Trifunctional imidazole dinitrile, wave-absorbing composite material and preparation method and application thereof

Abstract

The application belongs to the technical field of high polymer materials, and discloses a trifunctional imidazole dicyan, a wave-absorbing composite material and a preparation method and application thereof. First, a first intermediate is prepared by taking trichlorazizine and a hydroxy aldehyde compound as raw materials; then, a second intermediate is prepared by taking the first intermediate and a diamino maleonitrile as raw materials; and finally, a trifunctional imidazole dicyan is prepared by performing a ring closing reaction on the second intermediate. The trifunctional imidazole dicyan prepared by the application has excellent carbon nanotube dispersibility and stability and ion coordination, and can be used for preparing a wave-absorbing material. The wave-absorbing material prepared by the application has low reflection loss and very thin thickness, and thus is expected to become a new generation of wave-absorbing material.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and relates to a novel multifunctional polymer material, specifically a trifunctional imidazole dinitrile, microwave absorbing composite material, its preparation method and application. Background Technology

[0002] With the widespread use of electronic devices and the development of electronic technologies such as radar communication, electromagnetic pollution, especially high-frequency electromagnetic pollution, has attracted widespread attention from the whole society due to its potential harm to equipment performance, human health and the surrounding environment [1]. Electromagnetic interference is also becoming a new source of pollution in the new century. In this context, it is of great significance to eliminate harmful radiation by absorbing unwanted electromagnetic waves (EMW) using microwave absorbing materials (MAM). Generally speaking, an ideal microwave absorber should meet the requirements of thinness, light weight, wide bandwidth and high absorption intensity.

[0003] Traditional microwave absorbing materials such as silicon carbide, ferrite, and magnetic metal powders have been widely used. However, their high density results in a narrow effective absorption bandwidth. Carbon-based materials, on the other hand, possess advantages such as light weight, good conductivity, strong structural tunability, good stability, and high dielectric loss, making them a focus of attention in electromagnetic wave absorption. However, due to limited loss mechanisms and difficult-to-control electromagnetic parameters, the absorption capacity of single-component carbon materials at low filling levels is limited, making it difficult to achieve perfect impedance matching and strong electromagnetic wave attenuation. Currently effective solutions include: (1) combining carbon materials with various magnetic metals / nonmetals (e.g., Fe, Co, Ni and their oxides) to regulate impedance matching characteristics and introduce additional magnetic loss mechanisms; at the same time, the heterogeneous interface between carbon materials and magnetic materials also leads to increased polarization loss; (2) constructing highly heterogeneous interface structures such as porous / hollow / core-shell, regulating impedance matching by controlling dielectric properties, and consuming electromagnetic waves through polarization loss of heterogeneous interfaces and multiple reflections and scattering of the surface and interface; (3) by introducing heteroatoms such as B, N, S, O, and F, the electron transport path can be disrupted, improving the impedance matching characteristics of carbon materials, while increasing dipole polarization loss; therefore, composite materials based on carbon nanostructures can achieve better impedance matching and lower reflection loss under low density conditions, and have become the mainstream method for preparing ideal microwave absorbers. Common preparation methods for multi-component microwave absorbing materials include electrospinning, hydrothermal, solvothermal, chemical vapor deposition, electroplating, and in-situ polymerization coating. However, the complex preparation process and the large amount of solvent used are not conducive to large-scale preparation; at the same time, further improving its absorption capacity for EMW is very limited.

[0004] Precursor design is a bottom-up approach to customize the functionality of carbon materials with desired properties. Polymers are an important class of precursors, but they are constrained by additional polymerization processes. Molecular precursors, with their flexible structural and morphological tunability, have greatly expanded the performance boundaries and application areas of carbon materials. However, most molecular precursors are limited by low carbon yields and atom utilization efficiency. Therefore, developing a carbon-based production strategy that is highly atom-efficient, simple, green, and possesses excellent overall performance is an ongoing pursuit in this field, but it also faces significant challenges. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the existing technologies by providing a multifunctional molecular platform—a trifunctional imidazole dinitrile—containing a trifunctional branched compound with imidazole dinitrile and a triazine ring. This compound exhibits high char residue and atom utilization, as well as excellent carbon nanotube dispersibility and ion coordination. Based on these properties, the condensed-state structure of the trifunctional imidazole dinitrile derivative can be easily controlled, thereby regulating the composition, morphology, and pore structure of the derived carbon materials.

[0006] The trifunctional imidazole dinitrile provided by this invention has the following general structural formula:

[0007]

[0008] Where R is -H, -OCH3, -OCH2CH3 or -CF3.

[0009] The present invention also provides a method for preparing the above-mentioned trifunctional imidazole dinitrile, which includes the following steps:

[0010] (1) Using trichloromethazine and hydroxy aldehydes as raw materials, a first intermediate with the following general structural formula was prepared:

[0011]

[0012] Where R is -H, -OCH3, -OCH2CH3 or -CF3;

[0013] (2) Using the first intermediate and diaminomaleitrile as raw materials, a second intermediate with the following general structural formula was prepared:

[0014]

[0015] (3) The second intermediate was subjected to a ring-closing reaction to prepare a trifunctional imidazole dinitrile.

[0016] The chemical reaction equation for the preparation method of the above-mentioned trifunctional imidazole dinitrile is as follows:

[0017]

[0018] In step (1) above, the specific operation is as follows: trichlorochloroazine, hydroxy aldehyde compound, basic compound and first catalyst are mixed in a first organic solvent, and then reacted at 80-110℃ for 20-30h. Afterwards, the resulting reaction product is washed and rotary evaporated to obtain a white powder. The molar ratio of trichlorochloroazine (TCT), hydroxy aldehyde compound, basic compound and catalyst is 10:45-60:54-108:2.25-4.8. The hydroxy aldehyde compound is p-hydroxytolualdehyde (PHBA), vanillin or ethyl vanillin; the first catalyst is 18-crown ether-6, 15-crown ether-5 or cyclodextrin, etc.; the basic compound is sodium carbonate or potassium carbonate, etc.; the first organic solvent is benzene, toluene or xylene, etc.; the amount of the first organic solvent is calculated according to 8%-15% solid content. The reaction product obtained above is first filtered to obtain a first filtrate. The resulting filter cake is stirred in ethyl acetate at 65-75℃ for 0.5-1 h, and then filtered to obtain a second filtrate. The first and second filtrates are mixed and then extracted using alkaline solutions and deionized water, respectively, with each solution being extracted 2-3 times. The alkaline solution is an aqueous solution of sodium carbonate, potassium carbonate, sodium hydroxide, or potassium hydroxide, etc., with a concentration of 5wt%-10wt%. The washed organic phase is rotary evaporated at 70-80℃ to obtain a white powder, which is the first intermediate.

[0019] In step (2) above, the first intermediate and diaminomaleitrile (DMAN) are reacted in a mixed organic solvent at 25-80℃ for 6-15 hours. The resulting reaction solution is then added dropwise to a mixed solution of ethanol and deionized water. The precipitate obtained by filtration is washed and dried to obtain the second intermediate. The molar ratio of the first intermediate to diaminomaleitrile is 1:4.5-6. The mixed organic solvent includes a second organic solvent and a third organic solvent. The second organic solvent is N,N-dimethylformamide (DMF) or acetamide; the third organic solvent is methanol or ethanol. The volume ratio of the second organic solvent to the third organic solvent is 1:1-1:2. The amount of the mixed organic solvent used is measured according to a solid content of 10%-15% (mass of reactant:volume of solvent). The proportion of ethanol in the mixed solution of ethanol and deionized water is 10%-50%. The precipitate obtained by filtration is washed 3-4 times with deionized water, and the washed precipitate is dried at 70-80℃ to obtain the second intermediate.

[0020] In step (3) above, the second intermediate, N-chlorosuccinimide (NCS), and the second catalyst are reacted in a fourth organic solvent at 25-50°C for 10-24 hours; then the resulting reaction solution is added dropwise to deionized water, and the precipitate obtained by filtration is washed and dried to obtain a yellow powder, namely trifunctional imidazole dinitrile; the molar ratio of the second intermediate, N-chlorosuccinimide, and the second catalyst is 1:4-6:4-6. The fourth organic solvent is N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMAC), etc.; the amount of the fourth organic solvent used is measured according to a solid content of 10%-15%. The second catalyst is nicotinamide (NCT). The precipitate obtained by filtration is washed with deionized water 3-4 times, and the washed precipitate is dried at 70-80°C to constant weight to obtain trifunctional imidazole dinitrile.

[0021] The present invention also provides the application of the above-mentioned trifunctional imidazole dinitrile in the dispersion of carbon nanomaterials; wherein the carbon nanomaterials are carbon nanotubes, graphene, etc.

[0022] This invention also provides the application of the above-mentioned trifunctional imidazole dinitrile as a metal ion ligand; the metal ion is preferably a transition metal ion such as Fe, Zn, Mn, Sn, Sb, etc.

[0023] This invention also provides the application of the above-mentioned trifunctional imidazole dinitrile in the preparation of microwave absorbing materials. Because the above-mentioned trifunctional imidazole dinitrile possesses ion coordination and carbon nanotube dispersibility, it can be used as a precursor for carbon materials.

[0024] This invention also provides a method for preparing a microwave absorbing composite material, which includes the following steps:

[0025] (S1) Prepare transition metal salt solution;

[0026] (S2) Dissolve trifunctional imidazole dinitrile and ammonia in deionized water to obtain a carbon material precursor solution; the amount of ammonia in the ammonia solution is 10-25% excess relative to the amount of imidazole dinitrile in the trifunctional imidazole dinitrile.

[0027] (S3) Carbon nanotubes are added to a carbon material precursor solution and ultrasonically dispersed to obtain a dispersion; the mass ratio of carbon nanotubes to trifunctional imidazole dinitrile is 1:1-1:50.

[0028] (S4) Under stirring conditions, the transition metal salt solution is added dropwise to the dispersion obtained in step (S3) to obtain a viscous mixed solution; the molar ratio of the transition metal salt to the trifunctional imidazole dinitrile is 0.5:1-3:1.

[0029] (S5) A viscous mixed solution was freeze-dried to obtain a precursor for a microwave absorbing composite material;

[0030] (S6) The microwave absorbing composite material precursor is sintered at 600-800℃ to obtain the microwave absorbing composite material.

[0031] In step (S1) above, a transition metal salt is dissolved in deionized water to obtain a transition metal salt solution. The concentration of the transition metal salt in the solution is 0.01 mmol / mL to 0.1 mmol / mL. The transition metal salt can be one of ferric ammonium oxalate trihydrate, FeCl3, ZnCl2, MnCl2, etc.

[0032] In step (S2) above, the concentration of the trifunctional imidazole dinitrile is 2 mg / mL-10 mg / L. The mass concentration of ammonia in the ammonia water is 25-28%.

[0033] In step (S3) above, the preferred mass ratio of carbon nanotubes to trifunctional imidazole dinitrile is 1:25-30. Carbon nanotubes can achieve long-term uniform dispersion in the carbon material precursor solution, which helps to construct uniform conductive and thermally conductive pathways. The carbon nanotubes can be single-walled or multi-walled.

[0034] In step (S4) above, the trifunctional imidazole dinitrile coordinates with transition metal ions to regulate its condensed-state structure, thereby controlling the morphology and pore structure of the derived carbon material. This, in turn, modulates the electromagnetic parameters and impedance matching characteristics of the derived carbon material, while introducing abundant dipoles and heterostructures. Furthermore, the abundant pore structure facilitates multiple reflections and scattering of electromagnetic waves within the material, thus enhancing the microwave absorption performance of the derived carbon material.

[0035] In step (S5) above, freeze drying is performed using conventional equipment and operations in the art.

[0036] In the above step (S6), the sintering time is 1-5 hours.

[0037] The present invention also provides another method for preparing a microwave absorbing composite material, which includes the following steps:

[0038] The above-mentioned trifunctional imidazole dinitrile was sintered at 600-800℃ to obtain a microwave absorbing composite material;

[0039] Alternatively, trifunctional imidazole dinitrile and ammonia water can be dissolved in deionized water; the resulting solution can be freeze-dried to obtain a microwave absorbing composite material precursor; the microwave absorbing composite material precursor can be sintered at 600-800℃ to obtain a microwave absorbing composite material.

[0040] In the above-mentioned method for preparing microwave absorbing composite materials, the sintering time is preferably 2 hours.

[0041] In the preparation method of the above-mentioned microwave absorbing composite material, when the trifunctional imidazole dinitrile is dissolved first, the amount of ammonia in the ammonia water is 10-25% excess relative to the amount of imidazole dinitrile in the trifunctional imidazole dinitrile.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) The trifunctional imidazole dinitrile provided by the present invention has excellent carbon nanotube dispersibility and stability, and is suitable as a nanomaterial dispersant. It can also disperse graphene, nano BN, etc.

[0044] (2) The trifunctional imidazole dinitrile provided by the present invention has excellent ion coordination properties, can coordinate and complex with metal ions, and its multi-coordination site structure is conducive to forming stable five- or six-membered ring coordination structures.

[0045] (3) The trifunctional imidazole dinitrile provided by the present invention can control the composition, morphology and pore structure of carbon materials derived from trifunctional imidazole dinitrile by coordinating and complexing with metal ions, while introducing abundant dipoles and heterostructures; the abundant pore structure is conducive to multiple reflections and scattering of electromagnetic waves inside the material, thereby improving the wave absorption performance of carbon materials.

[0046] (3) The trifunctional imidazole dinitrile provided by the present invention can be used to prepare microwave absorbing materials, and the prepared microwave absorbing materials have low reflection loss and very thin thickness, so they are expected to become a new generation of microwave absorbing materials. Attached Figure Description

[0047] Figure 1 The structural analysis results of DQSQ, DQSXF, and DQSDCI prepared in Example 1 are shown in (A), where (A) represents the NMR results of DQSQ, DQSXF, and DQSDCI. 1 H NMR spectra, (B) are the infrared spectra obtained from DQSQ, DQSXF and DQSDCI infrared measurements, and (C)-(E) are the NMR spectra obtained from DQSDCI, DQSXF and DQSQ respectively. 13 CNMR;

[0048] Figure 2 The XCQSQ, XCQSXF, and XCQSDCI samples prepared in Example 2 were obtained through nuclear magnetic resonance testing. 1 HNMR spectrum;

[0049] Figure 3 The results of the YXCQSQ nuclear magnetic resonance test prepared in Example 3 are shown; where (a) corresponds to 1 HNMR spectrum, (b) corresponding 13 CNMR;

[0050] Figure 4TGA test results for DQSDCI prepared in Example 1 and XCQSDCI prepared in Example 2;

[0051] Figure 5 The dispersion effect of 15 mg MWCNT in different solutions is shown in the figure. Among them, (1) corresponds to 15 mg MWCNT dispersed in 15 mL of deionized water, (2) corresponds to 15 mg MWCNT dispersed in 15 mL of deionized water containing ammonia (0.69 mmol of ammonia), (3) corresponds to 15 mg MWCNT dispersed in 15 mL of deionized water containing 0.2 mmol DQSDCI and 0.69 mmol ammonia, (A) corresponds to sonication for 30 min and standing for 1 h, (B) corresponds to sonication for 30 min and standing for 1 week, (C) corresponds to sonication for 30 min and standing for 2 weeks, (D) corresponds to sonication for 30 min and standing for 1 month.

[0052] Figure 6 The infrared spectra are obtained from infrared measurements of DQSDCI, DQSDCI-NH4OH, and DQSDCI-NH4OH-Fe; where (A) is the infrared spectrum obtained from 500-4000 cm⁻¹. -1 The overall infrared spectrum corresponding to the wavenumber, (B) is 2200-2300 cm⁻¹ -1 The overall infrared spectrum corresponding to the wavenumber, (C) is 1400-1480 cm⁻¹ -1 The overall infrared spectrum corresponding to the wavenumber, (D) is 1240-1280 cm⁻¹ -1 Overall infrared spectrum corresponding to wavenumber,

[0053] Figure 7The images show the morphology test results of different microwave absorbing composite materials; where (A)-(C) are SEM images of DQSDCI-Fe-CNT-600, (D)-(E) are HRTEM images of DQSDCI-Fe-CNT-600; (F)-(H) are SEM images of DQSDCI-Fe-CNT-700, (I)-(J) are HRTEM images of DQSDCI-Fe-CNT-700; (K)-(M) are SEM images of DQSDCI-Fe-CNT-800, (N)-(O) are HRTEM images of DQSDCI-Fe-CNT-800; (P)-(R) are SEM images of DQSDCI-Fe-CNT-600, (D)-(E) are HRTEM images of DQSDCI-Fe-CNT-600, (F)-(H) are SEM images of DQSDCI-Fe-CNT-700, (I)-(J) are HRTEM images of DQSDCI-Fe-CNT-700; (K)-(M) are SEM images of DQSDCI-Fe-CNT-800, (N)-(O) are HRTEM images of DQSDCI-Fe-CNT-800; and (P)-(R) are HRTEM images of DQSDCI-Fe-CNT-800. (S)-(T) are SEM images of DQSDCI-700; (P)-(R) are SEM images of DQSDCI-700; (S)-(T) are HRTEM images of DQSDCI-700; (A′)-(C′) are SEM images of DQSDCI-CNT-700; (D′)-(E′) are HRTEM images of DQSDCI-CNT-700; (F′)-(H′) are SEM images of DQSDCI-Fe-700; (I′)-(J′) are HRTEM images of DQSDCI-Fe-700.

[0054] Figure 8 The N2 adsorption and desorption curves (a) and pore size distribution curves (b) of different microwave absorbing composite materials are shown.

[0055] Figure 9 3D RL plots, 2D contour RL plots, and |Zi plots at different thicknesses and frequencies in Two-dimensional contour map of / Z0| values; where (A), (E), and (I) correspond to DQSDCI-Fe-CNT-600, (B), (F), and (J) correspond to DQSDCI-Fe-CNT-700, (C), (G), and (K) correspond to DQSDCI-Fe-CNT-800, and (D), (H), and (L) correspond to DQSDCI-700. Detailed Implementation

[0056] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are part of the present invention.

[0057] The ammonia concentration in the ammonia solution used in the following examples is 25%-28% by mass.

[0058] Example 1

[0059] This embodiment prepares trifunctional imidazole dinitrile DQSDCI according to the following steps:

[0060] (1) 0.03 mol trichloromethazine (TCT), 0.162 mol p-hydroxybenzaldehyde (PHBA), 0.243 mol Na2CO3, 0.008 mol 18-crown ether-6 and 350 mL benzene were added to a single-necked flask and then refluxed at 80 °C for 24 h. The resulting reaction product was then washed: the first filtrate was obtained by filtration, and the filter cake was stirred with ethyl acetate at 70 °C for 20 min, and then filtered to obtain the second filtrate. The first and second filtrates were mixed and extracted twice with sodium carbonate aqueous solution (concentration of 10 wt%), stirring for 30 min each time. Then, the organic phase was extracted twice with deionized water, stirring for 30 min each time. The washed organic phase was rotary evaporated at 70 °C for 8 h to obtain a white powder, which is the first intermediate DQSQ.

[0061] (2) 0.01 mol of the first intermediate DQSQ, 0.045 mol of diaminomaleitrile (DMAN), 26 mL of DMF and 39 mL of ethanol were added to a single-necked flask and reacted at 30 °C for 12 h. The resulting reaction solution was then added dropwise to a mixed solution of ethanol and deionized water (ethanol content was 50%). The precipitate obtained by filtration was washed three times with deionized water to obtain a yellow filter cake. The yellow filter cake was dried in a vacuum oven at 80 °C for 12 h to obtain the second intermediate DQSXF.

[0062] (3) 0.01 mol of the second intermediate DQSXF, 0.045 mol of N-chlorosuccinimide (NCS), 0.045 mol of nicotinamide (NCT) and 47 mL of DMF were added to a single-necked flask and reacted at 25 °C for 6 h, and then the temperature was raised to 40 °C and reacted for another 6 h. The resulting reaction solution was then added dropwise to deionized water, and the precipitate was filtered and washed three times with deionized water. The washed precipitate was dried in a vacuum oven at 80 °C for 12 h to obtain a yellow powder, namely trifunctional imidazole dinitrile DQSDCI (yield 98%).

[0063] Example 2

[0064] This embodiment prepares trifunctional imidazole dinitrile XCQSDCI according to the following steps:

[0065] (1) 0.03 mol trichloromethazine (TCT), 0.15 mol vanillin, 0.18 mol Na2CO3, 0.008 mol 18-crown ether-6 and 350 mL benzene were added to a single-necked flask and then refluxed at 80 °C for 24 h. The resulting reaction product was then washed: the first filtrate was obtained by filtration, and the filter cake was stirred with ethyl acetate at 70 °C for 20 min, and then filtered to obtain the second filtrate. The first and second filtrates were mixed and extracted twice with sodium carbonate aqueous solution (concentration of 10 wt%), stirring for 30 min each time. Then, the organic phase was extracted twice with deionized water, stirring for 30 min each time. The washed organic phase was rotary evaporated at 70 °C for 8 h to obtain a white powder, which is the first intermediate XCQSQ.

[0066] (2) 0.01 mol of the first intermediate XCQSQ, 0.045 mol of diaminomaleonitrile (DMAN), 26 mL of DMF and 39 mL of ethanol were added to a single-necked flask and reacted at 30 °C for 12 h. The resulting reaction solution was then added dropwise to a mixed solution of ethanol and deionized water (ethanol content was 50%). The precipitate obtained by filtration was washed four times with deionized water to obtain a yellow filter cake. The yellow filter cake was dried in a vacuum oven at 80 °C for 12 h to obtain the second intermediate XCQSXF.

[0067] (3) 0.01 mol of the second intermediate XCQSXF, 0.045 mol of N-chlorosuccinimide (NCS), 0.045 mol of nicotinamide (NCT) and 47 mL of DMF were added to a single-necked flask and reacted at 25 °C for 6 h, and then the temperature was raised to 40 °C and reacted for another 6 h. The resulting reaction solution was then added dropwise to a deionizer, and the precipitate obtained by filtration was washed 4 times with deionized water. The washed precipitate was dried in a vacuum oven at 80 °C for 12 h to obtain a yellow powder, namely trifunctional imidazole dinitrile XCQSDCI.

[0068] Example 3

[0069] This embodiment prepares trifunctional imidazole dinitrile YXCQSDCI according to the following steps:

[0070] (1) 0.03 mol trichloromethazine (TCT), 0.16 mol ethyl vanillin, 0.18 mol K2CO3, 0.01 mol 18-crown ether-6 and 350 mL benzene were added to a single-necked flask and then refluxed at 83 °C for 20 h. The resulting reaction product was then washed: the first filtrate was obtained by filtration, and the filter cake was stirred with ethyl acetate at 70 °C for 20 min, and then filtered to obtain the second filtrate. The first and second filtrates were mixed and extracted twice with sodium carbonate aqueous solution (concentration of 10 wt%), stirring for 30 min each time. Then, the organic phase was stirred and extracted twice with deionized water, stirring for 30 min each time. The washed organic phase was rotary evaporated at 70 °C for 8 h to obtain a white powder, which is the first intermediate YXCQSQ.

[0071] (2) 0.01 mol of the first intermediate XCQSQ, 0.054 mol of diaminomaleitrile (DMAN), 26 mL of DMF and 39 mL of ethanol were added to a single-necked flask and reacted at 30 °C for 12 h. The resulting reaction solution was then added dropwise to a mixed solution of ethanol and deionized water (ethanol content was 50%). The precipitate obtained by filtration was washed four times with deionized water to obtain a yellow filter cake. The yellow filter cake was dried in a vacuum oven at 80 °C for 12 h to obtain the second intermediate YXCQSXF.

[0072] (3) 0.01 mol of the second intermediate XCQSXF, 0.045 mol of N-chlorosuccinimide (NCS), 0.045 mol of nicotinamide (NCT) and 47 mL of DMF were added to a single-necked flask and reacted at 25 °C for 6 h, and then the temperature was raised to 40 °C and reacted for another 6 h. The resulting reaction solution was then added dropwise to deionized water, and the precipitate obtained by filtration was washed 4 times with deionized water. The washed precipitate was dried in a vacuum oven at 80 °C for 12 h to obtain a yellow powder, namely trifunctional imidazole dinitrile YXCQSDCI.

[0073] Example 4

[0074] This embodiment prepares the microwave absorbing composite material DQSDCI-Fe-MWCNT according to the following steps:

[0075] (S1) Add 1.5 mmol of ferric ammonium oxalate trihydrate (AIOT) to 20 mL of deionized water and stir until completely dissolved to obtain an AIOT solution;

[0076] (S2) Add 1.5 mmol DQSDCI (1.06 g) and ammonia (5.18 mmol of ammonia in molar amount, 15% excess) to 60 mL of deionized water and stir until completely dissolved (the solution pH is about 7-8) to obtain a carbon material precursor solution.

[0077] (S3) Add 40 mg of multi-walled carbon nanotubes (MWCNTs) to the carbon material precursor solution and sonicate for 30 min to disperse evenly to obtain a dispersion.

[0078] (S4) Under stirring conditions, the AIOT solution is added dropwise to the dispersion obtained in step (S3). As the AIOT solution is continuously added, the viscosity of the mixed solution increases, and finally a viscous mixed solution is obtained.

[0079] (S5) A viscous mixed solution was freeze-dried to obtain a precursor for a microwave absorbing composite material;

[0080] (S6) Divide the microwave absorbing composite material precursor into three parts, and heat the three parts of the microwave absorbing composite material precursor to 600℃, 700℃ and 800℃ respectively at a heating rate of 5℃ / min. Then sinter at the corresponding temperatures for 2h to obtain microwave absorbing composite materials DQSDCI-Fe-MWCNT-600, DQSDCI-Fe-MWCNT-700 and DQSDCI-Fe-MWCNT-800.

[0081] Comparative Example 1

[0082] This comparative example prepared the microwave absorbing composite material DQSDCI-Fe-700 according to the following steps:

[0083] (S1′) Add 1.5 mmol of ferric ammonium oxalate trihydrate (AIOT) to 20 mL of deionized water and stir until completely dissolved to obtain an AIOT solution;

[0084] (S2′) Add 1.5 mmol DQSDCI (1.06 g) and ammonia (5.18 mmol of ammonia in molar amount, 15% excess) to 60 mL of deionized water and stir until completely dissolved (the solution pH is about 7-8) to obtain a carbon material precursor solution.

[0085] (S3′) Under stirring conditions, the AIOT solution is added dropwise to the dispersion obtained in step (S2). As the AIOT solution is continuously added, the viscosity of the mixed solution increases, and finally a viscous mixed solution is obtained.

[0086] (S4′) A viscous mixed solution was freeze-dried to obtain a precursor for a microwave absorbing composite material;

[0087] (S5′) The microwave absorbing composite material precursor was heated to 700℃ at a heating rate of 5℃ / min and sintered for 2h to obtain the microwave absorbing composite material DQSDCI-Fe-700.

[0088] Comparative Example 2

[0089] This comparative example prepared the microwave absorbing composite material DQSDCI-CNT-700 according to the following steps:

[0090] (S1′) Add 1.5 mmol DQSDCI (1.06 g) and ammonia (5.18 mmol of ammonia in molar amount, 15% excess) to 60 mL of deionized water and stir until completely dissolved (the solution pH is about 7-8) to obtain a carbon material precursor solution.

[0091] (S2′) Add 40 mg of multi-walled carbon nanotubes (MWCNTs) to the carbon material precursor solution and sonicate for 30 min to disperse them evenly;

[0092] (S3′) The dispersion obtained in step (S2′) is freeze-dried to obtain the precursor of the microwave absorbing composite material;

[0093] (S5′) The microwave absorbing composite material precursor was heated to 700℃ at a heating rate of 5℃ / min and sintered for 2h to obtain the microwave absorbing composite material DQSDCI-CNT-700.

[0094] Comparative Example 3

[0095] This comparative example prepared the microwave absorbing composite material DQSDCI-700 according to the following steps:

[0096] (S1″) Add 1.5 mmol DQSDCI (1.06 g) and ammonia (5.18 mmol of ammonia in molar amount, 15% excess) to 60 mL of deionized water and stir until completely dissolved (the solution pH is about 7-8) to obtain a carbon material precursor solution.

[0097] (S2″) The carbon material precursor solution was freeze-dried to obtain the microwave absorbing composite material precursor;

[0098] (S3″) The microwave absorbing composite material precursor was heated to 700℃ at a heating rate of 5℃ / min and sintered for 2h to obtain the microwave absorbing composite material DQSDCI-700.

[0099] (I) Analysis of the structure and properties of the trifunctional imidazole dinitrile prepared in Examples 1-3

[0100] 1. Structural Analysis

[0101] Nuclear magnetic resonance (NMR) and infrared (IR) analyses were performed on the DQSQ, DQSXF, and DQSDCI prepared in Example 1. The results are as follows: Figure 1 As shown, Figure 1 Elemental analysis results confirm that the aforementioned DQSQ, DQSXF, and DQSDCI have been successfully prepared.

[0102] Nuclear magnetic resonance analysis was performed on XCQSQ, XCQSXF, and XCQSDCI prepared in Example 2, and the results are as follows: Figure 2As shown in the figure, the elemental analysis results prove that the above-mentioned XCQSQ, XCQSXF and XCQSDCI have been successfully prepared.

[0103] Nuclear magnetic resonance analysis was performed on the YXCQSQ prepared in Example 3, and the results are as follows: Figure 3 As shown in the figure, the elemental analysis results prove that the above-mentioned DQSQ, DQSXF and DQSDCI have been successfully prepared.

[0104] 2. Thermal performance analysis

[0105] TGA tests were performed on the DQSDCI prepared in Example 1 and the XCQSDCI prepared in Example 2. The test results are as follows: Figure 4 As shown. From Figure 4 As can be seen, the trifunctional imidazole dinitrile prepared by the method of the present invention has excellent thermal stability and high char residue.

[0106] 3. Dispersion analysis of carbon nanotubes

[0107] 15 mg of MWCNT was dispersed in 15 mL of deionized water, 15 mL of deionized water containing 0.69 mmol of ammonia, and 15 mL of deionized water containing 0.2 mmol of DQSDCI, respectively. The three dispersions were sonicated for 30 min each, and then allowed to stand for 1 h, 1 week, 2 weeks, and 1 month. Images were then collected. The results are shown below. Figure 5 As shown. From Figure 5 As can be seen, MWCNT exhibits excellent dispersibility and stability in deionized water containing DQSDCI, making it suitable as a precursor dispersion for carbon materials.

[0108] 4. Ion coordination

[0109] To investigate the ionic coordination properties of trifunctional imidazole dinitrile, the following experiment was conducted:

[0110] (1) Add 1.5 mmol DQSDCI (1.06 g) and 5.18 mmol ammonia (15% excess) to 60 mL of deionized water and stir until completely dissolved (the solution pH is about 7-8); then freeze-dry the dissolved solution to obtain the product DQSDCI-NH4OH.

[0111] (2) Add 1.5 mmol of ferric ammonium oxalate trihydrate (AIOT) to 20 mL of deionized water and stir until completely dissolved to obtain an AIOT solution; add 1.5 mmol of DQSDCI (1.06 g) and 5.18 mmol of ammonia (15% excess) to 60 mL of deionized water and stir until completely dissolved (the solution pH is about 7-8); then add the dissolved AIOT solution dropwise to the above solution containing dissolved DQSDCI, and finally freeze-dry the resulting mixed solution to obtain the product DQSDCI-NH4OH-Fe.

[0112] Infrared analysis was performed on DQSDCI, DQSDCI-NH4OH, and DQSDCI-NH4OH-Fe, and the results are as follows: Figure 6 As shown.

[0113] Triazine rings, imidazole rings of azole dinitrile, and cyano groups can all coordinate with metal ions. This is mainly due to the lone pair of electrons on the nitrogen atom, which exhibits a strong interaction with metal ions. Furthermore, the multi-coordination site structure of DQSDCI favors the formation of stable five- and six-membered ring coordination structures. For example... Figure 6 As shown in (B), cyano group and Fe 3+ After coordination, the infrared characteristic peaks shift to lower wavenumbers, which may be due to Fe. 3+ This averages out the electron cloud density on -CN. And triazine rings, such as... Figure 6 As shown in (C) and (D), the imidazole ring with Fe 3+ After coordination, the infrared characteristic peak (1360 cm⁻¹) -1 1255cm -1 The shift towards higher wavenumbers (left and right) is likely due to the intrinsic highly conjugated aromatic heterocyclic structure of the triazine ring (where the electron cloud density is sufficiently averaged), Fe 3+ The introduction mainly serves an electron-withdrawing inductive effect. This indicates that Fe 3+ and NH 4+ It exhibits a strong interaction with imidazolidinone.

[0114] (II) Analysis of the performance of the microwave absorbing composite materials prepared in Example 4 and Comparative Examples 1-3

[0115] 1. Structural and Morphological Analysis

[0116] The morphology of the microwave absorbing composite materials prepared in Example 4 and Comparative Examples 1-3 was analyzed, and the results are shown in the figure. Figure 7 As shown. From Figure 7 As can be seen, the SEM morphology of DQSDCI-Fe-CNT-600, DQSDCI-Fe-CNT-700, DQSDCI-Fe-CNT-800, and DQSDCI-Fe-700 samples all exhibit folded nanosheets with thicknesses ranging from 53 to 155.6 nm. Compared to the samples with added iron salts, the nanowires of DQSDCI-700 and DQSDCI-CNT-700 without added iron salts mainly exhibit disordered nanoribbons with a small number of disordered small sheets. This suggests that the introduction of iron salts is beneficial to the growth and preparation of nanosheets. The formation of the two-dimensional nanosheet structure can be attributed to Fe. 3+ Multiple chelation with DQSDCI. Simultaneously, the high specific surface area of ​​the nanosheets and the disordered overlapping and grinding between them facilitate the formation of heterogeneous interfaces and conductive pathways, thereby enhancing electromagnetic wave attenuation.

[0117] from Figure 7 As can be seen from (C), (H), and (M), MWCNTs are uniformly dispersed on the nanosheets, which can be attributed to the good dispersion of MWCNTs in the DQSDCI solution. The introduction of MWCNTs facilitates the construction of conductive channels and the introduction of more heterogeneous interfaces, thereby improving the microwave absorption performance of the nanosheets.

[0118] Meanwhile, TEM results also showed morphological differences between iron-containing and iron-free samples. Furthermore, a uniform distribution of MWCNTs and Fe-based compounds was observed in the DQSDCI-Fe-CNT carbides. Based on selected area electron diffraction (SAED) results, these rings can be attributed to the diffraction of the graphite microcrystal structure, with bright spots indicating the formation of iron-based compounds. The indistinct rings suggest that the prepared carbon nanosheets are primarily of a disordered structure. Lattice fringes of 0.36 nm, 0.20 nm, and 0.12 nm were clearly observed in DQSDCI-Fe-CNT-600, corresponding to the lattice spacings of graphite-like, Fe3N(111), and C3N4(320), respectively. Figure 7 (E)). Lattice stripes belonging to Fe3N(300) and Fe3C(233) were observed in DQSDCI-Fe-CNT-700. Figure 7 (J)). The introduction of iron-based compounds is beneficial for constructing a heterogeneous interface between iron-based particles and nanosheets, which is conducive to introducing more interfacial polarization, thereby improving the dielectric loss of the material.

[0119] 2. Pore structure regulation

[0120] Studies have found that trifunctional imidazole dinitrile reacts with Fe... 3+ Coordination complexes can modulate the final pore structure of carbon materials. The pore structure and interfaces of carbon materials facilitate multiple reflections and scattering of electromagnetic waves within the material, thereby enhancing the wave absorption performance of carbon materials.

[0121] Here, the specific surface area and pore size distribution of DQSDCI-Fe-CNT and its comparative sample were characterized by N2 adsorption and desorption tests, and the results are as follows: Figure 8 As shown in (a) and (b).

[0122] As can be seen from the figure, DQSDCI-700 does not conform to the typical adsorption-desorption curve due to its too small specific surface area. DQSDCI-CNT-700 composites exhibit a typical Type I adsorption-desorption curve. DQSDCI-Fe, DQSDCI-Fe-CNT-600, DQSDCI-Fe-CNT-700, and DQSDCI-Fe-CNT-800 are more in line with the Type IV desorption curve. They show high adsorption amounts at low and high relative pressures, indicating that the system contains a large number of micropores and macropores; within the range of 0.45 < P / P0 < 1.0, there is an obvious hysteresis loop in the adsorption-desorption curve, indicating the presence of mesopores inside the material. Therefore, based on the non-local density functional theory (NLDFT) model, the pore size distribution of the materials was further studied. As shown in Figure 8 (b), for the Fe-containing material systems, they have a hierarchical pore structure with micropores, mesopores, and macropores. For the Fe-free material systems, there is no obvious micropore structure (pore size < 2 nm). At the same time, according to the specific surface areas obtained from the N2 adsorption and desorption curves (see Table 1), the addition of Fe ions and CNTs will increase the specific surface area of the final carbon materials, and the addition of Fe ions contributes more to the specific surface area. Generally speaking, micropores contribute more to the specific surface area. In the Fe-containing samples, a significant micropore distribution can be observed, while in the Fe-free samples, no obvious micropore distribution can be observed. The significant differences in the N2 desorption curve, BET specific surface area, and pore size distribution also indirectly confirm the obvious coordination effect between Fe ions and DQSDCI. Moreover, a high specific surface area and rich pore structure are beneficial to improving the dielectric loss and impedance matching performance of the materials, thereby improving the microwave absorption performance of the materials. At the same time, a high specific surface area is conducive to introducing more heterogeneous interfaces, strengthening the interfacial polarization, and enhancing the dielectric loss of the materials.

[0123] Table 1 BET specific surface areas and pore parameters of different samples

[0124]

[0125]

[0126] 3. Reflection loss (RL) analysis

[0127] For DQSDCI-Fe-CNT-600, DQSDCI-Fe-CNT-700, and DQSDCI-Fe-CNT-800 prepared in Example 4 and DQSDCI-700 prepared in Comparative Example 3, the electromagnetic parameters (relative permeability μ rand relative permittivity ε r Then, the reflection loss RL is calculated using the following formula, and the result is as follows: Figure 9 As shown.

[0128] Z in =Z0(μ r / v r 1 / 2 )tanh{j(2πfd / c)(μ r / ε r ) 1 / 2};

[0129]

[0130] In the formula, Z0 represents the free space impedance; μ r ε represents relative permeability; r d represents the relative permittivity; c represents the sample thickness; f represents the speed of light; and f represents the electromagnetic wave frequency.

[0131] according to Figure 9 The three-dimensional RL maps (A)-(D) show that DQSDCI-Fe-CNT-700 has the lowest RL value of -69.57 dB, and its thickness is only 2.25 mm, which is superior to most reported microwave absorbers. Meanwhile... Figure 9 As can be seen from (E)-(H), by adjusting the thickness of the absorbing composite material (1-5mm), its absorption bandwidth can cover a wide frequency range, among which DQSDCI-Fe-CNT-700 can cover a frequency range of 4-18GHz. Meanwhile, according to... Figure 9 As can be seen from (I)-(L), DQSDCI-Fe-CNT-700 exhibits the best impedance matching, while DQSDCI-Fe-CNT-800 shows the worst. This can be attributed to the increased conductivity and dielectric parameters of the materials at higher carbonization temperatures. The maximum effective absorption bandwidth (EAB) of DQSDCI-Fe-CNT-700 is... max The wavelength is 5.7 GHz, and the sample thickness is only 1.95 mm. The DQSDCI-700 exhibits excellent electromagnetic wave absorption performance. minThe absorption values ​​are -56.11 dB and 7.17 GHz. The excellent microwave absorption performance of DQSDCI-700 can be attributed to the rich variety and content of nitrogen dopants resulting from its unique molecular structure, and the heterogeneous interface introduced by the nanoribbon overlap. The even better microwave absorption performance of DQSDCI-Fe-CNT-700 can be attributed to the synergistic regulation of the composition and pore structure of the carbon material by the introduction of Fe salt and trace amounts of carboxyl MWCNTs, thereby controlling the dielectric parameters and thus the impedance matching characteristics and electromagnetic wave attenuation capability of the carbon material. Simultaneously, it introduces more dipoles, heterogeneous interfaces, and multiple reflection and scattering paths, thereby improving the material's microwave absorption performance. Compared with currently reported microwave absorbing materials, DQSDCI-Fe-CNT-700 and DQSDCI-700 are expected to become strong competitors for next-generation microwave absorbing materials.

[0132] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A tri-functional imidazole dinitrile, characterized in that, The structural general formula is: Wherein, R is -H, -OCH3, -OCH2CH3 or -CF3.

2. The process for the preparation of the tri-functional imidazole dicarbonitrile according to claim 1, characterized in that, The method comprises the following steps: (1) using trichloro-3, 3, 5, 5-tetramethylazetidine and hydroxy aldehyde compound as raw materials, a first intermediate with the following structural general formula is prepared: Wherein, R is -H, -OCH3, -OCH2CH3 or -CF3. (2) using the first intermediate and diamino maleonitrile as raw materials, a second intermediate with the following structural general formula is prepared: (3) the second intermediate is subjected to a ring closing reaction to prepare a trifunctional imidazole dinitrile.

3. The process for the preparation of trifunctional imidazole dicarbonitrile according to claim 2, characterized in that, In step (1), the structure general formula of the p-hydroxytoluene aldehyde compound is as follows: Wherein, R is -H, -OCH3, -OCH2CH3 or -CF3.

4. The process for the preparation of trifunctional imidazole dicarbonitrile according to claim 3, characterized in that, In step (1), the specific operation is as follows: trichloro-3, 3, 5, 5-tetramethylazetidine, hydroxy aldehyde compound, basic compound and first catalyst are mixed in a first organic solvent, and then the mixture is reacted at 80-110℃ for 20-30h, and then the obtained reaction product is washed and rotary evaporated to obtain white powder; the molar ratio of trichloro-3, 3, 5, 5-tetramethylazetidine, hydroxy aldehyde compound, basic compound and catalyst is 10:45-60:54-108:2.25-4.

8.

5. The process for the preparation of trifunctional imidazole dicarbonitrile according to claim 4, characterized in that, The first catalyst is 18-crown-6, 15-crown-5 or cyclodextrin; the basic compound is sodium carbonate or potassium carbonate; and the first organic solvent is benzene, toluene or xylene.

6. The process for the preparation of trifunctional imidazole dicarbonitrile according to claim 2, characterized in that, In step (2), the first intermediate and diamino maleonitrile are reacted in a mixed organic solvent at 25-80℃ for 6-15h, and then the obtained reaction solution is added dropwise into a mixed solution of ethanol and deionized water; the obtained precipitate is filtered, washed and dried to obtain the second intermediate; the molar ratio of the first intermediate and diamino maleonitrile is 1:4.5-6.

7. The process for the preparation of trifunctional imidazole dicarbonitrile according to claim 6, characterized in that, The mixed organic solvent comprises a second organic solvent and a third organic solvent; the second organic solvent is N, N-dimethylformamide or acetamide; the third organic solvent is methanol or ethanol; the volume ratio of the second organic solvent and the third organic solvent is 1:1-1:2; and the proportion of ethanol in the mixed solution of ethanol and deionized water is 10%-50%.

8. The process for the preparation of trifunctional imidazole dicarbonitrile according to claim 2, characterized in that, In step (3), the second intermediate, N-chlorosuccinimide and a second catalyst are reacted in a fourth organic solvent at 25-50℃ for 10-24h; and then the obtained reaction solution is added dropwise into deionized water, and the obtained precipitate is filtered, washed and dried to obtain yellow powder, i.e. the trifunctional imidazole dinitrile; the molar ratio of the second intermediate, N-chlorosuccinimide and the second catalyst is 1:4-6:4-6.

9. The process for the preparation of trifunctional imidazole dicarbonitrile according to claim 8, characterized in that, The fourth organic solvent is N, N-dimethylformamide or N, N-dimethylacetamide; and the second catalyst is nicotinamide.

10. Application of the trifunctional imidazole dinitrile in claim 1 in dispersion of carbon nanomaterials.

11. Application of the trifunctional imidazole dinitrile in claim 1 as a metal ion ligand.

12. Application of the trifunctional imidazole dinitrile in claim 1 in preparation of wave-absorbing materials.

13. A method of preparing a wave-absorbing composite material, characterized by, The method comprises the following steps: (S1) preparing a transition metal salt solution; (S2) dissolving the trifunctional imidazole dinitrile of claim 1 and aqueous ammonia in deionized water to obtain a carbon material precursor solution; the amount of substance of ammonia in the aqueous ammonia is 10-25% excess relative to the amount of substance of imidazole dinitrile in the trifunctional imidazole dinitrile; (S3) adding carbon nanotubes to the carbon material precursor solution and uniformly dispersing by ultrasonic to obtain a dispersion liquid; the mass ratio of the carbon nanotubes to the trifunctional imidazole dinitrile is 1:1-1:50; (S4) under stirring, adding a transition metal salt solution to the dispersion liquid obtained in step (S3) to obtain a viscous mixed solution; the molar ratio of the transition metal salt to the trifunctional imidazole dinitrile is 0.5:1-3:1; (S5) freeze-drying the viscous mixed solution to obtain a wave-absorbing composite material precursor; (S6) sintering the wave-absorbing composite material precursor at 600-800℃ to obtain a wave-absorbing composite material.

14. The method of claim 13, wherein the wave-absorbing composite material is prepared by a method comprising: mixing the metal oxide and the metal powder; and mixing the mixture with the resin. In step (S1), the transition metal salt is dissolved in deionized water to obtain a transition metal salt solution; the concentration of the transition metal salt in the transition metal salt solution is 0.01mmol / mL-0.1mmol / mL; the transition metal salt is one of ferric ammonium oxalate, FeCl3, ZnCl2, and MnCl2.

15. The method of claim 13, wherein the wave-absorbing composite material is prepared by a method comprising: mixing the metal nanoparticles and the polymer to form a mixture; and coating the mixture on a surface of a substrate to form the wave-absorbing composite material. In step (S6), the sintering time is 1-5h.

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