NO2 gas sensor as well as preparation method and application thereof

Abstract

The invention provides an NO2 gas sensor as well as a preparation method and application thereof, and belongs to the technical field of sensors. The NO2 gas sensor provided by the invention comprises a porous metal material, Cu2O loaded on the surface of the porous metal material and an MOF material loaded on the surface of the Cu2O. According to the invention, the porous metal material is used as the substrate, which not only has good mechanical properties, but also contributes to the transmission of high-pressure pulse airflow; cu2O is used as an NO2 sensing material with excellent performance, so that the NO2 gas sensor is endowed with good NO2 detection capability; the MOF material is used as a gas-sensitive material with excellent performance, so that the roughness of the NO2 gas sensor is increased, the gas-sensitive performance can be further improved, and the sensitivity of the NO2 gas sensor is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensors, and in particular relates to a NO2 gas sensor and a preparation method and application thereof. Background Art

[0002] Nitrogen dioxide (NO2), a typical harmful gas, is widely distributed in industrial waste, automobile exhaust, and chemical production, among other scenarios. It can irritate the respiratory tract and cause symptoms such as coughing and wheezing. Long-term exposure can also lead to decreased lung function, increase the risk of respiratory and cardiovascular diseases, and pose a serious threat to human health. Therefore, accurately detecting NO2 emissions and leaks is crucial for environmental protection, industrial safety, and ensuring the well-being of residents.

[0003] In recent years, new materials have shown great potential in the field of gas sensing. Cuprous oxide (Cu2O), a high-performance semiconductor material with a unique crystal structure and electrical properties, has attracted much attention in the field of gas sensing. It has a certain degree of adsorption and reactivity towards NO2, and can indicate the presence and concentration of NO2 through changes in its own electrical properties. However, cuprous oxide has a low sensitivity when detecting NO2. Therefore, how to modify Cu2O to improve its sensitivity for NO2 gas detection has become a technical challenge that needs to be solved urgently in this field. Summary of the Invention

[0004] The present invention aims to provide a NO2 gas sensor and its preparation method and application. The NO2 gas sensor provided by the present invention has excellent sensitivity.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a NO2 gas sensor, comprising a porous metal material, Cu2O loaded on the surface of the porous metal material, and a MOF material loaded on the surface of the Cu2O.

[0007] Preferably, the pore density of the porous metal material is 20-200 PPI, and the pore diameter of the porous metal material is 0.25-1.27 mm.

[0008] Preferably, the Cu2O is a rod-shaped structure, and the length of the Cu2O is 3 to 5 μm.

[0009] Preferably, the MOF material includes ZIF-8, ZIF-67, HKUST-1 or UIO-66, and the loading amount of the MOF material in Cu2O is ≤35 wt%.

[0010] The present invention also provides a method for preparing the NO2 gas sensor according to the above technical solution, comprising the following steps:

[0011] (1) mixing a porous metal material, a first solvent, an oxidant, and a hydroxide, and performing a precipitation reaction to obtain a porous metal material having copper hydroxide on the surface;

[0012] (2) sintering the porous metal material with copper hydroxide on the surface obtained in step (1) to obtain a porous metal material with Cu2O loaded on the surface;

[0013] (3) The porous metal material with surface-loaded Cu2O obtained in step (2), a metal salt, an organic ligand, and a second solvent are mixed and subjected to a polymerization reaction to obtain a NO2 gas sensor.

[0014] Preferably, the temperature of the precipitation reaction in step (1) is 50-80° C., the time of the precipitation reaction is 4-6 hours, and the pH value of the precipitation reaction is 10-12.

[0015] Preferably, the sintering temperature in step (2) is 500-700° C., and the sintering time is 2.5-4 hours.

[0016] Preferably, the molar ratio of the metal salt to the organic ligand in step (3) is 1:(6-10).

[0017] Preferably, the polymerization reaction temperature in step (3) is 75-95° C., and the polymerization reaction time is 3-6 hours.

[0018] The present invention also provides the use of the NO2 gas sensor described in the above technical solution or the NO2 gas sensor prepared by the preparation method described in the above technical solution in automobile exhaust detection.

[0019] The present invention provides a NO2 gas sensor comprising a porous metal material, Cu2O supported on the surface of the porous metal material, and a MOF material supported on the surface of the Cu2O. By utilizing the porous metal material as a substrate, the present invention not only exhibits excellent mechanical properties but also facilitates the transmission of high-pressure pulsed gas flow. Cu2O, as a high-performance NO2 sensing material, imparts excellent NO2 detection capabilities to the NO2 gas sensor. The MOF material, as a high-performance gas-sensitive material, increases the roughness of the NO2 gas sensor while further enhancing its gas-sensing performance, thereby increasing its sensitivity. Experimental results demonstrate that the NO2 gas sensor provided by the present invention exhibits a significant current signal at concentrations of 0 to 100 ppm and exhibits good stability at various NO2 gas concentrations. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Flowchart for preparing a NO2 gas sensor according to an embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of the signal output module and circuit control module in the NO2 gas monitoring system;

[0022] Figure 3 is a schematic diagram of a signal transmission unit;

[0023] Figure 4 This is a schematic diagram of the NO2 gas monitoring and alarm module;

[0024] Figure 5 This is a SEM image of the NO2 gas sensor prepared in Example 1;

[0025] Figure 6 for Figure 5 Enlarged image in box;

[0026] Figure 7 for Figure 6 Enlarged image in box;

[0027] Figure 8 for Figure 7 Enlarged image in box;

[0028] Figure 9 The current signal of the NO2 gas sensor prepared in Comparative Examples 1 to 5;

[0029] Figure 10 The current signal of the NO2 gas sensor prepared in Comparative Examples 6 to 13;

[0030] Figure 11 The current signal of the NO2 gas sensor prepared in Example 1;

[0031] Figure 12 The response time and recovery time curves of the NO2 gas sensor prepared in Example 1;

[0032] Figure 13 These are the current signals of the NO2 gas sensor prepared in Example 1 when the NO2 concentrations are 0 PPM, 50 PPM, and 500 PPM. DETAILED DESCRIPTION

[0033] The present invention provides a NO2 gas sensor, comprising a porous metal material, Cu2O loaded on the surface of the porous metal material, and a MOF material loaded on the surface of the Cu2O.

[0034] The NO2 gas sensor provided by the present invention comprises a porous metal material; the porous metal material preferably has a pore density of 20 to 200 PPI and a pore diameter of 0.25 to 1.27 mm. By controlling the pore density of the porous metal material within the above range, the present invention not only exhibits excellent flexibility and output performance, but also utilizes the impact of NO2 gas flow to induce a volume change in the NO2 gas sensor, resulting in triboelectric charging and, in turn, a change in current.

[0035] As an embodiment, the pore density of the porous metal material may be 30PPI, 40PPI, 50PPI, 60PPI, 70PPI, 80PPI, 90PPI, 100PPI, 110PPI, 120PPI, 130PPI, 140PPI, 150PPI, 160PPI, 170PPI, 180PPI or 190PPI; the pore size of the porous metal material may be 0.30mm, 0.35mm, 0.40mm, 045mm, 0.50mm, 0.51mm, 0.52mm, 0.60mm, 0.70mm, 0.80mm, 0.90mm, 1.00mm, 1.10mm or 1.20mm.

[0036] In the present invention, the pore density of the porous metal material affects the current intensity of the NO2 gas sensor, and is the highest at 100 PPI.

[0037] In the present invention, the porous metal material preferably comprises foamed copper. The porous metal material used in the present invention is cheap and readily available, and has good mechanical properties, which is conducive to the transmission of high-pressure pulsed airflow.

[0038] The present invention has no particular limitation on the size of the porous metal material, and the size can be adjusted according to the required size.

[0039] The NO2 gas sensor provided by the present invention also includes Cu2O supported on the surface of the porous metal material; the Cu2O is preferably rod-shaped and preferably has a length of 3 to 5 μm. In the present invention, the Cu2O serves as an excellent NO2 sensing material, endowing the NO2 gas sensor with excellent NO2 detection capabilities. Limiting the length of the Cu2O to the aforementioned range enables the NO2 gas sensor to exhibit excellent triboelectric performance.

[0040] As an embodiment, the length of the Cu2O may be 3.5 μm, 4.0 μm or 4.5 μm.

[0041] The NO2 gas sensor provided by the present invention also includes a MOF material supported on the Cu2O surface; the MOF material preferably includes ZIF-8, ZIF-67, HKUST-1, or UIO-66, with ZIF-8 being more preferred. In the present invention, the MOF material, as a high-performance gas-sensing material, increases the roughness of the NO2 gas sensor while further improving its gas-sensing performance.

[0042] In the present invention, the MOF material loading in Cu2O is preferably ≤35wt%. In one embodiment, the MOF material loading in Cu2O can be 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, or 30wt%. Limiting the MOF material loading in Cu2O to this range further improves the gas-sensing performance of the NO2 gas sensor.

[0043] In the present invention, the loading amount of the MOF material affects the current intensity of the NO2 gas sensor, and is the highest at 25 wt%.

[0044] The NO2 gas sensor provided by the present invention utilizes a porous metal substrate, which not only exhibits excellent mechanical properties but also facilitates the transmission of high-pressure pulsed airflow. Cu2O, a high-performance gas sensing material, imparts excellent gas detection capabilities to the NO2 gas sensor. The MOF material, a high-performance gas-sensitive material, exhibits specific adsorption for NO2 gas, increasing the sensor's roughness while further enhancing its gas-sensing performance. Therefore, the NO2 gas sensor provided by the present invention exhibits excellent sensitivity for NO2 gas detection.

[0045] The NO2 gas sensor provided by the present invention has excellent sensing performance and has excellent sensitivity, selectivity and stability for detecting low-concentration NO2 gas.

[0046] The present invention also provides a method for preparing the NO2 gas sensor according to the above technical solution, comprising the following steps:

[0047] (1) mixing a porous metal material, a first solvent, an oxidant, and a hydroxide, and performing a precipitation reaction to obtain a porous metal material having copper hydroxide on the surface;

[0048] (2) sintering the porous metal material with copper hydroxide on the surface obtained in step (1) to obtain a porous metal material with Cu2O loaded on the surface;

[0049] (3) The porous metal material with surface-loaded Cu2O obtained in step (2), a metal salt, an organic ligand, and a second solvent are mixed and subjected to a polymerization reaction to obtain a NO2 gas sensor.

[0050] The invention mixes a porous metal material, a first solvent, an oxidant and a hydroxide, and performs a precipitation reaction to obtain a porous metal material with copper hydroxide on the surface.

[0051] In the present invention, the porous metal material is preferably sequentially acid-washed, water-washed and dried before use.

[0052] The present invention has no special limitation on the pickling operation, and the oxides on the surface of the porous metal material are removed by an operation well known to those skilled in the art.

[0053] As an embodiment, the pickling operation may be to immerse the porous metal material in dilute hydrochloric acid for 2.5 to 10 minutes; the concentration of the dilute hydrochloric acid may be 0.02 to 0.1 mol / L.

[0054] The present invention has no particular limitation on the water washing operation, and the water washing can be performed until the mixture becomes neutral.

[0055] The present invention has no particular limitation on the drying operation, and the drying operation may be performed until the weight is constant. As an embodiment, the drying temperature may be 80°C.

[0056] In the present invention, the first solvent is preferably distilled water. The present invention has no particular limitation on the amount of the first solvent, and any amount known to those skilled in the art can be used to dissolve the raw materials.

[0057] In the present invention, the oxidant is preferably ammonium persulfate. In the present invention, the oxidant can be used to promote the oxidation reaction on the surface of the porous metal material.

[0058] The present invention has no particular limitation on the specific type of the hydroxide, as long as it can provide hydroxide.

[0059] As an embodiment, the hydroxide may be sodium hydroxide. In the present invention, the hydroxide is used to provide hydroxide.

[0060] In the present invention, the porous metal material, the first solvent, the oxidant and the hydroxide are preferably mixed by mixing the porous metal material with the first solvent, and then sequentially adding the oxidant and the hydroxide to obtain a mixture.

[0061] The present invention has no special limitation on the operation of mixing the porous metal material with the first solvent, and a technical solution for preparing a mixed material well known to those skilled in the art can be used.

[0062] The present invention has no particular limitation on the operation of sequentially adding the oxidant and the hydroxide, and a technical solution for preparing a mixed material well known to those skilled in the art may be used.

[0063] In the present invention, the total concentration of the oxides and hydroxides in the mixture is preferably 0.02 to 0.1 mol / L; the molar concentration ratio of the oxides to hydroxides in the mixture is preferably 1:(1.5 to 2.5). Limiting the total concentration of the oxides and hydroxides and the concentration ratio of the oxides to hydroxides within the above ranges is more conducive to preparing Cu(OH)2 with a uniform surface.

[0064] As an embodiment, the total concentration of oxides and hydroxides in the mixture may be 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L or 0.09 mol / L; the molar concentration ratio of oxides and hydroxides in the mixture may be 1:2.

[0065] In the present invention, the temperature of the precipitation reaction is preferably 50 to 80°C; the time of the precipitation reaction is preferably 4 to 6 hours; and the pH value of the precipitation reaction is preferably 10 to 12. Limiting the process parameters of the precipitation reaction within the above ranges is more conducive to preparing Cu(OH)2 with a uniform surface.

[0066] As an embodiment, the temperature of the precipitation reaction can be 55°C, 60°C, 65°C, 70°C or 75°C; the time of the precipitation reaction can be 4.5h, 5.0h or 5.5h; and the pH value of the precipitation reaction can be 11.

[0067] After the precipitation reaction is completed, the product obtained by the precipitation reaction is preferably filtered, washed with water and dried in sequence to obtain a porous metal material with copper hydroxide on the surface.

[0068] The present invention has no particular limitation on the filtering operation, and any operation well known to those skilled in the art may be used to obtain filter residue.

[0069] In the present invention, the number of water washing is preferably 3 to 5 times. The present invention has no particular limitation on the amount of water used in the water washing, as long as the residual impurities on the surface are removed.

[0070] The present invention has no particular limitation on the drying operation, and drying to a constant weight may be performed using an operation well known to those skilled in the art.

[0071] After obtaining the porous metal material with copper hydroxide on the surface, the present invention sintered the porous metal material with copper hydroxide on the surface to obtain the porous metal material with Cu2O loaded on the surface.

[0072] In the present invention, the sintering temperature is preferably 500-700°C; the sintering time is preferably 2.5-4 hours; and the rate of heating to the sintering temperature is preferably 5-15°C / min. As an embodiment, the sintering temperature can be 550°C, 600°C, or 650°C; the sintering time can be 3 hours or 3.5 hours; and the rate of heating to the sintering temperature can be 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 11°C / min, 12°C / min, 13°C / min, or 14°C / min. In the present invention, limiting the sintering temperature, time, and heating rate within the above ranges is more conducive to forming uniform Cu2O on the porous metal material.

[0073] In the present invention, the sintering is preferably performed in an argon atmosphere; the flow rate of the argon is preferably 30 to 70 mL / min. As an embodiment, the flow rate of the argon can be 35 mL / min, 40 mL / min, 45 mL / min, 50 mL / min, 55 mL / min, 60 mL / min, or 65 mL / min.

[0074] After the sintering is completed, the present invention preferably cools the sintered product to obtain a porous metal material with surface-loaded Cu2O.

[0075] The present invention has no particular limitation on the cooling operation, and cooling to room temperature may be performed using an operation well known to those skilled in the art.

[0076] As an embodiment, the sintering operation in an argon atmosphere can be performed by placing the porous metal material with copper hydroxide on the surface in a porcelain boat, pushing the porcelain boat into the constant temperature zone in the center of the tube furnace, closing the furnace body, and then using a vacuum pump to pump the air pressure to 100 Pa, and then introducing 99.99% argon to normal pressure, and repeating this three times to completely exclude other gases.

[0077] After obtaining the porous metal material with Cu2O loaded on the surface, the present invention mixes the porous metal material with Cu2O loaded on the surface, a metal salt, an organic ligand and a second solvent, and performs a polymerization reaction to obtain a NO2 gas sensor.

[0078] In the present invention, the second solvent is preferably formaldehyde. The present invention has no particular limitation on the amount of the second solvent, as long as the raw materials are mixed uniformly.

[0079] The present invention has no particular limitation on the specific types of the metal salt and the organic ligand. The corresponding metal salt and organic ligand can be selected according to the desired MOF material.

[0080] As an embodiment, the metal salt may be ZnNO 3 ·6H 2 O; and the organic ligand may be 2-methylimidazole.

[0081] In the present invention, the mixing of the surface-loaded Cu2O porous metal material, metal salt, organic ligand and second solvent is preferably performed by mixing the metal salt, organic ligand and second solvent to obtain a mixed solution, and then adding the surface-loaded Cu2O porous metal material.

[0082] The present invention has no special limitation on the operation of mixing the metal salt, the organic ligand and the second solvent, and the technical scheme for preparing the mixed material well known to those skilled in the art can be adopted.

[0083] In the present invention, the concentration of the metal salt in the mixed solution is preferably 0.05 to 0.15 mol / L, more preferably 0.10 mol / L; the concentration of the organic ligand in the mixed solution is preferably 0.5 to 0.1 mol / L, more preferably 0.8 mol / L; and the molar ratio of the metal salt to the organic ligand is preferably 1:(6 to 10). As an embodiment, the molar ratio of the metal salt to the organic ligand can be 1:7, 1:8, or 1:9. The present invention limits the concentration of the metal salt and the organic ligand and the molar ratio thereof to the above ranges to form a uniform MOF material on the Cu2O surface.

[0084] In the present invention, the polymerization reaction temperature is preferably 75-95°C, and the polymerization reaction time is preferably 3-6 hours. In one embodiment, the polymerization reaction temperature can be 80°C, 85°C, or 90°C, and the polymerization reaction time can be 4 hours or 5 hours. Limiting the polymerization reaction temperature and time within these ranges allows for the formation of a uniform MOF material on the Cu2O surface.

[0085] The present invention has no particular limitation on the ratio of the mixed solution to the porous metal material with surface-loaded Cu2O, as long as the loading amount of the MOF material is ensured to be ≤35wt%.

[0086] The present invention has no special limitation on the operation of adding the surface-loaded Cu2O porous metal material, and the technical solution for preparing the mixed material well known to those skilled in the art can be adopted.

[0087] After the polymerization reaction is completed, the present invention preferably filters, washes and dries the product obtained by the polymerization reaction in sequence to obtain a NO2 gas sensor.

[0088] The present invention has no particular limitation on the filtering operation, and any operation well known to those skilled in the art may be used to obtain filter residue.

[0089] The present invention has no particular limitation on the washing operation, as long as the washing is thorough.

[0090] The present invention has no particular limitation on the drying operation, and the product may be dried to a constant weight.

[0091] The flow chart of preparing NO2 gas sensor in the embodiment of the present invention is as follows Figure 1 shown.

[0092] from Figure 1 It can be seen that the present invention first forms Cu(OH)2 on the surface of the porous metal material (foam copper), then forms Cu2O through a sintering method, and finally prepares the NO2 gas sensor through an in-situ polymerization reaction.

[0093] The method provided by the invention is simple to operate, and the obtained NO2 gas sensor has excellent sensitivity.

[0094] The present invention also provides the use of the NO2 gas sensor described in the above technical solution or the NO2 gas sensor prepared by the preparation method described in the above technical solution in automobile exhaust detection.

[0095] In the present invention, the application of the NO2 gas sensor in automobile exhaust detection preferably includes: using the NO2 gas sensor as a signal output module of a NO2 gas monitoring system to determine the operating status of the automobile engine by monitoring the NO2 content.

[0096] In one embodiment of the present invention, the NO2 gas monitoring system preferably includes a signal output module (PPC-TENG), a circuit control module, a signal transmission unit and an alarm module connected in sequence.

[0097] In one embodiment of the present invention, the schematic diagram of the NO2 gas monitoring system is as follows: Figures 2-4 shown.

[0098] like Figure 2 As shown, in one embodiment of the present invention, the signal output module is a triboelectric generator, and the triboelectric generator is a NO2 gas sensor. The present invention uses the NO2 gas sensor as the signal output module. When the pulsed airflow passes through, charge transfer occurs at the solid-gas interface, outputting a triboelectric signal.

[0099] like Figure 2As shown, in one embodiment of the present invention, the circuit control module includes an air pump, a solenoid valve and a relay. In the present invention, the air pump, the solenoid valve and the relay are three control units that can be used to control the injection rate and output frequency of the pulsed airflow.

[0100] like Figure 3 As shown, in one embodiment of the present invention, the signal transmission unit is connected to the positive terminal of a current amplifier / oscilloscope via a wire, the negative terminal of the current amplifier / oscilloscope is connected to a data acquisition card, and the data acquisition card is connected to a USB port of a computer, and the data is analyzed and processed by a Labview program on the computer. The present invention can convert the electrical signal of the interface into a digital signal through the signal transmission unit.

[0101] like Figure 4 As shown, in one embodiment of the present invention, the NO2 gas monitoring alarm module is an alarm with Bluetooth function and a radio frequency module, an alarm bell with Bluetooth connection function, and a mobile phone with WIFI connection function.

[0102] In the present invention, when the alarm module is used as a siren or mobile phone, when the NO2 gas concentration exceeds 50ppm, the peak current generated will fall below the threshold set by the relay, causing the instantaneous current to turn on the alarm module. Furthermore, the alarm module provided by this invention also includes a radio frequency (RF) module and a Bluetooth module. When a signal passes through, the module emits electromagnetic waves (433.92MHz) and Bluetooth signals.

[0103] In the present invention, the alarm module consists of a signal receiving unit (mobile phone) and an alarm unit (alarm bell); the alarm bell uses Bluetooth signals to realize the alarm, while the radio frequency signal uploads the warning signal to the cloud via the Internet and WIFI, and the mobile phone application pushes it to the mobile device to realize real-time wireless alarm.

[0104] Since the NO2 gas sensor provided by the present invention has excellent sensitivity to NO2, the NO2 monitoring system obtained by using the NO2 gas sensor can be used to judge whether the automobile engine is running normally by monitoring low concentrations of NO2.

[0105] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0106] Example 1

[0107] A NO2 gas sensor comprises a porous metal material, Cu2O supported on the surface of the porous metal material, and ZIF-8 supported on the surface of the Cu2O;

[0108] The porous metal material is foam copper with a pore density of 100 PPI and a pore diameter of 0.25 mm;

[0109] The Cu2O has a rod-like structure and a length of 3 μm;

[0110] The loading amount of ZIF-8 in Cu2O is 30wt%;

[0111] The preparation method of the NO2 gas sensor is as follows:

[0112] (1) The copper foam was soaked in dilute hydrochloric acid for 5 minutes to remove the surface oxide, and then repeatedly rinsed with deionized water until neutral, and then placed in an oven to dry, and then distilled water was added, and then ammonium persulfate and sodium hydroxide were added in sequence, and stirred until completely dissolved to obtain a mixture, and then precipitation reaction was carried out at 80°C for 6 hours, and then filtered, and then washed with deionized water for 3 times, and dried to obtain a porous metal material with copper hydroxide on the surface; wherein the concentration of dilute hydrochloric acid is 0.02 mol / L; the total concentration of ammonium persulfate and sodium hydroxide in the mixture is 0.02 mol / L; the molar concentration ratio of ammonium persulfate and sodium hydroxide in the mixture is 1:1.5; the pH value of the precipitation reaction is 12;

[0113] (2) placing the porous metal material with copper hydroxide on the surface obtained in step (1) into a tube furnace, introducing pure argon gas for sintering, and naturally cooling to room temperature to obtain a porous metal material with Cu2O loaded on the surface; wherein the sintering temperature is 700°C; the sintering time is 4 hours; the heating rate to the sintering temperature is 5°C / min; and the flow rate of argon gas is 30 mL / min;

[0114] (3) The porous metal material with surface-loaded Cu2O obtained in step (2) is placed in a formaldehyde solution of ZnNO3·6H2O and 2-methylimidazole to carry out a polymerization reaction, and then filtered, washed and dried in sequence to obtain a NO2 gas sensor; wherein the concentration of ZnNO3·6H2O in the formaldehyde solution of ZnNO3·6H2O and 2-methylimidazole is 0.05 mol / L, the concentration of 2-methylimidazole is 0.5 mol / L, and the molar ratio of ZnNO3·6H2O to 2-methylimidazole is 1:10; the temperature of the polymerization reaction is 95°C; and the time of the polymerization reaction is 3 hours.

[0115] Figure 5 This is a SEM image of the NO2 gas sensor prepared in Example 1; Figure 6 for Figure 5 Enlarged image in box; Figure 7 for Figure 6 Enlarged image in box; Figure 8 for Figure 7 Enlarged image within the box.

[0116] from Figure 5 It can be seen that the foam copper has a porous network structure.

[0117] from Figure 7 It can be seen that the surface of the foam copper is covered by Cu2O.

[0118] from Figure 8 It can be seen that the surface roughness of Cu2O loaded on ZIF-8 increases, which is more conducive to the adsorption and desorption of NO2 gas and enhances the NO2 gas sensing ability of the NO2 gas sensor.

[0119] Example 2

[0120] A NO2 gas sensor comprises a porous metal material, Cu2O supported on the surface of the porous metal material, and ZIF-8 supported on the surface of the Cu2O;

[0121] The porous metal material is foam copper with a pore density of 60 PPI and a pore diameter of 0.52 mm;

[0122] The Cu2O has a rod-like structure and a length of 4 μm;

[0123] The loading amount of ZIF-8 in Cu2O is 20wt%;

[0124] The preparation method of the NO2 gas sensor is the same as that of Example 1.

[0125] Example 3

[0126] A NO2 gas sensor comprises a porous metal material, Cu2O supported on the surface of the porous metal material, and ZIF-8 supported on the surface of the Cu2O;

[0127] The porous metal material is foam copper with a pore density of 100 PPI and a pore diameter of 0.25 mm;

[0128] The Cu2O has a rod-like structure and a length of 5 μm;

[0129] The loading amount of ZIF-8 in Cu2O is 10 wt%;

[0130] The preparation method of the NO2 gas sensor is the same as that of Example 1.

[0131] Comparative Example 1

[0132] A NO2 gas sensor is composed of a porous metal material and Cu2O loaded on the surface of the porous metal material;

[0133] The porous metal material is foam copper with a pore density of 20 PPI and a pore diameter of 1.27 mm;

[0134] The Cu2O has a rod-like structure and a length of 3 μm;

[0135] Compared with Example 1, the preparation method of the NO2 gas sensor omits the preparation step of ZIF-8, and other conditions remain unchanged.

[0136] Comparative Example 2

[0137] Based on Comparative Example 1, only the pore density was modified to 50 PPI, and other conditions remained unchanged.

[0138] Comparative Example 3

[0139] Based on Comparative Example 1, only the pore density was modified to 100 PPI, and other conditions remained unchanged.

[0140] Comparative Example 4

[0141] Based on Comparative Example 1, only the pore density was modified to 150 PPI, and other conditions remained unchanged.

[0142] Comparative Example 5

[0143] Based on Comparative Example 1, only the pore density was modified to 200 PPI, and other conditions remained unchanged.

[0144] The current signals of the NO2 gas sensors prepared in Comparative Examples 1 to 5 are as follows: Figure 9 As shown ( Figure 9 The horizontal axis has no practical meaning and is only used to evenly separate different current signals).

[0145] from Figure 9 It can be seen that as the pore density (number of pores per inch) of the copper foam increases from 20 PPI to 100 PPI, the current increases from 2.1 μA to 4 μA. This is because the increase in the number of pores increases the friction area at the gas-solid interface, enhancing the output of the NO2 gas sensor. As the pore density of the copper foam further increases to 200 PPI, the current decreases from 4 μA to 1.6 μA. This is because the further increase in the number of pores hinders gas transmission, resulting in a decrease in output. Therefore, the NO2 gas sensor output is highest when the pore density of the porous metal material is 100 PPI.

[0146] Comparative Example 6

[0147] A NO2 gas sensor is composed of a porous metal material and ZIF-8 supported on the surface of the porous metal material;

[0148] The porous metal material is foam copper with a pore density of 100 PPI and a pore diameter of 0.50 mm;

[0149] The Cu2O has a rod-like structure and a length of 4 μm;

[0150] The loading amount of ZIF-8 in Cu2O is 5 wt%;

[0151] Compared with Example 1, the preparation method of the NO2 gas sensor omits the preparation step of Cu2O, and other conditions remain unchanged.

[0152] Comparative Example 7

[0153] Based on Comparative Example 6, only the loading amount of ZIF-8 in Cu2O was modified to 10 wt %, and other conditions remained unchanged.

[0154] Comparative Example 8

[0155] Based on Comparative Example 6, only the loading amount of ZIF-8 in Cu2O was modified to 15 wt %, and other conditions remained unchanged.

[0156] Comparative Example 9

[0157] Based on Comparative Example 6, only the loading amount of ZIF-8 in Cu2O was modified to 20 wt %, and other conditions remained unchanged.

[0158] Comparative Example 10

[0159] Based on Comparative Example 6, only the loading amount of ZIF-8 in Cu2O was modified to 25 wt %, and other conditions remained unchanged.

[0160] Comparative Example 11

[0161] Based on Comparative Example 6, only the loading amount of ZIF-8 in Cu2O was modified to 30 wt%, and other conditions remained unchanged.

[0162] Comparative Example 12

[0163] Based on Comparative Example 6, only the loading amount of ZIF-8 in Cu2O was modified to 35 wt%, and other conditions remained unchanged.

[0164] Comparative Example 13

[0165] Based on Comparative Example 6, ZIF-8 was omitted and other conditions remained unchanged.

[0166] The current signals of the NO2 gas sensors prepared in Comparative Examples 6 to 13 are as follows: Figure 10 As shown ( Figure 10 The horizontal axis has no practical meaning and is only used to evenly separate different current signals).

[0167] from Figure 10 As can be seen, as the ZIF-8 loading increases from 0wt% to 25wt%, the current gradually increases from 1.8μA to 4.1μA; however, when the ZIF-8 loading increases from 25wt% to 35wt%, the current decreases from 4.1μA to 3.7μA. This is because increasing the ZIF-8 loading increases the contact area, thereby improving the output; however, excessive ZIF-8 reduces gas transmission channels, thereby reducing the output of the NO2 gas sensor. Therefore, the NO2 gas sensor has the highest output when the ZIF-8 loading is 25%.

[0168] The NO2 gas sensor prepared in Example 1 is used to monitor NO2 gas. The installation diagram is shown in the figure below. Figure 2 As shown, the current signal of different NO2 gas concentrations was tested and the results were as follows Figure 11 As shown ( Figure 11 The horizontal axis has no practical meaning and is only used to evenly separate different current signals).

[0169] from Figure 11 It can be seen that at a concentration of 0 to 100 ppm, the NO2 gas sensor prepared in Example 1 has obvious current signals. This shows that the NO2 gas sensor prepared in the present invention has excellent sensitivity to low-concentration NO2 gas.

[0170] The response time and recovery time curve of the NO2 gas sensor prepared in Example 1 is as follows: Figure 12 shown.

[0171] from Figure 12 As can be seen, in the absence of NO₂ gas (0 ppm), the output of the NO₂ gas sensor prepared in Example 1 was approximately 3.8 μA. Upon sudden introduction of 500 ppm NO₂, the output gradually decreased to 1 μA and stabilized after 13 seconds. Upon removal of the NO₂ gas, the output gradually returned to its original value after 17 seconds. Therefore, the response time of the NO₂ gas sensor prepared in Example 1 was approximately 13 seconds, and its recovery time was approximately 17 seconds.

[0172] The current signals of the NO2 gas sensor prepared in Example 1 at NO2 concentrations of 0 PPM, 50 PPM and 500 PPM are as follows: Figure 13 shown.

[0173] from Figure 13 It can be seen that the NO2 gas sensor prepared by the present invention has good stability under different NO2 gas concentrations.

[0174] Application Example 1

[0175] The NO2 gas sensor prepared in Example 1 is used to monitor NO2. The installation diagram is as shown in the figure. Figures 2-4 As shown, it was then used to monitor NO2 concentration. The specific operation was as follows: the prepared gas sensor device was connected to the exhaust port of a car, the exhaust gas was connected to a gas control device, and the gas flow was directed to a triboelectric device to measure the current change. The current output of the TENG (triboelectric nanogenerator) was approximately 4.05μA under the empty bottle condition. In a normally operating engine, the sensor current dropped to 1.25μA, indicating that a concentration of 200PPM of NO2 gas had been generated. After placing a damaged engine in the vehicle, the current change was observed and the output current was 3.07μA, indicating that the gasoline was not fully burned and the NO2 concentration produced was approximately 10PPM. According to previous research, a NO2 concentration of 50PPM is sufficient to determine the quality of the engine. Therefore, the engine condition can be divided into three categories: normal (≥200PPM), general (50-200PPM), and damaged (<50PPM).

[0176] From the above results, it can be seen that the NO2 gas sensor prepared by the present invention has excellent sensitivity and selectivity to low concentrations of NO2, so it can judge the working condition of the engine by monitoring the NO2 content, providing a new method for monitoring the combustion condition of automobile engines.

[0177] It can be seen from the above embodiments and comparative examples that the NO2 gas sensor provided by the present invention has excellent sensitivity and stability.

[0178] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A NO2 gas sensor comprising a porous metal material, Cu2O supported on the surface of the porous metal material, and a MOF material supported on the surface of the Cu2O.

2. The NO2 gas sensor according to claim 1, characterized in that The pore density of the porous metal material is 20-200 PPI, and the pore diameter of the porous metal material is 0.25-1.27 mm.

3. The NO2 gas sensor according to claim 1, characterized in that The Cu2O has a rod-like structure, and the length of the Cu2O is 3 to 5 μm.

4. The NO2 gas sensor according to claim 1, characterized in that The MOF material includes ZIF-8, ZIF-67, HKUST-1 or UIO-66, and the loading amount of the MOF material in Cu2O is less than or equal to 35 wt%.

5. The method for preparing the NO2 gas sensor according to any one of claims 1 to 4, comprising the following steps: (1) mixing a porous metal material, a first solvent, an oxidant, and a hydroxide, and performing a precipitation reaction to obtain a porous metal material having copper hydroxide on the surface; (2) sintering the porous metal material with copper hydroxide on the surface obtained in step (1) to obtain a porous metal material with Cu2O loaded on the surface; (3) The porous metal material with surface-loaded Cu2O obtained in step (2), a metal salt, an organic ligand, and a second solvent are mixed and subjected to a polymerization reaction to obtain a NO2 gas sensor.

6. The preparation method according to claim 5, characterized in that The temperature of the precipitation reaction in step (1) is 50-80° C., the time of the precipitation reaction is 4-6 hours, and the pH value of the precipitation reaction is 10-12.

7. The preparation method according to claim 5, characterized in that The sintering temperature in step (2) is 500-700° C., and the sintering time is 2.5-4 hours.

8. The preparation method according to claim 5, characterized in that The molar ratio of the metal salt to the organic ligand in the step (3) is 1:(6-10).

9. The preparation method according to claim 5, characterized in that The polymerization reaction temperature in step (3) is 75-95° C., and the polymerization reaction time is 3-6 hours.

10. Use of the NO2 gas sensor according to any one of claims 1 to 4 or the NO2 gas sensor prepared by the preparation method according to any one of claims 5 to 9 in automobile exhaust detection.

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