Rare earth element doped transition metal molybdate nanosheet / N doped hollow carbon foam material, preparation method and application thereof

Abstract

The invention discloses a rare earth element doped transition metal molybdate nanosheet / N-doped hollow carbon foam material, a preparation method and application of the rare earth element doped transition metal molybdate nanosheet / N-doped hollow carbon foam material. And uniformly growing rare earth element-doped transition metal molybdate nanosheets on the surface of the N-doped hollow carbon foam through hydrothermal reaction and heat treatment. Wherein the N-doped hollow carbon foam effectively reduces the density of the composite material, is beneficial to multiple reflection and refraction loss of electromagnetic waves in the composite material, prevents aggregation of transition metal molybdate nanosheets and doping of rare earth elements, and enhances the magnetic loss capability of the composite material; the effective electromagnetic wave absorption bandwidth of the composite material moves towards low frequency, the dielectric loss capability of the N-doped hollow carbon foam is effectively improved, the matching thickness is reduced, and the composite material obtains more efficient electromagnetic wave absorption performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetic wave absorption, and relates to an electromagnetic wave absorption material, in particular to a rare earth element doped transition metal molybdate nanosheet / N doped hollow carbon foam material, a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of electronic technology, electromagnetic waves are widely used in the fields of Internet of Things, artificial intelligence, aerospace, etc., which also brings serious electromagnetic pollution problems, not only harming human health, but also interfering with the operation of large precision instruments. In addition, in the military field, in order to improve the service capability of weapon equipment, the development of stealth technology is essential. Electromagnetic wave absorption material is a kind of functional material that can effectively attenuate electromagnetic waves. As the core of radar stealth technology, the development of electromagnetic wave absorption material not only has important economic value and strategic significance, but also is the internal demand for the development of national economy and the maintenance of national security.

[0003] Compared with other electromagnetic wave absorption materials, carbon-based electromagnetic wave absorption materials with three-dimensional multi-hole structure are considered to be more promising electromagnetic wave absorption materials due to their small density, high specific surface area and strong designability. However, the electromagnetic wave loss capacity of single-component carbon materials is limited, which is difficult to meet the urgent demand of aerospace, weapon equipment and wearable devices for integrated wave absorption performance of "light, thin, wide and strong".

[0004] Transition metal nickel molybdate is considered to have high conductive loss and polarization loss potential due to the rich valence change and controllable electronic structure of transition metal and molybdenum bimetallic sites. However, the electromagnetic wave absorption performance of the composite material composed of carbon material and transition metal molybdate has the problems of narrow effective electromagnetic wave absorption bandwidth and large matching thickness. SUMMARY

[0005] In view of the defects and deficiencies of the prior art, the purpose of the present application is to provide a rare earth element doped transition metal molybdate nanosheet / N doped hollow carbon foam material, a preparation method and application thereof, to solve the technical problems of narrow effective electromagnetic wave absorption bandwidth and large matching thickness of the electromagnetic wave absorption performance of the composite material composed of carbon material and transition metal molybdate in the prior art.

[0006] In order to solve the above technical problems, the present application adopts the following technical solutions: A preparation method of a rare earth element doped transition metal molybdate nanosheet / N doped hollow carbon foam material, the method first prepares N doped hollow carbon foam by pyrolysis, and then grows rare earth element doped transition metal molybdate nanosheets on the surface of the N doped hollow carbon foam through hydrothermal reaction and heat treatment. Specifically, the method comprises the following steps: Step one, the amino-containing carbon foam is placed in a tube furnace, protective gas is introduced, the temperature is raised to 800-1100 DEG C at a rate of 1-10 DEG C / min, heat treatment is carried out for 1-4 hours, after the heat preservation, the temperature is reduced to room temperature at a rate of 1-10 DEG C / min, and N-doped hollow carbon foam with three-dimensional hollow structure is obtained; Step two, the molybdenum source, the transition metal source, the rare earth element source, the urea and the ammonium fluoride are dispersed and dissolved in a solvent, then the N-doped hollow carbon foam is added, after standing, the mixed solution containing the N-doped hollow carbon foam is placed in a reaction kettle, and hydrothermal reaction is carried out at 130-160 DEG C for 10-24 hours, after the hydrothermal reaction, the product is washed and dried, and a rare earth element-doped transition metal molybdate hydrate / N-doped hollow carbon foam is obtained. Step three, the rare earth element-doped transition metal molybdate hydrate / N-doped hollow carbon foam is placed in a tube furnace, protective gas is introduced, the temperature is raised to 300-450 DEG C at a rate of 1-10 DEG C / min, heat treatment is carried out for 1-3 hours, after the heat preservation, the temperature is reduced to room temperature at a rate of 1-10 DEG C / min, and a rare earth element-doped transition metal molybdate nanosheet / N-doped hollow carbon foam material is obtained. The application also comprises the following technical features: Specifically, in step two, the standing time is 4-12 hours.

[0007] Specifically, in step two, the final concentration of the molybdenum source is 0.03-0.3 M, the amount of the N-doped hollow carbon foam is 0.001-0.05 g, the molar ratio of the molybdenum source to the transition metal source is 1:0.33-3, and the molar ratio of the molybdenum source to the nitric acid compound of the rare earth element is 1:0.0013-0.2.

[0008] More specifically, in step two, the final concentration of the transition metal source is 9.9*10 -4 -0.9 M, the final concentration of the rare earth element source is 3.9*10 -5 -0.06 M, the final concentration of the urea is 0.03-0.6 M, and the final concentration of the ammonium fluoride is 0.03-0.6 M.

[0009] Specifically, in step two, the drying temperature is 60 DEG C, and the drying time is 24 hours.

[0010] Specifically, in step one and step three, the protective gas is argon.

[0011] Specifically, in step two, the rare earth element source is selected from one or more of La(NO3)3·6H2O, Ce(NO3)3·6H2O, Er(NO3)3·6H2O, Pr(NO3)3·6H2O, La(CH3COO)3·1.5H2O, Ce(CH3COO)3·1.5H2O, Er(CH3COO)3·H2O, Pr(CH3COO)3·4H2O; the molybdenum source is selected from one or more of Na2MoO4, Na2MoO4·2H2O, (NH4)6Mo7O 24 ·4H2O; and the transition metal source is selected from one or more of Ni(NO3)2·6H2O, Co(NO3)2·6H2O, Cu(NO3)2·6H2O, Ni(CH3COO)2·4H2O, Co(CH3COO)2·4H2O, Cu(CH3COO)2·H2O.

[0012] The application also protects a rare earth element doped transition metal molybdate nanosheet / N-doped hollow carbon foam material prepared by the preparation method described above, wherein the material has a substrate of N-doped hollow carbon foam with a three-dimensional hollow structure, and the substrate surface is uniformly distributed with rare earth element doped transition metal molybdate nanosheets.

[0013] Specifically, the rare earth element is selected from one or more of lanthanum, cerium, praseodymium, and erbium; the transition metal molybdate is selected from one or more of NiMoO4, CoMoO4, and CuMoO4; the N-doped hollow carbon foam is an amino-containing carbon foam after pyrolysis; the amino-containing carbon foam is a polymer-based foam material containing at least one -NH2, -NH-, or quaternary ammonium type nitrogen functional group on the polymer main chain or side chain; the amino-containing carbon foam has an open pore or semi-open pore structure, a porosity of 30%–99%, and can be in the form of a block, a sheet, a skeleton, a porous particle, or an aerogel structure; and the amino-containing carbon foam is selected from one or more of a polyamide foam (such as a nylon foam), a polyamide acid or prepolymer foam, a polyurethane foam (containing free or blocked amino groups), a polyethylenimine (PEI) or polyacrylamide foam, a chitosan foam, an amino-modified phenolic or melamine foam, and other amino-modified polymer foams.

[0014] The application also protects the use of the rare earth element doped transition metal molybdate nanosheet / N-doped hollow carbon foam material described above for absorbing electromagnetic waves. Compared with the prior art, the application has the following beneficial technical effects: (I) This invention uses a carbon skeleton matrix with a three-dimensional hollow structure, on which rare earth element-doped transition metal molybdate two-dimensional nanosheets are uniformly distributed. The NCF effectively reduces the density of the composite material, which is beneficial for electromagnetic waves to undergo multiple reflections and refractions within the composite material. At the same time, it prevents the aggregation of transition metal molybdate nanosheets. The doping of rare earth elements enhances the magnetic loss capability of the composite material, causing the effective electromagnetic wave absorption bandwidth of the composite material to shift to lower frequencies. It effectively improves the dielectric loss capability of N-doped hollow carbon foam, while reducing the matching thickness, so that the composite material obtains more efficient electromagnetic wave absorption performance.

[0015] (II) In this invention, rare earth elements with large ionic radii are used to introduce lattice distortion within transition metal molybdate nanosheets, thereby enhancing defect-induced polarization. The transition metal molybdate nanosheets loaded with rare earth elements increase the abundance of heterointerfaces, which is beneficial for enhancing interfacial polarization loss.

[0016] (III) In this invention, the filling amount of the composite material is only 4 wt%, which can obtain excellent electromagnetic wave absorption performance and the minimum reflection loss can reach -52.40 dB. Attached Figure Description

[0017] Figure 1 The microstructure diagram of N-doped hollow carbon foam with a three-dimensional hollow structure is shown in an embodiment of the present invention.

[0018] Figure 2 The microstructure diagram and elemental distribution diagram of LNM / NCF in the embodiments of the present invention are shown.

[0019] Figure 3 The X-ray diffraction (XRD) pattern of LNM / NCF in an embodiment of the present invention is shown.

[0020] Figure 4 The diagram illustrates the electromagnetic wave absorption performance test structure of the composite material in an embodiment of the present invention. (ab) represents the 2D and 3D reflection loss curves of NM / NCF, respectively; (cd) represents the 2D and 3D reflection loss curves of LNM / NCF, respectively; (ef) represents the 2D and 3D reflection loss curves of CNM / NCF, respectively; and (gh) represents the 2D and 3D reflection loss curves of LCM / NCF, respectively.

[0021] The technical solution of the present invention will be further described below with reference to the embodiments. Detailed Implementation

[0022] It should be noted that, unless otherwise specified, all raw materials used in this invention are known in the prior art.

[0023] Following the above technical solutions, specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0024] Example 1: This embodiment provides a rare earth element-doped transition metal molybdate nanosheet / N-doped hollow carbon foam material, the method specifically including the following steps: Step 1: Place melamine foam in a tube furnace, introduce argon gas, heat to 900°C at a rate of 5°C / min, hold for 3 hours to carry out pyrolysis reaction, and cool to room temperature at a rate of 5°C / min to obtain N-doped hollow carbon foam (NCF) with a three-dimensional hollow structure.

[0025] Step 2: Disperse and dissolve 0.0017 M La(NO3)3·6H2O, 0.033 M Na2MoO2·2H2O, 0.033 M Ni(NO3)2·6H2O, 0.05 M urea, and 0.067 M ammonium fluoride in deionized water; weigh 0.0035 g NCF and place it in the above mixed solution, let it stand for 4 hours; place the mixed solution containing NCF in a high-temperature reactor and react at 150°C for 8 hours; after the reaction is completed, wash the product and dry it at 60°C for 24 hours to obtain the intermediate product La-doped NiMoO4·xH2O / NCF.

[0026] Step 3: Place the intermediate product La-doped NiMoO4·xH2O / NCF in a tube furnace, introduce argon gas, heat to 300℃ at a rate of 5℃ / min, hold for 2 hours, and then cool to room temperature at a rate of 5℃ / min to obtain La-doped NiMoO4 nanosheets / NCF (LNM / NCF).

[0027] In this embodiment, the prepared La-doped NiMoO4 nanosheets / NCF were tested, and the minimum reflection loss was -38.41 dB. The effective absorption bandwidth was 6.08 GHz (11.92 to 18 GHz) when the matching thickness was 2.3 mm.

[0028] Example 2: This embodiment provides a rare earth element-doped transition metal molybdate nanosheet / N-doped hollow carbon foam material, the method specifically including the following steps: Step 1: Place melamine foam in a tube furnace, introduce argon gas, heat to 900°C at a rate of 5°C / min, hold for 3 hours to carry out pyrolysis reaction, and cool to room temperature at a rate of 5°C / min to obtain N-doped hollow carbon foam with a three-dimensional hollow structure.

[0029] Step 2: Disperse and dissolve 0.0017 M Ce(NO3)3·6H2O, 0.033 M Na2MoO4·2H2O, 0.033 M Ni(NO3)2·6H2O, 0.05 M urea, and 0.067 M ammonium fluoride in deionized water; weigh 0.0035 g NCF and place it in the above mixed solution, let it stand for 4 hours; place the mixed solution containing NCF in a high-temperature reactor and react at 150°C for 8 hours; after the reaction is completed, wash the product and dry it at 60°C for 24 hours to obtain the intermediate product Ce-doped NiMoO4·xH2O / NCF.

[0030] Step 3: Place the intermediate product Ce-doped NiMoO4·xH2O / NCF in a tube furnace, introduce argon gas, heat to 300°C at a rate of 5°C / min, hold for 2 hours, and then cool to room temperature at a rate of 5°C / min to obtain Ce-doped NiMoO4 nanosheets / NCF (CNM / NCF).

[0031] In this embodiment, the prepared Ce-doped NiMoO4 nanosheets / NCF were tested, and the minimum reflection loss was -18.85 dB. The effective absorption bandwidth was 4.16 GHz (13.84 to 18 GHz) when the matching thickness was 2.3 mm.

[0032] Example 3: This embodiment provides a rare earth element-doped transition metal molybdate nanosheet / N-doped hollow carbon foam material, the method specifically including the following steps: Step 1: Place melamine foam in a tube furnace, introduce argon gas, heat to 900°C at a rate of 5°C / min, hold for 3 hours to carry out pyrolysis reaction, and cool to room temperature at a rate of 5°C / min to obtain N-doped hollow carbon foam with a three-dimensional hollow structure.

[0033] Step 2: Disperse and dissolve 0.0017 M La(NO3)3·6H2O, 0.033 M Na2MoO4·2H2O, 0.033 M Co(NO3)2·6H2O, 0.05 M urea, and 0.067 M ammonium fluoride in deionized water; weigh 0.0035 g NCF and place it in the above mixed solution, and let it stand for 4 hours; place the mixed solution containing NCF in a high-temperature reactor and react at 150°C for 8 hours; after the reaction is completed, wash the product and dry it at 60°C for 24 hours to obtain the intermediate product La-doped CoMoO4·xH2O / NCF.

[0034] Step 3: Place the intermediate product La-doped CoMoO4·xH2O / NCF in a tube furnace, introduce argon gas, heat to 300°C at a rate of 5°C / min, hold for 2 hours, and then cool to room temperature at a rate of 5°C / min to obtain La-doped CoMoO4 nanosheets / NCF (LCM / NCF).

[0035] In this embodiment, the prepared La-doped CoMoO4 nanosheets / NCF were tested, and the minimum reflection loss was -52.4 dB. The effective absorption bandwidth was 6.26 GHz (11.92 to 18 GHz) with a matching thickness of 2.7 mm.

[0036] Example 4: This embodiment provides a rare earth element-doped transition metal molybdate nanosheet / N-doped hollow carbon foam material, the method specifically including the following steps: Step 1: Place melamine foam in a tube furnace, introduce argon gas, heat to 900°C at a rate of 5°C / min, hold for 3 hours to carry out pyrolysis reaction, and cool to room temperature at a rate of 5°C / min to obtain N-doped hollow carbon foam with a three-dimensional hollow structure.

[0037] Step 2: Disperse and dissolve 0.033 M Na2MoO4·2H2O, 0.033 M Ni(NO3)2·6H2O, 0.05 M urea, and 0.067 M ammonium fluoride in deionized water; weigh 0.0035 g NCF and place it in the above mixed solution, and let it stand for 4 hours; place the mixed solution containing NCF in a high-temperature reactor and react at 150°C for 8 hours; after the reaction is completed, wash the product and dry it at 60°C for 24 hours to obtain the intermediate product NiMoO4·xH2O / NCF.

[0038] Step 3: Place the intermediate product NiMoO4·xH2O / NCF in a tube furnace, introduce argon gas, heat to 300℃ at a rate of 5℃ / min, hold for 2 hours, and cool to room temperature at a rate of 5℃ / min to obtain NiMoO4 nanosheets / NCF (NM / NCF).

[0039] In this embodiment, the prepared NiMoO4 nanosheets / NCF were tested, and the minimum reflection loss was -13.98 dB. With a matching thickness of 2.5 mm, the effective absorption bandwidth was 2.8 GHz (13.36 to 16.16 GHz).

[0040] The following conclusions can be drawn from the above embodiments: This invention prepares N-doped hollow carbon foam with a three-dimensional hollow structure through high-temperature pyrolysis, such as... Figure 1As shown in the microscopic morphology diagram, this three-dimensional structure effectively reduces the density of the composite material and facilitates multiple reflections and refractions of electromagnetic waves within the composite material.

[0041] Figure 2 These are the microstructure diagram and elemental distribution diagram of LNM / NCF in Example 1. Figure 2 As shown in (a to b), lanthanum-doped NiMoO4 nanosheets are uniformly dispersed on the surface of the NCF framework. On the one hand, this helps to increase the specific surface area of ​​the composite material. On the other hand, the lanthanum-doped NiMoO4 nanosheets form a heterogeneous interface with the NCF matrix, which increases the interfacial polarization loss. At the same time, under an alternating electromagnetic field, the La elements doped on the NiMoO4 nanosheets are induced to oscillate as polarization centers, resulting in defect-induced polarization and enhancing the dielectric loss capability of the composite material against electromagnetic waves.

[0042] Figure 3 The image shows the XRD pattern of LNM / NCF in Example 1. In the image, 25.0°, 27.5°, 34.3°, 43.6° and 60.4° correspond to the (201), (20-2), (22-2), (42-2) and (620) crystal planes of NiMoO4, respectively (PDF#45-0142), which also confirms the preparation of NiMoO4 nanosheets.

[0043] Figure 4 These are electromagnetic wave absorption performance diagrams of the composite materials in Examples 1 to 4, for comparison. Figure 4 (ah) found that doping with rare earth elements effectively enhances the electromagnetic wave absorption performance of transition metal molybdate nanosheets / N-doped hollow carbon foams. The effective absorption bandwidth of LNM / NCF increased by 1.17 times compared with NM / NCF, and the effective absorption bandwidth of electromagnetic waves shifted to the low frequency region.

Claims

1. A method for preparing rare earth element-doped transition metal molybdate nanosheets / N-doped hollow carbon foam materials, characterized in that, The method specifically includes the following steps: Step 1: Place the amino-containing carbon foam in a tube furnace, introduce protective gas, heat it to 800-1100 ℃ at a rate of 1-10 ℃ / min, hold it at this temperature for 1-4 hours, and perform pyrolysis treatment. After holding, cool it to room temperature at a rate of 1-10 ℃ / min to obtain N-doped hollow carbon foam with a three-dimensional hollow structure. Step 2: Molybdenum source, transition metal source, rare earth element source, urea and ammonium fluoride are dispersed and dissolved in a solvent, and then N-doped hollow carbon foam is added. After standing, the mixed solution containing N-doped hollow carbon foam is placed in a reaction vessel and kept at 130-160℃ for 10-24 hours to carry out a hydrothermal reaction. After the hydrothermal reaction is completed, the product is washed and dried to obtain rare earth element-doped transition metal molybdate hydrate / N-doped hollow carbon foam. Step 3: Place the rare earth element-doped transition metal molybdate hydrate / N-doped hollow carbon foam in a tube furnace, introduce protective gas, heat to 300-450℃ at a rate of 1-10℃ / min, hold for 1-3 hours for heat treatment, and after holding, cool to room temperature at a rate of 1-10℃ / min to obtain rare earth element-doped transition metal molybdate nanosheets / N-doped hollow carbon foam material.

2. The method for preparing rare earth element-doped transition metal molybdate nanosheets / N-doped hollow carbon foam material as described in claim 1, characterized in that, In step one, the amino-containing carbon foam is a polymer-based foam material containing amino functional groups, and its polymer main chain or side chain contains at least one -NH2, -NH- or quaternary ammonium nitrogen functional group.

3. The method for preparing rare earth element-doped transition metal molybdate nanosheets / N-doped hollow carbon foam material as described in claim 2, characterized in that, In step one, the amino-containing polymer-based foam is one or more of the following: polyamide foam, polyamic acid and its prepolymer foam, polyurethane foam containing free or terminal amino groups, polyethyleneimine foam, polyacrylamide foam, chitosan foam, amino-modified phenolic foam, melamine foam, and other amino-modified polymer foams.

4. The preparation method of rare earth element-doped transition metal molybdate nanosheets / N-doped hollow carbon foam material as described in claim 1, characterized in that, In step one, the amino-containing carbon foam has an open or semi-open pore structure with a porosity of 30% to 99%, and has a block, sheet, skeleton, porous particle or aerogel structure.

5. The method for preparing rare earth element-doped transition metal molybdate nanosheets / N-doped hollow carbon foam material as described in claim 1, characterized in that, In step two, the final concentration of the molybdenum source is 0.03–0.3 M; the amount of N-doped hollow carbon foam used is 0.001–0.05 g.

6. The method for preparing rare earth element-doped transition metal molybdate nanosheets / N-doped hollow carbon foam material as described in claim 3, characterized in that, In step two, the molar ratio of molybdenum source to transition metal source is 1:0.33-3; the molar ratio of molybdenum source to rare earth element nitrate compound is 1:0.0013-0.

2.

7. The method for preparing rare earth element-doped transition metal molybdate nanosheets / N-doped hollow carbon foam material as described in claim 1, characterized in that, In step two, the rare earth element source is selected from one or more of La(NO3)3·6H2O, Ce(NO3)3·6H2O, Er(NO3)3·6H2O, Pr(NO3)3·6H2O, La(CH3COO)3·1.5H2O, Ce(CH3COO)3·1.5H2O, Er(CH3COO)3·H2O, and Pr(CH3COO)3·4H2O; the molybdenum source is selected from Na2MoO4, Na2MoO4·2H2O, and (NH4)6Mo7O. 24 One or more of ·4H2O; the transition metal source is selected from one or more of Ni(NO3)2·6H2O, Co(NO3)2·6H2O, Cu(NO3)2·6H2O, Ni(CH3COO)2·4H2O, Co(CH3COO)2·4H2O, and Cu(CH3COO)2·H2O.

8. A rare earth element-doped transition metal molybdate nanosheet / N-doped hollow carbon foam material prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The matrix of this material is an N-doped hollow carbon foam with a three-dimensional hollow structure, and rare earth element-doped transition metal molybdate nanosheets are uniformly distributed on the matrix surface.

9. The rare earth element-doped transition metal molybdate nanosheets / N-doped hollow carbon foam material as described in claim 8, characterized in that, The rare earth element is selected from one or more of lanthanum, cerium, praseodymium, and erbium; the transition metal molybdate is selected from one or more of NiMoO4, CoMoO4, and CuMoO4; and the N-doped hollow carbon foam is an amino-containing carbon foam obtained after pyrolysis.

10. The application of the rare earth element-doped transition metal molybdate nanosheets / N-doped hollow carbon foam material as described in claim 8 or 9 for absorbing electromagnetic waves.

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