Sea urchin-like hierarchical indium oxide microspheres gas sensing material, preparation method and application thereof

Abstract

The application discloses a kind of sea urchin-like hierarchical indium oxide microspheres gas-sensitive materials, preparation method and application thereof, which uses indium nitrate pentahydrate as indium source, ethylene glycol and deionized water as mixed solvent, sodium dodecyl sulfonate as morphology regulator, urea as precipitant, and obtains sea urchin-like hierarchical indium oxide microspheres after hydrothermal reaction, drying and calcination.The material prepared by the application is assembled into hierarchical microspheres with a diameter of 1-2 μm by one-dimensional nanoneedle, has high specific surface area, and the response value to 500 ppm methane at 100 ℃ low temperature can reach 4.84, the response time is only 3.6 s, and the selectivity to interference gases such as ammonia, carbon monoxide and water vapor in coal mine is excellent.The process of the application is simple and controllable, and the gas-sensitive material prepared has the advantages of low power consumption, high sensitivity and high anti-interference, and is suitable for real-time monitoring of methane gas in coal mine.

Description

Technical Field

[0001] This invention belongs to the field of gas-sensitive materials and gas detection technology, specifically relating to a sea urchin-shaped graded indium oxide microsphere gas-sensitive material, its preparation method, and its application in methane gas detection in underground coal mines. Background Technology

[0002] With the gradual expansion of coal mining in my country, the risks of gas exceeding limits, outbursts, and explosions in deep mines have increased significantly, becoming the primary hidden danger for coal mine gas disasters. The main component of methane is gas, with an explosive concentration range typically between 5% and 16%. Underground working environments are enclosed and densely populated; once a gas leak or explosion occurs, it will cause significant casualties and property damage. According to the "Coal Mine Safety Regulations," real-time and continuous monitoring of methane concentration is required in coal mines, with alarm concentrations typically set at 0.5% to 1.5%. This places more stringent requirements on the sensitivity, response rate, environmental adaptability, and anti-interference capabilities of detection sensors for deep working conditions.

[0003] Current methane detection technologies mainly include chromatographic analysis, spectroscopic analysis, and gas sensor methods. Among them, metal oxide semiconductor (MOS) gas sensors have become the core sensing devices in deep mine gas early warning and monitoring systems due to their advantages of simple structure, controllable cost, and suitability for long-term online monitoring in mines. Indium oxide (In2O3), an n-type semiconductor, has the characteristics of low intrinsic resistance, good chemical stability, and excellent response characteristics to reducing gases. Compared with materials such as zinc oxide and tin dioxide, it is more suitable for low-power, high-stability downhole detection scenarios.

[0004] However, existing indium oxide-based methane gas-sensitive materials still cannot meet the needs of complex disaster prevention and control in deep mines: First, conventional bulk or nanoparticle indium oxide has a limited specific surface area and insufficient gas adsorption active sites, resulting in low sensitivity to methane; second, traditional indium oxide-based sensors generally operate at temperatures above 200°C, resulting in high power consumption in high-temperature operating modes. In deep, high-humidity, hot, and oxygen-deficient environments, these sensors are prone to accelerated thermal aging and performance degradation, significantly reducing their long-term reliability; third, deep mine environments suffer from severe multi-component gas coupling interference, with coexisting interfering gases such as ammonia, carbon monoxide, and high-humidity water vapor. Existing materials have poor methane selectivity and weak anti-interference capabilities, easily leading to false alarms, missed alarms, and delayed alarms in gas monitoring. This directly affects the accuracy of gas disaster prediction, early warning, and prevention and control decisions in deep mines, making it difficult to meet the engineering requirements for precise prevention and control of disasters in deep mining.

[0005] Constructing hierarchical micro / nanomaterials is an important way to improve gas-sensing performance. Among them, the urchin-like hierarchical structure has the advantages of high specific surface area, abundant pore channels, and fast electron transport pathways. However, in the current technology, the preparation of urchin-like indium oxide often adopts highly toxic template agents or complex multi-step processes, and there is still a lack of methane-specific gas-sensing materials optimized for the complex working conditions in coal mines, making it difficult to simultaneously meet the requirements of low-temperature operation, high sensitivity, and high selectivity. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a sea urchin-shaped graded indium oxide microsphere gas-sensitive material and its preparation method, and to expand its application in methane detection in coal mines, thereby solving the problems of low methane response sensitivity, high operating temperature, weak anti-interference ability, and difficulty in adapting to the complex working conditions of underground coal mines in existing indium oxide gas-sensitive materials.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing urchin-shaped hierarchical indium oxide microsphere gas-sensitive materials, comprising the following steps: Step 1: Mix ethylene glycol and deionized water at a volume ratio of 1:2 to obtain a mixed solvent. Stir at room temperature for 30-40 minutes. Dissolve indium nitrate pentahydrate in the mixed solvent and stir at room temperature for 30-40 minutes until completely dissolved. Then add sodium dodecyl sulfonate and urea and stir at room temperature for 60 minutes until the solution is homogeneous to obtain a precursor solution. The corresponding amounts of indium nitrate pentahydrate, sodium dodecyl sulfonate, and urea are added to every 60 mL of the mixed solvent.

[0008] Step 2: Transfer the precursor solution to a polytetrafluoroethylene-lined reactor, seal it, and place it in an oven for hydrothermal reaction at 110°C for 11-12 hours. After the reaction is complete, allow it to cool naturally to room temperature, centrifuge to collect the precipitate, wash the precipitate alternately with anhydrous ethanol and deionized water, and then dry the precipitate in a drying oven to obtain the precursor powder.

[0009] Step 3: Place the precursor powder in a muffle furnace and heat it to 400°C at a heating rate of 5°C / min. Hold the temperature for 4 hours and allow it to cool naturally to room temperature to obtain the urchin-shaped graded indium oxide microsphere gas-sensitive material.

[0010] Furthermore, in step one, it is preferable to add 0.5g sodium dodecyl sulfonate and 0.78g urea to every 60mL of mixed solvent. This ratio can yield sea urchin-like microspheres with uniform morphology and complete hierarchical structure.

[0011] Furthermore, in step two, the washing process involves alternating between anhydrous ethanol and deionized water five times to remove residual surfactants and inorganic salt ions; the drying conditions are 45°C for 12 hours to avoid precursor aggregation caused by high-temperature drying.

[0012] Furthermore, the preferred conditions for the hydrothermal reaction in step two are: a temperature of 110°C and a reaction time of 11 hours. Under these conditions, the degree of nanoneedle assembly is moderate and the uniformity of microsphere morphology is optimal.

[0013] This invention also provides a hierarchical indium oxide microsphere gas-sensitive material with a sea urchin-like structure, prepared by the above method: the gas-sensitive material is a hierarchical microsphere, shaped like a sea urchin, with a diameter of 1-2 μm, self-assembled from one-dimensional nanoneedles with a diameter of 20-50 nm, and a specific surface area of ​​not less than 60 m². 2 / g; the material has good crystallinity and is cubic indium oxide.

[0014] The present invention also provides the application of the above-mentioned urchin-shaped graded indium oxide microsphere gas-sensitive material: for the preparation of methane gas sensors for methane gas detection, especially suitable for methane gas detection in underground coal mine environments.

[0015] Furthermore, the optimal operating temperature of the methane gas sensor is 100℃; at the operating temperature of 100℃, the response value of the gas-sensitive material to 500ppm methane is not less than 4.8, and the response time is not more than 4s; and the response values ​​to typical interfering gases in coal mines (ammonia, carbon monoxide, water vapor) are significantly lower than those to methane, demonstrating excellent selectivity and anti-interference ability.

[0016] Compared with the prior art, the present invention has the following advantages: 1. The optimal operating temperature of the urchin-shaped graded indium oxide microspheres prepared by this invention is only 100℃, which is much lower than the operating temperature of conventional indium oxide methane sensors. This can effectively reduce sensor power consumption and extend the service life and endurance of downhole equipment. At the same time, it has a high response value to 500ppm methane at 100℃ and a short response time, combining high sensitivity and fast response characteristics.

[0017] 2. The sea urchin-like hierarchical structure of the present invention is assembled from one-dimensional nanoneedles, which has both a high specific surface area and abundant gas adsorption active sites, as well as interconnected pore channels and fast electron transport paths, which can accelerate the gas adsorption-desorption process and electron transfer efficiency, thereby improving the gas-sensitive response performance from the structural level.

[0018] 3. The material of this invention has a much lower response value to typical interfering gases (ammonia, carbon monoxide, and water vapor) in coal mines than to methane, which can effectively reduce the false alarm probability in complex underground environments and improve the accuracy and reliability of methane detection.

[0019] 4. This invention adopts a one-step hydrothermal process combined with subsequent calcination, which does not require complex templates and expensive equipment. The raw materials are readily available, the reaction conditions are mild, and the morphology and properties of the product can be precisely controlled by solvent ratio, surfactant dosage, and hydrothermal parameters, making it suitable for large-scale production. Attached Figure Description

[0020] Figure 1 The image shows a scanning electron microscope (SEM) image of the urchin-shaped hierarchical indium oxide microspheres prepared in Example 1.

[0021] Figure 2 SEM image of the urchin-shaped hierarchical indium oxide microspheres prepared in Example 2.

[0022] Figure 3 The image shows a SEM image of the indium oxide microspheres prepared in Comparative Example 1.

[0023] Figure 4 The X-ray diffraction (XRD) pattern of the urchin-shaped hierarchical indium oxide microspheres prepared in Example 1.

[0024] Figure 5 The gas-sensitive response-recovery curve of the material prepared in Example 1 to 500 ppm methane at 100 °C.

[0025] Figure 6 The graph shows a comparison of the response values ​​of the material prepared in Example 1 to 500 ppm of different gases at 100°C. Detailed Implementation

[0026] The present invention will be further described below.

[0027] All reagents used in the following examples were of analytical grade, and the experimental water was deionized water; the volume of the polytetrafluoroethylene-lined reaction vessel was 50 mL, the muffle furnace was a box-type resistance furnace, and the gas sensitivity performance was tested using the static gas mixing method on a CGS-MT gas sensitivity analysis and testing system.

[0028] The gas-sensitive response value is defined as: S=Ra / Rg, where Ra is the stable resistance value of the element in clean air, and Rg is the stable resistance value of the element in the gas atmosphere to be measured; the response time is the time required for the resistance value to reach 90% of the total change after the element is introduced into the gas atmosphere to be measured; the recovery time is the time required for the resistance value to recover to 90% of the initial value after the element is removed from the gas atmosphere to be measured.

[0029] Example 1: A method for preparing a gas-sensitive material of urchin-shaped hierarchical indium oxide microspheres, the steps of which are as follows: Step 1: Measure 20 mL of ethylene glycol and 40 mL of deionized water into a beaker and stir at room temperature for 40 min to obtain a homogeneous mixed solvent; weigh 0.391 g of indium nitrate pentahydrate and add it to the above mixed solvent, stir at room temperature for 40 min until completely dissolved; then add 0.5 g of sodium dodecyl sulfonate and 0.78 g of urea in sequence, and continue stirring at room temperature for 60 min to obtain a clear and transparent precursor solution.

[0030] Step 2: Transfer the precursor solution to a 50 mL polytetrafluoroethylene-lined reactor, seal it, and place it in an oven at 110 °C for hydrothermal reaction for 11 h. After the reaction, allow it to cool naturally to room temperature and collect the white precipitate by centrifugation at 7000 r / min for 10 min. Wash the precipitate five times with anhydrous ethanol and deionized water alternately, centrifuging after each wash. After washing, place the precipitate in a drying oven and dry it at 45 °C for 12 h to obtain the precursor powder.

[0031] Step 3: Transfer the precursor powder into a ceramic crucible, place it in a muffle furnace, heat it to 400℃ at a rate of 5℃ / min, and calcine it at that temperature for 4 hours; after the program is completed, allow it to cool naturally to room temperature to obtain a light yellow, urchin-shaped, graded indium oxide microsphere gas-sensitive material.

[0032] Performance characterization: such as Figure 1 As shown, SEM characterization revealed that the product consisted of uniformly shaped sea urchin-like microspheres, approximately 1.5 μm in diameter, with the surface composed of numerous radially grown nanoneedles, each approximately 30 nm in diameter. Figure 2 As shown, the XRD pattern perfectly matches the cubic In₂O₃ standard card (JCPDS No. 71-2194), with no impurity peaks and good crystallinity; the BET specific surface area is 68.2 m². 2 / g.

[0033] Gas-sensitive performance testing: such as Figure 5 and 6 As shown, at a working temperature of 100℃, the response value for 500ppm methane is 4.84, the response time is 3.6s, and the recovery time is 3.8s; the response values ​​for 500ppm ammonia, 500ppm carbon monoxide, and saturated water vapor are 1.58, 3.12, and 1.07, respectively, all significantly lower than those for methane.

[0034] Example 2: A method for preparing a gas-sensitive material of urchin-shaped hierarchical indium oxide microspheres, the steps of which are as follows: Step 1: Measure 30 mL of ethylene glycol and 30 mL of deionized water into a beaker and stir at room temperature for 40 min to obtain a homogeneous mixed solvent; weigh 0.391 g of indium nitrate pentahydrate and add it to the above mixed solvent, stir at room temperature for 40 min until completely dissolved; then add 0.3 g of sodium dodecyl sulfonate and 0.78 g of urea in sequence, and continue stirring at room temperature for 60 min to obtain the precursor solution.

[0035] Steps two and three are the same as in Example 1, and finally indium oxide microsphere gas-sensitive material is obtained.

[0036] Performance characterization: such as Figure 2As shown, SEM characterization revealed that the product remained urchin-like microspheres, with a slight increase in nanoneedle diameter and slight aggregation in some microspheres; the surface nanoneedle density was lower than in Example 1; and the BET specific surface area was 65.7 m². 2 / g.

[0037] Gas-sensing performance test: At a working temperature of 100℃, the response value to 500ppm methane is 3.23, and the response time is 5.9s.

[0038] Example 3: A method for preparing a gas-sensitive material of urchin-shaped hierarchical indium oxide microspheres, the steps of which are as follows: Step 1: Measure 20 mL of ethylene glycol and 40 mL of deionized water into a beaker and stir at room temperature for 40 min to obtain a homogeneous mixed solvent; weigh 0.391 g of indium nitrate pentahydrate and add it to the above mixed solvent, stir at room temperature for 40 min until completely dissolved; then add 0.5 g of sodium dodecyl sulfonate and 0.9009 g of urea in sequence, and continue stirring at room temperature for 60 min to obtain the precursor solution.

[0039] Step 2: Transfer the precursor solution to the reactor and hydrothermally react at 110°C for 12 hours; the remaining washing and drying steps are the same as in Example 1.

[0040] Step 3 is the same as in Example 1, and finally indium oxide microsphere gas-sensitive material is obtained.

[0041] Gas-sensitive performance test: At a working temperature of 100℃, the response value to 500ppm methane is 1.25, and the response time is 8.3s.

[0042] Comparative Example 1 (Solvent Replacement Control): In this comparative example, ethylene glycol in Example 1 was replaced with anhydrous ethanol, and the amounts of other raw materials, preparation steps and parameters were completely consistent with those in Example 1, and indium oxide material was prepared.

[0043] Performance characterization: such as Figure 3 As shown, SEM characterization revealed that the product consisted of flower-like hierarchical microspheres, without the formation of sea urchin-like nanoneedle structures; the BET specific surface area was 42.3 m². 2 / g.

[0044] Gas sensitivity test: At a working temperature of 100°C, the response value to 500 ppm methane was 2.37 and the response time was 8.2 s, which was significantly lower than that of Example 1.

[0045] Comparative Example 2 (Commercial Indium Oxide Control): This comparative example uses commercial indium oxide nanoparticles (particle size 30~50nm) as a control and performs gas-sensing tests under the same conditions.

[0046] Gas sensitivity test: At a working temperature of 100℃, the response value to 500ppm methane is only 1.62, and the response time exceeds 15s; and the response value to carbon monoxide is close to that to methane, indicating poor selectivity.

[0047] The above examples and comparative examples demonstrate that the present invention can prepare well-structured, urchin-like hierarchical indium oxide microspheres by using an ethylene glycol-water mixed solvent system combined with the morphology control effect of sodium dodecyl sulfonate. This special hierarchical structure endows the material with excellent low-temperature methane gas sensing performance and anti-interference ability, which is significantly better than the flower-like materials prepared by the ethanol system and commercial indium oxide particles, and can be adapted to the complex detection conditions in coal mines.

[0048] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a gas-sensitive material of urchin-shaped hierarchical indium oxide microspheres, characterized in that, Includes the following steps: Step 1: Mix ethylene glycol and deionized water at a volume ratio of 1:2 to obtain a mixed solvent. Stir at room temperature for 30-40 minutes. Dissolve indium nitrate pentahydrate in the mixed solvent and stir at room temperature for 30-40 minutes until completely dissolved. Then add sodium dodecyl sulfonate and urea and stir at room temperature until the solution is homogeneous to obtain the precursor solution. The corresponding amounts of indium nitrate pentahydrate, sodium dodecyl sulfonate, and urea are added to every 60 mL of the mixed solvent. Step 2: Transfer the precursor solution to a polytetrafluoroethylene-lined reactor, seal it, and place it in an oven for hydrothermal reaction at 110~120℃ for 11~12h. After the reaction is completed, allow it to cool naturally to room temperature, centrifuge to collect the precipitate, wash the precipitate alternately with anhydrous ethanol and deionized water, and then dry the precipitate in a drying oven to obtain the precursor powder. Step 3: Place the precursor powder in a muffle furnace and heat it to 400°C at a heating rate of 3~5°C / min. Hold the temperature for calcination for 3~4 hours and allow it to cool naturally to room temperature to obtain urchin-shaped graded indium oxide microsphere gas-sensitive material.

2. The preparation method according to claim 1, characterized in that, In step one, 0.5g of sodium dodecyl sulfonate and 0.78g of urea are added to every 60mL of mixed solvent.

3. The preparation method according to claim 1, characterized in that, In step two, the washing process involves alternating between anhydrous ethanol and deionized water five times; the drying conditions are 45°C for 12 hours.

4. The preparation method according to claim 1, characterized in that, In step two, the hydrothermal reaction temperature is 110℃ and the reaction time is 11h.

5. A gas-sensitive material of urchin-shaped hierarchical indium oxide microspheres, characterized in that, The gas-sensitive material is prepared by the method according to any one of claims 1 to 4; the gas-sensitive material is a hierarchical microsphere, which is urchin-shaped, with a diameter of 1 to 2 μm, and is self-assembled from one-dimensional nanoneedles with a diameter of 20 to 50 nm, and has a specific surface area of ​​not less than 60 m². 2 / g.

6. An application of a gas-sensitive material consisting of urchin-shaped hierarchical indium oxide microspheres, characterized in that... Used to prepare a methane gas sensor for methane gas detection.

7. The application according to claim 6, characterized in that, The methane gas detection refers to the detection of methane gas in the underground environment of a coal mine.

8. The application according to claim 6, characterized in that, The optimal operating temperature of the methane gas sensor is 100℃. At the operating temperature of 100℃, the gas-sensitive material has a response value of not less than 4.8 to 500ppm methane and a response time of not more than 4s. The response values ​​to ammonia, carbon monoxide, and water vapor are all lower than those to methane.

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