Carbon monoxide sensor based on nickel-doped zinc oxide semiconductor and preparation method thereof

Abstract

The invention discloses a carbon monoxide sensor based on a nickel-doped zinc oxide semiconductor and a preparation method thereof, relates to the technical field of gas sensors, and solves the problems that a traditional carbon monoxide sensor is low in detection sensitivity, limited in carbon monoxide detection concentration and not suitable for large-scale application. A nickel-doped zinc oxide nanosheet is directly grown on an Al2O3 insulating ceramic substrate in one step through an aerosol-assisted chemical vapor deposition method, and the carbon monoxide sensor is prepared by welding and packaging according to a general indirectly-heated gas sensitive element. According to the carbon monoxide sensor provided by the invention, the conductivity, the cycling stability, the selectivity and the gas sensitivity of the carbon monoxide sensor are improved by utilizing the synergistic effect of nickel and ZnO, the response value of the nickel-doped zinc oxide sensor to 50ppb carbon monoxide at room temperature reaches 33%, and meanwhile, the carbon monoxide concentration as low as 5ppb can be detected.

Description

Technical Field

[0001] The present invention relates to the technical field of gas sensors, and particularly relates to a carbon monoxide sensor based on nickel-doped zinc oxide semiconductor and a preparation method thereof. Background Art

[0002] Carbon monoxide is colorless, odorless and highly toxic. Since people cannot directly perceive its presence, long-term or high-concentration exposure to carbon monoxide poses a serious threat to human health and even causes fatal accidents. Carbon monoxide has become the "invisible killer" in the indoor environment. A report by the Chinese Center for Disease Control and Prevention shows that when the carbon monoxide concentration exceeds 220 ppb, people can be poisoned within one hour. Timely detection and monitoring of the carbon monoxide concentration have become crucial. A carbon monoxide sensor can issue an alarm before the carbon monoxide concentration reaches the dangerous threshold, buying precious escape time for people and avoiding poisoning accidents. Therefore, researching and developing a carbon monoxide sensor with high selectivity and low detection limit for low concentrations is not only crucial for ensuring public safety but also a key technology for protecting human health and preventing catastrophic accidents.

[0003] Zinc oxide (ZnO) has become an ideal sensitive material for detecting gases such as carbon monoxide due to its excellent electrical properties, outstanding thermal stability and good controllability. However, pure ZnO nanomaterials have defects such as poor selectivity, low sensitivity and limitations in detecting low-concentration gases in gas-sensing applications. To solve the above problems, researchers have begun to prepare sensors by developing two-dimensional nanosheet materials of metal-ion-doped zinc oxide. For example, preparing a sensor by doping copper ions into ZnO can effectively increase the carrier concentration of ZnO, enhance the response to gases and improve the adsorption ability of gas molecules; however, the copper-doped ZnO sensor has poor stability and can respond to multiple gases simultaneously, with poor gas selectivity; preparing a sensor by doping aluminum into ZnO can increase its conductivity and improve the sensitivity to the target gas; however, its response time is long and the gas selectivity is poor; preparing a sensor by doping nickel into ZnO, nickel can increase the mobility of surface electrons of ZnO due to its excellent carbon monoxide adsorption ability and driving catalytic ability, improving the response speed and sensitivity of the sensor. However, the current method of doping nickel into metal oxides is complex in operation and has strict environmental requirements, which is not suitable for large-scale applications. Therefore, developing a simple and efficient Ni-doping ZnO strategy is of great significance for realizing the industrial application of gas-sensing sensors.

[0004] Researchers found that the specific surface area directly affects the number of oxygen vacancies on the surface of nanomaterials, thereby affecting their gas-sensing performance. Therefore, in order to synthesize two-dimensional ZnO nanosheet materials with a high specific surface area, researchers have proposed various methods to optimize the microstructure, including hydrothermal method, water bath method, electrochemical method, and thermal oxidation method, etc. However, in most cases, these methods are complex to operate and difficult to achieve large-scale production. For example, although the hydrothermal method can prepare high-quality nanomaterials, its reaction time is long and it is difficult to meet the requirements of industrial-scale production; although the water bath method has mild conditions, its reaction rate is slow and it is limited by temperature, which is not conducive to efficient preparation; the electrochemical method can achieve better morphology control, but the system is relatively complex and the applicable material range is limited; although the thermal oxidation method is simple and easy to operate, it usually requires high-temperature conditions, it is difficult to precisely control the morphology of the material, and it is easy to produce by-products, affecting the final performance of the material. Therefore, the current traditional methods still have problems such as low preparation efficiency, complex process, and poor repeatability, which hinder the further development of ZnO-based gas-sensing materials. Therefore, developing an efficient, controllable, and easy-to-scale preparation method to achieve the synthesis of Ni-doped ZnO two-dimensional nanosheets in one step will bring a breakthrough in the practical application of gas sensors. Summary of the Invention

[0005] In order to solve the problems of low detection sensitivity, limited carbon monoxide detection concentration, and inapplicability to large-scale applications in existing carbon monoxide sensors, the present invention proposes a carbon monoxide sensor based on nickel-doped zinc oxide semiconductor and its preparation method. The technical solution of the present invention is as follows:

[0006] A preparation method of a carbon monoxide sensor based on nickel-doped zinc oxide semiconductor, comprising the following steps:

[0007] S1: Add zinc acetate dihydrate to deionized water, continue to add nickel acetate and stir to dissolve after complete dissolution, and then add methanol solution;

[0008] S2: Add acetic acid to the solution prepared in S1, stir to form a homogeneous solution; place the solution in an ultrasonic humidifier to prepare an aerosol;

[0009] S3: Place an Al 2 O 3 insulating ceramic substrate with two interdigital electrodes on the outer surface into a tube furnace, using air as the carrier gas, place the aerosol in the central temperature zone of the tube furnace, heat up the tube furnace, and then anneal to obtain an Al 2 O 3 ceramic substrate with nickel-doped zinc oxide sensitive material between the interdigital electrodes;

[0010] S4: The Al 2 O 3A ceramic substrate, a heater, and a Pt wire are welded and encapsulated according to a general indirectly heated gas-sensitive element to prepare a carbon monoxide sensor based on nickel-doped zinc oxide semiconductor;

[0011] Further, the stirring time in the S1 is 5 min for all;

[0012] Further, the stirring time in the S2 is 10 min;

[0013] Further, the resonance frequency of the ultrasonic humidifier in the S2 is 1700 MHz;

[0014] Further, the flow rate of air in the S3 is 500 sccm;

[0015] Further, the temperature of the tubular furnace in the S3 is 400 °C;

[0016] Further, the annealing time in the S3 is 2 h.

[0017] A carbon monoxide sensor based on nickel-doped zinc oxide semiconductor is obtained by the above preparation method.

[0018] Compared with the prior art, the present invention solves the problems of low detection sensitivity, limited carbon monoxide detection concentration, and inapplicability to large-scale applications of traditional carbon monoxide sensors. The specific beneficial effects are as follows:

[0019] 1. The present invention directly grows nickel-doped zinc oxide nanosheets on an Al 2 O 3 insulating ceramic substrate by aerosol-assisted chemical vapor deposition. This method is usually operated under standard atmospheric pressure, further reducing the operation difficulty and production cost; by controlling the frequency of the ultrasonic nebulizer to control the uniformity of the aerosol and the size of the droplets, sensitive materials with specific morphologies and sizes are customized, which ensures unobstructed diffusion of carbon monoxide on the entire sensor surface and improves gas-sensing stability; the aerosol-assisted chemical vapor deposition method has doping consistency, and the stoichiometric ratio of the dopant to the matrix in the precursor is highly consistent with the stoichiometric ratio in the obtained thin film, effectively improving the defect that nickel is not easily doped into metal oxides.

[0020] 2. The present invention uses nickel acetate as a dopant to prepare carbon monoxide sensors with nickel-doped ZnO nano-sensitive materials of different mass ratios. The carbon monoxide sensors provided by the present invention have excellent conductivity, cyclic stability, and gas sensitivity. Since ZnO nanosheets have a large specific surface area, it is beneficial to the adsorption and desorption of carbon monoxide. At the same time, nickel has a high catalytic ability, which increases the active sites and promotes electron transfer, and promotes the redox reaction of carbon monoxide and oxygen. The synergistic effect of nickel and ZnO improves the gas sensitivity and selectivity of the carbon monoxide sensor. At room temperature, the response value to carbon monoxide with a concentration of 50 ppb reaches 33%, and at the same time, it can detect a carbon monoxide concentration as low as 5 ppb.

[0021] 3. The carbon monoxide sensor based on nickel-doped zinc oxide semiconductor provided by the present invention has a simple process, and the sensitive material film is uniform and has high crystallinity. Carbon monoxide molecules react with oxygen on the surface of the sensitive material, changing the conductivity of the surface of the sensitive material, and thus changing the resistance of the sensitive material. The circuit inside the sensor can convert the resistance change signal into a gas concentration signal, and transmit the electrochemical signal outward through the interdigital electrode and platinum wire; at the same time, the sensor uses Al 2 O 3 insulating ceramic sheet for electrical isolation, effectively preventing electrical interference between different electrodes. The working temperature of the sensor is controlled by a heater to maintain the structural stability of the sensor, and thus ensure the stable gas sensitivity performance of the sensor. The preparation cost of the sensor is reduced, and the gas selectivity and gas sensitivity performance are excellent, which is conducive to batch industrial production. Brief Description of the Drawings

[0022] Figure 1 are the top view and bottom view of the structure of the carbon monoxide sensor based on nickel-doped zinc oxide semiconductor;

[0023] Figure 2 is the standard working curve of the sensitivity response of the carbon monoxide sensor based on nickel-doped zinc oxide semiconductor to carbon monoxide with different concentrations (ppm level) at 230 °C;

[0024] Figure 3 is the standard working curve of the sensitivity response of the carbon monoxide sensor based on nickel-doped zinc oxide semiconductor to carbon monoxide with different concentrations (ppb level) at 230 °C;

[0025] Figure 4 is the cyclic response curve of the carbon monoxide sensor based on nickel-doped zinc oxide semiconductor at 230 °C and a carbon monoxide concentration of 50 ppb. Detailed Embodiments

[0026] To make the technical solution of the present invention clearer, the following will clearly and completely describe the technical solution in the embodiments of the present invention in conjunction with the accompanying drawings of the present invention. It should be noted that the following embodiments are only used to better understand the technical solution of the present invention and should not be construed as a limitation of the present invention.

[0027] Embodiment 1.

[0028] S1: Add 0.3 g of zinc acetate dihydrate to 3 mL of deionized water, stir for 5 min. After the zinc acetate dihydrate is completely dissolved, continue to add 0.0047 g of nickel acetate and stir for 5 min to dissolve it. Subsequently, add 27 mL of methanol solution;

[0029] S2: Add 1 mL of acetic acid to the solution prepared in S1, stir for 10 min to form a homogeneous solution; pour the solution into a flat-bottomed flask, and then place it on an ultrasonic humidifier. The resonant frequency of the ultrasonic humidifier is 1700 MHz, and start the ultrasonic humidifier to generate aerosol;

[0030] S3: Place the Al 2 O 3 insulating ceramic substrate with 2 interdigital electrodes on its outer surface into a tube furnace. Using air as the carrier gas with an air flow rate of 500 sccm, place the aerosol in the central temperature zone of the tube furnace. Heat the tube furnace to 400 °C, and then anneal at 400 °C for 2 h to obtain an Al 2 O 3 ceramic substrate with nickel-doped zinc oxide sensitive material between the interdigital electrodes;

[0031] S4: Weld and encapsulate the Al 2 O 3 ceramic substrate with nickel-doped zinc oxide sensitive material between the interdigital electrodes, the heater, and the Pt wire according to the general indirectly heated gas sensor to prepare a carbon monoxide sensor based on nickel-doped zinc oxide semiconductor.

[0032] As Figure 1 is the structural schematic diagram of the carbon monoxide sensor based on nickel-doped zinc oxide semiconductor. The left side is the top view of the sensor, and the right side is the bottom view of the sensor. Figure 1 In 2 O 3The insulating ceramic sheet is used for electrical isolation to prevent electrical interference between different electrodes while maintaining the structural stability of the sensor. The sensitive material is the core part of the sensor. Carbon monoxide molecules react with oxygen on the surface of the sensitive material, changing the conductivity of the sensitive material surface, and further causing a change in the resistance of the sensitive material. The circuit inside the sensor can convert the resistance change signal into a gas concentration signal.

[0033] Example 2.

[0034] The difference between this example and Example 1 is that the mass of nickel acetate in S1 is 0.014 g, and the remaining preparation steps and experimental conditions are the same as those in Example 1.

[0035] Example 3.

[0036] The difference between this example and Example 1 is that the mass of nickel acetate in S1 is 0.023 g, and the remaining preparation steps and experimental conditions are the same as those in Example 1.

[0037] Comparative Example 1.

[0038] The difference between this comparative example and Example 1 is that nickel acetate is not added, and the remaining preparation steps and experimental conditions are the same as those in Example 1.

[0039] Sensitivity test of carbon monoxide sensor:

[0040] Put the carbon monoxide sensor into the gas chamber, and measure the resistance value Ra of the sensor in the air. Use a micro syringe to inject 5 ppb - 1000 ppm of carbon monoxide into the gas chamber respectively, and measure the resistance value Rg of the sensor in ethanol with different concentrations. According to the definition formula of sensitivity S = Ra / Rg, calculate the sensitivity of the sensor under different concentrations of carbon monoxide, and finally obtain the standard working curve of carbon monoxide concentration - sensitivity. As Figure 2 For the standard working curves of the sensitivity responses of the nickel-doped zinc oxide semiconductor carbon monoxide sensors prepared in Examples 1 - 3 and Comparative Example 1 to carbon monoxide with different concentrations (ppm level) at 230 °C, it can be seen that for the same concentration of carbon monoxide gas, the change in the resistance of the sensors prepared in Examples 1 - 3 is significantly larger, and the detection time of the sensors prepared in Examples 1 - 3 is short and the speed is faster, which can prove that the sensors prepared in Examples 1 - 3 have higher detection sensitivity. As Figure 3 For the standard working curves of the sensitivity responses of the nickel-doped zinc oxide semiconductor carbon monoxide sensors prepared in Examples 1 - 3 and Comparative Example 1 to carbon monoxide with different concentrations (ppb level) at 230 °C, as Figure 3It can be seen that the detection limit of the sensor provided by the present invention is 5 ppb, which is significantly lower than that of the sensor in the comparative example. The sensor provided by the present invention exhibits good linear response in different carbon monoxide concentration ranges, ensuring the accuracy and stability of the detection results. At the same time, the sensor shows low cross-sensitivity to common interfering gases (such as carbon dioxide, methane, and ammonia), further improving the selectivity to carbon monoxide. This indicates that the carbon monoxide sensor provided by the present invention not only has excellent detection sensitivity but also has strong anti-interference ability, and is applicable to various application scenarios such as environmental monitoring, industrial safety warning, and home safety protection. For example Figure 4 is the cyclic response curve of the nickel-doped zinc oxide semiconductor carbon monoxide sensor prepared in Examples 1-3 at 230 °C and a carbon monoxide concentration of 50 ppb. As can be seen from Figure 4 it that the sensors prepared by the present invention show good consistency within five cycles, proving that the sensors have good stability. By adjusting the time of aerosol-assisted chemical vapor deposition, the gas-sensing performance of the sensors can be effectively adjusted. In Comparative Example 1, the pure zinc oxide semiconductor carbon monoxide sensor can only detect a minimum carbon monoxide concentration of 100 ppb.

[0041] In the present invention, nickel acetate is used as a dopant, and nickel-doped zinc oxide nanosheets are directly grown on an Al 2 O 3 insulating ceramic substrate in one step by aerosol-assisted chemical vapor deposition to prepare a nickel-doped zinc oxide semiconductor carbon monoxide sensor with excellent conductivity, cyclic stability, and gas-sensitivity. The synergistic effect of nickel and ZnO improves the gas-sensing performance and selectivity of the carbon monoxide sensor, and can detect a carbon monoxide concentration as low as 5 ppb. The response value to 50 ppb carbon monoxide at room temperature reaches 33%. The preparation process of the carbon monoxide sensor based on nickel-doped zinc oxide semiconductor provided by the present invention is simple, the sensitive material film is uniform and has high crystallinity, the gas-sensing performance is stable, the preparation cost is low, and it is conducive to batch industrial production.

[0042] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0043] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a carbon monoxide sensor based on nickel-doped zinc oxide semiconductor, characterized in that: The following steps are involved: S1: Add zinc acetate dihydrate to deionized water, and after it is completely dissolved, continue to add nickel acetate and stir to dissolve, and then add methanol solution; S2: adding acetic acid to the solution prepared in S1 and stirring to form a homogeneous solution; placing the solution in an ultrasonic humidifier to prepare an aerosol; S3: placing an Al2O3 insulating ceramic substrate with two interdigital electrodes on the outer surface into a tube furnace, using air as a carrier gas, placing the aerosol in the central temperature zone of the tube furnace, heating the tube furnace, and then annealing to obtain an Al2O3 ceramic substrate with nickel-doped zinc oxide sensitive material between the interdigital electrodes; S4: The Al2O3 ceramic substrate with nickel-doped zinc oxide sensitive material between the interdigital electrodes, the heater and the Pt wire are welded and packaged according to the general indirect heating gas sensor to prepare a nickel-doped zinc oxide semiconductor carbon monoxide sensor.

2. The method for preparing a carbon monoxide sensor based on nickel-doped zinc oxide semiconductor according to claim 1, characterized in that: The mass ratio of nickel acetate to zinc acetate dihydrate in S1 is 0.01-0.08:

1.

3. The method for preparing a carbon monoxide sensor based on nickel-doped zinc oxide semiconductor according to claim 1, characterized in that: The stirring time in S1 is 5 min.

4. The method for preparing a carbon monoxide sensor based on nickel-doped zinc oxide semiconductor according to claim 1, characterized in that: The stirring time in S2 is 10 min.

5. The method for preparing a carbon monoxide sensor based on nickel-doped zinc oxide semiconductor according to claim 1, characterized in that: The resonant frequency of the ultrasonic humidifier in S2 is 1700 MHz.

6. The method for preparing a carbon monoxide sensor based on nickel-doped zinc oxide semiconductor according to claim 1, characterized in that: The flow rate of air in S3 is 500 sccm.

7. The method for preparing a carbon monoxide sensor based on nickel-doped zinc oxide semiconductor according to claim 1, characterized in that: The temperature of the tube furnace in S3 is 400°C.

8. The method for preparing a carbon monoxide sensor based on nickel-doped zinc oxide semiconductor according to claim 1, characterized in that: The annealing time in S3 is 2 hours.

9. A carbon monoxide sensor based on nickel-doped zinc oxide semiconductor, characterized in that: Prepared by the preparation method described in any one of claims 1 to 8.

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