Composite doped neodymium ferrite-based gas sensitive material and application thereof in detecting carbon monoxide in pyrolysis gas

Abstract

The application discloses a kind of composite doped neodymium ferrite-based gas sensitive material and its application in detecting carbon monoxide in pyrolysis gas, it is related to gas sensitive material technical field.The application uses NdFeO3 as base material, and adopts Ag and Pd to modify and modify it to obtain composite doped neodymium ferrite-based gas sensitive material.The composite doped neodymium ferrite-based gas sensitive material prepared by the application maintains good gas sensitive response to CO gas in the temperature range of 160-220 DEG C, and also 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 application to 10ppm CO gas is 9.73 at 180 DEG C, and the response value change rate is less than 10% under relative humidity RH<60%, and the response value change rate is less than 5% within one month.

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. At a working temperature of 180℃, the response value of the composite doped neodymium ferrite-based gas sensitive material to 10ppm CO gas reaches 9.73. When the relative humidity is less than 60%, the response value change rate is less than 10%. The response value change within one month is less than 5%. In addition, in the pyrolysis gas in the simulated industrial environment, the detection result of the composite doped neodymium ferrite-based gas sensitive material prepared by the present application for the CO concentration in the pyrolysis gas environment is highly consistent with the gas chromatography method, and has good accuracy.

[0006] To achieve the above object, the present application adopts the following technical solutions:

[0007] In the first aspect of the present application, a composite doped neodymium ferrite-based gas sensitive material is provided, and the chemical formula of the composite doped neodymium ferrite-based gas sensitive material is Xwt%Ag-Ywt%Pd-NdFeO3, wherein X and Y respectively represent the doping amounts of Ag and Pd in the composite doped neodymium ferrite-based gas sensitive material, and 0X≤5 and 0Y≤10.

[0008] In the second aspect of the present application, a preparation method of the composite doped neodymium ferrite-based gas sensitive material is provided, and the preparation method comprises the following steps:

[0009] (1) Nd(NO3)3·6H2O and Fe(NO3)3·9H2O are mixed with citric acid and then added into water to mix uniformly, to obtain a mixed solution. NaOH solution is added into the mixed solution to react. After the reaction is completed, the NdFeO3 precursor is obtained by filtration, washing and drying;

[0010] (2) The NdFeO3 precursor is dispersed in water to obtain a NdFeO3 solution. AgNO3 and PdCl2 are added into the NdFeO3 solution to react. After the reaction is completed, the solid after reaction is collected, washed and dried, and then calcined at 400-600℃ under air atmosphere for 2.5-3.5h to obtain the composite doped neodymium ferrite-based gas sensitive material;

[0011] The adding 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.

[0012] Preferably, in step (1), the concentration of the NaOH solution is 1-2 mol / L.

[0013] Preferably, in step (1), the mass ratio of the mixed solution to the NaOH solution is 1:(1-2).

[0014] Preferably, in step (1), the reaction time is 1-2 h.

[0015] Preferably, in step (1), the washing operation is that the filtered solid is washed with ionized water and ethanol for 3-5 times in sequence.

[0016] Preferably, in step (1), the drying method is vacuum drying, the drying temperature is 70-90℃, and the drying time is 6-12 h.

[0017] Preferably, in step (2), the reaction temperature is 60-80℃, and the reaction time is 2-4 h.

[0018] Preferably, in step (2), the drying method is vacuum drying, the drying temperature is 70-90℃, and the drying time is 6-12 h.

[0019] In a third aspect, the application provides the use of the composite doped neodymium ferrite-based gas sensitive material in (1)-(2) as follows:

[0020] (1) detecting CO gas in a pyrolysis gas environment;

[0021] (2) preparing a carbon monoxide gas sensor.

[0022] Preferably, the concentration of the CO gas is 10-50 ppm.

[0023] Preferably, the preparation method of the carbon monoxide gas sensor is as follows:

[0024] The composite doped neodymium ferrite-based gas sensitive material, deionized water and terpineol are mixed in a ratio 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 50-200 μm; and the gas sensitive film is aged at 180-200℃ for 12-24 hours to obtain the carbon monoxide gas sensor.

[0025] Preferably, the working temperature of the carbon monoxide gas sensor is 100-280℃.

[0026] The application has the following advantages:

[0027] 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 good gas sensitive response to CO gas in the temperature range of 160-220 DEG C, and also 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% under the relative humidity RH < 60%, and the response value change rate is less than 5% within 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 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.

[0028] 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.

[0029] 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 also achieved.

[0030] 3.The composite doped neodymium ferrite-based gas sensitive material prepared by the co-precipitation method has a nanoparticle structure, the particle size is 80-200 nm, has a large specific surface area, can provide more adsorption and reaction sites for CO molecules, and further improves the sensitivity and response speed. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 XRD pattern of the composite doped neodymium ferrite-based gas sensitive material prepared in Example 1;

[0032] 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;

[0033] 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;

[0034] 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;

[0035] 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;

[0036] 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

[0037] 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.

[0038] 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 conjunction with specific embodiments.

[0039] 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.

[0040] Example 1: Preparation of composite doped neodymium ferrite-based gas sensitive material 3 wt% Ag-7 wt% Pd-NdFeO3

[0041] (1) mixed 4.383 g Nd(NO3)3·6H2O, 4.040 g Fe(NO3)3·9H2O and 10 g citric acid, and then added into 100 mL deionized water to obtain a mixed solution; 60 mL of 1 mol / L NaOH solution was added into the mixed solution, and reacted for 1.5 h; after the reaction was completed, the precipitate was collected after 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;

[0042] (2) the NdFeO3 precursor prepared in step (1) was dispersed in 50 mL deionized water to obtain a NdFeO3 solution; 0.103 g AgNO3 and 0.252 g PdCl2 were added into the NdFeO3 solution, and then in-situ deposited and reacted 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 composite doped neodymium ferrite-based gas sensitive material 3 wt% Ag-7 wt% Pd-NdFeO3, which was recorded as Ag-Pd-NFO.

[0043] The composite doped neodymium ferrite-based gas sensitive material 3 wt% Ag-7 wt% Pd-NdFeO3 prepared in this example was subjected to structural characterization, and the results are shown in Figures 1-3 .

[0044] As can be seen from Figure 1 , the crystal peaks correspond to (200), (121) and (002) crystal phases of NdFeO3 (No. 25-1149), indicating that the composite doped neodymium ferrite-based gas sensitive material prepared has a pure phase perovskite structure. As can be seen from Figure 2 , the composite doped neodymium ferrite-based gas sensitive material prepared has a typical nanoparticle structure, with a particle size of about 80-200 nm, a large specific surface area and porosity, which provides abundant reaction sites and transmission channels for gas molecules. As can be seen from Figure 3 , the elements in the composite doped neodymium ferrite-based gas sensitive material are uniformly distributed, which proves that Ag and Pd are successfully loaded on the surface of NdFeO3.

[0045] Example 2: Preparation of composite doped neodymium ferrite-based gas sensitive material 1 wt% Ag-3 wt% Pd-NdFeO3

[0046] (1) mixed 4.383 g of Nd(NO3)3.6H2O, 4.040 g of Fe(NO3)3.9H2O and 15 g of citric acid, and then added into 100 mL of deionized water to obtain a mixed solution; 55 mL of 1 mol / L NaOH solution was added into the mixed solution, and reacted for 2 h; after the reaction was completed, the precipitate was collected by filtration, washed with deionized water and ethanol for 4 times respectively, and then vacuum dried at 70°C for 12 h to obtain a NdFeO3 precursor;

[0047] (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 into the NdFeO3 solution, and then in-situ deposition reaction was carried out at 80°C for 2 h; the solid after reaction was collected, washed, 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.

[0048] Example 3: Preparation of a composite doped neodymium ferrite-based gas sensitive material 2 wt% Ag-5 wt% Pd-NdFeO3

[0049] (1) mixed 4.383 g of Nd(NO3)3.6H2O, 4.040 g of Fe(NO3)3.9H2O and 15 g of citric acid, and then added into 100 mL of deionized water to obtain a mixed solution; 55 mL of 1 mol / L NaOH solution was added into the mixed solution, and reacted for 2 h; after the reaction was completed, the precipitate was collected by filtration, washed with deionized water and ethanol for 4 times respectively, and then vacuum dried at 70°C for 12 h to obtain a NdFeO3 precursor;

[0050] (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 into the NdFeO3 solution, and then in-situ deposition reaction was carried out at 80°C for 2 h; the solid after reaction was collected, washed, 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.

[0051] Example 4: Preparation of a carbon monoxide gas sensitive sensor

[0052] The composite doped neodymium ferrite-based gas sensitive material 3 wt% Ag-7 wt% 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.

[0053] Preparation of a neodymium ferrite gas sensitive material NdFeO3

[0054] The difference between this comparative example and Example 1 is that the neodymium ferrite material was not modified using Ag and Pd elements. The specific preparation method is as follows:

[0055] 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, 60 mL of 1 mol / L NaOH solution was then added and the reaction was carried out for 1.5 h; after the reaction was completed, the precipitate was collected by filtration, washed with deionized water and ethanol for 3 times each, and then vacuum dried at 80 °C for 8 h to obtain a neodymium ferrite gas sensitive material NdFeO3, denoted as NFO.

[0056] Preparation of an Ag doped neodymium ferrite-based gas sensitive material 3 wt% Ag-NdFeO3

[0057] The difference between this comparative example and Example 1 is that the neodymium ferrite material was modified only using Ag elements. The specific preparation method is as follows:

[0058] (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, 60 mL of 1 mol / L NaOH solution was then added and the reaction was carried out for 1.5 h; after the reaction was completed, the precipitate was collected by filtration, washed with deionized water and ethanol for 3 times each, and then vacuum dried at 80 °C for 8 h to obtain a NdFeO3 precursor;

[0059] (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 was added to the NdFeO3 solution, and in-situ deposition reaction was carried out at 70 °C for 3 h; the solid after the reaction was collected, washed, vacuum dried at 80 °C for 8 h, and then calcined at 500 °C for 3 h to obtain an Ag doped neodymium ferrite-based gas sensitive material 3 wt% Ag-NdFeO3, denoted as Ag-NFO.

[0060] Comparative Example 3: Preparation of Pd-doped neodymium ferrite-based gas sensitive material 7wt% Pd-NdFeO3

[0061] The difference between this comparative example and Example 1 is that only Pd element is used to modify the neodymium ferrite material, and the specific preparation method is as follows:

[0062] (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;

[0063] (2) The NdFeO3 precursor prepared in step (1) was dispersed in 50 mL of deionized water to obtain a NdFeO3 solution. Then, 0.252 g of PdCl2 was added to the NdFeO3 solution, and 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 was denoted as Pd-NFO.

[0064] Test Example 1

[0065] The gas sensitive 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 3wt% Ag-NdFeO3 prepared in Comparative Example 2 and the Pd-doped neodymium ferrite-based gas sensitive material 7wt% Pd-NdFeO3 prepared in Comparative Example 3 were detected, and the specific method was as follows:

[0066] The gas sensitive materials prepared in Example 1 and Comparative Examples 1-3 were coated on a gas sensitive film respectively, and the gas sensitive response (Rg / Ra) of the gas sensitive materials to CO gas was detected, and the results are shown in Table 1. Figures 4-6

[0067] Figure 4 ​​It can be seen that the response value of the gas sensitive material prepared in Example 1 and Comparative Examples 1-3 to 10 ppm CO shows a trend of first increasing and then decreasing with the increase of temperature. Among them, the composite doped neodymium ferrite-based gas sensitive material 3 wt% Ag-7 wt% Pd-NdFeO3 prepared in Example 1 has a relatively high gas response to 10 ppm CO gas in the temperature range of 160-220℃, and the response value is the highest of 9.73 at the working temperature of 180℃, while the response value of the neodymium ferrite gas sensitive material NdFeO3 prepared in Comparative Example 1 is the highest of 1.97 at the working temperature of 220℃, the response value of the Ag-doped neodymium ferrite-based gas sensitive material 3 wt% Ag-NdFeO3 prepared in Comparative Example 2 is the highest of 4.61 at the working temperature of 200℃, and the response value of the Pd-doped neodymium ferrite-based gas sensitive material 7 wt% Pd-NdFeO3 prepared in Comparative Example 3 is the highest of 4.33 at the working temperature of 200℃. Therefore, it can be seen that the use of Ag and Pd to dope NdFeO3 material can greatly reduce the working temperature, and highlights the significant advantages of double noble metal doping in energy saving and low temperature detection.

[0068] In addition, at the working temperature of 180℃, the response value of the composite doped neodymium ferrite-based gas sensitive material 3 wt% Ag-7 wt% Pd-NdFeO3 prepared in Example 1 to 10 ppm CO gas is 9.73, the response value of the neodymium ferrite gas sensitive material NdFeO3 prepared in Comparative Example 1 to 10 ppm CO gas is 1.63, the response value of the Ag-doped neodymium ferrite-based gas sensitive material 3 wt% Ag-NdFeO3 prepared in Comparative Example 2 to 10 ppm CO gas is 3.56, and the response value of the Pd-doped neodymium ferrite-based gas sensitive material 7 wt% Pd-NdFeO3 prepared in Comparative Example 3 to 10 ppm CO gas is 3.31. Therefore, it can be seen that the use of Pd and Ag composite doping has a synergistic effect on providing the response value of the composite doped neodymium ferrite-based gas sensitive material to 10 ppm CO gas.

[0069] From the above data, it can be seen that the response value of the composite doped neodymium ferrite-based gas sensitive material 3 wt% Ag-7 wt% Pd-NdFeO3 prepared in Example 1 to 10 ppm CO gas is 9.73, which is 4.76 times that of the neodymium ferrite gas sensitive material NdFeO3 prepared in Comparative Example 1, 2.62 times that of the Ag-doped neodymium ferrite-based gas sensitive material 3 wt% Ag-NdFeO3 prepared in Comparative Example 2, and 2.28 times that of the Pd-doped neodymium ferrite-based gas sensitive material 7 wt% Pd-NdFeO3 prepared in Comparative Example 3. Figure 5 It can be seen that 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 <10% at a relative humidity of 60%, indicating that it has good humidity resistance.

[0070] 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 CO gas is shown in the following table. Figure 6 It can be seen that the response value change rate is <5% within one month, indicating that the material has extremely high gas sensitive stability.

[0071] Test Example 2: CO concentration detection in pyrolysis gas

[0072] The straw was used as a biomass raw material, and pyrolysis was carried out in a tubular furnace at 500°C to obtain pyrolysis gas. The pyrolysis gas was recovered and collected to simulate the waste heat utilization and gas treatment in the industrial process.

[0073] The present test example has 5 treatment groups, and the CO concentration in the pyrolysis gas is detected by different detection methods. The specific treatment groups are as follows:

[0074] Treatment group 1: gas chromatograph;

[0075] Treatment group 2: carbon monoxide gas sensitive sensor prepared in Example 4;

[0076] Treatment group 3: carbon monoxide gas sensitive sensor corresponding to the neodymium ferrite gas sensitive material NdFeO3 prepared in Comparative Example 1;

[0077] Treatment group 4: carbon monoxide gas sensitive sensor corresponding to the Ag-doped neodymium ferrite-based gas sensitive material 3wt% Ag-NdFeO3 prepared in Comparative Example 2;

[0078] Treatment group 5: carbon monoxide gas sensitive sensor corresponding to the Pd-doped neodymium ferrite-based gas sensitive material 7wt% Pd-NdFeO3 prepared in Comparative Example 3.

[0079] The preparation method of the carbon monoxide gas sensitive sensor in treatment groups 3-5 is the same as that in Example 4. The specific steps for detecting the CO concentration in the pyrolysis gas by the carbon monoxide gas sensitive sensor are as follows: expose the carbon monoxide gas sensitive sensor to the collected pyrolysis gas, set the gas flow rate to 100 mL / min, monitor the response value (Rg / Ra), and convert it to the CO concentration reading through the pre-calibration curve. The test lasts for 30 min, and the average value is recorded. The results are shown in Table 1.

[0080] Table 1. CO concentration data in pyrolysis gas detected by different gas sensitive materials

[0081]

[0082] The gas chromatograph is one of the most accurate and reliable methods for detecting gas concentration. In the present test 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. The reference CO concentration is 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 prepared by the present application (treatment group 2) 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 used in the present application to dope the NdFeO3 has a synergistic effect in improving the accuracy of the gas sensitive material in detecting the CO concentration in the pyrolysis gas.

[0083] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. 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. Application of a composite doped neodymium ferrite-based gas sensitive material in detecting CO gas in a pyrolysis gas environment, characterized in that, the chemical formula of the composite doped neodymium ferrite-based gas sensitive material is Xwt%Ag-Ywt%Pd-NdFeO3; in the formula, X and Y respectively represent the doping amount of Ag and Pd in the composite doped neodymium ferrite-based gas sensitive material, 0 < X ≤ 5, 0 < Y ≤ 10; the composite doped neodymium ferrite-based gas sensitive material is prepared by the following method: (1) Nd(NO3)3·6H2O, Fe(NO3)3·9H2O and citric acid are mixed and then added to water to mix uniformly to obtain a mixed solution, NaOH solution is added to the mixed solution to react, after the reaction is completed, the NdFeO3 precursor is obtained after filtration, washing and drying; (2) the NdFeO3 precursor is dispersed in water to obtain a NdFeO3 solution, AgNO3 and PdCl2 are added to the NdFeO3 solution to react, after the reaction is completed, the solid after reaction is collected, washed and dried, and then calcined at 400-600°C under air atmosphere for 2.5-3.5h to obtain the 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.

2. Use 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).

3. The use according to claim 1, wherein In step (1), the reaction time is 1-2h, the drying method is vacuum drying, the drying temperature is 70-90°C, and the drying time is 6-12h.

4. The use according to claim 1, wherein In step (2), the reaction temperature is 60-80°C, and the reaction time is 2-4h.

5. The use according to claim 1, wherein The concentration of the CO gas is 10-50ppm.

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