CuO / In2O3 two-dimensional porous nanosheet gas-sensitive material, gas-sensitive element and application of CuO / In2O3 two-dimensional porous nanosheet gas-sensitive material

Abstract

The invention discloses a CuO / In2O3 two-dimensional porous nanosheet gas sensitive material, a gas sensitive element and application of the gas sensitive element. A mixture of deionized water, ethanol and ethylene glycol is used as a solvent, indium nitrate is used as a precursor, and two-dimensional porous flaky indium oxide is obtained through hydrothermal and calcination treatment. Then, indium oxide is used as a matrix, copper oxide nanoparticles are compounded on the surface, and the CuO / In2O3 composite gas-sensitive material is obtained. The composite gas-sensitive material is a two-dimensional porous sheet, the two-dimensional porous sheet has a large effective surface area, the porous structure provides a rapid and continuous charge transfer channel and a gas diffusion channel, and CuO provides an alkaline site for adsorption of acidic H2S gas, so that the gas-sensitive material can be used as a gas-sensitive material for adsorption of acidic H2S gas. The CuO / In2O3 gas sensor has the advantages of high sensitivity, high selectivity, fast response and low detection limit on H2S gas at room temperature. The CuO / In2O3 composite gas-sensitive material prepared by the invention has a wide application prospect in the aspect of H2S gas detection, and the CuO / In2O3 composite gas-sensitive material is simple in synthesis process, short in synthesis time, low in cost and suitable for mass production.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal oxide semiconductor gas sensitive sensors, and specifically relates to a CuO / In2O3 two-dimensional porous nano-thin sheet gas sensitive material, a gas sensitive element and applications thereof. Background Art

[0002] Hydrogen sulfide (H2S) is a highly toxic, flammable, acidic gas that comes primarily from petroleum refining, decomposition of sulfur-containing organic matter, coal gasifiers, petrochemical plants, and natural gas processing. H2S can cause explosions and fires when exposed to open flames or high temperatures. Long-term exposure to H2S at even ppb levels can damage the respiratory system. Short-term exposure to high concentrations of H2S can also cause headaches, apnea, myocardial damage, coma, and even death. In addition, H2S can serve as a signal factor for certain disease states. For example, the H2S concentration in the exhaled gas of patients with periodontal disease is higher than 250 ppb. Currently, methods for detecting H2S, such as fluorescent probes, electrochemiluminescence, and chemical methods, are relatively complex and costly. Therefore, there is an urgent need to develop a cost-effective gas sensor that can perform high-performance detection of low-concentration H2S at room temperature.

[0003] Indium oxide (In2O3) is a cost-effective n-type semiconductor with a wide bandgap and excellent optoelectronic properties, and is often used for H2S detection. However, pure In2O3 still has problems such as high operating temperature, low response, slow response and poor selectivity. Summary of the invention

[0004] The present invention aims at the many shortcomings of the current In2O3-based H2S gas sensor, such as high operating temperature, poor selectivity, low sensitivity, and high detection limit, and provides a CuO / In2O3 two-dimensional porous nanosheet gas-sensitive material, a gas-sensitive element, and its application. A simple hydrothermal method and annealing process are used to obtain pure In2O3 material, and the obtained In2O3 is immersed in a copper nitrate solution of a certain concentration, and an annealing process is performed to obtain a composite gas-sensitive material of CuO and In2O3. The obtained material is made into a gas-sensitive element through coating, welding and other processes. The gas-sensitive element realizes room temperature detection of H2S, overcoming the problems of poor selectivity, low sensitivity, and high detection limit. The material powder obtained by the present invention has a two-dimensional porous structure. The prepared sensor can quickly identify low-concentration H2S at room temperature with high selectivity and high sensitivity.

[0005] The technical solution of the present invention to solve the technical problem is: designing a CuO / In2O3 two-dimensional porous nanosheet gas-sensitive material, characterized in that the gas-sensitive material is prepared by the following steps:

[0006] Step 1: At room temperature, mix 5-15 mL of deionized water, 5-15 mL of ethanol and 5-15 mL of ethylene glycol, and stir magnetically for 5-10 minutes to obtain a mixed solvent;

[0007] Step 2: Add 0.8-1.5 mmol indium nitrate to the above mixed solvent, stir magnetically for 20-30 min at a stirring rate of 500-800 rpm to obtain a mixed solution;

[0008] Step 3: Transfer the mixed solution to a 50-100 mL reactor and perform a hydrothermal reaction at 130-180°C for 13-18 hours;

[0009] Step 4: centrifuging the solution obtained by the hydrothermal reaction, and washing the precipitate obtained by centrifugation with deionized water and ethanol alternately for 4-8 times, and then placing the precipitate in a drying oven and drying it for 3-6 hours at a drying temperature of 55-65° C. to obtain a first precipitate powder;

[0010] Step 5: placing the first precipitate powder in a muffle furnace, calcining at 400-600° C. for 1.5-3 h at a heating rate of 1-3° C. / min, and then naturally cooling to room temperature to obtain a first calcined powder;

[0011] Step 6: 15-30 mg of the powder after the first calcination is placed in 15-30 mL of deionized water, subjected to ultrasonic treatment for 3-5 min, and then magnetically stirred, and 100-800 μL of copper nitrate solution is added while stirring to obtain a mixed suspension; the stirring time is 15-30 hours, the stirring rate is 100-200 rpm / min; the concentration of copper nitrate is 15-30 mg / mL; the dripping rate of the copper nitrate solution is 0.5-1 μL / s;

[0012] Step 7: centrifuging the mixed suspension, and washing the precipitate obtained by centrifugation with deionized water and ethanol alternately for 4-8 times, and then placing the precipitate in a drying oven for 3-6 hours at a drying temperature of 55-65° C. to obtain a second precipitate powder;

[0013] Step 8: Place the second precipitate powder in a muffle furnace, calcine at 300-600°C for 1.5-3h with a heating rate of 1-3°C / min, and then cool naturally to room temperature to obtain a CuO / In2O3 gas-sensitive material.

[0014] Furthermore, the present invention provides a gas sensor, which is a indirectly heated gas sensor, characterized in that the gas sensor is prepared by using the CuO / In2O3 gas-sensitive material as described above, and the preparation method thereof comprises the following steps:

[0015] Step 1: Take 1-3 mg of the above-mentioned CuO / In2O3 gas-sensitive material, add 10-20 μL of deionized water, mix into a paste, and evenly coat it on the surface of the ceramic tube between two annular and parallel metal electrodes of the indirectly heated gas-sensitive element; the coating thickness is 8-15 μm;

[0016] Step 2: Place the ceramic tube coated with the above-mentioned CuO / In2O3 gas-sensitive material under a drying lamp for 5-10 minutes, place it in a muffle furnace, anneal it at 400-600℃ for 1.5-3 hours, and the heating rate is 1-3℃ / min, and then naturally cool it to room temperature; then weld the ceramic tube to the hexagonal base, and set the resistance wire inside the ceramic tube to heat the ceramic tube. The two ends of the resistance wire are connected to the No. 1 and No. 6 connecting pins respectively through platinum wires. 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. 2, No. 3, No. 4, and No. 5 connecting pins through platinum wires to obtain a gas-sensitive element containing CuO / In2O3 gas-sensitive material.

[0017] Furthermore, the present invention provides an application of a gas sensor, characterized in that the gas sensor as described above is used, and the application process specifically includes the following steps:

[0018] Step 1: Connect the above gas sensor to the circuit, load the working voltage at both ends of the resistance wire, so that the resistance wire heats up and the gas sensor obtains different working temperatures; two annular metal electrodes connect the detection resistor of the gas sensor with a load resistor in series through their terminals to form a series resistance circuit, and the test voltage V is supplied to both ends of the series resistance circuit. c , the voltage across the load resistor is the output voltage V out , the resistance value of the detection resistor R1=V c / V out (1-R0), R0 is the resistance value of the load resistor; at the test voltage V c Under the condition of no change, the resistance value of the detection resistor changes with the temperature in the environment and the type and concentration of the target gas;

[0019] Step 2: Place the gas sensor in a 1L air bottle. At room temperature, wait for the resistance value of the gas sensor's detection resistor to stabilize and record the resistance value at this time as R a ;

[0020] Step 3: Transfer the gas sensor to a 1L glass container filled with a certain concentration of target gas, wait for the resistance value of the detection resistor to stabilize, and record the resistance value at this time as R g; Then transfer the gas sensor back to the air bottle. After 1-3 minutes, if the resistance value of the gas sensor's detection resistor changes by less than 1% of the stable resistance value in the air bottle, adjust the current on the resistance wire to 110-150mA. When the resistance value of the gas sensor's detection resistor stabilizes to R1, reduce the current on the resistance wire to 0mA and wait for the resistance value of the gas sensor's detection resistor to return to the initial resistance value R a , the desorption of the gas-sensitive element is completed;

[0021] Step 4: Use the obtained R a , R g Calculate the sensitivity S = R a / R g ; Using the gas-sensitive element that has completed desorption in step 3, select target gases of different concentrations, and repeat the process of step 3; according to the sensitivity of target gases of different concentrations, draw a correlation curve between the concentration and sensitivity of the target gas;

[0022] Step 5: Place the desorbed gas sensor in a 1L glass container filled with target gas of unknown concentration, wait for the resistance value of its detection resistor to stabilize, and record the resistance value R0 at this time; calculate the sensitivity R a / R0, substitute the sensitivity value into the correlation curve in step 4 to obtain the concentration value of the target gas of unknown concentration.

[0023] Compared with the prior art, the invention has the following beneficial effects: a CuO / In2O3 two-dimensional porous nanosheet gas-sensitive material of the invention uses a mixture of deionized water, ethanol and ethylene glycol as a solvent, indium nitrate as a precursor, and hydrothermal calcination treatment to obtain a two-dimensional porous thin sheet indium oxide. Indium oxide is used as a matrix, and copper oxide nanoparticles are composited on the surface to obtain a CuO / In2O3 composite gas-sensitive material. The composite gas-sensitive material is a two-dimensional porous thin sheet, the size of the thin sheet is uniform, and the material component distribution is relatively uniform; the two-dimensional porous thin sheet has a large effective surface area, and the porous structure provides a fast and continuous charge transfer channel and a gas diffusion channel, and CuO provides an alkaline site for the adsorption of acidic H2S gas, so that the gas sensor (i.e., gas sensor) prepared by using the CuO / In2O3 composite gas-sensitive material has high sensitivity (30000-60000, concentration is 10ppm H2S vapor), high selectivity, fast response (2-3s) and low detection limit (50-200ppb) to H2S gas at room temperature. The CuO / In2O3 composite gas-sensitive material prepared by the present invention has broad application prospects in detecting H2S gas, and its synthesis process is streamlined, the synthesis time is short, the cost is low, and it is suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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; 1 and 6 are connecting pins connected to both ends of the resistance wire, 2 and 3 are connecting pins connected to both ends of the No. 1 metal electrode, and 4 and 5 are connecting pins connected to both ends of the No. 2 metal electrode.

[0025] Figure 2 The figure shows the packaging state of the indirectly heated gas sensor.

[0026] Figure 3 This is a low-magnification SEM image of the In2O3 gas-sensitive material prepared in the comparative example of the present invention.

[0027] Figure 4 This is a high-magnification SEM image of the In2O3 gas-sensitive material prepared in the comparative example of the present invention.

[0028] Figure 5 This is a low-magnification SEM image of the CuO / In2O3 gas-sensitive material prepared in Example 2 of the present invention.

[0029] Figure 6 This is a high-magnification SEM image of the CuO / In2O3 gas-sensitive material prepared in Example 2 of the present invention.

[0030] Figure 7 This is a TEM morphology photograph of the CuO / In2O3 gas-sensitive material prepared in Example 2 of the present invention.

[0031] Figure 8 This is a high-magnification HRTEM image of the CuO / In2O3 gas-sensitive material prepared in Example 2 of the present invention.

[0032] Fig. 9 These are the XRD diagrams of the In2O3 gas-sensitive material obtained in the comparative example of the present invention and the CuO / In2O3 gas-sensitive materials obtained in Example 1, Example 2, and Example 3.

[0033] Fig.10 This is the response curve of the In2O3 gas sensor in the comparative example of the present invention to 10 ppm H2S at room temperature.

[0034] Fig.11 This is the response curve of the gas sensor obtained in Example 1 of the present invention to 10 ppm H2S at room temperature.

[0035] Fig.12 This is the response curve of the gas sensor obtained in Example 2 of the present invention to 10 ppm of H2S at room temperature.

[0036] Fig.13 This is the response curve of the gas sensor obtained in Example 3 of the present invention to 10 ppm of H2S at room temperature.

[0037] Fig.14 The gas sensing elements prepared by using the In2O3 gas-sensitive material obtained in the comparative example of the present invention and the CuO / In2O3 gas-sensitive material obtained in Example 1, Example 2 and Example 3 have sensitivities to different gases at room temperature.

[0038] Fig.15 The graph is a graph showing the relationship between the sensitivity of the gas sensor obtained in the comparative example of the present invention and the change in concentration.

[0039] Fig.16 The figure is a graph showing the relationship between the sensitivity of the gas sensor obtained in Example 2 of the present invention and the concentration in the low concentration range.

[0040] Fig.17 The graph is a graph showing the relationship between the sensitivity of the gas sensor obtained in Example 2 of the present invention and the concentration in a high concentration range. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further explained below in conjunction with specific implementation cases and drawings.

[0042] The present invention provides a CuO / In2O3 two-dimensional porous nanosheet gas-sensitive material, which is prepared by the following steps:

[0043] Step 1: At room temperature, mix 5-15 mL of deionized water, 5-15 mL of ethanol and 5-15 mL of ethylene glycol, and stir magnetically for 5-10 minutes to obtain a mixed solvent;

[0044] Step 2: Add 0.8-1.5 mmol indium nitrate to the above mixed solvent, stir magnetically for 20-30 min at a stirring rate of 500-800 rpm to obtain a mixed solution;

[0045] Step 3: Transfer the mixed solution to a 50-100 mL reactor and perform a hydrothermal reaction at 130-180°C for 13-18 hours;

[0046] Step 4: centrifuging the solution obtained by the hydrothermal reaction, and washing the precipitate obtained by centrifugation with deionized water and ethanol alternately for 4-8 times, and then placing the precipitate in a drying oven and drying it for 3-6 hours at a drying temperature of 55-65° C. to obtain a first precipitate powder;

[0047] Step 5: placing the first precipitate powder in a muffle furnace, calcining at 400-600° C. for 1.5-3 h at a heating rate of 1-3° C. / min, and then naturally cooling to room temperature to obtain a first calcined powder;

[0048] Step 6: 15-30 mg of the powder after the first calcination is placed in 15-30 mL of deionized water, and after ultrasonic treatment for 3-5 minutes, magnetic stirring is performed, and 100-800 μL of copper nitrate solution is added while stirring to obtain a mixed suspension; the stirring time is 15-30 hours, and the stirring rate is 100-200 rpm / min; the concentration of copper nitrate is 15-30 mg / mL; and the dripping rate of the copper nitrate solution is 0.5-1 μL / s.

[0049] Step 7: centrifuging the mixed suspension, and washing the precipitate obtained by centrifugation with deionized water and ethanol alternately for 4-8 times, and then placing the precipitate in a drying oven for 3-6 hours at a drying temperature of 55-65° C. to obtain a second precipitate powder;

[0050] Step 8: Place the second precipitate powder in a muffle furnace, calcine at 300-600°C for 1.5-3h, with a heating rate of 1-3°C / min, and then naturally cool to room temperature to obtain a CuO / In2O3 gas-sensitive material (i.e., a CuO / In2O3 two-dimensional porous nanosheet gas-sensitive material).

[0051] Furthermore, the present invention provides a gas sensor, which is a indirectly heated gas sensor. The gas sensor is prepared using the above-mentioned CuO / In2O3 gas-sensitive material, and the preparation method thereof comprises the following steps:

[0052] Step 1: Take 1-3 mg of the above-mentioned CuO / In2O3 gas-sensitive material, add 10-20 μL of deionized water, mix it into a paste with a fine brush, and evenly coat it on the surface of the ceramic tube between the two annular and parallel metal electrodes of the indirectly heated gas sensor; the coating thickness is 8-15 μm;

[0053] Step 2: Place the ceramic tube coated with the above-mentioned CuO / In2O3 gas-sensitive material under a drying lamp for 5-10 minutes, then place it in a muffle furnace, anneal it at 400-600℃ for 1.5-3 hours, with a heating rate of 1-3℃ / min, and then cool it naturally to room temperature. Then weld the ceramic tube to the hexagonal base, set the resistance wire inside the ceramic tube to heat the ceramic tube, and connect the two ends of the resistance wire to the No. 1 and No. 6 connection pins through platinum wires, respectively. Two annular metal electrodes are provided with a connection point at both ends of the outer diameter passing through the center of the circle, and the four connection points are connected to the No. 2, No. 3, No. 4, and No. 5 connection pins through platinum wires, and a gas-sensitive element containing CuO / In2O3 gas-sensitive material is obtained.

[0054] The gas sensor is connected to the circuit through its No. 1-No. 6 connection pins, wherein the No. 1 and No. 6 connection pins connect the resistance wire in parallel to the circuit so that the resistance wire obtains the working voltage and generates heat; the two connection pins on each annular metal electrode are connected in parallel to form a terminal, the coating between the two annular metal electrodes is the detection resistor, and the two terminals connect the detection resistor to the circuit.

[0055] The working principle of gas sensors is based on the oxidation and reduction reaction of gas on the surface of semiconductor, which causes the resistance of the sensitive element to change. When the semiconductor device is heated to a stable state, the gas contacts the semiconductor surface, and the adsorbed molecules react with the semiconductor, causing the charge layer on the semiconductor surface to change, thereby changing the carrier concentration of the semiconductor, which ultimately manifests as a change in resistance. The definition of sensitivity is the stable resistance value R of the sensor in the atmosphere. a The stable resistance value R of the sensor in the measured gas atmosphere g Ratio:

[0056] S=R a / R g

[0057] The response time is the time required for the device resistance value to change by 90% of the total change when the sensor device is transferred from air atmosphere to the target gas.

[0058] Furthermore, the present invention provides an application of a gas sensor, using the gas sensor as described above, and the application process specifically includes the following steps:

[0059] Step 1: Connect the above gas sensor to the circuit, load the working voltage at both ends of the resistance wire, so that the resistance wire heats up and the gas sensor obtains different working temperatures; two annular metal electrodes connect the detection resistor of the gas sensor with a load resistor in series through their terminals to form a series resistance circuit, and the test voltage V is supplied to both ends of the series resistance circuit. c , the voltage across the load resistor is the output voltage V out , the resistance value of the detection resistor R1=V c / V out (1-R0), R0 is the resistance value of the load resistor; at the test voltage V c When the resistance of the detection resistor remains unchanged, the resistance value of the detection resistor changes with the temperature in the environment and the type and concentration of the target gas.

[0060] Step 2: Place the gas sensor in a 1L air bottle at room temperature (i.e. no current is required for the resistor wire), wait for the resistance value of the gas sensor's detection resistor to stabilize, and record the resistance value at this time as R a .

[0061] Step 3: Transfer the gas sensor to a 1L glass container filled with a certain concentration of target gas, wait for the resistance value of the detection resistor to stabilize, and record the resistance value at this time as R g Then transfer the gas sensor back 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, causing the gas molecules to desorb on the surface of the material and the resistance value of the gas sensor's detection resistor to rise. The degree of desorption of the gas molecules can be determined based on the real-time resistance value of the gas sensor's detection resistor. After 1-3 minutes, if the resistance value of the gas sensor's detection resistor changes less than the stable resistance value (R a ), it means that the gas sensor cannot desorb autonomously at room temperature and needs to use pulse current to drive the recovery of the element resistance. Then adjust the current on the resistance wire to 110-150mA. At this time, the temperature of the ceramic tube is 225-325℃, and the charge transfer between the gas sensor and H2S is accelerated. Wait for 1-3 minutes until the resistance value of the gas sensor detection resistor stabilizes to R1, then reduce the current on the resistance wire to 0mA, and wait for the resistance value of the gas sensor detection resistor to return to the initial resistance value R a , the desorption of the gas sensitive element is completed.

[0062] Step 4: Use the obtained R a , R g Calculate the sensitivity S = R a / R g ; Use the gas-sensitive element that has completed desorption in step 3, select target gases of different concentrations, and repeat the process of step 3; according to the sensitivity of target gases of different concentrations, draw a correlation curve between the concentration and sensitivity of the target gas.

[0063] Step 5: Place the desorbed gas sensor in a 1L glass container filled with target gas of unknown concentration, wait for the resistance value of its detection resistor to stabilize, and record the resistance value at this time as R0. Calculate the sensitivity R a / R0, substitute the sensitivity value into the correlation curve in step 4 to obtain the concentration value of the target gas of unknown concentration.

[0064] The present invention prepares an oxide semiconductor gas-sensitive material that is sensitive to H2S. Under the auxiliary recovery of pulse current, it can realize high-performance recognition of H2S at room temperature and can detect the presence of H2S at the ppb level. The material preparation process is simple and has excellent properties such as high sensitivity, short response time, low detection limit and high selectivity at room temperature.

[0065] Example 1

[0066] This embodiment provides a CuO / In2O3 two-dimensional porous nanosheet gas-sensitive material, which is prepared by the following steps:

[0067] Step 1: At room temperature, mix 10 mL of deionized water, 10 mL of ethanol and 10 mL of ethylene glycol and stir magnetically for 10 min to obtain a mixed solvent;

[0068] Step 2: Add 1 mmol of indium nitrate to the above mixed solvent, stir magnetically for 20 min at a stirring rate of 600 rpm to obtain a mixed solution;

[0069] Step 3: The mixed solution was transferred to a 50 mL reactor and subjected to hydrothermal reaction at 160 °C for 15 h.

[0070] Step 4: centrifuging the solution obtained by the hydrothermal reaction, and washing the precipitate obtained by centrifugation with deionized water and ethanol alternately for 6 times, and then placing the precipitate in a drying oven and drying it for 5 hours at a drying temperature of 60° C. to obtain a first precipitate powder;

[0071] Step 5: placing the first precipitate powder in a muffle furnace, calcining at 500° C. for 2 h at a heating rate of 2° C. / min, and then naturally cooling to room temperature to obtain a first calcined powder;

[0072] Step 6: Take 20 mg of the above first calcined powder and place it in 20 mL of deionized water. After ultrasonic treatment for 5 minutes, stir it magnetically, and add 300 μL of copper nitrate solution while stirring to obtain a mixed suspension; the stirring time is 24 hours, and the stirring rate is 180 rpm / min; the concentration of copper nitrate is 19 mg / mL; the dripping rate of the copper nitrate solution is 0.5-1 μL / s.

[0073] Step 7: centrifuging the mixed suspension, and washing the precipitate obtained by centrifugation with deionized water and ethanol alternately for 6 times, and then placing the precipitate in a drying oven and drying it for 5 hours at a drying temperature of 60° C. to obtain a second precipitate powder;

[0074] Step 8: Place the second precipitate powder in a muffle furnace, calcine at 500°C for 2 hours with a heating rate of 2°C / min, and then naturally cool to room temperature to obtain a CuO / In2O3 gas-sensitive material (i.e., a CuO / In2O3 two-dimensional porous nanosheet gas-sensitive material).

[0075] Furthermore, this embodiment provides a gas sensor, which is a indirectly heated gas sensor. The gas sensor is prepared using the above-mentioned CuO / In2O3 gas-sensitive material, and the preparation method thereof includes the following steps:

[0076] Step 1: Take the above-mentioned CuO / In2O3 gas-sensitive material, add deionized water dropwise, with a solid-liquid ratio of 1mg:5μL, mix it into a paste with a fine brush, and evenly coat it on the surface of the ceramic tube between the two annular and parallel metal electrodes of the indirectly heated gas-sensitive element; the coating thickness is 10μm;

[0077] Step 2: Place the ceramic tube coated with the gas-sensitive material under a drying lamp for 10 minutes, then place it in a muffle furnace, anneal 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, set the resistance wire inside the ceramic tube to heat the ceramic tube, and connect the two ends of the resistance wire to the No. 1 and No. 6 connection pins through platinum wires. Two annular metal electrodes are provided with a connection point at each end of the outer diameter passing through the center of the circle, and the four connection points are connected to the No. 2, No. 3, No. 4, and No. 5 connection pins through platinum wires, so as to obtain a gas-sensitive element containing CuO / In2O3 gas-sensitive material.

[0078] Example 2

[0079] This embodiment provides a CuO / In2O3 two-dimensional porous nanosheet gas-sensitive material, which is prepared by the following steps:

[0080] Step 1: At room temperature, mix 10 mL of deionized water, 10 mL of ethanol and 10 mL of ethylene glycol and stir magnetically for 10 min to obtain a mixed solvent;

[0081] Step 2: Add 1 mmol of indium nitrate to the above mixed solvent, stir magnetically for 20 min at a stirring rate of 600 rpm to obtain a mixed solution;

[0082] Step 3: The mixed solution was transferred to a 50 mL reactor and subjected to hydrothermal reaction at 160 °C for 15 h.

[0083] Step 4: centrifuging the solution obtained by the hydrothermal reaction, and washing the precipitate obtained by centrifugation with deionized water and ethanol alternately for 6 times, and then placing the precipitate in a drying oven and drying it for 5 hours at a drying temperature of 60° C. to obtain a first precipitate powder;

[0084] Step 5: placing the first precipitate powder in a muffle furnace, calcining at 500° C. for 2 h at a heating rate of 2° C. / min, and then naturally cooling to room temperature to obtain a first calcined powder;

[0085] Step 6: Take 20 mg of the above first calcined powder and place it in 20 mL of deionized water. After ultrasonic treatment for 5 minutes, stir it magnetically, and add 400 μL of copper nitrate solution while stirring to obtain a mixed suspension; the stirring time is 24 hours, and the stirring rate is 180 rpm / min; the concentration of copper nitrate is 19 mg / mL; the dripping rate of the copper nitrate solution is 0.5-1 μL / s.

[0086] Step 7: centrifuging the mixed suspension, and washing the precipitate obtained by centrifugation with deionized water and ethanol alternately for 6 times, and then placing the precipitate in a drying oven and drying it for 5 hours at a drying temperature of 60° C. to obtain a second precipitate powder;

[0087] Step 8: Place the second precipitate powder in a muffle furnace, calcine at 500°C for 2 hours with a heating rate of 2°C / min, and naturally cool to room temperature to obtain a CuO / In2O3 gas-sensitive material (i.e., a CuO / In2O3 two-dimensional porous nanosheet gas-sensitive material).

[0088] The CuO / In2O prepared in this example 33 SEM images of gas-sensitive materials Figure 5 and 6 As shown, it can be observed that its morphology inherits the two-dimensional porous elongated flake structure of In2O3. Figure 7 In this embodiment, CuO / In2O 33 The local TEM image of the gas-sensitive material further confirms the porous structure of the material. Figure 8 CuO / In2O 33 In the HRTEM image of the gas-sensitive material, the interplanar spacings of adjacent regions correspond to In2O3 and CuO, respectively, confirming the formation of the CuO / In2O3 composite structure.

[0089] Furthermore, this embodiment provides a gas sensor, which is a indirectly heated gas sensor. The gas sensor is prepared using the above-mentioned CuO / In2O3 gas-sensitive material, and the preparation method thereof includes the following steps:

[0090] Step 1: Take the above-mentioned CuO / In2O3 gas-sensitive material, add deionized water dropwise, with a solid-liquid ratio of 1mg:5μL, mix it into a paste with a fine brush, and evenly coat it on the surface of the ceramic tube between the two annular and parallel metal electrodes of the indirectly heated gas-sensitive element; the coating thickness is 10μm;

[0091] Step 2: Place the ceramic tube coated with the gas-sensitive material under a drying lamp for 10 minutes, then place it in a muffle furnace, anneal 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, set the resistance wire inside the ceramic tube to heat the ceramic tube, and connect the two ends of the resistance wire to the No. 1 and No. 6 connection pins through platinum wires. Two annular metal electrodes are provided with a connection point at each end of the outer diameter passing through the center of the circle, and the four connection points are connected to the No. 2, No. 3, No. 4, and No. 5 connection pins through platinum wires, so as to obtain a gas-sensitive element containing CuO / In2O3 gas-sensitive material.

[0092] Example 3

[0093] This embodiment provides a CuO / In2O3 two-dimensional porous nanosheet gas-sensitive material, which is prepared by the following steps:

[0094] Step 1: At room temperature, mix 10 mL of deionized water, 10 mL of ethanol and 10 mL of ethylene glycol and stir magnetically for 10 min to obtain a mixed solvent;

[0095] Step 2: Add 1 mmol of indium nitrate to the above mixed solvent, stir magnetically for 20 min at a stirring rate of 600 rpm to obtain a mixed solution;

[0096] Step 3: The mixed solution was transferred to a 50 mL reactor and subjected to hydrothermal reaction at 160 °C for 15 h.

[0097] Step 4: centrifuging the solution obtained by the hydrothermal reaction, and washing the precipitate obtained by centrifugation with deionized water and ethanol alternately for 6 times, and then placing the precipitate in a drying oven and drying it for 5 hours at a drying temperature of 60° C. to obtain a first precipitate powder;

[0098] Step 5: placing the first precipitate powder in a muffle furnace, calcining at 500° C. for 2 h at a heating rate of 2° C. / min, and then naturally cooling to room temperature to obtain a first calcined powder;

[0099] Step 6: Take 20 mg of the above first calcined powder and place it in 20 mL of deionized water. After ultrasonic treatment for 5 minutes, stir it magnetically, and add 500 μL of copper nitrate solution while stirring to obtain a mixed suspension; the stirring time is 24 hours, and the stirring rate is 180 rpm / min; the concentration of copper nitrate is 19 mg / mL; the dripping rate of the copper nitrate solution is 0.5-1 μL / s.

[0100] Step 7: centrifuging the mixed suspension, and washing the precipitate obtained by centrifugation with deionized water and ethanol alternately for 6 times, and then placing the precipitate in a drying oven and drying it for 5 hours at a drying temperature of 60° C. to obtain a second precipitate powder;

[0101] Step 8: Place the second precipitate powder in a muffle furnace, calcine at 500°C for 2 hours with a heating rate of 2°C / min, and naturally cool to room temperature to obtain a CuO / In2O3 gas-sensitive material (i.e., a CuO / In2O3 two-dimensional porous nanosheet gas-sensitive material).

[0102] Furthermore, this embodiment provides a gas sensor, which is a indirectly heated gas sensor. The gas sensor is prepared using the above-mentioned CuO / In2O3 gas-sensitive material, and the preparation method thereof includes the following steps:

[0103] Step 1: Take the above-mentioned CuO / In2O3 gas-sensitive material, add deionized water dropwise, with a solid-liquid ratio of 1mg:5μL, mix it into a paste with a fine brush, and evenly coat it on the surface of the ceramic tube between the two annular and parallel metal electrodes of the indirectly heated gas-sensitive element; the coating thickness is 10μm;

[0104] Step 2: Place the ceramic tube coated with the gas-sensitive material under a drying lamp for 10 minutes, then place it in a muffle furnace, anneal 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, set the resistance wire inside the ceramic tube to heat the ceramic tube, and connect the two ends of the resistance wire to the No. 1 and No. 6 connection pins through platinum wires. Two annular metal electrodes are provided with a connection point at each end of the outer diameter passing through the center of the circle, and the four connection points are connected to the No. 2, No. 3, No. 4, and No. 5 connection pins through platinum wires, so as to obtain a gas-sensitive element containing CuO / In2O3 gas-sensitive material.

[0105] Comparative Example 1

[0106] This comparative example provides a gas-sensitive material, which is prepared by the following steps:

[0107] Step 1: At room temperature, mix 10 mL of deionized water, 10 mL of ethanol and 10 mL of ethylene glycol and stir magnetically for 10 min to obtain a mixed solvent;

[0108] Step 2: Add 1 mmol of indium nitrate to the above mixed solvent, stir magnetically for 20 min at a stirring rate of 600 rpm to obtain a mixed solution;

[0109] Step 3: The mixed solution was transferred to a 50 mL reactor and subjected to hydrothermal reaction at 160 °C for 15 h.

[0110] Step 4: centrifuging the solution obtained by the hydrothermal reaction, and washing the precipitate obtained by centrifugation with deionized water and ethanol alternately for 6 times, and then placing the precipitate in a drying oven and drying it for 5 hours at a drying temperature of 60° C. to obtain a first precipitate powder;

[0111] Step 5: placing the first precipitate powder in a muffle furnace, calcining at 500° C. for 2 h at a heating rate of 2° C. / min, and then naturally cooling to room temperature to obtain the gas-sensitive material (i.e., In2O3 gas-sensitive material);

[0112] The SEM image of the In2O3 gas-sensitive material prepared in this comparative example is shown in FIG. Figure 3 and 4 As shown, it can be observed that the morphology is two-dimensional porous elongated flakes with uniform size and even distribution, and there is a slight overlap between the flakes.

[0113] Furthermore, this comparative example provides a gas sensor, which is a indirectly heated gas sensor. The gas sensor is prepared using the above-mentioned gas-sensitive material, and the preparation method thereof comprises the following steps:

[0114] Step 1: Take the above-mentioned gas-sensitive material, add deionized water dropwise, with a solid-liquid ratio of 1mg:5μL, mix it into a paste with a fine brush, and evenly coat it on the surface of the ceramic tube between the two annular and parallel metal electrodes of the indirectly heated gas-sensitive element; the coating thickness is 10μm;

[0115] Step 2: Place the ceramic tube coated with the gas-sensitive material under a drying lamp for 10 minutes, then place it in a muffle furnace, anneal 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, set the resistance wire inside the ceramic tube to heat the ceramic tube, and connect the two ends of the resistance wire to the No. 1 and No. 6 connection pins through platinum wires. Two annular metal electrodes are provided with a connection point at each end of the outer diameter passing through the center of the circle, and the four connection points are connected to the No. 2, No. 3, No. 4, and No. 5 connection pins through platinum wires, so as to obtain a gas-sensitive element containing the gas-sensitive material.

[0116] The In2O3 gas-sensitive material obtained in the comparative example and the CuO / In2O3 gas-sensitive materials obtained in Example 1, Example 2, and Example 3 were subjected to XRD tests respectively. The results are as follows: Fig. 9As shown; the XRD diffraction peaks of the In2O3 gas-sensitive material in the comparative example correspond well to the hexagonal In2O3 structure (JCPDS No.73-1809); the XRD diffraction peaks of CuO / In2O3 in Example 1 correspond to the hexagonal In2O3 structure (JCPDS No.73-1809), but the peak corresponding to CuO is not observed, which may be due to the low crystallinity of CuO. The XRD diffraction peaks of CuO / In2O3 in Example 2 correspond to the hexagonal In2O3 structure (JCPDS No.73-1809), but the peak corresponding to CuO is not observed, which may be due to the low crystallinity of CuO. The XRD diffraction peaks of CuO / In2O3 in Example 3 correspond to the hexagonal In2O3 structure (JCPDS No.73-1809), but the peak corresponding to CuO is not observed, which may be due to the low crystallinity of CuO.

[0117] The gas sensing properties of the gas sensing elements prepared by the In2O3 gas sensing material obtained in the comparative example and the CuO / In2O3 gas sensing materials obtained in Examples 1, 2 and 3 were tested by a gas sensing test system (FLUKE).

[0118] Fig.10 It is shown that the response time of the In2O3 gas sensor in the comparative example to 10ppm H2S is 56s at room temperature. When there is no pulse current stimulation, the recovery time is greater than 60s. Within 60s, the resistance of the gas sensor shows no signs of recovery but decreases instead. Finally, the resistance must be restored under a pulse heating current (130mA, i.e. 275°C).

[0119] like Fig.11 As shown in the figure, the response recovery diagram of the gas sensor of the CuO / In2O3 gas-sensitive material prepared in Example 1 to 10ppmH2S at room temperature shows that, compared with the comparative example, the response time (2s) is greatly shortened. During the recovery process, without the stimulation of pulse current, the resistance of the gas sensor slightly recovers, but the stimulation of pulse heating current (120mA, i.e. 250°C) is still required to help the resistance of the gas sensor recover.

[0120] like Fig.12 As shown in the response recovery diagram of the gas sensor of the CuO / In2O3 gas-sensitive material prepared in Example 2 to 10ppm H2S at room temperature, compared with the comparative example, the response time (2s) is greatly shortened. During the recovery process, without the stimulation of pulse current, the resistance of the gas sensor is slightly restored, but the stimulation of pulse heating current (120mA, i.e. 250°C) is still required to help the resistance of the gas sensor recover.

[0121] like Fig.13As shown in the response recovery diagram of the gas sensor of the CuO / In2O3 gas-sensitive material prepared in Example 3 to 10ppm H2S at room temperature, compared with the comparative example, the response time (2s) is greatly shortened. During the recovery process, without the stimulation of pulse current, the resistance of the gas sensor is slightly restored, but the stimulation of pulse heating current (120mA, i.e. 250°C) is still required to help the resistance of the gas sensor recover.

[0122] Fig.14 The sensitivity of the gas-sensitive element prepared by the In2O3 gas-sensitive material obtained in the comparative example and the CuO / In2O3 gas-sensitive material obtained in Example 1, Example 2 and Example 3 to different gases at room temperature; the concentration of H2S gas is 10ppm, and the concentrations of other gases are all 100ppm; the results show that the sensitivity of the gas-sensitive element of Example 1 to different gases at room temperature, the sensitivity to 10ppm H2S (43333) is much higher than that of 100ppm other gases. The sensitivity of the gas-sensitive element of Example 2 to different gases at room temperature, the sensitivity to 10ppm H2S (58000) is much higher than that of 100ppm other gases, which is 2230 times that of the comparative example. The sensitivity of the gas-sensitive element of Example 3 to different gases at room temperature, the sensitivity to 10ppm H2S (13990) is much higher than that of 100ppm other gases; the response of the In2O3 gas-sensitive element in the comparative example to 10ppm H2S at room temperature is 26, which is higher than the response to other target gases, showing good selectivity.

[0123] Fig.15 It shows that the sensitivity of the In2O3 gas sensor in the comparative example is linearly related to the concentration in the entire test concentration range (500ppb-20ppm) at room temperature.

[0124] Fig.16 and 17 The gas sensor of Example 2 shows a good linear relationship between sensitivity and concentration in the low concentration range (50-1500 ppb) and high concentration range (3-20 ppm).

[0125] The above embodiments are for illustration only and are not intended to be limiting. Any equivalent modifications or changes made thereto without departing from the spirit and scope of the present invention shall be included in the scope of the claims of this application.

[0126] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A CuO / In2O3 two-dimensional porous nanosheet gas-sensitive material, characterized in that: The gas-sensitive material is prepared by the following steps: Step 1: At room temperature, mix 5-15 mL of deionized water, 5-15 mL of ethanol and 5-15 mL of ethylene glycol, and stir magnetically for 5-10 minutes to obtain a mixed solvent; Step 2: Add 0.8-1.5 mmol indium nitrate to the above mixed solvent, stir magnetically for 20-30 min at a stirring rate of 500-800 rpm to obtain a mixed solution; Step 3: Transfer the mixed solution to a 50-100 mL reactor and perform a hydrothermal reaction at 130-180°C for 13-18 hours; Step 4: centrifuging the solution obtained by the hydrothermal reaction, and washing the precipitate obtained by centrifugation with deionized water and ethanol alternately for 4-8 times, and then placing the precipitate in a drying oven and drying it for 3-6 hours at a drying temperature of 55-65° C. to obtain a first precipitate powder; Step 5: placing the first precipitate powder in a muffle furnace, calcining at 400-600° C. for 1.5-3 h at a heating rate of 1-3° C. / min, and then naturally cooling to room temperature to obtain a first calcined powder; Step 6: 15-30 mg of the powder after the first calcination is placed in 15-30 mL of deionized water, subjected to ultrasonic treatment for 3-5 min, and then magnetically stirred, and 100-800 μL of copper nitrate solution is added while stirring to obtain a mixed suspension; the stirring time is 15-30 hours, the stirring rate is 100-200 rpm / min; the concentration of copper nitrate is 15-30 mg / mL; the dripping rate of the copper nitrate solution is 0.5-1 μL / s; Step 7: centrifuging the mixed suspension, and washing the precipitate obtained by centrifugation with deionized water and ethanol alternately for 4-8 times, and then placing the precipitate in a drying oven for 3-6 hours at a drying temperature of 55-65° C. to obtain a second precipitate powder; Step 8: Place the second precipitate powder in a muffle furnace, calcine at 300-600°C for 1.5-3h with a heating rate of 1-3°C / min, and then cool naturally to room temperature to obtain a CuO / In2O3 gas-sensitive material.

2. The CuO / In2O3 two-dimensional porous nanosheet gas-sensitive material according to claim 1, characterized in that: The gas-sensitive material is prepared by the following steps: Step 1: At room temperature, mix 10 mL of deionized water, 10 mL of ethanol and 10 mL of ethylene glycol and stir magnetically for 10 min to obtain a mixed solvent; Step 2: Add 1 mmol of indium nitrate to the above mixed solvent, stir magnetically for 20 min at a stirring rate of 600 rpm to obtain a mixed solution; Step 3: Transfer the mixed solution to a 50 mL reactor and perform hydrothermal reaction at 160 °C for 15 h; Step 4: centrifuging the solution obtained by the hydrothermal reaction, and washing the precipitate obtained by centrifugation with deionized water and ethanol alternately for 6 times, and then placing the precipitate in a drying oven and drying it for 5 hours at a drying temperature of 60° C. to obtain a first precipitate powder; Step 5: placing the first precipitate powder in a muffle furnace, calcining at 500° C. for 2 h at a heating rate of 2° C. / min, and then naturally cooling to room temperature to obtain a first calcined powder; Step 6: 20 mg of the first calcined powder was placed in 20 mL of deionized water, subjected to ultrasonic treatment for 5 min, and then magnetically stirred, and 400 μL of copper nitrate solution was added while stirring to obtain a mixed suspension; the stirring time was 24 hours, the stirring rate was 180 rpm / min; the concentration of copper nitrate was 19 mg / mL; and the dripping rate of the copper nitrate solution was 0.5-1 μL / s; Step 7: centrifuging the mixed suspension, and washing the precipitate obtained by centrifugation with deionized water and ethanol alternately for 6 times, and then placing the precipitate in a drying oven and drying it for 5 hours at a drying temperature of 60° C. to obtain a second precipitate powder; Step 8: Place the second precipitate powder in a muffle furnace, calcine at 500°C for 2h with a heating rate of 2°C / min, and naturally cool to room temperature to obtain a CuO / In2O3 gas-sensitive material.

3. A gas sensor, which is a indirectly heated gas sensor, characterized in that: The gas sensor is prepared by using the CuO / In2O3 gas-sensitive material as claimed in any one of claims 1 or 2, and the preparation method thereof comprises the following steps: Step 1: Take 1-3 mg of the above-mentioned CuO / In2O3 gas-sensitive material, add 10-20 μL of deionized water, mix into a paste, and evenly coat it on the surface of the ceramic tube between two annular and parallel metal electrodes of the indirectly heated gas-sensitive element; the coating thickness is 8-15 μm; Step 2: Place the ceramic tube coated with the above-mentioned CuO / In2O3 gas-sensitive material under a drying lamp for 5-10 minutes, place it in a muffle furnace, anneal it at 400-600℃ for 1.5-3 hours, and the heating rate is 1-3℃ / min, and then naturally cool it to room temperature; then weld the ceramic tube to the hexagonal base, and set the resistance wire inside the ceramic tube to heat the ceramic tube. The two ends of the resistance wire are connected to the No. 1 and No. 6 connecting pins respectively through platinum wires. 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. 2, No. 3, No. 4, and No. 5 connecting pins through platinum wires to obtain a gas-sensitive element containing CuO / In2O3 gas-sensitive material.

4. A gas sensor according to claim 3, characterized in that: The preparation method comprises the following steps: Step 1: Take the CuO / In2O3 gas-sensitive material, add deionized water dropwise, with a solid-liquid ratio of 1mg:5μL, mix it into a paste with a fine brush, and evenly coat it on the surface of the ceramic tube between the two annular and parallel metal electrodes of the indirectly heated gas-sensitive element; the coating thickness is 10μm; Step 2: Place the ceramic tube coated with the above-mentioned gas-sensitive material under a drying lamp for 10 minutes, place it in a muffle furnace, anneal it at 500°C for 2 hours, and the heating rate is 2°C / min, and then naturally cool it to room temperature; then weld the ceramic tube to the hexagonal base, and set the resistance wire inside the ceramic tube to heat the ceramic tube. The two ends of the resistance wire are connected to the No. 1 and No. 6 connecting pins respectively through platinum wires. 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. 2, No. 3, No. 4, and No. 5 connecting pins through platinum wires to obtain a gas-sensitive element containing CuO / In2O3 gas-sensitive material.

5. An application of a gas sensor, characterized in that: The gas sensor as claimed in claim 3 is used, and the application process specifically includes the following steps: Step 1: Connect the above gas sensor to the circuit, load the working voltage at both ends of the resistance wire, so that the resistance wire heats up and the gas sensor obtains different working temperatures; two annular metal electrodes connect the detection resistor of the gas sensor with a load resistor in series through their terminals to form a series resistance circuit, and the test voltage V is supplied to both ends of the series resistance circuit. c , the voltage across the load resistor is the output voltage V out , the resistance value of the detection resistor R1=V c / V out (1-R0), R0 is the resistance value of the load resistor; at the test voltage V c Under the condition of no change, the resistance value of the detection resistor changes with the temperature in the environment and the type and concentration of the target gas; Step 2: Place the gas sensor in a 1L air bottle. At room temperature, wait for the resistance value of the gas sensor's detection resistor to stabilize and record the resistance value at this time as R a ; Step 3: Transfer the gas sensor to a 1L glass container filled with a certain concentration of target gas, wait for the resistance value of the detection resistor to stabilize, and record the resistance value at this time as R g ; Then transfer the gas sensor back to the air bottle. After 1-3 minutes, if the resistance value of the gas sensor's detection resistor changes by less than 1% of the stable resistance value in the air bottle, adjust the current on the resistance wire to 110-150mA. When the resistance value of the gas sensor's detection resistor stabilizes to R1, reduce the current on the resistance wire to 0mA and wait for the resistance value of the gas sensor's detection resistor to return to the initial resistance value R a , the desorption of the gas-sensitive element is completed; Step 4: Use the obtained R a , R g Calculate the sensitivity S = R a / R g ; Using the gas-sensitive element that has completed desorption in step 3, select target gases of different concentrations, and repeat the process of step 3; according to the sensitivity of target gases of different concentrations, draw a correlation curve between the concentration and sensitivity of the target gas; Step 5: Place the desorbed gas sensor in a 1L glass container filled with target gas of unknown concentration, wait for the resistance value of its detection resistor to stabilize, and record the resistance value R0 at this time; calculate the sensitivity R a / R0, substitute the sensitivity value into the correlation curve in step 4 to obtain the concentration value of the target gas of unknown concentration.

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