A composite membrane for capturing heavy metal ions and a method for preparing the same

Abstract

The application relates to a preparation method of a functional mixed matrix membrane for capturing heavy metal ions, which is prepared by a phase inversion method and takes a traditional hydrophobic polymer as a membrane substrate, polyethylene glycol as a pore-forming agent, a positively charged molecule chitosan and methyl methacrylic acid grafted nanosilica as functional components; the strong hydrophilic functional components are used to improve the permeability and anti-pollution performance of the membrane; meanwhile, the positively charged molecules are used to enhance the electrostatic repulsion of the membrane to heavy metal ions, and the functional groups of the methyl methacrylic acid are used to enhance the adsorption of the membrane to heavy metal ions, so that the heavy metal ion removal efficiency is comprehensively improved. The application has the advantages of mild preparation conditions, simple method, excellent permeability and heavy metal ion removal performance, low energy consumption in the operation process, and wide industrial application prospect.

Description

Technical Field

[0001] This invention relates to a functional hybrid matrix membrane for capturing heavy metal ions and its preparation method, belonging to the field of separation membrane preparation technology. The hybrid matrix membrane has advantages such as 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 Technology

[0002] The pollution of water bodies by toxic heavy metal ions in industrial wastewater discharge is a global environmental problem. Rapid industrial development has exacerbated the release of toxic heavy metal ions into natural water bodies. Mining, electroplating, metal processing, textiles, battery manufacturing, tanneries, oil refining, paint manufacturing, pesticides, pigment manufacturing, and printing industries are the main sources of heavy metal ion pollution. Lead, cadmium, copper, arsenic, nickel, chromium, zinc, and mercury are recognized as harmful heavy metals. Unlike other pollutants, heavy metal ions are not biodegradable and can accumulate in organisms, causing various diseases and even death after entering the human body. They are non-biodegradable and can accumulate in biological tissues, causing various diseases and disorders. Therefore, many countries have introduced very strict legislation to control water pollution from heavy metal ions. Different regulatory agencies have set maximum limits for the discharge of toxic heavy metal ions into aquatic systems. The World Health Organization (WHO) has set permissible limits for heavy metal ions in drinking water as follows: Ni(II) 0.02 ppm, Cu(I, II) 2 ppm, Cd(II) 0.003 ppm, Pb(II) 0.01 ppm, Cr(III) 0.05 ppm, and Fe(III) 0.2 ppm. Therefore, the simple and efficient removal of heavy metal ions from wastewater has become an important research topic.

[0003] Over the past few decades, various methods have been used to treat heavy metal ion wastewater, such as adsorption, ion exchange, chemical coprecipitation, coagulation, and electrochemical methods. However, these traditional methods suffer from problems such as low efficiency, high cost, sensitivity to operating conditions, and the generation of secondary sludge.

[0004] Existing solutions: Currently, mixed matrix films are prepared using a mixture of multiple functional components to remove heavy metal ions. For example, Chinese patent CN202311601123.6 discloses a positively charged mixed matrix film doped with etched zinc oxide nanoparticles and its preparation method, for removing Cu... 2+ Zn 2+ Ni 2+ It achieves a rejection rate of 95%-96% for heavy metal ions, but its operating pressure is 4 bar, resulting in high energy consumption and a flux of only 8 L·m⁻¹. -2 ·h -1 ·bar -1However, this approach cannot be widely applied in the treatment of heavy metal wastewater. Hybrid matrix membranes combine the advantages of polymer molecules and inorganic materials. Introducing hydrophilic functional molecules and nanomaterials into hydrophobic polymer membranes can improve membrane flux and enhance the removal efficiency of heavy metal ions due to the presence of amino and carboxyl groups. However, relying solely on the specific adsorption of chemical groups still suffers from problems such as easy saturation of adsorption sites and decreased efficiency and flux. Functionalized nano-oxide materials are used to increase surface adsorption sites, while positively charged chitosan molecules are introduced to enhance the electrostatic repulsion between the membrane and heavy metal ions, thus addressing the aforementioned problems from both chemical adsorption and charge repulsion perspectives. Summary of the Invention

[0005] To address the issues of low permeability and susceptibility to fouling in mixed matrix membranes, this invention provides a novel preparation method for mixed matrix membranes used to capture heavy metal ions. The mixed matrix membrane prepared by this method, containing positively charged functional molecules and functionalized modified nano-silica, can effectively improve membrane flux, heavy metal ion capture efficiency, and antifouling performance.

[0006] The technical solution of the present invention is as follows:

[0007] A functional hybrid matrix membrane for capturing heavy metal ions and its preparation method, the specific steps of which are as follows:

[0008] (1) Preparation of modified SiO2 nanoparticles

[0009] 2 g of nano-SiO2 powder was weighed and uniformly dispersed in 10 ml of deionized water at room temperature, and this solution was labeled as 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 weighed and dissolved in 8 ml of deionized water, and this solution was labeled as solution 2. Solution 2 was slowly added dropwise to solution 1 under magnetic stirring at 400 rpm. After magnetic stirring for 4 hours, the mixture was centrifuged, washed, and vacuum dried for 24 hours to obtain methacrylic acid-grafted nano-silica particles.

[0010] (2) Preparation of casting solution

[0011] 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 nano-silica, and the remainder being an organic solvent. The polymer and polyethylene glycol are dissolved in one organic solvent, denoted as solution A; the chitosan is dissolved in another organic solvent, denoted as solution B; and the methacrylic acid-grafted nano-silica particles are dispersed in another organic solvent, denoted as solution C. At 60°C, solutions A, B, and C are thoroughly stirred until a homogeneous casting solution is formed, and then allowed to stand to remove bubbles before use. All the above-mentioned organic solvents are the same.

[0012] (3) Preparation of functional hybrid matrix membranes

[0013] Using a doctor blade coating tester, the casting solution from step (2) is cast into a thin layer of a certain thickness on a clean, smooth glass plate. The doctor blade speed is set to 30-50 mm / s. After casting, the glass plate loaded with the casting solution layer is quickly immersed in deionized water, and the casting solution is converted into a film using the phase inversion method. The formed film is placed in deionized water and allowed to stand. The deionized water is changed every 3-4 hours until there are no more scum particles in the water.

[0014] In step (1), the preferred particle size of nano-SiO2 is one of 50 nm, 100 nm, or 200 nm.

[0015] In step (2), the molecular weight of chitosan is preferably one of 5 kDa, 10 kDa, or 20 kDa.

[0016] The preferred organic solvent in step (2) is one of N,N-dimethylformamide, N,N-dimethylacetamide, or dimethyl sulfoxide.

[0017] In preferred step (2), the polymer is selected from one of polyethersulfone, polyvinylidene fluoride, and polyacrylonitrile.

[0018] In preferred step (3), the thickness of the thin layer formed by spreading the casting solution on the glass plate surface is one of 100µm, 200µm, or 250µm.

[0019] This invention proposes a novel mixed matrix membrane prepared by combining positively charged functional molecules chitosan, functionalized nano-silica, and polymer molecules. This membrane improves the removal efficiency of heavy metal ions by employing a combination of chemical adsorption and charge repulsion strategies. The prepared novel mixed matrix membrane exhibits a pure water flux ≥280 L·m⁻¹ under a test pressure of 1 bar. -2 ·h -1 , for Cd 2+ Cr 3+ Cu2+ Pb 2+ The capture efficiency of heavy metal ions is ≥98%.

[0020] Beneficial effects:

[0021] Nano-sized silica modified with positively charged molecules and groups such as chitosan as functional components is added to hydrophobic polymer membrane substrates. On the one hand, this significantly enhances the membrane's hydrophilicity, permeability, and antifouling properties; on the other hand, it enhances the removal efficiency of heavy metal ions through electrostatic repulsion and group coordination. The membrane preparation process is simple, and the membrane separation process is easy to operate, energy-efficient, and produces no secondary pollution. Attached Figure Description

[0022] Figure 1 Electron micrograph of the membrane surface in Example 9 Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments.

[0024] Comparative Example 1:

[0025] (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 for 12 h in a constant temperature water bath at 60℃, then stop stirring and let stand at the original temperature to remove bubbles.

[0026] (2) Using a doctor blade coating tester, the casting liquid prepared in (1) is spread on the surface of a glass plate to form a film layer with a thickness of 100 μm. Then, it is quickly immersed in deionized water, solidified into a film by phase inversion, and then taken out and placed in deionized water. The deionized water is replaced every 4-6 hours until there is no foam in the water.

[0027] Tests showed that its pure water flux at 1 bar was 107.64 L·m. -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.

[0028] Example 1:

[0029] (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.

[0030] The mixture was continuously stirred for 4 hours in a constant temperature water bath at 60℃.

[0031] (2) Weigh 10g of chitosan with a molecular weight of 5 kD and 5g of methacrylic acid-grafted nano silica particles (nano SiO2 with a size of 50 nm) and dissolve them in 10g of N,N-dimethylformamide. Stir continuously for 4h in a constant temperature water bath at 60℃.

[0032] (3) Mix the solutions prepared in (1) and (2) respectively, and add N,N-dimethylformamide to make up to 100g. Stir continuously for 12h in a constant temperature water bath at 60℃, and then let stand to remove bubbles under the original temperature conditions.

[0033] (4) Using a doctor blade coating tester, the casting liquid prepared in (3) is spread on the surface of a glass plate to form a film layer with a thickness of 100 μm. Then, it is quickly immersed in deionized water, solidified into a film by phase inversion, and then taken out and placed in deionized water. The deionized water is replaced every 4-6 hours until there is no foam in the water.

[0034] Tests showed that its pure water flux at 1 bar was 326.8 L·m. -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.

[0035] Example 2:

[0036] (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 for 4 h in a constant temperature water bath at 60℃.

[0037] (2) Weigh 10 g of chitosan with a molecular weight of 5 kD and 5 g of methacrylic acid-grafted nano silica particles (nano SiO2 with a size of 100 nm) and dissolve them in 10 g of N,N-dimethylacetamide. Stir continuously for 4 h in a constant temperature water bath at 60℃.

[0038] (3) Mix the solutions prepared in (1) and (2) respectively, and add N,N-dimethylacetamide to make up to 100 g. Stir continuously for 12 h in a constant temperature water bath at 60℃, and let stand to remove bubbles under the original temperature conditions.

[0039] (4) Using a doctor blade coating tester, the casting liquid prepared in (3) is spread on the surface of a glass plate to form a film layer with a thickness of 100 μm. Then, it is quickly immersed in deionized water, solidified into a film by phase inversion, and then taken out and placed in deionized water. The deionized water is replaced every 4-6 hours until there is no foam in the water.

[0040] Tests showed that its pure water flux at 1 bar was 315.2 L·m. -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.

[0041] Example 3:

[0042] (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 for 4 h in a constant temperature water bath at 60℃.

[0043] (2) Weigh 10 g of chitosan with a molecular weight of 10 kD and 5 g of methacrylic acid-grafted nano silica particles (nano SiO2 with a size of 200 nm) and dissolve them in 10 g of dimethyl sulfoxide. Stir continuously for 4 h in a constant temperature water bath at 60℃.

[0044] (3) Mix the solutions prepared in (1) and (2) respectively, and add dimethyl sulfoxide to make up to 100 g. Stir continuously for 12 h in a constant temperature water bath at 60℃, and let stand to remove bubbles under the original temperature conditions.

[0045] (4) Using a doctor blade coating tester, the casting liquid prepared in (3) is spread on the surface of a glass plate to form a film layer with a thickness of 200 μm. Then, it is quickly immersed in deionized water, solidified into a film by phase inversion, and then taken out and placed in deionized water. The deionized water is replaced every 4-6 hours until there is no foam in the water.

[0046] Tests showed that its pure water flux at 1 bar was 297.4 L·m. -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.

[0047] Example 4:

[0048] (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 for 4 h in a constant temperature water bath at 60℃.

[0049] (2) Weigh 10 g of chitosan with a molecular weight of 20 kD and 5 g of methacrylic acid-grafted nano silica particles (nano SiO2 with a size of 50 nm) and dissolve them in 10 g of N,N-dimethylformamide. Stir continuously for 4 h in a constant temperature water bath at 60℃.

[0050] (3) Mix the solutions prepared in (1) and (2) respectively, and add N,N-dimethylformamide to 100 g. Stir continuously for 12 h in a constant temperature water bath at 60℃, and let stand to remove bubbles under the original temperature conditions.

[0051] (4) Using a doctor blade coating tester, the casting liquid prepared in (3) is spread on the surface of a glass plate to form a film layer with a thickness of 200 μm. Then, it is quickly immersed in deionized water, solidified into a film by phase inversion, and then taken out and placed in deionized water. The deionized water is replaced every 4-6 hours until there is no foam in the water.

[0052] Tests showed that its pure water flux at 1 bar was 312.5 L·m. -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.

[0053] Example 5:

[0054] (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 for 4 h in a constant temperature water bath at 60℃.

[0055] (2) Weigh 10 g of chitosan with a molecular weight of 10 kD and 5 g of methacrylic acid-grafted nano silica particles (nano SiO2 with a size of 100 nm) and dissolve them in 10 g of N,N-dimethylacetamide. Stir continuously for 4 h in a constant temperature water bath at 60℃.

[0056] (3) Mix the solutions prepared in (1) and (2) respectively, and add N,N-dimethylacetamide to make up to 100 g. Stir continuously for 12 h in a constant temperature water bath at 60℃, then stop stirring and let stand at the original temperature to remove bubbles.

[0057] (4) Using a doctor blade coating tester, the casting liquid prepared in (3) is spread on the surface of a glass plate to form a film layer with a thickness of 250 μm. Then, it is quickly immersed in deionized water, solidified into a film by phase inversion, and then taken out and placed in deionized water. The deionized water is replaced every 4-6 hours until there is no foam in the water.

[0058] Tests showed that its pure water flux at 1 bar was 282.3 L·m. -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.

[0059] Example 6:

[0060] (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 for 4 h in a constant temperature water bath at 60℃.

[0061] (2) Weigh 10 g of chitosan with a molecular weight of 20 kD and 5 g of methacrylic acid-grafted nano silica particles (nano SiO2 with a size of 200 nm) and dissolve them in 10 g of dimethyl sulfoxide. Stir continuously for 4 h in a constant temperature water bath at 60 °C.

[0062] (3) Mix the solutions prepared in (1) and (2) respectively, and add dimethyl sulfoxide to make up to 100 g. Stir continuously for 12 h in a constant temperature water bath at 60℃, and let stand to remove bubbles under the original temperature conditions.

[0063] (4) Using a doctor blade coating tester, the casting liquid prepared in (3) is spread on the surface of a glass plate to form a film layer with a thickness of 250 μm. Then, it is quickly immersed in deionized water, solidified into a film by phase inversion, and then taken out and placed in deionized water. The deionized water is replaced every 4-6 hours until there is no foam in the water.

[0064] Tests showed that its pure water flux at 1 bar was 289.6 L·m. -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.

[0065] Example 7:

[0066] (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 for 4 h in a constant temperature water bath at 60℃.

[0067] (2) Weigh 10 g of chitosan with a molecular weight of 20 kD and 5 g of methacrylic acid-grafted nano silica particles (nano SiO2 with a size of 50 nm) and dissolve them in 10 g of N,N-dimethylformamide. Stir continuously for 4 h in a constant temperature water bath at 60℃.

[0068] (3) Mix the solutions prepared in (1) and (2) respectively, and add N,N-dimethylformamide to 100 g. Stir continuously for 12 h in a constant temperature water bath at 60℃, and let stand to remove bubbles under the original temperature conditions.

[0069] (4) Using a doctor blade coating tester, the casting liquid prepared in (3) is spread on the surface of a glass plate to form a film layer with a thickness of 100 μm. Then, it is quickly immersed in deionized water, solidified into a film by phase inversion, and then taken out and placed in deionized water. The deionized water is replaced every 4-6 hours until there is no foam in the water.

[0070] Tests showed that its pure water flux at 1 bar was 336.9 L·m. -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.

[0071] Example 8:

[0072] (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 for 4 h in a constant temperature water bath at 60℃.

[0073] (2) Weigh 10 g of chitosan with a molecular weight of 5 kD and 5 g of methacrylic acid-grafted nano silica particles (nano SiO2 with a size of 100 nm) and dissolve them in 10 g of N,N-dimethylacetamide. Stir continuously for 4 h in a constant temperature water bath at 60℃.

[0074] (3) Mix the solutions prepared in (1) and (2) respectively, and add N,N-dimethylacetamide to make up to 100 g. Stir continuously for 12 h in a constant temperature water bath at 60℃, and let stand to remove bubbles under the original temperature conditions.

[0075] (4) Using a doctor blade coating tester, the casting liquid prepared in (3) is spread on the surface of a glass plate to form a film layer with a thickness of 200 μm. Then, it is quickly immersed in deionized water, solidified into a film by phase inversion, and then taken out and placed in deionized water. The deionized water is replaced every 4-6 hours until there is no foam in the water.

[0076] Tests showed that its pure water flux at 1 bar was 298.5 L·m. -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.

[0077] Example 9:

[0078] 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 for 4 h in a constant temperature water bath at 60℃.

[0079] (2) Weigh 10 g of chitosan with a molecular weight of 10 kD and 5 g of methacrylic acid-grafted nano silica particles (nano SiO2 with a size of 200 nm) and dissolve them in 10 g of dimethyl sulfoxide. Stir continuously for 4 h in a constant temperature water bath at 60℃.

[0080] (3) Mix the solutions prepared in (1) and (2) respectively, and add dimethyl sulfoxide to make up to 100 g. Stir continuously for 12 h in a constant temperature water bath at 60℃, and let stand to remove bubbles under the original temperature conditions.

[0081] (4) Using a doctor blade coating tester, the casting liquid prepared in (3) is spread on the surface of a glass plate to form a film layer with a thickness of 250 μm. Then, it is quickly immersed in deionized water, solidified into a film by phase inversion, and then taken out and placed in deionized water. The deionized water is replaced every 4-6 hours until there is no foam in the water.

[0082] Tests showed that its pure water flux at 1 bar was 284.1 L·m⁻¹. -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 hybrid matrix membrane for capturing heavy metal ions, comprising the following specific steps: (1) Preparation of modified SiO2 nanoparticles 2 g of nano-SiO2 powder was weighed and uniformly dispersed in 10 ml of deionized water at room temperature, and this was recorded as solution 1. Separately, 0.7 g of methacrylic acid, 0.03 g of potassium persulfate and 0.02 g of potassium metabisulfite were weighed and dissolved in 8 ml of deionized water, and this was recorded as solution 2. Under magnetic stirring at 400 rpm, solution 2 was slowly added dropwise to solution 1. After stirring magnetically for 4 hours, the mixture was centrifuged, washed, and vacuum dried for 24 hours to obtain methacrylic acid-grafted nano-silica particles. (2) Preparation of casting solution The casting 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 nano-silica, and the remainder being an organic solvent. The polymer and polyethylene glycol are dissolved in one organic solvent, denoted as solution A; the chitosan is dissolved in another organic solvent, denoted as solution B; the methacrylic acid-grafted nano-silica particles are dispersed in another organic solvent, denoted as solution C. At 60°C, solutions A, B, and C are thoroughly stirred until a homogeneous casting solution is formed, and then allowed to stand to remove bubbles before use. All the above-mentioned organic solvents are the same. (3) Preparation of functional hybrid matrix membranes Using a doctor blade coating tester, the casting solution from step (2) is cast into a thin layer of a certain thickness on a clean and smooth glass plate. The doctor blade speed is set to 30-50 mm / s. After casting, the glass plate loaded with the thin layer of casting solution is quickly immersed in deionized water, and the casting solution is converted into a film by phase inversion. The formed film is placed in deionized water and left to stand. The deionized water is replaced every 3-4 hours until there is no more foam in the water.

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

3. The preparation method according to claim 1, characterized in that... In step (2), the molecular weight of chitosan is one of 5 kDa, 10 kDa, or 20 kDa.

4. The preparation method according to claim 1, characterized in that... In step (2), the organic solvent 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 selected is one of polyethersulfone, polyvinylidene fluoride, or 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 solution on the glass plate surface is one of 100µm, 200µm, or 250µm.

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

Images