Preparation method of pure chitosan porous carbon fiber and its application

Abstract

The present invention discloses a preparation method and application of pure chitosan porous carbon fibers. The preparation method comprises the following steps: (1) dissolving chitosan in an acetic acid solution, then adding a water-soluble metal salt to the obtained chitosan solution, then adding excess water and continuously stirring to form a uniform and stable mixed solution for standby use. (2) freeze-drying the mixed solution, then placing the obtained solid product in a protective atmosphere for carbonization treatment; after completion, cooling to room temperature, washing the obtained carbonized product to remove the metal salt template, thereby forming porous carbon fibers. The method of the present invention uses pure chitosan as a raw material to prepare pure chitosan porous carbon fibers, and the preparation method of the present invention is simpler and more efficient, does not require the use of excess organic solvents, has low production costs and energy consumption, and is more suitable for large-scale production. Moreover, the metal salt template can be recycled and reused, which is more in line with the requirements of sustainable development and environmental friendliness.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon nanofiber material preparation, and in particular to a preparation method of pure chitosan porous carbon fiber and application thereof. Background Art

[0002] The following content in the background technology refers only to the information related to the present invention understood by the inventor, and is intended to increase the understanding of the present invention by explaining some basic technical knowledge related to the present invention. This information does not necessarily constitute knowledge known to ordinary technicians in this field.

[0003] In recent years, carbon nanofiber materials, especially porous carbon nanofibers, have attracted widespread attention from researchers in the fields of environment and new energy due to their advantages such as large specific surface area, multiple reactive sites, light weight, high specific strength, and unique morphology and structure. Among the various raw materials for preparing porous carbon materials, chitosan has become one of the most popular materials for research due to its wide availability, low cost, biodegradability, non-toxicity, good biocompatibility, and good film-forming properties. However, the preparation method of pure chitosan porous carbon fibers needs to be developed because chitosan has relatively poor fiber-forming properties, which limits the development and application of chitosan-based porous carbon fiber materials.

[0004] Patent publication number CN 110982124 A discloses a nanofiber chitosan porous material and its preparation method. This method involves mixing polyvinyl alcohol-ethylene copolymer nanofibers with a chitosan solution and freeze-drying the mixture to produce the nanofiber chitosan porous material. The preparation method disclosed in this patent document is a multi-step process. First, polyvinyl alcohol-ethylene copolymer nanofibers are prepared, which requires acetone extraction to remove cellulose acetate butyrate. Next, chitosan and polyvinyl alcohol-ethylene copolymer nanofibers are prepared into a solution. The two solutions are then mixed and finally freeze-dried. This complex preparation process, coupled with the use of acetone, makes it unsuitable for large-scale production.

[0005] In summary, in the current methods of preparing fibers or porous fibers based on chitosan, chitosan must rely on other polymer fiber-forming additives to become nanofibers, and the amount of chitosan in the prepared products is relatively small, which directly affects the specific properties of the finished products such as biocompatibility, adsorption, film-forming properties, and hygroscopicity. Summary of the Invention

[0006] To address the above-mentioned issues, the present invention discloses a method for preparing pure chitosan porous carbon fibers and its application. The present method utilizes pure chitosan as a raw material to prepare pure chitosan porous carbon fibers, and utilizes a simpler and more efficient synthesis method. To achieve the above-mentioned objectives, the present invention discloses the following technical solutions.

[0007] First, the present invention discloses a method for preparing pure chitosan porous carbon fibers, comprising the following steps:

[0008] (1) Dissolve chitosan in acetic acid solution, then add water-soluble metal salt to the obtained chitosan solution, and then add excess water and continue stirring to form a uniform and stable mixed solution for use.

[0009] (2) The mixed solution is freeze-dried, and the obtained solid product is then placed in a protective atmosphere for carbonization. After completion, the solid product is cooled to room temperature, and the obtained carbonized product is washed to remove the metal salt template, thereby forming porous carbon fibers.

[0010] Furthermore, in step (1), the chitosan has a deacetylation degree of 50-95%.

[0011] Furthermore, in step (1), the mass fraction of the acetic acid solution is 10-50 wt%. In the present invention, the acetic acid solution has the functions of dissolving chitosan to form a solution and promoting the complete dissolution of the metal salt (such as zinc chloride).

[0012] Furthermore, in step (1), the mass fraction of the chitosan solution is 0.5-5 wt%.

[0013] Furthermore, in step (1), the mass ratio of the metal salt to chitosan is 1:5 to 1:1. By changing the ratio of chitosan to metal salt, the size of the pores in the porous carbon fiber can be controlled.

[0014] Furthermore, in step (1), the metal salt includes at least one of sodium chloride, potassium chloride, ferric chloride, cobalt chloride, ferrous chloride, calcium chloride, magnesium chloride, zinc chloride, sodium hydroxide, potassium hydroxide, and the like. In the present invention, the metal salt is used as a fiber forming agent and pore-forming agent. In addition, the metal salt is easily soluble in water, making it easy to completely remove it during washing and also facilitating recycling of the metal salt.

[0015] Furthermore, in step (1), the mass of the water is 1 to 5 times the mass of the chitosan solution.

[0016] Furthermore, in step (2), the temperature of the freeze-drying treatment is -40~-80°C, and the vacuum degree is 10~50Pa.

[0017] Furthermore, in step (2), the carbonization treatment temperature is 600-800°C, and the treatment time is 2-6 hours (preferably 2-4 hours). Optionally, the protective atmosphere includes any one of nitrogen, inert gas (such as argon, etc.), etc.

[0018] Furthermore, in step (2), the carbonized product is washed with clean water for 3 to 5 times to obtain the porous carbon fiber. The metal salt is used as a sacrificial template agent. After washing with clean water, the washing liquid can be dried to remove moisture, and the metal salt can be recovered for further use, thereby achieving sustainable use of the metal salt.

[0019] Secondly, the present invention discloses the application of the porous carbon fibers obtained by the preparation method of pure chitosan porous carbon fibers in the energy field, and optionally, in photocatalytic hydrogen production, lithium-sulfur battery cathode catalyst, etc.

[0020] The present invention successfully achieves the preparation of porous carbon fibers using pure chitosan as raw material through the sol-gel combined with freeze-drying method. In order to achieve the above purpose: the present invention adopts acetic acid solution to dissolve chitosan to prepare chitosan solution. Since the viscosity of the chitosan solution is relatively large at this time, it is not conducive to the formation of chitosan fibers. For this reason, the present invention further adds water-soluble metal salts to the chitosan solution, so that chitosan and metal ions are complexed to form irregular complex precipitates. At this time, the metal ions and chitosan molecular chains are already combined together. However, irregular complex precipitates are not conducive to the formation of chitosan fibers. The present invention adopts the method of adding excess water to dissociate the complex formed by metal ions and chitosan to form a uniform and stable solution. At this time, the concentration of the chitosan and metal ion complex becomes smaller, and the low concentration of metal salts combines with the chitosan molecules, which is conducive to the stretching of the chitosan molecules into linear polymers. Because the freezing process occurs at extremely low temperatures, the unique "linear, polymer-like stretch" state is preserved after freezing. Freeze-drying gradually removes moisture, forming chitosan fibers containing metal salts. After carbonization and other steps, these chitosan fibers become porous carbon fibers. The above-mentioned method of the present invention differs significantly from other methods, such as template methods and electrospinning. First, the preparation method differs. The present invention simply prepares a solution and then freeze-dries it to produce pure chitosan fibers. Other methods primarily rely on electrospinning, which requires the addition of a fiber-forming agent (such as polyvinyl pyrrolidone or polyvinyl alcohol), aging the sol, and electrospinning using an electrospinning machine to produce fibers. Second, the principle differs. The present invention utilizes a complex formed between a metal salt and chitosan, and uses excess water to linearly stretch the chitosan molecular weight to produce fibers. Electrospinning relies on electrostatic forces, producing fibers by stretching a solution in an electrostatic field.

[0021] Compared with the existing technology, the preparation method of the present invention is simpler and more efficient, does not require the use of hydrofluoric acid and excess organic solvents, has low production costs and energy consumption, and is more suitable for large-scale production. Moreover, the metal salt template can be recycled and reused repeatedly, which is more in line with the requirements of sustainable development and environmental friendliness. This is unmatched by electrospinning and other template methods. Relevant experiments have verified that the porous carbon fibers prepared by the embodiment of the present invention are used for hydrogen production at 10 mA·cm -1 The polarization voltage corresponding to the current is as high as 140-200 mV, indicating that the porous carbon fibers have excellent electrocatalytic hydrogen evolution performance. When the porous carbon fibers prepared in the examples of the present invention are used as cathode catalysts in lithium-sulfur batteries, test results show that after 50 charge and discharge cycles at a charge and discharge voltage range of 1.5-3.0 V and current densities of 0.1C and 0.5C, their specific capacities stabilize at approximately 1020 and 800 mAh / g, respectively, demonstrating the excellent electrochemical performance of the porous carbon fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute undue limitations thereon. The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0023] Figure 1 The following is an SEM image of the pure chitosan porous carbon fiber prepared in Example 1.

[0024] Figure 2 The following is an SEM image of pure chitosan porous carbon fibers prepared in Example 2.

[0025] Figure 3 The following is an SEM image of pure chitosan porous carbon fibers prepared in Example 3.

[0026] Figure 4 This is a TEM image of pure chitosan porous carbon fibers prepared in Example 4 below.

[0027] Figure 5 The LSV curve of the pure chitosan porous carbon fiber prepared in Example 4 below.

[0028] Figure 6 The lithium-sulfur battery cycle performance of the pure chitosan porous carbon fiber prepared in the following Example 4.

[0029] Figure 7 This is a TEM image of pure chitosan porous carbon fibers prepared in Example 5 below.

[0030] Figure 8 The LSV curve of the pure chitosan porous carbon fiber prepared in Example 5 below.

[0031] Figure 9 The lithium-sulfur battery cycle performance of the pure chitosan porous carbon fiber prepared in Example 5 below. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present invention only and are not intended to limit the scope of the invention. The experimental methods in the following examples, for which specific conditions are not specified, are generally performed under conventional conditions or as recommended by the manufacturer.

[0033] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. The reagents or raw materials used in the present invention can be purchased through conventional channels. Unless otherwise specified, the reagents or raw materials used in the present invention are used in a conventional manner in the art or in accordance with the product instructions. In addition, any method and material similar to or equivalent to the described content can be applied to the method of the present invention. The present invention is further described with reference to the accompanying drawings and specific embodiments. The preferred embodiments and materials described in the present invention are for demonstration purposes only.

[0034] Example 1

[0035] A method for preparing pure chitosan porous carbon fiber comprises the following steps:

[0036] (1) Take 0.2g chitosan (85% deacetylation degree) and dissolve it in 19.8g 20wt% acetic acid solution. Stir continuously until the chitosan is completely dissolved to form a chitosan solution with a mass fraction of 1%.

[0037] (2) Add 0.8 g of potassium chloride to the chitosan solution and stir for 0.5 h. Then add 60 g of water and continue stirring for 1 h to form a uniform and stable mixed solution. Pour the mixture into a beaker for later use.

[0038] (3) The mixed solution was placed in the cold well of a freeze dryer and frozen at -70°C. After the mixed solution was completely frozen, the vacuum pump was turned on to evacuate the sample and the vacuum degree was set to 20 Pa. The sample was freeze-dried until it was completely dry.

[0039] (4) The dried product was placed in a tubular furnace and heated to 700°C at a heating rate of 3°C / min under a nitrogen atmosphere and kept at that temperature for 2 h. After completion, the temperature was cooled to room temperature and the obtained carbonized product was centrifuged and washed 5 times with distilled water to obtain porous carbon fibers.

[0040] The SEM image of the porous carbon fiber prepared in this embodiment is as follows Figure 1As shown, it can be seen that the porous carbon fiber presents obvious fiber morphology, the average diameter of the fiber is 218 nm, and the average pore size of the internal pores is 27 nm.

[0041] Example 2

[0042] A method for preparing pure chitosan porous carbon fiber comprises the following steps:

[0043] (1) Take 0.1g chitosan (95% deacetylation degree) and dissolve it in 19.9g 20wt% acetic acid solution. Stir continuously until the chitosan is completely dissolved to form a chitosan solution with a mass fraction of 0.5%.

[0044] (2) Add 0.5 g of potassium chloride to the chitosan solution and stir for 0.5 h. Then add 60 g of water and continue stirring for 1 h to form a uniform and stable mixed solution. Pour the mixture into a beaker for later use.

[0045] (3) The mixed solution was placed in the cold well of a freeze dryer and frozen at -70°C. After the mixed solution was completely frozen, the vacuum pump was turned on to evacuate the sample and the vacuum degree was set to 20 Pa. The sample was freeze-dried until it was completely dry.

[0046] (4) The dried product was placed in a tubular furnace and heated to 700°C at a heating rate of 3°C / min under a nitrogen atmosphere and kept at that temperature for 2 h. After completion, the temperature was cooled to room temperature and the obtained carbonized product was centrifuged and washed three times with distilled water to obtain porous carbon fibers.

[0047] The SEM image of the porous carbon fiber prepared in this embodiment is as follows Figure 2 As shown, it can be seen that the porous carbon fiber presents obvious fiber morphology, the average diameter of the fiber is 226 nm, and the average pore diameter of the internal pores is 34 nm.

[0048] Example 3

[0049] A method for preparing pure chitosan porous carbon fiber comprises the following steps:

[0050] (1) Take 0.2g chitosan (deacetylation degree 60%) and dissolve it in 19.8g acetic acid solution with a mass fraction of 20wt%. Continue stirring until the chitosan is completely dissolved to form a chitosan solution with a mass fraction of 1%.

[0051] (2) Add 0.8 g of potassium hydroxide to the chitosan solution and stir for 0.5 h. Then add 100 g of water and continue stirring for 1 h to form a uniform and stable mixed solution. Pour the mixture into a beaker for later use.

[0052] (3) The mixed solution was placed in the cold well of a freeze dryer and frozen at -70°C. After the mixed solution was completely frozen, the vacuum pump was turned on to evacuate the sample and the vacuum degree was set to 20 Pa. The sample was freeze-dried until it was completely dry.

[0053] (4) The dried product was placed in a tubular furnace and heated to 600°C at a heating rate of 3°C / min under a nitrogen atmosphere and kept at that temperature for 4 h. After completion, the temperature was cooled to room temperature and the obtained carbonized product was centrifuged and washed 5 times with distilled water to obtain porous carbon fibers.

[0054] The SEM image of the porous carbon fiber prepared in this embodiment is as follows Figure 3 As shown, it can be seen that the porous carbon fiber presents obvious fiber morphology, the average diameter of the fiber is 97 nm, and the average pore size of the internal pores is 28 nm.

[0055] Example 4

[0056] A method for preparing pure chitosan porous carbon fiber comprises the following steps:

[0057] (1) Take 0.2g chitosan (70% deacetylation degree) and dissolve it in 19.8g 20wt% acetic acid solution. Stir continuously until the chitosan is completely dissolved to form a chitosan solution with a mass fraction of 1%.

[0058] (2) Add 1 g of potassium hydroxide to the chitosan solution and stir for 0.5 h. Then add 40 g of water and continue stirring for 1 h to form a uniform and stable mixed solution. Pour the mixture into a beaker for later use.

[0059] (3) The mixed solution is placed in the cold well of a freeze dryer and frozen at -50°C. After the mixed solution is completely frozen, the vacuum pump is turned on to evacuate the sample and the vacuum degree is set to 40 Pa. Freeze drying is performed until the sample is completely dry.

[0060] (4) The dried product was placed in a tubular furnace and heated to 800°C at a heating rate of 3°C / min under a nitrogen atmosphere and kept at that temperature for 4 h. After completion, the temperature was cooled to room temperature and the obtained carbonized product was centrifuged and washed 5 times with distilled water to obtain porous carbon fibers.

[0061] The SEM image of the porous carbon fiber prepared in this embodiment is as follows Figure 4 As shown, it can be seen that the porous carbon fiber presents obvious fiber morphology, the average diameter of the fiber is 94 nm, and the average pore size of the internal pores is 42 nm.

[0062] A three-electrode system was used, with a silver chloride electrode as the counter electrode and a platinum electrode as the reference electrode. In this embodiment, the porous carbon fiber was used as the working electrode, 0.5 mol / L potassium hydroxide was used as the electrolyte, and an electrochemical workstation was used to perform an electrocatalytic hydrogen evolution test. The polarization curve obtained is shown in FIG. Figure 5 The result shows: 10 mA•cm -1 The corresponding polarization voltage is 154 mV, indicating that the porous carbon fiber has good electrocatalytic performance.

[0063] In addition, the porous carbon fiber prepared in this embodiment was used as the positive electrode catalyst of the lithium-sulfur battery, and the charge and discharge performance of the lithium-sulfur battery was tested using a Shenzhen Xinwei battery tester. The constant current charge and discharge specific capacity cycle test experiment was carried out at a current density of 0.2C, and the charge and discharge voltage range was 1.5~3.0V. The test results are shown in Figure 2. Figure 6 As shown, the results show that the specific capacity remains at about 1020 mA•h / g after 50 cycles, indicating that the porous carbon fiber has excellent electrochemical properties.

[0064] Example 5

[0065] A method for preparing pure chitosan porous carbon fiber comprises the following steps:

[0066] (1) Take 0.15g of chitosan (50% deacetylation degree) and dissolve it in 14.85g of 10wt% acetic acid solution. Stir continuously until the chitosan is completely dissolved to form a chitosan solution with a mass fraction of 1%.

[0067] (2) Add 0.3 g of sodium chloride to the chitosan solution and stir for 0.5 h. Then add 30 g of water and continue stirring for 2 h to form a uniform and stable mixed solution. Pour the mixture into a beaker for later use.

[0068] (3) The mixed solution is placed in the cold well of a freeze dryer and frozen at -60°C. After the mixed solution is completely frozen, the vacuum pump is turned on to evacuate the sample and the vacuum degree is set to 50 Pa. Freeze drying is performed until the sample is completely dry.

[0069] (4) The dried product was placed in a tubular furnace and heated to 800°C at a heating rate of 3°C / min under a nitrogen atmosphere and kept at that temperature for 4 h. After completion, the temperature was cooled to room temperature and the obtained carbonized product was centrifuged and washed 5 times with distilled water to obtain porous carbon fibers.

[0070] The SEM image of the porous carbon fiber prepared in this embodiment is as follows Figure 7 As shown, it can be seen that the porous carbon fiber presents obvious fiber morphology, the average diameter of the fiber is 110 nm, and the average pore size of the internal pores is 8 nm.

[0071] In addition, the porous carbon fiber prepared in this embodiment was used as the positive electrode catalyst of the lithium-sulfur battery, and the charge and discharge performance of the lithium-sulfur battery was tested using a Shenzhen Xinwei battery tester. The constant current charge and discharge specific capacity cycle test experiment was carried out at a current density of 0.5C, and the charge and discharge voltage range was 1.5~3.0V. The test results are shown in Figure 2. Figure 8 As shown, the results show that after 50 cycles, the specific capacity remains at about 800 mA•h / g, indicating that the porous carbon fiber has excellent electrochemical properties.

[0072] A three-electrode system was used, with a silver chloride electrode as the counter electrode and a platinum electrode as the reference electrode. In this embodiment, the porous carbon fiber was used as the working electrode, 0.5 mol / L potassium hydroxide was used as the electrolyte, and an electrochemical workstation was used to perform an electrocatalytic hydrogen evolution test. The polarization curve obtained is shown in FIG. Figure 9 The result shows: 10 mA•cm -1 The corresponding polarization voltage is 146 mV, indicating that the sample has good electrocatalytic performance.

[0073] Example 6

[0074] A method for preparing pure chitosan porous carbon fiber comprises the following steps:

[0075] (1) Take 1g of chitosan (80% deacetylation degree) and dissolve it in 19g of 50wt% acetic acid solution. Stir continuously until the chitosan is completely dissolved to form a chitosan solution with a mass fraction of 5%.

[0076] (2) Add 1 g of ferrous chloride to the chitosan solution and stir for 0.5 h. Then add 20 g of water and continue stirring for 1 h to form a uniform and stable mixed solution. Pour the mixture into a beaker for later use.

[0077] (3) The mixed solution is placed in the cold well of a freeze dryer and frozen at -80°C. After the mixed solution is completely frozen, the vacuum pump is turned on to evacuate the sample and the vacuum degree is set to 10 Pa. Freeze drying is performed until the sample is completely dry.

[0078] (4) The dried product was placed in a tubular furnace and heated to 600°C at a heating rate of 3°C / min under a nitrogen atmosphere and kept at this temperature for 6 hours. After completion, the temperature was cooled to room temperature and the obtained carbonized product was centrifuged and washed 5 times with distilled water to obtain porous carbon fibers. The average fiber diameter of the porous carbon fibers was measured to be 186 nm, and the average pore size of the internal pores was 19 nm.

[0079] Example 7

[0080] A method for preparing pure chitosan porous carbon fiber comprises the following steps:

[0081] (1) Take 0.4 g of chitosan (deacetylation degree of 60%) and dissolve it in 19.6 g of 30 wt% acetic acid solution. Continue stirring until the chitosan is completely dissolved to form a chitosan solution with a mass fraction of 2%.

[0082] (2) Add 0.8 g of magnesium chloride to the chitosan solution and stir for 0.5 h. Then add 40 g of water and continue stirring for 1 h to form a uniform and stable mixed solution. Pour the mixture into a beaker for later use.

[0083] (3) The mixed solution was placed in the cold well of a freeze dryer and frozen at -60°C. After the mixed solution was completely frozen, the vacuum pump was turned on to evacuate the sample and the vacuum degree was set to 30 Pa. The sample was freeze-dried until it was completely dry.

[0084] (4) The dried product was placed in a tubular furnace and heated to 700°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at this temperature for 3 hours. After completion, the temperature was cooled to room temperature and the obtained carbonized product was centrifuged and washed three times with distilled water to obtain porous carbon fibers. The average fiber diameter of the porous carbon fibers was measured to be 143 nm, and the average pore size of the internal pores was 21 nm.

[0085] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing pure chitosan porous carbon fiber, characterized in that: The steps include: (1) Dissolve chitosan in acetic acid solution, then add water-soluble metal salt or potassium hydroxide to the obtained chitosan solution, and then add excess water and continue stirring to form a uniform and stable mixed solution for use; (2) freeze-drying the mixture, and then placing the obtained solid product in a protective atmosphere for carbonization; after completion, cooling to room temperature, and washing the obtained carbonized product to remove the metal salt or potassium hydroxide template, thereby forming porous carbon fibers; In step (1), the metal salt is potassium chloride, and the mass ratio of potassium chloride to chitosan is 4:1 or 5:1; Or: in step (1), the mass ratio of potassium hydroxide to chitosan is 4:1 or 5:1; Or: in step (1), the metal salt is sodium chloride, and the mass ratio of sodium chloride to chitosan is 2:1; In step (1), the mass of the water is 1 to 5 times the mass of the chitosan solution.

2. The method for preparing pure chitosan porous carbon fiber according to claim 1, characterized in that: In step (1), the chitosan deacetylation degree is 50-95%.

3. The method for preparing pure chitosan porous carbon fiber according to claim 1, characterized in that: In step (1), the mass fraction of the acetic acid solution is 10-50 wt%.

4. The method for preparing pure chitosan porous carbon fiber according to claim 1, characterized in that: In step (1), the mass fraction of the chitosan solution is 0.5-5 wt%.

5. The method for preparing pure chitosan porous carbon fiber according to claim 1, characterized in that: In step (2), the temperature of the freeze-drying treatment is -40~-80°C, and the vacuum degree is 10~50Pa.

6. The method for preparing pure chitosan porous carbon fiber according to claim 1, characterized in that: In step (2), the temperature of the carbonization treatment is 600-800°C, and the treatment time is 2-6 hours.

7. The method for preparing pure chitosan porous carbon fiber according to claim 6, characterized in that: The processing time is 2~4h.

8. The method for preparing pure chitosan porous carbon fiber according to claim 1, characterized in that: The protective atmosphere includes any one of nitrogen and inert gas.

9. The method for preparing pure chitosan porous carbon fiber according to any one of claims 1 to 8, characterized in that: In step (2), the carbonized product is washed with clean water for 3 to 5 times to obtain the porous carbon fiber.

10. Application of the porous carbon fiber obtained by the method for preparing pure chitosan porous carbon fiber according to any one of claims 1 to 8 in the field of energy.

11. Application of the porous carbon fiber obtained by the preparation method of pure chitosan porous carbon fiber according to claim 10 in the field of energy, characterized in that: The application is to be used for photocatalytic hydrogen production and / or as a cathode catalyst for lithium-sulfur batteries.

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