Composite phosphorus removal agent and preparation method thereof

Abstract

The invention belongs to the technical field of sewage treatment, and particularly relates to a composite phosphorus removal agent and a preparation method thereof. The preparation method comprises the following steps: adding a chitosan derivative and sodium alginate into water, uniformly stirring, and then adding modified magnesium-aluminum layered bimetal hydroxide to obtain a mixed solution; and adding the mixed solution into a lanthanum nitrate solution to form gel microspheres, washing, and drying in vacuum. Modified magnesium-aluminum layered double hydroxides, chitosan derivatives and sodium alginate are used as raw materials, and the composite phosphorus removal agent is prepared through lanthanum ion crosslinking. The composite phosphorus removal agent has the advantages of high selectivity, large adsorption capacity, wide pH application range and excellent reusability.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a composite phosphorus removal agent and its preparation method. Background Technology

[0002] Eutrophication is a prominent water environment problem, and one of its key contributing factors is excessive phosphorus levels in water. Eutrophication leads to a sharp decline in water oxygen levels, causing aquatic organisms to die from lack of oxygen, ecosystem degradation, water quality deterioration, and significantly increasing the difficulty and cost of wastewater treatment. Therefore, effectively removing phosphorus from wastewater is of great significance for the prevention and control of eutrophication.

[0003] Currently, commonly used methods for phosphorus removal from wastewater mainly include chemical methods, biological methods, and adsorption methods. Chemical methods, which involve adding metal salt reagents to form phosphate precipitates, are effective but easily generate chemical sludge, causing secondary pollution, and have a limited applicable pH range. Biological methods rely on the phosphorus uptake of polyphosphate-accumulating bacteria; their effectiveness is greatly affected by microbial activity and fluctuations in influent water quality, making it difficult to consistently achieve the required phosphorus concentration in the effluent for advanced treatment, and their operation and control are relatively complex. Adsorption methods have attracted much attention due to their simple operation, fast phosphorus removal rate, environmental friendliness, and wide applicability. However, while natural adsorbent materials (such as zeolite and clay) have large specific surface areas, they generally suffer from low adsorption capacity, poor selectivity for phosphorus, and unstable performance under a wide range of pH conditions, limiting their practical application. Therefore, it is essential to develop an adsorbent material with high selectivity, large adsorption capacity, a wide pH applicable range, and good regeneration performance. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the primary objective of this invention is to provide a method for preparing a composite phosphorus removal agent. This method uses modified magnesium-aluminum layered bimetallic hydroxide, chitosan derivatives and sodium alginate as raw materials, and prepares the composite phosphorus removal agent through lanthanum ion crosslinking.

[0005] Another object of the present invention is to provide a composite phosphorus removal agent prepared by the above method, which has high selectivity, large adsorption capacity, wide pH range and good regeneration performance.

[0006] The objective of this invention is achieved through the following technical solution: The first aspect of this invention provides a method for preparing a composite phosphorus removal agent, comprising the following steps: Chitosan derivatives and sodium alginate were added to water and stirred until homogeneous. Then, modified magnesium-aluminum layered bimetallic hydroxide was added to obtain a mixed solution. The mixed solution was added to a lanthanum nitrate solution to form gel microspheres. After washing and vacuum drying, the composite phosphorus removal agent was obtained. The modified magnesium-aluminum layered bimetallic hydroxide was prepared by modifying magnesium-aluminum layered bimetallic hydroxide with N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt; the structural formula of the N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt is as follows: ; The preparation process of the chitosan derivative is as follows: (1) Add 4-azidobenzoic acid, N-hydroxysuccinimide and N,N'-dicyclohexylcarbodiimide to 1,4-dioxane and carry out the first light-protected reaction to obtain activated 4-azidobenzoic acid; add the dimethyl sulfoxide solution of activated 4-azidobenzoic acid to the acetic acid / water solution of chitosan and carry out the second light-protected reaction to obtain azido-chitosan; (2) The azide-modified chitosan is added to a mixed solvent of acetic acid / dimethyl sulfoxide, and then acetylacetic betaine, sodium ascorbate and CuSO4 solution are added to react and obtain chitosan derivatives; The structural formula of the acetylacetic betaine is as follows: .

[0007] Preferably, in step (1), the molar ratio of 4-azidobenzoic acid, N-hydroxysuccinimide, and N,N'-dicyclohexylcarbodiimide is 1:(1-1.5):(1-1.5); the mass ratio of chitosan to activated 4-azidobenzoic acid is 1:(0.5-0.8); the time for the first light-protected reaction is 12-18 h; and the time for the second light-protected reaction is 2-3 d.

[0008] Preferably, the mass ratio of azidochitosan, acetylacetic betaine, sodium ascorbate and CuSO4 in step (2) is 1:(0.8-1):(0.4-0.5):(0.17-0.21); and the reaction time is 24-48 h.

[0009] Preferably, the preparation process of the acetylated betaine in step (2) is as follows: adding propargylamine and N,N-diisopropylethylamine to dichloromethane, and then adding a dichloromethane solution of betaine chloride at 0°C to react and obtain the acetylated betaine; the molar ratio of propargylamine, betaine chloride and N,N-diisopropylethylamine is 1:(1.4-2):(3-4).

[0010] Preferably, the preparation process of the modified magnesium-aluminum layered bimetallic hydroxide is as follows: (a) Add magnesium nitrate and aluminum nitrate to water to obtain a precursor solution; add sodium nitrate and sodium hydroxide to water to obtain an alkaline solution; add the precursor solution to the alkaline solution at 60-70°C to carry out a hydrothermal reaction, and after post-treatment, obtain magnesium-aluminum layered bimetallic hydroxide; (b) The magnesium-aluminum layered bimetallic hydroxide was added to a solution of N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt, stirred and reacted, and then post-treated to obtain the modified magnesium-aluminum layered bimetallic hydroxide.

[0011] Preferably, in step (a), the concentrations of magnesium nitrate and aluminum nitrate in the precursor solution are 1-2 mol / L and 0.5 mol / L, respectively; the concentrations of sodium nitrate and sodium hydroxide in the alkaline solution are 2-3 mol / L and 3-5 mol / L, respectively; the volume ratio of the precursor solution to the alkaline solution is 1:1; the temperature of the hydrothermal reaction is 100-120℃, and the time is 12-18 h.

[0012] Preferably, in step (b), the ratio of the magnesium-aluminum layered bimetallic hydroxide to the N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt solution is 1 g: (100-200) mL; the concentration of the N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt solution is 0.02-0.05 mol / L; and the stirring reaction time is 3-5 h.

[0013] Preferably, the preparation process of the N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetate inner salt is as follows: ① Ethyl isonicotinic acid and 12-bromo-1-dodecene were added to ethanol and refluxed. After purification, intermediate 1 was obtained. The structural formula of intermediate 1 is as follows: ; ② The intermediate 1, mercaptoacetic acid and triethylamine were added to dichloromethane and reacted at room temperature. After purification, the N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt was obtained.

[0014] Preferably, in step ①, the molar ratio of isonicotinic acid ethyl ester to 12-bromo-1-dodecene is 1:(1-1.5), and the reflux reaction time is 48-60 h; in step ②, the molar ratio of intermediate 1, mercaptoacetic acid, and triethylamine is 1:(1-1.25):(0.5-0.6), and the reaction time at room temperature is 8-10 h.

[0015] A second aspect of the present invention provides a composite phosphorus removal agent, which is prepared by the above-described preparation method.

[0016] The present invention has the following advantages over the prior art: 1. This invention provides a composite phosphorus removal agent, which is a three-dimensional network gel microsphere prepared by cross-linking with lanthanum ions using modified magnesium-aluminum layered bimetallic hydroxide, chitosan derivatives, and sodium alginate as raw materials. This composite phosphorus removal agent exhibits high selectivity, large adsorption capacity, wide pH range, and excellent reusability.

[0017] 2. The modified magnesium-aluminum layered bimetallic hydroxide of the present invention is obtained by intercalation modification of magnesium-aluminum layered bimetallic hydroxide with N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetate inner salt. This intercalation structure has three functions: first, it expands the interlayer spacing, significantly reducing the diffusion resistance of phosphate; second, the zwitterion pair formed by its pyridinium and carboxylate enhances the selective recognition of phosphate and suppresses the interference of competing anions such as sulfate and chloride ions through electrostatic shielding effect; and third, it increases the hydrophilicity of the material surface and the number of ion exchange sites. These three functions work together to achieve a significant improvement in the selectivity, adsorption capacity, and adsorption rate of the phosphate remover.

[0018] 3. The chitosan derivative of this invention is prepared by a click chemistry reaction of azidated chitosan and acetylated betaine, introducing triazole ring linkers and terminal quaternary ammonium groups onto the chitosan backbone. The quaternary ammonium groups of this derivative can efficiently capture phosphate ions through strong electrostatic interactions over a wide pH range, solving the problem of reduced efficiency of traditional adsorbents under alkaline conditions due to weakened surface charge. Simultaneously, the conjugated structure of its triazole ring can further enhance phosphate adsorption through secondary interactions such as π–π stacking.

[0019] 4. The quaternary ammonium groups and triazole rings in the chitosan derivatives of this invention, as well as the pyridinium ions in the intercalating agent, all possess strong antibacterial activity. They can effectively inhibit bacterial growth on the material surface and within the pores, prevent biofilm formation, and avoid blockage of adsorption channels and deactivation of active sites. This synergistic and stable gel framework not only ensures the continuous stability of phosphorus removal efficiency during long-term operation of the phosphorus removal agent, but also provides it with excellent regeneration performance, enabling it to maintain a high adsorption capacity even during repeated use. Attached Figure Description

[0020] Figure 1 FT-IR images of chitosan, azidated chitosan, and chitosan derivatives in Preparation Example 4 are shown, where a corresponds to chitosan, b corresponds to azidated chitosan, and c corresponds to chitosan derivatives. Figure 2 This is a SEM image of the composite phosphorus removal agent in Example 1. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to specific embodiments. However, those skilled in the art should understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the reagents or instruments used are all conventional products obtained through commercial channels.

[0022] Preparation Example 1 Preparation Example 1 provides an acetylated betaine, prepared by the following process: Prolylamine (3.7 mmol) and N,N-diisopropylethylamine (13.0 mmol) were dissolved in 22 mL of dichloromethane, cooled to 0 °C, and a dichloromethane solution of betaine chloride (6.0 mmol, 20 mL) was added. The mixture was reacted at room temperature for 2 h, concentrated under vacuum, and purified by column chromatography (dichloromethane / methanol gradient elution of 100:1 to 5:1) to obtain acetylated betaine. 1 HNMR: (400MHz, DMSO-d6) δ : 3.06-3.10(t, H), 3.30(s, 9H), 4.13(s, 2H), 4.19-4.23(d, 2H), 8.18(s, H); MS (ESI) m / z=155.12[M].

[0023] Preparation Example 2 Preparation Example 2 provides an acetylated betaine, prepared by the following process: Proprynneamine (3.7 mmol) and N,N-diisopropylethylamine (11.1 mmol) were dissolved in 20 mL of dichloromethane, cooled to 0 °C, and a dichloromethane solution of betaine chloride (5.5 mmol, 20 mL) was added. The reaction was carried out at room temperature for 1 h, concentrated under vacuum, and purified by column chromatography (dichloromethane / methanol gradient elution of 100:1 to 5:1) to obtain acetylacetine; acetylacetine... 1 The HNMR and MS results were consistent with those of Preparation Example 1.

[0024] Preparation Example 3 Preparation Example 3 provides an acetylated betaine, prepared by the following process: Proprynneamine (3.7 mmol) and N,N-diisopropylethylamine (14.8 mmol) were dissolved in 25 mL of dichloromethane, cooled to 0 °C, and a dichloromethane solution of betaine chloride (7.4 mmol, 20 mL) was added. The reaction was carried out at room temperature for 3 h, concentrated under vacuum, and purified by column chromatography (dichloromethane / methanol gradient elution of 100:1 to 5:1) to obtain acetylacetine; acetylacetine... 1The HNMR and MS results were consistent with those of Preparation Example 1.

[0025] Preparation Example 4 Preparation Example 4 provides a chitosan derivative, the preparation process of which is as follows: (1) 4-Azidobenzoic acid (10 mmol), N-hydroxysuccinimide (12 mmol) and N,N'-dicyclohexylcarbodiimide (12 mmol) were dissolved in 45 mL of 1,4-dioxane and reacted at room temperature in the dark for 15 h. After filtration, the filtrate was evaporated to obtain activated 4-azidobenzoic acid. Activated 4-azidobenzoic acid (0.6 g) was dissolved in dimethyl sulfoxide to prepare an activated 4-azidobenzoic acid solution with a concentration of 15 g / L. Chitosan (1 g) was prepared in acetic acid / water solution (1:99, v / v) to prepare a chitosan solution with a concentration of 4 wt%. The activated 4-azidobenzoic acid solution was then added to the chitosan solution and reacted at room temperature in the dark for 2.5 d. After dialyzing with deionized water and freeze-drying, azido-chitosan was obtained. (2) Azide-modified chitosan (0.1 g) was dissolved in 10 mL of acetic acid / dimethyl sulfoxide solution (1:99, v / v), and acetylacetic betaine (0.09 g), sodium ascorbate (0.045 g) and CuSO4 solution (0.019 g, 1 mol / L) from Preparation Example 1 were added. After reacting at room temperature for 36 h, the mixture was dialyzed with deionized water and freeze-dried to obtain the chitosan derivative.

[0026] Preparation Example 5 Preparation Example 5 provides a chitosan derivative, the preparation process of which is as follows: (1) 4-Azidobenzoic acid (10 mmol), N-hydroxysuccinimide (10 mmol) and N,N'-dicyclohexylcarbodiimide (10 mmol) were dissolved in 40 mL of 1,4-dioxane and reacted at room temperature in the dark for 12 h. After filtration, the filtrate was evaporated to obtain activated 4-azidobenzoic acid. Activated 4-azidobenzoic acid (0.5 g) was dissolved in dimethyl sulfoxide to prepare an activated 4-azidobenzoic acid solution with a concentration of 15 g / L. Chitosan (1 g) was prepared in acetic acid / water solution (1:99, v / v) to prepare a chitosan solution with a concentration of 2 wt%. The activated 4-azidobenzoic acid solution was added to the chitosan solution and reacted at room temperature in the dark for 2 d. After dialyzing with deionized water and freeze-drying, azido-chitosan was obtained. (2) Azide-modified chitosan (0.1 g) was dissolved in 10 mL of acetic acid / dimethyl sulfoxide solution (1:99, v / v), and acetylacetic betaine (0.08 g), sodium ascorbate (0.04 g) and CuSO4 solution (0.017 g, 1 mol / L) from Preparation Example 2 were added. After reacting at room temperature for 24 h, the mixture was dialyzed with deionized water and freeze-dried to obtain the chitosan derivative.

[0027] Preparation Example 6 Preparation Example 6 provides a chitosan derivative, the preparation process of which is as follows: (1) 4-Azidobenzoic acid (10 mmol), N-hydroxysuccinimide (15 mmol) and N,N'-dicyclohexylcarbodiimide (15 mmol) were dissolved in 50 mL of 1,4-dioxane and reacted at room temperature in the dark for 18 h. After filtration, the filtrate was evaporated to obtain activated 4-azidobenzoic acid. Activated 4-azidobenzoic acid (0.8 g) was dissolved in dimethyl sulfoxide to prepare an activated 4-azidobenzoic acid solution with a concentration of 15 g / L. Chitosan (1 g) was prepared in acetic acid / water solution (1:99, v / v) to prepare a chitosan solution with a concentration of 5 wt%. The activated 4-azidobenzoic acid solution was then added to the chitosan solution and reacted at room temperature in the dark for 3 days. After dialyzing with deionized water and freeze-drying, azido-chitosan was obtained. (2) Azide-modified chitosan (0.1 g) was dissolved in 10 mL of acetic acid / dimethyl sulfoxide solution (1:99, v / v), and acetylacetic betaine (0.1 g), sodium ascorbate (0.05 g) and CuSO4 solution (0.021 g, 1 mol / L) from Preparation Example 3 were added. After reacting at room temperature for 48 h, the mixture was dialyzed with deionized water and freeze-dried to obtain the chitosan derivative.

[0028] Preparation Example 7 Preparation Example 7 provides an N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetate inner salt, the preparation process of which is as follows: ①Isonicotinic acid ethyl ester (8 mmol) and 12-bromo-1-dodecene (10 mmol) were dissolved in 40 mL of anhydrous ethanol and reacted under reflux for 55 h. The crude product was obtained by vacuum distillation. The crude product was recrystallized with ethyl acetate, filtered, washed with ethyl acetate, and dried naturally at room temperature to obtain intermediate 1. 1HNMR: (400MHz, DMSO-d6) δ: 1.24-1.35 (m, 17H), 1.99-2.03 (m, 2H), 2.11-2.15 (m, 2H), 4.28-4.32 (m, 2H), 4.86-4. 90 (m, 1H), 4.99-5.03 (t, 2H), 5.11-5.15 (m, 1H), 5.80-5.84 (m, 1H), 8.37-8.41 (d, 2H), 9.14-9.18 (d, 2H); MS (ESI) m / z=318.24[M].

[0029] ② Intermediate 1 (20 mmol), mercaptoacetic acid (22 mmol), and triethylamine (11 mmol) were dissolved in 65 mL of dichloromethane and reacted at room temperature for 9 h. The crude product was obtained by filtration. The crude product was dissolved in an appropriate amount of ethanol, and an excess of saturated sodium bicarbonate aqueous solution was slowly added under ice bath stirring. The mixture was stirred at room temperature for 45 min, and ethyl acetate was added to precipitate the product. The product was filtered, washed with ethyl acetate, and dried under vacuum to obtain N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt. 1 HNMR: (400MHz, DMSO-d6) δ: 1.23-1.35 (m, 17H), 1.40-1.44 (m, 2H), 1.55-1.59 (m, 2H), 1.99-2.03 (m, 2H), 2. 40-2.44 (t, 2H), 3.55 (s, 2H), 4.28-4.32 (m, 2H), 4.99-5.03 (t, 2H), 8.37-8.41 (d, 2H), 9.14-9.18 (d, 2H); MS (ESI) m / z=409.23[M].

[0030] Preparation Example 8 Preparation Example 8 provides an N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetate inner salt, the preparation process of which is as follows: ① Ethyl isonicotinic acid (8 mmol) and 12-bromo-1-dodecene (8 mmol) were dissolved in 30 mL of anhydrous ethanol and reacted under reflux for 48 h. The mixture was then distilled under reduced pressure to obtain the crude product. The crude product was recrystallized from ethyl acetate, filtered, washed with ethyl acetate, and then naturally dried at room temperature to obtain intermediate 1. Intermediate 1... 1 The HNMR and MS results were consistent with those of Preparation Example 1.

[0031] ② Intermediate 1 (20 mmol), mercaptoacetic acid (20 mmol), and triethylamine (10 mmol) were dissolved in 50 mL of dichloromethane and reacted at room temperature for 8 h. The crude product was obtained by filtration. The crude product was dissolved in an appropriate amount of ethanol, and an excess of saturated sodium bicarbonate aqueous solution was slowly added under ice bath stirring. The mixture was stirred at room temperature for 30 min, and ethyl acetate was added to precipitate the product. The product was filtered, washed with ethyl acetate, and dried under vacuum to obtain N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt. 1 The HNMR and MS results were consistent with those of Preparation Example 1.

[0032] Preparation Example 9 Preparation Example 9 provides an N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetate inner salt, the preparation process of which is as follows: ① Ethyl isonicotinic acid (8 mmol) and 12-bromo-1-dodecene (12 mmol) were dissolved in 50 mL of anhydrous ethanol and reacted under reflux for 48-60 h. The mixture was then distilled under reduced pressure to obtain the crude product. The crude product was recrystallized from ethyl acetate, filtered, washed with ethyl acetate, and then naturally dried at room temperature to obtain intermediate 1. Intermediate 1... 1 The HNMR and MS results were consistent with those of Preparation Example 1.

[0033] ② Intermediate 1 (20 mmol), mercaptoacetic acid (25 mmol), and triethylamine (12 mmol) were dissolved in 50-75 mL of dichloromethane and reacted at room temperature for 10 h. The crude product was obtained by filtration. The crude product was dissolved in an appropriate amount of ethanol, and an excess of saturated sodium bicarbonate aqueous solution was slowly added under ice bath stirring. The mixture was stirred at room temperature for 60 min, and ethyl acetate was added to precipitate the product. The product was filtered, washed with ethyl acetate, and dried under vacuum to obtain N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt. 1 The HNMR and MS results were consistent with those of Preparation Example 1.

[0034] Preparation Example 10 Preparation Example 10 provides a modified magnesium-aluminum layered bimetallic hydroxide, the preparation process of which is as follows: (a) Magnesium nitrate and aluminum nitrate were added to water to obtain a precursor solution with concentrations of 1.5 mol / L and 0.5 mol / L, respectively. Sodium nitrate and sodium hydroxide were added to water to obtain an alkaline solution with concentrations of 2.5 mol / L and 4 mol / L, respectively. The precursor solution was added dropwise to the alkaline solution at a volume ratio of 1:1 at 65°C. The mixture was then placed in a hydrothermal reactor and reacted at 110°C for 15 h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed with deionized water, and vacuum dried to obtain a magnesium-aluminum layered bimetallic hydroxide. (b) Add 1 g of magnesium-aluminum layered bimetallic hydroxide to 150 mL of 0.03 mol / L N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt aqueous solution, stir at room temperature for 4 h, centrifuge, collect the solid and wash with deionized water, and dry in a vacuum oven at 60 °C to obtain modified magnesium-aluminum layered bimetallic hydroxide.

[0035] Preparation Example 11 Preparation Example 11 provides a modified magnesium-aluminum layered bimetallic hydroxide, the preparation process of which is as follows: (a) Magnesium nitrate and aluminum nitrate were added to water to obtain a precursor solution with concentrations of 1 mol / L and 0.5 mol / L, respectively. Sodium nitrate and sodium hydroxide were added to water to obtain an alkaline solution with concentrations of 2 mol / L and 3 mol / L, respectively. The precursor solution was added dropwise to the alkaline solution at a volume ratio of 1:1 at 60°C. The mixture was then placed in a hydrothermal reactor and reacted at 100°C for 18 h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed with deionized water, and vacuum dried to obtain a magnesium-aluminum layered bimetallic hydroxide. (b) Add 1 g of magnesium-aluminum layered bimetallic hydroxide to 100 mL of 0.05 mol / L N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt aqueous solution, stir at room temperature for 3 h, centrifuge, collect the solid and wash with deionized water, and dry in a vacuum oven at 60 °C to obtain modified magnesium-aluminum layered bimetallic hydroxide.

[0036] Preparation Example 12 Preparation Example 12 provides a modified magnesium-aluminum layered bimetallic hydroxide, the preparation process of which is as follows: (a) Magnesium nitrate and aluminum nitrate were added to water to obtain a precursor solution with concentrations of 2 mol / L and 0.5 mol / L, respectively. Sodium nitrate and sodium hydroxide were added to water to obtain an alkaline solution with concentrations of 3 mol / L and 5 mol / L, respectively. The precursor solution was added dropwise to the alkaline solution at a volume ratio of 1:1 at 70°C. The mixture was then placed in a hydrothermal reactor and reacted at 120°C for 12 h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed with deionized water, and vacuum dried to obtain a magnesium-aluminum layered bimetallic hydroxide. (b) Add 1 g of magnesium-aluminum layered bimetallic hydroxide to 200 mL of 0.02 mol / L N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt aqueous solution, stir at room temperature for 5 h, centrifuge, collect the solid and wash with deionized water, and dry in a vacuum oven at 60 °C to obtain modified magnesium-aluminum layered bimetallic hydroxide.

[0037] Example 1 Example 1 provides a method for preparing a composite phosphorus removal agent, the specific process of which is as follows: The chitosan derivative (0.3 g) and sodium alginate (0.5 g) from Preparation Example 4 were added to 55 mL of deionized water and stirred until homogeneous. Then, the modified magnesium-aluminum layered bimetallic hydroxide (0.45 g) from Preparation Example 10 was added and mixed until homogeneous. The above solution was then added dropwise to a 5 wt% lanthanum nitrate solution to form gel microspheres. After washing with deionized water and vacuum drying, a composite phosphorus removal agent was obtained.

[0038] Example 1 also provides a composite phosphorus removal agent obtained by the above preparation method.

[0039] Example 2 Example 2 provides a method for preparing a composite phosphorus removal agent, the specific process of which is as follows: The chitosan derivative (0.6 g) and sodium alginate (0.6 g) from Preparation Example 5 were added to 60 mL of deionized water and stirred until homogeneous. Then, the modified magnesium-aluminum layered bimetallic hydroxide (0.45 g) from Preparation Example 11 was added and mixed until homogeneous. The above solution was then added dropwise to a 5 wt% lanthanum nitrate solution to form gel microspheres. After washing with deionized water and vacuum drying, a composite phosphorus removal agent was obtained.

[0040] Example 2 also provides a composite phosphorus removal agent obtained by the above preparation method.

[0041] Example 3 Example 3 provides a method for preparing a composite phosphorus removal agent, the specific process of which is as follows: The chitosan derivative (0.4 g) and sodium alginate (0.3 g) from Preparation Example 6 were added to 50 mL of deionized water and stirred until homogeneous. Then, the modified magnesium-aluminum layered bimetallic hydroxide (0.45 g) from Preparation Example 12 was added and mixed until homogeneous. The above solution was then added dropwise to a 5 wt% lanthanum nitrate solution to form gel microspheres. After washing with deionized water and vacuum drying, a composite phosphorus removal agent was obtained.

[0042] Example 3 also provides a composite phosphorus removal agent obtained by the above preparation method.

[0043] Comparative Example 1 Comparative Example 1 is basically the same as Example 1, except that the chitosan derivative in Example 1 is replaced with chitosan.

[0044] Comparative Example 2 Comparative Example 2 is basically the same as Example 1, except that the modified magnesium-aluminum layered bimetallic hydroxide in Example 1 is replaced with the magnesium-aluminum layered bimetallic hydroxide obtained in step (a) of Preparation Example 10.

[0045] Structural characterization FT-IR tests were performed on the chitosan, azido-chitosan, and chitosan derivatives obtained in Preparation Example 4, and the results are as follows: Figure 1 As shown, Figure 1 Curve a corresponds to chitosan, curve b corresponds to azidated chitosan, and curve c corresponds to chitosan derivatives. From Figure 1 It can be seen that, compared to chitosan, azidated chitosan has a higher content of 2130 cm⁻¹. -1 The presence of a characteristic absorption peak for azido groups at 2520 cm⁻¹ indicates successful preparation of azido-chitosan; compared to azido-chitosan, the chitosan derivative exhibits a higher absorption peak at 2520 cm⁻¹. -1 and 1474 cm -1 The presence of characteristic absorption peaks at C=CN=N and methyl groups on the quaternary ammonium salt indicates that the chitosan derivative was successfully prepared.

[0046] The composite phosphorus removal agent obtained in Example 1 was tested by scanning electron microscopy, and the results are as follows: Figure 2 As shown.

[0047] Performance testing (1) Removal rate: 8 mg of each of the phosphorus removal agents prepared in Examples 1-3 and Comparative Examples 1-2 were added to 50 mL of an aqueous solution of phosphate (KH2PO4) with an initial concentration of 30 mg / L. The solution was shaken at 25℃ until adsorption equilibrium was reached. The supernatant was filtered through a 0.45 μm filter membrane, and the concentration of phosphate in the filtrate was measured. The removal rate of the phosphorus removal agent was calculated according to the following formula: R (%) = (C0 - C t ) / C0×100%, where C0 and C tThe values ​​are the phosphate concentrations in the solution before and after adsorption, in mg / L. The results are shown in Table 1.

[0048] (2) Adsorption capacity: 8 mg of each of the phosphorus removal agents prepared in Examples 1-3 and Comparative Examples 1-2 were added to 50 mL of an aqueous solution of phosphate (KH2PO4) with an initial concentration of 30 mg / L. The solution was kept at 25℃ and shaken until adsorption equilibrium was reached. The supernatant was filtered through a 0.45 μm filter membrane, and the concentration of phosphate in the filtrate was measured. The adsorption capacity of the phosphorus removal agent was calculated according to the following formula: Q e =V(C0-C) e ) / m, where Q e V represents the amount of adsorbent adsorbed at adsorption equilibrium, in mg / g; V represents the volume of the phosphate solution, in L; C e C0 and C0 represent the phosphate concentrations in the equilibrium solution and the initial solution, respectively, in mg / L. m represents the mass of the phosphate removal agent in g. The results are shown in Table 1.

[0049] (3) Adsorption performance at different pH values: 50 mL of phosphate (KH2PO4) aqueous solution with an initial concentration of 30 mg / L was taken, and the pH value was adjusted to 3, 5, 7, 9 and 11 respectively with 0.1 mol / L HCl solution and NaOH solution. 8 mg of each of the phosphorus removal agent prepared in Examples 1-3 and Comparative Examples 1-2 was added to phosphate aqueous solutions with different pH values, and the solution was shaken at 25℃ until adsorption equilibrium was reached. After filtration through a 0.45 μm filter membrane, the concentration of phosphate in the filtrate was measured, and the adsorption rate of the phosphorus removal agent was calculated. The results are shown in Table 2.

[0050] (4) Reusability test: Take 8 mg of each of the phosphorus removal agent prepared in Examples 1-3 and Comparative Examples 1-2 and add them to 50 mL of phosphate (KH2PO4) aqueous solution with an initial concentration of 30 mg / L. Shake at 25℃ until adsorption equilibrium is reached. Filter through a 0.45 μm filter membrane to separate the phosphorus removal agent from the solution. Put the phosphorus removal agent into a 0.1 mol / L sodium hydroxide solution for desorption. After filtration, wash with deionized water until neutral. After drying, repeat the above adsorption-desorption cycle 10 times. After the 10th cycle, the concentration of residual phosphate in the filtrate is determined again by the molybdenum antimony spectrophotometric method. Calculate the adsorption rate after 10 cycles. The results are shown in Table 3.

[0051] (5) Anti-interference performance: Take 8 mg of each of the phosphorus removal agents prepared in Examples 1-3 and Comparative Examples 1-2 and add them to 50 mL of phosphate (KH2PO4) aqueous solution with an initial concentration of 30 mg / L. Add Na2SO4 (30 mg / L) or NaCl (30 mg / L) respectively. Shake at 25℃ until adsorption equilibrium is reached. Take the supernatant and filter it through a 0.45 μm filter membrane. Measure the concentration of phosphate in the filtrate and calculate the removal rate of the phosphorus removal agent. The results are shown in Table 3.

[0052] Table 1 Table 2 Table 3 As can be seen from the experimental data in Tables 1-3, the composite phosphorus removal agent prepared in Examples 1-3 has a large adsorption capacity, a wide pH range, high selectivity, and good regeneration performance.

[0053] Compared to Example 1, the phosphorus removal agents prepared in Comparative Examples 1-2 all showed varying degrees of decrease in adsorption capacity, pH range, anti-interference ability, and reusability, indicating that the modified magnesium-aluminum layered bimetallic hydroxide and chitosan derivative of the present invention can improve the adsorption effect of phosphorus removal agents to varying degrees.

[0054] A detailed analysis of the above results is as follows: ① The modified magnesium-aluminum layered bimetallic hydroxide of the present invention is obtained by intercalation modification of magnesium-aluminum layered bimetallic hydroxide with N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetate inner salt. This intercalation structure has three functions: first, it expands the interlayer spacing, significantly reducing the diffusion resistance of phosphate; second, the zwitterion pair formed by its pyridinium and carboxylate can enhance the selective recognition of phosphate and suppress the interference of competing anions such as sulfate and chloride ions through electrostatic shielding effect; third, it improves the hydrophilicity of the material surface and the number of ion exchange sites. The three functions work together to achieve a significant improvement in the selectivity, adsorption capacity and adsorption rate of the phosphate remover. ② The chitosan derivative of the present invention is prepared by click chemistry reaction of azidated chitosan and acetylated betaine, which introduces triazole ring linker arms and terminal quaternary ammonium groups into the chitosan backbone. The quaternary ammonium group of this derivative can efficiently capture phosphate ions through strong electrostatic interactions over a wide pH range, solving the problem of reduced efficiency of traditional adsorbents under alkaline conditions due to weakened surface charge. Simultaneously, the conjugated structure of its triazole ring can further enhance phosphate adsorption through secondary interactions such as π–π stacking. ③ The quaternary ammonium group and triazole ring in the chitosan derivative, as well as the pyridinium ion in the intercalating agent, all possess strong antibacterial activity, effectively inhibiting bacterial growth on the material surface and within pores, preventing biofilm formation, and avoiding blockage of adsorption channels and deactivation of active sites. This synergistic and stable gel framework not only ensures the continuous stability of phosphorus removal efficiency during long-term operation but also provides excellent regeneration performance, allowing it to maintain a high adsorption capacity even during repeated use.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. A method for preparing a composite phosphorus removal agent, characterized by, The method comprises the following steps: The chitosan derivative and sodium alginate are added into water and stirred uniformly, and then the modified magnesium-aluminum layered double hydroxide is added to obtain a mixed solution; the mixed solution is added into a lanthanum nitrate solution to form gel microspheres, and the gel microspheres are washed and vacuum dried to obtain the composite phosphorus removal agent; The modified magnesium-aluminum layered double hydroxide is prepared by modifying the magnesium-aluminum layered double hydroxide with N-dodecyl-4-(ethoxycarbonyl) pyridinium-S-acetic acid inner salt; the structural formula of the N-dodecyl-4-(ethoxycarbonyl) pyridinium-S-acetic acid inner salt is as follows: ； The preparation process of the chitosan derivative is as follows: (1) 4-azidobenzoic acid, N-hydroxysuccinimide and N,N'-dicyclohexyl carbodiimide are added into 1,4-dioxane to perform a first light-avoiding reaction to obtain activated 4-azidobenzoic acid; a dimethyl sulfoxide solution of the activated 4-azidobenzoic acid is added into an acetic acid / water solution of chitosan to perform a second light-avoiding reaction to obtain azidated chitosan; (2) the azidated chitosan is added into an acetic acid / dimethyl sulfoxide mixed solvent, and then ynyl betaine, sodium ascorbate and a CuSO4 solution are added to perform a reaction to obtain the chitosan derivative; The structural formula of the ynyl betaine is as follows: 。 2. The method of claim 1, wherein the composite phosphorus removal agent is prepared by the steps of: In step (1), the molar ratio of the 4-azidobenzoic acid, N-hydroxysuccinimide and N,N'-dicyclohexyl carbodiimide is 1:(1-1.5):(1-1.5); the mass ratio of the chitosan to the activated 4-azidobenzoic acid is 1:(0.5-0.8); the time of the first light-avoiding reaction is 12-18 h; and the time of the second light-avoiding reaction is 2-3 d.

3. The method of claim 1, wherein the composite phosphorus removal agent is prepared by the steps of: In step (2), the mass ratio of the azidated chitosan, ynyl betaine, sodium ascorbate and CuSO4 is 1:(0.8-1):(0.4-0.5):(0.17-0.21); and the reaction time is 24-48 h.

4. The method of claim 1, wherein the composite phosphorus removal agent is prepared by the steps of: In step (2), the preparation process of the ynyl betaine is as follows: propargylamine and N,N-diisopropylethylamine are added into dichloromethane, and then a dichloromethane solution of betaine chloride acid chloride is added at 0°C to perform a reaction to obtain the ynyl betaine; the molar ratio of the propargylamine, betaine chloride acid chloride and N,N-diisopropylethylamine is 1:(1.4-2):(3-4).

5. The method of claim 1, wherein the composite phosphorus removal agent is prepared by the steps of: The preparation process of the modified magnesium-aluminum layered double hydroxide is as follows: (a) magnesium nitrate and aluminum nitrate are added into water to obtain a precursor solution; sodium nitrate and sodium hydroxide are added into water to obtain an alkali solution; the precursor solution is added into the alkali solution at 60-70°C to perform a hydrothermal reaction, and after treatment, a magnesium-aluminum layered double hydroxide is obtained; (b) the magnesium-aluminum layered double hydroxide is added into a N-dodecyl-4-(ethoxycarbonyl) pyridinium-S-acetic acid inner salt solution, and stirred to perform a reaction, and after treatment, the modified magnesium-aluminum layered double hydroxide is obtained.

6. The method of claim 5, wherein the composite phosphorus removal agent is prepared by the steps of: The concentration of magnesium nitrate and aluminum nitrate in the precursor solution in step (a) is 1-2 mol / L and 0.5 mol / L respectively; the concentration of sodium nitrate and sodium hydroxide in the alkali solution is 2-3 mol / L and 3-5 mol / L respectively; the volume ratio of the precursor solution and the alkali solution is 1:1; the temperature of the hydrothermal reaction is 100-120℃, and the time is 12-18 h.

7. The method for preparing the composite phosphorus removal agent according to claim 5, characterized in that, In step (b), the ratio of the amount of the magnesium-aluminum layered double hydroxide and the N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt solution is 1 g:(100-200) mL; the concentration of the N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt solution is 0.02-0.05 mol / L; the stirring reaction time is 3-5 h.

8. The method of claim 7, wherein the composite phosphorus removal agent is prepared by the steps of: The preparation process of the N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt is as follows: ​ 1) ethyl isonicotinate and 12-bromo-1-dodecene are added to ethanol, and refluxed to obtain intermediate 1; the structural formula of the intermediate 1 is as follows: ； 2) the intermediate 1, mercaptoacetic acid and triethylamine are added to dichloromethane, and reacted at room temperature to obtain the N-dodecyl-4-(ethoxycarbonyl)pyridinium-S-acetic acid inner salt.

9. The method of claim 8, wherein the composite phosphorus removal agent is prepared by the steps of: In step 1), the molar ratio of ethyl isonicotinate and 12-bromo-1-dodecene is 1:(1-1.5), and the reflux reaction time is 48-60 h; in step 2), the molar ratio of the intermediate 1, mercaptoacetic acid and triethylamine is 1:(1-1.25):(0.5-0.6), and the reaction time at room temperature is 8-10 h. ​ 10. A composite phosphorus removal agent, characterized by, Prepared by the preparation method of any one of claims 1-9. Prepared by the preparation method of any one of claims 1-9.

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