Multifunctional MOFs derived metal selenide wave-absorbing powder as well as preparation method and application thereof

Abstract

The invention relates to multifunctional MOFs derived metal selenide wave-absorbing powder and a preparation method and application thereof.The wave-absorbing material is of a core-shell structure with a (CozNi1-z) xSey substance as a core and a carbon coating layer as a shell, the wave-absorbing powder is of a porous hollow spherical microstructure, and the particle size ranges from 6 micrometers to 10 micrometers. The bimetallic MOFs-derived (CozNi1-z) xSeyat C composite material with adjustable components is successfully prepared by fully utilizing heterogeneous interface engineering and a multi-loss synergistic mechanism derived from bimetallic MOFs, regulating and controlling the wave-absorbing performance of metal selenide wave-absorbing powder by virtue of a solvothermal method and a high-temperature selenylation method and adjusting the temperature in the selenylation reaction and pyrolysis process, and has the advantages that the preparation method is simple, the cost is low, and the application prospect is wide. The tunable characteristic of the absorption frequency band is realized; besides, due to improvement factors such as a unique core-shell microstructure, a rich heterogeneous interface, excellent impedance matching and the like, the electromagnetic wave absorption (EMWA) performance of the composite material can be enhanced, sufficient electromagnetic wave absorption is achieved within the range of 2-18 GHz, the RLmin value of-51.5 dB and the EAB value of 4 GHz are included, and excellent electromagnetic wave absorption is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-performance electromagnetic wave absorption functional materials, and relates to a multifunctional MOFs-derived metal selenide absorbing powder, a preparation method thereof, and an application thereof. Background Art

[0002] Microwave technology has been widely applied in military and civilian fields. With the further development of the fifth-generation mobile communication technology and the intelligentization of various fields, communication technologies using electromagnetic waves have brought great convenience to people's lives. However, at the same time, electromagnetic wave radiation has been generated, constituting harmful pollution. Electromagnetic pollution not only interferes with the normal operation of precision equipment, but also threatens human health and daily life, and even affects national defense security. Facing continuous electromagnetic pollution and high-frequency electromagnetic environments in the gigahertz frequency range, different from electromagnetic interference shielding materials, electromagnetic wave absorbing materials mainly convert electromagnetic energy into Joule energy, which is one of the effective means to purify the electromagnetic environment. In addition, military radar stealth materials also have higher requirements for electromagnetic wave absorbing materials. An ideal electromagnetic wave absorbing material (MAMs) should have the characteristics of thin thickness, light weight, wide absorption bandwidth, strong absorption, etc., to meet the requirements of various applications. Therefore, it has become an urgent need to develop high-performance microwave absorbing materials (MAMs) that can effectively absorb and attenuate electromagnetic waves.

[0003] In view of the different requirements for high-performance electromagnetic wave absorbing materials, porous metal-organic framework materials (MOFs) with high porosity, large specific surface area, and controllable morphology are expected to meet diverse application requirements and at the same time solve technical problems such as large density, large thickness, narrow absorption bandwidth, and low absorption intensity of traditional electromagnetic wave absorbing materials. Metal-organic framework (MOFs)-derived carbon materials are considered a reasonable choice for preparing high-performance electromagnetic wave absorbers due to their unique microstructure, multi-component synergistic effect, and modifiability. On the one hand, compared with other absorbers, MOFs-derived absorbers will generate a carbon matrix during the annealing process, which greatly increases the conductivity of the material, thereby improving the conductive loss. On the other hand, the unique morphology structure is conducive to improving the impedance matching characteristics of the material through various chemical methods. The synthesis of multiphase MAMs composed of porous carbon materials, metal oxides / carbides, and their composites can be achieved by the pyrolysis of MOF precursors.

[0004] In terms of material modification, metal chalcogenides such as metal sulfides and selenides have advantages as microwave absorbers over their corresponding oxides. Among them, the heterointerface engineering and multiple loss synergistic mechanism derived from bimetallic MOFs provide a new perspective for the preparation of high-performance electromagnetic wave absorption functional materials. Although the bimetallic MOFs-derived strategy has been used to develop high-performance electromagnetic wave absorption functional materials, there are still significant deficiencies in the electromagnetic wave absorption performance of existing bimetallic MOFs-derived composites, such as large density, large thickness, narrow absorption bandwidth, low absorption intensity, and other problems. Moreover, in the face of the requirements of various applications, especially in special fields such as military radar stealth, solving the technical problems of large density, large thickness, narrow absorption bandwidth, low absorption intensity, etc. of electromagnetic wave absorption materials has become a difficult point in the professional field. Therefore, it is of great value to study the structure regulation, structure-activity relationship, and controllable synthesis method of high-performance electromagnetic wave absorption functional materials (MAMs).

[0005] The present invention is precisely proposed based on this. Summary of the Invention

[0006] The purpose of the present invention is to provide a multifunctional MOFs-derived metal selenide absorbing powder, its preparation method and application, so as to solve the problems of large density, large thickness, narrow absorption bandwidth, low absorption intensity, etc. of existing electromagnetic wave absorption materials.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] On the one hand, the present invention provides a multifunctional MOFs-derived metal selenide absorbing powder, which shows that a dense and dispersed (agglomeration-free) layer of cobalt-nickel selenide nanoparticles (i.e., (Co z Ni 1-z ) x Se y ) is in-situ generated on the surface of the graphitized carbon shell. The (Co z Ni 1-z ) x Se y @C absorbing powder is a porous hollow spherical microstructure with a particle size of 6 - 10 μm. Specifically, the size of the distributed metal selenide nanoparticles is about 50 - 200 nm.

[0009] On the second hand, the present invention provides a preparation method of a multifunctional MOFs-derived metal selenide absorbing powder, including the following steps:

[0010] S1. Take soluble nickel salt, soluble cobalt salt, H3BTC, and PVP and dissolve them in a solvent. After stirring evenly, transfer them to an autoclave and seal it, and carry out a solvothermal reaction. The obtained reaction product is centrifuged, washed, and dried to obtain a CoNi-MOF precursor powder;

[0011] S2. Place the selenium powder and the CoNi-MOF precursor powder at the upwind and downwind of the tube furnace respectively, continuously introduce an Ar / H2 atmosphere, heat up for the selenization reaction to obtain the multifunctional MOFs-derived metal selenide microwave absorption powder.

[0012] Further, in S1, the soluble nickel salt is Ni(NO3)2 or its hydrate, and the soluble cobalt salt is Co(NO3)2 or its 6H2O.

[0013] Further, in S1, the addition ratio of the soluble nickel salt, the soluble cobalt salt, H3BTC, and PVP is 2 mmol : (3.5 - 4.5) mmol : (0.5 - 0.7) g : (1.8 - 2.2) g, preferably 2 mmol : 4 mmol : 0.6 g : 2.0 g.

[0014] Further, in S1, the solvent is composed of equal volumes of deionized water, absolute ethanol, and DMF.

[0015] Further, in S1, the temperature of the solvothermal reaction is 195 - 205 °C, preferably 200 °C, and the time is 12 - 18 h. Here, the main purpose of controlling the temperature and time of the solvothermal reaction is to make the solvothermal reaction complete and sufficient, and improve the yield of the CoNi-MOF precursor powder in the subsequent steps.

[0016] Meanwhile, after the solvothermal reaction, it is necessary to let it stand and cool to room temperature before taking out the product from the reaction kettle to prevent personal danger caused by the boiling of the solution and the too high pressure in the reaction kettle. Centrifuge at a rate of 6000 r / min, with a single centrifugation time of about 3 - 5 minutes. After each centrifugation, wash thoroughly and repeat the cycle 3 times or more to eliminate the influence of residual impurities as much as possible and retain the 6 - 10 μm spherical structure characteristics of the CoNi-MOF precursor.

[0017] Further, in S2, the mass ratio of the selenium powder to the CoNi-MOF precursor powder is 1.8 - 2.2 : 1, preferably 2 : 1. Here, the selenium powder and the CoNi-MOF precursor powder are respectively placed in two open and adjacent quartz crucibles. Place the selenium powder at the upwind, so that the gas-phase deposition distance between the selenium powder and the CoNi-MOF precursor can be shortened, greatly improving the success rate of the chemical reaction. At the same time, use a tube furnace with a furnace tube size of 60 mm * 1200 mm and a rated voltage of 3 kw. The flow rate of the H2 / Ar gas introduced should be set at 100 - 300 mL / min and should not be too high. Otherwise, after the selenium powder volatilizes, the gas-phase substances will be quickly discharged from the tube furnace with the flowing gas, which is not conducive to diffusing to the surface of the CoNi-MOF precursor, bringing a negative impact on the gas-phase deposition process of the selenization reaction, and further affecting the effect of the subsequent selenization reaction.

[0018] Further, in S2, the temperature of the selenization reaction is 500 - 700 °C, the time is 4 - 6 h, preferably 5 h. By controlling the temperature of the selenization reaction, (Co z Ni 1-z ) x Se y bimetal selenides with different stoichiometric ratios can be synthesized. However, the temperature should not be too high or too low, otherwise it will directly affect the effect of the selenization reaction and the physical and chemical properties of the selenized product.

[0019] Further, in S2, in the Ar / H2 atmosphere, the volume fraction of H2 is 5%.

[0020] In a third aspect, the present invention provides an application of a multifunctional MOFs-derived metal selenide absorbing powder as a high-performance electromagnetic wave absorbing functional material.

[0021] Through research, the present invention finds that selenium powder (Se) has the property of being easily volatilized by heat. Using the chemical vapor deposition (CVD) method, selenized products can be obtained with high efficiency. At the same time, the selenization reaction promotes the formation of heterogeneous interfaces in the microstructure of the material. According to the Maxwell-Wagner-Sillars theory, the interfacial polarization behavior results from the redistribution of charges caused by an inhomogeneous interface with different dielectric properties and conductivity differences. The electronic properties and bonding states in the heterogeneous interface region are different from those in the homogeneous interface region, leading to an uneven spatial charge distribution, thereby generating an electric dipole moment. Under the action of an alternating electromagnetic field, the aggregation of carriers and the subsequent polarization relaxation process result in the interfacial polarization phenomenon. Therefore, the construction of heterogeneous interfaces is beneficial to introducing a more intense interfacial polarization process, improving the polarization loss of electromagnetic wave materials, and thus improving the electromagnetic wave absorption (EMWA) performance of the composite material.

[0022] Based on this, the present invention makes full use of the solvothermal method and the high-temperature selenization method to regulate the wave absorption performance of the metal selenide absorbing powder by adjusting the temperature of the selenization reaction and the pyrolysis process, and successfully prepares a composition-tunable bimetal MOFs-derived (Co z Ni 1-z ) x Se y @C composite material. Specifically, by controlling the temperature of the selenization reaction, (Co z Ni 1-z ) x Se y with different stoichiometric ratios can be synthesized, further realizing the regulation of the morphology and structure by chemical components. According to the structure-activity relationship, the inherent dielectric and electromagnetic parameters can be adjusted, thereby adjusting the bandwidth absorption characteristics. Using trimesic acid (H3BTC) as the organic ligand, Co 2+ 、Ni 2+It is a metal main body. By using polyvinylpyrrolidone (PVP) as an adhesive, the preparation of spherical CoNi-MOF precursors can be achieved through a solvothermal method. In the chemical vapor deposition (CVD) process in a tubular furnace, taking advantage of the property that selenium powder (Se) is volatile when heated, the gas will drive the rapid diffusion of selenium powder (Se) to the surface of the CoNi-MOF precursor and a violent selenization reaction will occur. Due to the phase change and recrystallization during the selenization reaction and high-temperature pyrolysis process, a large number of spherical grains grow on the surface of the sphere, forming metal selenide nanoparticles with high surface energy. At the same time, it catalyzes the organic ligand to form a graphitized carbon shell, realizing a complete carbon-encapsulated structure. Using an Ar / H2 flowing atmosphere has two important functions: on the one hand, it can provide a suitable product combination environment for the selenization process, facilitating the targeted diffusion of the Se source to the surface of the CoNi-MOF precursor. On the other hand, the Ar / H2 atmosphere, as a reducing gas, is used to reduce the catalytic properties of Co and Ni metals, enabling cobalt-nickel selenide with high surface energy to catalyze the organic ligand (polyvinylpyrrolidone) to generate a graphitized carbon shell. In subsequent reactions, cobalt-nickel selenide can further in-situ grow into nanoparticles with the help of the graphitized carbon shell.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The present invention makes full use of the heterogeneous interface engineering and multiple loss synergistic mechanisms. By means of the solvothermal method and high-temperature selenization method, the electromagnetic wave absorption performance of metal selenide absorbing powder is regulated by adjusting the temperature of the selenization reaction and pyrolysis process, and a dual-metal MOFs-derived (Co z Ni 1-z ) x Se y @C composite material is successfully prepared. Specifically, by controlling the temperature of the selenization reaction, (Co z Ni 1-z ) x Se y with different stoichiometric ratios can be synthesized, further realizing the regulation of the morphology and structure by chemical components. According to the structure-activity relationship, the inherent dielectric and electromagnetic parameters can be adjusted to achieve the tunable characteristics of the absorption band, solving the problem of poor tunability of traditional absorbing materials.

[0025] (2) The present invention provides an innovative and reliable research design scheme. Due to improved factors such as rich heterogeneous interfaces and excellent impedance matching, the electromagnetic wave absorption (EMWA) performance of the composite material can be enhanced, which is of great significance for the preparation and use of high-performance electromagnetic wave absorption functional materials (MAMs). Specifically, selenization improves the impedance matching (Z in), allowing more electromagnetic waves to enter the interior of the wave-absorbing material; at the same time, affected by the in-situ grown selenide protrusions on the surface, the porous structure of the MOFs-derived skeleton, and the morphological and structural characteristics such as hollow spheres, the EMW transmission path is extended, promoting the reflection and scattering processes; after growth, (Co z Ni 1-z )) x Se y -C heterointerface can promote interfacial polarization and improve interfacial loss; under the combined action of the abundant functional groups (C-C, C=O, C-N / C=N) and selenium vacancy defects in the microspheres, under the condition of high-frequency electromagnetic fields, the charge balance is disrupted, acting as a polarization center to induce dipole polarization, combined with the conductive network, jointly improving the polarization loss and conduction loss.

[0026] (3) The present invention can prepare high-performance electromagnetic wave absorption functional materials with thin thickness, low density, wide absorption frequency band, and strong absorption, solving the problems of low absorption intensity, narrow absorption frequency band, large density, and large thickness of traditional wave-absorbing materials, meeting the requirements of various applications, especially in special fields such as military radar stealth. In the range of 2-18 GHz, the minimum reflection loss (R min ) can reach -51 dB, and the corresponding minimum thickness (d min ) is only 1.5 mm, and the effective absorption bandwidth (EAB) can reach 4 GHz, achieving excellent electromagnetic wave absorption. In addition, by adjusting the matching thickness of the composite material from 1.5 to 5.0 mm, sufficient electromagnetic wave absorption can be obtained in the entire S, C, X, and Ku bands. Brief Description of the Drawings

[0027] Figure 1 Synthesis schematic diagram of bimetallic MOFs-derived (Co z Ni 1-z )) x Se y @C composite material;

[0028] Figure 2 SEM image of the sample in Example 1;

[0029] Figure 3 SEM image of the sample in Example 2;

[0030] Figure 4 SEM image of the sample in Example 3;

[0031] Figure 5 XRD patterns of the samples in Examples 1, 2, and 3;

[0032] Figure 6 Raman spectra of the samples in Examples 1, 2, and 3;

[0033] Figure 7Reflection loss diagram of the sample in Example 1;

[0034] Figure 8 Reflection loss diagram of the sample in Example 2;

[0035] Figure 9 Reflection loss diagram of the sample in Example 3;

[0036] Figure 10 Impedance matching diagram of the samples in Examples 1, 2, and 3;

[0037] Figure 11 、 12 Dielectric constant diagram of the samples in Examples 1, 2, and 3;

[0038] Figure 13 Dielectric tangent value diagram of the samples in Examples 1, 2, and 3;

[0039] Figure 14 HRTEM diagram of the samples in Examples 1, 2, and 3. Detailed implementation manners

[0040] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0042] The selection scope of the terms “and / or”, “or / and”, and “and / or” used herein includes any one of two or more related listed items, and also includes any and all combinations of the related listed items. The said any and all combinations include combinations of any two related listed items, any more related listed items, or all related listed items. It should be noted that when at least two conjunctions selected from “and / or”, “or / and”, and “and / or” are used to connect at least three items, it should be understood that in this application, this technical solution undoubtedly includes the technical solution connected by “logical AND” and also undoubtedly includes the technical solution connected by “logical OR”.

[0043] In this application, among the technical features described in an open-ended manner, it includes a closed technical solution composed of the listed features, and also includes an open technical solution containing the listed features.

[0044] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as every value between such minimum and maximum values. Further, when the range refers to integers, every integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0045] Only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recited.

[0046] For the temperature parameters in this application, unless otherwise specified, both constant temperature treatment and treatment within a certain temperature range are allowed. The constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuation within ranges such as ±5°C, ±4°C, ±3°C, ±2°C, ±1°C is allowed.

[0047] In this article, the "suitable combination method", "suitable method", "any suitable method", etc., the "suitable" mentioned therein shall be subject to being able to implement the technical solution of this application, solve the technical problems of this application, and achieve the expected technical effects of this application.

[0048] In this application, "further", "even further", "especially", etc. are used for descriptive purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0049] In this application, "optionally", "optional", "option", mean optional, that is, it refers to any one of the two parallel options of "having" or "not having". If "optional" appears multiple times in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction relationship, each "optional" is independent of each other.

[0050] In the description of the application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise specifically limited.

[0051] Unless otherwise specified, all formulations and tests occur in an environment of 25°C in this article.

[0052] In this text, terms such as "include", "comprise", "contain", "have" or other variants are intended to cover non-closed inclusion, and no distinction is made among these terms. The term "comprise" means that other steps and components can be added without affecting the final result. The compositions and methods / processes of the present invention comprise, consist of, and consist essentially of the essential elements and limitations described herein, as well as any additional or optional components, ingredients, steps or limitations described herein. In this text, no distinction is made among the terms "efficacy", "performance", "effect", and "efficiency".

[0053] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution. If not otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0054] If not otherwise specified, all steps of the present application can be carried out sequentially or randomly, and preferably sequentially.

[0055] In order to solve the technical problems such as high density, large thickness, narrow absorption frequency band, and low absorption intensity of electromagnetic wave absorption materials, taking nickel nitrate hexahydrate as the soluble nickel salt and cobalt nitrate hexahydrate as the soluble cobalt salt as examples, the present invention provides a preparation of a bimetallic MOFs-derived (Co z Ni 1-z ) x Se y @C composite material, referring to the process shown in Figure 1 as follows:

[0056] S1 Magnetically stir and mix deionized (DI) water, anhydrous ethanol, and N, N-dimethylformamide (DMF) with appropriate concentration ratios to prepare a homogeneous solution, denoted as solution A;

[0057] S2 Dissolve appropriate amounts of Ni(NO3)2·6H2O, Co(NO3)2·6H2O, H3BTC, and PVP in solution A under magnetic stirring, continuously stir, and then transfer it to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene, seal it, and carry out a solvothermal reaction. Subsequently, collect the precipitate by centrifugation and wash it several times (with deionized water and ethanol), and finally dry it in a vacuum oven to obtain the CoNi-MOF precursor powder.

[0058] S3 Put selenium powder and CoNi-MOF precursor powder into a quartz crucible in a certain mass ratio, and place them in the upper and lower wind directions of a tube furnace respectively. Continuously and slowly introduce an Ar / H2 atmosphere, and carry out a selenization reaction at a certain heating rate and pyrolysis temperature to obtain the MOFs-derived multifunctional metal selenide microwave absorption powder.

[0059] In the following examples and comparative examples, nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 99%), cobalt nitrate hexahydrate (Co(NO3)2·6H2O, 99%) and trimesic acid (trimellitic acid, H3BTC, 99%) were purchased from Shanghai Aladdin Reagent Co., Ltd. Selenium powder (Se, 99.9%) was purchased from Shanghai Macklin Biochemical Co., Ltd. Reagents such as polyvinylpyrrolidone (PVP-K30), N,N-dimethylformamide (DMF), and absolute ethanol were provided by Sinopharm Chemical Reagent Co., Ltd. The Milli-Q system was used to provide deionized (DI) water.

[0060] Example 1:

[0061] Step 1: Solution preparation and solvothermal reaction

[0062] A binary MOF precursor was prepared by a solvothermal method. First, under constant stirring, 2 mmol of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), 4 mmol of cobalt nitrate hexahydrate (Co(NO3)2·6H2O), 0.6 g of trimesic acid (H3BTC), and 2.0 g of polyvinylpyrrolidone (PVP, K30) were dissolved in a homogeneous solution composed of 60 mL of equal volumes of deionized (DI) water, absolute ethanol, and DMF, and continuously stirred for 30 min. Then, it was transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene, sealed, and maintained at 200 °C for 12 hours. Finally, the purple precipitate was collected by centrifugation and washed several times (with deionized water and ethanol), and dried in a vacuum oven at 60 °C for 6 hours to obtain the product.

[0063] Step 2: Selenization reaction

[0064] The CoNi-MOF and selenium (Se) powder were placed in two quartz crucibles at a mass ratio of 1:2. Among them, the Se powder was placed upstream in the tubular furnace, while the CoNi-MOF was placed downstream. In a 5% Ar / H2 atmosphere, it was selenized at 500 °C for 5 hours at a heating rate of 2 °C min -1 to obtain (Co z Ni 1-z ) x Se y @C composite material.

[0065] Example 2

[0066] Step 1: Solution preparation and solvothermal reaction

[0067] Prepare a binary MOF precursor by the solvothermal method. First, under constant stirring, dissolve 2 mmol of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), 4 mmol of cobalt nitrate hexahydrate (Co(NO3)2·6H2O), 0.6 g of trimesic acid (H3BTC), and 2.0 g of polyvinylpyrrolidone (PVP, K30) in a homogeneous solution composed of 60 mL of equal volumes of deionized (DI) water, absolute ethanol, and DMF, and stir continuously for 30 min. Then, transfer it to a 100 mL stainless-steel autoclave lined with polytetrafluoroethylene, seal it, and maintain it at 200 °C for 12 hours. Finally, collect the purple precipitate by centrifugation and wash it several times (with deionized water and ethanol), and dry it in a vacuum oven at 60 °C for 6 hours to obtain the product.

[0068] Step 2: Selenization reaction

[0069] Place CoNi-MOF and selenium (Se) powder in two quartz crucibles at a mass ratio of 1:2. Among them, the Se powder is placed upstream in the tubular furnace, while the CoNi-MOF is placed downstream. In a 5% Ar / H2 atmosphere, at a heating rate of 2 °C min -1 and seleniumize at 600 °C for 5 hours to obtain (Co z Ni 1-z ) x Se y @C composite material.

[0070] Example 3

[0071] Step 1: Solution preparation and solvothermal reaction

[0072] Prepare a binary MOF precursor by the solvothermal method. First, under constant stirring, dissolve 2 mmol of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), 4 mmol of cobalt nitrate hexahydrate (Co(NO3)2·6H2O), 0.6 g of trimesic acid (H3BTC), and 2.0 g of polyvinylpyrrolidone (PVP, K30) in a homogeneous solution composed of 60 mL of equal volumes of deionized (DI) water, absolute ethanol, and DMF, and stir continuously for 30 min. Then, transfer it to a 100 mL stainless-steel autoclave lined with polytetrafluoroethylene, seal it, and maintain it at 200 °C for 12 hours. Finally, collect the purple precipitate by centrifugation and wash it several times (with deionized water and ethanol), and dry it in a vacuum oven at 60 °C for 6 hours to obtain the product.

[0073] Step 2: Selenization reaction

[0074] The CoNi-MOF and selenium (Se) powder were placed in two quartz crucibles at a mass ratio of 1:2. Among them, the Se powder was placed upstream of the tube furnace, while the CoNi-MOF was placed downstream. In a 5% Ar / H2 atmosphere, it was selenized at 700 °C for 5 hours at a heating rate of 2 °C min -1 to obtain (Co z Ni 1-z ) x Se y @C composite materials.

[0075] Sample analysis

[0076] The morphology of the multifunctional MOFs-derived metal selenide microwave absorption powder prepared in the examples was observed: Figures 2 - 4 They are the SEM images of the selenized products in Examples 1 to 3 respectively. From the figure, we can observe an obvious hollow microsphere morphology. After the selenization reaction, the carbon of the ligand was pyrolyzed to form a carbon-encapsulated structure of (Co z Ni 1-z ) x Se y @C composite materials, and the spherical structure of NiCo-MOF was maintained, with the microsphere particle size of 6 - 10 μm. The (Co z Ni 1-z ) x Se y nanoparticles in situ grown on the surface of the graphitized carbon shell have a size of about 50 - 100 nm and are relatively well dispersed. From Figures 2 - 4 the comparison, we can see that with the increase of the selenization reaction and pyrolysis temperature, the nanoparticle size decreases relatively, which is mainly due to the decomposition of NiSe2 and CoSe2 into NiSe and CoSe nanoparticles at high calcination temperatures.

[0077] The XRD characterization of the multifunctional MOFs-derived metal selenide microwave absorption powder prepared in the examples was carried out: Figure 5 They are the XRD patterns of the selenized products in Examples 1, 2, and 3. The sample numbers CoNi-MOF-Se-500 / 600 / 700 in the figure correspond to Examples 1 / 2 / 3 respectively. From the figure, it can be seen that the diffraction peaks of Co3Se4, CoSe, and CoSe2 show high purity and crystallinity, and controlling the selenization annealing temperature can effectively regulate the stoichiometric coefficient ratio of the selenized products. The results show that the selenization reaction at 500 °C produced CoSe2-NiSe2, and Co3Se4-NiSe2 and CoSe-NiSe were produced at 600 and 700 °C respectively, which can be attributed to the fact that metal selenides are more stable at lower temperatures. With the reaction temperature increasing from 500 °C to 700 °C, the selenized products are prone to decomposition at high temperatures, and selenium atoms tend to form 1:1 selenides with cobalt and nickel.

[0078] The Raman spectrum characterization was carried out on the multifunctional MOFs-derived metal selenide microwave absorption powder prepared in the examples: Figure 6 Figs. are the Raman spectra of the selenization products in Examples 1, 2, and 3. In the figures, the sample numbers NiCo-Se-MOF-500 / 600 / 700 correspond to Examples 1 / 2 / 3 respectively. It can be observed from the Raman curves that obvious diffraction peaks exist near 1322 cm -1 (D band) and 1598 cm -1 (G band), which originate from the crystal defects of C atoms and the in-plane stretching vibration of sp2 hybridization respectively. The intensity ratio (I D / I G ) of the D peak and the G peak is an important parameter for evaluating the lattice distortion and graphitization degree of carbon materials. The lower the I D / I G value, the higher the graphitization or defect degree. After calculation, the I D / I G values of NiCo-MOF-Se-500, NiCo-MOF-Se-600, and NiCo-MOF-Se-700 are 1.01, 1.00, and 0.98 respectively. Therefore, appropriately increasing the temperature of the selenization reaction and the pyrolysis process is beneficial to improving the graphitization degree of the sample, thereby affecting the increase in the dielectric constant related to conductivity. The lower I D / I G value means that there is a large amount of disordered carbon or defects in the composite material. The synergistic effect of the ideal defects combined with the selenium vacancies in the microspheres after the selenization reaction is conducive to being recognized as polarization centers under the excitation of the electromagnetic field, destroying the balance of the charge density between regions, and further inducing dipole polarization behavior, improving the EMWA performance of the composite material.

[0079] Figures 7 - 9 Figs. are the reflection loss diagrams of the samples in Examples 1 to 3: It can be seen from the figures that when the selenization reaction and the pyrolysis temperature are 500 and 600 °C, excellent RL min of -51.5 dB and -51.1 dB are achieved, the minimum thickness is only 1.5 mm, and the EAB value is as high as 4 GHz. Figure 10 Fig. is the impedance matching diagram of the samples in Examples 1, 2, and 3. The excellent impedance matching characteristics enable the electromagnetic wave to penetrate into the material as much as possible, which is conducive to the dissipation of the electromagnetic wave. Figure 11 , 12 Figs. are the dielectric constant diagrams of the samples in Examples 1, 2, and 3. For the ε’ curve, the ε’ value of the sample increases with the increase of the selenization temperature. A higher dielectric constant often produces a skin effect on the material surface, resulting in poor impedance matching characteristics. The ε” curve shows multiple resonance peaks in the high-frequency region (8 - 18 GHz), indicating the existence of multiple polarization relaxation phenomena.Figure 13 Dielectric tangent value graphs of the samples in Examples 1, 2, and 3. tan(ε) shows a relatively stable tangent value trend in the range of 2 - 18 GHz, indicating a stable dielectric loss ability. (Co z Ni 1-z ) x Se y Charge accumulation at the heterointerface between the Se substance and the carbon shell promotes interfacial polarization. Abundant defects such as Se vacancies and polar functional groups (C─O, C=O) become polarization centers, promoting dipole polarization.

[0080] Figure 14 HRTEM images of the crystal phases and interfaces of the cobalt nickel selenide products of the samples in Examples 1 - 3: Figure 14 a shows the HRTEM image of CoNi - MOF - Se - 500. Further processing of the interface information reveals a heterostructure composed of NiSe2 and CoSe2. Here, typical representative crystal phase information is presented. The lattice fringe with an interplanar spacing of 0.268 nm corresponds to the (210) crystal plane of NiSe2, and its lattice distortion is relatively obvious ( Figure 14 e). The lattice fringe with an interplanar spacing of 0.294 nm corresponds to the (200) crystal plane of CoSe2 ( Figure 14 d). There is an obvious grain boundary between the two phases, indicating the successful construction of a heterointerface at the nanoscale, which is conducive to triggering the interface effect. Similar interface characteristics are also observed in CoNi - MOF - Se - 700, a heterostructure composed of NiSe and CoSe, and there is also a significant grain boundary ( Figure 14 c). The lattice fringes with interplanar spacings of 0.149 nm and 0.320 nm correspond to hexagonal CoSe and NiSe ( Figure 14 f - g). In this technology, a precursor system with great phase change potential is created based on the solvothermal method. The catalytic properties of the metal can be effectively restored and the high diffusion and nucleation efficiency enable the organic ligands to be transformed into a complete carbon - encapsulated structure. We can clearly observe in all (Co z Ni 1-z ) x Se y @C microspheres that multiple inseparable heterointerfaces are formed between the selenide and the graphitized carbon shell (such as NiSe2 - C, CoSe2 - C, NiSe - C, and CoSe - C). In CoNi - MOF - Se - 600, a four - phase interface amplification of NiSe2, CoSe2, NiSe, and CoSe is successfully achieved ( Figure 14 b). In addition, a large number of lattice defects are observed in the CoNi - MOF - Se - 600 sample, such as point defects, lattice stacking, distortion, and disappearance, existing on the surfaces and interfaces of multiple phases ( Figure 14h). Therefore, by using cobalt and nickel atoms to compete for the control of the binding of the selenized product, through the ingenious introduction of element competition and multiphase fission, and at the same time screening out a bimetallic precursor system with great phase change potential, it is beneficial to achieve the maximized interfacial effect. In terms of performance, CoNi-MOF-Se-600 prepared by using this technology, which has a rich heterostructure and a maximized interfacial effect, exhibits the best electromagnetic wave absorption performance.

[0081] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. Obviously, those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A multifunctional MOFs-derived metal selenide absorbing powder, characterized in that: The microwave absorbing powder is obtained by in-situ generating a layer of dense and dispersed cobalt nickel selenide nanoparticles on the surface of the graphitized carbon shell. The microwave absorbing powder is a porous hollow spherical microstructure with a particle size of 6-10 μm.

2. The method for preparing a multifunctional MOFs-derived metal selenide absorbing powder according to claim 1, characterized in that: The following steps are involved: S1. Dissolve soluble nickel salt, soluble cobalt salt, H3BTC and PVP in a solvent, stir evenly and transfer to an autoclave, seal and perform a solvent thermal reaction. Centrifuge, wash and dry the reaction product to obtain a CoNi-MOF precursor powder. S2. Selenium powder and CoNi-MOF precursor powder are placed in the upper and lower wind directions of a tube furnace respectively, and an Ar / H2 atmosphere is continuously introduced, and the temperature is increased to perform a selenization reaction to obtain a multifunctional MOFs-derived metal selenide absorbing powder.

3. The method for preparing a multifunctional MOFs-derived metal selenide absorbing powder according to claim 2, characterized in that: In S1, the soluble nickel salt is Ni(NO3)2 or its hydrate, and the soluble cobalt salt is Co(NO3)2 or its 6H2O.

4. The method for preparing a multifunctional MOFs-derived metal selenide absorbing powder according to claim 2, characterized in that: In S1, the ratio of the added amounts of soluble nickel salt, soluble cobalt salt, H3BTC, and PVP is 2 mmol: (3.5-4.5) mmol: (0.5-0.7) g: (1.8-2.2) g.

5. The method for preparing a multifunctional MOFs-derived metal selenide absorbing powder according to claim 2, characterized in that: In S1, the solvent consists of equal volumes of deionized water, anhydrous ethanol and DMF.

6. The method for preparing a multifunctional MOFs-derived metal selenide absorbing powder according to claim 2, characterized in that: In S1, the temperature of the solvent thermal reaction is 195-205°C and the time is 12-18 hours.

7. The method for preparing a multifunctional MOFs-derived metal selenide absorbing powder according to claim 2, characterized in that: In S2, the mass ratio of selenium powder and CoNi-MOF precursor powder is 1.8-2.2:

1.

8. The method for preparing a multifunctional MOFs-derived metal selenide absorbing powder according to claim 2, characterized in that: In S2, the temperature of the selenization reaction is 500-700°C and the time is 4-6 hours.

9. The method for preparing a multifunctional MOFs-derived metal selenide absorbing powder according to claim 2, characterized in that: In S2, the volume fraction of H2 in the Ar / H2 atmosphere is 5%.

10. Use of the multifunctional MOFs-derived metal selenide absorbing powder as claimed in claim 1 as a high-performance electromagnetic wave absorbing functional material.

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