Multifunctional water purifying gel material and preparation method thereof

Abstract

The invention belongs to the technical field of water purification materials, and particularly relates to a multifunctional water purification gel material and a preparation method thereof. The composite material consists of an outer-layer film, a middle-layer framework and an inner-layer carbon core, the outer-layer film is prepared from the following raw materials: sodium alginate, carboxymethyl starch, NaCl and Tween-20; the middle-layer framework is prepared from the following raw materials: chitosan, modified sodium bentonite and Fe-P nano powder; the inner-layer carbon core is prepared from the following raw materials: rice hull biochar, nano CaCO3, FeCl3. 6H2O and FeSO4. 7H2O. Efficient water purification is achieved through a three-layer synergistic structure, and the outer layer Ca < 2 + > cross-linked sodium alginate / carboxymethyl starch porous membrane intercepts particles and buffers metal ions; the middle layer is integrated with chitosan to chelate heavy metals, CTAB-bentonite electrostatically adsorbs anions and Fe-P nanoparticles to precipitate phosphate / arsenate; and the biochar-Fe3O4 complex on the inner layer provides deep adsorption and catalytic oxidation functions.

Description

Technical Field

[0001] The present invention belongs to the technical field of water purification materials, and particularly relates to a multifunctional water purification gel material and a preparation method thereof. Background Art

[0002] At present, common traditional sewage treatment technologies, such as activated sludge method, biochemical oxidation method, chemical precipitation method, etc., although have achieved certain results in removing most conventional pollutants, the treatment efficiency for refractory pollutants and high-concentration heavy metal ions is still limited. In addition, traditional methods often have high energy consumption, expensive operating costs, and are prone to generate a large amount of sludge or residual monomers during the treatment process, leading to the risk of secondary pollution. In the face of the dual challenges of increasingly severe water resource shortage and water environmental pollution, there is an urgent need for a new type of water purification material that is efficient, low-consumption, easy to operate and environmentally friendly. Hydrogels are regarded as ideal water purification material platforms due to their three-dimensional porous network structure and excellent biomimetic characteristics. In early studies, although single-component hydrogels based on sodium alginate (SA) or polyvinyl alcohol (PVA) have certain adsorption capabilities, the problems of insufficient mechanical strength and limited adsorption capacity are prominent: under dynamic water flow conditions, pure SA hydrogels are prone to structural rupture, and the maximum adsorption capacity of traditional physically cross-linked gels for heavy metal ions is relatively low, which is difficult to meet the requirements for high-concentration wastewater treatment; at the same time, these materials lack specific recognition of pollutants, resulting in the treatment efficiency being greatly affected by the water body composition and environmental conditions (such as pH value, ionic strength); even some chemical cross-linking agents may have residual toxicity during the synthesis process, thus bringing new environmental risks. Therefore, based on the above problems, it is extremely necessary to develop a multifunctional water purification gel material with both high mechanical strength and long-term stability. Summary of the Invention

[0003] Aiming at the defects of the prior art, the purpose of the present invention is to provide a multifunctional water purification gel material and a preparation method thereof.

[0004] The technical effects of the present invention are achieved through the following technical solutions: a multifunctional water purification gel material, which is composed of an outer film, a middle skeleton and an inner carbon core; the raw materials of the outer film include, by weight: 8-10 parts of sodium alginate, 6-8 parts of carboxymethyl starch, 0.4-0.6 part of NaCl, and 0.03-0.05 part of Tween-20; the raw materials of the middle skeleton include, by weight: 10-15 parts of chitosan, 10-15 parts of modified sodium-based bentonite, 1-1.5 parts of Fe-P nanoflakes; the raw materials of the inner carbon core include, by weight: 38-45 parts of rice husk biochar, 10-12 parts of nano-CaCO3, 2-3 parts of FeCl3·6H2O, and 1-2 parts of FeSO4·7H2O.

[0005] Preferably, the specific preparation steps of the Fe-P nanoflakes are as follows: S1: Dissolve FeCl3·6H2O in deionized water, stir until evenly dissolved to obtain a 0.1M Fe 3+ solution; dissolve KH2PO4 in deionized water, stir until evenly dissolved to obtain a 0.1M PO4 3- solution; S2: Heat the 0.1M Fe 3+ solution obtained in step S1 to 70 °C, continuously stir at 500 rpm, and then slowly add dropwise the 0.1M PO4 3- solution obtained in step S1 at a rate of 1 mL / min. During the dropping process, adjust the pH to 6.5 - 7 using 1M NaOH solution. After the dropping is completed, continue to stir and age at 70 °C and 500 rpm for 2 - 3 h; S3: After completing the aging treatment in step S2, centrifuge at 8000 rpm for 10 - 15 min, take the precipitate, wash it 5 times repeatedly with deionized water, dry it in vacuum at 60 °C for 12 - 16 h, pulverize it, and screen it through a 200 - mesh sieve to obtain Fe - P nanometer powder; Preferably, in step S2, the volume ratio of the Fe 3+ solution to the PO4 3- solution is 1:1; Preferably, the specific preparation steps of the modified sodium - based bentonite are as follows: S101: Add sodium - based bentonite to deionized water, stir and disperse evenly at 60 °C, dropwise add 1M HCl solution to adjust the pH to 4.5 - 5.5 to obtain a sodium - based bentonite dispersion; add cetyltrimethylammonium bromide to deionized water, stir and dissolve evenly at 50 - 60 °C to obtain a CTAB solution; S102: Slowly add dropwise the CTAB solution to the sodium - based bentonite dispersion, stir at 500 rpm at 60 °C for 2 - 4 h. After the reaction is completed, dropwise add 1M NaOH solution to adjust the pH to 7, centrifuge, filter, wash with deionized water, dry at 80 °C for 12 - 16 h, and screen through a 200 - mesh sieve to obtain the modified sodium - based bentonite; Preferably, in step S101, the dosage ratio of the sodium - based bentonite to deionized water is 1 - 1.2 g:10 mL; the dosage ratio of the cetyltrimethylammonium bromide to deionized water is 1.4 - 1.5 g:50 mL; Preferably, in step S102, the volume ratio of the CTAB solution to the sodium - based bentonite dispersion is 1.5:1; Preferably, on the other hand, the present invention provides a preparation method of a multifunctional water - purification hydrogel material, including the following preparation steps: S201: Add rice husk biochar to 5 times its weight in deionized water, stir to disperse evenly, then add nano-CaCO3, and ultrasonically treat to disperse evenly. Perform vacuum impregnation, add 0.05M FeCl3·6H2O solution and 0.025M FeSO4·7H2O solution, remove bubbles with nitrogen, maintain a nitrogen atmosphere, stir at 60 °C for 20 - 30 min, then add 2M NaOH solution to adjust the pH to 9.5 - 10, continue aging treatment at 60 °C for 30 - 50 min, centrifuge, discard the supernatant, wash with deionized water until neutral, calcine in a nitrogen atmosphere at 150 - 250 °C for 1 - 2 h, sieve through a 20-mesh sieve, and dry with hot air at 40 °C for 2 h to obtain the inner carbon core; S202: Dissolve chitosan in a 1wt% glacial acetic acid solution to obtain a 3wt% chitosan solution; add modified sodium bentonite to deionized water and ultrasonically treat to disperse evenly to obtain a 3wt% modified bentonite dispersion; ultrasonically disperse Fe-P nanopowder into the chitosan solution, then combine it with the modified bentonite dispersion, and stir at 1000 rpm for 10 - 20 min to obtain an emulsion slurry; S203: Add the inner carbon core from step S201 to a magnetic stirring container, dropwise add the emulsion slurry from step S202, stir at 300 - 500 rpm for 10 - 15 min, then let it stand for 20 - 30 min; atomize and spray 1M NaOH solution at a ratio of 1 - 3 mL / g, let it stand and solidify for 10 - 20 min, wash with deionized water until neutral to obtain the coated beads; S204: Add sodium alginate and carboxymethyl starch to deionized water, add Tween - 20, stir at 600 rpm for 30 - 60 min, perform vacuum degassing for 10 min to obtain a 2.5wt% composite solution. Immerse the coated beads from step S203 in the composite solution for 10 s, spin - off the liquid at 300 rpm for 20 s, spray 1M CaCl2 solution at 1.5 mL / g, let it stand and solidify for 15 - 30 min, then add 10wt% NaCl solution for salting - out pore formation, soak in 0.05M CaCl2 solution for 1 - 3 min, wash with deionized water, and dry with hot air at 40 °C for 1 - 2 h to obtain the water purification hydrogel material; Preferably, in step S201, the specific parameters of the vacuum impregnation are: evacuate to 5 - 20 kPa, maintain for 30 - 60 min, and then return to normal pressure; Preferably, in step S204, the specific parameters of the salting - out pore formation are: treat at 40 °C for 15 - 25 min, treat at 50 °C for 30 - 50 min, and perform vacuum dehydration treatment at 60 °C for 20 - 30 min.

[0006] The beneficial effects of the present invention are as follows: The present invention utilizes the sodium alginate / carboxymethyl starch film through Ca 2+Crosslinking and NaCl-induced pore formation result in a porous outer shell with a stable thickness and a pore size distribution in the order of several micrometers. Water can permeate freely, while larger suspended particles and bacteria are retained on the membrane surface or at the pore openings. At the same time, the carboxyl groups evenly distributed on the film undergo reversible coordination with metal ions entering the water, buffering the metal ions to a lower concentration before flowing into the interior, thereby reducing the instantaneous load on the inner-layer adsorption sites. The overall film is negatively charged, and this surface electrical property can inhibit the deposition of natural organic matter and extend the time for the material to maintain flux and integrity under continuous water inflow conditions for up to twenty days. When the water body enters the middle-layer framework, the chitosan molecules are in a deprotonated state after alkali curing, and the free amino groups have a strong and rapid coordination ability with heavy metals such as Pb 2+ and Cd 2+ etc. The CTAB-bentonite intertwined with chitosan provides a dual adsorption mechanism. On the one hand, the quaternary ammonium cations of CTAB make the bentonite lamellae permanently positively charged, enabling electrostatic adsorption of anionic dyes, phosphate, and various antibiotics. On the other hand, the intercalated cetyl long chains increase the hydrophobic region between layers, showing an enrichment effect similar to microphase extraction for hydrophobic organic pollutants. In addition, Fe-P nanoparticles are uniformly embedded in the same framework network. The surface hydroxyl groups can coordinate and precipitate with phosphate or arsenate, and are stably anchored within the framework, not easily stripped by the water flow during long-term operation. Based on the positive electric field inherent in CTAB-bentonite, the negatively charged phosphate is first adsorbed on the periphery and then further combines with the surface of Fe-P to precipitate. There are also chitosan amino-metal coordination sites in the same space. After the heavy metal ions are captured by chitosan, they form insoluble complexes with the phosphate to be precipitated at the Fe-P interface, reducing the competition between the two types of pollutants and showing a synergistic adsorption behavior. When entering the innermost layer, the hierarchical pores and graphite-like lamellae of rice husk biochar provide π-π and hydrophobic interaction sites for further enrichment of persistent organic pollutants. The CaCO3 microparticles will gradually dissolve when encountering acidic wastewater or high-concentration metal ions, releasing carbonate ions and forming low-solubility carbonates with metals. This process not only neutralizes the acid shock that may be brought by industrial wastewater but also deposits some metal ions on the pore walls. In addition, the Fe3O4 nanocrystals obtained by the co-precipitation of FeCl3 / FeSO4 are dispersed in the biochar pores, and solid-liquid separation can be completed within dozens of seconds using an ordinary permanent magnet rod. Fe3O4 also has Fenton-like catalytic activity, generating hydroxyl radicals in the presence of trace amounts of hydrogen peroxide or dissolved oxygen to in-situ oxidize and decompose the dye molecules that have been enriched by the biochar. The carbonate ions buffered and released by CaCO3 maintain a near-neutral environment, avoiding damage to the outer layer structure caused by a sharp drop in pH during the Fenton reaction.

[0007] In summary, the outer layer intercepts large particles and some metals. The middle layer uses the synergistic effects of positively charged CTAB lamellae, amino chelation, and Fe-P precipitation to efficiently capture anions and metal ions. The inner layer uses the combination of biochar-Fe3O4 to complete deep adsorption and catalytic oxidation. Each functional component used in the present invention is connected to adjacent materials through electrostatic force, hydrogen bond, or coordination bond, rather than simple physical mixing, significantly avoiding the loss of active particles during operation; during the continuous influent simulation for twenty days, the pollutant removal rate always remains at a high level, ensuring that the particle structure is not significantly damaged. Description of the Drawings

[0008] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings described below are only those of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0009] Figure 1 It is a test result graph of calcium ion release of the water purification gel materials prepared in Examples 1-3 and Comparative Examples 1 and 4 of the present invention; Figure 2 It is a test result graph of PO4 3- adsorption of the water purification gel materials prepared in Examples 1-3 and Comparative Examples 1 and 4 of the present invention after the calcium ion release test; Figure 3 It is a test result graph of acidic buffer of the water purification gel materials prepared in Example 1 and Comparative Examples 1-4 of the present invention; Figure 4 It is a test result graph of Pb2+ adsorption of the water purification gel materials prepared in Example 1 and Comparative Examples 1-4 of the present invention; Figure 5 It is a test result graph of CrO4 2- adsorption of the water purification gel materials prepared in Example 1 and Comparative Examples 1-4 of the present invention; Figure 6 It is a SEM scanning electron microscope graph of the water purification gel material prepared in Example 1 of the present invention after the calcium ion release test. Detailed Embodiments

[0010] The following will clearly and completely describe the technical solutions of the present invention in combination with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. It should be noted that unless otherwise specified, the raw materials involved in the present invention are purchased through conventional commercial channels.

[0011] Example 1: A multifunctional water purification gel material, which consists of an outer film, a middle skeleton and an inner carbon core; the raw materials of the outer film include, by weight: 9 parts of sodium alginate, 7 parts of carboxymethyl starch, 0.5 part of NaCl and 0.04 part of Tween-20; the raw materials of the middle skeleton include, by weight: 12 parts of chitosan, 12 parts of modified sodium-based bentonite, 1.2 parts of Fe-P nanopowder; the raw materials of the inner carbon core include, by weight: 42 parts of rice husk biochar, 11 parts of nano CaCO3, 2.5 parts of FeCl3·6H2O and 1.5 parts of FeSO4·7H2O.

[0012] 1. The specific preparation steps of Fe-P nanopowder are as follows: S1: Dissolve 0.01 mol of FeCl3·6H2O in 100 mL of deionized water, stir and dissolve evenly to obtain a 0.1 M Fe 3+ solution; dissolve 0.01 mol of KH2PO4 in 100 mL of deionized water, stir and dissolve evenly to obtain a 0.1 M PO4 3- solution; S2: Heat 100 mL of the 0.1 M Fe 3+ solution in step S1 to 70 °C, continuously stir at 500 rpm, and then slowly dropwise add 100 mL of the 0.1 M PO4 3- solution in step S1 at a rate of 1 mL / min. During the dropping process, adjust the pH to 6.5 with 1 M NaOH solution. After the dropping is completed, continue to stir and age at 70 °C and 500 rpm for 2.5 h; S3: After the aging treatment in step S2, centrifuge at 8000 rpm for 12 min, take the precipitate, wash it repeatedly with deionized water 5 times, vacuum dry it at 60 °C for 15 h, pulverize it and screen it through a 200-mesh sieve to obtain Fe-P nanopowder; 2. The specific preparation steps of modified sodium-based bentonite are as follows: S101: Add 10 g of sodium-based bentonite to 100 mL of deionized water, stir and disperse evenly at 60 °C, and dropwise add 1 M HCl solution to adjust the pH to 5 to obtain a sodium-based bentonite dispersion; add 4.2 g of cetyltrimethylammonium bromide to 150 mL of deionized water, stir and dissolve evenly at 55 °C to obtain a CTAB solution; S102: Slowly drop 150 mL of the CTAB solution into 100 mL of the sodium-based bentonite dispersion, stir at 500 rpm at 60 °C for 3 h. After the reaction is completed, dropwise add 1 M NaOH solution to adjust the pH to 7, centrifuge, filter, wash with deionized water, dry at 80 °C for 15 h, and screen through a 200-mesh sieve to obtain modified sodium-based bentonite; 3. The preparation steps of the multifunctional water purification gel material are as follows: S201: Add rice husk biochar into 5 times its weight of deionized water, stir and disperse evenly. Then add nano-CaCO3, and disperse evenly by ultrasonic treatment. Evacuate to 10 kPa and keep for 50 min, then restore to normal pressure. Add 0.05 M FeCl3·6H2O solution and 0.025 M FeSO4·7H2O solution, remove bubbles with nitrogen. Maintain a nitrogen atmosphere and stir at 60 °C for 25 min, then add 2 M NaOH solution to adjust the pH to 9.5. Continue aging treatment at 60 °C for 40 min, centrifuge, discard the supernatant, wash with deionized water until neutral, calcine in a nitrogen atmosphere at 200 °C for 1.5 h, sieve through a 20-mesh sieve, and dry with hot air at 40 °C for 2 h to obtain the inner carbon core; S202: Dissolve chitosan in a 1 wt% glacial acetic acid solution to obtain a 3 wt% chitosan solution; add modified sodium bentonite into deionized water, and disperse evenly by ultrasonic treatment to obtain a 3 wt% modified bentonite dispersion; ultrasonically disperse Fe-P nanoflakes into the chitosan solution, then combine with the modified bentonite dispersion, and stir at 1000 rpm for 15 min to obtain an emulsion slurry; S203: Add the inner carbon core from step S201 into a magnetic stirring container, dropwise add the emulsion slurry from step S202, stir at 500 rpm for 12 min, then let stand for 25 min; atomize and spray 1 M NaOH solution at a ratio of 1.5 mL / g, let stand and solidify for 15 min, wash with deionized water until neutral to obtain the coated beads; S204: Add sodium alginate and carboxymethyl starch into deionized water, and add Tween-20, stir at 600 rpm for 50 min, and remove bubbles under vacuum for 10 min to obtain a 2.5 wt% composite solution. Immerse the coated beads from step S203 into the composite solution for 10 s, spin and drain at 300 rpm for 20 s, spray 1 M CaCl2 solution at a ratio of 1.5 mL / g, let stand and solidify for 25 min, then add 10 wt% NaCl solution for salting out and pore formation, treat at 40 °C for 20 min, treat at 50 °C for 40 min, perform vacuum dehydration treatment at 60 °C for 25 min, soak in 0.05 M CaCl2 solution for 2 min, wash with deionized water, and dry with hot air at 40 °C for 1.5 h to obtain the water purification gel material.

[0013] Example 2: A multifunctional water purification gel material, which consists of an outer film, a middle skeleton and an inner carbon core; the raw materials of the outer film include, by weight: 8 parts of sodium alginate, 6 parts of carboxymethyl starch, 0.4 part of NaCl and 0.03 part of Tween-20; the raw materials of the middle skeleton include, by weight: 10 parts of chitosan, 10 parts of modified sodium bentonite, 1 part of Fe-P nanoflakes; the raw materials of the inner carbon core include, by weight: 38 parts of rice husk biochar, 10 parts of nano-CaCO3, 2 parts of FeCl3·6H2O and 1 part of FeSO4·7H2O.

[0014] 1. The specific preparation steps of Fe-P nanometer powder are as follows: S1: Dissolve 0.01 mol of FeCl3·6H2O in 100 mL of deionized water, stir to dissolve evenly to obtain a 0.1 M Fe 3+ solution; dissolve 0.01 mol of KH2PO4 in 100 mL of deionized water, stir to dissolve evenly to obtain a 0.1 M PO4 3- solution; S2: Heat 100 mL of the 0.1 M Fe 3+ solution in step S1 to 70 °C, continuously stir at 500 rpm, and then slowly dropwise add 100 mL of the 0.1 M PO4 3- solution in step S1 at a rate of 1 mL / min. During the dropping process, use 1 M NaOH solution to adjust the pH to 7. After the dropping is completed, continue to stir and age at 70 °C and 500 rpm for 2 h; S3: After the aging treatment in step S2 is completed, centrifuge at 8000 rpm for 10 min, take the precipitate, wash it repeatedly with deionized water 5 times, dry it in vacuum at 60 °C for 12 h, crush it and screen it through a 200-mesh sieve to obtain Fe-P nanometer powder; 2. The specific preparation steps of modified sodium bentonite are as follows: S101: Add 11 g of sodium bentonite to 100 mL of deionized water, stir and disperse evenly at 60 °C, dropwise add 1 M HCl solution to adjust the pH to 5.5 to obtain a sodium bentonite dispersion; add 4.3 g of cetyltrimethylammonium bromide to 150 mL of deionized water, stir and dissolve evenly at 50 °C to obtain a CTAB solution; S102: Slowly drop 150 mL of the CTAB solution into 100 mL of the sodium bentonite dispersion, stir at 500 rpm at 60 °C for 2 h. After the reaction is completed, dropwise add 1 M NaOH solution to adjust the pH to 7, centrifuge, filter, wash with deionized water, dry at 80 °C for 12 h, and screen through a 200-mesh sieve to obtain modified sodium bentonite; 3. The preparation steps of the multifunctional water purification gel material are as follows: S201: Add rice husk biochar to 5 times the weight of deionized water, stir and disperse evenly, then add nano-CaCO3, ultrasonically disperse evenly, evacuate to 20 kPa and maintain for 60 min and then return to normal pressure, add 0.05 M FeCl3·6H2O solution and 0.025 M FeSO4·7H2O solution, remove bubbles with nitrogen, maintain a nitrogen atmosphere and stir at 60 °C for 20 min, then dropwise add 2 M NaOH solution to adjust the pH to 9.8, continue to age at 60 °C for 30 min, centrifuge, remove the supernatant, wash with deionized water until neutral, calcine in a nitrogen atmosphere at 150 °C for 2 h, screen through a 20-mesh sieve, and dry with hot air at 40 °C for 2 h to obtain the inner carbon core; S202: Dissolve chitosan in 1 wt% acetic acid solution to obtain a 3 wt% chitosan solution; add modified sodium bentonite to deionized water, and disperse it evenly by ultrasonic treatment to obtain a 3 wt% modified bentonite dispersion; ultrasonically disperse Fe-P nanoflour into the chitosan solution, then combine it with the modified bentonite dispersion, and stir at 1000 rpm for 10 min to obtain an emulsion slurry; S203: Add the inner carbon core of step S201 into a magnetic stirring container, dropwise add the emulsion slurry of step S202, stir at 300 rpm for 15 min, and then let it stand for 20 min; atomize and spray 1M NaOH solution at a ratio of 1 mL / g, let it stand and solidify for 10 min, wash with deionized water until neutral to obtain coated beads; S204: Add sodium alginate and carboxymethyl starch into deionized water, and add Tween-20, stir at 600 rpm for 30 min, and degas under vacuum for 10 min to obtain a 2.5 wt% composite solution. Immerse the coated beads of step S203 into the composite solution for 10 s, rotate and drain at 300 rpm for 20 s, spray 1M CaCl2 solution at 1.5 mL / g, let it stand and solidify for 15 min, then add 10 wt% NaCl solution for salting out and pore formation, treat at 40 °C for 15 min, treat at 50 °C for 30 min, perform vacuum dehydration treatment at 60 °C for 20 min, soak in 0.05M CaCl2 solution for 1 min, wash with deionized water, and dry at 40 °C with hot air for 1 h to obtain a water purification gel material.

[0015] Example 3: A multifunctional water purification gel material, which consists of an outer film, a middle skeleton and an inner carbon core; the raw materials of the outer film include, by weight: 10 parts of sodium alginate, 8 parts of carboxymethyl starch, 0.6 part of NaCl and 0.05 part of Tween-20; the raw materials of the middle skeleton include, by weight: 15 parts of chitosan, 15 parts of modified sodium bentonite, 1.5 parts of Fe-P nanoflour; the raw materials of the inner carbon core include, by weight: 45 parts of rice husk biochar, 12 parts of nano CaCO3, 3 parts of FeCl3·6H2O and 2 parts of FeSO4·7H2O.

[0016] 1. The specific preparation steps of Fe-P nanoflour are as follows: S1: Dissolve 0.01 mol of FeCl3·6H2O in 100 mL of deionized water, stir until dissolved evenly to obtain a 0.1M Fe 3+ solution; dissolve 0.01 mol of KH2PO4 in 100 mL of deionized water, stir until dissolved evenly to obtain a 0.1M PO4 3- solution; S2: Take 100 mL of the 0.1M Fe 3+The solution is heated to 70 °C and continuously stirred at 500 rpm. Then, 100 mL of 0.1 M PO4 from step S1 is slowly added dropwise at a rate of 1 mL / min. 3- During the dropping process, the pH is adjusted to 6.8 using 1 M NaOH solution. After the dropping is completed, stirring and aging are continued at 70 °C and 500 rpm for 3 h. S3: After the aging treatment in step S2 is completed, centrifugation is performed at 8000 rpm for 15 min. The precipitate is taken, washed 5 times repeatedly with deionized water, dried in vacuum at 60 °C for 16 h, pulverized, and screened through a 200-mesh sieve to obtain Fe-P nanoflour. 2. The specific preparation steps of the modified sodium bentonite are as follows: S101: Add 12 g of sodium bentonite to 100 mL of deionized water, stir and disperse evenly at 60 °C, and adjust the pH to 4.5 by dropping 1 M HCl solution to obtain a sodium bentonite dispersion. Add 4.5 g of cetyltrimethylammonium bromide to 150 mL of deionized water, stir and dissolve evenly at 60 °C to obtain a CTAB solution. S102: Slowly drop 100 mL of CTAB solution into 150 mL of sodium bentonite dispersion, stir at 500 rpm at 60 °C for 4 h. After the reaction is completed, add 1 M NaOH solution to adjust the pH to 7, centrifuge, filter, wash with deionized water, dry at 80 °C for 16 h, and screen through a 200-mesh sieve to obtain the modified sodium bentonite. 3. The preparation steps of the multifunctional water purification gel material are as follows: S201: Add rice husk biochar to 5 times the weight of deionized water, stir and disperse evenly, then add nano-CaCO3, and disperse evenly by ultrasonic treatment. Evacuate to 5 kPa and maintain for 30 min, then return to normal pressure. Add 0.05 M FeCl3·6H2O solution and 0.025 M FeSO4·7H2O solution, remove bubbles with nitrogen, maintain a nitrogen atmosphere, stir at 60 °C for 30 min, then add 2 M NaOH solution to adjust the pH to 10, continue aging treatment at 60 °C for 50 min, centrifuge, remove the supernatant, wash with deionized water until neutral, calcine in a nitrogen atmosphere at 250 °C for 1 h, screen through a 20-mesh sieve, and dry with hot air at 40 °C for 2 h to obtain the inner carbon core. S202: Dissolve chitosan in 1 wt% acetic acid solution to obtain a 3 wt% chitosan solution. Add the modified sodium bentonite to deionized water and disperse evenly by ultrasonic treatment to obtain a 3 wt% modified bentonite dispersion. Ultrasonically disperse the Fe-P nanoflour into the chitosan solution, then combine it with the modified bentonite dispersion, and stir at 1000 rpm for 20 min to obtain an emulsion slurry. S203: Add the inner carbon core from step S201 into a magnetic stirring container, dropwise add the emulsion slurry from step S202, stir at 450 rpm for 10 min, then let it stand for 30 min; atomize and spray 1 M NaOH solution at a ratio of 3 mL / g, let it stand and solidify for 20 min, wash with deionized water until neutral to obtain coated beads; S204: Add sodium alginate and carboxymethyl starch into deionized water, add Tween-20, stir at 600 rpm for 60 min, and perform vacuum degassing for 10 min to obtain a 2.5 wt% composite solution. Immerse the coated beads from step S203 into the composite solution for 10 s, perform rotary liquid drainage at 300 rpm for 20 s, spray 1 M CaCl2 solution at 1.5 mL / g, let it stand and solidify for 30 min, then add 10 wt% NaCl solution for salting-out pore formation, treat at 40 °C for 25 min, treat at 50 °C for 50 min, perform vacuum dehydration treatment at 60 °C for 30 min, soak in 0.05 M CaCl2 solution for 3 min, wash with deionized water, and dry at 40 °C with hot air for 2 h to obtain a hydrogel material for water purification.

[0017] Comparative Example 1: The operation process parameters of Comparative Example 1 are basically the same as those of Example 1. The main difference is that in Comparative Example 1, the salting-out pore formation process in step S204 is cancelled, and conventional crosslinking is used. That is, step S204: Add sodium alginate and carboxymethyl starch into deionized water, add Tween-20, stir at 600 rpm for 50 min, perform vacuum degassing for 10 min to obtain a 2.5 wt% composite solution. Immerse the coated beads from step S203 into the composite solution for 10 s, perform rotary liquid drainage at 300 rpm for 20 s, spray 1 M CaCl2, let it stand and solidify for 25 min, wash with deionized water, and dry at 40 °C with hot air for 1.5 h to obtain a multifunctional hydrogel material for water purification.

[0018] Comparative Example 2: The operation process parameters of Comparative Example 2 are basically the same as those of Example 1. The main difference is that in Comparative Example 2, sodium-based bentonite is used to replace the modified sodium-based bentonite.

[0019] Comparative Example 3: The operation process parameters of Comparative Example 3 are basically the same as those of Example 1. The main difference is that in Comparative Example 3, the addition of Fe-P nanoflakes is cancelled, and an FeCl3 solution with the same iron content is used for replacement.

[0020] Comparative Example 4: The operation process parameters of Comparative Example 4 are basically the same as those of Example 1. The main difference is that in Comparative Example 4, vacuum impregnation is cancelled, that is, rice husk biochar, nano-CaCO3, and nano-Fe3O4 are directly mixed, and the subsequent calcination step process is exactly the same.

[0021] Performance test: Calcium ion release test: Take 0.5 g of the water purification hydrogel materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 and place them in 100 mL of reaction solution (2 mM CaCl2 + 1 mM MgSO4 + 5 mg / L humic acid + 0.1 M NaCl, pH 7.5). Use HEPES buffer as the control group. After putting them in, the whole system should be in a slow flow state (0.6 m / s) to simulate the slight disturbance of a river channel or a circulating water body. This is defined as 0 h. At the time points of 0.5 h, 2 h, 6 h, 24 h, 72 h, and 168 h after putting them in, respectively take 5 mL of supernatant samples (immediately add fresh buffer with the same volume and composition after each sampling), and accurately quantify the calcium ion concentration with AAS, and calculate the cumulative release amount = calcium ion concentration measured by AAS at time t × total volume of the medium / initial mass of the dry gel. All examples and comparative examples were tested in parallel with 3 batches of independent samples, and the average value was taken for each data point. The results are as Figure 1 shown; Take out the material after releasing calcium and transfer it to a 500 mL solution containing 10 mg / L PO4 3- , and measure the residual phosphorus concentration after shaking at 25 °C for 24 h. All examples and comparative examples were tested in parallel with 3 batches of independent samples, and the average value was taken for each data point. The results are as Figure 2 shown.

[0022] From Figure 1 the results, it can be seen that the calcium ions of the water purification hydrogel materials prepared in Examples 1 to 3 of the present invention can be continuously released to achieve long-term effective use; from the result of Comparative Example 1, it can be seen that after salting out is cancelled, the outer membrane has high density and small pore size, and it is difficult for Na + to quickly enter the middle layer site to replace Ca 2+ , and the release in the first 24 h decreases significantly. Subsequently, it enters the CaCO3 diffusion-dissolution controlled stage, but the release rate shows a significant increase after 24 h, and the overall performance shows obvious non-uniform release. This may be due to the non-uniform erosion of the dense structure under the action of humic acid, resulting in the expansion of the pores; from the result of Comparative Example 2, it can be seen that the Ca 2+ exudation rate is slightly slower than that of the example. This may be because the positive electric lamella of CTAB is missing, and humic acid is more likely to adhere to the pore wall, resulting in a decrease in the release rate; from the result of Comparative Example 3, it can be seen that the Ca 2+ exudation rate is relatively fast. This may be due to the mild acidification brought by the hydrolysis of FeCl3, which promotes the dissolution of CaCO3 to a certain extent, and then leads to an increase in the Ca 2+ exudation rate; from the result of Comparative Example 4, it can be seen that without vacuum impregnation, CaCO3 mostly accumulates on the outer surface of the carbon nucleus or the large pore mouth, and has the largest direct contact area with the fluid. The instantaneous concentration of Ca 2+ in the first 24 h is significant; but the subsequent release gradually flattens and decreases. This may be due to the gradual passivation of the exposed CaCO3 within 72 h. From Figure 2The results show that after 7 days of flushing test, the Fe-P and Fe3O4 in the water purification gel material prepared by the present invention still have hydroxyl exchange sites, and cooperate with CTAB-bentonite to maintain a long-term positive charge, which can effectively adsorb residual PO4 3- , forming a very low detection value; from the results of Comparative Example 1, it can be seen that due to the outer membrane blockage, it is more difficult for Fe / lamellae to quickly contact the solution, and the residual amount of PO4 3- is relatively large; from the results of Comparative Example 2, it can be seen that the lack of CTAB-bentonite leads to a significant reduction in effective strong adsorption sites. Although Fe-P and chitosan are still present, their co-precipitation with PO4 3- needs to capture a certain concentration before it can be triggered. After the pre-concentration effect of CTAB is weakened, the entire precipitation-fixation process starts slowly and has low efficiency, resulting in a slightly increased residual amount of PO4 3- ; from the results of Comparative Example 3, it can be seen that after replacing Fe-P with FeCl3, Fe 3+ is mostly suspended as Fe(OH)3 under neutral / weak alkaline conditions, and there is little formation of FePO4 precipitation, losing the chemical precipitation locking function for PO4 3- , resulting in a significantly increased residual amount of PO4 3- ; from the results of Comparative Example 4, it can be seen that the exposed CaCO3 is passivated, and the positive electric lamellae have been partially covered by humic acid in flowing water for 168 h, and the residual amount of PO4 3- is significantly increased.

[0023] Acid buffer test: Take 1 g of the water purification gel materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 and place them in 500 mL of 0.1 M H2SO4 solution, record the pH change value, and calculate the buffer capacity (mmol H + / g)=(initial concentration of H+-concentration of H + after testing)×solution volume / sample mass. After placing for 2 h, record the weight loss (%)=(weight before testing-weight after testing) / weight before testing×100%. All examples and comparative examples were tested in parallel with 3 batches of independent samples, and the average value was taken for each data point. The results are as Figure 3 shown.

[0024] From Figure 3The results show that the hydrogel materials prepared in Examples 1 to 3 of the present invention have good instantaneous resistance and buffering properties to strong acid, and will not be easily broken through by strong acid, resulting in performance failure; from the results of Comparative Example 1, it can be seen that the dense membrane of Comparative Example 1 has poor buffering performance, and the weight change in 2h is large, which may be due to local corrosion forming pinholes, and the acid removes part of the chitosan skeleton edge and calcium carbonate along the pores; from the results of Comparative Example 2, after CTAB falls off, the bentonite layers are no longer stretched, and the hydrophobic chains and quaternary ammonium positively charged system The system is absent, the layers are closer together, and are more easily blocked by humic acid, resulting in a lower pH change, a slight increase in buffering capacity, and a slight increase in weight loss; from the results of Comparative Example 3, it can be seen that FeCl3 will immediately hydrolyze and dissolve under strong acid, which is equivalent to additional acid corrosion of the skeleton, the buffering capacity will decrease slightly, and the weight loss will increase significantly. From the results of Comparative Example 4, it can be seen that there is a lack of vacuum impregnation, and CaCO3 is mostly exposed in the carbon core. Although it shows excellent instantaneous buffering performance, the weight loss is significant, the subsequent endurance performance is almost zero, and the sustained release effect cannot be achieved.

[0025] Purified water adsorption test: prepare 20mg / L of Pb 2+ and CrO4 2- The solution was then added with 1 g of the clean hydrogel material prepared in Examples 1 to 3 and Comparative Examples 1 to 4 into 1 L of the above four heavy metal ion solutions, and treated in a constant temperature water bath at 25°C. 1 mL of samples were taken at 0.5 h, 1 h, 3 h, 6 h, 12 h and 24 h (the same volume of solution was added), the residual concentration was determined, and the adsorption rate (%) was calculated as (initial concentration - concentration at the test time point) / initial concentration × 100%. All examples and comparative examples were tested in parallel using 3 independent batches of samples, and the average value of each data point was taken. The results are shown in the figure. Figure 4 and Figure 5 shown.

[0026] Depend on Figure 4 and Figure 5 The results show that the hydrogel materials prepared in Examples 1 to 3 of the present invention have excellent heavy metal adsorption performance; the results of Comparative Example 1 show that there is no salting out and pores, acid / Na + Enter slowly, Ca 2+ The replacement and CaCO3 dissolution are both delayed, the adsorption is poor in the early stage, and the adsorption is significantly improved in the later stage; from the results of comparative example 2, it can be seen that the bentonite layer without modification no longer has a permanent positive charge, loses its strong adsorption of anions, and the pore wall is more easily recharged. The lack of hydrophobic chains makes the pore wall hydrophilic, and foreign anions are more likely to reversely occupy the site, CrO4 2- The adsorption decreased significantly; from the results of Comparative Example 3, it can be seen that there is no iron-phosphorus-metal co-precipitation site, Pb 2+ Need to rely on chitosan-NH2 and CaCO3 to treat separately, Pb 2+ The adsorption effect is reduced, and the use of FeCl3 with its own H+ , the framework is locally acidified, the charge degree of the CTAB lamella decreases, and the adsorption of CrO4 2- decreases significantly; from the results of Comparative Example 4, it can be seen that most of the CaCO3 is exposed outside, reacting violently with acid in the early stage, and the reduction of Cr(VI) by the Fe3O4 catalyst is limited, resulting in a significant decrease in the overall adsorption effect.

[0027] Spectrum test: The sample of the water purification hydrogel material of Example 1 after the calcium ion release test was scanned using a scanning electron microscope to obtain an SEM scanning electron micrograph, and the results are as Figure 6 shown.

[0028] From Figure 6 the results, it can be clearly seen in the figure that there are flakes with a side length of 5-10 µm and hexagonal or polygonal edges, which conform to the typical morphology of bentonite lamellae lying flat on the pore wall after drying; the picture shows that the outer membrane is peeled off after 168 h of flowing water shear, but the middle layer of chitosan-bentonite-Fe-P framework still remains intact, and the honeycomb / through channels still remain connected; in addition, a thinner and denser coating layer that is brighter than the main body can be seen at the edges of the lamellae and the intersections of the fibers, which may be the manifestation of the slightly thickened pore wall of the framework under long-term immersion and electrolyte environment, and the overall connectivity of the water purification hydrogel material still has good performance.

[0029] In summary, the water purification hydrogel materials prepared in Examples 1-3 have excellent slow-release performance and long-term water purification effect. In the early stage, heavy metal ions can be rapidly adsorbed to achieve the water purification effect, and in the middle and late stages, calcium ions can also be stably released to achieve phosphorus fixation and removal. At the same time, the water purification hydrogel materials prepared in Examples 1-3 have excellent acid resistance, which can ensure the stability of use in extreme environments; however, in-depth comparative analysis reveals that Example 1 performs better in key performance indicators and is the best choice with the best comprehensive performance: in the calcium ion release test, the CaCO3 content of Example 1 is at the best slow-release level, which can not only ensure the rapid release of a sufficient amount of Ca at the initial stage 2+ , raising the system pH to a range conducive to metal coordination (such as forming PbCO3 / Pb3(CO3)2(OH)2) and phosphorus precipitation (such as forming Ca5(PO4)3OH or CaHPO4), and avoiding the depletion of the alkali source in the short term; although the total amount of calcium ion release in Example 3 is slightly higher than that in Example 1 (this may be related to its slightly higher CaCO3 feeding amount), its phosphorus fixation effect after the 168 h slow-release test is significantly weaker than that in Example 1 because of the too fast Ca 2+The release may cause a denser calcium phosphate hard shell to form on the outer membrane surface of Example 3 faster than that of Example 1, clogging the pores and hindering the subsequent diffusion and precipitation of phosphorus, thereby resulting in an increase in the residual dissolved phosphorus. Therefore, Example 1 has more advantages in terms of slow-release effect and final phosphorus fixation efficiency. In terms of buffer capacity (β value), Example 3 is slightly higher than Example 1, which may be related to its higher CaCO3 content. However, under the same 2h acid shock condition, the weight loss of Example 3 (7.6%) is significantly higher than that of Example 1 (6.4%). This indicates that more CaCO3 on the surface layer of Example 3 is consumed in a one-time violent reaction, although it provides an instantaneous high buffer capacity, but this may come at the cost of sacrificing the material structure and subsequent long-term buffer capacity. When the acid shock weakens or subsequent shocks need to be dealt with, the effectiveness of its deep alkali source will be inferior to that of Example 1. Compared with the buffer capacity index, the excessive weight loss of Example 3 will lead to significantly weaker long-term use performance of the overall material than that of Example 1. For Example 2, due to the relatively low feed of both CaCO3 and Fe-P, the weight loss is higher than that of Example 1 and the buffer capacity decreases slightly, indicating that its outer membrane is more severely corroded and the reserve of effective alkali source is insufficient, and its acid shock resistance performance is significantly weaker than that of Example 1 and Example 3. Considering the β value and weight loss (especially the weight loss index), Example 1 exhibits better acid buffer stability and long-term effectiveness. Example 1 is significantly superior to Example 2 and Example 3 in both the adsorption start-up speed and the final removal efficiency. For the adsorption of Pb 2+ , the adsorption rate of Example 1 can reach about 80% within 0.5h and a high removal rate of 99% at 24h; while 2-4% remains in Example 2 and Example 3 at 24h. For CrO4 2- : Example 1 reaches the 70% removal rate line faster and has an adsorption rate of over 95% at 24h; the final adsorption rates of Example 2 and Example 3 are only between 94-95%; Example 1 shows a more stable adsorption rate throughout the adsorption process. Specifically, although Example 3 may perform slightly better in a single index (such as the total amount of calcium ion release, instantaneous buffer capacity), it has other obvious disadvantages (such as reduced phosphorus fixation efficiency, increased structural weight loss, impaired long-term effectiveness). Example 2 shows deficiencies in multiple indexes. In contrast, Example 1 demonstrates excellent and balanced performance in all key properties, including the long-term effectiveness of calcium ion slow release (effectively supporting phosphorus fixation), structural stability (low weight loss) and sustainable buffer capacity under acid shock, and rapid and efficient adsorption of multiple pollutants. Therefore, based on the above analysis, the optimal water purification hydrogel material with comprehensive performance can be obtained through the raw material ratio and process parameters of Example 1.

[0030] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill 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, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A multifunctional water purification gel material, characterized in that, It consists of an outer film, a middle skeleton and an inner carbon core; the raw materials of the outer film include, by weight: 8-10 parts of sodium alginate, 6-8 parts of carboxymethyl starch, 0.4-0.6 parts of NaCl, and 0.03-0.05 parts of Tween-20; the raw materials of the middle skeleton include, by weight: 10-15 parts of chitosan, 10-15 parts of modified sodium-based bentonite, 1-1.5 parts of Fe-P nanoflakes; the raw materials of the inner carbon core include, by weight: 38-45 parts of rice husk biochar, 10-12 parts of nano-CaCO3, 2-3 parts of FeCl3·6H2O, and 1-2 parts of FeSO4·7H2O; The preparation steps of the multifunctional water purification hydrogel material are as follows: S201: Add rice husk biochar into deionized water, stir and disperse evenly, then add nano-CaCO3, ultrasonically treat to disperse evenly, vacuum impregnate, add FeCl3·6H2O solution and FeSO4·7H2O solution, remove bubbles with nitrogen, maintain a nitrogen atmosphere, heat and stir, then add NaOH solution to adjust the pH, continue aging treatment, centrifuge, remove the supernatant, wash with deionized water until neutral, calcine in a nitrogen atmosphere, screen, and dry with hot air to obtain the inner carbon core; S202: Dissolve chitosan in an acetic acid solution to obtain a chitosan solution; add modified sodium-based bentonite into deionized water, ultrasonically treat to disperse evenly to obtain a modified bentonite dispersion; ultrasonically disperse Fe-P nanoflakes into the chitosan solution, then combine with the modified bentonite dispersion, stir to obtain an emulsion slurry; S203: Add the inner carbon core from step S201 into a magnetic stirring container, dropwise add the emulsion slurry from step S202, stir, and let stand; atomize and spray NaOH solution, let stand and solidify, wash with deionized water until neutral to obtain coated beads; S204: Add sodium alginate and carboxymethyl starch into deionized water, add Tween-20, stir, vacuum degas to obtain a composite solution, immerse the coated beads from step S203 into the composite solution, spin to remove liquid, spray CaCl2 solution, let stand and solidify, then add NaCl solution for salting-out pore formation, soak in CaCl2 solution, wash with deionized water, and dry with hot air to obtain the water purification hydrogel material.

2. The multifunctional water purification gel material according to claim 1, characterized in that, The specific preparation steps of the Fe-P nanoflakes are as follows: S1: Dissolve FeCl3·6H2O in deionized water, stir until dissolved evenly to obtain an Fe 3+ solution; dissolve KH2PO4 in deionized water, stir until dissolved evenly to obtain a PO4 3- solution; S2: Heat the Fe solution in step S1, continuously stir, and then slowly add dropwise the PO4 solution in step S1. During the addition process, adjust the pH with NaOH solution. After the addition is completed, continue to stir and age; 3+ solution, continuously stir, and then slowly add dropwise the PO4 3- solution. During the addition process, adjust the pH with NaOH solution. After the addition is completed, continue to stir and age; S3: After completing the aging treatment in step S2, centrifuge, take the precipitate, repeatedly wash with deionized water, vacuum dry, pulverize and screen to obtain Fe-P nanoflakes.

3. The multifunctional water purification gel material according to claim 2, wherein, In step S2, the Fe 3+ solution and the PO4 3- solution are used in a volume ratio of 1:

1.

4. A multifunctional water purification gel material according to claim 3, characterized in that, The specific preparation steps of the modified sodium-based bentonite are as follows: S101: Add sodium-based bentonite into deionized water, heat and stir to disperse evenly, add HCl solution to adjust the pH to obtain a sodium-based bentonite dispersion; add cetyltrimethylammonium bromide into deionized water, stir and dissolve evenly to obtain a CTAB solution; S102: Slowly drop the CTAB solution into the sodium-based bentonite dispersion, heat and stir, after the reaction is completed, add NaOH solution to adjust the pH, centrifuge, filter, wash with deionized water, dry, and screen to obtain the modified sodium-based bentonite.

5. The multifunctional water purification gel material according to claim 4, characterized in that, In step S101, the dosage ratio of the sodium-based bentonite to deionized water is 1 - 1.2 g: 10 mL; the dosage ratio of the cetyltrimethylammonium bromide to deionized water is 1.4 - 1.5 g: 50 mL.

6. The multifunctional water purification gel material according to claim 5, characterized in that, In step S102, the volume dosage ratio of the CTAB solution to the sodium-based bentonite dispersion is 1.5:

1.

7. The multifunctional water purification gel material according to claim 6, characterized in that, In step S201, the specific parameters of the vacuum impregnation are: evacuating to 5 - 20 kPa and maintaining for 30 - 60 min, then restoring to normal pressure.

8. A multifunctional water purification gel material according to claim 7, characterized in that, In step S204, the specific parameters of the salting-out pore formation are: treating at 40 °C for 15 - 25 min, treating at 50 °C for 30 - 50 min, and performing vacuum dehydration treatment at 60 °C for 20 - 30 min.

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