One-dimensional N-doped carbon nanorod material and its preparation method and application

Abstract

The present invention provides a one-dimensional N-doped carbon nanorod material. Zn(CH3COO)2·2H2O, CTAB, dimethylimidazole, and deionized water are uniformly mixed and subjected to a hydrothermal reaction. The dried product is calcined at different temperatures under a nitrogen atmosphere. The present invention prepares a one-dimensional rod-shaped ZIF-8, which is different from the traditional rhombic dodecahedron shape. The one-dimensional N-doped carbon nanorod absorber is obtained by high-temperature calcination. The present invention is simple and easy to operate, low in cost, and has excellent absorbing performance, a wide bandwidth, and a thin thickness. The low-dielectric network formed by the interlaced one-dimensional rod-shaped structures effectively improves impedance matching and effectively enhances the absorbing performance of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic absorbing materials, and in particular to a one-dimensional N-doped carbon nanorod absorbing material, a preparation method thereof, and application of the one-dimensional N-doped carbon nanorod absorbing material as an absorbing material. Background Art

[0002] With the advancement of society and the booming development of science and technology, more and more electronic devices are becoming part of our daily lives and learning. However, technology itself is a double-edged sword. While it brings us convenience, it also carries some negative consequences. These electronic devices emit electromagnetic waves of varying frequencies, exposing us to an increasing amount of electromagnetic waves and generating electromagnetic pollution. This not only interferes with our communication systems but can also seriously harm our health. The issue of electromagnetic pollution has attracted the attention of numerous experts and scholars both domestically and internationally, and addressing it is urgent. The essence of electromagnetic absorbing materials lies in the interaction between electromagnetic waves and materials. When electromagnetic waves pass through an absorbing material, they are converted into heat and other forms of energy, thereby attenuating the waves. The electromagnetic properties of electromagnetic absorbing materials are typically characterized by electromagnetic parameters: dielectric constant, magnetic permeability, and electromagnetic loss tangent. However, current electromagnetic absorbing materials suffer from complex preparation processes, lengthy preparation times, and poor electromagnetic wave absorption performance. Therefore, to address these issues, the search for new absorbing materials has become a research priority.

[0003] Porous carbon material is a new type of electromagnetic absorbing material. Due to its high stability, good conductivity, low price, and the introduction of pore structure, it has the characteristics of large specific surface area, controllable pore structure, and adjustable pore size, it has been developed into a potential absorbing material. Summary of the Invention

[0004] The present invention aims to address the problems of complex manufacturing processes, high costs, storage difficulties, narrow effective absorption bands, and heavy materials associated with absorbing materials. The present invention provides a method for preparing and applying a dielectric lossy electromagnetic absorbing material. By adding CTAB, the traditional rhombic dodecahedron morphology of ZIF-8 is modified to produce a one-dimensional rod-like structure. This simple, low-cost process allows for mass production, resulting in an electromagnetic absorbing material with a wide absorption bandwidth, strong absorption capacity, and thin thickness, exhibiting excellent electromagnetic wave absorption performance. The present invention prepares one-dimensional rod-shaped ZIF-8, which differs from the traditional rhombic dodecahedron, and then calcines it at high temperature to obtain a one-dimensional N-doped carbon nanorod absorbing material. The preparation method is simple, operational, and low-cost, resulting in excellent absorption performance with a wide absorption bandwidth and thin thickness. The high-temperature sublimation of the Zn element leaves defect sites, providing defect polarization. The abundant pores and defects in the material provide interfacial polarization and dipole polarization between nitrogen and carbon atoms. The unique anisotropy of the rod-like structure makes it easier to form axial carrier transport paths under the action of an alternating electromagnetic field, dissipating the energy of the electromagnetic wave through dielectric loss mode. At the same time, the low-dielectric network formed by the interlaced one-dimensional rod-like structures effectively improves impedance matching, all of which effectively enhance the material's microwave absorption performance. This work provides a new method and new ideas for synthesizing MOF materials with different morphologies and dimensions for future research on microwave-absorbing materials.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a one-dimensional N-doped carbon nanorod material, which is prepared by the following method:

[0007] (1) dissolving Zn(CH3COO)2·2H2O in deionized water A to obtain an aqueous solution of Zn(CH3COO)2; dissolving dimethylimidazole and a quaternary ammonium salt type cationic surfactant in deionized water B to obtain an aqueous solution of dimethylimidazole and a quaternary ammonium salt type cationic surfactant; adding the aqueous solution of Zn(CH3COO)2 to the aqueous solution of dimethylimidazole and a quaternary ammonium salt type cationic surfactant under ultrasonic and stirring conditions, continuing ultrasonication to make it uniform, and hydrothermally reacting the obtained mixture at 110-120°C for 12-120h (preferably at 120°C for 48h), and post-treating the obtained reaction solution (white milky solution) to obtain a ZIF-8 precursor;

[0008] The amount of substance ratio of the dimethylimidazole to the total amount of the deionized water A and the deionized water B is 1:40-80 (preferably 1:60); the amount of substance ratio of the Zn(CH3COO)2 to the total amount of the deionized water A and the deionized water B is 1:1200-2400 (preferably 1:1800), and the mass of the quaternary ammonium salt cationic surfactant is 0.2-0.4wt% (preferably 0.35wt%) of the total mass of the Zn(CH3COO)2·2H2O, dimethylimidazole, the quaternary ammonium salt cationic surfactant, the deionized water A and the deionized water B; the deionized waters A and B are both deionized water, and A and B are used herein to represent deionized water in order to distinguish different stages;

[0009] (2) placing the ZIF-8 precursor obtained in step (1) into a tube furnace and calcining it at 800-1000° C. for 1-2 h (preferably 900-1000° C., more preferably 900° C. for 2 h) to obtain the one-dimensional N-doped carbon nanorod material.

[0010] Furthermore, the quaternary ammonium salt cationic surfactant in step (1) is cetyltrimethylammonium chloride (CTAC), cetyltrimethylammonium bromide (CTAB) or octadecyltrimethylammonium chloride, preferably cetyltrimethylammonium bromide (CTAB).

[0011] Furthermore, the post-treatment in step (1) is as follows: deionized water is added to the reaction solution, followed by centrifugation (10,000 rpm for 10 minutes), removing the supernatant, and the resulting precipitate is sequentially resuspended with anhydrous methanol and anhydrous ethanol, centrifuged (10,000 rpm for 10 minutes), and the supernatant is removed, followed by drying at 70° C. overnight to obtain the ZIF-8 precursor. The purpose of the post-treatment is to remove impurities.

[0012] Furthermore, the addition of the aqueous solution of Zn(CH3COO)2 in step (1) can be completed by injection using a syringe. Injection can ensure a sufficiently large contact area and rapid addition, so that the ZIF-8 obtained has good morphological uniformity.

[0013] Preferably, the calcination temperature in step (2) is increased to 800-1000° C. at a heating rate of 2° C. / min, and then decreased to room temperature at a cooling rate of 5° C. / min.

[0014] The present invention also provides an application of the one-dimensional N-doped carbon nanorod material as a wave absorbing material.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. Compared with most existing methods for preparing absorbing materials, the preparation method of the present invention requires only a simple hydrothermal process and calcination, without the need for coating or doping with other materials or other preparation processes, thus avoiding the possibility of experimental failure. Moreover, the entire reaction process is carried out in an aqueous solution, without the addition of other organic solvents. Therefore, the preparation process is simple and the raw material cost is low. The resulting electromagnetic absorbing material has the advantages of strong absorbing ability, a wide effective absorption bandwidth, and a thin thickness, and has excellent application prospects.

[0017] 2. The one-dimensional N-doped carbon nanorod absorbing material prepared by the present invention has a unique one-dimensional nanorod structure and unique anisotropy, which makes it easier to form a carrier transport path in the axial direction under the action of an alternating electromagnetic field, consuming the energy of the electromagnetic wave through a dielectric loss mode. Among them, after the high-temperature sublimation of Zn, a defect structure is left at the corresponding site, providing defect polarization, forming a dipole polarization between the N and C atoms, and the one-dimensional porous structure induces interfacial polarization. This structure and loss mechanism are conducive to the attenuation of electromagnetic waves.

[0018] 3. The one-dimensional nanorod structures of the one-dimensional N-doped carbon nanorod absorbing material prepared by the present invention are intertwined to form a low dielectric network, which effectively improves impedance matching and has excellent absorbing performance. The minimum reflection loss value reaches -52.48dB at 17.6GHz, the thickness is only 1.5mm, and the effective absorption bandwidth reaches 13.6GHz. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 : (a) is the XRD pattern of the one-dimensional ZIF-8 precursor prepared in Example 1 of the present invention, and (b) is the XRD pattern of the one-dimensional N / C nanorod electromagnetic absorbing material prepared in Example 1 of the present invention.

[0020] Figure 2 This is an SEM image of the one-dimensional N / C nanorod electromagnetic absorbing material prepared in Example 1 of the present invention.

[0021] Figure 3 (a) is a dielectric constant test curve of the one-dimensional N / C nanorod electromagnetic absorbing material prepared in Example 1 of the present invention, and (b) is a dielectric loss tangent curve of the one-dimensional N / C nanorod electromagnetic absorbing material prepared in Example 1 of the present invention.

[0022] Figure 4 This is a graph showing the electromagnetic wave absorption curve of the one-dimensional N / C nanorod electromagnetic absorbing material prepared in Example 1 of the present invention.

[0023] Figure 5 This is an electromagnetic wave absorption curve of the one-dimensional N / C nanorod electromagnetic absorbing material prepared in Example 2 of the present invention.

[0024] Figure 6This is a scanning electron microscope image of the rhombic dodecahedron-shaped electromagnetic absorbing material prepared in Example 3 of the present invention.

[0025] Figure 7 This is a graph showing the electromagnetic wave absorption curve of the rhombic dodecahedron electromagnetic absorbing material prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0026] To facilitate understanding of the present invention by those skilled in the art, the following describes specific embodiments of the present invention in conjunction with the accompanying drawings. It should be understood that the following text is merely used to describe one or several specific embodiments of the present invention and does not strictly limit the scope of protection specifically claimed in the present invention.

[0027] Example 1

[0028] The preparation method of the one-dimensional N / C nanorod absorbing material of this embodiment specifically comprises the following steps:

[0029] Step 1: Add 216.4 mg of Zn(CH3COO)2·2H2O solid particles and 2 mL of deionized water to a 5 mL centrifuge tube and sonicate in an ultrasonic bath for 5 minutes. The resulting solution is recorded as solution A. Then, add 2428.3 mg of dimethylimidazole (Hmim), 120.3 mg of CTAB, and 30 mL of deionized water to a 250 mL beaker, place it in an ultrasonic bath and sonicate it evenly. The resulting solution is recorded as solution B. While solution B is stirring, take a 5 mL syringe to draw solution A and inject it into solution B. The resulting solution is sonicated for another 5 minutes. Finally, it is transferred to a 50 mL Teflon stainless steel reactor and reacted at 120°C for 48 hours. The obtained white solution was added to deionized water and centrifuged at 10000r / min for 10min, the supernatant was discarded, and the obtained precipitate was centrifuged again with anhydrous methanol and anhydrous ethanol under the same centrifugal conditions, the supernatant was removed until the supernatant became clear, and then the obtained precipitate was placed in a 70℃ oven and dried overnight. 2+ The molar ratio of / Hmim / H2O is 1:30:1800. Step 2: The product obtained in step 1 is placed in a tube furnace, heated to 900°C at a rate of 2°C / min, maintained for 2 hours, and then cooled to room temperature at a rate of 5°C / min to obtain the N / C-900 nanorod electromagnetic absorbing material.

[0030] The ZIF-8 and N / C nanorod materials prepared in Example 1 were subjected to XRD tests. The test results are shown in FIG. Figure 1 As shown: Figure 1(a) The diffraction peaks at 7.4°, 10.5°, 12.8°, 14.8°, 16.5°, and 18.1° correspond to the (011), (002), (112), (022), (013), and (222) crystal planes of ZIF-8 (PDF#602542), demonstrating the successful synthesis of one-dimensional rod-shaped ZIF-8. Figure 1 (b) There are two broad peaks at 25.6°C and 42.1°C, corresponding to the (002) and (100) crystal planes of graphite, but the diffraction peaks are very broad, indicating an amorphous state.

[0031] The N / C nanorod electromagnetic absorbing material prepared in Example 1 was subjected to SEM testing. Figure 2 As shown: We can clearly see the rod-like structure, with some ZnO particles on the nanorods. We can also see that due to the high-temperature sublimation of Zn, there are some defect structures and holes on the surface of the rods. These defect structures and holes provide the material with very high dielectric loss.

[0032] The dielectric loss of the one-dimensional N / C nanorod electromagnetic absorber prepared in Example 1 was tested. For microwave measurements, 30 wt% of the resulting composite material was mixed with paraffin wax and pressed into a ring with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm. The relevant parameters were measured using an Agilent PNA-N5234A electromagnetic wave vector network analyzer. The electromagnetic wave electromagnetic parameter test results of the absorber are shown in Figure 2. Figure 3 As shown in (a) and 3(b), we can see that the real part of the dielectric constant ε′ of the N / C nanorod electromagnetic absorber material shows a decreasing trend in the frequency range of 2-18 GHz, which is consistent with the Debye theory. The nanorods have higher ε′ values ​​because they have a good dispersion state and a certain degree of nanorod alignment. In addition, the loss tangent shows a resonance peak in the frequency range of 12 to 16 GHz. The imaginary part of the dielectric constant ε″ and the loss tangent have similar curves. This is due to the dipole polarization and interface polarization caused by the evaporation of zinc metal. Because ionic polarization and electronic polarization appear in the higher frequency region of 10 3 -10 6 GHz.

[0033] The electromagnetic wave absorption performance of the one-dimensional N / C nanorod electromagnetic absorbing material prepared in Example 1 was tested. The reflection loss is related to the electromagnetic parameters, absorption frequency and thickness of the sample. The electromagnetic wave absorption curve of the absorber is shown in FIG. Figure 4 As shown, we usually take the reflection loss of -10dB as the effective absorption value of the absorbing material, which means that when the electromagnetic wave is incident on the surface of the material, the reflected wave is only 10% of the incident wave. -1, meaning that 90% of the electromagnetic wave energy is absorbed, and the bandwidth less than -10dB is the effective absorption bandwidth. The effective absorption bandwidth and minimum reflection loss value are usually used as parameters to evaluate the material's wave absorption performance. As shown in the figure, when the material thickness is 1.5mm, the minimum reflection loss value reaches -52.48dB at 17.6GHz. Throughout the entire measured frequency range, the effective absorption bandwidth reaches 17.6GHz. The material's excellent wave absorption performance is attributed to its excellent electromagnetic wave attenuation ability and impedance matching characteristics with free space. At the same time, the material's defective structure and porous structure increase the transmission path of electromagnetic waves within the material, which is beneficial to electromagnetic wave attenuation. Therefore, this material is an excellent wave absorbing material due to its thin thickness, good performance, and wide effective absorption bandwidth.

[0034] Example 2

[0035] The preparation method of the one-dimensional N / C nanorod absorbing material in this embodiment specifically comprises the following steps:

[0036] Step 1: Add 216.4 mg of Zn(CH3COO)2·2H2O solid particles and 2 mL of deionized water to a 5 mL centrifuge tube and sonicate in an ultrasonic bath for 5 minutes. The resulting solution is recorded as Solution A. Then, add 2428.3 mg of dimethylimidazole, 120.3 mg of CTAB, and 30 mL of deionized water to a 250 mL beaker and sonicate until uniform. The resulting solution is recorded as Solution B. While Solution B is stirring, take a 5 mL syringe and inject Solution A into Solution B. The resulting solution is sonicated for another 5 minutes. Finally, it is transferred to a 50 mL Teflon stainless steel reactor and reacted at 120°C for 48 hours. The resulting white solution is added to an appropriate amount of deionized water and centrifuged at 10,000 rpm for 10 minutes. The supernatant is discarded, and the precipitate is resuspended and centrifuged in anhydrous methanol and anhydrous ethanol under the same conditions. The supernatant is discarded until the supernatant is clear. The resulting precipitate is then dried in a 70°C oven overnight. 2+ The molar ratio of / Hmim / H2O is 1:30:1800, and the mass fraction of CTAB is 0.35wt%.

[0037] Step 2: Place the product obtained in step 1 in a tube furnace, heat it to 1000°C at a rate of 2°C / min, maintain it for 2 hours, and then cool it to room temperature at a rate of 5°C / min to obtain N / C-1000 nanorod electromagnetic absorbing material.

[0038] The electromagnetic wave absorption performance of the one-dimensional N / C nanorod absorbing material prepared in Example 2 was calculated. The electromagnetic wave absorption curve of the absorber is shown in FIG. Figure 5As shown in the figure, compared to the material prepared in Example 1, the overall absorption performance of the material prepared in Example 2 is reduced. At a thickness of 1 mm, the minimum reflection loss value is -5.88 dB. This is due to the large complex dielectric constant of the material, which leads to a mismatch between the free space and the wave impedance of the material, resulting in a large amount of electromagnetic wave reflection and reduced absorption performance.

[0039] Example 3

[0040] The preparation method of the one-dimensional N / C nanorod absorbing material in this embodiment specifically comprises the following steps:

[0041] Step 1: Add 216.4 mg of Zn(CH3COO)2·2H2O solid particles and 2 mL of deionized water to a 5 mL centrifuge tube and sonicate in an ultrasonic bath for 5 minutes. The resulting solution is recorded as solution A. Then, add 2428.3 mg of dimethylimidazole and 30 mL of deionized water to a 250 mL beaker and place it in an ultrasonic bath for uniform sonication. The resulting solution is recorded as solution B. While solution B is stirring, take a 5 mL syringe to draw solution A and inject it into solution B. The resulting solution is sonicated for another 5 minutes. Finally, it is transferred to a 50 mL Teflon stainless steel reactor and reacted at 120°C for 48 hours. Add an appropriate amount of deionized water to the resulting white solution and centrifuge it at 10,000 r / min for 10 minutes. The supernatant is discarded, and the precipitate is resuspended and centrifuged with anhydrous methanol and anhydrous ethanol under the same conditions. The supernatant is removed until the supernatant becomes clear. The obtained precipitate is then placed in a 70°C oven to dry overnight. Among them, Zn 2+ The molar ratio of Hmim / H2O is 1:30:1800.

[0042] Step 2: The product obtained in step 1 was placed in a tube furnace, heated to 900°C at a rate of 2°C / min, maintained for 2 hours, and then cooled to room temperature at a rate of 5°C / min to obtain an electromagnetic absorbing material in the shape of a rhombic dodecahedron.

[0043] The rhombic dodecahedron electromagnetic absorbing material prepared in Example 3 was subjected to SEM testing, and the results are as follows: Figure 6 As shown, without adding CTAB, an absorbing material with a rhombic dodecahedron morphology of about 2 μm in diameter was obtained.

[0044] The electromagnetic wave absorption performance of the rhombic dodecahedron electromagnetic absorbing material prepared in Example 3 was tested. The reflection loss is related to the electromagnetic parameters, absorption frequency and thickness of the sample. The electromagnetic wave absorption curve of the absorber is shown in FIG. Figure 7As shown in the figure, when the filling amount is 35wt% and the material thickness is 2.5mm, the lowest reflection loss value reaches -30.448dB at 8.4GHz. In comparison, at the same temperature and filling ratio, the one-dimensional N / C nanorods obtain better absorbing performance.

[0045] The above description of the embodiments of the present invention is in detail combined with the embodiments, which does not limit the present invention in any form. For those skilled in the art, after knowing the contents described in the present invention, they can make several improvements and substitutions without departing from the principles of the present invention. These equivalent improvements and substitutions should be included in the scope of protection of the claims of the present invention.

Claims

1. A one-dimensional N-doped carbon nanorod material, characterized in that The one-dimensional N-doped carbon nanorod material is prepared as follows: (1) dissolving Zn(CH3COO)2·2H2O in deionized water A to obtain an aqueous solution of Zn(CH3COO)2; dissolving dimethylimidazole and a quaternary ammonium salt type cationic surfactant in deionized water B to obtain an aqueous solution of dimethylimidazole and a quaternary ammonium salt type cationic surfactant; dispersing the aqueous solution of Zn(CH3COO)2 into the aqueous solution of dimethylimidazole and a quaternary ammonium salt type cationic surfactant under ultrasonic and stirring conditions, continuing ultrasonication to make it uniform, subjecting the obtained mixed solution to a hydrothermal reaction at 110-120°C for 12-120h, and subjecting the obtained reaction solution to post-treatment to obtain a ZIF-8 precursor; the post-treatment comprises: adding deionized water to the reaction solution, centrifuging, removing the supernatant, resuspending the obtained precipitate in anhydrous methanol and anhydrous ethanol in sequence, centrifuging, removing the supernatant, and then drying at 70°C overnight; The molar ratio of the dimethylimidazole to the total amount of the deionized water A and the deionized water B is 1:40-80; the molar ratio of the Zn(CH3COO)2 to the total amount of the deionized water A and the deionized water B is 1:1200-2400; the mass of the quaternary ammonium salt cationic surfactant is 0.2-0.4wt% of the total mass of the Zn(CH3COO)2·2H2O, dimethylimidazole, the quaternary ammonium salt cationic surfactant, the deionized water A and the deionized water B; (2) placing the ZIF-8 precursor obtained in step (1) into a tubular furnace and calcining it at 800-1000°C for 1-2h to obtain the one-dimensional N-doped carbon nanorod material.

2. The one-dimensional N-doped carbon nanorod material according to claim 1, wherein: The quaternary ammonium salt cationic surfactant in step (1) is cetyltrimethylammonium chloride, cetyltrimethylammonium bromide or octadecyltrimethylammonium chloride.

3. The one-dimensional N-doped carbon nanorod material according to claim 1, wherein: The hydrothermal reaction in step (1) is carried out at 120° C. for 48 hours.

4. The one-dimensional N-doped carbon nanorod material according to claim 1, wherein: The molar ratio of the dimethylimidazole to the total amount of the deionized water A and the deionized water B in step (1) is 1:

60.

5. The one-dimensional N-doped carbon nanorod material according to claim 1, wherein: The molar ratio of Zn(CH3COO)2 to the total amount of deionized water A and deionized water B in step (1) is 1:1800.

6. The one-dimensional N-doped carbon nanorod material according to claim 1, wherein: The mass of the quaternary ammonium salt cationic surfactant in step (1) is 0.35wt% of the total mass of the Zn(CH3COO)2·2H2O, dimethylimidazole, quaternary ammonium salt cationic surfactant, deionized water A and deionized water B.

7. The one-dimensional N-doped carbon nanorod material according to claim 1, wherein: The calcination in step (2) is carried out at 900° C. for 2 h.

8. Use of the one-dimensional N-doped carbon nanorod material as claimed in claim 1 as a wave absorbing material.

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