A method for graphitizing mesophase pitch-based carbon fibers, carbon fibers and applications thereof

Abstract

The application provides a mesophase pitch-based carbon fiber graphitization method, carbon fiber and application thereof, and relates to the technical field of carbon fiber materials.The mesophase pitch-based carbon fiber graphitization method comprises the following steps: S1.catalyst loading: loading a catalyst Ag@TiO2 on mesophase pitch-based carbon fiber after pre-oxidation treatment;S2.laser activation: placing the catalyst-loaded mesophase pitch-based carbon fiber in a closed reaction chamber, introducing a mixed gas of nitrogen and hydrogen, and adopting a pulsed green wave laser with a wavelength of 532 nm and a pulse width of 50 ns for activation treatment; and S2.high-temperature graphitization.The mesophase pitch-based carbon fiber graphitization method provided by the application effectively improves the performance of mesophase pitch-based carbon fiber and the graphitization speed through a specific catalyst system, simultaneously reduces the reaction temperature, and accelerates the graphitization efficiency by up to 19%, and improves the fiber performance by up to 17%.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber materials technology, and in particular to a method for graphitizing mesophase pitch-based carbon fibers, carbon fibers and their applications. Background Technology

[0002] Mesophase pitch-based carbon fibers occupy an irreplaceable position in aerospace, defense, and high-end composite materials fields due to their ultra-high modulus, high thermal conductivity, and excellent mechanical properties. Their preparation process mainly includes four core stages: pitch modulation, melt spinning, pre-oxidation, and graphitization. Among these, the graphitization stage typically requires a high-temperature environment of 2500–3000℃ to improve the size and orientation of the microcrystals within the carbon fiber, ultimately achieving a key breakthrough in the high modulus and high thermal conductivity of mesophase pitch-based carbon fibers.

[0003] Currently, mainstream graphitization processes generally use iron (Fe) or boron (B) as catalysts, relying on high-temperature catalysis above 2500℃ to promote the ordered arrangement of carbon layers. Although iron catalysts are less expensive, they easily react with carbon at high temperatures to form carbides such as Fe3C, leading to an increase in fiber ash content exceeding 0.1%, significantly reducing material purity. While boron catalysts can improve graphitization to some extent, they easily introduce dislocation defects into the graphite lattice, manifested as an ID / IG value greater than 0.35 in Raman spectroscopy, adversely affecting the mechanical properties of the fiber. Furthermore, existing processes generally suffer from low graphitization efficiency and high energy consumption due to excessively high reaction temperatures.

[0004] The prior art CN109112826A discloses a method for preparing mesophase pitch-based carbon fiber woven fabric loaded with carbon nanofibers. The method uses mesophase pitch as raw material to spin mesophase pitch fibers with a diameter of 12-16 μm; subsequently, it undergoes pre-oxidation at 260-300℃ and low-temperature carbonization treatment at 500-800℃; the low-temperature carbonized fibers are woven into a two-dimensional carbon fiber fabric, and carbon nanofibers are grown in the gas phase on the carbon fiber surface; the carbon fiber woven fabric loaded with gas-phase carbon fibers is subjected to high-temperature carbonization treatment at 1200-1500℃ and graphitization treatment at 2600-3000℃ to obtain the mesophase pitch-based carbon fiber woven fabric loaded with carbon nanofibers. However, the graphitization temperature is between 2600 and 3000℃, which obviously cannot solve the problem of excessively high graphitization reaction temperature for mesophase pitch-based carbon fibers. Summary of the Invention

[0005] This invention addresses the shortcomings of current graphitization processes for mesophase pitch-based carbon fibers, which suffer from excessively high reaction temperatures, low graphitization efficiency, and unsatisfactory carbon fiber performance. It provides a graphitization method for mesophase pitch-based carbon fibers, employing a laser-Ag@TiO2 synergistic catalysis approach. Under specific wavelength laser excitation, the electron-hole separation behavior in the catalyst is precisely controlled, achieving efficient graphitization of mesophase pitch-based carbon fibers at relatively low temperatures. This simultaneously improves the purity, crystallinity, and mechanical properties of the final fiber product, effectively solving the problems of low graphitization efficiency, insufficient fiber performance, and excessive energy consumption in existing processes.

[0006] Another object of the present invention is to provide a mesophase pitch-based carbon fiber.

[0007] Another objective of this invention is to provide an application of mesophase pitch-based carbon fiber in the fields of aerospace, defense, and high-end composite materials.

[0008] In a first aspect, the present invention provides a method for graphitizing mesophase pitch-based carbon fibers, comprising the following steps: S1. Catalyst support: The pre-oxidized mesophase pitch-based carbon fiber is immersed in the catalyst Ag@TiO2 dispersion to obtain catalyst-supported mesophase pitch-based carbon fiber. The catalyst Ag@TiO2 has a core-shell structure, with the diameter of the Ag core being 20-50 nm and the thickness of the TiO2 shell being 5-10 nm. S2: Laser activation: The catalyst-supported mesophase pitch-based carbon fiber is placed in a closed reaction chamber and a mixture of nitrogen and hydrogen is introduced. The volume percentage of hydrogen in the mixture is 5-25%. A pulsed green wave laser with a wavelength of 532nm and a pulse width of 50ns is used for activation treatment. S3: High-temperature graphitization: The catalyst-supported mesophase pitch-based carbon fiber that has been laser-activated is subjected to high-temperature graphitization treatment. The high-temperature graphitization treatment temperature is 1800~2200℃, the treatment time is 10~30min, and the atmosphere is a mixture of argon and hydrogen, with hydrogen accounting for 1~3% of the volume of the mixture.

[0009] In the graphitization method of mesophase pitch-based carbon fibers provided by the present invention, preferably, the catalyst loading in S1 is 0.1 to 1.0% of the mass of the mesophase pitch-based carbon fibers.

[0010] In the graphitization method of mesophase pitch-based carbon fibers provided by the present invention, preferably, the catalyst Ag@TiO2 dispersion is an ethanol dispersion of Ag@TiO2, and the concentration of Ag@TiO2 is 0.5~2.0wt%.

[0011] In the graphitization method of mesophase pitch-based carbon fibers provided by the present invention, preferably, the laser power density of the laser activation treatment in S2 is set to 50~200W / cm², the scanning speed is controlled at 2~5mm / s, and the total irradiation time is 30~120s.

[0012] In the graphitization method of mesophase pitch-based carbon fibers provided by the present invention, preferably, the catalyst Ag@TiO2 in S1 is anatase phase Ag@TiO2.

[0013] In the graphitization method for mesophase pitch-based carbon fibers provided by the present invention, preferably, the full width at half maximum (FWHM) of the anatase (101) peak of the anatase phase Ag@TiO2 is 0.2~0.3. ° The Ag-TiO2 interface peak in Raman characterization is located at 510~514 cm⁻¹. -1 .

[0014] According to the graphitization method of mesophase pitch-based carbon fibers provided by the present invention, preferably, the catalyst Ag@TiO2 in S1 is prepared by the following method: Titanium precursor and silver salt were mixed and added to a mixed solution of polar solvent and water. The pH was adjusted to 2, and the reaction was carried out at 200℃ and 1 MPh until complete. The reactants were separated and then calcined at 300℃ for 1 h to prepare the catalyst Ag@TiO2.

[0015] Secondly, the present invention also provides a mesophase pitch-based carbon fiber, which is prepared by spinning pitch modulation, melt spinning, pre-oxidation and graphitization, wherein the graphitization is performed using the graphitization method of the mesophase pitch-based carbon fiber.

[0016] The mesophase pitch-based carbon fiber provided by the present invention preferably has an axial thermal conductivity of 900~1150 W / (m·K) and an ash content of less than or equal to 100 ppm.

[0017] Thirdly, the present invention also provides an application of mesophase pitch-based carbon fiber in the fields of aerospace, defense and military industry and high-end composite materials.

[0018] Beneficial effects: This invention provides a method for graphitizing mesophase pitch-based carbon fibers. By utilizing a green wave laser-multi-metal superstructure compound Ag@TiO2 catalytic system, the performance and graphitization rate of mesophase pitch-based carbon fibers are effectively improved, while simultaneously reducing the reaction temperature. Compared to traditional Fe-catalyzed graphitization at 2500℃, this graphitization process can accelerate graphitization efficiency by up to 19% and improve fiber performance by up to 17%. Attached Figure Description

[0019] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0020] Figure 1 The image shows the XRD pattern of Ag@TiO2.

[0021] Figure 2 The image shows the Raman spectrum of Ag@TiO2.

[0022] Figure 3 The graph shows the effect of H2 percentage on nitrogen free radical concentration.

[0023] Figure 4 The graph shows the effect of H2 content on the oxidation degree of Ag. Detailed Implementation

[0024] The following examples are for illustrative purposes only and are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the examples, they should be performed according to the techniques or conditions described in the literature in this field, or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased from legitimate channels.

[0025] In a specific embodiment, the present invention provides a method for graphitizing mesophase pitch-based carbon fibers, comprising the following steps: S1. Catalyst support: The pre-oxidized mesophase pitch-based carbon fiber is immersed in the catalyst Ag@TiO2 dispersion to obtain catalyst-supported mesophase pitch-based carbon fiber. The catalyst Ag@TiO2 has a core-shell structure, with the diameter of the Ag core being 20~50nm and the thickness of the TiO2 shell being 5~10nm. S2: Laser activation: The catalyst-supported mesophase pitch-based carbon fiber is placed in a closed reaction chamber and a mixture of nitrogen and hydrogen is introduced. The hydrogen volume concentration in the mixture is 5~20%. A pulsed green wave laser with a wavelength of 532nm and a pulse width of 50ns is used for activation treatment. S3: High-temperature graphitization: The catalyst-supported mesophase pitch-based carbon fiber that has been laser-activated is subjected to high-temperature graphitization treatment. The high-temperature graphitization treatment temperature is 1800-2200℃, the treatment time is 10-30min, and the atmosphere is a mixture of argon and hydrogen, with hydrogen accounting for 1-3% of the volume of the mixture.

[0026] It should be noted that: The graphitization method provided by this invention is a laser-Ag@TiO2 synergistic catalysis method. By precisely controlling the electron-hole separation behavior in the catalyst under the excitation of a specific wavelength laser, efficient graphitization of mesophase pitch-based carbon fibers is achieved under relatively low temperature conditions. This process can simultaneously improve the purity, crystallinity, and mechanical properties of the final carbon fiber product, effectively solving the problems of low graphitization efficiency, insufficient fiber performance, and excessive energy consumption in existing processes. The core of the graphitization method of this invention lies in utilizing the surface plasmon resonance effect of silver (Ag), which can efficiently extend light absorption to the visible light region. When Ag combines with TiO2 to form a composite structure, a Schottky barrier is generated at the interface. Under the irradiation of a green laser, the photogenerated electrons generated by TiO2 can quickly cross the interface and transfer to Ag nanoparticles, thereby effectively promoting the separation of electrons and holes. The highly active charge carriers after separation then participate in the catalytic reaction process, effectively realizing the graphitization treatment of mesophase pitch-based carbon fibers.

[0027] The catalyst Ag@TiO2 mentioned in this invention has a core-shell structure, which ingeniously combines the dual functions of plasma effect and anti-sulfur poisoning.

[0028] Firstly, the key role of the titanium dioxide shell lies in its chemical inertness, which effectively blocks the diffusion of thiophene sulfides from the mesophase pitch to the Ag nucleus, preventing the catalyst from being deactivated due to sulfur poisoning. When the shell thickness is less than 5 nm, its sulfur blocking efficiency will decrease significantly by more than 60%, while a thickness greater than 10 nm will hinder the effective tunneling of electrons.

[0029] Secondly, Ag nanoparticles undergo SPR (surface plasmon resonance) effect under visible light irradiation, generating localized surface plasmon polaritons (LSPs), which significantly enhance the absorption range and intensity of light. This effect not only expands the photoresponse range of TiO2 (from ultraviolet light to visible light), but also promotes the efficient separation of photogenerated electron-hole pairs by injecting hot electrons induced by LSPS into the conduction band of TiO2.

[0030] Third, the Schottky junction formed between Ag and TiO2 generates a built-in electric field at the interface, further accelerating the migration of photogenerated electrons from TiO2 to Ag while suppressing the recombination of holes and electrons. Furthermore, Ag's high conductivity acts as an electron "conductor," rapidly capturing electrons generated by TiO2 and suppressing the recombination of photogenerated carriers. Fourth, the TiO2 shell can protect the Ag core from photocorrosion (such as Ag⁺ oxidation) and agglomeration. Experiments have shown that after 50 hours of ultraviolet light irradiation, the activity retention rate of Ag@TiO2 reaches 90%, while that of pure Ag nanoparticles is only 50%.

[0031] In the S2 step laser activation operation, laser excitation induces a strong surface plasmon resonance effect in Ag@TiO2, with a local electric field intensity Log(E / E0) reaching 19, exciting the nitrogen / hydrogen mixture to transform into a plasma state. The plasma effect creates oxygen vacancy defects on the Ag@TiO2 surface, enhancing charge transport capabilities. Simultaneously, the strong electric field promotes the migration of holes from the titanium dioxide valence band to the surface, effectively oxidizing and removing sulfur impurities, as shown in the reaction: 2h⁺ + C₄H₄S → CO₂ + H₂O + SO₄²⁻.

[0032] The reason for choosing a 532nm pulsed green laser core is that its photon energy precisely matches the surface plasmon resonance (SPR) characteristics of the Ag@TiO2 core-shell structure, thereby driving the target reaction synergistically through multiple physical mechanisms. Specifically, the 532nm photon energy (approximately 2.33 eV) corresponds to the dipole plasmon resonance absorption peak of the Ag nanonucleus (the SPR peak red-shifts to this range after modulation by the TiO2 shell), and can simultaneously excite interband electronic transitions in TiO2 (band gap 3.0-3.2 eV, requiring ultraviolet light excitation, but 532nm photons can facilitate transitions through defect-assisted energy levels). This dual excitation effect, guided directionally by the interface Schottky junction (Ag-TiO2), promotes the efficient injection of photogenerated electrons into the sp² orbitals of the carbon layer, significantly reducing the activation energy required for graphitization. Furthermore, the SPR effect excited by the 532nm laser induces plasmaification of the surrounding gas. High-energy particles in the plasma bombard the TiO2 shell, generating oxygen vacancy defects. These defects act as charge transport channels, further accelerating electron migration and simultaneously driving the reconstruction of the six-membered carbon rings. Oxygen vacancies trap electrons to form a local reduction environment, lowering the energy barrier for carbon atom rearrangement and ultimately achieving directional graphitization of the carbon layer. At this wavelength, the synergistic effect of photothermal and plasma-induced effects avoids the strong photodegradation damage of short-wavelength lasers (such as ultraviolet) while overcoming the energy deficiency problem of long-wavelength lasers (such as infrared), making it an ideal choice for controlling the Ag@TiO2 interface reaction.

[0033] During the S3 high-temperature graphitization process, high-energy electrons enriched on silver nuclei are injected into the carbon layer structure of carbon fibers through quantum tunneling. This process significantly reduces the energy barrier required for sp² carbon atom reconstruction, thereby driving the directional transformation of polycyclic aromatic hydrocarbons into an ordered graphite microcrystalline structure. Active nitrogen species synergistically promote the ordered rearrangement of carbon atoms, transforming them into a graphite crystal structure, thus achieving fiber graphitization. Ultimately, the axial thermal conductivity of the resulting carbon fibers is increased to 1100 W / (m·K), a 40% improvement compared to traditional high-temperature graphitization processes.

[0034] The laser activation and high-temperature graphitization mentioned in this invention are both carried out under specific gas atmospheres. The core logic behind the S2 laser activation using nitrogen and hydrogen, and the S3 graphitization using hydrogen and Ar, lies in achieving multi-dimensional optimization of "plasma energy regulation - catalyst protection - structural ordering" through the synergistic effect of these three gases. The ionization energy of Ar (15.76 eV) is close to that of nitrogen (15.6 eV). Using a mixed atmosphere of hydrogen and Ar in S3 can optimize plasma characteristics in three aspects: By reducing the electron temperature from 2.8 eV to 2.3 eV through Ar⁺-N⁺ collisions, the carbon layer is prevented from being over-etched by high-energy electrons, while maintaining the N· radical concentration reduction rate of <10% to ensure nitrogen doping efficiency. Furthermore, the addition of Ar⁺ increases the plasma ion density by 15%, increasing the N⁺ ion implantation depth into the carbon layer from 0.5 nm to 1.2 nm, thereby enhancing the directional growth of the graphite layer. Its high specific heat capacity of Ar (0.52 J / g·K) absorbs the laser-induced local overheating energy, reducing the temperature fluctuation in the reaction region from ±50℃ to ±20℃, inhibiting the thermal aggregation of Ag nanonuclei (particle size growth rate decreased from 0.3 nm / min to 0.1 nm / min), while the inert environment reduces the unnecessary consumption of hydrogen and nitrogen, increasing the N· radical retention rate from 65% to 80%. Furthermore, Ar⁺ bombardment of the TiO2 shell induces the generation of oxygen vacancies (V0), which combine with H· to form H·-V0 complexes. Through the electron trap mechanism, the charge transfer resistance from Ag to the carbon layer is reduced from 25 Ω·cm² to 22.5 Ω·cm², achieving synergistic regulation of plasma energy, thermal environment and interface charge.

[0035] In laser activation and low-temperature graphitization processes, the selection of inert atmosphere follows a synergistic logic of "reaction regulation - catalytic protection - impurity removal".

[0036] S2 employs an inert atmosphere created by mixing nitrogen and hydrogen in a 4:1 volume ratio. Under the influence of a 532nm laser, a plasma environment is formed, driving the ordered carbon structure through a dual mechanism. The high-energy N⁺ and N・ radicals released by the nitrogen plasma act as "structural templates," embedding themselves into the carbon layers to replace unsaturated carbon sites, reducing five-membered ring defects and promoting the orderly arrangement of six-membered carbon rings towards a graphitic layered structure, thus reducing the graphitization degree (ID / IG value) from 1.2 to 0.9. Simultaneously, hydrogen maintains the metallic activity of the Ag nucleus through a reduction reaction (Ag₂O + H₂ → 2Ag + H₂O), preventing the SPR effect from decaying due to oxidation. Its lower ionization energy (13.6 eV) also lowers the plasma breakdown threshold, increasing the plasma density by 30% and enhancing energy transfer efficiency.

[0037] By controlling the proportion of hydrogen in the nitrogen-hydrogen mixture during S2 laser activation, the nitrogen source supply and plasma stability are balanced. For example, the proportion of hydrogen in the nitrogen-hydrogen mixture during S2 laser activation can be 5%, 10%, 15%, 20%, or 25%, with 20% being more preferred.

[0038] In the S3 high-temperature graphitization operation, an Ar / hydrogen mixture with a volume ratio of 1-3% H2 is used. The hydrogen gas, upon laser excitation, generates highly reactive hydrogen radicals (increasing reactivity by 10%). 2 (times), which means maintaining Ag catalytic activity through reduction reaction (Ag2O→Ag) 0 It can also crack sulfur impurities such as thiophene (C4H4S+4H2→CH4+H2S) and remove amorphous carbon through water-gas reaction (C+H2O→CO+H2). The 3% hydrogen concentration is not only below the explosion limit (the lower explosion limit of hydrogen in Ar is 4%), but also achieves the optimal balance between catalytic activity and carbon deposition inhibition.

[0039] The core mechanism of this invention lies in the dynamic matching between the 532nm pulsed green laser and the surface plasmon resonance absorption peak of the Ag@TiO2 core-shell structure. This plasmonic effect creates oxygen vacancy defects, enhancing surface charge transport capabilities. Simultaneously, nitrogen / hydrogen plasma provides active reactive species, extending the lifetime of photogenerated carriers to the nanosecond level through the built-in electric field effect of the Schottky junction. The high-energy electrons injected into the carbon layer effectively reduce the activation energy required for C / C bond recombination, active nitrogen species participate in the ordered carbon structure, and the holes migrating to the surface efficiently oxidize and remove sulfur impurities, reducing the final fiber ash content to below 100ppm. This synergistic effect of electrons and holes enables high-purity, high-efficiency graphitization of mesophase pitch-based carbon fibers at relatively low temperatures.

[0040] In some specific embodiments, the diameter of the mesophase pitch-based carbon fiber mentioned in this invention can be 8~12μm, more preferably 10μm.

[0041] The impregnation process mentioned in this invention is carried out at a temperature of 25°C for a duration of 25 to 35 minutes, preferably 30 minutes, to achieve the catalyst loading requirement. Nitrogen gas is then used to purge to remove residual solvent.

[0042] In some specific embodiments, the catalyst loading amount in the S1. catalyst loading step mentioned in this invention is 0.1 to 1.0% of the mass of the mesophase pitch-based carbon fiber, for example, it can be a point value or any range of values ​​such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%.

[0043] In some specific embodiments, the catalyst Ag@TiO2 dispersion mentioned in this invention is an ethanol dispersion of Ag@TiO2, and the concentration of Ag@TiO2 is 0.5-2.0 wt%.

[0044] Ethanol serves two main purposes: firstly, it effectively disperses the Ag@TiO2 catalyst, ensuring its uniform distribution in the solution and guaranteeing sufficient contact between the catalyst and the pre-oxidized mesophase pitch-based carbon fibers for uniform loading; secondly, its moderate volatility allows for rapid removal after impregnation via nitrogen purging, preventing residual solvent from interfering with subsequent laser activation and high-temperature graphitization processes. Furthermore, ethanol exhibits good compatibility with Ag@TiO2, stably maintaining the core-shell structure of the catalyst and preventing its aggregation or decomposition.

[0045] The concentration of the dispersion (0.5-2.0 wt%) directly affects the catalyst loading on the carbon fiber surface. By controlling the concentration, it is possible to ensure that the catalyst adheres uniformly and appropriately to the fiber surface: too low a concentration may result in insufficient loading and failure to fully exert its catalytic effect; too high a concentration may cause catalyst agglomeration, reduce the utilization rate of active sites, and even affect fiber performance. By setting a specific concentration, the loading can be precisely controlled within the target range, thereby ensuring the optimization of catalytic efficiency during laser activation and high-temperature graphitization, ultimately improving graphitization efficiency and fiber performance.

[0046] The Ag@TiO2 dispersion mentioned in this invention can also use dispersants such as methanol and isopropanol.

[0047] In some specific embodiments, the laser power density of the laser activation treatment mentioned in S2 of the present invention is set to 50~200W / cm², the scanning speed is controlled at 2~5mm / s, and the total irradiation time is 30~120s.

[0048] For example, the laser power density can be selected as a point value such as 50W / cm², 100W / cm², 150W / cm², 200W / cm², or any range thereof; the scanning speed can be controlled at a point value such as 2mm / s, 3mm / s, 4mm / s, 5mm / s, or any range thereof; the total irradiation time can be, for example, a point value such as 30s, 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s, 120s, or any range thereof.

[0049] In some specific embodiments, the catalyst Ag@TiO2 mentioned in this invention is preferably anatase phase Ag@TiO2.

[0050] Anatase Ag@TiO2 not only has a larger specific surface area for more uniform loading of Ag nanoparticles (reducing Ag agglomeration) and exposes more surface active sites, but also has superior photocatalytic activity. Its band gap of approximately 3.2 eV makes it easier to generate more photogenerated electron-hole pairs through defect-assisted electron transitions under 532 nm pulsed green wave laser excitation, thereby enhancing the synergistic effect with Ag nuclei and improving catalytic efficiency. Furthermore, the core-shell interface formed by the anatase phase TiO2 and Ag is more tightly bonded (Raman characterization shows that the Ag-TiO2 interface peak is located at 512 cm⁻¹), which is conducive to the formation of efficient Schottky junctions, accelerates the migration of photogenerated electrons from TiO2 to Ag, reduces carrier recombination, and provides more high-energy electrons for carbon fiber graphitization. In the mixed gas atmosphere of laser activation and high-temperature graphitization, the chemical stability is higher, which can more stably block impurities such as sulfur in the mesophase pitch to protect the Ag core from poisoning, and it is not prone to crystal phase transformation, which can maintain the persistence of catalytic activity (experiments show that the activity retention rate reaches 90% after 50 hours of ultraviolet light irradiation). At the same time, oxygen vacancy defects are more easily generated under laser excitation. As a charge transport channel, oxygen vacancy defects can enhance the interaction with the carbon fiber surface, promote the orderly rearrangement of carbon atoms, and help the graphitization process to proceed efficiently at a relatively low temperature of 1800-2200℃.

[0051] In some specific embodiments, the anatase phase Ag@TiO2 structure mentioned in this invention exhibits significant advantages, with high shell crystallinity and a full width at half maximum (FWHM) of 0.2~0.3 for the anatase (101) peak. ° More preferably 0.25 ° Furthermore, the interface bonding is strong, and the Ag-TiO2 interface peak in Raman characterization is located at 510~514 cm⁻¹. ⁻¹ 512cm is preferred. ⁻¹ .

[0052] By precisely controlling the reaction parameters, the shell thickness, crystallinity, and crystal orientation of the Ag@TiO2 catalyst can be precisely controlled. The strong interfacial bonding and the resulting tight interface are more conducive to charge transport, exhibiting higher activity and stability in catalysis and other applications.

[0053] The Ag@TiO2 core-shell structure mentioned in this invention is prepared using a hydrothermal / solvothermal method. The synthesis mechanism involves the hydrolysis of a titanium source in a high-temperature, high-pressure liquid environment to generate TiO2 nanocrystals, which then grow directionally on the Ag surface to form a shell. Furthermore, the crystal orientation can be controlled by the solvent polarity. Taking an ethanol-water mixed solvent as an example, the specific steps are as follows: Polyvinylpyrrolidone (0.5-1 times the mass of Ag nanoparticles), 0.01 mol / L AgNO3 and 0.02 mol / L Ti(SO4)2 were mixed, and the pH was adjusted to 2 (by nitric acid). The mixture was then added to a system of ethanol:water = 1:1 and reacted completely at 200℃ for 1 MPa. After natural cooling, the mixture was washed by centrifugation and then calcined at 300℃ for 1 h to obtain anatase phase Ag@TiO2 with a shell thickness of 5-10 nm.

[0054] This method uses surface ligand engineering to add polyvinylpyrrolidone (PVP) as a coating agent. The coordination effect of PVP-Ag guides TiO2 to grow along the

[001] crystal plane to form a shell layer that exposes a highly active crystal plane. At the same time, with the help of temperature-pressure synergy, such as at 200℃ and 1MPa, the growth rate of TiO2 shell layer can be increased to 5nm / h, which is 30% higher than the conventional 180℃ hydrothermal method.

[0055] The Ag@TiO2 prepared in this way has significant structural advantages, with high shell crystallinity. XRD shows that the full width at half maximum (FWHM) of the anatase (101) peak is only 0.25°, and the interfacial bonding is strong. In Raman characterization, the Ag-TiO2 interface peak is located at 512 cm⁻¹.

[0056] Compared to other methods, the hydrothermal / solvothermal method does not require complex vacuum equipment, has lower costs, and can achieve precise control of shell thickness, crystallinity, and crystal orientation by precisely adjusting reaction parameters. The resulting tight interface is more conducive to charge transport, exhibiting higher activity and stability in applications such as catalysis.

[0057] In a specific embodiment, the present invention also provides a mesophase pitch-based carbon fiber, which is prepared by spinning pitch modulation, melt spinning, pre-oxidation and graphitization, wherein the graphitization is performed using any of the above-mentioned mesophase pitch-based carbon fiber graphitization methods.

[0058] In a specific embodiment, the mesophase pitch-based carbon fiber prepared by the present invention has an axial thermal conductivity of 900~1150 (1100) W / (m·K) and an ash content of less than or equal to 100 ppm.

[0059] In a specific embodiment, the present invention also provides an application of mesophase pitch-based carbon fiber in the fields of aerospace, defense and military industry and high-end composite materials.

[0060] Examples 1-3 This embodiment provides a method for preparing anatase Ag@TiO2 catalyst, comprising the following steps: Polyvinylpyrrolidone (0.8 times the mass of Ag nanoparticles), 0.01 mol / L AgNO3 and 0.02 mol / L Ti(SO4)2 were mixed, and the pH was adjusted to 2 (adjusted with nitric acid). The mixture was then reacted completely at 200℃ and 1 MPa in a system of ethanol:water = 1:1. After natural cooling, the mixture was washed by centrifugation and then calcined at 300℃ for 1 h to obtain anatase phase Ag@TiO2 with a shell thickness of 5-10 nm.

[0061] Among them, the anatase Ag@TiO2 catalysts in Examples 1 to 3 have a core-shell structure, with the Ag core having a diameter of 30 nm and the TiO2 shell having thicknesses of 5, 8, and 10 nm, respectively.

[0062] The shell thickness is mainly adjusted by changing the concentration of the titanium precursor (such as tetrabutyl titanate) and the reaction time. When the titanium precursor concentration is low and the reaction time is short, the shell is thinner; as the concentration increases and the reaction time prolongs, the shell thickness gradually increases.

[0063] In Example 1 (5nm), the concentration of the titanium precursor was 0.015 mol / L, and the reaction time was 8 h. In Example 2 (8nm), the concentration of the titanium precursor was 0.020 mol / L, and the reaction time was 12 h. In Example 3 (10 nm), the concentration of the titanium precursor was 0.025 mol / L, and the reaction time was 16 h. The Ag@TiO2 prepared in this way has significant structural advantages, high shell crystallinity, and XRD (such as...) Figure 1 The results showed that the full width at half maximum (FWHM) of the anatase (101) peak was only 0.25°, and the interfacial bonding was strong. Raman characterization (e.g.) Figure 2 The Ag-TiO2 interface peak is located at 512 cm⁻¹.

[0064] By precisely controlling the reaction parameters, the shell thickness, crystallinity, and crystal orientation of the Ag@TiO2 catalyst can be accurately controlled. The strong interfacial bonding and the resulting tight interface facilitate charge transport, leading to higher activity and stability in catalytic and other applications. Examples 4-6 A method for graphitizing mesophase pitch-based carbon fibers includes the following steps: S1. Catalyst loading: Pre-oxidized mesophase pitch-based carbon fibers with a diameter of 10 μm were immersed in an Ag@TiO2 ethanol dispersion. The immersion process was carried out at 25°C for 30 min. Afterward, nitrogen was used to purge the residual solvent to obtain catalyst-loaded mesophase pitch-based carbon fibers. The Ag@TiO2 catalyst was the catalyst prepared in Example 1, the concentration of the dispersion was 1.0 wt%, and the catalyst loading on the fiber was controlled to be 0.5% of the carbon fiber mass. S2: Laser activation: The catalyst-supported mesophase pitch-based carbon fiber is placed in a sealed reaction chamber and a mixture of nitrogen and hydrogen is introduced. The volume ratio of hydrogen in the mixture is 20%. A pulsed green wave laser with a wavelength of 532nm and a pulse width of 50ns is used for activation treatment. The laser power density is set to 100W / cm², the scanning speed is controlled at 3mm / s, and the total irradiation time is 60s. S3: High-temperature graphitization: The catalyst-supported mesophase pitch-based carbon fiber, which has been laser-activated, is subjected to high-temperature graphitization treatment. The high-temperature graphitization treatment temperature is 2000℃, the heating rate is set to 50℃ / min, the treatment time is 20min, and the atmosphere is a mixed gas atmosphere of argon and 3% hydrogen by volume.

[0065] Examples 5 and 6 refer to the above-described graphitization method for mesophase pitch-based carbon fibers, the difference being that the catalysts Ag@TiO2 from Examples 1 and 3 are used respectively.

[0066] Comparative Examples 1-2 A method for graphitizing mesophase pitch-based carbon fibers, the specific steps of which are described in Example 4, differs in that the catalyst Ag@TiO2 with a TiO2 shell thickness of 3 nm is used and the catalyst Ag@TiO2 with a TiO2 shell thickness of 15 nm is used.

[0067] The preparation methods for Ag@TiO2 catalysts with a TiO2 shell thickness of 3 nm and 15 nm are the same as in Example 1, with the difference being: Comparative Example 1 (3 nm) had a titanium precursor concentration of 0.010 mol / L and a reaction time of 5 h; Comparative Example 2 (15 nm) had a titanium precursor concentration of 0.030 mol / L and a reaction time of 20 h.

[0068] Comparative Example 3 The traditional Fe-catalyzed graphitization at 2500℃ is carried out using the following method: Traditional graphitization methods (such as the Atcheson furnace process) mainly rely on high temperatures (2500-3000℃) to induce carbon atom rearrangement. However, for hard carbon or pitch-based materials that are difficult to graphitize, efficient graphitization is difficult to achieve even at high temperatures. Therefore, introducing transition metal catalysts such as Fe can significantly reduce the graphitization activation energy, allowing graphitization to be completed at lower temperatures.

[0069] 1. Loading the furnace: Load the product into the furnace and embed coke granules with a particle size of 5mm to form a conductive circuit.

[0070] 2. Preliminary heating stage: The temperature is raised to 1000℃ using resistance heating at a rate of 50℃ / h. During this stage, volatiles escape impurities.

[0071] 3. Heating stage: The temperature rises from 1000℃ to 2500℃. As the temperature increases, the resistance of the coke particles decreases, so the current needs to be increased. The heating rate is 100℃ / h.

[0072] 4. High-temperature recombination stage: Fe catalyst is added during carbonization. After the hard carbon precursor is mixed with Fe powder, the temperature is maintained at 2500-2800℃ and the whole process is kept at this temperature for 20-30 hours to allow the crystal lattice to recombine.

[0073] 5. Cooling: Allow to cool naturally for ≥7 days to avoid thermal stress cracking of the product.

[0074] Comparative Example 4 A graphitization method for mesophase pitch-based carbon fibers, the specific steps of which are described in Example 4, the difference being that the hydrogen volume concentration in the nitrogen and hydrogen mixture used for S2 laser activation in Comparative Example 4 is 30%.

[0075] Comparative Example 5 A graphitization method for mesophase pitch-based carbon fibers, the specific steps of which are described in Example 4, the difference being that the hydrogen volume concentration in the nitrogen and hydrogen mixture used for S2 laser activation in Comparative Example 4 is 3%.

[0076] Result detection The relevant results of Examples 1-3 and Comparative Examples 1-2 regarding the application of Ag@TiO2 core-shell structure catalysts with different shell thicknesses are as follows: Sulfur barrier efficiency: XPS was used to detect the residual sulfur content in the graphitized fibers and the differences in sulfur content among the groups were compared. Electron transport properties: The charge transfer resistance from Ag to the carbon layer was measured using an electrochemical workstation; Carbon fiber properties: Axial thermal conductivity was tested using the laser flare method, and ash content was tested using the high-temperature burning method.

[0077] The axial thermal conductivity was determined by laser flare method: Carbon fibers are made into axially oriented composite specimens (or single filament bundles are used directly) to ensure that heat is transferred along the fiber axis; A short-time energy pulse was emitted onto one side of the sample using a laser flare instrument, and the temperature change curve of the other side of the sample over time was recorded. Axial thermal conductivity is calculated using the formula (thermal conductivity = thermal diffusivity × density × specific heat capacity) based on the thermal diffusivity, material density, and specific heat capacity.

[0078] Graphitization efficiency was tested using the following method: The graphite interlayer spacing (d) of carbon fibers was determined using X-ray diffraction (XRD). 002 The degree of graphitization (g) and crystallite size (Lc) are calculated using the formula: g = (0.3440 - d) / (Lc) = 0.3440 - d ...002 / 0.3440-0.3354)×100% (where: 0.3440nm is the interlayer spacing of non-graphite carbon, 0.3354nm is the interlayer spacing of ideal graphite, d 002 (Measured interlayer spacing); Graphitization efficiency calculation: Based on the graphitization degree of Fe-catalyzed graphitization in the traditional process, the efficiency improvement of the improved method is calculated: Graphitization efficiency improvement rate = (Graphitization degree of this method − Graphitization degree of the traditional method) / Graphitization degree of the traditional method × 100%.

[0079] The methods for determining the elastic modulus and tensile strength are as follows: Following the international standard ASTM D4018, the monofilament tensile method is used. A high-precision electronic monofilament tensile tester is used. A single fiber is adhered to a standard specimen frame with a gauge length of 25 mm. A tensile load is applied at a rate of 0.5 mm / min until fracture. The testing environment is 23±1°C and 50±5%RH. At least 50 monofilaments are tested for each sample. The tensile strength is calculated from the fracture load and the monofilament diameter; the elastic modulus is calculated from the slope of the linear segment of the stress-strain curve.

[0080] Among them, the Ag@TiO2 catalyst with a shell thickness of 5 nm in Example 1 exhibits good sulfur barrier capability, effectively preventing most sulfur impurities from contacting the Ag core and ensuring the activity of the Ag core. It also demonstrates good electron tunneling capability, allowing electrons to transfer relatively smoothly from the Ag core to the TiO2 shell and carbon fiber layer, which is beneficial for the separation and transport of photogenerated electron-hole pairs, resulting in high catalytic efficiency. However, compared to the 8 nm thick catalyst, its sulfur barrier efficiency and electron transport performance are slightly inferior.

[0081] Example 2: Ag@TiO2 catalyst with an 8nm shell thickness: exhibits optimal overall performance. Sulfur residue is <50ppm, and sulfur barrier efficiency reaches over 90% (the 8nm shell effectively blocks the diffusion of thiophene sulfides), effectively protecting the Ag core from sulfur poisoning. It has low electron tunneling resistance, high electron transport efficiency, good photogenerated carrier separation, and a charge transfer resistance of 22.5Ω·cm² (Schottky junction is highly conductive). It fully leverages the synergistic catalytic effect of laser-Ag@TiO2, demonstrating the highest catalytic activity in the graphitization reaction of mesophase pitch-based carbon fibers.

[0082] Example 3: The Ag@TiO2 catalyst with a shell thickness of 10 nm showed good sulfur barrier properties, effectively blocking sulfur impurities. However, its electron tunneling ability was slightly lower than that of the 8 nm thick catalyst, as the resistance to electron transfer from the Ag core to the outside increased, leading to the recombination of some photogenerated electron-hole pairs. Consequently, its catalytic efficiency was slightly lower than that of the 8 nm thick catalyst.

[0083] Among them, the Ag@TiO2 catalyst with a shell thickness of 3 nm in Comparative Example 1 showed poor sulfur barrier performance, with sulfur residue >300 ppm and barrier efficiency reduced to <30%, a decrease of more than 60% compared to the catalyst with an 8 nm thickness. Due to the excessively thin shell, it could not effectively block sulfur impurities in the mesophase pitch, allowing sulfur to easily diffuse to the Ag core surface and react with it, leading to Ag core poisoning (XPS showed Ag-S bond formation), thus reducing catalyst activity. Simultaneously, the thin shell structure lacked stability, easily inducing Ag nanoparticle aggregation during the reaction, increasing the resistivity to 35 Ω·cm² (Ag core poisoning, decreased conductivity), further affecting the catalytic effect. The thermal conductivity of the prepared carbon fibers decreased to 750 W / (m·K) (loss of Ag catalytic activity), and the ash content increased to 500 ppm (sulfur impurity residue).

[0084] In Comparative Example 2, the catalyst with a shell thickness of 15 nm had an excessively thick shell, severely hindering efficient electron tunneling. This significantly increased the resistance to electron transfer from the Ag nucleus to the TiO2 shell and carbon fiber layers, suppressing the separation and transport of photogenerated electron-hole pairs. The resistivity rose to 40 Ω·cm² (the excessively thick shell hindered electron tunneling and charge transport), resulting in a significant decrease in catalytic efficiency and preventing efficient graphitization of mesophase pitch-based carbon fibers at lower temperatures. The thermal conductivity of the prepared carbon fibers decreased to 800 W / (m·K) (insufficient electron transport and incomplete graphitization).

[0085] The axial thermal conductivity of the carbon fibers obtained by the graphitization method of the mesophase pitch-based carbon fibers using the catalyst of Example 2 (Example 4) was increased to 1100 W / (m·K), which is 40% higher than that of the traditional high-temperature graphitization process, and the ash content was reduced to below 100 ppm.

[0086] The graphitization efficiency is increased by 19% (compared to the method of Comparative Example 3), and the carbon fiber performance is improved by 17% (reaching 1000 GPa and tensile strength reaching 4050 MPa) (compared to the method of Comparative Example 3).

[0087] The following analysis was conducted on the reaction results of laser activation in step S2 of the graphitization method for mesophase pitch-based carbon fibers using different nitrogen and hydrogen mixed gas atmospheres: Immediately after laser activation, XPS was used to detect the relative concentration of nitrogen free radicals (N·) in the residual gas in the reaction chamber; XPS analysis was used to analyze the oxidation state of Ag on the carbon fiber surface (calculation of Ag⁺ / (Ag)). 0 The ratio of Ag⁺ to Ag⁺ represents the degree of Ag oxidation. SEM was used to observe the catalyst morphology to confirm whether the abnormal hydrogen content caused Ag agglomeration or TiO2 shell damage.

[0088] The results are analyzed as follows: Nitrogen free radical concentration: such as Figure 3 As shown, Example 4 (20% hydrogen): The N· radical concentration was the highest, satisfying the requirement of "sufficient nitrogen supply", which can effectively assist in the ordering of carbon structure; Comparative Example 4 (30% hydrogen): The N· radical concentration decreased by about 35% compared with the control group (consistent with the conclusion of the cited document), because the excess hydrogen consumed high-energy particles and inhibited nitrogen dissociation; Comparative Example 5 (3% hydrogen): The N· radical concentration was slightly lower than that of the control group (but the decrease was <10%), because the insufficient hydrogen led to lower plasma activity.

[0089] Ag oxidation degree: such as Figure 4 As shown, Example 4 (20% hydrogen): Ag⁺ / (Ag 0 When the proportion of Ag⁺ is less than 5%, the Ag nucleus remains in a metallic state, and the SPR effect is significant. Comparative Example 4 (30% hydrogen): the oxidation degree of Ag is slightly lower than that of the control group (hydrogen has too strong a reducing power and there is no obvious oxidation), but the catalytic activity still decreases due to insufficient N·. Comparative Example 3 (3% hydrogen): the oxidation degree of Ag rises to more than 25%, but due to insufficient hydrogen, it is impossible to inhibit the oxidation of Ag by residual oxygen, the SPR effect weakens, and the electron transfer efficiency decreases.

[0090] Catalyst morphology: Example 4: The Ag@TiO2 core-shell structure is intact, with no obvious agglomeration; Comparative Examples 4 and 5: Slight Ag agglomeration may occur (due to imbalance of active particles), but the TiO2 shell remains stable. In step S2, the proportion of hydrogen in the mixed gas needs to be controlled between 5% and 20% to balance the nitrogen source supply and Ag activity.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for graphitizing mesophase pitch-based carbon fibers, characterized in that, Includes the following steps: S1. Catalyst support: The pre-oxidized mesophase pitch-based carbon fiber is immersed in the catalyst Ag@TiO2 dispersion to obtain catalyst-supported mesophase pitch-based carbon fiber. The catalyst Ag@TiO2 has a core-shell structure, with the diameter of the Ag core being 20-50 nm and the thickness of the TiO2 shell being 5-10 nm. S2: Laser activation: The catalyst-supported mesophase pitch-based carbon fiber is placed in a closed reaction chamber and a mixture of nitrogen and hydrogen is introduced. The volume percentage of hydrogen in the mixture is 5-25%. A pulsed green wave laser with a wavelength of 532nm and a pulse width of 50ns is used for activation treatment. S3: High-temperature graphitization: The catalyst-supported mesophase pitch-based carbon fiber that has been laser-activated is subjected to high-temperature graphitization treatment. The high-temperature graphitization treatment temperature is 1800~2200℃, the treatment time is 10~30min, and the atmosphere is a mixture of argon and hydrogen, with hydrogen accounting for 1~3% of the volume of the mixture.

2. The graphitization method for mesophase pitch-based carbon fibers according to claim 1, characterized in that, The catalyst loading in S1 is 0.1 to 1.0% of the mass of the mesophase pitch-based carbon fiber.

3. The graphitization method for mesophase pitch-based carbon fibers according to claim 2, characterized in that, The catalyst Ag@TiO2 dispersion is an ethanol dispersion of Ag@TiO2, and the concentration of Ag@TiO2 is 0.5~2.0wt%.

4. The graphitization method for mesophase pitch-based carbon fibers according to any one of claims 1 to 3, characterized in that, The laser power density for laser activation treatment described in S2 is set to 50~200W / cm², the scanning speed is controlled at 2~5mm / s, and the total irradiation time is 30~120s.

5. The graphitization method for mesophase pitch-based carbon fibers according to any one of claims 1 to 4, characterized in that, The TiO2 in the catalyst Ag@TiO2 described in S1 is anatase TiO2.

6. The graphitization method for mesophase pitch-based carbon fibers according to claim 5, characterized in that, The full width at half maximum (FWHM) of the anatase (101) peak in the Ag@TiO2 anatase phase is 0.2–0.

3. ° The Ag-TiO2 interface peak in Raman characterization is located at 510~514 cm⁻¹. ⁻¹ .

7. The graphitization method for mesophase pitch-based carbon fibers according to claim 5 or 6, characterized in that, The catalyst Ag@TiO2 described in S1 is prepared by the following method: The coating agent, titanium precursor and silver salt were mixed and added to a mixed solution of polar solvent and water. The pH was adjusted to 2 and the reaction was carried out at 200℃ and 1 MPh until complete. The reactants were separated and then calcined at 300℃ for 1 h to prepare the catalyst Ag@TiO2.

8. A mesophase pitch-based carbon fiber, characterized in that, It is obtained by processing pre-oxidized mesophase pitch-based carbon fibers through the graphitization method of mesophase pitch-based carbon fibers according to any one of claims 1 to 7.

9. The mesophase pitch-based carbon fiber according to claim 8, characterized in that, The mesophase pitch-based carbon fiber has an axial thermal conductivity of 900~1150 (1100) W / (m·K) and an ash content of less than or equal to 100 ppm.

10. The application of the mesophase pitch-based carbon fiber as described in claim 8 or 9 in the fields of aerospace, defense and military industry and high-end composite materials.

Images