CN110606503B - Gold-modified porous tin dioxide micro-nanosheet composite material and preparation method and application thereof - Google Patents
Gold-modified porous tin dioxide micro-nanosheet composite material and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a gold-modified porous stannic oxide micro-nano sheet composite material and a preparation method and application thereof.A nano flaky stannous chloride precursor is obtained by taking stannous chloride dihydrate and sodium hydroxide as raw materials through the steps of stirring, aging, filtering, washing and drying; then roasting the nanometer flaky basic stannous chloride precursor at high temperature to obtain porous flaky SnO2Micro-nano powder; finally, in the form of porous flakes SnO2The preparation method comprises the steps of taking micro-nano powder, chloroauric acid and sodium citrate as raw materials, stirring, heating, separating, washing, drying and the like to obtain Au modified porous SnO2Micro-nano sheet, Au modified porous SnO prepared by the method2The micro-nano sheet powder product is dark red powder, has large specific surface area, high purity and good product quality, and the prepared gas-sensitive sensing element has high sensitivity, and the sensitivity S value of the gas-sensitive sensing element to 100ppm ethanol gas reaches up to 94.2.
Description
Technical Field
The invention belongs to the technical field of nano materials, and particularly relates to a gold-modified porous tin dioxide micro-nano sheet composite material as well as a preparation method and application thereof.
Background
With the continuous development of science and technology, the human society has entered the information age. In the field of information materials, sensors have been developed very rapidly as one of the most direct and effective tools for acquiring information. The gas sensor generally comprises a sensing element and a conversion element, can detect the components and the concentration of gas, and converts related information into an outputable signal, thereby realizing the detection and alarm effects on harmful gas. The gas sensor has important application in the aspects of industrial production control, family life safety, food industry, medical detection, environmental protection, public safety and the like.
Tin dioxide (SnO)2) Is an important wide-band-gap n-type semiconductor material with the forbidden band width Eg3.6eV, it is an important functional material. While nano-scale SnO2The material has special photoelectric characteristics and good performanceThe performance of the catalyst is greatly concerned about the mechanical, catalytic, photosensitive and gas-sensitive performances, and the catalyst has wide application value in the aspects of gas-sensitive components, hydrogen storage materials, transparent photoelectrodes, solar cells and the like. Thus, for SnO2The preparation and property research of nano materials is always a hot topic of the scientific research community at present. At present, researches show that designing and synthesizing an oxide semiconductor with a porous structure and a large specific surface area is an effective way for improving the performance of sensitive materials.
The sensitive response mechanism of tin dioxide to gas belongs to a surface adsorption control type mechanism, namely a tin dioxide sensitive film at the working temperature can adsorb oxygen molecules in clean air (oxidizing atmosphere) and is combined with electrons in the material to be converted into oxygen anions (O)-And O2 -) A potential barrier is formed at the grain boundary of the nanocrystal, and the barrier can block the directional movement of electrons under the action of an electric field, so that the electrons are not easy to pass through the potential barrier, and the conductivity of the sensitive film is reduced; when the sensor is in the atmosphere of the reducing gas to be detected, the molecules of the reducing gas to be detected and the oxygen anions adsorbed on the sensitive film generate catalytic oxidation reaction, so that electrons on the oxygen anions are released and transferred onto the nano-crystal, the grain boundary potential barrier of the nano-crystal is reduced, the conductivity of the sensitive film is increased, and the gas detection is realized by measuring the conductivity change of the sensitive film.
Therefore, the sensitivity and selectivity of the tin dioxide gas sensor to gas response are closely related to the microstructure of the tin dioxide sensitive material and the preparation method thereof. In order to improve the sensitivity, selectivity and response speed of gas sensors, the research work done by researchers in the industry is mainly focused on the following aspects: firstly, the material particles are made to be as fine as possible, and the nano material or the graded nano material is preferably made, so that the specific surface area of the material is increased, and the sensitivity of the sensor is improved; secondly, making the gas-sensitive material into a film so as to increase the contact area with gas and improve the sensitivity of the sensor; and noble metal elements or rare earth elements are doped, so that the sensitivity and the selectivity of the sensor are further improved.
In the prior art, a sol-gel method or a hydrothermal method is mostly adopted to prepare heavy metal doped tin dioxide nano-materials, and although the performances of the gas sensor are improved to a certain extent, the microstructures of tin dioxide cannot be regulated, so that how to regulate the microstructures of tin dioxide, designing and synthesizing a tin dioxide composite material modified by noble metal, and further improving the sensitivity of the sensor still needs to be continuously explored.
Disclosure of Invention
In view of the defects in the prior art, the invention aims to provide a gold-modified porous tin dioxide micro-nanosheet composite material and a preparation method and application thereof. The gas-sensitive property of the tin dioxide is improved by regulating the micro-nano structure of the tin dioxide and carrying out noble metal nano particle modification on the tin dioxide.
The technical scheme adopted by the invention is as follows:
a preparation method of a gold-modified porous tin dioxide micro-nano sheet composite material comprises the following steps:
A. a mixing procedure: heating the stannous chloride solution and the sodium hydroxide solution to a certain temperature, mixing and stirring to obtain a milky white suspension solution; standing the milky white suspension solution at constant temperature, aging and crystallizing to obtain a white precipitate, and filtering, washing and drying the white precipitate to obtain a micro-nano flaky stannous chloride precursor;
B. A calcination procedure: roasting the micro-nano flaky stannous chloride precursor in an air atmosphere, and naturally cooling to room temperature to obtain porous flaky tin dioxide micro-nano powder;
C. a modification procedure: ultrasonically dispersing porous flaky tin dioxide micro-nano powder in a chloroauric acid solution to obtain a gray turbid liquid; and heating the gray turbid liquid to a certain temperature, adding a sodium citrate solution under stirring, continuously stirring for reaction, and filtering, washing and drying to obtain the dark red gold-modified porous tin dioxide micro-nanosheet composite material.
Further, in the step A, the stannous chloride solution is obtained by dissolving stannous chloride dihydrate in a mixed solution of ethylene glycol and water; the volume ratio of the ethylene glycol to the water is 1: 5-25; the concentration of the stannous chloride dihydrate in the mixed solution is 0.1-0.5 mol/L.
In the step A, the concentration of the sodium hydroxide solution is 0.2-3.0 mol/L; the molar ratio of sodium hydroxide to stannous chloride is 1: 1 to 3.
In the step A, the temperature is increased to 30-80 ℃; the mixing and stirring speed is 50-300 r/min, and the stirring time is 3-10 min; the constant-temperature standing and aging time is 8-48 hours, and the temperature is 30-80 ℃.
In the step B, the roasting temperature is 350-800 ℃, and the roasting time is 0.5-6 hours.
In the step C, the concentration of the porous flaky tin dioxide micro-nano powder relative to the chloroauric acid solution is 0.02-0.4M; the molar ratio of the chloroauric acid to the porous flaky tin dioxide micro-nano powder is 1-8: 100, respectively; the molar ratio of the sodium citrate to the chloroauric acid is 4-15: 1.
in the step C, the concentration of the chloroauric acid solution is 0.0002-0.032M; the concentration of the sodium citrate solution is 0.0008-0.48M.
In the step C, the temperature is increased to 70-99 ℃; the rotating speed of the stirring reaction is 50-300 r/min, and the stirring reaction time is 15-60 min.
The invention also provides the gold-modified porous tin dioxide micro-nano sheet composite material prepared by the preparation method.
The invention also provides application of the gold-modified porous tin dioxide micro-nano sheet composite material as a gas sensor, which has high sensitive responsiveness to organic volatile gases such as ethanol, acetone, n-butanol and the like and good stability.
In the preparation method disclosed by the invention, easily prepared micro-nano flaky stannous chloride hydroxide (Sn) 4(OH)6Cl2) The tin dioxide is used as a precursor, the stannous chloride hydroxide is decomposed and oxidized into tin dioxide, water and hydrogen chloride by roasting in the air atmosphere, and the reaction product water and hydrogen chloride gas are easy to volatilize and remove in the roasting process, so that the porous flaky tin dioxide micro-nano powder is directly obtained after high-temperature roasting; will be moreAnd dispersing the porous flaky tin dioxide in a chloroauric acid solution, and adding sodium citrate as a reducing agent at a certain temperature to prepare the gold-modified porous flaky tin dioxide composite material.
The chemical reaction formula involved in the reaction process is represented as follows:
4SnCl2+6NaOH→Sn4(OH)6Cl2↓+6NaCl
Sn4(OH)6Cl2+2O2→4SnO2+2HCl↑+2H2O↑
according to the invention, by controlling the reaction temperature and the raw material dosage, the micro-nano flaky stannous chloride hydroxide powder which belongs to an orthorhombic system and has high crystallinity and good product quality is obtained; the roasting temperature of the porous SnO in the air is controlled to obtain the porous flaky SnO2Micro-nano powder; then, under the conditions of controlling the dosage of chloroauric acid and sodium citrate and controlling the reaction temperature, obtaining dark red Au modified porous SnO2The specific surface area of the micron sheet powder is large (35-85 m)2The purity is high, the product quality is good, and the product has high sensitive response to organic volatile gas in the air.
The gold-modified porous tin dioxide micro-nano sheet composite material prepared by the invention is beneficial to developing the unique performance and application of a tin dioxide material and is also beneficial to the development and application of other new nano-structure devices. Compared with the prior art, the invention has the advantages of simple process and low cost, and the prepared resistance type gas sensor has high sensitivity. Compared with the prior art, the invention has the following outstanding advantages:
1. The prepared Au modified porous SnO2The micro-nano sheet has high purity, does not contain other appearances, and has uniform pore size distribution;
2. the prepared Au modified porous SnO2The micro nano sheet has large specific surface area (35-85 m)2/g)；
3. The prepared Au modified porous SnO2The micro-nano sheet has stable performance, stable structure in air and stable performance;
4. the production process is simple, the requirement on equipment is low, the conditions of microwaves, reaction kettles and the like are not needed, the raw materials are easy to obtain, the cost is low, and the batch production can be carried out.
Drawings
FIG. 1 is an SEM image of Au modified porous tin dioxide micro-nanosheets prepared in example 1;
FIG. 2 is an SEM image of Au modified porous tin dioxide micro-nano sheets prepared in example 2;
fig. 3 is an SEM image of stannous oxychloride microsheets prepared in example 3;
fig. 4 is an SEM image of porous tin dioxide micro-nanosheets prepared in example 3;
figure 5 is a TEM image of porous tin dioxide nanosheets prepared in example 3;
FIG. 6 is an XRD pattern of porous tin dioxide micro-nanosheets and Au-modified porous tin dioxide micro-nanosheets prepared in example 3;
FIG. 7 is an SEM image of Au modified porous tin dioxide micro-nanosheets prepared in example 3;
FIG. 8 is an EDS diagram of Au-modified porous tin dioxide nanosheets prepared in example 3;
FIG. 9 is a BET diagram of Au modified porous tin dioxide micro-nanosheets prepared in example 3;
fig. 10 is an SEM image of Au modified porous tin dioxide micro-nanosheets prepared in example 4;
fig. 11 is an SEM image of Au modified porous tin dioxide micro-nanosheets prepared in example 5;
fig. 12 shows the response sensitivity of the Au modified porous tin dioxide nanosheet prepared in example 3 to 100ppm of gases such as ethanol, acetone, n-butanol and isopropanol at the working temperature of 280 ℃.
Detailed Description
The present invention will be described in detail with reference to examples.
Example 1
A preparation method of a gold-modified porous tin dioxide micro-nano sheet composite material comprises the following steps:
A. dissolving stannous chloride dihydrate in a volume ratio of 1: 5, preparing 20 ml of 0.1M stannous chloride solution in a mixed solution of ethylene glycol and water;
dissolving sodium hydroxide in water to prepare 10 ml of 0.2M sodium hydroxide solution;
heating the two solutions to 30 ℃, adding the sodium hydroxide solution into a stannous chloride solution under magnetic stirring at a rotation speed of 50 revolutions per minute, then continuously stirring for 3 minutes at 30 ℃ to obtain a mixed suspension, standing and aging for 48 hours at 30 ℃ to obtain a white precipitate, filtering and washing the white precipitate, and drying for 24 hours at 40 ℃ to obtain an alkali stannous chloride micro-nanosheet;
B. Roasting the stannous chloride hydroxide nanosheets at 800 ℃ for 0.5 hour, and cooling to obtain gray porous flaky stannic oxide micro-nano powder;
C. ultrasonically dispersing 0.0002mol of porous flaky tin dioxide micro-nano powder in 10 ml of 0.0002M chloroauric acid solution to obtain gray turbid liquid; dissolving sodium citrate in water to prepare 10 ml of 0.0008M sodium citrate solution; and (2) adding the sodium citrate solution into the gray suspension under magnetic stirring at the rotation speed of 50 revolutions per minute at 70 ℃, then continuously stirring and reacting for 60 minutes at 70 ℃ to obtain a dark red precipitate, filtering and washing the precipitate, and drying at 40 ℃ for 24 hours to obtain the gold-modified porous tin dioxide micro-nanosheet composite material, wherein an SEM picture of the composite material is shown in figure 1.
Example 2
A preparation method of a gold-modified porous tin dioxide micro-nano sheet composite material comprises the following steps:
A. dissolving stannous chloride dihydrate in a volume ratio of 1: 10, preparing 20 ml of 0.2M stannous chloride solution in a mixed solution of ethylene glycol and water;
dissolving sodium hydroxide in water to prepare 10 ml of 0.5M sodium hydroxide solution;
heating the two solutions to 45 ℃, adding the sodium hydroxide solution into a stannous chloride solution under magnetic stirring at the rotating speed of 80 revolutions per minute, then continuously stirring for 8 minutes at 45 ℃ to obtain a mixed suspension, and standing and aging for 45 hours at 45 ℃ to obtain a white precipitate; filtering and washing the white precipitate, and drying at 50 ℃ for 20 hours to obtain an alkali stannous chloride nanosheet;
B. Roasting the stannous chloride hydroxide micro-nanosheets at 700 ℃ for 0.5 hour, and cooling to obtain gray porous flaky tin dioxide micro-nano powder;
C. ultrasonically dispersing 0.001mol of porous flaky tin dioxide micro-nano powder in 10 ml of 0.0015M chloroauric acid solution to obtain gray suspension; dissolving sodium citrate in water to prepare 10 ml of 0.009M sodium citrate solution; and (2) adding the sodium citrate solution into the gray turbid liquid under magnetic stirring at the rotation speed of 100 revolutions per minute at 75 ℃, then continuously stirring and reacting for 60 minutes at 75 ℃ to obtain a dark red precipitate, filtering and washing the precipitate, and drying for 24 hours at 60 ℃ to obtain the gold-modified porous tin dioxide micro-nanosheet composite material, wherein the SEM picture of the gold-modified porous tin dioxide micro-nanosheet composite material is shown in figure 2.
Example 3
A preparation method of a gold-modified porous tin dioxide micro-nano sheet composite material comprises the following steps:
A. dissolving stannous chloride dihydrate in a volume ratio of 1: 15, preparing 20 ml of 0.3M stannous chloride solution;
dissolving sodium hydroxide in water to prepare 10 ml of 1.2M sodium hydroxide solution;
heating the two solutions to 55 ℃, adding the sodium hydroxide solution into a stannous chloride solution under magnetic stirring at the rotating speed of 120 revolutions per minute, then continuously stirring for 10 minutes at 55 ℃ to obtain a mixed suspension, and standing and aging for 48 hours at 55 ℃ to obtain a white precipitate; filtering and washing the white precipitate, and drying at 60 ℃ for 18 hours to obtain stannous oxychloride micro-nanosheets, wherein an SEM image of the stannous oxychloride micro-nanosheets is shown in figure 3, and the stannous oxychloride micro-nanosheets are micro-nano tablets with smooth surfaces;
B. Roasting the stannous chloride hydroxide micro-nanosheets at 600 ℃ for 1 hour, and cooling to obtain gray porous flaky stannic oxide micro-nano powder, wherein an SEM image of the powder is shown in figure 4, and the powder can be seen to be in a flaky structure; the TEM image is shown in FIG. 5, which shows the porous microstructure; the XRD pattern is shown in figure 6, and the diffraction pattern proves that the prepared porous micro nano-sheet is square rutile structure tin dioxide.
C. Ultrasonically dispersing 0.002mol of porous flaky tin dioxide micro-nano powder in 10 ml of 0.008M chloroauric acid solution to obtain a gray turbid liquid; dissolving sodium citrate in water to prepare 10 ml of 0.08M sodium citrate solution; adding the sodium citrate solution into the gray suspension under magnetic stirring at the rotation speed of 150 revolutions per minute at 80 ℃, then continuing stirring and reacting for 50 minutes at 80 ℃ to obtain a dark red precipitate, filtering and washing the precipitate, and drying at 70 ℃ for 20 hours to obtain a gold-modified porous tin dioxide micro-nanosheet composite material, wherein an SEM picture of the composite material is shown in figure 7, and the composite material can be seen to be in a sheet structure; the EDS diagram is shown in FIG. 8, which can obtain the composition of Au, Sn and O, wherein the Si peak is from the silicon chip substrate when preparing SEM sample; the BET diagram is shown in FIG. 9, and the specific surface area is 45.2m 3(iv)/g, average pore size 9.5nm, indicating that it is a porous material; the XRD pattern is shown in FIG. 6, and the resulting diffraction pattern matches the peaks listed in standard card JCPDS no 411445, indicating that the composite material prepared contains tin dioxide. Because the content of the gold nanoparticles is less, XRD diffraction peaks of the gold nanoparticles are absent.
Example 4
A preparation method of a gold-modified porous tin dioxide micro-nano sheet composite material comprises the following steps:
A. dissolving stannous chloride dihydrate in a volume ratio of 1: 20 ml of 0.4M stannous chloride solution is prepared in the mixed solution of 20 percent of glycol and water;
dissolving sodium hydroxide in water to prepare 10 ml of 2.1M sodium hydroxide solution;
heating the two solutions to 65 ℃, adding the sodium hydroxide solution into a stannous chloride solution under magnetic stirring at the rotating speed of 200 revolutions per minute, then continuously stirring for 5 minutes at 65 ℃ to obtain a mixed suspension, and standing and aging for 12 hours at 65 ℃ to obtain a white precipitate; filtering and washing the white precipitate, and drying at 70 ℃ for 10 hours to obtain an alkali stannous chloride nanosheet;
B. roasting the stannous chloride hydroxide nanosheets for 4 hours at 500 ℃, and cooling to obtain gray porous flaky stannic oxide micro-nano powder;
C. Ultrasonically dispersing 0.003mol of porous flaky tin dioxide micro-nano powder in 10 ml of 0.018M chloroauric acid solution to obtain gray turbid liquid; dissolving sodium citrate in water to prepare 10 ml of 0.215M sodium citrate solution; and (2) adding the sodium citrate solution into the gray turbid liquid under magnetic stirring at the rotation speed of 200 revolutions per minute at 90 ℃, then continuously stirring and reacting for 30 minutes at 90 ℃ to obtain a dark red precipitate, filtering and washing the precipitate, and drying for 12 hours at 80 ℃ to obtain the gold-modified porous tin dioxide micro-nanosheet composite material, wherein an SEM picture of the composite material is shown in FIG. 10.
Example 5
A preparation method of a gold-modified porous tin dioxide micro-nano sheet composite material comprises the following steps:
A. dissolving stannous chloride dihydrate in a volume ratio of 1: 25 of mixed solution of ethylene glycol and water to prepare 20 ml of 0.5M stannous chloride solution;
dissolving sodium hydroxide in water to prepare 10 ml of 3.0M sodium hydroxide solution;
heating the two solutions to 80 ℃, adding the sodium hydroxide solution into a stannous chloride solution under magnetic stirring at the rotating speed of 300 revolutions per minute, then continuously stirring for 6 minutes at 80 ℃ to obtain a mixed suspension, and standing and aging for 8 hours at 80 ℃ to obtain a white precipitate; filtering and washing the white precipitate, and drying at 80 ℃ for 6 hours to obtain an alkali stannous chloride micro-nanosheet;
B. Roasting the stannous chloride hydroxide nanosheets at 350 ℃ for 6 hours, and cooling to obtain gray porous flaky stannic oxide micro-nano powder;
C. ultrasonically dispersing 0.004mol of porous flaky tin dioxide micro-nano powder in 10 ml of 0.032M chloroauric acid solution to obtain gray turbid liquid; dissolving sodium citrate in water to prepare 10 ml of 0.48M sodium citrate solution; and (2) adding the sodium citrate solution into the gray turbid liquid under magnetic stirring at the rotation speed of 300 revolutions per minute at 99 ℃, then continuously stirring and reacting for 15 minutes at 99 ℃ to obtain a dark red precipitate, filtering and washing the precipitate, and drying at 90 ℃ for 6 hours to obtain the gold-modified porous tin dioxide micro-nanosheet composite material, wherein the SEM image of the gold-modified porous tin dioxide micro-nanosheet composite material is shown in fig. 11.
Example 6
Application of gold-modified porous tin dioxide micro-nano sheet composite material in gas sensor
The gold-modified porous tin dioxide nanosheet composite prepared in example 5 was dispersed in absolute ethanol, then uniformly coated on a ceramic tube with an electrode to prepare a gas sensor, dried at 50 ℃ for 2h, and then heat-treated at 200 ℃ for 2 h. A small coil of nickel chromium alloy was then placed in the tube as a heater to provide the operating temperature for the sensor, the sensor was aged at 300 ℃ for 48 hours, and then various volatile organic gases were tested at the operating temperature. The specific test operation steps are as follows: the method comprises the steps of injecting a certain amount of organic steam into a sensor test box by using an injector, waiting for about two minutes, introducing dry air into the test box after a sensor output response value is stable, gradually recovering the sensor output response, and testing and recording the output response value of the sensor in dry air and target gas by using an electrochemical workstation and a computer. The sensitivity of the sensor to gas response is defined as S ═ R a/Rg(reducing gas), RaIs the resistance of the sensor in dry air, RgIs the resistance of the sensor in the test gas. The sensitive response of the sensor to common volatile organic gases is examined.
The performance test research shows that the prepared gold-modified porous flaky tin dioxide micro-nano sheet has good sensitive response to the common toxic and harmful organic gases in the air, as shown in figure 12. As can be seen from the figure, the gold-modified porous flaky tin dioxide micro-nanosheet prepared by the method is more sensitive to 100ppm of toxic and harmful gases such as ethanol, acetone, n-butanol and isopropanol, and the sensitivity is 94.2, 91.0, 86.8 and 93.0 respectively.
The above detailed description of a gold-modified porous tin dioxide nanosheet composite, and methods of making and using the same, with reference to the examples, is illustrative and not limiting, and several examples can be cited within the scope defined, thus changes and modifications that do not depart from the general inventive concept are intended to be within the scope of the present invention.
Claims (10)
1. A preparation method of a gold-modified porous tin dioxide micro-nano sheet composite material is characterized by comprising the following steps:
A. a mixing procedure: heating the stannous chloride solution and the sodium hydroxide solution to 30-80 ℃, and mixing and stirring to obtain a milky white suspension solution; standing and aging the milky white suspension solution at the constant temperature of 30-80 ℃ to obtain a white precipitate, and filtering, washing and drying the white precipitate to obtain a micro-nano flaky stannous chloride hydroxide precursor;
B. A calcination procedure: roasting the micro-nano flaky stannous chloride precursor in an air atmosphere, and naturally cooling to room temperature to obtain porous flaky tin dioxide micro-nano powder;
C. a modification procedure: ultrasonically dispersing porous flaky tin dioxide micro-nano powder in a chloroauric acid solution to obtain a gray turbid liquid; heating the gray turbid liquid to a certain temperature, adding a sodium citrate solution while stirring, continuously stirring for reaction, and filtering, washing and drying to obtain a dark red gold-modified porous tin dioxide nanosheet composite material;
in the step A, the stannous chloride solution is obtained by dissolving stannous chloride dihydrate in a mixed solution of ethylene glycol and water.
2. The method according to claim 1, wherein in step a, the volume ratio of the ethylene glycol to the water is 1: 5-25; the concentration of the stannous chloride dihydrate in the mixed solution is 0.1-0.5 mol/L.
3. The preparation method according to claim 1 or 2, wherein in the step A, the concentration of the sodium hydroxide solution is 0.2-3.0 mol/L; the molar ratio of sodium hydroxide to stannous chloride is 1: 1 to 3.
4. The preparation method according to claim 1 or 2, wherein in the step A, the rotation speed of the mixing and stirring is 50-300 r/min, and the stirring time of the mixing and stirring is 3-10 min; the constant-temperature standing and aging time is 8-48 hours.
5. The preparation method according to claim 1, wherein in the step B, the roasting temperature is 350-800 ℃, and the roasting time is 0.5-6 hours.
6. The preparation method according to claim 1, wherein in the step C, the concentration of the porous flaky tin dioxide micro-nano powder relative to the chloroauric acid solution is 0.02-0.4M; the molar ratio of the chloroauric acid to the porous flaky tin dioxide micro-nano powder is 1-8: 100, respectively; the molar ratio of the sodium citrate to the chloroauric acid is 4-15: 1.
7. the method according to claim 1, wherein in step C, the concentration of the chloroauric acid solution is 0.0002 to 0.032M; the concentration of the sodium citrate solution is 0.0008-0.48M.
8. The preparation method according to claim 1, wherein in the step C, the heating to a certain temperature is heating to 70-99 ℃; the rotating speed of the stirring reaction is 50-300 r/min, and the stirring reaction time is 15-60 min.
9. The gold-modified porous tin dioxide nanosheet composite material prepared by the preparation method of any one of claims 1 to 8.
10. Use of the gold-modified porous tin dioxide nanosheet composite of claim 9 in a gas sensor.
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