KR101746301B1 - Composite oxide semiconductors with hierarchical hollow structures and manufacturing method thereof - Google Patents
Composite oxide semiconductors with hierarchical hollow structures and manufacturing method thereof Download PDFInfo
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Abstract
The present invention relates to a member for a metal oxide hollow spherical-nanotube composite nano material gas sensor including a nanoparticle catalyst, and a method of manufacturing the same. Specifically, the metal oxide precursor / nanoparticle catalyst / polymer composite nanofiber is continuously subjected to a high-temperature heat treatment in a reducing atmosphere and a high-temperature heat treatment in an oxidizing atmosphere to form a composite nanomaterial consisting of a zero-dimensional hollow sphere and a one- And the nanoparticle catalyst is also uniformly distributed in the metal oxide sensing material, and a manufacturing method thereof. In particular, the principle of making a zero-dimensional metal oxide hollow ball is to use a metal having a relatively low melting point to melt the metal through high temperature and to elute through the carbon pores to form spherical metal particles, A hollow sphere having a spherical shape can be synthesized. The hollow spheres-nanotubes composite nanostructured metal oxide containing the synthesized nanoparticles have excellent sensitivity characteristics capable of detecting a very small amount of gas through a remarkably wide specific surface area and an effective catalytic reaction, A nanoparticle composite oxide nanoparticle containing a nanoparticle catalyst by a simple process, thereby producing a gas sensor member, a gas sensor, and a manufacturing method thereof capable of mass production, .
Description
The present invention relates to a composite metal oxide having a hierarchical hollow structure and a method of manufacturing the same. More specifically, the present invention relates to a one-dimensional polycrystalline nanofiber hollow structure having a hollow structure and a zero-dimensional metal oxide polycrystalline spherical particle having a hollow structure on the outer wall, Wherein the nanoparticle catalyst is uniformly distributed and bound in the composite sensing material having a one-dimensional structure of nanotubes and a zero-dimensional structure of a hollow sphere, and the composite metal oxide gas having a hierarchical hollow structure And a sensor member.
In order to minimize the problems caused by air pollution due to the development of industrial technology, development of gas sensors for detecting harmful gas outflows is actively under way. A gas sensor based on a metal oxide semiconductor detects a gas using a phenomenon in which the electrical resistance of a metal oxide semiconductor changes due to a surface reaction occurring when a specific gas is adsorbed and desorbed on a surface of a metal oxide semiconductor material . Research has been actively conducted to increase the gas sensor sensitivity characteristics by increasing the surface area of a metal oxide semiconductor material using the principle of sensing gas through surface reaction. In order to selectively detect a specific gas, a nanoparticle catalyst Studies to impart selectivity by bonding with metal oxide semiconductor sensing materials are also being actively pursued. In the case of a metal oxide-based gas sensor, it is easy to miniaturize and interlock with a smart device. Recently, commercialization studies for mounting the gas sensor device on a wearable device have been attempted. In addition to this, it is possible to mass-produce sensors based on low prices, and metal oxide-based gas sensors have been applied to various fields throughout the society, such as harmful environmental gas alarms, alcohol drinking meters, and sensors for preventing terrorism gases. In particular, recently, as people's interest in healthcare has increased, a very small amount of biomarker gas contained in the exhalation of the human body through the lungs has been detected, The research of the sensor of the expiration is active. Biological surface gases released in the body's exhalation include acetone, ammonia, nitrogen monoxide, hydrogen sulfide, and toluene. These gases are known as the biomarkers of diabetes, kidney disease, asthma, bad breath and lung cancer.
However, in order for gas sensors based on metal oxide semiconductor to be widely commercialized, the characteristic of the gas sensor must have high sensitivity and high selectivity so that a specific gas can be detected among a large number of gases and high reliability can be achieved. In order to develop such a high-performance gas sensor, it is necessary to develop a new nanostructure shape having a large specific surface area and develop effective nanoparticle catalyst binding technology. As described above, since the surface reaction between the metal oxide semiconductor material and the gas molecules is due to the surface reaction, the higher the surface area of the metal oxide reacting with the gases, the higher the sensitivity characteristic can be expected. From this point of view, nanostructure sensing materials can have excellent gas sensing properties because they have a relatively large area of reacting with the gases compared to thick films, and that gas molecules can spread rapidly into the sensing material Since it has a porous structure, ultrahigh-speed reaction characteristics can be derived. Particularly, the hollow structure of the hollow structure with a zero-dimensional structure (hollow structure with a hollow shell) and the hollow structure with a one-dimensional structure have a surface area several tens to several hundred times larger than that of the thin structure , The nanotube structure can have a specific surface area more than twice as high as that of the nanofiber structure filled with the nanotubes. Particularly, in the case of the hollow structure, gas diffusion into the nanostructure is easy, and both the outside and the inside of the hollow structure act as a reaction surface, thereby inducing an effective gas sensor reaction. In this respect, if a hollow structure of a zero-dimensional sphere and a hollow structure of a one-dimensional nanotube are combined, it is possible to show a specific surface area several times larger than that of a simple nanotube or hollow structure, Tubes and hollow spheres simultaneously and can be expected to have improved gas sensor characteristics. If the nanoparticle catalyst is uniformly bound to the nanostructure in which the 0-dimensional structure and the 1-dimensional structure are combined with each other, selectivity and sensitivity characteristics for a specific gas may be further improved. These catalysts can be categorized into two types: chemical sensitization which increases gas sensor characteristics by increasing the concentration of gases participating in the surface reaction by using a metal catalyst such as platinum (Pt) or gold (Au) Method or a metal oxide such as palladium (Pd), nickel (Ni), cobalt (Co), silver (Ag) or the like such as PdO, NiO, Co- 2 O 3 or Ag 2 O, There is an electronic sensitization method which improves the sensitivity.
As described above, in spite of the development of various nanostructures and research on utilizing sensing materials that are bound with various nanoparticle catalysts, there is a need for a technique capable of precisely measuring ultra-minute amounts of gas less than several hundreds of ppb Sensing materials based on metal oxide semiconductors having high sensitivity characteristics have not yet been commercialized. In order to realize an exhalation sensor for early diagnosis of disease, it is urgent to develop a sensing material capable of sensing a trace amount of gas.
From the viewpoint of synthesis of sensing materials having nanostructures, many methods for manufacturing nanostructures through chemical vapor deposition, physical vapor deposition, and chemical growth have been studied. However, these methods have a number of problems such as difficulty in mass production due to complicated and troublesome process steps in synthesizing a nanostructure, costly process cost, and long process time.
Particularly, when the zero-dimensional hollow structure and the one-dimensional hollow tube structure are separately synthesized and mixed with each other, the process time and manufacturing cost may increase. In order to measure the resistance change signals obtained after the reaction with the gas, it is important that the hollow structures are well contacted. If they are simply mixed with each other, a zero-dimensional hollow structure May exist as aggregated with each other, and it is difficult to form a uniformly dispersed complex.
In order to overcome these disadvantages, it is necessary to develop a sensing material having a large surface area that reacts with gases in a short time and in a simple and effective manner. In addition, a nanoparticle catalyst capable of dispersing a nanoparticle- Is required for nanostructure synthesis process. Particularly, by manufacturing a composite metal oxide having a nanoparticle catalyst-bound hierarchical hollow structure (i.e., a structure in which 0-dimensional hollow particles are bound to a one-dimensional tube structure without aggregation uniformly) The cost can be remarkably reduced.
In embodiments of the present invention, the metal oxide precursor / nanoparticle catalyst / polymer composite nanofiber synthesized by electrospinning is first subjected to a high-temperature heat treatment in a reducing atmosphere so that the metal oxide precursor is reduced to metal, and the metal is sequentially melted The present invention provides a carbon nanofiber electrospinning method in which a polymer in a nanofiber is carbonized to form a carbon nanofiber, a molten metal is eluted through pores formed in the carbon nanofiber, and metal particles are bound to the surface of the carbon nanofiber. At this time, the nanoparticle catalyst added to the added electrospinning solution is selectively present only in the molten metal.
In the embodiments of the present invention, the carbon nanofibers to which the synthesized metal particles are bound are decomposed in the form of carbon dioxide through the high-temperature heat treatment in an oxidizing atmosphere, and the metal particles are oxidized to form a 0-dimensional hollow metal oxide Particle and one-dimensional hollow structure nanotubes are formed at the same time, and the nanoparticle catalyst is a hollow-structure metal oxide composite material which is uniformly distributed throughout the synthesized metal oxide composite nano material, and a gas sensor application technology .
This is a method for solving the problems of the prior art, in which hollow particles having a large specific surface area and nanotube complex material are easily synthesized in a single process without any bonding process, and a reaction area capable of adsorbing even a very small amount of gas The present invention also provides a gas sensor member capable of detecting a trace amount of gas because the nanoparticle catalyst is dispersed evenly in the sensing material, and a gas sensor using the same and a method of manufacturing the same.
A nanoparticle catalyst having excellent dispersibility due to surface charge characteristics according to one aspect of the present invention can be synthesized and a nanoparticle catalyst can be easily produced in a single process using a high temperature heat treatment in a reducing atmosphere and a high temperature heat treatment in a continuous oxidizing atmosphere, The present invention provides a sensing material having a uniformly bound metal oxide hollow spheres and a metal oxide nanotube complex, and a method of manufacturing a member for a gas sensor using the same.
A method for manufacturing a sensing material and a gas sensor using the same according to the present invention comprises the steps of: (a) preparing an electrospinning solution containing a metal oxide precursor, a nanoparticle catalyst, and a polymer; (b) synthesizing a metal oxide precursor / nanoparticle catalyst / polymer composite nanofiber through electrospinning; (c) synthesizing carbon nanofibers to which the metal particles and the nanoparticle catalyst are bound through a high-temperature heat treatment in a reducing atmosphere; (d) removing carbon nanofibers through a high-temperature heat treatment, synthesizing a zero-dimensional hollow spherical metal oxide including a nanoparticle catalyst and a one-dimensional metal oxide nanotube hollow structure; And (e) dispersing or pulverizing the 0-dimensional hollow-sphere metal oxide and the one-dimensional metal oxide nanotube composite hollow structure including the nanoparticle catalyst, thereby forming a drop coating, a spin coating Forming a resistance variable semiconductor gas sensor by using at least one coating process such as spraying, ink jet printing, or dispensing, and a nano particle catalyst for a gas sensor capable of detecting a biomarker gas for diagnosis of environmentally harmful gases and diseases Nanotube complex nanostructured metal oxide sensing material having a hollow-nanotube complex formed thereon.
Here, the nanoparticle catalyst used in step (a) may be a highly dispersible nanoparticle catalyst using a protein template having a hollow structure. The total size of the hollow structure protein is about 12 nm and the size of the internal void space is about 8 nm. A variety of metal salts can be substituted in the hollow space surrounded by the outer wall of the protein, and nanoparticle catalysts can be easily synthesized through a reduction process. Typical salt-type catalysts include copper (II) nitrate, copper (II) chloride, cobalt (II) nitrate, cobalt (II) acetate, lanthanum (III) nitrate, lanthanum (III) (II) chloride, iron (III) chloride, iron (III) acetate, nickel (II) chloride, (III) chloride, Ruthenium Acetate, Iridium (III) chloride, iridium acetate, Tantalum (V) chloride and Palladium (II) chloride. In the case of salts containing metal ions, I do not. In the case of the metal oxide precursor used in step (a), metal (M), which is a reduced form of the corresponding metal ion (M n + ), should have a low melting point of 400 ° C or less. Typically, . Finally, in step (a), a nanoparticle catalyst is further dispersed in a solvent in which the polymer and the metal salt are dissolved to prepare an electrospinning solution.
The step (b) is a step of synthesizing a polymer composite nanofiber in which a nanoparticle catalyst and a metal oxide precursor are uniformly distributed. Composite nanofibers can be prepared by electrospinning.
In the step (c), the polymer composing the composite nanofibers electrospun through a high-temperature heat treatment in a reducing atmosphere is carbonized to form amorphous carbon nanofibers, the metal ions are reduced to a metal, and the reduced The metals become liquid, which is carbonized and flows out through the pores of the produced amorphous carbon nanofibers to form droplet-shaped particles on the surface of the carbon nanofibers. Particularly, the nanoparticle catalyst having a high melting point is kept in a solid form while being swept by the liquid metal and selectively located only in the metal particles and the metal inside the carbon nanofiber.
In the step (d), the carbon nanofibers synthesized in the step (c) are subjected to a high-temperature heat treatment in an oxidizing atmosphere to remove carbon components of the carbon nanofibers, The metal in the nanofiber is crystallized through the oxidation process and forms a metal oxide composite nanostructure having a composite of hollow spherical particles and nanotube shapes and uniformly binding the nanoparticle catalyst. Specifically, the carbon component is removed in the form of carbon dioxide through the high-temperature heat treatment in the oxidizing atmosphere, and the metal particles start to oxidize from the surface of the metal, and the kerchant effect due to the difference in diffusion speed between the metal oxide on the outer wall and the metal inside (Kirkendall effect) to form hollow spherical shapes and nanotubes. In addition, since the nanoparticle catalyst is selectively present only in the metal portion in the step (c), the nanoparticle catalyst is uniformly distributed in the hollow nanotube composite nanostructured metal oxide during the crystallization process as the metal oxide in the oxidative atmosphere heat treatment process.
In the step (e), the dispersion solution obtained by dispersing the hollow nanotube composite nanostructured metal oxide having the nanoparticle catalyst attached thereto in the step (d) in a solvent is applied to a previously prepared sensor electrode (measurement of electrical conductivity and electrical resistance change A coating method such as drop coating, spin coating, inkjet printing, or dispensing on an alumina insulator substrate on which a parallel electrode capable of being formed can be formed. Here, if the method includes a nanoparticle catalyst and uniformly coating the hollow spherical-nanotube composite nanostructured metal oxide, there is no restriction on the specific coating method.
In the hollow spherical-nanotube composite nanostructured metal oxide to which the nanoparticle catalyst is bound, the thickness between the inner wall and the outer wall of the nanotube can be set in a range of 10 nm to 50 nm, and the diameter of the nanotube And has a length range of 50 nm to 1 占 퐉. The length of the nanotubes may range from 1 占 퐉 to 20 占 퐉. In addition, the diameter of the hollow sphere structure coupled to the inner and outer walls of the nanotube may range from 50 nm to 1 m, and the thickness between the inner wall and the outer wall of the hollow sphere structure ranges from 10 to 50 nm do.
According to the present invention, in the production of a hollow spherical-nanotube composite nanostructure metal oxide in which a plurality of hollow spherical particles (50 nm-1 탆) are bound to inner and outer walls of a nanotube, In the reducing atmosphere, spherical metal particles melted and discharged on the surface of the carbon nanofibers are formed through high temperature heat treatment, and then crystallization is carried out by continuous heat treatment at an oxidizing atmosphere at a high temperature to produce a hollow spherical-nanotube composite nanostructured metal oxide , It has a specific surface area several tens of times or more higher than that of a general thin film structure, and has an increased specific surface area several times higher than that of a single type of nanotube and hollow tube, thereby improving the sensitivity to gas. In addition, by utilizing the presence of the nanoparticle catalyst in the molten metal, the nanoparticle catalyst is produced by a gas sensor using a sensing material uniformly distributed in the metal oxide sensing material after the oxidation heat treatment, Can be maximized. As mentioned above, by maximizing the surface area and the catalytic reaction effect of the gas sensor member, it is possible to provide a gas sensor having a high sensitivity characteristic capable of detecting a trace amount of gas, excellent selectivity for detecting a specific gas, Member, a gas sensor, and a manufacturing method thereof.
BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
FIG. 1 is a schematic view of a hollow spherical-nanotube composite nano-structured metal oxide gas sensor member in which a nanoparticle catalyst according to an embodiment of the present invention is uniformly bound.
2 is a flowchart of a method of manufacturing a gas sensor using a hollow spherical-nanotube composite nanostructured metal oxide with a nanoparticle catalyst uniformly bound according to an embodiment of the present invention.
FIG. 3 is a view illustrating a process for manufacturing a hollow spherical-nanotube composite nanostructured metal oxide in which a nanoparticle catalyst is uniformly bound using an electrospinning method according to an embodiment of the present invention.
FIG. 4 is a graph showing the results of the heat treatment of electrospun tin oxide precursor / nanoparticle catalyst / polymer composite nanofiber according to an embodiment of the present invention in a reducing atmosphere. It is a scanning electron microscope photograph.
FIG. 5 is a graph showing an energy dispersive X-ray spectrometer (EDS) showing nanoparticle catalyst migration when a nanoparticle catalyst is subjected to a high-temperature reduction heat treatment in a tin oxide precursor / nanoparticle catalyst / polymer composite nanofiber according to an embodiment of the present invention. ) It is a photograph.
6 is a view illustrating a principle of movement of a nanoparticle catalyst in a carbon nanofiber in a high-temperature reduction heat treatment process according to an embodiment of the present invention.
FIG. 7 is a cross-sectional view of a carbon nanotube according to an exemplary embodiment of the present invention. Referring to FIG. 7, when the electrospinning metal oxide precursor / nanoparticle catalyst / polymer composite nanofiber according to an embodiment of the present invention is subjected to reduction heat treatment, metal oxide precursor is reduced to become a metal, In-situ scanning electron microscope (SEM) photograph showing the phenomenon of elution through the membrane.
FIG. 8 is a graph showing the results of a high-temperature reduction heat treatment according to an embodiment of the present invention. FIG. 8 is a graph showing the results of experiments of a nanoparticle catalyst prepared by subjecting carbon nanofibers, Spherical-nanotube composite nanostructured metal oxide is a scanning electron microscope photograph.
9 is a transmission electron micrograph and an EDS (Energy Dispersive X-ray Spectrometer) photograph of a hollow spherical-nanotube composite nanostructured metal oxide according to an embodiment of the present invention.
10 is a scanning electron micrograph of a hollow-nanotube composite nano-structured metal oxide synthesized by a high-temperature heat treatment in an oxidizing atmosphere of carbon nanofibers obtained by a high-temperature reduction heat treatment according to an embodiment of the present invention to be.
FIG. 11 is a graph showing the relationship between the pore diameter of the tin oxide hollow nanotube composite nanostructure and the pure tin oxide hollow nanotube composite nanostructure including the Pt nanoparticle catalyst according to an embodiment of the present invention, ppm) for reactivity graphs, and toluene (C 6 H 5 CH 3) , biometric, such as hydrogen sulfide (H 2 S), nitrogen monoxide (NO), carbon monoxide (CO), pentane (C 5 H 12) and ammonia (NH 3) A graph of reactivity at 1 ppm for surface gases.
FIG. 12 is a graph showing the relationship between the concentration of toluene gas (1-5 ppm) at 350 ° C. of a tin oxide hollow nanotube composite nanostructure containing a Pd nanoparticle catalyst and pure tin oxide hollow spherical- ) And a biochemical indicator gas such as acetone (CH 3 COCH 3 ), hydrogen sulfide (H 2 S), nitrogen monoxide (NO), carbon monoxide (CO), pentane (C 5 H 12 ) and ammonia (NH 3 ) Lt; RTI ID = 0.0 > 1 ppm. ≪ / RTI >
BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and specific embodiments will be described in detail below with reference to the accompanying drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
The terms first, second, etc. may be used to describe various components, but the components are not limited by the terms, and the terms are used only for the purpose of distinguishing one component from another Is used.
Hereinafter, a member for a gas sensor using a hollow spherical-nanotube composite nanostructured metal oxide including a highly dispersible nanoparticle catalyst, a gas sensor and a method for manufacturing the same will be described in detail with reference to the accompanying drawings.
The present invention relates to a hollow spherical-nanotube composite nanostructured metal oxide having uniformly bound nanoparticle catalyst by melting a metal having a low melting point through a high-temperature reduction heat treatment, leaching phenomenon occurring on the surface of a carbon nanofiber, Is synthesized by a single process.
In order to improve the sensing characteristics of the gas sensor, studies have been conducted to broaden the specific surface area of the sensing material. In addition, a nanoparticle catalyst is attached to the sensing material, Studies have been carried out to improve the characteristics. However, among the research methods developed so far, in order to broaden the specific surface area, in order to form a structure of a hollow structure with spheres and nanotubes, it is necessary to independently perform synthesis of nanotubes and hollow spheres using a template, Has a disadvantage in that it has a very complicated process. In addition, the process of attaching the nanoparticle catalyst to the sensing material also requires a separate process. As described above, the complexity of the process of fabricating the sensing material can be time consuming and costly, and there is a disadvantage that mass production is difficult.
In order to overcome these disadvantages, in the present invention, spherical metal particles are formed on the surface of carbon nanotubes during a reduction heat treatment process using a metal having a relatively low melting point (400 DEG C or less) and then subjected to a continuous oxidation heat treatment process, Nanotube Composite Nanostructured Metal Oxide Nanoparticle Catalyst Nanostructured Gas Sensor Detection Material A mass synthesis method is provided. In the case of nanoparticle catalyst, it is combined with molten liquid metal during high-temperature reduction atmosphere heat treatment process, and it can be located at a place where metal is selectively located. The metal is oxidized to metal oxide through oxidation heat treatment and nanoparticle catalyst is uniformly It can be seen that it can be distributed. In addition, by the existence of metal oxide hollow spheres and nanotubes in combination, it is possible to expect a specific surface area that is several times larger than that of single-type nanotubes and hollow spheres. The hollow structure allows easy penetration of gases, Can be activated. In addition, nanoparticle catalysts that are uniformly distributed throughout the sensing material can maximize the catalytic effect of the gases when they react with the sensing material. A gas sensor member, a gas sensor, and a manufacturing method thereof are implemented in an efficient and easy process for manufacturing a gas sensor member having the above characteristics.
1 is a schematic view of a
The present invention provides a hollow spherical-nanotube composite nanostructured metal oxide (100) having a complex structure of a metal oxide hollow fiber (110) and a metal oxide nanotube (111) as a gas sensor member (100) The
In particular, the hollow spherical-nanotube composite
At this time, the hollow spherical-nanotube composite
The nanostructured metal oxide / nanoparticle catalyst / polymer composite nanofiber is subjected to a high-temperature heat treatment in a reducing atmosphere, and then a high-temperature heat treatment is conducted again in an oxidizing atmosphere continuously. In this simple heat treatment process, And has a feature of easily synthesizing a hollow spherical-nanotube composite nanostructured metal oxide having a catalyst attached thereto.
When the metal oxide precursor is reduced to a metal in a reducing atmosphere, the metal oxide precursor should be a metal that melts at a temperature of 400 ° C or lower. Typical metal salt precursors include In and Sn. The melting point of the metal should be at a temperature at which it does not form an alloy with the nanoparticle catalyst. After the metal is melted, it may be eluted through the pores of the carbon nanofibers, resulting in a metal sphere on the surface of the carbon nanofibers.
In the hollow-nanotube composite nano-structured metal oxide consisting of the metal oxide hollow structure of the 0-dimensional structure and the metal oxide nanotube of the one-dimensional structure, the elongated elliptical 10 nm-100 nm There is a crack in the size range and the reaction gas can be smoothly moved through the crack.
Copper (II) chloride, cobalt (II) nitrate, cobalt (II) acetate, lanthanum (III) nitrate and lanthanum (III) nitrate were used in the protein template of the hollow structure. (III) chloride, iron (III) chloride, iron (III) acetate, nickel (II) acetate, (II) acetate, Ruthenium (III) chloride, Ruthenium Acetate, Iridium (III) chloride, iridium acetate, Tantalum (V) chloride and Palladium , Nanoparticle catalysts such as Rh, Ru, Ni, Co, Cr, Ir, Au, Ag, Zn, W, Sr, Pb, Fe, Cu, V, Ta, Sb, Sc, Ti, can do. Thus, the size of the nanoparticle catalyst can be controlled by adjusting the amount of the precursor in the range of 0.1 nm to 8 nm using apoperi- tin as a template, and the nanoparticle catalysts are enclosed by the apoperator protein bark having a hollow structure Therefore, it has a great advantage that it is dispersed well even in an electrospinning solution. Gas sensor sensing A closer look at the role of nanoparticle catalysts in the sensing material is a chemical modifier that increases the concentration of adsorbed oxygen ions involved in surface reactions by promoting the decomposition of oxygen molecules between the metal oxide surface and the air layer platinum (Pt), gold (Au) may be the same noble metal type of nanoparticle catalyst, PdO, Co affecting improved detection characteristics 3 O 4, NiO, Cr 2 O 3, CuO, Fe 2
2 is a flowchart illustrating a method of manufacturing a member for a gas sensor using a hollow spherical-nanotube composite nanostructured metal oxide including a nanoparticle catalyst according to an embodiment of the present invention. As shown in the flowchart of FIG. 2, the manufacturing method of the gas sensor member includes the steps of manufacturing (S210) an electrospinning solution including a metal oxide precursor, a nanoparticle catalyst, and a polymer together; (S220) synthesizing a metal oxide precursor / nanoparticle catalyst / polymer composite nanofiber by electrospinning the prepared electrospinning solution using an electrospinning machine; (S230) synthesizing the metal oxide precursor / nanoparticle catalyst / polymer composite nanofibers with carbon nanofibers to which the metal particles and the nanoparticle catalyst are bound through a high-temperature heat treatment (240 ° C to 1000 ° C) in a reducing atmosphere; And a high-temperature heat treatment in an oxidizing atmosphere to remove the carbon component of the carbon nanofibers, and the hollow spherical-nanotube composite nanomaterial including the nanoparticle catalyst (i.e., the metal oxide hollow structure of the zero-dimensional structure and the metal oxide nano- Nanotube composite nanostructured metal oxide in which a nanoparticle catalyst is embedded and bound to a composite structure of nanotubes and tubes. Each of the above steps will be described in more detail below.
First, a step S210 of manufacturing an electrospinning solution containing a metal oxide precursor / nanoparticle catalyst / polymer will be described. The nanoparticle catalyst, the metal oxide precursor and the polymer which are embedded in the prepared hollow structure protein are dissolved in N, N'-dimethylformamide, dimethylsulfoxide, N, N'-dimethyl The metal oxide precursor / polymer is simultaneously dissolved using compatible solvents such as N, N'-dimethylacetamide, N-methylpyrrolidone, DI water and ethanol. Dissolve in solvent. In addition, the polymer which can be used here is not limited to a specific polymer if it is a polymer which can be dissolved together with a solvent and can be removed through a high-temperature heat treatment. Polymers which can be specifically used include polymers such as polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyacrylic copolymer, polyvinyl acetate copolymer, polyvinyl acetate (PVAc) Polyvinyl acetate, polyvinylpyrrolidone, polyvinyl alcohol, polypropyl alcohol, PP, polystyrene, polystyrene copolymer, polyethylene oxide (PEO), polyvinylpyrrolidone, Polypropylene oxide (PPO), polyethylene oxide copolymer, polypropylene oxide copolymer, polycarbonate (PC), polyvinyl chloride (PVC), polycaprolactone, polyvinyl fluoride, polyvinylidene fluoride copolymer, Polyimide, polyacrylonitrile, styrene-acrylonitrile (SAN), polyvinyl alcohol (P), polyacrylonitrile VA, polyvinyl alcohol), polycarbonate (PC), polyaniline (PANI), polyvinylchloride (PVC), polyvinylchloride (PVDF), polyvinylidene fluoride (PVDF), polyethylene terephthalate , Polyethylene terephthalate), polypropylene (PP), and polyethylene (PE) can be used. The metal precursor may be selected from the group consisting of tin chloride, tin chloride pentahydrate, tin acetate, tin sulfate, tin bis (acetylacetonate) dichloride ), Tin chloride dehydrate, indium chloride, indium chloride tetrahydrate, indium acetate, indium acetylacetonate, antimony trichloride, chloride, antimony acetate, and antimony sulfide may be used as the precursor.
In addition, the metal oxide precursor used in this step has a characteristic of being melted at 400 ° C or less when it is reduced to a metal in a high-temperature reduction heat treatment zone, and can be melted into a metal form through the pores of the carbon nanofiber . Typically, there are transition metals such as In and Sn. The ratio of the polymer to the metal oxide precursor to form the spinning solution is preferably about 1: 0.5 to 2, and the ratio of the polymer to the nanoparticle catalyst synthesized using apoferritin is in the range of 1: 0.00001 to 1: 0.1 . The process of preparing the electrospinning solution in step S210 first dissolves the metal oxide precursor and the polymer in the solvent, and then disperses the protein template-based nanoparticle catalyst in the electrospinning solution. Here, the stirring is carried out at room temperature and sufficiently stirred for 3-48 hours to uniformly disperse the nanoparticle catalyst and completely dissolve the polymer and the metal oxide precursor.
The synthesized metal oxide precursor / nanoparticle catalyst / polymer composite electrospinning solution is subjected to electrospinning in step S220 to produce a one-dimensional nanofiber form. First, the electrospinning solution is transferred to a syringe of an appropriate capacity, and then a syringe pump is used to apply pressure to the syringe at a constant speed so that a certain amount of solution is discharged at a constant time. The electrospinning system may include a high voltage generator, a grounded conductive substrate, a syringe, and a syringe nozzle. A high voltage of about 5 kV to about 30 kV is applied between the solution filled in the syringe and the conductive substrate to form an electric field. And the electrification is performed so that the spinning solution discharged through the syringe nozzle is drawn out in a nanofiber form due to the formed electric field. Nanofibers that are spun out in a one-dimensional form have a structure in which a metal oxide precursor / polymer / solvent is mixed, and the nanoparticle catalyst has a shape uniformly bound to the inside and the outside of the composite nanofiber.
Next, the prepared metal oxide precursor / nanoparticle catalyst / polymer composite nanofiber is subjected to a heat treatment process in a reducing atmosphere (H 2 or N 2 atmosphere) through step S230. When the metal oxide precursor / nanoparticle catalyst / polymer composite nanofiber is subjected to a high-temperature heat treatment in a reducing atmosphere, the polymer in the composite nanofiber is carbonized to form carbon nanofiber, the metal ion is reduced to metal, And the spherical metal particles are bound to the surface of the carbon nanofibers. In addition, the nanoparticle catalyst in the carbon nanofiber is combined with the molten liquid metal through heat treatment to move along the liquid metal and selectively located in the metal part. For this, in step S230, at least one kind of gas selected from nitrogen (N 2 ), ammonia (NH 3 ), argon (Ar), hydrogen (H 2 ) Lt; RTI ID = 0.0 > 400 C < / RTI >
The heat treatment temperature ranges from 250 ° C to 400 ° C to ensure that the reduced metal is sufficiently dissolved but does not form an alloy with the nanoparticle catalyst. During the high-temperature heat treatment process, the polymer is carbonized to form amorphous carbon nanofibers. The metal oxide precursor is reduced to metal, and at the same time, the molten metal is melted and eluted through the pores of the carbon nanofibers, To form metal particles. In the case of the nanoparticle catalyst, the nanoparticles also migrate along with the movement of the metal due to the merging of the liquid metal during the high-temperature reduction heat treatment process. Here, the protein template surrounding the nanoparticle catalyst is all decomposed and removed.
Finally, in step S240, the carbon nanofibers having the sphere-shaped metal particles formed through the high-temperature heat treatment in the reducing atmosphere are heat-treated in an oxidizing atmosphere to obtain hollow spherical-nanotube composite nanostructure metal oxide Can be formed. At this time, when the carbon nanofibers are subjected to a high-temperature heat treatment in an oxidizing atmosphere, the carbon nanofibers are removed in the form of carbon dioxide, the surface of the metal is preferentially oxidized, and the metal oxide hollow And a complex structure composed of spherical and metal oxide nanotubes can be formed. Here, the heat treatment temperature may range from 400 ° C. to 800 ° C., and the carbon nanofibers of the carbon component are all decomposed into the carbon dioxide form through the high-temperature heat treatment, and the spherical metal and the carbon nanofibers The metals inside are all oxidized to form hollow spherical-nanotube composite nanostructured metal oxide. In this case, the surface of the metal is preferentially oxidized during the oxidation heat treatment process, so that the metal surface becomes a metal oxide, and the hollow structure is formed by the difference in the diffusion speed between the metal oxide and the metal. Since the nanoparticle catalyst is also present only in the portion where the metal is selectively present in the step (S230), the nanoparticle catalyst may be uniformly dispersed throughout the metal oxide after the oxidation heat treatment. In other words, the nanoparticle catalyst is selectively present in the metal position in the metal-bound carbon nanofibers and can be uniformly bonded to the inside and the surface of the metal oxide after the heat treatment in the oxidizing atmosphere. A
FIG. 3 schematically shows a manufacturing process according to a method of manufacturing a hollow nano-tube composite nano-structured metal oxide gas sensor member including a nanoparticle catalyst using an electrospinning method according to an embodiment of the present invention. Specifically, a metal oxide precursor / nanoparticle catalyst / polymer composite nanofiber is formed using electrospinning, and a carbon nanotube is formed using a material characteristic of a low-melting metal through a high-temperature heat treatment (250-400 ° C.) A metal oxide particle is formed on the surface of the metal by the heat treatment of continuous oxidizing atmosphere to form a metal oxide and the diffusion rate of the metal oxide and the metal is used, Nanoparticle composite nanostructured metal oxide with a nanoparticle catalyst bound thereto.
Hereinafter, the present invention will be described in detail with reference to examples and comparative examples. The examples and comparative examples are merely intended to illustrate the present invention, and the present invention is not limited to the following examples.
Example 1: spherical nanoparticles selectively distributed in tin Tin particles Concluded Carbon nanofiber Produce
In order to produce carbon nanofibers in which spherical tin particles having nanoparticles are distributed, synthesis is performed as follows.
First, the metal oxide precursor / nanoparticle catalyst / polymer composite nanofiber synthesized by electrospinning mentioned in step S220 of FIG. 2 is directly put into a furnace capable of being heat-treated in a reducing atmosphere. It is preferable that the reducing atmosphere is performed in an atmosphere of nitrogen (100%) or hydrogen gas (100%), and when oxygen is introduced, tin is oxidized so that the melting point can not rise rapidly and can not be melted. During the reducing atmosphere heat treatment, the heating rate is preferably 0.1 ° C / min-10 ° C / min, and the heat treatment temperature is preferably in the range of 250 ° C to 400 ° C for 3 hours. If the heat treatment temperature is higher than 400 ° C, an alloy may be formed between the tin and the nanoparticle catalyst. In the reducing atmosphere high temperature heat treatment process, all the polymers are carbonized to form amorphous carbon nanofibers having many pores, and the protein template surrounding the nanoparticle catalyst is removed. In addition, the tin ions are reduced to tin during the reducing atmosphere heat treatment process using the low melting point (238 ° C) of tin, and at the same time, they are melted as a liquid and partially eluted through the pores of the carbon. The eluted liquid tin forms spherical metal particles and forms spherical metal particles on the carbon nanofiber surface while the temperature is lowered. At this time, the nanoparticle catalyst moves together with the liquid tin and is selectively present in the tin of the carbon nanofiber. As a result, the nanoparticle catalyst is selectively distributed in the tin and the nanofiber structure in which spherical tin particles are bound to the carbon nanofiber outer surface is formed.
FIG. 4 is a scanning electron micrograph showing a structure in which the nanoparticle catalyst prepared in the above process is selectively distributed in tin and spherical tin particles are bound to the surface of carbon nanofibers. The diameter of the hollow sphere structure may range from 50 nm to 1 m, and the thickness between the inner wall and the outer wall of the hollow sphere structure is in the range of 10-50 nm.
FIG. 5 is a graph showing an energy dispersive X-ray spectrometer (EDS) image indirectly showing the positional shift of a component existing in a nanofiber when a tin oxide precursor / nanoparticle catalyst / polymer composite nanofiber is carbonized through a high-temperature reduction heat treatment process to be. In the EDS analysis image, when the positions of the Pt nanoparticles and the Sn components are traced, it can be seen that Sn forms a spherical metal particle on the surface and inside of the carbon nanofibers as a liquid, and the Pt nanoparticles form liquid It can be confirmed that Sn is selectively positioned along the Sn.
FIG. 6 is a view illustrating a mechanism of a phenomenon in which a nanoparticle catalyst moves in accordance with the movement of tin metal in a reducing atmosphere high-temperature heat treatment process. Specifically, during the heat treatment, the tin is melted and the nanoparticle catalyst can be selectively positioned on the tin metal as the liquid tin passes through the nano-sized catalyst particles while diffusing through the pores of the non-crystallized carbon nanofiber.
FIG. 7 is a graph showing the process in which tin having a melting point of 238 DEG C is melted and eluted outside the amorphous carbon nanofibers when the tin oxide precursor / nanoparticle catalyst / polymer composite nanofiber is carbonized through a high-temperature heat treatment process in a reducing atmosphere. In-situ scanning electron microscopy (SEM).
Example 2: The nanoparticles uniformly Concluded Tin oxide Hollow ball - Nanotube composite nano structure manufacturing
The nanoparticles synthesized in Example 1 are selectively distributed in tin and the spherical tin particles are bound to the surface of carbon nanofibers. In the oxidative atmosphere heat treatment process, the temperature range is from 400 ° C. to 800 ° C. for 1 hour, and the temperature raising rate is preferably from 0.1 ° C. to 10 ° C.
Fig. 8 is a graph showing the relationship between the nanoparticle catalyst and the nano-particle catalyst nanoparticles after the nanoparticle catalyst is dispersed in the tin and the tin particles are bound to the carbon nanofiber outer surface. It is a scanning electron microscope photograph showing the material. Here, when a tin metal is in a hollow state such as a hollow sphere or a nanotube, the outer surface is preferentially oxidized to form a tin oxide shell, and the diffusion rate difference of the tin oxide in the tin and shell portions of the core portion A hollow sphere or a nanotube can be formed by the Kirkendall effect according to the present invention. In the case of the tin oxide hollow spheres distributed evenly on the outer wall and the inner wall of the nanotube, spherical tin particles adhered to the surface of the carbon nanofiber material produced in Example 1 were formed by oxidation. On the other hand, the tin oxide nanotubes are formed by oxidation of tin metal existing in the carbon nanofiber material produced in Example 1.
FIG. 9 shows shape, lattice analysis, SAED pattern analysis and EDS (Energy Dispersive X-ray Spectrometer) analysis of a tin oxide hollow-nanotube composite nano material to which a synthesized nanoparticle catalyst is bound using a transmission electron microscope There is a picture. Through the transmission electron microscope, it can be confirmed that the tin oxide hollow particle-nanotube composite nanomaterial with nanoparticle catalyst is well formed in the hollow structure. Through lattice analysis and SAED pattern analysis, tin oxide and nanoparticle catalyst Can be found independently of the alloy. Finally, it can be seen that the nanoparticle catalyst is uniformly distributed throughout the tin oxide hollow-nanotube composite nanomaterial sensing material through EDS (Energy Dispersive X-ray Spectrometer) analysis.
The prepared nanoparticle catalyst-bound tin oxide hollow spherical-nanotube composite nanostructure may have a thickness between 10 nm and 50 nm in thickness between the inner wall and the outer wall of the nanotube, and the diameter of the nanotube is 50 nm Lt; RTI ID = 0.0 > 1 < / RTI > The length of the nanotubes may range from 1 [mu] m to 5 [mu] m. In addition, the diameter of the hollow sphere structure coupled to the inner and outer walls of the nanotube may range from 50 nm to 1 m, and the thickness between the inner wall and the outer wall of the hollow sphere structure ranges from 10 to 50 nm do. In the case of the above structure, it is expected that hollow spheres and nanotubes will form a composite material and have smooth gas movement and high specific surface area. It is expected that gas sensor reaction will be excellent through uniformly dispersed nanoparticle catalyst effect can do.
Comparative Example 1: Pure tin oxide Hollow ball - Nanotube composite nano structure manufacturing
In Comparative Example 1, unlike Example 1 and Example 2, a pure tin oxide hollow hollow-nanotube composite nanostructure without nanoparticle catalyst was synthesized. The tin oxide precursor / nanoparticle catalyst / polymer composite nanofiber prepared by electrospinning was put into a reducing atmosphere (H 2 or
FIG. 10 is a scanning electron microscope (SEM) image of a pure tin oxide hollow hollow-nanotube composite nanostructure synthesized through the process of Comparative Example 1. FIG. The prepared tin oxide hollow spherical-nanotube composite nanostructure may have a thickness ranging from 10 nm to 50 nm between the inner wall and the outer wall of the hollow structure, and the diameter of the nanotube is in a range of 50 nm to 1 μm I have. The length of the nanotubes may range from 1 [mu] m to 5 [mu] m. In addition, the diameter of the hollow sphere structure coupled to the inner and outer walls of the nanotube may range from 50 nm to 1 m, and the thickness between the inner wall and the outer wall of the hollow sphere structure ranges from 10 to 50 nm do.
Experimental Example 1: Platinum or palladium nanoparticle catalyst Concluded Tin oxide Hollow ball - nanotube composite nanostructures and pure tin oxide Hollow ball - Fabrication and characterization of gas sensor using nanotube composite nanostructure
In order to manufacture the sensor material for gas sensor manufactured by Example 2 and Comparative Example 1 as a sensor capable of diagnosing disease by analyzing the exhalation, a platinum nanoparticle catalyst-bound tin oxide hollow-nanotube composite nano material , 7 mg of a tin oxide hollow particle-nanotube composite nanomaterial and a pure tin oxide hollow nanotube composite nanomaterial, each of which was bound with a palladium nanoparticle catalyst, were dispersed in 70 μl of ethanol, and ultrasonically cleaned for 1 hour It is pulverized. Tin oxide nanoparticles bonded to a platinum nanoparticle catalyst dispersed in ethanol, hollow-nanotube composite nanomaterials, and tin oxide hollow-nanotube composite nanomaterials bonded with a palladium nanoparticle catalyst were separated into two
FIG. 11 shows the result of the sensor test in which the reaction value at the time when the concentration of the acetone gas was reduced to 5, 4, 3, 2, 1, 0.6, 0.4, 0.2 and 0.1 ppm at 350 ° C. over time. As shown in FIG. 11, a gas sensor made of a tin oxide hollow particle-nanotube composite nano material to which a platinum nanoparticle catalyst is bound is about 10 times more sensitive to acetone gas than pure tin oxide hollow-nanotube composite nano material It shows a high reaction characteristic. In addition, as compared with the hydrogen sulfide (H 2 S), toluene (C 6 H 5 CH 3) , nitrogen monoxide (NO), carbon monoxide (CO), ammonia (NH 3) and pentane (C 5 H 12) gas for the acetone gas It can be seen that it exhibits an overwhelmingly high selective sensitivity characteristic.
12 is a result of a sensor test in which the degree of reaction when the concentration of toluene gas decreases at 5, 4, 3, 2, 1, 0.6, 0.4, 0.2 and 0.1 ppm at 350 캜 with time. As shown in FIG. 12, a gas sensor made of a tin oxide hollow hollow-nanotube composite nano material to which a palladium nanoparticle catalyst was bound was found to be about 3.5 times more transparent to toluene gas than a pure tin oxide hollow-nanotube composite nano material (CH 3 COCH 3 ), hydrogen sulfide (H 2 S), nitrogen monoxide (NO), carbon monoxide (CO), ammonia (NH 3 ) and pentane (C 5 H 12 ) gas The sensitivity to toluene is selectively superior to that of toluene. In the case of the tin oxide hollow particle-nanotube composite nanomaterials synthesized through the platinum or palladium nanoparticle catalyst synthesized in Example 2 above, a large specific surface area of each of the hollow spheres and nanotubes and a very small amount of biomarker Enabling the detection of gases. Particularly, it is applied to a gas sensor for a health care which can diagnose various diseases by detecting a specific biochemical surface gas among various bio-surface gases in the exhalation of a human body by changing the nanoparticle catalyst, .
The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments described in the present invention are not intended to limit the technical spirit of the present invention but to illustrate the present invention. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents thereof should be construed as being included in the scope of the present invention.
Claims (14)
The hollow spherical-nanotube composite nano-structured metal oxide may include a metal oxide hollow sphere having a zero-dimensional structure in which the nanoparticle catalyst is embedded and bound, and the metal oxide hollow sphere having the one- Is bonded to the inner wall and the outer wall of the gas sensor.
The hollow spherical-nanotube composite nanostructure metal oxide includes at least one metal oxide selected from the group consisting of tin oxide (SnO 2 ), indium oxide (In 2 O 3 ), and antimony oxide (Sb 2 O 3 ) A member for a gas sensor.
In the hollow spherical-nanotube composite nano-structured metal oxide, the thickness between the inner wall and the outer wall of the metal oxide nanotube ranges from 10 nm to 50 nm, and the diameter of the metal oxide nanotube ranges from 50 nm to 1 탆 Wherein the length of the metal oxide nanotubes ranges from 1 占 퐉 to 5 占 퐉.
In the hollow spherical-nanotube composite nano-structured metal oxide, the thickness between the inner wall and the outer wall of the metal oxide hollow has a length of 10 nm to 50 nm, the diameter of the metal oxide hollow is 50 nm to 1 μm Wherein the gas sensor has a width in a range of from 1 mm to 10 mm.
Wherein the weight ratio of the hollow spherical-nanotube composite nanostructured metal oxide to the nanoparticle catalyst is in the range of 0.001-10 wt%.
Wherein the hollow spherical-nanotube composite nano-structured metal oxide has cracks for movement of reaction gas on the surface of the metal oxide hollow spheres and the metal oxide nanotubes.
(b) synthesizing a metal oxide precursor / nanoparticle catalyst / polymer composite nanofiber by electrospinning the electrospinning solution;
(c) synthesizing the metal oxide precursor / nanoparticle catalyst / polymer composite nanofiber with carbon nanofibers bound to spherical metal particles and a nanoparticle catalyst through a high-temperature heat treatment in a reducing atmosphere; And
(d) removing the carbon component of the carbon nanofibers through a high-temperature heat treatment in an oxidizing atmosphere and introducing the nanoparticle catalyst into a composite structure composed of a metal oxide hollow structure having a zero-dimensional structure and a metal oxide nanotube having a one- Synthesizing a hollow hollow-nanotube composite nanostructured metal oxide;
Wherein the gas sensor member is made of a metal.
When the metal oxide precursor / nanoparticle catalyst / polymer composite nanofiber is heat-treated at a high temperature in a reducing atmosphere, the polymer in the composite nanofiber is carbonized to form amorphous carbon nanofiber, and the metal ion is reduced to metal Wherein the carbon nanofibers are melted at the same time and eluted through the pores of the carbon to bind spherical metal particles on the surface of the carbon nanofibers.
When the metal oxide precursor / nanoparticle catalyst / polymer composite nanofiber is heat-treated at a high temperature in a reducing atmosphere, the nanoparticle catalyst in the carbon nanofiber is combined with the molten liquid metal through the heat treatment to move along the liquid metal, Wherein the gas sensor element is selectively positioned in a portion of the gas sensor element.
When the carbon nanofibers are subjected to a high temperature heat treatment in an oxidizing atmosphere, the carbon nanofibers are removed in the form of carbon dioxide, the surface of the metal is preferentially oxidized, and the metal oxide hollow And forming a composite structure of the metal oxide nanotube and the metal oxide nanotube.
The step (c)
At least one kind of gas selected from nitrogen (N 2 ), ammonia (NH 3 ), argon (Ar), hydrogen (H 2 ) and helium (He) Wherein the gas sensor member is made of a metal.
Wherein the nanoparticle catalyst is selectively present in a metal position in the carbon nanofibers to which the metal is bound and is uniformly bound to the inside and the surface of the metal oxide after the heat treatment in the oxidizing atmosphere.
The metal oxide precursor may be selected from the group consisting of tin chloride, tin chloride pentahydrate, tin acetate, tin sulfate, tin bis (acetylacetonate) dichloride, tin chloride dehydrate, indium chloride, indium chloride tetrahydrate, indium acetate, indium acetylacetonate, antimony chloride antimony chloride, antimony acetate, antimony sulfide, antimony acetate, and antimony sulfide.
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| KR20220047151A (en) | 2020-10-08 | 2022-04-15 | 연세대학교 산학협력단 | Method for forming platinum nano-structures on gallium-based liquid metal surfaces and Liquid metal manufactured by the same method |
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| KR20220047151A (en) | 2020-10-08 | 2022-04-15 | 연세대학교 산학협력단 | Method for forming platinum nano-structures on gallium-based liquid metal surfaces and Liquid metal manufactured by the same method |
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