Positively-charged composite membrane based on sulfonated COF interlayer and application of positively-charged composite membrane

Abstract

The invention relates to a high-performance positively charged composite membrane and a preparation method thereof, in particular to a nanofiltration membrane containing a sulfonated imino covalent organic framework (TpPa-SO3H) interlayer. The nanofiltration membrane adopts a three-layer structure design, and comprises a base membrane layer, a TpPa-SO3H middle interlayer and a positively charged separation surface layer. Wherein the TpPa-SO3H interlayer is formed by in-situ growth of polyphenol and sulfated amine under the action of an oxidizing agent, and the separation surface layer is assembled and constructed through electrostatic attraction and hydrogen-bond interaction between positively charged polyelectrolyte and sulfonic acid groups. The TpPa-SO3H interlayer is introduced to effectively regulate and control the pore size distribution and hydrophilicity of the surface of the substrate, the formed negative electricity interlayer can promote the assembly of a polyelectrolyte positive electricity layer, and the interception performance and the operation stability of the composite membrane on heavy metal cations are remarkably improved. Compared with a traditional nanofiltration membrane, the composite membrane prepared through the method keeps high water flux (larger than or equal to 40 L.m <-2 >. H <-1 >. Bar <-1 >), meanwhile, the rejection rate of heavy metal cations such as Cr < 3 + >, Mn < 2 + > and Co < 2 + > is larger than or equal to 95%, and the composite membrane has excellent long-term operation stability. The preparation method is simple in process and low in cost, and has a wide application prospect in the field of heavy metal wastewater treatment.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically to a composite membrane based on layer-by-layer self-assembly technology and its preparation method. By incorporating a sulfonated covalent organic framework (COF) interlayer and a positively charged separation surface layer, this composite membrane exhibits high water flux, excellent heavy metal ion selectivity, and good anti-pollution properties, making it suitable for industrial wastewater treatment, heavy metal ion recovery, and other fields. Background Art

[0002] Industrial wastewater (such as mining wastewater, smelting wastewater, and coal-fired flue gas treatment sludge) often contains toxic heavy metals such as chromium (Cr), arsenic (As), and mercury (Hg). If discharged without effective treatment, these ions pose serious risks to the ecological environment and human health. Currently, the removal of heavy metal ions relies primarily on traditional methods such as chemical precipitation, ion exchange, adsorption, and electrochemical treatment. However, these methods generally suffer from low removal efficiency, high energy consumption, and the generation of secondary pollution (such as heavy metal sludge), making them difficult to meet increasingly stringent environmental protection requirements.

[0003] COF materials have shown great potential in the field of membrane separation due to their highly ordered pore structure, tunable chemical properties, and excellent stability. However, the interlayer pore size (1-5 nm) of traditional two-dimensional COF materials is much larger than the size of hydrated heavy metal ions (<1 nm), making it difficult to achieve efficient retention when used alone. In addition, existing COF-based nanofiltration membranes often face the following problems during the preparation process: (1) uneven COF dispersion, and direct addition of COF materials can easily lead to membrane pore blockage and reduce flux; (2) poor interfacial compatibility, and weak bonding between the COF layer and the base membrane, affecting the mechanical strength and long-term stability of the membrane.

[0004] In the prior art, patent CN202411308166 proposes a composite nanofiltration membrane containing COF, but it suffers from problems such as low removal efficiency, uneven COF dispersion clogging the pores, and a significant decrease in flux. To address the above-mentioned drawbacks, the present invention proposes a novel method for preparing a positively charged composite membrane: (1) introducing a sulfonated COF (TpPa-SO3H) interlayer and constructing an intermediate layer with uniform pore size and negative charge characteristics on the surface of the base membrane through in-situ growth technology, thereby enhancing interfacial bonding and optimizing the pore structure; (2) electrostatically self-assembling a positively charged separation layer, utilizing the negative charge of TpPa-SO3H to attract positively charged polyelectrolytes, forming a dense and high-charge-density separation layer, synergistically improving the membrane's screening capacity and electrostatic repulsion effect, preventing COF shedding and pore clogging, and ensuring the membrane's high flux and long-term stability.

[0005] Through the above innovative design, the present invention effectively solves the key problems of traditional nanofiltration membranes in the separation of heavy metal ions, such as the difficulty in balancing flux and selectivity, easy pollution, and poor durability, and has significant prospects for industrial application. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a positively charged composite membrane containing TpPa-SO3H by layer-by-layer self-assembly, thereby improving separation performance and long-term operational stability. The technical solution adopted by the present invention is: a method for preparing a positively charged composite membrane containing TpPa-SO3H by layer-by-layer self-assembly, the specific steps of which are as follows: (1) Basement membrane pretreatment Soak the basement membrane in 2 mol / L sodium hydroxide solution and place it in a 60°C constant temperature water bath for 2 h. After taking it out, wash it with pure water three times and then soak it in pure water for 24 h. (2) Preparation of TpPa-SO3H interlayer Prepare an aqueous solution containing 0.5-2.5% sulfonated amine organic compound, add 0.05-0.2% oxidant, and ultrasonicate for 0.1-0.5 h to obtain solution 1; prepare an organic solution of 1,3,5-triformylphloroglucinol and ultrasonically disperse until completely dissolved to obtain solution 2; mix solution 1 and solution 2 in proportion, stir for 5-30 seconds, and then immerse the pretreated basement membrane horizontally in the solution and allow in situ growth for 1-3 days; (3) Separation surface construction Prepare a polyelectrolyte solution of a certain concentration; take out the membrane obtained in step (2), wipe it dry, pour 15-25 mL of the polyelectrolyte solution on the membrane surface, and filter it under a vacuum condition of 0.1-1 bar; dry it at 60℃ for 5-20 min to obtain a finished composite membrane.

[0007] Preferably, the base film in step (1) is one of polyacrylonitrile, polyvinylidene fluoride, polyethersulfone and polysulfone.

[0008] Preferably, the sulfonated diamine compound in step (2) is one of 2,5-diaminobenzenesulfonic acid, 3,5-diaminobenzoic acid, and 4,4-diaminobenzenesulfonylanilide.

[0009] Preferably, the solvent for 1,3,5-triformylphloroglucinol in step (2) is one of ethanol, acetic acid and methanol.

[0010] Preferably, the oxide in step (2) is one of dopamine hydrochloride, tannic acid, and gallic acid.

[0011] Preferably, the polyelectrolyte in step (3) is one of polyethyleneimine, polylysine, and polypropyleneimine. Beneficial effects

[0012] This invention proposes constructing a sulfonated COF (TpPa-SO3H) interlayer on the surface of a base membrane through an in situ growth method. A positively charged polyelectrolyte separation layer is then electrostatically assembled on the TpPa-SO3H interlayer via vacuum filtration, forming a high-charge-density functional separation layer. By co-manipulating the pore size of the interlayer and the polyelectrolyte, this approach overcomes the pore mismatch between the hydrated heavy metal ion size and the pore size of conventional COF membranes. By optimizing interlayer charge interactions, this approach achieves high heavy metal rejection while maintaining high flux, thus overcoming the "high flux-high selectivity" trade-off inherent in conventional membrane materials. (1) Structural advantages The high specific surface area and modifiability of TpPa-SO3H significantly improve the hydrophilicity of the membrane; the negative charge of the interlayer effectively enables the uniform self-assembly of vaginal polyelectrolytes.

[0013] (2) Improved separation performance The ordered pores of TpPa-SO3H reduce mass transfer resistance and increase membrane flux; the electrostatic self-assembled layer makes the membrane isoelectric point pH ≥ 7.5, and has excellent retention rate for heavy metals such as Cr³⁺ and Cd²⁺.

[0014] (3) Long-term stability The in-situ growth technology ensures a strong interfacial bond between TpPa-SO3H and the base film; the semiquinone radicals generated by the oxidant firmly anchor the COF material on the base film surface through oxidative polymerization reaction, thus avoiding interlayer delamination. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the positively charged composite membrane with sulfonated COF interlayer in the present invention DETAILED DESCRIPTION

[0016] The present invention will be further described in detail below by way of specific embodiments. However, it will be understood by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention.

[0017] The positively charged nanofiltration membrane containing TpPa-SO3H prepared by the present invention can be used to remove heavy metal cations, so the heavy metal cation retention rate, water flux and long-term operation stability are three important parameters for evaluating the nanofiltration membrane.

[0018] The test conditions for water flux, heavy metal cation retention rate and long-term operation stability are as follows: dead-end filtration device, inorganic salts selected from heavy metal cations commonly found in industrial wastewater (Cr 3+ 、Mn 2+ 、Co 2+ 、Ni 2+ 、Zn 2+ and Cd 2+) chloride salt, where the total concentration of heavy metal cations is 600 mg / L (100 ppm each), the test temperature is 25℃, pH=7, and the test pressure is 0.6MPa.

[0019] The heavy metal cation rejection is defined as:

[0020] Where R1 represents the heavy metal cation retention rate, C p1 and C f1 are the concentrations of heavy metal cations in the permeate and feed solution, respectively.

[0021] Water flux is defined as the volume of water that passes through the effective area of ​​the membrane per unit time under unit pressure. Example

[0022] (1) Basement membrane pretreatment Immerse the commercial polyacrylonitrile membrane in 2 mol / L sodium hydroxide solution and place it in a 60°C constant temperature water bath for 2 h. After taking it out, wash it with pure water three times and then soak it in pure water for 24 h. (2) Preparation of TpPa-SO3H thin film Prepare 50 mL of an aqueous solution containing 1 g of 2,5-diaminobenzenesulfonic acid, add 0.1 g of dopamine hydrochloride, and sonicate for 10 min to obtain solution 1. Prepare 50 mL of an ethanol solution containing 50 mg of 1,3,5-triformylphloroglucinol and sonicate until completely dissolved to obtain solution 2. Mix solutions 1 and 2, stir for 10 s, and then immerse the pretreated basement membrane horizontally. Allow to grow in situ for 1 day. After cleaning, place the membrane in a 60°C oven to dry for 1 h. After drying, place the membrane in deionized water and store for later use.

[0023] (3) Preparation of nanofiltration membrane containing TpPa-SO3H Prepare 50 mL of polyelectrolyte aqueous solution containing 0.5 g of polyethyleneimine; take out the membrane obtained in step (2) and wipe it dry, pour 25 mL of polyelectrolyte solution on the membrane surface, and filter it under a vacuum condition of 0.1 bar; dry it at 60℃ for 20 min to obtain the finished composite membrane.

[0024] The performance test of the nanofiltration membrane prepared in Example 1 showed that the water flux of the nanofiltration membrane was 42.8 L·m -2 ·h -1 bar -1 , Cr 3+ 、Mn 2+ 、Co 2+ 、Ni 2+ 、Zn 2+ and Cd 2+The retention rates were 98.52%, 99.36%, 97.62%, 97.53%, 97.24% and 98.95% respectively, and the retention rates of the six heavy metal ions were all greater than 95% after 7 days of long-term operation. Example

[0025] (1) Basement membrane pretreatment Immerse the commercial polyacrylonitrile membrane in 2 mol / L sodium hydroxide solution and place it in a 60°C constant temperature water bath for 2 h. After taking it out, wash it with pure water three times and then soak it in pure water for 24 h. (2) Preparation of TpPa-SO3H thin film Prepare 50 mL of an aqueous solution containing 0.5 g of 2,5-diaminobenzenesulfonic acid, add 0.1 g of dopamine hydrochloride, and sonicate for 10 min to obtain solution 1. Prepare 50 mL of an ethanol solution containing 50 mg of 1,3,5-triformylphloroglucinol and sonicate until completely dissolved to obtain solution 2. Mix solutions 1 and 2, stir for 10 s, and then immerse the pretreated basement membrane horizontally. Allow to grow in situ for 2 days. After cleaning, dry in a 60°C oven for 1 h. After drying, store in deionized water for later use.

[0026] (3) Preparation of nanofiltration membrane containing TpPa-SO3H Prepare 50 mL of polyelectrolyte aqueous solution containing 0.5 g of polypropylene imine; take out the membrane obtained in step (2) and wipe it dry, pour 25 mL of polyelectrolyte solution on the membrane surface, and filter it under a vacuum condition of 1 bar; dry it at 60℃ for 20 min to obtain the finished composite membrane.

[0027] The performance test of the nanofiltration membrane prepared in Example 2 showed that the water flux of the nanofiltration membrane was 45.8 L·m -2 ·h -1 bar -1 , Cr 3+ 、Mn 2+ 、Co 2+ 、Ni 2+ 、Zn 2+ and Cd 2+ The retention rates were 96%, 96.13%, 98.66%, 96.05%, 96.59% and 95.99% respectively, and the retention rates of the six heavy metal ions were all greater than 94% after 7 days of long-term operation. Example

[0028] (1) Basement membrane pretreatment Immerse the commercial polyacrylonitrile membrane in 2 mol / L sodium hydroxide solution and place it in a 60°C constant temperature water bath for 2 h. After taking it out, wash it with pure water three times and then soak it in pure water for 24 h. (2) Preparation of TpPa-SO3H thin film Prepare 50 mL of an aqueous solution containing 2 g of 3,5-diaminobenzenesulfonic acid, add 0.2 g of dopamine hydrochloride, and sonicate for 10 min to obtain solution 1. Prepare 50 mL of an acetic acid solution containing 50 mg of 1,3,5-triformylphloroglucinol and sonicate until completely dissolved to obtain solution 2. Mix solutions 1 and 2, stir for 10 s, and then immerse the pretreated basement membrane horizontally. Let it grow in situ for 2 days. After cleaning, dry it in a 60°C oven for 1 h. After drying, store it in deionized water for later use.

[0029] (3) Preparation of nanofiltration membrane containing TpPa-SO3H Prepare 50 mL of polyelectrolyte aqueous solution containing 0.5 g of polypropylene imine; take out the membrane obtained in step (2) and wipe it dry, pour 25 mL of polyelectrolyte solution on the membrane surface, and filter it under a vacuum condition of 0.1 bar; dry it at 60℃ for 20 min to obtain the finished composite membrane.

[0030] The performance test of the nanofiltration membrane prepared in Example 3 showed that the water flux of the nanofiltration membrane was 50.9 L·m -2 ·h -1 bar -1 , Cr 3+ 、Mn 2+ 、Co 2+ 、Ni 2+ 、Zn 2+ and Cd 2+ The retention rates were 96.5%, 96.49%, 99.5%, 97.48%, 96.7% and 99.04% respectively, and the retention rates of the six heavy metal ions were all greater than 95% after 7 days of long-term operation. Example

[0031] (1) Basement membrane pretreatment Immerse the commercial polyacrylonitrile membrane in 2 mol / L sodium hydroxide solution and place it in a 60°C constant temperature water bath for 2 h. After taking it out, wash it with pure water three times and then soak it in pure water for 24 h. (2) Preparation of TpPa-SO3H thin film Prepare 50 mL of an aqueous solution containing 1.5 g of 3,5-diaminobenzenesulfonic acid, add 0.2 g of dopamine hydrochloride, and sonicate for 10 min to obtain solution 1. Prepare 50 mL of an acetic acid solution containing 50 mg of 1,3,5-triformylphloroglucinol and sonicate until completely dissolved to obtain solution 2. Mix solutions 1 and 2, stir for 10 s, and then immerse the pretreated basement membrane horizontally. Allow to grow in situ for 3 days. After cleaning, dry in a 60°C oven for 1 h. After drying, store in deionized water for later use.

[0032] (3) Preparation of nanofiltration membrane containing TpPa-SO3H Prepare 50 mL of polyelectrolyte aqueous solution containing 0.5 g of polypropylene imine; take out the membrane obtained in step (2) and wipe it dry, pour 25 mL of polyelectrolyte solution on the membrane surface, and filter it under a vacuum condition of 1 bar; dry it at 60℃ for 20 min to obtain the finished composite membrane.

[0033] The performance test of the nanofiltration membrane prepared in Example 4 showed that the water flux of the nanofiltration membrane was 52.9 L·m -2 ·h -1 bar -1 , Cr 3+ 、Mn 2+ 、Co 2+ 、Ni 2+ 、Zn 2+ and Cd 2+ The retention rates were 98.66%, 95.01%, 95.8%, 95.47%, 96.37% and 99.95% respectively, and the retention rates of the six heavy metal ions were all greater than 95% after 7 days of long-term operation. Example

[0034] (1) Basement membrane pretreatment Immerse the commercial polyacrylonitrile membrane in 2 mol / L sodium hydroxide solution and place it in a 60°C constant temperature water bath for 2 h. After taking it out, wash it with pure water three times and then soak it in pure water for 24 h. (2) Preparation of TpPa-SO3H thin film Prepare 50 mL of an aqueous solution containing 1.5 g of 4,4-diaminobenzenesulfonanilide, add 0.15 g of dopamine hydrochloride, and sonicate for 10 min to obtain solution 1. Prepare 50 mL of an acetic acid solution containing 50 mg of 1,3,5-triformylphloroglucinol, and sonicate until completely dissolved to obtain solution 2. Mix solutions 1 and 2, stir for 10 s, and then immerse the pretreated basement membrane horizontally. Allow to grow in situ for 1 day. After cleaning, dry in a 60°C oven for 1 h. After drying, store in deionized water for later use.

[0035] (3) Preparation of nanofiltration membrane containing TpPa-SO3H Prepare 50 mL of polyelectrolyte aqueous solution containing 0.5 g of polylysine; take out the membrane obtained in step (2) and wipe it dry, pour 25 mL of polyelectrolyte solution on the membrane surface, and filter it under a vacuum condition of 0.1 bar; dry it at 60℃ for 20 min to obtain the finished composite membrane.

[0036] The performance test of the nanofiltration membrane prepared in Example 5 showed that the water flux of the nanofiltration membrane was 48.3 L·m -2 ·h-1 bar -1 , Cr 3+ 、Mn 2+ 、Co 2+ 、Ni 2+ 、Zn 2+ and Cd 2+ The retention rates were 98.14%, 96.54%, 96.29%, 99.43%, 95.37% and 98.99% respectively, and the retention rates of the six heavy metal ions were all greater than 95% after 7 days of long-term operation. Example

[0037] (1) Basement membrane pretreatment Immerse the commercial polyacrylonitrile membrane in 2 mol / L sodium hydroxide solution and place it in a 60°C constant temperature water bath for 2 h. After taking it out, wash it with pure water three times and then soak it in pure water for 24 h. (2) Preparation of TpPa-SO3H thin film Prepare 50 mL of an aqueous solution containing 2.5 g of 4,4-diaminobenzenesulfonanilide, add 0.25 g of dopamine hydrochloride, and sonicate for 10 min to obtain solution 1. Prepare 50 mL of an acetic acid solution containing 50 mg of 1,3,5-triformylphloroglucinol and sonicate until completely dissolved to obtain solution 2. Mix solutions 1 and 2, stir for 10 s, and then immerse the pretreated basement membrane horizontally. Allow to grow in situ for 3 days. After cleaning, dry in a 60°C oven for 1 h. After drying, store in deionized water for later use.

[0038] (3) Preparation of nanofiltration membrane containing TpPa-SO3H Prepare 50 mL of polyelectrolyte aqueous solution containing 0.5 g of polylysine; take out the membrane obtained in step (2) and wipe it dry, pour 25 mL of polyelectrolyte solution on the membrane surface, and filter it under a vacuum condition of 1 bar; dry it at 60℃ for 20 min to obtain the finished composite membrane.

[0039] The performance test of the nanofiltration membrane prepared in Example 6 showed that the water flux of the nanofiltration membrane was 46.6 L·m -2 ·h -1 bar -1 , Cr 3+ 、Mn 2+ 、Co 2+ 、Ni 2+ 、Zn 2+ and Cd 2+ The retention rates were 97.49%, 96.27%, 96.2%, 99.94%, 95.33% and 97.94% respectively, and the retention rates of the six heavy metal ions were all greater than 95% after 7 days of long-term operation.

Claims

1. A method for preparing a positively charged composite membrane based on a sulfonated covalent organic framework (COF) interlayer, characterized in that The following steps are involved: (1) Basement membrane pretreatment Soak the basement membrane in 2 mol / L sodium hydroxide solution and place it in a 60°C constant temperature water bath for 2 h. After taking it out, wash it with pure water three times and then soak it in pure water for 24 h. (2) Preparation of TpPa-SO3H interlayer Prepare an aqueous solution containing 0.5-2.5% sulfonated amine organic compound, add 0.05-0.2% oxidant, and ultrasonicate for 0.1-0.5 h to obtain solution 1; prepare an organic solution of 1,3,5-triformylphloroglucinol and ultrasonically disperse until completely dissolved to obtain solution 2; mix solution 1 and solution 2 in proportion, stir for 5-30 seconds, and then immerse the pretreated basement membrane horizontally in the solution and allow in situ growth for 1-3 days; (3) Separation surface construction Prepare a polyelectrolyte solution of a certain concentration; take out the membrane obtained in step (2), wipe it dry, pour 15-25 mL of the polyelectrolyte solution on the membrane surface, and filter it under a vacuum condition of 0.1-1 bar; dry it at 60℃ for 5-20 min to obtain a finished composite membrane.

2. The preparation method according to claim 1, wherein: The base film is selected from one of polyacrylonitrile, polyvinylidene fluoride, polyethersulfone and polysulfone.

3. The preparation method according to claim 1, wherein: The sulfonated amine organic compound is selected from 2,5-diaminobenzenesulfonic acid, 3,5-diaminobenzoic acid or 4,4-diaminobenzenesulfonylanilide.

4. The preparation method according to claim 1, wherein: The solvent of the 1,3,5-triformylphloroglucinol is selected from one of ethanol, acetic acid and methanol.

5. The preparation method according to claim 1, wherein: The oxidant is selected from one of dopamine hydrochloride, tannic acid and gallic acid.

6. The preparation method according to claim 1, wherein: The polyelectrolyte is selected from one of polyethyleneimine, polylysine and polypropyleneimine.

7. A positively charged composite membrane prepared according to the method according to any one of claims 1 to 6, characterized in that: Pure water flux ≥40L·m -2 ·h -1 bar -1 , isoelectric point pH ≥ 7.5; for Cr 3+ 、Mn 2+ 、Co 2+ 、Ni 2+ 、Zn 2+ and Cd 2+ The retention rate of heavy metal cations is ≥95%, the flux recovery rate is ≥98%, it can operate stably for more than 7 days, and has significant anti-biological pollution performance.

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