Preparation method of nano tin oxide, nano tin oxide, tin oxide printing ink, gas sensor and preparation method of gas sensor

Abstract

The invention relates to the technical field of gas sensing, and discloses a preparation method of nano tin oxide, nano tin oxide, tin oxide ink, a gas sensor and a preparation method of the gas sensor. The preparation method of the nano tin oxide comprises the following steps: mixing tin chloride dehydrate and ethanolamine to obtain a precursor mixed solution; treating the precursor mixed solution to obtain a complex solution; adding propionic acid into the complex solution to obtain tin oxide precipitate; and carrying out sintering treatment on the tin oxide precipitate to obtain the nano tin oxide. Ethanolamine and propionic acid are added in the process of preparing the nano tin oxide by using a sol-gel method, so that the health and safety risks are avoided, the pH value stability is favorably controlled, the uniformity and consistency of the nano tin oxide are ensured, and the gas sensing performance can be improved when the nano tin oxide is applied to a gas sensor. According to the invention, a sol-gel method and an ink-jet printing technology are combined, so that the preparation process of the gas sensor is simplified.

Description

Technical Field

[0001] The present invention relates to the field of gas sensing technology, and in particular to a method for preparing nano tin oxide, nano tin oxide, tin oxide ink, a gas sensor and a method for preparing the same. Background Art

[0002] Gas sensors are crucial in monitoring environmental conditions, industrial processes, and ensuring environmental safety. Tin oxide is a gas-sensitive material that is sensitive and selective to various gases and can be used in gas sensors, especially nano-tin oxide.

[0003] In the prior art, tin oxide nanoparticles can be synthesized by using a template method, and the synthesis process includes: mixing and stirring a triblock copolymer Pluronic F127 as a soft template, ethanol as a solvent, and xylene as a micelle expansion agent; adding tin tetrachloride as a precursor to the stirred solution and continuing to stir; and finally adding deionized water to the solution and stirring and homogenizing it continuously. However, when the nano-tin oxide synthesized by the above template method is used in a gas sensor, there are the following defects: on the one hand, the pH value cannot be kept stable during the template method synthesis of nano-tin oxide (for example, the chemical reaction byproducts of the template method will change the pH value, and the use of ethanol as a solvent will absorb CO2 in the air to cause the pH value to fluctuate), which will lead to uneven size and shape of the nano-tin oxide particles, thereby affecting the gas sensing performance (such as sensitivity) of the gas sensor prepared using the nano-tin oxide; on the other hand, the ethanol and xylene used in the template method synthesis process are harmful chemicals, and inhalation or skin contact with these chemicals will bring health and safety risks. Summary of the invention

[0004] In view of the technical problems in the prior art such as unstable performance of nano-tin oxide synthesized by template method when used in gas sensors, the present invention provides a method for preparing nano-tin oxide, nano-tin oxide, tin oxide ink, a gas sensor and a method for preparing the same.

[0005] In a first aspect, the present invention provides a method for preparing nano tin oxide, comprising: mixing tin chloride dihydrate and ethanolamine to obtain a precursor mixed solution; treating the precursor mixed solution to obtain a complex solution; adding propionic acid to the complex solution to obtain tin oxide precipitate; The tin oxide precipitate is sintered to obtain nano tin oxide.

[0006] In a second aspect, the present invention provides a nano-tin oxide, which is prepared according to the preparation method of the first aspect.

[0007] In a third aspect, the present invention provides a tin oxide ink, wherein the tin oxide ink comprises nano tin oxide obtained according to the preparation method of the first aspect.

[0008] In a fourth aspect, the present invention provides a gas sensor, comprising a microsensor chip, wherein the microsensor chip comprises a tin oxide coating formed by printing the tin oxide ink of the third aspect.

[0009] In a fifth aspect, the present invention provides a method for preparing a gas sensor, comprising: Mixing an organic solvent with the nano-tin oxide obtained by the preparation method according to the first aspect to obtain a tin oxide ink; the viscosity of the tin oxide ink is 10-12 cP, and the surface tension is 25-40 mN / m; Printing the tin oxide ink layer by layer onto the surface of the microsensor substrate in an inkjet printing manner to form at least two layers of tin oxide coating; Annealing the microsensor substrate carrying at least two layers of the tin oxide coating to obtain a microsensor chip; The microsensor chip is packaged to obtain a gas sensor.

[0010] The present invention provides a method for preparing nano tin oxide. The method for preparing nano tin oxide adopts a sol-gel method based on tin chloride dihydrate, and uses ethanolamine as a solvent, thereby improving the safety of the solvent and reducing health and safety risks. At the same time, the addition of ethanolamine and propionic acid helps to control the pH stability of the solution. The present invention also provides nano tin oxide obtained by the method for preparing nano tin oxide, as well as tin oxide ink and gas sensor prepared based on the nano tin oxide. Since a stable pH value condition can be maintained during the preparation of nano tin oxide, the uniformity and consistency of the particle size, morphology and surface chemical properties of nano tin oxide are guaranteed, thereby improving the gas sensing performance of the gas sensor, and having higher sensitivity, selectivity and room temperature stability. The present invention also provides a method for preparing a gas sensor, which combines the sol-gel method with inkjet printing technology, realizes the efficient application of nano tin oxide, simplifies the preparation process of the gas sensor, and can significantly improve the gas sensing performance of the gas sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0012] Figure 1is an X-ray diffraction diagram of a product prepared by a method for preparing nano-tin oxide in one embodiment of the present invention; Figure 2 This is the response result of the gas sensor based on nano-tin oxide at different sintering temperatures to ammonia in one embodiment of the present invention. DETAILED DESCRIPTION

[0013] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0014] In a first aspect, an embodiment of the present invention provides a method for preparing nano tin oxide, comprising: mixing tin chloride dihydrate and ethanolamine to obtain a precursor mixed solution; treating the precursor mixed solution to obtain a complex solution; adding propionic acid to the complex solution to obtain tin oxide precipitate; The tin oxide precipitate is sintered to obtain nano tin oxide.

[0015] Furthermore, the present embodiment adopts a sol-gel method to prepare nano-tin oxide, including preparing a precursor mixed solution, preparing a complex solution, precipitating tin oxide, and forming nano-tin oxide at high temperature. Among them, preparing a precursor mixed solution is a process of dissolving a tin precursor in a solvent. In the present embodiment, dihydrated tin chloride is used as a tin precursor, ethanolamine is used as a solvent, and after ultrasonic treatment, dihydrated tin chloride is dissolved in ethanolamine to obtain a precursor mixed solution. Preparing a complex solution is a process of forming a tin complex from dihydrated tin chloride dissolved in ethanolamine, and stirring and standing are helpful to form a stable tin complex. Precipitating tin oxide precipitates is a process of causing a dissociation reaction of the tin complex under the action of propionic acid to precipitate tin oxide. Forming nano-tin oxide at high temperature is a process of forming a dense nano-tin oxide material by causing a solid-phase reaction between particles of the tin oxide precipitate through high-temperature sintering. In addition, further grinding after sintering can obtain powdered nano-tin oxide, so that the powdered nano-tin oxide can be subsequently inkjet printed to prepare a gas sensor.

[0016] Tin chloride dihydrate is an inorganic salt that has good solubility in water, but low solubility in organic solvents. Ethanolamine, as an organic solvent, is less toxic and easier to handle than ethanol, avoiding health and safety risks. Ultrasonic treatment is an effective physical method to promote the dissolution and dispersion of substances. Ultrasonic treatment generates strong local vibrations and microjets through high-frequency sound waves, which promote the penetration and diffusion of solvent molecules into solute particles, allowing tin chloride dihydrate and ethanolamine to mix more fully to form a precursor mixed solution.

[0017] For the tin chloride dihydrate and ethanolamine in the precursor mixed solution, since the amine group of ethanolamine has a lone pair of electrons, and the tin ion in the tin chloride dihydrate has an empty orbital, a complex reaction can occur between them, that is, the lone pair of electrons of ethanolamine enters the empty orbital of the tin ion to form a stable tin complex. The central ion of the tin complex is Sn 2+ , the ligand is C2H7NO, and the main chemical reaction is: 2SnCl2•2H2O + 4C2H7NO → 2[Sn(C2H7NO)2]Cl2+ 4H2O. The tin complex is more stable than the uncomplexed tin ion and has a greater solubility in aqueous solution. Stirring the precursor mixed solution obtained after ultrasonic treatment can make the components in the solution more evenly distributed and avoid the occurrence of local concentrations that are too high or too low. At the same time, stirring can also help further promote the complexation reaction and make the reaction more complete. Finally, the stirred solution is allowed to stand for a static treatment. During the static process, the complex will gradually stabilize to form a uniform and transparent solution. When propionic acid is added to the complex solution for stirring, the tin complex in the complex solution will undergo a dissociation reaction and tin oxide will precipitate. The main chemical reaction is: [Sn(C2H7NO)2]Cl2+ C2H5COOH → SnO2↓ + by-products. On the one hand, propionic acid acts as a promoter in the dissociation reaction, accelerating the occurrence of the dissociation reaction. On the other hand, propionic acid acts as a stabilizer in the dissociation reaction to maintain the stability of the pH value. By stirring, it can be ensured that propionic acid is in full contact with the tin complex, thereby improving the dissociation efficiency of the tin complex and the precipitation rate of tin oxide. At the same time, the chemical toxicity of propionic acid is lower than that of xylene, which significantly reduces the environmental impact and improves the safety of the preparation process.

[0018] When the obtained tin oxide precipitate is sintered, the high temperature causes a solid phase reaction between the tin oxide particles, the particle size of the tin oxide particles will be further reduced, and the bonding force between the particles will be strengthened, forming a dense nano-tin oxide material. Figure 1 The X-ray diffraction pattern of the product prepared by the nano-tin oxide preparation method shown in the figure shows that the grains after high-temperature sintering mainly grow along crystal planes such as (110), (101) and (211). The X-ray diffraction peaks in the figure are consistent with the PDF standard card of SnO2 phase (JPCD#41-1445), indicating that the prepared product is tin oxide grains.

[0019] The present invention provides a method for preparing nano tin oxide. The method for preparing nano tin oxide adopts a sol-gel method based on tin chloride dihydrate, and uses ethanolamine as a solvent, thereby improving the safety of the solvent and reducing health and safety risks. At the same time, the addition of ethanolamine and propionic acid helps to control the pH stability of the solution. The present invention also provides nano tin oxide obtained by the method for preparing nano tin oxide, as well as tin oxide ink and gas sensor prepared based on the nano tin oxide. Since a stable pH condition can be maintained during the preparation of nano tin oxide, the uniformity and consistency of the particle size, morphology and surface chemical properties of nano tin oxide are guaranteed, thereby improving the gas sensing performance of the gas sensor, and having higher sensitivity, selectivity and room temperature stability. The present invention also provides a method for preparing a gas sensor, which combines the sol-gel method with inkjet printing technology, realizes the efficient application of nano tin oxide, simplifies the preparation process of the gas sensor, and can significantly improve the gas sensing performance and integration of the gas sensor.

[0020] In the process of preparing nano-tin oxide, each step and parameter condition will affect the properties of nano-tin oxide (such as particle size, morphology and surface chemical properties, etc.), further affecting the application characteristics of nano-tin oxide in gas sensors and the gas sensing performance of gas sensors (such as sensitivity, selectivity and response time).

[0021] Optionally, the mixing of tin chloride dihydrate and ethanolamine to obtain a precursor mixed solution comprises: 0.8-1.0 g of tin chloride dihydrate is added to 9-12 mL of ethanolamine, and ultrasonic treatment is performed at 20-30° C. for 20-40 minutes to dissolve the tin chloride dihydrate in the ethanolamine to obtain a precursor mixed solution.

[0022] Furthermore, in the process of dissolving tin chloride dihydrate in ethanolamine, it is necessary to control the dosage ratio between ethanolamine and tin chloride dihydrate to ensure the sufficiency of the dissolution reaction. If the dosage of tin chloride dihydrate is too much, it may not be completely dissolved; if the dosage of tin chloride dihydrate is too little, it may not be possible to precipitate tin oxide later.

[0023] The parameter conditions for preparing the precursor mixed solution will affect the characteristics of nano tin oxide. The different usage ratios between ethanolamine and tin chloride dihydrate will change the concentration of tin chloride dihydrate in the precursor mixed solution, affect the balance between the nucleation and growth stages of tin oxide grains, and thus control the particle size of tin oxide. The higher the concentration of tin chloride dihydrate, the easier it is to promote nucleation, thereby forming smaller tin oxide particles. The lower the concentration of tin chloride dihydrate, the slower the nucleation rate, and the larger the tin oxide particles. At the same time, since ethanolamine can act as a complexing agent to form a tin complex with tin chloride dihydrate, therefore, adjusting the usage ratio between ethanolamine and tin chloride dihydrate can fine-tune the complex reaction rate, thereby affecting the subsequent particle size of tin oxide precipitated. In the present embodiment, 0.8~1.0 g of tin chloride dihydrate is added to 9~12 mL of ethanolamine. In addition, the purpose of ultrasonic treatment is to ensure that tin chloride dihydrate is fully mixed and dissolved with ethanolamine, and the temperature and duration of ultrasonic treatment can indirectly affect the formation of tin complexes and the precipitation of tin oxide. In this embodiment, the ultrasonic treatment temperature is room temperature of 20-30° C., and the duration is 20-40 minutes. The shorter the duration, the larger the tin oxide particles precipitated subsequently, and the longer the duration, the smaller the tin oxide particles precipitated subsequently.

[0024] In the process of preparing the precursor mixed solution in this embodiment, the dosage ratio between ethanolamine and tin chloride dihydrate, as well as the temperature and duration of ultrasonic treatment are limited, which can ensure that the dissolution reaction is fully carried out and help improve the crystallization performance of the finally prepared nano tin oxide.

[0025] Optionally, the precursor mixed solution is treated to obtain a complex solution, comprising: The precursor mixed solution is stirred under sealed conditions, and allowed to stand for 2 to 4 weeks after stirring to obtain a complex solution; wherein the stirring speed of the stirring treatment is 500 to 600 rpm, the stirring temperature is 65 to 75° C., and the stirring time is 2 to 2.5 hours.

[0026] Further, the parameter conditions for preparing the complex solution will affect the characteristics of nano-tin oxide. The stirring process can make the ethanolamine and dihydrate tin chloride in the precursor mixed solution more evenly distributed, and promote the complex reaction during the stirring process. The parameters of the stirring process include stirring speed, stirring temperature and stirring time. The stirring speed and stirring time will affect the uniformity of the solution mixing, and the stirring temperature will affect the completeness of the complex reaction, thereby affecting the precipitation of tin oxide. The temperature increase will accelerate the complex reaction, which is conducive to the growth of subsequent tin oxide particles. The temperature reduces the complex reaction, which is not conducive to the growth of subsequent tin oxide particles. In this embodiment, magnetic stirring is used for stirring in a sealed environment, the stirring speed is 500~600rpm, the stirring temperature is 65~75℃, and the stirring time is 2~2.5 hours, so that the complex reaction is more complete. After the stirring process is completed, the precursor mixed solution presents an obvious light yellow color, so that the precursor mixed solution is placed in a closed container that is not in contact with external moisture for standing, and the precursor mixed solution will continue to undergo a slow complex reaction, thereby forming a more uniform and consistent tin complex. Adjusting the standing time before crystallization can control the precipitated tin oxide particles. The longer the standing time, the more conducive it is to precipitate uniform tin oxide particles. In this embodiment, standing for 2 to 4 weeks after stirring can stabilize the tin complex, thereby improving the properties of the subsequent precipitated tin oxide, such as size distribution, crystallinity and morphology.

[0027] In the process of preparing the complex solution in this embodiment, the stirring speed, temperature, time and standing time are controlled to ensure that the complex reaction is fully carried out, forming a more uniform tin complex, which helps to improve the crystallization performance of the finally prepared nano-tin oxide.

[0028] Optionally, the step of adding propionic acid to the complex solution to obtain a tin oxide precipitate comprises: 0.55-0.60 mL of propionic acid is added dropwise to 1-1.2 mL of the complex solution and stirred to cause a dissociation reaction in the complex solution to obtain a precipitated tin oxide; wherein the stirring speed of the stirring treatment is 500-600 rpm, the stirring temperature is 20-25° C., and the stirring time is 2-2.5 hours.

[0029] Further, the parameter conditions for precipitating tin oxide will affect the characteristics of nano tin oxide. Adding propionic acid to the complex solution can cause the tin complex to undergo a dissociation reaction and precipitate tin oxide. During the dissociation reaction, the addition of propionic acid will make the pH value of the solution weakly acidic, which can increase the nucleation rate of tin oxide and promote the formation of smaller tin oxide precipitation particles. However, as the reaction proceeds, by-products will be produced while precipitating tin oxide, and these by-products will increase the pH value of the solution, resulting in the destruction of the weakly acidic pH value conditions. In order to control the pH value conditions to maintain a weakly acidic environment (such as pH = 6~7), propionic acid can be added in a slow dripping manner to ensure the controllability of the dissociation reaction and the uniformity of the precipitation of tin oxide. In this embodiment, 0.55~0.60mL of propionic acid (propionic acid purity is 99~100%) is added dropwise to 1~1.2mL of the complex solution, and the dripping speed is controlled to 0.25~0.3mL / h by a syringe pump, such as using a TJ1A single-channel syringe pump. Meanwhile, in this embodiment, the stirring speed of the stirring process is controlled to be 500-600 rpm, the stirring temperature is 20-25° C., and the stirring time is 2-2.5 hours, so as to further ensure the precipitation of uniform tin oxide precipitation.

[0030] In this embodiment, the amount of the complex solution and propionic acid used is controlled, and the propionic acid is added dropwise to the complex solution while stirring, which helps to maintain the pH stability of the solution, ensure the controllability of the dissociation reaction and the uniformity of the tin oxide precipitation. At the same time, controlling the stirring speed, temperature and time helps to precipitate a uniform tin oxide precipitate.

[0031] Optionally, the sintering treatment of the tin oxide precipitate to obtain nano tin oxide includes: The tin oxide precipitate is sintered in an oxygen-containing inert gas environment to obtain nano tin oxide; wherein the sintering temperature of the sintering treatment is 400-500° C., and the sintering time is 2-10 hours.

[0032] Optionally, the oxygen content in the oxygen-containing inert gas environment is 20% to 30%, the inert gas content is 70% to 80%, and the inert gas includes at least one of nitrogen, helium and argon.

[0033] Further, before the tin oxide precipitate is sintered, it is necessary to filter the tin oxide precipitate to remove impurities, unreacted tin precursors and by-products, which is helpful to obtain nano tin oxide particles with higher purity, so that the final prepared product is more consistent and controllable. When the tin oxide precipitate is sintered, it is necessary to carry out in an oxygen-containing inert gas environment to avoid the tin oxide precipitate from reacting with impurities in the air under high temperature conditions. In the present embodiment, the content of oxygen in the oxygen-containing inert gas environment is 20% to 30%, and the content of inert gas is 70% to 80%, and the inert gas includes at least one of nitrogen, helium and argon. The parameter conditions for sintering the tin oxide precipitate will affect the characteristics of nano tin oxide, especially the sintering temperature and sintering time. Too low sintering temperature or too short sintering time are not conducive to the solid phase reaction between tin oxide particles, and affect the size distribution, crystallinity and morphology of nano tin oxide.

[0034] In this embodiment, the tin oxide precipitate is sintered in an oxygen-containing inert gas environment, which can avoid the formation of impurities during the sintering process and control the sintering temperature and sintering time, which is helpful to improve the uniformity and crystallization performance of nano-tin oxide.

[0035] In a specific embodiment, a gas sensor is prepared based on nano-tin oxide prepared at different sintering temperatures (the sintering temperature of nano-tin oxide is different during the preparation of the gas sensor, and other conditions are the same), and the response sensitivity of the gas sensor under different ammonia concentrations is tested. Among them, the sintering temperature (Sintering Temperature) represents the sintering temperature when preparing nano-tin oxide, and the three groups of temperatures are 400°C, 450°C and 500°C respectively. The ammonia concentration range of the ammonia concentration (NH3Concentration) test is 10ppm, 50ppm and 100ppm respectively. The sensor response (Sensor Response) represents the relative change of the sensor resistance, that is, ΔR / R0, ΔR is the resistance change caused by the presence of ammonia, and R0 is the baseline resistance in the absence of ammonia. The sensor response is measured at a combination of three groups of temperatures and three groups of concentrations, and the sensor response of each temperature and concentration is recorded, and 9 groups of response results can be obtained. The test results are shown in Table 1.

[0036] Table 1 Response results of gas sensors based on nano-tin oxide at different sintering temperatures to ammonia In addition, if Figure 2 As shown in Table 1, the bar graph shows the response results of the gas sensor based on nano-tin oxide at different sintering temperatures to ammonia. Figure 2It can be seen that at different ammonia concentrations (10ppm, 50ppm and 100ppm), the sensor response increases with the increase of ammonia concentration. At the same ammonia concentration, the response value is the lowest when the sintering temperature is 400℃, and the highest response value is shown at all ammonia concentrations when the sintering temperature is 450℃. The response value when the sintering temperature is 500℃ is higher than the response value at 400℃ but lower than the response value at 450℃. Therefore, compared with 400℃ and 500℃, the sintering temperature of 450℃ is the best temperature to balance sensitivity and other factors, and has the best sensitivity and performance for detecting ammonia.

[0037] In a second aspect, an embodiment of the present invention further discloses a nano tin oxide, wherein the preparation method of the nano tin oxide comprises the following steps: subjecting tin chloride dihydrate and ethanolamine to a mixed ultrasonic treatment to obtain a precursor mixed solution; Stirring and standing the precursor mixed solution to obtain a complex solution; Adding propionic acid to the complex solution for stirring and dissociation reaction to obtain tin oxide precipitate; The tin oxide precipitate is sintered to obtain nano tin oxide.

[0038] In a third aspect, an embodiment of the present invention further discloses a tin oxide ink, wherein the tin oxide ink comprises nano tin oxide, and a method for preparing the nano tin oxide comprises the following steps: subjecting tin chloride dihydrate and ethanolamine to a mixed ultrasonic treatment to obtain a precursor mixed solution; Stirring and standing the precursor mixed solution to obtain a complex solution; Adding propionic acid to the complex solution for stirring and dissociation reaction to obtain tin oxide precipitate; The tin oxide precipitate is sintered to obtain nano tin oxide.

[0039] In a fourth aspect, an embodiment of the present invention further discloses a gas sensor, wherein the gas sensor comprises a micro sensor chip, wherein the micro sensor chip comprises a tin oxide coating formed by printing tin oxide ink, wherein the tin oxide ink comprises nano tin oxide, and a method for preparing the nano tin oxide comprises the following steps: subjecting tin chloride dihydrate and ethanolamine to a mixed ultrasonic treatment to obtain a precursor mixed solution; Stirring and standing the precursor mixed solution to obtain a complex solution; Adding propionic acid to the complex solution for stirring and dissociation reaction to obtain tin oxide precipitate; The tin oxide precipitate is sintered to obtain nano tin oxide.

[0040] In a fifth aspect, an embodiment of the present invention further discloses a method for preparing a gas sensor, comprising: Mixing an organic solvent with the nano-tin oxide obtained by the preparation method according to the first aspect to obtain a tin oxide ink; the viscosity of the tin oxide ink is 10-12 cP, and the surface tension is 25-40 mN / m; Printing the tin oxide ink layer by layer onto the surface of the microsensor substrate in an inkjet printing manner to form at least two layers of tin oxide coating; Annealing the microsensor substrate carrying at least two layers of the tin oxide coating to obtain a microsensor chip; The microsensor chip is packaged to obtain a gas sensor.

[0041] Furthermore, the tin oxide ink includes an organic solvent and nano tin oxide obtained according to the preparation method of the first aspect. The organic solvent includes at least one of propylene glycol methyl ether, tripropylene glycol methyl ether and diisobutyl ketone. The organic solvent is used as a diluent in the tin oxide ink, which can effectively help adjust the viscosity and surface tension (fluidity) of the tin oxide ink, thereby improving the printing effect. In addition, the organic solvent also has good solubility and volatility, can dry quickly during the printing process, and improve the printing quality. The viscosity of the tin oxide ink in this embodiment is 10~12cP, and the surface tension is 25~40mN / m.

[0042] After obtaining the tin oxide ink, the tin oxide ink is printed layer by layer onto the surface of the microsensor substrate by inkjet printing to form at least two layers of tin oxide coating. Compared with the traditional chemical vapor deposition method, the inkjet printing method is simple to operate, economical and suitable for large-scale production. After the last layer of tin oxide coating is printed and dried, the microsensor substrate carrying at least two layers of tin oxide coating is annealed to obtain a microsensor chip. The microsensor chip is packaged and assembled with a sensor component including a gold electrode to obtain a gas sensor.

[0043] This embodiment combines the sol-gel method with inkjet printing technology to achieve efficient application of nano-tin oxide, and directly integrates the chip formed by printing tin oxide ink into the gas sensor, which simplifies the preparation process of the gas sensor and can significantly improve the gas sensing performance of the gas sensor.

[0044] Optionally, before printing the tin oxide ink layer by layer onto the surface of the microsensor substrate in an inkjet printing manner, the method comprises: Set the printing distance to 0.5~1mm, the printing speed to 1.5~2mm / s, and the printing pressure to 3.5~6kPa.

[0045] Furthermore, the print distance refers to the distance between the needle tip and the microsensor substrate. The print speed refers to the speed at which the print head moves. The print pressure refers to the pressure applied to the ink. When using inkjet printing, adjusting the speed at which the print head moves and the pressure applied to the ink can ensure the consistency of droplet formation. By precisely controlling the distance between the print needle tip and the microsensor substrate, it can be ensured that the droplets land exactly where they are needed without splashing or excessive spreading.

[0046] This embodiment avoids the formation of satellite droplets by fine-tuning the inkjet printing parameters, achieves uniform printing, and ensures the consistency and accuracy of the printed droplets.

[0047] Optionally, printing the tin oxide ink layer by layer onto the surface of the microsensor substrate in an inkjet printing manner comprises: After a layer of tin oxide ink is printed onto the surface of the microsensor substrate and the layer of tin oxide ink is dried to form a dried tin oxide coating, the next layer of tin oxide ink is printed onto the surface of the dried tin oxide coating; the drying temperature of the drying treatment is 50-60° C. and the drying time is 25-35 minutes.

[0048] Furthermore, the tin oxide ink is printed layer by layer onto the surface of the microsensor substrate, and multiple layers of ink are printed to construct the active sensing layer. Between two adjacent layers, the previous layer of tin oxide ink needs to be dried to ensure that the tin oxide ink layer has proper adhesion and prevent fusion between the layers.

[0049] In this embodiment, the upper layer of tin oxide ink is dried before printing the next layer of tin oxide ink, thereby ensuring that the microsensor chip has a uniform and well-adhered tin oxide ink layer.

[0050] Optionally, the annealing temperature of the annealing treatment is 400-500° C., and the annealing time is 8-10 hours.

[0051] Furthermore, after the last layer of tin oxide ink is printed and dried, the microsensor substrate carrying the tin oxide coating is annealed at an annealing temperature of 400 to 500°C for 8 to 10 hours, which helps the nano-tin oxide crystallize to form a stable structure.

[0052] This embodiment controls the annealing temperature and time to enhance the structural and functional characteristics of the tin oxide coating, which helps to improve the gas sensing performance of the gas sensor.

[0053] In a specific embodiment, a laboratory-grade Dimatix inkjet printer (MP1100 microelectronic printer) is used for inkjet printing. First, tin oxide ink is prepared using nano-tin oxide prepared by sol-gel method, and the 60-microliter syringe of the print head is filled with tin oxide ink. The printing parameters of the print head and inkjet printer are set to ensure the viscosity and fluidity of the tin oxide ink. Secondly, the microsensor substrate is surface treated (cleaned with ethanol and isopropanol for 15 minutes), and the drop spacing is evaluated, so that the ink droplet diameter is 60 microns and the drop spacing is 20 microns, which can achieve continuous and visible printing and ensure good surface coverage. Then, the microsensor substrate is placed in a micro-electro-mechanical system (MEMS) device for printing. During the printing process, 50°C is used to dry for 30 minutes between adjacent printed layers. Finally, annealing is performed at 450°C for 10 hours to make the tin oxide ink coating more gas sensing active.

[0054] This example ensures that the printed tin oxide ink coating has the properties required for effective gas sensing, including uniformity, proper adhesion, and crystallinity. Precise control of viscosity, surface tension, printing speed, pressure, and the distance between the needle and the substrate are critical to achieving high-quality printing on MEMS devices.

[0055] Existing chemical vapor deposition methods require high-temperature equipment and complex multi-step procedures, making the process complex, costly, and not easy to accurately control. This embodiment can produce reliable and high-performance MEMS gas sensors that can operate at room temperature, reducing the need for external heating, making the sensor more energy-efficient, and suitable for a wider range of applications, such as environmental monitoring, industrial safety, and medical diagnosis. Chemical vapor deposition methods are difficult to mass-produce due to their complexity and the need for specialized equipment. The scalability of the inkjet printing method is suitable for large-scale manufacturing, ensuring consistency and uniformity in production. The inkjet printing method used in this embodiment is compatible with the MEMS manufacturing process and can be mass-produced on MEMS devices, promoting the development of compact, efficient, and high-performance gas sensors.

[0056] In order to verify the effect of the gas sensor of the present invention and the gas sensor prepared by the traditional chemical vapor deposition method, the gas sensor prepared by inkjet printing is used as an example, and the gas sensor prepared by chemical vapor deposition is used as a comparative example to detect the same concentration of ammonia. Compared with the gas sensor prepared by chemical vapor deposition, the inkjet-printed gas sensor performs better when detecting ammonia of different concentrations (3.5 ppm to 700 ppm) at room temperature. Specifically, it is manifested in higher sensitivity at low concentrations, faster response and recovery time, better selectivity, and enhanced stability at room temperature.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing nano tin oxide, characterized in that: include: mixing tin chloride dihydrate and ethanolamine to obtain a precursor mixed solution; treating the precursor mixed solution to obtain a complex solution; adding propionic acid to the complex solution to obtain tin oxide precipitate; The tin oxide precipitate is sintered to obtain nano tin oxide.

2. The method for preparing nano tin oxide according to claim 1, characterized in that: The mixing of tin chloride dihydrate and ethanolamine to obtain a precursor mixed solution comprises: 0.8-1.0 g of tin chloride dihydrate is added to 9-12 mL of ethanolamine, and ultrasonic treatment is performed at 20-30° C. for 20-40 minutes to dissolve the tin chloride dihydrate in the ethanolamine to obtain a precursor mixed solution.

3. The method for preparing nano tin oxide according to claim 1, characterized in that: The step of treating the precursor mixed solution to obtain a complex solution comprises: The precursor mixed solution is stirred under sealed conditions, and allowed to stand for 2 to 4 weeks after stirring to obtain a complex solution; wherein the stirring speed of the stirring treatment is 500 to 600 rpm, the stirring temperature is 65 to 75° C., and the stirring time is 2 to 2.5 hours.

4. The method for preparing nano tin oxide according to claim 1, characterized in that: The step of adding propionic acid to the complex solution to obtain tin oxide precipitation comprises: 0.55-0.60 mL of propionic acid is added dropwise to 1-1.2 mL of the complex solution and stirred to cause a dissociation reaction in the complex solution to obtain a precipitated tin oxide; wherein the stirring speed of the stirring treatment is 500-600 rpm, the stirring temperature is 20-25° C., and the stirring time is 2-2.5 hours.

5. The method for preparing nano tin oxide according to claim 1, characterized in that: The sintering treatment of the tin oxide precipitate to obtain nano tin oxide comprises: The tin oxide precipitate is sintered in an oxygen-containing inert gas environment to obtain nano tin oxide; wherein the sintering temperature of the sintering treatment is 400-500° C., and the sintering time is 2-10 hours.

6. The method for preparing nano tin oxide according to claim 5, characterized in that: The oxygen content in the oxygen-containing inert gas environment is 20% to 30%, and the inert gas content is 70% to 80%. The inert gas includes at least one of nitrogen, helium and argon.

7. A nano tin oxide, characterized in that: The nano tin oxide is prepared according to the preparation method according to any one of claims 1 to 6.

8. A tin oxide ink, characterized in that: The tin oxide ink comprises nano tin oxide obtained according to the preparation method according to any one of claims 1 to 6.

9. A gas sensor, characterized in that: The gas sensor comprises a micro sensor chip, and the micro sensor chip comprises a tin oxide coating formed by printing the tin oxide ink according to claim 8.

10. A method for preparing a gas sensor, characterized in that: include: Mixing an organic solvent with the nano-tin oxide obtained by the preparation method according to any one of claims 1 to 6 to obtain tin oxide ink; The viscosity of the tin oxide ink is 10-12 cP, and the surface tension is 25-40 mN / m; Printing the tin oxide ink layer by layer onto the surface of the microsensor substrate in an inkjet printing manner to form at least two layers of tin oxide coating; Annealing the microsensor substrate carrying at least two layers of the tin oxide coating to obtain a microsensor chip; The microsensor chip is packaged to obtain a gas sensor.

11. The method for preparing a gas sensor according to claim 10, characterized in that: Before printing the tin oxide ink layer by layer onto the surface of the microsensor substrate in an inkjet printing manner, the method comprises: Set the printing distance to 0.5~1mm, the printing speed to 1.5~2mm / s, and the printing pressure to 3.5~6kPa.

12. The method for preparing a gas sensor according to claim 11, characterized in that: The method of printing the tin oxide ink layer by layer onto the surface of the microsensor substrate in an inkjet printing manner comprises: After a layer of tin oxide ink is printed onto the surface of the microsensor substrate and the layer of tin oxide ink is dried to form a dried tin oxide coating, the next layer of tin oxide ink is printed onto the surface of the dried tin oxide coating; the drying temperature of the drying treatment is 50-60° C. and the drying time is 25-35 minutes.

13. The method for preparing a gas sensor according to claim 10, characterized in that: The annealing temperature of the annealing treatment is 400-500° C., and the annealing time is 8-10 hours.

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