Preparation method of Au atom modified Sn3O4 gas sensitive material and application thereof

Abstract

The application discloses a preparation method of Au atom modified Sn3O4 gas-sensitive material and application thereof, and the preparation method comprises the following steps: Sn3O4 is weighed and dispersed into distilled water and is ultrasonically treated, then under the condition of stirring, a HAuCl4 solution is slowly added into the Sn3O4, the solution is uniformly stirred to obtain a mixed solution; an ammonia solution is slowly added into the mixed solution, the pH is adjusted to 9-12, and the stirring is continued; then, an L-ascorbic acid solution is added into the solution, gold ions are reduced, and the solution is uniformly stirred under the condition of magnetic stirring at room temperature; the precipitate is collected through centrifugation, and is washed with deionized water and acetone for three times respectively, the obtained final product is dried in a vacuum drying box, and the Au atom modified Au / Sn3O4 gas-sensitive material is obtained. The synthesized Au / Sn3O4 gas-sensitive material is applied to a MEMS-based gas sensor, and the concentration of formaldehyde is detected at a lower working temperature.

Description

Technical Field

[0001] This invention relates to the field of semiconductor metal oxide gas sensor technology, specifically to a method for preparing an Au-atom-modified Sn3O4 gas-sensitive material and its application. Background Technology

[0002] Gas detection plays a vital role in many fields, such as environmental protection, industrial safety (detecting explosive gases), the food industry (e.g., fermentation control and seafood freshness control), and indoor gas detection (including combustible and toxic pollutants). Indoor gas detection is receiving increasing attention in these areas due to the growing number of human activities taking place indoors, where airtightness is crucial. Formaldehyde, a carcinogenic and teratogenic harmful indoor pollutant, can be slowly released from building / decorative materials, and even low concentrations can cause serious health problems. Therefore, developing accurate formaldehyde (HCHO) sensors to detect low concentrations of formaldehyde indoors is essential to ensure public health.

[0003] To date, various analytical instruments for detecting formaldehyde concentration have been developed, such as high performance liquid chromatographs, gas chromatographs, fluorescence gas sensors, electrochemical gas sensors, and semiconductor oxide gas sensors.

[0004] While the aforementioned methods can accurately detect formaldehyde, their high cost, complex processes, and time consumption limit their widespread application. In contrast, metal oxide semiconductor-based gas sensors exhibit unique advantages due to their low cost, ease of operation, ease of integration, fast response and recovery speeds, and high physical and chemical stability. However, existing semiconductor-based metal oxide formaldehyde gas sensors still cannot meet the actual needs of the vast market due to relatively high detection limits, low sensitivity and selectivity, and short lifespan caused by high operating temperatures. These problems are mainly attributed to the limited surface area and insufficient active sites of the gas-sensitive materials coated on the gas sensors, resulting in weak absorption and poor electron transport of gas molecules. Therefore, from a materials design perspective, there is still a need to develop high-performance gas-sensitive materials for formaldehyde gas sensors. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing Au / Sn3O4 gas-sensitive materials modified with Au atoms and their application. The method involves a two-step synthesis of Au / Sn3O4 gas-sensitive materials modified with Au atoms, and the synthesized Au / Sn3O4 gas-sensitive materials are applied to MEMS-based gas sensors to detect the concentration of formaldehyde at an operating temperature not exceeding 250°C.

[0006] In one aspect of the present invention, a method for preparing Au-atom-modified Sn3O4 gas-sensitive materials is provided. According to an embodiment of the present invention, the method includes the following steps:

[0007] S1. Weigh Sn3O4, disperse it in distilled water, and sonicate it. Then, under stirring, slowly add HAuCl4 solution dropwise to Sn3O4 and stir to mix it evenly to obtain a mixed solution.

[0008] S2. Slowly add the ammonia solution dropwise to the mixture, adjust the pH to 9-12, and continue stirring;

[0009] S3. Add L-ascorbic acid solution to the solution in step S2 to reduce gold ions, and stir magnetically until homogeneous at room temperature.

[0010] S4. Centrifuge to collect the precipitate, and wash it three times with deionized water and acetone respectively. The final product is dried in a vacuum drying oven to obtain Au / Sn3O4 gas-sensitive material modified with Au atoms.

[0011] In addition, the preparation method of the Au-atom-modified Sn3O4 gas-sensitive material according to the above embodiments of the present invention may also have the following additional technical features:

[0012] In some embodiments of the present invention, step S1, the preparation method of Sn3O4 specifically includes the following steps:

[0013] S101. Dissolve stannous chloride dihydrate and sodium citrate dihydrate completely in deionized water under rapid stirring and continue stirring to form a transparent solution;

[0014] S102. Slowly add sodium hydroxide solution dropwise to the above transparent solution and continue stirring;

[0015] S103. Transfer the solution to a high-pressure reactor and keep it at 150-200°C for 8-16 hours in an electric heating drying oven. After the reaction is complete, cool the high-pressure reactor to room temperature.

[0016] S104. The yellow precipitate obtained by centrifugation is collected and washed three times with deionized water and acetone respectively. Finally, the precipitate is dried in a vacuum drying oven to obtain pure Sn3O4 gas-sensitive material.

[0017] In some embodiments of the present invention, in step S101, the molar ratio of stannous chloride dihydrate to sodium citrate dihydrate ranges from 1:5 to 3:5; in step S102, the concentration of sodium hydroxide solution is 0.1 to 0.5 mol / L; and in step S104, the drying temperature is 40 to 80°C and the drying time is 8 to 16 h.

[0018] In some embodiments of the present invention, in step S1: the ultrasonic time is 10 to 20 min; the mass ratio of HAuCl4 to Sn3O4 is in the range of 1 to 5%; and the concentration of HAuCl4 is 10 to 30 mmol / L.

[0019] In some embodiments of the present invention, in step S2, the concentration of the ammonia solution is 1 to 3 mol / L.

[0020] In step S3, the concentration of the L-ascorbic acid solution is 0.1–1 mol / L, and the molar ratio of L-ascorbic acid to HAuCl4 is in the range of 1:1–50:1.

[0021] In step S4, the vacuum drying temperature is 40–80°C, and the drying time is 8–16 hours.

[0022] In another aspect of the present invention, the present invention provides a method for preparing the Au-atom-modified Sn3O4 gas-sensitive material to obtain the Au-atom-modified Sn3O4 gas-sensitive material.

[0023] In another aspect of the present invention, a MEMS-based formaldehyde gas sensor is proposed, comprising a gas-sensitive material, characterized in that: the gas-sensitive material is the Au-atom-modified Sn3O4 gas-sensitive material.

[0024] In another aspect, the present invention provides a method for fabricating a MEMS-based formaldehyde gas sensor, which, according to an embodiment of the present invention, includes the following steps:

[0025] S1. Sample preparation: Add the Au-atom-modified Sn3O4 gas-sensitive material and polyethylene glycol 400 to a centrifuge tube and mix them evenly to obtain the gas-sensitive material.

[0026] S2. Retrieve the chips: Arrange the chips sequentially on the chip box and observe under a microscope to check if the chips are intact;

[0027] S3. Applying material: Place the chip box containing the chip under a microscope, dip one end of a cotton swab into the gas-sensitive material, and lightly apply it to the chip material loading area under the microscope so that the gas-sensitive material completely covers the four sides of the chip material loading area. Then place the chip with the gas-sensitive material on the heating stage to remove the dispersant polyethylene glycol 400 and allow the gas-sensitive material to better adhere to the chip material loading area.

[0028] S4. Sealing: Use tweezers to pick up the shell, then use a needle to apply a small amount of black glue to the center of the groove in the shell. After applying the glue, under a microscope, use plastic tweezers to pick up the chip containing the gas-sensitive material and place it in the groove of the shell. Gently press the edge of the chip to make the chip and the bottom of the shell fit together. Then dry in an oven to fix the two together.

[0029] S5. Wire bonding: After the gas sensor is sealed, it is placed into the MEMS fixture, and then the four electrodes on the chip are bonded to the four corresponding gold electrodes on the casing by a gold wire bonding machine.

[0030] S6. Sealing: Finally, apply black glue to the four sides of the gas sensor and add a metal protective shell with round holes. Then put it in an oven to dry and fix the two together, thus obtaining the MEMS-based formaldehyde gas sensor.

[0031] In addition, the method for fabricating a MEMS-based formaldehyde gas sensor according to the above embodiments of the present invention may also have the following additional technical features:

[0032] In some embodiments of the present invention, in step S1, the ratio of Au-modified Sn3O4 gas-sensitive material to polyethylene glycol 400 is 100-300 μL of polyethylene glycol 400 per 0.1 g Au / Sn3O4 gas-sensitive material; in step S3, the temperature of the heating stage is 150-250°C, and the heating time is 10-20 min; in step S4, the drying temperature of the oven is 100-200°C, and the drying time is 10-30 min; in step S6, the drying temperature of the oven is 100-200°C, and the drying time is 10-30 min.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] The sensing mechanism of metal oxide semiconductor gas sensors is based on the space charge layer theory. Their gas-sensing response characteristics depend on the adsorption properties of the gas and the redox reaction between the analyte gas and chemisorbed oxygen. Therefore, the morphology and composition of the metal oxide semiconductor gas-sensing material both affect the gas-sensing response characteristics. Tin tetroxide (Sn3O4) is a typical gas sensor with different tin valences (Sn... 4+ Sn 2+ Sn3O4 is an n-type semiconductor material. Due to its unique structure, thermodynamic stability in the Sn-O phase diagram, and abundant oxygen vacancies, it exhibits excellent physical and chemical properties, such as low humidity dependence, large specific surface area, and abundant oxygen adsorption. This invention synthesizes an Au atom-modified Sn3O4 gas-sensitive material using a two-step method. The first step involves preparing Sn3O4 via a hydrothermal method, and the second step involves preparing the gold atom-modified Au / Sn3O4 gas-sensitive material via an impregnation method. Based on this, the Au / Sn3O4 gas-sensitive material synthesized in this invention is loaded onto a MEMS chip to fabricate a formaldehyde gas sensor.

[0035] Compared to pure Sn3O4 formaldehyde gas sensors, Au-modified Sn3O4 formaldehyde gas sensors exhibit higher response times and shorter response and recovery times for formaldehyde gas. The improved sensing performance of Au-modified Sn3O4 formaldehyde sensors can be attributed to two main factors. First, Au atoms are a far superior oxygen dissociation catalyst than Sn3O4, enabling more oxygen molecules to form chemisorbed oxygen ions on the metal oxide surface, thus increasing the resistance of Sn3O4. The high concentration of chemisorbed oxygen ions increases the thickness of the electron depletion layer, leading to an increase in baseline resistance in air; the thicker electron depletion region enhances sensitivity. Furthermore, due to the high conductivity and availability of free electrons in gold atoms, oxygen ion adsorption occurs on the gold atom surface at low temperatures. This process is believed to favor a larger and faster reaction between formaldehyde gas molecules and adsorbed oxygen. In addition, applying Au-modified Sn3O4 gas-sensitive materials to MEMS-based gas sensors offers advantages such as miniaturization, low power consumption, small size, easy integration, easy multifunctionality, fast response, high sensitivity, and high stability. Attached Figure Description

[0036] Figure 1 These are X-ray diffraction (XRD) patterns of Sn3O4 and Au / Sn3O4 prepared in Example 1 of this invention;

[0037] Figure 2 Sn3O4 (prepared in Example 1 of this invention) Figure 2 a) Scanning electron microscope (SEM) images of Au / Sn3O4 Figure 2 b) and the elemental distribution diagrams of O, Sn, and Au in Au / Sn3O4 ( Figure 2 cf);

[0038] Figure 3 This is the X-ray energy dispersive spectroscopy (EDS) pattern of Au / Sn3O4 prepared in Example 1 of this invention;

[0039] Figure 4 This is a flowchart of the preparation of Sn3O4 and Au / Sn3O4 gas-sensitive materials in Example 1 of the present invention;

[0040] Figure 5 This is the response recovery curve of the Sn3O4 gas sensor device prepared in Example 2 of the present invention to 10 ppm formaldehyde at 220°C;

[0041] Figure 6 The response recovery curve of the Au / Sn3O4 gas sensor device prepared in Example 2 of this invention to 10 ppm formaldehyde at 220°C is shown.

[0042] Figure 7The response curves of the Au / Sn3O4 gas sensor device prepared in Example 2 of this invention to different concentrations of formaldehyde at 220°C are shown.

[0043] Figure 8 This is the linear relationship between the response value of the Au / Sn3O4 gas sensor device prepared in Example 2 of the present invention to formaldehyde and the formaldehyde concentration;

[0044] Figure 9 These are 15 repeated cycle curves of the response recovery of the Au / Sn3O4 gas sensor device prepared in Example 2 of the present invention to 10ppm formaldehyde at 220℃;

[0045] Figure 10 This is the response of the Au / Sn3O4 gas sensor device prepared in Example 2 of the present invention to various 10ppm gases at 220℃;

[0046] Figure 11 This is a structural diagram of the MEMS-based formaldehyde gas sensor packaged in Embodiment 2 of the present invention;

[0047] In the figure, 1 is the measuring electrode, 2 is the tube shell, 3 is the gold electrode, 4 is the material loading area, 5 is the heating electrode, and 6 is the metal protective shell. Detailed Implementation

[0048] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0049] Example 1

[0050] The preparation method of Au-atom-modified Sn3O4 gas-sensitive material includes the following steps:

[0051] S1. One-step hydrothermal synthesis of Sn3O4

[0052] S101. Dissolve 0.90g of stannous chloride dihydrate and 2.94g of sodium citrate dihydrate in 10ml of deionized water under rapid stirring to form a transparent solution.

[0053] S102. Slowly add 10 ml of pre-prepared sodium hydroxide solution (0.2 M) dropwise to the above mixed solution and continue stirring;

[0054] S103. Transfer the solution to a 50ml high-pressure reactor and keep it at 180℃ for 12 hours in an electric heating drying oven. After the reaction is complete, cool the high-pressure reactor to room temperature.

[0055] S104. The yellow precipitate obtained by centrifugation is collected and washed three times each with deionized water and acetone (the precipitate generated in the reaction is insoluble in acetone solution; washing with acetone can fully separate the product and thus greatly improve the yield). Finally, the precipitate is dried in a vacuum drying oven at 60℃ for 12 hours to obtain pure Sn3O4 gas-sensitive material.

[0056] S2. Preparation of Au / Sn3O4 modified with Au atoms by impregnation method

[0057] S201. Weigh 1g of the prepared Sn3O4 and disperse it in 20ml of deionized water and sonicate for 10min. Then, under stirring, slowly add 507μL of HAuCl4 (20mM) solution to the turbid liquid containing Sn3O4 and stir to mix evenly.

[0058] S202. Slowly add the diluted ammonia solution (1 mol / L) dropwise to the mixture, adjust the pH to about 10, and continue stirring.

[0059] S203. Add 1 ml of L-ascorbic acid solution (0.1 M) to the mixture to reduce gold ions, and stir magnetically until homogeneous at room temperature. The molar ratio of L-ascorbic acid to HAuCl4 is 9.86:1.

[0060] S204, centrifuge to collect the precipitate, and wash it three times with deionized water and acetone (the precipitate generated in the reaction is insoluble in acetone solution, and washing with acetone can fully separate the product and thus greatly improve the yield). The final product is dried in a vacuum drying oven at a temperature of 60℃ for 12 hours to obtain Au atom modified Au / Sn3O4 gas-sensitive material.

[0061] like Figure 1 As shown, both Sn3O4 and Au / Sn3O4 samples exhibit strong diffraction peaks, which correspond to the JCPDS (16-0737) card for the standard of tin tetroxide, indicating that Sn3O4 was successfully synthesized in this invention. Furthermore, the diffraction peaks of the Au / Sn3O4 sample at 2θ = 38.2° and 2θ = 44.4° correspond to the JCPDS (04-0784) card for the standard of gold atoms, which also confirms the presence of gold atoms.

[0062] Figure 2 a and Figure 2 b are scanning electron microscope images of Sn3O4 and Au / Sn3O4, respectively. As shown in the figure, the microstructure of Sn3O4 and Au / Sn3O4 consists of rough spheres with a diameter of about 2 μm composed of tiny particles. Figure 2 c to Figure 2 e is the elemental distribution diagram of Au / Sn3O4. The elemental distribution diagram of Au / Sn3O4 confirms the presence of Sn, O, and Au, where Sn and O originate from Sn3O4, while Au originates from gold atoms. Furthermore, from... Figure 2 f indicates that the gold atoms are evenly distributed.

[0063] Figure 3 This is the X-ray energy spectrum of Au / Sn3O4. Characteristic peaks of Sn, O, and Au elements can be observed in the figure. The mass percentage of gold is close to the theoretical value, indicating that most of the gold ions were reduced to gold atoms and modified on the Au / Sn3O4 gas-sensitive material.

[0064] Example 2

[0065] A method for fabricating a MEMS-based formaldehyde gas sensor includes the following steps:

[0066] S1. Sample preparation: Add an appropriate amount of gas-sensitive material and polyethylene glycol 400 to a centrifuge tube and mix them evenly using a vortex mixer to obtain the gas-sensitive material. The ratio of Au-atom modified Sn3O4 gas-sensitive material to polyethylene glycol 400 is 200 μL of polyethylene glycol 400 per 0.1 g of Au / Sn3O4 gas-sensitive material.

[0067] S2. Remove the chip: Use plastic tweezers to hold the chip by both sides and shake it to remove it. Then arrange the chips in order on the chip box and observe whether the chips are intact under a microscope.

[0068] S3. Applying material: Place the chip box containing the chip under a microscope, dip one end of a cotton swab into the material, and lightly apply it to the chip material loading area 4 under the microscope so that the material completely covers the four sides of the chip material loading area 4. Then place the chip with the gas-sensitive material on the heating stage. The temperature of the heating stage is 200℃ and the heating time is 10 minutes to remove the dispersant polyethylene glycol 400 and allow the gas-sensitive material to better adhere to the chip material loading area.

[0069] S4. Sealing: Use tweezers to pick up the shell 2, then use a needle to apply a small amount of black glue to the center of the groove in the shell 2. After applying the glue, under a microscope, use plastic tweezers to pick up the chip carrying the gas-sensitive material and place it into the groove in the shell 2. Gently press the edge of the chip to make the chip and the bottom of the shell 2 fit together. Then dry in an oven to fix the two together. The drying temperature of the oven is 200℃ and the drying time is 20min.

[0070] S5. Wire bonding: Place the semi-finished gas sensor after the casing is completed into the MEMS fixture, and then use a gold wire bonding machine to solder the four electrodes on the chip (a pair of heating electrodes 5 and a pair of measuring electrodes 1) to the four corresponding gold electrodes 3 on the casing (the function of the gold electrodes 3 is to connect the gas sensor chip and the test circuit board fixture) with gold wire.

[0071] S6, Sealing: Finally, apply black glue to the four sides of the gas sensor and add a metal protective shell 6 with round holes. Then put it in an oven to dry and fix the two together. The drying temperature of the oven is 200℃ and the drying time is 30 minutes. The MEMS-based formaldehyde gas sensor, also known as Au / Sn3O4 gas sensor, is obtained.

[0072] S7. The packaged gas sensor is placed in the circuit board fixture, and its gas sensing performance is measured using the H1S-9010 gas sensor gas sensing performance testing system.

[0073] Figure 5 The figure shows the response and recovery curves of pure Sn3O4 to 10ppm formaldehyde gas at 220℃. As can be seen from the figure, the response of pure Sn3O4 to 10ppm formaldehyde gas is 1.9, the response time is 31 seconds, and the recovery time is 81 seconds. Figure 6 The image shows the response and recovery curves of Au / Sn3O4 to 10 ppm formaldehyde gas at 220℃. The response time of Au / Sn3O4 to 10 ppm formaldehyde gas is 4.3, the response time is 20 seconds, and the recovery time is 43 seconds. Compared with pure Sn3O4, Au / Sn3O4 has a higher response time and shorter response and recovery times to 10 ppm formaldehyde gas. This indicates that surface modification with Au atoms improves the gas-sensing performance of tin tetroxide for formaldehyde.

[0074] Figure 7 and Figure 8 The figures show the continuous response curves of Au / Sn3O4 at 220℃ to different formaldehyde concentrations (1ppm-50ppm) and their corresponding fitting curves. As can be seen from the figures, the response increases with the increase of formaldehyde concentration, showing an excellent linear relationship.

[0075] Figure 9 The figure shows the response and recovery curves of Au / Sn3O4 to 10ppm formaldehyde for 15 consecutive cycles at 220℃. As can be seen from the figure, the response value of Au / Sn3O4 formaldehyde gas sensor to 10ppm formaldehyde is not significantly different each time, and the response and recovery time do not change significantly, indicating that Au / Sn3O4 has good repeatability.

[0076] Figure 10 This is the preparation process of Au / Sn3O4 gas-sensitive materials. First, Sn3O4 is synthesized by hydrothermal reaction, and then Au-modified Au / Sn3O4 is prepared by impregnation method.

[0077] Figure 10 The figure shows the response of the Au / Sn3O4 gas sensor to various 10ppm gases at 220℃. As can be seen from the figure, the Au / Sn3O4 gas sensor has the highest response to formaldehyde, indicating that it has good selectivity (response of 4.3 for 10ppm formaldehyde and 16.7 for 50ppm formaldehyde). Figure 11 This is a microstructure diagram of the MEMS-based formaldehyde gas sensor packaged according to the present invention.

[0078] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the present invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for preparing an Au-atom-modified Sn3O4 gas-sensitive material, characterized in that, Includes the following steps: S1. Weigh Sn3O4, disperse it in distilled water, and sonicate it. Then, under stirring, slowly add HAuCl4 solution dropwise to Sn3O4 and stir to mix it evenly to obtain a mixed solution. S2. Slowly add the ammonia solution dropwise to the mixture, adjust the pH to 9-12, and continue stirring; S3. Add L-ascorbic acid solution to the solution in step S2 to reduce gold ions, and stir magnetically at room temperature until homogeneous. The concentration of L-ascorbic acid solution is 0.1~1 mol / L, and the molar ratio of L-ascorbic acid to HAuCl4 is 1:1~50:

1. S4. Centrifuge to collect the precipitate, and wash it three times with deionized water and acetone respectively. The final product is dried in a vacuum drying oven to obtain Au / Sn3O4 gas-sensitive material modified with Au atoms.

2. The method for preparing an Au-atom-modified Sn3O4 gas-sensitive material according to claim 1, characterized in that: In step S1, the preparation method of Sn3O4 specifically includes the following steps: S101. Dissolve stannous chloride dihydrate and sodium citrate dihydrate completely in deionized water under rapid stirring and continue stirring to form a transparent solution; S102. Slowly add sodium hydroxide solution dropwise to the above transparent solution and continue stirring; S103. Transfer the solution to a high-pressure reactor and keep it at 150~200℃ for 8~16 hours in an electric heating drying oven. After the reaction is complete, cool the high-pressure reactor to room temperature. S104. The yellow precipitate obtained by centrifugation is collected and washed three times with deionized water and acetone respectively. Finally, the precipitate is dried in a vacuum drying oven to obtain pure Sn3O4 gas-sensitive material.

3. The method for preparing an Au-atom-modified Sn3O4 gas-sensitive material according to claim 2, characterized in that: In step S101, the molar ratio of stannous chloride dihydrate to sodium citrate dihydrate is in the range of 1:5 to 3:

5. In step S102, the concentration of the sodium hydroxide solution is 0.1~0.5 mol / L; In step S104, the drying temperature is 40~80℃ and the drying time is 8~16h.

4. The method for preparing an Au-atom-modified Sn3O4 gas-sensitive material according to claim 1, characterized in that, In step S1: The ultrasound time is 10-20 minutes; The mass ratio of HAuCl4 to Sn3O4 ranges from 1% to 5%. The concentration of HAuCl4 is 10~30 mmol / L.

5. The method for preparing an Au-atom-modified Sn3O4 gas-sensitive material according to claim 1, characterized in that: In step S2, the concentration of the ammonia solution is 1~3 mol / L; In step S4, the vacuum drying temperature is 40~80℃ and the drying time is 8~16h.

6. An Au-atom-modified Sn3O4 gas-sensitive material prepared by a method according to any one of claims 1-5.

7. A MEMS-based formaldehyde gas sensor, comprising a gas-sensitive material, characterized in that: The gas-sensitive material is the Au-atom-modified Sn3O4 gas-sensitive material as described in claim 6.

8. A method for fabricating a MEMS-based formaldehyde gas sensor, characterized in that, Includes the following steps: S1. Sample preparation: Add the Au-atom-modified Sn3O4 gas-sensitive material and polyethylene glycol 400 as described in claim 6 to a centrifuge tube and mix them evenly to obtain the gas-sensitive material. S2. Retrieve the chips: Arrange the chips sequentially on the chip box and observe under a microscope to check if the chips are intact; S3. Applying material: Place the chip box containing the chip under a microscope, dip one end of a cotton swab into the gas-sensitive material, and lightly apply it to the chip material loading area under the microscope so that the gas-sensitive material completely covers the four sides of the chip material loading area. Then place the chip with the gas-sensitive material on the heating stage to remove the dispersant polyethylene glycol 400 and allow the gas-sensitive material to better adhere to the chip material loading area. S4. Sealing: Use tweezers to pick up the shell, then use a needle to apply a small amount of black glue to the center of the groove in the shell. After applying the glue, under a microscope, use plastic tweezers to pick up the chip containing the gas-sensitive material and place it in the groove of the shell. Gently press the edge of the chip to make the chip and the bottom of the shell fit together. Then dry in an oven to fix the two together. S5. Wire bonding: After the gas sensor is sealed, it is placed into the MEMS fixture, and then the four electrodes on the chip are bonded to the corresponding four electrodes on the casing by gold wire bonding machine. S6. Sealing: Finally, apply black glue to the four sides of the gas sensor and add a metal protective shell with round holes. Then put it in an oven to dry and fix the two together, thus obtaining the MEMS-based formaldehyde gas sensor.

9. The method for fabricating a MEMS-based formaldehyde gas sensor according to claim 8, characterized in that: In step S1, the ratio of Au-modified Sn3O4 gas-sensitive material to polyethylene glycol 400 is 100~300μL of polyethylene glycol 400 per 0.1g Au / Sn3O4 gas-sensitive material. In step S3, the temperature of the heating table is 150~250℃, and the heating time is 10~20min; In step S4, the drying temperature of the oven is 100~200℃, and the drying time is 10~30min; In step S6, the drying temperature of the oven is 100~200℃, and the drying time is 10~30min.

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