A cyclodextrin-based seawater uranium extraction material and a preparation method thereof

Abstract

This invention provides a uranium extraction material from seawater based on cyclodextrin. By grafting poly(amine oximes) onto the surface of the cyclodextrin, the uniform spatial distribution and high exposure of the amine oxime groups improve the contact efficiency with uranyl ions. Thanks to multi-point grafting and a three-dimensional high-density functional group arrangement, the material exhibits a significantly higher adsorption capacity than ordinary linear amine oxime polymers. The modified cyclodextrin still retains some hydroxyl structures, which improves the hydrophilicity of the material surface, facilitating the diffusion of uranyl ions from the aqueous phase to the adsorption sites, shortening the adsorption equilibrium time, and improving adsorption kinetics. The material has a stable structure, and the functional groups are not easily detached during adsorption-desorption. Its structure is not easily damaged in the high-salinity, complex ion background of seawater, making it suitable for long-term use.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a uranium extraction material from seawater based on cyclodextrin and its preparation method. Background Technology

[0002] The rapid development of artificial intelligence in recent years has led to a surge in human demand for electricity. Electricity generation reflects a nation's industrial capacity. my country boasts diverse power generation methods, including thermal power, hydropower, nuclear power, wind power, solar power, biomass power, and geothermal power. China's total installed nuclear power capacity, both completed and under construction, is 8.7 million kilowatts. It is projected that China's nuclear power capacity will reach approximately 20 million kilowatts by 2010 and 40 million kilowatts by 2020. Uranium is a crucial raw material in nuclear power generation and the nuclear fuel cycle, and its demand continues to increase with the development of nuclear energy utilization. Currently, uranium resources mainly originate from terrestrial uranium deposits. However, terrestrial deposits are characterized by limited exploitable reserves, gradually decreasing grades, high energy consumption during extraction, and significant environmental impact. With the increasing demand for nuclear energy and the gradual depletion of traditional deposits, it is difficult to meet the long-term needs of future nuclear energy development. my country suffers from a scarcity of terrestrial uranium resources, yet its demand for uranium continues to grow annually. In 2024, China's demand for natural uranium was 13,132 tons, a huge shortfall that necessitates substantial imports. Uranium extraction from seawater is considered a crucial pathway to achieving sustainable development of my country's nuclear energy sector. Although the concentration of uranium in seawater is extremely low (approximately 2-4 micrograms per liter), the sheer volume of global seawater means its total reserves far exceed those of terrestrial uranium deposits, making it a significant potential source of future uranium resources.

[0003] Currently, the most studied materials for uranium extraction from seawater are polymeric adsorbents containing amylopectin groups. Amylopectin groups are excellent nucleophilic ligands for uranium adsorption, forming stable coordination structures with uranyl ions and exhibiting good adsorption selectivity. Therefore, amylopectin-functionalized polymer adsorbents have great potential for uranium extraction from seawater. However, existing amylopectin-functionalized polymeric materials have some limitations. For example, linear polymer chains are prone to entanglement in the aqueous environment, leading to insufficient functional group exposure and low utilization of effective adsorption sites, making it difficult to achieve rapid adsorption in low-concentration seawater environments. Some materials have limited adsorption capacity, and the functional groups are easily deactivated during repeated use, affecting the material's stability.

[0004] Against this backdrop, developing a novel seawater uranium extraction adsorbent that can improve the utilization rate of amine oxime groups and operate stably in seawater environments is of great significance for improving the capture efficiency of uranium in seawater. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is that the uranium extraction material based on cyclodextrin provided has high capture efficiency of uranium in seawater.

[0006] This invention addresses the problem of low utilization of amylopectin ligands in seawater caused by molecular chain entanglement in existing linear polymer adsorbents. The invention uses acryloyl-β-cyclodextrin (Acryloyl-β-CD) as a matrix, grafting polyacrylonitrile chains onto this matrix, and then reacting it with hydroxylamine hydrochloride to generate amylopectin groups. The introduction of acryloyl-β-cyclodextrin aims to provide a hydrophilic polyhydroxy framework and construct a three-dimensional structure, thereby improving the accessibility and utilization of amylopectin sites and enhancing the adsorption capacity for uranyl ions. Experiments show that the adsorbent prepared by this invention has a high adsorption capacity for uranyl ions in uranium solutions and seawater. Furthermore, the adsorbent prepared by this invention has advantages such as low production cost, mass production capability, and reusability, showing great application potential in the field of uranium extraction from seawater.

[0007] This invention provides a cyclodextrin-based seawater uranium extraction material with the structure of formula (I): Formula (I) Where R is H or , where n is the statistical average repetition number of acrylonitrile structural units in the polymer. The number-average molecular weight (Mn = 13256 g / mol) measured by GPC has n of 180–260, preferably 200–240.

[0008] This invention provides a method for preparing uranium extraction materials from seawater based on cyclodextrin, comprising the following steps: A) Mix β-cyclodextrin, N,N-dimethylformamide and the polymerization inhibitor dibutylhydroxytoluene, add acryloyl chloride dropwise, and react to obtain acryloyl-β-cyclodextrin; B) The acryloyl-β-cyclodextrin, acrylonitrile and 2,2'-azobisisobutyronitrile are reacted in a solvent to obtain the compound of formula (II); C) Hydroxylamine hydrochloride is dissolved in a solvent, and after adjusting the pH value, it is mixed and reacted with the compound of formula (II) to obtain the cyclodextrin seawater uranium extraction material.

[0009] Equation (II); where R is H or n is 180–260.

[0010] The reaction formula of this invention is as follows:

[0011] The preparation method of seawater uranium extraction material based on cyclodextrin provided by the present invention firstly involves the preparation of acryloyl-β-cyclodextrin: β-cyclodextrin, N,N-dimethylformamide and the polymerization inhibitor dibutylhydroxytoluene are mixed, acryloyl chloride is added dropwise, and the reaction is carried out to obtain acryloyl-β-cyclodextrin. First, β-cyclodextrin was used as a polyhydroxy natural macromolecular matrix, and esterification with acryloyl chloride was carried out to obtain cyclodextrin with polymerizable double bonds.

[0012] Compound A; where R is H or .

[0013] According to one specific embodiment of the present invention, β-cyclodextrin (β-CD) was added to dry N,N-dimethylformamide (DMF), and the polymerization inhibitor butylated hydroxytoluene (BHT) was added. A solution of acryloyl chloride in DMF was then added dropwise at room temperature. After the addition was complete, the solution was stirred to react. After the reaction, the solution was added dropwise to water to precipitate the precipitate. The precipitate was allowed to stand until the viscous substance at the bottom solidified, then crushed and filtered. The filter cake was dried and washed with diethyl ether to obtain a white solid powder, which was then dried in a vacuum oven to obtain acryloyl-β-cyclodextrin for further use.

[0014] In some specific embodiments, the molar ratio of β-cyclodextrin to acryloyl chloride is 1:15; The molar ratio is chosen to fully activate the hydroxyl groups on the β-cyclodextrin molecules, ensuring that each β-cyclodextrin molecule can graft a sufficient number of acryloyl groups, thus providing ample polymerizable sites for subsequent copolymerization. In practice, precisely controlling the molar ratio to 1:15 helps to create a stable reaction environment in the reaction system, reduces the formation of byproducts, and improves the yield and purity of acryloyl-β-cyclodextrin, laying a good material foundation for the subsequent graft copolymerization reaction with acrylonitrile.

[0015] In some specific embodiments, the molar ratio of β-cyclodextrin, the polymerization inhibitor dibutylhydroxytoluene, and acryloyl chloride is 1:0.3:15.

[0016] The preferred polymerization inhibitor of the present invention is 5 wt% acryloyl chloride.

[0017] In some specific embodiments, the dropwise addition in step A) is carried out at room temperature; wherein the room temperature is preferably 20~30°C; The reaction temperature is 70–90°C, specifically 70°C, 75°C, 80°C, 85°C, or 90°C. Within this temperature range, the reaction proceeds at a suitable rate, which helps improve reaction efficiency and ensure product quality. For example, when the reaction temperature is controlled at 80°C, it avoids the problems of slow reaction rate and incomplete reaction caused by excessively low temperature, and also prevents the increase of side reactions and decomposition of raw materials or products that may be caused by excessively high temperature. In actual operation, an appropriate value within the above temperature range can be selected according to factors such as the specific reaction scale and the stirring efficiency of the reaction system. The reaction time is 4–6 hours. Within this time range, it ensures that the reaction proceeds fully, allowing the hydroxyl groups of β-cyclodextrin to be fully replaced by acryloyl groups, while avoiding the increase of by-products or excessive energy consumption due to excessively long reaction time.

[0018] The reaction process includes adding the reaction solution dropwise into water to precipitate, allowing it to stand and filter, drying the filter cake, washing it with ether, and then drying it.

[0019] Specifically, after the reaction was complete and the mixture cooled naturally to room temperature, the reaction solution was slowly added dropwise to an appropriate amount of deionized water under stirring. The dropping rate was controlled at 2-4 drops per second to ensure that acryloyl-β-cyclodextrin precipitated uniformly and formed relatively regular precipitates. After the addition was complete, stirring was continued for 30 minutes to allow the precipitate to fully coagulate. The mixture was then allowed to stand for 12 hours to allow the precipitate to settle naturally. Next, a Buchner funnel was used for vacuum filtration. During the filtration process, the filter cake was washed three times with deionized water, each time using 50 times the volume of the filter cake, to thoroughly remove unreacted raw materials (such as excess acryloyl chloride, acid-binding agents, etc.) and salts generated in the reaction. After filtration, the obtained filter cake was placed in a vacuum drying oven and dried at 50°C and a vacuum of -0.09 MPa for 12 hours to obtain preliminarily dried crude acryloyl-β-cyclodextrin. To further purify the product, the dried crude product was placed in a Soxhlet extractor and extracted by reflux in a 35°C water bath using diethyl ether as the extraction solvent for 12 h. This process effectively removed residual organic impurities (such as unreacted acryloyl chloride and low-boiling byproducts that may be generated during the reaction) by utilizing the good solubility of diethyl ether. After extraction, the solid product was removed and placed again in a vacuum drying oven at 50°C for 12 h, finally yielding a high-purity acryloyl-β-cyclodextrin white solid powder. Through the above-described post-treatment steps of precipitation, filtration, washing, and drying, impurities in the reaction system can be effectively removed, improving the purity of the target product and providing high-quality raw materials for subsequent graft copolymerization reactions.

[0020] The acryloyl-β-cyclodextrin, acrylonitrile, and 2,2'-azobisisobutyronitrile were reacted in a solvent to obtain the compound of formula (II).

[0021] In this invention, acryloyl-β-cyclodextrin is crosslinked with acrylonitrile: Acryloyl-β-cyclodextrin is added to a two-necked flask and dissolved in DMF. Acrylonitrile (AN) and 2,2'-azobisisobutyronitrile (AIBN) are then added, and the mixture is bubbled with nitrogen. A vacuum is then created using a water pump, and the nitrogen is replaced three times. After the reaction is complete, the solution is poured into a large amount of acetone, resulting in a precipitate. After thorough stirring, the precipitate is filtered, washed successively with acetone and ethanol, and dried under vacuum to obtain compound (II).

[0022] In some specific embodiments, the mass ratio of acryloyl-β-cyclodextrin to acrylonitrile is 1:200; The amount of acrylonitrile added is 15 wt%; The amount of 2,2'-azobisisobutyronitrile added is 0.5 mol of the amount of acrylonitrile added.

[0023] The reaction described in this invention includes bubbling with nitrogen gas for 25-35 minutes, specifically 28 minutes, 30 minutes, or 32 minutes. Nitrogen bubbling effectively removes oxygen from the reaction system, preventing it from inhibiting the free radical polymerization reaction and ensuring the smooth progress of the reaction. If the bubbling time is too short, oxygen cannot be sufficiently removed, potentially leading to incomplete polymerization or a wide molecular weight distribution of the product. While a longer bubbling time ensures effective oxygen removal, it increases experimental time and nitrogen consumption. Considering both reaction efficiency and cost, a nitrogen bubbling time of 25-35 minutes is deemed most suitable.

[0024] Then, use a water pump to evacuate and replace the nitrogen gas three times, and react at 60~70℃ for 20~30 h; specifically, it can be 62℃, 65℃, or 68℃, and the reaction time can be 22 h, 25 h, or 28 h.

[0025] This temperature range provides suitable activation energy for free radical polymerization, ensuring the reaction rate remains within a reasonable range. Too low a temperature results in a slow reaction rate, potentially preventing the reaction from proceeding fully within the specified time and affecting monomer conversion. Too high a temperature easily triggers side reactions, such as intensified chain transfer reactions, leading to a decrease in product molecular weight or an increase in structural defects. The 20-30 h reaction time setting is determined by comprehensively considering factors such as monomer concentration, initiator efficiency, and the target product molecular weight. Too short a reaction time results in insufficient monomer polymerization and low product yield; too long a reaction time not only increases energy consumption but may also degrade the generated polymer, similarly affecting the final product's performance. Precise control of the reaction temperature and time effectively ensures the smooth progress of the acryloyl-β-cyclodextrin-acrylonitrile graft copolymerization reaction, obtaining a copolymer intermediate with stable structure and properties.

[0026] The reaction process includes pouring the resulting solution into acetone to form a precipitate, stirring, filtering under vacuum, washing with acetone and ethanol successively, and then drying under vacuum at 50°C. The volume of acetone is approximately 10 times the volume of the reaction solution. The mixture is stirred for 1 hour, filtered by a water pump, and then washed with acetone, ethanol, and dichloromethane.

[0027] Specifically, the acryloyl-β-cyclodextrin prepared above, acrylonitrile as a comonomer, and 2,2'-azobisisobutyronitrile (AIBN) as an initiator are added to a suitable solvent in a specific ratio. In some specific embodiments, the mass ratio of acryloyl-β-cyclodextrin to acrylonitrile is set to 1:200 to ensure that acrylonitrile dominates the reaction system, thereby grafting sufficiently long polyacrylonitrile side chains. Simultaneously, the amount of acrylonitrile added relative to the total mass percentage of the reaction system is 15 wt%. This concentration ensures sufficient monomer reaction while avoiding problems such as overly vigorous polymerization or uneven molecular weight distribution of the product due to excessive concentration. The amount of the initiator 2,2'-azobisisobutyronitrile is even more precise, being 0.5 mol% of the acrylonitrile addition. This amount effectively initiates the free radical copolymerization reaction between the acryloyl groups on the acryloyl-β-cyclodextrin molecule and the acrylonitrile monomer, playing a crucial role in controlling the reaction rate and polymer molecular weight.

[0028] Hydroxylamine hydrochloride is dissolved in a solvent, and after adjusting the pH value, it is mixed and reacted with the compound of formula (II) to obtain cyclodextrin-based seawater uranium extraction material.

[0029] In some specific embodiments, the synthesis of the amine oxime group is as follows: Hydroxylamine hydrochloride is added to a beaker, dissolved in DMF and water, and sodium carbonate is added to adjust the pH to about 9. Then, the solution is poured into a flask, compound B is added, and the reaction is initiated. After the reaction is complete, the solution is poured into a large amount of water to form a precipitate. The precipitate is filtered, washed successively with water and ethanol, and dried under vacuum at 50°C to obtain the compound with the structure of formula (I).

[0030] The amount of hydroxylamine hydrochloride used must be strictly controlled, usually set to more than twice the molar amount of cyano group in compound (II), to ensure that the cyano group can be fully converted into a amine oxime group. The volume ratio of DMF to water is preferably 1:1. This mixed solvent system can ensure good dissolution of hydroxylamine hydrochloride and compound (II) and provide a suitable polar environment for the oxime reaction. The reaction temperature is generally controlled at 60-70℃. At this temperature, the reaction rate is moderate, which can effectively reduce the occurrence of side reactions. The reaction time usually lasts for 20-30 h until the starting material compound B is completely eliminated.

[0031] The resulting precipitate was filtered, washed with water to remove residual sodium carbonate and unreacted hydroxylamine hydrochloride, and then washed twice with ethanol to further purify the product and promote drying. Vacuum drying at 50°C for at least 12 hours ensured that the product's water content was below 0.5%, resulting in a pale yellow powder of formula (I). In some specific embodiments, the solvent comprises N,N-dimethylformamide and water; the volume ratio of N,N-dimethylformamide to water is 1:1; and the concentration of hydroxylamine hydrochloride in the solvent is 5 wt%.

[0032] In some specific embodiments, the pH adjustment is achieved by using sodium carbonate to adjust the pH to 8.5-9.5; preferably, the pH adjustment is achieved by using sodium carbonate to adjust the pH to 9.

[0033] The molar ratio of hydroxylamine hydrochloride to the cyano group in the compound of formula (II) of the present invention is greater than 2; preferably, the molar ratio of hydroxylamine hydrochloride to the nitrile group in the compound of formula (II) of the present invention is not less than 2.76:1.

[0034] The reaction temperature is 60-70℃, specifically 60℃, 62℃, 65℃, 68℃, or 70℃. Within this temperature range, not only is the high reactivity of the starting compound B ensured, promoting the reaction towards the formation of compound (I) efficiently, but it also avoids the problems of increased by-products and decomposition of the starting material or product due to excessively high temperatures. Simultaneously, it prevents the reaction rate from becoming too slow due to excessively low temperatures, thus prolonging the reaction cycle and reducing production efficiency. The reaction time is 20-30 h, specifically 20 h, 22 h, 25 h, 28 h, or 30 h. This reaction time range is chosen primarily because within 20-30 h, sufficient contact and reaction between the compound of formula (II) and hydroxylamine hydrochloride can be ensured, thereby achieving a high conversion rate. If the reaction time is too short, such as less than 20 hours, the raw materials may not react completely, leading to a decrease in product yield. Unreacted raw materials also increase the difficulty of subsequent separation and purification. Conversely, if the reaction time is too long, exceeding 30 hours, although it may slightly improve the conversion rate, it will significantly increase production time and energy consumption, raising production costs. Furthermore, an excessively long reaction time may trigger unnecessary side reactions, affecting product purity. Therefore, controlling the reaction time within 20-30 hours achieves a balance between production efficiency and cost while ensuring product yield and purity.

[0035] The reaction process includes precipitating the reaction solution in water, filtering, washing with water and ethanol successively, and then vacuum drying at 45-55°C. The volume of water is more than 10 times that of the reaction solution.

[0036] This invention provides a method for uranium extraction from seawater, using the cyclodextrin-based seawater uranium extraction material with the structure of formula (I) of the above-mentioned technical solution or the seawater uranium extraction material prepared by any of the preparation methods described in the above-mentioned technical solutions.

[0037] The specific steps include: First, the seawater uranium extraction material is loaded into an adsorption column or fixed on a specific carrier to form an adsorption device. Then, the seawater to be treated is passed through the adsorption device at a certain flow rate. Uranyl ions in the seawater chelate and coordinate with the amine oxime groups in the seawater uranium extraction material, thus being efficiently adsorbed onto the material surface. After adsorption, the adsorption-saturated material is eluted with a suitable desorbent (such as sodium carbonate-hydrogen peroxide solution (1M Na2CO3 + 0.1 M H2O2)) to desorb uranium ions from the material, obtaining a uranium-containing desorbate. Finally, the desorbate is further separated and purified to obtain a high-purity uranium product. The desorbed seawater uranium extraction material can be reused after regeneration, effectively reducing the cost of seawater uranium extraction. This method is simple to operate, has a large adsorption capacity, high selectivity, and is environmentally friendly, showing promising application prospects.

[0038] The present invention also provides the application of the cyclodextrin-based seawater uranium extraction material of the above-mentioned technical solution (I) structure or the seawater uranium extraction material prepared by any of the above-mentioned technical solutions in seawater uranium extraction.

[0039] This application specifically involves using the aforementioned seawater uranium extraction material to efficiently and selectively adsorb uranium from seawater. In practical applications, the material can be filled into an adsorption column to construct a seawater uranium extraction adsorption system, or it can be fixed to the surface of specific carriers such as fibers or membranes through coating or embedding to form easily operable adsorption modules. When seawater flows through these adsorption devices or modules, the amine oxime groups in the material can form stable coordination bonds with trace amounts of uranyl ions in the seawater. Simultaneously, the cavity structure of the cyclodextrin units further enhances the capture capacity of uranyl ions through host-guest recognition, thereby achieving efficient enrichment of uranium. After adsorption saturation, elution is performed using a sodium carbonate-hydrogen peroxide solution (1M Na₂CO₃ + 0.1 MH₂O₂) as a desorbent to desorb uranyl ions from the material, obtaining a high-concentration uranium-containing solution. Subsequent separation and purification processes yield uranium products. After desorption, the seawater uranium extraction material can regain its adsorption properties through simple washing and regeneration, allowing it to be reused in the seawater uranium extraction process. This significantly improves material utilization efficiency and reduces overall process costs. This application method is not only simple to operate and operates under mild conditions, but it is also environmentally friendly to the marine environment, demonstrating significant practical application value and broad market prospects in addressing the global uranium resource shortage.

[0040] This invention provides a method for preparing a seawater uranium extraction material based on cyclodextrin. First, β-cyclodextrin is used as a polyhydroxy natural macromolecular matrix, and an esterification reaction with acryloyl chloride is carried out to obtain cyclodextrin with polymerizable double bonds. The functionalized cyclodextrin is then subjected to free radical polymerization with acrylonitrile in solution, crosslinking acrylonitrile with acryloyl-β-cyclodextrin. Next, hydroxylamine hydrochloride is used to perform a cycloamine oxime reaction on the cyano groups in the polyacrylonitrile chain, converting the polyacrylonitrile chain into a polymer containing cycloamine oxime groups. After crosslinking and curing, an adsorbent material with cyclodextrin as the core and a large number of cycloamine oxime groups distributed on the periphery is obtained.

[0041] The adsorption capacity calculation formula of this invention is as follows:

[0042] In formula (1), q (mg / g) represents the adsorption capacity of uranium. C 0 (mg / L) represents the uranium concentration in the solution before adsorption. C t (mg / L) represents the uranium concentration in the solution after adsorption. V (L) represents the volume of the solution. M (g) represents the mass of the adsorbent.

[0043] The technical solution provided by this invention has the following beneficial effects: (1) By grafting polyamine oxime onto the surface of cyclodextrin, the spatial distribution of the amylamine oxime groups is uniform and the exposure is high, which improves the contact efficiency with uranyl ions.

[0044] (2) Thanks to multi-point grafting and three-dimensional high-density functional group arrangement, the material of the present invention has a significantly higher adsorption capacity than ordinary linear amine oxime polymers.

[0045] (3) The modified cyclodextrin still has a certain hydroxyl structure, which can improve the hydrophilicity of the material surface, facilitate the diffusion of uranyl ions in the aqueous phase to the adsorption site, shorten the adsorption equilibrium time, and improve the adsorption kinetics performance.

[0046] (4) The material has a stable structure and the functional groups are not easily detached during the adsorption-desorption process. The structure is not easily destroyed in the seawater environment with high salinity and complex ion background, and it is suitable for long-term use.

[0047] (5) The reaction conditions of this invention are mild, the process is mature, the raw materials are readily available, the preparation route is clear, it is easy to scale up production, and the product does not pollute the environment, which is in line with the concept of green chemistry. Attached Figure Description

[0048] Figure 1 The compound synthesized in Example 1 1 H NMR spectrum; Figure 2 The FT-IR spectrum of the compound synthesized in Example 1; Figure 3 The compound synthesized in Example 2 1 H NMR spectrum; Figure 4 The FT-IR spectrum of the compound synthesized in Example 2; Figure 5 The GPC spectrum of the compound synthesized in Example 2; Figure 6 The compound synthesized in Example 3 13 C CP-MAS NMR spectrum; Figure 7 The FT-IR spectrum of the compound synthesized in Example 3; Figure 8 The diagram shows the water contact angle of the compound synthesized in Example 3 and the linear PAO of Comparative Example 1, where a is the result of compound 3 and b is the result of Comparative Example 1. Figure 9 This is a graph showing the selective adsorption performance of the compound in Example 3 under conditions of coexistence of multiple metal ions; Figure 10 The reusability of the compound in Example 3; Figure 11 For Comparative Example 1 PAO 13 C CP-MAS NMR spectrum; Figure 12 The adsorption effects of adsorbent (Ⅰ) and adsorbent (Ⅱ) prepared in Example 3 and Comparative Example 1 are shown in the diagram. Detailed Implementation

[0049] This invention provides a cyclodextrin-based seawater uranium extraction material and its preparation method. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the same result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and fall within the scope of this invention. The method and application of this invention have been described through preferred embodiments. Those skilled in the art can obviously modify or appropriately change and combine the method and application described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0050] It should be understood that the expression “one or more of…” individually includes each of the objects described after the expression, as well as various different combinations of two or more of the described objects, unless otherwise understood from the context and usage. The expression “and / or” combined with three or more described objects should be understood to have the same meaning, unless otherwise understood from the context.

[0051] The terms “including,” “having,” or “containing,” including the use of their grammatical synonyms, should generally be understood as open-ended and non-restrictive, for example, not excluding other unstated elements or steps, unless otherwise specifically stated or understood from the context.

[0052] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0053] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items.

[0054] It should be understood that the order of the steps or the order in which certain actions are performed is not important as long as the invention remains operational. Furthermore, two or more steps or actions can be performed simultaneously.

[0055] The use of any and all instances or exemplary language such as “e.g.” or “including” in this document is merely intended to better illustrate the invention and is not intended to limit the scope of the invention unless the claims are made. No language in this specification should be construed as indicating that any unclaimed element is essential to the practice of the invention.

[0056] Furthermore, the numerical ranges and parameters used to define the present invention are approximate values, and the relevant values ​​in the specific embodiments have been presented as precisely as possible. However, any value inevitably contains standard deviations due to individual test methods. Therefore, unless explicitly stated otherwise, it should be understood that all ranges, quantities, values, and percentages used in this disclosure are modified with the word "approximately". Here, "approximately" generally means that the actual value is within plus or minus 10%, 5%, 1%, or 0.5% of a specific value or range.

[0057] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0058] The embodiments and comparative examples of this invention describe some examples, in which the embodiments illustrate certain implementations of the invention. However, this does not mean that the effects of the invention can only be achieved in these examples.

[0059] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a cyclodextrin-based seawater uranium extraction material and its preparation method provided by the present invention.

[0060] In this invention, all ICP-MS measurements were performed using an Agilent 7800 inductively coupled plasma mass spectrometer (ICP-MS). Before testing, the sample solution was filtered through a 0.45 μm filter membrane, acidified with 2% (v / v) nitric acid, and diluted to a suitable concentration range. A series of standard solutions for the analytes were prepared sequentially, and the concentration range of the calibration curve could be adjusted according to the measurement requirements. A certain volume of standard working solution was taken into a volumetric flask, and a series of standard curves were prepared using nitric acid solution with the following mass concentrations: 0 µg / L, 5 µg / L, 10.0 µg / L, 20 µg / L, 50.0 µg / L, 100 µg / L, 200 µg / L, and 500 µg / L. Rhodium was selected as the internal standard element and was automatically added via a peristaltic pump before sample nebulization. The standard solutions were measured using inductively coupled plasma mass spectrometry, and a calibration curve was established with the standard solution concentration as the abscissa and the ratio of the sample signal to the internal standard signal as the ordinate. The slope was obtained using linear regression analysis for calculating the sample content. Selected during the test 238 U was used to determine isotopes, and measurements were performed under standard instrument operating conditions. Each sample was measured in parallel at least three times, and the average value was taken as the final result.

[0061] Example 1

[0062] Preparation of Acryloyl-β-cyclodextrin

[0063] In a 100 mL round-bottom flask, add 2.5 g of β-cyclodextrin (β-CD) and 12 mL of dry N,N-dimethylformamide (DMF), and stir magnetically until fully dissolved. Add 0.145 g of butylated hydroxytoluene (BHT) as a polymerization inhibitor. At room temperature, dissolve 2.68 mL of acryloyl chloride in 5 mL of DMF beforehand, and add it dropwise to the β-CD solution, controlling the dropping rate to maintain homogeneity.

[0064] After the addition was complete, the reaction system was heated to 80°C and stirred continuously for 5 hours. After the reaction was complete, the reaction solution was slowly added dropwise to 100 mL of deionized water to precipitate the product. The precipitate was allowed to stand until it solidified, then crushed and filtered. The filter cake was dried and washed with anhydrous diethyl ether to remove unreacted monomers and organic impurities. After washing, the solid was dried in a vacuum drying oven to obtain compound A.

[0065] Figure 1 The acryloyl-β-cyclodextrin synthesized in Example 1 1 H NMR spectrum; Figure 2The FT-IR spectrum of the compound synthesized in Example 1 is shown below; Figure 1 and Figure 2 It can be seen that the present invention is confirmed to have the above-described structure. Compound 1 1 In the 1H NMR spectrum, three sets of olefin proton signals appeared in the region δ≈6.6–5.8 ppm, which can be attributed to the characteristic hydrogens of –CH= and –CH2= in the acryloyl group, typically appearing as one –CH= signal and two –CH2= signals. Simultaneously, broad peak signals of hydrogens on the sugar ring in the cyclodextrin backbone were still observed in the region δ≈5.0–3.0 ppm, indicating that the main sugar ring structure remained intact. The appearance of these olefin characteristic peaks proves that a polymerizable carbon-carbon double bond was successfully introduced into compound 1, providing a reaction site for subsequent free radical polymerization. Furthermore, according to… Figure 1 In 1 The degree of substitution was calculated using the integrated H NMR results, specifically the total integrated area of ​​the acryloyl double bond region (δ 6.6–5.8 ppm) and the integrated area of ​​the β-cyclodextrin H-1 proton peak (δ 4.97 ppm). Each substituent in the acryloyl group corresponds to three olefinic hydrogens, while each β-cyclodextrin molecule contains seven H-1 protons. The integrated area of ​​the acryloyl double bond region was 36.08, and the integrated area of ​​the H-1 proton peak was 7.00, indicating that approximately 12 acryloyl groups were introduced onto each β-cyclodextrin molecule on average in the product. 1 H NMR (400 MHz, Chloroform-d) δ 6.60–5.75(m, 36H), 4.97 (s,7H), 3.97 (s, 11H), 2.97 (s, 9H), 2.92 (s, 4H), 2.89 (s, 8H), 1.24 (s,6H).

[0066] like Figure 2 The FT-IR spectra of β-CD and the compound are shown, except at 3400 cm⁻¹. –1 A broad absorption band of cyclodextrin hydroxyl groups is visible at 2920 cm⁻¹. –1 In addition to the nearby C–H stretching vibrations, a vibration also appeared at 1730 cm⁻¹. –1 The strong absorption peak at 1634 cm⁻¹ can be attributed to the carbonyl (C=O) stretching vibration; simultaneously, at 1634 cm⁻¹... –1 Absorption peaks associated with alkenyl groups can be observed nearby, attributed to (C=C) stretching vibrations. Additionally, absorption peaks are observed in the 1150–1030 cm⁻¹ range. –1 The multiple absorption peaks in this region correspond to the C–O–C / C–O stretching vibrations of the sugar ring, representing a typical fingerprint region of the cyclodextrin backbone. (Summary) 1 The newly emerging olefin proton signal in H NMR and the appearance of carbonyl characteristic peaks in FT-IR confirm that compound 1 has successfully introduced an acryloyl functional group.

[0067] Example 2

[0068] Graft copolymerization of acryloyl-β-cyclodextrin and acrylonitrile

[0069] Add 30 mg of compound A to a 250 mL two-necked flask and then add 42 mL of DMF to dissolve and form a homogeneous solution. Add 7.4 mL of acrylonitrile (AN) and 90 mg of 2,2'-azobisisobutyronitrile (AIBN) to the system as free radical initiators.

[0070] Nitrogen gas was bubbled through the solution for 30 minutes to remove dissolved oxygen. Then, a vacuum-nitrogen purging process was used for three cycles of replacement to ensure the system was in an inert atmosphere. The reaction system was then heated to 65°C and maintained at this temperature for 24 hours.

[0071] After the reaction was complete, the reaction solution was slowly poured into a large amount of acetone to precipitate the product. The precipitate was stirred thoroughly and filtered, then washed successively with acetone, ethanol, and dichloromethane to remove unreacted monomers and DMF. The washed solid was dried under vacuum at 50°C to obtain the compound with formula II. Figure 3 The compound synthesized in Example 2 1 H NMR spectrum; Figure 4 The FT-IR spectrum of the compound synthesized in Example 2 is shown below; Figure 3 and Figure 4 As can be seen, the present invention is confirmed to have the structure described above.

[0072] Example 3

[0073] Amine oxime reaction of polyacrylonitrile chains

[0074] Add 15.2 g of hydroxylamine hydrochloride (NH₂OH·HCl) to a beaker, and dissolve it in a mixture of 156 mL DMF and 156 mL deionized water. Add 18.5 g of sodium carbonate to adjust the pH of the solution to approximately 9, thus converting the hydroxylamine from its salt form to its reactive state.

[0075] The above hydroxylamine solution was transferred to a 500 mL flask, 4.8 g of compound II was added, and the mixture was stirred magnetically until homogeneous. The mixture was then heated to 65 °C and maintained at that temperature for 24 h to induce a cyano group on the polyacrylonitrile chain to undergo a amine oxime reaction.

[0076] After the reaction was complete, the reaction solution was poured into a large amount of deionized water to precipitate the product. The solid product was obtained by filtration and washed successively with water and ethanol to remove inorganic salts, unreacted hydroxylamine, and residual solvent. Finally, the obtained solid was dried under vacuum at 50 °C to obtain the adsorbent compound (Ⅰ).

[0077] Figure 6 The compound synthesized in Example 3 13 C CP-MAS NMR spectrum; Figure 7 The FT-IR spectrum of the compound synthesized in Example 3; Figure 8 The diagram shows the water contact angles of the compound synthesized in Example 3 and the linear PAO of Comparative Example 1, where a represents the angle of compound 3 and b represents the angle of comparative example 1. It can be seen that... Figure 8 To compare the surface wetting properties of compound 3 and PAO, dynamic water contact angle tests were performed on both materials. The results are shown in Figures 1 and 2. Compound 3 exhibits a faster wetting rate and stronger hydrophilicity compared to PAO, indicating that the introduction of cyclodextrin improves the surface wetting properties of the materials. Good hydrophilicity facilitates rapid wetting and full contact of the materials in an aqueous environment, effectively reducing mass transfer resistance and promoting the diffusion and enrichment of uranyl ions from the solution to the adsorption sites.

[0078] Example 4

[0079] Choose VO2 + Ni 2+ Ba 2+ Cu 2+ Co 2+ and Fe 3+ As competing ions, and with UO2 2+ The concentration in natural seawater increased 100 times, and UO2 was used as a standard. 2+ VO2 + Ni 2+ Ba 2+ Cu 2+ Co 2+ and Fe 3+ A 1 L solution was prepared using standard solutions of seven metal ions and natural seawater (taken from Binhai New Area, Tianjin (39.103437°N, 117.847896°E)) filtered through a 0.22 µm filter membrane. The pH was adjusted to 8 ± 0.1 using 0.2 M NaOH and 0.2 M HNO3 solutions. 5 mg of adsorbent (Example 3) was weighed and added to the aforementioned seawater containing multiple ions. The mixture was stirred continuously at 25 °C and 800 rpm for 24 h. After the stirring was complete, the supernatant was collected, filtered through a 0.45 µm filter membrane, and a certain amount of the liquid was diluted 50 times with 2% HNO3. The concentrations of U, V, Ni, Ba, Cu, Co, and Fe in the solution were tested using ICP-MS, and the adsorption effect of the adsorbent was calculated using formula (1). See [link to relevant documentation]. Figure 9 , Figure 9 This is a graph showing the selective adsorption performance of the compound in Example 3 under conditions of coexistence of multiple metal ions.

[0080] Experimental results show that under conditions of multiple ion coexistence, the adsorbent maintains a high adsorption capacity for U(VI), while its adsorption capacity for Ni remains high. 2+ Ba 2+ Co 2+ The adsorption capacity of divalent metal ions is relatively low. Cu 2+ and Fe 3+ Due to its certain coordination ability, it may interact with UO2 to some extent. 2+ They compete for adsorption sites, but overall, their impact on U(VI) adsorption is limited.

[0081] This selective behavior is closely related to the coordination characteristics of the metallo-oxime group. Metallo-oximes can react with UO2. 2+ The formation of stable coordination structures is more favorable under weakly basic conditions. In contrast, Ba... 2+ Alkaline earth metals primarily rely on electrostatic interactions, exhibiting relatively weak coordination abilities. While some transition metals can coordinate with amine oximes, their stability is generally lower than that of uranyl ion coordination systems. Therefore, even with significantly increased concentrations of various metal ions, this adsorbent still demonstrates a certain selectivity for U(VI).

[0082] To determine the reusability of the adsorbent, continuous adsorption-desorption cycle tests were performed. Adsorption experiments were conducted for 24 h in 1 L of 8 ppm uranium-standard simulated seawater (NaCl (0.50 M) + NaHCO3 (2.0 mM)). Desorption experiments were conducted in sodium carbonate-hydrogen peroxide solution (1 M Na2CO3 + 0.1 M H2O2). The regenerated adsorbent was then used in subsequent adsorption cycles. The reusability of the adsorbent was analyzed by eluting bound uranium and performing adsorption-desorption cycle tests. See [link to relevant documentation] Figure 10 Based on the initial adsorption capacity, the uranium adsorption capacity gradually decreased with each cycle. After four cycles, the uranium adsorption capacity of the adsorbent was 425.68 mg / g, approximately 70% of the initial uranium adsorption capacity (603.34 mg / g).

[0083] Comparative Example 1

[0084] amine oxime reaction of polyacrylonitrile

[0085] Add 15.2 g of hydroxylamine hydrochloride (NH₂OH·HCl) to a beaker, and dissolve it in a mixture of 156 mL DMF and 156 mL deionized water. Add 18.5 g of sodium carbonate to adjust the pH of the solution to approximately 9, thus converting the hydroxylamine from its salt form to its reactive state.

[0086] The hydroxylamine solution was transferred to a 500 mL flask, 4.5 g of polyacrylonitrile was added, and the mixture was stirred magnetically until homogeneous. The mixture was then heated to 65 °C and maintained at that temperature for 24 h.

[0087] After the reaction was complete, the reaction solution was poured into a large amount of deionized water to precipitate the product. The solid product was obtained by filtration and washed successively with water and ethanol to remove inorganic salts, unreacted hydroxylamine, and residual solvent. Finally, the obtained solid was dried under vacuum at 50 °C to obtain adsorbent (II).

[0088] Figure 11 For Comparative Example 1 PAO 13 CCP-MAS NMR spectrum; to further analyze the existence of the amine oxime-related coordination structure in the material, solid-state nuclear magnetic resonance (CMR) was used. 13 The structures of compounds 3 and PAO were characterized by CCP-MAS NMR. In solid-state NMR spectroscopy, the signal at approximately 150 ppm was attributed to the cyclic iminodioxime-related carbon environment, while the signal near 157 ppm corresponded to the characteristic carbon in the amylopyrime structure. These results indicate that compounds 3 and PAO simultaneously contain amylopyrime and its potential cyclic iminodioxime-related structure. This type of coordination configuration has been widely reported to possess strong coordination ability during uranyl ion adsorption. A 4 L solution of 8 ppm uranyl nitrate was prepared using uranyl nitrate hexahydrate (UO2(NO3)2·6H2O). Seven groups of solutions, each 500 mL, were prepared, and the pH of the seven solutions was adjusted from 4.0 ± 0.1 to 10.0 ± 0.1 using 0.2 M NaOH and 0.2 M HNO3 solutions. The adsorbent was added at a dosage of 10 mg / L to 8 ppm uranium solutions at different pH values, and stirred continuously at 25 °C and 800 rpm for 24 h. After the stirring was complete, the supernatant was collected, filtered through a 0.45 µm filter membrane, and the concentration of U in the solution was measured by ICP-MS. The adsorption efficiency of the adsorbents (adsorbent (I) and adsorbent (II) prepared in Example 3 and Comparative Example 1) was calculated using the formula. See the results below. Figure 12 , Figure 12 The adsorption effect diagrams are for the adsorbents (Ⅰ) and (Ⅱ) prepared in Example 3 and Comparative Example 1.

[0089] The results showed that the adsorbent exhibited significantly different adsorption behaviors under different pH conditions, and the adsorption capacity of compound 3 was higher than that of PAO at all pH levels. Overall, the adsorption capacity was relatively low under acidic conditions (pH 4–5), while it significantly increased with increasing pH to the neutral and weakly alkaline regions (pH 6–8), reaching a relatively high value within a certain pH range. Further increases to strongly alkaline conditions (pH > 9) resulted in some changes in adsorption capacity.

[0090] Verification Example

[0091] Natural seawater test: Insoluble impurities were filtered out from seawater taken from the Bohai Sea, and 30 mg of adsorbent was added. The mixture was stirred continuously at 25°C for 10 days. A certain amount of seawater was filtered through a 0.45 µm filter membrane, and the concentration of residual uranium ions in the seawater was tested by ICP-MS. The adsorption effect of the adsorbent (adsorbent (Ⅰ) prepared in Example 3) on uranium was calculated using formula (1).

[0092] After a 10-day adsorption experiment in natural seawater, the material achieved an adsorption capacity of 2.15 mg / g. Compared to the adsorption capacity under higher concentration conditions in the simulated system, the uranium concentration in natural seawater is at the μg / L level, and the system contains complex ion backgrounds and competing factors such as carbonate complexes. Therefore, the significant decrease in adsorption capacity is reasonable. These results demonstrate that the constructed β-cyclodextrin-grafted poly(amine oxime) material can still achieve a certain degree of uranium enrichment in a real seawater environment, validating its practical application potential in complex systems.

[0093] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A cyclodextrin-based seawater uranium extraction material of formula (I): Equation (I) in, R is H or n is 180~260.

2. A method for preparing seawater uranium extraction materials based on cyclodextrin, characterized in that, Includes the following steps: A) Mix β-cyclodextrin, N,N-dimethylformamide and the polymerization inhibitor dibutylhydroxytoluene, add acryloyl chloride dropwise, and react to obtain acryloyl-β-cyclodextrin; B) The acryloyl-β-cyclodextrin, acrylonitrile and 2,2'-azobisisobutyronitrile are reacted in a solvent to obtain the compound of formula (II); C) Hydroxylamine hydrochloride is dissolved in a solvent, and after adjusting the pH value, it is mixed and reacted with the compound of formula (II) to obtain cyclodextrin-based seawater uranium extraction material; Equation (II); where R is H or n is between 180 and 260.

3. The preparation method according to claim 2, characterized in that, In step A), the molar ratio of β-cyclodextrin to acryloyl chloride is 1:15; The molar ratio of β-cyclodextrin, the polymerization inhibitor dibutylhydroxytoluene, and acryloyl chloride is 1:0.3:

15.

4. The preparation method according to claim 2, characterized in that, The addition in step A) is carried out at room temperature; the reaction temperature is 70~90℃ and the reaction time is 4~6 h.

5. The preparation method according to claim 2, characterized in that, Step A) involves adding the reaction solution dropwise to water to precipitate, allowing it to stand and filter, drying the filter cake, washing it with ether, and then drying it.

6. The preparation method according to claim 2, characterized in that, In step B), the mass ratio of acryloyl-β-cyclodextrin to acrylonitrile is 1:

200. The amount of acrylonitrile added is 15 wt%; The amount of 2,2'-azobisisobutyronitrile added is 0.5 mol of the amount of acrylonitrile added.

7. The preparation method according to claim 2, characterized in that, The reaction described in step B) includes: bubbling with nitrogen for 25-35 minutes, then evacuating with a water pump and replacing the nitrogen three times, and reacting at 60-70°C for 20-30 hours. The reaction process also includes pouring the resulting solution into acetone to form a precipitate, stirring, filtering, washing with acetone, ethanol, and dichloromethane successively, and then drying under vacuum at 50°C.

8. The preparation method according to claim 2, characterized in that, Step C) The solvent comprises N,N-dimethylformamide and water; the volume ratio of N,N-dimethylformamide and water is 1:1; the concentration of hydroxylamine hydrochloride in the solvent is 5 wt%.

9. The preparation method according to claim 2, characterized in that, Step C) involves adjusting the pH to 8.5-9.5 using sodium carbonate. The molar ratio of cyano groups in hydroxylamine hydrochloride and the compound of formula (II) is greater than 2; The reaction is carried out at a temperature of 60-70°C for 20-30 hours. The reaction process includes precipitating the reaction solution in water, filtering, washing with water and ethanol successively, and then vacuum drying at 45-55°C.

10. A method for uranium extraction from seawater, characterized in that, The seawater uranium extraction material based on cyclodextrin with the structure of formula (I) as described in claim 1, or the seawater uranium extraction material prepared by any one of claims 2 to 9.

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