CN112014439A - Graphene quantum dot functionalization-based composite nano film material and gas-sensitive sensing element - Google Patents
Graphene quantum dot functionalization-based composite nano film material and gas-sensitive sensing element Download PDFInfo
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Abstract
The invention discloses a graphene quantum dot functionalization-based composite nano film material, which is in a film shape, the main body of the composite nano film material is a ZnO nanosheet, and the surface of the composite nano film material is covered with graphene quantum dots and tin dioxide quantum grains; the ZnO nanosheet as the main body is hexagonal, the average side length is 1.5-2.4 mu m, and the average thickness is 50-100 nm; the average size of the graphene quantum dots is 3.2-4.3 nm, and the average size of the tin dioxide quantum grains is 3.5-5.2 nm. The invention comprehensively uses the hydrothermal method and the post-thermal steaming method to prepare the multi-level structure sensing material, and has simple synthesis method and low cost.
Description
Technical Field
The invention relates to the technical field of semiconductor oxide gas sensors, in particular to a gas-sensitive sensing element adopting a composite nano-film material based on graphene quantum dot functionalization.
Background
The noninvasive diagnosis technology based on the metal oxide semiconductor gas sensor has the advantages of fast dynamic process, low cost, good portability and the like. Real-time detection of biomarkers in exhaled breath has become a hotspot of current research. These sensors can diagnose diseases by detecting disease biomarkers that contain specific Volatile Organic Compounds (VOCs) in human exhaled breath, which have strong correlation with specific diseases. Previous studies have found that certain biomarkers in breath, such as hydrogen sulfide gas, are associated with halitosis. Compared with healthy people, the content of hydrogen sulfide gas exhaled by halitosis patients exceeds 0.1 ppm. Gas sensor pair H with metal oxide semiconductor material as core in recent years2S gas has good sensitivity and mature preparation process, but the S gas has the common defects of slow response speed at room temperature, low sensitivity and poor selectivity. The Chinese patent application with the application number of CN201910083504.7 discloses H of a Pt-supported NiO sensitive film nano material2S gas sensor, which is sensitive to 1ppmH at 80 DEG C2The gas sensitive response value of S is only 2.6. Due to H2S gas can cause great damage to human body in a short time, so that the gas-sensitive material can be used for treating extremely low-concentration H2S has a higher response value, and can show more value in practical application. Chinese patent with application number CN201810196908.2 discloses H based on La doped indium oxide nano sensitive material with hollow sphere structure2S sensor, which is sensitive to 1ppmH at 200 DEG C2The gas sensitive response value of S is only 2.5. Furthermore, the existing metal oxide semiconductor sensors are far from sensitive enough to respond to low concentrations, especially to ppb level changes, and thus their practical application in specific disease diagnosis is still challenging.
Various methods have been used to prepare metal oxide nanomaterials, such as sputtering, chemical vapour deposition, sol-gel methods, hydrothermal synthesis. Among them, hydrothermal synthesis is a liquid phase method for preparing various polycrystalline thin films and nanostructures, and has succeeded in preparing materials such as semiconductor and superconductor thin films. However, the hydrothermal synthesis method is not suitable for obtaining high-performance sensing materials because of its own characteristics, and the size of nano particles in the nano structure prepared by the hydrothermal synthesis method is usually more than 10 nm.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a novel composite nano film material which can be used for a gas sensor and has the performances of high sensitivity, good selectivity and the like.
In order to achieve the aim, the invention provides a graphene quantum dot functionalization-based composite nano film material which is in a film shape, the main body of the composite nano film material is a ZnO nanosheet, and the surface of the composite nano film material is covered with graphene quantum dots and tin dioxide quantum grains; the ZnO nanosheet as the main body is hexagonal, the average side length is 1.5-2.4 mu m, and the average thickness is 50-100 nm; the average size of the graphene quantum dots is 3.2-4.3 nm, and the average size of the tin dioxide quantum grains is 3.5-5.2 nm.
Further, by XPS surface elemental analysis: the composite nano film material contains 60-70% of ZnO element, 5-10% of graphene quantum dot element and 20-35% of tin dioxide quantum grain element.
In some embodiments, it is preferable that the ZnO element content in the composite nano thin film material is 64%, the graphene quantum dot element content is 8%, and the tin dioxide quantum grain element content is 28%.
The invention also provides the composite nano film material in H2And S gas detection.
The invention also provides a gas-sensitive sensing element prepared by adopting the composite nano film material, and the composite nano film material is arranged on the surface of the gas-sensitive sensing element.
The interdigital electrodes of the gas-sensitive sensing element are gold interdigital electrodes or platinum interdigital electrodes, the length and width of a square contact pad in the electrodes are 1-2mm, the distance between the two contact pads is 2.5-3.5mm, the two contact pads are symmetrical to each other, the distance between the interdigital in the interdigital array is 0.5-1.5um, and the length of the interdigital array part is 1-2 mm. The preparation process of the gas-sensitive sensor element is described in the literature (Nanoscale,2011,3, 4283).
The gas-sensitive sensing element is prepared by the following method:
(1) cleaning the gas sensitive sensing element;
(2) depositing a metal zinc film on the surface of the cleaned gas-sensitive sensing element;
(3) preparing the deposited metal zinc film into a one-dimensional zinc oxide film by adopting a hydrothermal synthesis method;
(4) preparation of graphene quantum dots/SnO by adopting post-thermal evaporation method2a/ZnO multilevel structure sensing material;
(5) and (4) roasting.
The specific method for cleaning the gas sensitive sensor in the step (1) is as follows: firstly, vacuumizing to remove gas in a plasma cleaning machine, wherein the pressure control range of a vacuum cavity is 1-10 Pa, and maintaining for 5-10 minutes; then, argon and oxygen are introduced through a double-way pipeline, and the flow ratio of the argon to the oxygen is 1: 1-3: 1; the frequency of the plasma generator is 40KHz, and the power is regulated and controlled between 120W and 180W.
The specific steps of depositing the metal zinc film in the step (2) are as follows: placing the cleaned gas-sensitive sensor in a vacuum chamber of a magnetron sputtering device, and performing sputtering deposition by using metal zinc with the mass purity of 99.99% as a target material and argon with the mass purity of 99.99% as a working gas; in the process of depositing the metal zinc film, the distance between the target and the base station is 50-150 mm, and the chamber is firstly vacuumized to 1 multiplied by 10-4～5×10-4And Pa, introducing argon, removing pollutants on the surface, adjusting the flow of the argon to be 8-28 SCCM to enable the pressure of the chamber to be 0.5-2.5 Pa, and setting the deposition power to be 90-120W.
Adjusting the pH value of a reaction system by the hydrothermal synthesis method in the step (3) through concentrated ammonia water, using carboxymethyl cellulose as a structure directing agent, controlling the reaction temperature to be 120-160 ℃, and controlling the reaction time to be 6-72 h; the using amount of the concentrated ammonia water is 2-8 ml, the using amount of deionized water in a reaction system is 20-25 mlml, and carboxymethyl cellulose is a carboxymethyl cellulose aqueous solution, the concentration is 1.4-4.2 g/L, and the using amount is 2-4 ml.
The post-heating steaming method adopted in the step (4) comprises the following specific steps: spin-coating a tin tetrachloride mixed solution (the concentrations of tin tetrachloride and graphene quantum dots in the solution are 0.1-0.4 g/ml and 0.02-0.05 g/ml respectively, preferably, the concentrations of tin tetrachloride and graphene quantum dots in the solution are 0.2g/ml and 0.04g/ml respectively) with uniformly dispersed graphene quantum dots on the surface of the one-dimensional zinc oxide film of the gas-sensitive sensor obtained in the step (3), repeatedly drying and spin-coating for 3-5 times, placing the gas-sensitive sensor into a closed container, regulating and controlling the humidity in the closed container to be 75-95%, the reaction temperature to be 120-150 ℃, and the reaction time to be 24-72 hours to obtain the graphene quantum dots/SnO2the/ZnO multilevel structure sensing material. After the mixed solution is spin-coated, the one-dimensional nano zinc oxide is partially dissolved, and the size is reduced. The residual one-dimensional nano zinc oxide is aggregated by a post-thermal evaporation method and further fused to form a nano sheet. The step realizes the self-assembly of the one-dimensional nano rods into nano sheets, and the nano sheets are further assembled to form the multi-level structure sensing material. The nanosheets form a porous structure during assembly. In the forming process of the nano-sheet, tin dioxide quantum grains are generated by simultaneous reaction, graphene quantum dots and the tin dioxide quantum grains are uniformly covered on the surface of the nano-sheet, and a large amount of n-p-n (SnO) exists in the nano-sheet2-GQD-ZnO) quantum tunnel junction.
The roasting method in the step (5) is as follows: loading the graphene quantum dots/SnO2And carrying out heat treatment on the gas-sensitive sensing element of the/ZnO multi-level structure sensing material in a programmed muffle furnace at 400-500 ℃ in a nitrogen atmosphere for 2-4 h, and controlling the heating rate to be less than 2 ℃/min.
Compared with the prior art, the invention has the following advantages:
1. the hydrothermal method and the post-thermal steaming method are comprehensively used for preparing the multi-level structure sensing material, the synthesis method is simple, and the cost is low.
2. SnO is compounded by using graphene quantum dots2the/ZnO nano sheet reduces the surface of a sensing materialSurface resistance, improved pair H2The sensitivity of S and the detection lower limit of the material are low, and the material has quick response recovery speed and good repeatability, and has good application prospect in the aspect of breath detection.
3. And the planar sensor is adopted, so that the device has simple process and small volume and is suitable for batch production.
4. Utilizing graphene quantum dots/SnO2the/ZnO heterojunction structure is used as a sensitive material, and on one hand, a ZnO nano sheet is used as a substrate, so that the transmission and detection of gas are facilitated; graphene quantum dots/SnO on the other hand2A large number of heterojunctions are formed between the ZnO and the/ZnO due to the difference of Fermi energy levels, and more active sites are provided for sensing reaction. The combined action of the two aspects greatly improves the reaction efficiency of the gas and the sensitive material, and further improves the sensitivity of the sensor.
5. Response and H of the gas sensor of the invention under the condition of room temperature2There is a good correlation between S concentration, with faster response/recovery time (13S/14S), and H2The selectivity of S gas is better than that of other contrast gases by more than 10 times.
6. The method firstly prepares a one-dimensional ZnO nanorod array as a precursor, and obtains SnO with uniform particle size and good dispersibility by a post-thermal evaporation method2H prepared by forming high-quality heterojunction by nano particles and graphene quantum dots2The S gas sensor has a significantly reduced operating temperature and a significantly improved sensitivity.
Drawings
FIG. 1 is an X-ray diffraction pattern of a one-dimensional zinc oxide nanorod array prepared in step 6 of example 1 of the present invention;
FIG. 2 is an X-ray diffraction pattern of the composite nano-film material prepared in step 7 of example 1 of the present invention;
FIG. 3 is an SEM image of one-dimensional zinc oxide nanorods prepared in step 6 of example 1 of the present invention;
FIG. 4 is an SEM image of a composite nano-film material prepared in step 7 of example 1 of the present invention;
FIG. 5 is a graph showing the comparison between the sensing performance of the one-dimensional zinc oxide nanorods prepared in example 1 of the present invention and the sensing performance of the composite nano-film material;
FIG. 6 is a diagram of the sensing selectivity of the composite nano-film material prepared in example 1 of the present invention;
FIG. 7 is an SEM image of a composite nano-film material prepared in example 2 of the invention;
FIG. 8 is a graph of the sensing performance of the composite nano-film material prepared in example 2 of the present invention;
fig. 9 is a diagram of the sensing selectivity of the composite nano-film material prepared in example 2 of the present invention.
Detailed Description
The present invention will be described in detail with reference to specific examples.
Example 1
H based on graphene quantum dot functionalized tin oxide/zinc oxide2The S sensor and the preparation method thereof comprise the following steps:
1. firstly, a gas-sensitive sensor (a preparation process reference document (New Journal of Chemistry,38 (2014)) and 2362-.
2. Placing the cleaned gas-sensitive sensing element in a vacuum chamber of a magnetron sputtering device, adopting metal zinc with the mass purity of 99.99 percent as a target material, adopting argon with the mass purity of 99.99 percent as a working gas, and sputtering and depositing a metal zinc film on the cleaned gas-sensitive sensing element;
3. in the process of depositing the metal zinc film, the distance between the target and the base station is 50mm, and the chamber is firstly vacuumized to 1 multiplied by 10-4Pa. Then Ar is introduced to remove the pollutants on the surface.
4. Regulating the flow of Ar to ensure that the pressure of the chamber is 1.5Pa, introducing gas, heating the gas-sensitive sensing element until the temperature reaches 300 ℃, the deposition power is 100W, pre-sputtering for about 15mins, and timing and sputtering for 30 mins.
5. And after the sputtering is finished, cooling the system to room temperature, filling nitrogen into the vacuum chamber, and opening the vacuum chamber to take out the loaded zinc gas-sensitive sensing device when normal air pressure is reached.
6. Preparing a one-dimensional zinc oxide gas-sensitive sensing film:
adopting a hydrothermal synthesis method, wherein 4ml of concentrated ammonia water, 24 ml of deionized water and 4ml of 2.8 g/L carboxymethyl cellulose are adopted, the reaction temperature is 120 ℃, and the reaction time is 36 hours; the one-dimensional zinc oxide gas-sensitive sensing film is prepared, as shown in fig. 1 and fig. 3, the obtained one-dimensional zinc oxide is in a shape of a nanorod, and the diameter range of the obtained one-dimensional zinc oxide is between 100 and 200 nanometers.
7. Graphene quantum dot/SnO2Preparing a/ZnO composite nanosheet sensing film:
dissolving 1g of stannic chloride in 5ml of ethanol, adding 0.2g of graphene quantum dots into the precursor solution, dripping 0.2 ml of concentrated hydrochloric acid into the mixed solution of the precursor and the graphene quantum dots, performing ultrasonic dispersion for 5 minutes, and performing magnetic stirring for 12 hours. And (3) spin-coating the mixed sol solution on a one-dimensional zinc oxide gas-sensitive thin film sensor at a relative humidity of 50% at a rotation speed of 4000 rpm for 30 seconds, drying at 60 ℃ for 1 hour, and repeating spin-coating for 4 times. The sensing device was placed in a closed container and the relative humidity in the closed container was adjusted to 95%. And (3) treating for 48 hours at the reaction temperature of 150 ℃, and then carrying out heat treatment on the synthesized nanosheet sensing film device for 2 hours at the temperature of 400 ℃ in a nitrogen atmosphere.
As shown in fig. 2 and 4, the prepared composite film on the surface of the sensor device takes ZnO as a main body and is in a nano-sheet shape, the ZnO nano-sheet is in a hexagonal shape, the average side length is 1.5 μm, and the average thickness is 50 nm; the average size of the graphene quantum dots is 3.2nm, and the average size of the tin dioxide quantum grains is 3.5 nm.
Surface elemental analysis by XPS:
in the composite nano film material, the content of ZnO is 64%, the content of graphene quantum dot elements is 8%, and the content of tin dioxide quantum grain elements is 28%.
8. And (2) performing gas-sensitive performance test on the prepared gas-sensitive sensing element (the gas-sensitive characteristic is generally characterized by sensitivity, wherein the sensitivity is defined as the ratio of the resistance value Ra of the element in the atmospheric atmosphere to the resistance value Rg of the element in a measured gas atmosphere with a certain concentration to the resistance value Rg:
)：
(1) gas sensor for different concentrations H2Testing of S gas:
graphene quantum dot/SnO prepared by using embodiment2H of/ZnO nano composite material2And S, carrying out performance test on the gas sensor. And testing the gas sensor by using a dynamic testing system. Waiting for the initial baseline to be substantially stable, and introducing H at a concentration of 25ppb to 5ppm2And S, introducing air into the test cavity after the resistance of the gas sensor is reduced and reaches balance until the baseline is stable again, and finishing the gas-sensitive test. Graphene quantum dot/SnO2The ZnO gas sensor can be used for measuring H with the concentration of 25ppb-5ppm at room temperature2The sensitivity of S is shown in fig. 5.
The volume of the gas detection cavity is controlled to be 200cm by adopting a dynamic gas-sensitive test method3Regulation and control of H2The concentration of S atmosphere is between 25ppb and 5ppm, the detection temperature is controlled between room temperature, and Keithley 6570A is adopted to collect gas-sensitive sensing data. As shown in FIG. 5, is a gas sensor pair H2Room temperature sensing sensitivity of gas to be measured with S concentration between 25ppb and 5ppm, with H2The sensing sensitivity of the gas sensitive element is improved along with the improvement of the concentration of S. For 50ppb (response Peak 1, ordered from left to right, the same applies below), 100ppb (response Peak 2), 250ppb (response Peak 3), 1ppm (response Peak 6), 2ppm (response Peak 8) and 5ppmH2The sensitivities of S (response peak 10) were 9.9, 16.3, 27.8, 96.4, 156.2, and 281.5, respectively.
(2) Selectivity test of gas sensor:
h of the nanocomposite prepared in this example2And S, carrying out performance test on the gas sensor. Firstly, the gas sensor works under the condition of room temperature, and the initial baseline is stableThen, H was introduced again at a concentration of 100ppb2And S, introducing air after the resistance of the gas-sensitive sensor is reduced and reaches balance until the baseline is stable again, and finishing the gas-sensitive test. In addition, under the same operation conditions, several gases with a concentration of 100ppb, including ammonia, methanol, isopropanol, diethyl ether, acetone, formaldehyde, and toluene, were introduced separately. FIG. 6 shows graphene quantum dots/SnO2The selectivity of the/ZnO gas sensor to different target gases under the room temperature condition can be seen from figure 62The sensitivity of S is far higher than that of ammonia gas, methanol, isopropanol, ether, acetone, formaldehyde and toluene and is more than 5 times that of other target gases, which shows that the graphene quantum dots/SnO2/ZnO gas sensor pair H2The S gas has excellent selectivity.
Example 2
H based on graphene quantum dot functionalized tin oxide/zinc oxide2The S sensor and the preparation method thereof comprise the following steps:
1. firstly, a gas-sensitive sensor (a preparation process reference document (New Journal of Chemistry,38 (2014)) and 2362-.
2. Placing the cleaned gas-sensitive sensing element in a vacuum chamber of a magnetron sputtering device, adopting metal zinc with the mass purity of 99.99 percent as a target material, adopting argon with the mass purity of 99.99 percent as a working gas, and sputtering and depositing a metal zinc film on the cleaned gas-sensitive sensing element;
3. in the process of depositing the metal zinc film, the distance between the target and the base station is 150mm, and the chamber is firstly vacuumized to 5 multiplied by 10-4Pa. Then Ar is introduced to remove the pollutants on the surface.
4. Regulating the flow of Ar to ensure that the pressure of the chamber is 1.5Pa, introducing gas, heating the gas-sensitive sensing element until the temperature reaches 300 ℃, the deposition power is 100W, pre-sputtering for about 15mins, and timing and sputtering for 30 mins.
5. And after the sputtering is finished, cooling the system to room temperature, filling nitrogen into the vacuum chamber, and opening the vacuum chamber to take out the loaded zinc gas-sensitive sensing device when normal air pressure is reached.
6. Preparing a one-dimensional zinc oxide gas-sensitive sensing film:
adopting a hydrothermal synthesis method, wherein the concentration of strong ammonia water is 8ml, the concentration of deionized water is 20 ml, the concentration of 3.2 g/L carboxymethyl cellulose is 2 ml, the reaction temperature is 150 ℃, and the reaction time is 24 hours; and preparing the one-dimensional zinc oxide gas-sensitive sensing film.
7. Graphene quantum dot/SnO2Preparing a/ZnO composite nanosheet sensing film:
dissolving 2g of stannic chloride in 5ml of ethanol, adding 0.16 g of graphene quantum dots into the precursor solution, dripping 0.2 ml of concentrated hydrochloric acid into the mixed solution of the precursor and the graphene quantum dots, performing ultrasonic dispersion for 5 minutes, and performing magnetic stirring for 12 hours. And (3) spin-coating the mixed sol solution on a one-dimensional zinc oxide gas-sensitive thin film sensor at a relative humidity of 50% at a rotation speed of 4000 rpm for 30 seconds, drying at 60 ℃ for 1 hour, and repeating spin-coating for 4 times. The sensing device was placed in a closed container and the relative humidity in the closed container was adjusted to 95%. And (3) treating for 60 hours at the reaction temperature of 150 ℃, and then carrying out heat treatment on the synthesized nanosheet sensing film device for 2 hours at the temperature of 400 ℃ in a nitrogen atmosphere.
As shown in fig. 7, the prepared composite film on the surface of the sensor device takes ZnO as a main body and is in a nano-sheet shape, the ZnO nanosheet is in a hexagonal shape, the average side length is 2.4 μm, and the average thickness is 100 nm; the average size of the graphene quantum dots is 4.3nm, and the average size of the tin dioxide quantum grains is 5.2 nm.
Surface elemental analysis by XPS:
the composite nano film material contains 68% of ZnO element, 6% of graphene quantum dot element and 26% of stannic oxide quantum grain element.
8. Performing gas sensitivity on the prepared gas-sensitive sensing elementThe sensitivity is defined as the ratio of the resistance value Ra of the element in the atmosphere to the resistance value Rg of the element in the measured gas atmosphere with a certain concentration:
(1) gas sensor for different concentrations H2Testing of S gas:
graphene quantum dot/SnO prepared by using embodiment2H of/ZnO nano composite material2And S, carrying out performance test on the gas sensor. And testing the gas sensor by using a dynamic testing system. Waiting for the initial baseline to be substantially stable, and introducing H at a concentration of 25ppb to 5ppm2And S, introducing air into the test cavity after the resistance of the gas sensor is reduced and reaches balance until the baseline is stable again, and finishing the gas-sensitive test. Graphene quantum dot/SnO2The ZnO gas sensor can be used for measuring H with the concentration of 25ppb-5ppm at room temperature2The sensitivity of S is shown in fig. 8.
The volume of the gas detection cavity is controlled to be 200cm by adopting a dynamic gas-sensitive test method3Regulation and control of H2The concentration of S atmosphere is between 25ppb and 5ppm, the detection temperature is controlled between room temperature, and Keithley 6570A is adopted to collect gas-sensitive sensing data. As shown in FIG. 8, is a gas sensor pair H2Room temperature sensing sensitivity of gas to be measured with S concentration between 25ppb and 5ppm, with H2The sensing sensitivity of the gas sensitive element is improved along with the improvement of the concentration of S. For 50ppb (response Peak 1, ordered from left to right, the same applies below), 100ppb (response Peak 2), 250ppb (response Peak 3), 1ppm (response Peak 6), 2ppm (response Peak 8) and 5ppmH2The sensitivity of S (response peak 10) was 8.9, 18.1, 24.6, 87.4, 142.4 and 258.5, respectively.
(2) Selectivity test of gas sensor:
h of the nanocomposite prepared in this example2And S, carrying out performance test on the gas sensor. Firstly, the gas sensor works under the condition of room temperature, and after the initial baseline is stable, H with the concentration of 100ppb is introduced2S gas, wait for gasAnd (4) introducing air after the resistance of the sensitive sensor is reduced and reaches balance until the base line is stable again, and finishing the gas-sensitive test. In addition, under the same operation conditions, several gases with a concentration of 100ppb, including ammonia, methanol, isopropanol, diethyl ether, acetone, formaldehyde, and toluene, were introduced separately. FIG. 9 shows graphene quantum dots/SnO2The selectivity of the/ZnO gas sensor to different target gases under the room temperature condition can be seen from figure 92The sensitivity of S is far higher than that of ammonia gas, methanol, isopropanol, ether, acetone, formaldehyde and toluene and is more than 5 times that of other target gases, which shows that the graphene quantum dots/SnO2/ZnO gas sensor pair H2The S gas has excellent selectivity.
Claims (10)
1. The graphene quantum dot functionalization-based composite nano film material is characterized in that the composite nano film material is in a film shape, the main body of the composite nano film material is a ZnO nanosheet, and graphene quantum dots and tin dioxide quantum grains are covered on the surface of the composite nano film material; the ZnO nanosheets are hexagonal, the average side length is 1.5-2.4 microns, and the average thickness is 50-100 nm; the average size of the graphene quantum dots is 3.2-4.3 nm, and the average size of the tin dioxide quantum grains is 3.5-5.2 nm.
2. The composite nano thin film material of claim 1, wherein the composite nano thin film material contains 60-70% of ZnO, 5-10% of graphene quantum dot, and 20-35% of tin dioxide quantum grain.
3. The composite nano thin film material of claim 2, wherein the composite nano thin film material contains 64% of ZnO, 8% of graphene quantum dot and 28% of tin dioxide quantum grain.
4. A composite nano film material of any one of claims 1 to 3 in H2And S gas detection.
5. The gas-sensitive sensor prepared from the composite nano film material of any one of claims 1 to 3, wherein the composite nano film material is arranged on the surface of the gas-sensitive sensor.
6. The gas-sensitive sensing element according to claim 5, wherein the interdigital electrode of the gas-sensitive sensing element is a gold interdigital electrode or a platinum interdigital electrode; the gas-sensitive sensing element is prepared by the following method:
(1) cleaning the gas sensitive sensing element;
(2) depositing a metal zinc film on the surface of the cleaned gas-sensitive sensing element;
(3) preparing the deposited metal zinc film into a one-dimensional zinc oxide film by adopting a hydrothermal synthesis method;
(4) preparation of graphene quantum dots/SnO by adopting post-thermal evaporation method2a/ZnO multilevel structure sensing material;
(5) and (4) roasting.
7. The gas sensor element made of the composite material of claim 6, wherein the post-thermal evaporation method adopted in the step (4) comprises the following specific steps: spin-coating the tin tetrachloride mixed solution uniformly dispersed with the graphene quantum dots on the surface of the one-dimensional zinc oxide film of the gas-sensitive sensor obtained in the step (3), repeating drying and spin-coating for 3-5 times, placing the gas-sensitive sensor into a closed container, regulating and controlling the humidity in the closed container to be 75% -95%, the reaction temperature to be 120-150 ℃, and the reaction time to be 24-72 hours, thus obtaining the graphene quantum dots/SnO2a/ZnO multilevel structure sensing material; the concentrations of the stannic chloride and the graphene quantum dots in the mixed solution are respectively 0.1-0.4 g/ml and 0.02-0.05 g/ml.
8. The gas sensor according to claim 7, wherein the specific method for cleaning the gas sensor in step (1) is as follows: first, a vacuum-pumping operation is performed to remove the gas in the plasma cleaning machineThe pressure control range of the vacuum cavity is 1-10 Pa, and the pressure is maintained for 5-10 minutes; then, argon and oxygen are introduced through a double-way pipeline, and the flow ratio of the argon to the oxygen is 1: 1-3: 1; the frequency of the plasma generator is 40KHz, and the power is regulated and controlled to be 120-180W; the specific steps of depositing the metal zinc film in the step (2) are as follows: placing the cleaned gas-sensitive sensor in a vacuum chamber of a magnetron sputtering device, and performing sputtering deposition by using metal zinc with the mass purity of 99.99% as a target material and argon with the mass purity of 99.99% as a working gas; in the process of depositing the metal zinc film, the distance between the target and the base station is 50-150 mm, and the chamber is firstly vacuumized to 1 multiplied by 10-4～5×10-4And Pa, introducing argon, removing pollutants on the surface, adjusting the flow of the argon to be 8-28 SCCM to enable the pressure of the chamber to be 0.5-2.5 Pa, and setting the deposition power to be 90-120W.
9. The gas-sensitive sensor element according to claim 7, wherein in the step (3), the hydrothermal synthesis method adjusts the acidity and alkalinity of the reaction system through concentrated ammonia water, carboxymethyl cellulose is used as a structure directing agent, the reaction temperature is controlled to be 120-160 ℃, and the reaction time is controlled to be 6-72 hours; the using amount of the concentrated ammonia water is 2-8 ml, the using amount of deionized water in a reaction system is 20-25 ml, the carboxymethyl cellulose adopts a carboxymethyl cellulose aqueous solution, the concentration is 1.4-4.2 g/L, and the using amount is 2-4 ml.
10. The gas sensor according to claim 7, wherein the baking in step (5) is performed by the following steps: loading the graphene quantum dots/SnO2And carrying out heat treatment on the gas-sensitive sensing element of the/ZnO multi-level structure sensing material in a programmed muffle furnace at 400-500 ℃ in a nitrogen atmosphere for 2-4 h, and controlling the heating rate to be less than 2 ℃/min.
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