KR102578618B1 - Gas sensor containing metal fluoride hydroxide - Google Patents

Abstract

One embodiment of the present invention provides a gas sensor containing metal fluoride hydroxide and a gas sensing method using the same. According to one embodiment of the present invention, metal fluoride hydroxide prepared by hydrothermal synthesis using microwaves can be applied to a gas sensor to exhibit higher detection characteristics for acetone and nitrogen dioxide gas compared to other gases. In addition, the gas sensor of the present invention operates at a temperature of 50 °C to 250 °C and can operate stably even when doped with fluorine.

Description

Gas sensor containing metal fluoride hydroxide and gas detection method using the same {GAS SENSOR CONTAINING METAL FLUORIDE HYDROXIDE}

The present invention relates to a gas sensor comprising metal fluoride hydroxide. More specifically, by applying metal fluoride hydroxide produced by hydrothermal synthesis using microwaves to a gas sensor, we provide a metal fluoride hydroxide gas sensor that can exhibit higher detection characteristics for acetone and nitrogen dioxide gas than other gases. .

A gas sensor is a device that detects specific chemicals contained in gas, converts the concentration into an electrical signal, and outputs it. There are many methods depending on the type of gas.

Representative examples include methods that use changes in solid properties due to gas adsorption or reaction (semiconductor sensors, ceramic wet temperature sensors, piezoelectric sensors, etc.), methods that use combustion heat (contact combustion sensors), and methods that use electrochemical reactions (solid electrolyte sensors). sensor, electrochemical sensor), and methods that use physical characteristic values (infrared absorption method, etc.).

Among the methods that utilize changes in solid properties due to gas adsorption or reaction, a semiconductor gas sensor can detect gas using an oxide semiconductor.

It is a sensor that uses the fact that the electrical conductivity of an oxide semiconductor changes when it comes in contact with a certain type of gas. Since this element is often used by heating to over 300℃, electrodes and heaters are incorporated into various structures such as thin film type, thick film type, and sintered type. use.

Depending on the detection gas, tin oxide or zinc oxide-based semiconductor materials are mainly used.

In addition, the gas detection device includes: ① When an electron-donating or electron-accepting gas is chemically adsorbed on the surface of a semiconductor, electron exchange occurs from the adsorbed molecule to the semiconductor, and the carrier density in the semiconductor changes, thereby changing surface conductivity; ② Metal oxide semiconductor It is reduced to a reducing gas, causing a change in composition, resulting in a change in conductivity; ③ The height of the potential barrier at the contact grain boundary in the semiconductor and the contact surface with catalytic metals such as palladium and platinum changes due to reaction with the gas phase; ④ On the surface Conductivity changes as the temperature of the device increases due to contact combustion between adsorbed gas molecules and oxygen molecules.

Semiconductor gas sensors are small, inexpensive, have high sensitivity and quick response, and have the advantage of detecting gas concentration through an electric signal.

It is used in gas leak alarms, fire alarms, alcohol detectors, engine combustion gas detection, etc.

At this time, in addition to the above fields, a field where gas sensors can be applied is the biomarker application field.

Biomarkers are biomarkers that can detect changes in the body using proteins, DNA, RNA, and metabolites.

Using the above biomarkers, the normal or pathological state of a living organism and the degree of response to drugs can be objectively measured.

The biomarker must be able to selectively detect low concentrations of nitrogen dioxide or acetone gas.

A method of doping fluorine has been attempted to improve the gas detection characteristics of existing oxide semiconductor materials, but gas sensors using oxide semiconductor materials are often used by heating to over 300℃, and doping with fluorine is unstable at high temperatures. There was a problem with not sufficiently improving the detection characteristics.

A material that can detect more effectively than existing oxide semiconductor-based materials is needed.

Republic of Korea Patent Publication No. 2012-0049057

In order to solve the problems of the prior art as described above, the technical problem to be achieved by the present invention is to apply metal fluoride hydroxide manufactured by hydrothermal synthesis using microwaves to a gas sensor, which has a higher level of accuracy for acetone and nitrogen dioxide gas compared to other gases. The aim is to provide a metal fluoride hydroxide gas sensor that can exhibit detection characteristics.

The technical problem to be achieved by the present invention is not limited to the technical problem mentioned above, and other technical problems not mentioned can be clearly understood by those skilled in the art from the description below. There will be.

In order to achieve the above technical problem, an embodiment of the present invention provides a gas sensor.

A gas sensor according to an embodiment of the present invention,

It includes a gas sensing layer containing metal fluoride hydroxide,

The gas sensing layer can selectively detect acetone or nitrogen dioxide gas.

The resistance of the gas sensing layer containing the metal fluoride hydroxide may change as a result of a reaction between oxygen ions adsorbed on the surface and the acetone or nitrogen dioxide gas.

In the metal fluoride hydroxide, fluorine can lower the resistance of the material coated on the gas sensor itself, thereby increasing the sensitivity of the reaction when adsorbed oxygen ions react with acetone or nitrogen dioxide gas.

The gas sensing layer can detect acetone or nitrogen dioxide gas of 1 ppm or less.

The metal fluoride hydroxide may include one selected from Co(OH)F, Zn(OH)F, and Co(OH)F/Zn(OH)F.

The metal fluoride hydroxide can be produced through a hydrothermal synthesis method using microwaves.

The gas sensor can operate at temperatures between 50 °C and 250 °C.

In order to achieve the above technical problem, an embodiment of the present invention provides a gas detection method using a gas sensor.

A gas detection method using a gas sensor according to an embodiment of the present invention,

Oxygen ions adsorbed on the surface of the gas sensing layer containing metal fluoride hydroxide react with acetone or nitrogen dioxide gas to change resistance, and the changed resistance can be measured.

When oxygen ions adsorbed on the surface of the gas sensing layer containing the metal fluoride hydroxide react with acetone or nitrogen dioxide gas, the resistance of the gas sensor may increase.

The metal fluoride hydroxide may include one selected from Co(OH)F, Zn(OH)F, and Co(OH)F/Zn(OH)F.

The fluorine of the metal fluoride hydroxide can lower the resistance of the material coated on the gas sensor itself, thereby increasing the sensitivity of the reaction when adsorbed oxygen ions react with acetone or nitrogen dioxide gas.

The gas sensor can operate at temperatures between 50 °C and 250 °C.

According to an embodiment of the present invention, it relates to a gas sensor containing metal fluoride hydroxide. By applying metal fluoride hydroxide prepared by hydrothermal synthesis using microwaves to a gas sensor, acetone and nitrogen dioxide gas are compared to other gases. It has the effect of showing high detection characteristics.

In addition, the gas sensor of the present invention operates at a temperature of 50 °C to 250 °C and can operate stably even when doped with fluorine.

The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description or claims of the present invention.

Figure 1 is a graph measuring the sensitivity after applying Zn(OH)F nanorods and Co(OH)F/Zn(OH)F heterostructures material according to an embodiment of the present invention to a nitrogen dioxide or acetone gas sensor, respectively.
Figure 2 is an XRD graph and SEM photo of Zn(OH)F nanorods according to an embodiment of the present invention.
Figure 3 is an XRD graph and SEM photo of Co(OH)F/Zn(OH)F heterostructures according to an embodiment of the present invention.
Figure 4 shows (a) the sensitivity of Zn(OH)F nanorods and ZnO material-based gas sensors to nitrogen dioxide gas according to an embodiment of the present invention, and (b) the change in nitrogen dioxide concentration of Zn(OH)F nanorods. Sensitivity according to gas type, (c) Sensitivity graph according to gas type of Zn(OH)F nanorods.
Figure 5 shows (a) Co(OH)F, Zn(OH)F, Co(OH)F/Zn(OH)F heterostructures (3:1, 1:1, 1:3) according to an embodiment of the present invention. ) Sensitivity of material-based gas sensor to acetone gas by operating temperature (b) Co(OH)F/Zn(OH)F heterostructures (3:1) Sensitivity of material-based gas sensor to acetone concentration change, (c) Co (OH)F/Zn(OH)F heterostructures (3:1) This is a sensitivity graph according to the gas type of the material-based gas sensor.
Figure 6 is a conceptual diagram showing the synthesis process of Zn(OH)F nanorods and ZnO caltrop-like according to an embodiment of the present invention.
Figure 7 is a TEM image of Zn(OH)F nanorods and ZnO caltrop-like according to an embodiment of the present invention.
Figure 8 is an XRD spectrum of Zn(OH)F nanorods according to an embodiment of the present invention after post-annealing at 250 °C, 350 °C, and 450 °C.
Figure 9 is an SEM image of Zn(OH)F nanorods according to an embodiment of the present invention after post-annealing at (a) 250 °C, (b) 350 °C, and (c) 450 °C.
Figure 10 is a TEM photo of Zn(OH)F nanorods according to an embodiment of the present invention after post-annealing at 250 °C, 350 °C, and 450 °C.
Figure 11 is a graph of the atomic ratios of F, O, and Zn and XPS spectra obtained from Zn(OH)F nanorods annealed at 250 °C, 350 °C, and 450 °C.
Figure 12 is a graph showing the detection characteristics of the reaction gas of Zn(OH)F.
Figure 13 is a stability graph for acetone detection of the Co(OH)F/Zn(OH)F heterostructure gas sensor.

Hereinafter, the present invention will be described with reference to the attached drawings. However, the present invention may be implemented in various different forms and, therefore, is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts that are not related to the description are omitted, and similar parts are given similar reference numerals throughout the specification.

Throughout the specification, when a part is said to be "connected (connected, contacted, combined)" with another part, this means not only "directly connected" but also "indirectly connected" with another member in between. "Includes cases where it is. In addition, when a part is said to “include” a certain component, this does not mean that other components are excluded, but that other components can be added, unless specifically stated to the contrary.

The terms used herein are only used to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as “comprise” or “have” are intended to indicate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features. It should be understood that this does not exclude in advance the possibility of the existence or addition of elements, numbers, steps, operations, components, parts, or combinations thereof.

Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

A gas sensor containing metal fluoride hydroxide according to an embodiment of the present invention will be described.

The gas sensor,

It includes a gas sensing layer containing metal fluoride hydroxide,

The gas sensing layer can selectively detect acetone or nitrogen dioxide gas.

The resistance of the gas sensing layer containing the metal fluoride hydroxide may change as a result of a reaction between oxygen ions adsorbed on the surface and the acetone or nitrogen dioxide gas.

In addition, fluorine in the metal fluoride hydroxide can lower the resistance of the material itself coated on the gas sensor, thereby increasing the sensitivity of the reaction when adsorbed oxygen ions react with acetone or nitrogen dioxide gas.

Additionally, the gas sensor can selectively detect acetone and nitrogen dioxide gas of 1 ppm or less by the metal fluoride hydroxide.

The gas sensor will be described through FIGS. 1 to 12.

Figure 1 is a graph measuring the sensitivity after applying Zn(OH)F nanorods and Co(OH)F/Zn(OH)F heterostructures materials according to an embodiment of the present invention to a nitrogen dioxide or acetone gas sensor, respectively.

Referring to FIG. 1, it can be seen that acetone and nitrogen dioxide gas of 1 ppm or less can be selectively detected by the metal fluoride hydroxide.

Additionally, Figure 1 is a graph of resistance against NO ₂ concentration and resistance against acetone concentration.

The resistance is expressed as Rg/Ra (Rg: sensor resistance in gas, Ra: sensor resistance in air), and it can be seen that the Rg/Ra value of resistance increases as the NO ₂ gas and acetone gas increase.

At this time, the introduced NO ₂ gas and acetone gas can be detected by the gas sensor containing the metal fluoride hydroxide.

The metal fluoride hydroxide may include one selected from Co(OH)F, Zn(OH)F, and Co(OH)F/Zn(OH)F.

Referring to FIG. 1, the gas sensor containing Zn(OH)F nanorods can first detect NO ₂ gas at 0.3 ppm, and the gas sensor containing Co(OH)F/Zn(OH)F can detect acetone. Gas can be first detected at 0.25ppm.

That is, a gas sensor containing metal fluoride hydroxide can selectively detect acetone and nitrogen dioxide gas of 1 ppm or less by the metal fluoride hydroxide.

At this time, if low concentrations of NO ₂ gas and acetone gas can be selectively detected through the use of a gas sensor, it can be used in the biomarker field to determine diabetes, periodontal disease, etc.

Figure 2 is an XRD graph and SEM photo of Zn(OH)F nanorods according to an embodiment of the present invention.

The XRD graph is an X-ray diffraction meter and is used to characterize the phase of Zn (OH) F.

The SEM image is used to analyze the morphology of the material using a scanning electron microscope.

Referring to FIG. 2(a), the XRD spectrum in FIG. 2(a) is a Zn(OH)F spectrum that confirms that the sensor detects NO ₂ gas with high sensitivity by the Zn(OH)F nanorod.

Also, referring to FIG. 2(b), it can be seen that the Co(OH) F and Zn(OH)F are in the form of nanorods.

Additionally, the length of Zn(OH)F may range from 1 μm to 3 μm.

The reason why the Co(OH)F and Zn(OH)F were manufactured in nano size was to increase the efficiency of the reaction by increasing the surface area.

Figure 3 is an XRD graph and SEM photo of Co(OH)F/Zn(OH)F heterostructures according to an embodiment of the present invention.

Referring to FIG. 3(a), the XRD spectrum in FIG. 3(a) confirms that the sensor detects acetone gas with high sensitivity due to Co(OH)F/Zn(OH)F heterostructures. This is the Co(OH)F/Zn(OH)F spectrum.

The heterostructure may mean a structure composed of a combination of several heterojunctions inside one material.

Additionally, referring to FIG. 3(b), it can be seen that Co(OH)F/Zn(OH)F of FIG. 2(b) is a mixture of nanorods and flowers.

The Co(OH)F/Zn(OH)F diameter may range from 4 μm to 5 μm.

Figure 4 shows (a) the sensitivity of Zn(OH)F nanorods and ZnO material-based gas sensors to nitrogen dioxide gas according to an embodiment of the present invention, and (b) the change in nitrogen dioxide concentration of Zn(OH)F nanorods. Sensitivity according to gas type, (c) Sensitivity graph according to gas type of Zn(OH)F nanorods.

FIG. 4 (a) is a graph showing the sensitivity of the nitrogen dioxide gas sensor based on (a) Zn(OH)F nanorods and ZnO material to nitrogen dioxide gas by operating temperature.

Referring to FIG. 4 (a), it can be seen that Zn(OH)F nanorods and ZnO material selectively detect nitrogen dioxide and have high sensitivity to nitrogen dioxide gas when the operating temperature is 100°C or less. It can be seen that sensitivity to nitrogen dioxide gas is low when the temperature is above °C.

This confirms that Zn(OH)F nanorods are more sensitive to nitrogen dioxide gas than ZnO, and that sensitivity decreases when Zn(OH)F nanorods are exposed to high temperatures above 150°C. You can check that.

FIG. 4 (b) is a graph showing the sensitivity of Zn(OH)F nanorods (b) according to changes in nitrogen dioxide concentration.

Referring to FIG. 4(b), it can be seen that Zn(OH)F nanorods can detect even at low concentrations, and that sensitivity increases as the concentration increases.

FIG. 4 (c) is a graph of the sensitivity of Zn(OH)F nanorods according to gas type.

Referring to FIG. 4 (c), the Zn(OH)F nanorods are nitrogen dioxide (NO ₂ ), hydrogen (H ₂ ), ethanol (C ₂ H ₅ OH), ammonia (NH ₃ ), and toluene (C ₆ H). The properties of ₅ CH ₃ ) and acetone (CH ₃ COCH ₃ ) can be confirmed.

In addition, the Zn(OH)F nanorods are nitrogen dioxide (NO ₂ ), hydrogen (H ₂ ), ethanol (C ₂ H ₅ OH), ammonia (NH ₃ ), toluene (C ₆ H ₅ CH ₃ ), and acetone ( It can be confirmed that nitrogen dioxide (NO ₂ ) can be selectively detected compared to CH ₃ COCH ₃ ).

At this time, when the nitrogen dioxide (NO ₂ ) gas is 1.3 ppm, it shows an Rg/Ra value of over 60, so it can be confirmed that the sensitivity to low concentrations of nitrogen dioxide is high.

Additionally, the metal fluoride hydroxide may be formed by coating the gas sensing layer of the gas sensor so that resistance changes when it comes into contact with gas.

The fluorine lowers the resistance of the material coated on the gas sensor itself and increases the sensitivity of the reaction when adsorbed oxygen ions react with acetone or nitrogen dioxide gas.

Fluorine, which has high electronegativity, plays a catalytic role. The fluorine increases the Lewis acidity of the material included in the gas sensor and allows the sensing material to easily provide electrons when adsorbing oxygen or detecting gas. .

The fluorine can protect surface defects and reduce carrier trapping of the material.

In addition, the fluorine-containing Zn(OH)F nanorod-based sensor has low carrier trapping compared to the resistance (more than 10MOhm) of the caltrop-type ZnO-based sensor applied to the existing gas sensor at an operating temperature of 100°C. Initial resistance can be lowered to less than 100kOhm.

Figure 5 shows (a) Co(OH)F, Zn(OH)F, Co(OH)F/Zn(OH)F heterostructures (3:1, 1:1, 1:3) according to an embodiment of the present invention. ) Sensitivity of material-based gas sensor to acetone gas by operating temperature (b) Co(OH)F/Zn(OH)F heterostructures (3:1) Sensitivity of material-based gas sensor to acetone concentration change, (c) Co (OH)F/Zn(OH)F heterostructures (3:1) This is a sensitivity graph according to the gas type of the material-based gas sensor.

Figure 5 (a) shows (a) Co(OH)F, Zn(OH)F, Co(OH)F/Zn(OH)F heterostructures (3:1, 1:1, 1:3) material-based gas sensor. This is a graph showing the sensitivity to acetone gas by operating temperature.

In Figure 5 (a), Co(OH)F is blue hatched, Zn(OH)F is pink hatched, Co(OH)F/Zn(OH)F heterostructures (3:1) is yellow hatched, and Co(OH) F/Zn(OH)F heterostructures (1:1) are shaded in white, and Co(OH)F/Zn(OH)F heterostructures (1:3) are shaded in green.

Referring to Figure 5 (a), it is a graph showing gas detection by a gas sensor coated with each material at 50°C, 100°C, 150°C, and 200°C, and at 50°C and 100°C is Co(OH)F, Zn(OH)F, Co(OH)F/Zn(OH)F heterostructures (3:1), Co(OH)F/Zn(OH)F heterostructures (1:1), Co It can be seen that all (OH)F/Zn(OH)F heterostructures (1:3) materials exhibit similar sensitivity.

Additionally, at 150°C, Co(OH)F/Zn(OH)F heterostructures (3:1) showed the highest sensitivity, followed by Co(OH)F/Zn(OH)F heterostructures (1:1). ), Co(OH)F/Zn(OH)F heterostructures (1:3), Co(OH)F, and Zn(OH)F show the highest strength in that order.

In addition, Figure 5 (b) is a graph showing the sensitivity of a gas sensor based on Co(OH)F/Zn(OH)F heterostructures (3:1) according to changes in acetone concentration.

At this time, the unit of resistance is MOhm and is 10 ⁶ Ohm.

Referring to FIG. 5(b), the highest resistance can be shown at 5 ppm in about 500 seconds.

Additionally, it can be seen that the resistance decreases as the concentration of acetone decreases over time.

At this time, referring to Figure 5 (b), it can be confirmed that resistance can be detected even at 0.25 ppm.

Figure 5 (c) Sensitivity graph according to gas type of gas sensor based on Co(OH)F/Zn(OH)F heterostructures (3:1) material.

Referring to FIG. 5 (c), nitrogen dioxide (NO ₂ ), hydrogen (H ₂ ), ethanol (C ₂ H ₅ OH), ammonia (NH ₃ ), toluene (C ₆ H ₅ CH ₃ ), acetone (CH It can be confirmed that it reacts to ₃ COCH ₃ ), and among them, it can be confirmed that it shows the highest sensitivity to acetone (CH ₃ COCH ₃ ).

Figure 6 is a conceptual diagram showing the synthesis process of Zn(OH)F nanorods and ZnO caltrop-like according to an embodiment of the present invention.

The metal fluoride hydroxide can be produced through a hydrothermal synthesis method using microwaves.

As an embodiment of the present invention, the manufacturing method of Zn(OH)F is as follows.

First, 5 mmol of zinc nitrate hexahydrate (Zn(NO ₃ ) ₂ 6H ₂ O), 5 mmol of ammonium fluoride (NH ₄ F), and 1 mmol of sodium hydroxide (NaOH) are added to 18.5 mL of distilled water.

Next, mix the solution for 10 minutes and transfer it to a 30ml vial.

Next, react in a microwave synthesis reactor at 120 °C for 20 min. (Used Anton Paar Monowave 300)

Next, the final solution in the reactor is naturally cooled to 55°C.

Next, the white powder is filtered, the precipitated white powder is washed with distilled water and ethanol, and then dried in an oven at 80 °C overnight.

The hydrothermal synthesis process using the microwave was performed to form a metal fluoride hydroxide with the chemical formula Zn(OH)F, which has high selective detection properties for low concentrations of acetone and nitrogen dioxide gas.

Referring to the above preparation example, Zn(OH)F can be produced when the reaction includes ammonium fluoride (NH ₄ F), and ZnO can be produced when the reaction excludes ammonium fluoride (NH ₄ F).

The mechanism for forming the Zn(OH)F structure is explained in Equations (1) and (2) below.

<Equation (1)>

Zn ²⁺ +F- →ZnF ⁺

<Equation (2)>

ZnF ⁺ +OH- →Zn(OH)F

At this time, in the reaction providing F-, NH ₄ F plays an important role in the synthesis process of forming the Zn(OH)F structure.

The hydrothermal synthesis process using the microwave has the effect of shortening the synthesis time to 20 minutes compared to 6 hours for the existing furnace-based synthesis.

At this time, the Zn(OH)F may be in the form of a rod, and ZnO may be in the form of a caltrop.

Figure 7 is a TEM image of Zn(OH)F nanorods and ZnO caltrop-like according to an embodiment of the present invention.

Referring to FIG. 7, FIG. 7 (a), (b) and (c) show the Zn(OH)F nanorod form and FIG. 7 (d), (e) and (f) show the form of ZnO. A caltrop-like shape can be identified.

At this time, Figures 7 (b) and (e) can show the single crystal properties of Zn(OH)F nanorods and ZnO caltrop-like, respectively.

In the single crystals shown in Figures 7 (b) and (e), the Zn(OH)F nanorod has a diaspore structure, and the ZnO caltrop-like has a wurtzite structure.

Additionally, Figures 7(c) and (f) can show lattice fringes with d spacings of 0.44 and 0.26 nm.

The d may represent the horizontal width of the Zn(OH)F nanorod and the ZnO caltrop-like material.

At this time, since the gas sensor generally operates at high temperatures, it is important to ensure the thermal stability of the sensing material.

Figure 8 is an XRD spectrum of Zn(OH)F nanorods according to an embodiment of the present invention after post-annealing at 250 °C, 350 °C, and 450 °C.

At this time, post-annealing was performed on Zn(OH)F nanorods at 250°C, 350°C, and 450°C for 2 hours to confirm the high-temperature properties of metal fluoride hydroxide prepared through a hydrothermal synthesis method using microwaves. This means annealing during

In addition, the annealing refers to a heat treatment method of heating to a certain temperature and then slowly cooling to correct internal deformation of metal, etc.

Referring to Figure 8, the spectrum of the Zn(OH)F nanorods annealed at 250 °C remains almost the same as that of the pristine sample, while the spectrum of the sample annealed at 450 °C is completely converted to that of ZnO. You can check that it works.

Additionally, the spectrum of Zn(OH)F heat-treated at 350 °C shows an intermediate state between Zn(OH)F and ZnO, which may mean that the material is evolving from Zn(OH)F to ZnO structure. .

Figure 9 is an SEM image of Zn(OH)F nanorods according to an embodiment of the present invention after post-annealing at (a) 250 °C, (b) 350 °C, and (c) 450 °C.

Referring to Figure 9, the microstructure evolution can be confirmed by SEM and TEM analysis as the annealing temperature increases.

The Zn(OH) nanorods remain in the nanorod shape regardless of the post-annealing temperature, but referring to Figure 6 (c), it can be seen that there are pores on the surface of the nanorods annealed at 450°C.

The pores may emit HF gas according to the following equation (3) after thermal decomposition of Zn(OH)F at high temperature.

<Equation (3)>

Zn(OH)F → ZnO+HF ↑

Figure 10 is a TEM photo of Zn(OH)F nanorods according to an embodiment of the present invention after post-annealing at 250 °C, 350 °C, and 450 °C.

The TEM analysis can show detailed information about the microstructural transformation, as shown in FIG. 10.

At this time, Figures 10 (a) to (c) may show Zn(OH)F nanorods annealed at 250°C.

It still maintains the single-crystal Zn(OH)F structure, showing a plane of Zn(OH)F (110), as shown in Figure 10 (c).

Additionally, referring to Figures 10 (f) and (i), it can be seen that the Zn(OH)F nanorods became polycrystalline due to thermal decomposition after annealing at 350°C and 450°C.

In addition, referring to FIGS. 10 (d) to (i), TEM analysis can confirm the porous structure of Zn(OH)F nanorods annealed at 350 °C and 450 °C.

The porous structure can be created by decomposing Zn(OH)F and HF flying away from Zn(OH)F according to equation (3).

In addition, referring to Figure 10 (i), the d-spacing (100,101) of Zn (OH) F post-annealed at 450 °C is 0.24 and 0.28 nm, respectively, which may correspond to the d-spacing interplanar distance of ZnO. .

On the other hand, Figure 10 (f) is Zn(OH)F post-annealed at 350 °C, and the d-spacing is 0.25 nm. As confirmed by XRD analysis, the material is in an intermediate state, so it is difficult to determine the d-spacing length of the material. I can't.

Through this, it can be confirmed that the Zn(OH)F is stable at a temperature of 250 °C or lower.

Figure 11 is a graph of the atomic ratios of F, O, and Zn and XPS spectra obtained from Zn(OH)F nanorods annealed at 250 °C, 350 °C, and 450 °C.

Figure 11 (a) is a graph showing the atomic ratio versus post-annealing temperature, Figure 11 (b) is a graph of Zn 2p of Zn(OH)F and ZnO, and Figure 11 (c) is a graph of Zn(OH) Shows the O 1s graph of F and ZnO.

Referring to Figure 11, it can be seen that the atomic ratio of F in Zn(OH)F is similar after annealing at 250 °C and 350 °C.

On the other hand, the fluorine (F) concentration drops sharply after post-annealing at 450°C.

The reason is that, as can be seen in equation (3), F inside Zn(OH)F evaporates at 450°C.

<Equation (3)>

Zn(OH)F → ZnO+HF ↑

In addition, referring to Figures 11 (b) and (c), the spectral evolution can be confirmed according to the chemical states of O1s (1s orbital of oxygen atom) and Zn2p (2p orbital of zirconium atom) depending on annealing temperature. .

Referring to (b) of FIG. 11, the spectrum of O1s can be deconvoluted into two sub-peaks (the spectral peaks are separated) when the post-annealing temperature is 350°C or higher.

That is, it can be deconvolute into two peaks: a peak corresponding to the Zn-O bond at about 530.0 eV and a peak corresponding to the Zn-OH bond at about 531.6 eV.

This is because the spectra of the raw and 250 °C annealed samples show only Zn-OH bonds, whereas in the ZnO structure, peaks corresponding to Zn-O bonds can appear in the spectrum of the sample post-annealed at 350 °C. am.

Additionally, the Zn-OH bond in the spectrum of the sample annealed at 450 °C is similar to that of the ZnO sample because it is completely converted from Zn(OH)F to ZnO.

Also, referring to (b) of Figure 11, the Zn 2p peak position can shift from high binding energy to low binding energy after post-annealing at 350 °C and 450 °C.

At this time, the peak of the Zn-O bond in FIG. 11(b) increases and the peak of the Zn-OH bond decreases, so it can be confirmed that there is a shift from high binding energy to low binding energy.

That is, the XPS analysis in FIG. 11 (c) shows that when the Zn(OH)F structure is post-annealed at 250 °C, the Zn(OH)F structure is maintained and begins to transform at 350 °C, and post-annealed above 450 °C. In the case of annealing, it can be confirmed that the Zn(OH)F structure is completely converted to the ZnO structure.

Through this, it can be confirmed that gas sensors containing metal fluoride hydroxide are stable at temperatures below 250 °C.

Figure 12 is a graph showing the detection characteristics of Zn (OH) F for the reaction gas.

The gas sensor can operate at temperatures between 50 °C and 250 °C.

The gas sensor containing the metal fluoride hydroxide is capable of detecting hydrogen (H ₂ ), ethanol (C ₂ H ₅ OH), ammonia (NH ₃ ), toluene (C ₆ H ₅ CH ₃ ), and acetone (CH ₃ COCH ₃ ). In contrast, nitrogen dioxide (NO ₂ ) can be selectively detected.

Figure 12 (a) is a graph showing the change in resistance over time of a gas sensor containing Zn(OH)F nanorods.

Referring to FIG. 12 (a), it can be seen that the Zn(OH)F material shows a high resistance change to NO ₂ gas.

Figure 12 (b) shows the correlation between sensors based on Zn(OH)F nanorods and caltrop-like ZnO at operating temperatures of 25°C, 50°C, 100°C, 150°C, 200°C, and 250°C. NO ₂ sensitivity comparison is shown.

The response graph shows a typical mountain shape, and at all operating temperatures, the gas sensor containing Zn(OH)F nanorods can exhibit a much higher response than the caltrop-like ZnO-based gas sensor toward NO ₂ .

At this time, the response at 100 °C, the optimal operating temperature of the Zn(OH)F nanorod-based gas sensor, is about 63.4, which is about 8.6 times higher than the response of the ZnO-based gas sensor.

Through this, it can be confirmed that the gas sensor can operate at a temperature of 50 °C to 250 °C, and the optimal operating temperature is 100 °C.

In addition, the gas sensor of the present invention operates at a temperature of 50 °C to 250 °C and can operate stably even when doped with fluorine.

Figure 12 (c) is a graph showing NO ₂ gas response to operating temperature of Zn(OH)F sample after post-annealing.

Additionally, referring to Figure 12(c), the response after post-annealing at 250°C is similar to that of the raw sample, but when the post-annealing temperature increases to 350°C and 450°C, the response to NO ₂ gas decreases sharply. You can check that it does.

Through this, it can be confirmed that the optimal temperature for the Zn(OH)F-based gas sensor is below 250 °C.

Figure 12 (d) is a graph showing the response of the gas sensor to the change in NO ₂ concentration of the Zn(OH)F nanorod-based gas sensor.

Referring to FIG. 12 (d), the Zn(OH)F-based gas sensor can respond when NO ₂ gas is at a low concentration, and it can be confirmed that the response increases as the concentration of NO ₂ gas increases. .

Figure 12 (e) shows nitrogen dioxide (NO ₂ ), hydrogen (H ₂ ), ethanol (C ₂ H ₅ OH), ammonia (NH ₃ ), and toluene (C) at 100 °C of the Zn(OH)F-based gas sensor. This is a graph showing the reaction to ₆ H ₅ CH ₃ ) and acetone (CH ₃ COCH ₃ ).

Figure 12 (e) shows H ₂ (5ppm), C ₂ H ₅ OH (10.6ppm), NH ₃ (10.6ppm), C ₆ H ₅ CH ₃ (36.2ppm) and CH ₃ COCH ₃ (2.8ppm). This may indicate high selectivity of the gas sensor for gas species.

Figure 12(e) shows the response of the Zn(OH)F nanorod-based gas sensor to 1.3ppm NO ₂ gas over time for 70 days.

Referring to Figure 12(e), the response of the gas sensor drops below 30 after 21 days.

The stability of the sensor can be improved by heterostructure to improve the long-term stability of the sensor for longer operation.

Figure 13 is a stability graph for acetone gas detection of the Co(OH)F/Zn(OH)F heterogeneous structure gas sensor.

Referring to Figure 13, it can be seen that the sensitivity of the Co(OH)F/Zn(OH)F heterogeneous gas sensor does not decrease even after 30 days and maintains high sensitivity even after 90 days.

A gas detection method using a gas sensor containing metal fluoride hydroxide according to an embodiment of the present invention will be described.

Oxygen ions adsorbed on the surface of the gas sensing layer containing metal fluoride hydroxide react with acetone or nitrogen dioxide gas to change resistance, and the changed resistance can be measured.

A gas detection method using a gas sensor containing metal fluoride hydroxide,

Preparing a gas sensor containing metal fluoride hydroxide (S100);

Injecting a gas containing acetone or nitrogen dioxide into the gas sensor to react the oxygen ions adsorbed on the gas sensor with the acetone or nitrogen dioxide gas (S200);

Measuring resistance increased as the gas sensor reacts (S300); may include.

In the first step, it may include preparing a gas sensor containing metal fluoride hydroxide. (S100)

The metal fluoride hydroxide may include one selected from Co(OH)F, Zn(OH)F, and Co(OH)F/Zn(OH)F.

In addition, the Co(OH)F/Zn(OH)F may be characterized as having a heterostructure.

The heterostructure of Co(OH)F/Zn(OH)F may be a mixture of flowers and nanorods.

In the second step, a gas containing acetone or nitrogen dioxide may be introduced into the gas sensor to react with the oxygen ions adsorbed on the gas sensor and the acetone or nitrogen dioxide gas. (S200)

The step of adsorbing oxygen ions can be expressed according to equation (4) below.

<Equation (4)>

O ₂ (gas) + 2e- → 2O-(ads)

At this time, in the step of adsorbing oxygen ions, a gas containing oxygen is introduced and reacts with electrons transferred by metal fluoride hydroxide, so that oxygen ions can be adsorbed to the gas sensor.

The step of reacting the adsorbed oxygen ions with acetone or nitrogen dioxide gas can be expressed by the following equations (5) and (6).

<Equation (5)>

NO ₂ (ads) + e ^- → NO ₂ ^- (ads)

<Equation (6)>

NO ₂ ^- (ads)+O ^- (ads)+2e ^- → NO(gas)+2O ^2- (ads)

When the gas containing nitrogen dioxide is introduced, it reacts with the electrons transferred by the metal fluoride hydroxide as shown in equation (5), and nitrogen dioxide ions can be adsorbed to the gas sensor.

When electrons are extracted from the Zn(OH)F, oxygen and nitrogen dioxide molecules are ionized, and the adsorbed nitrogen dioxide ions and oxygen ions can further extract electrons from the sensing material Zn(OH)F to generate nitrogen monoxide gas (NO).

The adsorbed nitrogen dioxide ions react with oxygen ions and remove electrons from the sensing material Zn(OH)F, thereby increasing the resistance of the gas sensor.

In the third step, the electrons that move as the gas sensor reacts increase resistance and may include measuring the increased resistance. (S300)

At this time, in the step of measuring the resistance,

The fluorine can lower the resistance of the material coated on the gas sensor and increase the sensitivity of the reaction when adsorbed oxygen ions react with acetone or nitrogen dioxide gas.

At this time, the NO ₂ detection response of the gas sensor can be improved by the fluorine (F) ions of the Zn(OH)F nanorods.

The fluorine (F) can reduce carrier trapping of the material by protecting surface defects.

If the Zn(OH)F nanorod-based gas sensor has low carrier trapping, the peripheral resistance can be lowered to less than 100kOhm than the ZnO-based sensor, which has a resistance of 10MOhm or more at an operating temperature of 100°C.

Carrier trapping by defects located in the crystal system results in charge accumulation and the formation of a dislocation barrier that impedes further charge transport across it.

At this time, if the carrier trapping is low, the formation of a potential barrier that hinders the accumulation and transport of charges can be prevented.

The low resistance of the Zn(OH)F nanorods is beneficial to the oxidation reaction and can maximize the increase in resistance.

In other words, the Zn(OH)F fluorine (F) can protect surface defects by lowering carrier trapping, and lowers the resistance of the material itself coated on the gas sensor, preventing the adsorbed oxygen ions and acetone or nitrogen dioxide gas from When reacting, the sensitivity of the reaction can be increased.

Manufacturing example

First, 5 mmol of zinc nitrate hexahydrate (Zn(NO ₃ ) ₂ 6H ₂ O), 5 mmol of ammonium fluoride (NH ₄ F) and 1 mmol of sodium hydroxide (NaOH) are added to 18.5 mL of distilled water.

Next, mix the solution for 10 minutes and transfer it to a 30ml vial.

Next, react in a microwave synthesis reactor at 120 °C for 20 min. (Used Anton Paar Monowave 300)

Next, the final solution in the reactor is naturally cooled to 55°C.

Next, the white powder is filtered, the precipitated white powder is washed with distilled water and ethanol, and then dried in an oven at 80 °C overnight.

The hydrothermal synthesis process using the microwave was performed to form a metal fluoride hydroxide with the chemical formula Zn(OH)F, which has high selective detection properties for low concentrations of acetone and nitrogen dioxide gas.

Experiment example

The Zn(OH)F formed according to the above preparation example may have selectively high sensing characteristics for acetone and nitrogen dioxide gas.

In order to study the selectively high detection characteristics of the acetone and nitrogen dioxide gases and the appropriate temperature characteristics of the gas sensor, a post annealing process is performed.

The post-annealing may have an effect on the properties of Zn(OH)F.

First, prepare metal fluoride hydroxide nanorod Zn(OH)F powder.

Next, it is placed in the furnace and annealed at temperatures of 250°C, 350°C, and 450°C for 2 hours.

At this time, post-annealing at a temperature higher than 350 C must be performed on a small scale or in a fume hood because toxic HF gas may be released as a by-product.

The description of the present invention described above is for illustrative purposes, and those skilled in the art will understand that the present invention can be easily modified into other specific forms without changing the technical idea or essential features of the present invention. will be. Therefore, the embodiments described above should be understood in all respects as illustrative and not restrictive. For example, each component described as single may be implemented in a distributed manner, and similarly, components described as distributed may also be implemented in a combined form.

The scope of the present invention is indicated by the patent claims described below, and all changes or modified forms derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present invention.

Claims (12)

It includes a gas sensing layer containing metal fluoride hydroxide,
The gas sensing layer selectively detects acetone or nitrogen dioxide gas,
The metal fluoride hydroxide is characterized in that it contains Co(OH)F nanorods, or Co(OH)F/Zn(OH)F, which is a mixture of Zn(OH)F nanorods and Co(OH)F flowers. gas sensor. According to paragraph 1,
A gas sensor, wherein the gas sensing layer containing the metal fluoride hydroxide changes resistance by reacting the oxygen ions adsorbed on the surface with the acetone or nitrogen dioxide gas. According to paragraph 1,
In the metal fluoride hydroxide, fluorine lowers the resistance of the material coated on the gas sensor itself, thereby increasing the sensitivity of the reaction when adsorbed oxygen ions react with acetone or nitrogen dioxide gas. According to clause 1,
A gas sensor characterized in that the gas sensing layer detects acetone or nitrogen dioxide gas of 1 ppm or less. delete According to clause 1,
A gas sensor, characterized in that the metal fluoride hydroxide is manufactured through a hydrothermal synthesis method using microwaves. According to clause 1,
The gas sensor is characterized in that it operates at a temperature of 50 °C to 250 °C. Measure the resistance changed by the reaction between oxygen ions adsorbed on the surface of the gas sensing layer containing metal fluoride hydroxide and acetone or nitrogen dioxide gas,
The metal fluoride hydroxide is characterized in that it contains Co(OH)F/Zn(OH)F, which is a mixture of Co(OH)F nanorods, or Zn(OH)F nanorods and Co(OH)F flowers. Gas detection method using a gas sensor. According to clause 8,
A gas sensing method using a gas sensor, wherein the resistance of the gas sensor increases when oxygen ions adsorbed on the surface of the gas sensing layer containing the metal fluoride hydroxide react with acetone or nitrogen dioxide gas. delete According to clause 8,
A gas detection method using a gas sensor, characterized in that the fluorine of the metal fluoride hydroxide lowers the resistance of the material itself coated on the gas sensor, thereby increasing the sensitivity of the reaction when adsorbed oxygen ions react with acetone or nitrogen dioxide gas. . According to clause 8,
A gas detection method using a gas sensor, characterized in that the gas sensor operates at a temperature of 50 °C to 250 °C.