Room temperature ammonia gas sensor based on PANI / Au / SnO2 sensing material and preparation method thereof

Abstract

The invention discloses a room temperature ammonia gas sensor based on a PANI / Au / SnO2 sensing material and a preparation method thereof. The room temperature ammonia gas sensor comprises a monocrystalline silicon substrate, silicon dioxide layers are arranged on the two faces of the monocrystalline silicon substrate, a gold interdigital electrode is arranged on the silicon dioxide layer on one side, gas sensitive material films are arranged on the surfaces of the silicon dioxide layers and the gold interdigital electrode, and the gas sensitive material films are made of a PANI / Au / SnO2 composite material. The monocrystalline silicon substrate, the silicon dioxide layer and the gold interdigital electrode jointly form a sensor chip; resistance changes before and after the gas sensitive material film is in contact with to-be-detected gas, namely ammonia gas, and related performance of a response value of the sensor is obtained by measuring the change of resistance between the gold interdigital electrodes; the sensor has the advantages of low detection limit and high response, the baseline drift condition can be obviously reduced, the response recovery capability and speed of the gas sensor are improved, and the sensor preparation method is simple and convenient.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas sensing, and in particular relates to a room temperature ammonia sensor based on PANI / Au / SnO2 sensing material and a preparation method thereof. Background Art

[0002] Ammonia detection research is of great significance in fields such as energy storage, environmental monitoring, and medical diagnostics. Resistive ammonia sensors, which use resistance changes to reflect minute changes in ammonia concentration, have attracted widespread attention due to their simple structure and low cost. Metal oxide semiconductor (MOS)-based gas sensors are currently the most widely used ammonia sensors due to their low cost, high stability, and high sensitivity. However, MOS gas sensors have low sensitivity and poor selectivity at room temperature, which severely limits the application range of metal oxide gas sensors. Conductive polymer gas sensors can further reduce energy consumption and sensor size, and have promising application prospects.

[0003] In recent years, functional organic semiconductors (OSCs) have been developed. For example, many polythiophene-based ammonia sensors have been developed. However, due to the inherent defects of the material itself, polythiophene as a gas-sensitive material has problems such as high detection limit, low response, and obvious baseline drift. Some studies, such as Shivam Kumar Gautam et al. functionalized PANI with metal nanocomposites to prepare a sensor for detecting ammonia at room temperature with strong stability (Shi vam Kumar Gautam, Siddhartha Panda, Field effect characteristics and gas sensing properties of verSncally grown PANI on no fibers Organic Electronics, Volume 123, 2023, 106938, 1566-1199.); another researcher Tran et al. improved the detection of ammonia by controlling the nanoporous structure, and used the shear-assisted phase separation method to finely control the morphology of nanopores to obtain a specific pore size (Tran, VV; Jeong, G.; Kim, KS; Kim, J.; Jung, HR; Park, B.; Park, JJ; Chang, M. Facile strategy for modulating the nanoporous structure of ultrathinπ-conjugated polymer films for high-performance gas sensors. ACS Sen s.2022,7,175–185.); These studies have brought new ideas for improving ammonia sensors, but there are still disadvantages such as complex preparation process and low sensor response value. Summary of the Invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a room-temperature ammonia sensor based on PANI / Au / SnO2 sensing material and a preparation method thereof. The sensor has a low detection limit, high response, and can significantly reduce baseline drift, improve the response recovery ability and speed of the gas sensor, and the sensor preparation method is simple and convenient.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A room-temperature ammonia sensor based on PANI / Au / SnO2 sensing material comprises a single-crystal silicon substrate 1, with silicon dioxide layers 2 provided on both sides of the single-crystal silicon substrate 1, gold interdigital electrodes 3 provided on the silicon dioxide layer 2 on one side, a gas-sensitive material film 4 provided on the surfaces of the silicon dioxide layer 2 and the gold interdigital electrodes 3, and the gas-sensitive material film 4 being composed of a PANI / Au / SnO2 composite material; the single-crystal silicon substrate 1, the silicon dioxide layer 2 and the gold interdigital electrodes 3 together constitute a sensor chip; the resistance of the gas-sensitive material film 4 changes before and after contact with a gas to be measured, i.e., ammonia, and the performance related to the sensor response value is obtained by measuring the change in resistance between the gold interdigital electrodes.

[0007] The gas sensitive material film 4 composed of the PANI / Au / SnO2 composite material is prepared by a drop coating method.

[0008] The PANI / Au / SnO2 composite gas-sensitive material is formed by mixing gold-coated polyaniline and tin dioxide nanoparticles in a mass ratio of 1:(0.1-5), and the average particle size of the tin dioxide nanoparticles is about 500nm.

[0009] The method for preparing a room temperature ammonia sensor based on PANI / Au / SnO2 sensing material comprises the following steps:

[0010] Step 1: Clean the sensor chip by ultrasonically cleaning the sensor chip with gold interdigital electrodes deposited on the surface with ethanol and water in sequence, and drying for later use;

[0011] Step 2: Prepare chloroauric acid solution by adding 1-5 ml of concentrated hydrochloric acid to the gold trichloride solution and adding 40-60 ml of water to make chloroauric acid solution;

[0012] Step 3, SnO2 hollow nanospheres are synthesized by a template-free hydrothermal method, 0.1-0.2g SnCl4·5H2O is dissolved in a mixed solution of 2-6ml deionized water and 20-40ml ethanol, and after being fully stirred at room temperature, 0.5-1ml concentrated hydrochloric acid is added; next, after ultrasonication for 30-50min, the mixed solution is transferred to a hydrothermal autoclave and reacted at 200-300°C for 24-36h; after the hydrothermal autoclave is naturally cooled to room temperature, the obtained white precipitate is collected and washed alternately with deionized water and ethanol for 6-8 times by centrifugation to remove excess impurity ions, and finally the white precipitate is dried in an oven at 80-100°C for 12-16h, and calcined in air at 400-600°C for 2-4h to obtain SnO2 hollow nanospheres;

[0013] Step 4: Au / SnO2 hollow nanospheres were prepared by a wet impregnation method. 100-200 mg of the SnO2 hollow nanospheres prepared in step 3 and 10-20 ml of chloroauric acid prepared in step 2 were dissolved in 10-20 ml of ethanol and ultrasonicated for 1-2 hours to obtain a uniform mixed solution. The mixed solution was then stirred continuously at 80-100°C until the ethanol was completely evaporated. Finally, the solid powder was collected and calcined in air at 300-500°C for 2-3 hours to obtain Au / SnO2 hollow nanospheres.

[0014] Step 5: PANI / Au / SnO2 hollow nanospheres PAS were prepared by in situ polymerization. 0.3-0.6 mmol aniline (purified by vacuum distillation) and 10-20 mg Au / SnO2 hollow nanospheres were added to 30-60 mL of 1-2 M HCl solution, and ultrasonicated in an ice bath for 30-60 min to obtain a uniform suspension. At the same time, 0.3-0.6 mmol PAS was added to 30-60 mL of 1-2 M HCl solution, stirred vigorously for 30-60 min, and then precooled in an ice bath. Thereafter, the precooled PAS solution was added to the ultrasonicated mixed solution of aniline and Au / SnO2 hollow nanospheres, and polymerized in an ice bath in the dark for 4-8 h. Finally, the precipitate was collected and washed alternately by centrifugation with deionized water and ethanol for 6-8 times to obtain a PANI / Au / SnO2 hollow nanosphere composite material.

[0015] Step 6: Prepare a PANI / Au / SnO2 gas sensitive material thin film by drop coating. Ultrasonic dispersion of the PANI / Au / SnO2 hollow nanosphere composite material prepared in step 5 in ethanol is performed. 0.5-2 μL of the prepared PANI / Au / SnO2 composite material is pipetted and vertically dropped onto the sensor chip prepared in step 1 to form a PANI / Au / SnO2 gas sensitive material thin film on its surface.

[0016] Step 7: Heat the PANI / Au / SnO2 gas sensitive material film prepared above to completely evaporate the solvent ethanol, thereby obtaining a PANI / Au / SnO2 room temperature ammonia sensor.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. Among all conductive polymers, polyaniline can achieve adsorption and desorption of low-concentration ammonia due to its unique doping mechanism. Moreover, the addition of SnO2 nanoparticles to the PANI / Au composite material will make the sensitive material more stable, so it has the advantage of improving the response of the gas sensor.

[0019] 2. As a typical catalytic medium, gold has the function of reducing the adsorption activation energy of gas molecules and accelerating the charge transfer between gas molecules and the surface of semiconductor sensitive materials. At the same time, gold can also form a Schottky barrier between itself and semiconductor sensitive materials, change the charge distribution at the interface, and increase the charge transfer rate between gas molecules and semiconductor sensitive materials, thereby improving the response recovery ability and speed of the gas sensor.

[0020] 3. Since the polyaniline used mainly conducts electricity through positively charged holes and exhibits P-type semiconductor characteristics, and tin dioxide mainly conducts electricity through negatively charged electrons and exhibits N-type semiconductor characteristics, the composite of polyaniline and tin dioxide can form a heterojunction between the two materials. When the sensor is exposed to a certain concentration of ammonia, the lone pairs of electrons in the ammonia molecules will interact with the polyaniline to reduce the hole concentration, causing energy band bending at the contact interface, increasing the width of the interface depletion layer, further hindering carrier transport, significantly increasing the resistance of the gas-sensitive film, and improving the sensitivity of the sensor, which has the advantages of low detection limit and high response.

[0021] 4. Due to the redox properties of aniline monomer and noble metal ions, the oxidative polymerization from aniline monomer to polyaniline and the reduction reaction from noble metal ions to nanoparticles can proceed simultaneously in the reaction system, thus having the advantage of realizing the simultaneous preparation of polyaniline / noble metal composite nanomaterials.

[0022] 5. Since the present invention adopts the drop coating method to realize the preparation of the PANI / Au / SnO2 resistive type room temperature ammonia sensor, it is simple and easy to operate, and the sensor can be conveniently manufactured, providing good conditions for mass production and processing. It solves the problems of traditional metal oxide gas sensors requiring high temperature sintering and complex processing, so it has the advantages of further reducing energy consumption and reducing costs.

[0023] 6. Compared with other room-temperature ammonia sensors, the PANI / Au / SnO2 resistive room-temperature ammonia sensor has a higher response value and selectivity to ammonia, which can improve the sensitivity of the composite gas sensor, lower the detection limit, and significantly reduce the baseline drift. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic structural diagram of an ammonia sensor according to Example 1 of the present invention.

[0025] Figure 2 This is a scanning electron microscope image of the PANI / Au / SnO2 gas sensitive material in Example 1 of the present invention.

[0026] Figure 3 This is the gas-sensitive response diagram of the PANI / Au / SnO2 gas-sensitive material in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0028] Example 1, with reference to Figure 1 A room-temperature ammonia sensor based on PANI / Au / SnO2 sensing material includes a single-crystal silicon substrate 1, a silicon dioxide layer 2 is provided on both sides of the single-crystal silicon substrate 1, a gold interdigital electrode 3 is provided on the silicon dioxide layer 2 on one side, a gas-sensitive material film 4 is provided on the surface of the silicon dioxide layer 2 and the gold interdigital electrode 3, and the gas-sensitive material film 4 is composed of a PANI / Au / SnO2 composite material and is prepared by a drop coating method; the single-crystal silicon substrate 1 is 500μm thick, the double-sided silicon dioxide layer 2 is 2μm thick, the interdigital width of the gold interdigital electrode 3 is 10μm, the gap between adjacent interdigits is 10μm, and the thickness of the gold electrode is 75nm; the resistance of the gas-sensitive material film 4 changes before and after it contacts the gas to be measured, namely ammonia, and the relevant performance of the sensor response value is obtained by measuring the change in resistance between the gold interdigital electrodes.

[0029] The PANI / Au / SnO2 composite gas-sensitive material is formed by mixing gold-coated polyaniline and tin dioxide nanoparticles in a mass ratio of 1:(0.1-5); the average particle size of the tin dioxide nanoparticles is 500nm.

[0030] The method for preparing a room temperature ammonia sensor based on PANI / Au / SnO2 sensing material comprises the following steps:

[0031] Step 1: Clean the sensor chip by ultrasonically cleaning the sensor chip with gold interdigital electrodes deposited on the surface with ethanol and water in sequence, and drying for later use;

[0032] Step 2: Prepare chloroauric acid solution by adding 1 ml of concentrated hydrochloric acid to the gold trichloride solution and then adding 40 ml of water to prepare chloroauric acid solution;

[0033] Step 3: SnO2 hollow nanospheres were synthesized by a template-free hydrothermal method. 0.1 g of SnCl4·5H2O was dissolved in a mixed solution of 2 ml of deionized water and 20 ml of ethanol. After sufficient stirring at room temperature, 0.5 ml of concentrated hydrochloric acid was added. Next, after ultrasonication for 30 minutes, the mixed solution was transferred to a hydrothermal autoclave and reacted at 200°C for 24 hours. After the hydrothermal autoclave was naturally cooled to room temperature, the obtained white precipitate was collected and washed alternately with deionized water and ethanol for 6 times by centrifugation to remove excess impurity ions. Finally, the white precipitate was dried in an oven at 80°C for 12 hours and calcined in air at 400°C for 2 hours to obtain SnO2 hollow nanospheres.

[0034] Step 4: Au / SnO2 hollow nanospheres were prepared by wet impregnation method. 100 mg of the SnO2 hollow nanospheres prepared in step 3 and 10 ml of chloroauric acid prepared in step 2 were dissolved in 10 ml of ethanol and ultrasonicated for 1 h to obtain a uniform mixed solution. Then, the mixed solution was continuously stirred at 80°C until the ethanol was completely evaporated. Finally, the solid powder was collected and calcined in air at 300°C for 2 h to obtain Au / SnO2 hollow nanospheres.

[0035] Step 5: PANI / Au / SnO2 hollow nanospheres PAS were prepared by in situ polymerization. 0.3 mmol aniline (purified by vacuum distillation) and 10 mg Au / SnO2 hollow nanospheres were added to 30 mL of 1 M HCl solution and ultrasonicated in an ice bath for 30 min to obtain a uniform suspension. At the same time, 0.3 mmol PAS was added to 30 mL of 1 M HCl solution, stirred vigorously for 30 min, and then precooled in an ice bath. Thereafter, the precooled PAS solution was added to the ultrasonicated mixed solution of aniline and Au / SnO2 hollow nanospheres, and polymerized in an ice bath for 4 h in the dark. Finally, the precipitate was collected and washed alternately by centrifugation with deionized water and ethanol for 6 times to obtain a PANI / Au / SnO2 hollow nanosphere composite material.

[0036] Step 6: Prepare a PANI / Au / SnO2 gas sensitive material thin film by drop coating. Ultrasonic dispersion of the PANI / Au / SnO2 hollow nanosphere composite material prepared in step 5 in ethanol is performed. 0.5 μL of the prepared PANI / Au / SnO2 composite material is pipetted and vertically dropped onto the sensor chip prepared in step 1 to form a PANI / Au / SnO2 gas sensitive material thin film on its surface.

[0037] Step 7: Heat the PANI / Au / SnO2 gas sensitive material film prepared above to completely evaporate the solvent ethanol, thereby obtaining a PANI / Au / SnO2 room temperature ammonia sensor.

[0038] The PANI / Au / SnO2 gas sensitive material prepared in this example was tested by scanning electron microscopy. Figure 2 As shown, the image shows the overall morphology of PANI / Au mixed with SnO2 nanoparticles, and PANI / Au aggregates on the SnO2 surface.

[0039] Reference Figure 3The performance of the resistive room-temperature ammonia sensor of this embodiment was tested using a gas-sensitive testing system. In a test environment with a room temperature of 20°C and a humidity of 60% RH, the sensitivity of the PANI@Au-SnO2 room-temperature ammonia sensor to 3ppm ammonia was 7%, and the baseline was relatively stable with a small drift difference. The test results show that the PANI / Au / SnO2 room-temperature ammonia sensor has good repeatability.

[0040] Example 2, a room temperature ammonia sensor based on PANI / Au / SnO2 sensing material is the same as Example 1; a method for preparing a room temperature ammonia sensor based on PANI / Au / SnO2 sensing material comprises the following steps:

[0041] Step 1: Clean the sensor chip by ultrasonically cleaning the sensor chip with gold interdigital electrodes deposited on the surface with ethanol and water in sequence, and drying for later use;

[0042] Step 2: Prepare chloroauric acid solution by adding 3 ml of concentrated hydrochloric acid to the gold trichloride solution and then adding 50 ml of water to prepare chloroauric acid solution;

[0043] Step 3: SnO2 hollow nanospheres were synthesized by a template-free hydrothermal method. 0.15 g of SnCl4·5H2O was dissolved in a mixed solution of 4 ml of deionized water and 30 ml of ethanol. After sufficient stirring at room temperature, 0.7 ml of concentrated hydrochloric acid was added. Next, after ultrasonication for 40 minutes, the mixed solution was transferred to a hydrothermal autoclave and reacted at 250°C for 30 hours. After the hydrothermal autoclave was naturally cooled to room temperature, the obtained white precipitate was collected and washed alternately with deionized water and ethanol for 7 times by centrifugation to remove excess impurity ions. Finally, the white precipitate was dried in an oven at 90°C for 14 hours and calcined in air at 500°C for 3 hours to obtain SnO2 hollow nanospheres.

[0044] Step 4: Au / SnO2 hollow nanospheres were prepared by wet impregnation method. 150 mg of the SnO2 hollow nanospheres prepared in step 3 and 15 ml of chloroauric acid prepared in step 2 were dissolved in 15 ml of ethanol and ultrasonicated for 1.5 h to obtain a uniform mixed solution. Then, the mixed solution was continuously stirred at 90°C until the ethanol was completely evaporated. Finally, the solid powder was collected and calcined in air at 400°C for 2.5 h to obtain Au / SnO2 hollow nanospheres.

[0045] Step 5: PANI / Au / SnO2 hollow nanospheres PAS were prepared by in situ polymerization. 0.5 mmol aniline (purified by vacuum distillation) and 15 mg Au / SnO2 hollow nanospheres were added to 50 mL of 1.5 M HCl solution, and ultrasonicated in an ice bath for 50 min to obtain a uniform suspension. At the same time, 0.5 mmol PAS was added to 50 mL of 1.5 M HCl solution, stirred vigorously for 50 min, and then precooled in an ice bath. Thereafter, the precooled PAS solution was added to the ultrasonicated mixed solution of aniline and Au / SnO2 hollow nanospheres, and polymerized in an ice bath for 6 h in the dark. Finally, the precipitate was collected and washed 7 times by alternating centrifugation with deionized water and ethanol to obtain a PANI / Au / SnO2 hollow nanosphere composite material.

[0046] Step 6: Prepare a PANI / Au / SnO2 gas sensitive material thin film by drop coating. Ultrasonic dispersion of the PANI / Au / SnO2 hollow nanosphere composite material prepared in step 5 in ethanol is performed. 1 μL of the prepared PANI / Au / SnO2 composite material is pipetted and vertically dropped onto the sensor chip prepared in step 1 to form a PANI / Au / SnO2 gas sensitive material thin film on its surface.

[0047] Step 7: Heat the PANI / Au / SnO2 gas sensitive material film prepared above to completely evaporate the solvent ethanol, thereby obtaining a PANI / Au / SnO2 room temperature ammonia sensor.

[0048] The performance of the resistive room temperature ammonia sensor of this embodiment is similar to that of embodiment 1.

[0049] Example 3, a room temperature ammonia sensor based on PANI / Au / SnO2 sensing material is the same as Example 1; a method for preparing a room temperature ammonia sensor based on PANI / Au / SnO2 sensing material comprises the following steps:

[0050] Step 1: Clean the sensor chip by ultrasonically cleaning the sensor chip with gold interdigital electrodes deposited on the surface with ethanol and water in sequence, and drying for later use;

[0051] Step 2: Prepare chloroauric acid solution by adding 5 ml of concentrated hydrochloric acid to the gold trichloride solution and adding 60 ml of water to make chloroauric acid solution;

[0052] Step 3: SnO2 hollow nanospheres were synthesized by a template-free hydrothermal method. 0.2 g of SnCl4·5H2O was dissolved in a mixed solution of 6 ml of deionized water and 40 ml of ethanol. After sufficient stirring at room temperature, 1 ml of concentrated hydrochloric acid was added. Next, after ultrasonication for 50 minutes, the mixed solution was transferred to a hydrothermal autoclave and reacted at 300°C for 36 hours. After the hydrothermal autoclave was naturally cooled to room temperature, the obtained white precipitate was collected and washed alternately with deionized water and ethanol for 8 times by centrifugation to remove excess impurity ions. Finally, the white precipitate was dried in an oven at 100°C for 16 hours and calcined in air at 600°C for 4 hours to obtain SnO2 hollow nanospheres.

[0053] Step 4: Au / SnO2 hollow nanospheres were prepared by wet impregnation method. 200 mg of SnO2 hollow nanospheres prepared in step 3 and 20 ml of chloroauric acid prepared in step 2 were dissolved in 20 ml of ethanol and ultrasonicated for 2 h to obtain a uniform mixed solution. Then, the mixed solution was continuously stirred at 100°C until the ethanol was completely evaporated. Finally, the solid powder was collected and calcined in air at 500°C for 3 h to obtain Au / SnO2 hollow nanospheres.

[0054] Step 5: PANI / Au / SnO2 hollow nanospheres PAS were prepared by in situ polymerization. 0.6 mmol aniline (purified by vacuum distillation) and 20 mg Au / SnO2 hollow nanospheres were added to 60 mL of 2M HCl solution and ultrasonicated in an ice bath for 60 min to obtain a uniform suspension. At the same time, 0.6 mmol PAS was added to 60 mL of 2M HCl solution, stirred vigorously for 60 min, and then precooled in an ice bath. Thereafter, the precooled PAS solution was added to the ultrasonicated mixed solution of aniline and Au / SnO2 hollow nanospheres, and polymerized in an ice bath for 8 h in the dark. Finally, the precipitate was collected and washed 8 times by alternating centrifugation with deionized water and ethanol to obtain a PANI / Au / SnO2 hollow nanosphere composite material.

[0055] Step 6: Prepare a PANI / Au / SnO2 gas sensitive material thin film by drop coating. Ultrasonic dispersion of the PANI / Au / SnO2 hollow nanosphere composite material prepared in step 5 is performed in ethanol. 2 μL of the prepared PANI / Au / SnO2 composite material is pipetted and vertically dropped onto the sensor chip prepared in step 1 to form a PANI / Au / SnO2 gas sensitive material thin film on its surface.

[0056] Step 7: Heat the PANI / Au / SnO2 gas sensitive material film prepared above to completely evaporate the solvent ethanol, thereby obtaining a PANI / Au / SnO2 room temperature ammonia sensor.

[0057] The performance of the resistive room temperature ammonia sensor of this embodiment is similar to that of embodiment 1.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A room-temperature ammonia sensor based on a PANI / Au / SnO2 sensing material, comprising a single-crystal silicon substrate (1), silicon dioxide layers (2) being provided on both sides of the single-crystal silicon substrate (1), a gold interdigital electrode (3) being provided on one side of the silicon dioxide layer (2), and a gas-sensitive material thin film (4) being provided on the surface of the silicon dioxide layer (2) and the gold interdigital electrode (3), wherein: The gas sensitive material film (4) is composed of a PANI@Au-SnO2 composite material; a single crystal silicon substrate (1), a silicon dioxide layer (2) and gold interdigital electrodes (3) together constitute a sensor chip; the resistance of the gas sensitive material film (4) changes before and after contact with a gas to be measured, i.e., ammonia gas, and the performance related to the sensor response value is obtained by measuring the change in resistance between the gold interdigital electrodes.

2. The room temperature ammonia sensor according to claim 1, characterized in that: The gas sensitive material film (4) composed of the PANI / Au / SnO composite material is prepared by a drop coating method.

3. The room temperature ammonia sensor according to claim 1, wherein: The PANI / Au / SnO composite gas-sensitive material is formed by mixing gold-coated polyaniline and tin dioxide nanoparticles in a mass ratio of 1:(0.1-5), and the average particle size of the tin dioxide nanoparticles is 500nm.

4. The method for preparing a room temperature ammonia sensor based on PANI / Au / SnO2 sensing material according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1: Clean the sensor chip by ultrasonically cleaning the sensor chip with gold interdigital electrodes deposited on the surface with ethanol and water in sequence, and drying for later use; Step 2: Prepare chloroauric acid solution by adding 1-5 ml of concentrated hydrochloric acid to the gold trichloride solution and adding 40-60 ml of water to make chloroauric acid solution; Step 3, synthesizing SnO2 hollow nanospheres, dissolving 0.1-0.2g SnCl4·5H2O in a mixed solution of 2-6ml deionized water and 20-40ml ethanol, stirring thoroughly at room temperature, and then adding 0.5-1ml concentrated hydrochloric acid; next, after ultrasonication, transferring the mixed solution to a hydrothermal autoclave, and collecting the resulting white precipitate after the autoclave naturally cools to room temperature after hydrothermal treatment. The white precipitate is washed alternately with deionized water and ethanol by centrifugation to remove excess impurity ions, and finally, the white precipitate is dried in an oven and calcined in air to obtain SnO2 hollow nanospheres; Step 4: Prepare Au / SnO2 hollow nanospheres by dissolving 100-200 mg of the SnO2 hollow nanospheres prepared in step 3 and 10-20 ml of chloroauric acid prepared in step 2 in 10-20 ml of ethanol, and ultrasonically obtain a uniform mixed solution; then, continuously stir the mixed solution until the ethanol is completely evaporated; finally, collect the solid powder and calcine it in air to obtain Au / SnO2 hollow nanospheres; Step 5: PANI / Au / SnO2 hollow nanospheres (PAS) were prepared by in situ polymerization; 0.3-0.6 mmol aniline and 10-20 mg Au / SnO2 hollow nanospheres were added to 30-60 mL of 1-2 M HCl solution, and ultrasonicated in an ice bath to obtain a uniform suspension; at the same time, 0.3-0.6 mmol PAS was added to 30-60 mL of 1-2 M HCl solution, stirred vigorously, and then precooled in an ice bath; thereafter, the precooled PAS solution was added to the ultrasonicated mixed solution of aniline and Au / SnO2 hollow nanospheres, and polymerized in an ice bath in the dark; finally, the precipitate was collected and washed by alternating centrifugation with deionized water and ethanol to obtain a PANI / Au / SnO2 hollow nanosphere composite material; Step 6: Prepare a PANI / Au / SnO2 gas sensitive material thin film by drop coating. Ultrasonic dispersion of the PANI / Au / SnO2 hollow nanosphere composite material prepared in step 5 is performed in ethanol. The prepared PANI / Au / SnO2 composite material is sucked up using a pipette and vertically dropped onto the sensor chip prepared in step 1 to form a PANI / Au / SnO2 gas sensitive material thin film on the surface of the sensor chip. Step 7: Heat the PANI / Au / SnO2 gas sensitive material film prepared above to completely evaporate the solvent ethanol, thereby obtaining a PANI / Au / SnO2 room temperature ammonia sensor.

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