CO2 gas sensor and preparation method thereof

Abstract

The invention relates to the technical field of gas sensor preparation, in particular to a CO2 gas sensor and a preparation method thereof.The preparation method comprises the following steps that a quartz wafer is pretreated, the pretreated quartz wafer is obtained, a CeO2 nanometer semiconductor material of a porous core-shell structure is prepared, polyethyleneimine, polyethylene glycol and water are mixed and stirred, and the CO2 gas sensor is obtained. The preparation method comprises the following steps: preparing a polyethyleneimine-polyethylene glycol mixed solution, adding a CeO2 nano semiconductor material with a porous core-shell structure into the polyethyleneimine-polyethylene glycol mixed solution, heating, carrying out ultrasonic mixing to obtain a PEI / PEG / CeO2 solution, and spin-coating a quartz wafer with the PEI / PEG / CeO2 solution to obtain the CO2 gas sensor. The response time and recovery time of the sensor to CO2 can be effectively shortened, and accurate detection of CO2 at room temperature is realized.

Description

Technical Field

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

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

[0003] The development of intelligent regulation technology for CO2 concentration is relatively slow. The main reason for this is that gas measurement is difficult, and CO2 molecules are non-polar linear structures, which give them extremely stable chemical properties, which makes the development of CO2 concentration detection instruments and sensors more difficult. At present, there are two main 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 require offline detection and cannot be detected in real time. The equipment is large, expensive, cumbersome to operate, and requires high professionalism. Although the infrared CO2 detector developed based on the CO2 gas sensor has a fast response and high detection accuracy, it also has a complex equipment structure and is expensive, and its core sensor mainly relies on foreign imports. Although the electrochemical CO2 detector is relatively cheap, it has high energy consumption and slow response. The sensor electrolyte is lost during use and is frequently replaced. The emergence of mass sensors based on quartz crystal microbalances provides a new solution for the detection of CO2 concentration. As a high-precision mass-sensitive analytical instrument, the QCM sensor can respond quickly to changes in nanogram-level mass. It is low-cost, highly accurate, and capable of continuous real-time detection. It is widely used in gas detection, chemical composition analysis, and other fields.

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

[0005] In view of the deficiencies of the above-mentioned prior art, an object of the present invention is to provide a CO2 gas sensor and a method for preparing the same. The method for preparing 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 accurate detection of CO2 at room temperature.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions: A method for preparing a CO2 gas sensor comprises the following steps: The quartz wafer is pre-treated to obtain a pre-treated quartz wafer.

[0007] Preparation of porous core-shell structured CeO2 nano-semiconductor materials.

[0008] The polyethyleneimine and polyethylene glycol are mixed with water and stirred to obtain a polyethyleneimine and polyethylene glycol mixed solution.

[0009] The porous core-shell 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. The PEI / PEG / CeO2 solution is spin-coated on a pretreated quartz wafer to obtain a CO2 gas sensor.

[0010] The present invention adds a CeO2 nano-semiconductor material with a porous core-shell structure into a mixed solution of polyethyleneimine and polyethylene glycol to obtain a PEI / PEG / CeO2 solution, and then spin-coats the PEI / PEG / CeO2 solution 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 amine groups, thereby promoting the reaction between CO2 and the amine 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 the polyethylene glycol matches the number of primary and secondary amine groups of the polyethyleneimine, the hydrogen bonds between the amine groups can be interrupted, so that more amine groups can contact with CO2, thereby achieving optimal CO2 adsorption. The CeO2 nano-semiconductor material with a porous core-shell structure is added to the mixed solution of polyethyleneimine and polyethylene glycol to effectively improve the ability to adsorb CO2, further reduce the response time and recovery time of the sensor to CO2, and achieve accurate detection of CO2 at room temperature.

[0011] 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.

[0012] In a preferred embodiment of the present invention, polyethyleneimine is used in the form of a polyethyleneimine aqueous solution with a mass fraction of 50%.

[0013] In a preferred embodiment of the present invention, the usage ratio of polyethylene glycol to water is 350 mg-450 mg: 35 mL-45 mL.

[0014] In a preferred embodiment of the present invention, the usage 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.

[0015] In a preferred embodiment of the present invention, the heating temperature is 40° C. to 45° C., and the ultrasonic time is 110 min to 120 min.

[0016] In a preferred embodiment of the present invention, the preparation method of the porous core-shell structured CeO2 nanomaterial 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 to carry out a hydrothermal reaction, and the hydrothermal reaction product is post-treated to obtain the porous core-shell structured CeO2 nanomaterial.

[0017] 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 usage ratio of Ce(NO3)3·6H2O to ethylene glycol and water is 280 mg~285 mg: 8 mL~9 mL: 56 mL~58 mL.

[0018] In a preferred embodiment of the present invention, the hydrothermal reaction temperature is 120° C. to 130° C., and the hydrothermal reaction time is 20 hours to 24 hours.

[0019] Another object of the present invention is to provide a CO2 gas sensor manufactured by any of the above-mentioned preparation methods.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention adds a CeO2 nano-semiconductor material with a porous core-shell structure to a mixed solution of polyethyleneimine and polyethylene glycol to obtain a PEI / PEG / CeO2 solution, and then spin-coats the PEI / PEG / CeO2 solution 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 amine groups, thereby promoting the reaction between CO2 and amine 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 amine groups of polyethyleneimine, the hydrogen bonds between the amine groups can be interrupted, so that more amine groups can contact CO2 and achieve optimal CO2 adsorption. The addition of the CeO2 nano-semiconductor material with a porous core-shell structure to a mixed solution of polyethyleneimine and polyethylene glycol can effectively improve the ability to adsorb CO2, further reduce the sensor's response time and recovery time to CO2, and achieve accurate detection of CO2 at room temperature.

[0021] 2. The present invention adopts a hydrothermal method to prepare a porous core-shell structure CeO2 nano-semiconductor material, and then ultrasonically mixes polyethyleneimine and polyethylene glycol in an appropriate proportion with the CeO2 nano-material, and drips the mixed solution on a QCM quartz wafer. A spin coater is used to spin off excess water, thereby preparing a new CO2 gas sensor, which is then tested for its gas-sensitive performance. The gas sensor of the present invention is simple to prepare, and in order to solve the lack of cost-effective, miniaturized instruments that can quickly and real-time detect CO2 in a greenhouse environment, it is of great practical significance to develop highly sensitive, low-cost, and highly stable CO2 sensor materials suitable for a greenhouse environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a frequency change curve of PEI-SnO2 prepared by prior art.

[0023] Figure 2 (a) to (d) are microscopic morphologies of CeO2 prepared in Example 1 of the present invention at different magnifications.

[0024] Figure 3 This is a frequency change curve of the gas sensor prepared in Example 1 of the present invention.

[0025] Figure 4 This is a frequency change curve of the PEI / PEG gas sensor prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0026] The following is a detailed description of the technical solutions in the embodiments of the present invention in combination with the preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] It should be noted that all professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods.

[0028] The novel CO2 gas sensor prepared by the present invention adopts a hydrothermal method to prepare a CeO2 nano-semiconductor material with a porous core-shell structure, which is added into a mixed solution of PEI / PEG to prepare a sensor gas-sensitive material, where polyethyleneimine is abbreviated as PEI with a molecular weight of 70,000, and polyethylene glycol is abbreviated as PEG with a molecular weight of 400. The optimal sensor material preparation process is determined, and a novel CO2 sensor is designed and manufactured for performance testing.

[0029] Cerium is a lanthanide element and the most abundant rare earth element on earth. It has a unique Ce 4f electronic structure, large oxygen vacancies, active sites and good Ce 3+ / Ce 4+Ions can be reversibly converted and are widely used in catalysis, fuel cells, antioxidant biology, ultraviolet absorption, sensors, and chemical mechanical polishing. The hydrothermal synthesis method refers to the chemical reaction of Ce source solution under high temperature and high pressure to generate precipitates. The precipitates are washed, centrifuged, dehydrated, and other processes to obtain finer particle powders. Its characteristics are that the CeO2 grain size, morphology, and structure can be controlled by means of hydrothermal reaction temperature, reaction time, addition of activators, template agents, and other means. The generated CeO2 nanoparticles have high purity, good dispersibility, and controllable morphology and structure. CeO2 nanomaterials can adsorb CO2 gas in the air, and controlling the morphology of CeO2 can greatly increase the specific surface area, thereby adsorbing CO2 molecules faster. Therefore, they are widely used in experimental preparation processes.

[0030] PEI in PEI / PEG materials contains primary, secondary and tertiary amines, which can easily adsorb CO2 molecules at room temperature. Therefore, a lot of research work has focused on the adsorption and sensing of CO2 using PEI. PEG can adsorb water molecules from the environment due to its hydroxyl groups. The adsorption of more water molecules can enhance the Le Chatelier principle reaction, thereby amplifying the electrical signal. PEI and PEG are used for non-covalent functionalization of graphene to detect CO2. The blending of PEI with hygroscopic PEG increases the number of protonated amine groups, thereby promoting the reaction between CO2 and amine groups in the presence of water molecules. This process is caused by the hygroscopic PEG promoting the adsorption of carbon dioxide molecules. Optimal CO2 adsorption can be achieved when the number of hydroxyl end groups of PEG matches the number of primary and secondary amine groups of PEI, which can interrupt the hydrogen bonds between amine groups, allowing more amine groups to contact CO2. In addition, the embedded PEG molecules themselves may not have a strong interaction with CO2, while reducing the overall polymer viscosity, allowing better CO2 diffusion. 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 surface of a solid support or by incorporating amines into the pore space by physical adsorption. Solid-supported amines physically impregnated with PEI / PEG into porous solid supports are promising adsorbents for capturing CO2.

[0031] Example 1 A method for preparing a CO2 gas sensor comprises the following steps: (1) Before modifying the sensitive film, the surface of the quartz wafer needs to be cleaned. Cleaning the quartz wafer mainly removes dust, grease and other impurities on the surface of the quartz wafer. For sensors that stop vibrating due to excessively thick sensitive films, the surface sensitive materials can be cleaned and reused to save costs. Four beakers with a range of 500 mL are used for cleaning. Two beakers are filled with 300 mL of anhydrous ethanol, and the other two beakers are filled with 300 mL of deionized water. The four beakers are placed in an ultrasonic cleaner, and water is added to the ultrasonic cleaner at a suitable height. The water bath temperature is set to 30°C and the power is set to 25%. Use tweezers to place the quartz wafer in the No. 1 anhydrous ethanol beaker for two minutes, then in the No. 1 deionized water beaker for two minutes, then in the No. 2 anhydrous ethanol beaker for two minutes, and finally in the No. 2 deionized water beaker for two minutes. After the QCM is cleaned, put it in a constant temperature drying oven, set the drying oven temperature to 40°C, and dry for 2 hours. After the temperature in the drying oven cools to room temperature, take it out to obtain the pretreated quartz wafer.

[0032] (2) 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 were dissolved in a mixture of 56 mL of ultrapure water and 8 mL of ethylene glycol and stirred for 20 minutes. 0.4 mL of H2O2 was added and stirred for 5 minutes. The mixture was then transferred to a 100 mL polytetrafluoroethylene container, which was placed in a reactor and heated to 130°C in a vacuum drying oven for 24 hours. After cooling, the precipitate was centrifuged, filtered using a circulating water multi-purpose vacuum pump, washed with deionized water and ethanol, and dried in a vacuum drying oven at 80°C for 4 hours to obtain a porous core-shell structured CeO2 nano-semiconductor material.

[0033] (3) Weigh 800 mg of 50% aqueous solution of PEI, 400 mg of PEG and 40 mL of deionized water, mix them, heat to 45°C with a magnetic stirrer, 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 at 45°C for 1 h. During spin coating, clamp the quartz wafer on the spin coater, control the spin coater speed at 1000 rpm, use a micro syringe to draw 10 μL of PEI / PEG / CeO2 solution, gently push the syringe to let the droplet drip naturally from the needle to the center of the quartz wafer, spin coat at 1000 rpm for 30 s, and then increase the spin coating speed to 2000 rpm for 30 s to spin off excess water, thereby preparing a thin film PEI / PEG / CeO2 composite gas sensor.

[0034] Example 2 A method for preparing a CO2 gas sensor comprises the following steps: (1) Pre-treating a quartz wafer to obtain a pre-treated quartz wafer.

[0035] (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. 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 reactor, heat it to 120°C in a vacuum drying oven for 20 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 hours to obtain a porous core-shell structured CeO2 nano-semiconductor material.

[0036] (3) Weigh 700 mg of 50% aqueous solution of PEI, 350 mg of PEG and 35 mL of deionized water, mix them, heat to 40°C with 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 and heat and ultrasonically mix them at 40°C for 1 h to obtain a PEI / PEG / CeO2 solution. During spin coating, clamp the quartz wafer on the spin coater, control the spin coater speed at 1000 rpm, use a micro syringe to draw 10 μL of PEI / PEG / CeO2 solution, gently push the syringe to let the droplet drip naturally from the needle to the center of the quartz wafer, spin coat at 1000 rpm for 30 s, and then increase the spin coating speed to 2000 rpm for 30 s to spin off excess water, thereby preparing a thin film PEI / PEG / CeO2 composite gas sensor.

[0037] Example 3 A method for preparing a CO2 gas sensor comprises the following steps: (1) Pre-treating a quartz wafer to obtain a pre-treated quartz wafer.

[0038] (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. 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 reactor, heat it to 125°C in a vacuum drying oven and place it 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 hours to obtain a porous core-shell structured CeO2 nano-semiconductor material.

[0039] (3) Weigh 900 mg of 50% aqueous solution of PEI, 450 mg of PEG and 45 mL of deionized water, mix them, heat to 43°C with a magnetic stirrer, and stir for 1 h. Then weigh 0.8 mg of CeO2 and 1.5 mL of PEI / PEG solution, put them into an ultrasonic cleaner and heat and ultrasonically mix them at 43°C for 1 h. During spin coating, clamp the quartz wafer on the spin coater, control the spin coater speed at 1000 rpm, use a micro syringe to draw 10 μL of the mixed PEI / PEG / CeO2 solution, gently push the syringe to let the droplet drip naturally from the needle to the center of the quartz wafer, spin coat at 1000 rpm for 30 s, and then increase the spin coating speed to 2000 rpm for 30 s to spin off excess water, thereby preparing a thin film PEI / PEG / CeO2 composite gas sensor.

[0040] The undisclosed steps in Examples 2 and 3 of the present invention are the same as those in Example 1. The gas sensors prepared by the methods of Examples 2 and 3 can reduce the response time and recovery time to CO2.

[0041] Comparative Example 1 A method for preparing a PEI / PEG gas sensor comprises the following steps: Weigh 800 mg of 50% aqueous solution of PEI, 400 mg of PEG and 40 mL of deionized water, mix them, heat to 45°C with a magnetic stirrer, and stir for 1 h. During spin coating, clamp the quartz wafer on the spin coater, control the spin coater speed at 1000 rpm, use a micro syringe to draw 10 μL of the mixed PEI / PEG solution, gently push the syringe to let the droplet drip naturally from the needle to the center of the quartz wafer, spin coat at 1000 rpm for 30 s, and then increase the spin coating speed to 2000 rpm for 30 s to shake off excess water, thereby preparing a thin film PEI / PEG gas sensor.

[0042] Gas Sensitive Performance Test The gas response test is divided into four steps: the first step is to continuously introduce dry nitrogen into the gas detection chamber to fully desorb the gas molecules adsorbed on the surface of the sensitive membrane. During this process, the oscillation frequency of the QCM increases rapidly until it stabilizes. At this time, the introduction of nitrogen is stopped, and the nitrogen purge time is recorded as t N2 The second step is to wait for the QCM frequency to stabilize again after stopping the nitrogen purge. This is because there are airflow and pressure effects during the purge process. After stopping the nitrogen purge, the QCM frequency will fluctuate. The frequency after stabilization is the fundamental frequency f of the QCM sensor. film The waiting time is t wait1 In the third step, the sample gas is introduced into the gas detection chamber for a period of time. At this time, the QCM frequency will drop rapidly. The time for the sample gas to be introduced is recorded as t samp ; The fourth step is to wait for the QCM frequency to stabilize again after the sample gas to be tested stops flowing. At this time, the adsorption and desorption of the sample gas by the sensitive membrane are in a dynamic equilibrium state. The waiting time is recorded as t wait2 , the frequency of the stabilized QCM is recorded as f resp , f film With f resp The difference corresponds to the frequency response value ▲f of the sample gas measured this time. N2 ,t wait1 and t wait2 It is directly related to the sensitive material. The response speed and recovery speed of sensors modified with different sensitive membranes are different. If the gas flow rate is too small during the nitrogen purge process, the recovery time of the sensor will be too long. At the same time, the gas molecules adsorbed on the surface of the sensitive membrane will not be completely desorbed, resulting in a weaker response. However, if the gas flow rate is too large, the sensor frequency will fluctuate greatly or even drop rapidly after the nitrogen purge is completed. This is because the pressure in the gas chamber suddenly decreases after the nitrogen purge is stopped.

[0043] Results Analysis The present invention uses a hydrothermal method to prepare CeO2 nanomaterials at a temperature of 130°C for 24 h, and uses a scanning electron microscope S-4800 to perform microscopic morphology analysis. Figure 2 In (a), we can see the spherical CeO2 with porous core-shell structure. Its spherical shape is very obvious. Figure 2 (b) shows the core in the damaged shell structure. Figure 2 From (c) in the figure, we can see that the shapes are all spherical in size and no other shapes. Figure 2It can be seen from (d) in the figure that the large area is also full of spheres with porous core-shell structure. The reasons why the CeO2 nano-semiconductor material with porous core-shell structure of the present invention can effectively improve the CO2 capacity by adding it to the mixed solution of polyethyleneimine and polyethylene glycol are mainly reflected in the following points: (1) CeO2 nano-semiconductor material is composed of many different spheres, which 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 CeO2 nano-semiconductor material, allowing CO2 to enter, thereby improving the adsorption performance; (3) PEI forms groups on the surface of CeO2 nano-semiconductor spheres, and these groups react reversibly with CO2, further improving the CO2 adsorption.

[0044] Figure 3 This is a frequency change curve of the gas sensor prepared in Example 1 of the present invention. After the N2 environment is stabilized, CO2 gas is injected to exhaust the N2 in the closed space. It can be found that its frequency drops significantly. Figure 3 It can be seen from the figure that the response time is about 30s. When the curve stabilizes, dry N2 gas is injected to exhaust the CO2 gas in the confined space. It can be found that its frequency rises significantly and slowly approaches the frequency of the original stable N2 environment. Figure 3 It can be seen that the recovery time is about 30s.

[0045] Figure 4 This is a frequency change curve of the PEI / PEG gas sensor prepared in Comparative Example 1 of the present invention. After the N2 environment is stabilized, CO2 gas is injected to exhaust the N2 in the confined space. It can be found that its frequency drops significantly. Figure 4 It can be seen from the figure that the response time is about 60s. When the curve stabilizes, dry N2 gas is injected to exhaust the CO2 gas in the confined space. It can be found that its frequency rises significantly and slowly approaches the frequency of the original stable N2 environment. Figure 4 It can be seen that the recovery time is about 50s. Through comparative analysis, it can be found that adding spherical shell structure CeO2 can significantly improve the response time and recovery time of the sensor.

[0046] In summary, the present invention adds a porous core-shell CeO2 nano-semiconductor material to a mixed solution of polyethyleneimine and polyethylene glycol to obtain a PEI / PEG / CeO2 solution, and then spin-coats the PEI / PEG / CeO2 solution 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 amine groups, thereby promoting the reaction between CO2 and amine 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 amine groups of polyethyleneimine, the hydrogen bonds between the amine groups can be interrupted, so that more amine groups can contact CO2 and achieve optimal CO2 adsorption. The addition of the porous core-shell CeO2 nano-semiconductor material to the mixed solution of polyethyleneimine and polyethylene glycol can effectively improve the ability to adsorb CO2, further reduce the sensor's response time and recovery time to CO2, and achieve accurate detection of CO2 at room temperature.

[0047] It should be noted that when the present invention relates to a numerical range, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundant description, the present invention describes a preferred embodiment. Although the preferred embodiments of the present invention have been described, once those skilled in the art know the basic creative concept, they can make other changes and modifications to these embodiments. Therefore, the attached protection scope is intended to be interpreted as including the preferred embodiment and all changes and modifications that fall within the scope of the present invention.

[0048] 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 protection scope of the present invention and its equivalent technology, the present invention is also intended to include these changes and variations.

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; Preparation of porous core-shell structured CeO2 nano-semiconductor materials; Mixing polyethyleneimine and polyethylene glycol with water and stirring to obtain a polyethyleneimine and polyethylene glycol mixed solution; The porous core-shell 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. The PEI / PEG / CeO2 solution is spin-coated on a pretreated 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 mass ratio of polyethyleneimine to polyethylene glycol is 700 mg~900 mg:350 mg~450 mg.

3. The method for preparing a CO2 gas sensor according to claim 1, characterized in that: The polyethyleneimine is used in the form of a 50% by mass polyethyleneimine aqueous solution.

4. The method for preparing a CO2 gas sensor according to claim 1, characterized in that: The dosage ratio of polyethylene glycol to water is 350 mg~450 mg:35 mL~45 mL.

5. The method for preparing a CO2 gas sensor according to claim 1, characterized in that: 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.

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

7. The method for preparing a CO2 gas sensor according to claim 1, characterized in that: The preparation method of porous core-shell CeO2 nanomaterials is as follows: 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 hydrothermal reaction, and the hydrothermal reaction product is post-treated to obtain the porous core-shell CeO2 nanomaterials.

8. The method for preparing a CO2 gas sensor according to claim 7, 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.

9. The method for preparing a CO2 gas sensor according to claim 7, characterized in that: The hydrothermal reaction temperature is 120°C to 130°C, and the hydrothermal reaction time is 20 hours to 24 hours.

10. A CO2 gas sensor made by the preparation method according to any one of claims 1 to 9.

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