Nanometer ZnO-NH2 / rGO composite material as well as preparation method and application thereof

Abstract

The invention discloses a nano ZnO-NH2 / rGO composite material as well as a preparation method and application thereof, and belongs to the technical field of gas sensitive materials. In the preparation process of the composite material, nano ZnO particles are pretreated through ultraviolet irradiation, a large number of oxygen vacancies are introduced to the surface of ZnO to form high-activity sites, adsorption and activation of carbon dioxide are effectively promoted, meanwhile, the oxygen vacancies serve as electron donors, Zn < 2 + > is exposed and positively charged, and in follow-up amino functional modification, the oxygen vacancies serve as electron donors, so that the oxygen vacancies and the Zn < 2 + > serve as electron donors. The ZnO nano-particles can be subjected to electrostatic attraction with sulfydryl (-SH) of aminothiol, so that directional combination is promoted, amino groups are more uniformly distributed on the surfaces of the ZnO nano-particles, and carbon dioxide adsorption point positions are more uniformly distributed. Through verification, the nanometer ZnO-NH2 / rGO composite material is higher in carbon dioxide detection sensitivity and better in stability when being used in a gas sensitive sensor.

Description

Technical Field

[0001] This application belongs to the field of gas-sensitive materials technology, specifically relating to a nano-ZnO-NH2 / rGO composite material, its preparation method, and its application. Background Technology

[0002] The development and utilization of energy by humankind has played a crucial role, particularly in the production and processing of carbon and carbon-containing compounds. However, this process inevitably generates a certain amount of carbon dioxide, some of which, without purification or remediation, is directly released into the atmosphere, contributing to global warming. Excessively high carbon dioxide concentrations in confined spaces can also cause harm to humans, even leading to death, posing a potential threat to human health. Therefore, improving the sensitivity of carbon dioxide detection in the environment is essential.

[0003] With the rapid development of nanotechnology, significant progress has been made in the development of gas sensors based on nanomaterials. Among them, nano-ZnO (zinc oxide) exhibits advantages in detecting gases such as carbon dioxide due to its high surface area, high surface activity, and chemical stability. rGO (reduced graphene oxide), with its large specific surface area, facilitates gas adsorption and possesses good conductivity at room temperature, effectively reducing the operating temperature of gas sensors. Therefore, gas sensors prepared using nano-ZnO and graphene composites have successfully achieved gas detection in ambient temperatures. To achieve more uniform dispersion of nano-ZnO in graphene and further improve the sensitivity to analytes, Chinese invention patent application CN112461907A discloses a composite material of nano-zinc oxide and reduced graphene oxide, its preparation method, and its application. This method involves pre-treating the surface of nano-zinc oxide with amino functionalization by adding 3-aminopropyltriethoxysilane (APTES), followed by stirring and mixing with the prepared reduced graphene oxide (GO). The two materials then self-assemble and disperse uniformly, resulting in more uniform ZnO dispersion and improved sensitivity to analytes. However, this patent does not consider the potential aggregation of amino groups on the surface of nano-zinc oxide due to the random hydrolysis and condensation of the traditional APTES method. This aggregation could lead to uneven amino group distribution, potentially affecting the distribution of carbon dioxide adsorption sites and consequently impacting the sensitivity and stability of detection.

[0004] In summary, there is an urgent need to develop a gas sensor with high sensitivity and strong stability for the accurate detection of carbon dioxide. Summary of the Invention

[0005] 1. The problem to be solved While existing technologies that pretreat nano-ZnO with amino functionalization improve the sensitivity of the nano-ZnO / graphene composite material to the measured substances, they do not consider the potential impact of uneven amino distribution on the nano-ZnO surface on the sensitivity and stability of the measured substances. This application provides a nano-ZnO-NH2 / rGO composite material. Before amino functionalization modification, the nano-ZnO particles are pretreated with ultraviolet light, introducing a large number of oxygen vacancies on the ZnO surface to form highly active sites. These oxygen vacancies not only effectively promote the adsorption and activation of carbon dioxide, but also act as electron donors, enabling ZnO to... 2+ Exposed and positively charged, it can electrostatically attract the thiol (-SH) group of aminothiol during subsequent amino functionalization modification, promoting directional binding and making the amino group more uniformly distributed on the surface of nano-ZnO particles. This results in a more uniform distribution of adsorption sites for carbon dioxide in the composite material, thereby improving the sensitivity and stability of its detection.

[0006] 2. Technical Solution To solve the above problems, the technical solution adopted in this application is as follows: This application provides a method for preparing nano-ZnO-NH2 / rGO composite materials, the method comprising: S1. Preparation of nano ZnO particles: Zinc nitrate was dissolved in deionized water, and then an alkaline solution was added. The mixture was stirred continuously during the reaction. After centrifugation, washing, and drying, nano ZnO particles were obtained. S2. Pretreatment: The nano ZnO particles in S1 are dispersed in an organic reagent and subjected to ultrasonic treatment. Then, they are placed under a UV lamp to activate the oxygen vacancies on their surface, thus obtaining a nano ZnO particle suspension rich in oxygen vacancies. S3, Aminofunctionalization modification: 2-aminoethanethiol was added to the suspension of nano-ZnO particles with oxygen-rich vacancies in S2, and the reaction was carried out under visible light irradiation at room temperature with continuous stirring; after centrifugation, washing and drying, nano-ZnO-NH2 powder was obtained. S4. Preparation of rGO: Disperse GO in deionized water, then add a reducing agent, stir continuously during the reaction, centrifuge, wash, and dry to obtain rGO; S5. Preparation of nano ZnO-NH2 / rGO composite material: The nano ZnO-NH2 powder in S3 and rGO in S4 are mixed and dispersed in deionized water. After ultrasonic treatment, the nano ZnO-NH2 / rGO composite material is prepared by hydrothermal method.

[0007] Furthermore, the concentration of zinc nitrate mentioned above is 0.1~0.4 g / mL.

[0008] Furthermore, the concentration of zinc nitrate mentioned above is 0.1 g / mL.

[0009] Furthermore, the alkaline solution mentioned above includes ammonia water, and the pH of the solution becomes 10-11 after its addition.

[0010] Furthermore, the reaction in S1 above is carried out at 8000~10000 rpm for 2.5~3.5 h.

[0011] Furthermore, the reaction in S1 above was carried out at 10,000 rpm for 3 h.

[0012] Furthermore, the above-mentioned nano-ZnO particles were dispersed in an organic reagent at a ratio of 1~5 mg / mL and subjected to ultrasonic treatment for 25~35 min.

[0013] Furthermore, the above-mentioned nano-ZnO particles were dispersed in an organic reagent at a ratio of 2 mg / mL and subjected to ultrasonic treatment for 30 min.

[0014] Furthermore, the aforementioned organic reagents include anhydrous ethanol.

[0015] Furthermore, the ultraviolet lamps mentioned above have a power of 300 W to 400 W and a wavelength of 320 to 400 nm.

[0016] Furthermore, the aforementioned ultraviolet lamp has a power of 300 W and a wavelength of 365 nm.

[0017] Furthermore, the duration of the above-mentioned ultraviolet lamp irradiation is 25-35 minutes.

[0018] Furthermore, the duration of the above-mentioned ultraviolet lamp irradiation is 30 minutes.

[0019] Furthermore, the above-mentioned 2-aminoethanethiol was added at a final concentration of 0.03~0.05 g / mL.

[0020] Furthermore, the above-mentioned 2-aminoethanethiol was added at a final concentration of 0.04 g / mL.

[0021] Furthermore, the wavelength of the aforementioned visible light source is 390~780 nm.

[0022] Furthermore, the wavelength of the aforementioned visible light source is 450 nm.

[0023] Furthermore, the reaction in S3 above is carried out at 8000~10000 rpm for 1.5~2.5 h.

[0024] Furthermore, the reaction in S3 above was carried out at 10,000 rpm for 2 h.

[0025] Furthermore, in S3 above, centrifugation is performed at 8000~10000 rpm for 10~15 min.

[0026] Furthermore, in S3 above, centrifugation is performed at 8000 rpm for 10 min.

[0027] Furthermore, in step S3 above, the washing process involves washing three times with ethanol and deionized water in sequence.

[0028] Furthermore, the S3 above is dried at 50℃~80℃ for 10~14 h under a nitrogen atmosphere.

[0029] Furthermore, the S3 above is dried at 60°C for 12 h under a nitrogen atmosphere.

[0030] Furthermore, the above-mentioned GO was dispersed in deionized water at a ratio of 1~3 mg / mL.

[0031] Furthermore, the above-mentioned GO was dispersed in deionized water at a ratio of 1 mg / mL.

[0032] Furthermore, the reducing agent mentioned above is added at a volume ratio of (1~1.5):100.

[0033] Furthermore, the reducing agent mentioned above includes any one of ascorbic acid and hydrazine hydrate.

[0034] Furthermore, the reducing agent mentioned above is ascorbic acid, which is added at a volume ratio of 1:100.

[0035] Furthermore, the reaction in S4 above is carried out at 80℃~120℃ and 8000~10000 rpm for 4~6 h.

[0036] Furthermore, the reaction in S4 was carried out at 100°C and 10,000 rpm for 5 h.

[0037] Furthermore, the above-mentioned nano ZnO-NH2 powder and rGO were mixed at a mass ratio of (0.8~1.2):1, and the mixture was dispersed in deionized water at a ratio of 1~1.5 mg / mL and subjected to ultrasonic treatment for 1~2 h.

[0038] Furthermore, the above-mentioned nano ZnO-NH2 powder was mixed with rGO at a mass ratio of 1:1, and the mixture was dispersed in deionized water at a ratio of 1 mg / mL and subjected to ultrasonic treatment for 1 h.

[0039] Furthermore, the above-mentioned hydrothermal reaction is carried out at 120~180℃ for 6~8 h.

[0040] Furthermore, the above-mentioned hydrothermal reaction was carried out at 180°C for 8 hours.

[0041] This application also provides nano-ZnO-NH2 / rGO composite materials prepared by the above method.

[0042] Furthermore, the above-mentioned composite material has a three-dimensional porous network structure, wherein the nano-ZnO-NH2 is in the form of particles and rGO is in the form of sheets, and the nano-ZnO-NH2 particles are uniformly loaded on the surface of the rGO sheets and in the interlayer voids.

[0043] Furthermore, the specific surface area of ​​the above-mentioned composite material is 200~400 m². 2 / g, with a porosity of 60%~80%.

[0044] Furthermore, the specific surface area of ​​the aforementioned composite material is 300 m². 2 / g, with a porosity of 75%.

[0045] Furthermore, the particle size of the above-mentioned nano-ZnO-NH2 is 20~50 nm.

[0046] Furthermore, the particle size of the aforementioned nano-ZnO-NH2 is 35 nm.

[0047] Furthermore, the lateral dimensions of the above-mentioned rGO are 1~5 μm and the thickness is 0.34~3.4 nm.

[0048] Furthermore, the lateral dimension of the above-mentioned rGO is 2 μm and the thickness is 3.4 nm.

[0049] This application also provides the application of the above-mentioned nano-ZnO-NH2 / rGO composite material in the preparation of gas sensors.

[0050] This application also provides a gas sensor for carbon dioxide detection, which includes any of the above-mentioned nano-ZnO-NH2 / rGO composite materials.

[0051] Furthermore, the gas sensor for carbon dioxide detection described above includes a flexible substrate and an electrode located on the surface of the flexible substrate, as well as any of the aforementioned nano-ZnO-NH2 / rGO composite materials coated on the surface of the substrate.

[0052] This application also provides the application of the above-mentioned gas sensor for carbon dioxide detection in carbon dioxide detection.

[0053] 3. Beneficial effects Compared with the prior art, the advantages of this application are as follows: (1) This application provides a nano-ZnO-NH2 / rGO composite material and its preparation method. The nano-ZnO is pretreated with ultraviolet light to generate a large number of oxygen vacancies on its surface, which serve as highly active sites to promote the adsorption and activation of carbon dioxide. Simultaneously, the oxygen vacancies act as electron donors, enabling ZnO to...2+ Exposed and positively charged, it can electrostatically attract the thiol (-SH) group of aminothiol during subsequent amino functionalization modification, thereby promoting directional binding and making the amino group more uniformly distributed on the surface of nano ZnO particles. This, in turn, makes the adsorption sites of carbon dioxide in the composite material more uniformly distributed.

[0054] (2) This application provides a nano ZnO-NH2 / rGO composite material and its preparation method and application. The gas sensor prepared by the nano ZnO-NH2 / rGO composite material in this application has been verified to have improved sensitivity to carbon dioxide detection and maintain good stability after multiple detections. It is suitable for accurate monitoring of carbon dioxide in the environment. Attached Figure Description

[0055] Figure 1 This is a SEM image of the nano-ZnO-NH2 / rGO composite material prepared in Example 1 of this application.

[0056] Figure 2 This is a SEM image of the nano-ZnO-NH2 / rGO composite material prepared in Comparative Example 1 of this application.

[0057] Figure 3 This is a diagram showing the electrode installation of the gas sensor in this application.

[0058] Figure 4 This is a graph showing the resistance response of the gas sensor prepared in Example 2 of this application to different concentrations of carbon dioxide.

[0059] Figure 5 This is a sensitivity curve of the gas sensor prepared in Example 2 of this application for detecting carbon dioxide at different concentrations.

[0060] Figure 6 This is a stability test diagram of the gas sensor prepared in Example 2 of this application for carbon dioxide detection. Detailed Implementation

[0061] The present application will be further described below with reference to specific embodiments.

[0062] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0063] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0064] As used herein, the term “about” is used to provide for the flexibility and imprecision associated with a given term, measure, or value. Those skilled in the art can readily determine the degree of flexibility for a particular variable. As used herein, the term “at least one of…” is intended to be synonymous with “one or more of…”. For example, “at least one of A, B, and C” explicitly includes only A, only B, only C, and combinations thereof. Concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as "less than about 4.5," which should be interpreted to include all the values ​​and ranges described above. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0065] Example 1 This embodiment provides a nano-ZnO-NH2 / rGO composite material and its preparation method.

[0066] like Figure 1 As shown, the nano-ZnO-NH2 / rGO composite material has a three-dimensional porous network structure, in which the nano-ZnO-NH2 is granular and the rGO is lamellar. The nano-ZnO-NH2 particles (amino-functionalized nano-zinc oxide particles) are uniformly loaded on the surface and interlayer voids of the rGO (reduced graphene oxide) sheets; the specific surface area of ​​the composite material is 300 m². 2 / g, with a porosity of 75%. Among them, the nano ZnO-NH2 particles have a particle size of 35 nm; the rGO has a lateral dimension of 2 μm and a thickness of 3.4 nm.

[0067] The specific preparation method is as follows: S1. Preparation of nano ZnO particles: Dissolve 10 g of zinc nitrate in 100 mL of deionized water, add ammonia to adjust the pH to 11, stir continuously (10000 rpm) for 3 hours, centrifuge, wash and dry to obtain nano ZnO particles. S2. Pretreatment: Disperse the nano ZnO particles (1 g) in S1 in 500 mL of anhydrous ethanol, sonicate for 30 minutes, and then irradiate under a 300 W ultraviolet lamp (wavelength 365 nm) for 30 minutes to activate the surface oxygen vacancies and obtain a nano ZnO particle suspension rich in oxygen vacancies. S3, Aminofunctionalization modification: 20 g of 2-aminoethanethiol was added to the suspension of nano-ZnO particles with oxygen-rich vacancies in S2, and the mixture was stirred at room temperature (10000 rpm) for 2 hours under visible light (wavelength 450 nm) for irradiation. After separation (8000 rpm, 10 min), the mixture was washed three times with ethanol and deionized water, and dried at 60 °C for 12 hours under a nitrogen atmosphere to obtain nano-ZnO-NH2 powder. S4. Preparation of rGO: 200 mg of GO (graphene oxide) was dispersed in 200 mL of deionized water, 2 mL of ascorbic acid was added, and the mixture was stirred at 100 °C (10000 rpm) for 5 hours. After centrifugation, washing and drying, rGO was obtained. S5. Preparation of nano-ZnO-NH2 / rGO composite material: 100 mg of nano-ZnO-NH2 powder and 100 mg of rGO were mixed and dispersed in 200 mL of deionized water, sonicated for 1 hour, and reacted at 180℃ for 8 hours by hydrothermal method. After centrifugation, washing and drying, ZnO-NH2 / rGO composite material was obtained.

[0068] Example 2 This embodiment provides a gas-sensitive sensor and its preparation method.

[0069] This gas sensor was prepared using the nano-ZnO-NH2 / rGO composite material from Example 1, specifically: 20 mg of the ZnO-NH2 / rGO composite material from Example 1 was dispersed in 20 mL of ethanol to form a uniform slurry. This slurry was then coated onto the surface of a ceramic substrate with interdigitated electrodes, dried, and encapsulated to obtain the desired product. Figure 3 The gas sensor shown.

[0070] Comparative Example 1 This embodiment provides a nano-ZnO-NH2 / rGO composite material and its preparation method.

[0071] Unlike Example 1, the nano-ZnO particles prepared in this comparative example did not undergo pretreatment to activate surface oxygen vacancies under ultraviolet light irradiation. Instead, the nano-ZnO particles were directly modified with amino groups using APTES (3-aminopropyltriethoxysilane), ultimately yielding the desired product. Figure 2 The nano-ZnO-NH2 / rGO composite material shown.

[0072] The preparation method includes the following steps: S1. Preparation of nano ZnO particles: Dissolve 10 g of zinc nitrate in 100 mL of deionized water, add ammonia to adjust the pH to 10, stir continuously (10000 rpm) for 2 hours, centrifuge, wash and dry to obtain nano ZnO particles. S2, Amino-functionalized modification: 1 g of nano ZnO particles from S1 were dispersed in 50 mL of anhydrous ethanol, 1 mL of APTES was added, and the mixture was stirred at 70 °C (10000 rpm) for 4 hours. After centrifugation, washing, and drying, nano ZnO-NH2 powder was obtained. S3. Preparation of rGO: 100 mg GO was dispersed in 100 mL of deionized water, 1 mL of hydrazine hydrate was added, and the mixture was stirred at 90 °C (10000 rpm) for 6 hours. After centrifugation, washing and drying, rGO was obtained. S4. Preparation of nano-ZnO-NH2 / rGO composite material: 50 mg of nano-ZnO-NH2 powder and 50 mg of rGO were mixed and dispersed in 100 mL of deionized water, sonicated for 30 minutes, and reacted at 150℃ for 6 hours by hydrothermal method. After centrifugation, washing and drying, nano-ZnO-NH2 / rGO composite material was obtained.

[0073] Comparative Example 2 This comparative example provides a gas-sensitive sensor and its preparation method.

[0074] The gas sensor was prepared using the nano-ZnO-NH2 / rGO composite material from Comparative Example 1. Specifically, 20 mg of the ZnO-NH2 / rGO composite material was dispersed in 20 mL of ethanol to form a uniform slurry, which was then coated onto the surface of a ceramic substrate with interdigitated electrodes. After drying, the slurry was encapsulated to obtain the gas sensor.

[0075] Example 3 This embodiment compares the sensitivity of the two gas sensors described above for carbon dioxide detection.

[0076] (1) Sensitivity detection The gas sensor was placed in clean air, its operating temperature was set to 30℃, and the initial resistance value R0 was recorded. Then, carbon dioxide at a concentration of 5000 ppm was introduced for detection for 5 minutes, and the real-time resistance change was recorded. Clean air was then introduced into the gas sensor until the resistance returned to baseline, and then carbon dioxide at a concentration of 1000 ppm was introduced for detection for another 5 minutes. The sensitivity was calculated using the formula: Sensitivity(%) = [(R0)] g –R0) / R0]×100%, where R0 is the initial resistance value, R g -R0 is the change in total resistance.

[0077] (2) Results analysis: The results are shown in Table 1. The gas sensor prepared using the nano-ZnO-NH2 / rGO composite material in Example 1 (Example 2) has a higher sensitivity for carbon dioxide detection than the gas sensor prepared using the nano-ZnO-NH2 / rGO composite material in Comparative Example 1 (Comparative Example 2). This indicates that the pretreatment of nano-ZnO-NH2 with ultraviolet light irradiation in this application can effectively improve the sensitivity of the gas sensor for carbon dioxide detection. Specifically, the introduction of oxygen vacancies may promote the adsorption and activation of carbon dioxide, and at the same time, make the amino groups on the surface of nano-ZnO particles more uniformly distributed in the subsequent amino functionalization modification, resulting in a more uniform distribution of carbon dioxide adsorption sites, thereby improving the sensitivity for carbon dioxide detection.

[0078] Table 1:

[0079] Example 4 This embodiment further explores the sensitivity of the gas sensor prepared in Example 2 for carbon dioxide detection.

[0080] (1) Sensitivity test: The gas sensor from Example 2 was placed in clean air, and its operating temperature was set to 30°C. The initial resistance (R0) was recorded. Carbon dioxide concentrations ranging from 1000 to 10000 ppm were then introduced sequentially. Similarly, after detecting carbon dioxide at the previous concentration gradient, the gas sensor was placed in clean air until the resistance returned to the baseline before introducing carbon dioxide at the next gradient concentration for detection. Each group was measured for 5 minutes, and the resistance changes were recorded. The sensitivity was calculated in the same way as in Example 3.

[0081] (2) Results analysis: The results are as follows Figures 4-5 As shown in Table 3, it can be observed that the sensitivity of the gas sensor continuously increases with the increase of carbon dioxide concentration. When the concentration is greater than 6000 ppm, such as... Figure 5 The sensitivity curve shown gradually flattens out, but is still rising slowly, indicating that the gas sensor has the characteristics of large range and high accuracy for carbon dioxide detection.

[0082] Table 3:

[0083] Example 5 This embodiment investigates the stability of the gas sensor prepared in Example 2 for carbon dioxide detection.

[0084] (1) Stability test The carbon dioxide concentration of 10,000 ppm in Example 4 was subjected to 17 consecutive repeated gas sensitivity tests. The specific detection method and sensitivity calculation method were the same as in Example 3.

[0085] (2) Results analysis: The results are as follows Figure 6 As shown, the gas sensor showed almost no change in response performance during 17 consecutive repeated gas sensitivity tests at 10,000 ppm carbon dioxide, demonstrating that the gas sensor has good stability for carbon dioxide detection.

Claims

1. A method for preparing a nano-ZnO-NH2 / rGO composite material, characterized in that, The method includes: S1. Preparation of nano ZnO particles: Zinc nitrate was dissolved in deionized water, and then an alkaline solution was added. The mixture was stirred continuously during the reaction. After centrifugation, washing, and drying, nano ZnO particles were obtained. S2. Pretreatment: The nano ZnO particles in S1 are dispersed in an organic reagent and subjected to ultrasonic treatment. Then, they are placed under a UV lamp to activate the oxygen vacancies on their surface, thus obtaining a nano ZnO particle suspension rich in oxygen vacancies. S3, Aminofunctionalization modification: 2-aminoethanethiol was added to the suspension of nano-ZnO particles with oxygen-rich vacancies in S2, and the reaction was carried out under visible light irradiation at room temperature with continuous stirring; after centrifugation, washing and drying, nano-ZnO-NH2 powder was obtained. S4. Preparation of rGO: Disperse GO in deionized water, then add a reducing agent, stir continuously during the reaction, centrifuge, wash, and dry to obtain rGO; S5. Preparation of nano ZnO-NH2 / rGO composite material: The nano ZnO-NH2 powder in S3 and rGO in S4 are mixed and dispersed in deionized water. After ultrasonic treatment, the nano ZnO-NH2 / rGO composite material is prepared by hydrothermal method.

2. The method according to claim 1, characterized in that, The nano-ZnO particles are dispersed in an organic reagent at a ratio of 1-5 mg / mL and subjected to ultrasonic treatment for 25-35 min; the organic reagent includes anhydrous ethanol; and / or The ultraviolet lamp has an irradiation power of 300~400 W; and / or a wavelength of 320~400 nm; and / or an irradiation duration of 25~35 min.

3. The method according to claim 1 or 2, characterized in that, The 2-aminoethanethiol is added at a final concentration of 0.03~0.05 g / mL; and / or the wavelength of the visible light source is 390~780 nm.

4. The method according to claim 3, characterized in that, The GO is dispersed in deionized water at a ratio of 1 to 3 mg / mL; the reducing agent is added at a volume ratio of (1 to 1.5):100; and / or the reducing agent includes any one of ascorbic acid and hydrazine hydrate.

5. The method according to claim 4, characterized in that, The nano ZnO-NH2 powder and rGO were mixed at a mass ratio of (0.8~1.2):1, and the mixture was dispersed in deionized water at a ratio of 1~1.5 mg / mL and subjected to ultrasonic treatment for 1~2 h.

6. The nano-ZnO-NH2 / rGO composite material prepared by the method according to any one of claims 1-5.

7. The nano-ZnO-NH2 / rGO composite material according to claim 6, characterized in that, The composite material has a three-dimensional porous network structure, wherein the nano-ZnO-NH2 is in the form of particles and rGO is in the form of sheets, and the nano-ZnO-NH2 particles are uniformly loaded on the surface of the rGO sheets and in the interlayer voids.

8. The application of the nano-ZnO-NH2 / rGO composite material according to claim 6 or 7 in the preparation of gas sensors.

9. A gas sensor for carbon dioxide detection, characterized in that, The gas sensor comprises the nano-ZnO-NH2 / rGO composite material as described in claim 6 or 7.

10. The gas sensor according to claim 9, characterized in that, The gas sensor includes a flexible substrate and electrodes located on the surface of the flexible substrate, as well as any of the aforementioned nano-ZnO-NH2 / rGO composite materials coated on the surface of the substrate.

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