A nano-hydrogel seawater uranium adsorption material with low cross-linking density and salt shrinkage resistance and a preparation method thereof

Abstract

The application discloses a kind of nanohydrogel seawater uranium adsorption materials with low crosslinking density and salt shrinkage resistance and a preparation method thereof, comprising preparing nanogel by precipitating polymerization of poly-amidoxime and glutaraldehyde, then mixing nanogel dispersion and poly-amidoxime alkaline solution and stirring uniformly at room temperature to obtain precursor solution, injecting the precursor solution into mold and heating to obtain PGP hydrogel by gelation;The PGP hydrogel is pre-frozen, then immersed in low-temperature seawater to obtain PGP-S hydrogel.The method uses nanogel as crosslinking point to prepare hydrogel and uses freeze-assisted salting-out strategy to endow the hydrogel with salt shrinkage resistance, so that the hydrogel has interconnected pore structure, ultra-low crosslinking density and high water permeability, thereby having excellent uranium adsorption rate and uranium adsorption selectivity.

Description

Technical Field

[0001] This invention relates to the field of functional polymer materials, and more particularly to a nano-hydrogel seawater uranium adsorption material with low crosslinking density and salt shrinkage resistance, and its preparation method. Background Technology

[0002] Uranium (U) is one of the most essential raw materials for nuclear power plant operation and plays an indispensable role in the sustainable development of nuclear power. It is estimated that terrestrial uranium reserves are only sufficient for about a century, necessitating the search for and utilization of unconventional uranium resources. Extracting uranium from seawater is considered the most efficient method for mining unconventional uranium resources. The ocean contains approximately 4.5 billion tons of uranium, nearly 1000 times more than current estimates of terrestrial uranium reserves (7.6 million tons). This reserve could meet global uranium demand for at least 10,000 years, but requires the development of corresponding chemical separation technologies and reductions in economic costs. Furthermore, compared to mining terrestrial uranium, seawater extraction causes less environmental pollution.

[0003] Adsorption is one of the most practical and effective methods due to its advantages such as low cost, simple operation, strong practicality, low environmental pollution, and easy regeneration of adsorbents. The key technology for seawater uranium extraction adsorption depends on the design and construction of materials. Commonly used adsorbents include porous carbon-based materials, metal-organic frameworks (MOFs), covalent organic frameworks (COFs), biomaterials, and amine oxime-based polymers. In recent years, continuous technological advancements have provided more possibilities for preparing high-performance adsorbents. The high efficiency and specificity of amine oxime-based materials for uranium ions have made them a research hotspot in this field. For example, Chinese patent CN202010378458.6 discloses a method for preparing an antibacterial amine oxime aerogel for seawater uranium extraction, utilizing the combination of chitosan and amine oxime. Although this enhances its antifouling ability and provides good uranium extraction performance, most amine oxime-based gel uranium extraction materials suffer from small pore sizes due to their non-connected honeycomb microporous structure and high cross-linking density, which is detrimental to water molecules and UO2. 2+ Rapid diffusion within polymer networks and slow adsorption rates limit their practical commercial application. Therefore, the development of a hydrogel adsorbent with a high uranium adsorption rate is crucial for advancing the application of amylopyrime-based materials in the commercial extraction of uranium from seawater. Summary of the Invention

[0004] In view of this, the present invention provides a method for preparing a nano-hydrogel seawater uranium adsorbent material, which solves the problem of slow adsorption rate of existing amylopyroxime-based gels.

[0005] This invention employs a method for preparing a nano-hydrogel seawater uranium adsorbent material, comprising the following steps:

[0006] First, the nanogel dispersion and poly(xylene oxime) sodium hydroxide solution were mixed and stirred evenly to obtain a hydrogel precursor solution. Then, the solution was poured into a mold and heated to gel, and the gel was formed. After washing, the nanostructured hydrogel was finally obtained. The nanostructured hydrogel was then pre-frozen and then immersed in low-temperature seawater until it was completely thawed. Finally, it was washed to obtain a salt-resistant nanostructured hydrogel. The mass ratio of nanogel to poly(xylene oxime) was 0.3:1.

[0007] Preferably, the concentration of the nanogel dispersion is 25 mg / mL, and the concentration of the poly(amine oxime) sodium hydroxide solution is 50 mg / mL.

[0008] Preferably, the low-temperature seawater is -1℃.

[0009] Preferably, the pre-freezing temperature of the nanostructured hydrogel is -25°C.

[0010] Preferably, the heating temperature is 60°C and the heating time is 2 hours.

[0011] Preferably, the nanogel dispersion is prepared by the following method: 100 mg of poly(ammonia oxime) powder is dissolved in 4 mL of sodium hydroxide solution with a concentration of 0.15 mol / L, and then 50 μL of glutaraldehyde and 25 mg of sodium dodecyl sulfate are added to the solution in sequence. The mixture is stirred at 50 °C for 1.5 h to obtain the nanogel dispersion.

[0012] The present invention provides a method for preparing a nano-hydrogel seawater uranium adsorbent material with low cross-linking density and salt shrinkage resistance. The process is simple, mild, economical, and efficient. First, poly(ammonia) oxime is used for pre-crosslinking to form a nanogel. Then, the nanogel serves as a nano-crosslinking point, and a certain proportion of poly(ammonia) oxime is used to further form a nano-hydrogel with ultra-low cross-linking density and a cleverly interconnected porous structure through hydrogen bonding. The hydrogel is further treated by freeze-assisted salting out to impart resistance to shrinkage in high-salinity environments. Ultimately, the synergistic effect gives the material ultra-high water permeability and strong salt shrinkage resistance, resulting in a rapid uranium adsorption rate and ion selectivity. Attached Figure Description

[0013] Figure 1 The infrared absorption spectrum of the nanostructured hydrogel (PGP) prepared in Example 1;

[0014] Figure 2 Scanning electron microscope image of the nanostructured hydrogel (PGP) prepared in Example 1;

[0015] Figure 3 The crosslinking density and pore size of the nanostructured hydrogel (PGP) prepared in Example 1 in deionized water and seawater;

[0016] Figure 4 Crosslinking structural parameters, water permeability, and swelling ratio of the PGP-S hydrogel prepared in Example 1;

[0017] Figure 5 Photographs of the PGP-S hydrogel prepared in Example 1 after immersion in seawater for different times, as well as the mesh size and crosslinking density;

[0018] Figure 6 The results show representative uranium adsorption kinetics of the PGP-S hydrogel prepared in Example 1.

[0019] Figure 7 The results of uranium competitive ion adsorption tests are shown for the PGP-S hydrogel prepared in Example 1. Detailed Implementation

[0020] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0021] The following examples use rheological frequency scanning curves to determine the average pore size and crosslinking density of hydrogels.

[0022] Example 1: A nano-hydrogel seawater uranium adsorbent material with low cross-linking density and salt shrinkage resistance, and its preparation method, comprising the following steps:

[0023] Preparation of S101-amine oxime-modified polyacrylonitrile (PAO)

[0024] Weigh 16g of hydroxylamine hydrochloride and add it to a round-bottom flask containing 100mL of DMF. Stir until completely dissolved. Add 6.9g of sodium hydroxide and stir in an oil bath at 45℃ for 2.5h until the solution turns milky white. Add 10g of polyacrylonitrile (PAN). After the PAN is completely dissolved, raise the temperature to 80℃ and continue the reaction for 12h. Finally, centrifuge at 11000rpm for 30min and collect the supernatant. Add deionized water dropwise to precipitate the precipitate. After washing with water, vacuum dry at 60℃ and grind to obtain poly(aminoamine) oxime powder.

[0025] Preparation of S102 nanogel (PG) dispersion

[0026] At room temperature, 100 mg of poly(ammonia oxime) powder was weighed and dissolved in 4 mL of 0.15 mol / L sodium hydroxide solution. Then, 50 μL of glutaraldehyde and 25 mg of sodium dodecyl sulfate were added to the solution in sequence. After stirring at 50 °C for 1.5 h, a nanogel dispersion with a concentration of 25 mg / mL was obtained.

[0027] Preparation of S103 poly(amine) oxime alkaline solution

[0028] 0.5 g of poly(xylene oxime) powder was completely dissolved in 10 mL of 0.15 mol / L sodium hydroxide solution to obtain a 50 mg / mL poly(xylene oxime) sodium hydroxide solution.

[0029] Preparation of S104 nanostructured hydrogel (PGP)

[0030] 1.2 mL of a 25 mg / mL nanogel dispersion and 2 mL of a 50 mg / mL poly(amine oxime) sodium hydroxide solution were mixed at a mass ratio of 0.3:1 (PG:PAO) and stirred until homogeneous to obtain a hydrogel precursor solution. 3 mL of the precursor solution was then poured into a polytetrafluoroethylene mold, and the sample was heated at 60 °C for 2 h to obtain a formed gel. Finally, the gel material was immersed in 1 L of water at room temperature for washing, with water replacement every 4 h, to obtain the final nanostructured hydrogel.

[0031] Preparation of S105 salt-resistant nanostructured hydrogel (PGP-S)

[0032] The fully swollen nanostructured hydrogel was frozen at -25°C for 4 hours. Then, the frozen nanostructured hydrogel was transferred to a low-temperature reaction bath filled with seawater and thawed at -1°C until completely thawed. Finally, the PGP hydrogel was rinsed with deionized water to remove residual salt ions, thus obtaining a salt-resistant nanostructured hydrogel.

[0033] Example 2: The difference between Example 1 and Example 2 lies in the different mass ratios of the nanogel dispersion and the poly(amine oxime) sodium hydroxide solution added in step S104. The properties of the hydrogel materials prepared with different masses of nanogel and poly(amine oxime) are shown in Table 2. As can be seen from the results in Table 1, when the amount of nanogel is less than 25 mg, PAO cannot form a hydrogel, while a porous gel material can be obtained when PG:PAO = 0.3-1.0:1 is added. However, the uranium extraction results in Table 2 show that the uranium adsorption time increases with the increase of nanogel content. This indicates that the nanogel content prepared in this invention is extremely low, and the lower the cross-linking density of the hydrogel, the more favorable it is to obtain an interconnected porous structure, which is conducive to the rapid diffusion of uranyl ions inside the hydrogel, thereby shortening the uranium adsorption time.

[0034] Table 1. Morphology of nanostructured hydrogel materials prepared by nanogels and poly(xime) at different mass ratios.

[0035] 25 100 Unable to form 30 100 Colorless hydrogel 40 100 Colorless hydrogel 50 100 Colorless hydrogel 70 100 Colorless hydrogel 100 100 Colorless hydrogel

[0036] Table 2. Uranium extraction performance of nanostructured hydrogel materials prepared by combining nanogels with poly(xyleneamine) at different mass ratios.

[0037]

[0038] Example 3: The difference between Example 3 and Example 1 lies in step S105, where the nanostructured hydrogel is treated with seawater of different supercooled degrees. The effects of actual seawater at 25℃ and 1.5 mol / L seawater at -5℃ on the crosslinking density and pore size of the nanostructured hydrogel are compared. Table 3 shows that after treatment with seawater at -1℃, the crosslinking density of the hydrogel (0.957 mol / L) is significantly reduced. 3 The lower temperature (12.14 nm) compared to 25℃ imparts shrinkage resistance to the material and results in a larger pore size, which facilitates the rapid diffusion of uranyl ions. However, treatment with 1.5 mol / L seawater at -5℃ significantly increases the crosslinking density and reduces the pore size, hindering the rapid diffusion of uranyl ions and preventing the achievement of a short adsorption equilibrium time. Therefore, the nanostructured hydrogel obtained through seawater treatment at -1℃ not only exhibits shrinkage resistance but also a high crosslinking density (0.957 mol / L). 3 The mesh size (12.14 nm) and the mesh size further improve the uranium adsorption rate.

[0039] Table 3. Effects of seawater treatment at different degrees of supercooling on the cross-linking structure of nanostructured hydrogels.

[0040] 25℃ 6.44 6.39 -1℃ 0.957 12.14 -5℃ 8.72 5.79

[0041] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that the poly(ammonia oxime) hydrogel was prepared using conventional chemical crosslinking, including the following steps: 200 mg of poly(ammonia oxime) powder was dissolved in a sodium hydroxide solution (0.15 mol / L, 4 mL), and then heated to 50 °C to obtain a homogeneous solution. Subsequently, the PAO solution was mixed with different volumes of GA (50 μL, 100 μL, 200 μL, 300 μL) at 50 °C, corresponding to the ratio of GA (μL) to PAO (mg) (0.25, 0.5, 1.0, 1.5), and then stirred for 20 min to obtain a precursor solution of GA / PAO hydrogel. Then, the precursor solution (3 mL) was transferred to a petri dish and heated in an oven at 60 °C for gelation. Finally, the freshly prepared GA / PAO hydrogel was immersed in deionized water for 24 h to remove residues.

[0042] As shown in Table 4, GA / PAO gel cannot form when there is too little crosslinking agent, and the minimum crosslinking density of GA / PAO hydrogel in deionized water is 0.19 mol / m³. 3 With a maximum mesh size of 22.91 nm, it is only close to the crosslinking density (0.10 mol / m²) of the nanostructured hydrogel PG:PAO (1.0:1) in Example 2. 3The results show that hydrogels prepared using conventional chemical crosslinking methods cannot achieve lower crosslinking density and larger pore size.

[0043] Table 4 Crosslinking parameters of conventionally chemically crosslinked poly(amine oxime) hydrogels

[0044] 200 40 —— —— 200 50 0.19 22.91 200 100 0.31 17.76 200 150 0.44 15.69

[0045] Example 4: The nanostructured hydrogel (PGP) and salt-resistant nanostructured hydrogel (PGP-S) prepared in Example 1 were characterized and their performance was tested. The results are as follows:

[0046] (1) The nanostructured hydrogel (PGP) was characterized using infrared spectroscopy, such as... Figure 1 The results show that the poly(amine oxime) powder clearly exhibits C≡N (2244 cm⁻¹). -1 The peak does not exist, but C = N(1654cm) appears. -1 ), C-N (1391cm) -1 ) and N-O (940cm -1 The infrared absorption peaks confirm that the poly(gamma-amino)oxime has been successfully oximated; and new CO (1037 cm⁻¹) appeared in the infrared spectra of both PG and PGP. -1 This demonstrates that the hydroxyl group (-OH) in PAO and the aldehyde group (-CHO) in glutaraldehyde underwent an acetal reaction, indicating the successful synthesis of nanogels and nanostructured hydrogels (PGP).

[0047] (2) Scanning electron microscopy was performed on the nanostructured hydrogel (PGP) of Example 1, such as... Figure 2 The scanning electron microscope image shows that the nanostructured hydrogel (PGP) has a linear network-like structure, indicating that the hydrogel of this invention has interconnected micropores that allow water and UO2 to pass through. 2+ It provides an effective channel for rapid transmission.

[0048] (3) The crosslinking density and pore size of the nanostructured hydrogel (PGP) of Example 1 were tested in deionized water and seawater, respectively. The results are as follows: Figure 3 As shown in Figure a, with the increase of PG nanogel content, the crosslinking density of PGP hydrogel in deionized water increases, and the calculated pore size gradually decreases with the increase of PG gel content. However, in uranium adsorption experiments conducted in seawater, a strong shrinkage phenomenon was observed in the PGP hydrogel when immersed in seawater. This phenomenon occurred within a very short time. Figure 3 As shown in b, the crosslinking density of PGP hydrogel in seawater is 0.02 mol / m 3 Increased to 12.69 mol / m 3Furthermore, the pore size decreased from 42.1 nm to 5.07 nm and remained essentially unchanged for a long period. This indicates that the nanostructured hydrogel (PGP) does not possess resistance to salt shrinkage.

[0049] (4) The crosslinking density and pore size of the PGP-S hydrogel in Example 1 were tested, such as... Figure 4 The results show that the crosslinking density of the PGP-S hydrogel is only 0.97 mol / m³. 3 It is far lower than the 12.69 mol / m of PGP hydrogel. 3 Meanwhile, the PGP-S hydrogel exhibits a pore size of up to 12.14 nm in seawater, a 2.4-fold improvement compared to the 5.07 nm pore size of the PGP hydrogel in seawater. Figure 4 As shown in b, the swelling rate of PGP-S hydrogel in seawater is several times higher than that of PGP-0.3 hydrogel, and the water permeability is also several times higher. This indicates that the PGP-S hydrogel prepared by this invention has a larger pore size, better water permeability, which helps the diffusion of water and uranyl ions and promotes the adsorption of ions.

[0050] (5) Test on the salt shrinkage resistance of the PGP-S hydrogel in Example 1

[0051] The results are as follows Figure 5 As shown in Figure a, the PGP-S hydrogel immersed in seawater showed virtually no shrinkage, indicating that the PGP-S hydrogel possesses certain anti-shrinkage properties in seawater. Figure 5 As shown in b, after immersion in seawater for up to 10 days, the pore size and cross-linking density of the PGP-S hydrogel remained stable and essentially unchanged, further confirming the anti-shrinkage properties of the PGP-S hydrogel in seawater.

[0052] (6) The uranium adsorption performance of the PGP-S hydrogel in Example 1 was tested. First, 5 mg of the hydrogel adsorbent was placed in 1 L of natural seawater spiked with 8 ppm uranium at room temperature (25°C) for adsorption kinetic testing. It was found that the nano-hydrogel with low cross-linking density and salt-cementation resistance reached adsorption equilibrium within 10 h. Figure 6 As shown, the equilibrium adsorption capacity was 166.19 mg / g, while the PGP hydrogel required 14 hours to reach adsorption equilibrium, indicating that the uranium adsorption rate of the PGP-S hydrogel was significantly improved.

[0053] (7) When performing uranium competitive ion adsorption tests on the PGP-S nanohydrogel of Example 1, it was adsorbed in 100L of natural seawater for 11 days. Figure 7 The results show that the nanohydrogel with low crosslinking density and salt-cementation resistance in Example 1, during the adsorption of uranyl ions, primarily competes with VO₄²⁻ as the ion. 2-The low adsorption of other ions indicates that the nanohydrogel with low cross-linking density and salt-condensation resistance has excellent ion selectivity for uranium.

[0054] In summary, the preparation method of the nano-hydrogel seawater uranium adsorbent material with low cross-linking density and salt shrinkage resistance provided by this invention is simple, mild, economical and efficient. It forms a nano-structured hydrogel with ultra-low cross-linking density and interconnected pores by using nanogels as nano-cross-linking points. The hydrogel is further treated by freeze-assisted salt precipitation to endow it with the ability to resist shrinkage in high salinity environments. This gives the material ultra-high water permeability and strong salt shrinkage resistance, thereby enabling the material to have a fast uranium adsorption rate and ion selectivity.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a nano-hydrogel seawater uranium adsorption material, characterized in that, Includes the following steps: First, a nanogel dispersion and a poly(xylene oxime) sodium hydroxide solution are mixed and stirred evenly to obtain a hydrogel precursor solution. This precursor solution is then poured into a mold and heated to gel, resulting in a shaped gel. After washing, a nanostructured hydrogel is finally obtained. The nanostructured hydrogel is pre-frozen and then immersed in low-temperature seawater until completely thawed. Finally, it is washed to obtain a salt-resistant nanostructured hydrogel. The mass ratio of nanogel to poly(xylene oxime) is 0.3:

1. The low-temperature seawater is -1℃. The pre-freezing temperature of the nanostructured hydrogel is -25℃. The nanogel dispersion is prepared by the following method: 100 mg of poly(xylene oxime) powder is dissolved in 4 mL of a 0.15 mol / L sodium hydroxide solution. Then, 50 μL of glutaraldehyde and 25 mg of sodium dodecyl sulfate are added sequentially to the solution. The mixture is stirred at 50℃ for 1.5 h to obtain the nanogel dispersion.

2. The method for preparing a nano-hydrogel seawater uranium adsorbent material according to claim 1, characterized in that, The concentration of the nanogel dispersion was 25 mg / mL, and the concentration of the poly(amine oxime) sodium hydroxide solution was 50 mg / mL.

3. The method for preparing a nano-hydrogel seawater uranium adsorbent material according to claim 1, characterized in that, The heating temperature is 60°C and the heating time is 2 hours.

4. A nano-hydrogel seawater uranium adsorbent material prepared by the method according to any one of claims 1-3.

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