A single-atom zinc-graphene composite material, a preparation method and application thereof

Abstract

The application discloses a monatomic zinc-graphene composite material, a preparation method thereof and application of the material in an NO2 gas sensor. The zinc is dispersed in a graphene framework in a monatomic form; and the monatomic zinc-graphene composite material has a two-dimensional nanosheet morphology. The material is used in the NO2 gas sensor, and has the advantages of simple preparation, convenient operation, rapid, sensitive and high-selectivity detection of NO2 gas molecules, and low cost.

Description

Technical Field

[0001] This application relates to a single-atom zinc-graphene composite material, its preparation method and application, belonging to the field of materials and environmental monitoring. Background Technology

[0002] Gas sensors are crucial for the rapid and efficient identification of hazardous and harmful gases in production and daily life. The core of a gas sensor is the gas detection component. Traditional gas sensors detect target gas molecules by relying on the reaction between the absorbed target gas molecules and chemically adsorbed oxygen species on the surface of the sensing material to detect the concentration of the target gas.

[0003] Traditional gas sensors suffer from significant drawbacks in selectivity, consistency, stability, and recyclability. To overcome these shortcomings, precious metal sensitization is often employed to achieve a dual effect of electronic and chemical sensitization. This not only improves the material's accessibility to target gas molecules but also enhances the thermodynamic processes of gas sensing. However, given the high cost of metals, the most crucial challenge lies in maximizing the activation of oxygen and the target gas by utilizing the interaction of each metal atom. Summary of the Invention

[0004] To address the aforementioned technical problems, the purpose of this application is to provide a single-atom zinc-graphene composite material, its preparation method, and its application in a gas sensor.

[0005] The inventive concept of this application is to use graphene containing oxygen functional groups as a framework to achieve efficient control over the coordination environment of Zn single atoms, effectively regulating the electronic structure of Zn single atoms and the adsorption strength of active sites for intermediates, thereby improving catalytic performance. Specifically, by utilizing the single-atom control within the graphene framework, catalytic performance in areas such as electron transfer and gas activation is achieved. This precise coordination structure at the atomic scale regulates the CUS-Zn site of Zn-2MI-G, exhibiting highly efficient redox reaction (ORR) activity. Under the dual effects of electronic sensitization and chemical sensitization, the dynamic processes in gas sensors can be significantly improved, enhancing sensing performance.

[0006] According to one aspect of this application, a single-atom zinc-graphene composite material is provided. This material, used in gas sensing, exhibits a customized interfacial electric field that significantly enhances the accessibility of target gas molecules. Its unique single-atom structure also provides extremely high selectivity. This material enables the detection of trace amounts of NO2 and can be used in gas sensors to detect target gases in production and daily life.

[0007] The single-atom zinc-graphene composite material is characterized in that the zinc is dispersed in the form of single atoms within the graphene framework;

[0008] The morphology of the single-atom zinc-graphene composite material is a two-dimensional nanosheet.

[0009] Optionally, the zinc content in the single-atom zinc-graphene composite material is between 2 wt.% and 5 wt.%. Preferably, the zinc content in the single-atom zinc-graphene composite material is between 2.4 wt.% and 4.8 wt.%.

[0010] Optionally, the thickness of the two-dimensional nanosheet is 0.9 nm to 1.5 nm. Preferably, the thickness of the two-dimensional nanosheet is 0.9 nm to 1.5 nm. More preferably, the thickness of the two-dimensional nanosheet is 0.98 nm.

[0011] Another objective of this application is to provide a simple and inexpensive method for preparing single-atom catalytic gas sensing materials. To this end, this application first provides a novel strategy for synthesizing single-atom zinc-graphene composite materials. Graphene, with its naturally occurring oxygen-containing functional groups, serves as a framework to achieve efficient control over the coordination environment of Zn single atoms. This effectively modulates the electronic structure of Zn single atoms and the adsorption strength of active sites for intermediates, thereby improving catalytic performance. These results provide new insights for the design, synthesis, and optimization of single-atom catalysts that precisely adjust the coordination environment of metal single atoms.

[0012] According to another aspect of this application, a method for preparing the single-atom zinc-graphene composite material is provided, characterized by comprising the following steps:

[0013] a) A solution containing graphene oxide is placed in liquid nitrogen, and then subjected to freeze-drying to remove water, vacuum heating to dry, and treatment in an H2 atmosphere to obtain graphene.

[0014] b) The solution containing zinc source and 2-methylimidazole is mixed with the solution containing graphene, placed in liquid nitrogen, and then subjected to freeze drying, vacuum heating drying, and treatment in an H2 atmosphere to obtain the single-atom zinc-graphene composite material.

[0015] Optionally, in step a), the concentration of graphene oxide in the solution containing graphene oxide is 0.15 mg / mL to 0.5 mg / mL.

[0016] Optionally, the graphene oxide-containing solution in step a) is obtained by mixing a commercially available graphene oxide solution with deionized water; when the commercially available graphene oxide solution has a concentration of 2 mg / mL, the volume ratio of the commercially available graphene oxide solution to deionized water is 5–10 mL: 35–50 mL.

[0017] Optionally, the graphene-containing solution described in step b) is obtained by mixing graphene and water in a ratio of 47.6 mg to 48.8 mg: 100 mL.

[0018] Optionally, in step b), the zinc source is selected from at least one of zinc chloride, zinc nitrate, and organozinc compounds.

[0019] Optionally, in step b), the mass ratio of the zinc source to 2-methylimidazole is 5-10:25-30.

[0020] Optionally, in step b), the mass ratio of the zinc source to the graphene is:

[0021] Zn:graphene = 2-5:95-98; wherein the mass of the zinc source is expressed as the mass of zinc atoms.

[0022] Preferably, in step b), the mass ratio of the zinc source to the graphene is:

[0023] Zn:graphene = 2.4–4.8:95.2–97.6; wherein the mass of the zinc source is expressed as the mass of zinc atoms.

[0024] Optionally, in steps a) and b), the freeze-drying time is not less than 24 hours.

[0025] Optionally, in steps a) and b), the vacuum heating drying temperature is 80–100°C and the time is 20–24 h.

[0026] Optionally, in steps a) and b), the conditions for treatment in the H2-containing atmosphere are:

[0027] The H2-containing atmosphere is a mixture of H2 and Ar2 gas;

[0028] The treatment temperature is 180–200℃, and the time is 3–4 hours.

[0029] Preferably, the H2 atmosphere is a mixture of H2 and Ar2 gases, with a volume ratio of H2 to Ar2 of 1:9.

[0030] According to another aspect of this application, an NO2 gas sensor is provided, which is simple to prepare, easy to operate, and achieves rapid, sensitive, and highly selective detection of NO2 gas molecules, and is low in cost.

[0031] The NO2 gas sensor includes the single-atom zinc-graphene composite material.

[0032] Preferably, the NO2 gas sensor has a detection limit of 160–300 ppb for NO2 when the operating temperature is 120°C.

[0033] As one embodiment, the preparation steps of the NO2 gas sensor include:

[0034] (1) Using interdigitated electrodes as gas sensing electrodes, the single-atom zinc-graphene composite material is added to a solvent and mixed to form a uniform slurry; the slurry is drop-coated onto the electrode surface and dried to obtain an electrode containing a sensing film.

[0035] (2) Then the electrode obtained in step (1) is aged to remove the solvent remaining on the electrode and a gas sensing electrode with stable resistance is obtained. The gas sensing electrode is connected to the testing instrument to obtain the NO2 gas sensor.

[0036] Optionally, in step (1), the solvent is selected from at least one of ultrapure water, anhydrous ethanol, and acetone.

[0037] According to another aspect of this application, the NO2 gas sensor is provided for use in NO2 gas detection, wherein the NO2 gas sensor has a detection limit of 160 to 300 ppb for NO2 at an operating temperature of 120°C.

[0038] In one implementation, the NO2 gas sensor is used to detect NO2 gas molecules, and the detection method includes:

[0039] (1) The static gas mixing method is used for testing, that is, the liquid containing NO2 is evaporated on the hot stage using a micro-injector to obtain a certain concentration of NO2 gas. The vaporized NO2 gas evaporates in the test chamber. The detection of NO2 gas molecules is achieved by recording the resistance change of the NO2 gas sensor before and after the gas is introduced.

[0040] (2) Record the initial resistance of the sensor in air as R. a Different concentrations of NO2 were introduced into the test chamber, and the resistance was recorded as R. g , with R g With R a A working curve was plotted to show the relationship between the ratio of NO2 to NO2 gas molecules.

[0041] In this application, "GO" is an abbreviation for graphene oxide; "2MI" is an abbreviation for 2-methylimidazole.

[0042] The beneficial effects of this application include, but are not limited to:

[0043] (1) The single-atom zinc-graphene composite material provided in this application has an ultra-thin nanosheet morphology, which has inherent advantages in gas sensing and provides a new idea for the reaction design of gas sensors.

[0044] (2) The method for preparing single-atom zinc-graphene composite material provided in this application is simple and provides a new strategy for single-atom regulation in catalysts / materials.

[0045] (3) The NO2 gas sensor provided in this application is simple to prepare and easy to operate. It realizes rapid, sensitive and highly selective detection of NO2 gas molecules, and is low in cost. It can realize the detection of trace amounts of NO2 gas and has market development prospects. Detailed Implementation

[0046] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0047] Unless otherwise specified, all raw materials and reagents used in this application are commercially purchased and used directly without processing. The instruments and equipment used adopt the manufacturer's recommended scheme and parameters.

[0048] As a specific implementation method, the present invention is achieved through the following technical solution:

[0049] 1. A method for preparing a zinc single-atom catalyst confined within a graphene framework and its application in NO2 gas sensing, wherein the preparation method comprises the following steps:

[0050] (1) Preparation of graphene

[0051] A certain amount of GO solution was weighed and added to a certain amount of deionized water, and mixed under magnetic stirring. The solution was then poured into liquid nitrogen and rapidly frozen, followed by freeze-drying for a certain period to dehydrate and form a solid. Finally, under a protective atmosphere of a mixture of H2 and Ar2 gases, the freeze-dried sample was annealed at 180-200℃ for 3-4 hours, and then ground into a uniform powder using an agate mortar.

[0052] (2) Preparation of Zn-2MI-G single-atom catalyst

[0053] Weigh a certain amount of Zn precursor and a certain amount of 2MI, dissolve them in a certain amount of deionized water, and stir to obtain a homogeneous system. This mixture is denoted as solution A.

[0054] Weigh a certain amount of GO solution, mix it with a certain amount of deionized water, stir well, and denote this mixture as solution B.

[0055] Solution A and solution B were mixed thoroughly and stirred vigorously for 5 minutes. The mixture was then poured into liquid nitrogen and rapidly frozen. The solution was then dehydrated by freeze-drying for a certain period to obtain a solid. The freeze-dried sample was then heated and dried in a vacuum oven for a period of time. Finally, under the protection of a mixed gas of H2 and Ar2 in a certain proportion, the dried sample was annealed at 180-200℃ for 3-4 hours and ground into a uniform powder using an agate mortar.

[0056] Step b: The specific steps for constructing the NO2 gas sensor are as follows:

[0057] (1) Using interdigitated electrodes as gas sensing electrodes, the prepared sample was added to an appropriate amount of solvent and mixed to form a uniform slurry. The slurry was then uniformly drop-coated onto the electrode surface to form a film. The interdigitated electrodes were dried in an oven to evaporate the solvent, resulting in a sensing film.

[0058] (2) Then the electrode obtained in step (1) is aged in an oven to remove the organic solvent remaining on the electrode and obtain a gas sensing electrode with stable resistance. The gas sensing electrode is then connected to the testing instrument to obtain the NO2 gas sensor.

[0059] Optionally, in step (1), the solvent is selected from at least one of ultrapure water, anhydrous ethanol, and acetone.

[0060] 2. The application of a single-atom catalytic gas sensor based on two-dimensional materials to the detection of NO2 gas molecules is characterized by the following specific detection method:

[0061] (1) Using interdigitated electrodes as gas sensing electrodes, 5-10 μL of slurry was dropped onto the surface of a substrate with Ag-Pd printed interdigitated electrodes. The electrodes were dried at 65-100 °C to form a sensing film.

[0062] (2) The modified interdigitated electrode is heated in an oven to 180-200°C for 12-24 hours to remove residual organic solvents and obtain the NO2 gas sensor to be tested.

[0063] (3) The gas sensing test adopts the static gas mixing method, that is, a certain amount of liquid containing NO2 is evaporated on the hot stage using a micro-injector to obtain a certain concentration of NO2 gas. The vaporized NO2 gas evaporates in the test chamber, and the NO2 gas molecules are detected by recording the resistance change of the sensor before and after the gas is introduced.

[0064] (4) Record the initial resistance of the sensor in air as R. a Different concentrations of NO2 were introduced into the test chamber, and the resistance was recorded as R. g , with R g With Ra A working curve was plotted to show the relationship between the ratio of NO2 to NO2 gas molecules.

[0065] In the examples, the graphene oxide (GO) aqueous solution used was purchased from Merck Sigma-Aldrich and had a concentration of 2 mg / mL.

[0066] In this embodiment, the instruments used for sample characterization are as follows:

[0067] Instrument Model Manufacturer RX I Fourier Transform Infrared Spectrometer Perkin Elmer, USA Model Smart Lab SE XRD Nippon Rigaku Co., Ltd. Gemini 300 Field Emission Scanning Electron Microscope Carl Zeiss AG Optoelectronic Integrated Test Platform CGS-MT

[0068] Example 1: Preparation of defect-rich single-atom zinc-graphene composite sample Zn-2MI-G 1#

[0069] (1) Preparation of graphene

[0070] Weigh 5 mL of commercially available GO aqueous solution (2 mg / mL) and add it to 35 mL of deionized water, mixing them under magnetic stirring. Then, pour the solution into liquid nitrogen and freeze rapidly, followed by freeze-drying for 24 hours to dehydrate and form a solid. Finally, under the protection of a mixed gas of H2 and Ar2 (volume ratio of H2:Ar2 = 1:9), anneal the freeze-dried sample at 200 °C for 3 hours, and grind it into a uniform powder using an agate mortar, thus obtaining the graphene, denoted as sample G1#.

[0071] (2) Preparation of Zn-2MI-G single-atom composite materials

[0072] Weigh 5 mg (containing 2.4 mg Zn atoms) of zinc chloride and 25 mg of 2MI, dissolve them in 35 mL of deionized water, and stir to obtain a homogeneous system. This mixture is denoted as solution A.

[0073] Weigh 97.6 mg of sample G1# obtained in step (1), mix it with 200 mL of deionized water, stir well, and denote this mixture as solution B.

[0074] Solution A and solution B were mixed homogeneously and stirred vigorously for 5 minutes. The mixture was then poured into liquid nitrogen and rapidly frozen, followed by freeze-drying for 24 hours to obtain a solid. The freeze-dried sample was then heated and dried in a vacuum oven at 100°C for 20 hours. Finally, under the protection of a mixed gas of H2 and Ar2 (volume ratio of H2:Ar2 = 1:9), the dried sample was annealed at 200°C for 4 hours and ground into a uniform powder using an agate mortar, designated as sample Zn-2MI-G 1#.

[0075] Example 2: Preparation of defect-rich single-atom zinc-graphene composite sample Zn-2MI-G 2#

[0076] (1) Preparation of graphene

[0077] Weigh 10 mL of commercially available GO aqueous solution (2 mg / mL) and add it to 50 mL of deionized water, mixing them under magnetic stirring. Then, pour the solution into liquid nitrogen and freeze rapidly, followed by freeze-drying for 24 hours to dehydrate and form a solid. Finally, under the protection of a mixed gas of H2 and Ar2 (volume ratio of H2:Ar2 = 1:9), anneal the freeze-dried sample at 180 °C for 4 hours, and grind it into a uniform powder using an agate mortar. This powder is designated as sample G2#.

[0078] (2) Preparation of Zn-2MI-G single-atom composite materials

[0079] Weigh 5 mg (containing 2.4 mg Zn atoms) of zinc chloride and 25 mg of 2MI, dissolve them in 50 mL of deionized water, and stir to obtain a homogeneous system. This mixture is denoted as solution A.

[0080] Weigh 97.6 mg of sample G2# obtained in step (1), mix it with 200 mL of deionized water, stir well, and denote this mixture as solution B.

[0081] Solution A and solution B were mixed thoroughly and stirred vigorously for 5 minutes. The mixture was then poured into liquid nitrogen and rapidly frozen. The resulting solid was dehydrated by freeze-drying for 24 hours. The freeze-dried sample was then heated and dried in a vacuum oven at 80°C for 24 hours. Finally, under the protection of a mixed gas of H2 and Ar2 (volume ratio of H2:Ar2 = 1:9), the dried sample was annealed at 180°C for 4 hours and ground into a uniform powder using an agate mortar. This powder was designated as sample Zn-2MI-G 2#.

[0082] Example 3: Preparation of defect-rich single-atom zinc-graphene composite sample Zn-2MI-G 3#

[0083] (1) Preparation of graphene

[0084] 10 mL of commercially available GO aqueous solution (2 mg / mL) was weighed and added to 40 mL of deionized water, and the mixture was stirred magnetically. The solution was then rapidly frozen in liquid nitrogen and freeze-dried for 24 hours to remove water and form a solid. Finally, under the protection of a mixed gas of H2 and Ar2 (volume ratio of H2:Ar2 = 1:9), the freeze-dried sample was annealed at 190 °C for 3.5 hours and ground into a uniform powder using an agate mortar. This powder was designated as sample G3#.

[0085] (2) Preparation of Zn-2MI-G single-atom composite materials

[0086] Weigh 5 mg (containing 2.4 mg Zn atoms) of zinc chloride and 25 mg of 2MI, dissolve them in 40 mL of deionized water, and stir to obtain a homogeneous system. This mixture is denoted as solution A.

[0087] Weigh 97.6 mg of sample G3# obtained in step (1), mix it with 200 mL of deionized water, stir well, and denote this mixture as solution B.

[0088] Solution A and solution B were mixed homogeneously and stirred vigorously for 5 minutes. The mixture was then poured into liquid nitrogen and rapidly frozen, followed by freeze-drying for 24 hours to obtain a solid. The freeze-dried sample was then heated and dried in a vacuum oven at 100°C for 20 hours. Finally, under the protection of a mixed gas of H2 and Ar2 (volume ratio of H2:Ar2 = 1:9), the dried sample was annealed at 190°C for 4 hours and ground into a uniform powder using an agate mortar, designated as sample Zn-2MI-G 3#.

[0089] Example 4: Preparation of defect-rich single-atom zinc-graphene composite sample Zn-2MI-G 4#

[0090] (1) Preparation of graphene

[0091] 10 mL of commercially available GO aqueous solution (2 mg / mL) was weighed and added to 50 mL of deionized water, and the mixture was stirred magnetically. The solution was then rapidly frozen in liquid nitrogen and freeze-dried for 24 hours to remove water and form a solid. Finally, under the protection of a mixed gas of H2 and Ar2 (volume ratio of H2:Ar2 = 1:9), the freeze-dried sample was annealed at 200 °C for 3.5 hours and ground into a uniform powder using an agate mortar. This powder was designated as sample G4#.

[0092] (2) Preparation of Zn-2MI-G single-atom composite materials

[0093] Weigh 10 mg (containing 4.8 mg Zn atoms) of zinc chloride and 25 mg of 2MI, dissolve them in 50 mL of deionized water, and stir to obtain a homogeneous system. This mixture is denoted as solution A.

[0094] Weigh 95.2 mg of sample G4# obtained in step (1), mix it with 200 mL of deionized water, stir well, and denote this mixture as solution B.

[0095] Solution A and solution B were mixed homogeneously and stirred vigorously for 5 minutes. The mixture was then poured into liquid nitrogen and rapidly frozen, followed by freeze-drying for 24 hours to obtain a solid. The freeze-dried sample was then heated and dried in a vacuum oven at 100°C for 20 hours. Finally, under the protection of a mixed gas of H2 and Ar2 (volume ratio of H2:Ar2 = 1:9), the dried sample was annealed at 200°C for 3 hours and ground into a uniform powder using an agate mortar, designated as sample Zn-2MI-G 4#.

[0096] Example 5: Preparation of defect-rich single-atom zinc-graphene composite sample Zn-2MI-G 5#

[0097] (1) Preparation of graphene

[0098] 10 mL of commercially available GO aqueous solution (2 mg / mL) was weighed and added to 35 mL of deionized water, and the mixture was stirred magnetically. The solution was then rapidly frozen in liquid nitrogen and freeze-dried for 24 hours to remove water and form a solid. Finally, under the protection of a mixed gas of H2 and Ar2 (volume ratio of H2:Ar2 = 1:9), the freeze-dried sample was annealed at 200 °C for 4 hours and ground into a uniform powder using an agate mortar. This powder was designated as sample G5#.

[0099] (2) Preparation of Zn-2MI-G single-atom composite materials

[0100] Weigh 10 mg of zinc nitrate (containing 3.45 mg of Zn atoms) and 25 mg of 2MI, dissolve them in 50 mL of deionized water, and stir to obtain a homogeneous system. This mixture is denoted as solution A.

[0101] Weigh 96.55 mg of sample G5# obtained in step (1), mix it with 200 mL of deionized water, stir well, and denote this mixture as solution B.

[0102] Solution A and solution B were mixed homogeneously and stirred vigorously for 5 minutes. The mixture was then poured into liquid nitrogen and rapidly frozen, followed by freeze-drying for 24 hours to obtain a solid. The freeze-dried sample was then heated in a vacuum oven at 90°C for 22 hours. Finally, under the protection of a mixed gas of H2 and Ar2 (volume ratio of H2:Ar2 = 1:9), the dried sample was annealed at 200°C for 3 hours and ground into a uniform powder using an agate mortar, designated as sample Zn-2MI-G 5#.

[0103] Example 6: Preparation of defect-rich single-atom zinc-graphene composite sample Zn-2MI-G 6#

[0104] (1) Preparation of graphene

[0105] 10 mL of commercially available GO aqueous solution (2 mg / mL) was weighed and added to 50 mL of deionized water, and the mixture was stirred magnetically. The solution was then rapidly frozen in liquid nitrogen and freeze-dried for 24 hours to remove water and form a solid. Finally, under the protection of a mixed gas of H2 and Ar2 (volume ratio of H2:Ar2 = 1:9), the freeze-dried sample was annealed at 200 °C for 3.5 hours and ground into a uniform powder using an agate mortar. This powder was designated as sample G6#.

[0106] (2) Preparation of Zn-2MI-G single-atom composite materials

[0107] Weigh 10 mg of zinc nitrate (containing 3.45 mg of Zn atoms) and 30 mg of 2MI, dissolve them in 50 mL of deionized water, and stir to obtain a homogeneous system. This mixture is denoted as solution A.

[0108] Weigh 96.55 mg of sample G6# obtained in step (1), mix it with 200 mL of deionized water, stir well, and denote this mixture as solution B.

[0109] Solution A and solution B were mixed homogeneously and stirred vigorously for 5 minutes. The mixture was then poured into liquid nitrogen and rapidly frozen, followed by freeze-drying for 24 hours to obtain a solid. The freeze-dried sample was then heated and dried in a vacuum oven at 100°C for 20 hours. Finally, under the protection of a mixed gas of H2 and Ar2 (volume ratio of H2:Ar2 = 1:9), the dried sample was annealed at 200°C for 3.5 hours and ground into a uniform powder using an agate mortar, designated as sample Zn-2MI-G6#.

[0110] Example 7: Preparation of defect-rich single-atom zinc-graphene composite sample Zn-2MI-G 7#

[0111] (1) Preparation of graphene

[0112] 10 mL of commercially available GO aqueous solution (2 mg / mL) was weighed and added to 50 mL of deionized water, and the mixture was stirred magnetically. The solution was then rapidly frozen in liquid nitrogen and freeze-dried for 24 hours to remove water and form a solid. Finally, under the protection of a mixed gas of H2 and Ar2 (volume ratio of H2:Ar2 = 1:9), the freeze-dried sample was annealed at 190 °C for 3 hours and ground into a uniform powder using an agate mortar. This powder was designated as sample G7#.

[0113] (2) Preparation of Zn-2MI-G single-atom composite materials

[0114] Weigh 10 mg of zinc nitrate (containing 3.45 mg of Zn atoms) and 30 mg of 2MI, dissolve them in 50 mL of deionized water, and stir to obtain a homogeneous system. This mixture is denoted as solution A.

[0115] Weigh 96.55 mg of sample G7# obtained in step (1), mix it with 50 mL of deionized water, stir well, and denote this mixture as solution B.

[0116] Solution A and solution B were mixed homogeneously and stirred vigorously for 5 minutes. The mixture was then poured into liquid nitrogen and rapidly frozen, followed by freeze-drying for 24 hours to obtain a solid. The freeze-dried sample was then heated and dried in a vacuum oven at 80°C for 24 hours. Finally, under the protection of a mixed gas of H2 and Ar2 (volume ratio of H2:Ar2 = 1:9), the dried sample was annealed at 190°C for 3 hours and ground into a uniform powder using an agate mortar, designated as sample Zn-2MI-G 7#.

[0117] Example 8: Preparation of defect-rich single-atom zinc-graphene composite sample Zn-2MI-G 8#

[0118] (1) Preparation of graphene

[0119] 10 mL of commercially available GO aqueous solution (2 mg / mL) was weighed and added to 50 mL of deionized water, and the mixture was stirred magnetically. The solution was then rapidly frozen in liquid nitrogen and freeze-dried for 24 hours to remove water and form a solid. Finally, under the protection of a mixed gas of H2 and Ar2 (volume ratio of H2:Ar2 = 1:9), the freeze-dried sample was annealed at 180 °C for 4 hours and ground into a uniform powder using an agate mortar. This powder was designated as sample G8#.

[0120] (2) Preparation of Zn-2MI-G single-atom catalyst

[0121] Weigh 10 mg of zinc nitrate (containing 3.45 mg of Zn atoms) and 30 mg of 2MI, dissolve them in 50 mL of deionized water, and stir to obtain a homogeneous system. This mixture is denoted as solution A.

[0122] Weigh 96.55 mg of sample G8# obtained in step (1), mix it with 200 mL of deionized water, stir well, and denote this mixture as solution B.

[0123] Solution A and solution B were mixed homogeneously and stirred vigorously for 5 minutes. The mixture was then poured into liquid nitrogen and rapidly frozen, followed by freeze-drying for 24 hours to obtain a solid. The freeze-dried sample was then heated and dried in a vacuum oven at 100°C for 20 hours. Finally, under the protection of a mixed gas of H2 and Ar2 (volume ratio of H2:Ar2 = 1:9), the dried sample was annealed at 180°C for 3 hours and ground into a uniform powder using an agate mortar, designated as sample Zn-2MI-G 8#.

[0124] Example 9: Construction of NO2 gas sensors NO2-S1# to NO2-S8#

[0125] (1) Using interdigitated electrodes as gas sensing electrodes, samples Zn-2MI-G 1#~8# were added to deionized water (the mass ratio of the single-atom zinc-graphene composite sample to water was 1:10) and mixed to form a homogeneous slurry. Then, 10 μL of the slurry was dropped onto the surface of the Ag-Pd printed interdigitated electrode substrate. The electrode was dried at 80℃ to form a sensing film.

[0126] (2) Then the electrodes obtained in step (1) are heated to 200°C in an oven for 5 hours to remove residual water, thus obtaining the NO2 gas sensor, which is denoted as sensor NO2-S1#~NO2-S8#.

[0127] Example 10: Construction of NO2 Gas Sensor NO2-S3#-EtOH

[0128] (1) Using interdigitated electrodes as gas sensing electrodes, the sample Zn-2MI-G 3# was added to anhydrous ethanol (the mass ratio of the single-atom zinc-graphene composite sample Zn-2MI-G 3# to ethanol was 1:10) and mixed to form a homogeneous slurry. Then, 5 μL of the slurry was dropped onto the surface of the Ag-Pd printed interdigitated electrode substrate. The electrode was dried at 60 °C to form a sensing film.

[0129] (2) Then the electrode obtained in step (1) is heated to 180°C in an oven for 3 hours to remove residual ethanol, thus obtaining the NO2 gas sensor, denoted as sensor NO2-S3#-EtOH.

[0130] Example 11

[0131] The NO2 gas sensors NO2-S1#~NO2-S8# and NO2-S3#-EtOH were respectively applied to the detection of NO2 gas molecules, and the steps are as follows:

[0132] (1) Preparation of gas sensing electrodes: NO2-S1#~NO2-S8# and NO2-S3#-EtOH were used as working electrodes respectively;

[0133] (2) Preparation of standard gas: In order to obtain the required gas, liquid NO2 is added to the test chamber using a micro-syringe and evaporated directly;

[0134] (3) Plotting the working curve: Connect the electrode described in (1) to the gas sensor detection device, and mix the gas in the gas chamber using the method described in (2); test the resistance of the sensor before and after gas is introduced in the chamber with constant relative humidity and temperature; plot the working curve based on the relationship between the obtained resistance change and NO2 concentration; the resistance change is represented by Rg / Ra, where Ra refers to the resistance in the ambient air and Rg is the resistance in the gas being measured; plot the working curve with the NO2 gas molecule concentration as the abscissa and Rg / Ra as the ordinate.

[0135] The results showed that NO2-S1#~NO2-S8# and NO2-S3#-EtOH all exhibited good linear range for NO2, with detection limits of 160~300 ppb at an operating temperature of 120℃.

[0136] Example 12 Selectivity test of NO2 gas by sensors NO2-S1#~NO2-S8# and NO2-S3#-1

[0137] Interfering gas molecules with the same concentration as NO2 were injected into the chamber, and their gas-sensing performance was tested to obtain the selectivity of sensors NO2-S1#~NO2-S8# and NO2-S3#-1 for NO2 gas. (The test method and test conditions were consistent with those for NO2 gas detection). The results showed that NO2-S1#~NO2-S8# and NO2-S3#-1 all had good selectivity for NO2 molecules.

[0138] Characterization of Samples Zn-2MI-G 1# to 8# in Example 13

[0139] The samples Zn-2MI-G 1# to 8# were characterized by Fourier transform infrared spectroscopy, XRD, and emission scanning electron microscopy, respectively.

[0140] The results showed that samples Zn-2MI-G 1# to 8# all had uniform two-dimensional ultrathin nanosheet morphology and good dispersion. The thickness of the nanosheets ranged from 0.9 to 1.5 nm, with most of them having a thickness of about 0.98 nm. Zinc was dispersed in the graphene framework in the form of single atoms.

[0141] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A single-atom zinc-graphene composite material, characterized in that, The zinc is dispersed in a single-atom form within the graphene framework; The morphology of the single-atom zinc-graphene composite material is a two-dimensional nanosheet.

2. The single-atom zinc-graphene composite material according to claim 1, characterized in that, The zinc content in the single-atom zinc-graphene composite material is between 2 wt.% and 5 wt.%. Preferably, the zinc content in the single-atom zinc-graphene composite material is between 2.4 wt.% and 4.8 wt.%.

3. The single-atom zinc-graphene composite material according to claim 1, characterized in that, The thickness of the two-dimensional nanosheet is 0.9 nm to 1.5 nm; Preferably, the thickness of the two-dimensional nanosheet is 0.9 nm to 1.0 nm.

4. The method for preparing the single-atom zinc-graphene composite material according to any one of claims 1 to 3, characterized in that, Includes the following steps: a) A solution containing graphene oxide is placed in liquid nitrogen, and then subjected to freeze-drying to remove water, vacuum heating to dry, and treatment in an H2 atmosphere to obtain graphene. b) The solution containing zinc source and 2-methylimidazole is mixed with the solution containing graphene and placed in liquid nitrogen. After freeze-drying and dehydration, vacuum heating and drying, and treatment in an H2 atmosphere, the single-atom zinc-graphene composite material is obtained.

5. The method according to claim 4, characterized in that, In step a), the concentration of graphene oxide in the solution containing graphene oxide is 0.15 mg / mL to 0.5 mg / mL; In step b), the graphene-containing solution is obtained by mixing graphene and water, with a graphene to water ratio of 47.6 mg to 48.8 mg: 100 mL.

6. The method according to claim 4, characterized in that, In step b), the zinc source is selected from at least one of zinc chloride, zinc nitrate, and organozinc compounds; The mass ratio of the zinc source to 2-methylimidazole is 5-10:25-30.

7. The method according to claim 4, characterized in that, In step b), the mass ratio of the zinc source to the graphene is: Zn:Graphene = 2-4:96-98; The mass of the zinc source is expressed as the mass of zinc atoms.

8. The method according to claim 4, characterized in that, In steps a) and b), The freeze-drying time is no less than 24 hours; The vacuum heating drying temperature is 80-100℃, and the time is 20-24 hours; The conditions for treatment in the H2-containing atmosphere are as follows: The H2-containing atmosphere is a mixture of H2 and Ar2 gas; The treatment temperature is 180–200℃, and the time is 3–4 hours.

9. A NO2 gas sensor, characterized in that, It includes the single-atom zinc-graphene composite material according to any one of claims 1 to 3.

10. The application of the NO2 gas sensor according to claim 9 in NO2 gas detection, characterized in that, The NO2 gas sensor has a detection limit of 160–300 ppb for NO2 at an operating temperature of 120°C.