JP4746366B2 - Titania fiber and method for producing titania fiber - Google Patents

Description

  The present invention relates to a titania fiber and a method for producing the same. More specifically, the present invention relates to a titania fiber useful as a photocatalyst and a method for producing the same.

  As the global environment deteriorates in recent years, environmental problems have been taken up as social problems, and their interest is only increasing. As environmental problems become more serious, development of advanced removal technology for harmful pollutants is required.

  As one of the techniques for decomposing and removing harmful pollutant chemical substances, titanium oxide having a photocatalytic action has attracted attention. That is, when a photocatalyst material made of titanium oxide is irradiated with light having a wavelength greater than the band gap, photoexcitation generates electrons in the conduction band and holes in the valence band. It has been proposed to decompose harmful substances using the high reducing power and oxidizing power of the pores.

  Since available titanium oxide is a particle, it is necessary to prevent scattering and outflow when used. As one of the techniques, production of titanium oxide fibers has been studied (for example, see Patent Document 1). However, since these titanium oxide fibers have a large fiber diameter, there is a problem that the surface area effective for obtaining high photocatalytic activity is small.

  In addition, use of an electrospinning method is known as a technique for producing a titanium oxide fiber having a small fiber diameter (see, for example, Non-Patent Documents 1 and 2).

However, in these methods, since the organic polymer that is a spinning aid contained in the fiber before firing is an organic polymer that is relatively easily decomposed by heating, amorphous titanium oxide is crystallized and has a morphology. It is expected that the organic polymer will decompose before being fixed. For this reason, the structure of the fiber surface becomes smooth, and a titanium oxide fiber having a high surface area may not be obtained.
JP 2000-218170 A Dan Li et al. (Dan Li, Younan Xia), “Direct Fabrication of Composites and Ceramic Hollow Nanofibers by Electrospinning and Ceramic Hollow Nanofibers by Electrospin, USA. ), (The American Chemical Society) The American Chemical Society, May 2004, Vol. 4, No. 5, P933-938 By Mi Yeon Song, Do Kyung Kim, Kyo Jin Ihn, Seong Mu Jo, Dong Young Kim, “Electrospun Tanim Geoxide Electro-Ford 2 Sensitized Solar Cells” sensitized solar cells), Nanotechnology, (USA), Institute of Physics, December 2004, Vol. 15, No. 12, P1861-1865

  An object of the present invention is to provide a titania fiber having a small fiber diameter and a large BET specific surface area, and a method for producing the same, which could not be achieved by the above-described prior art.

  As a result of intensive studies in view of the above prior art, the present inventors have completed the present invention.

That is, the object of the present invention is to
It can be achieved by titania fibers having an average fiber diameter of 50 to 1000 nm, a fiber length of 50 μm or more, and a BET specific surface area of more than 10 and 1000 m ² / g or less.

Furthermore, another object of the present invention is to
Preparing a solution comprising a compound that forms a complex with an alkyl titanate, an alkyl titanate, an organic solvent, and a carbon precursor organic polymer; spinning from the solution by an electrospinning method; and This is achieved by a method for producing a titania fiber, which includes a step of accumulating a fiber structure obtained by spinning and a step of firing the accumulated fiber structure.

Since the titania fiber of the present invention has a small average fiber diameter and a large BET specific surface area of 10 to 1000 m ² / g, the fiber surface structure is porous and useful as a photocatalyst.

  In addition, the obtained titania fibers can be formed into various structures by processing such as weaving, and can also be used in combination with ceramic fibers other than the present invention in accordance with handleability and other requirements. it can.

  Hereinafter, the present invention will be described in detail.

The titania fiber of the present invention has an average fiber diameter of 50 to 1000 nm, a fiber length of 50 μm or more, and a BET specific surface area of more than 10 and 1000 m ² / g or less.

Here, the titania fiber refers to a fiber structure made of an oxide-based ceramic mainly composed of titanium oxide. As subcomponents, 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 Examples include those containing oxide ceramics such as Cr ₂ O ₃ , MnO, Fe ₂ O ₃ , CoO, NiO, Y ₂ O ₃ , Lu ₂ O ₃ , Yb ₂ O ₃ , and HfO ₂ .

  The abundance ratio of the oxide-based ceramics other than titanium oxide is preferably 5% by weight or less based on the weight of the titania fiber, more preferably 1% by weight or less, more preferably 1% by weight or less. Preferably it is 0.1 weight% or less.

  Next, the crystal form of the titania fiber will be described. There are anatase type, rutile type and brookite type in the crystal form of titanium oxide, but the titania fiber of the present invention is preferably mainly composed of anatase type. In the X-ray diffraction pattern of the titania fiber, the abundance ratio of the anatase type crystal and the rutile type crystal is 1-30 in the peak intensity of 27-28 ° of the rutile crystal with respect to the peak intensity of 25-26 ° of the anatase crystal. Preferably there is. More preferably, it is 1-10. The presence of many crystal forms other than the anatase type is not preferable because the photocatalytic activity of the titania fiber decreases.

  Next, it will be described that the average fiber diameter is 50 to 1000 nm. When the average fiber diameter of the titania fiber of the present invention exceeds 1000 nm, the flexibility of the titania fiber becomes unfavorable. More preferably, it is in the range of 100 to 800 nm.

  Next, it will be described that the fiber length is 50 μm or more. When the fiber length of the titania fiber of the present invention is 50 μm or less, the mechanical strength of the titania fiber aggregate obtained thereby becomes insufficient. The fiber length is preferably 150 μm or more, more preferably 1 mm or more.

Next, it will be described that the BET specific surface area is more than 10 and 1000 m ² / g or less. When the BET specific surface area of the titania fiber of the present invention is 10 m ² / g or less, it indicates that the surface of the titania fiber is smooth and the photocatalytic activity is considered to be lowered, which is not preferable. Preferably, it is 20-1000 m < ² > / g, More preferably, it is 30-500 m < ² > / g, More preferably, it is 50-200 m < ² > / g.

  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 it can obtain a titania fiber that satisfies the above-mentioned requirements at the same time, but a compound that forms a complex with an alkyl titanate and titanium A step of preparing a solution comprising a mixture of an alkyl acid, a solvent, and a carbon precursor organic polymer, a step of spinning from the solution by an electrospinning method, and a step of accumulating the fiber structure obtained by the spinning. A preferred embodiment of the method for producing titania fibers includes a step of firing the accumulated fiber structure.

  First, the step of preparing a solution comprising a compound that forms a complex with an alkyl titanate, an alkyl titanate, an organic solvent, and an organic polymer will be described.

  Examples of the alkyl titanate used herein include titanium tetramethoxide, titanium tetraethoxide, titanium tetranormal propoxide, titanium tetraisopropoxide, titanium tetranormal butoxide, and titanium tetratertiary butoxide. From the standpoint of ease, titanium tetraisopropoxide and titanium tetranormal butoxide are preferred.

  Next, the addition amount of the alkyl titanate is not particularly limited as long as it is a concentration range in which fibers are formed. %.

  Next, a compound that forms a complex with an alkyl titanate will be described. Compounds that form complexes with alkyl titanates include coordinating compounds such as carboxylic acids, amides, esters, ketones, phosphines, ethers, alcohols, thiols, etc. From the viewpoint of stability, it is preferable that a strong complex is formed with the alkyl titanate and the solution has high stability. Therefore, acetic acid and acetylacetone are more preferable, and acetylacetone is more preferable.

  The amount of the compound that forms a complex with the alkyl titanate is not particularly limited as long as the amount of the solution for preparing the titania fiber of the present invention is prepared, but 2 equivalents or more with respect to the alkyl titanate. It is preferable that it is 3-5 equivalent.

  Next, the carbon precursor organic polymer used in the production method of the present invention will be described. The carbon precursor organic polymer referred to in the present invention may be any organic polymer that is carbonized by heating (firing). For example, polyacrylonitrile, polyvinyl alcohol, polyvinyl chloride, Arylate polyparaphenylene terephthalamide, polyparaphenylene terephthalamide-3,4'-oxydiphenylene terephthalamide copolymer, cellulose, cellulose diacetate, cellulose triacetate, methylcellulose, propylcellulose, benzylcellulose, polycarbodiimide, A phenol resin, a melamine resin, etc. are mentioned, Among them, polyacrylonitrile is more preferable from the viewpoint of solubility.

  Next, the addition amount of the carbon precursor organic polymer is not particularly limited as long as it is a concentration range in which fibers are formed, but is preferably 1 to 30% by weight. If the concentration of the carbon precursor organic polymer is less than 1% by weight, it is not preferable because the concentration is too low and it becomes difficult to form a fiber structure. On the other hand, if it is greater than 30% by weight, the fiber diameter of the resulting fiber structure is undesirably large. The concentration of the organic polymer with respect to the solution in a more preferable solution is 5 to 15% by weight.

  Next, the organic solvent used for the solution for producing the titania fiber of the present invention will be described. One organic solvent may be used alone, or a plurality of organic solvents may be combined. Examples of the organic solvent include acetone, chloroform, ethanol, isopropanol, methanol, toluene, tetrahydrofuran, water, benzene, benzyl alcohol, 1,4-dioxane, propanol, methylene chloride, carbon tetrachloride, cyclohexane, cyclohexanone, phenol, Examples include pyridine, trichloroethane, acetic acid, formic acid, hexafluoroisopropanol, hexafluoroacetone, N, N-dimethylformamide, acetonitrile, N-methylmorpholine-N-oxide, 1,3-dioxolane, methyl ethyl ketone, and mixed solvents of the above solvents. It is done.

  Of these, N, N-dimethylformamide and N, N-dimethylacetamide are preferable in view of handling properties and physical properties.

  Next, the electrostatic spinning method will be described. The titania fiber of the present invention is produced by an electrostatic spinning method. In the electrostatic spinning method, a solution in which a fiber-forming substrate is dissolved is discharged into an electrostatic field formed between the electrodes, and the solution is applied to the electrodes. In which the fibrous material formed is accumulated on a collection substrate to obtain a fiber structure, and the fibrous material is a solvent in which a fiber-forming substrate is dissolved. The figure shows not only the state of leaving the fiber laminate but also the state in which the solvent is contained in the fibrous material.

  Ordinary electrospinning is performed at room temperature, but the temperature of the spinning atmosphere and the temperature of the collection substrate can be controlled as necessary, such as when the solvent is not sufficiently volatilized. It is.

  Next, an apparatus used in the electrostatic spinning method will be described.

  The above-described electrode can be used as long as it has conductivity, and any metal, inorganic, or organic material has a thin film of conductive metal, inorganic, or organic material on an insulator. May be.

  The electrostatic field is formed between a pair or a plurality of electrodes, and a high voltage may be applied to any of the electrodes. This includes, for example, using two high-voltage electrodes with different voltage values (for example, 15 kV and 10 kV) and a total of three electrodes connected to the ground, or when using more than three electrodes. Shall also be included.

Next, the step of accumulating the fiber structure obtained by spinning will be described.
In the production method of the present invention, since the spinning is performed by the electrostatic spinning method, the fiber structure is laminated on the electrode that is the collection substrate. If a flat surface is used for the collection substrate, a planar nonwoven fabric can be obtained. However, by changing the shape of the collection substrate, a structure having a desired shape can be produced.

  In addition, when the uniformity is low, such as when the fiber structure is concentrated and laminated at one place on the substrate, the substrate can be swung or rotated.

  Moreover, since the fiber structure before baking of this invention has low intensity | strength, when peeling the fiber structure laminated | stacked on the collection board | substrate, a structure may be broken partially. Therefore, it is also possible to install a static eliminator or the like between the collection substrate and the nozzle and to laminate the fiber structure in a cotton shape between the nozzle and the static eliminator.

  Next, the step of firing the fiber structure will be described. In order to produce the titania fiber of the present invention, it is necessary to fire the fiber structure produced by spinning. 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 300 to 900 ° C. in order to suppress sufficient anatase type crystal growth and rutile type crystal dislocation. More preferably, it is 500-800 degreeC.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. The evaluation items in the following examples and comparative examples were carried out by the following methods.

Average fiber diameter:
The diameter of the filament was measured by randomly selecting 20 locations from a photograph obtained by photographing the surface of the obtained titania fiber with a scanning electron microscope (S-2400 manufactured by Hitachi, Ltd.) (magnification 2000 times). The average value of all the fiber diameters (n = 20) was determined and used as the average fiber diameter of titania fibers.

Confirmation of the presence of fibers having a fiber length of 50 μm or less:
A photograph obtained by photographing the surface of the obtained titania fiber with a scanning electron microscope (S-2400, manufactured by Hitachi, Ltd.) (magnification 400 times) is observed, and it is confirmed whether a fiber having a fiber length of 50 μm or less exists. did.

Method for measuring BET specific surface area:
The specific surface area of the obtained titania fiber was measured by the BET method using nitrogen gas.

X-ray diffraction pattern measurement:
The resulting titania fibers, using X-ray diffraction apparatus (manufactured by Rigaku Corporation), using K _alpha rays of Cu as an X-ray source to obtain an X-ray diffraction pattern with monochromatic by multilayer confocal mirror .

[Example 1]
In a solution comprising 1 part by weight of polyacrylonitrile (manufactured by Wako Pure Chemical Industries, Ltd.) and 9 parts by weight of N, N-dimethylformamide (manufactured by Wako Pure Chemical Industries, Ltd., special grade), titanium tetranormal butoxide (Wako Pure Chemical Industries, Ltd.) A spinning solution was prepared by mixing a solution consisting of 1 part by weight of company-made, first grade and 1 part by weight of acetylacetone (made by Wako Pure Chemical Industries, Ltd., special grade).

  A fiber structure was produced from the spinning solution using the apparatus shown in FIG. The inner diameter of the ejection nozzle 1 was 0.8 mm, the voltage was 15 kV, and the distance from the ejection nozzle 1 to the electrode 4 was 15 cm. The obtained fiber structure was heated to 600 ° C. for 10 hours in an air atmosphere using an electric furnace, and then held at 600 ° C. for 2 hours to produce a titania fiber.

When the obtained titania fiber was observed with an electron microscope, the fiber diameter was 600 nm, and fibers with a fiber length of 50 μm or less were not observed. Moreover, the BET specific surface area was 73 m < ² > / g. In the X-ray diffraction result of the obtained titania fiber, a peak was observed at 2θ = 25.3 °, which confirmed that anatase crystals were mainly formed. Scanning electron micrographs of the surface of the obtained titania fiber are shown in FIGS. 2 and 3, and an X-ray diffraction pattern is shown in FIG.

It is the figure which showed typically the manufacturing apparatus for manufacturing the titania fiber of this invention. FIG. 3 is a photograph obtained by photographing (400 times) the surface of titania fiber obtained by the operation of Example 1 with a scanning electron microscope. FIG. 3 is a photograph obtained by photographing the surface of titania fiber obtained by the operation of Example 1 with a scanning electron microscope (2000 times). 2 is an X-ray diffraction pattern of titania fiber obtained by the operation of Example 1. FIG.

Explanation of symbols

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

Claims (3)

Preparing a solution comprising a compound that forms a complex with an alkyl titanate, an alkyl titanate, an organic solvent, and a carbon precursor organic polymer; spinning from the solution by an electrospinning method; and A method for producing a titania fiber, comprising the steps of accumulating a fiber structure obtained by spinning and firing the accumulated fiber structure . The method for producing a titania fiber according to claim 1, wherein the carbon precursor organic polymer is polyacrylonitrile. The manufacturing method of the titania fiber of Claim 1 whose compound which forms a complex with an alkyl titanate is acetylacetone or an acetic acid.

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