KR20210120404A - Nano particle composite, gas sensor comprising the same and producing method of the same - Google Patents

Abstract

The present invention relates to a nanoparticle composite, a gas sensor having the same, and a manufacturing method of the same. The nanoparticle composite comprises graphene quantum dots, dopamine, and metal oxide nanoparticles.

Description

Nanoparticle composite, gas sensor including same, and method for manufacturing same {Nano particle composite, gas sensor comprising the same and producing method of the same}

The present invention relates to a nanoparticle composite, a gas sensor including the same, and a method for manufacturing the same. Specifically, it relates to a nanoparticle composite including graphene quantum dots, dopamine and metal oxide nanoparticles, a gas sensor having improved gas sensing properties by employing the same, and a method for manufacturing the nanoparticle composite.

Oxide semiconductors for gas sensing are being researched and developed in bulk, thick film, chip and thin film forms because they exhibit excellent reactivity, stability, durability, and productivity to reactive gases. The gas sensing characteristic of the oxide semiconductor gas sensor for the reactive gas is due to the change in the electrical characteristics of the semiconductor oxide due to the reversible chemical reaction that occurs when the reactive gas is adsorbed/desorbed on the oxide surface.

However, in the case of the conventional oxide semiconductor gas sensor, the material is limited, and the response and recovery rate to the reaction gas are not fast. The use of was a disadvantage of increasing the manufacturing cost.

In addition, a composite structure in which functionalization was attempted by introducing a carbon nanomaterial (eg, carbon nanotube (CNT), graphene, or reduced graphene) into the oxide semiconductor has been studied, but this is also a complex synthesis There were problems such as high cost according to the process, purity of a desired carbon material, low on-off current ratio due to a small band gap, and poor selectivity at low gas concentration.

One aspect is to provide novel nanoparticle composites comprising graphene quantum dots, dopamine and metal oxide nanoparticles.

Another aspect is to provide a gas sensor having improved gas sensing characteristics by employing the above-described nanoparticle composite as a gas sensing material.

Another aspect is to provide a method for preparing the above-described nanoparticle composite.

In one aspect, the present invention, graphene quantum dots (quantum dot);

dopamine; and

Provided is a nanoparticle composite comprising metal oxide nanoparticles.

In one embodiment, the dopamine may be bound to the surface of the graphene quantum dots.

For example, the dopamine may be represented by Formula 1 below, and a "-NH ₂ " moiety in Formula 1 may be bonded to the surface of the graphene quantum dot:

<Formula 1>

.

.

In one embodiment, the graphene quantum dots may be attached to the surface of the metal oxide nanoparticles.

In one embodiment, a portion of the graphene quantum dots that is not a portion to which the dopamine is bound may be attached to the surface of the metal oxide nanoparticles.

In one embodiment, the graphene quantum dots may have an average particle diameter (D50) in the range of 1 to 5 nm.

In one embodiment, the graphene quantum dots may have a band gap of 2.2 to 3.1 eV.

In one embodiment, the metal oxide nanoparticles may be one or more oxides selected from Ag, Ni, Si, Ti, Cr, Mn, Fe, Co, Cu, Sn, In, Pt, Au, and Mg.

In one embodiment, the metal oxide nanoparticles may have an average particle diameter (D50) of 1 to 5 nm.

For example, the surface of the metal oxide nanoparticles may include a depletion region.

In another aspect, the present invention provides a gas sensor comprising the above-described nanoparticle composite.

In one embodiment, the gas sensor may _{detect nitrogen oxide (NO x} (0<x≤2)) gas.

In another aspect, the present invention is a method for preparing the above-described nanoparticle composite,

(A) a process of synthesizing dopamine-coated graphene quantum dots by acid-treating dopamine; and

(B) mixing the dopamine-coated graphene quantum dots and metal oxide nanoparticles to prepare a nanoparticle composite; provides a method for producing a nanoparticle composite, including.

In one embodiment, the dopamine-coated graphene quantum dots may be synthesized by a hydrothermal synthesis method.

In one embodiment, the metal oxide nanoparticles may be synthesized by a heat up synthesis method.

In one embodiment, the dopamine-coated graphene quantum dots and metal oxide nanoparticles may be mixed _{in a CHCl 3 solvent.}

In one embodiment, after mixing the dopamine-coated graphene quantum dots and metal oxide nanoparticles, the process of spin coating the mixture may be further performed.

For example, after the spin coating, a process of heat-treating the mixture may be further performed.

Nanoparticle composite of the present invention is graphene quantum dots; By including dopamine and metal oxide nanoparticles together, when applied to a gas sensor, it is possible to exert the effect of easily detecting a low concentration gas even at a low temperature.

1 is a schematic diagram of a nanoparticle composite according to an embodiment.
2 is a schematic diagram illustrating a process of manufacturing a nanoparticle composite according to an embodiment and a gas sensing principle of a gas sensor including the same.
3 is an NMR graph of the nanoparticle composite synthesized in Synthesis Example 1.
4 is an XRD spectrum of the nanoparticle composite synthesized in Synthesis Example 1.
5A and 5B are FT-IR spectra of the nanoparticle composite synthesized in Synthesis Example 1. FIG.
_{6A and 6B are graphs in which the NO x} gas sensing reaction capability according to the temperature of the gas sensor of Example 1 is measured.
_{7A and 7B are graphs in which the NO x} gas sensing reaction capability according to the temperature of the gas sensor of Comparative Example 2 is measured.
8 is a graph comparing and measuring the gas sensing response capability of the gas sensors of Example 1, Comparative Example 1, and Comparative Example 2;
9 is a graph in which the gas sensor of Example 1 is measured for repeating gas sensing response capability.
10 is a graph of measuring _{the NO x} gas sensing reaction capability according to the gas concentration of the gas sensor of Example 1. Referring to FIG.
11 is a graph in which the detection limit of the gas sensor of Example 1 is measured.

Since the present invention can apply various transformations and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention. In describing the present invention, if it is determined that a detailed description of a related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted.

Terms such as first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In addition, in each drawing, components are exaggerated, omitted, or schematically illustrated for convenience and clarity of description, and the size of each component does not fully reflect the actual size.

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

Nanoparticle Composites

In one aspect, the present invention, graphene quantum dots (quantum dot); dopamine; And it provides a nanoparticle composite comprising metal oxide nanoparticles.

The graphene quantum dots can be used in various fields due to electrical and electronic properties similar to those of graphene, and furthermore, the graphene quantum dots have a smaller 0-dimensional size, high electron mobility, a large band gap, and the reactivity of surface atoms is high. It has high characteristics. Due to these characteristics, the gas sensing ability may be very good.

1 is a schematic diagram of a nanoparticle composite according to an embodiment.

Referring to FIG. 1 , the nanoparticle composite 1 includes graphene quantum dots 10 ; dopamine (20); and metal oxide nanoparticles 30 .

For example, the dopamine 20 may be bound to the surface of the graphene quantum dots 10 . Specifically, the dopamine 20 may be conjugated to the surface of the graphene quantum dots 10 .

The dopamine 20 is a basic group as an N-containing functional group, and the presence of this N-containing functional group can increase the basicity of graphene quantum dots, which promotes _{more NO 2 gas adsorption and diffusion on the active surface.} During exposure to the NO _2, wherein the dopamine 20. nanoparticle composite 1 that includes the NO ₂ shortest NO ₂ molecules doping atoms due to the distance NO ₂ gas molecules in the gas molecules is very low adsorption energy and the low-temperature can show much more adsorption for

The dopamine 20 is represented by the following Chemical Formula 1, and the "-NH ₂ " moiety 21 in the following Chemical Formula 1 may be bonded to the surface of the graphene quantum dot 10:

<Formula 1>

.

.

For example, the graphene quantum dots 10 may be attached to the surface of the metal oxide nanoparticles 30 .

For example, a portion 10b of the graphene quantum dots 10 other than the portion 10a to which the dopamine is bound may be attached to the surface of the metal oxide nanoparticles 30 .

That is, the nanoparticle composite 1 according to an embodiment may have a structure in which dopamine 20, graphene quantum dots 10, and metal oxide nanoparticles 30 are combined in an order (or reverse order).

When having such a structure, when the nanoparticle complex 1 is applied as a gas sensing material to be described later, a gas (eg, nitric acid gas) oxidizes the dopamine 20, and the electrons in the dopamine 20 It moves to the metal oxide 30 through the graphene quantum dots 10 and can be easily detected by a gas sensor while improving resistance.

For example, the graphene quantum dots 10 may have an average particle diameter (D50) of 1 to 5 nm. That is, the graphene quantum dots 10 may be substantially 0-dimensional particles. By having such a small average particle diameter (D50), the graphene quantum dots 10 may have a sufficient band gap range in a size-dependent manner due to the quantum confinement effect.

For example, the graphene quantum dots 10 may have a band gap of 2.2 to 3.1 eV. By having such a large band gap, the gas sensor employing the graphene quantum dots 10 may exhibit an excellent gas sensing effect.

For example, the graphene quantum dots 10 may be doped with a doping material other than the dopamine 20 and the metal oxide nanoparticles 30 .

For example, the doping material may include one or more of sulfur (S), boron (B), and nitrogen (N).

For example, the metal oxide nanoparticles 30 may be one or more oxides selected from Ag, Ni, Si, Ti, Cr, Mn, Fe, Co, Cu, Sn, In, Pt, Au, and Mg.

For example, the metal oxide nanoparticles 30 may be _{tin oxide (SnO 2 ). The SnO 2 , which} is a typical n-type semiconductor, _{can generate oxygen ion species (O 2} ⁻ , O ⁻ , O ² − ) on the surface by extracting electrons from the conduction band when exposed to air. Since the SnO ₂ adsorbed oxygen species, a depletion region was formed on the surface, and the concentration of the carrier decreased during electron extraction.

When the size of the metal oxide nanoparticles 30 is small, they may exhibit higher surface reactivity and have a larger adsorption area for gas molecules.

For example, the metal oxide nanoparticles 30 may have an average particle diameter (D50) of 1 to 5 nm. By having an average particle diameter (D50) in this range, the metal oxide nanoparticles 30 may have a high surface area and exhibit a quantum confinement effect.

Methods for the preparation of nanoparticle composites

In another aspect, the present invention is a method for preparing the above-described nanoparticle composite, (A) the process of synthesizing dopamine-coated graphene quantum dots by acid-treating dopamine; and (B) mixing the dopamine-coated graphene quantum dots and metal oxide nanoparticles to prepare a nanoparticle composite;

The acid treatment may be performed by, for example, citric acid, but is not limited thereto.

In this case, the dopamine-coated graphene quantum dots may be synthesized by a hydrothermal synthesis method.

Here, the hydrothermal synthesis may refer to the synthesis of a material made in an aqueous solution state under high temperature and high pressure conditions. The hydrothermal synthesis may be performed at a temperature of about 140°C to 250°C. The hydrothermal synthesis may be performed for about 8 hours to 36 hours. In this case, high-purity alcohol or distilled water may be used.

In this case, the metal oxide nanoparticles may be synthesized by a heat up synthesis method.

The heating synthesis (or temperature increase synthesis) may refer to a synthesis in which a reaction mixture including both a precursor and a stabilizer is slowly heated from a low temperature to a desired reaction temperature.

For example, the heating synthesis may be heating at a temperature increase rate of 1° C./min to 10° C./min, but may not be limited thereto. For example, the temperature increase rate is about 1 °C/min to about 10 °C/min, about 1 °C/min to about 8 °C/min, about 1 °C/min to about 6 °C/min, about 1 °C/min to about 4°C/min, about 1°C/min to about 2°C/min, about 1°C/min to about 1.8°C/min, about 1°C/min to about 1.6°C/min, about 1°C/min to about 1.4 °C/min, about 1 °C/min to about 1.2 °C/min, about 1.2 °C/min to about 10 °C/min, about 1.4 °C/min to about 10 °C/min, about 1.6 °C/min to about 10 °C/min min, from about 1.8°C/min to about 10°C/min, from about 2°C/min to about 10°C/min, from about 4°C/min to about 10°C/min, from about 6°C/min to about 10°C/min, Alternatively, it may be from about 8°C/min to about 10°C/min, but may not be limited thereto.

For example, the heating synthesis may be to increase the temperature range of about 90 ℃ to about 190 ℃, but may not be limited thereto. For example, the temperature raising process temperature is about 90 °C to about 190 °C, about 90 °C to about 170 °C, about 90 °C to about 151.5 °C, about 90 °C to about 150 °C, about 90 °C to about 130 °C, about 90°C to about 110°C, about 110°C to about 190°C, about 130°C to about 190°C, about 150°C to about 190°C, about 151.5°C to about 190°C, or about 170°C to about 190°C, , which may not be limited thereto.

For example, the dopamine-coated graphene quantum dots and metal oxide nanoparticles may be mixed _{in a CHCl 3 solvent.} For example, in addition to _{the CHCl 3 , CDCl 3} and the like may be further used.

For example, after mixing the dopamine-coated graphene quantum dots and metal oxide nanoparticles, a process of spin coating the mixture may be further performed.

For example, the spin coating may be performed for a time of about 1 second to about 1000 seconds. For example, the spin coating may be from about 1 second to about 900 seconds, from about 10 seconds to about 900 seconds, from about 10 seconds to about 800 seconds, from about 10 seconds to about 700 seconds, from about 10 seconds to about 600 seconds, about 10 seconds. Seconds to about 500 seconds, about 10 seconds to about 400 seconds, about 10 seconds to about 300 seconds, about 1 second to about 200 seconds, or about 10 seconds to about 100 seconds may be performed for a time period, but is not limited thereto. .

For example, the spin coating may be performed at a speed of 1000 RPM to 5000 RPM, but is not limited thereto.

For example, after the spin coating, a process of heat-treating the mixture may be further performed.

For example, the heat treatment may be performed by rapid thermal annealing (RTA).

For example, the RTA may be performed by setting a soak time of 700° C. to 1150° C. and maintaining the soak temperature for 10 seconds to 60 seconds. Alternatively, the RTA may be performed in which the soak time is maintained at 900°C to 1200°C. In this case, the RTA may be performed by omitting the pre-stable process for stabilization at a low temperature lower than the soak temperature before ramping up to the soak temperature, thereby reducing the overall process time.

gas sensor

In another aspect, the present invention provides a gas sensor comprising the above-described nanoparticle composite.

For example, the gas sensor may use the above-described nanoparticle composite as a gas sensing material.

For example, the gas sensor may _{detect nitrogen oxide (NO x} (0<x≤2)) gas.

A detailed description of the gas sensor may be understood with reference to a bar widely known in the art.

2 is a schematic diagram illustrating a process of manufacturing a nanoparticle composite according to an embodiment and a gas sensing principle of a gas sensor including the same.

Referring to FIG. 2 , first, the graphene quantum dots 10 and dopamine 20 react, and through an oxidation reaction according to electron movement, the graphene quantum dots 10 coated with dopamine 20 may be formed.

Subsequently, metal oxide nanoparticles 30 (eg, SnO ₂ ) are added to the dopamine 20-coated graphene quantum dots 10 to form a nanoparticle composite 1 .

When the nanoparticle composite 1 is applied to a gas sensor as a gas sensing material, a gas (eg, nitric acid gas) oxidizes dopamine 20 , while electrons in dopamine 20 become graphene quantum dots 10 ) through the metal oxide 30, and while improving resistance, it can be easily detected by a gas sensor.

The present invention will be described in more detail through the following examples and comparative examples. However, the examples are provided to illustrate the present invention and do not limit the scope of the present invention only to these examples.

[Example]

(Preparation of nanoparticle composites)

Synthesis Example 1

0.125 g of a dopamine precursor and 0.5 g of a citric acid precursor were reacted for 6 hours at 180° C. using a hydrothermal synthesis reactor with a volume of 50 ml, to synthesize 500 μl of dopamine-coated graphene quantum dots (average particle diameter of about 1-5 nm). .

500 μl of the dopamine-coated graphene quantum dots _{were added to SnO 2} nanoparticles (average particle diameter of 1-5 nm) 0.5 wt% aqueous ethanol solution (10 mL), followed by sonication for 15 minutes, and stirred overnight.

The mixture was subjected to a spin coating reaction in a spin coating reactor at 3000 RPM for 40 seconds.

Then, the obtained product was subjected to RTA at a temperature of 300° C. for 90 seconds to prepare a nanoparticle composite.

The NMR graph of the obtained nanoparticle composite is shown in FIG. 3, the XRD spectrum is shown in FIG. 4, and the FT-IR spectrum is shown in FIGS. 5A and 5B.

Comparative Synthesis Example 1

_{A graphene quantum dot-SnO 2} composite was prepared in the same manner as in Synthesis Example 1, except that graphene quantum dots were used instead of the dopamine-coated graphene quantum dots.

Example 1

A gas sensor was prepared by using the nanoparticle composite obtained in Synthesis Example 1 as a gas sensing material.

Specifically, after depositing Ti/Au (20/200 nm) as an electrode, the gas sensing material was spin-coated at 3000 RPM for 40 seconds. The finished sample was annealed for 90 seconds by rapid thermal annealing at 300° C. under ambient atmosphere to improve the ohmic contact between the gas sensing material and the electrode.

Comparative Example 1

A gas sensor was prepared in the same manner as in Example 1, except that the _{graphene quantum dot-SnO 2} composite obtained in Comparative Synthesis Example 1 was used as a gas sensing material instead of the nanoparticle composite.

Comparative Example 2

A gas sensor was manufactured in the same manner as in Example 1, except that _{SnO 2} was used as a gas sensing material instead of the nanoparticle composite.

Evaluation Example 1: Measurement of gas sensitivity according to temperature change

The gas sensor of Example 1 and Comparative Example 2 was placed inside a gas detection chamber composed of a quartz tube, and nitric oxide (NO _x ) gas was injected in an amount of about 0.1 to 1 ppm, respectively, 25 ℃, 50 ℃, 100 The resistance change of the gas sensor at ℃, 150℃, 200℃, and 250℃ was measured in real time. At this time, the gas sensitivity to the gas was defined as R _g /R _a (R _g : sensor resistance in gas, R _a : sensor resistance in air).

_{By measuring the NO x} gas sensing reaction capability according to the temperature of the gas sensor of Example 1, and shown in FIGS. 6A and 6B, by measuring the NO _x gas detection reaction capability according to the temperature of the gas sensor of Comparative Example 2, FIG. 7a and 7b.

6A and 7A, and 6B and 7B, respectively, it can be seen that the gas sensitivity of the gas sensor of Example 1 is significantly higher than that of the gas sensor of Comparative Example 2, particularly in the case of the gas sensor of Example 1 , it can be seen that, rather, it exhibits very high gas sensitivity even at low temperatures.

Evaluation Example 2

The gas sensor of Example 1, Comparative Example 1 and Comparative Example 2 was placed inside a gas detection chamber composed of a quartz tube, and nitrogen oxide (NO _x ) gas was injected at a content of 0.1 ppm, and the gas sensor at 150° C. The change in gas sensitivity was measured and shown in FIG. 8 .

Referring to FIG. 8 , it can be seen that the gas sensor of Example 1 has significantly higher initial gas sensitivity than the gas sensors of Comparative Examples 1 and 2.

Evaluation Example 3

The gas sensor of Example 1 was placed inside a gas detection chamber composed of a quartz tube, nitric oxide (NO _x ) gas was injected at a content of 0.1 ppm, and the resistance change of the gas sensor at 150° C. was measured in FIG. 9 . indicated.

Referring to FIG. 9 , it can be seen that the change in resistance of the gas sensor is continuously maintained no matter how long the detection time is increased, so that the gas detection ability is maintained.

Evaluation Example 4

The gas sensor of Example 1 was placed inside a gas detection chamber composed of a quartz tube, and nitric oxide (NO _x ) gas was applied at a concentration of 100 ppb, 200 ppb, 300 ppb, 500 ppb, and 700 ppb, respectively, at 150° C. was injected from

The resistance change of the gas sensor in each concentration condition was measured and shown in FIG. 10 , and the gas sensitivity (R _g /R _a ) was measured and measured in FIG. 11 .

10 and 11 , it can be seen that even when the gas concentration is very low as 100 ppb, the resistance of the gas sensor is changed, so that gas detection is possible.

As described above, although the present invention has been described with reference to limited embodiments and drawings, the present invention is not limited thereto, and the technical spirit of the present invention and the following by those of ordinary skill in the art to which the present invention pertains. It goes without saying that various modifications and variations are possible within the scope of equivalents of the claims to be described.

Claims (19)

graphene quantum dots;
dopamine; and
Nanoparticle composite comprising metal oxide nanoparticles. According to claim 1,
The dopamine is bound to the surface of the graphene quantum dots, nanoparticle complex. 3. The method of claim 2,
The dopamine is represented by the following Chemical Formula 1, and the "-NH ₂ " moiety in the following Chemical Formula 1 is bonded to the surface of the graphene quantum dot, a nanoparticle complex:
<Formula 1>

. According to claim 1,
The graphene quantum dots are attached to the surface of the metal oxide nanoparticles, nanoparticle composite. According to claim 1,
The nanoparticle composite, wherein a site other than the site to which the dopamine is bonded among the graphene quantum dots is attached to the surface of the metal oxide nanoparticles. According to claim 1,
The graphene quantum dots have an average particle diameter (D50) in the range of 1 to 5 nm, a nanoparticle composite. According to claim 1,
The graphene quantum dots have a band gap of 2.2 to 3.1 eV, a nanoparticle composite. According to claim 1,
The graphene quantum dots are doped with a doping material other than the dopamine and metal oxide nanoparticles, nanoparticle composite. 9. The method of claim 8,
The doping material comprises at least one of sulfur (S), boron (B), and nitrogen (N). According to claim 1,
The metal oxide nanoparticles are Ag, Ni, Si, Ti, Cr, Mn, Fe, Co, Cu, Sn, In, Pt, Au, and at least one oxide selected from Mg, the nanoparticle composite. According to claim 1,
The metal oxide nanoparticles have an average particle diameter (D50) in the range of 1 to 5 nm, the nanoparticle composite. A gas sensor comprising the nanoparticle composite according to any one of claims 1 to 11. 13. The method of claim 12,
The gas sensor detects a nitric oxide (NO _x (0<x≤2)) gas. A method for preparing a nanoparticle composite according to any one of claims 1 to 11,
(A) a process of synthesizing dopamine-coated graphene quantum dots by reacting graphene quantum dots with dopamine under an acid; and
(B) mixing the dopamine-coated graphene quantum dots and metal oxide nanoparticles to prepare a nanoparticle composite; Containing, a method for producing a nanoparticle composite. 15. The method of claim 14,
The dopamine-coated graphene quantum dots are synthesized by a hydrothermal synthesis method, a method of manufacturing a nanoparticle composite. 15. The method of claim 14,
The metal oxide nanoparticles are synthesized by a heat up synthesis method, a method of manufacturing a nanoparticle composite. 15. The method of claim 14,
The dopamine-coated graphene quantum dots and metal oxide nanoparticles are _{mixed under a CHCl 3} solvent, a method for producing a nanoparticle composite. 15. The method of claim 14,
After mixing the dopamine-coated graphene quantum dots and metal oxide nanoparticles, further performing a process of spin-coating the mixture, a method for producing a nanoparticle composite. 19. The method of claim 18,
After the spin coating, further performing a process of heat-treating the mixture, the method for producing a nanoparticle composite.

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