A method for preparing metal / nitrogen-doped helical carbon nanotube microwave absorbing materials

Abstract

This invention discloses a method for preparing metal / nitrogen-doped helical carbon nanotube microwave absorbing materials. The invention aims to address the technical problems of existing microwave absorbing materials, such as limited energy loss mechanisms, high filler ratios and densities, narrow microwave absorption bandwidth, and limited functionality, hindering their widespread application. This invention prepares high-performance M / N-HCNTs by in-situ loading metal ions into a helical carbon nanotube matrix and then performing an external thermal-driven process. The unique atomic configuration of M-N-C and the unique geometric configuration of the helical structure enable orbital coupling, spin polarization, and cross-polarization, synergistically regulating the electromagnetic wave absorption characteristics of the material. This material exhibits strong attenuation capabilities, broadband absorption, and excellent microwave absorption performance, making it highly valuable for both civilian and military applications.

Description

Technical Field

[0001] This invention relates to a method for preparing a metal / nitrogen-doped carbon microwave absorbing material. Background Technology

[0002] The emergence of 5G technology and the widespread adoption of wireless communication technologies and high-power electronic devices have led to a surge in electromagnetic (EM) pollution. Despite extensive development of electromagnetic wave absorbing (EMWA) materials, their practical application remains challenging. Atomic doping strategies offer an excellent option for preparing high-performance EMWA materials. This approach induces lattice distortion, strain, and active point defects, generating numerous dipole centers and in-plane topological defects. This accelerates electron accumulation, triggers Maxwell polarization, and ultimately modulates the EM properties of the material. Notably, the metal-nitrogen-carbon (MNC) configuration has garnered significant attention across various fields due to its high surface free energy, ultra-high atomic utilization, and quantum size effects. The orbital coupling between the 3d orbitals of metal and the 2p orbitals of N alters the charge arrangement, generating new electronic states (d-bands) near the Fermi level. This significantly improves conductivity and dielectric loss. Furthermore, the spin polarization generated by electron spin promotes the formation of high-spin states, enhancing electromagnetic attenuation.

[0003] The geometry of electromagnetic wave absorbers plays a crucial role in EMWA performance. Helical materials, with their unique symmetry and electromagnetic coupling properties, have attracted considerable research attention. Helical structures can increase electromagnetic losses by simultaneously inducing electric and magnetic polarization. Notably, Zuo et al. constructed a material using helical nanotubes and investigated the effect of spatial configuration on the dielectric constant, revealing additional cross-polarization and broadband electromagnetic wave absorption with a bandwidth of 6.7 GHz (Zuo X, Zhang H, Zhou C, Zhao Y, Huang H, Wen N, Sun C, Fan Z, Pan L, Hierarchical and porous structures of carbon nanotubes-anchored MOF derivatives bridged by carbon nanocoils as lightweight and broadband microwave absorbers, Small 2023, 19:2301992.). The results show that the helical structure effectively reduces the frequency sensitivity of the EMWA material, facilitating broadband absorption. Furthermore, Huang et al. demonstrated that the electromagnetic field is uniformly distributed along the length direction in electromagnetic simulations. However, the introduction of the helical structure disrupts this original electromagnetic field distribution, causing it to redistribute along the helix (Huang L, Duan Y, Shi Y, Ma X, Pang H, Zeng Q, Che R, Chiral asymmetric polarizations generated by bioinspired helical carbon fibers to induce broadband microwave absorption and multispectral photonic manipulation, Advanced Optical Materials, 2022, 10, 220024.). This phenomenon induces a strong electromagnetic resonance, further enhancing the attenuation of electromagnetic wave (EMW). Summary of the Invention

[0004] The present invention aims to address the technical problems of existing microwave absorbing materials, such as limited energy loss modes, high fill ratios and densities, narrow microwave absorption bandwidth, and limited functionality, which hinder their widespread application. The invention provides a method for preparing metal / nitrogen-doped helical carbon nanotube microwave absorbing materials.

[0005] The preparation method of the metal / nitrogen-doped helical carbon nanotube microwave absorbing material of the present invention is carried out according to the following steps:

[0006] 1. Dissolve phenylglycine and sodium hydroxide together in a mixed solution of acetone and deionized water, and denote this solution as solution A;

[0007] Dissolve palmitoyl chloride in acetone and denote this solution as solution B;

[0008] Sodium hydroxide is dissolved in deionized water and denoted as solution C.

[0009] Solution B and solution C were slowly added dropwise to solution A, and the mixture was stirred for 12-13 hours. The pH of the solution was adjusted to 0.9-1.1, and the stirring was continued for another 4-4.5 hours. The product was filtered and dried. The resulting white product was placed in a beaker, and petroleum ether was added. The mixture was heated to 90-95°C. The white product gradually dissolved. Heating was stopped when the white product re-precipitated as the petroleum ether evaporated. The mixture was then allowed to cool naturally to room temperature to obtain the purified template, denoted as AS.

[0010] The volume ratio of the petroleum ether to the acetone in solution A is 2:3;

[0011] When preparing solution A, the mass ratio of sodium hydroxide to phenylglycine is 1:(3.5-4), the volume ratio of acetone to deionized water is 1:(3-3.5), and the mass ratio of sodium hydroxide to acetone is 1g:(54mL-55mL).

[0012] When preparing solution B, the volume ratio of palmitoyl chloride to acetone is 1:(7.5-8);

[0013] When preparing solution C, the mass ratio of sodium hydroxide to deionized water is 1 g:(160 mL to 165 mL);

[0014] The sodium hydroxide in solution A and the sodium hydroxide in solution C have the same mass.

[0015] The mass ratio of sodium hydroxide in solution A to the volume ratio of palmitoyl chloride in solution B is 1 g:(6.5 mL to 7 mL).

[0016] 2. Dissolve AS and 3-aminophenol prepared in step 1 in methanol, stir thoroughly to obtain a transparent solution D;

[0017] The mass ratio of AS to 3-aminophenol is (0.01–0.1):(0.0199–1.9999).

[0018] The mass ratio of AS to methanol is 1 g:(225 mL to 230 mL);

[0019] 3. Add acetate to the transparent solution D prepared in step 2, stir thoroughly, then add deionized water and continue stirring for 40 min to 45 min to obtain solution E;

[0020] The mass ratio of the acetate to the 3-aminophenol in step two is 1:(0.4–9.1);

[0021] The mass ratio of the acetate to the volume of deionized water is 1 g:(124 mL to 2820 mL);

[0022] 4. Slowly add the formaldehyde aqueous solution dropwise to solution E prepared in step 3, heat to 62℃~63℃ and stir continuously for 3h~3.5h, let it cool naturally to room temperature, and then filter and dry in sequence to obtain the yellow precursor;

[0023] The formaldehyde aqueous solution has a mass concentration of 37% to 40%, and the volume ratio of the formaldehyde aqueous solution to the deionized water added in step three is 1:(305 to 315).

[0024] 5. The yellow precursor prepared in step 4 is calcined under a protective gas and at 600℃~900℃ for 2h~3h, and then naturally cooled to room temperature to obtain metal / nitrogen-doped spiral carbon nanotube microwave absorbing material.

[0025] This invention prepares a high-performance metal / nitrogen (M / N) doped helical carbon nanotube (M / N-HCNT) microwave absorbing material by introducing a unique MNC configuration onto a helical carbon nanotube matrix with special cross-polarization. The orbital coupling between the 3d orbitals of the metal and the 2p orbitals of N causes local charge rearrangement, enhancing polarization loss. Simultaneously, it converts electromagnetic waves into electrical energy, which is dissipated as heat, increasing conductivity loss. The unique spin polarization characteristics endow the material with additional electromagnetic losses, significantly improving electromagnetic wave absorption performance. The helical structure significantly increases multiple reflections and scattering of electromagnetic waves, and the induced cross-polarization forms electromagnetic coupling, thus exhibiting excellent electromagnetic attenuation characteristics.

[0026] The M / N-HCNT absorbing material prepared in this invention possesses superior dielectric and magnetic properties compared to single carbon materials, enabling its multifunctional application in various scenarios. Simulation using CST electromagnetic field software verified the material's low RCS characteristics. Designed as a metamaterial, it achieves ultra-wideband absorption of 12.16 GHz, covering 67.5% of the entire frequency band (2–18 GHz), meeting the requirements for applications in special environments such as military equipment, electronic devices, and protective clothing. It holds particular promise as a replacement for traditional absorbing materials in stealth aircraft. Furthermore, the preparation method of this invention is simple and low-cost, achieving ultra-wideband absorption, especially with low filler ratios and thin thicknesses, making it highly valuable for industrial production applications and widespread adoption.

[0027] The beneficial effects of this invention are:

[0028] 1. Unique Preparation Method: This invention uses a template method to prepare a helical carbon nanotube precursor (the product of step four), introduces metal particles in situ, and calcines to prepare a high-performance metal / nitrogen-doped nanocarbon microwave absorbing material. Electromagnetic simulation and density functional theory calculations show that the unique atomic configuration of the MNC and the special geometric configuration of the helical structure induce spin polarization, orbital coupling, and cross-polarization, which synergistically enhance electromagnetic attenuation.

[0029] 2. Excellent electromagnetic wave absorption capability: The method of preparing the metal / nitrogen-doped helical carbon nanotube microwave absorbing material in this invention is to precisely control the electromagnetic parameters by changing the type of metal (acetate), the ratio of metal to nitrogen source (3-aminophenol), and the temperature and time of sample heat treatment (step five). This improves impedance matching and achieves a synergistic effect of electromagnetic loss, thereby obtaining ideal electromagnetic wave absorption performance. The resulting composite microwave absorbing material, when mixed with paraffin, exhibits excellent lightweight microwave absorption performance at a low coating thickness. It achieves a super-strong absorption of -63.13dB at an ultra-thin thickness of 1.29mm and a broadband absorption of 6.08GHz at a thickness of 1.83mm.

[0030] 3. Multi-scenario applicability: Through electromagnetic synergy, this invention can achieve a radar absorption efficiency of over 90% across the entire frequency band; CST electromagnetic field simulation software analysis shows that the maximum reduction in radar stealth performance at 0° is 36.4 dB·m. 2 This means that the obtained material possesses excellent radar wave attenuation characteristics, which can suppress the reflection of electromagnetic waves from the PEC surface, and has broad application prospects in the military field. Through the construction of metamaterials, ultra-wideband absorption of 12.16 GHz was achieved at a thickness of 5 mm, which can meet most practical application scenarios. Attached Figure Description

[0031] Figure 1 The X-ray diffraction patterns of the products obtained in step five of experiments one through five;

[0032] Figure 2 Scanning electron microscope image of HMC-8 prepared for Experiment 1;

[0033] Figure 3 Scanning electron microscope image of SHMC-8 prepared for Experiment 2;

[0034] Figure 4 Scanning electron microscope image of SMC-8 prepared for Experiment 3;

[0035] Figure 5Scanning electron microscope image of LHMC-8 prepared for Experiment 4;

[0036] Figure 6 Scanning electron microscope image of LMC-8 prepared for Experiment 5;

[0037] Figure 7 A graph showing the electromagnetic reflection loss data of HMC-8 calculated through step six of Experiment 1;

[0038] Figure 8 A graph showing the electromagnetic reflection loss data of SHMC-8 calculated through step six of Experiment 2;

[0039] Figure 9 A graph showing the electromagnetic reflection loss data of SMC-8 calculated through step six of Experiment 3;

[0040] Figure 10 A graph showing the electromagnetic reflection loss data of LHMC-8 calculated through step six of Experiment 4;

[0041] Figure 11 A graph showing the electromagnetic reflection loss data of LMC-8 calculated through step six of Experiment 5;

[0042] Figure 12 The effective absorption bandwidth diagram of HMC-8 prepared for Experiment 1;

[0043] Figure 13 Simulation results of the electromagnetic metamaterial constructed for Experiment 7;

[0044] Figure 14 Calculated voltage standing wave ratio (VSWR) of the gradient metamaterial constructed for Experiment 7;

[0045] Figure 15 This is a schematic diagram for RCS calculation;

[0046] Figure 16 The graph shows the RCS reduction value in step seven of Experiment 2;

[0047] Figure 17 The RCS calculation results for step seven of Experiment 2. Figure 3 Vito;

[0048] Figure 18 The structure radar diagram for RCS calculation in step seven of Experiment 2;

[0049] Figure 19 The structure radar diagram for RCS calculation in step seven of Experiment 1;

[0050] Figure 20 The structure radar diagram for the RCS calculation in step seven of Experiment 3. Detailed Implementation

[0051] Specific Implementation Method 1: This implementation method is a preparation method of a metal / nitrogen-doped helical carbon nanotube microwave absorbing material, specifically carried out according to the following steps:

[0052] 1. Dissolve phenylglycine and sodium hydroxide together in a mixed solution of acetone and deionized water, and denote this solution as solution A;

[0053] Dissolve palmitoyl chloride in acetone and denote this solution as solution B;

[0054] Sodium hydroxide is dissolved in deionized water and denoted as solution C.

[0055] Solution B and solution C were slowly added dropwise to solution A, and the mixture was stirred for 12-13 hours. The pH of the solution was adjusted to 0.9-1.1, and the stirring was continued for another 4-4.5 hours. The product was filtered and dried. The resulting white product was placed in a beaker, and petroleum ether was added. The mixture was heated to 90-95°C. The white product gradually dissolved. Heating was stopped when the white product re-precipitated as the petroleum ether evaporated. The mixture was then allowed to cool naturally to room temperature to obtain the purified template, denoted as AS.

[0056] The volume ratio of the petroleum ether to the acetone in solution A is 2:3;

[0057] When preparing solution A, the mass ratio of sodium hydroxide to phenylglycine is 1:(3.5-4), the volume ratio of acetone to deionized water is 1:(3-3.5), and the mass ratio of sodium hydroxide to acetone is 1g:(54mL-55mL).

[0058] When preparing solution B, the volume ratio of palmitoyl chloride to acetone is 1:(7.5-8);

[0059] When preparing solution C, the mass ratio of sodium hydroxide to deionized water is 1 g:(160 mL to 165 mL);

[0060] The sodium hydroxide in solution A and the sodium hydroxide in solution C have the same mass.

[0061] The mass ratio of sodium hydroxide in solution A to the volume ratio of palmitoyl chloride in solution B is 1 g:(6.5 mL to 7 mL).

[0062] 2. Dissolve AS and 3-aminophenol prepared in step 1 in methanol, stir thoroughly to obtain a transparent solution D;

[0063] The mass ratio of AS to 3-aminophenol is (0.01–0.1):(0.0199–1.9999).

[0064] The mass ratio of AS to methanol is 1 g:(225 mL to 230 mL);

[0065] 3. Add acetate to the transparent solution D prepared in step 2, stir thoroughly, then add deionized water and continue stirring for 40 min to 45 min to obtain solution E;

[0066] The mass ratio of the acetate to the 3-aminophenol in step two is 1:(0.4–9.1);

[0067] The mass ratio of the acetate to the volume of deionized water is 1 g:(124 mL to 2820 mL);

[0068] 4. Slowly add the formaldehyde aqueous solution dropwise to solution E prepared in step 3, heat to 62℃~63℃ and stir continuously for 3h~3.5h, let it cool naturally to room temperature, and then filter and dry in sequence to obtain the yellow precursor;

[0069] The formaldehyde aqueous solution has a mass concentration of 37% to 40%, and the volume ratio of the formaldehyde aqueous solution to the deionized water added in step three is 1:(305 to 315).

[0070] 5. The yellow precursor prepared in step 4 is calcined under a protective gas and at 600℃~900℃ for 2h~3h, and then naturally cooled to room temperature to obtain the metal / nitrogen-doped spiral carbon nanotube microwave absorbing material M / N-HCNT.

[0071] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the pH of the solution is adjusted in step one by adding hydrochloric acid solution. Everything else is the same as in Specific Implementation Method One.

[0072] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the acetate mentioned in step three is manganese acetate, cobalt acetate, or nickel acetate. Everything else is the same as in Specific Implementation Method One or Two.

[0073] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the drying in step four is performed at 60°C for 12 hours. Everything else is the same as in Specific Implementation Methods One to Three.

[0074] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that the protective gas mentioned in step five is argon or nitrogen. Everything else is the same as in Specific Implementation Method Four.

[0075] The invention was verified using the following experiments:

[0076] Experiment 1: This experiment demonstrates a method for preparing a metal / nitrogen-doped helical carbon nanotube microwave absorbing material, specifically carried out according to the following steps:

[0077] 1. Dissolve 2.0709g of phenylglycine and 0.55g of sodium hydroxide together in a mixed solution of 30mL of acetone and 90mL of deionized water, and denote this solution as solution A.

[0078] Dissolve 3.8 mL of palmitoyl chloride in 30 mL of acetone, and denote this as solution B;

[0079] Dissolve 0.55g of sodium hydroxide in 90mL of deionized water and denote it as solution C;

[0080] Solution B and solution C were slowly added dropwise to solution A and stirred for 12 hours. Hydrochloric acid was added to adjust the pH to 1, and the mixture was stirred for another 4 hours. The white product was filtered and dried. The white product was placed in a beaker and 20 mL of petroleum ether was added. The mixture was heated to 90°C. The white product gradually dissolved. Heating was stopped when the white product re-precipitated as the petroleum ether evaporated. The mixture was allowed to cool naturally to room temperature to obtain the purified template, denoted as AS.

[0081] 2. Dissolve 0.035g of AS and 0.1997g of 3-aminophenol in 8mL of methanol and stir thoroughly to obtain a transparent solution D.

[0082] 3. Add 0.022g of manganese acetate to the transparent solution D, stir thoroughly, add 62mL of deionized water, stir for 40min, and obtain solution E.

[0083] 4. Slowly add 200 μL of formaldehyde aqueous solution to solution E, heat to 62°C and stir continuously for 3 hours, let it cool naturally to room temperature, filter, and dry at 60°C for 12 hours to obtain a yellow precursor; the mass concentration of the formaldehyde aqueous solution is 37% to 40%.

[0084] 5. Under argon protection, the yellow precursor was calcined at 800℃ for 2 hours and then naturally cooled to room temperature to obtain HMC-8; the heating rate was 5℃ / min.

[0085] 6. The prepared HMC-8 absorbing material was impregnated with molten paraffin as the substrate (HMC-8 to paraffin mass ratio of 3:7) and formed into a ring, with HMC-8 accounting for 30 wt.% of the total mass of the ring. The electromagnetic parameters of HMC-8 were measured using a vector network analyzer. According to transmission line theory, the reflection loss of the material to electromagnetic waves was calculated using the following equation:

[0086]

[0087] 7. The radar stealth performance of the HMC-8 was simulated using CST electromagnetic field simulation software. The reduction in its radar cross-section was calculated using the following formula:

[0088]

[0089] Experiment 2: The difference between this experiment and Experiment 1 is that the mass of 3-aminophenol mentioned in step 2 is 0.0999g;

[0090] The product obtained in step five is SHMC-8. Everything else is the same as in experiment one.

[0091] Experiment 3: The difference between this experiment and Experiment 1 is that the mass of 3-aminophenol mentioned in step 2 is 0.0499g;

[0092] The product obtained in step five is SMC-8. Everything else is the same as in experiment one.

[0093] Experiment 4: The difference between this experiment and Experiment 1 is that the mass of manganese acetate mentioned in step 3 is 0.11g; the product obtained in step 5 is LHMC-8. Everything else is the same as Experiment 1.

[0094] Experiment 5: The difference between this experiment and Experiment 1 is that the mass of manganese acetate mentioned in step 3 is 0.22g; the product obtained in step 5 is LMC-8. Everything else is the same as Experiment 1.

[0095] Experiment Six: The difference between this experiment and Experiment One is that the calcination temperature in step five is 700℃; the product obtained in step five is HMC-7. Everything else is the same as Experiment One.

[0096] Experiment 7: Constructing an electromagnetic metamaterial based on HMC-7, the product of Experiment 6: The electromagnetic parameters of HMC-7 obtained by the vector network analyzer were imported into the CST electromagnetic field simulation software. The frequency was set to 2-18 GHz, and the boundary was set to a periodic boundary. A three-layer gradient metamaterial was constructed. The side length and height of the bottom layer were 15 mm × 1 mm, the side length and height of the second layer were 13 mm × 2 mm, and the side length and height of the third layer were 11 mm × 2 mm.

[0097] Figure 1 The X-ray diffraction patterns of the products obtained in step five of experiments one through five are shown. The peaks observed at 34.9°, 40.5°, 58.7°, 70.2°, and 73.8° of the SMC-8 prepared in experiment three can be attributed to the (111), (200), (220), (311), and (222) crystal planes of MnO. The two broad characteristic peaks observed at approximately 23.5° and 43.8° in the other four groups of samples correspond to the (002) and (100) crystal planes of graphitized carbon, indicating the stability of the prepared manganese / nitrogen-doped nanocarbon materials, which is beneficial for industrial production and promotion.

[0098] Figure 2 The image shows a scanning electron microscope image of HMC-8 prepared for Experiment 1, from which a distinct helical structure can be seen.

[0099] Figure 3 The image shows a scanning electron microscope image of SHMC-8 prepared for Experiment 2. The image shows the coexistence of helical and spherical structures, with the spheres having a diameter of approximately 171 nm.

[0100] Figure 4 The image shows a scanning electron microscope image of the SMC-8 prepared for Experiment 3. The image shows that the structure consists entirely of small spherical structures with a diameter of approximately 171 nm.

[0101] Figure 5 The image shows a scanning electron microscope image of LHMC-8 prepared for Experiment 4. The image shows the coexistence of helical structures and large spherical structures, with the diameter of the large spheres being approximately 299 nm.

[0102] Figure 6 The image shows a scanning electron microscope image of LMC-8 prepared for Experiment 5. It can be seen from the image that the structures are all large spherical, with a diameter of about 299 nm.

[0103] Figure 7 The graph shows the electromagnetic reflection loss data of HMC-8 calculated through step six of Experiment 1. Figure 8 The graph shows the electromagnetic reflection loss data of SHMC-8 calculated through step six of Experiment 2. Figure 9 The graph shows the electromagnetic reflection loss data of SMC-8 calculated through step six of Experiment 3. Figure 10 The graph shows the electromagnetic reflection loss data of LHMC-8 calculated through step six of Experiment 4. Figure 11 The graph shows the electromagnetic reflection loss data of LMC-8 calculated through step six of experiment five. It can be seen that when the mass fill ratio is 30%, the minimum reflection losses of HMC-8, SHMC-8, SMC-8, LHMC-8 and LMC-8 can reach -63.13dB, -26.4dB, -42.49dB, -52.43dB and -42.92dB respectively, with matching thicknesses of 1.29mm, 1.34mm, 4.98mm, 1.67mm and 5mm respectively, all exhibiting excellent absorption performance.

[0104] Figure 12 The effective absorption bandwidth diagram of HMC-8 prepared for Experiment 1 shows that HMC-8 achieves an ultra-wideband absorption bandwidth of 5.12 GHz with a thickness of 1.83 mm.

[0105] Figure 13 The simulation results of the electromagnetic metamaterial constructed for Experiment 7 show that the metamaterial exhibits excellent electromagnetic wave absorption performance, exceeding 67% of the entire frequency band and reaching an ultra-wideband absorption of 12.16 GHz, demonstrating potential for practical applications and military applications.

[0106] Figure 14 The voltage standing wave ratio (VSWR) of the gradient metamaterial constructed for Experiment 7 is shown in the graph. The closer the VSWR value is to 1, the better the impedance of the material. The VSWR of the gradient metamaterial is significantly better than that of the bulk material, demonstrating the excellent impedance characteristics of the gradient metamaterial.

[0107] Figure 15 This is a schematic diagram for RCS calculation. Figure 16 This is a graph showing the RCS reduction value in step seven of Experiment 2. Figure 17 The RCS calculation results for step seven of Experiment 2. Figure 3 Vito, Figure 18 The radar chart for the RCS calculation in step seven of Experiment 2 shows that at a 0° angle, the RCS reduction is greater than 30 dB·m. 2 The maximum RCS reduction of SHMC-8 was 36.4 dB·m. 2 This demonstrates the excellent radar stealth performance of the SHMC-8.

[0108] Figure 19 The radar image of the structure for RCS calculation in step seven of Experiment 1 shows that the maximum RCS reduction is 35.19 dB·m. 2 .

[0109] Figure 20 The radar image for the RCS calculation in step seven of Experiment 3 shows that the maximum RCS reduction is 32.04 dB·m. 2 .

Claims

1. A method for preparing a metal / nitrogen-doped helical carbon nanotube microwave absorbing material, characterized in that... The preparation method of metal / nitrogen-doped helical carbon nanotube microwave absorbing material is carried out according to the following steps:

1. Dissolve phenylglycine and sodium hydroxide together in a mixed solution of acetone and deionized water, and denote this solution as solution A; Dissolve palmitoyl chloride in acetone and denote this solution as solution B; Sodium hydroxide is dissolved in deionized water and denoted as solution C. Solution B and solution C were slowly added dropwise to solution A, and the mixture was stirred for 12-13 hours. The pH of the solution was adjusted to 0.9-1.1, and the stirring was continued for another 4-4.5 hours. The product was filtered and dried. The resulting white product was placed in a beaker, and petroleum ether was added. The mixture was heated to 90-95°C. The white product gradually dissolved. Heating was stopped when the white product re-precipitated as the petroleum ether evaporated. The mixture was then allowed to cool naturally to room temperature to obtain the purified template, denoted as AS. The volume ratio of the petroleum ether to the acetone in solution A is 2:3; When preparing solution A, the mass ratio of sodium hydroxide to phenylglycine is 1:(3.5-4), the volume ratio of acetone to deionized water is 1:(3-3.5), and the mass ratio of sodium hydroxide to acetone is 1g:(54mL-55mL). When preparing solution B, the volume ratio of palmitoyl chloride to acetone is 1:(7.5-8); When preparing solution C, the mass ratio of sodium hydroxide to deionized water is 1 g:(160 mL to 165 mL); The sodium hydroxide in solution A and the sodium hydroxide in solution C have the same mass. The mass ratio of sodium hydroxide in solution A to the volume ratio of palmitoyl chloride in solution B is 1 g:(6.5 mL to 7 mL).

2. Dissolve AS and 3-aminophenol prepared in step 1 in methanol, stir thoroughly to obtain a transparent solution D; The mass ratio of AS to 3-aminophenol is (0.01–0.1):(0.0199–1.9999). The mass ratio of AS to methanol is 1 g:(225 mL to 230 mL); 3. Add acetate to the transparent solution D prepared in step 2, stir thoroughly, then add deionized water and continue stirring for 40 min to 45 min to obtain solution E; The mass ratio of the acetate to the 3-aminophenol in step two is 1:(0.4–9.1); The mass ratio of the acetate to the volume of deionized water is 1 g:(124 mL to 2820 mL); 4. Slowly add the formaldehyde aqueous solution dropwise to solution E prepared in step 3, heat to 62℃~63℃ and stir continuously for 3h~3.5h, let it cool naturally to room temperature, and then filter and dry in sequence to obtain the yellow precursor; The formaldehyde aqueous solution has a mass concentration of 37% to 40%, and the volume ratio of the formaldehyde aqueous solution to the deionized water added in step three is 1:(305 to 315).

5. The yellow precursor prepared in step 4 is calcined under a protective gas and at 600℃~900℃ for 2h~3h, and then naturally cooled to room temperature to obtain the metal / nitrogen-doped spiral carbon nanotube microwave absorbing material M / N-HCNT.

2. The method for preparing a metal / nitrogen-doped helical carbon nanotube microwave absorbing material according to claim 1, characterized in that... In step one, the pH of the solution is adjusted by adding hydrochloric acid solution.

3. The method for preparing a metal / nitrogen-doped helical carbon nanotube microwave absorbing material according to claim 1, characterized in that... The acetate mentioned in step three is manganese acetate, cobalt acetate, or nickel acetate.

4. The method for preparing a metal / nitrogen-doped helical carbon nanotube microwave absorbing material according to claim 1, characterized in that... The drying process described in step four involves drying at 60°C for 12 hours.

5. The method for preparing a metal / nitrogen-doped helical carbon nanotube microwave absorbing material according to claim 1, characterized in that... The protective gas mentioned in step five is argon or nitrogen.

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