Coal-based hollow carbon fiber membrane, and preparation method and application thereof

Abstract

The application discloses a coal-based hollow carbon fiber membrane and a preparation method and application thereof, and belongs to the technical field of water treatment. The preparation method comprises the following steps: collecting a hollow fiber precursor on an aluminum foil by using a coaxial electrospinning method according to a push injection speed ratio of a shell layer spinning solution and a core layer spinning solution being 18:(1-6), and then sequentially performing air low-temperature pre-oxidation and high-temperature carbonization treatment under inert gas to obtain the coal-based hollow carbon fiber membrane; wherein the shell layer spinning solution contains oxidized coal and polyacrylonitrile; and the core layer spinning solution contains polystyrene. That is, the coal-based hollow carbon fiber with different inner diameters is prepared by fixing the push injection speed of the shell layer spinning solution and adjusting the push injection speed of the core layer spinning solution. The hollow structure carbon fiber membrane has a larger specific surface area and can provide more active sites, so as to improve the deionization capacity and efficiency. The oxidized coal modified hollow carbon fiber can be used to prepare binder-free electrode materials, reduces the use of non-active materials, constructs a three-dimensional conductive network to improve the conductivity of the electrode, enhances the structural integrity of the electrode under the action of mechanical stress, and significantly improves the cycle service life of the electrode.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, and particularly relates to a coal-based hollow carbon fiber membrane, its preparation method, and its application. Background Technology

[0002] Of the world's total water resources, freshwater accounts for only 2.53%, and of these freshwater resources, only 13% is directly usable by humans. Meanwhile, climate change and population growth have negatively impacted drinking water from natural water resources such as rivers. In this context, brackish water is considered an ideal alternative water source for conversion into freshwater. To desalinate brackish water, various seawater desalination processes have been explored, such as reverse osmosis, nanofiltration, and electrodialysis. However, these processes face challenges in practical applications, including high energy consumption and membrane degradation due to scaling. Capacitive deionization (CDO) has become one of the ideal technologies for seawater desalination due to its advantages of no secondary pollution, easy regeneration, long cycle life, and low energy consumption. CDO is an electrochemical ion separation technology that utilizes porous carbon electrodes to achieve desalination and concentration through repeated adsorption and desorption processes.

[0003] Electrode materials, as a core component of capacitive deionization (CDO) technology, directly influence its development. Traditional methods for preparing electrode materials are cumbersome, requiring the addition of conductive agents and binders. The active material is mixed with a specific ratio of conductive agent and polymer binder, ground, and then attached to the current collector. If the active material is not uniformly distributed, unavoidable agglomeration may block some pores, affecting electron transfer and ion transport, further severely impacting the electrochemical reaction of the electrode material, ultimately leading to insufficient utilization of the electrode material and adversely affecting cycle performance.

[0004] Furthermore, many traditional carbon materials generally suffer from low desalination capacity and side reactions (co-ion repulsion and oxidative corrosion), limiting their practical application in capacitive deionization. Therefore, there is an urgent need to develop new materials or improve existing materials to enhance their electrochemical performance. Moreover, as the core component of capacitive deionization, electrode materials can also effectively improve the CDI performance of carbon materials through methods such as pore structure regulation and the construction of self-supporting structures. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a coal-based hollow carbon fiber membrane, its preparation method, and its applications. This invention, by adjusting the injection speed of the core layer spinning solution, yields coal-based hollow carbon fiber membranes with different inner diameters, exhibiting excellent conductivity and capacitance characteristics, and demonstrating many advantages in the field of capacitive deionization. The specific surface area of ​​the coal-based hollow carbon fiber membrane prepared by this invention can reach 378.30 cm². 2 g -1Among them, the macroporous structure of the coal-based hollow carbon fiber membrane provides more space for ions to enter the electrode interior, which is conducive to ion migration; the desalination capacity is 37.22 mg g. -1 It is solid coal-based carbon fiber (23.12 mg g) -1 It is 1.6 times that of other substances, and its desalination rate reaches 3.02 mg / g. -1 min -1 This demonstrates that the coal-based hollow carbon fibers prepared by this invention significantly improve the desalination capacity and desalination rate of carbon-based electrode materials.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] One of the technical solutions of this invention:

[0008] A method for preparing a coal-based hollow carbon fiber membrane includes the following steps:

[0009] Hollow fiber precursors were collected on aluminum foil using coaxial electrospinning with a feed rate ratio of 18:(1-6) for the shell spinning solution and the core spinning solution. The precursors were then subjected to pre-oxidation and carbonization treatments to obtain the coal-based hollow carbon fiber membrane.

[0010] The shell spinning solution contains oxidized coal and polyacrylonitrile;

[0011] The core spinning solution contains polystyrene.

[0012] Beneficial effects: This invention uses coaxial electrospinning to prepare coal-based hollow carbon fiber precursors. By fixing the injection speed of the shell spinning solution and adjusting the injection speed of the core spinning solution, coal-based hollow carbon fiber membranes with different inner diameters can be prepared. The hollow structure has a larger specific surface area and abundant pore structure, providing more active sites.

[0013] Preferably, the injection rate ratio is 18:1, 9:1, 6:1, 9:2, 18:5, or 3:1.

[0014] Preferably, the total concentration of oxidized coal and polyacrylonitrile in the shell spinning solution is 10-20 wt%.

[0015] The polystyrene concentration in the core spinning solution is 20–30 wt%.

[0016] Furthermore, the mass ratio of the oxidized coal to polyacrylonitrile is 1:1.

[0017] Furthermore, the shell spinning solution is obtained by adding coal oxide and polyacrylonitrile to N,N-dimethylformamide and magnetically stirring at 50-70°C for 12-24 hours until completely dissolved;

[0018] The core spinning solution is obtained by adding polystyrene to N,N-dimethylformamide and magnetically stirring at 50-70°C for 12-24 hours until it is completely dissolved.

[0019] Preferably, the condition parameters in the coaxial electrospinning process are:

[0020] The injection speed of the shell spinning solution is 0.1–1.0 mm / min. -1 The injection speed of the core spinning solution is 0.005–0.34 mm / min. -1 The positive and negative voltages are set to 10–22 kV and -3.0–0 kV, respectively; the aluminum foil is placed on a roller, and the roller speed is 50–150 r / min. -1 The receiving distance is 10-25cm.

[0021] Preferably, the conditions in the pre-oxidation process are:

[0022] In air atmosphere, at 2℃ min -1 The temperature was raised from room temperature to 280°C, and the pre-oxidation treatment was carried out at this temperature for 1 hour.

[0023] Beneficial effects: During the pre-oxidation stage, the oxygen-containing functional groups on the surface of oxidized coal promote the cyclization and cross-linking of polyacrylonitrile molecules, further stabilizing the fiber structure, reducing molecular chain breakage and shrinkage, thereby improving the thermal stability of the fiber.

[0024] Preferably, the conditions during the carbonization process are as follows:

[0025] Under an inert atmosphere, at 5℃ for min -1 The temperature is raised from room temperature to 800°C and carbonized at this temperature for 2 hours.

[0026] Beneficial effects: During the carbonization stage, the cross-linked network structure of the shell can reduce the shrinkage and deformation of carbon fibers during the carbonization process, which helps to maintain the fiber morphology, reduce porosity, and ultimately improve the mechanical properties of carbon fibers; the polystyrene in the core layer decomposes at high temperature, and hydrogen and oxygen are released in the form of gases, thereby forming a hollow structure inside the carbon fiber.

[0027] The second technical solution of the present invention:

[0028] A coal-based hollow carbon fiber membrane is prepared by the above-described preparation method.

[0029] Preferably, the inner diameter of the carbon fibers in the coal-based hollow carbon fiber membrane is 180-850 nm; more preferably, it is 187-209 nm, 209-313 nm, 313-480 nm, 480-542 nm, 584-667 nm, or 750-834 nm.

[0030] Preferably, the specific surface area of ​​the coal-based hollow carbon fiber membrane is 200-400 cm². 2 g -1 The total pore volume is 0.1-0.3 cm³. 3 g -1 The micropore volume reaches 0.05-0.25 cm³. 3 g -1 .

[0031] The third technical solution of this invention:

[0032] The above-mentioned coal-based hollow carbon fiber membrane is used in the preparation of binder-free capacitor deionization electrode materials.

[0033] Beneficial Effects: Using the coal-based hollow carbon fiber membrane prepared by this invention as a capacitive deionization electrode material offers several advantages. First, its unique hollow structure provides a larger specific surface area, which improves the utilization rate of active sites, resulting in excellent desalination performance. Second, the oxidized coal-modified hollow carbon fiber possesses excellent mechanical properties, allowing it to be directly used as a self-supporting electrode in capacitive deionization. Its three-dimensional conductive network structure maintains high conductivity, and its high modulus preserves the structural integrity of the self-supporting electrode during cycling, significantly extending its lifespan. In other words, the coal-based hollow carbon fiber membrane prepared by this invention, used as a self-supporting electrode material, eliminates the need for polymer binders, increases the loading of active materials, exposes more active sites, improves the utilization rate of active materials, and achieves efficient ion diffusion and storage.

[0034] Compared with the prior art, the present invention has the following advantages and technical effects:

[0035] 1. This invention introduces oxidized coal into a hollow carbon fiber matrix. On one hand, the abundant oxygen-containing functional groups of oxidized coal chemically crosslink with polyacrylonitrile to improve the overall mechanical properties of the carbon fiber; on the other hand, the microcrystalline structure of oxidized coal constructs graphite microcrystalline domains in the hollow tube wall, improving the desalination kinetics. Therefore, the coal-based hollow carbon fiber prepared by this invention has a higher specific surface area and better conductivity, thus exhibiting stronger ion adsorption capacity and a better desalination rate in capacitive deionization. Furthermore, when used as a capacitive deionization electrode material, it eliminates the need for binders as required in existing electrode material preparation techniques, avoiding their negative impact on the electrode's electrochemical performance and exhibiting better desalination performance and structural stability.

[0036] 2. This invention makes full use of the carbon element in coal resources, achieving efficient resource utilization, while simplifying the production process, reducing environmental pollution, and providing a sustainable technical solution for the development of green energy materials. Attached Figure Description

[0037] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0038] Figure 1 Scanning electron microscope (SEM) images of the hollow carbon fibers prepared in Examples 1-6 and the solid carbon fibers prepared in Comparative Example 1;

[0039] Wherein, a is Example 6, bf are Examples 1-5 respectively, and g is Comparative Example 1; in addition, 1 and 2 in a1 and a2 are scanning electron microscope images of the hollow fibers prepared in Example 6 under different scales, and so on;

[0040] Figure 2 The N2 adsorption / desorption curves (a) and pore size distribution (b) of the hollow carbon fibers prepared in Examples 1, 3 and 5 and the solid carbon fibers prepared in Comparative Example 1 are shown.

[0041] Figure 3 The tensile stress-strain curves of the hollow carbon fibers prepared in Examples 1-6 and the solid carbon fibers prepared in Comparative Example 1 are shown.

[0042] Figure 4 The hollow carbon fibers prepared in Example 1 and the solid carbon fibers prepared in Comparative Example 1 were subjected to a concentration of 500 mg / L. -1 Desalination capacity change curves (a) and Ragone curves (b) in NaCl solution;

[0043] Figure 5 The X-ray diffraction pattern of the binder-free capacitor deionization electrode material prepared in Example 1 is shown below.

[0044] Figure 6 The image shows the Raman diagram of the binder-free capacitor deionization electrode material prepared in Example 1.

[0045] Figure 7 Here is a photograph of the binder-free capacitor deionization electrode material prepared in Example 1;

[0046] Figure 8 The conductivity diagram is shown for the binder-free deionized capacitor electrode material prepared in Example 1.

[0047] The inset shows the IV curve. Detailed Implementation

[0048] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0049] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0050] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0051] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0052] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0053] This invention provides a method for preparing a coal-based hollow carbon fiber membrane, comprising the following steps:

[0054] Step 1: After the raw coal undergoes liquid-phase oxidation treatment, the precipitate obtained by centrifugation is oxidized coal;

[0055] Step 2: Add polyacrylonitrile and coal oxide to N,N-dimethylformamide and stir until completely dissolved to obtain a shell spinning solution;

[0056] Polystyrene was added to N,N-dimethylformamide and then stirred until completely dissolved to obtain a core spinning solution.

[0057] Step 3: The shell spinning solution and the core spinning solution from Step 2 are loaded into identical syringes, and the coal-based hollow carbon fiber precursor is obtained by collecting the solution on aluminum foil using coaxial electrospinning.

[0058] Step 4: The coal-based hollow carbon fiber precursor obtained in Step 3 is first placed in a muffle furnace for pre-oxidation treatment, and then placed in a tube furnace for carbonization treatment to obtain a flexible hollow carbon fiber membrane.

[0059] In some preferred embodiments, in step 1, the liquid-phase oxidation treatment involves oxidizing the raw coal with a mixed acid. Surface modification oxidizes some carbon atoms, resulting in abundant oxygen-containing functional groups, such as hydroxyl and carboxyl groups, which facilitates the dispersion and dissolution of the oxidized coal in organic solvents. The mixed acid is a solution of 98wt% concentrated sulfuric acid and 68wt% concentrated nitric acid in a volume ratio of 3:1.

[0060] In some preferred embodiments, the raw coal in step 1 is Xinjiang Heishan bituminous coal, which has not undergone chemical treatment.

[0061] In some preferred embodiments, in step 2, the total concentration of coal oxide and polyacrylonitrile in the shell spinning solution is 10-20 wt%. As the amount of coal oxide added increases, the concentration of the spinning solution will increase. The concentration of the spinning solution directly affects the degree of entanglement of polymer molecular chains in the solution. Only when the molecular chains are sufficiently entangled can continuous fibers be formed under the action of electric field force.

[0062] The polystyrene concentration in the core spinning solution is 20–30 wt%.

[0063] In some preferred embodiments, in step 2, oxidized coal and polyacrylonitrile are added to N,N-dimethylformamide and magnetically stirred at 50-70°C for 12-24 hours until completely dissolved to obtain a shell spinning solution.

[0064] Polystyrene was added to N,N-dimethylformamide and magnetically stirred at 50–70°C for 12–24 h until completely dissolved to obtain the core spinning solution.

[0065] In some preferred embodiments, in step 3, the coaxial electrospinning parameters are set as follows: the injection speed of the shell spinning solution is 0.1–1.0 mm / min. -1 The injection speed of the core spinning solution is 0.005–0.34 mm / min. -1 The positive and negative voltages are set to 10–22 kV and -3.0–0 kV, respectively; the aluminum foil is placed on a roller, and the roller speed is 50–150 r / min. -1 The receiving distance is 10-25cm.

[0066] In some preferred embodiments, in step 3, by fixing the injection speed of the shell spinning solution and adjusting the injection speed of the core spinning solution, coal-based hollow carbon fibers with different inner diameters can be obtained. The ratio of the injection speed of the shell spinning solution to the injection speed of the core spinning solution is 18:(1-6).

[0067] In some preferred embodiments, the ratio of the injection speed of the shell spinning solution to the injection speed of the core spinning solution is 18:1, 9:1, 6:1, 9:2, 18:5, and 3:1. The inner diameters of the prepared flexible hollow fibers are 187–209 nm, 209–313 nm, 313–480 nm, 480–542 nm, 584–667 nm, and 750–834 nm, respectively; and the tensile strengths are 4.62 MPa, 4.32 MPa, 3.92 MPa, 2.73 MPa, 2.26 MPa, and 2.06 MPa, respectively.

[0068] In some preferred embodiments, the pre-oxidation process in step 4 includes: being carried out in a muffle furnace at a pre-oxidation temperature of 280°C for 1 hour in an air atmosphere, at a rate of 2°C / min. -1 The temperature was increased from room temperature to 280°C;

[0069] In some preferred embodiments, the carbonization process in step 4 includes: the carbonization process is carried out in a tube furnace at a carbonization temperature of 800°C for 2 hours, under a nitrogen atmosphere, at a temperature of 5°C / min. -1 The temperature is increased from room temperature to 800°C.

[0070] The present invention also discloses the use of the above-mentioned coal-based hollow carbon fiber membrane as a binderless capacitor deionization electrode material. Because the addition of oxidized coal improves the mechanical and electrical properties of the hollow carbon fiber membrane, it can be used as a binderless capacitor deionization electrode material with both mechanical properties and flexibility. Moreover, as an independent electrode material, it does not require current collectors and binders, which not only eliminates the traditional coating process but also reduces the manufacturing cost of the electrode material.

[0071] Unless otherwise specified, "room temperature" in this invention refers to 20-30℃.

[0072] Unless otherwise specified, the term "parts" in this invention refers to parts by weight.

[0073] All raw materials used in this invention were purchased from the market.

[0074] The technical solution of the present invention will be further illustrated by the following embodiments.

[0075] Example 1

[0076] Step 1: Add raw coal to a mixed acid solution (concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1) and perform liquid-phase oxidation treatment for 2 hours. The precipitate obtained by centrifugation is oxidized coal.

[0077] Step 2: Add polyacrylonitrile and coal oxide to 5 mL of N,N-dimethylformamide at a mass ratio of 1:1 to prepare a solution with a mass fraction of 16.9 wt% (total mass fraction of polyacrylonitrile and coal oxide). Stir magnetically at 60 °C for 12 h until completely dissolved to obtain the shell spinning solution.

[0078] Step 3: Add polystyrene to 5 mL of N,N-dimethylformamide to prepare a solution with a mass fraction of 25.3 wt%. Stir magnetically at 60 °C for 12 h until completely dissolved to obtain the core spinning solution.

[0079] Step 4: Load the prepared spinning solutions into 5mL syringes, attach the coaxial electrospinning needles, and then spin at a ratio of 3:1 between the injection speed of the shell spinning solution and the injection speed of the core spinning solution (e.g., ...). Figure 1 (f) The positive and negative voltages are 18kV and -2.5kV respectively. The aluminum foil is placed on a roller, and the roller rotates at 100 r / min. -1 The receiving distance is 20cm;

[0080] Step 5: The prepared hollow carbon fiber precursor is first transferred to a muffle furnace for pre-oxidation. The pre-oxidation temperature is 280℃, the pre-oxidation time is 1 hour, and the atmosphere is air, with a firing rate of 2℃ / min. -1 The temperature was increased from room temperature to 280℃; the pre-oxidized hollow carbon fiber precursor was transferred to a tube furnace for carbonization treatment at 800℃ for 2 hours in a nitrogen atmosphere at a rate of 5℃ / min. -1 By heating from room temperature to 800℃, a coal-based carbon fiber membrane with a hollow structure—HCF(3∶1)—was obtained.

[0081] Example 2

[0082] The difference from Example 1 is that, in step 4, spinning is performed under the condition that the ratio of the shell spinning solution injection rate to the core spinning solution injection rate is 18:1 (e.g., Figure 1 (a) The positive and negative voltages are 14kV and -2.5kV respectively. The aluminum foil is placed on a roller, and the roller speed is 100 r / min. -1 The receiving distance is 20cm.

[0083] Example 3

[0084] The difference from Example 1 is that, in step 4, spinning is performed under the condition that the ratio of the shell spinning solution injection speed to the core spinning solution injection speed is 9:1 (e.g., Figure 1 (b) The positive and negative voltages are 15kV and -2.5kV respectively. The aluminum foil is placed on a roller, and the roller speed is 100 r / min. -1 The receiving distance is 20cm.

[0085] Example 4

[0086] The difference from Example 1 is that, in step 4, spinning is performed under the condition that the ratio of the shell spinning solution injection rate to the core spinning solution injection rate is 6:1 (e.g., Figure 1 c) The positive and negative voltages are 16kV and -2.5kV respectively. The aluminum foil is placed on a roller, and the roller speed is 100 r / min. -1 The receiving distance is 20cm.

[0087] Example 5

[0088] The difference from Example 1 is that, in step 4, spinning is performed under the condition that the ratio of the shell spinning solution injection rate to the core spinning solution injection rate is 9:2 (e.g., Figure 1 (d) The positive and negative voltages are 17kV and -2.5kV respectively. The aluminum foil is placed on a roller, and the roller speed is 100 r / min. -1 The receiving distance is 20cm.

[0089] Example 6

[0090] The difference from Example 1 is that, in step 4, spinning is performed under the condition that the ratio of the shell spinning solution injection rate to the core spinning solution injection rate is 18:5 (e.g., Figure 1 (e) The positive and negative voltages are 20kV and -2.5kV respectively. The aluminum foil is placed on a roller, and the roller speed is 100 r / min. -1 The receiving distance is 20cm.

[0091] Comparative Example 1

[0092] Step 1: Add raw coal to a mixed acid solution (concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1) and perform liquid-phase oxidation treatment for 2 hours. The precipitate obtained by centrifugation is oxidized coal.

[0093] Step 2: Add polyacrylonitrile and coal oxide to 5 mL of N,N-dimethylformamide at a mass ratio of 1:1 to prepare a solution with a mass fraction of 16.9 wt%. Stir magnetically at 60 °C for 12 h until completely dissolved to obtain the spinning solution.

[0094] Step 3: Load the prepared spinning solution into a 5mL syringe, attach the electrospinning needle, and then prepare solid carbon fibers by electrospinning at a injection speed of 0.1mm / min. -1 The positive and negative voltages are 13℃ and -2.5kV respectively. The aluminum foil is placed on a roller, and the roller speed is 100r / min. -1 The receiving distance is 20cm;

[0095] Step 4: The prepared solid carbon fiber precursor is first transferred to a muffle furnace for pre-oxidation at a temperature of 280℃ for 1 hour in an air atmosphere at a rate of 2℃ / min. -1 The carbon fiber precursor was heated from room temperature to 280℃; the pre-oxidized precursor was then transferred to a tube furnace for carbonization treatment at 800℃ for 2 hours in a nitrogen atmosphere at a rate of 5℃ / min. -1 By heating from room temperature to 800℃, coal-based carbon fiber membranes-CF (e.g.) were obtained. Figure 1 (g), with a specific surface area of ​​271.95 m². 2 g -1 .

[0096] Figure 1 The images show scanning electron microscope (SEM) images of the hollow carbon fibers prepared in Examples 1-6 and the solid carbon fibers prepared in Comparative Example 1; where a represents Example 6, bf represents Examples 1-5 respectively, and g represents Comparative Example 1; furthermore, 1 and 2 in a1 and a2 are SEM images of the hollow fibers prepared in Example 6 at different scales, and so on; from Figure 1 As can be seen from the examples, the carbon fibers prepared in Examples 1-6 of this invention have a hollow structure.

[0097] Figure 2 The N2 adsorption / desorption curves and pore size distribution diagrams are shown for the hollow carbon fibers prepared in Examples 1, 3, and 5, and the solid carbon fibers prepared in Comparative Example 1. The specific surface area of ​​the hollow carbon fiber membranes prepared in Examples 1, 3, and 5 is 200-400 cm². 2 g -1 The total pore volume is 0.1-0.3 cm³. 3 g -1 The micropore volume reaches 0.05-0.25 cm³. 3 g -1 .

[0098] Figure 3 The figures show the tensile stress-strain curves of the hollow carbon fibers prepared in Examples 1-6 and the solid carbon fibers prepared in Comparative Example 1. As can be seen from the figures, the mechanical properties of coal-based hollow carbon fibers decrease as the inner diameter of the hollow fibers increases, but the tensile strength of the coal-based hollow carbon fibers with the largest inner diameter can still reach 2.06 MPa.

[0099] Comparative Example 2

[0100] See the preparation process of the FUSFM-0.15 solid fiber material prepared in Example 1 of the existing patent CN 118477492 A.

[0101] Comparing the coal-based hollow carbon fiber membrane prepared in Example 1 of this invention with the coal-based fiber membrane prepared in Comparative Example 2, the following differences exist: ① The spinning technology and preparation objectives differ. In Comparative Example 2, oxidized coal was used for core spinning, and candle ash was used as the shell spinning solution to prepare solid fiber materials. In this invention, oxidized coal is used for the shell spinning solution to prepare hollow carbon fibers. Currently, there are no reports on coal-based hollow carbon fiber technology. ② The processing properties of the materials are completely different. Comparative Example 2, after pre-oxidation treatment at 300℃, was directly used as an oil-water separation material. Its fiber material is essentially a pre-oxidized polyacrylonitrile fiber material, intrinsically electronically insulating. The core of its material lies in the graded rough structure of candle ash on the fiber surface, which increases roughness and achieves oil-water separation. The role of oxidized coal in the carbon fiber is to provide a better fiber skeleton structure. The hollow carbon fiber finally obtained in Example 1 of this invention is a carbon material treated at high temperatures of 600-900℃ under inert gas, exhibiting excellent conductivity. Figure 6 As can be seen from the data, ID / IG = 1.03, indicating that the coal-based hollow carbon fiber membrane prepared in Example 1 not only has certain defects but also maintains the ordered carbon structure of graphite; from Figure 8 As can be seen from the data, the conductivity of Example 1 reaches 4443.8 S / m. -1 It exhibits excellent electrical conductivity and can be used as an electrode material in the field of electrochemistry. In particular, the hollow carbon fiber prepared using oxidized coal as a shell in Example 1 of this invention achieves a specific surface area of ​​378.30 cm². 2 g -1 The total pore volume is 0.20 cm³. 3 g -1 It has a large specific surface area and abundant pore structure; among them, hollow carbon fiber uses coal oxide as carbon source, which improves the mechanical properties of the fiber and forms graphite microcrystalline domains, improves the conductivity of carbon fiber, and improves the adsorption kinetics of sodium ions, and can be prepared into a self-supporting electrode material with cycle stability.

[0102] Effect verification

[0103] The coal-based hollow carbon fiber membrane prepared in Example 1 of this invention and the solid carbon fiber prepared in Comparative Example 1 were cut into 4*4cm squares (e.g., Figure 7 As shown, the electrode material was used as a capacitor deionization electrode, and the electrode material was subjected to desalination test.

[0104] Figure 4 The hollow carbon fibers prepared in Example 1 and the solid carbon fibers prepared in Comparative Example 1 were subjected to a concentration of 500 mg / L. -1 Desalination capacity change curves (a) and Ragone curves (b) in NaCl solution; from Figure 4 As can be seen from this, at a voltage of 1.2V, for 500mg L... -1The desalination capacity and maximum desalination rate of NaCl solution were determined from 23.12 mg / g of solid carbon fiber (CF). -1 and 0.80 mg g -1 min -1 Increased to 37.22 mg g -1 and 3.02mg g -1 min -1 .

[0105] Figure 5 The X-ray diffraction pattern of the binder-free capacitor deionization electrode material prepared in Example 1 is shown below; Figure 5 It can be seen that the material has broad peaks around 23° and 43°, which correspond to the (002) and (100) crystal planes of graphite, respectively, indicating that the coal-based hollow carbon fiber is mainly composed of amorphous carbon.

[0106] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a coal-based hollow carbon fiber membrane, characterized in that, Includes the following steps: Hollow fiber precursors were collected on aluminum foil using coaxial electrospinning with a feed rate ratio of 18:(1-6) for the shell spinning solution and the core spinning solution. The precursors were then subjected to pre-oxidation and carbonization treatments to obtain the coal-based hollow carbon fiber membrane. The shell spinning solution contains oxidized coal and polyacrylonitrile; The core spinning solution contains polystyrene; The total concentration of coal oxide and polyacrylonitrile in the shell spinning solution is 10-20 wt%. The polystyrene concentration in the core spinning solution is 20-30 wt%. The injection rate of the shell spinning solution is 0.1~1.0 mm / min. -1 The injection rate of the core spinning solution is 0.005~0.34 mm / min. -1 The positive and negative voltages are set to 10~22 kV and -3.0~0 kV, respectively; the aluminum foil is placed on a roller, and the roller speed is 50~150 r / min. -1 The receiving distance is 10~25 cm; The conditions for the pre-oxidation process are as follows: In air atmosphere, at 2 ℃ min -1 The temperature was raised from room temperature to 280°C, and pre-oxidized at this temperature for 1 hour. The conditions during the carbonization process are as follows: Under an inert atmosphere, at 5 °C for min -1 The temperature was increased from room temperature to 800°C, and carbonized at this temperature for 2 hours.

2. The method for preparing a coal-based hollow carbon fiber membrane according to claim 1, characterized in that, The injection rate ratio is 18:1, 9:1, 6:1, 9:2, 18:5, or 3:

1.

3. The method for preparing a coal-based hollow carbon fiber membrane according to claim 1, characterized in that, The mass ratio of the oxidized coal to polyacrylonitrile is 1:

1.

4. A coal-based hollow carbon fiber membrane, characterized in that, It is prepared by the preparation method according to any one of claims 1-3.

5. The coal-based hollow carbon fiber membrane according to claim 4, characterized in that, The inner diameter of the coal-based hollow carbon fiber membrane is 180-850 nm.

6. The application of the coal-based hollow carbon fiber membrane as described in claim 4 or 5 in the preparation of binderless capacitor deionization electrode materials.

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