Indium trioxide nanotube loaded cobalt oxyhydroxide composite material, and preparation method and application thereof

Abstract

The application discloses an indium trioxide nanotube loaded cobalt oxyhydroxide composite material and application of the composite material in detection of nitrogen oxide, and the composite material is obtained by uniformly mixing indium trioxide nanotubes and Co / MOF in an aqueous solution, adding an etchant to fully react, washing the reaction product to neutral, and then drying to obtain the composite material; the organic skeleton raw material in the Co / MOF is dimethyl imidazole; and the etchant is sodium hydroxide or potassium hydroxide. The method has the advantages of simple process, low cost and no pollution to the environment; the indium trioxide nanotube has the advantages of excellent conductivity, large surface area and chemical stability, and the synthesized low-cost sensing material has high response value at room temperature, rapid detection and good stability, and has excellent selectivity to nitrogen oxide; the composite material has excellent gas sensing performance, and has excellent long-term stability and cycle stability, and has wide application prospect in the field of detection of nitrogen oxide.

Description

Technical Field

[0001] This invention belongs to the field of metal oxide nanomaterials technology, and relates to a gas-sensitive material, specifically to an indium trioxide nanotube-supported cobalt hydroxyl oxide composite material, its preparation method, and its application. Background Technology

[0002] With the increasing severity of air pollution, controlling and improving air quality has attracted worldwide attention. Nitrogen oxides (NOx) are a major pollutant. x The vast majority of NO comes from vehicle exhaust emissions. When a car is running, the high temperature and oxygen-rich conditions during the combustion process in the internal combustion engine generate NO. x NO x As a primary pollutant, it can pose certain health risks. More importantly, nitrogen oxides (NOx)... x It also produces a variety of secondary pollutants. As one of the important substances that generate ozone (O3), its concentration is closely related to photochemical pollution. x It also causes soil acidification. NO released into the atmosphere... x Sulfur dioxide and nitrogen dioxide contribute to acid rain. NO x It also enters rivers, lakes, and oceans through rainwater, and seeps into groundwater, causing eutrophication. Eutrophication can also alter soil chemical composition, leading to soil acidification and ecosystem imbalance. Therefore, real-time and effective detection and monitoring are essential. However, existing detection methods largely rely on expensive laboratory equipment, such as gas chromatography, high-performance liquid chromatography, colorimetry, and luminescence methods. Therefore, convenient NO... x Real-time detection remains a key challenge in practical applications. Compared with other gas detection methods, metal oxide semiconductor-based gas sensors have attracted increasing attention due to their significant advantages such as low cost, small size, good manufacturing flexibility, compatibility with electronic systems, and ease of operation. Many metal oxides, such as cobalt tetroxide, tin dioxide, iron oxide, titanium dioxide, and chromium oxide, have been widely used in the fabrication of nitrogen oxide sensors.

[0003] Indium trioxide (In₂O₃) is a broadband semiconductor with a bandwidth of 3.55–3.75 eV, and is an n-type semiconductor. Nanostructured In₂O₃ has attracted widespread attention due to its good chemical stability and excellent gas-sensing performance. Recently, various composite materials or doped systems have been successfully introduced into In₂O₃-based sensors, such as ZnO-In₂O₃, SnO₂-In₂O₃, Al₂O₃-In₂O₃, CaO-In₂O₃, and CdO-In₂O₃. Adding appropriate dopants to the In₂O₃ matrix is ​​an effective way to improve its sensor performance. The morphology of a material is closely related to its electron transport. One-dimensional indium trioxide nanotubes have a large specific surface area, abundant channels, and unique physical and chemical properties. Their one-dimensional axis provides a pathway for rapid electrical signal transmission by reducing the large potential barrier, thus rapidly becoming a research hotspot in gas-sensing materials. However, indium trioxide is still limited by low conductivity, high operating temperature, and low sensitivity. To improve the gas-sensing performance of indium trioxide, many attempts have been made, such as modification with noble metals, doping with other metals, or combining with other sensor materials.

[0004] CoOOH (cobalt hydroxyoxide) is a non-dense hydroxy oxide, considered a p-type semiconductor with promising applications in catalysis, electrochemistry, and gas sensors. Several studies report that the gas-sensing properties of CoOOH can be enhanced by altering its structure and morphology or by modifying it with metal oxides and noble metals.

[0005] Currently reported gas sensing materials that significantly improve gas sensing performance are made of precious metals, which are expensive, have limited reserves, and are costly. Some composite materials, although they have good gas sensitivity, do not have ideal cycle stability and long-term stability, which leads to further increases in usage costs. Summary of the Invention

[0006] This invention addresses the aforementioned technical problems in the prior art by utilizing the superior conductivity, large surface area, and chemical stability of indium trioxide nanotubes to synthesize a low-cost sensing material with high response values, rapid detection, and good stability at room temperature. Based on this, the present invention protects the following technical solution:

[0007] A cobalt hydroxyl oxide composite material supported on indium oxide nanotubes is obtained by uniformly mixing indium oxide nanotubes and Co / MOF in an aqueous solution, adding an etchant and allowing it to react fully, washing the reaction product until neutral, and then drying it; the organic framework raw material in the Co / MOF is dimethylimidazole; the etchant is sodium hydroxide or potassium hydroxide.

[0008] The indium trioxide nanotubes are obtained by reacting indium nitrate and terephthalic acid as raw materials and N,N dimethylformamide as solvent via a solvothermal method. The reaction products are then washed and dried.

[0009] The Co / MOF is prepared using cobalt nitrate (Co(NO3)2·6H2O) or cobalt chloride (CoCl2) and dimethylimidazole as raw materials.

[0010] The preparation method of the indium trioxide nanotube-supported cobalt hydroxyl oxide composite material described in any of the above claims includes the following steps: indium trioxide nanotubes are added to water and ultrasonically dispersed evenly; Co / MOF is added and mixed evenly; an etchant is added and stirred to allow it to react fully; after the reaction is completed, the mixture is centrifuged, washed with water until neutral, and dried to obtain the target product.

[0011] The mass ratio of indium trioxide nanotubes to Co / MOF is (0.050-0.080):(0.003-0.011) or (0.060-0.080):(0.003-0.009) or (0.060-0.080):(0.005-0.009) or (0.065-0.075):(0.003-0.009) or (0.065-0.075):(0.005-0.009) or 0.07:0.007;

[0012] The amount of etchant added is such that the mass ratio of indium trioxide nanotubes to etchant is (0.050-0.080):(1.0-3.0) or (0.060-0.080):(1.3-2.7) or (0.060-0.080):(1.5-2.5) or (0.065-0.075):(1.5-2.5) or (0.065-0.075):(1.8-2.2) or 0.07:2.

[0013] In the above preparation method, indium trioxide nanotubes are added to deionized water and ultrasonically dispersed for 15-20 min to obtain a homogeneous solution. After adding Co / MOF, the solution is ultrasonically treated for 20-30 min to obtain a homogeneous solution. After adding an etchant, the solution is reacted under stirring for 12-30 h or 12-20 h. The solution is then centrifuged, washed with water until neutral, and dried in an oven at 50-100℃ under vacuum. The mass ratio of indium trioxide nanotubes to deionized water is (0.050-0.080):(10-100) or (0.060-0.080):(10-80) or (0.065-0.075):(10-50) or (0.065-0.075):(10-30) or 0.07:20.

[0014] The preparation method of the indium trioxide nanotubes is as follows: Indium nitrate (In(NO3)3·4.5H2O) is added to DMF for dispersion and dissolution, and then terephthalic acid is added to dissolve and disperse evenly to obtain a mixed solution. The mixed solution is placed in an oven for solvothermal reaction at 60-120℃ for 2-8 hours. After the reaction is completed and cooled to room temperature, the reaction product is washed and dried to obtain indium trioxide nanotubes. The ratio of raw materials to solvent is In(NO3)3·4.5H2O:terephthalic acid:DMF of 0.05-0.15g:0.03-0.07g:10-20mL or 0.07-0.12g:0.04-0.06g:12-18mL or 0.1g:0.05g:15mL.

[0015] Preferably, the mixed solution is placed in an oven at 80-120℃ or 90-110℃ for a solvothermal reaction for 4-8 hours. After the reaction is completed and cooled to room temperature, the reaction product is washed with ethanol and then placed in an oven at 50-100℃, 50-80℃ or 50-70℃ for 4-10 hours or 5-8 hours for drying.

[0016] The preparation method of Co / MOF is as follows: Cobalt nitrate is added to water to obtain a cobalt nitrate solution, dimethylimidazole is added to water to obtain a dimethylimidazole solution, the dimethylimidazole solution is slowly added to the cobalt nitrate solution, stirred and mixed, and allowed to stand until the reaction is complete. The product is centrifuged, washed, and dried to obtain Co / MOF. The mass ratio of cobalt nitrate to dimethylimidazole is 0.7-1.3:1, 0.9-1.1:1, or 1:1. The concentration of cobalt nitrate or cobalt chloride solution is 0.01-0.1 g / ml, 0.03-0.08 g / ml, 0.04-0.06 g / ml, or 0.05 g / ml. The concentration of dimethylimidazole solution is 0.01-0.1 g / ml, 0.03-0.08 g / ml, 0.04-0.06 g / ml, or 0.05 g / ml.

[0017] Preferably, the dimethylimidazole solution is slowly added to the cobalt nitrate solution, stirred and mixed, and then allowed to stand for 20-30h, 20-26h or 22-26h. The product is then centrifuged, washed with water, and dried in an oven at 50-100℃, 50-80℃ or 50-70℃ for 4-10h or 5-8h.

[0018] The application of the indium trioxide nanotube-supported cobalt hydroxyl oxide composite material prepared by any of the above preparation methods in the detection of nitrogen oxides, wherein the nitrogen oxides include NO and NO2; preferably, the nitrogen oxides are NO2.

[0019] In the above-mentioned application technical solutions, the concentration of nitrogen oxides is 0.07-100ppm or 0.08-70ppm or 0.09-50ppm or 0.07-50ppm or 0.07-20ppm or 0.1-30ppm or 0.1-10ppm.

[0020] Application of the indium trioxide nanotube-supported cobalt hydroxyl oxide composite material prepared by any of the above preparation methods in the preparation of sensing materials for detecting nitrogen oxides.

[0021] The principle of this invention is:

[0022] Specific surface area and morphology significantly influence gas sensing performance. Increasing the specific surface area of ​​materials, utilizing the size effect of nanomaterials, gives one-dimensional nanomaterials a greater advantage in gas sensing applications. The large specific surface area of ​​one-dimensional nanomaterials increases the contact between the material and reactants, facilitating the adsorption and desorption of more target gas molecules. Electrons can transport along the axis of one-dimensional nanomaterials, significantly improving the electron diffusion rate within the material. The presence of numerous active sites on the surface of one-dimensional nanomaterials enhances their gas sensing performance; however, the presence of numerous homojunctions between In₂O₃ molecules leads to severe electron scattering, resulting in high sensor resistance. The introduction of CoOOH promotes the formation of pn heterojunctions, allowing charge carriers (free electrons from In₂O₃ and holes from CoOOH) at the n-In₂O₃ and p-CoOOH interfaces to diffuse from high-concentration regions to low-concentration regions until the Fermi level reaches equilibrium. This results in a wide space charge region and a potential energy barrier at the interface, essentially creating a region of charge carrier depletion. Therefore, the sensor's resistance modulation capability is enhanced, which is the fundamental reason why heterojunction sensors outperform single-metal oxide sensors. In addition, the hierarchical structure formed by adding CoOOH provides abundant porosity and a large surface area. The synthesized product consists of a large number of nanotubes with an average length of approximately 3-10 μm and a diameter of approximately 1.4-1.5 μm, where CoOOH nanoparticles are loaded onto In2O3 nanotubes. Co / MOF is etched with a strong base to form CoOOH, which exhibits better stability and higher conductivity. Besides the homojunctions between In2O3 nanotubes, numerous In2O3 / CoOOH contacts are generated in the sensing layer after composite with CoOOH. Due to the different work functions of In2O3 and CoOOH, a Schottky barrier is formed. Therefore, electron diffusion is easier in the In2O3 nanotube / CoOOH composite material than in pure In2O3 nanotubes. When the sensor is in the air, oxygen molecules adsorb onto the In2O3 nanotube / CoOOH and spontaneously diffuse to the heterojunction due to the concentration gradient. The adsorbed oxygen can capture electrons in the conduction band of In2O3 nanotubes / CoOOH, forming chemisorbed oxygen ions (mainly O2). -(As can be seen from formulas 1 and 2). Therefore, an electron depletion layer forms on both the surface and interface of the In2O3 nanotube / CoOOH, resulting in a high potential barrier at the heterojunction. Thus, when equilibrium is reached, the resistance of the sensing layer remains at a relatively high level. The main reaction equations are as follows:

[0023]

[0024] O2(ad)+e - →O2 - (ad) (2)

[0025] NO+O2 - (ads)→NO3 - (3)

[0026] NO+O2 - (ads)→NO2 - +O (4)

[0027] NO + O → NO2 (5)

[0028] NO2+e - →NO2 - (6)

[0029] 2NO2+O2 - (ads)+e - →2NO3 - (7)

[0030] When the sensing layer is exposed to the target gas, nitrogen oxides (NOx) x It can react with O2 on the surface of nanotubes. - A reaction occurs, disrupting the equilibrium. O2 in the interface region... - It will diffuse back towards the surface and react with excess NO. x The reaction continues until a new equilibrium state is formed. In NO... x and O2 - During the reaction, trapped electrons are released, causing the electron depletion layer to narrow. Therefore, the barrier height at the heterojunction decreases to a relatively low level, leading to an increase in the conductivity of the sensing layer. The higher surface area and the provision of numerous active sites facilitate the absorption / diffusion of gas molecules, which will improve NO sensing. x The reaction between the In₂O₃ nanotube / CoOOH sensor and the chemisorbed oxygen. Therefore, the sensitivity of the In₂O₃ nanotube / CoOOH sensor is higher than that of the pure In₂O₃ sensor. When NO x This phenomenon is more pronounced at higher concentrations because more NO is produced. x The gas diffuses into the sensing layer and reacts with oxygen ions chemically adsorbed on the surface.

[0031] The beneficial effects of this invention are:

[0032] 1. The method of the present invention is simple, low-cost, and does not pollute the environment.

[0033] 2. Taking advantage of the superior conductivity, large surface area and chemical stability of indium trioxide nanotubes, a low-cost sensing material with high response value, fast detection and good stability at room temperature is synthesized. It has excellent selectivity for nitrogen oxides, with a response value of over 80 for 10 ppm nitrogen oxides at room temperature and a response time of 141s.

[0034] 3. The composite material of the present invention has excellent gas-sensing properties, as well as excellent long-term stability and cyclic stability, and has broad application prospects in the field of nitrogen oxide detection. Attached Figure Description

[0035] Figure 1 The XRD patterns of the indium trioxide nanotube-supported cobalt hydroxyl oxide composite material of the present invention and the control indium trioxide nanotube are shown.

[0036] Figure 2 This is a scanning SEM image of the indium trioxide nanotube-supported cobalt hydroxyl oxide composite material of the present invention;

[0037] Figure 3 The diagram shows the dynamic response of the indium trioxide nanotube-supported cobalt hydroxyl oxide composite material and the control indium trioxide nanotube to different concentrations of nitrogen oxides.

[0038] Figure 4 The figure shows the results of five cycles of stability testing of the indium trioxide nanotube-supported cobalt hydroxyl oxide composite material of the present invention and the control indium trioxide nanotube against 10 ppm nitrogen oxides.

[0039] Figure 5 The linear fitting of the response values ​​of different concentrations of nitrogen oxides to the indium trioxide nanotube-supported cobalt hydroxyl oxide composite material and the control indium trioxide nanotube of the present invention is shown.

[0040] Figure 6 The graph shows the selectivity test results of nitrogen oxides for the indium trioxide nanotube-supported cobalt hydroxyl oxide composite material of the present invention and the control indium trioxide nanotube.

[0041] Figure 7 The figure shows the long-term stability test results of the indium trioxide nanotube-supported cobalt hydroxyl oxide composite material and the control indium trioxide nanotube for nitrogen oxides in this invention.

[0042] Explanation of reference numerals in the figures: In2O3 indicates the indium trioxide nanotube control prepared by the method in Example 1, and In2O3 / CoOOH indicates the indium trioxide nanotube-supported cobalt hydroxyl oxide composite material of the present invention. In the preparation process, the raw material ratio is 0.07g indium trioxide nanotubes to 0.007g Co / MOF. Detailed Implementation

[0043] The present invention will be further described below with reference to embodiments, but these embodiments are not intended to limit the scope of the invention.

[0044] Unless otherwise specified, the experimental methods in the following examples are conventional methods; the chemical reagents and materials used are conventional reagents and materials in the art and can be obtained commercially.

[0045] Example 1: Preparation of Indium Trioxide Nanotubes

[0046] Prepared according to the method described in the following literature: Yuanyuan, L., et al. (2021). "Metal-organic framework (MOF) derived In2O3 and g-C3N4 composite for superior NOx gas-sensing performance at room temperature." Sensors and Actuators B: Chemical.

[0047] The specific steps are as follows:

[0048] 1) Weigh 0.1g of indium nitrate (In(NO3)3·4.5H2O) and add it to 15mL of N-N dimethylformamide (DMF). Sonicate for 30min to disperse and dissolve it. Then weigh and add 0.05g of terephthalic acid (H2BDC). Stir for 30min and then sonicate for 30min.

[0049] 2) The mixed solution obtained in step 1) was placed into a 25 mL reaction vessel with a polytetrafluoroethylene liner and placed in an oven at 100℃ (i.e., solvothermal temperature) for 4 h (i.e., solvothermal time). After the reaction was completed and cooled to room temperature, the product was washed three times with ethanol and dried in a 60℃ oven under vacuum for 6 h to obtain indium trioxide nanotubes (In2O3 nanotubes).

[0050] This embodiment also tested the gas-sensing properties of In2O3 nanotubes prepared with different solvothermal times and temperatures for nitrogen oxides (NO2), and the testing method was the same as that in Example 3.

[0051] Comparison of different solvothermal temperatures: Using the above method, the In2O3 nanotubes were solvothermal at 60, 80, 100, and 120℃ for 4 hours respectively. The results showed that the response values ​​of In2O3 nanotubes prepared at 60, 80, 100, and 120℃ to 10 ppm nitrogen oxides at room temperature were 19.7, 22.6, 30.4, and 23.5 respectively, indicating that the In2O3 nanotubes prepared at 100℃ had the highest response value to 10 ppm nitrogen oxides.

[0052] Comparison of different solvothermal times: Using the above method, solvothermal treatment was performed at 100℃ for 2, 4, 6, and 8 hours respectively. The response values ​​of In2O3 nanotubes prepared by solvothermal treatment for 2, 4, 6, and 8 hours to 10 ppm nitrogen oxides at room temperature were 12.1, 33.4, 25.3, and 26.1 respectively. This shows that the In2O3 nanotubes prepared by solvothermal treatment for 4 hours at 100℃ had the highest response value to 10 ppm nitrogen oxides.

[0053] Example 2: Preparation of Co / MOF

[0054] Follow these steps:

[0055] 1 g of cobalt nitrate (Co(NO3)2·6H2O) was weighed and added to 20 mL of deionized water, and sonicated for 10 min to obtain solution A. 1 g of dimethylimidazole (CAS No.: 693-98-1) was weighed and added to 20 mL of deionized water, and stirred for 10 min to obtain solution B. Solution B was slowly added to solution A, stirred for 10 min, and then allowed to stand for 24 h. The product was centrifuged, washed three times with water, and dried in a vacuum oven at 60 °C for 6 h to obtain the cobalt precursor, i.e., the cobalt-organic framework (Co / MOF) material.

[0056] Example 3: Preparation of the indium trioxide nanotube-supported cobalt hydroxyl oxide composite material of the present invention and performance testing.

[0057] I. Preparation Method

[0058] Follow these steps:

[0059] Weigh 70 mg of the In2O3 nanotubes prepared in Example 1 and add them to 20 mL of deionized water. Sonicate for 15 min, then add 7 mg of the Co / MOF prepared in Example 2 and sonicate for 30 min to obtain a homogeneous solution. Add 2 g of sodium hydroxide and stir for 12 h. Centrifuge, wash with water until neutral, and dry in a 60 °C oven under vacuum for 6 h to obtain the indium trioxide nanotube-supported cobalt hydroxyl oxide composite material of the present invention (denoted as In2O3 / CoOOH-7).

[0060] The XRD patterns of the composite material show its crystal structure and diffraction planes, such as... Figure 1As shown, the XRD pattern of the control In2O3 nanotubes prepared in Example 1 shows that their peak positions are 21.5°, 30.58°, 33.10°, 34.46°, 45.7°, 51.03°, and 60.67°, respectively.

[211] ,

[222] ,

[321] ,

[400] ,

[431] ,

[440] , and

[622] represent the diffraction planes. All diffraction peaks in the XRD pattern are indexed to the orthorhombic phase In2O3 with JCPDS card number (06-0416).

[0061] No diffraction peaks of CoOOH were observed in the XRD pattern of In2O3 / CoOOH-7, which is attributed to the low content of CoOOH.

[0062] SEM image of In2O3 / CoOOH-7 as shown below Figure 2 As shown, the synthesized product consists of a large number of nanotubes with a length of about 3-10 μm, with CoOOH nanoparticles loaded on In2O3 nanotubes.

[0063] II. Gas Sensing Performance Test for Nitrogen Oxides

[0064] Test method:

[0065] The target gas is NO2, which diffuses within an 18L air-filled chamber to create a test atmosphere of a specific concentration. The gas sensitivity test is conducted entirely at room temperature. The gas sensor performance testing instrument consists of an electrical signal generation system, a testing system, and an information collection system and information processor. The testing system is a gas sensitivity tester (model: WS-30B, made in Zhengzhou, China).

[0066] Preparation before testing: Fabrication of the gas-sensitive element. Take 1 mg of the previously prepared In2O3 / CoOOH-7 composite material in a mortar, add 1 mL of anhydrous ethanol, and mix into a paste. Use a brush to evenly and thinly apply the paste to the surface of the interdigitated electrode (size: 10×8×0.15 mm). Transfer to an 80℃ forced-air oven to dry for 6 hours to ensure complete evaporation of the ethanol.

[0067] Gas Sensitive Tester Operating Procedures: Insert the gas-sensitive element into the test circuit board, and adjust the test baseline to a suitable position by adjusting the load resistor. After the baseline stabilizes, begin the formal test. For the first 300 seconds, measure the air resistance R of the gas-sensitive element in clean air. a Turn on the built-in fan inside the chamber, and inject a certain amount of target gas into the test chamber after 300 seconds, then quickly seal it. The resistance reading at this time is the resistance value R of the gas-sensitive element in the target gas. g The gas concentration and the volume of the volatile liquid are calculated using formula (8). After the data acquisition is completed, the sealed cavity is opened, the target gas in the cavity is drained, the target gas concentration is changed, and the above steps are repeated.

[0068] The formulas for calculating gaseous concentration and corresponding liquid volume are derived from the ideal gas law PV = nRT:

[0069] V 气 =(P 瓶 *C ppm *V 瓶 *M 气 ) / (22.4*ρ 气 *ω 气 (8)

[0070] In formula (8), M 气 V 气 ρ 气 ω 气 , , and , respectively, represent the molar mass, volume, density, and mass fraction of the liquid corresponding to the target gas; P 瓶 and V 瓶 and are the pressure and volume of the space containing the gas, respectively; that is, C ppm The desired gas concentration is given. The material's sensitivity (response value) is defined as: R = R0 g / R a R represents the response value.

[0071] 1. Dynamic response test

[0072] The results are as follows Figure 3 As shown, experimental results indicate that the response value increases with increasing NO2 gas concentration. At room temperature (25℃), the response values ​​of In2O3 nanotubes (i.e., the control prepared in Example 1) to 0.1, 0.3, 0.5, 0.7, 1, 3, 5, 7, and 10 ppm NO2 were 1.0, 1.2, 2.1, 5.2, 8.7, 11.4, 18.3, 26.5, and 33.4, respectively. The response values ​​of the composite material In2O3 / CoOOH-7 of this invention to 0.1, 0.3, 0.5, 0.7, 1, 3, 5, 7, and 10 ppm NO2 were 1.2, 2.1, 3, 6, 17, 55, 71, 75, and 87, respectively.

[0073] 2. Cyclic stability test

[0074] Test Method: Insert the gas-sensitive element into the test circuit board and adjust the test baseline to a suitable position by adjusting the load resistor. After the baseline stabilizes, begin the formal test. Turn on the built-in fan inside the chamber and measure the air resistance R of the gas-sensitive element in clean air for the first 300 seconds. a After 300 seconds, 10 ppm NO2 gas is injected into the test chamber and quickly sealed. The resistance reading at this time is the resistance value R of the gas-sensitive element in the target gas. gAfter data acquisition is complete, open the sealed cavity, purge the target gas from the cavity, and repeat the above steps four times to measure the material's cyclic stability.

[0075] The results of five cycles of testing at 25℃ with 10ppm NO2 gas are as follows: Figure 4 As shown, the results indicate that the response value fluctuations of both the control In2O3 nanotube and the composite material In2O3 / CoOOH-7 of this invention are less than 5% of the mean, indicating that both materials have good stability.

[0076] 3. Linear fitting of NOx concentrations and response values

[0077] Figure 5 (a) and Figure 5 (b) illustrates the relationship between the sensor's response value y and the gas concentration x. The fitting function equations for pure In2O3 and the In2O3 / CoOOH-7 composite material are (9) and (10), respectively, where the fitting correlation coefficients are R0 and R1, respectively. 2 =0.98742 and R 2 =0.9836, reflecting a good functional relationship between the response values ​​of the two samples and the NO2 gas concentration. The fitting function equations for low gas concentration and sensor response value are (11) and (12). Based on the empirical equations (13) and (14), the detection limits of pure In2O3 and In2O3 / CoOOH-7 composite material were calculated to be 82 ppb and 70 ppb, respectively.

[0078] y = -0.24456x 2 +0.16503x-0.01179(R 2 =0.98742) (9)

[0079] y = -0.90681x 2 +21.14584x-2.79413(R 2 =0.9836) (10)

[0080] y = 2.72737x + 1.1695(R) 2 =0.9895) (11)

[0081] y = 10.74302x + 0.97207(R) 2 =0.98137) (12)

[0082]

[0083]

[0084] In the formula, S represents the standard deviation of the linear fitting curve, N represents the total number of data collection points, slope is the slope of empirical equations (11) and (12), and D L This is the lowest detection limit.

[0085] 4. Gas selectivity test

[0086] Following the previously described method for testing the gas-sensing performance of NO2, gas selectivity tests were conducted on the prepared pure In2O3 nanotubes and the In2O3 / CoOOH-7 composite material by introducing 10 ppm of ammonia, methanol, ethanol, hydrogen sulfide, and acetone, respectively.

[0087] The results are as follows Figure 6 As shown, experimental results indicate that the pure In2O3 and the In2O3 / CoOOH-7 composite material of the present invention exhibit excellent selectivity for nitrogen oxides in the presence of 10 ppm interfering gases (ammonia, methanol, ethanol, hydrogen sulfide, acetone).

[0088] 5. Long-term stability test

[0089] Following the previous method for testing the gas-sensitivity of nitrogen oxides, the long-term stability of the prepared In2O3 / CoOOH-7 composite material was tested, with the NO2 gas sensitivity being tested every five days for thirty consecutive days.

[0090] The results are as follows Figure 7 As shown, the results indicate that after 30 days of continuous testing, the response value of the In2O3 / CoOOH-7 composite material decays very little, with the fluctuation range of the maximum and minimum values ​​within 5%, indicating that the composite material of the present invention has good long-term stability.

[0091] Example 4: Experiments with different ratios of indium trioxide and Co / MOF

[0092] In2O3 / CoOOH composite materials with different ratios of In2O3 nanotubes and Co / MOF were prepared according to the method in Example 3. 70 mg of indium trioxide nanotubes were weighed and mixed with different masses of Co / MOF. Different amounts of Co / MOF were added: 0.003, 0.005, 0.007, 0.009, and 0.011 g. The gas-sensing performance of the prepared samples for nitrogen oxides (NO2) was tested (using the same method as in Example 3). The results are as follows:

[0093] Sample 1: The mass ratio of In2O3 nanotubes to Co / MOF was 0.07:0.003, and the response value of the prepared In2O3 / CoOOH-3 to 10 ppm nitrogen oxides was 43.6.

[0094] Sample 2: The mass ratio of In2O3 nanotubes to Co / MOF was 0.07:0.005, and the prepared In2O3 / CoOOH-5 had a response value of 71.8 to 10 ppm nitrogen oxides.

[0095] Sample 3: The mass ratio of In2O3 nanotubes to Co / MOF is 0.07:0.007 (i.e. the sample prepared in Example 2). The prepared In2O3 / CoOOH-7 has a response value of 87 to 10 ppm nitrogen oxides.

[0096] Sample 4: The mass ratio of In2O3 nanotubes to Co / MOF was 0.07:0.009, and the prepared In2O3 / CoOOH-9 had a response value of 64.1 to 10 ppm nitrogen oxides.

[0097] Sample 5: The mass ratio of In2O3 nanotubes to Co / MOF was 0.07:0.011, and the prepared In2O3 / CoOOH-11 had a response value of 50.7 to 10 ppm nitrogen oxides.

[0098] The results above show that when the mass ratio of indium trioxide to Co / MOF is 0.07:0.007, the prepared In2O3 / CoOOH-7 exhibits the highest response value to 10 ppm nitrogen oxides.

Claims

1. The application of indium trioxide nanotube-supported cobalt hydroxyl oxide composite material in the detection of nitrogen oxides or in the preparation of sensing materials for detecting nitrogen oxides, characterized in that: The nitrogen oxides include NO and NO2. The preparation method of the composite material includes the following steps: indium trioxide nanotubes are added to water and ultrasonically dispersed evenly; Co / MOF is added and mixed evenly; an etchant is added and the mixture is reacted under stirring for 12-30 h; after the reaction is completed, the mixture is centrifuged, washed with water until neutral, and dried to obtain the target product; the organic framework raw material in the Co / MOF is dimethylimidazole, and the Co / MOF is prepared using cobalt nitrate or cobalt chloride and dimethylimidazole as raw materials; the etchant is sodium hydroxide or potassium hydroxide. The mass ratio of indium trioxide nanotubes to Co / MOF is (0.050-0.080) : (0.003-0.011). The amount of etchant added is such that the mass ratio of indium trioxide nanotubes to etchant is (0.050-0.080): (1.0-3.0).

2. The application according to claim 1, characterized in that: The concentration of the nitrogen oxides is 0.07-100 ppm.

3. The application according to claim 1, characterized in that: The preparation method of the composite material includes the following steps: adding indium trioxide nanotubes to deionized water and ultrasonically dispersing for 15-20 min to obtain a uniform solution; adding Co / MOF and ultrasonically treating for 20-30 min to obtain a uniform solution; adding an etchant and reacting under stirring for 12-30 h; centrifuging; washing with water until neutral; and drying in an oven at 50-100 ℃ under vacuum conditions; the mass ratio of indium trioxide nanotubes to deionized water is (0.050-0.080): (10-100).

4. The application according to claim 1, characterized in that: The preparation method of the indium trioxide nanotubes is as follows: Indium nitrate is added to DMF for dispersion and dissolution, then terephthalic acid is added to dissolve and disperse evenly to obtain a mixed solution. The mixed solution is placed in an oven at 60-120 ℃ for solvothermal reaction for 2-8 h. After the reaction is completed and cooled to room temperature, the reaction product is washed and dried to obtain indium trioxide nanotubes. The ratio of raw materials to solvent is In(NO3)3•4.5H2O : terephthalic acid : DMF = 0.05-0.15g : 0.03-0.07g : 10-20 mL.

5. The application according to claim 1, characterized in that: The preparation method of Co / MOF is as follows: Cobalt nitrate is added to water to obtain a cobalt nitrate solution, dimethylimidazole is added to water to obtain a dimethylimidazole solution, the dimethylimidazole solution is slowly added to the cobalt nitrate solution, stirred and mixed, and allowed to stand until the reaction is complete. The product is centrifuged, washed, and dried to obtain Co / MOF; wherein, the mass ratio of cobalt nitrate to dimethylimidazole is 0.7-1.3:1, the concentration of cobalt nitrate or cobalt chloride solution is 0.01-0.1 g / ml, and the concentration of dimethylimidazole solution is 0.01-0.1 g / ml.

6. The application according to claim 5, characterized in that: Slowly add dimethylimidazole solution to cobalt nitrate solution, stir and mix well, let stand for 20-30 hours, centrifuge the product, wash with water, and dry in an oven at 50-100 ℃ for 4-10 hours.

Images