A high water flux polymer permeable membrane and its preparation method and application

Abstract

A high-water-flux polymer permeable membrane, its preparation method, and application include the following steps: spin-coating a substrate with methyl methacrylate (PMMA), PVA, or S1813 polymer material and heating and curing it to form a sacrificial layer; plasma-etching the sacrificial layer, cross-linking the surface with CF4 and CHF3 to form a polymer membrane; spin-coating PVA on the etched surface to form a support layer and curing it; dissolving the sacrificial layer with a solvent to suspend the composite membrane; transferring the suspended composite membrane to a porous support substrate; cleaning to remove residual solvent and sacrificial layer material; and removing the support layer to obtain a self-supporting permeable porous polymer membrane. The membrane prepared by this method has a salt rejection rate of up to 98% and a water flux of 2.16×10 6 L / h / m 2 .

Description

Technical Field

[0001] The present invention relates to the technical field of permeable membrane preparation, and in particular to a high-water-flux polymer permeable membrane and a controllable preparation method and application thereof. Background Art

[0002] Global freshwater shortages are becoming increasingly severe, and seawater desalination and wastewater reuse have become key approaches to alleviating the imbalance between supply and demand. Reverse osmosis (RO) technology is a mainstream desalination method, and the performance of its core component, the membrane, directly determines system efficiency and cost. Currently, commercial RO membranes are primarily polyamide thin film composite membranes (TFCs), consisting of a polysulfone-based membrane and a polyamide active layer. However, this technology still suffers from drawbacks such as a conflict between water flux and retention rate. In recent years, attempts have been made to improve membrane performance through modification with nanomaterials such as carbon nanotubes and MOFs, but these efforts face challenges such as complex preparation processes, high costs, and uneven material dispersion. One approach proposes embedding TiO2 nanoparticles into the polyamide layer to improve fouling resistance, but this approach results in nanoparticle aggregation, leading to structural defects in the membrane. Another approach uses sulfonated polyethersulfone-based membranes to enhance hydrophilicity, but this approach compromises the membrane's mechanical strength. Summary of the Invention

[0003] In order to solve the above problems, the present invention discloses a polymer permeable membrane with high water flux and high ion rejection rate.

[0004] Technical solution:

[0005] A method for preparing a high water flux polymer permeable membrane comprises the following steps:

[0006] S1, spin coating a first polymer material on a substrate and heating and curing the substrate to form a sacrificial layer;

[0007] S2, performing plasma etching on the sacrificial layer to form a cross-linked porous structure on the surface;

[0008] S3, spin coating a second polymer material on the etched surface to form a support layer and curing the layer;

[0009] S4, dissolving the sacrificial layer by a solvent to suspend the composite membrane;

[0010] S5, transferring the suspended composite membrane to a porous support substrate;

[0011] S6, cleaning to remove residual solvent and sacrificial layer material;

[0012] S7, removing the support layer to obtain an independently supported permeable porous polymer membrane.

[0013] Furthermore, in step S1, the substrate is a silicon wafer, a quartz wafer or an alumina ceramic substrate; the first polymer material is polymethyl methacrylate (PMMA), PVA or S1813 polymer material; and the spin coating adopts a three-step method: pre-spin coating at 500 r / min for 5-10 seconds → increasing to 6000-8000 r / min for spin coating for 30-60 seconds → decreasing to 500-1000 r / min for spin coating for 5-10 seconds.

[0014] Furthermore, in step S2, the plasma etching parameters include: etching gas is a mixture of CF4 and CHF3, the volume ratio is (3-5):1, the chamber pressure is 20-50 mTorr, the source power is 30-400 W, the bias power is 10-200 W, and the etching time is 5-30 seconds.

[0015] Furthermore, step S2 includes:

[0016] S201, clamping the sacrificial layer on a substrate of an ICP device, and setting the substrate temperature to 15° C.;

[0017] S202, placing it in an inductively coupled plasma etching chamber and evacuating it;

[0018] S203, introduce CF4 and CHF3, and set the steady-state pressure in the cavity;

[0019] S204, setting the source power, setting the bias power after stabilization, and performing the reaction;

[0020] S205. Turn off ventilation and power and cool for one minute.

[0021] Furthermore, in step S3, the second polymer material is PVA, the spin coating thickness is 200-500 nm, the curing temperature is 60-80° C., and the curing time is 5-15 minutes.

[0022] Furthermore, in step S4, the dissolving solvent is acetone, chloroform or dichloromethane, the dissolving temperature is 40-80° C., and the dissolving time is 30-60 minutes.

[0023] Furthermore, in step S5, the porous support substrate is a silicon nitride wafer with a pore size of 0.5-2 μm and a pore number of 5-20, which is prepared by plasma etching combined with chemical etching.

[0024] Furthermore, step S6 includes: washing with isopropyl alcohol at 60-80° C. for 5-15 minutes; and drying on a hot plate at 70-80° C. for 5-15 minutes.

[0025] Furthermore, step S7 specifically includes: placing the composite membrane in deionized water and shaking and washing it 2-3 times, each time for 3-5 minutes, so as to dissolve and remove the support layer.

[0026] Furthermore, the permeable porous polymer membrane has a thickness of 7-30 nm, an asymmetric pore structure, a salt rejection rate ≥98%, and a water flux ≥2×10^6 L / h / m².

[0027] The present invention also discloses a permeable porous polymer membrane prepared by the above preparation method. The permeable porous polymer membrane has a thickness of 7-30 nm and an asymmetric pore structure, with sub-nanometer pores on the front side and 20-120 nm pores on the back side.

[0028] The invention also discloses an application of a permeable porous polymer membrane, wherein the permeable membrane is used for water treatment.

[0029] Beneficial effects

[0030] (1) This method uses plasma etching to induce PMMA cross-linking to form a controllable porous structure, and combines sacrificial layer dissolution and support layer transfer technology to prepare a free-standing polymer permeable membrane. By adjusting the spin coating parameters and plasma etching process, the membrane thickness (7-30 nm) and the pore structure can be synergistically controlled, showing unique advantages in the fields of salt water desalination and precision filtration. In particular, the self-supporting nature of the membrane can maintain the integrity of the membrane structure, so that the resulting permeable membrane has excellent mechanical strength and transmembrane mass transfer efficiency.

[0031] (2) This method uses the synergistic effect of plasma etching gas ratio and energy parameters to induce directional cross-linking of PMMA molecular chains, forming three-dimensional through-hole channels. Compared with the traditional phase inversion method, the water flux of this structure reaches 2×10^6 L / h / m², while maintaining a salt retention rate of ≥98%. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the preparation process of the porous polymer membrane of this application;

[0033] Figure 2 This is a large-area porous polymer film directly prepared on PET material in this application;

[0034] Figure 3 For this application, transfer to a self-supporting porous polymer membrane with a 0.8 cm diameter circular hole;

[0035] Figure 4 This is a sample image on a silicon nitride substrate under a 100x optical microscope in this application;

[0036] Figure 5 This is an atomic force microscope image of the porous polymer film of this application;

[0037] Figure 6 Atomic force microscope images of the front and back sides of the porous polymer film of this application;

[0038] Figure 7 This is a scanning electron microscope (SEM) image of a single layer of amorphous carbon film on the TEM microgate of this application;

[0039] Figure 8 The retention rate of the porous polymer film for different salt ions in this application;

[0040] Figure 9 The water flux of the porous polymer film obtained under different parameters and different precursors in this application;

[0041] Figure 10 Schematic diagram of the salt retention rate test device for this application;

[0042] Figure 11 Schematic diagram of the cross-flow device for water flux testing in this application.

[0043] Reference numerals:

[0044] 1-Porous polymer film under atomic force microscopy, 2-Silicon oxide wafer substrate under atomic force microscopy, 3-Atomic force microscopy image of the front side of the polymer film, 4-Atomic force microscopy image of the back side of the polymer film, 5-Porous polymer film, 6-Through hole, 7-Support membrane, 8-Conductivity measurement electrode, 9-25ml 2.5M KCl solution, 10-25ml deionized water, 11-50ml simulated seawater solution, 12-50ml deionized water, 13-Customized chemical cell, 14-Peristaltic pump. DETAILED DESCRIPTION

[0045] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be interpreted as limiting the present invention.

[0046] The following materials and instruments are required for the implementation of the present invention:

[0047] The PMMA 495 A2 with a 2% anisole concentration used in the examples was purchased from Kayaku Co., Ltd.

[0048] The PVA used in the examples had an alcoholysis degree of 72.5-74.5 mol% and was purchased from Aladdin Reagent Co., Ltd.

[0049] The silicon wafer used in the embodiment is an oxidized silicon wafer with a silicon oxide thickness of 285 nanometers and a silicon wafer thickness of 535 micrometers, purchased from Suzhou Jingsi Electronic Technology Co., Ltd.

[0050] The silicon nitride wafer used in the embodiment has a silicon nitride thickness of 450 nanometers and a silicon wafer thickness of 525 micrometers;

[0051] The acetone used in the examples was purchased from Sinopharm Chemical Reagent Co., Ltd. with a purity of 99.7%.

[0052] The isopropyl alcohol used in the examples was purchased from Aladdin Reagent Co., Ltd. with a purity of 99.9%.

[0053] The U-shaped chemical cell used in the examples had a capacity of 30 ml and was purchased from Airuite Mechanical and Electrical Equipment Co., Ltd.

[0054] The cross-flow test device used in the embodiment includes a peristaltic pump, an analytical balance, and a custom chemical cell. The peristaltic pump is purchased from Lifu Automation Technology Co., Ltd., and the analytical balance is purchased from Xiniu Technology Co., Ltd.

[0055] The spin coater (SPS POLOS), heating stage (STUART), and ICP (Leuven HAASRODEPishow® A) used in the examples. Example 1

[0056] like Figures 1 to 11 As shown, this embodiment provides a controllable preparation method for a porous polymer film with a thickness of 7 nm. The preparation process of the method specifically includes:

[0057] S1. Spin-coating polymethyl methacrylate (PMMA) on a silicon wafer and heating and curing the wafer. The specific steps are as follows:

[0058] S101, placing a clean silicon oxide wafer on a spin coater;

[0059] S102, spin coating PMMA 495 A2 with a 2% anisole concentration to a thickness of 50 nm in three steps; the three steps are: spin coating at 500 r / min for one minute, spin coating at 6000-8000 r / min for one minute, and spin coating at 500 r / min for one minute;

[0060] S103. After spin coating, heat on a hot plate at 180°C for 5 minutes to ensure complete curing.

[0061] S2. Place the silicon wafer in an inductively coupled plasma etching chamber and use CF4 and CHF3 to react with PMMA on the surface. The specific steps are as follows:

[0062] S201, clamping the silicon wafer on the substrate of the ICP device, and setting the ICP substrate temperature to 15°C;

[0063] S202, place it in the inductively coupled plasma etching chamber and evacuate it to a vacuum degree of less than 5×10 -4 mbar;

[0064] S203, introduce 80 sccm CF4 and 20 sccm CHF3, and set the steady-state pressure in the chamber to 30 mTorr;

[0065] S204, set the source power for exciting inductive coupling to 30W, wait for three seconds for stabilization, set the bias power to 10W, and react for 12 seconds;

[0066] S205. Turn off ventilation and power and cool for one minute.

[0067] S3: Spin-coat 4% PVA (300 nm thick) at 3000 rpm and then heat-cure on a hot plate at 70°C.

[0068] S4. Place the silicon wafer cured by heating in S3 in 97% analytical grade acetone at 60°C for half an hour to dissolve the PMMA at the bottom, until a thin film of the PVA and PMMA reaction product is suspended in the acetone.

[0069] S5. Transfer the suspended film obtained in S4 to a silicon nitride wafer with holes and remove it.

[0070] S6. Place the silicon nitride wafer treated in S5 into 99.9% chromatographically pure isopropyl alcohol at 70°C and heat for 5 minutes to remove the PMMA residual glue and acetone.

[0071] S7. Place the silicon nitride wafer treated in S6 on a 70°C heating table for 10 minutes to dry the isopropyl alcohol.

[0072] S8. Place the silicon nitride wafer treated in S7 in 70°C ultrapure water and wash it 2 to 3 times to dissolve the PVA.

[0073] S9. Use an air gun to dry the surface moisture of the membrane treated in S8, and dry it on a hot plate at 70°C for 10 minutes to obtain an independently supported permeable porous polymer membrane.

[0074] In this embodiment, the silicon nitride film was placed in the middle of a U-shaped chemical cell. 20 ml of deionized water and 20 ml of 2.5 M KCl solution were added to both sides of the cell respectively. Samples were taken continuously to obtain the salt retention rate of the film.

[0075] In this embodiment, a silicon nitride film with a membrane is placed in a cross-flow test device, with deionized water and simulated seawater on both sides of the cross-flow, respectively. Continuous sampling is performed to obtain the membrane water flux.

[0076] like Figure 2 As shown, Figure 2 It is a large-area film directly made on transparent PET material, showing its uniformity and high light transmittance.

[0077] like Figure 3 As shown, Figure 3To transfer the porous polymer membrane onto a hole with a diameter of 8 mm and demonstrate its self-supporting property.

[0078] like Figure 5 As shown, Figure 5 These are atomic force microscope (AFM) images of a porous polymer film, approximately 8nm thick. Image 1 shows the porous polymer film under AFM, and image 2 shows the silicon oxide substrate under AFM. The film's precise thickness and good uniformity were measured.

[0079] like Figure 6 As shown, Figure 6 These are atomic force microscopy images of the front and back sides of a porous polymer film, demonstrating its asymmetric pore microstructure. Image 3 shows an AFM image of the front side of the film, showing subnanometer pores that appear smooth under AFM. Image 4 shows an AFM image of the back side of the film, showing pores ranging from 20 to 200 nm.

[0080] like Figure 7 As shown, Figure 7 This is a scanning electron microscope (SEM) image of a porous polymer film on a TEM microgrid. In the figure, 5 is the porous polymer film, 6 is the through hole, and 7 is the support membrane. Example 2

[0081] This embodiment provides a controllable preparation method for a porous polymer film with a thickness of 30 nanometers. The preparation process of the method specifically includes:

[0082] S1. Spin-coat the quartz wafer with photoresist S1813 and heat-cure it. The specific steps are as follows:

[0083] S101, placing a clean quartz wafer on a spin coater;

[0084] S102, spin coating a 50 nm thick benzene photoresist S1813 in three steps; the three steps are 500 r / min spin coating for one minute, 6000-8000 r / min spin coating for one minute, and 500 r / min spin coating for one minute;

[0085] S103, after spin coating, heat on a hot plate at 125°C for 1 minute to ensure complete curing;

[0086] S2. Place the quartz wafer in an inductively coupled plasma etching chamber and use CF4 and CHF3 to react with the surface S1813. The specific steps are as follows:

[0087] S201, clamping the quartz plate on the substrate of the ICP device;

[0088] S202, place it in the etching chamber and evacuate it to a vacuum level of less than 5×10 -4 mbar;

[0089] S203, introduce 80 sccm CF4 and 20 sccm CHF3, and set the steady-state pressure in the chamber to 30 mTorr;

[0090] S204, set the source power for exciting inductive coupling to 400W, wait for three seconds for stabilization, set the bias power to 100W, and react for 4 seconds;

[0091] S205, turn off ventilation and power and cool for one minute;

[0092] S3, spin coating 4% PVA (300 nm thickness) at 3000 rpm and then heating and curing on a hot plate at 70°C;

[0093] S4. Place the quartz plate in 97% analytical grade acetone at 60°C for half an hour to dissolve the S1813 at the bottom, until a thin film of the PVA and S1813 reaction product is suspended in the acetone;

[0094] S5, transferring the suspended film obtained in S4 to a silicon nitride wafer with holes and removing the film;

[0095] S6. Place the silicon nitride wafer treated in S5 in 99.9% chromatographically pure isopropyl alcohol at 70°C and heat for 5 minutes to remove the S1813 residual glue and acetone;

[0096] S7, placing the silicon nitride wafer treated in S6 on a 70° C. heating table for 10 minutes to dry the isopropyl alcohol;

[0097] S8. Wash the silicon nitride wafer treated in S7 in 70°C ultrapure water 2-3 times to dissolve the PVA.

[0098] S9. Use an air gun to dry the surface moisture of the membrane treated in S8, and dry it on a hot plate at 70°C for 10 minutes to obtain an independently supported permeable porous polymer membrane.

[0099] In this embodiment, the silicon nitride film was placed in the middle of a U-shaped chemical cell. 20 ml of deionized water and 20 ml of 2.5 M KCl solution were added to both sides of the cell respectively. Samples were taken continuously to obtain the salt retention rate of the film.

[0100] In this embodiment, a silicon nitride film with a membrane is placed in a cross-flow test device, with deionized water and simulated seawater on both sides of the cross-flow, respectively. Continuous sampling is performed to obtain the membrane water flux.

[0101] like Figure 8 As shown, Figure 8 To penetrate the porous polymer film to K + 、Na + 、Ga 2+ Mg 2+The ion retention rate of the membrane for different salt ions reaches more than 98%, which has a very high salt retention rate.

[0102] like Figure 9 As shown, Figure 9 This is the water flux permeating the porous polymer film obtained under different parameters and different precursors. The test solution is simulated seawater.

[0103] like Figure 10 As shown, Figure 10 This is a test device for the salt ion rejection rate of a porous polymer film. 8 is a conductivity measurement electrode, 9 is 25 ml of a 2.5 M KCl solution, and 10 is 25 ml of deionized water.

[0104] like Figure 11 As shown, Figure 11 This is a test device for water flux through porous polymer membranes. 11 is 50 ml of simulated seawater solution, 12 is 50 ml of deionized water, 13 is a customized chemical pool, and 14 is a peristaltic pump. Example 3

[0105] This embodiment discloses the application of a high water flux polymer permeable membrane for seawater desalination, clean water regeneration, and water / ion separation.

[0106] Finally, it should be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, and the present invention is not limited thereto. Those skilled in the art will be able to make various modifications and improvements without departing from the principles and essence of the present invention, and such modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a high water flux polymer permeable membrane, characterized in that: The steps include: S1. Spin-coating a substrate with polymethyl methacrylate (PMMA), PVA, or S1813 polymer material and heating and curing the substrate to form a sacrificial layer; wherein the substrate is a silicon wafer, a quartz wafer, or an alumina ceramic substrate; the spin-coating adopts a three-step method: the first step is pre-spin coating at 500 rpm for 5-10 seconds, the second step is increasing the speed to 6000-8000 rpm and spin coating for 30-60 seconds, and the third step is reducing the speed to 500-1000 rpm and spin coating for 5-10 seconds; S2. Plasma etching the sacrificial layer to form a cross-linked porous structure on the surface, thereby obtaining a thin film of PMMA reactant; wherein the plasma etching parameters include: etching gas is a mixture of CF4 and CHF3 in a volume ratio of (3-5):1, chamber pressure is 20-50 mTorr, source power is 30-400 W, bias power is 10-200 W, and etching time is 5-30 seconds; S3, spin coating PVA on the etched surface to form a support layer and solidifying it; S4, dissolving the sacrificial layer by a solvent to suspend a thin film of the PVA and PMMA reactants; S5, transferring the film of the suspended PVA and PMMA reactant to a porous support substrate; S6. Clean and remove the residual solvent and sacrificial layer material, and remove the support layer to obtain an independently supported permeable porous polymer membrane.

2. The preparation method according to claim 1, characterized in that Step S2 includes: S201, clamping the sacrificial layer on a substrate of an ICP device, and setting the substrate temperature to 15° C.; S202, placing it in an inductively coupled plasma etching chamber and evacuating it; S203, introduce CF4 and CHF3, and set the steady-state pressure in the cavity; S204, setting the source power, setting the bias power after stabilization, and performing the reaction; S205. Turn off ventilation and power and cool for one minute.

3. The preparation method according to claim 1, characterized in that In step S3, the spin coating thickness is 200-500 nm, the curing temperature is 60-80° C., and the curing time is 5-15 minutes.

4. The preparation method according to claim 1, characterized in that In step S4, the dissolving solvent is acetone, chloroform or dichloromethane, the dissolving temperature is 40-80° C., and the dissolving time is 30-60 minutes.

5. The preparation method according to claim 1, characterized in that In step S5, the porous support substrate is a silicon nitride wafer with a pore size of 0.5-2 μm and a pore number of 5-20, which is prepared by plasma etching combined with chemical etching.

6. The preparation method according to claim 1, characterized in that Step S6 includes: washing with isopropyl alcohol at 60-80° C. for 5-15 minutes; drying on a hot plate at 70-80° C. for 5-15 minutes; and washing the composite membrane in deionized water for 2-3 times, each time for 3-5 minutes, to dissolve and remove the support layer.

7. A high water flux polymer permeable membrane, characterized in that: The membrane is prepared by the preparation method according to any one of claims 1 to 6, wherein the thickness of the membrane is 7-30 nm, and the membrane has an asymmetric pore structure, with sub-nanometer pores on the front side and 20-120 nm pores on the back side.

8. The use of the polymer permeable membrane according to claim 7, characterized in that: The permeable membrane is used for water treatment.

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