High-water-flux polymer permeable membrane as well as preparation method and application thereof

Abstract

The invention discloses a high-water-flux polymer permeable membrane as well as a preparation method and application thereof. The preparation method comprises the following steps: spin-coating a substrate with a methyl methacrylate PMMA (Polymethyl Methacrylate) or PVA (Polyvinyl Alcohol) or S1813 polymer material, and heating and curing to form a sacrificial layer; performing plasma etching treatment on the sacrificial layer, and using CF4 and CHF3 to crosslink the surface to form a polymeric membrane; pVA is spin-coated on the etched surface to form a supporting layer, and the supporting layer is cured; dissolving the sacrificial layer through a solvent to suspend the composite membrane; transferring the suspended composite membrane to a porous support substrate; cleaning to remove the residual solvent and the sacrificial layer material; and removing the support layer to obtain the independently supported permeable porous polymeric membrane. The film prepared by the preparation method disclosed by the invention has the salt rejection rate of 98% and the water flux of 2.16 * 10 < 6 > L / h / m < 2 >.

Description

Technical Field

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

[0002] The problem of global freshwater shortage is becoming increasingly severe, and seawater desalination and wastewater reuse have become key ways to alleviate the contradiction between supply and demand. As the mainstream desalination method, the performance of the filter membrane, the core component of the reverse osmosis (RO) technology, directly determines the system efficiency and cost. At present, commercial reverse osmosis membranes are mainly polyamide thin film composite membranes (TFCs), which are composed of a polysulfone substrate membrane and a polyamide active layer. However, this technology still has defects such as the contradiction between water flux and rejection rate. In recent years, there have been methods to improve the membrane performance by modifying with nanomaterials such as carbon nanotubes and MOFs, but they face problems such as complex preparation processes, high costs, or uneven dispersion of materials. There is a method of embedding TiO2 nanoparticles into the polyamide layer to improve anti-fouling performance, but in this method, the nanoparticles are prone to agglomeration, resulting in membrane structure defects; there is a method of using a sulfonated polyethersulfone substrate membrane to enhance hydrophilicity, but this method affects the mechanical strength of the thin film. Summary of the Invention

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

[0004] Technical Solution: A preparation method of a high water flux polymer permeable membrane specifically includes the following steps: S1. Spin-coat a first polymer material on a substrate and heat-cure to form a sacrificial layer; S2. Perform plasma etching treatment on the sacrificial layer to form a cross-linked porous structure on the surface; S3. Spin-coat a second polymer material on the etched surface to form a support layer and cure it; S4. Dissolve the sacrificial layer with a solvent to suspend the composite membrane; S5. Transfer the suspended composite membrane to a porous support substrate; S6. Wash to remove the residual solvent and sacrificial layer material; S7. Remove the support layer to obtain an independently supported permeable porous polymer membrane.

[0005] Further, in step S1, the substrate is a silicon wafer, a quartz wafer, or an alumina ceramic substrate; the first polymer material is poly(methyl methacrylate) PMMA, PVA, or S1813 polymer material; the spin-coating adopts a three-step method: pre-spin-coat at 500 r / min for 5 - 10 seconds → raise the speed to 6000 - 8000 r / min and spin-coat for 30 - 60 seconds → lower the speed to 500 - 1000 r / min and spin-coat for 5 - 10 seconds.

[0006] Further, in step S2, the plasma etching parameters include: the etching gas is a mixed gas of CF4 and CHF3, with a volume ratio of (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.

[0007] Further, step S2 includes: S201: Clamp the sacrificial layer on the substrate of the ICP device, and set the substrate temperature to 15°C; S202: Place it in the inductively coupled plasma etching chamber and evacuate; S203: Introduce CF4 and CHF3, and set the steady-state gas pressure in the chamber; S204: Set the source power, and after stabilization, set the bias power and carry out the reaction; S205: Turn off the gas supply and the power supply and cool for one minute.

[0008] Further, 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 time is 5 - 15 minutes.

[0009] Further, in step S4, the dissolving solvent is acetone, chloroform or dichloromethane, the dissolving temperature is 40 - 80°C, and the time is 30 - 60 minutes.

[0010] Further, in step S5, the porous support substrate is a silicon nitride wafer with a pore diameter of 0.5 - 2 μm and 5 - 20 pores, and is prepared by plasma etching combined with chemical etching method.

[0011] Further, step S6 includes: cleaning with isopropyl alcohol at 60 - 80°C for 5 - 15 minutes; drying on a hot plate at 70 - 80°C for 5 - 15 minutes.

[0012] Further, step S7 is specifically: placing the composite membrane in deionized water and shaking and cleaning it 2 - 3 times, 3 - 5 minutes each time, to dissolve and remove the support layer.

[0013] Further, the thickness of the permeable porous polymer membrane is 7 - 30 nm, it has an asymmetric pore structure, the salt rejection rate is ≥98%, and the water flux is ≥2×10^6 L / h / m².

[0014] The present invention also discloses a permeable porous polymer membrane prepared by the above preparation method. The thickness of the permeable porous polymer membrane is 7 - 30 nm, it has an asymmetric pore structure, with sub-nanometer pores on the front side and 20 - 120 nm pores on the back side.

[0015] The present invention also discloses an application of a permeable porous polymer membrane, and the permeable membrane is used for water treatment.

[0016] Beneficial effects (1) In this method, plasma etching is used to induce the cross-linking of PMMA to form a controllable porous structure. Combining the sacrificial layer dissolution and support layer transfer techniques, a freestanding polymer permeable membrane is prepared. By adjusting the spin-coating parameters and plasma etching process, the synergetic regulation of the membrane thickness (7 - 30 nm) and pore structure can be achieved, showing unique advantages in the fields of desalination, precision filtration, etc. In particular, the self-supporting property of the membrane can maintain the integrity of the membrane structure, making the finally obtained permeable membrane have excellent mechanical strength and transmembrane mass transfer efficiency.

[0017] (2) Through the synergistic effect of the plasma etching gas ratio and energy parameters, the PMMA molecular chains are induced to cross-link directionally to form three-dimensional through pores. Compared with the traditional phase inversion method, the water flux of this structure reaches 2×10^6 L / h / m², and at the same time, a salt rejection rate of ≥98% can be maintained. Description of the drawings

[0018] Figure 1 It is a schematic diagram of the preparation process of the permeable porous polymer membrane of this application; Figure 2 It is a diagram of a large-area porous polymer membrane directly prepared on a PET material in this application; Figure 3 It is a diagram of a porous polymer membrane transferred to a self-supporting circular hole with a diameter of 0.8 cm in this application; Figure 4 It is a diagram of a sample on a silicon nitride substrate under a 100-fold optical microscope in this application; Figure 5 It is an atomic force microscope image of the porous polymer thin film in this application; Figure 6 It is an atomic force microscope image of the front and back sides of the porous polymer thin film in this application; Figure 7 It is a scanning electron microscope (SEM) image of a single-layer amorphous carbon film on a TEM microgrid in this application; Figure 8 It is the salt rejection rate of the permeable porous polymer thin film in this application for different salt ions; Figure 9 It is the water flux of the permeable porous polymer thin film obtained in this application under different parameters and different precursors; Figure 10 It is a schematic diagram of the salt rejection rate test device in this application; Figure 11 It is a schematic diagram of the cross-flow device for water flux test in this application.

[0019] Reference numerals: 1 - Porous polymer film under atomic force microscope, 2 - Silicon oxide wafer substrate under atomic force microscope, 3 - Atomic force microscope image of the front side of the polymer film, 4 - Atomic force microscope image of the back side of the polymer film, 5 - Porous polymer film, 6 - Through hole, 7 - Support film, 8 - Conductivity measurement electrode, 9 - 25 ml of 2.5 M KCl solution, 10 - 25 ml of deionized water, 11 - 50 ml of simulated seawater solution, 12 - 50 ml of deionized water, 13 - Customized chemical cell, 14 - Peristaltic pump. Detailed implementation mode

[0020] The following details the implementation modes of the present invention, and examples of the implementation modes are shown in the drawings. The implementation modes described below with reference to the drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0021] The implementation of the present invention requires the following materials and instruments: The PMMA 495 A2 with an anisole concentration of 2% used in the examples was purchased from Kayaku Co., Ltd.; The PVA used in the examples had a degree of alcoholysis of 72.5 - 74.5 mol% and was purchased from aladdin reagent Co., Ltd.; The silicon wafers used in the examples were silicon oxide wafers with a silicon oxide thickness of 285 nm and a silicon wafer thickness of 535 μm, and were purchased from Suzhou Jingsi Electronic Technology Co., Ltd.; The silicon nitride wafers used in the examples had a silicon nitride thickness of 450 nm and a silicon wafer thickness of 525 μm; The acetone used in the examples had a purity of 99.7% and was purchased from Sinopharm Chemical Reagent Co., Ltd.; The isopropanol used in the examples had a purity of 99.9% and was purchased from aladdin reagent Co., Ltd.; The U-shaped chemical cell used in the examples had a capacity of 30 ml and was purchased from Arit Precision Electromechanical Equipment Co., Ltd.; The cross-flow test device used in the examples included a peristaltic pump, an analytical balance, and a customized chemical cell. The peristaltic pump was purchased from Lifu Automatic Control Technology Co., Ltd., and the analytical balance was purchased from Xiniu Technology Co., Ltd.; The spin coater (SPS POLOS), heating stage (STUART), and ICP (Leuven HAASRODEPishow® A) used in the examples. Example 1

[0022] As Figures 1 to 11 shown, this example provides a method for controllably preparing a porous polymer film with a thickness of 7 nm. The preparation process of this method specifically includes: S1. Spin-coat the silicon wafer with polymethyl methacrylate (PMMA) and heat it for curing. The specific steps are as follows: S101. Place the clean silicon oxide wafer on the spin coater. S102. Spin-coat PMMA 495 A2 with a concentration of 2% in anisole with a thickness of 50 nm by a three-step method. The three-step method is to spin-coat at 500 r / min for one minute, at 6000 - 8000 r / min for one minute, and at 500 r / min for one minute. S103. After spin-coating, heat it on a hot plate at 180 °C for 5 minutes to ensure complete curing.

[0023] S2. Place the silicon wafer into the inductively coupled plasma etching chamber and use CF4 and CHF3 to react with the surface PMMA. The specific steps are as follows: S201. Clamp the silicon wafer on the substrate of the ICP device, and set the temperature of the ICP substrate to 15 °C. S202. Place it into the inductively coupled plasma etching chamber and evacuate it. The vacuum degree is less than 5×10 -4 mbar. S203. Introduce 80 sccm CF4 and 20 sccm CHF3, and set the steady-state gas pressure in the chamber to 30 mTorr. S204. Set the source power of the inductively coupled excitation to 30 W. After waiting for three seconds to stabilize, set the bias power to 10 W and react for 12 seconds. S205. Turn off the gas supply and the power supply and cool for one minute.

[0024] S3. Spin-coat PVA with a mass fraction of 4% (thickness 300 nm) at 3000 rpm and then heat it on a hot plate at 70 °C for curing.

[0025] S4. Place the silicon wafer after heating and curing in step S3 into 97% analytical pure acetone at 60 °C for half an hour to dissolve the bottom PMMA until the film of the PVA and PMMA reaction product is suspended in the acetone.

[0026] S5. Transfer the suspended film obtained in S4 to a silicon nitride wafer with holes and fish it out.

[0027] S6. Place the silicon nitride wafer after treatment in S5 into 99.9% chromatographically pure isopropyl alcohol at 70 °C and heat it for 5 minutes to remove the residual PMMA glue and acetone.

[0028] S7. Place the silicon nitride wafer after treatment in S6 on a hot plate at 70 °C for 10 minutes to dry the isopropyl alcohol.

[0029] S8. Place the silicon nitride wafer after treatment in S7 into ultrapure water at 70 °C and wash it 2 - 3 times to dissolve the PVA.

[0030] S9. Air gun is used to dry the moisture on the surface of the membrane after S8 treatment, and then it is dried on a hot stage at 70 °C for 10 minutes to obtain an independently supported permeable porous polymer membrane.

[0031] In this embodiment, the silicon nitride with the membrane is placed in the middle of a U-shaped chemical cell. 20 ml of deionized water and 20 ml of 2.5 M KCl solution are added to both sides of the chemical cell respectively, and continuous sampling is carried out to obtain the salt rejection rate of the thin film.

[0032] In this embodiment, the silicon nitride with the membrane is placed in a cross-flow test device. Deionized water and simulated seawater are on both sides of the cross-flow respectively, and continuous sampling is carried out to obtain the water flux of the thin film.

[0033] As Figure 2 shown, Figure 2 It is a large-area thin film directly prepared on a transparent PET material, showing its uniformity and high light transmittance.

[0034] As Figure 3 shown, Figure 3 It is to transfer the porous polymer membrane to a hole with a diameter of 8 mm, showing its self-supporting property.

[0035] As Figure 5 shown, Figure 5 It is an atomic force microscope (AFM) image of the porous polymer thin film, with a thickness of about 8 nm. Among them, 1 is the porous polymer thin film under the atomic force microscope, 2 is the silicon oxide wafer substrate under the atomic force microscope, and the precise thickness and good uniformity of the thin film are measured.

[0036] As Figure 6 shown, Figure 6 It is an atomic force microscope image of the front and back sides of the porous polymer thin film, showing its asymmetric pore microstructure. Among them, 3 is the AFM image of the front side of the membrane, and the sub-nanometer pores on the surface show a smooth surface under the AFM. 4 is the AFM image of the back side of the membrane, and the pore distribution is 20 - 200 nm.

[0037] As Figure 7 shown, Figure 7 It is a scanning electron microscope (SEM) image of the porous polymer thin film on a TEM microgrid. In the figure, 5 is the porous polymer thin film, 6 is the through hole, and 7 is the support film. Example 2

[0038] This embodiment provides a controllable preparation method for a porous polymer thin film with a thickness of 30 nanometers. The preparation process of this method specifically includes: S1. Spin-coat photoresist S1813 on the quartz wafer and heat it for curing. The specific steps are as follows: S101. Place the clean quartz wafer on the spin coater; S102. Spin-coat a 50-nm-thick benzene photoresist S1813 using a three-step method; the three-step method is to spin-coat at 500 r / min for one minute, at 6000 - 8000 r / min for one minute, and at 500 r / min for one minute; S103. After spin-coating, heat on a hot plate at 125°C for 1 minute to ensure complete curing; S2. Place the quartz wafer into an inductively coupled plasma etching chamber and react the surface of S1813 using CF4 and CHF3. The specific steps are as follows: S201. Clamp the quartz wafer on the substrate of the ICP device; S202. Place it into the etching chamber and evacuate, with the vacuum degree less than 5×10 -4 mbar; S203. Introduce 80 sccm of CF4 and 20 sccm of CHF3, and set the steady-state gas pressure in the chamber to 30 mTorr; S204. Set the source power for exciting the inductively coupled plasma to 400 W. After waiting for three seconds to stabilize, set the bias power to 100 W and react for 4 seconds; S205. Turn off the gas supply and the power supply and cool for one minute; S3. Spin-coat a 4% mass fraction of PVA (thickness 300 nm) at 3000 rpm and then heat and cure on a hot plate at 70°C; S4. Place the quartz wafer in 97% analytical pure acetone at 60°C for half an hour to dissolve the bottom S1813 until the film of the reaction product of PVA and S1813 is suspended in acetone; S5. Transfer the suspended film obtained in S4 to a perforated silicon nitride wafer and fish it out; S6. Place the silicon nitride wafer treated in S5 into 99.9% chromatographic pure isopropyl alcohol at 70°C and heat for 5 minutes to remove the residual glue of S1813 and acetone; S7. Place the silicon nitride wafer treated in S6 on a hot plate at 70°C for 10 minutes to dry the isopropyl alcohol; S8. Place the silicon nitride wafer treated in S7 into ultrapure water at 70°C and wash 2 - 3 times to dissolve PVA; S9. Blow dry the moisture on the surface of the film treated in S8 with an air gun and dry it on a hot plate at 70°C for 10 minutes to obtain an independently supported permeable porous polymer membrane.

[0039] In this embodiment, place the silicon nitride with the film in the middle of a U-shaped chemical cell, add 20 ml of deionized water and 20 ml of 2.5 M KCl solution to both sides of the chemical cell respectively, and sample continuously to obtain the salt rejection rate of the film.

[0040] In this embodiment, the silicon nitride with a film is placed in a cross-flow test device. Deionized water and simulated seawater are on both sides of the cross-flow, and continuous sampling is carried out to obtain the water flux of the thin film.

[0041] As Figure 8 shown, Figure 8 is the ion rejection rate of the permeable porous polymer film for K + , Na + , Ga 2+ , Mg 2+ . The rejection rate of the film for different salt ions reaches over 98%, showing a very high salt rejection rate.

[0042] As Figure 9 shown, Figure 9 is the water flux of the permeable porous polymer film obtained under different parameters and different precursors. The test solution is simulated seawater.

[0043] As Figure 10 shown, Figure 10 is the test device for the salt ion rejection rate of the permeable porous polymer film. 8 is the conductivity measurement electrode, 9 is 25 ml of 2.5 M KCl solution, and 10 is 25 ml of deionized water.

[0044] As Figure 11 shown, Figure 11 is the test device for the water flux of the permeable porous polymer film. 11 is 50 ml of simulated seawater solution, 12 is 50 ml of deionized water, 13 is a customized chemical cell, and 14 is a peristaltic pump. Example 3

[0045] This embodiment discloses an application of a high water flux polymer permeable membrane for seawater desalination, clean water regeneration, and water / ion separation.

[0046] Finally, it can be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principles of the present invention. However, the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the principles and essence of the present invention, and these modifications and improvements are also considered within the protection scope 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 polymethyl methacrylate PMMA or PVA or S1813 polymer material on the substrate and heating and curing to form a sacrificial layer; S2, performing plasma etching on the sacrificial layer to form a cross-linked porous structure on the surface; 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 the composite film; S5, transferring the suspended composite membrane to a porous support substrate; S6, cleaning to remove the residual solvent and sacrificial layer material, and removing the support layer to obtain an independently supported permeable porous polymer membrane.

2. The preparation method according to claim 1, characterized in that: In step S1, the substrate is a silicon wafer, a quartz wafer or an alumina ceramic substrate; the spin coating adopts a three-step method: pre-spin coating at 500 r / min for 5-10 seconds → increase to 6000-8000 r / min for spin coating for 30-60 seconds → reduce the speed to 500-1000 r / min for spin coating for 5-10 seconds.

3. The preparation method according to claim 1, characterized in that: In step S2, the plasma etching parameters include: the etching gas is a mixed gas of CF4 and CHF3, the volume ratio is (3-5):1, the chamber pressure is 20-50 mTorr, the source power is 30-400W, the bias power is 10-200W, and the etching time is 5-30 seconds.

4. The preparation method according to claim 3, 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 in an inductively coupled plasma etching chamber and evacuating the chamber; S203, introducing CF4 and CHF3 to set the steady-state gas pressure in the cavity; S204, setting source power, setting bias power after stabilization, and reacting; S205. Turn off ventilation and power and cool for one minute.

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

6. 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.

7. 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.

8. The preparation method according to claim 1, characterized in that: Step S6 includes: washing with isopropanol 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.

9. 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 8, the thickness of the membrane is 7-30 nm, and it has an asymmetric pore structure, with sub-nanometer pores on the front side and 20-120 nm pores on the back side.

10. The use of the polymer permeable membrane according to claim 9, characterized in that: The permeable membrane is used for water treatment.

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