KR20140021745A - Graphene catalyst-decorated metal oxide nanorod, method for fabricating the same and sensors comprising the same - Google Patents

Abstract

The present invention relates to a sensor which prevents the modulation of resistance change characteristics of metal oxide nanorod on gas by combining minute graphene or graphene fine aggregates on the surface of the metal oxide nanorod. The present invention provides improved sensitivity characteristics, rapid response rates and recovery rates, selectivity, and low drive characteristics by adopting metal oxide nanorod combined with graphene or graphene aggregate to the gas sensor.

Description

TECHNICAL FIELD The present invention relates to a metal oxide nanorod and a graphene composite, a method of manufacturing the same, and a sensor including the metal oxide nanorod,

The present invention relates to a metal oxide nanorod and a graphene composite, a method of manufacturing the same, and a sensor including the same. More particularly, the present invention relates to a method of manufacturing a metal oxide nanorod, which comprises graphene catalysts having a finer size compared to a metal oxide nanorod, which are locally bound to the surface of the metal oxide nanorod, To a metal oxide nano-rod and a graphene composite, a production method thereof, and a sensor including the same.

In a gas sensor using a metal oxide semiconductor, an oxidizing gas (for example, NO ₂ ) and a reducing gas (for example, Cl ₂ , C ₂ H ₅ OH, CO, and H ₂ ) are adsorbed / desorbed on the surface of the metal oxide semiconductor It is driven by the principle of recognizing the change of resistance. Since the adsorption / desorption process of the gas proceeds relatively slowly, the gas sensor using the metal oxide semiconductor has a disadvantage that the reaction rate and the recovery rate are slow. Metal oxide semiconductors are classified into n-type semiconductors (SnO ₂ , In ₂ O ₃ , ZrO ₂ ) and p-type (NiO, CuO and Co ₃ O ₄ ) semiconductors. Carrier paper It is distinguished according to whether it is electron or hole. When n-type metal oxide semiconductors are adsorbed on the surface of the atmosphere, electrons acting as conduction in the semiconductor are localized on the surface of the adsorbed oxygen due to high electronegativity of the adsorbed oxygen species , Captive state). As a result, electrons are deficient on the surface of the metal oxide semiconductor, and an electron depletion layer (surface depletion layer) is formed. When a reducing gas (for example, CO) is adsorbed on the surface of the n-type metal oxide semiconductor having such an electron depletion layer, adsorbed oxygen on the surface reacts with these gas species to desorb the adsorbed oxygen on the surface. At this time, the trapped electrons around oxygen can be freed again to contribute to the electrical conductivity. Therefore, the electrical conductivity of the semiconductor sensor is changed according to the type of the target gas to be detected, and thus the presence or concentration of the gas species can be known.

Korean Patent Publication No. 2011-0013742 discloses a carbon-based nanocomposite comprising a substrate, a graphene sheet formed on the substrate, and a carbon-based nanomaterial formed on the other surface of the graphene sheet so as to be orthogonal to graphene have.

An object of the present invention is to provide a composite in which a graphene catalyst is bound to the surface of a metal oxide nanorod, and a sensor using the composite and a manufacturing method thereof.

It is another object of the present invention to provide a method of manufacturing a metal oxide nano-rods, in which a graphene catalyst is locally bound to a surface of a metal oxide nano-rods so that an electrical resistance characteristic of the metal oxide as well as an electrical resistance characteristic of the graphene are combined, Oxide nano-rod composite and a method of manufacturing the same.

It is another object of the present invention to provide a method of manufacturing a composite sensor material in which p-type graphene catalysts are combined with n-type metal oxide nano-rods or p-type metal oxide nano-rods and have pn junctions or pp junctions And applies it to a sensor array.

The metal oxide nanorod and the graphene composite which are one aspect of the present invention include a metal oxide nanorod; And graphene or agglomerates bound to the surface of the metal oxide nanorod.

Another aspect of the present invention is to provide a method for producing a metal oxide nanorod and a graphene composite, which comprises: (a) spinning a metal oxide precursor and a polymer spinning solution to prepare a composite nanofiber; (b) heat-treating the composite nanofibers to prepare metal oxide nanofibers, (c) pulverizing the metal oxide nanofibers to prepare metal oxide nanorods, and (d) And mixing the fin dispersion solution to prepare a graphene complex with a metal oxide nanorod having graphene or graphene aggregates bound thereto.

The sensor, which is another aspect of the present invention, may comprise the metal oxide nanorod and the graphene complex.

According to the present invention, it is possible to produce a composite containing both a one-dimensional nano-rod and two-dimensional graphene electrical characteristics at the same time by binding fine-graphene grains to the surface of a metal oxide nano- Sensor material and an exhaled breath detection sensor material, it is possible to provide a sensor material having high sensitivity and excellent selectivity.

As the graphene having the p-type characteristic is bound to the n-type or p-type metal oxide nanorod, the electron concentration on the surface is changed and the selectivity to the specific gas can be increased.

Through the change of the content of graphene bound to the metal oxide nanorod, it is possible to control the detection characteristic of the sensor. Due to the excellent gas binding characteristics of graphene, it is possible to operate at a temperature lower than the sensor operating temperature of a conventional metal oxide semiconductor. That is, there is an advantage that a low temperature operation gas sensor can be realized.

1 is a conceptual diagram of a metal oxide nanorod and a graphene composite in which graphenes are bound to the surface of the metal oxide nanorod according to one embodiment of the present invention.
FIG. 2 is a scanning electron microscope (SEM) photograph of the metal oxide precursor / polymer composite nanofiber prepared by electrospinning in Example 1. FIG.
FIG. 3 is a scanning electron microscope (SEM) photograph of a metal oxide nanorod obtained by heat treatment of a metal oxide precursor / polymer composite nanofiber prepared through electrospinning in Example 1 and pulverization.
4 is a scanning electron microscope (SEM) photograph of a metal oxide nanorod having a graphene catalyst obtained by dispersing a graphene catalyst in the metal oxide nanorod of Example 1. Fig.
5 is an enlarged scanning electron microscope (SEM) photograph of FIG.
FIG. 6 shows the results of gas sensor reactivity of the metal oxide nanorods and the pure metal oxide nanorods bound to the graphene catalysts of Example 2 and Comparative Example 1 for H ₂ S gas at 200 ° C. FIG.
FIG. 7 shows the results of gas sensor reactivity of the metal oxide nanorods and the pure metal oxide nanorods bound to the graphene catalyst of Example 2 and Comparative Example 1 at 350 ° C for H ₂ S gas.
8 is a graph showing gas sensor reactivity results of the metal oxide nanorods and the pure metal oxide nanorods bound to the graphene catalyst of Example 2 and Comparative Example 1 at 200 ° C for acetone gas.
9 is a graph showing gas sensor reactivity results of the metal oxide nanorods and the pure metal oxide nanorods bonded with the graphene catalyst of Example 2 and Comparative Example 1 at 350 ° C for acetone gas.
10 is a graph showing gas sensor reactivity results of the metal oxide nanorods and the pure metal oxide nanorods bound to the graphene catalyst of Example 2 and Comparative Example 1 at 200 ° C for toluene gas.
FIG. 11 shows the results of gas sensor reactivity of the metal oxide nanorods and the pure metal oxide nanorods bound to the graphene catalyst of Example 2 and Comparative Example 1 at 300 ° C for toluene gas.

The metal oxide nanorod and the graphene composite which are one aspect of the present invention include a metal oxide nanorod; And graphene or agglomerates bound to the surface of the metal oxide nanorod.

In the composite, graphene or agglomerates thereof can bind to some of the surfaces of the metal oxide nanorods. In the composite, graphene or agglomerates thereof are bound to catalyze the modification of the electrical properties of the metal oxide nanorod when it comes into contact with a gas or the like. Therefore, in the composite of the present invention, a small amount of graphene or an agglomerate thereof is adhered to the surface of the metal oxide nanorod.

When graphene binds to the surface of the metal oxide nanorod, it is important that the entire surface of the metal oxide nanorod is not covered by graphene. When graphene binds to the front surface of the metal oxide nanorod, the adsorption / desorption with the external gas is performed by graphene coated on the outer wall of the metal oxide nanorod. Therefore, the gas detection characteristic . Therefore, it is preferable that the graphene is locally bound so that a part of the surface of the metal oxide nanorod is exposed to the gas.

The ratio of the surface of the metal oxide nanorod that is not bound to the graphene or the aggregate thereof may be 5% to 98%, preferably 70% to 90%. If the exposed surface of the metal oxide nanorod is less than 5%, the characteristics of graphene become significant, and if the exposed surface of the nanorod exceeds 98%, the effect due to graphene addition becomes insufficient.

In the composite, graphene or agglomerates thereof can be bound to a plurality of surfaces of the metal oxide nanorods. Graphene can better perform its catalytic role by binding a plurality of graphenes or agglomerates thereof.

In the composite, graphene or its aggregates are bound to a finer size relative to the metal oxide nanorods. If the size of the graphene or agglomerate thereof is larger than that of the nano-rods, the electrical characteristics may be influenced by graphene when the gas is adsorbed. The ratio of the length of the metal oxide nanorod to the maximum diameter of graphene or agglomerates thereof may be 3 to 30,000, preferably 15 to 300. [

In the composite, graphene or agglomerates thereof may be included in the composite in an amount of 0.0001 to 10 wt%, preferably 0.001 to 1 wt%, more preferably 0.001 to 0.005 wt%. In this range, graphene can sufficiently perform the role of a catalyst, and may have an effect of lowering the driving temperature of the sensor and increasing the reactivity to the gas.

In the composite, graphene or agglomerates thereof may be bound in a direction perpendicular or perpendicular to the longitudinal direction of the metal oxide nanorods. The graphenes include those which form the agglomerates and bind to the metal oxide nanorods in a horizontal or vertical direction, can be bound in various directions, and have no specific binding direction.

In the composite, graphene or agglomerates thereof can be discrete bonded to a portion of the surface of the metal oxide nanorod. This is due to the manufacturing process of the composite because it involves a process of mixing the graphene or agglomerate thereof with the metal oxide nanorod in the process of producing the composite.

In this specification, 'graphene' may include not only graphene but also graphene oxide, reduced graphene oxide, or a mixture thereof.

In the composite, graphene or agglomerates thereof may have a graphene initial shape, but may preferably have at least one of a graphene slice, a graphene quantum dot, a graphene ribbon, or a graphene flake. This is due to the manufacturing process of the composite because it involves a process of mixing the graphene or agglomerate thereof with the metal oxide nanorod in the process of producing the composite.

In the composite, graphene or aggregates thereof may be formed from single or multilayer graphene.

In the composite, the metal oxide nanorod is manufactured by electrospinning technology, and the formed metal oxide nanofiber is pulverized and manufactured into a nanorod shape. Metal oxide nanorods are formed from precursor salts through nucleation and particle growth during heat treatment. As a result, the metal oxide nanorods can have a polycrystalline structure composed of fine nanoparticles.

In the composite, a one-dimensional metal oxide nanorod does not limit the specific crystallinity. The single-crystal metal oxide nanorods obtained by the hydrothermal synthesis method or the vapor deposition method may be combined with fine graphene pieces to form a graphene composite with the metal oxide nanorods.

Since metal oxide nanorods are produced through the grinding process of nanofibers, the length of the nanorods composing the composite is variable. Preferably, the length of the nano-rods may be between 1 [mu] m and 30 [mu] m. When the thickness is less than 1 탆, the aspect ratio is small, so that the basic resistance of the whole composite may increase. When the thickness is larger than 30 탆, nonuniformity may occur during coating of the sensor electrode.

In the composite, pores are present in the metal oxide nanorod. As a result, the movement of the gas molecules can occur rapidly, and the gas having a high specific surface area can be expected to have excellent gas reaction characteristics. In addition, excellent gas sensing characteristics can be expected based on excellent mass transfer characteristics of a one-dimensional shape. The diameter of the pores formed in the metal oxide nanorods in the composite can be from 1 nm to 50 nm.

In the composite, fine graphene binds to the surface of the metal oxide nanorod to form a composite. This is due to the high surface energy of graphene, and the metal oxide nanorods and graphene are bound together by a van der waals force.

The metal oxide constituting the metal oxide nanorod can be n-type or p-type, and graphene is p-type. Accordingly, the composite of the present invention can have selective detection characteristics for various gases by bonding the metal oxide nanorod and graphene to each other to form an n-p junction structure or a p-p junction structure.

The metal oxide constituting the metal oxide nanorod has a semiconductor property. For example, the metal oxide may be selected from the group consisting of WO ₃ , ZnO, SnO ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , NiO, TiO ₂ , CuO, In ₂ O ₃ , Zn ₂ SnO ₄ , Co ₃ O ₄ , PdO, LaCoO ₃ , NiCo ₂ O ₄ , Ca ₂ Mn ₃ O ₈ , V ₂ O ₅ , Ag ₂ V ₄ O ₁₁ , Ag ₂ O, MnO ₂ , InTaO ₄ , InTaO _{4 , CaCu 3 Ti 4 O 12,} Ag 3 PO 4, BaTiO 3, NiTiO 3, SrTiO 3, Sr 2 Nb 2 O 7, Sr 2 Ta 2 O 7, Ba 0 .5 Sr 0 .5 Co 0 .8 Fe 0 _.2 O ₃ It may include one or more of.

The graphene may have a diameter of 1 nm to 300 nm, preferably 1 nm to 50 nm. Since graphene having a size of less than 1 nm is difficult to synthesize and graphene larger than 300 nm is used, the metal oxide nano-rods can be completely coated with graphene, It can be influenced by initiative.

The diameter of the metal oxide nanorods may be between 50 nm and 1.5 탆. In the case of a nanorod having an average diameter smaller than 50 nm, it is difficult to maintain a stable shape because most of the nanorod is crushed during the grinding process of the nanofiber. In the case of a nanorod having a thickness larger than 1.5 탆, the surface area may decrease.

The length of the metal oxide nanorod may be from 1 [mu] m to 30 [mu] m. Within this range, there may be an effect of lowering the driving temperature and increasing the reactivity to the gas.

The graphene in the composite may be contained in an amount of 0.0001 to 10% by weight, preferably 0.001 to 1% by weight, more preferably 0.001 to 0.005% by weight. When the content of graphene is less than 0.0001% by weight, the effect of graphene addition is small. When the content of graphene is more than 10% by weight, the characteristics of graphene, which is not a metal oxide nano-rod characteristic, .

The graphene may be formed as a single layer or a multilayer.

The graphene and metal oxide nanorod composites can be used as a gas sensor by calculating the resistance change in contact with the gas. Generally, the gas sensor reaction is carried out at a high temperature of 300 ° C or higher, but when graphene is added, the reactivity largely changes even at a low temperature of 200 ° C or lower. The operating temperature of the gas is consumed by the battery to heat the heating element heater, so developing a sensor with low power consumption is a very important technology. Therefore, it is very important to fabricate a sensor capable of operating at low temperatures using metal oxide nanorods and graphene composites.

By using graphene, graphene oxide, and three kinds of reduced graphene oxides, respectively, or graphene mixed with some of them, it is expected that various characteristics such as high detection characteristics, reaction rate / recovery rate, selectivity can be improved have.

Since graphene exists in a colloidal form in a solution with irregular shape and size, the size and shape of the graphene attached to the surface of the metal oxide nanorod are also different. Therefore, the shape of the graphene bonded to the metal oxide nanorod varies greatly depending on the uniformity of the graphene used.

1 is a conceptual diagram of a metal oxide nanorod and a graphene composite according to an embodiment of the present invention. 1, the composite 1 comprises a metal oxide nanorod 2 having a single layer or multi-layered graphene sheet 3 and graphenes having various sizes and shapes (single layer or multi-layered graphenes 3) 4) can be constituted.

Another method of manufacturing a metal oxide nano-rod and a graphene composite according to another aspect of the present invention may include a step of mixing a metal oxide nano-rod and graphene to prepare a metal oxide nano-rod and a graphene composite.

In one embodiment, the method of making the complex of the present invention can include the methods described below:

(a) spinning a polymer spinning solution containing a metal salt precursor to prepare a metal oxide precursor / polymer composite nanofiber and subjecting the metal oxide precursor / polymer composite nanofiber to heat treatment to produce a metal oxide nanofiber; (b) pulverizing the metal oxide nanofibers to produce metal oxide nanorods; And (c) mixing the metal oxide nanorod and a graphene dispersion solution dispersed in a finer size to prepare a composite in which graphene is bound to the surface of the metal oxide nanorod.

The polymer can impart a viscosity to the spinning solution to form a fiber phase upon spinning, and control the structure of the spinning fiber by compatibility with the precursor for metal and metal oxide formation.

The polymer may have a weight average molecular weight (Mw) of 100,000 g / mol to 1,500,000 g / mol. Within this range, nanofibers can be formed through electrospinning. Preferably, it can be from 500,000 g / mol to 1,300,000 g / mol.

The glass transition temperature (Tg) of the polymer may be from 25 ° C to 200 ° C. Preferably, it may be 35 ° C to 190 ° C.

The polymer is not particularly limited as long as it meets the above-mentioned weight-average molecular weight and glass transition temperature. For example, it is possible to use PVAc (polyvinyl acetate), PVP (polyvinylpyrrolidone), PVA (polyvinyl alcohol), PEO (polyethylene oxide), PANi (polyaniline), PAN (polyacrylonitrile) Methacrylate), PAA (polyacrylic acid), or PVC (polyvinyl chloride).

The metal salt precursor capable of forming the semiconductor metal oxide nanorod may be a metal-containing salt, for example, an organic acid salt, a halogen salt, an inorganic acid salt, an alkoxy salt, a sulfide salt, an amide salt and the like. Specifically, there may be mentioned, for example, acetates, chlorides, acetylacetonates, nitrates, methoxides, ethoxides, butoxides, isopropoxide, sulfides, oxytriisopropoxide, (ethyl or cetylethyl) hexanoate, , Ethyl amide, amide, and the like, or a mixture of two or more thereof.

The solvent may affect the shape of the nanofibers due to the volatilization rate after electrospinning.

The solvent may be a solvent having a boiling point higher than that of water, preferably a solvent having a boiling point of 100 ° C to 170 ° C. For example, dimethylformamide (DMF, boiling point: 153 占 폚) or a mixed solvent thereof may be used, but is not limited thereto.

The spinning solution can be prepared by controlling the content of the metal salt precursor and the polymer, which are solutes, and the content of the solvent. For example, the spinning solution may comprise from 5 to 30% by weight of the metal salt precursor, from 5 to 20% by weight of the polymer, and a residual amount of solvent.

In the spinning solution, the precursor may be included in an amount of 50 to 300 parts by weight based on 100 parts by weight of the polymer.

The spinning solution may further comprise additives for smooth spinning in addition to precursors, polymers, and solvents. The additives may include, but are not limited to, surfactants, acids, bases, oils, organic salts, or mixtures thereof. The additive may be added in an amount of 0.1 to 10% by weight in the spinning solution.

As the additive, a surfactant including cetyltrimethylammonium bromide and the like, and an acid such as acetic acid, stearic acid, adipic acid, ethoxyacetic acid, benzoic acid or nitric acid can be used.

In the spinning solution, the precursor, which is a solute, and the order of addition of the polymer to the solvent, the stirring temperature and the agitation time can be suitably adjusted.

The polymer in the solute is first added to prepare a polymer solution, and then a precursor and various additives are added to prepare a spinning solution. After adding both the polymer and the precursor, the mixture is stirred. The stirring temperature may be from 25 to 80 ° C., and the stirring time may be from 1 hour to 48 hours.

The viscosity of the spinning solution may be 70 cps to 3000 cps at 25 ° C. Preferably, the viscosity may be between 100 cps and 2000 cps.

After the spinning solution is prepared, the spinning solution is electrospun to form a precursor / polymer composite nanofiber in which the precursor and the polymer are combined.

In the electrospinning, the electrospinning device consists of a spray nozzle connected to a metering pump, a high voltage generator, and a grounded conductive substrate, which can quantitatively inject the spinning solution. The conductive substrate is a metal plate and electrospun using a spinning nozzle spaced 10 cm to 20 cm from the metal plate.

During the electrospinning, the spinning rate of the spinning solution may be 5 μl / min to 100 μl / min. The ejection speed may preferably be 10 μl / min to 100 μl / min.

The operating voltage for electrospinning can be from 8 kV to 30 kV.

The ambient humidity during electrospinning can be from 10% to 50%, and the ambient temperature during electrospinning can be from 15 ° C to 25 ° C.

The discharge speed of the spinning solution, the operating voltage, the distance between the nozzle and the current collector, the humidity and the temperature can be fixed but can be changed.

In electrospinning, the diameter of the nanofibers can be controlled according to the hole size of the spinning nozzle, the discharge speed, the concentration of the precursor in the spinning solution, and the spinning length.

By electrospinning, a precursor / polymer composite fiber in which the precursor and the polymer are combined can be formed, and the composite fiber can have a web shape.

After electrospinning, the formed precursor and the precursor / polymer composite nanofiber in which the polymer is complexed are heat-treated. The heat treatment allows the polymer contained in the composite fiber to be carbonized or removed, and at the same time, the precursor can be oxidized to form a metal oxide.

The heat treatment can be performed in an oxidizing atmosphere. The heat treatment is performed at a rate of 4 ° C / min. Per minute. After the heat treatment time is maintained for at least 30 minutes at a temperature range of 300 ° C to 600 ° C for a maximum of 5 hours, the heat treatment is performed at a rate of 4 ° C / minute per minute.

After the nanofibers are prepared, the nanofibers may be pulverized to form metal oxide nanorods.

The method of pulverizing the nanofibers can be carried out in a conventional manner, for example, through a ball milling process.

Next, the nano-rods of the metal oxide nanofibers in a pulverized shape are mixed with graphene to prepare a metal oxide nanorod and a graphene composite. That is, graphene is dispersed in an organic solvent, and the metal oxide nanorods are mixed to prepare a graphene composite with a metal oxide nanorod.

The diameter (size) of the graphene may be in the range of 1 nm to 300 nm, and the graphene may be partially agglomerated to further include a graphene agglomerate having a size of 100 nm to 500 nm. In the above range, the graphene in the form of particles may uniformly adhere to the metal oxide nanorod, which may lead to an improvement in the sensing characteristics for various gases. Preferably, the two-dimensional surface of the graphene binds to the surface of the metal oxide nanorod.

The organic solvent for dispersing graphene is typically ethanol, dimethylformamide, isopropyl alcohol or the like, and other organic solvents may be used for the degree of dispersion and are not limited to specific organic solvents.

The graphene dispersion method includes various physical and chemical dispersion methods such as dispersion through ultrasonic treatment and dispersion through incorporation of a surfactant in a dispersion solvent, and is not limited to any one dispersion method. In the case of dispersion through ultrasonic treatment, which is a physical dispersing process which is one aspect of the present invention, dispersion can be performed between 1 minute and 3 hours. When the graphene dispersion is from 1 minute to 10 minutes, graphene is not dispersed, and graphenes aggregate to form large graphene. When the graphene dispersion is 1 hour to 3 hours, fine grains such as graphene particles, graphene quantum dot, graphene ribbon and graphene flake, which are sufficiently dispersed graphene sheets are formed .

When the metal oxide nanorods and the graphene catalyst are mixed with each other, when the metal oxide nanorods and the graphene are mixed at an appropriate ratio, the graphene acts as a catalyst to form a complex in a suitable ratio to the metal oxide nanorods have. As a result, when the present invention is applied to an exhalation sensor for diagnosing diseases due to its high surface area and high electrical conductivity, it can improve the detection characteristics of various gases.

The graphene of the metal oxide nanorod and the graphene composite is mixed in the range of 0.0001 wt% to 10 wt%, preferably 0.001 wt% to 1 wt%, and more preferably 0.001 wt% to 0.005 wt%. When the content of graphene is less than 0.0001% by weight, the effect of graphene addition is small. When the content of graphene is more than 10% by weight, the characteristics of graphene, rather than the properties of metal oxide nanorods, .

In the metal oxide nanorod and the graphene composite, graphene can be uniformly coated on the surface of the cylindrical nano-rod without discriminating the upper and lower or side surfaces of the metal oxide nanorod, and an electron depletion layer is formed on the composite interface , It is possible to effectively exhibit the external gas adsorption / desorption action of graphene having a high surface area, thereby exhibiting various characteristics such as high sensing characteristics, reaction rate / recovery speed, selectivity, and low sensor driving temperature as a gas sensor.

In graphene-bound metal oxide nanorod composites, graphene may bind to the metal oxide nanorods in the form of agglomerates through aggregation of graphene.

The sensor, which is another aspect of the present invention, may comprise a metal oxide nanorod composite on which the graphene catalyst is bound. At this time, the graphene catalyst may be bonded in the form of a two-dimensional plane or graphene may be aggregated. The graphene catalyst-metal oxide nanorod composite can be coated on a sensor substrate that can recognize resistance change to detect various gases and other substances. For example, the sensor may include a semiconductor gas sensor capable of detecting exhaled gas (H ₂ S, Acetone, NH ₃ , Toluene, Pentane, Isoprene, NO, etc.) for disease diagnosis.

The gas sensor may be manufactured by coating the sensor substrate with the graphene catalyst and the metal oxide nanorod composite.

When applied to a gas sensor using a metal oxide nano-rod composite having a graphene catalyst attached thereto, the large surface area and open pore size of the metal oxide nanorod structure alone as well as the large surface area of the graphene catalyst, It is possible to add excellent reaction characteristics to the gas through the formation of the depletion layer. In addition, the high electrical conductivity of graphene enables electrons to migrate, allowing for fast response / recovery rates for gases and low sensor operating temperatures.

Another aspect of the present invention is an article comprising a metal oxide nanorod and a graphene composite. For example, the article may include, but is not limited to, a sensing material for a resistance-changing gas sensor, a negative electrode active material and a positive electrode active material for a secondary battery, a positive electrode and a negative electrode material for a fuel cell, a lithium air battery, and a catalyst material for a fuel cell.

Hereinafter, the present invention will be described in more detail by way of examples. However, it should be understood that the present invention is not limited thereto.

Example 1: Preparation of a composite in which a tin oxide nano rod was bonded to a graphene catalyst

As shown in the conceptual diagram of FIG. 1, the metal oxide nano-rods of the present invention are produced by grinding metal oxide nanofibers obtained by electrospinning. The produced metal oxide nanorods are bound to a graphene catalyst, Rod-graphene composites. The graphene catalyst may be bonded to the metal oxide nanorods having a fine shape in the form of graphene fragments, graphene quantum dots, graphene ribbons, and the graphene having a large area into pieces. It may be attached to form agglomerates of several hundred nanometers through.

(1) Production of tin oxide nano-rods

0.2 g of polyvinylpyrrolidone (PVP), Aldrich having a molecular weight of 1,300,000 g / mol and 0.2 g of poly (methyl methacrylate (PMMA), Aldrich) having a molecular weight of 350,000 g / N, N -dimethylformamide (DMF) solution, and dissolved in 25 ℃ to 2.831 g., insert a tin precursor tin acetate (IV) 0.4 g ( Aldrich) and acetic acid 0.11 g (Junsei Chemical) in the solution at 25 ℃ 48 sigan Immediately prior to electrospinning, the spinning solution is dispersed in an ultrasonic cleaner for 5 minutes and placed in a plastic syringe of 12 ml capacity.

The polymer solution was poured into a syringe and connected to a syringe pump (KD Scientific, model 781200), the spinning solution was pushed out at a discharge rate of 10 μl / min, and the spinning solution was injected into the injection needle A voltage of 15 kV is applied to the tin oxide precursor / polymer composite fiber web while maintaining 15 cm between the current collecting substrates.

When a sufficient amount of nanofibers were stacked, the tin oxide precursor / polymer composite fiber stacked on a stainless steel (SUS) substrate was heat-treated in an air atmosphere (oxidizing atmosphere). The heat treatment was carried out in a Ney Vulcan 3-550 electric furnace at 500 ° C (at a heating rate of 4 ° C / min) in an atmospheric environment, maintained for 30 minutes, and then naturally cooled in an electric furnace without any external change. At this time, due to the high heat treatment temperature, the internal polymer constituting the nanofiber is oxidized and removed, and the tin precursors dissolved therein are oxidized to form tin oxide. The heat-treated tin oxide nanofibers are pulverized at the time of collection or exhibit a nanorod shape through an additional milling process.

2 is a scanning electron microscope (SEM) image of a tin oxide precursor / polymer composite fiber prepared by electrospinning in Example 1. Fig. The tin oxide precursor polymer composite fibers exhibit a web shape with a thickness of 400 nm - 700 nm and a smooth surface.

FIG. 3 is a scanning electron microscope (SEM) image of a tin oxide nano-rod obtained by subjecting the tin oxide precursor / polymer composite fiber obtained in Example 1 to thermal treatment in air and pulverization. Dimensional shape similar to that of the tin oxide precursor / polymer composite fiber before the heat treatment. The polymer composing the composite fiber is removed during the heat treatment process, and the precursor is oxidized to form tin oxide. At this time, as the precursor salt crystallizes, tin oxide nano-rods composed of fine nano-particles having polycrystals are formed.

(2) Production of graphene-bound tin oxide nanorod composites

A graphene catalyst-tin oxide nano-rod composite was prepared by attaching a graphene catalyst having a size smaller than the diameter of the nano-rods to the surface of the tin oxide nano-rods manufactured through the above-described Examples.

The dispersion solution of UniThink Inc. was dispersed in 30 ml of DMF with 0.3 mg of graphene using an ultrasonic washing machine. Followed by dispersion treatment for about 3 hours. Through the long-time ultrasonic dispersion process, the graphene was dispersed in the form of ultra-fine particles (flakes) in a wide sheet form. After the dispersion treatment, 0.005 wt% of graphene based on the weight of the tin oxide nano-rods was mixed to prepare a tin oxide nano-rod composite having a graphene catalyst. The graphene was added to the tin oxide in a very small proportion in comparison with the tin oxide so that the graphene acts as a catalyst.

Figure 4 shows a scanning electron micrograph (SEM) of a composite of graphene catalyst-tin oxide nano-rods as described above. As shown in FIG. 4, the graphene catalyst adhered to the metal oxide nanorod, and the graphene adhered not only as fine nanoparticles as a catalyst but also aggregated to form graphene agglomerates.

FIG. 5 is a scanning electron microscope (SEM) photograph of the above-mentioned graphene catalyst when aggregates were formed. It was confirmed that aggregates formed by aggregation of graphenes existed up to about 500 nm in size. When graphene is excessively aggregated, a large number of graphenes are consumed in the agglomeration process, which is not preferable. The size of graphene agglomerates is preferably within a range not exceeding 500 nm. Since graphene agglomerates can also affect the reactivity of the gas, it is not necessary to complicate the process in order to forcibly remove the graphene agglomerates, and the graphene catalyst partially including these graphene agglomerates is used in the composite oxide bound to the metal oxide nanorod .

Example 2 Preparation of Gas Sensor Using Tin Oxide Nanorods Containing Graphene Catalyst

In order to investigate the characteristics of a gas sensor for implementing an aerosol sensor using the above-described analysis of the mouth odor of the graphene catalyst-tin oxide nano-rod composite, the manufacture and characteristics of the sensor were evaluated as described below.

The exhalation sensor was fabricated on an alumina substrate in which two electrodes were patterned in parallel using the above-described graphene catalyst-tin oxide nano-rod complex as a sensing material.

The area of the alumina substrate is 460 μm. The two electrodes on the alumina substrate are spaced about 70 μm apart, and the patterned electrode is about 25 μm thick and about 345 μm long. A heater is placed on the opposite side of the alumina substrate to control the temperature of the substrate.

In order to fabricate the graphene catalyst-tin oxide nano-rod composite as a sensor-sensing material, the graphene catalyst and the main oxide nano-rods were dispersed in ethanol, and the graphene catalyst-tin oxide nano- Rod composite. The graphene catalyst-tin oxide nano-rod composite dispersed in ethanol was coated on an alumina substrate through a drop coating method.

In order to apply the graphene catalyst-tin oxide nanorod composites prepared above to the expiratory sensor, sensitivity characteristics were analyzed by flowing three kinds of gases of hydrogen sulfide (H ₂ S), acetone, and toluene. In order to characterize it as an expiratory sensor, the characterization was carried out with a relative humidity of 85% -90%, similar to the humid environment of expiration. Sensitivity of the sensor is measured by Agilent's Model 34972A, which changes when a specific gas flows. Response to each gas (Response: change of R _air / R _gas resistance, R _air : resistance in air, R _gas : resistance at the time of flowing the measuring gas) was analyzed to confirm the sensitivity. In order to evaluate the characteristics according to the gas concentration, the resistance change was recorded while varying the concentration of the flowing gas in the order of 5 ppm, 4 ppm, 3 ppm, 2 ppm and 1 ppm. The operating temperature of the gas sensor was adjusted using the E3647A model, a DC voltage generator from Agilent.

Comparative Example 1: Sensor fabrication using pure tin oxide nano-rods

In order to observe more clearly the effect on the gas sensor characteristics of the graphene catalyst - tin oxide nanorod composite, a gas sensor was fabricated using pure tin oxide nano - rods without a graphene catalyst. Using the pure tin oxide nano-rod network obtained in Example 1, the same alumina sensor substrate used in Example 2 was coated. For the purpose of a reasonable comparison, tin oxide nano-rods were dispersed in ethanol and then dropped on an alumina substrate by the same method as the sensor manufactured in Example 2, using a drop coating method.

The sensor test was carried out in the same manner as in Example 2.

In the above embodiment, a method of manufacturing a tin oxide nano-rod composite having a graphene catalyst bound thereto has been described. In order to demonstrate the superiority of a tin oxide nano-rod to which a graphene catalyst is attached, a pure tin oxide nano- Direct comparison with the sensor was made.

FIG. 6 is a graph showing the relationship between a gas sensor gas sensor for detecting a volatile organic compound gas emitted from the mouth using a network of tin oxide nano-rod complexes and pure tin oxide nano rods bonded with a graphene catalyst prepared according to Example 2 and Comparative Example 1 The test results are shown. At this time, the reaction gas was hydrogen sulfide (H ₂ S) and a graph showing the gas reaction (resistance change due to hydrogen sulfide injection) at 200 ° C. Also as it is shown in 6, compared with the sensor of the 0.005 wt% yes the detectability of that sensor complexed to the tin oxide nanorods the pin into the catalyst using only the pure tin oxide as compared to the pure tin oxide nanorods sensor produced under the same conditions H ₂ It was confirmed that the reaction to the S gas was remarkably improved. In this case, the reaction (R _air / R _gas ) value of the tin oxide nano-rod complex with the graphene catalyst attached at 5 ppm showed a resistance change of about 5.5 times higher than that of the pure tin oxide nano-rod structure. This is a very encouraging result with the sensor sensitivity value obtained at a low temperature of 200 ° C.

7 is a graph showing the relationship between the hydrogen sulfide (H ₂ S) gas of the disease diagnosis sensor using the pure tin oxide nano-rods without the graphene catalyst-attached tin oxide nano-rod complex and the graphene catalyst- The graph shows the reaction results at 350 ° C. As shown in FIG. 7, when the same sample was heated to 350 ° C and subjected to a sensitivity test for H ₂ S under the same conditions, the sensitivity of the graphene catalyst-attached tin oxide was drastically decreased. However, the sensitivity characteristic of the pure tin oxide not adhering to the graphene catalyst was rather improved, showing a sensitivity of about 17 (R _air / R _gas ) at a gas concentration of 5 ppm. 6 and 7, when the composite was formed by attaching the graphene catalyst to the tin oxide, not only the sensitivity characteristic was improved but the driving temperature of the sensor was also remarkably reduced. This reduction in the driving temperature has an advantage that power consumption can be minimized. In addition, since the gas reactivity varies depending on the temperature, graphene addition is advantageous in that it can impart selectivity to the temperature.

FIG. 8 is a graph showing the relationship between the acetone gas of the disease diagnosis sensor using a pure tin oxide nano-rod having no graphene catalyst attached thereto and the graphene catalyst-tin oxide nano-rod composite prepared according to Example 2 and Comparative Example 1 at 200 ° C This is a graph showing the results. As shown in FIG. 8, the tin oxide nano-rod composite without graphene catalyst-tin oxide nano-rod composite and the graphene catalyst-free tin oxide nano-rod sensor showed sensitivity at a level close to 1 at 200 ° C for each sample . From the above results, it can be seen that the graphene catalyst-tin oxide nano-rods have an excellent selectivity for acetone gas and preferentially detect H ₂ S gas when compared with the 200 ° C. H ₂ S gas test result shown in FIG. 6 .

9 is a graph showing the results of reaction of acetone gas at 350 DEG C of a disease diagnosis sensor using a tin oxide nano rod with no graphene catalyst-attached graphene catalyst-tin oxide nano-rod composite prepared according to Example 2 and Comparative Example 1 FIG. As shown in FIG. 9, the temperature was raised to 350 ° C and the reactivity against acetone gas was confirmed. As a result, the reactivity of the graphene catalyst-tin oxide nano-rod complex and the tin oxide nano-rod without the graphene catalyst was improved It looked. Particularly, the reactivity of the tin oxide nano-rods with graphene catalysts was more improved than that of tin oxide nano-rods without graphene catalysts.

10 is a graph showing the results of reaction of toluene gas at 200 ° C of a disease diagnosis sensor using a tin oxide nano rod without a graphene catalyst attached thereto and a graphene catalyst-tin oxide nano-rod composite prepared according to Example 2 and Comparative Example 1 FIG. As shown in FIG. 10, it can be seen that both the graphene catalyst-tin oxide nano-rod complex and the tin oxide nano-rod without the graphene catalyst did not react with the toluene gas at a sensitivity close to 1 at 200 ° C. From the above results, it was confirmed that the graphene catalyst-tin oxide nanorod selectively senses H ₂ S gas with respect to toluene gas as compared with the 200 ° C. H ₂ S gas test result shown in FIG.

11 is a graph showing the results of the reaction of toluene gas at 300 DEG C of the disease diagnosis sensor using the tin oxide nano-rods without graphene catalyst attached thereto and the graphene catalyst-tin oxide nano-rod composite prepared according to Example 2 and Comparative Example 1 FIG. As shown in FIG. 11, it can be seen that both the graphene catalyst-tin oxide nano-rod complex and the tin oxide nano-rod without the graphene catalyst do not react with the toluene gas at a sensitivity close to 1 at 300 ° C. From the above results, it was confirmed that the graphene catalyst-tin oxide nanorod composite selectively senses acetone gas against toluene gas as compared with the test result for acetone gas at 350 ° C. shown in FIG.

In the above embodiment, tin oxide (SnO ₂ ) is used as an example. However, any metal oxide semiconductor that can be produced through electrospinning can be used, and ZnO, SnO ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , NiO, TiO ₂ , CuO, In ₂ O ₃ , Zn ₂ SnO ₄ , Co ₃ O ₄ , PdO, LaCoO ₃ , NiCo ₂ O ₄ , Ca ₂ Mn ₃ O ₈ , V ₂ O ₅ , Ag ₂ V ₄ O ₁₁ , Ag _{2 O, MnO 2, InTaO 4} , InTaO 4, CaCu 3 Ti 4 O 12, Ag 3 PO 4, BaTiO 3, NiTiO 3, SrTiO 3, Sr 2 Nb 2 O 7, Sr 2 Ta 2 O 7, Ba 0.5 Sr _0.5 Co _0.8 Fe _0.2 O ₃ , or a combination thereof. It is possible to form a complex through mixing with any of the above-mentioned metal oxides with the graphene catalyst. (H ₂ S, Acetone, NH ₃ , Toluene, Pentane, Isoprene, NO ₃ , etc.) for diagnosis of diseases is applied not only to the H ₂ S gas shown in the concrete results of the above embodiment, Etc.) as well as harmful gases (CO, NOx, SOx, etc.) for environmental diagnosis. It is possible to improve not only the reaction value but also various characteristics such as the reaction rate / recovery speed and the low sensor driving temperature from the specific gas sensor results shown in the above embodiments.

Claims (18)

Metal oxide nanorods; And
Metal oxide nanorods and graphene composite comprising one or more of graphene or aggregates thereof bonded to the surface of the metal oxide nanorods. The metal oxide nanorods and graphene composite of claim 1, wherein a ratio of the length of the metal oxide nanorods to the maximum diameter of the graphene or aggregates thereof is 30,000. The graphene composite according to claim 1, wherein the ratio of the surface of the metal oxide nanorod that is not bound to the graphene or the aggregate thereof is 5% to 98%. The composite of claim 1, wherein the metal oxide nanorod has pores formed in the metal oxide nanorod. The graphene composite of claim 1, wherein the graphene or aggregate thereof is a graphene composite with a metal oxide nanorod having a shape of at least one of a graphene piece, a graphene quantum dot, a graphene ribbon, and a graphene flake. 2. The graphene composite of claim 1, wherein the graphene or aggregate thereof is a graphene complex with a metal oxide nanorod comprising graphene oxide, reduced graphene oxide, or a mixture thereof. The graphene composite according to claim 1, wherein the graphene has a size distribution of 1 nm to 300 nm and the graphene aggregate has a size distribution of 100 nm to 500 nm. The metal oxide nanorods and graphene composite of claim 1, wherein the graphene or graphene aggregate of the composite is present in an amount of 0.0001 to 10 wt%. The graphene composite according to claim 1, wherein the graphene is a graphene having a single layer or a multilayer structure. According to claim 1, wherein said metal oxide nanorod is _{WO 3, ZnO, SnO 2,} Fe 2 O 3, Fe 3 O 4, NiO, TiO 2, CuO, In 2 O 3, Zn 2 SnO 4, Co 3 O _{4, PdO, LaCoO 3, NiCo} 2 O 4, Ca 2 Mn 3 O 8, V 2 O 5, Ag 2 V 4 O 11, Ag 2 O, MnO 2, InTaO 4, InTaO 4, CaCu 3 Ti 4 O 12 , at least one of _{Ag 3 PO 4, BaTiO 3,} NiTiO 3, SrTiO 3, Sr 2 Nb 2 O 7, Sr 2 Ta 2 O 7, Ba 0 .5 Sr 0 .5 Co 0 .8 Fe 0 .2 O 3 Metal oxide nanorods and graphene composites. The graphene composite according to claim 1, wherein the metal oxide nanorod has a diameter of 50 nm to 1.5 占 퐉 and a length of 1 占 퐉 to 30 占 퐉. 2. The graphene composite according to claim 1, wherein the metal oxide nanorod is a polycrystalline metal oxide nanorod composed of nanoparticles. And mixing the metal oxide nanorod and the graphene dispersion solution to prepare a graphene complex with the metal oxide nanorod having the graphene or graphene aggregate bound thereto,
Wherein the ratio of the length of the metal oxide nanorod to the maximum diameter of the graphene is 3 to 30,000. 14. The method of claim 13, wherein the metal oxide nanorod and the graphene are dispersed in a solvent selected from the group consisting of ethanol, methanol, propanol, butanol, isopropanol, dimethylformamide, acetone, tetrahydrofuran, toluene, water, Method for preparing mixed metal oxide nanorods and graphene composites. 14. The method of claim 13, wherein the metal oxide nanorods are obtained by grinding nanofibers produced by an electrospinning method. 14. The method of claim 13, wherein the metal oxide constituting the metal oxide nanorod is selected from the group consisting of WO ₃ , ZnO, SnO ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , NiO, TiO ₂ , CuO, In ₂ O ₃ , Zn ₂ SnO ₄ , Co ₃ O ₄ , PdO, LaCoO ₃ , NiCo ₂ O ₄ , Ca ₂ Mn ₃ O ₈ , V ₂ O ₅ , Ag ₂ V ₄ O ₁₁ , Ag ₂ O, MnO ₂ , InTaO ₄ , InTaO ₄ , CaCu _{3 Ti 4 O 12, Ag 3} PO 4, BaTiO 3, NiTiO 3, SrTiO 3, Sr 2 Nb 2 O 7, Sr 2 Ta 2 O 7, Ba 0 .5 Sr 0 .5 Co 0 .8 Fe 0 .2 O ₃ and a metal oxide nanorod that is a complex of at least one selected from the group consisting of a metal oxide nanorod and a graphene composite. A sensor comprising the metal oxide nanorod of claim 1 and a graphene composite. 18. The method of claim 17, wherein the sensor is a sensor for detecting H ₂ S, acetone, NH _3, toluene, pentane, isoprene, CO, NOx, SOx, H ₂ and one or more of the NO.

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