JP2012030172A - Method of manufacturing visible light responsive photocatalyst and visible light responsive photocatalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To establish a method for manufacturing a visible light responsive photocatalyst easily and reliably at low costs.SOLUTION: The method of manufacturing a visible light responsive photocatalyst comprises irradiating titanium oxide with a femtosecond laser beam under the atmospheric pressure to form at least one of oxygen defects and Tiin crystals of the titanium oxide. The irradiation energy of the femtosecond laser is 133-533 GW/cm, the pulse width is 50-1,000 fs, and the wavelength is 250-1,600 nm. The method provides a visible light responsive photocatalyst having at least one of oxygen defects and Tiin crystals of titanium oxide.

Description

  The present invention relates to a method for producing a visible light responsive photocatalyst, and a visible light responsive photocatalyst obtained by the method.

A typical photocatalyst is titanium oxide (TiO ₂ ). When titanium oxide is irradiated with ultraviolet light having energy larger than the band gap, electrons in the valence band are excited to the conduction band and holes are generated in the valence band. Since these holes have a strong oxidizing action, they are effective for the decomposition, antifouling and sterilization of malodorous substances and pollutants.

  However, ordinary titanium oxide (anatase type) exhibits photocatalytic activity only when irradiated with ultraviolet light having a wavelength of about 400 nm or less. Accordingly, sunlight or fluorescent light mainly containing a large amount of visible light or infrared light cannot generate holes efficiently because the proportion of ultraviolet light of about 400 nm or less is small. In view of this, various attempts have been made for titanium oxide to develop photocatalytic activity even when irradiated with visible light.

  For example, cation-doped titanium oxide in which a small amount of cations such as B, P, V, Cr, Mn, and Fe is contained in titanium oxide is known (see, for example, Patent Document 1). According to Patent Literature 1, when titanium oxide is doped with a cation, the electronic state is changed in the crystal structure of titanium oxide, and as a result, the photocatalytic activity is expressed even for visible light.

  In addition, a method of subjecting titanium oxide to plasma treatment has been proposed (see, for example, Patent Document 2). According to Patent Document 2, hydrogen plasma treatment or rare gas plasma treatment is performed on titanium oxide under reduced pressure. As a result, stable oxygen defects are generated in the crystal structure of titanium oxide, and photocatalytic activity is obtained even when irradiated with visible light.

JP 2000-237598 A International Publication No. WO00 / 10706 Pamphlet

  However, the methods disclosed in Patent Document 1 and Patent Document 2 have several problems. In Patent Document 1, in order to introduce a cation into titanium oxide, a solution containing the cation is impregnated into titanium oxide. However, since such a method is performed in a wet condition, processing steps such as drying and heating are necessary later. In addition, since the solution impregnates the entire titanium oxide in the impregnation treatment, it is impossible to design a precise catalyst such as doping a cation only at a predetermined site. Furthermore, the introduction of cations into titanium oxide adds impurities in a sense. Therefore, once the cation is doped, it is difficult to regenerate the original pure titanium oxide.

  In Patent Document 2, it is necessary to perform plasma treatment under reduced pressure. This complicates the device configuration and increases the manufacturing cost. Further, under reduced pressure, there is a high possibility that impurities are mixed during the plasma treatment, and the impurities may be injected into the titanium oxide together with the target ions.

  Thus, at present, a method for effectively obtaining a visible light responsive photocatalyst has not been sufficiently established. The present invention has been made in view of the above problems, and its object is obtained by establishing a method for producing a visible light responsive photocatalyst that can be realized simply, reliably, and at a low cost. The object is to provide a visible light responsive photocatalyst.

The characteristic configuration of the method for producing a visible light responsive photocatalyst according to the present invention for solving the above problems is as follows.
The titanium oxide is irradiated with a femtosecond laser under atmospheric pressure to form at least one of oxygen defects and Ti ^{3+ in} the titanium oxide crystal.

As described in the above problem, the conventional method for expressing the photocatalytic activity of titanium oxide with visible light is a complicated manufacturing process, precise catalyst design is impossible, and regeneration is difficult. There are problems such as complicated apparatus configuration, high cost, and the possibility of contamination.
In this regard, according to the method for producing a visible light responsive photocatalyst having this configuration, visible light responsive titanium oxide can be obtained by a simple method of irradiating the titanium oxide with a femtosecond laser. Here, the irradiation with the femtosecond laser is performed so that at least one of an oxygen defect and Ti ³⁺ is formed in the titanium oxide crystal. It is considered that oxygen defects or Ti ³⁺ formed in the crystal continues to exist in a relatively stable state. As a result, titanium oxide exhibits effective absorption not only for ultraviolet light but also for visible light.
If it is the manufacturing method of the visible light response type photocatalyst of this structure, a visible light absorption characteristic can be expressed in titanium oxide, without performing cation doping like the past. That is, a reproducible visible light responsive titanium oxide containing no impurities can be realized. In addition, the method of irradiating a femtosecond laser can easily perform a selective treatment on a specific portion of titanium oxide. This makes it possible to design a precise catalyst according to the purpose of use. Furthermore, the method for producing a visible light responsive photocatalyst having this configuration can be carried out under atmospheric pressure. Therefore, the configuration of the manufacturing apparatus can be simplified, which can contribute to the reduction of manufacturing cost.

In the method for producing a visible light responsive photocatalyst according to the present invention,
The irradiation energy of the femtosecond laser is preferably 133 to 533 GW / cm ² .

According to the method for producing a visible light responsive photocatalyst having this configuration, the oxygen energy and Ti ³⁺ are reduced in the titanium oxide crystal by setting the irradiation energy of the femtosecond laser for irradiating the titanium oxide to 133 to 533 GW / cm ^2. It can be reliably formed.

In the method for producing a visible light responsive photocatalyst according to the present invention,
The pulse width of the femtosecond laser is preferably 50 to 1000 fs.

According to the method for producing a visible light responsive photocatalyst of this configuration, oxygen defects and Ti ³⁺ are reliably formed in the titanium oxide crystal by setting the pulse width of the femtosecond laser irradiated to the titanium oxide to 50 to 1000 fs. can do.

In the method for producing a visible light responsive photocatalyst according to the present invention,
The wavelength of the femtosecond laser is preferably 250 to 1600 nm.

According to the method for producing a visible light responsive photocatalyst having this configuration, oxygen defects and Ti ³⁺ are reliably formed in the titanium oxide crystal by setting the wavelength of the femtosecond laser irradiated to the titanium oxide to 250 to 1600 nm. be able to.

In the method for producing a visible light responsive photocatalyst according to the present invention,
It is preferable to use titanium oxide to which a dopant is added as the titanium oxide.

  According to the method for producing a visible light responsive photocatalyst of this configuration, the titanium oxide photocatalyst absorbs visible light by irradiating a titanium oxide to which a dopant having a certain absorption characteristic with respect to visible light is added with a femtosecond laser. The characteristics can be further improved. As a result, a strong visible light responsive photocatalyst can be generated.

The characteristic configuration of the visible light responsive photocatalyst according to the present invention for solving the above problems is as follows:
It exists in having at least one of an oxygen defect and Ti3 ⁺ in the crystal | crystallization of a titanium oxide.

In the visible light responsive photocatalyst having this configuration, it is considered that oxygen defects or Ti ³⁺ continues to exist in a relatively stable state in the crystal. As a result, titanium oxide exhibits effective absorption not only for ultraviolet light but also for visible light.
In the case of the visible light responsive photocatalyst having this configuration, unlike the conventional cation-doped titanium oxide, the visible light absorption characteristic is manifested only by reproducible pure titanium oxide. In addition, the visible light responsive photocatalyst having this configuration enables precise catalyst design according to the purpose of use. Furthermore, since the visible light responsive photocatalyst having this configuration can be manufactured under atmospheric pressure, the configuration of the manufacturing apparatus can be simplified, and the manufacturing cost can be reduced.

FIG. 1 is a schematic view of a film forming apparatus used for forming a titanium oxide film on a glass substrate. FIG. 2 is a schematic diagram of a laser beam irradiation apparatus. FIG. 3 is a diagram illustrating an irradiation pattern of laser light in the first embodiment. FIG. 4 is an overall photograph of the surface of the titanium oxide film after irradiation with laser light, and an enlarged photograph of a part of the surface of the titanium oxide film taken by a scanning electron microscope (SEM). FIG. 5 is a diagram illustrating an irradiation pattern of laser light in the second embodiment. FIG. 6 is a schematic diagram of a test apparatus for performing an acetaldehyde decomposition test. FIG. 7 is a graph showing the results of an acetaldehyde decomposition test using ultraviolet light. FIG. 8 is a graph showing the results of an acetaldehyde decomposition test using visible light.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not intended to be limited to the configurations described in the examples and drawings described below, and includes configurations equivalent thereto.

  One major feature of the visible light responsive photocatalyst of the present invention is that it can be composed of pure titanium oxide substantially free of impurities. Therefore, recycling and recycling are easy. As the crystal form of the raw material titanium oxide, rutile titanium oxide and brookite type titanium oxide can be used in addition to anatase type titanium oxide widely used for photocatalysts. However, in view of the photocatalytic activity and availability, anatase-type titanium oxide is preferable. As the raw material titanium oxide, commercially available titanium oxide powder can be used as it is. On the other hand, titanium oxide may be synthesized from an organic titanium compound. For example, a desired titanium oxide can be synthesized by a sol-gel reaction of titanium alkoxide. The property of titanium oxide to be used can be any property such as powder, film, solid, etc. depending on the application. Also, a support type in which titanium oxide is supported on a catalyst carrier such as a porous body, or a film type in which titanium oxide is formed on a substrate can be used. In this embodiment, a titanium oxide film in which titanium oxide is formed on a glass substrate is used.

  FIG. 1 is a schematic view of a film forming apparatus 100 used for forming a titanium oxide film on a glass substrate. The film forming apparatus 100 mainly includes a process chamber 1, an aerosol chamber 2, a gas cylinder 3, a mechanical booster pump 4, and a rotary pump 5.

  A process stage 11 for disposing a substrate is provided inside the process chamber 1, and a nozzle 12 for spraying a titanium oxide aerosol is provided so as to face the process stage 11. The process stage 11 is movable, and the sample placed on the process stage 11 can be moved relative to the nozzle 12 in the vertical direction (Y direction) and the horizontal direction (X direction) by the controller 13. After disposing the substrate A on the process stage 11, the mechanical booster pump 4 and the rotary pump 5 are operated to decompress the inside of the process chamber 1.

  Inside the aerosol chamber 2, titanium oxide fine particles as a film forming raw material are introduced in advance. In addition, a gas cylinder 3 for supplying an inert gas (for example, helium, nitrogen, etc.) as a flow gas is connected to the aerosol chamber 2. When an inert gas is introduced into the aerosol chamber 2 from the gas cylinder 3, the titanium oxide fine particles are blown up into the aerosol chamber 2 to be mixed with the inert gas (aerosol) and pass through the upper hose 21 to the downstream nozzle 12. To be supplied. Here, the aerosol chamber 2 is provided with a vibration device 22 as necessary in order to improve the dispersibility of the titanium oxide fine particles. In the process chamber 1, a jet of titanium oxide fine particles (aerosol beam) is sprayed from the nozzle 12 toward the substrate A disposed on the process stage 11 at an incident angle θ. Here, the process stage 11 is moved relative to the nozzle 12 during spraying. The movement pattern of the process stage 11 is programmed in the controller 13 according to the shape of the designed titanium oxide film. When the titanium oxide aerosol collides with the surface of the substrate A, the aerosol is destroyed and thinned. At this time, an active new surface is generated on the surface of the thin film. When another aerosol that arrives later collides with this active new surface, a new titanium oxide film is formed on the new surface. By repeating this collision, a thin film grows and becomes a dense and strong titanium oxide film.

  In order to change the titanium oxide film formed by the film forming apparatus 100 into a visible light responsive photocatalyst, the titanium oxide film is irradiated with a femtosecond laser. In this specification, the “femtosecond laser” is a laser beam having a pulse width on the order of femtoseconds. Irradiation with a femtosecond laser can be performed under normal atmospheric pressure without requiring a decompression chamber or the like. FIG. 2 shows a schematic diagram of a femtosecond laser irradiation apparatus 200. The irradiation apparatus 200 mainly includes a femtosecond laser transmitter 51, an energy attenuator 52, a reflection mirror 53, a condenser lens 54, and an irradiation stage 55.

The irradiation energy of the femtosecond laser emitted from the femtosecond laser transmitter 51 (hereinafter referred to as “laser light”) is adjusted by the energy attenuator 52. Thereafter, the laser light whose energy has been adjusted passes through the reflection mirror 53 and the condenser lens 54 and irradiates the titanium oxide film S on the substrate A placed on the irradiation stage 55. Here, the laser beam irradiation from the femtosecond laser transmitter 51 is performed so that at least one of oxygen defects and Ti ³⁺ is formed in the crystal of the titanium oxide film S. That is, laser irradiation is performed so that a new donor level is formed in the band structure of titanium oxide. Specifically, the laser light reaching the titanium oxide film S, so that the irradiation energy by the energy attenuator 52 is 133～533GW (GW) / cm ^2, the 267~533GW / cm ² and more preferably The attenuation is adjusted as follows. When the irradiation energy is smaller than 133 GW / cm ² , oxygen defects or Ti ³⁺ is not sufficiently formed. On the other hand, if the irradiation energy becomes too large, the titanium oxide film S may be damaged. The pulse width of the laser light is adjusted to 50 to 1000 fs, more preferably 100 to 200 fs. Within these ranges, the titanium oxide film S becomes black and absorbs visible light when irradiated with laser light. When the pulse width is smaller than 50 fs, oxygen defects or Ti ³⁺ is not sufficiently formed. On the other hand, when the pulse width is larger than 1000 fs, the titanium oxide film S may be melted. Furthermore, the wavelength of the laser light is adjusted to 250 to 1600 nm, more preferably 700 to 800 nm. When the wavelength is smaller than 250 nm or larger than 1600 nm, oxygen defects or Ti ³⁺ is not sufficiently formed.

Under the above irradiation conditions, when the laser light is irradiated onto the titanium oxide film S by the femtosecond laser transmitter 51, the irradiated portion is changed from brown to black, and oxygen defects or Ti ³⁺ is formed in the crystal of the titanium oxide film S. . This oxygen defect and Ti ³⁺ are considered to continue to exist in a relatively stable state. As a result, titanium oxide exhibits effective absorption not only for ultraviolet light but also for visible light. Further, the electrical resistance was measured by irradiating ultraviolet light or visible light with respect to the titanium oxide film S changed in color to brown or black by laser light irradiation. As a result, it was confirmed that the electrical resistance of the titanium oxide film S is lower than that before the discoloration not only during the ultraviolet light irradiation but also during the visible light irradiation. This new and unique phenomenon is considered to occur because a new donor level is formed 0.75 to 1.18 eV lower than the conduction band in the band structure of titanium oxide. As described above, in the present invention, it is possible to form a visible light responsive photocatalyst that can exhibit excellent activity with respect to visible light.

  Examples relating to the visible light responsive photocatalyst of the present invention will be described. In the examples described below, first, the titanium oxide film S was formed using the film forming apparatus 100 shown in FIG. Next, the titanium oxide film S was irradiated with laser beams having different irradiation energies from the femtosecond laser transmitter 51 to generate the visible light responsive photocatalyst of the present invention. The deposition conditions for the titanium oxide film S common to the examples are as follows.

<Film formation conditions>
(1) Raw material: Anatase-type titanium oxide powder (average particle size 200 nm)
(2) Carrier gas: helium (3) Gas flow rate: 17 L / sec (4) Substrate: glass slide (5) Nozzle-substrate distance: 10 mm
(6) Aerosol beam incident angle: 40 degrees (7) Sweep speed: 3 mm / sec (8) Aerosol beam processing area: 10 × 20 mm ²
(9) Processing temperature: room temperature

<Example 1>
In Example 1, a test for confirming an irradiation energy range of laser light suitable for forming a visible light responsive photocatalyst from the titanium oxide film S was performed. The irradiation of the laser beam by the femtosecond laser transmitter 51 was performed using the irradiation apparatus 200 shown in FIG. The irradiation conditions of the laser beam in Example 1 are as follows.

<Irradiation conditions>
(1) Wavelength: 775 nm
(2) Pulse width: 150 fs
(3) Repetition frequency: 1 kHz
(4) Lens focal length: 100 mm
(5) Beam spot diameter: 250 μm
(6) Irradiation energy: 67 GW / cm ^{2 in} the range of 67 to 1267 GW / cm ² (7) Sweep speed: 1 μm / pulse (8) Irradiation atmosphere: air

FIG. 3 shows an irradiation pattern of the laser beam in Example 1. As shown in the figure, a laser beam whose irradiation energy was adjusted every 67 GW / cm ^{2 in} a range of 67 to 1267 GW / cm ² was irradiated on the titanium oxide film S in a line shape.

FIG. 4 shows an overall photograph of the surface of the titanium oxide film S after irradiation with laser light, and an enlarged photograph of a part of the surface of the titanium oxide film S taken by a scanning electron microscope (SEM). From the figure, when the irradiation energy was adjusted to 133 GW / cm ² or more, the white titanium oxide film S changed from brown to black. However, when the irradiation energy was increased to 1200 GW / cm ^2, changes in the shape of the titanium oxide film S such as cracks were observed. From these results, in order to change the titanium oxide film S into a visible light responsive photocatalyst, it is considered preferable to adjust the irradiation energy of the laser light to about 133 to 1067 GW / cm ² .

<Example 2>
In Example 2, a decomposition test of acetaldehyde using a visible light responsive photocatalyst was performed. The visible light responsive photocatalyst used in Example 2 is obtained by irradiating the titanium oxide film S with laser light using the irradiation apparatus 200 shown in FIG. The irradiation conditions of the laser beam in Example 2 are as follows.

<Irradiation conditions>
(1) Wavelength: 775 nm
(2) Pulse width: 150 fs
(3) Repetition frequency: 1 kHz
(4) Lens focal length: 100 mm
(5) Beam spot diameter: 250 μm
(6) Irradiation energy: Every 133 GW / cm ^{2 in} the range of 133 to 800 GW / cm ² (7) Sweep speed: 1 μm / pulse (8) Irradiation atmosphere: Air

In FIG. 5, the irradiation pattern of the laser beam in Example 2 is shown. As shown in FIG. 5A, the entire surface of the titanium oxide film S was irradiated with a laser beam with adjusted irradiation energy to obtain a sample of a visible light responsive photocatalyst. Samples were prepared specimen irradiated every 133GW / cm ² in the range of 133~800GW / cm ² (total six samples). FIG. 5B shows an example of a surface photograph of the titanium oxide film S after irradiation with laser light. From the figure, it can be confirmed that the white titanium oxide film S has changed from brown to black.

  An acetaldehyde decomposition test was performed using the above six samples. FIG. 6 shows a schematic diagram of a test apparatus 300 for performing the acetaldehyde decomposition test. As shown in FIG. 6A, a stage 62 is arranged inside a transparent container 61 having a capacity of 1 L, and a sample (titanium oxide film S formed on the substrate A) irradiated with each irradiation energy is placed on the stage 62. I put it. Then, a gas containing 100 ppm of acetaldehyde was introduced into the transparent container 61, and ultraviolet light was irradiated from below the transparent container toward each sample. The ultraviolet light has a spectrum shown in FIG. Irradiation with ultraviolet light continued for 4 hours, and the gas concentration was measured using the gas detection tube 63 every hour. As a control test, a similar acetaldehyde decomposition test was performed on the titanium oxide film S not irradiated with laser light. The test results are shown in the graph of FIG.

  Next, an acetaldehyde decomposition test using visible light was performed using the test apparatus 300 of FIG. Visible light has the spectrum shown in FIG. The test conditions are the same as the test conditions in the ultraviolet light irradiation test. The test results are shown in the graph of FIG.

From the test results shown in FIGS. 7 and 8, the visible light responsive photocatalyst obtained by irradiating the titanium oxide film S with the irradiation energy of 133 to 533 GW / cm ² by the femtosecond laser transmitter 51 is excellent in acetaldehyde decomposition. It was confirmed to show performance. In the case of irradiation with ultraviolet light, acetaldehyde could be decomposed by 80% or more at maximum. Even when irradiated with visible light, about 50% of acetaldehyde could be decomposed. In particular, the photocatalytic activity that is manifested by irradiation with visible light is a new finding that cannot be found in conventional pure titanium oxide that has not been subjected to a treatment such as cation doping. The reason for this has not been fully elucidated yet, but is due to the fact that oxygen defects or Ti ³⁺ formed in the titanium oxide crystal by laser irradiation continued to exist in a relatively stable state. Conceivable. Thus, the visible light responsive photocatalyst of the present invention showed significant photocatalytic activity not only for ultraviolet light but also for visible light, and an excellent effect in decomposing organic substances was observed.

<Another embodiment>
In the above embodiment (example), pure titanium oxide containing substantially no impurities is used as the titanium oxide irradiated with the femtosecond laser. However, the technical idea of the present invention is that at least one of oxygen defects and Ti ³⁺ is formed in the titanium oxide crystal by irradiating the titanium oxide with a femtosecond laser, and as a result, the visible light response characteristic is improved. It is in. Therefore, as a titanium oxide to be irradiated, not only pure titanium oxide but also titanium oxide to which a dopant is added, for example, boron (B), phosphorus (P), vanadium (V), chromium (Cr), manganese (Mn ), Cation-doped titanium oxide doped with iron (Fe) or the like, or anion-doped titanium oxide doped with sulfur (S), nitrogen (N) or the like can be used. In this case, the visible light absorption characteristic originally provided in the titanium oxide photocatalyst can be further improved by irradiating the titanium oxide to which the dopant having a certain absorption characteristic with respect to visible light is added with the femtosecond laser. . Therefore, in order to generate a strong visible light responsive photocatalyst, it is also effective to irradiate titanium oxide to which a dopant is added with a femtosecond laser.

  The visible light responsive photocatalyst of the present invention is particularly useful in a room where a lighting device such as a fluorescent lamp is installed or outdoors where sunlight can be used. The decomposition, antifouling and sterilizing of malodorous substances and pollutants Etc. can be used for the purpose.

DESCRIPTION OF SYMBOLS 1 Process chamber 2 Aerosol chamber 3 Gas cylinder 4 Mechanical booster pump 5 Rotary pump 11 Process stage 12 Nozzle 51 Femtosecond laser transmitter 52 Energy attenuator 53 Reflection mirror 54 Condensing lens 55 Irradiation stage 100 Film-forming apparatus 200 Irradiation apparatus

Claims (6)

A method for producing a visible light responsive photocatalyst, wherein a femtosecond laser is irradiated to titanium oxide under atmospheric pressure to form at least one of oxygen defects and Ti ^{3+ in} the titanium oxide crystal. The method for producing a visible light responsive photocatalyst according to claim 1, wherein irradiation energy of the femtosecond laser is 133 to 533 GW / cm ² .   The method for producing a visible light responsive photocatalyst according to claim 1 or 2, wherein a pulse width of the femtosecond laser is 50 to 1000 fs.   The method for producing a visible light responsive photocatalyst according to any one of claims 1 to 3, wherein a wavelength of the femtosecond laser is 250 to 1600 nm.   The method for producing a visible light responsive photocatalyst according to any one of claims 1 to 4, wherein titanium oxide to which a dopant is added is used as the titanium oxide. A visible light responsive photocatalyst having at least one of an oxygen defect and Ti ³⁺ in a crystal of titanium oxide.

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