KR20190046320A - Porous Metal Oxide Nanotube, Gas Sensing Layers Using the Same, and Their Fabrication Method - Google Patents

Abstract

The present invention relates to a member for a gas sensor, a gas sensor using the same, and a manufacturing method thereof and, specifically, to a porous metal oxide nanotube including multiple p-n junctions formed as a part of metal oxides forming a metal oxide nanofiber is substituted to the metal oxide having an n-type property due to a galvanic substitution reaction to the metal oxide nanofiber having a p-type property, a member for a gas sensor using the same, a gas sensor, and manufacturing methods thereof. According to embodiments of the present invention, specifically, the member for a gas sensor forms a porous nanotube structure using the easy galvanic substitution reaction and can effectively detect gas by the p-n junction formed by the metal oxide having the n-type property substituted with the residual metal oxide having the p-type property at the same time. So, the member for a gas sensor, the gas sensor and the manufacturing method thereof are effectively provided due to convenient mass-production through an easy process.

Description

TECHNICAL FIELD [0001] The present invention relates to a metal oxide porous nanotube, a gas sensor member using the metal oxide porous nanotube,

The present invention relates to a member for a gas sensor, a gas sensor using the same, and a method of manufacturing the same. More specifically, the present invention relates to a method of manufacturing a metal oxide nanofiber having p- Type metal oxide nanotubes having a pn junction formed by converting some of the p-type metal oxides constituting the metal oxide nanofibers having the n-type metal oxide into n-type metal oxides, and a gas sensor using the same Member, a gas sensor, and a manufacturing method thereof.

As interest in personal health care has increased rapidly as the lifespan has increased, attention has been paid to health care, and as volatile organic compound gas, which is a biomarker of diseases included in the exhalation for diagnosing human diseases, The technology to detect and monitor specific gases by receiving and monitoring harmful environment gas in real time is receiving great attention. In order to increase the sensitivity and selectivity of gas, many researches such as porous metal oxide, pn bonding, and catalytic bonding have been developed to detect volatile organic compound gas and harmful environmental gas. It is actively proceeding. The resistive gas sensor using the metal oxide semiconductor based material analyzes the relative ratio (R _gas / R _air or R _air / R _gas ) of the resistance to the specific gas relative to the air resistance so that the concentration of the gas is quantitatively Can be detected. The metal oxide semiconductor type gas sensor using the above principle has a great merit that it can be easily manufactured in an extremely small size and is inexpensive. Therefore, much research has been made on the commercialization of an alcohol drinking measuring instrument, an air pollution measuring instrument, a noxious gas leak alarm, and the like. Recently, attempts have been made to commercialize a metal oxide semiconductor based gas sensor in cooperation with a mobile or a small electronic device. Especially, researches on a healthcare ventilation sensor capable of monitoring a specific disease by detecting a living body gas present in an exhalation are getting attention.

Since more than 3,500 kinds of mixed gases are contained in the body's exhalation, it is necessary to be able to selectively detect a specific bio-surface gas. In addition, since the biomass gas contained in a person's exhalation is emitted at a low concentration ranging from 10 ppb (part per billion) to 5 ppm (part per million) depending on a specific disease, It is necessary to develop a highly sensitive gas sensor that can detect the gas. Since a gas sensor based on a metal oxide semiconductor is a principle for measuring a change in electrical resistance due to a surface reaction occurring in the process of adsorption and desorption of a specific gas on the surface, the selectivity to react only with a specific gas is low, It is difficult to measure the concentration of the gas. Therefore, it is urgently required to develop a gas sensor sensing material having high sensitivity and high selectivity in order to be used as a healthcare aeration sensor using a metal oxide semiconductor gas sensor.

In order to have a high sensitivity and high selectivity, gas sensor based on metal oxide semiconductor is designed to have a relatively large surface area compared to the thin film structure, through nanostructure design of nanofibers, nanotubes, nanotubes, nanocubes, There are many researches to increase the resistance change, which is a method of representing the resistance. In addition, as the large and small pores are formed in the nanostructure in order to further maximize the wide specific surface area, the gas permeability into the sensing material increases and higher sensitivity can be expected. In particular, the porous nanotube structure has an ideal structure as a gas sensor. In addition, if the porous nanotube structure is made of a composite metal oxide having p-type and n-type characteristics, energy banding due to a difference in work function between metal oxides between different kinds of interfaces is formed, The resistance of the material is increased, and when exposed to the reducing gas, a larger resistance change is brought about, so that high sensitivity can be expected.

In addition to the development of various types of nanostructures, research on the use of sensing materials having various pn junctions has been conducted. However, a sensing material based on a metal oxide semiconductor synthesized by an additional single process has not been commercialized yet, In order to realize the healthcare aerosol sensor, it is urgent to develop a sensing material capable of selectively sensing a very small amount of gas.

Conventional methods for synthesizing porous nanostructures include chemical vapor deposition, physical vapor deposition, and a method using a sacrificial layer template. However, these methods have many problems, including complicated and cumbersome process steps, which are difficult to mass-produce, that are expensive to process, and that the process takes a long time.

In order to overcome the disadvantages mentioned above, it is necessary to develop a sensing material having a wide surface area in which a porous structure and a p-n junction are reacted with gases by a simple and effective manufacturing method in a single process.

Examples of the present invention include a technique capable of synthesizing metal oxide nanofibers having p-type characteristics through electrospinning and heat treatment and then synthesizing metal oxide porous nanotubes having n-type characteristics through additional galvanic substitution reaction .

Particularly, metal oxide nanofibers having p-type characteristics can be formed by an additional galvanic substitution reaction to form a porous nanotube structure having a wide specific surface area and a n-type metal oxide and a pn junction to increase the sensitivity Material synthesis technology and gas sensor application technology using it are presented.

This is a method for solving the problems of the prior art, which is a member for a gas sensor capable of detecting a trace amount of gas using metal oxide porous nanotubes having n-type characteristics including a pn junction, a gas sensor using the same, And a manufacturing method thereof.

a part of the metal oxides constituting the metal oxide nanofibers is replaced with a metal oxide having an n-type characteristic through a galvanic substitution reaction on metal oxide nanofibers having p-type characteristics, The present invention provides a member for a pn junction one-dimensional metal oxide porous nanotube-based gas sensor, which is characterized by forming an oxide porous nanotube.

According to an aspect of the present invention, the metal oxide porous nanotube has a diameter of 50 nm to 10 μm, an inner diameter of 5 nm to 5 μm, a thickness between the outer wall and the inner wall Is included in the thickness range of 45 nm - 5 μm, and the length is included in the range of 1 μm - 100 μm.

According to another aspect of the present invention, the metal oxide porous nanotubes form a plurality of p-n junction structures between the remaining p-type metal oxide existing after the galvanic substitution reaction on the fiber surface and inside of the fiber.

According to another aspect of the present invention, in the metal oxide porous nanotube, a portion of the p-type metal oxide constituting the metal oxide nanofibers having the p-type characteristic during the galvanic substitution reaction is substituted with an n-type metal oxide, And a plurality of pores having a diameter in the range of 2 nm to 50 nm are formed in the inside.

According to another aspect, the average grain size of the metal oxide nanofibers having p-type characteristics is in the range of 50 nm to 300 nm, and the average grain size of the metal oxide porous nanotubes is 10 nm to 200 nm The present invention is not limited thereto.

According to another aspect of the present invention, the metal oxide nanofibers having p-type characteristics include Co ₃ O ₄ , CuO, Fe ₂ O ₃ , Ag ₂ O, PdO, RuO ₂ , Rh ₂ O ₃ , NiO, Fe ₃ O ₄ , V ₂ O _5, and Cr ₂ O ₃ , and the metal oxide porous nanotubes may include at least one of TiO ₂ , ZnO, WO ₃ , SnO ₂ , In ₂ O ₃ , V ₂ O _3, and MoO ₃ .

(a) preparing an electrospinning solution in which a metal oxide precursor and a polymer are dissolved; (b) forming a metal oxide precursor / polymer composite nanofiber by electrospinning the electrospinning solution; (c) synthesizing the metal oxide precursor / polymer composite nanofiber into a p-type-based metal oxide nanofiber through a high-temperature heat treatment; And (d) substituting a part of the p-type metal oxide constituting the p-type-based metal oxide nanofibers with an n-type metal oxide using a galvanic substitution reaction to form a metal oxide porous nano- Wherein the porous nanotube-based gas sensor is formed of a porous metal oxide nanoparticle.

The step (a) is a step of preparing an electrospinning solution for electrospinning, wherein a metal oxide precursor and a polymer which gives a certain viscosity are mixed in a solvent to prepare an electrospinning solution. Representative polymers used in this case include polypropyl alcohol (PPFA), polymethyl methacrylate (PMMA), polyacrylic copolymer, polyvinyl acetate (PVAc), polyvinyl acetate copolymer, polystyrene (PS), polystyrene, polyvinylpyrrolidone (PVP), polystyrene copolymer, polyethylene oxide (PEO), polyethylene oxide copolymer, polycarbonate (PC), polyvinyl chloride (PVC) , Polypropylene oxide copolymer, polycaprolactone, polyvinyl fluoride, polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymer, polyimide, polyacrylate (PAN, polyacrylonitrile), polyethylene terephthalate (PET), polypropylene oxide (PPO) Polyvinyl alcohol (PVA), styrene-acrylonitrile (SAN), polycarbonate (PC), polyaniline (PANI), polypropylene (PP) , And polyethylene) may be used. The polymer constituting the electrolytic solution may be prepared in a weight ratio of 0.1 to 90 wt% with respect to each specific solvent. In the electrospinning solution, the solvent is selected from the group consisting of water (Deionized water), tetrahydrofuran, methanol, isopropanol, formic acid, acetonitrile, nitromethane ), Acetic acid, ethanol, acetone, ethylene glycol (EG), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide DMAc, Dimethylacetamide) and toluene (Toluene) may be used. At this time, the thickness of the p-type-based metal oxide nanofiber used as the sacrificial layer template in the galvanic substitution reaction can be controlled by controlling the viscosity of the electrospinning solution in the step (a).

The step (b) is a step of spinning the metal oxide precursor / polymer composite nanofiber using the electrospinning process of the electrospinning solution synthesized in step (a), wherein the metal oxide precursor is uniformly dissolved, Shape. Also, the composite nanofibers are formed as a matrix having large and small pores, thereby increasing the gas permeability.

The step (c) is a step of synthesizing a metal oxide nanofiber structure having a p-type property through a high-temperature heat treatment process. The polymer is thermally decomposed and removed through heat treatment, and the metal precursor is oxidized to form a metal oxide nanofiber . At this time, the shape of the nanofiber is maintained even after the heat treatment.

In the step (d), a portion of the p-type metal oxide constituting the metal oxide nanofibers having p-type characteristics is replaced with an n-type metal oxide using a galvanic substitution reaction to form a metal containing a plurality of pn junctions Oxide porous nanotubes can be produced. The p-type metal oxide may be a metal oxide particle formed by oxidizing the metal oxide precursor in step (c). Part of the p-type metal oxide may be replaced with an n-type metal oxide through a galvanic substitution reaction. A plurality of pn junctions can be formed. The metal oxide porous nanotubes formed through galvanic substitution are characterized in that the type conversion occurs through the oxidation and reduction reactions between the metal oxide and the ions. The amount of the metal oxide to be substituted is controlled by the substitution reaction time, -type or n-type metal oxide) can be controlled. The thickness of the metal oxide porous nanotube between the outer wall and the inner wall, and the amount of pores formed on the surface and inside can be controlled.

The manufacturing method of the pn junction one-dimensional metal oxide porous nanotube-based gas sensor member may further include a step of applying a cleaning process and a drying process using centrifugal separation to the metal oxide porous nanotube obtained in the step (d) have.

According to the present invention, a metal oxide precursor / polymer composite nanofiber is synthesized, and then a metal oxide nanofiber having p-type characteristics is synthesized through an additional high-temperature heat treatment. The metal oxide nanofiber having a p- By simply fabricating the nanotubes, the nanotubes have a porous nanotube structure compared to conventional p-type metal oxides, which can provide a relatively larger specific surface area, and can effectively maximize the resistance change as the pn junction is formed The gas sensor characteristic can be improved.

As mentioned above, through the conversion of the semiconductor characteristic type and the single process galvanic substitution reaction that can be formed with porous nanotubes, it is possible to maximize the specific surface area by the porous nanotube structure of the gas sensor member and detect the trace gas by forming the pn junction It is possible to disclose a member for a gas sensor, a gas sensor and a method of manufacturing the same, which have high selectivity for detecting a specific gas, which can be mass-produced.

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 this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
1 is a schematic view of a member for an n-type metal oxide porous nanotube gas sensor according to an embodiment of the present invention.
2 is a flowchart of a method of manufacturing a gas sensor using an n-type metal oxide porous nanotube structure according to an embodiment of the present invention.
FIG. 3 is a view showing a process of manufacturing an n-type metal oxide porous nanotube using a heat treatment and a galvanic substitution reaction according to an embodiment of the present invention.
FIG. 4 is a graph showing the results of a galvanic substitution reaction according to Example 1 of the present invention. FIG. 4 is a graph showing the results of scanning electron microscopy of p-type SnO ₂ / Co ₃ O ₄ and n-type SnO ₂ / Co ₃ O ₄ porous nanotubes It is a photograph.
FIG. 5 is a graph showing the transmission electron microscope (SEM) of p-type SnO ₂ / Co ₃ O ₄ and n-type SnO ₂ / Co ₃ O ₄ porous nanotubes after 1 hour and 4 hours of galvanic substitution reaction according to Example 1 of the present invention It is a photograph.
6 is a scanning electron micrograph of p-type Co- ₃ O ₄ nanofibers according to Comparative Example 1 of the present invention.
FIG. 7 is a graph showing the results of comparison of p-type SnO ₂ / Co ₃ O ₄ produced with 1-hour and 4-hour galvanic substitution reaction with p-type Co- ₃ O ₄ nanofibers through Comparative Example 1 and Example 1 of the present invention It is a graph of change in resistance when n-type SnO ₂ / Co ₃ O ₄ porous nanotubes are exposed to acetone gas.
FIG. 8 is a graph showing the results of comparison of p-type SnO ₂ / Co ₃ O ₄ produced with p-type Co- ₃ O ₄ nanofibers through galvanic substitution reaction for 1 hour and 4 hours through Comparative Example 1 and Example 1, The n-type SnO ₂ / Co ₃ O ₄ porous nanotubes are graphs of reactivity against acetone gas (0.4-5 ppm) at 400 ° C.
9 is a graph _{showing the results of} measurement of ethanol (C ₂ H ₆ O), mercaptan (CH ₃ CO ₃ ), and mercapto (CH ₃ COCH ₃ ) in n-type SnO ₂ / Co ₃ O ₄ porous nanotubes according to Example 1 of the present invention at 400 ° C. ₃ SH), toluene (C ₇ H ₈ ), hydrogen sulfide (H ₂ S), carbon monoxide (CO), pentane (C ₅ H ₁₂ ) and ammonia (NH ₃ ) gas (5 ppm).

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, a gas sensor, and a manufacturing method thereof using a principle in which a part of a p-type metal oxide constituting metal oxide nanofibers having p-type characteristics is substituted with an n-type metal oxide through a galvanic substitution reaction Will be described in detail with reference to the accompanying drawings.

The embodiments of the present invention synthesize metal oxide nanofibers having p-type characteristics through electrospinning and heat treatment, and synthesize metal oxide porous nanotubes having n-type characteristics through an additional galvanic substitution reaction by a solution process .

It has been reported that metal oxide nanofibers having p-type characteristics, which have been studied in the past, have poor reactivity and selectivity to specific gases compared with n-type metal oxides. In order to increase this reactivity, a sacrificial layer template is generally used, a method of increasing the surface area by controlling the shape of a belt or a tube, a method of attaching a nano-sized catalyst to induce more surface chemical reaction with gas molecules According to the chemical sensitization method, a chemical sensitization method that increases the concentration of adsorbed ions participating in the selectivity and surface reaction to a specific gas and an electronic sensitization method that improves the sensitivity based on the change of the oxidation state are used So that the sensitivity can be improved. However, these methods have limitations in that the problems of the continuous price increase of the rare metals used as the additional process and the catalyst can lead to an increase in the process and the unit price in terms of mass production of the gas sensor.

In order to overcome these limitations, in embodiments of the present invention, metal oxides having p-type characteristics are synthesized through electrospinning and heat treatment, and metal oxides having n-type characteristics with good detection characteristics through additional galvanic substitution reaction A member for a gas sensor having a porous tube structure having a large specific surface area and a pn junction between a remaining p-type metal oxide and a substituted n-type metal oxide, thereby maximizing sensing characteristics for a specific gas, Gas sensor and a manufacturing method thereof.

FIG. 1 is a schematic view of a member for an n-type metal oxide porous nanotube 100 gas sensor according to an embodiment of the present invention. Here, the n-type metal oxide porous nanotube 100 may include a metal oxide porous nanotube having an n-type property as at least a part of the metal oxide having p-type specificity is substituted with n-type The metal oxide porous nanotubes are characterized in that a metal oxide 111 having n-type characteristics and a metal oxide 110 having p-type characteristics are pn-bonded to each other. The porous metal nanotube having a porous nanotube structure .

In other words, the metal oxide porous nanotubes may be characterized by forming a plurality of p-n junction structures between the fiber surface and the remaining p-type metal oxide existing after the galvanic substitution reaction inside the fiber surface.

At this time, the metal oxide porous nanotubes are n-type TiO ₂ , ZnO, WO ₃ , SnO ₂ , In ₂ O ₃ , V ₂ O ₃ , MoO _3, and the like. The p-type may include any of metal oxides such as Co ₃ O ₄ , CuO, Fe ₂ O ₃ , Ag ₂ O, PdO, RuO ₂ , Rh At least one metal oxide selected from the group consisting of all kinds of metal oxides having p-type characteristics such as ₂ O ₃ , NiO, Fe ₃ O ₄ , V ₂ O ₅ , Cr ₂ O ₃ and MnO ₂ .

In addition, the metal oxide porous nanotubes have an outer diameter in the range of 50 nm to 10 μm, an inner diameter in the range of 5 nm to 5 μm, a thickness between the outer wall and the inner wall of 45 nm - 5 μm, and the length is in the range of 1 μm to 100 μm.

In addition, it is possible to control the amount of metal oxide and the pore size of the n-type characteristic formed according to the galvanic substitution reaction time, and thus, the main surface characteristics of the metal oxide porous tube structure are n-type and p- have. More specifically, it is possible to control the content ratio of the p-type metal oxide and the n-type metal oxide in the metal oxide porous nanotube by controlling the progress time of the galvanic substitution reaction.

For example, a metal oxide porous nanotube has a structure in which a portion of a p-type metal oxide constituting a metal oxide nanofiber having p-type characteristics during a galvanic substitution reaction is substituted with an n-type metal oxide, And forming a plurality of pores in the range of 2 nm to 50 nm.

FIG. 2 is a cross-sectional view illustrating a method of synthesizing metal oxide nanofibers having p-type characteristics through electrospinning and heat treatment according to an embodiment of the present invention. Then, the metal oxide nanofibers having n-type characteristics (more specifically, And a method of manufacturing a member for a gas sensor using the metal oxide porous nanotube structure (including the metal oxide porous nanotube structure). 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 in which a metal oxide precursor and a polymer are dissolved; Forming a metal oxide precursor / polymer composite nanofiber by electrospinning the electrospinning solution (S220); (S230) synthesizing the metal oxide precursor / polymer composite nanofiber with a p-type based metal oxide nanofiber through a high-temperature heat treatment; A metal oxide porous nanotube including a plurality of pn junctions is prepared by substituting a part of a p-type metal oxide constituting the p-type based metal oxide nanofibers with an n-type metal oxide using a galvanic substitution reaction Step S240; And applying a washing process and a drying process using centrifugal separation to the metal oxide porous nanotube including the p-n junction fabricated at step S240. Each of the above steps will be described in more detail below.

First, a step S210 of manufacturing an electrospinning solution in which a metal oxide precursor and a polymer are dissolved will be described. This step (S210) may be a process for preparing a metal oxide precursor / polymer mixed electrospinning solution. The polymer used in the spinning solution is not limited as long as it has a high weight average molecular weight and can have a sufficient viscosity.

The solvent used in the electrospinning solution does not limit the specific solvent as long as it can dissolve the polymer used for electrospinning. For example, solvents selected from ethanol, methanol, propanol, butanol, IPA, dimethylformamide (DMF), acetone, tetrahydrofuran, toluene, water and mixtures thereof can be used.

In addition, the metal oxide precursor used in this step must be dissolved in a solvent, and TiO ₂ , ZnO, WO ₃ , SnO ₂ , IrO ₂ , In ₂ O ₃ , V ₂ O ₃ , There is no limitation on a specific metal salt as long as it is a precursor including a metal salt capable of forming a semiconductor metal oxide nanofiber in which resistance changes upon adsorption and desorption of a gas such as MoO ₃ .

The weight ratio of the metal oxide precursor and the polymer for forming the electrospinning solution is preferably about 1: 1-2.

The electrospun solution is prepared by first dissolving the metal oxide precursor in a solvent and then adding a certain amount of the polymer to a solvent in which the metal oxide precursor is dissolved so that the electrospinning can be easily performed Allow the polymer to stir at a temperature sufficient to melt. Prepare a homogeneous mixture of electrolytic solution by sufficient agitation. At this time, the thickness of the p-type-based metal oxide nanofiber used as a sacrificial layer template in the galvanic substitution reaction can be controlled by controlling the viscosity of the electrospinning solution.

Step S220 may be a step of performing electrospinning using the composite electrospinning solution prepared in step S210. To this end, the composite electrospinning solution is filled into a syringe of a predetermined size, And discharges the electrospinning solution at a predetermined rate. The electrospinning system may include a high voltage generator, a grounded conductive substrate, a syringe, and a syringe nozzle. A high voltage of about 5-30 kV is applied between the solution filled in the syringe and the conductive substrate to form an electric field. The electrospinning is performed so that the spinning solution discharged through the syringe nozzle due to the electric field is formed into a nanofiber shape. During the electrospinning process, the spinning liquid may form solid polymeric fibers as the solvent of the spinning solution volatilizes until collecting on the collector plate. In detail, the discharge speed can be adjusted to about 0.01-1 ml / min, and the precursor / polymer composite nanofiber having a desired diameter can be manufactured through controlling the rate of discharge and the voltage to be transferred.

Next, in step S230, a heat treatment process is performed to oxidize the fabricated composite nanofibers to metal oxides. The heat treatment is preferably performed at a temperature in the range of 200-1000 ° C. During the heat treatment, the nanofibers are thermally decomposed and oxidized to form metal oxide nanofibers having p-type characteristics. The metal precursor for forming the p-type metal oxide is Cu ₂ (CNS) ₄ , Ni ₄ (C ₃ H ₃ N ₂ ) _8, Mg ₃ O ₃ (CO ₂ ) ₃ and Co ₃ O ₃ (CO ₂ ) _{3, Ni 3 O 3 (CO} 2) 3, Mn 3 O 3 (CO 2) 3, Fe 3 O 3 (CO 2) 3, Cu 3 O 3 (CO 2) 3, Al (OH) (CO 2) _{2, VO (CO 2) 2} , Co (NO 3) 2, Co (O 2 CCH 3), Cr 3 O (CO 2) 6, Ga 3 O (CO 2) 6, Cu 2 O (CO 2) 4 , Zn ₂ O (CO ₂ ) ₄ , _{Mo 2 O (CO 2) 4} , Cr 2 O (CO 2) 4, Co 2 O (CO 2) 4, Ru 2 O (CO 2) 4, Zr 6 O 4 (OH 4), Zr 6 O 4 ( _{CO 2) 12, Zr 6 O} 8 (CO 2) 8, In (C 5 HO 4 N 2) 4, Na (OH) 2 (SO- 3) may comprise more than one type, such as the type _3, p -type If the precursor is capable of forming a metal oxide, there is no restriction on the specific metal salt.

In step S240, at least a part of the p-type metal oxide constituting the metal oxide nanofibers having the p-type characteristic is converted into a metal oxide porous nanotube material having an n-type characteristic by a galvanic substitution reaction. . Since the metal oxide nanofibers having p-type characteristics are etched and ionized through a galvanic replacement process, a number of pores can be formed on the surface, and a nanotube, which is a hollow fiber, can be formed in the nanofiber structure Have. In addition, since the n-type metal oxide existing in an ion state precipitates as a metal oxide in the ion state, the porous nanotube structure can be maintained. Here, the galvanic substitution reaction proceeds in a solution state chemical reaction at a temperature ranging from room temperature to 100 ° C, and can be generated through a uniform stirring process. For example, a solution in which metal oxide nanofibers having p-type characteristics are uniformly dispersed is maintained at a temperature of 80 ° C to 100 ° C, and hydrochloric acid, oleic acid and Oleylamine may be added to conduct a galvanic substitution reaction.

Further, by controlling the progress time of the galvanic substitution reaction, the thickness of the metal oxide porous nanotubes including the pn junction, the thickness between the outer wall and the inner wall, the amount of pores formed on the surface and inside, the grain size, Or the content ratio of the n-type metal oxide) can be controlled.

Finally, in step S250, to obtain the metal oxide porous nanotube material having the n-type characteristics, the metal oxide porous nanotubes having n-type characteristics dispersed in the solution are separated through centrifugation , And a metal oxide porous nanotube powder having n-type characteristics can be obtained through a drying process. The centrifugal rotation speed is preferably in the range of 1000 rpm to 3000 rpm.

A metal oxide porous nanotube having substantially n-type characteristics includes a p-type n-type metal oxide and a substituted n-type metal oxide, and at the same time, a metal oxide porous nanotube having n-type characteristics . The content ratio of the p-type metal oxide and the n-type metal oxide may be controlled depending on the progress of the galvanic substitution reaction, and the case where the p-type metal oxide is substituted with the n-type metal oxide may be considered.

(NO _x , SO _x ) and biomarker gases (CH ₃ COCH ₃ , H ₂ S, C ₇ H ₈ , EtOH) using a metal oxide porous nanotube containing a pn junction according to an embodiment The method comprising the steps of: preparing a gas sensor capable of detecting at least one gas among the gas sensors.

FIG. 3 is a cross-sectional view illustrating a method of manufacturing a metal oxide porous nanotube-based gas sensor member having n-type characteristics by using a galvanic substitution reaction of metal oxide nanofibers having p-type characteristics according to an embodiment of the present invention Which schematically illustrates the process. Specifically, a metal oxide precursor / polymer composite nanofiber is formed through electrospinning, and then a metal oxide nanofiber having p-type characteristics is obtained through additional heat treatment. Thereafter, the metal oxide nanotubes having n-type characteristics are synthesized by substituting p-type metal oxide nanofibers with n-type metal oxide porous nanotubes using a galvanic substitution reaction.

Example 1: Preparation of n-type SnO ₂ / Co ₃ O ₄  Porous nanotube manufacturing

In order to synthesize n-type SnO ₂ / Co ₃ O ₄ porous nanotubes, 0.06 g of p-type metal oxide nanofibers synthesized through Comparative Example 1 was mixed with 2 g of oleylamine, 0.14 g Of oleic acid is added to 10 mL of xylene solvent and dispersed at about 90 DEG C for 2 hours with stirring. In addition, 2 ml of 2 M SnCl ₂ solution and 0.7 ml of 37% strength hydrochloric acid are added to the solution and reacted for 1 hour and 4 hours. According to the galvanic substitution reaction, the surface properties of the metal oxide can be controlled depending on the amount of SnO ₂ additionally bound.

FIG. 4 is a scanning electron micrograph of n-type SnO ₂ / Co ₃ O ₄ porous nanotubes as described above. As shown in the scanning electron microscope photograph, it can be confirmed that the Co ₃ O ₄ metal oxide nanofiber is substituted with the SnO ₂ metal oxide through the galvanic reaction to form a hollow nanotube shape and a grain size becomes smaller. For example, the average grain size of the metal oxide nanofibers having p-type characteristics may be in the range of 50 nm to 300 nm, and the average grain size of the metal oxide porous nanotubes may be in the range of 10 nm to 200 nm .

FIG. 5 is a photograph showing a transmission electron microscope photograph, a high-resolution transmission electron microscope photograph and a SAED pattern of the n-type SnO ₂ / Co ₃ O ₄ porous nanotube formed by the above process. TEM analysis shows that the size of the nanotube hollow structure is controlled according to the time of galvanic substitution reaction and the characteristics of the metal oxide forming nanotubes through the high resolution transmission electron microscope and SAED pattern are n-type and p-type It is possible to form SnO ₂ / Co ₃ O ₄ porous nanotubes having the characteristics of the present invention. Specifically, in the case proceed with galvanic substituted react for 1 hour substitution of a p-type characteristics of SnO ₂ / Co ₃ O ₄ is porous nanotube SnO ₂ / Co ₃ having an n-type characteristic O ₄ porous nanotube as a whole uniform Type SnO ₂ / N-type SnO ₂ / N-type SnO ₂ / N-type SnO ₂ / N-type SnO ₂ / Co ₃ O ₄ porous nanotubes can be formed.

Comparative Example 1. A pure p-type Co ₃ O ₄  Manufacture of nanofibers

As compared with Example 1, metal oxide nanofibers having p-type characteristics were synthesized, unlike Example 1. Specifically, 0.75 g of a cobalt oxide precursor, cobalt acetate, was dissolved in 2 g of a DMF solvent and polyvinylpyrrolidone (PVP) 0.25 (weight average) having a weight average of 1,300,000 g / mol was added to give a viscosity to the solution. g, and sufficiently stirred. The stirring conditions referred to herein means stirring at room temperature for at least 5 hours at a rotation speed of 500 rpm. The cobalt oxide precursor / polymer mixed electrospinning solution thus formed was placed in an electric syringe (Henke-Sass Wolf, 10 mL NORM-JECT), connected to a syringe pump, and pumped at a discharge rate of 0.2 ml / min The needle used for electrospinning was a 23 gauge needle while maintaining a distance of 20 cm from the collector collecting the nozzle and nanofibers while applying a high voltage of about 15 kV to the cobalt oxide precursor / Respectively.

The synthesized cobalt oxide precursor / polymer composite nanofiber is subjected to high temperature heat treatment to remove the polymer and form a cobalt oxide through oxidation of the cobalt oxide precursor. The high temperature heat treatments were performed at 600 ℃ for 1 hour, and the heating rate was kept constant at 5 ℃ / min. The temperature lowering rate was kept constant at 40 ℃ / min. By this method, pure p-type Co ₃ O ₄ nanofiber can be synthesized.

6 is a scanning electron micrograph of pure p-type Co- ₃ O ₄ nanofibers synthesized through the process of Comparative Example 1. FIG. The fabricated pure p-type Co- ₃ O ₄ nanofibers are characterized by having a size range of 200-300 nm.

EXPERIMENTAL EXAMPLE 1 Preparation of n-type SnO ₂ / Co ₃ O ₄  Fabrication and characterization of gas sensor using porous nanotubes

In order to fabricate the sensing material for the gas sensor fabricated in Example 1 and Comparative Example 1 with an exhalation disease diagnosis sensor, n-type SnO ₂ / Co ₃ O ₄ porous nanotubes, p-type SnO ₂ / Co ₃ O ₄ Porous nanotubes and pure p-type Co ₃ O ₄ nanofibers were dispersed in 300 μl of ethanol and then subjected to ultrasonic washing for 1 minute. The nanotubes of n-type SnO ₂ / Co ₃ O ₄ porous nanotubes dispersed in ethanol, p-type SnO ₂ / Co ₃ O ₄ porous nanotubes and pure p-type Co ₃ O ₄ nanofibers were dispersed at 150 μm intervals A drop coating method was applied to an upper surface of a 3 mm × 3 mm alumina substrate on which two parallel gold (Au) electrodes were formed. In the coating process, 5 μl of nanomaterials dispersed in ethanol prepared above was coated on an alumina substrate having a sensor electrode portion and then dried on a hot plate at 60 ° C., The process was repeated. In addition, the gas sensor manufactured for the evaluation of the characteristics of the expiratory flow sensor has an acetone (CH ₃ COCH ₃ ) gas as an indicator gas for diagnosis of diabetes at a relative humidity of 85 to 95 RH%, which is similar to the humidity of the gas coming out from a human mouth. The reaction temperature was maintained at 400 ℃ and the reactivity characteristics of each gas were evaluated. In addition, in order to confirm the selectivity of the gas sensor, ethanol (C ₂ H ₆ O), mercaptan (CH ₃ SH), toluene (C ₇ H ₈ ), hydrogen sulfide (H ₂ S), carbon monoxide ), Pentane (C ₅ H ₁₂ ), and ammonia (NH ₃ ) gas (5 ppm).

FIG. 7 is a graph _{showing the relation} between p-type SnO ₂ / Co ₃ O ₄ and n-type SnO ₂ / Co ₃ O _{4 prepared by the} p-type Co- ₃ O ₄ nanofibers and galvanic substitution reaction for 1 hour and 4 hours through Comparative Example 1 and Example 1, -type SnO ₂ / Co ₃ O ₄ Porous nanotubes and pure p-type Co ₃ O ₄ nanofibers are the result of varying resistance changes when exposed to acetone gas

Generally, in the case of metal oxide having p-type characteristics, the resistance of the metal oxide increases when exposed to reducing gas, while the resistance of metal oxide having n-type characteristics decreases. The p-type SnO ₂ / Co ₃ O ₄ porous nanotubes obtained from the pure p-type Co ₃ O ₄ nanofibers and the galvanic substitution reaction for 1 hour, Quot ;. < / RTI > On the other hand, the n-type SnO ₂ / Co ₃ O ₄ porous nanotubes exhibited a reduced resistance when the galvanic substitution reaction proceeded for 4 hours. As a result, it is possible to control the n-type and p-type surface characteristics according to the galvanic substitution reaction time.

FIG. 8 shows a result of a sensor test in which the degree of reaction when the concentration of acetone gas decreased at 5, 4, 3, 2, 1, 0.6, and 0.4 ppm at 400 ° C. over time. As shown in the graph, the n-type SnO ₂ / Co ₃ O ₄ porous nanotube material exhibits an enhanced sensitivity of 55 times or more as compared to the pure p-type Co ₃ O ₄ nanofiber. This increases the surface reaction with acetone through the porous nanotube structure through the galvanic substitution, and the p-type Co ₃ O ₄ and the n-type SnO _{2 form} the pn junction, Is interpreted.

9 is _{n-type SnO 2 / Co 3} O 4 Porous a graph showing the selectivity characteristics of the acetone the nanotube material ethanol (C ₂ H ₆ O), mercaptan (CH ₃ SH), toluene (C ₇ H ₈ ), Hydrogen sulfide (H ₂ S), carbon monoxide (CO), pentane (C ₅ H ₁₂ ) and ammonia (NH ₃ ) gas (5 ppm). Based on these results, the present invention can be applied not only to a gas sensor for health care, but also to a gas sensor for detecting harmful environmental gas, which can detect various kinds of diseases by sensing specific biochemical surface gas among various bio-surface gases in the exhalation of the human body

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.

100: n-type metal oxide porous nanotubes that represent hollow tube structures.
110: n-type metal oxide Part showing a metal oxide having p-type characteristics in a porous nanotube.
111: n-type metal oxide Part showing a metal oxide having n-type characteristics in a porous nanotube.

Claims (12)

a part of the metal oxides constituting the metal oxide nanofibers is replaced with a metal oxide having an n-type characteristic through a galvanic substitution reaction on metal oxide nanofibers having p-type characteristics, Wherein the porous nanotubes are formed of oxide porous nanotubes. The method according to claim 1,
The metal oxide porous nanotube has an outer diameter in the range of 50 nm to 10 μm, an inner diameter in the range of 5 nm to 5 μm, a thickness between the outer wall and the inner wall of 45 nm to 5 μm and the length is in the range of from 1 μm to 100 μm. A member for a gas sensor based on a one-dimensional pn-junction metal oxide porous nanotube. The method according to claim 1,
Wherein the metal oxide porous nanotube forms a plurality of pn junction structures between the surface of the fiber and the remaining p-type metal oxide existing after the galvanic substitution reaction in the fiber surface. The pn junction 1-dimensional metal oxide porous nanotube Member for a base gas sensor. The method according to claim 1,
In the metal oxide porous nanotube, a portion of the p-type metal oxide constituting the metal oxide nanofibers having the p-type characteristic during the galvanic substitution reaction is substituted with an n-type metal oxide, nm to 50 nm. The present invention also relates to a member for a pn junction one-dimensional metal oxide porous nanotube-based gas sensor. The method according to claim 1,
The average grain size of the metal oxide nanofibers having the p-type characteristic is in the range of 50 nm to 300 nm,
Wherein the average grain size of the metal oxide porous nanotubes is in the range of 10 nm to 200 nm. The method according to claim 1,
The p-type metal oxide is _{Co 3 O 4, CuO, Fe} 2 O 3, Ag 2 O, PdO, RuO 2, Rh 2 O 3, NiO, Fe 3 O 4, V 2 O 5, MnO 2 , and Cr ₂ O ₃ ,
The n-type metal oxide may include TiO ₂ , ZnO, WO ₃ , SnO ₂ , In ₂ O ₃ , V ₂ O _3, and MoO _{3. The} member for a gas sensor based on a one-dimensional metal oxide porous nano tube having pn junctions. (a) preparing an electrospinning solution in which a metal oxide precursor and a polymer are dissolved;
(b) forming a metal oxide precursor / polymer composite nanofiber by electrospinning the electrospinning solution;
(c) synthesizing the metal oxide precursor / polymer composite nanofiber into a p-type-based metal oxide nanofiber through a high-temperature heat treatment; And
(d) substituting at least a portion of the p-type metal oxide constituting the p-type based metal oxide nanofibers with an n-type metal oxide using a galvanic substitution reaction to form a metal oxide porous nano- Steps to make tube
Wherein the porous nanotube-based gas sensor comprises a pn-bonded one-dimensional metal oxide porous nanotube-based gas sensor. 8. The method of claim 7,
(e) applying a cleaning process and a drying process using centrifugal separation to the metal oxide porous nanotube including the pn junction fabricated above
The method of claim 1, wherein the porous nanotube-based gas sensor comprises a pn-bonded one-dimensional metal oxide porous nanotube-based gas sensor. 8. The method of claim 7,
Wherein the thickness of the p-type-based metal oxide nanofiber used as the sacrificial layer template in the galvanic substitution reaction is controlled by adjusting the viscosity of the electrospinning solution in the step (a) A method for manufacturing a member for a porous nanotube-based gas sensor. 8. The method of claim 7,
The step (d)
The solution in which the metal oxide nanofibers having the p-type characteristics are uniformly dispersed is maintained at a temperature of 80 ° C to 100 ° C, and hydrochloric acid, oleic acid and oleyl amine oleylamine is added to proceed the galvanic substitution reaction. The method for manufacturing a member for a gas sensor of a pn junction one-dimensional metal oxide porous nanotube. 8. The method of claim 7,
The step (d)
By adjusting the time for the progress of the galvanic substitution reaction, the thickness of the metal oxide porous nanotubes including the pn junction, the thickness between the outer wall and the inner wall, the amount of the pores formed on the surface and inside, the grain size, Or the content ratio of the n-type metal oxide) is controlled. The method for manufacturing a member for a pn junction one-dimensional metal oxide porous nanotube-based gas sensor. 8. The method of claim 7,
(NO _x , SO _x ) and biomarker gas (CH ₃ COCH ₃ , H ₂ S, C ₇ H ₈ , EtOH) using the metal oxide porous nanotubes containing the pn junction A step of producing a gas sensor capable of detecting one gas
The method of claim 1, wherein the porous nanotube-based gas sensor comprises a pn-bonded one-dimensional metal oxide porous nanotube-based gas sensor.

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