KR101539526B1 - Metal oxide nanofibers including nanoscale pores, fabrication method for preparing the same, and gas sensor comprising the same - Google Patents

Abstract

The present invention relates to a metal oxide nanofiber including a multiple pore distribution structure, a manufacturing method thereof and a gas sensor including the same and, more specifically, to a metal oxide precursor/polymer composite nanofiber whose outer surface and inner surface are attached to sacrificial layer templates, which is manufactured by dispersing a polymer bead template on the sacrificial layer to be separated with heat in an electrospinning solution where metal oxide precursors and polymers are dissolved and electrospins the same, and to a manufacturing method of metal oxide nanofibers with the multiple pore distribution structure made by including different sized polymer beads, removing the sacrificial layer template and polymers with use of post-heat treatment and oxidizing metal oxide. The metal oxide nanofiber with a multiple pore distribution structure includes increased porosity, whose surface area is increased with large pore distribution structure, and is accordingly used in a high sensitivity exhalation sensing sensor and a good harmful-environment sensing sensor because the metal oxide nanofiber with the multiple pore distribution structure has efficient surface gas reaction and good performance of permeating and dispersing gas.

Description

TECHNICAL FIELD [0001] The present invention relates to a metal oxide nanofiber having a multi-pore distribution structure, a method of manufacturing the same, and a gas sensor including the same. BACKGROUND ART < RTI ID = 0.0 >

The present invention relates to metal oxide nanofibers including nanoscale pores, a method for producing nanofibers, and a gas sensor for analyzing exhaled gas containing nanofibers. More particularly, the present invention relates to a method of forming a plurality of pores on the inside and the surface of a metal oxide nanofiber fabricated by electrospinning. In the preparation of an electrospinning solution, the spinning solution containing a polymer / metal oxide precursor, A method of manufacturing nanofibers, nanofibers, nanofibers, nanofibers, nanofibers, nanoparticles, nanoparticles, nanoparticles, nanoparticles, nanoparticles, nanoparticles, nanoparticles, The present invention relates to a gas sensor for analyzing an exhalation gas.

Studies on the application of gas sensors using metal oxides have been developed as nanoparticles and materials with various nanostructures that can have further improved sensing properties from gas sensor materials using thin film. The basic principle of a gas sensor using a metal oxide is that ionized oxygen (O ^- , O ^2- ) adsorbed on the surface of a metal oxide semiconductor and oxidation (Cl ₂ , NO, NO _2, and the like) and a reducing gas (CH ₃ COCH ₃ , C ₂ H ₅ OH, CO, H _2, and the like) react with each other. Research on the synthesis of metal oxide sensing materials with various nanostructures, such as nanoparticles, nanotubes, and nanowires, has been presented as an effective research method for producing highly sensitive gas sensors by broadening the surface area capable of reacting with gases.

In recent years, electrospinning technology that can easily fabricate nanofiber structures has been actively applied to gas sensor research. Fabrication of metal oxide nanofibers through electrospinning technology begins with the preparation of electrospinning solutions. The electrospinning solution is prepared by dissolving a specific polymer in a solvent and a metal oxide precursor for forming a metal oxide together. The electrospinning solution thus prepared is put into a syringe pump and pushed to a certain discharge amount. At the same time, when a high voltage is applied between the nozzle and the current collector on the syringe pump, the spinning solution is collected on the top of the collector in the form of nanofiber. The collected nanofibers are thermally treated at high temperature to remove polymer components, and the metal oxide precursor can be oxidized at high temperatures to form metal oxide nanofibers. Particularly, as the metal oxide precursor salts undergo nucleation and grain growth during the oxidation process, a polycrystalline nanofiber shape composed of fine nanoparticles can be obtained. By studying this principle, it is possible to prepare a polycrystalline nanofiber structure including fine pores of less than 100 nm by controlling the phase fluidity between the precursor salt and the polymer (refer to Korean Patent No. 10-1337914, inventor: Kim, , The preparation of a nanofiber structure including a macropore stretched in the longitudinal direction of several hundreds to several micrometers by increasing the discharge speed during electrospinning under the condition having a phase fluidity between the precursor salt and the polymer Research has been presented. In addition, studies have been made on the synthesis of metal oxide nanofibers containing fine pores having a size of 20 nm by dispersing carbon nanotubes having a size of 20 nm in a carbon template together with an electrospinning solution and heat-treating them at a high temperature . Carbon particles such as carbon black, however, generally require high temperature heat treatment above 600 ° C to decompose. If the heat treatment is performed at a temperature of 600 ° C or higher, the nanofiber-like structure containing a large amount of pores may easily collapse. It is therefore important to easily remove the sacrificial layer template at an excessively high temperature.

In addition, researches and developments have been actively made on an exhalation sensor for diagnosing diseases by precisely analyzing volatile organic compounds emitted from the exhalation of human body as well as environmental sensors for monitoring harmful environments in the atmosphere. In particular, volatile organic compounds such as acetone, toluene, isoprene, and pentane, known as biomarkers of a specific disease, are considerably larger in size compared to the atmospheric environment (NO _x , CO, SO _x, etc.) , It is very important that the large pores are capable of rapidly diffusing large-sized volatile organic compound gases in the sensing material. When these pores have a size of 50 nm or more, they can have an effect of increasing surface area as well as diffusion of fast molecules. In a polycrystalline nanofiber structure composed of fine nanoparticles, a pore size distribution of nanoparticles having a size of 50 nm or less formed between nanoparticles and a pore size distribution of bi- modal pore distribution structure, it is possible to detect an effective gas component even for a volatile organic compound gas having a large molecular structure.

Therefore, it is necessary to develop a process capable of easily synthesizing polycrystalline metal oxide nanofibers having micropores of 1 to 50 nm size and macropores of 100 to 500 nm size simultaneously.

An object of the present invention is to provide a method for producing a metal oxide nanofiber having a multi-pore distribution structure in which a plurality of pores having a size of several tens nm to several hundreds of nanometers are formed on the inside and the surface of the metal oxide nanofiber.

Another object of the present invention is to provide an electrospinning device for a polymer bead having a size selected from various sizes (50 nm to 500 nm) in an electrospinning solution to conduct electrospinning and subsequent heat treatment to remove polymer beads And a pore having a size similar to the size of the selected polymer beads formed by the metal oxide nanofibers.

It is still another object of the present invention to provide a polymeric bead comprising two or more kinds of polymer beads having different sizes in an electrospinning solution to conduct electrospinning and subsequent heat treatment to remove polymer beads to form pores of two or more different sizes And a metal oxide nanofiber.

 It is another object of the present invention to provide a high-sensitivity harmful environmental gas sensing sensor and an exhaled gas sensing sensor using metal oxide nanofibers having a multi-pore distribution structure as a sensing material.

In order to produce porous metal oxide nanofibers which are one aspect of the present invention, a metal oxide precursor and a polymer having high viscosity are dissolved together in a solution in which a sacrificial layer template (spherical polymer bead) is dispersed, Metal oxide precursor composite nanofibers in which the sacrificial layer template is bound to the inside and the surface of the sacrificial layer template, and a multi-pore distribution structure including the inside and the surface of the nanofiber, The metal oxide nanofiber can be produced.

In one embodiment, the diameter of the sacrificial layer template may be 50 nm to 500 nm, and the sacrificial layer template material may be a polymer (polymethylmethacrylate (PMMA), polyvinylpyrrolidone (PVP), polyvinyl acetate (PVA), polyvinyl alcohol (PVA), polystyrene (PS) and polyacrylonitrile (PAN), polyvinylidene fluoride Lt; / RTI >

In another aspect of the present invention, a method for producing a metal oxide nanofiber having a multi-pore distribution structure includes the steps of: (a) preparing an electrospinning solution by dissolving a metal oxide precursor and a polymer together in a solution in which a sacrificial layer template is dispersed; (b) electrospinning the prepared electrospinning solution to form nanofibers bound to the inside and the surface of the polymer / metal oxide precursor composite nanofibers by the template; And (c) removing the sacrificial layer template by heat-treating the metal oxide precursor / polymer composite fiber bound to the inside and the surface of the nanofiber by a high temperature, and oxidizing the metal oxide precursor to form a metal oxide nano- And forming a fiber.

According to the embodiments of the present invention, the polymer / metal oxide precursor composite nanofibers including sacrificial polymer beads of different sizes are electrospun and then heat-treated to form pores having different sizes on the inside and the surface of the metal oxide nanofiber Polycrystalline metal oxide nanofibers having a multi-pore distribution structure can be produced.

Pores of various sizes formed on the surface and pores formed in the surface are oxidized gas (Cl ₂ , NO, NO _2, etc.) and reducing gas (CH ₃ COCH ₃ , C ₂ H ₅ OH, CO, H _2, etc.) are injected, And thus can exhibit high sensitivity gas sensing characteristics.

The polycrystalline metal oxide nanofiber sensing material having a multi-pore distribution structure can be used as an environmental sensor and an exhaled breath detection sensor material.

FIG. 1 is a conceptual diagram of a metal oxide having a multi-pore distribution formed by using a polymer bead template to explain one embodiment of the present invention.
2 is a schematic diagram for explaining an electrospinning technique used in one embodiment of the present invention.
3 is a flowchart illustrating a process for fabricating a metal oxide nanofiber having a multi-pore distribution using a polymer bead template according to Example 1 of the present invention.
4 is a scanning electron microscope (SEM) photograph of nanofibers in which polystyrene bead templates of 500 nm diameter obtained according to Example 1 of the present invention are bound to the surface and inside of a tungsten oxide precursor / polymer composite nanofiber.
5 is a scanning electron microscope (SEM) photograph of the tungsten oxide nanofiber obtained after heat treatment of a 500 nm diameter polystyrene bead template-bound tungsten oxide precursor / polymer composite nanofiber obtained according to Example 1 of the present invention at a high temperature .
6 is a scanning electron microscope (SEM) photograph of a tungsten oxide nanofiber obtained after heat treatment of a tungsten oxide precursor / polymer composite nanofiber with a polystyrene bead template of 100 nm diameter obtained according to Example 1 of the present invention at a high temperature .
7 is a scanning electron microscope (SEM) image of tungsten oxide nanofibers obtained after heat treatment of a 200 nm diameter polystyrene bead template-bound tungsten oxide precursor / polymer composite nanofiber obtained according to Example 1 of the present invention at a high temperature .
8 is a graph showing the results of the injection of tungsten oxide nanofibers obtained after heat treatment at high temperature of tungsten oxide precursor / polymer composite nanofibers obtained by binding polystyrene bead templates having different diameters of 200 nm and 500 nm diameters obtained according to Example 2 of the present invention It is an electron microscope (SEM) photograph.
9 is a scanning electron microscope (SEM) photograph of a tungsten oxide precursor / polymer composite nanofiber prepared without the addition of polystyrene beads according to Comparative Example 1 of the present invention.
10 is a scanning electron microscope (SEM) photograph of a dense structure tungsten oxide nanofiber obtained by heat-treating a tungsten oxide precursor / polymer composite nanofiber prepared without containing polystyrene beads according to Comparative Example 1 of the present invention at a high temperature.
11 is a graph showing the relationship between the hydrogen sulfide detection characteristic at 300 [deg.] C using dense tungsten oxide nanofibers prepared without inclusion of tungsten oxide and polystyrene beads having multi-pore distribution structures obtained according to Example 1, Example 2 and Comparative Example 1 of the present invention Fig.

In one aspect of the present invention, the metal oxide nanofibers having a multi-pore distribution structure may include pores having various sizes on the surface and inside of the nanofiber.

The metal oxide nanofibers can be synthesized by using the electrospinning technique, and the polymer bead templating method can be used as a method for forming pores on the surface and inside of the metal oxide.

FIG. 1 is a schematic view of a metal oxide nanofiber having a multi-pore structure shown in one embodiment of the present invention. As shown in FIG. 1, a web structure in which metal oxide nanofibers are mutually entangled can be formed (001). The metal oxide nanofibers formed by electrospinning have not only a cylindrical structure (002) It can also have a nano-belt shape (003). The pores formed through the templating method proposed in one embodiment of the present invention are formed by using a polymer bead template having a size of 50 nm to 500 nm so that pores having small diameters (005) and large pores (004) May be formed on the inside and on the surface of the metal oxide nanofibers. Particularly, when a large size polymer bead having a size of 300 to 500 nm and a small size polymer bead having a size of 50 to 200 nm are included at the same time and used as a template, it is possible to obtain a polymer having a triple pore distribution or a multi- Metal oxide nanofibers may be formed.

When polymer beads larger than 500 nm are used as the template, the size of the pores after heat treatment is too large to make the metal oxide nanofibers hard to have stable mechanical strength. When polymer beads of less than 50 nm are used as the template, The size is relatively small, and it is difficult to expect fast gas diffusion. Therefore, it is important to synthesize metal oxide nanofibers having a multi-pore distribution structure including small pores and large pores at the same time.

The electrospinning apparatus shown in FIG. 2 includes a plastic syringe (Henke-Sass Wolf, 10 ml NORM-JECT ^? ) Capable of holding an electrospinning solution, a DC power supply capable of applying a high electric field, A collector, and a syringe pump capable of discharging the electrospinning solution. The polymer / metal oxide precursor composite nanofiber structure can be easily fabricated by placing an electrospinning solution in a syringe and discharging it at a constant speed while applying a high voltage between the nozzle on the syringe and the collector substrate.

The method for preparing an electrospinning solution for forming a metal oxide nanofiber can be achieved by dissolving a metal oxide precursor and a polymer in a specific solvent. The solvent does not limit the specific solvent as long as it is a metal oxide precursor used for electrospinning and a solvent capable of dissolving the polymer. For example, solvents selected from ethanol, methanol, propanol, butanol, IPA, dimethylformamide (DMF), acetone, tetrahydrofuran, toluene, water and mixtures thereof can be used. The polymer does not have any specific restriction as long as it is a polymer dissolved in the solvent for the electrospinning. As a specific example, the polymer may be selected from the group consisting of polymethylmethacrylate (PMMA), polyvinylpyrrolidone (PVP), polyvinyl acetate (PVAc), polyvinyl alcohol (PVA), polystyrene (PS) and polyacrylonitrile Polyvinylidene fluoride (PVDF), or a mixture of two or more thereof. The metal oxide precursor may be a metal-containing salt, 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. Specific examples include but are not limited to acetate, chloride, acetylacetonate, nitrate, methoxide, ethoxide, butoxide, isopropoxide, sulfide, oxytriisopropoxide, (ethyl or cetylethyl) hexanoate, , Ethylamide, amide, and the like can be used. When the metal-containing salt is oxidized at a high temperature, it is preferred that the metal oxide is selected from the group consisting of 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 , Cr 3 O 4, CeO 2} , Pr 6 O 11, Nd 2 O 3, Sm 2 O 3, Eu 2 O 3, Gd 2 O 3, Tb 4 O 7, Dy 2 O 3, Ho 2 O 3, Er _{2 O 3, Yb 2 O 3} , Lu 2 O 3, 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 y (Cr x Mn 2-x) O 4 + z, LiCoMnO 4, Ag 3 PO 4, BaTiO 3, NiTiO 3, SrTiO ₃ , Sr ₂ Nb ₂ O ₇ , Sr ₂ Ta ₂ O _{7, and} Ba _0.5 Sr _0.5 Co _0.8 Fe _0.2 O _3-7 .

In the polymer bead templating method, polymer beads are further dispersed in an electrospinning solution in which the polymer and the metal oxide precursor are dissolved together to form nanofibers through electrospinning, and further heat treatment is performed to remove the template It is a method of forming pores. It is important to select polymers that are insoluble in the electrospinning solution. The prepared metal oxide precursor / polymer composite fiber including the polymer bead template may be spun. At this time, the polymer beads can be distributed not only on the inside of the composite fiber but also on the surface. Then, all the polymer components constituting the composite fiber are decomposed and removed in a high-temperature heat treatment process, and the metal oxide precursor salts are oxidized to form polycrystalline metal oxide nanofibers. At this time, the polymer bead template is also removed, leaving pores corresponding to the size of the beads on the inside and the surface of the nanofiber.

The template may include polymers and proteins and does not have template surface specific limitations that are removed during the high temperature heat treatment subsequent to electrospinning. For example, the template may be made of a polymer selected from the group consisting of polymethylmethacrylate (PMMA), polyvinylpyrrolidone (PVP), polyvinyl acetate (PVAc), polyvinyl alcohol (PVA), polystyrene (PS) and polyacrylonitrile PAN, polyvinylidene fluoride (PVDF), ferritin, virus, and the like, and one or a combination of two or more thereof may be used as a template.

The shape of the sacrificial layer template may have a polygonal shape such as a ball structure, a hexagon, a pentagon, a quadrangle, a triangle, or the like, and if the template can be used, the structure is not limited.

The diameter of the sacrificial layer template may be 50 nm to 500 nm, and the template having a size within this range may be included in the electrospinning solution without any specific size limitation.

The size of the sacrificial layer template may be one or two or more sizes may be combined to form a polymer bead template to synthesize metal oxide nanofibers having a dual pore distribution or a multi-pore distribution structure.

The electrospinning solution containing the sacrificial layer template can be easily discharged by injecting a high voltage between the nozzle attached to the syringe and the current collector while discharging the electrospinning solution in the syringe at a constant speed. At this time, the size of the nozzle is larger than the diameter of the sacrificial layer template so that the sacrificial layer template does not block the nozzle during electrospinning.

When the electrospinning solution containing the sacrificial layer template is electrospun to form nanofibers, the applied voltage may be between 5 kV and 30 kV.

The discharge rate of the spinning solution for preparing the metal oxide precursor / polymer composite fiber in which the sacrificial layer template is bound to the surface and the interior of the sacrificial layer template through electrospinning may be 5 to 100 μl per minute.

The metal oxide precursor / polymer composite fiber in which the sacrificial layer template formed through electrospinning is bound to the surface and inside can be formed in the range of 100 nm to 10 μm in diameter.

The surface of the sacrificial layer formed by electrospinning and the metal oxide precursor / polymer composite fiber bound to the inside may have the form of a web.

 The metal oxide precursor / polymer composite fiber in which the sacrificial layer template formed through the electrospinning is bound to the surface and inside can exhibit a nano-belt structure as well as a nanofiber shape.

By subjecting the sacrificial layer template and the polymer to heat treatment at a high temperature, metal oxide nanofibers having a multi-pore distribution structure in which a large number of pores are distributed can be manufactured. The heat treatment process can be performed at a temperature between 400 ° C and 800 ° C, at which the sacrificial layer template and the polymer can be decomposed. The heat treatment can proceed to raise the temperature at a rate of 4 ° C / min. Per minute, and can be maintained at a rate of 4 ° C / min per minute after maintaining the heat treatment time for at least 30 minutes to a maximum of 5 hours in the heat treatment temperature range.

The metal oxide nanofibers having a double-to-multiple pore distribution structure including a plurality of pores formed through heat treatment at a high temperature of the metal oxide precursor / polymer composite nanofibers in which the sacrificial layer template is bonded to the surface and the interior are crushed and split, Metal oxide nanorods can be formed.

By subjecting to heat treatment at a high temperature, the diameter of the metal oxide precursor / polymer composite nanofiber can be reduced, and the diameter of the shrinked porous metal oxide can be formed in the range of 50 nm to 5 μm.

The polymer bead template contained in the surface and inside of the metal oxide precursor / polymer composite nanofiber can be shrunk during the pyrolysis process, and the size of the shrunk pore may have a shrinkage ratio of about 1% to 50% have.

3 is a flowchart illustrating a process for fabricating a metal oxide nanofiber having a multi-pore distribution using a polymer bead template according to Example 1 of the present invention. A method for producing a metal oxide nanofiber having a double to multi-pore distribution structure according to another aspect of the present invention may include the following steps. Herein, steps 310 to 330 illustrate a process for producing metal oxide nanofibers having a multi-pore distribution structure, and step 340 is a step for fabricating metal oxide nanofibers using a metal oxide nanofiber having a multi- Showing a process of manufacturing a semiconductor type gas sensor.

(a) preparing (310) an electrospinning solution by dissolving a metal oxide precursor and a polymer together in a solution in which polymer bead sacrificial layer templates having the same diameter or different diameters are dispersed;

(b) electrospinning the prepared electrospinning solution to form composite fibers bound to the inside and the surface of the metal oxide precursor / polymer composite nanofiber by the polymer bead sacrificial layer template (320);

(c) heat treating the metal oxide precursor / polymer composite nanofiber including the polymer bead sacrificial layer template to remove the polymer bead sacrificial layer template, and oxidizing the metal oxide precursor to form a multi- Forming 330 a metal oxide nanofiber having a pore distribution structure, and

(d) A biomarker gas (oxide gas: NO ₂ , NO, reduction) for diagnosing harmful environmental gas and disease by coating metal oxide nanofibers having multiple pore distributions on a sensor substrate capable of recognizing resistance change (340) a semiconductor type gas sensor capable of detecting a gas: H ₂ , CO, C ₂ H ₅ OH, H ₂ S, CH _4, and the like;

The metal oxide gas sensor having a double or multi-pore distribution including a plurality of pores manufactured by the above-described method has a large surface area and a large number of open pore structures capable of moving gases faster than a general flat surface membrane. It can have sensitivity.

Hereinafter, the present invention will be described in detail with reference to more specific embodiments. However, it should be understood that the present invention is not limited thereto.

Example 1: Tungsten oxide having a double pore distribution structure prepared using a polymer bead template (WO ₃ Manufacture of Nanofibers.

0.25 g of polyvinyl pyrrolidone (PVP) (Aldrich) having a molecular weight of 1,300,000 g / mol and 0.2 g of tungsten oxide precursor ammonium metatungstate hydrate (Aldrich) were dispersed in polystyrene Dissolved in 1.5 g of water. The polystyrene-dispersed water is a polystyrene latex microsphere (Alfa Aesar) in which 2.5 wt% polystyrene having a 500 nm ball structure is dispersed in water. The tungsten oxide precursor / polymer blend solution containing the polystyrene beads was placed in a syringe and connected to a syringe pump (Henke-Sass Wolf, 10 ml NORM-JECT ^? ) To prepare a spinning solution at a discharge rate of 0.1 ml / And a voltage of 14 kV is applied between a needle (25 gauge) and a current collector for obtaining a nanofiber web to discharge the spinning solution, thereby forming a metal oxide precursor / polymer bonded on the surface and inside of the polystyrene template To produce a composite nanofiber web.

Scanning electron micrographs of the metal oxide precursor / polymer composite nanofiber web in which the polystyrene template obtained by the above electrospinning method are bound to the surface and inside can be observed in FIG. 4, polystyrene beads having a diameter of 500 nm were uniformly bound to the surface and inside of the tungsten oxide precursor / polymer composite nanofiber. The diameter of the formed tungsten oxide precursor / polymer composite nanofiber was found to be in the range of 500 nm to 1 μm. Electrospinning tungsten oxide precursor / polymer composite nanofibers may have a nano-belt shape during their formation. As the polymer beads are uniformly distributed inside the composite fiber, it is confirmed that some beads protrude from the surface. If the size of the polymeric beads is less than 50 nm and the size distribution is very fine, most of the beads may be embedded in the metal oxide precursor / polymer composite fiber and it may be difficult to observe the shape protruding to the surface as shown in Fig. . This is a unique microstructure observed because the size of the polymer bead is about half the diameter of the nanofiber and a very large polymer bead template is used.

The polystyrene beads and the polymer were removed, and the tungsten oxide precursor was subjected to heat treatment at a high temperature to oxidize the precursor. The high temperature annealing process was performed at 500 ° C for 1 hour, and the temperature rise and fall were kept constant at 4 ° C / min. In FIG. 5, the heat-treated tungsten oxide nanofibers were shrunk to 300 nm to 600 nm in diameter, and polystyrene beads were removed to form pores. It can be confirmed that the formed pores have a diameter of 100 nm to 300 nm which is shrunk compared with the polystyrene template having a size of 500 nm used in the preparation of the electrospinning solution. In this case, the heat shrinkage of the polymer occurs during the heating process, and the tungsten precursor salts flow through the polymer to move the polymer, and the size of the polymer bead template is 3/5 to 1/5 It can be confirmed that the formed pores are formed. This is a unique phenomenon that is also related to the glass transition temperature of the polymer beads used and can be observed only in the metal oxide nanofibers formed through the heat treatment process. The formation of retracted pores is closely related to the glass transition temperature of the polymer mixed with the bound polymer template and metal oxide precursor. In the case of polystyrene bead templates, glass transition temperature is 100 ° C, whereas polyvinyl pyrrolidone, a polymer mixed with a metal oxide precursor, has a glass transition temperature range of 150 to 180 ° C. Thus, the polystyrene bead template having a relatively low glass transition temperature first begins to undergo glass transition, and additionally the polyvinylpyrrolidone undergoes glass transition later. Therefore, it can be confirmed that the pores formed from the polystyrene bead template are shrunk by the polyvinyl pyrrolidone causing the glass transition later. As a result, metal oxide nanofibers capable of controlling the pore shrinkage due to the polymer template can be produced if a suitable combination of the polymer template and the polymer mixed with the metal oxide precursor is achieved. For example, if the glass transition temperature of the polymer template is higher than the glass transition temperature of the polymer mixed with the metal oxide precursor, the pore contraction due to the polymer template can be minimized to enable enlarged pore formation.

In the same way, if the size of polystyrene beads dispersed in water is made different, the size of pores formed after heat treatment can be easily controlled. 6, it can be seen that the pores formed are reduced to 20 nm to 100 nm in size by using polystyrene beads having a diameter of 100 nm. In FIG. 7, it can be seen that pores formed are formed in a size of 50 nm to 150 nm by using polystyrene beads having a diameter of 200 nm. It is interesting to note that despite the use of homogeneous polymeric beads of one size as described above, it exhibits a broad pore distribution. The reason for having such a wide pore distribution is that the polymer template in the metal oxide precursor / polymer composite nanofiber depends on whether it is located in the metal oxide precursor domain or the polymer domain. For example, if polystyrene, which is a polymer template, is located in a domain containing a large amount of polymer polyvinylpyrrolidone, it is advantageous to form relatively large pores while decomposing the template polystyrene and polyvinylpyrrolidone in a high-temperature heat treatment . However, in the domain containing a large amount of the metal oxide precursor, the polystyrene undergoes the glass transition temperature at a high temperature, thereby inducing the diffusion and oxidation of the metal oxide precursor to the periphery, thereby reducing the pore size.

As described above, the pores formed on the surface and inside of the tungsten oxide have the effect of widening the surface area. Further, when the gas to be measured is measured through a plurality of pore distributions, active gas diffusion can be performed to exhibit excellent detection characteristics for a specific gas.

Example 2: Preparation of tungsten oxide nanofibers having a multi-pore distribution structure using polymer bead templates having diameters of 200 nm and 500 nm.

In order to further increase the size of the pores formed in the porous tungsten oxide nanofibers using the prepared polystyrene bead template in a specific size range, polystyrene beads having two or more size distributions were added to prepare tungsten oxide nano- Fibers can be produced. That is, an electrospinning solution was prepared by mixing polystyrene bead templates having diameters of 200 nm and 500 nm, respectively, at a ratio of 1: 1. It is also possible to adjust the concentration of the pores having a specific size while changing the relative ratio of the polymer beads of different sizes.

More specifically, the electrospinning solution was prepared by dissolving 0.25 g of polyvinylpyrrolidone (PVP) (Aldrich) having a molecular weight of 1,300,000 g / mol and 0.25 g of ammonium metatungstate hydrate (Aldrich) 0.2, a tungsten oxide precursor g is dissolved in 1.5 g of polystyrene-dispersed water. Here, 1.5 g of the polystyrene-dispersed water was prepared by mixing 0.75 g of a water dispersion of 2.5 wt% of polystyrene beads with 200 nm and 0.75 g of a 2.5 wt% dispersion of 500 nm polystyrene beads.

Electrospinning was carried out in the same manner as described above. Specifically, a tungsten oxide precursor / polymer blend solution containing polystyrene beads was placed in a syringe and syringe pump (Henke-Sass Wolf, 10 ml NORM-JECT ^? And the spinning solution was pushed out at a discharge rate of 0.1 ml / min. A voltage of 14 kV was applied between a needle for discharging the spinning solution (25 gauge) and a collector substrate for obtaining a nanofiber web A tungsten oxide precursor / polymer composite nanofiber web having a polystyrene template bound to the surface and inside thereof was prepared.

In order to remove the polymer bead template and the polymer constituting the nanofiber in the tungsten oxide precursor / polymer composite nanofiber including the polystyrene bead template having a size of 200 nm and 500 nm, the heat treatment was performed under the same conditions as in Example 1 . Specifically, the high temperature heat treatment process was performed at 500 ° C for 1 hour, and the temperature rise and fall temperature were kept constant at 4 ° C / min.

8 is a scanning electron micrograph of a tungsten oxide nanofiber obtained after heat treatment of a tungsten oxide precursor / polymer composite nanofiber including polystyrene bead templates having sizes of 200 nm and 500 nm at 500 ° C for 1 hour. As can be seen from FIG. 8, porous tungsten oxide nanofibers having a wide pore distribution are well formed. Particularly, pores having a diameter of 100 nm to 300 nm are formed in a region where polymer beads having a size of 500 nm are removed, and pores having a diameter of 50 nm to 150 nm are removed in a region where polymer beads having a size of 200 nm are removed As shown in FIG. As a result, it was confirmed that tungsten oxide nanofibers having a multi-pore distribution size can be easily prepared by two different polymer bead templating techniques.

Comparative Example 1: Fabrication of tungsten oxide nanofibers without using polystyrene bead templates.

In order to more clearly observe the microstructure change effect of the tungsten oxide nanofibers including the micropores prepared by the template method of polymer beads and the large pores, tungsten oxide nanofibers prepared without using polystyrene beads as a template were synthesized, As a comparative example for testing the sensor.

The tungsten oxide nanofiber prepared without using polystyrene beads as a template used the same manufacturing method except that the polystyrene bead template was not added in the manufacturing method described in Example 1 above. Specifically, 0.25 g of polyvinylpyrrolidone (PVP) (Aldrich) having a molecular weight of 1,300,000 g / mol and 0.25 g of ammonium metatungstate hydrate (Aldrich) 0.2, which is a tungsten oxide precursor, g is dissolved in 1.5 g of water. Here, 1.5 g of water is used in which polystyrene bead template is not dispersed.

Specifically, the tungsten oxide precursor / polymer mixed solution was placed in a syringe and connected to a syringe pump (Henke-Sass Wolf, 10 ml NORM-JECT ^? ), The spinning solution was pushed out at a discharge rate of 0.1 ml / min, and a voltage of 14 kV was applied between a needle (25 gauge) through which the spinning solution was discharged and a collector substrate for obtaining a nanofiber web to form a tungsten oxide precursor / Polymer composite nanofiber webs were prepared.

The process of removing the polymer through heat treatment proceeded in the same manner as described above. Specifically, the high temperature heat treatment process was performed at 500 ° C for 1 hour, and the temperature rise and fall temperature was kept constant at 4 ° C / min .

9 is a scanning electron micrograph of a tungsten oxide precursor / polymer composite nanofiber prepared by electrospinning. As a result of observing the surface shape, it is impossible to observe the bead shape bound to the surface without using the polystyrene bead template, and it can be confirmed that the surface has a smooth shape. Further, not only the cylindrical shape of the nanofiber, but also the nanobelt structure can be observed.

10 is a photograph of a surface morphology obtained by heat treatment of the tungsten oxide precursor / polymer composite nanofiber prepared through the above electrospinning at 500 ° C for 1 hour under a scanning electron microscope. As a result of observing the surface shape, it was found that the pores formed by removing the polystyrene bead template were not observed, and the tungsten oxide particles formed a dense polycrystalline microstructure. It can be confirmed that the tungsten oxide nanofiber maintains the cylindrical nanofiber shape and the nanobelt structure during the high temperature heat treatment. At this time, nanofibers and nano-belts have a polycrystalline structure composed of fine nanoparticles.

Therefore, it was confirmed through scanning electron microscope observation that the difference in surface shape between the case of using the sacrificial layer template and the case of not using the sacrificial layer template was confirmed through Example 1, Example 2 and Comparative Example 1, and the polystyrene bead When the template was used, tungsten oxide nanofibers having a multi-pore distribution structure having a large surface area and containing a large number of pores could be fabricated.

Although the metal oxide nanofibers including tungsten oxide (WO ₃ ) are mentioned as an example in the above embodiments, the metal oxide nanofibers that can be produced by electrospinning using the sacrificial layer template do not limit the specific material . For _{example, 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, Cr 3 O 4, CeO 2 _{, Pr 6 O 11, Nd 2} O 3, Sm 2 O 3, Eu 2 O 3, Gd 2 O 3, Tb 4 O 7, Dy 2 O 3, Ho 2 O 3, Er 2 O 3, Yb 2 O 3 Li ₂ O ₃ , 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, (Ni, Mn, Co) O ₂ , LiFePO ₄ , Li (Mn, Co, Ni), Li ₂ MnO ₄ , LiCoO ₂ , LiMn ₂ O ₄ , Ga ₂ O ₃ , LiNiO ₂ , CaCu ₃ Ti ₄ O ₁₂ , PO _4, Li (Mn, Fe) O ₂ , Li _y (Cr _x Mn _{2 -x} ) O _{4 + z} , LiCoMnO ₄ , Ag ₃ PO ₄ , BaTiO ₃ , NiTiO ₃ , SrTiO ₃ , Sr ₂ Nb ₂ O ₇ , Sr ₂ Ta ₂ O _{7, and} Ba _0.5 Sr _0.5 Co _0.8 Fe _0.2 O _3-7 , may be fabricated.

Experimental Example 1: Comparison of tungsten oxide nanofibers having a multi-pore distribution structure obtained by using polystyrene bead templates of various sizes and tungsten oxide nanofiber gas sensors having a dense structure.

The tungsten oxide nanofibers having the multi-pore distribution structure using the polystyrene bead template prepared in Examples 1 and 2 of the present invention can be used to detect a harmful gas present in the surrounding environment or a volatile organic compound gas The bioassistive gas sensor was developed for the diagnosis of health condition by the concentration of biomass surface gas. In addition, as shown in Comparative Example 1, the characteristics and the characteristics of the dense tungsten oxide nanofibers produced without using the polystyrene bead template were compared and analyzed. The manufacturing process of the gas sensor is as follows.

Area 3 mm? An Au positive electrode having a thickness of 25 μm and a length of 345 μm is formed on a 3 mm alumina (Al ₂ O ₃ ) substrate at intervals of about 300 μm. A micro heater was attached to the opposite side of the alumina substrate on which the Au electrode was formed so that the temperature of the substrate could be adjusted according to the applied voltage. The applied voltage was adjusted so that the temperature of the substrate was 300 ° C.

The tungsten oxide nanofibers prepared in Examples 1 and 2 and Comparative Example 1 were dispersed in a solvent to prepare a dispersion solution of tungsten oxide nanofibers, which was then coated on the alumina substrate by a drop coating method And the sensor characteristics were evaluated after the gas sensor was manufactured. In the concrete coating method, the prepared tungsten oxide was dispersed in ethanol, and 3 μl of a mixed solution was applied on a substrate having sensor electrodes using a micropipette, and then dried on a hot plate at 80 ° C. It was repeated 2 ~ 3 times so as to apply the gas sensing material between the electrode and the electrode.

The characteristics of the expiratory sensor were evaluated at 85-95 RH% relative humidity, similar to that of the human mouth. H ₂ S, known as the bad breath gas, was measured at gas concentrations of 5, 4, 3 , 2, and 1 ppm, respectively, and the characteristics were evaluated at a sensor operating temperature of 300 ° C. Sensitivity of the sensor was measured using Agilent's Model 34972A, which varies when each specific gas is flowed. The response to each gas (Response: change in R _gas / R _air resistance, R _air : Resistance, and R _gas : resistance at the time of flowing the measuring gas).

The metal oxide nanofibers having a multi-pore distribution structure manufactured by the polymer bead templating method can adsorb gas on a wider surface, and also actively diffuse gas through the pores to detect gas emitted through exhalation Can be applied to a high sensitivity expiratory sensor. Specifically, hydrogen sulfide (H ₂ S) gas contained in human exhalation is known as the main gas causing bad breath. If the hydrogen sulfide gas is analyzed precisely, it is possible to judge the presence or absence of bad breath and to judge whether or not the treatment is possible.

FIG. 11 is an example of evaluating the hydrogen sulfide gas sensing characteristics using the tungsten oxide nanofibers prepared in Examples 1 and 2 and Comparative Example 1. FIG. As shown in FIG. 11, tungsten oxide nanofibers including large pores and small pores fabricated using a polystyrene bead template exhibited remarkably improved hydrogen sulfide (Pb) compared to dense tungsten oxide nanofibers prepared without using a polystyrene bead template It can be confirmed that it represents the sensing characteristic. In addition, tungsten oxide nanofibers prepared by mixing polystyrene bead templates having diameters of 200 nm and 500 nm in diameter compared to tungsten oxide nanofibers produced using polystyrene bead templates having a diameter of 200 nm were found to have higher hydrogen sulfide It can be confirmed that it represents the sensing characteristic. This enhanced sensing property can be expected because the pores formed during the removal of the polystyrene bead template at a high temperature are effectively developed to increase the surface area where the gas can react and to provide a diffusion space in which the gas can effectively penetrate . In addition, by deriving the results that can obtain excellent sensor characteristics in a sensing material having a wide pore distribution, it is possible to use two kinds of polymer beads having different sizes, rather than using one size of polymer beads, It is more preferable to produce a metal oxide nanofiber sensor having a metal oxide nanofiber.

Claims (18)

(a) preparing an electrospinning solution by dissolving a metal oxide precursor and a polymer together in a solution in which a polymer bead sacrificial layer template is dispersed;
(b) electrospinning the prepared electrospinning solution to form conjugate fibers bound to the inside and the surface of the metal oxide precursor / polymer composite nanofiber by the polymer bead sacrificial layer template; And
(c) heat treating the metal oxide precursor / polymer composite nanofiber including the polymer bead sacrificial layer template to remove the polymer bead sacrifice layer template, and the metal oxide precursor is oxidized to simultaneously contain the micropores and the macropores A step of forming a metal oxide nanofiber having a multi-pore distribution structure
Lt; / RTI >
The micropores and the macropores are formed by (1) a polymer bead sacrificial layer template having different diameters, or (2) when the polymer bead sacrificial layer template is mixed with different kinds of polymers, Or (3) when the polymer bead sacrificial layer template has the same diameter, the metal oxide precursor / polymer composite nanofiber may have the same effect as that of the metal Wherein the metal oxide nanofibers are produced by binding to a domain containing a large amount of oxide precursor or a domain having a high content of the polymer. The method according to claim 1,
Wherein the polymeric bead sacrificial layer template is fabricated through electrospinning using at least one polymer selected from the group consisting of a ball structure, a hexagonal shape, a pentagonal shape, a quadrangular shape, and a triangular shape, and the metal oxide nanofibers having a multi- Way. The method according to claim 1,
Wherein the polymeric bead sacrificial layer template has a size distribution in the range of 50 nm to 500 nm. The method according to claim 1,
The micropores have a size range of 1 to 50 nm,
Wherein the macropores have a size range of 100 to 500 nm. ≪ RTI ID = 0.0 > 21. < / RTI > The method according to claim 1,
Wherein at least one of the diameter and the circumference of the metal oxide nanofiber having the multi-pore distribution structure has a size range of 100 nm to 2 占 퐉. The method according to claim 1,
Wherein the metal oxide nanofiber having the multi-pore distribution structure includes a crater-like surface uneven structure formed at the time of thermal decomposition of the polymer bead sacrifice layer template. Way. The method according to claim 1,
The polymeric bead sacrificial layer template may be formed of at least one polymer selected from the group consisting of polymethylmethacrylate (PMMA), polyvinylpyrrolidone (PVP), polyvinyl acetate (PVAc), polyvinyl alcohol (PVA), polystyrene (PS), and polyacrylonitrile PAN), and polyvinylidene fluoride (PVDF). The method of manufacturing a metal oxide nanofiber having a multiple pore distribution structure according to claim 1, The method according to claim 1,
The metal oxide nanofibers having the multi-pore distribution structure may be selected from the group consisting of 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, Cr 3 O 4, CeO} 2, Pr 6 O 11, Nd 2 O 3, Sm 2 O 3, Eu 2 O 3, Gd 2 O 3, Tb 4 O 7, Dy 2 O 3, Ho 2 O 3, _{Er 2 O 3, Yb 2 O} 3, Lu 2 O 3, 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, LiCoMnO 4, Ag 3 PO 4, BaTiO 3, NiTiO 3, SrTiO 3, Sr 2 Nb 2 O 7 and Sr ₂ Ta ₂ O _{7, Ba 0.5 Sr 0.5 Co 0.8} Fe 0.2 O metal oxide nano-fiber having a multi-pore distribution structure according to any one or characterized in that the at least one complex selected from the group consisting of _3-7 method. The method according to claim 1,
(d) fabricating a gas sensor including the metal oxide nanofibers having the multi-pore distribution structure as a sensing material
Wherein the metal oxide nanofibers have a multi-pore distribution structure. The method according to claim 1,
(e) coating the metal oxide nanofibers having the multi-pore distribution structure on a sensor substrate capable of recognizing the change in resistance to remove biomarker gas (oxidizing gas: NO ₂ , NO, reduction, Step of producing a semiconductor type gas sensor so as to be able to detect gas: H ₂ , CO, C ₂ H ₅ OH, H ₂ S, CH ₄ )
Wherein the metal oxide nanofibers have a multi-pore distribution structure. The method according to claim 1,
Wherein the metal oxide nanofibers having the multi-pore distribution structure have at least one of a cylindrical structure and a plate-like structure. The method according to claim 1,
The sizes of the micropores and the macropores formed from pyrolysis of the polymer bead sacrificial layer template are thermally shrunk to the range of 20% to 60% of the size of the beads of the polymer used, and the metal having the multi- Wherein the metal oxide nanofibers are distributed on the inside and the surface of the oxide nanofibers. The method according to claim 1,
Wherein the polymer bead sacrificial layer template is a polymer having a glass transition temperature of 20 ^o C to 200 ^o C. delete delete delete delete delete

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