A DMMP gas sensor based on gold-modified ZnFe2O4 sensing material and S-1 molecular sieve and its preparation method.

Abstract

The application relates to a DMMP gas sensor based on gold-modified ZnFe2O4 sensitive material and S-1 molecular sieve and a preparation method thereof, and belongs to the technical field of semiconductor oxide gas sensors. The sensor is composed of a commercially available Al2O3 substrate with two separate L-shaped gold electrodes on the outer surface, gold-modified ZnFe2O4 sensitive material coated on the outer surface of the Al2O3 substrate and the L-shaped gold electrode, and S-1 molecular sieve spin-coated on the gold-modified ZnFe2O4 sensitive material. The gold-modified ZnFe2O4 sensitive material is prepared by a simple solvothermal method, and a great leap in gas-sensitive characteristics is realized; the sensor prepared by further spin-coating S-1 molecular sieve on the sensitive material exhibits excellent selectivity and sensitivity to DMMP, and has good long-term stability and repeatability. The sensor has the characteristics of simple device process, small size and suitability for mass production, and has a wide application prospect in detecting DMMP pollutants.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor oxide gas sensor technology, specifically relating to a DMMP gas sensor based on gold-modified ZnFe2O4 sensitive material and S-1 molecular sieve and its preparation method. Background Technology

[0002] The paper "Porous Graphene Oxide-Metal Ion Composite for Selective Sensing of Organophosphate Gases" published in ACS SENSORS, Volume 5, Issue 6, pp. 1573-1581, mentions that sarin is a typical organophosphate compound with a complex structure. In addition, the paper "Multidimensional polypyrrole / iron oxyhydroxide hybrid nanoparticles for chemical nerve gas agent sensing application" published in ACS NANO, Volume 7, Issue 11, pp. 10139-10147, also mentions that sarin is used as a pesticide and insecticide in agriculture, causing environmental pollution. The paper "Application of polymethyl[4-(2,3-difluoro-4-hydroxyphenoxy)butyl]siloxane in surface acoustic wave gas sensors for dimethyl methylphosphonate detection," published in Volume 329 of *SENSORS AND ACTUATORS B-CHEMICAL*, mentions that sarin's mechanism of harm to humans involves inhibiting acetylcholinesterase, leading to the inability to properly hydrolyze acetylcholine, resulting in acetylcholine accumulation and symptoms such as nicotine-like and muscarinic symptoms. In severe cases, it can lead to death from respiratory failure. The paper "The effects of repeated low-dose sarin exposure," published in Volume 215, Issue 2, pp. 119-134 of *TOXICOLOGY AND APPLIED PHARMACOLOGY*, reports that the toxic dose of sarin gas is 0.5 ppm, and the lethal dose is 50–150 ppm. Since dimethyl methylphosphonate (DMMP) is the most common simulant of sarin, the detection of low concentrations of DMMP is of great significance for national defense and human safety.

[0003] Among the many types of gas sensors, resistive gas sensors using semiconductor oxides as sensing materials have advantages such as simple fabrication, good selectivity, high sensitivity, fast response and recovery speed, high stability, and low cost, making them one of the most widely used gas sensors. With the development of nanoscience and technology, modifying gas-sensitive materials with noble metals can greatly increase the specific surface area of ​​the material and form heterojunctions, thereby improving the gas-sensing characteristics and obtaining better gas-sensing properties.

[0004] Zinc ferrite (ZnFe₂O₄) is an important N-type metal oxide semiconductor, widely used in solar energy, photocatalysis, and gas sensors due to its stable chemical and electrical properties. Studies on the sensing performance of ZnFe₂O₄ materials show that although its sensitivity is not significantly superior to some N-type metal oxide semiconductors, zinc ferrite exhibits excellent catalytic activity in the oxidation of DMMP, making the modification of ZnFe₂O₄ sensitive materials meaningful. This invention utilizes a solvothermal method to synthesize a gold-modified ZnFe₂O₄ to improve its gas-sensing properties. This noble metal modification can effectively enhance the gas-sensing characteristics of gas sensors. Summary of the Invention

[0005] The purpose of this invention is to provide a DMMP gas sensor based on gold-modified ZnFe2O4 sensitive material and S-1 molecular sieve (S-1 molecular sieve was purchased from Dalian Zeer Catalytic Materials Co., Ltd.) and its preparation method. This invention uses gold-modified ZnFe₂O₄ prepared by a solvothermal two-step synthesis method as the sensing material. Firstly, Au nanoparticles have long been proven to be excellent catalysts for gas-sensitive reactions, their main function being to generate more adsorbed oxygen on the surface of the sensing material, thereby lowering the activation energy of the chemical reaction. Secondly, due to the high Fermi level of Au, electrons will flow from Au to ZnFe₂O₄ to balance the Fermi level, resulting in a composite material with an even higher Fermi level and a lower work function. This will increase the number of active electrons on the surface of the composite material, further enhancing its oxygen adsorption capacity. The combined effect of these two aspects significantly improves the reaction efficiency of the gas with the gold-modified ZnFe₂O₄ sensing material. Compared with DMMP gas sensors based on ZnFe₂O₄, the DMMP gas sensor based on gold-modified ZnFe₂O₄ shows a significant improvement in sensitivity to DMMP gas in the range of 50-1000 ppb. Finally, the selective catalysis of S-1 molecular sieves can significantly reduce the sensor's response to interfering gases such as acetone and ethanol. This aspect focuses on improving the selectivity of the sensor. The commercially available planar sensor used in this invention has a simple manufacturing process, small size, and is suitable for mass production in industry, thus having significant application value.

[0006] The present invention discloses a method for preparing a DMMP gas sensor based on gold-modified ZnFe2O4 sensing material and S-1 molecular sieve, the steps of which are as follows:

[0007] (1) Take 0.08-0.12g of gold-modified ZnFe2O4 nanoparticles and mix them with 4-6mL of n-butanol to form a paste. Then, take a small amount of paste and drop it onto the surface of an Al2O3 substrate with two discrete L-shaped gold electrodes on the outer surface. Spin-coat at 800-1000r / min for 2-4 minutes to form a 12-16μm thick sensitive material film, and make the sensitive material completely cover the outer surface of the Al2O3 substrate and the L-shaped gold electrodes.

[0008] (2) After the sensitive material film is dried, the Al2O3 substrate obtained in step (1) is calcined at 200-300℃ for 1.5-3 hours and then cooled to room temperature; 0.01-0.02g of S-1 molecular sieve is added to 400-600μL of isopropanol, and the resulting S-1 molecular sieve solution is dropped onto the sensitive material film and spin-coated at a speed of 300-500r / min for 1-3 minutes; finally, the above device is welded and packaged as a side-heated gas sensing element to obtain a DMMP gas sensor based on gold-modified ZnFe2O4 sensitive material and S-1 molecular sieve.

[0009] The gold-modified ZnFe2O4 nanoparticles are prepared by the following steps:

[0010] (1) Mix 2-6 mL of glycerol and 14-18 mL of isopropanol, then add 0.1-0.2 g of Zn(NO3)2·6H2O and 0.4-0.5 g of Fe(NO3)3·9H2O, and stir continuously until completely dissolved. Then add 0.05-0.07 g of urea (CO(NH2)2) and stir for 20-40 minutes.

[0011] (2) Transfer the solution obtained in step (1) to a hydrothermal reactor, keep it at 160-200℃ for 20-25 hours, take it out, cool it naturally to room temperature, wash the precipitate with deionized water and anhydrous ethanol by centrifugation several times, dry the centrifuged product at 70-90℃ for 10-15 hours, and finally anneal at 400-500℃ for 1-3 hours to obtain ZnFe2O4 nanoparticles;

[0012] (3) Add 0.01-0.02g HAuCl4·3H2O and 0.005-0.01g NaBH4 to 4-6mL of deionized water respectively, and stir for 20-40 minutes;

[0013] (4) Add 0.08-0.12 g of ZnFe2O4 nanoparticles obtained in step (2) to 15-25 mL of deionized water and stir continuously until completely dissolved; then add 2-6 mL of HAuCl4 solution obtained in step (3) and stir for 20-40 minutes; then add 2-6 mL of NaBH4 solution obtained in step (3) and stir for 40-60 minutes; finally, wash the precipitate repeatedly by centrifugation with deionized water and anhydrous ethanol, and dry the centrifuged product at 70-90℃ for 10-15 hours to obtain gold-modified ZnFe2O4 nanoparticles.

[0014] This invention discloses a DMMP gas sensor based on gold-modified ZnFe2O4 sensing material and S-1 molecular sieve, which is prepared by the method described above. The Al2O3 substrate has a length of 2.5–3.5 mm, a width of 2.5–3.5 mm, and a thickness of 0.2–0.3 mm. The Al2O3 substrate has four discrete rectangular gold electrodes on its front and back sides. The two electrodes on the back side serve a heating function, while the two electrodes on the front side are electrically connected to two discrete L-shaped gold electrodes for measuring the sensor's resistance. The L-shaped gold electrodes have a length of 1.5–2 mm, a width of 1.5–2 mm, and a thickness of 0.02–0.06 mm.

[0015] The DMMP gas sensor based on gold-modified ZnFe2O4 sensing material prepared in this invention has the following advantages:

[0016] 1. ZnFe2O4 nanoparticles were successfully prepared using a simple solvothermal method. Then, gold-modified ZnFe2O4 nanoparticles were prepared using sodium borohydride and chloroauric acid, which improved the response value and response recovery time of the material. The synthesis method is simple and low in cost.

[0017] 2. By using S-1 molecular sieve, the selectivity of gold-modified ZnFe2O4 nanoparticles for DMMP gas was improved, and they exhibited good repeatability and stability, showing broad application prospects in the detection of DMMP pollution in the environment.

[0018] 3. It adopts commercially available planar sensors, which have simple manufacturing processes, small size, and are suitable for mass production. Attached Figure Description

[0019] Figure 1 a: A schematic diagram of the front structure of the sensor described in this invention; Figure 1 b: Schematic diagram of the reverse side structure of the sensor described in this invention;

[0020] Figure 2 a: SEM morphology of ZnFe2O4 nanoparticles; Figure 2 b: SEM morphology of gold-modified ZnFe2O4 nanoparticles; Figure 2 c: SEM morphology of S-1 molecular sieve;

[0021] Figure 3 a: TEM image of gold-modified ZnFe2O4 nanoparticles; Figure 3 b: HRTEM image of gold-modified ZnFe2O4 nanoparticles;

[0022] Figure 4 XRD patterns of ZnFe2O4 and ZnFe2O4 nanoparticles modified with gold in different proportions;

[0023] Figure 5 a: Sensitivity curves of the sensors in the comparative examples and embodiments for 1ppm DMMP gas at different operating temperatures; Figure 5 b: Comparative and example histograms of the selectivity of the sensor for 7 1ppm analytes at 330°C;

[0024] Figure 6 Sensitivity-DMMP concentration characteristic curves of the sensors in Comparative Example 2 and Example 1 at the optimal operating temperature (330°C);

[0025] Figure 7 a: The response recovery curve of the sensor with respect to the DMMP concentration gradient at the optimal operating temperature (330°C) in Example 1; Figure 7 b: The response recovery curve of the sensor in Comparative Example 2 with respect to the DMMP concentration gradient at the optimal operating temperature (330℃);

[0026] Figure 8 The response recovery curve of the sensor to 1 ppm DMMP gas at the optimal operating temperature (330°C) in the embodiment;

[0027] Figure 9 a: Stable resistance curve of the sensor in the DMMP atmosphere at the optimal operating temperature for 30 consecutive days; Figure 9 b; Long-term stability curve of the sensor for 1ppm DMMP gas at the optimal operating temperature in the embodiment;

[0028] like Figure 1 As shown, the device consists of an Al2O3 substrate, two discrete L-shaped gold electrodes and two discrete rectangular electrodes on the front side of the Al2O3 substrate, and two discrete rectangular electrodes on the back side of the Al2O3 substrate.

[0029] like Figure 2 The images show the morphology of ZnFe2O4, gold-modified ZnFe2O4, and S-1 molecular sieve at low magnification. Figure 2As can be seen in a, ZnFe2O4 is composed of many nanoparticles with a diameter of approximately 145~165 nm. Figure 2 The diameter of gold-modified ZnFe2O4 in b is approximately 147~170 nm. Figure 2 c. The S-1 molecular sieve is composed of porous plates.

[0030] like Figure 3 As shown, the morphology of the gold-modified ZnFe2O4 nanoparticles is consistent with that shown in the TEM and SEM images. The nanoparticles have a diameter of approximately 155 nm. The high-resolution TEM image shows a lattice spacing of 0.235 mm, which matches the (111) crystal plane of Au, and a lattice spacing of 0.486 mm, which matches the (111) crystal plane of ZnFe2O4.

[0031] like Figure 4 As shown, the XRD patterns of ZnFe2O4 and ZnFe2O4 nanoparticles modified with gold in different proportions are presented (the preparation methods of ZnFe2O4 nanoparticles modified with gold in different proportions can be referred to Comparative Example 2, the difference being the different volumes of HAuCl4 solution and NaBH4 solution added in step (4). The volumes of HAuCl4 solution and NaBH4 solution required to prepare 1% wt Au modified ZnFe2O4 nanoparticles, 3% wt Au modified ZnFe2O4 nanoparticles, 5% wt Au modified ZnFe2O4 nanoparticles, and 7% wt Au modified ZnFe2O4 nanoparticles are 0.625 mL, 1.875 mL, 3.125 mL, and 4.375 mL, respectively. 5% wt Au modified ZnFe2O4 nanoparticles correspond to Comparative Example 2). No other phase impurity peaks were observed, which is consistent with the ZnFe2O4 standard card. Furthermore, in the XRD pattern of the prepared 7% wt Au modified ZnFe2O4 material, not only the aforementioned ZnFe2O4 diffraction peaks are present, but also the Au nanoparticle (111) peaks are present.

[0032] like Figure 5 As shown, the optimal operating temperature of the sensors in the comparative examples and embodiments is 330°C. At this temperature, the sensitivities of the devices to 1 ppm DMMP gas are 1.7 (Comparative Example 1), 1.66 (Example 1), and 1.52 (Comparative Example 2), respectively. However, the sensors in Comparative Example 1 and Comparative Example 2 have higher sensitivities to 1 ppm acetone than to the same concentration of DMMP. This means that the selectivity of Comparative Example 1 and Comparative Example 2 sensors is relatively poor. In contrast, the sensor in Example 1 has the best selectivity to DMMP gas.

[0033] like Figure 6As shown, with the increase of DMMP gas concentration, the sensitivity of the sensor in Example 1 and the sensor in Comparative Example 2 is significantly improved, and the two sensors show a good saturation curve relationship between sensitivity and concentration.

[0034] like Figure 7 As shown, for both the Example 1 sensor and the Comparative Example 2 sensor exposed to DMMP, the resistance of the semiconductor decreases, a characteristic consistent with the gas-sensing characteristics of N-type oxide semiconductors. Furthermore, the sensors exhibit excellent response and recovery characteristics to different concentrations of DMMP. When the Example device operates at 330°C, the sensitivity increases with increasing DMMP concentration. The Example sensor's sensitivities to 50, 100, 200, 500, 800, and 1000 ppb DMMP are 1.085, 1.22, 1.28, 1.47, 1.57, and 1.66, respectively. Although the Comparative Example 2 device's sensitivity to 50–1000 ppb DMMP is only 1.1–1.7, slightly higher than the Example device, the Comparative Example 2 device has poor selectivity for DMMP gas. Comparative Example 1, due to its very poor recovery characteristics, has no concentration gradient data. Overall, the gas-sensing characteristics of the Example device are superior to those of the Comparative Example device.

[0035] like Figure 8 As shown, the sensor in the embodiment showed no significant fluctuations in its response recovery curve to 1 ppm DMMP gas at an operating temperature of 330°C, with response recovery times of 50 s and 103 s, respectively.

[0036] like Figure 9 As shown, during a month of continuous testing, the sensor in the embodiment operating at 330°C exhibited minimal fluctuations in its stable resistance curve in a DMMP atmosphere and its corresponding sensitivity curve in 1ppm DMMP gas, demonstrating its good long-term stability.

[0037] Note: The sensitivity of a device (N-type semiconductor) in a reducing gas test is defined as the ratio of its resistance in the gas being tested to its resistance in air, i.e., S = R. a / R g During the testing process, a static testing system was used. The device was placed in a 50-80L gas chamber, a certain amount of the organic gas to be tested was injected, and the change in resistance was observed and recorded. The corresponding sensitivity value was then calculated. Detailed Implementation

[0038] Comparative Example 1:

[0039] The specific fabrication process of using ZnFe2O4 as the sensing material to create a DMMP sensor is as follows:

[0040] (1) Measure 4 mL of glycerin and 16 mL of isopropanol and mix them together.

[0041] (2) Add 0.149g Zn(NO3)2·6H2O and 0.404g Fe(NO3)3·9H2O to the mixed solution and stir continuously until they are completely dissolved. Then add 0.06g urea (CO(NH2)2) and stir for 30 minutes.

[0042] (3) Transfer the solution obtained in step (2) to a hydrothermal reactor, keep it at 180°C for 21 hours, take it out, cool it naturally to room temperature, wash the precipitate with deionized water and anhydrous ethanol by centrifugation several times, dry it at 80°C for 12 hours, and finally anneal it at 450°C for 2 hours to obtain ZnFe2O4 nanoparticles.

[0043] (4) Take 0.1g of ZnFe2O4 nanoparticles obtained in (3) and mix with 5mL of n-butanol to form a paste. Then, use a dropper to take a small amount of paste and drop it onto the surface of an Al2O3 substrate with two discrete L-shaped gold electrodes on the outer surface. Use an automatic spin coater to spin coat at a speed of 900r / min for 3 minutes to form a 15μm thick sensitive material film, and make the sensitive material completely cover the outer surface of the Al2O3 substrate and the L-shaped gold electrodes.

[0044] (5) Finally, the above devices are welded and packaged according to the general side-heated gas sensing element to obtain the DMMP gas sensor of ZnFe2O4 sensitive material.

[0045] Comparative Example 2:

[0046] The specific fabrication process of using gold-modified ZnFe2O4 as the sensing material to create a DMMP sensor is as follows:

[0047] (1) Measure 4 mL of glycerol and 16 mL of isopropanol and stir them together. Add 0.149 g of Zn(NO3)2·6H2O and 0.404 g of Fe(NO3)3·9H2O to the mixed solution and stir continuously until they are completely dissolved. Then add 0.06 g of urea (CO(NH2)2) and stir for 30 minutes.

[0048] (2) Transfer the solution obtained in step (1) to a hydrothermal reactor, keep it at 180°C for 21 hours, take it out, cool it naturally to room temperature, wash the precipitate with deionized water and anhydrous ethanol by centrifugation several times, dry it at 80°C for 12 hours, and finally anneal it at 450°C for 2 hours to obtain ZnFe2O4 nanoparticles.

[0049] (3) Take two 5 mL portions of deionized water, add 0.0197 g of HAuCl4·3H2O and 0.009 g of NaBH4 to them respectively, stir for 30 minutes to prepare a HAuCl4 solution with a concentration of 0.01 mol / L and a NaBH4 solution with a concentration of 0.05 mol / L.

[0050] (4) Take 20 mL of deionized water, add 0.1 g of ZnFe2O4 nanoparticles obtained in step (2) to the deionized water, and stir continuously until they are completely dissolved. First, add 3 mL of HAuCl4 solution from step (3) to the solution and stir for 30 minutes. Then, add 3.125 mL of NaBH4 solution from step (3) to the solution and stir for 60 minutes. Wash the precipitate repeatedly by centrifugation with deionized water and anhydrous ethanol, and then dry it at 80 °C for 12 hours to obtain 5 wt% gold-modified ZnFe2O4 nanoparticles.

[0051] (5) Take 0.1g of gold-modified ZnFe2O4 nanoparticles from (4) and mix them with 5mL of n-butanol to form a paste. Then, use a dropper to take a small amount of paste and drop it onto the surface of an Al2O3 substrate with two discrete L-shaped gold electrodes on the outer surface. Use an automatic spin coater to spin coat at a speed of 900r / min for 3 minutes to form a 15μm thick sensitive material film, and make the sensitive material completely cover the outer surface of the Al2O3 substrate and the L-shaped gold electrodes.

[0052] (6) Finally, the above devices are welded and packaged according to the general side-heated gas sensing element to obtain the DMMP gas sensor with Au modified ZnFe2O4 sensing material.

[0053] Example 1:

[0054] The fabrication process of a DMMP gas sensor modified with gold ZnFe2O4 nanoparticles and S-1 molecular sieve:

[0055] (1) Measure 4 mL of glycerol and 16 mL of isopropanol and stir them together. Add 0.149 g of Zn(NO3)2·6H2O and 0.404 g of Fe(NO3)3·9H2O to the mixed solution and stir continuously until they are completely dissolved. Then add 0.06 g of urea (CO(NH2)2) and stir for 30 minutes.

[0056] (2) Transfer the solution obtained in step (1) to a hydrothermal reactor, keep it at 180°C for 21 hours, take it out, cool it naturally to room temperature, wash the precipitate with deionized water and anhydrous ethanol by centrifugation several times, dry the centrifuged product at 80°C for 12 hours, and finally anneal at 450°C for 2 hours to obtain ZnFe2O4 nanoparticles.

[0057] (3) Take two 5 mL portions of deionized water, add 0.0197 g of HAuCl4·3H2O and 0.009 g of NaBH4 to them respectively, stir for 30 minutes to prepare a HAuCl4·3H2O solution with a concentration of 0.01 mol / L and a NaBH4 solution with a concentration of 0.05 mol / L.

[0058] (4) Take 20 mL of deionized water, add 0.1 g of ZnFe2O4 nanoparticles obtained in step (2) to the deionized water, and stir continuously until they are completely dissolved. First, add 3 mL of HAuCl4 solution from step (3) to the solution and stir for 30 minutes. Then, add 3.125 mL of NaBH4 solution from step (3) to the solution and stir for 60 minutes. Wash the precipitate repeatedly by centrifugation with deionized water and anhydrous ethanol, and then dry it at 80 °C for 12 hours to obtain 5 wt% gold-modified ZnFe2O4 nanoparticles.

[0059] (5) Take 0.1g of gold-modified ZnFe2O4 nanoparticles from (4) and mix them with 5mL of n-butanol to form a paste. Then, use a dropper to take a small amount of paste and drop it onto the surface of an Al2O3 substrate with two discrete L-shaped gold electrodes on the outer surface. Use an automatic spin coater to spin coat at a speed of 900r / min for 3 minutes to form a sensitive material film with a thickness of about 15μm, and make the sensitive material completely cover the outer surface of the Al2O3 substrate and the L-shaped gold electrodes.

[0060] (6) After the sensitive material is dried, the Al2O3 substrate is calcined at 250°C for 2 hours and then cooled to room temperature. 500 μL of isopropanol is measured, and 0.015 g of purchased S-1 molecular sieve is added to it. The S-1 molecular sieve solution is then dropped onto the surface of the sensitive material film and spin-coated at 400 r / min for 2 minutes. Finally, the above device is welded and packaged as a side-heated gas sensing element to obtain a DMMP gas sensor based on gold-modified ZnFe2O4 sensitive material and S-1 molecular sieve.

Claims

1. A method for preparing a DMMP gas sensor based on gold-modified ZnFe2O4 sensing material and S-1 molecular sieve, comprising the following steps: (1) Take 0.08-0.12g of gold-modified ZnFe2O4 nanoparticles and mix them with 4-6mL of n-butanol to form a paste. Then, take a small amount of paste and drop it onto the surface of an Al2O3 substrate with two discrete L-shaped gold electrodes on the outer surface. Spin-coat at 800-1000r / min for 2-4 minutes to form a 12-16μm thick sensitive material film, and make the sensitive material completely cover the outer surface of the Al2O3 substrate and the L-shaped gold electrodes. (2) After the sensitive material film is dried, the Al2O3 substrate obtained in step (1) is calcined at 200-300℃ for 1.5-3 hours and then cooled to room temperature; 0.01-0.02g of S-1 molecular sieve is added to 400-600μL of isopropanol, and the resulting S-1 molecular sieve solution is dropped onto the sensitive material film and spin-coated at a speed of 300-500r / min for 1-3 minutes; finally, it is welded and packaged according to the side-heated gas sensing element to obtain the DMMP gas sensor based on gold-modified ZnFe2O4 sensitive material and S-1 molecular sieve.

2. The method for preparing a DMMP gas sensor based on gold-modified ZnFe2O4 sensing material and S-1 molecular sieve as described in claim 1, characterized in that: Gold-modified ZnFe2O4 nanoparticles were prepared by the following steps. (1) Mix 2-6 mL of glycerol and 14-18 mL of isopropanol, then add 0.1-0.2 g of Zn(NO3)2·6H2O and 0.4-0.5 g of Fe(NO3)3·9H2O, and stir continuously until completely dissolved. Then add 0.05-0.07 g of urea (CO(NH2)2) and stir for 20-40 minutes. (2) Transfer the solution obtained in step (1) to a hydrothermal reactor, keep it at 160-200℃ for 20-25 hours, take it out, cool it naturally to room temperature, wash the precipitate with deionized water and anhydrous ethanol by centrifugation several times, dry the centrifuged product at 70-90℃ for 10-15 hours, and finally anneal at 400-500℃ for 1-3 hours to obtain ZnFe2O4 nanoparticles; (3) Add 0.01-0.02g HAuCl4·3H2O and 0.005-0.01g NaBH4 to 4-6mL of deionized water respectively, and stir for 20-40 minutes; (4) Add 0.08-0.12 g of ZnFe2O4 nanoparticles obtained in step (2) to 15-25 mL of deionized water and stir continuously until completely dissolved; then add 2-6 mL of HAuCl4 solution obtained in step (3) and stir for 20-40 minutes; then add 2-6 mL of NaBH4 solution obtained in step (3) and stir for 40-60 minutes; finally, wash the precipitate repeatedly by centrifugation with deionized water and anhydrous ethanol, and dry the centrifuged product at 70-90℃ for 10-15 hours to obtain gold-modified ZnFe2O4 nanoparticles.

3. The method for preparing a DMMP gas sensor based on gold-modified ZnFe2O4 sensing material and S-1 molecular sieve as described in claim 1, characterized in that: The Al2O3 substrate has a length of 2.5–3.5 mm, a width of 2.5–3.5 mm, and a thickness of 0.2–0.3 mm; the L-shaped gold electrode has a length of 1.5–2 mm, a width of 1.5–2 mm, and a thickness of 0.02–0.06 mm.

4. A DMMP gas sensor based on gold-modified ZnFe2O4 sensing material and S-1 molecular sieve, characterized in that: It is prepared by the method described in claim 1, 2 or 3.

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