JP5660419B2 - Composite oxide semiconductor, and yellow pigment and photocatalyst using the same. - Google Patents

Description

The present invention relates to a titanium oxide-iron oxide composite oxide semiconductor containing no harmful metal, and a yellow pigment and a photocatalyst using the same.

Conventionally, lead chromate (PbCrO ₄ ), cadmium yellow (CdS), bismuth vanadium yellow (BiVO ₄ ), nickel yellow (TiO ₂ —NiSb ₂ O ₆ ) and the like have been used as inorganic yellow pigments. However, since these yellow pigments contain a large amount of toxic substances such as chromium, cadmium, vanadium and nickel, their use has been limited. Therefore, development of an alternative yellow pigment is expected.

  In Non-Patent Document 1, a part of oxynitride represented by tantalum oxynitride (CaLaTaON) is reported as a yellow pigment. Although this yellow pigment is composed of harmless elements, it is necessary to use toxic ammonia gas in the process of oxide oxynitride formation, and hue variations are likely to occur due to changes in ammonia concentration.

  In Patent Document 1, as a yellow pigment based on titanium, which is a non-toxic metal, titanium oxide treated with hydrogen peroxide is reported. However, when it is exposed to light, it gradually decomposes to become titanium oxide or titanium hydroxide and returns to white. Thus, this material is inferior in weather resistance.

In addition, iron-based pigments have been reported as yellow pigments made of harmless metals. Yellow iron oxide (FeOOH) is one of them (Patent Document 2), but there is a big problem in heat resistance, and yellow iron oxide becomes reddish at a temperature of 180 ° C or higher (Non-Patent Document 2). ). Therefore, it cannot be used for plastic materials that are molded at a temperature of 200 ° C. or higher.

Furthermore, as other yellow pigments, composite oxide yellow pigments mainly composed of Zn, Fe or Al, Fe have been reported. As shown in Non-Patent Document 3, the yellow pigment mainly composed of Zn and Fe has a very low L * value of about 37-43 in the CIE-L * a * b * color system. It lacks. There is also a drawback that the color changes drastically when blended with a resin and heated at 250 ° C. (Patent Document 3). Further, although yellow pigments mainly composed of Al and Fe have been reported, as shown in Patent Document 3, the value of L * in the CIE-L * a * b * color system is 54- It is as low as 59 and lacks brightness.

JP 2006-265366 JP 10-194747 JP-A-8-104824 M. Jansen and HP. Letschert, Nature, Vol 404, pp. 980-982.Macmillan Publishers Limited (April 27, 2000). Y.X. Han, X.S.Ma, H.M.Cao, H.Y.Zhang, Q.F.Wu, Materials Research Bulletin, Vol 39, pp.1159-1166.Elsevier Limited (June 8, 2004). CS Xavier, RA Candeia, MIB Bernardi, SJG Lima, E. Longo, CA Paskocimas, LEB Soledade, AG Souza and IMG Santos, Journal of Thermal Analysis and Calorimetry, Vol. 87, pp.709-713. Akademiai Kiado, co- published with Springer Science and Business Media BV (March 9, 2007).

  In view of such circumstances, the present invention provides a titanium oxide-iron oxide composite oxide semiconductor composed of nontoxic elements and having high heat resistance, and provides a nontoxic yellow pigment and a photocatalyst using the same. Objective.

In addition, pigments are used in various materials such as plastics. However, in order to increase the added value, the pigments may be difficult to get dirty and may need a function of removing harmful substances (for example, deodorization). Therefore, it is expected to develop a yellow pigment that imparts photocatalytic properties to the yellow pigment itself and also has a function of decomposing and removing organic harmful substances and a function of decomposing dirt by a photocatalytic reaction caused by ultraviolet light and visible light excitation.
The present invention seeks to meet these needs.

Composite oxide semiconductors invention 1, rutile type titanium oxide - a composite oxide semiconductor rutile oxidation ferrous general _{formula; A x B y M (1} -x) O (2 + 2.5y _-0.5x) (where 0 <x <0.5, 0 <x / y <1.1, A is any trivalent selected from the group _consisting of Fe or Fe and Ga, Al, In, Y, La, and Ce. It is composed of a metal, B is composed of Nb, Ta, M is composed of Ti or any tetravalent metal selected from the group of Ti and Zr, Ge, Si, Sn. To do.

The yellow pigment of the invention 2 is characterized by comprising the composite oxide semiconductor powder of the invention 1.

The photocatalyst of the invention 3 is characterized by comprising the composite oxide semiconductor powder of the invention 1.

Invention 1 has provided a composite oxide semiconductor having excellent heat resistance.
This can be used as a good yellow pigment for the following reasons, and is also useful as a photocatalyst.

  The present inventors performed band gap control by making full use of band engineering so that the pigment has a yellow color. In particular, if the pigment has a yellow color, it is necessary to absorb blue to violet light, which is the complementary color. Therefore, by using impurity doping etc. in a material with a band gap of about 3 eV, the band or doping level-conduction We decided to narrow the gap derived from the transition between the bottoms of the bands.

Titanium oxide with a band gap of 3 eV satisfies this condition and was therefore selected as a constituent element of the yellow pigment. That is, the bottom of the conduction band and the top of the valence band that make up the band structure of titanium oxide are composed of Ti3d orbitals and O2p orbitals, respectively, and a level slightly lower in potential than this O2p orbitals is introduced into the bandgap. Therefore, it is considered that the band gap becomes small and the material becomes yellow. As a result of accumulating data on various complex oxides and conducting intensive research, titanium oxide exhibits a yellow color when doped with a predetermined amount of Fe ₂ O ₃ and Ta ₂ O ₅ or Nb ₂ O _5. Successful development of complex oxides has led to success in imparting significant visible light photocatalytic properties.
The present invention has been made based on these findings. The configuration is as described below.

The present invention 2 is a yellow pigment composed of a complex oxide semiconductor composed of titanium, iron, oxygen, tantalum or niobium, and these ratios cover a very wide range. Because it consists of non-toxic metal elements, it is a very safe material compared to conventional yellow pigments (lead chromate, cadmium yellow, etc.). Furthermore, it has a high CIE-L * a * b * color system L * (L *> 70) value compared to complex oxide yellow pigments mainly composed of Zn, Fe or Al, Fe. And a brighter yellow pigment.

The yellow pigment has not only ultraviolet light but also a special effect that can efficiently decompose 2-propyl alcohol (IPA), one of the VOCs most often used in factories and the like using visible light. It is. This photocatalytic property is not limited to this, and the ability to decompose and remove various harmful substances such as aldehyde gas, which is one of the cause gases of sick house syndrome, by irradiating light. Have.
The present invention 3 is a photocatalyst that makes use of such functions, and has the photocatalytic activity in the visible light and ultraviolet light regions as described above. It is expected that it can be used for various purposes, and its role will be very large in the future.

The yellow pigment of the present invention is prepared by mixing the metal component oxides, metal carbonates, metal nitrates, metal sulfates, or metal chlorides in the ratio of the target composition in the usual solid phase reaction method. It can be synthesized by firing in compressed air.

Desirably, it is synthesized using a method (for example, complex polymerization method) in which iron, tantalum or niobium is highly dispersed in the atomic order. This gives a yellow pigment with a larger value of L *.

_{X and y} in the general formula constituting this yellow pigment; A _x B _y M _(1-x) O _{(2 + 2.5y-0.5x)} may satisfy the following conditions.
The condition is that x is greater than 0 and less than 0.5, preferably 0.4 or less, more preferably 0.3 or less, and y is greater than 0 and 1.1 or less in the x / y ratio. That is, when x is 0.5 or more, the L * value of the CIE-L * a * b * color system is too low to be suitable as a yellow pigment, and the photocatalytic activity is too small to be suitable as a photocatalytic material. Furthermore, if the x / y ratio exceeds 1.1, the interaction between Fe atoms increases and the color tone tends to be reddish, which makes it unsuitable as a yellow pigment. In addition, the redness suggests that the amount of impurity levels existing between the bands becomes excessive, and the photocatalytic activity decreases. Therefore, this condition is not suitable as a photocatalytic material.

In addition to the above raw materials, metal alkoxides and metal salts are used as raw materials, which can be prepared by various methods such as so-called sol-gel method, coprecipitation method, sputtering method, chemical vapor deposition method, hydrothermal synthesis method, etc. It can also be carried out by a preparation process. The firing temperature for firing the prepared blended raw material may be any temperature at which the raw material is decomposed and converted into an oxide, and a sintered body made of the oxide is obtained. Specifically, the temperature range may be 300 ° C. or higher and 1500 ° C. or lower, and more preferably 400 ° C. or higher and 1300 ° C. or lower.

The catalyst is prepared by the general formula : A _x B _y M _(1-x) O _{(2 + 2.5y-0.5x )} ( 0 <x <0.5, 0 <x / y <1.1, where A is Fe or Fe and Ga , Al, In, Y, La, Ce, etc., B is composed of Nb, Ta, M is Ti or Ti and tetravalent metals, such as Zr, Ge, Si, Sn) It is determined. It is prepared by blending the raw materials so as to satisfy this general formula and firing. The meaning and meaning of this general formula are those that can function as a yellow pigment as long as iron, titanium, tantalum or niobium satisfies the specified amounts.

This pigment is a material mainly composed of iron, titanium, tantalum or niobium. Even if a part of the pigment is replaced with another element, the property as a yellow pigment can be maintained, and the visible light responsive photocatalytic property can be maintained. Can show. Therefore, the present invention may include such aspects and is not excluded.
Specifically, a part of iron may be replaced up to 1/2 mole with other trivalent metal elements Ga, Al, In, Y, La, Ce, etc. per mole of iron, or a part of titanium may be replaced. In addition, even if the tetravalent metal element Zr, Si, Ge, Sn or the like is replaced by 1/10 mol per 1 mol of titanium, it can be used as a yellow pigment. The mixing / substitution of these other components cannot be uniquely defined. That is, when the function as a yellow pigment is improved by mixing / substitution of these other components, it can be said that mixing / substitution of these other components is rather preferable and does not need to be excluded.

The shape and particle size of the yellow pigment of the present invention are desirably designed so that the surface area becomes as large as possible in order to effectively use light when imparting photocatalytic properties.
Specifically, it is desirable that the specific surface area be 1 m ² g ⁻¹ or more, preferably 1.5 m ² g ⁻¹ or more, more preferably 10 m ² g ⁻¹ or more. In addition, although a specific surface area is so preferable that it is larger, it is difficult to clarify an absolute numerical value. Therefore, it is desirable to synthesize at a low temperature, but complex oxides produced by the solid-phase reaction method can be obtained as large moldings or lumps, so this can be crushed with a ball mill or etched with acid or the like By doing so, the surface area can be further increased. Further, the surface area may be increased by synthesizing so as to have a mesoporous structure.

Furthermore, in order to suppress the photocatalytic properties of the yellow pigment of the present invention, it is desirable to synthesize at a high temperature so as to reduce the surface area. When used as a pigment, the specific surface area is preferably 200 m ² g ⁻¹ or less, preferably 2 m ² g ⁻¹ or less, more preferably 0.2 m ² g ⁻¹ or less. In other words, the smaller the specific surface area, the larger the particle size, the more the recombination rate of electrons and holes contributing to the photocatalytic reaction, and the amount of electrons and holes reaching the surface is drastically reduced. This is because the effect is increased.
In addition, the photocatalytic property of the pigment having a large specific surface area synthesized at a low temperature can be suppressed by applying an amorphous treatment.

  The yellow pigment of the present invention can be made yellowish by mixing it with various materials such as plastics, cosmetics, paints for coating, or coating the material surface.

  Hazardous substances that can be removed by decomposition or oxidation or reduction reaction based on the photocatalytic properties of the yellow pigment of the present invention include environmental hormones, agricultural chemicals, insecticides, molds, bacteria, viruses, algae, environmental pollutants, chlorofluorocarbons, hydrocarbons, alcohols Aldehyde, ketone, carboxylic acid, carbon monoxide, amine, oil, aromatic compound, organic halogen compound, nitrogen compound, sulfur compound, organic phosphorus compound, protein and the like. In addition, soap and oil, hand stains, tea astringents, and slimes such as kitchen sinks that cause personal contamination can be decomposed by the photocatalytic reaction of this photocatalytic material.

Hereinafter, although the present invention is explained in detail based on a concrete example and a drawing, these do not limit the present invention. In the examples described below, the general formula : A _x B _y M _(1-x) O _{(2 + 2.5y-0.5x )} ( 0 <x <0.5, 0 <x / y <1.1, A is Fe Or Fe and trivalent metals such as Ga, Al, In, Y, La and Ce, B is Nb, Ta, M is Ti or Ti and tetravalent metals such as Zr, Ge, Si and Sn As an example, Fe _0.005 Nb _0.005 Ti _0.995 O _2.01 , Fe _0.01 Ta _0.01 Ti _0.99 O _2.02 , and Fe _0.2 Ta _0.2 Ti _0.8 O _2.4, which are specific values of the composite oxide represented by It is an Example at the time of disclosing and synthesize | combining this by the solid-phase reaction method or the complex polymerization method.

Fe _0.01 Ta _0.01 Ti _0.99 O _2.02 which is one of yellow pigments composed of iron, titanium and tantalum was synthesized by a solid phase reaction method as described below.
First, 1.3 g of iron oxide (Fe ₂ O ₃ ) and 3.7 g of tantalum oxide were weighed, and this was thoroughly pulverized and mixed using a pulverizing and mixing device such as a ball mill or mortar, and then placed in an alumina crucible. Sintering was performed for 5 hours at 1250 ° C. (indicated in units of 10 ° C., hereinafter the same) in a pneumatic atmosphere to obtain FeTaO ₄ powder. Thereafter, 2.9 g of rutile type titanium oxide and 0.11 g of FeTaO ₄ were weighed, sufficiently pulverized and mixed, and then placed in an alumina crucible and sintered at 1250 ° C. for 5 hours in an atmospheric air atmosphere. Got. When this powder sample was measured using an X-ray diffractometer, it was found that a material having a single-phase rutile structure was obtained.
The specific surface area was evaluated by adsorbing nitrogen after cooling the pigment to −200 ° C. using the BET specific surface area measurement method. The specific surface area of this pigment was 0.4 m ² / g. Next, the color tone of the powder was measured with a color difference meter using BaSO ₄ as a reference sample. The L * value of the CIE-L * a * b * color system is 86.69, which is sufficiently large, the a * value indicating the red degree is negative, and the b * value indicating the yellow degree is 20 or more (Table 1). Furthermore, when the heat resistance was confirmed by heating at 400 ° C. for 1 hour, no change was seen in the color tone, and it can be said that the heat resistance was excellent. Therefore, this pigment is effective as a yellow pigment.
A decomposition test of 2-propyl alcohol was conducted using 0.4 g of this yellow pigment. A 300 W Xe lamp was used as a light source, and visible light (light quantity: 0.9 mWcm ⁻² ) from 400 nm to 520 nm was irradiated to the reaction vessel using a cutoff filter. Detection and quantification of 2-propyl alcohol and its decomposition substance acetone were performed by gas chromatography (detector is FID), and the time change of the amount of intermediate acetone generated when 2-propyl alcohol was decomposed was examined. . As a result, 3.5 ppm of acetone was produced in 1 hour, and this material was also shown to show visible light activity under visible light irradiation (FIG. 1).

Fe _0.005 Nb _0.005 Ti _0.995 O _2.01 which is one of yellow pigments composed of iron, titanium and niobium was synthesized by the solid phase reaction method in the same manner as in Example 1. They were weighed so that the molar ratio was Fe ₂ O ₃ : Nb ₂ O ₅ = 1: 1, sufficiently pulverized and mixed, and then sintered at 1250 ° C. for 5 hours to obtain FeNbO ₄ powder. This FeNbO ₄ and rutile type titanium oxide were mixed at a molar ratio of 1: 199 and sintered at 1250 ° C. for 5 hours to obtain a sample. When this powder sample was measured using an X-ray diffractometer, it was found that a material having a single-phase rutile structure was obtained. The specific surface area of this pigment was 0.4 m ² / g.
Next, the color tone of this powder was measured with a color difference meter. The L * value, a *, and b * value of the CIE-L * a * b * color system were almost the same as those in Example 1. Further, as a heat resistance test, the sample was heated at 400 ° C. for 1 hour in the same manner as in Example 1, but no change in color tone was observed. Therefore, it can be said that this pigment is also effective as a yellow pigment (Table 1). Furthermore, when the photocatalytic activity was evaluated by the method shown in Example 1, 2.1 ppm of acetone was produced in 1 hour, and it was also revealed that this pigment showed visible light activity under visible light irradiation (FIG. 1). ).

Fe _0.01 Ta _0.01 Ti _0.99 O _2.02 shown in Example 1 was synthesized by a complex polymerization method as described below. First, titanium tetraisopropoxide (7.3 mL), 0.1 mol / L tris (acetylacetonato) iron (III) -ethanol solution (2.4 mL), 0.1 mol / L tantalum ethoxide-ethanol solution (2.4 mL) Was weighed into each container, then further diluted with ethanol and sufficiently stirred. Then, citric acid and polyethylene glycol were added to each container and stirred. Thereafter, the three solutions were mixed together and stirred to obtain a mixed solution. The amounts of citric acid, polyethylene glycol, and ethanol added were 46 g, 61 g, and 89 g, respectively. The mixed solution was aged at 80 ° C. for 10 minutes and then calcined at 250 ° C. for 2 hours. As a result, a foamy solid was obtained, which was further calcined at 400 ° C. for 2 hours and at 800 ° C. for 5 hours to obtain a sample. When the powder was measured using an X-ray diffractometer, it was found that a powder having a single-phase rutile structure was obtained. Its specific surface area was 1.6 m ² / g.
As a result of measurement with a color difference meter, the L * value of the CIE-L * a * b * color system was sufficiently large as 96.14, and the b * value was close to 30 (Table 1). Furthermore, the heat resistance was confirmed by heating at 400 ° C. for 1 hour, but no change in color tone was observed and the heat resistance was excellent. Therefore, it can be said that this powder is also suitable for a yellow pigment (Table 1).
Photocatalytic activity was evaluated under the same conditions as in Example 1. As a result, as much as 27 ppm of acetone was produced in 1 hour, and this material having a large specific surface area was 8 times stronger in visible light photocatalytic activity than the material shown in Example 1 (FIG. 1). Therefore, when this material is used as a yellow pigment, it can be said that a more significant harmful substance removal effect and dirt decomposition effect can be imparted.
(Reference example)

Fe _0.2 Ta _0.2 Ti _0.8 O _2.4 was synthesized by the complex polymerization method used in Example 3. First, according to the composition ratio, titanium tetraisopropoxide (5.9 mL), 0.1 mol / L tris (acetylacetonato) iron (III) -ethanol solution (48 mL), 0.1 mol / L tantalum ethoxide-ethanol solution ( 48 mL) was weighed into each container, then diluted with ethanol and stirred well. Then, citric acid and polyethylene glycol were added to each container, and after thorough stirring, the three solutions were mixed together and further stirred. The ratio of the amounts of citric acid, polyethylene glycol, and ethanol added was 1: 4: 8. The mixed solution was aged at 80 ° C. for 10 minutes and then calcined at 250 ° C. for 2 hours and further at 400 ° C. for 2 hours to obtain a sample. When this powder was measured using an X-ray diffractometer, it was found that a substance having a single-phase anatase structure was obtained. The specific surface area of this pigment was 180 m ² / g.
The color was yellow, and as a result of measuring with a color difference meter, the L * value of the CIE-L * a * b * color system was 75.76, and the b * value was 39.12, which was sufficiently large. Furthermore, although the heat resistance was confirmed by heating at 400 ° C. for 1 hour, no change was seen in the color tone, and the heat resistance was excellent, so it can be said that the material is suitable as a yellow pigment. (Table 1) Further, when the photocatalytic activity was evaluated by the method shown in Example 1, 4.0 ppm of acetone was produced in 1 hour, and it was also revealed that this material shows visible light activity under visible light irradiation. (FIG. 1).

Comparative Example 1

A rutile type titanium oxide was fired at 1250 ° C. for 5 hours to prepare a comparative sample. As a result of measuring with a color difference meter, the L * value of the CIE-L * a * b * color system was sufficiently large as 94.69, but the b * value was as small as 4.32, and it was hardly yellowish (Table 1). ) Further, when the photocatalytic activity was evaluated by the method shown in Example 1, 0.5 ppm of acetone was produced in 1 hour, but the activity was low enough to be less than that of Example 1-3 and Reference Example (FIG. 1). . Therefore, it can be said that the yellow pigments of Examples 1-3 and Reference Examples have significant visible light responsive photocatalytic properties.

Comparative Example 2

Fe _0.01 Ti _0.99 O _1.995 , one of the complex oxides of iron and titanium, was synthesized by a solid phase reaction method as described below. First, according to the composition ratio, 0.05 g of iron oxide (Fe ₂ O ₃ ) and 4.95 g of titanium oxide were weighed, and this was thoroughly pulverized and mixed using a pulverizing and mixing device such as a ball mill or a mortar, and then placed in an alumina crucible. And was sintered for 5 hours at 1250 ° C. in an atmospheric air atmosphere to obtain a powder. The color was orange, and as a result of measuring with a color difference meter, the L * value of the CIE-L * a * b * color system was relatively small at 62.45 and the a * value was very large at 21.20 (Table 1). A large a * value indicates redness, and this powder is not suitable for yellow pigments.
As described above, the powder shows yellow when Fe and Ta are mixed in a highly dispersed manner in the titanium oxide lattice at a predetermined ratio (Examples 1 to 3, Reference Example ), and if Ta and Nb are missing. As shown in Comparative Example 2, the composite oxide turns red and becomes unsuitable as a yellow pigment. Further, when Fe is missing, as shown in Comparative Example 1, it lacks yellowishness, which is also inappropriate.

The above results are shown in Table 1 as described above. That is, the composite oxide composed of iron, titanium, tantalum, or niobium is a harmless inorganic yellow pigment, indicating that the development of a material that meets the above-mentioned purpose has been successful. In addition, since the material is synthesized by high-temperature firing, the heat resistance is also high. Furthermore, this yellow pigment exhibits photocatalytic activity with respect to visible light and ultraviolet light, and is expected to contribute more effectively to and contribute to uses such as decomposition of harmful substances and prevention of contamination.

As described above, the present invention can be represented by the general formula: general formula; A _x B _y M _(1-x) O _{(2 + 2.5y-0.5x)} (0 <x <0.5, 0 <x / y < 1.1, A consists of Fe or Fe and trivalent metals such as Ga, Al, In, Y, La, Ce, B is Nb, Ta, M is Ti or Ti and 4 such as Zr, Ge, Si, Sn The complex oxide represented by (valent metal) is a pigment exhibiting a bright yellow color, and since it is composed of a harmless metal, yellow can be added to various materials. Furthermore, considering that most of the practical inorganic yellow pigments so far are composed of harmful metals, it is very significant that bright new yellow pigments composed of harmless metals and heat resistant can be developed. Furthermore, the photocatalytic property which responds with visible light and ultraviolet light can also be provided as needed. As a result, harmful substances and dirt can be decomposed to create a clean space. According to the present invention, this pigment is heat-resistant and made of a harmless metal, so it is possible to add a yellow color to various materials such as paint and plastic, and also provide photocatalytic properties as necessary. In this way, environmental protection technology used to make harmful substances such as sterilizing, decomposing, removing, etc. by using visible light and ultraviolet light to act on various harmful compounds such as environmental hormones and bacteria. It is expected to contribute to the development of industry by being used for various chemical reactions.

Photocatalytic activity of the prepared sample

Claims (3)

Rutile titanium oxide - a composite oxide semiconductor rutile oxidation ferrous general _{formula; A x B y M (1} -x) O (2 + 2.5y-0.5x) ( where 0 < x <0.5, 0 <x / y <1.1, A is Fe or any trivalent metal selected from the group consisting of Fe and Ga, Al, In, Y, La, Ce, and B is Nb, Ta , M is composed of Ti or Ti and any tetravalent metal selected from the group consisting of Ti and Zr, Ge, Si, and Sn).   An inorganic pigment which absorbs blue and violet light and exhibits a yellow color, comprising the composite oxide semiconductor powder according to claim 1. A photocatalyst for decomposing an organic substance with light, comprising the composite oxide semiconductor powder according to claim 1.