Reduced graphene oxide@nickel catalyzed nitrogen-doped carbon nanotube heterostructure filler, preparation method and application thereof

Abstract

The application provides a reduced graphene oxide@nickel catalytic nitrogen-doped carbon nanotube heterostructure filler and a preparation method and application thereof, and belongs to the technical field of electromagnetic shielding materials.The heterostructure filler comprises reduced graphene oxide and a plurality of one-dimensional nitrogen-doped carbon nanotubes grown in situ on the surface of the reduced graphene oxide; the top end of the nitrogen-doped carbon nanotube is coated with magnetic nickel nanoparticles, and the nitrogen-doped carbon nanotube is vertically distributed on the surface of the reduced graphene oxide.The filler provided by the application has a morphology of one-dimensional carbon nanotubes vertically distributed on the surface of two-dimensional reduced graphene oxide, which significantly improves the lapping efficiency and the conductive network construction capability of the filler, reduces the percolation threshold, and multiplies the number of contact points between the fillers, so that a high-efficiency three-dimensional conductive network can be formed in aerogel at a low filler dosage, thereby realizing excellent electromagnetic shielding performance while maintaining good lightweight characteristics and mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic shielding materials technology, specifically to a reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler, its preparation method, and its application. Background Technology

[0002] Two-dimensional graphene (2D) is widely used as a conductive filler due to its high specific surface area, high electrical conductivity, excellent Young's modulus, and enhanced effect on multiple reflections of electromagnetic waves, making it an ideal choice for preparing polymer-based electromagnetic shielding composites. However, single 2D graphene sheets tend to stack when constructing 3D conductive networks, resulting in low contact efficiency. In contrast, 1D fillers, with their aspect ratio advantage, can effectively act as bridges connecting other morphological fillers, thereby constructing more complete 3D conductive networks. Based on this, researchers often combine 1D fillers with 2D sheets to construct multidimensional hybrid systems to improve the electromagnetic shielding performance of composite materials. However, existing studies often simply stack 1D fillers on the surface of 2D sheets, resulting in a low proportion of heterogeneous structures in 3D space and unsatisfactory overlap efficiency between fillers. This limits the efficient construction of 3D conductive networks, leading to high percolation thresholds and difficulty in achieving efficient electromagnetic shielding with low filler content.

[0003] Therefore, the key to improving the electromagnetic shielding performance of polymer-based composite materials is to achieve a highly efficient three-dimensional conductive network with low filler content through innovative structural design. Summary of the Invention

[0004] The purpose of this invention is to provide a heterostructure filler consisting of reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotubes, its preparation method, and its applications. The technical solution of this invention utilizes an "in-situ growth-heat treatment" technique to grow essentially perpendicular nickel-catalyzed nitrogen-doped carbon nanotubes in situ on the surface of two-dimensional reduced graphene oxide, forming a unique three-dimensional structure of one-dimensional linear fillers standing on a two-dimensional surface. This significantly improves the overlap efficiency between fillers, enabling the construction of a highly efficient conductive network even with low filler content. Simultaneously, the heterostructure enhances the interfacial polarization effect, thereby achieving excellent broadband electromagnetic shielding performance.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a heterostructure filler consisting of reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotubes. The heterostructure filler includes reduced graphene oxide and a plurality of one-dimensional nitrogen-doped carbon nanotubes grown in situ on the surface of the reduced graphene oxide. The top of the nitrogen-doped carbon nanotubes is coated with nickel nanoparticles, and the nitrogen-doped carbon nanotubes stand upright on the surface of the reduced graphene oxide.

[0007] The present invention relates to a heterostructure filler consisting of reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotubes. Nickel-catalyzed nitrogen-doped carbon nanotubes are vertically grown in situ on the surface of reduced graphene oxide, with nickel coating at the top. The structure is a two-dimensional surface with a one-dimensional linear filler. This structure mimics the tentacle-like protrusions of the pyloric membrane of animals in nature, maximizing contact efficiency with electromagnetic waves, significantly improving filler overlap efficiency and conductive network integrity, reducing the percolation threshold, and achieving low-filling, high-performance, and multifunctional integration.

[0008] This invention discloses a method for preparing the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler as described above, comprising the following steps:

[0009] Step S1: Prepare graphene oxide;

[0010] Step S2: Nickel nanoparticles are grown in situ on the surface of the graphene oxide by hydrothermal reduction to obtain a reduced graphene oxide@nickel precursor.

[0011] Step S3 involves mixing the reduced graphene oxide@nickel precursor with a carbon-nitrogen source and heat-treating it under a nitrogen atmosphere. This allows the nickel nanoparticles to catalyze the growth of the carbon and nitrogen sources, forming nitrogen-doped carbon nanotubes, resulting in a reduced graphene oxide@nickel catalyzed nitrogen-doped carbon nanotube heterostructure filler. Due to the tip growth mechanism, the carbon nanotubes lift the nickel particles, forming an "standing" structure perpendicular to the surface of the reduced graphene oxide.

[0012] This technical solution uses a "hydrothermal reduction-heat treatment" process to prepare a heterostructure filler of reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotubes. Nickel-catalyzed nitrogen-doped carbon nanotubes with nickel-coated tips are grown vertically in situ on the surface of reduced graphene oxide, resulting in a multidimensional heterostructure of one-dimensional conductive material standing on the surface of two-dimensional sheets. This significantly improves the filler overlap efficiency and the integrity of the conductive network, thereby effectively reducing the percolation threshold of the composite material and achieving excellent electrical conductivity and electromagnetic shielding performance with a low filler content.

[0013] As a further improvement of the present invention, the carbon and nitrogen source is at least one selected from melamine, urea, and dicyandiamide. More specifically, the carbon and nitrogen source is melamine.

[0014] Preferably, the mass ratio of the graphene oxide@nickel precursor to melamine is 1:5~15. Further, the mass ratio of the reduced graphene oxide@nickel precursor to melamine is 1:5, 1:10, and 1:15. Further, the mass ratio of the graphene oxide@nickel precursor to melamine is 1:10. Using this technical solution, the length and morphology of carbon nanotubes can be controlled, avoiding excessively short nanotubes or the formation of carbon spheres.

[0015] Preferably, step S1 uses a modified Hummers method to prepare graphene oxide, obtaining monolayer or few-layer graphene oxide. Further, this step includes: adding 3 g of graphite powder, 4 g of potassium persulfate, and 4 g of phosphorus pentoxide to a three-necked flask containing 20 mL of concentrated sulfuric acid, and then... o Stir mechanically at C for 6 hours. Add 500 mL of deionized water, and obtain pre-oxidized graphite by vacuum filtration, washing, and drying. Add 3 g of pre-oxidized graphite to 120 mL of concentrated sulfuric acid, stir mechanically in an ice-water bath, slowly add 9 g of potassium permanganate, and heat to 35°C. o React at step C for 2 hours. Slowly add 125 mL of deionized water and 20 mL of hydrogen peroxide sequentially, and continue stirring for 15 minutes. Dilute with 2 L of deionized water, let stand for 12 hours, collect the precipitate at the bottom, dialyze to neutral, and freeze-dry to obtain graphene oxide.

[0016] Step S2: Nickel nanoparticles are grown in situ on the surface of the graphene oxide by hydrothermal reduction to obtain a graphene@nickel precursor.

[0017] Preferably, step S2 includes adding the graphene oxide to water to obtain an aqueous dispersion of graphene oxide; mixing the aqueous dispersion of graphene oxide with an ethylene glycol solution of nickel chloride hexahydrate and stirring thoroughly, wherein the mass ratio of graphene oxide to nickel chloride hexahydrate is 1~3:1; then adding sodium hydroxide solution and hydrazine hydrate sequentially; mixing thoroughly; and transferring the mixture to a high-pressure reactor and heating at 85~95°C. o The reaction was carried out at C for 0.5~2 hrs; the product was collected by vacuum filtration, washed, and dried to obtain the reduced graphene oxide@nickel precursor.

[0018] Preferably, the mass ratio of graphene oxide to nickel chloride hexahydrate is 2:1.

[0019] Preferably, in step S3, heat treatment is performed in a tubular furnace under nitrogen protective gas pressure of 0.2 MPa, at a pressure of 3~7. o C / min increased to 850~950 o Keep warm at C for 1~3 hours, and apply 1~3% heat with the furnace. o Cooling to room temperature at C / min yields a heterostructure filler with nickel-catalyzed nitrogen-doped carbon nanotubes vertically erected on the surface of reduced graphene oxide.

[0020] This invention discloses the application of the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler as described above for the preparation of composite aerogels.

[0021] This invention discloses a composite aerogel comprising a polymer matrix and a reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler as described above, dispersed in the polymer matrix. The polymer matrix is ​​polyimide, and the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler accounts for 50% to 90% by mass. Further, the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler accounts for 80% by mass.

[0022] The filler in this technical solution is based on a biomimetic strategy, giving the aerogel a three-dimensional porous network structure, excellent compression resilience, and ultra-wideband (gigahertz to terahertz) high electromagnetic shielding effectiveness. This aerogel achieves an average total electromagnetic shielding effectiveness (EMI SE) in the gigahertz band. T The performance reaches 52 dB in the high-frequency band and 54 dB in the terahertz band, and maintains a performance retention rate of over 95% under extreme environments such as high temperature, humid heat aging, and long-term storage.

[0023] This invention discloses a method for preparing the composite aerogel as described above, comprising the following steps:

[0024] Step S10: The reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler is mixed with a polyamic acid solution and dispersed evenly to obtain a dispersion.

[0025] Step S20: The dispersion is subjected to directional freeze-drying to obtain a composite aerogel precursor. This step utilizes a temperature gradient to induce the directional growth of ice crystals, and after freeze-drying, an aerogel precursor with an oriented porous structure is formed.

[0026] Step S30: The composite aerogel precursor is subjected to thermal imidization treatment to convert polyamic acid into polyimide, thereby obtaining reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube / polyimide composite aerogel.

[0027] As a further improvement of the present invention, in step S10, the solvent of the polyamic acid solution is water, and the dispersion also contains triethylamine;

[0028] And / or, in step S20, the directional freeze-drying is performed by placing a mold containing the dispersion on a cooling copper plate in contact with liquid nitrogen, followed by a temperature of -80 to -60°C. o C, freeze-drying under a pressure not exceeding 2 Pa;

[0029] And / or, in step S30, the thermal imidization treatment is carried out under an inert atmosphere at a temperature of 250~350°C. o C, keep warm for 1-3 hours; then keep warm for 1-3 hours. o The composite aerogel was obtained by cooling the temperature at a rate of C / min to room temperature.

[0030] As a further improvement of the present invention, in the obtained reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube / polyimide composite aerogel, the mass fraction of the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler is 50%~90%. Further, the mass fraction of the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler is 80%.

[0031] As a further improvement of the present invention, in step S10, the polyamic acid is prepared by the following steps: 4,4'-diaminodiphenyl ether is mixed with N,N-dimethylacetamide solvent and stirred until the 4,4'-diaminodiphenyl ether is completely dissolved. Then, pyromellitic dianhydride is added and mixed evenly. The mixture is stirred in an ice-water bath for 2 hours until the rod-climbing phenomenon occurs. Triethylamine is then added, and stirring is continued for 5 hours to obtain a water-soluble polyamic acid precursor solution. The solution is subjected to solvent exchange in an ice-water bath and collected. After low-temperature freezing and freeze-drying, water-soluble polyamic acid is obtained for later use.

[0032] This invention discloses the application of the composite aerogel described above, which is used to prepare electromagnetic shielding materials.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] First, by employing the technical solution of this invention, based on a biomimetic strategy and in-situ growth process, a heterogeneous filler structure of one-dimensional carbon nanotubes erected on the surface of two-dimensional sheets was successfully constructed. Unlike traditional hybrid structures, this unique erected structure greatly improves the overlap efficiency between fillers and the ability to build a conductive network, reduces the percolation threshold, and multiplies the number of contact points. A highly efficient three-dimensional conductive network can be formed with relatively low filler dosage, achieving excellent performance and helping to maintain the lightweight and good mechanical properties of the composite material. Furthermore, by adjusting the carbon-nitrogen source ratio and heat treatment process, the length, morphology, and perpendicularity of nickel-catalyzed nitrogen-doped carbon nanotubes can be precisely controlled, achieving adjustable performance. The technical solution of this invention solves the problems of easy agglomeration, low overlap efficiency, and difficulty in balancing lightweight and shielding performance in traditional conductive fillers. The process is simple and highly controllable, and the resulting material has broad application prospects in 5G / 6G communications, aerospace, and precision electronic protection.

[0035] Secondly, the aerogel obtained by combining the filler and polyimide using the technical solution of this invention exhibits excellent performance. At a filler content of 80 wt%, the composite aerogel shows an average EMI SE in the gigahertz band (5.4~40 GHz). T Up to 52 dB, with an average EMI SE in the terahertz band (0.3–2 THz). TUp to 54 dB, achieving ultra-wideband high-efficiency shielding; it also possesses excellent stability against extreme environments (humid heat, strong acid corrosion, strong ultraviolet radiation, etc.), at 400 o After being exposed to high temperatures and stored for a long period of time, the performance retention rate is ≥95%. Attached Figure Description

[0036] Figure 1 This is a microscopic morphology diagram of the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler of Example 1 of the present invention.

[0037] Figure 2 The images show the microstructure and structural characterization of the reduced graphene oxide@nickel precursor and the reduced graphene oxide@nickel catalytic nitrogen-doped carbon nanotube heterostructure filler of Example 1 of the present invention; wherein, (a) and (b) are SEM images of reduced graphene oxide@nickel at different magnifications; (c) and (d) are SEM images of reduced graphene oxide@nickel catalytic nitrogen-doped carbon nanotube heterostructure filler at different magnifications.

[0038] Figure 3 These are microscopic morphology images of the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler of Examples 2 and 3 of the present invention; wherein, (a) and (a') are SEM images of the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler of Example 2 at different magnifications; (b) and (b') are SEM images of the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler of Example 3 at different magnifications.

[0039] Figure 4 The figures show the electrical conductivity and electromagnetic shielding performance of the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube / polyimide composite aerogel according to embodiments of the present invention; wherein, (a) is the electrical conductivity of the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube / polyimide composite aerogel with different mass fractions of reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotubes; (b) is the EMI SE of the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube / polyimide composite aerogel with different mass fractions of reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotubes. T (c) Real-time received signal strength (RSSI) test setup in different test scenarios in a microwave anechoic chamber: direct exposure, open window, covered with pure polyimide aerogel, covered with reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube / polyimide composite aerogel; a smartphone is used as a 5 GHz Wi-Fi signal transmitter; (d) RSSI measured curves within 100 seconds in all test scenarios.

[0040] Figure 5The results show the comparison of electrical conductivity and electromagnetic shielding performance of the composite aerogels in Examples 4, 8, and 9 of this invention; wherein, (a) is the electrical conductivity of the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube / polyimide composite aerogels prepared by reducing graphene oxide@nickel precursor to melamine at mass ratios of 1:5, 1:10, and 1:15, respectively; (b) is the electromagnetic shielding effectiveness (EMI SE) of the reduced graphene oxide@nickel precursor to melamine composite aerogel samples prepared by reducing graphene oxide@nickel precursor to melamine at mass ratios of 1:5, 1:10, and 1:15, respectively; and (c) is the reflectance coefficient (R) of the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube / polyimide composite aerogel samples prepared by reducing graphene oxide@nickel precursor to melamine at mass ratios of 1:5, 1:10, and 1:15, respectively.

[0041] Figure 6 These are the environmental stability test results of the composite aerogel of Example 4 of the present invention; wherein, (a) is the durability and stability of the composite aerogel of Example 4 under different extreme environments; (b) is the EMI SE of the composite aerogel of Example 4 under different high temperature conditions. T (c) EMI SE of the composite aerogel of Example 4 after long-term storage. T .

[0042] Figure 7 These are the electromagnetic shielding performance test results of the composite aerogel of Example 4 of the present invention; wherein, (a) is the EMI SE of the composite aerogel of Example 4 in the 0.3~2 THz band. T (b) EMI SE of the composite aerogel in Example 4 in the 5.4~40 GHz band. T ; Detailed Implementation

[0043] The preferred embodiments of the present invention will be described in further detail below.

[0044] Example 1

[0045] A heterostructure filler consisting of reduced graphene oxide (rGO)@nickel-catalyzed nitrogen-doped carbon nanotubes (ni-NCNTs) is disclosed. The heterostructure filler comprises reduced graphene oxide (rGO) and multiple one-dimensional nitrogen-doped carbon nanotubes (Ni-NCNTs) grown in situ on the surface of the reduced graphene oxide. The Ni-NCNTs are topped with nickel nanoparticles and stand upright on the surface of the rGO. This filler is prepared using the following steps:

[0046] Step S1, Preparation of graphene oxide (GO); Graphite is oxidized using a modified Hummers method:

[0047] Add 3 g of graphite powder, 4 g of potassium persulfate, and 4 g of phosphorus pentoxide to a three-necked flask containing 20 mL of concentrated sulfuric acid. 80 o Stir mechanically at C for 6 hours. Add 500 mL of deionized water, and obtain pre-oxidized graphite by vacuum filtration, washing, and drying. Add 3 g of pre-oxidized graphite to 120 mL of concentrated sulfuric acid, stir mechanically in an ice-water bath, slowly add 9 g of potassium permanganate, and heat to 35°C. o React at C for 2 hours. Slowly add 125 mL of deionized water and 20 mL of hydrogen peroxide sequentially, and continue stirring for 15 minutes. Dilute with 2 L of deionized water, let stand for 12 hours, collect the precipitate at the bottom, dialyze to neutral, and freeze-dry to obtain GO.

[0048] Step S2 involves in-situ growth of nickel nanoparticles on the surface of the graphene oxide via hydrothermal reduction to obtain a reduced graphene oxide@nickel (rGO@Ni) precursor; specifically including:

[0049] 0.2 g of GO was added to 40 mL of deionized water to obtain an aqueous GO dispersion. The obtained GO dispersion was then added to 68 mL of 0.0025 mol / L NiCl₂·6H₂O ethylene glycol solution and stirred thoroughly. Subsequently, 10.8 mL of 1 mol / L NaOH ethylene glycol solution and 8.2 mL of hydrazine hydrate were added, mixed thoroughly, and then transferred to a high-pressure reactor. The mixture was incubated at 90 °C. o React in a C oven for 1 hour. Collect the product by vacuum filtration, wash repeatedly with deionized water and ethanol, and then... o Dry in an oven at C for 12 hours to obtain rGO@Ni powder.

[0050] Step S3: After uniformly mixing rGO@Ni and melamine at a mass ratio of 1:10, place the mixture in a tube furnace. Heat at 5°C under a nitrogen atmosphere. o Heating rate increased to 900 °C / min o Keep warm at 2°C for 2 hours, then at 2°C... o Heating rate increased to 1600 °C / min o Keep warm at 2°C for 2 hours, and finally at 2°C. o The temperature was reduced to room temperature at a rate of C / min, yielding rGO@Ni-NCNTs heterostructure packing material. This step utilized the catalytic effect of Ni and the carbon (C source) and nitrogen (N source) sources provided by melamine to grow Ni-NCNTs on the rGO surface. Due to the apical growth mechanism, the growth direction of Ni-NCNTs was perpendicular to the rGO substrate, thus successfully constructing an rGO@Ni-NCNTs heterostructure packing material with a two-dimensional surface supporting a one-dimensional linear packing material spatial configuration. The microstructure of this packing material is as follows: Figure 1 As shown.

[0051] The microstructure comparison image of rGO@Ni in step S2 is shown below. Figure 2 (a) and Figure 2 As shown in (b), it can be seen that magnetic Ni nanoparticles can be successfully grown on the GO surface by hydrothermal reduction, and GO will also be initially reduced, successfully preparing rGO@Ni and rGO@Ni-NCNTs obtained in step S3.

[0052] like Figure 2 (c) and Figure 2 (d) is a SEM image of the rGO@Ni-NCNTs prepared in this embodiment. It can be seen that one-dimensional linear Ni-NCNTs can be grown in situ on the surface of two-dimensional sheet-like rGO through high-temperature reduction. This is attributed to the decomposition of melamine at high temperature, which provides C and N sources. Ni nanoparticles are excited under high-temperature conditions, acting as catalytic sites to absorb C and N atoms. When saturation is reached, C and N precipitate from the bottom of the Ni nanoparticles, growing NCNTs and simultaneously lifting the Ni particles, resulting in a structure composed of carbon nanotubes (C, O, and N elements) with Ni particles at the top. By rationally controlling the content of C and N sources, the grown one-dimensional Ni-NCNTs can exhibit a vertically upright state.

[0053] Example 2

[0054] Based on Example 1, the difference in this example is that the mass ratio of rGO@Ni to melamine in step S3 is 1:5, and the resulting filler is named rGO@Ni-NCNTs-5. The microstructure of the filler obtained in this example is as follows. Figure 3 As shown in (a) and 3(a'), it can be seen that the length of the one-dimensional filler on the surface of the two-dimensional sheet is relatively short.

[0055] Example 3

[0056] Based on Example 1, the difference in this example is that the mass ratio of rGO@Ni to melamine in step S3 is 1:15, and the resulting filler is named rGO@Ni-NCNTs-15. The microstructure of the filler obtained in this example is as follows. Figure 3 As shown in (b) and 3(b'), the filler morphology on the surface of the two-dimensional sheet is close to spherical.

[0057] Example 4

[0058] Composite aerogels were prepared using the rGO@Ni-NCNTs heterostructure filler prepared in Example 1; the preparation method included the following steps:

[0059] Step S10, Preparation of polyamic acid (PAA): Add 4.00 g of 4,4'-diaminodiphenyl ether (ODA) to a three-necked round-bottom flask, then add 48 g of N,N-dimethylacetamide (DMAc) as a solvent, and stir until the ODA is completely dissolved. Next, add 4.42 g of pyromellitic dianhydride (PMDA) and mix thoroughly. Stir the mixture in an ice-water bath for 2 hours until the rod-climbing phenomenon occurs. Then add 2.02 g of triethylamine (TEA) and continue stirring for 5 hours to obtain a water-soluble PAA precursor solution. Perform solvent exchange on the solution in an ice-water bath and collect the solution. After low-temperature freezing and lyophilization, obtain water-soluble PAA for later use.

[0060] Dissolve 0.5 g PAA in 20 mL of deionized water, add 0.3 g TEA while stirring, and add a certain amount of rGO@Ni-NCNTs after PAA is completely dissolved. After homogenization by a high-speed homogenizer, a dispersion is obtained.

[0061] Step S20: Pour the dispersion into a rectangular polytetrafluoroethylene mold of a specific size (23 mm in length and 12 mm in width) placed on a copper plate. Introduce liquid nitrogen into the copper plate and, after the sample is completely frozen, place it at a temperature of -70°C. o C, under a pressure not exceeding 2 Pa, freeze-drying was performed to obtain rGO@Ni-NCNTs / PAA composite aerogel precursor; this step utilizes the temperature gradient to induce the directional growth of ice crystals, and after freeze-drying, an aerogel precursor with an oriented porous structure is formed.

[0062] Step S30: Place the composite aerogel precursor in a tube furnace and heat it under a nitrogen atmosphere at 5°C. o Temperature increased to 300 °C / min o Keep warm at 2°C for 2 hours, then at 2°C. o The PAA was converted to polyimide (PI) by cooling at a rate of C / min to room temperature, resulting in rGO@Ni-NCNTs / PI composite aerogel. The mass percentage of rGO@Ni-NCNTs in the composite aerogel was 80 wt%.

[0063] Examples 5-7

[0064] Based on Example 4, Examples 5-7 differ in that the mass percentages of rGO@Ni-NCNTs in the composite aerogel are 20 wt%, 40 wt%, and 60 wt%, respectively.

[0065] Methods for testing aerogel properties:

[0066] Conductivity was measured using a four-probe instrument.

[0067] Electromagnetic shielding performance was tested using a vector network analyzer and waveguide method, covering C-band (5.4-8.2 GHz), X-band (8.2-12.4 GHz), Ku-band (12.4-18 GHz), Ka-band (18-26.5 GHz), and K-band (26.5-40 GHz), according to ASTM D5568-2008 standard.

[0068] Terahertz time-domain signal testing was conducted in transmission mode using a self-built angle-resolved terahertz time-domain spectroscopy system (THz-TDS). A femtosecond fiber laser oscillator with a center wavelength of 1560 nm and a repetition frequency of 100 MHz was used to pump a low-temperature grown gallium arsenide photoconductive antenna to generate horizontally polarized terahertz pulses.

[0069] The durability of aerogels in real-world environments was assessed using accelerated aging tests: 200... o The chemical resistance was evaluated by continuous heating at C for 6 hrs; immersion in liquid nitrogen for 30 min; immersion in 98% concentrated sulfuric acid and analytical grade NaOH solution for 24 hrs respectively; ultrasonication in water for 1 hr to simulate mechanical vibration; and exposure in a UV aging chamber for 48 hrs at an irradiance of 0.76 W·m. -2 ·nm -1 (340 nm), temperature 60 o C; 60 o C. Damp heat aging at 95%±5% relative humidity for 48 hours; thermal shock cycling: 150 o After holding at 4°C for 4 hours, quickly transfer to 40°C. o Keep warm at C for 2 hours, for a total of 8 cycles.

[0070] Environmental stability: The sample was placed at a high temperature (400°C). o C) After undergoing extreme conditions such as 100 days of natural placement, its EMI SE was tested. T Retention rate.

[0071] The performance of the aerogels obtained in Examples 4-7 was tested, and the results are as follows: Figure 4 As shown in the figure, it can be seen that the conductivity of the composite aerogel gradually increases with the increase of the mass fraction of rGO@Ni-NCNTs (e.g., ...). Figure 4 (as shown in (a)) This is mainly attributed to the increased density of the conductive filler inside, which promotes the overlap and contact between the fillers, thereby constructing a more complete three-dimensional conductive network. The improved conductivity exacerbates the impedance mismatch of the material, enhances its ability to reflect electromagnetic waves, and thus effectively improves the EMI SE of the aerogel. T (like Figure 4(b) shows that when the mass fraction of rGO@Ni-NCNTs is 80 wt%, the EMI SE of the rGO@Ni-NCNTs / PI composite aerogel is... T The maximum value reached was 47 dB. Compared with single conductive fillers, the prepared rGO@Ni-NCNTs heterostructure filler showed a significant advantage in improving the electromagnetic shielding performance of the composite material, indicating that its unique microstructure and interface structure contribute to enhancing the electromagnetic shielding performance of the material.

[0072] To evaluate the shielding effect of rGO@Ni-NCNTs / PI composite aerogel in practical applications, RSSI testing was conducted in a microwave anechoic chamber using the 5 GHz Wi-Fi band (a widely used electronic communication band). During the test, a smartphone was used as a Wi-Fi hotspot transmitter to radiate a 5 GHz electromagnetic signal, while another smartphone ran a corresponding program to continuously record the RSSI value over 100 seconds at a distance of 1 meter. The test scenarios included four conditions: direct exposure, open window, open window covering PI aerogel, and open window covering the rGO@Ni-NCNTs / PI aerogel from Example 4. The results are as follows: Figure 4 As shown in (c). The results show that RSSI remained at a high level in all three cases: direct exposure, open window, and open window covering with PI aerogel, indicating that the signal could be transmitted effectively. However, when covered with the rGO@Ni-NCNTs / PI composite aerogel of Example 4, RSSI decreased significantly, confirming that the electromagnetic signal was almost completely blocked, as shown in (c). Figure 4 As shown in (d). The above results further confirm that the prepared rGO@Ni-NCNTs / PI composite aerogel can effectively shield electromagnetic signals in the target frequency band, demonstrating its potential in practical electromagnetic shielding applications.

[0073] Example 8

[0074] Based on Example 4, the difference in this example is that the filler from Example 2 is used to prepare rGO@Ni-NCNTs-5 / PI composite aerogel. In the composite aerogel, the mass percentage of rGO@Ni-NCNTs-5 is 80 wt%.

[0075] Example 9

[0076] Based on Example 4, the difference in this example is that the filler from Example 3 is used to prepare rGO@Ni-NCNTs-15 / PI composite aerogel. In the composite aerogel, the mass percentage of rGO@Ni-NCNTs-15 is 80 wt%.

[0077] The electromagnetic shielding performance of composite aerogels obtained from different mass ratios of rGO@Ni and melamine in Examples 4, 8, and 9 was tested. Figure 5 As shown. In Example 4, the rGO@Ni-NCNTs prepared at a mass ratio of 1:10 exhibited a microstructure of Ni-NCNTs vertically grown on the rGO surface. The resulting composite aerogel showed good conductivity and EMI SE. T The highest values ​​for R indicate that using a 1:10 mass ratio of rGO@Ni-NCNTs facilitates effective overlap between fillers. In Example 8, the rGO@Ni-NCNTs prepared with a 1:5 mass ratio resulted in shorter Ni-NCNTs lengths compared to those prepared with a 1:10 mass ratio. In Example 9, the rGO@Ni-NCNTs prepared with a 1:10 mass ratio produced fillers with near-spherical morphology grown on the surface of the two-dimensional sheets. The electrical conductivity and EMI SE of the composite aerogels from Examples 8 and 9 were also observed. T Both R and R are improved, indicating that the filler can achieve effective overlap. However, when the mass ratio is higher than 1:5, due to the low melamine content and insufficient C and N sources, the grown Ni-NCNTs are short, making it difficult to form a good three-dimensional overlap structure. When the mass ratio is lower than 1:15, excess C and N sources rapidly accumulate at the catalytic sites, promoting the formation of a large number of spherical carbon particles. Compared to one-dimensional carbon nanotubes, this morphology is not conducive to the overlap between fillers and the overlap of the conductive network.

[0078] Composite aerogels prepared from rGO@Ni-NCNTs with three different mass ratios exhibit varying degrees of electromagnetic shielding performance due to differences in their microstructures, resulting in the formation of three-dimensional conductive networks. The composite aerogel prepared at a mass ratio of 1:10 demonstrates the best conductivity, exhibiting the largest impedance mismatch at its surface-to-air interface, thus reflecting the most electromagnetic waves and showing the highest Rconductivity (e.g., Rconductivity). Figure 5 (c) shown), thereby obtaining the best electromagnetic shielding performance.

[0079] Example 10

[0080] Environmental stability tests were conducted using the rGO@Ni-NCNTs / PI composite aerogel from Example 4. Figure 6 As shown in (a), the composite aerogel of Example 4 exhibits improved EMI SE after undergoing various extreme environmental treatments. T The retention rates are all above 95%, demonstrating excellent stability in extreme environments. For example... Figure 6 As shown in (b), at 400 o In high-temperature environments, the electromagnetic shielding performance of C remains stable and slightly improves with increasing temperature. This is mainly attributed to the fact that high temperatures promote electronic transitions between local defects in the conductive network, thereby enhancing ohmic loss capability by increasing carrier mobility. Figure 6As shown in (c), the electromagnetic shielding performance of the aerogel remained basically unchanged after being placed in a normal atmospheric environment for 100 days, demonstrating good long-term durability.

[0081] Example 11

[0082] Electromagnetic shielding properties of the rGO@Ni-NCNTs / PI composite aerogel from Example 4 were tested. Figure 7 As shown in (a), the electromagnetic shielding performance in the terahertz band was tested, with an average EMI SE in the range of 0.3–2 THz. T It can reach 54dB. For example... Figure 7 As shown in (b), the broadband electromagnetic shielding characteristics of the rGO@Ni-NCNTs / PI composite aerogel of Example 4 were tested in the C, Ku, K, and Ka bands. It can be seen that the composite aerogel exhibits excellent broadband electromagnetic shielding performance in the C, Ku, K, and Ka bands, and its EMI SE (Electromagnetic Shielding Performance) is also good. T It increases with frequency, and its average EMI SE increases in the 5.4-40 GHz ultrawide range. T It reached 52 dB.

[0083] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler, characterized in that: It includes reduced graphene oxide and multiple one-dimensional nitrogen-doped carbon nanotubes grown in situ on the surface of the reduced graphene oxide; the top of the nitrogen-doped carbon nanotubes is coated with nickel nanoparticles, and the nitrogen-doped carbon nanotubes stand on the surface of the reduced graphene oxide.

2. The preparation method of the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler according to claim 1, characterized in that: Includes the following steps: Step S1: Graphene oxide is prepared using the modified Hummers method; Step S2: The graphene oxide is mixed with a nickel source, ethylene glycol, and hydrazine hydrate, and subjected to a hydrothermal reduction reaction under alkaline conditions to obtain a reduced graphene oxide@nickel precursor. Step S3: The reduced graphene oxide@nickel precursor is mixed with a carbon-nitrogen source and heat-treated under a nitrogen atmosphere to obtain a reduced graphene oxide@nickel catalytic nitrogen-doped carbon nanotube heterostructure filler.

3. The method for preparing reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler according to claim 2, characterized in that: The nickel source is nickel chloride hexahydrate, the carbon and nitrogen source is melamine, and the mass ratio of the reduced graphene oxide@nickel precursor to melamine is 1:5~15.

4. The method for preparing reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler according to claim 2, characterized in that: Step S1 uses the modified Hummers method to prepare graphene oxide, obtaining monolayer or few-layer graphene oxide; Step S2 includes adding the graphene oxide to water to obtain an aqueous dispersion of graphene oxide; mixing the aqueous dispersion with an ethylene glycol solution of nickel chloride hexahydrate, wherein the mass ratio of graphene oxide to nickel chloride hexahydrate is 1-3:1; stirring thoroughly; then sequentially adding an ethylene glycol solution of sodium hydroxide and hydrazine hydrate; mixing evenly; and transferring the mixture to a high-pressure reactor; and heating at 85-95°C. o The reaction was carried out at C for 0.5~2 hrs; the product was collected by vacuum filtration, washed, and dried to obtain reduced graphene oxide@nickel precursor; In step S3, heat treatment is performed under a nitrogen atmosphere at 3~7°C. o C / min increased to 850~950 o Keep warm at C for 1 hour, and apply 1~3% heat with the furnace. o Cooling to room temperature at C / min yields a heterostructure filler with nickel-catalyzed nitrogen-doped carbon nanotubes vertically erected on the surface of reduced graphene oxide.

5. The application of the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler as described in claim 1, characterized in that: Used to prepare composite aerogels.

6. A composite aerogel, characterized in that: The invention comprises a polymer matrix and the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler of claim 1 dispersed in the polymer matrix, wherein the polymer matrix is ​​polyimide and the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler accounts for 50% to 90% by mass.

7. The composite aerogel according to claim 6, characterized in that: The mass fraction of the reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler is 70%~85%.

8. The method for preparing the composite aerogel as described in claim 6 or 7, characterized in that: Includes the following steps: Step S10: The reduced graphene oxide@nickel-catalyzed nitrogen-doped carbon nanotube heterostructure filler is mixed with a polyamic acid solution and dispersed evenly to obtain a dispersion. Step S20: The dispersion is subjected to directional freezing and freeze-drying to obtain a composite aerogel precursor; Step S30: The composite aerogel precursor is subjected to thermal imidization treatment to obtain the composite aerogel.

9. The method for preparing the composite aerogel according to claim 8, characterized in that: In step S10, the solvent of the polyamic acid solution is water, and the dispersion also contains triethylamine; the concentration of the polyamic acid solution is 1-3 wt%. And / or, in step S20, the directional freezing is performed by placing a mold containing the dispersion on a cooling copper plate in contact with liquid nitrogen, followed by freezing at a temperature of -80 to -60°C. o C, freeze-drying under a pressure not exceeding 2 Pa; And / or, in step S30, the thermal imidization treatment is carried out under an inert atmosphere at a temperature of 250~350°C. o C, keep warm for 1-3 hours; then keep warm for 1-3 hours. o The composite aerogel was obtained by cooling the temperature at a rate of C / min to room temperature.

10. The application of the composite aerogel as described in claim 6 or 7, characterized in that: The composite aerogel is used to prepare electromagnetic shielding materials.

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