WO3 / Al2O3 / graphite composite materials and their preparation and application

Abstract

The present invention discloses a WO3 / Al2O3 / graphite composite material, its preparation and application. In the composite material, WO3 nanoparticles and Al2O3 nanoparticles are tightly attached to graphite sheets. The gas-sensitive material has a large specific surface area and more gas interaction centers. Al2O3 nanoparticles account for 2-12% of the total mass of WO3 nanoparticles and Al2O3 nanoparticles. Through simple doping and stirring, it can be directly used as a gas-sensitive material. When it is used to detect 2-CEES gas, the optimal operating temperature of the gas sensor is 340°C. At an operating temperature of 340°C, the gas sensor has a response time of 5s to 2-CEES gas with a concentration of 5.70ppm, a recovery time of 42s, and a sensitivity of 69%.

Description

Technical Field

[0001] The present invention relates to the technical field of gas sensors, and in particular to a composite material based on WO3 / Al2O3 / graphite and its application in detecting 2-CEES gas sensors. Background Art

[0002] Toxic and hazardous gases can be categorized as blistering agents, nerve agents, blood agents, and lung agents based on their mechanisms of toxicity. Dichlorodiethyl sulfide, commonly known as a blistering agent, targets the skin as a primary target organ. Absorption of large doses of dichlorodiethyl sulfide through the skin, respiratory tract, and digestive tract can lead to systemic toxicity. Therefore, detection and real-time monitoring of dichlorodiethyl sulfide are essential to prevent its presence in the atmosphere and potential harm to humans and the environment. Due to the high toxicity of toxic and hazardous gases, direct laboratory experiments using them is extremely dangerous. Therefore, simulants with similar physical, chemical, and structural properties to those of toxic and hazardous gases are often used in experiments. These simulants are less toxic and therefore suitable for experimental use. The chemical gas 2-chloroethyl sulfide (2-CEES) is often used as a simulant for dichlorodiethyl sulfide. Previous reports have reported on semiconductor metal oxide gas sensors for detecting 2-CEES. For example, Patil et al. reported on the detection of 2-CEES using platinum-doped CdSnO3 thin films. However, the sensitivity of this gas sensor to 2-CEES gas at a concentration of 4 ppm was only 33.46, with a recovery time of 125 s, indicating a low response to 2-CEES gas and poor recovery. Yoo et al. reported synthesizing Al-doped ZnO nanoparticles via a hydrothermal method for 2-CEES gas detection. However, the operating temperature of this gas sensor was 500°C, and the recovery time was 127 s. This indicates that the required operating temperature of this gas sensor was too high and the recovery effect was poor. Aliha et al. also reported fabricating a SnO2-based semiconductor thick-film gas sensor for detecting chlorinated volatile organic compounds. However, the response time of this gas sensor was 50 s, the recovery time was 1200 s, and its selectivity was not studied. Summary of the Invention

[0003] To address the aforementioned issues encountered in the prior art, the present invention provides a WO3 / Al2O3 / graphite composite material with high response, good recovery, and excellent selectivity, and its application in 2-CEES gas sensors. This composite material, characterized by its high number of gas interaction centers and large specific surface area, exhibits excellent potential for application in 2-CEES gas sensors, and its preparation method is simple.

[0004] Specifically, the present invention is implemented using the following technical solutions:

[0005] The WO3 / Al2O3 / graphite composite material of the present invention comprises WO3 nanoparticles and Al2O3 nanoparticles tightly attached to a graphite sheet. This gas-sensitive material exhibits a large specific surface area and numerous gas interaction centers, resulting in a more sensitive response to 2-CEES gas. The WO3 particle size is preferably no larger than 100 nm, and the gamma-type Al2O3 particle size is preferably 10-50 nm. The Al2O3 nanoparticles preferably constitute 2-12% of the total mass of the WO3 and Al2O3 nanoparticles, more preferably 2-8%, very preferably 4-5%, and most preferably 4%.

[0006] The method for preparing the WO3 / Al2O3 / graphite composite material of the present invention comprises the following steps:

[0007] 1) Mixing WO3 and Al2O3: Weigh appropriate amounts of WO3 and Al2O3, put them into a mortar, grind them until they are evenly mixed, and then pour them into a crucible;

[0008] 2) High-temperature calcination of the WO3 and Al2O3 mixture: placing the mixture prepared in step 1) into a muffle furnace, calcining at different temperatures and collecting the solid product after high-temperature calcination;

[0009] 3) Prepare graphite solution: Add ethanol and deionized water to a beaker and stir with a rotor. Then add graphite to the beaker where the ethanol and deionized water are mixed. Continue stirring with the rotor to disperse the graphite evenly in the solution.

[0010] 4) Mixing WO3, Al2O3, and graphite: adding the solid product obtained in step 2) to the graphite solution obtained in step 3), and continuously stirring to obtain a WO3 / Al2O3 / graphite solution;

[0011] 5) Preparation of WO3 / Al2O3 / graphite composite material: The WO3 / Al2O3 / graphite solution obtained in step 4) was placed in an oven to dry.

[0012] In the preparation method described above, preferably, in the step 1), based on the total mass of WO3 and Al2O3, the mass proportion of Al2O3 is preferably 2%-12%, more preferably 2%-8%, very preferably 4%-5%, and optimally 4%, and the grinding time is 20-40 min.

[0013] In the above-mentioned preparation method, preferably, in step 2), the high temperature calcination heating rate is 3-6°C min -1The inventors have found that a step-by-step heat preservation method can produce a composite material with better performance. For example, the temperature can be raised to 105-115°C for calcination for 1-3 hours, then to 580-620°C for calcination for 1-3 hours, and finally to 680-720°C for calcination for 1-3 hours. In particular, calcination at 110°C for 1 hour, then to 600°C for 1 hour, and finally to 700°C for 1 hour is more preferred. The composite material calcined in this manner has the highest response to 2-CEES gas.

[0014] In the above-mentioned preparation method, preferably, in step 3), the volume ratio of ethanol to deionized water is 20-25:5-10, and the concentration of graphite is 0.05-0.5 mg ml -1 More preferably, the volume ratio of ethanol to deionized water is 20:5 or 25:5, and the concentration of graphite is 0.08-0.1 mg ml -1 , the amount of graphite used is related to the total volume of ethanol and deionized water.

[0015] In the above-described preparation method, preferably, in step 4), the stirring time is 6-30 h, more preferably 10-30 h, and most preferably 20-25 h.

[0016] In the above-mentioned preparation method, preferably, in the step 5), when the drying temperature is 55-65° C., the drying time is 6-24 h.

[0017] The WO3 / Al2O3 / graphite composite material described herein can be used as a gas-sensitive material or gas sensor for gas detection. In this application, the WO3 / Al2O3 / graphite composite material can be mixed with deionized water to form a slurry, which can then be evenly applied to a ceramic tube and dried in an oven. The slurry can then be used as a gas sensor for detecting 2-CEES gas.

[0018] The technical advantages of the present invention are:

[0019] (1) The present invention provides a method for preparing and applying a WO3 / Al2O3 / graphite 2-CEES gas sensor. The gas-sensitive material has a large specific surface area and a large number of gas interaction centers, and is highly sensitive to 2-CEES gas. A gas sensor with an Al2O3 content of 4 wt% exhibits optimal gas-sensing properties to 2-CEES gas. The optimal operating temperature of the gas sensor is 340°C. At an operating temperature of 340°C, the gas sensor has a response time of 5 s, a recovery time of 42 s, and a sensitivity of 69% to a 2-CEES gas concentration of 5.70 ppm.

[0020] (2) The gas-sensitive material WO3 / Al2O3 / graphite of the present invention has the advantage of a simple preparation method. It can be directly used as a gas-sensitive material through simple doping and stirring. This synthesis method is simple, controllable, and highly reproducible, which is conducive to its industrialization.

[0021] (3) Compared with other types of gas sensors, the semiconductor metal oxide WO3 / Al2O3 / graphite 2-CEES gas sensor of the present invention has the advantages of wide applicability, simplicity and ease of use, low power consumption, small size, low cost, and easy integration. In addition, when the gas-sensitive material WO3 / Al2O3 / graphite is applied to the 2-CEES gas sensor, it has the advantages of better gas molecule adsorption effect and gas interaction, and higher carrier mobility of the sensing material, and has great application potential in the field of gas sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Flow chart of the WO3 / Al2O3 / graphite gas-sensitive material produced by the present invention;

[0023] Figure 2 a is a photo of a gas sensor made of WO3 / Al2O3 / graphite 2-CEES of the present invention. Figure 2 b is a schematic diagram of the WO3 / Al2O3 / graphite 2-CEES gas sensor of the present invention, Figure 2 c is the measurement circuit of the WO3 / Al2O3 / graphite2-CEES gas sensor of the present invention;

[0024] Figure 3 a is the XRD pattern of the WO3 / Al2O3 / graphite gas-sensitive material of the present invention, Figure 3 b is the SEM image of the WO3 / Al2O3 / graphite gas-sensitive material of the present invention;

[0025] Figure 4 a is the response curve of the WO3 / Al2O3 / graphite gas sensor of the present invention to 2-CEES gas and the working temperature, Figure 4 b is the sensing response of the WO3 / Al2O3 / graphite gas sensor of the present invention to 2-CEES gas with a concentration of 5.70 ppm and interfering gases (ammonia, ethanol, acetone and acetonitrile) with a concentration of 5.70 ppm at different operating temperatures, Figure 4 c is the response time and recovery time of the WO3 / Al2O3 / graphite gas sensor of the present invention to 2-CEES gas with a concentration of 5.70 ppm at an operating temperature of 340°C. Figure 4d is the sensing response of the WO3 / Al2O3 / graphite gas sensor of the present invention to 2-CEES gas with a concentration of 0.10 ppm at an operating temperature of 340°C; based on the total mass of WO3 and Al2O3, S1 is 2% by mass of Al2O3, S2 is 4% by mass of Al2O3, S3 is 8% by mass of Al2O3, and S4 is 12% by mass of Al2O3;

[0026] Figure 5 a is the response and recovery curve of the WO3 / Al2O3 / graphite gas sensor of the present invention at an operating temperature of 340°C to 2-CEES gas with concentrations of 0.10, 0.22, 0.42, 1.00, 2.10, 3.10, 4.10, 7.20, 9.30 and 11.40 ppm, respectively. Figure 5 b is the linear correlation between the response of the WO3 / Al2O3 / graphite gas sensor of the present invention to different concentrations of 2-CEES gas at an operating temperature of 340°C and the 2-CEES gas concentration. Figure 5 c is the sensing response of the WO3 / Al2O3 / graphite gas sensor of the present invention after six cycles of testing 2-CEES gas with a concentration of 5.70 ppm. Figure 5 d is the sensing response of the WO3 / Al2O3 / graphite gas sensor of the present invention in a long-term stability test of 2-CEES gas with a concentration of 5.70 ppm at an operating temperature of 340°C for 6 consecutive days. DETAILED DESCRIPTION

[0027] The following embodiments are further descriptions of the present invention to illustrate the technical content of the present invention, but the essential content of the present invention is not limited to the following embodiments. Ordinary technicians in this field can and should know that any simple changes or replacements based on the essential spirit of the present invention should fall within the scope of protection required by the present invention.

[0028] Example 1

[0029] A method for preparing a WO3 / Al2O3 / graphite 2-CEES gas sensor comprises the following steps:

[0030] 1) Mix WO3 and Al2O3: Weigh 96 mg of WO3 and 4 mg of Al2O3, then put them into a mortar and grind them for 30 minutes to mix them evenly, then pour them into a crucible;

[0031] 2) High-temperature calcination of the WO3 and Al2O3 mixture: The mixture prepared in step 1) was placed in a muffle furnace and calcined at 110°C, 600°C, and 700°C for 1 h, respectively, and the solid products after high-temperature calcination were collected;

[0032] 3) Prepare graphite solution: Add ethanol and deionized water to a beaker in a 5:1 volume ratio and stir thoroughly with a rotor. Then, add 2.7 mg of graphite to the mixture and continue stirring until the graphite is evenly dispersed in the solution.

[0033] 4) Mixing WO3, Al2O3, and graphite: Add the solid product obtained in step 2) to the graphite solution obtained in step 3), and stir for 24 hours to obtain a WO3 / Al2O3 / graphite solution;

[0034] 5) Preparation of WO3 / Al2O3 / graphite gas sensor: The WO3 / Al2O3 / graphite solution obtained in step 4) was dried in an oven at 60°C for 24 hours. An appropriate amount of WO3 / Al2O3 / graphite solid material was then weighed and mixed with an appropriate amount of deionized water. The mixture was evenly applied to a ceramic tube and dried in an oven.

[0035] Performance test of the WO3 / Al2O3 / graphite gas sensor prepared in this embodiment:

[0036] The prepared WO3 / Al2O3 / graphite gas sensor was used to test its gas sensing performance to 2-CEES gas. Figure 1 The actual photo of WO3 / Al2O3 / graphite 2-CEES gas sensor is shown in Figure 2 a; the structural diagram of the smeared ceramic tube is shown in Figure 2 b; the measurement circuit of WO3 / Al2O3 / graphite gas sensor for detecting 2-CEES gas is shown in Figure 2 As shown in c.

[0037] The XRD pattern of the WO3 / Al2O3 / graphite gas-sensitive material of the present invention is as follows: Figure 3As shown in Figure a, the XRD pattern shows that the characteristic diffraction peaks at 23.55°, 34.11° and 49.88° can correspond to the (020), (202) and (400) crystal planes of WO3 nanoparticles (JCPDS No.83-950), respectively, and they are related to the structure of WO3 nanoparticles. The SEM image of WO3 / Al2O3 / graphite gas sensing material is shown in Figure 2. Figure 3 As shown in b, the SEM image shows that WO3 nanoparticles and Al2O3 nanoparticles are tightly attached to the graphite sheets.

[0038] The responses of various gas sensors to 2-CEES gas with a concentration of 5.70 ppm at different operating temperatures and different Al2O3 doping amounts are shown in Figure 2. Figure 4 As shown in a, Figure 4 As can be seen in a, the gas sensor with an Al2O3 content of 4wt.% (based on the total mass of WO3 and Al2O3, WO3 accounts for 96% and Al2O3 accounts for 4%) shows the greatest sensitivity to 2-CEES gas with a concentration of 5.70ppm at each operating temperature. Gas sensors with other Al2O3 contents have relatively small responses to 2-CEES gas with a concentration of 5.70ppm at all operating temperatures. The selectivity of the gas sensor with an Al2O3 content of 4wt.% to 2-CEES gas, as shown in Figure 1, is as follows: Figure 4 As shown in b. Figure 4 As can be seen from b, the gas sensor with an Al2O3 content of 4wt.% has low responses to ammonia water, ethanol and acetonitrile with a concentration of 5.70ppm at working temperatures of 260℃, 300℃, 340℃ and 440℃, and the changes are not significant. However, the responses to 2-CEES gas with a concentration of 5.70ppm are relatively large. The response to 2-CEES gas is much higher than the response to ammonia water, ethanol and acetonitrile. However, when the working temperature of the gas sensor becomes higher and higher, the response to acetone also becomes larger and larger. So in summary, the optimal working temperature of the gas sensor with an Al2O3 content of 4wt.% when detecting 2-CEES gas is 340℃. The response time and recovery time of the gas sensor with an Al2O3 content of 4wt.% to 2-CEES gas with a concentration of 5.70ppm are 5s and 42s respectively, as shown in Figure 2. Figure 4 c. The gas sensor with Al2O3 content of 4wt.% has a sensing response to 2-CEES gas with a concentration of 0.10ppm at the optimal working temperature of 340℃. Figure 4d. When 0.10 ppm of 2-CEES gas was injected into the sealed test apparatus, the gas sensor exhibited a sensitivity of 27%. This demonstrates that a gas sensor with a 4 wt.% Al2O3 content can detect and monitor extremely low concentrations of 2-CEES gas. This facilitates the real-world application of WO3 / Al2O3 / graphite gas sensors for detecting and monitoring 2-CEES gas, and can quickly detect 2-CEES gas leaks.

[0039] The response of the gas sensor with Al2O3 content of 4wt.% to 2-CEES gas in the concentration range of 0.10-11.40ppm was tested, as shown in Figure 2. Figure 5 As shown in a. Figure 5 As can be seen in a, as the concentration of 2-CEES gas increases, the response of the gas sensor to 2-CEES gas also increases. This shows that the gas sensor with an Al2O3 content of 4wt.% has good response recovery characteristics to 2-CEES gas. Next, the linear correlation curve between the response of the gas sensor with an Al2O3 content of 4wt.% to 2-CEES gas and the 2-CEES gas concentration was studied, as shown in Figure 1. Figure 5 As shown in Figure b. Initially, the sensitivity of the gas sensor to 2-CEES gas increases with the increase in 2-CEES gas concentration. However, when the 2-CEES gas concentration exceeds 3.10 ppm, the gas sensor's response to 2-CEES gas begins to saturate. This indicates that the gas sensor with an Al2O3 content of 4 wt.% has a relatively wide detection range when detecting 2-CEES gas. The repeatability and long-term stability of the sensing response of the gas sensor with an Al2O3 content of 4 wt.% when detecting 2-CEES gas with a concentration of 5.70 ppm are shown in Figure 2. Figure 5 c and Figure 5 At the optimal working temperature of 340℃, the gas sensor with Al2O3 content of 4wt.% was subjected to 6 repeated cycle tests with 2-CEES gas concentration of 5.70ppm. The results are shown in Figure d. Figure 5 As shown in c. Figure 5 As can be seen from c, the sensitivity of the gas sensor to 2-CEES gas with a concentration of 5.70ppm was maintained at about 69% in 6 repeated cycle tests. And at the end of each detection cycle of the gas sensor to 2-CEES gas, the resistance of the gas sensor will return to its initial value. These data show that the gas sensor with an Al2O3 content of 4wt.% has good repeatability for 2-CEES gas. Next, the gas sensor with an Al2O3 content of 4wt.% was tested for its gas sensing performance to 2-CEES gas with a concentration of 5.70ppm for 6 consecutive days. Figure 5 d. Figure 5 As shown in Figure d, the gas sensor with a 4 wt.% Al2O3 content maintained a nearly constant response of around 69% for 5.70 ppm of 2-CEES gas over six consecutive days, despite some minor fluctuations. These results demonstrate that the gas sensor with a 4 wt.% Al2O3 content exhibits excellent repeatability and long-term stability for 2-CEES gas.

[0040] The WO3 / Al2O3 / graphite gas sensor for 2-CEES gas detection prepared in the present invention has the advantages of simple preparation, low cost, good cycle stability, etc.

[0041] It should be noted that, in the technical solution of the present invention, in the embodiments, although some numerical values ​​with better effects are given, for example, 96 mg of WO3 and 4 mg of Al2O3 are put into a mortar, ground for 30 minutes to make them evenly mixed, and then poured into a crucible, the present invention is not limited to the masses of WO3 and Al2O3 given in the above embodiments, and the specific masses of WO3 and Al2O3 should be determined according to actual needs; for example, the stirring time of WO3, Al2O3 and graphite is 24 hours in the embodiments, but the present invention is not limited to the stirring time given in the above embodiments. Since the stirring time is 6-24 hours, the 6 hours in the embodiments can be taken, and 10 hours, 24 hours, etc. can also be taken. The specific stirring time needs to be determined according to actual conditions; that is, the content claimed to be protected by the present invention is based on the scope recorded and explained in the claims.

[0042] Example 2

[0043] A preparation method of a WO3 / Al2O3 / graphite 2-CEES gas sensor is similar to that of Example 1, except that in step 1), the mass ratio of WO3:Al2O3 is 98:2.

[0044] Example 3

[0045] A preparation method of a WO3 / Al2O3 / graphite 2-CEES gas sensor is similar to that of Example 1, except that in step 1), the mass ratio of WO3:Al2O3 is 92:8.

[0046] Example 4

[0047] A preparation method of a WO3 / Al2O3 / graphite 2-CEES gas sensor is similar to that of Example 1, except that in step 2), the high-temperature calcination is performed at 110°C, 600°C, and 700°C for 2h respectively.

[0048] Example 5

[0049] A preparation method of a WO3 / Al2O3 / graphite 2-CEES gas sensor is similar to that of Example 1, except that in step 2), the high-temperature calcination is performed at 110°C, 600°C, and 700°C for 3 hours respectively.

[0050] Example 6

[0051] A preparation method of a WO3 / Al2O3 / graphite 2-CEES gas sensor is similar to that of Example 1, except that in step 3), the volume fraction ratio of ethanol to deionized water is 20:5, and the amount of graphite is 2.7 mg.

[0052] Example 7

[0053] A preparation method of a WO3 / Al2O3 / graphite 2-CEES gas sensor is similar to that of Example 1, except that in step 3), the volume fraction ratio of ethanol to deionized water is 20:10, and the amount of graphite is 2.7 mg.

[0054] Example 8

[0055] A preparation method of a WO3 / Al2O3 / graphite 2-CEES gas sensor is similar to that of Example 1, except that in step 4), the stirring time is 6 hours.

[0056] Example 9

[0057] A preparation method of a WO3 / Al2O3 / graphite 2-CEES gas sensor is similar to that of Example 1, except that in step 4), the stirring time is 10 h.

[0058] Example 10

[0059] A preparation method of a WO3 / Al2O3 / graphite 2-CEES gas sensor is similar to that of Example 1, except that in step 4), the stirring time is 16 hours.

[0060] Example 11

[0061] A preparation method of a WO3 / Al2O3 / graphite 2-CEES gas sensor is similar to that of Example 1, except that in step 5), the drying temperature is 55°C and the drying time is 20 hours.

[0062] Example 12

[0063] A preparation method of a WO3 / Al2O3 / graphite 2-CEES gas sensor is similar to that of Example 1, except that in step 5), when the drying temperature is 65°C, the drying time is 18 hours.

[0064] It should be noted that the technical contents of the present invention described above are only for the purpose of explaining and illustrating the technical essence of the present invention to enable those skilled in the art to understand the technical essence of the present invention. Therefore, the technical contents described above are not intended to limit the substantial protection scope of the present invention. The substantial protection scope of the present invention shall be based on the claims. Those skilled in the art should be aware that any modifications, equivalent substitutions, and improvements based on the substantial spirit of the present invention shall fall within the substantial protection scope of the present invention.

Claims

1. A method for preparing a WO3 / Al2O3 / graphite composite material, characterized in that: The steps include: 1) Mixing WO3 and Al2O3: Weigh appropriate amounts of WO3 and Al2O3, put them into a mortar, grind them until they are evenly mixed, and then pour them into a crucible; 2) High-temperature calcination of the WO3 and Al2O3 mixture: placing the mixture prepared in step 1) into a muffle furnace, calcining at different temperatures and collecting the solid product after high-temperature calcination; 3) Prepare graphite solution: Add ethanol and deionized water to a beaker and stir with a rotor. Then add graphite to the beaker, stirring the ethanol and deionized water. Continue stirring with the rotor to disperse the graphite evenly in the solution. 4) Mixing WO3, Al2O3, and graphite: Add the solid product obtained in step 2) to the graphite solution obtained in step 3), and continuously stir to obtain a WO3 / Al2O3 / graphite solution; 5) Preparation of WO3 / Al2O3 / graphite composite material: The WO3 / Al2O3 / graphite solution obtained in step 4) was placed in an oven to dry.

2. The preparation method according to claim 1, wherein In the step 1), based on the total mass of WO3 and Al2O3, the mass of WO3 accounts for 88%-98%, the mass of Al2O3 accounts for 2%-12%, and the grinding time is 20-40 minutes.

3. The preparation method according to claim 1, wherein In step 2), the high temperature calcination heating rate is 3-6°C min -1 , the temperature is raised to 105-115℃ and calcined for 1~3h, the temperature is raised to 580-620℃ and calcined for 1~3h, and finally the temperature is raised to 680-720℃ and calcined for 1~3h.

4. The preparation method according to claim 1, wherein In step 3), the volume ratio of ethanol to deionized water is 20-25:5-10, and the amount of graphite used is 0.05-0.5 mg ml -1 .

5. The preparation method according to claim 1, wherein In the step 5), when the drying temperature is 55-65° C., the drying time is 6-24 hours.

6. Use of the WO3 / Al2O3 / graphite composite material obtained by the preparation method according to any one of claims 1 to 5 as a gas-sensitive material or a gas sensor in gas detection.

7. The use according to claim 6, characterized in that Mix the WO3 / Al2O3 / graphite composite material with deionized water, apply it evenly on the ceramic tube, and put it in an oven to dry.

8. The use according to claim 6 or 7, characterized in that Used for the detection of gas 2-CEES.

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