Method for preparing ZnO nanoparticles by using multi-walled carbon nanotubes as template and application of ZnO nanoparticles in methane gas detection

Abstract

The invention relates to a method for preparing ZnO nanoparticles by using a multi-walled carbon nanotube as a template and application of the ZnO nanoparticles in methane gas detection. The preparation method comprises the following steps: dissolving zinc acetate dihydrate and a multi-walled carbon nanotube in absolute ethyl alcohol, and vigorously stirring to enable the multi-walled carbon nanotube to fully adsorb zinc acetate to obtain a mixed solution; carrying out vacuum filtration on the obtained mixed solution to remove the solvent, collecting a solid product, and drying to obtain a precursor; and transferring the obtained precursor into a tubular furnace, carrying out heat treatment in a high-purity air atmosphere, and naturally cooling to room temperature to obtain the ZnO nanoparticles. The optimal working temperature of the methane sensor prepared from the ZnO nanoparticles is 150 DEG C, and the gas-sensitive performance is excellent.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor gas sensing materials, and particularly to a method for preparing ZnO nanoparticles using multi-walled carbon nanotubes as a template and its application in methane gas detection. Background Art

[0002] To achieve the sustainable development goals of the energy environment, the production and consumption of natural gas are increasing at an unprecedented rate. The government has strongly promoted the clean heating project of "replacing coal with gas" in winter in the northern region, and the popularity of natural gas in residents' lives has continued to deepen. However, explosion and asphyxiation poisoning accidents caused by natural gas leakage or improper use occur frequently, sounding the safety alarm. At the same time, with the rapid advancement of the intensive layout of natural gas pipelines and the construction of urban underground utility tunnels, incorporating natural gas pipelines into utility tunnels has become a development trend. However, hidden dangers such as pipeline aging, corrosion, and defects have led to frequent natural gas pipeline leakage accidents. In the field of coal mining, the accumulation of gas in poorly ventilated areas is particularly prominent. When the gas concentration reaches the explosion limit (5% - 15% volume fraction), any open flame or electric spark may trigger an explosion or fire, causing catastrophic consequences. Methane, as the main component of natural gas and coalbed methane, poses a major threat to the safety of life and property due to its flammable and explosive characteristics, and the potential risk of economic losses cannot be ignored. To build a safety defense line for residential gas use, natural gas pipeline operation, and coal mine production, it is urgent to achieve real-time monitoring and accurate detection of methane gas concentration. The research and development of high-performance methane gas sensors have become a key technical support for ensuring energy security.

[0003] The existing methane gas sensor technologies show a diversified development trend, covering types such as catalytic combustion type, quartz crystal resonance type, metal oxide semiconductor type, infrared absorption type, gas chromatography type, and solid electrolyte type. Among them, semiconductor gas sensors based on metal oxides (such as SnO2, ZnO, WO3, etc.) are widely used in industrial, environmental protection, and household fields due to their fast response, high sensitivity, stable performance, simple structure, and low cost. ZnO is an n-type semiconductor material. However, gas sensors prepared from pure ZnO still have disadvantages such as high operating temperature and poor long-term stability.

[0004] Carbon nanotubes are ideal one-dimensional quantum materials. They are nanotubes formed by curling graphene sheets with a hexagonal close-packed structure. During the weaving process of the hexagons, pentagons or heptagons will appear, showing the concavity and convexity of the tube. Therefore, in carbon nanotubes, in addition to hexagons, pentagons and heptagons also play important roles. Carbon nanotubes can be divided into multi-walled carbon nanotubes and single-walled carbon nanotubes. Depending on their diameter and chiral vector (n, m), carbon nanotubes exhibit many strange electrical, magnetic, and mechanical properties. They are expected to be widely used in many fields such as structural enhancement, nanoelectronic devices, field emission, hydrogen storage, sensors, etc. Therefore, carbon nanotubes have always been a hot topic in world scientific research. In recent years, due to their unique physical and chemical properties, carbon nanotubes have been applied to the detection of gases such as NO2, H2, and NH4. However, there are few reports on the research of using carbon nanotubes as raw materials to prepare gas-sensitive materials for detecting methane gas. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing ZnO nanoparticles using multi-walled carbon nanotubes as a template and its application in the detection of methane gas.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: A method for preparing ZnO nanoparticles using multi-walled carbon nanotubes as a template, comprising the following steps: (1) Dissolve zinc acetate dihydrate and multi-walled carbon nanotubes in absolute ethanol, and stir vigorously to enable the multi-walled carbon nanotubes to fully adsorb zinc acetate to obtain a mixed solution; subject the obtained mixed solution to vacuum filtration to remove the solvent, collect the solid product and dry it to obtain a precursor; (2) Transfer the precursor obtained in step (1) into a tubular furnace, perform heat treatment under the atmosphere of high-purity air, and naturally cool to room temperature to obtain ZnO nanoparticles; Further, in step (1), the amount of zinc acetate dihydrate used is 3.29265 g, the amount of multi-walled carbon nanotubes used is 0.5 g, the amount of absolute ethanol used is 60 mL, the stirring temperature is 60 °C, and the stirring time is 1 h; Further, in step (1), the vacuum degree of the vacuum filtration is 0.06 MPa, the time is 10 min, the drying temperature is 60 °C, and the drying time is 9 h; Further, in step (2), the heat treatment procedure is: first heat up to 350 °C at a heating rate of 5 °C / min and hold for 0.5 h, and then continue to heat up to 800 °C at a heating rate of 5 °C / min and hold for 5 h.

[0007] A kind of ZnO nanoparticles, which are prepared by the above method.

[0008] The application of the above-mentioned ZnO nanoparticles in the detection of methane gas.

[0009] The above application of ZnO nanoparticles in the preparation of a gas sensor for methane gas detection.

[0010] A gas sensor for methane gas detection, the gas sensor comprising the above ZnO nanoparticles.

[0011] The above preparation method of a gas sensor comprises the following steps: (1) Take ZnO nanoparticles and put them into an agate mortar, add absolute ethanol, grind thoroughly to make a slurry, and then evenly coat the slurry on the outer surface of an alumina ceramic tube. After drying at room temperature, a gas-sensitive coating is formed, and the gas-sensitive coating can completely cover the gold electrodes at both ends of the outer surface of the alumina ceramic tube; then weld the platinum wire leads connected to the gold electrodes on the alumina ceramic tube to the corresponding electrodes of the gas-sensitive element base respectively; then pass a nickel-chromium alloy heating wire through the inside of the ceramic tube and weld the two ends to the corresponding electrodes of the gas-sensitive element base respectively to obtain an assembled gas-sensitive element; (2) Age the assembled gas-sensitive element obtained in step (1) at 175 °C for 4 h to obtain a gas sensor.

[0012] The above application of a gas sensor in methane gas detection.

[0013] The remarkable advantages of the present invention are as follows: In the traditional hard template method, the template material (such as ceramics, metal oxides, etc.) may remain in the final product during the preparation process, which will not only affect the gas-sensitive performance of the material, but may also introduce impurities, affecting the stability and reliability of the material. In the present invention, by using multi-walled carbon nanotubes as a template, due to its combustible property at high temperature, it can be easily removed in subsequent processing, thus avoiding the problem of template residue, simplifying the steps of removing the template, reducing the need for chemical treatment, and thereby reducing the preparation cost and environmental impact. The present invention utilizes the unique properties of multi-walled carbon nanotubes to improve the porosity, specific surface area and gas-sensitive performance of ZnO nanomaterials. The optimal working temperature of ZnO nanoparticles prepared with multi-walled carbon nanotubes as a template is 150 °C. At this working temperature, the material has high sensitivity to methane, short response and recovery times, meeting the requirements for high-performance gas-sensitive materials in practical applications. Description of the Drawings

[0014] Figure 1 : a, XRD pattern of the multi-walled carbon nanotube template ZnO nanoparticle material; b, ZnO Three strong peaks.

[0015] Figure 2 : a-b, SEM images of the multi-walled carbon nanotube template ZnO nanoparticle material; c, EDS spectrum of the multi-walled carbon nanotube template ZnO nanoparticles.

[0016] Figure 3 : FTIR spectrum of ZnO nanoparticles material with multi-walled carbon nanotube template.

[0017] Figure 4 : BJH pore size distribution curve of ZnO nanoparticles material with multi-walled carbon nanotube template.

[0018] Figure 5 : Response and recovery curves of the gas sensor prepared from ZnO nanoparticles material with multi-walled carbon nanotube template to methane gas at different operating temperatures.

[0019] Figure 6 : a, Curve of the relationship between the response time and methane gas concentration of the gas sensor prepared from ZnO nanoparticles material with multi-walled carbon nanotube template at different operating temperatures; b, Curve of the relationship between the recovery time and methane gas concentration of the gas sensor prepared from ZnO nanoparticles material with multi-walled carbon nanotube template at different operating temperatures.

[0020] Figure 7 : a, Curve of the relationship between the sensitivity and methane gas concentration of the gas sensor prepared from ZnO nanoparticles material with multi-walled carbon nanotube template at different operating temperatures; b, Linear relationship diagram of the sensitivity of the gas sensor prepared from ZnO nanoparticles material with multi-walled carbon nanotube template at the operating temperature of 150 °C. Detailed implementation manners

[0021] To make the content of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation manners, but the present invention is not limited thereto.

[0022] The multi-walled carbon nanotubes (MWCNTs) used in the present invention were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., CAS No.: 308068-56-6, product number: C313046.

[0023] For the preparation method of the coal-based carbon used in the present invention, see: Wang Chicheng, Liu Tianhao, Wu Haoyu, etc. Preparation of ZnO gas-sensitive materials using coal-based carbon hard template and its 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, particle size 2-3 μm.

[0024] Example 1: A method for preparing ZnO nanoparticles using multi-walled carbon nanotubes as a template, the steps are as follows: (1) Dissolve 3.29265 g of zinc acetate dihydrate and 0.5 g of multi-walled carbon nanotubes in 60 mL of absolute ethanol, and stir vigorously at 60 °C for 60 min to allow the multi-walled carbon nanotubes to fully adsorb zinc acetate, obtaining a mixed solution; subject the obtained mixed solution to vacuum filtration at 0.06 MPa for 10 min to remove the solvent, collect the solid product and dry it at 60 °C for 9 h to obtain a precursor. (2) Transfer the precursor obtained in step (1) into a tubular furnace, and perform heat treatment under the atmosphere of high-purity air (flow rate 100 mL / min), and naturally cool to room temperature to obtain ZnO nanoparticles (also known as "MWCNTs-template ZnO nanoparticle material"). Among them, the heat treatment procedure is as follows: first, heat up to 350 °C at a heating rate of 5 °C / min and hold at 350 °C for 0.5 h; then continue to heat up to 800 °C at a heating rate of 5 °C / min and hold at 800 °C for 5 h.

[0025] The X-ray diffraction pattern of the MWCNTs-template ZnO nanoparticle material is as Figure 1 shown. The results show that all XRD diffraction peaks can correspond to the hexagonal crystal structure of ZnO. Its diffraction peak intensity is high, the symmetry is good, and there are no other impurity peaks in the material, indicating that the ZnO nanoparticles have high purity and good crystallinity.

[0026] The scanning electron microscope image and EDS energy spectrum of the MWCNTs-template ZnO nanoparticle material are as Figure 2 shown. The sizes of the ZnO nanoparticles are uneven, concentrated in the range of 100 - 300 nm, and the nanoparticle clusters form microflowers. There are C, Zn, and O in the energy spectrum peaks. The C peak in the energy spectrum, combined with the results of XRD and SEM analysis, may be due to the residual of a very small amount of template and the conductive glue of the substrate, further proving that the ZnO nanoparticles prepared with multi-walled carbon nanotubes as the template have high purity and almost no other impurities.

[0027] The FTIR spectrum of the MWCNTs-template ZnO nanoparticle material is as Figure 3 shown. In the range of wavenumbers from 3200 to 3600 cm -1 , due to the O-H stretching vibration of water molecules, a broad and strong absorption peak is generated at 3430 cm -1 ; in the range of wavenumbers from 1600 to 1700 cm -1 , due to the bending vibration of two hydrogen atoms around the oxygen atom in water molecules, a weaker H-O-H bending vibration peak is generated at 1630 cm -1 ; in the range of wavenumbers from 1350 to 1450 cm -1 , due to the reaction of adsorbed water and carbon dioxide on the material surface to produce CO3 2- , CO3 2-The symmetric stretching vibration of the two O-C=O groups in the ion produced an absorption peak at 1382 cm -1 ; in the wavenumber range of 400 - 500 cm -1 , two strong absorption peaks produced at 435 cm -1 and 500 cm -1 were both due to the vibration of the Zn-O bond in ZnO. No characteristic absorption peaks of other non-ZnO crystals were found in the ZnO nanoparticles prepared using multi-walled carbon nanotubes as a template, indicating that the purity of the ZnO nanoparticles was relatively high and the residual amount of the template was low.

[0028] The BJH pore size distribution curve of the MWCNTs template ZnO nanoparticle material is as Figure 4 shown. The mesopore size of the MWCNTs template ZnO nanomaterial is concentrated in the range of 2.4 - 3.7 nm, and the specific surface area of the material is 5.9150 m 2 / g, which can provide more active sites for methane gas and help improve the efficiency of the material in specific reactions.

[0029] Comparative Example 1: A method for preparing ZnO nanoparticles using coal-based carbon as a template, the steps are as follows: (1) Dissolve 3.29265 g of zinc acetate dihydrate and 0.5 g of coal-based carbon in 60 mL of absolute ethanol, stir vigorously at 60 °C for 60 min to obtain a mixed solution; vacuum filter the obtained mixed solution at 0.06 MPa for 10 min to remove the solvent, collect the solid product and dry it at 60 °C for 9 h to obtain a precursor.

[0030] (2) Transfer the precursor obtained in step (1) into a tubular furnace, and perform heat treatment in an atmosphere of high-purity air (flow rate 100 mL / min), and naturally cool to room temperature to obtain ZnO nanoparticles (also known as "coal-based carbon template ZnO nanomaterial"). Among them, the heat treatment program is: first heat up to 350 °C at a heating rate of 5 °C / min and hold at 350 °C for 0.5 h; then continue to heat up to 800 °C at a heating rate of 5 °C / min and hold at 800 °C for 5 h.

[0031] The nanoparticle size of the coal-based carbon template ZnO nanomaterial is concentrated in the range of 50 - 100 nm, the mesopore size is concentrated in the range of 2.2 - 3.2 nm, and the BET specific surface area is 8.2761 m 2 / g.

[0032] Comparative Example 2: A method for preparing ZnO nanorods using activated carbon as a template, the steps are as follows: (1) Dissolve 3.29265 g of zinc acetate dihydrate and 0.5 g of activated carbon in 60 mL of absolute ethanol, and vigorously stir the mixture at 60 °C for 60 min to obtain a mixed solution; vacuum filter the obtained mixed solution at 0.06 MPa for 10 min to remove the solvent, collect the solid product, and dry it at 60 °C for 9 h to obtain a precursor.

[0033] (2) Transfer the precursor obtained in step (1) into a tube furnace, and perform heat treatment in an atmosphere of high-purity air (flow rate 100 mL / min), and naturally cool to room temperature to obtain ZnO nanorods (also known as "activated carbon template ZnO nanomaterials"). Among them, the heat treatment procedure is as follows: first, heat up to 350 °C at a heating rate of 5 °C / min and hold at 350 °C for 0.5 h; then continue to heat up to 800 °C at a heating rate of 5 °C / min and hold at 800 °C for 5 h.

[0034] The activated carbon template ZnO nanomaterials exhibit a hexagonal prism structure with a length of about 1 μm and a width of 200 - 300 nm. The nanorod clusters form microflower-like shapes, the mesopore diameter is concentrated in the range of 2.0 - 3.7 nm, and the BET specific surface area is 3.5044 m 2 / g.

[0035] Application example: Use the MWCNTs template ZnO nanoparticle material as a gas-sensitive material to prepare a gas sensor, and test its methane gas sensing performance. 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 length of the alumina ceramic tube is 4 mm, the inner diameter is 1.2 mm, and the outer diameter is 0.9 mm; at both ends of the outer surface of the alumina ceramic tube, there are distributed annular, discrete, and parallel gold electrodes, the distance between the two gold electrodes is 1.15 mm, the width of the gold electrode is 0.5 mm, and two platinum wire leads are connected to each gold electrode, and the length of the platinum wire leads 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) Take 0.5 g of the gas-sensitive material and put it into an agate mortar, add 0.5 mL of absolute ethanol, fully grind it into a slurry, and then evenly coat it on the outer surface of the alumina ceramic tube. After drying at room temperature for 0.5 h, a gas-sensitive coating is formed, and the gas-sensitive coating can completely cover the gold electrodes at both ends of the outer surface of the alumina ceramic tube; then, respectively weld the platinum wire leads connected to the gold electrodes on the alumina ceramic tube to the corresponding electrodes of the gas-sensitive element base; then pass the nickel-chromium alloy heating wire through the inside of the ceramic tube and weld the two ends to the corresponding electrodes of the gas-sensitive element base to obtain an assembled gas-sensitive element; (2) Place the assembled gas-sensitive element obtained in step (1) on a WS-30B gas-sensing test bench and age it at 175 °C for 4 h to obtain a gas sensor.

[0036] Figure 5 Figure a is the response and recovery curve of a gas sensor prepared from MWCNTs-template ZnO nanoparticle material to methane gas at different working temperatures. During the test, the response and recovery effects of the sensor to methane gas at 300 ppm, 600 ppm, 900 ppm, 1200 ppm, and 1500 ppm were detected at each working temperature. As can be seen from the figure, the sensor resistance decreases continuously with the increase of the working temperature, showing a typical n-type semiconductor response; however, compared with the gas sensor prepared from activated carbon-template ZnO nanomaterial, the resistance of the gas sensor prepared from MWCNTs-template ZnO nanoparticle material does not change significantly with the increase of the working temperature. The resistance value in air is the lowest at a working temperature of 125 °C, and at a working temperature of 175 °C, when methane gas is exhausted, with the desorption process of methane gas, the resistance drifts significantly and cannot return to the initial level within a short time.

[0037] Figure 5 Figure b is the response and recovery diagram of a gas sensor prepared from MWCNTs-template ZnO nanoparticle material to 1500 ppm methane gas at different working temperatures. At 1 min, methane gas was introduced, and the resistance of the sensor began to decrease. Among them, the resistance of the sensor changed the fastest and reached stability at a working temperature of 150 °C, while the recovery times at each working temperature were relatively close, and the recovery rate at a working temperature of 175 °C was relatively slow.

[0038] The response and recovery curves of the gas sensor prepared from MWCNTs-template ZnO nanoparticle material to methane gas at different working temperatures are as Figure 6 shown. At each working temperature, the response time of the sensor basically becomes longer with the increase of the methane gas concentration; at a working temperature of 150 °C, the response time of the sensor to methane gas at each concentration (600 - 1500 ppm) is the shortest. The recovery time of the sensor at each working temperature has no obvious change law with the methane gas concentration, and the recovery time for the same methane gas concentration does not significantly shorten with the increase of the working temperature.

[0039] The sensitivity of the gas sensor prepared from MWCNTs-template ZnO nanoparticle material to methane gas at each working temperature is as Figure 7 shown. At each working temperature, the sensitivity of the sensor to methane gas increases with the increase of the methane gas concentration; at a working temperature of 125 °C, the sensitivity of the sensor to methane gas is the lowest; at a working temperature of 175 °C, the sensitivity of the sensor to methane gas is the highest. At each working temperature, the sensor shows a good linear response to methane gas. Considering the comprehensive response / recovery rate and sensitivity, 150 °C is selected as the optimal working temperature of the sensor. At this working temperature, the linear relationship of the sensor sensitivity to methane gas is asFigure 7 As shown in Figure b, its sensitivities to methane at 300 ppm, 600 ppm, 900 ppm, 1200 ppm, and 1500 ppm are 3.62, 4.00, 4.17, 4.28, and 4.50, respectively.

[0040] The above are only the preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims

1. A method for preparing ZnO nanoparticles using multi-walled carbon nanotubes as a template, characterized in that: It includes the following steps: (1) Dissolve zinc acetate dihydrate and multi-walled carbon nanotubes in absolute ethanol, and stir vigorously to allow the multi-walled carbon nanotubes to fully adsorb zinc acetate to obtain a mixed solution; subject the obtained mixed solution to vacuum filtration to remove the solvent, collect the solid product and dry it to obtain a precursor; (2) Transfer the precursor obtained in step (1) into a tubular furnace, perform heat treatment under the atmosphere of high-purity air, and naturally cool to room temperature to obtain ZnO nanoparticles.

2. The method according to claim 1, wherein: In step (1), the dosage of zinc acetate dihydrate is 3.29265 g, the dosage of multi-walled carbon nanotubes is 0.5 g, the dosage of absolute ethanol is 60 mL, the stirring temperature is 60 °C, and the time is 1 h.

3. The method according to claim 1, wherein: In step (1), the vacuum degree of the vacuum filtration is 0.06 MPa and the time is 10 min, and the drying temperature is 60 °C and the time is 9 h.

4. The method according to claim 1, characterized in that: In step (2), the heat treatment procedure is: first heat up to 350 °C at a heating rate of 5 °C / min and hold for 0.5 h, and then continue to heat up to 800 °C at a heating rate of 5 °C / min and hold for 5 h.

5. A ZnO nanoparticle, characterized in that: Prepared by the method according to any one of claims 1 to 4.

6. Application of the ZnO nanoparticles according to claim 4 in detecting methane gas.

7. Application of the ZnO nanoparticles according to claim 4 in preparing a gas sensor for methane gas detection.

8. A gas sensor for methane gas detection, characterized in that: The gas sensor includes the ZnO nanoparticles according to claim 4.

9. The preparation method of the gas sensor according to claim 8, characterized in that: It includes the following steps: (1) Take ZnO nanoparticles and put them into an agate mortar, add absolute ethanol, fully grind to make a slurry and evenly coat it on the outer surface of an alumina ceramic tube. After drying at room temperature, a gas-sensitive coating is formed, and the gas-sensitive coating can completely cover the gold electrodes at both ends of the outer surface of the alumina ceramic tube; then weld the platinum wire leads connected to the gold electrodes on the alumina ceramic tube to the corresponding electrodes of the gas-sensitive element base respectively; then pass a nickel-chromium alloy heating wire through the inside of the ceramic tube and weld the two ends to the corresponding electrodes of the gas-sensitive element base respectively to obtain an assembled gas-sensitive element; (2) Age the assembled gas-sensitive element obtained in step (1) at 175 °C for 4 h to obtain a gas sensor.

10. Application of the gas sensor according to claim 9 in methane gas detection.

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