Gas sensor for carbon monoxide detection

Abstract

The invention discloses a gas-sensitive sensor for carbon monoxide detection, and belongs to the technical field of gas-sensitive sensors, the gas-sensitive sensor comprises an alumina ceramic tube, two annular gold electrodes, four platinum wire leads, a sensitive inner layer, an outer layer, a palladium-platinum heating wire and a six-pin tube seat; the two annular gold electrodes are arranged on the aluminum oxide ceramic tube in parallel at an interval; each annular gold electrode is connected with the two platinum wire leads; the palladium-platinum heating wire penetrates through the inside of the aluminum oxide ceramic tube; two ends of the palladium-platinum heating wire and the four platinum wire leads are jointly welded on the six-pin tube seat; the sensitive inner layer is coated on the outer surfaces of the aluminum oxide ceramic tube and the annular gold electrode; and the sensitive inner layer is made of a nano tin dioxide material of which the surface is grafted with silicon dioxide. According to the scheme, the sensitivity and stability of the sensor on carbon monoxide detection can be improved.

Description

Technical Field

[0001] This application relates to the field of gas sensors, and particularly to a gas sensor for carbon monoxide detection. Background Art

[0002] CO gas is a very common gas and has been widely used in multiple fields. In the chemical industry, CO is an important raw material for synthesizing a series of basic organic chemical products and intermediates; in the metallurgical industry, CO can be used as a reducing agent for refining metals; in other fields, CO can also be used as a fuel; and in the long term in the future, the application frequency of CO will not decrease. CO is a colorless, odorless and toxic gas that can cause great harm to the human body. It destroys the oxygen transport function of the human body by acting on hemoglobin, causing people to lack oxygen and leading to death or permanent brain damage; moreover, this gas is flammable and explosive, and will explode if exposed to an open flame, resulting in serious economic losses and casualties. In daily life, incomplete combustion of automobile gasoline, leakage of kitchen gas, and poor ventilation in coal mines may all produce a large amount of CO gas.

[0003] With the expansion of the usage amount and application fields of CO, new and more challenging requirements have been put forward for the monitoring of CO gas. Due to the concealment and universality of CO leakage incidents, it is crucial to use a fast and effective method to monitor the concentration of CO. The gas sensing alarm can detect the change in gas concentration before the gas concentration reaches the dangerous threshold and trigger an alarm, realizing the effective detection of the CO gas concentration. The key to the CO alarm is the CO gas sensor. Currently, the main sensors in domestic gas industry alarms generally include semiconductor sensors, catalytic combustion sensors, infrared sensors, and laser sensors. Many traditional sensors rely on metal oxide semiconductor materials, such as tin oxide (SnO 2 )), which can only work effectively at high temperatures. This not only increases energy consumption but also limits the application of the sensor in low-temperature environments. In addition, such materials have poor selectivity for carbon monoxide and are easily interfered by other gases such as nitrogen dioxide and formaldehyde, resulting in a decrease in detection accuracy. The stability of the material is also a significant problem. When exposed to air for a long time or affected by a humid environment, the sensor material is prone to oxidation or reduction reactions, leading to a decrease in sensitivity and response speed. In addition, traditional materials often require complex processes such as high-temperature sintering during the preparation process, increasing the manufacturing cost and process difficulty, and also restricting the miniaturization and integration development of the sensor. Moreover, many conventional materials have the problem of limited cyclic service life. Frequent adsorption and desorption processes will cause the material performance to gradually degrade, shortening the service life of the sensor.

[0004] Therefore, there is an urgent need for a technical solution to improve the sensitivity and stability of carbon monoxide detection. Summary of the Invention

[0005] To solve the deficiencies of the prior art, an embodiment of the present application discloses a gas sensor for carbon monoxide detection. The present application solves the technical problems such as insufficient sensitivity and poor stability in the prior art.

[0006] An embodiment of the present application discloses a gas sensor for carbon monoxide detection, including: an alumina ceramic tube, two annular gold electrodes, four platinum wire leads, a sensitive inner layer, an outer layer, a palladium-platinum heating wire, and a six-pin socket; the two annular gold electrodes are arranged in parallel at intervals on the alumina ceramic tube; each annular gold electrode is connected to two of the platinum wire leads; the palladium-platinum heating wire passes through the inside of the alumina ceramic tube; both ends of the palladium-platinum heating wire are welded to the six-pin socket together with the four platinum wire leads; the sensitive inner layer is coated on the outer surfaces of the alumina ceramic tube and the annular gold electrodes; the material of the sensitive inner layer is a nano-tin dioxide material with surface-grafted silica.

[0007] In a possible implementation manner, the preparation method of the sensitive inner layer includes: adding tin grains to concentrated nitric acid and stirring, and grinding and calcining the dried product and then grinding it again to obtain nano-tin dioxide powder; mixing the powder with hydrogen peroxide, ammonia water, and deionized water, and performing ultrasonic oscillation treatment to obtain a tin dioxide hydroxide intermediate; adding 3-aminopropyltriethoxysilane and toluene to the intermediate and then magnetically stirring to obtain a tin dioxide material with surface-grafted silica through calcination.

[0008] In a possible implementation manner, adding tin grains to concentrated nitric acid and stirring, and grinding and calcining the dried product and then grinding it again to obtain nano-tin dioxide powder includes: adding tin grains to concentrated nitric acid in batches and performing magnetic stirring until no brownish-red gas is generated; centrifuging and washing the obtained precipitate until it is neutral; placing the washed precipitate in a vacuum drying oven for drying; grinding the dried product and then placing it in a muffle furnace for calcination; grinding the calcined light yellow solid to obtain nano-tin dioxide powder.

[0009] In a possible implementation manner, mixing the powder with hydrogen peroxide, ammonia water, and deionized water, and performing ultrasonic oscillation treatment to obtain a tin dioxide hydroxide intermediate includes: mixing the nano-tin dioxide powder with hydrogen peroxide, ammonia water, and deionized water; performing ultrasonic oscillation treatment on the mixture; separating and drying the ultrasonically treated mixture to obtain a tin dioxide hydroxide intermediate.

[0010] In one possible implementation, after adding aminopropyltriethoxysilane and toluene to the intermediate, magnetic stirring is performed to obtain a tin dioxide material with surface-grafted silica through calcination, including: adding aminopropyltriethoxysilane and toluene to the tin dioxide hydroxide intermediate, and magnetically stirring the mixture; centrifuging the stirred mixture; drying the centrifuged product; placing the dried product in a muffle furnace for calcination to obtain a tin dioxide material with surface-grafted silica.

[0011] In one possible implementation, the calcined light yellow solid is ground to obtain nano-tin dioxide powder, including: placing the preliminarily ground powder in a zirconia ball mill tank, and the ball milling medium is zirconia balls; controlling the mass ratio of the ball milling medium to the powder and the filling degree of the ball mill tank, and performing intermittent ball milling in an inert atmosphere; performing air classification on the ball-milled powder, and performing classification by adjusting the main air velocity and the rotation speed of the classification wheel; dispersing the classified powder in absolute ethanol and performing homogenization treatment using a shear disperser; performing vacuum drying on the homogenized slurry, and sieving the dried powder to obtain nano-tin dioxide powder.

[0012] In one possible implementation, adding aminopropyltriethoxysilane and toluene to the tin dioxide hydroxide intermediate and magnetically stirring the mixture includes: dispersing the tin dioxide hydroxide intermediate in a mixed solvent of toluene and n-hexane; dissolving the aminopropyltriethoxysilane coupling agent in absolute ethanol and slowly dropping it into the dispersion at the target temperature; continuously introducing dry nitrogen during the dropping process, and heating and stirring after completion.

[0013] In one possible implementation, adding aminopropyltriethoxysilane and toluene to the tin dioxide hydroxide intermediate and magnetically stirring the mixture further includes: establishing a transfer equation for the silyl group flux, diffusion coefficient, local concentration, and sound field-induced flow velocity; adjusting the sound field amplitude parameter according to the target flux value; dropping the aminopropyltriethoxysilane coupling agent solution at the target temperature while applying an ultrasonic field.

[0014] In a gas-sensitive sensor for carbon monoxide detection disclosed above, in the embodiments of the present application, by using the hydroxyl groups on the surface of SnO 2 as the anchor points, the siloxane groups react with them chemically, and a uniform assembly of highly dispersed Si functional groups is achieved on the surface of the oxide. This grafting modification method can not only introduce a finely dispersed phase at the molecular level, but more importantly, by eliminating the hydroxyl groups on the surface of the oxide and using the strong chemical bond between silicon and the oxide to firmly pin the second phase between the oxide grain boundaries, effectively preventing the migration of the second phase, and synergistically improving the sensitivity and stability of the nano gas-sensitive material from multiple dimensions. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 The embodiment of the present application discloses a method of using nano SnO 2 Surface grafting modified SiO 2 The structural principle diagram and physical diagram of the CO sensor which is a gas sensitive element;

[0017] Figure 2 A sensitive inner layer material prepared by SiO2 2 Surface grafted SnO 2 TEM and SEM images;

[0018] Figure 3 A sensitive inner layer material prepared by SiO2 2 Surface grafted SnO 2 IR spectrum analysis and XRD diffraction pattern;

[0019] Figure 4 A sensitive inner layer material prepared by SiO2 2 Surface grafted SnO 2 TGA-DTA curve diagram;

[0020] Figure 5 A sensitive inner layer material prepared by SiO2 2 Surface grafted SnO 2 Sensitivity to different gases and the relationship between sensitivity and gas concentration;

[0021] Figure 6 A sensitive inner layer material prepared by SiO2 2 Surface grafted SnO 2 Sensitivity to different concentrations of CO and response recovery characteristics of CO elements;

[0022] Figure 7 A sensitive inner layer material prepared by SiO2 2 Surface grafted SnO 2 Resistance change under periodic pulse voltage and long-term stability of the CO element. Detailed Implementation Modes

[0023] Various exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. It should be noted that: Unless otherwise specifically stated, the relative arrangements of components and steps, numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present disclosure.

[0024] Those skilled in the art can understand that terms such as "first", "second", etc. in the embodiments of the present disclosure are only used to distinguish different steps, devices, or modules, etc., and neither represent any specific technical meaning nor indicate an inevitable logical order between them. It should also be understood that in the embodiments of the present disclosure, "a plurality of" may refer to two or more, and "at least one" may refer to one, two, or more. It should also be understood that for any component, data, or structure mentioned in the embodiments of the present disclosure, without clear limitation or contrary indication in the context, it can generally be understood as one or more. In addition, the term "and / or" in the present disclosure is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in the present disclosure generally represents an "or" relationship between the associated objects before and after. It should also be understood that the present disclosure emphasizes the differences between various embodiments, and the same or similar parts can be referred to each other. For the sake of brevity, they will not be elaborated one by one.

[0025] At the same time, it should be understood that for the sake of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present disclosure and its application or use. Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and devices should be regarded as part of the specification. It should be noted that: Similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts fall within the scope of protection of the present application.

[0027] An embodiment of the present application discloses a gas sensor for carbon monoxide detection, including: an alumina ceramic tube, two annular gold electrodes, four platinum wire leads, a sensitive inner layer, an outer layer, a palladium-platinum heating wire, and a six-pin socket; the two annular gold electrodes are arranged in parallel at intervals on the alumina ceramic tube; each annular gold electrode is connected to two of the platinum wire leads; the palladium-platinum heating wire passes through the inside of the alumina ceramic tube; both ends of the palladium-platinum heating wire and the four platinum wire leads are welded to the six-pin socket together; the sensitive inner layer is coated on the outer surfaces of the alumina ceramic tube and the annular gold electrodes; the material of the sensitive inner layer is a nano-tin dioxide material with surface-grafted silica.

[0028] It should be understood that traditional carbon monoxide sensors mainly use semiconductor metal oxide SnO 2 as the basic gas-sensitive material, and its preparation process usually adopts simple redox reaction and heat treatment process, and there are obvious technical shortcomings in this process route. In terms of the action mechanism between the gas-sensitive material and CO gas, in the conventional SnO 2 material surface, only spontaneous adsorption of oxygen forms a negative charge layer. When CO molecules react with the surface-adsorbed oxygen, electrons are released, resulting in a change in the conductivity of the material. This single gas-sensing mechanism severely restricts the sensitivity and response speed of the sensor. In the embodiment of the present application, by introducing Pd atoms on the SnO 2 surface as electron donors, the electron capture ability of surface oxygen is significantly enhanced, the oxygen ion concentration is increased, the reaction amount with CO gas is increased, and fundamentally, the interaction process between electrons and surface oxygen anions is accelerated, realizing a qualitative improvement in gas-sensing performance.

[0029] In terms of the structural stability of the material, the SnO 2 nanomaterials prepared by the conventional process have inherent defects such as unstable grain boundary structure and easy agglomeration growth of grains. This is mainly because nanocrystals have a large specific surface area and surface energy, and grain growth is extremely likely to occur during service, resulting in deterioration of gas-sensing performance. In the embodiment of the present application, through the introduction of SiO 2 grafting modification process, the pinning effect is formed at the crystal grain interface by the highly discrete second phase, effectively reducing the crystal interface curvature, significantly increasing the activation energy barrier for crystal growth, and suppressing the abnormal growth of crystals from both the thermodynamic and kinetic levels. More importantly, in the embodiment of the present application, by controlling the grafting process of siloxane groups, it is ensured that the second phase is evenly distributed on the surface of the oxide, and it is firmly pinned at the grain boundary through strong chemical bonds, effectively preventing the migration and agglomeration of the second phase during service, thereby ensuring the long-term stability of the gas-sensitive material structure from the mechanism.

[0030] In one implementation scenario, the embodiment of the present application first prepares SnO 2, prepare SnO by using nitric acid oxidation method and Sol-Gel method 2 . Secondly, prepare the gas-sensitive material to obtain SnO grafted and modified on the surface with SiO 2 . 2 Finally, prepare the SiO 2 surface-grafted modified nano-SnO 2 -based CO sensor.

[0031] Specifically, the preparation method of the sensitive inner layer includes:

[0032] Add tin grains to concentrated nitric acid and stir, and grind and calcine the dried product and then grind it again to obtain nano-tin dioxide powder. It includes: adding tin grains to concentrated nitric acid in batches and performing magnetic stirring until no brownish-red gas is generated; centrifuging and washing the obtained precipitate until it is neutral; placing the washed precipitate in a vacuum drying oven for drying; grinding the dried product and placing it in a muffle furnace for calcination; grinding the calcined light yellow solid to obtain nano-tin dioxide powder.

[0033] In one embodiment, to prepare the sensitive inner layer material: SiO 2 surface-grafted modified SnO 2 , the typical tin grain-nitric acid oxidation method can be used to prepare nano-SnO 2 . First, measure 100 ml of concentrated nitric acid into a three-necked flask with a tail gas treatment device, add 25 g of tin grains in batches, and perform magnetic stirring for 3 h until no brownish-red gas is generated. Then, centrifuge and wash the obtained precipitate until it is neutral, dry it in a 95 °C vacuum drying oven for 24 h, grind it and place it in a muffle furnace for calcination at 450 °C for 2 h to obtain a light yellow solid, and grind it again to obtain nano-SnO 2 powder.

[0034] Among them, grinding the calcined light yellow solid to obtain nano-tin dioxide powder includes: placing the preliminarily ground powder in a zirconia ball milling tank, and the ball milling medium is zirconia balls; controlling the mass ratio of the ball milling medium to the powder and the filling degree of the ball milling tank, and performing intermittent ball milling in an inert atmosphere; performing air classification treatment on the ball-milled powder and performing classification by adjusting the main air speed and the rotation speed of the classification wheel; dispersing the classified powder in absolute ethanol and performing homogenization treatment with a shear disperser; performing vacuum drying on the homogenized slurry and sieving the dried powder to obtain nano-tin dioxide powder.

[0035] Preferably, for particle size classification and homogenization treatment, the preliminarily ground powder sample can be placed in a mechanical ball milling tank made of zirconia with a platinum-plated inner wall. The ball milling medium is zirconia balls with a diameter of 4.7 mm. The ball-to-powder mass ratio is controlled at 8:1, and the filling degree of the ball milling tank is 45%. Ball milling is carried out in an inert atmosphere at a rotation speed of 290 r / min. Each ball milling time is 45 minutes, with an intermittent time of 10 minutes, and the total number of cycles is 7 times. The ball-milled powder is classified by an air classification system. The main air velocity of the classification system is 28 m / s, and the rotation speed of the classification wheel is 4730 r / min. The powder with a particle size in the range of 87 - 326 nm is collected. The classified powder is dispersed in absolute ethanol at a dispersion concentration of 26 g / L, and homogenization treatment is carried out using a shear disperser. The shear rotation speed is 8460 r / min, and the treatment time is 30 minutes. During the treatment, 3 - 5 mL of absolute ethanol is supplemented every 7 minutes. The homogenized slurry is dried in vacuum, and the drying vacuum degree is 0.08 MPa. Finally, the dried powder is passed through an 80-mesh sieve to obtain nano-tin dioxide powder.

[0036] It should be noted that before preparing the nano-SnO 2 powder, the raw materials can be purified and pretreated. First, the tin grains are placed in a 400 mL hydrochloric acid solution with a concentration of 3.2 mol / L and soaked at 42 °C to remove the surface oxide layer. After taking out, it is immediately rinsed with deionized water 3 times, and the water consumption per time is at least 500 mL. The cleaned tin grains are put into an ethanol solution for ultrasonic cleaning. The ethanol concentration is 95%, the ultrasonic power is set at about 250 W, and the cleaning time is 25 - 35 minutes. The treated tin grains are dried in vacuum for 60 - 75 minutes. The concentrated nitric acid used in the experiment is pretreated. The concentrated nitric acid is left standing at 4 °C for 12 hours to allow the insoluble matter to settle, and then filtered through a PTFE filter membrane with a pore size of about 0.2 μm. The purified nitric acid needs to be stored in a brown reagent bottle at 4 °C. When preparing the reaction solution, 87 mL of purified concentrated nitric acid is added to a three-necked flask. After heating to 28 °C, the treated tin grains are added in batches, with each batch addition amount of 4.2 g and an interval time of 15 minutes. Dry air is continuously introduced during the reaction, with a flow rate of 0.4 - 0.5 L / min, and the reaction temperature is controlled within 30 °C.

[0037] Furthermore, after obtaining the nano-tin dioxide powder, the powder can be mixed with hydrogen peroxide, ammonia water, and deionized water, and an ultrasonic oscillation treatment is carried out to obtain a tin dioxide hydroxide intermediate. This includes: mixing the nano-tin dioxide powder with hydrogen peroxide, ammonia water, and deionized water; carrying out ultrasonic oscillation treatment on the mixture; separating and drying the ultrasonically treated mixture to obtain the tin dioxide hydroxide intermediate.

[0038] In one embodiment, 10 g of nano-SnO 2Powder, 10 ml of hydrogen peroxide, 10 ml of ammonia water and 10 ml of deionized water were ultrasonically oscillated at 70 °C for 30 min, separated and dried to obtain SnO 2 hydroxide intermediate.

[0039] Next, aminopropyltriethoxysilane and toluene were added to the intermediate and magnetically stirred to obtain a tin dioxide material with surface-grafted silica by calcination. This included: adding aminopropyltriethoxysilane and toluene to the tin dioxide hydroxide intermediate and magnetically stirring the mixture; centrifuging the stirred mixture; drying the centrifuged product; and calcining the dried product in a muffle furnace to obtain a tin dioxide material with surface-grafted silica.

[0040] Specifically, the prepared intermediate was transferred to a 100 ml beaker, 0.92 g of 3-aminopropyltriethoxysilane (KH-550) and 40 ml of toluene were added, and magnetically stirred for 3 h. The reaction product was centrifuged and dried, and calcined at 600 °C for 2 h to obtain SnO with SiO 2 grafted on the surface. 2 The sensitive inner layer material is SiO 2 surface-grafted and modified SnO 2 In the sensitive inner layer material, the grafting rate of SiO 2 is 1-3 wt%; the thickness of the sensitive inner layer is 0.05-0.2 mm.

[0041] Among them, adding aminopropyltriethoxysilane and toluene to the tin dioxide hydroxide intermediate and magnetically stirring the mixture includes: dispersing the tin dioxide hydroxide intermediate in a mixed solvent of toluene and n-hexane; dissolving the aminopropyltriethoxysilane coupling agent in absolute ethanol and slowly dropping it into the dispersion at the target temperature; continuously introducing dry nitrogen during the dropping process, and after completion, raising the temperature and stirring.

[0042] Preferably, during the modification with the silane coupling agent, the pretreated SnO 2 can be dispersed in a mixed solvent, and the mixed solvent is prepared from toluene and n-hexane according to a volume ratio of 4.25:1, with a total volume of 187 mL. A solution of 3-aminopropyltriethoxysilane (KH-550) was slowly added dropwise to the dispersion, and the dosage of KH-550 was 8.73% of the mass of SnO 2 . KH-550 was first dissolved in 22 mL of absolute ethanol, and the dropping rate was controlled at 0.4 mL / min. Dry nitrogen was continuously introduced during the dropping process, and the temperature was maintained at 58 °C. After the dropping was completed, the temperature was raised to 73 °C, and the stirring rate was 360 r / min. At

[0043] After the reaction is completed, the mixture is cooled to 40 °C, and 187 mL of n-hexane is added for extraction. After standing for phase separation, the organic phase is separated. The organic phase is washed successively with absolute ethanol and deionized water at washing temperatures of 37 °C and 28 °C, respectively. Finally, the product is dried in vacuo, and the obtained powder is ground in a mortar to a fine state.

[0044] In one embodiment, aminopropyltriethoxysilane and toluene are added to the tin dioxide hydroxide intermediate, and the mixture is magnetically stirred. It further includes: establishing a transfer equation for the flux of silane groups, diffusion coefficient, local concentration, and sound field-induced flow velocity; adjusting the sound field amplitude parameter according to the target flux value; dropping the aminopropyltriethoxysilane coupling agent solution at the target temperature while applying an ultrasonic field.

[0045] Preferably, when performing sound field-driven grafting, first establish the mass transfer equation in the sound field: where J is the flux of silane groups, D is the diffusion coefficient (3.8×10 -9 m 2 / s), c is the local concentration, and v(t) is the sound field-induced flow velocity: v(t) = A·ω·cos(ωt)·exp(-αx), where A is the sound wave amplitude, ω is the angular frequency, and α is the attenuation coefficient (0.046 dB / cm). Control the sound field parameters according to this equation: when J is less than the target value 0.85J * (the target flux J * is 2.4×10 -6 mol / (m 2 ·s)), increase the amplitude A by 15%; when J is in the range of 0.85J * to 1.8J * , keep the amplitude unchanged; when J exceeds 1.8J*, reduce the amplitude A by 10 - 12%.

[0046] In one example, the KH-550 solution is dropped at a rate of 0.45 mL / min at 28 ± 0.5 °C while applying an ultrasonic field with a frequency of 42 - 44 kHz and an initial amplitude of 12 μm, and the sound power density is 1.2 W / cm 2 . During the dropping process, the value of the silane group flux J is collected every 90 seconds, and the amplitude is dynamically adjusted according to the ratio of the collected J value to the target flux J * . By controlling the local concentration gradient within the range of 0.015 - 0.025 mol / L·mm, precise control of the grafting process is achieved. After the dropping is completed, continue to maintain the same parameter adjustment rule for ultrasonic treatment for 15 minutes. The experimental results show that using this parameter system can control the standard deviation of the grafting degree within ±4%, effectively improving the uniformity of grafting.

[0047] It should be noted that SiO2 The SnO after graft modification 2 material, in the organic phase, uses the hydroxyl groups on the SnO 2 surface as the anchoring sites, and the siloxane groups on the siloxane react chemically with the hydroxyl groups to uniformly assemble highly dispersed Si functional groups on the oxide surface. On the one hand, this can introduce a fine and dispersed second phase, and it is even possible to introduce a second phase as small as the molecular level. On the other hand, it eliminates the hydroxyl groups on the oxide surface, and at the same time uses the strong chemical bond between silicon and the oxide to fix the second phase, making the second phase more firmly pinned between the oxide grain boundaries and preventing the second phase from moving. The combined action of these three aspects improves the stability of the nanometer gas-sensitive material. On the SnO 2 surface, grafting the active groups of silicon as the second phase, and the unreacted siloxane groups grafted are also the initiation points for the next polymerization reaction, enabling the in-situ formation of a uniformly distributed coating layer in these initiation points during the hydrolysis polymerization reaction of the organosiloxane in the second step. Then, by using the differences in the number and size of the alkyl groups connected to the silicon atoms in the organosiloxane, the alkyl groups are decomposed during the post-treatment calcination process, and the film layer structure is controlled by controlling the size and amount of the organic alkyl groups, making the film layer a reticular partial coating structure to ensure the gas-sensing performance of the coated nanometer semiconductor.

[0048] Figure 1 This is a schematic diagram of the structure and a physical diagram of a CO sensor with a gas-sensitive element formed by grafting and modifying SiO 2 on the surface of nanometer SnO 2 as the gas-sensitive element.

[0049] As can be seen from the (a) sensor schematic diagram, this sensor adopts a semiconductor metal oxide side-heating design, and the main structure is composed of Al 2 O 3 ceramic tube, two circular gold electrodes, four platinum wire leads, a sensitive inner layer, an outer layer, a palladium-platinum heating wire, and a six-pin socket, a total of seven parts. Among them, the Al 2 O 3 ceramic tube has a tubular structure, and the two circular gold electrodes are arranged in parallel at intervals on the surface of the Al 2 O 3 ceramic tube. Each gold electrode is connected to two platinum wire leads. The sensitive inner layer material is coated on the outer surfaces of the Al 2 O 3 ceramic tube and the gold electrodes. The palladium-platinum heating wire passes through the hollow area inside the Al 2 O 3 ceramic tube. At the bottom of the device, the two ends of the palladium-platinum heating wire and the four platinum wire leads of the Al 2 O 3 ceramic tube are jointly welded to the six-pin socket to form a complete circuit connection.

[0050] (b) The physical picture of the sensor shows the actual prepared finished product of the CO sensor. It can be observed that the overall device has a cylindrical structure, with a six-pin socket at the bottom and a white Al 2 O 3 ceramic tube body. The metallic luster of the gold electrodes and the evenly coated grayish-white sensitive layer can be seen on the surface of the ceramic tube.

[0051] Figure 2 This is a TEM image and an SEM image of a prepared sensitive inner layer material of SiO 2 surface-grafted modified SnO 2 .

[0052] TEM images (a) and (b) show the morphological characteristics of the material at the nanoscale. It can be observed that the size distribution of the SnO 2 nanoparticles is in the range of 20 - 50 nm, and the particle shape is relatively regular, presenting an approximately spherical structure. A uniformly thick coating layer can be seen on the surface of the nanoparticles, which is a surface modification layer formed by SiO 2 grafting modification. There is an obvious interfacial structure between the particles, indicating that the coating of SiO 2 effectively prevents the aggregation of nanoparticles.

[0053] SEM images (c) and (d) show the microscopic morphology and surface characteristics of the material, revealing the three-dimensional packing structure of the nano-SnO 2 particles. As can be seen from the figure, the particles have good dispersion and no obvious aggregation phenomenon. The surface of the material presents a typical porous structure with uniform pore distribution, which is beneficial to the diffusion and adsorption of gas molecules. The surface of the particles is relatively smooth, which is related to the uniform coating of SiO 2 . Overall, the morphological characteristics of the material show good dispersion and uniformity, which have an important impact on the performance of the gas-sensitive material.

[0054] Figure 3 This is an infrared spectrum analysis and an XRD diffraction pattern of a prepared sensitive inner layer material of SiO 2 surface-grafted modified SnO 2 .

[0055] The infrared spectrum shows multiple characteristic absorption peaks. Among them, the broad peak near 3400 cm-1 corresponds to the stretching vibration of surface hydroxyl groups (-OH), and the absorption peak at 1630 cm-1 belongs to the bending vibration of adsorbed water molecules. In the low wavenumber region, strong absorption peaks in the range of 600 - 700 cm-1 can be observed, which are the characteristic vibration peaks of the Sn-O bond. At the same time, the absorption peak near 1080 cm-1 belongs to the asymmetric stretching vibration of the Si-O-Si bond, confirming the presence of SiO 2 on SnO2 Successful surface grafting.

[0056] The XRD pattern shows the crystal phase structure information of the material. The main diffraction peaks can all be attributed to the characteristic diffraction peaks of tetragonal rutile SnO 2 , and the corresponding crystal plane indices are (110), (101), (200), (211), (220), (002), and (310). The peak shapes of the diffraction peaks are sharp, indicating that the material has good crystallinity. The grain size can be estimated to be in the nanometer range from the full width at half maximum of the diffraction peaks. It is worth noting that no obvious SiO 2 diffraction peaks are observed in the XRD pattern, which indicates that SiO 2 exists in an amorphous form on the surface of SnO 2 . By analyzing the integrated intensity of the main diffraction peaks, the relative crystallinity information of the material can be obtained.

[0057] Figure 4 This is a TGA-DTA curve of SnO 2 surface-grafted and modified with SiO 2 for the sensitive inner layer material prepared in the embodiment of the present application.

[0058] The TGA curve shows the mass change of the material during the heating process. A mass loss of about 2% is observed in the temperature range from room temperature to 200 °C, which is mainly attributed to the removal of physically adsorbed water. In the temperature range of 200 - 400 °C, the curve shows a slow mass loss plateau, and the mass loss is about 3%, which may be due to the removal of surface chemically adsorbed water and the decomposition of some organic groups. Above 400 °C, the mass remains basically stable, and the curve tends to be flat.

[0059] The DTA curve reflects the thermal effect change of the material during heating. An endothermic peak appears near 100 °C, corresponding to the removal process of physically adsorbed water. The weak endothermic peak near 300 °C can be attributed to the decomposition of surface organic groups. It is worth noting that no obvious thermal effect peaks are observed in the temperature range of 400 - 600 °C, indicating that the material has good thermal stability in this temperature range. Overall, the TGA-DTA analysis results show that the material has stable thermodynamic properties above 400 °C, which has important guiding significance for the selection of working temperature in practical applications.

[0060] Figure 5 This is a graph showing the sensitivity of a SiO 2 surface-grafted and modified SnO 2 for different gases and the relationship between sensitivity and gas concentration in the embodiment of the present application.

[0061] The left figure shows the sensitivity of the material to CO, H 2, CH 4 Response curves for different gases such as etc. The horizontal axis represents the gas type, and the vertical axis represents the sensitivity value. From the curves, it can be seen that the material shows the highest response value to CO gas, followed by H 2 , while the response to CH 4 is relatively low. The right figure shows the sensitivity curve of the material to CO gas at different concentrations. The horizontal axis represents the CO concentration (ppm), and the vertical axis represents the sensitivity value. As the CO concentration increases, the sensitivity value shows a non-linear growth trend. In the low-concentration region (0 - 100 ppm), the sensitivity increases rapidly with the concentration, while in the high-concentration region, the growth rate gradually decreases and finally tends to saturation.

[0062] Through the analysis of these two figures, it can be seen that the material shows excellent selectivity at a working temperature of 300 °C, and the response to CO gas is significantly higher than that of other interfering gases. The relationship curve between sensitivity and concentration follows the characteristics of the typical Langmuir adsorption isotherm, indicating that the adsorption process of gas molecules on the material surface conforms to the monolayer adsorption mechanism. In the concentration range of 100 - 500 ppm, there is a good correspondence between sensitivity and concentration, which discloses the basis for quantitative concentration detection in practical applications.

[0063] Figure 6 A sensitive inner layer material prepared in the embodiment of this application is a SnO grafted and modified on the surface of SiO 2 for the sensitivity to different concentrations of CO and the response and recovery characteristics of the CO element. 2

[0064] The left figure shows the response-recovery curves of the material to CO gas at different concentrations such as 50, 100, 200 ppm, etc. The horizontal axis represents time (s), and the vertical axis represents the resistance value (kΩ). When CO gas is introduced, the resistance value of the material rapidly decreases and remains constant after reaching the stable value; when the introduction of CO gas stops, the resistance value gradually returns to the initial state. The right figure gives the detailed kinetic curve of a single response-recovery process, and the change process of the response time and recovery time can be clearly observed.

[0065] From the shape characteristics of the response-recovery curve, it can be seen that the response process of the material to CO gas is relatively fast, usually reaching 90% of the response value within 20 seconds, while the recovery process is relatively slow and takes about 60 seconds to fully recover. This asymmetric kinetic characteristic is related to the adsorption-desorption mechanism of gas molecules on the material surface. Under the same test conditions, a higher concentration of CO gas will cause a greater change in resistance, but the change in response time and recovery time is not obvious, indicating that the kinetic characteristics of the material are mainly controlled by the surface reaction process.

[0066] Figure 7 A sensitive inner layer material prepared in the embodiment of this application is a SnO grafted and modified on the surface of SiO​2 Surface-grafted modified SnO 2 Resistance change graph under periodic pulse voltage and long-term stability graph of the CO element.

[0067] The left figure shows the resistance change curve of the material under the action of periodic pulse voltage. The abscissa is time (s), and the ordinate is the resistance value (kΩ). It can be observed that under the pulse voltage of constant amplitude, the resistance value of the material shows regular periodic changes, and the amplitude of resistance change within each period is basically the same, indicating that the material has good electrical response reversibility.

[0068] The right figure gives the stability test results of the material under long-term working conditions. The abscissa is time (days), and the ordinate is the sensitivity value. During the continuous 30-day test period, the response value of the material to CO gas of a specific concentration fluctuates little, and the relative standard deviation is controlled within 5%. From the curve trend, it can be seen that the sensitivity of the material does not show an obvious attenuation phenomenon, and the response value basically remains at a stable level. This stable long-term working performance is closely related to the structural stability brought by the surface modification of SiO 2 Surface modification is closely related.

[0069] In summary, existing CO gas sensors generally have technical problems such as poor stability of gas-sensitive materials and insufficient sensitivity. This is mainly due to the key technical bottlenecks in the preparation process of traditional SnO 2 Based gas-sensitive materials, such as difficulty in controlling grain growth and unstable interface structure. In the embodiments of this application, by implementing SiO 2 Surface grafting modification on the surface of nano-SnO 2 The above technical problems are solved. Specifically, this solution uses the hydroxyl groups on the surface of SnO 2 in the organic phase as the anchor points, enabling the siloxane groups to undergo chemical reactions with them, and achieving the uniform assembly of highly dispersed Si functional groups on the oxide surface. This grafting modification method can not only introduce fine dispersed phases at the molecular level, but more importantly, by eliminating the hydroxyl groups on the oxide surface and using the strong chemical bond between silicon and the oxide to firmly pin the second phase between the oxide grain boundaries, effectively preventing the migration of the second phase, and synergistically improving the stability of the nano-gas-sensitive material from multiple dimensions.

[0070] Furthermore, in the preparation process of the embodiments of the present application, strict purification pretreatment of raw materials, particle size grading and homogenization treatment, and grafting process assisted by sound field driving are carried out. In the link of raw material purification pretreatment, the oxide layer on the surface of tin particles is removed by designing a soaking process with a hydrochloric acid solution at 42 °C and 3.2 mol / L, combined with 250 W ultrasonic cleaning and vacuum drying, ensuring the high purity of the raw materials; in terms of particle size control, zirconia ball milling media are used, and by optimizing the ball-powder ratio of 8:1, a filling degree of 45%, and ball milling parameters of 290 r / min, combined with an air classification system with a main air velocity of 28 m / s and a classifier wheel speed of 4730 r / min, particle size control in the range of 87 - 326 nm is achieved; in terms of the grafting process, a sound field driving mechanism is introduced, and by establishing a mass transfer equation in the sound field and adjusting the sound field parameters in real time, the grafting uniformity is significantly improved.

[0071] In terms of the material structure design, the embodiments of the present application achieve a controllable network partial coating structure. Specifically, the unreacted siloxanyl groups grafted on the surface of SnO 2 serve as the polymerization reaction initiation points for in-situ hydrolysis polymerization of organosiloxane to form a uniformly distributed coating layer. By regulating the number and size of alkyl groups connecting silicon atoms in the organosiloxane, controllable decomposition of the alkyl groups is achieved during the subsequent calcination process, and finally a network partial coating structure that can maintain both the semiconductor gas sensing performance and structural stability is formed. This precisely controllable structure design solves the technical contradiction that traditional gas sensing materials often lose gas sensing performance while improving stability.

[0072] Furthermore, the embodiments of the present application also disclose a computer program product, which, when running on a terminal device, enables the terminal device to execute any one of the above methods.

[0073] From the description of the above embodiments, those skilled in the art can clearly understand that all or part of the steps in the above embodiment methods can be implemented by means of software plus a necessary general hardware platform. Based on such an understanding, the technical solution of the present application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a storage medium, such as ROM / RAM, magnetic disk, optical disc, etc., and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network communication device such as a media gateway, etc.) to execute the methods described in each embodiment or some parts of the embodiments of the present application.

[0074] It should be noted that the various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple. For the relevant parts, reference can be made to the description in the method part.

[0075] It should also be noted that in this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the existence of additional identical elements in the process, method, article or device comprising the said element.

[0076] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A gas sensor for carbon monoxide detection, characterized in that: include: An alumina ceramic tube, two annular gold electrodes, four platinum wire leads, a sensitive inner layer, an outer layer, a palladium-platinum heating wire and a six-pin tube holder; the two annular gold electrodes are arranged in parallel and spaced apart on the alumina ceramic tube; each annular gold electrode is connected to two platinum wire leads; the palladium-platinum heating wire passes through the interior of the alumina ceramic tube; both ends of the palladium-platinum heating wire and the four platinum wire leads are welded together on the six-pin tube holder; the sensitive inner layer is coated on the outer surfaces of the alumina ceramic tube and the annular gold electrodes; the material of the sensitive inner layer is a nano-tin dioxide material with silicon dioxide grafted on the surface.

2. The gas sensor according to claim 1, characterized in that: The preparation method of the sensitive inner layer comprises: Add tin particles to concentrated nitric acid and stir, grind and calcine the dried product and then grind it again to obtain nano tin dioxide powder; The powder is mixed with hydrogen peroxide, ammonia water and deionized water, and subjected to ultrasonic vibration treatment to obtain a tin dioxide hydroxylate intermediate; Aminopropyltriethoxysilane and toluene are added to the intermediate, followed by magnetic stirring, so as to obtain a tin dioxide material with silica grafted on the surface thereof through calcination.

3. The gas sensor according to claim 2, characterized in that: in, Add tin particles to concentrated nitric acid and stir, grind and calcine the dried product, and then grind it again to obtain nano tin dioxide powder, including: Add tin particles to concentrated nitric acid in batches and stir magnetically until no brown-red gas is generated; The obtained precipitate is washed by centrifugation until it becomes neutral; The washed precipitate is placed in a vacuum drying oven for drying; The dried product is ground and then placed in a muffle furnace for calcination; The calcined light yellow solid is ground to obtain nano tin dioxide powder.

4. The gas sensor according to claim 2, characterized in that: in, The powder is mixed with hydrogen peroxide, ammonia water and deionized water, and subjected to ultrasonic vibration treatment to obtain a tin dioxide hydroxylate intermediate, including: Mixing nano-tin dioxide powder with hydrogen peroxide, ammonia water and deionized water; subjecting the mixture to ultrasonic vibration; The sonicated mixture is separated and dried to obtain a tin dioxide hydroxide intermediate.

5. The gas sensor according to claim 2, characterized in that: in, Adding aminopropyltriethoxysilane and toluene to the intermediate and then stirring with magnetic force to obtain a tin dioxide material with surface grafted silicon dioxide by calcination, comprising: Adding aminopropyltriethoxysilane and toluene to the tin dioxide hydroxylate intermediate, and magnetically stirring the mixture; centrifuging the stirred mixture; Drying the centrifuged product; The dried product is placed in a muffle furnace for calcination to obtain a tin dioxide material with silicon dioxide grafted on the surface.

6. The gas sensor according to claim 3, characterized in that: in, The calcined light yellow solid is ground to obtain nano tin dioxide powder, including: The preliminarily ground powder is placed in a zirconia ball mill, wherein the ball milling medium is zirconia balls; The mass ratio of the ball milling medium to the powder and the filling degree of the ball milling jar are controlled, and intermittent ball milling is performed under an inert atmosphere; The ball-milled powder is subjected to airflow classification and classification is performed by adjusting the main air speed and the speed of the classifying wheel; The classified powder is dispersed in anhydrous ethanol and homogenized using a shear disperser; The homogenized slurry is vacuum dried, and the dried powder is sieved to obtain nano-tin dioxide powder.

7. The gas sensor according to claim 5, characterized in that: in, Adding aminopropyltriethoxysilane and toluene to the tin dioxide hydroxide intermediate and magnetically stirring the mixture comprises: dispersing the tin dioxide hydroxide intermediate in a mixed solvent of toluene and n-hexane; Dissolve aminopropyltriethoxysilane coupling agent in anhydrous ethanol and slowly add it dropwise into the dispersion at the target temperature; Dry nitrogen was continuously introduced during the dropwise addition, and the temperature was raised and the mixture was stirred after completion.

8. The gas sensor according to claim 5, characterized in that: in, Adding aminopropyltriethoxysilane and toluene to the tin dioxide hydroxylate intermediate and subjecting the mixture to magnetic stirring, further comprising: The transfer equations of silane group flux and diffusion coefficient, local concentration and acoustic field induced flow velocity were established; adjusting the acoustic field amplitude parameter according to the target flux value; The aminopropyltriethoxysilane coupling agent solution was added dropwise at the target temperature while applying an ultrasonic field.

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