Carbon dioxide gas sensor and method for manufacturing the same

Abstract

The application discloses a carbon dioxide gas sensor and a preparation method thereof. The carbon dioxide gas sensor comprises an electrode, and a sensitive layer formed by a BP / APTES composite material is covered on the surface of the electrode. The BP / APTES composite material is prepared by a BP / APTES composite material solution formed by uniformly dispersing APTES in anhydrous ethanol / BP dispersion liquid. The carbon dioxide gas sensor disclosed by the application takes the BP / APTES composite material as the sensitive layer, realizes the rapid response to low-concentration CO2 (5-30 ppm) at room temperature, the response / recovery time is less than 5 s, has excellent selectivity and long-term stability, can work for a long time in a humidity environment (20% RH-62% RH), and has the advantages of simple operation, low cost and the like.

Description

Technical Field

[0001] This invention relates to the field of gas detection technology, specifically to a carbon dioxide gas sensor and its preparation method, in order to achieve rapid ion conduction and detection of CO2 gas at the ppm level. Background Technology

[0002] The continuous emission of carbon dioxide (CO2) is a major factor contributing to the greenhouse effect, leading to global warming, sea-level rise, and biodiversity loss. However, because CO2 is a non-reactive gas, the challenges of room-temperature, high-sensitivity detection, and especially real-time, rapid response for low concentrations of CO2 (below 30 ppm) urgently need to be addressed.

[0003] Most current carbon dioxide detection methods are based on infrared detection, which is based on the principle that the absorption spectrum of a gas varies depending on the substance. Different gas molecules have different chemical structures, and therefore absorb infrared radiation of different wavelengths to varying degrees. Thus, when infrared radiation of different wavelengths irradiates a substance sequentially, certain wavelengths of radiation are selectively absorbed and weakened by the sample, producing an infrared absorption spectrum. Therefore, knowing the infrared absorption spectrum of a substance allows us to determine its absorption peak in the infrared region. Different concentrations of the same substance will exhibit different absorption intensities at the same absorption peak position, and the absorption intensity is directly proportional to the concentration. That is, different gas molecules have different chemical structures, corresponding to different absorption spectra, and each gas has a strong absorption of specific wavelengths of light within its spectrum. Therefore, by detecting the effect of a gas on the wavelength and intensity of light, the concentration of the gas can be determined. Common infrared detection sensors consist of an infrared light source, a measuring gas chamber, an adjustable interference filter, a photodetector, an optical modulation circuit, and an amplification system. However, infrared detection is costly and not suitable for real-time detection.

[0004] Current technology also includes chemical CO2 gas sensors with sensitive layers based on polymers or hybrid polysiloxanes. Their main advantages are extremely low power consumption and the ability to reduce size for microelectronic systems. On the downside, short-term and long-term drift effects and a relatively low overall lifetime are major drawbacks. Most CO2 sensors are fully calibrated before leaving the factory. Over time, the sensor's zero point needs to be calibrated to maintain long-term stability.

[0005] Existing technologies also include chemical resistance sensors based on sensitive materials such as metal oxides and perovskites. These sensors often require high operating temperatures (200-600℃), resulting in high power consumption and unsuitability for flammable and explosive environments.

[0006] In addition, their minimum detection limits are usually over several hundred ppm, which is not conducive to the identification of trace amounts (below 30 ppm).

[0007] Although gas-sensitive films based on conductive carbon nanomaterials have enabled some studies of carbon dioxide gas at room temperature, they are still not satisfactory. They can often only perform qualitative measurements to observe the changing trend of carbon dioxide, or the response rate is extremely slow, the detection limit is limited, and the reaction is weak.

[0008] There is an urgent need to solve the technical problem that existing carbon dioxide gas sensors cannot respond and recover quickly to trace amounts of low concentration (ppm level) CO2 gas. Summary of the Invention

[0009] The purpose of this invention is to provide a carbon dioxide gas sensor and its preparation method, so as to solve the technical problem that existing carbon dioxide gas sensors cannot respond and recover quickly to trace low concentrations (ppm level) of CO2 gas.

[0010] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0011] A carbon dioxide gas sensor includes an electrode, the surface of which is covered with a sensitive layer formed by a BP / APTES composite material; the BP / APTES composite material is prepared by a BP / APTES composite material solution formed by uniformly dispersing APTES in anhydrous ethanol / BP dispersion.

[0012] Preferably, in the BP / APTES composite material, the weight ratio of BP to APTES ranges from 1:52.5 to 1:420.

[0013] Preferably, in the BP / APTES composite material, the weight ratio of BP to APTES is 1:210.

[0014] Preferably, in the BP / APTES composite material, BP is a multi-layered three-dimensional spatial structure formed by stacking nanosheets, namely black phosphorus nanosheets, the length of which is 200nm~5μm and the thickness is 1nm~6nm.

[0015] Preferably, in the BP / APTES composite material, BP is a multi-layered three-dimensional spatial structure formed by stacking nanosheets, namely black phosphorus nanosheets, and the length of the black phosphorus nanosheets is 200nm~400nm.

[0016] Preferably, the electrode is a planar interdigitated electrode device.

[0017] This invention also discloses a method for preparing a carbon dioxide gas sensor, which utilizes the carbon dioxide gas sensor described above and includes the following steps:

[0018] S1. An NMP / BP / NaOH dispersion with black phosphorus nanosheets was prepared by alkaline NMP solvent exfoliation method;

[0019] S2. The NMP and NaOH in the NMP / BP / NaOH dispersion were washed away with anhydrous ethanol to obtain anhydrous ethanol / BP dispersion;

[0020] S3. Add APTES to the anhydrous ethanol / BP dispersion obtained in step S2 and perform ultrasonic composite to obtain a BP / APTES composite solution.

[0021] S4. The BP / APTES composite material solution is drop-coated onto the surface of the electrode device and dried to obtain a carbon dioxide gas sensor with the BP / APTES composite material as the sensitive layer.

[0022] Preferably, the alkaline NMP solvent stripping method described in step S1 includes the following steps:

[0023] S1.1 Grind BP crystals and NaOH solid of a predetermined mass into powder in sequence, and add them to alkaline NMP solvent in sequence to obtain the first mixture;

[0024] S1.2. The first mixture is used to peel off the BP crystals under preset conditions to obtain an NMP / BP / NaOH dispersion with black phosphorus nanosheets.

[0025] Preferably, in step S2, anhydrous ethanol is used to wash away NMP and NaOH from the NMP / BP / NaOH dispersion, including the following steps:

[0026] S2.1 Centrifuge the NMP / BP / NaOH dispersion obtained in step S1 to obtain the supernatant from the alkaline NMP solvent, and replace the alkaline NMP solvent supernatant with an anhydrous ethanol solution of the same volume as the supernatant.

[0027] S2.2 Repeat step S2.1 multiple times to wash away NMP and NaOH from the NMP / BP / NaOH dispersion to obtain anhydrous ethanol / BP dispersion.

[0028] Preferably, in the BP / APTES composite material obtained in step S4, the weight ratio of BP to APTES is 1:210.

[0029] The present invention has the following beneficial effects:

[0030] 1. The carbon dioxide gas sensor disclosed in this invention uses BP / APTES composite material as the sensitive layer to achieve a rapid response to low concentrations of CO2 (5~30ppm) at room temperature, with response / recovery times of less than 5s. It has excellent selectivity and long-term stability, can work for a long time in humid environments (20%RH~62%RH), and has the advantages of simple operation and low cost.

[0031] 2. The multilayer spatial structure of BP in the carbon dioxide gas sensor disclosed in this invention provides ample space for CO2 adsorption and desorption. The primary amino groups in APTES molecules are dispersed and attached to the BP surface at the optimal density, effectively increasing the CO2 attachment sites. The excellent specific surface area of ​​BP provides abundant modification sites for amino modification. The amine polymers are uniformly distributed in the BP interlayer, ensuring the high responsivity of the carbon dioxide gas sensor.

[0032] 3. The carbon dioxide gas sensor disclosed in this invention allows the bicarbonate produced during the adsorption process to undergo a reversible reaction in the opposite direction after the concentration of the carbon dioxide to be measured decreases. Combined with the BP multilayer spatial structure, it provides sufficient space for the entry and diffusion of CO2 molecules and serves as an excellent conductive platform. Therefore, the carbon dioxide sensor can detect trace amounts of carbon dioxide gas at different concentrations with high sensitivity and speed, and has complete desorption capability. Attached Figure Description

[0033] To make the objectives, technical solutions, and advantages of the invention clearer, the invention will now be described in further detail with reference to the accompanying drawings, wherein:

[0034] Figure 1 This is a schematic diagram of the carbon dioxide gas sensor of the present invention.

[0035] Figure 2 This is a molecular structure diagram of APTES of the present invention.

[0036] Figure 3 This is a molecular structure diagram of NMP according to the present invention.

[0037] Figure 4 The image shows the SEM surface morphology of the BP and BP / APTES carbon dioxide sensors of the present invention.

[0038] Figure 5 This is a test diagram of the gas-sensing performance of the BP / APTES carbon dioxide sensor of the present invention.

[0039] Explanation of reference numerals in the attached figures: 1. Electrode device; 2. BP / APTES composite material solution; 3. Sensitive layer; 4. Carbon dioxide gas sensor with BP / APTES composite material as the sensitive layer. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0041] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the figures, or the orientation or positional relationship commonly used when the product is in use. They are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance. In addition, the terms "horizontal," "vertical," etc., do not indicate that the component is required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted. In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0042] This invention solves the technical problem that existing carbon dioxide gas sensors cannot respond and recover quickly to trace amounts of low concentration (ppm level) CO2 gas.

[0043] The present invention aims to achieve rapid response and high sensitivity detection of low concentrations of CO2 (ppm) at room temperature.

[0044] like Figure 1 As shown, based on the above-mentioned technical problems to be solved, the present invention discloses a carbon dioxide gas sensor, including an electrode, and a sensitive layer 3 formed by a BP / APTES composite material is covered on the surface of the electrode; the BP / APTES composite material is prepared by a BP / APTES composite material solution formed by uniformly dispersing APTES in anhydrous ethanol / BP dispersion.

[0045] Preferably, in the BP / APTES composite material, the weight ratio of black phosphorus (BP) to APTES ranges from 1:52.5 to 1:420.

[0046] Preferably, in the BP / APTES composite material, the weight ratio of black phosphorus (BP) to APTES is 1:210.

[0047] Preferably, in the BP / APTES composite material, BP is a multi-layered three-dimensional spatial structure formed by stacking nanosheets, namely black phosphorus nanosheets (BP NSs). The length of the black phosphorus nanosheets (BP NSs) is 200nm~5μm, the thickness is 1nm~10nm, and the number of layers is 1~12. Preferably, the length of the black phosphorus nanosheets (BP NSs) is 200nm~400nm; preferably, the thickness of the black phosphorus nanosheets (BP NSs) is 1nm~6nm; preferably, the number of layers of the black phosphorus nanosheets (BP NSs) is 1~5.

[0048] Each black phosphorus nanosheet in this invention has a layered structure. Related studies have shown that when the number of black phosphorus atoms inside the black phosphorus nanosheet is more than 10, the black phosphorus nanosheet material has the characteristics of a bulk metallic material and has high electrical conductivity. The black phosphorus nanosheets used in this invention have more than 50% of the black phosphorus atoms inside less than 10 layers, resulting in lower electrical conductivity. The black phosphorus nanosheets used in this invention have the advantages of structural stability and large specific surface area, and can serve as a good main structural support in BP / APTES composite materials and a good adsorption and desorption carrier for carbon dioxide gas.

[0049] Preferably, the electrode is a planar interdigitated electrode device.

[0050] The CO2 detection limit of the carbon dioxide gas sensor disclosed in this invention is 5ppm to 30ppm.

[0051] The working mechanism of the carbon dioxide gas sensor disclosed in this invention is as follows: When the carbon dioxide sensor is working, pre-adsorbed water molecules will ionize into H under the action of the primary amino groups in the APTES molecules. + and OH - Ion pairs; after the introduction of CO2 gas, the primary amines on the BP surface bind H. + Forming non-movable NH3 + At the same time, CO2 combines with OH- - Formation of HCO3 - When exposed to CO2 gas, free amines react with carbon dioxide molecules to form a liquid state, reducing the concentration of free amines on the BP surface. This decreases the conductivity of the carbon dioxide gas sensor with the BP / APTES composite material as the sensitive layer, ultimately increasing the sensor's resistance. Depending on the CO2 gas concentration, the increase in resistance during the carbon dioxide gas sensor's response will vary. Therefore, based on the relationship between the resistance value and the CO2 gas concentration, the detected CO2 gas concentration can be deduced.

[0052] In this invention, the primary amino group in APTES is more chemically active than the secondary amino group. Compared with the secondary amino group in branched polyethyleneimine, the primary amino group has a stronger ability to lose electrons. Therefore, when the carbon dioxide gas sensor responds, the primary amino group in APTES can more sensitively identify low concentrations of CO2 and can also combine with CO2 more quickly, giving the carbon dioxide gas sensor higher sensitivity and a faster response speed. This enables it to respond quickly and detect low concentrations of CO2 (ppm) at room temperature with high sensitivity.

[0053] In this invention, the BP material refers to black phosphorus (abbreviated as BP), which is an allotrope of elemental phosphorus. Among all allotropes of phosphorus, it has the lowest reactivity. At room temperature and pressure, black phosphorus has an orthorhombic crystal structure. Black phosphorus is also a semiconductor with a density of 2.70 g / cm³ and a hardness of 2. The crystal lattice of black phosphorus is an interconnected six-membered ring, with each atom connected to three other atoms. In these chains, the PPP bond angle is 90° and the PP bond distance is 2.17 angstroms. The thickness of a single layer of black phosphorus atoms is approximately 10.47 angstroms (1.047 nanometers).

[0054] In this invention, APTES refers to a compound with the Chinese name 3-aminopropyltriethoxysilane, and other Chinese names including: γ-aminopropyltriethoxysilane; 3-triethoxysilyl-1-propylamine; (3-aminopropyl)triethoxysilane; triethoxy-3-aminopropylsilane; 3-aminopropyltriethoxysilane; (3-aminopropyl)triethoxysilane; 3-aminopropyltriethoxysilane.

[0055] The molecular formula of APTES is C9H 23 NO3Si can also be written as H2NCH2CH2CH2Si(OC2H5)3, with the following molecular structure: Figure 2 As shown, the CAS number is 919-30-2, the molecular weight is 221.369, and the density is 0.9 g / cm³. 3 It is a pale yellow liquid that is toxic if inhaled.

[0056] APTES is readily hydrolyzed, releasing ethanol and forming the corresponding silanol condensate. The amino group within the C—NH2 bond of the molecule can react with acids, carboxylic acid esters, aldehydes, ketones, halogenated hydrocarbons, amides, and nitriles. It is soluble in organic solvents, but acetone and carbon tetrachloride are unsuitable as release agents; it is soluble in water; it hydrolyzes in water, forming an alkaline solution. APTES is generally prepared by reacting chloropropyltriethoxysilane with NH3 in an autoclave.

[0057] APTES can also be used as a silane coupling agent. Commercial brands include Kehua KH550, Wuhan WD-50, and the American A1100. This product is alkaline, highly versatile, and suitable for various thermoplastic and thermosetting resins such as epoxy, PBT, phenolic resins, polyamide, and polycarbonate.

[0058] In this invention, the response of the carbon dioxide gas sensor is defined as (R-R0) / R0, where R is the stable resistance value under a specific target gas and R0 is the initial resistance value of the device.

[0059] This invention also discloses a method for preparing a carbon dioxide gas sensor, utilizing the carbon dioxide gas sensor described above, such as... Figure 1 As shown, it includes the following steps:

[0060] S1. An NMP / BP / NaOH dispersion containing black phosphorus nanosheets (BP NSs) was prepared by alkaline NMP solvent exfoliation method;

[0061] S2. The NMP and NaOH in the NMP / BP / NaOH dispersion were washed away with anhydrous ethanol to obtain anhydrous ethanol / BP dispersion;

[0062] S3. Add APTES to the anhydrous ethanol / BP dispersion obtained in step S2 and perform ultrasonic composite to obtain BP / APTES composite solution 2.

[0063] S4. The BP / APTES composite material solution is drop-coated onto the surface of electrode device 1 and dried to obtain carbon dioxide gas sensor 4 with BP / APTES composite material as the sensitive layer.

[0064] Specifically, the length of the black phosphorus nanosheets obtained in step S1 is 200 nm to 5 μm, preferably 200 nm to 400 nm; the lattice spacing is 0.25 nm.

[0065] Preferably, the alkaline NMP solvent stripping method described in step S1 includes the following steps:

[0066] S1.1 Grind BP crystals and NaOH solid of a predetermined mass into powder in sequence, and add them to alkaline NMP solvent in sequence to obtain the first mixture;

[0067] S1.2. The first mixture is used to peel off the BP crystals under preset conditions to obtain an NMP / BP / NaOH dispersion containing black phosphorus nanosheets (BPNSs).

[0068] Specifically, at room temperature, a predetermined mass of BP crystals is weighed and ground into powder; then a predetermined mass of NaOH solid is weighed, and the BP crystals and NaOH solid are simultaneously added to a predetermined volume of alkaline NMP solvent to obtain the first mixture.

[0069] The alkaline NMP solvent is composed of NMP and NaOH, with a weight ratio of NMP to NaOH of 1.028:1.

[0070] The weight ratio of BP crystals to NaOH solids ranges from 1:1 to 1:3, with a preferred weight ratio of 1:2.

[0071] After the BP crystals are dissolved in an alkaline NMP solvent, the concentration of the BP material is in the range of 0.5~1 mg / mL, preferably 0.5 mg / mL; after the NaOH solid is dissolved in an alkaline NMP solvent, the concentration of the NaOH is in the range of 0.5~1.5 mg / mL, preferably 1 mg / mL.

[0072] Specifically, the first mixture was ultrasonically broken up using an ultrasonic breaker at an ambient temperature of 0°C, in a light-protected environment and under nitrogen protection for 720 minutes. The ultrasonic frequency was 20 kHz to 23 kHz. This process was used to peel off the BP crystals, resulting in black phosphorus crystals being exfoliated into black phosphorus nanosheets (BP NSs) with a layered structure. Ultrasonic peeling was performed under nitrogen protection because black phosphorus is easily oxidized and degraded in air, which affects its gas-sensitive properties.

[0073] Preferably, in step S2, anhydrous ethanol is used to wash away NMP and NaOH from the NMP / BP / NaOH dispersion, including the following steps:

[0074] S2.1 Centrifuge the NMP / BP / NaOH dispersion obtained in step S1 to obtain the supernatant from the alkaline NMP solvent, and replace the alkaline NMP solvent supernatant with an anhydrous ethanol solution of the same volume as the supernatant.

[0075] S2.2 Repeat step S2.1 multiple times to wash away NMP and NaOH from the NMP / BP / NaOH dispersion to obtain anhydrous ethanol / BP dispersion.

[0076] Specifically, in step S2.1, the centrifugation speed is 10,000 rpm and the centrifugation time is 15 min.

[0077] Specifically, in step S3, a preset volume of APTES is added to anhydrous ethanol / BP dispersion, then stirred thoroughly and ultrasonically composited. The ultrasonic frequency is 20 kHz to 23 kHz, and the ultrasonic time is 120 min. The stirring and ultrasonic composite are carried out at an ambient temperature of 0℃, protected from light, and in an N2 environment to further obtain BP / APTES composite material solution 2.

[0078] The APTES is used as an ammonia modifier to functionalize BP with amino groups. The volume fraction of APTES is between 0% and 20%. The volume fraction refers to the volume fraction of liquid pure ammonia modifier relative to the total volume of the composite solution, that is, the volume fraction of liquid pure APTES relative to the total volume of anhydrous ethanol / BP dispersion. In other words, the volume percentage range of liquid pure APTES to anhydrous ethanol / BP dispersion is 0% to 20%.

[0079] Preferably, the volume percentage of the liquid pure APTES relative to the total volume of the anhydrous ethanol / BP dispersion is 10%.

[0080] Specifically, the drying process described in step S4 refers to vacuum drying and heating (45°C) the electrode device coated with the BP / APTES composite material solution for 2 hours, so that the BP / APTES composite material solution forms a thin film sensitive layer 3 on the surface of the electrode device, and finally prepares a carbon dioxide gas sensor 4 with the BP / APTES composite material as the sensitive layer.

[0081] Preferably, in the BP / APTES composite material obtained in step S4, the weight ratio of black phosphorus (BP) to APTES is 1:210.

[0082] Specifically, the electrode is a planar interdigitated electrode device, and the spacing and width of the planar interdigitated electrode device are 50 μm.

[0083] In this invention, the alkaline NMP solvent refers to N-methylpyrrolidone, CAS number 872-50-4, molecular weight 99.131, molecular formula C5H9NO, and molecular structure as shown below. Figure 3 As shown, its English name is N-Methylpyrrolidone; N-methylpyrrolidone (basic NMP solvent) is a polar aprotic solvent with advantages such as low toxicity, high boiling point, strong dissolving power, non-flammability, strong selectivity, good stability, biodegradability, recyclability, safe use, and suitability for a variety of formulations.

[0084] If only APTES molecules are present, there may be a situation where the APTES molecules have sufficient reaction strength, but the interior of the APTES molecules cannot come into contact with CO2. This will lead to a decrease in the sensitivity of the carbon dioxide gas sensor.

[0085] In this invention, the BP material used has an excellent specific surface area, thus providing abundant modification sites for amino modification. The multilayer spatial structure of BP provides ample space for CO2 adsorption and desorption, as well as for the entry and diffusion of CO2 gas molecules. Since the two ends of the APTES molecule are respectively composed of a siloxane and a relatively free primary amino group, the use of 10% by volume APTES modification allows the amino functional groups to be distributed at the optimal density between the BP atomic layers. Thus, with the BP material providing good adsorption and desorption space, and the APTES molecules providing good sensitivity and response speed to CO2 gas at room temperature, the carbon dioxide gas sensor disclosed in this invention achieves rapid response and high sensitivity detection of low concentrations of CO2 (ppm) at room temperature.

[0086] The carbon dioxide gas sensor and its preparation method disclosed in this invention have the following technical advantages:

[0087] 1. Response speed and responsiveness

[0088] Compared to other two-dimensional nanocomposites that often require response / recovery times on the order of minutes or hours, the carbon dioxide gas sensor with BP / APTES composite material as the sensitive layer exhibits extremely fast response-recovery characteristics, with response / recovery times of 4.7 s and 4.8 s, respectively. The carbon dioxide gas sensor prepared using the method disclosed in this invention has high responsivity (reaching 28% response to 10 ppm CO2). The multilayer spatial structure of BP provides ample space for CO2 adsorption and desorption. The primary amino groups within the APTES molecules are dispersed and attached to the BP surface at optimal density, effectively increasing CO2 attachment sites. The excellent specific surface area of ​​BP provides abundant modification sites for amino group modification. The uniform distribution of APTES molecules in the BP interlayer ensures the high responsivity of the carbon dioxide gas sensor.

[0089] 2. Working conditions

[0090] The carbon dioxide gas sensor disclosed in this invention can operate normally at room temperature. Compared with the disadvantages of high power consumption caused by high temperature detection of CO2 by sensitive materials such as metal oxides and perovskites, the carbon dioxide gas sensor of this invention has low power consumption and can also operate normally in humid environments (20%RH~62%RH). This is because in humid environments, when water vapor is present, the reaction between CO2 and water will transfer the reaction product from carbamate to bicarbonate. This reversible reaction explains the complete desorption capability of the device in humid environments.

[0091] 3. Desorption capacity

[0092] When the carbon dioxide concentration decreases, the bicarbonate produced during the adsorption process can easily undergo a reversible reaction in the opposite direction. Combined with the BP multilayer spatial structure, which provides ample space for the entry and diffusion of CO2 molecules and serves as an excellent conductive platform, the carbon dioxide sensor can detect trace amounts of carbon dioxide gas at different concentrations with high sensitivity and speed, and has complete desorption capability.

[0093] 4. Innovation

[0094] Although there are existing literature reports on CO2 detection based on two-dimensional nanocomposite materials, this is the first time that composite materials prepared using BP and APTES polymers have been used for CO2 detection. This invention provides a rapid ion conduction scheme for detecting CO2 gas at the ppm level, which broadens the detection range of BP-based gas sensing and explores a CO2 gas sensitive system modified with BP-based amino functionalization.

[0095] Example 1

[0096] A carbon dioxide gas sensor with a BP / APTES composite material as the sensitive layer was prepared according to the carbon dioxide gas sensor preparation method disclosed in the instruction manual. The specific amounts of the materials used were: 20 mg of BP raw material, 40 mg of NaOH solid, 40 mL of alkaline NMP solvent, and 4 mL of APTES. After preparation, a BP / APTES composite material solution was obtained. 40-60 μL of the obtained BP / APTES composite material solution was deposited on the surface of the planar interdigitated electrode device using a drop-coating method and then dried to obtain a carbon dioxide gas sensor with a BP / APTES composite material as the sensitive layer.

[0097] (I) The microscopic characterization analysis of the carbon dioxide gas sensor prepared with BP / APTES composite material as the sensitive layer is shown below:

[0098] The device used in this experiment is a resistive gas sensor based on interdigitated electrodes, with a BP / APTES composite material as the sensing layer. The microstructure comparison between this and a pure BP sensing layer is as follows: Figure 4 As shown, where Figure 4 (a) shows the microstructure of the pure BP sensitive layer. Figure 4 (b) shows the microstructure of the BP / APTES carbon dioxide sensor.

[0099] The morphology image shows that the exfoliated BP nanosheets have a sheet-like structure, and the surface of the BP / APTES composite material has a viscous substance, indicating that the APTES polymer has been successfully attached to the BP nanosheets.

[0100] (II) The gas-sensing performance of the prepared carbon dioxide gas sensor with BP / APTES composite material as the sensitive layer was tested, as shown below:

[0101] This study investigated the repeatability, concentration-dependent real-time resistance change, operational stability, and selectivity of a carbon dioxide gas sensor with a 10% APTES volume fraction and a BP / APTES composite material as the sensing layer. Gas-sensing performance experiments were conducted at room temperature (22℃) and humidity (36%RH), including response / recovery time, repeatability, concentration gradient, and selectivity.

[0102] Meanwhile, another new carbon dioxide sensor was periodically exposed to 10 ppm CO2 to determine its long-term stable operation. Air or nitrogen was used as the carrier gas; the difference in response was negligible. The gas-sensing performance test results are as follows: Figure 5 As shown.

[0103] in, Figure 5 (a) is a schematic diagram of single-cycle response / recovery time. Figure 5 (b) is a graph showing the real-time changes in the concentration gradient resistance. Figure 5 (c) is the fitted curve of the response magnitude as a function of concentration. Figure 5 (d) is a graph showing the real-time changes in repetitive resistance. Figure 5 (e) is the error bar analysis plot for long-term stability. Figure 5 (f) shows the error bar analysis and response comparison of the gas-sensitive thin film to the interfering gas.

[0104] A diagram illustrating single-cycle response / recovery time is shown below. Figure 5 As shown in (a), after 10 ppm CO2 gas is introduced, the resistance of the gas-sensitive carbon dioxide sensor rises rapidly, and the curve is close to a square wave. It has an extremely fast response / recovery time (4.7 s / 4.8 s), which breaks the limitation of existing gas sensors that respond extremely slowly to low concentrations of CO2 in the 100 ppm range. Moreover, the detection limit for low concentrations of CO2 is expected to reach the ppb level.

[0105] CO2 gas at concentrations of 5 ppm to 30 ppm was introduced sequentially, such as... Figure 5 As shown in (b), the saturation resistance increases monotonically with increasing CO2 concentration, exhibiting a clear concentration gradient response. A linear fit was performed on the magnitude of the resistance response with the level of the introduced gas concentration, as follows: Figure 5 As shown in (c). The results indicate that the membrane is highly sensitive to CO2 (fitting slope Slope = 3.252 × 10⁻⁶). -2 / ppm), and the response magnitude has an excellent linear relationship with the gas concentration (fit coefficient R). 2 =0.992).

[0106] When 10ppm CO2 is introduced and the process is repeated for 4 cycles, the resistance changes in real time as follows: Figure 5As shown in (d), the mean response is 28.5% and the variance is 0.6%, indicating that the carbon dioxide sensor meets the excellent repeatability requirement.

[0107] Meanwhile, another new BP / APTES gas-sensitive carbon dioxide sensor was periodically exposed to 10 ppm CO2, and its repeatability was repeatedly tested every 1–3 days at 22°C room temperature and constant 36% RH humidity using a multi-functional gas analyzer and a multi-component automated gas mixing system. The response differences over 14 days were minimal. Figure 5 (e), with a mean response of 28% and a mean square error of 1.9%, indicates that the gas-sensitive composite film prepared in this study provides good operational stability for room temperature, real-time, and high-sensitivity detection of low-concentration CO2 (ppm).

[0108] The response of the composite sensitive thin film to interfering gases was tested, and the magnitude of the response was compared to that of... Figure 5 As shown in (f), the carbon dioxide sensor exhibits a mean response of 28.57% and a variance of 0.65% to CO2 under ambient temperature (22°C) and humidity (36%RH) conditions, while the mean response to interfering gases is only around 1%. This indicates that the carbon dioxide sensor has a selectivity for CO2 that is more than 20 times higher than that for interfering gases, thus demonstrating excellent selectivity for CO2.

[0109] The above embodiments lead to the following conclusions: The carbon dioxide gas sensor with BP / APTES composite material as the sensitive layer disclosed in this invention achieves high sensitivity, high response, and selective detection of CO2 with a concentration limit of 5 ppm under humidity and room temperature conditions: BP is used as a substrate, and amino groups are modified on the BP surface using the amine modifier APTES, wherein the mass fraction of BP dispersion is 0.5 mg / mL, and the volume fraction of APTES in the composite material solution is 10%; the multilayer spatial structure of BP provides sufficient space for CO2 adsorption and desorption, primary amino groups are dispersed and attached to the BP surface at the optimal density, effectively increasing CO2 attachment sites, and the excellent specific surface area of ​​BP provides abundant modification sites for amino modification. The amine polymer is uniformly distributed in the BP interlayer, ensuring the high responsiveness of the film.

[0110] The APTES molecule is composed of a siloxane and a relatively free primary amino group at each end. Pre-adsorbed water molecules ionize into H+ under the influence of the primary amino group. + and OH - Ion pairs; after the introduction of CO2 gas, the primary amines on the BP surface bind H. + Forming non-movable NH3 + At the same time, CO2 combines with OH- - Formation of HCO3 -When exposed to CO2 gas, the free amine reacts with the carbon dioxide molecules to form a liquid state, which reduces the concentration of free amines on the BP surface. This decreases the conductivity of the BP / APTES gas-sensitive composite carbon dioxide sensor, ultimately increasing the resistance of the sensing element.

[0111] The carbon dioxide gas sensor disclosed in this invention can operate normally at room temperature. Compared with the disadvantages of high power consumption caused by high temperature detection of CO2 by sensitive materials such as metal oxides and perovskites, the carbon dioxide gas sensor of this invention has low power consumption and can also operate normally in humid environments (20%RH~62%RH). This is because in humid environments, when water vapor is present, the reaction between CO2 and water will transfer the reaction product from carbamate to bicarbonate. This reversible reaction explains the complete desorption capability of the device in humid environments.

[0112] Compared to other two-dimensional nanocomposites that often require response / recovery times on the order of minutes or hours, the carbon dioxide gas sensor with BP / APTES composite material as the sensitive layer exhibits extremely fast response-recovery characteristics, with response / recovery times of 4.7 s and 4.8 s, respectively. The carbon dioxide gas sensor prepared using the method disclosed in this invention has high responsivity (reaching 28% response to 10 ppm CO2). The multilayer spatial structure of BP provides ample space for CO2 adsorption and desorption. The primary amines within the APTES molecules are dispersed and attached to the BP surface at optimal density, effectively increasing CO2 attachment sites. The excellent specific surface area of ​​BP provides abundant modification sites for amine modification. The uniform distribution of amine polymers within the BP interlayer ensures the high responsivity of the carbon dioxide gas sensor.

[0113] When the carbon dioxide concentration decreases, the bicarbonate produced during the adsorption process can easily undergo a reversible reaction in the opposite direction. Combined with the BP multilayer spatial structure, which provides ample space for the entry and diffusion of CO2 molecules and serves as an excellent conductive platform, the carbon dioxide sensor can detect trace amounts of carbon dioxide gas at different concentrations with high sensitivity and speed.

[0114] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Under the teachings of the present invention, modifications can be made to these features and embodiments to adapt to specific situations and materials without departing from the spirit and scope of the invention. The embodiments described in this invention are only a part of the embodiments of the invention, not all of them. The components of the embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. Therefore, the invention is not limited to the specific embodiments disclosed herein, and all other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A carbon dioxide gas sensor, comprising electrodes, characterized in that, A sensitive layer formed by a BP / APTES composite material is coated on the electrode surface; the BP / APTES composite material is prepared by a BP / APTES composite material solution uniformly dispersed in anhydrous ethanol / BP dispersion; wherein, BP is black phosphorus; The method for preparing the carbon dioxide gas sensor includes the following steps: S1. An NMP / BP / NaOH dispersion containing black phosphorus nanosheets is prepared using an alkaline NMP solvent exfoliation method; the alkaline NMP solvent exfoliation method includes the following steps: S1.1 Grind BP crystals and NaOH solid of a predetermined mass into powder in sequence, and add them to alkaline NMP solvent in sequence to obtain the first mixture; S1.

2. The first mixture is used to peel off the BP crystals under preset conditions to obtain an NMP / BP / NaOH dispersion with black phosphorus nanosheets; wherein, the specific method of peeling off the BP crystals with the first mixture is to use an ultrasonic disruptor to sonicate the first mixture for 720 minutes in an environment with an ambient temperature of 0°C, in the dark and under nitrogen protection, with an ultrasonic frequency of 20 kHz~23 kHz, thereby peeling off the BP crystals. S2. The NMP and NaOH in the NMP / BP / NaOH dispersion were washed away with anhydrous ethanol to obtain anhydrous ethanol / BP dispersion; S3. Add APTES to the anhydrous ethanol / BP dispersion obtained in step S2 and perform ultrasonic composite to obtain a BP / APTES composite solution; wherein, stirring and ultrasonic composite are carried out at an ambient temperature of 0°C, in the dark and under N2 environment; S4. The BP / APTES composite material solution is drop-coated onto the surface of the electrode device and dried to obtain a carbon dioxide gas sensor with the BP / APTES composite material as the sensitive layer.

2. The carbon dioxide gas sensor according to claim 1, characterized in that, In the BP / APTES composite material, the weight ratio of BP to APTES is 1:52.5 to 1:

420.

3. The carbon dioxide gas sensor according to claim 1, characterized in that, In the BP / APTES composite material, the weight ratio of BP to APTES is 1:

210.

4. The carbon dioxide gas sensor according to any one of claims 1 to 3, characterized in that, In the BP / APTES composite material, BP is a multi-layered three-dimensional spatial structure formed by stacking nanosheets, namely black phosphorus nanosheets, with a length of 200nm~5μm and a thickness of 1nm~6nm.

5. The carbon dioxide gas sensor according to any one of claims 1 to 3, characterized in that, In the BP / APTES composite material, BP is a multi-layered three-dimensional spatial structure formed by stacking nanosheets, namely black phosphorus nanosheets, and the length of the black phosphorus nanosheets is 200nm~400nm.

6. The carbon dioxide gas sensor according to claim 1, characterized in that, The electrode is a planar interdigitated electrode device.

7. The carbon dioxide gas sensor according to claim 1, characterized in that, In step S2, anhydrous ethanol is used to wash away NMP and NaOH from the NMP / BP / NaOH dispersion, including the following steps: S2.1 Centrifuge the NMP / BP / NaOH dispersion obtained in step S1 to obtain the supernatant from the alkaline NMP solvent, and replace the alkaline NMP solvent supernatant with an anhydrous ethanol solution of the same volume as the supernatant. S2.2 Repeat step S2.1 multiple times to wash away NMP and NaOH from the NMP / BP / NaOH dispersion to obtain anhydrous ethanol / BP dispersion.

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