CN110412088B - In doping based on Au2O3Xanthate gas sensitive element of nanosphere and preparation method thereof - Google Patents

Abstract

The invention discloses a xanthate gas gas sensor based on Au-doped In ₂ O ₃ nanospheres and a preparation method thereof, belonging to the field of gas sensors of metal oxide semiconductor materials. The invention uses indium nitrate as the indium source and chloroauric acid as the gold source, and adopts a hydrothermal method to prepare Au-doped In ₂ O ₃ nanospheres with a hexagonal crystal structure and a diameter of 75-125 nm. The prepared Au-doped In ₂ O ₃ nanospheres are dispersed in an ethanol solution to prepare a gas-sensing slurry, which is then uniformly coated on the surface of an electrode element to prepare a gas-sensing element. The Au-doped In ₂ O ₃ nanospheres of the invention have a simple synthesis method, low cost, no pollution and stable structure. The gas sensing element of the invention has high sensitivity, good response and recovery characteristics, and good response reversibility, repeatability and stability, and can fill the gap in the quantitative detection of this type of gas in the current market. The life, health and safety of the workers in the flotation workshop is of great significance.

Description

A xanthate gas sensor based on Au-doped In2O3 nanospheres and its preparation method

technical field

The invention belongs to the field of metal oxide semiconductor gas sensors, in particular to a xanthate gas gas sensor element based on Au-doped In ₂ O ₃ nanospheres and a preparation method thereof.

Background technique

In the process of comprehensive utilization of mineral resources, the first step is to enrich the useful elements in the ore. Common separation methods include gravity separation, magnetic separation, and flotation. Among them, flotation is a widely used ore sorting method. Its basic principle is to use the difference in physical and chemical properties of the surface of different minerals to selectively attach to the air bubbles in the pulp, and float to the pulp with the bubbles. surface, thereby separating useful minerals from gangue. During the flotation process, in order to control the physical and chemical properties of the ore surface and the properties of the pulp, certain flotation agents must be added to the pulp. Xanthate, one of the most common flotation agents, is often used in the flotation of sulfide ores. However, xanthate solution is easy to decompose and volatilize, and its volatile gas has a strong irritating odor, which has serious irritating effects on eyes, skin, respiratory system, central and peripheral nervous systems, and acute exposure to high concentrations (>0.05%) Can cause anesthesia or psychosis. Therefore, the preparation of high-performance gas sensors to quantitatively monitor the xanthate gas in the flotation workshop is of great significance to protect the life and health of the workers in the flotation workshop.

At present, there are many different types of gas sensors such as semiconductor type, catalytic combustion type, photochemical type, electrochemical type, etc. on the market, and the types of detected gases have covered most of the common gases. However, no high-performance gas sensor has been developed that can effectively detect xanthate gas.

SUMMARY OF THE INVENTION

Aiming at the lack of effective xanthate gas detection methods in the flotation workshop of the current mineral processing plant, the present invention provides a xanthate gas gas sensing element based on Au-doped In ₂ O ₃ nanospheres and a preparation method thereof. The purpose is to control the synthesis of Au-doped In ₂ O ₃ nanospheres with good dispersion and large specific surface area by optimizing the preparation process parameters, and use this as a gas-sensing material to prepare a gas sensor capable of real-time detection of xanthate gas. Therefore, the flotation workshop can effectively prevent the occurrence of accidents in which the health of workshop workers is endangered due to the high concentration of xanthate gas in the flotation workshop.

The present invention provides a xanthate gas sensor based on Au _- doped _{In 2 O 3} nanospheres. The Au-doped In ₂ O ₃ nano-spheres have a hexagonal crystal structure, a diameter of 75-125 nm, a rough and porous surface, a uniform morphology and good dispersibility.

Further, in the above technical solution, the electrode element is a ceramic electrode.

Further, in the above technical solution, the shape of the electrode element is a tubular electrode or a planar electrode.

Further, in the above technical solution, the Au-doped In ₂ O ₃ nanospheres are prepared according to the following method:

①Add indium nitrate, citric acid monohydrate, and urea to a mixed solution of deionized water and ethylene glycol in a molar ratio of 1:2:1.5. The volume ratio of deionized water and ethylene glycol is 1:1, stir at room temperature until completely dissolved;

② During the stirring process, slowly add a certain amount of chloroauric acid solution with a molar ratio of 1:100 to 5:100 to indium nitrate into the solution obtained in step ①;

3. transfer the solution obtained in step 2. to the hydrothermal reactor, and then place it in an oven to react for 6-24 h under the conditions of 120-180 °C;

④ After the reaction is completed, after the hydrothermal reaction kettle is cooled to room temperature, the product obtained by the reaction is washed and dried, and then heat-treated in a tube furnace at 200-400 ° C for 2-5 hours to obtain Au-doped In ₂ O ₃ nanospheres.

Further, in the above technical solution, the washing and drying process in step 4 is to wash the precipitated product with deionized water and absolute ethanol at least twice, respectively, and then place the precipitated product in a drying oven at 30 to 80 ° C for 12 to 48 hours.

The present invention also provides a method for preparing a xanthate gas sensor based on Au-doped In ₂ O ₃ nanospheres, comprising the following steps:

①Add indium nitrate, citric acid monohydrate, and urea to a mixed solution of deionized water and ethylene glycol in a molar ratio of 1:2:1.5. The volume ratio of deionized water and ethylene glycol is 1:1, and stirred at room temperature until completely dissolved; during the stirring process, a certain amount of chloroauric acid solution with a molar ratio of 1:100 to 5:100 to indium nitrate was slowly added to the above solution; the above obtained The solution was transferred to the hydrothermal reactor, and then placed in an oven to react at 120-180 °C for 6-24 h; after the reaction, after the hydrothermal reactor was cooled to room temperature, the product obtained by the reaction was washed and dried Then, heat treatment in a tube furnace at 200-400° C. for 2-5 hours to obtain Au-doped In ₂ O ₃ nanospheres;

② Disperse the Au-doped In ₂ O ₃ nanospheres obtained in step 1 into anhydrous ethanol, and after wet grinding for 10 minutes, make a paste-like slurry to obtain a gas-sensing slurry;

③ Evenly coat the gas-sensing slurry obtained in step ② on the surface of the electrode element;

④ Connect the electrode element coated with Au-doped In ₂ O ₃ nanospheres in step ③ on the hexagonal base, then install it on the gas sensor aging table, and age it at 300 ° C for 12 to 24 hours, that is, Au based Xanthate gas sensor doped with In ₂ O ₃ nanospheres.

Further, in the above technical solution, the washing and drying process in step ① is to wash the precipitated product with deionized water and absolute ethanol at least twice, respectively, and then place the precipitated product in a drying oven at 30 to 80 ° C for 12 to 48 hours.

Further, in the above-mentioned technical scheme, the concrete operation of wet grinding in the step 2. is: placing the Au-doped In ₂ O ₃ nanospheres dispersed in ethanol in an agate mortar, and under a fluid environment with ethanol , grind into a paste slurry.

Further, in the above technical scheme, the slurry coating method in step 3 is to dip the Au-doped In ₂ O ₃ nano-sphere slurry with a hook pen, and then evenly coat it on the electrode elements, so that the electrode elements The surface is completely covered and uniform in thickness.

Compared with the prior art, the characteristics and beneficial effects of the present invention are:

The invention provides a synthesis method of Au-doped In ₂ O ₃ nanospheres and a gas sensing element for detecting xanthate gas based on the material. First of all, there is currently a lack of high-performance gas sensors on the market that can effectively detect xanthate gas, so this gas sensor can fill this gap. The gas sensor has high sensitivity, good stability, selectivity and repeatability. Meanwhile, the gas-sensing material used in the gas-sensing element of the present invention has the characteristics of simple synthesis method, low cost, stable structure and the like.

Description of drawings

Fig. 1 is the X-ray diffraction pattern of Au-doped In ₂ O ₃ nanospheres prepared by the present invention;

Fig. 2 is (a) low magnification and (b) high magnification scanning electron microscope photographs of Au-doped In ₂ O ₃ nanospheres prepared by the present invention;

3 is a schematic diagram of the structure of the ceramic electrodes in Examples 1 to 4; wherein, 1: ceramic tube; 2: gas-sensitive coating; 3: heating resistance wire; 4: gold film; 5: platinum lead wire; 6: hexagonal base ;

4 is a graph showing the relationship between the sensitivity of the gas sensor prepared by the present invention to 20ppm xanthate gas and the working temperature;

Fig. 5 is the dynamic response curve of the gas sensor prepared by the present invention to different concentrations of xanthate gas when the working temperature is 300°C;

FIG. 6 is a graph showing the sensitivity of the gas sensor prepared by the present invention to different detected gases when the working temperature is 300°C;

Fig. 7 is the repeatability curve of 50ppm xanthate gas for 6 cycles of the gas sensor prepared by the present invention when the working temperature is 300°C.

Detailed ways

The following non-limiting examples may enable those of ordinary skill in the art to more fully understand the present invention, but do not limit the present invention in any way.

The test methods described in the following examples are conventional methods unless otherwise specified; the reagents, materials and equipment can be obtained from commercial sources unless otherwise specified.

The gas-sensing test system described in the following examples is Weisheng Technology WS-30A gas-sensing test system; the aging table is Weisheng Technology TS-60 aging table.

Example 1

The xanthate gas sensor based on Au-doped In ₂ O ₃ nanospheres described in this embodiment has a schematic structural diagram as shown in FIG. 3 , including a ceramic tube 1 , a gas sensing coating 2 , a heating resistance wire 3 , a gold Membrane 4, platinum lead 5 and hexagonal base 6, wherein the gold membrane 4 covers both ends of the ceramic tube 1 to make ceramic tube electrodes, and the gas-sensitive coating 2 is evenly coated on the entire surface of the ceramic tube 1 and the gold membrane 4, The heating resistance wire 3 traverses the ceramic tube 1 and is welded to the heating electrode of the hexagonal base 6; one end of the platinum lead wire 4 is welded to the surface of the gold film 4, and the other end is welded to the four measuring electrodes of the hexagonal base 6. Xanthate gas sensor based on Au-doped In ₂ O ₃ nanospheres. The raw material of the gas sensitive coating 2 is Au-doped In ₂ O ₃ nanospheres, the Au-doped In ₂ O ₃ nanospheres have uniform appearance and good dispersibility, and have a diameter of 75-125 nm. The preparation process of the Au-doped In ₂ O ₃ nanospheres is carried out according to the following steps:

①Add 1 mmol of indium nitrate, 2 mmol of citric acid monohydrate, and 1.5 mmol of urea to a mixed solution of 15 ml of deionized water and 15 ml of ethylene glycol in sequence, and stir at room temperature until completely dissolved.

② Slowly add 3 ml of chloroauric acid solution (4.256 g/L) to the solution obtained in step ① while stirring.

③ Transfer the solution obtained in step ② to a polytetrafluoroethylene hydrothermal reactor, and then place it in an oven to react at 160° C. for 12 hours.

④ After the reaction is completed, after the hydrothermal reactor is naturally cooled to room temperature, the product obtained by the reaction is washed with deionized water and ethanol at least twice to remove the impurity ions therein.

⑤ The cleaned product was dried in a vacuum drying oven at 30°C for 12 hours, and then heat-treated in a tube furnace at 400°C for 4 hours to obtain Au-doped In ₂ O ₃ nanospheres.

Figure 1 is the XRD pattern of the as-prepared Au-doped In ₂ O ₃ nanospheres. It can be seen from the figure that the prepared Au-doped In ₂ O ₃ nanospheres are composed of cubic phase elemental Au and hexagonal phase In ₂ O ₃ and have good crystallinity. FIG. 2 is a scanning electron microscope photograph of the prepared Au-doped In ₂ O ₃ nanospheres. It can be seen that the obtained product is spherical with a diameter of 75-125 nm, the surface is relatively rough and porous, and is composed of In ₂ O ₃ nanoparticles with good dispersibility.

A preparation method of a xanthate gas gas sensor based on Au-doped In ₂ O ₃ nanospheres, which is carried out according to the following steps:

① Disperse 0.01 g of the above Au-doped In ₂ O ₃ nanospheres into 10 mL of anhydrous ethanol, grind in an agate mortar for 10 minutes in a fluid environment with ethanol, and then adjust to a paste-like slurry to obtain a gas-sensing slurry .

② The above-mentioned gas _- sensing slurry is evenly coated _on the surface of the ceramic tube electrode to prepare a gas-sensitive coating. It is coated on the electrode element so that the surface of the electrode element is completely covered and the thickness is uniform.

③ Weld the electrodes prepared above to the hexagonal base, and then age them on the gas sensor aging table at 300°C for 24 hours to obtain a xanthate gas sensor based on Au-doped In ₂ O ₃ nanospheres .

4 is a graph showing the relationship between the sensitivity of the gas sensor prepared by the present invention to 20 ppm xanthate gas and the working temperature. It can be seen that the sensitivity of the gas sensor to xanthate gas of the same concentration increases with the increase of the working temperature. The trend of decreasing after increasing, and the maximum sensitivity to xanthate gas was obtained at the working temperature of 300 °C. Figure 5 shows the sensitivity of the gas sensor to different concentrations of xanthate gas when the working temperature is 300°C. It can be seen that the sensitivity of the gas sensor increases with the increase of the concentration of xanthate gas. At the same time, the gas sensor also exhibits excellent reversibility, repeatability and stability. Figure 6 shows the sensitivity of the gas sensor to different gases at an operating temperature of 300°C. It can be seen that the sensitivity of the gas sensor to xanthate gas is much higher than the sensitivity to other common interfering gases, indicating that the gas sensor has good selectivity for xanthate gas and can be used for xanthate gas detection. specific identification. Figure 7 is the repeatability curve of the gas sensor for 6 cycles of 50ppm xanthate gas when the working temperature is 300°C. It can be seen that the gas sensor has almost the same response and recovery characteristics in 6 consecutive test cycles, and the fluctuation is small. At the same time, after 6 consecutive tests, its resistance can still quickly recover to the initial value, indicating its excellent stability.

Example 2

The xanthate gas sensor based on Au-doped In ₂ O ₃ nanospheres described in this embodiment has a schematic structural diagram as shown in FIG. 3 , including a ceramic tube 1 , a gas sensing coating 2 , a heating resistance wire 3 , a gold Film 4, platinum lead 5 and hexagonal base 6, wherein gold film 4 covers both ends of ceramic tube 1 to form ceramic tube electrodes, gas-sensitive coating 2 is evenly coated on the entire surface of ceramic tube 1 and gold film 4, heating The resistance wire 3 traverses the ceramic tube 1 and is welded on the heating electrode of the hexagonal base 6; one end of the platinum lead 4 is welded on the surface of the gold film 4, and the other end is welded on the four measuring electrodes of the hexagonal base 6. Xanthate gas sensor based on Au- _{doped In2O3} nanospheres. The raw material of the gas sensitive coating 2 is Au-doped In ₂ O ₃ nanospheres, the Au-doped In ₂ O ₃ nanospheres have uniform appearance and good dispersibility, and have a diameter of 75-125 nm. The preparation process of the Au-doped In ₂ O ₃ nanospheres is carried out according to the following steps:

①Add 1 mmol of indium nitrate, 2 mmol of citric acid monohydrate, and 1.5 mmol of urea to a mixed solution of 15 ml of deionized water and 15 ml of ethylene glycol in sequence, and stir at room temperature until completely dissolved.

② Slowly add 3 ml of chloroauric acid solution (4.256 g/L) to the solution obtained in step ① while stirring.

③ Transfer the solution obtained in step ② to a polytetrafluoroethylene hydrothermal reactor, and then place it in an oven to react at 160° C. for 8 hours.

④ After the reaction, after the hydrothermal reactor is naturally cooled to room temperature, the product obtained by the reaction is washed at least twice with deionized water and ethanol to remove the impurity ions therein.

⑤ The cleaned product was dried in a vacuum drying oven at 40°C for 15h, and then heat-treated in a tube furnace at 400°C for 4h to obtain Au-doped In ₂ O ₃ nanospheres.

The obtained Au-doped In ₂ O ₃ nanospheres have a hexagonal crystal structure and good crystallinity. The diameter of the nanosphere is 75-125nm, the surface is relatively rough and porous, it is composed of In ₂ O ₃ nanoparticles, and the dispersibility is good.

A preparation method of a xanthate gas gas sensor based on Au-doped In ₂ O ₃ nanospheres, which is carried out according to the following steps:

① Disperse 0.01 g of the above Au-doped In ₂ O ₃ nanospheres in 10 mL of anhydrous ethanol, grind in an agate mortar for 10 minutes in a fluid environment with ethanol, and then adjust to a paste-like slurry to obtain a gas-sensing slurry .

② The above-mentioned gas-sensitive slurry is uniformly coated on the surface of the electrode element to prepare a gas-sensitive coating. The coating method is to dip the Au-doped In ₂ O ₃ nano-sphere slurry with a hook pen, and then evenly apply Cover the electrode element so that the surface of the electrode element is completely covered and the thickness is uniform.

③ Weld the electrodes prepared above to the hexagonal base, and age them on the gas sensor aging table at 300° C. for 24 hours to obtain a xanthate gas sensor based on Au-doped In ₂ O ₃ nanospheres.

After testing, the gas-sensing element prepared in this example has good gas-sensing properties for xanthate gas under the condition of working temperature of 200-325°C.

Example 3

The xanthate gas sensor based on Au-doped In ₂ O ₃ nanospheres described in this embodiment has a schematic structural diagram as shown in FIG. 3 , including a ceramic tube 1 , a gas sensing coating 2 , a heating resistance wire 3 , a gold Film 4, platinum lead 5 and hexagonal base 6, wherein gold film 4 covers both ends of ceramic tube 1 to form ceramic tube electrodes, gas-sensitive coating 2 is evenly coated on the entire surface of ceramic tube 1 and gold film 4, heating The resistance wire 3 traverses the ceramic tube 1 and is welded on the heating electrode of the hexagonal base 6; one end of the platinum lead 4 is welded on the surface of the gold film 4, and the other end is welded on the four measuring electrodes of the hexagonal base 6. Xanthate gas sensor based on Au- _{doped In2O3} nanospheres. The raw material of the gas sensitive coating 2 is Au-doped In ₂ O ₃ nanospheres, the Au-doped In ₂ O ₃ nanospheres have uniform appearance and good dispersibility, and have a diameter of 75-125 nm. The preparation process of the Au-doped In ₂ O ₃ nanospheres is carried out according to the following steps:

①Add 1 mmol of indium nitrate, 2 mmol of citric acid monohydrate, and 1.5 mmol of urea to a mixed solution of 15 ml of deionized water and 15 ml of ethylene glycol in sequence, and stir at room temperature until completely dissolved.

② Slowly add 3 ml of chloroauric acid solution (4.256 g/L) to the solution obtained in step ① while stirring.

③ Transfer the solution obtained in step ② to a polytetrafluoroethylene hydrothermal reactor, and then place it in an oven to react at 180° C. for 8 hours.

④ After the reaction, after the hydrothermal reactor is naturally cooled to room temperature, the product obtained by the reaction is washed at least twice with deionized water and ethanol to remove the impurity ions therein.

⑤ The cleaned product was dried in a vacuum drying oven at 30°C for 12 hours, and then heat-treated in a tube furnace at 400°C for 4 hours to obtain Au-doped In ₂ O ₃ nanospheres.

The obtained Au-doped In ₂ O ₃ nanospheres have a hexagonal crystal structure and good crystallinity. The diameter of the nanosphere is 75-125nm, the surface is relatively rough and porous, and it is composed of In ₂ O ₃ nanoparticles with good dispersibility.

A preparation method of a xanthate gas gas sensor based on Au-doped In ₂ O ₃ nanospheres, which is carried out according to the following steps:

① Disperse 0.01 g of the above Au-doped In ₂ O ₃ nanospheres in 10 mL of anhydrous ethanol, grind in an agate mortar for 10 minutes in a fluid environment with ethanol, and then adjust to a paste-like slurry to obtain a gas-sensing slurry .

② The above-mentioned gas-sensitive slurry is uniformly coated on the surface of the electrode element to prepare a gas-sensitive coating. The coating method is to dip the Au-doped In ₂ O ₃ nano-sphere slurry with a hook pen, and then evenly apply Cover the electrode element so that the surface of the electrode element is completely covered and the thickness is uniform.

③ Weld the electrode prepared above to the hexagonal base, and age it on the gas sensor aging table at 300°C for 12-24 hours, to obtain a xanthate gas gas sensor based on Au-doped In ₂ O ₃ nanospheres element.

After testing, the gas-sensing element prepared in this example has good gas-sensing properties for xanthate gas under the condition of working temperature of 200-325°C.

Example 4

The xanthate gas sensor based on Au-doped In ₂ O ₃ nanospheres described in this embodiment has a schematic structural diagram as shown in FIG. 3 , including a ceramic tube 1 , a gas sensing coating 2 , a heating resistance wire 3 , a gold Film 4, platinum lead 5 and hexagonal base 6, wherein gold film 4 covers both ends of ceramic tube 1 to form ceramic tube electrodes, gas-sensitive coating 2 is evenly coated on the entire surface of ceramic tube 1 and gold film 4, heating The resistance wire 3 traverses the ceramic tube 1 and is welded on the heating electrode of the hexagonal base 6; one end of the platinum lead 4 is welded on the surface of the gold film 4, and the other end is welded on the four measuring electrodes of the hexagonal base 6. Xanthate gas sensor based on Au- _{doped In2O3} nanospheres. The raw material of the gas sensitive coating 2 is Au-doped In ₂ O ₃ nanospheres, the Au-doped In ₂ O ₃ nanospheres have uniform appearance and good dispersibility, and have a diameter of 75-125 nm. The preparation process of the Au-doped In ₂ O ₃ nanospheres is carried out according to the following steps:

①Add 1 mmol of indium nitrate, 2 mmol of citric acid monohydrate, and 1.5 mmol of urea to a mixed solution of 15 ml of deionized water and 15 ml of ethylene glycol in sequence, and stir at room temperature until completely dissolved.

② Slowly add 3 ml of chloroauric acid solution (4.256 g/L) to the solution obtained in step ① while stirring.

③ Transfer the solution obtained in step ② to a polytetrafluoroethylene hydrothermal reactor, and then place it in an oven at 160° C. for 12 hours.

④ After the reaction, after the hydrothermal reactor is naturally cooled to room temperature, the product obtained by the reaction is washed at least twice with deionized water and ethanol to remove the impurity ions therein.

⑤ The cleaned product was dried in a vacuum drying oven at 30°C for 12 hours, and then heat-treated in a tube furnace at 300°C for 4 hours to obtain Au-doped In ₂ O ₃ nanospheres.

The obtained Au-doped In ₂ O ₃ nanospheres have a hexagonal crystal structure and good crystallinity. The diameter of the nanosphere is 75-125nm, the surface is relatively rough and porous, and it is composed of In ₂ O ₃ nanoparticles with good dispersibility.

A preparation method of a xanthate gas gas sensor based on Au-doped In ₂ O ₃ nanospheres, which is carried out according to the following steps:

① Disperse 0.01 g of the above Au-doped In ₂ O ₃ nanospheres into 10 mL of anhydrous ethanol, grind in an agate mortar for 10 minutes in a fluid environment with ethanol, and then adjust to a paste-like slurry to obtain a gas-sensing slurry .

② The above-mentioned gas-sensitive slurry is uniformly coated on the surface of the electrode element to prepare a gas-sensitive coating. The coating method is to dip the Au-doped In ₂ O ₃ nano-sphere slurry with a hook pen, and then evenly apply Cover the electrode element so that the surface of the electrode element is completely covered and the thickness is uniform.

③ Weld the electrode prepared above to the hexagonal base, and age it on the gas sensor aging table at 300°C for 12-24 hours, to obtain a xanthate gas gas sensor based on Au-doped In ₂ O ₃ nanospheres element.

After testing, the gas-sensing element prepared in this example has good gas-sensing properties for xanthate gas under the condition of working temperature of 200-325°C.

Claims (8)

1. A xanthate gas sensor based on Au-doped In ₂ O ₃ nanospheres, wherein the gas sensor is mainly composed of electrode elements and Au-doped In ₂ O uniformly coated on the electrode elements ₃ nanospheres, the Au-doped In ₂ O ₃ nanospheres have a hexagonal crystal structure, a diameter of 75-125 nm, a rough and porous surface, uniform morphology and good dispersibility; The Au-doped In ₂ O ₃ nanospheres are prepared as follows: ①Add indium nitrate, citric acid monohydrate, and urea to a mixed solution of deionized water and ethylene glycol in a molar ratio of 1:2:1.5. The volume ratio of deionized water and ethylene glycol is 1:1, stir at room temperature until completely dissolved; ② During the stirring process, slowly add a certain amount of chloroauric acid solution to the solution obtained in step ①, wherein the molar ratio of chloroauric acid to indium nitrate is 1:100 to 5:100; ③ Transfer the solution obtained in step ② to a hydrothermal reactor, and then place it in an oven to react at 120-180° C. for 6-24 hours; ④ After the reaction is completed, after the hydrothermal reaction kettle is cooled to room temperature, the product obtained by the reaction is washed and dried, and then heat-treated in a tube furnace at 200-400 ° C for 2-5 hours to obtain Au-doped In ₂ O ₃ nanospheres. 2 . The gas sensor according to claim 1 , wherein the electrode element is a ceramic electrode. 3 . 3 . The gas sensor according to claim 1 , wherein the shape of the electrode element is a tubular electrode or a planar electrode. 4 . 4. gas sensor element according to claim 1, is characterized in that, the washing in described step 4., drying process is to wash the precipitated product with deionized water and dehydrated alcohol respectively at least 2 times and then be placed in a drying box in a drying oven. Dry at 30～80℃ for 12～48h. 5. The preparation method of gas sensor element according to claim 1, is characterized in that, comprises the steps: ①Add indium nitrate, citric acid monohydrate, and urea to a mixed solution of deionized water and ethylene glycol in a molar ratio of 1:2:1.5. The volume ratio of deionized water and ethylene glycol is 1:1, stir at room temperature until completely dissolved; in the stirring process, slowly add chloroauric acid solution with a molar ratio of 1:100 to 5:100 to indium nitrate into the above solution; transfer the obtained solution to The hydrothermal reaction kettle was then placed in an oven to react at 120-180 °C for 6-24 hours; after the reaction was completed, after the hydrothermal reaction kettle was cooled to room temperature, the product obtained by the reaction was washed and dried. Au-doped In ₂ O ₃ nanospheres can be obtained by heat treatment at 200 to 400° C. for 2 to 5 hours in a furnace; ② Disperse the Au-doped In ₂ O ₃ nanospheres obtained in step 1 into anhydrous ethanol, and after wet grinding for 10 minutes, make a paste-like slurry to obtain a gas-sensing slurry; ③ Evenly coat the gas-sensing slurry obtained in step ② on the surface of the electrode element; ④ Connect the electrode element coated with Au-doped In ₂ O ₃ nanospheres in step ③ on the hexagonal base, then install it on the gas sensor aging table, and age it at 300 ° C for 12 to 24 hours, that is, Au based Xanthate gas sensor doped with In ₂ O ₃ nanospheres. 6. preparation method according to claim 5 is characterized in that, washing in described step 1., drying process is to wash precipitated product with deionized water and dehydrated alcohol respectively at least 2 times and then place in drying box at 30 ℃. Dry at ~80℃ for 12~48h. 7. preparation method according to claim 5, is characterized in that, the concrete operation of wet grinding in described step 2. is: the Au _- doped In ₂ O that is dispersed in ethanol is placed in agate mortar , in a fluid environment with ethanol, grinding into a paste-like slurry. 8. preparation method according to claim 5 is characterized in that, in described step 3., the slurry coating method is to dip the Au-doped In ₂ O ₃ nanometer ball slurry with a hook pen, and then evenly coat On the electrode element, the surface of the electrode element is completely covered and the thickness is uniform.

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