阅读说明：本技术 复合材料的制备方法及应用和气体传感器 (Preparation method and application of composite material and gas sensor ) 是由 高健 郭美圆 郜蕾 朱亚峰 韩一帆 詹自立 于 2019-08-30 设计创作，主要内容包括：本发明提供了一种钯/二氧化锡/石墨烯复合材料的制备方法及应用和气体传感器。所述制备方法包括以下步骤：将锡盐溶于去离子水中以形成锡盐溶液,搅拌并调节锡盐溶液的pH值至7～9,以生成白色沉淀,然后洗涤和干燥,得到白色晶体,将白色晶体研磨成粉末,然后焙烧制得二氧化锡纳米颗粒；向石墨烯溶液中加入二氧化锡纳米颗粒,超声分散均匀得到混合液,并经过离心分离、干燥和焙烧得到二氧化锡/石墨烯复合材料；将二氧化锡/石墨烯复合材料加入氯化钯溶液中,超声分散均匀得到混合液,并经过离心分离、干燥和焙烧得到钯/二氧化锡/石墨烯复合材料。本发明制备得到的复合材料具有在较低工作温度条件下对CO气体的高气敏传感性能。(The invention provides a preparation method and application of a palladium/tin dioxide/graphene composite material and a gas sensor. The preparation method comprises the following steps: dissolving tin salt in deionized water to form a tin salt solution, stirring and adjusting the pH value of the tin salt solution to 7-9 to generate white precipitate, then washing and drying to obtain white crystals, grinding the white crystals into powder, and then roasting to obtain tin dioxide nanoparticles; adding tin dioxide nanoparticles into the graphene solution, uniformly dispersing by using ultrasonic waves to obtain a mixed solution, and performing centrifugal separation, drying and roasting to obtain a tin dioxide/graphene composite material; adding the tin dioxide/graphene composite material into a palladium chloride solution, uniformly dispersing by ultrasonic to obtain a mixed solution, and performing centrifugal separation, drying and roasting to obtain the palladium/tin dioxide/graphene composite material. The composite material prepared by the invention has high gas-sensitive sensing performance on CO gas under the condition of lower working temperature.)

1. A preparation method of a palladium/tin dioxide/graphene composite material is characterized by comprising the following steps:

A. Dissolving tin salt in deionized water to form a tin salt solution, stirring and adjusting the pH value of the tin salt solution to 7-9 to generate white precipitate, then washing and drying to obtain white crystals, grinding the white crystals into powder, and then roasting to obtain tin dioxide nanoparticles;

B. Adding the tin dioxide nanoparticles into the graphene solution, uniformly dispersing by using ultrasonic waves to obtain a mixed solution, and performing centrifugal separation, drying and roasting to obtain a tin dioxide/graphene composite material;

C. And adding the tin dioxide/graphene composite material into a palladium chloride solution, uniformly dispersing by ultrasonic to obtain a mixed solution, and performing centrifugal separation, drying and roasting to obtain the palladium/tin dioxide/graphene composite material.

2. The method for preparing the palladium/tin dioxide/graphene composite material according to claim 1, wherein in the step A, the step B and the step C, the roasting temperature is 300-400 ℃.

3. The preparation method of the palladium/tin dioxide/graphene composite material according to claim 1, wherein the tin salt is at least one of tin tetrachloride, stannous sulfate, stannous chloride and tin chloride, and the concentration of the tin salt solution is 0.025-0.25 mol/L.

4. The method for preparing a palladium/tin dioxide/graphene composite material according to claim 1, wherein in the drying step of the step A, the composite material is dried at 40 to 170 ℃ for 5 to 48 hours.

5. The preparation method of the palladium/tin dioxide/graphene composite material according to claim 1, wherein in the step A, the roasting time is 1-6 hours; in the step B and the step C, the roasting time is 0.5-10 hours.

6. The preparation method of the palladium/tin dioxide/graphene composite material according to claim 1, wherein in the step B, graphene is dispersed in low carbon alcohol, and is subjected to ultrasonic treatment until the graphene is uniformly dispersed, so as to prepare the graphene solution;

and C, dispersing palladium chloride in low-carbon alcohol, and performing ultrasonic treatment until the palladium chloride is uniformly dispersed to obtain the palladium chloride solution.

7. The preparation method of the palladium/tin dioxide/graphene composite material according to claim 6, wherein in the step B, the addition amount of the graphene is 0.1-0.35% by mass of the tin dioxide nanoparticles;

In the step C, the mass percentage of palladium in the tin dioxide graphene composite material is 0.5% -2%.

8. The preparation method of the palladium/tin dioxide/graphene composite material according to claim 1, wherein in the preparation step B and the step C, the ultrasonic treatment is performed for 1-10 hours.

9. Use of a palladium/tin dioxide/graphene composite material as a gas sensitive material for detecting CO, the palladium/tin dioxide/graphene composite material being prepared by the preparation method of any one of claims 1 to 8.

10. A gas sensor comprising a gas-sensitive layer formed of a palladium/tin dioxide/graphene composite material produced by the production method according to any one of claims 1 to 8.

Technical Field

the invention relates to a composite material, in particular to a preparation method of a palladium/tin dioxide/graphene composite material, application of the palladium/tin dioxide/graphene composite material as a gas-sensitive material for detecting CO, and a gas sensor using the gas-sensitive material.

Background

With the rapid development of human society, people increasingly demand and rely on energy, and the problem of air pollution is also highlighted. The atmospheric pollutants are various, wherein carbon monoxide (CO) is one of the main pollutants which are most widely distributed, most harmful and most produced in the atmosphere, the binding capacity of the carbon monoxide (CO) and hemoglobin in human blood is 240 times of that of oxygen, once the carbon monoxide enters the blood circulation system of a human body, the carbon monoxide (CO) and the hemoglobin in the blood compete with the oxygen to block the transportation of the hemoglobin in the blood to the oxygen, so that human tissue cells are anoxic, the central nervous system is damaged, and even the life is threatened. Therefore, it is necessary to develop a CO gas sensor with high sensitivity, high selectivity and fast response/recovery to realize efficient monitoring and early warning of CO gas.

The semiconductor gas sensor is a common gas sensor, and is widely applied to places needing real-time gas monitoring because of the advantages of being capable of being miniaturized, real-time monitoring, simple to use, low in price, high in precision and the like; however, the gas-sensitive material of such a gas sensor often has poor gas-sensitive performance under low temperature conditions, and needs to work under heating conditions at a relatively high working temperature, so that it is particularly important to prepare a gas-sensitive material that can still have stable, reliable, fast, accurate, high-sensitivity, and high-selectivity sensing response to a target gas CO at a relatively low working temperature even without heating conditions.

Disclosure of Invention

in view of the deficiencies in the prior art, it is an object of the present invention to address one or more of the problems in the prior art as set forth above. For example, an object of the present invention is to provide a method for preparing a palladium/tin dioxide/graphene composite material having a low-temperature gas-sensitive response to CO gas, and a gas sensor using the gas-sensitive material.

One aspect of the present invention provides a preparation method of a palladium/tin dioxide/graphene composite material, including the following steps: A. dissolving tin salt in deionized water to form a tin salt solution, stirring and adjusting the pH value of the tin salt solution to 7-9 to generate white precipitate, then washing and drying to obtain white crystals, grinding the white crystals into powder, and then roasting to obtain tin dioxide nanoparticles; B. adding tin dioxide nanoparticles into the graphene solution, uniformly dispersing by using ultrasonic waves to obtain a mixed solution, and performing centrifugal separation, drying and roasting to obtain a tin dioxide/graphene composite material; C. adding the tin dioxide/graphene composite material into a palladium chloride solution, uniformly dispersing by ultrasonic to obtain a mixed solution, and performing centrifugal separation, drying and roasting to obtain the palladium/tin dioxide/graphene composite material.

Alternatively, in the step A, the step B and the step C, the roasting temperature may be 300-400 ℃.

Optionally, the tin dioxide nanoparticles have a particle size of no more than 20 nm.

Alternatively, the tin salt may be at least one of tin tetrachloride, stannous sulfate, stannous chloride and tin chloride, and the concentration of the tin salt solution may be 0.025 to 0.25 mol/L. Preferably, the concentration of the tin salt solution can be 0.1-0.125 mol/L.

Alternatively, in step a, a weak base or an organic strong base is added dropwise to adjust the pH. For example, ammonia and tetraethylammonium hydroxide.

Optionally, in the step A, the stirring time can be 1-48 hours. Preferably, the stirring time may be 1 to 6 hours.

Optionally, in the step A, the drying can be carried out for 5 to 48 hours at 40 to 170 ℃. Preferably, the drying is carried out at 80 to 160 ℃ for 10 to 24 hours.

Optionally, in the step A, the roasting time can be 1-6 hours; preferably, the time for the calcination may be 2 to 4 hours. In the step B and the step C, the roasting time is 0.5-10 hours. Preferably, the time for the calcination may be 0.5 to 2.5 hours.

Optionally, in step B, the graphene is dispersed in a low carbon alcohol, and is subjected to ultrasonic treatment until the graphene is uniformly dispersed, so as to obtain a graphene solution.

Optionally, in step C, the palladium chloride is dispersed in a lower alcohol and subjected to ultrasonic treatment until the palladium chloride is uniformly dispersed, to prepare a palladium chloride solution.

Alternatively, the lower alcohol may be at least one of methanol, ethanol, ethylene glycol, propanol, and isopropanol.

Optionally, in the step B, the addition amount of the graphene may be 0.1% to 0.35% by mass of the tin dioxide nanoparticles. Preferably, the addition amount of the graphene can be 0.1 to 0.25 percent of the mass of the tin dioxide nanoparticles by mass percentage.

Optionally, in step C, the mass percentage of palladium in the tin dioxide graphene composite material may be in a range of 0.5% to 2%. Preferably, the mass percentage of palladium in the tin dioxide graphene composite material may be preferably 1% to 1.5%.

Optionally, in the preparation step B and the step C, the time of ultrasonic treatment is 1-10 hours. Preferably, the time of the ultrasonic treatment may be 2 to 3 hours.

Another aspect of the present invention provides use of a palladium/tin dioxide/graphene composite material as a gas sensitive material for detecting CO, the palladium/tin dioxide/graphene composite material being prepared by the preparation method as described above.

Still another aspect of the present invention provides a gas sensor including a gas sensing layer formed of the palladium/tin dioxide/graphene composite material prepared by the preparation method as described above.

Compared with the prior art, the invention has the beneficial effects that: graphene with excellent conductivity and high specific surface is used as a carrier, palladium/tin dioxide nanoparticles are uniformly loaded, the agglomeration degree and particle size of the nanoparticles are effectively reduced, and high gas-sensitive sensing performance on CO gas under the condition of lower working temperature is realized.

Drawings

the above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is an XRD pattern of a palladium/tin dioxide/graphene composite material prepared by the method for preparing a palladium/tin dioxide/graphene composite material according to an exemplary embodiment of the present invention;

Fig. 2 is a TEM image of a palladium/tin dioxide/graphene composite material prepared by the method for preparing a palladium/tin dioxide/graphene composite material according to an exemplary embodiment of the present invention;

Fig. 3 is a response/recovery curve of a palladium/tin dioxide/graphene composite material at 75 ℃ to 100ppm of carbon monoxide gas, which is prepared by the method for preparing the palladium/tin dioxide/graphene composite material according to the exemplary embodiment of the present invention;

Fig. 4 is a continuous dynamic response/recovery curve of the palladium/tin dioxide/graphene composite material prepared by the preparation method of the palladium/tin dioxide/graphene composite material according to the exemplary embodiment of the present invention at 75 ℃ for carbon monoxide gas with different concentrations;

Fig. 5 is a sensitivity curve of the palladium/tin dioxide/graphene composite material prepared by the preparation method of the palladium/tin dioxide/graphene composite material according to the exemplary embodiment of the present invention at 75 ℃ for carbon monoxide gas with different concentrations;

Fig. 6 is a comparison of the sensitivity of the palladium/tin dioxide/graphene composite material prepared by the method for preparing the palladium/tin dioxide/graphene composite material according to the exemplary embodiment of the present invention to 5 different gases (100ppm) at 75 ℃.

Detailed Description

hereinafter, a preparation method and application of the palladium/tin dioxide/graphene composite material and the gas sensor according to the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.

The invention designs and synthesizes the palladium/tin dioxide/graphene composite material with high sensing performance on CO gas by aiming at the defects of low response value, poor sensitivity, higher working temperature and the like of the traditional gas sensor in practical application.

Tin dioxide is an n-type semiconductor material with the forbidden band width of 3.6eV, has high surface activity, a special crystal structure and adsorption characteristics, and a gas sensor made of the tin dioxide as a gas sensitive material has the advantages of long service life, low cost, small volume, simplicity in operation, stable performance and the like. In order to further improve the gas-sensitive sensing performance of the semiconductor gas-sensitive material on CO, researchers improve the gas-sensitive sensing performance of the semiconductor gas-sensitive material by reducing the particle size of tin dioxide on one hand, and introduce noble metal and obtain a corresponding composite material by adopting a doping mode by utilizing the chemical sensitization and electronic sensitization effects of the noble metal on the other hand to improve the sensitivity of the semiconductor gas-sensitive material on reducing gas CO and find that the influence of the environmental humidity on the gas-sensitive performance of the sensing material can be effectively reduced by regulating the particle size and the quantity of the noble metal.

Although the introduction of metal heteroatoms can significantly improve the gas-sensitive performance of the sensing material, the response/recovery speed of the sensing material to the target gas CO needs to be improved. Graphene as a carbon material is essentially a two-dimensional nano material, the surface is uneven, and the surface with atomic-level folds has a high specific surface area and can provide more active sites. In addition, the graphene also has excellent physicochemical properties such as ultrahigh carrier mobility, high thermal conductivity, strength and flexibility; and the novel high-performance metal oxide-graphene composite material can be obtained by introducing the graphene oxide into the preparation of the metal oxide semiconductor gas-sensitive material, and is an effective method for effectively improving the gas-sensitive sensing performance of the semiconductor sensing material.

A preparation method of a palladium/tin dioxide/graphene composite according to an exemplary embodiment of an aspect of the present invention includes the steps of:

A. Preparing tin dioxide nanoparticles: dissolving tin salt in deionized water to form a tin salt solution, stirring and adjusting the pH value of the tin salt solution to 7-9 to generate white precipitate, then washing and drying to obtain white crystals, grinding the white crystals into powder, and then roasting to obtain the tin dioxide nanoparticles.

Wherein, the roasting temperature can be 300-400 ℃. The roasting temperature is selected within the temperature range, so that impurities can be removed, and the prepared material is ensured not to have a serious agglomeration phenomenon.

The roasting time can be 1-6 hours; preferably, the time for the calcination may be 2 to 4 hours. Within this calcination time range, the prepared material has a higher crystallinity. If the time is less than the 1 hour, the prepared material has more impurities and poor crystallinity; above this 6 hours, the resulting material may agglomerate, increasing its particle size.

The tin salt can be at least one of stannic chloride, stannous sulfate, stannous chloride and stannic chloride, and the concentration of the tin salt solution can be 0.025-0.25 mol/L. Preferably, the concentration of the tin salt solution can be 0.1-0.125 mol/L.

And the precipitate can be generated by adjusting the pH value to 7-9, and the generated precipitate can be washed after being stirred, so that alkali is not needed. Preferably, the pH is adjusted to 8. Preferably, the pH can be adjusted by dropwise addition of a weak base or a strong organic base. For example, ammonia and tetraethylammonium hydroxide. The tin dioxide is dropwise added, so that the phenomenon of serious agglomeration of the tin dioxide, which leads to the increase of the particle size, can be avoided.

The stirring time can be 1-48 hours. Preferably, the stirring time may be 1 to 6 hours.

Preferably, the drying time can be 5 to 48 hours at 40 to 170 ℃. More preferably, the drying may be carried out at 80 to 160 ℃ for 10 to 24 hours.

the grain diameter of the prepared stannic oxide nano-particles is not more than 20 nm.

B. Preparing a tin dioxide/graphene composite material: and adding tin dioxide nanoparticles into the graphene solution, uniformly dispersing by using ultrasonic waves to obtain a mixed solution, and performing centrifugal separation, drying and roasting to obtain the tin dioxide/graphene composite material.

The graphene solution can be prepared by dispersing graphene in low-carbon alcohol and performing ultrasonic treatment until the graphene is uniformly dispersed. The lower alcohol may be at least one of methanol, ethanol, ethylene glycol, propanol, and isopropanol.

The addition amount of the graphene can be 0.1-0.35% of the mass of the tin dioxide nanoparticles in percentage by mass. When the addition amount of the graphene is less than 0.1% of the mass of the tin dioxide nanoparticles, the dispersion effect of the graphene on the tin dioxide is limited, and the sensing performance of the composite material is low. When the addition amount of the graphene exceeds 0.25% of the mass of the tin dioxide nanoparticles, the amount of tin dioxide contained in the graphene per unit area is reduced, which leads to a reduction in the number of active sites and a reduction in the sensing performance. Preferably, the addition amount of the graphene can be 0.1 to 0.25 percent of the mass of the tin dioxide nanoparticles by mass percentage.

The time of ultrasonic treatment can be 1-10 hours, so that the solution is fully and uniformly dispersed. Preferably, the time of the ultrasonic treatment may be 2 to 3 hours.

Preferably, the firing is performed under protection of an inert atmosphere (e.g., nitrogen atmosphere) to avoid oxidative decomposition of the graphene. The roasting temperature can be 300-400 ℃. The roasting temperature is selected within the temperature range, so that impurities can be removed, and the prepared material is ensured not to have a serious agglomeration phenomenon. The roasting time can be 0.5-10 hours. In the roasting time range, the prepared material has larger specific surface area and higher dispersion degree. If the time is less than 0.5 hour, the amount of tin dioxide dispersed on the surface of the graphene is small; if the time is more than 10 hours, the tin dioxide is agglomerated on the surface of the graphene, and even the morphology and the structure of the graphene are changed. Preferably, the time for the calcination may be 0.5 to 2.5 hours.

C. Preparing a palladium/tin dioxide/graphene composite material: adding the tin dioxide/graphene composite material into a palladium chloride solution, uniformly dispersing by ultrasonic to obtain a mixed solution, and performing centrifugal separation, drying and roasting to obtain the palladium/tin dioxide/graphene composite material.

The palladium chloride solution can be prepared by dispersing palladium chloride in low-carbon alcohol and performing ultrasonic treatment until the palladium chloride is uniformly dispersed. The lower alcohol may be at least one of methanol, ethanol, ethylene glycol, propanol, and isopropanol.

The mass percentage of palladium in the tin dioxide graphene composite material can be 0.5-2%. If the mass percentage of the palladium and tin dioxide graphene composite material is lower than 0.5%, the effect of improving the gas-sensitive sensing performance is weaker; if the mass percentage of the palladium and tin dioxide graphene composite material exceeds 2%, the palladium chloride is easy to agglomerate. Preferably, the mass percentage of palladium in the tin dioxide graphene composite material may be preferably 1% to 1.5%. The concentration of the palladium chloride solution may be 2.5 mmol/L.

The ultrasonic treatment time can be 1-10 hours, so that the palladium is uniformly dispersed. Preferably, the time of the ultrasonic treatment may be 2 to 3 hours.

Preferably, the firing is performed under protection of an inert atmosphere (e.g., nitrogen atmosphere) to avoid oxidative decomposition of the graphene. The roasting temperature can be 300-400 ℃. The roasting temperature is selected within the temperature range, so that impurities can be removed, and the prepared material is ensured not to have a serious agglomeration phenomenon. The calcination time can be 0.5-10 hours. In the roasting time range, the prepared material has larger specific surface area and higher dispersion degree of the active components. If the time is less than 0.5 hour, the tin dioxide cannot be well dispersed on the surface of the graphene and the palladium species cannot be well dispersed on the surface of the tin dioxide/graphene composite material; if the time is more than 10 hours, the tin dioxide is agglomerated on the surface of the graphene, and even the morphology and the structure of the graphene are changed. Preferably, the roasting time may be 0.5 to 2.5 hours.

according to the invention, graphene with excellent conductivity and high specific surface area is used as a carrier, palladium/tin dioxide nanoparticles are uniformly loaded, the agglomeration degree and particle size of the nanoparticles are effectively reduced, and the high gas-sensitive sensing performance for CO gas under the condition of lower working temperature is realized. Because the graphene has a large specific surface area, the agglomeration of tin dioxide particles can be effectively inhibited, and the size of a tin dioxide metal cluster is obviously reduced, so that the tin dioxide particles can be more uniformly dispersed on the surface of the graphene, and more tin dioxide active sites can be exposed. Meanwhile, the graphene has excellent electrical characteristics, and can accelerate the transfer speed of electrons among noble metal palladium, tin dioxide and target gas molecules, so that the carrier concentration of the composite material prepared by the method is increased, the resistance is reduced, and the gas-sensitive performance of CO is improved.

In another exemplary embodiment of the present invention, the preparation method of the palladium/tin dioxide/graphene composite material of the present invention can also be obtained by the following method:

Step 1: preparing tin dioxide nanoparticles: dissolving tin tetrachloride pentahydrate in deionized water to form a solution, adding ammonia water into the solution in the stirring process, keeping the pH of the solution at 7-9 after adding the ammonia water to generate a white precipitate, continuing stirring for 1-48 hours, centrifugally washing, and drying at 40-170 ℃ for 5-48 hours to obtain a white crystal; grinding the mixture to powder, and roasting the powder for 1 to 6 hours at the temperature of between 300 and 400 ℃ to obtain the tin dioxide.

Step 2: preparing a tin dioxide/graphene composite material: and dispersing graphene in ethanol to prepare a graphene solution by ultrasonic, adding the prepared tin dioxide into the solution, dispersing the solution by ultrasonic to obtain a mixed solution uniformly, drying the mixed solution, and roasting the dried mixed solution in nitrogen at 300-400 ℃ for 0.5-10 hours to obtain the tin dioxide/graphene composite material. Wherein the time of ultrasonic treatment can be 1-10 hours.

step 3: preparing a palladium/tin dioxide/graphene composite material: dispersing palladium chloride in ethanol, performing ultrasonic dispersion to obtain a palladium chloride solution, adding the prepared stannic oxide/graphene composite material into the palladium chloride solution, performing ultrasonic dispersion to obtain a uniform mixed solution, drying, and roasting in nitrogen at 300-400 ℃ for 0.5-10 hours to obtain the palladium/stannic oxide/graphene composite material. Wherein the time of ultrasonic treatment can be 1-10 hours.

According to another exemplary embodiment of the present invention, a palladium/tin dioxide/graphene composite material, which is prepared by the above-described preparation method, is used as a gas sensitive material for detecting CO.

According to still another aspect of the present invention, a gas sensor includes a gas sensing layer formed of a palladium/tin dioxide/graphene composite material prepared by the above preparation method.

The method for preparing the palladium/tin dioxide/graphene composite material according to the present invention will be described in detail with reference to specific examples, however, it should be understood that these examples are only illustrative and are not intended to limit the scope of the present invention.

Example 1

Preparing a tin dioxide nano material: dissolving 0.263g of tin tetrachloride pentahydrate in 30mL of deionized water to form a solution, adding ammonia water into the solution in the stirring process until the pH value of the solution is 7 to generate a white precipitate, continuously stirring for 1 hour, centrifugally washing, and drying at 40 ℃ for 48 hours to obtain a white crystal; grinding the mixture to powder, and roasting the powder for 6 hours at 300 ℃ to prepare the tin dioxide nano particles.

Preparing a tin dioxide/graphene composite material: dispersing 0.2mg of graphene in 50mL of ethanol, performing ultrasonic dispersion to obtain a graphene solution, adding 200mg of prepared tin dioxide into the solution, performing ultrasonic dispersion to obtain a mixed solution, drying, and roasting at 300 ℃ for 10 hours in a nitrogen atmosphere to obtain the tin dioxide/graphene composite material.

Preparing a palladium/tin dioxide/graphene composite material: dispersing 4.5mg of palladium chloride in 25ml of ethanol, performing ultrasonic dispersion on the obtained solution to obtain a palladium chloride solution, adding 175mg of the prepared stannic oxide/graphene composite material into the palladium chloride solution, performing ultrasonic dispersion on the obtained solution for 1 hour to obtain a mixed solution, drying the mixed solution at the temperature of 60 ℃ for 6 hours, and roasting the dried mixed solution at the temperature of 300 ℃ for 10 hours in a nitrogen atmosphere to obtain the palladium/stannic oxide/graphene composite material.

Example 2

preparing a tin dioxide nano material: dissolving 1.95g of tin tetrachloride pentahydrate in 30mL of deionized water to form a solution, adding ammonia water into the solution in the stirring process until the pH value of the solution is 9 to generate a white precipitate, continuously stirring for 2 hours, centrifugally washing, and drying at 170 ℃ for 5 hours to obtain a white crystal; grinding the mixture to powder, and roasting the powder for 1 hour at 400 ℃ to prepare the tin dioxide nano particles.

Preparing a tin dioxide/graphene composite material: dispersing 0.5mg of graphene in 50mL of ethanol, performing ultrasonic dispersion to obtain a graphene solution, adding 200mg of prepared tin dioxide into the solution, performing ultrasonic dispersion to obtain a mixed solution, drying, and roasting at 400 ℃ for 0.5 hour in a nitrogen atmosphere to obtain the tin dioxide/graphene composite material.

preparing a palladium/tin dioxide/graphene composite material: dispersing 4.5mg of palladium chloride in 25ml of ethanol, performing ultrasonic dispersion to obtain a palladium chloride solution, adding 150mg of the prepared stannic oxide/graphene composite material into the palladium chloride solution, performing ultrasonic dispersion to obtain a mixed solution, drying at 80 ℃ for 4 hours, and roasting at 400 ℃ for 0.5 hour in a nitrogen atmosphere to obtain the palladium/stannic oxide/graphene composite material.

Example 3

preparing a tin dioxide nano material: dissolving 1.0518g of tin tetrachloride pentahydrate in 30mL of deionized water to form a solution, adding ammonia water into the solution in the stirring process until the pH value of the solution is 8 to generate a white precipitate, continuously stirring for 4 hours, centrifugally washing, and drying for 12 hours at 80 ℃ to obtain a white crystal; grinding the mixture to powder, and roasting the powder for 2 hours at 350 ℃ to prepare the tin dioxide nano particles.

preparing a tin dioxide/graphene composite material: dispersing 0.4mg of graphene in 50mL of ethanol, performing ultrasonic dispersion to obtain a graphene solution, adding 200mg of prepared tin dioxide into the solution, performing ultrasonic dispersion to obtain a mixed solution, drying, and roasting at 350 ℃ for 2 hours in a nitrogen atmosphere to obtain the tin dioxide/graphene composite material.

Preparing a palladium/tin dioxide/graphene composite material: dispersing 4.5mg of palladium chloride in 25ml of ethanol, performing ultrasonic dispersion to obtain a palladium chloride solution, adding 200mg of the prepared stannic oxide/graphene composite material into the palladium chloride solution, performing ultrasonic dispersion to obtain a mixed solution, drying at 70 ℃ for 10 hours, and roasting at 350 ℃ for 2 hours in a nitrogen atmosphere to obtain the palladium/stannic oxide/graphene composite material.

fig. 1 shows an XRD spectrum of the palladium/tin dioxide/graphene composite material prepared from example 1. The peak positions of all diffraction peaks in the composite material are matched with those in a rutile-structure tin dioxide standard spectrogram, and no obvious impurity diffraction peak appears in the spectrogram, which indicates that the tin dioxide is successfully synthesized, and the crystal structure of the tin dioxide is not obviously influenced by the doping of the graphene.

Fig. 2 shows a TEM image of the palladium/tin dioxide/graphene composite material prepared from example 1. The tin dioxide is uniformly dispersed on the graphene sheet layer, the particle size range is 4-6 nm, and meanwhile, noble metal palladium is also uniformly dispersed on the graphene and tin dioxide nanoparticles respectively, and the particle size range is 1-2 nm.

Fig. 3 shows the response/recovery curve of the palladium/tin dioxide/graphene composite material prepared from example 1 at 75 ℃ to 100ppm of carbon monoxide gas. As can be seen from FIG. 3, the gas sensitive material has a relatively fast response/recovery speed at 75 ℃ to 100ppm of carbon monoxide gas, and the response time and the recovery time are only 7s and 10s, respectively. The response time is the time required to reach 90% of the change from the initial resistance value of the sensor in the atmosphere to the resistance value after the sensor reaches an equilibrium state in the target gas. The recovery time is the time required to reach 90% of the variation from the resistance value of the sensor in the target gas to the resistance value after the sensor remains stable in the environment.

Figure 4 shows the continuous dynamic response/recovery curves of the palladium/tin dioxide/graphene composite material prepared from example 2 at 75 ℃ for different concentrations of carbon monoxide gas. As can be seen from FIG. 4, the gas sensing material has faster response/recovery speed for different concentrations of CO gas at 75 ℃, and the sensitivity increases with the increase of CO concentration.

Fig. 5 shows the sensitivity profiles at 75 ℃ for different concentrations of carbon monoxide gas for the palladium/tin dioxide/graphene composite material prepared in example 3. As can be seen from fig. 4, the palladium/tin dioxide/graphene composite material has higher sensitivity to carbon monoxide gas at 75 ℃ in different concentrations, wherein the sensitivity value for 100ppm of carbon monoxide reaches 56. The sensitivity is the ratio of Ra to Rg, wherein Ra is the initial resistance value of the gas-sensitive material which is kept stable in the environment; rg is the stable resistance value of the gas sensitive material in target gas.

Fig. 6 shows a comparison of the sensitivity of the palladium/tin dioxide/graphene composite material prepared from example 3 at 75 ℃ to 5 different gases (i.e. carbon monoxide, ethanol, acetone, toluene and hydrogen, all at 100 ppm). As can be seen from fig. 5, the palladium/tin dioxide/graphene composite material has good gas selectivity for carbon monoxide gas.

Compared with the prior art, the invention has the following advantages:

(1) The graphene is used as a carrier, so that the agglomeration of tin dioxide nanoparticles can be effectively inhibited, the cluster size of tin dioxide is reduced, the dispersion degree of the tin dioxide nanoparticles is improved, and the loading and dispersion degree of metal palladium on the surfaces of the tin dioxide nanoparticles are improved.

(2) In the prepared palladium/tin dioxide/graphene composite material, due to the high specific surface of the graphene and the obtained tin dioxide metal oxide nanoparticles with smaller particle size and uniform dispersion, the gas-sensitive material can provide more active sites, the adsorption and desorption processes of target gas CO are improved, the gas molecule transmission and reaction processes are accelerated, and the gas-sensitive sensing performance of the gas CO is improved.

(3) in the prepared palladium/tin dioxide/graphene composite material, the graphene is doped, so that the conductivity of the composite material can be improved, the electron transmission speed is increased, and the gas-sensitive response/recovery speed to CO is increased.

(4) The prepared palladium/tin dioxide/graphene composite material is used for a resistance type gas sensor, has high sensitivity and selectivity on CO gas, and still has higher gas-sensitive sensing performance in a lower temperature range (for example, lower than 100 ℃).

(5) The preparation method of the palladium/tin dioxide/graphene composite material is simple to operate, wide in raw material source and low in preparation cost.

Although the present invention has been described above in connection with exemplary embodiments, it will be apparent to those skilled in the art that various modifications and changes may be made to the exemplary embodiments of the present invention without departing from the spirit and scope of the invention as defined in the appended claims.