Multifunctional polyvinylidene fluoride adsorption membrane and preparation method thereof

Abstract

The application provides a preparation method of a multifunctional polyvinylidene fluoride adsorption membrane, and comprises the following steps: S1. blending polyvinylidene fluoride and polyacrylonitrile modified under alkaline conditions to prepare a polyvinylidene fluoride / modified polyacrylonitrile blended membrane; and S2. modifying the blended membrane under alkaline conditions, and grafting polyethylene imine to form the multifunctional polyvinylidene fluoride adsorption membrane. The membrane can adsorb metal ions in an aprotic solvent, and has good stability.

Description

Technical Field

[0001] This invention relates to the field of polymer membrane preparation technology, specifically to a multifunctional polyvinylidene fluoride adsorption membrane and its preparation method. Background Technology

[0002] In high-purity organic solvents, the removal of trace particulate impurities and metal ion contaminants is a key challenge. Traditional adsorption materials, such as ion exchange resins, are ineffective in treating organic solutions because the leaching of impurities can introduce secondary pollutants. To address these challenges, membrane adsorption technology can be used to remove trace metal ions. Membrane adsorption technology can replace conventional ion exchange technology or be coupled with ion exchange technology to achieve better removal of metal ions without introducing additional impurities.

[0003] Polyvinylidene fluoride (PVDF) is a widely used semi-crystalline polymer with excellent corrosion resistance, heat resistance, aging resistance, radiation resistance and chemical stability. It also has good mechanical properties and good film-forming properties, so it is widely used in the field of water treatment membrane materials.

[0004] Polyacrylonitrile (PAN) hydrolyzes to produce amide bonds and carboxylic acids (-COOH), and undergoes a certain degree of cyclization and cross-linking. It is often used as a metal ion adsorbent. However, PAN is generally difficult to form films when used to prepare electrospun structural materials. Furthermore, blending polyvinylidene fluoride (PVDF) with PAN is also difficult to form films. Currently, the common practice is to activate PVDF with UV light and then polymerize PAN using free radicals, a complex preparation method. Summary of the Invention

[0005] To address the problems existing in the background art, the present invention provides a multifunctional polyvinylidene fluoride (PVDF) adsorption membrane and its preparation method. This multifunctional PVDF adsorption membrane can effectively remove Cu from water and organic solvents. 2+ .

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a multifunctional polyvinylidene fluoride adsorption membrane, comprising the following steps:

[0008] S1. Polyvinylidene fluoride (PVDF) was blended with polyacrylonitrile modified under alkaline conditions to prepare a PVDF / modified polyacrylonitrile blend membrane;

[0009] S2. Modify the blended membrane under alkaline conditions by grafting polyethyleneimine to form the multifunctional polyvinylidene fluoride adsorption membrane.

[0010] Furthermore, the modification method of the polyacrylonitrile is as follows: the polyacrylonitrile powder is modified in sodium hydroxide solution. After the polyacrylonitrile powder turns yellow, it is filtered to obtain yellow powder. Then, it is washed with deionized water until neutral and placed in an oven to dry to obtain modified polyacrylonitrile powder. The concentration of sodium hydroxide is 5-15%, the modification time is 20-30 min, and the drying temperature is 40-80℃.

[0011] Furthermore, the polyvinylidene fluoride / modified polyacrylonitrile blend membrane described in step S1 is prepared by a phase inversion method.

[0012] Further, the specific steps of step S1 are as follows: polyvinylidene fluoride and modified polyacrylonitrile powder are mixed and dissolved in a nonpolar protic solvent to form a membrane liquid, the membrane liquid is scraped onto a nonwoven fabric for support, and after the coating is completed, it is placed in pure water for 12-24 hours until phase separation is completed and the membrane structure is cured.

[0013] Furthermore, in step S1, the mass ratio of polyvinylidene fluoride to modified polypropylene powder is (4-5):2, the mass concentration of polyvinylidene fluoride in the mixed solution is 15-20%, and the nonpolar protic solvent is N,N-dimethylacetamide or N,N-dimethylformamide.

[0014] Furthermore, the specific steps of the blend membrane alkalization in step S2 are as follows: the blend membrane is immersed in the alkalization solution at room temperature for a certain period of time, the membrane is taken out, rinsed with pure water and stored in water. The alkalization solution is a NaOH ethanol solution with a mass fraction of 10% to 20%, and the alkalization time is 10 to 15 minutes.

[0015] Furthermore, the specific method for grafting polyethyleneimine in step S2 is as follows: the alkalized blended membrane is immersed in a grafting solution containing polyethyleneimine for grafting. After grafting, it is placed in hydrochloric acid solution for activation at room temperature for 3–8 hours at a temperature of 50–80°C for 2–12 hours. The grafting time is preferably, more preferably, 7–8 hours.

[0016] Furthermore, the grafting solution is prepared by dissolving polyethyleneimine in sodium carbonate solution, wherein the mass concentration of polyethyleneimine is 1-15%, the concentration of sodium carbonate is 1-1.5 mol / L, and the pH of the hydrochloric acid solution is 1-3.

[0017] Furthermore, the polyethyleneimine is a branched polyethyleneimine, and the molecular weight of the branched polyethyleneimine is 50k to 100k.

[0018] Secondly, the present invention provides a polyvinylidene fluoride adsorption membrane prepared by the above preparation method.

[0019] The beneficial effects of this invention are:

[0020] Alkaline hydrolysis of polyacrylonitrile yields a random copolymer of acrylamide and acrylate, an electronegative intermediate with strong nucleophilic ability. This intermediate can further undergo nucleophilic addition reactions with adjacent cyano groups to form a six-membered ring structure. In the presence of water, the six-membered ring combines with water and undergoes tautomerism to form an amide. The amide is further attacked by OH- in an alkaline environment, hydrolyzing to form sodium carboxylate and releasing ammonia gas.

[0021] Polyethylene imine (PEI) grafts and crosslinks the polyvinylidene fluoride backbone through an addition reaction. The PEI molecule contains a large number of primary, secondary, and tertiary amine groups, which have a strong chelating and coordination effect with metal ions under neutral or alkaline conditions. The removal of metal ions can be achieved by relying on the chelation effect between the amino and imino groups (-NH2 and -NH-) in PEI and the metal ions. At the same time, polyacrylonitrile (PAN) after alkaline hydrolysis can also interact with polyethyleneimine (PEI) to form a PAN-PEI ionic bond structure, thereby increasing the active adsorption sites of metal ions.

[0022] Due to the cross-linking effect of PEI on PVDF and the self-cross-linking after PAN hydrolysis, the prepared multifunctional polyvinylidene fluoride adsorption membrane has excellent stability and solvent resistance in aprotic solvents. It can be used effectively in aprotic solvents without causing secondary pollution to reagents. After adsorbing metal ions, it can be desorbed and recycled more than 5 times and is non-toxic and harmless.

[0023] Compared with traditional polyacrylonitrile (PAN) modification, this invention creatively first alkalizes, then blends polyvinylidene fluoride (PVDF) and then grafts polyethyleneimine (PEI), creating more active adsorption sites and effectively improving the adsorption performance of the adsorption membrane.

[0024] The multifunctional polyvinylidene fluoride adsorption membrane prepared by this invention exhibits good adhesion to Cu in water and organic solvents. 2+ Both methods can achieve relatively good adsorption effects. For Cu in water with an initial concentration of 50 ppm... 2+ The maximum adsorption capacity can reach 103 mg / g. At an initial concentration of 30 ppm, this membrane effectively adsorbs Cu in methanol solution. 2+ The adsorption capacity is approximately 60 mg / g, for Cu in ethanol solution. 2+ The adsorption capacity is approximately 55 mg / g. Attached Figure Description

[0025] Figure 1 The multifunctional polyvinylidene fluoride adsorption membrane prepared in Example 1 of this invention, with an initial Cu concentration of 10 ppm in pure water, 2+ Adsorption curves over time;

[0026] Figure 2The multifunctional polyvinylidene fluoride adsorption membrane prepared in Example 1 of this invention was used to adsorb different concentrations of Cu in pure water. 2+ The maximum adsorption capacity;

[0027] Figure 3 The maximum adsorption capacity of the multifunctional polyvinylidene fluoride adsorption membrane prepared in Example 1 of this invention varies with different Cu concentrations in methanol or ethanol solutions. 2+ Changes;

[0028] Figure 4 The re-adsorption capacity of the polyvinylidene fluoride adsorption membrane prepared in Example 1 of this invention after multiple elution cycles is shown. Detailed Implementation

[0029] The principles and features of the present invention are described below with reference to the accompanying drawings and specific embodiments. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0030] This invention provides a multifunctional polyvinylidene fluoride (PVDF) adsorption membrane and its preparation method. Polyacrylonitrile is alkali-hydrolyzed and then blended with PVDF to form a membrane. After strong alkali modification, polyethyleneimine is grafted onto the membrane to form a multifunctional PVDF adsorption membrane with chelating or ion-exchange capabilities. The specific preparation method is as follows:

[0031] Step 1: Take polyacrylonitrile (PAN) powder and place it in a 5%-15% NaOH solution for 20-30 minutes for modification. After the polyacrylonitrile powder turns yellow, filter it to obtain a yellow powder. Then rinse it with deionized water until neutral and place it in an oven at 40-80℃ to dry it, thus obtaining alkalized modified polyacrylonitrile powder.

[0032] Step 2: Place the alkali-modified polyacrylonitrile powder into a nonpolar protic solvent, and then add a certain amount of polyvinylidene fluoride (PVDF) powder. The mass fraction of PVDF in the mixed solution is 15-20%. After stirring, place it in an oven overnight. After taking it out, observe that there are no bubbles in the solution. The mass ratio of polyvinylidene fluoride to alkali-modified polyacrylonitrile powder is (4-5):2.

[0033] Step 3: Apply the prepared membrane solution onto the nonwoven fabric using a scraper. After coating, quickly place it in pure water for 12-24 hours until phase separation is complete and the membrane structure solidifies.

[0034] Step 4: Prepare a 10%-20% NaOH ethanol solution. After preparation, immerse the entire membrane in the solution for alkalization for 10-15 minutes. At this time, you can observe that the membrane quickly turns dark brown. Remove the membrane, rinse it with pure water, and store it in water.

[0035] Step 5: After alkalization, prepare a sodium carbonate solution and add polyethyleneimine to make a solution with a mass fraction of 1-15%. Place the membrane in the solution and react in an oven at 50-80℃ for 3-8 hours, then remove it.

[0036] Step 6: After the reaction is complete, clean the membrane with deionized water, then prepare a hydrochloric acid solution with a pH of 1-3, activate it for 2-12 hours, and then remove it. The preparation of the multifunctional polyvinylidene fluoride adsorption membrane is complete.

[0037] The present invention will be further described below with reference to specific embodiments.

[0038] Example 1

[0039] Weigh 4g of polyacrylonitrile powder and place it in a 10% NaOH solution for alkalization treatment for 20 minutes. After the polyacrylonitrile powder turns yellow, filter it to obtain a yellow powder. Then rinse it with deionized water until neutral and place it in an oven to dry at 40-80℃ to obtain alkalized modified polyacrylonitrile powder.

[0040] Weigh 9g of polyvinylidene fluoride powder, put the alkali-modified polyacrylonitrile powder into 50ml of nonpolar protic solvent N,N-dimethylacetamide (dmac), and then add the weighed polyvinylidene fluoride powder to prepare a PVDF-PAN mixed solution with a polyvinylidene fluoride mass fraction of 18%. After stirring, place it in an oven overnight. After taking it out, observe that there are no bubbles in the solution.

[0041] The prepared membrane solution was coated onto a nonwoven fabric using a doctor blade. After coating, the membrane was quickly placed in pure water for 12 hours to allow phase separation to complete and the membrane structure to solidify.

[0042] Prepare a 10% NaOH ethanol solution. After preparation, immerse the entire membrane in the solution for alkalization for 10 minutes. At this time, the membrane can be observed to turn blackish-brown rapidly. Remove the membrane, rinse it with pure water, and then store it in water.

[0043] After alkalization, a 1 mol / L sodium carbonate solution was prepared, and 5% (w / w) of branched polyethyleneimine (molecular weight 70K) was added. The membrane was placed in the solution and reacted in an oven at 70°C for 8 hours before being removed.

[0044] After the reaction was completed, the membrane was cleaned with deionized water, and then a hydrochloric acid solution with a pH of 1 was prepared. After activation for 12 hours, the membrane was taken out, and the preparation of the multifunctional polyvinylidene fluoride adsorption membrane was completed.

[0045] Example 2

[0046] Weigh 4g of polyacrylonitrile powder and place it in a 10% NaOH solution for alkalization treatment for 20 minutes. After the polyacrylonitrile powder turns yellow, filter to obtain yellow powder, rinse with deionized water until neutral, and dry in an oven at 60℃ to obtain alkalized modified polyacrylonitrile powder.

[0047] Weigh 8g of polyvinylidene fluoride powder, put the alkali-modified polyacrylonitrile powder into 50ml of nonpolar protic solvent dmac, and then add the weighed polyvinylidene fluoride powder to prepare a PVDF-PAN mixed solution with a PVDF concentration of 16%. After stirring, place it in an oven overnight. After taking it out, observe that there are no bubbles in the solution.

[0048] The prepared membrane solution was coated onto a nonwoven fabric using a scraper. After coating, the membrane was quickly placed in pure water for 8 hours to allow phase separation to complete and the membrane structure to solidify.

[0049] Prepare a 10% NaOH ethanol solution. After preparation, immerse the entire membrane in the solution for alkalization for 8 minutes. At this time, the membrane can be observed to turn blackish-brown rapidly. Remove the membrane, rinse it with pure water, and then store it in water.

[0050] After alkalization, a 1.5 mol / L sodium carbonate solution was prepared, and 8% (w / w) polyethyleneimine was added. The membrane was placed in the solution and reacted in an oven at 80°C for 6 hours before being removed.

[0051] After the reaction was complete, the membrane was cleaned with deionized water, then activated with a hydrochloric acid solution at pH 1 for 12 hours, and finally removed. The multifunctional polyvinylidene fluoride adsorption membrane was thus prepared.

[0052] Example 3

[0053] Weigh 4g of polyacrylonitrile powder and place it in a 10% NaOH solution for alkalization treatment for 20 minutes. After the polyacrylonitrile powder turns yellow, filter to obtain yellow powder, rinse with deionized water until neutral, and dry in an oven at 60℃ to obtain alkalized modified polyacrylonitrile powder.

[0054] Weigh 10g of polyvinylidene fluoride powder, put the alkali-modified polyacrylonitrile powder into 50ml of nonpolar protic solvent dmac, and then add the weighed polyvinylidene fluoride powder to prepare a PVDF-PAN mixed solution with a PVDF concentration of 20%. After stirring, place it in an oven overnight. After taking it out, observe that there are no bubbles in the solution.

[0055] The prepared membrane solution was coated onto a nonwoven fabric using a scraper. After coating, the membrane was quickly placed in pure water for 8 hours to allow phase separation to complete and the membrane structure to solidify.

[0056] Prepare a 10% NaOH ethanol solution. After preparation, immerse the entire membrane in the solution for alkalization for 8 minutes. At this time, the membrane can be observed to turn blackish-brown rapidly. Remove the membrane, rinse it with pure water, and then store it in water.

[0057] After alkalization, a 1.5 mol / L sodium carbonate solution was prepared, and 15% polyethyleneimine was added. The membrane was placed in the solution and reacted in an oven at 80°C for 6 hours before being removed.

[0058] After the reaction was completed, the membrane was cleaned with deionized water, and then a hydrochloric acid solution with a pH of 1 was prepared. After activation for 12 hours, the membrane was removed, and the preparation of the multifunctional polyvinylidene fluoride adsorption membrane was completed.

[0059] The multifunctional polyvinylidene fluoride (PVDF) adsorption membrane prepared in the above embodiments has the dual function of removing particulate impurities and metal ions. Furthermore, due to the stable cross-linked structure formed during the preparation process, it exhibits good stability, showing no dissolution when processing organic solvents and generating no additional impurities. It also demonstrates good adsorption performance for metal ions in organic solvents. It can effectively remove metal ions from non-protic solvents.

[0060] Experimental Example 1

[0061] Prepare Cu solutions with concentration gradients ranging from 2 ppm to 20 ppm 2+ An aqueous solution was prepared by placing the multifunctional polyvinylidene fluoride adsorption membrane prepared in Example 1 in the solution at room temperature and stirring for 4 hours. Small samples were taken from the solution at regular intervals for measurement. Cu 2+ Concentrations were measured using an ICP-OES instrument, and the maximum adsorption capacity at different concentrations was as follows: Figure 2 As shown.

[0062] As can be seen from the figure, with Cu 2+ With the increase of initial concentration, Cu 2+ The adsorption capacity is also gradually increasing. Figure 1 For Cu in pure water 2+ Cu at an initial concentration of 10 ppm 2+ Adsorption curves over time.

[0063] Simultaneously, it was measured that at an initial concentration of 50 ppm, the maximum adsorption capacity reached 103 mg / g, and it conformed to the Langmuir isotherm adsorption equation. Therefore, it can be concluded that this multifunctional polyvinylidene fluoride adsorption membrane effectively adsorbs Cu in aqueous solution. 2+ It has excellent adsorption properties and can effectively remove Cu from aqueous solutions. 2+ .

[0064] Experimental Example 2

[0065] Take 500 ml of methanol (AR) solution and prepare Cu solutions with different concentration gradients from 5 ppm to 30 ppm. 2+ An alcohol solution was prepared by placing a small amount of the finished film in the solution at room temperature and stirring for 4 hours. Small samples were taken from the solution at regular intervals for measurement. Cu 2+ Concentration was measured using an ICP-OES instrument;

[0066] Take 500 ml of ethanol (AR) solution and prepare Cu solutions with different concentration gradients from 5 ppm to 30 ppm. 2+ An alcohol solution was prepared by placing a small amount of the finished film in the solution at room temperature and stirring for 4 hours. Small samples were taken from the solution at regular intervals for measurement. Cu 2+ Concentration was measured using an ICP-OES instrument.

[0067] Adsorption effect such as Figure 3 As shown, even in high-purity methanol or ethanol organic reagents, the multifunctional polyvinylidene fluoride adsorption membrane of this invention can still adsorb Cu. 2+ It exhibits excellent adsorption performance. At an initial concentration of 30 ppm, the membrane effectively adsorbs Cu in a methanol solution. 2+ The adsorption capacity is approximately 60 mg / g, for Cu in ethanol solution. 2+ The adsorption capacity was approximately 55 mg / g. Furthermore, infrared spectroscopy analysis of the adsorbed solution revealed the absence of other functional groups, indicating that the membrane was not contaminated in methanol and ethanol organic solvents. This demonstrates the membrane's high solubility and excellent adsorption performance in methanol and ethanol solvents.

[0068] Experimental Example 3

[0069] A hydrochloric acid solution with a pH of 1 was prepared. The saturated polyvinylidene fluoride (PVDF) adsorption membrane was placed in the hydrochloric acid solution for 12 hours. After desorption was completed, Experiments 1 and 2 were repeated. The maximum adsorption capacity measured was almost the same as the first maximum adsorption capacity. After five cycles of this experimental procedure, the maximum adsorption capacity decreased as shown in the results. Figure 4 As shown, this indicates that the adsorption membrane has good regeneration and recycling performance and does not produce any environmental pollution.

[0070] The polyvinylidene fluoride adsorption membranes prepared in Examples 2 and 3 both exhibit high solvent resistance and good adsorption effect in organic solvents, and are effective against Cu. 2+ It has a good adsorption effect.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a multifunctional polyvinylidene fluoride (PVDF) adsorption membrane, characterized in that, Includes the following steps: S1. Polyvinylidene fluoride (PVDF) was blended with polyacrylonitrile (PA) modified under alkaline conditions to prepare a PVDF / modified PA blend membrane; S2. Modify the blended membrane under alkaline conditions by grafting polyethyleneimine to form the multifunctional polyvinylidene fluoride adsorption membrane, wherein the polyethyleneimine is a branched polyethyleneimine with a molecular weight of 50k~100k. The modification method of the polyacrylonitrile is as follows: the polyacrylonitrile is modified in sodium hydroxide solution, dried after modification, washed with deionized water, and dried to obtain modified polyacrylonitrile powder. The concentration of the sodium hydroxide solution is 5~15%, the modification time is 20~30 min, and the drying temperature is 40~80℃. The specific steps for modifying the blended membrane under alkaline conditions in step S2 are as follows: the blended membrane is immersed in an alkaline solution and alkalized at room temperature for a certain period of time. The membrane is then removed, rinsed with pure water, and stored in water. The alkaline solution is a 10%~20% NaOH ethanol solution by mass, and the alkalization time is 10~15 minutes.

2. The method for preparing the multifunctional polyvinylidene fluoride adsorption membrane according to claim 1, characterized in that, The polyvinylidene fluoride / modified polyacrylonitrile blend membrane described in step S1 is prepared by phase inversion method.

3. The method for preparing the multifunctional polyvinylidene fluoride adsorption membrane according to claim 2, characterized in that, The specific steps of step S1 are as follows: polyvinylidene fluoride and modified polyacrylonitrile powder are mixed and dissolved in a nonpolar protic solvent to form a membrane liquid. The membrane liquid is scraped onto a nonwoven fabric for support. After the coating is completed, it is placed in pure water for 12-24 hours until phase separation is completed and the membrane structure is cured.

4. The method for preparing the multifunctional polyvinylidene fluoride adsorption membrane according to claim 3, characterized in that, In step S1, the mass ratio of polyvinylidene fluoride to modified polyacrylonitrile powder is (4~5):2, the mass concentration of polyvinylidene fluoride in the membrane solution is 15~20%, and the nonpolar protic solvent is N,N-dimethylacetamide or N,N-dimethylformamide.

5. The method for preparing the multifunctional polyvinylidene fluoride adsorption membrane according to claim 1, characterized in that, The specific method for grafting polyethyleneimine in step S2 is as follows: the alkalized blended membrane is immersed in a grafting solution containing polyethyleneimine for grafting. After grafting, it is placed in hydrochloric acid solution for activation. The grafting time is 3-8 hours, the temperature is 50-80℃, and the activation time is 2-12 hours.

6. The method for preparing the multifunctional polyvinylidene fluoride adsorption membrane according to claim 5, characterized in that, The grafting solution is prepared by dissolving polyethyleneimine in sodium carbonate solution, wherein the mass concentration of polyethyleneimine is 1-15%, the concentration of sodium carbonate is 1-1.5 mol / L, and the pH of the hydrochloric acid solution is 1-3.

7. A multifunctional polyvinylidene fluoride adsorption membrane, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

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