A CO2 gas sensor and its preparation method

Abstract

The present invention relates to the technical field of gas sensor preparation, and specifically relates to a CO2 gas sensor and a preparation method thereof, comprising the following steps: pre-treating a quartz wafer to obtain a pre-treated quartz wafer, preparing a porous core-shell structured CeO2 nano-semiconductor material, mixing polyethyleneimine and polyethylene glycol with water and stirring to obtain a polyethyleneimine and polyethylene glycol mixed solution, adding the porous core-shell structured CeO2 nano-semiconductor material into the polyethyleneimine and polyethylene glycol mixed solution, heating and ultrasonically mixing to obtain a PEI / PEG / CeO2 solution, spin-coating the PEI / PEG / CeO2 solution on the quartz wafer to obtain a CO2 gas sensor. The preparation method of the CO2 gas sensor of the present invention is simple, can effectively reduce the response time and recovery time of the sensor to CO2, and realizes accurate detection of CO2 at room temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of gas sensor preparation, and particularly relates to a CO2 gas sensor and a preparation method thereof. Background Art

[0002] Smart agriculture is to use sensors to monitor environmental factors such as CO2 concentration, temperature, humidity, and light intensity in real time, and regulate these environmental factors during different growth periods of crops to create a suitable growth environment for crops, thereby improving the yield and quality of crops. Currently, smart agriculture is mainly applied in greenhouse greenhouses, which can greatly solve problems such as low crop yields caused by factors such as climate and altitude. The application of smart greenhouse technology can greatly reduce the planting costs of farmers and improve planting efficiency.

[0003] The intelligent regulation technology of CO2 concentration has developed relatively slowly. The main reason for this situation is that gas measurement is difficult, and the CO2 molecule has a non-polar linear structure, which makes its chemical properties extremely stable, further increasing the development difficulty of CO2 concentration detection instruments and sensors. Currently, there are mainly two types of instruments for detecting CO2 concentration: gas chromatographs and instruments developed based on CO2 gas sensors. Gas chromatographs have the highest detection accuracy, but they need to be detected offline, cannot detect in real time, have a large equipment volume, are expensive, have cumbersome operations, and require high professionalism. Among the instruments developed based on CO2 gas sensors, although the infrared CO2 detector has a rapid response and high detection accuracy, its equipment structure is also complex, the price is high, and its core sensor mainly relies on foreign imports. Although the electrochemistry type CO2 detector is relatively cheap, it has high energy consumption, slow response, and the electrolyte of the sensor is consumed during use and needs to be replaced frequently. The emergence of the mass-type sensor based on quartz crystal microbalance provides a new solution for the detection of CO2 concentration. As a high-precision mass-sensitive analytical instrument, the QCM sensor can quickly respond to changes in nanogram-level mass, has low cost, high accuracy, and can continuously detect in real time. It is widely used in the fields of gas detection, chemical composition analysis, etc.

[0004] In the prior art, a QCM gas sensor is prepared to detect CO2. Take 2 mg of SnO2, add 20 mL of N,N-dimethylformamide, and magnetically stir for 20 minutes to obtain a uniformly dispersed SnO2 solution. Dilute 0.5 mL of the PEI aqueous dispersion with deionized water to 7.5 mg / mL, and magnetically stir for thirty minutes to form a stable and uniform PEI solution. Take 0.5 mL of the SnO2 solution and deposit it on a clean and dry QCM device by spraying method, and place it in a vacuum drying oven at 60 °C for one hour. After natural cooling, the SnO2 support film is formed. Then, spin-coat the diluted PEI solution on the device containing the SnO2 support film, and vacuum dry at 60 °C for 48 hours to form a PEI-MWCNTs multilayer film. The QCM gas sensor prepared by this method has a response speed as Figure 1 shown, and it can be seen from Figure 1 that its response time is more than 500 s, and the speed is slow. The QCM gas sensor judges the CO2 gas concentration by the material adsorbing gas to generate different frequencies. Ordinary tin oxide does not have a large specific surface area and the selectivity for CO2 gas is reduced, so its response time and recovery time are slow. Summary of the Invention

[0005] Aiming at the deficiencies of the above prior art, the purpose of the present invention is to provide a CO2 gas sensor and its preparation method. The preparation method of the CO2 gas sensor of the present invention is simple, can effectively reduce the response time and recovery time of the sensor to CO2, and realize the accurate detection of CO2 at room temperature.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A preparation method of a CO2 gas sensor includes the following steps:

[0008] Pretreat the quartz wafer to obtain a pretreated quartz wafer.

[0009] Prepare a porous core-shell structured CeO2 nano-semiconductor material.

[0010] Mix and stir polyethyleneimine and polyethylene glycol with water to obtain a polyethyleneimine and polyethylene glycol mixed solution.

[0011] Add the porous core-shell structured CeO2 nano-semiconductor material into the polyethyleneimine and polyethylene glycol mixed solution, and simultaneously perform heating and ultrasonic mixing to obtain a PEI / PEG / CeO2 solution. Spin-coat the PEI / PEG / CeO2 solution on the pretreated quartz wafer to obtain a CO2 gas sensor.

[0012] In the present invention, a porous core-shell structured CeO2 nano-semiconductor material is added to a mixed solution of polyethyleneimine and polyethylene glycol to obtain a PEI / PEG / CeO2 solution. Then, the PEI / PEG / CeO2 solution is spin-coated onto a pretreated quartz wafer to obtain a CO2 gas sensor. In the present invention, the blending of polyethyleneimine and hygroscopic polyethylene glycol increases the number of protonated amino groups, thereby promoting the reaction between CO2 and amino groups in the presence of water molecules. This process is caused by the hygroscopic polyethylene glycol promoting the adsorption of carbon dioxide molecules. When the number of hydroxyl end groups of polyethylene glycol matches the number of primary and secondary amino groups of polyethyleneimine, the hydrogen bonds between amino groups can be interrupted, enabling more amino groups to come into contact with CO2, achieving optimal CO2 adsorption. Moreover, adding the porous core-shell structured CeO2 nano-semiconductor material to the mixed solution of polyethyleneimine and polyethylene glycol can effectively improve the ability to adsorb CO2, further reducing the response time and recovery time of the sensor to CO2, and achieving precise detection of CO2 at room temperature.

[0013] In a preferred embodiment of the present invention, the mass ratio of polyethyleneimine to polyethylene glycol is 700 mg - 900 mg: 350 mg - 450 mg.

[0014] In a preferred embodiment of the present invention, polyethyleneimine is used in the form of an aqueous solution of polyethyleneimine with a mass fraction of 50%.

[0015] In a preferred embodiment of the present invention, the dosage ratio of polyethylene glycol to water is 350 mg - 450 mg: 35 mL - 45 mL.

[0016] In a preferred embodiment of the present invention, the dosage ratio of the porous core-shell structured CeO2 nano-semiconductor material to the mixed solution of polyethyleneimine and polyethylene glycol is 0.5 mg - 1 mg: 1 mL - 2 mL.

[0017] In a preferred embodiment of the present invention, the heating temperature is 40°C - 45°C, and the ultrasonic time is 110 min - 120 min.

[0018] In a preferred embodiment of the present invention, the preparation method of the porous core-shell structured CeO2 nano-material is as follows: Ce(NO3)3·6H2O, urea, and citric acid are dissolved in a mixed solution of ethylene glycol and water, and H2O2 is added, followed by a hydrothermal reaction. The hydrothermal reaction product is post-treated to obtain the porous core-shell structured CeO2 nano-material.

[0019] In a preferred embodiment of the present invention, the mass ratio of Ce(NO3)3·6H2O, urea and citric acid is 280 mg - 285 mg : 40 mg - 42 mg : 68 mg - 70 mg, and the dosage ratio of Ce(NO3)3·6H2O to ethylene glycol and water is 280 mg - 285 mg : 8 mL - 9 mL : 56 mL - 58 mL.

[0020] In a preferred embodiment of the present invention, the hydrothermal reaction temperature is 120°C - 130°C, and the hydrothermal reaction time is 20 hours - 24 hours.

[0021] Another object of the present invention is to provide a CO2 gas sensor prepared by the preparation method described in any one of the above.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. In the present invention, the CeO2 nano-semiconductor material with a porous core-shell structure is added to the mixed solution of polyethyleneimine and polyethylene glycol to obtain a PEI / PEG / CeO2 solution. Then, the PEI / PEG / CeO2 solution is spin-coated onto the pretreated quartz wafer to obtain a CO2 gas sensor. In the present invention, the blending of polyethyleneimine and hygroscopic polyethylene glycol increases the number of protonated amino groups, thereby promoting the reaction between CO2 and amino groups in the presence of water molecules. This process is caused by the hygroscopic polyethylene glycol promoting the adsorption of carbon dioxide molecules. When the number of hydroxyl end groups of polyethylene glycol matches the number of primary and secondary amino groups of polyethyleneimine, the hydrogen bonds between amino groups can be interrupted, so that more amino groups can contact CO2, achieving the best CO2 adsorption. Moreover, adding the CeO2 nano-semiconductor material with a porous core-shell structure to the mixed solution of polyethyleneimine and polyethylene glycol can effectively improve the ability to adsorb CO2, further reducing the response time and recovery time of the sensor to CO2, and achieving accurate detection of CO2 at room temperature.

[0024] 2. The present invention uses the hydrothermal method to prepare a CeO2 nano-semiconductor material with a porous core-shell structure, then ultrasonically mixes polyethyleneimine and polyethylene glycol in a suitable ratio with the CeO2 nano-material, drops the mixed solution on the QCM quartz wafer, and uses a spin coater to spin out the excess water, thereby preparing a novel CO2 gas sensor. Then, its gas-sensing performance is tested. The gas sensor of the present invention is simple to prepare, and it has very important practical significance for developing a CO2 sensor material with high sensitivity, low cost, and high stability suitable for greenhouse environments to solve the lack of instruments with high cost performance, miniaturization, and rapid real-time detection of CO2 in greenhouse environments. Description of the Drawings

[0025] Figure 1Frequency change curve of PEI-SnO2 prepared by the prior art.

[0026] Figure 2 Among them, (a)-(d) are the microscopic morphology diagrams of CeO2 with different magnification factors prepared in Example 1 of the present invention.

[0027] Figure 3 Frequency change curve of the gas sensor prepared in Example 1 of the present invention.

[0028] Figure 4 Frequency change curve of the PEI / PEG gas sensor prepared in Comparative Example 1 of the present invention. Detailed implementation manners

[0029] The following combines the embodiments of the present invention, and uses preferred embodiments and accompanying drawings for detailed description. The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0030] It should be noted that all the professional terms used in the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the protection scope of the present invention. Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be obtained through market purchase or prepared by existing methods.

[0031] The novel CO2 gas sensor prepared by the present invention uses a hydrothermal method to prepare a porous core-shell structured CeO2 nanosemiconductor material, and adds it to a mixed solution of PEI / PEG to prepare a sensor gas-sensitive material. Polyethyleneimine is abbreviated as PEI, the molecular weight of PEI is 70000, polyethylene glycol is abbreviated as PEG, the molecular weight of PEG is 400, the optimal preparation process of the sensor material is determined, and a novel CO2 sensor is designed and manufactured for performance detection.

[0032] Cerium is a lanthanide element and the most abundant rare earth element on the earth. Due to its unique Ce 4f electron structure, large oxygen vacancies, active sites and good Ce 3+ / Ce 4+Ionic reversible conversion is widely used in fields such as catalysis, fuel cells, antioxidant biology, ultraviolet absorption, sensors, and chemical mechanical polishing. The hydrothermal synthesis method refers to the chemical reaction of a Ce source solution under high temperature and pressure to form a precipitate, and the precipitate is obtained as a powder with finer particles through processes such as washing, centrifugation, and dehydration. Its characteristics are that the characteristics such as the grain size and morphology structure of CeO2 can be controlled by means of hydrothermal reaction temperature, reaction time, addition of activators, templating agents, etc. The generated CeO2 nanoparticles have high purity, good dispersibility, and controllable morphology structure. CeO2 nanomaterials can adsorb CO2 gas in the air, and controlling the morphology of CeO2 can greatly increase the specific surface area, thus adsorbing CO2 molecules faster. Therefore, it is widely used in the experimental preparation process.

[0033] In the PEI / PEG material, PEI contains primary amines, secondary amines, and tertiary amines, and it is extremely easy to adsorb CO2 molecules at room temperature. Therefore, a large amount of research work focuses on using PEI for CO2 adsorption and sensing. Due to the presence of its hydroxyl groups, PEG can adsorb water molecules from the environment. Adsorbing more water molecules can enhance the Le Chatelier's principle reaction, thereby amplifying the electrical signal. PEI and PEG are used for the non-covalent functionalization of graphene to detect CO2. The blending of PEI with hygroscopic PEG increases the number of protonated amino groups, thus promoting the reaction between CO2 and amino groups in the presence of water molecules. This process is caused by the hygroscopic PEG promoting the adsorption of CO2 molecules. When the number of hydroxyl end groups of PEG matches the number of primary and secondary amino groups of PEI, the best CO2 adsorption can be achieved, which can disrupt the hydrogen bonds between amino groups, enabling more amino groups to come into contact with CO2. In addition, the embedded PEG molecules themselves may not have a strong interaction with CO2, while reducing the overall polymer viscosity, thus allowing better CO2 diffusion. And the addition of short-chain PEG may lead to an increase in polymer fluidity. Solid-supported amines are usually prepared by grafting amines onto the solid support surface or by physically adsorbing amines into the pore space. The solid-loaded amine obtained by physically impregnating PEI / PEG into a porous solid support is a promising adsorbent for capturing CO2.

[0034] Example 1

[0035] A preparation method of a CO2 gas sensor includes the following steps:

[0036] (1) Before modifying the sensitive film on the surface of the quartz wafer, cleaning work needs to be carried out. Cleaning the quartz wafer mainly aims to remove impurities such as dust and grease on the surface of the quartz wafer. For sensors with the sensitive film being too thick and causing oscillation stop, after cleaning off the surface sensitive material, they can also be reused to save costs. When cleaning, use four beakers with a measuring range of 500 mL. Add 300 mL of absolute ethanol to two beakers respectively, and add 300 mL of deionized water to the other two beakers. Place the four beakers into an ultrasonic cleaner, add water to an appropriate height in the ultrasonic cleaner, set the water bath temperature to 30 °C and the power to 25%. Use tweezers to put the quartz wafer into the first absolute ethanol beaker for cleaning for two minutes, then into the first deionized water beaker for cleaning for two minutes, then into the second absolute ethanol beaker for cleaning for two minutes, and finally into the second deionized water beaker for cleaning for two minutes. After the QCM is cleaned, put it into a constant temperature drying oven, set the drying oven temperature to 40 °C and the drying time to 2 h. Take it out after the temperature in the drying oven has cooled to room temperature to obtain the pretreated quartz wafer.

[0037] (2) Dissolve 282.67 mg, 0.651 mmol of Ce(NO3)3·6H2O, 40.18 mg, 0.669 mmol of CO(NH2)2, and 68.59 mg, 0.326 mmol of C6H8O7·H2O in a mixture of 56 mL of ultrapure water and 8 mL of ethylene glycol and stir for 20 minutes. Then add 0.4 mL of H2O2 and mix and stir for 5 minutes. Then transfer the mixture to a 100 mL polytetrafluoroethylene container, place the polytetrafluoroethylene container into a reaction kettle and heat it to 130 °C in a vacuum drying oven and place it for 24 hours. After cooling, centrifuge the precipitate, filter it using a circulating water type multi-purpose vacuum pump, wash it with deionized water and ethanol, and dry it in a vacuum drying oven at 80 °C for 4 h to obtain a porous core-shell structured CeO2 nano-semiconductor material.

[0038] (3) Weigh 800 mg of 50% aqueous solution of PEI, 400 mg of PEG, and 40 mL of deionized water and mix them. Use a magnetic stirrer to heat it to 45 °C and stir for 1 h. Then weigh 1 mg of CeO2 and 2 mL of PEI / PEG solution, put them into an ultrasonic cleaner and heat and ultrasonically mix them evenly at 45 °C for 1 h. When spin-coating, clamp the quartz wafer on the spin coater, control the spin coater speed at 1000 rpm, use a micro syringe to suck 10 μL of PEI / PEG / CeO2 solution, gently push the syringe to let the liquid drop naturally fall from the needle tip to the center of the quartz wafer, and spin-coat for 30 s at a spin-coating speed of 1000 rpm, then increase the spin-coating speed to 2000 rpm and spin-coat for 30 s to throw out the excess water, thereby preparing a thin film type PEI / PEG / CeO2 composite material gas sensor.

[0039] Example 2

[0040] A preparation method of a CO2 gas sensor, comprising the following steps:

[0041] (1) Pretreat the quartz wafer to obtain a pretreated quartz wafer.

[0042] (2) Dissolve 280 mg of Ce(NO3)3·6H2O, 40 mg of CO(NH2)2 and 68 mg of C6H8O7·H2O in a mixture of 57 mL of ultrapure water and 8.5 mL of ethylene glycol, and stir for 20 minutes. Then add 0.4 mL of H2O2 and stir for 5 minutes. Then transfer the mixture to a 100 mL polytetrafluoroethylene container, place the polytetrafluoroethylene container in a reaction kettle, heat it to 120 °C in a vacuum drying oven and place it for 20 hours. After cooling, centrifuge the precipitate, filter it using a circulating water type multi-purpose vacuum pump, wash it with deionized water and ethanol, and dry it in a vacuum drying oven at 80 °C for 4 h to obtain a porous core-shell structured CeO2 nanosemiconductor material.

[0043] (3) Weigh 700 mg of 50% aqueous solution of PEI, 350 mg of PEG and 35 mL of deionized water, mix them, heat them to 40 °C using a magnetic stirrer and stir for 1 h. Then weigh 0.5 mg of CeO2 and 1 mL of PEI / PEG solution, put them into an ultrasonic cleaner, heat and ultrasonically mix them at 40 °C for 1 h to obtain a PEI / PEG / CeO2 solution. When spin-coating, clamp the quartz wafer on the spin coater, control the spin coater speed at 1000 rpm, use a micro syringe to suck 10 μL of the PEI / PEG / CeO2 solution, gently push the syringe to let the liquid drop naturally fall to the center of the quartz wafer, spin coat at a spin coating speed of 1000 rpm for 30 s, and then increase the spin coating speed to 2000 rpm and spin coat for 30 s to spin out the excess water, thereby preparing a thin film type PEI / PEG / CeO2 composite material gas sensor.

[0044] Example 3

[0045] A preparation method of a CO2 gas sensor, comprising the following steps:

[0046] (1) Pretreat the quartz wafer to obtain a pretreated quartz wafer.

[0047] (2) Dissolve 285 mg of Ce(NO3)3·6H2O, 42 mg of CO(NH2)2, and 70 mg of C6H8O7·H2O in a mixture of 58 mL of ultrapure water and 9 mL of ethylene glycol, and stir for 20 minutes. Then add 0.4 mL of H2O2 and stir for 5 minutes. Next, transfer the mixture to a 100 mL Teflon container, place the Teflon container in a reaction kettle, and heat it to 125 °C in a vacuum drying oven for 22 hours. After cooling, centrifuge the precipitate, filter it using a circulating water multi-purpose vacuum pump, wash it with deionized water and ethanol, and dry it in a vacuum drying oven at 80 °C for 4 h to obtain a porous core-shell structured CeO2 nanosemiconductor material.

[0048] (3) Weigh 900 mg of 50% aqueous solution of PEI, 450 mg of PEG, and 45 mL of deionized water, mix them, and heat to 43 °C using a magnetic stirrer and stir for 1 h. Then weigh 0.8 mg of CeO2 and 1.5 mL of PEI / PEG solution, place them in an ultrasonic cleaner, and heat and ultrasonically mix them at 43 °C for 1 h. When spin-coating, clamp the quartz wafer on the spin coater, control the spin coater speed at 1000 rpm, use a micro syringe to aspirate 10 μL of the mixed PEI / PEG / CeO2 solution, gently push the syringe to let the liquid drop naturally fall onto the center of the quartz wafer from the needle tip, spin-coat for 30 s at a spin-coating speed of 1000 rpm, and then increase the spin-coating speed to 2000 rpm and spin-coat for 30 s to spin out the excess water, thereby preparing a thin-film type PEI / PEG / CeO2 composite gas sensor.

[0049] The steps not disclosed in Example 2 and Example 3 of the present invention are the same as those in Example 1. The gas sensors prepared by the methods of Example 2 and Example 3 can both reduce the response time and recovery time to CO2.

[0050] Comparative Example 1

[0051] A preparation method of a PEI / PEG gas sensor, comprising the following steps:

[0052] Weigh 800 mg of 50% aqueous solution of PEI, 400 mg of PEG, and 40 mL of deionized water, mix them, and heat to 45 °C using a magnetic stirrer and stir for 1 h. When spin-coating, clamp the quartz wafer on the spin coater, control the spin coater speed at 1000 rpm, use a micro syringe to aspirate 10 μL of the mixed PEI / PEG solution, gently push the syringe to let the liquid drop naturally fall onto the center of the quartz wafer from the needle tip, spin-coat for 30 s at a spin-coating speed of 1000 rpm, and then increase the spin-coating speed to 2000 rpm and spin-coat for 30 s to spin out the excess water, thereby preparing a thin-film type PEI / PEG gas sensor.

[0053] Gas-sensing performance test

[0054] The gas response test is divided into four steps: In the first step, dry nitrogen is continuously introduced into the gas detection chamber to fully desorb the gas molecules adsorbed on the surface of the sensitive film. During this process, the oscillation frequency of the QCM rapidly increases until it stabilizes. At this time, the introduction of nitrogen is stopped, and the time of nitrogen purging is recorded as t N2 ; In the second step, wait for the QCM frequency to stabilize again after stopping nitrogen purging. This is because there are effects of air flow and air pressure during the purging process. After stopping nitrogen purging, the QCM frequency will fluctuate, and the frequency after re-stabilization is the fundamental frequency f of the QCM sensor film , and the waiting time is recorded as t wait1 , In the third step, introduce the sample gas into the gas detection chamber for a period of time. At this time, the QCM frequency will rapidly decrease, and the time of sample gas introduction is recorded as t samp ; In the fourth step, wait for the QCM frequency to stabilize again after stopping the introduction of the sample gas to be measured. At this time, the adsorption and desorption of the sample gas by the sensitive film are in a dynamic equilibrium state, and the waiting time is recorded as t wait2 , and the stabilized QCM frequency is recorded as f resp , f film and f resp The difference corresponds to the frequency response value ▲f of the sample gas measured this time. t N2 , t wait1 and t wait2 are directly related to the sensitive material. The response speed and recovery speed of sensors modified with different sensitive films are different. If the gas flow rate is too small during nitrogen purging, it will lead to too long recovery time of the sensor, and at the same time, the gas molecules adsorbed on the surface of the sensitive film are not thoroughly desorbed, resulting in weakened response. However, if the gas flow rate is too large, it will lead to large fluctuations or even a rapid decrease in the sensor frequency after the end of nitrogen purging, which is caused by the sudden decrease in the air chamber pressure after stopping nitrogen purging

[0055] Result analysis

[0056] In this invention, CeO2 nanomaterials are prepared by hydrothermal method at 130 °C for 24 h. Microscopic morphology analysis is carried out by scanning electron microscope S-4800. From Figure 2 (a) in it, it can be seen that spherical CeO2 with a porous core-shell structure, and its spherical shape is very obvious. From Figure 2 (b) in it, it can be seen the core in the damaged shell structure. From Figure 2 (c) in it, it can be seen that the morphologies are all spherical with different sizes and there are no other shapes. From Figure 2As can be seen from (d) therein, spheres with a porous core-shell structure also exist throughout a large range. The reasons why the porous core-shell structured CeO₂ nano-semiconductor material of the present invention can effectively improve the CO₂ capture ability when added to a mixed solution of polyethyleneimine and polyethylene glycol are mainly reflected in the following points: (1) The CeO₂ nano-semiconductor material is composed of many different spheres, and these spheres are composed of many small spheres. The gaps between these small spheres improve the adsorption performance of CO₂; (2) PEG prevents PEI from entering the mesopores of the CeO₂ nano-semiconductor material, allowing CO₂ to enter, thereby improving the adsorption performance. (3) PEI forms groups on the spherical surface of CeO₂, and these groups undergo a reversible reaction with CO₂, further improving the CO₂ adsorption.

[0057] Figure 3 This is the frequency change curve of the gas sensor prepared in Example 1 of the present invention. After a stable N₂ environment, CO₂ gas is injected to displace N₂ in the closed space. It can be found that its frequency drops significantly, from Figure 3 As can be seen, the response time is about 30 s. When the curve stabilizes, dry N₂ gas is injected to displace CO₂ gas in the closed space. It can be found that its frequency rises significantly and slowly approaches the frequency of the original stable N₂ environment. As can be seen from Figure 3 As can be seen, the recovery time is about 30 s.

[0058] Figure 4 This is the frequency change curve of the PEI / PEG gas sensor prepared in Comparative Example 1 of the present invention. After a stable N₂ environment, CO₂ gas is injected to displace N₂ in the closed space. It can be found that its frequency drops significantly, from Figure 4 As can be seen, the response time is about 60 s. When the curve stabilizes, dry N₂ gas is injected to displace CO₂ gas in the closed space. It can be found that its frequency rises significantly and slowly approaches the frequency of the original stable N₂ environment. As can be seen from Figure 4 As can be seen, the recovery time is about 50 s. Through comparative analysis, it can be found that adding CeO₂ with a spherical shell structure can significantly improve the response time and recovery time of the sensor.

[0059] In summary, in the present invention, a porous core-shell structured CeO2 nano-semiconductor material is added to a mixed solution of polyethyleneimine and polyethylene glycol to obtain a PEI / PEG / CeO2 solution. Then, the PEI / PEG / CeO2 solution is spin-coated onto a pretreated quartz wafer to obtain a CO2 gas sensor. In the present invention, the blending of polyethyleneimine and hygroscopic polyethylene glycol increases the number of protonated amino groups, thereby promoting the reaction between CO2 and amino groups in the presence of water molecules. This process is caused by the hygroscopic polyethylene glycol promoting the adsorption of carbon dioxide molecules. When the number of hydroxyl end groups of polyethylene glycol matches the number of primary and secondary amino groups of polyethyleneimine, the hydrogen bonds between amino groups can be interrupted, enabling more amino groups to come into contact with CO2 and achieving optimal CO2 adsorption. Moreover, adding the porous core-shell structured CeO2 nano-semiconductor material to the mixed solution of polyethyleneimine and polyethylene glycol can effectively improve the ability to adsorb CO2, further reduce the response time and recovery time of the sensor to CO2, and achieve precise detection of CO2 at room temperature.

[0060] It should be noted that when the present invention involves numerical ranges, it should be understood that any value between the two endpoints of each numerical range and the two endpoints themselves can be selected. Since the steps and methods adopted are the same as those in the embodiments, to avoid redundancy, the present invention describes the preferred embodiments. Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended protection scope is intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0061] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the present invention and its equivalent technologies, the present invention also intends to include these changes and modifications.

Claims

1. A method for preparing a CO2 gas sensor, characterized in that: The following steps are involved: Pre-treating the quartz wafer to obtain a pre-treated quartz wafer; Ce(NO3)3·6H2O, urea and citric acid are dissolved in a mixed solution of ethylene glycol and water, and H2O2 oxidant is added to carry out a hydrothermal reaction, and the hydrothermal reaction product is post-treated to obtain a CeO2 nano-semiconductor material with a porous core-shell structure; Mixing polyethyleneimine and polyethylene glycol with water and stirring to obtain a polyethyleneimine and polyethylene glycol mixed solution; The mass ratio of polyethyleneimine to polyethylene glycol is 700 mg~900 mg:350 mg~450 mg, polyethyleneimine is used in the form of a polyethyleneimine aqueous solution with a mass fraction of 50%, and the amount ratio of polyethylene glycol to water is 350 mg~450 mg:35 mL~45 mL; The porous core-shell structured CeO2 nano-semiconductor material is added to a mixed solution of polyethyleneimine and polyethylene glycol, and heated and ultrasonically mixed to obtain a PEI / PEG / CeO2 solution, wherein the amount ratio of the porous core-shell structured CeO2 nano-semiconductor material to the mixed solution of polyethyleneimine and polyethylene glycol is 0.5 mg to 1 mg: 1 mL to 2 mL; The PEI / PEG / CeO2 solution was spin-coated on the pre-treated quartz wafer to obtain a CO2 gas sensor.

2. The method for preparing a CO2 gas sensor according to claim 1, characterized in that: The heating ultrasonic temperature is 40℃~45℃.

3. The method for preparing a CO2 gas sensor according to claim 1, characterized in that: The mass ratio of Ce(NO3)3·6H2O, urea and citric acid is 280 mg~285 mg: 40 mg~42 mg: 68 mg~70 mg, and the dosage ratio of Ce(NO3)3·6H2O to ethylene glycol and water is 280 mg~285 mg: 8 mL~9 mL: 56 mL~58 mL.

4. The method for preparing a CO2 gas sensor according to claim 1, characterized in that: The hydrothermal reaction temperature is 120°C to 130°C, and the hydrothermal reaction time is 20 hours to 24 hours.

5. A CO2 gas sensor made by the preparation method according to any one of claims 1 to 4.

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