阅读说明：本技术 一种Pd/In2O3气敏材料及其制备方法、气敏传感器 (Pd/In2O3Gas sensitive material, preparation method thereof and gas sensor ) 是由 王燕 张赛赛 张波 曹建亮 张博文 张豪爽 姚梦霞 张战营 于 2021-08-27 设计创作，主要内容包括：本发明属于气敏材料技术领域,具体涉及一种Pd/In-(2)O-(3)气敏材料及其制备方法、气敏传感器。本发明的制备方法包括以下步骤：将铟源溶于由丙三醇和异丙醇组成的混合溶液中,在高压反应釜中加热反应,反应后所得固体洗涤、干燥、煅烧得In-(2)O-(3)微米球粉末,然后按比例将氯化钯和所述In-(2)O-(3)微米球粉末加入到乙二醇中,超声、搅拌、加热反应,对反应产物固液分离,所得固体洗涤、干燥后得到Pd/In-(2)O-(3)气敏材料。本发明提供的Pd/In-(2)O-(3)气敏材料,具体为一种微米球气敏材料,在较低工作温度下可实现甲烷的高响应、低浓度检测。(The invention belongs to the technical field of gas-sensitive materials, and particularly relates to Pd/In 2 O 3 Gas sensitive material, preparation method thereof and gas sensor. The preparation method comprises the following steps: dissolving indium source In mixed solution composed of glycerol and isopropanol, heating and reacting In a high-pressure reaction kettle, washing, drying and calcining the obtained solid after reaction to obtain In 2 O 3 Micro-sphere powder, then proportionally mixing palladium chloride and the In 2 O 3 Adding the micron sphere powder into ethylene glycol, performing ultrasonic, stirring and heating reaction, performing solid-liquid separation on a reaction product, washing and drying the obtained solid to obtain Pd/In 2 O 3 A gas sensitive material. The Pd/In provided by the invention 2 O 3 The gas sensitive material is a microsphere gas sensitive material, and can realize high-response and low-concentration detection of methane at a lower working temperature.)

1. Pd/In₂O₃The preparation method of the gas sensitive material is characterized by comprising the following steps of:

step one, dissolving an indium source in a mixed solution composed of glycerol and isopropanol to obtain a mixed solution A;

secondly, placing the mixed solution A in a high-pressure reaction kettle for heating reaction, and cooling after the reaction to obtain a mixture;

step three, carrying out solid-liquid separation on the mixture, washing and drying the obtained solid to obtain a precipitate A;

step four, calcining the precipitate A to obtain In₂O₃Micro-sphere powder;

step five, proportionally mixing palladium chloride and the In₂O₃Adding the micro-sphere powder into ethylene glycol, and performing ultrasonic stirring to obtain a mixed solution B;

step six, heating the mixed solution B for reaction, carrying out solid-liquid separation on a reaction product, and washing the obtained solid to obtain a precipitate B;

step seven, drying the precipitate B to obtain Pd/In₂O₃A gas sensitive material.

2. Pd/In according to claim 1₂O₃The preparation method of the gas-sensitive material is characterized in that in the first step, every 1g of indium source corresponds to 100-150 mL of mixed solution consisting of glycerol and isopropanol;

preferably, the indium source is a water-soluble indium salt or hydrate thereof;

more preferably, the indium source is one or more of indium nitrate, indium chloride, indium sulfate, indium acetate, indium nitrate hydrate, indium chloride hydrate, indium sulfate hydrate, and indium acetate hydrate.

3. Pd/In according to claim 1₂O₃The preparation method of the gas sensitive material is characterized in that in the step one, the volume ratio of glycerol to isopropanol in a mixed solution consisting of glycerol and isopropanol is 4: (10-20).

4. Pd/In according to claim 1₂O₃The preparation method of the gas sensitive material is characterized in that in the second step, the volume of the mixed solution A accounts for 60-70% of the volume of the high-pressure reaction kettle;

preferably, in the second step, the temperature of the heating reaction is 150-200 ℃;

more preferably, the heating reaction time is 1-2 h.

5. Pd/In according to claim 1₂O₃The preparation method of the gas sensitive material is characterized in that in the third step, the solid-liquid separation is centrifugal separation, and the rotating speed of the centrifugal separation is 6000-8000 r/min;

preferably, the centrifugal separation time is 5-10 min.

6. Pd/In according to claim 1₂O₃The preparation method of the gas-sensitive material is characterized in that in the fourth step, the calcining temperature is 300-400 ℃;

preferably, the calcining time is 3-3.5 h, and the heating rate is 1-3 ℃/min.

7. Pd/In according to claim 1₂O₃The preparation method of the gas sensitive material is characterized in that in the fifth step, the proportion is as follows: the atomic mole ratio of Pd to In is 0.2 or less.

8. Pd/In according to claim 1₂O₃The preparation method of the gas-sensitive material is characterized in that in the sixth step, the temperature of the heating reaction is 90-110 ℃;

preferably, in the sixth step, the heating reaction time is 2-4 h.

9. Use of the Pd/In compound of any one of claims 1 to 8₂O₃Pd/In prepared by preparation method of gas-sensitive material₂O₃A gas sensitive material.

10. A gas sensor comprising the Pd/In according to claim 9₂O₃A gas sensitive material.

Technical Field

The invention belongs to the technical field of gas-sensitive materials, and particularly relates to Pd/In₂O₃Gas sensitive material, preparation method thereof and gas sensor.

Background

CH₄The gas is colorless, tasteless, flammable and explosive, when the concentration reaches a certain concentration, people can suffocate due to oxygen deficiency, and when the volume concentration of the gas mixed with air reaches an explosion limit (4.9-15.4%), severe combustion or explosion is easily caused when the gas meets a high-temperature fire source, so that huge economic loss and casualties can be caused. China has abundant coal resources, can release a large amount of gas in the process of mining, and has the main component of methane (CH)₄) Every year, China has casualty accidents caused by coal mine gas explosion, and great harm is caused to family happiness and national stability. The gas becomes one of important factors harming coal mine safety, and the accurate identification and concentration measurement of the mine gas can effectively prevent coal mine gas explosion, so that the important significance in ensuring coal mine safety production is achieved. The metal oxide semiconductor gas sensor becomes an effective means for detecting gas because of the advantages of high sensitivity, good stability, low cost, easy integration, easy manufacture and the like, and still needs to solve the problems of high working temperature, low response value, poor selectivity and difficult detection of low-concentration gas for adapting to complex underground coal mine environment. The core component of the metal oxide semiconductor gas sensor is a gas sensitive material, and the reports of the metal oxide semiconductor gas sensitive material for detecting methane of scholars at home and abroad at present cover ZnO and SnO₂、In₂O₃、TiO₂、NiO、WO₃And the like. In₂O₃The N-type semiconductor material has the characteristics of large forbidden band width, high conductivity, high catalytic activity, surface defects and the like, and shows excellent application prospect.

In is currently concerned₂O₃There are a few reports of the use of materials in the study of gas sensors. Vuong et al developed a Ni₂O₃Nanoparticle modified In₂O₃Nanostructure of thin film and preparation of highly responsive CH₄The results for the gas sensor show that the material has a response of about 52% to 200ppm CH4 at 350 ℃ (Vuong et al, Ni₂O₃ decoration of In₂O₃nanostructures for catalytically enhanced methane sensing[J]Applied Surface Science,2014,317:765- & 770). Cao et al prepared In composed of porous nanoparticles₂O₃Micro-sphere, and on CH₄The gas-sensitive property of the material is researched, and the result shows that the material can resist 5000ppm CH at 350 DEG C₄A response value of 6.50(Cao et al, Synthesis of porous In)₂O₃ microspheres as a sensitive material for early warning of hydrocarbon explosions[J]RSC Advances,2015,5: 5424-. Shaalan et al developed a thin film type In₂O₃Radical CH₄Gas sensor studied for CH at different operating temperatures and concentrations₄The result shows that the film is paired with CH₄Has good sensing performance and stability (Shaalan et al, reproducibility of indium oxide gas sensors for detecting methane at low temperature [ J)]Materials Science in Semiconductor Processing,2016,56: 260-. Xue et al synthesized In with porous structure by one-step hydrothermal method₂O₃The nano-sheet shows that the material can resist 500ppm CH at 190 DEG C₄The response value of (A) was 3.24(Xue et al, Hydrothermal synthesis of methane sensitive positive In)₂O₃ nanosheets[J]Materials Letters, 2019; 252:169). In the detection of inflammable and explosive gases, the higher working temperature not only limits the application range of the sensor, but also greatly reduces the safety,at the same time, it means a large energy consumption and a shortened service life and higher maintenance costs for the production plant.

In recent years, two approaches are mainly adopted in improving the gas sensitivity performance of a gas sensor: firstly, the surface appearance is regulated, a porous structure with larger specific surface area, such as a hollow sphere structure, a core-shell structure, a hierarchical structure and the like, is synthesized, and the chemical reaction of gas molecules on the surface of the sensitive membrane and the diffusion of the gas molecules in the material can be accelerated; secondly, functional modification, at present, most researches are carried out on noble metal loading and heterojunction construction, and the effect of improving the gas-sensitive performance of the sensor is achieved through the catalysis of the noble metal and the heterojunction and the like. However, the existing methane sensor has high working temperature, low response value, poor selectivity and difficult low concentration detection, and can not meet the requirements of practical application.

Therefore, there is a need to provide an improved solution to the above-mentioned deficiencies of the prior art.

Disclosure of Invention

The invention aims to provide Pd/In₂O₃A gas sensitive material, a preparation method thereof and a gas sensor solve the problems of high working temperature, low response value, poor selectivity and difficult low concentration detection of the existing methane sensor.

In order to achieve the purpose, the invention provides the following technical scheme:

Pd/In₂O₃A method for preparing a gas sensitive material, the method comprising the steps of:

step one, dissolving an indium source in a mixed solution composed of glycerol and isopropanol to obtain a mixed solution A;

secondly, placing the mixed solution A in a high-pressure reaction kettle for heating reaction, and cooling after the reaction to obtain a mixture;

step three, carrying out solid-liquid separation on the mixture, washing and drying the obtained solid to obtain a precipitate A;

step four, calcining the precipitate A to obtain In₂O₃Micro-sphere powder;

step five, proportionally mixing palladium chloride and the In₂O₃Adding the micro-sphere powder into ethylene glycol, and performing ultrasonic stirring to obtain a mixed solution B;

step six, heating the mixed solution B for reaction, carrying out solid-liquid separation on a reaction product, and washing the obtained solid to obtain a precipitate B;

step seven, drying the precipitate B to obtain Pd/In₂O₃A gas sensitive material.

In the preparation method, preferably, in the first step, 100 to 150mL of a mixed solution composed of glycerol and isopropanol is used for every 1g of indium source.

Preferably, the indium source is a water soluble indium salt or hydrate thereof.

More preferably, the indium source is one or more of indium nitrate, indium chloride, indium sulfate, indium acetate, indium nitrate hydrate, indium chloride hydrate, indium sulfate hydrate, and indium acetate hydrate.

In the above production method, preferably, in the first step, the volume ratio of glycerin to isopropyl alcohol in the mixed solution composed of glycerin and isopropyl alcohol is 4: (10-20).

In the preparation method, preferably, in the second step, the volume of the mixed solution a accounts for 60-70% of the volume of the high-pressure reaction kettle.

Preferably, in the second step, the temperature of the heating reaction is 150-200 ℃.

More preferably, the heating reaction time is 1-2 h.

In the preparation method, preferably, in the third step, the solid-liquid separation is centrifugal separation, and the rotation speed of the centrifugal separation is 6000 to 8000 r/min.

Preferably, the centrifugal separation time is 5-10 min.

In the preparation method, preferably, in the fourth step, the calcining temperature is 300-400 ℃.

Preferably, the calcining time is 3-3.5 h, and the heating rate is 1-3 ℃/min.

In the above preparation method, preferably, in step five, the ratio is: the atomic mole ratio of Pd to In is 0.2 or less (i.e., the atomic mole ratio of Pd to In is greater than 0 but not greater than 0.2), and preferably 0.08 to 0.16.

In the preparation method, preferably, in the sixth step, the temperature of the heating reaction is 90-110 ℃.

Preferably, in the sixth step, the heating reaction time is 2-4 h.

The invention also provides the Pd/In₂O₃Pd/In prepared by preparation method of gas-sensitive material₂O₃A gas sensitive material.

The invention also provides a gas sensor, wherein the gas sensor adopts the Pd/In₂O₃A gas sensitive material.

Has the advantages that:

the invention utilizes the strong catalytic activity of Pd nano-particles to promote the dissociation adsorption of oxygen molecules and methane molecules and activate the overflow process of the oxygen molecules and the methane molecules, accelerates the capture and release speed of electrons, and leads the electrons to be transferred by the difference between work functions to cause the bending of an energy band at a metal-semiconductor interface, thereby forming a Schottky barrier to be used as an electron trap, further regulating the resistivity of the material and improving the Pd/In₂O₃The response of the base sensor. Pd/In prepared by solvothermal method₂O₃The gas sensitive material has high component purity and good dispersibility.

The invention provides a proper Pd and In proportioning scheme, which not only saves resources and cost, but also enables the response of the sensor to methane to be the highest at a lower working temperature, and can detect methane at a low concentration.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention. Wherein:

FIG. 1 shows In obtained In comparative example 1, example 2 and example 3₂O₃Micro-spheres and Pd/In₂O₃An X-ray diffraction pattern of the gas sensitive material;

FIG. 2Is In prepared In comparative example 1 and example 2 of the present invention₂O₃Micro-spheres (FIG. 2a, FIG. 2b, respectively) and Pd/In₂O₃(corresponding to FIGS. 2c and 2d, respectively) low-magnification and high-magnification transmission electron micrographs of the gas-sensitive material;

FIG. 3 shows In obtained by using comparative example 1, example 2 and example 3 of the present invention₂O₃Micro-spheres and Pd/In₂O₃The sensor assembled by gas sensitive materials can be used for detecting 500ppm CH at different working temperatures₄(ii) a response of (d);

FIG. 4 shows In obtained by using comparative example 1 and example 2 of the present invention₂O₃Micro-spheres and Pd/In₂O₃Response value and CH of sensor assembled by gas sensitive materials₄A line graph of gas concentration;

FIG. 5 shows In obtained by using comparative example 1 and example 2 of the present invention₂O₃Micro-spheres and Pd/In₂O₃The response results of the sensor assembled by the gas sensitive material to different gases at 50 ℃.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments that can be derived by one of ordinary skill in the art from the embodiments given herein are intended to be within the scope of the present invention.

The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

The invention provides a method for modifying metal oxide In by adopting noble metal Pd₂O₃Preparation of Pd/In by using microspheres₂O₃Gas-sensitive material, for CH₄And the system shows higher response value, lower working temperature and detection limit.

The Pd/In provided by the invention₂O₃The gas sensitive material is a micron sphere gas sensitive material which can be realized at a lower working temperatureHigh response, low concentration detection of methane.

Pd/In of the invention₂O₃The preparation method of the gas sensitive material comprises the following steps:

step one, adding a certain amount of indium source into a mixed solution composed of glycerol and isopropanol, and dissolving the indium source by magnetic stirring (namely dissolving the indium source into the mixed solution composed of glycerol and isopropanol) to obtain a mixed solution A;

step two, putting the mixed solution A obtained in the step one into a high-pressure reaction kettle with a polytetrafluoroethylene lining, wherein the volume of the mixed solution A accounts for 60-70% (such as 60%, 62%, 65%, 67% or 70%) of the volume of the high-pressure reaction kettle, then putting the mixed solution A into an oven for heating reaction, and naturally cooling to room temperature after the reaction is finished to obtain a mixture;

step three, centrifugally separating the mixture obtained in the step two at a rotating speed of 6000-8000 r/min (such as 6000r/min, 6500r/min, 7000r/min, 7500r/min or 8000r/min) for 5-10 min (such as 5min, 6min, 7min, 8min, 9min or 10min), removing supernatant, alternately centrifugally washing the residual solid matters with deionized water and absolute ethyl alcohol, and then placing the washed solid matters in an oven for drying to obtain a precipitate A;

step four, placing the precipitate A obtained In the step three In a muffle furnace for calcining (air atmosphere) to obtain In₂O₃Micro-sphere powder;

step five, weighing a certain amount of In according to the atomic mole ratio of Pd to In₂O₃Adding the microsphere powder and palladium chloride into ethylene glycol, performing ultrasonic treatment for 5-10 min (for example, 5min, 6min, 7min, 8min, 9min or 10min), and performing magnetic stirring to obtain a mixed solution B;

step six, transferring the mixed solution B obtained in the step five into an oven for heating reaction, removing supernatant of the obtained mixture, and alternately centrifuging and washing by using distilled water and absolute ethyl alcohol to obtain a precipitate B;

step seven, transferring the precipitate B obtained In the step six to an oven for drying to obtain Pd/In₂O₃A gas sensitive material.

Preferably, in the first step, the indium source is a water-soluble indium salt capable of providing indium ions and hydrates thereof, such as one or more of indium nitrate, indium chloride, indium sulfate, indium acetate, indium nitrate hydrate, indium chloride hydrate, indium sulfate hydrate, and indium acetate hydrate.

Preferably, in the first step, the volume ratio of glycerol to isopropanol in the mixed solution consisting of glycerol and isopropanol is 4: (10-20) (e.g., 4: 10, 4: 12, 4: 14, 4: 15, 4: 17, 4: 18, or 4: 20).

Preferably, a constant-temperature magnetic stirrer is used for stirring in the first step and the fifth step, the rotating speed is 850r/min, and the stirring is carried out for 0.5-1 h (for example, 0.5h, 0.6h, 0.7h, 0.8h, 0.9h or 1 h).

Preferably, the second step and the sixth step are heated by an oven, the second step is heated at a temperature of 150-200 ℃ (e.g. 150 ℃, 160 ℃, 170 ℃, 180 ℃, 190 ℃ or 200 ℃), preferably 180 ℃ for 1 hour, and the sixth step is heated at a temperature of 90-110 ℃ (e.g. 90 ℃, 95 ℃, 100 ℃, 105 ℃ or 110 ℃) for 2-4 hours (e.g. 2 hours, 3 hours or 4 hours).

Preferably, the residual solid matters in the third step and the sixth step are washed by alternate centrifugation with distilled water and absolute ethyl alcohol for 3 times.

Preferably, the fourth step is placed in a muffle furnace for calcination, the calcination temperature is 300-400 ℃ (such as 300 ℃, 320 ℃, 340 ℃, 350 ℃, 360 ℃, 380 ℃ or 400 ℃), the heating rate is 1-3 ℃/min (such as 1 ℃/min, 2 ℃/min or 3 ℃/min), and the calcination is carried out at constant temperature for 3-3.5 h (such as 3h, 3.1h, 3.2h, 3.3h, 3.4h or 3.5 h).

Preferably, the drying in the third step and the drying in the seventh step are carried out by using an electrothermal blowing drying oven, the drying temperature in the third step is 60 ℃, the drying time is 12 hours, and the drying temperature in the seventh step is 105 ℃, and the drying time is 12 hours.

The invention also provides an optimized comparison of the modification amount of Pd, and the proportion is preferably carried out according to the atomic mole ratio of Pd to In of less than 0.2 (such as 0.04, 0.08, 0.12, 0.16 or 0.2). In the following examples, Pd/In ratios of 0, 0.08, 0.12 and 0.16 In terms of atomic mole ratio of Pd to In were examined₂O₃Gas-sensitive materials, i.e. In₂O₃，4.0at％Pd/In₂O₃，6.0at％Pd/In₂O₃，8.0at％Pd/In₂O₃。

The invention also provides a method for preparing the Pd/In₂O₃A gas sensor for gas sensitive materials.

The present invention will be further described with reference to the following examples.

Example 1

Pd/In of the present example₂O₃The preparation method of the gas sensitive material comprises the following steps:

adding 0.6g of indium nitrate hydrate into a mixed solution consisting of 16mL of glycerol and 60mL of isopropanol, and magnetically stirring for 30min to dissolve the indium nitrate hydrate to obtain a mixed solution A; putting the obtained mixed solution A into a high-pressure reaction kettle with a polytetrafluoroethylene lining, wherein the volume of the mixed solution A accounts for 65% of the volume of the reaction kettle, then placing the reaction kettle into an oven, keeping the temperature of the reaction kettle at 180 ℃ for 1 hour, and naturally cooling the reaction kettle to room temperature after the reaction is finished to obtain a mixture; centrifuging the obtained mixture at 8000r/min for 5min, removing supernatant, alternately centrifuging the rest solid substance with deionized water and anhydrous ethanol for 3 times, and drying in 60 deg.C electrothermal blowing dry box for 12 hr to obtain precipitate A; calcining the obtained precipitate A In a muffle furnace, heating to 350 ℃, heating at the rate of 3 ℃/min, and calcining at constant temperature for 3h to obtain In₂O₃Micro-sphere powder; weighing 0.2mmol of prepared In according to the atomic mole ratio of Pd to In of 0.08₂O₃Adding the microsphere powder and 0.032mmol of palladium chloride into 12mL of ethylene glycol, performing ultrasonic treatment for 8min, and performing magnetic stirring for 1h to obtain a mixed solution B; transferring the obtained mixed solution B into an oven, keeping the temperature of 100 ℃ for 3 hours, removing supernatant of the obtained mixture, and alternately centrifuging and washing for 3 times by using distilled water and absolute ethyl alcohol to obtain a precipitate B; transferring the obtained precipitate B into an electrothermal blowing dry box at 105 ℃, and drying for 12h to obtain 4.0 at% Pd/In₂O₃A gas sensitive material.

Example 2

Pd/In of the present example₂O₃The preparation method of the gas sensitive material comprises the following steps:

adding 0.6g of indium nitrate hydrate into the mixtureIn a mixed solution composed of L glycerol and 60mL isopropanol, magnetically stirring for 30min to dissolve the L glycerol and the 60mL isopropanol to obtain a mixed solution A; putting the obtained mixed solution A into a high-pressure reaction kettle with a polytetrafluoroethylene lining, wherein the volume of the mixed solution A accounts for 65% of the volume of the reaction kettle, then placing the reaction kettle into an oven, keeping the temperature of the reaction kettle at 180 ℃ for 1 hour, and naturally cooling the reaction kettle to room temperature after the reaction is finished to obtain a mixture; centrifuging the obtained mixture at 8000r/min for 5min, removing supernatant, alternately centrifuging the rest solid substance with deionized water and anhydrous ethanol for 3 times, and drying in 60 deg.C electrothermal blowing dry box for 12 hr to obtain precipitate A; calcining the obtained precipitate A In a muffle furnace, heating to 350 ℃, heating at the rate of 3 ℃/min, and calcining at constant temperature for 3h to obtain In₂O₃Micro-sphere powder; weighing 0.2mmol of prepared In according to the atomic mole ratio of Pd to In of 0.12₂O₃Adding the microsphere powder and 0.048mmol of palladium chloride into 12mL of ethylene glycol, performing ultrasonic treatment for 8min, and performing magnetic stirring for 1h to obtain a mixed solution B; transferring the obtained mixed solution B into an oven, keeping the temperature of 100 ℃ for 3 hours, removing supernatant of the obtained mixture, and alternately centrifuging and washing for 3 times by using distilled water and absolute ethyl alcohol to obtain a precipitate B; transferring the obtained precipitate B into an electrothermal blowing dry box at 105 ℃, and drying for 12h to obtain 6.0 at% Pd/In₂O₃A gas sensitive material.

Example 3

Pd/In of the present example₂O₃The preparation method of the gas sensitive material comprises the following steps:

adding 0.6g of indium nitrate hydrate into a mixed solution consisting of 16mL of glycerol and 60mL of isopropanol, and magnetically stirring for 30min to dissolve the indium nitrate hydrate to obtain a mixed solution A; putting the obtained mixed solution A into a high-pressure reaction kettle with a polytetrafluoroethylene lining, wherein the volume of the mixed solution A accounts for 65% of the volume of the reaction kettle, then placing the reaction kettle into an oven, keeping the temperature of the reaction kettle at 180 ℃ for 1 hour, and naturally cooling the reaction kettle to room temperature after the reaction is finished to obtain a mixture; centrifuging the obtained mixture at 8000r/min for 5min, removing supernatant, alternately centrifuging the rest solid substance with deionized water and anhydrous ethanol for 3 times, and drying in 60 deg.C electrothermal blowing dry box for 12 hr to obtain precipitate A; the obtained precipitate ACalcining In a muffle furnace at the temperature of 350 ℃ and the heating rate of 3 ℃/min for 3h at constant temperature to obtain In₂O₃Micro-sphere powder; weighing 0.2mmol of prepared In according to the atomic mole ratio of Pd to In of 0.16₂O₃Adding the microsphere powder and 0.064mmol of palladium chloride into 12mL of ethylene glycol, performing ultrasonic treatment for 8min, and magnetically stirring for 1h to obtain a mixed solution B; transferring the obtained mixed solution B into an oven, keeping the temperature of 100 ℃ for 3 hours, removing supernatant of the obtained mixture, and alternately centrifuging and washing for 3 times by using distilled water and absolute ethyl alcohol to obtain a precipitate B; transferring the obtained precipitate B into an electrothermal blowing dry box at 105 ℃, and drying for 12h to obtain 8.0 at% Pd/In₂O₃A gas sensitive material.

Comparative example 1

The preparation method of the gas sensitive material of this comparative example was as follows:

adding 0.6g of indium nitrate hydrate into a mixed solution consisting of 16mL of glycerol and 60mL of isopropanol, and magnetically stirring for 30min to dissolve the indium nitrate hydrate to obtain a mixed solution A; putting the obtained mixed solution A into a high-pressure reaction kettle with a polytetrafluoroethylene lining, wherein the volume of the mixed solution A accounts for 65% of the volume of the reaction kettle, then placing the reaction kettle into an oven, keeping the temperature of the reaction kettle at 180 ℃ for 1 hour, and naturally cooling the reaction kettle to room temperature after the reaction is finished to obtain a mixture; centrifuging the obtained mixture at 8000r/min for 5min, removing supernatant, alternately centrifuging the rest solid substance with deionized water and anhydrous ethanol for 3 times, and drying in an electrothermal blowing drying oven at 60 deg.C for 12 hr to obtain precipitate A; calcining the obtained precipitate A In a muffle furnace, heating to 350 ℃, heating at the rate of 3 ℃/min, and calcining at constant temperature for 3h to obtain In₂O₃The gas sensitive material is microspheres.

Examples of the experiments

The experiment adopts a CGS-4TPs intelligent gas-sensitive analysis test system manufactured by Beijing Airit science and technology Limited company, and carries out gas-sensitive performance test on the prepared gas-sensitive element by using a static gas distribution method. The preparation process of the gas sensor comprises the following steps: and (3) taking a proper amount of gas-sensitive material into an agate mortar, dropwise adding a proper amount of distilled water to disperse the sample, and then forcibly grinding the sample to be uniform and viscous by using an agate grinding rod. Dipping the slurry by a clean brush, uniformly brushing the slurry on a planar ceramic substrate (13.4mm multiplied by 7mm) to form a sensitive film with proper thickness, brushing for a plurality of times to ensure that the slurry completely covers the Ag-Pd interdigital electrode, and finally drying the prepared gas-sensitive element in the shade for later use. In order to improve the stability and the repeatability of the gas sensor, the prepared gas sensor is placed on a heating table at 120 ℃ for aging for 48 h.

1. In obtained In comparative example 1, example 2 and example 3₂O₃Micro-spheres and Pd/In₂O₃The gas sensitive material is detected by X-ray powder diffraction, and the result is shown In figure 1 (four curves of a, b, c and d In the figure correspond to comparative example 1, example 2 and example 3 In sequence), which shows that In is successfully prepared by the solvothermal method₂O₃Micro-spheres and Pd nanoparticles have been successfully loaded to In₂O₃The surface of the microsphere.

2. In obtained In comparative example 1 and example 2₂O₃Micro-sphere Pd/In₂O₃The transmission electron microscope test of the gas-sensitive material shows that the result is shown In fig. 2 (a and b In the figure correspond to the transmission electron microscope with low magnification and high magnification of comparative example 1 In sequence, and c and d In the figure correspond to the transmission electron microscope with low magnification and high magnification of example 2 In sequence), the prepared material is obviously observed to be In a spherical structure, the surface is rough, a plurality of small protrusions are formed, and meanwhile, the fact that Pd nanoparticles are successfully loaded to In is further shown₂O₃The surface of the microsphere.

3. In obtained In comparative example 1, example 2 and example 3₂O₃Micro-spheres and Pd/In₂O₃The gas sensitive material is assembled into a sensor and is used for detecting 500ppm CH at different working temperatures₄The gas sensitive performance test was performed, and the results are shown in fig. 3. As can be observed from the figure, 4 sensor pairs CH₄The response of the display screen is increased along with the continuous increase of the working temperature, the overall trend of the graph is the same, and the graph presents a 'fire hill type', which is increased firstly and then decreased. In addition, except for pure phase In₂O₃At 140 ℃ to CH₄The response of (2) is beyond the maximum value (11.964), and the remaining 3 Pd/In₂O₃The sensors all reached a maximum at 50 ℃. Wherein Pd is negativePd/In at 6.0 at%₂O₃Sensor pair CH₄The response of (2) reaches a maximum of 15.317, so In after loading Pd₂O₃The optimal working temperature of the micro-spheres is reduced from 140 ℃ to 50 ℃. Therefore, the Pd load with proper concentration can reduce the optimal working temperature of the sensor.

4. In obtained In comparative example 1 and example 2₂O₃Micro-spheres and Pd/In₂O₃The gas-sensitive material of the micro-spheres is assembled into a sensor for detecting CH with different concentrations of 10ppm to 5000ppm at 50 DEG C₄The results are shown in fig. 4. As can be seen, in the lower concentration range (10-100 ppm), the concentration is dependent on CH₄Gas concentration increases, gas sensor pair CH₄The response value of (a) increases linearly; when CH is present₄When the gas concentration is more than 100ppm, the response value changes slowly, which indicates that the sensor is on CH₄Gradually towards saturation. The inset of FIG. 4b shows two gas sensors at low CH concentrations₄Has good linear relation In the range of (10-100 ppm), pure phase In₂O₃Response y and CH₄The linear fit equation for the gas concentration x is: y is 1.84361+0.00406x, and the fitting coefficient is 0.96417; and 6.0 at.% Pd/In₂O₃Response y and CH₄The linear fit equation for the gas concentration x is: y is 5.35662+0.0583x and the fitting coefficient is 0.93856. Therefore, the sensitivity of the two sensors is 4.06X 10 in the concentration range (10-100 ppm)^-3ppm^-1And 5.83X 10^-2ppm^-1The higher fitting coefficient and the good linear relation show that the sensor can effectively monitor CH₄The gas concentration. According to the definition of the International Union of Pure and Applied Chemistry (IUPAC), the formula for calculating the limit of detection is defined as: LoD ═ 3 (S)_D/m) wherein S_DThe standard deviation of the noise in the response curve is calculated by taking 30 points at the baseline of the response curve without injecting the target gas, and m is the slope of the linear portion of the response curve, i.e., the sensor pair CH₄The sensitivity of (2). According to the above calculation formula, pure phase In₂O₃And 6.0 at.% Pd/In₂O₃Detection limit of2.53ppm and 1.78ppm, respectively. With pure phase In₂O₃In contrast, 6.0 at.% Pd/In₂O₃Lower detection limit of, for CH₄Has higher sensitivity and can realize the CH₄Trace detection of gases.

5. In obtained In comparative example 1 and example 2₂O₃Micro-spheres and Pd/In₂O₃The gas-sensitive material of the microspheres is assembled into a sensor, and the response of the sensor to different gases at 50 ℃ is detected, and the result is shown in figure 5. According to the latest regulation of coal mine safety regulations, CO and NH₃Are 24ppm and 40ppm, respectively, CH₄The minimum alarm concentration and the power-off concentration of the sensor are 5000ppm, the maximum allowable concentration of formaldehyde, toluene and methanol is 1ppm, and in addition, the coal mine gas contains a small amount of H₂O, so 50ppm H is selected₂O test selectivity. Meanwhile, the formula K is S according to the selectivity (K)_{Target gas}/S_{Interfering gas}(S_{Target gas}Is the response value of the sensor to the target gas; s_{Interfering gas}Response value of sensor to interfering gas) to obtain pure phase In₂O₃For interfering gases CO and NH₃、H₂O、HCHO、C₇H₈And CH₃The OH selectivities were 2.18, 2.51, 2.73, 2.85, 4.17 and 2.66, respectively; 6.0 at% Pd/In₂O₃For interfering gases CO and NH₃、H₂O、HCHO、C₇H₈And CH₃The OH selectivities were 3.13, 4.57, 5.58, 3.06, 5.54 and 6.69, respectively. The experimental result shows that In is obviously improved after noble metal Pd is loaded₂O₃Microsphere pair CH₄Selectivity of (2).

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.