Composite membrane for capturing heavy metal ions and preparation method thereof

Abstract

The invention relates to a preparation method of a functional mixed matrix membrane for capturing heavy metal ions, and the functional mixed matrix membrane is prepared by taking a traditional hydrophobic polymer as a membrane substrate, polyethylene glycol as a pore-foaming agent and positively charged molecular chitosan and methacrylic acid grafted nano silicon dioxide as functional components through a phase inversion method. The permeability and the anti-pollution performance of the membrane are improved by using functional components with strong hydrophilicity; meanwhile, the electrostatic repulsion effect of the membrane on heavy metal ions is enhanced by utilizing positively charged molecules, the adsorption effect of the membrane on the heavy metal ions is enhanced by utilizing functional groups of methacrylic acid, and the removal efficiency of the heavy metal ions is comprehensively improved. The preparation method has the advantages of mild preparation conditions and simple method; the permeability and the heavy metal ion removal performance are excellent, the energy consumption in the operation process is low, and the industrial application prospect is wide.

Description

Technical Field

[0001] The present invention relates to a functional mixed matrix membrane for capturing heavy metal ions and a preparation method thereof, belonging to the technical field of separation membrane preparation. The mixed matrix membrane has the advantages of high pure water flux and high capture efficiency for heavy metal ions, and is suitable for fields such as heavy metal ion wastewater treatment. Background Art

[0002] Water pollution from industrial wastewater discharges of toxic heavy metal ions is a global environmental problem. Rapid industrialization has exacerbated the release of toxic heavy metal ions into natural water bodies. Mining, electroplating, metal processing, textiles, battery manufacturing, tanneries, petroleum refining, paint manufacturing, pesticide and pigment manufacturing, and printing are major sources of heavy metal ion pollution. Heavy metals such as lead, cadmium, copper, arsenic, nickel, chromium, zinc, and mercury are recognized as hazardous heavy metals. Unlike other pollutants, heavy metal ions are not biodegradable and can accumulate in living organisms, causing various illnesses and even death upon entry into the human body. As a result, many countries have introduced very strict legislation to control water pollution from heavy metal ions. Various regulatory bodies have established maximum regulatory limits for the discharge of toxic heavy metal ions into aquatic systems. The World Health Organization (WHO) stipulates that the permissible limits for drinking water are 0.02 ppm for Ni(II), 2 ppm for Cu(I, II), 0.003 ppm for Cd(II), 0.01 ppm for Pb(II), 0.05 ppm for Cr(III), and 0.2 ppm for Fe(III). Therefore, the simple and efficient removal of heavy metal ions from wastewater has become an important issue today.

[0003] In the past few decades, there have been many methods for treating heavy metal ion wastewater, such as adsorption, ion exchange, chemical co-precipitation, coagulation and electrochemical means. However, these traditional methods have problems such as low efficiency, high cost, sensitive operating conditions and easy generation of secondary sludge.

[0004] Existing solutions: Currently, mixed matrix membranes are prepared by mixing multiple functional components to remove heavy metal ions. For example, Chinese patent No. CN202311601123.6 discloses a positively charged mixed matrix membrane doped with etched zinc oxide nanoparticles and its preparation method. 2+ 、Zn 2+ 、Ni 2+ The rejection rate of heavy metal ions reaches 95%-96%, but its operating pressure is 4 bar, the energy consumption is high, and the flux is only 8 L·m -2 ·h -1 bar -1, and cannot be widely used in the field of heavy metal wastewater treatment. Mixed matrix membranes can combine the advantages and characteristics of polymer molecules and inorganic materials. Introducing hydrophilic functional molecules and nanomaterials into hydrophobic polymer membranes can not only improve the flux of the membrane, but also enhance the removal efficiency of the membrane for heavy metal ions because it is rich in coordinating groups such as amino and carboxyl groups. However, relying solely on the specific adsorption of chemical groups still has problems such as easy saturation of adsorption sites, decreased efficiency and flux. Functionally modified nano-oxide materials are used to increase surface adsorption sites, and positively charged molecules such as chitosan are introduced to enhance the electrostatic repulsion between the membrane and heavy metal ions, solving the above problems from the two aspects of chemical adsorption and charged repulsion. Summary of the Invention

[0005] In response to the problems of low permeability and easy contamination of mixed matrix membranes, the present invention provides a new method for preparing mixed matrix membranes for capturing heavy metal ions. The mixed matrix membrane prepared by this method, which contains positively charged functional molecules and functionally modified nano-silica, can effectively improve the membrane flux, heavy metal ion capture efficiency and anti-pollution performance.

[0006] The technical solutions of the present invention are as follows: A functional mixed matrix membrane for capturing heavy metal ions and a preparation method thereof, wherein the specific steps are: (1) Preparation of modified SiO2 nanoparticles At room temperature, 2 g of nano-SiO2 powder was uniformly dispersed in 10 ml of deionized water (Solution 1). Separately, 0.7 g of methacrylic acid (MA), 0.03 g of potassium persulfate (K2S2O8), and 0.02 g of potassium metabisulfite (K2S2O5) were dissolved in 8 ml of deionized water (Solution 2). Under magnetic stirring at 400 rpm, Solution 2 was slowly added dropwise to Solution 1. After magnetic stirring for 4 hours, the mixture was centrifuged for washing and then vacuum dried for 24 hours to obtain methacrylic acid-grafted nano-SiO2 particles (MA-g-SiO2).

[0007] (2) Configuration of casting solution The membrane solution is prepared from the following components by mass percentage: 17-20% polymer powder for membrane preparation, 20-40% polyethylene glycol-400, 2-10% functional chitosan, 0.5-5.0% methacrylic acid-grafted nanosilica, and the remainder being organic solvent. The polymer and polyethylene glycol are dissolved in one organic solvent, designated Solution A; chitosan is dissolved in another organic solvent, designated Solution B; and MA-g-SiO2 particles are dispersed in another organic solvent, designated Solution C. Solutions A, B, and C are thoroughly stirred at 60°C until a uniform membrane casting solution is formed, then allowed to stand to degas before use. All of the above organic solvents are the same.

[0008] (3) Preparation of functional mixed matrix membranes Use a doctor blade coating tester to cast the casting solution in step (2) into a thin layer of a certain thickness on a clean, smooth glass plate. Set the doctor blade speed to 30-50 mm / s. After casting, quickly immerse the glass plate loaded with the thin layer of casting solution in deionized water. Use the phase inversion method to convert the casting solution into a film. Place the formed film in deionized water and let it stand. Replace the deionized water every 3-4 hours until there is no more foam in the water.

[0009] Preferably, the particle size of the nano-SiO2 in step (1) is one of 50 nm, 100 nm, and 200 nm.

[0010] Preferably, the molecular weight of chitosan in step (2) is one of 5 kDa, 10 kDa and 20 kDa.

[0011] Preferably, the organic solvent in step (2) is one of N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide.

[0012] Preferably, the polymer in step (2) is selected from the group consisting of polyethersulfone, polyvinylidene fluoride, and polyacrylonitrile.

[0013] Preferably, the thickness of the thin layer formed by spreading the casting liquid on the surface of the glass plate in step (3) is one of 100 μm, 200 μm and 250 μm.

[0014] This paper proposes a mixed matrix membrane prepared by combining positively charged functional molecules chitosan, functionalized nano-silica, and polymer molecules. The removal efficiency of the membrane for heavy metal ions is improved by combining chemical group adsorption and charge repulsion strategies. The prepared new mixed matrix membrane has a water flux of ≥280 L·m under a test pressure of 1 bar. -2 ·h -1 , for Cd 2+ Cr 3+ 、Cu 2+ , Pb 2+ The capture efficiency of heavy metal ions is ≥98%. Beneficial effects

[0015] Positively charged molecules like chitosan and group-modified nanosilica are added as functional components to a hydrophobic polymer membrane substrate. This significantly enhances the membrane's hydrophilicity, permeability, and anti-fouling properties. Furthermore, it enhances heavy metal ion removal efficiency through electrostatic repulsion and group coordination. The membrane preparation process is simple, and the membrane separation process is easy to operate, energy-efficient, and pollution-free. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Scanning electron microscope image of the membrane surface of Example 9 DETAILED DESCRIPTION

[0017] The present invention will be further described below with reference to specific embodiments.

[0018] Comparative Example 1: (1) Weigh 20 g of polyethersulfone powder and 20 g of polyethylene glycol-400 powder and dissolve them in 30 g of dimethyl sulfoxide. Stir continuously in a constant temperature water bath at 60 °C for 12 h. Then stop stirring and let it stand at the original temperature to degas.

[0019] (2) Use a doctor blade coating tester to spread the casting solution prepared in (1) on the surface of the glass plate to form a 100 μm thick film layer, then quickly immerse it in deionized water, solidify it into a film using the phase inversion method, take it out, and put it into deionized water. Replace the deionized water every 4-6 hours until there is no foam in the replaced water.

[0020] After testing, its pure water flux is 107.64 L·m at 1 bar. -2 ·h -1 , Cd 2+ Cr 3+ 、Cu 2+ , Pb 2+ The removal efficiencies were 0.6%, 0.3%, 1.0% and 0.8% respectively.

[0021] Example 1 (1) Weigh 20 g of polyethersulfone powder and 20 g of polyethylene glycol-400 powder and dissolve them in 30 g of N,N-dimethylformamide. The mixture was stirred continuously in a water bath at 60 °C for 4 h. (2) Weigh 10 g of chitosan with a molecular weight of 5 kD and 5 g of MA-g-SiO2 (nano-SiO2 with a size of 50 nm) and dissolve them in 10 g of N,N-dimethylformamide. Stir continuously in a constant temperature water bath at 60 °C for 4 h. (3) Mix the solutions prepared in (1) and (2) and make up to 100 g with N,N-dimethylformamide. Stir continuously in a constant temperature water bath at 60 °C for 12 h, and then let it stand at the original temperature to degas. (4) Using a doctor blade coating tester, spread the casting solution prepared in (3) on the surface of the glass plate to form a 100 μm thick film layer, then quickly immerse it in deionized water, solidify it into a film using the phase inversion method, take it out, and put it into deionized water. Replace the deionized water every 4-6 hours until there is no foam in the replaced water; The test shows that its pure water flux is 326.8 L·m at 1 bar. -2·h -1 , Cd 2+ Cr 3+ 、Cu 2+ , Pb 2+ The removal efficiencies were 98.2%, 99.1%, 98.7% and 99.3% respectively. Example

[0022] (1) Weigh 20 g of polyethersulfone powder and 20 g of polyethylene glycol-400 powder and dissolve them in 30 g of N,N-dimethylacetamide. Stir continuously in a constant temperature water bath at 60°C for 4 h. (2) Weigh 10 g of chitosan with a molecular weight of 5 kD and 5 g of MA-g-SiO2 (nano-SiO2 with a size of 100 nm) and dissolve them in 10 g of N,N-dimethylacetamide. Stir continuously in a constant temperature water bath at 60 °C for 4 h. (3) Mix the solutions prepared in (1) and (2) and make up to 100 g with N,N-dimethylacetamide. Stir continuously for 12 h in a constant temperature water bath at 60 °C and allow to stand at the original temperature to degas. (4) Using a doctor blade coating tester, spread the casting solution prepared in (3) on the surface of the glass plate to form a 100 μm thick film layer, then quickly immerse it in deionized water, solidify it into a film using the phase inversion method, take it out, and put it into deionized water. Replace the deionized water every 4-6 hours until there is no foam in the replaced water; After testing, its pure water flux is 315.2 L·m at 1 bar. -2 ·h -1 , Cd 2+ Cr 3+ 、Cu 2+ , Pb 2+ The removal efficiencies were 98.4%, 99.1%, 98.6% and 98.9% respectively. Example

[0023] (1) Weigh 20 g of polyvinylidene fluoride powder and 20 g of polyethylene glycol-400 powder and dissolve them in 30 g of dimethyl sulfoxide. Stir continuously in a constant temperature water bath at 60°C for 4 h. (2) Weigh 10 g of chitosan with a molecular weight of 10 kD and 5 g of MA-g-SiO2 (nano-SiO2 with a size of 200 nm) and dissolve them in 10 g of dimethyl sulfoxide. Stir continuously in a constant temperature water bath at 60 °C for 4 h. (3) Mix the solutions prepared in (1) and (2) and make up to 100 g with dimethyl sulfoxide. Stir continuously for 12 h in a constant temperature water bath at 60 °C and allow to stand at the original temperature to degas. (4) Using a doctor blade coating tester, spread the casting solution prepared in (3) on the surface of the glass plate to form a 200 μm thick film layer, then quickly immerse it in deionized water, solidify it into a film using the phase inversion method, take it out, and put it into deionized water. Replace the deionized water every 4-6 hours until there is no foam in the replaced water; After testing, its pure water flux is 297.4 L·m at 1 bar. -2 ·h -1 , Cd 2+ Cr 3+ 、Cu 2+ , Pb 2+ The removal efficiencies were 99.1%, 99.5%, 98.9% and 99.2% respectively. Example

[0024] (1) Weigh 20 g of polyacrylonitrile powder and 20 g of polyethylene glycol-400 powder and dissolve them in 30 g of N,N-dimethylformamide. Stir continuously in a constant temperature water bath at 60°C for 4 h. (2) Weigh 10 g of chitosan with a molecular weight of 20 kD and 5 g of MA-g-SiO2 (nano-SiO2 with a size of 50 nm) and dissolve them in 10 g of N,N-dimethylformamide. Stir continuously in a constant temperature water bath at 60 °C for 4 h. (3) Mix the solutions prepared in (1) and (2) and make up to 100 g with N,N-dimethylformamide. Stir continuously for 12 h in a constant temperature water bath at 60 °C and allow to stand at the original temperature to degas. (4) Using a doctor blade coating tester, spread the casting solution prepared in (3) on the surface of the glass plate to form a 200 μm thick film layer, then quickly immerse it in deionized water, solidify it into a film using the phase inversion method, take it out, and put it into deionized water. Replace the deionized water every 4-6 hours until there is no foam in the replaced water; After testing, its pure water flux is 312.5 L·m at 1 bar. -2 ·h -1 , Cd 2+ Cr 3+ 、Cu 2+ , Pb 2+ The removal efficiencies were 98.6%, 98.1%, 98.4% and 99.0% respectively. Example

[0025] (1) Weigh 20 g of polyacrylonitrile powder and 20 g of polyethylene glycol-400 powder and dissolve them in 30 g of N,N-dimethylacetamide. Stir continuously in a constant temperature water bath at 60°C for 4 h. (2) Weigh 10 g of chitosan with a molecular weight of 10 kD and 5 g of MA-g-SiO2 (nano-SiO2 with a size of 100 nm) and dissolve them in 10 g of N,N-dimethylacetamide. Stir continuously in a constant temperature water bath at 60 °C for 4 h. (3) Mix the solutions prepared in (1) and (2) and make up to 100 g with N,N-dimethylacetamide. Stir continuously in a constant temperature water bath at 60 °C for 12 h. Then stop stirring and let it stand at the original temperature to degas. (4) Using a doctor blade coating tester, spread the casting solution prepared in (3) on the surface of the glass plate to form a 250 μm thick film layer, then quickly immerse it in deionized water, solidify it into a film using the phase inversion method, take it out, and put it into deionized water. Replace the deionized water every 4-6 hours until there is no foam in the replaced water; After testing, its pure water flux is 282.3 L·m at 1 bar. -2 ·h -1 , Cd 2+ Cr 3+ 、Cu 2+ , Pb 2+ The removal efficiencies were 98.0%, 98.2%, 98.7% and 99.1% respectively. Example

[0026] (1) Weigh 20 g of polyvinylidene fluoride powder and 20 g of polyethylene glycol-400 powder and dissolve them in 30 g of dimethyl sulfoxide. Stir continuously in a constant temperature water bath at 60°C for 4 h. (2) Weigh 10 g of chitosan with a molecular weight of 20 kD and 5 g of MA-g-SiO2 (nano-SiO2 with a size of 200 nm) and dissolve them in 10 g of dimethyl sulfoxide. Stir continuously in a constant temperature water bath at 60 °C for 4 h. (3) Mix the solutions prepared in (1) and (2) and make up to 100 g with dimethyl sulfoxide. Stir continuously for 12 h in a constant temperature water bath at 60 °C and allow to stand at the original temperature to degas. (4) Using a doctor blade coating tester, spread the casting solution prepared in (3) on the surface of the glass plate to form a 250 μm thick film layer, then quickly immerse it in deionized water, solidify it into a film using the phase inversion method, take it out, and put it into deionized water. Replace the deionized water every 4-6 hours until there is no foam in the replaced water; After testing, its pure water flux is 289.6 L·m at 1 bar. -2 ·h -1 , Cd 2+ Cr 3+ 、Cu 2+ , Pb 2+The removal efficiencies were 98.6%, 98.1%, 98.9% and 98.8% respectively. Example

[0027] (1) Weigh 20 g of polyvinylidene fluoride powder and 20 g of polyethylene glycol-400 powder and dissolve them in 30 g of N,N-dimethylformamide. Stir continuously in a constant temperature water bath at 60°C for 4 h. (2) Weigh 10 g of chitosan with a molecular weight of 20 kD and 5 g of MA-g-SiO2 (nano-SiO2 with a size of 50 nm) and dissolve them in 10 g of N,N-dimethylformamide. Stir continuously in a constant temperature water bath at 60 °C for 4 h. (3) Mix the solutions prepared in (1) and (2) and make up to 100 g with N,N-dimethylformamide. Stir continuously for 12 h in a constant temperature water bath at 60 °C and allow to stand at the original temperature to degas. (4) Using a doctor blade coating tester, spread the casting solution prepared in (3) on the surface of the glass plate to form a 100 μm thick film layer, then quickly immerse it in deionized water, solidify it into a film using the phase inversion method, take it out, and put it into deionized water. Replace the deionized water every 4-6 hours until there is no foam in the replaced water; After testing, its pure water flux is 336.9 L·m at 1 bar. -2 ·h -1 , Cd 2+ Cr 3+ 、Cu 2+ , Pb 2+ The removal efficiencies were 98.7%, 98.3%, 99.4% and 99.1% respectively. Example

[0028] (1) Weigh 20 g of polyacrylonitrile powder and 20 g of polyethylene glycol-400 powder and dissolve them in 30 g of N,N-dimethylacetamide. Stir continuously in a constant temperature water bath at 60°C for 4 h. (2) Weigh 10 g of chitosan with a molecular weight of 5 kD and 5 g of MA-g-SiO2 (nano-SiO2 with a size of 100 nm) and dissolve them in 10 g of N,N-dimethylacetamide. Stir continuously in a constant temperature water bath at 60 °C for 4 h. (3) Mix the solutions prepared in (1) and (2) and make up to 100 g with N,N-dimethylacetamide. Stir continuously for 12 h in a constant temperature water bath at 60 °C and allow to stand at the original temperature to degas. (4) Using a doctor blade coating tester, spread the casting solution prepared in (3) on the surface of the glass plate to form a 200 μm thick film layer, then quickly immerse it in deionized water, solidify it into a film using the phase inversion method, take it out, and put it into deionized water. Replace the deionized water every 4-6 hours until there is no foam in the replaced water; After testing, its pure water flux is 298.5 L·m at 1 bar. -2 ·h -1 , Cd 2+ Cr 3+ 、Cu 2+ , Pb 2+ The removal efficiencies were 98.3%, 98.7%, 99.6% and 99.8% respectively. Example

[0029] (1) Weigh 20 g of polyethersulfone powder and 20 g of polyethylene glycol-400 powder and dissolve them in 30 g of dimethyl sulfoxide. Stir continuously in a constant temperature water bath at 60°C for 4 h. (2) Weigh 10 g of chitosan with a molecular weight of 10 kD and 5 g of MA-g-SiO2 (nano-SiO2 with a size of 200 nm) and dissolve them in 10 g of dimethyl sulfoxide. Stir continuously in a constant temperature water bath at 60 °C for 4 h. (3) Mix the solutions prepared in (1) and (2) and make up to 100 g with dimethyl sulfoxide. Stir continuously for 12 h in a constant temperature water bath at 60 °C and allow to stand at the original temperature to degas. (4) Using a doctor blade coating tester, spread the casting solution prepared in (3) on the surface of the glass plate to form a 250 μm thick film layer, then quickly immerse it in deionized water, solidify it into a film using the phase inversion method, take it out, and put it into deionized water. Replace the deionized water every 4-6 hours until there is no foam in the replaced water; After testing, its pure water flux is 284.1 L·m at 1 bar. -2 ·h -1 , Cd 2+ Cr 3+ 、Cu 2+ , Pb 2+ The removal efficiencies were 98.7%, 98.4%, 98.8% and 99.5% respectively.

Claims

1. A method for preparing a functional mixed matrix membrane for capturing heavy metal ions, comprising the following steps: (1) Preparation of modified SiO2 nanoparticles At room temperature, 2 g of nano-SiO2 powder was uniformly dispersed in 10 ml of deionized water (Solution 1). Separately, 0.7 g of methacrylic acid (MA), 0.03 g of potassium persulfate (K2S2O8), and 0.02 g of potassium metabisulfite (K2S2O5) were dissolved in 8 ml of deionized water (Solution 2). Under magnetic stirring at 400 rpm, Solution 2 was slowly added dropwise to Solution 1. After magnetic stirring for 4 hours, the mixture was centrifuged, washed, and vacuum-dried for 24 hours to obtain methacrylic acid-grafted nano-SiO2 particles (MA-g-SiO2). (2) Configuration of casting solution The casting solution is prepared by the following components in mass percentage: 17-20% polymer powder for membrane preparation, 20-40% polyethylene glycol-400, 2-10% functional molecule chitosan, 0.5-5.0% methacrylic acid grafted nano-silica, and the rest is organic solvent. The polymer and polyethylene glycol are dissolved in an organic solvent, recorded as solution A; chitosan is dissolved in an organic solvent, recorded as solution B; MA-g-SiO2 particles are dispersed in an organic solvent, recorded as solution C. Under the condition of 60°C, the three solutions A, B, and C are fully stirred to form a uniform casting solution, and then allowed to stand for degassing and standby. The above organic solvents are all the same solvent; (3) Preparation of functional mixed matrix membranes Use a doctor blade coating tester to cast the casting solution in step (2) into a thin layer of a certain thickness on a clean, smooth glass plate. Set the doctor blade speed to 30-50 mm / s. After casting, quickly immerse the glass plate loaded with the thin layer of casting solution in deionized water. Use the phase inversion method to convert the casting solution into a film. Place the formed film in deionized water and let it stand. Replace the deionized water every 3-4 hours until there is no more foam in the water.

2. The preparation method according to claim 1, wherein The particle size of the nano-SiO2 in step (1) is one of 50 nm, 100 nm, and 200 nm.

3. The preparation method according to claim 1, wherein The molecular weight of chitosan in step (2) is one of 5 kDa, 10 kDa and 20 kDa.

4. The preparation method according to claim 1, characterized in that The organic solvent in step (2) is one of N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide.

5. The preparation method according to claim 1, characterized in that In step (2), the polymer is selected from one of polyethersulfone, polyvinylidene fluoride and polyacrylonitrile.

6. The preparation method according to claim 1, characterized in that In step (3), the thickness of the thin layer formed by spreading the casting liquid on the surface of the glass plate is one of 100 μm, 200 μm, and 250 μm.

7. A high-flux ultrafiltration membrane for efficiently capturing heavy metal ions prepared by the functional mixed matrix membrane for capturing heavy metal ions and the preparation method thereof according to any one of claims 1 to 6, characterized in that: The pure water flux of the prepared mixed matrix membrane is ≥280 L·m -2 ·h -1 , for Cd 2+ Cr 3+ 、Cu 2+ , Pb 2+ The capture efficiency of heavy metal ions is ≥98%.

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