COF nanofiber membrane, preparation method thereof and application of COF nanofiber membrane in uranium enrichment

Abstract

According to the COF nanofiber membrane, the preparation method thereof and the application of the COF nanofiber membrane to uranium enrichment, adsorptive COF powder is synthesized through a solvothermal method, the maximum uranium enrichment amount of the adsorptive COF powder can reach 520 mg / g under the condition that the pH of the adsorptive COF powder is equal to 5, and the adsorptive COF powder is processed into the COF nanofiber membrane through an electrostatic spinning method. The COF nanofiber membrane prepared by the method can retain the properties of COF powder, not only has adsorption capacity to U (VI), but also has photocatalytic reaction capacity, and can convert soluble U (VI) into insoluble uranium and release additional adsorption sites, so that the enrichment capacity of a COF material to uranium is improved, and the enrichment efficiency of the COF material to uranium in water reaches 97% or above. In addition, the COF nanofiber membrane is also beneficial to use and recovery, and is more conveniently applied to the fields of uranium-containing wastewater treatment, uranium extraction from seawater and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite fiber materials, and particularly relates to a COF nanofiber membrane, a preparation method thereof, and applications in the treatment of uranium-containing wastewater and uranium extraction from seawater. Background Art

[0002] Nuclear energy is considered an efficient and clean energy source and has been vigorously developed recently. Uranium is a key raw material for nuclear power generation. However, the extraction and production of uranium generate a large amount of uranium-containing wastewater, and the discharge of this wastewater into the environment will seriously affect human health. Developing efficient and environmentally friendly uranium enrichment materials is one of the feasible methods to solve the pollution of uranium-containing wastewater. Porous materials have a large specific surface area and porous structure and have been developed for the treatment of uranium-containing wastewater and the extraction of trace uranium in seawater, such as porous polymer materials, porous aromatic framework materials, metal-organic frameworks, and covalent organic framework materials. Among them, covalent organic framework materials (COF) are crystalline porous materials composed of organic molecules connected by covalent bonds. By selecting different building monomers, more adsorption active sites can be constructed within the COF material to achieve efficient enrichment of uranium. Usually, when the adsorption sites in the COF material are completely occupied by uranium ions U(VI), the enrichment of U(VI) will stop. To further improve the adsorption capacity of COF for U(VI), the ability of COF to photocatalytically convert U(VI) is imparted, that is, soluble U(VI) is converted into insoluble uranium through a photocatalytic reaction, thereby releasing additional adsorption sites and improving the uranium enrichment ability of the COF material. Summary of the Invention

[0003] (I) Technical Problems to be Solved

[0004] The present invention provides a COF nanofiber membrane, a preparation method thereof, and an application in uranium enrichment to solve the technical problem of how to improve the adsorption capacity of COF for U(VI).

[0005] (II) Technical Solutions

[0006] To solve the above technical problems, the present invention provides a preparation method of a COF nanofiber membrane. The preparation method is to uniformly mix adsorptive COF powder with a dispersant and a solvent to obtain a spinning solution, and perform electrospinning using the uniform spinning solution to obtain a COF nanofiber membrane.

[0007] Furthermore, the adsorptive COF powder is prepared by reacting an amino monomer with an aldehyde monomer; wherein, the amino monomer is 1,3,6,8-tetra-(p-aminophenyl)-pyrene, and the aldehyde monomer is one or more of 4,4'-biphenyldicarboxaldehyde, 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarboxaldehyde, 2,2'-bipyridine-5,5'-dicarboxaldehyde, 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarboxaldehyde, and p-phthalaldehyde.

[0008] Furthermore, the dispersant is one or more of polyacrylonitrile, polystyrene, and polyvinylpyrrolidone; the solvent is one or more of acetonitrile, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0009] Furthermore, the mass ratio of the adsorptive COF powder, the dispersant, and the solvent is 1:(1-10):(10-50); the loading amount of the adsorptive COF powder is 20-80 g / m 2 ; before electrospinning, the particle size of the adsorptive COF powder is controlled below 50 μm.

[0010] Furthermore, the parameters of electrospinning are: the negative voltage is -0.5 to -1 kV, the positive voltage is 5.0 kV to 20 kV, the injection rate is 0.05 to 0.5 mm / min, the distance between the needle and the receiving device is 10 to 30 cm, the roller rotation speed is 20 to 80 r / min, and the spinning temperature is from room temperature to 40 °C; the material for receiving the COF nanofiber membrane is one of tin foil, aluminum foil, and non-woven fabric.

[0011] Furthermore, the adsorptive COF powder can enrich uranium (VI) ions at a pH of 2-6, and at pH = 5, the maximum enrichment amount reaches 520 mg / g.

[0012] In addition, the present invention also provides a COF nanofiber membrane, which is prepared by the above method.

[0013] In addition, the present invention also provides an application of the COF nanofiber membrane in uranium enrichment. The above COF nanofiber membrane is placed in a solution to be treated containing uranium (VI), irradiated under sunlight, soluble uranium (VI) is adsorbed onto the surface of the COF nanofiber membrane, and soluble uranium (VI) is converted into insoluble uranium through a photocatalytic reaction to achieve the enrichment of uranium ions.

[0014] Furthermore, in the solution to be treated containing uranium (VI), the uranium content is 0.003-200 ppm; the addition amount of the COF nanofiber membrane in the solution to be treated is 0.05-1 g / L.

[0015] Further, after the COF nanofiber membrane realizes the enrichment of uranium ions, it is regenerated by pickling. The acid used is one of sulfuric acid, hydrochloric acid, and nitric acid, and the concentration is 0.1 - 1 mol / L.

[0016] (III) Beneficial Effects

[0017] The present invention provides a COF nanofiber membrane, its preparation method, and its application in uranium enrichment. An adsorptive COF powder is synthesized by a solvothermal method. The maximum enrichment amount of the adsorptive COF powder for uranium can reach 520 mg / g at pH = 5, and the adsorptive COF powder is processed into a COF nanofiber membrane by electrospinning. The COF nanofiber membrane prepared by this method can retain the properties of the COF powder. It not only has the ability to adsorb U(VI), but also has the ability of photocatalytic reaction, which can convert soluble U(VI) into insoluble uranium, release additional adsorption sites, improve the uranium enrichment ability of the COF material, and the enrichment efficiency of uranium in water reaches more than 97%. In addition, the COF nanofiber membrane is beneficial for use and recycling, and is more convenient for application in fields such as the treatment of uranium-containing wastewater and uranium extraction from seawater. Description of the Drawings

[0018] Figure 1 Synthesis route of PyTTA-DHTA powder and PyTTA-DHTA nanofiber membrane in the example;

[0019] Figure 2 Measured PXRD pattern and Pawley refinement pattern of PyTTA-DHTA powder in the example;

[0020] Figure 3 Adsorption isotherm diagram of uranyl ions by PyTTA-DHTA powder in the example;

[0021] Figure 4 Adsorption kinetics diagram of uranyl ions by PyTTA-DHTA powder in the example;

[0022] Figure 5 Photocatalytic kinetics curve diagram of the enrichment of uranyl ions by PyTTA-DHTA powder in the example;

[0023] Figure 6 PXRD pattern of PyTTA-DHTA powder after photocatalytic reaction in the example. Detailed Embodiments

[0024] To make the objectives, contents, and advantages of the present invention clearer, the following further describes the detailed embodiments of the present invention in conjunction with the drawings and examples.

[0025] This example is about a preparation method of PyTTA-DHTA nanofiber membrane and its application in uranium enrichment. The preparation processes of PyTTA-DHTA powder and PyTTA-DHTA nanofiber membrane are as follows Figure 1 shown.

[0026] 1. Preparation of PyTTA-DHTA powder, static adsorption of uranium and photocatalytic enrichment experiment of uranium

[0027] (1) Add 1,3,6,8-tetra-(p-aminophenyl)pyrene (PyTTA, 11.3 mg, 0.02 mmol) and 2,5-dihydroxyterephthalaldehyde (DHTA, 6.6 mg, 0.04 mmol) into a Pyrex tube, then add n-butanol (0.5 ml), o-dichlorobenzene (0.5 ml) and ultrasonicate for 10 min, then add 6M acetic acid (0.1 ml), and then ultrasonicate for about 10 s. Then quickly freeze in a liquid nitrogen bath at 77K and perform freeze-thaw cycling degassing three times. Subsequently, place the Pyrex tube in an oven at 120 °C for 3 days and then cool to room temperature. Filter and collect the solid powder, and wash the solid powder three times with tetrahydrofuran and acetone respectively. Dry the obtained solid powder in vacuo at 60 °C overnight to obtain red PyTTA-DHTA powder with a yield of 91%.

[0028] As Figure 2 shown, the PXRD pattern of PyTTA-DHTA has obvious small-angle diffraction peaks. The strongest peak positions are at 2θ = 3.76°, corresponding to the (100) crystal plane, indicating the successful construction of the COF crystal structure. The crystal cell structure of COF and Pawley refinement were simulated by Materials Studio software, and the simulated diffraction peaks of the AA stacking model of the three are in good agreement with the experimental values.

[0029] (2) Static adsorption experiment of uranium. Adsorption isotherm experiments were carried out under the condition of pH = 5.0. Add PyTTA-DHTA (5.0 mg) into 50 mL of uranium ion solutions with different concentrations (10 - 120 ppm). Take uranium solution samples (500 μL) at different times and filter them using a 0.22 μm filter. Mix the filtered samples with 0.1M HCl aqueous solution (250 μL), 0.5 g / L arsenazo-III solution (1000 μL) and 3.25 mL of deionized water, and measure the change in absorbance at a wavelength of 651 nm on a UV-visible spectrophotometer to detect the concentration of the uranium solution. In the kinetic study, add 5 mg of PyTTA-DHTA into 50 mL of uranium solution with a concentration of 50 ppm and pH = 5, mix and stir for a period of time, and collect the filtrate at different times. Use UV-visible spectrophotometry to detect the concentration of the uranium solution. The adsorption capacity calculation formula is as follows: q e =(C0 - Ce ) × V / m. Where q e is the adsorption capacity, in mg / g; V is the volume of the mixed solution, in L; m is the dosage of PyTTA-DHTA, in g; C0 is the initial concentration of uranium ion U(VI), in mg / L; C e is the equilibrium concentration of uranium ion U(VI), in mg / L. The results show that at pH = 5, the adsorption capacity of PyTTA-DHTA increases continuously with the increase of the initial uranium concentration until the adsorption equilibrium is reached. Adsorption isotherm analysis shows that the adsorption law conforms to the Langmuir model, indicating that PyTTA-DHTA has monolayer adsorption on uranium ion U(VI), and finally reaches an equilibrium adsorption capacity of 520 mg / g, as Figure 3 shown.

[0030] The adsorption kinetics of COF was studied at an initial U(VI) concentration of 50 ppm, and the quasi-first-order model and quasi-second-order model were used to further explore the mechanism of the adsorption process. The data fit well with the quasi-second-order kinetic model, indicating that the adsorption of the material on U(VI) is chemisorption, as Figure 4 shown.

[0031] (3) Photocatalytic enrichment experiment of uranium. The uranium photocatalytic experiment was carried out in a 100 mL photoreactor cooled by circulating water. In each experiment, 5 mg of PyTTA-DHTA was suspended in 50 mL of a solution containing U(VI) (20 ppm), and 1% methanol solution was added as a hole scavenger. The pH was adjusted to 5 using nitric acid or sodium hydroxide solution. The solution was stirred in the dark for 3 hours to achieve adsorption-desorption equilibrium of U(VI) on the surface of the gPyTTA-DHTA powder. A 300 W xenon lamp (wavelength range 420 nm ≤ λ ≤ 780 nm, light intensity 1 kWm -2 ) was used as the light source to simulate sunlight.

[0032] After adding light after adsorption equilibrium in the dark, the content of U(VI) in the solution decreased rapidly, and the removal rate of U(VI) reached more than 95% after three hours; comparing the enrichment of U(VI) by PyTTA-DHTA under light conditions and the adsorption of U(VI) under dark conditions, the contribution rate of the adsorption of U(VI) by PyTTA-DHTA in the dark to the removal of uranium in the whole reaction was about 53%, as Figure 5 shown.

[0033] After the photocatalytic reaction, obvious peaks appeared at positions such as 16.9°, 20.2°, and 23.4°, corresponding to the peaks of (UO2)O2·2H2O (PDF#35-0571), indicating that U(VI) in the solution was converted into insoluble (UO2)O2·2H2O during the photocatalytic process, improving the adsorption capacity of PyTTA-DHTA, asFigure 6 as shown

[0034] 2. Preparation of PyTTA-DHTA nanofiber membrane, static adsorption of uranium, and photocatalytic enrichment experiment of uranium

[0035] After grinding PyTTA-DHTA, it is passed through a 200-mesh sieve (particle size about 50 μm). Then, 50 mg of PyTTA-DHTA, 100 mg of polyacrylonitrile, and 2 mL of N,N-dimethylformamide are fully stirred to form a spinning solution. The spinning solution is then transferred to an electrospinning device. The specific parameter settings are a negative voltage of -0.7 kV, a positive voltage of 10.0 kV, an injection rate of 0.10 mm / min, the distance between the needle and the receiving device is 15 cm, the roller rotation speed is 30 r / min, the spinning temperature is 25 °C, and the material for receiving the fiber membrane is tin foil. The material collected by electrospinning is placed in a vacuum drying oven at 85 °C for 12 h to obtain the PyTTA-DHTA nanofiber membrane.

[0036] The static adsorption of uranium and the photocatalytic enrichment experiment of uranium by the PyTTA-DHTA nanofiber membrane are similar to those of the PyTTA-DHTA powder. The adsorption capacity of the PyTTA-DHTA nanofiber membrane for uranium is proportional to the content of PyTTA-DHTA. Using 5 mg of the PyTTA-DHTA nanofiber membrane prepared under the above conditions (its loading rate of PyTTA-DHTA powder is about 45%), the adsorption amount of uranium is about 210 mg / g. This nanofiber membrane can be regenerated by pickling with 1 mol / L nitric acid.

[0037] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a COF nanofiber membrane, characterized in that, The preparation method is as follows: an adsorbent COF powder is mixed evenly with a dispersant and a solvent to obtain a spinning solution, and electrospinning is carried out using the homogeneous spinning solution to obtain a COF nanofiber membrane.

2. The preparation method of the COF nanofiber membrane according to claim 1, wherein The adsorbent COF powder is prepared by reacting an amino monomer with an aldehyde monomer; among them, the amino monomer is 1,3,6,8-tetra-(p-aminophenyl)-pyrene, and the aldehyde monomer is one or more of 4,4'-biphenyldicarboxaldehyde, 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarboxaldehyde, 2,2'-bipyridine-5,5'-dicarboxaldehyde, 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarboxaldehyde, and p-phthalaldehyde.

3. The preparation method of the COF nanofiber membrane according to claim 1, wherein, The dispersant is one or more of polyacrylonitrile, polystyrene, and polyvinylpyrrolidone; the solvent is one or more of acetonitrile, N,N-dimethylformamide, and N,N-dimethylacetamide.

4. The preparation method of the COF nanofiber membrane according to claim 1, characterized in that, The mass ratio of the adsorbent COF powder, the dispersant and the solvent is 1:(1-10):(10-50); the loading amount of the adsorbent COF powder is 20-80 g / m 2 ; before electrospinning, the particle size of the adsorbent COF powder is controlled below 50 μm.

5. The preparation method of the COF nanofiber membrane according to claim 1, wherein, The parameters of the electrospinning are as follows: the negative voltage is -0.5 to -1 kV, the positive voltage is 5.0 kV to 20 kV, the injection rate is 0.05 to 0.5 mm / min, the distance between the needle and the receiving device is 10 to 30 cm, the roller rotation speed is 20 to 80 r / min, and the spinning temperature is from room temperature to 40 °C; the material for receiving the COF nanofiber membrane is one of tin foil, aluminum foil, and non-woven fabric.

6. The preparation method of the COF nanofiber membrane according to claim 1, characterized in that, The adsorbent COF powder can enrich uranium (VI) ions at a pH of 2 to 6, and at pH = 5, the maximum enrichment amount reaches 520 mg / g.

7. A COF nanofiber membrane, characterized in that, The COF nanofiber membrane is prepared by the method described in any one of claims 1 to 6.

8. An application of a COF nanofiber membrane in uranium enrichment, characterized in that the COF nanofiber membrane described in claim 7 is placed in a solution to be treated containing uranium (VI), irradiated under sunlight, the soluble uranium (VI) is adsorbed onto the surface of the COF nanofiber membrane, and the soluble uranium (VI) is converted into insoluble uranium through a photocatalytic reaction to achieve the enrichment of uranium ions.

9. The application of the COF nanofiber membrane in uranium enrichment as described in claim 8, characterized in that in the solution to be treated containing uranium (VI), the uranium content is 0.003 to 200 ppm; the addition amount of the COF nanofiber membrane in the solution to be treated is 0.05 to 1 g / L.

10. The application of the COF nanofiber membrane in uranium enrichment as described in claim 8, characterized in that after the COF nanofiber membrane realizes the enrichment of uranium ions, it is regenerated by pickling, and the acid used is one of sulfuric acid, hydrochloric acid, and nitric acid, with a concentration of 0.1 to 1 mol / L.

Images