Preparation method of phosphorus removal polymer gel

Abstract

This invention relates to the field of water pollution control technology, specifically disclosing a method for preparing a phosphorus-removing polymer gel. The method involves reacting sodium alginate, modified iron oxide-hydroxyapatite, N-(hydroxymethyl)acrylamide, acrylamide, and a crosslinking agent to obtain the phosphorus-removing polymer gel. The nano-hydroxyapatite and nano-iron oxide in the polymer gel possess abundant micropores and specific surface area, resulting in rich adsorption sites. Sodium alginate forms a three-dimensional network structure, providing support and fixation, increasing the specific surface area and adsorption sites of the material. Through the synergistic effect of adsorption and precipitation, the polymer gel achieves efficient removal of phosphates. The nano-iron oxide exhibits superparamagnetism, enabling rapid separation and effective recovery through magnetic separation, simplifying the recovery process, reducing recovery costs, minimizing secondary pollution, and promoting environmental friendliness.

Description

Technical Field

[0001] This invention relates to the field of water pollution control technology, specifically to a method for preparing phosphorus removal polymer gel. Background Technology

[0002] Phosphorus in nature is mainly distributed in the biosphere in the form of phosphates and is one of the essential elements for human, animal, and plant life activities. Unrestrained human production and lifestyle activities have disrupted the normal phosphorus cycle in nature. Every year, excessive phosphorus enters the aquatic environment through sewage discharge and agricultural runoff, causing eutrophication of water bodies, resulting in the proliferation of algae, a sharp decline in dissolved oxygen, and seriously threatening the survival of aquatic organisms and human health.

[0003] Phosphorus in water exists mainly in three forms: organic phosphorus, orthophosphate, and polymeric phosphorus, with orthophosphate and polymeric phosphorus accounting for the vast majority. Traditional phosphorus removal technologies include chemical precipitation, biological methods, and electrolysis. However, these technologies can lead to the formation of new polymers in the water, causing secondary pollution. Adsorption phosphorus removal is simple to operate, recyclable, and produces no secondary pollution, making it a key research focus for the treatment of phosphorus-containing water pollution.

[0004] Chinese patent application CN102614854A discloses a method for preparing a phosphorus-removing iron-loaded activated carbon adsorbent. The method involves soaking powdered activated carbon in hydrochloric acid, washing it with water, impregnating it in a strong oxidizing acid solution, mixing it with an inorganic iron salt solution, and drying it to obtain a highly efficient phosphorus-removing activated carbon adsorbent rich in iron oxides. This phosphorus-removing iron-loaded activated carbon adsorbent has mild preparation conditions, is easy to implement, and is highly operable, but its phosphorus removal rate in high-concentration phosphorus-containing wastewater is relatively low. Chinese patent application CN104785177A discloses a method for preparing alginate-graphene composite double-network gel spheres. The method involves stirring an aqueous solution of graphene oxide and alginate to form a homogeneous mixed solution, adding it dropwise to a divalent salt ion solution, and then adding it to an aqueous solution containing a reducing agent. The mixture is then heated in a water bath to obtain alginate-graphene composite double-network gel spheres. This alginate-graphene composite double-network gel sphere process is simple and easy to promote, has a large specific surface area, and strong adsorption capacity. However, it relies on a single separation method and cannot achieve efficient separation after adsorption, easily leading to resource waste.

[0005] Therefore, developing a high-efficiency, stable, and environmentally friendly phosphorus removal material is of great significance. Summary of the Invention

[0006] (1) Technical problems solved

[0007] To address the aforementioned technical problems, this invention provides a method for preparing a phosphorus removal polymer gel. The prepared polymer gel can rapidly and efficiently remove phosphates from water, and can also achieve efficient separation and recovery after adsorption.

[0008] (2) Technical solution

[0009] To achieve the above objectives, this invention discloses a method for preparing a phosphorus-removing polymeric gel, comprising the following steps:

[0010] S1. Nano-hydroxyapatite was ultrasonically dispersed in N,N-dimethylformamide. After uniform ultrasonic dispersion, 2-buten-1-ylsuccinic anhydride, 4-dimethylaminopyridine and sodium hydroxide were added, stirred and mixed, and the reaction was carried out. After the reaction was completed, the mixture was filtered, washed with 75% ethanol solution, and dried under vacuum at 60℃ for 12h to obtain modified hydroxyapatite.

[0011] S2. Nano-iron oxide was ultrasonically dispersed in anhydrous ethanol. After uniform dispersion, γ-aminopropyltriethoxysilane was added, stirred and mixed, and the reaction was carried out. After the reaction was completed, the mixture was washed with anhydrous ethanol and dried under vacuum at 60°C for 12 hours to obtain aminated iron oxide.

[0012] S3. Mix toluene, modified hydroxyapatite, aminated iron oxide and triethylamine evenly, heat to allow the reaction to occur, filter after the reaction is complete, wash with anhydrous ethanol, and dry under vacuum at 60℃ for 24h to obtain modified iron oxide-hydroxyapatite.

[0013] S4. Sodium alginate, modified iron oxide-hydroxyapatite, N-(hydroxymethyl)acrylamide, acrylamide, and deionized water are mixed evenly. Under a nitrogen atmosphere, a crosslinking agent, initiator, and catalyst are added, the mixture is heated and stirred to allow the reaction to occur. After the reaction is complete, the mixture is washed with anhydrous ethanol and deionized water and then freeze-dried to obtain a phosphorus-removing polymer gel.

[0014] Preferably, the mass ratio of nano-hydroxyapatite, N,N-dimethylformamide, 2-buten-1-ylsuccinic anhydride, 4-dimethylaminopyridine and sodium hydroxide in S1 is 100:2500-3000:52-60:2-3:1-1.5.

[0015] Preferably, the reaction temperature in S1 is 85-95℃, and the reaction time is 6-9h.

[0016] Preferably, the mass ratio of nano-iron oxide, anhydrous ethanol, and γ-aminopropyltriethoxysilane in S2 is 100:1800-2100:65-75.

[0017] Preferably, the reaction temperature in S2 is 25-35℃, and the reaction time is 2-4h.

[0018] Preferably, the mass ratio of toluene, modified hydroxyapatite, aminated iron tetroxide, and triethylamine in S3 is 4500-6000:100:20-30:1-2.

[0019] Preferably, the reaction temperature in S3 is 80-90℃, and the reaction time is 12-14h.

[0020] Preferably, the mass ratio of sodium alginate, modified iron oxide-hydroxyapatite, N-(hydroxymethyl)acrylamide, acrylamide, deionized water, crosslinking agent, initiator and catalyst in S4 is 100:15-20:75-105:240-320:1200-1500:28-40:1-3:2-3.5.

[0021] Preferably, the reaction temperature in S4 is 55-65℃, and the reaction time is 5-8h.

[0022] Preferably, in S4, the crosslinking agent is methylenebisacrylamide, the initiator is ammonium persulfate, and the catalyst is tetramethylethylenediamine.

[0023] (III) Beneficial Technical Effects

[0024] In this invention, 2-buten-1-ylsuccinic anhydride is used to modify nano-hydroxyapatite. The anhydride on the 2-buten-1-ylsuccinic anhydride reacts with the hydroxyl groups on the nano-hydroxyapatite, introducing alkenyl and carboxyl groups onto the nano-hydroxyapatite to obtain modified hydroxyapatite. γ-aminopropyltriethoxysilane is used to modify nano-ferric oxide, introducing amino groups onto the nano-ferric oxide to obtain aminated ferric oxide. The carboxyl groups on the modified hydroxyapatite and the amino groups on the aminated ferric oxide undergo an amidation reaction to obtain modified ferric oxide-hydroxyapatite. Sodium alginate, modified ferric oxide-hydroxyapatite, N-(hydroxymethyl)acrylamide, and acrylamide undergo polymerization and crosslinking under the action of a crosslinking agent and an initiator to obtain a phosphorus-removing polymer gel.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) In this invention, nano-hydroxyapatite is an effective phosphorus adsorbent. The calcium ions on its surface can combine with phosphate ions in water to form insoluble calcium phosphate precipitates. At the same time, the hydroxyl groups on the surface of hydroxyapatite can undergo an exchange reaction with phosphate ions in water, adsorbing phosphate ions onto the material surface through electrostatic adsorption and chemical bonding, thereby achieving the purpose of removing phosphorus from the water. Nano-ferric oxide carries a positive charge on its surface, which can electrostatically attract negatively charged phosphate ions, adsorbing them onto the material surface. Furthermore, the iron ions on the surface of nano-ferric oxide can undergo a ligand exchange reaction with phosphate ions to form stable complexes, thereby achieving phosphorus removal. Modified hydroxyapatite and aminated ferric oxide react to obtain modified ferric oxide-hydroxyapatite, which is then polymerized and crosslinked with other raw materials to prepare a polymer gel. This effectively avoids the agglomeration of nano-hydroxyapatite and nano-ferric oxide, allowing them to be uniformly dispersed in the gel matrix and improving the overall performance of the gel.

[0027] (2) In this invention, sodium alginate serves as the framework structure of the polymer gel, combining with nano-hydroxyapatite, nano-ferric oxide, N-(hydroxymethyl)acrylamide, and acrylamide to form a polymer gel with excellent phosphorus removal performance. Sodium alginate can form a three-dimensional network structure, providing support and fixation for the polymer gel material, while increasing the specific surface area and adsorption sites of the material. The hydroxyl groups in sodium alginate can undergo ligand exchange reactions with phosphate ions, adsorbing phosphate ions onto the material surface or in micropores. The polyacrylamide introduced into the polymer gel has a good flocculation effect, mainly playing a role in improving and strengthening solid-liquid separation during phosphorus removal. The introduced N-(hydroxymethyl)acrylamide is reactive; the hydroxymethyl group can react with phosphorus, which helps in phosphorus removal. Its cross-linking ability allows it to form a network structure on the material surface, enhancing the stability and performance of the material, and greatly enhancing its mechanical properties. Through synergistic effects, the various components in the polymer gel can rapidly and efficiently remove phosphorus from water through adsorption and chemical bonding.

[0028] (3) In this invention, modified hydroxyapatite and aminated iron oxide have abundant micropores and specific surface area, providing rich adsorption sites. Phosphate molecules are adsorbed onto the surface or micropores of the gel material through physical forces such as van der Waals forces, thereby reducing the phosphorus content in the water. The network structure in the polymer gel can trap and sweep up suspended particles and colloidal substances in the water, including phosphate precipitates, thereby accelerating their sedimentation and removal. The polymer chains in the polymer gel can act as bridges, connecting multiple phosphate molecules or precipitate particles together to form larger aggregates, accelerating the removal of phosphate from the water. The amide bonds introduced during the reaction can improve the hydrophilicity and surface charge of the material, thereby enhancing its phosphorus adsorption capacity, increasing the adsorption capacity of the material for phosphorus, and improving the adsorption efficiency. The gel material has good stability and can maintain its phosphorus removal performance under different environmental conditions. The raw materials used in the preparation process are environmentally friendly substances, harmless to the environment, and in line with the development trend of green chemistry. Through the synergistic effect of adsorption and precipitation, this polymer gel can achieve efficient removal of phosphate. Furthermore, the nano-Fe3O4 exhibits superparamagnetism, which enables rapid separation and effective recovery through magnetic separation, simplifying the recovery process, reducing recovery costs, achieving recycling, and reducing the generation of secondary pollution. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] Example 1

[0031] A method for preparing a phosphorus removal polymer gel includes the following steps:

[0032] S1. Nano-hydroxyapatite was ultrasonically dispersed in N,N-dimethylformamide. After uniform ultrasonic dispersion, 2-buten-1-ylsuccinic anhydride, 4-dimethylaminopyridine, and sodium hydroxide were added. The mass ratio of nano-hydroxyapatite, N,N-dimethylformamide, 2-buten-1-ylsuccinic anhydride, 4-dimethylaminopyridine, and sodium hydroxide was 100:2500:52:2:1. The mixture was stirred and reacted at 85°C for 9 hours. After the reaction was completed, the mixture was filtered, washed with 75% ethanol solution, and vacuum dried at 60°C for 12 hours to obtain modified hydroxyapatite.

[0033] S2. Nano-iron oxide was ultrasonically dispersed in anhydrous ethanol. After uniform dispersion, γ-aminopropyltriethoxysilane was added, wherein the mass ratio of nano-iron oxide, anhydrous ethanol, and γ-aminopropyltriethoxysilane was 100:1800:65. The mixture was stirred and reacted at 25°C for 4 hours. After the reaction was completed, the mixture was washed with anhydrous ethanol and dried under vacuum at 60°C for 12 hours to obtain aminated iron oxide.

[0034] S3. Toluene, modified hydroxyapatite, aminated iron oxide and triethylamine were mixed evenly in a mass ratio of 4500:100:20:1, and the mixture was heated to allow the reaction to occur at 80°C for 14 hours. After the reaction was completed, the mixture was filtered, washed with anhydrous ethanol, and dried under vacuum at 60°C for 24 hours to obtain modified iron oxide-hydroxyapatite.

[0035] S4. Sodium alginate, modified iron(III) oxide-hydroxyapatite, N-(hydroxymethyl)acrylamide, acrylamide, and deionized water are mixed evenly. Under a nitrogen atmosphere, crosslinking agent methylenebisacrylamide, initiator ammonium persulfate, and catalyst tetramethylethylenediamine are added. The mass ratio of sodium alginate, modified iron(III) oxide-hydroxyapatite, N-(hydroxymethyl)acrylamide, acrylamide, deionized water, crosslinking agent, initiator, and catalyst is 100:15:75:240:1200:28:1:2. The mixture is heated and stirred, and the reaction takes place at 55°C for 8 hours. After the reaction is completed, the mixture is washed with anhydrous ethanol and deionized water and freeze-dried to obtain a phosphorus-removing polymer gel.

[0036] Example 2

[0037] A method for preparing a phosphorus removal polymer gel includes the following steps:

[0038] S1. Nano-hydroxyapatite was ultrasonically dispersed in N,N-dimethylformamide. After uniform ultrasonic dispersion, 2-buten-1-ylsuccinic anhydride, 4-dimethylaminopyridine, and sodium hydroxide were added. The mass ratio of nano-hydroxyapatite, N,N-dimethylformamide, 2-buten-1-ylsuccinic anhydride, 4-dimethylaminopyridine, and sodium hydroxide was 100:2800:80:2.5:1.2. The mixture was stirred and reacted at 90°C for 8 hours. After the reaction was completed, the mixture was filtered, washed with 75% ethanol solution, and vacuum dried at 60°C for 12 hours to obtain modified hydroxyapatite.

[0039] S2. Nano-iron oxide was ultrasonically dispersed in anhydrous ethanol. After uniform dispersion, γ-aminopropyltriethoxysilane was added, wherein the mass ratio of nano-iron oxide, anhydrous ethanol, and γ-aminopropyltriethoxysilane was 100:2000:72. The mixture was stirred and reacted at 30°C for 3 hours. After the reaction was completed, the mixture was washed with anhydrous ethanol and dried under vacuum at 60°C for 12 hours to obtain aminated iron oxide.

[0040] S3. Toluene, modified hydroxyapatite, aminated iron oxide and triethylamine were mixed evenly in a mass ratio of 5000:100:24:1.4, and the mixture was heated to allow the reaction to occur at 85°C for 13 hours. After the reaction was completed, the mixture was filtered, washed with anhydrous ethanol, and dried under vacuum at 60°C for 24 hours to obtain modified iron oxide-hydroxyapatite.

[0041] S4. Sodium alginate, modified iron(III) oxide-hydroxyapatite, N-(hydroxymethyl)acrylamide, acrylamide, and deionized water are mixed evenly. Under a nitrogen atmosphere, crosslinking agent methylenebisacrylamide, initiator ammonium persulfate, and catalyst tetramethylethylenediamine are added. The mass ratio of sodium alginate, modified iron(III) oxide-hydroxyapatite, N-(hydroxymethyl)acrylamide, acrylamide, deionized water, crosslinking agent, initiator, and catalyst is 100:16:90:280:1350:32:1.8:2.5. The mixture is heated and stirred, and the reaction takes place at 60°C for 6 hours. After the reaction is completed, the mixture is washed with anhydrous ethanol and deionized water, and then freeze-dried to obtain a phosphorus-removing polymer gel.

[0042] Example 3

[0043] A method for preparing a phosphorus removal polymer gel includes the following steps:

[0044] S1. Toluene, modified hydroxyapatite, aminated iron oxide and triethylamine were mixed evenly in a mass ratio of 5000:100:28:1.6, and the mixture was heated to allow the reaction to occur at 85°C for 13 hours. After the reaction was completed, the mixture was filtered, washed with anhydrous ethanol, and dried under vacuum at 60°C for 24 hours to obtain modified iron oxide-hydroxyapatite.

[0045] S2. Sodium alginate, modified iron(III) oxide-hydroxyapatite, N-(hydroxymethyl)acrylamide, acrylamide, and deionized water are mixed evenly. Under a nitrogen atmosphere, crosslinking agent methylenebisacrylamide, initiator ammonium persulfate, and catalyst tetramethylethylenediamine are added. The mass ratio of sodium alginate, modified iron(III) oxide-hydroxyapatite, N-(hydroxymethyl)acrylamide, acrylamide, deionized water, crosslinking agent, initiator, and catalyst is 100:16:90:280:1350:32:1.8:2.5. The mixture is heated and stirred, and the reaction takes place at 60°C for 6 hours. After the reaction is completed, the mixture is washed with anhydrous ethanol and deionized water, and then freeze-dried to obtain a phosphorus-removing polymer gel.

[0046] The preparation methods of modified hydroxyapatite and aminated iron oxide are the same as those in Example 2.

[0047] Example 4

[0048] A method for preparing a phosphorus removal polymer gel includes the following steps:

[0049] S1. Sodium alginate, modified iron(III) oxide-hydroxyapatite, N-(hydroxymethyl)acrylamide, acrylamide, and deionized water are mixed evenly. Under a nitrogen atmosphere, crosslinking agent methylenebisacrylamide, initiator ammonium persulfate, and catalyst tetramethylethylenediamine are added. The mass ratio of sodium alginate, modified iron(III) oxide-hydroxyapatite, N-(hydroxymethyl)acrylamide, acrylamide, deionized water, crosslinking agent, initiator, and catalyst is 100:18:100:300:1450:38:2.5:3. The mixture is heated and stirred, and the reaction takes place at 60°C for 6 hours. After the reaction is completed, the mixture is washed with anhydrous ethanol and deionized water, and then freeze-dried to obtain a phosphorus-removing polymer gel.

[0050] The preparation method of the modified iron tetroxide-hydroxyapatite is the same as that of the modified iron tetroxide-hydroxyapatite in Example 3.

[0051] Example 5

[0052] A method for preparing a phosphorus removal polymer gel includes the following steps:

[0053] S1. Nano-hydroxyapatite was ultrasonically dispersed in N,N-dimethylformamide. After uniform ultrasonic dispersion, 2-buten-1-ylsuccinic anhydride, 4-dimethylaminopyridine, and sodium hydroxide were added. The mass ratio of nano-hydroxyapatite, N,N-dimethylformamide, 2-buten-1-ylsuccinic anhydride, 4-dimethylaminopyridine, and sodium hydroxide was 100:3000:60:3:1.5. The mixture was stirred and reacted at 95°C for 6 hours. After the reaction was completed, the mixture was filtered, washed with 75% ethanol solution, and vacuum dried at 60°C for 12 hours to obtain modified hydroxyapatite.

[0054] S2. Nano-iron oxide was ultrasonically dispersed in anhydrous ethanol. After uniform dispersion, γ-aminopropyltriethoxysilane was added, wherein the mass ratio of nano-iron oxide, anhydrous ethanol, and γ-aminopropyltriethoxysilane was 100:2100:75. The mixture was stirred and reacted at 35°C for 2 hours. After the reaction was completed, the mixture was washed with anhydrous ethanol and dried under vacuum at 60°C for 12 hours to obtain aminated iron oxide.

[0055] S3. Toluene, modified hydroxyapatite, aminated iron oxide and triethylamine in a mass ratio of 6000:100:30:2 were mixed evenly and heated to allow the reaction to occur at 90°C for 12 hours. After the reaction was completed, the mixture was filtered, washed with anhydrous ethanol, and dried under vacuum at 60°C for 24 hours to obtain modified iron oxide-hydroxyapatite.

[0056] S4. Sodium alginate, modified iron(III) oxide-hydroxyapatite, N-(hydroxymethyl)acrylamide, acrylamide, and deionized water are mixed evenly. Under a nitrogen atmosphere, crosslinking agent methylenebisacrylamide, initiator ammonium persulfate, and catalyst tetramethylethylenediamine are added. The mass ratio of sodium alginate, modified iron(III) oxide-hydroxyapatite, N-(hydroxymethyl)acrylamide, acrylamide, deionized water, crosslinking agent, initiator, and catalyst is 100:20:105:320:1500:40:3:3.5. The mixture is heated and stirred, and the reaction takes place at 65°C for 5 hours. After the reaction is completed, the mixture is washed with anhydrous ethanol and deionized water, and then freeze-dried to obtain a phosphorus-removing polymer gel.

[0057] Comparative Example 1

[0058] A method for preparing a phosphorus removal polymer gel includes the following steps:

[0059] S1. Nano-hydroxyapatite was ultrasonically dispersed in N,N-dimethylformamide. After uniform ultrasonic dispersion, 2-buten-1-ylsuccinic anhydride, 4-dimethylaminopyridine, and sodium hydroxide were added. The mass ratio of nano-hydroxyapatite, N,N-dimethylformamide, 2-buten-1-ylsuccinic anhydride, 4-dimethylaminopyridine, and sodium hydroxide was 100:2800:80:2.5:1.2. The mixture was stirred and reacted at 90°C for 8 hours. After the reaction was completed, the mixture was filtered, washed with 75% ethanol solution, and vacuum dried at 60°C for 12 hours to obtain modified hydroxyapatite.

[0060] S2. Nano-iron oxide was ultrasonically dispersed in anhydrous ethanol. After uniform dispersion, γ-aminopropyltriethoxysilane was added, wherein the mass ratio of nano-iron oxide, anhydrous ethanol, and γ-aminopropyltriethoxysilane was 100:2000:72. The mixture was stirred and reacted at 30°C for 3 hours. After the reaction was completed, the mixture was washed with anhydrous ethanol and dried under vacuum at 60°C for 12 hours to obtain aminated iron oxide.

[0061] S3. Sodium alginate, modified hydroxyapatite, aminated iron(III) oxide, N-(hydroxymethyl)acrylamide, acrylamide, and deionized water are mixed evenly. Under a nitrogen atmosphere, crosslinking agent methylenebisacrylamide, initiator ammonium persulfate, and catalyst tetramethylethylenediamine are added. The mass ratio of sodium alginate, modified hydroxyapatite, aminated iron(III) oxide, N-(hydroxymethyl)acrylamide, acrylamide, deionized water, crosslinking agent, initiator, and catalyst is 100:14:4:100:300:1450:38:2.5:3. The mixture is heated and stirred, and the reaction takes place at 60°C for 6 hours. After the reaction, the mixture is washed with anhydrous ethanol and deionized water, and then freeze-dried to obtain a phosphorus-removing polymer gel.

[0062] Comparative Example 2

[0063] A method for preparing a phosphorus removal polymer gel includes the following steps:

[0064] S1. Sodium alginate, nano-hydroxyapatite, nano-ferric oxide, N-(hydroxymethyl)acrylamide, acrylamide, and deionized water are mixed evenly. Under a nitrogen atmosphere, crosslinking agent methylenebisacrylamide, initiator ammonium persulfate, and catalyst tetramethylethylenediamine are added. The mass ratio of sodium alginate, nano-hydroxyapatite, nano-ferric oxide, N-(hydroxymethyl)acrylamide, acrylamide, deionized water, crosslinking agent, initiator, and catalyst is 100:14:4:100:300:1450:38:2.5:3. The mixture is heated and stirred, and the reaction takes place at 60°C for 6 hours. After the reaction, the mixture is washed with anhydrous ethanol and deionized water and freeze-dried to obtain a phosphorus-removing polymer gel.

[0065] Comparative Example 3

[0066] A method for preparing a phosphorus removal polymer gel includes the following steps:

[0067] S1. Sodium alginate, modified iron tetroxide-hydroxyapatite, and deionized water are mixed evenly under a nitrogen atmosphere. The mass ratio of sodium alginate, modified iron tetroxide-hydroxyapatite, and deionized water is 100:18:1450. The mixture is heated and stirred, and the reaction takes place at 60°C for 6 hours. After the reaction is completed, the mixture is washed with anhydrous ethanol and deionized water and then freeze-dried to obtain a phosphorus-removing polymer gel.

[0068] The preparation method of the modified iron tetroxide-hydroxyapatite is the same as that of the modified iron tetroxide-hydroxyapatite in Example 3.

[0069] The nano-ferric oxide described in the embodiments and comparative examples of this invention is prepared by the following steps: FeCl3·6H2O and FeCl2·4H2O are added to a reactor, followed by deionized water and hydrochloric acid. The mixture is stirred under a nitrogen atmosphere. A sodium hydroxide solution is then added, with a mass ratio of sodium hydroxide to deionized water of 3:100. The mass ratio of FeCl3·6H2O, FeCl2·4H2O, deionized water, hydrochloric acid, and sodium hydroxide solution is 4.8:2:100:2:103. The mixture is stirred and mixed to allow the reaction to occur. After the reaction is complete, the mixture is separated using an external magnetic field, washed with deionized water and anhydrous ethanol, and vacuum dried at 60°C for 12 hours to obtain nano-ferric oxide.

[0070] In the embodiments and comparative examples of this invention, nano-hydroxyapatite was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; sodium alginate was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; other undisclosed raw materials and reagents were commercially available.

[0071] The phosphorus-removing polymer gels from Examples 1-5 and Comparative Examples 1-3 were used as samples for performance testing, and the relevant performance tests are as follows:

[0072] (1) Phosphorus removal test: A 10 mg / L potassium dihydrogen phosphate solution was prepared for adsorption experiments. 100 mL of potassium dihydrogen phosphate solution was placed in an Erlenmeyer flask, and 0.1 g of phosphorus removal polymer gel was added. The mixture was stirred and placed in a constant temperature shaker for adsorption. The residual phosphorus concentration in the Erlenmeyer flask was measured at 1 h, 2 h, and 4 h. Q = (C0 - C1) / C0 × 100%, where Q is the phosphorus removal rate, C0 is the initial concentration of inorganic phosphorus in the solution, and C1 is the concentration of inorganic phosphorus in the solution after adsorption. The inorganic phosphorus content in the solution was tested using the national standard method of ammonium molybdate visible spectrophotometry. The Q value was calculated. Each group was tested three times, and the average value was taken. The test results are shown in Table 1.

[0073] Table 1

[0074]

[0075] (2) Swelling performance test: The phosphorus-removing polymer gel was made into cylindrical specimens with a diameter of 1.0 cm and a height of 1 mm. After drying to constant weight, the specimens were immersed in hydrochloric acid solution with pH 1 and PBS solution with pH 7 for 6 h. The specimens were weighed every 2 h and the swelling ratio Q was calculated. W Q W = (W1-W0) / W0, where W0 is the dry weight of the sample and W1 is the weight of the sample after soaking. Each group was tested three times, and the average value was taken. The test results are shown in Table 2.

[0076] Table 2

[0077]

[0078] The test results in Tables 1 and 2 show that the polymeric gels corresponding to Examples 1-5 exhibit excellent phosphorus removal rates and stable swelling ratios, enabling efficient removal of phosphorus from water. During adsorption, these gels maintain a relatively constant volume and morphology, facilitating thorough contact and adsorption with phosphates, rapidly reaching a stable equilibrium, and minimizing gel loss during adsorption, thus improving adsorption efficiency. Furthermore, the polymeric gels maintain stable swelling ratios under different pH conditions, showing good stability and absorbing more water in neutral solutions and less in acidic solutions. In Comparative Example 1, modified hydroxyapatite and aminated iron oxide were used instead of modified iron oxide-hydroxyapatite, resulting in poorer dispersibility, increased swelling ratio, decreased stability, and a longer time to reach equilibrium, leading to a lower phosphorus removal rate and a longer adsorption equilibrium time. In Comparative Example 2, no modification was performed on the nano-hydroxyapatite and nano-iron oxide, resulting in significantly reduced overall performance, a significantly increased swelling ratio, and a significantly lower phosphorus removal rate. In Comparative Example 3, sodium alginate, modified iron oxide-hydroxyapatite, and deionized water were directly mixed to obtain a phosphorus removal polymer gel. No cross-linking occurred, the swelling rate was greatly improved, and the phosphorus removal rate was low.

[0079] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A method for preparing a phosphorus-removing polymeric gel, characterized in that: Includes the following steps: S1. Nano-hydroxyapatite was ultrasonically dispersed in N,N-dimethylformamide. After uniform ultrasonic dispersion, 2-buten-1-ylsuccinic anhydride, 4-dimethylaminopyridine and sodium hydroxide were added, stirred and mixed, and the reaction was carried out. After the reaction was completed, the mixture was filtered, washed, and vacuum dried at 60℃ for 12h to obtain modified hydroxyapatite. S2. Nano-Fe3O4 is ultrasonically dispersed in anhydrous ethanol. After uniform dispersion, γ-aminopropyltriethoxysilane is added, stirred and mixed, and the reaction occurs. After the reaction is completed, the mixture is washed and dried under vacuum at 60°C for 12 hours to obtain aminated Fe3O4. S3. Mix toluene, modified hydroxyapatite, aminated iron oxide and triethylamine evenly, heat to allow the reaction to occur, filter after the reaction is complete, wash, and dry under vacuum at 60℃ for 24h to obtain modified iron oxide-hydroxyapatite. S4. Sodium alginate, modified iron oxide-hydroxyapatite, N-(hydroxymethyl)acrylamide, acrylamide, and deionized water are mixed evenly. Under a nitrogen atmosphere, a crosslinking agent, initiator, and catalyst are added, the mixture is heated and stirred to allow the reaction to occur. After the reaction is complete, the mixture is washed and freeze-dried to obtain a phosphorus-removing polymer gel.

2. The method for preparing a phosphorus-removing polymeric gel according to claim 1, characterized in that: The mass ratio of nano-hydroxyapatite, N,N-dimethylformamide, 2-buten-1-ylsuccinic anhydride, 4-dimethylaminopyridine, and sodium hydroxide in S1 is 100:2500-3000:52-60:2-3:1-1.

5.

3. The method for preparing a phosphorus-removing polymeric gel according to claim 1, characterized in that: The reaction temperature in S1 is 85-95℃, and the reaction time is 6-9h.

4. The method for preparing a phosphorus-removing polymeric gel according to claim 1, characterized in that: The mass ratio of nano-ferric oxide, anhydrous ethanol, and γ-aminopropyltriethoxysilane in S2 is 100:1800-2100:65-75.

5. The method for preparing a phosphorus-removing polymeric gel according to claim 1, characterized in that: The reaction temperature in S2 is 25-35℃, and the reaction time is 2-4h.

6. The method for preparing a phosphorus-removing polymeric gel according to claim 1, characterized in that: The mass ratio of toluene, modified hydroxyapatite, aminated iron tetroxide, and triethylamine in S3 is 4500-6000:100:20-30:1-2.

7. The method for preparing a phosphorus removal polymer gel according to claim 1, characterized in that: The reaction temperature in S3 is 80-90℃, and the reaction time is 12-14h.

8. The method for preparing a phosphorus removal polymer gel according to claim 1, characterized in that: The mass ratio of sodium alginate, modified iron oxide-hydroxyapatite, N-(hydroxymethyl)acrylamide, acrylamide, deionized water, crosslinking agent, initiator and catalyst in S4 is 100:15-20:75-105:240-320:1200-1500:28-40:1-3:2-3.

5.

9. The method for preparing a phosphorus removal polymer gel according to claim 1, characterized in that: The reaction temperature in S4 is 55-65℃, and the reaction time is 5-8h.

10. The method for preparing a phosphorus-removing polymeric gel according to claim 1, characterized in that: In S4, the crosslinking agent is methylenebisacrylamide, the initiator is ammonium persulfate, and the catalyst is tetramethylethylenediamine.

Images