Aerogel for sewage treatment and preparation method thereof

Abstract

The invention provides aerogel for sewage treatment and a preparation method thereof.The preparation method comprises the steps that a fluosilicate solution and a silicon source material are mixed, then a metal ion targeting polymer is added for a reaction, and fluosilicate modified silica sol is obtained; adding a titanium-based photocatalyst into the fluosilicate modified silica sol, and uniformly mixing to obtain a mixed solution; transferring the aerogel sol into a mold, keeping a constant temperature for gelatinization for 24 hours, putting into a freezing environment of-40 DEG C for freeze-drying, heating to 300 DEG C, and keeping the temperature for 3 hours to obtain the aerogel. Therefore, the adsorption capacity of the aerogel and the degradation effect on pollutants are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment materials, and particularly relates to an aerogel for sewage treatment and a preparation method thereof. Background Art

[0002] Industrial sewage contains various pollutants, such as suspended solids, colloidal substances, and oils. Aerogels have extremely high porosity (>90%) and specific surface area, providing a large number of accessible surface sites for adsorbing pollutants. The hierarchical pore channels of aerogels are conducive to water penetration and pollutant molecule diffusion, making the adsorption process faster and reducing resistance. Therefore, aerogels are excellent materials for industrial sewage treatment.

[0003] However, the aerogels in related technologies have the following disadvantages. On the one hand, most traditional silicon-based or inorganic aerogels only have surface hydroxyl groups (–OH) or a small amount of silicon-oxygen bonds (Si–O–Si), resulting in insufficient selective adsorption of heavy metal ions (such as lead, cadmium, mercury, chromium, etc.) and refractory organic compounds (such as petroleum hydrocarbons, benzene series) in industrial sewage. The adsorption mainly relies on physical adsorption or weak charge interactions, making it difficult to achieve targeted and selective capture. On the other hand, once ordinary silica, alumina-based aerogels are adsorbed saturated, the aerogels need to be regenerated or replaced, and they cannot degrade pollutants for continuous treatment. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an aerogel for sewage treatment and a preparation method thereof, aiming to solve the problems of insufficient adsorption capacity of aerogels and difficulty in degrading pollutants.

[0005] To solve the above technical problems, the present invention is realized as follows. The present invention provides a preparation method of an aerogel, and the steps include: S1. Mix a fluorosilicate solution with a silicon source material, and then add a metal ion-targeting polymer for reaction to obtain a fluorosilicate-modified silica sol; S2. Add a titanium-based photocatalyst to the fluorosilicate-modified silica sol and mix evenly to obtain a mixed solution; S3. Transfer the above aerogel sol to a mold, maintain a constant temperature for 24 h of gelation, place it in a freezing environment at -40°C for freeze-drying, and then heat it to 300°C and keep it warm for 3 h to obtain the aerogel.

[0006] In some embodiments of the present invention, in step S1, the fluorosilicate solution includes at least one of sodium fluorosilicate, ammonium fluorosilicate, and aluminum fluorosilicate, the silicon source material includes at least one of tetraethoxysilane, sodium silicate, and aluminum silicate, and the metal ion-targeting polymer includes at least one of sulfonated polystyrene, sodium polyacrylate, and polyethyleneimine.

[0007] In some embodiments of the present invention, by mass ratio, the fluorosilicate solution: the silicon source material: the metal ion-targeting polymer = 1:2 to 3:0.05 to 0.2.

[0008] In some embodiments of the present invention, step S1 includes: S1.1. Dissolve an appropriate amount of fluorosilicate in deionized water, with the solution concentration being 10% by mass ratio, control the temperature at 25 °C, and use a magnetic stirrer for stirring, with the stirring speed set at 200 to 300 rpm to obtain a fluorosilicate solution; S1.2. Gradually add the silicon source material to the fluorosilicate solution, and then add an acidic catalyst after the addition is completed. Adjust the pH value of the solution to 4.5 to 5.5, maintain the temperature at 25 °C and stir for 4 hours to obtain a fluorosilicate-silicon solution; S1.3. Add the metal ion-targeting polymer to the fluorosilicate-silicon solution, raise the temperature to 40 to 50 °C, and stir for 1 hour to obtain a fluorosilicate-modified silica sol.

[0009] In some embodiments of the present invention, in step S2, the titanium-based photocatalyst includes at least one of titanium dioxide, nitrogen-doped titanium dioxide, and copper-doped titanium dioxide. By mass ratio, the titanium-based photocatalyst: the fluorosilicate-modified silica sol = 1:20 to 50.

[0010] In some embodiments of the present invention, step S2 includes: S2.1. Suspend the titanium-based photocatalyst in deionized water, add epichlorohydrin with a mass ratio of 1%, and perform ultrasonic treatment at 40 kHz for 20 min to obtain a modified titanium-based photocatalyst solution; S2.2. Mix the modified titanium-based photocatalyst solution with an organic solvent, and eject it through an electrospinning device under high voltage to form nano-scale catalyst fibers; S2.3. Add the nano-scale catalyst fibers and the fluorosilicate-modified silica sol to a supercritical carbon dioxide solvent, heat to a temperature of 40 °C, and stir for 1 hour under the condition of a pressure of 7 to 8 MPa to obtain a mixed solution.

[0011] In some embodiments of the present invention, step S2 includes: S2.1. Transfer the fluorosilicate-modified silica sol to a reaction chamber and let it stand, adjust the air pressure to -0.08 MPa, adjust the temperature to 40 °C and dry for 10 to 20 min; S2.2. First, introduce gaseous titanium-based photocatalyst for 0.5 - 1 s, with the flow rate of the titanium-based photocatalyst being 0.1 - 10 sccm. Stop introducing the gaseous titanium-based photocatalyst and purge with nitrogen for 5 - 10 s. Then, introduce water vapor or ozone for 0.5 - 1 s, stop introducing water vapor or ozone and purge with nitrogen for 5 - 10 s; S2.3. Execute step S2.2 according to the set number of cycles. After the cycle is completed, maintain nitrogen purging until the reaction chamber slowly cools down to room temperature, and perform ultrasonic dispersion to obtain a mixed solution.

[0012] In some embodiments of the present invention, step S3 includes: S3.1. Transfer the mixed sol to a mold, ensuring that the volume of the sol occupies 90% of the mold. Evacuate to remove air bubbles; S3.2. Place the degassed mixed solution under constant temperature conditions, maintain the temperature at 25°C, and perform gelation for 24 hours to obtain a gel; S3.3. After taking out the gel from the mold, put it into a freeze-drying chamber, set the temperature at -40°C for pre-freezing treatment. After pre-freezing to -40°C, adjust to an air pressure of -0.1 MPa and perform freeze-drying operation for 24 hours. After freeze-drying is completed, gradually raise the temperature to -20°C to obtain an aerogel preform; S3.4. Put the freeze-dried aerogel preform into a high-temperature furnace with an inert atmosphere, set the heating temperature at 300°C, and the heating time at 3 h to obtain an aerogel.

[0013] The present invention provides an aerogel, which is made by the preparation method of an aerogel as described above. The aerogel includes a silicon source material, a fluorosilicate solution, a metal ion-targeting polymer, and a titanium-based photocatalyst; wherein, The silicon source material is used to form the main framework of the aerogel, improving the specific surface area, pore distribution rate, and mechanical strength of the aerogel; The fluorosilicate solution is used to provide fluoride ions and react with the silicon element in the silicon source material, enhancing the hydrophilicity, chemical stability, and adsorption capacity of the aerogel; The metal ion-targeting polymer is used to improve the targeted adsorption performance of the aerogel for heavy metal ions; The titanium-based photocatalyst is used to generate photoinduced electron-hole pairs under light illumination conditions to achieve photocatalytic degradation of organic pollutants in water.

[0014] Compared with the prior art, the beneficial effects of an aerogel for sewage treatment and its preparation method in the present invention are as follows: Mix the fluorosilicate solution with the silicon source material, and then add the metal ion-targeting polymer to introduce fluorine elements into the silica sol framework. Fluorine elements have strong electronegativity and can form a silicon fluoride network or fluorine-containing sites on the material surface, thereby enhancing the adsorption capacity of the aerogel for positively charged or polar pollutants. The combined action of fluorine element modification and the metal ion-targeting polymer greatly improves the hydrophilicity, specific surface area of the aerogel, and its targeted adsorption capacity for specific pollutants, laying a good foundation for the subsequent in-depth removal of heavy metal ions and refractory organic compounds.

[0015] Add the titanium-based photocatalyst to the fluorosilicate-modified silica sol and mix evenly under appropriate conditions. Since the silica sol is still in the sol state, the titanium-based photocatalyst can be dispersed and embedded into the upcoming aerogel framework. This enables the photocatalyst to be uniformly distributed on the surface or inside the pores of the framework at the nanoscale, maximizing the exposure of photocatalytic active sites. This stable loading method ensures that the aerogel can continuously and efficiently photocatalytically degrade the organic pollutants or bacteria adsorbed into the pores under light, rather than simply physically adsorbing them. While retaining a high porosity, the fluorosilicate-modified silica sol and the titanium-based photocatalyst form an adsorption-degradation coupling system, realizing an efficient sewage treatment mechanism of first adsorption and then degradation or synchronous degradation. Brief Description of the Drawings

[0016] Figure 1 is a schematic flow chart of the preparation method of the aerogel for sewage treatment in an embodiment of the present invention. Detailed Embodiments

[0017] In order to make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] Please refer to Figure 1 , the present invention proposes a preparation method of an aerogel for sewage treatment, and the steps include: S1. Mix the fluorosilicate solution with the silicon source material, and then add the metal ion-targeting polymer to react to obtain the fluorosilicate-modified silica sol.

[0019] In step S1, the fluorosilicate solution includes at least one of sodium fluorosilicate, ammonium fluorosilicate, and aluminum fluorosilicate, the silicon source material includes at least one of tetraethoxysilane, sodium silicate, and aluminum silicate, and the metal ion-targeting polymer includes at least one of sulfonated polystyrene, sodium polyacrylate, and polyethyleneimine. Calculated by mass ratio, fluorosilicate solution: silicon source material: metal ion-targeting polymer = 1:2-3:0.05-0.2.

[0020] Step S1 includes: S1.1. Dissolve an appropriate amount of fluorosilicate in deionized water. The solution concentration is 10% by mass ratio, and the temperature is controlled at 25°C. Stir using a magnetic stirrer with the stirring speed set at 200 - 300 rpm to obtain a fluorosilicate solution.

[0021] By stirring at 25°C, the fluorosilicate (such as sodium fluorosilicate, ammonium fluorosilicate, or aluminum fluorosilicate) is fully and evenly dissolved in deionized water, forming a solution with a constant concentration and uniform dispersion, laying a uniform chemical environment for the subsequent reaction with the silicon source material. The appropriate temperature (25°C) and stirring speed (200 - 300 rpm) can avoid local high concentration or crystallization precipitation phenomena, ensuring that fluoride ions are in a relatively stable and active chemical state in the solution, providing good conditions for the subsequent hydrolysis and polycondensation reactions of the silicon source. By maintaining a moderate rotation speed and temperature, it can effectively prevent the precipitation or decomposition of fluorosilicate due to local supersaturation, ensuring that the entire solution remains in a homogeneous system of a single phase, which is conducive to the smooth progress of the subsequent sol - gel process. Obtaining a uniform and stable fluorosilicate solution in the early stage ensures that fluorine elements can fully combine with the silicon source and achieve modification in subsequent steps, thereby enhancing the hydrophilicity, chemical stability, and adsorption performance of the aerogel towards pollutants.

[0022] S1.2. Gradually add the silicon source material to the fluorosilicate solution. After the addition is completed, add an acidic catalyst and adjust the pH value of the solution to 4.5 - 5.5. Maintain the temperature at 25°C and stir for 4 hours to obtain a fluorosilicate - silicon solution.

[0023] Adopting the method of gradual addition can ensure that the silicon source material (such as tetraethoxysilane, sodium silicate, or aluminum silicate) is fully mixed with the fluorosilicate solution, avoiding local high concentration or uneven reaction caused by one - time feeding, thus ensuring the uniformity of sol formation. Adding an acidic catalyst and adjusting the pH value to the range of 4.5 - 5.5 is conducive to the moderate progress of the hydrolysis and polycondensation reactions of the silicon source material. Within this pH range, the formation and cross - linking reaction of silicon - OH bonds occur at a relatively moderate rate, which can not only smoothly form the silicon sol skeleton but also not be too rapid to cause precipitation or excessive colloidal aggregation. Stirring continuously at 25°C for 4 hours creates sufficient time for the hydrolysis and polycondensation of silicon source molecules, thereby forming a molecular - level or nano - level uniformly dispersed silicon - oxygen network. At the same time, fluoride ions can interact synergistically with some silicon - OH bonds or silicon ions to achieve the modification of the silicon sol skeleton. Gradual addition and moderate acidic adjustment ensure the stability and controllability of the sol - gel reaction, obtaining a silicon sol containing fluorine elements, which has a uniform cross - linked structure microscopically and lays a foundation for subsequent functionalization and high - specific - surface - area skeleton.

[0024] S1.3. Add the metal - ion - targeted polymer to the fluorosilicate - silicon solution, raise the temperature to 40 - 50°C, and stir for 1 hour to obtain a fluorosilicate - modified silicon sol.

[0025] Select metal ion-targeting polymers such as sulfonated polystyrene, sodium polyacrylate, or polyethyleneimine, which can rapidly dissolve and uniformly disperse in the silica sol system when heated to 40-50 °C. An appropriate increase in temperature can promote the stretching of polymer segments and form better interactions with the silica sol. Metal ion-targeting polymers carry abundant functional groups (such as sulfonic acid groups, carboxylic acid groups, or amino groups, etc.), which will be anchored to the surface or pores of the silica sol network during the skeleton formation process, achieving targeted adsorption or ion exchange capabilities for pollutants such as heavy metal ions, organic dyes, and ionic compounds. The polymer reacts fully or uniformly disperses with the fluorosilicate silica solution at a slightly higher temperature, and can be grafted into the silicon-oxygen network at the molecular level, not only enhancing the mechanical toughness of the sol but also providing specific surface chemical properties for the final aerogel. Through temperature control conditions (40-50 °C) and 1 hour of stirring, the metal ion-targeting polymer is fully dispersed and combined in the silica sol, endowing the final material with high adsorption capacity and stability for various pollutants (organic, metal ions, etc.), while ensuring the uniformity and flow characteristics of the sol itself.

[0026] S2. Add the titanium-based photocatalyst to the fluorosilicate-modified silica sol and mix evenly to obtain a mixed solution. In step S2, the titanium-based photocatalyst includes at least one of titanium dioxide, nitrogen-doped titanium dioxide, and copper-doped titanium dioxide. Calculated by mass ratio, the titanium-based photocatalyst: fluorosilicate-modified silica sol = 1:20-50.

[0027] In one embodiment, step S2 includes: S2.1. Suspend the titanium-based photocatalyst in deionized water, add epichlorohydrin with a mass ratio of 1%, and perform ultrasonic treatment at 40 kHz for 20 min to obtain a modified titanium-based photocatalyst solution.

[0028] Under the action of ultrasonic waves, epichlorohydrin can introduce hydrophilic functional groups such as epoxy groups on the surface of the titanium-based photocatalyst, enhancing the hydrophilicity of the photocatalyst surface and the binding force with the fluorosilicate-modified silica sol.

[0029] Through such surface modification, more uniform dispersion can be achieved in subsequent solution or sol systems. Ultrasonic treatment at 40 kHz can effectively break up the agglomeration of photocatalyst particles, making the photocatalytic particles at the nanoscale more uniformly dispersed, greatly increasing its specific surface area, and thus obtaining more stable and efficient catalytic performance in subsequent processes. Enhancing the surface activity and hydrophilicity of the photocatalyst, avoiding the agglomeration of large particles in subsequent processing, and achieving nanoscale uniform dispersion lay a good foundation for efficient photocatalysis.

[0030] S2.2. Mix the modified titanium-based photocatalyst solution with an organic solvent and eject it under high voltage through an electrospinning device to form nanoscale catalyst fibers.

[0031] Electrospinning can eject a well-dispersed photocatalyst solution and solidify it into a nanofiber morphology. Compared with conventional powder particles, fibrous materials have continuity and a higher aspect ratio, significantly increasing the surface contact area and improving the photocatalytic reaction efficiency. Such one-dimensional nanofibers can better expose active sites and reduce agglomeration, further enhancing light absorption and pollutant capture. By adjusting parameters such as the solution viscosity, high voltage intensity, and collection distance of electrospinning, the diameter, pore distribution, and microstructure of the photocatalytic fibers can be precisely controlled, so as to optimize for different water pollutants or light conditions. Using electrospinning to form nanoscale catalyst fibers provides a higher specific surface area and a controllable microstructure, making the photocatalytic effect more efficient and targeted.

[0032] Specifically, electrospinning can control the diameter of the generated nanoscale catalyst fibers by adjusting the solution viscosity , solution flow rate , applied voltage and parameters. The control equation is as follows: where the solution viscosity , solution flow rate can obtain numerical values through a viscometer and a flowmeter. refers to the voltage actually applied between the electrospinning needle and the collector, usually in kV (kilovolts). This is the voltage value output by the high-voltage power supply, and the solution jet is stretched into fibers through the electric field between the needle and the collector. represents the critical voltage for electrospinning to start. Only when the actual applied voltage exceeds this critical value , can the surface tension be overcome at the needle to stretch the droplet into a jet and continue into the spinning stage. If does not reach , a stable jet cannot be formed at the needle, making it difficult to produce fibers. represents the actual effective voltage. When the diameter of the nanoscale catalyst fibers is less than the preset diameter value, the actual voltage can be reduced to increase . When the diameter of the nanoscale catalyst fibers is greater than the preset diameter value, the actual voltage can be increased to reduce .

[0033] is the pre-exponential factor. Under the same parameter conditions, if is larger, the diameter of the nanoscale catalyst fibers will be larger; if is smaller, the overall size of the nanoscale catalyst fibers will decrease. is an empirical constant. Using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) to statistically measure the fiber morphology and diameter, a dataset of a set of parameters and nanoscale catalyst fibers is obtained. Using the least squares method or other regression algorithms, the measured is subjected to logarithmic linear regression. According to the linear fitting slope of the experimental data, can be obtained, and the intercept gives ln(K). α can be 0.5 to 1.

[0034] The diameter of the nanoscale catalyst fibers is finer, resulting in a larger specific surface area of the nanoscale catalyst fibers, leading to more sufficient light exposure and pollutant adsorption, improving the photocatalytic efficiency, and also affecting the pore distribution of the aerogel skeleton. If the diameter of the nanoscale catalyst fibers is too large, a lower porosity appears in the aerogel, or dense agglomeration forms during subsequent drying. If the nanoscale catalyst fibers are evenly distributed, a more stable network structure can be formed with the fluorosilicate-modified silica sol, ensuring that the final aerogel is not easily cracked macroscopically and has a high density of photocatalytic active regions microscopically. When the dispersion is poor, local aggregation leads to pore structure collapse or agglomerated regions, reducing the specific surface area and weakening the photocatalytic effect. Through surface modification before electrospinning and regulation of the solution formulation during the spinning process, the surface of the nanoscale catalyst fibers has more functional groups or defect sites for capturing pollutants and promoting photocatalytic reactions.

[0035] S2.3. Add the nanoscale catalyst fibers and the fluorosilicate-modified silica sol to a supercritical carbon dioxide solvent, heat to a temperature of 40 °C, and stir for 1 hour under the condition of a pressure of 7 - 8 MPa to obtain a mixed solution.

[0036] Supercritical carbon dioxide has a high density similar to that of a liquid and a low viscosity and high diffusivity similar to those of a gas, enabling sufficient penetration and fusion between the catalytic fiber and silica sol. Compared with traditional organic solvents, supercritical carbon dioxide is more likely to enter the internal pores of the material, achieving a more uniform and thorough mixing. Under high pressure, carbon dioxide is in a supercritical state, which can reduce the interfacial tension between the conventional liquid and solid phases, and is not easily caused by the collapse or agglomeration of the nanofiber or silica sol network structure, retaining the nano-pores and fiber continuity of the material. Stirring for 1 hour at 40 °C and 7 - 8 MPa can disperse the nano-catalyst fibers in the fluorosilicate-modified silica sol, and better combine them into a composite solution. In this way, during the subsequent preparation of the aerogel, the uniform distribution of the photocatalyst and the overall stability of the material are greatly improved. Utilizing the excellent penetration and dissolution ability of supercritical carbon dioxide, the nano-catalyst fibers and the modified silica sol are mixed at the molecular level, avoiding pore collapse and agglomeration phenomena, laying a foundation for the subsequent formation of an aerogel with outstanding photocatalytic function and stable structure.

[0037] In one embodiment, step S2 includes: S2.1. Transfer the fluorosilicate-modified silica sol to the reaction chamber and let it stand, adjust the air pressure to -0.08 MPa, and adjust the temperature to 40 °C for drying for 10 - 20 min.

[0038] Under the low-pressure condition of -0.08 MPa and the mild temperature of 40 °C, short-time drying of the fluorosilicate-modified silica sol can remove some surface or free water and volatile solvents, avoiding excessive adsorption or liquid interference on the sol surface when subsequently introducing the gaseous titanium-based photocatalyst. This step ensures that there are appropriate hydroxyl groups (–OH) or active sites on the surface, but they are not covered by too much liquid, thus providing good surface conditions for subsequent reactions. The active sites (such as silanol groups) on the sol surface can be moderately excited in a low-pressure environment, laying a foundation for the adsorption of subsequent gaseous precursors. The temperature of 40 °C is relatively mild, which can prevent the sol skeleton from undergoing thermoplastic deformation or structural collapse, and can fully volatilize the excess solvent. By short-time low-pressure drying, the water content on the sol surface and in the pores is controlled, stabilizing the structure and activity of the fluorosilicate-modified silica sol, and creating a suitable surface environment for the subsequent deposition of the titanium-based photocatalyst.

[0039] S2.2. First, introduce the gaseous titanium-based photocatalyst for 0.5 - 1 s, the flow rate of the titanium-based photocatalyst is 0.1 - 10 sccm, stop introducing the gaseous titanium-based photocatalyst and purge with nitrogen for 5 - 10 s, then introduce water vapor or ozone for 0.5 - 1 s, stop introducing water vapor or ozone and purge with nitrogen for 5 - 10 s.

[0040] Among them, the gas flow rate of water vapor is 0.1 - 5 sccm, and the gas flow rate of ozone is 10 - 100 sccm. The gaseous titanium-based photocatalyst adsorbs only at the active sites on the surface of the sol (or the surface of the pores) within the gas introduction time of 0.5 - 1 s, and no longer accumulates after reaching saturation. This can ensure the uniformity of deposition, avoid rough or irregular accumulation, and form an ultrathin film at the atomic / molecular level. Purge with nitrogen for 5 - 10 s to remove unadsorbed gas precursors or by-products, ensuring that no non-self-limiting mixing reaction occurs when introducing the oxidant in the next step. Introduce water vapor or ozone for 0.51 s to react with the titanium precursor adsorbed on the surface to form titanium-oxygen bonds, that is, the titanium dioxide deposition film layer. Then purge again for 5 - 10 s to remove excess oxidant and reaction by-products. If ozone is used, the reaction is more thorough and a dense titanium dioxide film can be formed at a lower temperature; using water vapor is suitable for deposition under mild conditions. A uniform and controllable thickness titanium-based photocatalytic thin film is formed on the surface of the fluorosilicate-modified silica sol, avoiding particle agglomeration or uneven coverage. Each gas introduction cycle can precisely grow a titanium dioxide film layer with a thickness of sub-nanometers.

[0041] S2.3. Execute step S2.2 according to the set number of cycles. After the cycle is completed, maintain nitrogen purging until the reaction chamber slowly cools down to room temperature, and perform ultrasonic dispersion to obtain a mixed solution. Each cycle of step S2.2 will grow a titanium dioxide thickness of 0.03 - 0.05 nm, and the overall titanium dioxide thickness can be 5 - 50 nm. The power of ultrasonic dispersion is 5 - 10 kHz.

[0042] Repeating the cycle of gaseous precursor pulses and oxidant pulses can accumulate multiple layers of titanium dioxide film on the surface of the sol, and the thickness has an approximately linear relationship with the number of cycles. If specific doping is required (such as nitrogen-doped titanium dioxide), a nitrogen-containing precursor (such as ammonia, hydrazine, ethylenediamine, triethylamine) can be introduced in some cycles; or for the design of multi-layer films to meet different photocatalytic response requirements. Keep nitrogen purging after the cycle ends and gradually cool down to room temperature, which can avoid cracks or stress concentration in the film layer or sol during rapid cooling, ensuring a firm combination of the film layer and the framework. Finally, through ultrasonic dispersion, the framework particles or networks with titanium-based photocatalytic films deposited on the surface of the sol are further dispersed to form a more uniform mixed solution, preventing local agglomeration and facilitating subsequent shaping or drying processes. By setting the number of cycles, the required film thickness and properties are obtained, and after completion, sufficient cooling, purging, and ultrasonic dispersion are carried out to make the photocatalyst-sol system stable and uniform, laying a foundation for further preparation of aerogels or other composite materials.

[0043] S3. Transfer the above aerogel sol to a mold, maintain a constant temperature for gelation for 24 h, place it in a freezing environment at -40°C for freeze-drying, and then heat it to 300°C and keep it warm for 3 h to obtain an aerogel.

[0044] Step S3 includes: S3.1. Transfer the mixed sol to the mold, making sure that the volume of the sol occupies 90% of the mold. Vacuum the mold to remove the bubbles.

[0045] Controlling the sol to about 90% of the mold volume can reserve space for the sol in the subsequent gelation process, prevent the gel from overflowing due to expansion or flow, and ensure the integrity of the gel shape. By vacuuming to remove bubbles in the sol, the uneven internal structure of the aerogel (such as holes, cracks, etc.) caused by residual bubbles can be avoided, and local defects that occur during subsequent freeze-drying or heating can also be reduced. Controlling the sol injection molding ratio and eliminating bubbles can improve the overall uniformity and mechanical strength of the aerogel, prevent internal structural defects, and lay a stable foundation for subsequent gelation and drying.

[0046] S3.2. The mixed solution after degassing is placed under a constant temperature condition, maintained at 25°C, and gelled for 24 hours to obtain a gel.

[0047] After being placed at 25°C for 24 hours, the silicon source material and functional components in the sol can be hydrolyzed, polycondensed and gradually cross-linked at a moderate rate to form a three-dimensional network structure. Sufficient gelation time ensures that the active sites in the sol react fully, so that the gel has a more uniform and solid skeleton, and allows the introduced titanium-based photocatalyst and metal ion-targeted polymer to be evenly distributed in the gel skeleton. Gelation is carried out for 24 hours under mild conditions to allow the internal reaction of the material to be sufficient, forming a uniform and stable gel structure, laying the foundation for subsequent drying and high-temperature treatment to obtain a high specific surface area and uniform pore distribution.

[0048] S3.3. After taking the gel out of the mold, put it into a freeze-drying tank and set the temperature to -40°C for pre-freezing. After pre-freezing to -40°C, adjust the air pressure to -0.1MPa and perform freeze-drying operation for 24 hours. After freeze-drying is completed, the temperature gradually rises to -20°C to obtain an aerogel preform.

[0049] First, the gel temperature is lowered to -40°C so that the water therein forms ice crystals, thus preventing the capillary force caused by the evaporation of conventional liquid water from destroying the pore structure. This process ensures that the pore walls of the gel are not pulled. Freeze-drying for 24 hours under vacuum conditions of -0.1MPa can allow the ice crystals to sublime directly, minimize the damage of the solvent to the skeleton, and maintain the microscopic pore structure of the aerogel. After freeze-drying, the temperature is gradually raised to -20°C to allow the dried gel preform to adapt to the ambient temperature and avoid structural stress or cracks caused by sudden temperature increases. Through low-temperature pre-freezing and vacuum freeze-drying processes, pore collapse can be significantly reduced, the three-dimensional network structure and high specific surface area of ​​the aerogel can be retained, and an aerogel preform with stable morphology can be obtained.

[0050] S3.4. Place the freeze-dried aerogel preform into a high-temperature furnace with an inert atmosphere, set the heating temperature to 300 °C, and the heating time to 3 h to obtain the aerogel for sewage treatment.

[0051] Heating up in an inert gas (such as nitrogen or argon) environment can prevent the aerogel from being oxidized or decomposed during heating, especially providing a certain degree of protection for the introduced polymers and some active elements in the photocatalyst. A temperature of 300 °C is sufficient to decompose and remove most of the organic solvents or a small amount of unreacted precursors, further strengthening the silicon-oxygen skeleton, and at the same time enabling the fluorosilicate modification and the titanium-based photocatalyst to bind more stably in the skeleton. This high-temperature process can promote a certain degree of sintering and condensation reactions in the aerogel skeleton, improving the mechanical strength and environmental corrosion resistance of the aerogel, making it more durable in applications such as sewage treatment and photocatalysis. By heating at 300 °C for 3 hours in an inert atmosphere, the aerogel is further stabilized and purified, strengthening the combination between the skeleton structure and the functional components, and obtaining a final aerogel product with excellent chemical stability, high porosity, and good mechanical properties.

[0052] The present invention provides an aerogel for sewage treatment, which is prepared by a preparation method of an aerogel for sewage treatment. The aerogel includes a silicon source material, a fluorosilicate solution, a metal ion-targeting polymer, and a titanium-based photocatalyst; wherein, The silicon source material is used to form the main skeleton of the aerogel, improving the specific surface area, pore distribution rate, and mechanical strength of the aerogel; The fluorosilicate solution is used to provide fluoride ions and react with the silicon element in the silicon source material, enhancing the hydrophilicity, chemical stability, and adsorption capacity of the aerogel; The metal ion-targeting polymer is used to enhance the targeted adsorption performance of the aerogel for heavy metal ions; The titanium-based photocatalyst is used to generate photoinduced electron-hole pairs under light illumination conditions to achieve photocatalytic degradation of organic pollutants in water.

[0053] Fluorosilicate-modified and metal-ion targeted polymers significantly enhance hydrophilicity, surface charge characteristics, and specific molecular recognition ability. The formed three-dimensional porous framework has a large specific surface area and convenient mass transfer channels, allowing pollutants to quickly enter the interior of the framework and be captured by surface active sites. The titanium-based photocatalyst is loaded in the porous framework and rapidly generates active free radicals under light irradiation, which can effectively decompose the adsorbed pollutants. During long-term use or cyclic regeneration, the photocatalyst is not easily lost, and at the same time, the framework is strengthened by heat treatment, making it resistant to aging and corrosion. Since most pollutants in the solution will first be rapidly enriched in the pores by the aerogel framework, the photocatalytic reaction is more efficient. At the same time, the surface functional groups and photocatalytic sites act synergistically to continuously degrade the adsorbed organic matter into inorganic small molecules or carbon dioxide, avoiding saturation failure and improving the treatment ability for various pollutants.

[0054] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of an aerogel for sewage treatment, characterized in that the steps Including: S1. Mix the fluorosilicate solution with the silicon source material, and then add the metal ion-targeting polymer for reaction to obtain fluorosilicate-modified silica sol. S2. Add the titanium-based photocatalyst to the fluorosilicate-modified silica sol and mix evenly to obtain a mixed solution. S3. Transfer the above aerogel sol to a mold, maintain a constant temperature for gelation for 24 h, place it in a freezing environment at -40 °C for freeze-drying, and then heat it to 300 °C and keep it warm for 3 h to obtain the aerogel for sewage treatment.

2. The preparation method of an aerogel for sewage treatment according to claim 1, characterized in that In step S1, the fluorosilicate solution includes at least one of sodium fluorosilicate, ammonium fluorosilicate, and aluminum fluorosilicate, the silicon source material includes at least one of tetraethoxysilane, sodium silicate, and aluminum silicate, and the metal ion-targeting polymer includes at least one of sulfonated polystyrene, sodium polyacrylate, and polyethyleneimine.

3. The preparation method of an aerogel for sewage treatment according to claim 1 or 2, characterized in that, Calculated by mass ratio, the fluorosilicate solution: the silicon source material: the metal ion-targeting polymer = 1:2 - 3:0.05 - 0.

2.

4. The preparation method of an aerogel for sewage treatment according to claim 1, wherein Step S1 includes: S1.

1. Dissolve an appropriate amount of fluorosilicate in deionized water, with the solution concentration being 10% by mass ratio, control the temperature at 25 °C, and use a magnetic stirrer for stirring, with the stirring speed set at 200 - 300 rpm to obtain the fluorosilicate solution. S1.

2. Gradually add the silicon source material to the fluorosilicate solution, and then add an acidic catalyst after the addition is complete, adjust the pH value of the solution to 4.5 - 5.5, and maintain the temperature at 25 °C for stirring for 4 hours to obtain the fluorosilicate-silica solution. S1.

3. Add the metal ion-targeting polymer to the fluorosilicate-silica solution, raise the temperature to 40 - 50 °C, and stir for 1 hour to obtain the fluorosilicate-modified silica sol.

5. The preparation method of an aerogel for sewage treatment according to claim 1, wherein, In step S2, the titanium-based photocatalyst includes at least one of titanium dioxide, nitrogen-doped titanium dioxide, and copper-doped titanium dioxide. Calculated by mass ratio, the titanium-based photocatalyst: the fluorosilicate-modified silica sol = 1:20 - 50.

6. The preparation method of an aerogel for sewage treatment according to claim 1, wherein, Step S2 includes: S2.

1. Suspend the titanium-based photocatalyst in deionized water, add epichlorohydrin with a mass ratio of 1%, perform ultrasonic treatment at 40 kHz, and the ultrasonic treatment time is 20 min to obtain the modified titanium-based photocatalyst solution. S2.

2. Mix the modified titanium-based photocatalyst solution with an organic solvent, and eject it through an electrospinning device under high voltage to form nano-scale catalyst fibers. S2.

3. Add the nano-scale catalyst fibers and the fluorosilicate-modified silica sol to a supercritical carbon dioxide solvent, heat it to a temperature of 40 °C, and stir for 1 hour under the condition of a pressure of 7 - 8 MPa to obtain a mixed solution.

7. The preparation method of an aerogel for sewage treatment according to claim 1, wherein, Step S2 includes: S2.

1. Transfer the fluorosilicate-modified silica sol to a reaction chamber and let it stand, adjust the air pressure to -0.08 MPa, adjust the temperature to 40 °C and dry for 10 - 20 min. S2.

2. First, introduce gaseous titanium-based photocatalyst for 0.5 - 1 s with a flow rate of 0.1 - 10 sccm. Then stop introducing the gaseous titanium-based photocatalyst and purge with nitrogen for 5 - 10 s. Next, introduce water vapor or ozone for 0.5 - 1 s, and then stop introducing water vapor or ozone and purge with nitrogen for 5 - 10 s; S2.

3. Execute step S2.2 according to the set number of cycles. After the cycle is completed, maintain nitrogen purging until the reaction chamber slowly cools down to room temperature, and then perform ultrasonic dispersion to obtain a mixed solution.

8. The preparation method of an aerogel for sewage treatment according to claim 1, characterized in that, Step S3 includes: S3.

1. Transfer the mixed sol to a mold, ensuring that the volume of the sol occupies 90% of the mold. Evacuate to remove air bubbles; S3.

2. Place the degassed mixed solution under constant temperature conditions, maintain the temperature at 25°C, and perform gelation for 24 hours to obtain a gel; S3.

3. After taking out the gel from the mold, put it into a freeze-drying chamber, set the temperature at -40°C for pre-freezing. After pre-freezing to -40°C, adjust to a pressure of -0.1 MPa and perform freeze-drying for 24 hours. After freeze-drying is completed, gradually raise the temperature to -20°C to obtain an aerogel preform; S3.

4. Put the freeze-dried aerogel preform into a high-temperature furnace with an inert atmosphere, set the heating temperature at 300°C, and the heating time at 3 h to obtain an aerogel for sewage treatment.

9. An aerogel for sewage treatment, characterized in that, Prepared by the preparation method of an aerogel for sewage treatment according to any one of claims 1 - 8, the aerogel includes a silicon source material, a fluorosilicate solution, a metal ion-targeting polymer, and a titanium-based photocatalyst; wherein, The silicon source material is used to form the main framework of the aerogel for sewage treatment, improving the specific surface area, pore distribution rate, and mechanical strength of the aerogel; The fluorosilicate solution is used to provide fluoride ions and react with the silicon element in the silicon source material, enhancing the hydrophilicity, chemical stability, and adsorption capacity of the aerogel for sewage treatment; The metal ion-targeting polymer is used to enhance the targeted adsorption performance of the aerogel for sewage treatment towards heavy metal ions; The titanium-based photocatalyst is used to generate photoinduced electron-hole pairs under light irradiation conditions to achieve photocatalytic degradation of organic pollutants in water.

Images