Preparation method and application of three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material

Abstract

The invention relates to a preparation method of a three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material, which comprises the following steps: preparing polystyrene (PS) microspheres by adopting an emulsion polymerization method, cleaning a glass substrate by using a piranha solution, preparing an opal photonic crystal template by adopting a heating convection self-assembly method, and preparing the three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material. The preparation method comprises the following steps: preparing a precursor solution by a sol-gel method, filling the obtained opal photonic crystal template with the precursor solution, filling the opal photonic crystal template with the precursor solution in a manual dropwise adding manner to obtain a template / precursor compound, placing the template / precursor compound in a muffle furnace, and carrying out heat preservation for 2-4 hours to obtain the opal photonic crystal template. Calcining and annealing at high temperature to remove the polystyrene colloidal microsphere template to obtain a three-dimensional ordered macroporous metal oxide material; in a word, the catalyst has the advantages of simple preparation method, low preparation cost, good long-term stability, high selectivity and high response to nitrogen dioxide at low working temperature.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor gas sensors, and particularly relates to a preparation method and application of a three-dimensionally ordered macroporous metal oxide / polyaniline composite gas sensing material. Background Art

[0002] Nitrogen dioxide (NO 2 ) is a harmful gas that has a fatal impact on humans and the environment. Its reaction with water vapor can generate acid rain, photochemical smog, and cause damage to the tropospheric ozone layer. The exposure limit of nitrogen dioxide permitted by the Occupational Safety and Health Administration (OSHA) is only 5 ppm. Exposure to nitrogen dioxide can lead to respiratory diseases such as bronchitis, emphysema, and heart disease. Some studies have shown that direct exposure to 150 ppm NO 2 can cause pulmonary edema and inflammatory death, and the consequences are very serious.

[0003] A gas sensor is a type of transducer that uses the physical and chemical properties of a gas to detect it and converts the gas concentration information into an easily collectable signal such as an electrical signal according to a certain rule. It mainly consists of a sensing element, a heating circuit, and a hardware housing, etc. It plays an important role in many fields, helping to monitor and control the gas concentration in the environment, thereby protecting people's health and safety and promoting the sustainable development of production and the environment. Therefore, in the current background, there is an urgent need for a NO 2 gas sensor that can detect at low concentrations (ppm / ppb) and has high sensitivity, high selectivity, and fast response / recovery to achieve efficient monitoring and early warning of NO 2 gas and thus solve the problem of excessive nitrogen dioxide gas.

[0004] Spinel MFe 2 O 4 (M = Zn, Ni, Co) is an important multifunctional material that has received extensive attention and great interest in many fields such as photocatalysis, magnetic materials, lithium-ion batteries, and gas sensors. Spinel oxides (AB 2 O 4 ) have a better response to certain gases and thus have more advantages than single metal oxides. Among spinel ferrites, ZnFe 2 O 4 with a unique chemical structure has been studied as a good gas sensing material due to its high sensitivity, high selectivity, and excellent response to nitrogen dioxide; however, its response to the target gas NO 2The response / recovery speed needs to be improved, and the optimal working temperature is high, and the long-term stability is poor. As an excellent conductive polymer, polyaniline (PANI) has the characteristics of simple and reversible doping-undoping process, easy synthesis, stable conductive mechanism, and high environmental stability. However, due to its poor chemical stability and mechanical strength at high temperatures, the practical application of polyaniline as a good sensing material still faces many challenges.

[0005] An invention patent with application number "CN201811533460.5" titled "Ultrafine zinc ferrite nanoparticles, preparation method and gas sensing application thereof" mentions a nanoparticle with a diameter of 8-10nm and a specific surface area of ​​70-90m 2 / g zinc ferrite nanoparticle microspheres and a preparation method and application thereof, the method comprises mixing zinc nitrate hexahydrate, ferric nitrate nonahydrate and an ethanol solution, after the mixture is evenly mixed, dripping ammonia water into the mixed solution, adjusting the pH value of the solution to 9-11, and then placing the mixed solution on a magnetic stirrer for continuous stirring, after sufficient stirring, bathing the mixed solution in water and ultrasonicating, and then transferring the mixed solution to a polytetrafluoroethylene-lined high-pressure reactor and placing it in an oven for reaction; washing the mixture to remove the supernatant by centrifugation, placing the mixture in an oven for drying to obtain a zinc ferrite nanoparticle precursor, and finally drying the dried ultrafine zinc ferrite nanoparticle precursor. Ultrafine zinc ferrite nanoparticles are prepared by high-temperature calcination. The prepared ultrafine zinc ferrite nanoparticles have good gas-sensitive properties and can be directly used as gas-sensitive materials for gas-sensitive research on nitrogen dioxide and its harmful gases. The ultra-large specific surface area provided by the ultrafine zinc ferrite nanoparticles increases the contact area between the gas and the material, which is beneficial to the detection of the gas, and has outstanding selectivity and excellent gas-sensitive performance. Although the above invention can achieve rapid response detection of nitrogen dioxide, the detection limit and long-term stability still have a lot of room for improvement, and the operating temperature is also relatively high. These problems have seriously limited its further application in the field of gas sensing.

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides a zinc ferrite / polyaniline composite material and a preparation method and application thereof, which can effectively prepare a composite material for a nitrogen dioxide sensor with low power consumption, fast response and good stability, effectively improve the gas-sensitive sensing performance for nitrogen dioxide, and can not only be effectively used at lower temperatures, but also have a higher specific surface area, more reactive sites and good gas accessibility. Summary of the invention

[0007] In view of this, the present invention proposes a preparation method and application of a three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensor material, which is applied to the field of nitrogen dioxide sensor technology to solve the technical problems of the existing complex preparation method, high preparation cost, poor gas sensitive sensing performance for nitrogen dioxide, slow response speed and poor stability.

[0008] To achieve the above technical objectives, the specific technical solution adopted by the present invention is as follows:

[0009] A preparation method of a three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material, comprising the following steps:

[0010] S1. Prepare polystyrene (PS) microspheres by emulsion polymerization.

[0011] S2. Clean the glass substrate with piranha solution, perform multiple ultrasonic cleanings on the glass substrate using piranha solution to remove surface dirt and increase hydrophilicity, and prepare an opal photonic crystal template by heating convection self-assembly method. Select monodisperse polystyrene microspheres with a particle size of 150 - 300 nm. Place the glass substrate treated with piranha solution on a hot plate, take a certain amount of polystyrene (PS) microspheres and spread them flat on the surface of the glass substrate, and obtain an opal photonic crystal template after heat curing treatment.

[0012] S3. Prepare a precursor solution by sol-gel method. Dissolve the metal salt in a lower carbon alcohol with citric acid as a chelating agent, stir evenly at room temperature to obtain a transparent metal alkoxide precursor solution, and the molar fraction range of citric acid is 5.0% - 20.0%.

[0013] S4. Fill the opal photonic crystal template obtained in step S2 with the precursor solution. Fill the opal photonic crystal template with the precursor solution by manual dropping, allow the precursor solution to completely diffuse through capillary action, and then further dry it in an oven to obtain a template / precursor complex.

[0014] S5. Place the template / precursor complex in step S4 in a muffle furnace, and remove the polystyrene colloidal microsphere template by high-temperature calcination annealing to obtain a three-dimensional ordered macroporous metal oxide material.

[0015] S6. For the three-dimensional ordered macroporous metal oxide material calcined in step S5, perform an in-situ composite reaction in an aniline, oxidant and protonic acid precursor solution by dip-coating method, and then dry it in an oven to obtain a three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material.

[0016] Further, in step S2, the metal salt is any one of zinc nitrate, iron nitrate, tin chloride, indium nitrate and tungsten chloride. In step S2, the lower carbon alcohols are one or more of methanol, ethanol, ethylene glycol, propanol and isopropanol, and the concentration of the precursor solution is 0.5 M - 2 M.

[0017] Further, when the metal salt is dissolved in the lower carbon alcohol solution in step S3, the addition amount of the citric acid chelating agent is 5.0% - 20.0% by atomic percentage.

[0018] Further, in step S4, the temperature of the oven is 30 - 80 °C, and the drying time is 12 - 48 h. In step S5, the heating rate of the muffle furnace is 1 - 10 °C / min, and the temperature for calcining to remove the polystyrene colloidal microsphere template is 400 - 850 °C.

[0019] Further, in step S6, the oxidant is any one of potassium persulfate and ammonium persulfate, the dosage of the oxidant is 0.05 - 0.5 ml, the protonic acid is any one of hydrochloric acid, sulfuric acid and nitric acid, the dosage of the protonic acid is 10 - 100 ml, the impregnation times are 1 - 50 times, and the impregnation time is 0.5 - 5 min.

[0020] A gas sensor element comprising a three - dimensionally ordered macroporous metal oxide / polyaniline composite gas - sensing material, and the three - dimensionally ordered macroporous metal oxide / polyaniline composite gas - sensing material is attached to the gas sensor element by means of coating.

[0021] A preparation method of a gas sensor element comprising a three - dimensionally ordered macroporous metal oxide / polyaniline composite gas - sensing material, comprising the following steps: grinding the three - dimensionally ordered macroporous metal oxide / polyaniline composite gas - sensing material and uniformly coating it on a planar interdigital electrode sheet, and obtaining a gas sensor element with a three - dimensionally ordered macroporous metal oxide / polyaniline composite gas - sensing material coating through drying and aging.

[0022] Further, after grinding, the three - dimensionally ordered macroporous metal oxide / polyaniline composite gas - sensing material is dispersed in a small amount of ethanol, the drying time after coating is 1 - 24 h, and the aging time is 24 - 48 h.

[0023] An application of a three - dimensionally ordered macroporous metal oxide / polyaniline composite gas - sensing material in a gas sensor.

[0024] In the present invention, polyaniline is coated on the surface of the three - dimensionally ordered macroporous metal oxide material by the dip - coating method. While retaining the high stability of the metal oxide and the high specific surface area of the inverse opal structure material, the optimal operating temperature of the material for NO 2 is significantly reduced (from 300 °C to 98 °C or even room temperature), and moreover, the sensitivity and selectivity of the material for NO 2 are improved, realizing the improvement of the gas - sensing performance for NO 2 .

[0025] The principle of the present invention is mainly based on the stable physical and chemical properties of ZnFe 2 O 4 and the relatively low manufacturing cost. ZnFe 2 O 4As a spinel-type ferrite material, it has strong magnetic and catalytic properties and is also an excellent inorganic pigment. It is usually an n-type semiconductor with a band gap between 1.70 eV and 1.90 eV. The special feature of zinc ferrite is that it has magnetism and can be applied to magnetic sensors, and the response speed and sensitivity of the sensor can be improved through the action of a magnetic field; its band gap is small and it has more active sites, thus improving the sensitivity to gases. Therefore, a gas sensor made of zinc ferrite as a gas-sensitive material has the advantages of low production cost, long service life, small volume, accurate detection of target gases, and stable performance during long-term use. Currently, in order to further improve the gas-sensing performance of such semiconductor gas-sensitive materials to NO 2 On the one hand, through morphology control, the specific surface area of the material is increased, and the contact area between the material and gas molecules is increased to improve the gas-sensing performance. On the other hand, noble metal sensitization is used to improve or endow the material with new properties by doping different types of noble metals, and the sensitivity of the material to the oxidizing gas NO 2 is improved.

[0026] The three-dimensional ordered macroporous metal oxide / polyaniline composite material prepared by the template method, sol-gel method and dip-coating method adopted in the present invention has a surface structure similar to a honeycomb, and its surface with an atomic-level regular inverse opal structure has a high specific surface area, which can provide more active sites. Moreover, the outer layer of polyaniline material further improves the sensitivity selectivity of the material to NO 2 and greatly reduces the working temperature.

[0027] Adopting the above technical solution, the present invention can also bring the following beneficial effects:

[0028] 1. The present invention mentions a preparation method and application of a three-dimensional ordered macroporous metal oxide / polyaniline composite gas-sensing material. The three-dimensional ordered macroporous metal oxide / polyaniline composite material is prepared by the template method, sol-gel method and dip-coating method. Polyaniline is coated on the inverse opal zinc ferrite framework by the dip-coating method. While retaining the high stability of the metal oxide and the high specific surface area of the inverse opal structure material, the optimal working temperature of the gas-sensitive material is greatly reduced, so that it has high selectivity and fast response recovery for the detection of NO 2 gas under low working temperature conditions.

[0029] 2. The present invention relates to a preparation method and application of a three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material. The prepared three-dimensional ordered macroporous metal oxide / polyaniline composite material has an inverse opal structure, which increases its specific surface area, improves the utilization rate of atoms, and has a highly ordered porous structure. The porous interstitial material has good connectivity, and the gas accessibility on the pore wall surface is good, which is conducive to the diffusion of target gases and gas sensing behavior. Therefore, the gas-sensitive material can provide more active sites, improving the adsorption and desorption processes of the target gas NO 2 and accelerating the gas molecule transmission and reaction process, enhancing the gas-sensitive sensing performance of NO 2 . By the dip-coating method, during the synthesis of the three-dimensional ordered macroporous metal oxide / polyaniline composite material, the coating amount of polyaniline on the inverse opal framework of zinc ferrite metal oxide is changed by varying the number of immersion times and immersion time, thereby controlling the loading amount of polyaniline. Through structural synergy and performance synergy, the sensitivity is improved, and the response and recovery performance of the composite material is optimized, enhancing the gas-sensitive sensing performance of NO 2 . ZnFe 2 O 4 itself is one of the best catalysts, which can significantly improve the sensitivity of the gas sensor to NO 2 , accelerate the adsorption and desorption processes of NO 2 gas molecules on the sensor surface, and make the material surface have a higher adsorbed oxygen content, enabling the material to quickly dissociate NO 2 even at low working temperatures, greatly enhancing the desorption performance of the material.

[0030] 3. The present invention relates to a preparation method and application of a three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material. The prepared three-dimensional ordered macroporous metal oxide / polyaniline composite material has a highly ordered porous structure and a stable framework. This characteristic endows the material with an extremely high specific surface area, more reactive sites, and excellent gas accessibility. Not only is the preparation method simple to operate, the raw materials are widely available and the preparation cost is low, but it is also suitable for large-scale promotion, which can effectively drive the development of related industries. When used in a resistive gas sensor, it has high sensitivity and selectivity to NO 2 , and still has high gas-sensitive sensing performance in a relatively low temperature range (for example, below 100 °C and even at room temperature), greatly expanding the scope of application of the present invention and having very positive significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0032] Figure 1 is the XRD pattern of the three-dimensional ordered macroporous metal oxide (zinc ferrite) / polyaniline composite material prepared by the preparation method of the three-dimensional ordered macroporous metal oxide / polyaniline composite material in Example 2 of the present invention;

[0033] Figure 2 is the TEM image of the three-dimensional ordered macroporous metal oxide (zinc ferrite) / polyaniline composite material prepared by the preparation method of the three-dimensional ordered macroporous metal oxide / polyaniline composite material in Example 2 of the present invention;

[0034] Figure 3 is the response / recovery curve of the three-dimensional ordered macroporous metal oxide (zinc ferrite) / polyaniline composite material prepared by the preparation method of the three-dimensional ordered macroporous metal oxide / polyaniline composite material in Example 2 of the present invention to 100 ppm of nitrogen dioxide at room temperature;

[0035] Figure 4 is the response / recovery curve of the three-dimensional ordered macroporous metal oxide (zinc ferrite) / polyaniline composite material prepared by the preparation method of the three-dimensional ordered macroporous metal oxide / polyaniline composite material in Example 2 of the present invention to 100 ppm of nitrogen dioxide at 98 °C;

[0036] Figure 5 is the resistance response / recovery curve of the three-dimensional ordered macroporous metal oxide / polyaniline composite material prepared in Example 2 of the present invention to 100 ppm of nitrogen dioxide at room temperature with different numbers of polyaniline coating times;

[0037] Figure 6 is the resistance response / recovery curve of the three-dimensional ordered macroporous metal oxide / polyaniline composite material prepared in Example 2 of the present invention to 100 ppm of nitrogen dioxide at 98 °C with different numbers of polyaniline coating times;

[0038] Figure 7 is the continuous dynamic response / recovery curve of the three-dimensional ordered macroporous metal oxide (zinc ferrite) / polyaniline composite material prepared by the preparation method of the three-dimensional ordered macroporous metal oxide / polyaniline composite material in Example 2 of the present invention to nitrogen dioxide with different concentrations at room temperature;

[0039] Figure 8It is the continuous dynamic response / recovery curve of the three-dimensional ordered macroporous metal oxide (zinc ferrite) / polyaniline composite material prepared by the preparation method of the three-dimensional ordered macroporous metal oxide / polyaniline composite material in Example 2 of the present invention to nitrogen dioxide with different concentrations at 98 °C;

[0040] Figure 9 It is the short-term continuous dynamic response / recovery curve of the three-dimensional ordered macroporous metal oxide (zinc ferrite) / polyaniline composite material prepared by the preparation method of the three-dimensional ordered macroporous metal oxide / polyaniline composite material in Example 2 of the present invention to 100 ppm of nitrogen dioxide at room temperature;

[0041] Figure 10 It is the short-term continuous dynamic response / recovery curve of the three-dimensional ordered macroporous metal oxide (zinc ferrite) / polyaniline composite material prepared by the preparation method of the three-dimensional ordered macroporous metal oxide / polyaniline composite material obtained in Example 2 of the present invention to 100 ppm of nitrogen dioxide at 98 °C;

[0042] Figure 11 It is the sensitivity change curve of the three-dimensional ordered macroporous metal oxide (zinc ferrite) / polyaniline composite material prepared by the preparation method of the three-dimensional ordered macroporous metal oxide / polyaniline composite material obtained in Example 2 of the present invention to 100 ppm of nitrogen dioxide at different temperatures;

[0043] Figure 12 It is the sensitivity comparison diagram of the three-dimensional ordered macroporous metal oxide (zinc ferrite) / polyaniline composite material prepared by the preparation method of the three-dimensional ordered macroporous metal oxide / polyaniline composite material in Example 2 of the present invention to 6 different gases (100 ppm) at room temperature;

[0044] Figure 13 It is the sensitivity comparison diagram of the three-dimensional ordered macroporous metal oxide (zinc ferrite) / polyaniline composite material prepared by the preparation method of the three-dimensional ordered macroporous metal oxide / polyaniline composite material in Example 2 of the present invention to 6 different gases (100 ppm) at 98 °C. Detailed implementation mode

[0045] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0046] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand the other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0047] It should be noted that the following describes various aspects of the embodiments within the scope of the appended claims. It should be obvious that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is illustrative only. Based on the present invention, those skilled in the art should understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects described herein can be used to implement the device and / or practice the method. In addition, this device can be implemented and this method can be practiced using other structures and / or functions in addition to one or more of the aspects described herein.

[0048] It also needs to be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present invention schematically. The drawings only show the components related to the present invention, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0049] In addition, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0050] Embodiment 1

[0051] S1: Preparation of opal photonic crystal template: Place the glass substrate treated with piranha solution on a hot plate at 85°C. Pipette 700 μL of monodisperse polymer microsphere emulsion onto the surface of the glass substrate. Obtain the opal photonic crystal template through the heating convection self-assembly method, and then cure it at a high temperature of 100°C for 3 hours to enhance the template strength.

[0052] S2. Preparation of precursor solution: Weigh 2.424 g of ferric nitrate nonahydrate and 1.78 g of zinc nitrate hexahydrate, dissolve them in 6 ml of absolute ethanol, stir magnetically for 30 min to fully dissolve, then add 0.08 g of citric acid, continue to stir for 1 h, and obtain the precursor solution, which is sealed for standby.

[0053] S3. Preparation of three-dimensional ordered macroporous zinc ferrite material: Use capillary action to fill the opal photonic crystal template with the precursor solution, let it stand overnight at room temperature, and then calcine at 600 °C for 4 hours to obtain the three-dimensional ordered macroporous metal oxide zinc ferrite material.

[0054] S4. Preparation of three-dimensional ordered macroporous zinc ferrite / polyaniline composite material: Weigh 0.76 g of aniline and 0.56 g of ammonium persulfate, add them to 80 ml of 1 M HCl respectively. The zinc ferrite nanomaterial on the prepared glass substrate is subjected to the dip-coating method, and it is repeatedly immersed 5 times (the immersion time is 1 min) in beakers containing aniline and HCl, ammonium persulfate and HCl, and pure HCl, washed several times with absolute ethanol and deionized water, dried in vacuum for 24 h. The obtained zinc ferrite / polyaniline composite material is ground and coated on a planar interdigital electrode sheet, dried at room temperature, and then aged on an aging table for 48 h to obtain a gas sensor element coated with a gas-sensitive layer of zinc ferrite / polyaniline composite material.

[0055] Example 2

[0056] S1: Preparation of opal photonic crystal template: Place the glass substrate treated with piranha solution on a hot plate at 85 °C, transfer 700 μL of monodisperse polymer microsphere emulsion and spread it on the surface of the glass substrate. The opal photonic crystal template is prepared by the heating convection self-assembly method, and then cured at 100 °C for 3 hours to enhance the template strength.

[0057] S2. Preparation of precursor solution: Weigh 2.424 g of ferric nitrate nonahydrate and 1.78 g of zinc nitrate hexahydrate, dissolve them in 6 ml of absolute ethanol, stir magnetically for 30 min to fully dissolve, then add 0.08 g of citric acid, continue to stir for 1 h, and obtain the precursor solution, which is sealed for standby.

[0058] S3. Preparation of three-dimensional ordered macroporous zinc ferrite material: Use capillary action to fill the opal photonic crystal template with the precursor solution, let it stand overnight at room temperature, and then calcine at 600 °C for 4 hours to obtain the three-dimensional ordered macroporous metal oxide zinc ferrite material.

[0059] S4: Preparation of three-dimensional ordered macroporous zinc ferrite / polyaniline composite: Weigh 0.76 g of aniline and 0.56 g of ammonium persulfate, and add them to 80 ml of 1 M HCl respectively. The zinc ferrite nanomaterial on the prepared glass substrate is subjected to the dip-coating method, and is repeatedly immersed 10 times (the immersion time is 1 min) in beakers containing aniline and HCl, ammonium persulfate and HCl, and pure HCl. After washing several times with absolute ethanol and deionized water, it is vacuum dried for 24 h. The obtained zinc ferrite / polyaniline composite is ground and coated on a planar interdigital electrode sheet. After drying at room temperature, it is further aged on an aging table for 48 h to obtain a gas sensor element coated with a gas-sensitive layer of zinc ferrite / polyaniline composite.

[0060] Example 3

[0061] S1: Preparation of opal photonic crystal template: Place the glass substrate treated with piranha solution on a hot plate at 85 °C, pipette 700 μL of monodisperse polymer microsphere emulsion onto the surface of the glass substrate, and obtain the opal photonic crystal template by the method of heating convection self-assembly. Then, it is cured at a high temperature of 100 °C for 3 hours to enhance the template strength.

[0062] S2: Preparation of precursor solution: Weigh 2.424 g of ferric nitrate nonahydrate and 1.78 g of zinc nitrate hexahydrate, dissolve them in 6 ml of absolute ethanol, and magnetically stir for 30 min to fully dissolve. Then add 0.08 g of citric acid and continue to stir for 1 h to prepare the precursor solution, which is sealed and reserved.

[0063] S3: Preparation of three-dimensional ordered macroporous zinc ferrite material: Use capillary action to fill the precursor solution into the opal photonic crystal template, let it stand overnight at room temperature, and then calcine it at 600 °C for 4 hours to obtain the three-dimensional ordered macroporous metal oxide zinc ferrite material.

[0064] S4: Preparation of three-dimensional ordered macroporous zinc ferrite / polyaniline composite: Weigh 0.76 g of aniline and 0.56 g of ammonium persulfate, and add them to 80 ml of 1 M HCl respectively. The zinc ferrite nanomaterial on the prepared glass substrate is subjected to the dip-coating method, and is repeatedly immersed 20 times (the immersion time is 1 min) in beakers containing aniline and HCl, ammonium persulfate and HCl, and pure HCl. After washing several times with absolute ethanol and deionized water, it is vacuum dried for 24 h. The obtained zinc ferrite / polyaniline composite is ground and coated on a planar interdigital electrode sheet. After drying at room temperature, it is further aged on an aging table for 48 h to obtain a gas sensor element coated with a gas-sensitive layer of zinc ferrite / polyaniline composite.

[0065] The preparation of the three-dimensional ordered macroporous zinc ferrite / polyaniline composites in Example 1, Example 2, and Example 3 was tested for their gas-sensing performance by inputting different working temperatures through a WS-30A gas-sensing element tester to obtain the corresponding response values. The data are shown in the following table:

[0066]

[0067] It can be concluded that the three-dimensional ordered macroporous zinc ferrite / polyaniline composite prepared in Example 2 has the highest output response value, indicating that the three-dimensional ordered macroporous zinc ferrite / polyaniline composite prepared in Example 2 has the highest sensitivity to nitrogen dioxide and is most suitable as a gas-sensing material for a nitrogen dioxide sensor. However, although the performance of the three-dimensional ordered macroporous zinc ferrite / polyaniline composites prepared in Examples 1 and 3 is lower than that of the three-dimensional ordered macroporous zinc ferrite / polyaniline composite in Example 2, they still have very excellent performance compared with existing gas-sensing materials and can be used as materials for gas sensors.

[0068] Corresponding analysis was carried out on the three-dimensional ordered macroporous zinc ferrite / polyaniline composite with the best gas-sensing performance in Example 2. The analysis results are shown in Figures 1 to 6 , where Figure 1 shows the XRD pattern of the three-dimensional ordered macroporous zinc ferrite / polyaniline composite prepared in Example 2. The peak positions of all diffraction peaks in the composite are consistent with those in the standard XRD pattern of spinel-structured zinc ferrite, and no obvious impurity diffraction peaks appear in the standard zinc ferrite spectrum. In addition, no obvious characteristic peaks of polyaniline are found in the XRD pattern, which may be due to the low coating amount of polyaniline in the sample.

[0069] Figure 2 shows the TEM image of the three-dimensional ordered macroporous zinc ferrite / polyaniline composite prepared in Example 2. The zinc ferrite material forms an inverse opal structure after calcination to remove the PS microsphere template, and at the same time, polyaniline is also uniformly coated on the zinc ferrite inverse opal framework, with a particle size range of 150 - 300 nm.

[0070] Figure 3 and Figure 4The sensitivity response / recovery curves of the three-dimensional ordered macroporous zinc ferrite / polyaniline composite prepared in Example 2 to 100 ppm of nitrogen dioxide at room temperature and 98 °C are shown. It can be seen that this gas-sensitive material has a fast response / recovery speed to 100 ppm of nitrogen dioxide at room temperature and 98 °C. The response time at room temperature is less than 2 seconds, and the recovery time is 62 seconds. The response time at 98 °C is 90 seconds, and the recovery time is less than 10 seconds. The response time is the time required to reach 90% of the change amount, and the change amount is the change in the initial resistance value of the sensor in the atmosphere to the resistance value of the sensor after reaching the equilibrium state in the target gas. The recovery time is the time required to reach 90% of the change amount, and the change amount is the change in the resistance value of the sensor in the target gas to the resistance value of the sensor after remaining stable in the environment.

[0071] Figure 5 and Figure 6 The resistance response / recovery curves of the three-dimensional ordered macroporous zinc ferrite / polyaniline composite prepared in Example 2 to 100 ppm of nitrogen dioxide at room temperature and 98 °C with different coating times of polyaniline are shown. It can be seen that the gas-sensitive material with 10 coating times of polyaniline has a faster response / recovery speed and higher sensitivity to 100 ppm of nitrogen dioxide at room temperature and 98 °C than those with 5 and 20 coating times of polyaniline respectively.

[0072] Figure 7 and Figure 8 The continuous dynamic response / recovery curves of the three-dimensional ordered macroporous zinc ferrite / polyaniline composite prepared in Example 2 to nitrogen dioxide with different concentrations at room temperature and 98 °C are shown. It can be seen that this gas-sensitive material has a fast response / recovery speed to nitrogen dioxide with different concentrations at room temperature and 98 °C, and the sensitivity increases positively with the concentration of nitrogen dioxide.

[0073] Figure 9 and Figure 10 The short-term continuous dynamic response / recovery curves of the three-dimensional ordered macroporous zinc ferrite / polyaniline composite prepared in Example 2 to 100 ppm of nitrogen dioxide at room temperature and 98 °C are shown. It can be seen that this gas-sensitive material has good stability and can still maintain stable performance after adsorbing and desorbing nitrogen dioxide multiple times in the short term.

[0074] Figure 11The sensitivity change curve of the prepared three-dimensionally ordered macroporous zinc ferrite / polyaniline composite prepared in Example 2 to 100 ppm of nitrogen dioxide at different temperatures is shown. The prepared three-dimensionally ordered macroporous zinc ferrite / polyaniline composite has a relatively high sensitivity to 100 ppm of nitrogen dioxide at 98 °C, where the sensitivity value for 100 ppm of nitrogen dioxide reaches 261. The sensitivity is the ratio of Ra to Rg, where Ra is the initial resistance value of the gas-sensitive material that remains stable in the environment; Rg is the resistance value of the gas-sensitive material that reaches stability in the target gas.

[0075] Figure 12 and Figure 13 The sensitivity comparison of the prepared three-dimensionally ordered macroporous zinc ferrite / polyaniline composite prepared in Example 2 to 6 different gases (i.e., nitrogen dioxide, methane, acetone, ammonia, methanol, and ethanol, all at a concentration of 100 ppm) at room temperature and 98 °C is shown, thus indicating that the prepared three-dimensionally ordered macroporous zinc ferrite / polyaniline composite has good gas selectivity for nitrogen dioxide.

[0076] Combined Figures 1 to 13 With this, the present invention prepares a three-dimensionally ordered macroporous zinc ferrite / polyaniline composite by using the template method, sol-gel method, and dip-coating method. By dip-coating polyaniline on the zinc ferrite inverse opal framework, while retaining the good gas-sensitive properties of metal oxides, the high specific surface area of the inverse opal structure material, etc., it significantly reduces the optimal working temperature of the material for nitrogen dioxide, enabling it to have high selectivity, fast response and recovery, etc. gas-sensitive sensing properties for nitrogen dioxide gas under low working temperature conditions. In short, the present invention prepares a gas-sensitive sensing material with a simple preparation method, low preparation cost, good long-term stability, high selectivity, and high response to nitrogen dioxide even at low working temperatures.

[0077] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for preparing a three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material, characterized in that: The following steps are involved: S1, preparing polystyrene microspheres by emulsion polymerization; S2, washing the glass substrate with piranha solution and preparing the opal photonic crystal template by heating convection self-assembly method; S3, preparing a precursor solution by a sol-gel method, dissolving a metal salt in a low-carbon alcohol with citric acid as a chelating agent, stirring evenly at room temperature to obtain a transparent metal alkoxide precursor solution, wherein the molar fraction of citric acid ranges from 5.0% to 20.0%; S4, filling the opal photonic crystal template obtained in step S2 with a precursor solution, manually dripping the precursor solution into the opal photonic crystal template, and further drying in an oven to obtain a template / precursor complex; S5, placing the template / precursor complex of step S4 in a muffle furnace, removing the polystyrene colloidal microsphere template by high-temperature calcination annealing, and obtaining a three-dimensional ordered macroporous metal oxide material; S6. The material calcined in step S5 is subjected to an in-situ composite reaction in a precursor solution of aniline, an oxidant and a protonic acid by a pulling and impregnation method, and then dried in an oven to obtain a three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material.

2. The method for preparing a three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material according to claim 1, characterized in that: In step S2, the metal salt is any one of zinc nitrate, iron nitrate, tin chloride, indium nitrate and tungsten chloride, and the low-carbon alcohol in step S2 is one or more of methanol, ethanol, ethylene glycol, propanol and isopropanol. The concentration of the precursor solution is 0.5M to 2M.

3. The method for preparing a three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material according to claim 2, characterized in that: When the metal salt is dissolved in the low-carbon alcohol solution in step S3, the amount of the citric acid chelating agent added is 5.0% to 20.0% in terms of atomic percentage.

4. The method for preparing a three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material according to claim 3, characterized in that: In step S4, the temperature of the oven is 30-80° C., the drying time is 12-48 hours, the heating rate of the muffle furnace in step S5 is 1-10° C. / min, and the temperature for calcining and removing the polystyrene colloidal microsphere template is 400-850° C.

5. The method for preparing a three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material according to claim 4, characterized in that: In step S6, the oxidant is any one of potassium persulfate and ammonium persulfate, the amount of the oxidant is 0.05-0.5 ml, the protonic acid is any one of hydrochloric acid, sulfuric acid and nitric acid, the amount of the protonic acid is 10-100 ml, the number of immersions is 1-50 times, and the immersion time is 0.5-5 min.

6. A gas sensing element comprising the three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material as claimed in claim 1, characterized in that: The three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material is attached to the gas sensing element by means of a coating.

7. A method for preparing a gas sensing element comprising a three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material as claimed in claim 6, characterized in that: The method comprises the following steps: grinding a three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material and uniformly coating it on a plane interdigitated electrode sheet, and drying and aging the material to obtain a three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material coating gas sensitive element.

8. The method for preparing a gas sensor comprising a three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material according to claim 7, characterized in that: The three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material is dispersed in a small amount of ethanol after grinding, and the drying time after coating is 1 to 24 hours, and the aging time is 24 to 48 hours.

9. Use of the three-dimensional ordered macroporous metal oxide / polyaniline composite gas sensing material as claimed in claim 1 in a gas sensor.

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