Activated aluminum oxide modified activated carbon fiber felt as well as preparation method and application thereof

Abstract

The invention discloses an activated aluminum oxide modified activated carbon fiber felt and a preparation method and application thereof, and belongs to the technical field of adsorption materials, and the preparation method comprises the following steps: S1, preparing an activated activated carbon fiber felt; s2, adding urea and aluminum chloride hexahydrate into deionized water, stirring and dissolving, then adding the activated activated carbon fiber felt, stirring and mixing uniformly, transferring into a reaction kettle for reaction, cooling, taking out, washing and drying to obtain an aluminum oxide precursor modified activated carbon fiber felt; s3, transferring the alumina precursor modified activated carbon fiber felt into a tubular furnace, performing annealing treatment in a nitrogen atmosphere, and cooling to room temperature to obtain an activated alumina modified activated carbon fiber felt; the preparation method is simple and easy to implement, the used materials are wide in source and low in cost, and the prepared activated aluminum oxide modified activated carbon fiber felt shows excellent fluorine ion removal rate and removal efficiency on a water body containing low-concentration fluorine ions and has wide application prospects.

Description

Technical Field

[0001] This invention belongs to the field of adsorption materials technology, specifically relating to an activated alumina-modified activated carbon fiber felt, its preparation method, and its application. Background Technology

[0002] With the booming development of industries such as photovoltaics and semiconductors, fluoride pollution has become increasingly serious, especially as fluoride ions enter aquatic ecosystems, gradually becoming a major problem of surface water pollution. Even relatively low concentrations of fluoride ions in water can seriously affect human health. Studies have shown that if an adult's daily fluoride intake exceeds 3.4 mg, it can cause fluorosis, leading to diseases such as dental fluorosis and skeletal fluorosis. In severe cases, it can even cause cancer and paralysis, greatly endangering public health. Therefore, the "GB 3838-2002 Surface Water Environmental Quality Standard" requires that the fluoride ion concentration in Class I-III water be ≤1 mg / L, and the fluoride ion concentration in Class IV-V water be ≤1.5 mg / L.

[0003] In recent years, many new methods for removing fluoride ions from water have emerged, such as chemical precipitation, coagulation sedimentation, and membrane separation. However, most of these methods are only suitable for water with high fluoride concentrations and have not been effectively applied in real-world situations. Compared to these methods, adsorption has the advantages of not producing other byproducts and providing stable performance during fluoride ion removal. Activated carbon fiber felt is one of the most common adsorbents, possessing high adsorption capacity and wide availability, and is currently widely used in drinking water filter cartridges. However, ordinary activated carbon fiber felt lacks specificity for fluoride ion adsorption, resulting in low removal rates and efficiencies in water containing low concentrations of fluoride ions. Therefore, developing an adsorbent material based on activated carbon fiber felt that maintains low cost while achieving superior removal performance for low concentrations of fluoride ions in water is a technical problem that needs to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide an activated alumina-modified activated carbon fiber felt, its preparation method, and its application, so as to solve the problems in the background art.

[0005] The objective of this invention can be achieved through the following technical solutions: A method for preparing activated carbon fiber felt modified with activated alumina includes the following steps: S1. Add the pretreated activated carbon fiber felt to sodium hydroxide solution and ultrasonically disperse for 3-5 minutes. Then, transfer the mixture to a hydrothermal reactor and react at 110-130℃ for 12 hours. After cooling to room temperature, remove the reactor and wash it 3-5 times with deionized water to obtain activated activated carbon fiber felt. Modifying activated carbon fiber felt with sodium hydroxide solution is beneficial to the subsequent adhesion of aluminum salts on the activated carbon fiber felt, thereby obtaining a higher aluminum salt loading. S2. Add urea and aluminum chloride hexahydrate to deionized water and stir to dissolve. Then add activated carbon fiber felt and stir for 10 min. Transfer to a reaction vessel and keep warm at 110-130℃ for 12 h. After cooling to room temperature, take it out, wash it with deionized water 3-5 times, and dry it to obtain alumina precursor modified activated carbon fiber felt. S3. The alumina precursor-modified activated carbon fiber felt is transferred into a tube furnace, and then nitrogen is introduced to purge the air while maintaining a nitrogen flow rate of 100 mL / min. Under a nitrogen atmosphere, the problem of excessive oxidation of the activated carbon fiber felt leading to excessively large pore size can be avoided. The temperature is then raised to 400-500℃ and annealed at a constant temperature for 2 hours. After cooling to room temperature, the activated alumina-modified activated carbon fiber felt is obtained.

[0006] This invention modifies alumina, which is originally prone to agglomeration and difficult to fully exert its effect, onto activated carbon fiber felt with a large specific surface area. This allows the alumina to be uniformly dispersed and loaded in the pores of the activated carbon fiber felt, thus fully exerting the adsorption efficiency of alumina for fluoride ions. After annealing, the bound water can be completely removed, generating a gas pore-forming effect, which greatly improves the treatment efficiency for fluoride ions.

[0007] Furthermore, the pretreatment consists of cutting, washing, and drying steps, specifically including: cutting the activated carbon fiber felt into small pieces, then washing them sequentially with ethanol and deionized water, and then drying them in an oven at 100-110°C until constant weight.

[0008] Furthermore, the ratio of the pretreated activated carbon fiber felt to sodium hydroxide solution is 1g:50-100mL; the concentration of sodium hydroxide solution is 1mol / L.

[0009] Furthermore, the ratio of urea, aluminum chloride hexahydrate, deionized water, and activated carbon fiber felt is 7g:6g:100mL:1g. This invention selects aluminum salts with chloride ions as the anion, as chloride ions have less interference with the adsorption of fluoride ions compared to carbonate and sulfate ions. Although nitrate ions have the least interference with the adsorption of fluoride ions, they are prone to high-temperature decomposition during subsequent annealing, rapidly generating large amounts of nitrogen oxides and oxygen, thus affecting the nitrogen atmosphere. This poses a safety hazard of localized oxygen-rich explosions at high temperatures. Additionally, because nitrogen oxides are denser than air, they tend to accumulate near the exhaust gas outlet of the boiler, potentially causing poisoning. Therefore, this invention preferentially uses aluminum chloride hexahydrate as the aluminum salt.

[0010] Furthermore, the heating rate is 5°C / min.

[0011] An activated alumina-modified activated carbon fiber felt is prepared by the above method.

[0012] Application of alumina-modified activated carbon fiber felt in the removal of low concentrations of fluoride ions from water.

[0013] Furthermore, the application of the activated alumina-modified activated carbon fiber felt specifically includes the following steps: The activated carbon fiber felt modified with activated alumina was added to a water sample with a low concentration of fluoride ions at a pH of 6.5-7. The sample was then subjected to full adsorption treatment for 2 hours at room temperature and with stirring at a speed of 150 r / min to obtain the purified water sample.

[0014] Furthermore, the ratio of the amount of the activated alumina-modified activated carbon fiber felt to the low-concentration fluoride ion water sample is 0.2-0.3g:200mL.

[0015] Furthermore, the fluoride ion concentration in the low-concentration fluoride ion water sample is ≤10mg / L.

[0016] Beneficial effects: This invention uses activated carbon fiber felt as a substrate. First, a hydrothermal reaction is carried out using sodium hydroxide solution to obtain activated activated carbon fiber felt. Then, a reaction is carried out in an aqueous solution containing urea and aluminum chloride hexahydrate to obtain amorphous alumina precursor modified activated carbon fiber felt. Finally, annealing is performed under a nitrogen atmosphere to obtain the activated alumina modified activated carbon fiber felt of this invention. The preparation method of this invention is simple and easy to implement. The materials used in the preparation process are widely available and inexpensive, and will not cause further pollution to water bodies, thus having broad application prospects. The activated alumina-modified activated carbon fiber felt prepared by this invention combines the high specific surface area of ​​activated carbon fiber with the selective adsorption capacity of activated alumina for fluoride ions, significantly improving the removal efficiency and adsorption capacity of fluoride ions, and is suitable for the deep treatment of low-concentration fluoride-containing wastewater; the specific advantages are as follows: 1. By uniformly loading alumina precursors onto the surface of activated carbon fiber felt, the specific surface area of ​​activated carbon fiber is increased, which can provide more metal sites for effective adsorption of fluoride ions, and give full play to the adsorption efficiency of activated carbon fiber felt modified with activated alumina for fluoride ions. 2. Annealing effectively alters the crystal structure of alumina, transforming it from an amorphous to an ordered γ-Al2O3 crystal structure. Simultaneously, it removes bound water, reducing pore blockage and further increasing the specific surface area of ​​the activated alumina-modified activated carbon fiber felt. Utilizing the porous structure, it adsorbs fluoride ions in water through van der Waals forces and electrostatic attraction, exhibiting superior adsorption performance. 3. The activated alumina formed by annealing has a large number of hydroxyl groups and a polar surface, which can undergo ion exchange reaction with fluoride ions to form soluble complex ions with strong adsorption capacity. At the same time, the aluminum ions in the activated alumina can form coordinate bonds with fluoride ions to generate stable Al-F coordination compounds, forming a significant strong coordination effect, which stably adsorbs fluoride ions on the surface of activated carbon fiber felt, further fixing the fluoride ions. The above advantages enable the activated alumina-modified activated carbon fiber felt prepared by this invention to not only achieve a removal rate of up to 85% for low-concentration fluoride ions in water, but also to have superior adsorption and removal efficiency, enabling it to adsorb and remove fluoride ions from water in a shorter time. Attached Figure Description

[0017] The invention will now be further described with reference to the accompanying drawings.

[0018] Figure 1 This is a physical image of the activated alumina-modified activated carbon fiber felt prepared in Example 2 of the present invention; Figure 2 This is a scanning electron microscope image of the activated alumina-modified activated carbon fiber felt prepared in Example 2 of the present invention at a resolution of 10 μm. Figure 3 This is a scanning electron microscope image of the activated alumina-modified activated carbon fiber felt prepared in Example 2 of the present invention at a resolution of 2 μm. Figure 4 This is a picture of the actual activated carbon fiber felt in Comparative Example 1; Figure 5 This is a scanning electron microscope image of the activated carbon fiber felt in Comparative Example 1 at a resolution of 10 μm. Figure 6 This is a graph showing the removal rate versus adsorption time of the adsorbent in Example 2 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 This embodiment provides an activated alumina-modified activated carbon fiber felt, which is prepared by the following method: S1. Cut the activated carbon fiber felt into small pieces of 1cm×1cm×0.1cm, then wash them with ethanol and deionized water in sequence, and then dry them in an oven at 100℃ until constant weight; add 1g of the pretreated activated carbon fiber felt to 50mL of 1mol / L sodium hydroxide solution and ultrasonically disperse for 5min, then transfer them together into a hydrothermal reactor and keep them at 110℃ for 12h. After cooling to room temperature, wash them three times with deionized water to obtain activated carbon fiber felt. S2. Add 7g of urea and 6g of aluminum chloride hexahydrate to 100mL of deionized water and stir to dissolve. Then add 1g of activated carbon fiber felt and stir to mix for 10min. Transfer to a reaction vessel and keep warm at 110℃ for 12h. After cooling to room temperature, take it out, wash it 3 times with deionized water, and dry it to obtain alumina precursor modified activated carbon fiber felt. S3. The alumina precursor modified activated carbon fiber felt is transferred into a tube furnace, and then nitrogen is introduced to purge the air while maintaining a nitrogen flow rate of 100 mL / min. The temperature is then increased to 400℃ at a heating rate of 5℃ / min, and the temperature is kept constant for 2 hours. After cooling to room temperature, activated alumina modified activated carbon fiber felt is obtained.

[0021] Example 2 This embodiment provides an activated alumina-modified activated carbon fiber felt, which is prepared by the following method: S1. Cut the activated carbon fiber felt into small pieces of 1cm×1cm×0.1cm, then wash them with ethanol and deionized water in sequence, and then dry them in an oven at 105℃ until constant weight; add 1g of pretreated activated carbon fiber felt to 80mL of 1mol / L sodium hydroxide solution and ultrasonically disperse for 4min, then transfer them together into a hydrothermal reactor and keep them at 120℃ for 12h. After cooling to room temperature, wash them 4 times with deionized water to obtain activated carbon fiber felt. S2. Add 7g of urea and 6g of aluminum chloride hexahydrate to 100mL of deionized water and stir to dissolve. Then add 1g of activated carbon fiber felt and stir to mix for 10min. Transfer to a reaction vessel and keep warm at 120℃ for 12h. After cooling to room temperature, take it out, wash it 4 times with deionized water, and dry it to obtain alumina precursor modified activated carbon fiber felt. S3. The alumina precursor-modified activated carbon fiber felt is transferred into a tube furnace, and then nitrogen is introduced to purge the air while maintaining a nitrogen flow rate of 100 mL / min. The temperature is then increased to 450°C at a heating rate of 5°C / min, and the temperature is kept constant for 2 hours. After cooling to room temperature, the activated alumina-modified activated carbon fiber felt is obtained, denoted as Al2O3@ACFF.

[0022] Depend on Figure 1 It is evident that the activated carbon fiber felt modified with activated alumina contains a large amount of activated alumina. Depend on Figure 2 It can be seen that the adsorbent retains the interwoven network structure of the activated carbon fiber felt, with a large number of open pores between the fibers. This network porous structure is a typical feature of activated carbon fibers, providing channels for fluid transport and diffusion, and also providing a substrate with a high specific surface area for the material; the surface of the activated carbon fibers is not smooth, but is uniformly covered with a large number of fluffy materials, indicating that activated alumina has been successfully loaded onto the surface of the activated carbon fibers; Depend on Figure 3 It can be seen that the activated alumina on the surface of activated carbon fiber exists in the form of fine needles (or filaments). These needle-like structures are intertwined and form a dense and rough needle-like layer on the surface of activated carbon fiber. The needle-like alumina is evenly distributed and there is no obvious agglomeration or shedding, indicating that the loading effect is good and the dispersibility and binding force are excellent.

[0023] Example 3 This embodiment provides an activated alumina-modified activated carbon fiber felt, which is prepared by the following method: S1. Cut the activated carbon fiber felt into small pieces of 1cm×1cm×0.1cm, then wash them with ethanol and deionized water in sequence, and then dry them in an oven at 110℃ until constant weight; add 1g of pretreated activated carbon fiber felt to 100mL of 1mol / L sodium hydroxide solution and ultrasonically disperse for 3min, then transfer them together into a hydrothermal reactor and keep them at 130℃ for 12h. After cooling to room temperature, wash them 5 times with deionized water to obtain activated carbon fiber felt. S2. Add 7g of urea and 6g of aluminum chloride hexahydrate to 100mL of deionized water and stir to dissolve. Then add 1g of activated carbon fiber felt and stir for 10min. Transfer to a reaction vessel and keep warm at 130℃ for 12h. After cooling to room temperature, take it out, wash it 5 times with deionized water, and dry it to obtain alumina precursor modified activated carbon fiber felt. S3. The alumina precursor modified activated carbon fiber felt is transferred into a tube furnace, and then nitrogen is introduced to purge the air while maintaining a nitrogen flow rate of 100 mL / min. The temperature is then increased to 500℃ at a heating rate of 5℃ / min, and the temperature is kept constant for annealing for 2 hours. After cooling to room temperature, activated alumina modified activated carbon fiber felt is obtained.

[0024] Application Example 1 0.3g of the activated alumina-modified activated carbon fiber felt (hereinafter referred to as adsorbent in Table 1) prepared in Example 1 was added to 200mL of a low-concentration fluoride ion water sample with pH 6.5. The fluoride ion concentration in the low-concentration fluoride ion water sample was 1mg / L. The water was fully adsorbed for 2h at room temperature and stirring at 150r / min to obtain the purified water sample.

[0025] Application Example 2 0.2g of the activated alumina-modified activated carbon fiber felt prepared in Example 2 was added to 200mL of a low-concentration fluoride ion water sample with a pH of 6.5. The fluoride ion concentration in the low-concentration fluoride ion water sample was 10mg / L. The sample was fully adsorbed for 2h at room temperature and stirring at a speed of 150r / min to obtain the purified water sample.

[0026] Application Example 3 0.2g of the activated alumina-modified activated carbon fiber felt prepared in Example 3 was added to 200mL of a low-concentration fluoride ion water sample with a pH of 7. The fluoride ion concentration in the low-concentration fluoride ion water sample was 5mg / L. The sample was fully adsorbed for 2h at room temperature and stirring at a speed of 150r / min to obtain the purified water sample.

[0027] Comparative Application Example 1 The difference between this comparative application example and application example 2 is that the amount of activated alumina modified activated carbon fiber felt prepared in example 2 is 0.1g, while all other conditions are the same.

[0028] Comparative Application Example 2 The difference between this comparative application example and application example 2 is that the amount of activated alumina modified activated carbon fiber felt prepared in example 2 is 0.4g, while all other conditions are the same.

[0029] Comparative Application Example 3 The difference between this comparative application example and application example 2 is that the pH of the water sample is 5, while all other conditions are the same.

[0030] Comparative Application Example 4 The difference between this comparative application example and application example 2 is that the pH of the water sample is 9, while all other conditions are the same.

[0031] Comparative Application Example 5 The difference between this comparative application example and application example 2 is that the initial fluoride ion concentration in the water sample is 20 mg / L, while all other conditions are the same.

[0032] The purified water samples obtained from Application Examples 1-3 and Comparative Application Examples 1-5 were measured using a PXSJ-216F ion meter. The residual fluoride ion concentration was recorded and the fluoride ion removal rate was calculated. The results are shown in Table 1 below: Table 1 As can be seen from the data in Table 1, the activated alumina-modified activated carbon fiber felt prepared in this invention is suitable for water samples with a concentration ≤10 mg / L when used to adsorb and remove fluoride ions from water. Above this concentration, its removal rate of fluoride ions decreases, indicating that its adsorption capacity is limited. Furthermore, the optimal ratio of adsorbent to water sample is 1-1.5 g / L; exceeding this range also reduces the removal rate of fluoride ions. Meanwhile, pH value is a crucial factor affecting the adsorption effect; the activated alumina-modified activated carbon fiber felt prepared in this invention is only suitable for neutral water bodies, and its effect is poor in acidic or alkaline water bodies.

[0033] Comparative Example 1 This comparative example is an untreated activated carbon fiber felt, denoted as ACFF. Its morphology and microstructure are shown in [reference needed]. Figure 4 and Figure 5 As shown.

[0034] Comparative Example 2 This comparative example is a mixture of commercially available ordinary activated carbon fiber felt and commercially available activated alumina at a mass ratio of 2:1, denoted as ACFF+Al2O3.

[0035] Comparative Example 3 The difference between this comparative example and Example 2 is that step S3 is not performed, and the activated carbon fiber felt modified with alumina precursor is directly used as the final product, denoted as precursor Al2O3@ACFF.

[0036] The adsorbents obtained in Example 2 and Comparative Examples 1-3 were subjected to performance testing. 0.2 mg of adsorbent was added to 200 mL of water samples with pH 6.5 and initial fluoride ion concentrations of 1 mg / L, 5 mg / L, and 10 mg / L, respectively. After sufficient adsorption treatment, the residual fluoride ion concentration in the treated water samples was measured using a PXSJ-216F ion meter to calculate the fluoride ion adsorption removal rate. The adsorption capacity Qe (mg / g) was calculated according to the following formula: Wherein, Co represents the initial concentration of fluoride ions in the solution, mg / L; Ce represents the concentration of fluoride ions at equilibrium, mg / L; V represents the solution volume, L; and M represents the mass of the adsorbent, g. 0.2 g of the adsorbent from Examples 2 and Comparative Examples 1-3 was added to 200 mL of water sample with a pH of 6.5 and a fluoride ion concentration of 10 mg / L. The fluoride ion concentration in the water sample was measured at time points of 10 min, 20 min, 30 min, 60 min, 120 min, 180 min, 240 min, 360 min, and 720 min, and the fluoride ion adsorption removal rate was calculated. The adsorption removal rate versus adsorption time curve was recorded. The test results are shown in Table 2 and... Figure 6 As shown: Table 2 As can be seen from the data in Table 2, the activated alumina-modified activated carbon fiber felt prepared in this invention has superior adsorption performance for fluoride ions. In Comparative Example 1, the untreated activated carbon fiber felt showed poor adsorption and removal of fluoride ions, with the removal rate decreasing as the fluoride ion concentration increased. In Comparative Example 2, the simple mixture of activated carbon fiber felt and activated alumina also exhibited poor adsorption performance for fluoride ions, as both could not achieve optimal results due to issues such as dispersibility. In Comparative Example 3, the activated carbon fiber felt modified with an unannealed alumina precursor showed improved adsorption performance, but still lagged significantly behind the invention. The activated alumina-modified activated carbon fiber felt prepared in this invention maintains a stable and high removal level even for low concentrations of fluoride ions.

[0037] Depend on Figure 6 It can be seen that the curves of the four adsorbents in Example 2 and Comparative Examples 1-3 all show a trend of "fast at first and slow later", but the levels are significantly different. The removal rate of fluoride ions in Comparative Example 1 remains at a low level, only about 1.8% at 720 min; the removal rate of Comparative Example 2 improves in the first 60 min (to 5.2%), and then slowly increases to 10.4% at 720 min; the overall removal rate of Comparative Example 3 is improved, reaching 8.4% at 60 min and 15.6% at 720 min; while Example 2 performs the best, with a significant improvement in the removal rate in the first 60 min, reaching 68.8% at 60 min, and basically reaching quasi-equilibrium at 120 min, and then stabilizing at about 85%, showing higher adsorption efficiency.

[0038] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0039] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for producing an activated alumina-modified activated carbon fiber felt, characterized by, The preparation method comprises the following steps: S1, the pretreated activated carbon fiber felt is added into a sodium hydroxide solution and uniformly dispersed by ultrasonic, and then the mixture is transferred into a hydrothermal reaction kettle, and reacted at 110-130℃ for 12h, and then cooled to room temperature, washed with deionized water, and an activated activated carbon fiber felt is obtained; S2, urea and aluminum chloride hexahydrate are added into deionized water and stirred to dissolve, and then the activated activated carbon fiber felt is added and stirred to mix uniformly, and then transferred into a reaction kettle, and reacted at 110-130℃ for 12h, and then cooled to room temperature, taken out, washed with deionized water, and dried, and an alumina precursor modified activated carbon fiber felt is obtained; S3, the alumina precursor modified activated carbon fiber felt is transferred into a tube furnace, and then nitrogen is introduced to remove air and keep the nitrogen flow at 100mL / min, and then heated to 400-500℃, and annealed for 2h, and then cooled to room temperature, and an active alumina modified activated carbon fiber felt is obtained.

2. The method for preparing activated alumina-modified activated carbon fiber felt according to claim 1, characterized in that, The pretreatment is a cutting, washing and drying step, specifically comprising: cutting the activated carbon fiber felt into small pieces, and then washing with ethanol and deionized water in sequence, and then drying in an oven at 100-110℃ to constant weight.

3. The method for preparing activated alumina-modified activated carbon fiber felt according to claim 1, characterized in that, The use amount ratio of the pretreated activated carbon fiber felt to the sodium hydroxide solution is 1g:50-100mL; and the concentration of the sodium hydroxide solution is 1mol / L.

4. The method for preparing activated alumina-modified activated carbon fiber felt according to claim 1, characterized in that, The use amount ratio of the urea, aluminum chloride hexahydrate, deionized water and activated activated carbon fiber felt is 7g:6g:100mL:1g.

5. The method for preparing activated alumina-modified activated carbon fiber felt according to claim 1, characterized in that, The heating rate is 5℃ / min.

6. An activated alumina-modified activated carbon fiber felt, characterized by, The active alumina modified activated carbon fiber felt is prepared by the preparation method according to any one of claims 1-5.

7. The application of the active alumina modified activated carbon fiber felt according to claim 6 in removing low-concentration fluoride ions in water.

8. Use of an activated alumina-modified activated carbon fiber felt according to claim 7, characterized in that, The preparation method comprises the following steps: The active alumina modified activated carbon fiber felt is added into a low-concentration fluoride ion water sample with pH of 6.5-7, and under stirring at room temperature, the sample is fully adsorbed and treated for 2h, and a purified water sample is obtained.

9. Use of an activated alumina-modified activated carbon fiber felt according to claim 8, characterized in that, The use amount ratio of the active alumina modified activated carbon fiber felt to the low-concentration fluoride ion water sample is 0.2-0.3g:200mL.

10. The use of the activated alumina-modified activated carbon fiber felt according to claim 8, characterized by, The fluoride ion concentration in the low-concentration fluoride ion water sample is ≤10mg / L.

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