A UV-assisted nitrogen dioxide gas sensor, its preparation method and application

Abstract

This invention discloses a UV-assisted nitrogen dioxide gas sensor, its preparation method, and its application, belonging to the field of gas sensor technology. It includes a metal electrode and an In / ZnO-g-C3N4 nanocomposite material made of g-C3N4 nanosheets and In / ZnO grown on the surface of the g-C3N4 nanosheets. g-C3N4 prepared by a combination of sintering and ultrasonication is mixed uniformly with indium nitrate and zinc nitrate, followed by a hydrothermal reaction to obtain the In / ZnO-g-C3N4 nanocomposite material. This material is then coated onto the surface of the metal electrode and annealed to obtain the UV-assisted nitrogen dioxide gas sensor. The prepared UV-assisted nitrogen dioxide gas sensor overcomes the high operating temperature drawback of most gas sensing materials, detecting NO2 at room temperature. It exhibits stable NO2 detection, a completely reversible sensing process, and a wide operating temperature range. It demonstrates excellent gas sensing performance and high specificity for low concentrations of NO2, with a short response time and ultra-fast recovery. It also exhibits good repeatability and cyclic performance for different concentrations of NO2, and possesses excellent selectivity and anti-interference capabilities.

Description

Technical Field

[0001] This invention belongs to the field of gas sensor technology, specifically relating to a UV-assisted nitrogen dioxide gas sensor, its preparation method, and its application. Background Technology

[0002] NO2, a typical air pollutant, mainly originates from industrial waste gas and vehicle exhaust emissions. NO2 not only forms highly destructive acid rain but also poses significant health risks to the human respiratory and cardiovascular systems, causing conditions such as asthma and myocardial infarction. Therefore, developing a low-cost gas sensing technology capable of detecting NO2 at room temperature with rapid response and ultra-fast recovery is of great importance.

[0003] Currently, the most common gas sensors used for NO2 detection are resistive gas sensors based on semiconductor metal oxide materials. The biggest drawback of these materials is that they can only operate at high temperatures, which greatly limits their practical applications while causing power consumption. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a UV-assisted nitrogen dioxide gas sensor, its preparation method and application, and solve the problems of high operating temperature, high power consumption, slow desorption at room temperature and low response value for low concentration of NO2 gas in the gas sensors used for NO2 detection in the prior art.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] This invention discloses a UV-assisted nitrogen dioxide gas sensor, which includes a gas sensing material and a metal electrode;

[0007] The gas sensing material is an In / ZnO / g-C3N4 nanocomposite material, which is made of g-C3N4 nanosheets and In / ZnO grown on the surface of g-C3N4 nanosheets;

[0008] The gas sensing material is coated on the surface of the metal electrode.

[0009] Ideally, with UV assistance, NO2 gas at a concentration of 500–1 ppb can be detected at room temperature.

[0010] Ideally, the metal electrode is a ceramic tube electrode.

[0011] This invention also discloses a method for preparing the above-mentioned UV-assisted nitrogen dioxide gas sensor, comprising the following steps:

[0012] S1. First, melamine is sintered at medium temperature to obtain bulk C3N4. Then, bulk C3N4 is placed in water and ultrasonically dispersed to obtain g-C3N4. Then, indium nitrate, zinc nitrate and g-C3N4 are mixed evenly and subjected to hydrothermal reaction to obtain In / ZnO-g / C3N4 nanocomposite material.

[0013] S2. After coating the In / ZnO / g-C3N4 nanocomposite material obtained in step S1 onto the surface of the metal electrode, perform annealing treatment to obtain a UV-assisted NO2 gas sensor.

[0014] Optimally, in step S1, the mass ratio of indium nitrate: zinc nitrate: g-C3N4 is (0.02~0.05):(1.00~1.40):(0.03~0.06).

[0015] Ideally, in step S1, the sintering temperature is 400–800°C; the ultrasonic dispersion time is 0.3–1 h; and the ultrasonic power is 220–280 W.

[0016] Ideally, in step S1, the temperature of the hydrothermal reaction is 150–200°C, and the time is 12–20 h.

[0017] Ideally, in step S2, the annealing temperature is 300–600°C.

[0018] Ideally, in step S2, the annealing process takes 1 to 3 minutes.

[0019] The present invention also discloses the application of the above-mentioned UV-assisted nitrogen dioxide gas sensor in the detection of NO2 gas at room temperature.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention discloses a UV-assisted nitrogen dioxide gas sensor, comprising a gas sensing material and a metal electrode. The gas sensing material is made of g-C3N4 nanosheets and In / ZnO grown on the surface of the g-C3N4 nanosheets. The conductivity of ZnO is significantly improved after doping with In. When combined with g-C3N4, which has photoactivated properties, the resulting In / ZnO / g-C3N4 exhibits a lower and more stable resistivity at room temperature. This is because In has a higher electronegativity (1.7) than Zn (1.6), making it less prone to oxide formation and more likely to exist in the crystal lattice as substitution sites, thus achieving effective doping. The low and stable resistivity facilitates rapid charge transfer, a crucial factor in overcoming the high-temperature operation of the gas sensor. The growth marks formed by In / ZnO on the g-C3N4 surface make the surface rougher, further increasing the specific surface area of ​​the two-dimensional g-C3N4 nanosheets. This higher specific surface area enriches the active sites on the surface, facilitating NO2 adsorption and increasing the response value. Furthermore, the heterostructure formed by In / ZnO and g-C3N4, which possess UV-activated properties, achieves rapid cleaning of adsorbed NO2 under intermittent UV operation (UV excitation before and after gas adsorption, respectively). This is also an important characteristic of its superior gas-sensing properties. Therefore, the In / ZnO / g-C3N4 nanocomposite material prepared in this application overcomes the drawback of high operating temperature of most gas sensing materials, enabling NO2 detection at room temperature with low power consumption. It also exhibits good stability and repeatability in NO2 detection, as well as a wide operating temperature range. The In / ZnO-g / C3N4 nanocomposite material coated on the metal electrode surface gives the UV-assisted NO2 gas sensor good chemical stability, a completely reversible sensing process, and enables ultrafast desorption at room temperature under UV assistance, while also exhibiting a high response value for low-concentration NO2 gas detection.

[0022] Furthermore, with UV assistance, the response value to NO2 gas has been greatly improved, enabling the detection of NO2 concentrations of 500–1 ppb at room temperature. It exhibits excellent gas-sensing performance and high specificity for low concentrations of NO2, with a short response time and ultra-fast recovery.

[0023] Furthermore, the metal electrode is a ceramic tube electrode, which has good contact with the gas-sensitive sensing material. As a side-heated electrode, the ceramic tube electrode adopts a side-heated middle layer heating method, which has the function of rapid heating (high temperature) annealing, and the process of preparing the gas sensor is simple.

[0024] This invention also discloses a method for preparing the aforementioned UV-assisted nitrogen dioxide gas sensor. First, two-dimensional g-C3N4 nanomaterials are prepared using a simple two-step method of sintering and ultrasonic exfoliation. Two-dimensional nanomaterials have the advantage of a large specific surface area, and using two-dimensional g-C3N4 as a template to prepare two-dimensional nanocomposite materials is an important strategy for optimizing sensing performance. Second, In is doped with ZnO and grown on the surface of two-dimensional g-C3N4 nanosheets to form an In / ZnO-g-C3N4 nanocomposite material. Due to the effective doping of In in the ZnO lattice and its growth on the surface of two-dimensional g-C3N4, this strategy further increases the specific surface area of ​​two-dimensional g-C3N4. Simultaneously, the composite In / ZnO / g-C3N4 nanocomposite material exhibits significantly excellent gas-sensing performance under UV excitation, overcoming the high operating temperature limitation of most gas sensing materials. This provides more options and greater practicality in real-world applications. Third, in the fabrication of the NO2 gas sensor, this invention employs a rapid annealing process to prepare the In / ZnO-g-C3N4 nanocomposite material. Rapid high-temperature annealing helps to preserve its microstructure and removes water of crystallization and organic groups from the gas-sensitive material, thus extending its lifespan. The entire fabrication process is simple, energy-efficient, and inexpensive, meeting the needs of commercial NO2 sensors and providing a new approach for the design of room-temperature NO2 gas sensors.

[0025] The present invention also discloses the application of the above-mentioned UV-assisted nitrogen dioxide gas sensor in the detection of NO2 gas at room temperature. When applied, it has good cycling performance for different concentrations of NO2, and has good selectivity and anti-interference performance for NO2. In practical applications, it can demonstrate more choices and stronger practicality. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the sensor of the present invention in the operation of a self-made gas sensing test;

[0027] Figure 2 This is a 50Kx SEM image of the In / ZnO / g-C3N4 nanocomposite material prepared in Example 1 of this invention;

[0028] Figure 3 The response curves of the In / ZnO / g-C3N4 nanocomposite material prepared in Example 1 of the present invention to different concentrations of NO2 when used as a sensor device;

[0029] Figure 4 The In / ZnO / g-C3N4 nanocomposite material prepared in Example 1 of this invention is used as a sensor device, and the test curves of NO2 cycle stability at 500 ppb and 1 ppb are shown.

[0030] Figure 5 Comparison of response values ​​to NO2 and interfering substances when the In / ZnO / g-C3N4 nanocomposite material prepared in Example 1 of this invention is used as a sensor. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0033] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0034] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0035] In this invention, unless otherwise specified, the components involved or their preferred components can be combined to form new technical solutions.

[0036] In this invention, unless otherwise specified, the numerical range "a~b" represents an abbreviation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" means that all real numbers between "6~22" have been listed in this document, and "6~22" is simply an abbreviation of these numerical combinations.

[0037] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0038] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0039] In this invention, unless otherwise stated, the various reactions or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0040] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0041] This invention discloses a UV-assisted nitrogen dioxide gas sensor, wherein the NO2 gas sensor comprises a gas sensing material and a metal electrode; the gas sensing material is an In / ZnO / g-C3N4 nanocomposite material, which is made of g-C3N4 nanosheets and In / ZnO grown on the surface of g-C3N4 nanosheets; the gas sensing material is coated on the surface of the metal electrode.

[0042] With UV assistance, NO2 gas at a concentration of 500–1 ppb can be detected at room temperature.

[0043] Metal electrodes are limited to ceramic tube electrodes.

[0044] A method for fabricating a UV-assisted nitrogen dioxide gas sensor includes the following steps:

[0045] S1. First, melamine is sintered at medium temperature to obtain bulk C3N4. Then, bulk C3N4 is placed in water and ultrasonically dispersed to obtain g-C3N4. Then, indium nitrate, zinc nitrate and g-C3N4 are mixed evenly and subjected to hydrothermal reaction to obtain In / ZnO / g-C3N4 nanocomposite material.

[0046] Preferably, the mass ratio of indium nitrate: zinc nitrate: g-C3N4 is (0.02~0.05):(1.00~1.40):(0.03~0.06).

[0047] Preferably, the sintering temperature is 400–800℃; the ultrasonic dispersion time is 0.3–1h; and the ultrasonic power is 220–280W.

[0048] Preferably, the hydrothermal reaction temperature is 150–200℃ and the time is 12–20 h.

[0049] Preferably, the annealing temperature is 300–600°C.

[0050] S2. After coating the In / ZnO / g-C3N4 nanocomposite material obtained in step S1 onto the surface of the metal electrode, annealing is performed immediately to obtain a UV-assisted NO2 gas sensor.

[0051] Preferably, the annealing time is 1 to 3 minutes.

[0052] Another technical solution of the present invention: the application of a UV-assisted nitrogen dioxide gas sensor in the detection of NO2 gas at room temperature.

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0054] Unless otherwise specified, the raw materials or devices used in the embodiments can be purchased from conventional commercial channels or obtained through existing technical methods. The ceramic tube electrode used in this invention is a commercially available Al2O3 ceramic tube electrode and a nickel-chromium heating wire; the ceramic tube electrode includes: one pair of gold electrodes and four platinum electrode wires; the distance between the two gold electrodes is 3 mm.

[0055] Example 1

[0056] 1) Preparation of g-C3N4 nanosheets

[0057] 4g of melamine was placed in a crucible and reacted at 600℃ for 3h. After cooling to room temperature, a yellow solid C3N4 was obtained. The block-shaped C3N4 was ground in a mortar, and 0.92g was weighed and placed in a beaker (100mL) containing 60mL of deionized water. The solution was stirred for 10min and then sonicated for 30min (250W, 40KHz) to obtain a g-C3N4 suspension with a concentration of 0.17mol / L. The thickness of the g-C3N4 nanosheets was about 7nm.

[0058] 2) Preparation of In / ZnO / g-C3N4 nanocomposite materials

[0059] Mix 0.019 g of indium nitrate and 1.19 g of zinc nitrate (4 mmol) in a mass ratio of 1% with 1.40 g of C6H 12 10 mmol of N4 was added sequentially to the polytetrafluoroethylene liner, followed by 5 mL of the suspension prepared in step 1) and 25 mL of distilled water. The entire reaction system was stirred at room temperature for 10 min. Then, the liner was placed in the reactor and hydrothermally reacted at 180 °C for 12 h. After the hydrothermal reaction was completed, the hydrothermal product was centrifuged at 5000 r / min for 3 min, washed with distilled water 3 to 5 times, and the centrifuged precipitate was dried in an oven at 60 °C to obtain the In / ZnO / g-C3N4 nanocomposite material.

[0060] 3) Fabrication of NO2 gas sensor

[0061] The In / ZnO / g-C3N4 nanomaterials prepared in step 2) were mixed with anhydrous ethanol to form a slurry of 10 mg / mL. The slurry was ground evenly in a mortar and pestle. An appropriate amount of the slurry was taken with a syringe and evenly coated on the surface of the ceramic tube welded to the test base to form a 1 mm film. The device containing the coating was dried in a 60°C oven. Then the dried device was directly connected to the test platform and rapidly heated by a nickel-chromium heating wire. It was aged at 400°C for 1-3 minutes. The resulting sensor can detect NO2 at room temperature.

[0062] See Figure 1 The diagram shows the working process of the sensor of the present invention in a self-made gas sensing test. The gas preparation process is as follows: take a certain volume of commercially purchased NO2 with a concentration of 1000ppm, mix it with air in a sealed container of a certain volume, prepare NO2 test gases with different concentrations and different humidity, and then use the NO2 sensor prepared above to detect it in the sealed container.

[0063] See Figure 2 The image shows a 50Kx SEM image of the In / ZnO / g-C3N4 nanocomposite material prepared in Example 1 of this invention. The growth of In / ZnO on the g-C3N4 nanosheets can be clearly seen from the image.

[0064] See Figure 3 The figure shows the response value of the In / ZnO / g-C3N4 nanocomposite material prepared in Example 1 of this invention as a sensor device to different concentrations of NO2. As can be seen from the figure, under UV assistance, its response value to low concentrations of NO2 is around 100, the response time is 70-100s, and the ultrafast recovery time is 1s.

[0065] See Figure 4 The figure shows the cycle stability test curves of the In / ZnO / g-C3N4 nanocomposite material prepared in Example 1 of this invention when used as a sensor device for 500ppb and 1ppb NO2. As can be seen from the figure, it has good repeatability and cycle performance for different concentrations of NO2.

[0066] See Figure 5 The figure shows a comparison of the response values ​​of the In / ZnO / g-C3N4 nanocomposite material prepared in Example 1 of this invention to NO2 and interfering gases. The interfering gases include NH3, ethanol, acetone, xylene, and formaldehyde. As can be seen from the figure, at room temperature, the sensor exhibits good selectivity and anti-interference performance for NO2. The NO2 sensing performance of other embodiments is similar to that of Example 1.

[0067] Example 2

[0068] 1) Preparation of g-C3N4 nanosheets

[0069] 2g of melamine was placed in a crucible and reacted at 550℃ for 3h. After cooling to room temperature, a yellow solid C3N4 was obtained. The block-shaped C3N4 was ground in a mortar, and 0.46g was weighed and placed in a beaker (100mL) containing 60mL of deionized water. The solution was stirred for 10min and then sonicated for 30min (250W, 40KHz) to obtain a g-C3N4 suspension with a concentration of 0.08mol / L. The thickness of the g-C3N4 nanosheets was about 3nm.

[0070] 2) Preparation of In / ZnO / g-C3N4 nanocomposite materials

[0071] Mix 0.039 g of indium nitrate and 1.19 g of zinc nitrate (4 mmol) in a mass ratio of 2% with 1.68 g of C6H 12 12 mmol of N4 was added sequentially to the polytetrafluoroethylene liner, followed by 6 mL of the suspension prepared in step 1) and 25 mL of distilled water. The entire reaction system was stirred at room temperature for 10 min. Then, the liner was placed in a reaction vessel and hydrothermally reacted at 170 °C for 18 h. After the hydrothermal reaction was completed, the hydrothermal product was centrifuged at 5000 r / min for 3 min, washed with distilled water 3 to 5 times, and the centrifuged precipitate was dried in a 60 °C oven to obtain the In / ZnO / g-C3N4 nanocomposite material.

[0072] 3) Fabrication of NO2 gas sensor

[0073] The In / ZnO / g-C3N4 nanomaterials prepared in step 2) were prepared into a slurry of 10 mg / mL using anhydrous ethanol and ground evenly in a mortar. An appropriate amount of the slurry was taken with a coating applicator and evenly coated onto the surface of the ceramic tube welded to the test base to form a 1 mm film. The device containing the coating was dried in a 60°C oven. Then, the dried device was directly connected to the test platform and rapidly heated by a nickel-chromium heating wire. It was aged at 500°C for 1–3 min. The resulting sensor can detect NO2 at room temperature.

[0074] Example 3

[0075] 1) Preparation of g-C3N4 nanosheets

[0076] 3g of melamine was placed in a crucible and reacted at 500℃ for 5h. After cooling to room temperature, a yellow solid C3N4 was obtained. The block-shaped C3N4 was ground in a mortar, and 0.46g was weighed and placed in a beaker (100mL) containing 50mL of deionized water. The solution was stirred for 10min and then sonicated for 30min (250W, 40KHz) to obtain a g-C3N4 suspension with a concentration of 0.1mol / L. The thickness of the g-C3N4 nanosheets was about 8nm.

[0077] 2) Preparation of In / ZnO / g-C3N4 nanocomposite materials

[0078] 0.078 g of indium nitrate and 1.19 g of zinc nitrate (4 mmol by mass) were mixed with 1.96 g of C6H 12 14 mmol of N4 was added sequentially to the polytetrafluoroethylene liner, followed by 4 mL of the suspension prepared in step 1) and 25 mL of distilled water. The entire reaction system was stirred at room temperature for 10 min. Then, the liner was placed in the reactor and hydrothermally reacted at 170 °C for 14 h. After the hydrothermal reaction was completed, the hydrothermal product was centrifuged at 5000 r / min for 3 min, washed with distilled water 3 to 5 times, and the centrifuged precipitate was dried in an oven at 60 °C to obtain the In / ZnO / g-C3N4 nanocomposite material.

[0079] 3) Fabrication of NO2 gas sensor

[0080] The In / ZnO / g-C3N4 nanomaterials prepared in step 2) were prepared into a slurry with anhydrous ethanol at a concentration of 8 mg / mL and ground evenly in a mortar. An appropriate amount of the slurry was taken with a coating applicator and evenly coated onto the surface of the ceramic tube welded to the test base to form a 2 mm film. The device containing the coating was dried in a 60°C oven. Then, the dried device was directly connected to the test platform and rapidly heated by a nickel-chromium heating wire. It was aged at 400°C for 1–3 min. The resulting sensor can detect NO2 at room temperature.

[0081] Example 4

[0082] 1) Preparation of g-C3N4 nanosheets

[0083] 3g of melamine was placed in a crucible and reacted at 550℃ for 5h. After cooling to room temperature, a yellow solid C3N4 was obtained. The block-shaped C3N4 was ground in a mortar, and 0.84g was weighed and placed in a beaker (100mL) containing 60mL of deionized water. The solution was stirred for 10min and then sonicated for 30min (250W, 40KHz) to obtain a g-C3N4 suspension with a concentration of 0.1mol / L. The thickness of the g-C3N4 nanosheets was about 6nm.

[0084] 2) Preparation of In / ZnO / g-C3N4 nanocomposite materials

[0085] 0.117 g of indium nitrate and 1.19 g of zinc nitrate (4 mmol) in a mass ratio of 6% were mixed with 1.96 g of C6H 12 14 mmol of N4 was added sequentially to the polytetrafluoroethylene liner, followed by 3 mL of the suspension prepared in step 1) and 25 mL of distilled water. The entire reaction system was stirred at room temperature for 10 min. Then, the liner was placed in the reactor and hydrothermally reacted at 180 °C for 18 h. After the hydrothermal reaction was completed, the hydrothermal product was centrifuged at 5000 r / min for 3 min, washed with distilled water 3 to 5 times, and the centrifuged precipitate was dried in an oven at 60 °C to obtain the In / ZnO / g-C3N4 nanocomposite material.

[0086] 3) Fabrication of NO2 gas sensor

[0087] The In / ZnO / g-C3N4 nanomaterials prepared in step 2) were mixed with anhydrous ethanol to form a slurry of 15 mg / mL and ground evenly in a mortar. An appropriate amount of the slurry was taken with a coating applicator and evenly coated on the surface of the ceramic tube welded to the test base to form a 2 mm film. The device containing the coating was dried in a 60°C oven. Then the dried device was directly connected to the test platform and rapidly heated by a nickel-chromium heating wire. It was aged at 550°C for 1-3 minutes. The resulting sensor can detect NO2 at room temperature.

[0088] Example 5

[0089] 1) Preparation of g-C3N4 nanosheets

[0090] 2g of melamine was placed in a crucible and reacted at 550℃ for 3h. After cooling to room temperature, a yellow solid C3N4 was obtained. The block-shaped C3N4 was ground in a mortar, and 0.46g was weighed and placed in a beaker (100mL) containing 60mL of deionized water. The solution was stirred for 10min and then sonicated for 30min (250W, 40KHz) to obtain a g-C3N4 suspension with a concentration of 0.8mol / L. The thickness of the g-C3N4 nanosheets was about 12nm.

[0091] 2) Preparation of In / ZnO / g-C3N4 nanocomposite materials

[0092] Mix 0.039 g of indium nitrate and 1.19 g of zinc nitrate (4 mmol) in a mass ratio of 2% with 1.68 g of C6H 1212 mmol of N4 was added sequentially to the polytetrafluoroethylene liner, followed by 5 mL of the suspension prepared in step 1) and 25 mL of distilled water. The entire reaction system was stirred at room temperature for 10 min. Then, the liner was placed in a reaction vessel and hydrothermally reacted at 200 °C for 12 h. After the hydrothermal reaction was completed, the hydrothermal product was centrifuged at 5000 r / min for 3 min, washed with distilled water 3 to 5 times, and the centrifuged precipitate was dried in an oven at 60 °C to obtain the In / ZnO / g-C3N4 nanocomposite material.

[0093] 3) Fabrication of NO2 gas sensor

[0094] The In / ZnO / g-C3N4 nanomaterials prepared in step 2) were mixed with anhydrous ethanol to form a slurry of 12 mg / mL and ground evenly in a mortar. An appropriate amount of the slurry was taken with a coating applicator and evenly coated on the surface of the ceramic tube welded to the test base to form a 2 mm film. The device containing the coating was dried in a 60°C oven. Then the dried device was directly connected to the test platform and rapidly heated by a nickel-chromium heating wire. It was aged at 350°C for 1-3 minutes. The resulting sensor can detect NO2 at room temperature.

[0095] The sensor operates at room temperature. The NO2 sensing performance was tested using a constant voltage mode with a resistance of 20V. The gas sensor is compared with the original meter (Keithley 2450 Source). The instrument is connected via wires. The testing process involves recording the resistance of the sensor after it stabilizes in air as R. a Place the sensor in a NO2 test bottle with a specific concentration and humidity. Wait for the resistance change curve to plateau; the resistance at this point is recorded as R. g The gas sensor was removed from the NO2 atmosphere and simultaneously irradiated with UV light to aid in rapid resistance recovery. The test signal in the original table is resistivity, where the response signal is defined as R... g / R a The response time is defined as 90% of the time taken from the baseline resistance to the response plateau; similarly, the recovery time is defined. Based on this, a graph was drawn. Figure 2 Response value versus concentration curve and Figure 3 Cyclic stability at different NO2 concentrations.

[0096] The preparation method provided by this invention enables the fabrication of a low-concentration NO2 gas sensor. We have also demonstrated that this sensor exhibits excellent sensing performance and high specificity for low-concentration NO2 under UV-assisted conditions. Furthermore, the sensing material, composed of metal oxides and two-dimensional g-C3N4, possesses good chemical stability, and the sensing process is completely reversible. This invention offers a simple, low-energy-consumption, and inexpensive preparation and testing method, meeting the needs of commercial NO2 sensors.

[0097] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A UV-assisted nitrogen dioxide gas sensor, characterized in that, The UV-assisted nitrogen dioxide gas sensor includes a gas sensing material and a metal electrode. The gas sensing material is an In / ZnO / g-C3N4 nanocomposite material, which is made of g-C3N4 nanosheets and In / ZnO grown on the surface of g-C3N4 nanosheets; in the In / ZnO, In enters the ZnO lattice in the form of doping to form a solid solution. The gas sensing material is coated on the surface of the metal electrode; With UV assistance, NO2 gas at a concentration of 500~1 ppb can be detected at room temperature; The method for preparing the UV-assisted nitrogen dioxide gas sensor includes the following steps: S1. First, melamine is sintered at medium temperature to obtain bulk C3N4. Then, the bulk C3N4 is ultrasonically dispersed in water to obtain g-C3N4. Then, indium nitrate, zinc nitrate and g-C3N4 are mixed evenly and subjected to hydrothermal reaction to obtain In / ZnO-g / C3N4 nanocomposite material. The mass ratio of indium nitrate:zinc nitrate:g-C3N4 is (0.02~0.05):(1.00~1.40):(0.03~0.06). S2. After coating the In / ZnO / g-C3N4 nanocomposite material obtained in step S1 onto the surface of the metal electrode, perform annealing treatment to obtain a UV-assisted NO2 gas sensor; the annealing treatment time is 1~3 min.

2. The UV-assisted nitrogen dioxide gas sensor according to claim 1, characterized in that, The metal electrode is a ceramic tube electrode.

3. The UV-assisted nitrogen dioxide gas sensor according to claim 1, characterized in that, In step S1, the sintering temperature is 400~800 ℃; the ultrasonic dispersion time is 0.3~1 h; and the ultrasonic power is 220~280 W.

4. The UV-assisted nitrogen dioxide gas sensor according to claim 1, characterized in that, In step S1, the temperature of the hydrothermal reaction is 150~200 ℃; the time is 12~20 h.

5. The UV-assisted nitrogen dioxide gas sensor according to claim 1, characterized in that, In step S2, the annealing temperature is 300~600 ℃.

6. The application of the UV-assisted nitrogen dioxide gas sensor according to any one of claims 1 to 5 in the detection of NO2 gas at room temperature.

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