JP2008038314A - Titania fiber and method for producing titania fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a titania fiber having a small fiber diameter, exhibiting sufficient photocatalytic activities, facilitating the post-processing, and capable of being used as a catalyst without being fixed by the addition of a binder or the like; and to provide a method for producing the titania fiber. <P>SOLUTION: The titania fiber having an average fiber diameter of ≥50 nm and ≤1,000 nm, and containing ≥0.1 mass% and ≤10 mass% niobium element expressed in terms of niobium oxide based on the mass of the whole fiber is produced by producing a fiber assembly from a composition containing a niobium element as the fiber-forming composition for forming the titania fiber, by a static spinning method using the composition, and firing the resultant fiber assembly. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a titania fiber and a method for producing the titania fiber. More specifically, as a photocatalytic filter or a semiconductor material that has a small fiber diameter, expresses sufficient photocatalytic activity, is easy to be processed later, and can be used as a catalyst as it is without being fixed by adding a binder or the like. The present invention relates to a useful titania fiber and a method for producing the titania fiber.

  The ceramic fiber is a useful material that can be used in various fields such as an electrical insulating material, a heat insulating material, a filler, and a filter by making use of properties such as electrical insulation, low thermal conductivity, and high elasticity. Such ceramic fibers are usually produced by a melting method, a spindle method, a blowing method, or the like, and the fiber diameter is generally several μm (see Patent Document 1).

  By the way, in recent years, particularly in the field of fillers and filters, thinner ceramic fibers have been demanded in order to increase the adhesion area with the matrix material and improve the filter efficiency.

Here, as a method for producing a fiber thinner than a conventional fiber, an electrospinning method (electrostatic spinning method) is known with a focus on materials made of organic polymers. The electrospinning method (electrostatic spinning method) is a method in which a high voltage is applied to a solution in which a fiber-forming solute such as an organic polymer is dissolved, and the solution is ejected toward the electrode. Since the solvent evaporates by this, an ultrafine fiber structure can be easily obtained (see Patent Document 2).
And also about a titania fiber, the method of producing a fiber by such an electrospinning method is already known (refer nonpatent literature 1-2).

  It is also known to support titania with a metal such as platinum, rubidium or silver or a metal oxide such as tungsten oxide, molybdenum oxide or vanadium oxide for the purpose of improving the photocatalytic activity of titania. Among them, the titania photocatalyst containing a specific amount of niobium oxide exhibits equivalent activity as compared to the case of supporting other metals and metal oxides, and is safe for the human body and free from environmental pollution. And it can manufacture at low cost (refer patent document 3).

JP 2003-105658 A JP 2002-249966 A Japanese Patent Laid-Open No. 09-267037 Dan Li, Younan Xia, “Direct Fabrication of Composite and Ceramic Hollow Nanofibers by Electrospinning”, NanoLetters, US, The American Chemical Society, May 2004, Vol. 4, No. 5, P933-938 Mi Yeon Song, Do Kyun Kim, Kyo Jin Ihn, SeongMu Jo, Dong Young Kim, “ElectrospunTiO2 electrodes for dye-sensitized solar cells”, Nanotechnology, US, Institute Of Physics, December 2004, Vol. 15, No. 12 , P1861-1865

  However, in the method described in Non-Patent Document 1, it is necessary to add 0.1 to 0.5 times as much organic polymer as the titania raw material compound. For this reason, the titania fiber obtained by the method described in Non-Patent Document 1 is expected to have a porous structure.

  Since the titania fiber having a porous structure is considered to have a relatively large surface area, it seems to be suitable for use as a support material such as a metal catalyst. However, the titania fiber having a porous structure generally has low mechanical strength, and therefore, it has been difficult to use it for applications requiring strength. Furthermore, since the titania fiber with a porous structure is considered to be low in crystallinity containing a lot of lattice defects, a large amount of recombination of electrons and holes occurs due to the inclusion of many lattice defects, and a sufficient photocatalyst. It is considered that the activity cannot be expressed.

  In addition, since the titania photocatalyst described in Patent Document 3 is a powder-shaped catalyst, it is essential to fix it to something in use. Examples of the immobilization method include a method of forming a film as a powder slurry, a method of bonding with an organic or inorganic binder, etc., all of which are new steps such as slurrying, film formation, mixing, and coating. Will occur.

  Furthermore, the titania film obtained from the slurry is brittle in strength and low in durability. Moreover, when using an organic binder, since a binder will be decomposed | disassembled together in the case of a photocatalytic reaction, the fall of titania powder will generate | occur | produce. On the other hand, when using an inorganic binder, it is durable, but in order to ensure a sufficient reaction area (area exposed to the surface of titania), a large amount of binder must be used, and as a result There was a problem that the catalyst efficiency was lowered.

  The present invention has been made in view of the above problems, and its object is that the fiber diameter is small, sufficient photocatalytic activity is expressed, subsequent processing is easy, and a binder or the like is added and fixed. An object of the present invention is to provide a titania fiber that can be used as a catalyst as it is without being converted into a catalyst, and a method for producing the titania fiber.

  The present inventors have made extensive studies in view of the above problems. As a result, by using a composition containing niobium element as a fiber-forming composition for forming titania fibers, a fiber assembly is produced from the composition by an electrostatic spinning method, and this is fired. The present invention has found that a fiber having a small fiber diameter, expressing a sufficient photocatalytic activity, easy to be processed later, and capable of being used as a catalyst as it is without being fixed by adding a binder or the like is obtained. It came to complete.

  That is, the present invention is a titania fiber having an average fiber diameter of 50 nm or more and 1000 nm or less and containing niobium element in an amount of 0.1% by mass or more and 10% by mass or less in terms of niobium oxide with respect to the total mass of the fiber.

  Another embodiment of the present invention is a fiber-forming composition for preparing a fiber-forming composition comprising an alkyl titanate, a complex-forming compound with an alkyl titanate, and a mixture containing niobium alkoxide, water, and a fiber-forming solute. A composition preparing step, a spinning step of obtaining fibers by ejecting the fiber-forming composition by an electrostatic spinning method, a cumulative step of accumulating the fibers to obtain a fiber aggregate, and the fiber aggregate And a firing process for obtaining a fiber structure by firing.

  Since the average fiber diameter of the titania fiber of the present invention is as small as nanoscale, it becomes a flexible fiber. In addition, since the surface area is larger than that of conventional titania fibers, sufficient catalytic efficiency can be exhibited when used for a photocatalyst filter, a catalyst-supporting substrate, or the like.

  Furthermore, since the titania fiber of the present invention can suppress the formation of a porous structure, it can retain a mechanical strength while having a certain surface area. In addition, recombination of electrons and holes can be suppressed as compared with a fiber containing many lattice defects, and thus sufficient photocatalytic activity can be exhibited.

  Moreover, since the titania fiber of the present invention contains a niobium element, the catalytic activity when used as a photocatalyst can be improved.

  Furthermore, because of the fiber shape, it is easy to process later compared to conventional powder photocatalyst materials, and can be used as a catalyst as it is without adding a binder or the like. When used as a filter or the like, it is possible to prevent the particles from dropping off due to the binder decomposition, and the catalyst efficiency from being lowered due to the excessive binder content.

  Accordingly, the titania fiber of the present invention has a small fiber diameter, expresses sufficient photocatalytic activity, is easy to be processed later, and can be left as it is without being fixed by adding a binder or the like. It is very useful as a catalyst support substrate and a semiconductor material.

  Furthermore, the titania fiber of the present invention can form various structures by processing such as weaving. Moreover, it can also be used in combination with ceramic fibers other than the titania fiber of the present invention in accordance with handleability and other requirements.

Hereinafter, the present invention will be described in detail.
<Titania fiber>
The titania fiber of the present invention is a titania fiber having an average fiber diameter in a specific range and containing a specific amount of niobium element. That is, the titania fiber of the present invention is a titania fiber having an average fiber diameter of 50 nm or more and 1000 nm or less and containing niobium element in an amount of 0.1% by mass or more and 10% by mass or less in terms of niobium oxide with respect to the mass of the entire fiber.

Here, the “titania fiber” refers to a fiber structure made of an oxide ceramic mainly composed of titanium oxide. In the present invention, niobium element is contained as an auxiliary component in an amount of 0.1% by mass or more and 10% by mass or less in terms of niobium oxide, and as other auxiliary components, Al ₂ O ₃ , SiO ₂ , Li ₂ O, Na ₂ O, _{MgO, CaO, SrO, BaO,} B 2 O 3, P 2 O 5, SnO 2, ZrO 2, K 2 O, Cs 2 O, ZnO, Sb 2 O 3, As 2 O 3, CeO 2, V 2 O ₅ , oxide systems such as Cr ₂ O ₃ , MnO, Fe ₂ O ₃ , CoO, NiO, Y ₂ O ₃ , Lu ₂ O ₃ , Nb ₂ O ₃ , Er ₂ O ₃ , Yb ₂ O ₃ , HfO ₂ Ceramics may be included.

[Niobium element content]
The content of the niobium element in the titania fiber of the present invention is in the range of 0.1% by mass or more and 10% by mass or less, more preferably 0.3% by mass in terms of niobium oxide based on the mass of the entire titania fiber. It is the range of 5 mass% or less. When the content of niobium element is less than 0.1% by mass, the effect of improving the activity as a photocatalyst is low. On the other hand, when the content exceeds 10% by mass, the solution is formed in the fiber forming composition preparation step. Since it is gelled, it becomes difficult to adjust, and it is difficult to obtain an additional effect even in the fiber obtained thereafter.

  The abundance ratio of oxide ceramics (subcomponents) other than titanium oxide and niobium oxide is preferably 5% by mass or less with respect to the mass of the titania fiber from the viewpoint of crystallinity of the titania fiber. More preferably, it is 1 mass% or less, Most preferably, it is 0.1 mass% or less.

[Average fiber diameter of titania fiber]
Next, the average fiber diameter of the titania fiber will be described. The average fiber diameter of the titania fiber of the present invention is 50 nm or more and 1000 nm or less. More preferably, it is the range of 100 nm or more and 500 nm or less. When the average fiber diameter of the titania fiber exceeds 1000 nm, the flexibility of the titania fiber becomes poor, which is not preferable.

[Fiber length of titania fiber]
Next, the average fiber length of the titania fiber will be described. The fiber length of the titania fiber of the present invention is preferably 100 μm or more. More preferably, it is 150 micrometers or more, Most preferably, it is 1 mm or more. When the fiber length of the titania fiber is less than 100 μm, the mechanical strength of the titania fiber structure obtained by collecting the fibers becomes insufficient.

[BET specific surface area of titania fiber]
Next, the BET specific surface area of the titania fiber will be described. The BET specific surface area of the titania fiber of the present invention is preferably 0.1 m ² / g or more and 10 m ² / g or less. More preferably not more than 0.1 m ² / g or more ^{5 m} 2 / g, more preferably not more than 0.1 m ² / g or more ^{1 m} 2 / g, particularly preferably 0.1 m ² / g or more 0.5m ² / g or less. When the titania fiber has a BET specific surface area of less than 0.1 m ² / g, the photocatalytic activity decreases when the titania fiber is used as a photocatalyst, or the titania fiber is supported when the titania fiber is used as a catalyst support substrate. It is not preferable because the amount of catalyst to be reduced is decreased. On the other hand, when the BET specific surface area is larger than 10 m ² / g, since the titania fiber surface has a porous structure, the strength of the titania fiber is not preferable.

[Crystal form of titania fiber]
Next, the crystal form of the titania fiber will be described. The crystal form of titanium oxide includes anatase type, rutile type, and brookite type. Among these, the titania fiber of the present invention is preferably composed mainly of anatase type. If a crystal form other than the anatase type is present, the strength of the titania fiber is lowered, and the photocatalytic activity of the titania fiber is lowered.

  The presence of anatase-type crystals and rutile-type crystals is confirmed in the X-ray diffraction pattern of titania fibers with a peak intensity of 25-26 ° indicating anatase crystals and a peak intensity of 27-28 ° showing rutile-type crystals. be able to. In the titania fiber of the present invention, it is preferable that no diffraction peak other than the anatase type is confirmed in the X-ray diffraction pattern.

<Method for producing titania fiber>
Next, an embodiment for producing the titania fiber of the present invention will be described.
In order to produce the titania fiber of the present invention, any technique can be used as long as the titania fiber satisfies the above-mentioned requirements at the same time, but alkyl titanate and complex formation with alkyl titanate are possible. A fiber-forming composition preparation step of preparing a fiber-forming composition containing a compound and a mixture containing niobium alkoxide, water, and a fiber-forming solute; and the fiber-forming composition by an electrostatic spinning method. A method for producing titania fibers, comprising: a spinning step for obtaining fibers by jetting; a cumulative step for accumulating the fibers to obtain a fiber aggregate; and a firing step for firing the fiber aggregate to obtain a fiber structure. Can be mentioned as a preferred embodiment.

  Below, the component of the composition for fiber formation used as one aspect | mode of the preferable manufacturing method for obtaining the titania fiber of this invention, and each manufacturing process are demonstrated.

[Configuration of Fiber Forming Composition]
The fiber-forming composition used in one embodiment of a preferred production method for obtaining the titania fiber of the present invention will be described. The fiber-forming composition used as a preferred embodiment is an alkyl titanate, a complex-forming compound with an alkyl titanate, a mixture containing niobium alkoxide, water, and a composition containing a fiber-forming solute. The structure of the fiber forming composition will be described below.

[Alkyl titanate]
Examples of preferred alkyl titanates used in the production method include titanium tetramethoxide, titanium tetraethoxide, titanium tetranormal propoxide, titanium tetraisopropoxide, titanium tetranormal butoxide, titanium tetratertiary butoxide and the like. Can be mentioned. Among these, titanium tetraisopropoxide and titanium tetranormal butoxide are preferable from the viewpoint of availability.

[Complex-forming compound with alkyl titanate]
Next, a complex-forming compound with an alkyl titanate will be described. Examples of the complex-forming compound with alkyl titanate include coordination compounds such as carboxylic acids, amides, esters, ketones, phosphines, ethers, alcohols, and thiols.

  In the fiber-forming composition preparation step described later, a mixture containing alkyl titanate, a complex-forming compound with alkyl titanate, and niobium alkoxide is mixed with water. For this reason, as a complex-forming compound with alkyl titanate, it is not preferable to use a compound that forms a strong complex to such an extent that it does not show reactivity with water at room temperature. From this viewpoint, it is preferable to use carboxylic acids as the complex-forming compound with alkyl titanate, more preferably aliphatic carboxylic acids, and particularly preferably acetic acid.

  Further, the addition amount of the complex-forming compound with the alkyl titanate is not particularly limited as long as it is an amount capable of producing the fiber-forming composition for producing the titania fiber of the present invention. Is preferably 5 equivalents or more, more preferably 7 equivalents or more and 10 equivalents or less.

[Niobium alkoxide]
Examples of the niobium alkoxide used in the preferred embodiment include niobium tetramethoxide, niobium tetraethoxide, niobium tetranormal propoxide, niobium tetraisopropoxide, niobium tetranormal butoxide, niobium tetratertiary butoxide and the like. It is done. Among these, niobium ethoxide is preferable from the viewpoint of availability.

〔water〕
The water used in the preferred embodiment of the production method is not particularly limited. However, if metal ions are contained as impurities, the metal remains in the produced titania fiber, which is not preferable. For this reason, as water used for a preferable manufacturing method, distilled water and ion exchange water are preferable.

  The amount of water to be added is not particularly limited as long as titania fibers can be produced from the fiber-forming composition, but it is 0.5 times or more of the mass of the alkyl titanate. The amount is preferably 10 times or less. More preferably, it is 0.5 to 3 times the mass of the alkyl titanate, and particularly preferably 0.5 to 1.5 times.

[Fiber-forming solute]
Next, the fiber-forming solute will be described. In an embodiment of a preferable production method for obtaining the titania fiber of the present invention, it is necessary to dissolve a fiber-forming solute in the fiber-forming composition for the purpose of giving the fiber-forming composition a kite string. The fiber-forming solute used is not particularly limited as long as it can produce the titania fiber of the present invention, but from the viewpoint of ease of handling and needs to be removed in the firing step, it is organic. It is preferable to use a polymer.

  Examples of the organic polymer used include polyethylene glycol, polyvinyl alcohol, polyvinyl ester, polyvinyl ether, polyvinyl pyridine, polyacrylamide, ether cellulose, pectin, starch, polyvinyl chloride, polyacrylonitrile, polylactic acid, polyglycolic acid, poly Lactic acid-polyglycolic acid copolymer, polycaprolactone, polybutylene succinate, polyethylene succinate, polystyrene, polycarbonate, polyhexamethylene carbonate, polyarylate, polyvinyl isocyanate, polybutyl isocyanate, polymethyl methacrylate, polyethyl methacrylate, polynormal Propyl methacrylate, polynormal butyl methacrylate, polymethyl acrylate, polyethyl acetate Rate, polybutyl acrylate, polyethylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polyparaphenylene terephthalamide, polyparaphenylene terephthalamide-3,4'-oxydiphenylene terephthalamide copolymer, polymetaphenylene Isophthalamide, cellulose diacetate, cellulose triacetate, methyl cellulose, propyl cellulose, benzyl cellulose, fibroin, natural rubber, polyvinyl acetate, polyvinyl methyl ether, polyvinyl ethyl ether, polyvinyl normal propyl ether, polyvinyl isopropyl ether, polyvinyl normal butyl ether, polyvinyl isobutyl Ether, polyvinyl tertiary butyl ether, polyvinylidenek Lido, poly (N-vinylpyrrolidone), poly (N-vinylcarbazole), poly (4-vinylpyridine), polyvinyl methyl ketone, polymethyl isopropenyl ketone, polypropylene oxide, polycyclopentene oxide, polystyrene sulfone, nylon 6 , Nylon 66, nylon 11, nylon 12, nylon 610, nylon 612, and copolymers thereof. Among these, from the viewpoint of solubility in water, polyethylene glycol, polyvinyl alcohol, polyvinyl ester, polyvinyl ether, polyvinyl pyridine, polyacrylamide, ether cellulose, pectin, and starch are preferable, and polyethylene glycol is particularly preferable.

  The average molecular weight of the organic polymer to be used is not particularly limited as long as the titania fiber of the present invention can be produced, but when the average molecular weight is low, the addition amount of the organic polymer must be increased. Therefore, the amount of gas generated in the firing step increases, and the possibility of defects occurring in the structure of the obtained titania fiber increases, which is not preferable. On the other hand, when the average molecular weight is high, the viscosity becomes too high and spinning becomes difficult, which is not preferable. In the case of polyethylene glycol, the preferred average molecular weight of the organic polymer used is in the range of 100,000 to 6,000,000, more preferably in the range of 100,000 to 600,000.

  The addition amount of the fiber-forming solute is preferably as small as possible in the concentration range where the fiber can be formed from the viewpoint of improving the denseness of the surface structure of the titania fiber, and the entire fiber-forming composition The range of 0.01% by mass or more and 2% by mass or less is preferable, and the range of 0.01% by mass or more and 1.5% by mass or less is more preferable.

[Other ingredients]
In an embodiment of a preferable production method for obtaining the titania fiber of the present invention, fibers can be formed from the fiber-forming composition, and components other than the above essential components are formed as long as they do not exceed the gist of the present invention. It may be contained as a component of the composition for use.

  In the fiber forming composition of a preferred embodiment, water is used as an essential component, and this water also serves as a solvent. In the fiber-forming composition, from the viewpoint of improving the stability of the composition and the spinning stability, it is possible to add a solvent other than water, for example, an alcohol, a salt such as ammonium chloride, hydrochloric acid, etc. It is also possible to add the acid.

[Fiber-forming composition preparation step]
In the fiber-forming composition preparation step, an alkyl titanate, a complex-forming compound with alkyl titanate, a mixture containing niobium alkoxide, water, and a fiber-forming composition containing a fiber-forming solute are prepared. .

  In an embodiment of a preferable production method for obtaining the titania fiber of the present invention, first, a mixture containing an alkyl titanate, a complex-forming compound with an alkyl titanate, and a niobium alkoxide is obtained. Note that a mixture obtained by mixing alkyl titanate, a complex-forming compound with alkyl titanate, and niobium alkoxide becomes a uniform solution.

  The mixing method is not particularly limited, and a known method such as stirring can be employed. Also, the order of mixing is not particularly limited, and it may be simultaneous addition or sequential addition.

  Subsequently, the alkyl titanate obtained above, a complex-forming compound with alkyl titanate, and a mixture containing niobium alkoxide are mixed with water. When these are mixed, a gel is formed. In the fiber forming composition preparation step, a transparent titanium-containing solution is finally prepared by dissociating the generated gel.

  When water is added to a mixture containing an alkyl titanate, a complex-forming compound with an alkyl titanate, and a niobium alkoxide, a gel that is difficult to dissociate may be generated if the concentration of water is locally increased. is there. For this reason, it is preferable to add water gradually, stirring the mixture containing the alkyl titanate and the complex-forming compound of alkyl titanate and niobium alkoxide.

  In the dissociation of the generated gel, the gel can be dissociated by further stirring. When the gel is dissociated, a transparent titanium-containing solution can be obtained.

  Subsequently, a fiber-forming solute is added to the titanium-containing solution obtained above to finally obtain a fiber-forming composition. The method for adding the fiber-forming solute is not particularly limited as long as the titanium-containing solution and the fiber-forming solute can be mixed almost uniformly. Also, the order of addition is not particularly limited, and a form in which one is added as a base or a form in which the same amount is added simultaneously may be employed.

  Note that the fiber-forming solute may be added at the time of preparing the titanium-containing solution. In this case, it may be time to obtain a mixture containing alkyl titanate, a complex-forming compound with alkyl titanate, and niobium alkoxide, or may be a time to mix the mixture and water. . In the case where the fiber-forming solute is added simultaneously with water, for example, water and the fiber-forming solute are mixed in advance, and an alkyl titanate, a complex-forming compound with an alkyl titanate, and a niobium alkoxide are included. It is also possible to add gradually to the mixture.

  In the present invention, from the viewpoint of the stability of the fiber-forming composition solution and spinning stability, when adding a solvent other than water to the fiber-forming composition, or when adding other optional components, Either when obtaining a mixture containing alkyl titanate, a complex-forming compound with alkyl titanate, and niobium alkoxide, when mixing the mixture with water, or when adding a fiber-forming solute. Although it is possible to add at the time, it is preferable to add the fiber-forming solute in order not to affect the complex formation.

[Spinning process]
In the spinning step, fibers are produced by ejecting the fiber-forming composition obtained above by an electrostatic spinning method. The spinning method and spinning device in the spinning process will be described below.

[Spinning method]
In the spinning process of a preferred embodiment, fibers are produced by an electrostatic spinning method. Here, the “electrostatic spinning method” is a method in which a solution or dispersion containing a fiber-forming substrate or the like is discharged into an electrostatic field formed between electrodes, and the solution or dispersion is directed toward the electrodes. This is a method for forming a fibrous substance. In addition, the fibrous substance obtained by spinning is laminated | stacked on the electrode which is a collection board | substrate in the accumulation process mentioned later.

  In addition, the fibrous substance to be formed is not only in a state where the fiber-forming solute and solvent contained in the fiber-forming composition are completely distilled off, but also remains in the fibrous substance. Including state.

  In addition, although normal electrospinning is performed at room temperature, in the present invention, when the volatilization of a solvent or the like is insufficient, the temperature of the spinning atmosphere is controlled as necessary, or in an accumulation process described later. It is also possible to control the temperature of the collection substrate used.

[Spinning equipment]
Next, an apparatus used in the electrostatic spinning method will be described.
The electrode for forming the electrostatic field may be any material such as a metal, an inorganic material, or an organic material as long as it exhibits conductivity. Alternatively, a thin film made of a metal, an inorganic material, an organic material, or the like having conductivity may be provided over an insulator.

  The electrostatic field used in the electrostatic spinning method is formed between a pair or a plurality of electrodes, and a high voltage may be applied to any electrode that forms the electrostatic field. This includes, for example, the case of using two high-voltage electrodes having different voltage values (for example, 15 kV and 10 kV) and one electrode connected to the ground, or a total of more than three electrodes. Including the case of using.

[Cumulative process]
In the accumulation step, the fibers obtained in the spinning step are accumulated to obtain a fiber assembly. Specifically, a fiber aggregate is obtained by accumulating (stacking) the fibrous material formed in the spinning process on an electrode as a collection substrate.

  Therefore, a planar fiber assembly can be obtained by using a flat surface as an electrode to be a collection substrate, but a fiber assembly having a desired shape can be produced by changing the shape of the collection substrate. Further, when the uniformity is low, such as when the fiber aggregate is concentrated (stacked) in one place on the collection substrate, the substrate can be shaken or rotated.

  In addition, since the fiber assembly before baking has low intensity | strength, when peeling the fiber assembly accumulated (laminated | stacked) on the collection board | substrate, a part of the structure may be broken. For this reason, it is also possible to install a static eliminator or the like between the collection substrate and the nozzle, and to laminate the fiber assembly in a cotton shape between the nozzle and the static eliminator.

  Further, in the same manner as described above, the fiber aggregate was not only in a state where the solvent and the like contained in the fiber-forming composition were completely distilled off to form an aggregate, but the solvent and the like were contained in the fibrous substance. The state which remains is also included.

[Baking process]
In the firing step, the fiber aggregate obtained in the accumulation step is fired to obtain the titania fiber fiber structure of the present invention.

  For firing, a general electric furnace can be used, but an electric furnace capable of replacing the gas in the furnace may be used as necessary. The firing temperature is preferably in the range of 300 ° C. or higher and 900 ° C. or lower, and more preferably in the range of 500 ° C. or higher and 800 ° C. or lower in order to suppress sufficient anatase type crystal growth and rutile type crystal dislocation. .

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these unless it exceeds the gist.

<Measurement and evaluation method>
In Examples and Comparative Examples, the following items were measured and evaluated by the following methods.

[Average fiber diameter]
The surface of the obtained titania fiber was photographed (magnification: 2000 times) with a scanning electron microscope (manufactured by Hitachi, Ltd., trade name: S-2400) to obtain a photograph. Twenty spots were selected at random from the obtained photograph and the filament diameter was measured. The average value of all the measurement results (n = 20) of the fiber diameter was obtained and used as the average fiber diameter of the titania fiber.

[Fiber length]
The surface of the obtained titania fiber was photographed with a scanning electron microscope (manufactured by Hitachi, Ltd., model: S-2400) (magnification 400 times), and the resulting photographic diagram was observed, and fibers with a fiber length of 100 μm or less were observed. Confirmed that it exists.

[Photocatalytic activity]
Evaluation of the photocatalytic activity of the obtained titania fiber was performed using a fading reaction of methylene blue. Specifically, 5 mL of 10 ppm methylene blue aqueous solution was poured into a petri dish with a diameter of 37 mm, and 5 mg of titania fiber (or titania particles) was immersed in this solution. Subsequently, the photocatalytic activity was evaluated by irradiating a solution soaked with titania fibers (or titania particles) with ultraviolet light having an intensity of 14 mW / cm ² and measuring the absorbance at 665 nm when the ultraviolet irradiation time was 30 minutes. In addition, the light absorbency before ultraviolet irradiation was 1.896A.

[X-ray diffraction (crystal form)]
Use X-ray diffractometer (manufactured by Rigaku Corporation), using K _alpha rays of Cu as an X-ray source, monochromatic by multilayer confocal mirror, per resulting titania fiber was obtained X-ray diffraction pattern .

<Example 1>
[Fiber-forming composition preparation step]
1 part by mass of titanium tetranormal butoxide (manufactured by Wako Pure Chemical Industries, Ltd., first grade) and 0.008 parts by mass of niobium ethoxide (manufactured by Wako Pure Chemical Industries, Ltd., 99.9%), acetic acid (Wako Pure Chemical Industries, Ltd.) A uniform solution was obtained by adding and mixing 1.3 parts by mass of a company-made, special grade). A solution obtained by mixing 1 part by mass of ion-exchanged water and 0.016 part by mass of polyethylene glycol (manufactured by Wako Pure Chemical Industries, Ltd., first grade, average molecular weight: 300,000 to 500,000) with the obtained solution is stirred. When added, a gel was formed in the solution. By further stirring, the produced gel was dissociated, and a transparent fiber-forming composition (spinning solution) could be prepared.

[Spinning process / Cumulative process]
Using the fiber-forming composition (spinning solution) obtained above, the fiber-forming composition was ejected by an electrostatic spinning device shown in FIG. 1 to spin the fiber. Furthermore, fibers were accumulated by continuous spinning to produce a fiber assembly. At this time, the inner diameter of the ejection nozzle 1 was 0.2 mm, the voltage was 15 kV, and the distance from the ejection nozzle 1 to the electrode 4 was 15 cm.

[Baking process]
The fiber assembly obtained above was heated to 600 ° C. over 10 hours using an electric furnace in an air atmosphere, and then held at 600 ° C. for 2 hours to obtain a fiber structure of titania fibers. It was.

[Measurement / Evaluation]
The above-described various measurements and evaluations were performed on the obtained titania fibers. As a result, the average fiber diameter was 150 nm, and fibers with a fiber length of 100 μm or less were not confirmed. Moreover, when the light absorbency after ultraviolet irradiation was measured in evaluating photocatalytic activity, the result was 0.423A. Further, when X-ray diffraction measurement was performed on the obtained titania fiber, a sharp peak was observed at 2θ = 25.4 °, confirming the formation of an anatase type crystal.
A scanning electron micrograph of the surface of the titania fiber is shown in FIG. 2, and an X-ray diffraction pattern is shown in FIG.

<Comparative Example 1>
Titania particles (manufactured by Titanium Industry Co., Ltd., trade name: PC-101A) were prepared. And about this titania particle, said photocatalytic activity was evaluated. When the absorbance after ultraviolet irradiation was measured, the result was 1.391A.

  The absorbance in the case of the titania fiber of Example 1 is smaller than that in the case of the titania particles of Comparative Example 1, indicating that the methylene blue fading reaction is more advanced, and therefore the photocatalytic activity is higher. I understand.

It is the figure which showed typically the manufacturing apparatus for manufacturing the titania fiber of this invention. It is the photograph figure obtained by image | photographing (2000 times) the surface of the titania fiber obtained in Example 1 with the scanning electron microscope. 2 is an X-ray diffraction pattern of the titania fiber obtained in Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fiber formation composition ejection nozzle 2 Fiber formation composition 3 Fiber formation composition holding tank 4 Electrode 5 High voltage generator

Claims (8)

  A titania fiber having an average fiber diameter of 50 nm or more and 1000 nm or less and containing 0.1 to 10% by mass of niobium element in terms of niobium oxide with respect to the mass of the entire fiber.   The titania fiber according to claim 1, wherein the titania fiber is made of anatase type crystal. Alkyl titanate, a complex-forming compound with alkyl titanate, and a mixture containing niobium alkoxide, water, and a fiber-forming composition preparation step for preparing a fiber-forming composition containing a fiber-forming solute;
A spinning step of obtaining fibers by ejecting the fiber-forming composition by an electrostatic spinning method;
A cumulative step of accumulating the fibers to obtain a fiber aggregate;
And a firing step of firing the fiber assembly to obtain a fiber structure.   The fiber forming composition preparation step dissociates the gel produced by mixing the alkyl titanate, a complex-forming compound with the alkyl titanate, and a mixture containing niobium alkoxide and water. The manufacturing method of the titania fiber of Claim 3 which includes the process of preparing the composition for fiber formation by this.   The method for producing a titania fiber according to claim 3 or 4, wherein the fiber-forming solute is an organic polymer.   The method for producing a titania fiber according to claim 5, wherein the organic polymer is polyethylene glycol.   The method for producing a titania fiber according to any one of claims 3 to 6, wherein the complex-forming compound with an alkyl titanate is a carboxylic acid.   The method for producing a titania fiber according to claim 7, wherein the carboxylic acid is acetic acid.

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