KR20170044979A - Metal oxide compoties nanotubes including multiple pores and nanocatalysts, fabrication method for preparing the same, and gas sensor comprising the same - Google Patents
Metal oxide compoties nanotubes including multiple pores and nanocatalysts, fabrication method for preparing the same, and gas sensor comprising the same Download PDFInfo
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- G01N27/403—Cells and electrode assemblies
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Abstract
The present invention relates to a porous metal oxide nanotube to which a nanoparticle catalyst is bound, a process for producing the same, and a gas sensor including the same. More particularly, the present invention relates to a method for preparing a porous metal oxide nanotube having a plurality of pores by using an electrospinning method using a dual nozzle and a thermally decomposable sacrificial layer polymer bead template, wherein a metal oxide precursor and a polymer And can be produced using dissolved electrospinning solution. Further, when the nanoparticle catalyst is further dispersed in the spinning solution during the electrospinning of the dual nozzle, porous metal oxide nanotubes to which catalyst particles are bound can be produced. Wherein the plurality of pores formed are connected to the inner pores of the metal oxide nanotubes and the outer pores and the nanoparticle catalyst is uniformly distributed on the surface of the porous metal oxide nanotubes. To provide a method for manufacturing oxide nanotubes. The porous metal oxide nanotube to which the catalyst is bound can be applied to a high sensitivity expiration sensor and an excellent harmful environment sensor through effective surface gas reaction, smooth gas penetration and diffusion due to improved pores, surface area and catalytic effect by nanoparticles.
Description
The present invention relates to metal oxide composite nanotubes including a plurality of pores and nanocatalysts at the same time, a method for producing nanotubes, and a sensor for analyzing harmful environmental gases and exhaled gas including nanotubes. More particularly, the present invention relates to a method for forming a plurality of pores on the surface of a metal oxide composite nanotube fabricated by electrospinning using a dual nozzle and functioning as a catalyst, and more particularly, to a method for producing a polymer / metal oxide precursor A template polymer and a nanocatalyst that do not dissolve in the spinning solution together with the spinning solution are dispersed and electrospinning is performed and then the template polymer is removed in a subsequent heat treatment process so that a plurality of pores and a nano- A method for manufacturing a sensing material for a high sensitivity, high selectivity gas sensor is provided.
In order to develop a highly sensitive gas sensor, various attempts have been made to develop a structure that maximizes the surface area by using various metal oxide nanomaterials and includes a large number of pores in the metal oxide nanomaterial to facilitate gas infiltration. Basically, a gas sensor using a metal oxide sensing material is adsorbed on the surface of the atmosphere, and by evaluating the electrical resistance change characteristics by reacting with ionized oxygen (O - , O 2- ) and a target gas to be detected Loses. Since this reaction occurs on the surface of the sensing material, a material having a large surface area and a high porosity should be used to improve the sensing characteristics of the metal oxide gas sensor. For this reason, studies have been conducted on the synthesis of metal oxide sensing materials having various nanostructures such as nanoparticles, nanotubes, and nanowires, and various studies have been conducted actively on the influence of the improvement of surface area and porosity on the sensor characteristics .
In recent years, electrospinning technology that can easily fabricate a one-dimensional nanofiber structure has been actively applied to gas sensor research. Synthesis of metal oxide nanofibers begins with the preparation of electrospinning solution. The electrospinning solution is prepared by dissolving together a polymer capable of dispersing in a specific solvent and a metal oxide precursor (metal salt) for forming a metal oxide. When the electrospinning solution thus prepared is put into a syringe pump and pushed to a certain discharge amount and a high voltage is applied between the nozzle attached to the syringe pump and the current collector, the spinning solution is collected at the top of the collector in the form of nanofiber . The collected nanofibers are subjected to high temperature heat treatment to remove polymer components, and the metal oxide precursor can be oxidized at high temperatures to form metal oxide nanofibers. In order to develop a sensitive gas sensor sensing material, it is necessary to have a high specific surface area and an improved porosity as described above. From this point of view, a pore-type nanotube structure in which the central portion of the nanofiber is empty is presented, and an improved gas sensing characteristic in the nanotube structure has been reported. Typically, a method of developing a metal oxide-based nanotube sensing material includes physical vapor deposition (PVD), chemical vapor deposition (CVD), and chemical vapor deposition ) Or atomic layer deposition (ALD) method, the polymer nanofiber outer surface is coated with a metal or metal oxide material, and then subjected to a high-temperature heat treatment process to remove the inner polymer nanofiber, A method of oxidizing the oxide layer to develop a metal oxide nanotube structure has been proposed. In addition, since the core / shell structure can be easily fabricated by electrospinning using dual nozzles, the nanotube structure can also be fabricated without using physical vapor deposition, chemical vapor deposition, or atomic layer deposition methods It can be easily produced. Specifically, as a core spinning solution, a polymer or oil which is easily decomposed at high temperature is used, and as a shell spinning solution, a metal oxide precursor / polymer mixed solution is used, so that a nanotube structure can be formed after high temperature heat treatment do. However, although the nanotube structure having a dense outer wall has a specific surface area, the nanotube structure has a structure that diffuses gas to the inside of the nanotube and does not easily cause a reaction on the surface, so that it may have a limit to exhibit high sensitivity characteristics. In particular, in the case of a one-dimensional tube structure, open structure design capable of rapid diffusion of gas into the inner layer is important because gas diffusion is possible through longitudinal openings in order to penetrate into the inner layer.
In addition to improving the surface area and porosity of metal oxides, studies have been conducted to bind precious metal catalysts as a method for improving the properties of metal oxide based gas sensors. For example, it has been reported that when a noble metal catalyst such as gold (Au), platinum (Pt), silver (Ag), and palladium (Pd) is combined with a metal oxide material, gas sensor characteristics are greatly improved. Particularly, it has been reported that noble metal catalysts bound to metal oxides should be very small in size of several nanometers, and evenly dispersed without being agglomerated on the metal oxide surface, thereby maximizing the catalyst characteristics. Since these experimental results have been derived, various nanocatalyst synthesis methods have been suggested, and improved gas sensor characteristics have been suggested when complexed with metal oxides.
Gas sensor applications based on metal oxide semiconductors on which catalysts are bound include precise analysis of volatile organic compounds emitted from the human body's exhalation as well as environmental sensors for monitoring the harmful environment in the atmosphere, Research and development on an exhalation sensor for diagnosing is being actively carried out. In particular, volatile organic compounds such as acetone, toluene, isoprene and pentane, known as biomarkers of certain diseases, have a considerably larger size compared to the atmospheric environment's harmful gases (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 inside the sensing material. When these pores have a size of 100 nm or more, diffusion of fast gas molecules can be expected, and a new edge surface can be formed due to the formation of pores, so that the surface area can be increased. It is also important to synthesize structures with mesopores in the size range of 2 nm to 50 nm in order to increase the reactivity between the sensing material and the gas.
Accordingly, a metal oxide nanomaterial having a porous structure that facilitates diffusion of a target gas and having a high specific surface area capable of causing an effective surface reaction can be developed. At the same time, the nanocatalyst can be effectively bound to the surface, It is necessary to develop a process that can produce materials. Particularly, a process technology capable of easily fabricating metal oxide composite nanotubes containing multiple pores and a nanoparticle catalyst simultaneously in a single electrospinning process without introducing a physical or chemical deposition method on the surface of the polymer nanofibers .
SUMMARY OF THE INVENTION An object of the present invention is to provide a method of forming a plurality of pores having a size of tens to hundreds of nanometers on the surface of metal oxide nanotubes by electrospinning using a dual nozzle capable of easily fabricating a core / shell structure, (Nanoparticle catalyst-porous metal oxide composite nanotubes) having nanoparticle catalyst-functionalized porous metal oxide composite nanotubes of the type in which a particle catalyst is further ligated.
It is another object of the present invention to provide a method for producing a metal oxide precursor, which comprises using an electrospinning method using a dual nozzle, wherein oil which is easily decomposed at high temperature is used as a spinning solution in a core, / Polymer composite spinning solution is used to form a core / shell composite structure after electrospinning, the oil located in the core is decomposed and removed through a high-temperature heat treatment process, and the metal oxide precursor salt located in the shell is oxidized to form a metal oxide nanotube Lt; RTI ID = 0.0 > structure. ≪ / RTI >
It is another object of the present invention to provide a polymer bead which comprises polymer beads in an electrospinning solution forming a shell by using a polymer bead which is easily decomposed at a high temperature to conduct electrospinning using a dual nozzle, And a method of manufacturing a metal oxide nanotube including pores having a size similar to or smaller than the size of a polymer bead through thermal decomposition of beads.
It is another object of the present invention to provide a nanoparticle catalyst which comprises a nanoparticle catalyst in an electrospinning solution forming a shell to conduct electrospinning using a dual nozzle and then subjecting the polymer bead to thermal decomposition Porous metal oxide nanotubes having uniformly functionalized (bound) surfaces on the surfaces of the porous metal oxide nanotubes formed through the porous metal oxide nanotubes.
It is another object of the present invention to provide a highly sensitive noxious environmental gas detection sensor and an expiratory flow sensor using nanoparticle catalyst-porous metal oxide composite nanotubes as a sensing material.
In order to produce porous metal oxide nanotubes to which a nano catalyst is bound, which is an aspect of the present invention, a metal oxide precursor and a polymer having a high viscosity are added to a solution in which a sacrificial layer template (spherical polymer bead) After dissolving, the oil is easily decomposed in the core at high temperature using the dual nozzle electrospinning technology, and the core / shell is formed by using the metal oxide precursor / polymer composite spinning solution having the sacrificial layer template and the nanocatalyst simultaneously dispersed in the shell. After the formation of the structure, the sacrificial layer template is removed by a subsequent heat treatment process to form a plurality of pores on the surface of the metal oxide nanotube, and nanoparticle catalyst-porous metal oxide composite nanotubes to which the nanocatalyst particles are bound are prepared .
In one embodiment, the electrospinning solution of the core may be a mixed solution comprising a polymer material, and may be a sacrificial layer template that can be easily decomposed during heat treatment at a high temperature, such as mineral oil.
In one embodiment, the sacrificial layer template may have a diameter of 200 nm, and the sacrificial layer template material may be a polymer (polymethylmethacrylate (PMMA), polyvinylpyrrolidone (PVP), polyvinyl acetate (PVAc) May be a template that can be removed through a high temperature heat treatment such as polyvinyl alcohol (PVA), polystyrene (PS) and polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF) . The size (diameter) of the sacrificial layer template can be freely adjusted in the range of 50 nm to 1 μm. Since the sacrificial layer template is accompanied by a shrinkage process in the heat treatment process of the composite nanofiber and is thermally decomposed and removed, it is possible to simultaneously manufacture the sacrificial layer template including the sacrificial layer template having various size ranges. In this case, metal oxide nanotubes having different average pore sizes can be produced.
In one embodiment, the nanocatalyst particles may be prepared by methods such as polyol synthesis, hydrothermal synthesis, solvothermal synthesis, mechanical powder milling, and synthesis using a ferritin (virus) .
In another aspect of the present invention, there is provided a method for manufacturing a nanocatalyst-bound porous metal oxide nanotube, comprising: (a) simultaneously dissolving a metal oxide precursor and a polymer in a solution in which a sacrificial layer template and a nanocatalyst are dispersed, And a core spinning solution using mineral oil; (b) forming a shell (a sacrificial layer template and a metal oxide precursor / polymer) composite nanofiber wrapping the core (mineral oil) through the dual nozzle electrospinning with the prepared core / shell spinning solution ; And (c) removing the sacrificial layer template and the mineral oil by heat treatment of the metal oxide precursor / polymer composite core / shell nanofibers on which the sacrificial layer template and nanocatalyst particles are bound at a high temperature to oxidize the metal oxide precursor, To form the porous metal oxide composite nanotubes to which the catalyst is bound.
According to the embodiments of the present invention, a composite nanofiber having a core (mineral oil) / shell (metal oxide precursor / polymer bonded with a sacrificial layer template and nanocatalyst particles) is formed through electrospinning using a dual nozzle The nanoparticle catalyst-porous metal oxide composite nanotubes may be prepared by forming porous metal oxide nanotubes containing a plurality of pores through heat treatment and simultaneously binding the nanotubes to the surfaces of the metal oxide nanotubes.
By further forming a plurality of pores in the nanotube surface and to be manufactured by using this increased the metal oxide nanotube structure surface area, using the sacrificial layer template dual nozzle electrospinning process, the oxidizing 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 into the metal oxide nanotube, And a catalyst-porous metal oxide composite nanotube structure capable of exhibiting a highly sensitive gas sensing property by exhibiting an excellent catalytic effect by further binding the nano catalyst can be manufactured.
The catalyst-porous metal oxide composite nanotube sensing material can be used as an environment sensor for detecting harmful gas and an exhaled breath detection sensor material for disease diagnosis.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a conceptual view of a catalyst-porous metal oxide composite nanotube prepared by dual nozzle electrospinning of a polymer bead template and a nanocatalyst for explaining one embodiment of the present invention.
2 is a schematic diagram for explaining a dual nozzle electrospinning technique used in one embodiment of the present invention.
3 is a flowchart illustrating a process for fabricating a catalyst-porous metal oxide composite nanotube in which spinning solution containing a polymer bead template and a nanocatalyst according to Example 1 of the present invention is synthesized by a dual nozzle electrospinning method.
4 is a scanning electron microscope (SEM) photograph of a polystyrene bead template of 200 nm size used to fabricate a tungsten oxide precursor / polymer composite nanofiber structure with palladium nanocatalyst particles and a polystyrene bead template bonded according to Example 1 of the present invention to be.
5 is a transmission electron microscope (TEM) photograph of palladium catalyst nanoparticles used for preparing a tungsten oxide precursor / polymer composite nanofiber structure in which palladium nanocatalyst particles and a polystyrene bead template are bound according to Example 1 of the present invention.
FIG. 6 is a graph showing the relationship between the diameter of the core / shell nano-particles having a 200 nm diameter polystyrene bead template and the palladium nanocatalyst particles obtained according to Example 1 of the present invention formed with a composite of a tungsten oxide precursor / It is a scanning electron microscope (SEM) photograph of the fiber structure.
FIG. 7 is a graph showing the relationship between the particle diameter of the core / shell nano-particles of the present invention and the core / shell nano- It is an enlarged scanning electron microscope (SEM) photograph of the fiber structure.
FIG. 8 is a graph showing the relationship between the particle size distribution of the core / shell nano-particles having a 200 nm diameter polystyrene bead template and palladium nanocatalyst particles obtained according to Example 1 of the present invention formed with a composite of a tungsten oxide precursor / (SEM) photographs of porous tungsten oxide nanotubes to which palladium particles obtained after heat treatment at a high temperature of a fiber structure are bonded.
FIG. 9 is a graph showing the results of a comparison between a core / shell having mineral oil formed therein and a core / shell formed by forming a polystyrene bead template having a diameter of 200 nm and a tungsten oxide precursor / (SEM) photographs of porous tungsten oxide nanotubes obtained after heat treatment of the nanofiber structure at a high temperature.
FIG. 10 is a graph showing the results of measurement of a core / shell nanofiber structure having mineral oil formed on its inner core, without forming a palladium nanocatalyst obtained according to Comparative Example 2 of the present invention and a polystyrene bead template without a tungsten oxide precursor / (SEM) photographs of the present invention.
11 is a view showing a core / shell nanofiber structure in which a shell composed of a composite of tungsten oxide precursor / polymer is formed without containing the palladium nano catalyst and polystyrene bead template obtained according to Comparative Example 2 of the present invention, Is a scanning electron microscope (SEM) photograph of a dense structure tungsten oxide nanotube obtained after heat treatment at a high temperature.
Fig. 12 is a graph showing the results of measurement of the average particle diameter of the porous tungsten oxide nanotube, the porous tungsten oxide nanotube, and the palladium nanocatalyst particle obtained without binding of the palladium nanocatalyst particles obtained in Example 1, Comparative Example 1 and Comparative Example 2, (H 2 S) sensing characteristics at 450 ° C of gas sensors using a dense tungsten oxide nanotube fabricated without the polystyrene bead template.
The porous metal oxide nanotubes to which the catalyst nanoparticles are bound may include pores connecting the inner pores of the nanotubes and the outer pores.
The metal oxide nanotubes containing multiple pores can be synthesized by electrospinning using a dual nozzle. As a method for forming pores connecting the inner pores and the outer pores of the metal oxide nanotube, there is a method of polymer bead templating Can be used. In addition, as a method for deriving excellent gas sensing characteristics, metal oxide nanotubes can be produced in which the nanoparticle catalyst is uniformly bound to the surface by further including catalyst nanoparticles during the dual nozzle electrospinning process.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a porous metal oxide nanotube to which catalyst nanoparticles are bound according to one embodiment of the present invention (001). As shown in FIG. 1, the porous metal oxide nanotubes to which the catalyst nanoparticles were bound were fabricated using dual nozzle electrospinning and had a one-dimensional structure (002). In the dual nozzle electrospinning process, The solution can be easily disassembled and removed, and the inside of the tube can be subjected to a high temperature heat treatment to have an empty nanotube structure (003). In addition, in the dual nozzle electrospinning process, after the sacrificial layer template beads are further included in the shell solution to perform electrospinning, the sacrificial layer template is decomposed at a high temperature to form a plurality of pores on the surface of the metal oxide . Here, if the size of the sacrificial layer polymer beads is 200 nm, pores having a size of 100 nm - 180 nm (diameter) smaller than that of the used sacrificial layer polymer beads can be formed. The shape of the pores may form pores connecting the inner pores of the nanotubes with the outer pores (004), and may form pores outside the inner pores of the nanotubes without connecting the outer pores (005). In order to form the pores connecting the inner pores and the outer pores of the metal oxide nanotube, a sacrificial layer polymer template having a larger size such as 500 nm or 1 μm can be used. In addition, when electrospinning is performed by further containing catalyst nanoparticles in the shell solution in the dual nozzle electrospinning process, the metal nanocatalyst can be uniformly bound to the surface of the porous metal oxide nanotube after an additional high temperature heat treatment process (006 ).
FIG electrospinning apparatus with a dual-nozzle shown in Figure 2, if the plastic syringe to hold the electrospinning solution (Henke-Sass Wolf, 20 ml NORM-JECT), can perform a dual-nozzle electrospinning dual nozzle (Inovenso TM that A DC power supply capable of applying a high electric field, a current collector, and a syringe pump capable of discharging an electrospinning solution. A one-dimensional composite nanofiber shape of the core / shell structure is manufactured (100) using a dual nozzle electrospinning device, and metal oxide nanotubes can be manufactured through high temperature heat treatment. Here, the spinning solution for the core and the shell can be synthesized differently, and the solution of the core is easily decomposed at high temperature (101), and the solution of the shell is spinning solution containing the metal oxide precursor / polymer (111), a metal oxide nanotube can be formed after high-temperature heat treatment. Also, dispersing the sacrificial
If the electrospinning solution of the core and the shell are placed in different syringes and a high voltage is applied between the dual nozzle attached to the syringe and the current collecting substrate (when a high voltage is applied) while discharging at different discharging speeds, The metal oxide precursor / polymer composite core / shell nanofiber structure in which the template beads are bound to the surface can be produced. In a metal oxide precursor / polymer composite core / shell nanofiber structure in which catalyst nanoparticles and sacrificial layer template beads are bound to the surface, a one-dimensional core / shell nanofiber structure is formed from a metal oxide precursor / polymer mixture solution ), The sacrificial layer template beads may be irregularly bound (202) to the surface of the one-dimensional core / shell nanofiber structure, and the catalyst nanoparticles may have a one-dimensional structure of the metal oxide precursor / polymer
A method for preparing a dual-nozzle electrospinning solution for forming porous metal oxide nanotubes with catalytic nanoparticles is mainly composed of core spinning solution preparation and shell spinning solution preparation. The core spinning solution is a solution which can be easily decomposed during the high temperature heat treatment process, but it does not limit the specific solvent if the solution is not easily mixed with the shell spinning solution. For example, mineral oil and the like may be used. The shell spinning solution can be obtained by dissolving the metal oxide precursor and the 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 possible to oxidize the metal salt at a high temperature, such as 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, Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-7 Or a metal oxide composed of one or more of these metals.
The method of forming the pores using the sacrificial layer template can further perform dual nozzle electrospinning by further dispersing the polymer template beads in the electrospinning solution in which the polymer and the metal oxide precursor are dissolved together. It is important to select polymers that are insoluble in the electrospinning solution.
In addition, the catalyst nanoparticles can be additionally dispersed in the shell electrospinning solution to perform dual nozzle electrospinning. A nanoparticle catalyst means a metal or non-metal nanoparticle that is not dissolved in a shell electrospinning solution, and does not limit the specific catalyst material. For example, the catalyst nanoparticles may be selected from Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Os, Ir, Pt, Au, Si, and Ge.
The core / shell spinning solution may be discharged through dual nozzle electrospinning to form a metal oxide precursor / polymer composite core / shell nanofiber structure in which catalyst nanoparticles and sacrificial layer template are bound. Then, all the polymer components constituting the composite core / shell nanofiber structure are decomposed and removed in a high-temperature heat treatment process, and the metal oxide precursor salts are oxidized to form polycrystalline metal oxide nanotubes. At this time, the polymer bead template is also removed, leaving pores having a size similar to the size of the beads on the surface of the nanotube. In fact, when the shrinkage process of the polymer bead is accompanied by the heat treatment process, pores having a size smaller than that of the initial bead are formed.
The sacrificial layer template may include polymers and proteins and does not limit the template surface specific material that is removed during the high temperature heat treatment after 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 rectangle, or a triangle. If the template can be used to form pores on the surface of the metal oxide nanotube by heat treatment, Do not.
The diameter of the sacrificial layer template may be 50 nm to 1 탆, and the template having a size within this range may be included in the electrospinning solution without any specific size limitation.
The core / shell spinning solution can easily form a core / shell nanofiber structure by applying a high voltage between the nozzle attached to the syringe and the current collecting substrate while discharging the spinning solution in different syringes at different discharge speeds. At this time, the size of the nozzle of the shell spinning solution is larger than the diameter of the sacrificial layer template so that the sacrificial layer template does not block the nozzle during dual spinning. In the dual nozzle electrospinning discharge rate, the core spinning solution must emit slower than the shell spinning solution to form the nanofiber structure of the core / shell structure. For example, the ejection speed of the core spinning solution can be set in the range of 1 μL / min to 50 μL / min, and the shell spinning solution can be ejected at a rate of 10 μL / min to 500 μL / min faster than the core spinning solution Can be achieved.
When performing electrospinning using a dual nozzle, the voltage applied between the dual nozzle and the current collector may be between 10 kV and 50 kV.
The diameter of the tungsten oxide precursor / polymer composite nanofiber having a core / shell structure in which the catalyst nanoparticles formed through dual nozzle electrospinning and the sacrificial layer template are bonded can be formed in the range of 500 nm to 5 μm. Preferably in the range of 150 nm to 2 占 퐉.
In the tungsten oxide precursor / polymer composite nanofiber structure in which the catalyst nanoparticles formed by dual nozzle electrospinning and the sacrificial layer template are bound, the sacrificial layer template is bound to the surface, and the metal oxide precursor / polymer composite fiber is in the form of a web Lt; / RTI >
In a tungsten oxide precursor / polymer composite nanofiber structure in which the catalyst nanoparticles formed through dual nozzle electrospinning and the sacrificial layer template are bound, the catalyst nanoparticles may have a size of 1 nm to 20 nm.
The tungsten oxide precursor / polymer composite nanofiber structure in which the catalyst nanoparticles formed by dual nozzle electrospinning and the sacrificial layer template are bonded has not only a nanofiber structural shape of the core / shell but also a core / Nanotube structures or irregular nanofiber structures.
In the case of conjugated fibers having the structure of the most common cylindrical core (mineral oil) / shell (metal oxide precursor / polymer) structure, the diameter of the core may range from 400 nm to 4 μm and the diameter of the shell may range from 500 nm to 5 μm And the thickness of the formed shell may be 50 nm to 1 μm.
By subjecting the sacrificial layer template and the polymer to heat treatment at a high temperature, metal oxide nanotubes having a large number of pores can be produced. The heat treatment process can be performed at temperatures 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 5 ° C / min and can proceed to a cooling rate of 5 ° 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.
As a result of the heat treatment at high temperature, the diameter of the tungsten oxide precursor / polymer composite nanofiber structure formed by the catalyst nanoparticles formed through the dual nozzle electrospinning and the sacrificial layer template can be shrunk to the range of 300 nm to 1 μm .
In the tungsten oxide precursor / polymer composite nanofiber structure in which the catalyst nanoparticles and the sacrificial layer template are bonded, the pores formed by the sacrificial layer template may be shrunk during the pyrolysis process, and the size of the shrunk pores may be larger than the size of the polymer beads It may have a shrinkage ratio of about 5/10 to 9/10.
The pores formed through the heat treatment process may be equal to or smaller than the size of the sacrificial layer template, and may have a size range of preferably 1 nm to 500 nm. In addition, the formed pores may exhibit a circular structure, and the sacrificial layer template may aggregate to have pores of an elliptical structure stretched in the longitudinal direction. The formed pores connect the inner pores of the metal oxide nanotube with the outer pores, and the cross-section exposed to the surface by the formed pores may have an effect of increasing the overall surface area of the metal oxide nanotube. Because of the pores generated in the process of removing the sacrificial layer beads from the surface of the metal oxide natto tube, pores having the same shape as a hole opened two-dimensionally are formed.
3 is a flowchart illustrating a process for fabricating porous metal oxide nanotubes to which catalyst nanoparticles are bound using catalyst nanoparticles and sacrificial layer templating method using dual nozzle electrospinning according to Embodiment 1 of the present invention. A method of manufacturing porous metal oxide nanotubes to which catalyst nanoparticles are bound, which is another aspect of the present invention, may include the following steps. Here, steps 301 to 303 show a process for preparing porous metal oxide nanotubes to which catalyst nanoparticles are bound, and step 304 is a step for preparing porous metal oxide nanotubes To thereby produce a semiconductor type gas sensor.
(a) preparing (301) a sacrificial layer polymer bead template, a solution in which catalyst particles are dispersed, a shell spinning solution in which a metal oxide precursor and a polymer are dissolved, and a core spinning solution composed of a mineral oil;
(b) using the dual-nozzle electrospinning method, the prepared core / shell electrospinning solution is mixed with the sacrificial layer polymer bead template and the core (mineral oil) / shell (metal oxide precursor / polymer) composite nanofiber structure (302);
(c) The prepared core / shell composite nanofibers are heat treated at a high temperature to remove the sacrificial layer polymer bead template and the oil, and the metal oxide precursor is oxidized to form a porous nanotube (303), < / RTI > and
(d) A porous metal oxide nanotube having a catalyst attached thereto is coated on a sensor substrate capable of recognizing a change in resistance, thereby forming a biomarker gas (oxidizing gas: NO 2 , NO, reduction (304) a semiconductor type gas sensor capable of detecting gases (H 2 , CO, C 2 H 5 OH, H 2 S, CH 4, etc.);
The porous metal oxide nanotube-based gas sensor formed by the above-mentioned method has a high porosity and an effective catalytic effect, so that the gases move rapidly, and the pores formed by using the sacrificial layer template form a cross- To enhance the surface area, and it is possible to have a high sensitivity by activating the reaction on the surface by enlarging the surface electron-rich layer.
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: Palladium nanocatalyst particles and polymer Bead Template The palladium particles prepared using Concluded Porous tungsten oxide (WO 3 Manufacture of nanotubes.
0.25 g of polyvinyl pyrrolidone (PVP) (Aldrich) having a molecular weight of 1,300,000 g / mol and 0.2 g of ammonium metatungstate hydrate (Aldrich) as a precursor of tungsten oxide were mixed with 0.2 g of polystyrene dispersed polystyrene It dissolves 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 spherical structure of 200 nm is dispersed in water. Further, palladium nanoparticles having a size of 5 nm or less are further dispersed in the mixed solution. The content of palladium nanoparticles is maintained at 0.1 wt% with respect to the tungsten oxide finally produced through heat treatment, thereby maximizing catalytic activity.
The palladium nanocatalyst particles and the polystyrene bead-added tungsten oxide precursor / polymer blend solution are used as a shell solution in the dual nozzle electrospinning method. Mineral oil is used as the core solution. The two core / shell solutions were placed in respective syringes and connected to a syringe pump (Henke-Sass Wolf, 20 ml NORM-JECT), the core solution was pushed out at a discharge rate of 10 μl / min, The solution is pushed out at a discharge rate of 100 μl / min. The dual nozzles to be ejected are arranged in a concentric circular form, and a dual nozzle (Inovenso TM ) having a core nozzle diameter of 0.8 mm and a shell nozzle diameter of 1.6 mm is used. A voltage of 30 kV is applied between the dual nozzle and the collector substrate to obtain a nanofiber web of composite core / shell structure to prepare a metal oxide precursor / polymer composite nanofiber structure web having the palladium catalyst particles and the polystyrene template surface-bonded .
In the metal oxide precursor / polymer composite nanofiber structure in which the palladium catalyst particles and the polystyrene template are surface-bonded, the palladium catalyst nanoparticles are synthesized by polyol synthesis, hydrothermal synthesis, solid phase synthesis, mechanical powder milling and sacrificial layer template synthesis And the like. FIG. 4 is a scanning electron microscope photograph showing the palladium nanoparticle catalyst prepared in the present invention, and it can be confirmed that it has a size distribution of 5 nm or less.
In the metal oxide precursor / polymer composite nanofiber structure in which the palladium catalyst particles and the polystyrene template are surface-bonded, the polystyrene bead template is a material that can be decomposed upon heat treatment at a high temperature. The polystyrene bead template is a polygonal structure such as a ball structure, hexagonal, pentagonal, Shape. FIG. 5 is a scanning electron micrograph of the polystyrene of the ball structure used in the present invention, and it is confirmed that the polystyrene has an average diameter of 200 nm.
Scanning electron micrographs of the web of the metal oxide precursor / polymer composite nanofiber structure in which the palladium catalyst particles obtained by the electrospinning method and the polystyrene template were surface-bonded can be observed in FIG. 6, polystyrene beads having a diameter of 200 nm were uniformly bound to the surface of the tungsten oxide precursor / polymer composite nanofiber. In the enlarged scanning electron microscope photograph shown in FIG. 7, a shape in which polystyrene beads having a diameter of 200 nm are bound to the surface can be confirmed. The diameter of the formed tungsten oxide precursor / polymer composite nanofiber structure was found to be in the range of 500 nm to 5 μm. However, since the palladium catalyst particles bound to the surface have a very small size of 5 nm or less, they could not be confirmed by scanning electron microscopy. In addition, mineral oil injected into the nanofiber structure using the core solution can not be confirmed by scanning electron microscope photograph. Electrospinned tungsten oxide precursor / polymer composite nanostructures may have a nanobelt pattern during the formation process. In addition, the injection of the core mineral oil is uneven and may have an irregular shape. Specifically, the core mineral oil may be excessively injected to have a nanofiber structure protruding from the surface, and the core mineral oil may not be injected, so that the mineral oil may not penetrate into the nanofiber structure. In addition, injection of the shell mixed solution may be uneven and may have an irregular shape. Specifically, if the injection amount of the shell mixed solution is insufficient, an open nanotube structure can be formed after the heat treatment. From this point of view, it is possible to control the nanotube structure formed after the heat treatment by controlling the discharge amount of the shell solution.
The polystyrene bead template and the polymer are removed, and the tungsten oxide precursor is subjected to a heat treatment at a high temperature to oxidize the precursor. The high temperature heat treatment process was performed at 600 ℃ for 1 hour, and the temperature rise and fall temperature were kept constant at 5 ℃ / min. In FIG. 8, the heat-treated tungsten oxide nanotubes were shrunk to 300 nm to 1 μm in diameter. In the core / shell composite nanofiber structure, the mineral solution of the core portion was decomposed at high temperatures to form pores therein, As shown in Fig. Also, it can be seen that the polystyrene beads are removed on the surface, and the pores of the inner pores of the nanotubes and the outer pores are connected to each other. It can be seen that the formed pores have a diameter of 100 nm ~ 180 nm which is shrunk compared with the 200 nm polystyrene bead template used in the preparation of the electrospinning solution. The size of the shrunk pores is about 5/10 to 9/10 times larger than the polymer bead template used at the initial stage of polymerization because the polymer shrinks during the heating process and the tungsten precursor salt flows through the polymer. It can be confirmed that pores having a reduced size are formed. Similarly, palladium catalyst particles can not be observed by scanning electron microscopy because they have a very small size of 5 nm or less.
As described above, by forming the pores connecting the inside and the outside of the tungsten oxide, the gas to be measured can be easily injected into the nanotube. In the case of the nanotube having a dense outer wall developed conventionally, The nanotube having a large number of pores on its surface can actively react with the gas in a wider area to exhibit excellent gas sensing characteristics.
Comparative Example 1: polymer Bead Template Porous tungsten oxide (WO < RTI ID = 0.0 > 3 Manufacture of nanotubes.
In order to compare and evaluate the change of the gas sensing characteristics according to the palladium nanocatalyst particles, tungsten oxide nanotubes were synthesized using only the polymer beads as the template without the palladium nanocatalyst and used as a comparative example for testing the gas sensor .
In the core / shell electrospinning solution prepared in Example 1, the mineral oil solution of the core was used as it is, except that the palladium catalyst nanoparticles were removed from the mixed solution of the shell, Porous tungsten oxide nanotubes can be produced.
Specifically, 0.25 g of polyvinyl pyrrolidone (PVP) (Aldrich) having a molecular weight of 1,300,000 g / mol and 0.2 g of ammonium metatungstate hydrate (Aldrich) as a precursor of tungsten oxide were mixed with polystyrene Dissolve in 1.5 g of dispersed water. Polystyrene latex microspheres (Alfa Aesar) were prepared by dispersing 2.5 wt% of polystyrene with 200 nm ball structure in water.
The polystyrene bead-added tungsten oxide precursor / polymer blend solution is used as a shell solution in a dual nozzle electrospinning process. Mineral oil is used as the core solution. The two core / shell solutions were placed in respective syringes and connected to a syringe pump (Henke-Sass Wolf, 20 ml NORM-JECT), the core solution was pushed out at a discharge rate of 10 μl / min, The solution is pushed out at a discharge rate of 100 μl / min. The dual nozzles to be ejected are arranged in a concentric circular form, and a dual nozzle (Inovenso TM ) having a core nozzle diameter of 0.8 mm and a shell nozzle diameter of 1.6 mm is used. A voltage of 30 kV is applied between the dual nozzle and the current collecting substrate to obtain a composite core / shell structure nano-web to prepare a metal oxide precursor / polymer composite nanofiber structure web having a polystyrene template surface-bonded.
The polystyrene beads and the polymer are removed, and the tungsten oxide precursor is subjected to a heat treatment at a high temperature to oxidize the precursor. The high temperature heat treatment process was performed at 600 ℃ for 1 hour, and the temperature rise and fall temperature were kept constant at 5 ℃ / min. 9, the heat-treated tungsten oxide nanotube shrank to 300 nm to 1 μm in diameter. In the core / shell composite nanofiber structure, the mineral solution of the core portion was decomposed at a high temperature to form pores therein, As shown in Fig. Also, it can be seen that the polystyrene beads are removed on the surface, and the pores of the inner pores of the nanotubes and the outer pores are connected to each other. It can be seen that the formed pores have a diameter of 100 nm ~ 180 nm which is shrunk compared with the 200 nm polystyrene template used in the preparation of the electrospinning solution. The size of the shrunk pores is about 5/10 to 9/10 times larger than the polymer bead template used at the initial stage of polymerization because the polymer shrinks during the heating process and the tungsten precursor salt flows through the polymer. It can be confirmed that pores having a reduced size are formed. As a result, it can be confirmed that pure porous tungsten oxide nanotubes having no adhesion to the surface of the palladium catalyst nanoparticles are fabricated.
Comparative Example 2: Tungsten oxide of dense structure (WO 3 Manufacture of nanotubes.
In order to more clearly observe the effect of changing the microstructure of the tungsten oxide nanotubes including a plurality of pores prepared by the polymerizing method of the polymer beads, it is preferable to use a catalyst having a dense structure prepared without using palladium catalyst particles and polystyrene beads as templates Tungsten oxide nanotubes were synthesized and used as a comparative example for testing gas sensors.
In the core / shell electrospinning solution prepared in Example 1, the mineral oil solution of the core was used as it was, and the same spinning solution was synthesized except for the palladium nanocatalyst particles and the polystyrene bead template in the mixed solution of the shell, It is possible to produce a dense tungsten oxide nanotube having no nanoparticles and polystyrene beads.
Specifically, 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 dissolved in 1.5 g of pure water Lt; / RTI >
The tungsten oxide precursor / polymer blend solution is used as a shell solution in a dual nozzle electrospinning process. Mineral oil is used as the core solution. The two core / shell solutions were placed in respective syringes and connected to a syringe pump (Henke-Sass Wolf, 20 ml NORM-JECT), the core solution was pushed out at a discharge rate of 10 μl / min, The solution is pushed out at a discharge rate of 100 μl / min. The dual nozzles to be ejected are arranged in a concentric circular form, and a dual nozzle (Inovenso TM ) having a core nozzle diameter of 0.8 mm and a shell nozzle diameter of 1.6 mm is used. A voltage of 30 kV is applied between the dual nozzle and the current collecting substrate to obtain a composite core / shell structure nano-web to prepare a metal oxide precursor / polymer composite nanofiber structure web having a polystyrene template surface-bonded.
A scanning electron microscope photograph of the web of the metal oxide precursor / polymer composite nanofiber structure obtained by the above electrospinning method can be observed in FIG. In Fig. 10, it can be confirmed that the tungsten oxide precursor / polymer composite nanostructure exhibits a nanofiber shape. However, the inside of the nanofiber shape shows the core / shell structure by injecting mineral oil into the core through dual nozzle electrospinning. Likewise, the amount of mineral oil injected into the core may be uneven and may have an irregularly shaped core / shell nanofiber structure. The diameter of the formed tungsten oxide precursor / polymer composite nanofiber structure was found to be in the range of 500 nm to 5 μm.
The polymer is subjected to a heat treatment at high temperature to remove the tungsten oxide precursor and oxidize the tungsten oxide precursor. The high temperature heat treatment process was performed at 600 ℃ for 1 hour, and the temperature rise and fall temperature were kept constant at 5 ℃ / min. In FIG. 11, the heat-treated tungsten oxide nanotubes were shrunk to 300 nm to 1 μm in diameter. In the core / shell composite nanofiber structure, the mineral solution of the core portion was decomposed at high temperature to form pores therein, As shown in Fig. In particular, since tungsten oxide nanotubes were prepared without using polystyrene bead templates, it was confirmed that many pores were not formed on the surface, and as a result, tungsten oxide nanotubes having a dense outer wall structure were produced.
Therefore, through the above-described Example 1, Comparative Example 1, and Comparative Example 2, it was confirmed by 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, and the polystyrene bead template It is possible to obtain an effect that the penetration of gas is advantageous because a large number of pores are formed on the surface, and as a result, a large number of pores can effectively react with the inner surface of the nanotube, thereby widening the surface area. In addition, since the porous tungsten oxide nanotube structure was prepared in a very similar manner with and without palladium catalyst nanoparticles, it is possible to clearly observe how the gas sensor characteristics change depending on whether the catalyst is bound or not have.
Although the porous metal oxide nanotubes including tungsten oxide (WO 3 ) are used as an example in the above embodiments, it is possible to use a sacrificial layer template to limit the specific substance to metal oxide nanotubes that can be fabricated through dual nozzle electrospinning. I do not. 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
In addition, although porous metal oxide nanotubes including palladium (Pd) catalyst particles are mentioned as an example in the above embodiment, the present invention is not limited to specific materials as long as they are catalytic materials capable of binding to the surfaces of metal oxide nanotubes and serving as catalysts. For example, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, Catalyst particles further comprising at least one selected from Pt, Au, Si, and Ge, or two or more complexes may be bound to the surface of the metal oxide nanotube.
Experimental Example 1: Palladium nano-catalyst Concluded Porous tungsten oxide nanotubes, palladium nanocatalyst particles Settlement Porous tungsten oxide nanotubes and palladium nanocatalyst particles and polystyrene Bead Template Comparison of gas sensor characteristics of dense - structured tungsten oxide nanotubes fabricated without.
Using the porous tungsten oxide nanotubes with the palladium catalyst attached using the palladium catalyst nanoparticles prepared in Example 1 of the present invention and the polystyrene bead template, it is possible to detect the noxious gas in the surrounding environment or the volatile organic compounds The diagnostic gas sensor for the diagnosis of health condition by the concentration of compound gas (biomarker gas) was fabricated and its characteristics were analyzed. In addition, as shown in Comparative Example 1 and Comparative Example 2, it was confirmed that the porous porous tungsten oxide nanotubes prepared without using the palladium nanocatalyst particles and the porous porous tungsten oxide nanotubes having a dense structure without using both the palladium nanocatalyst particles and the polystyrene bead template Tungsten oxide nanotubes. The manufacturing process of the gas sensor is as follows.
An Au positive electrode having a thickness of 25 μm and a length of 345 μm is formed on a 3 mm 3 mm alumina (Al 2 O 3 ) substrate with an interval 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 substrate temperature was 450 ° C.
The tungsten oxide nanotubes prepared in Example 1, Comparative Example 1 and Comparative Example 2 were dispersed in a solvent to prepare a dispersion solution of tungsten oxide nanotubes, 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 a sensor electrode using a micropipette, followed by drying on a hot plate at 60 ° 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 in a dry environment similar to that of the room air, and the hydrogen concentration (H 2 S), known as bad breath gas, was changed to 20, 10, and 5 ppm, . Sensitivity of the sensor was measured using Agilent's Model 34972A, which varies when each specific gas is flowed. The response of 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 nanotube having a porous structure manufactured by the polymeric polystyrene bead templating method can not only adsorb a gas on a wider surface but also actively diffuse the gas contained in a living body And can exhibit high sensitivity characteristics for sensing the surface gas. Specifically, hydrogen sulfide (H 2 S) gas is classified as a harmful gas in the atmosphere and is known to be harmful to health when continuously inhaled. In addition, a trace amount of hydrogen sulphide gas contained in human exhalation is known as the main gas causing bad breath. By precisely analyzing the hydrogen sulfide gas, it is possible not only to analyze the harmful gas in the atmosphere, but also to judge the presence or absence of bad breath and to judge whether or not the treatment is possible.
FIG. 12 is an example of evaluating the hydrogen sulfide gas sensing characteristics using the tungsten oxide nanotubes prepared in Example 1, Comparative Example 1 and Comparative Example 2. FIG. As shown in FIG. 12, the porous tungsten oxide nanotubes fabricated by using the palladium nanocatalyst particles and the polystyrene bead template each had porous metal oxide nanotubes that did not use the palladium nanocatalyst, and both the palladium nanocatalyst particles and the polystyrene bead template It can be confirmed that the hydrogen sulfide-sensing property is remarkably improved as compared with the dense-structured tungsten oxide nanotubes produced without use. Specifically, porous metal oxide nanotubes without using the porous tungsten oxide nanotube palladium nanocatalyst prepared by using the palladium nanocatalyst particles and the polystyrene bead template, and the porous metal oxide nanotubes prepared without using both the palladium nanocatalyst particles and the polystyrene bead template It can be confirmed that the hydrogen sulfide detection characteristic is improved by about 2.4 times and 5 times, respectively, compared with the hydrogen sulfide concentration of 20 ppm at a driving temperature of 450 캜, as compared with a dense tungsten oxide nanotube. In addition, in the case of pure tungsten oxide nanotubes fabricated using polystyrene bead templates alone, the detection of hydrogen sulfide was improved by about 1.5 times compared with the dense structure of tungsten oxide nanotubes fabricated without polystyrene bead templates at the same temperature and the same hydrogen sulfide concentration Respectively. This enhanced sensing property can be expected because the pores formed during the removal of the polystyrene bead template at high temperature are 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, it can be expected that when palladium nanocatalyst particles are bound, the gas reaction is activated by inducing an excellent catalytic effect with improved specific surface area and porosity. In this way, in the fabrication of a metal oxide sensing material having a nanotube structure through electrospinning using a dual nozzle, a polystyrene bead template was introduced to provide a structure suitable for a gas reaction, and a nanoparticle catalyst in a dual nozzle electrospinning process It has been proved through the present invention that it is possible to develop a very excellent gas sensing material.
Claims (26)
A mixed solution obtained by dispersing a polymer bead sacrificial layer template and a nanoparticle catalyst in an electrospinning solution in which a metal oxide precursor and a polymer are dissolved is used as a shell solution and a mineral oil is used as a core solution, To form a composite nanofiber having a core (mineral oil) / shell (composite in which a polymer, a metal precursor, and a sacrificial layer template and a nanoparticle catalyst are bound at the same time), and the composite nanofiber having the core / shell structure formed is heat- Wherein the mineral oil is obtained by removing the mineral oil.
Wherein the polymeric bead sacrificial layer template has a polygonal or irregular particle shape including at least one of spherical, hexagonal, pentagonal, rectangular, and triangular shapes and is removed through the heat treatment to form the plurality of pores. Porous metal oxide nanotube composite.
Wherein the polymeric bead sacrificial layer template comprises a polystyrene sacrificial layer template and wherein the plurality of pores include oval pores of a longitudinally elongated shape removed through the heat treatment after the polystyrene sacrificial layer template has agglomerated Catalyst - Porous Metal Oxide Nanotube Composites.
Wherein the polymeric bead sacrificial layer template has a diameter distribution ranging from 50 nm to 1 < RTI ID = 0.0 > um. ≪ / RTI >
In the composite nanofiber of the core / shell structure, the diameter of the core is in the range of 400 nm to 4 μm, the diameter of the shell is in the range of 500 nm to 5 μm, and the thickness of the formed shell is 50 nm to 1 lt; RTI ID = 0.0 > g / m2. < / RTI >
In the formed core / shell structure, the shell has a cylindrical structure in which the oxidized metal oxide particles gather to form an empty space,
Wherein at least a portion of the cylindrical structure includes a structure in which the mineral oil is swollen and protruded as the injection of the mineral oil is uneven, or a shrinking structure.
The composite bead sacrificial layer template and the nanoparticle catalyst are bound to the surface through electrospinning using a dual nozzle to synthesize composite nanofibers of a core / shell structure including convex protruded shapes on the surface, Wherein the catalyst-porous metal oxide nanotube composite comprises a plurality of pores on the surface by removing the polymer bead sacrificial layer template through heat treatment of the catalyst particles and simultaneously includes the nanoparticle catalyst.
Wherein the pores connecting the inner pores and the outer pores of the nanotubes have a diameter ranging from 1 nm to 500 nm.
Wherein the diameter of the nanoparticle catalyst is in the range of 1 nm to 20 nm.
Wherein the surface area of the catalyst-porous metal oxide nanotube composite is increased as the cross-section of the polycrystalline metal oxide nanotube formed by the plurality of pores is exposed to the surface.
Wherein the nanoparticle catalyst comprises a metal or a nonmetal and is selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ta, Re, Os, Ir, Pt, Au, Si and Ge.
(b) electrospinning the core spinning solution using the prepared shell spinning solution and mineral oil through a dual nozzle to form a metal oxide precursor / polymer composite core / shell structure in which the sacrificial layer template and the nanoparticle catalyst are bound step; And
(c) heat treating the metal oxide precursor / polymer composite core / shell structure to remove the sacrificial layer template and the mineral oil, and oxidizing the metal oxide precursor to form a porous metal oxide Step of forming nanotube
Wherein the porous metal oxide nanotube is bound to a catalyst.
(d) coating the porous metal oxide nanotube on a sensor substrate capable of recognizing the change in resistance to manufacture a semiconductor type gas sensor capable of detecting a biomarker gas for environmental noxious gas and disease diagnosis
Wherein the porous metal oxide nanotubes are bonded to each other.
Wherein the porous metal oxide nanotube comprises a hollow cylindrical structure, a nanobelt structure, or a structure having an irregular shape due to uneven injection of core mineral oil. ≪ / RTI >
The size of the pores formed as the sacrificial layer template is removed through the heat treatment is thermally contracted to a size ranging from 10 to 50% of the size of the beads of the polymer used as the sacrificial layer template, Wherein the inner pore and the outer pore of the porous metal oxide nanotube are connected to each other.
The step (b)
The nanoparticle catalyst and the bead of the sacrificial layer template are mixed with each other by applying a high voltage between the core spinning liquid and the shell spinning solution in different syringes and discharging them at different discharge speeds, Wherein the metal oxide precursor / polymer composite core / shell structure nanofiber bound to the surface of the porous metal oxide nanotube is formed.
In the metal oxide precursor / polymer composite core / shell structure, the core includes a portion penetrated by the mineral oil, and the mineral oil flows out from the core of the metal oxide precursor / polymer composite core / shell structure to form pores in the core And a heat treatment process is performed at a high temperature to form a hollow nanotube structure in the core, wherein the porous metal oxide nanotube is bound to the catalyst.
In the dual nozzle electrospinning, the discharge amount of the core spinning solution is smaller than the discharge amount of the shell spinning solution,
The ejection speed of the core spinning solution is in the range of 1 μL / min to 50 μL / min,
Wherein the discharge rate of the shell spinning solution is in the range of 10 μL / min to 500 μL / min, and the discharge speed of the shell spinning solution is selected at a rate higher than the discharge speed of the core spinning solution. A method for producing porous metal oxide nanotubes to which a catalyst is bound.
The metal oxide precursor / polymer composite core / shell structure may further include a nanobelt structure, an open nanotube structure, or an irregular nanofiber structure depending on the nanofiber structure of the core / shell as well as the discharge amount of the core spinning solution. A method for producing porous metal oxide nanotubes to which a catalyst is bound.
Wherein the diameter of the metal oxide precursor / polymer composite core / shell structure is in the range of 500 nm to 5 占 퐉.
Wherein the diameter of the metal oxide precursor / polymer composite core / shell structure is reduced to a range of 300 nm to 1 占 퐉 through a heat treatment process.
Wherein the nanoparticle catalyst is bound to the surface of the metal oxide precursor / polymer composite core / shell structure at a concentration ranging from 0.001 wt% to 20 wt% relative to the porous metal oxide nanotube. Oxide nanotube.
Wherein the sacrificial layer template is bound to the surface of the metal oxide precursor / polymer composite core / shell structure at a concentration ranging from 1 wt% to 10 wt% relative to the solvent of the shell spinning solution. Oxide nanotube.
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