A preparation method of In2O3@CeO2 core-shell structure nanomaterials with excellent sensing performance for hydrogen

Abstract

The application discloses a preparation method of In2O3@CeO2 core-shell structure nanomaterial with excellent sensing performance for hydrogen. The preparation method of the material is as follows: taking a mixed aqueous solution of Ce(NO3)4 and InCl3 as a precursor, adopting a flame aerosol synthesis technology, using a premixed stagnation flame synthesis method, breaking the precursor into mist drops through an atomizing device, conveying the mist drops to a burner with a carrier gas to form a premixed gas with ethylene and oxygen, making the precursor react through a planar flame formed by combustion, depositing the product on a water-cooled substrate under a huge thermal convection force, and annealing the product to obtain the In2O3@CeO2 core-shell structure nanomaterial. The material has uniform size, small particle size, and high purity, and has excellent performance for hydrogen detection. The hydrogen synthesis method is simple, fast and low in cost.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation and gas sensing technology, specifically relating to a method for preparing In2O3@CeO2 core-shell structured nanomaterials with excellent hydrogen sensing performance. Background Technology

[0002] With the rapid increase in people's demand for energy, hydrogen, as a new energy source, has been widely used in various industries due to its advantages such as rapid combustion and zero pollution. However, hydrogen is colorless and odorless, has a low ignition point, and a wide explosion limit range, making it prone to combustion and explosion accidents that can cause serious losses. Timely detection of hydrogen leaks is crucial to preventing accidents. Existing single In2O3 hydrogen sensors and CeO2 hydrogen sensors often suffer from poor selectivity, low sensitivity, and slow response speed. However, a core-shell structure formed by two metal oxides can effectively improve hydrogen sensing performance.

[0003] Currently, research on the synthesis of In2O3 and CeO2 nanomaterials commonly employs hydrothermal methods, sol-gel methods, vapor deposition, and magnetron sputtering. However, these methods are complex, costly, and produce large-sized products. In contrast, flame synthesis of In2O3@CeO2 core-shell nanomaterials yields small, uniformly sized In2O3@CeO2 nanomaterials with effectively controlled particle size and structure. The synthesis process is simple and yields high output. This is beneficial for improving the hydrogen sensing performance of In2O3@CeO2 core-shell nanomaterials. Furthermore, there are no reports in existing research on the use of flame synthesis to prepare In2O3@CeO2 core-shell nanomaterials. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of complex experimental procedures, uneven product size, and large product particle size in the preparation methods of existing In2O3 and CeO2 nanomaterials, as well as their poor selectivity for hydrogen, low sensitivity, and slow response speed. The invention provides an In2O3@CeO2 core-shell structured nanomaterial with excellent gas-sensing performance for hydrogen.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing In2O3@CeO2 core-shell structured nanomaterials with excellent hydrogen sensing properties is disclosed. A mixed aqueous solution of Ce(NO3)4 and InCl3 is used as a precursor, placed in a jet atomization device. A breaking gas is introduced to atomize the precursor into an aerosol. A carrier gas is introduced to mix the precursor with ethylene and oxygen to form a premixed gas. After ignition, a high-temperature planar flame is formed between the burner nozzle and a water-cooled substrate. The precursor rapidly passes through the flame, undergoing processes such as vaporization, decomposition, oxidation, and collision nucleation during its passage. Under the influence of the large thermophoretic force caused by the steep temperature difference, it is deposited onto the surface of the water-cooled substrate below. The product is then annealed to obtain the In2O3@CeO2 core-shell structured nanomaterials.

[0007] In the above synthesis process, the carrier gas and the atomizing gas used are nitrogen or argon. The flow rate of each component of the premixed gas is the most important factor affecting the particle size and structure of the product. In this invention, the flow rate of ethylene is 0.72 L / min, the flow rate of oxygen is 3.81 L / min, the flow rate of the carrier gas is 8.81 L / min, and the flow rate of the atomizing gas is 4.07 L / min.

[0008] The total flow rate of the premixed gas is a key factor affecting the particle size and structure of the product. A lower premixed gas flow rate slows down the movement of the precursor, thus increasing its time in the flame and resulting in a longer growth time for the particles, which is not conducive to the formation of small-diameter nanoparticles. A higher premixed gas flow rate leads to a higher flame temperature and a faster particle growth rate in the flame, which is also not conducive to the formation of small-diameter nanoparticles.

[0009] The high-temperature planar flame in this invention has a center temperature of 900°C and a flame thickness of 1 mm.

[0010] In this invention, the preheating temperature of the precursor delivery pipeline is 60°C. If preheating is not performed, the precursor will condense and accumulate inside the pipeline, subsequently dripping into the flame and onto the water-cooled substrate in the form of droplets, severely affecting product formation.

[0011] In this invention, the water-cooled substrate is a stainless steel plate that can be circulated with cooling water, and an aluminum nitride ceramic plate is placed on top of it, which is 100mm long, 100mm wide and 10mm thick.

[0012] In this invention, the temperature of the water-cooled substrate is maintained at 10-15°C. Higher temperatures will reduce the temperature gradient between the flame and the substrate, thereby reducing the thermophoretic force on the particles, resulting in the particles spending more time in the flame, which is not conducive to the formation of small-particle-size products.

[0013] The burner nozzle in this invention has a nozzle radius of 15 mm. The inventors discovered that a nozzle radius that is too small will reduce the temperature range of the planar flame, thus affecting product yield. A nozzle radius that is too large will be detrimental to achieving a stable planar flame.

[0014] In the precursor of this invention, the indium source is provided by InCl3 at a concentration of 0.15 M, the cerium source is provided by Ce(NO3)4 at a concentration of 0.015 M, and the molar ratio of cerium to indium is 1:10.

[0015] Increasing the Ce(NO3)4 concentration in the precursor will result in larger product particle size and severe agglomeration, which is detrimental to improving hydrogen sensing performance. Decreasing the Ce(NO3)4 concentration in the precursor will prevent the formation of an In2O3@CeO2 core-shell structure in the product.

[0016] In this invention, the product collected on the water-cooled substrate is annealed at 600°C for 1.5 hours. The inventors discovered that excessive annealing time and temperature will cause sintering of the product, resulting in increased particle size. Insufficient annealing time and temperature will lead to insufficient crystallinity and an amorphous crystal structure, which is detrimental to improving hydrogen sensing performance.

[0017] The In2O3@CeO2 core-shell structured nanomaterials synthesized by the method provided in this invention have a particle size of 15–24 nm.

[0018] The In2O3@CeO2 core-shell structured nanomaterial synthesized by the method provided in this invention exhibits high response value to hydrogen, short response / recovery time, high selectivity, and a suitable operating temperature, resulting in excellent hydrogen sensing performance.

[0019] The present invention has significant advantages over the prior art as follows:

[0020] 1. This invention utilizes premixed stagnant planar flame technology to achieve the synthesis of In2O3@CeO2 core-shell structured nanomaterials for the first time, providing support for their excellent gas-sensing properties to hydrogen. Compared with other cumbersome synthesis methods that produce products with large particle sizes, the synthesis process of this invention is simple, low-cost, and the prepared In2O3@CeO2 core-shell structured nanomaterials have small particle sizes and uniform size distribution.

[0021] 2. The present invention can easily control the size and structure of the product by changing parameters such as the flow rate of each component of the premixed gas, the type and concentration of the precursor, the burner size, and the substrate temperature, and the synthesis process is highly reproducible.

[0022] 3. The In2O3@CeO2 core-shell structured nanomaterial synthesized in this invention forms an n-heterojunction between In2O3 and CeO2, resulting in a higher response value to hydrogen, a lower optimal operating temperature, and better sensing performance compared to pure In2O3. Attached Figure Description

[0023] Figure 1 The XRD pattern of the synthesized In2O3@CeO2 core-shell structured nanomaterial.

[0024] Figure 2 SEM image of the synthesized In2O3@CeO2 core-shell structured nanomaterial.

[0025] Figure 3 TEM image of the synthesized In2O3@CeO2 core-shell structured nanomaterial.

[0026] Figure 4 HRTEM for the synthesis of In2O3@CeO2 core-shell structured nanomaterials.

[0027] Figure 5 SAED image for the synthesis of In2O3@CeO2 core-shell structured nanomaterials.

[0028] Figure 6 The elemental mapping diagrams for synthesizing In2O3@CeO2 core-shell nanomaterials are: (a) HAADF diagram, (b) In elemental diagram, (c) Ce elemental diagram, and (d) O elemental spectrum.

[0029] Figure 7 XPS spectra of the synthesized In2O3@CeO2 core-shell nanomaterials: (a) full spectrum, (b) In3d elemental spectrum, (c) Ce3d elemental spectrum, and (d) O1s elemental spectrum.

[0030] Figure 8 The images show the XRD patterns of the composite materials of Comparative Example 1 and Comparative Example 2.

[0031] Figure 9 The image shows the SEM image of the composite material in Comparative Example 1.

[0032] Figure 10 The image shows the SEM image of the composite material in Comparative Example 2.

[0033] Figure 11 The graph shows a comparison of the responses of the three materials in the examples and comparative examples to 300 ppm hydrogen gas.

[0034] Figure 12 This is a comparison chart showing the selectivity of the three materials for hydrogen in the examples and comparative examples. Detailed Implementation

[0035] To make the contents of this invention easier to understand, the invention will be further described below through embodiments and comparative examples, but the contents of this invention are not limited to the following contents.

[0036] Example 1

[0037] Weigh 0.3318 g of InCl3 powder and 0.0582 g of Ce(NO3)4 using an analytical balance. Mix the InCl3 and Ce(NO3)4 powders, add 10 mL of deionized water and a trace amount of dilute hydrochloric acid, and stir until homogeneous to obtain a mixed solution of InCl3 and Ce(NO3)4 with a cerium-indium molar ratio of [Ce]:[In] = 1:10, which serves as the precursor. The InCl3 concentration is 0.15 M. Pour the precursor into a jet atomization device, set up the experimental setup, and set the preheating device temperature of the delivery pipeline to 60℃. The premixed gas conditions are: oxygen 3.81 L / min, ethylene 0.72 L / min, carrier gas 8.81 L / min, atomizing gas 4.07 L / min, and protective gas 2.56 L / min. The temperature of the water-cooled substrate was controlled at approximately 10℃ using a circulating liquid cooler; the distance between the substrate and the flame nozzle was 30 mm; synthesis experiments were conducted using a premixed stagnant planar flame synthesis technique, with the product deposition time on the water-cooled substrate around 20 minutes, resulting in the synthesis of In2O3@CeO2 core-shell structured nanomaterials. Finally, to improve the crystallinity of the product, it was annealed at 600℃ in a tube furnace. The XRD, SEM, TEM, HRTEM, SAED, mapping, and XPS images of the prepared In2O3@CeO2 core-shell structured nanomaterials are shown below. Figure 1 , 2 As shown in 3, 4, 5, and 6.

[0038] Figure 1 The image shows the XRD pattern of In2O3@CeO2. The product exhibits strong and well-formed diffraction peaks, indicating high crystallinity. The main diffraction peaks at 2θ values ​​of 21.50°, 30.59°, 35.46°, 51.02°, and 60.67° correspond to the (220), (222), (400), (440), and (622) crystal planes in the In2O3 standard card PDF#71-2194. Similarly, the main diffraction peaks at 2θ values ​​of 28.55°, 33.08°, 47.49°, and 56.34° correspond to the (111), (200), (110), and (311) crystal planes in the CeO2 standard card PDF#34-0394. Since no other impurity peaks are observed, the product exists as a high-purity CeO2 and In2O3 crystal. The average particle size of the product can be calculated to be approximately 19.76 nm using the Scherrer formula.

[0039] Figure 2 and Figure 3 SEM and TEM images of In2O3@CeO2 are presented. The images show that the synthesized product exhibits good dispersion with a particle size of approximately 20 nm, and no sintering is observed.

[0040] Figure 4The HRTEM image of the sample shows clear lattice fringes and high crystallinity. Calculations from the image show that the interplanar spacing inside the particle is 0.292 nm, corresponding to the (222) crystal plane in the In2O3 standard card, and the interplanar spacing of the outer layer of the particle is 0.312 nm, corresponding to the (111) crystal plane in the CeO2 standard card, proving that some CeO2 is coated on the In2O3 surface. Figure 5 The diffraction rings obtained from the SEAD test show that the particles in the selected area have a polycrystalline structure. In addition to the diffraction rings of In2O3, the diffraction rings of CeO2 are also marked in the figure. The bright spots correspond to its (111), (002), (022), (113) and (024) crystal planes, which are consistent with the information in the standard card. Figure 6 The mapping diagram of In2O3@CeO2 shows that the distribution range of In elements is relatively concentrated, while the distribution of Ce is wider than that of In. In addition, there are also O elements distributed outside of In elements, which proves that there is CeO2 coating on the surface of In2O3.

[0041] Figure 7 The XPS full spectrum, elemental XPS spectra of In2O3@CeO2, In3d, Ce3d, and O1s are shown. The full spectrum reveals that the product contains In, Ce, and O elements. The two asymmetric binding energies of 451.7 eV and 444.1 eV in the In3d elemental XPS spectrum correspond to the In3d binding energies, respectively. 3 / 2 With In3d 5 / 2 The orbitals demonstrate the presence of numerous oxygen vacancies. The binding energy peaks of 915.9 eV, 906.4 eV, and 900.7 eV in the figure correspond to Ce3d. 3 / 2 The binding energy peaks at 897.9 eV, 887.5 eV, and 881.9 eV correspond to Ce3d orbitals. 5 / 2 Orbit. It was proven that the Ce element simultaneously... 4+ With Ce 3+ It exists in the form of more Ce 3+ This will lead to crystal defects, generating a large number of oxygen vacancies, which will help the adsorption of gases and improve its sensing performance.

[0042] Comparative Example 1

[0043] The precursor concentration ratio in Example 1 was changed, and the precursor was replaced with a mixed solution of InCl3 and Ce(NO3)4 with a cerium-indium molar ratio of 1:20, wherein the InCl3 concentration was 0.15M. The remaining steps and conditions were the same as in Example 1.

[0044] XRD and SEM analyses of the prepared In2O3-CeO2 (1:20) nanomaterials are as follows: Figure 8 , 9As shown in the figure, the XRD pattern shows a weakening of the characteristic CeO2 diffraction peaks, indicating a low CeO2 content in the product. The SEM image shows that the product particle size has increased, and the product has failed to form a core-shell structure.

[0045] Comparative Example 2

[0046] The precursor concentration ratio in Example 1 was changed, and the precursor was replaced with a mixed solution of InCl3 and Ce(NO3)4 with a cerium-indium molar ratio of 1:5, wherein the InCl3 concentration was 0.15M. The remaining steps and conditions were the same as in Example 1.

[0047] XRD and SEM analyses of the prepared In2O3-CeO2(1:5) nanomaterials are as follows: Figure 8 , 10 As shown in the figure, the characteristic diffraction peaks of CeO2 in the XRD pattern are stronger, indicating a higher CeO2 content in the product. The SEM image shows that the product particle size is larger, the aggregation phenomenon is obvious, and the product has failed to form a core-shell structure.

[0048] Figure 11 This section describes the response of the three composite materials to 300 ppm hydrogen at different operating temperatures. In Example 1, the In2O3@CeO2 composite material exhibited a maximum response value of 12.38 to 500 ppm hydrogen, with an optimal operating temperature of 280°C. In contrast, the composite materials in the two comparative examples showed maximum response values ​​of 9.41 and 4.05, respectively, with optimal operating temperatures of 300°C and 280°C, respectively. The comparison demonstrates that the In2O3@CeO2 core-shell structured nanomaterial synthesized in Example 1 exhibits a high response value to hydrogen, a low optimal operating temperature, and excellent hydrogen sensing performance.

[0049] Figure 12 These are the highest response values ​​of the three composite materials to several other combustible gases at a concentration of 300 ppm. It was found that the three composite materials synthesized by premixed stagnant planar flame all showed good selectivity for hydrogen, with the In2O3@CeO2 core-shell nanomaterial synthesized in Example 1 exhibiting the highest response value and strongest selectivity for hydrogen.

Claims

1. A method for preparing In2O3@CeO2 core-shell structured nanomaterials with excellent hydrogen sensing properties, characterized in that: A mixed aqueous solution of Ce(NO3)4 and InCl3 was used as a precursor. The precursor was atomized into an aerosol by a jet atomizer using a breaking gas. A carrier gas was introduced to mix the precursor with ethylene and oxygen to form a premixed gas, which was then ignited at the nozzle of a burner to form a 1 mm thick planar flame at 900 °C. The precursor passed through the flame rapidly and underwent gasification, decomposition, oxidation, and collision nucleation processes in the flame. Under the action of huge thermophoretic force caused by the steep temperature difference, it was deposited on the surface of the water-cooled substrate below. The product was annealed to obtain In2O3@CeO2 core-shell structured nanomaterials. The concentration of InCl3 aqueous solution was 0.15 M, the concentration of Ce(NO3)4 aqueous solution was 0.015 M, and the molar ratio of cerium to indium was 1:

10.

2. The preparation method according to claim 1, characterized in that, The carrier gas and the breakup gas used are nitrogen or argon.

3. The preparation method according to claim 1, characterized in that, in, The flow rate of ethylene is 0.72 L / min, the flow rate of oxygen is 3.81 L / min, the flow rate of carrier gas is 8.81 L / min, and the flow rate of atomizing and breaking gas is 4.07 L / min.

4. The preparation method according to claim 1, characterized in that, The preheating temperature of the precursor transport pipeline is 60℃.

5. The preparation method according to claim 1, characterized in that, The water-cooled base plate is a stainless steel plate that circulates cooling water, with an aluminum nitride ceramic plate on top, measuring 100mm in length, 100mm in width, and 10mm in thickness.

6. The preparation method according to claim 1, characterized in that, The temperature of the water-cooled substrate is maintained at 10~15℃.

7. The preparation method according to claim 1, characterized in that, The burner nozzle orifice radius is 15mm.

8. The preparation method according to claim 1, characterized in that, The product collected from the water-cooled substrate was annealed at 600°C for 1.5 hours.

9. The In2O3@CeO2 core-shell structured nanomaterial prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The particle size of In2O3@CeO2 core-shell structured nanomaterials is 15~24nm.

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