A xylene gas sensor based on C / MnWO4 core-shell nanocomposite material and its preparation method

Abstract

The application discloses a kind of xylene gas sensor based on C / MnWO4 core-shell structure nanocomposite and preparation method thereof, belong to gas sensor technical field.Sensor is composed of Al2O3 substrate, Pd metal interdigital electrode, three parts of C / MnWO4 core-shell structure nanocomposite sensitive layer coated on Al2O3 substrate and Pd metal interdigital electrode using hydrothermal method preparation.C / MnWO4 core-shell structure nanocomposite is prepared by growing, crystallizing and enriching MnWO4 nanoparticles on porous loose carbon microspheres and forming active semiconductor shell.The sensor prepared by the application has the characteristics of simple preparation method, low cost and low equipment requirement.The sensor has good selectivity, high response and fast response speed for xylene gas, and has good detection performance for low concentration xylene, is suitable for mass production, and has important application value.

Description

Technical Field

[0001] This invention belongs to the field of gas sensor technology, specifically relating to a xylene gas sensor based on C / MnWO4 core-shell structured nanocomposite material and its preparation method. Background Technology

[0002] With the development of the national economy, while people enjoy the abundant material wealth of today's society, they are also suffering from the harm and troubles caused by environmental pollution. People are paying more and more attention to the safety of their environment, especially the safety of the gaseous environment. While modern industrial society is developing rapidly, due to relatively imperfect technological development and the high cost of pollutant emissions and subsequent treatment, some complex environments contain toxic gases (such as nitrogen oxides), industrial organic gases (such as benzene derivatives, organic alcohols, aldehydes, ketones, esters, etc.), flammable and explosive gases (such as hydrogen, CO, acetylene, etc.), and indoor volatile organic compounds (such as formaldehyde, xylene, etc.). Rapid and intelligent detection of these gases makes the development of high-performance gas sensors necessary. Xylene is one of the main pollutants in indoor air, and developing a low-cost, rapid sensor for detecting xylene is of great significance.

[0003] Semiconductor gas sensors utilize the direct adsorption of gases by sensitive materials, causing changes in the material's electrical properties. These changes are then detected by an external circuit monitoring the output signal of the sensitive element, thus determining the gas concentration. Many semiconductor materials can be used for gas sensing, with multi-metal oxide semiconductors being one of the industry's research directions. Manganese tungstate (MnWO4) is a multi-metal oxide with excellent catalytic activity, often used as a catalyst and battery material. MnWO4 possesses a suitable band structure and band gap (2.6 eV–2.8 eV). The splitting and hybridization of d-orbital energy levels within the dual transition metal atoms in MnWO4 enhances metal-to-metal charge transfer within the material, demonstrating its significant potential as a gas-sensitive material.

[0004] Furthermore, the gas-sensing performance of multi-metal oxide semiconductor sensitive materials is also affected by material morphology, composite or doped metals, ions, etc. Therefore, the gas-sensing performance of materials can be improved by synthesizing sensitive materials with different morphologies and composites. Carbon microspheres, as a new generation of carbon materials, have great potential for modifying multi-metal oxides. The porous surface of carbon microspheres increases the surface area for gas molecule adsorption, thereby enhancing the gas adsorption capacity of the composite material. In addition, the surface of carbon microspheres possesses a large number of hydrophilic groups, which can coordinate and electrostatically bind with ions before oxide crystallization. This process reduces ion aggregation during crystallization, allowing oxides to nucleate and crystallize on the microsphere surface, forming a core-shell morphology. During this process, oxide crystals undergo granulation, resulting in smaller particle size and increased specific surface area. Simultaneously, the increase in dangling bonds on the material surface significantly reduces the activation energy of the reaction, improving gas-sensing performance. Therefore, by combining manganese tungstate with carbon microspheres, under the combined effect of external conditions, a change in the Fermi level position can be achieved, reducing the activation energy of the reaction. At the same time, it promotes surface charge transfer and enhances surface catalytic activity, thus exhibiting excellent gas-sensing performance. Summary of the Invention

[0005] The purpose of this invention is to provide a xylene gas sensor based on a C / MnWO4 core-shell nanocomposite material and its preparation method. This method is simple, easy to implement, involves few steps, is low-cost, and has low equipment requirements. The C / MnWO4 core-shell nanocomposite material can improve the gas sensor's gas-sensitive response to xylene, making it suitable for mass production and possessing significant application value.

[0006] The xylene gas sensor based on C / MnWO4 core-shell nanocomposite material of the present invention consists of three parts from bottom to top: an Al2O3 substrate, a Pd metal interdigitated electrode, and a C / MnWO4 core-shell nanocomposite material sensitive layer prepared by hydrothermal method coated on the Al2O3 substrate and the Pd metal interdigitated electrode. The C / MnWO4 core-shell nanocomposite material is prepared by growing, crystallizing, enriching MnWO4 nanoparticles on porous carbon microspheres and forming an active semiconductor shell.

[0007] The present invention discloses a method for preparing a xylene gas sensor based on a C / MnWO4 core-shell structured nanocomposite material, the steps of which are as follows:

[0008] 1. Treatment of Pd metal interdigitated electrodes:

[0009] Pd metal interdigitated electrodes were prepared by screen printing technology: The raw materials were mixed and stirred into a paste according to the mass ratio of ink [Jiahua JX07500487]: Pd powder: ink product diluent of 1:1:2~2.5. The paste was then injected onto a screen printing plate with an interdigitated electrode pattern. The paste was scraped at an angle of 30°~45° and a pressure of 5~10N to print the interdigitated electrodes onto an Al2O3 substrate. After UV curing, the Pd metal interdigitated electrodes were prepared. The width and electrode spacing of the interdigitated electrodes were 0.15~0.20 mm, the thickness was 100~150 nm, and the number of pairs was 5~10.

[0010] Wipe the Al2O3 substrate with interdigitated electrodes with acetone and ethanol cotton balls until clean. Then place the Al2O3 substrate with Pd metal interdigitated electrodes in acetone, ethanol and deionized water in sequence and ultrasonically clean for 5-10 minutes each. Finally, dry it at 100-120℃ for later use.

[0011] 2. Preparation of carbon microsphere materials and C / MnWO4 core-shell structured nanocomposites:

[0012] (1) Preparation of carbon microspheres:

[0013] At room temperature, using 40-50 mL of deionized water as the reaction solvent, 3.96-5.12 g of glucose monohydrate was added and magnetically stirred at room temperature until the raw materials were completely dissolved to obtain a colorless and transparent reaction solution. Subsequently, the reaction solution was reacted in a reaction vessel at 180-200 °C for 8-10 hours. After the reaction was completed and completely cooled, the product was taken out and washed with deionized water and anhydrous ethanol alternately 3-5 times. Then, it was dried in air at 60-80 °C to obtain carbon microsphere materials.

[0014] (2) Preparation of C / MnWO4 core-shell structured nanocomposites

[0015] At room temperature, using 20-25 mL of deionized water as the reaction solvent, add 50-150 mg of the carbon nanospheres obtained in step (1), and then ultrasonically disperse the resulting dark brown mixed turbidity for 30-60 minutes; after ultrasonic dispersion, add 20-25 mL of anhydrous ethanol to the dispersion turbidity, and add 1.0-2.0 mmol of sodium tungstate dihydrate and 1.0-2.0 mmol of manganese acetate, and magnetically stir to fully dissolve the raw materials, wherein Mn 2+ With WO4 2-The molar ratio is 1:1~1.5. Stir for 30~60 minutes until the solution gradually turns into a dark gray turbid liquid. Then add 0.1~0.5 mL of 1~2 mol / L NaOH solution to control the pH value of the solution system between 8 and 9. After standing for 10~15 minutes, transfer the resulting mixture into a reaction vessel and react at 180~200℃ for 12~14 hours. After cooling to room temperature, wash the reaction product with deionized water by centrifugation. After drying the centrifuged product at 60~80℃, anneal it in a muffle furnace at 400~800℃ for 0~2 hours with a heating rate of 4~6℃ to obtain 250~400 mg of C / MnWO4 core-shell structured nanocomposite material.

[0016] 3. Fabrication of gas-sensitive devices

[0017] Take 1-2 mg of C / MnWO4 core-shell structured nanocomposite material and grind it for 20-30 minutes. Then add 0.1-0.5 mL of ethanol and continue grinding for another 20-30 minutes to obtain a viscous slurry. Take a small amount of this slurry and coat it onto an Al2O3 substrate with Pd metal interdigitated electrodes. Then dry it at 60-80℃ to obtain a C / MnWO4 core-shell structured nanocomposite material sensitive layer with a thickness of 10-30 μm. Finally, age it for 48-72 hours at 50-65 mA DC in an environment with a relative humidity of 30-50%RH and a temperature of 20-35℃ to obtain a xylene gas sensor with C / MnWO4 core-shell structured nanocomposite material as the sensitive layer.

[0018] After the gas sensor was prepared, its xylene gas-sensing performance was tested (using the CGS-1TP gas-sensing performance tester from Beijing Elite Technology Co., Ltd.).

[0019] The xylene gas sensor prepared by this invention based on C / MnWO4 core-shell structured nanocomposite material has the advantages of simple preparation method, low cost, fast response recovery speed, and potential for large-scale production. It has good selectivity and high responsivity for xylene and can respond to low concentrations of xylene. Attached Figure Description

[0020] Figure 1 Figures (a) to (b) are SEM images of carbon microsphere material (S0), and figures (c) to (d) are SEM images of C / MnWO4 core-shell structured nanocomposite material (S1). It can be seen that the size of carbon microspheres is 1~1.1μm; the particle size of C / MnWO4 core-shell structured nanocomposite material is 1.1~1.2μm.

[0021] Figure 2: Schematic diagram of the basic device (S1~S6) of the present invention; the device consists of an Al2O3 substrate 1, a Pd metal interdigitated electrode 2, and a C / MnWO4 core-shell structured nanocomposite sensitive layer 3;

[0022] Figure 3 XRD images of C / MnWO4 core-shell nanocomposites; line 1 corresponds to the standard card PDF#:13-0434 for manganese tungstate; lines 2 to 4 correspond to the C / MnWO4 core-shell nanocomposites (S1, S2, S4), respectively. It can be seen that the XRD spectra of the composite materials all show characteristic peaks of MnWO4, indicating that the three examples above all have crystal structure and crystalline phase characteristics highly correlated with MnWO4.

[0023] Figure 4 XPS images of the C / MnWO4 core-shell nanocomposite material (S1) prepared in this invention, where Figures a to d correspond to the spectra of Mn2p, W4f, O1s, and C1s, respectively; the spectra of each element indicate the presence of Mn, W, O, and C elements in the prepared composite material.

[0024] Figure 5 The bar chart shows the response of the device (S1) of the present invention to acetone, triethylamine, formaldehyde, xylene, methanol, and ethyl acetate at an operating temperature of 157°C. It indicates that the responsivity of the device varies with the type of gas, with the highest responsivity to xylene. (The responsivity refers to the ratio of the resistance value of the p-type semiconductor gas sensor in the test gas or test environment to the resistance value in room temperature air environment when the device is in the working state, i.e., S=Rg / Ra, where S is the responsivity, Rg is the instantaneous resistance value of the device measured in the test environment, and Ra is the resistance value of the device in room temperature air environment, Ra is less than Rg. The highest responsivity or maximum responsivity refers to the maximum value that S can achieve during the process of maintaining a stable resistance change in the test environment for a period of time and then returning to room temperature air environment and maintaining a stable resistance change. It can be further seen that Rg should be the highest value at this time. Ra is a parameter formed with the completion of device fabrication, which only changes with the operating temperature. When the operating temperature is constant, Ra is constant, so Ra is also called the baseline resistance.)

[0025] Figure 6 The repeatability test curve of the device (S1) of the present invention against xylene (100ppm) at an operating temperature of 157℃; each repetition corresponds to the highest responsivity, and the calculated responsivity value is within the allowable error range (±2), proving that the device prepared by the present invention has good repeatability and commercial potential; the fourth group has a longer time span than the first three groups, and when the device is removed from the xylene gas environment, its highest responsivity can still remain relatively constant, which shows that the device has no maximum operating time limitation during use and has good device stability;

[0026] Figure 7 The device (S1) of this invention displays a time-resistance graph (inset is an enlarged view of the 0~300s region) for different concentrations of xylene (1ppm, 10ppm, 20ppm, 50ppm, 100ppm, 200ppm, 500ppm, 1000ppm) at an operating temperature of 157°C. This graph shows that as the concentration of the test gas increases, the resistance (Rg) of the sensor increases, and the responsiveness of the device (S1) to xylene increases. This graph illustrates that the device has a relatively wide xylene concentration testing range.

[0027] Figure 8 The graph shows the long-term stability curve of the device (S1) of this invention. Line 1 represents the broken line showing the change in the highest responsivity over time, and line 2 represents the broken line showing the change in the baseline resistance (the resistance value measured when the device is in operation under ambient air at room temperature, i.e., Ra) over time. This graph shows the fluctuation of the initial resistance and the change in the highest responsivity of the device at different time points over a long period when it is operating at its optimal operating temperature. It can be clearly seen that as the time span increases, i.e., the time interval increases, the slope of the change in the highest response approaches zero, and the response always fluctuates within 52 to 54, which meets the requirements of long-term use and testing of the device in production and daily life.

[0028] Figure 9 The device (S1) of this invention has a time-resistance diagram of a single response (i.e., one inflation and one deflation process) to xylene. It can be seen that the response time (the time required from the moment the device is placed in the xylene concentration stable space to the moment when the resistance value is 90% of the highest stable resistance) is 26s, and the recovery time (the time required from the moment the device is removed from the xylene concentration stable environment and placed in the room temperature air environment to the moment when the stable resistance is close to the minimum of the baseline resistance) is 40s.

[0029] Figure 10 The response curves of the devices prepared in Examples 1-6 to xylene at different temperatures show that the devices in Examples 1-6 have different responses to xylene at different temperatures. The figures show that the response of the devices prepared in Examples 4-6 (S4-S6) is much smaller than that in Examples 1-2 (S1, S2), indicating that calcination to remove carbon has a significant impact on material properties. The higher the calcination annealing temperature and the lower the carbon content, the smaller the response. Example 3 (S3) demonstrates that more carbon is not necessarily better; excessive carbon inhibits the sensitive activity that manganese tungstate should possess, leading to a decrease in device response. Detailed Implementation

[0030] Next, the technical solutions of the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention,

[0031] Example 1

[0032] 1. Processing procedure for Pd metal interdigitated electrodes

[0033] Pd metal interdigitated electrodes were prepared using screen printing technology: The raw materials were mixed and stirred into a paste according to the mass ratio of ink [Jiahua JX07500487]: Pd powder: matching diluent of 1:1:2. The paste was then injected onto a screen printing plate with an interdigitated electrode pattern. The paste was scraped at a 35° tilt angle and a pressure of 5 Newtons to print electrodes on an Al2O3 substrate. After drying and UV curing, the metal interdigitated electrodes were prepared. The width and electrode spacing of the metal interdigitated electrodes were both 0.15 mm, the thickness was 150 nm, and the number of interdigitated electrode pairs was 6.

[0034] Then, the Al2O3 substrate with Pd interdigitated metal electrodes was wiped clean with acetone and ethanol cotton balls respectively. The Al2O3 substrate with Pd interdigitated metal electrodes was then placed in acetone, ethanol and deionized water in sequence and ultrasonically cleaned for 5 minutes each. Finally, it was placed in 100... o Dry in a drying oven (C) for later use.

[0035] 2. Preparation process of carbon microspheres and C / MnWO4 core-shell structured nanocomposites

[0036] At room temperature, 40 mL of deionized water was added to a clean reaction vessel as the reaction solvent, followed by 3.96 g of glucose monohydrate. The reaction solution was then stirred on a magnetic stirrer at room temperature for 30 minutes until completely dissolved, resulting in a colorless and transparent solution. The solution was then completely transferred to a Teflon-lined container, which was placed in a steel reactor and reacted at 180°C for 9 hours. After the reaction was complete and cooled, the product was removed and washed four times alternately with deionized water and anhydrous ethanol, followed by drying in air at 70°C to obtain carbon microspheres, labeled S0. The obtained material was weighed, sealed, and stored for future use.

[0037] C / MnWO4 core-shell nanocomposites were prepared using a hydrothermal method: At room temperature, 100 mg of the prepared carbon microspheres and 20 mL of deionized water were added to a clean conical flask, and the resulting dark brown mixed turbidity was placed on an ultrasonic dispersion table for 60 minutes. After ultrasonic dispersion, 20 mL of anhydrous ethanol, 1 mmol of sodium tungstate dihydrate, and 1 mmol of manganese acetate were added to the carbon microsphere dispersion turbidity, and the mixture was magnetically stirred for 20 minutes to ensure complete dissolution of the added compounds. The added Mn... 2+ With WO4 2- The molar ratio of ions was 1:1. The mixed turbid liquid was stirred for another 30 minutes until it gradually turned a dark gray turbid liquid. Then, 0.5 mL of a pre-prepared 1 mol / L NaOH solution was added to maintain the pH of the solution at 8. After dispersion, the mixture was allowed to stand for 15 minutes. The final mixture was then transferred to a reaction vessel, and the reaction temperature was 180 °C for 12 hours. After cooling to room temperature, the reaction product was washed with deionized water by centrifugation and dried at 60 °C to obtain 275 mg of C / MnWO4 core-shell structured nanocomposite material. The composite material product obtained in this embodiment was not annealed in a muffle furnace.

[0038] 3. Fabrication and assembly process of gas-sensitive devices

[0039] 1 mg of the dried C / MnWO4 core-shell nanocomposite was placed in a mortar and ground for 25 minutes. Then, 0.2 mL of ethanol was added to the mortar, and grinding continued for another 25 minutes to obtain a viscous slurry. A small amount of the slurry was coated onto an Al2O3 substrate with Pd interdigitated metal electrodes and then heated at 70°C. o Drying at C conditions yielded a 15 μm thick MnWO4@C core-shell structured nanocomposite sensitive layer; finally, it was dried at a relative humidity of 40%RH and a temperature of 30°C. o In an environment of C, the xylene gas sensor was aged for 48 hours under a DC current of 65mA to obtain a C / MnWO4 core-shell structured nanocomposite material as the sensitive layer, labeled as S1.

[0040] After the gas sensor was prepared, its xylene gas-sensing performance was tested (using the CGS-1TP gas-sensing performance tester from Beijing Elite Technology Co., Ltd.).

[0041] Example 2

[0042] The processing of the Pd metal interdigitated electrode and the preparation process of the carbon microspheres are the same as in Example 1.

[0043] In this embodiment, the C / MnWO4 core-shell structured nanocomposite material was also prepared by hydrothermal method, but the quality of the carbon microspheres differed from that in Example 1:

[0044] C / MnWO4 core-shell nanocomposites were prepared using a hydrothermal method: At room temperature, 50 mg of the prepared carbon microspheres and 20 mL of deionized water were added to a reaction conical flask, and the resulting dark brown mixed turbidity was placed on an ultrasonic dispersion table. The ultrasonic dispersion time was set to 60 minutes. After ultrasonic dispersion, 20 mL of anhydrous ethanol, 1 mmol of sodium tungstate dihydrate, and 1 mmol of manganese acetate were added to the above carbon microsphere dispersion turbidity, and the mixture was magnetically stirred for 20 minutes to fully dissolve the newly added compounds. The added Mn... 2+ With WO4 2- The molar ratio of ions was 1:1. The mixed turbid solution was stirred for another 30 minutes until it gradually turned a dark gray turbidity. Then, 0.5 mL of a pre-prepared 1 mol / L NaOH solution was added to maintain the pH at 8. After dispersion, the mixture was allowed to stand for 15 minutes. The final mixture was then transferred to a reaction vessel, and the reaction temperature was 180°C for 12 hours. After cooling to room temperature, the reaction product was washed with deionized water by centrifugation and dried at 60°C to obtain 244 mg of C / MnWO4 core-shell structured nanocomposite material. The composite material obtained in this embodiment was not annealed in a muffle furnace.

[0045] The process for fabricating the device is as described in Example 1. This device is labeled as S2.

[0046] Example 3

[0047] The processing of the Pd metal interdigitated electrode and the preparation process of the carbon microspheres are the same as in Example 1.

[0048] In this embodiment, the C / MnWO4 core-shell structured nanocomposite material was also prepared by hydrothermal method, but the quality of the carbon microspheres differed from that in Examples 1-2:

[0049] C / MnWO4 core-shell nanocomposites were prepared using a hydrothermal method: At room temperature, 150 mg of the prepared carbon microspheres and 20 mL of deionized water were added to a reaction conical flask, and the resulting dark brown mixed turbidity was placed on an ultrasonic dispersion table. The ultrasonic dispersion time was set to 60 minutes. After ultrasonic dispersion, 20 mL of anhydrous ethanol, 1 mmol of sodium tungstate dihydrate, and 1 mmol of manganese acetate were added to the carbon microsphere dispersion turbidity, and the mixture was magnetically stirred for 20 minutes to fully dissolve the newly added compounds. The added Mn... 2+ With WO4 2-The molar ratio of ions was 1:1. The mixed turbid solution was stirred for another 30 minutes until it gradually turned a dark gray turbidity. Then, 0.5 mL of a pre-prepared 1 mol / L NaOH solution was added to maintain the pH at 8. After dispersion, the mixture was allowed to stand for 15 minutes. The final mixture was then transferred to a reaction vessel, and the reaction temperature was 180°C for 12 hours. After cooling to room temperature, the reaction product was washed with deionized water by centrifugation and dried at 60°C to obtain 310 mg of C / MnWO4 core-shell structured nanocomposite material. The composite material obtained in this embodiment was not annealed in a muffle furnace.

[0050] The process for fabricating the device is as described in Example 1. The device in this example is labeled as S3.

[0051] Example 4

[0052] The processing of the Pd metal interdigitated electrode and the preparation process of the carbon microspheres are the same as in Example 1.

[0053] In this embodiment, the C / MnWO4 core-shell structured nanocomposite material was also prepared by hydrothermal method, but the annealing step differed from that in Example 1:

[0054] C / MnWO4 core-shell nanocomposites were prepared using a hydrothermal method: At room temperature, 100 mg of the prepared carbon microspheres and 20 mL of deionized water were added to a reaction conical flask, and the resulting dark brown mixed turbidity was placed on an ultrasonic dispersion table. The ultrasonic dispersion time was set to 60 minutes. After ultrasonic dispersion, 20 mL of anhydrous ethanol, 1 mmol of sodium tungstate dihydrate, and 1 mmol of manganese acetate were added to the carbon microsphere dispersion turbidity, and the mixture was magnetically stirred for 20 minutes to fully dissolve the newly added compounds. The added Mn... 2+ With WO4 2- The molar ratio of ions was 1:1. The mixed turbid liquid was stirred for another 30 minutes until it gradually turned a dark gray turbid liquid. Then, 0.5 mL of a pre-prepared 1 mol / L NaOH solution was added to maintain the pH of the solution at 8. After dispersion, the mixture was allowed to stand for 15 minutes. The final mixture was then transferred to a reaction vessel, and the reaction temperature was 180℃ for 12 hours. After cooling to room temperature, the reaction product was washed with deionized water by centrifugation and dried at 60℃. Finally, it was annealed in a muffle furnace at 400℃ for 2 hours with a heating rate of 5℃ to obtain 225 mg of the C / MnWO4 core-shell structured nanocomposite material.

[0055] The fabrication process for the device is as described in Example 1. This device is labeled as S4.

[0056] Example 5

[0057] The processing of the Pd metal interdigitated electrode and the preparation process of the carbon microspheres are the same as in Example 1.

[0058] In this embodiment, the C / MnWO4 core-shell structured nanocomposite material was also prepared by hydrothermal method, but the annealing temperature differed from that in Example 4:

[0059] C / MnWO4 core-shell nanocomposites were prepared using a hydrothermal method: At room temperature, 100 mg of the prepared carbon microspheres and 20 mL of deionized water were added to a reaction conical flask, and the resulting dark brown mixed turbidity was placed on an ultrasonic dispersion table. The ultrasonic dispersion time was set to 60 minutes. After ultrasonic dispersion, 20 mL of anhydrous ethanol, 1 mmol of sodium tungstate dihydrate, and 1 mmol of manganese acetate were added to the carbon microsphere dispersion turbidity, and the mixture was magnetically stirred for 20 minutes to fully dissolve the newly added compounds. The added Mn... 2+ With WO4 2- The molar ratio of ions was 1:1. The mixed turbid solution was stirred for 30 minutes until it gradually turned a dark gray turbidity. Then, 0.5 mL of a pre-prepared 1 mol / L NaOH solution was added to maintain the pH at 8. After dispersion, the mixture was allowed to stand for 15 minutes. The final mixture was then transferred to a reaction vessel, and the reaction temperature was 180 °C for 12 hours. After cooling to room temperature, the reaction product was washed with deionized water by centrifugation and dried at 60 °C. Finally, it was annealed in a muffle furnace at 500 °C for 2 hours with a heating rate of 5 °C to obtain 129 mg of C / MnWO4 core-shell structured nanocomposite material.

[0060] The fabrication process for the device is as described in Example 1. This device is labeled as S5.

[0061] Example 6

[0062] The processing of the Pd metal interdigitated electrode and the preparation process of the carbon microspheres are the same as in Example 1.

[0063] In this embodiment, the C / MnWO4 core-shell structured nanocomposite material was also prepared by hydrothermal method, but the annealing temperature differed from that in Example 4:

[0064] C / MnWO4 core-shell nanocomposites were prepared using a hydrothermal method: At room temperature, 100 mg of the prepared carbon microspheres and 20 mL of deionized water were added to a reaction conical flask, and the resulting dark brown mixed turbidity was placed on an ultrasonic dispersion table. The ultrasonic dispersion time was set to 60 minutes. After ultrasonic dispersion, 20 mL of anhydrous ethanol, 1 mmol of sodium tungstate dihydrate, and 1 mmol of manganese acetate were added to the carbon microsphere dispersion turbidity, and the mixture was magnetically stirred for 20 minutes to fully dissolve the newly added compounds. The added Mn... 2+ With WO4 2-The ion ratio was 1:1. The mixed turbid liquid was stirred for another 30 minutes until it gradually turned a dark gray turbid liquid. Then, 0.5 mL of a pre-prepared 1 mol / L NaOH solution was added to maintain the pH of the solution at 8. After dispersion, the mixture was allowed to stand for 15 minutes. The final mixture was then transferred to a reaction vessel, and the reaction temperature was 180℃ for 12 hours. After cooling to room temperature, the reaction product was washed with deionized water by centrifugation and dried at 60℃. Finally, it was annealed in a muffle furnace at 750℃ for 2 hours with a heating rate of 5℃ to obtain 129 mg of C / MnWO4 core-shell structured nanocomposite material.

[0065] The fabrication process for the device is as described in Example 1. This device is labeled as S6.

[0066] The gas sensing performance of the C / MnWO4 core-shell nanocomposite sensitive layer and the gas sensor with Pd as the metal interdigitated electrode prepared in the above embodiments was tested using a CGS-1TP gas sensing performance tester from Beijing Elite Technology Co., Ltd. The optimal gas sensing performance indicators are as follows (corresponding to Example 1):

[0067] The sensitivity was 53.43 (100 ppm xylene).

[0068] Xylene gas testing range: 1~1000 ppm;

[0069] The response time is 26 seconds, and the recovery time is 40 seconds.

[0070] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and improvements made in accordance with the scope of the present invention patent application should still fall within the scope of the present invention patent.

Claims

1. A method for preparing a xylene gas sensor based on a C / MnWO4 core-shell structured nanocomposite material, comprising the following steps: (1) Treatment of Pd metal interdigitated electrodes Wipe the Al2O3 substrate with Pd metal interdigitated electrodes with acetone and ethanol cotton balls until clean. Then place the Al2O3 substrate with Pd metal interdigitated electrodes in acetone, ethanol and deionized water in sequence and ultrasonically clean for 5-10 minutes each. Finally, dry it at 100-120℃. (2) Preparation of carbon microsphere materials and C / MnWO4 core-shell structured nanocomposites ① Preparation of carbon microspheres At room temperature, using 40-50 mL of deionized water as the reaction solvent, 3.96-5.12 g of glucose monohydrate was added and magnetically stirred at room temperature until the raw materials were completely dissolved to obtain a colorless and transparent reaction solution. Subsequently, the reaction solution was reacted in a reaction vessel at 180-200 °C for 8-10 hours. After the reaction was completed and completely cooled, the product was taken out and washed with deionized water and anhydrous ethanol alternately 3-5 times. Then, it was dried in air at 60-80 °C to obtain carbon microsphere materials. ② Preparation of C / MnWO4 core-shell structured nanocomposites At room temperature, using 20-25 mL of deionized water as the reaction solvent, add 50-150 mg of the carbon nanospheres obtained in step ①, and then ultrasonically disperse the resulting dark brown mixed turbidity for 30-60 minutes. After ultrasonic dispersion, add 20-25 mL of anhydrous ethanol to the dispersion, and add 1.0-2.0 mmol of sodium tungstate dihydrate and 1.0-2.0 mmol of manganese acetate. Stir magnetically to fully dissolve the raw materials, wherein Mn... 2+ With WO4 2- The molar ratio is 1:1~1.

5. Stir for 30~60 minutes until the solution gradually turns into a dark gray turbid liquid. Then add 0.1~0.5 mL of 1~2 mol / L NaOH solution to control the pH value of the solution system between 8 and 9. After standing for 10~15 minutes, transfer the resulting mixture into a reaction vessel and react at 180~200℃ for 12~14 hours. After cooling to room temperature, wash the reaction product with deionized water by centrifugation. After drying the centrifuged product at 60~80℃, anneal it in a muffle furnace at 400~800℃ for 0~2 hours with a heating rate of 4~6℃ to obtain 250~400 mg of C / MnWO4 core-shell structured nanocomposite material. (3) Fabrication of gas-sensitive devices Take 1-2 mg of the C / MnWO4 core-shell nanocomposite material prepared in step (2) and grind it for 20-30 minutes. Then add 0.1-0.5 ml of ethanol and continue grinding for another 20-30 minutes to obtain a viscous slurry. Take a small amount of the slurry and coat it onto the Al2O3 substrate with Pd metal interdigitated electrodes obtained in step (1). Then dry it at 60-80℃ to obtain a C / MnWO4 core-shell nanocomposite material sensitive layer with a thickness of 10-30 μm. Finally, age it for 48-72 hours at 50-65 mA DC in an environment with a relative humidity of 30-50%RH and a temperature of 20-35℃ to obtain a xylene gas sensor with C / MnWO4 core-shell nanocomposite material as the sensitive layer.

2. The method for preparing a xylene gas sensor based on a C / MnWO4 core-shell structured nanocomposite material as described in claim 1, characterized in that: The raw materials are mixed and stirred to form a paste according to the mass ratio of ink:Pd powder:ink product diluent of 1:1:2~2.

5. The paste is then injected onto a screen printing plate with interdigitated electrode pattern. The paste is scraped at an inclination angle of 30°~45° and a pressure of 5~10N to print the interdigitated electrodes on an Al2O3 substrate. After UV curing, the Pd metal interdigitated electrodes are prepared. The width and electrode spacing of the interdigitated electrodes are 0.15~0.20mm, the thickness is 100~150nm, and the number of pairs is 5~10.

3. The method for preparing a xylene gas sensor based on a C / MnWO4 core-shell structured nanocomposite material as described in claim 1, characterized in that: C / MnWO4 core-shell nanocomposite materials are prepared by growing, crystallizing, enriching MnWO4 nanoparticles on porous carbon microspheres and forming an active semiconductor shell. The size of the carbon microspheres is 1~1.1μm; the particle size of the C / MnWO4 core-shell nanocomposite materials is 1.1~1.2μm.

4. A xylene gas sensor based on a C / MnWO4 core-shell structured nanocomposite material, characterized in that: It is prepared by the method described in claim 1, 2 or 3.

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