A method for preparing a modified PTFE forward osmosis membrane

Abstract

This invention aims to provide a method for preparing a modified PTFE forward osmosis membrane for heavy metal ion separation. Due to the advantages of PTFE membranes, such as chemical stability, high mechanical strength, and anti-aging properties, this invention uses a PTFE membrane as the substrate. First, the PTFE membrane is soaked in anhydrous ethanol and deionized water for a certain period to remove surface impurities and clear pores. Then, plasma treatment is performed using nitrogen as the active gas, causing some C-F bonds to break, forming a PTFE membrane with surface defects. The modified PTFE membrane is then completely immersed in a silane coupling agent solution, followed by the addition of a specific amount of UiO-66-NH2 and a certain amount of polyethyleneimine (PEI). The coupling agent mainly contains two functional groups: one group has an affinity for UiO-66-NH2 and can effectively bind to inorganic fillers; the other group has an affinity for organic groups and can effectively bind to polyethyleneimine. The resulting UiO-66-NH2-silane coupling agent-polyethyleneimine composite structure is connected to the defective PTFE membrane through chemical bonds, ultimately forming a modified PTFE composite membrane. This modified membrane, when applied to a heavy metal separation system, achieves a mercury ion removal rate of up to 99%.

Description

Technical Field

[0001] This invention relates to a method for preparing a modified PTFE forward osmosis membrane for the separation of heavy metal ions, belonging to the field of membrane preparation technology. The prepared modified PTFE forward osmosis membrane has advantages such as strong acid and alkali resistance, high flux, high mechanical strength, and simple preparation, and is suitable for heavy metal ion separation systems. Background Technology

[0002] With the advancement of industrial development and urbanization, the management, efficient recycling, and reuse of heavy metal resources can effectively alleviate the current resource and energy crisis.

[0003] Traditional methods for separating heavy metal ions include chemical precipitation, adsorption, ion flotation, ion exchange, coagulation / flocculation, and electrochemical methods. However, these methods have several significant drawbacks, such as the need for further treatment due to high sludge production, low removal efficiency, and high energy demands. In recent years, newer, more efficient, more economical, and innovative technologies have been researched. Recently, photocatalysis, electrodialysis, hydrogels, membrane separation technologies, and the introduction of newer adsorbents have been developed to achieve better adsorption. Patent CN202411924014 provides a modified covalent organic framework material for simultaneously adsorbing multiple heavy metal ions, its preparation method, and its application. The modified covalent organic framework material is prepared using a simple room-temperature synthesis method and a rapid ultrasonic modification strategy with a neutral solution. Compared to the traditional high-temperature, high-pressure hydrothermal method combined with chemical synthesis, this method significantly shortens the preparation time. However, the modified covalent organic framework material's connection to the substrate is not strong enough, and it is prone to detachment during long-term operation. Patent CN202411924014 also provides a biodegradable positively charged nanofiltration composite membrane, its preparation method, and its application. Using viscose fiber nonwoven fabric with cellulose as the main component as the substrate, a nanocellulose support layer is first prepared using a vacuum filtration method. Then, a positively charged ultrathin chitosan-based macromolecular separation layer is prepared using a spin-coating method and a chemical cross-linking method. The preparation process is somewhat cumbersome, and the membrane's antifouling ability is somewhat lacking.

[0004] Therefore, preparing a high-efficiency, economical heavy metal ion separation membrane with high mechanical strength is an urgent technical problem that needs to be solved. Summary of the Invention

[0005] A method for preparing a modified PTFE forward osmosis membrane, the specific steps of which are as follows:

[0006] The PTFE commercial membrane was first pretreated by soaking it in anhydrous ethanol and deionized water for 1 hour each to remove surface impurities and unclog pores. The PTFE membrane was then pretreated by plasma treatment with nitrogen as the active gas. Subsequently, a certain mass fraction of silane coupling agent aqueous solution was prepared. A certain amount of UiO-66-NH2 powder and a certain amount of polyethyleneimine (PEI) were added to the silane coupling agent aqueous solution and mixed evenly to form solution A. The pretreated PTFE membrane was then soaked in solution A for a period of time. After the reaction was completed, the modified membrane was removed, rinsed with deionized water, and dried to finally form a PTFE heavy metal ion separation composite membrane.

[0007] The silane coupling agent is one of vinyltriethoxysilane, vinyltrimethoxysilane, and vinyltri(β-methoxyethoxy)silane;

[0008] The content of the silane coupling agent in the aqueous solution is 0.5-2.0 wt%;

[0009] The content of UiO-66-NH2 in the aqueous solution of the silane coupling agent is 0.2-1.0 wt%.

[0010] The content of PEI in the aqueous solution of the silane coupling agent is 0.1-0.3 wt%;

[0011] The pretreated PTFE membrane is immersed in the mixed solution for 2-5 hours.

[0012] This invention modifies PTFE membranes using nitrogen as the active gas through plasma treatment, causing partial breakage of the CF bonds in the PTFE membrane. Subsequently, a specific amount of UiO-66-NH2 and a certain amount of PEI are added. The coupling agent's structure mainly contains two functional groups: one group has an affinity for UiO-66-NH2, effectively binding to inorganic fillers; the other group has an affinity for organic groups, effectively binding to polyethyleneimine. The resulting UiO-66-NH2-silane coupling agent-polyethyleneimine composite structure is chemically bonded to the defective PTFE membrane, and UiO-66-NH2 grows in situ on the membrane surface, ultimately forming sub-nanochannels. Simultaneously, both the UiO-66-NH2 nanomaterial and the long chain of PEI contain a large number of amine groups. The prepared heavy metal ion separation membrane exhibits strong positive charge, and the synergistic effect of pore size sieving and the Donnan effect demonstrates excellent separation performance of heavy metal ions, showing broad application prospects. Detailed Implementation

[0013] Compare with Example 1:

[0014] The commercial PTFE membrane was pretreated by soaking it in anhydrous ethanol and deionized water for 1 hour each to remove surface impurities and unclog pores. The membrane's performance was then tested using simulated wastewater. Analysis of the COD results showed a COD removal rate of 13.21%. The PTFE membrane's ability to remove Hg... 2+ The rejection rate can reach 16.17%, and the flux is 200.48 L·m⁻¹. -2 ·h -1 .

[0015] Example 1:

[0016] The commercial PTFE membrane was pretreated by soaking it in anhydrous ethanol and deionized water for 1 hour each to remove surface impurities and unclog pores. The PTFE membrane was then pretreated with plasma treatment using nitrogen as the active gas. Following this, a 0.5 wt% aqueous solution of A151 silane coupling agent, containing 0.2 wt% UiO-66-NH2 powder and 0.1 wt% PEI, was prepared. The pretreated PTFE membrane was then immersed in this mixed solution for 2 hours. After the reaction, the modified membrane was removed, rinsed with deionized water, and dried to form a modified PTFE heavy metal ion separation composite membrane. Performance tests were conducted on the modified PTFE membrane using simulated wastewater. Analysis of the COD results showed a COD removal rate of 90.21%, and the PTFE membrane effectively separated Hg... 2+ The rejection rate can reach 86.17%, and the flux is 45.78 L·m⁻¹. -2 ·h -1 .

[0017] Example 2:

[0018] The commercial PTFE membrane was pretreated by soaking it in anhydrous ethanol and deionized water for 1 hour each to remove surface impurities and unclog pores. The PTFE membrane was then pretreated with plasma treatment using nitrogen as the active gas. Following this, a 1.0 wt% aqueous solution of A171 silane coupling agent, containing 0.4 wt% UiO-66-NH2 powder and 0.2 wt% PEI, was prepared. The pretreated PTFE membrane was then immersed in this mixed solution for 3 hours. After the reaction, the modified membrane was removed, rinsed with deionized water, and dried to form a modified PTFE heavy metal ion separation composite membrane. Performance tests were conducted on the modified PTFE membrane using simulated wastewater. Analysis of the COD results showed a COD removal rate of 94.67%, and the PTFE membrane effectively separated Hg... 2+ The rejection rate can reach 92.79%, and the flux is 36.35 L·m⁻¹. -2 ·h -1 .

[0019] Example 3:

[0020] The commercial PTFE membrane was pretreated by soaking it in anhydrous ethanol and deionized water for 1 hour each to remove surface impurities and unclog pores. The PTFE membrane was then pretreated with plasma treatment using nitrogen as the active gas. Following this, a 1.5 wt% aqueous solution of A172 silane coupling agent, containing 0.6 wt% UiO-66-NH2 powder and 0.3 wt% PEI, was prepared. The pretreated PTFE membrane was then immersed in this mixed solution for 5 hours. After the reaction, the modified membrane was removed, rinsed with deionized water, and dried to form a modified PTFE heavy metal ion separation composite membrane. Performance tests were conducted on the modified PTFE membrane using simulated wastewater. Analysis of the COD results showed a COD removal rate of 98.32%, and the PTFE membrane effectively separated Hg... 2+ The rejection rate can reach 98.54%, and the flux is 28.98 L·m⁻¹. -2 ·h -1 .

[0021] Table 1. Heavy metal ion separation effect of a modified PTFE forward osmosis membrane

[0022] project <![CDATA[Flux (L·m -2 ·h -1 )]]> <![CDATA[Hg 2+ Retention rate (%) COD removal rate (%) Compare with Example 1 200.48 16.17% 13.21% Example 1 45.78 86.17% 90.21% Example 2 36.35 92.79% 94.67% Example 3 28.98 98.54% 98.32%

[0023] As shown in Table 1, compared with conventional PTFE commercial membranes (Control Example 1), the modified PTFE heavy metal ion separation composite membrane exhibits significantly lower Hg levels through performance testing with simulated wastewater and TOC analysis. 2+ The rejection rate increased from 16.17% to 98.54%, and the COD removal rate increased from 13.21% to 98.32%. The decrease in flux is due to the sub-nanopores formed by the in-situ growth of UiO-66-NH2 nanomaterials on the surface of the modified PTFE heavy metal ion separation composite membrane. The pore size is smaller than the effective radius of heavy metal ions, which greatly improves the rejection rate of heavy metal ions.

Claims

1. A method for preparing a modified PTFE forward osmosis membrane, comprising the following steps: The commercial PTFE membrane is first pretreated by soaking it in anhydrous ethanol and deionized water for 1 h each to remove surface impurities and unclog pores. Then, the PTFE membrane is treated with plasma using nitrogen as the active gas. Subsequently, a certain mass fraction of silane coupling agent aqueous solution is prepared. A certain amount of UiO-66-NH2 powder and a certain amount of polyethyleneimine (PEI) are added to the silane coupling agent aqueous solution and mixed evenly to obtain solution A. The pretreated PTFE membrane is then immersed in solution A for a period of time. After the reaction is complete, the modified membrane is removed, rinsed with deionized water, and dried to finally form a modified PTFE forward osmosis membrane. The silane coupling agent is one of vinyltriethoxysilane, vinyltrimethoxysilane, or vinyltri(β-methoxyethoxy)silane.

2. The method for preparing a modified PTFE forward osmosis membrane according to claim 1, characterized in that: The content of the silane coupling agent in the aqueous solution is 0.5-2.0 wt%.

3. The method for preparing a modified PTFE forward osmosis membrane according to claim 1, characterized in that: The content of UiO-66-NH2 in the aqueous solution of silane coupling agent is 0.2-1.0 wt%.

4. The method for preparing a modified PTFE forward osmosis membrane according to claim 1, characterized in that: The content of PEI in the aqueous solution of silane coupling agent is 0.1-0.3 wt%.

5. The method for preparing a modified PTFE forward osmosis membrane according to claim 1, characterized in that: The PTFE membrane after pretreatment is immersed in solution A for 2-5 hours.