Self-assembled multi-nuclear defluorination gel material, preparation method and application thereof

Abstract

The application relates to the field of drinking water treatment, and specifically discloses a self-assembled multi-core defluorination gel material, a preparation method and application thereof. The gel material is formed by stacking high-density, medium-density and low-density gel units along a preset water flow direction; the three kinds of gel units each comprise a three-dimensional network gel matrix formed by cross-linking sodium alginate and metal ions, and a mesoporous reinforcing phase uniformly dispersed in the three-dimensional network gel matrix; and the mesoporous reinforcing phase is a mesoporous silica carrier modified by a phosphate on the surface and gradient amino modification. Through the synergistic effect of the sodium alginate multi-metal ion cross-linking network and the mesoporous reinforcing phase modified by phosphorylation and gradient amino modification, high adsorption capacity, rapid adsorption kinetics, low pressure drop and super-long continuous operation stability are simultaneously achieved, the problems of easy loss, easy cementation, high pressure drop and rapid capacity attenuation of traditional defluorination materials are effectively solved, and the defluorination material is particularly suitable for continuous purification of fluorine-containing water in village and town centralized water supply and the like.

Description

Technical Field

[0001] This application relates to the field of advanced drinking water treatment, and more specifically, to a self-assembled multinucleated defluorination gel material, its preparation method, and its application. Background Technology

[0002] With the gradual implementation and improvement of regulations such as the "Standards for Drinking Water Quality" (GB 5749-2022) in my country, the limits on fluoride ion concentration in drinking water are becoming increasingly stringent, posing a greater challenge to the safety of centralized water supply in rural and remote areas. Excessive fluoride in water has become one of the important issues affecting drinking water safety in villages and towns. Currently, purification technologies for fluoride-containing water (especially when the fluoride ion concentration is ≤5 mg / L) mainly include adsorption, precipitation, and membrane separation. Among these, adsorption is widely used in decentralized water supply scenarios due to its relatively simple operation and controllable cost.

[0003] Currently, the mainstream adsorption and defluorination materials are mainly in powder or micro-particle form, such as activated alumina and bone char. Although these materials have a large specific surface area and a certain adsorption capacity, they have obvious drawbacks in actual dynamic water treatment processes: the materials are easily lost with the water flow, causing secondary pollution and are difficult to recover; solid-liquid separation is difficult, requiring the addition of sedimentation or filtration units, which increases the complexity of the system and operating costs; when used in packed columns, the powder is prone to clogging and caking, leading to a significant increase in operating pressure drop and even equipment failure.

[0004] In recent years, researchers have developed various nanocomposite adsorption materials to improve adsorption performance, increasing specific surface area and the number of active sites through nano-sizing. However, nanomaterials are prone to aggregation in aqueous phases, significantly increasing mass transfer resistance and reducing the effective adsorption rate, and have not fundamentally solved the problems of solid-liquid separation and material loss. On the other hand, membrane separation technologies (such as reverse osmosis and nanofiltration) can achieve high fluoride ion removal rates, but these technologies suffer from high equipment investment, membrane modules being susceptible to fouling by organic matter and colloids, requiring frequent chemical cleaning, and high energy consumption, making them unsuitable for rural water supply scenarios with relatively weak economic foundations and limited operation and maintenance capabilities.

[0005] To improve the engineering applicability of adsorbents, some improvements have emerged in the existing technology, such as:

[0006] (1) Powder immobilization technology: The active components are loaded onto porous supports such as zeolite and silica gel. However, the pores of the support are easily blocked, resulting in a decrease in effective adsorption capacity of more than 40%.

[0007] (2) Granulation technology: Adsorbent powder is pressed into granules using a binder. Although this method improves the mechanical strength of the material, it reduces the internal mass transfer channels and decreases the adsorption kinetics performance by up to 50%.

[0008] (3) Fluidized bed reactor: The adsorbent is fluidized by water or air flow to avoid caking, but the system energy consumption increases by about 3 times, and the material wear is severe, and the fine powder generated further aggravates the loss problem.

[0009] In summary, existing drinking water defluoridation materials and technologies often struggle to simultaneously achieve key performance indicators such as high adsorption capacity (>40 mg / g), rapid adsorption kinetics (equilibrium time <1 h), and low operating pressure drop (<10 kPa) during actual dynamic operation. Furthermore, they commonly suffer from material loss, capacity decay, clogging, and secondary pollution risks during long-term operation. Therefore, developing a defluoridation material and equipment that combines high adsorption performance, good hydraulic characteristics, easy solid-liquid separation, and suitability for modular continuous purification has significant practical application value. Summary of the Invention

[0010] To address the industry challenge of existing drinking water defluoridation technologies failing to achieve long-term stable operation while maintaining high adsorption capacity, rapid kinetics, and low pressure drop during dynamic operation, this application provides a self-assembled multinuclear defluoridation gel material, its preparation method, and its application.

[0011] This application provides the following technical solution:

[0012] In a first aspect, this application provides a self-assembled multinucleus defluoridation gel material, which is formed by stacking a high-density gel unit layer, a medium-density gel unit layer and a low-density gel unit layer sequentially along a predetermined water flow direction;

[0013] The high-density, medium-density, and low-density gel units each include: a three-dimensional network gel matrix formed by crosslinking sodium alginate with metal ions, and a mesoporous reinforcing phase uniformly dispersed in the gel matrix;

[0014] The mesoporous reinforcing phase is a mesoporous silica support with a surface modified by phosphate and amino groups; the metal ions include Ca²⁺ as the main crosslinking ion, and Al³⁺, Fe³⁺, and Ti as fluoride removal active sites. 4 ⁺, La³⁺ and Zr 4 At least two of the following: ⁺

[0015] The difference between the high-density, medium-density, and low-density gel units lies in the decreasing density of amino-modified mesoporous reinforcing phases in that they are respectively.

[0016] Furthermore, in the aforementioned metal ions, the total molar ratio of Ca²⁺ to the polyvalent metal ions of the fluoride-removing active sites is 1-2:0.8-1.6.

[0017] Furthermore, the above-mentioned mesoporous reinforcing phase is prepared by the following method:

[0018] A dry mesoporous silica support is reacted with a silane reagent containing phosphate ester groups under an inert atmosphere and at 70-90°C under reflux to obtain phosphate-modified silica, denoted as P-SiO2.

[0019] The obtained P-SiO2 was divided into three parts and reacted with different amounts of aminosilane reagents at 65-75℃ to prepare mesoporous reinforced phases with high, medium and low amino modification densities.

[0020] Furthermore, in the process of preparing the mesoporous reinforced phase described above:

[0021] When preparing a mesoporous reinforcing phase with high amino-modified density, the mass ratio of P-SiO2 to 5% aminosilane reagent is 4:4.5~5.5.

[0022] When preparing a mesoporous reinforcing phase with medium amino-modified density, the mass ratio of P-SiO2 to 5% aminosilane reagent is 4:2.5~3.5.

[0023] When preparing a mesoporous reinforcing phase with low amino modification density, the mass ratio of P-SiO2 to 5% aminosilane reagent is 4:0.5~1.5.

[0024] Furthermore, carbon nanotubes are dispersed in the aforementioned gel material to form a conductive network within the gel material.

[0025] Secondly, this application provides a method for preparing the above-mentioned self-assembled multinucleated defluorination gel material, comprising:

[0026] The contents include Ca²⁺, as well as Al³⁺, Fe³⁺, and Ti, which serve as active sites for fluoride removal. 4 ⁺, La³⁺ and Zr 4 A mixed metal salt solution of at least two of the metals in ⁺ is mixed with a sodium alginate solution and a mesoporous reinforcing phase with a specific amino-modified density to obtain a homogeneous precursor solution;

[0027] The precursor liquid is injected into a mold and allowed to stand at 20-30°C to complete the primary gelation, forming a gel block.

[0028] The gel block was heat-treated at 50-70℃ for 1-3 hours to enhance cross-linking. The resulting gel material was then cut to obtain gel units modified with different amino densities.

[0029] Gel units modified with different amino densities were arranged in a gradient along the water flow direction according to the amino density from high to low, forming a self-assembled multinucleated defluorination gel material with gradient mass transfer channels.

[0030] Furthermore, the aforementioned gel material is cut into cubic gel units with a side length of 3-10 mm, and the packing density of the gel units when arranged in a gradient is 0.7-0.8 g / cm³.

[0031] Furthermore, the process also includes adding carbon nanotubes to the mixture and ultrasonically dispersing them, wherein the mass ratio of the carbon nanotubes to the sodium alginate is 1:6~8.

[0032] Thirdly, this application also provides a purification device for fluoride-containing water, which includes at least one filled column module, wherein the filled column module is sequentially filled with the above-mentioned high-density gel unit, medium-density gel unit and low-density gel unit along the water flow direction.

[0033] In summary, this application has the following beneficial effects:

[0034] 1. This application utilizes a three-dimensional network gel matrix formed by cross-linking sodium alginate with multivalent metal ions. This matrix firmly anchors multinucleated fluoride removal active sites and a mesoporous reinforcing phase within the matrix, utilizing them in a macroscopically ordered gel unit form. This achieves complete immobilization of the adsorbent, fundamentally solving the inherent defects of traditional powder or microparticle adsorbents, such as easy loss in dynamic water flow and difficulty in solid-liquid separation. This design achieves a solid-liquid separation efficiency exceeding 99%, completely avoiding the risk of secondary pollution caused by adsorbent loss, and eliminating the need for additional complex solid-liquid separation units.

[0035] 2. This application creatively constructs a "gradient mass transfer channel" on a mesoporous reinforced phase. By modifying the mesoporous silica support with phosphate and gradient density amino groups, a continuous distribution of amino group density from high to low is formed along the water flow direction during column packing. This unique charge gradient structure can actively attract and accelerate the directional diffusion of fluoride ions into the active sites inside the pores, significantly reducing the internal mass transfer resistance. This drastically shortens the adsorption equilibrium time from over 1 hour for traditional particulate materials to approximately 30 minutes, improving adsorption kinetics performance by up to 2 times and achieving the goal of rapid purification.

[0036] 3. This application achieves high and stable adsorption capacity while ensuring the mechanical strength of the material through a strategy of "synergistic effect of polynuclear metal ions" and "dispersion enhancement of mesoporous supports". The main crosslinking network composed of Ca²⁺ provides the basic framework strength, while Al³⁺, Fe³⁺, and Ti... 4 The doping of polynuclear ions such as ⁺ provides abundant specific adsorption sites; the mesoporous reinforcing phase not only contributes to the capacity, but its gradient channels also ensure the efficient utilization of all active sites. Therefore, the gel material exhibits an adsorption capacity as high as 42 mg / g, and its mechanical properties are stable after heat treatment, with slow capacity decay during long-term dynamic adsorption.

[0037] 4. To overcome the challenges of clogging and caking in fixed-bed systems, which can lead to increased operating pressure drop, this invention prepares the gel material into regular cubic units with sides of 3-10 mm and stacks them in a packed column at a loose density of 0.7-0.8 g / cm³. This structure creates stable, uniform, and unobstructed water flow channels within the bed, effectively controlling the operating pressure drop below 6 kPa, a 60% reduction compared to traditional granular beds. Furthermore, it enables continuous processing up to 1000 BV (bed volume) without caking, ensuring long-term stable operation and low energy consumption.

[0038] In summary, this invention successfully integrates key advantages such as high adsorption capacity, rapid adsorption kinetics, low operating pressure drop, and resistance to leakage and easy maintenance, providing an efficient, stable, and practical ideal technical solution for the deep purification of fluoride-containing water in scenarios such as centralized water supply in villages and towns. Attached Figure Description

[0039] Figure 1 This is a structural diagram of the modular infill column system in Embodiment 6 of this application;

[0040] Figure 2 This is the curve showing the change in adsorption capacity of the cementitious material over time in the performance test example;

[0041] Figure 3 This is a comparison chart of pressure drop at different flow rates in the performance test examples;

[0042] Figure 4 This is a graph showing the change in fluoride ion removal rate during continuous treatment in a performance test case. Detailed Implementation

[0043] The embodiments of the present invention will be described in detail below with reference to the examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Specific conditions not specified in the examples shall be carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0044] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0045] Preparation Example 1

[0046] This preparation example provides three mesoporous reinforcing phases modified with different amino densities, and their preparation methods include:

[0047] (1) Phosphate modification:

[0048] SiO2 microspheres were vacuum dried at 120℃ for 4 h to remove adsorbed water; 10 g of dried microspheres and 100 mL of anhydrous toluene were mixed, and 5 mL of (CH3)3Si3PO4 and 0.5 mL of triethylamine were added in sequence. The mixture was refluxed at 80℃ for 12 h under nitrogen protection to obtain phosphate-modified silica (P-SiO2).

[0049] The modification reaction is as follows:

[0050] ≡Si-OH + (CH3)3Si-O-PO(O - )2 → ≡Si-O-PO(O - )2+ (CH3)3Si-OH

[0051] (2) Modification with different amino densities

[0052] The P-SiO2 obtained in the above steps was divided into three portions, and gradient amino-modified mesoporous silica supports were prepared separately for each portion:

[0053] A. High-density modified P-SiO2: P-SiO2 microspheres and APTES (3-aminopropyltriethoxysilane) (5%) were added to ethanol at a mass ratio of 4:5, ultrasonically dispersed for 30 min, and then stirred at 70 °C for 2 h. The outer high-density modified material was obtained by centrifugation.

[0054] B. Medium-density modified P-SiO2: P-SiO2 microspheres and APTES (5%) were added to ethanol at a mass ratio of 4:3, ultrasonically dispersed for 30 min, and then stirred at 70 °C for 4 h. The medium-density modified material was obtained by centrifugation.

[0055] C. Low-density modified P-SiO2: P-SiO2 microspheres and APTES (5%) were added to ethanol at a mass ratio of 4:1, ultrasonically dispersed for 30 min, and then stirred at 70 °C for 6 h. The inner low-density modified material was obtained by centrifugation.

[0056] Preparation Example 2

[0057] The difference between this preparation example and preparation example 1 lies in the amount of aminosilane reagent used in step (2), specifically:

[0058] In high-density modified P-SiO2, the ratio of P-SiO2 to APTES is 4:5.5;

[0059] In medium-density modified P-SiO2, the ratio of P-SiO2 to APTES is 4:3.5;

[0060] In low-density modified P-SiO2, the ratio of P-SiO2 to APTES is 4:1.5.

[0061] Preparation Example 3

[0062] The difference between this preparation example and preparation example 1 lies in the amount of aminosilane reagent used in step (2), specifically:

[0063] In high-density modified P-SiO2, the ratio of P-SiO2 to APTES is 4:4.5;

[0064] In medium-density modified P-SiO2, the ratio of P-SiO2 to APTES is 4:2.5;

[0065] In low-density modified P-SiO2, the ratio of P-SiO2 to APTES is 4:0.5.

[0066] Preparation Example 4

[0067] The difference between this preparation example and Preparation Example 1 is that the SiO2 microspheres are directly modified with amino groups without phosphorylation modification. For specific steps, refer to Preparation Example 1.

[0068] Example 1

[0069] This embodiment provides a self-assembled multinucleated defluorination gel material, the preparation method of which includes:

[0070] (1) Prepare a mixed salt solution by mixing calcium nitrate tetrahydrate, aluminum nitrate, ferric nitrate and tetraisopropyl titanate in a molar ratio of Ca:Al:Fe:Ti = 1.5:0.75:0.35:0.03;

[0071] (2) Mix the mixed salt solution, 2% sodium alginate solution and the high-density modified P-SiO2 provided in Preparation Example 1 (preferably with the positive and negative charges being basically equal), stir at room temperature for 30 min to obtain a precursor solution; inject the precursor solution into a mold, let it stand at room temperature for 12 h to complete the primary gelation, and form a gel block; heat-treat the obtained gel block at 60 °C for 2 h to strengthen the crosslinking, and then cut the obtained gel material into 5 mm³ units to obtain a high-density gel unit;

[0072] (3) Mix the mixed salt solution, 2% sodium alginate solution and the medium-density modified P-SiO2 provided in Preparation Example 1 (preferably with the positive and negative charges being basically equal), stir at room temperature for 30 min to obtain a precursor solution; inject the precursor solution into a mold, let it stand at room temperature for 12 h to complete the primary gelation, and form a gel block; heat-treat the obtained gel block at 60 °C for 2 h to strengthen the crosslinking, and then cut the obtained gel material into 5 mm³ units to obtain medium-density gel units;

[0073] (4) Mix the mixed salt solution, 2% sodium alginate solution and the low-density modified P-SiO2 provided in Preparation Example 1 (preferably with the positive and negative charges being basically equal), stir at room temperature for 30 min to obtain a precursor solution; inject the precursor solution into a mold, let it stand at room temperature for 12 h to complete the primary gelation, and form a gel block; heat-treat the obtained gel block at 60 °C for 2 h to strengthen the crosslinking, and then cut the obtained gel material into 5 mm³ units to obtain low-density gel units;

[0074] (5) The obtained high-density gel units, medium-density gel units and low-density gel units are arranged and stacked in sequence along the water flow direction to form a composite module with gradient mass transfer channels. A gap of 0.2 mm is left between each gel unit and the stacking density is controlled to be 0.75 g / cm³.

[0075] Example 2

[0076] This embodiment provides a self-assembled multinucleated defluorination gel material, the preparation method of which includes:

[0077] (1) Prepare a mixed salt solution by mixing calcium nitrate tetrahydrate, lanthanum nitrate hexahydrate, and zirconium nitrate pentahydrate in a molar ratio of Ca:La:Zr=1.5:2:1;

[0078] The remaining steps are the same as in Example 1, except that the gel block is heat-treated at 70°C for 1.5 hours.

[0079] Example 3

[0080] This embodiment provides a self-assembled multinucleated defluorination gel material, the preparation method of which includes:

[0081] (1) Prepare a mixed salt solution by mixing calcium nitrate tetrahydrate, aluminum nitrate, ferric nitrate and tetraisopropyl titanate in a molar ratio of Ca:Al:Fe:Ti=1:0.5:0.3:0.01;

[0082] The remaining steps are the same as in Example 1, except that the gel block is heat-treated at 60°C for 1.2 hours.

[0083] Example 4

[0084] This embodiment provides a self-assembled multinucleated defluorination gel material, the preparation method of which includes:

[0085] (1) Prepare a mixed salt solution by mixing calcium nitrate tetrahydrate, aluminum nitrate, ferric nitrate and tetraisopropyl titanate in a molar ratio of Ca:Al:Fe:Ti=2:1:0.5:0.05;

[0086] The remaining steps are the same as in Example 1, except that the gel block is heat-treated at 50°C for 2.8 hours.

[0087] Example 5

[0088] This embodiment provides a self-assembled multinuclear defluorination gel material, in which carbon nanotubes are also dispersed. The preparation method of this material differs from that of Example 1 in that:

[0089] In steps (2) to (4), after obtaining the precursor liquid, 5 wt% of carbon nanotubes are added to the precursor liquid, ultrasonically dispersed for 1 h, and then injected into the mold. The primary gelation is completed by standing at room temperature for 12 h to form a gel block. The obtained gel block is heat-treated at 60°C for 2 h to strengthen cross-linking. The obtained gel material is then cut into 5 mm³ units to obtain high, medium and low density gel units respectively.

[0090] Example 6

[0091] This embodiment provides a purification device for fluoride-containing water, which includes a packed column module, an inlet pump and flow controller, a pressure drop monitoring unit and a regeneration unit. It mainly adsorbs fluoride in water through the packed column module, ensures constant flow of water through the inlet pump and flow controller, monitors the pressure drop changes in the column in real time through the pressure drop monitoring unit, and regenerates the adsorbent material through the regeneration unit.

[0092] Among them, the filling column module is as follows Figure 1 As shown, the self-assembled multinucleated defluorination gel material prepared in Examples 1-5 is packed into an organic glass column with an inner diameter of 50 mm to form a packed column with an amino density decreasing sequentially from top to bottom.

[0093] Comparative Example 1

[0094] The difference between this comparative example and Example 1 is that: the unphosphorylated, high-, medium-, and low-density amino-modified P-SiO2 provided in Preparation Example 4 is used as the mesoporous reinforcing phase, while everything else remains the same.

[0095] Comparative Example 2

[0096] The difference between this comparative example and Example 1 is that only high-density amino-modified P-SiO2 is used for stacking, and the stacking density is controlled to be 0.75 g / cm³.

[0097] Comparative Example 3

[0098] The difference between this comparative example and Example 1 is that only medium-density amino-modified P-SiO2 is used for stacking, and the stacking density is controlled at 0.75 g / cm³.

[0099] Comparative Example 4

[0100] The difference between this comparative example and Example 1 is that only low-density amino-modified P-SiO2 is used for stacking, and the stacking density is controlled to be 0.75 g / cm³.

[0101] Performance testing

[0102] 1. Modular filled column operation test:

[0103] The self-assembled multinuclear defluorination gel material prepared in Example 1, with a stacking density of 0.75 g / cm³, was packed into an plexiglass column with an inner diameter of 50 mm. Continuous experiments were conducted using raw water with a fluoride ion concentration of 5 mg / L, while using conventional granular bed adsorption as a comparison. The adsorption capacity, pressure drop at different flow rates, and fluoride ion removal rate during continuous treatment were investigated. The results are as follows: Figure 2 , 3 and Figure 4 As shown.

[0104] Figure 2 This is a curve showing the adsorption capacity changing over time. Figure 2 It can be seen that the gel block of the present invention maintains a stable adsorption capacity of approximately 41-42 mg / g during an adsorption process lasting up to 120 minutes, without significant decay. In contrast, the adsorption capacity of traditional particulate adsorbents can only be maintained at 30 mg / g. This result indicates that the stable structure of the present invention, based on a three-dimensional network gel matrix and a gradient mesoporous reinforced phase, can effectively lock active sites and prevent rapid performance decay caused by scouring or local concentration saturation in dynamic water flow, thus exhibiting superior long-term adsorption stability.

[0105] Figure 3 This is a comparison graph of pressure drop at different flow rates. (Example) Figure 3 As shown, during the process of increasing the flow rate from 1 BV / h to 5 BV / h, the operating pressure drop of the packed column of the present invention only gradually increases from about 1 kPa to about 5 kPa, with a linear and gradual growth trend. In contrast, the pressure drop of the conventional granular bed increases sharply from about 3 kPa to more than 18 kPa within the same flow rate range. This comparative data fully demonstrates that the structured gel units used in the present invention and their controlled loose stacking density (0.75 g / cm³) can form uniform and unobstructed water flow channels in the packed bed, reducing the operating pressure to less than 30% of that of the conventional granular bed. This effectively solves the problem of increased energy consumption caused by easy clogging and caking in the conventional fixed bed, and provides a guarantee for the long-term stable and low-energy operation of the system.

[0106] Figure 4 This is a graph showing the change in fluoride ion removal rate during continuous treatment. From... Figure 4As can be seen, during long-term continuous operation at a processing volume of 1200 BV (bed volume), the fluoride ion removal rate of the packed column of this invention consistently remained above 95%, demonstrating extremely stable purification efficiency. In contrast, while the removal rate of traditional particulate adsorption beds was close to 100% in the initial stage of treatment, it began to decline rapidly after the processing volume exceeded 400 BV, dropping to less than 60% at 1200 BV. This result directly confirms that this invention, by "gelling" the adsorbent components and constructing a "gradient mass transfer channel," not only completely solves the problem of loss of powder or microparticle adsorbents but also maintains high adsorption kinetics through gradient amino modification, thereby achieving a highly efficient, stable, and continuous processing capacity at the level of thousands of times the bed volume, far exceeding traditional technologies.

[0107] 2. Adsorption performance test

[0108] Referring to the aforementioned method, the adsorption performance of the gel materials provided in the examples and comparative examples was tested under the same conditions. The structures are shown in Table 1. The column pressure drop is the test data at a flow rate of 2 BV / h, and the continuous processing capacity is the percentage of the adsorption capacity that remains at the initial value after running for 1000 BV.

[0109] Table 1.

[0110]

[0111] As can be seen from Table 1:

[0112] (1) As can be seen from the comparison between Example 1 and Comparative Example 1, compared with Comparative Example 1 which uses SiO2 without phosphorylation and only with gradient amino modification, the adsorption capacity, adsorption rate and long-term stability of Example 1 are comprehensively and significantly improved. This proves that the phosphate group introduced in the phosphate modification step provides an initial capture site with high affinity for fluoride ions through a strong ligand exchange mechanism, and forms a "capture-transfer" synergy with the electrostatic attraction of amino groups. This not only improves the intrinsic adsorption capacity, but also ensures the efficient and stable utilization of active sites in long-term dynamic operation.

[0113] (2) A comparison of Example 1 with Comparative Examples 2-4 shows that Comparative Examples 2-4, which use a single amino density structure, all have obvious shortcomings in performance and insufficient long-term stability: only the high density (Comparative Example 2) has fast initial adsorption (25 min), but the internal mass transfer resistance is large, resulting in low capacity and high pressure drop. Moreover, the capacity retention rate is only 75% after long-term operation, indicating low utilization of internal sites and easy local saturation and inactivation. Only the low density (Comparative Example 4) has smooth internal mass transfer, but weak surface capture ability, resulting in extremely slow kinetics and a low capacity retention rate (78%). Only the medium density (Comparative Example 3) has mediocre performance in all aspects.

[0114] In contrast, the "high-medium-low" gradient structure used in Example 1 cleverly balances the relationship between rapid inlet capture, efficient mid-stage transport, and deep end-stage utilization, thereby achieving the highest long-term operational stability while realizing high adsorption capacity (42 mg / g), rapid kinetics (30 min), and low pressure drop (5.8 kPa).

[0115] (2) Data from Examples 2 and 5 show that, under the premise that the core gradient gel remains unchanged, by adjusting the type of metal ions or introducing conductive components, the material can still maintain excellent comprehensive performance and develop specific advantages. For example, Example 2 is suitable for high-hardness water and has enhanced resistance to calcium and magnesium interference; Example 5 has electrochemical regeneration potential.

[0116] In summary, this invention achieves high adsorption capacity, rapid mass transfer, low operating pressure drop, and strong anti-caking performance through the synergistic effect of a sodium alginate multi-metal ion crosslinking network and a phosphorylated, amino-gradient modified mesoporous reinforcing phase. The modular design of the system facilitates installation, operation, maintenance, and regeneration, making it particularly suitable for the continuous purification of fluoride-containing water in centralized water supply stations in rural towns and villages, demonstrating significant technical advantages and application prospects.

[0117] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A self-assembled multinucleated fluoride-removing gel material, characterized in that, The gel material is composed of high-density gel unit layers, medium-density gel unit layers, and low-density gel unit layers stacked sequentially along a predetermined water flow direction. Each of the high-density, medium-density, and low-density gel units comprises: a three-dimensional network gel matrix formed by crosslinking sodium alginate with metal ions, and a mesoporous reinforcing phase uniformly dispersed within the gel matrix. The mesoporous reinforcing phase is a mesoporous silica carrier with a surface modified by phosphate and amino groups. The metal ions include Ca²⁺ as the main crosslinking ion, and Al³⁺, Fe³⁺, and Ti as fluoride removal active sites. 4 ⁺, La³⁺ and Zr 4 At least two of the following: ⁺; The difference between the high-density, medium-density, and low-density gel units lies in the decreasing density of amino-modified mesoporous reinforcing phases contained therein; The gel material is cut into cubic gel units with a side length of 3-10 mm, and the packing density of the gel units when arranged in a gradient is 0.7-0.8 g / cm³.

2. The self-assembled multinucleated defluorination gel material according to claim 1, characterized in that, In the metal ions, the total molar ratio of Ca²⁺ to the polyvalent metal ions of the fluoride removal active sites is 1-2:0.8-1.

6.

3. The self-assembled multinucleated defluorination gel material according to claim 1, characterized in that, The mesoporous reinforcing phase is prepared by the following method: A dry mesoporous silica support is reacted with a silane reagent containing phosphate ester groups under an inert atmosphere and at 70-90°C under reflux to obtain phosphate-modified silica, denoted as P-SiO2; The obtained P-SiO2 is divided into three parts and reacted with different amounts of aminosilane reagents at 65-75°C to obtain mesoporous reinforcing phases with high, medium and low amino modification densities, respectively.

4. The self-assembled multinucleated defluorination gel material according to claim 3, characterized in that, In the preparation of the mesoporous reinforcing phase: When preparing a mesoporous reinforcing phase with high amino modification density, the mass ratio of P-SiO2 to 5% aminosilane reagent is 4:4.5~5.5; When preparing a mesoporous reinforcing phase with medium amino modification density, the mass ratio of P-SiO2 to 5% aminosilane reagent is 4:2.5~3.5; When preparing a mesoporous reinforcing phase with low amino modification density, the mass ratio of P-SiO2 to 5% aminosilane reagent is 4:0.5~1.

5.

5. The self-assembled multinucleated defluorination gel material according to claim 1, characterized in that, The gel material also contains dispersed carbon nanotubes, which are used to construct a conductive network within the gel material.

6. A method for preparing a self-assembled multinucleated defluorination gel material as described in any one of claims 1-5, characterized in that, It includes: The contents include Ca²⁺, as well as Al³⁺, Fe³⁺, and Ti, which serve as active sites for fluoride removal. 4 ⁺, La³⁺ and Zr 4 A mixed solution of at least two metal salts from ⁺ is mixed with a sodium alginate solution and a mesoporous reinforcing phase with a specific amino-modified density to obtain a uniform precursor solution. The precursor solution is injected into a mold and allowed to stand at 20-30°C to complete primary gelation, forming a gel block. The gel block is heat-treated at 50-70°C for 1-3 hours to strengthen cross-linking. The resulting gel material is then cut to obtain gel units modified with different amino densities. The gel units modified with different amino densities are arranged in a gradient along the water flow direction according to the amino density from high to low, forming a self-assembled multinucleated defluorination gel material with gradient mass transfer channels.

7. The method for preparing the self-assembled multinucleated defluorination gel material according to claim 6, characterized in that, It also includes the process of adding carbon nanotubes to the mixture and ultrasonically dispersing them, wherein the mass ratio of the carbon nanotubes to the sodium alginate is 1:6~8.

8. A purification device for fluoride-containing water, characterized in that, It includes at least one filled column module, wherein the filled column module is sequentially filled with high-density gel units, medium-density gel units and low-density gel units as described in any one of claims 1-5 along the water flow direction.

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