PVDF-HFP (Polyvinylidene Fluoride-Hexafluoropropylene)-based polymer containing membrane and preparation method and application thereof

Abstract

The invention discloses a PVDF-HFP (Polyvinylidene Fluoride-Hexafluoropropylene)-based polymer containing membrane as well as a preparation method and application thereof, and belongs to the technical field of heavy metal polluted water treatment. And the polymer raw material of the PVDF-HFP based polymer containing membrane is polyvinylidene fluoride-hexafluoropropylene. Compared with a conventional polymer-based containing membrane, the PVDF-HFP-based polymer containing membrane prepared by using polyvinylidene fluoride-hexafluoropropylene as a polymer has obviously higher separation efficiency on copper ions in a water body. Besides, an MOFs material is further introduced on the basis of the PVDF-HFP-based polymer containing membrane, so that the separation efficiency of the polymer containing membrane on the copper ions in the water body is improved, and the problem that the MOFs are easy to generate skeleton collapse in the water is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of treating heavy metal-polluted water bodies, and particularly relates to a PVDF-HFP-based polymer inclusion membrane, a preparation method thereof, and an application thereof. Background Art

[0002] Copper, as an essential element for the health of organisms, exists in proteins and is beneficial to human health in trace amounts. However, when the copper content in organisms exceeds the standard, it will affect health. As a common heavy metal pollutant, copper ions have the characteristics of a long half-life, high mobility, and strong bioaccumulation, and can enter the human body through the food chain and drinking water.

[0003] Currently, the main methods for treating copper ions in water include advanced oxidation methods, biological treatment methods, ion exchange methods, adsorption methods, and membrane filtration methods, etc.

[0004] ① Advanced oxidation method

[0005] The advanced oxidation method refers to directly mineralizing pollutants in water into CO2, H2O, or other small-molecule inorganic substances through chemical or physicochemical means. When the advanced oxidation technology is used to treat Cu 2+ ions, for Cu-EDTA, free radicals that can break the coordination bond of Cu-EDTA are generated to achieve the purpose of removal. In 2021, Han Zijian used the advanced oxidation technology under the conditions of a solution pH of 3, a current density of 10 mA / cm 2 , a PDS dosage of 6 mmol / L, and an electrode spacing of 3 cm. The removal rate of Cu 2+ reached 92.62% within 4 h.

[0006] ② Biological treatment method

[0007] The biological treatment method uses microorganisms and plants to complete the purification of wastewater through biotechnology means. The biological treatment method includes biological precipitation method and biological adsorption method. When treating Cu 2+ ions, the biological adsorption method is mainly used, and the adsorption of Cu 2+ ions by microorganisms produces a solidification effect. The biological method has a low secondary pollution rate or no secondary pollution when treating harmful substances, and the biological method is easy to industrialize. The cost of microbial treatment is low, and the treatment effect is good. It is an environmentally friendly sewage treatment material with development prospects. In 2021, the black algae-based magnetic nanocomposite synthesized by Gao Hairong et al. had an adsorption rate of up to 97.12% for Cu 2+ ions in water, and the adsorption capacity reached 24.28 mg / g. In the same year, Zeng Fancheng screened out a combination of biological strains and graphene additives, and the adsorption rate of Cu 2+ ions reached 86.01%.

[0008] ③ Ion exchange method

[0009] The ion exchange method mainly uses ion exchange resins to remove heavy metals. When using the ion exchange method, the heavy metals to be treated need to exist in the form of ions so as to exchange with the exchangeable ions in the resin. Yang Jin et al. used 001×7 resin to treat Cu 2+ After treatment, the concentration decreased from the initial 1680 mg / L to below 0.5 mg / L, meeting the discharge standard.

[0010] ④ Adsorption method

[0011] The adsorption method uses the characteristics of large specific surface area and porosity of substances to adsorb and remove target substances. Common adsorbents include activated carbon, bio-adsorbents, nanotubes, etc. New adsorption materials include metal-organic framework materials (MOFs). The huge specific surface area, special pore structure, and unique metal sites of MOFs materials enable them to exhibit excellent performance in the adsorption field. In 2014, Jiang Yujuan used modified activated carbon to increase the adsorption rate of Cu-EDTA complex to 97%, and the adsorption rate did not decrease significantly after the activated carbon was regenerated three times.

[0012] ⑤ Membrane filtration method

[0013] The membrane filtration method uses membrane materials to filter and separate pollutants to achieve the purpose of purification. It can be divided into: ultrafiltration, reverse osmosis, nanofiltration, and electroosmosis according to different types of technologies. Membrane separation technology uses the permeability of polymer membranes and, with the help of chemical potential difference or other energy drives, enables pollutants to enter the analytical phase through the polymer membrane, achieving the separation state of pollutants and the aqueous phase and completing purification. Membrane separation technology can achieve the functions of adsorption, separation, and extraction simultaneously. In 2017, Zhao Kai et al. used the EC-UF technology to achieve a 99.6% removal rate of copper ions in 20 minutes. In 2012, Wei Yuqing used the complexing agent acrylic maleic acid copolymer and self-made PVB hollow fiber ultrafiltration membrane to achieve a 99.8% treatment rate of Cu 2+

[0014] In addition to the traditional methods for treating copper ions in water, whether new removal methods can be provided is a research direction worthy of attention in this field currently. Summary of the Invention

[0015] The purpose of the present invention is to provide a PVDF-HFP-based polymer inclusion membrane, its preparation method, and application. By using polyvinylidene fluoride-hexafluoropropylene as the polymer and bis(2-ethylhexyl) phosphate as the carrier, a polymer inclusion membrane (PIM) capable of efficiently separating copper ions in water is prepared. Adding MOFs to the PIM can further enhance the separation efficiency of copper ions in water.

[0016] To achieve the above purpose, the present invention provides the following technical solutions:

[0017] ​One of the technical solutions of the present invention: Provide a PVDF-HFP-based polymer inclusion membrane, wherein the polymer inclusion membrane uses polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) as the polymer and bis(2-ethylhexyl) phosphate (D2EHPA) as the carrier.

[0018] Preferably, the mass of the bis(2-ethylhexyl) phosphate accounts for 30-60% of the total mass of the polyvinylidene fluoride-hexafluoropropylene and the bis(2-ethylhexyl) phosphate.

[0019] More preferably, the mass of the bis(2-ethylhexyl) phosphate accounts for 60% of the total mass of the polyvinylidene fluoride-hexafluoropropylene and the bis(2-ethylhexyl) phosphate.

[0020] Two of the technical solutions of the present invention: Provide a preparation method of the above PVDF-HFP-based polymer inclusion membrane, including the following steps:

[0021] Blend polyvinylidene fluoride-hexafluoropropylene and bis(2-ethylhexyl) phosphate in a solvent to prepare a casting solution, and volatilize the solvent in the casting solution to obtain the PVDF-HFP-based polymer inclusion membrane.

[0022] Preferably, the solvent is acetone.

[0023] More preferably, the volatilization temperature is 60°C.

[0024] Three of the technical solutions of the present invention: Provide a MOFs-modified PVDF-HFP-based polymer inclusion membrane, wherein the MOFs-modified PVDF-HFP-based polymer inclusion membrane uses polyvinylidene fluoride-hexafluoropropylene as the polymer, MOFs as the filler, and bis(2-ethylhexyl) phosphate as the carrier.

[0025] Due to the weak binding bonds between elements, common MOFs materials are extremely prone to framework collapse in water and are limited in their application in water. However, the structure of PIM is stable. Combining MOFs with PIM not only improves the separation efficiency of PIM for copper ions but also solves the problem of easy framework collapse of MOFs in water.

[0026] Preferably, the mass ratio of the polyvinylidene fluoride-hexafluoropropylene to the bis(2-ethylhexyl) phosphate is 4:6; the addition amount of the MOFs does not exceed 2% of the total mass of the polyvinylidene fluoride-hexafluoropropylene and the bis(2-ethylhexyl) phosphate.

[0027] Four of the technical solutions of the present invention: Provide a preparation method of the above MOFs-modified PVDF-HFP-based polymer inclusion membrane, including the following steps:

[0028] A casting solution is prepared by blending polyvinylidene fluoride - hexafluoropropylene, MOFs, and bis(2 - ethylhexyl) phosphate in a solvent. The solvent in the casting solution is volatilized to obtain a MOFs - modified PVDF - HFP - based polymer inclusion membrane.

[0029] Preferably, the solvent is acetone.

[0030] More preferably, the temperature of volatilization is 60 °C.

[0031] Technical solution five of the present invention: Provide an application of the above PVDF - HFP - based polymer inclusion membrane in separating copper ions in water.

[0032] Technical solution six of the present invention: Provide an application of the above MOFs - modified PVDF - HFP - based polymer inclusion membrane in separating copper ions in water.

[0033] The beneficial technical effects of the present invention are as follows:

[0034] Compared with conventional polymer - based inclusion membranes, the PVDF - HFP - based polymer inclusion membrane prepared by using polyvinylidene fluoride - hexafluoropropylene as the polymer in the present invention has significantly higher separation efficiency for copper ions in water. In addition, on the basis of the PVDF - HFP - based polymer inclusion membrane, further introducing MOFs materials not only improves the separation efficiency of the polymer inclusion membrane for copper ions in water, but also solves the problem that MOFs are prone to framework collapse in water. Description of the Drawings

[0035] Figure 1 For testing the Cu 2+ separation ability of the present invention, the Cu 2+ separation device.

[0036] Figure 2 For the separation performance of each PIM membrane prepared in Example 1 and Comparative Examples 1 - 2 for Cu 2+ .

[0037] Figure 3 For the dynamic separation situation of the PVDF - HFP - based PIM with 60% D2EHPA content in Example 1 for Cu 2+ .

[0038] Figure 4 SEM images of PVDF - HFP - based PIMs with different D2EHPA contents prepared in Example 1.

[0039] Figure 5 The infrared spectra of the PVDF - HFP - based PIM with 60% D2EHPA content in Example 1 and the raw materials used are shown in Figure 5, where a is the infrared spectrum of the PVDF-HFP-based PIM, and b is the infrared spectrum of the PVDF-HFP-based PIM and its raw materials.

[0040] Figure 6 It is the infrared spectrum of the PVDF-based PIM with 30% D2EHPA content in Comparative Example 1 and its raw materials used. Among them, a is the infrared spectrum of the PVDF-based PIM, and b is the infrared spectrum of the PVDF-based PIM and its raw materials.

[0041] Figure 7 It is the infrared spectrum of the PVC-based PIM with 60% D2EHPA content in Comparative Example 2 and its raw materials used. Among them, a is the infrared spectrum of the PVC-based PIM, and b is the infrared spectrum of the PVC-based PIM and its raw materials.

[0042] Figure 8 It is the mechanical properties of the PVDF-HFP-based PIM with different D2EHPA contents prepared in Example 1. Among them, a is the tensile strength, and b is the stress-strain curve.

[0043] Figure 9 It is the mechanical properties of the PVDF-HFP-based PIM with different volatilization temperatures prepared in Example 2. Among them, a is the tensile strength, and b is the stress-strain curve.

[0044] Figure 10 It is the SEM image of the MOF-modified PVDF-HFP-based PIM with different MOF contents prepared in Example 3.

[0045] Figure 11 It is the infrared spectrum of the MOF-modified PVDF-HFP-based PIM with 1.5 g of Zn-MOFs added in Example 3 and its raw materials used. Among them, a is the infrared spectrum of the MOF-modified PVDF-HFP-based PIM, and b is the infrared spectrum of the MOF-modified PVDF-HFP-based PIM and its raw materials.

[0046] Figure 12 It is the separation performance of the MOF-modified PVDF-HFP-based PIM with different MOF contents prepared in Example 3 for Cu 2+ .

[0047] Figure 13 It is the dynamic separation situation of the MOF-modified PVDF-HFP-based PIM with 1.5 g of Zn-MOFs added in Example 3 for Cu 2+ .

[0048] Figure 14 It is the best separation rate of each PIM prepared in Example 1, Example 3, and Comparative Examples 1-2 for Cu 2+ . Detailed Embodiments

[0049] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation on the present invention, but rather as a more detailed description of certain aspects, features, and implementation schemes of the present invention. It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention.

[0050] It should be noted that the aspects not described in detail in the present invention are all conventional operation means in the art and are not the focus of the present invention.

[0051] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0052] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention.

[0053] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0054] The MOFs material used in the present invention is self-made Zn-MOFs, and the preparation steps are as follows:

[0055] Add Zn(NO3)2·6H2O (0.893 g, 0.3 mmol), 5-chloro-8-hydroxyquinoline (0.0539 g, 0.3 mmol), 2,5-thiophenedicarboxylic acid (0.0517 g, 0.3 mmol) and 5 mL of N,N-dimethylformamide (DMF) into a 50 mL beaker. After shaking for 1 min, pour the well-mixed solution into a reaction kettle. Place the reaction kettle in an oven at 120 °C and heat for 3 days. After three days, cool the temperature by 5 °C per hour to room temperature. Then wash it 3 times with DMF, filter, and dry to obtain yellow block-shaped crystals, which are Zn-MOFs. The yield is 62.9% (0.033 g) based on Zn(NO3)2·6H2O.

[0056] All other materials used in the present invention except the MOFs material are commercially available products.

[0057] In the examples and comparative examples of the present invention, the normal temperature refers to a temperature of 20 ± 10 °C.

[0058] Example 1

[0059] Preparation of PVDF - HFP - based PIM:

[0060] Weigh 1.2 g of PVDF - HFP in a conical flask and dissolve it in 20 mL of acetone. Add different masses of D2EHPA (the addition amounts are 20%, 30%, 40%, 50%, 60% and 70% of the total mass of D2EHPA and PVDF - HFP, corresponding to 0.3 g, 0.51 g, 1.13 g, 1.2 g, 1.8 g and 2.8 g respectively). Seal it with plastic wrap, place it on a constant - temperature magnetic stirrer, and stir at room temperature for 4 h. Pour the clear, transparent and colorless solution into a 150×150 mm film former. After the liquid covers the film former, put it into an oven at 60 °C. Take it out after 30 min, soak it in deionized water for 10 min, take it out with tweezers to obtain a uniform and semi - transparent PVDF - HFP - based PIM, and then put it into a self - sealing bag for storage.

[0061] Comparative Example 1

[0062] Preparation of PVDF - based PIM:

[0063] Weigh 1.2 g of PVDF in a conical flask and dissolve it in 20 mL of DMF. Stir at 70 °C for 3 h. After the temperature cools to 45 °C, add different masses of D2EHPA (the addition amounts are 20%, 30%, 40%, 50%, 60% and 70% of the total mass of D2EHPA and PVDF, corresponding to 0.3 g, 0.51 g, 1.13 g, 1.2 g, 1.8 g and 2.8 g respectively), and stir for 4 h. Seal the flask with plastic wrap during the stirring process. After the stirring is completed, pour the clear, transparent and colorless solution into a 150×150 mm film former, and put it into a constant - temperature drying oven to volatilize and dry at 140 °C for 30 min to obtain a colorless and transparent PVDF - based PIM. Put the obtained product into a self - sealing bag for storage.

[0064] Comparative Example 2

[0065] Preparation of PVC - based PIM:

[0066] Weigh 1.2 g of PVC in a conical flask and dissolve it in 20 mL of tetrahydrofuran (THF). Add different masses of D2EHPA (the addition amounts are 20%, 30%, 40%, 50%, 60% and 70% of the total mass of D2EHPA and PVC, corresponding to 0.3 g, 0.51 g, 1.13 g, 1.2 g, 1.8 g and 2.8 g respectively). Seal it with plastic wrap and stir in a magnetic stirrer for 4 h. Pour the obtained clear, transparent and colorless solution into a 150×150 mm film former, and volatilize at 70 °C for 30 min to obtain a colorless and transparent PVC - based PIM, which is put into a self - sealing bag for storage.

[0067] Measure the separation performance of each PIM membrane prepared in Example 1 and Comparative Examples 1-2 for Cu 2+ , Cu 2+ The separation device is shown in Figure 1 , Cu 2+ The separation device consists of two left and right cylinders, separation clips, and fixing bolts. The volumes of the two left and right cylinders are 160 mL, and the diameter of the clip is 30 mm.

[0068] During separation, 150 mL of a feed liquid phase with a concentration of 10 mg / mL of Cu 2+ and 150 mL of a stripping phase with pH = 9 are respectively added to the two left and right chambers. After adding a magnetic stir bar, it is placed on a T09-1S magnetic stirrer, and the rotation speed is set to 1300 r / min. During the separation process, liquid samples are taken every 1 h, 0.5 mL each time, and 0.5 mL of the liquid is replenished; the liquid samples are added to a 10 mL colorimetric tube, 2 mL of EDTA color-developing solution is added, and then it is made up to 10 mL with deionized water. The absorbance is measured using an ultraviolet spectrophotometer at a wavelength of 750 nm, and each sample is detected three times and the average value is taken. According to the Cu 2+ standard curve fitting formula (y = 0.1898x + 0.0928, where y is the absorbance and x is the Cu 2+ concentration in mg / mL), calculate the Cu 2+ content and separation rate (separation rate Z = (10 - x×2) / 10×100%, where x is the Cu 2+ concentration in mg / mL).

[0069] The measured separation performance of each PIM membrane prepared in Example 1 and Comparative Examples 1-2 for Cu 2+ is shown in Figure 2 .

[0070] From Figure 2 it can be seen that as the carrier content increases, the change rules of the separation rates of the three different substrate PIMs for Cu 2+ are the same (the best is when the carrier content is 60%), but the overall separation rate of the PVDF-HFP-based PIM is higher than that of the PVDF-based PIM and the PVC-based PIM. By comparison, it is found that when the modified material PVDF-HFP of PVDF is used as the film-forming substrate, the separation effect for Cu 2+ can be greatly improved. PVDF-HFP contains more polar functional groups. With the addition of D2EHPA, the polar interaction between the functional groups causes the molecular chain arrangement to be more regular, and it is easier to establish a continuous transport channel. Therefore, the separation effect based on PVDF-HFP is better.

[0071] The PVDF-HFP-based PIM with 60% D2EHPA content in Example 1 for Cu2+ The dynamic separation situation is shown in Figure 3 .

[0072] Figure 3 It shows that the Cu 2+ concentration continuously decreases with time, and the separation rate continuously increases with time. The separation rate is relatively large within the first 12 hours, reaching a maximum of 0.992 mg / h. After 12 hours, the separation rate gradually reaches stability. Since the transport separation relies on the self-concentration difference, when the concentration of the feed liquid phase decreases and the concentration of the stripping phase increases, the transport rate gradually decreases until it stops.

[0073] SEM images of PVDF-HFP-based PIMs with different D2EHPA contents prepared in Example 1 are shown in Figure 4 .

[0074] Figure 4 It shows that with the increase of the carrier content, the microscopic imaging of PVDF-HFP-based PIMs presents obvious changes. When the carrier content is 20%, it can be seen from the microscopic imaging that the membrane structure is relatively disordered and shows filamentous entanglement; when the carrier content is greater than 30%, the membrane structure becomes more regular, the filamentous entanglement phenomenon disappears, the membrane composition distribution is relatively uniform, and the pore diameter of the membrane shows an increasing trend with the increase of the carrier content. When the carrier content is 50%, the distribution of each component is the most uniform, the pore distribution is dense, but the pore diameter is small. When the carrier content is 60%, dark dot-like structures appear in the microscopic imaging, but there is no obvious difference from the microscopic view of the membrane, and the pore diameter of the membrane is relatively ideal at this time. When the carrier content is 70%, a circular distribution appears in the membrane structure distribution, and with the increase of the carrier content, the pores of the membrane gradually increase.

[0075] Infrared spectra of PVDF-HFP-based PIM with 60% D2EHPA content in Example 1 and the raw materials used are shown in Figure 5 , where a is the infrared spectrum of PVDF-HFP-based PIM, and b is the infrared spectrum of PVDF-HFP-based PIM and the raw materials.

[0076] Figure 5 It shows that in a, the stretching vibration peak of C=O is at 3391.54 cm -1 ; the symmetric stretching vibration of -CH2- is at 2960.56 cm -1 , 2933.09 cm -1 , and the bending vibration peak of -CH2- is at 1403.52 cm -1 ; the symmetric stretching vibration of CF2 is at 1179.57 cm -1 ; the characteristic peaks of PVDF crystallization are at 875.35 cm -1 , 837.32 cm -1 ; and at 1025.35 cm-1 is the characteristic peak of P-O. Combining with Figure 5 b in

[0077] The infrared spectra of the PVDF-based PIM with 30% D2EHPA content in Comparative Example 1 and the raw materials used are shown in Figure 6 , where a is the infrared spectrum of the PVDF-based PIM, and b is the infrared spectra of the PVDF-based PIM and the raw materials.

[0078] Figure 6 It shows that the symmetric stretching vibration of -CH2- in a is at 2960.56 cm -1 , 2930.98 cm -1 , 2861.26 cm -1 . The bending vibration peak of -CH2- is at 1401.78 cm -1 . The symmetric stretching vibration of CF2 is at 1169.01 cm -1 . The characteristic peaks of PVDF crystallization are at 875.35 cm -1 , 839.43 cm -1 . The characteristic peak of P-O is at 1023.23 cm -1 . Combining with Figure 6 b in

[0079] proves that the carrier D2EHPA participates in film formation. Figure 7 , where a is the infrared spectrum of the PVC-based PIM, and b is the infrared spectra of the PVC-based PIM and the raw materials.

[0080] Figure 7 It shows that the symmetric stretching vibration of -CH2- in a is at 2958.45 cm -1 , 2930.98 cm -1 , 2861.26 cm -1 . The bending vibration peak of -CH2- is at 1464.78 cm -1 . The stretching vibration peaks of -CHCl- are at 1380.28 cm -1 and 1202.81 cm -1 . The characteristic peak of P-O is at 1021.12 cm -1 . Combining with Figure 7 b in

[0081] The mechanical properties of the PVDF-HFP-based PIMs with different D2EHPA contents prepared in Example 1 are shown in Figure 8 , where a is the tensile strength and b is the stress-strain curve.

[0082] Figure 8 It shows that as the carrier content increases, the tensile force that the PVDF-HFP-based PIM can withstand gradually decreases. When the carrier content is 20%, the tensile force that the PIM can withstand is the largest, which is 2.129 MPa. From Figure 8 b in it, it can be seen that as the carrier content increases, the elongation at break of the PIM also decreases. When the carrier content is 20%, the strain value is the largest. The PVDF-HFP molecule contains halogen functional groups and has a certain polarity; the polar functional groups contained in D2EHPA itself will actively attack the polar functional groups of PVDF-HFP during the film-forming reaction, resulting in a decrease in the intermolecular interaction force of the PVDF-HFP molecular chain, thereby leading to a decrease in the mechanical properties of the polymer inclusion membrane.

[0083] Example 2

[0084] Investigate the effect of the volatilization temperature on the mechanical properties of the PVDF-HFP-based PIM:

[0085] Compared with Example 1, D2EHPA is fixed at 1.8 g, and the volatilization temperatures are set at 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, 80 °C, and 90 °C respectively.

[0086] The mechanical properties of the PVDF-HFP-based PIMs with different volatilization temperatures prepared in Example 2 are shown in Figure 9 , where a is the tensile strength and b is the stress-strain curve.

[0087] Figure 9 It shows that as the volatilization temperature increases, the maximum value of the force that the PVDF-HFP-based PIM can withstand shows a trend of first increasing and then decreasing. When the temperature reaches 60 °C, the PVDF-HFP-based PIM withstands the maximum tensile force of 2.12 MPa. From Figure 9 b in it, it can be seen that as the temperature increases, the change law of the strain of the PVDF-HFP-based PIM is consistent with the change law of the maximum value of the force. The change in temperature causes changes in the mechanical properties of the film, and the reasons can be analyzed from two aspects: First, the solvent of the PVDF-HFP-based PIM is acetone, and the boiling point is 56.5 °C. When the film is formed below 60 °C, the solvent volatilizes incompletely, and the remaining organic solvent results in poor mechanical properties of the film. As the temperature increases, the solvent volatilizes in large amounts and the remaining amount decreases, and the mechanical properties of the film decrease. Second, as the temperature increases, while the solvent volatilization rate increases, the movement of the molecular chain also accelerates, and the structural regularity of the film gradually improves, and the mechanical properties are enhanced. However, when the volatilization temperature exceeds 60 °C, the solvent volatilization rate is too fast, resulting in a decrease in the structural regularity of the film, thereby leading to a decrease in the mechanical properties of the film.

[0088] Example 3

[0089] Preparation of MOFs-modified PVDF-HFP-based PIM:

[0090] Add 1.2 g of PVDF-HFP, 20 mL of acetone, 1.8 g of D2EHPA and different masses of Zn-MOFs (0.015 g, 0.030 g, 0.046 g, 0.061 g, 0.077 g and 0.093 g respectively) into a conical flask. Place it on a magnetic stirrer, set the rotation speed to 600 r / min, and stir for 4 h. Then pour the casting solution into a self-made 150 mm×150 mm film-making square tank, let it level naturally. After it covers the casting tank, put it into an oven at 60 °C. Take it out after the solvent has completely evaporated, and store it in a plastic-sealed bag.

[0091] The SEM images of MOFs-modified PVDF-HFP-based PIM with different MOFs contents prepared in Example 3 are shown in Figure 10 .

[0092] Figure 10 It shows that with the increase of the Zn-MOFs content, the optical microscopic imaging of the PVDF-HFP-based PIM presents obvious changes. With the increase of the Zn-MOFs content, obvious crystallization aggregation occurs in the PVDF-HFP-based PIM. This is because the dissolving ability of the solvent is limited. When the Zn-MOFs content is greater than 2.0%, it cannot be completely dissolved and uniformly filled in the membrane structure. When the Zn-MOFs content is less than 2.0%, compared with the optical microscopic imaging of the pure PVDF-HFP-based PIM, the surface of the membrane is more delicate, there is no imaging of dark impurities, and the distribution of each component is uniform. After the Zn-MOFs enter the membrane structure, they occupy the pore structure of the membrane material, resulting in a decrease in the imaging degree of the membrane pore structure. The introduction of Zn-MOFs greatly improves the surface performance of the PVDF-HFP-based PIM, which helps to improve the separation performance for Cu 2+ .

[0093] The infrared spectra of the MOFs-modified PVDF-HFP-based PIM with 1.5 g of Zn-MOFs added in Example 3 and the raw materials used are shown in Figure 11 , where a is the infrared spectrum of the MOFs-modified PVDF-HFP-based PIM, and b is the infrared spectrum of the MOFs-modified PVDF-HFP-based PIM and the raw materials.

[0094] Figure 11 It shows that at 3378.87 cm -1 in a is the stretching vibration peak of O-H; the stretching vibration at 1644.36 cm -1 is the characteristic absorption peak of the carbonyl group of the tertiary amide; they respectively correspond to the H2O molecule and the DMF molecule in the Zn-MOFs; combined with Figure 11In b, it is proved that the Zn-MOFs material is incorporated into the PVDF-HFP polymer inclusion membrane. The symmetric stretching vibration of -CH2- is at 2960.56 cm -1 , 2930.98 cm -1 ; 1405.63 cm -1 is the bending vibration peak of -CH2-; at 1181.69 cm -1 is the symmetric stretching vibration of CF2; 873.23 cm -1 is the PVDF crystallization characteristic peak; 1021.12 cm -1 is the characteristic peak of P-O, which fully proves that the carrier D2EHPA participates in film formation.

[0095] The separation performance of the MOFs-modified PVDF-HFP-based PIM with different MOFs contents prepared in Example 3 for Cu 2+ is shown in Figure 12 (The separation method is the same as above).

[0096] Figure 12 It shows that with the increase of the Zn-MOFs content, the separation of Cu 2+ by the PVDF-HFP-based PIM shows a trend of first increasing and then decreasing. When the Zn-MOFs content is less than 1.5%, with the increase of the addition amount of Zn-MOFs, the separation of PIM for Cu 2+ gradually increases. When the Zn-MOFs content is greater than 1.5%, with the increase of the MOFs content, the separation rate of PIM for Cu 2+ gradually decreases. This detection result conforms to the optical microscope imaging law. With the addition of Zn-MOFs, the Zn-MOFs material gradually occupies the pores of the PIM, plays a supporting role in the pores, enhances the pore structure of the PIM, accelerates the separation rate relying on the concentration difference as the driving force, and enhances the adsorption of Cu 2+ by relying on its own adsorption performance. However, when the Zn-MOFs content exceeds 1.5%, the film volatilization will cause the recrystallization and precipitation of Zn-MOFs, form agglomerates in the PIM structure, block the pore structure of the PIM, and lead to a decrease in the separation rate.

[0097] The dynamic separation of the MOFs-modified PVDF-HFP-based PIM with a Zn-MOFs addition amount of 1.5 g in Example 3 for Cu 2+ is shown in Figure 13 .

[0098] Figure 13 It shows that with the passage of the separation time, the content of Cu 2+ is gradually decreasing, and the change amount tends to be stable after 24 h. The adsorption rate continuously increases with time, tends to be stable after 24 h, and the maximum separation rate is 75.076% when the separation stops at 36 h.

[0099] The best separation rates of the various PIMs prepared in Example 1, Example 3 and Comparative Examples 1-2 for Cu 2+ are shown in Figure 14 .

[0100] It can be seen from Figure 14 that the order of the separation rates for Cu 2+ from small to large is: PVC-based PIM < PVDF-based PIM < PVDF-HFP-based PIM < MOFs-modified PVDF-HFP-based PIM.

[0101] The above-described embodiments are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A PVDF-HFP-based polymer inclusion membrane, characterized in that, The polymer inclusion membrane uses poly(vinylidene fluoride - hexafluoropropylene) as the polymer and bis(2-ethylhexyl) phosphate as the carrier.

2. The PVDF-HFP based polymer inclusion membrane according to claim 1, wherein The mass of the bis(2-ethylhexyl) phosphate accounts for 30 - 60% of the total mass of the poly(vinylidene fluoride - hexafluoropropylene) and the bis(2-ethylhexyl) phosphate.

3. The PVDF-HFP based polymer inclusion membrane according to claim 2, wherein The mass of the bis(2-ethylhexyl) phosphate accounts for 60% of the total mass of the poly(vinylidene fluoride - hexafluoropropylene) and the bis(2-ethylhexyl) phosphate.

4. A method for preparing the PVDF-HFP based polymer inclusion membrane according to any one of claims 1 to 3, characterized in that, It includes the following steps: Blend poly(vinylidene fluoride - hexafluoropropylene) and bis(2-ethylhexyl) phosphate in a solvent to prepare a casting solution, and volatilize the solvent in the casting solution to obtain the PVDF-HFP-based polymer inclusion membrane.

5. The preparation method of the PVDF-HFP-based polymer inclusion membrane according to claim 4, wherein, The solvent is acetone.

6. A MOFs modified PVDF-HFP based polymer inclusion membrane, characterized in that, The MOFs-modified PVDF-HFP-based polymer inclusion membrane uses poly(vinylidene fluoride - hexafluoropropylene) as the polymer, MOFs as the filler, and bis(2-ethylhexyl) phosphate as the carrier.

7. The MOFs modified PVDF-HFP based polymer inclusion membrane according to claim 6, characterized in that, The mass ratio of the poly(vinylidene fluoride - hexafluoropropylene) to the bis(2-ethylhexyl) phosphate is 4:6; the addition amount of the MOFs does not exceed 2% of the total mass of the poly(vinylidene fluoride - hexafluoropropylene) and the bis(2-ethylhexyl) phosphate.

8. A method for preparing the MOF-modified PVDF-HFP-based polymer inclusion membrane according to claim 6 or 7, characterized in that, It includes the following steps: Blend poly(vinylidene fluoride - hexafluoropropylene), MOFs, and bis(2-ethylhexyl) phosphate in a solvent to prepare a casting solution, and volatilize the solvent in the casting solution to obtain the MOFs-modified PVDF-HFP-based polymer inclusion membrane.

9. Application of the PVDF-HFP-based polymer inclusion membrane according to any one of claims 1 - 3 in separating copper ions in water.

10. Application of the MOFs-modified PVDF-HFP-based polymer inclusion membrane according to claim 6 or 7 in separating copper ions in water.

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