Radio frequency negative dielectric nano material derived from zeolite imidazate skeleton and preparation method thereof

Abstract

The invention relates to the technical field of negative dielectric materials, in particular to a radio frequency negative dielectric nano material derived from a zeolite imidazate framework and a preparation method, and the preparation method comprises the following steps: 1) dissolving 2-methylimidazole and polyvinylpyrrolidone in deionized water, and recording as a solution A; 2) dissolving zinc acetate and cobalt chloride hexahydrate in deionized water to obtain a solution B; the molar ratio of zinc acetate to cobalt chloride hexahydrate is 1: 2; 3) mixing the solution A and the solution B, stirring at 80 DEG C, and then stirring the mixture at room temperature; centrifuging the mixture, and performing freeze drying to obtain ZIF (at) ZnCo; and 4) heating the ZIF (at) ZnCo in argon at 900 DEG C to obtain the radio frequency negative dielectric nano material derived from the zeolite imidazate skeleton. According to the invention, the radio frequency negative dielectric characteristic in the nanostructure is successfully proved by using a method derived from a zeolite imidazate framework (ZIF) for the first time.

Description

Technical Field

[0001] The present invention relates to the technical field of negative dielectric materials, and specifically relates to a radio frequency negative dielectric nanomaterial derived from a zeolite imidazolate skeleton and a preparation method thereof. Background Art

[0002] Dielectric near-zero (ENZ) materials have attracted widespread attention due to their unique properties such as near-zero phase transition, refractive index, and perfect absorption. ENZ materials can be easily realized in the infrared and optical bands because the intrinsic plasma frequency is located in or near these bands (some semiconductors are located in the infrared band, while gold, silver, and copper are close to the optical band). Therefore, ENZ materials have been widely used in the infrared and optical bands, promoting the development of some new devices such as nano-optical circuits, super lenses, and photocatalysts.

[0003] However, with the development towards lower frequencies, single-phase materials have not been found to have intrinsic plasma frequencies in the RF band, that is, single-phase materials cannot achieve RF ENZ, which is a material problem. So far, RF ENZ properties are mainly achieved by metamaterials containing artificial arrays, and their properties are closely related to geometric factors, including the shape, size and arrangement of the units. The research group of the inventor proposed the academic idea of ​​deconstructing and reconstructing metamaterials using composite technology. That is, the plasma material in the artificial array is deconstructed into a functional filler in the composite material, while the insulating substrate acts as the matrix in the composite material. Reconstruction refers to the assembly of micro-nano fillers into a specific orientation or no orientation, and a percolation effect occurs, which is called a percolation supercomposite material. This idea has been used to achieve RF ENZ properties. For example, RF ENZ is obtained in polyolefin elastomer @ graphene / carbon nanotube (PGC) materials, and the ENZ performance is adjusted by component content, Lego-style lamination and photothermal strategy. RF ENZ can only be obtained in polyvinyl alcohol / Ni @ CNTs films when the content of Ni @ CNTs filler is higher than the percolation threshold, and the percolation behavior is dominant. Fundamentally, the ENZ obtained from these infiltrated composites have the same properties, which are closely related to the microstructure and material size. Unfortunately, the random microstructure of the infiltrated composites may lead to unstable ENZ performance. Specifically, the macroscopic size of the composite may fluctuate during the material processing, resulting in failure of equivalent performance.

[0004] Therefore, how to design a nanostructure to achieve ENZ performance in the RF band has become one of the important research directions in this field. Summary of the invention

[0005] The object of the present invention is to provide a radio frequency negative dielectric nanomaterial derived from a zeolite imidazolate framework and a preparation method thereof.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing a radio frequency negative dielectric nanomaterial derived from a zeolite imidazolate framework comprises the following steps:

[0008] (1) Dissolve 2-methylimidazole and polyvinylpyrrolidone in deionized water, referred to as solution A;

[0009] (2) dissolving zinc acetate and cobalt chloride hexahydrate in deionized water, which is referred to as solution B; the molar ratio of zinc acetate to cobalt chloride hexahydrate is 1:2;

[0010] (3) Solution A and solution B were mixed and stirred at 80°C, and then the mixture was stirred at room temperature; the mixture was centrifuged and freeze-dried to obtain ZIF@ZnCo;

[0011] (4) ZIF@ZnCo was heated at 900 °C in argon to obtain RF negative dielectric nanomaterials derived from the zeolite imidazolate framework.

[0012] Specifically, step (1) comprises dissolving 80 mmol 2-methylimidazole and 2.5 g polyvinyl pyrrolidone in 200 mL deionized water, which is referred to as solution A.

[0013] Specifically, step (2) comprises dissolving 5 mmol of zinc acetate and 10 mmol of cobalt chloride hexahydrate in 200 mL of deionized water, which is referred to as solution B.

[0014] Specifically, step (3) comprises mixing solution A and solution B and stirring at 80° C. for 3 hours. Then, the mixture is stirred at room temperature for 12 hours, and the mixture is washed several times by centrifugation at a speed of 10,000 rpm for 5 minutes, and freeze-dried for 24 hours to obtain ZIF@ZnCo.

[0015] Wherein, the step (4) is specifically to heat ZIF@ZnCo in argon at 5°C·min -1 The heating rate was 1000-900℃ for 3 hours to obtain radio frequency negative dielectric nanomaterials derived from zeolite imidazolate framework.

[0016] Wherein, the radio frequency negative dielectric nanomaterial derived from the zeolite imidazolate framework is a hexagonal nanostructure.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] Unlike optical and infrared bands, RF ENZ materials face ongoing challenges as single-phase materials are not available or equivalent performance in percolation supercomposites may fail. This paper successfully demonstrated RF negative dielectric properties in nanostructures for the first time using a method derived from zeolitic imidazolate framework (ZIF). By carbonization-doped ZIF, hexagonal-shaped nanostructures were designed, in which cobalt (Co) nanoparticles were encapsulated within carbon sheets and carbon nanotubes (CNTs) formed on the surface of the sheets. The hexagonal-shaped nanostructures achieved a negative dielectric constant in the frequency range of 10k-1MHz. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 (a) SEM image of ZIF@ZnCo(1:2). (b) SEM image of hexagonal structure. (cd) TEM images of hexagonal structure.

[0020] Figure 2 TEM and mapping of hexagonal structure.

[0021] Figure 3 This is a test graph of the real part of the dielectric constant and frequency of the radio frequency negative dielectric nanomaterial (hexagonal structure) prepared in the example. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Example

[0024] A method for preparing a radio frequency negative dielectric nanomaterial (hexagonal structure) derived from a zeolite imidazolate framework, the specific method being:

[0025] 80 mmol of 2-methylimidazole and 2.5 g of polyvinyl pyrrolidone were dissolved in 200 mL of deionized water, which was recorded as solution A.

[0026] 5 mmol of zinc acetate and 10 mmol of cobalt chloride hexahydrate were dissolved in 200 mL of deionized water, which was recorded as solution B.

[0027] Then, solution A and solution B were mixed and stirred at 80°C for 3 hours. Then, the mixture was stirred at room temperature for 12 hours. The mixture was rinsed several times, centrifuged at 10,000 rpm for 5 minutes several times, and freeze-dried for 24 hours to obtain ZIF@ZnCo(1:2), where 1:2 means that the molar ratio of the added Zn element to the Co element is 1:2. Among them, the regular hexagonal ZIF@ZnCo(1:2) is as follows Figure 1 As shown in a.

[0028] Finally, ZIF@ZnCo(1:2) was heated in argon at 5 °C min -1 After heating at 900℃ for 3 hours, a hexagonal carbon sheet with a nanostructure was obtained. The carbon sheet was filled with metal Co particles. Carbon nanotubes were distributed on the surface of the carbon sheet, and the carbon nanotubes also wrapped metal Co particles, which were labeled as Co@HCNTs. It showed the morphology of hexagonal carbon sheets covered by CNTs ( Figure 1 b and Figure 1 c). TEM image ( Figure 1 d) It is confirmed that Co nanoparticles are also distributed in the hexagonal carbon sheets and encapsulated in CNTs. HAADF-STEM and corresponding EDS images ( Figure 2 ) also proved the Co nanoparticles in CNTs.

[0029] The prepared hexagonal structure was tested using an LCR digital bridge (E4980Al) to obtain the relationship between the real part of the dielectric constant and the frequency, as shown in Figure 3 As shown in Figure 2, from 10kHz to 1MHz, the real part of the dielectric constant is negative, achieving negative dielectric properties.

[0030] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a radio frequency negative dielectric nanomaterial derived from a zeolite imidazolate framework, characterized in that: The following steps are involved: (1) Dissolve 2-methylimidazole and polyvinylpyrrolidone in deionized water, referred to as solution A; (2) dissolving zinc acetate and cobalt chloride hexahydrate in deionized water, which is referred to as solution B; the molar ratio of zinc acetate to cobalt chloride hexahydrate is 1:2; (3) Solution A and solution B were mixed and stirred at 80°C, and then the mixture was stirred at room temperature; the mixture was centrifuged and freeze-dried to obtain ZIF@ZnCo; (4) ZIF@ZnCo was heated at 900 °C in argon to obtain RF negative dielectric nanomaterials derived from the zeolite imidazolate framework.

2. The method for preparing the radio frequency negative dielectric nanomaterial derived from the zeolite imidazolate framework according to claim 1, characterized in that: Specifically, the step (1) comprises dissolving 80 mmol of 2-methylimidazole and 2.5 g of polyvinyl pyrrolidone in 200 mL of deionized water, which is referred to as solution A.

3. The method for preparing the radio frequency negative dielectric nanomaterial derived from the zeolite imidazolate framework according to claim 1, characterized in that: The step (2) is specifically as follows: dissolving 5 mmol of zinc acetate and 10 mmol of cobalt chloride hexahydrate in 200 mL of deionized water, which is referred to as solution B.

4. The method for preparing the radio frequency negative dielectric nanomaterial derived from the zeolite imidazolate framework according to claim 1, characterized in that: Specifically, the step (3) includes mixing solution A and solution B and stirring at 80° C. for 3 hours. Then, the mixture is stirred at room temperature for 12 hours, and the mixture is washed several times by centrifugation at a speed of 10,000 rpm for 5 minutes, and freeze-dried for 24 hours to obtain ZIF@ZnCo.

5. The method for preparing the radio frequency negative dielectric nanomaterial derived from the zeolite imidazolate framework according to claim 1, characterized in that: The step (4) is specifically to heat ZIF@ZnCo in argon at 5°C·min -1 The heating rate was 900 °C for 3 h to obtain the radio frequency negative dielectric nanomaterials derived from the zeolite imidazolate framework.

6. The method for preparing the radio frequency negative dielectric nanomaterial derived from the zeolite imidazolate framework according to claim 1, characterized in that: The radio frequency negative dielectric nanomaterial derived from the zeolite imidazolate framework is a hexagonal nanostructure.

7. The radio frequency negative dielectric nanomaterial prepared by the preparation method according to any one of claims 1 to 6.

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