Preparation Method of a NiCo2O4-In2O3 Composite Gas-Sensing Material Formaldehyde Sensor

Abstract

Preparation method of NiCo2O4-In2O3 composite gas-sensitive material formaldehyde sensor, which relates to a preparation method of a formaldehyde sensor. In the design and preparation process of the gas-sensitive material, a simple and efficient two-step hydrothermal method is adopted. By changing the ratio of raw materials, the optimal structure of the NiCo₂O₄-In₂O₃ composite material is constructed, so that it has excellent application performance. The whole production process has simple technology, low cost, good controllability, non-toxic and harmless. The prepared material has high purity, good crystallization and good dispersibility, and is suitable for large-scale industrial production. The NiCo₂O₄-In₂O₃ composite material prepared by the invention shows high sensitivity, good selectivity and stability to formaldehyde at room temperature, making it show broad application prospects in detecting organic volatile gases in the indoor environment.

Description

Technical Field

[0001] The present invention relates to a method for preparing a formaldehyde sensor, in particular to a method for preparing a formaldehyde sensor based on a NiCo2O4-In2O3 composite gas-sensitive material. Background Art

[0002] Formaldehyde is a colorless gas with a very strong pungent smell and is very volatile. It is a carcinogen with relatively high toxicity. Formaldehyde has currently been recognized by the World Health Organization as an invisible substance that can cause deformities and cancer. In China, formaldehyde has been recognized as a highly polluting and highly toxic chemical. Formaldehyde can cause very strong irritation to human skin, mucous membranes, eyes, etc., may trigger problems such as system dysfunction, and may also lead to problems such as damage to the central nervous system and liver. It can cause fetal deformities, chronic respiratory diseases, leukemia, nasopharyngeal carcinoma, acute mental depression, menstrual disorders in women, etc. Therefore, it is of great significance to effectively and real-time monitor the formaldehyde concentration.

[0003] In recent years, with the rapid development of the Internet of Things, gas sensors have great application prospects in the fields of industrial production safety detection, atmospheric environmental pollution monitoring, intelligent mobile terminals, and emerging smart homes. Metal oxide semiconductor gas sensors have become widely commercialized gas sensors due to their low cost and excellent gas-sensing characteristics. However, they still have disadvantages such as high working temperature, poor selectivity, and poor stability, and thus cannot meet the requirements of integrating environmental information into Internet of Things technology. Therefore, developing low-power, integrated, and intelligent room-temperature metal oxide gas sensors to realize the identification and detection of toxic, flammable, and explosive gases can inject new vitality into the environmental monitoring field in the Internet of Things era.

[0004] Indium oxide (In2O3) is an n-type semiconductor material with a direct bandgap of 3.55 - 3.75 eV and an indirect bandgap of 2.62 eV. Due to the good conductivity, unique gas adsorption and catalytic characteristics, and low electron affinity of In2O3, it has broad application prospects in the microelectronics field. Therefore, it is of important commercial value to use In2O3 as a gas-sensitive material and study its sensitive performance to volatile organic compounds such as formaldehyde. With the rise and vigorous development of nanotechnology, using advanced nanotechnology to synthesize In2O3 nanostructure sensitive materials with excellent performance and designing and constructing a gas-sensing platform by regulating the microstructure and composition of the materials are effective technical means to improve the gas-sensing performance. Summary of the Invention

[0005] The object of the present invention is to provide a preparation method of a NiCo2O4-In2O3 composite gas-sensitive material formaldehyde sensor. The present invention uses a hydrothermal synthesis method to prepare a NiCo2O4-In2O3 material assembled by nanosheets, which exhibits good detection characteristics for formaldehyde gas. The greatest advantage is that it can be detected at room temperature, which will provide a simple and fast technical means for on-site online monitoring of indoor air pollutants. The equipment used is simple, the cost is low, the product purity is high, and it is suitable for large-scale industrial production.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] The advantages and effects of the present invention are:

[0008] (1) The present invention uses indium chloride, cobalt nitrate, nickel nitrate and urea as raw materials to prepare a NiCo2O4-In2O3 composite material by a two-step hydrothermal method. It has the advantages of low cost, good controllability, high purity, good crystallization and good dispersibility of the prepared material, and is suitable for large-scale industrial production.

[0009] (2) The gas sensor prepared with the NiCo2O4-In2O3 composite material prepared by the present invention as a gas-sensitive material exhibits high sensitivity, good selectivity and stability to formaldehyde at room temperature, and has broad application prospects in detecting organic volatile gases in the indoor environment.

[0010] (3) The NiCo2O4-In2O3-based formaldehyde gas sensor fabricated by the present invention has a simple manufacturing process and low cost, and is suitable for industrial batch production. Description of the Drawings

[0011] Figure 1 It is a schematic structural diagram of the formaldehyde sensor of the present invention;

[0012] Figure 2 It is a sensitivity graph of the gas sensor of the present invention to 10 ppm formaldehyde gas at room temperature;

[0013] Figure 3 It is the response and recovery curve of the sensor of Example 3 of the present invention to 10 ppm formaldehyde gas at room temperature;

[0014] Figure 4 It is a selectivity test graph of the sensor of Example 3 of the present invention to 10 ppm gas at room temperature. Detailed Embodiments

[0015] The present invention will be described in detail below with reference to the embodiments shown in the drawings.

[0016] The starting materials of the present invention are inexpensive and readily available indium chloride, cobalt nitrate, nickel nitrate and urea, which are processed through hydrothermal reaction, centrifugation, washing, drying and calcination. The NiCo2O4-In2O3 composite material is prepared into a gas sensor, which shows high sensitivity, good selectivity and stability to formaldehyde at a relatively low working temperature due to its unique spatial structure.

[0017] A method for preparing the NiCo2O4-In2O3 composite material comprises the following steps:

[0018] Step 1: Weigh indium chloride and terephthalic acid, dissolve them in 10 mL of N,N-dimethylacetamide solution, add an anhydrous sodium acetate solution, and stir all the mixed solutions in a constant temperature water bath at 100 °C for 30 minutes to obtain a precursor reaction solution;

[0019] Step 2: Centrifuge the solution obtained in Step 1 to obtain a reaction product, and then wash it repeatedly with distilled water and absolute ethanol; then put the washed reaction product into a drying oven at a constant temperature of 60 °C for 12 hours for drying treatment, and a white powder is obtained after drying;

[0020] Step 3: Ultrasonically treat the powder in Step 2 with deionized water, then add nickel nitrate, cobalt nitrate and urea, and stir all the mixed solutions in a constant temperature water bath at 100 °C for 30 minutes to obtain a reaction product;

[0021] Step 4: Centrifuge the solution obtained in Step 3 to obtain a reaction product, and then wash it repeatedly with distilled water and absolute ethanol;

[0022] Step 5: Put the reaction product washed in Step 4 into a drying oven at a constant temperature of 60 °C for 12 hours for drying treatment, and cool it after drying is completed;

[0023] Step 6: Put the product dried in Step 5 into a clean crucible and place it in a muffle furnace, calcine it at 500 °C for 4 hours to obtain the NiCo2O4-In2O3 composite material, and store it in a desiccator for analysis and testing. [[ID=2,3]]

[0024] Example 1

[0025] Preparation of In2O3 material

[0026] Step 1: Weigh 0.3810 g of indium chloride and 0.1661 g of terephthalic acid, dissolve them in 10 mL of N,N-dimethylacetamide solution, add an anhydrous sodium acetate solution, and stir all the mixed solutions in a constant temperature water bath at 100 °C for 30 minutes to obtain a precursor reaction solution;

[0027] Step 2: Centrifuge the solution after the reaction in Step 1 to obtain the reaction product, and then wash it repeatedly with distilled water and absolute ethanol; then place the washed reaction product in a drying oven at a constant temperature, and dry it at 60 °C for 12 hours to obtain a white powder;

[0028] Step 3: Place the product dried in Step 2 in a clean crucible and put it into a muffle furnace, calcine it at 500 °C for 4 hours to obtain In2O3 material, and store it in a desiccator for analysis and testing.

[0029] Example 2

[0030] Preparation of NiCo2O4-In2O3 composite material

[0031] Step 1: Weigh 0.3810 g of indium chloride and 0.1661 g of terephthalic acid, dissolve them in 10 mL of N,N-dimethylacetamide solution, add anhydrous sodium acetate solution, and stir all the mixed solutions with a constant temperature water bath at 100 °C for 30 minutes to obtain a precursor reaction solution;

[0032] Step 2: Centrifuge the solution after the reaction in Step 1 to obtain the reaction product, and then wash it repeatedly with distilled water and absolute ethanol; then place the washed reaction product in a drying oven at a constant temperature, and dry it at 60 °C for 12 hours to obtain a white powder;

[0033] Step 3: Ultrasonically treat 0.0895 g of the powder in Step 2 with deionized water, then add 0.0020 g of nickel nitrate, 0.0073 g of cobalt nitrate and 0.0112 g of urea, and stir all the mixed solutions with a constant temperature water bath at 100 °C for 30 minutes to obtain a reaction product;

[0034] Step 4: Centrifuge the solution after the reaction in Step 3 to obtain the reaction product, and then wash it repeatedly with distilled water and absolute ethanol;

[0035] Step 5: Place the reaction product washed in Step 4 in a drying oven at a constant temperature, and dry it at 60 °C for 12 hours, and cool it after drying;

[0036] Step 6: Place the product dried in Step 5 in a clean crucible and put it into a muffle furnace, calcine it at 500 °C for 4 hours to obtain NiCo2O4-In2O3 composite material, and store it in a desiccator for analysis and testing.

[0037] Example 3

[0038] Preparation of NiCo2O4-In2O3 composite material

[0039] Steps 1, 2, 4, 5, and 6 are the same as those in Example 2.

[0040] Step 3: Add 0.0895 g of the powder obtained in Step 2 to deionized water and perform ultrasonic treatment. Then add 0.0045 g of nickel nitrate, 0.0014 g of cobalt nitrate, and 0.0219 g of urea. Stir the resulting mixed solution in a constant temperature water bath at 100 °C for 30 minutes to obtain a reaction product;

[0041] Example 4

[0042] Preparation of NiCo2O4-In2O3 composite material

[0043] Steps 1, 2, 4, 5, and 6 are the same as those in Example 2.

[0044] Step 3: Add 0.0895 g of the powder obtained in Step 2 to deionized water and perform ultrasonic treatment. Then add 0.0045 g of nickel nitrate, 0.0014 g of cobalt nitrate, and 0.0219 g of urea. Stir the resulting mixed solution in a constant temperature water bath at 100 °C for 30 minutes to obtain a reaction product;

[0045] Using the prepared NiCo2O4-In2O3 composite material product to make a gas sensor, relevant gas-sensing performance tests on formaldehyde were carried out:

[0046] Weigh a certain amount of the NiCo2O4-In2O3 composite material product and add water to make a slurry. Coat it on an alumina ceramic tube. There are two gold electrodes and four platinum wires on the alumina ceramic tube, and a nickel-chromium heating wire is in the tube. Weld the ceramic tube on a six-pin base to obtain a gas sensor element, as Figure 1 shown.

[0047] The sensitivity curve of the gas sensor to 10 ppm formaldehyde gas at room temperature is as shown in Figure 2 shown. It can be clearly seen from the figure that several gas sensors all have a response characteristic to formaldehyde gas at room temperature, and their sensitivities are 2.6 for the sensor in Example 1, 2.9 for the sensor in Example 2, 3.1 for the sensor in Example 3, and 2 for the sensor in Example 4. Through comparison, it is found that the sensor in Example 3 performs more excellently in terms of response characteristics. Here, the sensor in Example 3 is selected as the best sensor, and its sensitive performance is further analyzed. Figure 3 Shown is the response-recovery curve of the sensor in Example 3 to 10 ppm formaldehyde gas at room temperature. As can be seen from the figure, the sensor in Example 3 has good response-recovery characteristics to formaldehyde. Figure 4 Shown is the test result of the selectivity of the sensor in Example 3 to 6 kinds of gases at 10 ppm at room temperature. It can be seen that the sensitivity of this sensor to formaldehyde gas is higher than that to methanol, ethanol, toluene, benzene, and acetone gases, indicating excellent selectivity to formaldehyde.

Claims

1. A preparation method of a NiCo2O4-In2O3 composite gas-sensitive material formaldehyde sensor, characterized in that, The method includes the following preparation process: Step 1: Weigh 0.3810 g of indium chloride and 0.1661 g of terephthalic acid, dissolve them in 10 mL of N,N-dimethylacetamide solution, add an anhydrous sodium acetate solution. After stirring the mixed solution in a constant temperature water bath at 100 °C for 30 minutes, a precursor reaction solution is obtained. Step 2: Centrifuge the solution after the reaction in Step 1 to obtain the reaction product, and then wash it repeatedly with distilled water and anhydrous ethanol. Then put the washed reaction product into a drying oven at a constant temperature of 60 °C for 12 hours for drying treatment. After drying, a white powder is obtained. Step 3: Add 0.0895 g of the powder in Step 2 to deionized water for ultrasonic treatment, then add 0.0020 g of nickel nitrate, 0.0073 g of cobalt nitrate and 0.0112 g of urea. Stir the mixed solution in a constant temperature water bath at 100 °C for 30 minutes to obtain the reaction product. Step 4: Centrifuge the solution after the reaction in Step 3 to obtain the reaction product, and then wash it repeatedly with distilled water and anhydrous ethanol. Step 5: Put the reaction product after washing in Step 4 into a drying oven at a constant temperature of 60 °C for 12 hours for drying treatment. After drying is completed, cool it. Step 6: Put the product after drying in Step 5 into a clean crucible and place it in a muffle furnace, calcine it at 500 °C for 4 hours to obtain the NiCo2O4-In2O3 composite material. Use the above NiCo2O4-In2O3 composite material as a gas-sensitive material to fabricate a gas sensor.

2. A preparation method of a NiCo2O4-In2O3 composite gas-sensitive material formaldehyde sensor, characterized in that, The method includes the following preparation process: Step 1: Weigh 0.3810 g of indium chloride and 0.1661 g of terephthalic acid, dissolve them in 10 mL of N,N-dimethylacetamide solution, add an anhydrous sodium acetate solution. After stirring the mixed solution in a constant temperature water bath at 100 °C for 30 minutes, a precursor reaction solution is obtained. Step 2: Centrifuge the solution after the reaction in Step 1 to obtain the reaction product, and then wash it repeatedly with distilled water and anhydrous ethanol. Then put the washed reaction product into a drying oven at a constant temperature of 60 °C for 12 hours for drying treatment. After drying, a white powder is obtained. Step 3: Add 0.0895 g of the powder in Step 2 to deionized water for ultrasonic treatment, then add 0.0045 g of nickel nitrate, 0.0014 g of cobalt nitrate and 0.0219 g of urea. Stir the mixed solution in a constant temperature water bath at 100 °C for 30 minutes to obtain the reaction product. Step 4: Centrifuge the solution after the reaction in Step 3 to obtain the reaction product, and then wash it repeatedly with distilled water and anhydrous ethanol. Step 5: Put the reaction product after washing in Step 4 into a drying oven at a constant temperature of 60 °C for 12 hours for drying treatment. After drying is completed, cool it. Step 6: Put the product after drying in Step 5 into a clean crucible and place it in a muffle furnace, calcine it at 500 °C for 4 hours to obtain the NiCo2O4-In2O3 composite material. Use the above NiCo2O4-In2O3 composite material as a gas-sensitive material to fabricate a gas sensor.

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