Metal oxide aerogels, methods of making and using the same, and gas sensors and uses thereof

Abstract

The present application relates to the technical field of gas sensor, and discloses a metal oxide aerogel, a preparation method and application thereof, and a gas sensor and application thereof.The specific surface area of the metal oxide aerogel is 150-300m 2 / g, the pore size is 100-1000nm, and the compressive strength is 10-50kPa.The method comprises the following steps: (1) preparing a dispersion liquid by mixing a metal oxide nanowire, a hydrophilic and lipophilic polymer compound and a dispersion medium; (2) freeze-drying the dispersion liquid; and (3) sintering the product obtained in step (2) in the presence of an oxidizing gas, wherein the sintering temperature is 600-900 DEG C.The metal oxide aerogel provided by the present application has a porous structure, good gas sensitivity and high mechanical strength, can promote the electron transfer between nanowires, and improve the reliability of the aerogel in the sensing process.

Description

Technical Field

[0001] This invention relates to the field of gas sensor technology, specifically to a metal oxide aerogel, its preparation method and application, and a gas sensor and its application. Background Technology

[0002] Metal oxides such as WO3, SnO2, ZnO, and Co3O4 are important semiconductor materials, widely used in solar cells, light-emitting diodes, and gas sensors due to their excellent optical, electrical, and magnetic properties. Among them, WO3 gas sensors play a crucial role in environmental monitoring, industrial production control, and safety protection due to their high sensitivity and selectivity to various gases. However, traditional WO3 gas sensors typically form a gas-sensitive thin film on the sensor surface using methods such as spraying and screen printing. While this method is simple and easy to implement, the high density of the gas-sensitive film makes it difficult for the target gas to penetrate the internal gas-sensitive material, resulting in low response performance. To address these issues, researchers have proposed several improved methods. For example, porous WO3 thin films can be prepared using anodic oxidation, bio-templating, block copolymer self-assembly, and colloidal templating methods. Although existing technologies have improved the performance of WO3-based gas sensors to some extent, several problems and challenges remain. First, these improved methods often require complex experimental conditions and precise control, consuming significant human and material resources, making large-scale production impossible. Second, due to stress mismatch, these porous WO3 gas-sensitive materials are prone to cracking and detachment, affecting the stability of the sensor. Therefore, how to improve the response performance and stability of WO3 while maintaining its excellent gas-sensing properties remains an urgent problem to be solved.

[0003] CN105301062A proposes a gas sensor based on hierarchical porous WO3 microspheres and its preparation method. However, the porous WO3 microspheres obtained in this patent are still dense films after being coated on the surface of ceramic tubes, resulting in low response performance.

[0004] CN110983254A proposes a method for preparing porous WO3 electrochromic thin films and their applications. The method uses anodic oxidation to prepare porous films, which is complex and uses a fluorine-containing electrolyte, which is highly toxic and harmful to the environment and human health. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of existing metal oxide aerogels, such as high density leading to poor response performance and stability, and complex preparation processes requiring etching molds. This invention provides a metal oxide aerogel, its preparation method, its applications, and a gas sensor with the same application. The metal oxide aerogel provided by this invention has a porous structure, good gas-sensing performance, and high mechanical strength, which can promote electron transfer between nanowires and improve the reliability of the aerogel in the sensing process.

[0006] To achieve the above objectives, the present invention provides a metal oxide aerogel with a specific surface area of ​​150–300 m². 2 / g, pore size 100~1000nm, compressive strength 10~50kPa.

[0007] Preferably, the metal oxide aerogel is selected from at least one of WO3 aerogel, SnO aerogel, ZnO aerogel and Co3O4 aerogel.

[0008] A second aspect of this invention provides a method for preparing WO3 aerogel, the method comprising the following steps:

[0009] (1) A dispersion was prepared by combining metal oxide nanowires, hydrophilic and lipophilic polymers and a dispersion medium;

[0010] (2) The dispersion was freeze-dried;

[0011] (3) The product obtained in step (2) is sintered in the presence of an oxidizing gas, wherein the sintering temperature is 600-900°C.

[0012] Preferably, in step (1), the concentration of metal oxide nanowires in the dispersion is 25-100 mg / mL, more preferably 50-80 mg / mL.

[0013] Preferably, in step (1), the metal oxide nanowires are selected from at least one of WO3 nanowires, SnO nanowires and ZnO nanowires.

[0014] Preferably, in step (1), the weight ratio of the metal oxide nanowires to the hydrophilic and lipophilic polymer compound is 0.1 to 2:1, more preferably 0.2 to 1.6:1.

[0015] Preferably, the hydrophilic and lipophilic polymeric compound is selected from at least one of polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, polyvinyl alcohol, polyethylene glycol, and methylcellulose.

[0016] Preferably, the process of preparing the dispersion in step (1) includes: adding metal oxide nanowires to the dispersion medium, then adding a hydrophilic and lipophilic polymer compound, and then sonicating the resulting mixture.

[0017] Preferably, the dispersion medium is water.

[0018] Preferably, the ultrasound duration is 20–50 minutes.

[0019] Preferably, in step (2), the freeze-drying conditions include: a freezing temperature of -50 to -190°C, a drying time of 12 to 48 hours, and a pressure of 1 to 10 Pa.

[0020] Preferably, in step (3), the oxidizing gas is oxygen.

[0021] Preferably, in step (3), the sintering time is 2-5 hours.

[0022] A third aspect of the present invention provides a metal oxide aerogel prepared by the method described above.

[0023] A fourth aspect of the present invention provides an application of the aforementioned metal oxide aerogel as a gas-sensitive material.

[0024] The fifth aspect of the present invention provides a gas sensor, which includes a gas-sensitive material and two electrodes, the two electrodes being fixed at both ends of the gas-sensitive material respectively;

[0025] The gas-sensitive material is the metal oxide aerogel described above.

[0026] The sixth aspect of this invention provides an application of the gas sensor described above in gas monitoring;

[0027] Preferably, the gas is selected from at least one of hydrogen, hydrogen sulfide, and carbon monoxide.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects:

[0029] (1) The metal oxide aerogel provided by the present invention has a porous structure with a large specific surface area and pore size, and has good porous properties. Compared with existing block and powder metal oxide aerogels, it has better gas sensing performance. At the same time, the metal oxide aerogel provided by the present invention has high mechanical strength, which can promote electron transfer between nanowires and improve the stability of metal oxide aerogel in the sensing process.

[0030] (2) The method described in this invention involves freeze-drying a dispersion of metal oxide nanowires and then sintering it at high temperature to obtain a metal oxide aerogel with a porous structure. Simultaneously, sintering at a specific high temperature achieves fusion between the nanowires, enhancing the mechanical strength of the aerogel, promoting electron transfer between the nanowires, and improving its gas-sensing performance and reliability in the sensing process. The preparation process described in this invention is simple, overcoming the shortcomings of existing technologies that are complex and require template etching. Furthermore, the resulting aerogel possesses excellent porosity and gas-sensing properties, making it suitable for detecting various toxic and harmful gases.

[0031] (3) The gas sensor provided by the present invention uses the metal oxide aerogel provided by the present invention as the gas-sensitive material, and fixes the two ends of the gas-sensitive material on the gas-sensitive material respectively. Compared with the traditional method of fixing the electrodes on the chip, the sensing performance is greatly improved. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of one embodiment of the gas sensor described in this invention;

[0033] Figure 2 Here is a SEM image of the WO3 aerogel prepared in Example 1;

[0034] Figure 3 This is the XRD pattern of the WO3 aerogel prepared in Example 1;

[0035] Figure 4 This is a SEM image of the SnO2 aerogel prepared in Example 9;

[0036] Figure 5 This is the XRD pattern of the SnO2 aerogel prepared in Example 9;

[0037] Figure 6 Here is a SEM image of the ZnO aerogel prepared in Example 10;

[0038] Figure 7 This is the XRD pattern of the ZnO aerogel prepared in Example 10;

[0039] Figure 8 Here is a SEM image of the Co3O4 aerogel prepared in Example 11;

[0040] Figure 9 This is the XRD pattern of the Co3O4 aerogel prepared in Example 12. Detailed Implementation

[0041] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0042] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0043] The metal oxide aerogel provided by this invention has a porous structure and strong mechanical properties. Specifically, the specific surface area of ​​this metal oxide aerogel can be 150–300 m². 2 / g, pore size can be 100~1000nm, compressive strength is 10~50kPa.

[0044] In this invention, the metal oxide in the metal oxide aerogel can be any conventionally chosen material in the art, as long as it can exist in the form of an aerogel. In some embodiments, the metal oxide aerogel can be selected from at least one of WO3 aerogel, SnO aerogel, ZnO aerogel, and Co3O4 aerogel, preferably WO3 aerogel.

[0045] Compared with existing block or powdered metal oxide aerogels, the metal oxide aerogel of the present invention has good porous properties and better gas-sensing performance. At the same time, the metal oxide aerogel provided by the present invention has high mechanical strength, which can promote electron transfer between nanowires and improve the reliability of metal oxide aerogel in the sensing process.

[0046] The method for preparing WO3 aerogel provided by this invention includes the following steps:

[0047] (1) A dispersion was prepared by combining metal oxide nanowires, hydrophilic and lipophilic polymers and a dispersion medium;

[0048] (2) The dispersion was freeze-dried;

[0049] (3) The product obtained in step (2) is sintered in the presence of an oxidizing gas, wherein the sintering temperature is 600-900°C.

[0050] The preparation method described in this invention is simple. It only requires freeze-drying a dispersion containing metal oxide nanowires, hydrophilic and lipophilic polymer compounds, and a dispersion medium, followed by sintering, to obtain a metal oxide aerogel with a porous structure. At the same time, sintering at a specific high temperature achieves the fusion of nanowires, enhances the mechanical strength of the aerogel, promotes electron transfer between nanowires, and improves the gas-sensing performance and the reliability of the aerogel in the sensing process.

[0051] In this invention, the metal oxide in the metal oxide nanowires can be a conventional choice in the art. In some embodiments, the metal oxide nanowires can be selected from at least one of WO3 nanowires, SnO nanowires, ZnO nanowires, and Co3O4 nanowires, preferably WO3 nanowires.

[0052] In some embodiments, the concentration of metal oxide nanowires in the dispersion can be 25–100 mg / mL. Too low a concentration of metal oxide nanowires in the dispersion results in too few contact points between the freeze-dried nanowires, leading to low mechanical strength and even preventing the formation of an aerogel. Too high a concentration of metal oxide nanowires in the dispersion leads to uneven dispersion and nanowire aggregation, which is detrimental to the formation of porous aerogels. Therefore, in some preferred embodiments, the concentration of metal oxide nanowires in the dispersion can be controlled to be 50–80 mg / mL.

[0053] In this invention, the metal oxide nanowires can be commercially available products commonly used in the art, or they can be self-made products. In a preferred embodiment, WO3 nanowires can be prepared as follows: 0.84 g of WCl6 is accurately weighed and placed in a 500 mL beaker, 240 mL of anhydrous ethanol is poured in, and the mixture is magnetically stirred for 30 min. The mixture is then transferred to eight 50 mL polytetrafluoroethylene-lined high-temperature reaction vessels and placed in a microwave digester with a maximum microwave power of 800 kW and a maximum pressure of 40 bar. The temperature is increased from room temperature to 200 °C over 30 min and maintained for 2 h. After the reaction is complete, the mixture is cooled to room temperature, and the liquid in the reaction vessel is poured into centrifuge tubes and centrifuged at 10000 r / 5 min. The precipitate is washed three times with deionized water and a small amount of ethanol. Then, it is dried at 80 °C for 6 h to obtain a blue powder.

[0054] In this invention, the hydrophilic and lipophilic polymer compound is amphiphilic. On the one hand, it can be well dispersed in the dispersion medium, and on the other hand, it can coat the surface of the metal oxide nanowires to prevent the metal oxide nanowires from agglomerating during the dispersion process.

[0055] In some embodiments, the weight ratio of the metal oxide nanowires to the hydrophilic-lipophilic polymer compound can be 0.1 to 2:1. Insufficient amounts of the hydrophilic-lipophilic polymer compound will not provide adequate dispersion, leading to agglomeration of the metal oxide nanowires; excessive amounts will result in insufficient contact between the metal oxide nanowires in the aerogel, preventing them from fusing during high-temperature sintering and reducing mechanical strength. Therefore, in some preferred embodiments, the weight ratio of the metal oxide nanowires to the hydrophilic-lipophilic polymer compound can be controlled to be 0.2 to 1.6:1.

[0056] In this invention, the hydrophilic and lipophilic polymeric compounds include, but are not limited to, at least one of polyvinylpyrrolidone (PVP), polyacrylamide, polyacrylic acid, polyvinyl alcohol, polyethylene glycol, and methylcellulose.

[0057] In a preferred embodiment, the step (1) of preparing the dispersion includes: adding metal oxide nanowires to a dispersion medium, then adding a hydrophilic and lipophilic polymer compound, and then sonicating the resulting mixture. The sonication time can be 20–50 min. In this invention, water is preferably used as the dispersion medium to facilitate freeze-drying of the dispersion.

[0058] In one embodiment, the freeze-drying process includes: freezing the dispersion in liquid nitrogen, and then drying it in a freeze dryer. In this invention, the freeze-drying temperature is -50 to -190°C, the drying time is 12 to 48 hours, and the pressure is 1 to 10 Pa.

[0059] In the method described in this invention, the sintering of the dispersion at a high temperature of 600-900°C after freeze-drying is a necessary means to improve the mechanical strength of metal oxide aerogel. In-situ TEM can reveal that adjacent metal oxide nanowires will fuse together under high temperature conditions, thus forming a whole. This not only prevents slippage between nanowires after the aerogel is subjected to force, but also facilitates the flow of electrons between nanowires, thereby improving the gas-sensing performance and the reliability of the aerogel in the sensing process.

[0060] In some embodiments, the sintering temperature can be 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, or 900°C. In another embodiment, the sintering time is 2-5 hours.

[0061] In the method described in this invention, the oxidizing gas may be oxygen. In one embodiment, the oxidizing gas exists in the form of a mixture, such as a mixture of oxygen and nitrogen, or air; preferably, the mixture is air.

[0062] In a preferred embodiment, the method for preparing WO3 aerogel includes the following steps:

[0063] (1) A dispersion is prepared by mixing metal oxide nanowires, hydrophilic and lipophilic polymers and a dispersion medium, wherein the concentration of metal oxide nanowires in the dispersion is 50-80 mg / mL and the weight ratio of the amount of metal oxide nanowires to the amount of hydrophilic and lipophilic polymers is 0.2-1.6:1.

[0064] (2) The dispersion was freeze-dried;

[0065] (3) The product obtained in step (2) is sintered in the presence of an oxidizing gas, wherein the sintering temperature is 600-900°C.

[0066] The metal oxide aerogel prepared using this preferred embodiment has better porous properties, better gas-sensing properties, and higher mechanical strength.

[0067] This invention also provides a metal oxide aerogel prepared by the method described above. In some embodiments, the specific surface area of ​​the metal oxide aerogel is 150–300 m². 2 / g, pore size 100~1000nm, compressive strength 10~50kPa.

[0068] In some embodiments, the metal oxide in the metal oxide aerogel is selected from at least one of WO3 aerogel, SnO aerogel, ZnO aerogel and Co3O4 aerogel.

[0069] This invention also provides an application of the aforementioned metal oxide aerogel as a gas-sensitive material. The metal oxide aerogel provided by this invention, as a gas-sensitive material, can be used to detect toxic and harmful gases and combustible gases in petrochemical enterprises and hydrogen refueling stations.

[0070] The present invention also provides a gas sensor, which includes a gas-sensitive material and two electrodes, the two electrodes being fixed at both ends of the gas-sensitive material; wherein the gas-sensitive material is the metal oxide aerogel described above.

[0071] Because the metal oxide aerogel described in this invention possesses excellent gas-sensing properties and stability, the sensing performance of gas sensors prepared using this metal oxide aerogel as the gas-sensing material is significantly improved. Furthermore, in traditional gas sensors, the electrodes are located on a chip, while in this invention, the electrodes are fixed at both ends of the gas-sensing material, meaning that the two electrodes are in contact with both ends of the gas-sensing material, thereby improving the sensing performance of the gas sensor.

[0072] In a more specific implementation, such as Figure 1 As shown, an electrode is fixed at each end of the gas-sensitive material, and a wire is led out from each electrode to connect to a power source, forming a gas sensor. The electrodes can be copper, platinum, or gold electrodes.

[0073] This invention also provides the application of the gas sensor described above in gas detection. The gases that the gas sensor can detect include, but are not limited to, toxic and harmful gases and combustible gases in petrochemical plants and hydrogen refueling stations.

[0074] In a more specific embodiment, the gas is selected from at least one of hydrogen, hydrogen sulfide, and carbon monoxide.

[0075] In this invention, the gas-sensing performance testing method for a gas sensor using metal oxide aerogel as the gas-sensitive material includes: placing the gas sensor in a sealed container, turning on the power supply, applying a 0.1V power supply, and then introducing the target gas, calculating the resistance change at this time. During the test, the sensor's response value S = (R0 - Rx) / R0, where R0 is the resistance value of the gas sensor in air, and Rx is the resistance value of the gas sensor after the gas is introduced; the gas sensor's response time is the time when the resistance change reaches 90% of the total change after the gas is introduced; the recovery time is the time when the resistance change reaches 90% of the total change after the air is introduced.

[0076] The following examples further illustrate the metal oxide aerogel, its preparation method, its application, and the gas sensor and its application described in this invention. These examples are implemented based on the technical solution of this invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of this invention is not limited to the following examples.

[0077] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0078] Example 1

[0079] Preparation of WO3 nanowires:

[0080] Accurately weigh 0.84 g of WCl6 into a 500 mL beaker, pour in 240 mL of anhydrous ethanol, and stir magnetically for 30 min. Then transfer the mixture to eight 50 mL polytetrafluoroethylene-lined high-temperature reaction vessels and place them in a microwave digester. The microwave power was set to a maximum of 800 kW, and the pressure to a maximum of 40 bar. The temperature was increased from room temperature to 200 °C over 30 min and maintained for 2 h. After the reaction, cool to room temperature, pour the liquid from the reaction vessels into centrifuge tubes, and centrifuge at 10000 rpm for 5 min. Wash the precipitate three times with deionized water and a small amount of ethanol. Then dry at 80 °C for 6 h to obtain a blue powder, which is WO3 nanowires.

[0081] Preparation of WO3 aerogel:

[0082] (1) Accurately weigh 0.5g of WO3 nanowires, put them into 10mL of deionized water, add 0.5g of PVP, and sonicate the resulting mixture for half an hour to obtain a dispersion.

[0083] (2) The dispersion was frozen in liquid nitrogen and then dried in a freeze dryer. The freeze drying conditions included: freezing temperature of -190℃, drying time of 24h, and pressure of 1Pa.

[0084] (3) Place the freeze-dried aerogel in a tube furnace, introduce air, heat to 600℃ for sintering, and hold for 3 hours to obtain the final WO3 aerogel.

[0085] Fabrication of the gas sensor:

[0086] like Figure 1 As shown, a copper foil is fixed at each end of a WO3 aerogel as an electrode using conductive silver paste. A wire is led out from each electrode and connected to a power source to form a gas sensor.

[0087] Example 2

[0088] Preparation of WO3 nanowires:

[0089] Accurately weigh 0.84 g of WCl6 into a 500 mL beaker, pour in 240 mL of anhydrous ethanol, and stir magnetically for 30 min. Then transfer the mixture to eight 50 mL polytetrafluoroethylene-lined high-temperature reaction vessels and place them in a microwave digester. The microwave power was set to a maximum of 800 kW, and the pressure to a maximum of 40 bar. The temperature was increased from room temperature to 200 °C over 30 min and maintained for 2 h. After the reaction, cool to room temperature, pour the liquid from the reaction vessels into centrifuge tubes, and centrifuge at 10000 rpm for 5 min. Wash the precipitate three times with deionized water and a small amount of ethanol. Then dry at 80 °C for 6 h to obtain a blue powder, which is WO3 nanowires.

[0090] Preparation of WO3 aerogel:

[0091] (1) Accurately weigh 0.8g of WO3 nanowires, put them into 10mL of deionized water, add 0.5g of PVP, and sonicate the resulting mixture for half an hour to obtain a dispersion.

[0092] (2) The dispersion was frozen in liquid nitrogen and then dried in a freeze dryer. The freeze drying conditions included: freezing temperature of -50℃, drying time of 12h, and pressure of 10Pa.

[0093] (3) Place the freeze-dried aerogel in a tube furnace, introduce air, heat to 700℃ for sintering, and hold for 4 hours to obtain the final WO3 aerogel.

[0094] Fabrication of the gas sensor:

[0095] like Figure 1As shown, a copper foil is fixed at each end of a WO3 aerogel as an electrode using conductive silver paste. A wire is led out from each electrode and connected to a power source to form a gas sensor.

[0096] Example 3

[0097] Preparation of WO3 nanowires:

[0098] Accurately weigh 0.84 g of WCl6 into a 500 mL beaker, pour in 240 mL of anhydrous ethanol, and stir magnetically for 30 min. Then transfer the mixture to eight 50 mL polytetrafluoroethylene-lined high-temperature reaction vessels and place them in a microwave digester. The microwave power was set to a maximum of 800 kW, and the pressure to a maximum of 40 bar. The temperature was increased from room temperature to 200 °C over 30 min and maintained for 2 h. After the reaction, cool to room temperature, pour the liquid from the reaction vessels into centrifuge tubes, and centrifuge at 10000 rpm for 5 min. Wash the precipitate three times with deionized water and a small amount of ethanol. Then dry at 80 °C for 6 h to obtain a blue powder, which is WO3 nanowires.

[0099] Preparation of WO3 aerogel:

[0100] (1) Accurately weigh 0.5g of WO3 nanowires, put them into 10mL of deionized water, add 2.5g of PVP, and sonicate the resulting mixture for half an hour to obtain a dispersion.

[0101] (2) The dispersion was frozen in liquid nitrogen and then dried in a freeze dryer. The freeze drying conditions included: freezing temperature of -100℃, drying time of 24h, and pressure of 5Pa.

[0102] (3) Place the freeze-dried aerogel in a tube furnace, introduce air, heat to 800℃ for sintering, and hold for 3.5h to obtain the final WO3 aerogel.

[0103] Fabrication of the gas sensor:

[0104] like Figure 1 As shown, a copper foil is fixed at each end of a WO3 aerogel as an electrode using conductive silver paste. A wire is led out from each electrode and connected to a power source to form a gas sensor.

[0105] Example 4

[0106] Preparation of WO3 nanowires:

[0107] Accurately weigh 0.84 g of WCl6 into a 500 mL beaker, pour in 240 mL of anhydrous ethanol, and stir magnetically for 30 min. Then transfer the mixture to eight 50 mL polytetrafluoroethylene-lined high-temperature reaction vessels and place them in a microwave digester. The microwave power was set to a maximum of 800 kW, and the pressure to a maximum of 40 bar. The temperature was increased from room temperature to 200 °C over 30 min and maintained for 2 h. After the reaction, cool to room temperature, pour the liquid from the reaction vessels into centrifuge tubes, and centrifuge at 10000 rpm for 5 min. Wash the precipitate three times with deionized water and a small amount of ethanol. Then dry at 80 °C for 6 h to obtain a blue powder, which is WO3 nanowires.

[0108] Preparation of WO3 aerogel:

[0109] (1) Accurately weigh 0.5g of WO3 nanowires, put them into 10mL of deionized water, add 0.5g of polyvinyl alcohol, and sonicate the resulting mixture for half an hour to obtain a dispersion.

[0110] (2) The dispersion was frozen in liquid nitrogen and then dried in a freeze dryer. The freeze drying conditions included: freezing temperature of -70℃, drying time of 16h, and pressure of 3Pa.

[0111] (3) Place the freeze-dried aerogel in a tube furnace, introduce air, heat to 650℃ for sintering, and hold for 4 hours to obtain the final WO3 aerogel.

[0112] Fabrication of the gas sensor:

[0113] like Figure 1 As shown, a copper foil is fixed at each end of a WO3 aerogel as an electrode using conductive silver paste. A wire is led out from each electrode and connected to a power source to form a gas sensor.

[0114] Example 5

[0115] Preparation of WO3 nanowires:

[0116] Accurately weigh 0.84 g of WCl6 into a 500 mL beaker, pour in 240 mL of anhydrous ethanol, and stir magnetically for 30 min. Then transfer the mixture to eight 50 mL polytetrafluoroethylene-lined high-temperature reaction vessels and place them in a microwave digester. The microwave power was set to a maximum of 800 kW, and the pressure to a maximum of 40 bar. The temperature was increased from room temperature to 200 °C over 30 min and maintained for 2 h. After the reaction, cool to room temperature, pour the liquid from the reaction vessels into centrifuge tubes, and centrifuge at 10000 rpm for 5 min. Wash the precipitate three times with deionized water and a small amount of ethanol. Then dry at 80 °C for 6 h to obtain a blue powder, which is WO3 nanowires.

[0117] Preparation of WO3 aerogel:

[0118] (1) Accurately weigh 0.65g of WO3 nanowires, put them into 10mL of deionized water, add 0.5g of PVP, and sonicate the resulting mixture for 1 hour to obtain a dispersion.

[0119] (2) The dispersion was frozen in liquid nitrogen and then dried in a freeze dryer. The freeze drying conditions included: freezing temperature of -150℃, drying time of 40h, and pressure of 10Pa.

[0120] (3) Place the freeze-dried aerogel in a tube furnace, introduce air, heat to 900℃ for sintering, and hold for 3 hours to obtain the final WO3 aerogel.

[0121] Fabrication of the gas sensor:

[0122] like Figure 1 As shown, a copper foil is fixed at each end of a WO3 aerogel as an electrode using conductive silver paste. A wire is led out from each electrode and connected to a power source to form a gas sensor.

[0123] Example 6

[0124] The method of Example 1 was implemented, except that in step (1), 0.5g of WO3 nanowires was replaced with 0.25g of WO3 nanowires.

[0125] Example 7

[0126] The method of Example 1 was implemented, except that in step (1), 0.5g of WO3 nanowires was replaced with 1g of WO3 nanowires.

[0127] Example 8

[0128] The method is implemented according to Example 1, except that in step (1), 0.5g PVP is replaced with 5g PVP.

[0129] Example 9

[0130] Preparation of SnO2 nanowires:

[0131] Dissolve 2 mmol H₂C₂O₄ in 3 mL ethanol, add 9 mL polyethylene glycol (PEG 400), and continue stirring until dissolved. Then centrifuge to separate the solid product. Wash the solid product alternately with deionized water and ethanol, and then dry it in a vacuum oven at 50 °C for 12 hours. The precursor is then exposed to air at 400 °C at a 1 °C rate. · min -1 SnO2 nanowires were obtained by calcining at a rate of 2 hours.

[0132] Preparation of SnO2 aerogel:

[0133] (1) Accurately weigh 0.8g of SnO2 nanowires, put them into 10mL of deionized water, add 0.5g of PVP, and sonicate the resulting mixture for half an hour to obtain a dispersion.

[0134] (2) The dispersion was frozen in liquid nitrogen and then dried in a freeze dryer. The freeze drying conditions included: freezing temperature of -50℃, drying time of 12h, and pressure of 10Pa.

[0135] (3) Place the freeze-dried aerogel in a tube furnace, introduce air, heat to 700℃ for sintering, and hold for 4 hours to obtain the final SnO2 aerogel.

[0136] Fabrication of the gas sensor:

[0137] Reference Figure 1 A copper foil is fixed at both ends of a SnO2 aerogel using conductive silver paste as an electrode. A wire is led out from each electrode and connected to a power source to form a gas sensor.

[0138] Example 10

[0139] Preparation of ZnO nanowires:

[0140] Prepare 100 mL of 0.1 M zinc acetate solution, then add 100 mL of urea dropwise to the zinc acetate solution. After stirring evenly, add polyvinylpyrrolidone (PVP), where zinc acetate:urea:PVP = 1:2:0.01. Stir evenly and place in a reaction vessel. Microwave heat to 120 °C (microwave power 1200 kW) for 30 min, and react for 30 min. Then wash the product twice with ethanol and deionized water, and remove moisture by freeze drying to obtain basic zinc carbonate powder. Place the basic zinc carbonate powder in a tube furnace and sinter at 400 °C for 4 h in air atmosphere to obtain ZnO nanowires.

[0141] Preparation of ZnO aerogel:

[0142] (1) Accurately weigh 0.8g of ZnO nanowires, put them into 10mL of deionized water, add 0.5g of PVP, and sonicate the resulting mixture for half an hour to obtain a dispersion.

[0143] (2) The dispersion was frozen in liquid nitrogen and then dried in a freeze dryer. The freeze drying conditions included: freezing temperature of -50℃, drying time of 12h, and pressure of 10Pa.

[0144] (3) Place the freeze-dried aerogel in a tube furnace, introduce air, heat to 700℃ for sintering, and hold for 4 hours to obtain the final ZnO aerogel.

[0145] Fabrication of the gas sensor:

[0146] Reference Figure 1 A copper foil is fixed at both ends of a ZnO aerogel using conductive silver paste as an electrode. A wire is led out from each electrode and connected to a power source to form a gas sensor.

[0147] Example 11

[0148] Preparation of Co3O4 nanowires:

[0149] 5 mM Co(NO3)2, 10 mM NH4F and 25 mM urea were dispersed in 70 mL of ultrapure water and magnetically stirred for 30 minutes to form a pink solution. The solution and a piece of FTO were transferred to a Teflon-lined stainless steel autoclave (100 mL). After cooling to room temperature, Co(OH)2 was washed three times with deionized water. Finally, Co(OH)2 was annealed in air at 350 °C for 2 hours to generate Co3O4 nanowires.

[0150] Preparation of Co3O4 aerogel:

[0151] (1) Accurately weigh 0.8g of Co3O4 nanowires, put them into 10mL of deionized water, add 0.5g of PVP, and sonicate the resulting mixture for half an hour to obtain a dispersion.

[0152] (2) The dispersion was frozen in liquid nitrogen and then dried in a freeze dryer. The freeze drying conditions included: freezing temperature of -50℃, drying time of 12h, and pressure of 10Pa.

[0153] (3) The freeze-dried aerogel was placed in a tube furnace and air was introduced. It was heated to 700°C and sintered. The temperature was maintained for 4 hours to obtain the final Co3O4 aerogel.

[0154] Fabrication of the gas sensor:

[0155] Reference Figure 1 A copper foil is fixed at both ends of a Co3O4 aerogel using conductive silver paste as an electrode. A wire is led out from each electrode and connected to a power source to form a gas sensor.

[0156] Comparative Example 1

[0157] The method is implemented according to Example 1, except that PVP is not added in step (1).

[0158] Result: Aerogel could not be obtained; only WO3 powder was obtained.

[0159] Comparative Example 2

[0160] The method of Example 1 is implemented, except that in step (3), the temperature is heated to 300°C for sintering.

[0161] Result: Aerogel could not be obtained; only WO3 powder was obtained.

[0162] Comparative Example 3

[0163] The method described in Example 1 was followed, except that the fabrication process of the gas sensor was different.

[0164] Specifically, the fabrication process of the gas sensor includes:

[0165] WO3 aerogel was crushed in a mortar, mixed with terpineol to form a gas-sensitive slurry, and coated onto a ceramic tube to prepare a gas sensor. The sensing performance was significantly reduced.

[0166] Test Example 1

[0167] The WO3 aerogel prepared in the examples was characterized by SEM and XRD.

[0168] Figure 2 SEM image of the WO3 aerogel prepared in Example 1, from Figure 2 As can be seen, WO3 aerogel is mainly a porous material formed by interconnected WO3 nanowires, with a pore size of 100-1000 nm.

[0169] Figure 3 The image shows the XRD pattern of the WO3 aerogel prepared in Example 1. Figure 3 It can be seen that WO3 aerogel has a good crystal structure and corresponds to the standard peak of WO3.

[0170] The SEM and XRD images of the WO3 aerogels prepared in Examples 2-8 are similar to those in Example 1, and will not be repeated here.

[0171] Figure 4 This is a SEM image of the SnO2 aerogel prepared in Example 9. Figure 4 As can be seen, aerogels are mainly porous materials formed by interconnected SnO2 nanowires, with pore sizes ranging from 100 to 1000 nm.

[0172] Figure 5 This is the XRD pattern of the SnO2 aerogel prepared in Example 9. Figure 5 As can be seen, SnO2 aerogel has a good crystal structure.

[0173] Figure 6 This is a SEM image of the ZnO aerogel prepared in Example 10. Figure 6As can be seen, aerogels are mainly porous materials formed by interconnected ZnO nanowires, with pore sizes ranging from 100 to 500 nm.

[0174] Figure 7 This is the XRD pattern of the ZnO aerogel prepared in Example 10. Figure 7 As can be seen, ZnO aerogel has a good crystal structure.

[0175] Figure 8 This is a SEM image of the Co3O4 aerogel prepared in Example 11. Figure 8 As can be seen, aerogels are mainly porous materials formed by interconnected Co3O4 nanowires, with pore sizes ranging from 300 to 1000 nm.

[0176] Figure 9 This is the XRD pattern of the Co3O4 aerogel prepared in Example 12. Figure 9 As can be seen, Co3O4 aerogel has a good crystal structure.

[0177] Test Example 2

[0178] The specific surface area of ​​the aerogels prepared in the examples was tested using a specific surface area analyzer, and the results are shown in Table 1.

[0179] Table 1

[0180] serial number <![CDATA[Specific surface area (m 2 / g)]]> Example 1 290 Example 2 275 Example 3 262 Example 4 257 Example 5 248 Example 6 244 Example 7 235 Example 8 196 Example 9 183 Example 10 192 Example 11 177

[0181] As can be seen from Table 1, the metal oxide aerogel prepared by the method described in this invention has a large specific surface area.

[0182] Test Example 3

[0183] The mechanical strength of the WO3 aerogel prepared in the test examples was tested, and the results are shown in Table 2.

[0184] The mechanical strength testing methods include: using a universal testing machine to compress the gas-sensitive material and test its compressive strength.

[0185] Table 2

[0186] serial number Compressive strength (kPa) Example 1 48.1 Example 2 46.7 Example 3 45.2 Example 4 37.8 Example 5 31.9 Example 6 27.7 Example 7 24.6 Example 8 22.5 Example 9 19.7 Example 10 19.4 Example 11 18.3

[0187] As can be seen from Table 2, the metal oxide aerogel prepared by the method described in this invention has a large mechanical strength.

[0188] Test Example 4: Testing Gas Sensing Performance

[0189] The gas sensors prepared in the examples and comparative examples were placed in a sealed container. A 0.1V power supply was turned on, and then the target gas (hydrogen) was introduced. The resistance change was calculated. During the test, the sensor's response value S = (R0 - Rx) / R0, where R0 is the resistance of the gas sensor in air, and Rx is the resistance of the gas sensor after the gas is introduced. The response time of the gas sensor is the time when the resistance change reaches 90% of the total change after the gas is introduced; the recovery time is the time when the resistance change reaches 90% of the total change after the air is introduced. The results are shown in Table 3.

[0190] Table 3

[0191]

[0192]

[0193] As can be seen from Table 3, compared with the comparative example, the gas sensor prepared by the method described in this invention has significantly improved gas-sensing performance.

[0194] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A metal oxide aerogel, characterized in that, The specific surface area of ​​this metal oxide aerogel is 150–300 m². 2 / g, pore size 100~1000nm, compressive strength 10~50kPa.

2. The metal oxide aerogel according to claim 1, characterized in that, The metal oxide aerogel is selected from at least one of WO3 aerogel, SnO aerogel, ZnO aerogel, and Co3O4 aerogel.

3. A method for preparing WO3 aerogel, characterized in that, The method includes the following steps: (1) A dispersion was prepared by combining metal oxide nanowires, hydrophilic and lipophilic polymers and a dispersion medium; (2) The dispersion was freeze-dried; (3) The product obtained in step (2) is sintered in the presence of an oxidizing gas, wherein the sintering temperature is 600 to 900°C.

4. The method according to claim 1, characterized in that, In step (1), the concentration of metal oxide nanowires in the dispersion is 25-100 mg / mL, preferably 50-80 mg / mL; Preferably, in step (1), the metal oxide nanowires are selected from at least one of WO3 nanowires, SnO nanowires, ZnO nanowires and Co3O4 nanowires.

5. The method according to claim 3 or 4, characterized in that, In step (1), the weight ratio of the metal oxide nanowires to the hydrophilic and lipophilic polymer compound is 0.1 to 2:1, preferably 0.2 to 1.6:1; Preferably, the hydrophilic and lipophilic polymeric compound is selected from at least one of polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, polyvinyl alcohol, polyethylene glycol, and methylcellulose.

6. The method according to any one of claims 3-5, characterized in that, The process of preparing the dispersion in step (1) includes: adding metal oxide nanowires to the dispersion medium, then adding a hydrophilic and lipophilic polymer compound, and then sonicating the resulting mixture. Preferably, the dispersion medium is water; Preferably, the ultrasound duration is 20–50 minutes.

7. The method according to any one of claims 3-6, characterized in that, In step (2), the freeze-drying conditions include: freezing temperature of -50 to -190°C, drying time of 12 to 48 hours, and pressure of 1 to 10 Pa.

8. The method according to any one of claims 3-7, characterized in that, In step (3), the oxidizing gas is oxygen.

9. The method according to any one of claims 3-8, characterized in that, In step (3), the sintering time is 2-5 hours.

10. A metal oxide aerogel prepared by the method according to any one of claims 3-9.

11. The use of the metal oxide aerogel according to any one of claims 1, 2 or 10 as a gas-sensitive material.

12. A gas sensor, characterized in that, The gas sensor includes a gas-sensitive material and two electrodes, which are respectively fixed at both ends of the gas-sensitive material. The gas-sensitive material is the metal oxide aerogel as described in any one of claims 1, 2 or 10.

13. The application of the gas sensor according to claim 12 in gas detection; Preferably, the gas is selected from at least one of hydrogen, hydrogen sulfide, and carbon monoxide.

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