Copper ion-modified titanium oxide, method for producing the same, and photocatalyst

The present invention relates to a copper ion-modified titanium oxide suitable for a photocatalyst that exhibits activity by irradiation with visible light, a method for producing the same, and a photocatalyst containing the copper ion-modified titanium oxide as a main component.

Titanium oxide is a substance widely known as a photocatalyst, but it hardly functions in the absence of ultraviolet rays. Therefore, at present, attempts are being made to impart the property of allowing titanium oxide to absorb visible light.

One attempt is to dope titanium oxide with copper ions. A composite of copper ion and titanium oxide can exhibit photocatalytic activity under visible light irradiation (see, for example, Patent Document 1). However, the above method does not clarify whether the additive metal is present on the surface or in the bulk of titanium oxide. On the other hand, the copper ion modification only to the surface of titanium oxide is performed for the purpose of improving the ultraviolet light activity or the antibacterial property, and the volatile organic compound decomposition performance under visible light irradiation has not been investigated ( For example, see Patent Documents 2 and 3).

On the other hand, it has been reported in Non-Patent Document 1 that by modifying copper ions, a visible light absorption band and a multi-electron reduction function due to interfacial charge transfer are imparted to titanium oxide, and isopropanol can be decomposed under visible light irradiation. .. However, in this report, only the adaptation to rutile-type titanium oxide is examined, and it is not applicable to anatase or brookite, which are generally considered to have high activity.

<p><patcit num="1"><text>Japanese Unexamined Patent Publication No. 9-192496</text></patcit><patcit num="2"><text>Japanese Patent Application Laid-Open No. 6-205977</text></patcit><patcit num="3"><text>Japanese Patent Application Laid-Open No. 6-65012</text></patcit><nplcit num="1"><text>Chemical Physics Letters 457 (2008) 202-205 Hiroshi Irie, Shuhei Miura, Kazuhide Kamiya, Kazuhito Hashimoto</text></nplcit></p>

<p> From the above, the present invention provides a copper ion-modified titanium oxide and a method for producing the same, which can exhibit good catalytic activity under visible light irradiation when used as a photocatalyst, and a photocatalyst containing the copper ion-modified titanium oxide as a main component. The purpose is to do.</p>

<p> The present inventors have come up with the following invention and found that the above problems can be solved. That is, the present invention is as follows.</p><p>[1] Copper ion-modified titanium oxide whose surface is modified with copper ions and contains brookite-type crystals. [2] The copper ion-modified titanium oxide according to [1], wherein the diffraction line is detected at least 2.90 ± 0.02 Å in the plane spacing d (Å) measured by powder X-ray diffraction using Cu-Kα1 line. [3] The copper ion according to [1] or [2], wherein the content of brookite-type crystals in Rietveld analysis using 10% by mass of nickel oxide as an internal standard substance is 14% by mass or more and 60% by mass or less. Modified titanium oxide. [4] The copper ion-modified titanium oxide according to any one of [1] to [3], wherein the brookite-type crystal obtained from Scheller's equation has a crystallite size of 24 nm or less. [5] The copper ion-modified titanium oxide according to any one of [1] to [4], wherein the copper ion is derived from copper (II) chloride. [6] The copper ion-modified titanium oxide according to any one of [1] to [5], which is modified with 0.05 to 0.3% by mass of copper ions in terms of metal.</p><p>[7] A hydrolysis step in which a titanium compound that produces titanium oxide is hydrolyzed in a reaction solution, and a surface modification in which an aqueous solution containing copper ions is mixed with the hydrolyzed solution to modify the surface of the titanium oxide. A method for producing copper ion-modified titanium oxide, which includes steps. [8] The method for producing copper ion-modified titanium oxide according to [7], wherein the titanium compound is titanium tetrachloride or titanium trichloride. [9] The method for producing copper ion-modified titanium oxide according to [7] or [8], wherein the temperature of the reaction solution at the time of hydrolysis is 70 ° C. or higher and lower than the boiling point of the reaction solution. [10] The method for producing copper ion-modified titanium oxide according to any one of [7] to [9], wherein oxygen or ozone is bubbled in the reaction solution at the time of hydrolysis. [11] The method for producing copper ion-modified titanium oxide according to any one of [7] to [10], wherein the temperature at which the surface is modified in the surface modification step is 80 to 95 ° C. [12] Copper ion-modified titanium oxide obtained by the production method according to any one of the above [7] to [11]. [13] A photocatalyst containing 70% by mass or more of the copper ion-modified titanium oxide according to any one of [1] to [6] and [12] above.</p>

<p> According to the present invention, there is provided a copper ion-modified titanium oxide and a method for producing the same, which can exhibit good catalytic activity under visible light irradiation when used as a photocatalyst, and a photocatalyst containing the copper ion-modified titanium oxide as a main component. can do.</p>

<figref num="1">It is a figure which shows the X-ray diffraction pattern of the copper ion modified titanium oxide of Example 1.</figref>

[Copper-modified titanium oxide] At least a part of the crystal structure of the copper ion-modified titanium oxide of the present invention is a brookite type crystal. Then, as long as it contains brookite-type crystals, titanium hydroxide-containing titanium hydroxide, titanium hydroxide, titanium acid, amorphous, anatase-type crystals, rutile-type crystals and the like may be mixed.

The presence of brookite-type crystals can be confirmed by powder X-ray diffraction using Cu-Kα1 rays. That is, it can be confirmed by detecting the diffraction line at least 2.90 ± 0.02 Å in the plane spacing d (Å) measured by the powder X-ray diffraction.

Then, by comparing the peaks of 2.90 Å derived from brookite type crystal, 2.38 Å derived from anatase type crystal, and 3.25 Å derived from rutile type crystal, it was confirmed that each crystal phase was present to some extent in titanium oxide. The relative abundance ratio can be estimated. However, since the relative intensities of these three peaks and the ratio of each crystal phase contained in titanium oxide do not completely match and the existence of amorphous material is ignored, the content rate of each crystal phase is measured. It is preferable to use the Rietveld method using an internal standard substance.

That is, the content of brookite-type crystals can be determined by Rietveld analysis by mixing nickel oxide so as to be 10% by mass as an internal standard substance. The abundance ratio of each crystal can be determined by Rietveld analysis software in PANalytical's X'Pert High Score Plus program.

The content of the brookite-type crystal is preferably 14% by mass or more and 60% by mass or less, and more preferably 14% by mass or more and 40% by mass or less. When it is 14% by mass or more, it is preferable because the dispersibility of the titanium oxide sol and the adsorptivity of copper ions to titanium oxide are improved. In addition, excellent catalytic ability can be exhibited when used as a photocatalyst. On the other hand, when it is 60% by mass or less, the crystallite size does not become too large, and the interaction between the copper ion modified on the surface and titanium oxide can be maintained in a good state.

The crystallite size of the brookite-type crystal is preferably 24 nm or less, more preferably 18 nm or less, further preferably 5 to 18 nm, particularly preferably 5 to 12 nm, and 9 to 9 to 9. Most preferably, it is 12 nm. A crystallite size of 24 nm or less is preferable because the interaction with copper ions is improved. In addition, the reactivity between the surface of the photocatalyst particles and the copper ions changes, and the visible light activity can be increased.

The crystallite size of the crystal is t (nm) for the crystallite size, λ (Å) for the X-ray wavelength, and B for the half width of the sample._M, Reference (SiO)₂) Is calculated by the following Scheller's equation, where Bs is the half width and θ is the diffraction angle.

<maths num="1"><img file="JP2011079713A_D0001.tif" /></maths>

The surface of the copper ion-modified titanium oxide of the present invention is modified by copper ions, and the copper ions include copper (II) chloride, copper (II) acetate, copper (II) sulfate, copper (II) nitrate, and foot. Examples thereof include those derived from copper (II) oxide, copper (II) iodide, copper (II) bromide and the like. Among them, it is preferably derived from copper (II) chloride in consideration of availability and productivity. Copper ions are generated by the above-mentioned precursors undergoing chemical reactions such as decomposition and oxidation on titanium oxide and physical changes such as precipitation.

The amount of modification with copper ions is preferably 0.05 to 0.3% by mass, more preferably 0.1 to 0.2% by mass, in terms of metal (Cu) with respect to titanium oxide. When the modification amount is 0.05% by mass or more, the photocatalytic activity when used as a photocatalyst can be improved. When it is 0.3% by mass or less, agglutination of copper ions is unlikely to occur, and it is possible to prevent a decrease in photocatalytic ability when used as a photocatalyst.

Although the mechanism of interaction between copper ions and rutile-type titanium oxide is not clear, Non-Patent Document 1 describes the following mechanism. That is, when light is irradiated, a direct transition from the valence band of rutile-type titanium oxide to copper ions occurs, so that photocatalytic activity is exhibited even under visible light irradiation.

Even in the brookite-type crystal-containing titanium oxide having a small crystallite size of the present invention, visible light response can be achieved by the above mechanism, and the interaction with copper ions is promoted due to the difference in crystal structure, so that the conventional titanium oxide It is considered that more excellent photocatalytic activity can be exhibited. In particular, when two types of crystal forms having different band gaps, anatase type and rutile type, are mixed, charge separation of photogenerated electrons and holes is promoted, and photocatalytic activity may be increased. Therefore, it is presumed that the mixture of titanium oxides having different band gaps promotes charge separation and greatly contributes to the excellent properties of the brookite-type crystal-containing titanium oxide of the present invention.

[Manufacturing method of copper-modified titanium oxide] In the method for producing titanium oxide modified titanium oxide of the present invention, a hydrolysis step of hydrolyzing a titanium compound that produces titanium oxide in a reaction solution and an aqueous solution containing copper ions are mixed with the hydrolyzed solution to oxidize the titanium oxide. It includes a surface modification step of modifying the surface of titanium. Hereinafter, each step will be described.

(Hydrolyzed step) In this step, for example, a titanium oxide slurry is obtained by hydrolyzing an aqueous solution of a titanium compound capable of producing titanium oxide such as titanium chloride. By changing the conditions of the solution at the time of hydrolysis, it can be formed into an arbitrary crystal form, and for example, titanium oxide particles having a brookite content of 7 to 60% by mass can be obtained. In addition, the half width of the X-ray diffraction peak and the crystallite size obtained from Scheller's equation can be created separately, for example, at 9 to 24 nm. The crystal structure or crystallite size of titanium oxide has a great influence on the mobility of photogenerated carriers. It also affects the interaction with copper ions. Specifically, when the hydrolysis temperature is 80 ° C or less, the rutile type is likely to be formed, from 80 to 90 ° C, the anatase type is likely to be formed, and at 95 ° C, the brookite type is likely to be formed. Addition of hydrochloric acid can reduce the anatase-type content and increase the brookite or rutile-type content. With these, the crystal phase can be made separately.

Examples of the titanium compound include titanium tetrachloride, titanium trichloride, titanium sulfate, titanium tetraethoxyside, titanium tetraisopropoxyside and the like, and among them, titanium tetrachloride and titanium trichloride are preferable.

The temperature of the reaction solution at the time of hydrolysis is preferably 70 ° C. or higher and lower than the boiling point of the reaction solution. Within such a temperature range, titanium oxide sol can be efficiently synthesized.

Further, at the time of hydrolysis, it is preferable to bubble oxygen or ozone in the reaction solution. Thereby, the crystal structure and the crystallite diameter can be controlled.

(Surface modification process) In the surface modification step, the temperature at the time of surface modification is preferably 80 to 95 ° C, more preferably 90 to 95 ° C. By setting the temperature to 80 to 95 ° C, copper ions can be efficiently modified on the surface of titanium oxide.

For the modification with copper ions, the method described in Non-Patent Document 1 can be used. (1) A method in which titanium oxide particles and copper chloride are mixed in a medium under heating and then washed with water for recovery. , (2) A method in which titanium oxide particles and copper chloride are mixed in a medium under heating and then evaporated to dryness for recovery and the like can be mentioned. The method (1) is preferable because the counter anion can be removed without heat treatment.

The copper ion-modified titanium oxide obtained by the production method of the present invention has its particle surface modified with copper ions. State analysis of modified copper ions is difficult due to the small amount. Therefore, if an absorption band that cannot be observed only with titanium oxide or copper ions can be observed in the diffuse reflection spectrum (spectrophotometer with integrating sphere, manufactured by Shimadzu Corporation) (in the vicinity of 420 to 500 nm, it is included in copper ion modification. The qualification and quantification of ions can also be achieved by ICP analysis.

[photocatalyst] The photocatalyst of the present invention contains the copper ion-modified titanium oxide of the present invention as a main component. Here, the "main component" means 70% by mass or more, preferably 75% by mass or more of the total amount of the photocatalyst. In addition, examples of other components include amorphous titanium oxide and hydrous titanium. The photocatalyst of the present invention is used in various forms, but is preferably used in powder form.

The photocatalyst of the present invention can exhibit its photocatalytic activity even with light having a wavelength of 420 nm or less, but it also exhibits its catalytic ability even under visible light having a wavelength of 420 nm or more. The photocatalytic activity in the present invention includes functions such as antibacterial, deodorant, antifouling, air purification, water purification and other environmental purification. Specifically, the following functions can be exemplified, but the functions are not particularly limited to these. In particular, when there are substances in the system that adversely affect the environment, such as photocatalytic powder and organic compounds such as aldehydes, the concentration of organic substances decreases and oxidative decomposition products occur when compared with dark places under light irradiation. There is an increase in carbon dioxide concentration.

<p> Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The crystal structures of the copper ion-modified titanium oxide obtained in each example were specified by XRD measurement, and the abundance ratio of various crystals and the crystallite size of brookite-type crystals were determined. For XRD measurement, using a copper target and Cu-Kα1 wire, the tube voltage is 45 kV, the tube current is 40 mA, the measurement range is 2θ = 20 to 80 deg, the sampling width is 0.0167 deg, and the scanning speed is 1.1 deg / min. I went there. The device used for the measurement was PANalytical's X'pert PRO.</p><p>(Example 1) 690 mL of distilled water was injected into a reaction vessel equipped with a reflux condenser, and 60 g of a titanium trichloride aqueous solution (20% mass solution, density 1.23 g / ml) was added dropwise to the reaction vessel at a rate of 1 g / min. Then, while bubbling oxygen through the ozone generator, the temperature was raised to 101 ° C over 30 minutes and held for 90 minutes. The obtained sol was dechlorinated with an electrodialyzer until the pH reached 4. To 200 mL of the obtained slurry solution (containing powder content 1.5 g), 0.5 mL of copper chloride aqueous solution (TiO)₂As copper, equivalent to 0.1% by mass) was added. Then, after heat-treating at 90 ° C for 1 hour with stirring, the mixture was allowed to cool to room temperature, washed and recovered by centrifugation, dried at 120 ° C for 1 day and night, crushed in an agate mortar, and brookite type. The copper ion-modified titanium oxide of the present invention having a pale yellow color containing 40% by mass of crystals was obtained. FIG. 1 shows the X-ray diffraction pattern of the copper ion-modified titanium oxide.</p><p>(Example 2) 690 mL of distilled water was injected into a reaction vessel with a reflux condenser and heated to 95 ° C to maintain it. While maintaining the stirring speed at 300 rpm, 60 g of a titanium tetrachloride aqueous solution (Ti content 17.0% by mass, specific gravity 1.52) was added dropwise to the reaction vessel at a rate of 1 g / min. Immediately after the dropping, the reaction solution began to become cloudy in the reaction vessel, but was kept at the same temperature, and after the dropping was completed, the temperature was further raised and maintained at a temperature near the boiling point for 60 minutes. The obtained sol was dechlorinated with an electrodialyzer until the pH reached 4. To 100 mL of the obtained slurry solution (containing powder content 1.5 g), 0.5 mL of copper chloride aqueous solution (TiO)₂As copper, equivalent to 0.1% by mass) was added. Next, the mixture was heat-treated at 90 ° C for 1 hour with stirring, allowed to cool to room temperature, washed and recovered by centrifugation, dried at 120 ° C for 1 day and night, and then crushed in an agate mortar. The copper ion-modified titanium oxide of the present invention having a pale yellow color containing 35% by mass of brookite-type crystals was obtained.</p><p>(Example 3) 690 mL of distilled water was injected into a reaction vessel equipped with a reflux condenser, and 60 g of a titanium tetrachloride aqueous solution (Ti content 17.0% by mass, specific gravity 1.52) was added dropwise to the reaction vessel at a rate of 1 g / min. Then, the temperature was raised to 101 ° C. and held for 120 minutes. The obtained sol was dechlorinated with an electrodialyzer until the pH reached 4 . To 200 mL of the obtained slurry solution (containing powder content 1.5 g), 0.5 mL of copper chloride aqueous solution (TiO)₂As copper, equivalent to 0.1% by mass) was added. Next, the mixture was heat-treated at 90 ° C for 1 hour with stirring, allowed to cool to room temperature, washed and recovered by centrifugation, dried at 120 ° C for 1 day and night, and then crushed in an agate mortar. The copper ion-modified titanium oxide of the present invention having a pale yellow color containing 24% by mass of brookite-type crystals was obtained.</p><p>(Example 4) 690 mL of distilled water was injected into a reaction vessel with a reflux condenser and heated to 70 ° C to maintain it. While maintaining the stirring speed at 300 rpm, 60 g of a titanium tetrachloride aqueous solution (Ti content 17.0% by mass, specific gravity 1.52) was added dropwise to the reaction vessel at a rate of 1 g / min. Immediately after the dropping, the reaction solution began to become cloudy in the reaction vessel, but the temperature was maintained as it was, and after the dropping was completed, the temperature was further raised to 75 ° C. and maintained for 60 minutes. The obtained sol was dechlorinated with an electrodialyzer until the pH reached 4. To 100 mL of the obtained slurry solution (containing powder content 1.5 g), 0.5 mL of copper chloride aqueous solution (TiO)₂As copper, equivalent to 0.1% by mass) was added. Then, after heat-treating at 90 ° C for 1 hour with stirring, the mixture was allowed to cool to room temperature, washed and recovered by centrifugation, dried at 120 ° C for 1 day and night, crushed in an agate mortar, and brookite type. A pale yellow copper ion-modified titanium oxide containing 14% by mass of crystals was obtained.</p><p>(Example 5) 690 mL of distilled water was injected into a reaction vessel with a reflux condenser and heated to 95 ° C to maintain it. While keeping the stirring speed at 300 rpm and bubbling oxygen through the ozone generator, 60 g of titanium trichloride aqueous solution (20 mass% solution, density 1.23 g / ml) was dropped into the reaction vessel at a rate of 1 g / min. did. Then, bubbling of oxygen through the ozone generator was completed, and the temperature was maintained as it was, and after the dropping was completed, the temperature was further raised and maintained at a temperature near the boiling point for 60 minutes. The obtained sol was dechlorinated with an electrodialyzer until the pH reached 4. To 150 mL of the obtained slurry solution (containing powder content 1.5 g), 0.5 mL of copper chloride aqueous solution (TiO)₂As copper, equivalent to 0.1% by mass) was added. Then, after heat-treating at 90 ° C for 1 hour with stirring, the mixture was allowed to cool to room temperature, washed and recovered by centrifugation, dried at 120 ° C for 1 day and night, crushed in an agate mortar, and brookite type. The copper ion-modified titanium oxide of the present invention having a pale yellow color containing 54% by mass of crystals was obtained.</p><p>(Example 6) 690 mL of distilled water was injected into a reaction vessel with a reflux condenser and heated to 95 ° C to maintain it. While keeping the stirring speed at 300 rpm and bubbling oxygen through the ozone generator, 60 g of titanium trichloride aqueous solution (20 mass% solution, density 1.23 g / ml) was dropped into the reaction vessel at a rate of 1 g / min. did. It was kept at the same temperature, and after the completion of dropping, the temperature was further raised and maintained at a temperature near the boiling point for 60 minutes. The obtained sol was dechlorinated with an electrodialyzer until the pH reached 4. To 150 mL of the obtained slurry solution (containing powder content 1.5 g), 0.5 mL of copper chloride aqueous solution (TiO)₂As copper, equivalent to 0.1% by mass) was added. Then, after heat-treating at 90 ° C for 1 hour with stirring, the mixture was allowed to cool to room temperature, washed and recovered by centrifugation, dried at 120 ° C for 1 day and night, crushed in an agate mortar, and brookite type. The copper ion-modified titanium oxide of the present invention having a pale yellow color containing 60% by mass of crystals was obtained.</p><p>(Comparative example 1) 690 mL of distilled water was injected into a reaction vessel with a reflux condenser and heated to 80 ° C to maintain it. While maintaining the stirring speed at 300 rpm, 60 g of a titanium tetrachloride aqueous solution (Ti content 17.0% by mass, specific gravity 1.52) was added dropwise to the reaction vessel at a rate of 1 g / min. Immediately after the dropping, the reaction solution began to become cloudy in the reaction vessel, but it was kept at the same temperature. The obtained sol was dechlorinated with an electrodialyzer until the pH reached 4. To 100 mL of the obtained slurry solution (containing powder content 1.5 g), 0.5 mL of copper chloride aqueous solution (TiO)₂As copper, equivalent to 0.1% by mass) was added. Then, after heat-treating at 90 ° C for 1 hour with stirring, the mixture was allowed to cool to room temperature, washed and recovered by centrifugation, dried at 120 ° C for 1 day and night, and then crushed in an agate mortar. A copper ion-modified titanium oxide consisting only of rutile-type crystals was obtained.</p><p>(Comparative example 2) 1.5 g of commercially available titanium oxide (trade name: Super Titania (registered trademark) F6, manufactured by Showa Denko), which is mainly anatase type, is suspended in 200 ml of ion-exchanged water, and treated with copper chloride in the same manner as in Example 1. This was carried out to obtain copper ion-modified titanium oxide.</p><p>(Comparative example 3) A commercially available titanium oxide (trade name: ST01, manufactured by Ishihara Sangyo Co., Ltd.) consisting only of anatase type was modified with copper ions in the same manner as in Comparative Example 2 to obtain copper ion-modified titanium oxide.</p><p>(Measurement of carbon dioxide generation) A glass petri dish with a diameter of 1.5 cm was placed in a closed glass reaction vessel (capacity 0.5 L), and 0.3 g of particulate titanium oxide obtained in each Example and Comparative Example was placed on the petri dish. .. Replace the inside of the reaction vessel with a mixed gas having a volume ratio of oxygen and nitrogen of 1: 4, 5.2 μL of water (equivalent to 50% relative humidity (25 ° C)), 5.1% acetaldehyde (mixed gas standard with nitrogen). A state of 25 ° C (1 atm) was sealed in 5.0 mL, and visible light was irradiated from outside the reaction vessel. For the irradiation of visible light, a xenon lamp equipped with a filter (trade name: Y-44 Asahi Techno Glass) that cuts ultraviolet rays with a wavelength of 420 nm or less was used as a light source. The rate of decrease of acetaldehyde and the rate of generation of carbon dioxide, which is an oxidative decomposition product, were measured over time by gas chromatography. The value obtained by subtracting the amount immediately before the light irradiation from the amount of carbon dioxide generated 8 hours after the light irradiation was taken as the amount of carbon dioxide generated from the true acetaldehyde. The results are shown in Table 1 below.</p><p><tables num="1"><img file="JP2011079713A_D0002.tif" /></tables></p><p> From the above results, the titanium oxide containing the brookite-type crystal modified with copper ions of the present invention produces 1.3 to 2.4 times as much carbon dioxide as the titanium oxide containing no brookite-type crystal modified with copper ions. It is clearly a highly active photocatalyst. Up to a brookite-type crystal content of 40% by mass, the photocatalytic activity improved as the content increased. Above that, the photocatalytic activity decreased. Up to 40% by mass, the proportion of brookite-type crystal particles increases, so that the photocatalytic ability is improved. However, if it exceeds 40% by mass, the crystallite size of the brookite-type crystal increases to about 20 nm, so that the interaction between copper ions and titanium oxide becomes small and the photocatalytic activity decreases.</p>