Composite neodymium ferrite-doped gas-sensitive material and application thereof in detection of carbon monoxide in pyrolysis gas

Abstract

The invention discloses a composite doped neodymium ferrite-based gas-sensitive material and application thereof in detection of carbon monoxide in pyrolysis gas, and relates to the technical field of gas-sensitive materials. According to the invention, NdFeO3 is used as a substrate material, and two elements of Ag and Pd are adopted to modify the NdFeO3 to prepare the composite doped neodymium ferrite-based gas sensitive material. The composite neodymium ferrite-doped gas-sensitive material prepared by the invention keeps good gas-sensitive response to CO gas within the temperature range of 160-220 DEG C, and also has good moisture resistance and long-term stability. Specifically, the response value of the prepared composite doped neodymium ferrite-based gas sensitive material to 10 ppm CO gas at 180 DEG C is 9.73, the change rate of the response value is less than 10% when the relative humidity RH is less than 60%, and the change rate of the response value within one month is less than 5%.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of gas-sensitive materials, in particular to a composite doped neodymium ferrite-based gas-sensitive material and application thereof in detecting carbon monoxide in pyrolysis gas. BACKGROUND

[0002] As a key process for the resource utilization of organic solid waste (such as biomass, sludge, plastic), the pyrolysis process produces pyrolysis gas with high calorific value, which can be used as fuel or chemical raw material. The pyrolysis gas is complex in composition and mainly contains H2, CH4, CO, CO2 and a small amount of high-order hydrocarbons.

[0003] CO is a colorless and odorless gas, which is one of the main pollutants produced in the pyrolysis process. Detecting the CO concentration in the pyrolysis gas is a rigid requirement for safety. As a toxic gas, direct emission of CO will cause poisoning of operating personnel, oxygen deficiency and symptoms such as headache and nausea, which poses a threat to ecological balance and human health. Studies have shown that when the CO concentration in the pyrolysis gas exceeds the threshold, the poisoning effect is more obvious, and high-concentration CO will cause dizziness, poisoning and other symptoms in the human body, and increase the risk of cardiovascular disease. At the same time, CO is also an easily flammable and explosive gas, which can easily cause explosion when its concentration is within the explosion limit (12.5%-74.2%) and meets a naked flame. It poses a serious threat to life and property safety. In addition, with the increasingly stringent environmental regulations, the emission of pyrolysis gas has become a red line for project operation permission. As an air pollutant, the emission concentration of CO is strictly limited. Therefore, detecting the CO concentration in the pyrolysis gas is an indispensable key link for preventing explosion and poisoning accidents, ensuring personnel safety and meeting environmental regulations.

[0004] In the prior art, gas chromatography, infrared absorption and mass spectrometry are used to detect CO in the pyrolysis gas, but the detection process usually requires manual sampling and transportation to the laboratory, and after complex sample pretreatment, the final data can be obtained by on-machine analysis. These methods are time-consuming, costly and dependent on large special equipment. The new type of gas-sensitive sensor designed by using the characteristics of gas-sensitive materials has the advantages of fast response speed, low cost, portability and controllable process, and can realize online real-time detection, but there is no report on the use of gas-sensitive materials for detecting the CO concentration in the special environment of pyrolysis gas. SUMMARY

[0005] In view of the prior art, the present application aims to provide a composite doped neodymium ferrite-based gas sensitive material and its application in detecting carbon monoxide in pyrolysis gas. The composite doped neodymium ferrite-based gas sensitive material is prepared by doping NdFeO3 with Ag and Pd. The composite doped neodymium ferrite-based gas sensitive material has a high gas response to CO gas in the temperature range of 160-220℃, and has good humidity resistance and stability. In particular, the response value of the composite doped neodymium ferrite-based gas sensitive material to 10ppm CO gas reaches 9.73 at a working temperature of 180℃, the response value change rate is less than 10% when the relative humidity is less than 60%, and the response value change is less than 5% within one month. In addition, the composite doped neodymium ferrite-based gas sensitive material prepared by the present application has a detection result of CO concentration in pyrolysis gas environment that is highly consistent with that of gas chromatography, and has good accuracy.

[0006] To achieve the above object, the present application adopts the following technical solutions: In a first aspect, the present application provides a composite doped neodymium ferrite-based gas sensitive material, which has a chemical formula of Xwt%Ag-Ywt%Pd-NdFeO3, wherein X and Y represent the doping amounts of Ag and Pd in the composite doped neodymium ferrite-based gas sensitive material, and 0X≤5 and 0Y≤10.

[0007] In a second aspect, the present application provides a preparation method of the composite doped neodymium ferrite-based gas sensitive material, which comprises the following steps: (1) mixing Nd(NO3)3·6H2O and Fe(NO3)3·9H2O with citric acid, then adding water to mix them uniformly to obtain a mixed solution, adding NaOH solution to the mixed solution to react, and after the reaction is completed, filtering, washing and drying the reaction product to obtain a NdFeO3 precursor; (2) dispersing the NdFeO3 precursor in water to obtain a NdFeO3 solution, adding AgNO3 and PdCl2 to the NdFeO3 solution to react, collecting the solid after the reaction, washing and drying the solid, and then calcining the solid in an air atmosphere at 400-600℃ for 2.5-3.5h to obtain the composite doped neodymium ferrite-based gas sensitive material; The amounts of Nd(NO3)3·6H2O, Fe(NO3)3·9H2O, PdCl2, AgNO3 and citric acid added are (0.01-0.05) mol:(0.01-0.05) mol:(0.01-2) g:(0.01-1) g:(5-20) g, respectively.

[0008] Preferably, in step (1), the concentration of the NaOH solution is 1-2mol / L.

[0009] As preferred, in step (1), the mass ratio of the mixed solution and the NaOH solution is 1:(1-2).

[0010] As preferred, in step (1), the reaction time is 1-2h.

[0011] As preferred, in step (1), the washing operation is that the filtered solid is washed with ionized water and ethanol for 3-5 times in sequence.

[0012] As preferred, in step (1), the drying mode is vacuum drying, the drying temperature is 70-90℃, and the drying time is 6-12h.

[0013] As preferred, in step (2), the reaction temperature is 60-80℃, and the reaction time is 2-4h.

[0014] As preferred, in step (2), the drying mode is vacuum drying, the drying temperature is 70-90℃, and the drying time is 6-12h.

[0015] In the third aspect of the present application, the above-mentioned composite doped neodymium ferrite-based gas sensitive material is applied to (1)-(2) as follows: (1) detecting CO gas in a pyrolysis gas environment; (2) preparing a carbon monoxide gas sensitive sensor.

[0016] As preferred, the concentration of the CO gas is 10-50ppm.

[0017] As preferred, the preparation method of the carbon monoxide gas sensitive sensor is as follows: The above-mentioned composite doped neodymium ferrite-based gas sensitive material, deionized water and terpineol are mixed in the adding amount of (1-3) g:(5-10) mL:(1-3) mL to prepare a slurry; the slurry is spin-coated on an alumina ceramic substrate to form a gas sensitive film with a thickness of 50-200μm, and the gas sensitive film is aged at 180-200℃ for 12-24 hours to obtain a carbon monoxide gas sensitive sensor.

[0018] As preferred, the working temperature of the carbon monoxide gas sensitive sensor is 100-280℃.

[0019] The present application has the following advantages: 1.The composite doped neodymium ferrite-based gas sensitive material is prepared by using NdFeO3 as a base material and modifying the base material by Ag and Pd elements. The composite doped neodymium ferrite-based gas sensitive material prepared by the method has a good gas sensitive response to CO gas in a temperature range of 160-220 DEG C, and has good humidity resistance and long-term stability. Specifically, the response value of the composite doped neodymium ferrite-based gas sensitive material prepared by the method to 10 ppm of CO gas is 9.73 at 180 DEG C, the response value change rate is less than 10% at a relative humidity RH < 60%, and the response value change rate is less than 5% in one month. In addition, the composite doped neodymium ferrite-based gas sensitive material prepared by the method is used for detecting the concentration of CO gas in an industrial simulated pyrolysis gas environment, and the detection result is highly consistent with the detection result of a gas chromatograph, with only a 6% error. Therefore, the composite doped neodymium ferrite-based gas sensitive material prepared by the method is very suitable for detecting the concentration of CO in a pyrolysis gas environment, and has high accuracy.

[0020] 2.The method optimizes the NdFeO3 material by using Ag elements and Pd elements as doping elements, which can not only reduce the working temperature of the composite doped neodymium ferrite-based gas sensitive material, but also improve the gas sensitive sensitivity of the composite doped neodymium ferrite-based gas sensitive material. In addition, the combination of Ag elements and Pd elements has a synergistic effect on improving the response value of the composite doped neodymium ferrite-based gas sensitive material.

[0021] Specific principle analysis is as follows: the Ag-Pd combination modification forms a five-fold synergy of "interface strain-oxygen vacancy-electronic structure-double oxygen source-potential barrier regulation" on NdFeO3. Specifically, the metal / oxide lattice mismatch and strain reduce the surface and subsurface oxygen vacancy formation energy, fine-tune the Fe-O bond length and improve the Fe 3+ / Fe 2+ reversibility; the high work function of Pd and the lower work function of Ag construct an asymmetric Schottky barrier and an internal electric field, form a hole-rich layer and reduce the low-temperature transmission barrier; Ag-Pd local alloying causes the d-band center to move downward, moderately adjusts the CO adsorption strength, avoids low-temperature poisoning, and promotes CO / active oxygen overflow coupling; the reversible oxidation and reduction of Pd / Ag and the O2 activation and Mars-van Krevelen lattice oxygen supply of the substrate are synergistic, which reduces the "adsorption-activation-reaction-reoxidation" full-path energy barrier, so that high response and fast kinetics to low-concentration CO are achieved at a lower working temperature, and good humidity stability and selectivity are achieved.

[0022] 3.The composite doped neodymium ferrite-based gas sensitive material prepared by the co-precipitation method has a nanoparticle structure, a particle size of 80-200 nm, and a large specific surface area, which can provide more adsorption and reaction sites for CO molecules, and further improve the sensitivity and response speed. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 XRD pattern of the composite doped neodymium ferrite-based gas sensitive material prepared in Example 1; Figure 2 SEM images of the composite doped neodymium ferrite-based gas sensitive material prepared in Example 1 at different scales; wherein, (a) is the SEM image at the scale of 5 μm, (b) is the SEM image at the scale of 2 μm, (c) is the SEM image at the scale of 1 μm, and (d) is the SEM image at the scale of 500 nm; Figure 3 EDS Mapping images of Ag, Pd and Nd elements in the composite doped neodymium ferrite-based gas sensitive material prepared in Example 1; Figure 4 Relationship diagram of the gas sensitive performance of the gas sensitive materials prepared in Example 1 and Comparative Examples 1-3 and the temperature to 10 ppm CO gas; Figure 5 Relationship diagram of the gas sensitive performance of the gas sensitive materials prepared in Example 1 and Comparative Examples 1-3 and the humidity to 10 ppm CO gas; Figure 6 Schematic diagram of the long-term gas sensitive stability of the composite doped neodymium ferrite-based gas sensitive material prepared in Example 1 to 10 ppm CO gas. DETAILED DESCRIPTION

[0024] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. 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 application belongs.

[0025] In order to enable those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in combination with specific embodiments.

[0026] The experimental materials used in the embodiments of the present application are all conventional experimental materials in the art and can be purchased through commercial channels.

[0027] Example 1: Preparation of composite doped neodymium ferrite-based gas sensitive material 3 wt% Ag-7 wt% Pd-NdFeO3 (1) 4.383 g of Nd(NO3)3·6H2O, 4.040 g of Fe(NO3)3·9H2O and 10 g of citric acid were mixed and added to 100 mL of deionized water to obtain a mixed solution; 60 mL of 1 mol / L NaOH solution was added to the mixed solution and reacted for 1.5 h, and after the reaction was completed, the precipitate after filtration was collected, washed with deionized water and ethanol each for 3 times, and then vacuum dried at 80°C for 8 h to obtain a NdFeO3 precursor; (2) The NdFeO3 precursor prepared in step (1) was dispersed in 50 mL of deionized water to obtain a NdFeO3 solution; 0.103 g of AgNO3 and 0.252 g of PdCl2 were added to the NdFeO3 solution, and the mixture was subjected to in-situ deposition reaction at 70°C for 3 h. The solid after the reaction was collected, washed, and vacuum-dried at 80°C for 8 h, and then calcined at 500°C for 3 h to obtain a composite doped neodymium ferrite-based gas-sensitive material 3 wt% Ag-7 wt% Pd-NdFeO3, which was recorded as Ag-Pd-NFO.

[0028] The structure of the composite doped NdFeO-based gas-sensitive material 3 wt% Ag-7 wt% Pd-NdFeO3 prepared in this embodiment was characterized. Figures 1-3 shown.

[0029] Depend on Figure 1 It can be seen that the crystallization peaks correspond to the (200), (121) and (002) crystal phases of NdFeO3 (No.25-1149), indicating that the prepared composite doped NdFeO3-based gas-sensitive material has a pure phase perovskite structure. Figure 2 It can be seen that the prepared composite doped neodymium ferrite-based gas-sensitive material presents a typical nanoparticle structure with a particle size of about 80-200 nm, a large specific surface area and porosity, and provides abundant reaction sites and transmission channels for gas molecules. Figure 3 It can be seen that the elements in the composite doped NdFeO3-based gas-sensitive material are evenly distributed, proving that Ag and Pd are successfully loaded on the NdFeO3 surface.

[0030] Example 2: Preparation of composite doped neodymium ferrite-based gas-sensitive material 1 wt% Ag-3 wt% Pd-NdFeO3 (1) 4.383 g of Nd(NO3)3·6H2O, 4.040 g of Fe(NO3)3·9H2O, and 15 g of citric acid were mixed and added to 100 mL of deionized water to obtain a mixed solution. 55 mL of 1 mol / L NaOH solution was added to the mixed solution and reacted for 2 h. After the reaction was completed, the mixture was filtered and the filtered precipitate was collected. The precipitate was washed with deionized water and ethanol four times each, and then dried in vacuum at 70 °C for 12 h to obtain a NdFeO3 precursor. (2) The NdFeO3 precursor prepared in step (1) was dispersed in 50 mL of deionized water to obtain a NdFeO3 solution; 0.034 g of AgNO3 and 0.108 g of PdCl2 were added to the NdFeO3 solution, and the mixture was subjected to in-situ deposition reaction at 80°C for 2 h. The solid after the reaction was collected, washed, and vacuum-dried at 70°C for 12 h, and then calcined at 600°C for 2.5 h to obtain a composite doped neodymium ferrite-based gas-sensitive material 1 wt% Ag-3 wt% Pd-NdFeO3.

[0031] Example 3: Preparation of composite doped neodymium ferrite-based gas sensitive material 2wt% Ag-5wt% Pd-NdFeO3 (1) 4.383 g of Nd(NO3)3·6H2O, 4.040 g of Fe(NO3)3·9H2O and 8 g of citric acid were mixed and then added to 100 mL of deionized water to obtain a mixed solution; 70 mL of 1 mol / L NaOH solution was added to the mixed solution and reacted for 1 h; after the reaction was completed, the precipitate was collected by filtration, washed with deionized water and ethanol for 5 times respectively, and then vacuum dried at 90°C for 6 h to obtain a NdFeO3 precursor; (2) The NdFeO3 precursor prepared in step (1) was dispersed in 50 mL of deionized water to obtain a NdFeO3 solution; 0.068 g of AgNO3 and 0.180 g of PdCl2 were added to the NdFeO3 solution, and then in-situ deposition reaction was carried out at 60°C for 4 h; the solid after reaction was collected, washed, vacuum dried at 90°C for 6 h, and then calcined at 400°C for 3.5 h to obtain the composite doped neodymium ferrite-based gas sensitive material 2wt% Ag-5wt% Pd-NdFeO3.

[0032] Example 4: Preparation of a carbon monoxide gas sensitive sensor The composite doped neodymium ferrite-based gas sensitive material 3wt% Ag-7wt% Pd-NdFeO3 prepared in Example 1, deionized water and terpineol were mixed in a ratio of 1 g:5 mL:1 mL to obtain a slurry; the slurry was spin-coated on the surface of an alumina ceramic substrate at a rotation speed of 800 rpm to form a gas sensitive film with a thickness of 100 μm; the gas sensitive film was placed in air and aged at 180°C for 18 hours to obtain a carbon monoxide gas sensitive sensor.

[0033] Comparative Example 1: Preparation of neodymium ferrite gas sensitive material NdFeO3 The difference between this comparative example and Example 1 is that Ag element and Pd element are not used to modify the neodymium ferrite material. The specific preparation method is as follows: 4.383 g of Nd(NO3)3·6H2O, 4.040 g of Fe(NO3)3·9H2O and 10 g of citric acid were mixed and then added to 100 mL of deionized water; 60 mL of 1 mol / L NaOH solution was added and reacted for 1.5 h; after the reaction was completed, the precipitate was collected by filtration, washed with deionized water and ethanol for 3 times respectively, and then vacuum dried at 80°C for 8 h to obtain the neodymium ferrite gas sensitive material NdFeO3, which is denoted as NFO.

[0034] Comparative Example 2: Preparation of Ag doped neodymium ferrite-based gas sensitive material 3wt% Ag-NdFeO3 The difference between the present comparative example and Example 1 is that only Ag element is used to modify the neodymium ferrite material, and the specific preparation method is as follows: (1) 4.383 g of Nd(NO3)3·6H2O, 4.040 g of Fe(NO3)3·9H2O and 10 g of citric acid were mixed and then added to 100 mL of deionized water. After adding 60 mL of 1 mol / L NaOH solution, the mixture was reacted for 1.5 h. After the reaction was completed, the precipitate was collected by filtration, washed with deionized water and ethanol for 3 times respectively, and then vacuum dried at 80°C for 8 h to obtain a NdFeO3 precursor; (2) The NdFeO3 precursor prepared in step (1) was dispersed in 50 mL of deionized water to obtain a NdFeO3 solution. After adding 0.103 g of AgNO3 to the NdFeO3 solution, in-situ deposition reaction was carried out at 70°C for 3 h. The solid after reaction was collected, washed, vacuum dried at 80°C for 8 h, and then calcined at 500°C for 3 h to obtain a Pd-doped neodymium ferrite-based gas sensitive material 7wt% Pd-NdFeO3, which is denoted as Pd-NFO.

[0035] Preparation of Pd-doped neodymium ferrite-based gas sensitive material 7wt% Pd-NdFeO3 The difference between the present comparative example and Example 1 is that only Ag element is used to modify the neodymium ferrite material, and the specific preparation method is as follows: (1) 4.383 g of Nd(NO3)3·6H2O, 4.040 g of Fe(NO3)3·9H2O and 10 g of citric acid were mixed and then added to 100 mL of deionized water. After adding 60 mL of 1 mol / L NaOH solution, the mixture was reacted for 1.5 h. After the reaction was completed, the precipitate was collected by filtration, washed with deionized water and ethanol for 3 times respectively, and then vacuum dried at 80°C for 8 h to obtain a NdFeO3 precursor; (2) The NdFeO3 precursor prepared in step (1) was dispersed in 50 mL of deionized water to obtain a NdFeO3 solution. After adding 0.103 g of AgNO3 to the NdFeO3 solution, in-situ deposition reaction was carried out at 70°C for 3 h. The solid after reaction was collected, washed, vacuum dried at 80°C for 8 h, and then calcined at 500°C for 3 h to obtain a Pd-doped neodymium ferrite-based gas sensitive material 7wt% Pd-NdFeO3, which is denoted as Pd-NFO.

[0036] Test Example 1: The gas sensing properties of the composite doped neodymium ferrite-based gas-sensitive material 3 wt% Ag-7 wt% Pd-NdFeO3 prepared in Example 1, the neodymium ferrite gas-sensitive material NdFeO3 prepared in Comparative Example 1, the Ag-doped neodymium ferrite-based gas-sensitive material 3 wt% Ag-NdFeO3 prepared in Comparative Example 2, and the Pd-doped neodymium ferrite-based gas-sensitive material 7 wt% Pd-NdFeO3 prepared in Comparative Example 3 were tested. The specific method is as follows: The gas-sensitive materials prepared in Example 1 and Comparative Examples 1-3 were coated on the gas-sensitive film, and their gas-sensitive responses to CO gas (Rg / Ra) were tested. The results are shown in FIG. Figures 4-6 Here, Ra is the sensor's resistance in air, and Rg is the sensor's resistance in the gas being measured. The experimental environment was: relative humidity (RH) 20% and ambient temperature 20°C.

[0037] Depend on Figure 4 It can be seen that the response values ​​of the gas-sensitive materials prepared in Example 1 and Comparative Examples 1-3 to 10 ppm CO show a trend of first increasing and then decreasing with increasing temperature. Among them, the composite doped neodymium ferrite-based gas-sensitive material 3 wt% Ag-7 wt% Pd-NdFeO3 prepared in Example 1 maintains a high gas response to 10ppm CO gas in the temperature range of 160-220°C, and its response value is as high as 9.73 at an operating temperature of 180°C, while the neodymium ferrite gas-sensitive material NdFeO3 prepared in Comparative Example 1 has a maximum response value of 1.97 at an operating temperature of 220°C, the Ag-doped neodymium ferrite-based gas-sensitive material 3wt% Ag-NdFeO3 prepared in Comparative Example 2 has a maximum response value of 4.61 at an operating temperature of 200°C, and the Pd-doped neodymium ferrite-based gas-sensitive material 7wt% Pd-NdFeO3 prepared in Comparative Example 3 has a maximum response value of 4.33 at an operating temperature of 200°C. It can be seen that the present invention uses Ag and Pd to dope NdFeO3 material to significantly reduce the operating temperature, highlighting the significant advantages of dual precious metal doping in energy saving and low-temperature detection.

[0038] In addition, when the composite doped neodymium ferrite-based gas sensitive material 3 wt% Ag-7 wt% Pd-NdFeO3 prepared in Example 1 is used to detect 10 ppm of CO gas at a working temperature of 180℃, the response value is 9.73; the neodymium ferrite-based gas sensitive material NdFeO3 prepared in Comparative Example 1 has a response value of 1.63; the Ag-doped neodymium ferrite-based gas sensitive material 3 wt% Ag-NdFeO3 prepared in Comparative Example 2 has a response value of 3.56; and the Pd-doped neodymium ferrite-based gas sensitive material 7 wt% Pd-NdFeO3 prepared in Comparative Example 3 has a response value of 3.31. Therefore, the Pd and Ag composite doping has a synergistic effect on the response value of the composite doped neodymium ferrite-based gas sensitive material to 10 ppm of CO gas.

[0039] By Figure 5 As can be seen, when the relative humidity is 60%, the response value change rate of the composite doped neodymium ferrite-based gas sensitive material 3 wt% Ag-7 wt% Pd-NdFeO3 prepared in Example 1 is less than 10%, indicating that the material has good humidity resistance.

[0040] Figure 6 The long-term stability of the composite doped neodymium ferrite-based gas sensitive material 3 wt% Ag-7 wt% Pd-NdFeO3 prepared in Example 1 to 10 ppm of CO gas is shown in Figure 4. Figure 6 As can be seen, the response value change rate is less than 5% within one month, indicating that the material has extremely high gas sensitivity stability.

[0041] Test Example 2: Detection of CO concentration in pyrolysis gas Straw is used as a biomass raw material to prepare pyrolysis gas at 500℃ in a tube furnace. The pyrolysis gas is recovered and collected to simulate the waste heat utilization and gas treatment in an industrial process.

[0042] In this test example, five treatment groups are set up to detect the CO concentration in the pyrolysis gas by using different detection methods. Specifically, the treatment groups are as follows: Treatment Group 1: gas chromatograph; Treatment Group 2: carbon monoxide gas sensitive sensor prepared in Example 4; Treatment Group 3: carbon monoxide gas sensitive sensor corresponding to the neodymium ferrite-based gas sensitive material NdFeO3 prepared in Comparative Example 1; Treatment Group 4: carbon monoxide gas sensitive sensor corresponding to the Ag-doped neodymium ferrite-based gas sensitive material 3 wt% Ag-NdFeO3 prepared in Comparative Example 2; Treatment Group 5: carbon monoxide gas sensitive sensor corresponding to the Pd-doped neodymium ferrite-based gas sensitive material 7 wt% Pd-NdFeO3 prepared in Comparative Example 3.

[0043] The preparation method of the carbon monoxide gas sensor in the treatment group 3-5 is the same as that in Example 4. The specific steps of detecting the CO concentration in the pyrolysis gas by the carbon monoxide gas sensor are as follows: exposing the carbon monoxide gas sensor to the collected pyrolysis gas, setting the gas flow rate to be 100 mL / min, monitoring the response value (Rg / Ra), and converting the CO concentration reading by the pre-calibration curve, the test lasts for 30 min, the average value is recorded, and the results are shown in Table 1.

[0044] Table 1. CO concentration data in pyrolysis gas detected by different gas sensitive materials The gas chromatograph is one of the most accurate and reliable methods for detecting gas concentration. In the present experimental example, the gas chromatograph is used to quantitatively detect the CO content in the pyrolysis gas, and the detected CO concentration is taken as the reference concentration, and the reference CO concentration is measured to be 25 ppm (error ± 1 ppm). As can be seen from Table 1, the error of detecting the CO concentration in the pyrolysis gas by using the 3wt% Ag-7wt% Pd-NdFeO3 (treatment group 2) prepared by the present application is only 6%, while the error of detecting the CO concentration in the pyrolysis gas by using the NdFeO3 without doping treatment (treatment group 3) is 37%, and the error of detecting the CO concentration in the pyrolysis gas by using the Ag or Pd doped NdFeO3 (treatment group 4 and treatment group 5) is 21% and 24%, respectively. It can be seen that the Ag and Pd combination for doping NdFeO3 has a synergistic effect in improving the accuracy of the gas sensitive material for detecting the CO concentration in the pyrolysis gas.

[0045] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Various modifications and changes can be made by those skilled in the art based on the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A composite doped neodymium ferrite-based gas-sensitive material, characterized in that: The chemical formula of the composite doped neodymium ferrite-based gas-sensitive material is Xwt%Ag-Ywt%Pd-NdFeO3, wherein X and Y represent the doping amounts of Ag and Pd in ​​the composite doped neodymium ferrite-based gas-sensitive material, respectively. <X≤5,0<Y≤10。 2. The method for preparing the composite doped neodymium ferrite-based gas-sensitive material according to claim 1, characterized in that: The following steps are involved: (1) Nd(NO3)3·6H2O, Fe(NO3)3·9H2O and citric acid were mixed and then added into water and mixed evenly to obtain a mixed solution. NaOH solution was added into the mixed solution to react. After the reaction was completed, the mixture was filtered, washed and dried to obtain a NdFeO3 precursor. (2) Dispersing the NdFeO3 precursor in water to obtain a NdFeO3 solution; adding AgNO3 and PdCl2 to the NdFeO3 solution and reacting them; after the reaction is completed, collecting the reacted solid, washing, drying, and then calcining it at 400-600°C in an air atmosphere for 2.5-3.5 hours to obtain a composite doped neodymium ferrite-based gas-sensitive material; The added amounts of Nd(NO3)3·6H2O, Fe(NO3)3·9H2O, PdCl2, AgNO3 and citric acid are (0.01-0.05) mol: (0.01-0.05) mol: (0.01-2) g: (0.01-1) g: (5-20) g, respectively.

3. The method for preparing a composite doped neodymium ferrite-based gas-sensitive material according to claim 1, wherein: In step (1), the concentration of the NaOH solution is 1-2 mol / L, and the mass ratio of the mixed solution to the NaOH solution is 1:(1-2).

4. The method for preparing a composite doped neodymium ferrite-based gas-sensitive material according to claim 1, wherein: In step (1), the reaction time is 1-2 hours; the drying method is vacuum drying, the drying temperature is 70-90° C., and the drying time is 6-12 hours.

5. The method for preparing a composite doped neodymium ferrite-based gas-sensitive material according to claim 1, wherein: In step (2), the reaction temperature is 60-80°C and the reaction time is 2-4h.

6. Application of the composite doped neodymium ferrite-based gas-sensitive material according to claim 1 in the following (1)-(2): (1) Detect CO gas in pyrolysis environment; (2) Preparation of carbon monoxide gas sensor.

7. The use according to claim 6, characterized in that The concentration of CO gas is 10-50 ppm.

8. The use according to claim 6, characterized in that The operating temperature of the carbon monoxide gas sensor is 100-280℃.

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