Gas-sensitive nano-material formed by compounding multi-walled carbon nanotubes and zinc oxide nanosheets and application of gas-sensitive nano-material in methane gas detection

Abstract

The invention belongs to the technical field of gas-sensitive materials, and particularly relates to a high-performance gas-sensitive nano material formed by compounding multi-walled carbon nanotubes and zinc oxide nanosheets and application of the high-performance gas-sensitive nano material in methane gas detection. A traditional zinc oxide-based gas-sensitive material is insufficient in sensitivity when being used for detecting methane gas. By compounding the multi-walled carbon nanotubes and the zinc oxide nanosheets, the sensitivity of the gas-sensitive material to methane gas is improved. In addition, many gas-sensitive materials need to work at higher temperature to obtain better performance, which limits their application in low temperature environments. According to the invention, the high-performance gas-sensitive nano material is prepared by compounding the multi-walled carbon nanotubes and the zinc oxide nanosheets, so that efficient gas-sensitive performance at a relatively low temperature (50 DEG C) is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas-sensitive materials, and particularly relates to a high-performance gas-sensitive nanomaterial composited with multi-walled carbon nanotubes and zinc oxide nanosheets, and its application in methane gas detection. Background Art

[0002] To achieve sustainable energy and environmental goals, natural gas production and consumption are growing at an unprecedented rate. However, frequent explosions and asphyxiation accidents caused by natural gas leaks or improper use have sounded a safety alarm. At the same time, with the increasing density of natural gas pipelines and the rapid development of urban underground integrated pipeline corridors, the integration of natural gas pipelines into these corridors has become a growing trend. However, hidden dangers such as pipeline aging, corrosion, and defects contribute to frequent natural gas pipeline leaks. In coal mining, gas accumulation in poorly ventilated areas is particularly prominent. When gas concentrations reach the explosive limit (5% to 15% by volume), any open flame or spark can trigger an explosion or fire, resulting in catastrophic consequences. Methane, as a major component of natural gas and coalbed methane, is flammable and explosive, posing a significant threat to life and property, and the potential for economic losses cannot be ignored. To ensure safety in residential gas use, natural gas pipeline operations, and coal mine production, real-time monitoring and accurate detection of methane gas concentrations are imperative. The development of high-performance methane gas sensors has become a key technological support for ensuring energy security.

[0003] Existing methane gas sensor technologies are diversified, encompassing catalytic combustion, quartz crystal resonator, metal oxide semiconductor, infrared absorption, gas chromatography, and solid electrolyte types. Metal oxide semiconductor gas sensors, with their high sensitivity, fast response, low cost, excellent integration, strong safety, and long life, have gained widespread application in industrial, environmental, and household applications. Their operating principle is based on the detection gas inducing a redox reaction on the semiconductor surface, resulting in a significant change in resistance. However, these sensors still suffer from inherent drawbacks such as high operating temperature, nonlinear correlation between the output signal and gas concentration, and insufficient selectivity.

[0004] Carbon nanotubes, a novel material discovered in 1991, offer broad application prospects in the field of gas-sensing materials due to their unique pore structure, large specific surface area, and ultra-high surface energy. However, research on the preparation of gas-sensing materials using carbon nanotubes for methane gas detection has been rare. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-performance gas-sensitive nanomaterial composed of multi-walled carbon nanotubes and zinc oxide nanosheets and its application in methane gas detection.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A gas-sensitive nanomaterial, the gas-sensitive nanomaterial being composited by multi-walled carbon nanotubes and zinc oxide nanosheets; Furthermore, the molar ratio of the multi-walled carbon nanotubes to the zinc oxide nanosheets is 1:1.

[0007] The method for preparing the above-mentioned gas-sensitive nanomaterial comprises the following steps: (1) dispersing multi-walled carbon nanotubes in a mixture of deionized water and anhydrous ethanol, stirring at room temperature, then adding zinc nitrate hexahydrate, ammonium carbonate and polyethylene glycol 6000, stirring at room temperature to obtain a precursor solution; (2) transferring the precursor solution obtained in step (1) to a PTFE substrate hydrothermal reactor, performing a hydrothermal reaction, naturally cooling to room temperature, and centrifuging to obtain a solid product; washing the obtained solid product with deionized water and anhydrous ethanol, and then drying it in an oven to obtain a precursor material; (3) placing the precursor material obtained in step (2) in a tube furnace, heat-treating it under an inert gas atmosphere, and naturally cooling it to room temperature to obtain a MWCNTs / ZnO composite material, that is, a gas-sensitive nanomaterial composed of multi-walled carbon nanotubes and zinc oxide nanosheets; Furthermore, step (1) is specifically as follows: 0.5 g of multi-walled carbon nanotubes is dispersed in a mixture consisting of 40 mL of deionized water and 40 mL of anhydrous ethanol, stirred at room temperature for 0.5 h, and then 0.595 g of zinc nitrate hexahydrate, 0.384 g of ammonium carbonate and 0.1 g of polyethylene glycol 6000 are added, and stirred at room temperature for 1 h to obtain a precursor solution; Furthermore, step (2) is specifically as follows: transferring the precursor solution obtained in step (1) to a PTFE substrate hydrothermal reactor, performing a hydrothermal reaction at 180° C. for 24 hours, naturally cooling to room temperature, and centrifuging to obtain a solid product; washing the obtained solid product with deionized water and anhydrous ethanol alternately for 3 times, and then drying it in an oven at 60° C. for 9 hours to obtain a precursor material; Furthermore, step (3) is specifically as follows: placing the precursor material obtained in step (2) in a tube furnace, heating the tube furnace to 400°C at a heating rate of 5°C / min under an argon atmosphere, and keeping the temperature for 2 hours, and naturally cooling to room temperature to obtain a MWCNTs / ZnO composite material, that is, a gas-sensitive nanomaterial composed of multi-walled carbon nanotubes and zinc oxide nanosheets.

[0008] The application of the above-mentioned gas-sensitive nanomaterial in methane gas detection.

[0009] Application of the above-mentioned gas-sensitive nanomaterial in the preparation of a gas sensor; Furthermore, the gas sensor is used for detecting methane gas.

[0010] A gas sensor comprises the above-mentioned gas-sensitive nanomaterial.

[0011] The significant advantages of the present invention are: Conventional methane gas sensors suffer from insufficient sensitivity when detecting low concentrations. Many gas-sensing materials require higher temperatures for optimal performance, limiting their application in low-temperature environments and increasing energy consumption. The present invention utilizes zinc oxide, a typical n-type semiconductor, as the metal oxide methane gas-sensing material. By combining multi-walled carbon nanotubes with zinc oxide nanosheets, the sensitivity to methane gas detection is improved, enabling detection of lower concentrations of methane gas and maintaining high gas-sensing performance at lower operating temperatures. This broadens the application range and reduces energy consumption. The present invention also features a simple preparation process and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 : Preparation process of ZnO nanosheets.

[0013] Figure 2 : Preparation process of MWCNTs / ZnO composite materials.

[0014] Figure 3 : a, XRD patterns of ZnO nanosheets and MWCNTs / ZnO composites; b, three strong peaks of ZnO after enlarging area a.

[0015] Figure 4 : a, SEM image of ZnO nanosheets; b, SEM image of MWCNTs / ZnO composite material.

[0016] Figure 5 ; a, nitrogen adsorption isotherm and BJH pore size distribution curve of ZnO nanosheets; b, nitrogen adsorption isotherm and BJH pore size distribution curve of MWCNTs / ZnO composite materials.

[0017] Figure 6 : a, Response-recovery characteristic curves of the gas sensor prepared by pure ZnO nanosheets to methane gas of different concentrations at different temperatures; b, sensitivity; c, response time; d, recovery time.

[0018] Figure 7 : a, Response-recovery characteristic curves of the gas sensor prepared by MWCNTs / ZnO composite material to methane gas of different concentrations at different temperatures; b, sensitivity; c, response time; d, recovery time. DETAILED DESCRIPTION

[0019] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0020] The multi-walled carbon nanotubes (MWCNTs) used in the present invention were purchased from Aladdin Reagents (Shanghai) Co., Ltd., CAS No.: 308068-56-6, Product No.: C313046.

[0021] For the preparation method of the coal-based carbon used in the present invention, see: Wang Chicheng, Liu Tianhao, Wu Haoyu, et al. Preparation of ZnO gas-sensitive materials using coal-based carbon hard templates and their detection of low-mass fraction ethanol gas [J]. Mining and Metallurgical Engineering, 2024, 44(6): 129-133. The activated carbon used in the present invention was purchased from Aladdin Reagent (Shanghai) Co., Ltd., CAS No.: 7440-44-0, with a particle size of 2 to 3 μm.

[0022] Example 1: A method for preparing a gas-sensitive nanomaterial composed of a composite of multi-walled carbon nanotubes and zinc oxide nanosheets, comprising the following steps: (1) Disperse 0.163 g of multi-walled carbon nanotubes in a mixture of 40 mL of deionized water and 40 mL of anhydrous ethanol, stir at room temperature for 0.5 h, then add 0.595 g of zinc nitrate hexahydrate, 0.384 g of ammonium carbonate, and 0.1 g of polyethylene glycol 6000, and stir at room temperature for 1 h to obtain a precursor solution; (2) The precursor solution obtained in step (1) was transferred to a PTFE substrate hydrothermal reactor with a volume of 100 mL, and the reaction was carried out at 180° C. for 24 h, and then naturally cooled to room temperature, and centrifuged to obtain a solid product; the obtained solid product was washed alternately with deionized water and anhydrous ethanol for 3 times, and then placed in a 60° C. oven for 9 h to obtain a precursor material; (3) The precursor material obtained in step (2) is placed in a tube furnace, and the tube furnace is heated to 400°C at a heating rate of 5°C / min under an argon atmosphere (flow rate of 100 mL / min), and kept warm for 2 h, and then naturally cooled to room temperature to obtain a MWCNTs / ZnO composite material, that is, a gas-sensitive nanomaterial composed of multi-walled carbon nanotubes and zinc oxide nanosheets.

[0023] Comparative Example 1: A method for preparing ZnO nanosheets, comprising the following steps: (1) Add 0.595 g of zinc nitrate hexahydrate, 0.384 g of ammonium carbonate, and 0.1 g of polyethylene glycol 6000 to the same beaker, add a mixture consisting of 40 mL of deionized water and 40 mL of anhydrous ethanol, and stir at room temperature for 1 h to obtain a precursor solution; (2) The precursor solution obtained in step (1) was transferred to a PTFE substrate hydrothermal reactor with a volume of 100 mL, and the reaction was carried out at 180° C. for 24 h, and then naturally cooled to room temperature, and centrifuged to obtain a solid product; the obtained solid product was washed alternately with deionized water and anhydrous ethanol for 3 times, and then placed in a 60° C. oven for 9 h to obtain a precursor material; (3) The precursor material obtained in step (2) was placed in a tube furnace, and the temperature of the tube furnace was raised to 400°C at a heating rate of 5°C / min under an argon atmosphere (flow rate of 100 mL / min), and kept at this temperature for 2 h, and then naturally cooled to room temperature to obtain ZnO nanosheets.

[0024] Comparative Example 2: A method for preparing a coal-based carbon / ZnO nanosheet composite material, comprising the following steps: (1) Disperse 0.163 g of coal-based carbon in a mixture of 40 mL of deionized water and 40 mL of anhydrous ethanol, stir at room temperature for 0.5 h, then add 0.595 g of zinc nitrate hexahydrate, 0.384 g of ammonium carbonate, and 0.1 g of polyethylene glycol 6000, and stir at room temperature for 1 h to obtain a precursor solution; (2) The precursor solution obtained in step (1) was transferred to a PTFE substrate hydrothermal reactor with a volume of 100 mL, and the reaction was carried out at 180° C. for 24 h, and then naturally cooled to room temperature, and centrifuged to obtain a solid product; the obtained solid product was washed alternately with deionized water and anhydrous ethanol for 3 times, and then placed in a 60° C. oven for 9 h to obtain a precursor material; (3) The precursor material obtained in step (2) was placed in a tubular furnace, and the temperature of the tubular furnace was raised to 400°C at a heating rate of 5°C / min under an argon atmosphere (flow rate of 100 mL / min), and kept at this temperature for 2 h, and then naturally cooled to room temperature to obtain a coal-based carbon / ZnO nanosheet composite material.

[0025] Comparative Example 3: A method for preparing an activated carbon / ZnO nanosheet composite material comprises the following steps: (1) Disperse 0.163 g of activated carbon in a mixture of 40 mL of deionized water and 40 mL of anhydrous ethanol, stir at room temperature for 0.5 h, then add 0.595 g of zinc nitrate hexahydrate, 0.384 g of ammonium carbonate, and 0.1 g of polyethylene glycol 6000, and stir at room temperature for 1 h to obtain a precursor solution; (2) The precursor solution obtained in step (1) was transferred to a PTFE substrate hydrothermal reactor with a volume of 100 mL, and the reaction was carried out at 180° C. for 24 h, and then naturally cooled to room temperature, and centrifuged to obtain a solid product; the obtained solid product was washed alternately with deionized water and anhydrous ethanol for 3 times, and then placed in a 60° C. oven for 9 h to obtain a precursor material; (3) The precursor material obtained in step (2) was placed in a tube furnace, and under an argon atmosphere (flow rate 100 mL / min), the tube furnace was heated to 400°C at a heating rate of 5°C / min and kept warm for 2 h, and then naturally cooled to room temperature to obtain an activated carbon / ZnO nanosheet composite material.

[0026] Figure 3 The XRD patterns of ZnO nanosheets and MWCNTs / ZnO composites are shown. As can be seen, the baseline of the MWCNTs / ZnO composite is stable. The diffraction peak at 25.8448° corresponds to the (002) crystal plane of the graphite phase after multi-walled carbon nanotube deposition (JCPDS No. 41-1487). All other XRD diffraction peaks correspond to the hexagonal structure of ZnO (JCPDS No. 36-1451). The three strongest peaks of the MWCNTs / ZnO composite exhibit good symmetry. Compared with ZnO nanosheets, the width of the three strongest peaks of the MWCNTs / ZnO composite remains unchanged, and their positions do not shift significantly. This indicates that the MWCNTs / ZnO composite has good crystallinity. The introduction of MWCNTs does not change the lattice parameters of ZnO or its crystal structure, but the intensity of the ZnO characteristic peaks decreases slightly.

[0027] Figure 4 The SEM images of ZnO nanosheets and MWCNTs / ZnO composites are shown in Figure 2. Figure 4 (a) It can be observed that the edges of the pure ZnO nanosheets are clear, the thickness of the pure ZnO nanosheets is 20-50nm, the length is 0.5-2μm, and the width is 200-500nm. The nanosheets are evenly dispersed without agglomeration, indicating that the synthesized pure ZnO nanosheets are well crystallized and grow evenly. Figure 4 As shown in (b), ZnO nanosheets are encapsulated in MWCNTs, where the edges of the ZnO nanosheets are clear. Compared with pure ZnO nanosheets, the size of the ZnO nanosheets in the MWCNTs / ZnO composite material is reduced, with the length concentrated in the range of 200-500nm and the width concentrated in the range of 100-200nm. Smaller ZnO nanosheets can provide more gas adsorption sites. According to the Scherr formula, the XRD diffraction peak intensity of smaller ZnO nanosheets will be weakened, which is consistent with the Figure 3 The XRD patterns are consistent.

[0028] Figure 5The nitrogen adsorption / desorption curves and mesopore size distribution curves of ZnO nanosheets and MWCNTs / ZnO composites are shown in the figure. As can be seen from the figure, the MWCNTs / ZnO composites also exhibit type IV nitrogen adsorption / desorption curves, similar to ZnO nanosheets, but the MWCNTs / ZnO composites exhibit a larger adsorption capacity, which is related to the high BET specific surface area of ​​the MWCNTs / ZnO composites (the BET specific surface area of ​​the MWCNTs / ZnO composites is 114.0116 m 2 / g, which is 3.5 times that of ZnO nanosheets), the mesopore diameter of MWCNTs / ZnO composites is more concentrated in 2-4 nm, which is more beneficial for methane gas sensing.

[0029] Application examples: A gas sensor was prepared using either MWCNTs / ZnO composite material or ZnO nanosheets as the gas-sensitive material, and its methane gas sensing performance was tested. The gas sensor mainly consists of a gas-sensitive coating, an alumina ceramic tube, a nickel-chromium alloy heating wire, and a gas-sensitive element base. The alumina ceramic tube is 4 mm long, with an inner diameter of 1.2 mm and an outer diameter of 0.9 mm. Annular, separate, and parallel gold electrodes are distributed at both ends of the outer surface of the alumina ceramic tube. The distance between the two gold electrodes is 1.15 mm, and the width of the gold electrodes is 0.5 mm. Two platinum wires are connected to each gold electrode, and the length of the platinum wire is 6 mm. The resistance value of the nickel-chromium alloy heating wire is 30 Ω. The preparation steps of the gas sensor are as follows: (1) 0.05 g of gas-sensitive material was placed in an agate mortar, 0.5 mL of anhydrous ethanol was added, and the mixture was thoroughly ground into a slurry, which was then evenly coated on the outer surface of the alumina ceramic tube. After drying at room temperature for 0.5 h, a gas-sensitive coating was formed, and the gas-sensitive coating was made to completely cover the gold electrodes at both ends of the outer surface of the alumina ceramic tube; then, the platinum wires connected to the gold electrodes on the alumina ceramic tube were welded to the corresponding electrodes on the base of the gas sensor; then, a nickel-chromium alloy heating wire was passed through the interior of the ceramic tube, and the two ends were welded to the corresponding electrodes on the base of the gas sensor, thereby obtaining an assembled gas sensor; (2) The gas sensor assembled in step (1) was placed on a WS-30B gas-sensitive test bench and aged at 90° C. for 24 h to obtain a gas sensor.

[0030] Figure 6 The response-recovery characteristic curves of the gas sensor prepared with ZnO nanosheets to methane gas at concentrations of 300, 600, 900, 1200, and 1500 ppm at RT (room temperature) -200°C. Figure 6As shown in (a), the resistance of pure ZnO nanosheets decreases as the temperature rises. This is because the concentration and migration rate of free electrons, the main carriers of n-type semiconductors, increase with the temperature, which causes the resistance of the material to decrease. When methane gas is introduced, methane gas competes with oxygen for adsorption and reacts with the adsorbed oxygen on the surface of pure ZnO nanosheets. The free electrons captured by oxygen are released, and the resistance of the material decreases. After the methane gas is discharged, the resistance of the material cannot return to its original level and drift occurs. This indicates that the desorption rate of methane gas in ZnO nanomaterials is slow. The sensitivity of pure ZnO to methane at various temperatures is shown in Figure 2. Figure 6 As shown in (b), at 150℃, pure ZnO nanosheets have the best sensitivity to methane, with response values ​​of 2.1, 3.0, 3.6, 3.9, and 4.1 to 300, 600, 900, 1200, and 1500 ppm of methane gas, respectively. The response recovery time of ZnO nanosheets to methane is shown in Figure 6 As shown in (c) and (d), the ZnO resistance drifts during the gas-sensing process due to the influence of methane gas desorption rate, resulting in no significant increase in the ZnO response recovery time with increasing methane concentration at various temperatures. In summary, pure ZnO nanosheets exhibit optimal sensitivity to methane at 150°C. However, the slow desorption rate of methane from the ZnO nanosheet material at various temperatures adversely affects the response / recovery of the ZnO nanosheet resistance during the experiment.

[0031] Figure 7 The following is a graph showing the response recovery time of a gas sensor made from MWCNTs / ZnO composite materials. As can be seen from the graph, at various operating temperatures, the sensor's response recovery time increases with increasing methane concentration. However, for methane gas at the same concentration, the sensor's response recovery time does not show an increasing trend with increasing operating temperature. This is because, while rising operating temperature accelerates the thermal motion of methane gas molecules, which helps speed up gas adsorption and desorption, the adsorption and desorption effects of MWCNTs on gas deteriorate with increasing operating temperature. Therefore, the response recovery rate of the gas sensor made from the MWCNTs / ZnO composite material is significantly enhanced regardless of rising operating temperature. At 50°C, the material exhibits the best sensitivity to methane, and the response recovery time to methane is also low. Therefore, 50°C is considered to be the optimal operating temperature of the MWCNTs / ZnO composite material. At this time, the sensitivity of the MWCNTs / ZnO composite material to 300, 600, 900, 1200 and 1500 ppm methane gas is 1.4, 1.6, 1.8, 2.1 and 2.2, respectively, showing a linear response to methane gas.

[0032] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A gas-sensitive nanomaterial, characterized in that: The gas-sensitive nanomaterial is composited from multi-walled carbon nanotubes and zinc oxide nanosheets.

2. The gas-sensitive nanomaterial according to claim 1, characterized in that: The molar ratio of the multi-walled carbon nanotubes to the zinc oxide nanosheets is 1:

1.

3. The method for preparing the gas-sensitive nanomaterial according to any one of claims 1 to 2, wherein: The following steps are involved: (1) dispersing multi-walled carbon nanotubes in a mixture of deionized water and anhydrous ethanol, stirring at room temperature, then adding zinc nitrate hexahydrate, ammonium carbonate, and polyethylene glycol 6000, stirring at room temperature to obtain a precursor solution; (2) transferring the precursor solution obtained in step (1) to a PTFE substrate hydrothermal reactor, performing a hydrothermal reaction, naturally cooling to room temperature, and centrifuging to obtain a solid product; washing the obtained solid product with deionized water and anhydrous ethanol, and then drying it in an oven to obtain a precursor material; (3) The precursor material obtained in step (2) is placed in a tube furnace, heat-treated under an inert gas atmosphere, and naturally cooled to room temperature to obtain a MWCNTs / ZnO composite material, that is, a gas-sensitive nanomaterial composed of multi-walled carbon nanotubes and zinc oxide nanosheets.

4. The gas-sensitive nanomaterial according to claim 3, characterized in that: Step (1) is specifically as follows: 0.163 g of multi-walled carbon nanotubes are dispersed in a mixture of 40 mL of deionized water and 40 mL of anhydrous ethanol, stirred at room temperature for 0.5 h, and then 0.595 g of zinc nitrate hexahydrate, 0.384 g of ammonium carbonate and 0.1 g of polyethylene glycol 6000 are added, and stirred at room temperature for 1 h to obtain a precursor solution.

5. The gas-sensitive nanomaterial according to claim 3, characterized in that: Step (2) is specifically as follows: the precursor solution obtained in step (1) is transferred to a PTFE substrate hydrothermal reactor, hydrothermally reacted at 180° C. for 24 hours, naturally cooled to room temperature, and centrifuged to obtain a solid product; the obtained solid product is washed alternately with deionized water and anhydrous ethanol three times, and then placed in a 60° C. oven for drying for 9 hours to obtain a precursor material.

6. The gas-sensitive nanomaterial according to claim 3, characterized in that: Step (3) is specifically as follows: placing the precursor material obtained in step (2) in a tube furnace, heating the tube furnace to 400°C at a heating rate of 5°C / min under an argon atmosphere, and keeping the temperature for 2 hours, and naturally cooling to room temperature to obtain a MWCNTs / ZnO composite material, that is, a gas-sensitive nanomaterial composed of multi-walled carbon nanotubes and zinc oxide nanosheets.

7. Use of the gas-sensitive nanomaterial according to claim 1 in methane gas detection.

8. Use of the gas-sensitive nanomaterial according to claim 1 in the preparation of a gas sensor.

9. The use according to claim 8, characterized in that: The gas sensor is used for detecting methane gas.

10. A gas sensor, characterized in that: The gas-sensitive nanomaterial comprises the gas-sensitive nanomaterial according to any one of claims 1 to 2.

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