Graphene fiber for terahertz wave enhancement and preparation method thereof

Abstract

The invention provides a graphene fiber for terahertz wave enhancement and a preparation method thereof, and aims to solve the technical problems of low efficiency, narrow tuning range and complex preparation process of the existing terahertz enhancement material. The graphene fiber has a gradient multilevel structure and sequentially comprises a graphene fiber core layer, a graphene / terahertz functional material composite layer and a metal nanoparticle surface layer formed by self-assembly of metal nanoparticles from a core part to a surface, according to the invention, a three-channel microfluidic device is adopted, and a gradient structure is constructed by respectively controlling the flow velocity of a precursor solution in each layer; then carrying out reduction treatment under the action of a vitamin C-iron-based catalyst to reduce the graphene oxide into high-conductivity graphene, and carrying out in-situ reduction and self-assembly on the metal precursor to form metal nanoparticles which are attached to the surface of the fiber; and finally, performing electric field cooperative treatment on the fibers, and performing performance activation.

Description

Technical Field

[0001] This invention belongs to the field of terahertz functional materials and nanocomposite materials technology, specifically relating to a graphene fiber for terahertz wave enhancement and its preparation method. Background Technology

[0002] Terahertz waves typically refer to electromagnetic waves with frequencies ranging from 0.1 to 10 THz. Terahertz technology holds significant promise for applications in biomedical imaging, security scanning, wireless communication, and spectral sensing. However, the efficient generation, modulation, and detection of terahertz waves remain a technological bottleneck due to the lack of high-performance functional materials and devices. For example, many traditional terahertz devices can only operate within limited frequency bands, exhibiting low energy conversion or modulation efficiency, which fails to meet practical application requirements. Currently, the main approaches to enhancing or controlling terahertz waves include artificial metamaterials / metasurfaces and special dielectric materials. However, such metamaterials typically function only near the designed frequency, with a narrow tuning range and a fixed peak response. Furthermore, the fabrication of metamaterials relies on expensive micro- and nano-fabrication processes, which are complex and difficult to mass-produce, limiting their practical application. Existing patent CN110003660A discloses a terahertz active ceramic sphere made from various raw materials, including natural minerals, through terahertz wave pretreatment and high-temperature sintering. Experimental measurements show that it can stably emit terahertz waves with wavelengths ranging from 4 to 16 μm, with a normal emissivity exceeding 85%. This indicates that broadband terahertz emission materials can be obtained through specific processes. However, the preparation of such materials involves a wide variety of raw materials, sintering temperatures as high as 1100℃, enormous energy consumption, and demanding equipment requirements. Furthermore, the resulting ceramics must be used indirectly as additives, limiting their applications. Therefore, although some mineral ceramics possess the potential for broadband terahertz response, existing preparation processes are complex and costly, hindering their widespread adoption.

[0003] In summary, existing terahertz enhancement technologies suffer from drawbacks such as low efficiency, narrow tuning bandwidth, and complex fabrication processes, necessitating the development of new material structures and fabrication methods for improvement. This invention addresses these issues by providing a terahertz wave-enhanced graphene-based material that combines high efficiency, wide tuning bandwidth, and a simple fabrication process. Summary of the Invention

[0004] The purpose of this invention is to provide a graphene fiber for terahertz wave enhancement and its preparation method, thereby solving the problems in the prior art; A graphene fiber for terahertz wave enhancement and its preparation method are disclosed below: S1: Prepare a graphene oxide dispersion by mixing graphene oxide powder with deionized water; weigh 2-3 parts by mass of functional material, 0.2-0.3 parts by mass of graphene oxide powder and 45-55 parts by mass of deionized water, and sonicate for 30 minutes while stirring to obtain a functional material-graphene oxide composite dispersion; add 1.5-2.5 parts by mass of metal precursor to 95-105 parts by mass of deionized water, then add 9-11 parts by mass of polyvinyl alcohol powder, heat and stir until completely dissolved to obtain a surface precursor solution; S2: Using a three-channel coaxial microfluidic spinneret, the graphene oxide dispersion, functional material-graphene oxide composite dispersion, and surface precursor liquid prepared in step S1 are loaded into syringes and connected to the inner, middle, and outer channel inlets of the spinneret through hoses. After the flow rate of the three injection pumps is adjusted and the coaxial jet is formed and stabilized at the nozzle, the nozzle is moved above the tank containing a coagulation bath containing a 5% calcium chloride solution dissolved in ethanol-water at a volume ratio of 7:3 (ethanol:calcium chloride). The coaxial jet enters the coagulation bath at room temperature. A rotating roller is placed at the bottom of the tank to pull the fiber at a linear speed of 5 cm / s. The fiber is washed three times with water to obtain wet fiber. S3: Place the wet fiber prepared in step S2 into a reducing solution, which is prepared by adding 1-3 parts of vitamin C reducing agent and 0.1-0.2 parts of reducing agent to 90-100 parts of deionized water; add citric acid dropwise until the pH is 4, carry out microwave-assisted thermal reduction reaction, take out the fiber and rinse it with deionized water 3 times, and then dry it in a vacuum drying oven at 60°C for 6 hours to obtain dry fiber; S4: The dry fibers prepared in step S3 are placed in an inert atmosphere furnace for electric field synergistic treatment to obtain the graphene fibers of the present invention.

[0005] Further, the graphene oxide dispersion mentioned in step S1 is specifically prepared by adding graphene oxide dry powder to deionized water and ultrasonically dispersing it for 1 hour to obtain a graphene oxide dispersion with a concentration of 10-12 mg / mL.

[0006] Furthermore, the functional material described in step S1 is selected as silicon carbide.

[0007] Furthermore, the metal precursor mentioned in step S1 is selected from chloroauric acid or silver nitrate.

[0008] Furthermore, in step S2, the inner diameters of the inner, middle, and outer channels of the three-channel coaxial microfluidic spinneret are 0.2 mm, 0.5 mm, and 1.0 mm, respectively.

[0009] Furthermore, the flow rates of the three-way injection pumps mentioned in step S2 are specifically 0.2–0.4 mL / min for the graphene oxide dispersion, 0.2–0.4 mL / min for the functional material-graphene oxide composite dispersion, and 0.5–0.7 mL / min for the surface precursor solution.

[0010] Furthermore, the reducing agent mentioned in step S3 is selected from FeSO4 or FeCl3.

[0011] Furthermore, the microwave-assisted thermal reduction reaction described in step S3 has the following specific parameters: 160–180°C, 400–500 W, and a reaction time of 2–3 hours.

[0012] Furthermore, the electric field synergistic treatment described in step S4 specifically involves first performing medium-temperature thermal annealing at 400–500°C for 30 minutes; then applying a DC electric field of 1–5 V / μm for 10–20 minutes.

[0013] The beneficial effects of this invention are: 1. This invention features a multi-level synergistic composite structure that integrates highly crystalline graphene, high dielectric / emission minerals, and metal plasmon nanostructures into a single fiber, constructing a gradient-distributed multi-level functional structure. The graphene core layer provides a low-loss transmission channel and adjustable carrier concentration, the intermediate mineral layer generates a broadband polarization response, and the surface metal nanoparticle layer generates strong local field enhancement. The superposition of these three elements significantly improves the absorption and modulation efficiency of terahertz waves.

[0014] 2. This invention breaks through the limitations of narrowband operation of traditional devices by selecting different functional materials and metal components and combining them with terahertz wave activation treatment.

[0015] 3. This invention utilizes microfluidic shear-enhanced liquid crystal orientation spinning technology to produce graphene fiber core layers with crystallinity and orientation that are far superior to those of ordinary wet-spun fibers. The highly oriented and reduced graphene sheets form a graphite-like lattice, providing a near-macroscopically continuous conductive path and high carrier mobility. The highly crystallinity of the core layer improves the mechanical properties of the fiber, facilitating subsequent coating of functional layers and practical assembly applications.

[0016] 4. This invention uses vitamin C as a reducing agent, supplemented by a small amount of iron salt catalysis, which significantly reduces the toxicity and energy consumption of the reduction process. The vitamin C reduction method is mild and controllable, and can partially retain the oxygen-containing functional groups on the graphene surface. These residual functional groups are actually conducive to the in-situ nucleation and uniform distribution of metal nanoparticles, realizing the one-step simultaneous completion of graphene reduction and metal nanoparticle synthesis. This avoids the cumbersome process of first reducing and then loading metal in traditional multi-step methods. The generated metal nanoparticles form a continuous conductive network on the fiber surface through self-assembly. The process is simple and the effect is stable. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the preparation process of graphene fibers for terahertz wave enhancement according to the present invention.

[0018] Figure 2 The image shows the SEM characterization of the test results in Experiment Example 1.

[0019] Figure 3 The image shows the EDS characterization of Experiment Example 1.

[0020] Figure 4 The image shows the Raman spectrum obtained from Experiment Example 2.

[0021] Figure 5 This is a comparison chart of the absorption rate and enhancement ratio test results for Experiment Example 3. Detailed Implementation

[0022] The following embodiments further explain and illustrate the technical solutions of the present invention. It is particularly noted that each specific embodiment is a specific interpretation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention. (See attached...) Figure 1 The diagram shows a fabrication process for graphene fibers used for terahertz wave enhancement. The detailed fabrication steps are as follows: The graphene fiber of this invention possesses a gradient multi-level functional structure. From the fiber core to the surface layer, it sequentially comprises: a highly crystalline graphene fiber core layer, a graphene / terahertz functional material composite intermediate layer, and a metal nanoparticle composite surface layer supported by a carbonized polymer matrix. The core layer provides excellent electrical conductivity and a mechanical framework, the intermediate layer introduces terahertz functional materials to impart broadband response characteristics, and the metal nanoparticle array on the surface layer generates surface plasmon resonance to enhance the local electromagnetic field. Each layer is tightly bound together through a gradient transition, forming a synergistic effect and improving the overall enhancement effect on terahertz waves.

[0023] 1. Raw material preparation This invention selects graphene oxide as the graphene source, disperses graphene oxide in deionized water to prepare a high-concentration dispersion, thoroughly ultrasonically exfoliates and homogenizes it, and uses it as a core layer precursor solution. The selection of terahertz functional materials can be based on the target frequency band. This invention uses silicon carbide. An appropriate amount of mineral powder is added to another part of the graphene oxide dispersion, and ultrasonic and mechanical stirring are used to uniformly disperse the mineral particles in the graphene oxide colloid to obtain a composite precursor solution for the intermediate layer. The metal precursor uses gold or silver nanoparticles. When preparing the surface layer precursor solution, an aqueous solution of chloroauric acid or silver nitrate is selected as the metal ion source. Since the viscosity of pure aqueous solution is low, which is not conducive to fiber formation, a small amount of thickener can be added to the surface layer precursor solution to increase the solution viscosity and ensure the stability of the fluid interface, forming a metal nanoparticle surface layer.

[0024] 2. Microfluidic coaxial spinning and solidification The three precursor solutions were loaded into precision injection pumps and connected to the inlet of a three-channel microfluidic spinning chip. The three-channel microfluidic chip consists of three concentric flow channels. Before spinning begins, the propulsion speed of each channel injection pump is adjusted to ensure that the three liquid streams form a stable coaxial laminar jet at the confluence. By optimizing the chip's flow channel structure and flow rate, the graphene oxide dispersion is ensured to form an anisotropic liquid crystal state during flow, aligning the graphene sheets along the fiber axis. After the coaxial jet leaves the microfluidic chip, it immediately enters the solidification medium to fix the structure.

[0025] A coaxial jet is directly injected into a pre-prepared coagulation bath. The coagulation bath can be an organic solvent, salt solution, or other medium that can induce the formation of graphene oxide fibers. In this invention, an aqueous solution of calcium chloride is used as the coagulation bath. Polyvalent cations can rapidly coordinate / electrostatically interact with functional groups such as carboxyl and hydroxyl groups on the graphene oxide sheets, causing the graphene oxide to aggregate into gel fibers along the jet trajectory. Simultaneously, the polymers in the outer solution also gel or precipitate in the presence of calcium chloride, helping to capture and fix the metal salt and graphene oxide sheets. During fiber formation, the liquid flow from the microfluidic nozzle can be observed coiling into fine hydrogel filaments in the coagulation bath. The fibers are drawn and wound in the coagulation bath, with the drawing speed controlled slightly higher than the jet speed to appropriately stretch and orient the fibers. After about a few seconds of coagulation, the fiber strength is sufficient to lift it out of the coagulation bath. After the continuous fibers are removed, they are washed multiple times with deionized water to remove residual calcium chloride and unreacted substances, yielding wet fibers.

[0026] 3. Reduction and Nanoassembly The wet fiber was transferred into the reduction reaction solution, which consisted of vitamin C aqueous solution and ferrous salt. Citric acid was added appropriately to adjust the pH to accelerate the reaction. Then, a microwave-assisted thermal reduction reaction was carried out in a high-pressure microwave hydrothermal reaction device. Vitamin C is a green and mild reducing agent. Its functions are as follows: (1) It gradually reduces graphene oxide, and the fiber color gradually changes from brown to black, indicating that the conjugated structure of graphene is restored; (2) It reduces the metal ions in the outer precursor solution to zero-valent metal atoms. These in-situ generated metal atoms nucleate on the surface of graphene and minerals, and attach and grow at the oxygen functional group sites that were not completely removed by vitamin C, thereby spontaneously forming nanoparticles; (3) It acts as an antioxidant to stabilize the generated nanoparticles and prevent them from being over-oxidized or growing and sintering. Iron ions play a catalytic role in this process: Fe 2+ / Fe 3+ It can catalyze the decomposition of peroxide byproducts to generate free radicals, thereby promoting reduction reactions and accelerating the reduction rate of certain metals. Simultaneously, Fe... 2+The graphene oxide itself may also be partially reduced to form iron nanoparticles or iron oxide particles, which adhere to the fiber. After the reaction, most of the graphene oxide is converted into reduced graphene, and the metal ions are converted into metal nanoparticles. These nanoparticles are uniformly distributed on the fiber surface and in the shallow layer, fixed to the graphene / mineral matrix by van der Waals forces and residual functional group bonding. After the fiber is removed from the reducing solution, it is thoroughly rinsed several times with pure water to remove excess vitamin C, iron salts, and byproducts. The fiber is then dried in a vacuum drying oven to constant weight. The resulting fiber is blackish-gray and opaque with metallic luster spots on the surface. At this point, the fiber is conductive, and the graphene network is essentially interconnected. Simultaneously, the surface metal nanoparticle film also imparts certain metallic properties.

[0027] 4. Electric field synergistic activation processing The dried fibers were placed in an inert atmosphere furnace and subjected to medium-temperature thermal annealing, followed by the application of a DC electric field. Thermal annealing provides sufficient energy to the graphene network, promoting the rearrangement of carbon atoms within its sheets. This helps repair lattice defects remaining after the reduction of graphene oxide and increases sp0. 2 The area of ​​the carbon domain significantly improves the carrier mobility and conductivity of the fiber core layer, which helps to strengthen the interfacial bonding between the graphene core layer, functional material particles and metal nanoparticles, and reduce contact resistance. During the thermal annealing process, atomic diffusion and chemical bonding occur at the interface between graphene and the intermediate and surface metal nanoparticles, which enhances structural stability and makes the metal particles more firmly anchored to the fiber surface. Under the influence of a strong DC electric field, free electrons / holes in graphene undergo directional migration, forming a space charge layer at the interface. This pre-set charge distribution enhances the polarization response of the material under terahertz wave excitation, enabling pre-tuning to electromagnetic waves in specific frequency bands. Under the influence of the electric field, Joule heating is generated in the highly conductive graphene fibers due to the passage of current, further repairing graphene lattice defects, promoting the orientation of graphene sheets along the electric field direction, inducing further graphitization of residual carbon in polyvinyl alcohol, and improving the continuity and stability of the surface conductive network.

[0028] Example 1 Table 1 Raw Material Information Table A graphene fiber for terahertz wave enhancement is prepared as follows: S1: Add graphene oxide powder to deionized water and sonicate for 1 hour to obtain a graphene oxide dispersion with a concentration of 11 mg / mL; weigh 2.5 parts by mass of silicon carbide, 0.25 parts by mass of graphene oxide powder and 50 parts by mass of deionized water, and sonicate for 30 minutes while stirring to obtain a functional material-graphene oxide composite dispersion; add 2 parts by mass of chloroauric acid to 100 parts by mass of deionized water, then add 10 parts by mass of polyvinyl alcohol powder, heat and stir until completely dissolved to obtain a surface precursor solution; S2: A three-channel coaxial microfluidic spinneret is used, with inner diameters of 0.2 mm, 0.5 mm, and 1.0 mm for the inner, middle, and outer channels, respectively. The graphene oxide dispersion, functional material-graphene oxide composite dispersion, and surface precursor solution prepared in step S1 are loaded into syringes and connected to the inlets of the inner, middle, and outer channels of the spinneret through tubing. The flow rates of the three injection pumps are adjusted as follows: 0.3 mL / min for graphene oxide dispersion, 0.3 mL / min for functional material-graphene oxide composite dispersion, and 0.6 mL / min for surface precursor solution. After the coaxial jet is formed and stabilized at the nozzle, the nozzle is moved above a coagulation bath containing a 5% calcium chloride solution dissolved in ethanol-water at a volume ratio of 7:3 (ethanol:calcium chloride volume ratio). The coaxial jet enters the coagulation bath at room temperature. A rotating roller is placed at the bottom of the tank to pull the fiber at a linear speed of 5 cm / s. The fiber is washed three times to obtain wet fiber. S3: The wet fibers prepared in step S2 are placed in a reducing solution, which is prepared by adding 2 parts of vitamin C reducing agent and 0.15 parts of FeSO4 to 95 parts of deionized water; citric acid is added dropwise until the pH is 4, and then a microwave-assisted reaction is carried out in a high-pressure microwave hydrothermal reaction device. The temperature is set at 170℃, the power at 450W, and the reaction is carried out for 2.5 hours. The fibers are then taken out and rinsed with deionized water 3 times, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain dried fibers. S4: The dry fibers prepared in step S3 are placed in an inert atmosphere furnace for electric field synergistic treatment. First, they are subjected to medium-temperature thermal annealing at 450°C for 30 minutes; then a DC electric field of 3V / μm is applied for 15 minutes to obtain the graphene fibers of the present invention.

[0029] Example 2 S1: Add graphene oxide powder to deionized water and sonicate for 1 hour to obtain a graphene oxide dispersion with a concentration of 10 mg / mL; weigh 2 parts by mass of silicon carbide, 0.2 parts by mass of graphene oxide powder and 45 parts by mass of deionized water, and sonicate for 30 minutes while stirring to obtain a functional material-graphene oxide composite dispersion; add 1.5 parts by mass of silver nitrate to 95 parts by mass of deionized water, then add 9 parts by mass of polyvinyl alcohol powder, heat and stir until completely dissolved to obtain a surface precursor solution; S2: A three-channel coaxial microfluidic spinneret is used, with inner diameters of 0.2 mm, 0.5 mm, and 1.0 mm for the inner, middle, and outer channels, respectively. The graphene oxide dispersion, functional material-graphene oxide composite dispersion, and surface precursor solution prepared in step S1 are loaded into syringes and connected to the inlets of the inner, middle, and outer channels of the spinneret through tubing. The flow rates of the three injection pumps are adjusted as follows: 0.2 mL / min for graphene oxide dispersion, 0.2 mL / min for functional material-graphene oxide composite dispersion, and 0.5 mL / min for surface precursor solution. After the coaxial jet is formed and stabilized at the nozzle, the nozzle is immediately moved above a coagulation bath containing a 5% calcium chloride solution dissolved in ethanol-water at a volume ratio of 7:3 (ethanol:calcium chloride volume ratio). The coaxial jet enters the coagulation bath at room temperature. A rotating roller is placed at the bottom of the tank to pull the fiber at a linear speed of 5 cm / s. The fiber is washed three times with water to obtain wet fiber. S3: Place the wet fiber prepared in step S2 into the reducing solution, which is prepared by adding 1 part vitamin C reducing agent and 0.1 part FeCl3 to 90 parts deionized water; add citric acid dropwise until the pH is 4, and then carry out a microwave-assisted reaction in a high-pressure microwave hydrothermal reaction device, setting the temperature to 160℃, the power to 400W, and the reaction time to 3 hours. Take out the fiber and rinse it 3 times with deionized water, and then dry it in a vacuum drying oven at 60℃ for 6 hours to obtain dry fiber. S4: The dry fibers prepared in step S3 are placed in an inert atmosphere furnace for electric field synergistic treatment. First, they are subjected to medium-temperature thermal annealing at 400°C for 30 minutes; then a DC electric field of 1V / μm is applied for 20 minutes to obtain the graphene fibers of the present invention.

[0030] Example 3 S1: Add graphene oxide powder to deionized water and sonicate for 1 hour to obtain a graphene oxide dispersion with a concentration of 12 mg / mL; weigh 3 parts by mass of silicon carbide, 0.3 parts by mass of graphene oxide powder and 55 parts by mass of deionized water, and sonicate for 30 minutes while stirring to obtain a functional material-graphene oxide composite dispersion; add 2.5 parts by mass of chloroauric acid to 105 parts by mass of deionized water, then add 11 parts by mass of polyvinyl alcohol powder, heat and stir until completely dissolved to obtain a surface precursor solution; S2: A three-channel coaxial microfluidic spinneret is used, with inner diameters of 0.2 mm, 0.5 mm, and 1.0 mm for the inner, middle, and outer channels, respectively. The graphene oxide dispersion, functional material-graphene oxide composite dispersion, and surface precursor solution prepared in step S1 are loaded into syringes and connected to the inlets of the inner, middle, and outer channels of the spinneret through tubing. The flow rates of the three injection pumps are adjusted as follows: 0.4 mL / min for graphene oxide dispersion, 0.4 mL / min for functional material-graphene oxide composite dispersion, and 0.7 mL / min for surface precursor solution. After the coaxial jet is formed and stabilized at the nozzle, the nozzle is immediately moved above a coagulation bath containing a 5% calcium chloride solution dissolved in ethanol-water at a volume ratio of 7:3 (ethanol:calcium chloride volume ratio). The coaxial jet enters the coagulation bath at room temperature. A rotating roller is placed at the bottom of the tank to pull the fiber at a linear speed of 5 cm / s. The fiber is washed three times with water to obtain wet fiber. S3: Place the wet fiber prepared in step S2 into a reducing solution, which is prepared by adding 3 parts vitamin C reducing agent and 0.2 parts FeSO4 to 100 parts deionized water; add citric acid dropwise until the pH is 4, and then carry out a microwave-assisted reaction in a high-pressure microwave hydrothermal reaction device, setting the temperature to 180℃, the power to 500W, and the reaction time to 2 hours. Take out the fiber and rinse it 3 times with deionized water, and then dry it in a vacuum drying oven at 60℃ for 6 hours to obtain dry fiber. S4: The dry fibers prepared in step S3 are placed in an inert atmosphere furnace for electric field synergistic treatment. First, they are subjected to medium-temperature thermal annealing at 500°C for 30 minutes; then a DC electric field of 5V / μm is applied for 10 minutes to obtain the graphene fibers of the present invention.

[0031] Comparative Example 1 Referring to the preparation method of Example 1, but step S2 is modified as follows: Graphene oxide dispersion, tourmaline powder, and HAuCl4 solution are directly mixed together. The concentration of the graphene oxide dispersion is 11 mg / mL, the tourmaline powder accounts for 20% of the mass of the graphene oxide dispersion, and the HAuCl4 concentration is 0.05 mol / L. This yields a mixed spinning solution. Using a single-channel injection pump and a nozzle, this mixture is extruded into a 5% calcium chloride coagulation bath at a rate of 0.5 mL / min. Details are as follows: S1: Add graphene oxide powder to deionized water and sonicate for 1 hour to obtain a graphene oxide dispersion with a concentration of 11 mg / mL; weigh 2.5 parts by mass of silicon carbide, 0.25 parts by mass of graphene oxide powder and 50 parts by mass of deionized water, and sonicate for 30 minutes while stirring to obtain a functional material-graphene oxide composite dispersion; add 2 parts by mass of chloroauric acid to 100 parts by mass of deionized water, then add 10 parts by mass of polyvinyl alcohol powder, heat and stir until completely dissolved to obtain a surface precursor solution; S2: A mixed spinning solution was prepared by mixing graphene oxide dispersion, tourmaline powder and HAuCl4 solution. The mixture was then extruded into a 5% calcium chloride coagulation bath at a rate of 0.5 mL / min using a single-channel injection pump and a nozzle to obtain fibers. The fibers were washed with water three times to obtain wet fibers. S3: The wet fibers prepared in step S2 are placed in a reducing solution, which is prepared by adding 2 parts of vitamin C reducing agent and 0.15 parts of FeSO4 to 95 parts of deionized water; citric acid is added dropwise until the pH is 4, and then a microwave-assisted reaction is carried out in a high-pressure microwave hydrothermal reaction device. The temperature is set at 170℃, the power at 450W, and the reaction is carried out for 2.5 hours. The fibers are then taken out and rinsed with deionized water 3 times, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain dried fibers. S4: The dry fibers prepared in step S3 are placed in an inert atmosphere furnace for electric field synergistic treatment. First, they are subjected to medium-temperature thermal annealing at 450°C for 30 minutes; then a DC electric field of 3V / μm is applied for 15 minutes to obtain the graphene fibers of the present invention.

[0032] Comparative Example 2 The preparation method is the same as in Example 1, but no metal substance is added to the surface precursor solution in step S1, i.e., there are no surface metal nanoparticle fibers; specifically as follows: S1: Add graphene oxide powder to deionized water and sonicate for 1 hour to obtain a graphene oxide dispersion with a concentration of 11 mg / mL; weigh 2.5 parts by mass of silicon carbide, 0.25 parts by mass of graphene oxide powder and 50 parts by mass of deionized water, and sonicate for 30 minutes while stirring to obtain a functional material-graphene oxide composite dispersion; take 100 parts by mass of deionized water, add 10 parts by mass of polyvinyl alcohol powder, heat and stir until completely dissolved to obtain a surface precursor solution; S2: A three-channel coaxial microfluidic spinneret is used, with inner diameters of 0.2 mm, 0.5 mm, and 1.0 mm for the inner, middle, and outer channels, respectively. The graphene oxide dispersion, functional material-graphene oxide composite dispersion, and surface precursor solution prepared in step S1 are loaded into syringes and connected to the inlets of the inner, middle, and outer channels of the spinneret through tubing. The flow rates of the three injection pumps are adjusted as follows: 0.3 mL / min for graphene oxide dispersion, 0.3 mL / min for functional material-graphene oxide composite dispersion, and 0.6 mL / min for surface precursor solution. After the coaxial jet is formed and stabilized at the nozzle, the nozzle is moved above a coagulation bath containing a 5% calcium chloride solution dissolved in ethanol-water at a volume ratio of 7:3 (ethanol:calcium chloride volume ratio). The coaxial jet enters the coagulation bath at room temperature. A rotating roller is placed at the bottom of the tank to pull the fiber at a linear speed of 5 cm / s. The fiber is washed three times to obtain wet fiber. S3: The wet fibers prepared in step S2 are placed in a reducing solution, which is prepared by adding 2 parts of vitamin C reducing agent and 0.15 parts of FeSO4 to 95 parts of deionized water; citric acid is added dropwise until the pH is 4, and then a microwave-assisted reaction is carried out in a high-pressure microwave hydrothermal reaction device. The temperature is set at 170℃, the power at 450W, and the reaction is carried out for 2.5 hours. The fibers are then taken out and rinsed with deionized water 3 times, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain dried fibers. S4: The dry fibers prepared in step S3 are placed in an inert atmosphere furnace for electric field synergistic treatment. First, they are subjected to medium-temperature thermal annealing at 450°C for 30 minutes; then a DC electric field of 3V / μm is applied for 15 minutes to obtain the graphene fibers of the present invention.

[0033] Comparative Example 3 The preparation method of Example 1 is followed, but without the electric field coordination treatment, i.e., without step S4; specifically as follows: S1: Add graphene oxide powder to deionized water and sonicate for 1 hour to obtain a graphene oxide dispersion with a concentration of 11 mg / mL; weigh 2.5 parts by mass of silicon carbide, 0.25 parts by mass of graphene oxide powder and 50 parts by mass of deionized water, and sonicate for 30 minutes while stirring to obtain a functional material-graphene oxide composite dispersion; add 2 parts by mass of chloroauric acid to 100 parts by mass of deionized water, then add 10 parts by mass of polyvinyl alcohol powder, heat and stir until completely dissolved to obtain a surface precursor solution; S2: A three-channel coaxial microfluidic spinneret is used, with inner diameters of 0.2 mm, 0.5 mm, and 1.0 mm for the inner, middle, and outer channels, respectively. The graphene oxide dispersion, functional material-graphene oxide composite dispersion, and surface precursor solution prepared in step S1 are loaded into syringes and connected to the inlets of the inner, middle, and outer channels of the spinneret through tubing. The flow rates of the three injection pumps are adjusted as follows: 0.3 mL / min for graphene oxide dispersion, 0.3 mL / min for functional material-graphene oxide composite dispersion, and 0.6 mL / min for surface precursor solution. After the coaxial jet is formed and stabilized at the nozzle, the nozzle is moved above a coagulation bath containing a 5% calcium chloride solution dissolved in ethanol-water at a volume ratio of 7:3 (ethanol:calcium chloride volume ratio). The coaxial jet enters the coagulation bath at room temperature. A rotating roller is placed at the bottom of the tank to pull the fiber at a linear speed of 5 cm / s. The fiber is washed three times to obtain wet fiber. S3: The wet fiber prepared in step S2 is placed in a reducing solution, which is prepared by adding 2 parts of vitamin C reducing agent and 0.15 parts of FeSO4 to 95 parts of deionized water; citric acid is added dropwise until the pH is 4, and then a microwave-assisted reaction is carried out in a high-pressure microwave hydrothermal reaction device. The temperature is set at 170℃, the power at 450W, and the reaction is carried out for 2.5 hours. The fiber is then taken out and rinsed 3 times with deionized water, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain the fiber of the present invention.

[0034] Experimental Example 1 The fibers prepared in Example 1 were characterized by SEM and EDS. The dried fibers were then immersed in liquid nitrogen for brittle fracture. The cross-sections were vertically fixed on the sample stage and sputter-coated with gold. Field emission scanning electron microscopy was then used with an accelerating voltage of 1-5 kV, a working distance of 3-8 mm, and a mixed-signal detector. The EDS parameters were an accelerating voltage increased to 15 kV and a scanning step size of 50-100 nm. The scanning results are as follows: SEM characterization: such as Figure 2 As shown, the core layer exhibits a highly oriented layered stacked structure, with high-concentration graphene oxide liquid crystals arranged under the shear force of the microchannels and forming a dense rGO network after microwave reduction; the middle layer shows clearly embedded particles between the graphene layers, corresponding to the added SiC functional material, with uniform particle distribution, proving the effectiveness of the ultrasonic dispersion process; the surface layer shows a carbonized PVA matrix with uniformly attached high-contrast bright nanoparticles, which are Au nanoparticles generated by in-situ reduction of chloroauric acid with vitamin C. EDS characterization: such as Figure 3 As shown, (1) EDS line scan: C element is distributed radially, with the strongest and most stable signal in the core region; the signal in the surface layer is slightly lower, reflecting the step difference in density between carbonized PVA and graphene; Si element shows a characteristic bimodal distribution, with the signal concentrated in the middle layer region, and the core and outermost layers approaching zero, proving that SiC is precisely confined within the preset flow channel without interlayer crosstalk; Au element shows a sharp peak at the outermost edge of the fiber. This confirms that Au ions are successfully anchored on the PVA surface during the reduction process and do not undergo large-scale penetration and diffusion into the fiber interior; O element shows a gradient with a low center and a high edge, with the core layer being the most fully reduced and having the lowest oxygen content; the surface layer contains residual functional groups from carbonized PVA, resulting in a relatively significant oxygen signal; (2) EDS surface scan: The figure shows a perfect concentric circle structure; Si elements form a bright ring (middle layer), Au elements form an outermost extremely thin bright ring, and C elements cover the entire circular area; the signals of each element have slight overlap at the interface, indicating that molecular-level contact and good gradient transition are achieved between the layers through microfluidic coaxial extrusion.

[0035] Experiment Example 2 The fibers prepared in Example 1 were vertically embedded in epoxy resin and cured. The embedded block was then polished across its cross-section using an ultrathin slicer to expose a smooth and flat fiber cross-section. A 532nm laser was used with a 100× long focal length objective lens, laser power <1mW, and a scanning range of 500cm. -1 -3200cm -1 Data collection time: single-point integration time 10-30 seconds, accumulated twice; test results are as follows. Figure 4 As shown, Core-bottom curve: The main component is reduced graphene oxide, which forms the highly conductive skeleton of the fiber.

[0036] Peak (1350cm) -1 The intensity is significant. This corresponds to the process of vitamin C reducing graphene oxide in step S3; it indicates that large graphene oxide crystal domains are divided into more fine sp... 2 Graphitized microcrystals, a typical characteristic of chemical reduction processes; peak (1580 cm⁻¹) -1 ) Sharp and symmetrical, representing sp 2 The in-plane vibrations of carbon atoms confirmed the recovery of the graphene conjugated network; the D peak (2700 cm⁻¹) -1 The presence of a relatively obvious 2D peak indicates that the graphene layers are stacked in an ordered manner and the network is basically interconnected. Intermediate Layer - Intermediate Curve: This layer, constructed from a mixture of graphene oxide and silicon carbide mineral particles, is used to introduce terahertz response characteristics. SiC (796 / 972cm³) -1 The TO and LO modes of SiC were clearly observed in the low wavenumber region; the D, G and 2D peaks were still present, proving that the SiC particles were uniformly dispersed in the graphene conductive network; compared with pure SiC or pure rGO, the characteristic peak positions may have slight shifts, reflecting the interfacial stress or chemical interaction between the nanoparticles and the graphene sheets. Surface-top curve: This layer is supported by a polyvinyl alcohol matrix and embedded with in-situ reduced gold nanoparticles. Polymer characteristics (1000-1400 cm⁻¹) -1 The peaks show CC skeletal vibration and COO group vibration. Since step S3 only involved microwave hydrothermal treatment and drying, PVA was not completely carbonized into glassy carbon, retaining some polymer chain structural features; CH stretching vibration (2900 cmT) was also observed. -1 A broad and strong CH peak appears in the high wavenumber region, which is a typical sign of incompletely carbonized organic polymers, contrasting sharply with the all-carbon material in the core layer; although gold itself has no Raman peak, it enhances the signal intensity of the surrounding PVA residual functional groups.

[0037] Experimental Example 3 The comprehensive properties of the fibers prepared in Examples 1-3 and Comparative Examples 1-3 were measured: Absorption performance testing: The transmission / absorption spectra of the fiber in the range of 0.5–2.5 THz were tested using a terahertz time-domain spectroscopy system. The fiber sample was prepared into a uniform thin film and placed in the sample cavity optical path of the THz-TDS system. The absorptivity α(ω) was calculated using the formula α(ω) = 1−T(ω)−R(ω), where T(ω) is the transmittance and R(ω) is the reflectance. Terahertz wave testing: THz-TDS testing was performed on the fiber samples before performance activation, and the initial absorbance A0 in the target frequency band (0.8-2.5 THz sweep) was recorded. For the samples after performance activation treatment, THz-TDS testing was performed again under the same conditions, and the absorbance A0 was recorded. m Calculate the absorption enhancement ratio = (A m -A0) / A0×100%.

[0038] The specific test comparison results are shown in Table 2. Figure 5 As shown: Table 2. Comparison of overall performance between Examples 1-3 and Comparative Examples 1-3 The comparison results show that, in Comparative Example 1, the fiber exhibits low absorption performance in the terahertz band. Due to the mixture of all components, the graphene network is not sufficiently oriented and continuous, and the minerals and metals fail to play their respective roles, resulting in poor overall enhancement. In Comparative Example 2, the absence of a metal nanoparticle layer prevents the material from enhancing the coupling of terahertz waves at specific frequencies, resulting in relatively smooth absorption and low enhancement. In Comparative Example 3, the initial absorption rate is the lowest, and there is no enhancement effect. This demonstrates that the electric field synergistic activation treatment is crucial for activating the synergistic response of graphene, minerals, and metal nanoparticles within the fiber and achieving a sustained and optimized enhancement effect on terahertz waves at specific frequencies. The enhancement potential of the fiber without this treatment was not activated.

Claims

1. A graphene fiber for terahertz wave enhancement, having a gradient multi-level functional structure, characterized in that, The gradient multi-level functional structure comprises, from the fiber core to the surface layer, a graphene fiber core layer, a graphene / terahertz functional material composite intermediate layer, and a metal nanoparticle composite surface layer supported by a carbonized polymer matrix; the core layer contains a graphene network formed by reduced graphene oxide; the intermediate layer contains a composite of reduced graphene oxide and functional materials; and the surface layer contains carbonized polyvinyl alcohol and metal nanoparticles.

2. The graphene fiber for terahertz wave enhancement according to claim 1, characterized in that, The intermediate layer is prepared from functional materials, graphene oxide powder, and deionized water, with the following amounts: 2-3 parts by mass of functional materials, 0.2-0.3 parts by mass of graphene oxide powder, and 45-55 parts by mass of deionized water; the functional material is selected as silicon carbide.

3. The graphene fiber for terahertz wave enhancement according to claim 1, characterized in that, The raw materials for preparing the surface layer consist of a metal precursor, deionized water, and polyvinyl alcohol powder, with the following amounts: 1.5–2.5 parts metal precursor, 95–105 parts deionized water, and 9–11 parts polyvinyl alcohol powder.

4. A method for preparing graphene fibers for terahertz wave enhancement according to any one of claims 1-3, characterized in that, S1: Mix graphene oxide powder with deionized water and ultrasonically disperse for 1 hour to obtain a graphene oxide dispersion with a concentration of 10-12 mg / mL; mix the functional material, graphene oxide powder and deionized water and ultrasonically treat for 30 minutes while stirring to obtain a functional material-graphene oxide composite dispersion; add the metal precursor to deionized water, then add polyvinyl alcohol powder, heat and stir until completely dissolved to obtain a surface precursor solution; S2: Using a three-channel coaxial microfluidic spinneret, the graphene oxide dispersion, functional material-graphene oxide composite dispersion, and surface precursor liquid prepared in step S1 are loaded into syringes and connected to the inner, middle, and outer channel inlets of the spinneret through hoses. After the flow rate of the three injection pumps is adjusted and the coaxial jet is formed and stabilized at the nozzle, the nozzle is moved above the tank containing a coagulation bath containing a 5% calcium chloride solution dissolved in ethanol-water at a volume ratio of 7:3 (ethanol:calcium chloride). The coaxial jet enters the coagulation bath at room temperature. A rotating roller is placed at the bottom of the tank to pull the fiber at a linear speed of 5 cm / s. The fiber is washed three times with water to obtain wet fiber. S3: Place the wet fiber prepared in step S2 into a reducing solution, which is prepared by adding 1-3 parts of vitamin C reducing agent and 0.1-0.2 parts of reducing agent to 90-100 parts of deionized water; add citric acid dropwise until the pH is 4, carry out microwave-assisted thermal reduction reaction, take out the fiber and rinse it with deionized water 3 times, and then dry it in a vacuum drying oven at 60°C for 6 hours to obtain dry fiber; S4: The dry fibers prepared in step S3 are placed in an inert atmosphere furnace for electric field synergistic treatment to obtain the graphene fibers of the present invention.

5. The method for preparing graphene fibers for terahertz wave enhancement according to claim 4, characterized in that, The metal precursor mentioned in step S1 is selected from chloroauric acid or silver nitrate.

6. The method for preparing graphene fibers for terahertz wave enhancement according to claim 4, characterized in that, The three-channel coaxial microfluidic spinneret described in step S2 has inner diameters of 0.2 mm, 0.5 mm, and 1.0 mm for its inner, middle, and outer channels, respectively.

7. The method for preparing graphene fibers for terahertz wave enhancement according to claim 4, characterized in that, The flow rates of the three-way injection pumps mentioned in step S2 are specifically 0.2–0.4 mL / min for the graphene oxide dispersion, 0.2–0.4 mL / min for the functional material-graphene oxide composite dispersion, and 0.5–0.7 mL / min for the surface precursor solution.

8. The method for preparing graphene fibers for terahertz wave enhancement according to claim 4, characterized in that, The reducing agent mentioned in step S3 is selected from FeSO4 or FeCl3.

9. The method for preparing graphene fibers for terahertz wave enhancement according to claim 4, characterized in that, The microwave-assisted thermal reduction reaction described in step S3 has the following parameters: 160–180°C, 400–500 W, and a reaction time of 2–3 hours.

10. A method for preparing graphene fibers for terahertz wave enhancement according to claim 4, characterized in that, The electric field synergistic treatment described in step S4 specifically involves first performing medium-temperature thermal annealing at 400–500°C for 30 minutes; then applying a DC electric field of 1–5 V / μm for 10–20 minutes.

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