A porous alumina fiber and its preparation method

Abstract

This disclosure belongs to the field of ceramic materials technology. This disclosure provides a porous alumina fiber and its preparation method. The method includes the following steps: soaking chitosan fiber in an aqueous solution of aluminum salt to make the chitosan fiber swell, and then the aqueous solution of aluminum salt enters the interior of the swollen chitosan fiber to obtain a fiber template; drying the fiber template, and then heating it to a holding temperature of 950-1250℃ for heat treatment to remove the chitosan fiber and obtain the porous alumina fiber.

Description

Technical Field

[0001] This disclosure belongs to the field of ceramic materials technology and relates to a porous alumina fiber and its preparation method. Background Technology

[0002] Hollow alumina materials, with their excellent mechanical properties and thermal stability, have shown significant application potential in high-temperature insulation and radiative cooling. Hollow alumina materials not only possess the high thermal stability inherent in alumina but also effectively reduce thermal conductivity through their hollow structure, improving insulation performance and meeting the needs of various high-temperature environments and high-reflectivity applications. Currently, research on hollow alumina materials mainly focuses on the preparation of hollow alumina spheres. However, compared with hollow alumina fibers, hollow alumina microspheres have significant shortcomings in mechanical properties, thermal conductivity, and reactivity. Especially in terms of compressive strength, tensile strength, and long-term thermal insulation stability, the microsphere structure is easily affected by external factors (such as stress and thermal shock), exhibiting relatively low mechanical stability and poor long-term thermal insulation stability. These characteristics limit their practical application in high-temperature insulation, especially in scenarios requiring high strength and stable insulation performance.

[0003] In comparison, hollow alumina fibers are considered a more ideal candidate material. However, current technologies for preparing hollow alumina fibers have certain shortcomings. For example, Chinese invention patent CN113737315A proposes the preparation of hollow alumina-based insulating fibers using reed fibers. Although the fibers possess hollow characteristics, the shape and size of the reeds themselves are uncontrollable due to natural growth factors, resulting in uncontrollable dimensions of the resulting hollow alumina fibers. Furthermore, the hollow structure is prone to deformation. These defects not only affect the mechanical properties of the fibers but also lead to instability and uncontrollability in their thermal insulation performance, failing to meet the demands of industrial production for high-performance thermal insulation materials. Therefore, developing a new technology for preparing hollow alumina fibers and improving the thermal insulation performance of the resulting hollow alumina fibers has become a critical challenge that urgently needs to be overcome. Summary of the Invention

[0004] This disclosure provides a porous alumina fiber and its preparation method, which can effectively solve the above-mentioned problems.

[0005] This disclosure is implemented as follows:

[0006] On the one hand, this disclosure provides a method for preparing porous alumina fibers, including the following steps:

[0007] Chitosan fibers are soaked in an aqueous solution of aluminum salts to swell the chitosan fibers. The aqueous solution of aluminum salts then enters the interior of the swollen chitosan fibers to obtain a fiber template.

[0008] The fiber template is dried, and then heated to a holding temperature of 950-1250°C for heat treatment to remove the chitosan fibers and obtain the porous alumina fibers.

[0009] On the other hand, this disclosure provides a porous alumina fiber prepared by the above method.

[0010] The beneficial effects of this disclosure are:

[0011] This disclosure provides a porous alumina fiber and its preparation method. By using chitosan fiber as a template fiber, the chitosan fiber can swell in an aqueous solution of aluminum salt, allowing the aluminum salt to enter its interior and complex with the internal groups to form a gel network. This gel network forms a loose porous structure during the heat treatment stage, which can improve the thermal insulation performance of the prepared porous alumina fiber. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a macroscopic morphology diagram of the porous alumina fibers prepared in Example 1 of this disclosure.

[0014] Figure 2 This is a macroscopic morphology diagram of the hollow alumina fiber prepared in Comparative Example 1 of this disclosure.

[0015] Figure 3 This is a microscopic morphology diagram of the porous alumina fibers prepared in Example 1 of this disclosure.

[0016] Figure 4 This is a microscopic morphology diagram of the hollow alumina fiber prepared in Comparative Example 1 of this disclosure.

[0017] Figure 5 This is an X-ray powder diffraction pattern of the porous alumina fibers prepared in Example 1 of this disclosure. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure. Therefore, the following detailed description of the embodiments of this disclosure provided in the accompanying drawings is not intended to limit the scope of the claimed disclosure, but merely represents selected embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.

[0019] This disclosure provides a method for preparing porous alumina fibers, characterized by comprising the following steps:

[0020] Chitosan fibers are soaked in an aqueous solution of aluminum salts to swell the chitosan fibers. The aqueous solution of aluminum salts then enters the interior of the swollen chitosan fibers to obtain a fiber template.

[0021] The fiber template is dried, and then heated to a holding temperature of 950-1250°C for heat treatment to remove the chitosan fibers and obtain the porous alumina fibers.

[0022] In some embodiments, the aluminum salt is aluminum nitrate nonahydrate or anhydrous aluminum chloride.

[0023] The aluminum salt dissolves in an aqueous solution to form hydrated aluminum oxide. For example, aluminum nitrate nonahydrate is hydrated as [Al(H₂O)₆] in aqueous solution. 3+ Primarily, due to electrostatic adsorption and hydrogen bonding, an amorphous Al(OH)3 / AlOOH layer of 50-300nm will be deposited on the fiber surface.

[0024] In some embodiments, the aluminum salt is aluminum nitrate nonahydrate.

[0025] Fibers soaked in anhydrous aluminum chloride solution will produce hypochlorous acid when heated, which is highly corrosive to heat treatment equipment such as ovens and furnaces. However, using aluminum nitrate nonahydrate does not have this problem and is more in line with the requirements of green production.

[0026] In some embodiments, the mass fraction of aluminum nitrate nonahydrate in the aqueous solution is 5 wt.%-50 wt.%; and the mass fraction of anhydrous aluminum chloride in the aqueous solution is 5 wt.%-25 wt.%. Using a suitable mass fraction of aluminum salt ensures the porous structure morphology of the porous alumina fibers obtained in subsequent heat treatment. If the mass fraction of aluminum salt is too low, the Al in the solution will be insufficient. 3+ Low concentrations prolong the time it takes for the chitosan fibers to penetrate the interior, resulting in low alumina fiber yields. Furthermore, prolonged immersion in the aluminum salt solution can damage the chitosan fiber structure, preventing the formation of a complete gel network and leading to poor porous structure morphology. Conversely, if the aluminum salt mass fraction is too high, the H₂ generated by the ionization of the aluminum salt will... + As the concentration increases, the pH of the solution decreases. Due to the increased solubility of chitosan fibers in acidic solutions, their structure is also destroyed, rendering them unable to function as templates.

[0027] In some embodiments, the mass fraction of aluminum nitrate nonahydrate in the aqueous solution is 15 wt.%-40 wt.%.

[0028] In some embodiments, the mass fraction of aluminum nitrate nonahydrate in the aqueous solution is 25 wt.%-35 wt.%.

[0029] In some embodiments, the mass fraction of anhydrous aluminum chloride in the aqueous solution of the anhydrous aluminum chloride is 5 wt.%-20 wt.%.

[0030] In some embodiments, the mass fraction of anhydrous aluminum chloride in the aqueous solution of the anhydrous aluminum chloride is 5 wt.%-15 wt.%.

[0031] In some embodiments, the mass ratio of the chitosan fiber to the aluminum salt is 1:1-20. This mass ratio is set to strike a balance between “sufficiently loaded aluminum precursor on the fiber” and “solution economy”.

[0032] In some embodiments, the mass ratio of the chitosan fiber to the aluminum salt is 1:6-20.

[0033] In some embodiments, the aqueous solution of the aluminum salt has a pH of 1.4-3. The aluminum salt ionizes in water to form an acidic solution, but an excessively high mass fraction of the aluminum salt can result in an excessively low pH.

[0034] In some embodiments, the soaking time is 30-120 min.

[0035] When chitosan fibers are immersed in an Al-containing 3+In aqueous solutions of aluminum salts, the abundant amino and hydroxyl groups on the fiber surface can react with Al. 3+ A coordination complexation reaction occurs, forming a stable organic-inorganic complex layer at the interface. This layer initially acts as a "diffusion barrier," inhibiting the diffusion of Al. 3+ Penetration into the fiber interior, and Al 3+ The slow diffusion rate results in a relatively dense layer structure, leading to a more complete and dense shell morphology during subsequent drying and heat treatment. Simultaneously, chitosan fibers exhibit a significant swelling effect in acidic aqueous solutions of aluminum salts. The protonated amino groups increase the hydrophilicity within the fibers, allowing partial penetration of the solution into the fiber interior. During this process, Al... 3+ The weak coordination between the fiber and chitosan macromolecules, along with the phase separation induced by local dehydration, results in the formation of a non-uniform gel network within the fiber.

[0036] Through the soaking stage, intermediates with different structures of aluminum salts and chitosan groups are formed on the outer surface and inside of chitosan fibers.

[0037] During the drying process, the surface of the fiber template loses water first, and the complex layer cross-links and densifies. Inside, the water vapor and decomposition gases generated during the drying of the gel network are blocked by the surface complex layer and cannot escape smoothly, resulting in increased internal pressure and the formation of pores or honeycomb structures in some areas inside the fiber template.

[0038] In some implementations, the drying temperature is 60-70°C.

[0039] In some implementations, the drying time is 60-90 min.

[0040] In some embodiments, heat treatment is performed at a holding temperature of 950-1250°C, including a holding temperature of 950-1050°C.

[0041] In some embodiments, heat treatment is performed at a holding temperature of 950-1250°C, including a holding temperature of 1050-1250°C.

[0042] When heat treatment is performed at a holding temperature of 950-1050℃, γ-Al2O3 transforms into an intermediate state of δ-Al2O3 / θ-Al2O3, with the θ phase dominating. This θ phase exhibits higher thermal stability compared to the γ phase. If the holding temperature is further increased to 1050-1250℃, the transformation to the thermodynamically stable α-Al2O3 occurs through a nucleation-growth mechanism. This process not only improves the overall thermal stability of the material but also significantly optimizes its thermal insulation performance for the following reasons: First, the more regular crystal structure of α-Al2O3 effectively reduces the propagation of lattice vibrations. Since heat conduction primarily depends on lattice vibrations, a regular crystal structure significantly reduces the material's thermal conductivity, thereby improving thermal insulation performance. Second, at high temperatures, the pores in the porous structure become further stabilized, increasing the crystallinity of the pore walls and further reducing the heat conduction path, thus enhancing the thermal insulation effect. Third, the high crystallinity of α-Al₂O₃ reduces internal defects and impurities. These defects and impurities can become heat conduction channels at high temperatures, leading to increased heat conduction efficiency. Through the phase transformation process, internal defects and impurities are effectively reduced, thereby further lowering heat conduction efficiency and improving thermal insulation performance.

[0043] In some implementations, the heating rate is 5-10°C / min.

[0044] In some embodiments, heat treatment is performed in an oxygen atmosphere.

[0045] In some implementations, the temperature is raised to 950-1250°C and held for 60-120 minutes for heat treatment.

[0046] Chitosan in the fiber template begins to thermally decompose at around 300℃, with its main chain (COC, CN bonds) gradually breaking down and the chitosan being gradually oxidized. The intermediates produced during the soaking stage transform into an alumina / aluminum hydroxide transition state structure. The dense shell structure inherits the outer surface morphology of the template fiber.

[0047] Furthermore, when the temperature is raised to 600℃-800℃, due to the dense distribution of high-energy functional groups (-OH / -NH2) in the chitosan backbone and the low energy barrier of the glycosidic bond, chitosan undergoes a violent secondary decomposition at this stage. The decomposition is characterized by exothermic reaction, releasing a large amount of gases such as CO2, H2O, and NH3 instantaneously. The local temperature rise can reach tens of degrees Celsius. However, due to the outer shell layer of the template fiber, the alumina particles inside the shell layer are "blown away" by the gas flow. The loose and disordered porous structure formed during drying further forms interconnected pores, thus transforming into a porous structure region composed of a honeycomb-like structure.

[0048] Because the porous structure region has open channels, trace amounts of SiO(g) or SiO2 particles that may come from the crucible or chitosan fiber ash will be carried away by the airflow and cannot be deposited inside the prepared porous alumina fiber.

[0049] The porous structure of the porous region provides a “compressible space” that ensures that the lattice shrinkage of the porous alumina fiber during the transformation to the α phase is mainly absorbed by the pores, without having to release the strain through macroscopic size reduction, thereby avoiding cracks and maintaining structural integrity.

[0050] The heat preservation stage can further densify and homogenize the porous alumina fibers and the stress generated during the α-phase transformation.

[0051] In some embodiments, the diameter of the template fiber is 1-100 µm.

[0052] The porous alumina fiber provided in this embodiment exhibits a "two-layer gradient structure," consisting of a porous region with a loose porous structure and a relatively dense surface layer. The porous region is a honeycomb-like porous structure, while the surface layer is a relatively dense shell. In contrast, traditional hollow alumina fibers are thin-walled hollow structures, possessing only a thin-walled surface layer while remaining hollow internally, lacking the porous region found in the porous alumina fiber. Therefore, the porous alumina fiber provides a hollow structure distinct from traditional thin-walled hollow structures. This porous alumina fiber is a novel type of hollow alumina fiber.

[0053] First, thin-walled hollow structures are prone to deformation due to the lack of internal support, making it difficult to maintain the same external surface morphology as their template, leading to structural collapse. In contrast, the porous structure of the porous alumina fiber determines that its mechanical strength is much higher than that of the thin-walled hollow alumina fiber. Based on the density of its surface shell and the supporting effect of its internal porous structure, it has better structural stability and a more fibrous morphology.

[0054] Secondly, traditional hollow alumina fibers employ a thin-walled, hollow structure. This structure lacks internal support and is prone to deformation or collapse under external forces or thermal stress, thereby compromising the integrity of the insulation layer and reducing its insulation effect. Furthermore, the thin-walled structure has relatively high thermal conductivity, making it difficult to effectively block heat conduction. In contrast, the porous alumina fiber's porous structure contains numerous micropores filled with air or other gases, whose thermal conductivity is far lower than that of solid materials. The porous structure of the porous regions effectively hinders heat conduction, significantly reducing heat transfer efficiency and thus improving insulation performance. Its dense surface structure not only provides good mechanical strength and structural stability but also effectively prevents rapid heat transfer through the fiber surface, further enhancing the insulation effect. The synergistic effect of the dense surface layer and the porous regions allows the fiber to achieve excellent insulation performance while maintaining high strength.

[0055] Furthermore, existing technologies using biomass fibers as templates result in hollow alumina fibers that only inherit the morphology of natural fibers. The uniformity and stability of the diameter and length of natural fibers are limited by the raw materials and difficult to precisely control. This leads to inconsistent thermal insulation performance across different batches and locations, failing to meet the stability and reliability requirements for thermal insulation in industrial applications. In contrast, the porous alumina fibers used are industrially produced fibers. This template can be freely adjusted according to needs, allowing for the regulation of parameters such as the overall size and surface wall thickness of the product, resulting in a more uniform and stable product. The preparation method offers higher repeatability, lower cost, and higher production volume. This precise control capability gives porous alumina fibers a significant advantage in thermal insulation performance, enabling the optimization of fiber size and structure according to different application scenarios, further enhancing the thermal insulation effect. Due to the industrial production characteristics of chitosan fibers, the resulting porous alumina fibers exhibit high uniformity and stability in size and structure. This uniformity ensures consistent thermal insulation performance across different batches and locations, improving product reliability and repeatability, and meeting the stringent requirements for thermal insulation materials in industrial applications.

[0056] The preparation method described above provides a way to prepare porous alumina fibers based on chitosan fiber templates, which can prepare alumina fibers with porous structures under low-cost and environmentally friendly conditions. The prepared porous alumina fibers have excellent pore distribution, structural stability and thermal insulation performance, and the method has high repeatability and controllability, filling the gap in industrialized preparation technology of porous alumina fibers and solving the problems of high energy consumption, complex processes and unstable material properties.

[0057] The preparation method described above allows for precise control of the wall thickness, porosity, crystal phase, and surface characteristics of the porous alumina fibers by adjusting the mass fraction of aluminum salt in the aqueous solution, the soaking time, and the heat treatment temperature. This further enhances the performance of the porous alumina fibers, enabling them to meet the specific needs of various industrial fields. For example, in high-temperature insulation, the pore structure of the porous region can be optimized to improve insulation performance; in catalytic applications, the specific surface area can be adjusted to enhance catalytic activity; and in filtration and adsorption applications, the pore distribution can be adjusted to optimize adsorption performance.

[0058] This disclosure provides a porous alumina fiber, prepared using the method described in any of the above embodiments.

[0059] The porous alumina fibers, based on their dense surface structure, retain the high reflectivity of alumina materials, making them applicable in the field of radiative cooling. Furthermore, the porous structure of the porous regions of these alumina fibers provides a high specific surface area, resulting in a rich distribution of active sites, enabling their application in wastewater purification, impurity adsorption, biocatalysis, and electrochemical catalysis.

[0060] The porous structure of the porous alumina fibers helps improve the toughness of the material. As a hollow structure, it effectively reduces the density of the alumina material and increases its hollow strength. Compared to traditional solid alumina fibers, the porous alumina fibers significantly reduce density while maintaining high strength, making them an ideal reinforcing phase for lightweight, high-performance composite materials. Furthermore, the porous structure maintains stable mechanical properties even at high temperatures, making it suitable for reinforcement applications in aerospace, automotive manufacturing, and other high-temperature structural components.

[0061] The porous alumina fibers, prepared at relatively low sintering temperatures (950-1050℃), exhibit a high specific surface area and abundant pore structure, making them promising for applications in catalyst supports, filter materials, and adsorbents. The porous structure of its porous regions effectively improves the distribution of active sites on the catalyst, enhancing catalytic reaction efficiency, while also providing excellent filtration capabilities in high-temperature filtration and gas purification processes.

[0062] Information on the raw materials and instruments used in the following embodiments is shown in Table 1.

[0063] Table 1 Information on raw materials and instruments

[0064]

[0065] Example 1

[0066] This disclosure provides a method for preparing alumina fibers with a porous structure based on chitosan fiber templates, specifically including the following steps:

[0067] Step 1: Mix 30 g of anhydrous aluminum chloride (purity 99%) and 270 g of deionized water evenly to prepare an aluminum chloride solution with a mass fraction of 10 wt.%.

[0068] Step 2: Immerse 5 g of chitosan fiber (diameter: 10 μm) in the aluminum chloride solution prepared in step 1 for 120 min.

[0069] Step 3: Squeeze out excess impregnation liquid from the soaked fibers and place them in an electric constant temperature drying oven at 60°C for 60 minutes to dry.

[0070] Step 4: Place the dried fibers into a muffle furnace and heat them in an oxygen atmosphere. The heating process involves raising the temperature from room temperature to 1200°C at a rate of 5°C per minute and holding it at that temperature for 120 minutes. Then, cool the fibers to room temperature with the furnace to remove the chitosan fibers and obtain porous alumina fibers.

[0071] The macroscopic morphology of the prepared porous alumina fibers is as follows: Figure 1 As shown.

[0072] The thermal conductivity of the porous alumina fibers was tested using a flash laser thermal conductivity meter.

[0073] The porous alumina fibers were tested and found to have a thermal conductivity of 0.363 W / (m·K), exhibiting excellent thermal insulation performance.

[0074] Example 2

[0075] This embodiment provides a method for preparing alumina fibers with a porous structure based on chitosan fiber templates, specifically including the following steps:

[0076] Step 1: Mix 90 g of aluminum nitrate nonahydrate (99% purity) and 210 g of deionized water evenly to prepare an aluminum nitrate solution with a mass fraction of 30 wt.%.

[0077] Step 2: Immerse 10 g of chitosan fiber (diameter: 10 μm) in the aluminum nitrate solution prepared in step 1 for 30 min.

[0078] Step 3: Squeeze out excess impregnation liquid from the soaked fibers and place them in an electric constant temperature drying oven at 70°C for 90 minutes to dry.

[0079] Step 4: Place the dried fibers into a muffle furnace and heat them in an oxygen atmosphere. The heating process involves raising the temperature from room temperature to 1000°C per minute and holding it at that temperature for 60 minutes. Then, cool the fibers to room temperature with the furnace to remove the chitosan fibers and obtain porous alumina fibers.

[0080] Example 3

[0081] This embodiment provides a method for preparing alumina fibers with a porous structure based on chitosan fiber templates, specifically including the following steps:

[0082] Step 1: Mix 60 g of aluminum nitrate nonahydrate (99% purity) and 240 g of deionized water evenly to prepare an aluminum nitrate solution with a mass fraction of 20 wt.%.

[0083] Step 2: Immerse 3 g of chitosan fiber (diameter: 10 μm) in the aluminum chloride solution prepared in step 1 for 120 min.

[0084] Step 3: Squeeze out excess impregnation liquid from the soaked fibers and place them in an electric constant temperature drying oven at 60°C for 60 minutes to dry.

[0085] Step 4: Place the dried fibers into a muffle furnace and heat them in an oxygen atmosphere. The heating process involves raising the temperature from room temperature to 1250°C at a rate of 5°C per minute and holding it at that temperature for 100 minutes. Then, cool the fibers to room temperature with the furnace to remove the chitosan fibers and obtain porous alumina fibers.

[0086] Comparative Example 1

[0087] This comparative example provides a method for preparing hollow alumina fibers based on a degreased cotton fiber template, specifically including the following steps:

[0088] Step 1: Mix 30 g of anhydrous aluminum chloride (purity 99%) and 270 g of deionized water evenly to prepare an aluminum chloride solution with a mass fraction of 10 wt.%.

[0089] Step 2: Immerse 5 g of degreased cotton fibers (diameter: 10 μm) in the aluminum chloride solution prepared in step 1 for 120 min.

[0090] Step 3: Squeeze out excess impregnation liquid from the soaked fibers and place them in an electric constant temperature drying oven at 60°C for 60 minutes to dry.

[0091] Step 4: Place the dried fibers into a muffle furnace and heat them in an oxygen atmosphere. The heating process involves raising the temperature from room temperature to 1200°C at a rate of 5°C per minute and holding it at that temperature for 120 minutes. Then, cool the fibers in the furnace to room temperature to remove the degreased cotton fibers and obtain hollow alumina fibers.

[0092] The macroscopic morphology of the prepared hollow alumina fibers is as follows: Figure 2 As shown.

[0093] The porous alumina fibers prepared in Example 1 and the hollow alumina fibers prepared in Comparative Example 1 were observed using SEM.

[0094] from Figure 3 As can be seen, the porous alumina fiber prepared in Example 1 consists of a surface layer and a porous region inside. The porous region is a porous structure region composed of a honeycomb-like structure, while the surface layer is a dense shell layer.

[0095] from Figure 4As can be seen, the hollow alumina fibers prepared in Comparative Example 1 have a thin-walled hollow structure and do not have porous regions. This is mainly because the prerequisite for a porous structure is the swelling of chitosan fibers in an aluminum salt aqueous solution. However, during the process of soaking the degreased fiber cotton template in aluminum salt, only aluminum salt coating can be achieved. Therefore, after the degreased fiber cotton template is removed, only a hollow structure can be obtained.

[0096] The porous alumina fibers prepared in Example 1 were subjected to X-ray powder diffraction analysis.

[0097] from Figure 5 It can be seen that the porous alumina fibers prepared in Example 1 have obvious α-Al2O3 phase diffraction peaks.

[0098] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A method for producing porous alumina fibers, characterized by, The method comprises the following steps: immersing chitosan fibers in an aqueous solution of an aluminum salt, so that the chitosan fibers are swelled, and the aqueous solution of the aluminum salt enters the inside of the swelled chitosan fibers to obtain a fiber template, wherein the pH value of the aqueous solution of the aluminum salt is 1.4-3; drying the fiber template, and then heating to a holding temperature of 950-1250℃ for heat treatment to remove the chitosan fibers and obtain the porous alumina fibers, which are composed of a surface layer and a porous region inside the surface layer, wherein the porous region is a porous structure region composed of a honeycomb-like structure, and the surface layer is a dense shell layer.

2. The method of claim 1, wherein, The aluminum salt is aluminum nitrate nonahydrate or anhydrous aluminum chloride.

3. The method of claim 2, wherein, The mass fraction of the aluminum nitrate nonahydrate in the aqueous solution of the aluminum nitrate nonahydrate is 5 wt.%-50 wt.%, and the mass fraction of the anhydrous aluminum chloride in the aqueous solution of the anhydrous aluminum chloride is 5 wt.%-25 wt.%.

4. The method of claim 1, wherein, The mass ratio of the chitosan fibers to the aluminum salt is 1:1-20.

5. The method of claim 1, wherein, The immersion time is 30-120 min.

6. The method of claim 1, wherein, The holding temperature is 1050-1250℃.

7. The method of claim 1, wherein, The diameter of the fiber template is 1-100 µm.

8. A porous alumina fiber, characterized by, The porous alumina fibers are prepared by the method of any one of claims 1-7.

Images