A polyacrylonitrile-based uranium extraction membrane with in-situ grown composite catalyst and a preparation method thereof

Abstract

The application discloses a polyacrylonitrile-based uranium extraction film with in-situ growth of a composite catalyst and a preparation method thereof. The method uses an electrospun polyacrylonitrile (PAN) film as a substrate, and through soaking and in-situ hydrothermal reaction, ZnCdS and graphene quantum dots are firmly anchored in the PAN fiber network. The application overcomes the defects of difficult recovery of powder catalyst, poor mechanical properties of pure PAN film and easy loosening. The obtained composite film has high tensile strength and excellent hydrophilicity, can resist long-term impact of sea current, and can realize efficient uranium extraction through synergistic effect of adsorption and catalytic reduction under illumination, and is suitable for ocean uranium extraction and radioactive wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of marine resource extraction and water treatment materials technology, and more specifically, to a polyacrylonitrile-based uranium extraction film with in-situ grown composite catalyst and its preparation method. Background Technology

[0002] In the field of uranium extraction from seawater, loading powdered photocatalysts or adsorbents onto macroscopic substrates is a common strategy for achieving the engineering application and recycling of materials. Currently, commonly used macroscopic supports mainly include ordinary fabrics and electrospun membranes. However, while traditional ordinary fabric substrates possess certain macroscopic shaping characteristics, their excessively large fiber spacing results in a small overall specific surface area, making it difficult to achieve high-density loading and uniform dispersion of catalyst materials. In contrast, polyacrylonitrile (PAN) spun membranes, with their smaller fiber gaps and abundant pore structure, are more ideal support substrates. However, pure PAN membranes themselves possess virtually no uranium extraction activity (the uranium extraction effect is extremely poor); furthermore, pure PAN membranes exhibit significant physical defects when used in liquid environments. Their texture is too soft, and their mechanical elasticity is generally poor, making them prone to structural loosening or even breakage when subjected to water flow impacts, thus failing to meet the long-term operational requirements of actual marine environments.

[0003] The inventors had previously developed a ZnCdS-JPQD composite material with excellent uranium extraction performance (patent number: 2026100498217; for ease of description, JQPD will be referred to as graphene quantum dots (GQDs) below), but this material was in powder form. In practical marine applications, if powdered catalysts are directly added to seawater, they will face serious problems of agglomeration and loss, and their recovery from seawater is extremely difficult and costly, easily causing secondary pollution. The difficulty in recovering powdered materials greatly limits the practical application of this high-performance catalyst.

[0004] Therefore, how to effectively combine high-performance powdered catalysts with macroscopic substrates with small pores, solving the problem of powder material recycling while overcoming the inherent defects of poor mechanical properties and easy disintegration of pure PAN membranes, is a technical problem urgently needing to be solved in this field. Based on the above background, this invention proposes a method for constructing PAN / GQDs@ZCS-NCs thin films. Through in-situ growth technology, ZnCdS-JPQD-type catalysts are firmly anchored onto PAN spun membranes, imparting highly efficient uranium extraction performance to the substrate while significantly improving the macroscopic mechanical properties of the PAN membrane, thus completely solving the problem of difficult recovery of powdered catalysts in seawater. Summary of the Invention

[0005] To address the problems of poor mechanical properties, easy breakage, and lack of uranium extraction activity in existing pure polyacrylonitrile (PAN) films, the primary objective of this invention is to provide a PAN-based uranium extraction film with in-situ grown composite catalyst and its preparation method. This method achieves robust catalyst loading by in-situ growing ZnCdS and graphene quantum dots (GQDs) on a PAN substrate, thereby significantly improving the tensile mechanical properties of the PAN film and endowing it with excellent seawater uranium extraction capability.

[0006] To achieve the above objectives, this invention provides an in-situ grown composite catalyst polyacrylonitrile-based uranium extraction film and its preparation method, the method comprising the following steps:

[0007] Step 1: Place orange peel in a quartz crucible and transfer it to a tube furnace. Heat under nitrogen protection using a programmed temperature rise method. Grind the pyrolysis product into powder, disperse it in an organic solvent, and then transfer it to a hydrothermal reactor for further heating. Allow it to cool naturally to room temperature, remove it, and transfer it to a dialysis bag for dialyzing at room temperature. After dialysis, discard the solid residue in the bag and collect all the external liquid. Concentrate the external liquid by rotary evaporation under reduced pressure to obtain graphene quantum dots (GQDs).

[0008] Step 2: Add DMF to polyacrylonitrile and stir at room temperature to form a PAN spinning solution. Then, inject the PAN solution into a syringe for electrospinning, with the spinneret scanning above a cylindrical collector. After spinning, remove the PAN film from the collector. Dissolve 2-methylimidazole and 1-methylimidazole in an organic solvent to form solution A. Dissolve zinc acetate hexahydrate in an organic solvent to form solution B. Immerse the PAN film in a mixture of solutions A and B, then rinse with an organic solvent. Immerse the PAN film in a tannic acid solution (tannic acid dissolved in an organic solvent at room temperature using ultrasound), then rinse with an organic solvent. Immerse the PAN film in a thioacetamide solution (thioacetamide dissolved in an organic solvent at room temperature using ultrasound), heat in a water bath, then rinse with an organic solvent. Add the PAN film to an organic solvent containing cadmium acetate dihydrate dissolved in an ultrasonic solvent, transfer to a hydrothermal reactor, and heat in a high-temperature oven to generate ZnCdS in situ on the PAN film surface. After naturally cooling to room temperature, the PAN film loaded with ZnCdS is added to an organic solvent containing GQDs and immersed at room temperature to obtain in-situ grown PAN / GQDs@ZCS-NCs.

[0009] Preferably, in step one, the dialysis uses anhydrous ethanol as the external solution, and the solution is changed every 6 hours for 24 hours. The temperature of the external solution concentrated by vacuum rotary evaporation is 40 °C.

[0010] Preferably, in step two, the mass ratio of DMF to polyacrylonitrile is 20:1 to 1:1; the stirring speed is 200 to 700 rpm; and the stirring time is 5 to 20 h.

[0011] Preferably, in step two, the scanning speed of the spinning process is 10~70 mm / s, and the scanning range is 10~40 cm.

[0012] Preferably, in step two, the soaking time is 0.5 to 30 hours, and the number of times the organic solvent is rinsed is 1 to 6.

[0013] Preferably, the organic solvent used in each step of the method is independently selected from any one or a mixture of two of methanol, ethanol, ethylene glycol, isopropanol and n-octanol.

[0014] Preferably, in step two, the molar ratio of 2-methylimidazole to zinc acetate hexahydrate is 2:1 to 50:1; the concentration of the tannic acid solution is 5 to 20 mg / ml; and the molar ratio of thioacetamide to cadmium acetate dihydrate is 30:1 to 100:1.

[0015] Another object of the present invention is to provide a polyacrylonitrile-based uranium extraction film for in-situ growth of a composite catalyst obtained by the above preparation method.

[0016] Another object of the present invention is to provide the application of the above-mentioned polyacrylonitrile-based uranium extraction film in the treatment of uranium-containing radioactive wastewater or uranium extraction in marine environments.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) By growing composite catalysts in situ, the physicochemical properties of the pure PAN membrane surface are changed, making it more wettable and contactable in the aqueous environment, which is conducive to the rapid entry of uranium-containing wastewater or seawater into the membrane pores and reaction with the catalyst.

[0019] (2) The in-situ growth of the composite material not only does not damage the substrate, but also has the effect of structural reinforcement. The prepared composite film has excellent tensile properties and toughness, and can withstand water flow fluctuations and multiple impacts in the actual marine environment for a long time, which completely solves the defects of traditional pure PAN film that is too soft and easily loosened and damaged.

[0020] (3) The composite film combines the excellent photocatalytic / adsorption uranium extraction performance of ZnCdS-GQDs with the advantages of easy recovery of macroscopic films; during the long-term seawater uranium extraction process, the macroscopic structure of the film does not deform or collapse, and the catalyst is firmly anchored and does not fall off, which solves the problem of easy loss and difficult recovery of traditional powder catalysts in seawater. Attached Figure Description

[0021] Figure 1 These are SEM microscopic images of Comparative Example 1 and Example 1 of the present invention.

[0022] Figure 2The XRD diffraction patterns are those of Example 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0023] Figure 3 The images shown are FTIR infrared spectra of Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0024] Figure 4 This is a comparison diagram of the surface contact angle test between Comparative Example 1 and Example 1 of the present invention.

[0025] Figure 5 This is a tensile force-time curve for Comparative Example 1 and Example 1 of the present invention.

[0026] Figure 6 This is a 50% strain reciprocating tensile test diagram of Embodiment 1 of the present invention.

[0027] Figure 7 This is a bar chart comparing the uranium extraction rates of Comparative Example 1 and Example 1 in seawater spiked at 8 ppm.

[0028] Figure 8 This is a SEM microstructure image of the uranium extraction reaction in Example 1 of the present invention.

[0029] Figure 9 This is a comparison of XRD spectra before and after uranium extraction in Example 1 of the present invention.

[0030] Figure 10 This is a comparison of FTIR spectra before and after uranium extraction in Example 1 of the present invention. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] A polyacrylonitrile-based uranium extraction film with an in-situ grown composite catalyst and its preparation method are detailed below:

[0034] 50 g of orange peel was placed in a quartz crucible and transferred to a tube furnace. Under nitrogen protection, the temperature was increased to 200 °C at a rate of 5 °C / min and heated for 2 h. The pyrolysis product was ground into powder, and 50 ml of ethanol was added. The mixture was then transferred to a 100 ml hydrothermal reactor and heated at 180 °C for 15 h. After naturally cooling to room temperature, the powder was transferred to a dialysis bag and dialyzed at room temperature using anhydrous ethanol as the external solution. The solution was changed every 6 h for 24 h. After dialysis, the solid residue in the bag was discarded, and all the external solution was collected. The external solution was concentrated to a concentration of 20 mg / ml by rotary evaporation under reduced pressure at 40 °C to obtain graphene quantum dots (GQDs).

[0035] 27 g of DMF was added to 3 g of polyacrylonitrile, and the mixture was stirred at 500 rpm for 12 h at room temperature to form a PAN spinning solution. The PAN solution was then injected into a syringe, and the spinneret was scanned over a cylindrical collector at a speed of 20 mm / s over a 20 cm area. After spinning for several hours, the PAN membrane was removed from the collector. 656.8 mg of 2-methylimidazole and 2.05 μl of 1-methylimidazole were dissolved in 25 ml of methanol to form solution A. 219.5 mg of zinc acetate hexahydrate was dissolved in 25 ml of methanol to form solution B. The cut PAN was placed in the mixture of solutions A and B, soaked for 24 h, and then rinsed three times with anhydrous ethanol. It was then placed in a tannic acid solution (500 mg of tannic acid dissolved in 50 ml of methanol at room temperature via ultrasonication), soaked for 30 min, and then rinsed three times with anhydrous ethanol. The PAN film was immersed in a thioacetamide solution (600 mg thioacetamide dissolved in 10 ml anhydrous ethanol via ultrasonication at room temperature), heated in a water bath at 50 °C for 48 h, and then rinsed once with anhydrous ethanol. The solution was then added to 20 ml ethylene glycol containing 35 mg cadmium acetate dihydrate dissolved via ultrasonication, transferred to a 100 ml hydrothermal reactor, and heated in a high-temperature oven at 160 °C for 6 h to generate ZnCdS in situ on the PAN film surface. After natural cooling to room temperature, the ZnCdS-loaded PAN film was added to 0.1 ml GQDs in 30 ml anhydrous ethanol and immersed at room temperature for 48 h to obtain in-situ grown PAN / GQDs@ZCS-NCs.

[0036] Comparative Example 1

[0037] A method for preparing a PAN film:

[0038] 27 g of DMF was added to 3 g of polyacrylonitrile, and the mixture was stirred at 500 rpm for 12 h at room temperature to form a PAN spinning solution. The PAN solution was then injected into a syringe, and the spinneret was scanned over a cylindrical collector at a speed of 20 mm / s over a range of 20 cm. After spinning for several hours, the PAN film was removed from the collector.

[0039] Comparative Example 2

[0040] A method for preparing a ZnCdS-JPQD composite material with a dodecahedral core-shell structure fully coated with GQDs (Example 1 of Patent No.: 2026100498217):

[0041] (1) Preparation of JPQD (orange peel graphene quantum dots)

[0042] Place 50g of orange peel into a quartz crucible, transfer it to a tube furnace, and heat it to 200℃ at a rate of 5℃ / min for 2 hours under nitrogen protection. Grind the pyrolysis product into powder, add 50ml of ethanol, transfer it to a 100ml hydrothermal reactor, heat it at 180℃ for 15 hours, allow it to cool naturally to room temperature, remove it, centrifuge it, discard the solid residue, and obtain JPQD.

[0043] (2) Preparation of etched ZnO

[0044] Dissolve 8 mmol of 2-methylimidazole and 0.025 mmol of 1-methylimidazole in 25 mL of methanol, and mix with 25 mL of methanol containing 1 mmol of zinc acetate. Stir the solution continuously for 24 h to form a white powder. Wash the powder three times with ethanol and dry at 40 °C to obtain ZnO. Dissolve 20 mg of ZnO and 500 mg of tannic acid in 50 mL of methanol, stir for 30 min, centrifuge, and wash three times with ethanol to obtain etched ZnO.

[0045] (3) Preparation of ZnCdS

[0046] Dissolve 600 mg of thioacetamide in 10 ml of ethanol, add the etched ZnO to the solution, heat in a 50 °C water bath and stir for 48 h, centrifuge, add to 20 ml of ethylene glycol containing 35 mg of cadmium acetate, stir, add to a 100 ml hydrothermal reactor, heat at 160 °C for 6 h, remove and sonicate for 30 min, centrifuge, wash three times with ethanol, and dry at 40 °C to obtain ZnCdS.

[0047] (4) Preparation of ZnCdS-JPQD with GQDs fully encapsulated core-shell structure

[0048] Take 0.1 ml of JPQD and add it together with 20 mg of ZnCdS into 50 ml of ethanol. Stir at room temperature for 24 h, let stand for 24 h, centrifuge, and dry at 40 °C to obtain GQDs fully coated dodecahedral core-shell structure ZnCdS-JPQD.

[0049] Figure 1The images show the SEM microstructure of Comparative Example 1 and Example 1 of this invention. As can be seen from the figures, Comparative Example 1 has smaller fiber gaps and a rich pore structure, but the fiber arrangement is relatively loose. After in-situ growth treatment, the fiber network of Example 1 is more densely interwoven, while still retaining a good three-dimensional pore structure. This dense and porous structure not only improves the overall stability of the film but also provides ample sites for the penetration and adhesion of uranyl ions.

[0050] Figure 2 The figures show the XRD diffraction patterns of Example 1, Comparative Example 1, and Comparative Example 2 of this invention. As can be seen from the figures, the pattern of Example 1 exhibits characteristic diffraction peaks of both Comparative Example 1 and Comparative Example 2, without any extraneous peaks. This strongly demonstrates the success of the in-situ composite growth strategy, and the target composite film was successfully prepared.

[0051] Figure 3 The figures show the FTIR spectra of Example 1, Comparative Example 1, and Comparative Example 2 of this invention. As can be seen from the figures, Example 1 successfully retained the key characteristic absorption peaks of Comparative Example 2. The results of the FTIR spectra correspond to the XRD results, further confirming the successful in-situ loading of the catalyst material (Comparative Example 2) onto the polymer-based film (Comparative Example 1).

[0052] Figure 4 This is a comparison diagram of the surface contact angle tests for Comparative Example 1 and Example 1 of the present invention. The test results show that the contact angle of Comparative Example 1 remained between 25° and 45° at 0.5 s and 1 s; while the contact angle of Example 1 rapidly decreased to 12° to 19° at 0.5 s, and further decreased to 11° to 17° at 1 s. The significant reduction in contact angle indicates that Example 1, after in-situ growth treatment, possesses stronger hydrophilicity, which can greatly promote the rapid penetration and mass transfer of uranium-containing aqueous solutions inside the membrane, thereby effectively improving the efficiency of uranium extraction from seawater.

[0053] Figure 5 The figures show the tensile force-time curves of Comparative Example 1 and Example 1 of this invention. As can be seen from the figures, the maximum breaking force of Comparative Example 1 is only 6.3 N, and its tensile force-time curve exhibits a clear rightward dip. This indicates that during constant-speed stretching, the macromolecular chains of Comparative Example 1 are highly prone to slippage, exhibiting physical defects such as easy yielding and irreversible plastic deformation. In contrast, the maximum breaking force of Example 1 of this invention is significantly increased to 10.5 N. More importantly, the tensile force-time curve of Example 1 maintains a constant linear slope before fracture, exhibiting characteristics of a perfectly elastic body. This indicates that the in-situ grown nanoparticles effectively restrict the slippage of the polymer molecular chains, significantly improving the stiffness and deformation resistance of the film.

[0054] Figure 6This is a 50% strain reciprocating tensile test diagram of Example 1 of the present invention. The results show that Example 1 only fractured after undergoing up to 9 cycles of 50% high strain reciprocating tensile testing. (Combined with...) Figure 5 The tensile test fully confirmed that the composite film of the present invention has excellent tensile strength and high resilience, which is sufficient to resist the long-term physical impact of waves and currents in the real marine environment.

[0055] Experimental Example 1: Evaluation of uranium extraction performance in seawater spiked with 8 ppm under sunlight

[0056] This experiment aimed to investigate the uranium extraction capability of membrane materials from seawater spiked with 8 ppm under natural sunlight irradiation. The specific process is as follows:

[0057] Films of Example 1 and Comparative Example 1, each measuring 5 cm × 5 cm, were cut and completely immersed in a reactor containing 1 L of spiked seawater with an initial concentration of 8 ppm. The films were irradiated under natural sunlight for 4–5 hours daily (after each day's irradiation, the films were removed and stored in a dark, sealed container). After a cumulative irradiation time of 20 hours, a suitable amount of spiked seawater sample was taken and treated using the azoarsine III colorimetric method. The initial uranyl concentration was denoted as C0, and the residual uranyl concentration after 20 hours of cumulative irradiation was denoted as C. The residual uranyl concentration in the sample was detected using UV-vis ultraviolet-visible absorption spectroscopy, and the uranium extraction and photocatalytic reduction capacity of the material were calculated and evaluated accordingly.

[0058] Figure 7 This is a bar chart comparing the uranium extraction yield of Comparative Example 1 and Example 1 in seawater spiked at 8 ppm. As can be clearly seen from the chart, after 20 hours of sunlight exposure, the uranium extraction yield of Comparative Example 1 was only 0.89 mg / g; while the uranium extraction yield of Example 1 was as high as 19.53 mg / g, which is 21.94 times that of Comparative Example 1. This indicates that the composite film of the present invention possesses extremely superior photocatalytic uranium extraction efficiency.

[0059] Figure 8 This is a SEM microstructure image of the composite film after uranium extraction in Example 1 of the present invention. Observation shows that the three-dimensional network framework of the composite film after uranium extraction remains intact, with no obvious structural collapse or cracking deformation, exhibiting excellent structural stability.

[0060] Figure 9 The image shows a comparison of XRD spectra before and after uranium extraction in Example 1 of this invention. As can be seen from the figure, the spectrum of Example 1 after uranium extraction exhibits obvious characteristic diffraction peaks of UO3⋅H2O. This confirms that uranium was indeed successfully captured and immobilized on the thin film, demonstrating the potential of this material for practical engineering applications of uranium extraction from seawater.

[0061] Figure 10The image shows a comparison of the FTIR spectra before and after uranium extraction in Example 1 of this invention. The results show that the main characteristic functional groups of the material remained unchanged after uranium extraction, demonstrating the stability of its chemical structure. Simultaneously, a distinct uranium-oxygen bond vibration peak appeared at 980 cm⁻¹. This result indicates that the present invention not only involves the physicochemical adsorption of uranyl but also a catalytic reduction under light irradiation.

[0062] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A polyacrylonitrile-based uranium extraction film with in-situ grown composite catalyst and its preparation method, characterized in that, The preparation method includes the following steps: Step 1: Orange peel is placed in a quartz crucible and transferred to a tube furnace for programmed heating under nitrogen protection; the pyrolysis product is ground into powder, dispersed in an organic solvent, and then transferred to a hydrothermal reactor for heating and reaction; after natural cooling to room temperature, it is removed and transferred to a dialysis bag for dialysis at room temperature. After dialysis, the solid residue in the bag is discarded, and all external liquid is collected. The external liquid is concentrated by rotary evaporation under reduced pressure to obtain graphene quantum dots (GQDs). Step 2: DMF is added to polyacrylonitrile and stirred at room temperature to form a PAN spinning solution. Then, the PAN solution is injected into a syringe for electrospinning, with the spinneret scanning above a cylindrical collector. After spinning, the PAN membrane is removed from the collector. 2-methylimidazole and 1-methylimidazole are dissolved in an organic solvent to form solution A. Zinc acetate hexahydrate is dissolved in an organic solvent to form solution B. PAN is placed in the mixture of solution A and solution B, soaked, and then rinsed with an organic solvent. The PAN film was immersed in a tannic acid solution (tannic acid dissolved in an organic solvent by ultrasonication at room temperature), then rinsed with the organic solvent. Next, it was immersed in a thioacetamide solution (thioacetamide dissolved in an organic solvent by ultrasonication at room temperature), heated in a water bath, and then rinsed with the organic solvent. Finally, it was added to an organic solvent containing cadmium acetate dihydrate dissolved by ultrasonication, transferred to a hydrothermal reactor, and heated in a high-temperature oven to generate ZnCdS in situ on the PAN film surface. After natural cooling to room temperature, the ZnCdS-loaded PAN film was added to an organic solvent containing GQDs and immersed at room temperature to obtain in-situ grown PAN / GQDs@ZCS-NCs.

2. The preparation method according to claim 1, characterized in that, In step one, the dialysis uses anhydrous ethanol as the external solution, and the solution is changed every 6 hours for 24 hours. The temperature of the external solution is 40 ℃ during the vacuum rotary evaporation concentration.

3. The preparation method according to claim 1, characterized in that, In step two, the mass ratio of DMF to polyacrylonitrile is 20:1 to 1:1; the stirring speed is 200 to 700 rpm; and the stirring time is 5 to 20 h.

4. The preparation method according to claim 1, characterized in that, In step two, the scanning speed of the spinning process is 10~70 mm / s, and the scanning range is 10~40 cm.

5. The preparation method according to claim 1, characterized in that... In step two, the soaking time is 0.5 to 30 hours, and the number of times the organic solvent is rinsed is 1 to 6.

6. The preparation method according to claim 1, characterized in that, The organic solvents used in each step of the method are independently selected from any one or a mixture of two of methanol, ethanol, ethylene glycol, isopropanol, and n-octanol.

7. The preparation method according to claim 1, characterized in that, In step two, the molar ratio of 2-methylimidazole to zinc acetate hexahydrate is 2:1 to 50:1; the concentration of the tannic acid solution is 5 to 20 mg / ml; and the molar ratio of thioacetamide to cadmium acetate dihydrate is 30:1 to 100:

1.

8. A polyacrylonitrile-based uranium extraction film with an in-situ grown composite catalyst obtained by the preparation method according to any one of claims 1-7.

9. The application of the polyacrylonitrile-based uranium extraction film as described in claim 8 in the treatment of uranium-containing radioactive wastewater or uranium extraction in marine environments.

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