Preparation method of tin dioxide gas-sensitive material, nitrogen dioxide sensor and preparation method thereof

Abstract

The present disclosure provides a method for preparing a tin dioxide gas-sensitive material, a nitrogen dioxide sensor and a method for preparing the same. The method for preparing the tin dioxide gas-sensitive material comprises the following steps: placing a tin dioxide nanosheet in a plasma chamber, introducing a nitrogen-containing gas into the plasma chamber to generate a nitrogen-containing plasma, and performing a surface treatment on the tin dioxide nanosheet by the nitrogen-containing plasma, wherein the duration of the surface treatment is 10s to 1800s. The method for preparing the tin dioxide gas-sensitive material can improve the response value of the prepared tin dioxide gas-sensitive material to nitrogen dioxide gas.

Description

Technical Field

[0001] The present invention relates to the technical field of gas sensors, and in particular to a method for preparing a tin dioxide gas-sensitive material, a nitrogen dioxide sensor and a preparation method thereof. Background Art

[0002] With the rapid development of industrialization and urbanization, automobile exhaust and other waste emissions have led to serious air pollution, among which nitrogen dioxide is a typical pollutant gas. Long-term exposure to an atmosphere of excessive nitrogen dioxide will cause serious damage to human health. Therefore, it is very necessary to monitor it in a timely manner through high-performance nitrogen dioxide sensors, which is of great significance for protecting the environment and human health.

[0003] Tin dioxide is one of the most commonly used metal oxide semiconductor gas-sensitive materials. It has been widely used in commercial gas sensors and exhibits good gas-sensing performance. The morphology of tin dioxide in gas sensors is usually nanoparticles. During detection, gases such as hydrogen, carbon monoxide, ozone and nitrogen dioxide can be adsorbed on the surface of tin dioxide nanoparticles and change the resistance of tin dioxide. The current tin dioxide gas-sensitive materials have a low response value for the detection of nitrogen dioxide gas. Correspondingly, the selectivity of tin dioxide-based gas sensors for nitrogen dioxide gas is also poor. Summary of the invention

[0004] Based on this, it is necessary to provide a method for preparing a tin dioxide gas-sensitive material in order to improve the response value of the prepared tin dioxide gas-sensitive material to nitrogen dioxide gas in order to address the problems in the above-mentioned background technology.

[0005] According to some embodiments of the present disclosure, a method for preparing a tin dioxide gas-sensitive material is provided, comprising the following steps: placing a tin dioxide nanosheet in a plasma chamber, introducing a nitrogen-containing gas into the plasma chamber to generate a nitrogen-containing plasma, and surface-treating the tin dioxide nanosheet by the nitrogen-containing plasma, wherein the duration of the surface treatment is 10s to 1800s.

[0006] In some embodiments of the present disclosure, the nitrogen-containing gas is selected from nitrogen; and / or the gas flow rate of the nitrogen-containing gas is 50 sccm~300 sccm.

[0007] In some embodiments of the present disclosure, the power of the power supply for generating the nitrogen-containing plasma is 120W~200W.

[0008] In some embodiments of the present disclosure, the duration of the surface treatment is 120s~150s.

[0009] In some embodiments of the present disclosure, the thickness of the tin dioxide nanosheets is 1 nm to 5 nm.

[0010] In some embodiments of the present disclosure, the maximum radial dimension of the tin dioxide nanosheets is 1 μm to 20 μm.

[0011] In some embodiments of the present disclosure, the method for preparing the tin dioxide nanosheets comprises the following steps:

[0012] dispersing a graphene material and a tin precursor in an acidic aqueous solution to obtain a mixed precursor solution;

[0013] hydrolyzing the tin precursor to obtain a composite precursor material containing tin dioxide and graphene material;

[0014] The composite precursor material is calcined to remove the graphene material therein and form the tin dioxide nanosheets.

[0015] In some embodiments of the present disclosure, the step of hydrolyzing the tin precursor includes: heating the mixed precursor solution in a water bath, wherein the water bath heating temperature is 60° C. to 80° C., and the duration of the water bath heating is 3 h to 6 h.

[0016] In some embodiments of the present disclosure, after the tin precursor is hydrolyzed, the reaction system is centrifuged to separate the composite precursor material in the reaction system.

[0017] In some embodiments of the present disclosure, before the composite precursor material is calcined, the composite precursor material is further subjected to freezing and freeze-drying treatments.

[0018] In some embodiments of the present disclosure, in the step of calcining the composite precursor material, the calcination temperature is 600° C. to 800° C., and the calcination time is 2 h to 4 h.

[0019] Furthermore, the present disclosure also provides a nitrogen dioxide sensor, which includes a gas-sensitive coating, the material of the gas-sensitive coating includes a tin dioxide gas-sensitive material, and the tin dioxide gas-sensitive material is prepared by the preparation method of the tin dioxide gas-sensitive material described in any of the above embodiments.

[0020] Furthermore, the present disclosure also provides a method for preparing a nitrogen dioxide sensor as described in any of the above embodiments, comprising the following steps:

[0021] Prepare a tin dioxide gas-sensitive material according to the method for preparing a tin dioxide gas-sensitive material as described in any of the above embodiments;

[0022] Dispersing the tin dioxide gas-sensitive material in a dispersant to form a dispersed system;

[0023] The dispersed system is coated on a sensor substrate and subjected to vacuum drying treatment to form the gas-sensitive coating.

[0024] In the preparation method of the tin dioxide gas-sensitive material of at least one of the above-mentioned embodiments, tin dioxide nanosheets are used as raw materials, and the tin dioxide nanosheets can produce oxygen vacancy defects during the treatment of nitrogen-containing plasma. The present disclosure has found in the research process that the treatment of tin dioxide nanosheets with nitrogen-containing plasma for 10s to 1800s can introduce an appropriate amount of oxygen vacancy defects on the surface of the tin dioxide nanosheets. These oxygen vacancy defects can serve as adsorption active sites for nitrogen dioxide gas, enhance the adsorption of nitrogen dioxide gas by the tin dioxide nanosheets, and improve the response value of the tin dioxide gas-sensitive material to nitrogen dioxide gas. Experiments have shown that the sensor using the tin dioxide gas-sensitive material as the gas-sensitive coating has excellent selectivity for nitrogen dioxide gas.

[0025] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 A schematic diagram of the steps of a method for preparing a tin dioxide gas-sensitive material;

[0028] Figure 2 The surface morphology of the tin dioxide nanosheets prepared in Example 1 was observed using a scanning electron microscope;

[0029] Figure 3 This is a graph of an X-ray diffraction test of the tin dioxide nanosheets after surface treatment in Example 1;

[0030] Figure 4 The electron paramagnetic resonance test results of the tin dioxide nanosheets that have not been surface treated and those that have been surface treated in Example 1 are respectively;

[0031] Figure 5 is the response value of the gas sensors prepared in Examples 1 to 4 and Comparative Example 1 when nitrogen dioxide at a concentration of 50 ppb is introduced during the test at 80°C; Figure 5 The left figure in is the response curve diagram of Example 1, Figure 5The right figure in the figure is the response value of each embodiment and comparative example;

[0032] Figure 6 The response curve of the gas sensor prepared in Example 1 is shown at 80° C. when nitrogen dioxide with a concentration of 0.5 ppb to 50 ppb is introduced sequentially during the test process;

[0033] Figure 7 The response values ​​of the gas sensor prepared in Example 1 at 80° C. when 50 ppb nitrogen dioxide, 1 ppm carbon monoxide, 1 ppm sulfur dioxide, 50 ppm ammonia, 50 ppm hydrogen and 50 ppm methane are introduced respectively;

[0034] Figure 8 The response value change curve of the gas sensor prepared in Example 1 is taken every week during the process of being placed for 5 weeks. DETAILED DESCRIPTION

[0035] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0037] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0038] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0039] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0040] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0041] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0042] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0043] The present disclosure provides a method for preparing a tin dioxide gas-sensitive material, which comprises the following steps: placing a tin dioxide nanosheet in a plasma chamber, introducing a nitrogen-containing gas into the plasma chamber to generate a nitrogen-containing plasma, and surface treating the tin dioxide nanosheet by the nitrogen-containing plasma, wherein the duration of the surface treatment is 10s to 1800s.

[0044] In the preparation method of the tin dioxide gas-sensitive material, tin dioxide nanosheets are used as raw materials, and the tin dioxide nanosheets can produce oxygen vacancy defects during the treatment of nitrogen-containing plasma. The present disclosure found in the research process that the tin dioxide nanosheets are treated with nitrogen-containing plasma for 10s to 1800s, which can introduce an appropriate amount of oxygen vacancy defects on the surface of the tin dioxide nanosheets. These oxygen vacancy defects can serve as adsorption active sites for nitrogen dioxide gas, enhance the adsorption of nitrogen dioxide gas by the tin dioxide nanosheets, and improve the response value of the tin dioxide gas-sensitive material to nitrogen dioxide gas. Experiments have shown that the sensor using the tin dioxide gas-sensitive material as a gas-sensitive coating has excellent selectivity for nitrogen dioxide gas.

[0045] Figure 1 Schematic diagram of the steps of the preparation method of the tin dioxide gas sensitive material disclosed in the present invention. Figure 1 As shown, the preparation method includes steps S1 and S2.

[0046] Step S1, preparing tin dioxide nanosheets.

[0047] In this embodiment, the preparation method of tin dioxide nanosheets includes the following steps: dispersing graphene material and tin precursor in an acidic aqueous solution to obtain a mixed precursor solution. Hydrolyzing the tin precursor to obtain a composite precursor material containing tin dioxide and graphene material. Calcining the composite precursor material to remove the graphene material therein to form tin dioxide nanosheets.

[0048] As an example of this embodiment, the acidic solute in the acidic aqueous solution may include one or more of hydrochloric acid and sulfuric acid. Further, the acidic aqueous solution may also include glycine. The solvent in the acidic aqueous solution includes one or both of water and ethylene glycol. The ratio of water to ethylene glycol may be adjusted according to actual needs.

[0049] It can be understood that in the mixed precursor solution, the graphene material is used as a growth template for tin dioxide, the acidic aqueous solution is used to inhibit the hydrolysis of the tin precursor, and glycine is used to control the hydrolysis rate of the tin precursor to grow larger and thinner tin dioxide nanosheets.

[0050] As an example of this embodiment, the graphene material is graphene oxide. Graphene oxide has good dispersion performance in aqueous solution, is not easy to agglomerate, is conducive to spreading to form sheet materials, and plays a better template role.

[0051] As an example of this embodiment, the tin precursor may include tin tetrachloride. The tin precursor may also be selected from other tin salts that can be hydrolyzed. The advantage of tin tetrachloride is that the reaction byproducts are easier to remove, which is conducive to obtaining purer tin dioxide nanosheets.

[0052] As an example of this embodiment, the step of hydrolyzing the tin precursor includes: heating the mixed precursor solution in a water bath.

[0053] As a further example of this embodiment, the temperature of the water bath heating is 60° C. to 80° C. For example, the temperature of the water bath heating can be 60° C., 62° C., 65° C., 68° C., 70° C., 72° C., 75° C., 78° C., 80° C., or the temperature of the water bath heating can also be between any two of the above temperatures.

[0054] As a further example of this embodiment, the duration of water bath heating is 3h~6h. For example, the duration of water bath heating can be 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, or the duration of water bath heating can also be between any two of the above times.

[0055] It can be understood that the above-mentioned reaction conditions of water bath heating are conducive to obtaining a moderate hydrolysis rate and enabling the tin precursor to be fully hydrolyzed, thereby growing into thinner and uniformly thick tin dioxide nanosheets based on the nucleation of graphene materials.

[0056] As a further example of this embodiment, during the water bath heating process, the heating medium is water or silicone oil.

[0057] As a further example of this embodiment, during the water bath heating process, the mixed precursor solution is also continuously stirred to promote uniform deposition of tin dioxide. The stirring speed may be 100 rpm to 500 rpm.

[0058] As an example of this embodiment, after the tin precursor is hydrolyzed, the reaction system is centrifuged to separate the composite precursor material in the reaction system.

[0059] As a further example of this embodiment, the centrifugal speed is 4000 rpm to 8000 rpm. For example, the centrifugal speed can be 4000 rpm, 4500 rpm, 5000 rpm, 5500 rpm, 6000 rpm, 6500 rpm, 7000 rpm, 7500 rpm, 8000 rpm, or the centrifugal speed can also be between any two of the above centrifugal speeds.

[0060] As a further example of this embodiment, the centrifugation time is 5 min to 20 min. For example, the centrifugation time can be 5 min, 6 min, 8 min, 10 min, 12 min, 15 min, 20 min, or the centrifugation time can also be between any two of the above times.

[0061] It is understood that after the centrifugal treatment, the supernatant is removed and the lower precipitate is separated to obtain the composite precursor material including tin dioxide and graphene material. Further, after the centrifugal treatment, the composite precursor material can also be cleaned.

[0062] As an example of this embodiment, before the composite precursor material is calcined, the composite precursor material is also subjected to freezing and freeze drying. The freeze drying is used to remove residual water in the composite precursor material while ensuring the spacing between the tin dioxide nanosheets to avoid the problem of agglomeration between the tin dioxide nanosheets.

[0063] As a further example of this embodiment, the temperature of the freezing treatment may be -20°C to -10°C; and the time of the freezing treatment may be 6h to 12h.

[0064] As a further example of this embodiment, the temperature of the freeze-drying process may be -60°C to -40°C; and the time of the freeze-drying process may be 12h to 24h.

[0065] As a further example of this embodiment, in the step of calcining the composite precursor material, the calcination temperature is 600° C. to 800° C. For example, the calcination temperature may be 600° C., 620° C., 650° C., 680° C., 700° C., 720° C., 750° C., 780° C., 800° C., or the calcination temperature may be between any two of the above temperatures.

[0066] As a further example of this embodiment, in the step of calcining the composite precursor material, the calcination time is 2 hours to 4 hours. For example, the calcination time can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, or the calcination time can also be between any two of the above times.

[0067] It is understood that the calcination process may be performed under an atmosphere of air or oxygen to remove the graphene material.

[0068] After step S1, the tin dioxide nanosheets used in the present disclosure can be obtained.

[0069] As an example of this embodiment, the thickness of the tin dioxide nanosheet is 1 nm to 5 nm. For example, the thickness of the tin dioxide nanosheet can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, or the thickness of the tin dioxide nanosheet can be between any two of the above thicknesses.

[0070] As an example of this embodiment, the maximum radial dimension of the tin dioxide nanosheet is 1 μm to 20 μm. For example, the maximum radial dimension of the tin dioxide nanosheet is 1 μm, 2 μm, 3 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 20 μm, or the maximum radial dimension of the tin dioxide nanosheet may be between any two of the above dimensions.

[0071] In conventional technology, tin dioxide nanoparticles are usually used as gas-sensitive materials. In the present disclosure, tin dioxide nanosheets are selected because the surface of tin dioxide nanosheets is larger, and more adsorption sites for nitrogen dioxide can be generated during the treatment of nitrogen-containing plasma, so that the response value to nitrogen dioxide gas is significantly improved. In addition, the adsorption effect of tin dioxide nanosheets on other gases is relatively poor. The above two factors work together to improve the selectivity of the sensor for nitrogen dioxide gas.

[0072] Step S2, using nitrogen-containing plasma to perform surface treatment on the tin dioxide nanosheets.

[0073] In this embodiment, the tin dioxide nanosheets can be placed in a plasma chamber, a nitrogen-containing gas is introduced into the plasma chamber and a nitrogen-containing plasma is generated, and the tin dioxide nanosheets are surface treated by the nitrogen-containing plasma. Further, the duration of the surface treatment is 10s~1800s. When the duration of the surface treatment is short, it is difficult to form enough oxygen vacancy defects on the surface of the tin dioxide nanosheets, and it has no significant effect on the response value of nitrogen dioxide gas. When the duration of the surface treatment is long, there are too many oxygen vacancy defects on the surface of the tin dioxide nanosheets, and the resistance of the tin dioxide nanosheets will be significantly reduced, which will also cause its response value to nitrogen dioxide gas to be significantly reduced or even difficult to detect.

[0074] It is understood that the plasma chamber refers to a chamber capable of generating plasma. As an example of this embodiment, the plasma chamber may be a chamber of a plasma treatment apparatus. In other examples, the plasma chamber may also be other chambers capable of generating plasma.

[0075] As an example of this embodiment, before the surface treatment, the tin dioxide nanosheets may be spread on the substrate to avoid the accumulation of the tin dioxide nanosheets and ensure that the surfaces of the tin dioxide nanosheets can be treated by the nitrogen-containing plasma.

[0076] As a further example of this embodiment, the step of laying the tin dioxide nanosheets on the substrate includes: dispersing the tin dioxide nanosheets in a solvent to form a dispersion, applying the dispersion on the substrate and performing a vacuum drying process so that the tin dioxide nanosheets can be laid on the substrate. The solvent may include one or more of water, ethanol and ethylene glycol. The ratio of water, ethanol and ethylene glycol can be adjusted according to actual needs.

[0077] As a further example of this embodiment, the mass concentration of the tin dioxide nanosheets in the dispersion can be 1 mg / mL to 10 mg / mL. When dispersing the tin dioxide nanosheets in the solvent, ultrasonic treatment can be used to assist dispersion, the ultrasonic frequency of the ultrasonic treatment is 50 kHz to 100 kHz, and the ultrasonic treatment time is 10 min to 30 min.

[0078] As a further example of this embodiment, the temperature of the vacuum drying process is 50° C. to 80° C., and the time of the vacuum drying process is 1 hour to 2 hours. After the vacuum drying process, the tin dioxide nanosheets can be adsorbed and fixed on the surface of the substrate.

[0079] As an example of this embodiment, the nitrogen-containing gas is selected from nitrogen. Compared with other nitrogen compound gases, nitrogen contains only nitrogen atoms. Using nitrogen as the nitrogen-containing gas can form oxygen vacancy defects without introducing impurity atoms, thereby ensuring the purity of the tin dioxide material.

[0080] As an example of this embodiment, the gas flow rate of the nitrogen-containing gas is 50 sccm to 300 sccm. For example, the gas flow rate of the nitrogen-containing gas can be 50 sccm, 70 sccm, 100 sccm, 120 sccm, 150 sccm, 180 sccm, 200 sccm, 250 sccm, 300 sccm, or the gas flow rate of the nitrogen-containing gas can also be between any two of the above flow rates. The use of the nitrogen-containing gas at the above flow rate is conducive to forming a plasma with a relatively suitable density, ensuring that the surface of the tin dioxide nanosheets can be fully treated.

[0081] As an example of this embodiment, the power of the power supply for generating the nitrogen-containing plasma is 120 W to 200 W. For example, the power of the power supply for generating the nitrogen-containing plasma is 120 W, 130 W, 140 W, 150 W, 160 W, 170 W, 180 W, 200 W, or the power of the power supply may be between any two of the above powers.

[0082] As an example of this embodiment, the duration of the surface treatment is 120s to 150s. Compared with other times, when the duration of the surface treatment is 120s to 150s, the response value of the tin dioxide nanosheets to nitrogen dioxide gas can be greatly improved. Further, the duration of the surface treatment is 120s, 125s, 130s, 135s, 140s, 145s, 150s, or the duration of the surface treatment can also be between any two of the above times.

[0083] It can be understood that after the above steps S1 to S2, tin dioxide nanosheets treated with nitrogen-containing plasma can be formed, and the tin dioxide nanosheets can be used as tin dioxide gas-sensitive materials.

[0084] Furthermore, the present disclosure also provides a tin dioxide gas-sensitive material, which is prepared by the preparation method of the tin dioxide gas-sensitive material in the above embodiment.

[0085] The present disclosure also provides a nitrogen dioxide sensor, which includes a gas-sensitive coating. The material of the gas-sensitive coating includes a tin dioxide gas-sensitive material. The tin dioxide gas-sensitive material is prepared by the preparation method of the tin dioxide gas-sensitive material in the above embodiment.

[0086] The present disclosure also provides a method for preparing a nitrogen dioxide sensor, which comprises the following steps:

[0087] The tin dioxide gas-sensitive material is prepared according to the preparation method of the tin dioxide gas-sensitive material in the above embodiment. The tin dioxide gas-sensitive material is dispersed in a dispersant to form a dispersion system. And the dispersion system is coated on a sensor substrate and vacuum dried to form a gas-sensitive coating.

[0088] As an example of this embodiment, the dispersant may include one or two of water, ethanol and ethylene glycol, wherein the ratio of water, ethanol and ethylene glycol can be adjusted according to actual needs.

[0089] As an example of this embodiment, the mass concentration of the tin dioxide gas-sensitive material in the dispersion system can be 1 mg / mL to 10 mg / mL. When dispersing the tin dioxide gas-sensitive material in the dispersant, ultrasonic treatment can be used to assist dispersion, the ultrasonic frequency of the ultrasonic treatment is 50 kHz to 100 kHz, and the ultrasonic treatment time is 10 min to 30 min.

[0090] As an example of this embodiment, the temperature of the vacuum drying process is 50° C. to 80° C., and the time of the vacuum drying process is 1 hour to 2 hours. After the vacuum drying process, the tin dioxide gas-sensitive material can be adsorbed and fixed on the surface of the sensor substrate.

[0091] As an example of this embodiment, the sensor substrate may be a common commercial ceramic tube gas-sensitive test device, or may be other devices known in the prior art that can be used to carry a gas-sensitive coating.

[0092] The present application is further described in detail below in conjunction with several specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0093] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0094] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used without specifying the manufacturer are all conventional products that can be obtained commercially.

[0095] Example 1

[0096] 0.376g of glycine was dispersed in a mixed solvent consisting of 16mL of deionized water and 84mL of ethylene glycol, and 0.366mL of concentrated hydrochloric acid was added to the mixed solvent and stirred evenly, then 200mg of graphene oxide was added to the mixed solvent, and ultrasonic treatment was performed for 30min to mix evenly, then 430mg of tin tetrachloride pentahydrate was added to the mixed solvent, and ultrasonic treatment was continued for 30min to mix evenly to obtain a mixed precursor solution. The mixed precursor solution was hydrolyzed under 70°C oil bath conditions for 4h. Finally, the above product was repeatedly centrifuged and washed with deionized water and collected to obtain a composite precursor material containing tin dioxide and graphene materials. After freeze-drying, the composite precursor material was calcined at 650°C in a muffle furnace for 2 hours to obtain tin dioxide nanosheets.

[0097] 5 mg of tin dioxide nanosheets were dispersed in 1 mL of ethanol, coated on a glass sheet, transferred to a vacuum drying oven, and vacuum dried at 60°C for 1 hour. Then, the nanosheets were transferred to a plasma treatment instrument, 100 sccm of high-purity nitrogen was introduced, the power supply was set to 160 W, and the treatment was continued for 150 seconds to obtain a tin dioxide gas-sensitive material.

[0098] The tin dioxide gas-sensitive material was dispersed in 1 mL of ethanol to form a dispersed system, and then the dispersed system was coated on the surface of a commercial ceramic tube device, transferred to a vacuum drying oven, and vacuum dried at 60°C for 1 hour to form a nitrogen dioxide gas sensor that can be used and measured.

[0099] Example 2

[0100] The only difference between Example 2 and Example 1 is that when nitrogen-containing plasma is used for surface treatment, the duration is 120 seconds.

[0101] Example 3

[0102] The only difference between Example 3 and Example 1 is that when nitrogen-containing plasma is used for surface treatment, the duration is 90 seconds.

[0103] Example 4

[0104] The only difference between Example 4 and Example 1 is that when nitrogen-containing plasma is used for surface treatment, the duration is 180 seconds.

[0105] Comparative Example 1

[0106] The only difference between Comparative Example 1 and Example 1 is that the surface of the tin dioxide nanosheets is not treated by nitrogen-containing plasma.

[0107] Experiment 1: The surface structure of the tin dioxide nanosheets prepared in Example 1 was observed using a scanning electron microscope. The obtained surface morphology can be seen in Figure 2 .

[0108] Reference Figure 2 As shown, it can be clearly observed that the tin dioxide is in the form of nanosheets, the maximum radial size of the tin dioxide nanosheets does not exceed 20 μm, and there is stacking between the tin dioxide nanosheets but no obvious agglomeration occurs.

[0109] Experiment 2: X-ray diffraction test was performed on the surface treated SnO2 nanosheets in Example 1. The X-ray diffraction pattern can be seen at Figure 3 .

[0110] Reference Figure 3 As shown in the figure, after the tin dioxide nanosheets were treated with nitrogen plasma, their diffraction peaks still fully matched those of the tin dioxide standard card (PDF#41-1445), and the tin dioxide nanosheets still had good crystal purity and crystallinity. This shows that the nitrogen plasma treatment does not significantly destroy or affect the crystal structure of the material.

[0111] Experiment 3: Electron paramagnetic resonance (EPR) tests were performed on the SnO2 nanosheets that were not surface treated and those that were surface treated in Example 1. The test results can be found in Figure 4 .

[0112] Reference Figure 4As shown, compared with the tin dioxide nanosheets that have not been surface treated, the EPR signal intensity at the g factor of 2.003 of the surface treated tin dioxide nanosheets has been significantly improved, indicating that there are more unpaired electrons in the surface treated tin dioxide nanosheets, which further proves that the surface treatment with nitrogen plasma introduces abundant oxygen vacancies into the tin dioxide nanosheets.

[0113] Test 4: The gas sensors prepared in Examples 1 to 4 and Comparative Example 1 were placed in an air environment at 80°C, and nitrogen dioxide at a concentration of 50 ppb was introduced during the test. The response values ​​of the examples and comparative examples were tested. The results can be seen in Figure 5 . Figure 5 The left figure in is the response curve diagram of Example 1, Figure 5 The right figure in the figure is the response value of each embodiment and comparative example. The response value in this article is defined as the resistance value of the sensor in air / the resistance value of the sensor in the test gas atmosphere.

[0114] Reference Figure 5 As shown in the left figure, during the test, the resistance value of the gas sensor of Example 1 remained stable in the air environment. When nitrogen dioxide was introduced, the response value began to rise rapidly and reached a maximum value of 2.72. Then, after the nitrogen dioxide was stopped and air was introduced, the response value gradually decreased to 1.

[0115] Reference Figure 5 As shown in the right figure, the tin dioxide nanosheets of comparative example 1 have not been surface treated, and its response value is only 1.39. The response values ​​of Examples 1 to 4 are significantly higher than those of comparative example 1, indicating that the use of nitrogen-containing plasma to treat the tin dioxide nanosheets in the present disclosure can indeed improve its response value to nitrogen dioxide. Further, compared with comparative example 1, the response values ​​of Examples 3 and 4 are actually only increased by 0.06 and 0.3, respectively, while the response values ​​of Examples 1 and 2 are increased by 1.1 and 1.33, respectively. That is to say, the improvement of Examples 1 and 2 is significantly higher than that of Examples 3 and 4, which indicates that when the duration of the surface treatment is 120s to 150s, the response value of the tin dioxide gas-sensitive material can be greatly improved.

[0116] Experiment 5: The gas sensor prepared in Example 1 was placed in an air environment at 80°C, and nitrogen dioxide with concentrations ranging from 0.5 ppb to 50 ppb was introduced in sequence to test its corresponding response values. The concentration gradient response curve of nitrogen dioxide can be seen in Figure 6 .

[0117] Reference Figure 6As shown, it can be found that the gas sensor prepared in Example 1 can still observe a complete response recovery curve when the concentration is as low as 0.5 ppb, and its response value is about 1.005. As the concentration gradually increases, the response value also begins to increase significantly.

[0118] Test 6: The gas sensor prepared in Example 1 was placed in an air environment at 80°C, and 50 ppb nitrogen dioxide, 1 ppm carbon monoxide, 1 ppm sulfur dioxide, 50 ppm ammonia, 50 ppm hydrogen and 50 ppm methane were introduced respectively, and its response values ​​were tested respectively. The test results can be seen in Figure 7 .

[0119] Reference Figure 7 As shown, during the test, when the gas concentration of nitrogen dioxide was significantly lower than that of other gases, the response value of the gas sensor of Example 1 to nitrogen dioxide was significantly higher than that to other gases, which indicates that the gas sensor has extremely excellent gas selectivity for nitrogen dioxide.

[0120] Experiment 7: The gas sensor prepared in Example 1 was placed for 5 weeks, and the test as in Experiment 4 was performed every other week. The response value obtained in each test was recorded. The results can be seen in Figure 8 .

[0121] Reference Figure 8 As shown in the figure, the response value of the gas sensor to nitrogen dioxide showed a slow downward trend during the placement process. However, even after 5 weeks of placement, the response value of the gas sensor only decayed by 14%, indicating that the gas sensor has good long-term stability.

[0122] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing a tin dioxide gas-sensitive material, characterized in that: The steps include: dispersing a graphene material and a tin precursor in an acidic aqueous solution to obtain a mixed precursor solution; The mixed precursor solution is heated in a water bath to obtain a composite precursor material containing tin dioxide and graphene material, the water bath heating temperature is 60° C. to 80° C., and the time is 3 h to 6 h; The composite precursor material is calcined to obtain tin dioxide nanosheets, the calcination temperature is 600° C. to 800° C., and the time is 2 h to 4 h; Placing the tin dioxide nanosheets in a plasma chamber, introducing nitrogen gas into the plasma chamber to generate nitrogen plasma, and performing surface treatment on the tin dioxide nanosheets by the nitrogen plasma to obtain the tin dioxide gas-sensitive material; The flow rate of the nitrogen gas is 50 sccm to 300 sccm, the power of the power supply for generating the nitrogen plasma is 150 W to 200 W, and the duration of the surface treatment is 10 s to 300 s.

2. The method for preparing a tin dioxide gas-sensitive material according to claim 1, characterized in that: The flow rate of the nitrogen gas is 80 sccm-120 sccm.

3. The method for preparing the tin dioxide gas-sensitive material according to claim 2, characterized in that: The power of the power supply for generating the nitrogen plasma is 150W~170W.

4. The method for preparing a tin dioxide gas-sensitive material according to claim 1, characterized in that: The duration of the surface treatment is 120s to 150s.

5. The method for preparing a tin dioxide gas-sensitive material according to any one of claims 1 to 4, characterized in that: The thickness of the tin dioxide nanosheet is 1 nm to 5 nm.

6. The method for preparing a tin dioxide gas-sensitive material according to any one of claims 1 to 4, characterized in that: The maximum radial dimension of the tin dioxide nanosheets is 1 μm to 20 μm.

7. The method for preparing a tin dioxide gas-sensitive material according to claim 1, characterized in that: The reaction system after the mixed precursor liquid is heated in a water bath is centrifuged to separate the composite precursor material in the reaction system.

8. The method for preparing a tin dioxide gas-sensitive material according to claim 1, characterized in that: Before the composite precursor material is calcined, the composite precursor material is frozen and freeze-dried.

9. A nitrogen dioxide sensor, characterized in that: The nitrogen dioxide sensor includes a gas-sensitive coating, the material of the gas-sensitive coating includes a tin dioxide gas-sensitive material, and the tin dioxide gas-sensitive material is prepared by the method for preparing a tin dioxide gas-sensitive material according to any one of claims 1 to 8.

10. The method for preparing a nitrogen dioxide sensor according to claim 9, characterized in that: The steps include: The tin dioxide gas-sensitive material is prepared by the method for preparing the tin dioxide gas-sensitive material according to any one of claims 1 to 8; Dispersing the tin dioxide gas-sensitive material in a dispersant to form a dispersed system; The dispersed system is coated on a sensor substrate and subjected to vacuum drying treatment to form the gas-sensitive coating.

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