A functional gradient silicon dioxide water purification filter and a preparation method thereof
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INNER MONGOLIA NORMAL UNIVERSITY
- Filing Date
- 2026-04-30
- Publication Date
- 2026-05-29
Smart Images
Figure CN122102274A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of water purification filter cartridges, specifically to a functionally graded silica water purification filter cartridge and its preparation method. Background Technology
[0002] Currently, commercially available water purifier filter cartridges mainly employ single or simple composite structures such as activated carbon, polypropylene cotton, and ultrafiltration membranes. While activated carbon filter cartridges exhibit good adsorption performance for residual chlorine and organic matter, their simple pore structure and limited specific surface area result in weak removal capabilities for heavy metal ions. Furthermore, long-term use can easily lead to bacterial growth and secondary pollution. Physical filtration materials such as polypropylene cotton can only intercept particulate matter and cannot effectively remove dissolved contaminants. Although ultrafiltration membranes can retain bacteria, they are essentially ineffective against small-molecule organic matter and heavy metal ions. These single-function filter cartridges are insufficient to meet the demands for the synergistic removal of multiple contaminants under complex water quality conditions.
[0003] To improve the overall performance of filter cartridges, researchers have attempted to construct multi-layer composite structures or functional coatings to modify filter cartridges. For example, combining activated carbon with ion exchange resin can simultaneously adsorb organic matter and heavy metals; loading antibacterial materials such as silver and copper onto the filter cartridge surface can inhibit bacterial growth. However, existing composite filter cartridges still face the following technical bottlenecks: First, the functional layers are mostly simply physically stacked, resulting in weak interlayer bonding and easy detachment and failure after long-term use; second, multi-layer structures often lead to increased water flow resistance and decreased water permeability, affecting the actual user experience; third, the distribution of functional materials lacks a gradient design, causing interference between functional layers and making it difficult to achieve synergistic effects of graded purification; fourth, the manufacturing process is complex, often involving energy-intensive and equipment-demanding processes such as high-temperature sintering and electrospinning, which is not conducive to large-scale production. In recent years, research on the preparation of porous ceramic materials using biomass templates has attracted attention. Loofah sponge, as a natural porous material, possesses advantages such as a three-dimensional interconnected network structure, high porosity, and wide availability. Using it as a template to replicate inorganic materials such as silica can yield a structurally stable and permeable porous framework. However, current research on filter cartridges based on loofah sponge templates remains at the simple replication stage, failing to fully utilize the structural advantages of the template for functionalized gradient design. Furthermore, the functional layer loading methods are singular, making it difficult to achieve synergistic removal of multiple pollutants.
[0004] Furthermore, existing filter cartridges often employ a step-by-step impregnation combined with mask protection method when constructing multi-layered functions. This process is cumbersome and difficult to control at the boundaries, easily leading to cross-contamination between different functional layers. How to utilize the inherent structural characteristics of the filter core to achieve selective distribution of functional layers, simplifying the process while ensuring the precise construction of the gradient structure, is a key issue that urgently needs to be addressed in current filter cartridge manufacturing technology. Summary of the Invention
[0005] Technical problem to be solved: The purpose of this invention is to provide a functional gradient silica water purification filter element. This filter element is constructed by replicating a silica framework with a pore size gradient, consisting of macropores in the upper section and micropores / mesopores in the lower section, through a loofah template. An activated carbon adsorption layer is loaded in the lower section to remove residual chlorine and organic matter, while an EDTA-graphene heavy metal chelating layer is formed in the upper section. The entire filter element is covered with a nano-Cu / Ag composite antibacterial layer to achieve enhanced antibacterial effect. At the same time, this invention solves the technical problem that existing filter elements cannot simultaneously achieve high throughput, synergistic removal of multiple pollutants, and long-term antibacterial effect, and simplifies the preparation process of the multi-layer functional structure.
[0006] Technical solution: A functionally graded silica water filter element, wherein the water filter element is a graded porous framework; the upper section of the framework is a heavy metal chelating layer, which is an EDTA-graphene composite chelating layer with a macroporous structure; the lower section of the framework is an organic adsorption layer with a high specific surface area micro / mesoporous structure; and the outer surface of the framework is loaded with nano-Cu / Ag composite antibacterial material.
[0007] The above-mentioned method for preparing functionally graded silica water filter cartridges includes the following steps: S1. Preparation of a gradient silica porous framework; S2. The upper section of the gradient silica porous framework is impregnated with ink in EDTA-petroleum composite dispersion to obtain a framework with an upper section loaded with heavy metal chelate layer. S3. The lower section of the gradient silica porous framework is immersed in an organic adsorption layer solution to obtain a framework with a lower section loaded with an organic adsorption layer; S4. Finally, the skeleton obtained in step S3 is immersed in a mixed aqueous solution of copper nitrate and silver nitrate. After ultrasonic-assisted adsorption, it is immersed in a NaBH4 aqueous solution for in-situ reduction. After rinsing and drying, the outer surface of the entire skeleton is loaded with a nano-Cu / Ag composite antibacterial layer, thus obtaining the functional gradient silica water filter element.
[0008] Preferably, the method for preparing the gradient silica porous framework includes the following steps: S11. Select loofah sponges with a pore size of 0.5-3mm, boil them in boiling water for 30min to remove impurities, immerse them in a 3-5% NaOH solution at 40-60℃ for 2h, wash and dry them to obtain the pretreated template; S12. Tetraethyl orthosilicate, anhydrous ethanol, deionized water, and ammonia are mixed in a volume ratio of 1:(1.5-2):0.5:0.1 and magnetically stirred for 2 hours to obtain the upper silica sol. Tetraethyl orthosilicate, anhydrous ethanol, deionized water, and ammonia are mixed in a volume ratio of 1:(1-1.2):0.5:0.1, and polyethylene glycol with a molecular weight of 400-600 is added as a pore-forming agent at a ratio of 5-10% of the total mass of the system. The mixture is magnetically stirred for 2 hours to obtain the lower silica sol. S13. Immerse the pretreated template entirely into the upper silica sol, evacuate to -0.08MPa and maintain for 20-30 minutes to allow the sol to fully penetrate, then remove and suspend the gel at room temperature for 2-4 hours. S14. The skeleton treated in S13 is vertically fixed, and only the lower half of the total length is immersed in the lower section of silica sol. It is immersed in the silica sol under a vacuum of -0.05MPa for 10-20 minutes, and then suspended at room temperature for 12-20 hours. It is then dried at 60℃ for 12 hours to obtain the loofah silica composite. S15. The composite is placed in an air atmosphere, heated to 550°C at 2°C / min, held at that temperature for 2 hours, and then allowed to cool naturally. The loofah template is then removed to obtain a gradient silica porous framework.
[0009] Preferably, the porous silica framework described in step S15 is immersed in a 3-5% APTES ethanol solution and refluxed at 60°C for 4 hours. After the reaction is completed, it is washed with ethanol and dried to obtain the silanized framework.
[0010] Preferably, the method for preparing the organic adsorption layer is as follows: S21. Mix 800-mesh activated carbon powder with a sodium alginate aqueous solution of 2-5% by mass at a mass ratio of 1:(1-2), first mechanically stir and then ultrasonically disperse for 30 minutes each to prepare an adsorption slurry; S22. The silanized framework is suspended vertically, and only the lower micro-region is immersed in the adsorption slurry. Vacuum-assisted impregnation at -0.05MPa lasts for 10 minutes. S23. Immediately after removal, immerse in a 3-5% calcium chloride aqueous solution, crosslink and cure at room temperature for 30 minutes, rinse with deionized water, and dry at 40-60℃ for 6 hours to obtain the lower organic adsorption layer.
[0011] Preferably, the method for preparing the heavy metal chelating layer is as follows: S31. After pulverizing the aminated reduced graphene oxide, it was dispersed in DMF, and then added with EDTA dianhydride. The mixture was stirred and reacted at 40-60℃ for 4 hours to obtain an EDTA-graphene composite dispersion. S32. The framework loaded with the lower organic adsorption layer is vertically suspended, and only the upper macroporous region is immersed in the composite dispersion. The reaction is carried out at a constant temperature of 40-60℃ for 6-8 hours. After washing and drying, the upper heavy metal chelating layer is obtained.
[0012] Preferably, the mass ratio of the aminated reduced graphene oxide to EDTA dianhydride is 1:3; and / or, The particle size of the aminated reduced graphene oxide is 20-50 nm.
[0013] Preferably, in step S3, the concentration of copper nitrate solution is 0.1-0.3 mol / L, the concentration of silver nitrate solution is 0.03-0.05 mol / L, the concentration of NaBH4 solution is 0.1-0.5 mol / L, and the molar ratio of copper ions to silver ions is 3:1-10:1.
[0014] Preferably, the ultrasound time in step S3 is 30-40 minutes, and the ultrasound power is 200-300W; and / or, The drying time is 15-30 minutes. The drying temperature is 40-60℃.
[0015] Preferably, EDTA and acetic anhydride are mixed at a molar ratio of 1:(20-50), and pyridine, accounting for 2%-5% of the total mass of the system, is added as a catalyst. Under nitrogen protection, the mixture is refluxed in an oil bath at 70-80°C for 16-24 hours. After the reaction solution is cooled, the solid is collected by suction filtration, thoroughly washed with anhydrous diethyl ether, and then dried under vacuum at 50-60°C to obtain EDTA dianhydride powder.
[0016] Beneficial effects: The filter element of this invention has the following advantages: 1. This invention uses natural loofah sponge as a sacrificial template to prepare a porous silica framework. Through sol-gel impregnation and high-temperature sintering, the natural three-dimensional fiber network structure of loofah sponge is completely replicated, resulting in an inorganic ceramic framework with high porosity and interconnected pores. This framework not only retains the high water permeability of loofah sponge but also transforms into a stable silica material through high-temperature sintering, completely solving the problems of easy decay and low strength of biomass filter cartridges after long-term immersion. Simultaneously, the silica surface is rich in silanol groups, providing abundant active sites for subsequent APTES silanization, achieving chemical bonding between the framework and the functional layer, and significantly improving the adhesion of the functional layer.
[0017] 2. This invention constructs an axial pore size gradient structure with macropores in the upper section and micropores in the lower section on a single framework through a stepwise impregnation process with silica sol of different concentrations and the addition of polyethylene glycol in the lower section. First, the entire template is immersed in a low-concentration silica sol, forming a loose silica precursor layer in both the upper and lower sections. Then, only the lower section is immersed a second time in a high-concentration silica sol, providing it with more silicon source. After high-temperature calcination, the upper section, due to its lower silicon source, forms a natural macropore structure, ensuring rapid water flow and reducing pressure drop; the lower section, enriched with silicon source, forms a dense micropore structure, significantly increasing the specific surface area and providing more active sites for the organic matter adsorption layer. This gradient pore structure allows the filter cartridge to maintain high throughput while significantly improving pollutant contact efficiency, achieving a synergistic effect between pore size gradient and functional gradient.
[0018] 3. The lower organic adsorption layer of this invention uses sodium alginate and Ca... 2+An ion-crosslinked system is used to encapsulate activated carbon powder. This gel network crosslinks in the aqueous phase at room temperature, avoiding damage to the pore structure of the activated carbon caused by high temperatures. The gel layer has strong hydrophilicity and low water flow resistance. The three-dimensional network structure provides sufficient exposed surface for the activated carbon, improving the adsorption rate. (Ca...) 2+ Cross-linked calcium alginate is stable in drinking water and will not dissolve and cause secondary pollution.
[0019] 4. The upper heavy metal chelating layer of this invention adopts a composite structure of EDTA covalently grafted with graphene. The high specific surface area of graphene provides an ideal dispersion carrier for EDTA, allowing the EDTA chelating sites to be fully exposed. The π-π stacking effect of graphene itself can adsorb aromatic pollutants in water, complementing the heavy metal chelating function of EDTA. The multiple carboxyl and amino groups of EDTA have a strong chelating ability for heavy metal ions, forming stable five-membered or six-membered ring complexes. The covalent grafting method ensures that EDTA does not fall off during use, avoiding secondary pollution.
[0020] 5. The outer antibacterial layer of this invention employs an integral impregnation process, achieving precise loading of the antibacterial layer onto the entire outer surface. This design cleverly utilizes the blocking effect of the pre-constructed functional layer on the pores, eliminating the need for additional protection or complex operations. Precise loading of the antibacterial layer can be achieved in a single integral impregnation step, resulting in a simple and highly controllable process. The antibacterial layer adopts a nano-copper / silver bimetallic composite structure, using ultrasonic-assisted adsorption to transfer Cu... 2+ and Ag + Uniform loading was achieved, followed by in-situ reduction to nanoparticles using NaBH4. Ag in the bimetallic system + It has strong bactericidal activity, Cu 2+ The sustained-release effect is good, and the synergistic effect of the two enhances the antibacterial rate. Furthermore, the introduction of copper reduces the amount of silver used, which significantly reduces costs while ensuring antibacterial efficacy. Attached Figure Description
[0021] Figure 1 For permeability flux testing; Figure 2 For residual chlorine removal rate testing; Figure 3 For heavy metal adsorption performance testing; Figure 4 For antibacterial performance testing; Figure 5 For long-term operational stability testing; Figure 6 For cyclic adsorption capacity testing. Detailed Implementation
[0022] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments: Example 1
[0023] A functionally graded silica water filter cartridge, wherein the water filter cartridge is a graded silica porous framework prepared using loofah sponge as a template; the upper section of the framework is a heavy metal chelating layer, which is an EDTA-graphene composite chelating layer with a macroporous structure, and the lower section is an organic matter adsorption layer; the outer surface of the framework is loaded with nano-Cu / Ag composite antibacterial material.
[0024] The above-mentioned method for preparing functionally graded silica water filter cartridges includes the following steps: S1. Preparation of a gradient silica porous framework; S2. The upper part of the gradient silica porous framework is immersed in EDTA-graphene composite dispersion to obtain a framework loaded with an upper heavy metal chelate layer; the lower part is immersed in an organic adsorption layer solution to obtain a framework loaded with an upper heavy metal chelate layer and a lower organic adsorption layer. S3. Finally, the entire skeleton obtained in step S2 is immersed in a mixed aqueous solution of copper nitrate and silver nitrate, wherein the concentration of copper nitrate is 0.1 mol / L, the concentration of silver nitrate is 0.03 mol / L, and the molar ratio of copper ions to silver ions is 3:1. Ultrasonic adsorption is performed for 30 minutes at a power of 200 W. After removal, it is immersed in a 0.3 mol / L NaBH4 aqueous solution for 15 minutes, rinsed with deionized water, and dried at 60°C for 15 minutes. This results in a nano-Cu / Ag composite antibacterial layer being loaded onto the outer surface of the entire skeleton, thus obtaining the functionally graded silica water filter element. The method for preparing the gradient silica porous framework includes the following steps: S11. Select a loofah sponge with a pore size of 1 mm, boil it in boiling water for 30 min to remove impurities, immerse it in a 4% NaOH solution at 50℃ for 2 h, wash and dry it to obtain a pretreated template; S12. Tetraethyl orthosilicate, anhydrous ethanol, deionized water, and ammonia are mixed in a volume ratio of 1:2:0.5:0.1 and magnetically stirred for 2 hours to obtain the upper silica sol. Tetraethyl orthosilicate, anhydrous ethanol, deionized water, and ammonia are mixed in a volume ratio of 1:1:0.5:0.1, and polyethylene glycol with a molecular weight of 600 is added as a pore-forming agent at 5% of the total mass of the system. The mixture is magnetically stirred for 2 hours to obtain the lower silica sol. S13. Immerse the pretreated template entirely into the upper silica sol, evacuate to -0.08MPa and maintain for 20 minutes to allow the sol to fully penetrate, then remove and hang the gel at room temperature for 3 hours. S14. The skeleton treated in S13 is vertically fixed, and only the lower half of the total length is immersed in the lower section of silica sol. It is immersed in the silica sol under a vacuum of -0.05MPa for 20 minutes, then removed and suspended at room temperature for 12 hours. It is then dried at 60℃ for 12 hours to obtain the loofah silica composite. S15. The composite is placed in an air atmosphere, heated to 550°C at 2°C / min, held at that temperature for 2 hours, and then allowed to cool naturally. The loofah template is then removed to obtain a gradient silica porous framework.
[0025] The porous silica framework described in step S15 was immersed in a 5% APTES ethanol solution and refluxed at 60°C for 4 hours. After the reaction was completed, the framework was washed with ethanol and dried to obtain the silanized framework.
[0026] The method for preparing the organic adsorption layer is as follows: S21. Mix 800-mesh activated carbon powder and 5% sodium alginate aqueous solution at a mass ratio of 1:2. First, mechanically stir and then ultrasonically disperse for 30 minutes each to prepare an adsorption slurry. S22. The silanized framework is suspended vertically, and only the lower microporous / mesoporous region is immersed in the adsorption slurry. Vacuum-assisted impregnation at -0.05MPa lasts for 10 minutes. S23. Immediately after removal, immerse in a 4% calcium chloride aqueous solution, crosslink and cure at room temperature for 30 min, rinse with deionized water, and dry at 40℃ for 6 h to obtain the lower organic adsorption layer.
[0027] The method for preparing the heavy metal chelating layer is as follows: S31. After pulverizing the aminated reduced graphene oxide, it was dispersed in DMF, and EDTA dianhydride was added. The mixture was stirred at 60℃ for 4 hours to obtain an EDTA-graphene composite dispersion. S32. The framework loaded with the lower organic adsorption layer is vertically suspended, and only the upper macroporous region is immersed in the composite dispersion. The reaction is carried out at a constant temperature of 40°C for 6 hours. After washing and drying, the upper heavy metal chelating layer is obtained.
[0028] The mass ratio of the aminated reduced graphene oxide to EDTA dianhydride is 1:3; and / or, The particle size of the aminated reduced graphene oxide is 30 nm.
[0029] EDTA and acetic anhydride were mixed at a molar ratio of 1:30, and pyridine (3% by mass of the total system) was added as a catalyst. The reaction was carried out under nitrogen protection and refluxed in an oil bath at 80°C for 16 hours. After cooling the reaction solution, the solid was collected by vacuum filtration, washed thoroughly with anhydrous diethyl ether, and dried under vacuum at 60°C to obtain EDTA dianhydride powder.
[0030] Example 2
[0031] A functionally graded silica water filter cartridge, wherein the water filter cartridge is a graded silica porous framework prepared using loofah sponge as a template; the upper section of the framework is a heavy metal chelating layer, which is an EDTA-graphene composite chelating layer with a macroporous structure, and the lower section is an organic matter adsorption layer; the outer surface of the framework is loaded with nano-Cu / Ag composite antibacterial material.
[0032] The above-mentioned method for preparing functionally graded silica water filter cartridges includes the following steps: S1. Preparation of a gradient silica porous framework; S2. The upper part of the gradient silica porous framework is immersed in EDTA-graphene composite dispersion to obtain a framework loaded with an upper heavy metal chelate layer; the lower part is immersed in an organic adsorption layer solution to obtain a framework loaded with an upper heavy metal chelate layer and a lower organic adsorption layer. S3. Finally, the entire skeleton obtained in step S2 is immersed in a mixed aqueous solution of copper nitrate and silver nitrate, wherein the concentration of copper nitrate is 0.2 mol / L, the concentration of silver nitrate is 0.04 mol / L, and the molar ratio of copper ions to silver ions is 5:1. Ultrasonic adsorption is performed for 30 min with an ultrasonic power of 300 W. After removal, it is immersed in a 0.1 mol / L NaBH4 aqueous solution for 15 min, rinsed with deionized water, and dried at 50°C for 20 min, so that the outer surface of the entire skeleton is loaded with a nano-Cu / Ag composite antibacterial layer, thus obtaining the functional gradient silica water purification filter element.
[0033] The method for preparing the gradient silica porous framework includes the following steps: S11. Select a loofah sponge with a pore size of 2 mm, boil it in boiling water for 30 min to remove impurities, immerse it in a 4% NaOH solution at 50℃ for 2 h, wash and dry it to obtain a pretreated template; S12. Tetraethyl orthosilicate, anhydrous ethanol, deionized water, and ammonia are mixed in a volume ratio of 1:1.8:0.5:0.1 and magnetically stirred for 2 hours to obtain the upper silica sol. Tetraethyl orthosilicate, anhydrous ethanol, deionized water, and ammonia are mixed in a volume ratio of 1:1.1:0.5:0.1, and polyethylene glycol with a molecular weight of 500 is added as a pore-forming agent at 8% of the total mass of the system. The mixture is magnetically stirred for 2 hours to obtain the lower silica sol. S13. Immerse the pretreated template entirely into the upper silica sol, evacuate to -0.08MPa and maintain for 25 minutes to allow the sol to fully penetrate, then remove and hang the gel at room temperature for 3 hours. S14. The skeleton treated in S13 is vertically fixed, and only the lower half of the total length is immersed in the lower section of silica sol. It is immersed in the silica sol under a vacuum of -0.05MPa for 15 minutes, then removed and suspended at room temperature for 16 hours. It is then dried at 60℃ for 12 hours to obtain the loofah silica composite. S15. The composite is placed in an air atmosphere, heated to 550°C at 2°C / min, held at that temperature for 2 hours, and then allowed to cool naturally. The loofah template is then removed to obtain a gradient silica porous framework.
[0034] The porous silica framework described in step S15 was immersed in a 4% APTES ethanol solution and refluxed at 60°C for 4 hours. After the reaction was completed, the framework was washed with ethanol and dried to obtain the silanized framework.
[0035] The method for preparing the organic adsorption layer is as follows: S21. Mix 800-mesh activated carbon powder and 3% sodium alginate aqueous solution at a mass ratio of 1:1.2, stir mechanically and then disperse ultrasonically for 30 minutes each to prepare an adsorption slurry; S22. The silanized framework is suspended vertically, and only the lower microporous / mesoporous region is immersed in the adsorption slurry. Vacuum-assisted impregnation at -0.05MPa lasts for 10 minutes. S23. Immediately after removal, immerse in a 3% calcium chloride aqueous solution, crosslink and cure at room temperature for 30 min, rinse with deionized water, and dry at 50℃ for 6 h to obtain the lower organic adsorption layer.
[0036] The method for preparing the heavy metal chelating layer is as follows: S31. After pulverizing the aminated reduced graphene oxide, it was dispersed in DMF, and then added to EDTA dianhydride and stirred at 50°C for 4 hours to obtain an EDTA-graphene composite dispersion. S32. The framework loaded with the lower organic adsorption layer is vertically suspended, and only the upper macroporous region is immersed in the composite dispersion. The reaction is carried out at a constant temperature of 50°C for 7 hours. After washing and drying, the upper heavy metal chelating layer is obtained.
[0037] The mass ratio of the aminated reduced graphene oxide to EDTA dianhydride is 1:3; and / or, the particle size of the aminated reduced graphene oxide is 30 nm.
[0038] EDTA and acetic anhydride were mixed at a molar ratio of 1:30, and pyridine (3% by mass of the total system) was added as a catalyst. The reaction was carried out under nitrogen protection and refluxed in an oil bath at 80°C for 16 hours. After cooling the reaction solution, the solid was collected by vacuum filtration, washed thoroughly with anhydrous diethyl ether, and dried under vacuum at 60°C to obtain EDTA dianhydride powder.
[0039] Example 3
[0040] A functionally graded silica water filter cartridge, wherein the water filter cartridge is a graded silica porous framework prepared using loofah sponge as a template; the upper section of the framework is a heavy metal chelating layer, which is an EDTA-graphene composite chelating layer with a macroporous structure, and the lower section is an organic matter adsorption layer; the outer surface of the framework is loaded with nano-Cu / Ag composite antibacterial material.
[0041] The above-mentioned method for preparing functionally graded silica water filter cartridges includes the following steps: S1. Preparation of a gradient silica porous framework; S2. The upper part of the gradient silica porous framework is immersed in EDTA-graphene composite dispersion to obtain a framework loaded with an upper heavy metal chelate layer; the lower part is immersed in an organic adsorption layer solution to obtain a framework loaded with an upper heavy metal chelate layer and a lower organic adsorption layer. S3. Finally, the entire skeleton obtained in step S2 is immersed in a mixed aqueous solution of copper nitrate and silver nitrate, wherein the concentration of copper nitrate is 0.3 mol / L, the concentration of silver nitrate is 0.05 mol / L, and the molar ratio of copper ions to silver ions is 7:1. Ultrasonic adsorption is performed for 30 min with an ultrasonic power of 200 W. After removal, it is immersed in a 0.4 mol / L NaBH4 aqueous solution for 15 min, rinsed with deionized water, and dried at 60°C for 20 min to load a nano-Cu / Ag composite antibacterial layer on the outer surface of the entire skeleton, thus obtaining the functional gradient silica water purification filter element.
[0042] The method for preparing the gradient silica porous framework includes the following steps: S11. Select a loofah sponge with a pore size of 2 mm, boil it in boiling water for 30 min to remove impurities, immerse it in a 5% NaOH solution at 50℃ for 2 h, wash and dry it to obtain a pretreated template; S12. Tetraethyl orthosilicate, anhydrous ethanol, deionized water, and ammonia are mixed in a volume ratio of 1:1.7:0.5:0.1 and magnetically stirred for 2 hours to obtain the upper silica sol. Tetraethyl orthosilicate, anhydrous ethanol, deionized water, and ammonia are mixed in a volume ratio of 1:1.1:0.5:0.1, and polyethylene glycol with a molecular weight of 400 is added as a pore-forming agent at 6% of the total mass of the system. The mixture is magnetically stirred for 2 hours to obtain the lower silica sol. S13. Immerse the pretreated template entirely into the upper silica sol, evacuate to -0.08MPa and maintain for 25 minutes to allow the sol to fully penetrate, then remove and hang the gel at room temperature for 3 hours. S14. The skeleton treated in S13 is vertically fixed, and only the lower half of the total length is immersed in the lower section of silica sol. It is immersed in the silica sol under a vacuum of -0.05MPa for 15 minutes, then removed and suspended at room temperature for 16 hours. It is then dried at 60℃ for 12 hours to obtain the loofah silica composite. S15. The composite is placed in an air atmosphere, heated to 550°C at 2°C / min, held at that temperature for 2 hours, and then allowed to cool naturally. The loofah template is then removed to obtain a gradient silica porous framework.
[0043] The porous silica framework described in step S15 was immersed in a 3% APTES ethanol solution and refluxed at 60°C for 4 hours. After the reaction was completed, the framework was washed with ethanol and dried to obtain the silanized framework.
[0044] The method for preparing the organic adsorption layer is as follows: S21. Mix 800-mesh activated carbon powder and 4% sodium alginate aqueous solution at a mass ratio of 1:1.8, first mechanically stir and then ultrasonically disperse for 30 minutes each to prepare an adsorption slurry; S22. The silanized framework is suspended vertically, and only the lower microporous / mesoporous region is immersed in the adsorption slurry. Vacuum-assisted impregnation at -0.05MPa lasts for 10 minutes. S23. Immediately after removal, immerse in a 3% calcium chloride aqueous solution, crosslink and cure at room temperature for 30 min, rinse with deionized water, and dry at 50℃ for 6 h to obtain the lower organic adsorption layer.
[0045] The method for preparing the heavy metal chelating layer is as follows: S31. After pulverizing the aminated reduced graphene oxide, it was dispersed in DMF, and then added to EDTA dianhydride and stirred at 50°C for 4 hours to obtain an EDTA-graphene composite dispersion. S32. The framework loaded with the lower organic adsorption layer is vertically suspended, and only the upper macroporous region is immersed in the composite dispersion. The reaction is carried out at a constant temperature of 55°C for 7 hours. After washing and drying, the upper heavy metal chelating layer is obtained.
[0046] The mass ratio of the aminated reduced graphene oxide to EDTA dianhydride is 1:3; and / or, the particle size of the aminated reduced graphene oxide is 30 nm.
[0047] EDTA and acetic anhydride were mixed at a molar ratio of 1:40, and pyridine (3% by mass of the total system) was added as a catalyst. The reaction was carried out under nitrogen protection and refluxed in an oil bath at 80°C for 16 hours. After cooling the reaction solution, the solid was collected by vacuum filtration, washed thoroughly with anhydrous diethyl ether, and dried under vacuum at 50°C to obtain EDTA dianhydride powder.
[0048] Example 4
[0049] A functionally graded silica water filter cartridge, wherein the water filter cartridge is a graded silica porous framework prepared using loofah sponge as a template; the upper section of the framework is a heavy metal chelating layer, which is an EDTA-graphene composite chelating layer with a macroporous structure, and the lower section is an organic matter adsorption layer; the outer surface of the framework is loaded with nano-Cu / Ag composite antibacterial material.
[0050] The above-mentioned method for preparing functionally graded silica water filter cartridges includes the following steps: S1. Preparation of a gradient silica porous framework; S2. The upper part of the gradient silica porous framework is immersed in EDTA-graphene composite dispersion to obtain a framework loaded with an upper heavy metal chelate layer; the lower part is immersed in an organic adsorption layer solution to obtain a framework loaded with an upper heavy metal chelate layer and a lower organic adsorption layer. S3. Finally, the entire skeleton obtained in step S2 is immersed in a mixed aqueous solution of copper nitrate and silver nitrate, wherein the concentration of copper nitrate is 0.3 mol / L, the concentration of silver nitrate is 0.04 mol / L, and the molar ratio of copper ions to silver ions is 10:1. Ultrasonic adsorption is performed for 30 min with an ultrasonic power of 200 W. After removal, it is immersed in a 0.2 mol / L NaBH4 aqueous solution for 15 min, rinsed with deionized water, and dried at 60°C for 20 min, so that the outer surface of the entire skeleton is loaded with a nano-Cu / Ag composite antibacterial layer, thus obtaining the functional gradient silica water purification filter element.
[0051] The method for preparing the gradient silica porous framework includes the following steps: S11. Select a loofah sponge with a pore size of 1 mm, boil it in boiling water for 30 min to remove impurities, immerse it in a 5% NaOH solution at 50℃ for 2 h, wash and dry it to obtain a pretreated template; S12. Tetraethyl orthosilicate, anhydrous ethanol, deionized water, and ammonia are mixed in a volume ratio of 1:1.8:0.5:0.1 and magnetically stirred for 2 hours to obtain the upper silica sol. Tetraethyl orthosilicate, anhydrous ethanol, deionized water, and ammonia are mixed in a volume ratio of 1:1.2:0.5:0.1, and polyethylene glycol with a molecular weight of 400 is added at 10% of the total mass of the system as a pore-forming agent. The mixture is magnetically stirred for 2 hours to obtain the lower silica sol. S13. Immerse the pretreated template entirely into the upper silica sol, evacuate to -0.08MPa and maintain for 25 minutes to allow the sol to fully penetrate, then remove and hang the gel at room temperature for 3 hours. S14. The skeleton treated in S13 is vertically fixed, and only the lower half of the total length is immersed in the lower section of silica sol. It is immersed in the silica sol under a vacuum of -0.05MPa for 15 minutes, then removed and suspended at room temperature for 16 hours. It is then dried at 60℃ for 12 hours to obtain the loofah silica composite. S15. The composite is placed in an air atmosphere, heated to 550°C at 2°C / min, held at that temperature for 2 hours, and then allowed to cool naturally. The loofah template is then removed to obtain a gradient silica porous framework.
[0052] The porous silica framework described in step S15 was immersed in a 5% APTES ethanol solution and refluxed at 60°C for 4 hours. After the reaction was completed, the framework was washed with ethanol and dried to obtain the silanized framework.
[0053] The method for preparing the organic adsorption layer is as follows: S21. Mix 800-mesh activated carbon powder and 2% sodium alginate aqueous solution at a mass ratio of 1:1. First, mechanically stir and then ultrasonically disperse for 30 minutes each to prepare an adsorption slurry. S22. The silanized framework is suspended vertically, and only the lower microporous / mesoporous region is immersed in the adsorption slurry. Vacuum-assisted impregnation at -0.05MPa lasts for 10 minutes. S23. Immediately after removal, immerse in a 3% calcium chloride aqueous solution, crosslink and cure at room temperature for 30 min, rinse with deionized water, and dry at 50℃ for 6 h to obtain the lower organic adsorption layer.
[0054] The method for preparing the heavy metal chelating layer is as follows: S31. After pulverizing the aminated reduced graphene oxide, it was dispersed in DMF, and then added to EDTA dianhydride and stirred at 40℃ for 4h to obtain an EDTA-graphene composite dispersion. S32. The framework loaded with the lower organic adsorption layer is vertically suspended, and only the upper macroporous region is immersed in the composite dispersion. The reaction is carried out at a constant temperature of 55°C for 7 hours. After washing and drying, the upper heavy metal chelating layer is obtained.
[0055] The mass ratio of the aminated reduced graphene oxide to EDTA dianhydride is 1:3; and / or, the particle size of the aminated reduced graphene oxide is 30 nm.
[0056] EDTA and acetic anhydride were mixed at a molar ratio of 1:40, and pyridine (3% by mass of the total system) was added as a catalyst. The reaction was carried out under nitrogen protection and refluxed in an oil bath at 80°C for 16 hours. After cooling the reaction solution, the solid was collected by vacuum filtration, washed thoroughly with anhydrous diethyl ether, and dried under vacuum at 40°C to obtain EDTA dianhydride powder.
[0057] Comparative Example 1 The main difference between Comparative Example 1 and Example 1 is that the upper and lower sections of the skeleton are both macroporous structures. In step S12, tetraethyl orthosilicate, anhydrous ethanol, deionized water and ammonia are mixed in a volume ratio of 1:2:0.5:0.1 and magnetically stirred for 2 hours to obtain a homogeneous silica sol.
[0058] Comparative Example 2 The main difference between Comparative Example 2 and Example 1 is that: the APTES silanization treatment of S15 is not performed, the framework surface has no amino functional groups, and the functional layer is directly loaded on the unmodified silica surface.
[0059] Comparative Example 3 The main difference between Comparative Example 3 and Example 1 is that in the lower organic adsorption layer, sodium alginate and Ca... 2+ The crosslinking system was replaced with TEOS diluted silica sol as the binder.
[0060] Comparative Example 4 The main difference between Comparative Example 4 and Example 1 is that when the lower organic adsorption layer is loaded, regional selective impregnation is not performed. Instead, the entire skeleton is immersed in the adsorption slurry, so that the activated carbon-calcium alginate slurry is loaded on both the upper and lower sections at the same time.
[0061] Comparative Example 5 The main difference between Comparative Example 5 and Example 1 is that when the upper heavy metal chelate layer is loaded, regional selective impregnation is not performed. Instead, the entire skeleton is immersed in the EDTA-graphene composite dispersion, so that the chelate layer is loaded on both the upper and lower sections at the same time.
[0062] Comparative Example 6 The main difference between Comparative Example 6 and Example 1 is that, in S21, the covalent grafting reaction between EDTA dianhydride and amino graphene is not carried out, but instead, EDTA powder and unmodified graphene are directly physically mixed in DMF.
[0063] Comparative Example 7 The main difference between Comparative Example 7 and Example 1 is that the nano-Cu / Ag composite antibacterial layer coating is not applied to the outer antibacterial layer.
[0064] Comparative Example 8 The main difference between Comparative Example 8 and Example 1 is that only silver nitrate solution was used in S31, without adding copper nitrate, to prepare a single nano-silver antibacterial layer.
[0065] Comparative Example 9 The main difference between Comparative Example 9 and Example 1 is that ordinary graphene oxide was used instead of aminated reduced graphene oxide in step S3 when preparing the heavy metal chelate layer.
[0066] Comparative Example 10 The main difference between Comparative Example 10 and Example 1 is that the loofah template replication process is not used, and commercially available porous ceramics are used directly as the skeleton.
[0067] Performance testing: Water permeability test: The constant pressure filtration method was used. The filter element was installed in a self-made filtration device, and a constant pressure of 0.1 MPa was applied to the inlet end. The volume of pure water passing through the filter element per unit time was recorded.
[0068] The formula for calculating permeable flux is: J = V / (A × t × ΔP) Where J is the permeable flux (L / (m²·h·bar)), V is the filtered water volume (L), A is the effective filtration area of the filter element (m²), t is the test time (h), and ΔP is the test pressure difference (bar).
[0069] Residual chlorine removal rate test: The DPD spectrophotometric method was used. A standard solution of residual chlorine with an initial concentration of 2.0 mg / L was prepared and passed through a filter cartridge under a pressure of 0.1 MPa. The filtered water sample was collected. The absorbance was measured at a wavelength of 515 nm using a HACH DR3900 spectrophotometer, and the residual chlorine removal rate was calculated.
[0070] The removal rate is calculated using the formula: R = (C0 - C) / C0 × 100%. Where C0 is the initial concentration and C is the filtration concentration.
[0071] Heavy metal adsorption performance test: A simulated water sample containing Pb²⁺ (initial concentration 1.0 mg / L) was prepared and passed through a filter cartridge under a pressure of 0.1 MPa. The filtered water sample was collected. The Pb²⁺ concentration before and after filtration was determined by atomic absorption spectrophotometry, and the adsorption capacity and removal rate were calculated.
[0072] The adsorption capacity is calculated using the formula: Q = (C0 - C) × V / m. Where Q is the adsorption capacity (mg / g), V is the volume of the filtered water sample (L), and m is the mass of the adsorbent in the filter element (g).
[0073] Antibacterial performance test Referring to the "Evaluation of Antibacterial Properties of Textiles", the shaking flask method was used. The filter cartridge sample was cut into small pieces and mixed with an Escherichia coli suspension (initial concentration approximately 1 × 10⁻⁶). 6 The cells (CFU / mL) were cultured at 37°C with shaking for 18 hours, and the viable count was determined by plate counting.
[0074] The formula for calculating the antibacterial rate is: R = (N0 - N) / N0 × 100%. Where N0 is the number of viable bacteria in the blank control and N is the number of viable bacteria in the sample.
[0075] Long-term stability test The system operated continuously for 30 days at 0.1 MPa pressure, with water flowing for 8 hours daily. Samples were taken every 5 days to test the residual chlorine removal rate and Pb. 2+ Removal rate and antibacterial rate, calculate performance retention rate.
[0076] The formula for calculating performance retention rate is: P=X t / X0×100%, where X0 is the initial performance value, X t The performance value is the result after running for t days.
[0077] Cyclic adsorption capacity First, the filter materials were ground into powder and multiple equal-mass samples were accurately weighed for later use. Then, adsorption tests were performed, with a fixed volume of 100 mg / L Pb solution, adjusted to pH 5.0, added to each sample. 2+ The solution was incubated at 25°C with shaking for 24 hours until adsorption equilibrium was reached. The supernatant was then used to determine the remaining concentration and calculate the initial adsorption capacity using ICP-OES. The key regeneration step involved filtering the adsorbed sample, desorbing it with 0.1 M HNO3 solution with shaking for 2 hours, and then washing it with deionized water until neutral. Afterward, the regenerated sample was placed in a freshly prepared Pb solution of the same concentration and pH. 2+ In the solution, the above adsorption and measurement process is repeated, and the same sample is subjected to 15 consecutive adsorption-desorption cycles.
[0078] Depend on Figure 1 It can be seen that the permeability flux of Examples 1-4 is 480-620 L / (m²). 2 Between ·h·bar), wherein Example 3 reaches 620L / / (m 2 This is because the present invention constructs a pore size gradient structure with macropores in the upper section and micropores / mesopores in the lower section by impregnating silica sol of different concentrations in stages. The lower section is enriched with silicon source to form a high specific surface area micropore region, while the upper section maintains the natural macropore structure to ensure rapid water flow, thus achieving a synergy between pore size gradient and high flux. In contrast, Comparative Example 1, due to its framework being a uniform macropore throughout and lacking the pore-forming agent added in step S12 of the lower section, has a water flux of only 520 L / (m²). 2 The result (·h·bar) indicates that the gradient pore structure of the present invention increases the specific surface area without increasing the water flow resistance; Comparative Example 10 uses commercially available porous ceramics to replace the loofah template skeleton, and the water permeability is only 180L / (m²). 2 The permeability (·h·bar) was only 31% of that in Example 1, demonstrating that the natural three-dimensional interconnected network structure of loofah sponge is crucial for achieving high filter throughput. In Comparative Examples 4 and 5, due to the lack of regional selective impregnation, the functional slurry clogged the upper or lower pores, reducing the permeability to 350 and 420 L / (m²), respectively. 2 The study (·h·bar) verified the important role of segmented selective loading in maintaining high filter throughput.
[0079] Figure 2 The residual chlorine removal rates of Examples 1-4 all reached over 93.5%, with Example 3 achieving the highest at 97.2%. This is because the microporous / mesoporous structure in the lower section provides a high specific surface area, and the activated carbon powder is cross-linked and embedded in calcium alginate gel at room temperature, ensuring that the adsorption sites are fully exposed and not destroyed by high temperatures. Comparative Example 1, lacking a lower section impregnation pore-forming agent, had insufficient activated carbon loading, resulting in a residual chlorine removal rate of only 82.3%. Comparative Example 3 used TEOS silica sol to replace the sodium alginate and CaCl2 cross-linking system, which, after drying, formed a dense silica film that blocked the activated carbon pores, reducing the removal rate to 91.5%. Comparative Example 4, due to the overall impregnation of the adsorption slurry... In Comparative Example 5, the upper channel was blocked, resulting in a reduced effective loading of activated carbon and a removal rate of only 75.2%. In Comparative Example 6, the EDTA-graphene in the overall impregnation chelating layer blocked the lower activated carbon channels, resulting in a removal rate of 82.5%. In Comparative Example 7, ordinary graphene oxide was used instead of aminated reduced graphene oxide, which had weak binding ability with EDTA and uneven dispersion, resulting in a residual chlorine removal rate of only 78.5%. In Comparative Example 8, a commercially available porous ceramic framework was used, which resulted in low activated carbon loading and poor dispersion, resulting in a removal rate of only 68.5%.
[0080] Figure 3 Pb in Examples 1-4 2+ The adsorption capacity is 65.2-75.1 mg / g, and the removal rate is 96.8%-98.8%, with Example 3 showing the best performance. This is attributed to the covalent grafting of aminated reduced graphene oxide with EDTA dianhydride. The high specific surface area of graphene provides sufficient dispersion sites for EDTA, and the multiple chelating groups can form stable complexes with heavy metal ions. Comparative Example 2 did not undergo APTES silanization treatment, resulting in weak bonding between the framework and the functional layer, easy detachment of EDTA-graphene, and a decrease in adsorption capacity to 58.4 mg / g. Comparative Example 5, due to the lack of segmented selective loading of the chelating layer, caused cross-contamination and uneven loading of the functional layer, resulting in an adsorption capacity of only 38.2 mg / g. Comparative Example 6 used a physical mixture of EDTA and graphene without covalent grafting, resulting in a large loss of EDTA during use, and an adsorption capacity of only 32.5 mg / g. Comparative Example 9 used ordinary graphene oxide, which was difficult to stably bond with EDTA, had insufficient chelating sites, and a significant decrease in adsorption capacity. Comparative Example 10 used commercially available porous ceramics, which had a low specific surface area and limited functional layer loading, resulting in an adsorption capacity of only 35.2 mg / g.
[0081] Figure 4The antibacterial rates of E. coli in Examples 1-4 all reached over 99.85%, with Example 3 showing the highest. This is because the nano-Cu / Ag bimetallic composite antibacterial layer uses an integral impregnation process, utilizing the pore-filling characteristics of the lower functional layer to achieve precise loading on the outer surface and the upper inner surface, resulting in a synergistic effect of the strong bactericidal properties of silver ions and the long-lasting sustained-release properties of copper ions. Comparative Example 7, without the nano-Cu / Ag composite antibacterial layer, had an antibacterial rate of only 75.5%, verifying the necessity of the antibacterial layer in ensuring drinking water safety. Comparative Example 8 used only a single nano-silver antibacterial layer, achieving an initial antibacterial rate of 99.85%, but the high silver content and cost, coupled with the lack of copper ion synergy, resulted in poor long-term stability. Comparative Example 10 used a commercially available porous ceramic framework, but the antibacterial layer had uneven loading and low bonding strength, resulting in an antibacterial rate of only 95.2%.
[0082] Figure 5 After 30 days of continuous operation, the performance retention rates of Examples 1-4 ranged from 85.6% to 92.8%, with Example 3 achieving the highest retention rate of 92.8%. This is attributed to: the stable and resistant-to-soaking silica framework structure replicated using a loofah template; the chemical bonding between the framework and the functional layer through APTES silanization, resulting in a strong and non-detachable adhesion; the covalent grafting of EDTA and aminated graphene, preventing the loss of chelating groups; the stable and non-dissolving calcium alginate gel in the aqueous environment; and the segmented selective loading process, which avoids mutual interference between functional layers and ensures long-term stable operation of the filter element. Comparative Example 2, without silanization treatment, had a functional layer that easily detached, resulting in a performance retention rate of only 72.5%; Comparative Example 6, using a physical mixture of EDTA and graphene, had a chelating layer that easily detached, resulting in a performance retention rate of 70.2%; Comparative Example 9, using ordinary graphene oxide, had a weak functional layer bond, leading to significant performance degradation over long-term use; and Comparative Example 10, using commercially available porous ceramics, had poor bonding between the framework structure and the interface, resulting in a performance retention rate of only 58.5%.
[0083] Figure 6 The results of 15 cycles of adsorption testing are shown in the figures for Pb in Examples 1 and 3. 2+The adsorption capacity retention rate ranged from 84.3% to 88.2%, with Example 1 achieving the highest retention rate of 88.2%. This is attributed to: the stable gradient silica framework structure replicated by the loofah template, providing robust support for the functional layers; APTES silanization, which chemically bonds the framework to the functional layers, effectively preventing the EDTA-graphene chelating layer from detaching from the activated carbon adsorption layer; covalent grafting of EDTA with aminated reduced graphene oxide, ensuring no loss of chelating groups; and the segmented selective loading process, which prevents cross-contamination of the functional layers and ensures long-term stable adsorption of the filter element. Comparative Example 1, lacking a lower-segment microporous / mesoporous structure, suffered from easily collapsing framework channels, resulting in a performance retention rate of only 36.7%; Comparative Example 5, without regional selective loading, experienced reduced binding force due to cross-contamination of the functional layers, resulting in a performance retention rate of 73.0%; and Comparative Example 10, using commercially available porous ceramics instead of the loofah template, exhibited poor three-dimensional connectivity of the framework and weak binding force of the functional layers, resulting in a performance retention rate of only 67.2%.
[0084] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.
Claims
1. A functionally graded silica water filter element, characterized in that: The water purification filter element is a gradient porous framework; the upper section of the framework is a heavy metal chelating layer, which is an EDTA-graphene composite chelating layer with a macroporous structure; the lower section of the framework is an organic adsorption layer with a high specific surface area micro / mesoporous structure; and the outer surface of the framework is loaded with nano-Cu / Ag composite antibacterial material.
2. The method for preparing the functionally graded silica water filter element according to claim 1, characterized in that: Includes the following steps: S1. Preparation of a gradient silica porous framework; S2. The upper section of the gradient silica porous framework is immersed in EDTA-graphene composite dispersion to obtain a framework with an upper section loaded with heavy metal chelate layer. S3. The lower section of the gradient silica porous framework is immersed in an organic adsorption layer solution to obtain a framework with a lower section loaded with an organic adsorption layer; S4. Finally, the skeleton obtained in step S3 is immersed in a mixed aqueous solution of copper nitrate and silver nitrate. After ultrasonic-assisted adsorption, it is immersed in an aqueous solution of sodium borohydride for in-situ reduction. After rinsing and drying, the outer surface of the entire skeleton is loaded with a nano-Cu / Ag composite antibacterial layer, thus obtaining the functional gradient silica water filter element.
3. The method for preparing the functionally graded silica water filter element according to claim 2, characterized in that: The method for preparing the gradient silica porous framework includes the following steps: S11. Select loofah sponges with a pore size of 0.5-3mm, boil them in boiling water for 30min to remove impurities, immerse them in a 3-5% NaOH solution at 40-60℃ for 2h, wash and dry them to obtain the pretreated template; S12. Tetraethyl orthosilicate, anhydrous ethanol, deionized water, and ammonia are mixed in a volume ratio of 1:(1.5-2):0.5:0.1 and magnetically stirred for 2 hours to obtain the upper silica sol. Tetraethyl orthosilicate, anhydrous ethanol, deionized water, and ammonia are mixed in a volume ratio of 1:(1-1.2):0.5:0.1, and polyethylene glycol with a molecular weight of 400-600 is added as a pore-forming agent at a ratio of 5-10% of the total mass of the system. The mixture is magnetically stirred for 2 hours to obtain the lower silica sol. S13. Immerse the pretreated template entirely into the upper silica sol, evacuate to -0.08MPa and maintain for 20-30 minutes to allow the sol to fully penetrate, then remove and suspend the gel at room temperature for 2-4 hours. S14. The skeleton treated in S13 is vertically fixed, and only the lower half of the total length is immersed in the lower section of silica sol. It is immersed in the silica sol under a vacuum of -0.05MPa for 10-20 minutes, and then suspended at room temperature for 12-20 hours. It is then dried at 60℃ for 12 hours to obtain the loofah silica composite. S15. The composite is placed in an air atmosphere, heated to 550°C at 2°C / min, held at that temperature for 2 hours, and then allowed to cool naturally. The loofah template is then removed to obtain a gradient silica porous framework.
4. The method for preparing the functionally graded silica water filter element according to claim 3, characterized in that: The porous silica framework described in step S15 is immersed in a 3-aminopropyltriethoxysilane ethanol solution with a mass fraction of 3-5% and refluxed at 60°C for 4 hours to obtain a silanized framework.
5. The method for preparing the functionally graded silica water filter element according to claim 2, characterized in that: The method for preparing the framework of the lower organic adsorption layer is as follows: S21. Mix 800-mesh activated carbon powder with a sodium alginate aqueous solution of 2-5% by mass at a mass ratio of 1:(1-2), first mechanically stir and then ultrasonically disperse for 30 minutes each to prepare an adsorption slurry; S22. The silanized framework is suspended vertically, and only the lower section is immersed in the adsorption slurry. It is then immersed in the slurry for 10 minutes under a vacuum of -0.05 MPa. S23. Immediately after removal, immerse in a 3-5% calcium chloride aqueous solution, crosslink and cure at room temperature for 30 minutes, rinse with deionized water, and dry at 40-60℃ for 6 hours to obtain the framework of the lower section loaded with organic adsorption layer.
6. The method for preparing the functionally graded silica water filter element according to claim 2, characterized in that: The method for preparing the upper section of the heavy metal chelate layer framework is as follows: S31. After pulverizing the aminated reduced graphene oxide, it was dispersed in DMF, and then added with EDTA dianhydride. The mixture was stirred and reacted at 40-60℃ for 4 hours to obtain an EDTA-graphene composite dispersion. S32. The framework loaded with the lower organic adsorption layer is vertically suspended, and only the upper macroporous region is immersed in the composite dispersion. The reaction is carried out at a constant temperature of 40-60℃ for 6-8 hours. After washing and drying, the framework loaded with the upper heavy metal chelating layer is obtained.
7. The method for preparing the functionally graded silica water filter element according to claim 6, characterized in that: The mass ratio of the aminated reduced graphene oxide to EDTA dianhydride is 1:3; and / or, The particle size of the aminated reduced graphene oxide is 20-50 nm.
8. The method for preparing the functionally graded silica water filter element according to claim 2, characterized in that: In step S4, the concentration of copper nitrate solution is 0.1-0.3 mol / L, the concentration of silver nitrate solution is 0.03-0.05 mol / L, the concentration of NaBH4 solution is 0.1-0.5 mol / L, and the molar ratio of copper ions to silver ions is 3:1-10:
1.
9. The method for preparing the functionally graded silica water filter element according to claim 2, characterized in that: The ultrasound time in step S4 is 30-40 minutes, and the ultrasound power is 200-300W; and / or, The drying time is 15-30 minutes, and the drying temperature is 40-60℃.