Carbon dioxide sensitive material and carbon dioxide sensor

Abstract

The invention discloses a carbon dioxide sensitive material and a carbon dioxide sensor, the carbon dioxide sensitive material is formed by compounding Co-Ni LDH and PEI, and the mass ratio of Co-Ni LDH to PEI is (0.2-20): 1; the invention also provides a carbon dioxide sensor prepared from the sensitive material, the carbon dioxide sensor can realize high-sensitivity detection on 15-900ppm carbon dioxide under the environment of room temperature and 50-70% RH humidity, the response value on 15ppm carbon dioxide can reach 25%, the response value on 500ppm CO2 can reach 377.8%, the response value on 900ppm carbon dioxide can reach 713%, and the response value on 15ppm CO2 can reach 377.8%. The problems that an existing carbon dioxide sensor is high in working temperature and low in detection sensitivity are solved, the testing environment range is widened, and high-sensitivity detection of carbon dioxide can be achieved in the environment with the RH of 50%-70%.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon dioxide detection, and particularly relates to a carbon dioxide sensitive material and a carbon dioxide sensor. Background Art

[0002] Carbon dioxide (CO2), as an important component of air, is not only closely related to the survival of plants through photosynthesis, but also plays a key role in many fields such as healthcare, space technology, and biological processes. In the healthcare industry, precise CO2 monitoring is crucial for early disease detection in angiography; in the International Space Station, CO2 detection is a key link to ensure the health and safety of astronauts; in the field of biological processes, a slight change in CO2 concentration can significantly affect the morphology of microbial cells and their metabolites and rates. Therefore, CO2 gas monitoring has extremely important application value.

[0003] Traditionally, the monitoring of CO2 gas relies on mass-sensitive, electro-chemical, and optical sensors. Although these methods can provide effective monitoring results to a certain extent, their high costs, lack of portability, and operational complexity limit their widespread application. In contrast, semiconductor resistive CO2 sensors have gradually become a promising alternative due to their advantages such as easy manufacturing, strong portability, and high cost-effectiveness.

[0004] However, currently common semiconductor CO2 gas-sensitive materials, such as CeO2, CuO, and graphene, have problems such as low sensitivity and high working temperature. Moreover, as a chemically stable gas, CO2 molecules have strong chemical inertness and are difficult to effectively exchange electrons with the sensitive layer, thus increasing the detection difficulty.

[0005] Infrared detection technology is another commonly used CO2 detection method, but its response value is much lower than that of semiconductor sensors, making it difficult to meet the precise requirements of indoor air quality monitoring or human respiration monitoring. At the same time, the MEMS manufacturing process of infrared sensors is complex, the large-scale production cost is high, and the sensing system is large in size and high in power consumption.

[0006] In summary, existing CO2 sensors have many problems such as high operating temperature, low sensitivity, and complex processes. Against this background, organic-inorganic composite films have received extensive attention as an effective means to improve sensor performance. By adding inorganic components to an organic polymer matrix, the intrinsic properties of inorganic materials and the new functions induced by the synergistic effect of the organic-inorganic interface can be effectively integrated, while maintaining the flexibility and processability of the polymer system, thus better realizing carbon dioxide detection. For example, the Guodong Wu team developed a sensor based on Ti3C2T / Polyaniline (PANI) composite materials (Chemical Engineering Journal, 2023, 475, 146228) for monitoring carbon dioxide and human respiration rate. At room temperature, the response to 500 ppm CO2 is 15.2%, and the response and recovery times are 115 s and 26 s respectively. Although its response and recovery speed is relatively fast, the 15.2% response is relatively low, and the response value of the sensor to CO2 needs to be further optimized. Summary of the Invention

[0007] Aiming at the above deficiencies of the existing technology, the purpose of the present invention is to provide a carbon dioxide sensitive material and a carbon dioxide sensor to solve the problems of high operating temperature and low sensitivity in detecting carbon dioxide in the existing technology.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0009] A carbon dioxide sensitive material is composed of Co-Ni LDH and PEI, and the mass ratio of Co-Ni LDH to PEI is 0.2 - 20:1.

[0010] Furthermore, the mass ratio of Co-Ni LDH to PEI is 1 - 10:1.

[0011] Furthermore, the preparation steps of Co-Ni LDH include:

[0012] (1) After adding Co(NO3)2·6H2O and 2-methylimidazole to methanol, quickly stir for 3 - 5 minutes, then place it under the condition of 25 - 30 °C, age for 24 - 30 h, after centrifugal separation, wash the obtained precipitate, and then first dry the washed precipitate at 50 - 55 °C for 24 - 30 h; then heat it at a heating rate of 1 - 2 °C / min to 400 - 450 °C, and keep it warm for 1 - 2 hours to obtain ZIF-67;

[0013] (2) Disperse ZIF-67 evenly in ethanol, then add Ni(NO3)2 and stir until dissolved. Then place it in a reaction at 120 - 130 °C for 2 - 3 h. After centrifugation, wash and dry the obtained precipitate to obtain Co-Ni LDH powder.

[0014] Further, in step (1), the molar ratio of Co(NO3)2·6H2O to 2-methylimidazole is 1 - 2:4.

[0015] Further, in step (2), the mass ratio of ZIF-67 to Ni(NO3)2 is 1:2 - 3.

[0016] A carbon dioxide sensor is prepared using the above carbon dioxide sensitive material.

[0017] Further, the preparation steps include: Dissolve Co-Ni LDH and PEI in ethanol, and stir at 35 - 40 °C for 6 - 7 h. Then use the drop coating method to coat the mixed solution on the surface of the electrode device, with a film thickness of 50 nm - 1 μm. After that, dry the film device to obtain the carbon dioxide sensor.

[0018] Further, the drying temperature is 45 - 50 °C, and the drying time is 2 - 3 h.

[0019] Further, the detection conditions of the sensor are room temperature and 20 - 90% RH. The preferred humidity is 50 - 70% RH.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention provides a carbon dioxide sensitive material, which is composed of Co-Ni LDH (cobalt-nickel layered double hydroxide) and PEI (polyethyleneimine). Through the synergistic effect of the two, the carbon dioxide sensor prepared with this composite material can achieve high-sensitivity detection of 15 - 900 ppm carbon dioxide at room temperature and in a humidity environment of 50 - 70% RH. The response value to 15 ppm carbon dioxide can reach 25%, the response value to 500 ppm CO2 can reach 377.8%, the response value to 900 ppm carbon dioxide can reach 713%, the sensitivity to 15 - 40 ppm carbon dioxide is 3.3×10 -2 / ppm, and the sensitivity to 200 - 900 ppm carbon dioxide is 6.6×10 -3 / ppm. It solves the problems of high working temperature and low detection sensitivity of existing carbon dioxide sensors, and expands the test environment range, enabling high-sensitivity detection of carbon dioxide in a humidity environment of 50 - 70% RH.

[0022] 2. In the CO₂-sensitive material provided by the present invention, Co-Ni LDH has a large specific surface area, providing a highly dispersed loading platform for PEI and more active sites for CO₂ adsorption. Moreover, the good layered structure of Co-Ni LDH is conducive to gas adsorption and diffusion, thereby improving the sensitivity of CO₂ detection. The amine polymer PEI requires a humid environment for CO₂ detection at room temperature. Because PEI is rich in amine functional groups, under the excitation of a water vapor environment, the amine functional groups inside PEI undergo protonation reactions, which is conducive to the adsorption of CO₂ molecules and the occurrence of acid-base neutralization reactions with them, consuming the protons in the film and causing the resistance of the sensor to increase, as shown in equations (1), (2), and (3), thereby achieving highly sensitive detection of CO₂. And in a humid environment, the activation energy of CO₂ molecules can also be reduced by the participation of water molecules in the adsorption / desorption reaction, thereby achieving high-performance detection at a lower working temperature (room temperature).

[0023]

[0024] After the present invention composes Co-Ni LDH on the basis of PEI, since Co-Ni LDH contains rich hydrophilic groups, it can pre-adsorb water molecules to form a local humid microenvironment, enabling the prepared sensor to achieve highly sensitive detection of CO₂ under the condition of a humidity range of 50-70% RH, making up for the defect that pure PEI needs to rely on external high humidity to maintain the CO₂ detection reaction and expanding the test environment range. Moreover, after the two are compounded, PEI and Co-Ni LDH form an organic-inorganic heterostructure. When PEI adsorbs CO₂ to generate bicarbonate, the protonation process of the amine group causes a band offset, resulting in a significant change in the interfacial potential barrier of the heterostructure and amplifying the resistance response signal, thereby further improving the detection sensitivity of CO₂; and because Co-Ni LDH has good conductivity, it can quickly transmit the resistance signal change caused by the protonation of PEI. The combination of the two can also reduce the response time of detection. Finally, through the synergistic effect of the two, the CO₂ sensor prepared by the present invention can achieve rapid detection of CO₂ as low as 15 ppm at room temperature and a humidity environment of 50-70% RH.

[0025] In addition, the rigid layered structure of Co-Ni LDH effectively inhibits the physical swelling and structural collapse of PEI during the CO₂ adsorption / desorption process. Its hydrophilic groups pre-adsorb water molecules to maintain a local humid microenvironment, reducing the chemical degradation of PEI caused by external humidity fluctuations; at the same time, the inorganic skeleton of Co-Ni LDH disperses the stress concentration of PEI and stabilizes the amine active sites through interfacial interactions (such as hydrogen bonds), delaying the oxidation or hydrolysis failure of the amine functional groups, thereby significantly improving the mechanical stability and chemical durability of the composite material. Description of the Drawings

[0026] Figure 1 This is the flow chart of carbon dioxide testing for the present invention;

[0027] Figure 2 This is the characterization result diagram of the Co-Ni LDH / PEI composite material obtained in Example 1 of the present invention. Among them, a is the SEM diagram of pure Co-Ni LDH, b is the SEM diagram after Co-Ni LDH-PEI composite; c is the adsorption / desorption diagram, and d is the pore size distribution diagram.

[0028] Figure 3 This is the response result diagram of Co-Ni LDH / PEI sensors with different ratios of the present invention to 100 ppm carbon dioxide at different humidities;

[0029] Figure 4 This is the schematic diagram of the response results of the Co-Ni LDH / PEI sensor obtained in Example 1 of the present invention to different CO2 concentrations; among them, a is the schematic diagram of the response time and resistance change of the sensor to 15-40 ppm CO2 concentration; b is the corresponding response fitting straight line diagram of Figure a; c is the schematic diagram of the response time and resistance change of the sensor to 200-900 ppm CO2 concentration; d is the corresponding response fitting straight line diagram of Figure c;

[0030] Figure 5 This is the long-term stability detection diagram of the Co-Ni LDH / PEI composite sensor obtained in Example 1 of the present invention. Detailed implementation manners

[0031] The following combines specific examples to further describe in detail the specific implementation manners of the present invention.

[0032] The numerical ranges in the present invention should be understood as specifically disclosing each intermediate value between the upper and lower limits of the range. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0033] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail. Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0034] Unless otherwise specified, the experimental methods used in the present invention are all conventional methods.

[0035] The materials, reagents, etc. used in the present invention can be purchased or synthesized by known methods unless otherwise specified.

[0036] In the quantitative tests of the present invention, three repeated experiments are set, and the results are averaged.

[0037] Example 1

[0038] This example provides a preparation method of a carbon dioxide sensor, including the following steps:

[0039] (1) Preparation of ZIF-67

[0040] After adding 0.01 mol of Co(NO3)2·6H2O and 0.04 mol of 2-methylimidazole to 200 mL of methanol, rapidly stir for 3 minutes, then place it in an oven at a constant temperature of 25 °C for aging for 24 h, and centrifuge to obtain a purple precipitate.

[0041] Wash the purple precipitate alternately with methanol and deionized water for several times, then place it in an oven at 50 °C for drying for 24 h, and then put it into a tube furnace for heating. Heat it to 400 °C at a heating rate of 1 °C / min, and keep it warm for 1 hour to remove the impurities physically attached to its surface. After the heating is completed, ZIF-67 is obtained.

[0042] (2) Preparation of Co-Ni LDH powder

[0043] Disperse 0.04 g of ZIF-67 evenly into 25 mL of ethanol by ultrasonic wave, then add 0.08 g of Ni(NO3)2 and stir until dissolved. Then transfer the mixture to a 50 mL polytetrafluoroethylene autoclave and react at 120 °C for 2 h. After centrifugation, wash the obtained precipitate several times, and then dry it at 50 °C for 12 h to obtain Co-Ni LDH powder.

[0044] (3) Preparation of Co-Ni LDH / PEI composite material solution

[0045] After mixing 20 mg of Co-Ni LDH powder and 8 μL of PEI solution (0.5 mg / μL, PEI molecular weight is 2000), dissolve it in 5 mL of absolute ethanol, and stir at 35 °C for 6.5 h to obtain Co-Ni LDH / PEI composite material solution.

[0046] (4) Electrode coating

[0047] The obtained Co-Ni LDH / PEI composite material solution was drop-coated onto the surface of a planar interdigital electrode device by a simple drop-coating method, with a film thickness of 50 nm - 1 μm. Then, the film-forming device was dried and heated at 45 °C for 2 hours, and finally, a Co-Ni LDH / PEI composite film unit carbon dioxide sensor was prepared.

[0048] Examples 2 - 4

[0049] Examples 2 - 4 all provided a preparation method of a carbon dioxide sensor, which was mainly the same as Example 1, except that the mass ratio of Co-Ni LDH powder and PEI was different, and the concentration of Co-Ni LDH powder in the obtained Co-Ni LDH / PEI composite material solution was different, as shown in Table 1.

[0050] Table 1 Comparison table of the mass ratio of Co-Ni LDH powder and PEI in Examples 1 - 4

[0051]

[0052] As Figure 1 shown is the carbon dioxide test flow chart. The ratio of a carbon dioxide gas cylinder and two bottles of dry air is controlled by a mass flow controller (MFC). A bubbler is connected between one bottle of dry air and the MFC, thereby changing the concentration of the target gas introduced into the test chamber and the humidity of the test environment. The humidity of the test environment is displayed by a hygrometer. After the gas enters the test chamber, the sensor detects the carbon dioxide concentration in the gas. The detection signal is transmitted to a computer through a data line, and the detection data is visually presented by the computer, thereby obtaining the carbon dioxide concentration.

[0053] Figure 2 Schematic diagrams for SEM characterization and BET characterization of the Co-Ni LDH / PEI composite material obtained in Example 1 of the present invention. Among them, a is the SEM image of pure Co-Ni LDH, and b is the SEM image after Co-Ni LDH-PEI composite; from Figure 2 a and 2b, it can be seen that after Co-Ni LDH-PEI composite, the elements are still evenly distributed, which can provide more carbon dioxide binding sites, enhance the carbon dioxide capture ability, improve the detection sensitivity, and the even distribution is also good for the structural stability of the material, and it is not easy to break, peel off or degrade; c is the adsorption / desorption diagram, and d is the pore size distribution diagram. From Figure 2As can be seen from c and 2d, after the Co-Ni LDH / PEI composite, compared with pure Co-Ni LDH, the specific surface area and pore size of the material decrease, but this does not affect the improvement of the performance of the sensor of the present invention, indicating that the large differences in the performance of different sensors are not related to the surface area parameters. After the Co-Ni LDH / PEI composite, the CO2 capture ability is improved through a chemical mechanism (rather than physical pores).

[0054] Figure 3 This is the response result diagram of Co-Ni LDH / PEI sensors with different ratios of the present invention to 100 ppm carbon dioxide at different humidities; from Figure 3 As can be seen, for the gas-sensing test of the Co-Ni LDH / PEI composite sensor, under the test conditions of room temperature (20±2 °C) and different humidities (50% RH - 70% RH), the response results of the sensor to 100 ppm carbon dioxide are as follows: when the working humidity is 52.7%, the response value is the largest, reaching 209.6%; at the same time, under the condition of nearly 70% RH, the response can still be maintained above 20%. It can be seen that the sensor of the present invention is suitable for the determination of carbon dioxide under the conditions of room temperature and 50% RH - 70% RH, and the response value is large.

[0055] Figure 4 This is the schematic diagram of the response results of the Co-Ni LDH / PEI sensor obtained in Example 1 of the present invention to different CO2 concentrations; among them, a is the schematic diagram of the response time and resistance change of the sensor to 15 - 40 ppm CO2 concentration; b is the corresponding response fitting straight-line diagram of Figure a; c is the schematic diagram of the response time and resistance change of the sensor to 200 - 900 ppm CO2 concentration; d is the corresponding response fitting straight-line diagram of Figure c; from Figure 4 As can be seen, the Co-Ni LDH / PEI sensor can not only detect carbon dioxide in a relatively high concentration range (200 - 900 ppm), but also detect low-concentration (15 - 40 ppm) carbon dioxide. The response of the sensor changes from 25% to 713%. The sensitivity to 15 - 40 ppm carbon dioxide is 3.3×10 -2 / ppm, and the sensitivity to 200 - 900 ppm carbon dioxide is 6.6×10 -3 / ppm, which can achieve carbon dioxide detection in a large range, with a large response value and high sensitivity. In addition, the linearity of the fitting straight line is also good.

[0056] Figure 5 This is the long-term stability detection diagram of the Co-Ni LDH / PEI composite sensor obtained in Example 1 of the present invention. From Figure 5 As can be seen, within 41 days of the composite sensor, the response of the sensor hardly changes. It can be seen that the Co-Ni LDH / PEI sensor has good stability.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than limiting them. Those of ordinary skill in the art should understand that any modifications or equivalent replacements made to the technical solutions of the present invention without departing from the purpose and scope of the technical solutions shall be covered by the scope of the claims of the present invention.

Claims

1. A carbon dioxide sensitive material, characterized in that: The composite material is composed of Co-Ni LDH and PEI, wherein the mass ratio of Co-Ni LDH to PEI is 0.2-20:

1.

2. The carbon dioxide sensitive material according to claim 1, characterized in that: The mass ratio of the Co-Ni LDH to PEI is 1 to 10:

1.

3. The carbon dioxide sensitive material according to claim 1 or 2, characterized in that: The preparation steps of the Co-Ni LDH include: (1) After adding Co(NO3)2·6H2O and 2-methylimidazole to methanol, the mixture was rapidly stirred for 3 to 5 minutes, and then aged for 24 to 30 hours at 25 to 30°C. After centrifugation, the obtained precipitate was washed, and then the washed precipitate was dried at 50 to 55°C for 24 to 30 hours; then the temperature was increased to 400 to 450°C at a heating rate of 1 to 2°C / min, and the temperature was kept for 1 to 2 hours to obtain ZIF-67; (2) ZIF-67 was evenly dispersed in ethanol, and then Ni(NO3)2 was added and stirred until dissolved, and then placed at 120-130°C for reaction for 2-3 hours. After centrifugation, the obtained precipitate was washed and dried to obtain Co-Ni LDH powder.

4. The carbon dioxide sensitive material according to claim 3, characterized in that: In step (1), the molar ratio of Co(NO3)2·6H2O to 2-methylimidazole is 1 to 2:

4.

5. The carbon dioxide sensitive material according to claim 3, characterized in that: In step (2), the mass ratio of ZIF-67 to Ni(NO3)2 is 1:2 to 3.

6. A carbon dioxide sensor, characterized in that: It is prepared by using the carbon dioxide sensitive material described in any one of claims 1 to 5.

7. The carbon dioxide sensor according to claim 6, characterized in that: The preparation steps include: dissolving Co-Ni LDH and PEI in ethanol, stirring at 35-40°C for 6-7 hours, applying the mixed solution on the surface of the electrode device by drop coating, and forming a film with a thickness of 50nm-1μm. After that, the film-formed device is dried to obtain a carbon dioxide sensor.

8. The carbon dioxide sensor according to claim 7, characterized in that: The drying temperature is 45-50°C and the drying time is 2-3 hours.

9. The carbon dioxide sensor according to claim 7, characterized in that: The detection conditions of the sensor are room temperature and 20-90% RH.

10. The carbon dioxide sensor according to claim 9, characterized in that: The detection conditions of the sensor are room temperature and 50-70% RH.

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