Preparation method and application of RuO2 / In2O3 gas-sensitive material derived from metal organic framework

Abstract

The invention discloses a preparation method and application of a metal organic framework derived RuO2 / In2O3 gas sensitive material, and the method uses a metal organic framework material MIL-68 as a precursor, and obtains a pure In2O3 material in an annealing process. And then taking pure In2O3 as a substrate, adopting Rucl3.xH2O as a noble metal loading agent, and successfully loading RuO2 nanoparticles on the surface of In2O3 by regulating and controlling parameters such as noble metal loading proportion, reaction conditions and annealing temperature, so as to form the composite RuO2 / In2O3 gas sensitive material. The gas-sensitive element prepared from the gas-sensitive material overcomes the problems of poor moisture resistance, poor selectivity, low sensitivity and the like of the existing sensor, maintains the gas-sensitive characteristic in a high-humidity environment, and has important application value for detecting low-concentration trimethylamine under a high-humidity condition. The preparation method provided by the invention is simple in process, low in manufacturing cost, short in production period and suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal oxide semiconductor gas sensors, and particularly relates to a preparation method of a metal-organic framework-derived RuO 2 / In 2 O 3 gas-sensitive material and its application in the detection of trimethylamine under high humidity conditions. Background Art

[0002] Trimethylamine is a colorless organic compound with a strong fishy smell and high volatility, and is widely used in the fields of medicine, pesticides, and chemical organic raw materials. However, long-term exposure to trimethylamine gas may cause serious discomfort reactions such as nausea, headache, red eyes, and respiratory obstruction, and even cause death at high concentrations. The safe concentrations for humans in long-term and short-term exposure to trimethylamine gas are 5 ppm and 10 ppm, respectively. Since trimethylamine is the gas produced by seafood decay, the freshness of seafood can be judged according to its concentration; when the trimethylamine concentration exceeds 10 ppm, it indicates that the fish is no longer fresh. In addition, by detecting the concentration of sub-ppm-level trimethylamine gas exhaled by patients, their health conditions can be evaluated, which is very important for the diagnosis of kidney diseases. Currently, there are various detection methods such as gas chromatography, spectrophotometry, and liquid chromatography to detect trimethylamine. However, due to high costs and complex test procedures, their application popularity is limited. Therefore, it is crucial to develop a trimethylamine gas sensor with low cost and meeting the requirements of high sensitivity, good selectivity, wide detection range, and simplicity.

[0003] A gas sensor is a device that converts the detected gas type and concentration into an electrical signal that is easier to identify; metal oxide (MOS) sensors have the characteristics of high sensitivity, fast response, and strong environmental adaptability, and are more likely to realize miniaturized and integrated gas detection devices. Among metal oxide semiconductor sensitive materials, the N-type semiconductor In 2 O 3 has characteristics such as a wide bandgap (3.55 - 3.75 eV), stable chemical properties, and high electron mobility; these special properties enable In 2 O 3 to prepare high-performance gas sensors. However, pure In 2 O 3 -based gas sensors have poor selectivity and sensitivity to trimethylamine. Since the environment for detecting trimethylamine is often high humidity, in actual test requirements, pure In 2 O 3 shows poor moisture resistance and usually requires a larger probe in the circuit to achieve the expected effect; therefore, it needs to be improved to increase sensitivity to meet actual test requirements. Summary of the Invention

[0004] Aiming at the problems of poor selectivity, poor moisture resistance and low sensitivity of the current In 2 O 3 -based trimethylamine gas sensor element, this study proposed a preparation method of metal-organic framework-derived RuO 2 / In 2 O 3 gas-sensitive material and applied it to the detection of trimethylamine under high humidity. This method uses the metal-organic framework material MIL-68 as a precursor to obtain pure In 2 O 3 material during the annealing process. Using pure In 2 O 3 as the substrate, Rucl 3 ·xH 2 O is used as the noble metal loading agent. By adjusting parameters such as the noble metal loading ratio, reaction conditions and annealing temperature, RuO 2 O 3 nanoparticles are successfully loaded on the surface of In 2 to form a composite RuO 2 / In 2 O 3 gas-sensitive material. Finally, the material is made into a slurry and coated on the surface of a ceramic tube, and a gas sensor element is prepared after annealing and welding treatments. The obtained element overcomes the problems of poor moisture resistance, poor selectivity and low sensitivity of the existing devices and maintains the gas-sensing characteristics in a high-humidity environment. In addition, the prepared material has the characteristics of small size and large specific surface area. The obtained gas sensor element not only has strong moisture resistance, large sensitivity (338 - 100 ppm) and low detection limit (50 ppb), but also exhibits good repeatability and excellent selectivity. The preparation method proposed in this study has the advantages of simple process, low manufacturing cost and short production cycle, and is suitable for large-scale production.

[0005] The technical solution of the present invention to solve the above technical problems is: designing a preparation method of metal-organic framework-derived RuO 2 / In 2 O 3 gas-sensitive material, which is characterized in that the method includes the following steps:

[0006] Step 1: At room temperature, mix 25 - 35 mL of N,N-dimethylformamide with 0.8 - 3 mmol of terephthalic acid and stir magnetically for 5 - 15 min to obtain a mixed solvent;

[0007] Step 2: Add 0.8 - 1.5 mmol of indium nitrate to the above mixed solvent and stir magnetically at a speed of 400 - 800 rpm / min for 20 - 30 min to obtain a mixed solution;

[0008] Step 3: Transfer the above mixed solution into a 50 - 100 mL autoclave, and carry out hydrothermal reaction at 120 - 160 °C for 2 - 4 h;

[0009] Step 4: Centrifuge the mixed solution after hydrothermal reaction, and alternately centrifuge and wash the obtained turbid liquid with ethanol and N,N - dimethylformamide for 4 - 8 times. Then transfer the turbid liquid obtained from the last centrifugation into an evaporating dish, and dry it in an oven for 2 - 4 h at a drying temperature of 55 - 65 °C to obtain the MIL - 68 precursor material;

[0010] Step 5: Transfer the MIL - 68 precursor material into a muffle furnace, calcine it at 300 - 500 °C for 1.5 - 3 h with a heating rate of 1 - 3 °C / min, and then naturally cool it to room temperature. Collect the annealed powder to obtain the metal - organic - framework - derived In 2 O 3 material;

[0011] Step 6: Take 10 - 25 mg of the above - obtained In 2 O 3 powder and place it in 20 - 40 mL of deionized water together with 2 - 3 mmol of sodium citrate. After ultrasonic treatment for 3 - 5 min, stir magnetically, and while stirring, dropwise add 10 - 65 μL of Rucl 3 ·xH 2 O solution to obtain a mixed solution; the stirring time is 20 - 40 min; the stirring rate is 100 - 200 rpm / min; the concentration of Rucl 3 ·xH 2 O is 0.1 g / mL; the dropping rate of the Rucl 3 ·xH 2 O solution is 0.5 - 1 μL / s;

[0012] Step 7: Centrifuge the mixed solution in Step 6, and alternately wash the obtained precipitate with deionized water and absolute ethanol for 4 - 8 times. Subsequently, place the precipitate in an oven and dry it for 2 - 4 hours at a drying temperature of 55 - 65 °C to obtain the RuO 2 / In 2 O 3 precursor powder;

[0013] Step 8: Place the above - mentioned RuO 2 / In 2 O 3 precursor powder in a muffle furnace, calcine it at 300 - 500 °C for 1.5 - 3 h with a heating rate of 1 - 3 °C / min. After the calcination is completed, naturally cool it to room temperature to obtain the metal - organic - framework - derived RuO 2 / In 2 O3 Gas-sensitive material.

[0014] Furthermore, a RuO derived from a metal-organic framework is designed 2 / In 2 O 3 For the application of the gas-sensitive material, it is characterized in that the RuO 2 / In 2 O 3 The gas-sensitive material is obtained by the above preparation method, and the application method includes the following steps:

[0015] Step 1) Use the above RuO 2 / In 2 O 3 The gas-sensitive material as the gas-sensitive material of the gas-sensitive element to fabricate a side-heated gas-sensitive element;

[0016] Step 2) Connect the above gas-sensitive element to the circuit, apply a working voltage across the two ends of the resistance wire, and obtain different working temperatures of the gas-sensitive element by adjusting the voltage across the resistance wire; two annular metal electrodes connect the detection resistance of the gas-sensitive element and a load resistance in series through their terminals to form a series resistance circuit; a test voltage V is applied across the two ends of this series resistance circuit c， The voltage across the load resistance is the output voltage V out , the value of the load resistance is R 0 , then the resistance value R of the detection resistance l = V c / V out (1 - R 0 ); Without changing the test voltage, the resistance value of the detection resistance will change with the change of the ambient temperature and the type and concentration of the target gas;

[0017] Step 3) Put the above gas-sensitive element into a 1L air bottle, and at the target working temperature, after its resistance value stabilizes, record the resistance value at this time as R a ;

[0018] Step 4) Put the above gas-sensitive element into a gas bottle filled with trimethylamine at a certain concentration, and at the target working temperature, after its resistance stabilizes, record the resistance value at this time as R g ; Then transfer the gas-sensitive element to the air bottle and wait for the reaction between oxygen molecules in the air and gas molecules on the material surface to promote the desorption of gas molecules on the material surface. When the resistance value of the detection resistance of the gas-sensitive element returns to R a , the desorption of the gas-sensitive element is completed;

[0019] Step 5) Use the obtained R a and R g to calculate the sensitivity R of the trimethylamine gas at the current concentrationa / R g ; Using the gas-sensitive element that has completed desorption in step 4), select trimethylamine gas of different concentrations and repeat the process of step 4); record the sensitivity at different concentrations and draw a correlation curve between the trimethylamine gas concentration and the sensitivity at the target operating temperature;

[0020] Step 6) Place the gas sensor that has completed desorption in step 4) in a 1L glass container filled with trimethylamine gas of unknown concentration, wait for the resistance value of its detection resistor to stabilize at the target operating temperature, and record the resistance value at this time as R p ; Calculate sensitivity R a / R p , substitute the sensitivity value into the correlation curve in step 5), and obtain the concentration value of the unknown concentration of trimethylamine gas, thus completing the concentration detection of trimethylamine gas.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention uses the metal organic framework MIL-68 as a precursor and prepares pure In by annealing 2 O 3 Powder. 2 O 3 Powder is the base material, using RuCl 3 ·xH 2 O as a precious metal additive, sodium citrate as a reducing agent, and by regulating In 2 O 3 With RuCl 3 ·xH 2 O mass ratio, amount of sodium citrate, reaction temperature and annealing temperature to achieve the loading of In 2 O 3 The surface of the mesoporous nanorod structure is formed. 2 The electron sensitization effect and the effect of In 2 O 3 The regulation of the morphology is helpful to improve the response performance of the gas sensor to trimethylamine gas. 2 The work function is better than that of indium oxide. 2 Load In 2 O 3 When the electrons are on the surface of RuO 2 To In 2 O 3 Transfer and form a Schottky barrier. Therefore, the number of electrons in the conduction band increases, thereby improving the response performance of the gas sensor.

[0023] (2) The metal organic framework derived RuO prepared by the present invention2 / In 2 O 3 The gas-sensitive material has high sensitivity and excellent selectivity to trimethylamine gas. The gas-sensitive element designed with the prepared gas-sensitive material shows a response value of 338 to 100 ppm trimethylamine gas at 200 °C, and its detection limit can reach 0.05 ppm. The gas-sensitive element has the characteristics of high sensitivity, strong moisture resistance, fast response, good selectivity and stability. Therefore, the metal-organic framework-derived RuO 2 / In 2 O 3 The gas-sensitive material has broad application prospects in the field of trimethylamine detection.

[0024] (3) The metal-organic framework-derived RuO 2 / In 2 O 3 The gas-sensitive material prepared in this invention shows strong moisture resistance. This is because the catalytic effect of RuO 2 regulates the morphology of the In 2 O 3 material, resulting in an increase in its surface defects and further binding of more water molecules. At the same time, the electron sensitization effect of RuO 2 activates the surface sensing region of In 2 O 3 and accelerates the adsorption and desorption process of water molecules. In this way, only a few water molecules participate in the process of competing with trimethylamine for charges, improving the moisture resistance. It should be noted that improving the humidity problem can be applied to the monitoring of fish health status and the diagnosis of kidney diseases; at the same time, it also provides new ideas for detecting trimethylamine in high-humidity environments.

[0025] (4) The metal-organic framework-derived RuO 2 / In 2 O 3 The gas-sensitive material prepared in this invention has the characteristics of easily obtainable and low-cost raw materials, simple process flow, and fast cycle, and is suitable for large-scale production requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to better illustrate the technical solutions of the embodiments of the present invention or the prior art, the following is a brief introduction to the drawings required in the description of the embodiments of the invention or the prior art. The following drawings are the comparative examples and some embodiments of the present invention

[0027] Figure 1The figure shows the structure of the indirectly heated gas sensor; wherein A is a resistance wire, B is an insulating ceramic tube, C is a No. 1 annular metal electrode, D is a No. 2 annular metal electrode, and E is a gas-sensitive material coating; wherein 1 and 2 are connecting pins connected to both ends of the resistance wire, 3 and 5 are connecting pins connected to both ends of the No. 1 metal electrode, and 4 and 6 are connecting pins connected to both ends of the No. 2 metal electrode.

[0028] Figure 2 Schematic diagram of the packaging status of the indirectly heated gas sensor.

[0029] Figure 3 The RuO obtained in Example 2 of the present invention 2 / In 2 O 3 Scanning electron microscope image of gas-sensitive material.

[0030] Figure 4 This is a sensitivity diagram of the gas sensor obtained in Example 1 of the present invention to different gases at a working temperature of 200°C.

[0031] Figure 5 This is a sensitivity diagram of the gas sensor obtained in Example 2 of the present invention to different gases at a working temperature of 200°C.

[0032] Figure 6 This is a sensitivity diagram of the gas sensor obtained in Example 3 of the present invention to different gases at a working temperature of 175°C.

[0033] Figure 7 This is a sensitivity diagram of the gas sensor obtained in Comparative Example 1 of the present invention to different gases at a working temperature of 200°C.

[0034] Figure 8 This is a line graph showing how the sensitivity of the gas sensors obtained in Examples 1-3 of the present invention changes with the concentration of trimethylamine at the optimal temperature.

[0035] Figure 9 The figure is a line graph showing the change in the sensitivity of the gas sensor obtained in Comparative Example 1 of the present invention with respect to the concentration of trimethylamine at 200°C.

[0036] Figure 10 The sensitivity dynamic response curve of the gas sensor obtained in Comparative Example 1 of the present invention to the concentration gradient of trimethylamine at 200°C.

[0037] Figure 11 The sensitivity dynamic response curve of the gas sensor obtained in Example 2 of the present invention to the concentration gradient of trimethylamine at 200°C is shown.

[0038] Figure 12 The sensitivity diagrams of the gas sensors obtained in Examples 1 to 3 of the present invention and Comparative Example 1 at different temperatures are shown.

[0039] Figure 13 This is the dynamic response diagram of the sensitivity of the gas sensor element obtained in Example 2 of the present invention at different relative humidities at 25°C.

[0040] Figure 14 This is the sensitivity diagram of the gas sensor elements obtained in Examples 1 to 3 and Comparative Example 1 of the present invention at different relative humidities at 25°C. Detailed implementation manners

[0041] In order to clearly explain the purpose, improved advantages and technical solutions of the embodiments of the present invention, the following will describe the specific implementation manners in detail and completely with reference to the accompanying drawings. It should be noted that the described embodiments are only part of the embodiments of the present invention, not all; all other invention embodiments that can be obtained without creative labor based on the existing embodiments in the present invention belong to the protection scope of the present invention.

[0042] The present invention provides a preparation method of a metal-organic framework-derived RuO 2 / In 2 O 3 gas-sensitive material, and the method includes the following steps:

[0043] Step 1: At room temperature, mix 25-35 mL of N,N-dimethylformamide with 0.8-3 mmol of terephthalic acid, and stir magnetically for 5-15 min to obtain a mixed solvent;

[0044] Step 2: Add 0.8-1.5 mmol of indium nitrate to the above mixed solvent, and stir magnetically at a speed of 400-800 rpm / min for 20-30 min to obtain a mixed solution;

[0045] Step 3: Transfer the above mixed solution to a 50-100 mL reaction kettle, and carry out hydrothermal reaction at 120-160°C for 2-4 h;

[0046] Step 4: Centrifuge the mixed solution after the hydrothermal reaction, and alternately centrifuge and wash the obtained turbid liquid with ethanol and N,N-dimethylformamide for 4-8 times, and then transfer the turbid liquid obtained by the last centrifugation to an evaporating dish, and dry it in an oven for 2-4 h, and the drying temperature is 55-65°C to obtain the MIL-68 precursor material;

[0047] Step 5: Transfer the MIL-68 precursor material to a muffle furnace, calcine it at 300-500°C for 1.5-3 h, and the heating rate is 1-3°C / min, and then naturally cool it to room temperature, and collect the annealed powder to obtain a metal-organic framework-derived In 2 O 3 material;

[0048] Step 6: Take 10 - 25 mg of the obtained In 2 O 3 powder, place it with 2 - 3 mmol of sodium citrate in 20 - 40 mL of deionized water, perform ultrasonic treatment for 3 - 5 min and then magnetic stirring, and while stirring, dropwise add 10 - 65 μL of Rucl 3 ·xH 2 O solution to obtain a mixed solution; the stirring time is 20 - 40 min; the stirring rate is 100 - 200 rpm / min; the concentration of Rucl 3 ·xH 2 O is 0.1 g / mL; the dropping rate of the Rucl 3 ·xH 2 O solution is 0.5 - 1 μL / s;

[0049] Step 7: Centrifuge the mixed solution in Step 6, and alternately wash the precipitate obtained by centrifugation 4 - 8 times with deionized water and absolute ethanol. Subsequently, place the precipitate in a drying oven and dry it for 2 - 4 hours at a drying temperature of 55 - 65 °C to obtain the RuO 2 / In 2 O 3 precursor powder;

[0050] Step 8: Place the above-mentioned RuO 2 / In 2 O 3 precursor powder in a muffle furnace, calcine it at 300 - 500 °C for 1.5 - 3 h with a heating rate of 1 - 3 °C / min. After the calcination is completed, naturally cool it to room temperature to obtain the metal-organic framework-derived RuO 2 / In 2 O 3 gas-sensitive material.

[0051] In the present invention, aiming at the problems of low sensitivity, poor moisture resistance, poor selectivity, and high detection limit existing in indium oxide-based gas-sensitive elements, the present invention uses metal-organic framework-derived In 2 O 3 as the substrate material, and through the loading and calcination treatment of RuO 2 obtains the MOF-derived RuO 2 / In 2 O 3 nanomaterials. Through morphology analysis and gas-sensing test result analysis, the examples of the present invention have a large specific surface area and defect sites, which helps to increase the number of gas reaction sites. At the same time, RuO 2 plays an electron-sensitizing role and has advantages in constructing an activated sensing layer, which can accelerate the reaction process of gas molecules and reduce the interference of water molecules, and can achieve high-sensitivity sensing of trimethylamine in a high-humidity environment.

[0052] In derived from mesoporous hollow short rod-shaped MOF is used as the substrate material in the present invention 2 O 3 Rucl is used 3 ·xH 2 O as the noble metal dopant. By regulating parameters such as the mass ratio of the two, reaction temperature, drying temperature, stirring rate, etc., RuO 2 nanoparticles are loaded on the surface of In 2 O 3 A Schottky barrier is formed between RuO 2 and In 2 O 3 which accelerates the flow of electrons to the conduction band, thereby improving the sensitivity for trimethylamine detection.

[0053] In the present invention, the preparation of the substrate MOF-derived In 2 O 3 material and the preparation of the MOF-derived RuO 2 / In 2 O 3 material are both carried out at room temperature. The preparation process of the present invention is simple, has low requirements for the preparation environment, short preparation cycle and stable performance, and is suitable for mass production.

[0054] The RuO prepared in the present invention 2 / In 2 O 3 The microstructure of the gas-sensitive material is mesoporous nanorods, the bottom surface of which is a planar hexagon, the average particle size is 100-200 nm, and there are defects and local fractures on the surface.

[0055] The metal-organic framework-derived RuO prepared in this study 2 / In 2 O 3 nanomaterials have excellent sensitivity, moisture anti-interference performance, reduced detection limit and excellent selectivity, etc. The reason is that on the one hand, RuO 2 plays a role in morphology regulation, increasing the specific surface area and the number of defect sites of the material, thereby increasing the number of gas reaction sites and the probability of the main reaction occurring, and the defect sites can also bind water molecules, reducing the probability of side reactions occurring and further enhancing the moisture anti-interference performance; on the other hand, during the construction of the activated sensing layer, due to RuO 2 and In 2 O 3A Schottky barrier effect is formed, the electron transfer speed to the conduction band is accelerated, the response time is significantly reduced, and the response value is increased. At the same time, in the presence of the activated sensing layer, the adsorption and desorption speeds of water molecules on the surface are accelerated, and the probability of side reactions is reduced. In summary, in this study, a nano-sized RuO 2 / In 2 O 3 gas-sensitive material with high sensitivity, moisture anti-interference performance, and excellent selectivity to trimethylamine was successfully prepared.

[0056] Furthermore, the present invention also provides an application of a metal-organic framework-derived RuO 2 / In 2 O 3 gas-sensitive material. The RuO 2 / In 2 O 3 gas-sensitive material is obtained by the above preparation method. The application method includes the following steps:

[0057] Step 1) Use the above RuO 2 / In 2 O 3 gas-sensitive material as the gas-sensitive material of a gas-sensitive element to fabricate a side-heated gas-sensitive element. Specifically, it includes the following steps:

[0058] Step 1.1: Take 1-3 mg of the above RuO 2 / In 2 O 3 gas-sensitive material, add 10-25 μL of deionized water, and mix it into a paste. Then evenly coat it on the surface of the ceramic tube between two annular and parallel metal electrodes of the side-heated gas-sensitive element. The coating thickness is 10-15 μm;

[0059] Step 1.2: Place the ceramic tube coated with the above RuO 2 / In 2 O 3 gas-sensitive material under a drying lamp for 5-10 min, then transfer it to a muffle furnace, calcine it at 300-500 °C for 1.5-3 h, with a heating rate of 1-3 °C / min, and then naturally cool it to room temperature; then weld the ceramic tube to a hexagonal base. The heating wire is located inside the ceramic tube to heat the ceramic tube. The two ends of the heating wire are respectively connected to the No. 1 and No. 2 connection pins of the gas-sensitive element. Each of the two annular metal electrodes has a connection point at both ends of its outer diameter passing through the center of the circle. The 4 connection points are respectively connected to the No. 3, No. 4, No. 5, and No. 6 connection pins of the gas-sensitive element, thus obtaining a gas-sensitive element containing RuO 2 / In 2 O 3 gas-sensitive material.

[0060] In the present invention, a schematic structural diagram of a gas sensor element for detecting trimethylamine is shown in Fig. (2). After annealing treatment, the surface of the ceramic tube is coated with a dense RuO 2 / In 2 O 3 nanomaterial film. The ceramic tube is welded to a rubber base to prepare a semi-direct-heating type gas sensor element. As shown in Fig. (1), the gas sensor element is connected to a circuit through its connection pins No. 1 - No. 6. Among them, connection pins No. 1 and No. 6 connect the resistance wire in parallel to the circuit, so that the resistance wire obtains a working voltage to generate heat to heat the ceramic tube; two connection pins on each annular metal electrode are connected in parallel to form a terminal, and the coating between the two annular metal electrodes is the detection resistor, and the two terminals connect the detection resistor to the circuit.

[0061] According to the change of the resistance value of the detection resistor with the gas concentration in the environment, it can be judged whether there is trimethylamine gas in the environment. It should be noted that the RuO 2 / In 2 O 3 gas-sensitive material prepared by the present invention is not limited to the semi-direct-heating type gas sensor element.

[0062] In the prior art, a metal oxide semiconductor sensor (i.e., a gas sensor element) belongs to a resistive sensor, which uses the change in resistance before and after the adsorption and redox reaction of gas molecules on the surface of the sensing layer to sense the gas. This ability to measure according to the degree of resistance change is called sensitivity, and generally sensitivity is used to evaluate the ability of the gas sensor element to detect the target gas. When the gas sensor element is in an air environment, oxygen molecules in the air will adsorb to the surface of the sensing layer and turn into an adsorbed state, while absorbing electrons in the conduction band. In this way, an electron depletion region is formed, and a high resistance is shown in this state. Mark the resistance of the sensor in the air at this time as R a ; when the target molecule adsorbs to the surface of the sensing layer and reacts with the existing adsorbed state and releases electrons back to the conduction band, the thickness of the electron depletion region decreases, thus presenting a low-resistance state. Mark the resistance of the sensor in the target gas at this time as R g . Therefore, the sensitivity can be defined as the ratio of R a / R g . The response time is the time it takes for the device resistance value to change by 90% of the total resistance change when the sensor is moved from an air atmosphere into a target gas bottle.

[0063] Step 2) Connect the above gas sensor element to a circuit, apply a working voltage across the two ends of the resistance wire, and adjust the voltage across the resistance wire to make the gas sensor element obtain different working temperatures; the two annular metal electrodes connect the detection resistor of the gas sensor element in series with a load resistor through their terminals to form a series resistance circuit. A test voltage V is applied across the two ends of this series resistance circuit c，The voltage across the load resistor is the output voltage V out , and the value of the load resistor is R 0 . Then, the resistance value R l of the detection resistor is equal to V c divided by V out (1 - R 0 ); Without changing the test voltage, the resistance value of the detection resistor will change with the change of the environmental temperature and the type and concentration of the target gas.

[0064] Step 3) Place the above gas-sensitive element into a 1L air bottle. At the target working temperature, after its resistance value stabilizes (that is, the resistance value remains unchanged for a certain period of time, which is 10s in this implementation), record the resistance value at this time as R a ;

[0065] Step 4) Place the above gas-sensitive element into a gas bottle filled with trimethylamine of a certain concentration. At the target working temperature, after its resistance stabilizes, record the resistance value at this time as R g ; Then transfer the gas-sensitive element to the air bottle and wait for the reaction between oxygen molecules in the air and gas molecules on the material surface to promote the desorption of gas molecules on the material surface. When the resistance value of the detection resistor of the gas-sensitive element returns to R a , the desorption of the gas-sensitive element is completed.

[0066] Step 5) Using the obtained R a and R g , calculate the sensitivity R a of trimethylamine gas at the current concentration divided by R g ; Using the gas-sensitive element that has completed desorption in Step 4), select trimethylamine gases with different concentrations and repeat the process of Step 4); Record the sensitivities at different concentrations and plot the correlation curve between the concentration of trimethylamine gas and the sensitivity at the target working temperature.

[0067] Step 6) Place the gas-sensitive element that has completed desorption in Step 4) into a 1L glass container filled with trimethylamine gas of unknown concentration. At the target working temperature, wait for the resistance value of its detection resistor to stabilize and record the resistance value at this time as R p . Calculate the sensitivity R a divided by R p . Substitute this sensitivity value into the correlation curve in Step 5) to obtain the concentration value of the trimethylamine gas of unknown concentration, and complete the concentration detection of the trimethylamine gas.

[0068] The above target working temperature ranges from room temperature to 250 °C.

[0069] To more clearly illustrate the technical solution and advantages of the present invention, the following uses several embodiments to describe a RuO derived from a metal-organic framework2 / In 2 O 3 The preparation and application of the gas-sensitive material will be described in detail.

[0070] Example 1

[0071] This example provides a method for preparing a metal-organic framework-derived RuO 2 / In 2 O 3 gas-sensitive material, and the preparation method includes the following steps:

[0072] Step 1: At room temperature, mix 30 mL of N,N-dimethylformamide and 2 mmol of terephthalic acid, and stir magnetically for 10 min to obtain a mixed solvent;

[0073] Step 2: Add 1.5 mmol of indium nitrate to the above mixed solvent, and stir magnetically at a speed of 600 rpm / min for 30 min to obtain a mixed solution;

[0074] Step 3: Transfer the above mixed solution to a 100 mL reaction kettle and perform a hydrothermal reaction at 120 °C for 2 h;

[0075] Step 4: Centrifuge the mixed solution after the hydrothermal reaction, and alternately centrifuge and wash the resulting turbid solution with ethanol and N,N-dimethylformamide 6 times. Then transfer the turbid solution obtained from the last centrifugation to an evaporating dish, and then dry it in an oven at 60 °C for 2 h to obtain the MIL-68 precursor material;

[0076] Step 5: Transfer the MIL-68 precursor material to a muffle furnace, calcine it at 500 °C for 2 h, with a heating rate of 2 °C / min, and then naturally cool it to room temperature. Collect the annealed powder to obtain the metal-organic framework-derived In 2 O 3 material;

[0077] Step 6: Take 10 mg of the above-obtained In 2 O 3 powder and 2 mmol of sodium citrate and place them in 30 mL of deionized water. After ultrasonic treatment for 5 min, stir magnetically, and while stirring, dropwise add 10 μL of Rucl 3 ·xH 2 O solution to obtain a mixed solution; the stirring time is 30 min; the stirring rate is 200 rpm / min; the concentration of Rucl 3 ·xH 2 O is 0.1 g / mL; the dropping rate of the Rucl 3 ·xH 2 O solution is 1 μL / s;

[0078] Step 7: Centrifuge the mixed solution in Step 6, and wash the precipitate obtained by centrifugation 6 times alternately with deionized water and absolute ethanol. Then place the precipitate in an oven and dry it at 60 °C for 2 h to obtain RuO 2 / In 2 O 3 precursor powder;

[0079] Step 8: Place the above RuO 2 / In 2 O 3 precursor powder in a muffle furnace, calcine it at 500 °C for 2 h with a heating rate of 2 °C / min. After the calcination is completed, cool it naturally to room temperature to obtain a metal-organic framework-derived RuO 2 / In 2 O 3 gas-sensitive material.

[0080] Example 2

[0081] This example provides a method for preparing a metal-organic framework-derived RuO 2 / In 2 O 3 gas-sensitive material, and the preparation method includes the following steps:

[0082] Step 1: At room temperature, mix 30 mL of N,N-dimethylformamide and 2 mmol of terephthalic acid, and stir magnetically for 10 min to obtain a mixed solvent;

[0083] Step 2: Add 1.5 mmol of indium nitrate to the above mixed solvent, and stir magnetically at a speed of 600 rpm for 30 min to obtain a mixed solution;

[0084] Step 3: Transfer the above mixed solution to a 100 mL reaction kettle and carry out a hydrothermal reaction at 120 °C for 2 h;

[0085] Step 4: Centrifuge the mixed solution after the hydrothermal reaction, and alternately centrifuge and wash the obtained turbid liquid 6 times with ethanol and N,N-dimethylformamide. Then transfer the turbid liquid obtained by the last centrifugation to an evaporating dish, and then dry it in an oven for 2 h at a drying temperature of 60 °C to obtain a MIL-68 precursor material;

[0086] Step 5: Transfer the MIL-68 precursor material to a muffle furnace, calcine it at 500 °C for 2 h with a heating rate of 2 °C / min, and then cool it naturally to room temperature. Collect the annealed powder to obtain a metal-organic framework-derived In 2 O 3 material;

[0087] Step 6: Take the obtained In 2 O 3 powder 10 mg and 2 mmol of sodium citrate and place them in 30 mL of deionized water. After ultrasonic treatment for 5 min, stir magnetically and dropwise add 15 μL of Rucl 3 ·xH 2 O solution to the solution to obtain a mixed solution; the stirring time is 30 min; the stirring rate is 200 rpm / min; the concentration of Rucl 3 ·xH 2 O is 0.1 g / mL; the dropping rate of Rucl 3 ·xH 2 O solution is 1 μL / s;

[0088] Step 7: Centrifuge the mixed solution in Step 6, and alternately wash the precipitate obtained by centrifugation with deionized water and absolute ethanol 6 times. Then place the precipitate in a drying oven and dry it for 2 h at a drying temperature of 60 °C to obtain RuO 2 / In 2 O 3 precursor powder;

[0089] Step 8: Place the above RuO 2 / In 2 O 3 precursor powder in a muffle furnace and calcine it at 500 °C for 2 h with a heating rate of 2 °C / min. After the calcination is completed, cool it naturally to room temperature to obtain a metal-organic framework-derived RuO 2 / In 2 O 3 gas-sensitive material;

[0090] The scanning electron microscope (SEM) image of the metal-organic framework-derived RuO 2 / In 2 O 3 gas-sensitive material obtained in this example is as shown in Figure 3 , and its morphology presents a mesoporous hollow short rod structure with a hexagonal bottom surface. Due to the hollow structure, local damage may occur during the reaction.

[0091] Example 3

[0092] This example provides a method for preparing a metal-organic framework-derived RuO 2 / In 2 O 3 gas-sensitive material, and the preparation method includes the following steps:

[0093] Step 1: At room temperature, mix 30 mL of N,N-dimethylformamide and 2 mmol of terephthalic acid and stir magnetically for 10 min to obtain a mixed solvent;

[0094] Step 2: Add 1.5 mmol of indium nitrate into the above-mentioned mixed solvent, and magnetically stir for 30 min at a speed of 600 rpm / min to obtain a mixed solution;

[0095] Step 3: Transfer the above-mentioned mixed solution to a 100 mL autoclave and carry out hydrothermal reaction at 120 °C for 2 h;

[0096] Step 4: Centrifuge the mixed solution after the hydrothermal reaction, and alternately centrifuge and wash the resulting turbid solution with ethanol and N,N-dimethylformamide for 6 times. Then transfer the turbid solution obtained from the last centrifugation to an evaporating dish, and then dry it in an oven at 60 °C for 2 h to obtain the MIL-68 precursor material;

[0097] Step 5: Transfer the MIL-68 precursor material to a muffle furnace, calcine it at 500 °C for 2 h with a heating rate of 2 °C / min, and then naturally cool it to room temperature. Collect the annealed powder to obtain the metal-organic framework-derived In 2 O 3 material;

[0098] Step 6: Take 10 mg of the above-obtained In 2 O 3 powder and 2 mmol of sodium citrate and place them in 30 mL of deionized water. After ultrasonic treatment for 5 min, magnetically stir, and while stirring, dropwise add 20 μL of Rucl 3 ·xH 2 O solution to obtain a mixed solution; the stirring time is 30 min; the stirring rate is 200 rpm / min; the concentration of Rucl 3 ·xH 2 O is 0.1 g / mL; the dropping rate of the Rucl 3 ·xH 2 O solution is 1 μL / s;

[0099] Step 7: Centrifuge the mixed solution in Step 6, and alternately wash the obtained precipitate with deionized water and absolute ethanol for 6 times. Then place the precipitate in an oven and dry it for 2 h at 60 °C to obtain the RuO 2 / In 2 O 3 precursor powder;

[0100] Step 8: Place the above-mentioned RuO 2 / In 2 O 3 precursor powder in a muffle furnace, calcine it at 500 °C for 2 h with a heating rate of 2 °C / min. After the calcination is completed, naturally cool it to room temperature to obtain the metal-organic framework-derived RuO2 / In 2 O 3 Gas-sensitive material;

[0101] Comparative Example 1

[0102] This example provides a preparation method of a metal-organic framework-derived In 2 O 3 gas-sensitive material, and the preparation method includes the following steps:

[0103] Step 1: At room temperature, mix 30 mL of N,N-dimethylformamide and 2 mmol of terephthalic acid, and stir magnetically for 10 min to obtain a mixed solvent;

[0104] Step 2: Add 1.5 mmol of indium nitrate to the above mixed solvent, and stir magnetically at a speed of 600 rpm for 30 min to obtain a mixed solution;

[0105] Step 3: Transfer the above mixed solution to a 100 mL reaction kettle and perform hydrothermal reaction at 120 °C for 2 h;

[0106] Step 4: Centrifuge the mixed solution after the hydrothermal reaction, and alternately centrifuge and wash the turbid solution obtained after centrifugation 6 times with ethanol and N,N-dimethylformamide. Then transfer the turbid solution obtained by the last centrifugation to an evaporating dish, and then dry it in an oven for 2 h at a drying temperature of 60 °C to obtain the MIL-68 precursor material;

[0107] Step 5: Transfer the MIL-68 precursor material to a muffle furnace, calcine it at 500 °C for 2 h with a heating rate of 2 °C / min, and then naturally cool it to room temperature. Collect the annealed powder to obtain the metal-organic framework-derived In 2 O 3 gas-sensitive material.

[0108] The above examples are only for illustration and do not play a restrictive role. Any equivalent modification or change without departing from the spirit and scope of the present invention shall be included in the scope of the claims of this application.

[0109] The three metal-organic framework-derived RuO 2 / In 2 O 3 gas-sensitive materials obtained in Example 1, Example 2, and Example 3, as well as the metal-organic framework-derived In 2 O 3 gas-sensitive material obtained in Comparative Example 1 are used as gas-sensitive materials, and are respectively prepared into a side-heated gas-sensitive element according to the following method:

[0110] Step 1: Take 2 mg of a gas-sensitive material as described above, add 10 μL of deionized water to make a paste, and then evenly coat it on the surface of a ceramic tube between two annular and parallel metal electrodes of a indirectly heated device, with a coating thickness of 10 μm;

[0111] Step 2: Place the ceramic tube coated with the above-mentioned gas-sensitive material under a drying lamp for 10 minutes, then transfer it to a muffle furnace, calcine it at 500°C for 2 hours, with a heating rate of 2°C / min, and then cool it naturally to room temperature; then weld the ceramic tube to the hexagonal base, and the resistance wire is located inside the ceramic tube to heat the ceramic tube. The two ends of the resistance wire are respectively connected to the No. 1 and No. 2 connecting pins of the gas-sensitive element. Two annular metal electrodes are respectively provided with a connection point at both ends of the outer diameter passing through the center of the circle. The four connection points are respectively connected to the No. 3, No. 4, No. 5, and No. 6 connecting pins of the ceramic tube to obtain a gas-sensitive element containing the corresponding gas-sensitive material.

[0112] That is, four gas sensors are obtained from Example 1, Example 2, Example 3, and Comparative Example 1, and the preparation methods of the above gas sensors are prior art.

[0113] The gas-sensitive element is tested for its gas-sensitive properties using a gas-sensitive test system (FLUKE). The gas-sensitive test system (FLUKE) is a prior art. The test conditions are set as follows:

[0114] A) Measure the sensitivity of the gas sensors of four gas-sensitive materials to ethanol, methanol, acetone, trimethylamine, triethylamine, formaldehyde and toluene at a certain working temperature. The concentration of the above gases is 100ppm. Record the sensitivity of each gas at this time and draw a gas selectivity bar graph. Then change the reaction temperature and repeatedly measure the sensitivity of the above different gases at 100ppm. Draw a gas selectivity bar graph at this temperature. The measurement results are shown in Figures 4 - 7 The results show that the sensitivity of the gas sensor obtained by the preparation method of the present invention to trimethylamine is improved by at least 5 times, and the selectivity is significantly improved.

[0115] Figure 4 The sensitivity test diagram of the gas sensor obtained in Example 1 of the present invention to different gases at the optimal temperature of 200°C shows that the response to trimethylamine gas is significantly better than that to other gases. At this time, the response of the gas sensor to 100ppm trimethylamine is 145; at a temperature of 200°C, Figure 5 The results show that compared with other interfering gases, the gas sensor obtained in Example 2 of the present invention exhibits higher sensitivity to trimethylamine, and the sensitivity of the gas sensor to 100 ppm trimethylamine reaches 338.

[0116] like Figure 6As shown, it can be seen that the gas sensor element obtained in Example 3 of the present invention has a significantly better response to trimethylamine gas than other gases. At this time, the response of the gas sensor element to 100 ppm trimethylamine is 160. It is worth noting that the operating temperature of the gas sensor element obtained in Example 3 of the present invention drops to 175 °C, which is suitable for low-power consumption detection.

[0117] B) Measure the sensitivity of the gas sensor elements prepared from four gas-sensitive materials to 100 ppm trimethylamine gas at different temperatures, record the sensitivity of 100 ppm trimethylamine gas at different temperatures until the sensitivity value reaches the maximum. At this time, the temperature is the optimal operating temperature of the gas sensor element, and plot the relationship between the sensitivity of trimethylamine gas and temperature; The measurement results are as Figure 12 shown. It can be seen that the optimal operating temperature of the gas sensor element obtained in Comparative Example 1 and the gas sensor elements obtained in Examples 1-2 is 200 °C, and the optimal operating temperature of the gas sensor element obtained in Example 3 is 175 °C, indicating that as the RuO 2 loading increases, it has the effect of reducing the operating temperature. The sensitivity of the gas sensor elements obtained in Examples 1-3 is much greater than that of the gas sensor element obtained in Comparative Example 1, indicating that RuO 2 loading improves the sensitivity of In 2 O 3 .

[0118] C) Measure the sensitivity of the gas sensor elements prepared from four gas-sensitive materials to different concentrations of trimethylamine at their optimal operating temperatures. The measurement results are as Figures 8 - 9 shown. It can be seen that the linearity is good, and it is piecewise linear at 0.05 ppm - 1 ppm and 10 ppm - 100 ppm. This phenomenon is suitable for application in devices for detecting trimethylamine in the environment;

[0119] In addition, Figure 11 shows the dynamic sensitivity curve of the gas sensor element obtained in Example 2 of the present invention to the trimethylamine concentration gradient. It can be observed that the detection limit of trimethylamine is 50 ppb, indicating that the gas sensor element obtained in Example 2 of the present invention has an extremely low detection limit.

[0120] D) Measure the sensitivity of the gas sensor elements prepared from four gas-sensitive materials to 100 ppm at 25 °C and different relative humidities. The results are as Figure 14 shown. As the relative humidity increases, the sensitivity of the gas sensor elements obtained in Examples 1-3 changes less and remains stable overall. On the contrary, the sensitivity of the gas sensor element obtained in Comparative Example 1 decreases sharply as the relative humidity increases, indicating that the gas-sensitive material in Comparative Example 1 has poor moisture resistance. By comparing the sensitivity curves of the gas sensor elements obtained in Comparative Example 1 and Examples 1-3 with respect to the change in relative humidity, it can be seen that RuO 2 loading improves the moisture resistance of In 2 O 3 .

[0121] Under different relative humidity conditions (see Figure 13 ), the gas-sensitive elements obtained in Example 2 showed stable and consistent sensitivity dynamic response characteristics, which proved that the gas-sensitive material prepared in Example 2 of the present invention has strong moisture resistance.

[0122] By performing gas-sensing tests on the gas-sensitive elements obtained in each embodiment of the present invention, the sensitivity value to 100 ppm trimethylamine at 200 °C is extremely high (338), and the sensitivity response time to trimethylamine is extremely short (3 s). At the same time, the gas-sensitive elements provided in the embodiments of the present invention have good moisture resistance. When the gas-sensitive element detects trimethylamine at a relative humidity of 80% RH, its sensitivity value can reach 88% of the sensitivity value under normal humidity, belonging to the category of high moisture resistance. In addition, this gas-sensitive element has excellent properties such as good cross-selectivity, a low detection limit (50 ppb), and excellent selectivity.

[0123] In this study, a liquid-phase synthesis method was successfully used to prepare an In 2 O 3 metal-organic framework MIL-68 precursor, and an In 2 O 3 nanomaterial with a metal-organic framework structure was obtained by annealing. On this basis, deionized water was innovatively used as a solvent, sodium citrate as a reducing agent, and Rucl 3 ·xH 2 O as a noble metal ligand, and a RuO 2 / In 2 O 3 composite nanomaterial for gas sensing was successfully synthesized. The material is in the shape of mesoporous hollow short rods with a hexagonal bottom surface structure, an average particle size of about 100 - 200 nm, and shows a certain degree of surface defects and microfractures compared with the pure material.

[0124] Matters not described in the present invention apply to the prior art.

Claims

1. A method for preparing a metal organic framework derived RuO2 / In2O3 gas sensitive material, characterized in that: The method comprises the following steps: Step 1: At room temperature, 25-35 mL of N,N-dimethylformamide and 0.8-3 mmol of terephthalic acid were mixed and magnetically stirred for 5-15 min to obtain a mixed solvent; Step 2: adding 0.8-1.5 mmol of indium nitrate to the above mixed solvent, and magnetically stirring at a speed of 400-800 rpm / min for 20-30 min to obtain a mixed solution; Step 3: Transfer the mixed solution to a 50-100 mL reactor and perform a hydrothermal reaction at 120-160° C. for 2-4 h; Step 4: centrifuge the mixed solution after the hydrothermal reaction, and wash the turbid liquid obtained after the centrifugation with ethanol and N,N-dimethylformamide alternately by centrifugation for 4 to 8 times, and then transfer the turbid liquid obtained by the last centrifugation to an evaporating dish, and then dry it in a drying oven for 2 to 4 hours at a drying temperature of 55 to 65° C. to obtain a MIL-68 precursor material; Step 5: The MIL-68 precursor material is transferred to a muffle furnace, calcined at 300-500°C for 1.5-3h, with a heating rate of 1-3°C / min, and then naturally cooled to room temperature, and the annealed powder is collected to obtain a metal organic framework-derived In2O3 material; Step 6: Take 10-25 mg of the In2O3 powder obtained above, place it with 2-3 mmol of sodium citrate in 20-40 mL of deionized water, ultrasonicate it for 3-5 min, stir it magnetically, and add 10-65 μL of Rucl3·xH2O solution while stirring to obtain a mixed solution; the stirring time is 20-40 min; the stirring rate is 100-200 rpm / min; the concentration of Rucl3·xH2O is 0.1 g / mL; the dripping rate of the Rucl3·xH2O solution is 0.5-1 μL / s; Step 7: centrifuge the mixed solution in step 6, and wash the precipitate obtained by centrifugation with deionized water and anhydrous ethanol alternately for 4 to 8 times, then place the precipitate in a drying oven and dry it for 2 to 4 hours at a drying temperature of 55 to 65° C. to obtain RuO2 / In2O3 precursor powder; Step 8: Place the above-mentioned RuO2 / In2O3 precursor powder in a muffle furnace and calcine it at 300-500°C for 1.5-3h with a heating rate of 1-3°C / min. After the calcination is completed, cool it naturally to room temperature to obtain the metal organic framework-derived RuO2 / In2O3 gas-sensitive material.

2. The method for preparing a metal organic framework derived RuO2 / In2O3 gas sensitive material according to claim 1, characterized in that: The method comprises the following steps: Step 1: At room temperature, 30 mL of N,N-dimethylformamide and 2 mmol of terephthalic acid were mixed and magnetically stirred for 10 min to obtain a mixed solvent; Step 2: Add 1.5 mmol of indium nitrate to the above mixed solvent, and stir magnetically at 600 rpm / min for 30 min to obtain a mixed solution; Step 3: Transfer the mixed solution to a 100 mL reactor and perform hydrothermal reaction at 120 °C for 2 h; Step 4: centrifuge the mixed solution after the hydrothermal reaction, and wash the turbid solution obtained after the centrifugation with ethanol and N,N-dimethylformamide alternately by centrifugation for 6 times, and then transfer the turbid solution obtained by the last centrifugation to an evaporating dish, and then dry it in a drying oven for 2 hours at a drying temperature of 60°C to obtain a MIL-68 precursor material; Step 5: The MIL-68 precursor material was transferred to a muffle furnace and calcined at 500°C for 2 h at a heating rate of 2°C / min, then naturally cooled to room temperature, and the annealed powder was collected to obtain a metal organic framework-derived In2O3 material; Step 6: Take 10 mg of the In2O3 powder obtained above and 2 mmol of sodium citrate and place them in 30 mL of deionized water. After ultrasonic treatment for 5 min, stir them magnetically. Add 15 μL of Rucl3·xH2O solution to the solution while stirring to obtain a mixed solution. The stirring time is 30 min. The stirring rate is 200 rpm / min. The concentration of Rucl3·xH2O is 0.1 g / mL. The dripping rate of the Rucl3·xH2O solution is 1 μL / s. Step 7: centrifuge the mixed solution in step 6, and wash the precipitate obtained by centrifugation with deionized water and anhydrous ethanol alternately for 6 times, then place the precipitate in a drying oven and dry it for 2 hours at a drying temperature of 60°C to obtain RuO2 / In2O3 precursor powder; Step 8: Place the RuO2 / In2O3 precursor powder in a muffle furnace and calcine at 500°C for 2 hours with a heating rate of 2°C / min. After the calcination is completed, cool it naturally to room temperature to obtain the metal organic framework-derived RuO2 / In2O3 gas-sensitive material.

3. A method for preparing a metal organic framework derived RuO2 / In2O3 gas sensitive material according to any one of claims 1-2, characterized in that: The obtained metal organic framework derived RuO2 / In2O3 gas sensitive material has a microscopic morphology of mesoporous nanorods with an average particle size of 100-200 nm, and has defects and local fragmentation on its surface.

4. Application of a metal organic framework derived RuO2 / In2O3 gas sensitive material, characterized in that: The RuO2 / In2O3 gas-sensitive material is obtained by the preparation method according to any one of claims 1 to 2, and the application method comprises the following steps: Step 1) using the RuO2 / In2O3 gas-sensitive material as the gas-sensitive material of the gas-sensitive element to prepare a indirectly heated gas-sensitive element; Step 2) Connect the above-mentioned gas sensor to the circuit, load the working voltage at both ends of the resistance wire, and adjust the voltage at both ends of the resistance wire to make the gas sensor obtain different working temperatures; connect the detection resistor of the gas sensor and a load resistor in series through the connection terminals of the two annular metal electrodes to form a series resistance circuit; connect the test voltage V c， The voltage across the load resistor is the output voltage V out , the load resistance is R0, then the resistance value of the detection resistor is R l =V c / V out (1-R0); Without changing the test voltage, the resistance value of the detection resistor will change with the change of ambient temperature and the type and concentration of the target gas; Step 3) Place the gas sensor in a 1L air bottle and wait for its resistance to stabilize at the target operating temperature. Record the resistance value as R a ; Step 4) Place the gas sensor into a gas bottle containing a certain concentration of trimethylamine, and record the resistance value R after its resistance stabilizes at the target operating temperature. g ; Then transfer the gas sensor to the air bottle and wait for the oxygen molecules in the air to react with the gas molecules on the surface of the material to promote the desorption of the gas molecules on the surface of the material. When the resistance value of the detection resistor of the gas sensor returns to R a When , the desorption of the gas sensor is completed; Step 5) Using the above obtained R a With R g , calculate the sensitivity R of the current concentration of trimethylamine gas a / R g ; Using the gas-sensitive element that has completed desorption in step 4), select trimethylamine gas of different concentrations and repeat the process of step 4); record the sensitivity at different concentrations and draw a correlation curve between the trimethylamine gas concentration and the sensitivity at the target operating temperature; Step 6) Place the gas sensor that has completed desorption in step 4) in a 1L glass container filled with trimethylamine gas of unknown concentration, wait for the resistance value of its detection resistor to stabilize at the target operating temperature, and record the resistance value at this time as R p ; Calculate sensitivity R a / R p , substitute the sensitivity value into the correlation curve in step 5), and obtain the concentration value of the unknown concentration of trimethylamine gas, thus completing the concentration detection of trimethylamine gas.

5. The use of a metal organic framework derived RuO2 / In2O3 gas sensitive material according to claim 4, characterized in that: The target operating temperature range is from room temperature to 250°C.

6. The use of a metal organic framework derived RuO2 / In2O3 gas sensitive material according to claim 4, characterized in that: The production of the indirectly heated gas sensor specifically includes the following steps: Step 1.1: Take 1-3 mg of the RuO2 / In2O3 gas-sensitive material, add 10-25 μL of deionized water, mix into a paste, and then evenly coat the paste on the surface of the ceramic tube between two annular and parallel metal electrodes of the indirectly heated gas-sensitive element, with a coating thickness of 10-15 μm; Step 1.2: Place the ceramic tube coated with the above-mentioned RuO2 / In2O3 gas-sensitive material under a drying lamp for 5 to 10 minutes, then transfer it to a muffle furnace, calcine it at 300 to 500°C for 1.5 to 3 hours, and the heating rate is 1 to 3°C / min, and then naturally cool it to room temperature; then weld the ceramic tube to a hexagonal base, and the resistance wire is located inside the ceramic tube to heat the ceramic tube. The two ends of the resistance wire are respectively connected to the No. 1 and No. 2 connecting pins of the gas sensor, and the two annular metal electrodes are respectively provided with a connection point at both ends of the outer diameter passing through the center of the circle. The four connection points are respectively connected to the No. 3, No. 4, No. 5, and No. 6 connecting pins of the gas sensor, so as to obtain a gas sensor containing RuO2 / In2O3 gas-sensitive material.

7. The use of a metal organic framework derived RuO2 / In2O3 gas sensitive material according to claim 4, characterized in that: The production of the indirectly heated gas sensor specifically includes the following steps: Step 1: Take 2 mg of the RuO2 / In2O3 gas-sensitive material, add 10 μL of deionized water to make a paste, and then evenly coat it on the surface of the ceramic tube between two annular and parallel metal electrodes of the indirectly heated device, with a coating thickness of 10 μm; Step 2: Place the ceramic tube coated with the above-mentioned gas-sensitive material under a drying lamp for 10 minutes, then transfer it to a muffle furnace, calcine it at 500°C for 2 hours, with a heating rate of 2°C / min, and then cool it naturally to room temperature; then weld the ceramic tube to a hexagonal base, and the resistance wire is located inside the ceramic tube to heat the ceramic tube. The two ends of the resistance wire are respectively connected to the No. 1 and No. 2 connecting pins of the gas-sensitive element. Two annular metal electrodes are each provided with a connection point at both ends of the outer diameter passing through the center of the circle. The four connection points are respectively connected to the No. 3, No. 4, No. 5, and No. 6 connecting pins of the ceramic tube, thereby obtaining a gas-sensitive element containing RuO2 / In2O3 gas-sensitive material.

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