Clay mineral-based room temperature gas sensing material and preparation method thereof

Abstract

The invention discloses a clay mineral-based room-temperature gas sensing material and a preparation method thereof, and the method comprises the following steps: by taking ultrapure water as a dispersion medium, carrying out ultrasonic dispersion on layered aluminosilicate clay mineral to prepare a suspension, then uniformly coating the suspension on the surface of an interdigital electrode with a specific electrode distance, and carrying out vacuum drying to obtain the clay mineral-based room-temperature gas sensing material. And drying and curing at room temperature to form the sensitive film. The gas sensing material prepared by the method can work at room temperature, and realizes high-selectivity detection of polar gas through unique interaction between polar gas molecules and clay mineral interlayer cations, adsorbed water and laminate electrons. The preparation process is simple, low in cost and environment-friendly, the high-temperature working condition required by a traditional semiconductor gas sensor is completely avoided, and a new material and a new way are provided for developing a low-power-consumption and high-selectivity room-temperature gas sensing platform.

Description

Technical Field

[0001] This invention relates to a method for preparing gas sensing materials, specifically to a room temperature gas sensing material based on clay minerals, its preparation method, and its application in polar gas detection, belonging to the interdisciplinary technical fields of biomimetic surface and interface materials and functional textiles. Background Technology

[0002] Gas sensors have significant applications in environmental monitoring, industrial safety, and medical diagnostics. Gas sensors based on metal oxides (such as SnO2, ZnO, and WO3) have long dominated the gas detection field due to their high sensitivity and fast response. Their sensing mechanism primarily relies on the change in conductivity caused by the redox reaction on the material surface: oxygen molecules in the air adsorb onto the material surface, forming adsorbed oxygen species (O2⁻, O⁻, O⁻). 2 (⁻), which consumes surface electrons to form a high-resistivity electron depletion layer; when in contact with reducing gas, the gas reacts with adsorbed oxygen to release electrons, reducing resistance and thus enabling gas detection.

[0003] However, such sensors still face many challenges in practical applications. Chinese invention patent CN202510813957.6 discloses a gas sensor based on WO3 nanosheets, which shows high sensitivity to unsymmetrical dimethylhydrazine, but its operating temperature needs to reach above 200℃. Chinese invention patent CN202411366371.1 uses SnO2 composite material activated by surfactant to improve gas sensitivity, but it needs to be prepared in a reaction chamber with specific gas pressure, gas flow rate, AC voltage and discharge frequency, and the preparation process is complicated. More importantly, this type of sensing mechanism based on surface redox reaction has inherent limitations: (1) It requires a high operating temperature (usually >200℃) to activate the surface reaction, resulting in high energy consumption and shortened device life; (2) It has poor selectivity for specific gases, and different reducing gases can react with adsorbed oxygen; (3) It is easily affected by environmental humidity, and water molecules will compete for surface adsorption sites; (4) It has a weak response to nonpolar or weakly polar gases (such as alkanes) because it is difficult for them to interact effectively with adsorbed oxygen species. These drawbacks highlight the urgent need for alternative sensing materials with tunable surface properties, low energy consumption, and better adaptability to diverse gaseous environments.

[0004] To overcome the aforementioned technical bottlenecks, researchers began exploring clay mineral materials with unique layered structures and surface physicochemical properties. Clay minerals are a class of naturally occurring layered or fibrous silicate materials, whose structural units are mainly composed of silicon-oxygen tetrahedral sheets and aluminum (magnesium)-oxygen octahedral sheets stacked in different proportions and arrangements. These materials generally possess characteristics such as large specific surface area, tunable pore structure, and abundant active sites such as hydroxyl groups on the surface. Furthermore, the presence of exchangeable cations between layers promotes ion-dipole interactions and electrostatic attraction, giving them excellent adsorption performance and interaction potential for various gas molecules, especially polar molecules. Unlike the sensing mechanisms of metal oxides that rely on surface redox reactions, clay minerals, with their inherent composite adsorption mechanism due to their layered structure, offer the possibility of realizing novel gas-sensitive sensors. Chinese invention patent CN201810275617.2 uses organomontmorillonite as a filler component of modified nylon to prepare the shell of a gas sensor connection device. Its main purpose is to improve the material's resistance to vapor corrosion, rather than to utilize the gas-sensitive properties of montmorillonite. Another Chinese invention patent, CN201110413620.4, developed a neuronal harmful gas sensor based on a ZnO surface coating of Y-type zeolite material. This technology uses zeolite as a carrier for ZnO, and prepares a thick-film sensitive material through high-temperature calcination (550℃) and high-pressure molding (5000 tons). The sensor's operating temperature needs to be maintained in the high-temperature range of 250-350℃, and it needs to detect impedance changes under a 3000Hz high-frequency signal. Chinese invention patent CN201810990340.1 uses an electrospinning process to prepare tin dioxide / ZSM-5 type zeolite composite nanofibers. Through a complex preparation process (including high-pressure electrospinning and 600℃ high-temperature calcination), zeolite is composited with metal oxides. The final gas sensor still needs to operate in a high-temperature environment.

[0005] Existing research shows that clay minerals, especially montmorillonite and zeolite, are mostly used as auxiliary reinforcing components of metal oxide sensors or as adsorption aids for other sensitive materials. Their potential as main sensitive materials has not been fully explored. There is still a lack of systematic research and in-depth theoretical explanation of their intrinsic gas-sensing properties as pure phase materials at room temperature for gases of different polarities, especially their selective response mechanism and structure-activity relationship.

[0006] Therefore, developing a novel gas sensing material that can operate at room temperature, has high selectivity for polar gases, and does not depend on surface redox reactions has become an urgent technical problem to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a room temperature gas sensing material based on clay minerals. This material can achieve high sensitivity and high selectivity for detecting polar gases at room temperature, and the preparation process is simple and low cost, thereby further improving the overall performance of gas sensing materials and expanding their application fields.

[0008] I. Preparation of clay mineral room temperature gas sensing materials (1) Using ultrapure water as the dispersion medium, clay mineral powder is added and ultrasonically dispersed to form a uniform and stable suspension; (2) The obtained suspension is coated on the surface of the interdigitated electrode and dried and cured for 1 to 24 hours in an environment with an ambient temperature of -10 to 50°C and a relative humidity of less than 60% to form a sensitive film and obtain a gas sensing material. The clay mineral is selected from at least one of montmorillonite, attapulgite, kaolin, bentonite, soapstone, vermiculite, illite, sepiolite, chlorite, or halloysite. These are all aluminosilicate materials with a layered structure. The interlayer domains of the clay mineral contain exchangeable cations, which act as active sites to selectively interact with polar gas molecules, thereby achieving highly selective sensing. The cation is selected from Na. + Al 3+ Li + Ca 2+ Mg 2+ One or more of these technologies can be used to selectively sense polar gases at room temperature through the interaction between interlayer cations, adsorbed water, and layer electrons of clay minerals and polar gas molecules.

[0009] The mass concentration of clay minerals in the suspension is 1% to 20%, preferably 2% to 10%. The ultrasonic dispersion power is 100 to 300 W, and the time is 20 to 60 minutes.

[0010] The substrate of the interdigitated electrodes is selected from ceramic, silicon wafer, glass, or flexible polymer materials, and the electrode material is selected from gold, silver, platinum, or conductive carbon materials. The spacing between the interdigitated electrodes is designed to be 1~500 μm, preferably 200 μm.

[0011] The thickness of the sensitive membrane is controlled within the range of 10 to 500 μm. If the membrane is too thin, there are fewer active sites and the response is low; if the membrane is too thick, the gas diffusion resistance is high and the response recovery is slow. Preferably, the thickness is controlled within the range of 100 to 300 μm.

[0012] The ambient temperature for drying and curing should be selected from -10 to 50°C, which covers normal room temperature and possible refrigeration or slightly higher room temperature environments. The relative humidity should be below 60% to avoid excessive moisture affecting the drying effect and film quality. The processing time should be 1 to 24 hours to ensure that the solvent evaporates fully and the film is cured stably.

[0013] This invention utilizes clay minerals themselves as the sensing material, rather than as a carrier or additive. The unique layered structure and interlayer exchangeable cations of clay minerals provide abundant active sites and unique interaction mechanisms for gas sensing.

[0014] II. Performance of Clay Mineral Room Temperature Gas Sensing Materials The clay mineral gas sensing material prepared in this invention possesses excellent room-temperature gas sensing performance. Its sensing mechanism is primarily based on physicochemical adsorption, such as ion-dipole interactions, electrostatic attraction, and hydrogen bonding of surface hydroxyl groups between exchangeable cations in the clay mineral interlayer and polar gas molecules, rather than the surface redox reactions of traditional metal oxides. This makes the material: It exhibits significant polar selectivity: it responds extremely highly to strongly polar gases (such as NH3), responds weakly to weakly polar gases (such as acetone), and shows no significant response to nonpolar gases (such as toluene). The intensity of its response increases significantly with the increasing polarity of the gas molecules.

[0015] Operating at room temperature: No high-temperature activation is required, reducing energy consumption, extending device lifespan, and simplifying device structure.

[0016] Specifically, its performance is as follows: it exhibits a response of up to 380% to 420% to the highly polar gas NH3, with response / recovery times of only 48 seconds and 45 seconds, respectively; a response of approximately 20% to the weakly polar gas acetone; and no significant response to the nonpolar gas toluene. This sensor demonstrates significant polarity selectivity, with its response intensity increasing significantly with increasing gas molecule polarity.

[0017] To verify the reliability of the clay mineral gas sensing material prepared in this invention in practical applications, its stability was systematically evaluated, including continuous testing stability, environmental humidity stability, and long-term baseline stability. Stability was assessed by testing changes in the sensor signal response value, baseline drift rate, and recovery rate; smaller changes in these parameters indicate better stability.

[0018] Continuous stability testing: Based on the dynamic gas-sensitive testing standard, the sensor was subjected to 100 consecutive response-recovery cycle tests in a 500 ppm NH3 atmosphere. Test results showed that the response value of the 100th cycle decreased by less than 5% compared to the first cycle, the response / recovery time fluctuation was within ±10%, and the baseline recovery rate remained above 95%.

[0019] Environmental humidity stability: The sensor was placed in an environmental chamber at 25℃ and relative humidity of 20%-80%, and 200 ppm NH3 was introduced for testing. Under high humidity of 80%, the sensor's response to NH3 remained above 85% of the response value under dry conditions, and the baseline drift rate was less than 10%.

[0020] Long-term baseline stability: The fabricated sensor chip was tested after being left to stand in an atmospheric environment at room temperature for 30 days. The results showed that its response value to 500 ppm NH3 decreased by less than 8%, and the rate of change of the initial baseline resistance was controlled within ±5%, demonstrating excellent long-term operational stability.

[0021] In summary, the present invention has the following outstanding advantages over the prior art: (1) Innovative sensing mechanism: This invention utilizes the unique layered structure and interlayer chemical environment of clay minerals to realize room temperature gas sensing based on the interaction of "interlayer cation-water molecule-electron", breaking the limitation of traditional semiconductor sensors that rely on surface redox reactions.

[0022] (2) Excellent polarity selectivity: The clay mineral sensing material prepared by the present invention has unique polarity selectivity. It exhibits high response and fast response to strongly polar gases, while the response to non-polar gases is negligible, effectively solving the technical problem of poor selectivity of traditional metal oxide sensors.

[0023] (3) Room temperature operation and low power consumption: The clay mineral gas sensor provided by the present invention can operate at room temperature and has extremely low power consumption, overcoming the disadvantages of traditional metal oxide sensors that require high temperature operation, resulting in high energy consumption and short lifespan.

[0024] (4) Simple preparation process and low cost: The present invention can prepare high-performance gas sensors through simple solution ultrasonic dispersion and coating process, which completely avoids traditional processes such as high temperature treatment, complex nanostructure construction and precious metal doping. The raw materials are natural clay minerals, which are abundant and environmentally friendly, and have significant cost advantages and large-scale production potential.

[0025] (5) Good stability and environmental adaptability: The sensing material of the present invention has shown good stability in continuous cyclic testing, different humidity environments and long-term placement. The baseline drift is small and the response decay rate is low, showing potential for practical application.

[0026] (6) Broad application prospects: The sensing materials and sensors of the present invention are particularly suitable for application scenarios with strict requirements for low power consumption, low cost and miniaturization, such as Internet of Things, wearable devices, smart homes, environmental monitoring, agricultural greenhouses, and food preservation, and have broad industrial application prospects. Attached image description: Figure 1 The response curve of NH3 to CMS-1 sample.

[0027] Figure 2 Response curve of C3H6O to CMS-2 sample.

[0028] Figure 3 Response curves of CMS-3 samples at 200, 500, 1000 and 1500 ppm H2O2.

[0029] Figure 4 Response curve of C2H5OH (500 ppm) to CMS-4 sample. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0031] Example 1 50 mg of montmorillonite powder was weighed and added to 1 mL of ultrapure water. The mixture was ultrasonically dispersed at 150 W for 30 minutes to obtain a homogeneous suspension with a mass fraction of 5%. 50 μL of this suspension was taken using a micropipette and uniformly coated onto the surface of a ceramic-based interdigitated silver electrode (electrode size: 7 mm × 13 mm, electrode spacing: 200 μm). The electrode was then naturally dried at 25℃ and <50% relative humidity for 24 hours to form a sensitive film with a thickness of approximately 200 μm, thus obtaining the clay mineral room temperature gas sensing chip (CMS-1). The response of 500 ppm NH3 to the CMS-1 sample reached 410% (…). Figure 1 ).

[0032] Example 2 30 mg of kaolin powder was weighed and added to 1.5 mL of ultrapure water. The mixture was ultrasonically dispersed at 250 W for 40 minutes to obtain a homogeneous suspension with a mass fraction of 2%. The suspension was uniformly coated onto the surface of an interdigitated silver electrode on a ceramic substrate using spin coating (2000 rpm, 30 s). The electrode was then naturally dried at 30℃ and <60% relative humidity for 18 hours to form a sensitive film with a thickness of approximately 150 μm, thus obtaining the clay mineral room temperature gas sensing chip (CMS-2). The response of 50 ppm C3H6O to the CMS-2 sample reached 23% (…). Figure 2 ).

[0033] Example 3 75 mg of sepiolite powder was weighed and added to 1 mL of ultrapure water. The mixture was ultrasonically dispersed at 100 W for 60 minutes to obtain a homogeneous suspension with a mass fraction of 7%. 80 μL of the suspension was coated twice onto the surface of an interdigitated silver electrode on a ceramic substrate using a drop-coating method. After each coating, the electrode was pre-dried at 25 °C for 1 hour, and finally continuously dried at room temperature for 24 hours to form a sensitive film with a thickness of approximately 220 μm, thus obtaining the clay mineral room temperature gas sensing chip (CMS-3). The responses of the CMS-3 sample to 200, 500, 1000, and 1500 ppm H2O2 reached 80%, 180%, 390%, and 760%, respectively. Figure 3 ).

[0034] Example 4 90 mg of attapulgite powder was weighed and added to 0.9 mL of ultrapure water. The mixture was ultrasonically dispersed at 300 W for 20 minutes to obtain a homogeneous suspension with a mass fraction of 9%. Interdigitated silver electrodes were immersed in this suspension using an dip-coating method (coating speed 100 mm / min). The electrodes were then allowed to dry at 25°C and <50% relative humidity for 24 hours to form a sensitive membrane with a thickness of approximately 190 μm, thus obtaining the clay mineral room temperature gas sensing chip (CMS-4). The response of 500 ppm C2H5OH to the CMS-4 sample reached 180% (…). Figure 4 ).

[0035] Performance testing The gas-sensing performance of the sensor chips (CMS-1 to CMS-4) prepared in Examples 1-4 was tested at 25°C using a CGS-MT multifunctional probe station. The test results are shown in the table below: Test results show that all sensor chips prepared in the embodiments can significantly respond to the highly polar gas NH3 at room temperature, and the response value is positively correlated with the coating concentration of clay minerals. The montmorillonite-based sensor performed best, followed by sepiolite and attapulgite, while the kaolin-based sensor also showed a significant response. Meanwhile, all chips exhibited incomplete baseline recovery characteristics to the weakly polar gas acetone, verifying the universality and effectiveness of the sensing mechanism described in this invention in different clay mineral materials.

Claims

1. A method for preparing a room-temperature gas sensing material based on clay minerals, characterized in that, Includes the following steps: (1) Using ultrapure water as the dispersion medium, clay mineral powder is ultrasonically dispersed to form a uniform suspension; the clay mineral is an aluminosilicate material with a layered structure, and its interlayer domains contain exchangeable cations; (2) The suspension is uniformly coated on the surface of the interdigitated electrode and dried and cured for 1 to 24 hours at -10~50℃ and relative humidity <60% to form a sensitive film and obtain a gas sensing material.

2. The method for preparing room temperature gas sensing materials based on clay minerals as described in claim 1, characterized in that: The clay mineral is selected from at least one of montmorillonite, attapulgite, kaolinite, bentonite, saponite, vermiculite, illite, sepiolite, chlorite, and halloysite; the cation is Na. + Al 3+ Li + Ca 2+ Mg 2+ One or more of them.

3. The method for preparing room temperature gas sensing materials based on clay minerals as described in claim 1, characterized in that: The mass concentration of clay mineral powder in the suspension is 1% to 20%; the ultrasonic dispersion power is 100 to 300 W, and the time is 20 to 60 minutes.

4. The method for preparing room temperature gas sensing materials based on clay minerals as described in claim 1, characterized in that: The substrate of the interdigitated electrode is selected from ceramic, silicon wafer, glass or flexible polymer material, and the electrode material of the interdigitated electrode is selected from gold, silver, platinum or conductive carbon material; the spacing of the interdigitated electrodes is 1~500 μm.

5. The method for preparing room temperature gas sensing materials based on clay minerals as described in claim 1, characterized in that: The thickness of the sensitive membrane is 10~500 μm.

6. The room temperature gas sensing material prepared by the method according to any one of claims 1 to 5, characterized in that, The sensing material exhibits a high response to strongly polar gases, a weaker response to weakly polar gases, and no significant response to non-polar gases.

7. The room temperature gas sensing material according to claim 6, characterized in that, The sensing material has a response value ≥380% for strongly polar gases, a response time ≤50 seconds, and a recovery time ≤55 seconds; a response value ≤30% for weakly polar gases; and no significant response for non-polar gases. The strongly polar gas includes NH3, H2O2 or C2H5OH, the weakly polar gas includes acetone, and the non-polar gas includes toluene.

8. The room temperature gas sensing material according to claim 6, characterized in that, The stability of the sensing material meets the following requirements: response value decay rate < 5% after 100 consecutive response-recovery cycles, response value retention rate ≥ 85% within an ambient humidity range of 20%-80%, and response value decay rate < 8% after standing at room temperature for 30 days.

9. The application of the room temperature gas sensing material according to any one of claims 6 to 8 in polar gas detection.

10. The application according to claim 9, characterized in that, The polar gas includes strongly polar gases such as NH3, H2O2, and C2H5OH, or weakly polar gases such as acetone; the detection is performed at room temperature.

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