Preparation method of modified PTFE forward osmosis membrane

Abstract

The invention aims to provide the preparation method of the modified PTFE forward osmosis membrane, the modified PTFE forward osmosis membrane is used for heavy metal ion separation, because the PTFE membrane has the advantages of stable chemical property, high mechanical strength, aging resistance and the like, the PTFE membrane is selected as a substrate, the PTFE membrane is firstly soaked in absolute ethyl alcohol and deionized water for a certain period of time, surface impurities are removed, holes are dredged, and the PTFE forward osmosis membrane is prepared; nitrogen is used as active gas for plasma treatment, part of C-F bonds are broken, a PTFE film with defects on the surface is formed, the modified PTFE film is completely soaked in a silane coupling agent solution, and then a certain amount of UiO-66-NH2 and a certain amount of polyethyleneimine (PEI) are added. The structure of the coupling agent mainly comprises two functional groups: a part of the groups have affinity to UiO-66-NH2 and can be effectively combined with the inorganic filler; a part of groups of the UiO-66-NH2-silane coupling agent have affinity to organic groups and can be effectively combined with polyethyleneimine, a formed UiO-66-NH2-silane coupling agent-polyethyleneimine composite structure is connected with a defective PTFE film through chemical bonds, and finally the modified PTFE composite film is formed. The modified membrane is applied to a heavy metal separation system, and the removal rate of mercury ions reaches up to 99%.

Description

Technical Field

[0001] The present invention relates to a preparation method of a modified PTFE forward osmosis membrane, belonging to the technical field of membrane preparation, and specifically relates to a preparation method of a PTFE heavy metal ion separation composite membrane. The PTFE heavy metal ion separation composite membrane has the advantages of strong acid and alkali resistance, high flux, high mechanical strength of the membrane, simple preparation, etc., and is applicable to the heavy metal ion separation system. Background Art

[0002] The governance, efficient recovery and reuse of heavy metal resources can effectively alleviate the current resource and energy crises.

[0003] Traditional separation methods of heavy metal ions include: chemical precipitation, adsorption, ion flotation, ion exchange, coagulation / flocculation and electrochemical methods. However, these methods have some serious drawbacks, such as high sludge production requiring further treatment, low removal efficiency, and high energy demand. In recent years, newer, more efficient, more economical and innovative technologies are being studied. 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 application. The modified covalent organic framework material is prepared by a simple room-temperature synthesis method and a neutral solution rapid ultrasonic modification strategy. Compared with the traditional high-temperature and high-pressure hydrothermal method combined with chemical synthesis method, the preparation time of this method is greatly shortened, but the connection between the modified covalent organic framework material and the substrate is not strong enough and is prone to fall off during long-term operation; Patent CN202411924014 provides a degradable positively charged nanofiltration composite membrane, its preparation method and application. Using viscose fiber non-woven fabric mainly composed of cellulose as the substrate, first a nanocellulose support layer is prepared by the suction filtration method, and then a positively charged ultrathin chitosan-based macromolecular separation layer is prepared by the spin coating method and the chemical cross-linking method. The preparation process is a bit cumbersome, and at the same time, the anti-pollution ability of the membrane is lacking.

[0004] Therefore, it is an urgent technical problem to be solved to prepare a heavy metal ion separation membrane with high efficiency, economy and high mechanical strength. Summary of the Invention

[0005] A preparation method of a modified PTFE forward osmosis membrane, the specific steps are as follows: The PTFE commercial membrane was first pretreated by soaking it in absolute ethanol and deionized water for 1 h respectively, aiming to remove surface impurities and open pores. The PTFE membrane was pretreated by plasma treatment using nitrogen as the reactive gas. Subsequently, an aqueous solution of silane coupling agent with a certain mass fraction was prepared. A certain amount of UiO-66-NH2 powder and a certain amount of polyethyleneimine (PEI) were added to the aqueous solution of silane coupling agent. The pretreated PTFE membrane was soaked in this mixed solution for a period of time. After the reaction ended, the modified membrane was taken out, rinsed with deionized water and dried, and finally a PTFE heavy metal ion separation composite membrane was formed.

[0006] Among them, the silane coupling agent is one of A151 (vinyltriethoxysilane), A171 (vinyltrimethoxysilane), and A172 (vinyltris(β-methoxyethoxy)silane); Among them, the content of the silane coupling agent in the aqueous solution is 0.5 - 2.0 wt%; Among them, the content of UiO-66-NH2 in the silane coupling agent is 0.2 - 1.0 wt%; Among them, the content of PEI in the silane coupling agent is 0.1 - 0.3 wt%; Among them, the time for the pretreated PTFE membrane to be soaked in this mixed solution is 2 - 5 h; In the present invention, the PTFE membrane is modified by plasma treatment using nitrogen as the reactive gas, causing partial C-F bonds in the PTFE membrane to break. Subsequently, a certain amount of UiO-66-NH2 and a certain amount of PEI are respectively added. The structure of the coupling agent mainly contains two functional groups: one part of the group has an affinity for UiO-66-NH2 and can effectively bind to the inorganic filler; while the other part of the group has an affinity for the organic group and can effectively bind to polyethyleneimine, forming a UiO-66-NH2-silane coupling agent-polyethyleneimine composite structure that is connected to the defective PTFE membrane through chemical bonds. UiO-66-NH2 grows in-situ on the membrane surface and finally forms sub-nanometer channels. At the same time, both UiO-66-NH2 nanomaterials and PEI long chains carry a large number of amine groups. The prepared heavy metal ion separation membrane has a strong positive charge, and the synergistic effect of pore size screening and Donnan effect. The modified membrane has a good effect on the separation of heavy metal ions and has broad application prospects. Detailed implementation mode

[0007] The PTFE commercial membrane was first pretreated by soaking it in absolute ethanol and deionized water for 1 h respectively, aiming to remove surface impurities and open pores. The performance of the membrane was tested with simulated wastewater. Through the analysis of the COD results, the COD removal rate was 13.21%. The PTFE membrane's... for Hg 2+The rejection rate can reach 16.17%, and the flux is 200.48 L·m -2 ·h -1 . Example

[0008] The PTFE commercial membrane was first pretreated by soaking it in absolute ethanol and deionized water for 1 h respectively, aiming to remove surface impurities and unblock pores. The PTFE membrane was pretreated by plasma treatment using nitrogen as the reactive gas. Subsequently, an aqueous solution of 0.5 wt% A151 silane coupling agent containing 0.2 wt% UiO-66-NH2 powder and 0.1 wt% PEI was prepared. The pretreated PTFE membrane was immersed in this mixed solution. After 2 h of reaction, the modified membrane was taken out, rinsed with deionized water and dried, finally forming a modified PTFE heavy metal ion separation composite membrane. The performance of the modified PTFE membrane was tested with simulated wastewater. Through the analysis of COD results, the removal rate of COD was 90.21%. The rejection rate of the PTFE membrane for Hg 2+ The rejection rate can reach 86.17%, and the flux is 45.78 L·m -2 ·h -1 . Example

[0009] The PTFE commercial membrane was first pretreated by soaking it in absolute ethanol and deionized water for 1 h respectively, aiming to remove surface impurities and unblock pores. The PTFE membrane was pretreated by plasma treatment using nitrogen as the reactive gas. Subsequently, an aqueous solution of 1.0 wt% A171 silane coupling agent containing 0.4 wt% UiO-66-NH2 powder and 0.2 wt% PEI was prepared. The pretreated PTFE membrane was immersed in this mixed solution. After 3 h of reaction, the modified membrane was taken out, rinsed with deionized water and dried, finally forming a modified PTFE heavy metal ion separation composite membrane. The performance of the modified PTFE membrane was tested with simulated wastewater. Through the analysis of COD results, the removal rate of COD was 94.67%. The rejection rate of the PTFE membrane for Hg 2+ The rejection rate can reach 92.79%, and the flux is 36.35 L·m -2 ·h -1 . Example

[0010] The PTFE commercial membrane was first pretreated by soaking it in absolute ethanol and deionized water for 1 h respectively, aiming to remove surface impurities and open pores. The PTFE membrane was pretreated by plasma treatment using nitrogen as the reactive gas. Subsequently, an aqueous solution of 1.5 wt% A172 silane coupling agent containing 0.6 wt% UiO-66-NH2 powder and 0.3 wt% PEI was prepared. The pretreated PTFE membrane was soaked in this mixed solution. After 5 h of reaction, the modified membrane was taken out, rinsed with deionized water and dried, finally forming a modified PTFE heavy metal ion separation composite membrane. The performance of the modified PTFE membrane was tested with simulated wastewater. Through the analysis of COD results, the removal rate of COD was 98.32%. The rejection rate of the PTFE membrane for Hg 2+ could reach 98.54%, and the flux was 28.98 L·m -2 ·h -1 .

[0011] Table 1 Heavy metal ion separation effect of a modified PTFE forward osmosis membrane Project <![CDATA[Flux (L·m -2 ·h -1 ).]]> <![CDATA[Hg 2+ Retention rate (%)]]> COD Removal Rate (%) Control 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% As can be seen from Table 1: Compared with the conventional PTFE commercial membrane (Control Example 1), through the performance test with simulated wastewater and the analysis of TOC results, the rejection rate of Hg of the modified PTFE heavy metal ion separation composite membrane 2+ increased from the original 16.17% to 98.54%, and the removal rate of COD increased from the original 13.21% to 98.32%. The reason for the decrease in flux is that 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 have pore sizes smaller than the effective radius of heavy metal ions, greatly improving the rejection rate of heavy metal ions.

Claims

1. A method for preparing a modified PTFE forward osmosis membrane, the specific steps of which are as follows: The commercial PTFE membrane was pretreated by soaking it in anhydrous ethanol and deionized water for 1 h respectively, in order to remove surface impurities and dredge holes. The PTFE membrane was pretreated by plasma treatment using nitrogen as the active gas. Then, a certain mass fraction of silane coupling agent aqueous solution was prepared, and a certain amount of UiO-66-NH2 powder and a certain amount of polyethyleneimine (PEI) were added to the silane coupling agent aqueous solution. The pretreated PTFE membrane was soaked in the mixed solution for a period of time. After the reaction was completed, the modified membrane was taken out, rinsed with deionized water, and dried to finally form a PTFE heavy metal ion separation composite membrane.

2. A method for preparing a PTFE heavy metal ion separation composite membrane as claimed in claim 1, characterized in that: The silane coupling agent is one of A151 (vinyl triethoxy silane), A171 (vinyl trimethoxy silane) and A172 (vinyl tri (β-methoxyethoxy) silane).

3. A method for preparing a PTFE heavy metal ion separation composite membrane as claimed in claim 1, characterized in that: The content of the silane coupling agent in the aqueous solution is 0.5-2.0 wt%.

4. A method for preparing a PTFE heavy metal ion separation composite membrane as claimed in claim 1, characterized in that: The content of UiO-66-NH2 in the silane coupling agent is 0.2-1.0 wt%.

5. A method for preparing a PTFE heavy metal ion separation composite membrane as claimed in claim 1, characterized in that: The content of PEI in the silane coupling agent is 0.1-0.3 wt%.

6. A method for preparing a PTFE heavy metal ion separation composite membrane as claimed in claim 1, characterized in that: The pretreated PTFE membrane is immersed in the mixed solution for 2-5 hours.