CN113522039A - Preparation method of forward osmosis membrane based on PVA (polyvinyl alcohol) grafting modification - Google Patents
Preparation method of forward osmosis membrane based on PVA (polyvinyl alcohol) grafting modification Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0039—Inorganic membrane manufacture
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/002—Forward osmosis or direct osmosis
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0081—After-treatment of organic or inorganic membranes
- B01D67/0088—Physical treatment with compounds, e.g. swelling, coating or impregnation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/30—Chemical resistance
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/36—Hydrophilic membranes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A20/00—Water conservation; Efficient water supply; Efficient water use
- Y02A20/124—Water desalination
- Y02A20/131—Reverse-osmosis
Abstract
The invention discloses a preparation method of a PVA (polyvinyl alcohol) graft modification-based forward osmosis membrane, which comprises the following steps of: 1-1.8: 1 of HCl, LiF and Ti3AlC2Sequentially adding the materials into a reactor, heating and stirring for 24-48 h at 30-40 ℃, then repeatedly washing and centrifuging, then ultrasonically stripping and centrifuging again to obtain a supernatant fluid, thus obtaining the MXene two-dimensional nanosheet; then, carrying out suction filtration on the MXene two-dimensional nano sheet on the surface of a nylon membrane by adopting a vacuum filtration method to obtain a forward osmosis membrane; then pouring a Glutaraldehyde (GA) water solution with the concentration of 0.05-0.1 wt% onto the surface of the forward osmosis membrane, and contacting for a certain time; and pouring a polyvinyl alcohol (PVA) water solution with the concentration of 100-300 mg/L onto the surface of the forward osmosis membrane soaked with GA, keeping for a certain time, and finally naturally drying the membrane sample to obtain the forward osmosis membrane based on PVA grafting modification. Book (I)The preparation method is simple, and the obtained forward osmosis membrane has smooth surface and high retention rate and water flux, can be used in the fields of emergency water bags, seawater desalination, industrial wastewater and the like, and has good application potential.
Description
Technical Field
The invention belongs to the technical field of membrane separation, and particularly relates to a preparation method of a forward osmosis membrane based on PVA (polyvinyl alcohol) grafting modification.
Background
China is a country extremely short of water resources, and the occupied amount of people is only one fourth of the average level of the world. The growing population and the rapid development of industry make the problem of water resource shortage increasingly serious. The development of water treatment technology provides a direction for people to solve the problem of water resource shortage. The membrane separation technology is a novel separation technology with high efficiency, environmental protection and energy saving, and plays an important role in the water treatment technology, and mainly comprises microfiltration, ultrafiltration, nanofiltration, reverse osmosis, forward osmosis and the like. The microfiltration and ultrafiltration precision is not high, and the membrane is easy to pollute; the nanofiltration membrane can intercept small-molecular organic matters and salts, the operation pressure is low, but the pollution problem is serious; the reverse osmosis has high operation pressure, high energy consumption and serious membrane pollution, and has certain limitation in practical application. Compared with the membrane separation technologies, the forward osmosis technology has the advantages of low energy consumption, high desalination rate, strong pollution resistance and the like, and has attracted extensive attention in recent years.
Currently, research on forward osmosis technology is mainly focused on two aspects: preparation of high-performance membrane material and selection of high-efficiency drawing liquid. The membrane is the core of the whole forward osmosis separation process, so that the preparation of high-performance membrane material is crucial to improve the overall performance of the system. Polysulfone, cellulose acetate, polyethersulfone and the like are the most commonly used film-forming materials. Among them, polyethersulfone is widely used because of its good chemical stability, thermal stability, and film-forming mechanical properties. However, in practical application, the conventional polyethersulfone membrane has large pore diameter, small porosity and rough membrane surface, which causes the problems of small water flux, poor desalting effect, easy pollution and the like. Therefore, the development and preparation of the high-performance forward osmosis membrane are of great significance, the modification of the porous support layer is an important way for improving the performance of the forward osmosis membrane, and the commonly used modification method comprises the following steps: blending modification, surface grafting modification, coating modification, plasma modification and the like.
In recent years, two-dimensional membranes formed by combining two-dimensional nanosheets are a new type of membrane materials which are of great interest, have unique physicochemical properties and excellent separation performance, and have wide application prospects in the separation field. MXene is a two-dimensional material which is successfully prepared in 2011, has been applied to the fields of electrochemistry, adsorption, membrane separation and the like for several years, and shows ultrahigh performance. In the field of membrane separation, MXene membranes exhibit excellent performance in aspects of gas separation, ion screening, dye interception and the like. The two-dimensional film formed by stacking MXene nanosheet units has regular controllable transmission channels, abundant surface functional groups and hydrophilic property, can realize the transmission of water and organic solvents, and can effectively screen molecules with different sizes. Therefore, the MXene nano flake solution with excellent performance is filtered on the nylon membrane substrate to prepare the forward osmosis membrane, and the PVA is adopted to carry out graft modification on the surface of the forward osmosis membrane to obtain the forward osmosis membrane based on PVA graft modification. The membrane not only can effectively improve the water flux and the retention rate of the forward osmosis membrane, but also can improve the antifouling performance of the membrane, and provides technical support for the wide application of the membrane technology in water treatment.
Currently, forward osmosis membranes based on PVA graft modification are less studied.
Chinese patent application No. CN201610453209.2 entitled preparation and application of graphene oxide modified cellulose acetate forward osmosis membrane discloses a method for preparing a forward osmosis membrane by using cellulose triacetate as a raw material and graphene oxide as a modifier through a phase inversion method. The method has the advantages of simple operation and the like, but the forward osmosis membrane taking the cellulose triacetate as the raw material has the problems of no high temperature resistance, easy hydrolysis, no acid and alkali resistance, easy biodegradation, low water flux and the like.
Chinese patent application No. CN201710506514.8 entitled "graphene oxide modified high-performance forward osmosis composite membrane and preparation method" discloses a method for preparing a forward osmosis membrane by taking polysulfone as a raw material, preparing a membrane casting solution by a blending mode, preparing a supporting layer by a phase inversion method and preparing an active layer by an interfacial polymerization method. The method has the advantages of good membrane selectivity and the like, but the preparation process is complex, and the problems of incomplete dissolution, uneven dispersion and the like of graphene oxide caused by the preparation of the membrane casting solution in a blending mode are solved, so that the water flux is not obviously improved.
Therefore, it is necessary to develop a forward osmosis membrane with acid and alkali resistance, good mechanical properties, high water flux, good retention rate and good antifouling property.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides the preparation method of the forward osmosis membrane based on PVA graft modification, which is simple in method, high in acid and alkali resistance, high in water flux, good in retention rate and good in antifouling performance.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
preparation method of forward osmosis membrane based on PVA (polyvinyl alcohol) grafting modificationThe method is characterized in that the mass ratio of the raw materials is 10-20: 1-1.8: 1 of HCl, LiF and Ti3AlC2Sequentially adding the materials into a reactor, heating and stirring for 24-48 h at 30-40 ℃, transferring the mixture in the reactor into a centrifuge tube, repeatedly washing and centrifuging, transferring the washed clay-like precipitate into a white jar, carrying out ultrasonic stripping, centrifuging and taking supernatant to obtain MXene two-dimensional nano flakes; then, carrying out suction filtration on the MXene two-dimensional nano sheet on the surface of a nylon membrane by adopting a vacuum filtration method to obtain a forward osmosis membrane; then, pouring a GA water solution with the concentration of 0.05-0.1 wt% onto the surface of the forward osmosis membrane, after contacting for a certain time, discharging the redundant solution from the surface of the forward osmosis membrane, then thoroughly washing the GA impregnated forward osmosis membrane with deionized water to remove unreacted GA molecules, and air-drying until no liquid remains; and then pouring a PVA water solution with the concentration of 100-300 mg/L onto the surface of the forward osmosis membrane soaked with GA, keeping for a certain time, discharging the redundant solution from the surface of the membrane, and finally naturally drying the membrane sample to obtain the forward osmosis membrane based on PVA graft modification.
The method specifically comprises the following steps:
1) mixing the following components in a mass ratio of 10-20: 1-1.8: HCl, LiF and Ti3AlC2 of 1 are sequentially and slowly added into the reactor, and the reactor is heated and stirred for 24-48 h at the temperature of 30-40 ℃.
2) Transferring the mixture obtained in the step 1) into a centrifugal tube, and centrifuging for 3-5 min at 3000-3500 rpm by using a high-speed centrifuge. And repeatedly washing and centrifuging until the pH value of the upper layer solution is close to 6-7.
3) Transferring the clay-like precipitate washed in the step 2) into a white jar, adding deionized water, and performing ultrasonic treatment for 1-2 h in an ice bath and argon atmosphere. And transferring the suspension liquid after the ultrasonic treatment into a centrifugal tube, and centrifuging for 1-2 h at 3000-3500 rpm. And after centrifugation, sucking the upper solution by using a liquid transfer gun, collecting the upper solution into a container, wherein the upper solution is the MXene nanosheet solution, and storing the MXene nanosheet solution in an argon atmosphere for later use after film extraction.
4) And (3) carrying out vacuum filtration on the MXene two-dimensional nanosheet obtained in the step 3) on the surface of a nylon membrane to obtain the forward osmosis membrane.
5) And (3) pouring a GA aqueous solution with the concentration of 0.05-0.1 wt% onto the surface of the forward osmosis membrane obtained in the step 4), contacting for 5-10 min, discharging the redundant solution from the surface of the forward osmosis membrane, then thoroughly washing the GA impregnated forward osmosis membrane with deionized water to remove unreacted GA molecules, and air-drying until no liquid remains.
6) And pouring a PVA water solution with the concentration of 100-300 mg/L onto the surface of the forward osmosis membrane soaked with GA, keeping for 2-5 min, discharging redundant solution from the surface of the membrane, and finally naturally drying the membrane sample to obtain the forward osmosis membrane based on PVA graft modification.
Wherein: HCl, LiF and Ti as described in step 1)3AlC2The mass ratio of (A) to (B) is 10-20: 1-1.8: 1. by selective etching, titanium-aluminium-carbon (Ti)3AlC2) As raw materials, HCl and LiF were used as etchants. The principle is that HF is generated in situ by reaction of HCl and LiF and reacts with an Al atomic layer to realize etching. When HCl, LiF and Ti3AlC2Is less than 10: 1: 1, the amounts of HCl and LiF were too small to allow Ti3AlC2 to be completely etched. When HCl, LiF and Ti3AlC2Is higher than 20: 1.8: 1, the amount of HCl and LiF is too much, the etching strength is too large, and the yield of MXene slices obtained by stripping is low, and the number of slice defects is large.
The sequential slow addition described in step 1) is Ti3AlC2The LiF should be completely dissolved in HCl before being slowly added to the reactor. Because if LiF is not completely dissolved in HCl, HF can not be completely generated in situ by reaction, thereby resulting in incomplete etching; if Ti is present3AlC2Too fast an addition will not allow complete contact reaction with HF, resulting in incomplete etching.
Heating and stirring for 24-48 h at 30-40 ℃ in the step 1). When the temperature is lower than 30 ℃, the reaction strength is not enough, and the etching is not complete; when the temperature is higher than 40 ℃, the reaction is too violent, the etching is excessive, the yield of the thin slices is reduced, and the defects of the thin slices are increased. When the time is less than 24 hours, the reaction time is insufficient, and the etching is incomplete; when the time is more than 48 hours, the reaction time is too long, the etching is excessive, the yield of the thin slice is reduced, and the defect of the thin slice is increased.
Centrifuging at 3000-3500 rpm for 3-5 min in the step 2) for repeated washing until the pH value of the upper layer solution is close to 6-7. The repeated washing centrifugation is to remove the aluminum and impurities etched away, and when the number of revolutions is less than 3000rpm, the aluminum and impurities cannot be completely centrifuged away. When the number of revolutions is higher than 3500rpm, it is uneconomical. When the centrifugation time is less than 3min, the centrifugation is incomplete. When the centrifugation time is more than 5min, it is uneconomical. When the pH is below 6, the solution is not completely washed off in acid. When the pH is higher than 7, it is not necessary.
And 3) carrying out ultrasonic treatment for 1-2 h in an ice bath and an argon atmosphere. When the ultrasonic time is less than 1h, the ultrasonic time is insufficient, and the multiple layers of MXene nano flakes can not be completely peeled into single-layer or few-layer MXene nano flakes, so that the yield of MXene two-dimensional nano flakes is low. When the ultrasonic time is higher than 2h, the ultrasonic time is too long, and a single layer or few layers of MXene nano flakes are shattered, so that the MXene two-dimensional nano flakes are smaller and the defects of the lamella are increased.
Pouring the GA aqueous solution with the concentration of 0.05-0.1 wt% on the surface of the forward osmosis membrane obtained in the step 4) in the step 5), and contacting for 5-10 min. When the concentration of the aqueous GA solution is less than 0.05 wt%, the amount of GA is too small, and it is not sufficiently tightly cross-linked with-OH groups on the surface of the forward osmosis membrane. When the concentration of the aqueous GA solution is higher than 0.1 wt%, the amount of GA is excessive, and the amount of residual GA molecules is large, which is uneconomical. When the contact time is less than 5min, the GA does not react completely with the hemiacetal on the membrane surface. When the contact time is more than 10min, GA reacts excessively with hemiacetal on the membrane surface.
Pouring the PVA water solution with the concentration of 100-300 mg/L on the surface of the forward osmosis membrane soaked with GA and keeping for 2-5 min in the step 6). When the concentration of the aqueous PVA solution is less than 100mg/L, the amount of PVA is too small to completely react with the other half of the aldehyde groups in GA, and the crosslinking is incomplete. When the concentration of the aqueous PVA solution is higher than 300mg/L, the amount of PVA is excessive, resulting in an increase in water resistance and a decrease in water flux. When the holding time is less than 2min, the reaction of PVA with GA is incomplete. When kept above 5min, PVA reacted excessively with GA.
Compared with the prior art, the invention has the following beneficial effects:
1. the preparation method disclosed by the invention is simple to operate, low in energy consumption and high in economic feasibility.
2. The forward osmosis membrane active layer prepared by the invention has a unique regular channel structure and good permeation and separation performance.
3. The forward osmosis membrane prepared by the invention has the characteristics of high hydrophilicity, antifouling property and the like, and can simultaneously ensure that the composite membrane has higher water flux and interception rate.
Detailed Description
The present invention will be described in further detail with reference to specific examples, wherein the raw materials used are common commercial products unless otherwise specified.
Example 1:
a forward osmosis membrane based on PVA graft modification was prepared in the following manner:
1) accurately weighing the components in a mass ratio of 10: 1.2: 1 of HCl, LiF and Ti3AlC2The mixture is added into a reactor slowly in turn and heated and stirred for 24 hours at the temperature of 30 ℃.
2) Transferring the mixture obtained in the step 1) into a centrifuge tube, and centrifuging for 3min at 3000rpm by using a high-speed centrifuge. The centrifugation was repeated until the pH of the supernatant solution was close to 6.
3) Transferring the clay-like precipitate washed in the step 2) into a white jar, adding deionized water, and performing ultrasonic treatment for 1h in an ice bath and argon atmosphere. The suspension after sonication was transferred to a centrifuge tube and centrifuged at 3000rpm for 1 h. And after centrifugation, sucking the upper solution by using a liquid transfer gun, collecting the upper solution into a container, wherein the upper solution is the MXene nanosheet solution, and storing the MXene nanosheet solution in an argon atmosphere for later use after film extraction.
4) And (3) carrying out vacuum filtration on the MXene two-dimensional nanosheet obtained in the step 3) on the surface of a nylon membrane to obtain the forward osmosis membrane.
5) Pouring a 0.05 wt% aqueous solution of GA on the surface of the forward osmosis membrane obtained in step 4), after contacting for 5min, draining the excess solution from the membrane surface, and then thoroughly rinsing the GA-impregnated forward osmosis membrane with deionized water to remove unreacted GA molecules and air-drying until no liquid remains.
6) And pouring a PVA aqueous solution with the concentration of 100mg/L onto the surface of the GA-impregnated forward osmosis membrane, keeping the surface for 2min, discharging the redundant solution from the surface of the membrane, and finally naturally drying the membrane sample to obtain the PVA graft modification-based forward osmosis membrane.
Example 2:
a forward osmosis membrane based on PVA graft modification was prepared in the following manner:
1) accurately weighing the components in a mass ratio of 15: 1.4: 1 of HCl, LiF and Ti3AlC2The mixture is added into the reactor slowly in turn and heated and stirred for 36h at the temperature of 35 ℃.
2) Transferring the mixture obtained in the step 1) into a centrifuge tube, and centrifuging for 3min at 3500rpm by using a high-speed centrifuge. The centrifugation was repeated until the pH of the supernatant solution was close to 6.5.
3) Transferring the clay-like precipitate washed in the step 2) into a white jar, adding deionized water, and performing ultrasonic treatment for 1.5h in an ice bath and argon atmosphere. The suspension after sonication was transferred to a centrifuge tube and centrifuged at 3500rpm for 1 h. And after centrifugation, sucking the upper solution by using a liquid transfer gun, collecting the upper solution into a container, wherein the upper solution is the MXene nanosheet solution, and storing the MXene nanosheet solution in an argon atmosphere for later use after film extraction.
4) And (3) carrying out vacuum filtration on the MXene two-dimensional nanosheet obtained in the step 3) on the surface of a nylon membrane to obtain the forward osmosis membrane.
5) Pouring a 0.07 wt% aqueous solution of GA onto the surface of the forward osmosis membrane obtained in step 4), after contacting for 7min, discharging the excess solution from the membrane surface, and then thoroughly rinsing the GA-impregnated forward osmosis membrane with deionized water to remove unreacted GA molecules and air-drying until no liquid remains.
6) And pouring 150mg/L PVA aqueous solution onto the surface of the GA-impregnated forward osmosis membrane, keeping the surface for 3min, discharging the redundant solution from the surface of the membrane, and finally naturally drying the membrane sample to obtain the PVA graft modification-based forward osmosis membrane.
Example 3:
a forward osmosis membrane based on PVA graft modification was prepared in the following manner:
1) accurately weighing the components in a mass ratio of 15: 1.6: 1 of HCl, LiF and Ti3AlC2The mixture is added into a reactor slowly in turn and heated and stirred for 24 hours at the temperature of 35 ℃.
2) Transferring the mixture obtained in the step 1) into a centrifuge tube, and centrifuging for 5min at 3000rpm by using a high-speed centrifuge. The centrifugation was repeated until the pH of the supernatant solution was close to 7.
3) Transferring the clay-like precipitate washed in the step 2) into a white jar, adding deionized water, and performing ultrasonic treatment for 1h in an ice bath and argon atmosphere. The suspension after sonication was transferred to a centrifuge tube and centrifuged at 3000rpm for 2 h. And after centrifugation, sucking the upper solution by using a liquid transfer gun, collecting the upper solution into a container, wherein the upper solution is the MXene nanosheet solution, and storing the MXene nanosheet solution in an argon atmosphere for later use after film extraction.
4) And (3) carrying out vacuum filtration on the MXene two-dimensional nanosheet obtained in the step 3) on the surface of a nylon membrane to obtain the forward osmosis membrane.
5) Pouring a 0.1 wt% aqueous solution of GA on the surface of the forward osmosis membrane obtained in step 4), after contacting for 10min, draining the excess solution from the membrane surface, and then thoroughly rinsing the GA-impregnated forward osmosis membrane with deionized water to remove unreacted GA molecules and air-drying until no liquid remains.
6) And pouring the PVA aqueous solution with the concentration of 200 mg/L onto the surface of the GA-impregnated forward osmosis membrane, keeping the surface for 2min, discharging the redundant solution from the surface of the membrane, and finally naturally drying the membrane sample to obtain the PVA graft modification-based forward osmosis membrane.
Example 4:
a forward osmosis membrane based on PVA graft modification was prepared in the following manner:
1) accurately weighing the components in a mass ratio of 20: 1.8: 1 of HCl, LiF and Ti3AlC2The mixture is added into the reactor slowly and heated and stirred for 24 hours at 40 ℃.
2) Transferring the mixture obtained in the step 1) into a centrifuge tube, and centrifuging for 5min at 3500rpm by using a high-speed centrifuge. The centrifugation was repeated until the pH of the supernatant solution was close to 6.
3) Transferring the clay-like precipitate washed in the step 2) into a white jar, adding deionized water, and performing ultrasonic treatment for 1h in an ice bath and argon atmosphere. The suspension after sonication was transferred to a centrifuge tube and centrifuged at 3500rpm for 2 h. And after centrifugation, sucking the upper solution by using a liquid transfer gun, collecting the upper solution into a container, wherein the upper solution is the MXene nanosheet solution, and storing the MXene nanosheet solution in an argon atmosphere for later use after film extraction.
4) And (3) carrying out vacuum filtration on the MXene two-dimensional nanosheet obtained in the step 3) on the surface of a nylon membrane to obtain the forward osmosis membrane.
5) Pouring a 0.05 wt% aqueous solution of GA on the surface of the forward osmosis membrane obtained in step 4), after contacting for 10min, draining the excess solution from the membrane surface, and then thoroughly rinsing the GA-impregnated forward osmosis membrane with deionized water to remove unreacted GA molecules and air-drying until no liquid remains.
6) And pouring a PVA aqueous solution with the concentration of 300mg/L onto the surface of the GA-impregnated forward osmosis membrane, keeping the surface for 3min, discharging the redundant solution from the surface of the membrane, and finally naturally drying the membrane sample to obtain the PVA graft modification-based forward osmosis membrane.
Example 5:
a forward osmosis membrane based on PVA graft modification was prepared in the following manner:
1) accurately weighing the components in a mass ratio of 20: 1.6: 1 of HCl, LiF and Ti3AlC2The mixture is added into a reactor slowly in turn and heated and stirred for 24 hours at the temperature of 35 ℃.
2) Transferring the mixture obtained in the step 1) into a centrifuge tube, and centrifuging for 5min at 3500rpm by using a high-speed centrifuge. The centrifugation was repeated until the pH of the supernatant solution was close to 6.5.
3) Transferring the clay-like precipitate washed in the step 2) into a white jar, adding deionized water, and performing ultrasonic treatment for 1.5h in an ice bath and argon atmosphere. The suspension after sonication was transferred to a centrifuge tube and centrifuged at 3500rpm for 1.5 h. And after centrifugation, sucking the upper solution by using a liquid transfer gun, collecting the upper solution into a container, wherein the upper solution is the MXene nanosheet solution, and storing the MXene nanosheet solution in an argon atmosphere for later use after film extraction.
4) And (3) carrying out vacuum filtration on the MXene two-dimensional nanosheet obtained in the step 3) on the surface of a nylon membrane to obtain the forward osmosis membrane.
5) Pouring a 0.1 wt% aqueous solution of GA on the surface of the forward osmosis membrane obtained in step 4), after contacting for 7min, draining the excess solution from the membrane surface, and then thoroughly rinsing the GA-impregnated forward osmosis membrane with deionized water to remove unreacted GA molecules and air-drying until no liquid remains.
6) Pouring the PVA water solution with the concentration of 250mg/L onto the surface of the forward osmosis membrane soaked with GA, keeping for 5min, discharging the redundant solution from the surface of the membrane, and finally naturally drying the membrane sample to obtain the forward osmosis membrane based on PVA graft modification.
Respectively measuring the forward osmosis membranes prepared in the embodiments 1-5 and based on PVA graft modification, with the thickness of 100nm, under a dead-end filtering device self-made in a laboratory, using 3.5mol/L NaCl solution as a raw material solution, applying a pressure of 1bar to test the salt cut-off rate, and under an AL-FS mode, using 1mol/L NaCl solution as a driving solution, using deionized water as a raw material solution, and testing the water flux and the reverse salt flux. Antifouling performance was tested by cross-flow filtration apparatus, the model contaminant was methylene blue (MB, 2 μ M) and the test parameters were Flux Decline Rate (FDR) and corresponding Flux Recovery Rate (FRR). The data are detailed in table 1.
TABLE 1 Performance testing of PVA graft-modified based Forward osmosis membranes
| Product(s) | Salt cut (%) | Water flux (LMH) | Reverse salt flux (LMH) | Flux Decline Rate (FDR) | Flux Recovery Rate (FRR) |
| Example 1 | 96.3 | 93.3 | 7.5 | 29.6 | 73.5 |
| Example 2 | 97.1 | 94.7 | 6.9 | 27.6 | 74.9 |
| Example 3 | 98.9 | 91.8 | 7.3 | 28.4 | 75.3 |
| Example 4 | 98.7 | 94.2 | 6.7 | 26.3 | 78.2 |
| Example 5 | 99.2 | 93.6 | 7.1 | 27.1 | 76.4 |
As can be seen from the above table 1, the forward osmosis membrane based on PVA graft modification has high water flux and rejection rate, low reverse salt flux and good antifouling performance. The preparation method effectively improves the performance of the forward osmosis membrane.
Finally, it should be noted that the above-mentioned examples of the present invention are only examples for illustrating the present invention, and are not intended to limit the embodiments of the present invention. Variations and modifications in other variations will occur to those skilled in the art upon reading the foregoing description. Not all embodiments are exhaustive. All obvious changes and modifications of the present invention are within the scope of the present invention.
Claims (5)
1. A preparation method of a PVA (polyvinyl alcohol) graft modification-based forward osmosis membrane is characterized by comprising the following steps of: 1-1.8: 1 of HCl, LiF and Ti3AlC2Sequentially adding the materials into a reactor, heating and stirring for 24-48 h at 30-40 ℃, transferring the mixture in the reactor into a centrifuge tube, repeatedly washing and centrifuging, transferring the washed clay-like precipitate into a white jar, carrying out ultrasonic stripping, centrifuging and taking supernatant to obtain MXene two-dimensional nano flakes; then, carrying out suction filtration on the MXene two-dimensional nano sheet on the surface of a nylon membrane by adopting a vacuum filtration method to obtain a forward osmosis membrane; then, pouring a GA water solution with the concentration of 0.05-0.1 wt% onto the surface of the forward osmosis membrane, after contacting for a certain time, discharging the redundant solution from the surface of the forward osmosis membrane, then thoroughly washing the GA impregnated forward osmosis membrane with deionized water to remove unreacted GA molecules, and air-drying until no liquid remains; and then pouring a PVA water solution with the concentration of 100-300 mg/L onto the surface of the GA-impregnated forward osmosis membrane, keeping the surface for a certain time, discharging the redundant solution from the surface of the membrane, and finally naturally drying the membrane sample to obtain the PVA graft modification-based forward osmosis membrane.
2. The method for preparing a forward osmosis membrane based on PVA graft modification of claim 1, wherein Ti is added3AlC2The LiF should be completely dissolved in HCl before being slowly added to the reactor.
3. The preparation method of the PVA graft modification-based forward osmosis membrane according to claim 1, wherein the repeated washing and centrifugation conditions are centrifugation at 3000-3500 rpm for 3-5 min; and repeatedly washing and centrifuging until the pH value of the upper layer solution is close to 6-7.
4. The preparation method of the PVA graft modification-based forward osmosis membrane according to claim 1, wherein the ultrasonic stripping is performed under the condition of ultrasonic treatment for 1-2 hours in an ice bath with power of 160-250W and in an argon atmosphere.
5. The preparation method of the PVA graft modification-based forward osmosis membrane according to claim 1, wherein the contact time of the GA aqueous solution on the surface of the MXene membrane is 5-10 min, and the contact time of the PVA aqueous solution on the surface of the MXene membrane immersed in the GA is 2-5 min.
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