configurations, methods, processes, shapes, materials, numerical values, and the like given in the above-described embodiments and examples are merely examples, and different configurations, methods, processes, shapes, materials, numerical values, and the like are necessary as necessary. May be used.

  The configurations, methods, processes, shapes, materials, numerical values, and the like of the above-described embodiments and examples can be combined with each other without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 10 Photocatalyst functional member 11 Base material 12 Surface layer 12A Nanoparticle 13 Intermediate | middle layer

Claims (12)

A substrate;
A surface layer formed on the surface of the base material and having a rutile-type titanium oxide crystal as a main phase or a rutile-type titanium oxide crystal and a brookite-type titanium oxide crystal as a main phase and containing a noble metal; Photocatalyst functional member provided.   The photocatalytic functional member according to claim 1, wherein the noble metal is at least one of gold, silver, platinum, and palladium.   The photocatalytic functional member according to claim 1 or 2, wherein the noble metal contained in the surface layer constitutes a nanoparticle.   The photocatalytic functional member according to claim 3, wherein the concentration of the nanoparticles in the surface layer is the highest at or near the surface of the surface layer.   The photocatalytic functional member according to claim 3 or 4, wherein the average particle diameter of the nanoparticles is 100 nm or less.   The photocatalytic functional member according to any one of claims 1 to 5, wherein at% of the amount of the noble metal contained in the surface layer is 0.007 or more with respect to the total amount of titanium and the noble metal contained in the surface layer. .   The photocatalytic functional member according to any one of claims 1 to 6, wherein the noble metal is dissolved in the surface layer.   The photocatalytic functional member according to claim 1, wherein the base material contains titanium and a noble metal.   A method for producing a photocatalytic functional member, comprising a step of thermally oxidizing a base material containing titanium and a noble metal in an atmosphere containing oxygen.   The method for producing a photocatalytic functional member according to claim 9, wherein a temperature of the thermal oxidation treatment is 673 K or more and 1073 K or less.   The method for producing a photocatalytic functional member according to claim 9 or 10, wherein the atmosphere containing oxygen is an air atmosphere.   The method for producing a photocatalytic functional member according to any one of claims 9 to 11, wherein the content of the noble metal contained in the substrate is 2 at% or more.