Neodymium oxide indium oxide composite porous nanorod material and preparation method and application thereof

Abstract

The application discloses a neodymium oxide-indium oxide composite porous nanorod material and a preparation method and application thereof, and comprises an indium oxide porous nanorod and a neodymium oxide layer loaded on the surface of the indium oxide porous nanorod; and the indium oxide porous nanorod is assembled by indium oxide nanoparticles. The prepared neodymium oxide-indium oxide composite porous nanorod material is composed of a large number of nanoparticle accumulations, the unique micro-morphology characteristics of the material are utilized, the specific surface area and gas diffusion path of the material are significantly increased, and therefore the sensitivity and identification capability of the material to H2S gas are improved.

Description

Technical Field

[0001] This invention belongs to the field of gas-sensitive materials technology, specifically relating to a neodymium oxide-indium oxide composite porous nanorod material, its preparation method, and its application. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Hydrogen sulfide (H2S) is a colorless, toxic gas with a strong, rotten egg-like odor. It is produced in large quantities during the production processes of synthetic fibers, petroleum refining, gas manufacturing, wastewater treatment, and papermaking, as well as during the decomposition of organic matter. Excessive emissions of hydrogen sulfide pose a significant threat to the atmospheric environment and human health. Furthermore, hydrogen sulfide is considered a biomarker for diseases such as asthma, chronic obstructive pulmonary disease (COPD), and halitosis, and its concentration in exhaled breath can be used for early, non-invasive diagnosis.

[0004] Resistive semiconductor metal oxide gas sensors are commonly used H2S concentration sensors. They work by exchanging electrons between gas molecules and metal oxides, altering the material's resistance after gas adsorption, thus demonstrating a response to gas molecules. However, current H2S sensor applications often involve high humidity environments. Under high humidity conditions, traditional semiconductor metal oxide gas sensors suffer from performance degradation because water molecules in the testing environment react with pre-adsorbed oxygen ions on the material surface to form stable surface hydroxyl groups. This reduces the material's resistivity and occupies gas-sensing adsorption sites, inhibiting its gas-sensing performance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a neodymium oxide-indium oxide composite porous nanorod material, its preparation method, and its applications.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] In a first aspect, the present invention provides a neodymium oxide-indium oxide composite porous nanorod material, comprising indium oxide porous nanorods and a neodymium oxide layer supported on the surface of the indium oxide porous nanorods; the indium oxide porous nanorods are assembled from indium oxide nanoparticles;

[0008] The indium oxide nanorods have a diameter of 300-500 nm and a length of 1-5 μm;

[0009] The particle size of indium oxide nanoparticles is 0.2-1 nm, and the particle size of neodymium oxide is 0.2-1 nm.

[0010] The molar ratio of neodymium oxide to indium oxide is 0.01-0.2:1.

[0011] Indium oxide (IO) is an n-type semiconductor with high conductivity and a narrow bandgap. As a composite matrix, it provides the main gas-sensitive reaction sites. Neodymium oxide (NdO) is also an n-type semiconductor. When loaded onto the surface of IO, it can form a heterojunction at the interface between heteromaterials, increasing the intergranular barrier and widening the space charge layer thickness, which is beneficial for optimizing gas-sensitive performance. In addition, NdO is also a highly hygroscopic material. Loading it onto the surface of IO can reduce the adsorption of water vapor on the surface of IO and inhibit the formation of surface hydroxyl groups, thereby effectively protecting the gas-sensitive reaction sites of IO from environmental humidity interference and improving the material's humidity resistance.

[0012] In some embodiments, the indium oxide nanorods have a cubic phase crystal structure. Compared to rhombic corundum phase indium oxide, the cubic phase structure has higher structural stability, ensuring the stability of the material structure and the application of the corresponding sensors over a wide temperature range.

[0013] In some embodiments, the neodymium oxide has a hexagonal crystal structure. Compared to other neodymium oxide crystal structures, cubic neodymium oxide has a lower semiconductor band gap, better electrical conductivity, and higher carrier concentration. When combined with an indium oxide matrix, it can provide more free electrons to the indium oxide matrix, further optimizing the gas-sensing performance.

[0014] Secondly, the present invention provides a method for preparing the neodymium oxide-indium oxide composite porous nanorod material, comprising the following steps:

[0015] Indium source and weakly reducing or non-reducing alkaline source are dissolved in a molar ratio of 1:5-15, mixed well, and then subjected to a solvothermal reaction under closed conditions to prepare indium hydroxide precursor. The indium hydroxide precursor is then annealed to obtain indium oxide porous nanorods.

[0016] Indium oxide porous nanorods were uniformly dispersed in a solvent, and then a neodymium source was added to dissolve and mix. The mixture was then dried, and the dried product was annealed to obtain a neodymium oxide-indium oxide composite porous nanorod material.

[0017] In this synthesis, the indium source provides indium ions for the solvothermal reaction, while the alkali source adjusts the pH conditions of the solvothermal reaction, providing hydroxide ions to combine with indium ions to form the indium hydroxide precursor. However, alkali sources with strong reducing properties (such as hydrazine hydrate and ethylenediamine) also provide a strong reducing atmosphere for the solvothermal reaction, causing the final precursor product to change from indium hydroxide to indium oxide. This results in a metastable rhombic corundum phase indium oxide structure instead of a cubic phase indium oxide, affecting both the morphology and crystal structure of the synthesized product. Therefore, weakly reducing or non-reducing raw materials are selected as the alkali source in the synthesis.

[0018] In this invention, an alkaline source is used as a reactant to regulate the alkalinity of the solution. Without the addition of an additional template directing agent, more nucleation sites are generated during the growth of the indium hydroxide precursor, which eventually grows into a nanorod structure with a large number of nanoparticles. Such a material structure is beneficial for providing a larger specific surface area, abundant gas adsorption sites and diffusion paths, which helps to improve the gas-sensing performance.

[0019] The temperature of the solvothermal reaction is 100-110℃, and the time is 2-24h.

[0020] Furthermore, a neodymium oxide-indium oxide composite structure was prepared using a simple chemical deposition process. The loose structure between the grains provides composite deposition sites for neodymium oxide. At the same time, the loading of neodymium oxide on the surface will not cover the effective gas-sensitive adsorption sites of indium oxide in large quantities, thus avoiding serious deterioration of gas-sensitive performance. This is beneficial for multi-level and comprehensive protection of the gas-sensitive sites of indium oxide to improve its humidity resistance stability. Meanwhile, the synthesis design scheme is simple, feasible, safe and environmentally friendly, which is conducive to industrial production.

[0021] In some embodiments, the indium source is selected from any one or a combination of indium chloride (InCl3), indium nitrate (In(NO3)3), or indium acetate (In(CH3COO)3).

[0022] In some embodiments, the alkali source is selected from urea (CH4N2O) and hexamethylenetetramine (C6H2O). 12 One or a combination of N4, sodium hydroxide (NaOH) or ammonia (NH3·H2O).

[0023] In some embodiments, the solvent used in the solvothermal reaction is one or a mixture of anhydrous ethanol (C2H6O), ethylene glycol (C2H6O2), or deionized water (H2O). All selected reaction solvents are polar solvents, while the precursor product obtained by solvothermal reaction is nonpolar indium hydroxide. Therefore, the precipitation rate of indium hydroxide is inhibited by the polar solvent, which helps to form a nanorod-like morphology and avoids the large-scale nucleation of indium hydroxide in an alkaline environment, ultimately forming a nanoparticle structure.

[0024] In some embodiments, the indium hydroxide precursor is annealed at a temperature of 400-600°C for 1-3 hours.

[0025] In some embodiments, the neodymium source is one or a combination of neodymium acetate (Nd(CH3COO)3), neodymium sulfate (Nd2(SO4)3), or neodymium nitrate (Nd(NO3)3).

[0026] Preferably, the mass ratio of indium oxide porous nanorods to neodymium source is 0.01-0.2:1.

[0027] In some embodiments, the temperature for drying the mixed solution is 60-120°C.

[0028] In some embodiments, the temperature for annealing the dried product is 300-500°C, and the annealing time is 1-5 hours.

[0029] Thirdly, the present invention provides the application of the neodymium oxide-indium oxide composite porous nanorod material in the preparation of gas-sensitive elements or the detection of H2S concentration.

[0030] Fourthly, the present invention provides a gas-sensitive element comprising a ceramic substrate and a gas-sensitive material, wherein the gas-sensitive material is the neodymium oxide-indium oxide composite porous nanorod material, and the gas-sensitive material is attached to the ceramic substrate.

[0031] The method for preparing a gas-sensitive element includes the following steps:

[0032] The prepared neodymium oxide and indium oxide composite porous nanorod material was mixed with a solvent at a certain mass ratio and then ground evenly to form a slurry. The slurry was then evenly coated onto a ceramic substrate, which was then placed in an oven for drying. After drying at a certain temperature for a period of time, the substrate was removed and the coating and drying process was repeated several times. Finally, the ceramic substrate coated with the gas-sensitive material was placed in an oven and dried thoroughly at a certain temperature to obtain the gas-sensitive element.

[0033] The solvent is one or a combination of deionized water (H2O), anhydrous ethanol (C2H6O) and N,N-dimethylformamide (C3H7NO); the mass ratio of neodymium oxide indium oxide composite porous nanorod material to solvent is 1:3-1, such as 1:3, 1:4, 1:5, 1:6, 1:7, or 1:1.

[0034] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0035] (1) The neodymium oxide and indium oxide composite porous nanorod material prepared by the present invention is composed of a large number of nanoparticles. By utilizing its unique microstructure characteristics, the specific surface area and gas diffusion path of the material are significantly increased, thereby improving the material's sensitivity and recognition ability to H2S gas.

[0036] This invention utilizes a simple chemical deposition method to achieve uniform loading of neodymium oxide onto indium oxide components. This composite system leverages the high affinity of neodymium oxide for water molecules and surface hydroxyl groups, enabling preferential adsorption of these molecules under high humidity conditions. This avoids the deterioration of the gas-sensing performance of the indium oxide matrix material and the occupation of saturated gas adsorption sites caused by high ambient humidity, thus exhibiting excellent humidity resistance to gas sensing performance.

[0037] (2) The neodymium oxide-indium oxide composite porous nanorod material prepared in this invention exhibits extremely excellent humidity resistance stability in H2S detection under high environmental humidity conditions. At 10% RH and 300℃, the response value for 10 ppm H2S reaches 10.1, which is higher than 93.5% under a dry testing environment (30% RH). Simultaneously, it still exhibits excellent selectivity in H2S detection under high environmental humidity conditions, effectively avoiding the influence of other interfering gases on the gas-sensitive material's H2S detection. These advantages ensure the gas-sensitive material's ability to detect H2S under various high humidity environments and effectively eliminate the severe interference caused by changes in relative humidity and various interfering gases on the sensor's operating signal.

[0038] (3) The neodymium oxide-indium oxide composite porous nanorod material prepared in this invention exhibits excellent H2S sensitivity over a wide temperature range. The optimal response value for 10 ppm H2S reaches 523.7 at 100℃, and the response value for 10 ppm H2S also reaches 10.1 at 300℃. It also exhibits excellent selectivity for H2S, enabling effective detection and identification of H2S molecular signals in different interference environments under wide operating temperature conditions, adapting to different sensor application temperature conditions.

[0039] (4) The preparation process of the present invention is simple, the raw materials and equipment are readily available, the synthesis does not pollute the environment, the synthesis efficiency is high, and it has a high economic effect, making it suitable for industrial production. Attached Figure Description

[0040] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0041] Figure 1 The XRD diffraction patterns are those of indium oxide porous nanorods and neodymium oxide indium oxide composite porous nanorods prepared in Examples 1-5 of this invention.

[0042] Figure 2The images show the SEM images of indium oxide porous nanorods and neodymium oxide-indium oxide composite porous nanorods prepared in Examples 1-5 of this invention, and the EDS image of the material prepared in Example 5. Figures a1 and a2 are SEM images of the indium oxide porous nanorod sample prepared in Example 1; Figures b1 and b2 are SEM images of the neodymium oxide-indium oxide composite porous nanorod material prepared in Example 2; Figures c1 and c2 are SEM images of the neodymium oxide-indium oxide composite porous nanorod material prepared in Example 3; Figures d1 and d2 are SEM images of the neodymium oxide-indium oxide composite porous nanorod material prepared in Example 4; and Figures e1 and e2 are SEM images of the neodymium oxide-indium oxide composite porous nanorod material prepared in Example 5. Figures f, g, h, and i are EDS images of the material prepared in Example 5, where g, h, and i correspond to the elemental distributions of In, O, and Nd, respectively.

[0043] Figure 3 The images show the TEM and HRTEM spectra of the indium oxide porous nanorods and neodymium oxide indium oxide composite porous nanorods prepared in Examples 1 and 5 of this invention. In Figures a1 and a2, the indium oxide porous nanorods prepared in Example 1 are TEM images, Figure a3 is an HRTEM image of the sample prepared in Example 1, and Figures a4 and a5 are magnified lattice fringes in Figure a3, respectively. In Figures b1 and b2, the neodymium oxide indium oxide composite porous nanorods prepared in Example 2 are TEM images, Figure b3 is an HRTEM image of the sample prepared in Example 2, and Figures b4 and b5 are magnified lattice fringes in Figure b3, respectively.

[0044] Figure 4 The XPS spectra of the neodymium oxide and indium oxide composite porous nanorod material prepared in Example 5 of this invention are shown in Figure a, where Figure a is the full XPS spectrum; Figure b is the fine spectrum of In 3d; Figure c is the fine spectrum of O 1s; and Figure d is the fine spectrum of Nd 3d.

[0045] Figure 5 The images show the BET and BJH spectra of the indium oxide porous nanorod materials and the neodymium oxide-indium oxide composite porous nanorod materials prepared in Examples 1 and 5 of this invention, where a is the BET spectrum of the material prepared in Example 1; b is the BJH spectrum of the material prepared in Example 1; c is the BET spectrum of the material prepared in Example 5; and d is the BJH spectrum of the material prepared in Example 5.

[0046] Figure 6The images show the FTIR spectra of indium oxide porous nanorods and neodymium oxide-indium oxide composite porous nanorod materials prepared in Examples 1 and 5 of this invention. In Example 1, a represents the indium oxide porous nanorods prepared at 100°C; c represents the indium oxide porous nanorods prepared in Example 1 at 300°C; b represents the neodymium oxide-indium oxide composite porous nanorod material prepared in Example 5 at 100°C; and d represents the neodymium oxide-indium oxide composite porous nanorod material prepared in Example 5 at 300°C.

[0047] Figure 7 The selectivity of the neodymium oxide-indium oxide composite porous nanorod material prepared in Example 5 of the present invention under different relative humidity conditions at 300℃.

[0048] Figure 8 The figures (a) show the response values ​​of indium oxide porous nanorods and neodymium oxide-indium oxide composite porous nanorods prepared in Examples 1-5 of this invention to 10 ppm H2S under different relative humidity conditions from 100 to 300℃, and the ratio of response values ​​under different relative humidity conditions (b). In a1-a5 and b1-b5, 1-5 correspond to Examples 1-5, respectively.

[0049] Figure 9 This is a schematic diagram of the gas-sensitive element prepared in Embodiment 1 of the present invention. Detailed Implementation

[0050] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0051] The present invention will be further described below with reference to the embodiments.

[0052] Example 1

[0053] A method for preparing indium oxide porous nanorod gas-sensitive materials includes the following steps:

[0054] (1) Dissolve InCl3 and NaOH in 10 mL of ethylene glycol at a molar mass ratio of 1:15. After stirring evenly at room temperature, transfer the solution to a 100 mL reaction vessel and carry out a solvothermal reaction at 150 °C for 12 h. After the reaction is completed and cooled to room temperature, centrifuge, wash and dry the product to obtain the indium hydroxide precursor.

[0055] (2) The indium hydroxide precursor obtained in step (1) was annealed at 600℃ and 5℃ for 5 min for 2 h to obtain indium oxide porous nanorod material.

[0056] Example 2

[0057] A method for preparing a neodymium oxide-indium oxide composite porous nanorod material includes the following steps:

[0058] (1) Dissolve InCl3 and CH4N2O in 15 mL of anhydrous ethanol at a molar mass ratio of 1:5. After stirring evenly at room temperature, transfer the solution to a 100 mL reaction vessel and carry out a solvothermal reaction at 100 °C for 2 h. After the reaction is completed and cooled to room temperature, centrifuge, wash and dry the product to obtain the indium hydroxide precursor.

[0059] (2) The indium hydroxide precursor obtained in step (1) was annealed at 400℃ and 1℃ for 5 min for 3 h to obtain indium oxide porous nanorod material.

[0060] (3) Take a portion of the indium oxide porous nanorod material obtained in step (2) and dissolve it in 10 mL of deionized water. Stir for 30 min until it is uniformly dispersed. Then, dissolve Nd(CH3COO)3 in the above solution and stir until uniform. The molar ratio of indium oxide porous nanorods to Nd(CH3COO)3 is 0.01:1. Then, place the solution in a 60°C oven and dry it thoroughly for 36 h. Then, anneal the dried product at a heating rate of 300°C and 1°C for 5 min for 5 h to obtain neodymium oxide indium oxide composite porous nanorod material.

[0061] Example 3

[0062] A method for preparing a neodymium oxide-indium oxide composite porous nanorod material includes the following steps:

[0063] (1) Dissolve In(NO3)3 and NH3·H2O in 25 mL of deionized water at a molar mass ratio of 1:10. After stirring evenly at room temperature, transfer the solution to a 100 mL reaction vessel and carry out a solvothermal reaction at 110 °C for 6 h. After the reaction is completed and cooled to room temperature, centrifuge, wash and dry the product to obtain the indium hydroxide precursor.

[0064] (2) The indium hydroxide precursor obtained in step (1) was annealed at a heating rate of 500℃ and 2℃ for 5 min for 1 h to obtain indium oxide porous nanorod material.

[0065] (3) Take a portion of the indium oxide porous nanorod material obtained in step (2) and dissolve it in 10 mL of ethylene glycol. Stir for 30 min until it is uniformly dispersed. Then, dissolve Nd2(SO4)3 in the above solution and stir until uniform. The molar ratio of indium oxide porous nanorods to Nd2(SO4)3 is 0.05:1. Then, place the solution in a 10°C oven and dry it thoroughly for 12 h. Then, anneal the dried product at a heating rate of 500°C and 4°C for 5 min for 5 h to obtain neodymium oxide indium oxide composite porous nanorod material.

[0066] Example 4

[0067] A method for preparing a neodymium oxide-indium oxide composite porous nanorod material includes the following steps:

[0068] (1) Dissolve In(NO3)3 and NH3·H2O in 25 mL of deionized water at a molar mass ratio of 1:10. After stirring evenly at room temperature, transfer the solution to a 100 mL reaction vessel and carry out a solvothermal reaction at 110 °C for 6 h. After the reaction is completed and cooled to room temperature, centrifuge, wash and dry the product to obtain the indium hydroxide precursor.

[0069] (2) The indium hydroxide precursor obtained in step (1) was annealed at a heating rate of 500℃ and 2℃ for 5 min for 1 h to obtain indium oxide porous nanorod material.

[0070] (3) Take a portion of the indium oxide porous nanorod material obtained in step (2) and dissolve it in 10 mL of ethylene glycol. Stir for 30 min until it is uniformly dispersed. Then, dissolve Nd2(SO4)3 in the above solution and stir until uniform. The molar ratio of indium oxide porous nanorods to Nd2(SO4)3 is 0.1:1. Then, place the solution in a 10°C oven and dry it thoroughly for 12 h. Then, anneal the dried product at a heating rate of 500°C and 4°C for 5 min for 5 h to obtain neodymium oxide indium oxide composite porous nanorod material.

[0071] Example 5

[0072] A method for preparing a neodymium oxide-indium oxide composite porous nanorod material includes the following steps:

[0073] (1) Add In(CH3COO)3 and C6H 12 N4 was dissolved in 40 mL of deionized water at a molar mass ratio of 1:15. After stirring evenly at room temperature, the solution was transferred to a 100 mL reaction vessel and subjected to a solvothermal reaction at 100 °C for 2 h. After the reaction was completed and cooled to room temperature, the product was centrifuged, washed and dried to obtain the indium hydroxide precursor.

[0074] (2) The indium hydroxide precursor obtained in step (1) was annealed at 400℃ and 1℃ for 5 min for 3 h to obtain indium oxide porous nanorod material.

[0075] (3) Take a portion of the indium oxide porous nanorod material obtained in step (2) and dissolve it in 10 mL of anhydrous ethanol. Stir for 30 min until it is uniformly dispersed. Then, dissolve Nd(CH3COO)3 in the above solution and stir until uniform. The molar ratio of indium oxide porous nanorods to Nd(CH3COO)3 is 0.2:1. Then, place the solution in a 120℃ oven and dry it thoroughly for 36 h. Then, anneal the dried product at a heating rate of 300℃ and 1℃ for 5 min for 5 h to obtain neodymium oxide indium oxide composite porous nanorod material.

[0076] Example 6

[0077] A method for preparing a neodymium oxide-indium oxide composite porous nanorod material includes the following steps:

[0078] (1) Dissolve InCl3 and NaOH in 60 mL of ethylene glycol in a molar mass ratio of 1:12. After stirring evenly at room temperature, transfer the solution to a 100 mL reaction vessel and carry out a solvothermal reaction at 120 °C for 24 h. After the reaction is completed and cooled to room temperature, centrifuge, wash and dry the product to obtain the indium hydroxide precursor.

[0079] (2) The indium hydroxide precursor obtained in step (1) was annealed at 600℃ and 3℃ for 5 min for 2 h to obtain indium oxide porous nanorod material.

[0080] (3) Take a portion of the indium oxide porous nanorod material obtained in step (2) and dissolve it in 40 mL of deionized water. Stir for 30 min until it is uniformly dispersed. Then, dissolve Nd(NO3)3 in the above solution and stir until uniform. The molar ratio of indium oxide porous nanorods to Nd(NO3)3 is 0.15:1. Then, place the solution in a 100℃ oven and dry it thoroughly for 11 h. Then, anneal the dried product at a heating rate of 500℃ and 1℃ for 5 min for 2 h to obtain neodymium oxide indium oxide composite porous nanorod material.

[0081] Example 7

[0082] A method for preparing a neodymium oxide-indium oxide composite porous nanorod material includes the following steps:

[0083] (1) Dissolve In(CH3COO)3 and CH4N2O in 35 mL of anhydrous ethanol at a molar mass ratio of 1:1. After stirring evenly at room temperature, transfer the solution to a 100 mL reaction vessel and carry out a solvothermal reaction at 150 °C for 6 h. After the reaction is completed and cooled to room temperature, centrifuge, wash and dry the product to obtain the indium hydroxide precursor.

[0084] (2) The indium hydroxide precursor obtained in step (1) was annealed at 450℃ and 1.5℃ for 5 min for 3 h to obtain indium oxide porous nanorod material.

[0085] (3) Take a portion of the indium oxide porous nanorod material obtained in step (2) and dissolve it in 10 mL of ethylene glycol. Stir for 30 min until it is uniformly dispersed. Then, dissolve Nd2(SO4)3 in the above solution and stir until uniform. The molar ratio of indium oxide porous nanorods to Nd2(SO4)3 is 0.01:1. Then, place the solution in a 60°C oven and dry it thoroughly for 12 h. Then, anneal the dried product at a heating rate of 350°C and 6°C for 5 min for 5 h to obtain neodymium oxide indium oxide composite porous nanorod material.

[0086] Example 8

[0087] A gas-sensitive element includes a ceramic substrate, a platinum wire, a gas-sensitive sensing material, and a gold electrode. The fabrication method specifically includes the following steps:

[0088] The prepared indium oxide porous nanorod material or neodymium oxide indium oxide composite gas-sensitive material was mixed with deionized water at a mass ratio of 1:5 and ground evenly to form a slurry. The gold electrode was attached to a ceramic substrate, and then the obtained slurry was evenly coated onto the ceramic substrate. The ceramic substrate was placed in a 10°C oven to dry for 5 minutes and then removed. The coating and drying process was repeated five times. The ceramic substrate coated with the gas-sensitive material was then placed in a 100°C oven to dry for 12 hours. Platinum wire was then connected to obtain the gas-sensitive element.

[0089] Performance testing:

[0090] Figure 1 The XRD diffraction patterns are those of indium oxide porous nanorods and neodymium oxide indium oxide composite porous nanorods prepared in Examples 1-5 of this invention. Figure 1 As shown in (a), the prepared indium oxide porous nanorod material has a cubic indium oxide crystal structure, exhibiting good crystallinity and the absence of other impurities. After surface loading with neodymium oxide, the bulk indium oxide crystal structure of the prepared material remained unchanged, and no obvious neodymium oxide diffraction peaks were observed. This may be due to either an excessively low actual neodymium oxide content or a high degree of neodymium oxide dispersion on the surface of the indium oxide nanorods. Figure 1 (b) further shows Figure 1 (a) shows the diffraction peak positions of the indium oxide (222) crystal plane. It can be seen that after surface neodymium oxide chemical deposition, the indium oxide crystal plane did not shift, which indicates that Nd... 3+ The fact that ions cannot exist in the indium oxide lattice as ion dopants indirectly proves that neodymium oxide can only exist on the surface of indium oxide nanorods as a second-phase deposit.

[0091] Figure 2The images show the SEM images of the indium oxide porous nanorods and neodymium oxide-indium oxide composite porous nanorods prepared in Examples 1-5 of this invention, and the EDS image of the material prepared in Example 5. The prepared indium oxide material exhibits a typical nanorod morphology, with some nanorods overlapping to form a flower-like structure. The diameter of the nanorods is approximately 500 nm. After surface loading with neodymium oxide, the morphology of the indium oxide nanorod matrix is ​​not significantly damaged, and the size and morphology of the nanorods are similar to those of the pure indium oxide material. The EDS results show the presence of In, Nd, and O elements in the neodymium oxide-indium oxide composite porous nanorod material, proving the presence of neodymium oxide on the surface of the prepared material.

[0092] Figure 3 The images show the TEM and HRTEM spectra of the indium oxide porous nanorods and neodymium oxide-indium oxide composite porous nanorods prepared in Examples (a) 1 and (b) 5 of this invention. The pure indium oxide material exhibits a porous nanorod morphology, with the nanorod structure composed of numerous nanoparticles. The lattice fringe spacings measured in the HRTEM images are 0.217 nm and 0.406 nm, corresponding to the (222) and (211) crystal planes of cubic In₂O₃, confirming that the synthesized material is cubic indium oxide. After neodymium oxide loading, the main morphology of the nanorods did not change significantly, but short lamellar structures appeared on the nanorod surface. The lattice fringe spacings in the HRTEM images show spacings of 0.217 nm and 0.300 nm, corresponding to the (222) crystal plane of cubic In₂O₃ and the (002) crystal plane of hexagonal Nd₂O₃, respectively, confirming the successful loading of neodymium oxide onto the porous indium oxide surface.

[0093] Figure 4 The XPS spectrum of the neodymium oxide-indium oxide composite porous nanorod material prepared in Example 5 of this invention shows the peak positions related to In, O, and Nd elements in the prepared material. Two sets of spin-coupled peaks are present in the In3d fine spectrum, which are attributed to In. 1-2+ and In 3+ In 1-2+ The appearance of the relevant peaks indicates that there are many positively charged defects, i.e., oxygen vacancies, in the synthesized indium oxide material. In is generated due to the material's own electron compensation. 1-2+The O1s fine spectrum further confirmed the presence of three types of oxygen in the material: lattice oxygen, oxygen vacancies, and chemisorbed oxygen. It was observed that the material contains a relatively high number of oxygen vacancies (35.05%). This high oxygen vacancy content provides numerous high-energy defect sites for the gas-sensing reaction, facilitating gas adsorption. Furthermore, the material itself has a low chemisorbed oxygen content (only 2.26%). Chemisorbed oxygen can act as a reactant to promote the gas-sensing reaction, while its low content inhibits the reaction. H2S can directly interact with indium oxide lattice oxygen through a sulfidation mechanism, initiating a sulfidation reaction and thus exhibiting H2S gas-sensing performance. Therefore, the low chemisorbed oxygen content is also highly beneficial for improving the material's H2S gas-sensing selectivity.

[0094] Figure 5 The figures show the BET and BJH spectra of the indium oxide porous nanorods and the neodymium oxide-indium oxide composite porous nanorods prepared in Examples 1 and 5 of this invention. Figures a and c show the BET results, which indicate that both the indium oxide porous nanorods and the neodymium oxide-indium oxide composite porous nanorods exhibit typical type IV adsorption curves and H3 hysteresis loops. This suggests that the prepared materials all possess mesoporous structures. The calculated specific surface areas of the indium oxide porous nanorods and the neodymium oxide-indium oxide composite porous nanorods are 23.92 m², respectively. 3 5g and 22.97m 3 5g. This indicates that loading neodymium oxide onto the surface does not significantly reduce the specific surface area of ​​the material. The main indium oxide gas-sensitive adsorption sites are not occupied and can still react. The BJH results in Figures b and d show that the diameter of the main mesopores in the indium oxide porous nanorod material and the neodymium oxide-indium oxide composite porous nanorod material is about 9nm. After loading neodymium oxide onto the surface, the mesopore structure with a pore size of about 25nm is occupied and disappears, but the main mesopore structure is not affected. The higher specific surface area helps to provide more gas adsorption sites and enhance the gas-sensitive response. The abundant mesopore structure provides a large number of channels for gas diffusion, which is beneficial to the conduction process of gas molecules.

[0095] Figure 6 The images show the FTIR spectra of indium oxide porous nanorods and neodymium oxide-indium oxide composite porous nanorod materials prepared in Examples 1 and 5 of this invention, with the 1430 cm⁻¹ value being the highest. -1 3420cm -1The peaks on the left and right correspond to the infrared peak positions of physically adsorbed water molecules and surface hydroxyl groups, respectively. For pure indium oxide materials, there are no significant changes in the number of water molecules and surface hydroxyl species on the material surface at low temperature (100℃) and high temperature (300℃), which confirms that the humidity resistance stability of pure indium oxide materials does not change significantly under different conditions. However, for indium oxide materials with surface loading of neodymium oxide, the number of physically adsorbed water molecules on the surface increases significantly with the increase of relative humidity at low temperature (100℃), indicating that the neodymium oxide component has strong hygroscopicity and can improve the affinity of the material for water molecules. Therefore, the material with neodymium oxide loading is more sensitive to relative humidity at low temperature. Tests at higher temperatures (300℃) show that surface loading of neodymium oxide helps to eliminate physically adsorbed water on the surface. At the same time, the surface hydroxyl groups of the material tend to combine with neodymium oxide to form the Nd-OOH peak (at 3400 cm⁻¹). -1 The flat peaks (generated on both sides) indicate that neodymium oxide can effectively eliminate water molecules and surface hydroxyl groups on the surface of indium oxide at higher temperatures, thereby protecting the gas-sensing properties of indium oxide from interference by ambient humidity.

[0096] Figure 7 The selectivity of the neodymium oxide-indium oxide composite porous nanorod material prepared in Example 5 of this invention under different relative humidity conditions at 300℃ is shown. It can be seen that the prepared material exhibits high selectivity for H2S; simultaneously, under high humidity conditions (10% RH), the material's response value to H2S remains almost unchanged, while still exhibiting excellent H2S selectivity. This indicates that the prepared gas-sensitive material has good H2S detection capability and excellent humidity resistance stability, which can meet the gas detection requirements under high humidity conditions.

[0097] Figure 1 The figures show the response values ​​of indium oxide porous nanorods and neodymium oxide-indium oxide composite porous nanorods prepared in Examples 1-5 of this invention to 10 ppm H2S under different relative humidity conditions ranging from 100-300℃, and the ratio of response values ​​under different relative humidity conditions. The prepared gas-sensitive materials exhibit excellent responses to H2S at different operating temperatures. At different operating temperatures, the response value of pure indium oxide to H2S decreases significantly with increasing relative humidity; while the sample with neodymium oxide loaded on its surface shows a significant improvement in humidity resistance with increasing operating temperature. The optimal group maintains a response value of over 93.5% of that at 20% RH at 10% RH, demonstrating excellent humidity resistance.

[0098] Figure 9This is a schematic diagram of the gas-sensitive element prepared in Embodiment 1 of the present invention. It includes a ceramic substrate, gold electrodes, four platinum wires, and sensing material. The prepared gas-sensitive material is coated onto the ceramic substrate, uniformly coated and dried. The ceramic substrate is then welded to a four-corner base via the four platinum wires to obtain the gas-sensitive element.

[0099] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a neodymium oxide-indium oxide composite porous nanorod material, characterized in that: The method for preparing the neodymium oxide and indium oxide composite porous nanorod material includes the following steps: dissolving an indium source and a weakly reducing or non-reducing alkaline source in a molar ratio of 1:5-15, mixing them, and then carrying out a solvothermal reaction under closed conditions to prepare an indium hydroxide precursor; annealing the indium hydroxide precursor to obtain indium oxide porous nanorods. Indium oxide porous nanorods were uniformly dispersed in a solvent, and then a neodymium source was added to it. After dissolving and mixing, the mixed solution was dried, and the dried product was annealed to obtain neodymium oxide indium oxide composite porous nanorod material. The neodymium oxide and indium oxide composite porous nanorod material includes indium oxide porous nanorods and a neodymium oxide layer supported on the surface of the indium oxide porous nanorods; the indium oxide porous nanorods are assembled from indium oxide nanoparticles; The indium oxide nanorods have a diameter of 300-500 nm and a length of 1-5 μm; The particle size of indium oxide nanoparticles is 0.2-1 nm, and the particle size of neodymium oxide is 0.2-1 nm. The molar ratio of neodymium oxide to indium oxide is 0.01-0.2:

1.

2. The method for preparing the neodymium oxide-indium oxide composite porous nanorod material according to claim 1, characterized in that: The indium oxide nanorods have a cubic phase crystal structure.

3. The method for preparing the neodymium oxide-indium oxide composite porous nanorod material according to claim 1, characterized in that: The crystal structure of the neodymium oxide is hexagonal.

4. The method for preparing the neodymium oxide-indium oxide composite porous nanorod material according to claim 1, characterized in that: The indium source is selected from any one or a combination of indium chloride, indium nitrate, or indium acetate. Alternatively, the alkali source is selected from one or a combination of urea, hexamethylenetetramine, sodium hydroxide, or ammonia water; Alternatively, the solvent used in the solvothermal reaction is one of anhydrous ethanol, ethylene glycol, or deionized water, or a mixture thereof; Alternatively, the neodymium source may be one or a combination of neodymium acetate, neodymium sulfate, or neodymium nitrate.

5. The method for preparing the neodymium oxide-indium oxide composite porous nanorod material according to claim 1, characterized in that: The indium hydroxide precursor is annealed at a temperature of 400-600℃ for 1-3 hours.

6. The method for preparing the neodymium oxide-indium oxide composite porous nanorod material according to claim 1, characterized in that: The mass ratio of indium oxide porous nanorods to neodymium source is 0.01-0.2:

1.

7. The method for preparing the neodymium oxide-indium oxide composite porous nanorod material according to claim 1, characterized in that: The dried product is annealed at a temperature of 300-500℃ for 1-5 hours.

8. The application of the neodymium oxide-indium oxide composite porous nanorod material obtained by any of the preparation methods described in claims 1-7 in the preparation of gas-sensitive elements or in the detection of H2S concentration.

9. A gas-sensitive element, characterized in that: It includes a ceramic substrate and a gas-sensitive material, wherein the gas-sensitive material is a neodymium oxide-indium oxide composite porous nanorod material obtained by any of the preparation methods described in claims 1-7, and the gas-sensitive material is attached to the ceramic substrate.

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