Preparation method of modified activated carbon reduced by ammonia water

Abstract

This invention discloses a method for preparing ammonia-modified activated carbon, which includes the following steps: (1) mixing grapefruit peel powder and sodium carbonate activator in a weight ratio of 3:1 and placing them in a corundum crucible, then heating and carbonizing them in a muffle furnace at 700°C for 2 h, and cooling them to room temperature; (2) grinding the carbonized material into powder, washing it with nitric acid solution, and then drying it in an oven to obtain grapefruit peel-based activated carbon; (3) mixing the grapefruit peel-based activated carbon with ammonia solution of 5-15% by mass and placing it in a three-necked flask; (4) refluxing the reaction at 65°C for 4 h, and repeatedly washing the activated carbon with deionized water until the filtrate is neutral; (5) drying it in an oven at 60°C to constant weight to obtain ammonia-modified activated carbon. This invention optimizes the pore structure of activated carbon through ammonia modification, improves its specific surface area and adsorption capacity, enhances its adsorption capacity for dye molecules, and improves its selectivity for different types of dyes.

Description

Technical Field

[0001] This invention relates to the preparation process of new materials for dye wastewater treatment, specifically a method for preparing ammonia-modified activated carbon. Background Technology

[0002] Dye wastewater is a significant pollutant discharged during industrial processes such as textiles, printing and dyeing, papermaking, and leather manufacturing. It is characterized by high color intensity, complex composition, strong chemical stability, and difficulty in degradation. Direct discharge without treatment can severely impact aquatic ecosystems. Therefore, developing efficient, economical, and sustainable dye wastewater treatment technologies is crucial. Among various wastewater treatment methods, adsorption has become an important means of purifying dye wastewater due to its simplicity, high efficiency, and strong adaptability to different types of dyes. Activated carbon, with its large specific surface area and well-developed pore structure, is widely used in dye wastewater treatment. However, unmodified activated carbon has limited surface chemical properties and insufficient variety and quantity of functional groups, resulting in low adsorption capacity for certain dyes, which restricts its practical application.

[0003] Currently, there are also technical solutions for improving the adsorption performance of activated carbon through modification. The main methods for modifying activated carbon include surface physical structure modification, surface chemical property modification, and surfactant modification. Surface physical structure modification has the advantages of simple operation, increased specific surface area, increased micropore number, and enhanced physical adsorption capacity. However, its disadvantages include low selectivity for specific pollutants, limited functionality, and high energy consumption. Surface chemical property modification has the advantages of high selectivity and enhanced chemical adsorption capacity for specific pollutants through functional groups. However, its disadvantages include complex processes, high cost, the need for strong acids or alkalis or toxic reagents, and safety risks. Surfactant modification has the advantages of directional modification, significantly enhanced adsorption of hydrophobic organic matter or charged ions, and the ability to select different surfactants to control surface properties. However, its disadvantages include limited effectiveness on non-polar pollutants, high cost of some surfactants, and narrow applicability.

[0004] Therefore, there is a need to develop a method for preparing modified activated carbon that is low in modification cost, has strong adsorption capacity, is safe, and has high selectivity. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing ammonia-modified activated carbon. By modifying with ammonia, the pore structure of activated carbon is optimized, the specific surface area and adsorption capacity are increased, and the adsorption capacity for dye molecules is enhanced, thereby improving the selectivity for different types of dyes.

[0006] The present invention solves the above-mentioned technical problems by means of the following technical solution:

[0007] This invention discloses a method for preparing ammonia-modified activated carbon, comprising the following steps:

[0008] Step 1: Mix grapefruit peel powder and sodium carbonate activator in a weight ratio of 3:1 and place them evenly in a high-temperature resistant corundum crucible. Then place the crucible in a muffle furnace and heat at 700°C for 2 hours to carbonize. Cool to room temperature to obtain carbonized material.

[0009] Step 2: Grind the obtained carbon into powder that passes through a 40-mesh sieve, wash off the sodium carbonate activator with a 1 mol / L nitric acid solution, filter, and then dry in an oven at 60°C to obtain grapefruit peel-based activated carbon.

[0010] Step 3: Mix grapefruit peel-based activated carbon with ammonia water with a mass concentration of 5-15% at a weight ratio of 1:100 and place it in a three-necked flask;

[0011] Step 4: Reflux the reaction at 65°C for 4 hours. After the reaction is complete, wash the activated carbon repeatedly with deionized water until the filtrate is neutral.

[0012] Step 5: Finally, place the activated carbon in an oven at 60°C and dry it to constant weight to obtain ammonia-reduced modified activated carbon.

[0013] The method for preparing grapefruit peel powder in step (1) of this invention is as follows:

[0014] (1) Remove the pulp from the Shatin pomelo, then cut the remaining pomelo peel into small pieces and wash it clean;

[0015] (2) Place the cleaned grapefruit peel in an electric heating drying oven and dry it at 80 ℃ for more than 8 hours until its quality no longer changes, and obtain grapefruit peel residue. Then, pulverize the grapefruit peel residue by high-speed electric mill and pass it through a 40-mesh sieve to obtain grapefruit peel powder. Seal it in a desiccator for storage.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. The activated carbon obtained by the method of the present invention has significantly improved adsorption performance: After ammonia reduction modification, the grapefruit peel-based activated carbon has a significantly enhanced adsorption capacity for methylene blue. The activated carbon modified with 15% ammonia water has a 32% higher removal rate than the original carbon and a higher adsorption capacity (maximum adsorption capacity reaches 37.15 mg / g).

[0018] 2. The method of this invention optimizes the material structure, provides more adsorption sites, and introduces nitrogen-containing functional groups and basic groups, thereby enhancing the interaction with cationic dyes (such as methylene blue) and improving the selectivity for different types of dyes such as cationic dyes, anionic dyes and nonpolar dyes.

[0019] 3. The preparation process of this invention is safe and low-cost: the ammonia reduction modification process is simple and requires little equipment. It does not require the use of strong acids, strong alkalis or toxic reagents, and the production is safe and low-cost, making it suitable for large-scale application.

[0020] 4. This invention makes full use of waste resources and has environmental benefits: Activated carbon is prepared from grapefruit peel, realizing the high-value utilization of agricultural waste, reducing environmental pollution, and having both economic and ecological benefits, which is in line with the concept of sustainable development.

[0021] 5. The adsorption mechanism used in this invention is clear and efficient: the adsorption process conforms to the pseudo-first-order kinetic model and the Langmuir isotherm model, the adsorption rate is fast, the removal efficiency of low-concentration methylene blue wastewater is high, and the applicability is strong. Attached Figure Description

[0022] Figure 1 This is a SEM image of the grapefruit peel-based activated carbon from Example 1 of this invention.

[0023] Figure 2 This is a SEM image of ammonia-reduced activated carbon obtained by modifying activated carbon with ammonia water at a concentration of 5% in Example 1 of this invention.

[0024] Figure 3 This is a SEM image of ammonia-reduced activated carbon obtained by modifying activated carbon with ammonia water at a concentration of 10% in Example 1 of the present invention.

[0025] Figure 4 This is a SEM image of ammonia-reduced activated carbon obtained by modifying activated carbon with ammonia water at a concentration of 15% in Example 1 of this invention.

[0026] Figure 5 This is the nitrogen adsorption-desorption isotherm of the grapefruit peel-based activated carbon modified with ammonia water in Example 1 of this invention.

[0027] Figure 6 This is a pore size distribution diagram of grapefruit peel-based activated carbon (AC) obtained in Example 1 of the present invention and grapefruit peel-based activated carbon modified with ammonia water of different concentrations.

[0028] Figure 7 This is the high-resolution XPS spectrum of grapefruit peel-based activated carbon in Example 1 of the present invention.

[0029] Figure 8 This is the high-resolution XPS spectrum of ammonia-reduced modified activated carbon (AC-N15) obtained in Example 1 of this invention. Detailed Implementation

[0030] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0031] Example 1

[0032] This invention discloses a method for preparing ammonia-modified activated carbon, comprising the following steps:

[0033] 1. Preparation of grapefruit peel-based activated carbon: The specific steps are as follows:

[0034] (1) Prepare Shatin pomelo, remove the pulp and cut the remaining pomelo peel into small pieces, then wash it repeatedly with deionized water;

[0035] (2) Place the cleaned broken grapefruit peel in an electric heating drying oven and dry it at 80°C for more than 8 hours until its quality no longer changes, and obtain grapefruit peel residue. Then, pulverize the grapefruit peel residue by high-speed electric mill and pass it through a 40-mesh sieve to obtain grapefruit peel powder. Seal it in a desiccator for storage.

[0036] (3) After mixing the pretreated grapefruit peel powder and sodium carbonate activator in a weight ratio of 3:1, place them in a high-temperature resistant corundum crucible, then put them in a muffle furnace and heat them at 700 °C for 2 h to carbonize them. Then cool them to room temperature to obtain carbonized products.

[0037] (4) Grind the obtained carbonized material into powder passing through 40 mesh, wash off the sodium carbonate activator with nitric acid solution with a concentration of 1 mol / L, filter, and then dry it in an oven at 60 °C to constant weight to obtain grapefruit peel-based activated carbon after pyrolysis carbonization treatment, labeled as AC.

[0038] 2. The specific steps for preparing ammonia-modified activated carbon are as follows:

[0039] (1) Prepare ammonia solutions with mass concentrations of 5%, 10%, and 15%, respectively. Weigh three equal amounts of grapefruit peel-based activated carbon and place them in 500 mL three-necked flasks. Add the prepared ammonia solutions of three different concentrations at a weight ratio of 1:100.

[0040] (2) Reflux the reaction at 65 °C for 4 h. After the reaction is complete, wash the activated carbon repeatedly with deionized water until the filtrate is neutral.

[0041] (3) Finally, the activated carbon is placed in an oven at 60°C and dried until constant, thus obtaining three kinds of ammonia-modified activated carbon with different concentrations (5%, 10%, and 15%) of ammonia water, which are labeled as AC-N5, AC-N10, and AC-N15 respectively.

[0042] Characterization of the ammonia-reduced modified activated carbon of this invention:

[0043] This invention employs scanning electron microscopy (SEM) analysis technology to scan and photograph grapefruit peel-based activated carbon samples modified with ammonia water of different concentrations. By adjusting the magnification, the pore size, surface morphology, pore structure, and other properties can be clearly observed. Figure 1 This is a SEM image of unmodified grapefruit peel-based activated carbon AC (raw carbon). Figure 2 , Figure 3 , Figure 4 These are SEM images of ammonia-reduced modified activated carbons AC-N5, AC-N10, and AC-N15 obtained in Example 1 of this invention. Analysis of the microstructure of the ammonia-reduced modified activated carbon using scanning electron microscopy (SEM) clearly reveals a complex porous structure on its surface. The surface of the ammonia-modified grapefruit peel-based activated carbon is covered with micropores of varying sizes. These micropores exhibit an irregular, blocky distribution and significant defect structures, resulting in a rough and porous overall surface. Compared to the unmodified raw carbon, the chemically activated carbon shows significant changes in its microstructure. Specifically, the surface pore density of the modified activated carbon is significantly increased, the pore size distribution is more uniform, and the specific surface area is effectively improved. This structural optimization provides the activated carbon with more adsorption sites and greater adsorption capacity, which is one of the key factors significantly improving the adsorption performance of modified activated carbon for pollutants.

[0044] This invention uses BET surface area analysis to characterize grapefruit peel-based activated carbon before and after modification, determining its specific surface area, pore size, and other parameters. See [link / reference]. Figure 6 As shown, during the ammonia modification process, ammonia molecules chemically react with the activated carbon surface, causing partial pore wall structure reconstruction and adjusting the original pore structure. Simultaneously, the active components in the ammonia react with the oxygen-containing functional groups on the activated carbon surface, promoting the introduction of nitrogen-containing functional groups. This leads to the shrinkage or blockage of some micropores and mesopores, resulting in a decrease in specific surface area and pore size. Although the pore structure parameters are reduced, the modification process effectively increases the chemically active sites on the material surface, improves surface polarity and the number of functional groups, and enhances the interaction between the material and the target pollutant.

[0045] To further clarify, the ammonia modification method employed in this invention does not simply rely on specific surface area to enhance adsorption performance. Instead, it modulates the surface chemical properties and functional group composition of activated carbon to transform the material's adsorption mechanism from a single physical adsorption to a synergistic effect of physical and chemical adsorption. Therefore, even with some reduction in pore structure, the modified grapefruit peel-based activated carbon still exhibits superior adsorption performance and pollutant removal capacity. Thus, the method of this invention, while maintaining material structural stability, effectively constructs surface active sites, providing a foundation for subsequent improvements in adsorption performance.

[0046] like Figure 5 As shown, the nitrogen adsorption-desorption isotherm of the grapefruit peel-based activated carbon modified with ammonia water according to the present invention is... Classification, belonging to Type and The isotherm pattern is as follows: In the region of lower relative pressure, due to the micropore filling effect, nitrogen molecules rapidly enter the microporous structure of activated carbon, resulting in a significant increase in adsorption. In the region of higher relative pressure, as the relative pressure increases, nitrogen molecules begin to undergo multilayer adsorption in the mesopore and macropore structures of activated carbon, thus the adsorption capacity continues to increase, and the isotherm shows a slow upward trend. This isotherm characteristic fully demonstrates that the ammonia-reduced modified activated carbon obtained in this invention has a rich microporous and mesoporous structure.

[0047] The specific surface area data of ammonia-reduced activated carbon modified with ammonia water of different concentrations in Example 1 of this invention are shown in Table 1.

[0048] Table 1

[0049]

[0050] Table 1 shows that the specific surface area and pore size distribution of grapefruit peel-based activated carbon exhibited significant changes after modification with different concentrations of ammonia. BET specific surface area testing and pore size distribution analysis revealed that modification with 5% ammonia reduced the specific surface area of ​​the activated carbon from 317.0587 m² / g to 84.3856 m² / g; modification with 10% ammonia reduced it to 190.9739 m² / g; and modification with 15% ammonia reduced it to 160.9416 m² / g. The micropore size also decreased from 32.004 nm to approximately 25 nm. This is because during the ammonia modification process, ammonia molecules react chemically with the activated carbon surface, causing partial erosion of carbon atoms in the microporous structure, thus producing a shrinkage effect. Ions react with oxygen-containing functional groups on the surface of activated carbon, causing partial removal of carbon atoms from the pore walls, ultimately leading to a reduction in pore size and specific surface area. However, the functional groups introduced during the modification process further enhance the surface chemical activity of the activated carbon, thereby improving its adsorption capacity.

[0051] This invention uses XPS (X-ray photoelectron spectroscopy) surface analysis technology to determine the elemental composition, chemical state, and electronic structure information of the surface of the ammonia-reduced modified activated carbon material obtained by this invention. For example... Figure 7As shown, the high-resolution XPS spectral analysis results of the N1s region of the original activated carbon (AC) are clearly displayed, successfully identifying two characteristic peaks: one at 400.4 eV, corresponding to graphitic nitrogen (amino, -NH2); and the other at 407.4 eV, corresponding to oxidized nitrogen (nitro, -NO2). This is because a special processing technique was used in the preparation of the original activated carbon, namely, washing with dilute nitric acid after carbonizing the grapefruit peel-based activated carbon, thereby introducing abundant oxidized nitrogen active sites on the material surface. And as... Figure 8 As shown, only graphitic nitrogen XPS characteristic peaks could be identified in the activated carbon samples after ammonia modification, indicating that the oxidized nitrogen bond configuration was completely converted to graphitic nitrogen during the modification process. Test results showed that the XPS peak area of ​​graphitic nitrogen in the original carbon was 10486.59 au, while the corresponding peak area of ​​the modified activated carbon significantly increased to 14879.18 au, an increase of 4392.59 au. The XPS analysis results fully confirm that although both nitrogen forms can serve as catalytic active sites for pollutant adsorption on activated carbon, graphitic nitrogen sites exhibit more prominent adsorption activity. Therefore, by using ammonia reduction modification, more alkaline activation sites were successfully constructed on the activated carbon surface, thereby significantly improving its adsorption performance.

[0052] The effect of different concentrations of ammonia water on the adsorption performance of the ammonia-modified activated carbon of this invention:

[0053] Experimental method: The concentration of MB in simulated wastewater was determined by spectrophotometry.

[0054] Preparation of MB solution: Accurately weigh 0.1000 g MB into a 100 mL volumetric flask using an electronic balance, and dilute to the mark with deionized water to obtain a 100 mg / L MB standard stock solution. Then, take 50 mL of the MB standard stock solution and place it into a 1000 mL volumetric flask, and dilute to the mark with deionized water to obtain a 50 mg / L MB standard solution.

[0055] Accurately pipette 2, 4, 10, 20, 30, 40, and 50 mL of 50 mg / L MB standard solution into 100 mL volumetric flasks, then add deionized water to dilute to volume, preparing MB standard solutions of 1, 2, 5, 10, 15, 20, and 25 mg / L. Then, use a visible spectrophotometer to measure the absorbance of the MB standard solutions at the maximum absorption peak of 663 nm to plot the MB standard curve.

[0056] Prepare 100 mL of methylene blue solutions with concentrations of 10, 20, 30, 50, 80, 100, 150, and 200 mg / L, pour them into a 250 mL Erlenmeyer flask, add 0.100 g of the ammonia-modified activated carbon of this invention, and place the flask in an air bath constant temperature shaker. Adsorb the activated carbon at 25°C for 240 min, then take a sample and filter it.

[0057] Determination of the adsorption efficiency of the ammonia-reduction modified activated carbon of this invention:

[0058] The absorbance of the methylene blue standard solution at a wavelength of 663 nm was measured using a visible spectrophotometer, and its standard curve was plotted. The adsorption capacity and removal rate of the ammonia-modified activated carbon for the MB solution were calculated using equations (1-1) and (1-2).

[0059] (1-1)

[0060] (1-2)

[0061] In the formula: q t t represents the adsorption capacity of activated carbon for methylene blue solution at time t, in mg / g; w represents the removal rate of methylene blue by activated carbon, in %; c0 represents the concentration of MB solution before adsorption, in mg / L; c t denoted as the concentration of the MB solution after adsorption (mg / L); V is the volume of the MB solution in the conical flask (L); and m is the mass of the added biological activated carbon (g).

[0062] The adsorption efficiency of the ammonia-reduced modified activated carbon before and after modification is shown in Table 2.

[0063] Table 2

[0064]

[0065] Table 2 shows that the adsorption effect varies with the concentration of ammonia. Before modification, the adsorption rate of activated carbon was 62.58%. After modification with 5% ammonia, the adsorption rate of grapefruit peel-based activated carbon was 64.46%. After modification with 10% and 15% ammonia, the adsorption rates of grapefruit peel-based activated carbon reached 83.29% and 94.77%, respectively, showing a significant enhancement in adsorption capacity. This is because the surface chemical modification of activated carbon increases the number of basic functional groups, which is beneficial for providing adsorption active sites. Therefore, the modified activated carbon is more conducive to the adsorption of methylene blue.

[0066] Adsorption kinetics analysis of ammonia-modified activated carbon according to the present invention:

[0067] To investigate the adsorption kinetics of methylene blue on activated carbon, pseudo-first-order kinetic equations (Equation 2-1) and pseudo-second-order kinetic equations (Equation 2-2) were used to fit the adsorption behavior of methylene blue on activated carbon, and the controlling steps of the adsorption rate of modified activated carbon were determined.

[0068] The formula for the pseudo-first-order dynamic model is as follows:

[0069] (2-1)

[0070] The formula for the pseudo-second-order dynamic model is as follows:

[0071] (2-2)

[0072] In the above formula: q t Adsorption capacity (mg / g) of grapefruit peel-based activated carbon MB at time t, q e Adsorption capacity at equilibrium (mg / g), t: sampling time (h), k1: rate constant of pseudo-first-order kinetic model (min) -1 k2: the rate constant of the pseudo-second-order kinetic model (g•min / mg). The results of calculation and testing are shown in Table 3.

[0073] Table 3. Kinetic fitting parameters of AC adsorption on MB by different concentrations of ammonia water

[0075] Table 3 shows that the R² parameter of the pseudo-first-order kinetic model for both the original activated carbon and the grapefruit peel-based activated carbon modified with different ammonia concentrations is greater than that of the pseudo-second-order kinetic model. Therefore, the pseudo-first-order kinetic model is most suitable for describing the adsorption kinetics of methylene blue on the activated carbon surface, indicating that the adsorption of the reduced-modified activated carbon is mainly dominated by physical adsorption. However, compared with the original activated carbon, the number of chemical adsorption sites in the modified activated carbon is significantly increased, thus improving the adsorption capacity of the activated carbon.

[0076] Adsorption isotherm analysis of ammonia-modified activated carbon in this invention

[0077] This invention employs two isotherm models, Langmuir and Freundlich, to fit and analyze experimental data. The Langmuir formula describes the adsorption of target molecules, which are similar in size to water molecules, on activated carbon surfaces as a monolayer. The Freundlich formula, on the other hand, describes the adsorption of target molecules on heterogeneous surfaces. The model formulas are as follows:

[0078] Langmuir adsorption isotherm model formula:

[0079] (3-1)

[0080] Freundlich adsorption isotherm model formula:

[0081] (3-2)

[0082] In the above formulas (3-1) and (3-2): C e q represents the concentration of MB in the solution (mg / L) at adsorption equilibrium. e Q represents the equilibrium adsorption capacity (mg / g) of MB. m K represents the theoretical maximum adsorption capacity of MB. F It is the Freundlich adsorption isotherm model constant, K L is the Langmuir adsorption isotherm model constant, and N is a constant related to adsorption strength. The test results are shown in Table 4.

[0083]

[0084] Table 4 shows that the R-value of the Langmuir adsorption isotherm model is... 2 All values ​​were greater than 0.99, indicating better consistency between activated carbon and the Langmuir model. The results show that the MB adsorption sites of grapefruit peel-based activated carbon are monolayered and uniform, consistent with the assumptions of the Langmuir model. Therefore, the adsorption mechanism of MB by ammonia-reduced modified activated carbon is a combination of physical and chemical monolayer adsorption.

[0085] In summary, the preparation method of ammonia-modified activated carbon of the present invention has the following advantages:

[0086] 1. This invention utilizes pomelo peel, an agricultural waste, as raw material, combined with sodium carbonate activator, and carbonizes it in an oxygen-limited muffle furnace at 700℃ for 2 hours to achieve a high-yield, high-specific-surface-area (317.0587 m² / g) biochar in a green manner. The process of this invention is simple, controllable, and highly reproducible, effectively solving the problems of high raw material costs and insufficient waste resource utilization in traditional activated carbon production.

[0087] 2. This invention uses an ammonia solution refluxed at 65°C for 4 hours to reduce and modify activated carbon. Surface chemical properties are controlled under mild conditions: oxidized nitrogen... Transformation into graphitic nitrogen (The XPS peak area increased by 4392.59 au), significantly increasing the content of basic functional groups and enhancing the electrostatic adsorption capacity for cationic dyes.

[0088] 3. The modified activated carbon of this invention has a smaller pore size of 25–26 nm (original carbon 32.004 nm), forming a more uniform microporous-mesoporous composite structure, which enhances the dye molecule retention capacity. The adsorption rate of methylene blue is increased by 32% (the removal rate reaches 94.77% after modification with 15% ammonia water, compared to only 62.58% for the original carbon).

[0089] 4. The ammonia-modified activated carbon of this invention is used to treat low-concentration methylene blue wastewater (≤50 mg / L), achieving a decolorization rate of >94% and an adsorption capacity of 98.38 mg / g under neutral conditions at 25℃. The adsorption mechanism conforms to physical-dominated monolayer adsorption (pseudo-first-order kinetic model R²>0.97, Langmuir model R²>0.99), solving the problem of poor selectivity of traditional activated carbon for cationic dyes.

Claims

1. A method for preparing ammonia-modified activated carbon, characterized in that, The method includes the following steps: (1) Mix grapefruit peel powder and sodium carbonate activator in a weight ratio of 3:1 and place them evenly in a high-temperature resistant corundum crucible. Then place them in a muffle furnace and heat them at 700°C for 2 hours to carbonize them. Cool them to room temperature to obtain carbonized products. (2) Grind the obtained carbon into powder that passes through a 40-mesh sieve, wash off the sodium carbonate activator with a 1 mol / L nitric acid solution, filter, and then dry in an oven at 60°C to obtain grapefruit peel-based activated carbon. (3) Mix grapefruit peel-based activated carbon with ammonia water with a mass concentration of 5-15% at a weight ratio of 1:100 and place it in a three-necked flask; (4) Reflux the reaction at 65℃ for 4 h. After the reaction is complete, wash the activated carbon repeatedly with deionized water until the filtrate is neutral. (5) Finally, the activated carbon is placed in an oven at 60°C and dried to constant weight to obtain ammonia-reduced modified activated carbon.

2. The method for preparing ammonia-modified activated carbon according to claim 1, characterized in that, The method for preparing the grapefruit peel powder described in step (1) is as follows: (1) Remove the pulp from the Shatin pomelo, then cut the remaining pomelo peel into small pieces and wash it clean; (2) Place the cleaned grapefruit peel in an electric heating drying oven and dry it at 80°C for more than 8 hours until its quality no longer changes, and obtain grapefruit peel residue. Then, pulverize the grapefruit peel residue by high-speed electric mill and pass it through a 40-mesh sieve to obtain grapefruit peel powder. Seal it in a desiccator for storage.

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