KR102485055B1 - Porous metal nanotubes, preparing method thereof and gas detector using the same - Google Patents

Abstract

The present invention provides a porous metal nanotube in which one or more metals form a hollow shell, and the shell has a plurality of pores formed thereon to have an open structured surface.

Description

Porous metal nanotube, manufacturing method thereof, and gas sensor using the same

The present invention relates to a porous metal nanotube, a manufacturing method thereof, and a gas sensor using the same. More specifically, the present invention relates to a hollow porous metal nanotube containing one or more metals formed through electrospinning and etching processes, a manufacturing method thereof, and a gas sensor using the same.

In general, nanotubes have characteristics of a high volume-to-surface area ratio and, in particular, have very unique mechanical and electrical properties including thermal conductivity, and thus are applied as additives to various structural materials. In particular, when nanotubes are applied as gas sensors, they have relatively high sensitivity and selectivity, fast response, and can be manufactured in a small size, so that the device can be easily miniaturized. Therefore, it is important to maximize the specific surface area capable of reacting with gas and to facilitate diffusion of the target gas to form a structure capable of effectively undergoing surface gas reaction.

In order for recent metal oxide semiconductor-based gas sensors to have high sensitivity and high selectivity, through the design of nanostructures such as nanofibers, nanobelts, nanotubes, and nanocubes, which have a relatively large surface area compared to thin film structures, A lot of research is being conducted to increase the resistance change, which is a method of expressing sensitivity, and to further maximize the wide specific surface area, small and large pores are formed in the nanostructure to increase gas permeability into the sensing material, resulting in higher sensitivity. technology is being developed.

However, a porous metal nanotube for a gas sensor capable of sensing a very small amount of gas, such as a transformer fuel gas, and having high sensitivity characteristics has not yet been disclosed.

The background art of the present invention is disclosed in Korean Patent Publication No. 10-2017-0047432 and the like.

An object of the present invention is a metal that is formed into nanoparticles so that one or more metals can be catalytically functionalized, has hollowness and porosity, shows a high specific surface area, and has a greatly increased porosity, allowing easy penetration even in the case of a very small amount of gas molecules. It is to provide porous nanotubes.

Another object of the present invention is to provide a method for effectively preparing hollow and porous metal nanotubes by controlling electrospinning and etching processes while using one or more metal oxide precursors.

Another object of the present invention is to provide a gas sensor including metal nanotubes that responds quickly even to a very small amount of gas and has improved response speed and recovery speed, including porous metal nanotubes.

The above and other objects of the present invention can all be achieved by the present invention described below.

1. One aspect of the invention relates to porous metal nanotubes.

In the porous metal nanotube, one or more types of metal may form a hollow shell, and the shell may have a surface having an open structure by forming a plurality of pores.

2. In the first embodiment, the porous metal nanotube may not contain a metal oxide.

3. In the above 1 or 2 embodiments, in the porous metal nanotube, an aggregate of one or more types of metal particles may form a hollow shell.

4. In the specific example of any one of 1 to 3 above, the metal may include palladium (Pd).

5. In the embodiment of any one of 1 to 4, the metal includes a first metal and a second metal, the precursor of the first metal has higher oxide formation energy than the precursor of the second metal, 2 The distribution of metals may increase from the center to the surface.

6. In any one of the embodiments of 1 to 5, the porous metal nanotube may have an average diameter of 100 nm to 5 μm.

7. In any one embodiment of 1 to 6, the shell may have an average thickness of 10 nm to 500 nm.

8. In any one of the embodiments 1 to 7, the pores may have an average diameter of 3 nm to 60 nm.

9. Another aspect of the present invention relates to a method for manufacturing porous metal nanotubes.

The manufacturing method of the porous metal nanotube includes (a) preparing primary nanofibers by electrospinning a spinning solution containing at least one metal oxide precursor and a polymer;

(b) preparing core-shell composite nanofibers by heat-treating the primary nanofibers to remove the polymer and oxidizing the metal oxide precursor;

(c) etching the core of the composite nanofiber to prepare a metal oxide nanotube in the form of a hollow shell; and

(d) preparing a metal nanotube having a shell in which one or more metals are bonded by reducing the metal oxide by heat-treating the metal oxide nanotube.

10. In the ninth embodiment, the spinning solution includes two or more metal oxide precursors having different oxide formation energies.

11. In the 9th or 10th embodiment, the electrospinning in step (a) may form a nanofiber web by spinning an electrospinning solution containing one or more metal oxide precursors at a voltage of 10 to 20 kV.

12. In any one embodiment of 9 to 11, the heat treatment in step (b) may be performed at 500 to 1,000 ° C.

13. In any one embodiment of 9 to 12, the shell in step (b) is PdO, SnO ₂ , SnO, ZnO, Fe ₂ O ₃ , Fe ₃ O ₄ , NiO, TiO ₂ , CuO, Cu ₂ One or more of O, In ₂ O ₃ , Co ₃ O ₄ , PdO, NiCo ₂ O ₄ , Ag ₂ O, MnO ₂ , MnO, Mn ₃ O ₄ , and Ta ₂ O ₅ may be included.

14. In any one of the specific examples of 9 to 13, the etching in step (c) may remove only the core by introducing a core-reactive solvent.

15. In any one embodiment of 9 to 14, the core reactive solvent is sodium hydroxide (NaOH), potassium hydroxide (KOH), nitric acid, hydrochloric acid, hydrofluoric acid, sulfuric acid (sulfuric acid), methanol (methanol), ethanol (ethanol), and ammonium persulfate (ammonium persulfate).

16. In any one embodiment of 9 to 15, the heat treatment in step (d) may reduce the metal oxide by heat treatment at 300 to 500 ° C. in a reducing gas atmosphere.

17. Another aspect of the present invention relates to a gas sensor comprising porous metal nanotubes.

The gas sensor may include a substrate;

a sensing layer formed on the substrate; and

and electrodes wire-bonded to both ends of the sensing film, and includes the porous nanotubes.

18. In the 17th embodiment, the gas sensor including the porous nanotubes can detect environmentally harmful gases or vapor gases generated from transformer insulating oil.

The present invention provides hollow porous metal nanotubes formed by forming primary nanotubes by controlling electrospinning and etching processes using at least one metal oxide precursor, reducing metal oxide nanoparticles, and having high porosity. Metal nanotubes having can be used as a sensing layer in a gas sensor, so that a very small amount of gas generated from an environmentally harmful gas or transformer insulating oil can be quickly detected.

1 is a schematic diagram showing a process of forming a porous metal nanotube according to one embodiment of the present invention.
2 is a process flow chart of a method for manufacturing a porous metal nanotube according to another aspect of the present invention.
3 is a scanning electron micrograph of composite nanofibers having a core-shell structure in the method for manufacturing porous metal nanotubes according to one embodiment of the present invention.
4 shows a transmission electron micrograph and element concentration analysis results of composite nanofibers having a core-shell structure in a method for manufacturing porous metal nanotubes according to an embodiment of the present invention.
5 is a scanning electron microscope (SEM) photograph of a metal oxide nanotube having a shell structure by etching a core in a method for manufacturing a porous metal nanotube according to an embodiment of the present invention.
6 is a graph of X-ray diffraction analysis of a porous palladium-nickel metal alloy and a porous palladium nanotube in a method for manufacturing a porous metal nanotube according to an embodiment of the present invention.
7 is a scanning electron micrograph of porous palladium-nickel metal alloy nanotubes in the method for manufacturing porous metal nanotubes according to one embodiment of the present invention.
8 is a scanning electron microscope (SEM) photograph of palladium-tin, palladium-silver, and palladium-copper alloy nanotubes in each process step in the method for manufacturing a porous metal nanotube according to an embodiment of the present invention.
9 is a gas sensor according to another aspect of the present invention, in which hydrogen gas of a gas sensor including porous palladium-nickel metal alloy nanotubes, porous palladium-tin metal alloy nanotubes, and porous palladium-silver metal alloy nanotubes It is a graph showing the sensing characteristics for

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. However, the following drawings are only provided to aid understanding of the present invention, and the present invention is not limited by the drawings. In addition, since the shape, size, ratio, angle, number, etc. disclosed in the drawings are exemplary, the present invention is not limited to the illustrated details.

Like reference numbers designate like elements throughout the specification. In addition, in describing the present invention, if it is determined that a detailed description of related known technologies may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted.

When 'includes', 'has', 'consists of', etc. mentioned in this specification is used, other parts may be added unless 'only' is used. In the case where a component is expressed in the singular, the case including the plural is included unless otherwise explicitly stated.

In interpreting the components, even if there is no separate explicit description, it is interpreted as including the error range.

When the positional relationship of two parts is described by 'over', 'over', 'under', 'beside', etc., unless 'immediately' or 'directly' is used, there is a One or more other parts may be located.

Positional relationships such as 'top', 'top', 'bottom', and 'bottom' are described based on the drawings, and do not represent absolute positional relationships. That is, the positions of 'upper' and 'lower' or 'upper surface' and 'lower surface' may be changed depending on the observation position.

In this specification, "a to b" representing a numerical range is defined as "≥a and ≤b".

The present invention will be described in detail with reference to the drawings below.

1 is a schematic diagram showing a process of forming a porous metal nanotube according to one embodiment of the present invention.

Referring to FIG. 1, the porous metal nanotube 1000 according to the present invention has an open structure in which one or more metals form a hollow shell 100 and a plurality of pores 200 are formed in the shell 100. (Open structure) surface.

The surface of the open structure has a plurality of surface pores non-uniformly formed.

The porous metal nanotube 1000 does not include metal oxide.

In a specific embodiment, the porous metal nanotube 1000 is a composite nanofiber having a core 21-shell 220 structure by forming primary nanofibers 10 with a metal oxide precursor and heat-treating the nanofibers 10. After the fibers 20 are formed, the core 21 is removed through an etching process, and metal oxide nanotubes 30 having a hollow shell structure in which a plurality of pores 31 are formed are formed, and the metal oxide is finally reduced. it is formed

In the porous metal nanotube 1000, a plurality of pores 200 are formed in the shell 100, the specific surface area is greatly increased, and the porous metal nanotube 1000 is used as a catalyst for diffusion of gas molecules. A very small amount of gas molecules are rapidly penetrated into the nanotubes.

In the porous metal nanotube 1000, an aggregate of one or more types of metal particles forms a hollow shell.

The porous metal nanotube 1000 is etched to form a hollow shell, and one or more types of metal particles are aggregated.

In one embodiment, the metal includes palladium (Pd).

When palladium is in contact with hydrogen gas, external hydrogen molecules are dissociated into atoms on the surface of palladium and adsorbed on the surface, and then atoms move to the interstitial site of palladium atoms by diffusion to form palladium hydride (PdHx). The volume expands and the electrical conductivity of palladium changes. Since the solubility of hydrogen gas in palladium increases as the temperature decreases, it is possible to detect highly reduced hydrogen gas when using palladium because the electrical conductivity is changed by hydrogen gas at room temperature (25° C.).

In the case of detecting hydrogen by manufacturing a gas sensor only with palladium, there is a disadvantage in that diffusion of hydrogen dissolved in palladium is very slow even if the solubility of hydrogen gas is high, and in this case, the response time and recovery time of the gas sensor are increased.

When the porous metal nanotube 1000 contains palladium and is aggregated with other metals to form a shell, it is easy to support the structure of the nanotube and has a high volume-to-surface area ratio, so hydrogen diffusion in palladium is greatly increased. Therefore, it is possible to effectively detect the change in the hydrogen gas concentration that changes in real time.

The at least one metal may form a metal alloy nanotube and a primary nanostructure.

In one embodiment, the metal includes a first metal and a second metal, the precursor of the first metal has higher oxide formation energy than the precursor of the second metal, and the second metal is distributed from the center to the surface. It increases.

A core-shell structure may be formed by selecting metals having different oxide formation energies (enthalpy) from among the metals and forming a concentration gradient according to the oxide formation energy.

In embodiments, the metal is one or more of Pd, Sn, Ag, Cu, Fe, Ni, Mn, Co, Ti, and Ta.

The metals of this kind aggregate to form a shell in the process of reducing metal oxides, combine to form nanotubes in an alloy state, and form primary nanostructures without a separate template.

In one embodiment, the porous metal nanotube 1000 may have an average diameter of 100 nm to 5 μm.

Nanotubes having an average diameter within the above range have catalytic properties that promote diffusion according to the inflow of gas molecules according to the increase in specific surface area.

The shell 100 may have an average thickness of 10 nm to 500 nm.

Porous metal nanotubes containing metals or metal alloys may be formed by forming and reducing one or more metal oxide precursors into nanotubes within the above range. It is difficult to maintain, and if it exceeds the above range, there is a concern that the promotion of gas molecule diffusion may be reduced.

The pores 200 may have an average diameter of 3 nm to 60 nm.

The pores 200 are formed by partially removing one or more metal oxides disposed in the shell during an etching process.

When the pores 200 have an average diameter within the above range, gas molecules such as H ₂ , C ₂ H ₂ , C ₂ H ₄ , C ₂ H ₆ , CH ₄ , CO, and CO ₂ easily penetrate.

When the porous metal nanotube 1000 is used as a sensing layer of a gas sensor, even a very small amount of gas molecules can easily enter and show a change in resistance.

Another aspect of the present invention relates to a method for manufacturing porous metal nanotubes.

2 is a process flow chart of a method for manufacturing a porous metal nanotube according to another aspect of the present invention.

Referring to FIG. 2, the method of manufacturing the porous metal nanotube includes (a) electrospinning a spinning solution containing at least one metal oxide precursor and a polymer to prepare primary nanofibers;

(b) preparing core-shell composite nanofibers by heat-treating the primary nanofibers to remove the polymer and oxidizing the metal oxide precursor;

(c) etching the core of the composite nanofiber to prepare a metal oxide nanotube in the form of a hollow shell; and

(d) preparing a metal nanotube having a shell in which one or more metals are bonded by reducing the metal oxide by heat-treating the metal oxide nanotube.

First, a primary nanofiber is prepared by electrospinning a spinning solution containing one or more metal oxide precursors and a polymer (S100).

In one embodiment, the spinning solution includes two or more metal oxide precursors having different oxide formation energies.

When metal oxide precursors having different oxide formation energies are included, nanofibers having a core-shell structure may be manufactured through a heat treatment process.

More specifically, the primary nanofibers include two or more types of metal oxide precursors, and when the oxide formation energies (enthalpy) of the metal oxide precursors are different from each other, an oxide concentration gradient is formed to form a metal having low oxide formation energy. The oxide precursor first forms an oxide, which increases its concentration on the surface to form a concentration gradient. The concentration of the metal oxide precursor having higher oxide formation energy increases toward the inside, so that two or more metal oxide precursors eventually form a core-shell structure.

In a specific example, a spinning solution is prepared by mixing and adding the one or more metal oxide precursors to the spinning solution, further adding a polymer to the nanofiber support and then stirring.

The spinning solution is not limited as long as it can be electrospun by uniformly dispersing the metal oxide precursor and the polymer, and specifically, distilled water, ethanol, methanol, propanol, butanol, isopropyl alcohol, dimethylformamide, acetone, detrahydrofuran , toluene and mixtures thereof.

The polymer is a support for the primary nanofibers, and is not limited as long as it is mixed with the metal oxide precursor to disperse the metal oxide precursor for electrospinning, and then thermally decomposes in a heat treatment process.

The spinning solution is electrospun to prepare primary nanofibers.

The electrospinning can produce primary nanofibers by controlling the electric field and using a single nozzle.

In a specific example, the electrospinning in S100 may form a nanofiber web by spinning an electrospinning solution containing one or more metal oxide precursors at a voltage of 10 to 20 kV using a single nozzle.

The electrospinning may produce a primary nanofiber web by applying a high voltage within the above range using a single nozzle, and it is difficult to prepare a primary nanofiber web if the voltage is not a single nozzle or is out of the above voltage range.

The primary nanofiber is heat treated to remove the polymer, and the metal oxide precursor is oxidized to prepare a composite nanofiber having a core-shell structure (S200).

The heat treatment thermally decomposes and removes the polymer, which is the support of the primary nanofibers.

In one embodiment, the heat treatment of S200 may be performed at 500 to 1,000 ° C. for 1 to 3 hours to thermally decompose the polymer.

When the heat treatment is performed within the above range, the polymer may be thermally decomposed and removed, and the metal oxide precursor may be oxidized and changed into a metal oxide.

The shell of step (b) in S200 is PdO, SnO ₂ , SnO, ZnO, Fe ₂ O ₃ , Fe ₃ O ₄ , NiO, TiO ₂ , CuO, Cu ₂ O, In ₂ O ₃ , Co ₃ O ₄ , PdO, NiCo ₂ O ₄ , Ag ₂ O, MnO ₂ , MnO, Mn ₃ O ₄ , and Ta ₂ O ₅ .

The metal oxide of the above type is introduced in the form of a metal oxide precursor and heat-treated to form a composite nanofiber having a core-shell structure in the form of a metal oxide.

The core of the composite nanofiber is etched to prepare a metal oxide nanotube in the form of a hollow shell in which a plurality of pores are formed (S300).

In the etching process, when the core is etched to form a hollow, a nanotube shape is formed.

In the etching step S300, a core-reactive solvent is introduced to change the metal oxide present in the core of the metal oxide nanofiber into a metal salt, and the metal salt can be etched by dissolving in water.

In one embodiment, the core reactive solvent is sodium hydroxide (NaOH), potassium hydroxide (KOH), nitric acid, hydrochloric acid, hydrofluoric acid, sulfuric acid, methanol , at least one of ethanol and ammonium persulfate.

It is preferable to form a metal salt using the above kind of solvent, but a solvent capable of dissolving the metal oxide as a salt is not limited.

In one embodiment, the at least one metal oxide includes a first metal oxide and a second metal oxide, and the weights of the first metal oxide and the second metal oxide are different from each other in content ratio within 100 wt%. and, for example, when the content of the first metal oxide is excessive and the second metal oxide is selected from the excess domain and the second metal oxide is etched, an open structure porous nanotube having a plurality of pores is formed. can

The metal oxide nanotube is heat-treated to reduce the metal oxide to prepare a metal nanotube having a shell in which one or more metals are bonded (S400).

In the heat treatment of S400, the metal oxide may be reduced by heat treatment at 300 to 500° C. for 1 to 3 hours under a reducing gas atmosphere containing hydrogen and nitrogen.

Porous metal nanotubes, which are metals or metal alloys, can be produced by reducing metal oxides under the heat treatment conditions under the reducing gas. When the metal oxides are out of the above range, the reduction reaction does not occur, and the metal oxides remain in the nanotubes, resulting in gas diffusion catalytic properties. this is reduced

Another aspect of the invention relates to a gas sensor comprising porous metal nanotubes.

The gas sensor may include a substrate; a sensing layer formed on the substrate; and electrodes wire-bonded to both ends of the sensing film.

The sensing layer includes the porous metal nanotubes 1000 .

The gas sensor includes a sensing film on a substrate and an electrode for recognizing a change in resistance of the sensing film.

The sensing film is applied to the porous metal nanotubes by any one of spray coating, drop coating, screen printing, electrohydrodynamic coating (EHD), direct coating through electrospray, and application through transfer of the metal nanotubes on the substrate. It is formed from aggregates.

The gas sensor including the sensing film including the porous metal nanotubes may detect resistance that is changed when an environmentally harmful gas or a gas generated from transformer insulating oil permeates the sensing film.

In one embodiment, the vapors are H ₂ , C ₂ H ₂ , C 2 H 4 , C 2 H 6 , H 2 , C 2 H 2 , C ₂ H ₄ , C ₂ H ₆ , CH ₄ , CO, CO ₂ and the like.

The gas sensor exhibits excellent selectivity capable of detecting various gases, having a faster response and recovery rate because the gas molecules of the above type are easily permeable.

Hereinafter, preferred examples are presented to aid understanding of the present invention, but the following examples are only illustrative of the present invention, and the scope of the present invention is not limited to the following examples.

Experimental Example 1. Preparation of primary nanofibers

Composite nanofibers containing silicon dioxide (SiO ₂ ), palladium oxide (PdO), and nickel oxide (NiO) were prepared to confirm the shape and distribution of metal particles.

0.396 g of palladium acetylacetonate (Pd(C ₅ H ₇ O ₂ ) ₂ , Sigma-Aldrich) as a precursor of palladium oxide and nickel nitrate hydrate (nickel nitrate hydrate; Ni(NO ₃ ) ₂ as a precursor of nickel oxide) 0.130 g of 6H ₂ O, Sigma-Aldrich) was added to a 3.0 g solution of N,N-dimethylformamide (DMF) and ethanol 1:1, and stirred at 500 RPM for 1 hour.

Then, 100 μl of tetraethyl orthosilicate (Aldrich), a silicon dioxide precursor, was added to the solution in which the palladium oxide precursor/nickel oxide precursor was dissolved, stirred at 500 RPM for 1 hour and 30 minutes, and polyvinyl chloride having a molecular weight of 1,300,000 g/mol was added to the solution. Pyrrolidone [poly(vinyl pyrrolidone); After dissolving 0.380 g of 'PVP', Aldrich], the electrospinning solution was prepared by further stirring for 6 hours.

The stirred silicon dioxide precursor/palladium oxide precursor/nickel oxide precursor/PVP polymer mixture spinning solution was placed in a syringe and connected to a syringe pump (Henke-Sass Wolf, 10ml NORM-JECT), and spinning was performed at a discharge rate of 100ml per minute. .

The distance between the needle (25 gauge) from which the spinning solution is discharged and the current collector substrate for obtaining the nanofiber web was maintained at 17 cm, and a high voltage of 18 kV was applied to form a silicon dioxide precursor / palladium oxide precursor / nickel oxide precursor / PVP polymer. A primary nanofibrous web containing was prepared.

Experimental Example 2. Preparation of composite nanofibers

It was confirmed whether composite nanofibers having a core-shell structure could be prepared by heat-treating the primary nanofibers.

The silicon dioxide precursor/palladium oxide precursor/nickel oxide precursor/PVP polymer mixed primary nanofiber web prepared by electrospinning using a single nozzle according to Experimental Example 1 was mixed with Ney's Vulcan 3 in an air atmosphere. High-temperature heat treatment was performed at 600° C. for 2 hours using a -550 small electric furnace.

At this time, the temperature increase rate was kept constant at 10 ° C. Due to the high-temperature heat treatment process, the PVP polymer that supports the silicon dioxide precursor / palladium oxide precursor / nickel oxide precursor / PVP polymer composite nanofiber web is thermally decomposed and removed, and the polymer fiber The silicon dioxide precursor, the palladium oxide precursor, and the nickel oxide precursor dissolved therein were oxidized to form a silicon dioxide/palladium oxide/nickel oxide composite nanofiber.

3 is a scanning electron micrograph of composite nanofibers having a core-shell structure in the method for manufacturing porous metal nanotubes according to one embodiment of the present invention.

Referring to FIG. 3, it was confirmed that the composite nanofibers including the silicon dioxide precursor/palladium oxide precursor/nickel oxide precursor/PVP polymer had a smooth surface and a uniform diameter distribution of 400 nm on average, and the silicon dioxide precursor/palladium It was confirmed that the oxide precursor/nickel oxide precursor/PVP polymer composite nanofibers can be prepared into nanofibers by preparing an electrospinning solution and controlling electrospinning conditions.

4 shows a transmission electron micrograph and element concentration analysis results of composite nanofibers having a core-shell structure in a method for manufacturing porous metal nanotubes according to an embodiment of the present invention.

Referring to FIG. 4 , it can be seen from the transmission electron micrograph that the nanofibers including silicon dioxide/palladium oxide/nickel oxide are composed of polycrystalline nanoparticles and have a relatively dense surface. In addition, as a result of element concentration analysis (TEM energy dispersive spectroscopy) of a transmission electron microscope, it was confirmed that silicon (Si) was concentrated in the central part, and palladium (Pd) and nickel (Ni) were evenly distributed throughout. did

Therefore, silicon dioxide (SiO ₂ ) is relatively located in the central part, and the silicon dioxide/palladium oxide/nickel oxide composite nanofiber is composed of mostly silicon dioxide in the central part and mostly palladium oxide (PdO)/nickel oxide (NiO) in the outer part. It was confirmed that it was made. This is because the ethalpy energy of silicon dioxide is greater than that of palladium oxide and nickel oxide, so palladium and nickel are oxidized from the surface of the nanofiber to form palladium oxide and nickel oxide, and palladium and nickel are formed on the outside and inside of the nanofiber. It was confirmed that an element concentration gradient was formed, and palladium and nickel elements diffused to the surface, and silicon dioxide was oxidized and formed inside the nanofibers.

Experimental Example 3. Preparation of metal oxide nanotubes

The composite nanofiber was etched to prepare a metal oxide nanotube in the form of a hollow shell in which a plurality of pores were formed.

The composite nanofibers according to Experimental Example 2 were additionally etched.

For the etching process, 50 mg of silicon dioxide/palladium oxide/nickel oxide composite nanofibers were impregnated with an aqueous solution of 0.04 g of sodium hydroxide (NaOH) dissolved in 100 ml of distilled water for 10 hours.

The temperature of the sodium hydroxide aqueous solution containing the silicon dioxide/palladium oxide/nickel oxide composite nanofibers was maintained at 60°C.

5 is a scanning electron microscope (SEM) photograph of a metal oxide nanotube having a shell structure by etching a core in a method for manufacturing a porous metal nanotube according to an embodiment of the present invention.

Referring to FIG. 5 , it was confirmed that silicon dioxide concentrated in the central portion was selectively etched to form porous palladium oxide/nickel oxide nanotubes having an empty central portion.

In the etching process, only silicon dioxide is selectively etched by sodium hydroxide in an atmosphere of about pH 12, and is etched according to Formula 1 below.

[Formula 1]

2NaOH + SiO ₂ → Na ₂ SiO ₃ + H ₂ O

Etching was carried out by the above reaction, and the silicate (Na ₂ SiO ₃ ) formed by the above reaction is soluble in water and can be easily removed through an additional washing process, thereby forming a palladium oxide/nickel oxide nanotube with an empty central portion. It was confirmed that it could be produced.

Example 1. Preparation of porous palladium-nickel metal alloy nanotubes

Porous metal nanotubes were prepared by reduction with the metal oxide nanotubes prepared according to Experimental Example 3.

The metal oxide nanotubes containing palladium oxide and nickel oxide were subjected to high-temperature heat treatment at 400° C. for 2 hours using a tubular electric furnace in a 20% H ₂ /N ₂ atmosphere.

At this time, the temperature increase rate was kept constant at 5°C/min. Due to the reduction heat treatment process, palladium oxide and nickel oxide were reduced to form porous palladium/nickel metal alloy nanotubes.

Example 2. Preparation of porous palladium nanotubes

Porous metal nanotubes were prepared in the same manner as in Example 1 without adding nickel nitrate hydrate, which is a nickel oxide precursor.

Experimental Example 4. Structure of Porous Metal Alloy Nanotube

Structures of the porous palladium/nickel metal alloy nanotubes according to Examples 1 and 2 were confirmed.

6 is an X-ray diffraction analysis graph of porous palladium-nickel metal alloys and porous palladium nanotubes according to Examples 1 and 2 of the present invention, and FIG. 7 is a graph of porous palladium-nickel metal alloy nanotubes prepared in Example 1. This is a scanning electron micrograph.

Referring to FIG. 6, it was confirmed that the hollow porous palladium and nickel metal alloy nanotubes and the porous palladium metal nanotubes were generally well formed in the palladium metal single phase, and referring to FIG. 7, the palladium prepared in Example 1 - It was confirmed that a plurality of pores were formed in the nickel metal alloy nanotube, and it was formed into a porous and hollow nanotube.

Example 3. Preparation of porous palladium-tin metal alloy nanotubes

To prepare porous palladium and tin metal alloy nanotubes, 0.396 g of palladium acetylacetonate [Pd(C ₅ H ₇ O ₂ ) ₂ , Sigma-Aldrich], a palladium oxide precursor, and tin chloride hydrate [SnCl ₂ xH ₂ , a tin oxide precursor] O, Sigma-Aldrich] 0.113g was added to a 3.0g solution of N,N-dimethylformamide (DMF) and ethanol mixed in a 1:1 ratio and stirred at 500 RPM for 1 hour.

Thereafter, porous palladium and tin metal alloy nanotubes were prepared in the same manner as in Example 1.

Example 4. Preparation of porous palladium-silver metal alloy nanotubes

0.396 g of palladium acetylacetonate [Pd(C ₅ H ₇ O ₂ ) ₂ , Sigma-Aldrich], a palladium oxide precursor, and silver chloride [AgCl, Sigma-Aldrich], a silver oxide precursor, were used to prepare porous palladium and silver metal alloy nanotubes. 0.062g was added to a 3.0g solution of N,N-dimethylformamide (DMF) and ethanol mixed at a ratio of 1:1 and stirred at 500 RPM for 1 hour.

Thereafter, porous palladium and silver metal alloy nanotubes were prepared in the same manner as in Example 1.

Example 5. Preparation of porous palladium-copper metal alloy nanotubes

To prepare porous palladium and copper metal alloy nanotubes, 0.396 g of palladium acetylacetonate [Pd(C ₅ H ₇ O ₂ ) ₂ , Sigma-Aldrich], a palladium oxide precursor, and copper acetylacetonate [Cu(C ₅ H ₇ , Sigma-Aldrich], a copper oxide precursor) 0.080 g of O ₂ ) ₂ , Sigma-Aldrich] was added to a 3.0 g solution of N,N-dimethylformamide (DMF) and ethanol mixed in a 1:1 ratio and stirred at 500 RPM for 1 hour.

Thereafter, porous palladium and copper metal alloy nanotubes were prepared in the same manner as in Example 1.

Experimental Example 5. Porous Metal Alloy Nanotube Structure

8 is scanning electron micrographs of the palladium-tin, palladium-silver, and palladium-copper alloy nanotubes according to Examples 3 to 5 at each step of the process.

Referring to FIG. 8 , it was confirmed that a hollow porous metal alloy nanotube was formed through an electrospinning process, an etching process, and a reduction process.

Example 6. Gas sensor

After applying the porous palladium-nickel metal alloy nanotube prepared according to Example 1 to an alumina substrate by drop coating, a gas sensor was manufactured using a platinum wire.

Example 7. Gas sensor

A gas sensor was manufactured in the same manner as in Example 6 using the porous palladium-tin metal alloy nanotube prepared in Example 3.

Example 8. Gas sensor

A gas sensor was manufactured in the same manner as in Example 6 using the porous palladium-silver metal alloy nanotubes prepared in Example 4.

Experimental Example 6. Gas sensor detection characteristics

9 shows the hydrogen gas sensing characteristics of gas sensors including porous palladium-nickel metal alloy nanotubes, porous palladium-tin metal alloy nanotubes, and porous palladium-silver metal alloy nanotubes according to Examples 6 to 8; it's a graph

Referring to FIG. 9 , it was confirmed that the gas sensor according to the embodiment exhibits hydrogen sensing characteristics with a fast reaction speed and recovery speed.

This sensing characteristic is achieved by removing silicon dioxide from the central portion through an etching process to form nanotubes with a large surface area and many mesopores, so that hydrogen, the target gas, is applied to the surface of the sensing material as well as the sensing layer. This is because it provides more diffusion space and gas reaction sites that can effectively penetrate into the lower interior.

As such, it was confirmed that a sensor composed of porous nanotubes having a large surface area can be manufactured by showing that excellent sensor characteristics can be obtained from a sensing material having a large surface area and a large number of pores.

Therefore, the porous metal nanotube according to the present invention is applied to a palladium-based gas sensor for detecting harmful environmental gases operated at room temperature, as well as various hydrogen gas detection sensors dissolved in transformer insulating oil, quickly detects gas, and detects time It is possible to provide a gas sensor with a very short recovery time.

So far, the present invention has been looked at mainly through embodiments. Those skilled in the art to which the present invention pertains will be able to understand that the present invention may be implemented in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments are to be considered in an illustrative rather than a limiting sense. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the equivalent range should be construed as being included in the present invention.

10: primary nanofiber
20: metal oxide nanofiber
21: Core
22: shell
30: shell structure metal oxide nanotube
31: pores
1000: porous metal nanotubes
100: shell
200: pores

Claims (18)

One or more metals form a hollow shell, and the shell has a surface of an open structure in which a plurality of pores are formed,
In the shell, one or more metals are diffused by forming a concentration gradient,
The shell includes any one metal alloy of palladium-nickel, palladium-tin and palladium-silver,
Porous metal nanotubes.
The porous metal nanotube of claim 1 , wherein the porous metal nanotube does not contain a metal oxide.
The porous metal nanotube according to claim 1, wherein an aggregate of one or more metal particles forms a hollow shell.
delete delete The porous metal nanotube according to claim 1, wherein the porous metal nanotube has an average diameter of 100 nm to 5 μm.
The porous metal nanotube according to claim 1, wherein the shell has an average thickness of 10 nm to 500 nm.
The porous metal nanotube according to claim 1, wherein the pores have an average diameter of 3 nm to 60 nm.
(a) preparing primary nanofibers by electrospinning a spinning solution containing at least one metal oxide precursor and a polymer;
(b) preparing core-shell composite nanofibers by heat-treating the primary nanofibers to remove the polymer and oxidizing the metal oxide precursor;
(c) etching the core of the composite nanofiber to prepare a metal oxide nanotube in the form of a hollow shell; and
(d) preparing a metal nanotube having a shell in which one or more metals are bonded by reducing the metal oxide by heat-treating the metal oxide nanotube;
In the step (a), a concentration gradient of one or more metal oxides is formed and diffused in the shell of the primary nanofiber,
The shell includes any one metal alloy of palladium-nickel, palladium-tin and palladium-silver,
A method for producing porous metal nanotubes.
10. The method of claim 9, wherein the spinning solution comprises two or more metal oxide precursors having different oxide formation energies.
The porous metal nanotube according to claim 9, wherein the electrospinning in step (a) is performed by spinning an electrospinning solution containing one or more metal oxide precursors at a voltage of 10 to 20 kV to form a nanofiber web. manufacturing method.
10. The method of claim 9, wherein the heat treatment in step (b) is performed at 500 to 1,000 °C.
delete 10. The method of claim 9, wherein the etching in step (c) is performed by adding a core-reactive solvent to remove only the core.
The method of claim 14, wherein the core reactive solvent is sodium hydroxide (NaOH), potassium hydroxide (KOH), nitric acid (nitric acid), hydrochloric acid (hydrochloric acid), hydrofluoric acid (hydrofluoric acid), sulfuric acid (sulfuric acid), methanol (methanol) ), a method for producing a porous metal nanotube, characterized in that at least one of ethanol and ammonium persulfate.
10. The method of claim 9, wherein the heat treatment in step (d) is performed at 300 to 500° C. under a reducing gas atmosphere to reduce the metal oxide.
Board;
a sensing layer formed on the substrate; and
Including; electrodes wire-bonded to both ends of the sensing layer,
The sensing layer is a gas sensor comprising a porous metal nanotube according to any one of claims 1 to 3 and 6 to 8.
[Claim 18] The gas sensor according to claim 17, wherein the gas sensor including porous metal nanotubes detects an environmentally harmful gas or a gas generated from transformer insulating oil.

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