阅读说明：本技术 三维石墨烯气体敏感传感器及其制备方法 (Three-dimensional graphene gas sensitive sensor and preparation method thereof ) 是由 刘欢 赵季杰 贾金梅 杜宇轩 文帅 白民宇 解飞 谢万鹏 刘卫国 于 2020-12-31 设计创作，主要内容包括：本发明公开了一种三维石墨烯气体敏感传感器及其制备方法,属于传感器及低维材料技术领域。该传感器由气体敏感层和上下电极构成,其中气体敏感层是被量子点修饰的三维石墨烯,当传感器周围出现目标检测气体时,气体敏感层吸附气体,电阻率发生改变,通过电阻变化情况判断目标检测气体的浓度变化情况。所述的被量子点修饰的三维石墨烯是通过本发明提出的一种新型合成方法制备而成,它具有比表面积大,电子传输速率快、探测灵敏度高以及机械强度好等优点,解决了传统气体传感器转换效率低、传输速率慢、耗能大、灵敏度低以及易被腐蚀的问题。可以广泛应用于冶金、化工、燃气、消防、煤炭深加工等领域。(The invention discloses a three-dimensional graphene gas sensitive sensor and a preparation method thereof, and belongs to the technical field of sensors and low-dimensional materials. The sensor is composed of a gas sensitive layer and an upper electrode and a lower electrode, wherein the gas sensitive layer is three-dimensional graphene modified by quantum dots, when target detection gas appears around the sensor, the gas sensitive layer adsorbs the gas, the resistivity changes, and the concentration change condition of the target detection gas is judged according to the resistance change condition. The three-dimensional graphene modified by the quantum dots is prepared by the novel synthesis method provided by the invention, has the advantages of large specific surface area, high electronic transmission rate, high detection sensitivity, good mechanical strength and the like, and solves the problems of low conversion efficiency, low transmission rate, high energy consumption, low sensitivity and easiness in corrosion of the traditional gas sensor. Can be widely applied to the fields of metallurgy, chemical industry, gas, fire fighting, coal deep processing and the like.)

1. A three-dimensional graphene gas sensitive sensor is characterized in that: the sensor comprises a three-dimensional graphene block body modified by quantum dots synthesized by a one-step method, an upper electrode (1) arranged on the upper surface of a gas sensitive layer (2), and a lower electrode (3) arranged on the lower surface of the gas sensitive layer (2), wherein when target detection gas appears around the sensor, the gas sensitive layer (2) adsorbs the gas, the resistivity changes, and the concentration change condition of the target detection gas is judged according to the resistance change condition.

2. The method for preparing the three-dimensional graphene gas-sensitive sensor according to claim 1, wherein the method comprises the following steps: the method comprises the following steps:

the method comprises the following steps: preparing a gas sensitive layer:

preparing a precursor: preparing a graphene oxide dispersion liquid by adopting an improved Hummers method, and adjusting the viscosity of the graphene oxide dispersion liquid to enable bubbles in the graphene oxide dispersion liquid to reach a non-volatile degree, wherein the graphene oxide dispersion liquid is used as a precursor;

preparing a gas core: preparing quantum dots with a core-shell structure, wherein ligand molecules are attached to the surfaces of the quantum dots to serve as shell parts for generating gas, so that the gas core can generate gas under certain conditions;

foaming: uniformly dispersing the gas core in the graphene oxide dispersion liquid to form a mixed liquid, and enabling a shell part of the gas core to react with a corresponding reagent by adopting a chemical reaction method to generate gas so as to form a dense bubble distribution in the mixed liquid;

consolidation: under certain pressure and temperature, freeze-drying the mixed liquid filled with bubbles to solidify the mixed liquid;

finally, reducing the consolidated graphene oxide into graphene by using a high-temperature heating method, volatilizing gas in bubbles, and leaving holes to obtain a porous three-dimensional graphene structure;

step two: preparing an electrode: a conductive film is prepared on the upper surface of the gas sensitive layer to serve as an upper electrode (1), and a conductive film is prepared on the lower surface of the gas sensitive layer to serve as a lower electrode (3).

3. The method for preparing the three-dimensional graphene gas-sensitive sensor according to claim 2, wherein the method for adjusting the viscosity of the graphene oxide dispersion liquid comprises the following steps: and drying the graphene oxide dispersion liquid to enable the dispersion liquid to be partially volatilized, so that the concentration of the graphene oxide is improved, the volume of the fluid is reduced, the intermolecular distance is shortened, the interaction is enhanced, and the viscosity is increased.

4. The preparation method of the three-dimensional graphene gas sensitive sensor according to claim 2, wherein the viscosity is that as the corrosion effect on the gas core shell part is increased, the gas is increased, the size of the bubble is 1-100 um, and the bubble cannot float out of a viscous solution, and the bubble is continuously increased under the action of external force.

5. The method for preparing the three-dimensional graphene gas-sensitive sensor according to claim 2, wherein the quantum dot with the core-shell structure comprises a core part and a shell part, and the shell part is reacted with a corresponding chemical reagent by a chemical reaction method to generate bubbles and the product is easily removed, and the core part does not react.

6. The method for preparing the three-dimensional graphene gas-sensitive sensor according to claim 2, wherein the chemical reaction is a reaction of a shell part and a chemical reagent, and the shell part is: any one of long carbon chain substances such as oleic acid, oleylamine and phosphonic acid, and the chemical reagent is as follows: any one of carbonates such as sodium carbonate and calcium carbonate.

7. The method for preparing the three-dimensional graphene gas sensitive sensor according to claim 2, wherein the certain pressure during consolidation is in a pressure range of 1Pa to 15 Pa.

8. The method for preparing the three-dimensional graphene gas-sensitive sensor according to claim 2, wherein the certain temperature during consolidation is a low-temperature environment ranging from-10 ℃ to-100 ℃.

9. The method for preparing the three-dimensional graphene gas sensitive sensor according to claim 2, wherein the conductive film is a metal film plated by magnetron sputtering and thermal evaporation, or a breathable conductive mesh film prepared from metal nanowires.

Technical Field

The invention belongs to the technical field of sensors and low-dimensional materials, and particularly relates to a three-dimensional graphene gas sensitive sensor and a preparation method thereof.

Background

With the development of production, the living standard of human beings is continuously improved, liquefied petroleum gas, city gas and natural gas are rapidly popularized as household fuel, explosion and toxic accidents caused by the leakage of the combustible gas are increased day by day, various combustible gases are needed for ensuring safety and preventing accidents, and the toxic gases are quantitatively analyzed and detected, so that the sensor with gas sensitivity is applied.

Since the advent of semiconductor metal oxide ceramic gas sensors in 1962, semiconductor gas sensors have become the most common and practical gas sensor for use today. It is widely used because of its advantages of low cost, simple manufacture, etc. However, the traditional semiconductor gas sensitive sensor has the defects of poor selectivity to gas or smell, dispersed element parameters, unsatisfactory stability, high power, low sensitivity, incapability of accurately positioning harmful gas, non-corrosion resistance and the like because of the necessity of working at high temperature. Greatly limiting its application. Therefore, a high-performance gas sensitive sensor is urgently needed.

Disclosure of Invention

In order to overcome the problems in the prior art, the invention aims to provide a three-dimensional graphene gas sensitive sensor and a preparation method thereof.

In order to achieve the purpose, the invention adopts the following technical scheme:

a three-dimensional graphene gas sensitive sensor comprises a three-dimensional graphene block body modified by quantum dots synthesized by a one-step method and serving as a gas sensitive layer 2, an upper electrode 1 arranged on the upper surface of the gas sensitive layer 2 and a lower electrode 3 arranged on the lower surface of the gas sensitive layer 2, wherein when target detection gas appears around the sensor, the gas sensitive layer 2 adsorbs the gas, the resistivity changes, and the concentration change condition of the target detection gas is judged according to the resistance change condition.

The preparation method of the three-dimensional graphene gas sensitive sensor comprises the following steps:

the method comprises the following steps: preparing a gas sensitive layer:

preparing a precursor: preparing a graphene oxide dispersion liquid by adopting an improved Hummers method (reference document: Marcano D C, Kosynkin D V, Berlin J M, et al, improved synthesis of graphene oxide [ J ]. Acs Nano,2010,4(8):4806.), adjusting the viscosity of the graphene oxide dispersion liquid to enable air bubbles in the graphene oxide dispersion liquid to reach a non-volatile degree, and taking the graphene oxide dispersion liquid as a precursor;

preparing a gas core: preparing quantum dots with a core-shell structure, wherein appropriate ligand molecules are attached to the surfaces of the quantum dots to serve as shell parts for generating gas, so that the gas core can generate gas under certain conditions;

foaming: uniformly dispersing the gas core in the graphene oxide dispersion liquid to form a mixed liquid, and enabling a shell part of the gas core to react with a corresponding reagent by adopting a chemical reaction method to generate gas so as to form a dense bubble distribution in the mixed liquid;

consolidation: under certain pressure and temperature, freeze-drying the mixed liquid filled with bubbles to solidify the mixed liquid;

finally, reducing the consolidated graphene oxide into graphene by using a high-temperature heating method, volatilizing gas in bubbles, and leaving holes to obtain a porous three-dimensional graphene structure;

step two: preparing an electrode: a conductive film is prepared on the upper surface of the gas sensitive layer to serve as an upper electrode 1, and a conductive film is prepared on the lower surface of the gas sensitive layer to serve as a lower electrode 3.

The method for adjusting the viscosity of the graphene oxide dispersion liquid comprises the steps of drying the graphene oxide dispersion liquid, volatilizing part of the dispersion liquid, improving the concentration of graphene oxide, reducing the volume of a fluid, shortening the distance between molecules, strengthening the interaction and increasing the viscosity.

The viscosity be along with the increase to gas core shell portion corrosion, gaseous increasing, the bubble can constantly increase under the exogenic action, its size is 1um-100um, but the bubble can not float out viscous solution.

The quantum dot with the core-shell structure comprises a core part and a shell part, wherein the shell part is reacted with a corresponding chemical reagent by a chemical reaction method to generate bubbles, the product is easy to remove, and the core part does not react.

The chemical reaction is the reaction of the shell and a chemical reagent, and the shell part can be: any one of long carbon chain substances such as oleic acid, oleylamine and phosphonic acid, and the chemical reagent can be: any one of carbonates such as sodium carbonate and calcium carbonate.

The certain pressure during consolidation is in the pressure range of 1Pa to 15 Pa.

The certain temperature during consolidation is a low-temperature environment from minus 10 ℃ to minus 100 ℃.

The conductive film can be a metal film plated by magnetron sputtering and thermal evaporation, and can also be a breathable conductive mesh film prepared by metal nanowires.

The three-dimensional graphene gas sensitive sensor is simple and easy to prepare, adopts a one-step method to prepare the three-dimensional graphene modified by the quantum dots sensitive to the gas, and adopts a novel synthesis method, namely, the shell part or the ligand part of the quantum dots and the bubbles generated by the reaction of the chemical reagent assist to form a pore structure in the three-dimensional graphene, so that the specific surface area of the three-dimensional graphene is effectively increased. The three-dimensional graphene has the advantages of higher electronic transmission speed, higher mechanical strength, visibility by naked eyes and convenience in operation; meanwhile, after the nano-scale quantum dots are used for modifying, the sensitive gas can be accurately positioned.

According to the three-dimensional graphene gas sensitive sensor prepared by the technical scheme, due to the introduction of the three-dimensional graphene, the electronic conversion efficiency of the gas sensor is increased, the transmission rate is increased, and the quantum dots sensitive to the gas are distributed in each hole of the three-dimensional graphene, so that the sensitivity to the gas is increased, and the gas is accurately positioned.

Drawings

Fig. 1 is a schematic structural diagram of a three-dimensional graphene gas-sensitive sensor.

Fig. 2 is a side view of a three-dimensional graphene gas-sensitive sensor.

Fig. 3 is a schematic structural diagram of a quantum dot-modified three-dimensional graphene.

FIG. 4 is a schematic diagram of the structure of the gas core.

FIG. 5 is a schematic view of the generation of bubbles by the gas core reaction.

Detailed Description

In order to make the technical scheme and advantages of the invention more clear, the invention is described in detail below with reference to the accompanying drawings and specific embodiments:

examples

As shown in fig. 1, the three-dimensional graphene gas-sensitive sensor of this embodiment is composed of a three-dimensional graphene block modified by quantum dots synthesized by a one-step method as a gas-sensitive layer 2, an upper electrode 1 prepared on an upper surface of the three-dimensional graphene block, and a lower electrode 3 prepared on a lower surface of the three-dimensional graphene block. A side view thereof is shown in figure 2.

Firstly, preparing a gas sensitive layer:

the quantum dot modified three-dimensional graphene gas sensitive material shown in fig. 3 inherits the excellent performance of two-dimensional graphene, has the advantages of larger specific surface area, higher electron transmission speed, higher mechanical strength, visibility by naked eyes, convenience in operation, higher sensitivity to gas under the modification of quantum dots, higher gas detection accuracy and more suitability for specific application.

Preparation of precursor

Weighing machine5g of natural graphite flakes and 2.5g of NaNO₃130mL of 98 wt% H was added₂SO₄The three are put together, mixed evenly and stirred continuously for 2h under the ice bath condition. Then KMnO is weighed₄15g of the reaction solution is put into a reaction beaker and the reaction is continued for 2 hours. The reaction beaker was then transferred to a 37 ℃ water bath for 1 h. Then, the temperature was raised to 98 ℃, 230mL of deionized water was measured and added to the reaction beaker, and the reaction was continued for 30 min. 400mL of deionized water and 10mLH were then added₂O₂And placing the mixture on a magnetic stirrer to stir for 1h, washing the mixture by using HCL to remove sulfate radicals after the reaction is finished, and repeatedly washing the mixture by using deionized water until the pH value is 7 to obtain the graphene oxide dispersion liquid. The method has the advantages that the graphene oxide is uniformly dispersed in the solution by using the principle that the surface of the graphene oxide can be close to the surface of the dispersion liquid, the method can keep the excellent electric conduction and heat conduction characteristics of the graphene oxide, the viscosity of the graphene oxide dispersion liquid is adjusted, the more the graphene oxide is, the less the dispersion liquid is, the higher the viscosity of the prepared graphene oxide dispersion liquid is, and finally the graphene oxide dispersion liquid is made to reach the degree that bubbles in the dispersion liquid are not volatile and is used as a precursor.

(II) preparation of gas core (taking PbSe quantum dot sensitive to NO as an example)

As shown in fig. 4, the preparation method of the quantum dot with the core-shell structure is as follows:

1. 1.784g of Pbo powder is taken, 5.4ml of oleic acid is taken by an injector, 32.56ml of octadecene is taken by a measuring cylinder, poured into a three-neck flask, and magnetons are placed in the flask.

2. Obtaining Se-TOP solution. The powder 1.28gSe was dissolved in 12.8ml of TOP solution, washed with ultrasound and stirred to dissolve.

3. The temperature of the electric heating jacket is set to be 30 ℃, the electric heating jacket is stirred, the vacuum knob is slowly turned on, the vacuum is pumped for 25min, and nitrogen is introduced for about 15min after the vacuum is finished. Then, after the temperature is raised to 180 ℃, the temperature is kept for 1 hour, thereby ensuring that liquid with uniform temperature is obtained.

4. The Se-TOP solution is injected quickly, the reaction is carried out for different time (the time range is between 0min and 5 min), and ice water bath is carried out immediately after the reaction is finished.

5. When the temperature is reduced to 60 ℃, 4ml of methanol-ammonium chloride solution (0.19mol/L) is immediately added and kept at 60 ℃ for 10 min.

6. Preparing cleaning liquid, namely mixing the acetone and the isopropanol in a ratio of 2:1, putting the mixture into a centrifuge for cleaning twice and centrifuging three times, wherein the rotating speed is required to be as follows: 7000rpm, time: 10 min; the gas core material with the core-shell structure quantum dots can be obtained.

(III) foaming

The gas nucleus solution and the graphene are subjected to ultrasonic oscillation to be fully and uniformly mixed, the gas nucleus is surrounded by the oleic acid ligand, the sensitivity characteristic to gas and the electron transmission characteristic are influenced, sodium carbonate is added into the mixed solution, the sodium carbonate and the oleic acid react to generate sodium oleate, water and carbon dioxide gas, and bubbles are increased and grow under the action of corrosion and external force. As the bubbles appear and grow further, the isocladder part or the ligand part is completely corroded, the generated gas surrounds the quantum dot clusters, and a corrosion process schematic diagram of the quantum dots with the core-shell structure is shown in fig. 5. Due to the fact that the content of the gas core in the graphene solution is large, the quantum dots surrounded by the bubbles are filled in the whole mixed solution, and a dense bubble distribution is formed in the graphene solution.

(IV) consolidation

The mixture, filled with air bubbles, was cooled to about 2 ℃ and then placed in a lyophilization chamber at about-40 ℃ (13.33 Pa). Closing the drying box, rapidly introducing refrigerant (Freon, ammonia), freezing, and sublimating after the mixed solution is completely frozen. Sublimation of the frozen mixed liquor mass is carried out under a high vacuum and during the pressure reduction the frozen state of the contents of the tank must be maintained to prevent spillage from the container. After the pressure in the box is reduced to a certain degree, the vacuum diffusion pump is opened, when the pressure is reduced to 1.33Pa and the temperature is below-60 ℃, the ice begins to sublimate, and the sublimated water vapor is frozen into ice crystals in the condenser. In order to ensure the sublimation of the ice, the heating system is started to heat the shelf and continuously supply heat required by the sublimation of the ice. During the sublimation stage, the ice sublimes to a greater extent, and the temperature should not exceed the minimum eutectic point, in order to prevent the formation of lumps in the product or defects in the product appearance, during which stage the shelf temperature is usually controlled to be within + -10 ℃. The water removed in the re-drying stage of the product is bound water, and the water vapor pressure on the solid surface is reduced to a different extent, and the drying speed is significantly reduced. On the premise of ensuring the product quality, the temperature of the shelf should be properly increased in this stage, which is beneficial to the evaporation of water, and the shelf is generally heated to 30-35 ℃ until the temperature of the product is coincident with the temperature of the shelf to dry. And obtaining the gas sensitive layer of the three-dimensional conductive net structure modified by the quantum dots.

Second, preparation of upper and lower electrodes

And sputtering a metal film on the upper surface of the gas sensitive layer to be used as an upper electrode (1), and sputtering a metal film on the lower surface of the gas sensitive layer to be used as a lower electrode (3).

The metal Au is selected as a sputtering target, the diameter of the sputtering target is 60mm, the thickness of the sputtering target is 3mm, and the purity of the sputtering target is 99.99 percent. The deposition of Au thin film is in Ar and O₂The method is carried out in a mixed atmosphere, and an upper electrode (1) and a lower electrode (3) are obtained after 0.5um is deposited at a certain temperature.

And obtaining the three-dimensional graphene gas sensitive sensor after the sensitive material layer and the upper and lower electrodes are prepared.