CN117482766A - Hydrophobic porous separation membrane and preparation method and application thereof - Google Patents
Hydrophobic porous separation membrane and preparation method and application thereof Download PDFInfo
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- 239000002994 raw material Substances 0.000 claims description 8
- BGHCVCJVXZWKCC-UHFFFAOYSA-N tetradecane Chemical compound CCCCCCCCCCCCCC BGHCVCJVXZWKCC-UHFFFAOYSA-N 0.000 claims description 8
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- 229920012266 Poly(ether sulfone) PES Polymers 0.000 claims description 3
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- 239000004745 nonwoven fabric Substances 0.000 claims description 3
- 229920000052 poly(p-xylylene) Polymers 0.000 claims description 3
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- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/76—Macromolecular material not specifically provided for in a single one of groups B01D71/08 - B01D71/74
- B01D71/80—Block polymers
-
- 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
- B01D61/36—Pervaporation; Membrane distillation; Liquid permeation
- B01D61/364—Membrane distillation
-
- 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
- B01D67/0002—Organic membrane manufacture
-
- 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
- B01D69/12—Composite membranes; Ultra-thin membranes
-
- 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
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Water Supply & Treatment (AREA)
- Manufacturing & Machinery (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Abstract
The invention provides a hydrophobic porous separation membrane, which is prepared from a block copolymer, wherein the block copolymer comprises a bulk phase block A and a hydrophobic disperse phase block B; in the porous separation membrane, a framework is formed by the main block A, and the surface of the membrane and the surface of the pore canal inside the membrane are rich in the hydrophobic disperse phase block B; the water contact angle of the hydrophobic disperse phase block B is more than 90 DEG, and the specific surface energy gamma is less than 30mN m ‑1 . The invention also provides a composite separation membrane with hydrophobic surface, comprising a porous basal layer and a hydrophobic porous surface layer; the surface layer is the hydrophobic porous separation membrane; the composite separating film has integral through pore canal with surface pore canal in the pore diameter of 10-10Between 0 nm. The invention also provides a method for preparing the hydrophobic porous separation membrane and the composite separation membrane, and application of the hydrophobic porous separation membrane and the composite separation membrane in membrane distillation. The separation membrane has the advantages of high porosity, small pore diameter, narrow pore diameter distribution, good hydrophobicity, stable structure and simple preparation method, and is suitable for industrial production.
Description
Technical Field
The invention mainly relates to a separation membrane, in particular to a porous membrane material with hydrophobic surface, a preparation method thereof and application thereof in membrane distillation.
Background
Membrane Distillation (MD) is a membrane separation technology combining a membrane technology and a distillation process, and adopts a hydrophobic porous membrane as a separation medium, and because of the hydrophobicity of the membrane surface, the membrane pores only allow gaseous molecules to pass through (liquid water cannot pass through the membrane pores), one side of the membrane directly contacts a solution to be treated (hot side) with a higher temperature, the other side of the membrane is connected with a cooling medium (cold side), and under the action of a vapor pressure difference caused by a temperature difference on two sides of the membrane, water vapor generated by the solution on the hot side permeates the membrane pores and condenses on the cold side, thereby obtaining produced water or realizing the concentration of the solution on the hot side. Compared with the traditional separation method, the membrane distillation has the advantages of high rejection rate, simple and convenient operation and the like, thereby having wide application prospect in the fields of utilizing low-grade heat sources, treating high-salt wastewater, desalting seawater and the like.
Separation membranes used in existing membrane distillation are in addition to SiO 2 、Al 2 O 3 And ZrO(s) 2 Most of the ceramic films fired with metal oxides are organic films which are relatively inexpensive. The current method for preparing the hydrophobic organic porous membrane mainly comprises the following two steps: firstly, the cold stretching method is mainly suitable for insoluble polymers with high crystallinity, has a certain limit on polymer materials, and the obtained porous membrane has poor hydrophobicity and is easy to wet. And the phase inversion method, which uses organic solvent and generates a large amount of waste water, thus causing pollution and increasing production cost.
In the prior art, there is also a report of coating or depositing a natural hydrophobic polymer on the surface of a porous membrane to prepare a hydrophobic membrane, for example, polydimethylsiloxane (PDMS) is deposited or dip-coated on the porous surface, and although this method can prepare a hydrophobic porous membrane for membrane distillation, since PDMS is a rubbery substance and has high fluidity, immobilization cannot be achieved only by dip-coating or deposition, and thus an additional step of crosslinking is generally required to chemically connect rubbery PDMS to the surface of the porous membrane, so that the membrane has practical use properties. Therefore, the process for preparing the hydrophobic porous membrane by the method is complex and high in cost, and is not beneficial to industrial production.
Therefore, it is necessary to develop a new preparation method of the hydrophobic porous membrane, so as to solve the problems of unstable performance, high preparation cost or easy generation of harmful solvents of the hydrophobic porous membrane prepared in the prior art.
Disclosure of Invention
The primary object of the present invention is: a hydrophobic porous separation membrane is provided, which has stable structure, good porosity, hydrophobicity, pressure resistance and other properties.
Another object of the invention is: providing a method for preparing the hydrophobic porous separation membrane, wherein only non-toxic and harmless swelling agents such as alkanes and the like are used, and the swelling agents are non-toxic and harmless and can be recycled; the swelling process can be carried out at room temperature, the energy consumption is low, the environment is protected, and the method is suitable for large-scale industrial popularization.
Still another object of the present invention is: the application of the hydrophobic porous separation membrane in membrane distillation is provided, so that the rejection rate of the porous separation membrane to NaCl exceeds 99.99 percent.
The above object of the present invention is achieved by the following technical solutions:
in a first aspect, the present invention provides a hydrophobic porous separation membrane made from a block copolymer comprising a bulk phase block a and a hydrophobic disperse phase block B; in the porous separation membrane, a framework is formed by the main block A, and the surface of the membrane and the surface of the pore canal inside the membrane are rich in the hydrophobic disperse phase block B.
In the embodiment of the present invention, the bulk block a of the block copolymer may be selected from any one of Polysulfone (PSF), polyethersulfone (PES), polystyrene (PS), preferably PSF or PS; the water contact angle of the hydrophobic disperse phase block B is more than 90 DEG, and the specific surface energy gamma is less than 30mN m -1 The preferred water contact angle of the block B is greater than 100 DEG, and the specific surface energy gamma is less than 25 mN.m -1 The polymer chain segment with the properties can have proper mobility and hydrophobicity, and has important significance for ensuring pore forming and hydrophobicity of the membrane. In a preferred embodiment of the invention, the block B may in particular be Polydimethylsiloxane (PDMS) or polymethylphenylsiloxane.
The block copolymer may be an A-B diblock copolymer, or may be an A-B-A or B-A-B triblock copolymer.
In an embodiment of the invention, the block copolymer has a total molecular weight of 5 to 500kDa. The invention has found through the experiment that when the mass ratio of the hydrophobic disperse phase block B in the block copolymer is too high, the rigid structure cannot be maintained, therefore, the mass ratio of the block A in the copolymer is preferably more than 50%, and the mass ratio of the block B in the copolymer is not more than 50%; it is further preferable that the mass ratio of the block B in the copolymer is not more than 40%.
In a preferred embodiment of the invention, the block copolymer is a PS-PDMS-PS block copolymer, i.e., the bulk phase block A of the block copolymer is PS and the hydrophobic disperse phase block B is PDMS. When the block copolymer is prepared into a separation membrane, a glassy PS block forms a membrane framework at room temperature, and meanwhile, a rubber PDMS chain segment with high mobility can freely move, so that the surface of the porous membrane framework and the surface of a pore channel in the framework can be guaranteed to have hydrophobicity due to the fact that the PDMS chain segment is covered.
In a further preferred embodiment of the present invention, the PDMS is present in the block copolymer in an amount of 10wt% to 50wt%, more preferably 15wt% to 40wt%.
In a further preferred embodiment of the invention, the molecular weight of the PDMS segments in the block copolymer is preferably from 5kDa to 25kDa.
In a second aspect, the present invention also provides a method of preparing a hydrophobic porous separation membrane, comprising: the preparation method comprises the steps of preparing an initial compact film by taking a block copolymer as a raw material, wherein the block copolymer structure comprises a bulk phase block A and a hydrophobic disperse phase block B, the water contact angle of the disperse phase block B is more than 90 degrees (preferably more than 100 degrees), and the specific surface energy gamma is higher than that of the block copolymer PDMS Below 30 mN.m -1 (preferably below 25 mN.m) -1 ) The method comprises the steps of carrying out a first treatment on the surface of the Immersing the initial compact membrane in a selective solvent for treatment, swelling the hydrophobic disperse phase block B and further forming pore channels after the solvent volatilizes, thus obtaining the hydrophobic porous separation membrane.
In the swelling process of the preparation method, the hydrophobic disperse phase block B is subjected to severe expansion after absorbing the solvent, after the swelling is finished and the swelling agent volatilizes, the volume occupied by the expansion of the block B is converted into a pore canal, and the hydrophobic block B is attached to the inside of the pore canal and the surface of the membrane. In the swelling process, the bulk block A moves along with the block B, but the movement of the blocks is difficult to be completely synchronous, so that the surface roughness of the film is increased. Thus the longer the swelling time, the more severe the movement of the blocks, the higher the surface roughness. Along with the extension of the swelling time, the surface roughness of the membrane is continuously improved in the swelling process, and the hydrophobic disperse phase block B is largely migrated to the surface, so that the porous separation membrane with the hydrophobic surface and the hydrophobic internal pore channels is finally formed.
In the preferred preparation method of the invention, the interaction parameter of the selective solvent and the disperse phase block B is less than 0.5, and the interaction parameter of the selective solvent and the bulk phase block A is more than 0.5. In a more preferred method of the present invention, the interaction parameter of the selective solvent with the dispersed phase block B is between 0.3 and 0.45, and the interaction parameter with the bulk phase block is between 0.9 and 1.3.
In one embodiment of the present invention, the disperse phase block B and the bulk phase block a are PDMS and PS, respectively, and the selective solvent is an alkane, preferably any one or a mixture of two or more of n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, undecane, dodecane, tridecane, tetradecane, or petroleum ether.
In the preparation method of the present invention, there are various methods for preparing the initial dense film, for example, solid block copolymer may be prepared into the dense film by melt pressing, casting, extrusion, etc., or the block copolymer may be prepared into the dense film by spin coating, spray coating, soaking or natural evaporation of the solvent after solvent dissolution.
In the preferred preparation method of the invention, the initial compact membrane is immersed in a selective solvent for 1min-24h at 0-90 ℃; more preferably, the soaking treatment is performed at room temperature for 1 to 4 hours, followed by washing off the solvent or allowing the solvent to evaporate naturally, and further drying treatment.
In a third aspect, the present invention also provides a composite separation membrane having a hydrophobic surface, comprising a porous substrate layer and a hydrophobic porous surface layer; the surface layer is the hydrophobic porous separation membrane according to the first aspect of the invention; the composite separation membrane is integrally provided with through pore channels, the surface layer is provided with uniformly distributed surface pore channels, and the pore diameter of the surface pore channels is between 10 and 100 nm; the preferred surface pore size is between 10-50 nm. The surface of the composite separation membrane has hydrophobicity, and liquid water cannot pass through the composite separation membrane.
In the preferred composite separation membrane of the present invention, the porous substrate layer may be a large Kong Jimo, nonwoven fabric or paper. The macroporous base membrane material can be further selected from polyvinylidene fluoride PVDF, polysulfone PSF, polyacrylonitrile PAN, poly-p-xylylene PET or polypropylene PP; PVDF or PSF is preferred.
In a fourth aspect, the present invention also provides a method of preparing the composite separation membrane, comprising: coating a block copolymer on the surface of a macroporous substrate film to obtain a surface compact non-porous composite film, wherein the block copolymer comprises a bulk phase block A and a hydrophobic disperse phase block B, the water contact angle of the disperse phase block B is more than 90 degrees (preferably more than 100 degrees), and the specific surface energy gamma is higher than that of the bulk phase block A PDMS Below 30 mN.m -1 (preferably below 25 mN.m) -1 ) The method comprises the steps of carrying out a first treatment on the surface of the And then soaking the compact and nonporous composite membrane on the surface with a selective solvent to swell the block B of the block copolymer, and removing the solvent to obtain the composite separation membrane with the hydrophobic surface. The interaction parameter of the selective solvent and the disperse phase block B is smaller than 0.5, and the interaction parameter of the selective solvent and the bulk phase block A is larger than 0.5. In a more preferred method of the present invention, the interaction parameter of the selective solvent with the dispersed phase block B is between 0.3 and 0.45, and the interaction parameter with the bulk phase block is between 0.9 and 1.3.
The method for preparing the composite separation membrane can realize the rapid modification of the material based on the existing porous membrane material (especially the macroporous membrane). The macroporous substrate membrane can be hydrophilic or non-hydrophilic, that is, any macroporous substrate can be quickly changed into a hydrophobic membrane with surface holes of tens of nanometers by the method for preparing the composite separation membrane. For example, some polyethylene and polypropylene macroporous base films can be made to have increased surface hydrophobicity even if they do not show hydrophilicity, after being prepared as base films.
In a fifth aspect, the present invention also provides the use of the hydrophobic porous separation membrane or the composite separation membrane having a hydrophobic surface in membrane distillation.
In the prior art, although a few hydrophobic membranes have been prepared and used for membrane distillation, the phenomenon of membrane wetting inevitably occurs during long-term use of the hydrophobic membranes, which affects the water production quality and salt rejection rate. Preventing wetting of hydrophobic membranes is therefore a critical issue to be addressed in the field of membrane distillation. In addition, the current method for preparing the hydrophobic membrane mainly comprises a melt stretching method, a phase inversion method, an electrostatic spinning method and the like, wherein the pore diameter of the hydrophobic membrane prepared by the melt stretching method is generally between hundreds of nanometers and a few micrometers, and the hydrophobic membrane is generally not high, so that the long-term use stability is not good; the phase inversion method requires a large amount of organic solvents, generates organic wastewater, and has high pollution. Research shows that PVDF microporous hydrophobic membrane with high flux and high hydrophobicity can be prepared by utilizing the electrostatic spinning technology, but the application of the process for preparing the hydrophobic membrane by electrostatic spinning is very limited, and the large-scale production is difficult to realize at present. In addition, there have been studies on preparing composite separation membranes from hydrophobic polymer materials (e.g., PDMS and the like) and other polymer materials, but in view of the high fluidity of hydrophobic materials such as PDMS, it is often difficult to obtain separation membranes with stable structures, and a step of curing or crosslinking is required. And the preparation process of the composite membrane is complex in multiple steps, harsh in conditions and high in pollution.
The invention aims to develop a hydrophobic membrane with stable performance, which is suitable for large-scale industrial production. The inventors have selected a block copolymer containing a hydrophobic block as a film-forming material. Because the hydrophobic structure in the separation membrane exists in the surface and the internal structure of the membrane in the form of the disperse phase block, and the chemical connection rather than the physical mixing or lamination contact exists between the hydrophobic structure and the skeleton structure formed by the bulk phase block, compared with the existing hydrophobic membrane containing PDMS, the hydrophobic membrane not only has the hydrophobicity on the surface of the membrane, but also has the hydrophobicity in the pore canal finally formed in the membrane, and more importantly, the chemical connection ensures the stability of the connection between the hydrophobic structure and the skeleton, so that the hydrophobic component of the membrane cannot be lost along with the extension of the service time. Experiments prove that the hydrophobic separation membrane or the composite membrane can still have good hydrophobicity after long-term use. In addition, in order to provide the separation membrane with desirable hydrophobicity on both the surface and the internal pore channels, it is necessary to have a large distribution of the hydrophobic blocks of the block copolymer within and on the membrane. The inventor fully considers the influence of the property of the hydrophobic block on the hydrophobicity of the membrane surface when selecting the membrane forming raw material, selects a hydrophobic chain segment (such as a rubbery chain segment) with proper fluidity, realizes the movement of the hydrophobic chain segment to the membrane surface by utilizing the fluidity of the hydrophobic chain segment, and ensures a large amount of distribution of the hydrophobic structure on the membrane surface. Based on the selection of the film-forming raw materials described above, the inventors also fully utilized the difference between the interactions of the solvent and the polymer block, and used a solvent selective for the hydrophobic block for the swelling treatment. With the progress of swelling, the roughness of the membrane surface is increased, and the rubbery dispersed phase block is moved to the membrane surface in advance, so that the surface of the obtained porous membrane has hydrophobicity, and the dispersed phase block is attached to the surface of the pore canal after the solvent is volatilized, and the surface of the pore canal also has hydrophobicity. In the present invention, it is also possible to obtain separation membranes of different properties by adjusting a plurality of influencing factors. For example, during the swelling process, the overall porosity and surface hydrophobicity of the hydrophobic porous membrane can be adjusted by adjusting the degree of swelling of the membrane by selecting the chain length of the solvent, the temperature of swelling, and the swelling time; for example, in the aspect of raw material selection, the surface pore size and the surface porosity of the hydrophobic porous membrane can be regulated by changing the block ratio of the block copolymer and the molecular weight of the disperse phase, so as to regulate the membrane distillation performance of the hydrophobic membrane.
In summary, the hydrophobic porous separation membrane is prepared from a single raw material through simple selective swelling. The raw materials and the preparation method complement each other and complement each other. Compared with other existing methods, the preparation method provided by the invention has the advantages that raw materials are simple, auxiliary components are not required to be added, the used swelling agent is low-cost and easily-obtained linear alkane, swelling pore forming can be completed under mild conditions (a certain preferred scheme is even under normal temperature), a large amount of solvents are not required to be used in treatment, the solvents can be recycled, the obtained separation membrane has higher porosity, smaller pore diameter and narrow pore diameter distribution, and the preparation method is an environment-friendly and convenient membrane preparation method, can obviously reduce the production cost of the overall hydrophobic membrane, and can be used for industrially producing the hydrophobic porous separation membrane on a large scale.
Drawings
Fig. 1 is a surface SEM image of the hydrophobic porous membrane obtained in example 2.
Fig. 2 is an enlarged SEM image of the surface of the hydrophobic porous membrane obtained in example 2.
Fig. 3 is a water contact angle diagram of the hydrophobic porous membrane obtained in example 2.
Fig. 4 is a surface SEM image of the hydrophobic porous membrane obtained in example 3.
Fig. 5 is a cross-sectional SEM image of the hydrophobic porous membrane obtained in example 3.
Fig. 6 is a surface SEM image of the hydrophobic porous membrane obtained in example 4.
FIG. 7 is a graph showing membrane distillation performance of the hydrophobic composite membrane obtained in example 5.
Fig. 8 is a surface SEM image of the hydrophobic porous membrane obtained in example 6.
FIG. 9 is a graph showing membrane distillation performance of the hydrophobic composite membrane obtained in example 6.
Fig. 10 is a surface SEM image of the hydrophobic porous membrane obtained in example 7.
FIG. 11 is a graph showing membrane distillation performance of the hydrophobic composite membrane obtained in example 7.
Fig. 12 is a surface SEM image of the hydrophobic porous membrane obtained in example 8.
FIG. 13 is a graph showing membrane distillation performance of the hydrophobic composite membrane obtained in example 8.
Detailed Description
The hydrophobic porous separation membrane provided by the invention is prepared from a block copolymer, wherein the block copolymer comprises a main body phase block A and a hydrophobic disperse phase block B; in the porous separation membrane, a framework is formed by the main block A, and the surface of the membrane and the surface of the pore canal inside the membrane are rich in the hydrophobic disperse phase block B.
The block copolymer can be an A-B diblock copolymer or an A-B-A or B-A-B triblock copolymer, wherein the bulk phase block A is selected from any one of Polysulfone (PSF), polyethersulfone (PES) and Polystyrene (PS), the water contact angle of the block B is more than 90 DEG, and the specific surface energy gammase:Sub>A is less than 30 mN.m -1 Preferably, the contact angle of water is more than 100 DEG, and the specific surface energy gamma is less than 25 mN.m -1 More preferably, the block B is Polydimethylsiloxane (PDMS) or polymethylphenylsiloxane. The block copolymer has a total molecular weight of 5-500kDa.
In a preferred embodiment, the bulk phase block A is PS and the disperse phase block B is PDMS. In a further preferred embodiment, the block copolymer has a molecular weight of PS 20k -PDMS 5k 、PS 10k -PDMS 5k 、PS 8k -PDMS 5k 、PS 40k -PDMS 10k 、PS 30k -PDMS 10k 、PS 20k -PDMS 10k 、PS 40k -PDMS 25k 、PS 30k -PDMS 25k 、PS 20k -PDMS 10k -PS 20k 、PS 15k -PDMS 10k -PS 15k 、PS 10k -PDMS 10k -PS 10k 、PS 10k -PDMS 5k -PS 10k 、PS 25k -PDMS 25k -PS 25k 、PS 20k -PDMS 25k -PS 20k 、PS 15k -PDMS 25k -PS 15k 、PS 28k -PDMS 10k -PS 28k 、PS 18k -PDMS 10k -PS 18k 、PS 9k -PDMS 5k -PS 9k In kilodaltons.
The method for preparing the hydrophobic porous separation membrane provided by the invention is a method for preparing the hydrophobic porous separation membrane based on selective swelling, and specifically comprises the following steps of:
1) Preparing a compact film by taking the block copolymer as a film forming material through a solution film forming or melt film forming method;
the preparation of the compact film can be realized by fusing the segmented copolymer, forming the film by pressing, casting, extruding and the like, or can be realized by spin coating, spraying and solvent volatilization after the two blocks are dissolved together by good solvents.
2) Immersing the compact membrane obtained in the step 1) in a selective solvent, heating in a water bath at 0-90 ℃ for 1min-24h to enable the disperse phase block B to swell under the action of the solvent, volatilizing the solvent to form a pore channel structure, and drying to obtain the separation membrane with a porous structure integrally provided with continuous open pores; the selective solvent can be alkane, and specifically can be any one or more than two selected from n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, undecane, dodecane, tridecane, tetradecane or petroleum ether.
In a preferred embodiment of the present invention, step 2) is immersing the dense film obtained in step 1) in a selective solvent, and treating at room temperature for 1min-24h, wherein the selective solvent is n-hexane or n-heptane.
In another preferred embodiment of the present invention, step 2) is immersing the dense film obtained in step 1) in a selective solvent, and treating at 35-65 ℃ for 1min-24h, wherein the selective solvent is n-octane or n-decane.
The composite separation membrane with the surface having hydrophobicity comprises a porous basal layer and a hydrophobic porous surface layer; the porous substrate layer can be large Kong Jimo, non-woven fabric or paper; the surface layer is the hydrophobic porous separation membrane; the composite separation membrane is integrally provided with through pore channels, the surface layer is provided with uniformly distributed surface pore channels, and the pore diameter of the surface pore channels is between 10 and 100 nm; the preferred surface pore size is between 10-50 nm. The macroporous membrane material can be further selected from polyvinylidene fluoride PVDF, polysulfone PSF, polyacrylonitrile PAN, poly-p-xylylene PET or polypropylene PP; PVDF or PSF is preferred.
The method for preparing the composite separation membrane with the hydrophobic surface is also a method for rapidly modifying the surface property of large Kong Jimo based on selective swelling, and comprises the following steps: spin coating, spray coating or dip coating the segmented copolymer on the surface of a macroporous substrate film to obtain a composite film with compact and nonporous surface, and then carrying out the same swelling treatment process as the step 2) on the composite film to obtain the composite separation film with the surface of tens of nanometer pore channels and hydrophobic surface.
In the preparation of the surface hydrophobic composite membrane, pore forming can be realized by one-step swelling without other treatment, and compared with the method of adopting crosslinking on the surface of the hydrophobic PDMS in the prior art, the method has the advantages of simpler operation, smaller pore canal and more stable hydrophobicity of the surface of the membrane.
In the aspect of membrane distillation performance of the hydrophobic porous separation membrane, unlike the prior hydrophobic membrane reported in literature, the hydrophobic membrane provided by the invention has a pore diameter of between 10 and 100nm and even between 10 and 50nm, has smaller pore diameter, is more difficult to wet in the use process, and has longer service time. The separation membrane prepared by the invention has more excellent salt rejection rate which is more than 99.99 percent.
The invention is further explained below with reference to examples. The following examples are only illustrative of the present invention and are not intended to limit the scope of the invention.
Example 1
PS is processed 28k -PDMS 10k -PS 28k Preparing into a solution, spin-coating the solution on a silicon wafer, and putting the silicon wafer into n-hexane for soaking treatment for 1h at 25 ℃. Immediately after the completion of the treatment, the sample was taken out and dried at room temperature to obtain a hydrophobic porous membrane.
The hydrophobic porous membrane prepared in this example had a porosity of 41.3%, a surface porosity of 8.7%, a surface average pore size of 23.8nm, and a membrane surface water contact angle of 115.8 °.
Example 2
PS is processed 28k -PDMS 10k -PS 28k Is configured to dissolveThe solution is coated on a silicon wafer in a spin mode, and the silicon wafer is placed into normal hexane for soaking treatment for 4 hours at 25 ℃. Immediately after the completion of the treatment, the sample was taken out and dried at room temperature to obtain a hydrophobic porous membrane.
The hydrophobic porous membrane prepared in this example had a porosity of 43.3%, a surface porosity of 9.8%, a surface average pore size of 24.3nm, and a membrane surface water contact angle of 119.5 °.
Fig. 1 and 2 are SEM images of the surface and the enlarged surface of the hydrophobic porous membrane prepared in this example, and fig. 3 is a water contact angle chart of this example.
Example 3
PS is processed 28k -PDMS 10k -PS 28k Preparing into a solution, spin-coating the solution on a silicon wafer, and putting the silicon wafer into n-octane for soaking treatment for 1h at 55 ℃. Immediately after the completion of the treatment, the sample was taken out and dried at room temperature to obtain a hydrophobic porous membrane.
The hydrophobic porous membrane prepared in this example had a porosity of 52.8%, a surface porosity of 27.2% and a surface average pore size of 39.1nm.
Fig. 4 and 5 are SEM images of the surface and cross-section of the hydrophobic porous membrane prepared in this example, respectively.
This example uses a high temperature treatment compared to example 1, under which conditions the swelling agent interacts more strongly with PS, and thus the resulting porosity is higher and the pore size is larger.
Example 4
PS is processed 18k -PDMS 10k -PS 18k Preparing into a solution, spin-coating the solution on a silicon wafer, and putting the silicon wafer into n-hexane for soaking treatment for 1h at 25 ℃. Immediately after the completion of the treatment, the sample was taken out and dried at room temperature to obtain a hydrophobic porous membrane.
The hydrophobic porous membrane prepared in this example had a porosity of 50.4%, a surface porosity of 17.2%, a surface average pore size of 17.7nm, and a membrane surface water contact angle of 119.7 °.
Fig. 6 is a surface SEM image of the hydrophobic porous membrane prepared in this example.
This example, compared to example 2, uses a higher PDMS content block copolymer, which can achieve a porosity of over 50% and a hydrophobicity of 119.7 ° at room temperature.
Example 5
PS is processed 18k -PDMS 10k -PS 18k Preparing a solution, spin-coating the solution on a hydrophilic PVDF macroporous base film to form a composite film, and putting the composite film into n-hexane for soaking treatment for 1h at 25 ℃. And taking out the composite membrane immediately after the treatment is finished, and drying the composite membrane at room temperature to obtain the hydrophobic porous composite membrane.
The properties of the composite membrane are substantially the same as those of example 4, but since it is integrated with a macroporous base membrane, the whole membrane has through-channels, surface hydrophobicity and surface pores of several tens nanometers make liquid water unable to pass through the composite membrane even under pressure, and gas can pass through, so that the membrane is applied to membrane distillation. The membrane obtained in this example has a water flux of 13.2.+ -. 0.9 kg.m -2 ·h -1 The salt cut-off rate is 99.99%.
Fig. 7 is a graph of membrane distillation performance of the hydrophobic composite membrane prepared in this example, wherein the left ordinate represents water flux, the right ordinate represents salt rejection rate, the upper broken line represents salt rejection rate test results at each time point, the lower broken line represents water flux test results at each time point, and water flux data are respectively from three sets of parallel tests.
Example 6
PS is processed 28k -PDMS 10k -PS 28k Preparing a solution, spin-coating the solution on a hydrophilic PVDF macroporous base film to form a composite film, and putting the composite film into n-hexane for soaking treatment for 1min at 25 ℃. And taking out the composite membrane immediately after the treatment is finished, and drying the composite membrane at room temperature to obtain the hydrophobic porous composite membrane.
The hydrophobic porous composite membrane prepared in this example had a porosity of 34.6%, a surface porosity of 3.6% and a surface average pore size of 17.7nm.
Fig. 8 is a surface SEM image of the hydrophobic porous composite membrane prepared in this example.
Fig. 9 is a graph of membrane distillation performance of the hydrophobic porous composite membrane prepared in this example, wherein the left ordinate represents water flux, the right ordinate represents salt rejection rate, the upper broken line represents salt rejection rate test results at each time point, the lower broken line represents water flux test results at each time point, and water flux data are respectively from three sets of parallel tests.
This example swells for only 1min at room temperature, i.e. a higher porosity is achieved, as well as a uniform distribution of surface pore sizes. The water flux of the composite membrane obtained in this example was 7.6.+ -. 0.3 kg.m -2 ·h -1 The salt cut-off rate is 99.99%.
Example 7
PS is processed 9k -PDMS 5k -PS 9k Preparing a solution, spin-coating the solution on a hydrophilic PVDF macroporous base film to form a composite film, and putting the composite film into n-hexane for soaking treatment for 1h at 25 ℃. And taking out the composite membrane immediately after the treatment is finished, and drying the composite membrane at room temperature to obtain the hydrophobic porous composite membrane.
The hydrophobic porous composite membrane prepared in this example had a porosity of 40.2%, a surface porosity of 8.9% and a surface average pore size of 13.9nm.
Fig. 10 is a surface SEM image of the hydrophobic porous composite membrane prepared in this example.
FIG. 11 is a graph showing membrane distillation performance of the hydrophobic porous composite membrane prepared in this example, wherein the left ordinate represents water flux, the right ordinate represents salt rejection rate, the upper broken line represents salt rejection rate test results at each time point, the lower broken line represents water flux test results at each time point, and water flux data are respectively from three sets of parallel tests.
This example shows that a higher porosity can be achieved by swelling at room temperature and a smaller surface pore size using a block copolymer with a lower PDMS molecular weight than example 1. The water flux of the composite membrane obtained in this example was 15.96.+ -. 0.2 kg.m -2 ·h -1 The salt cut-off rate is 99.99%.
Example 8
PS is processed 45k -PDMS 25k -PS 45k Preparing into solution, spin-coating on hydrophilic PVDF macroporous base film to form composite film, and spin-coating the composite filmSoaking in n-hexane at 25deg.C for 1 hr. Immediately after the completion of the treatment, the composite film was taken out and dried at room temperature to obtain a hydrophobic porous film.
The hydrophobic porous composite membrane prepared in this example had a porosity of 30.2%, a surface porosity of 4.8% and a surface average pore size of 35.7nm.
Fig. 12 is a surface SEM image of the hydrophobic porous composite membrane prepared in this example.
Fig. 13 is a graph of membrane distillation performance of the hydrophobic porous composite membrane prepared in this example, wherein the left ordinate represents water flux, the right ordinate represents salt rejection rate, the upper broken line represents salt rejection rate test results at each time point, the lower broken line represents water flux test results at each time point, and water flux data are respectively from three sets of parallel tests.
This example shows a reduction in porosity achieved by swelling at room temperature but a larger surface pore size using a block copolymer of a PDMS molecular weight compared to example 1. The water flux of the composite membrane obtained in this example was 11.0.+ -. 0.1 kg.m -2 ·h -1 The salt cut-off rate is 99.99%.
Comparative example 1
A porous membrane was prepared by the method described in example 1, using n-hexadecane at room temperature, following the following protocol:
PS is processed 28k -PDMS 10k -PS 28k Preparing into a solution, spin-coating the solution on a silicon wafer, and putting the silicon wafer into n-hexadecane for soaking treatment for 1h at 25 ℃. Immediately after the completion of the treatment, the silicon wafer was taken out and dried at room temperature.
In this comparative example, although alkane was used for swelling at room temperature, the interaction between n-hexadecane and the block copolymer was too low, and the interaction parameters with the PS and PDMS blocks were 1.80 and 1.05, respectively, so that there was no swelling effect on the membrane, no pore formation was observed on the surface of the obtained membrane, and the membrane thickness was not increased.
Comparative example 2
A porous membrane was prepared by the method described in example 1, with an increase in swelling temperature, as follows:
PS is processed 28k -PDMS 10k -PS 28k Preparing into a solution, spin-coating the solution on a silicon wafer, and putting the silicon wafer into normal hexane for soaking treatment for 1h at 65 ℃. Immediately after the end of the treatment, the sample was taken out and dried at room temperature.
In this comparative example, as compared with example 1, although n-hexane was used for swelling, the interaction between n-hexane and PS was too strong at 65 ℃, so that the PS block was highly mobile in the swelling agent, micelle formation occurred on the surface of the obtained membrane, collapse of the membrane skeleton occurred, and it was difficult to obtain a porous membrane with stable pore size and dimension.
Comparative example 3
A porous membrane was prepared according to the method described in example 1 to increase the PDMS content, in particular as follows:
PS is processed 5k -PDMS 10k -PS 5k Preparing into a solution, spin-coating the solution on a silicon wafer, and putting the silicon wafer into n-hexane for soaking treatment for 1h at 25 ℃. Immediately after the end of the treatment, the sample was taken out and dried at room temperature.
In this comparative example, as compared with example 1, n-hexane was used for swelling, but the PDMS content was too high, and n-hexane had a strong interaction with PDMS, so that the movement of the PDMS block was likely to bring about the movement of the PS block, and the membrane after swelling had a frame collapse, which was difficult to obtain a porous membrane with stable pore diameter.
Claims (17)
1. A hydrophobic porous separation membrane characterized by: made of a block copolymer comprising a bulk phase block a and a hydrophobic dispersed phase block B; in the porous separation membrane, a framework is formed by the main block A, and the surfaces of the membrane and the pore channel inside the membrane are rich in the hydrophobic disperse phase block B; the water contact angle of the hydrophobic disperse phase block B is more than 90 DEG, and the specific surface energy gamma is less than 30 mN.m -1 The method comprises the steps of carrying out a first treatment on the surface of the Preferably, the water contact angle of the block B is greater than 100 DEG and the specific surface energy gamma is less than 25 mN.m -1 。
2. The separation membrane of claim 1, wherein: the bulk phase block A of the block copolymer is selected from any one of Polysulfone (PSF), polyether sulfone (PES) and Polystyrene (PS), preferably PSF or PS; the hydrophobic block B is Polydimethylsiloxane (PDMS) or polymethylphenylsiloxane.
3. The separation membrane according to any one of claims 1 or 2, characterized in that: the mass ratio of the block A in the copolymer exceeds 50%, and the mass ratio of the block B in the copolymer is not higher than 50%; it is further preferable that the mass ratio of the block B in the copolymer is not more than 40%.
4. The separation membrane of claim 1, wherein: the block copolymer is a PS-PDMS-PS block copolymer, i.e. the bulk phase block A of the block copolymer is PS and the hydrophobic disperse phase block B is PDMS.
5. The separation membrane of claim 4, wherein: the PDMS is present in the block copolymer in an amount of 10wt% to 50wt%, more preferably 15wt% to 40wt%.
6. The separation membrane according to any one of claims 4 to 5, wherein: the molecular weight of the PDMS segment in the block copolymer is 5kDa-25kDa.
7. A method of making a hydrophobic porous separation membrane comprising: the preparation method comprises the steps of preparing an initial compact membrane by taking a block copolymer as a raw material, wherein the block copolymer structure comprises a bulk phase block A and a hydrophobic disperse phase block B, the water contact angle of the disperse phase block B is more than 90 degrees (preferably more than 100 degrees), and the specific surface energy gamma PDMS is lower than 30 mN.m -1 (preferably below 25 mN.m) -1 ) The method comprises the steps of carrying out a first treatment on the surface of the Immersing the initial compact membrane in a selective solvent for treatment, swelling the hydrophobic disperse phase block B and further forming pore channels after the solvent volatilizes, thus obtaining the hydrophobic porous separation membrane.
8. The method of claim 7, wherein: the interaction parameter of the selective solvent and the disperse phase block B is smaller than 0.5, and the interaction parameter of the selective solvent and the bulk phase block A is larger than 0.5; more preferably, the interaction parameter of the selective solvent with the disperse phase block B is between 0.3 and 0.45, while the interaction parameter with the bulk phase block is between 0.9 and 1.3.
9. The method of claim 7, wherein: the disperse phase block B and the bulk phase block A are PDMS and PS respectively; the selective solvent is an alkane, preferably any one or a mixture of more than two of n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, undecane, dodecane, tridecane, tetradecane or petroleum ether, more preferably n-hexane, n-octane or n-decane.
10. The method of claim 7, wherein: the initial compact membrane is immersed in a selective solvent for 1min-24h at 0-90 ℃; preferably, the soaking treatment is carried out at room temperature for 1 to 4 hours, followed by washing off the solvent or allowing the solvent to evaporate naturally, and further drying treatment.
11. A composite separation membrane with hydrophobic surface, comprising a porous basal layer and a hydrophobic porous surface layer; the surface layer is the hydrophobic porous separation membrane of claim 1; the composite separation membrane is integrally provided with through pore channels, the surface of the composite separation membrane is provided with uniformly distributed surface pore channels, and the pore diameter of the surface pore channels is between 10 and 100 nm; the preferred pore size is between 10-50 nm.
12. The composite separation membrane of claim 11, wherein: the porous substrate layer is large Kong Jimo, non-woven fabric or paper; the macroporous base membrane is preferably made of polyvinylidene fluoride PVDF, polysulfone PSF, polyacrylonitrile PAN, poly-p-xylylene PET or polypropylene PP; more preferably PVDF or PSF.
13. A method of making the composite separation membrane of claim 12, comprising: coating a block copolymer on the surface of a macroporous substrate film to obtain a compact surface nonporous composite film, wherein the block copolymer is coated withComprising a bulk phase block A and a hydrophobic disperse phase block B, said disperse phase block B having a water contact angle of greater than 90 DEG (preferably greater than 100 DEG) and a specific surface energy γPDMS of less than 30 mN.m -1 (preferably below 25 mN.m) -1 ) The method comprises the steps of carrying out a first treatment on the surface of the Then soaking the compact and nonporous composite membrane with a selective solvent to swell the block B of the block copolymer, and removing the solvent to obtain a composite separation membrane with hydrophobic surface; the interaction parameter of the selective solvent and the disperse phase block B is smaller than 0.5, and the interaction parameter of the selective solvent and the bulk phase block A is larger than 0.5; preferably, the interaction parameter of the selective solvent with the disperse phase block B is between 0.3 and 0.45, while the interaction parameter with the bulk phase block is between 0.9 and 1.3.
14. A method for rapidly modifying the hydrophobicity of a large Kong Jimo surface, comprising: coating a block copolymer on the surface of a macroporous substrate film to obtain a surface compact non-porous composite film, wherein the block copolymer comprises a bulk phase block A and a hydrophobic disperse phase block B, the water contact angle of the disperse phase block B is more than 90 degrees (preferably more than 100 degrees), and the specific surface energy gamma PDMS is lower than 30 mN.m -1 (preferably below 25 mN.m) -1 ) The method comprises the steps of carrying out a first treatment on the surface of the Then soaking the compact and nonporous composite membrane with a selective solvent to swell the block B of the block copolymer, and removing the solvent to obtain a composite separation membrane with hydrophobic surface; the interaction parameter of the selective solvent and the disperse phase block B is smaller than 0.5, and the interaction parameter of the selective solvent and the bulk phase block A is larger than 0.5; preferably, the interaction parameter of the selective solvent with the disperse phase block B is between 0.3 and 0.45, while the interaction parameter with the bulk phase block is between 0.9 and 1.3.
15. The method of any one of claims 13 or 14, wherein: the selective solvent is an alkane, preferably any one or a mixture of more than two of n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, undecane, dodecane, tridecane, tetradecane or petroleum ether, more preferably n-hexane, n-octane or n-decane.
16. The method of any one of claims 13 or 14, wherein: immersing the compact and nonporous composite membrane in a selective solvent for 1min-24h at 0-90 ℃; preferably, the soaking treatment is carried out at room temperature for 1 to 4 hours, followed by washing off the solvent or allowing the solvent to evaporate naturally, and further drying treatment.
17. Use of the hydrophobic porous separation membrane of claim 1 or the composite separation membrane having a hydrophobic surface of claim 11 in membrane distillation.
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