KR101284610B1 - Nanofiber with elliptical pore structure, method for fabricating the same and articles comprising the same - Google Patents

Abstract

PURPOSE: Nano fiber having an oval pore is provided to have a gas sensor with excellent sensitivity by utilizing the metal Nano fiber which greatly enlarged the specific surface area or the metallic oxide Nano fiber as a sensing material of the gas sensor. CONSTITUTION: Nano fiber is formed with metal, metal oxide, compound metal oxide or the mixture of these. The inner and surface of the Nano fiber has the corrugated structure and multiple fibril structures or shell structures and forms pore extended in a longitudinal direction of the Nano fiber on the surface of the Nano fiber. The metal is selected from Pt, Au, Ag, Fe, Ni, Ti, Sn, Si, Al, Cu, Mg, Sc, V, Cr, Mn, Co, Zn, Sr, W, Ru, Ir, Ta, Sb, In, Pb, Pd or the alloy of these.

Description

Nanofibers with elliptical pores, method for manufacturing the same, and articles containing same {Nanofiber with elliptical pore structure, method for fabricating the same and articles comprising the same}

The present invention relates to a nanofiber, a method of manufacturing the same and an article comprising the same. More specifically, the present invention includes non-uniform elliptic surface pores, and ripple structure and fibril structure or shell structure are formed on and inside the fiber. The present invention relates to a nanofiber having a greatly increased specific surface area, a method of manufacturing the same, and an article including the same.

Unlike bulk structures, one-dimensional nanostructures are used for environmental sensors, nanocatalysts, secondary batteries, fuel cells, and solar cells due to their high specific surface area, fast material transfer characteristics in the longitudinal direction, and unique physical and chemical properties. It is widely applied to electrodes and catalyst materials. Various one-dimensional nanomaterial manufacturing process methods, such as physical vapor deposition, chemical vapor deposition, and template method, have been introduced, but recently, electrospinning technology, which is a method for manufacturing large quantities of one-dimensional nanostructures in large areas, has been attracting much attention. It is widely used commercially.

Related prior arts include Korean Patent No. 10-1092606 (name of the invention: metal and metal oxide nanofibers having a hollow structure and a method of manufacturing the same).

It is an object of the present invention to provide metal nanofibers or metal oxide nanofibers comprising non-uniform micropores elongated in the longitudinal direction of a fiber and a method for producing the same.

Another object of the present invention is to form a wrinkle structure on the surface and the inside of the fiber, a plurality of shells are stacked in a stack, there is a large pore between the shell and the shell, metal nanofibers or metal with a large increase in specific surface area The present invention relates to an oxide nanofiber and a method of manufacturing the same.

Yet another object of the present invention is to provide a method for producing a large amount of microporous metal nanofibers or metal oxide nanofibers in rapid yield.

Still another object of the present invention is a microporous metal nanofiber or metal oxide nano that can be used for a resistance change gas sensor, a cathode active material and a cathode active material for a secondary battery, a cathode and anode material for a fuel cell, a catalyst material for a lithium air battery, and a fuel cell. It is to provide a nanorod obtained by grinding from fibers or nanofibers.

Nanofibers, which is an aspect of the present invention, are formed of a metal, a metal oxide, a composite metal oxide, or a mixture thereof, and the inside and the surface of the nanofiber include a corrugated structure and a plurality of fibril structures or shell structures, and the nano The surface of the fiber may be formed pores elongated in the longitudinal direction of the nanofibers.

According to another aspect of the present invention, a method of preparing nanofibers includes the steps of: a) dissolving a metal, metal oxide or metal complex oxide-forming precursor and a polymer in a solvent to prepare a spinning solution, b) electrospinning the spinning solution, Forming a precursor / polymer composite fiber in which the precursor and the polymer are complexed, and c) heat treating the composite fiber in a reducing or oxidizing atmosphere to prepare nanofibers.

According to the present invention, a gas sensor detects metal nanofibers or metal oxide nanofibers having non-uniform micropores elongated in the longitudinal direction of the fiber and having wrinkled structures formed on the surface and the inside of the fiber to increase specific surface area. By using it as a material, it is possible to realize a gas sensor with excellent sensitivity. In particular, the open pore structure allows the harmful gases to move quickly, so the gas sensor characteristics can be expected to react quickly and recover quickly. Nanofibers containing non-uniform micropores and corrugated structures drawn in the longitudinal direction of the fibers, or nanorods obtained by pulverizing them, are used for the cathode active materials and cathode active materials for secondary batteries, the anode and cathode materials for fuel cells, lithium air batteries and catalysts for fuel cells. It can be expected to be applied to the material, excellent energy material properties. In particular, this technology, which can easily produce porous metal or metal oxide nanofibers in preparation for hollow structures or other similar technologies that require two or more complex processes to make porous structures, is time-consuming in terms of mass production. It is cost effective.

1 is a scanning electron microscope (SEM) photograph of the precursor / polymer composite nanofibers of Example 1. FIG.
Figure 2 is a scanning electron micrograph of the nanofiber of Example 1.
Figure 3 is a scanning electron micrograph of the nanofiber of Example 1.
Figure 4 is a scanning electron micrograph of the nanofiber of Example 1.
5 is a scanning electron micrograph showing an enlarged fracture surface of the nanofiber of Example 1. FIG.
Figure 6 is a scanning electron micrograph of the nanofiber of Example 1.
7 is a transmission electron microscope (TEM) photograph of the nanofibers of Example 1. FIG.
FIG. 8 is an electron beam diffraction pattern (SAD) photograph of the nanofiber of FIG. 7.
FIG. 9 is a scanning electron micrograph of the precursor / polymer composite nanofiber of Example 2. FIG.
10 is a scanning electron micrograph of the nanofiber of Example 2.
11 is a transmission electron micrograph of the nanofiber of Example 2.
12 is a scanning electron micrograph of the precursor / polymer composite nanofiber of Comparative Example 1. FIG.
13 is a scanning electron micrograph of the nanofiber of Comparative Example 1.
14 is a transmission electron micrograph of the nanofiber of Comparative Example 1.

Nanofibers, which is an aspect of the present invention, are formed of a metal, a metal oxide, a composite metal oxide, or a mixture thereof.

The metal is Pt, Au, Ag, Fe, Ni, Ti, Sn, Si, Al, Cu, Mg, Sc, V, Cr, Mn, Co, Zn, Sr, W, Ru, Ir, Ta, Sb, In , Pb, Pd or alloys thereof.

The metal oxide is ZnO, SnO ₂ , WO ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , NiO, TiO ₂ , CuO, In ₂ O ₃ , Zn ₂ SnO ₄ , Li ₄ Ti ₅ O ₁₂ , Li ₄ Ti ₅ O ₁₂ , Co ₃ O ₄ , PdO, LaCoO ₃ , NiCo ₂ O ₄ , Ca ₂ Mn ₃ O ₈ , ZrO ₂ , Al ₂ O ₃ , B ₂ O ₃ , V ₂ O ₅ , Ag ₂ V ₄ O ₁₁ , _{Ag 2 O, Li 0 .3 La} 0 .57 TiO 3, LiV 3 O 8, RuO 2, IrO 2, MnO 2, InTaO 4, ITO, IZO, InTaO 4, MgO, Li 2 MnO 4, LiCoO 2, LiMn ₂ O ₄ , Ga ₂ O ₃ , LiNiO ₂ , CaCu ₃ Ti ₄ O ₁₂ , Li (Ni, Mn, Co) O ₂ , LiFePO ₄ , Li (Mn, Co, Ni) PO _4, Li (Mn, Fe) O ₂ , Li (Cr _x Mn _{2 -x} ) O ₄ (x is 0-0.5), LiCoMnO ₄ , Ag ₃ PO ₄ , BaTiO ₃ , NiTiO ₃ , SrTiO ₃ , Sr ₂ Nb ₂ O ₇ , Sr ₂ Ta It may be at least one or more complexes selected from ₂ O _{7 ,} Ba _0.5 Sr _0.5 Co _0.8 Fe _0.2 O _3-7 .

On the surface of the nanofibers, pores elongated in the longitudinal direction of the nanofibers are formed. The pores may be elliptical in shape and have a length of 2 nm-2 μm in the major axis and 1 nm-500 nm in the minor axis.

The pores are unevenly and irregularly distributed on the surface of the nanofibers. These pores can significantly increase the specific surface area of the nanofibers.

Nanofibers include mesopore-sized pore structures. As a result, rapid gas diffusion and movement of the liquid electrolyte can be expected, and the specific surface area is greatly increased compared to the dense nanofibers, so that the sensing material for the resistance change type gas sensor, the cathode active material and anode active material for secondary batteries, the anode for fuel cells, and It can be used as a material having a structure that is very suitable for the use of negative electrode material, lithium air battery and fuel cell catalyst material.

Nanofibers have a complex pore structure that includes both micropores and macropores on the inside and inside of the fiber. As a result, the rapid diffusion of gases and liquids is possible. The micropores can have a size of 1 nm-200 nm and the macropores can have a size of 500 nm-5000 nm.

The porosity of the nanofibers can be 20-70%. As a result, the present invention can increase the specific surface area increase effect and the degree of reaction of liquid or gas and nanofibers.

Nanofibers may include internal pores inside the fiber. Internal pores can be 10-50% of the average diameter of the nanofibers.

The inside and the surface of the nanofibers are formed with a corrugated structure and a plurality of fibril structures or shell structures. The wrinkle structure, fibril structure or shell structure of the nanofibers can significantly improve the specific surface area of the nanofibers. The specific surface area of the nanofibers can be 20-200 m ² / g. Nanofibers made of fibril and shell structures may also include wrinkles and pore structures that are stretched in the longitudinal direction.

The wrinkle structure refers to a structure in which irregularities are formed in the nanofibers based on the length direction of the nanofibers, similar to the wave pattern. The wrinkle structure, that is, the irregularities may be regularly or irregularly distributed along the length direction of the nanofibers.

Due to the corrugated structure described above, single nanofibers have a regular or irregular diameter distribution along the length of the nanofibers. Specifically, the maximum and minimum diameters in a single nanofiber vary in the range of 0.01-100% of the average diameter of the nanofibers.

The average diameter of the nanofibers may be 50 nm-3 μm. Within this range, it can have high specific surface area characteristics and stable mechanical strength. When the diameter is less than 50 nm, the nanofibers may be easily broken, and when the diameter is more than 3 μm, the specific surface area may be small, so that it may be difficult to expect excellent sensitivity characteristics.

The fibril structure refers to a structure in which nanofibers constituting nanofibers or aggregates thereof are crystallized and connected in the longitudinal direction to form nanofibers in the form of a bundle.

The shell structure refers to a structure in which a plurality of shells having a plate-like structure composed of nanoparticles constituting nanofibers or aggregates thereof are piled up along the length direction of the nanofibers to form nanofibers. A hollow structure including macropores or micropores is formed between the shell structure to increase the specific surface area.

Another aspect of the present invention, a method for producing a nanofiber may include the following steps:

a) dissolving a precursor and a polymer for forming a metal, a metal oxide or a metal complex oxide in a solvent to prepare a spinning solution,

b) electrospinning the spinning solution to form precursor / polymer composite nanofibers in which the precursor and the polymer are complexed, and

c) heat treating the composite nanofibers in a reducing or oxidizing atmosphere to produce nanofibers.

Details of the metal, metal oxide, and metal composite oxide are as described above.

The precursor for forming a metal, a metal oxide, or a metal complex oxide may be a salt containing the above-described metal, for example, an organic acid salt, a halogen salt, an inorganic acid salt, an alkoxy salt, a sulfide salt, an amide salt, or the like. Specifically, there may be mentioned, for example, acetates, chlorides, acetylacetonates, nitrates, methoxides, ethoxides, butoxides, isopropoxide, sulfides, oxytriisopropoxide, (ethyl or cetylethyl) hexanoate, , Ethyl amide, amide, and the like, or a mixture of two or more thereof.

The polymer may give a viscosity to the spinning solution to form a fibrous phase during spinning, and control the structure of the spun fiber by compatibility with the metal, metal oxide precursors. In the present invention, by using only a single type of polymer, a nanofiber having the above-described wrinkle structure, fibril structure, shell structure was implemented.

The polymer may have a weight average molecular weight (Mw) of 100,000-1,500,000 g / mol. In the above range, having the above-described corrugated structure and a plurality of fibril structures or shell structures can form pores elongated in the longitudinal direction on the surface. Preferably, it may be 500,000-1,300,000 g / mol.

The glass transition temperature (Tg) of the polymer may be 25-200 ° C. In the above range, having the above-described corrugated structure and a plurality of fibril structures or shell structures can form pores elongated in the longitudinal direction on the surface. Preferably, it may be 35-190 ° C.

The polymer is not particularly limited as long as it meets the above-mentioned weight-average molecular weight and glass transition temperature. For example, it is possible to use PVAc (polyvinyl acetate), PVP (polyvinylpyrrolidone), PVA (polyvinyl alcohol), PEO (polyethylene oxide), PANi (polyaniline), PAN (polyacrylonitrile) Methacrylate), PAA (polyacrylic acid), or PVC (polyvinyl chloride).

The solvent may affect the shape of the nanofibers due to the volatilization rate after electrospinning.

The solvent may be a solvent having a boiling point higher than that of water, preferably a solvent having a boiling point of 100 to 170 ° C. For example, dimethylformamide (DMF, boiling point: 153 DEG C), or a mixed solvent thereof may be used, but is not limited thereto. A solvent having a boiling point lower than that of water may also be used.

Preferably, a solvent having a low volatilization temperature such as DMF may be preferable in order to sufficiently obtain turbulent flow characteristics.

The spinning solution may be prepared by controlling the content of the precursor and the polymer, which are solutes, and the content of the solvent. For example, the spinning solution may comprise from 5 to 30% by weight of the precursor, from 5 to 20% by weight of the polymer and balance of the solvent. In the above range, pores elongated in the longitudinal direction may be formed on the surface of the nanofibers described above.

In the spinning solution, the precursor may be included in the amount of 50 to 300 parts by weight based on 100 parts by weight of the polymer. In the above range, pores elongated in the longitudinal direction may be formed on the surface of the nanofibers described above.

The spinning solution may further comprise additives for smooth spinning in addition to precursors, polymers, and solvents. The additives may include, but are not limited to, surfactants, acids, bases, oils, organic salts, or mixtures thereof. The additive may be added at 0.1-10% by weight in the spinning solution.

As the additive, a surfactant including cetyltrimethylammonium bromide and the like, and an acid such as acetic acid, stearic acid, adipic acid, ethoxyacetic acid, benzoic acid or nitric acid can be used.

In the spinning solution, the precursor, which is a solute, and the order of addition of the polymer to the solvent, the stirring temperature and the agitation time can be suitably adjusted.

The polymer in the solute is first added to prepare a polymer solution, and then a precursor and various additives are added to prepare a spinning solution. In this case, pores elongated in the longitudinal direction may be formed on the surface of the nanofiber described above. After adding both the polymer and the precursor, the mixture is stirred. The stirring temperature may be from 25 to 80 ° C., and the stirring time may be from 1 hour to 48 hours. In the above range, pores elongated in the longitudinal direction may be formed on the surface of the nanofibers described above.

The viscosity of the spinning solution may be 70 cps to 3000 cps at 25 ° C. Within this range, pores elongated in the longitudinal direction are formed on the surface of the nanofibers, and wrinkles and fibril structures or shell structures may be formed on and inside the fibers. Preferably, the viscosity may be between 100 cps and 2000 cps.

Depending on the phase fluidity (mixing degree) between the precursor and the polymer can also be greatly affected. If the phase fluidity is bad, it is possible to obtain nanofibers with more developed wrinkles or pore structures.

After the spinning solution is prepared, the spinning solution is electrospun to form a precursor / polymer composite nanofiber in which the precursor and the polymer are combined.

In the electrospinning, the electrospinning device consists of a spray nozzle connected to a metering pump, a high voltage generator, and a grounded conductive substrate, which can quantitatively inject the spinning solution. The conductive substrate is a metal plate and electrospun using a spinning nozzle spaced 10 cm to 20 cm from the metal plate.

The discharge rate of the spinning solution during electrospinning is 5 to 100 µl / min . In the above range, unstable turbulent behavior causes phase separation between the polymer and the precursor, thereby changing the microstructure of the nanofibers, and as a result, as described above, the pores stretched in the longitudinal direction on the surface of the nanofibers. This is formed, and a corrugated structure and a fibril structure or a shell structure may be formed on and inside the fiber. That is, within the above range, when radiated, precursors and polymers present in the polymer are stretched in the longitudinal direction, and after the heat treatment, the precursors are connected to each other to have a fibril structure or a shell structure. In addition, within the discharge rate range of 10 μl / min or less, the solvent may be uniformly volatilized during spinning, and deformation may not occur in the fiber shape. In addition, within the discharge rate range of 15 μl / min or less, the polymer twisted in an irregular coil form may be aligned in the spray direction, thereby generating interlayer pores having fibril-like pores or shells inside the fibers. If less than 10 μl / min, the nanofibers obtained after the final heat treatment do not form surface pores and wrinkle structures, and a dense and uniform nanofiber can be produced. In the case of electrospinning at very high speeds in excess of 100 [mu] l / min, there is a problem that many drops are dropped from the nozzles and the spinning solution can be lost. The discharge rate may preferably be 10-100 μl / min.

The operating voltage during electrospinning can be 8-30 kV. Within this range, pores elongated in the longitudinal direction are formed on the surface of the nanofibers, and wrinkles and fibril structures or shell structures may be formed on and inside the fibers.

The ambient humidity during electrospinning can be 10-50% and the ambient temperature during electrospinning can be 15-25 ° C.

The discharge speed of the spinning solution, the operating voltage, the distance between the nozzle and the current collector, the humidity and the temperature can be fixed but can be changed. Through this, pores elongated in the longitudinal direction may be formed on the surface of the nanofibers.

In electrospinning, the diameter of the nanofibers can be controlled according to the hole size of the spinning nozzle, the discharge speed, the concentration of the precursor in the spinning solution, and the spinning length.

By electrospinning, a precursor / polymer composite fiber in which the precursor and the polymer are combined can be formed, and the composite fiber can have a web shape.

After electrospinning, the formed precursor and the precursor / polymer composite nanofiber in which the polymer is complexed are heat-treated. The heat treatment carbonizes or removes the polymers contained in the composite fibers while simultaneously oxidizing or reducing the precursors to form metals, metal oxides or metal composite oxides.

The heat treatment can be carried out in an oxidizing or reducing atmosphere. Specifically, when the metal nanofibers are to be formed, the composite fiber is heat-treated in a reducing atmosphere (for example, air or nitrogen / hydrogen mixed gas), and when the metal oxide nanofibers are to be formed, the composite fibers are oxidized atmosphere. (For example, a gas containing oxygen).

The heat treatment is performed at a rate of 4 ° C / min. Per minute. After maintaining the heat treatment time for at least 30 minutes at a temperature range of 300 - 600 ° C for a maximum of 5 hours, the heat treatment is performed at a rate of 4 ° C / minute per minute.

In the heat treatment, the heat treatment temperature and air pressure of the nanofibers can be made constant, but can be changed, and if changed, can be changed regularly or irregularly. Through this, pores elongated in the longitudinal direction may be formed on the surface of the nanofibers.

The manufacturing method of the nanofibers may further include the step of pulverizing the nanofibers after the production of the nanofibers. By pulverization, pores elongated in a non-uniform longitudinal direction are formed on the surface, and nanorods having wrinkled structures or the like formed on the surface and the inside thereof may be formed.

In the production method of the present invention, nanofibers having a specific structure can be produced in a rapid yield by adjusting the discharge structure and the like.

An article which is another aspect of the invention may comprise the nanofibers. The article uses a large specific surface area of the nanofibers, an elliptical irregular open pore structure formed on the surface, which can increase the reaction rate and recovery rate, thereby increasing the sensitivity of the gas sensor. For example, the article may include, but is not limited to, a sensing material for a resistance change gas sensor, a cathode active material and a cathode active material for a secondary battery, a cathode and anode material for a fuel cell, a catalyst material for a lithium air cell and a fuel cell, and the like.

Hereinafter, the present invention will be described in more detail by way of examples. However, it should be understood that the present invention is not limited thereto.

Example  1: Preparation of Tin Oxide Nanofibers

0.666 g of PVAc (Aldrich) with a weight average molecular weight of 500,000 g / mol and a glass transition temperature of 39.5 ° C was dissolved in 25 ml of 4 ml of dimethyl formamide (DMF) (Aldrich) solution. 1 g (Aldrich) and 0.13 g (Junsei Chemical), a tin precursor, tin precursor, were added to this solution and stirred at 500 RPM for 7 hours at 25 ° C to prepare a spinning solution (viscosity: 400 cps at 25 ° C). It was. Immediately prior to electrospinning, the spinning solution is dispersed in an ultrasonic cleaner for 5 minutes and placed in a plastic syringe with a capacity of 12 ml.

Electrospinning was performed while maintaining a discharge rate of 25 µl / min under conditions of 30% relative humidity and 15 ° C or lower. The needle was perpendicular to the collector plate and kept at a distance of 15 cm and moved from side to side at a constant speed. After placing the stainless steel plate on the current collector plate directly below the injection needle for nanofiber collection, the injection needle was subjected to an anode voltage of 16.5 kV, and the current collector was grounded to obtain a tin oxide precursor / polymer composite fiber on the current collector. .

When sufficient amount of nanofibers accumulated after spinning for 2 hours or more, the tin oxide precursor / polymer composite fibers stacked on the stainless steel plate were heat treated in an air atmosphere (oxidizing atmosphere). The heat treatment was carried out from Ney's Vulcan 3-550 compact electric furnace to 400 ℃ to 500 ℃ in the atmospheric atmosphere (temperature rising rate: 4 ℃ / min), it was maintained for 30 minutes and then naturally cooled inside the furnace without any external changes. . At this time, due to the high heat treatment temperature, the internal polymer used as a template of the nanofibers is burned out and the tin precursors dissolved therein are oxidized to form a tin oxide precursor. As a result, nanofibers having many fine pores and wrinkled structures inside and outside the composite fiber were prepared.

1 is a scanning electron microscope (Scanning electron microscopy, SEM) photograph of the tin oxide precursor / polymer composite nanofibers in Example 1. It can be seen that when the nanofibers are pulled out along the nozzle wall due to the high discharge rate, the surface layer is partially torn due to unstable turbulent behavior inside the fiber (see yellow box). The separation of material inside and outside the fiber can also be confirmed by the contrast differences in this area. The diameters of the nanofibers vary due to unstable fluid behavior, and the diameters of the fibers are not constant, but vary from 200 nm to 500 nm. It is preferable that the convex and convex diameters of the fibers in the average fiber diameter are in the range of 100%. If the change in diameter is too large, the fiber may be mechanically weakened and broken after the heat treatment. The size of cracks on the surface is measured from 10 nm to 1 μm, with no particular regularity. Micropores up to 50 nm are also observed (see blue arrows).

2 and 3 are scanning electron micrographs of the nanofibers of Example 1. It can be seen that the gap of the surface layer of FIG. 1 developed into micropores on the surface of the nanofiber due to the loss of the internal polymer after heat treatment (see yellow box). The pore distribution is finely distributed on the surface of the nanofibers, about 104 per square micrometer, which serves as a passage through which gas molecules can move rapidly as the pore structure develops inside. It can be seen that the micropores confirmed in Figure 1 also maintain its form. In addition, according to FIG. 3, the elliptical pores elongated in the longitudinal direction of the fiber on the surface of the fiber can be confirmed.

Figure 4 is a photograph taken with a scanning electron microscope of the nanofiber of Example 1. The wrinkle structure formed on the nanofibers can be confirmed.

5 is an enlarged scanning microscope photograph of the fracture surface of the nanofiber of Example 1. FIG. The shell structure formed on the nanofibers can be confirmed. Inside the nanofibers, several layers of porous tin oxide membranes can be seen surrounded by layers like cockscomb petals. Due to the concentration separation of the extreme polymer and the tin precursor, such a porous composite layer structure is produced. At this time, the thickness of each porous membrane is relatively constant, about 20 to 30 nm. This means that the material has consistent and predictable physicochemical properties, which means that certain performances can be expected in many applications. It is also possible to see the presence of very large internal cavities (macropores formed in the longitudinal direction of the fiber) between the surface pores between each oxide shell. This makes it possible to obtain a specific surface area superior to that of other manufactured fibers. In particular, micropores (see blue arrow) formed on the surface of the nanofibers and macropores formed between the shell structure inside the nanofibers coexist, and very fast gas and liquid transfer characteristics can be expected.

Figure 6 is a photograph taken with a scanning electron microscope of the nanofiber of Example 1. Fibril structure formed on the nanofibers can be confirmed.

FIG. 7 is a photograph taken of a nanofiber of Example 1 with a transmission electron microscopy (TEM). FIG. In contrast to the contrast created by the transmission of the electron beam, the bright part (see yellow box) is an internal cavity. The size of the inner cavity is about 50% of the diameter of the nanofibers in cross-sectional area, and its length is measured from several hundred nanometers to several micrometers in length.

8 is an electron diffraction analysis (Selected Area Diffraction, SAD) photograph of the nanofiber of Example 1. The clear diffraction pattern confirms that the material is tin oxide (SnO ₂ ) with a rutile crystal structure of polycrystalline nature.

Example  2: Preparation of Tin Oxide Nanofibers

Nanofibers were prepared in the same manner as in Example 1 except that the discharge rate was changed to 15 μl / min.

FIG. 9 shows a scanning electron micrograph (SEM) of tin oxide precursor / polymer composite nanofibers of Example 2. FIG. As the flow of the internal fluid is diverted from the normal laminar flow into turbulent flow, it is possible to observe wrinkles on the surface as the solution flow changes. Due to the irregular fluid behavior and the high discharge rate, traces of water flowing on the fiber surface are observed. In addition, the diameter of the nanofibers are mostly measured at about 250 nm, but due to fluid instability during spraying, a diameter difference of about ± 100 nm may be observed for each fiber.

 10 is a photograph taken with a scanning electron microscope after the heat treatment of the composite nanofiber of Example 2. It can be seen that the wave pattern confirmed in FIG. 9 remains on the surface of the fiber even after the heat treatment. At this time, partial fiber shrinkage occurs during heat treatment due to an uneven internal concentration gradient caused by fast turbulent behavior. The low concentration of tin precursor shrinks during heat treatment, and the high concentration of tin precursor tends to maintain fiber form by converting to tin oxide after heat treatment. This is the cause of the tortuous fiber shape as a whole.

11 is a photograph taken with a transmission electron microscope of the nanofiber of Example 2. In the form of tin oxide, it is possible to infer traces of the polymer chain aligned in the spraying direction due to the high discharge rate. The structure of the pores arranged in the date is the part where the polymer was located during spinning, and the polymer having a high molecular weight spontaneously aligned in the spray direction in a dynamic flow state. It also serves to push relatively insoluble tin precursors into the surrounding space, and eventually serves to make tin oxide crystallized into a micropillar (fibril) structure after heat treatment.

In Example 1-2 described above, tin oxide (SnO ₂ ) is taken as an example, but any nanofiber in which an electrospinable precursor is dissolved may be used. It is possible to easily manufacture metal nanofibers or metal oxide nanofibers including non-uniform pore and corrugated structure, and have a specific surface area, and metal nanofibers or metal oxide nanofibers having an open pore structure are resistive gas sensors. It can be applied to various fields such as a sensing material, a cathode active material and a cathode active material for a secondary battery, a cathode and an anode material for a fuel cell, a catalyst material for a lithium air battery and a fuel cell.

Comparative example  1: Preparation of Tin Oxide Nanofibers

In Example 1, nanofibers were prepared in the same manner, except that the discharge rate was changed to 5 μl / min.

12 is a photograph taken with a scanning electron microscope of the composite fiber in Comparative Example 1. The low discharge rate creates a stable laminar flow inside the injected fiber and keeps the flow of the internal fluid in a steady state. At this time, in Examples 1 and 2, the phase separation between the polymer and the precursor is not observed in the nanofibers, and the tin salt is uniformly distributed in the matrix of the polymer nanofibers. It is hard to find patterns or cracks due to irregular fluid behavior anywhere on the surface, and most of them remain smooth. In addition, due to the stable fluid behavior during spraying is characterized by a constant fiber diameter of about 250 nm. 13-14 are scanning electron micrographs and transmission electron micrographs of the nanofibers of Comparative Example 1, respectively. The nanofibers are observed in a very uniform nanofiber characteristics consisting of nanoparticles in the form of rice grains.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood that the invention may be embodied in other specific forms without departing from the essential characteristics thereof. Therefore, it should be understood that the above-described embodiments are illustrative and non-restrictive in every respect.

Claims (16)

Nanofibers formed of metals, metal oxides, composite metal oxides or mixtures thereof,
The inside and the surface of the nanofibers include a wrinkle structure and a plurality of fibrillated structure or shell structure, the surface of the nanofibers nanopores are formed in the pores elongated in the longitudinal direction of the nanofibers. The method of claim 1, wherein the metal is Pt, Au, Ag, Fe, Ni, Ti, Sn, Si, Al, Cu, Mg, Sc, V, Cr, Mn, Co, Zn, Sr, W, Ru, Ir , Nanofibers selected from Ta, Sb, In, Pb, Pd or alloys thereof. The method of claim 1, wherein the metal oxide is ZnO, SnO ₂ , WO ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , NiO, TiO ₂ , CuO, In ₂ O ₃ , Zn ₂ SnO ₄ , Li ₄ Ti ₅ O ₁₂ , Li ₄ Ti ₅ O ₁₂ , Co ₃ O ₄ , PdO, LaCoO ₃ , NiCo ₂ O ₄ , Ca ₂ Mn ₃ O ₈ , ZrO ₂ , Al ₂ O ₃ , B ₂ O ₃ , V ₂ O ₅ , Ag _{2 V 4 O 11, Ag 2} O, Li 0 .3 La 0 .57 TiO 3, LiV 3 O 8, RuO 2, IrO 2, MnO 2, InTaO 4, ITO, IZO, InTaO 4, MgO, Li 2 MnO ₄ , LiCoO ₂ , LiMn ₂ O ₄ , Ga ₂ O ₃ , LiNiO ₂ , CaCu ₃ Ti ₄ O ₁₂ , Li (Ni, Mn, Co) O ₂ , LiFePO ₄ , Li (Mn, Co, Ni) PO _4, Li (Mn, Fe) O ₂ , Li (Cr _x Mn _{2 -x} ) O ₄ (x is 0-0.5), LiCoMnO ₄ , Ag ₃ PO ₄ , BaTiO ₃ , NiTiO ₃ , SrTiO ₃ , Sr ₂ Nb ₂ Nanofiber which is at least one or more composites selected from O ₇ , Sr ₂ Ta ₂ O _{7 ,} Ba _0.5 Sr _0.5 Co _0.8 Fe _0.2 O _3-7 . The nanofiber of claim 1, wherein the pores have an ellipse shape and a long axis has a length of 2 nm −2 μm and a short axis has a length of 1 nm −500 nm. The nanofiber of claim 1, wherein the nanofibers have a diameter of 50 nm −3 μm. The nanofiber of claim 1, wherein the specific surface area of the nanofiber is 20-200 m ² / g. a) dissolving a precursor and a polymer for forming a metal, a metal oxide or a metal complex oxide in a solvent to prepare a spinning solution,
b) electrospinning the spinning solution to form precursor / polymer composite fibers having a corrugated structure elongated in the longitudinal direction in which the precursor and the polymer are complexed,
c) heat treating the composite fiber in a reducing or oxidizing atmosphere to produce a nanofiber including a plurality of irregular elliptical pores elongated in the longitudinal direction of the nanofiber. The method of claim 7, wherein the polymer has a weight average molecular weight of 100,000-1,500,000 g / mol. The method according to claim 7, wherein the glass transition temperature of the polymer is 25 to 200 ℃. The method of claim 7, wherein the polymer is PVAc, PVP, PVA, PEO, PANi, PAN, PMMA, PAA or PVC. The method of claim 7, wherein the spinning solution is spun at a discharge rate of 20-100 μl / min. The method of claim 7, wherein the spinning solution has a viscosity at 25 ° C. of 70-3000 cps. The method of claim 7, wherein the heat treatment is performed at 300-600 ° C. The method of claim 7, wherein the spinning solution further comprises a surfactant, an acid, a base, an oil, an organic salt, and a mixture thereof. According to claim 7, wherein the nanofibers comprising a plurality of irregular oval pores stretched in the longitudinal direction has a diameter of 50 nm ~ 3 ㎛, the length of 2 nm-2 ㎛ long axis and the length of 1 nm-500 nm short axis Method for producing nanofibers containing other oval pores. Nanofibers produced by the method of any one of claims 7 to 15.

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