Composite nanofiber membrane as well as preparation method and application thereof

Abstract

The invention relates to a composite nanofiber membrane and a preparation method and application thereof.The preparation method comprises the steps that polyacrylonitrile and polyethyleneimine are dissolved in N, N-dimethylformamide according to a certain proportion, stirring is conducted, and condition parameters such as electrostatic voltage, propelling speed and receiving distance are set; preparing a PEI / PAN composite nanofiber membrane which is uniform in diameter and good in shape by adopting an electrostatic spinning technology; respectively weighing a proper amount of zinc nitrate hexahydrate and 2-methylimidazole, respectively adding a proper amount of methanol, and carrying out ultrasonic treatment for later use; and soaking the prepared PEI / PAN composite nanofiber membrane in a zinc nitrate hexahydrate ligand solution, carrying out oscillation reaction for a certain time, slowly pouring a 2-methylimidazole ligand solution along the cup wall, and carrying out sufficient oscillation reaction at a specific temperature to prepare the finished product of the composite nanofiber membrane. A pre-deposition and in-situ growth technology is adopted, and ZIF-8 crystals are uniformly loaded on the PEI / PAN blending electrospinning composite nanofiber membrane, so that not only is the loading capacity of the ZIF-8 improved, but also the uniform distribution of the ZIF-8 crystals on the fiber surface is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, in particular to a composite nanofiber membrane and a preparation method and application thereof. Background Art

[0002] At present, scholars at home and abroad have invested a lot of time and energy in researching effective methods to remove Cr(VI) from wastewater. The main methods include chemical methods (chemical reduction precipitation method, electrolytic reduction method), physical and chemical methods (ion exchange method, adsorption method, membrane separation method) and biological methods. Each method has its own characteristics. Among them, the most widely used methods are adsorption and membrane separation technology. Adsorption has become the most commonly used method for removing Cr(VI) from wastewater due to its advantages such as simple operation, strong adaptability and high utilization rate. However, existing adsorption technologies have shortcomings such as poor removal effect and long regeneration cycle, and there are still many difficulties in practical application. Therefore, the development of an adsorbent with high adsorption efficiency, durability and environmental friendliness is the key to the efficient removal of Cr(VI) from wastewater.

[0003] As an emerging crystalline material with a porous structure, metal organic framework (MOF) has shown wide application potential in many fields, including catalytic reactions, adsorption separation, etc., due to its high specific surface area and abundant active sites. In particular, the zeolitic imidazolate framework (ZIF-8), which has a structure similar to MOFs and is constructed by a stable MN bond formed between a metal center (Zn2+) and an organic ligand (imidazole), has the advantages of excellent thermochemical stability and environmental friendliness, making it an effective material for removing Cr(VI) from wastewater. However, ZIF-8 has a large void space and a hydrophilic surface, and ZIF-8 alone cannot show a good adsorption effect. Therefore, combining ZIF-8 with a highly hydrophilic polymer material and fixing it on various substrates has become an innovative and effective strategy.

[0004] In recent years, electrospun nanofiber membranes have shown promising application prospects in heavy metal wastewater treatment due to their large surface area, strong adsorption properties, easy regeneration, and flexible utilization. The research team previously prepared polyacrylonitrile and regenerated cellulose composite nanofiber membranes using electrospinning technology and chemical modification. Their studies demonstrated that the resulting amidoxime groups, through the formation of coordination / chelation bonds, possess strong adsorption capacity for heavy metal ions, effectively removing heavy metal ions from wastewater. Furthermore, electrospun nanofibers, due to their inherent flexibility and self-supporting properties, serve as an ideal porous substrate for loading ZIF-8. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a composite nanofiber membrane and its preparation method and application. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0006] A method for preparing a composite nanofiber membrane, the method comprising the following steps:

[0007] Step 1: Dissolve polyacrylonitrile and polyethyleneimine in N,N-dimethylformamide in a certain proportion, stir to prepare a spinning precursor solution, set condition parameters such as electrostatic voltage, propulsion speed, receiving distance, etc., and use electrospinning technology to prepare a PEI / PAN composite nanofiber membrane with uniform diameter and good morphology;

[0008] Step 2: Weigh appropriate amounts of zinc nitrate hexahydrate and 2-methylimidazole respectively, and then add appropriate amounts of methanol respectively, and set aside after ultrasonic treatment;

[0009] Step 3: Immerse the prepared PEI / PAN composite nanofiber membrane in the zinc nitrate hexahydrate ligand solution and oscillate for a certain time, then slowly pour the 2-methylimidazole ligand solution along the wall of the cup, and carry out sufficient oscillation reaction at a specific temperature to prepare the finished composite nanofiber membrane.

[0010] Step 1 includes the following steps: Weigh polyacrylonitrile and polyethyleneimine and add them to a reaction vessel, then add N,N-dimethylformamide, where the solute accounts for 10-13% of the total solution mass, stir with a magnetic stirrer at 60 °C for 8-14 h, then place the spinning solution in a syringe, and at room temperature, extrude the spinning solution from the nozzle onto the surface of the spunlace non-woven fabric receiving roller, the spinning speed is 0.4-1.0 ml / h, the voltage is 12-18 kV, the spinning distance is 12-15 cm, the spinning time is 24 h, and after solvent evaporation, the fibers are solidified.

[0011] Step 2 includes the following steps: Weigh 1 mmol of zinc nitrate hexahydrate and add it to a reaction vessel, and add 20 ml of methanol, and set aside after ultrasonic treatment for 20 min; then weigh 2-5 mmol of 2-methylimidazole and add it to different reaction vessels, and add 20 ml of methanol respectively, and set aside after ultrasonic treatment for 20 min.

[0012] Step 3 includes the following steps: Immerse the prepared PEI / PAN composite nanofiber membrane in the zinc nitrate hexahydrate ligand solution, oscillate at a temperature of 40 °C and an oscillation speed of 120 rpm for 2 h, then slowly pour different contents of the 2-methylimidazole ligand solution along the wall of the cup, and carry out a 12-h sufficient oscillation reaction to prepare the composite nanofiber membrane.

[0013] The present invention provides a composite nanofiber membrane, which is prepared by the above-mentioned preparation method.

[0014] The present invention also provides an application of a composite nanofiber membrane, and the application includes using the composite nanofiber membrane in a flat membrane for water treatment to perform an adsorption operation.

[0015] The beneficial effects of the present invention are as follows: By using the pre-deposition and in-situ growth techniques, ZIF-8 crystals are uniformly loaded on the PEI / PAN blend electrospun composite nanofiber membrane. This method not only increases the loading amount of ZIF-8 but also ensures its uniform distribution on the fiber surface, thereby improving the overall performance of the composite nanofiber membrane. In addition, the abundant adsorption sites on the fiber surface also provide favorable conditions for subsequent adsorption experiments.

[0016] Regarding the adsorption mechanism of the ZIF-8@PEI / PAN adsorption membrane, there is a high degree of synergy between polyethyleneimine and ZIF-8, which not only increases the adsorption capacity of the adsorption membrane but also enhances its reduction ability, solving the problem of low adsorption capacity of the adsorption membrane. The combination of the two enables the adsorption membrane to exhibit high efficiency and high selectivity during the adsorption process.

[0017] In an acidic environment, the ZIF-8@PEI / PAN adsorption membrane can still maintain high adsorption performance and stability, providing new ideas and methods for preparing adsorption membrane materials for treating heavy metal ions in wastewater, and also demonstrating its great potential in the field of wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described below in conjunction with the drawings and embodiments.

[0019] Figure 1 It is the SEM image of the ZIF-8@PEI / PAN adsorption membranes with different ratios in the present invention;

[0020] Figure 2 It is the SEM image of the ZIF-8@PEI / PAN adsorption membrane after adsorbing Cr(Ⅵ) in the present invention;

[0021] Figure 3 It is a schematic diagram comparing the adsorption amounts of the ZIF-8@PEI / PAN and PEI / PAN adsorption membranes in the present invention with temperature changes;

[0022] Figure 4 It is a schematic diagram showing the influence of different pH conditions on the ZIF-8@PEI / PAN adsorption membrane in the present invention;

[0023] Figure 5 It is a schematic diagram showing the influence of different times on the ZIF-8@PEI / PAN adsorption membrane in the present invention;

[0024] Figure 6 It is a schematic diagram showing the influence of the initial concentration on the ZIF-8@PEI / PAN adsorption membrane at different temperatures in the present invention;

[0025] Figure 7 Schematic diagram of the solution change before and after the ZIF-8@PEI / PAN adsorption membrane of the present invention adsorbs Cr(VI). Specific embodiments

[0026] In order to enable those skilled in the art to better understand the technical solution of the present invention, the following will combine the accompanying drawings in the embodiments to more clearly and completely elaborate on the present invention. Of course, the described embodiments are only a part of the present invention, not all of it. Based on this embodiment, other embodiments obtained by those skilled in the art without creative efforts are within the protection scope of the present invention.

[0027] A preparation method of a composite nanofiber membrane, the method comprising the following steps:

[0028] Step 1: Dissolve polyacrylonitrile and polyethyleneimine in N,N-dimethylformamide in a certain proportion, stir to prepare a spinning precursor solution, set condition parameters such as electrostatic voltage, propulsion speed, receiving distance, etc., and use electrospinning technology to prepare a PEI / PAN composite nanofiber membrane with uniform diameter and good morphology;

[0029] Step 2: Weigh appropriate amounts of zinc nitrate hexahydrate and 2-methylimidazole respectively, then add appropriate amounts of methanol respectively, and ultrasonically treat for later use;

[0030] Step 3: Immerse the prepared PEI / PAN composite nanofiber membrane in the zinc nitrate hexahydrate ligand solution and oscillate for a certain time, then slowly pour the 2-methylimidazole ligand solution along the cup wall, and carry out sufficient oscillation reaction at a specific temperature to prepare the finished composite nanofiber membrane.

[0031] Step 1 includes the following steps: Weigh polyacrylonitrile and polyethyleneimine and add them to a reaction vessel, then add N,N-dimethylformamide, where the solute accounts for 10-13% of the total solution mass, stir with a magnetic stirrer at 60°C for 8-14 h, then place the spinning solution in a syringe, and at room temperature, extrude the spinning solution from the nozzle onto the surface of a hydroentangled nonwoven receiving roller, with a spinning speed of 0.4-1.0 ml / h, a voltage of 12-18 kV, a spinning distance of 12-15 cm, and a spinning time of 24 h. After solvent evaporation, the fibers are solidified;

[0032] Polyethyleneimine is a cationic polymer. A considerable proportion of primary amines, secondary amines, and tertiary amines are contained in its macromolecular chains, which can form stable coordination bonds with metal ions, thus having a high adsorption capacity. At the same time, it has the advantages of good hydrophilicity, large adsorption capacity, fast coordination rate, good selectivity, environmental friendliness, etc., and can also reduce Cr(VI) to harmless Cr(III). As a highly water-soluble polymer, polyethyleneimine is prone to free movement and diffusion in solution, affecting its use efficiency and adsorption effect. Through Step 1, polyethyleneimine can be fixed on other substrates to maintain the stability of polyethyleneimine, and at the same time, it can show a high adsorption capacity for different heavy metals.

[0033] Step 2 includes the following steps: Weigh 1 mmol of zinc nitrate hexahydrate and add it to a reaction vessel, and add 20 ml of methanol, then ultrasonically treat for 20 min for standby; Subsequently, weigh 2 - 5 mmol of 2-methylimidazole and add it to different reaction vessels, and respectively add 20 ml of methanol, then ultrasonically treat for 20 min for standby.

[0034] Step 3 includes the following steps: Immerse the prepared PEI / PAN composite nanofiber membrane in the zinc nitrate hexahydrate ligand solution first, and carry out an oscillating reaction at a temperature of 40 °C and an oscillating speed of 120 rpm for 2 h. Subsequently, slowly pour different contents of the 2-methylimidazole ligand solution along the wall of the cup, and carry out a sufficient oscillating reaction for 12 h to prepare the composite nanofiber membrane;

[0035] In the prior art, the method of co-electrospinning ZIF-8 powder with a polymer to embed it in nanofibers is complex in steps and time-consuming on the one hand, and on the other hand, it also reduces the utilization rate. In the present invention, through pretreatment and pre-deposition in Step 2 and Step 3, ZIF-8 can be loaded on the nanofibers by deposition and in-situ growth. This process not only modifies the fiber surface but also significantly improves the loading amount of ZIF-8.

[0036] The present invention provides a composite nanofiber membrane, which is prepared by the above-mentioned preparation method.

[0037] The present invention also provides an application of the composite nanofiber membrane, and the application includes using the composite nanofiber membrane in a flat membrane for water treatment to perform adsorption operations.

[0038] The present invention includes the following embodiments:

[0039] Example 1

[0040] 1. First, weigh polyacrylonitrile and polyethyleneimine and add them to a beaker. Then add N,N-dimethylformamide, where the solute accounts for 10% of the total solution mass. Stir with a magnetic stirrer at 60 °C for 8 h. Then place the spinning solution in a syringe. At room temperature, extrude the spinning solution from the nozzle onto the surface of a spunlace nonwoven receiving roll. The spinning speed is 0.4 ml / h, the voltage is 12 kV, and the spinning distance is 12 cm. The spinning time is 24 h. After solvent evaporation, the fibers are solidified.

[0041] 2. Weigh 1 mmol of zinc nitrate hexahydrate and add it to a beaker, and add 20 ml of methanol. Ultrasonically treat for 20 min for standby. Subsequently, weigh 2 mmol of 2-methylimidazole and add it to a different beaker, and add 20 ml of methanol. Ultrasonically treat for 20 min for standby.

[0042] 3. First, soak the prepared PEI / PAN composite nanofiber membrane in the zinc nitrate hexahydrate ligand solution and react with oscillation at a temperature of 40 °C and an oscillation speed of 120 rpm for 2 h. Subsequently, slowly pour the 2-methylimidazole ligand solution along the wall of the cup and conduct a full oscillation reaction for 12 h. Take it out and wash it 3 times with methanol, and dry it at 40 °C for 4 h to obtain the ZIF-8@PEI / PAN composite nanofiber membrane.

[0043] 4. Using the single variable method, investigate the adsorption performance of the ZIF-8@PEI / PAN composite nanofiber membrane for Cr(VI). During the adsorption experiment, add the ZIF-8@PEI / PAN composite nanofiber membrane (20 mg) to the Cr(VI) solution and oscillate at 120 rpm for 10 - 2880 min. Among them, the volume is 25 mL, the concentration is 100 - 500 mg / L, the pH is 2 - 8, and the temperature is 298 - 318 K. Use a (SHIMADZU UV mini1285) ultraviolet spectrophotometer (540 nm) to detect the residual concentration of Cr(VI) after equilibrium adsorption, calculate the adsorption capacity Qe (mg / g), and investigate the removal efficiency of the ZIF-8@PEI / PAN composite nanofiber membrane for Cr(VI).

[0044] Example Two

[0045] 1. First, weigh polyacrylonitrile and polyethyleneimine and add them to a beaker. Then add N,N-dimethylformamide, where the solute accounts for 11% of the total solution mass. Stir with a magnetic stirrer at 60 °C for 10 h. Then place the spinning solution in a syringe. At room temperature, extrude the spinning solution from the nozzle onto the surface of a spunlace nonwoven receiving roll. The spinning speed is 0.6 ml / h, the voltage is 14 kV, and the spinning distance is 13 cm. The spinning time is 24 h. After solvent evaporation, the fibers are solidified.

[0046] 2. Weigh 1 mmol of zinc nitrate hexahydrate and add it to a beaker. Then add 20 ml of methanol and ultrasonically treat it for 20 min for later use. Subsequently, weigh 3 mmol of 2-methylimidazole and add it to a different beaker. Then add 20 ml of methanol and ultrasonically treat it for 20 min for later use.

[0047] 3. Immerse the prepared PEI / PAN composite nanofiber membrane in the zinc nitrate hexahydrate ligand solution first, and carry out an oscillating reaction at a temperature of 40 °C and an oscillating speed of 120 rpm for 2 h. Subsequently, slowly pour the 2-methylimidazole ligand solution along the wall of the cup and carry out a sufficient oscillating reaction for 12 h. Take it out and wash it 3 times with methanol, and dry it at 40 °C for 4 h to obtain the ZIF-8@PEI / PAN composite nanofiber membrane.

[0048] 4. Adopt the single variable method to investigate the adsorption performance of the ZIF-8@PEI / PAN composite nanofiber membrane for Cr(VI). During the adsorption experiment, add the ZIF-8@PEI / PAN composite nanofiber membrane (20 mg) into the Cr(VI) solution and oscillate it at 120 rpm for 10 - 2880 min. Among them, the volume is 25 mL, the concentration is 100 - 500 mg / L, the pH is 2 - 8, and the temperature is 298 - 318 K. Use a (SHIMADZU UV mini1285) ultraviolet spectrophotometer (540 nm) to detect the residual concentration of Cr(VI) after equilibrium adsorption, calculate the adsorption capacity Qe (mg / g), and investigate the removal efficiency of the ZIF-8@PEI / PAN composite nanofiber membrane for Cr(VI).

[0049] Example 3

[0050] 1. First, weigh polyacrylonitrile and polyethyleneimine and add them to a beaker. Then add N,N-dimethylformamide, where the solute accounts for 12% of the total solution mass. Stir it with a magnetic stirrer at 60 °C for 12 h. Then place the spinning solution in a syringe. At room temperature, extrude the spinning solution from the nozzle onto the surface of the spunlace non-woven fabric receiving roller. The spinning speed is 0.8 ml / h, the voltage is 16 kV, and the spinning distance is 14 cm. The spinning time is 24 h. After solvent evaporation, the fibers are solidified.

[0051] 2. Weigh 1 mmol of zinc nitrate hexahydrate and add it to a beaker. Then add 20 ml of methanol and ultrasonically treat it for 20 min for later use. Subsequently, weigh 4 mmol of 2-methylimidazole and add it to a different beaker. Then add 20 ml of methanol and ultrasonically treat it for 20 min for later use.

[0052] 3. Immerse the prepared PEI / PAN composite nanofiber membrane in the zinc nitrate hexahydrate ligand solution first, oscillate and react for 2 h at a temperature of 40 °C and an oscillation speed of 120 rpm. Subsequently, slowly pour the 2-methylimidazole ligand solution along the wall of the cup, carry out a full oscillation reaction for 12 h, take it out, wash it 3 times with methanol, and dry it at 40 °C for 4 h to obtain the ZIF-8@PEI / PAN composite nanofiber membrane.

[0053] 4. Adopt the single variable method to investigate the adsorption performance of the ZIF-8@PEI / PAN composite nanofiber membrane for Cr(VI). During the adsorption experiment, add the ZIF-8@PEI / PAN composite nanofiber membrane (20 mg) into the Cr(VI) solution and oscillate at 120 rpm for 10 - 2880 min. Among them, the volume is 25 mL, the concentration is 100 - 500 mg / L, the pH is 2 - 8, and the temperature is 298 - 318 K. Use a (SHIMADZU UV mini1285) ultraviolet spectrophotometer (540 nm) to detect the residual concentration of Cr(VI) after equilibrium adsorption, calculate the adsorption capacity Qe (mg / g), and investigate the removal efficiency of the ZIF-8@PEI / PAN composite nanofiber membrane for Cr(VI).

[0054] Example 4

[0055] 1. First, weigh polyacrylonitrile and polyethyleneimine and add them to a beaker, then add N,N-dimethylformamide, where the solute accounts for 13% of the total solution mass. Stir with a magnetic stirrer at 60 °C for 14 h. Then place the spinning solution in a syringe. At room temperature, extrude the spinning solution from the nozzle onto the surface of the spunlace non-woven fabric receiving roller. The spinning speed is 1.0 ml / h, the voltage is 18 kV, and the spinning distance is 15 cm; the spinning time is 24 h, and after solvent evaporation, the fibers are solidified.

[0056] 2. Weigh 1 mmol of zinc nitrate hexahydrate and add it to a beaker, and add 20 ml of methanol. Ultrasonically treat it for 20 min for standby; subsequently, weigh 5 mmol of 2-methylimidazole and add it to different beakers, and add 20 ml of methanol. Ultrasonically treat it for 20 min for standby.

[0057] 3. Immerse the prepared PEI / PAN composite nanofiber membrane in the zinc nitrate hexahydrate ligand solution first, oscillate and react for 2 h at a temperature of 40 °C and an oscillation speed of 120 rpm. Subsequently, slowly pour the 2-methylimidazole ligand solution along the wall of the cup, carry out a full oscillation reaction for 12 h, take it out, wash it 3 times with methanol, and dry it at 40 °C for 4 h to obtain the ZIF-8@PEI / PAN composite nanofiber membrane.

[0058] 4. The single-variable method was adopted to investigate the adsorption performance of the ZIF-8@PEI / PAN composite nanofiber membrane for Cr(VI). During the adsorption experiment, the ZIF-8@PEI / PAN composite nanofiber membrane (20 mg) was added to the Cr(VI) solution, and the mixture was oscillated at 120 rpm for 10 - 2880 min. Among them, the volume was 25 mL, the concentration was 100 - 500 mg / L, the pH was 2 - 8, and the temperature was 298 - 318 K. The residual concentration of Cr(VI) after equilibrium adsorption was detected by a (SHIMADZU UV mini1285) ultraviolet spectrophotometer (540 nm), and the adsorption capacity Qe (mg / g) was calculated to investigate the removal efficiency of the ZIF-8@PEI / PAN composite nanofiber membrane for Cr(VI).

[0059] It can be seen from Figure 1 that the ZIF-8 crystals grow tightly and orderly on the surface of the ZIF-8@PEI / PAN composite nanofibers, presenting a uniform pseudo-cubic and hexagonal nanoparticle morphology, effectively preventing the aggregation and agglomeration of ZIF-8 nanoparticles, and thus easily forming a hierarchical surface morphology. In addition, by comparing the samples grown at different ligand ratios, it can be clearly seen that the in-situ growth process has a significant impact on the ZIF-8 loading amount. The loading amount of ZIF-8 crystals on the nanofiber surface is significantly increased. However, after adding an excessive amount of 2-methylimidazole, although the loading amount of ZIF-8 crystals increases, obvious agglomeration phenomena appear on the fiber surface. Figure 2 It shows that after the ZIF-8@PEI / PAN composite nanofiber membrane adsorbs Cr(Ⅵ), there are obvious residual particles on the surface, indicating that a large amount of HCrO4- is effectively adsorbed and retained on the nanofibers to form crystals.

[0060] The 20 mg ZIF-8@PEI / PAN adsorption membrane prepared in Example 1 and the PEI / PAN adsorption membrane with the same solute mass fraction were added to a certain concentration of Cr(VI) solution (volume: 25 ml; concentration: 100 mg / L; pH = 3), and static adsorption was carried out at 298 K, 308 K, and 318 K for 24 h respectively. The residual concentration of Cr(VI) in the solution after the filtration experiment was detected by a Shimadzu UV mini1285 ultraviolet spectrophotometer (540 nm), and the adsorption capacity Qe was calculated. The adsorption capacity of the nanofiber membrane for Cr(VI) is positively correlated with the temperature. Compared with the PEI / PAN nanofiber membrane, the ZIF-8@PEI / PAN CNFM always shows stronger Cr(VI) adsorption performance. The results are as Figure 3 shown.

[0061] Add the 20 mg of ZIF-8@PEI / PAN adsorption membrane prepared in Example 1 to a Cr(VI) solution with a certain concentration (volume: 25 ml; concentration: 100 mg / L; temperature: 298 K), and perform static adsorption for 24 h under the condition of pH 2 - 8. At regular intervals, use a Shimadzu UV mini1285 ultraviolet spectrophotometer (540 nm) to detect the concentration of residual Cr(VI) in the solution after the filtration experiment, and calculate the adsorption capacity Qe. When the pH value decreases from 8 to 3, the adsorption capacity increases from 39.68 mg / g to 112.61 mg / g, and the adsorption ability is enhanced. When the pH value is 3, the adsorption capacity reaches the highest value, and the results are as Figure 4 shown.

[0062] Add the 20 mg of ZIF-8@PEI / PAN adsorption membrane prepared in Example 1 to a Cr(VI) solution with a certain concentration (volume: 25 ml; concentration: 100 mg / L; pH = 3; temperature: 318 K), and perform static adsorption for 48 h. At regular intervals, use a Shimadzu UV mini1285 ultraviolet spectrophotometer (540 nm) to detect the concentration of residual Cr(VI) in the solution after the filtration experiment, and calculate the adsorption capacity Qe. As the adsorption time increases, the adsorption capacity gradually increases and basically reaches the adsorption equilibrium at 1440 min. The results are as Figure 5 shown.

[0063] Add the 20 mg of ZIF-8@PEI / PAN adsorption membrane prepared in Example 1 to a Cr(VI) solution with a certain concentration (volume: 25 ml; concentration: 100 - 500 mg / L; pH = 3), and perform static adsorption for 24 h at temperatures of 298 K, 308 K, and 318 K respectively. Use a Shimadzu UVmini1285 ultraviolet spectrophotometer (540 nm) to detect the concentration of residual Cr(VI) in the solution after the filtration experiment, and calculate the adsorption capacity Qe. At 298 K, its adsorption capacity increases from 97.71 mg / g to 162.71 mg / g. At 308 K, this range is increased to 114.99 mg / g to 227.97 mg / g. And at 318 K, the adsorption capacity reaches a wide range of 124.41 mg / g to 288.92 mg / g. Temperature has a positive impact on the adsorption performance, and the results are as Figure 6 shown.

[0064] In summary, Figure 3-6 Generally speaking, through pretreatment or pre-deposition, ZIF-8 is loaded on the PEI / PAN composite nanofiber membrane in an in-situ growth manner, providing modification for the fiber surface, increasing the loading rate of ZIF-8 crystals, and significantly improving the adsorption performance of Cr(VI). At the same time, Figure 7By comparing the color change of the solution before and after Cr(VI) adsorption, strong evidence is also provided, and the preparation of a ZIF-8@PEI / PAN adsorption membrane with a high loading rate and a high removal rate is realized.

[0065] According to the above embodiments and experimental data, it can be seen that the present invention has found the optimal parameter combination suitable for different application scenarios by optimizing the ratio of zinc nitrate hexahydrate and 2-methylimidazole, achieving a significant improvement in the high loading capacity and high removal rate of the ZIF-8@PEI / PAN adsorption membrane. The process innovation and parameter optimization also provide important support for the performance improvement of the adsorption membrane, and it has a wide range of application prospects. In addition, different ratios can be applied to different application scenarios to meet diverse water treatment needs.

[0066] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification is only the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a composite nanofiber membrane, characterized in that: The method comprises the following steps: Step 1: Dissolve polyacrylonitrile and polyethyleneimine in N,N-dimethylformamide in a certain proportion, stir to prepare a spinning precursor solution, set condition parameters such as electrostatic voltage, propulsion speed, receiving distance, etc., and use electrospinning technology to prepare a PEI / PAN composite nanofiber membrane with uniform diameter and good morphology; Step 2: Weigh appropriate amounts of zinc nitrate hexahydrate and 2-methylimidazole respectively, then add appropriate amounts of methanol respectively, and set aside after ultrasonic treatment; Step 3: Immerse the prepared PEI / PAN composite nanofiber membrane in the zinc nitrate hexahydrate ligand solution first and oscillate for a certain time, then slowly pour the 2-methylimidazole ligand solution along the cup wall, and carry out sufficient oscillating reaction at a specific temperature to prepare the finished composite nanofiber membrane.

2. The preparation method of a composite nanofiber membrane according to claim 1, characterized in that: Step 1 includes the following steps: Weigh polyacrylonitrile and polyethyleneimine and add them to a reaction vessel, then add N,N-dimethylformamide, where the solute accounts for 10-13% of the total solution mass, stir with a magnetic stirrer at 60 °C for 8-14 h, then place the spinning solution in a syringe, and at room temperature, extrude the spinning solution from the nozzle onto the surface of a spunlace nonwoven fabric receiving roller, with a spinning speed of 0.4-1.0 ml / h, a voltage of 12-18 kV, a spinning distance of 12-15 cm, and a spinning time of 24 h. After solvent evaporation, the fibers are solidified.

3. The preparation method of a composite nanofiber membrane according to claim 1, characterized in that: Step 2 includes the following steps: Weigh 1 mmol of zinc nitrate hexahydrate and add it to a reaction vessel, and add 20 ml of methanol, set aside after ultrasonic treatment for 20 min; then weigh 2-5 mmol of 2-methylimidazole and add it to different reaction vessels, and add 20 ml of methanol respectively, set aside after ultrasonic treatment for 20 min.

4. The preparation method of a composite nanofiber membrane according to claim 1, characterized in that: Step 3 includes the following steps: Immerse the prepared PEI / PAN composite nanofiber membrane in the zinc nitrate hexahydrate ligand solution first, oscillate and react at a temperature of 40 °C and an oscillation speed of 120 rpm for 2 h, then slowly pour different amounts of the 2-methylimidazole ligand solution along the cup wall, and carry out sufficient oscillating reaction for 12 h to prepare the composite nanofiber membrane.

5. A composite nanofiber membrane, characterized in that: The composite nanofiber membrane is prepared by the preparation method according to any one of claims 1 to 4.

6. An application of a preparation method of a composite nanofiber membrane, characterized in that: the application includes applying the composite nanofiber membrane according to claim 5 in a flat membrane for water treatment, so as to carry out an adsorption operation.

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