Metal oxide fiber gas sensor as well as preparation method and application thereof

Abstract

The invention provides a metal oxide fiber gas sensor. The metal oxide fiber gas sensor comprises silicon dioxide composite fibers, a gas detection electrode, a metal oxide semiconductor gas sensitive layer, a heating electrode and a breathable film, the silicon dioxide composite fibers comprise hollow silicon dioxide fibers and liquid metal filled in the hollow silicon dioxide fibers; the gas detection electrodes are arranged at two ends of the silicon dioxide composite fiber; the surface of the silicon dioxide composite fiber is coated with the metal oxide semiconductor gas sensitive layer; the heating electrodes are arranged at two ends of the silicon dioxide composite fiber and are in contact with the liquid metal; the surface of the metal oxide semiconductor gas-sensitive layer is coated with the breathable film. The invention further provides a preparation method and application of the gas sensor. The gas sensor provided by the invention is high in heat source utilization rate, high in flexibility and small in size, meanwhile, no additional heating wire is needed to provide heat energy for the sensor, and the silicon dioxide composite fiber can generate higher heat energy under lower voltage.

Description

Technical Field

[0001] The present invention relates to the technical field of gas sensors, and in particular to a metal oxide fiber gas sensor, a preparation method thereof and applications thereof. Background Art

[0002] A gas sensor is a device that can detect the type and concentration of a target gas and output it as an electrical signal. Gas sensors can be divided into semiconductor gas sensors, solid electrolyte gas sensors, contact combustion gas sensors, electrochemical gas sensors, and optical gas sensors.

[0003] Metal oxide semiconductor gas sensors are the most popular type of gas sensors due to their unique electrical properties and large specific surface area. x , NH3, SO2 and H2S and other toxic gases have attracted widespread attention. Gas-sensitive materials will have electron depletion zones of different widths in different environments. When the gas-sensitive material is in the air, the oxygen on the surface of the material will exchange electrons with the gas-sensitive layer, and the electrons of the gas-sensitive material will transfer to the oxygen around the material, so that the oxygen around the material is converted into oxygen anions and adsorbed on the surface of the gas-sensitive material, causing the electron depletion zone of the gas-sensitive material to change, and the resistance will also change accordingly. When the gas-sensitive material is in a certain concentration of the response gas, the response gas will react with the oxygen anions adsorbed on the surface of the gas-sensitive material, so that the electrons are released back to the gas-sensitive layer, causing the electron depletion zone to change, and the resistance will change accordingly. Therefore, metal oxide nanostructures have many advantages in gas sensing, such as strong controllability and low cost, but they have a lot of problems in wearable applications, such as poor flexibility, the need to provide sufficient thermal energy to achieve optimal response and low thermal utilization, which limits their development in wearable applications.

[0004] Metal oxide semiconductor gas sensors are usually of two forms: gas-sensitive materials coated on ceramic tubes and directly grown on hard substrates such as microelectromechanical systems (MEMS). Among them, for gas sensors with ceramic tube structures, the process of built-in heating wires in the ceramic tube is generally used to provide the required thermal energy for the gas-sensitive layer. The heating layer of this method has a large space and fast air flow, which will also cause heat loss faster, affecting the thermal insulation effect, thereby greatly increasing power consumption.

[0005] The structure commonly used in silicon-based gas sensors made based on MEMS processing technology is as follows: a silicon nitride film layer is deposited on the upper surface of a single-crystal silicon substrate as a lower insulating layer, and an insulating groove is prepared on the lower surface of the single-crystal silicon substrate; when preparing the insulating groove, a backside wet etching process can be used, or a cantilever beam can be etched out of the lower insulating layer first, and then an inverted pyramid insulating groove is wet-etched downward; the two insulating grooves can better prevent heat loss to reduce power consumption; a platinum heating wire layer is processed above the lower insulating layer by a lift-off process, and heat can be generated by energizing the heating wire to form the temperature required for the gas sensor to work; a silicon nitride layer is deposited on the surface of the platinum heating wire as an upper insulating layer, and finally a temperature sensitive layer and a gas sensitive layer are deposited. After the insulating groove is etched out by the above method, the heating layer and the gas sensitive layer are supported by only a thin film structure of silicon nitride layer, and the thin film is supported only by the supporting substrate of the cantilever structure at both ends. The insulating layer of this thin film structure has poor mechanical properties and is prone to rupture when the device is vibrated or collided, resulting in device failure. In addition, due to the difference in thermal expansion coefficients between the insulation layer and the heating wire, the insulation layer is prone to warping at high temperatures, causing the heating wire to easily fall off the insulation layer, which also leads to device failure. At the same time, the insulation groove of the cantilever structure uses the air between the cantilevers for thermal insulation. Due to the large space and fast air flow, heat dissipation will also occur quickly, affecting the insulation effect. Moreover, the preparation process of this type of insulation groove is complicated and requires high control conditions, which increases the processing difficulty.

[0006] Therefore, in order to broaden the application field of metal oxide semiconductor gas sensors, it is of great significance to provide a metal oxide semiconductor gas sensor with high heat source utilization, good flexibility and small size. Summary of the invention

[0007] The technical problem solved by the present invention is to provide a metal oxide fiber gas sensor. The gas sensor provided by the present application has the advantages of high heat source utilization, good flexibility and small size.

[0008] In view of this, the present application provides a metal oxide fiber gas sensor, comprising: a silica composite fiber, a gas detection electrode, a metal oxide semiconductor gas sensitive layer, a heating electrode and a gas permeable film; the silica composite fiber comprises a hollow silica fiber and a liquid metal filled inside the hollow silica fiber;

[0009] Gas detection electrodes disposed at both ends of the silica composite fiber;

[0010] A metal oxide semiconductor gas-sensitive layer coated on the surface of the silica composite fiber;

[0011] Heating electrodes disposed at both ends of the silica composite fiber and in contact with the liquid metal;

[0012] A breathable film coated on the surface of the metal oxide semiconductor gas-sensitive layer.

[0013] Preferably, the metal in the liquid metal includes one or more of mercury, cesium, rubidium, gallium, indium, tin, lead, zinc, copper, gold and silver.

[0014] Preferably, the outer diameter of the silica composite fiber is ≥30 μm, and the inner diameter is ≥1 μm.

[0015] Preferably, the gas detection electrode comprises a silver wire, a platinum wire or a gold wire, the heating electrode comprises a silver wire, a platinum wire or a gold wire, and the silica composite fiber and the heating electrode are connected via a solidified conductive metal paste.

[0016] Preferably, the metal oxide in the metal oxide semiconductor gas sensing layer includes one or more of ZnO, SnO2, Fe2O3, In2O3, WO3, TiO2, Co3O4, the above metal oxides doped with metals and the above metal oxides modified with metals; the thickness of the metal oxide semiconductor gas sensing layer is ≥10nm; the microscopic morphology of the metal oxide in the metal oxide semiconductor gas sensing layer is one or more of nanoparticles, nanorods, nanowires, nanobelts, nanotubes, nanocombs, nanosheets, nano-ization and nanoclusters.

[0017] The present application also provides a method for preparing the metal oxide fiber gas sensor, comprising the following steps:

[0018] S1) filling the interior of the hollow silica fiber with liquid metal to obtain a silica composite fiber;

[0019] S2) forming gas detection electrodes at both ends of the silica composite fiber;

[0020] In-situ forming a metal oxide semiconductor gas-sensitive layer on the surface of the silica composite fiber;

[0021] inserting a heating electrode into the liquid metal of the silica composite fiber so that the heating electrode is in contact with the liquid metal;

[0022] A gas-permeable film is formed on the surface of the metal oxide semiconductor gas-sensitive layer.

[0023] Preferably, step S1) is specifically:

[0024] The hollow glass tube is heated and melted, and air pressure is applied to the inner wall of the hollow glass tube, softened, cooled, and then drawn to obtain hollow silica fibers;

[0025] The hollow silica fiber is fixed, and liquid metal is filled into the hollow silica fiber to obtain silica composite fiber.

[0026] Preferably, the preparation method of the metal oxide semiconductor gas sensitive layer includes one or more of vapor deposition, atomic layer deposition, template method, solvent thermal method, solid phase reaction method, sol-gel method, electrospinning and microwave assisted method.

[0027] The present application also provides a flexible substrate sensor, comprising a flexible substrate and a plurality of gas sensors formed on the flexible substrate, wherein the gas sensor is the metal oxide fiber gas sensor or the metal oxide fiber gas sensor prepared by the preparation method.

[0028] The present application also provides a sensor system, comprising the metal oxide fiber gas sensor or the metal oxide fiber gas sensor prepared by the preparation method.

[0029] The present application provides a metal oxide fiber gas sensor, which includes a silica composite fiber, a gas detection electrode, a metal oxide semiconductor gas sensitive layer, a heating electrode and a breathable film, wherein the silica composite fiber includes a hollow silica fiber and a liquid metal filled in the hollow silica fiber; the gas detection electrode is arranged at both ends of the silica composite fiber, the metal oxide semiconductor gas sensitive layer is coated on the surface of the silica composite fiber, the heating electrode is arranged at both ends of the silica composite fiber and is in contact with the liquid metal, and the breathable film is coated on the surface of the metal oxide semiconductor gas sensitive layer; the metal oxide fiber provided in the present application In the oxide fiber gas sensor, the liquid metal core is used as the heat source, and the hollow silica fiber is used as the insulating substrate. The Joule heat generated after the core is energized can directly provide heat for the gas-sensitive response process of the metal oxide semiconductor gas-sensitive layer through heat conduction, realizing the maximum utilization of electric thermal energy. At the same time, the hollow silica fiber has good flexibility; further, the hollow silica fiber can be used as an insulating substrate material to directly grow the metal oxide semiconductor gas-sensitive material in situ, reducing the technical difficulty of setting the gas-sensitive layer on the substrate. Compared with the substrate in the prior art, the fibrous insulating substrate material can significantly reduce the overall volume of the gas sensor. In summary, the metal oxide fiber gas sensor provided by the present application has the advantages of high heat source utilization, good flexibility, and small volume, making it possible to use it in flexible wearable applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the structure of the metal oxide fiber gas sensor of the present invention;

[0031] Figure 2 A schematic diagram of preparing silica composite fibers according to the present invention;

[0032] Figure 3 A schematic diagram of the process of preparing a metal oxide fiber gas sensor according to the present invention;

[0033] Figure 4 This is a SEM photo of the metal oxide semiconductor gas-sensitive layer prepared in Example 1 of the present invention;

[0034] Figure 5 This is a SEM photograph of the gas-sensitive material of the metal oxide semiconductor gas-sensitive layer prepared in Example 1 of the present invention;

[0035] Figure 6 This is a gas response curve diagram of the metal oxide fiber gas sensor prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0037] In view of the application fields and performance requirements of metal oxide semiconductor gas sensors in the prior art, the present application provides a metal oxide fiber gas sensor, the key of which is the introduction of a silica composite fiber including a hollow silica fiber and a liquid metal filled inside the hollow silica fiber, with the liquid metal core as the heat source and the hollow silica fiber as the insulating substrate. The Joule heat generated after the core is energized can provide heat for the gas-sensitive response process of the gas-sensitive layer through heat conduction, thereby achieving maximum utilization of thermal energy and solving the problem of large heat transfer loss during heating of the existing metal oxide gas sensor; and, the hollow silica fiber as the insulating substrate material can directly grow the metal oxide semiconductor gas-sensitive material in situ, reducing the technical difficulty of setting the gas-sensitive layer on the substrate, and the process threshold is relatively low; further, using the silica composite fiber as the substrate material, compared with the traditional ceramic tube and MEMS substrate, the overall volume of the gas sensor can be significantly reduced, and the gas sensor can be made to have a certain flexibility, making the flexible wearable application of the metal oxide semiconductor gas sensor possible. Specifically, the embodiment of the present invention discloses a metal oxide fiber gas sensor, comprising: a silica composite fiber, a gas detection electrode, a metal oxide semiconductor gas sensitive layer, a heating electrode and a gas permeable film; the silica composite fiber comprises a hollow silica fiber and a liquid metal filled inside the hollow silica fiber;

[0038] Gas detection electrodes disposed at both ends of the silica composite fiber;

[0039] A metal oxide semiconductor gas-sensitive layer coated on the surface of the silica composite fiber;

[0040] Heating electrodes disposed at both ends of the silica composite fiber and in contact with the liquid metal;

[0041] A breathable film coated on the surface of the metal oxide semiconductor gas-sensitive layer.

[0042] like Figure 1 As shown, Figure 1 This is a schematic diagram of the structure of the metal oxide fiber gas sensor provided in the present application, in which 6 is liquid metal, 7 is hollow silica fiber, 8 is a metal oxide semiconductor gas sensitive layer, 9 is a breathable film, 10 is a gas detection electrode, and 11 is a heating electrode.

[0043] In the present application, the silica composite fiber is composed of a hollow silica fiber and a liquid metal filled in the hollow silica fiber, wherein the liquid metal is used as the fiber core and the hollow silica fiber is used as the cladding layer; in the silica composite fiber, the hollow part of the hollow silica fiber is filled with liquid metal, and the liquid metal can generate Joule heat as long as it can achieve the connection of current. For example, the metal in the liquid metal includes one or more of mercury, cesium, rubidium, gallium, indium, tin, lead, zinc, copper, gold and silver; the above metals can exist alone or in any combination. Different metal compositions are formed according to the method known to those skilled in the art, and the metals in the liquid metal include gallium, indium and tin. More specifically, the metals in the liquid metal include 50-70wt% gallium, 20-35wt% indium and 5-15wt% tin. In a specific embodiment, the metals in the liquid metal include 68.5wt% gallium, 21.5wt% indium and 10wt% tin. The raw material ratio of the above liquid metal is not particularly limited in this application, and it can be in accordance with the ratio known to those skilled in the art. The outer diameter of the silica composite fiber can be adjusted according to actual needs. For example, the outer diameter of the silica composite fiber is ≥30μm and the inner diameter is ≥1μm. Specifically, the outer diameter of the silica composite fiber is 50-100μm and the inner diameter is 10-50μm. More specifically, the outer diameter of the silica composite fiber is 60-90μm and the inner diameter is 20-40μm.

[0044] The surface of the silica composite fiber is coated with a metal oxide semiconductor gas-sensitive layer. The metal oxide in the metal oxide semiconductor gas-sensitive layer serves as a gas-sensitive material and provides a site for the adsorption of the target gas to achieve the purpose of detecting the target gas. The metal oxide in the metal oxide semiconductor gas-sensitive layer includes one or more of ZnO, SnO2, Fe2O3, In2O3, WO3, TiO2, Co3O4, the above metal oxides doped with metals, and the above metal oxides surface modified with metal particles; in a specific embodiment, the metal oxide is zinc oxide surface modified with Au particles. The thickness of the metal oxide semiconductor gas-sensitive layer is ≥10nm. Specifically, the thickness of the metal oxide semiconductor gas-sensitive layer is 1 to 5μm; for example, the thickness of the metal oxide semiconductor gas-sensitive layer is 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm. The microscopic morphology of the metal oxide in the metal oxide semiconductor gas sensing layer is one or more of nanoparticles, nanorods, nanowires, nanobelts, nanotubes, nanocombs, nanosheets, nano-nization and nanoclusters; in a specific embodiment, the microscopic morphology of the metal oxide in the metal oxide semiconductor gas sensing layer is nanorods.

[0045] The gas detection electrodes are formed at both ends of the silica composite fiber, and are used to detect the resistance of the metal oxide semiconductor gas-sensitive layer, convert the interaction between the target gas and the metal oxide in the gas-sensitive layer into a change in resistance, and realize gas detection. The gas detection electrode includes a silver wire, a platinum wire or a gold wire. The gas detection electrode is connected to the hollow silica fiber in the silica composite fiber, and needs to be in contact with the metal oxide gas-sensitive layer to realize the detection of the resistance of the gas-sensitive layer; that is, the gas detection electrodes are arranged at both ends of the surface where the silica composite fiber and the metal oxide gas-sensitive layer are in contact.

[0046] The heating electrodes are arranged at both ends of the silica composite fiber and in contact with the liquid metal to apply current to the liquid metal so that the liquid metal generates Joule heat. The heating electrodes include silver wire, platinum wire or gold wire. The heating electrode contacts the liquid metal in the silica composite fiber and can be inserted into the liquid metal or not inserted into the liquid metal but only in contact with it, as long as the heating electrode can apply current to the liquid metal. The materials of the gas detection electrode and the heating electrode can be the same or different, and this application does not impose any special restrictions on this.

[0047] A permeable film is formed on the surface of the metal oxide semiconductor gas-sensitive layer, which can prevent the semiconductor gas-sensitive layer from falling off. The permeable film specifically includes: polytetrafluoroethylene (PTFE), polypropylene (PP), PDMS and Teflon AF2400.

[0048] The metal oxide fiber gas sensor provided in the present application has high heat source utilization, high flexibility, and small size. At the same time, no additional heating wire is required to provide thermal energy for the sensor. The fiber itself can generate higher thermal energy at a lower voltage.

[0049] The present application also provides a method for preparing a metal oxide fiber gas sensor, comprising the following steps:

[0050] S1) filling the interior of the hollow silica fiber with liquid metal to obtain a silica composite fiber;

[0051] S2) forming gas detection electrodes at both ends of the silica composite fiber;

[0052] In-situ forming a metal oxide semiconductor gas-sensitive layer on the surface of the silica composite fiber;

[0053] inserting a heating electrode into the liquid metal of the silica composite fiber so that the heating electrode is in contact with the liquid metal;

[0054] A gas-permeable film is formed on the surface of the metal oxide semiconductor gas-sensitive layer.

[0055] In the preparation method of the metal oxide fiber gas sensor, the present application first prepares a silica composite fiber, specifically as follows Figure 2 As shown, Figure 2 1 is a hollow glass tube, 2 is a pressurized ventilation device, 3 is a high-frequency induction heater, 4 is a capstan, and 5 is a hollow silica fiber; the preparation method of the hollow silica fiber is specifically as follows:

[0056] The hollow glass tube is heated and melted, and air pressure is applied to the inner wall of the hollow glass tube, softened, cooled, and then drawn to obtain hollow silica fibers;

[0057] The hollow silica fiber is fixed, and liquid metal is filled into the hollow silica fiber to obtain silica composite fiber.

[0058] use Figure 2 The preparation process of the hollow silica fiber preparation device shown is specifically as follows:

[0059] The hollow glass tube 1 is cleaned and dried for pretreatment; then it is fixed on the stage, and the upper end of the hollow glass tube 1 is connected to the pressurized ventilation device 2; then the pressurized ventilation device 2 is used to ventilate it, and at the same time, the high-frequency induction heater 3 is turned on to heat it, and the temperature and air flow rate are set to heat and melt the hollow glass tube 1, and a certain air pressure is applied to the inner wall of the hollow glass tube; after the hollow glass tube is heated to the softening point, it is led down with a glass rod, and after the condensed water is condensed, it is wound on the capstan 4 and drawn to obtain the hollow silica fiber 5.

[0060] In the preparation process of the hollow silica fiber, the hollow glass tube is well known to those skilled in the art and is not particularly limited in this application. The heating temperature is 1300-1700°C, and the gas flow rate is 0.001-0.010MPa; specifically, the heating temperature is 1400-1650°C, and the gas flow rate is 0.003-0.006MPa. The drawing speed is 1-10m / min, and specifically, the drawing speed is 3-7m / min.

[0061] After the hollow silica fiber is obtained, liquid metal is filled into the hollow silica fiber to obtain silica composite fiber; the specific process is as follows:

[0062] Use a syringe to extract liquid metal;

[0063] Tightly connect the two ends of the hollow silica fiber to a hollow glass tube whose inner diameter is larger than the outer diameter of the hollow silica fiber, seal them with an adhesive, and tightly connect the hollow glass tube to the syringe through the adhesive so that the hollow silica fiber and the syringe are in a sealed state;

[0064] The syringe is fixed to a micro-injector, and the driving force of the micro-injector is used to inject the liquid metal in the syringe into the hollow silica fiber. When the liquid metal overflows from the other end of the fiber, the hollow silica fiber is removed from the syringe, and the hollow glass tubes at both ends of the hollow fiber are removed to obtain a silica composite fiber.

[0065] The present application further forms gas detection electrodes at both ends of the hollow silica fiber of the silica composite fiber, and the formation method is not particularly limited in the present application; in a specific embodiment, the gas detection electrodes are respectively wound around the two ends of the hollow silica fiber, and then the conductive metal slurry is coated on the connection between the gas detection electrode and the hollow silica fiber, and then annealed to sinter the silica composite fiber and the gas detection electrode together; in the above process, the material selection of the gas detection electrode and the conductive metal slurry can be the same or different. In some specific embodiments, the gas detection electrode is a platinum wire and the conductive metal slurry is a silver paste. The annealing temperature is 400-500°C and the time is 10-30min; specifically, the annealing temperature is 420-480°C and the time is 15-25min. There is no particular limitation on the diameter of the gas detection electrode in the present application. For example, the diameter of the gas detection electrode is 50 to 200 μm, specifically, the diameter of the gas detection electrode is 80 to 160 μm, and more specifically, the diameter of the gas detection electrode is 100 to 150 μm.

[0066] According to the present invention, a metal oxide semiconductor gas-sensitive layer is then formed on the surface of the silica composite fiber; the preparation method of the metal oxide semiconductor gas-sensitive layer includes one or more of a vapor deposition method, an atomic layer deposition method, a template method, a solvent thermal method, a solid phase reaction method, a sol-gel method, an electrostatic spinning method and a microwave-assisted method; in a specific embodiment, the preparation method of the metal oxide semiconductor gas-sensitive layer is a sol-gel method, and more specifically, a ZnO nanorod modified with gold particles can be in situ grown on the surface of the silica coating layer by a hydrothermal method, firstly, ZnO nanoparticles are coated on the surface of the silica coating layer by a sol-gel method to form a seed layer, then ZnO nanorods are grown by a hydrothermal method, and finally Au nanoparticles are grown on the surface of the ZnO nanorods by an ultraviolet reduction method.

[0067] After this application, the heating electrode is inserted into the liquid metal of the silica composite fiber to make the heating electrode contact with the liquid metal; in order to ensure that the heating electrode and the liquid metal in the silica composite fiber are tightly connected, a thermal conductive slurry is applied to the connection between the heating electrode and the silica composite fiber, and after annealing, the silica composite fiber and the heating electrode are sintered together to form an ideal ohmic contact; the annealing temperature is 100-200°C, and the time is 10-30min; specifically, the annealing temperature is 120-180°C, and the time is 15-25min.

[0068] According to the present invention, a breathable film is finally formed on the surface of the gas-sensitive layer to form a protective layer on the surface of the gas-sensitive layer to prevent the gas-sensitive layer from falling off; the method for forming the breathable film is not particularly limited in this application. In a specific embodiment, the formation method is an immersion pulling method.

[0069] Figure 3 FIG. 1 is a schematic diagram of a specific process of the metal oxide semiconductor fiber gas sensor of the present invention, which includes sequentially preparing hollow glass fiber by hot drawing, injecting liquid metal and preparing the sensor, as shown in FIG. Figure 3 shown.

[0070] The present invention uses a liquid metal fiber core as a heat source and silicon dioxide as an insulating substrate. The Joule heat generated after the fiber core is energized can provide heat for the gas-sensitive response process of the gas-sensitive layer through heat conduction, thereby realizing the maximum utilization of thermal energy and solving the problem of large heat transfer loss when the existing metal oxide semiconductor gas sensor is heated. Moreover, the insulating substrate material (silicon dioxide) in this scheme can directly grow metal oxide semiconductor materials in situ, reducing the technical difficulty of setting a gas-sensitive layer on the substrate, and the process implementation threshold is low, which is more conducive to commercial promotion. In addition, since this scheme uses a fiber substrate material, compared with traditional ceramic tubes and MEMS substrates, the overall volume of the gas sensor can be significantly reduced, and the gas sensor can have a certain flexibility, making the flexible wearable application of metal oxide semiconductor gas sensors possible.

[0071] The present application also provides a flexible substrate sensor, comprising a flexible substrate and a plurality of gas sensors formed on the flexible substrate, wherein the gas sensor is the gas sensor described in the above scheme; and the number of gas sensors among the plurality of gas sensors is ≥1, so as to realize the detection of multiple gases at the same time.

[0072] The present application also provides a sensor system, which includes the metal oxide fiber gas sensor described in the above scheme.

[0073] The metal oxide fiber gas sensor provided in the present application can be used alone to detect the concentration of the gas, and can also be integrated with other components to still play its own role, while other components can play their respective roles to form a sensor system with multiple functions.

[0074] The present invention provides a metal oxide fiber gas sensor and a preparation method and application thereof. The gas sensor provided by the present invention has the advantages of high heat source utilization, high flexibility and small size. At the same time, no additional heating wire is required to provide thermal energy for the sensor. The liquid metal of the silica composite fiber itself will generate sufficient Joule heat to provide thermal energy for the gas-sensitive material when current passes through, so as to achieve high-sensitivity response.

[0075] In order to further improve the gas-sensitive response of the metal oxide semiconductor gas-sensitive layer, the metal oxide gas-sensitive layer can be doped and / or modified, including but not limited to the doping of metals and / or metal oxides; for example, the noble metals Au, Ag, Pd and / or metal oxides CuO, SnO2 can be used to sensitize the gas-sensitive layer, and UV light can be used to improve the gas-sensitive performance. Doping and / or modification may form a heterojunction or cause changes in the lattice, thereby causing changes in the electron depletion layer, an increase in the oxygen content adsorbed on the surface of the gas-sensitive layer, and improving the gas-sensitive response of the sensor. The methods of doping and / or modification include: sol-gel method, reduction method, sputtering method and flame spray pyrolysis, etc.

[0076] In order to further understand the present invention, the metal oxide fiber gas sensor and the preparation method thereof provided by the present invention are described in detail below in conjunction with the embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0077] Example

[0078] This embodiment provides a metal oxide semiconductor gas sensor based on a hollow fiber substrate, and the specific preparation process is as follows:

[0079] (1) Preparation of hollow glass fiber

[0080] The hollow glass tube was ultrasonically cleaned for 10 minutes using acetone, alcohol and deionized water respectively, and dried in a 60°C oven for 4 hours; the pretreated hollow glass tube was then fixed on a stage, and the upper end of the hollow glass tube was connected to a gas pipeline; then, it was heated and ventilated, the high-frequency induction heater and the pressurized ventilation device were turned on, the temperature was set to 1650°C, the gas flow rate was 0.003Mpa, the hollow glass tube was heated and melted, and a certain air pressure was applied to the inner wall of the hollow glass tube; finally, when the hollow glass tube was heated to the softening point, it was led down with a glass rod, and after the condensed water was condensed, it was wound onto a capstan, and a tensile force was applied by the capstan, and the hot pulling speed was 1m / min, forming a hollow glass fiber with an outer diameter of 90μm and an inner diameter of 40μm;

[0081] The hollow glass fiber prepared above was cut into 5 cm lengths for flexibility test. The specific test process and test results are as follows:

[0082] A squeezing force is applied to both ends of the fiber axially to make it bend. The bending angle of the fiber is 80 degrees through calculation and analysis. This proves that the hollow glass fiber prepared in this embodiment has good flexibility.

[0083] (2) Injection of liquid metal

[0084] The hollow glass fiber was cut into a length of 2 cm, and ultrasonically cleaned with acetone, ethanol and deionized water for 10 minutes in turn to remove surface pollutants, and dried in air at 60°C; then the two ends of the hollow glass fiber passed through two hollow glass tubes with an inner diameter of 100 μm and an outer diameter of 120 μm, and the contact port was sealed by heating and curing PDMS; then it was connected to a syringe carrying a certain amount of liquid metal, and it was tightly connected through PDMS, so that the hollow fiber was tightly connected to the hollow glass tube and the syringe, and there would be no air leakage; finally, a micro-injector was used to inject the liquid metal in the syringe into the interior of the hollow fiber through the hollow glass tube. After the liquid metal completely filled the hollow glass tube and the hollow fiber, the hollow quartz tubes at both ends of the syringe and the fiber were removed to form a silica composite fiber with a fiber shell structure with liquid metal as the core and silica coating layer; wherein the ratio of the liquid metal was: 68.5wt% gallium, 21.5wt% indium, and 10wt% tin;

[0085] (3) Preparation of sensor gas detection electrodes

[0086] Platinum wires with a diameter of 100 μm were wound around the two ends of the composite fiber as gas detection electrodes, silver paste was applied to the connection between the platinum wire and the hollow fiber, and annealed at 450°C for 15 min to sinter the fiber and the platinum wire together;

[0087] (4) Growth of Metal Oxide Semiconductor Gas Sensing Layer

[0088] First, a zinc oxide seed layer is grown on the surface of the silica composite fiber connected to the gas detection electrode prepared in step (3) by a sol-gel method. The specific operation steps are as follows:

[0089] ① Treat the silica composite fiber with air plasma for 120 seconds to improve the hydrophilicity of the fiber and make the seed layer solution more easily adhere to the surface of the fiber; ② Prepare a 0.03 mol / L Zn(CH3COO)2·2H2O ethanol solution, and use the pulling method to evenly disperse the seed layer solution on the surface of the fiber to form a film, and then dry it, and repeat the pulling and drying for 5 times; then anneal it at 350°C for 30 minutes to thermally decompose Zn(CH3COO)2·2H2O to form zinc oxide nanoparticles, and form a uniform and dense zinc oxide seed layer with high crystallinity on the fiber surface, so that the zinc oxide nanorods grown later have better orientation;

[0090] Then, based on the above zinc oxide seed layer, zinc oxide nanorods are in situ grown on the fiber surface by a hydrothermal method. The specific operation steps are as follows:

[0091] ① Prepare a 0.025 mol / L Zn(NO3)2·6H2O aqueous solution and an equimolar HMTA aqueous solution, then mix the two solutions and stir at room temperature for 1 hour to mix them evenly; ② Transfer the mixed solution to a reactor, place the prepared fiber in the reactor at an angle, react at 95°C for 2 hours, take out the fiber after the reactor temperature drops to room temperature, wash with deionized water to remove excess material on the surface, and dry at 60°C; ③ Anneal at 500°C for 2 hours to remove impurities in the zinc oxide nanorods and reduce structural defects; finally, a metal oxide semiconductor gas-sensitive layer with a thickness of about 2 μm is obtained on the fiber surface; finally, Au nanoparticles are grown on the surface of the ZnO nanorods by ultraviolet reduction: the concentration is 1×10 -3 mol / L HAuCl4 solution, adjust the pH of the HAuCl4 solution to 7 using 0.5 mol / L NaOH, then immerse the fiber in the HAuCl4 solution until the solution just covers the fiber, and use 365 nm ultraviolet light at 150 mW / cm -2 The power density of the fiber was irradiated with Au 3+ After the reaction, the fiber was washed with deionized water to remove the unreacted material on the surface, and dried at 60°C for later use;

[0092] The morphology of the gas-sensitive layer can be observed by field emission scanning electron microscopy, such as Figure 4 , Figure 5 As shown, Figure 4 , Figure 5 They are the cross-sectional view of the in-situ grown metal oxide semiconductor fiber and the morphology of the gas-sensitive material, from which the fiber shell structure of the silica composite fiber and the nanorod-shaped gas-sensitive layer can be clearly observed.

[0093] (5) Preparation of sensor heating electrode

[0094] Cut two 25mm platinum wires and insert them into both ends of the silica composite fiber. Then use silver paste to connect the platinum wire and the outer wall of the fiber. Anneal at 150℃ for 15min to sinter the fiber and the platinum wire together. By sintering the silver paste at high temperature, an ideal ohmic contact is formed.

[0095] The silica composite fiber prepared in this example was subjected to a thermal effect test, and the specific test process and test results are as follows:

[0096] The heating electrode of the silica composite fiber was connected to the circuit, and voltage was applied to examine its heat generation. The result was: at a voltage of 2V, the temperature of the silica composite fiber could reach 350°C; this proves that the silica composite fiber prepared in this example has a good thermal effect.

[0097] The gas sensor prepared in this embodiment was subjected to a gas sensitivity test. The specific test process included: placing the sensor prepared above in a gas chamber, connecting a heating electrode and a detection electrode, setting the voltage of the heating electrode to 2V, and passing acetone gas of different concentrations to perform a gas sensitivity test; the experimental results are shown in FIG. Figure 6 As shown in the figure, it can be seen that when the concentration of ammonia is 10ppm, the response of the sensor is 4.33.

[0098] The metal oxide semiconductor gas sensor provided in this embodiment uses fiber material as a substrate, has good flexibility, and can be woven onto a flexible substrate such as clothing.

[0099] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0100] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A metal oxide fiber gas sensor, comprising: Silica composite fiber, gas detection electrode, metal oxide semiconductor gas sensitive layer, heating electrode and breathable film; the silica composite fiber comprises hollow silica fiber and liquid metal filled in the hollow silica fiber; Gas detection electrodes disposed at both ends of the silica composite fiber; A metal oxide semiconductor gas-sensitive layer coated on the surface of the silica composite fiber; Heating electrodes disposed at both ends of the silica composite fiber and in contact with the liquid metal; A breathable film coated on the surface of the metal oxide semiconductor gas-sensitive layer.

2. The gas sensor according to claim 1, characterized in that The metal in the liquid metal includes one or more of mercury, cesium, rubidium, gallium, indium, tin, lead, zinc, copper, gold and silver.

3. The gas sensor according to claim 1, characterized in that: The outer diameter of the silica composite fiber is ≥30 μm, and the inner diameter is ≥1 μm.

4. The gas sensor according to claim 1, characterized in that: The gas detection electrode comprises a silver wire, a platinum wire or a gold wire, the heating electrode comprises a silver wire, a platinum wire or a gold wire, and the silica composite fiber and the heating electrode are connected via a solidified conductive metal paste.

5. The gas sensor according to claim 1, characterized in that: The metal oxide in the metal oxide semiconductor gas sensing layer includes one or more of ZnO, SnO2, Fe2O3, In2O3, WO3, TiO2, Co3O4, the above metal oxides doped with metals and the above metal oxides modified with metals; the thickness of the metal oxide semiconductor gas sensing layer is ≥10nm; the microscopic morphology of the metal oxide in the metal oxide semiconductor gas sensing layer is one or more of nanoparticles, nanorods, nanowires, nanobelts, nanotubes, nanocombs, nanosheets, nano-ization and nanoclusters.

6. The method for preparing the metal oxide fiber gas sensor according to claim 1, comprising the following steps: S1) filling the interior of the hollow silica fiber with liquid metal to obtain a silica composite fiber; S2) forming gas detection electrodes at both ends of the silica composite fiber; In-situ forming a metal oxide semiconductor gas-sensitive layer on the surface of the silica composite fiber; inserting a heating electrode into the liquid metal of the silica composite fiber so that the heating electrode is in contact with the liquid metal; A gas-permeable film is formed on the surface of the metal oxide semiconductor gas-sensitive layer.

7. The preparation method according to claim 6, characterized in that: Step S1) is specifically: The hollow glass tube is heated and melted, and air pressure is applied to the inner wall of the hollow glass tube to soften and then cool, and then drawn to obtain hollow silica fibers; The hollow silica fiber is fixed, and liquid metal is filled into the hollow silica fiber to obtain silica composite fiber.

8. The preparation method according to claim 6, characterized in that: The preparation method of the metal oxide semiconductor gas sensitive layer includes one or more of vapor phase deposition, atomic layer deposition, template method, solvent thermal method, solid phase reaction method, sol-gel method, electrostatic spinning and microwave assisted method.

9. A flexible substrate sensor, comprising a flexible substrate and a plurality of gas sensors formed on the flexible substrate, wherein the gas sensor is a metal oxide fiber gas sensor as described in any one of claims 1 to 5 or a metal oxide fiber gas sensor prepared by the preparation method as described in any one of claims 6 to 8.

10. A sensor system, comprising the metal oxide fiber gas sensor according to any one of claims 1 to 5 or the metal oxide fiber gas sensor prepared by the preparation method according to any one of claims 6 to 8.

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