A sewage separation membrane capable of adsorbing metal ions and a preparation method thereof

Abstract

The present application belongs to the technical field of water treatment membranes, wherein a wastewater separation membrane capable of adsorbing metal ions is provided, comprising: a polyethylene microporous membrane; and a metal ion adsorption layer arranged on at least one side of the polyethylene microporous membrane, wherein: the metal ion adsorption layer contains a sulfonated chitosan modified molecule connected with the polyethylene microporous membrane. Since the functional groups with adsorption function contained in the wastewater separation membrane capable of adsorbing metal ions stably exist, after the water body is treated by adsorption using the separation membrane, the separation membrane can be repeatedly used after being cleaned, and the valuable metal ions in the water body can be efficiently recovered.

Description

Technical Field

[0001] This invention relates to a separation membrane, and more particularly to a separation membrane for reducing the concentration of metal ions contained in water. Background Technology

[0002] Industrial wastewater discharged from processing or manufacturing industries, such as electroplating, electronics, smelting, chemical, dyeing and finishing, or battery industries, mostly contains heavy metal ions. Wastewater containing heavy metal ions poses a significant hazard to agriculture, aquaculture, animal husbandry, and domestic water use. To reduce its destructive impact on human health and the natural ecosystem, the main methods currently used are membrane separation, electrochemical precipitation, or ion exchange to separate heavy metal ions from industrial wastewater.

[0003] However, in traditional separation methods: membrane separation has limited effectiveness in reducing the concentration of heavy metal ions in wastewater because it cannot selectively adsorb metal ions; electrochemical precipitation requires additional treatment of the solid sediments obtained, otherwise there is a risk of secondary pollution; and the ion exchange resins added during ion exchange are easily poisoned, leading to a risk of re-polluting the water. Therefore, it is understandable that current treatment methods for heavy metal wastewater cannot effectively and with low risk remove heavy metal ions from wastewater. In view of the above problems, a simple, effective separation membrane that can effectively remove heavy metal ions from wastewater is urgently needed. Summary of the Invention

[0004] The purpose of this invention is to provide a water separation membrane that has a high removal efficiency for metal ions contained in water and does not produce secondary pollution.

[0005] To achieve the above objectives, the present invention provides a method for preparing a wastewater separation membrane capable of adsorbing metal ions, characterized by comprising the following steps in sequence: (S1) wetting a polyethylene microporous membrane in a wetting agent; (S2) removing the polyethylene microporous membrane from the wetting agent and immersing it in a reaction solution, wherein the reaction solution contains a sulfonated chitosan modified molecule; and (S3) heat-treating the polyethylene microporous membrane to connect the sulfonated chitosan modified molecule to the polyethylene microporous membrane and form a metal ion adsorption layer on the polyethylene microporous membrane, thereby obtaining the wastewater separation membrane capable of adsorbing metal ions.

[0006] More preferably, the method for preparing the reaction solution comprises: mixing a chitosan powder, a dilute acid and a sulfonating agent to obtain a sulfonated chitosan solution, wherein the sulfonated chitosan solution contains the sulfonated chitosan modified molecules; and mixing the sulfonated chitosan solution with a crosslinking agent and a solvent to prepare the reaction solution.

[0007] More preferably, it further includes: (S4) removing the wastewater separation membrane capable of adsorbing metal ions from the reaction solution and washing and drying it.

[0008] More preferably, the structural formula of the sulfonated chitosan modified molecule is: .

[0009] More preferably, the wetting agent is one or more selected from the group consisting of solvents such as ethanol, isopropanol, dimethylacetamide (DMAC), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP).

[0010] More preferably, the chitosan powder has an average molecular weight of 30,000 to 80,000.

[0011] More preferably, the dilute acid is 0.1 wt% to 5 wt% acetic acid.

[0012] More preferably, the sulfonating agent comprises one or more of concentrated sulfuric acid and chlorosulfonic acid.

[0013] More preferably, the crosslinking agent comprises one or more of glutaraldehyde, succinate, and silane coupling agents.

[0014] More preferably, the solvent comprises water and an organic solvent, wherein the organic solvent is one or more selected from the group consisting of dimethylacetamide, dimethylformamide, ethanol, acetone, dimethyl sulfoxide, and N-methylpyrrolidone.

[0015] More preferably, the reaction solution comprises, by total weight: 1 wt% to 5 wt% of the sulfonated chitosan solution, 0.1 wt% to 10 wt% of the crosslinking agent, and 85 wt% to 98.9 wt% of the solvent.

[0016] More preferably, in step (S2), the chitosan powder, the dilute acid and the sulfonating agent are mixed at a temperature of ≤5 °C and reacted for 2 to 5 hours.

[0017] More preferably, in step (S3), the polyethylene microporous membrane is heated at a temperature of 40 °C to 80 °C for 2 min to 10 min.

[0018] More preferably, in step (S2), the chitosan powder is first mixed with the dilute acid to obtain an acidic aqueous solution of chitosan, and then the sulfonating agent is added to the acidic aqueous solution of chitosan to obtain the sulfonated chitosan solution.

[0019] More preferably, the sulfonated chitosan solution contains, by weight, 0.5 wt% to 5 wt% of the chitosan powder, 85 wt% to 98.5 wt% of the dilute acid, and 1 wt% to 10 wt% of the sulfonating agent.

[0020] The present invention also provides a wastewater separation membrane capable of adsorbing metal ions, characterized in that it comprises: a polyethylene microporous membrane; and a metal ion adsorption layer disposed on at least one side of the polyethylene microporous membrane, wherein: the metal ion adsorption layer contains a sulfonated chitosan modified molecule, which is connected to the polyethylene microporous membrane.

[0021] It is understood that since the parameters, conditions, composition and proportions of each component in this embodiment have been explained in the above method, they will not be repeated here.

[0022] The advantages of this invention over prior art are: the polyethylene microporous membrane possesses excellent mechanical strength, flexibility and chemical stability at low temperatures, resistance to strong acids and alkalis, does not react with water or oils and other compounds, and exhibits good solvent stability at room temperature. However, the polyethylene microporous membrane is a chain-like crystalline polymer with (-CH2-CH2-) as its structural unit, therefore it cannot selectively adsorb heavy metal ions in water, requiring additional surface modification treatment. Specifically, to enable the polyethylene microporous membrane to selectively adsorb heavy metal ions in water, amino or hydroxyl groups need to be introduced into the polyethylene microporous membrane. Although chitosan contains hydroxyl and amino groups that can chelate and complex with metal ions, and thus has a certain adsorption effect on metal ions, in order to significantly improve the ability of polyethylene microporous membranes to adsorb metal ions contained in water, this invention modifies chitosan by sulfonation to introduce sulfonic acid groups with higher ion exchange capacity and electrophilicity. Therefore, the adsorption performance and selectivity of chitosan for metal ions can be greatly enhanced. When polyethylene microporous membranes are wetted with reaction solution, the adsorption rate of polyethylene microporous membranes for metal ions contained in water can be greatly enhanced.

[0023] Specifically, the reaction solution is a highly negatively charged chitosan sulfate. When it wets a polyethylene microporous membrane and adheres to its surface and pore structure, the numerous amino, hydroxyl, and sulfonic acid groups in the reaction solution can combine with the empty orbitals of metal ions in the water via ionic or coordinate bonds, forming a network structure to adsorb and remove metal ions from the water. Furthermore, after wetting the polyethylene microporous membrane with the reaction solution, the large specific surface area of ​​the membrane and the abundance of oxygen-containing functional groups enhance the hydrophilicity of the membrane, resulting in better wettability in water. Furthermore, by heat-treating the polyethylene microporous membrane immersed in the reaction solution, the sulfonated modified material can be uniformly diffused into the pore structure of the polyethylene microporous membrane and the voids in the polyethylene main chain segments to form an intertwined network structure or cross-linked structure. Therefore, the functional groups in the reaction solution can be attached to the polyethylene microporous membrane for a long time and stably. It can be understood that since the functional groups with adsorption function contained in the wastewater separation membrane that can adsorb metal ions are stably present, after the separation membrane adsorbs water, it can be washed and reused repeatedly, and valuable metal ions in the water can be efficiently recovered. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the preparation process of the wastewater separation membrane capable of adsorbing metal ions according to the present invention. Figure 2 This is a flowchart illustrating the preparation process of the wastewater separation membrane capable of adsorbing metal ions according to the present invention. Figure 3 This is a planar diagram used to illustrate the structural features of a wastewater separation membrane that can adsorb metal ions. Detailed Implementation

[0025] To make the above and / or other objects, effects, and features of the present invention more apparent and understandable, preferred embodiments are described in detail below: One objective of this invention is to provide a method for preparing a wastewater separation membrane capable of adsorbing metal ions, such as... Figure 1As shown, the process sequentially includes: (S1) wetting a polyethylene microporous membrane 1 in a wetting agent; (S2) removing the polyethylene microporous membrane 1 from the wetting agent and immersing it in a reaction solution, wherein the reaction solution contains a sulfonated chitosan modified molecule; and (S3) heat-treating the polyethylene microporous membrane 1 to connect the sulfonated chitosan modified molecule to the polyethylene microporous membrane 1 and form a metal ion adsorption layer 2 on the polyethylene microporous membrane 1, thereby obtaining the wastewater separation membrane capable of adsorbing metal ions. In a preferred embodiment, the method for preparing the reaction solution includes: mixing a chitosan powder, a dilute acid, and a sulfonating agent to obtain a sulfonated chitosan solution, wherein the sulfonated chitosan solution contains the sulfonated chitosan modified molecule; and mixing the sulfonated chitosan solution with a crosslinking agent and a solvent to prepare the reaction solution. In another preferred embodiment, to avoid carbonization of sulfonated chitosan and the generation of a large amount of heat during the preparation of the sulfonated chitosan solution, in step (S2), the chitosan powder is first mixed with the dilute acid to obtain an acidic aqueous solution of chitosan, and then the sulfonating agent is added to the acidic aqueous solution of chitosan to obtain the sulfonated chitosan solution. In another preferred embodiment, the sulfonated chitosan solution contains, by weight, 0.5 wt% to 5 wt% of the chitosan powder, 85 wt% to 98.5 wt% of the dilute acid, and 1 wt% to 10 wt% of the sulfonating agent, but is not limited thereto. In yet another preferred embodiment, such as Figure 2 As shown, it further includes: (S4) removing the wastewater separation membrane capable of adsorbing metal ions from the reaction solution, and washing and drying it. In another preferred embodiment, the structural formula of the sulfonated chitosan modified molecule is: .

[0026] More preferably, to wet the polyethylene microporous membrane 1, the wetting agent is one or more selected from the group consisting of ethanol, isopropanol, dimethylacetamide (DMAC), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP), but not limited thereto. In a preferred embodiment, the average molecular weight of the chitosan powder is 30,000 to 80,000, more preferably 40,000 to 70,000, and even more preferably 50,000 to 60,000, but not limited thereto. In another preferred embodiment, the dilute acid is 0.1 wt% to 5 wt% acetic acid, but not limited thereto. In another preferred embodiment, in order to modify the acidic aqueous solution of chitosan to contain sulfonic acid groups with large ion exchange capacity and high electrophilicity, the sulfonating agent comprises one or more of concentrated sulfuric acid and chlorosulfonic acid. Preferably, the sulfonating agent comprises concentrated sulfuric acid and chlorosulfonic acid, and the weight ratio of concentrated sulfuric acid to chlorosulfonic acid is 2:1 to 4, but not limited thereto.

[0027] More preferably, to enable cross-linking between the polyethylene microporous membrane 1 and the reaction solution, the amino, hydroxyl, and sulfonic acid groups contained in the reaction solution can be stably attached to the surface or pore structure of the polyethylene microporous membrane 1, thus selectively adsorbing heavy metal ions contained in the water. The cross-linking agent comprises one or more of glutaraldehyde, succinate, and silane coupling agents, but is not limited thereto. In a preferred embodiment, the solvent comprises water and an organic solvent, wherein the organic solvent is one or more selected from the group consisting of dimethylacetamide, dimethylformamide, ethanol, acetone, dimethyl sulfoxide, and N-methylpyrrolidone, but is not limited thereto. In another preferred embodiment, the reaction solution, by total weight, comprises: 1 wt% to 5 wt% of the sulfonated chitosan solution, 0.1 wt% to 10 wt% of the cross-linking agent, and 85 wt% to 98.9 wt% of the solvent, but is not limited thereto. In another preferred embodiment, to prevent the chitosan powder from carbonizing and causing the sample to turn black, in step (S2), the chitosan powder, the dilute acid, and the sulfonating agent are mixed at a temperature of ≤5 °C and reacted for 2 to 5 hours. In yet another preferred embodiment, to allow the modified material in the reaction solution to completely and uniformly diffuse into the pore structure of the polyethylene microporous membrane 1 and the voids in the polyethylene main chain segments, and to form an intertwined network structure and cross-linked structure, so that the modified material can adhere to the polyethylene microporous membrane 1 for a long time and stably, in step (S3), the polyethylene microporous membrane 1 is heated at a temperature of 40 °C to 80 °C for 2 to 10 minutes, but not limited thereto.

[0028] Another object of the present invention is to provide a wastewater separation membrane capable of adsorbing metal ions, such as... Figure 3 As shown, it comprises: a polyethylene microporous membrane 1; and a metal ion adsorption layer 2, which is disposed on at least one side of the polyethylene microporous membrane 1, wherein: the metal ion adsorption layer 2 contains a sulfonated chitosan modified molecule, which is connected to the polyethylene microporous membrane 1. It is understood that since the various parameters, conditions, composition, and proportions of the components in this embodiment have already been explained in the above method, they will not be repeated here.

[0029] Examples 1 to 5 are provided below to illustrate different process parameters of wastewater separation membranes that can adsorb metal ions, and the test results of the performance parameters of wastewater separation membranes that can adsorb metal ions are summarized in Table 1 below.

[0030] Example 1 The preparation method of the reaction solution used in this embodiment includes: (S1A) selecting chitosan powder with a degree of deacetylation ≥90% and a molecular weight of 50,000, dissolving it in 1.5 wt% acetic acid to prepare a 2 wt% acidic aqueous solution of chitosan; (S2A) transferring the acidic aqueous solution of chitosan to a three-necked flask, and slowly adding a sulfonating agent dropwise, then stirring and mixing at a temperature of ≤5 ℃ for 4 hours, and then removing the unreacted chitosan gel to obtain a sulfonated chitosan solution, wherein the sulfonating agent contains concentrated sulfuric acid and chlorosulfonic acid in a weight ratio of 1:1; and (S3A) slowly adding the sulfonated chitosan solution to a mixed solution and stirring and mixing for 2 hours to obtain a reaction solution, wherein the total weight of the mixed solution contains: 1 wt% glutaraldehyde and 99 wt% water.

[0031] The method for preparing the wastewater separation membrane capable of adsorbing metal ions in this embodiment includes, in sequence: (S4A) wetting a polyethylene microporous membrane 1 with dimethylacetamide (DMAC); (S5A) removing the polyethylene microporous membrane 1 from the dimethylacetamide (DMAC), immersing it in a reaction solution at room temperature for 2 min, then heating the temperature to 70 °C and maintaining it for 2 min, so that the polyethylene microporous membrane 1 and the reaction solution undergo a crosslinking reaction; and (S6A) removing the polyethylene microporous membrane 1 from the reaction solution and soaking it in water for 12 hr, then removing it from the water and drying it to obtain a wastewater separation membrane capable of adsorbing metal ions.

[0032] Example 2 The preparation method of the reaction solution used in this embodiment includes: (S1B) selecting chitosan powder with a degree of deacetylation ≥90% and a molecular weight of 30,000, dissolving it in 2 wt% acetic acid to prepare a 4 wt% acidic aqueous solution of chitosan; (S2B) transferring the acidic aqueous solution of chitosan to a three-necked flask, and slowly adding a sulfonating agent dropwise, then stirring and mixing at a temperature of ≤5 ℃ for 4 hours, and then removing the unreacted chitosan gel to obtain a sulfonated chitosan solution, wherein the sulfonating agent contains concentrated sulfuric acid and chlorosulfonic acid in a weight ratio of 1:2; and (S3B) slowly adding the sulfonated chitosan solution to a mixed solution and stirring and mixing for 2 hours to obtain a reaction solution, wherein the total weight of the mixed solution contains: 2 wt% glutaraldehyde and 50 wt% dimethylacetamide.

[0033] The method for preparing the wastewater separation membrane capable of adsorbing metal ions in this embodiment includes, in sequence: (S4B) wetting the polyethylene microporous membrane 1 with dimethylacetamide (DMAC); (S5B) removing the polyethylene microporous membrane 1 from the dimethylacetamide (DMAC), immersing it in the reaction solution at room temperature for 2 min, then heating the temperature to 80 °C and maintaining it for 10 min, so that the polyethylene microporous membrane 1 and the reaction solution undergo a crosslinking reaction; and (S6B) removing the polyethylene microporous membrane 1 from the reaction solution and soaking it in water for 12 hr, then removing it from the water and drying it to obtain the wastewater separation membrane capable of adsorbing metal ions.

[0034] Example 3 The preparation method of the reaction solution used in this embodiment includes: (S1C) selecting chitosan powder with a degree of deacetylation ≥90% and a molecular weight of 30,000, dissolving it in 3 wt% acetic acid to prepare a 5 wt% acidic aqueous solution of chitosan; (S2C) transferring the acidic aqueous solution of chitosan to a three-necked flask, and slowly adding a sulfonating agent dropwise, then stirring and mixing at a temperature of ≤5 ℃ for 4 hours, and then removing the unreacted chitosan gel to obtain a sulfonated chitosan solution, wherein the sulfonating agent contains concentrated sulfuric acid and chlorosulfonic acid in a weight ratio of 1:1; and (S3C) slowly adding the sulfonated chitosan solution to a mixed solution and stirring and mixing for 2 hours to obtain a reaction solution, wherein the total weight of the mixed solution contains: 10 wt% glutaraldehyde and 70 wt% dimethylacetamide.

[0035] The method for preparing the wastewater separation membrane capable of adsorbing metal ions in this embodiment includes, in sequence: (S4C) wetting a polyethylene microporous membrane 1 with dimethylacetamide (DMAC); (S5C) removing the polyethylene microporous membrane 1 from the dimethylacetamide (DMAC), immersing it in a reaction solution at room temperature for 2 min, then heating the temperature to 80 °C and maintaining it for 4 min, so that the polyethylene microporous membrane 1 and the reaction solution undergo a crosslinking reaction; and (S6C) removing the polyethylene microporous membrane 1 from the reaction solution and soaking it in water for 12 hr, then removing it from the water and drying it to obtain a wastewater separation membrane capable of adsorbing metal ions.

[0036] Example 4 The preparation method of the reaction solution used in this embodiment includes: (S1D) selecting chitosan powder with a degree of deacetylation ≥90% and a molecular weight of 80,000, dissolving it in 1 wt% acetic acid to prepare a 1 wt% chitosan acidic aqueous solution; (S2D) transferring the chitosan acidic aqueous solution to a three-necked flask, and slowly adding a sulfonating agent dropwise, then stirring and mixing at a temperature ≤5 ℃ for 4 hours, and then removing the unreacted chitosan gel to obtain a sulfonated chitosan solution, wherein the sulfonating agent contains concentrated sulfuric acid and chlorosulfonic acid in a weight ratio of 2:1; and (S3D) slowly adding the sulfonated chitosan solution to a mixed solution and stirring and mixing for 2 hours to obtain a reaction solution, wherein the total weight of the mixed solution contains: 10 wt% glutaraldehyde and 90 wt% water.

[0037] The method for preparing the wastewater separation membrane capable of adsorbing metal ions in this embodiment includes, in sequence: (S4D) wetting a polyethylene microporous membrane 1 with dimethylacetamide (DMAC); (S5D) removing the polyethylene microporous membrane 1 from the dimethylacetamide (DMAC), immersing it in a reaction solution at room temperature for 2 min, then heating the temperature to 70 °C and maintaining it for 2 min, so that the polyethylene microporous membrane 1 and the reaction solution undergo a crosslinking reaction; and (S6D) removing the polyethylene microporous membrane 1 from the reaction solution and soaking it in water for 12 hr, then removing it from the water and drying it to obtain a wastewater separation membrane capable of adsorbing metal ions.

[0038] Example 5 The preparation method of the reaction solution used in this embodiment includes: (S1E) selecting chitosan powder with a degree of deacetylation ≥90% and a molecular weight of 30,000, dissolving it in 2 wt% acetic acid to prepare a 4 wt% acidic aqueous solution of chitosan; (S2E) transferring the acidic aqueous solution of chitosan to a three-necked flask, and slowly adding a sulfonating agent dropwise, then stirring and mixing at a temperature of ≤5 ℃ for 4 hours, and then removing the unreacted chitosan gel to obtain a sulfonated chitosan solution, wherein the sulfonating agent contains concentrated sulfuric acid and chlorosulfonic acid in a weight ratio of 1:2; and (S3E) slowly adding the sulfonated chitosan solution to a mixed solution and stirring and mixing for 2 hours to obtain a reaction solution, wherein the total weight of the mixed solution contains: 2 wt% glutaraldehyde and 50 wt% ethanol.

[0039] The method for preparing the wastewater separation membrane capable of adsorbing metal ions in this embodiment includes, in sequence: (S4E) wetting a polyethylene microporous membrane 1 with dimethylacetamide (DMAC); (S5E) removing the polyethylene microporous membrane 1 from the dimethylacetamide (DMAC), immersing it in a reaction solution at room temperature for 2 min, then heating the temperature to 80 °C and maintaining it for 4 min, so that the polyethylene microporous membrane 1 and the reaction solution undergo a crosslinking reaction; and (S6E) removing the polyethylene microporous membrane 1 from the reaction solution and soaking it in water for 12 hr, then removing it from the water and drying it to obtain a wastewater separation membrane capable of adsorbing metal ions.

[0040] Comparative Example 1 The preparation method of the reaction solution used in this comparative example includes: (S1F) selecting chitosan powder with a degree of deacetylation ≥90% and a molecular weight of 30,000, dissolving it in 3 wt% acetic acid to prepare a 5 wt% acidic aqueous solution of chitosan; (S2F) transferring the acidic aqueous solution of chitosan to a three-necked flask, and slowly adding a sulfonating agent dropwise, then stirring and mixing at 8°C for 2 hours, and then removing the unreacted chitosan gel to obtain a sulfonated chitosan solution, wherein the sulfonating agent contains concentrated sulfuric acid and chlorosulfonic acid in a weight ratio of 1:1; and (S3F) slowly adding the sulfonated chitosan solution to a mixed solution and stirring and mixing for 2 hours to obtain a reaction solution, wherein the mixed solution contains 10 wt% glutaraldehyde and 70 wt% dimethylacetamide by weight.

[0041] The preparation method of the wastewater separation membrane capable of adsorbing metal ions in this comparative example includes, in sequence: (S4F) wetting polyethylene microporous membrane 1 with ethanol; (S5F) removing polyethylene microporous membrane 1 from ethanol, immersing it in a reaction solution at room temperature for 2 min, then heating the temperature to 80 °C and maintaining it for 4 min to allow polyethylene microporous membrane 1 to undergo a crosslinking reaction with the reaction solution; and (S6F) removing polyethylene microporous membrane 1 from the reaction solution and immersing it in water for 12 hr, then removing it from the water and drying it to obtain a wastewater separation membrane capable of adsorbing metal ions.

[0042] Comparative Example 2 The preparation method of the reaction solution used in this comparative example includes: (S1G) selecting chitosan powder with a degree of deacetylation ≥90% and a molecular weight of 30,000, dissolving it in 2 wt% acetic acid to prepare a 4 wt% acidic aqueous solution of chitosan; (S2G) transferring the acidic aqueous solution of chitosan to a three-necked flask, and slowly adding a sulfonating agent dropwise, then stirring and mixing at 5°C for 2 hours, and then removing the unreacted chitosan gel to obtain a sulfonated chitosan solution, wherein the sulfonating agent contains concentrated sulfuric acid and chlorosulfonic acid in a weight ratio of 1:2; and (S3G) slowly adding the sulfonated chitosan solution to a pure water and stirring and mixing for 2 hours to obtain the reaction solution.

[0043] The preparation method of the wastewater separation membrane capable of adsorbing metal ions in this comparative example includes, in sequence: (S4G) wetting polyethylene microporous membrane 1 with ethanol; (S5G) removing polyethylene microporous membrane 1 from ethanol, immersing it in a reaction solution at room temperature for 2 min, then heating the temperature to 80 °C and maintaining it for 4 min to allow polyethylene microporous membrane 1 to undergo a crosslinking reaction with the reaction solution; and (S6G) removing polyethylene microporous membrane 1 from the reaction solution and soaking it in water for 12 hr, then removing it from the water and drying it to obtain a wastewater separation membrane capable of adsorbing metal ions.

[0044] Comparative Example 3 The preparation method of the reaction solution used in this comparative example includes: (S1H) selecting chitosan powder with a degree of deacetylation ≥90% and a molecular weight of 50,000, dissolving it in 1 wt% acetic acid to prepare a 1 wt% acidic aqueous solution of chitosan; (S2H) transferring the acidic aqueous solution of chitosan to a three-necked flask, and slowly adding a sulfonating agent dropwise, then stirring and mixing at 5°C for 4 hours, and then removing the unreacted chitosan gel to obtain a sulfonated chitosan solution, wherein the sulfonating agent contains concentrated sulfuric acid and chlorosulfonic acid in a weight ratio of 2:1; and (S3H) slowly adding the sulfonated chitosan solution to a dimethylacetamide solvent and stirring and mixing for 2 hours to obtain a reaction solution, wherein: based on the total weight of the dimethylacetamide solvent, it contains 80 wt% dimethylacetamide and 20 wt% water.

[0045] The preparation method of the wastewater separation membrane capable of adsorbing metal ions in this comparative example includes, in sequence: (S4H) wetting polyethylene microporous membrane 1 with ethanol; (S5H) removing polyethylene microporous membrane 1 from ethanol, first immersing it in a reaction solution at room temperature for 2 min, then heating the temperature to 25 °C and maintaining it for 10 min, so that polyethylene microporous membrane 1 and reaction solution undergo cross-linking reaction; and (S6H) removing polyethylene microporous membrane 1 from the reaction solution and soaking it in water for 12 hours, then removing it from the water and drying it to obtain a wastewater separation membrane capable of adsorbing metal ions.

[0046] Comparative Example 4 The preparation method of the reaction solution used in this comparative example includes: (S1I) selecting chitosan powder with a degree of deacetylation ≥90% and a molecular weight of 50,000, dissolving it in 1.5 wt% acetic acid to prepare a 2 wt% acidic aqueous solution of chitosan; (S2I) stirring and mixing the acidic aqueous solution of chitosan with a glutaraldehyde aqueous solution for 2 hours to obtain the reaction solution, wherein: based on the total weight of the glutaraldehyde aqueous solution, it contains 1 wt% glutaraldehyde and 99 wt% water.

[0047] The preparation method of the wastewater separation membrane capable of adsorbing metal ions in this comparative example includes, in sequence: (S3I) wetting polyethylene microporous membrane 1 with DMAC; (S4I) removing polyethylene microporous membrane 1 from DMAC, first immersing it in the reaction solution at room temperature for 2 min, then heating the temperature to 70 °C and maintaining it for 2 min, so that polyethylene microporous membrane 1 and reaction solution undergo crosslinking reaction; and (S5I) removing polyethylene microporous membrane 1 from the reaction solution and soaking it in water for 12 hr, then removing it from the water and drying it to obtain wastewater separation membrane capable of adsorbing metal ions.

[0048] The wastewater separation membranes capable of adsorbing metal ions prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were subjected to (1) hydrophilicity test, specifically by injecting deionized water onto the separation membrane to measure the static contact angle of the separation membrane, and taking the average value of the parameter results obtained from three measurements; and (2) copper ion adsorption efficiency test, specifically by using a standard 100 mg / L Cu(II) solution, adjusting the solution to pH=5 with NaOH and HCl, and then filtering a copper ion solution with a volume of 10 ml and a concentration of 10 mg / L through the separation membrane to test the concentration of copper ions in the filtrate obtained after the copper ion solution is filtered through the separation membrane. The adsorption efficiency of the separation membrane for metal ions is calculated according to the following formula, where: E is the metal ion adsorption efficiency, C0 is the initial concentration of metal ions in the unfiltered water (mg / L), and C is the concentration of metal ions in the water filtered through the separation membrane (mg / L). Table 1 below shows the test results of the contact angle and copper ion adsorption efficiency of the wastewater separation membranes capable of adsorbing metal ions in each embodiment and comparative example. Additionally, Table 2 below shows the compiled results of various process parameters for the wastewater separation membranes capable of adsorbing metal ions in each embodiment and comparative example.

[0049]

[0050] Table 1. Test results of contact angle and copper ion adsorption efficiency of the separation membrane in each embodiment.

[0051] Table 2. Summary of process parameters for the separation membranes in each embodiment

[0052] The advantages of this invention over prior art are that the polyethylene microporous membrane 1 possesses excellent mechanical strength, flexibility and chemical stability at low temperatures, resistance to strong acids and alkalis, does not react with water or other compounds such as oils, and exhibits good solvent stability at room temperature. However, the polyethylene microporous membrane 1 is a chain-like crystalline polymer with (-CH2-CH2-) as its structural unit, therefore it cannot selectively adsorb heavy metal ions in water, requiring additional surface modification treatment. Specifically, to enable the polyethylene microporous membrane 1 to selectively adsorb heavy metal ions in water, amino or hydroxyl groups need to be introduced into the polyethylene microporous membrane 1. Although chitosan contains hydroxyl and amino groups that can chelate and complex with metal ions, thus exhibiting a certain adsorption effect on metal ions, this invention significantly enhances the adsorption capacity of the polyethylene microporous membrane 1 for metal ions in water by sulfonating chitosan to introduce sulfonic acid groups with higher ion exchange capacity and electrophilicity. This greatly enhances the adsorption performance and selectivity of chitosan for metal ions. When the polyethylene microporous membrane 1 is wetted with the reaction solution, the adsorption rate of the polyethylene microporous membrane 1 for metal ions in water is greatly increased. Specifically, the reaction solution is a highly negatively charged chitosan sulfate ester. When it wets the polyethylene microporous membrane 1 and adheres to its surface and pore structure, the numerous amino, hydroxyl, and sulfonic acid groups in the reaction solution can combine with the empty orbitals of metal ions in the water through ionic or coordinate bonds, forming a network structure to adsorb and remove metal ions from the water. Furthermore, after the polyethylene microporous membrane 1 is wetted with the reaction solution, the large specific surface area of ​​the reaction solution attached to the polyethylene microporous membrane 1, as well as its rich content of oxygen-containing functional groups, can enhance the hydrophilicity of the polyethylene microporous membrane 1, giving it better wettability in water. In addition, by heat-treating the polyethylene microporous membrane 1 immersed in the reaction solution, the sulfonated modified material can be uniformly diffused into the pore structure of the polyethylene microporous membrane 1 and the voids in the polyethylene main chain segments to form an intertwined network structure or cross-linked structure. Therefore, the functional groups in the reaction solution can be attached to the polyethylene microporous membrane 1 for a long time and stably. It is understood that since the adsorption functional groups contained in the wastewater separation membrane capable of adsorbing metal ions are stably present, after the separation membrane has been used to adsorb and treat water, it can be repeatedly used after washing, and valuable metal ions in the water can be efficiently recovered.

[0053] However, the above description is only a preferred embodiment of the present invention, and should not be construed as limiting the scope of patent protection of the present invention. Therefore, any simple equivalent changes and modifications made in accordance with the scope of patent protection and the contents of the specification of the present invention shall still fall within the scope of patent protection of the present invention.

Claims

1. A wastewater separation membrane capable of adsorbing metal ions, characterized in that, Include: A polyethylene microporous membrane; and A metal ion adsorption layer is disposed on at least one side of the polyethylene microporous membrane, wherein: the metal ion adsorption layer contains sulfonated chitosan modified molecules and is connected to the polyethylene microporous membrane; The method for preparing the wastewater separation membrane capable of adsorbing metal ions includes, in sequence: (S1) The polyethylene microporous membrane is placed in a wetting agent for wetting; (S2) The polyethylene microporous membrane is removed from the wetting agent and placed in a reaction solution for wetting, wherein the reaction solution contains the sulfonated chitosan modified molecules; and (S3) The polyethylene microporous membrane is heat-treated to connect the sulfonated chitosan modified molecules to the polyethylene microporous membrane and form the metal ion adsorption layer on the polyethylene microporous membrane to obtain the wastewater separation membrane that can adsorb metal ions.

2. The wastewater separation membrane capable of adsorbing metal ions according to claim 1, characterized in that, The structural formula of the sulfonated chitosan modified molecule is: 。 3. The wastewater separation membrane capable of adsorbing metal ions according to claim 1, characterized in that, The wetting agent is selected from one or more solvents in the group consisting of ethanol, isopropanol, dimethylacetamide (DMAC), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP).

4. The wastewater separation membrane capable of adsorbing metal ions according to claim 1, characterized in that, The method for preparing the reaction solution includes: mixing chitosan powder, dilute acid and sulfonating agent to obtain sulfonated chitosan solution; and mixing the sulfonated chitosan solution with crosslinking agent and solvent to prepare the reaction solution.

5. The wastewater separation membrane capable of adsorbing metal ions according to claim 4, characterized in that, The average molecular weight of the chitosan powder is between 30,000 and 80,000.

6. The wastewater separation membrane capable of adsorbing metal ions according to claim 4, characterized in that, The dilute acid is 0.1 wt% to 5 wt% acetic acid.

7. The wastewater separation membrane capable of adsorbing metal ions according to claim 4, characterized in that, The sulfonating agent includes one or more of concentrated sulfuric acid and chlorosulfonic acid.

8. The wastewater separation membrane capable of adsorbing metal ions according to claim 4, characterized in that, The crosslinking agent comprises one or more of glutaraldehyde, succinal, and silane coupling agents.

9. The wastewater separation membrane capable of adsorbing metal ions according to claim 4, characterized in that, The solvent comprises water and an organic solvent, wherein the organic solvent is one or more selected from the group consisting of dimethylacetamide, dimethylformamide, ethanol, acetone, dimethyl sulfoxide, and N-methylpyrrolidone.

10. The wastewater separation membrane capable of adsorbing metal ions according to claim 4, characterized in that, The reaction solution comprises, by total weight, 1 wt% to 5 wt% of the sulfonated chitosan solution, 0.1 wt% to 10 wt% of the crosslinking agent, and 85 wt% to 98.9 wt% of the solvent.

11. The wastewater separation membrane capable of adsorbing metal ions according to claim 4, characterized in that, The chitosan powder is first mixed with the dilute acid to obtain an acidic aqueous solution of chitosan, and then the sulfonating agent is added to the acidic aqueous solution of chitosan to obtain the sulfonated chitosan solution.

12. The wastewater separation membrane capable of adsorbing metal ions according to claim 11, characterized in that, The sulfonated chitosan solution contains, by total weight, 0.5 wt% to 5 wt% of the chitosan powder, 85 wt% to 98.5 wt% of the dilute acid, and 1 wt% to 10 wt% of the sulfonating agent.

13. The wastewater separation membrane capable of adsorbing metal ions according to claim 1, characterized in that, The method for preparing the wastewater separation membrane capable of adsorbing metal ions further includes: (S4) removing the wastewater separation membrane capable of adsorbing metal ions from the reaction solution and washing and drying it.

14. The wastewater separation membrane capable of adsorbing metal ions according to claim 4, characterized in that, In step (S2), the chitosan powder, the dilute acid and the sulfonating agent are mixed at a temperature of ≤5 °C and reacted for 2 to 5 hours.

15. The wastewater separation membrane capable of adsorbing metal ions according to claim 1, characterized in that, In step (S3), the polyethylene microporous membrane is heated at a temperature of 40 ℃ to 80 ℃ for 2 min to 10 min.

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