A ZIF-8 / graphene oxide-based aerogel adsorption material and a preparation method and application thereof

Abstract

The application belongs to the technical field of composite materials, and particularly relates to a ZIF-8 / graphene oxide-based aerogel adsorption material and a preparation method and application thereof. The material is composed of graphene oxide, sodium alginate and ZIF-8, and has a three-dimensional porous network structure. The preparation method comprises the following steps: performing in-situ composite reaction on graphene oxide and a precursor of ZIF-8 in a methanol system to obtain ZG composite powder; dissolving the obtained ZG composite powder and sodium alginate in water, mixing uniformly to obtain a composite precursor solution; adding the obtained composite precursor solution into a divalent metal ion crosslinker solution to form a hydrogel bead, and performing freeze-drying to obtain the target product. The application solves the problems of traditional adsorption materials, such as easy agglomeration, difficult solid-liquid separation and low adsorption capacity. The material is used for the synergistic adsorption of Cu(II) and U(Ⅵ) in water, and the adsorption retention rate is more than 80% after multiple cycles.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, and particularly relates to a ZIF-8 / graphene oxide-based aerogel adsorbent material, its preparation method and application, which is suitable for the synergistic removal of heavy metal ions and nuclides in water. Background Technology

[0002] With the rapid development of modern industry, wastewater discharge from industries such as non-ferrous metal smelting, electroplating, electronics manufacturing, and nuclear energy utilization has been increasing year by year, leading to increasingly serious pollution problems of heavy metal ions (such as copper, lead, and cadmium) and radioactive nuclides (such as uranium and thorium) in water bodies. Taking copper ions as an example, they are highly toxic, difficult to degrade, and bioaccumulate in water bodies, and long-term exposure will seriously threaten aquatic ecosystems and human health. Uranium, as a core strategic resource in the nuclear energy field, poses a risk of radioactive pollution when released into the aquatic environment, and also leads to the waste of valuable mineral resources. According to statistics, my country loses tens of thousands of tons of copper resources annually due to industrial wastewater discharge, and uranium-containing wastewater generated during nuclear facility operation and uranium mining, if not treated thoroughly, will pose a long-term threat to surrounding soil and groundwater. Therefore, developing functional materials that can simultaneously and efficiently remove heavy metal ions and recover radioactive nuclides has the dual significance of environmental safety and strategic resource recycling.

[0003] Currently, technologies for removing heavy metal ions and nuclides from water mainly include adsorption, chemical precipitation, ion exchange, membrane separation, and electrochemical treatment. Among these, adsorption has become one of the most popular deep purification technologies due to its advantages such as simple operation, low cost, environmental friendliness, and high designability. Its core lies in the development of high-performance adsorption materials. However, traditional adsorption materials such as activated carbon, ion exchange resins, clay minerals, and chitosan gels generally suffer from low adsorption capacity, poor selectivity, and insufficient mechanical stability. For example, although activated carbon has a high specific surface area, its surface functional groups are limited, resulting in weak chelation ability for low concentrations of heavy metals and nuclides; ion exchange resins are prone to swelling after long-term immersion in water, leading to the collapse of the internal pore structure and a significant decrease in adsorption kinetics; natural clay materials, due to their high impurity content and disordered pore structure, are difficult to achieve selective adsorption. More importantly, in actual aquatic environments where multiple ions coexist (such as those containing competing ions like calcium, magnesium, and sodium), traditional materials are less effective at targeting pollutants (such as Cu). 2+ and UO2 2+ The adsorption selectivity of the solid deteriorates rapidly, and the solid-liquid separation process is cumbersome, making it difficult to meet the needs of continuous engineering applications.

[0004] Metal-organic frameworks (MOFs) exhibit great potential in adsorption and separation due to their ultra-high specific surface area, tunable pore structure, abundant coordination unsaturated metal sites, and diverse functional group modification capabilities. Among them, the zeolite imidazolate framework ZIF-8, composed of Zn... 2+ It is self-assembled with 2-methylimidazole via coordination bonds, combining the high porosity of MOFs with the high thermodynamic / chemical stability of zeolites. ZIF-8 has a pore size of approximately 0.34 nm, close to the kinetic diameter of various heavy metal hydrated ions and uranyl ions, theoretically enabling a molecular / ionic scale sieving effect. Simultaneously, the nitrogen atom on its imidazole ring possesses a lone pair of electrons, which can react with Cu... 2 + UO2 2+ The metal ions coordinate and complex, thus endowing the material with strong adsorption affinity. In recent years, ZIF-8 powder has been shown to have good adsorption capacity for Cu(II) and U(VI) in water, with some studies reporting that its maximum adsorption capacity can reach more than 300 mg / g.

[0005] However, when ZIF-8 is used alone in nanoparticle form, there are obvious application bottlenecks: First, the particle size is small (usually tens to hundreds of nanometers) and the surface energy is high, making it prone to agglomeration in water, resulting in a significant decrease in effective specific surface area and active site utilization. Second, ZIF-8 crystals are brittle and have poor mechanical strength, making them easy to break and pulverize in stirred or flowing systems, producing fine particles that are difficult to recover and causing secondary pollution. Third, due to its low density, ZIF-8 powder is difficult to separate into solid and liquid phases through natural sedimentation or conventional filtration after dispersion in water, requiring high-energy-consuming operations such as high-speed centrifugation, which greatly limits its direct application in continuous flow adsorption processes.

[0006] However, the existing ZIF-8 / GO aerogel system still has the following shortcomings: (1) The uniformity of ZIF-8 loading on GO sheets needs to be further improved, and the distribution of active components in some composite systems is uneven, affecting the adsorption stability; (2) There are few studies on the synergistic adsorption of heavy metal ions and radionuclides in water under coexisting conditions, and there is a lack of systematic discussion on the adsorption behavior of binary pollution systems. Therefore, it is urgent to develop a ZIF-8 / graphene oxide-based aerogel adsorption material with uniform loading and synergistic adsorption performance for Cu(II) and U(VI). Summary of the Invention

[0007] The present invention aims to overcome the shortcomings of the prior art and provide a ZIF-8 / graphene oxide-based aerogel adsorbent material and its preparation method, which have high adsorption capacity, excellent mechanical stability and convenient solid-liquid separation characteristics. The material has high synergistic removal efficiency of Cu(II) and U(VI) in water and requires a small amount of adsorbent material.

[0008] This invention also provides an application of ZIF-8 / graphene oxide-based aerogel adsorbent material in the synergistic removal of heavy metal ions and radionuclides in water.

[0009] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0010] In a first aspect, the present invention provides a method for preparing a ZIF-8 / graphene oxide-based aerogel adsorbent material, comprising the following steps:

[0011] (1) In situ composite reaction of graphene oxide and ZIF-8 precursor in methanol system to obtain ZG composite powder with ZIF-8 nanocrystals loaded on the surface of graphene oxide sheets.

[0012] (2) Dissolve the ZG composite powder obtained in step (1) and sodium alginate in water and mix them evenly to obtain a composite precursor solution;

[0013] (3) The composite precursor solution obtained in step (2) is added to the divalent metal ion crosslinking agent solution to form hydrogel beads. After freeze drying, the target product ZGSA aerogel adsorbent material is obtained.

[0014] Further, in step (1), the precursors of ZIF-8 are zinc nitrate hexahydrate and 2-methylimidazole; the in-situ composite reaction includes: dispersing graphene oxide in methanol, dissolving zinc nitrate hexahydrate and 2-methylimidazole in methanol respectively, mixing and reacting, and then centrifuging, washing and drying to obtain ZG composite powder.

[0015] Further, in step (1), the mass ratio of graphene oxide, zinc nitrate hexahydrate, and 2-methylimidazole is 0.5:15-20:12-18.

[0016] Further, in step (1), after the reaction is completed, the product is collected by centrifugation at 5500-7000 rpm for 8-12 minutes, the centrifugation is repeated 3-5 times, the product is washed with deionized water, and then freeze-dried to obtain ZG composite powder.

[0017] Furthermore, in step (2), the mass ratio of ZG composite powder to sodium alginate is 0.25-0.4:0.6-1.

[0018] Further, in step (2), 0.32g of ZG composite powder and 0.8g of sodium alginate are dissolved in 40mL of deionized water for 1 hour under magnetic stirring. The two solutions are mixed and stirred for 2 hours to obtain a composite precursor solution.

[0019] Further, in step (3), the divalent metal ion crosslinking agent is calcium chloride, and its solution concentration is 2.5–4 mol / L; the composite precursor solution is prepared at a concentration of 2.5–4.0 d·s. -1 The solution of divalent metal ion crosslinking agent is added dropwise at a rate of 100%, and the resulting hydrogel beads are soaked for 8–12 hours.

[0020] Furthermore, in step (3), the freeze-drying is carried out under vacuum freeze-drying. First, the water is pre-frozen at -30 to -50°C for 15 to 30 minutes, and then vacuum freeze-dried at -60 to -40°C for 8 to 12 hours. The freeze-drying process allows the ice crystals in the hydrogel beads to sublimate and detach directly under vacuum low temperature conditions, thus preserving the three-dimensional porous network structure intact.

[0021] Secondly, the present invention also provides a ZIF-8 / graphene oxide-based aerogel adsorbent material prepared by the above preparation method, wherein the aerogel adsorbent material has a three-dimensional porous network structure, and ZIF-8 nanocrystals are uniformly loaded on the surface and between the graphene oxide sheets.

[0022] Thirdly, the present invention also provides an application of the above-mentioned aerogel adsorbent material in the synergistic removal of heavy metal ions and radionuclides in water. The aerogel adsorbent material is added to wastewater containing Cu(II) and U(VI) for adsorption treatment. After adsorption treatment, the wastewater is recovered by filtration through a screen or by sedimentation. The aerogel adsorbent material is used to fill an adsorption column and treats the wastewater at a flow rate of 2 to 10 BV / h. After multiple adsorption-desorption cycles, the adsorption retention rate of the aerogel adsorbent material for Cu(II) and U(VI) both exceeds 80%.

[0023] This invention addresses the problems of easy agglomeration and difficult recovery of ZIF-8 nanopowder, easy stacking of graphene sheets, and uneven distribution of active components in traditional aerogel preparation by proposing the following specific solutions: First, the precursors of ZIF-8 (zinc nitrate hexahydrate and 2-methylimidazole) are reacted in situ in a methanol dispersion of graphene oxide, allowing ZIF-8 nanocrystals to grow and composite in situ on the surface of graphene oxide sheets, forming ZG composite powder. This utilizes the abundant oxygen-containing functional groups on the surface of graphene oxide as nucleation sites to guide the heterogeneous nucleation and growth of ZIF-8, inhibiting self-agglomeration of ZIF-8 from the source. Simultaneously, the steric hindrance effect of ZIF-8 nanocrystals prevents graphene sheets from re-stacking, ensuring uniform loading of the active component (ZIF-8) on the graphene oxide carrier. Second, the ZG composite powder and sodium alginate are dissolved together in water, forming hydrogel beads through cross-linking with divalent calcium ions, followed by vacuum freeze-drying to obtain a three-dimensional porous aerogel. Sodium alginate acts as a crosslinking agent and structural support, assembling ZG composite powder into millimeter-sized spherical aerogels, thus endowing the material with solid-liquid separation capabilities. Vacuum freeze-drying avoids the pore collapse caused by traditional thermal drying, fully preserving the three-dimensional porous network structure. If ZIF-8 is directly mixed with sodium alginate without in-situ composite processing, the agglomeration problem of ZIF-8 cannot be solved; without crosslinking with sodium alginate, the material remains in a powder state, making solid-liquid separation difficult.

[0024] Graphene oxide (GO), as an important derivative of graphene, is characterized by its unique two-dimensional sheet structure and extremely high theoretical specific surface area (up to 2600 m²). 2 ZIF-8 nanocrystals, with their abundant oxygen-containing functional groups (hydroxyl, epoxy, carboxyl, etc.) and good hydrophilicity and dispersibility, are considered ideal carriers for nanoparticles. Through π-π stacking, electrostatic interactions, or coordination bonding, ZIF-8 nanocrystals can grow in situ or heterogeneously assemble on the surface of GO sheets, effectively suppressing the self-aggregation of ZIF-8 and leveraging the macroscopic layered structure of GO to impart good manufacturability to the composite material. Furthermore, crosslinking the ZIF-8 / GO composite system with natural polymers such as sodium alginate (SA) and combining it with freeze-drying technology to construct a three-dimensional porous aerogel not only solves the problem of solid-liquid separation in powder materials but also utilizes the large pore channels of the aerogel to promote mass transfer and improve adsorption kinetics. In the preparation method of a ZIF-8 / graphene oxide-based aerogel adsorbent material of this invention, graphene oxide provides a high specific surface area and oxygen-containing functional groups, sodium alginate serves as a crosslinking framework to impart mechanical stability and spherical morphology to the material, and ZIF-8 provides pore size sieving effects and coordination active sites.

[0025] The three components GO, ZIF-8, and SA have clearly defined functions and synergistic coupling, jointly constructing a three-dimensional porous spherical aerogel of ZGSA that combines high adsorption capacity, mechanical stability, and easy separation. The independent functions of each component and the overall synergistic mechanism are described below:

[0026] (1) GO has a lamellar surface rich in oxygen-containing functional groups such as hydroxyl, epoxy, and carboxyl groups, which can provide a matrix platform and abundant heterogeneous nucleation sites for the uniform growth of ZIF-8. At the same time, based on the electrostatic adsorption and coordination between the oxygen-containing functional groups on the surface and the zinc ions of the ZIF-8 precursor, it helps to induce the uniform in-situ growth of ZIF-8 on the lamellar surface and prevents agglomeration. The multi-layered structure of GO gives it a high specific surface area, which can lay the foundation for improving the adsorption performance of the derived gel material.

[0027] (2) ZIF-8 is the core adsorption component of the ZGSA aerogel adsorption material mentioned in this invention. Its intrinsic pore size of 0.34 nm matches the pore size of the target ion complex, enabling ion-scale sieving, improving the selectivity of target ion adsorption, and interfering with the influence of other ion complexes on adsorption performance. The N contained in the imidazole ring framework also has a large number of lone pairs of electrons, which can serve as coordination complexation sites for Cu(II) and U(VI). Utilizing the steric hindrance of ZIF-8 crystals for interpenetrating growth between GO sheets not only prevents the stacking of adjacent GO sheets due to π-π interactions, but also broadens the ion diffusion channels, thereby facilitating the full exposure of adsorption active sites and accelerating the adsorption kinetic rate.

[0028] (3) SA is the crosslinking support medium for the ZGSA aerogel adsorbent material mentioned in this invention. As a crosslinking agent and structural support, SA forms a specific eggshell structure through calcium ion crosslinking, and solidifies in situ to form the basic framework of hydrogel microspheres, solving the defects of ZIF-8 powder such as excessively small particle size, difficulty in settling in water, and high energy consumption for centrifugal recovery. At the same time, SA crosslinks with other components of the gel material to form a continuous three-dimensional polymer network framework, which helps to effectively enhance the mechanical stability and spherical morphology of the gel material.

[0029] Prepared according to the above formula, the aerogel material was tested in the treatment of simulated wastewater containing Cu(II) and U(VI) at a mass ratio of 1:800 (i.e., 1g of material treats 800mL of wastewater). Compared with the ZIF-8 powder dosage disclosed in existing technical literature (usually 1g treats 100-200mL), a higher removal rate was achieved (Cu(II) and U(VI) removal rates are both >95%). This is because the three-dimensional porous network constructed by graphene oxide and sodium alginate promotes the uniform dispersion of ZIF-8, prevents its aggregation, and fully exposes the active sites of ZIF-8, thereby enabling more efficient coordination adsorption of Cu(II) and U(VI) in the wastewater. This allows the pollutants in the treated water to quickly meet the discharge standards, thus achieving the goal of reducing the amount of adsorbent material used.

[0030] In the synergistic removal process of heavy metals and nuclides, the aerogel adsorbent material has the characteristics of high dispersibility and easy separation, which can reduce the initial amount of adsorbent material added and achieve the goal of reducing wastewater treatment costs. Attached Figure Description

[0031] Figure 1 This is the SEM image of the ZIF-8 / graphene oxide-based aerogel of the present invention.

[0032] Figure 2 This is a performance graph showing the effect of the number of cycles on the copper removal efficiency of the material in this invention.

[0033] Figure 3 This is a performance graph showing the effect of the number of cycles on the uranium removal efficiency of the material in this invention.

[0034] Figure 4 The images show the XRD patterns of the ZGSA aerogel adsorbent material, ZIF-8, and ZIF-8 standard card used in this invention.

[0035] Figure 5 This is an FT-IR image of the ZGSA aerogel adsorbent material and the intermediate products composed of each component in this invention.

[0036] Figure 6 These are the adsorption isotherms and adsorption kinetic curves of the ZGSA aerogel adsorbent material in this invention.

[0037] Figure 7 This is a diagram showing the selective adsorption performance of the ZGSA aerogel adsorbent material in this invention.

[0038] Figure 8 This invention illustrates the effect of the amount of ZGSA aerogel adsorbent material used on the removal efficiency.

[0039] Figure 9 This invention illustrates the effect of the amount of ZGSA aerogel adsorbent material used on the adsorption capacity.

[0040] Figure 10 This invention illustrates the effect of ZGSA aerogel adsorbent material on adsorption capacity at different pH values.

[0041] Figure 11 This illustrates the effect of the gel materials prepared in the three embodiments and two comparative examples of this invention on the removal efficiency. Detailed Implementation

[0042] The present invention will now be described in detail through specific embodiments. These embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art. As used throughout the specification and claims, the terms "comprising" or "including" are open-ended and are interpreted as "comprising but not limited to". The following description is a preferred embodiment for carrying out the invention; however, this description is intended to illustrate the general principles of the specification and is not intended to limit the scope of the invention. The scope of protection of the invention is determined by the appended claims. Unless otherwise specified, all reagents and materials used in the present invention are commercially available.

[0043] Example 1

[0044] (1) Disperse 0.5g of graphene oxide (GO) in 100mL of methanol, dissolve 18.1g of zinc nitrate hexahydrate in 50mL of methanol, and dissolve 15g of 2-methylimidazole in 50mL of methanol; treat each solution with ultrasonic power of 60W for 1 hour.

[0045] (2) Add zinc salt solution and imidazole solution to GO dispersion in sequence. After mixing, continue to sonicate the suspension for 1 hour, and then stir magnetically at room temperature for 24 hours. After the reaction is completed, collect the product by centrifugation at 6000 rpm for 10 minutes. Repeat the centrifugation 3 times, wash with deionized water, and freeze dry to obtain ZG powder.

[0046] (3) Take 0.32g ZG powder and 0.8g sodium alginate (SA), and dissolve them in 40mL deionized water for 1 hour under magnetic stirring. Mix the two solutions and stir continuously for 2 hours to obtain a composite precursor solution.

[0047] (4) The composite precursor solution was prepared at 3.3 d·s -1 The solution was added dropwise to a 3 mol / L calcium chloride solution using a peristaltic pump to form spherical hydrogel beads, which were soaked overnight (12 hours). After rinsing with deionized water to remove surface moisture, the solution was pre-frozen at -40°C for 20 minutes and then transferred to a vacuum freeze dryer to dry at -50°C for 10 hours to obtain ZGSA aerogel adsorbent material.

[0048] (5) The obtained aerogel material was used in simulated wastewater containing Cu(II) and U(VI) (initial concentration of 50 mg / L). The material dosage was 0.5 g / L, and the adsorption was carried out by shaking at 25℃ for 2 hours. The removal rate of Cu(II) was 96.2%, and the removal rate of U(VI) was 97.5%. After desorption with 0.1 mol / L HCl, the adsorption retention rate was more than 80% after repeated cycles.

[0049] Example 2

[0050] (1) Disperse 0.5g GO in 100mL methanol, dissolve 20.0g zinc nitrate hexahydrate in 60mL methanol, and dissolve 18g 2-methylimidazole in 60mL methanol; each solution is ultrasonically treated with 80W ultrasonic power for 1.5 hours.

[0051] (2) After mixing, the suspension was sonicated for 1.5 hours and then magnetically stirred for 30 hours; centrifuged at 7000 rpm for 12 minutes, washed 5 times, and freeze-dried to obtain ZG powder.

[0052] (3) Take 0.40g ZG powder and 1.0g SA, dissolve them in 50mL of deionized water for 1.5 hours, mix them and stir for 2.5 hours.

[0053] (4) The composite precursor solution was prepared at 4.0 d·s -1 The solution was added dropwise to a 4 mol / L calcium chloride solution and soaked overnight (10 hours); it was pre-frozen at -50°C for 30 minutes and then freeze-dried under vacuum (-60°C, 12 hours) to obtain ZGSA aerogel.

[0054] (5) The adsorption test was the same as in Example 1, and the removal rate of Cu(II) was 97.8% and the removal rate of U(VI) was 98.9%.

[0055] Example 3

[0056] (1) Disperse 0.5g GO in 100mL methanol, dissolve 16.0g zinc nitrate hexahydrate in 50mL methanol, and dissolve 12g 2-methylimidazole in 50mL methanol; treat each solution with 50W ultrasonic power for 0.5 hours.

[0057] (2) After mixing, the suspension was sonicated for 0.5 hours and magnetically stirred for 20 hours; centrifuged at 5500 rpm for 8 minutes, washed 4 times, and freeze-dried to obtain ZG powder.

[0058] (3) Take 0.25g ZG powder and 0.6g SA, dissolve them in 30mL of deionized water for 1 hour, mix them and stir for 1.5 hours.

[0059] (4) The composite precursor solution was prepared at 2.5 d·s-1 The solution was added dropwise to a 2.5 mol / L calcium chloride solution and soaked overnight (8 hours); it was pre-frozen at -35°C for 15 minutes and then freeze-dried under vacuum (-45°C, 8 hours) to obtain ZGSA aerogel.

[0060] (5) The adsorption test was the same as in Example 1, and the removal rate of Cu(II) was 94.5% and the removal rate of U(VI) was 95.8%.

[0061] Comparative Example 1

[0062] ZIF-8 powder is directly physically mixed with GO and SA, and then cross-linked and molded.

[0063] (1) Preparation of pure ZIF-8 powder alone: ​​Take 0.5 g of graphene oxide in equal amount of methanol solvent, 18.1 g of zinc nitrate hexahydrate, and 15 g of 2-methylimidazole. The in-situ growth step of GO dispersion was cancelled. The zinc salt and imidazole solution were directly mixed and stirred at room temperature for 24 h. After centrifugation at 6000 r / min for 10 min, the mixture was washed 3 times with deionized water and freeze-dried to obtain pure ZIF-8 nanoparticles.

[0064] (2) Preparation of composite precursor solution: Weigh 0.32 g of pure ZIF-8 powder, 0.32 g of GO and 0.8 g of sodium alginate respectively, add 40 mL of deionized water and stir magnetically for 1 h to dissolve. After mixing the three solutions, continue stirring for 2 h to obtain the physical blended precursor solution.

[0065] (3) Crosslinking molding and drying: The precursor solution was prepared at 2.5 d·s -1 2.5 mol / L CaCl2 solution was added dropwise at a rate of 10 h, and the hydrogel beads were soaked for 10 h and rinsed with deionized water. The mixture was pre-frozen at -40℃ for 20 min and then freeze-dried under vacuum at -50℃ for 10 h to obtain control sample 1 (ZIF / GO-SA physical blend aerogel).

[0066] (4) The adsorption test was the same as in Example 1, and the removal rate of Cu(II) was 76.2% and the removal rate of U(VI) was 82.3%.

[0067] Comparative Example 2

[0068] First, GO-SA aerogel was prepared, and then ZIF-8 was impregnated and loaded into the pores.

[0069] (1) Preparation of blank GO-SA aerogel framework: Take 0.32 g GO and 0.8 g SA, dissolve them in 40 mL deionized water and stir for 1 h, mix and stir for 2 h to obtain GO-SA precursor solution; at 2.5 d·s -1Dropwise into 3 mol / L CaCl2 solution at a rate of [missing information] to form beads, soak for 12 h, and freeze-dry to obtain ZIF-8-free spherical GO-SA aerogel framework.

[0070] (2) Post-impregnation loading ZIF-8: Prepare a mixture of zinc nitrate hexahydrate and 2-methylimidazolium methanol in the same proportion as in Example 1. Completely immerse the blank GO-SA aerogel in the mixture and seal it at room temperature for 24 h. Take it out, wash it with methanol 3 times, and freeze dry to obtain post-impregnation loading ZIF-8@GO-SA aerogel.

[0071] (3) The adsorption test was the same as in Example 1, and the removal rate of Cu(II) was 80.2% and the removal rate of U(VI) was 88.3%.

[0072] Experimental results

[0073] The ZGSA aerogel adsorbent material prepared in Example 1 was examined by scanning electron microscopy, and the results are as follows: Figure 1 As shown in the figure, the prepared composite material has a three-dimensional porous network structure. ZIF-8 nanoparticles are uniformly loaded on the surface and between layers of graphene oxide sheets. The particle size is about 50-150 nm, and the distribution is uniform with no obvious agglomeration. The gel skeleton formed by sodium alginate crosslinking is intact and no obvious structural collapse is observed.

[0074] A comparison of the adsorption performance and cycling stability of the aerogel materials prepared in Examples 1-3 revealed that Example 1 exhibited the best overall performance, with a saturated adsorption capacity of 328 mg / g for Cu(II) and 462 mg / g for U(VI). Furthermore, in the presence of Ca... 2+ Mg 2+ Na + After immersion in simulated seawater containing competing ions for 72 hours, the adsorption capacity retention rate of the material still reached over 92%, indicating that the aerogel material has good structural stability and anti-interference ability in complex aquatic environments. After multiple adsorption-desorption cycles, the adsorption retention rate of the material in Example 1 still remained above 86%, indicating that the material has excellent recyclability.

[0075] In contrast, Comparative Example 1, which used a process of direct physical mixing and cross-linking of ZIF-8 powder with GO and SA, showed a Cu(II) removal rate of 76.2% and a U(VI) removal rate of 82.3%, indicating a significant deterioration in overall performance. The root cause was the failure to anchor ZIF-8 through in-situ reaction, resulting in severe agglomeration of ZIF-8 particles and extremely uneven distribution within the graphene oxide sheets and aerogel framework. A large number of adsorption active sites were encapsulated by agglomerated particles, and the pores were blocked, making it difficult for pollutant ions to fully contact the active sites. At the same time, the agglomerated ZIF-8 was easily detached and lost during the recycling process, ultimately leading to a significant decrease in adsorption capacity and cycle stability. Comparative Example 2 involved a process of first preparing a GO-SA aerogel framework and then impregnating it with ZIF-8. Its Cu(II) removal rate was 80.2% and U(VI) removal rate was 88.3%. Although the performance was better than Comparative Example 1, it was still far lower than Examples 1-2. This is because the ZIF-8 precursor was difficult to penetrate into the dense three-dimensional channels inside the molded aerogel. The ZIF-8 nanocrystals were only deposited in large quantities on the outer surface of the aerogel beads, and the loading inside the material framework was extremely low. The pore space inside the aerogel and the carrier layers could not fully play their role in carrying the active components. A large number of internal adsorption sites were vacant. The ZIF-8 accumulated on the surface would also block the ion diffusion channels and reduce the mass transfer efficiency. Moreover, the ZIF-8 loaded on the surface was easily stripped and lost during water scouring and desorption regeneration. Therefore, the overall adsorption capacity and recycling performance of the material had obvious shortcomings.

[0076] It is understood that the above specific description of the present invention is only for illustrating the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention to achieve the same technical effect; as long as the use needs are met, they are all within the protection scope of the present invention.

Claims

1. A method for preparing a ZIF-8 / graphene oxide-based aerogel adsorbent material, characterized in that, Includes the following steps: (1) In situ composite reaction of graphene oxide and ZIF-8 precursor in methanol system to obtain ZG composite powder with ZIF-8 nanocrystals loaded on the surface of graphene oxide sheets. (2) Dissolve the ZG composite powder obtained in step (1) and sodium alginate in water and mix them evenly to obtain a composite precursor solution; (3) The composite precursor solution obtained in step (2) is added to the divalent metal ion crosslinking agent solution to form hydrogel beads. After freeze drying, the target product ZGSA aerogel adsorbent material is obtained.

2. The preparation method of the ZIF-8 / graphene oxide-based aerogel adsorbent material according to claim 1, characterized in that, In step (1), the precursors of ZIF-8 are zinc nitrate hexahydrate and 2-methylimidazole; the in-situ composite reaction includes: dispersing graphene oxide in methanol, dissolving zinc nitrate hexahydrate and 2-methylimidazole in methanol respectively, mixing and reacting, and then centrifuging, washing and drying to obtain ZG composite powder.

3. The preparation method of the ZIF-8 / graphene oxide-based aerogel adsorbent material according to claim 2, characterized in that, In step (1), the mass ratio of graphene oxide, zinc nitrate hexahydrate, and 2-methylimidazole is 0.5:15-20:12-18.

4. The preparation method of the ZIF-8 / graphene oxide-based aerogel adsorbent material according to claim 3, characterized in that, In step (1), after the reaction is completed, the product is collected by centrifugation at 5500-7000 rpm for 8-12 minutes. The centrifugation is repeated 3-5 times. The product is washed with deionized water and freeze-dried to obtain ZG composite powder.

5. The preparation method of the ZIF-8 / graphene oxide-based aerogel adsorbent material according to claim 4, characterized in that, In step (2), the mass ratio of ZG composite powder to sodium alginate is 0.25-0.4:0.6-1.

6. The preparation method of the ZIF-8 / graphene oxide-based aerogel adsorbent material according to claim 4, characterized in that, In step (2), 0.32g of ZG composite powder and 0.8g of sodium alginate are dissolved in 40mL of deionized water for 1 hour under magnetic stirring. The two solutions are then mixed and stirred for 2 hours to obtain a composite precursor solution.

7. The preparation method of the ZIF-8 / graphene oxide-based aerogel adsorbent material according to claim 6, characterized in that, In step (3), the divalent metal ion crosslinking agent is calcium chloride, and its solution concentration is 2.5–4 mol / L; the composite precursor solution has a concentration of 2.5–4.0 d·s. -1 The solution of divalent metal ion crosslinking agent is added dropwise at a rate of 100%, and the resulting hydrogel beads are soaked for 8–12 hours.

8. The preparation method of the ZIF-8 / graphene oxide-based aerogel adsorbent material according to claim 7, characterized in that, In step (3), the freeze-drying is carried out under vacuum. First, the water is pre-frozen at -30 to -50°C for 15 to 30 minutes, and then vacuum freeze-dried at -60 to -40°C for 8 to 12 hours. The freeze-drying process allows the ice crystals in the hydrogel beads to sublimate and detach directly under vacuum and low temperature conditions, thus preserving the three-dimensional porous network structure.

9. The ZIF-8 / graphene oxide-based aerogel adsorbent material prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The aerogel adsorbent material has a three-dimensional porous network structure, with ZIF-8 nanocrystals uniformly loaded on the surface and between layers of graphene oxide sheets.

10. The application of the aerogel adsorbent material as described in claim 9 in the synergistic removal of heavy metal ions and radionuclides in water, characterized in that: The aerogel adsorbent material is added to wastewater containing Cu(II) and U(VI) for adsorption treatment. After adsorption treatment, it is recovered by filtration through a screen or sedimentation separation. The aerogel adsorbent material is used to fill an adsorption column and treat wastewater at a flow rate of 2-10 BV / h. After multiple adsorption-desorption cycles, the adsorption retention rate of the aerogel adsorbent material for Cu(II) and U(VI) both exceeds 80%.

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