CN110836913A - Iron-doped porous indium oxide gas-sensitive material and preparation method and application thereof - Google Patents

Abstract

The present invention relates to NO₂The technical field of gas sensitive materials, in particular to an iron-doped porous indium oxide gas sensitive material and a preparation method and application thereof. The gas-sensitive material consists of a matrix phase and a doping phase, wherein the matrix phase is porous indium oxide and is a monodisperse porous nanorod, and the porous nanorod consists of particles with a pore channel structure; the doped phase is iron ions, and the doped phase is doped in the matrix phase crystal lattice in the form of the iron ions. The iron-doped porous indium oxide gas-sensitive material effectively improves the effect of pure indium oxide as the gas-sensitive material on low-concentration NO₂Low sensitivity, poor selectivity and long response recovery time. Through tests, the gas sensitive element prepared by adopting the gas sensitive material is specific to NO₂The gas has excellent selectivity and low concentration of NO₂The gas has high sensitivity, and the working temperature is reduced to be below 100 ℃, so that the power requirement on instrument equipment is obviously reduced.

Description

A kind of iron-doped porous indium oxide gas sensing material and preparation method and application thereof

technical field

The invention relates to the technical field of NO ₂ gas-sensing materials, in particular to an iron-doped porous indium oxide gas-sensing material and a preparation method and application thereof.

Background technique

The information disclosed in this Background of the Invention is only for enhancement of understanding of the general background of the invention and should not necessarily be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person of ordinary skill in the art.

Nitrogen dioxide (NO ₂ ) gas is a brown-red, irritating, toxic gas, and is one of the main pollutants in the atmosphere. As a typical polluting gas in industrial waste gas and domestic waste gas, NO ₂ gas has high chemical activity and strong corrosiveness, and can react with moisture or hydrocarbons in the air to form acid rain, photochemical smog and fog. The main source of secondary pollutants such as haze is a serious threat to people's health and living environment. According to the American Association of Governmental Industrial Hygiene (ACGIH) and the Occupational Safety and Health Administration (US ₎ , the threshold limit for exposure to NO2 gas is 3ppm, of which the exposure time to 1ppm _NO2 gas is not more than 15min. Therefore, designing gas-sensing sensing materials with high sensitivity and selectivity is of great significance for detecting low _- concentration NO2 gas.

Porous indium oxide material has great application prospects in the field of gas detection due to its tunable pore structure, high specific surface area and strong ion exchange performance, which is conducive to the reaction of reactants at the active site. Indium oxide materials are widely used in the field of gas sensing. However, a large number of studies have shown that the gas-sensing properties of a single In ₂ O ₃ gas-sensing material are controlled by the material's morphology, structure, crystal form, specific surface area, energy band structure and other factors. Disadvantages such as poor selectivity. At the same time, the inventors found that the working temperature of some existing porous In ₂ O ₃ gas-sensing materials is too high. Above 300 ℃ (see document 1); Zhang Meng of Taiyuan University of Technology and others proposed that noble metal modified indium oxide microstructure gas-sensing material has good sensitivity and response recovery speed to test gas at about 200 ℃ (see document 2); Shanghai University of Technology Second University The nano-indium oxide and composite materials proposed by Chen Yang et al. can effectively improve the gas sensing performance at low temperature, but the working temperature is still above 150 °C when detecting NO ₂ gas (see Reference 3). The operating temperature of these gas sensors, which can reach hundreds of degrees Celsius, requires extremely high power requirements of the instruments and equipment, which limits the practical application of indium oxide in the field of gas sensors.

Existing literature:

Literature 1: Deng Ni, Preparation of metal element-doped mesoporous indium oxide and its gas sensing properties [D], China Jiliang University, 2016.

Literature 2: Zhang Meng, Preparation, modification and sensitivity of indium oxide microstructure [D], Taiyuan University of Technology, 2017.

Literature 3: Chen Yang, Preparation and gas sensing properties of nano-In ₂ O ₃ and its composites [D], Shanghai Second Polytechnic University, 2018.

SUMMARY OF THE INVENTION

Aiming at the shortcomings of low sensitivity, poor selectivity and high working temperature of indium oxide for low-concentration nitrogen dioxide gas detection, the present invention aims to provide an iron-doped porous indium oxide gas sensing material and a preparation method and application thereof. The gas sensing element prepared with iron-doped porous indium _oxide gas sensing material has the advantages of high sensitivity and excellent selectivity to NO gas including low concentration at low temperature, and also has a fast response recovery speed.

The first objective of the present invention is to provide an iron-doped porous indium oxide gas-sensing material.

The second object of the present invention is to provide a preparation method of an iron-doped porous indium oxide gas-sensing material.

The third object of the present invention is to provide the application of the iron-doped porous indium oxide gas-sensing material.

For realizing the above-mentioned purpose of the invention, the technical means adopted in the present invention are:

First, the present invention discloses an iron-doped porous indium oxide gas sensing material, which is composed of a matrix phase and a doping phase, the matrix phase is porous indium oxide, which is a monodisperse porous nanorod, and the porous nanorod is composed of Particle composition with pore structure; the doped phase is iron ions, and the doped phase is doped inside the lattice of the matrix phase in the form of iron ions.

One of the characteristics of the iron-doped porous indium oxide gas-sensing material of the present invention is: because the gas-sensing material is a monodispersed porous nanorod, it has a very high specific surface area; The adsorption provides more active sites, and the porous structure provides abundant channels for gas diffusion _on the surface of the material, which are beneficial to improve the sensitivity and response recovery speed _of the _In2O3 material to NO2 gas.

The second characteristic of the iron-doped porous indium oxide gas-sensing material of the present invention is that in the iron-doped porous indium oxide gas-sensing material, the doping of metal iron (Fe) can increase the oxygen vacancies on the surface of the porous indium oxide material on the one hand. concentration, improve the electrical properties of the material at low temperature, increase the number of NO ₂ gas adsorbed on the surface of the material at low temperature and the number of molecules participating in the gas-sensing reaction; The surface activity at low temperature increases the sensitivity of In ₂ O ₃ material to NO ₂ gas at low temperature, thus realizing the detection of NO ₂ gas of In ₂ O ₃ material at low temperature.

Secondly, the present invention discloses a preparation method of an iron-doped porous indium oxide gas-sensing material, comprising the following steps:

(1) Dissolving the matrix raw material, the doped phase raw material and the organic ligand in an organic solvent, and solvothermally prepares a coordination polymer of indium iron; the matrix raw material is indium salt, and the doped phase raw material is iron Salt;

(2) calcining the coordination polymer of indium-iron to obtain.

Finally, the present invention discloses the application of the iron-doped porous indium oxide gas sensing material in gas detection.

Compared with the prior art, the present invention has achieved the following beneficial effects:

(1) The iron-doped porous indium oxide gas-sensing material of the present invention effectively improves the problems of low sensitivity, poor selectivity and long response recovery time to low-concentration NO ₂ when pure indium oxide is used as a gas-sensing material. After testing, the gas-sensing element prepared by using the gas-sensing material of the invention has excellent selectivity for NO ₂ gas, high sensitivity to low-concentration NO ₂ gas, and the working temperature drops below 80°C, which significantly reduces the need for instruments and equipment. power requirements.

(2) The iron-doped porous indium oxide gas-sensing material of the present invention is a nanorod with uniform size and monodispersity, and has good dispersibility, which can avoid the problem of uneven coating caused by agglomeration during the preparation of the gas-sensing element.

(3) The preparation method of the present invention is a one-step synthesis of gas-sensitive materials. This is because the matrix phase and the doping are generated under the same solvothermal conditions. Since the ratio of the matrix raw materials is higher than that of the doping phase raw materials, the matrix phase becomes the main body during crystallization. Therefore, The one-step method not only directly synthesizes the gas-sensitive material, but also has a simple and time-saving operation, and the effect is better.

(4) The present invention provides an iron-doped porous indium _oxide gas sensing element for NO2 gas prepared by a safe and effective method. The preparation method is safe and effective, and the required equipment is simple and easy to operate, the process parameters are easy to control, and the raw materials and low cost of equipment and equipment.

Description of drawings

The accompanying drawings forming a part of the present invention are used to provide further understanding of the present invention, and the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, and do not constitute an improper limitation of the present invention.

FIG. 1 is a scanning electron microscope (SEM) photograph of the iron-doped porous indium oxide gas-sensing material prepared in Example 1 of the present invention.

2 is a transmission electron microscope (TEM) photograph of the iron-doped porous indium oxide gas-sensitive material prepared in Example 1 of the present invention.

3 is a BET specific surface area spectrum of the iron-doped porous indium oxide gas sensing material prepared in Example 1 of the present invention.

4 is an energy dispersive spectrum diagram of the iron-doped porous indium oxide gas-sensing material prepared in Example 1 of the present invention.

FIG. 5 is the XRD patterns of the iron-doped porous indium oxide gas sensing material prepared in Example 1 of the present invention and the iron-doped porous indium oxide without iron prepared in the comparative example.

6 is the O1s peak energy spectrum of the X-ray photoelectron diffraction of the iron-doped porous indium oxide gas sensitive material prepared in Example 1 of the present invention.

FIG. 7 is the O1s peak energy spectrum of the X-ray photoelectron diffraction of the iron-undoped porous indium oxide prepared by the comparative example of the present invention.

FIG. 8 is a schematic diagram of a bypass heat sensor in an embodiment of the present invention. In the figure, 1 represents the alumina ceramic substrate; 2 represents the tested gold electrode; 3, 4 represents the tested platinum electrode; 5 represents the heating electrode; 6, 7 represents the Ni-Cr electrode; 8 represents the gas-sensing material layer.

9 shows the response values of the iron-doped porous indium oxide nanorods prepared in Examples 1 and 2 of the present invention and the undoped iron-doped porous indium oxide prepared in the comparative example to 2 ppm NO ₂ gas at 80°C.

10 is a graph showing the gas sensing performance of the iron-doped porous indium oxide gas sensing material prepared in Example 1 of the present invention for NO ₂ gas at different concentrations at 80°C.

11 is a bar graph of the response values of the iron-doped porous indium oxide gas sensing material prepared in Example 1 of the present invention and the undoped iron-doped porous indium oxide prepared in the comparative example to 2 ppm of different gases at 80°C.

Detailed ways

It should be noted that the following detailed description is exemplary and intended to provide further explanation of the invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It should be noted that the terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural as well, furthermore, it is to be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates that There are features, steps, operations, devices, components and/or combinations thereof.

As mentioned above, the gas sensing performance of a single _{In 2} O ₃ gas sensing material is controlled by the material's morphology, structure, crystal form, specific surface area, energy band structure and other factors. Disadvantages such as low sensitivity and poor selectivity. At the same time, the temperature required for the operation of some existing porous In ₂ O ₃ gas-sensing materials is too high. To this end, the present invention provides an iron-doped porous indium oxide gas sensing material and a preparation method thereof.

In some typical embodiments, the doping amount of the iron ions is 0.5-20 mol%; preferably 3-20 mol%, more preferably 5-10 mol%. For iron-doped porous indium oxide gas-sensing materials, with the increase of iron doping content, the increase of oxygen vacancies on the surface of gas-sensing materials is conducive to the adsorption of NO ₂ gas on the surface of the material and participating in the gas-sensing reaction, improving the material's ability to _The sensitivity of NO2 gas, however, excessive iron doping causes the destruction of the lattice structure of indium oxide, which is not conducive to the optimization of its electrical properties, which reduces its electron transfer efficiency and inhibits the improvement of its gas sensing properties.

In some typical embodiments, the porous nanorods have a diameter of 0.5-3 μm and a length of 1-9 μm.

In some typical embodiments, the molar ratio of the doping phase raw materials to the matrix phase raw materials is 0.5-20 mol %; preferably 3-10 mol %. The test results show that when the iron ion doping amount within the above range is selected , the obtained gas _- sensing material has better sensitivity to low concentrations of NO.

In some typical embodiments, the organic ligand is 0.5-2 times the molar amount of the base material.

In some typical embodiments, the indium salt includes one or more of indium chloride, indium nitrate, and indium sulfate.

In some typical embodiments, the iron salt includes one or more of ferric nitrate, ferric chloride, and ferric acetylacetonate.

In some typical embodiments, the organic ligand is terephthalic acid, and in the solvothermal reaction process, octahedral groups (InO ₄ (OH) ₂ , FeO ₄ (OH) centered on indium and iron ) ₂ ) through terephthalic acid, the organic chains are coupled to each other and grow into a hexagonal indium-iron coordination polymer with nano-rod nanostructures.

In some typical embodiments, the organic solvent is N,N-dimethylacetamide. The added amount of the solvent can fully dissolve the matrix raw materials, the doping phase raw materials and the organic ligands.

In some typical embodiments, the temperature of the solvothermal method is 80-150° C., and the reaction time is 5-20 min.

In some typical embodiments, the calcination temperature is 450-540° C., and the calcination time is 1.5-2.5 h.

In some typical embodiments, the present invention uses the prepared iron-doped porous indium oxide gas-sensing material for preparing a NO ₂ gas-sensing element; including a ceramic substrate 1 and a gas-sensing material layer 8 ; the gas-sensing material layer 8 attached to the surface of the ceramic substrate 1 .

In some typical embodiments, the preparation method of the NO ₂ gas sensing element is as follows: coating the gas sensing material slurry on the surface of the ceramic substrate, and drying to obtain the NO ₂ gas sensing element.

In some typical embodiments, the preparation method of the gas-sensing material slurry is as follows: adding the iron-doped porous indium oxide gas-sensing material to the mixed solution of ethyl cellulose and terpineol, and stirring it evenly.

Optionally, the ratio of the ethyl cellulose to terpineol is 1:5-10, preferably 1:9.

In some typical embodiments, the NO ₂ gas sensing element is used to prepare a bypass heat sensor, one side of the NO ₂ gas sensing element is provided with a test electrode and a platinum wire, and the other side of the NO ₂ gas sensing element is provided There are heating electrodes and Ni-Cr electrodes.

Further, the material of the ceramic substrate is any one of aluminum oxide and silicon oxide; the materials of the test electrode and the heating electrode are both gold.

In order to enable those skilled in the art to understand the technical solutions of the present invention more clearly, the present invention will now be further described with reference to the accompanying drawings and specific embodiments of the description.

The first embodiment , a preparation method of an iron-doped porous indium oxide gas sensing material, includes the following steps:

(1) Add 0.39g base material In(NO ₃ ) ₃ ·4.5H ₂ O, 0.0175g doped phase raw material Fe(C ₁₅ H ₂₁ O ₆ ), 0.18g organic ligand H ₂ BDC to 75ml organic solvent N , stir in N-dimethylacetamide until dissolved;

(2) The clear liquid stirred in step (1) is placed in an oil bath at 100° C. for 10 min to react, so that the raw materials undergo a coordination polymerization reaction to obtain a coordination polymer of indium iron, and then the polymer is centrifuged to separate out , washed with methanol for 5 times, and dried in an oven at 80 °C.

(3) The dried coordination polymer of indium iron is calcined in a muffle furnace at 500° C. for 2 hours to obtain a powdery iron-doped porous indium oxide gas sensing material.

The second embodiment , a preparation method of an iron-doped porous indium oxide gas sensing material, is the same as the embodiment 1, except that the molar ratio of the doping phase to the base material in step (1) is 3mol%, 10mol%, 20mol% %.

The third embodiment , a preparation method of an iron-doped porous indium oxide gas sensing material, includes the following steps:

(1) Add 0.39g base material indium chloride, 0.0175g doped phase raw material Fe(NO ₃ ) ₃ and 0.09g organic ligand H ₂ BDC into 75ml organic solvent N,N-dimethylacetamide and stir until dissolve;

(2) The clear liquid stirred in step (1) is placed in an oil bath at 80° C. for 20 min to react, so that the raw material undergoes a coordination polymerization reaction to obtain a coordination polymer of indium iron, and then the polymer is centrifuged to separate out , washed with methanol for 5 times, and dried in an oven at 80 °C.

(3) calcining the dried indium-iron coordination polymer at 450° C. for 2.5 hours in a muffle furnace to obtain a powdered iron-doped porous indium oxide gas sensing material.

The fourth embodiment , a preparation method of an iron-doped porous indium oxide gas sensing material, includes the following steps:

(1) Add 0.39g base material In ₂ (SO ₃ ) ₃ , 0.0175g doped phase raw material FeCl ₃ and 0.36g organic ligand H ₂ BDC into 75ml organic solvent N,N-dimethylacetamide and stir until dissolve;

(2) The clear liquid stirred in step (1) is placed in an oil bath at 150° C. for 5 min to react, so that the raw material undergoes a coordination polymerization reaction to obtain a coordination polymer of indium iron, and then the polymer is centrifuged to separate out , washed with methanol for 5 times, and dried in an oven at 80 °C.

(3) The dried coordination polymer of indium iron is calcined in a muffle furnace at 540° C. for 1.5 hours to obtain a powdered iron-doped porous indium oxide gas sensing material.

In the comparative example, the preparation method of the undoped porous indium oxide gas sensing material includes the following steps:

(1) 0.39g of base material In(NO ₃ ) ₃ ·4.5H ₂ O and 0.18g of organic ligand H ₂ BDC were added to 75ml of organic solvent N,N-dimethylacetamide and stirred until dissolved;

(2) The clear liquid stirred in step (1) is placed in an oil bath at 100° C. for 10 min to react, so that the raw materials undergo a coordination polymerization reaction to obtain a coordination polymer of indium iron, and then the polymer is centrifuged to separate out , washed with methanol for 5 times, and dried in an oven at 80 °C.

(3) The dried coordination polymer of indium iron is calcined in a muffle furnace at 500° C. for 2 hours to obtain a powdery iron-doped porous indium oxide gas sensing material.

Performance Testing:

Figure 1 is the SEM image of the iron-doped porous indium oxide gas-sensing material prepared in Example 1. It can be seen that the doped gas-sensing material is a monodisperse nanorod, and the diameter of the nanorod is about 0.5-3 μm. , the length is about 1-9 μm.

Figure 2 is a TEM image of the iron-doped porous indium oxide gas-sensing material prepared in Example 1. It can be seen that the iron-doped porous indium oxide nanorods are porous nanorods composed of small particles, showing abundant pore structure.

FIG. 3 is the BET specific surface area result of the iron-doped porous indium oxide gas sensing material prepared in Example 1, which shows that the specific surface area of the iron-doped porous indium oxide is as high as 52.7 m ² /g. Compared with bulk indium oxide gas sensing materials, the large specific surface area provides favorable channels and active surfaces for gas adsorption and desorption, which is beneficial to the improvement of material sensitivity and response recovery speed.

Fig. 4 is the energy dispersive spectrum of the iron-doped porous indium oxide gas-sensing material prepared in Example 1. The results show that the iron-doped porous indium oxide nanorods obtained by solvothermal calcination include In, Fe, O elements, and the three elements are uniformly distributed on the surface of the material.

5 is the X-ray spectrum of the iron-doped porous indium oxide gas sensing material prepared in Example 1 and the porous indium oxide nanorod prepared in Comparative Example 1. It can be seen from the figure that after doping the porous indium oxide, and No other crystal phases appeared, but their diffraction peaks tended to shift to high angles; in addition, after the doping treatment of porous indium oxide, the intensity of its diffraction peaks decreased and the peak width became wider. The above results show that metallic iron successfully enters the lattice of pure porous indium oxide in the form of ions, and regulates the oxygen vacancy concentration on the surface of the material.

Figures 6 and 7 are the O1s peak energy spectra of the X-ray photoelectron diffraction of the iron-doped porous indium oxide gas sensing material prepared in Example 1 and the undoped iron-doped porous indium oxide prepared in the comparative example, respectively. After the porous indium oxide was doped with metal iron, the oxygen vacancy concentration on its surface increased from 24.6% to 25.4%. The significant increase in the oxygen vacancy concentration was conducive to the adsorption of nitrogen dioxide gas on the surface of the gas sensing material, which could improve the gas sensitivity Sensitivity of materials to nitrogen dioxide gas.

The iron-doped porous indium oxide gas-sensing materials prepared in Examples 1 and 2 are prepared into gas-sensing elements, and the preparation method is as follows:

1. Preparation of gas sensor:

(1) Add the powdered iron-doped porous indium oxide gas-sensing material prepared according to the method of Example 1 into a mixed solution of ethyl cellulose and terpineol (mass ratio 1:9), stir evenly, and the obtained gas Sensitive material slurry, the mass ratio of the gas-sensitive material to the mixed solution is 1:4.

(2) Apply the gas-sensitive material slurry of step (1) on the surface of the alumina ceramic substrate 1 to form a gas-friendly material layer 8, and dry to obtain a gas-sensitive element.

2. Preparation of the side-heating sensor: its schematic diagram is shown in Figure 8. The right picture is the back of the left picture. The alumina ceramic substrate 1 is used as the carrier, and gold electrodes are coated on both sides. They are the test electrode 2 and the heating element. Electrode 5, and lead out test platinum electrodes 3, 4 and heated Ni-Cr electrodes 6, 7, the side of alumina ceramic substrate 1 coated with test electrode 2 is coated with gas-sensitive material layer 8.

At the same time, the non-iron-doped porous indium oxide prepared in the comparative example was also made into a gas sensor according to the above method, and the obtained five groups of gas sensors were assembled into a side-heat sensor, and were heated at 80 °C and 2 ppm NO ₂ gas conditions. The gas-sensing properties of iron-doped porous indium oxide have a certain change after changing the doping phase concentration, but the gas-sensing properties of iron-doped porous indium oxide have a certain change. It exhibits high sensitivity, especially when the doping phase is 5 mol%, and its response value reaches 9 times that of the doping phase zero.

10 is the response value of the sensor prepared by the iron-doped porous indium oxide gas sensing material prepared in Example 1 to different concentrations of NO ₂ gas at 80°C. It can be seen from the figure that at the working temperature of 80 °C, the response value of the material increases steadily with the increase of gas concentration. Iron-doped porous indium oxide nanorods exhibit high response values (82) and fast response recovery times (75/60s) when the NO gas concentration is ₂ ppm, the response values of the material in the gas environment The ratio of resistance to its resistance in air; at the same time, it also shows that the iron-doped porous indium oxide gas sensing material of the present invention can reduce the working temperature of the sensor to below 100 °C, and still has excellent sensitivity to low-concentration NO ₂ gas; In addition, other experimental test results show that the iron-doped porous indium oxide gas-sensing material prepared by the method of the present invention can still achieve good detection of low-concentration NO ₂ gas at a working temperature as low as 80°C.

Figure 11 shows the response values of the iron-doped porous indium oxide gas sensing material prepared in Example 1 and the sensor made of the undoped iron-doped porous indium oxide prepared in the comparative example to 2 ppm different gases at 80 °C; it can be seen that, Compared with the undoped porous indium oxide, the iron-doped porous indium _oxide gas-sensing material exhibits a higher response to NO gas (82), which is the response of pure porous indium oxide nanorods to 2 ppm NO. 29 times the gas response value ( ₉ ). The response value for other gases is close to 1, which means almost no response, which indicates that the iron-doped porous indium _oxide gas sensing material significantly improves the selectivity of pure porous indium oxide nanorods to NO gas and exhibits excellent of selectivity.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. An iron-doped porous indium oxide gas-sensing material, characterized in that, it is composed of a matrix phase and a doping phase, and the matrix phase is porous indium oxide, which is a monodispersed porous nanorod, and the porous nanorod is It is composed of particles with a channel structure; the doped phase is iron ions, and the doped phase is doped inside the lattice of the matrix phase in the form of iron ions. 2 . The iron-doped porous indium oxide gas sensing material according to claim 1 , wherein the doping amount of the iron ions is 0.5-20 mol %; preferably 3-10 mol %. 3 . 3 . The iron-doped porous indium oxide gas sensing material according to claim 1 , wherein the porous nanorods have a diameter of 0.5-3 μm and a length of 1-9 μm. 4 . 4. A preparation method of iron-doped porous indium oxide gas-sensing material, characterized in that the steps are: (1) Dissolving the matrix raw material, the doped phase raw material and the organic ligand in an organic solvent, and solvothermally prepares a coordination polymer of indium iron; the matrix raw material is indium salt, and the doped phase raw material is iron Salt; (2) calcining the coordination polymer of indium-iron to obtain. 5 . The preparation method of iron-doped porous indium oxide gas sensing material according to claim 4 , wherein the molar ratio of the doped phase raw material to the matrix phase raw material is 0.5-20 mol %; preferably 3-20 mol 5 . %, more preferably 5-10 mol%; Alternatively, the organic ligand is 0.5-2 times the molar amount of the base material. 6. The preparation method of iron-doped porous indium oxide gas sensing material according to claim 4, wherein the indium salt comprises one or more of indium chloride, indium nitrate, and indium sulfate; Or, described ferric salt includes one or more in ferric nitrate, ferric chloride, ferric acetylacetonate; Alternatively, the organic ligand is terephthalic acid; Alternatively, the organic solvent is N,N-dimethylacetamide. 7. The preparation method of iron-doped porous indium oxide gas sensitive material according to claim 4, wherein the temperature of the solvothermal method is 80-150°C, and the reaction time is 5-20min; Alternatively, in some typical embodiments, the calcination temperature is 450-540° C., and the calcination time is 1.5-2.5 h. 8 . A NO ₂ gas sensor, characterized in that it comprises a ceramic substrate and a gas-sensitive material layer; the gas-sensitive material layer is made of the iron-doped porous indium oxide gas sensor according to any one of claims 1-3. The material and/or the iron-doped porous indium oxide gas-sensing material prepared by the method of any one of claims 4-7 is formed by adhering to the surface of the ceramic substrate; Any kind of silicon. 9 . The NO ₂ gas sensing element according to claim 8, wherein the preparation method of the NO ₂ gas sensing element is as follows: coating the gas sensing material slurry on the surface of the ceramic substrate, and drying to obtain NO ₂ gas sensor; Preferably, the preparation method of the gas-sensing material slurry is as follows: adding the iron-doped porous indium oxide gas-sensing material into the mixed solution of ethyl cellulose and terpineol, and stirring evenly, that is, to obtain; Preferably, the ratio of the ethyl cellulose to terpineol is 1:5-10, preferably 1:9. 10. Application of the NO ₂ gas sensor according to claim 8 or 9 in gas detection.

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