Metal adsorbing membrane and method for manufacturing the same

Abstract

The application provides a metal adsorption membrane and a preparation method and application thereof, and comprises the following steps: S1, blending polyvinylidene fluoride and a first molecular weight polyethylene imine to prepare a polyvinylidene fluoride / polyethylene imine blending membrane; S2, modifying the blending membrane under alkaline conditions, grafting a second molecular weight polyethylene imine to form the metal adsorption membrane, wherein the first molecular weight polyethylene imine has a molecular weight of 70-700K, and the second molecular weight polyethylene imine has a molecular weight of 2-70K. The metal adsorption membrane solves the problem that a macromolecular weight polyethylene imine cannot be grafted on the membrane, and increases the content of the polyethylene imine on the metal adsorption membrane.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer film preparation, and in particular to a metal adsorption film and a preparation method thereof. Background Art

[0002] Industrial development has led to increasingly severe water pollution. Metallurgical, chemical, and electronic production processes generate large amounts of wastewater containing heavy metal ions, posing a significant threat to human health. Common treatment methods for heavy metal wastewater include chemical precipitation, electrolysis, and ion exchange. However, these methods suffer from high energy consumption, secondary pollution, high costs, complex operations, and difficult post-processing. Adsorption is a widely used method for removing heavy metal ions from industrial wastewater.

[0003] The adsorbents that have been developed so far mainly include activated carbon, synthetic resins, cheap adsorbents, etc., including industrial by-products, agricultural waste, biomass and polymer materials such as zeolite, viscoelastic, kaolin, fly ash, peat, as well as biomass, biologically activated sludge, etc., oxides such as aluminum oxide, iron oxide, silicon oxide, etc., and biological adsorbents such as chitin, chitosan, cyclodextrin, starch, etc.

[0004] Polyethyleneimine (PEI) is a typical water-soluble polymer, structurally classified into linear polyethyleneimine (L-PEI) and branched polyethyleneimine (B-PEI). Both have a large number of amino N atoms on their molecular chains. The abundance of N atoms in the PEI macromolecule makes it highly protonic. In a solution with a pH below 10, most of the amino groups on its molecular chain are in a protonated state, effectively adsorbing metal ions. At the same time, the primary and secondary amine functional groups in the PEI molecule can form coordination bonds with metal ions, thereby adsorbing them.

[0005] However, the existing polyethyleneimine exists mainly as free ions in water. Using polyethyleneimine alone as an adsorbent will make it difficult to separate and recover it, and it is easy to introduce ions in the polyethyleneimine, causing secondary pollution. Summary of the Invention

[0006] In order to solve the problems existing in the background technology, the present invention provides a metal adsorption membrane and a preparation method thereof, which solves the problem that high molecular weight polyethyleneimine cannot be grafted onto the membrane, increases the content of polyethyleneimine on the metal adsorption membrane, and improves the adsorption effect on metal ions.

[0007] The technical solution of the present invention to solve the above technical problems is as follows:

[0008] In a first aspect, the present invention provides a method for preparing a metal adsorption film, comprising the following steps:

[0009] S1, blending polyvinylidene fluoride with polyethyleneimine of a first molecular weight to prepare a polyvinylidene fluoride / polyethyleneimine blend membrane;

[0010] S2, modifying the blended film under alkaline conditions and grafting a second molecular weight polyethyleneimine to form the metal adsorption film;

[0011] The molecular weight of the first molecular weight polyethyleneimine is 70-700K, and the molecular weight of the second molecular weight polyethyleneimine is 2-70K.

[0012] Furthermore, the polyvinylidene fluoride / polyethyleneimine blend membrane in step S1 is prepared by a phase inversion method.

[0013] Furthermore, the specific steps of step S1 are: dissolving polyvinylidene fluoride and first molecular weight polyethyleneimine powder in a non-polar protic solvent to form a membrane liquid, coating the membrane liquid on a non-woven fabric support, and placing it in pure water for 12 to 24 hours after the coating is completed, until the phase separation is completed and the membrane structure is completed.

[0014] Furthermore, in step S1, the mass ratio of polyvinylidene fluoride to first molecular weight polyethyleneimine is 9:2-5, the mass concentration of polyvinylidene fluoride in the mixed solution is 8%-18%, and the non-polar protic solvent is N,N-dimethylacetamide or N,N-dimethylformamide.

[0015] Furthermore, the specific steps of alkalizing the blended membrane in step S2 are: immersing the entire blended membrane in an alkalizing solution at room temperature for a certain period of time, taking out the membrane, rinsing it with pure water, and then storing it in water. The alkalizing solution is a NaOH ethanol solution with a mass fraction of 10% to 20%, and the alkalization time is 10 to 15 minutes.

[0016] Furthermore, the specific method for grafting the second molecular weight polyethyleneimine in step S2 is: immersing the alkalized blended membrane in a grafting solution containing the second molecular weight polyethyleneimine for grafting, and after the grafting is completed, placing it in a hydrochloric acid solution for activation, the grafting time is 3~8h, the temperature is 50~80℃, and the activation time is 2~12h.

[0017] Furthermore, the grafting solution is prepared by dissolving second molecular weight polyethyleneimine in sodium carbonate solution, the mass concentration of the second molecular weight 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.

[0018] Furthermore, the first molecular weight polyethyleneimine and the second molecular weight polyethyleneimine are branched polyethyleneimine.

[0019] In a second aspect, the present invention provides a metal adsorption film prepared by the above preparation method.

[0020] The beneficial effects of the present invention are as follows: the present invention prepares a blend film by preparing polyvinylidene fluoride and high molecular weight polyethyleneimine, and then grafts low molecular weight polyethyleneimine on the blend film to prepare a metal adsorption film, thereby avoiding the problem that high molecular weight polyethyleneimine cannot be grafted on the film, increasing the content of polyethyleneimine on the metal adsorption film, and improving the adsorption effect on metal ions.

[0021] Polyethyleneimine has excellent hydrophilicity and exists in the form of large molecules in the aqueous phase, which allows it to adsorb metal ions very quickly. The content of groups (primary amines and secondary amines) that can be used for coordination in PEI molecules is very high, with a weight ratio of 34.9%. The amount of metal ions adsorbed per unit mass is very large. Due to its high adsorption capacity, the amount of adsorbent required is much lower than that of conventional adsorbents. PEI is suitable for solutions with a wide range of metal ion concentrations, has a high adsorption rate and adsorption capacity, as well as high selectivity, and is biosoluble, and will not cause secondary pollution to the environment during use. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The metal adsorption film prepared in Example 1 of the present invention has different initial concentrations of Cu 2+ The maximum adsorption capacity;

[0023] Figure 2 The metal adsorption film prepared in Example 2 of the present invention has different initial concentrations of Cu 2+ The maximum adsorption capacity;

[0024] Figure 3 The adsorption film prepared in comparative example 3 of the present invention has different initial concentrations of Cu 2+ The maximum adsorption capacity;

[0025] Figure 4 The metal adsorption film prepared in Example 1 of the present invention has a great influence on the Cu 2+ Dynamic adsorption effect;

[0026] Figure 5 The metal adsorption film prepared in Example 1 of the present invention is subjected to different flow rates on Cu 2+ Dynamic adsorption effect;

[0027] Figure 6 The metal adsorption films prepared in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention are 2+ Static adsorption effect. DETAILED DESCRIPTION

[0028] 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 used to explain the present invention and are not used to limit the scope of the present invention.

[0029] The present invention provides a metal adsorption film and its preparation method. Polyvinylidene fluoride is blended with a first molecular weight polyethyleneimine to form a film. After strong base modification, a second molecular weight polyethyleneimine is grafted to form a metal adsorption film with metal adsorption capacity. The specific preparation method is as follows:

[0030] Step 1: Dissolve polyvinylidene fluoride (PVDF) powder in a nonpolar protic solvent. Add polyethyleneimine (PEI) powder of a first molecular weight to create a PVDF / PEI solution. Stir and place in an oven overnight. Remove the solution and inspect for bubbles. The mass ratio of PVDF to polyethyleneimine of the first molecular weight is 9:2-5, and the molecular weight of the polyethyleneimine of the first molecular weight is 70-700K.

[0031] Step 2: Use a doctor blade to apply the prepared membrane solution onto the non-woven fabric and place it in water for 12 to 24 hours to form a membrane.

[0032] Step 3. After the membrane conversion is completed, prepare a 10%-20% NaOH ethanol or methanol solution and immerse the entire membrane in the solution for 10-15 minutes to alkalinize. At this time, it can be observed that the membrane quickly turns dark brown. Take out the membrane, rinse it with pure water, and store it in water.

[0033] Step 4: After alkalization, prepare a sodium carbonate solution and add the second molecular weight polyethyleneimine to a solution with a mass fraction of 1-15%. Place the membrane in the solution and place it in an oven at 50-80°C for 3-8 hours before removing it. The molecular weight of the second molecular weight polyethyleneimine is 2-70k.

[0034] Step 5: After the reaction is completed, the membrane is cleaned with deionized water, and then a hydrochloric acid solution with a pH of 1 to 3 is prepared. After activation for 2 to 12 hours, the membrane is taken out and placed in pure water. The metal adsorption membrane is prepared.

[0035] The present invention will be further described below with reference to specific embodiments.

[0036] Example 1

[0037] Weigh 9g of polyvinylidene fluoride powder and dissolve it in 50ml of non-polar protic solvent. Then add 2.5g of first molecular weight polyethyleneimine powder with a molecular weight of 700k. After stirring, place it in an oven overnight. After taking it out, observe whether there are bubbles in the solution.

[0038] The prepared membrane liquid is coated on the non-woven fabric with a doctor blade. After coating, it is quickly placed in pure water for 12 hours until the phase separation is completed and the membrane structure is solidified.

[0039] Prepare a 10% NaOH ethanol solution. After completion, immerse the entire membrane in the solution for alkalinization treatment for 10 minutes. At this time, it can be observed that the membrane quickly turns dark brown. Take out the membrane, rinse it with pure water, and store it in water.

[0040] After alkalization, 0.1 mol of sodium carbonate was weighed and added to 100 ml of water to prepare a sodium carbonate solution. 5 g of polyethyleneimine with a molecular weight of 70k was added. The membrane was placed in the solution and reacted in an oven at 70°C for 1 h before being removed.

[0041] After the reaction is completed, the membrane is cleaned with deionized water, and then a hydrochloric acid solution with a pH of 1 is prepared. After activation for 12 hours, it is taken out and the preparation of the metal adsorption membrane is completed.

[0042] Example 2

[0043] Weigh 8g of polyvinylidene fluoride powder and dissolve it in 50ml of non-polar protic solvent. Then add 4g of first molecular weight polyethyleneimine powder with a molecular weight of 700k. After stirring, place it in an oven overnight. After taking it out, observe whether there are bubbles in the solution.

[0044] The prepared membrane liquid is coated on the non-woven fabric with a doctor blade. After coating, it is quickly placed in pure water for 12 hours until the phase separation is completed and the membrane structure is solidified.

[0045] Prepare a 10% NaOH ethanol solution. After completion, immerse the entire membrane in the solution for alkalinization treatment for 15 minutes. At this time, it can be observed that the membrane quickly turns dark brown. Take out the membrane, rinse it with pure water, and store it in water.

[0046] After alkalization, weigh 0.15 mol of sodium carbonate and add it to 100 ml of water to prepare a 1.5 mol / L sodium carbonate solution. Add 4 g of 70k molecular weight polyethyleneimine. Place the membrane in the solution and react in an oven at 70°C for 7 hours before removing it.

[0047] After the reaction is completed, the membrane is cleaned with deionized water, and then a hydrochloric acid solution with a pH of 1 is prepared. After activation for 12 hours, it is taken out and the preparation of the metal adsorption membrane is completed.

[0048] Example 3

[0049] Weigh 2g of polyvinylidene fluoride powder and dissolve it in 50ml of non-polar protic solvent. Then add 5g of first molecular weight polyethyleneimine powder with a molecular weight of 100k. After stirring, place it in an oven overnight. After taking it out, observe whether there are bubbles in the solution.

[0050] The prepared membrane liquid is coated on the non-woven fabric with a doctor blade. After coating, it is quickly placed in pure water for 12 hours until the phase separation is completed and the membrane structure is solidified.

[0051] Prepare a 10% NaOH ethanol solution. After completion, immerse the entire membrane in the solution for alkalinization treatment for 15 minutes. At this time, it can be observed that the membrane quickly turns dark brown. Take out the membrane, rinse it with pure water, and store it in water.

[0052] After alkalization, weigh 0.12 mol of sodium carbonate and add it to 100 ml of water to prepare a 1.2 mol / L sodium carbonate solution. Add 15 g of polyethyleneimine (30k molecular weight). Place the membrane in the solution and allow it to react in an oven at 70°C for 7 hours before removing it from the oven.

[0053] After the reaction is completed, the membrane is cleaned with deionized water, and then a hydrochloric acid solution with a pH of 1 is prepared. After activation for 12 hours, it is taken out and the preparation of the metal adsorption membrane is completed.

[0054] Comparative Example 1

[0055] In this comparative example, the molecular weight of the second molecular weight polyethyleneimine used for grafting is 2k, and the rest is the same as in Example 1.

[0056] Comparative Example 2

[0057] In this comparative example, the molecular weight of the second polyethyleneimine used for grafting is 100K, and the rest is the same as in Example 1.

[0058] Comparative Example 3

[0059] In this comparative example, the mass of polyvinylidene fluoride added in step 1 is 9 g, polyethyleneimine of the first molecular weight is not added, and the other steps are the same as in Example 1.

[0060] The metal adsorption film can effectively remove metal ion pollutants in water.

[0061] Test Example 1

[0062] Take copper nitrate to prepare different concentration gradients of Cu from 2ppm to 20ppm 2+ Aqueous solution, the metal adsorption films prepared in Example 1 and Example 2 were placed in the solution at room temperature, stirred at room temperature for 4 hours, and a small amount of sample was taken from the solution at regular intervals for measurement. 2+ The concentration was measured by an icp-oes instrument. The maximum adsorption capacity of the metal adsorption film of Example 1 at different initial concentrations is as follows Figure 1 As shown in the figure, with the increase of initial concentration, the adsorption amount also gradually increases. At the same time, it is measured that when the initial concentration is 20ppm, the adsorption amount can reach about 50mg / g, and it conforms to the kinetic adsorption equation. It can be seen that the metal adsorption film has a good adsorption effect on Cu 2+ It has a good adsorption effect and can effectively remove trace Cu in the solution 2+ .

[0063] The maximum adsorption capacity of the metal adsorption film prepared in Example 2 at different initial concentrations is as follows Figure 2 shown.

[0064] The maximum adsorption capacity of the membrane prepared in Comparative Example 3 at different initial concentrations is as follows Figure 3 As shown, when the initial concentration is 20 ppm, the adsorption amount can reach about 22 mg / g.

[0065] Test Example 2

[0066] Prepare three different concentrations of Cu: 2ppm, 5ppm, and 10ppm 2+ 500ml of aqueous solution, the metal adsorption membrane prepared in Example 1 was placed at the bottom of the pressure tank and pressed with a rubber ring. The size of the modified membrane was 21.7cm 2 , Cu 2+ The entire solution is inverted into a pressure tank, and the pressure is adjusted to 0.2 bar, with a flow rate of 1 ml / min. The concentration of the outlet solution is recorded at intervals, and the outlet concentration is compared with the initial concentration to obtain a breakthrough curve.

[0067] Figure 4 The metal adsorption film at different concentrations of Cu 2+ The dynamic adsorption effect of Cu 2+ As the concentration increases, the penetration time becomes shorter, and the penetration curve gradually becomes steeper, the membrane penetration point moves forward, and the membrane penetration saturation rate gradually accelerates. This is because when the initial concentration is lower, the concentration gradient between the solid and liquid is smaller, and the mass transfer driving force is smaller, so it takes longer to make the membrane stack penetrate. Increasing the initial concentration is conducive to increasing the Cu 2+ The concentration gradient increases the mass transfer driving force between the solid and liquid phases, thereby enabling the adsorption sites on the surface of the functional separation membrane to be quickly occupied by Cu 2+ The ions occupy the membrane, thereby increasing the adsorption rate and shortening the breakthrough time of the membrane stack.

[0068] Test Example 3

[0069] Prepare Cu with a concentration of 2ppm 2+ 500ml of aqueous solution, place the finished membrane at the bottom of the pressure tank and press it with a rubber ring. The size of the modified membrane is 21.7cm 2 , Cu 2+ The solution was placed in a pressure tank and the pressure was adjusted to control the flow rate at different speeds, such as 1 ml / min and 2 ml / min. The concentration of the outlet solution was recorded at regular intervals and compared with the initial concentration to obtain a penetration curve.

[0070] The results are as follows Figure 5As shown in the figure, it can be seen that as the flow rate increases, the puncture point gradually moves forward. This is because the increase in flow rate reduces the contact between the membrane stack and Cu 2+ ion contact time, reducing the Cu 2+ The opportunity for ions to be chelated by the amino sites in the membrane leads to a decrease in the equilibrium adsorption capacity; while the lower flow rate provides more residence time for mass transfer into the pores in the membrane, subsequently allowing Cu 2+ It can enter more active centers in the adsorbent, thus obtaining better adsorption capacity.

[0071] Test Example 4

[0072] The metal adsorption films prepared in Example 1, Comparative Example 1 and Comparative Example 2 were placed in 10 ppm Cu 2+ The static adsorption capacity was tested in the solution, and the results were as follows Figure 6 As shown in the figure, it can be seen that the adsorption effect is best when the PEI molecular weight is 70k, and there is almost no adsorption effect when it is 100k. This is because as the molecular weight increases, the PEI molecular chain becomes larger and cannot be broken and grafted onto polyvinylidene fluoride, so no adsorption effect can be produced.

[0073] 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 in the scope of protection of the present invention.

Claims

1. A method for preparing a metal adsorption film, characterized in that: The steps include: S1, blending polyvinylidene fluoride with polyethyleneimine of a first molecular weight to prepare a polyvinylidene fluoride / polyethyleneimine blend membrane; S2, modifying the blended film under alkaline conditions and grafting a second molecular weight polyethyleneimine to form the metal adsorption film; The molecular weight of the first molecular weight polyethyleneimine is 70~700K, and the molecular weight of the second molecular weight polyethyleneimine is 2~70K; The polyvinylidene fluoride / polyethyleneimine blend membrane described in step S1 is prepared by a phase inversion method; The specific steps of alkalizing the blended membrane in step S2 are: immersing the entire blended membrane in an alkalizing solution at room temperature for a certain period of time, taking out the membrane, rinsing it with pure water, and then storing it in water. The alkalizing solution is a NaOH ethanol solution with a mass fraction of 10% to 20%, and the alkalization time is 10 to 15 minutes.

2. The method for preparing a metal adsorption film according to claim 1, wherein: The specific steps of step S1 are: dissolving polyvinylidene fluoride and first molecular weight polyethyleneimine powder in a non-polar protic solvent to form a membrane liquid, scraping the membrane liquid onto a non-woven fabric support, and placing it in pure water for 12 to 24 hours after the coating is completed, until the phase separation is completed and the membrane structure is completed.

3. The method for preparing a metal adsorption film according to claim 2, wherein: In step S1, the mass ratio of polyvinylidene fluoride to first molecular weight polyethyleneimine is 9:2-5, the mass concentration of polyvinylidene fluoride in the mixed solution is 8%-18%, and the non-polar protic solvent is N,N-dimethylacetamide or N,N-dimethylformamide.

4. The method for preparing a metal adsorption film according to claim 1, wherein: The specific method for grafting the second molecular weight polyethyleneimine in step S2 is: immersing the alkalized blended membrane in a grafting solution containing the second molecular weight polyethyleneimine for grafting, and after the grafting is completed, placing it in a hydrochloric acid solution for activation, the grafting time is 3~8h, the temperature is 50~80℃, and the activation time is 2~12h.

5. The method for preparing a metal adsorption film according to claim 4, wherein: The grafting solution is prepared by dissolving second molecular weight polyethyleneimine in sodium carbonate solution, wherein the mass concentration of the second molecular weight polyethyleneimine is 1-15%, the concentration of sodium carbonate is 1-1.5 mol / L, and the pH value of the hydrochloric acid solution is 1-3.

6. The method for preparing a metal adsorption film according to any one of claims 1 to 5, characterized in that: The first molecular weight polyethyleneimine and the second molecular weight polyethyleneimine are branched polyethyleneimines.

7. A metal adsorption film, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 6.

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