JP4785641B2 - Method for producing photocatalytic material and photocatalytic material - Google Patents

Description

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

Photocatalytic materials such as titanium oxide usually exhibit high catalytic ability by ultraviolet light, but when limited to visible light, the catalytic activity is significantly reduced. For this reason, giving visible light responsiveness to titanium oxide etc. is examined. For example, it is disclosed that a metal having a high ionic valence is dissolved in titanium dioxide (Patent Document 1). Further, doping titanium dioxide with nitrogen, which is a trivalent metal element, is also disclosed (Patent Document 2). Furthermore, it is also disclosed that a metal having an ionic valence of III and a metal having a valence of V or VI are dissolved in titanium dioxide (Patent Document 3).
JP 2004-195439 A International Publication WO01 / 010522 Pamphlet JP 2004196664

  However, there is a limit in solidifying a metal element having a high ionic valence in titanium dioxide, and there is a limit in improving visible light responsiveness by solid solution. In addition, when titanium dioxide is doped with nitrogen, it becomes unstable with respect to oxidation, and there is a problem that stable photocatalytic performance is difficult to obtain. Furthermore, in order to solid-dissolve a metal having a large ionic valence of a V-valent or VI-valent metal by dissolving a III-valent metal in titanium dioxide, the same amount or more of the III-valent metal must be dissolved. As a result, sufficient photocatalytic activity could not be obtained.

  On the other hand, conventionally, an oxide of a metal element with an ionic valence of I or a metal element with a valence of II and titanium dioxide form a double oxide, so that the solid solution is also slight. Moreover, it has not been reported that such a low ionic valence metal element is dissolved in order to improve the photoresponsiveness of titanium dioxide.

  Furthermore, hitherto, sufficient resolution has not been achieved for the deterioration of the photocatalytic properties of titanium oxide by imparting visible light responsiveness.

  An object of the present invention is to provide a photocatalytic material having a solid solution having a new composition and a method for producing the same. Another object of the present invention is to provide a photocatalytic material having good visible light response and photocatalytic properties and a method for producing the photocatalytic material. Another object of the present invention is to provide a photocatalytic material that can stably exhibit visible light responsiveness and photocatalytic properties. Furthermore, another object of the present invention is to provide a photocatalytic material in which photocatalytic activity and visible light responsiveness are controlled, and a method for producing the same.

  The present inventors have previously made it difficult to achieve solid solution by simultaneously adding a metal element having an ionic valence of V or VI and a metal element having an ionic valence of I or II to titanium dioxide. And found that titanium dioxide having such a solid solution composition has good visible light responsiveness and photocatalytic properties, and based on these findings, The present invention has been completed as a solution to at least one. That is, according to the present invention, the following means are provided.

  According to the present invention, the photocatalytic material includes titanium, a first metal element having an ionic valence of V or VI, and a second metal element having an ionic valence of I or II. A material having a titanium-containing oxide solid solution is provided.

  In the photocatalytic material of the present invention, the first metal element is preferably one or more selected from the group consisting of tungsten, niobium, tantalum, vanadium, molybdenum and antimony, more preferably tungsten. , One or more selected from the group consisting of niobium, tantalum and antimony. More preferably, the first metal element is tungsten.

  In the photocatalytic material of the present invention, the ionic valence is preferably selected from II-valent metal elements. Further, the second metal element may be one or more selected from a typical metal element and an alkaline earth metal element. More preferably, the second metal element is one or more selected from magnesium, calcium, strontium and copper. More preferably, it is magnesium.

  In the photocatalytic material of the present invention, the first metal element is preferably tungsten, and the second metal element is preferably one or more selected from magnesium, calcium, strontium and copper.

In the solid solution, x is preferably 0.01 or more and 0.29 or less, and y is preferably 0.01 or more and 0.29 or less in the following formula (1). Further, (x + y) is preferably 0.3 or less.
^{_{Ti (1-X-Y)}} M 1 x M 2 y O 2 ··· (1)
(M ¹ represents the first metal element, x represents the number of moles thereof, M ² represents the second metal element, and y represents the number of moles thereof)

  In the photocatalytic material of the present invention, the solid solution preferably has an anatase type crystal structure or a rutile type crystal structure.

According to the present invention, a method for producing a photocatalytic material comprising:
A raw material containing a titanium compound, a metal compound of a first metal element having an ionic valence of V or VI, and a metal compound of a second metal element having an ionic valence of I or II The process of preparing
Synthesizing a titanium-containing oxide solid solution containing titanium, the first metal element, and the second metal element from the raw material;
A manufacturing method is provided.

  The visible light responsive photocatalytic material of the present invention includes titanium, a first metal element having an ionic valence of V or VI, a second metal element having an ionic valence of I or II, A titanium-containing oxide solid solution. Including a metal element having an ionic valence of I or II together with a metal element having an ionic valence of V or VI, both of these metallic elements may have a solid solution in which titanium dioxide is dissolved. it can. A photocatalytic material having such a solid solution is a novel photocatalytic material.

  In addition, according to the photocatalytic material of the present invention, good visible light responsiveness can be obtained even if the amount of the V-valent or VI-valent metal element is small by simultaneously dissolving the I-valent or II-valent metal element. It can be demonstrated. Therefore, visible light responsiveness can be imparted without greatly reducing the titanium ratio. Therefore, according to the present invention, a photocatalytic material having both visible light responsiveness and photocatalytic characteristics can be provided. In addition, since the photocatalytic material of the present invention exhibits visible light responsiveness and photocatalytic properties by dissolving a metal element, these properties can be exhibited stably. Furthermore, the photocatalyst material of the present invention can easily and effectively increase the solid solution amount of the V-valent or VI-valent metal element that contributes to the visible light response due to the solid solution amount of the I-valent or II-valent metal element. Therefore, the photocatalytic material is capable of adjusting the visible light responsiveness and the photocatalytic characteristics in a wide range. Hereinafter, the photocatalytic material of the present invention and the production method thereof will be described in detail.

(Photocatalytic material)
The photocatalytic material of the present invention includes titanium, one or more first metal elements selected from metal elements having an ionic valence of I or II, and an ionic valence of V or VI. And a titanium-containing oxide solid solution phase containing one or more second metal elements selected from the metal elements.

(Solid solution components)
The first metal element is not particularly limited as long as the ionic valence is selected from V-valent or VI-valent metal elements. Examples of the V-valent or VI-valent metal element include tungsten (W), tantalum (Ta), niobium (Nb), antimony (Sb), molybdenum (Mo), and vanadium (V). These metal elements can be dissolved in the lattice space of titanium dioxide, and can exhibit visible light responsiveness. Further, according to these metal elements, a solid solution having a rutile crystal structure or an anatase crystal structure can be obtained. Among these metal elements, tungsten, molybdenum, vanadium, and antimony are preferable from the viewpoint of enhancing visible light response. Among them, tungsten was hardly dissolved in titanium dioxide alone, and could not be changed to an electronic structure exhibiting visible light responsiveness. The present invention is preferably applied in that the effective amount to be expressed can be dissolved. Tungsten is also preferred in that it exhibits good visible light response even with a small amount of solid solution.

    The second metal element is not particularly limited as long as it has one or more ionic valences selected from I-valent or II-valent metal elements. Examples of the I-valent or II-valent metal elements include alkali metals such as Li, Na, K, Rb and Cs, alkaline earth metals such as Be, Mg, Ca, Sr, Ba and Ra, Mn, Co, Ni and Cu. Transition metal elements such as and Zn. In consideration of elution in an aqueous solution, alkaline earth metals such as Mg, Ca and Sr are preferable, and Mg or Ca is more preferable. Of the transition metal elements, Cu is preferable.

  In the solid solution of this material, by adding the second metal element in addition to the first metal element, these metal elements that are difficult to dissolve in titanium dioxide can be dissolved in titanium dioxide. Will be able to. Moreover, since the second metal element is I-valent or II-valent, the V-valent or VI-valent first metal element can be dissolved in a small amount as compared with the case where the III-valent metal element is used. Therefore, the solid solution amount of the first metal element contributing to photoresponsiveness can be increased while maintaining the titanium content. For this reason, the photoresponsiveness and the photocatalytic property of this material are adjusted, and the material has properties as required.

  The first metal element and the second metal element can be appropriately combined within the above ranges, but when tungsten is used as the first metal element, magnesium, calcium, and strontium are used as the second metal element. And one or more selected from copper, and more preferably Mg. It is also preferable to use only tungsten as the first metal element and only magnesium as the second metal element.

The composition of these metal elements in the titanium-containing oxide solid solution containing titanium, the first metal element, and the second metal element can be a composition represented by the following formula (1). In the present invention, x is preferably 0.01 or more and 0.49 or less in the following formula. More preferably, it is 0.01 or more and 0.29 or less. Moreover, it is preferable that y is 0.01 or more and 0.49 or less. Moreover, it is more preferable that it is 0.01 or more and 0.29 or less.
^{_{Ti (1-X-Y)}} M 1 x M 2 y O 2 ··· (1)
(M ¹ represents the first metal element, x represents the number of moles thereof, M ² represents the second metal element, and y represents the number of moles thereof)

  Further, (x + y) is preferably 0.5 or less. This is because when (x + y) is 0.5 or less, Ti is 0.5 or more, and the photocatalytic properties of the present material can be ensured. More preferably, (x + y) is 0.3 or less. Within this range, good photocatalytic properties and stable photocatalytic properties can be ensured. More preferably, (x + y) is 0.1 or less.

The molar ratio x: y between the first metal element and the second metal element has a preferable range depending on the valence of the first metal element and the second metal element used. For example, the combinations of the first metal element: second metal element and the preferred molar ratio range can be listed in Table 1 below.

  In this solid solution, zirconium (Zr) and hafnium (Hf) may be included as metal elements together with titanium. Zirconium and hafnium can be dissolved in the anatase crystal structure, and can contribute to the stability and photocatalytic properties of the anatase crystal structure.

  The solid solution phase of the material can have a crystal structure such as anatase, rutile, brookite, monoclinic crystal, and badelite structure. Anatase type, brookite type or rutile type is preferred. More preferred are anatase type and / or rutile type. Moreover, it does not exclude that the solid solution phase of this material contains an amorphous phase. In addition to such a solid solution phase, the present material can have another solid solution phase, a crystalline phase, or an amorphous phase as long as the properties of the material are not hindered.

  This material can take various forms such as powder, thin film, thick film, porous body, sintered body, polycrystalline body, and single crystal. Moreover, this material may be combined with other materials. Other materials to be combined include, for example, activated carbon, zeolite, catalyst carrier, metal, glass, ceramics, paint, resin, dispersed or held in organic materials or attached or supported on a part of these surfaces by coating or the like. Can do.

(Method for producing photocatalytic material)
The method for producing a photocatalytic material of the present invention includes a titanium compound, a metal compound of a first metal element whose ionic valence is V or VI, and a second metal whose ionic valence is I or II. A step of preparing a raw material containing a metal compound of an element, and a titanium-containing oxidation containing titanium, the first metal element, the low ionic valence metal element, and the high ionic valence metal element from the raw material. Synthesizing an oxide having a solid-solid solution composition.

The production method of the present invention is a preferred method for producing the photocatalytic material of the present invention. As the titanium compound, the metal compound of the first metal element, and the metal compound of the second metal element in this production method, metal salts, metal organic compounds, metal alkoxides, and the like for these metals can be used. Examples of the metal salt include halides represented by chlorides including oxychlorides, nitrates, acetates, hydroxides, and sulfates including oxysulfides. Examples of the metal organic compound include MO (C ₅ H ₇ O ₂ ) ₂ and organic acid ammonium salt. Examples of the metal alkoxide include metal isoprooxide and butoxide.

  For example, the titanium compound may be one or more selected from alkoxides such as titanium isopropoxide and titanium butoxide, titanium oxysulfate, titanium chloride, titanium hydroxide and the like, depending on the synthesis method. Of these, titanium chloride, titanium hydroxide and the like can be preferably used. Among the metal compounds of the first metal element, tungsten compounds include tungstic acid, ammonium tungstate, tungsten hexachloride, tungsten hexabromide, tungsten oxychloride, tungsten bromide, tungsten fluoride, hexaethoxy tungsten, hexa One or more selected from methoxytungsten, hexa-i-propoxytungsten, hexa-n-propoxytungsten, hexa-n-butoxytungsten, hexa-n-butoxytungsten, hexa-sec-butoxytungsten, etc. It is done. Of these, tungstic acid, ammonium tungstate, and the like are preferably used. Moreover, the tantalum compound, niobium compound, antimony compound, molybdenum compound, and vanadium compound of the same aspect are mentioned, A preferable aspect can be used preferably similarly.

  These raw materials are dissolved in an appropriate solvent and prepared as a raw material solution. As the solvent, an organic solvent such as alcohol or THF, or an aqueous solution such as aqueous hydrogen peroxide can be appropriately selected and used. In the raw material solution, the molar ratio (1-xy): x: y in the above formula (1) of titanium, the first metal element and the second metal element in the photocatalytic material to be obtained is desired. Each compound is mix | blended so that it may become a ratio.

  Next, a known ceramic synthesis method is applied to such a raw material solution to synthesize a titanium-containing oxide. The synthesis method is not particularly limited, and examples thereof include vapor phase methods such as chemical vapor deposition, reactive vapor deposition, and reactive sputtering, and liquid phase methods such as sol-gel method, spray pyrolysis method, and hydrothermal method. . In the synthesis, typically, the material can be synthesized by a hydrothermal reaction at a temperature of 80 ° C. or higher and 200 ° C. or lower in the presence of an acid or an alkali.

  According to this production method, the first metal element that is a V-valent or VI-valent metal element and the second metal element that is an I-valent or II-valent metal element, which have been difficult to dissolve in titanium dioxide conventionally. Can be obtained in a solid solution with titanium dioxide. As a result, a photocatalytic material having good visible light response can be obtained. In addition, by synthesizing a titanium-containing oxide solid solution containing the first metal element and the second metal element, the solid solution amount of the first metal element is increased without reducing the titanium content in the solid solution. Therefore, a photocatalytic material having good visible light response and photocatalytic properties can be produced. Furthermore, since the solid solution amount of the first metal element can be adjusted by the solid solution amount of the second metal element, the visible light response and the photocatalytic property can be easily controlled. .

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, these Examples are not intending limiting this invention.

Example 1
(Synthesis of photocatalytic materials)
Titanium chloride and tungstic acid as raw materials for synthesizing powder A (Ti _0.9 W _0.05 Mg _0.05 O ₂ ) and powder B (Ti _0.7 W _0.15 Mg _0.15 O ₂ ) And magnesium acetate were used. These raw materials were dissolved in hydrogen peroxide so as to be 0.9: 0.05: 0.05 and 0.7: 0.15: 0.15, respectively. From this solution, a crystalline powder was synthesized by a spray pyrolysis method using a spray pyrolysis apparatus. Specifically, the solution is atomized by ultrasonic vibration, and the atomized fine particles are introduced into an electric furnace held at 200 ° C., 400 ° C., 600 ° C., and 800 ° C. by carrier gas (air), and atomized droplets The product was dried, decomposed, and crystallized, and the resulting fine particle powder was collected with a filter. The carrier gas (air) flow rate was 5 L / min.

(Evaluation)
Powder X-ray diffraction spectra were measured for the two types of powders A and B obtained, and the photocatalytic performance of each powder under visible light was evaluated based on the methylene blue decomposition rate. As test conditions, a 300 W lamp was used, and light intensity (wavelength: 500 nm): 50 μW cm ⁻² (410 nm or less was cut with an optical filter). In addition, it evaluated similarly about the titanium dioxide (Ishihara Sangyo Co., Ltd. make, ST-01) as a control example. The X-ray diffraction spectrum of each powder synthesized in this example is shown in FIG. 1, and the evaluation results of the photocatalytic performance under visible light are shown in FIG.

  As shown in FIG. 1, powders A and B are both powders having a crystalline phase at a high ratio, and it was found that a solid solution was obtained by the composition of any of powders A and B. It was estimated that powder A had a higher ratio of anatase type crystal structure phase than powder B. Further, as shown in FIG. 2, powders A and B both had a visible light-responsive photocatalytic activity superior to that of the control example (titanium dioxide), but had a smaller number of moles of tungsten and a mole of titanium. The higher number of powder A had higher visible light responsive photocatalytic activity.

  From the above, by simultaneously using tungsten, which is a VI metal element that can hardly be dissolved in titanium dioxide, and magnesium, which is a II metal element that can hardly be dissolved in titanium dioxide, both of them can be converted into titanium dioxide. It was found that it can be solidified. Moreover, in order to obtain effective visible light responsive photocatalytic activity, the metal element for obtaining the necessary visible light response performance by maintaining the titanium content ratio as well as solidifying the metal element contributing to the visible light response. It was found that it is important to make the solution solid. Furthermore, it has been found that a photocatalytic material having both the visible light responsiveness and the photocatalytic property can be obtained by solidifying these two kinds of metal elements.

(Example 2)
(Synthesis of photocatalytic materials)
As raw materials for synthesizing powders A and C to F shown in Table 1 below, titanium chloride, tungstic acid, and acetate are used, and these raw materials have the number of moles of metal elements shown in Table 2. Dissolved in hydrogen peroxide water. From this solution, a crystalline powder was synthesized by a spray pyrolysis method using a spray pyrolysis apparatus. Specifically, the solution is atomized by ultrasonic vibration, and the atomized fine particles are introduced into an electric furnace held at 200 ° C., 400 ° C., 600 ° C., and 800 ° C. by carrier gas (air), and atomized droplets The product was dried, decomposed, and crystallized, and the resulting fine particle powder was collected with a filter. The carrier gas (air) flow rate was 5 L / min. In addition, the powder F is a powder of the comparative example with respect to the powders A and C to E of the present invention.

(Evaluation)
While measuring a powder X-ray diffraction spectrum about two types of obtained powder A and CF, it carried out similarly to Example 1, and evaluated the photocatalytic performance under visible light of each powder. In addition, it evaluated similarly about the titanium dioxide (Ishihara Sangyo Co., Ltd. make, ST-01) as a control example. The X-ray diffraction spectrum of each powder synthesized in this example is shown in FIG. 3, and the evaluation results of the photocatalytic performance under visible light are shown in FIG.

  As shown in FIG. 3, powders A and C-F are all powders having a crystalline phase at a high ratio, and it was found that a solid solution was obtained by the composition of any powder. Moreover, as shown in FIG. 4, although powder A, C, and E all had the visible-light-responsive photocatalytic activity superior to the control example (titanium dioxide), powder D (utilization of strontium) However, depending on the molar ratio of the metal elements, it was speculated that either or both of the visible light responsiveness and the photocatalytic property were not satisfied. Moreover, although the solid solution was formed in powder F (aluminum utilization), the visible light responsive photocatalytic activity lower than the control example was shown.

  From the above, it has been found that the use of a valent metal element in titanium dioxide can also solidify a valent metal element such as tungsten, but the visible light responsive photocatalytic activity may be reduced. . That is, the visible light responsive photocatalytic activity is sufficient when the metal element solidified together with the metal element contributing to the visible light responsiveness is trivalent even if the titanium content can be maintained to some extent. It was found that it was difficult to impart the active photocatalytic activity.

The figure which shows the powder X-ray-diffraction spectrum of powder A and B. The figure which shows the evaluation result of the visible light responsive photocatalytic activity of powder A and B. The figure which shows the powder X-ray-diffraction spectrum of powder A, C-F. The figure which shows the evaluation result of the visible light responsive photocatalytic activity of powder A, C-F.

Claims (3)

A photocatalytic material,
Titanium, a first metal element that is tungsten, and one or more second metal elements selected from magnesium, calcium, strontium, and copper are represented by the following formula (1). And a material containing a titanium-containing oxide solid solution in which (x + y) is 0.3 or less.
^{_{Ti (1-X-Y)}} M 1 x M 2 y O 2 ··· (1)
(M ¹ represents the first metal element, x represents the number of moles thereof, M ² represents the second metal element, and y represents the number of moles thereof)   The material according to claim 2, wherein (x + y) is 0.1 or less in the formula (1).   The material according to claim 1 or 2, wherein the solid solution has an anatase type crystal structure or a rutile type crystal structure.