Different morphologies of molybdate prepared by using molybdenum trioxide as substrate, and preparation method and application thereof

Abstract

This invention discloses molybdates with different morphologies prepared using molybdenum trioxide as a substrate, their preparation methods, and applications. The preparation method includes the following steps: dispersing molybdenum trioxide nanorods in deionized water, adding copper acetate or zinc acetate, then adding ammonia dropwise until the pH of the system is 8-9, stirring and mixing evenly, and then hydrothermally reacting at 110-130℃ for 10-14 hours. After filtration, washing, and drying, a precursor is obtained. Finally, the precursor is calcined in an air atmosphere. This invention uses molybdenum trioxide nanorods as a substrate and, by adding different types of acetate, prepares molybdates with nanosheet or micron-sized morphologies under the same preparation steps and conditions. Furthermore, the molybdates, when used to make resistive gas sensors, exhibit high gas sensing sensitivity.

Description

Technical Field

[0001] This invention belongs to the field of micro and nanomaterials technology, specifically relating to molybdates with different morphologies prepared using molybdenum trioxide as a substrate, their preparation methods, and applications. Background Technology

[0002] Due to the rapid development of the information age and severe environmental pollution, gas detection tools have become indispensable. Several traditional techniques for gas detection include gas chromatography and spectroscopy, such as proton transfer reaction mass spectrometry (PTMS) and ion mobility spectrometry-mass spectrometry (IMS). However, they share common drawbacks: high cost, time-consuming operation, and complex sample processing, significantly limiting their practical application. Gas sensors convert detected gas information into electrical signals, and their low cost and portability have led to their widespread use in daily life.

[0003] Molybdenum trioxide (MoO3) is an important wide-bandgap n-type semiconductor material with a bandgap width E g =3.02 eV, MoO3 has numerous applications in gas sensing, hydrogen storage, photocatalysis, and batteries. Therefore, the preparation and properties of MoO3 materials remain a hot topic in scientific research. Chinese patent CN 110879238A discloses a molybdenum trioxide nanostructure sensitive material and a corresponding ammonia sensor, along with its preparation method. Specifically, it discloses the process of mixing appropriate amounts of sodium molybdate, thiourea, citric acid, and hexadecyltrimethylammonium bromide into a solution, followed by heating and drying to obtain MoS2 powder. This powder is then calcined at a suitable temperature to obtain MoO3 powder sensitive material. This sensitive material is then formulated into a slurry, coated onto a substrate surface, sintered at a suitable temperature, and electrodes are added accordingly. A heating layer is installed inside the substrate's leads to produce the sensor. This sensor exhibits extremely high sensitivity to ammonia, with a response of 4000 to 100 ppm ammonia and a detection limit of 100 ppb. However, the preparation method of the molybdenum trioxide nanostructure sensitive material disclosed in this patent is complex, and its ability to sense a limited range of gases is limited, with relatively low sensitivity.

[0004] In existing technologies, the sensitivity of molybdenum trioxide (MoO) to gas sensing is typically improved by modifying it. For example, Chinese patent CN 116046852A discloses a high-performance ethanol gas sensor with a ZnO nanoparticle-modified α-MoO heterojunction. Specifically, it discloses that a one-dimensional α-MoO3 nanoribbon is used as a matrix, and zinc oxide nanoparticles are uniformly loaded onto the surface of the one-dimensional α-MoO3 nanoribbon using a simple liquid-phase chemical method to modify the surface, forming an N-type heterojunction composite material. A high-performance ethanol gas sensor is then prepared based on this composite material. This patent improves the sensing sensitivity to ethanol gas by loading and modifying it with zinc oxide nanoparticles; however, it only responds to ethanol gas, limiting its application range, and the loading of zinc oxide nanoparticles does not change the morphology of the one-dimensional α-MoO3 nanoribbon. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing molybdates with different morphologies based on molybdenum trioxide and their applications. Using molybdenum trioxide nanorods as a substrate, different types of acetates and ammonia are added to prepare molybdates with nanosheet or micron-sized morphologies under the same preparation steps and conditions. Furthermore, the sensitivity of resistive gas sensors made from molybdates is significantly higher than that of gas sensors made from molybdenum trioxide nanorods.

[0006] The technical solution adopted in this invention is as follows:

[0007] A method for preparing molybdates with different morphologies using molybdenum trioxide as a substrate, the method comprising the following steps:

[0008] (1) Mix the ammonium molybdate nitric acid solution and the aspartic acid nitric acid solution evenly, and then perform a hydrothermal reaction at 160-200℃ for 20-26 hours. After filtration, washing and drying, molybdenum trioxide nanorods are prepared.

[0009] (2) Disperse molybdenum trioxide nanorods in deionized water, add copper acetate or zinc acetate, then add ammonia dropwise until the pH of the system is 8-9, stir and mix evenly, and then perform hydrothermal reaction at 110-130℃ for 10-14h. After filtration, washing and drying, the precursor is obtained.

[0010] (3) The precursor is calcined in an air atmosphere to prepare porous copper molybdate nanosheets or porous zinc molybdate microflowers.

[0011] In step (1), the mass ratio of ammonium molybdate to aspartic acid is 2.5-3.0:1.0-1.3.

[0012] In step (1), the concentration of ammonium molybdate in the nitric acid solution is 0.125–0.2 g / mL; the mass percentage concentration of the nitric acid solution is 65–68%; the concentration of ammonium molybdate in the nitric acid solution of aspartic acid is 0.05–0.1 g / mL; the mass percentage concentration of the nitric acid solution is 65–68%.

[0013] In step (2), the mass ratio of molybdenum trioxide nanorods to copper acetate is 0.1-0.15:0.1-0.3; the mass ratio of molybdenum trioxide nanorods to zinc acetate is 0.1-0.15:0.1-0.3.

[0014] In step (2), the mass percentage concentration of the ammonia water is 25-28%.

[0015] In step (2), the mixing speed is 50-300 rpm and the mixing time is 40-60 min.

[0016] In step (3), the calcination conditions are heating at 500-550℃ and holding for 0.5-2 hours.

[0017] The present invention also provides porous copper molybdate nanosheets or porous zinc molybdate microflowers prepared by the method, wherein the porous copper molybdate nanosheets have a particle size of 200-250 nm and an average pore size of 15.8 nm; and the porous zinc molybdate microflowers have an average particle size of 10-20 μm and an average pore size of 15.5 nm.

[0018] The present invention also provides the application of the porous copper molybdate nanosheets or porous zinc molybdate microflowers in gas sensors. The porous copper molybdate nanosheets or porous zinc molybdate microflowers have high sensitivity to ethanol, isopropanol and methanol gases and good stability.

[0019] The method for preparing molybdates with different morphologies based on molybdenum trioxide provided by this invention first prepares molybdenum trioxide nanorods using a simple preparation method. Then, using the molybdenum trioxide nanorods as a substrate, a precursor is obtained by adding copper acetate or zinc acetate and ammonia water through a hydrothermal reaction. The precursor is then calcined in an air atmosphere to decompose and oxidize the precursor into molybdates, water, and carbon dioxide. The reaction products, water and carbon dioxide gas, are easily volatilized and removed during the calcination process. Therefore, after high-temperature calcination, porous copper molybdate nanosheets or porous zinc molybdate micro-flowers with different morphologies are directly obtained.

[0020] When porous copper molybdate nanosheets or porous zinc molybdate microflora are used to fabricate resistive gas sensors, their sensitivity is significantly higher than that of gas sensors made of molybdenum trioxide. Furthermore, they exhibit higher sensitivity to ethanol, isopropanol, and methanol gases, and also demonstrate good stability.

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

[0022] 1. The preparation method provided by this invention is simple, with short reaction time and low temperature; and by changing the type of acetate using the same preparation method, molybdates with different morphologies and uniform size with high specific surface area and high crystallinity can be prepared, which are structurally stable and have stable properties in air.

[0023] 2. The molybdate provided by this invention has a high sensitivity to volatile organic gases in the air;

[0024] 3. The preparation method provided by this invention has low equipment requirements, does not require complex conditions such as microwaves, the raw materials are readily available, the cost is low, and it can be mass-produced. Attached Figure Description

[0025] Figure 1 SEM image of the molybdenum trioxide nanorods prepared in Example 1;

[0026] Figure 2 The image shows the XRD pattern of the molybdenum trioxide nanorods prepared in Example 1.

[0027] Figure 3 EDS image of the molybdenum trioxide nanorods prepared in Example 1;

[0028] Figure 4 The BET diagram is of the molybdenum trioxide nanorods prepared in Example 1;

[0029] Figure 5 SEM image of the sheet-like precursor prepared in Example 1;

[0030] Figure 6 XRD pattern of the sheet-like precursor prepared in Example 1;

[0031] Figure 7 SEM image of the copper molybdate nanosheets prepared in Example 1;

[0032] Figure 8 The image shows the XRD pattern of the copper molybdate nanosheets prepared in Example 1.

[0033] Figure 9 EDS image of copper molybdate nanosheets prepared in Example 1;

[0034] Figure 10 The image shows the BET plot of the copper molybdate nanosheets prepared in Example 1.

[0035] Figure 11 SEM image of the micronized precursor prepared in Example 2;

[0036] Figure 12 XRD pattern of the micronized precursor prepared in Example 2;

[0037] Figure 13 SEM image of zinc molybdate microflora prepared in Example 2;

[0038] Figure 14 XRD pattern of zinc molybdate microflora prepared in Example 2;

[0039] Figure 15 EDS image of zinc molybdate microflora prepared in Example 2;

[0040] Figure 16 BET plot of zinc molybdate microflora prepared in Example 2;

[0041] Figure 17 SEM image of the product prepared in Comparative Example 1;

[0042] Figure 18 SEM image of the product prepared in Comparative Example 2;

[0043] Figure 19 SEM image of the product prepared in Comparative Example 3;

[0044] Figure 20 SEM image of the product prepared in Comparative Example 4;

[0045] Figure 21 The optimal operating temperature for molybdenum trioxide nanorods and copper molybdate nanosheets;

[0046] Figure 22 The optimal operating temperature for molybdenum trioxide nanorods and zinc molybdate microflowers;

[0047] Figure 23 The response sensitivity of molybdenum trioxide nanorods and copper molybdate nanosheets to gases such as acetone, isopropanol, and ethanol at 100 ppm at the optimal operating temperature was determined.

[0048] Figure 24 The sensitivity of molybdenum trioxide nanorods and zinc molybdate nanosheets to gases such as 100 ppm ethanol, isopropanol, and methanol at the optimal operating temperature was determined. Detailed Implementation

[0049] The present invention will now be described in detail with reference to the embodiments.

[0050] Example 1

[0051] A method for preparing copper molybdate nanosheets includes the following steps:

[0052] (1) 2.5 g of ammonium molybdate was dissolved in 16 mL of deionized water and 4 mL of 65% nitric acid solution to obtain a nitric acid solution of ammonium molybdate; 1.0 g of aspartic acid was dissolved in 16 mL of deionized water and 4 mL of 65% nitric acid solution to obtain a nitric acid solution of aspartic acid; the two solutions were stirred and mixed for 50 minutes under magnetic stirring at 50 rpm to obtain a mixed transparent liquid, which was then transferred to a high-pressure reactor and hydrothermally reacted at 180℃ for 24 hours to obtain a white precipitate. The white precipitate was filtered, washed, and dried at 60℃ for 24 hours to obtain molybdenum trioxide nanorods, the SEM image of which is shown below. Figure 1 As shown in the figure, it can be seen that it has a rod-like structure; its XRD pattern is as follows. Figure 2 As shown, its EDS plot is as follows Figure 3 As shown, its BET chart is as follows: Figure 4 As shown.

[0053] (2) 0.12 g of molybdenum trioxide nanorods were added to 20 mL of distilled water, followed by 0.25 g of copper acetate. Then, 25% ammonia solution was added dropwise until the pH of the system reached 8. The mixture was stirred for 40 minutes under magnetic stirring at 80 rpm to obtain a mixed suspension. The suspension was transferred to a high-pressure reactor and reacted at 120 °C for 12 hours to obtain a green precipitate. The green precipitate was filtered, washed, and dried at 60 °C for 5 hours to obtain a sheet-like precursor. Its SEM image is shown below. Figure 5 As shown in the figure, it can be seen that it has a sheet-like structure; its XRD pattern is as follows. Figure 6 As shown.

[0054] (3) The sheet-like precursor was calcined at 500℃ for 2 hours, and after cooling, a yellowish-brown porous sheet-like copper molybdate powder was obtained; its SEM image is shown below. Figure 7 As shown in the figure, it can be seen that it has a sheet-like structure; its XRD pattern is as follows. Figure 8 As shown, the obtained diffraction pattern matches the peaks listed in the standard card for copper molybdate, JCPDS No. 24-0055, indicating that the final material prepared in this example is copper molybdate; its EDS plot is shown below. Figure 9 As shown in the figure, it can be seen from the figure that it is composed of three elements: Cu, Mo, and O; its BET diagram is as follows. Figure 10 As shown, its specific surface area is 19.2 m². 3 The average pore size is 15.8 nm, indicating that it is a porous material.

[0055] Example 2

[0056] A method for preparing zinc molybdate micron flowers includes the following steps:

[0057] (1) The preparation method of molybdenum trioxide nanorods is the same as in Example 1.

[0058] (2) 0.12 g of molybdenum trioxide nanorods were added to 20 mL of distilled water, followed by 0.25 g of zinc acetate. Then, 25% ammonia solution was added dropwise until the pH of the system reached 9. The mixture was stirred for 40 minutes under magnetic stirring at 80 rpm to obtain a mixed suspension. The suspension was transferred to a high-pressure reactor and reacted at 120 °C for 12 hours to obtain a white precipitate. The white precipitate was filtered, washed, and dried at 60 °C for 5 hours to obtain a micron-shaped flower-like precursor. Its SEM image is shown below. Figure 11 As shown in the figure, it can be seen that it has a sheet-like structure; its XRD pattern is as follows. Figure 12 As shown.

[0059] (3) The micronized precursor was calcined at 500℃ for 2 hours, and after cooling, white zinc molybdate micronized pollen particles were obtained. Its SEM image is shown below. Figure 13 As shown in the figure, it can be seen that it has a micron-sized flower-like structure. Its XRD pattern is as follows. Figure 14 As shown, the obtained diffraction pattern matches the peaks listed in the standard card for zinc molybdate, JCPDS No. 86-1771, indicating that the final material prepared in this example is zinc molybdate; its EDS plot is shown below. Figure 15 As shown in the figure, it can be seen from the figure that it is composed of three elements: Zn, Mo, and O; its BET graph is as follows. Figure 16 As shown, its specific surface area is 22.4 m². 3 The average pore size is 15.5 nm, indicating that it is a porous material.

[0060] Comparative Example 1

[0061] Everything else is the same as in Example 1, except that in step (2), 25% ammonia solution is added dropwise until the pH of the system reaches 7. The SEM image of the final product is shown below. Figure 17 As shown in Figure 17, if the pH of the reaction system is too low, the product is flat and plate-shaped with a large size.

[0062] Comparative Example 2

[0063] Everything else is the same as in Example 1, except that in step (2), 25% ammonia solution is added dropwise until the pH of the system reaches 10. The SEM image of the final product is shown below. Figure 18 As shown in Figure 18, if the pH of the reaction system is too high, the product will be a blocky product with uneven size and a large thickness.

[0064] Comparative Example 3

[0065] The rest is the same as in Example 2, except that in step (2), 25% ammonia solution was added dropwise until the pH of the system reached 7. The SEM image of the final product is shown below. Figure 19 As shown in Figure 19, the final product has an irregular morphology and cannot form micron-sized flowers.

[0066] Comparative Example 4

[0067] The rest is the same as in Example 2, except that in step (2), 25% ammonia solution is added dropwise until the pH of the system reaches 10. The SEM image of the final product is shown below. Figure 20 As shown in Figure 20, the final product has an irregular morphology and exhibits a state that is about to form the morphology of Example 2.

[0068] Application examples

[0069] Application of molybdate materials in gas sensors

[0070] The copper molybdate nanosheets prepared in Example 1, the zinc molybdate microflowers prepared in Example 2, and the molybdenum trioxide nanorods were dispersed in anhydrous ethanol, and then uniformly coated onto ceramic tubes with electrodes to fabricate copper molybdate gas sensors, zinc molybdate gas sensors, and molybdenum trioxide gas sensors, respectively. These sensors were dried at 50°C for 2 hours, followed by heat treatment at 200°C for 2 hours. Then, a small nickel-chromium alloy coil was placed inside the tube as a heater to provide the operating temperature for the sensors, and the sensors were aged at 300°C for 48 hours.

[0071] The following tests were conducted at different temperatures: acetone gas at a concentration of 100 pm was injected into the test chambers of the copper molybdate gas sensor and the molybdenum trioxide gas sensor, respectively. After approximately two minutes, when the sensor output response value stabilized, the acetone gas was then withdrawn from the test chamber, and the sensor response gradually recovered. The gas response values ​​of the sensors in dry air and in the presence of the target gas were tested and recorded using an electrochemical workstation and a computer. The sensor's gas response sensitivity is defined as S = R a / R g (Reducing gas), R a It is the resistance of the sensor in dry air, R g This refers to the sensor's resistance in the test gas. The optimal temperature for testing copper molybdate and molybdenum trioxide sensors with acetone is also specified. Figure 21 As shown in the figure, the optimal response temperature of copper molybdate to 100 ppm acetone gas is 210℃, and that of molybdenum trioxide is 240℃. The optimal response values ​​for the two materials are 145.4 and 21.1, respectively.

[0072] Ethanol gas at a concentration of 100 ppm was injected into the zinc molybdate gas sensor and the molybdenum trioxide sensor respectively using a syringe. After waiting for about two minutes, when the sensor output response value stabilized, the acetone gas in the test chamber was then withdrawn, and the sensor response gradually recovered. This determined the optimal temperature for the zinc molybdate sensor to respond to 100 ppm ethanol. Figure 22As shown in the figure, the optimal response temperature of zinc molybdate material to 100 ppm ethanol gas is 220℃, and the optimal response value is 58.3.

[0073] Eight different gases with a concentration of 100 ppm were injected into the copper molybdate sensor and the molybdenum trioxide sensor using a syringe. Each gas was kept for one minute, then withdrawn, and the next gas was injected after the response recovered. Figure 23 It can be seen that the copper molybdate sensor responds to the following eight gases: acetone (145.4), isopropanol (102.3), ethanol (90.3), methanol (51.1), toluene (48.0), benzene (44.1), formaldehyde (42.7), and ammonia (31.6), while the molybdenum trioxide sensor responds to the following gases: 21.1, 10.3, 11.3, 2.9, 6.3, 1.7, 4.3, and 2.2, respectively. All of these performances are lower than those of the copper molybdate sensor.

[0074] Twelve different gases at a concentration of 100 ppm were injected into the zinc molybdate sensor and the molybdenum trioxide sensor using a syringe. Each gas was retained for one minute, then withdrawn, and the next gas was injected only after the response recovered. The zinc molybdate sensor responded to the following 12 gases: ethanol (58.3), isopropanol (47.5), methanol (45.6), acetone (34.6), benzene (16.5), formaldehyde (15.5), ammonia (12.0), toluene (9.4), hydrogen (4.9), carbon monoxide (4.6), nitrogen dioxide (3.9), and sulfur dioxide (2.4). The molybdenum trioxide sensor responded to the following gases: 21.1, 10.3, 2.9, 2.5, 1.7, 4.3, 2.2, 6.3, 1.4, 1.6, 1.3, and 1.6.

[0075] in Figure 23 The test temperature for the copper molybdate gas sensor in the test was 210℃. Figure 23 and Figure 24 The test temperature of the molybdenum trioxide gas sensor in the test is 240℃; Figure 24 The zinc molybdate gas sensor in the test was tested at 220℃, which is its optimal operating temperature.

[0076] Performance testing studies have shown that the prepared copper molybdate nanosheets exhibit good sensitivity to common toxic and harmful organic gases in the air. Figure 23 As can be seen, the copper molybdate nanosheets prepared in Example 1 are more sensitive to toxic and harmful gases such as acetone, isopropanol, and ethanol at 100 ppm, with sensitivities of 145.4, 102.3, and 90.3, respectively. The zinc molybdate microflower sensor prepared in Example 2 also shows good response to a variety of gases, such as... Figure 24As shown in the figure, zinc molybdate microflora is more sensitive to toxic and harmful gases such as ethanol, isopropanol, and methanol at 100 ppm, with sensitivities of 58.3, 47.5, and 45.6, respectively.

[0077] The above-described detailed description of different morphologies of molybdates prepared on a molybdenum trioxide substrate, their preparation methods, and applications is illustrative rather than limiting. Several embodiments may be listed within the defined scope. Therefore, variations and modifications that do not depart from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing molybdates of different morphologies using molybdenum trioxide as a substrate, characterized in that, The method includes the following steps: (1) Mix the ammonium molybdate nitric acid solution and the aspartic acid nitric acid solution evenly, and then perform a hydrothermal reaction at 160-200℃ for 20-26 hours. After filtration, washing and drying, molybdenum trioxide nanorods are prepared. (2) Disperse molybdenum trioxide nanorods in deionized water, add copper acetate or zinc acetate, then add ammonia dropwise until the pH of the system is 8-9, stir and mix evenly, and then perform hydrothermal reaction at 110-130℃ for 10-14h. After filtration, washing and drying, the precursor is obtained. (3) The precursor is calcined in an air atmosphere to prepare porous copper molybdate nanosheets or porous zinc molybdate microflowers. In step (3), the calcination conditions are heating at 500-550℃ and holding for 0.5-2 hours; The porous copper molybdate nanosheets have a particle size of 200–250 nm and an average pore size of 15.8 nm; the porous zinc molybdate microflora have an average particle size of 10–20 μm and an average pore size of 15.5 nm. The molybdate is used in a gas sensor.

2. The method for preparing molybdates of different morphologies using molybdenum trioxide as a substrate according to claim 1, characterized in that, In step (1), the mass ratio of ammonium molybdate to aspartic acid is 2.5-3.0:1.0-1.

3.

3. The method for preparing molybdates of different morphologies using molybdenum trioxide as a substrate according to claim 1, characterized in that, In step (1), the concentration of ammonium molybdate in the nitric acid solution is 0.125–0.2 g / mL; the mass percentage concentration of the nitric acid solution is 65–68%; the concentration of aspartic acid in the nitric acid solution is 0.05–0.1 g / mL; the mass percentage concentration of the nitric acid solution is 65–68%.

4. The method for preparing molybdates of different morphologies using molybdenum trioxide as a substrate according to claim 1, characterized in that, In step (2), the mass ratio of molybdenum trioxide nanorods to copper acetate is 0.1–0.15: 0.1–0.3; The mass ratio of molybdenum trioxide nanorods to zinc acetate is 0.1–0.15:0.1–0.

3.

5. The method for preparing molybdates of different morphologies using molybdenum trioxide as a substrate according to claim 1, characterized in that, In step (2), the mass percentage concentration of the ammonia water is 25-28%.

6. The method for preparing molybdates of different morphologies using molybdenum trioxide as a substrate according to claim 1, characterized in that, In step (2), the mixing speed is 50-300 rpm and the mixing time is 40-60 min.

7. Porous copper molybdate nanosheets or porous zinc molybdate microflowers prepared by the method according to any one of claims 1-6.

8. The application of porous copper molybdate nanosheets or porous zinc molybdate microflowers as described in claim 7 in gas sensors.

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