JP2008260011A - Visible light-responsive photocatalyst and its producing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a titanium oxide-based photocatalyst which can exhibit high photocatalytic activity to visible light and can be mass-produced and to provide a photocatalyst-functional member. <P>SOLUTION: Titanium oxide is mixed with a bismuth compound and the obtained mixture is fired to obtain the visible light-responsive photocatalyst in which bismuth is deposited on titanium oxide and on the surface of which bismuth is thickened. When lower-valent bismuth is contained in bismuth oxide, the visible light-responsive photocatalyst having higher activity can be obtained. When at least one element selected from Si, Zr, Al, W, Mo, Mg, Hf and B is contained in titanium oxide, the activity of the visible light-responsive photocatalyst is promoted much more by the bismuth compound. It is preferable that the atomic ratio of Bi to Ti is 0.0001-10. The promotion of the activity of the visible light-responsive photocatalyst by deposition of the oxide of lower-valent bismuth can be applied even to the titanium oxide-based photocatalyst available commercially. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a visible light responsive photocatalyst capable of exhibiting a photocatalytic action not only by ultraviolet rays but also by irradiation with visible light, and a method for producing the same.

  The photocatalytic action exhibited by titanium oxide has been applied to various environmental purification technologies such as deodorization, antibacterial and antifouling. The band gap of anatase-type titanium oxide generally used as a photocatalyst is about 3.2 eV, and the reaction proceeds upon receiving ultraviolet light having a wavelength shorter than about 380 nm. Therefore, ultraviolet light is required for operation. Therefore, in order to use this photocatalyst, there has been a problem that installation environment, usage, and the like are limited.

  If visible light that is abundant in sunlight or indoor light can be used as an energy source for the photocatalyst, the photocatalyst can be used in various places. In response to this, development of a visible light responsive photocatalyst that exhibits photocatalytic activity by irradiation with visible light has been energetically advanced in recent years.

Photocatalysts having visible photocatalytic activity include the following:
(1) Nitrogen type in which nitrogen is contained in titanium oxide (for example, Chem. Phys. Lett 123 (1986) 126-128; Journal of the Chemical Society of Japan, 1986 (8), p. 1084, and WO 01/010552);
(2) Oxygen defect type in which oxygen defects are introduced into titanium oxide (for example, JP-A-2001-205103);
(3) A metal dope type in which another metal (ion) is contained in titanium oxide or a metal oxide is combined.

Various examples of the metal-doped type (3) have been proposed as described below.
JP-A-9-262482 discloses titanium oxide in which vanadium or chromium is ion-implanted.

Chem. Commun. 2001, 2718-2719 reports titanium oxides having visible light activity, containing transition metals such as V, Cr, Nb, and Mo.
In JP-A-2004-43282, various metal compounds and titanium compounds are mixed in a dissolved state, co-precipitated as hydroxides, and then the precipitates are fired, whereby titanium oxide having visible light activity is obtained. A manufacturing method is disclosed.

  The photocatalyst having visible light activity described in JP-A-2004-275999 is selected from Si, Ti, V, Sn, Sb, W, Nb, Bi, P, Mo, Cs, Ge, As, Ce, and the like. Made of titanium oxide containing a metal compound. This photocatalyst is produced by a method comprising contacting titanium oxide or a precursor thereof with a gas containing a metal halide.

On the other hand, J. Mat. Sci. Lett. 21, 2002, 1655-1656 reports on the effect of enhancing the ultraviolet activity of a titanium oxide photocatalyst containing bismuth and increasing the wavelength of the absorption spectrum. More recently, ultraviolet rays of titanium oxide with addition of bismuth prepared by mixing titanium alkoxide and bismuth chloride in a liquid as a precursor of titanium oxide and bismuth oxide in Mat. Lett., 60, 2006, 1296-1305, respectively. There have been reports on degradation activity and superhydrophilicity.
JP 2001-205103 A JP-A-9-262482 JP 2004-43282 A JP 2004-275999 A WO 01/010552 Chem. Phys. Lett 123 (1986) 126-128 The Chemical Society of Japan, 1986 (8), p.1084 Chem. Commun. 2001, 2718-2719 J. Mat. Sci. Lett. 21, 2002, 1655-1656 Mat. Lett., 60, 2006, 1296-1305

  The titanium oxide photocatalyst having visible light responsiveness described above cannot be said to have high activity under visible light irradiation in any of nitrogen type, oxygen defect type and metal dope type. In addition, many of them require an ion implantation apparatus and a sputtering apparatus for manufacturing, and have another problem that they are not suitable for mass production.

  The present invention provides a photocatalyst capable of exhibiting excellent visible photocatalytic activity and a production method thereof that is simple and suitable for mass production.

According to the present invention, the above problem is solved by a visible light responsive photocatalyst made of titanium oxide having a specific bismuth compound supported on the surface.
The visible light responsive photocatalyst according to the present invention has been completed based on the following findings (1) to (3).

(1) Preferably, bismuth oxide is supported on the surface of titanium oxide containing anatase-type crystals, and the bismuth content is concentrated on the surface of titanium oxide, preferably bismuth contained as an oxide is mixed atoms. The valence state, that is, a part of bismuth is in a low-order valence state of bivalence (Bi ²⁺ ) or less, and is supported in the state of a low-order oxide expressed as BiO _x (x <1.5) as a whole. Then, it becomes a highly active visible light responsive photocatalyst.

  (2) In addition, when a photocatalyst contains other elements such as silicon, zirconium, and aluminum, preferably in the base titanium oxide, a highly active visible light responsive photocatalyst is obtained.

  (3) The visible light responsive photocatalyst of the above (1) is a titanium oxide or a solid precursor thereof, BiOX (X = anions such as halogen ion, nitrate ion, organic acid ion, hydroxide ion) or halogenated. It is simply manufactured by mixing a bismuth compound such as bismuth and then firing the mixture. In order to produce the photocatalyst of (2) above, the compound of elements such as silicon, aluminum and zirconium is added to titanium oxide in advance, or the compound of other elements coexists when the titanium oxide is mixed with the bismuth compound. You can do it.

  As described above, there has been a report example in which visible light activity is exhibited by adding and including a metal element including bismuth in titanium oxide. However, as far as the present inventors know, bismuth oxide is supported on titanium oxide having photocatalytic activity, preferably anatase type titanium oxide as in the present invention, and bismuth is concentrated on the surface of titanium oxide as a result. Further, there has been no known knowledge that if the bismuth in the bismuth oxide is supported in a state containing low-order bismuth, it becomes a photocatalyst having excellent visible light response activity.

In one aspect, the present invention is a visible light responsive photocatalyst comprising titanium oxide having a bismuth oxide supported on the surface, wherein bismuth is concentrated on the surface, more preferably bismuth in the bismuth oxide is mixed. It is a titanium oxide-based visible light responsive photocatalyst characterized by containing a valence state, that is, low-order bismuth and represented by BiO _x (x <1.5) as a whole.

Here, the “titanium oxide” is any of titanium dioxide, oxygen-deficient titanium oxide, and titanium oxide containing elements other than Ti and O (for example, nitrogen, carbon, sulfur, and other metal elements). May be. As the existence form of other elements, any of the following is possible:
(1) Combined with titanium oxide at a certain ratio like metal titanate to form a composite oxide (when other elements are metals),
(2) contained in titanium oxide as a doping element occupying the position of O or Ti in the titanium oxide crystal lattice,
(3) It is microscopically and uniformly mixed with titanium oxide at an indefinite ratio.

  “Supporting” bismuth oxide means that the bismuth oxide is attached to the surface of titanium oxide with some bond. Further, the fact that bismuth is concentrated on the surface means that the concentration of bismuth is higher than the inside on the surface of titanium oxide. The supporting of bismuth oxide and the concentration of bismuth on the surface can be confirmed, for example, by surface analysis of titanium oxide by XPS. That is, if the Bi concentration of the titanium oxide surface obtained by XPS is higher than the Bi concentration of the entire titanium oxide obtained by chemical analysis of the titanium oxide, it is confirmed that bismuth is concentrated on the surface and supported on the surface. means. In the present invention, when the surface Bi concentration is at least 2.0 times higher than the chemical analysis value of Bi (which indicates the average Bi concentration in the entire titanium oxide), it is called “concentration”.

In the present invention, bismuth is supported as an oxide on the surface of titanium oxide, and preferably the bismuth is in a mixed valence state, that is, a low order (bivalent or less) represented by BiO _x (x <1.5) as a whole. ) Containing bismuth oxide. The fact that bismuth is supported on the surface of titanium oxide in this low-order oxide state can also be confirmed by surface analysis of titanium oxide by XPS, for example.

  “Titanium oxide-based visible light responsive photocatalyst” means a visible light responsive photocatalyst utilizing the photocatalytic function of titanium oxide. Titanium oxide is not necessarily the main component of the photocatalyst.

The visible light responsive photocatalyst of the present invention includes the following embodiments:
The bismuth oxide covers at least part of the surface of the titanium oxide;
The atomic ratio (Bi / Ti) of Bi and Ti contained in the photocatalyst is 0.001 or more and 1.0 or less;
The peak ratio R (the ratio of the second peak / first peak) of the radial distribution around the bismuth atom when the photocatalyst is analyzed by XAFS is 0.4 or less;
The peak ratio R of the radial distribution is 0.15 or less;
The photocatalyst contains at least one element M selected from silicon, zirconium, aluminum, tungsten, molybdenum, magnesium, hafnium, and boron;
The content of the element M in the photocatalyst (the total amount when two or more elements are contained) is such that the atomic ratio (M / Ti) to Ti is 0.0001 or more and less than 1.0. ;
The element M is contained in titanium oxide;
-Titanium oxide is at least partly crystalline and the main crystal form of the crystals is anatase.

  The element M is “contained in titanium oxide” means that the element M is mixed with titanium oxide at a molecular level, for example, incorporated into the crystal structure of titanium oxide (for example, Ti at a lattice point). M is substituted, M is present at the crystal grain interface, etc.). On the other hand, the photocatalyst contains the element M when the element M is contained in the titanium oxide as described above, or when the element M is in a physically mixed state with the titanium oxide, or when the element M is oxidized. This includes cases where the surface of titanium is coated or supported on the surface.

  From another aspect, the present invention provides a step of mixing titanium oxide or a solid precursor thereof with a bismuth compound, preferably at a ratio such that the Bi / Ti atomic ratio is 0.001 to 1.0 or less. And firing the mixture to obtain titanium oxide having the bismuth oxide supported on the surface thereof. The method for producing the titanium oxide-based visible light responsive photocatalyst is characterized by comprising:

This manufacturing method includes the following embodiments:
The firing step is stopped at the stage where the anatase-type titanium oxide is predominant in the X-ray diffraction pattern of the product obtained by firing;
-The baking temperature in the said baking process is 50-800 degreeC;
The bismuth compound is at least one selected from BiOX (X = halogen ion, nitrate ion, hydroxide ion, organic ion), bismuth halide, bismuth nitrate, bismuth sulfate, and bismuth sulfide;
The titanium oxide or its solid precursor contains at least one element M selected from silicon, zirconium, aluminum, tungsten, molybdenum, magnesium, hafnium and boron;
In the mixing step, in addition to titanium oxide or its solid precursor and bismuth compound, at least one selected from silicon compounds, zirconium compounds, aluminum compounds, tungsten compounds, molybdenum compounds, magnesium compounds, hafnium compounds and boron compounds Mixing the compounds;
-At least one of the compounds to be mixed is an oxide in a dispersion state.

The present invention further encompasses the following various forms:
A photocatalytic functional member having the visible light responsive photocatalyst on the surface of a substrate.
A dispersion for forming a visible light responsive photocatalyst, characterized by containing a dispersed titanium oxide and a dispersed or dissolved bismuth compound in a liquid medium.

A photocatalyst dispersion liquid comprising the visible light responsive photocatalyst dispersed in a liquid medium.
A visible light responsive photocatalytic coating liquid characterized by containing a dispersed titanium oxide, a dispersed or dissolved bismuth compound and a binder in a liquid medium.

  A visible light responsive photocatalyst coating comprising the visible light responsive photocatalyst and a binder in a liquid medium, wherein the content of the photocatalyst is 5 to 95% by mass based on the total amount of nonvolatile components. liquid.

-The manufacturing method of the photocatalyst functional member characterized by performing heat processing, after apply | coating the said dispersion liquid or the said coating liquid to a base material.
A visible light responsive activity enhancer for a titanium oxide photocatalyst, characterized by comprising a bismuth compound.

According to the present invention, the bismuth oxide is supported on the surface of the titanium oxide, preferably at least partially containing anatase crystals, thereby concentrating it on the surface of the titanium oxide, and more preferably included as an oxide. Bismuth is in a mixed valence state, that is, a part of bismuth is in a low-order state less than divalent (Bi ²⁺ ) and is an oxide state represented by BiO _x (x <1.5) as a whole By allowing bismuth to be supported on titanium oxide, a visible light responsive photocatalyst having excellent visible light response can be reliably provided.

  The raw material titanium oxide may not be visible light responsiveness, for example, anatase type titanium oxide. Even in that case, a visible light responsive photocatalyst having high visible light activity can be obtained by the present invention. When the raw material is originally titanium oxide having visible light responsiveness, the visible light catalytic activity can be remarkably enhanced by the present invention.

  The visible light responsive photocatalyst according to the present invention is one in which bismuth in an oxide state is supported on a surface of titanium oxide having photocatalytic activity in response to at least ultraviolet rays so that the surface is concentrated. Gains visible light responsiveness. It is not necessary for all of the bismuth oxide in the photocatalyst to be supported on titanium oxide (that is, to adhere to the surface), and some bismuth oxide is not supported but may be present in a mixed state with titanium oxide. Alternatively, it may be contained in titanium oxide. However, bismuth needs to be concentrated on the surface of titanium oxide as an oxide. Preferably, bismuth coats at least a part of the surface of titanium oxide as an oxide.

Although the mechanism by which the visible light responsive photocatalyst of the present invention exhibits visible light activity (visible light responsiveness) is not known at present, titanium oxide and bismuth oxide concentrated on its surface, preferably low-order bismuth, are used. Visible light is absorbed as a new transition generated by the interaction with the oxide containing (BiO _x : x <1.5), and the generated carrier is involved by the involvement of titanium oxide (preferably anatase) and low-order bismuth oxide. It is considered that the charge is effectively separated and the visible light activity is expressed or enhanced.

  Various substances can be used as titanium oxide. However, a titanium oxide that at least partially contains crystalline titanium oxide having an anatase structure is preferable from the viewpoint of catalytic activity. Preferably, anatase-type titanium oxide provided with visible light responsiveness by doping nitrogen, fluorine, hydrogen, carbon, transition metal, sulfur or the like can also be used. Among these, it is preferable to use anatase-type titanium oxide imparted with visible light responsiveness by nitrogen doping (containing nitrogen) because high visible light catalytic performance can be obtained. Even in the case of ordinary titanium oxide having no visible light responsiveness or titanium oxide exhibiting visible light responsive photocatalytic properties, it is preferable that low-order bismuth be added so that bismuth is concentrated on the surface of titanium oxide according to the present invention. A photocatalyst having high visible light activity can be obtained by supporting it in the form of an oxide containing.

The detailed structure of the bismuth oxide supported on titanium oxide is still unclear. From the structural analysis by XAFS (X-ray absorption fine structure), it seems that bismuth may partially make a new compound with titanium oxide. However, it has been found that a state in which bismuth is supported on the surface of titanium oxide as fine oxide particles is preferable. Bismuth oxide is not only trivalent (Bi ³⁺ ) but also low-order divalent (Bi ²⁺ ), monovalent (Bi ¹ ), and zero valence (Bi) from surface analysis by XPS and the like. ⁰ )), that is, a low-order oxide (BiO _x : x <1.5) as a whole, and the result suggesting the possibility that oxygen vacancies exist around bismuth Have gained. Bismuth hardly affects bulk titanium oxide, and the titanium oxide maintains the original crystal structure (eg, anatase).

  From various elemental analyzes, it is known that the bismuth concentration in titanium oxide of bismuth supported as an oxide in this catalyst is overwhelmingly higher on the surface than on the bulk. The surface is concentrated in an oxide state. This is consistent with the FT-IR result that OH groups on the surface of titanium oxide are reduced by the presence of bismuth oxide. The interaction between bismuth oxide (high concentration) present on the surface and anatase titanium oxide is strengthened, and a new visible light absorption transition occurs. After absorption of visible light, it is thought that carriers are efficiently transferred between an anatase crystal having high charge separation efficiency and a low-order oxide of bismuth, and as a result, high visible light activity can be obtained.

  By contacting BiOX (X is an anion such as nitrate ion, chlorine ion, hydroxyl ion, etc.), bismuth halide, bismuth nitrate with titanium oxide or a solid precursor, and applying heat treatment as necessary Bismuth oxide supported on titanium oxide has been found to be most effective.

  In the visible light responsive photocatalyst of the present invention, when at least one element M such as silicon, aluminum, zirconium or the like is originally contained in titanium oxide, an ideal structure can be easily obtained, and therefore, more excellent visible light activity and higher Performance stability is provided. There are many possible roles for element M. One is to suppress the crystal transition during the firing of titanium oxide, maintain the original crystal structure, preferably the anatase structure, and maintain a high specific surface area of titanium oxide. is there. On the other hand, by being contained in titanium oxide, the surface state is changed, the surface wettability is increased, and the solid acid point is further increased. These make it easier for the bismuth compound to react with the titanium oxide (surface) during production, and the low-order oxidation state such as a low-coordinate structure in which the bismuth compound is finely bonded to the surface of the titanium oxide. The change to bismuth oxide is promoted.

  Furthermore, as an important finding, visible light absorption after supporting a bismuth compound on titanium oxide often increases to a considerably long wavelength when the element M is not contained or is outside the proper range. On the other hand, if the titanium oxide contains an element M in an appropriate range in advance, the visible light absorption after supporting the bismuth compound is located on the relatively short wavelength side and the intensity is not so strong. From these facts, it seems that the main role of the element M in the titanium oxide is also effective in suppressing the solid reaction between the titanium oxide and the bismuth compound (for example, incorporation of bismuth into the titanium oxide lattice). It is.

Regarding the enhancement of the visible light responsive photocatalytic activity by the bismuth compound, the present inventors have further obtained the following findings.
The activity of a visible light responsive photocatalyst composed of titanium oxide containing bismuth is related to the structure of bismuth contained in titanium oxide, and is contained in titanium oxide revealed by XAFS (X-ray absorption fine structure) analysis. The activity changes according to the arrangement of atoms of bismuth, that is, the atomic correlation. Specifically, when the peak ratio R (second peak / first peak) of the radial distribution around the bismuth atom when the XAFS analysis of the photocatalyst is 0.4 or less, the visible light activity increases. The peak ratio R of the radial distribution is preferably 0.15 or less. The small second peak that is considered to exist if there are two or more layers of bismuth oxide on the titanium oxide surface is that bismuth oxide (BiO _x : x <1.5) is supported on the titanium oxide surface in a state close to a monolayer. Means that

In a preferred embodiment, the visible light responsive photocatalyst of the present invention is obtained by using titanium oxide (or a solid precursor thereof) containing anatase crystal as a raw material and supporting bismuth oxide thereon. Bismuth in titanium oxide is concentrated on the surface of titanium oxide, and more preferably, bismuth contained as an oxide is in a mixed valence state, that is, it contains low-order bismuth (Bi ²⁺ ) or less. However, it is important to support in a low-order oxide state represented by BiO _x (x <1.5) as a whole.

  The supported state can be a state in which the low-order bismuth oxide is adhered to the surface of the anatase-type titanium oxide in the form of fine particles or is coordinated on the surface, or the surface of the titanium oxide is coated or monolayered. A preferable support is a state in which a bismuth oxide containing low-order bismuth coats at least a part of titanium oxide. In the vicinity of the interface between the supported bismuth oxide and titanium oxide, solid solution or generation of a new compound may partially occur. The fact that bismuth oxide is supported on the surface of titanium oxide and that it is coated with bismuth oxide means that SEM (scanning electron microscope), FT-IR (Fourier transform infrared spectrophotometry), various absorptions. It can be confirmed by desorption heat analysis (for example, ammonia TPD <temperature-programmed desorption gas analysis> method, BAT method <benzaldehyde-ammonia titration method>).

  More bismuth supported on the surface of titanium oxide as bismuth oxide is present on the surface than inside titanium oxide, that is, it is necessary to concentrate on the surface. Concentration of bismuth can be most easily achieved by mixing a bismuth compound with titanium oxide so that it diffuses to the surface and selectively reacting with the surface (avoid reaction with the bulk).

Regarding the surface concentration of bismuth, the bismuth content of the extreme surface layer (depth of several nm or less) obtained by XPS is compared with the bismuth content obtained by chemical analysis of titanium oxide indicating the bismuth concentration of the entire catalyst particles. Can be confirmed. Chemical analysis is a method in which a catalyst is once dissolved and the amount of ions contained in the solution is measured. ICP-MASS, luminescence analysis, or the like is used for the analysis. Instead of chemical analysis, the bismuth content obtained by XPS after scraping the surface layer of titanium oxide by sputtering or etching (10 nm or more, preferably 20 nm or more in terms of SiO ₂ ) may be used for comparison. Alternatively, as will be described later, in some cases, the amount of Ni in the titanium oxide can be approximated by the amount of Bi charged.

  In the photocatalyst of the present invention, the bismuth concentration of the titanium oxide surface layer measured by XPS is higher than the bismuth concentration of the deep portion measured after removing the surface layer by sputtering or the like or the bismuth concentration measured by chemical analysis. Specifically, the bismuth surface layer concentration (at%) quantitatively analyzed by XPS is twice or more the chemical analysis value. When compared with the concentration when the surface layer is removed by sputtering or the like, the concentration measured after removing the surface layer with a thickness of at least 20 nm is used, and the bismuth concentration of the surface layer is 1.5 times or more of the concentration after sputtering. Preferably, it may be twice or more.

The bismuth oxide only needs to have a bond of Bi—O, but bismuth is in a mixed valence state, that is, contains low-order bismuth less than divalent (Bi ²⁺ ), and BiO _x as a whole. It is preferable to carry in a state containing a low-order oxide represented by (x <1.5). Specific examples include ultrafine particles, those having oxygen vacancies and unsaturated bonds, and those having a structure coordinated on the surface of titanium oxide. Bismuth compounds composed of Bi ³⁺ , for example, bismuth oxide (Bi ₂ O ₃ ), bismuth titanate (Bi ₃ Ti ₄ O ₁₂ ), bismuth oxyoxide (BiOX, X = acid anions such as halogen ions and nitrate ions), water Oxide ions, organic acid ions) and the like may be partially included, and the bismuth oxide existing on the titanium oxide surface may be represented by BiO _x : x <1.5.

In order to determine BiO _x (x <1.5) most simply, the Bi-4f core level spectrum obtained by XPS analysis of the titanium oxide photocatalyst of the present invention is
(A) 165 to 162.5 eV and 159.7 to 157.2 eV,
(B) 163-161 eV and 157.7-155.7 eV, and (c) 162.5-160 eV and 157.2-154.7 eV,
It is preferable to have at least two pairs of peak pairs out of the three pairs of peaks located in each range.

According to Journal of Electron Spectroscopy and Related Phenomena, 25 (1982) 181-189, in the XPS spectrum diagram based on the Bi-4f core level of the titanium oxide photocatalyst, (a) 165 to 162.5 eV and 159.7 to The peaks located in each range of 157.2 eV are attributed to the Bi-4f 5/2 state and Bi-4f 7/2 state of Bi ³⁺ (Bi ₂ O ₃ ), respectively (c) 162.5 to 160 eV and The peaks located in the respective ranges of 157.2 to 154.7 eV are attributed to the Bi-4f 5/2 state and the Bi-4f 7/2 state of Bi ⁰ (metal Bi), respectively. According to Chemistry of Materials, 8 (1996), p.1287-1291, in addition to the above documents, (b) peaks located in the ranges of 163 to 161 eV and 157.7 to 155.7 eV are represented by Bi ²⁺ ( Are attributed to the Bi-4f 5/2 and Bi-4f 7/2 states, respectively. As can be seen, the energy difference between the Bi-4f 5/2 state and the Bi-4f 7/2 state in each pair is 5.3 (± 0.1) eV.

Accordingly, the fact that the XPS spectrum diagram has at least two pairs of peaks among the three pairs of peaks located in the ranges of (a) to (c) above indicates that oxidation in the titanium oxide photocatalyst of the present invention The bismuth contained in titanium is not only trivalent bismuth (Bi ³⁺ ) but also at least partially divalent (Bi ²⁺ ) and / or zero valent (Bi ⁰ ), that is, compared to trivalent. It means that it exists in a low order (low valence) state. In this low-order bismuth state, it is presumed that excellent visible light catalytic performance is exhibited.

Further, the spectral diagram is more preferably one of the following:
(1) having three pairs of peaks of (a), (b) and (c);
(2) The total area of the pairs of peaks in each of the groups (a), (b), and (c) is a, b, and c, respectively, and the value of the peak area ratio of (b + c) / a is 0.15 or more. is there;
The visible light responsive photocatalyst of the present invention includes silicon, germanium, boron, aluminum, gallium, indium, zinc, lithium, sodium potassium, cesium, rubidium, magnesium, scandium, zirconium, hafnium, niobium, tantalum, barium, strontium, calcium When at least one other element selected from tungsten is contained, the visible light catalytic activity is improved.

These elements have the characteristics of maintaining the anatase structure of titanium oxide and maintaining its specific surface area higher than when it is not added. In addition, the wettability of the titanium oxide surface can be increased, or the surface can be provided with a solid acid point. In particular, bismuth compounds are easily decomposed on the surface of titanium oxide due to solid acid sites strengthened both in strength and in quantity by adding M, resulting in a state of fine low-order bismuth oxide (BiO _x : x <1.5). It will be easier. Further, in the firing step during the production of the photocatalyst, miniaturization proceeds even at a low temperature, so that Bi is not easily incorporated into the basic crystal structure of titanium oxide more than necessary, and there is an effect that high activity can be maintained.

  Among these, silicon, zirconium, aluminum, tungsten, molybdenum, magnesium, hafnium, and boron are preferable because of higher activity. Accordingly, preferred visible light responsive photocatalysts contain at least one of these elements.

  The existence form of the other element (M) in the photocatalyst may be either supported on the titanium oxide as an oxide (attached to the surface or coated) or contained in the titanium oxide. The inclusion in titanium oxide may be either metal substitution of the Ti network of titanium oxide or formation of a composite oxide by combination with titanium oxide. Further, the metal element may be transferred into the bismuth compound after being supported. However, in order to obtain higher activity, these elements are preferably contained in titanium oxide. The element contained in the titanium oxide is most preferably silicon from the viewpoints of the active surface, cost, and ease of handling.

It is very preferable that the titanium oxide in the visible light responsive photocatalyst of the present invention contains at least a part of titanium oxide having an anatase structure. Titanium dioxide having a TiO ₃ unit such as titanium dioxide (TiO ₂ ) and strontium titanate can be used. In the case of titanium dioxide (TiO ₂ ), in addition to the anatase type, a rutile type crystal, a brookite type crystal or an amorphous part may be contained. The crystal form of titanium oxide can be confirmed by an X-ray diffraction pattern.

  For those that can only absorb ultraviolet rays, such as anatase type titanium oxide, nitrogen, fluorine, hydrogen, sulfur, carbon, hydrogen, bismuth, transition metals such as iron, vanadium, chromium, platinum compounds, silver compounds, etc. Visible light-responsive titanium oxide imparted with visible light responsiveness by doping at least one element selected from noble metals may be used. If visible light responsiveness is previously imparted to the base titanium oxide, the visible light activity may be significantly improved by supporting the bismuth oxide. The doping amount varies depending on the kind of the doping element, but the doping amount and the doping method are not particularly limited as long as visible light responsiveness can be imparted.

  In the case of visible light-responsive titanium oxide, anatase-type titanium oxide doped (containing) nitrogen is preferable from the viewpoints of performance, availability, and activity stability. In this case, the doping amount of nitrogen in the titanium oxide is preferably 0.0005% by mass or more and 1.0% by mass or less. The nitrogen doping form may be any of a NO doping type, a TiN doping type, or a mixture thereof.

  The amount of the bismuth compound contained in the visible light responsive photocatalyst of the present invention should be such that the atomic ratio (Bi / Ti) of bismuth and Ti contained in the photocatalyst is 0.001 or more and 1.0 or less. preferable. If the amount of bismuth is outside this range, the effect of promoting visible light catalytic activity is low, and sufficient visible light catalytic activity cannot be obtained. The more preferable range of the Bi / Ti atomic ratio depends on the type and cost of the target photocatalytic reaction, but from the viewpoint of reactivity (photodecomposition characteristics, superhydrophilic characteristics), it is generally about 0.01 or more, 0 .30 or less is recommended. The Bi / Ti atomic ratio can be adjusted by the amount of Bi compound charged during the production of the catalyst of the present invention.

  On the other hand, when the visible light responsive photocatalyst contains other elements M such as silicon, zirconium, aluminum, tungsten, molybdenum, and boron, the content of other elements M in the photocatalyst (contains two or more elements M). The total amount in this case) is preferably such that the atomic ratio (M / Ti) to Ti in the photocatalyst is 0.0001 or more and less than 1.0, and this atomic ratio is more preferably 0.001 or more. , Less than 0.3. When the amount of the other element M is within this range, the effect of enhancing the visible light catalytic activity by supporting the bismuth compound becomes more remarkable, and a highly active visible light responsive photocatalyst can be obtained.

  In the visible light responsive photocatalyst according to the present invention, it has been found that the structure of bismuth supported on titanium oxide is greatly involved in the expression of activity, and when this is a specific structure, high visible light activity can be obtained. That is, the visible light catalytic activity differs depending on the arrangement of atoms of bismuth contained in titanium oxide, that is, the atomic correlation, which is clarified by XAFS analysis. Specifically, when the structure is such that the peak ratio R (second peak / first peak) of the radial distribution around the bismuth atom observed by the XAFS method is 0.4 or less, high visible light It becomes a photocatalyst showing activity.

  The XAFS method will be briefly described. An X-ray absorption spectrum XAFS (X-ray absorption fine structure) spectrum is observed when photoelectrons generated by irradiating a specific atom with X-rays are scattered or interfered with the surrounding atoms. On the other hand, if a Fourier transform is performed in an appropriate region, a radial distribution function is obtained. This function is a one-dimensional distribution of electron density centered on the element of interest, and there is some atom at the distance showing the maximum value, and its intensity is proportional to the electron density of the atom that is located. ing. When this radial distribution function is numerically analyzed, structural information about the element of interest (coordination number, interatomic distance, etc.) can be obtained. The measurement may be performed in the atmosphere or at room temperature, and any of solid, liquid, and gas may be used.

  A specific example of the radial distribution function obtained by the above method will be described. XAFS measurement was performed by a transmission method using a Si (111) 2 crystal monochrome and scanning between X-ray energies in a range of 1 to 6 eV. The integration time was 2 to 10 seconds / point. The radial distribution from XAFS was determined as follows. The background was subtracted from the measured EXAFS spectrum using the Victorian equation with a constant term, the absorbance of isolated atoms was estimated by the Cubic-Spline method, and the EXAFS signal was extracted. The extracted EXAFS signal was multiplied by overlap kn (n = 2) and Fourier transformed to derive a radial structure function which is a function of the distance from the absorbing atom.

FIG. 2 shows the result of obtaining the radial distribution around the bismuth atom by the XAFS method in the procedure as described above. First, the reference material Bi ₂ O ₃ (manufactured by Wako Pure Chemical Industries, Ltd. -α type (slightly containing β)) has a peak with a maximum intensity in the vicinity of 1.7 A in the radial distribution, and is between 3 and 4 km. It has a high intensity peak. The positions of these peaks indicate the distance from bismuth to adjacent atoms. The peak corresponding to bismuth and the nearest atom, that is, the oxygen atom is the first peak in the vicinity of 1.7Å in FIG. 2, and the peak corresponding to bismuth and the second adjacent atom, that is, the nearest bismuth atom is 3- It is a peak between 4A. In the present invention, based on the radial distribution of Bi ₂ O ₃ (measured in the same manner), the peak near Bi ₂ O ₃ 1.7 Å is the first peak, and the peak between _{3 and 4}と す る is the second peak. . In consideration of the influence of measurement accuracy and the like, a predetermined peak is defined in consideration of an error of ± 0.5 mm, and the intensity of each peak is defined. When a plurality of peaks are present in the specified range or overlap, peak separation is performed as necessary, a predetermined peak is extracted, and a peak indicating the maximum intensity in the range is set as the predetermined peak.

  In the case of titanium oxide supporting bismuth, the peak ratio R (second peak / first peak) of the radial distribution around the bismuth atom observed by the XAFS method in the above method is 0.4 or less. The activity of the visible light responsive acid photocatalyst is increased. R is preferably 0.15 or less. This means that the existence probability of the second adjacent atom is low, that is, bismuth exists in a state of extremely fine dispersion and / or a low coordination number.

When the Bi / Ti atomic ratio of the photocatalyst exceeds 1.0, a structure close to Bi ₄ Ti ₃ O ₁₂ is obtained, the R value increases, and the visible photocatalytic activity decreases. In this sense, the preferred Bi / Ti atomic ratio is 0.5 or less.

Next, the manufacturing method of the visible light responsive photocatalyst of this invention is demonstrated.
The visible light responsive photocatalyst of the present invention includes a step of mixing titanium oxide or a solid precursor thereof with a bismuth compound, and a step of firing the obtained mixture. By calcination, bismuth oxide is supported on the surface of titanium oxide, and bismuth takes a concentrated form on the surface of titanium oxide. Furthermore, normally, bismuth supported as an oxide on the surface of titanium oxide contains a mixed valence state, that is, low-order bismuth having a valence of 2 (Bi ²⁺ ) or less, and BiO _x (x <1 as a whole). It becomes an oxide state represented by .5).

  The firing is preferably stopped at the stage where anatase is predominant in the X-ray diffraction pattern of the fired powder. For the reasons described above, the bismuth compound is preferably mixed with titanium oxide or a solid precursor thereof in such a ratio that the Bi / Ti atomic ratio is 0.001 to 1.0 or less. When the Bi compound is supported on titanium oxide as a bismuth oxide via hydrolysis, substantially all Bi is supported on titanium oxide, so the Bi / Ti atomic ratio of the produced catalyst is titanium oxide (or It can also be approximated by a value calculated from the precursor) and the amount of Bi compound charged.

  Instead of using a liquid or gaseous titanium oxide precursor (such as titanium alkoxides or titanium tetrachloride) that becomes titanium oxide by hydrolysis or the like as a titanium oxide supply source used as a raw material, titanium oxide or its precursor is already used. Uses isolated in solid form as a solid. If the raw material is not in a solid state, the titanium oxide is homogeneously mixed with the bismuth oxide, and the visible light responsive photocatalyst of the present invention supported so that the bismuth oxide is concentrated on the surface of the titanium oxide. I can't get it.

  Among the titanium oxides used, anatase-type titanium oxide is preferable, and titanium oxide that can already function as a photocatalyst alone is more preferable. This is because the present catalyst uses some of the electronic state of the original titanium oxide by the bismuth oxide. However, even a precursor, a solid product can be used in this production method. Examples of the solid precursor include titanium hydroxide and titania sol (titanium is not completely an oxide, and at least partially contains titanium hydroxide).

  Bismuth compound mixed with raw material titanium oxide or its solid precursor (hereinafter simply referred to as titanium oxide) undergoes hydrolysis or heat treatment to form bismuth oxide, and is supported on titanium oxide in that form. Is preferred. The state of the bismuth compound at the time of mixing may be any of a solid phase (eg, powder), a liquid phase (eg, a solution or dispersion), or a gas phase.

  Examples of the means for mixing the titanium oxide and the bismuth compound include various methods such as solid mixing, impregnation using a bismuth compound in a liquid phase, ion exchange, hydrothermal treatment, and deposition of a bismuth compound in a gas phase. Mixing may or may not be accompanied by stirring. The impregnation method can be carried out, for example, by immersing titanium oxide in a solution containing a bismuth compound or dropping a solution containing a bismuth compound onto titanium oxide. When both the bismuth compound and titanium oxide are powder raw materials, they may be mixed with a ball mill or a blender.

  When titanium oxide forms a liquid phase as a dispersoid, that is, a dispersion (including a sol), mixing this dispersion with a bismuth compound in a liquid phase causes mixing on very small particles, so mixing In many cases, a uniform and highly active visible light responsive photocatalyst is obtained. Therefore, this mixing method is particularly preferred. However, an organic solvent-based ultrafine titanium oxide sol (including some water) obtained by a sol-gel method using a titanium oxide precursor does not provide sufficient activity even when a bismuth compound is introduced. This is presumably because a substance that inhibits the reaction with the bismuth compound remains on the surface or inside of the titanium oxide where the hydrolysis of the precursor is insufficient in the organic solvent. In this case, it is preferable to isolate titanium oxide from the sol solution and then use it as a raw material after sufficient hydrolysis or further baking.

  A dispersion of titanium oxide mixed with a bismuth compound, that is, a dispersion containing a dispersed titanium oxide and a dispersed or dissolved bismuth compound can be treated as a dispersion for forming a visible light responsive photocatalyst of the present invention. it can. This is because the visible light responsive photocatalyst of the present invention can be formed on the surface of the substrate when the dispersion is directly applied to the substrate and subjected to heat treatment. Moreover, it can also use as a coating liquid for manufacturing the photocatalyst functional member base material of this invention by adding a suitable binder as needed. In particular, a water-based titanium oxide dispersion containing a bismuth compound is preferred from the viewpoint of photocatalytic performance, environmental aspects, and cost.

  A mixture of the bismuth compound and titanium oxide is dried as necessary and then fired. The firing is preferably stopped at the stage where the anatase-type titanium oxide is predominant in the X-ray diffraction pattern of the fired powder. This applies to both cases where the raw material titanium oxide contains anatase-type titanium oxide and not. Even if the raw material does not contain anatase-type titanium oxide, titanium oxide becomes anatase during firing, but if firing proceeds further (for example, if the firing temperature is high or the firing is too long), oxidation other than anatase Visible photocatalytic activity is reduced due to increased crystal formation of titanium (eg, rutile) and bismuth oxides.

  The specific heat treatment temperature (firing temperature) in firing is from 80 ° C to 800 ° C, more preferably from 200 ° C to 600 ° C. This is the most active visible light responsive photocatalyst in this temperature range. When the raw material is anatase titanium oxide and the bismuth compound is also bismuth oxide, a relatively low firing temperature can be employed. On the other hand, when the raw material is non-anatase type titanium oxide or a solid precursor of titanium oxide and / or when the bismuth compound is not an oxide, the firing temperature necessary for the production of anatase type titanium oxide and bismuth oxide is set. use.

  The firing time (heat treatment temperature holding time) is not particularly limited, but a range of 10 minutes to 6 hours is appropriate. The rate of temperature increase is not particularly limited, but is preferably 1 ° C./min or more from the viewpoint of photocatalytic activity and productivity.

The atmosphere of the heat treatment may be any of an oxidizing atmosphere such as air, pure air and oxygen, an inert atmosphere such as nitrogen and argon, or a reducing atmosphere containing a reducing gas such as hydrogen and ammonia, and a combination of these. But it ’s okay. Even when fired in an oxidizing atmosphere, bismuth becomes a low-order oxide (BiO _x : x <1.5) during firing due to the reaction between titanium oxide and the bismuth compound. The amount of moisture in the atmosphere is not limited, but is preferably 10% by volume or less. When this concentration is exceeded, the specific surface area of the photocatalyst after heat treatment tends to be small.

  Of the raw materials, titanium oxide is in a solid state, but the bismuth compound mixed therein may be in any state of a solid phase, a liquid phase, and a gas phase. Accordingly, any compound containing bismuth can be used as the bismuth compound. Specific examples include an oxybismuth compound represented by BiOX, bismuth halide, bismuth nitrate, bismuth sulfate, bismuth citrate, bismuth oxide, bismuth alkoxide, and bismuth sulfide. Examples of oxybismuth compounds include bismuth oxybenzoate, bismuth oxynitrate (basic), bismuth oxyhydroxide, bismuth oxychloride, bismuth oxyfluoride, bismuth oxyiodide, dibismuth oxycarbonate, dibismuth oxysulfate, bismuth oxyacetate Bismuth oxyperchlorate, bismuth oxyhydroxide, bismuth oxyoxalate and the like. Bismuth halides include (3) bismuth chloride, (3) bismuth fluoride, (3) bismuth iodide, and (3) bismuth bromide. One or more selected from these bismuth compounds are used for mixing with titanium oxide. It is preferable to use a bismuth compound such as a bismuth salt or an oxybismuth salt that undergoes hydrolysis and condensation to produce bismuth oxide.

  As the raw material titanium oxide, titanium oxide, strontium titanate, and visible light responsive titanium oxide or strontium titanate containing or doped with nitrogen, carbon, transition metal, platinum compound, silver compound or the like can be used. . Of these, titanium oxide doped with nitrogen is preferably used as a raw material in terms of cost and catalyst performance. The nitrogen doping amount and the doping form are as described above. Further, a titanium oxide dispersion, particularly titania sol, can be used as a raw material, and the use of this dispersion is preferred as described above.

  As described above, a titanium oxide precursor such as a hydroxide can be used as a titanium oxide raw material as long as it is solid. Examples of usable precursors include titanium peroxide and hydrated titanium oxide in addition to hydroxide. In the heat treatment step and / or the firing step after the solid titanium oxide precursor is brought into contact with the bismuth compound, the titanium oxide precursor is converted into titanium oxide, so that the present invention comprises titanium oxide carrying a bismuth compound. The visible light responsive photocatalyst is obtained. Again, the titanium oxide precursor can be used in the form of a dispersion (sol).

  The raw material titanium oxide may be a commercially available titanium oxide-based visible light responsive photocatalyst. In that case, when the photocatalyst is brought into contact with a bismuth compound according to the present invention, the visible light responsive photocatalytic activity can be enhanced. Therefore, in this case, the bismuth compound functions as an activity enhancer for the visible light responsive photocatalyst.

  As described above, titanium oxide (including its solid precursor) used as a raw material contains at least one element M selected from silicon, zirconium, aluminum, tungsten, molybdenum, magnesium, hafnium, and boron. Is preferred.

  When the titanium oxide contains the element M, the contact between the bismuth compound and the titanium oxide is optimized during mixing with the bismuth compound, particularly under heating, and as a result, a highly active visible light responsive photocatalyst is obtained. It is done. As described above, it is presumed that the element M promotes the fine support of the bismuth compound by increasing the specific surface area of titanium oxide or providing a solid acid point.

  When a compound of element M, for example, a silicon compound is contained in titanium oxide, the incorporation of bismuth itself into the skeleton of titanium oxide is reduced, and the electronic state of titanium oxide is easily maintained. As a result, it is assumed that carriers generated by the interaction between titanium oxide and bismuth oxide are less likely to be recombined with titanium oxide, resulting in high activity. Most preferably, the silicon compound or the like is incorporated in the form of a silicon oxide such as a composite oxide with a visible light absorbing substance or a bismuth compound or a phase separated oxide.

Non-Patent Document 5 describes that tetraethylorthosilicate serving as a silicon compound is added to an ultraviolet-responsive photocatalyst composed of titanium oxide containing Bi. However, it is specified in the literature that tetraethylorthosilicate is used as a binder for fixing a TiO ₂ photocatalyst that has already incorporated Bi to a glass substrate, and it is an oxidation having visible light response as in the present invention. It does not affect the contact between titanium and bismuth compounds.

Although inclusion of the element M in titanium oxide is not limited, it can be performed by any of the following three methods.
1. At the stage of titanium oxide synthesis, a compound containing element M is added and contained;
2. After synthesizing titanium oxide, a compound containing element M is supported by a method such as a deposition method or an impregnation method (pretreatment of titanium oxide);
3. When mixing the bismuth compound and titanium oxide, a compound containing the element M is added to the system.

  In any method, the visible light responsive photocatalyst of the present invention can be obtained by supporting a bismuth compound. In terms of performance, the method 1 can provide the most active photocatalyst. On the other hand, in the methods of (2) and (3), a highly active photocatalyst can be produced using, for example, an ultraviolet-responsive or visible-light-responsive titanium oxide photocatalyst that is commercially available.

  The above method 1 will be described by taking as an example the synthesis of titanium oxide containing at least one of silicon, zirconium, aluminum, tungsten, molybdenum, magnesium, hafnium, and boron (abbreviated as M).

  A compound such as a chloride containing the element M or an alkoxide is added to a hydrolyzable titanium compound such as titanium tetrachloride, titanium trichloride, titanium alkoxide, or titanium sulfate. Examples of usable silicon compounds include inorganic silicon compounds such as silicon tetrachloride, silicon iodide, silicon nitride, silicon nitrate, and silicon sulfide, as well as alkoxysilanes such as tetraethoxysilane and methyltriethoxysilane, and silicon acetate. And organosilicon compounds such as silicone resins, silica, and silica colloid. Examples of the aluminum compound include inorganic aluminum compounds such as aluminum, aluminum chloride, aluminum fluoride, aluminum hydroxide, aluminum nitrate, and aluminum sulfate, and organic aluminum compounds such as aluminum ethoxide and aluminum isoprooxide. Examples of zirconium compounds include zirconium oxide, zirconium oxide colloid, zirconium chloride, zirconium trichloride, zirconium nitrate, zirconium nitrate oxide, zirconium sulfate, and other inorganic zirconium compounds, as well as zirconium isoproxide, acetylacetonatozirconium, zirconium butoxide, zirconium Examples include organic zirconium compounds such as ethoxide. As the tungsten compound, tungsten chloride or tungsten sulfate can be used (the same applies to the molybdenum compound). In the case of boron, boric acid, boron chloride, boron ethoxide, or the like can be used. The addition amount of the compound containing the element M is 0.0001 to 0.5, preferably 0.001 to 0.30 as the M / Ti ratio.

  Thereafter, nitrogen-containing compounds such as ammonia water, amine, urea, thiourea and the like are added to proceed with hydrolysis, the deposited precipitate is collected, and the obtained solid is baked at about 200 to 700 ° C. A titanium oxide having visible light responsiveness can be prepared. In addition, when the salt by-produced by hydrolysis is difficult to evaporate by baking (for example, when titanium tetrachloride is neutralized with sodium hydroxide, by-produced NaCl, etc.), after the hydrolysis is completed, it is washed thoroughly with water and the surface of titanium oxide By removing more salt, a visible light responsive photocatalyst having high activity is finally obtained. In addition, by performing incomplete firing, a solid titanium oxide precursor in which titanium remains in a hydroxide state can be obtained.

  In the method for producing a photocatalyst of the present invention, at least one of a raw material bismuth compound, visible light-responsive titanium oxide, and, in some cases (in the case of the above-described method 3), a compound containing an element such as silicon, aluminum, or zirconium. It is preferable that one compound has crystallinity. This is because when at least one raw material has crystallinity, the contact during mixing of the bismuth compound and titanium oxide is optimized, resulting in a highly active photocatalyst.

  Examples of the shape of the visible light responsive photocatalyst of the present invention include a particulate shape, a fiber shape, and a thin film shape. In the case of particles, the particles range from a fine powder of about several nm to a granulated body of about several tens of microns, and the size and form are not limited. In the case of a thin film, it is common to fix on a base material.

  When forming into an arbitrary shape such as a thin film or a fiber, it is desirable to add a binder in addition to the photocatalyst particles. By adding a binder, the thickness of the thin film and the fiber diameter can be increased, and the strength and workability of the thin film and fiber can be increased.

  The visible light responsive photocatalyst of the present invention produced by the above method may be used as it is in a powder state. However, from the viewpoint of handling, it is convenient to use this as a photocatalytic functional member that is fixed on the surface of the substrate.

  The form of immobilization can be selected according to the surface shape or application of the substrate, and examples thereof include a thin film shape, a particle shape, and a fiber shape. The type of substrate is not limited, but carbon steel, plated steel, chromate-treated steel, metal materials such as steel, stainless steel, titanium and aluminum, inorganic materials such as ceramic, glass, ceramics and quartz, plastic, resin, activated carbon, etc. These organic materials are exemplified. Moreover, the material which these combined, for example, a coated steel plate, etc. may be sufficient.

  A preferred substrate is one in which the metal or its surface is coated with a material that does not decompose with a photocatalyst. The base material whose whole or the surface is an organic material may be deteriorated or decomposed by the oxidizing power of the photocatalyst. In this case, the base material surface is previously coated with a material that is not decomposed by the photocatalyst. Even an organic material, for example, a silicone resin is not easily deteriorated by a photocatalyst, so that it may not be coated depending on conditions.

  The shape of the substrate is not particularly limited, and may be any shape such as a thin plate, a thick plate, a fibrous shape (including a knitted fabric and a nonwoven fabric), a net shape, and a tubular shape. It may be an object having a complicated shape as it is used as a product as it is, or an existing or in-use object. The surface of the substrate may be porous or dense.

  The most general production of the photocatalytic functional member can be performed by applying a dispersion liquid in which the particles of the visible light responsive photocatalyst of the present invention are dispersed in a solvent to a substrate and drying the coating film. Alternatively, the visible light responsive photocatalyst-forming dispersion in which the visible light responsive titanium oxide and bismuth compound are dispersed in a solvent is applied to a substrate, and the coating film is dried. You may apply | coat, after adding additives, such as a binder, to the said dispersion liquid suitably as a coating liquid. Furthermore, after applying visible light responsive titanium oxide to the substrate, the bismuth compound is contacted by a gas phase treatment such as impregnation or CVD, and then heat treatment is applied as necessary, so that the photocatalytic functional member of the present invention It can also be.

  Thus, the photocatalyst of this invention can also be formed by making a bismuth compound contact with this titanium oxide in the manufacturing stage of the photocatalyst functional member using visible light responsive titanium oxide. For example, a bismuth compound is added to a dispersion medium in which visible light responsive titanium oxide is dispersed, or a film of visible light responsive titanium oxide is formed, and then a bismuth compound is brought into contact therewith.

  The coating solution can also be prepared by simply mixing the visible light responsive photocatalyst of the present invention thoroughly with a medium and a binder. However, the visible light responsive photocatalyst produced by the above-described method is generally very easy to aggregate because the average primary particle system is as fine as several nanometers to hundred nanometers. When the aggregate becomes an aggregate, its diameter is several tens of μm. It becomes difficult to disperse uniformly in the medium.

  Therefore, in a preferred embodiment of the present invention, the visible light responsive photocatalyst particles are sufficiently dispersed in a medium in advance to prepare a photocatalyst particle dispersion. It is preferable to prepare a coating liquid by using this dispersion and incorporating a binder therein. When this coating solution is used, a thinner and more homogeneous photocatalytic film can be formed, and the film characteristics and photocatalytic activity are improved.

  The average particle size of the photocatalyst in the dispersion (particle size of the aggregate) is preferably 500 nm or less. When it is larger than this particle size, the film properties are poor, for example, peeling or adhesion is deteriorated, and the storage stability of the dispersion itself is lowered. The average particle size of the photocatalyst is more preferably 300 nm or less, still more preferably 200 nm.

  Examples of the liquid medium in which the photocatalyst particles are dispersed include water such as distilled water, ion exchange water, and ultrapure water; alcohols such as methanol, ethanol, and 2-propanol; ketones such as methyl ethyl ketone; aroma such as benzene, toluene, and xylene. Group hydrocarbons and the like. These may be arbitrarily mixed and used, but in that case, a combination of solvents compatible with each other is used.

  The dispersion treatment is preferably performed by mixing the photocatalyst with a medium so that the solid content concentration is in the range of several mass% to 50 mass%. When the solid content concentration is outside this range, the dispersibility may be lowered. A dispersant and a peptizer may be added as necessary. Examples of the dispersant include carbonyl and sulfone, and examples of the peptizer include nitric acid, hydrochloric acid, and sulfuric acid. Moreover, you may add a base and an acid for pH adjustment.

  The dispersion treatment can be performed using a paint shaker commonly used for the preparation of a coating solution, but is performed by a more powerful dispersion means such as media mill, shearing using a rotary blade, thin film swirl, and ultrasonic waves. It is preferable to do. Two or more types of dispersing means may be used in combination.

  When the obtained dispersion contains aggregated coarse particles, it is preferable to remove them by filtration or centrifugation. This is because coarse particles tend to be the starting point of peeling and powdering in the film. A solid content concentration can also be adjusted by adding a solvent to the dispersion after the dispersion treatment.

  This dispersion can be used as a coating solution as it is and applied to a substrate. When the photocatalyst is a fine particle having an average particle diameter of 500 nm or less, a film can be formed without a binder, and a film substantially consisting of only photocatalyst particles can be formed. However, since the film strength and adhesion are low as they are, a binder solution may be applied thereon to impregnate the binder between the photocatalyst particles.

  A preferred coating liquid contains a binder in addition to the photocatalyst and the medium. The medium may be similar to that described for the above dispersion but is selected so that the binder dissolves or emulsifies. When a coating liquid is prepared by mixing a binder with the above-described dispersion containing a visible light responsive photocatalyst, a coating film having excellent photocatalytic particle dispersibility, good storage stability, and high photocatalytic activity can be formed. Ting solution can be obtained.

  The amount of the binder is adjusted so that the content of the visible light responsive photocatalyst in the formed film is 5 to 95% by mass. A film having a photocatalyst content of less than 5% by mass exhibits almost no photocatalytic activity by visible light irradiation. When the content of the photocatalyst in the film exceeds 95% by mass, the binder component is too small and the film is easily peeled off. The content of the photocatalyst in the film is preferably 30 to 90% by mass, and more preferably 50% by mass or more in order to sufficiently obtain the photocatalytic activity.

  Binder components include metal oxide sols such as silica, alumina, titania, magnesia, and zirconia (becomes gels in the film), organic silane compounds, and organic resins such as silicone resins, fluororesins, urethane resins, and acrylic resins. Available. When the binder component is decomposed by the oxidizing power of the photocatalyst, it is desirable to use a hard-to-decompose material such as a metal oxide sol, silicone resin, acrylic silicone, or acrylic urethane. Further, when strong workability and high strength are required for the photocatalytic functional member, it is required by adding an appropriate amount of an organic resin such as a fluororesin, an acrylic resin, or a urethane resin to the hardly decomposable binder component. Characteristics can be secured.

  A preferable binder component is a silicon compound such as silica (eg, silica sol), a hydrolyzate / condensate of an organic silane compound, a silicone resin, and the like. The silica may be a silica sol (colloidal silica) produced by hydrolysis and condensation of a silicate ester (eg, ethyl silicate). As the organic silane compound, a film-forming hydrolyzable organic silane compound such as an alkoxysilane or a silane coupling agent can be used. The binder component may be uniformly dissolved in the medium, or may be emulsified in the medium to form an emulsion.

  The coating liquid may contain components other than those described above. Examples of such other components include a photocatalyst that is not a visible light responsive type (eg, a conventional titanium oxide photocatalyst) and a carrier when the photocatalyst is a supported particle. In addition, minor components such as coloring materials (preferably inorganic pigments) and extender pigments can also be included in the film.

  Application | coating of a coating liquid can be selected from well-known various methods according to the property of a coating liquid, and the shape of a base material. After application, the coating film is dried (further cured in some cases) while heating as necessary. The drying (curing) temperature may be determined in accordance with the composition of the coating liquid (type of solvent or binder), the heat resistant temperature of the substrate, and the like. When the coating liquid contains a precursor of a titanium oxide photocatalyst, heating is performed so as to change from the precursor to titanium oxide.

  The thickness of the film containing the photocatalyst formed on the substrate is preferably 0.1 μm or more. When the film is thinner than 0.1 μm, the amount of the photocatalyst is too small, and the photocatalytic activity due to irradiation with visible light becomes very low. The thickness of the film can be appropriately selected depending on the required catalyst performance and cost, but is more preferably 1 μm or more and even more preferably 5 μm or more from the viewpoint of stability of catalyst performance and catalyst activity. The upper limit of the thickness is not particularly specified, but is 50 μm or less, preferably 20 μm or less in consideration of cost and saturation of effects.

  The visible light responsive photocatalyst of the present invention and the photocatalytic functional member provided on the surface of the photocatalyst exhibit a photocatalytic action by contacting a substance to be treated under irradiation with visible light having a wavelength of 400 nm or more as well as ultraviolet light. Thus, various harmful substances and adhered substances can be decomposed, removed, or made harmless. The photocatalyst may be used in an environment in which a substance to be decomposed can be brought into contact therewith and can be irradiated with visible light. The light source only needs to include at least a part of the wavelength range of visible light. For example, sunlight, a fluorescent lamp, a halogen lamp, a black light, a xenon lamp, a mercury lamp, or the like can be used. Since the photocatalyst of the present invention exhibits activity even with ultraviolet rays, the light source may contain visible light and ultraviolet light, and the photocatalytic activity becomes higher.

Examples of harmful substances or deposits that can be treated by the visible light responsive photocatalyst of the present invention include VOC gases such as formaldehyde, acetaldehyde, and toluene; air pollution gases such as No _x , SO _x , and chlorofluorocarbon; ammonia, hydrogen sulfide, and mercaptans. Odor gases such as: Organic compounds such as alcohols, BTX, phenols, etc .; Organic halogen compounds such as trihalomethanes, trichloroethylene, and chlorofluorocarbons; Various pesticides such as herbicides, fungicides, and insecticides; Oxygen-requiring substances; surfactants; inorganic compounds such as cyanide and sulfur compounds; various heavy metal ions; fungi such as Escherichia coli, staphylococci, and green bacteria; microorganisms such as molds and algae; In addition, the visible light responsive photocatalyst of the present invention is superparent by light irradiation. Exhibit sex. In the functional member having the photocatalyst of the present invention on the surface, antifogging property, antifouling property, dustproof property and the like are obtained by the superhydrophilizing action.

The following examples illustrate the invention. However, the examples do not limit the present invention. The ratios such as Bi / Ti and Si / Ti in the examples all mean metal atomic ratios.
Example 1
[Preparation of titanium oxide]
Sample No. 1:
Titanium hydroxide obtained by hydrolyzing titanium tetrachloride with aqueous ammonia (7% by mass) was calcined in the atmosphere at 500 ° C. for 2 hours to obtain titanium oxide. The amount of nitrogen in the titanium oxide was 0.004% by mass. As a result of X-ray diffraction, the main crystal structure of titanium oxide was anatase type.

Sample No. 2:
Titanium oxide containing silicon was obtained by the same method as Sample No. 1 except that silicon tetrachloride was added to titanium tetrachloride (Si / Ti = 0.13). The amount of nitrogen in the titanium oxide was 0.007% by mass. As a result of X-ray diffraction, titanium oxide was anatase type.

(Preparation of bismuth compound)
Sample No. 3:
Bismuth chloride was dissolved in 3N-HCl, and aqueous ammonia (7% by mass) was added to the resulting solution to hydrolyze bismuth chloride. The white powder obtained by filtering the precipitate was dried at 80 ° C. to obtain a bismuth compound used for preparing a visible light responsive photocatalyst according to the present invention. As a result of X-ray diffraction, this compound was identified as bismuth oxychloride.

(Preparation of visible light responsive photocatalyst)
Sample No. 4:
The powder of the bismuth compound of sample No. 3 was added to the powdered titanium oxide of sample No. 1 so that Bi / Ti = 0.09, and kneaded well in a mortar. By calcination at 500 ° C. for 2 hours, a visible light responsive photocatalyst made of titanium oxide carrying bismuth oxide was obtained. When the X-ray diffraction pattern of this sample was taken, the main peak was that of the titanium oxide anatase crystal.

Sample No. 5:
A visible light responsive photocatalyst made of titanium oxide carrying bismuth oxide was prepared in the same manner as in sample No. 4 except that the silicon-containing visible light responsive titanium oxide of sample No. 2 was used. As a result of X-ray diffraction of this sample, titanium oxide was composed of anatase crystals.

Sample No. 6:
Bismuth chloride was added to a liquid titanium tetrachloride aqueous solution (9.3 wt%) so that Bi / Ti = 0.09 and mixed, and then hydrolyzed with aqueous ammonia (7% by mass), and the resulting Bi-containing hydroxide Titanium was baked for 2 hours at 500 ° C. in the atmosphere to obtain titanium oxide containing bismuth oxide. As a result of X-ray diffraction, titanium oxide was an anatase crystal.

Sample No. 7:
After adding liquid silicon tetrachloride and bismuth chloride to a liquid titanium tetrachloride aqueous solution (9.3 wt%) so that Bi / Ti = 0.09 and Si / Ti = 0.13, aqueous ammonia ( 7% by mass), and the resulting Bi-containing titanium hydroxide was calcined in the atmosphere at 500 ° C. for 2 hours to obtain titanium oxide containing bismuth oxide and silicon. As a result of X-ray diffraction, titanium oxide was an anatase crystal.

  Samples Nos. 6 and 7 are comparative titanium oxide photocatalysts produced by hydrolyzing the titanium oxide raw material and the bismuth raw material in a liquid or dissolved state by a coprecipitation method.

[Measurement of FT-IR]
About the support state of Bi, it is estimated from the stretching vibration peak intensity of the OH group in the FT-IR spectrum showing the surface structure. FIG. 1 shows the peak intensity of stretching vibration of Samples 2, 3, 5, and 7. There are almost no OH groups on the surface of bismuth oxychloride (sample No. 3) or bismuth oxide. On the other hand, when bismuth oxide is supported on the surface of titanium oxide, as shown in sample No. 5, the stretching vibration peak intensity of the OH group decreases with respect to base sample No. 2. On the other hand, in the photocatalyst of sample No. 7 synthesized by a coprecipitation method using a liquid titanium oxide precursor and a bismuth compound, the OH group hardly changes. From this, it is considered that the bismuth oxide of Sample No. 7 is not supported on the titanium oxide surface but is mainly taken into the titanium oxide. It is considered that the bismuth compound is taken in at the molecular level when titanium oxide is formed in the liquid from the titanium oxide precursor. In the visible light responsive photocatalyst of the present invention, since titanium oxide is used as a raw material, the bismuth compound reacts mainly on the surface of titanium oxide.

[Measurement of XPS]
XPS analysis was performed under the following conditions:
Equipment used: Scanning X-ray photoelectron spectrometer PHI Quantum 2000 manufactured by ULVAC-PHI
X-ray source used: mono-Al Kα ray 44.8W, 17kV
Extraction angle: 45 °
X-ray beam diameter: about 200μmφ
Neutralizing gun: 1.0V, 20mA (Combined with Ar + low-speed ion gun)
Energy resolution: Pure Ag Ag3d 5/2 peak (368.1 eV) and half-width of about 0.7 5 eV Vacuum degree: about 2.0 × 10 ⁻⁸ torr.

  The spectrum diagram of the Bi-4f core level of sample Nos. 3 to 5 obtained by XPS analysis is shown in FIG. This spectrum is measured without performing the sputtering treatment and reflects the surface state of the outermost surface of titanium oxide.

In the XPS spectrum diagram of the Bi-4f core level of the titanium oxide photocatalysts of No. 4 and No. 5 according to the present invention, (a) 165 to 162.5 eV and 159.7 to 157.2 eV that can be attributed to Bi ³⁺ In addition to the peak, it had (b) 163 to 161 eV and 157.7 to 155.7 eV to be Bi0. From these, it is understood that bismuth is partially reduced, that is, in an oxide state containing low-order bismuth (BiOx: x <1.5).

Table 1 shows the quantitative analysis values obtained by XPS analysis before and after sputtering of Samples 4, 5, 6, and 7 and the chemical analysis values of the catalyst. Ar sputtering was performed for 10 minutes under the conditions of an acceleration voltage of 3 KV and a sputtering rate of 3.8 nm / min (in terms of SiO ₂ ), and about 38 nm was sputtered from the surface layer. The chemical analysis is a value obtained by dissolving the catalyst once and measuring the obtained solution by ICP emission analysis.

  From Table 1, in the samples 4 and 5 of the present invention, the Bi / Ti value of the outermost surface shown by XPS measurement for Bi contained in the titanium oxide is 2. from the Bi / Ti value calculated from the chemical analysis value. It is more than 0 times higher. Therefore, in the catalyst of the present invention, it is clear that Bi existing as an oxide is concentrated on the surface of titanium oxide. In the samples 6 and 7 as comparative examples, the Bi / Ti value on the outermost surface is larger than the Bi / Ti value calculated from the chemical analysis, but is below the range defined by the present invention (twice or more), and is concentrated. Is not enough. Even in bismuth titanate known as a photocatalyst, the Bi concentration (Bi / Ti) on the outermost surface is close to the concentration calculated from the chemical formula, and there is no bias in the concentration.

[Measurement of photocatalytic activity (acetaldehyde degradation test)]
After the sample was dispersed in distilled water, the dispersion was applied to a 40 mm square glass plate and then dried at 80 ° C. to obtain a test piece for photocatalytic activity measurement. The coating amount was 40 g / m ² . The test piece was placed in a quartz reaction cell, connected to a closed circulation line (total internal volume: about 3.7 L), and acetaldehyde (about 240 ppm-40 μmol) diluted with nitrogen gas containing 20 vol% oxygen was introduced into the system. . Visible light was irradiated from a 250 W high pressure mercury lamp through an ultraviolet cut filter (L42 manufactured by Toshiba) while circulating the gas. The reaction was traced by measuring the concentration of carbon dioxide (CO ₂ ) produced by decomposition of acetaldehyde over time with a gas chromatograph. The photocatalytic activity was evaluated by the production rate of carbon dioxide. Also in the following examples, the photocatalytic activity was examined by the same method. The results are summarized in Table 2.

  As is apparent from Table 2, the visible light responsive photocatalysts (Nos. 4 and 5) of the present invention containing a bismuth compound (BiOCl) in contact with visible light responsive titanium oxide are independent of visible light responsiveness. It can be seen that the activity is higher than that of titanium oxide having No. 1 and No. 2 (respectively No. 1 and 2), and the activity is enhanced by supporting bismuth oxide (BiOx: x <1.5). Sample No. 5 is more active than sample No. 4, and the effect of addition by Si is clear. In addition, No. 4 was more than twice as active as the comparative sample No. 6, which was prepared by coprecipitation using titanium tetrachloride and bismuth chloride as precursors for titanium oxide. No. 5 containing Si also showed visible light activity two times or more higher than No. 7 produced by the coprecipitation method containing Si. Thus, the enhancement of visible photocatalytic activity according to the present invention is evident.

  By the way, the samples of No. 6 and No. 7 had all two pairs or more of the above-mentioned pairs (a) to (c) in the XPS spectrum, and the presence of low-order bismuth was recognized. However, as shown in Table 1, the Bi concentration (Bi / Ti) of the surface existing as an oxide is somewhat larger than the Bi concentration in the bulk and Bi / Ti calculated from chemical analysis. Thus, there was no significant difference compared to the catalysts of the present invention (No. 4 and 5), and no surface concentration of Bi was observed. Further, as revealed by FT-IR, it is considered that sufficient activity could not be obtained because Bi oxide was not supported on the titanium oxide surface.

(Example 2)
Sample Nos. 8-12:
After adding silicon tetrachloride, zirconium chloride, tungsten chloride, or aluminum hydroxide to titanium tetrachloride (M / Ti = 0.03), hydrolysis with ammonia water (7% by mass) gave a solid (M The compound-containing titanium hydroxide) was dried and then calcined at 450 ° C. for 2 hours in the air to obtain titanium oxide containing the additive element. To this titanium oxide, the powder of bismuth oxychloride prepared in Sample No. 3 of Example 1 was added so that Bi / Ti = 0.09, and kneaded well in a mortar. By calcination for 2 hours, a visible light responsive photocatalyst of the present invention consisting of titanium oxide carrying bismuth oxide was obtained. As a result of the X-ray diffraction pattern, titanium oxide was anatase type. The results of measuring the activity by the method described in Example 1 are summarized in Table 3.

  From Table 3, the activity of the visible light responsive photocatalyst of the present invention supported by bismuth oxide by using titanium oxide obtained by adding metal elements such as silicon, zirconium, tungsten, and aluminum to visible light responsive titanium oxide. Is clearly larger than that in the case of no addition (sample No. 12). Of these, silicon has the greatest enhancement effect. In addition to the elements listed in this table, boron, magnesium, hafnium, molybdenum, and the like were added to visible light-responsive titanium oxide, and the same enhancement effect was recognized.

(Example 3)
Sample Nos. 13 to 23:
In sample No. 4 (Si-containing titanium oxide) of Example 1, the visible light responsive photocatalyst of the present invention was prepared in the same manner except that the calcination temperature after kneading was changed. Table 4 shows the aldehyde decomposition activity determined by the method described in Example 1.

  The activity enhancement effect by supporting bismuth oxide is such that the firing temperature is 25 compared with the activity (1.1 μmol / h) of visible light responsive titanium oxide (sample No. 2 in Example 1) to which no bismuth compound is added. Although there is no effect at 0 ° C., the activity enhancement effect by the heat treatment appears clearly from 80 ° C. Furthermore, a remarkable enhancement effect was exhibited in the range of 300 ° C. to 700 ° C., and the effect continued even at 800 ° C.

FIG. 3 shows SEM diagrams of these catalysts, and FIG. 4 shows the intensity of a peak at 3400 cm ⁻¹ (derived from OH group stretching) in the FT-IR spectrum.
It can be seen from the SEM diagram of FIG. 3 that bismuth oxide is supported on titanium oxide, more specifically, covers at least part of the surface of titanium oxide. The SEM diagram will be described in more detail. At the stage of 80 ° C., which was only dried after kneading, the bismuth compound was slightly adhered to the base particles themselves as compared with the containing titanium oxide (Si—TiO 2) as the base particles. When the temperature reached 300 ° C., bismuth bismuth oxide was supported in the form of fine particles on the surface of the base particles. When the firing temperature reached 500 ° C., the fine particles of the bismuth compound almost disappeared, and at 600 ° C., the particle surface became smooth, and the bismuth compound covered most of the surface of the base particles.

On the other hand, in the result of the FT-IR spectrum shown in FIG. 4, a broad peak corresponding to the expansion and contraction of the OH group derived from titanium oxide is 3400 cm ^{− in} the state of 80 ° C. in which the base Si-containing titanium oxide and the kneaded material are dried after kneading. It can be seen near ¹ . As the firing temperature was raised, this OH group peak gradually weakened. These behaviors indicate that as the firing temperature increases, the bismuth compound coats the surface of the base titanium oxide (Si / TiO2) as a bismuth oxide.

  This result agrees with the particle observation result by SEM described above. From these measurement results, it was found that in the visible light responsive photocatalyst of the present invention, the bismuth compound is supported on titanium oxide, and it becomes more active by coating at least part of the titanium oxide surface.

Example 4
Sample No. 24-32:
Titanium oxide containing silicon was produced by the same method as Sample No. 2 in Example 1 except that the firing temperature of titanium hydroxide was changed to a range of 100 to 600 ° C. The produced titanium oxide was kneaded with a bismuth compound and calcined (at 500 ° C. in air for 2 hours) in the same manner as in Sample No. 4 of Example 1, and the bismuth oxide was supported on the titanium oxide. In addition, a visible light responsive photocatalyst of the present invention was prepared. Table 5 summarizes the acetaldehyde decomposition activity determined by the method described above.

  The raw material silicon-containing titanium oxide changes in photocatalytic activity depending on the firing temperature at the time of production, and the photocatalytic activity increases as the firing temperature increases up to about 600 ° C. Reflecting this, similar results were obtained for the visible photocatalytic activity of the photocatalyst of the present invention in which the bismuth compound was supported by mixing with a bismuth compound and heat treatment.

(Example 5)
Sample No. 33-38:
For the titanium oxide containing silicon of sample No. 2 in Example 1, bismuth nitrate, bismuth oxynitrate, bismuth oxyhydroxide, bismuth chloride, bismuth oxide (Bi ₂ O ₃ ) or bismuth oxyacetate are used as bismuth compounds. Each of the present invention (Bi / Ti = 0.09 to 0.11), kneaded well, and then baked at 450 ° C. or 500 ° C. for 2 hours in the atmosphere to form titanium oxide carrying bismuth oxide. The visible light responsive photocatalyst was obtained. The main peak in the X-ray diffraction pattern was attributed to anatase-type titanium oxide. The results obtained by determining the visible light activity in the same manner as described above are summarized in Table 6.

  In the production of the visible light responsive photocatalyst of the present invention, the activity of the bismuth compound is superior or inferior, but any compound containing bismuth can be used. However, if the bismuth compound is a stable oxide, the activity enhancement effect is small, and the bismuth compound is oxybismuth BiOX (X = halogen ion, nitrate ion, hydroxide ion, organic ion), bismuth halide or bismuth nitrate. It was highly effective. In addition, bismuth sulfate and bismuth sulfide have been confirmed to show high effects.

  On the other hand, Sample No. 37, in which the mixed bismuth compound was bismuth oxide, had a slightly improved visible photocatalytic activity compared to Sample No. 2, which was a titanium oxide raw material, but the improvement was negligible.

(Example 6)
Sample No. 39:
A bismuth compound (bismuth oxychloride) prepared in Sample No. 3 of Example 1 was added as an activity enhancer to powdery visible light responsive titanium oxide available on the market (Bi / Ti = 0.09). After that, the mixture was well kneaded in a mortar and then calcined at 500 ° C. for 2 hours in the atmosphere to produce the visible light responsive photocatalyst of the present invention. The main peak in the X-ray diffraction pattern was attributed to anatase-type titanium oxide. When the activity of this photocatalyst was examined, the activity after contact mixing with a bismuth compound and firing was 5.9 μmol / Hr, more than double the activity of the raw material titanium oxide (2.6 μmol / Hr). It was found that the activity was enhanced and the bismuth compound was effective as an activity enhancer for the already produced visible light responsive titanium oxide photocatalyst.

Sample No. 40:
Commercially available visible light responsive titanium oxide used in sample No. 39 was added to 0.1N nitric acid and dispersed well, and then ethyl orthosilicate was added so that Si / Ti = 0.12 and stirred for 3 hours or more. did. The powder obtained after filtration was dried and baked at 500 ° C. for 2 hours in the air to obtain visible light-responsive titanium oxide containing silicon. A bismuth compound was added as an activity enhancer to this titanium oxide in the same manner as in Sample No. 39, and calcined in the atmosphere at 500 ° C. for 2 hours to produce the visible light responsive photocatalyst of the present invention. The main peak in the X-ray diffraction pattern was attributed to anatase-type titanium oxide.

  The visible light activity of this photocatalyst was 8.6 μmol / Hr, and the activity was further enhanced by the silicon content as compared with Sample No. 39. That is, it has been clarified that, when a bismuth compound is used as an activity enhancer, a higher enhancement effect can be obtained by applying a metal element such as silicon in advance.

Sample No. 41:
Titanium oxide containing Si of Sample No. 2 of Example 1 was dispersed in deionized water using an organic dispersant to prepare a dispersion having a pH of 7 and a solid content of 20% by mass. To this dispersion was added a dispersion of bismuth oxychloride in water (pH 7) (Bi / Ti = 0.09) and stirred sufficiently to prepare a dispersion for forming a visible light responsive photocatalyst according to the present invention. This dispersion was applied to a glass plate (coating amount of about 40 g / m ² ) and then baked at 400 ° C. in the atmosphere for 2 hours to obtain a photocatalytic functional member having a visible light responsive photocatalyst layer of the present invention. The main peak in the X-ray diffraction pattern was attributed to titanium oxide.

  This photocatalytic functional member was subjected to an acetaldehyde decomposition test by the method described in Example 1. The activity of the photocatalytic functional member prepared by applying the Si-containing titanium oxide sol of sample No. 2 used as a raw material to a glass member and heat-treating the same was 2 μmol / H, whereas the photocatalytic function of the present invention was used. The activity of the member is 12 μmol / H, and it is confirmed that the member coated with the visible light responsive photocatalyst of the present invention obtained by contacting with a bismuth compound improves the visible light catalytic activity (achieves the activity enhancement effect). It was done.

Sample No. 42:
Dispersion liquid (pH 7, solid content 10 mass%) prepared from commercially available visible light responsive titanium oxide used in sample No. 39 using the same organic dispersant and deionized water as used in sample No. 41 ) Is added with an aqueous dispersion (pH 7) of bismuth oxychloride serving as a photocatalytic activity enhancer (Bi / Ti = 0.10), and sufficiently stirred, the visible light responsive photocatalyst forming dispersion of the present invention is prepared. Produced. The dispersion was directly applied to a glass plate (about 40 g / m ² ) and baked at 80 ° C. for 2 hours in the atmosphere to produce a photocatalytic functional member having a visible light responsive photocatalyst layer of the present invention.

Sample No. 43:
A dispersion (pH 7, solid content 10 mass%) prepared from the commercially available visible light responsive titanium oxide used in Sample No. 39 using the same organic dispersant and deionized water as used in Sample No. 36 ), Silica sol (Snowtech O) was added (Si / Ti = 0.12), and after sufficient stirring, a dispersion of bismuth oxynitrate (pH 7) serving as a photocatalytic activity promoter was added (Bi / Ti = 0). 10) and sufficiently stirred to produce a dispersion for forming a visible light responsive photocatalyst according to the present invention. The dispersion was directly applied to a glass plate (about 40 g / m ² ) and baked at 80 ° C. for 2 hours in the atmosphere to produce a photocatalytic functional member having a visible light responsive photocatalyst layer of the present invention. The main peak in the X-ray diffraction pattern was attributed to anatase-type titanium oxide.

The photocatalytic functional members prepared in Samples No. 42 and No. 43 were subjected to the acetaldehyde decomposition test by the method described in Example 1. As a result, 2.3 μmol / Hr in the sample No. 42 and 4.0 μmol / Hr in the sample No. 43 with respect to the activity (1.6 μmol / Hr) of the sample coated with the raw material visible light responsive titanium oxide sol. It was active. Therefore, the activity enhancer containing the bismuth compound of the present invention is also effective for the sol of the titanium oxide photocatalyst, and further, the enhancement action is higher by adding silicon (in this example, SiO ₂ ). It became clear that

(Example 7)
(XAFS measurement)
For various photocatalysts including Sample No. 4 and No. 5, the peak ratio R (second peak / first peak) of the radial distribution around the bismuth atom was determined by the XAFS method. The measurement was performed with SPring8-BL19-B2. The measurement results are shown in Table 7 together with the photocatalytic activity (CO ₂ generation rate) determined by the method described above.

In Table 7, as samples having different R values, the above sample Nos. 4 and 5, bismuth titanate (Bi ₃ Ti ₄ O ₁₂ ) and Bi ₂ O _3, and the amount of bismuth as Bi / Ti = 0.30. For the sample No. 44 produced by the same method as the sample No. 4 except that, the R value and the photocatalytic activity measurement results are also shown.

  As can be seen from the results in Table 7, high visible light catalytic activity is exhibited when the peak ratio R of the radial distribution is 0.4 or less. Further, it can be seen that when the peak ratio is 0.15 or less, it has extremely high activity. Even in the case of a single titanium oxide that does not contain other elements M, the titanium oxide is mixed with a bismuth compound and baked, so that the R value becomes 0.4 or less, and the visible light activity is sufficiently higher than that of the parent titanium oxide. It becomes like this.

  Thus, in titanium oxide containing bismuth, the peak ratio (second peak / first peak) in the radial distribution around Bi atoms obtained by XAFS measurement is set to 0.4 or less, which is extremely high. A visible light responsive photocatalyst having visible light activity can be provided.

The FT-IR spectra of various samples prepared in Example 1 are shown. The spectrum figure of the Bi-4f core level of sample No. 3-5 produced in Example 1 is shown. The SEM observation photograph of the sample of the visible light response type photocatalyst obtained in Example 3 is shown. The figure which put together the absorption value of 3400 cm < ^-1 > of the FT-IR spectrum of the sample of the visible light response type photocatalyst obtained in Example 3 is shown. The result of having calculated | required radial distribution around the bismuth of a sample by the XAFS method about the sample of the visible light response type photocatalyst obtained in Example 7 is shown.

Claims (24)

  A titanium oxide-based visible light responsive photocatalyst characterized in that it is a visible light responsive photocatalyst comprising titanium oxide having a bismuth oxide supported on the surface, wherein bismuth is concentrated on the surface. 2. The photocatalyst according to claim 1, wherein the bismuth oxide is represented by BiO _x (x <1.5).   The visible light responsive photocatalyst according to claim 1 or 2, wherein the bismuth oxide covers at least a part of the surface of titanium oxide.   The visible light responsive photocatalyst according to any one of claims 1 to 3, wherein an atomic ratio (Bi / Ti) of Bi and Ti contained in the photocatalyst is 0.001 or more and 1.0 or less.   The visible light ray according to any one of claims 1 to 4, wherein a peak ratio R (second peak / first peak ratio) of a radial distribution around a bismuth atom when the photocatalyst is analyzed by XAFS is 0.4 or less. Photoresponsive acid photocatalyst.   6. The visible light responsive acid photocatalyst according to claim 5, wherein a peak ratio R of the radial distribution is 0.15 or less.   The visible light responsive photocatalyst according to any one of claims 1 to 6, wherein the photocatalyst contains at least one element M selected from silicon, zirconium, aluminum, tungsten, molybdenum, magnesium, hafnium, and boron.   The content of the element M in the photocatalyst (the total amount when containing two or more elements) is such that the atomic ratio to Ti (M / Ti) is 0.0001 or more and less than 1.0. The visible light responsive photocatalyst according to claim 7.   The visible light responsive photocatalyst according to claim 7 or 8, wherein the element M is contained in titanium oxide.   The visible light responsive photocatalyst according to any one of claims 1 to 9, wherein the titanium oxide is at least partially crystalline and the main crystal form of the crystal is anatase.   It includes a mixing step of mixing titanium oxide or a solid precursor thereof with a bismuth compound, and a baking step of baking the resulting mixture to obtain titanium oxide having the bismuth oxide supported on the surface. The manufacturing method of the titanium oxide type visible light responsive photocatalyst in any one of Claims 1-10.   The method according to claim 11, wherein the firing step is stopped at a stage where anatase-type titanium oxide is predominant in an X-ray diffraction pattern of a product obtained by firing.   The method according to claim 11 or 12, wherein a firing temperature in the firing step is 50 to 800 ° C.   The bismuth compound is at least one selected from BiOX (X = halogen ion, nitrate ion, hydroxide ion, organic ion), bismuth halide, bismuth nitrate, bismuth sulfate, and bismuth sulfide. The method of crab.   The method according to any one of claims 11 to 14, wherein the titanium oxide or a solid precursor thereof contains at least one element M selected from silicon, zirconium, aluminum, tungsten, molybdenum, magnesium, hafnium and boron.   In the mixing step, in addition to titanium oxide or its solid precursor and bismuth compound, at least one compound selected from silicon compounds, zirconium compounds, aluminum compounds, tungsten compounds, molybdenum compounds, magnesium compounds, hafnium compounds and boron compounds The method according to any one of claims 11 to 15, which is mixed.   The method according to any one of claims 11 to 16, wherein at least one of the compounds to be mixed is an oxide in a dispersion state.   A photocatalytic functional member comprising the visible light responsive photocatalyst according to any one of claims 1 to 10 on the surface of a substrate.   A visible light responsive photocatalyst-forming dispersion, comprising a liquid medium containing dispersed titanium oxide and a dispersed or dissolved bismuth compound.   A photocatalyst dispersion liquid comprising the visible light responsive photocatalyst according to claim 1 dispersed in a liquid medium.   A visible light responsive photocatalyst coating liquid characterized by containing a dispersed titanium oxide, a dispersed or dissolved bismuth compound and a binder in a liquid medium.   The visible light responsive photocatalyst according to any one of claims 1 to 10 and a binder are contained in a liquid medium, and the content of the photocatalyst is 5 to 95% by mass based on the total amount of nonvolatile components. A visible light responsive photocatalytic coating solution.   A method for producing a photocatalytic functional member, wherein the dispersion liquid according to claim 19 or 20 or the coating liquid according to claim 21 or 22 is applied to a substrate, followed by heat treatment.   Visible light responsive activity enhancer for titanium oxide photocatalyst comprising bismuth compound.

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