Preparation of Tm-Cu-In < 2 > O < 3 > composite material, gas sensor based on Tm-Cu-In < 2 > O < 3 > composite material, preparation method and application

Abstract

The invention discloses preparation of a Tm-Cu-In < 2 > O < 3 > composite material, a gas sensor based on the Tm-Cu-In < 2 > O < 3 > composite material, a preparation method and application, and belongs to the technical field of gas sensor materials. Thulium chloride, copper sulfate, indium salt and an organic solvent are used as raw materials, In2O3 is doped with double metal elements Cu and Tm, a composite gas sensitive material is prepared, and a gas sensor based on the composite gas sensitive material is obtained. Compared with other In2O3-based H2S sensors, the gas sensor prepared by the invention has high sensitivity, high selectivity and good stability to H2S, and still has relatively high response in a high-humidity H2S environment, so that the gas sensor has excellent gas sensitivity to H2S gas in the environment. The sensor is simple in production process, low in energy consumption in the production process, low in cost and suitable for industrial batch production.

Description

Technical Field

[0001] The present invention relates to the technical field of gas sensor materials, and more specifically to a preparation method of a Tm-Cu@In2O3 nano-spherical composite H2S gas sensor based on Cu and Tm bimetal doping. Background Technique

[0002] Hydrogen sulfide (H2S) is a reducing gas with a rotten egg smell at room temperature and normal pressure, and it also has the characteristics of being colorless, flammable, highly corrosive, and highly toxic. Since its density is greater than that of air, it is likely to accumulate in enclosed spaces or areas with poor air circulation. Hydrogen sulfide mainly comes from the decomposition process of organic matter, the manufacturing process of fossil fuels, and the waste gas emitted by the fossil industry. It can enter the human body through human breathing activities. The pungent smell of hydrogen sulfide will not only cause serious environmental pollution problems but also pose a serious threat to human health. For example, hydrogen sulfide will stimulate human tissues, damage the central nervous system and respiratory system, leading to difficulty in breathing and olfactory dysfunction, and in severe cases, it will cause syncope or even death. According to the data of the National Institute for Occupational Safety and Health of the United States, the concentration of hydrogen sulfide that poses a direct threat to life and health is 100 ppm. Therefore, realizing the real-time monitoring of H2S gas with high sensitivity and high selectivity is very important for the detection and early warning of hydrogen sulfide, and it is of great significance for protecting human health and the natural environment.

[0003] Among many gas-sensitive materials, semiconductor gas-sensitive materials (MOSs) formed by combining MOFs and metal oxides have stood out. Due to their many advantages such as low raw material cost, simple preparation process, high practical benefits, light weight, and low carbon and low consumption in the preparation process, a large number of studies have been carried out in semiconductor gas sensing. So far, scholars have constructed some MOSs-based sensors based on different metal oxide materials, such as WO3, MoS2, SnO2, ZnO, In2O3, ZIF-67, NiO, etc. Among them, In2O3 belongs to a typical wide-bandgap N-type semiconductor material, and due to its significant surface effect and good electrical, optical, and chemical properties, it shows higher selectivity and response degree than other materials in the detection of H2S. According to previous research work, scholars have explored various methods to improve the gas-sensitive performance of In2O3 materials, including changing the surface morphology of the material, doping metal elements, and forming heterojunctions by compounding other semiconductor materials.

[0004] However, for sensors based on In2O3 materials doped with Cu elements (or one of the doping elements), since H2S will undergo a sulfonation reaction with the doped Cu in the gas-sensitive material, some of these types of sensors have the disadvantages of low response degree, poor long-term stability, and low selectivity.

[0005] Therefore, how to prepare a composite material by metal doping to improve the gas adsorption performance of H2S and optimize the gas-sensing performance of the sensor for H2S is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a gas sensor based on Tm-Cu@In2O3, a preparation method thereof and an application. In the present invention, two metal elements, Cu and Tm, are doped into the original In2O3 material by a solvothermal method to prepare a Tm-Cu@In2O3 nano three-dimensional spherical composite material sensor, which improves the gas adsorption performance of H2S and optimizes the gas-sensing performance of the sensor for H2S. The preparation method of the present invention has the advantages of simple operation, low cost, high product purity, etc., and is suitable for large-scale industrial production, providing new design insights for the development of metal oxide semiconductor gas-sensing materials for detecting H2S gas.

[0007] One of the purposes of the present invention is to provide a preparation method of a Tm-Cu@In2O3 composite gas-sensing material, comprising the following steps:

[0008] (1) Add indium salt to isopropanol and stir for 0.5 - 1 h to disperse evenly to obtain an indium salt solution;

[0009] (2) Add glycerol to the indium salt solution and stir for 0.5 - 1 h to fully mix glycerol and the indium salt solution, then add equimolar percentages (x mol%) of TmCl3·6H2O and Cu(NO3)2, and continuously stir for 0.5 - 2 h to obtain a mixed solution;

[0010] (3) Ultrasonically treat the mixed solution for 5 - 10 min, transfer it to a high-pressure reaction kettle, react at a certain temperature and then take it out, naturally cool to room temperature, separate the generated precipitate, and wash it by centrifugation with deionized water and ethanol multiple times (10000 rpm, 10 min) to obtain a solid product;

[0011] (4) Dry the solid product at 60 - 80 °C overnight, and then calcine it in air at a rate of 5 °C / min -1 at 300 - 500 °C for 1.5 - 2.5 h, take it out after cooling to room temperature to obtain Tm-Cu@In2O3 composite gas-sensing material powder.

[0012] Preferably, in step (1), the indium salt is selected from one or more of InCl3·4H2O, In(NO3)3·4.5H2O, In(NO3)3·6H2O, In(NO3)3·nH2O.

[0013] Preferably, in step (1), the solid-liquid ratio of the indium salt to isopropanol is 0.5 - 1:30 - 60 g / mL.

[0014] Preferably, in step (2), the mass ratio of the indium salt to the glycerol is 0.5-1:10-30; the addition amounts of TmCl3·6H2O and Cu(NO3)2 are based on the molar percentages of Tm and Cu to the indium salt respectively, and the molar percentage x = 0-6. Further preferably, x is 2, 4, or 6.

[0015] Further preferably, when x = 0, it is a pure In2O3 material, which is used as a control for the doped bimetallic Tm-Cu@In2O3 composite material.

[0016] Preferably, in step (3), the reaction is carried out at 160-180 °C for 6-10 h.

[0017] The second object of the present invention is to provide an H2S gas sensor based on the Tm-Cu@In2O3 composite gas-sensitive material, which is composed of a ceramic tube substrate with gold electrodes at both ends, the Tm-Cu@In2O3 composite material coated on the ceramic tube substrate and the gold electrodes, and a nickel-chromium heating coil placed inside the ceramic tube.

[0018] The third object of the present invention is to provide a preparation method of a gas sensor, including the following steps:

[0019] a. Take the Tm-Cu@In2O3 composite gas-sensitive material and mix it with absolute ethanol to form a paste-like slurry; then use a brush to dip a small amount of the slurry and evenly coat it on the outer surface of the ceramic tube with two gold electrodes and four platinum wires, so as to completely cover the outer surface of the ceramic tube and the gold electrodes at both ends;

[0020] b. Naturally air-dry the ceramic tube substrate coated with the composite material at room temperature. After the composite material is dried, weld the platinum wire leads connecting the ceramic tube surface to the gold electrodes to the measuring electrodes of the hexagonal base, and then cap and encapsulate to obtain an H2S gas sensor element based on the Tm-Cu@In2O3 composite gas-sensitive material;

[0021] c. Place the fabricated gas sensing element on an aging table and age it for 8-12 h under a heating current of 100-120 mA in an air environment.

[0022] Preferably, in step a, the mass ratio of the Tm-Cu@In2O3 composite gas-sensitive material to absolute ethanol is 0.1-0.5:1, and the coating thickness is 10-40 μm.

[0023] The present invention prepares a Tm-Cu@In2O3 composite material by a solvothermal method combined with subsequent calcination treatment. The composite material sensor has good selectivity and reproducibility, and still has high sensitivity to H2S under high relative humidity, showing good detection performance for H2S gas. The prepared Tm-Cu@In2O3 sensor has a simple manufacturing process, small size, low cost, and a green manufacturing process, which is suitable for industrial production, providing a promising method for realizing high-performance In2O3-based H2S gas sensors, and is expected to sensitively and accurately detect H2S in a complex environment, showing good practical application prospects.

[0024] As can be seen from the above technical solutions, compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0025] 1. A three-dimensional nano-spherical Tm-Cu@In2O3 composite sensitive material is prepared by a solvothermal synthesis method introducing two metal elements, Cu and Tm, as doping components. The raw materials are easily obtained and the preparation process is simple, which is suitable for batch production.

[0026] 2. The dual-metal doping changes the surface microstructure of the sensitive material, increases the specific surface area, enhances the formation of oxygen vacancies, and increases its active sites. Moreover, the p-n heterojunction, unique three-dimensional structure generated after doping, and the special affinity of Cu for H2S endow the Tm-Cu@In2O3 sensitive material sensor with good sensitivity, selectivity, and stability to H2S, and still has a good response to H2S under high relative humidity.

[0027] 3. In terms of the invention design, the Tm-Cu@In2O3 sensor provides a promising method for realizing high-performance In2O3-based H2S gas sensors, and is expected to sensitively and accurately detect H2S in a complex environment, showing good practical application prospects. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0029] Figure 1 XRD image of the product prepared for the embodiment.

[0030] Figure 2 SEM image of the product prepared for the embodiment.

[0031] Figure 3For the dynamic concentration response relationship of the sensor in the embodiment within the range of 2 - 100 ppm H2S at 173°C.

[0032] Figure 4 For the dynamic concentration response fitting curve of the sensor in the embodiment within the range of 2 - 100 ppm H2S at 173°C.

[0033] Figure 5 For the selectivity comparison of the sensor in Example 3 and Example 1 to 20 ppm H2S and 100 ppm of other interfering gases at 173°C.

[0034] Figure 6 For the response of the sensor in Example 3 to different relative humidities at 173°C and 100 ppm H2S.

[0035] Figure 7 For the long-term stability of the sensor in Example 3 within 30 days at 173°C and 100 ppm H2S.

[0036] Figure 8 For the continuous cyclic response test of the sensor in Example 3 to 20 ppm H2S at 173°C on the 30th day. Detailed implementation manners

[0037] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0038] Example 1

[0039] Preparation of Tm-Cu@In2O3 sensitive material

[0040] Add 0.8 g of indium salt to 50 mL of isopropanol and stir for 40 min to obtain an indium salt solution. Add 20 g of glycerol to the indium salt solution and stir for 1 h to fully mix the glycerol and the indium salt solution. Subsequently, add 0 mol% of TmCl3·6H2O and Cu(NO3)2 respectively, and continue to stir for 2 h. Then, perform ultrasonic treatment for 5 min, transfer it to a high-pressure reaction kettle, react at 180°C for 8 h, take it out, and after naturally cooling to room temperature, wash the generated precipitate with deionized water and ethanol by centrifugation multiple times (10,000 rpm, 10 min) to obtain a solid product. Dry the product at 60 - 80°C overnight, and calcine the obtained powder in air at a rate of 5 °C / min -1 at 350°C for 2 h, take it out after cooling to room temperature, and obtain the Tm-Cu@In2O3 sensitive material powder.

[0041] Example 2

[0042] The preparation of the Tm-Cu@In2O3 sensitive material is similar to that of Example 1, except that the addition amounts of TmCl3·6H2O and Cu(NO3)2 are each 2 mol%.

[0043] Example 3

[0044] The preparation of the Tm-Cu@In2O3 sensitive material is similar to that of Example 1, except that the addition amounts of TmCl3·6H2O and Cu(NO3)2 are each 4 mol%.

[0045] Example 4

[0046] The preparation of the Tm-Cu@In2O3 sensitive material is similar to that of Example 1, except that the addition amounts of TmCl3·6H2O and Cu(NO3)2 are each 6 mol%.

[0047] Example 5

[0048] Preparation of the Tm-Cu@In2O3 nanospherical composite gas sensor

[0049] Take the Tm-Cu@In2O3 sensitive material powder, and the mass ratio with absolute ethanol is 0.2:1. Mix to form a paste-like slurry. Then, dip a small amount of the slurry with a brush and evenly coat it on the outer surface of the ceramic tube with two gold electrodes and four platinum wires. The coating thickness is 25 μm, so that it completely covers the outer surface of the ceramic tube and the two end gold electrodes. Subsequently, let the ceramic tube substrate coated with the sensitive material dry naturally at room temperature. After the sensitive material is dried, weld the platinum wire connected to the gold electrode on the surface of the ceramic tube to the measuring electrode of the hexagonal base, and then cap and encapsulate it to obtain the H2S gas sensor element based on the Tm-Cu@In2O3 sensitive material. Finally, place the fabricated gas sensing element on the aging table and age it for 12 h under a heating current of 110 mA in an air environment.

[0050] Example 6

[0051] The preparation of the Tm-Cu@In2O3 nanospherical composite gas sensor is similar to that of Example 5, except that the mass ratio of the Tm-Cu@In2O3 sensitive material powder to absolute ethanol is 0.1:1, and the coating thickness is 30 μm.

[0052] Example 7

[0053] Preparation of the Tm-Cu@In2O3 nano-spherical composite gas sensor is similar to Example 5, except that the mass ratio of the Tm-Cu@In2O3 sensitive material powder to absolute ethanol is 0.5:1, and the coating thickness is 15 μm.

[0054] Experiment 1: Dynamic response test between four example sensors and H2S concentration

[0055] The relationship between the sensor response and H2S concentration (2 - 100 ppm) was investigated at 173 °C ( Figure 3 ). As the concentration of H2S gas increased, all sensors showed an increase in the response value to the target gas, and there was no baseline drift. It is worth noting that the responses of the sensors in Example 3 and Example 4 showed a jump-like increase as the gas concentration increased. In particular, the response degree of Example 3 was the best, indicating that the gas sensing performance of the Tm-Cu@In2O3 sensitive material of the present invention has been greatly improved. The dynamic response fitting curve is as Figure 4 shown. The linearity and fitting degree (R 2 ) of each example were relatively high, indicating a good relationship between the H2S response value and the concentration of the example sensors.

[0056] Experiment 2: Selectivity test of the sensor in Example 3

[0057] Subsequent experimental studies were carried out using Example 3 with the best response degree. The selectivity of the sensor in Example 3 to 20 ppm H2S and 100 ppm of other interfering gases was tested at 173 °C and compared with the sensor in Example 1 ( Figure 5 ). The two example sensors were successively exposed to 20 ppm H2S gas and 12 gases such as 100 ppm CO, SO2, NO2, CO2, CH4, and CH2O. The results showed that the response value of the sensor in Example 3 to H2S gas was significantly higher than that of other gases, and the response value (781.97) was 7 times that of the sensor in Example 1 (112.58), indicating its excellent selectivity to H2S.

[0058] Experiment 3: Humidity resistance test of the sensor in Example 3

[0059] Figure 6 The sensing response of the sensor in Example 3 to H2S (20 ppm) at different relative humidities (RH) at 173 °C. As shown, the response of the sensor to H2S remained at a relatively high response value at 50% - 65% RH. After exceeding 65% RH, the response decreased more significantly, but at 95% RH, the sensor in Example 3 could still achieve a response value of 94.37. This indicates that the sensor has good humidity resistance.

[0060] Experiment 4: Long-term stability test of the sensor in Example 3

[0061] As Figure 7 shown, the response of the sensor of Example 3 to 100 ppm H2S was tested at 173°C. With a 5-day test cycle, during the 30-day period, the response value of the sensor of Example 3 remained at a relatively high level all the time, and the overall change was stable, indicating its good long-term stability.

[0062] Test 5: Repeatability cycle test of the sensor of Example 3

[0063] On the 30th day, the sensor of Example 3 was placed in an environment of 173°C and 20 ppm H2S for five consecutive cyclic response tests ( Figure 8 ), and Example 3 showed a good response recovery trend, and the response value did not show obvious attenuation.

[0064] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a Tm-Cu@In2O3 composite material, characterized in that, It includes the following steps: (1) Add indium salt into isopropanol and stir evenly to obtain an indium salt solution; (2) Add glycerol into the indium salt solution, mix well, then add an equal amount of TmCl3·6H2O and Cu(NO3)2, and continuously stir to obtain a mixed solution; (3) Ultrasonically treat the mixed solution, react at a certain temperature, then naturally cool to room temperature, separate the precipitate, and wash it by centrifugation with deionized water and ethanol for multiple times to obtain a solid product; (4) Dry the solid product at 60 - 80 °C overnight, and then calcine it in air at a rate of 5 °C min -1 at 300 - 500 °C for 1.5 - 2.5 h. After cooling to room temperature, the Tm-Cu@In2O3 composite material is obtained.

2. The preparation method of a Tm-Cu@In2O3 composite material according to claim 1, wherein In step (1), the indium salt is selected from one or more of InCl3·4H2O, In(NO3)3·4.5H2O, In(NO3)3·6H2O, and In(NO3)3·nH2O.

3. The preparation method of a Tm-Cu@In2O3 composite material according to claim 1, characterized in that, In step (1), the solid-liquid ratio of the indium salt to isopropanol is 0.5 - 1:30 - 60 g / mL.

4. The preparation method of a Tm-Cu@In2O3 composite material according to claim 1, characterized in that, In step (2), the mass ratio of the indium salt to the glycerol is 0.5 - 1:10 - 30; the addition amounts of TmCl3·6H2O and Cu(NO3)2 are expressed as the molar percentages of Tm and Cu to the indium salt respectively, denoted as x mol%, and x = 0 - 6.

5. The preparation method of a Tm-Cu@In2O3 composite material according to claim 4, characterized in that, The x is 2, 4, or 6.

6. The preparation method of a Tm-Cu@In2O3 composite material according to claim 1, characterized in that, In step (3), the reaction is carried out at 160 - 180 °C for 6 - 10 h.

7. A H2S gas sensor based on Tm-Cu@In2O3 composite material, characterized in that, It consists of a ceramic tube substrate with gold electrodes at both ends, a Tm-Cu@In2O3 composite material coated on the ceramic tube substrate and the gold electrodes, and a nickel-chromium heating coil placed inside the ceramic tube. Among them, The Tm-Cu@In2O3 composite material is the composite material obtained by the preparation method described in any one of claims 1 - 6.

8. A preparation method of a gas sensor, which is the H2S gas sensor based on the Tm-Cu@In2O3 composite material as described in claim 7, characterized in that, It includes the following steps: a. Take the Tm-Cu@In2O3 composite material, mix it with absolute ethanol to form a paste-like slurry; then use a brush to dip a small amount of the slurry and evenly coat it on the outer surface of the ceramic tube with two gold electrodes and four platinum wires, so that it completely covers the outer surface of the ceramic tube and the gold electrodes at both ends; b. Naturally air-dry the ceramic tube substrate coated with the composite material at room temperature. After the composite material is dried, weld the platinum wire connected to the gold electrode on the surface of the ceramic tube to the measurement electrode of the hexagonal base, and then cap and package it to obtain an H2S gas sensor element based on the Tm-Cu@In2O3 composite material; c. Place the fabricated gas sensing element on an aging table and age it for 8 - 12 h under a heating current of 100 - 120 mA in an air environment.

9. The preparation method of a gas sensor according to claim 8, characterized in that, In step a, the mass ratio of the Tm-Cu@In2O3 composite material to absolute ethanol is 0.1 - 0.5:1, and the coating thickness is 10 - 40 μm.

10. Application of a gas sensor in detecting H2S gas, characterized in that, It is the gas sensor obtained by the preparation method described in any one of claims 8 - 9.

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