JP2006335619A - Titanium oxide particle, and production method and application thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide rutile type titanium oxide particles exhibiting high photocatalytic activity to a practical light source such as a white fluorescent lamp; and a method for producing the titanium oxide particles by which the titanium oxide particles can be easily produced by performing hydrolysis of an aqueous solution of titanium tetrachloride under a certain condition. <P>SOLUTION: The titanium oxide particles have a rutile content of 50-99.9 mass% and a BET specific surface area of >50 and ≤300 m<SP>2</SP>/g. The method for producing the titanium oxide particles comprises mixing titanium tetrachloride and hydrochloric acid each in an amount of 1-5 mass% to water of 65-90°C and then performing hydrolysis while keeping the temperature of the resulting mixed liquid within a temperature range of 65°C to the boiling point of the mixed liquid. In the method for producing the titanium oxide particles, a process for incorporating one or more kinds of elements selected from nitrogen, carbon, sulfur, and chromium into the titanium oxide particles is not provided. A photocatalyst, an aqueous dispersion titanium oxide sol, and a titanium oxide thin film, obtained by using the titanium oxide particles, and an article and a base material, obtained by using the titanium oxide thin film, are provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention is directed to a rutile structure as a main structure of the crystal structure, i.e. a rutile content of 50 to 99.9% by weight, wherein the BET specific surface area of 50m ² / g~300m ² / g And, without adding impurities such as nitrogen and chromium, titanium oxide particles having high photocatalytic activity for light sources used in general life such as white fluorescent lamps and daylight white fluorescent lamps, and titanium tetrachloride or The present invention relates to a method for producing a titanium tetrachloride aqueous solution by hydrolysis.

  Titanium oxide is known to have three crystal phases of brookite type, anatase type and rutile type. The latter two are used separately for photocatalyst use and ultraviolet shielding use, respectively. Of these, the anatase type is more frequently used than the rutile type for photocatalytic applications. The reason is that the photocatalytic ability is higher in the anatase type. This difference in activity is due to the energy gap between the two, and this band gap is about 0.2 eV higher than the rutile type. (Non-Patent Document 1)

  Environmental purification such as antibacterial, deodorizing, antifouling, air purification, water quality purification using this photocatalytic function has been studied.

  However, in order to use the excellent photocatalytic function of titanium oxide, ultraviolet light having a wavelength of 400 nm or less is necessary, and thus it is difficult to use the photocatalytic function in a space where it is difficult to obtain ultraviolet light such as indoors or in a vehicle. It was. Therefore, studies on so-called visible light responsive photocatalysts that absorb light having a wavelength longer than 400 nm have been made in various places.

  For example, in Patent Document 1 and Patent Document 2, it is studied that titanium oxide is doped with nitrogen to narrow the band gap and absorb visible light. In Patent Document 1, titanium oxide doped with nitrogen is produced by a reaction between a titanium trichloride solution and aqueous ammonia, and the decomposition of acetaldehyde gas by visible light is confirmed. In Patent Document 2, nitrogen is doped by sputtering, and methylene blue is decomposed by visible light.

  In addition, the metal optical elements such as Cr (chromium) and V (vanadium) are ion-implanted into anatase-type titanium dioxide with high catalytic activity, and the material is modified to shift the maximum light absorption wavelength of titanium dioxide to the longer wavelength side. Some reports have made it possible to operate the titanium dioxide catalyst with visible light. (Patent Document 3)

  As another example of high activation, it has recently been reported that a remarkable improvement in activity is observed by combining rutile and anatase particles. This is because the rutile crystal absorbs light efficiently like an antenna, and the electron-hole separation is promoted by the electron transfer between the rutile-anatase crystals, resulting in a decrease in the recombination rate of the electron-hole pair. This is considered to be the cause of high activity (rutile-anatase combined effect). (Non-Patent Document 2)

  In addition to the development of rutile-type titanium oxide fine particles for conventional UV shielding, the development of rutile-type titanium oxide having phototactility has recently been proposed. For example, the following production method has been proposed. Yes.

  (1) A method of producing titanium oxide having a rutile content ratio of 99% or more by changing the ratio of hydrogen in a mixed gas of oxygen and hydrogen in a gas phase reaction (Patent Document 4).

  (2) A method of producing titanium oxide fine particles having a high rutile content by burning titanium tetrachloride, hydrogen and oxygen in a specific range of molar ratio and hydrolyzing titanium tetrachloride (Patent Document 5).

  (3) Ultrafine particulate amorphous titanium oxide produced by heating and evaporating a titanium compound such as titanium alkoxide and thermally decomposing it in a gas phase is converted into a rutile type by aging in an aqueous inorganic acid solution. To produce ultrafine particulate rutile-type titanium oxide (Patent Document 6).

(4) A method for producing rutile titanium dioxide by hydrolysis of titanium (III) sulfate in an aqueous solution using an alkali (for example, ammonium hydroxide or alkali metal hydroxide). This rutile titanium dioxide has a BET specific surface area of 250 m ² / g or more, and is shown to be active against light of 420 nm (Patent Document 7).

In addition, titanium oxide containing a rutile crystal exhibiting photocatalytic activity has also been proposed.
(5) The average particle diameter of the aggregated particles is 0.1 to 10 μm, the average particle diameter of the primary particles is 10 to 1000 nm, the BET specific surface area is 0.5 to 50 m ² / g, and the rutile ratio is 10 to 100%. It has been shown that titanium oxide powder characterized by this shows photocatalytic activity, and that this titanium oxide for photocatalyst can be produced without using various known production methods (Patent Document 8).

  (6) A dilute sulfuric acid suspension of rutile titanium oxide fine particles is heated to reflux and neutralized to produce rutile titanium oxide having amorphous titanium hydroxide deposited on the surface. There is provided a titanium oxide photocatalyst in which the deposited titanium oxide is baked under conditions for crystallization into anatase-type titanium oxide, and anatase-type and rutile-type crystals are directly adhered to each other (Patent Document 9).

JP 2001-72419 A JP 2001-205094 A JP-A-9-262482 JP-A-3-252315 JP-A-6-340423 JP-A-7-291629 JP 2004-123481 A JP-A-11-349328 Japanese Patent Laid-Open No. 2004-025147 Ceramics 31 (1996) No. 10, p. 817 Published by Yoshio Nosaka and Atsuko Nosaka “Introductory Photocatalyst”, Tokyo Book 2004, 1st Edition

  In so-called nitrogen-doped visible light responsive photocatalysts described in Patent Documents 1 and 2, recombination of holes and electrons occurs due to impurity levels generated in the band gap of titanium oxide. The photocatalytic ability is lowered to decrease. In addition, the ion implantation of metal elements as in Patent Document 3 is expensive because the manufacturing apparatus becomes large, and there is a problem that it is not practical for industrial production.

  Patent Documents 4 to 6 are titanium oxide synthesizing methods by a vapor phase method, and it is difficult to produce a rutile type titanium oxide having a high BET specific surface area because a baking treatment at a high temperature is necessary. Moreover, in patent document 7 or 9, the baking process at high temperature is required similarly to the above.

  Furthermore, many of the conventional visible light responsive photocatalysts, including the patent documents cited above, also require a powerful light source such as a xenon lamp in order to fully exhibit their catalytic ability. I have to say that the reality is scarce. For example, sufficient photocatalytic activity cannot be obtained for a practical light source such as a white fluorescent lamp or a day white fluorescent lamp that is commonly used in general life.

  In other words, various studies have been made to improve the activity of the photocatalyst and impart visible light responsiveness, but the photocatalytic ability is not sufficient, and the production process is a very complicated process. Therefore, if an existing inexpensive light source, for example, a titanium oxide that exhibits a sufficient photocatalytic effect with a light source that is commonly used indoors, such as a white fluorescent lamp, that is, a highly sensitive titanium oxide can be easily manufactured, it is of great practical use. There are benefits.

  The present invention relates to rutile-type titanium oxide particles exhibiting high photocatalytic activity for a practical light source such as a white fluorescent lamp, and the titanium oxide particles by hydrolyzing a titanium tetrachloride aqueous solution under certain conditions. The object is to provide a method of manufacturing easily.

  In order to solve the above problems, the present inventors have conducted intensive research. As a result, by hydrolyzing titanium tetrachloride or titanium tetrachloride aqueous solution in an acidic aqueous solution under certain conditions, high rutile and high high catalytic activity against practical light sources such as fluorescent lamps. The present inventors have found that BET specific surface area titanium oxide particles can be produced and completed the present invention. Generally, titanium oxide having a rutile structure has a small specific surface area. Therefore, the fact that the rutile ratio is high and the specific surface area is high is epoch-making.

That is, this invention consists of the following invention.
(1) Titanium oxide particles having a rutile content of 50 to 99.9% by mass and a BET specific surface area of more than 50 m ² / g and 300 m ² / g or less.

(2) The titanium oxide particles according to (1), wherein the average particle diameter of the primary particles is in the range of 5 to 100 nm.
(3) The titanium oxide particles according to (1) or (2), wherein the titanium oxide contains at least one kind of titanium oxide among anatase type titanium oxide and brookite type titanium oxide.

(4) The titanium oxide particles according to any one of (1) to (3), wherein the content of each element of nitrogen, carbon, sulfur, and chromium is 100 ppm by mass or less.
(5) 1 to 5% by mass of titanium tetrachloride and hydrochloric acid are each mixed with water at 65 to 90 ° C. and hydrolyzed while maintaining the temperature of the mixed solution within the temperature range of 65 ° C. to the boiling point of the mixed solution. (1) The manufacturing method of the titanium oxide particle of any one of (4).

(6) The method for producing titanium oxide particles according to (5), wherein the chlorine ion concentration in the reaction vessel is maintained within a range of 10,000 to 50,000 mass ppm.
(7) The method for producing titanium oxide particles according to (5) or (6), wherein the titanium tetrachloride is hydrolyzed while preventing deviation of hydrogen chloride from the reaction vessel.

(8) A method for producing titanium oxide particles, comprising filtering and drying an aqueous dispersion sol of titanium oxide particles obtained by the production method according to any one of (5) to (7).
(9) A method for producing titanium oxide particles in which titanium tetrachloride is hydrolyzed in an acidic aqueous solution, wherein the titanium oxide particles are provided with one or more elements selected from nitrogen, carbon, sulfur, and chromium. The method for producing titanium oxide particles according to any one of (1) to (4).

(10) A photocatalyst comprising the titanium oxide particles according to any one of (1) to (4).
(11) The photocatalyst according to (10), which exhibits photocatalytic activity with respect to light from a white fluorescent lamp.

(12) A coating agent comprising the titanium oxide particles according to any one of (1) to (4).
(13) A water-dispersed titanium oxide sol in which the titanium oxide particles according to any one of (1) to (4) are dispersed in an amount of 0.1 to 30% by mass.

(14) The water-dispersed titanium oxide sol according to (13), wherein the chlorine ion concentration is 50 to 10,000 mass ppm.
(15) A titanium oxide thin film comprising the water-dispersed titanium oxide sol according to (13) or (14).

(16) The titanium oxide thin film according to (15), wherein the base material is a heat-resistant substance and the titanium oxide thin film is fired.
(17) A method for forming a titanium oxide thin film, wherein the mixture of the water-dispersed titanium oxide sol and the inorganic binder according to (13) or (14) is applied to a substrate surface.

(18) An article having the titanium oxide thin film according to (15) or (16).
(19) A substrate having the titanium oxide thin film according to (15) or (16) on the surface.

  The titanium oxide having a rutile structure as a main structure obtained by the present invention has a large BET specific surface area, and can exhibit a photocatalytic effect even for practical light such as a white fluorescent lamp and a daylight fluorescent lamp. . Further, the production method is easy, and it can be produced industrially at low cost. That is, the application range of the photocatalyst can be greatly expanded by the titanium oxide obtained by the present invention.

Hereinafter, the present invention will be described in more detail.
In the present invention, the rutile content indicates the result of calculating the peak of a rutile crystal in powder X-ray diffraction of titanium oxide by Rietveld analysis. The titanium oxide particles in the present invention have a rutile ratio of 50 to 99.9% by mass and a BET specific surface area of more than 50 m ² / g and 300 m ² / g or less. When the rutile ratio is less than 50% by mass, the photocatalytic activity which is a feature of the present invention cannot be obtained. Even if the rutile ratio is 100%, the performance cannot be obtained. That is, it is important to have a large BET specific surface area with a rutile type as a main structure and an anatase type, brookite type, or amorphous crystal structure portion.

The BET specific surface area is preferably larger when considering the mechanism of the photocatalytic activity. On the other hand, the rutile type titanium oxide is easier to produce when the BET specific surface area is smaller. It is generally difficult to obtain one having a large specific surface area while having a rutile structure as a main structure. In the present invention, in order to obtain a high photocatalytic activity, it is necessary to have a BET specific surface area of at least more than 50 m ² / g. However, since the rutile structure is the main structure, it is difficult to industrially obtain titanium oxide having a BET specific surface area greater than 300 m ² / g.

Preferably, rutile content from 55 to 99.5 wt%, a BET specific surface area of 100 to 250 m ² / g, more preferably, rutile content 55 to 99 wt%, BET specific surface area from 150 to 230 wt% m ² / g.

  The titanium oxide particles in the present invention preferably have a small primary particle size and are uniform. The average particle diameter of the primary particles is preferably in the range of 5 to 100 nm. More preferably, it exists in the range of 7-80 nm, Most preferably, it exists in the range of 10-50 nm.

  The method for measuring the powder X-ray diffraction and the BET specific surface area in the present invention may be a known method, and is not particularly limited thereto. The method for measuring the average particle diameter of the primary particles may be a known method such as an X-ray diffraction method or a method using an electron microscope, and is not particularly limited thereto.

  In the titanium oxide particles of the present invention, there is no limitation on the crystal form of titanium oxide having a phase other than the rutile structure. An anatase type and brookite type may be included, and these may be mixed crystals. Moreover, an amorphous phase may be included. Furthermore, even if these phases exist in a single phase, particles including a plurality of crystal phases may be dispersed. At least, it is necessary that the crystalline phase having the rutile-type characteristics can be confirmed to be more than 50% by mass to 99.9% by mass, but there is no limitation on the crystal form and mixed state of other parts.

  The most simple and practical method for confirming the presence of the rutile-type crystal phase is to measure by powder X-ray diffraction. The Rietveld analysis may be a known method and generally used conditions.

  The sol of the present invention or the titanium oxide powder obtained by drying the sol can exhibit photocatalytic activity even with light from a practical fluorescent lamp, and does not necessarily require an ultraviolet light source. Examples of practical light such as fluorescent lamps include, but are not limited to, lights such as white fluorescent lamps, daylight white fluorescent lamps, daylight color fluorescent lamps, warm white fluorescent lamps, and light bulb color fluorescent lamps. Any light source generally used in daily life can be used.

  As described above, the titanium oxide particles of the present invention can exhibit photocatalytic activity with practical light such as a fluorescent lamp, but nitrogen, carbon, sulfur, It is not necessary to perform treatment such as adding a visible light ray by narrowing the band gap by positively adding an element such as chromium. Further, since titanium tetrachloride having a purity of 99% or more can be used as a raw material, the purity of the obtained titanium oxide is very high. For example, titanium oxide having nitrogen, carbon, sulfur, and chromium elements of 100 mass ppm or less can be obtained. However, it is not an active addition that impurities present in a minute amount in the titanium tetrachloride raw material are contained in the manufactured titanium oxide. In the present invention, active substances such as nitrogen, carbon, sulfur, and chromium, which have been reported to increase visible light responsiveness when added, are added to raw materials or doped into products. It does not have to be done. That is, it is not necessary to provide a step of incorporating these substances into the obtained titanium oxide. In this state, titanium oxide particles exhibiting high activity with respect to a light source such as a fluorescent lamp can be obtained. In addition, since no treatment such as ion doping is performed, it can be manufactured at low cost.

  The photocatalytic activity exhibited by the titanium oxide powder of the present invention includes functions such as antibacterial, deodorizing, antifouling, air purification, water purification, and other environmental purification functions. Specifically, the following functions can be exemplified, but not particularly limited thereto.

(1) When the sol of the present invention or a solid content obtained therefrom and an organic compound such as methylene blue or aldehyde, or a substance having an adverse effect on the environment such as NH ₃ , H ₂ S, NOx, SOx exists in the system In addition, a decrease in the concentration of the organic substance or the inorganic substance is observed when compared with a dark place under light irradiation.
(2) When a sol is applied on a substrate or article, a phenomenon occurs in which the water droplet contact angle becomes smaller when compared with a dark place under light irradiation.

  The water-dispersed titanium oxide sol in the present invention refers to the following. The liquid medium needs to contain 50% by mass or more of water, but need not be 100% pure water, and may contain less than 50% by mass of a water-soluble organic solvent or some ions. Additives for dispersion may be included. The content of titanium oxide particles is the solid content when the sol is sufficiently dried in a dryer at 100 ° C. or higher, and this is characterized by being in the range of 0.1% by mass to 30% by mass. is there. Preferably, the content of titanium oxide particles is in the range of 1 to 20% by mass.

  The water-dispersed titanium oxide sol of the present invention preferably contains 50 to 10,000 ppm by mass of chlorine ions in order to maintain better dispersibility.

  Next, a method for producing a titanium oxide sol and titanium oxide particles will be described. A method for producing a titanium oxide sol having a rutile structure as a main crystal structure according to the present invention is characterized in that a titanium tetrachloride aqueous solution and water containing hydrochloric acid are mixed to hydrolyze titanium tetrachloride under specific conditions. To do. In the method of hydrolyzing titanium tetrachloride to obtain a water-dispersed titanium oxide sol, hydrogen chloride is generated by the reaction. It is desirable that the generated hydrogen chloride is prevented from escaping from the reaction vessel and remains in the sol as much as possible. When the titanium tetrachloride is hydrolyzed while the generated hydrogen chloride is escaped, the titanium oxide in the sol is less likely to have a small particle size and has poor crystallinity. Hydrogen chloride generated by this hydrolysis may be suppressed even if escape is not completely prevented. The method is not particularly limited as long as it can also be suppressed. For example, it is possible to apply pressure, but the easiest and most effective method is to install a reflux condenser in the hydrolysis reaction tank and perform hydrolysis. It is a method to do. If the concentration of titanium tetrachloride in the mixture of hydrolyzed titanium tetrachloride and hydrochloric acid is too low, the productivity is poor, and when forming a thin film from the water-dispersed titanium oxide sol, the efficiency is low, and if the concentration is too high, the reaction occurs. The resulting titanium oxide particles are less likely to be fine and the dispersibility is also deteriorated. In addition, a titanium oxide sol having a high rutile content can be obtained by adjusting the titanium oxide concentration to 0.5 g / l to 2.5 g / l. Therefore, it is not preferable to produce a sol with a high titanium oxide concentration by hydrolysis and dilute it with a large amount of water to adjust the titanium oxide concentration to 0.5 g / l to 2.5 g / l. The concentration of titanium oxide should be within the above range at the time of sol formation. For this purpose, the concentration of titanium tetrachloride in the aqueous solution of titanium tetrachloride to be hydrolyzed is not significantly different from the concentration of titanium oxide produced as described above. Value, that is, approximately 0.5 g / l to 2.5 g / l, and if necessary, the concentration is adjusted to 0.5 g / l to 2.5 g / l by adding or concentrating a small amount of water in the subsequent steps. You may adjust it.

  The temperature in the hydrolysis is preferably in the range of 50 ° C. or higher and the boiling point of the reaction liquid (mixed liquid). Below 50 ° C., the hydrolysis reaction takes a long time. The hydrolysis is carried out by raising the temperature to the above temperature and holding it for about 10 minutes to 12 hours. This holding time may be shorter as the hydrolysis temperature is higher. Hydrolysis of titanium tetrachloride may be performed by heating a mixture of titanium tetrachloride and water to a predetermined temperature in a reaction vessel, or by preheating water in the reaction vessel, A titanium tetrachloride aqueous solution may be added to a predetermined temperature. This hydrolysis generally provides titanium oxide in which an anatase type and / or a brookite type are mixed with a rutile type. In order to increase the content of rutile-type titanium oxide, water is heated in advance to 65 to 90 ° C. in a reaction vessel, and titanium tetrachloride or a titanium tetrachloride aqueous solution is added thereto, and 65 ° C. to the reaction solution. A method of hydrolyzing in the temperature range of the boiling point of is suitable. Of the total titanium oxide produced by the method, the rutile-type content can be 50% by mass or more.

From the viewpoint of catalytic action, titanium oxide is preferably crystalline.
The faster the rate of temperature rise of the reaction solution in the hydrolysis, the finer the particles obtained, so that it is preferably at least 0.2 ° C./min, more preferably at least 0.5 ° C./min. The production method of the water-dispersed titanium oxide sol of the present invention is not limited to a batch type, and while continuously feeding titanium tetrachloride and water in a continuous tank, the reaction solution is taken out on the opposite side of the inlet, and subsequently dechlorinated. Such a continuous method is also possible.

  The dechlorination treatment may be performed by a general known means, and electrodialysis, ion exchange resin, electrolysis and the like are possible. The degree of dechlorination may be based on the pH of the sol, and a preferable range is about 5 to 1. In particular, when it is desired to obtain a powder photocatalyst, the obtained photocatalyst sol may be dried, crushed and pulverized by a known method such as heating or freeze drying.

The titanium oxide concentration in the sol was measured by weighing 100 g of the sol in a Pyrex (registered trademark) beaker, leaving it in a constant temperature dryer at 120 ° C. for 24 hours or more, weighing the remaining solid content, The solid content concentration X [mass%] can be calculated. The sedimentation component amount Z [g] in the present invention is defined as follows. First, 100 g of the sol having a solid content concentration of X [mass%] was placed in a sealed container and allowed to stand at room temperature for 240 hours, and then 90 vol% was separated from the liquid surface by decantation, and the rest was kept at a constant temperature of 120 ° C Allow the water to evaporate by standing in a dryer for at least 24 hours. Since the obtained solid content includes not only the amount of sedimentation but also the amount dispersed in the lower layer liquid that was not removed by decantation, from the obtained solid content Y [g], The amount obtained by subtracting 0.1X [g] expected to be dispersed is defined as the amount of sedimentation component Z [g]. That is, the sedimentation component amount Z [g] can be expressed by (Formula 1).
Z = Y-0.1X (Formula 1)

When forming a thin film of titanium oxide from the rutile crystal-containing titanium oxide sol of the present invention, it is preferable to apply the sol produced by the hydrolysis reaction to the substrate using the sol as it is without going through the dry powder. . Moreover, the base material which has photocatalytic property can be manufactured by adding an inorganic binder arbitrarily to this sol, making it a coating agent, and apply | coating to the surface of a base material. That is, it can be used in the form of a paint, a coating composition or the like.
Examples of the substrate include ceramics, metal, glass, plastic, paper, and wood.
If the base material is a heat-resistant substance such as ceramics, metal, or glass, the titanium oxide thin film can be fired to form a film.

  The article having such a base material to which photocatalytic properties and hydrophilicity are imparted is not particularly limited, but various building materials, fluorescent lamps, window glass, machines, vehicles, glass products, home appliances, pure water producers, agriculture Materials, electronic equipment, tools, tableware, bath products, toilet products, furniture, clothing, fabric products, textiles, leather products, paper products, sports equipment, baskets, containers, glasses, signs, piping, wiring, metal fittings, sanitary materials, automobiles An article etc. can be illustrated.

  It is also applied to environmental purification equipment and devices effective for measures against sick houses, decomposition of organic chlorine compounds such as PCBs and dioxins in water, air and soil, and decomposition of residual agricultural chemicals and environmental hormones in water and soil. it can. In that case, the titanium oxide of the present invention can be kneaded into the resin in advance or mixed with the fiber can be mixed with raw materials for molding such as articles, or can be used by forming a film on the article. However, it is not particularly limited.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention does not receive any limitation by these description.

Example 1:
651 mL of distilled water and 39.4 g of hydrochloric acid (concentration: 35% by mass, special grade manufactured by Kanto Chemical Co., Inc.) were charged into a reaction tank equipped with a reflux condenser and heated to 75 ° C. to maintain it. While maintaining the stirring speed at about 200 rpm, 60 g of an aqueous solution of titanium tetrachloride (Ti content: 15.4% by mass, manufactured by Showa Titanium Co., Ltd.) was dropped into the reaction vessel at a rate of about 2 g / min. At this time, care was taken not to lower the temperature of the reaction solution. In the reaction vessel, the reaction solution started to become cloudy immediately after the dropping, but kept at the same temperature, and after the dropping was finished, the temperature was further raised and maintained at a temperature near the boiling point (101 ° C.) for 60 minutes. The obtained sol was cooled, and residual chlorine produced by the reaction was removed by electrodialysis. Electrodialysis of the obtained sol was performed while monitoring the pH of the sol solution using an electrodialysis apparatus G3 type manufactured by Asahi Kasei Kogyo Co., Ltd. As a result, a water-dispersed titanium oxide sol was obtained.

The obtained water-dispersed titanium oxide sol was dried with a 120 ° C. dryer and then pulverized in a mortar to obtain titanium oxide powder.
The physical properties and photocatalytic activity of the titanium oxide particles obtained in this manner were each carried out by the following methods.

(Crystal ratio)
For X-ray diffraction, the powder was measured with a powder X-ray diffractometer manufactured by Panalical. The crystal ratio was determined by Rietveld analysis software attached to the apparatus.

(BET specific surface area)
The BET specific surface area was measured after degassing a 0.15 g powder sample at 200 ° C. for 15 minutes using Shimadzu Flowsorb II.

(Primary particle size)
The water-dispersed titanium oxide sol was dried on a conductive sample stage and observed at a magnification of 100,000 or more using a scanning electron microscope, and the particle size range in one field of view was measured.

(Photocatalytic activity: acetaldehyde decomposition test)
The synthesized catalytic activity was evaluated by an acetaldehyde decomposition test. The outline of the test is as follows.
(1) 20 mg of titanium oxide powder was accurately weighed in a petri dish having an inner diameter of 90 mm. A small amount of ion-exchanged water was added, and the suspension was developed on the entire surface of the petri dish, and then placed in a dryer at 120 ° C. for 30 minutes for drying.

(2) A petri dish was placed in the chamber and sealed. This chamber was placed in a dark place, and the inside of the chamber was replaced with pure air.
(3) A predetermined amount of 4.80 vol-% acetaldehyde standard gas was injected into the chamber, and the inside of the chamber was adjusted to a predetermined concentration.

(4) Ion exchange water was inserted into the chamber to obtain a predetermined humidity.
(5) The sample was left in a dark place for a predetermined time, and the chamber was in an equilibrium state.
(6) Light was irradiated and the gas in the chamber was analyzed by GC every hour.
Judgment of the photocatalytic activity was based on the carbon dioxide generation rate (defined by Formula 2) generated by the decomposition of acetaldehyde by the photocatalytic reaction.
Carbon dioxide generation rate (%) = (carbon dioxide generation amount (mol) × 1/2) / (acetaldehyde charge amount (mol)) × 100 (Formula 2)

  GC used Shimadzu Corporation GC-14A (FID detector) in combination with a metanizer MTN-1, and the column used was CP-PoraBOND Q (0.53 mm ID × 25 m df = 10 μm). As pure air, G3 manufactured by Japan Fine Products was used. The acetaldehyde standard gas cylinder was manufactured by Japan Fine Products and used 4.80 vol-% acetaldehyde (nitrogen base). All measurements were performed in a room where the room temperature was controlled at about 25 ° C. with an air conditioner. The other conditions were the measurement conditions for the powder sample in Table 1.

Example 2:
Titanium oxide particles were obtained in the same manner as in Example 1 except that the amount of hydrochloric acid added was 29.6 g.

Example 3:
Titanium oxide particles were obtained in the same manner as in Example 1 except that the dropping rate of the titanium tetrachloride aqueous solution was about 4 g / min.

Example 4:
Titanium oxide particles were obtained in the same manner as in Example 1 except that the amount of the titanium tetrachloride aqueous solution was 30 g.

Example 5:
A reflux condenser was used for 651 mL of distilled water, 39.4 g of hydrochloric acid (concentration 35 mass%, special grade manufactured by Kanto Chemical Co., Ltd.) and 60 g aqueous solution of titanium tetrachloride (Ti content 15.4 mass%, Showa Titanium Co., Ltd.). The reaction vessel was charged and heated to 60 ° C. and maintained for 30 minutes. While maintaining the stirring speed at about 200 rpm, the inside of the reaction vessel was uniformly dispersed. At this time, care was taken not to lower the temperature of the reaction solution. In the reaction vessel, the reaction solution started to become cloudy from about 50 ° C., kept at a temperature of 60 ° C. for 30 minutes, further heated and maintained at a temperature near the boiling point (101 ° C.) for 60 minutes. After cooling the obtained sol, residual chlorine generated by the reaction was removed by electrodialysis. Electrodialysis of the obtained sol was performed while monitoring the pH of the sol solution using an electrodialysis apparatus G3 type manufactured by Asahi Kasei Kogyo Co., Ltd. Thereby, titanium oxide particles were obtained.

Example 6:
Titanium oxide particles were obtained in the same manner as in Example 5 except that the amount of the titanium tetrachloride aqueous solution was 30 g and the temperature in the reaction vessel was maintained at 75 ° C. for 30 minutes.

Example 7:
Titanium oxide particles were obtained in the same manner as in Example 5 except that the temperature in the reaction vessel was 75 ° C.

Example 8:
Titanium oxide particles were obtained in the same manner as in Example 5 except that the temperature in the reaction vessel was maintained at 75 ° C. for 60 minutes.

Example 9:
A zirconium ammonium carbonate solution was added as a binder component to the water-dispersed titanium oxide sol obtained in Example 5 to prepare a coating agent. At this time, the titanium oxide powder was 1.0% by mass, and the ZrO ₂ / titanium oxide powder (mass ratio) was 20%. This coating agent was applied on a 7.5 cm × 7.5 cm square glass plate and heat-treated in air at 120 ° C. for 15 minutes to obtain a titanium oxide thin film. The obtained thin film had a pencil scratch strength of 4H and was colorless and transparent.
The photocatalytic activity was measured under the conditions of the thin film sample on the glass plate shown in Table 1 by placing the glass plate on which this thin film was formed instead of the petri dish in the acetaldehyde decomposition test in a chamber.

Comparative Example 1:
689 mL of distilled water and 0.81 g of phosphoric acid (concentration 85% by mass, special grade manufactured by Kanto Chemical Co., Ltd.) were charged into a reaction tank equipped with a reflux condenser and heated to 100 ° C. to maintain it. While maintaining the stirring speed at about 200 rpm, 60 g of an aqueous solution of titanium tetrachloride (Ti content: 15.4% by mass, manufactured by Showa Titanium Co., Ltd.) was dropped into the reaction vessel at a rate of about 1 g / min. At this time, care was taken not to lower the temperature of the reaction solution. After completion of the dropwise addition, the temperature was further raised and maintained at a temperature near the boiling point (101 ° C.) for 60 minutes. The obtained sol was cooled, and residual chlorine produced by the reaction was removed by electrodialysis. Electrodialysis of the obtained sol was performed while monitoring the pH of the sol solution using an electrodialysis apparatus G3 type manufactured by Asahi Kasei Kogyo Co., Ltd.

Comparative Example 2:
Distilled water (690 mL) was charged into a reaction vessel equipped with a reflux condenser and heated to 95 ° C. to maintain it. While maintaining the stirring speed at about 200 rpm, 60 g of an aqueous solution of titanium tetrachloride (Ti content: 15.4% by mass, manufactured by Showa Titanium Co., Ltd.) was dropped into the reaction vessel at a rate of about 1 g / min. At this time, care was taken not to lower the temperature of the reaction solution. After completion of the dropwise addition, the temperature was further raised and maintained at a temperature near the boiling point (101 ° C.) for 60 minutes. The obtained sol was cooled, and residual chlorine produced by the reaction was removed by electrodialysis. Electrodialysis of the obtained sol was performed while monitoring the pH of the sol solution using an electrodialysis apparatus G3 type manufactured by Asahi Kasei Kogyo Co., Ltd.

Comparative Example 3:
A titanium oxide thin film on a glass plate was obtained in the same manner as in Example 9, except that the water-dispersed titanium oxide sol obtained in Comparative Example 1 was used instead of the water-dispersed titanium oxide sol obtained in Example 5. It was. The obtained thin film had a pencil scratch strength of 4H and was slightly cloudy.

  Table 2 shows the physical property values and photocatalytic activity of the titanium oxide particles obtained in Examples 1 to 9 and Comparative Examples 1 and 2. It is clear that the titanium oxide particles obtained in the present invention decompose acetaldehyde even under a white fluorescent lamp. Moreover, the thin film obtained in Example 9 clearly has higher photocatalytic activity under the white fluorescent lamp than the thin film obtained in Comparative Example 3.

Claims (19)

Titanium oxide particles having a rutile content of 50 to 99.9% by mass and a BET specific surface area of more than 50 m ² / g and not more than 300 m ² / g.   The titanium oxide particles according to claim 1, wherein the average particle diameter of the primary particles is in the range of 5 to 100 nm.   The titanium oxide particles according to claim 1 or 2, wherein the titanium oxide contains at least one titanium oxide of anatase type titanium oxide and brookite type titanium oxide.   The titanium oxide particles according to any one of claims 1 to 3, wherein the content of each element of nitrogen, carbon, sulfur, and chromium is 100 ppm by mass or less.   The titanium tetrachloride and hydrochloric acid are each mixed in an amount of 1 to 5% by mass with respect to water at 65 to 90 ° C, and hydrolyzed while maintaining the temperature of the mixed solution in a temperature range of 65 ° C to the boiling point of the mixed solution. The manufacturing method of the titanium oxide particle of any one of thru | or 4.   The manufacturing method of the titanium oxide particle of Claim 5 which maintains the chlorine ion concentration in a reaction tank in the range of 10,000-50,000 mass ppm.   The method for producing titanium oxide particles according to claim 5 or 6, wherein the titanium tetrachloride is hydrolyzed while preventing deviation of hydrogen chloride from the reaction vessel.   The manufacturing method of the titanium oxide particle which filters and dries the water dispersion sol of the titanium oxide particle obtained by the manufacturing method of any one of Claim 5 thru | or 7.   A method for producing titanium oxide particles in which titanium tetrachloride is hydrolyzed in an acidic aqueous solution, and does not include a step of incorporating one or more elements selected from nitrogen, carbon, sulfur, and chromium into titanium oxide particles. Item 5. The method for producing titanium oxide particles according to any one of Items 1 to 4.   The photocatalyst containing the titanium oxide particle of any one of Claims 1 thru | or 4.   The photocatalyst of Claim 10 which shows photocatalytic activity with respect to the light of a white fluorescent lamp.   The coating agent containing the titanium oxide particle of any one of Claims 1 thru | or 4.   A water-dispersed titanium oxide sol in which the titanium oxide particles according to any one of claims 1 to 4 are dispersed in an amount of 0.1 to 30% by mass.   The water-dispersed titanium oxide sol according to claim 13, having a chlorine ion concentration of 50 to 10,000 ppm by mass.   A titanium oxide thin film comprising the water-dispersed titanium oxide sol according to claim 13 or 14.   The titanium oxide thin film according to claim 15, wherein the base material is a heat-resistant substance and the titanium oxide thin film is fired.   A method for forming a titanium oxide thin film, wherein the mixture of the water-dispersed titanium oxide sol according to claim 13 or 14 and an inorganic binder is applied to a substrate surface.   An article comprising the titanium oxide thin film according to claim 15 or 16.   The base material which has a titanium oxide thin film of Claim 15 or 16 on the surface.