A method for preparing Pd-doped CeO2 / ZnO nanofibers by ultrasonication and its application

Abstract

This invention discloses a method for preparing and applying Pd-doped CeO2 / ZnO nanofibers using an ultrasonic method, belonging to the field of gas sensor technology. Zinc acetate dihydrate and cerium acetate are dissolved in N-N-dimethylformamide, and a polyvinylpyrrolidone / DMF solution is added to obtain a Ce-Zn solution. The Ce-Zn solution is transferred to a syringe for electrospinning, and the spun material is collected and dried in a vacuum drying oven. The dried material is transferred to a boat, and the boat is calcined in a muffle furnace to obtain a CeO2 / ZnO composite nanofiber material. The CeO2 / ZnO composite nanofiber material is ultrasonically mixed in a palladium nitrate / DMF solution to obtain a palladium salt-CeO2 / ZnO composite material. The palladium salt-CeO2 / ZnO composite material is calcined in H2 / Ar to obtain a CeO2 / ZnO-Pd nanofiber material. This invention provides a method for preparing Pd-doped CeO2 / ZnO nanofibers by ultrasonication and their application. CeO2 / ZnO nanofibers are prepared by electrospinning and then Pd is doped by ultrasonication, which improves the selectivity to acetone gas.

Description

Technical Field

[0001] This invention relates to the field of gas sensor technology, specifically to a method for preparing Pd-doped CeO2 / ZnO nanofibers by ultrasonication and their application. Background Technology

[0002] In recent years, rapid industrial development has led to severe air pollution from the production of various toxic, harmful, and polluting gases, even impacting human health. Acetone is a volatile organic solvent that easily diffuses and evaporates at room temperature. Inhalation can cause dizziness, nausea, and other symptoms, and large amounts may cause significant damage to the nervous system. Furthermore, acetone vapor can irritate the skin and eyes. Studies have shown that the concentration of acetone vapor exhaled by a normal human exceeds 1800 ppm, while that exhaled by a diabetic patient is only 300-900 ppm. Therefore, the development of highly selective, low-concentration acetone sensors is of great significance.

[0003] Because gas-sensitive materials prepared from single oxides have limited response and selectivity to gases, the method of constructing heterojunctions using composite materials to improve the performance of gas sensors is widely used. For example, Chinese patent CN109632893 discloses a gas sensor based on pn heterostructure NiO-In2O3 composite nanospheres with high selectivity for NO2; Chinese patent CN109107358B discloses a cerium oxide / copper oxide heterojunction composite oxide, which has better gas-sensing performance for H2S than single copper oxide-based materials, and can more accurately detect the content of H2S. Binary material compositing can effectively improve the gas-sensing performance of materials, but to further improve the selectivity of the sensor, other metals can be added to construct ternary materials.

[0004] Due to electronic sensitization and spillover effects, doping with noble metals has become a common and effective method to improve the gas-sensing performance of materials. For example, Chinese patent CN208383710U discloses a Pd-doped ZnO acetone gas sensor with high sensitivity for acetone gas detection; Chinese patent CN114935594B discloses a gas sensor sensitive membrane and gas sensor based on Fe@Pt / C core-shell nanocatalytic material, and the sensor prepared by it has high sensitivity to H2S, reaching 3.49 uA / ppm. However, due to the high cost of noble metals, large doping amounts are not conducive to mass production. Therefore, it is of great significance to use appropriate methods to efficiently utilize noble metals, reduce costs, and effectively improve gas-sensing performance. To address the above problems, this invention provides a method for preparing Pd-doped CeO2 / ZnO nanofiber materials by ultrasonic doping and its application. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing Pd-doped CeO2 / ZnO nanofibers by ultrasonication and its application. CeO2 / ZnO nanofibers are prepared by electrospinning and then Pd is doped by ultrasonication, thereby improving the selectivity for acetone gas.

[0006] To achieve the above objectives, this invention provides a method for preparing Pd-doped CeO2 / ZnO nanofibers using an ultrasonic method, specifically comprising the following steps:

[0007] (1) After zinc acetate dihydrate and cerium acetate are completely dissolved in NN dimethylformamide, polyvinylpyrrolidone / DMF solution is added and stirred evenly to obtain Ce-Zn solution;

[0008] (2) Transfer the Ce-Zn solution into a syringe, perform electrospinning, collect the spun material and dry it in a vacuum drying oven;

[0009] (3) The dried material was transferred to the ark and the ark was placed in a muffle furnace for calcination to obtain CeO2 / ZnO composite nanofiber material;

[0010] (4) The CeO2 / ZnO composite nanofiber material was placed in a palladium nitrate / DMF solution and ultrasonically mixed to obtain a palladium salt-CeO2 / ZnO composite material;

[0011] (5) The palladium salt-CeO2 / ZnO composite material was placed in H2 / Ar and calcined to obtain CeO2 / ZnO-Pd nanofiber material.

[0012] Preferably, in step (1), the mass ratio of polyvinylpyrrolidone, zinc acetate dihydrate, cerium acetate, and N,N-dimethylformamide is 1:0.8-1.2:0.8-1.2:6-10.

[0013] Preferably, in step (2), during the electrospinning process, the voltage is 13-17kV, the solution flow rate is 0.4-0.7mL / h, and the spinning receiving distance is 13-17cm.

[0014] Preferably, in step (2), the temperature of the vacuum drying oven is 50-80°C and the heat preservation time is 12-24 hours.

[0015] Preferably, in step (3), the calcination heating rate is 1-3℃ / min, the calcination temperature is raised to 280-300℃ and held for 1-3 hours, and then raised to 600-700℃ and held for 1-3 hours.

[0016] Preferably, in step (4), the mass ratio of palladium nitrate / DMF solution to CeO2 / ZnO composite nanofiber material is 1:500-1000.

[0017] Preferably, in step (5), the calcination heating rate is 1-3℃ / min, and the calcination temperature is maintained at 600-700℃ for 1-3 hours.

[0018] The present invention also provides the application of the Pd-doped CeO2 / ZnO nanofiber material prepared above in an acetone gas sensor.

[0019] Therefore, this invention provides a method for preparing Pd-doped CeO2 / ZnO nanofibers by ultrasonication and its application, with the following specific benefits:

[0020] (1) This invention prepares CeO2 / ZnO nanofibers by electrospinning and then dops Pd by ultrasonication to finally obtain CeO2 / ZnO-Pd nanofiber materials. The preparation method is simple and easy to operate.

[0021] (2) The CeO2 / ZnO-Pd nanofiber material prepared in this invention constructs an npn heterojunction, which enhances the resistance control capability. In the above heterojunction, PdO is a p-type semiconductor. Electrons from the CeO2 and ZnO surfaces transfer to PdO, and holes in PdO transfer to CeO2 and ZnO. An electron accumulation layer is formed on the surface of PdO. The active electrons on the charge accumulation layer combine with adsorbed oxygen molecules on the material surface to form more adsorbed oxygen ions, thereby promoting the reaction between the target gas and the adsorbed oxygen ions on the material, thus increasing the gas-sensing performance of the sensor for acetone vapor;

[0022] (3) The CeO2 / ZnO-Pd nanofiber material of the present invention uses ultrasonic doping of Pd, which has a higher utilization rate of Pd. It can use less Pd to have a better response and selectivity to acetone gas, and has a faster response speed and a lower detection limit.

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0024] Figure 1 This is a TEM image of the CeO2 / ZnO-Pd nanofiber material prepared in Example 1 of this invention;

[0025] Figure 2 This is a mapping image of the CeO2 / ZnO-Pd nanofiber material prepared in Example 1 of this invention;

[0026] Figure 3These are X-ray photoelectron spectra of the materials prepared in Example 1 and Comparative Example 2 of the present invention, wherein the upper curve is the X-ray photoelectron spectrum of Example 1 and the lower curve is the X-ray photoelectron spectrum of Comparative Example 2.

[0027] Figure 4 This is a graph showing the relationship between the response values ​​of the materials prepared in Example 1 and Comparative Examples 1-3 of the present invention to 50 ppm acetone gas and the operating temperature.

[0028] Figure 5 This is a radar chart showing the selectivity of the materials prepared in Example 1 and Comparative Examples 1-3 of the present invention to different gas response values ​​of 50 ppm;

[0029] Figure 6 This is a graph showing the resistance of the CeO2 / ZnO-Pd acetone sensor prepared in Example 1 of the present invention to 50ppm acetone gas over time at an operating temperature of 300℃.

[0030] Figure 7 This is a graph showing the change in resistance of the CeO2 / ZnO-Pd acetone sensor prepared in Example 1 of the present invention to 330ppb acetone gas over time at an operating temperature of 300℃.

[0031] Figure 8 This is a graph showing the response value of the CeO2 / ZnO-Pd acetone sensor prepared in Example 1 of the present invention to 50ppm acetone gas over 40 days at an operating temperature of 300℃. Detailed Implementation

[0032] The following detailed description of embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0033] Example 1

[0034] This embodiment provides a method for preparing Pd-doped CeO2 / ZnO nanofibers using ultrasonication, specifically including the following steps:

[0035] (1) Add 0.45g zinc acetate dihydrate and 0.65g cerium acetate to 2mL of NN dimethylformamide (DMF) and dissolve completely. Then add 0.8g polyvinylpyrrolidone / 4mL DMF solution and stir until homogeneous to obtain Ce-Zn solution.

[0036] (2) Transfer the Ce-Zn solution into a syringe and perform electrospinning under the conditions of 15kV voltage, 0.5mL / h solution flow rate and 15cm distance between the spinneret and the receiver. Collect the spun material and dry it in a vacuum drying oven at 60℃ for 24h.

[0037] (3) Transfer the dried material to the boat, place the boat in the muffle furnace for calcination, and heat it at a rate of 1℃ / min. After the calcination temperature rises to 280℃, keep it at that temperature for 1h, and then heat it again at a rate of 1℃ / min to 600℃ and keep it at that temperature for 2h to obtain CeO2 / ZnO composite nanofiber material.

[0038] (4) 0.1g of CeO2 / ZnO composite nanofiber material was placed in 0.5mL of 0.00265g / mL palladium nitrate / DMF solution and ultrasonically mixed to obtain palladium salt-CeO2 / ZnO composite material.

[0039] (5) The palladium salt-CeO2 / ZnO composite material was placed in H2 / Ar and calcined. The temperature was increased at a rate of 1℃ / min. After the calcination temperature reached 600℃, it was kept at the temperature for 2h to obtain CeO2 / ZnO-Pd nanofiber gas-sensitive material.

[0040] like Figure 1 As shown, the TEM image reveals that some particles are embedded in the nanofiber gas-sensitive material; such as Figure 2 As shown in the mapping diagram, Zn, Ce, and Pd are uniformly distributed in the fiber, indicating that Pd is uniformly incorporated.

[0041] Comparative Example 1

[0042] This comparative example provides a method for preparing CeO2 / ZnO composite nanofiber materials, specifically including the following steps:

[0043] (1) Add 0.45g zinc acetate dihydrate and 0.65g cerium acetate to 2mL of NN dimethylformamide (DMF) and dissolve completely. Then add 0.8g polyvinylpyrrolidone / 4mL DMF solution and stir until homogeneous to obtain Ce-Zn solution.

[0044] (2) Transfer the Ce-Zn solution into a syringe and perform electrospinning under the conditions of 15kV voltage, 0.5mL / h solution flow rate and 15cm distance between the spinneret and the receiver. Collect the spun material and dry it in a vacuum drying oven at 60℃ for 24h.

[0045] (3) Transfer the dried material to the boat, place the boat in the muffle furnace for calcination, and heat it at a rate of 1℃ / min. After the calcination temperature rises to 280℃, keep it at that temperature for 1h, and then heat it again at a rate of 1℃ / min to 600℃ and keep it at that temperature for 2h to obtain CeO2 / ZnO composite nanofiber material.

[0046] Comparative Example 2

[0047] This comparative example provides a method for preparing CeO2 / ZnO-PdO composite nanofiber material, specifically including the following steps:

[0048] (1) Dissolve 0.22 g zinc acetate dihydrate and 0.32 g cerium acetate in 1 mL of NN dimethylformamide (DMF) completely, then add 2.5 mL of 0.00265 g / mL palladium nitrate / DMF solution, and finally add 0.4 g polyvinylpyrrolidone / 3 mL DMF solution. Stir well to obtain Pd-CeZn solution.

[0049] (2) Transfer the Pd-CeZn solution into a syringe and perform electrospinning under the conditions of 15kV voltage, 0.5mL / h solution flow rate and 15cm distance between the spinneret and the receiver. Collect the spun material and dry it in a vacuum drying oven at 60℃ for 24h.

[0050] (3) The dried material was transferred to the boat and placed in a muffle furnace for calcination. The temperature was increased at a rate of 1℃ / min. After the calcination temperature reached 280℃, it was kept at that temperature for 1h. Then, the temperature was increased again at a rate of 1℃ / min to 600℃ and kept at that temperature for 2h to obtain CeO2 / ZnO-PdO composite nanofiber material.

[0051] Comparative Example 3

[0052] This comparative example provides a method for preparing Pd-doped CeO2 / ZnO nanofibers using a stirring method, specifically including the following steps:

[0053] (1) Add 0.45g zinc acetate dihydrate and 0.65g cerium acetate to 2mL of NN dimethylformamide (DMF) and dissolve completely. Then add 0.8g polyvinylpyrrolidone / 4mL DMF solution and stir until homogeneous to obtain Ce-Zn solution.

[0054] (2) Transfer the Ce-Zn solution into a syringe and perform electrospinning under the conditions of 15kV voltage, 0.5mL / h solution flow rate and 15cm distance between the spinneret and the receiver. Collect the spun material and dry it in a vacuum drying oven at 60℃ for 24h.

[0055] (3) Transfer the dried material to the boat, place the boat in the muffle furnace for calcination, and heat it at a rate of 1℃ / min. After the calcination temperature rises to 280℃, keep it at that temperature for 1h, and then heat it again at a rate of 1℃ / min to 600℃ and keep it at that temperature for 2h to obtain CeO2 / ZnO composite nanofiber material.

[0056] (4) 0.1g of CeO2 / ZnO composite nanofiber material was placed in 0.5mL of 0.00265g / mL palladium nitrate / DMF solution and stirred to obtain palladium salt-CeO2 / ZnO composite material.

[0057] (5) The palladium salt-CeO2 / ZnO composite material was placed in H2 / Ar and calcined. The temperature was increased at a rate of 1℃ / min. After the calcination temperature reached 600℃, it was kept at the temperature for 2h to obtain CeO2 / ZnO-Pd nanofiber gas-sensitive material.

[0058] X-ray electron spectroscopy analysis was performed on Example 1 and Comparative Example 2, and the results are as follows: Figure 3 As shown, by Figure 3 It can be seen that Pd is present in the CeO2 / ZnO-Pd nanofiber material prepared in Example 1. 0 and Pd 2+ The CeO2 / ZnO-PdO composite nanofiber material prepared in Comparative Example 2 contains only Pd. 2+ .

[0059] The composite materials obtained in Example 1 and Comparative Examples 1-3 were applied to acetone gas sensors. The preparation method of the acetone gas sensors is as follows:

[0060] Using Al2O3 ceramic as a substrate, a circular gold electrode is formed at each end of the ceramic tube, and each gold electrode has two platinum wires as leads. The composite material prepared above is ground into powder, and 1-3 drops of terpineol are added and stirred into a paste. The paste is then evenly coated onto the outer surface of the ceramic tube using a fine brush. The coated ceramic tube is placed in an oven to dry for 2 hours. Then, a nickel-chromium alloy heating wire is inserted into the inside of the ceramic tube at room temperature. Finally, the leads are soldered onto the sensor base and heated on an aging bench for 48 hours to complete the preparation of the acetone gas sensor.

[0061] Test experiment:

[0062] The optimal temperature for testing 50 ppm acetone was determined using sensors assembled from the composite materials of Examples 1 and 1-3, respectively. The temperature ranged from 200°C to 400°C in 50°C intervals, and the relationship between the test temperature and the response to acetone vapor was measured for the four sensors. The results are as follows: Figure 4As shown, all four sensors reached their optimal temperature at 300℃. However, CeO2 / ZnO-Pd showed a higher response to acetone at the optimal temperature, reaching 22.54, while the response values ​​of Comparative Examples 1 to 3 were 6.23, 6.62, and 8.03, respectively.

[0063] Sensors assembled using the composite materials from Examples 1 and 1-3 were tested for selectivity at 300°C for 50 ppm acetone, methanol, ethanol, DMF, H2, CO, and C2H4. The response values ​​of the four sensors to various gases were measured. The results are as follows: Figure 5 As shown in the radar chart, all four sensors have a higher response to acetone, but the radar chart of the CeO2 / ZnO-Pd sensor is sharper, indicating that CeO2 / ZnO-Pd has better selectivity for acetone.

[0064] The sensor assembled using the composite material of Example 1 was tested at 300°C for a response to 50 ppm acetone gas, and the change in resistance over time was calculated. The results are as follows: Figure 6 As shown, the sensor assembled in Example 1 has a response time of 0.6s and a recovery time of 24.3s, indicating that the sensor has a relatively fast response speed.

[0065] The sensor assembled using the composite material from Example 1 was used to test the change in resistance over time in acetone gas at 330 ppb and 300°C. The results are as follows: Figure 7 As shown, the sensor assembled in Example 1 still has a response value of 2.3 for 330 ppb acetone, indicating that the sensor has a low detection limit.

[0066] The stability of the sensor assembled from the composite material described in Example 1 was tested. The results are as follows: Figure 8 As shown, the sensor's response to 50 ppm acetone gas at 300℃ remained almost unchanged for forty days, and the response value was still 18.97 after 40 days, indicating that the sensor has good stability.

[0067] This invention provides a method for preparing Pd-doped CeO2 / ZnO nanofibers using an ultrasonic method and its application. CeO2 / ZnO nanofibers are prepared by electrospinning, and then Pd is doped using an ultrasonic method, improving the selectivity for acetone gas. Compared to sensors doped with Pd by stirring, the ultrasonically prepared sensor exhibits higher response and selectivity to acetone gas. The CeO2 / ZnO-Pd nanofiber gas-sensitive material prepared by this invention possesses excellent acetone sensing performance and has high application value.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an ultrasonic doped Pd modified CeO2 / ZnO nanofiber material for acetone gas sensor, characterized in that, Specifically, the following steps are included: (1) After zinc acetate dihydrate and cerium acetate are completely dissolved in NN dimethylformamide, polyvinylpyrrolidone / DMF solution is added and stirred evenly to obtain Ce-Zn solution; (2) Transfer the Ce-Zn solution into a syringe, perform electrospinning, collect the spun material and dry it in a vacuum drying oven; (3) The dried material was transferred to the ark and the ark was placed in a muffle furnace for calcination to obtain CeO2 / ZnO composite nanofiber material; (4) The CeO2 / ZnO composite nanofiber material was placed in a palladium nitrate / DMF solution and ultrasonically mixed to obtain a palladium salt-CeO2 / ZnO composite material; In step (4), the mass ratio of palladium nitrate / DMF solution to CeO2 / ZnO composite nanofiber material is 1:500~1000; (5) The palladium salt-CeO2 / ZnO composite material was calcined in H2 / Ar to obtain CeO2 / ZnO-Pd nanofiber material; In step (5), the calcination heating rate is 1~3℃ / min, and the calcination temperature is kept at 600~700℃ for 1~3h.

2. The preparation method of the ultrasonic doped Pd modified CeO2 / ZnO nanofiber material for acetone gas sensor according to claim 1, characterized in that: In step (1), the mass ratio of polyvinylpyrrolidone, zinc acetate dihydrate, cerium acetate, and N,N dimethylformamide is 1:0.8~1.2:0.8~1.2:6~10. 3.The method for preparing the ultrasonic doped Pd modified CeO 2 / ZnO nanofiber material for acetone gas sensor according to claim 1, characterized in that: In step (2), during electrospinning, the voltage is 13~17kV, the solution flow rate is 0.4~0.7mL / h, and the spinning receiving distance is 13~17cm.

4. The method according to claim 1, wherein the method for preparing the ultrasonic doped Pd modified CeO2 / ZnO nanofiber material for acetone gas sensor is characterized by: In step (2), the temperature of the vacuum drying oven is 50~80℃ and the heat preservation time is 12~24h.

5. The method according to claim 1, wherein the method for preparing the ultrasonic doped Pd modified CeO2 / ZnO nanofiber material for acetone gas sensor is characterized by: In step (3), the calcination heating rate is 1~3℃ / min, the calcination temperature is raised to 280~300℃ and held for 1~3h, and then raised to 600~700℃ and held for 1~3h.

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