JP2009056398A - Tungsten oxide visible light responsive type photocatalyst body, and visible light responsive type photocatalyst coating material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a tungsten oxide visible light responsive type photocatalyst synthetic method capable of remarkably improving photocatalytic performance, and to provide a photocatalyst body. <P>SOLUTION: The tungsten oxide visible light responsive type photocatalyst body is composed of tungsten oxide particles having an average particle size of 0.01-0.05 μm, and has a peak strength at the angle: 2θ=24.380±0.3° by XRD crystal structure observation using a CuKα target. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a tungsten oxide visible light responsive photocatalyst and a visible light responsive photocatalyst coating.

  Currently, titanium oxide is mainly used as a photocatalytic material. Titanium oxide photocatalysts are widely used in antifouling, deodorant and other applied products, but they have the property of being excited by ultraviolet rays, so there is a problem that sufficient photocatalytic performance cannot be obtained for indoor applications where ultraviolet rays are low. is there. As a countermeasure, a so-called visible light responsive photocatalyst has been actively researched and developed. Specifically, a type in which titanium oxide is doped with nitrogen and a type in which platinum is supported on titanium oxide have been developed. However, since this type of photocatalyst has a wavelength range of 400 to 410 nm of main excitation light, the photocatalytic performance is insufficient for indoor illumination light.

Further, tungsten oxide and iron oxide have been studied as a visible light responsive photocatalyst. Tungsten oxide has a band gap of 2.5 eV and a yellow color, and is an advantageous material when applied to building materials. In addition, the material is less harmful and relatively inexpensive. As a visible-response type tungsten oxide photocatalyst, a film prepared by a reactive sputtering method (Patent Document 1) and a powder obtained by adjusting the oxygen valence of tungsten oxide within a predetermined range (Patent Document 2) are known. Yes.
JP 2001-152130 A JP 2007-98293 A

  Since the photocatalyst of Patent Document 1 is formed by sputtering, the surface area is small and the photocatalytic action is not sufficiently exhibited. Moreover, the photocatalyst of Patent Document 2 needs to adjust the oxygen valence in the crystal by oxidation / reduction treatment, and is not practical as a material for mass production.

  By the way, tungsten trioxide is stable in room temperature air, but this tungsten trioxide has a characteristic that the crystal structure is complex and easily changes. Normally, tungsten trioxide made from para-tungsten ammonium, ammonium methanetungstate, and tungstic acid is monoclinic, but the crystal structure easily changes due to stress during processing of the powder and changes to triclinic. (J. Solid State Chemistry 143, 2432 (1999)). In the photocatalyst, electrons and holes excited by light need to move to the surface, and there are few defects that become recombination centers in the crystal, and it is necessary to make the particles small.

Conventionally, sufficient photocatalytic effect could not be obtained with tungsten oxide powder because the crystal change partially occurred during processing in the powder pretreatment, and different crystals were mixed. This is thought to be due to a defect that causes bonding. The commercially available WO ₃ fine particles have a large particle size of 1 to 100 μm, and it is necessary to carry out a dispersion treatment with a ball mill or a bead mill in order to make the WO ₃ photocatalyst powder into a paint. However, there is also a problem that when the dispersion treatment is performed, the catalytic activity is reduced and a highly active paint cannot be obtained.

  Usually, tungsten oxide fume obtained by heating and burning metallic tungsten has a variation in crystal structure depending on heating conditions and atmosphere, and it has been difficult to obtain a stable crystal structure. Furthermore, the tungsten oxide fine particles obtained by the combustion method have a problem that the particle diameter is large and the adsorption ability of the gas component is low even when compared with the titanium oxide photocatalyst powder of about 0.05 μm. Furthermore, when creating a paint using tungsten oxide photocatalyst powder, the activity of the photocatalyst is reduced if physical dispersion treatment such as ball milling or bead milling is performed as described above.

  The present invention has been made to solve such problems, and an object of the present invention is to provide a tungsten oxide visible light responsive photocatalyst and a visible light responsive photocatalyst coating which can greatly improve the photocatalytic performance.

  (1) The tungsten oxide visible light responsive photocatalyst according to claim 1 is composed of tungsten oxide particles having an average particle diameter of 0.01 to 0.05 μm, and an angle 2θ = in XRD crystal structure observation using a CuKα target. It has a peak intensity of 24.380 ± 0.3 °. Here, when the average particle diameter is less than 0.02 μm, the dispersibility of the particles is lowered and it becomes difficult to form a coating, and when it exceeds 0.05 μm, the photocatalytic reaction generated on the particle surface is lowered, which is not preferable. Moreover, the remarkable photocatalytic effect was not recognized in the case where the angle 2θ does not exist within the range of 24.080 to 24.680 °.

  (2) The tungsten oxide visible light responsive photocatalyst according to claim 2 is characterized in that the particles are tungsten trioxide fine particles having a band gap energy of 2.4 to 2.8 eV obtained by optical measurement. And Here, the band gap energy (BG energy) is preferably 2.4 to 2.6 eV, and more preferably 2.4 to 2.5. When the BG energy is less than 2.4 eV, the photocatalytic activity decreases, and when it exceeds 2.6 eV, it has been confirmed that sufficient visible light responsiveness cannot be obtained.

  (3) The tungsten oxide visible light responsive photocatalyst according to claim 3 includes particles of cubic, monoclinic and triclinic crystal structures in all oddities (1) or (2). It is characterized by being.

  (4) The visible light responsive photocatalyst paint according to claim 4 includes the tungsten oxide visible light responsive photocatalyst according to any one of claims 1 to 3, and is a metal oxide of any one of Al, Zr, and Si. 1-10 mass% of binder or the complex oxide binder of Al-Si is included with respect to the said visible light responsive type photocatalyst medium, It is characterized by the above-mentioned.

  (5) The tungsten oxide visible light responsive photocatalyst according to claim 4 according to claim 5 is characterized in that a photocatalytic film is formed by applying a visible light responsive photocatalyst coating amount.

  According to the present invention, tungsten oxide particles having an average particle diameter of 0.01 to 0.05 μm and a peak intensity of an angle 2θ = 24.380 ± 0.3 ° in XRD crystal structure observation using a CuKα target By virtue of the constitution, it is possible to obtain a visible light responsive photocatalyst body and a visible light responsive photocatalyst coating material that can greatly improve the photocatalytic performance.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
Please refer to FIG. However, FIG. 1 shows a schematic view of an apparatus for synthesizing tungsten oxide fine particles. FIG. 2 shows a schematic diagram of a measuring apparatus for the acetaldehyde gas decomposition test. FIG. 3 shows the band gap energy states of the two samples. FIG. 4 shows the results of structural analysis by XRD of two samples. FIG. 5 illustrates an acetaldehyde gas decomposition effect of a tungsten oxide film according to an embodiment of the present invention.

  In FIG. 1, reference numeral 1 indicates a tungsten wire spool (hereinafter referred to as a spool) that feeds out a metal tungsten wire 2. The metal tungsten wire 2 is heated and burned by the gas burner 3 to become fumes 4 of tungsten oxide fine particles. The fume 4 is collected by a fume suction pipe 6 provided in an electric dust collector 5 as a collection device. A part of the fume suction pipe 6 is disposed in the electric furnace 7.

First, a metal tungsten wire is heated by a burner at about 1000 to 1700 ° C. for a short time (5 to 15 seconds per 1 cm). As a result, the metallic tungsten is sublimated by burning and rapidly oxidized to release fumes of tungsten trioxide (WO ₃ ) fine particles to the atmosphere. The generated fumes include three or more types of cubic, triclinic, and monoclinic, and contain ultrafine particles of 0.005-0.05 μm rich in cubic. Next, the fumes are collected by the electric dust collector 5 to obtain WO ₃ fine particles. Subsequently, the fume 4 is placed in an electric furnace 7 in an oxidizing atmosphere of 600 to 1000 ° C. in order to suppress the crystal grain growth of the WO ₃ fine particles and to change the crystal structure from triclinic to cubic or monoclinic. It is introduced and heat-treated in a short time to synthesize highly active tungsten oxide fine particles.

  The results of measuring the band gap energy of the tungsten oxide fine particles obtained as described above are shown in FIG. The measurement is performed by irradiating a powder sample made of tungsten oxide fine particles with light of each wavelength corresponding to the band gap energy, and plotting the light absorption rate from the reflectance for each wavelength, and from this result, the band gap of the metal oxide semiconductor is plotted. This was done in a way that required energy.

Sa Sample A were measured tungsten oxide microparticles were synthesized as described above, (intersection of the imaginary straight line K ₁ and the horizontal axis) band gap energy was 2.46EV. Further, Sample B, which was measured by adding a heat treatment to the tungsten oxide particles, (intersection of the imaginary straight line K ₂ and the horizontal axis) band gap energy was 2.49EV. From FIG. 3, it was found that the crystal structure of sample B was higher than that of sample A, and the activity was higher. In FIG. 3, plots indicating the data of samples A and B are illustrated for convenience in a mixed state, but virtual straight lines K ₁ and K ₂ are obtained based on the respective data for each sample.

  When the band gap energy was measured by the method described above, the tungsten oxide fine particles of the present embodiment were in the range of 2.4 to 2.6 eV. In addition, it was confirmed that the photocatalyst by visible light becomes low for those outside the band gap energy range.

  Further, when the obtained tungsten oxide fine particles were observed by XRD (X-ray diffraction) using a CuKα target, the crystal structure was observed, and the result was as shown in FIG. That is, sample A has a peak intensity at 2θ = 24.381 ° as shown in FIG. 4A, and sample B has the strongest peak at 2θ = 24.380 ° as shown in FIG. 4B. It was found to have strength.

  In FIG. 2, reference numeral 8 indicates a measuring container having a capacity of 3000 cc, a watch glass 9 containing photocatalyst powder (mass: 0.1 g) is disposed therein, and a fan 10 is disposed below the watch glass 9. In addition, a white LED (using NSPW500BS) as the light source 11 is disposed on the upper portion of the measurement container 8. A multi-gas monitor 12 as a measuring instrument is connected to the measurement container 8 via a pipe 13. Note that 10 ppm of acetaldehyde is used as the introduced gas.

  When the tungsten trioxide fine particles were subjected to the acetaldehyde gas decomposition test using the measuring apparatus of FIG. 2, the characteristic diagram shown in FIG. 5 was obtained. The line a in FIG. 5 shows the case of the tungsten oxide fine particle photocatalyst of sample A, and the line b shows the case of the tungsten oxide fine particle photocatalyst of sample B.

  According to the tungsten oxide visible light responsive photocatalyst according to the above-described embodiment, the band gap energy including particles of cubic, monoclinic and triclinic crystal structures is 2.4 to 2.5. It is a tungsten oxide fine particle, has an average particle diameter of 0.01 to 0.05 μm, and has peak intensities at 2θ = 24.380 ° and 24.381 ° in XRD crystal structure observation using a CuKα target. As a result, according to the photocatalyst body, tungsten oxide fine particles having high photocatalytic activity can be obtained. As in the present embodiment, it has been confirmed that the tungsten oxide fine particles satisfying an angle of 2θ = 24.380 ± 0.3 ° by observation of the XRD crystal structure exhibit a remarkably high photocatalytic effect. . Although the reason has not been elucidated, no significant photocatalytic effect was observed when the 2θ was outside the predetermined range.

Further, when XRD data of the WO ₃ photocatalyst fine particles (average particle size: 0.01 to 0.1 μm) was examined, for example, characteristic diagrams as shown in FIGS. 6A and 6B were obtained. 6A is synthesized by the same method as that of the present embodiment except that heat treatment is not sufficiently performed, and a monoclinic crystal (002) in the vicinity of a predetermined angle 2θ (degrees). ) Plane and monoclinic (200) plane have high peak intensity. FIG. 6B shows the WO ₃ photocatalyst fine particles of the present embodiment. The monoclinic (002) plane has a high peak intensity in the vicinity of the same angle 2θ as in FIG. 6A, and is higher than this plane. It has a peak intensity of cubic (100) plane of peak intensity.

  Furthermore, when the band gap energy is in an appropriate numerical range (2.4 to 2.8 eV) defined in the present invention, high photocatalytic activity can be reliably obtained.

(Second Embodiment)
7 is a cross-sectional view schematically showing a configuration of a fluorescent lamp as a photocatalyst according to the present invention, FIG. 7A is a cross-sectional view including a cut-out cross section, and FIG. 7B is a configuration of the fluorescent lamp. The typical sectional view of the photocatalyst film which is is shown.
Reference numeral 40 in the drawing indicates a fluorescent lamp as a photocatalyst body, which is composed of a fluorescent lamp body 50 and a photocatalyst film 60 formed on the surface of the fluorescent lamp body 50. The fluorescent lamp body 50 includes a translucent discharge vessel 51, a phosphor layer 52, a pair of electrodes 53 and 53, a discharge medium (not shown), and a base 54.

  The translucent discharge vessel 51 includes an elongated glass bulb 51a and a pair of flare stems 51b. The glass bulb 51a is made of soda lime glass. The flare stem 51b includes an exhaust pipe, a flare, an internal introduction line, and an external introduction line. The exhaust pipe is used to communicate the inside and outside of the translucent discharge vessel 51 to exhaust the inside of the translucent discharge vessel 51 and enclose a discharge medium. The exhaust pipe is sealed after the discharge medium is sealed. The flare is sealed at both ends of the glass bulb 51a to form a translucent discharge vessel 51.

  The phosphor layer 52 is made of a three-wavelength light emitting phosphor and is formed on the inner surface of the translucent discharge vessel 51. The pair of electrodes 53, 53 are connected between the distal end portions of the pair of internal lead-in wires facing each other inside the both ends of the translucent discharge vessel 51. The electrode 53 is made of a tungsten coil filament and an electron-emitting material deposited on the coil filament.

  The discharge medium is made of mercury and argon, and is enclosed in the translucent discharge vessel 51. An appropriate amount of mercury is sealed through an exhaust pipe. The base 54 includes a base body 54a and a pair of base pins 54b and 54b. The base body 54 a has a cap shape and is bonded to both ends of the translucent discharge vessel 51. The pair of base pins 54b, 54b are supported by the base body 54a in an insulative relationship with each other and are connected to external lead-in wires, respectively.

  The photocatalyst film 60 is a film made of a photocatalyst paint mainly composed of tungsten trioxide fine particles (average particle diameter: 0.1 μm), and has a film thickness of about 0.5 to 3 μm. The tungsten trioxide fine particles maintain the crystal structure of the above embodiment even after the coating is completed. The photocatalyst film 60 is formed of photocatalyst fine particles 61 and a binder 52 having a good ultraviolet or visible light transmission property such as alumina fine particles, silica fine particles, or zirconia fine particles. The photocatalyst fine particles 51 are composed of tungsten trioxide fine particles 51a and calcium carbonate fine particles 51b attached to the surfaces of the tungsten trioxide fine particles 51a. The binder 52 is added in a range of 10 to 50% by mass with respect to the tungsten trioxide fine particles 51a. Moreover, when acrylic modified silicone or silicone resin is used for the binder 52, it can be set as the photocatalyst film | membrane hardened | cured at 20-200 degreeC. The calcium carbonate fine particles 51b function as a substance that adsorbs NOx (nitrogen oxide) or SOx (sulfur oxide). If it is not necessary to suppress the deterioration of the tungsten trioxide fine particles 51a by NOx or SOx, the calcium carbonate is obtained. The attachment of the fine particles 51b is not essential.

FIG. 8 is an explanatory view schematically showing a configuration of a deodorizing unit as a photocatalyst according to the invention, FIG. 8 (A) is a schematic perspective view of the deodorizing unit, and FIG. 8 (B) is FIG. ) Is a schematic side view. In FIG. 8B, the tungsten trioxide fine particles are not shown for convenience.
Reference numeral 61 in the figure denotes a deodorizing unit as a photocatalyst, which has a corrugated plate-like cross section arranged between upper and lower flat mesh-like first and second filters 62a and 62b and these filters 62a and 62b. And a third filter 63. Each of the filters 62a, 62b, 63 carries tungsten trioxide fine particles (average particle size: 0.1 μm) 64 according to the present invention. A plurality of GaN blue light emitting diodes 65 are disposed below the second filter 62b. Instead of the diode 65, a white light emitting diode using a phosphor excited by blue light may be arranged. In the deodorizing unit having such a configuration, when the air passes through the third filter 63 between the first and second filters 62a and 62, for example, from the left side to the right side, the air touches the trioxide fine particles carried on each filter. The deodorization is performed.

  The tungsten oxide fine particles of the present invention can also be prepared by the method described in paragraphs [0022] to [0031] of the specification of Japanese Patent Application No. 2007-184488 filed earlier by the present applicant. .

  The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the spirit of the invention in the stage of implementation. Furthermore, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, the particle diameter, the angle by XRD crystal structure observation, and the like shown in the embodiment may be arbitrarily changed within the range defined in the claims. Furthermore, you may combine the component covering different embodiment suitably.

FIG. 1 shows a schematic view of an apparatus for synthesizing tungsten oxide according to the present invention. FIG. 2 shows a schematic diagram of a measuring apparatus for the acetaldehyde gas decomposition test. FIG. 3 shows the band gap energy states of the two samples. FIG. 4 shows the results of structural analysis by XRD of two samples. FIG. 5 illustrates an acetaldehyde gas decomposition effect of a tungsten oxide film according to an embodiment of the present invention. FIG. 6 shows a characteristic diagram of XRD data of a WO ₃ fine particle photocatalyst having different crystal planes. FIG. 7 is a schematic explanatory view of a fluorescent lamp as a photocatalyst according to the present invention. FIG. 8 is a schematic explanatory diagram of a deodorizing unit as a photocatalyst according to the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Tungsten wire cable, 2 ... Metal tungsten wire, 3 ... Gas burner, 4 ... Hume, 5 ... Electric dust collector, 6 ... Hume suction pipe, 7 ... Electric furnace, 8 ... Desiccator, 12 ... Multi-gas monitor, 13 ... Piping .

Claims (5)

It consists of tungsten oxide particles having an average particle diameter of 0.01 to 0.05 μm, and has a peak intensity of an angle 2θ = 24.380 ± 0.3 ° in XRD crystal structure observation using a CuKα target. Tungsten oxide visible light responsive photocatalyst. 2. The tungsten oxide visible light responsive photocatalyst according to claim 1, wherein the particles are tungsten trioxide fine particles having a band gap energy of 2.4 to 2.8 eV obtained by optical measurement. The tungsten oxide visible light responsive photocatalyst according to claim 1 or 2, comprising particles having a cubic, monoclinic or triclinic crystal structure. A tungsten oxide visible light responsive photocatalyst according to any one of claims 1 to 3, and any one of Al, Zr, and Si metal oxide binders or Al-Si composite oxide binders as the visible light responsive type. A visible light responsive photocatalyst coating material, comprising 1 to 10% by mass based on the photocatalyst medium. A visible light responsive photocatalyst body, wherein the visible light responsive photocatalyst coating amount according to claim 4 is applied to form a photocatalyst film.

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