Ion exchange nanofiber membrane with high ion adsorption function and preparation method

Abstract

The invention provides an ion exchange nanofiber membrane with a high ion adsorption function and a preparation method, the preparation method comprises the following steps: 1) respectively preparing a polyacrylonitrile spinning solution and a polyethyleneimine spinning solution, and mixing and stirring the two obtained spinning solutions to obtain a mixed solution; and 2) carrying out an electrostatic spinning process on the mixed solution to prepare the polyacrylonitrile / polyethyleneimine nanofiber membrane. The polyacrylonitrile / polyethyleneimine nanofiber membrane disclosed by the invention has an excellent adsorption effect on Cu < 2 + >, Cr < 6 + > and CR. The optimal adsorption pH values of the material to Cu < 2 + >, Cr < 6 + > and CR are 6, 2 and 6 respectively, the optimal initial adsorption concentrations are 900 mg / L, 300 mg / L and 35 mg / L respectively, and the optimal adsorption time is 3.5 h, 3.5 h and 3.5 h respectively.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor filtration and wastewater treatment, and specifically relates to an ion exchange nanofiber membrane with high ion adsorption function and a preparation method thereof. Background Art

[0002] With the growing development of printing and dyeing, textile and other industries, the dye wastewater discharged enters rivers, lakes, seas and groundwater, causing irreversible damage to the human body. At present, the methods for treating dye wastewater at home and abroad are mostly physical adsorption, biological methods, chemical oxidation and membrane separation. Adsorption technology has attracted widespread attention due to its low adsorption cost, universal applicability to various pollutants and convenient operation. The nanofiber membrane prepared by electrospinning has the characteristics of small fiber diameter, large specific surface area, tortuous pore channels, high porosity, small pore size and high surface energy. It has ultra-high removal characteristics for small particles, that is, high filtration efficiency and large adsorption capacity.

[0003] Patent publication number CN115591417A discloses a composite membrane capable of purifying dye wastewater and a preparation method thereof. The composite membrane capable of purifying dye wastewater is composed of graphene oxide and polyacrylonitrile fibers; graphene oxide is interspersed between staggered and stacked polyacrylonitrile fibers to form a three-dimensional network support structure; the composite membrane capable of purifying dye wastewater has a porosity of 18% to 27% and a water flux of 330 to 850 L / m 2 h, specific surface area is 15~400m 2 / g; the preparation method is: conjugate electrospinning of an inorganic dispersion of graphene oxide and a polyacrylonitrile solution to obtain a composite membrane that can purify dye wastewater. Patent Publication No. CN112376166A discloses a method for preparing a carbon nanotube-modified polyacrylonitrile nanofiber membrane and its application, using acrylonitrile, 2-methylene-4-phenyl-1,3-dioxolane, methyl methacrylate silyl ester, initiator and solvent to prepare modified polyacrylonitrile by free radical polymerization; then electrospinning is used to prepare a carbon nanotube-modified polyacrylonitrile nanofiber membrane. Although the prior art discloses a series of methods for improving the adsorption performance of fiber membranes by doping inorganic nanoparticles such as graphene oxide, carbon nanotubes, and zinc oxide, their effects on Cu 2+ Cr 6+ The adsorption amount of CR is still low, and the adsorption performance needs to be further improved. Summary of the invention

[0004] In order to solve the technical problem of poor adsorption performance of electrospun fiber membranes, the present invention provides an ion exchange nanofiber membrane with high ion adsorption function and a preparation method thereof. The nanofiber membrane prepared by the present invention has the characteristics of excellent adsorption performance and diverse adsorption types.

[0005] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] A method for preparing an ion exchange nanofiber membrane with high ion adsorption function comprises the following steps:

[0007] 1) preparing a polyacrylonitrile spinning solution and a polyethyleneimine spinning solution respectively, and mixing and stirring the obtained two spinning solutions to obtain a mixed solution;

[0008] 2) The mixed solution is subjected to an electrostatic spinning process to prepare a polyacrylonitrile / polyethyleneimine nanofiber membrane.

[0009] Furthermore, in step 1), the polyacrylonitrile spinning solution preparation process includes: adding polyacrylonitrile to N,N-dimethylformamide solvent, stirring and dissolving at 40° C. for at least 4 hours, to obtain a spinning solution with a polyacrylonitrile concentration of 10%.

[0010] Furthermore, in step 1), the polyethyleneimine spinning solution preparation process includes: adding polyethyleneimine to N,N-dimethylformamide solvent, stirring and dissolving at 60° C. for at least 4 hours, to obtain a spinning solution with a polyethyleneimine concentration of 27%.

[0011] Furthermore, in step 1), during the preparation of the mixed solution, the polyethyleneimine spinning solution is poured into the polyacrylonitrile spinning solution and stirred at room temperature for at least 2 hours, wherein the mass ratio of polyacrylonitrile:polyethyleneimine is 3:2, and then allowed to stand for at least 10 hours.

[0012] Furthermore, in step 2), the electrospinning conditions are: voltage of 17 kV, flow rate of 0.0003 mm·s -1 , the syringe advancement speed is 1.5mL / h, and the distance between the nozzle and the receiver is 18cm.

[0013] An ion exchange nanofiber membrane with high ion adsorption function is obtained by using any of the above methods.

[0014] An application of the polyacrylonitrile / polyethyleneimine nanofiber membrane in semiconductor filtration and wastewater treatment, removing Cu by the polyacrylonitrile / polyethyleneimine nanofiber membrane 2+ Cr 6+ and CR.

[0015] Beneficial effects of the present invention:

[0016] The average diameter of the polyacrylonitrile / polyethyleneimine nanofibers of the present invention is 743.33 nm. The structures and properties of various nanofiber membranes are characterized by mechanical properties, contact angle, Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction spectroscopy (XRD). It can be seen that the surface of the PAN / PEI nanofiber membrane is hydrophilic.

[0017] The polyacrylonitrile / polyethyleneimine nanofiber membrane of the present invention is effective for Cu 2+ Cr 6+ The adsorption effect of CR was excellent, reaching 124 mg / g, 176 mg / g and 35 mg / g respectively. The adsorption of Cu by polyacrylonitrile / polyethyleneimine nanofiber membrane was 2+ Cr 6+ The optimal adsorption pH of and CR were 6, 2 and 6 respectively, the optimal adsorption starting concentrations were 900 mg / L, 300 mg / L and 35 mg / L respectively, and the optimal adsorption times were 3.5 h, 3.5 h and 3.5 h respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 The SEM images and diameter distribution diagrams of the nanofibers of the embodiments of the present invention are as follows: (a) PAN nanofibers; (b) PAN / PEI nanofibers; (c) PAN / PEI / PVP nanofibers; (d) PAN / β-cyclodextrin nanofibers; (e) PAN / CNT nanofibers; (f) PAN / ZnO nanofibers

[0020] Figure 2 FTIR graphs of PAN, PAN / PEI, PAN / β-cyclodextrin, PAN / PEI / PVP, PAN / CNT and PAN / ZnO nanofiber membranes according to the embodiments of the present invention.

[0021] Figure 3 These are the XRD patterns of PAN, PAN / PEI, PAN / PEI / PVP, PAN / β-cyclodextrin, PAN / CNT and PAN / ZnO nanofiber membranes according to the embodiments of the present invention.

[0022] Figure 4 The contact angle diagrams of the nanofiber membranes of the embodiments of the present invention are as follows: (a) PAN nanofiber membrane; (b) PAN / PEI nanofiber membrane; (c) PAN / β-cyclodextrin nanofiber membrane; (d) PAN / CNT nanofiber membrane; (e) PAN / ZnO nanofiber membrane

[0023] Figure 5 Graphs showing the mechanical properties of PAN, PAN / PEI, PAN / β-cyclodextrin, PAN / PEI / PVP, PAN / CNT and PAN / ZnO nanofiber membranes according to the embodiments of the present invention.

[0024] Figure 6 The effect of initial concentration on adsorption performance of the embodiment of the present invention: (a) Cu 2+ ; (b) Cr 6+ ; (c)CR.

[0025] Figure 7 The effect of solution pH on adsorption performance of the embodiment of the present invention: (a) Cu 2+ ; (b) Cr 6+ ; (c)CR.

[0026] Figure 8 The effect of contact time on adsorption performance of the embodiment of the present invention: (a) Cu 2+ ; (b) Cr 6+ ; (c)CR.

[0027] Fig. 9 This is a comparison chart of the adsorption capacity of the nanofiber membranes according to the embodiments of the present invention. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] Example 1

[0030] An ion exchange nanofiber membrane with high ion adsorption function, the preparation method comprises the following steps:

[0031] A certain amount of PAN (Mw = 150000) powder was weighed into a glass bottle using a 1 / 10,000 balance, and DMF solution was added. The bottle was then sealed with a sealing film, and the solution was placed on a magnetic stirrer at 40°C for 4 hours to prepare a PAN solution with a mass concentration of 10%.

[0032] Weigh a certain amount of PEI (Mw=70000, 50% aqueous solution) with a 1 / 10,000 balance and dissolve it in DMF. Stir at 60°C for 4 hours to prepare a 27% PEI spinning solution. Preparation of PAN / PEI spinning solution: Pour the PEI spinning solution into the PAN spinning solution (the mass ratio of PAN:PEI is 3:2), and continue to stir the mixed solution at room temperature for 2 hours. After standing for 10 hours, spin the solution. The electrospinning conditions are: voltage: 17kV, flow rate: 0.0003mm·s -1 , propulsion speed is 1.5mL / h, receiving distance: 18cm.

[0033] Example 2

[0034] An ion exchange nanofiber membrane with high ion adsorption function, the preparation method comprises the following steps:

[0035] PAN nanofiber membrane: Weigh a certain amount of PAN (Mw = 150000) powder in a glass bottle using a 1 / 10,000 balance, add DMF solution. Then seal with a sealing film, place the solution on a magnetic stirrer at 40°C and stir and dissolve for 4 hours to prepare a PAN solution with a mass concentration of 10%. After standing for 10 hours, the solution was spun. The spinning conditions were the same as those in Example 1.

[0036] Example 3

[0037] An ion exchange nanofiber membrane with high ion adsorption function, the preparation method comprises the following steps:

[0038] PAN / PEI / PVP nanofiber membrane: A small amount of PVP was added to the PAN / PEI solution prepared under the conditions of Example 1, and then stirred under a magnetic stirrer for 6 hours to obtain a PAN / PEI / PVP blended solution. After standing for 10 hours, the solution was spun. The spinning conditions were the same as those of Example 1.

[0039] Example 4

[0040] An ion exchange nanofiber membrane with high ion adsorption function, the preparation method comprises the following steps:

[0041] PAN / β-cyclodextrin nanofiber membrane: 40% β-cyclodextrin solution was added to 10% PAN solution and sealed with a sealing film. The solution was placed on a magnetic stirrer at 40°C and stirred for 4 hours. The spinning conditions were the same as those in Example 1.

[0042] Example 5

[0043] An ion exchange nanofiber membrane with high ion adsorption function, the preparation method comprises the following steps:

[0044] PAN / CNT nanofiber membrane: CNT accounting for 4% of PAN was added to a 12% PAN solution and then sealed with a sealing film. The solution was placed on a magnetic stirrer and the temperature was set to 40°C for stirring and dissolving for 4 hours. After the stirring was completed, the solution was allowed to stand for 10 hours before spinning. The spinning conditions were the same as those in Example 1.

[0045] Example 6

[0046] An ion exchange nanofiber membrane with high ion adsorption function, the preparation method comprises the following steps:

[0047] PAN / ZnO nanofiber membrane: Add 1% ZnO to a 12% PAN solution and seal it with a sealing film. Place the solution on a magnetic stirrer and set the temperature to 40°C for 4 hours to make ZnO fully and evenly distributed in the solution. After stirring, let it stand for 10 hours. The spinning conditions are the same as those in Example 1.

[0048] Results and Discussion

[0049] Nanofiber morphology observation and analysis

[0050] from Figure 1 It can be seen that when PEI is added to the spinning solution, the viscosity of the spinning solution will be higher, resulting in droplets appearing at the nozzle during the spinning process. However, under the action of voltage, the droplets will form fibers that stick together, and the average fiber diameter reaches 743.33 mm. The addition of CNT, ZnO and β-cyclodextrin will increase the porosity of the nanofiber membrane and the appearance of microsphere structure due to their own characteristics, so the morphology does not change, but the fiber diameter increases to varying degrees, which are 370.07nm, 188.37nm and 316.96nm respectively. This is because the addition of another substance increases the viscosity of the spinning solution.

[0051] Infrared spectroscopy (FTIR) analysis

[0052] Figure 2 It can be seen that at 1454cm -1 、2252cm -1 There are significant absorption peaks in all four nanofiber membranes, which are characteristic peaks formed by the vibration of -CH and C≡N groups. This shows that the molecular structure of PAN has not changed during the mixing and stirring process with PEI, β-cyclodextrin and PEI / PVP materials. The infrared spectrum of PAN / PEI nanofiber membrane is at 1645cm -1 There is an absorption peak at 2252 cm-1, which is the imide group and indicates the presence of PEI. -1 and 1454cm -1 There is an absorption peak at 1060cm -1 A characteristic absorption peak of —O— appeared at , which is the group contained in β-cyclodextrin, indicating the presence of β-cyclodextrin in the membrane.

[0053] The infrared spectrum of PAN / PEI / PVP nanofiber membrane shows that -1There is a sharp strong peak at the position. This is because of the presence of the nitrile group C≡N and its stretching vibration. Due to the excellent hydrophilicity of PVP and the small number of methyl structures, the infrared shows this trend. It can be seen that the PAN / CNT nanofiber membrane is not much different from the PAN nanofiber membrane. This is because the added CNT does not have an obvious infrared characteristic peak, but it has infrared absorption characteristics, so it will cause the peak intensity of the characteristic absorption peak of the nanofiber membrane to be weaker, and the peak position will be slightly shifted. The addition of ZnO to the PAN / ZnO nanofiber membrane makes the peak at 1680cm -1 The intensity of the absorption peak at is higher than that of several other nanofiber membranes, which proves the successful spinning of ZnO.

[0054] X-ray diffraction (XRD) analysis

[0055] Depend on Figure 3 It can be seen that there are two crystallization peaks near 14.5° and 26°, which correspond to PAN (010), and the (300) plane proves the existence of PAN. After adding PEI, it can be seen that its diffraction peak is basically consistent with that of PAN nanofiber membrane, indicating that PEI does not destroy the crystal structure of PAN. The diffraction peaks of PAN nanofiber membrane and PAN / β-cyclodextrin at 2θ=5°-60° are very similar. No new crystallization peaks appear after adding β-cyclodextrin, indicating that the addition of β-CD does not form new molecular agglomerations. There is a strong diffraction peak at 2θ=25.5°, corresponding to the crystal plane (002), which proves that PAN / CNT nanofiber membrane contains CNT. The characteristic peaks of ZnO are 31.8°, 34.4° and 36.3°, which belong to the (100), (002) and (101) of the ZnO crystal plane. It can be observed in the figure that these positions have peaks, thus proving that ZnO is successfully spun in.

[0056] Surface wettability analysis

[0057] Figure 4 From left to right, the state of the droplet just contacting the nanofiber membrane, the state of the droplet contacting the nanofiber membrane for 1 second, and the state of the droplet contacting the nanofiber membrane for 3 seconds are shown. It can be seen from the figure that the state change of the PAN nanofiber membrane within 3 seconds is the smallest, so its contact angle is the largest, which shows that the PAN nanofiber membrane has a certain hydrophobicity. The PAN / PEI nanofiber has obvious changes within 3 seconds and the droplet almost disappears at 3 seconds, indicating that the nanofiber membrane with the addition of PEI is more hydrophilic. From the above figure, it can be observed that the droplet is immediately absorbed by the membrane when it contacts the PAN / β-cyclodextrin, PAN / ZnO and PAN / CNT nanofiber membranes, and the droplet is almost invisible on the membrane, which shows that the addition of β-cyclodextrin, ZnO and CNT makes the membrane have excellent hygroscopicity.

[0058] Mechanical properties analysis

[0059] according to Figure 5 It can be seen that the mechanical properties and elongation at break of the nanofiber membrane with the addition of PEI have been significantly improved. This shows that PEI increases the mechanical properties of the nanofiber membrane. The mechanical properties of the nanofiber membrane with the addition of a small amount of PVP have been improved, indicating that adding a small amount of polymers with good mechanical properties during the spinning solution preparation process can greatly improve the mechanical properties of the nanofiber membrane. The strength of the PAN / β-cyclodextrin nanofiber membrane is not high, which means that the presence of β-cyclodextrin cannot increase the strength of the nanofiber membrane. The strength of the PAN / CNT nanofiber membrane is not much different from the mechanical properties of the PAN / PEI nanofiber membrane, which shows that the addition of CNT also increases the mechanical properties of the PAN nanofiber membrane. The nanofiber membrane with the addition of ZnO has also greatly improved the mechanical properties of the nanofiber membrane.

[0060] Analysis of factors affecting adsorption experiments

[0061] (1) Effect of initial solution concentration on adsorption performance

[0062] Figure 6 (a) Figure 6 (b) and Figure 6 (c) The effects of five nanofiber membranes on Cu at different initial concentrations 2+ Cr 6+ The adsorption curves of Cu and CR were shown in Figure 2. The solution pH was adjusted to the optimal level and adsorption was performed at room temperature for 6 h. 2+ Cr 6+ As the initial concentration of CR increases, the adsorption amount of the five nanofiber membranes increases. After reaching the optimal initial concentration, the adsorption amount tends to remain unchanged. This shows that when the initial concentration is small, the nanofiber membrane can provide enough adsorption sites and the adsorption sites are effectively utilized. As the initial concentration increases, the adsorption sites are insufficient and the nanofiber membrane adsorbs Cu. 2+ Cr 6+ and CR has reached saturation.

[0063] (2) Effect of solution pH on adsorption performance

[0064] During the adsorption process, changes in the pH value of the solution will affect the surface charge of the adsorbent and the existence form of the adsorbate, thereby affecting the binding of the adsorbent to the adsorbate. Figure 7 (a), (b) and (c) are the effects of four nanofiber membranes on Cu at different pH values. 2 + Cr 6+ And the adsorption curves of CR.

[0065] (3) Effect of contact time on adsorption performance

[0066] Figure 8 The curve of the adsorption amount of nanofiber membrane over time. In the experiment, the optimal adsorption concentration was used and the pH was adjusted to the optimal value. The adsorption process can be roughly divided into three stages, including the acceleration stage, the rate-limiting stage and the equilibrium stage. In the initial stage, due to the high content of heavy metal ions, they are generally diffused and distributed on the surface of nanofibers through concentration differences. A part of Cu 2+ Cr 6+ The CR diffuses into the nanofibers and reacts with the adsorption sites on the fibers. In this stage, physical adsorption and chemical adsorption exist simultaneously, mainly due to coordination. As time goes by, some heavy metal ions begin to distribute and accumulate inside and on the surface of the fibers, and the concentration difference at the adsorption interface begins to disappear. The reaction gradually enters the rate-limiting stage. In this stage, the adsorption process is mainly chemical adsorption, which mainly relies on the coordination of the active groups of heavy metal ions. When the heavy metal ions fully cover the adsorption sites of the fibers, the adsorption reaches saturation.

[0067] According to the results shown in the figure, the adsorption of Cr 6+ The adsorption capacity of PAN / PEI nanofiber membrane is much higher than that of other nanofiber membranes, reaching 176 mg / g. 2+ In terms of adsorption, the adsorption capacity of PAN / PEI nanofiber membrane is the highest, reaching 124 mg / g. In terms of adsorption of CR, the adsorption capacity of PAN / PEI nanofiber membrane reaches 35 mg / g. The adsorption of CR by PAN / PEI nanofiber membrane is not much different from that of other nanofiber membranes. This is because the initial concentration of CR is very small, but it also shows that other substances have a high adsorption capacity for CR. In summary, PAN / PEI nanofiber membrane has great advantages in adsorbing heavy metal ions. PAN / PEI nanofiber membrane can be used to adsorb heavy metal ions in the treatment of water pollution.

[0068] The embodiments described above provide a detailed description of the preparation scheme of the present invention. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing an ion exchange nanofiber membrane with high ion adsorption function, characterized in that: The following steps are involved: 1) preparing polyacrylonitrile spinning solution and polyethyleneimine spinning solution respectively, and mixing and stirring the obtained two spinning solutions to obtain a mixed solution; 2) The mixed solution is subjected to an electrostatic spinning process to prepare a polyacrylonitrile / polyethyleneimine nanofiber membrane, namely, an ion exchange nanofiber membrane with high ion adsorption function.

2. The method for preparing the ion exchange nanofiber membrane with high ion adsorption function according to claim 1, characterized in that: In step 1), the polyacrylonitrile spinning solution preparation process includes: adding polyacrylonitrile to N,N-dimethylformamide solvent, stirring and dissolving at 40° C. for at least 4 hours, to obtain a spinning solution with a polyacrylonitrile mass concentration of 10%.

3. The method for preparing the ion exchange nanofiber membrane with high ion adsorption function according to claim 1, characterized in that: In step 1), the polyethyleneimine spinning solution preparation process includes: adding polyethyleneimine to N,N-dimethylformamide solvent, stirring and dissolving at 60° C. for at least 4 hours, to obtain a spinning solution with a polyethyleneimine mass concentration of 27%.

4. The method for preparing the ion exchange nanofiber membrane with high ion adsorption function according to claim 1, characterized in that: In step 1), during the preparation of the mixed solution, the polyethyleneimine spinning solution is poured into the polyacrylonitrile spinning solution and stirred at room temperature for at least 2 hours, wherein the mass ratio of polyacrylonitrile:polyethyleneimine is 3:2, and then allowed to stand for at least 10 hours.

5. The method for preparing the ion exchange nanofiber membrane with high ion adsorption function according to claim 1, characterized in that: In step 2), the electrospinning conditions are: voltage of 17 kV, flow rate of 0.0003 mm·s-1, syringe propulsion speed of 1.5 mL / h, and distance between nozzle and receiver of 18 cm.

6. An ion exchange nanofiber membrane with high ion adsorption function, characterized in that: The method is obtained by any one of claims 1 to 5.

7. Application of the ion exchange nanofiber membrane with high ion adsorption function as claimed in claim 6 in semiconductor filtration or wastewater treatment, characterized in that: Removal of Cu by the polyacrylonitrile / polyethyleneimine nanofiber membrane 2+ Cr 6+ and CR.

Images