Activated carbon fiber and composite modification preparation method thereof

Abstract

The invention discloses an activated carbon fiber and a composite modification preparation method thereof, and relates to the technical field of activated carbon fibers. The composite modification preparation method of the activated carbon fiber comprises the following steps: S1, cleaning and drying activated carbon fiber cloth; s2, adding the activated carbon fiber cloth treated in the step S1 into a soaking solution for hydrothermal modification treatment to obtain modified activated carbon fibers; wherein the soaking solution is one of a phosphoric acid solution, a diammonium hydrogen phosphate solution and a mixed solution of the phosphoric acid solution and the diammonium hydrogen phosphate solution. According to the composite modification method, the ACF-SO2 adsorption capacity can be obviously improved, the optimal modification effect is achieved through composite modification under the condition that 6% of phosphoric acid and 4% of diammonium hydrogen phosphate are subjected to hydrothermal treatment for 1 h at the temperature of 120 DEG C, the ACF-SO2 adsorption capacity can reach 19.275 mg / g and is improved by 154.29% compared with an unmodified original sheet, the modification effect is quite remarkable, time and cost can be better saved, and energy consumption is lower.

Description

Technical Field

[0001] This invention relates to the field of activated carbon fiber technology, specifically to an activated carbon fiber and a method for preparing its composite modification. Background Technology

[0002] Activated carbon fiber, a novel fibrous activated carbon material, is typically obtained by activating carbon fiber materials. Compared to traditional activated carbon, activated carbon fiber possesses advantages such as stable chemical properties, well-developed pores, large adsorption capacity, fast adsorption rate, large specific surface area, and good regeneration performance. Therefore, it has been widely researched and applied in the field of SO2 waste gas treatment.

[0003] To increase the adsorption capacity of adsorbates and expand the application prospects of activated carbon fibers, researchers have carried out a series of modification treatments on activated carbon fibers. However, in existing technologies, researchers use strong acid or strong alkali solutions for immersion treatment, resulting in relatively violent reaction conditions; on the other hand, they use metal ion loading modification treatment, which can easily cause environmental pollution. Summary of the Invention

[0004] The purpose of this invention is to at least solve one of the technical problems existing in the prior art, and to provide an activated carbon fiber and a method for preparing the composite modification thereof.

[0005] Activated carbon fiber (ACF) typically has a fiber diameter between 5 and 50 μm, exhibiting a highly fibrous structure. The pore structure of activated carbon fiber is predominantly micropores, but also includes mesopores and macropores. Micropores are the main contributor to the adsorption performance of activated carbon fiber, with pore sizes typically less than 2 nm, providing a large specific surface area for adsorption. Mesopores and macropores facilitate the diffusion and transport of adsorbates, increasing the adsorption rate. Simultaneously, the surface of activated carbon fiber is rich in functional groups, such as hydroxyl, carboxyl, and ester groups. The presence of these functional groups not only enhances the hydrophilicity of activated carbon fiber but also provides active sites for adsorption reactions. Through certain modification methods, the microporous structure, specific surface area, and active functional groups on the fiber surface of carbon fibers can be further optimized, thereby further improving the material's adsorption capacity for pollutant gases such as SO2. Immersion in acidic solutions can induce acid oxidation of ACF, increasing the number of oxygen-containing functional groups on the material surface. The acidic solution also etches the surface, increasing the roughness of the carbon fiber surface, thus increasing the specific surface area and active sites, ultimately improving the material's adsorption performance. Immersion in ammonium salts increases the number of nitrogen-containing functional groups on the ACF surface. Both of these reactions effectively enhance the material's adsorption performance. Traditional methods typically employ multi-step sequential immersion treatments of ACF, which are time-consuming. In this study, ACF was immersed in a buffer solution composed of phosphoric acid and diammonium hydrogen phosphate at different concentrations, followed by a one-step composite modification in a reactor at 120°C. This reaction allows the carbon fiber to undergo simultaneous acid oxidation modification with phosphoric acid and nitrogen modification with diammonium hydrogen phosphate under high-temperature hydrothermal conditions. Through this one-step reaction, significant etching occurs on the surface of the carbon fiber material, and the number of oxygen- and nitrogen-containing functional groups on the surface further increases, significantly improving the adsorption performance of the ACF material. The best modification effect of ACF was observed under hydrothermal conditions of 1 hour at 120℃ with a mixture of 4% diammonium hydrogen phosphate and 6% phosphoric acid. The adsorption capacity of ACF-SO2 reached 19.275 mg / g, and the adsorption rate was 154.29% higher than that of the unmodified original tablet. This method uses a buffer solution composed of phosphoric acid and diammonium hydrogen phosphate, which can stabilize the hydrothermal environment in the hydrothermal reaction system and achieve significant modification effect.

[0006] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing composite modified activated carbon fibers, comprising the following steps: S1. Clean and dry the activated carbon fiber cloth; S2. The activated carbon fiber cloth treated in S1 is added to the soaking solution for hydrothermal modification treatment to obtain modified activated carbon fiber; wherein, the soaking solution is one of phosphoric acid solution, diammonium hydrogen phosphate solution, or a mixture of phosphoric acid solution and diammonium hydrogen phosphate solution.

[0007] Optionally, the cleaning method in S1 includes: adding activated carbon fiber cloth into a container filled with water, then placing the container into an ultrasonic cleaner for ultrasonic treatment, changing the water every 10-20 minutes, and performing ultrasonic treatment twice.

[0008] Optionally, the drying method in S1 includes: taking out the cleaned activated carbon fiber cloth and placing it in an oven at 95~105℃ for 2~4 hours to dry.

[0009] Optionally, in S2, the hydrothermal modification treatment is carried out at a temperature of 110~130℃ for a time of 0.5~3h.

[0010] Optionally, in S2, when the soaking solution is a phosphoric acid solution, the volume fraction of the phosphoric acid solution is 2% to 10%.

[0011] Optionally, in S2, when the soaking solution is a diammonium hydrogen phosphate solution, the volume fraction of the diammonium hydrogen phosphate solution is 2%~10%.

[0012] Optionally, in S2, when the soaking solution is a mixed solution of phosphoric acid solution and diammonium hydrogen phosphate solution, the volume ratio of phosphoric acid solution to diammonium hydrogen phosphate solution is 1:1, the volume fraction of phosphoric acid in the mixed solution is 2%~10%, and the volume fraction of diammonium hydrogen phosphate in the mixed solution is 2%~10%.

[0013] Optionally, in S2, when the soaking solution is a mixture of phosphoric acid solution and diammonium hydrogen phosphate solution, the volume ratio of added phosphoric acid solution and diammonium hydrogen phosphate solution is 1:1, the volume fraction of phosphoric acid in the mixture is 6%, and the volume fraction of diammonium hydrogen phosphate in the mixture is 4%.

[0014] Optionally, S2 specifically includes the following steps: The activated carbon fiber cloth treated with S1 is placed in a container, and an immersion solution is added to the container to submerge the activated carbon fiber cloth. The cloth is then subjected to ultrasonic treatment to remove air bubbles. Transfer the container to the inner liner of the reactor and tighten the reactor; place the reactor in an electric heating drying oven, set the temperature to 110~130℃, and remove it after reacting for 0.5~3 hours. After the temperature of the reactor drops to room temperature, open the reactor, take out the activated carbon fiber cloth for cleaning, and then put it into an electric heating drying oven at 90~110℃ for 2~4 hours to dry, thus obtaining the modified activated carbon fiber.

[0015] Secondly, the present invention provides a composite modified activated carbon fiber, which is obtained by the aforementioned composite modification preparation method.

[0016] Optionally, the surface of the composite modified activated carbon fiber has oxygen-containing functional groups and / or nitrogen-containing functional groups.

[0017] Optionally, the composite modified activated carbon fiber has an adsorption capacity of up to 19.275 mg / g for SO2.

[0018] This invention has at least one of the following beneficial effects: 1. The composite modification method of the present invention can significantly improve the adsorption capacity of ACF-SO2. The best modification effect is obtained by composite modification under the conditions of 6% phosphoric acid + 4% diammonium hydrogen phosphate at 120°C for 1 hour, which can make the adsorption capacity of ACF-SO2 reach 19.275 mg / g, which is 154.29% higher than the unmodified original tablet, and the modification effect is very significant.

[0019] 2. Traditional multi-step modification methods typically involve immersion followed by high-temperature heat treatment, which is time-consuming and energy-intensive. Furthermore, high-temperature ablation can cause significant quality loss in the ACF, further increasing product costs and impacting the material's ultimate market application prospects. The method of this invention uses a one-step hydrothermal composite modification process, which saves time and costs, consumes less energy, and results in almost no quality loss before and after modification, allowing for better cost control. Attached Figure Description

[0020] Figure 1 The graph shows the adsorption capacity of hydrothermally modified ACF-SO2 at different times.

[0021] Figure 2 The adsorption capacity of ACF-SO2 after hydrothermal modification with different concentrations of phosphoric acid is shown in the figure.

[0022] Figure 3 The adsorption capacity of ACF-SO2 modified by hydrothermal diammonium hydrogen phosphate at different concentrations is shown in the figure.

[0023] Figure 4 The adsorption capacity of ACF-SO2 under different hydrothermal composite modification conditions is shown in the figure.

[0024] Figure 5 FT-IR spectra of ACF materials modified by hydrothermal phosphoric acid at different concentrations.

[0025] Figure 6 FT-IR spectra of hydrothermally modified ACF materials with different concentrations of diamine hydrogen phosphate.

[0026] Figure 7 FT-IR spectra of ACF materials modified by hydrothermal treatment with different concentrations of diamine hydrogen phosphate + 6% phosphoric acid.

[0027] Figure 8 SEM images of ACF materials under different optimal modification conditions are shown, where (a) original ACF sheet; (b) hydrothermal treatment at 120℃ for 1 h; (c) hydrothermal treatment with 6% phosphoric acid; (d) hydrothermal treatment with 6% diammonium hydrogen phosphate; and (e) hydrothermal treatment with a composite of 6% phosphoric acid and 4% diammonium hydrogen phosphate. Detailed Implementation

[0028] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0029] This invention investigates the effect of hydrothermal treatment on the adsorption performance of activated carbon fiber (ACF)-SO2 by first immersing ACF in deionized water and then conducting a hydrothermal reaction in a reactor, thus determining the optimal hydrothermal time. Next, it explores whether the hydrothermal reaction of these two reagents can improve the adsorption performance of activated carbon fiber by immersing ACF in different concentrations of phosphoric acid or diammonium hydrogen phosphate. After determining the optimal hydrothermal concentrations for both reagents, the invention further investigates whether hydrothermal reactions of ACF with different concentration ratios of phosphoric acid and diammonium hydrogen phosphate can further enhance the adsorption performance. The results show that both phosphoric acid and diammonium hydrogen phosphate hydrothermal reactions significantly improve the adsorption performance of ACF-SO2. The 6% phosphoric acid hydrothermal reaction showed the best effect, achieving an ACF-SO2 adsorption capacity of 16.644 mg / g, representing a 119.59% improvement in adsorption performance. The 6% diammonium hydrogen phosphate hydrothermal modification also showed the best effect, achieving an ACF-SO2 adsorption capacity of 17.724 mg / g, representing a 133.84% improvement in adsorption performance. In the subsequent investigation of mixed buffer solution modification, the adsorption performance of the material was further improved on the basis of the previous results. Among them, the modification effect of 6% phosphoric acid + 4% hydrogen diamine phosphate hydrothermal for 1 hour at 120℃ was the best, and the adsorption capacity of ACF-SO2 reached 19.275 mg / g, which improved the adsorption performance by 154.29%.

[0030] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited to the following specific embodiments.

[0031] Example 1 A method for preparing composite modified activated carbon fibers includes the following steps: 1. Ultrasonic pretreatment Polyacrylonitrile activated carbon fiber cloth (hereinafter referred to as ACF) is cut into 5*4cm square pieces, weighing approximately 0.4~0.5g. The cut ACF pieces are placed in a clean beaker, and distilled water is poured in to completely submerge them. If the ACF pieces float, a clean funnel is used to invert them to ensure complete immersion. The beaker is then placed in an ultrasonic cleaner for ultrasonic treatment, with the water changed every 15 minutes, and the process repeated twice to remove grease and other impurities from the surface of the ACF pieces. The ACF pieces are then removed and placed in an oven at 100℃ for 3 hours to remove surface moisture. Finally, clean and dry ACF pieces are obtained.

[0032] 2. Investigation into the optimal hydrothermal modification time Four ultrasonically treated ACF sheets were placed in the inner liner of a 50ml reactor. Deionized water was poured to the mark, the reactor lid was tightened, and the inner liner was placed in the reactor and screwed on tightly. The reactor was placed in an electric heating drying oven at 120℃ and reacted for 0.5h, 1h, 2h, and 3h respectively. After the reactor cooled to room temperature, it was opened, the ACF sheets were removed, placed in a 250ml beaker, and dried in an electric heating drying oven at 100℃ for 3h. The SO2 adsorption capacity was then tested to determine the optimal hydrothermal treatment time.

[0033] The method for calculating the SO2 absorption content of activated carbon fiber is as follows: In the formula: K : SO2 adsorption content of activated carbon fiber (mg / g); C 0: Concentration of injected SO2 (mg / ml); V nd : Volume of SO2 injected (ml); C (1 / 2 I2): Concentration of iodine standard solution (mol / L); V 1: The volume (ml) of iodine standard solution consumed by the remaining SO2 after adsorption by activated carbon fiber; 32.0: The mass (mg) of sulfur dioxide equivalent to 1 ml of 1 mol / L iodine standard solution; m ACF Mass of activated carbon fiber (g).

[0034] Table 1 shows the adsorption capacity of activated carbon fiber (ACF)-SO2 after ultrasonication and hydrothermal modification at different times. After hydrothermal modification, the adsorption capacity of ACF-SO2 was improved to a certain extent. The best effect was achieved by hydrothermal modification at 1 hour, with the adsorption capacity of ACF-SO2 reaching 10.547 mg / g, an increase of 39.15%.

[0035] Table 1. Adsorption capacity of hydrothermally modified ACF-SO2 at different times Figure 1The graph shows the adsorption capacity of ACF-SO2 after hydrothermal modification at different times. It is clear that high-pressure hydrothermal treatment alone can effectively improve the adsorption performance of the material. The modification effect is best with a 1-hour hydrothermal treatment time. Because the reactor remains at a high temperature after 1 hour of hydrothermal treatment, it takes 3-4 hours to cool down. Therefore, the actual hydrothermal time is more than 1 hour. We only counted the 1-hour time starting from when the reactor is placed in a forced-air drying oven and heated to 120℃. Prolonged hydrothermal reaction will lead to a gradual decrease in the material's adsorption performance.

[0036] In summary, the results show that a hydrothermal treatment time of 1 hour is the optimal time. The adsorption capacity of ACF-SO2 reached 10.547 mg / g, and the adsorption performance was improved by 39.15%. Therefore, we selected 1 hour of hydrothermal treatment as the optimal hydrothermal time for subsequent composite modification.

[0037] 3. Investigation on the modification of phosphoric acid by hydrothermal composite treatment Five ACF tablets, after ultrasonic pretreatment, were placed in a beaker and submerged in phosphoric acid solutions with volume fractions of 2%, 4%, 6%, 8%, and 10%. After ultrasonication for 30 minutes to remove excess air bubbles, the tablets were transferred to the inner liner of a reaction vessel and the vessel was tightened. The reaction vessel was placed in an electrically heated drying oven at 120°C. Timing was started after the oven temperature stabilized at 120°C, and the reaction was carried out for 1 hour. After the reaction vessel cooled to room temperature, the ACF tablets were opened, removed, and placed in a 250ml beaker. The tablets were ultrasonically washed with water (changing the water every 15 minutes for 30 minutes). The tablets were then dried in an electrically heated drying oven at 100°C for 3 hours, and the SO2 adsorption capacity was tested. The optimal concentration of phosphoric acid for immersion in the aqueous solution was determined.

[0038] Table 2 shows the adsorption capacity of ACF-SO2 after hydrothermal modification with different concentrations of phosphoric acid. After 2% phosphoric acid hydrothermal modification, the adsorption performance of activated carbon fiber was significantly improved. Subsequently, with increasing phosphoric acid hydrothermal concentration, the overall adsorption performance of ACF-SO2 improved to some extent, reaching its maximum at a 6% phosphoric acid hydrothermal modification concentration, where the ACF-SO2 adsorption capacity reached 16.644 mg / g, and the adsorption rate increased by 119.59%.

[0039] Table 2. ACF-SO2 adsorption capacity after hydrothermal composite modification treatment with different concentrations of phosphoric acid.

[0040] Figure 2The figure shows the adsorption capacity of ACF-SO2 after hydrothermal composite modification with different concentrations of phosphoric acid. As can be seen from the figure, compared with simple hydrothermal treatment, hydrothermal modification with phosphoric acid significantly improves the adsorption performance of activated carbon fibers. A 2% phosphoric acid hydrothermal modification shows a significant improvement, and the adsorption performance further improves with increasing phosphoric acid concentration, with 6% phosphoric acid hydrothermal modification showing the most ideal effect. However, with further increases in phosphoric acid hydrothermal concentration, the adsorption performance of the ACF material decreases significantly, indicating that under excessively high concentrations of phosphoric acid immersion and high-temperature hydrothermal conditions, the structure of the carbon fiber is excessively damaged, leading to a significant decline in material performance.

[0041] In summary, the results show that initially, the ACF-SO2 adsorption capacity increases significantly with increasing phosphoric acid hydrothermal concentration, with a 2% phosphoric acid concentration showing a very significant modification effect. After 2% phosphoric acid hydrothermal treatment, the ACF-SO2 adsorption capacity reached 15.398 mg / g, an increase of 103.15% in adsorption rate. However, the effects of 2% to 6% phosphoric acid hydrothermal modification are not significantly different. Among them, 6% phosphoric acid hydrothermal modification has the best effect, with an ACF-SO2 adsorption capacity of 16.644 mg / g, an increase of 119.59% compared to the unmodified original sheet. However, with further increases in phosphoric acid hydrothermal concentration, the material's adsorption performance decreases significantly. This is likely because phosphoric acid itself is a moderately strong acid, and under the high-temperature hydrothermal environment of 120℃, its acid etching ability is further enhanced. At excessively high concentrations, it can over-etch the carbon fiber tube, causing excessive damage to the material structure and leading to a significant decrease in material performance.

[0042] 4. Investigation on the modification of diammonium hydrogen phosphate by hydrothermal composite treatment Five ACF (Acrylic Acid Fluoride) tablets, after ultrasonic pretreatment, were placed in a beaker and submerged in diammonium hydrogen phosphate solutions with mass fractions of 2%, 4%, 6%, 8%, and 10%. The tablets were ultrasonicated for 30 minutes to remove excess air bubbles, then transferred to the inner liner of a reaction vessel and tightened. The reaction vessel was placed in an electrically heated drying oven at 120°C. Timing was started after the oven temperature stabilized at 120°C, and the reaction was carried out for 1 hour. After the reaction vessel cooled to room temperature, the tablets were opened, removed, and placed in a 250ml beaker. The tablets were ultrasonically washed with water (changing the water every 15 minutes for 30 minutes). The tablets were then dried in an electrically heated drying oven at 100°C for 3 hours, and the SO2 adsorption capacity was tested. The optimal concentration of diammonium hydrogen phosphate for immersion in the water was determined.

[0043] Table 3 shows the adsorption capacity of ACF-SO2 modified with different concentrations of diammonium hydrogen phosphate via hydrothermal modification. As the water solubility of diammonium hydrogen phosphate increases, the adsorption performance of the ACF material gradually improves, reaching its maximum at a hydrothermal concentration of 6% diammonium hydrogen phosphate, where the ACF-SO2 adsorption capacity reaches 17.724 mg / g, and the adsorption rate increases by 133.84%. However, with further increases in the hydrothermal concentration of diammonium hydrogen phosphate, the adsorption performance of ACF-SO2 decreases. Next, we will use 6% phosphoric acid as a base and prepare mixed solutions by adding different concentrations of diammonium hydrogen phosphate to conduct further composite hydrothermal modification research, exploring whether a one-step composite modification process can further improve the adsorption performance of the ACF material.

[0044] Table 3. Adsorption capacity of ACF-SO2 under different concentrations of diammonium hydrogen phosphate Figure 3 The figure shows the SO2 adsorption capacity of ACF after hydrothermal composite modification with different concentrations of diammonium hydrogen phosphate. As can be seen from the figure, initially, the adsorption performance of the ACF material continuously improves with increasing diammonium hydrogen phosphate concentration, reaching its maximum at 6%. When the diammonium hydrogen phosphate concentration is further increased, the SO2 adsorption performance of the material begins to decline.

[0045] In summary, the results show that hydrothermal modification with diammonium hydrogen phosphate (DAP) can further improve the adsorption performance of the material compared to hydrothermal modification alone. Furthermore, the ACF-SO2 adsorption performance continuously improves with increasing DAP hydrothermal concentration, reaching its maximum at 6% DAP hydrothermal treatment, with an ACF-SO2 adsorption capacity of 17.724 mg / g, representing a 133.84% increase compared to the original tablet. However, with further increases in the DAP hydrothermal concentration, the adsorption performance of the material reaches an inflection point and begins to decline. Our next step is to investigate whether mixing phosphoric acid and DAP in different proportions can further improve the material's performance.

[0046] 5. Investigation of Optimal Composite Modification Conditions We conducted further research using 6% phosphoric acid as a base. First, 25 ml of a 12% (v / v) phosphoric acid solution was added to each of five beakers. Then, 25 ml of diamine hydrogen phosphate (DHP) with mass fractions of 4%, 8%, 12%, 16%, and 20% were added to these five beakers respectively, and the mixtures were stirred to form mixed solutions of 6% phosphoric acid + 2% DHP, 6% phosphoric acid + 4% DHP, 6% phosphoric acid + 6% DHP, 6% phosphoric acid + 8% DHP, and 6% phosphoric acid + 10% DHP. Five pieces of ACF (acetic acid fluoride) pre-treated by sonication were placed into each of the five beakers until fully submerged. After sonication to remove excess air bubbles, the ACF was transferred to the inner liner of the reaction vessel and the vessel was tightened. The reaction vessel was placed in an electrically heated drying oven at 120°C and reacted for 1 hour before being removed. After the reaction vessel cooled to room temperature, the container was opened, the ACF sheet was removed, and placed in a 250ml beaker. It was then ultrasonically washed with water (water changed every 15 minutes, ultrasonication for 30 minutes). The beaker was then dried in an electric heating drying oven at 100℃ for 3 hours, and the SO2 adsorption capacity was tested. The optimal composite modification treatment conditions were obtained.

[0047] Table 4 shows the adsorption capacity of ACF-SO2 after hydrothermal composite modification with different concentrations of diammonium hydrogen phosphate + 6% phosphoric acid. The data in the table shows that the modification effect is optimal when using 4% diammonium hydrogen phosphate + 6% phosphoric acid at 120℃ for 1 hour, with an ACF-SO2 adsorption capacity of 19.275 mg / g, representing a 154.29% improvement compared to the original sheet. However, as the concentration of diammonium hydrogen phosphate further increases, the modification effect of the ACF material declines significantly. This indicates that excessively high hydrothermal concentrations in the mixed solution damage the structure of the carbon fiber material, leading to a significant decline in material performance after reaching an inflection point.

[0048] Table 4. Adsorption capacity of ACF-SO2 modified by hydrothermal composite of different concentrations of diammonium hydrogen phosphate + 6% phosphoric acid Figure 4 The graph shows the adsorption capacity of ACF-SO2 under different hydrothermal composite modification conditions. It is evident that hydrothermal modification with diammonium hydrogen phosphate (DHP) + 6% phosphoric acid further enhances the adsorption performance compared to single hydrothermal modification. The 4% DHP + 6% phosphoric acid hydrothermal modification shows the best effect. However, with further increases in DHP concentration, the material performance declines significantly, even falling short of single DHP hydrothermal modification. This may be because high-concentration hydrothermal conditions cause excessive etching of the ACF carbon fiber surface, affecting the carbon skeleton structure and leading to a significant decrease in adsorption performance. To further explore the intrinsic mechanism of this modification technique on ACF, we will characterize the materials before and after modification using FT-IR and SEM.

[0049] In summary, the results show that the optimal composite modification effect was achieved by hydrothermal composite modification treatment of 6% phosphoric acid + 4% diammonium hydrogen phosphate for 1 hour. The adsorption capacity of ACF-SO2 reached 19.275 mg / g, and the adsorption rate increased by 154.29%. Subsequently, with the increase of the mass fraction of diammonium hydrogen phosphate, the modification effect of ACF reached an inflection point and showed a significant downward trend. Therefore, this experimental investigation is meaningful. The experiment not only proved that hydrothermal composite modification of activated carbon fiber in a mixed solution of phosphoric acid and diammonium hydrogen phosphate can further improve the adsorption performance of the material, but also explored the optimal mixing ratio. Excessively high mixing concentrations can further reduce the adsorption performance of the material.

[0050] Next, FT-IR characterization of ACF before and after modification was performed to explore the intrinsic mechanism of the effect of modification methods on ACF materials under single and composite modification conditions. The results are as follows: Figures 5-8 As shown.

[0051] Figure 5 The images show the FT-IR spectra of ACF materials modified with hydrothermally at different concentrations of phosphoric acid. After hydrothermal modification with phosphoric acid, the materials exhibit spectra in the range of 3100–3500 cm⁻¹. -1 and 1260-1400cm -1 Distinct absorption peaks are observed, consisting of the -OH stretching vibration and bending vibration absorption peaks, at 1650–1740 cm⁻¹. -1 A distinct absorption peak is observed, which is the C=O stretching vibration absorption peak. These results indicate that hydrothermal modification with phosphoric acid can undergo a significant oxidation reaction with carbon fibers, generating a large number of oxygen-containing functional groups such as -OH, -C=O, and -COOH. These oxygen-containing functional groups can effectively improve the material's adsorption performance for acidic gases such as SO2. Simultaneously, it can be observed from the figure that initially, with increasing phosphoric acid concentration, the absorption peaks of the oxygen-containing functional groups in ACF gradually increase, reaching their most pronounced after 6% phosphoric acid hydrothermal modification. This result best corresponds to the adsorption capacity test results of 6% phosphoric acid hydrothermal modification. However, with further increases in phosphoric acid hydrothermal concentration, the related functional group absorption peaks continuously weaken. This may be due to structural damage to the material, resulting in a significant reduction in surface oxygen-containing functional groups. The infrared results clearly demonstrate the effect of phosphoric acid hydrothermal treatment on the functional groups of ACF surface, and partly explain why excessively high concentrations of phosphoric acid hydrothermal treatment can lead to a decline in material performance.

[0052] Figure 6 The images show the FT-IR spectra of ACF modified with diammonium hydrogen phosphate at different concentrations via hydrothermal modification. After hydrothermal modification with diammonium hydrogen phosphate, the material exhibits wavelengths in the range of 1020–1340 cm⁻¹. -1 An absorption peak appears, which is the CN stretching vibration peak, and it is also present in the range of 3300~3500 cm⁻¹. -1 and 1550~1650cm -1The presence of distinct absorption peaks indicates the presence of -NH stretching and bending vibration peaks. Therefore, it can be inferred that hydrothermal modification of the ACF material surface resulted in significant nitrogen modification, generating a large number of -NH basic functional groups, effectively enhancing the AC-SO2 adsorption performance. Furthermore, it was observed that the nitrogen-containing functional group absorption peaks on the ACF surface were most pronounced after hydrothermal modification with 6% diammonium hydrogen phosphate, a result consistent with the ACF-SO2 adsorption results after hydrothermal modification with different concentrations of diammonium hydrogen phosphate.

[0053] Figure 7 The images show the FT-IR spectra of ACF materials modified by hydrothermal treatment with different concentrations of diamine hydrogen phosphate + 6% phosphoric acid. The spectra show that ACF exhibits high activity in the 3300–3500 cm⁻¹ range. -1 and 1550~1650cm -1 The material exhibits both -NH stretching and bending vibration peaks. Simultaneously, the material shows peak values ​​between 1650 and 1740 cm⁻¹. -1 An absorption peak for C=O stretching vibrations appears, particularly in the range of 3200–3500 cm⁻¹. -1 and 1260-1400cm -1 The presence of distinct -OH stretching vibration and bending vibration absorption peaks indicates that under the hydrothermal conditions of diammonium hydrogen phosphate-phosphoric acid composite, the material undergoes simultaneous oxidation and nitrogen modification, resulting in a large number of oxygen- and nitrogen-containing functional groups on the material surface, further enhancing the ACF-SO2 adsorption capacity. The ACF infrared functional group absorption peaks are most pronounced after hydrothermal treatment with 4% diammonium hydrogen phosphate + 6% phosphoric acid. Subsequently, as the concentration of the composite modifying reagent further increases, the overall functional group absorption peaks weaken after hydrothermal modification, likely due to varying degrees of structural damage. Therefore, we will next observe the surface microstructure of the material under different modification conditions using SEM to further analyze the intrinsic mechanism of the modification.

[0054] Figure 8Figure 1 shows SEM images of ACF materials under different optimal modification conditions. Figure (a) shows the original ACF sheet. Figure (b) shows that after hydrothermal treatment at 120℃ for 1 hour, the surface roughness and etching of the ACF fiber increased to some extent compared to the original sheet. Figure (c) shows that after hydrothermal treatment with 6% phosphoric acid, the surface roughness and texture of the fiber increased significantly, producing a good etching effect, increasing the specific surface area and active sites of the material, and significantly improving the adsorption performance of SO2. Figure (d) shows that after hydrothermal modification with diamine hydrogen phosphate, the carbon fiber surface also had a certain etching effect, but it was not as obvious as that of hydrothermal modification with phosphoric acid. However, there were obvious fine crystalline particles in the fiber texture, indicating that diamine hydrogen phosphate crystals were loaded on the material, which enhanced the adsorption performance of SO2. Figure (e) shows the SEM image of the material surface after hydrothermal treatment with 6% phosphoric acid + 4% diamine hydrogen phosphate. As can be seen from the figure, the surface of the material after composite hydrothermal treatment produced obvious etching and diamine hydrogen phosphate crystal loading phenomena. In particular, as the etching of the carbon fiber surface intensifies, the rough surface of the carbon fiber is more conducive to the loading of diamine hydrogen phosphate crystals. The increase in amine groups helps to improve the material's adsorption capacity for SO2, thus further improving the material's adsorption performance.

[0055] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for the composite modification of activated carbon fibers, characterized by, The method comprises the following steps: S1, washing and drying the activated carbon fiber cloth; S2, adding the activated carbon fiber cloth treated in S1 into a soaking solution for hydrothermal modification treatment to obtain modified activated carbon fiber; wherein the soaking solution is one of phosphoric acid solution, diammonium hydrogen phosphate solution, and a mixed solution of the two.

2. The composite modification manufacturing method of claim 1, wherein, In S2, the temperature for the hydrothermal modification treatment is 110-130℃, and the time is 0.5-3h.

3. The composite modification manufacturing method of claim 1, wherein, In S2, when the soaking solution is the phosphoric acid solution, the volume fraction of the phosphoric acid solution is 2%-10%.

4. The composite modification manufacturing method of claim 1, wherein, In S2, when the soaking solution is the diammonium hydrogen phosphate solution, the volume fraction of the diammonium hydrogen phosphate solution is 2%-10%.

5. The composite modification manufacturing method of claim 1, wherein, In S2, when the soaking solution is the mixed solution of the phosphoric acid solution and the diammonium hydrogen phosphate solution, the volume ratio of the two is 1:1, the volume fraction of the phosphoric acid in the mixed solution is 2%-10%, and the volume fraction of the diammonium hydrogen phosphate in the mixed solution is 2%-10%.

6. The composite modification manufacturing method of claim 1, wherein, In S2, when the soaking solution is the mixed solution of the phosphoric acid solution and the diammonium hydrogen phosphate solution, the volume ratio of the two for addition is 1:1, the volume fraction of the phosphoric acid in the mixed solution is 6%, and the volume fraction of the diammonium hydrogen phosphate in the mixed solution is 4%.

7. The composite modification manufacturing method of claim 1, wherein S2 specifically comprises the following steps: placing the activated carbon fiber cloth treated in S1 into a container, adding the soaking solution into the container to immerse the activated carbon fiber cloth, ultrasonic treatment, and removing air bubbles; transferring the container into the inner container of a reaction kettle, tightening the reaction kettle, placing the reaction kettle into an electric heating air drying oven, setting the temperature to 110-130℃, and taking out the reaction kettle after 0.5-3h of reaction; opening the reaction kettle after the temperature of the reaction kettle decreases to room temperature, taking out the activated carbon fiber cloth, washing, and then placing the activated carbon fiber cloth into the electric heating air drying oven for 90-110℃, 2-4h of drying to obtain the modified activated carbon fiber.

8. A composite modified activated carbon fiber, characterized by, obtained by the composite modification method in any one of claims 1-7.

9. The composite modified activated carbon fiber according to claim 8, characterized by The composite modified activated carbon fiber has oxygen-containing functional groups and / or nitrogen-containing functional groups on the surface.

10. The composite modified activated carbon fiber according to claim 8, wherein The adsorption capacity of the composite modified activated carbon fiber for SO2 is as high as 19.275mg / g.

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