CN110882632A - Reverse osmosis membrane and preparation method thereof - Google Patents
Reverse osmosis membrane and preparation method thereof Download PDFInfo
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- CN110882632A CN110882632A CN201811052153.5A CN201811052153A CN110882632A CN 110882632 A CN110882632 A CN 110882632A CN 201811052153 A CN201811052153 A CN 201811052153A CN 110882632 A CN110882632 A CN 110882632A
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- B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
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Abstract
The invention discloses a reverse osmosis membrane and a preparation method thereof, relates to the technical field of filtration membranes, and aims to solve the problem of low water yield of the reverse osmosis membrane in the water treatment process. The reverse osmosis membrane comprises: a support layer comprising a flat ultrafiltration membrane; a functional layer formed on the support layer, the functional layer comprising stacked overlapping graphene oxide sheets. The preparation method of the reverse osmosis membrane comprises the following steps: compounding the dispersion liquid of the graphene oxide on the surface of the supporting layer to form a composite film; and (3) performing coordination ion reinforcement on the composite membrane to obtain the required reverse osmosis membrane. The reverse osmosis membrane can effectively improve the water yield in the water treatment process.
Description
Technical Field
The invention relates to the technical field of filtering membranes, in particular to a reverse osmosis membrane and a preparation method thereof.
Background
Water resource shortage is one of the biggest challenges facing the world today, and as 70% of the earth is covered by seawater, fresh water resources also have serious water pollution problems, and therefore, seawater desalination and sewage treatment are increasingly attracting attention. The reverse osmosis technology refers to a separation method for separating solute from solvent in a solution under a certain pressure by means of selective permeability of a reverse osmosis membrane. The reverse osmosis membrane technology has the advantages of low energy consumption, stable structure, excellent separation performance and the like, and is widely concerned and applied in the fields of seawater desalination and water treatment.
The functional layer materials of the existing reverse osmosis membrane mainly comprise cellulose acetate, linear polyamide and aromatic polyamide, and the reverse osmosis membrane manufactured by adopting the three materials has the problem of low water yield (the yield of water filtered by the reverse osmosis membrane) in water treatment.
Disclosure of Invention
In view of the problems in the prior art, embodiments of the present invention provide a reverse osmosis membrane and a preparation method thereof, so as to solve the problem of low water yield of the reverse osmosis membrane in a water treatment process.
In order to achieve the above purpose, the embodiment of the present invention adopts the following technical solutions:
in a first aspect, embodiments of the present invention provide a reverse osmosis membrane comprising: a support layer comprising a flat ultrafiltration membrane; a functional layer formed on the support layer, the functional layer comprising stacked overlapping graphene oxide sheets.
In the reverse osmosis membrane provided by the embodiment of the invention, the graphene oxide has good hydrophilicity and an ion recognition function, and the functional layer adopts the stacked and overlapped graphene oxide, so that a selective two-dimensional nano channel can be formed between graphene oxide sheet layers, and a high-speed transmission channel is provided for water molecules, thereby realizing high-efficiency water treatment and increasing the water yield in the water treatment process. Meanwhile, the two-dimensional nanochannel formed by the stacked graphene oxide sheets can prevent solute macromolecules from passing through, and the support layer with the flat ultrafiltration membrane can also separate solute molecules with small and medium apertures in water, so that the separation performance of the reverse osmosis membrane is greatly improved under the combined action of the functional layer and the support layer.
Preferably, the graphene oxide sheets have a sheet diameter of 8-20 μm and 2-10 layers.
Preferably, the thickness of the functional layer is 0.1 to 0.5 μm.
Preferably, the surface pore diameter of the flat ultrafiltration membrane is 0.1-1 μm.
Preferably, the functional layer is bonded with the support layer through an adhesive, and the adhesive comprises any one or more of polyethylene glycol, polyvinylpyrrolidone and polyvinyl alcohol.
In a second aspect, embodiments of the present invention also provide a method of preparing a reverse osmosis membrane, for preparing a reverse osmosis membrane according to the first aspect, the method comprising: compounding the dispersion liquid of the graphene oxide on the surface of the supporting layer to form a composite film; and (3) performing coordination ion reinforcement on the composite membrane to obtain the required reverse osmosis membrane. The support layer comprises a flat ultrafiltration membrane.
According to the preparation method of the reverse osmosis membrane provided by the embodiment of the invention, the functional layer is further reinforced by utilizing chemical crosslinking through the coordination ion reinforcement of the composite membrane, so that the prepared reverse osmosis membrane has higher stability and firmness. The beneficial effects of the reverse osmosis membrane prepared by the preparation method of the reverse osmosis membrane provided by the embodiment of the invention are the same as those of the reverse osmosis membrane provided by the first aspect, and are not repeated herein.
Preferably, the step of forming a composite film by compositing the dispersion of graphene oxide on the surface of the support layer includes: spraying the dispersion of graphene oxide onto the surface of the support layer; wherein the spraying pressure is 0.1-0.5 MPa, and the spraying time is 1-10 s.
Preferably, the step of performing coordination ion reinforcement on the composite membrane to obtain the required reverse osmosis membrane comprises: putting the composite membrane into a reaction solution to carry out a coordination ion strengthening reaction; the reaction solution comprises a coordination ion aqueous solution and ethanol with the same volume as the coordination ion aqueous solution; and (3) showering the composite membrane by using ethanol, and standing the composite membrane for a certain time to obtain the required reverse osmosis membrane.
Preferably, the coordination ion aqueous solution comprises one or more of a calcium chloride solution, a magnesium chloride solution and an aluminum chloride solution, and the mass percentage of the solute in the coordination ion aqueous solution is 3-10%.
Preferably, the time of the complex ion strengthening reaction is 1 to 4 hours.
Preferably, before the step of forming a composite film by combining the dispersion of graphene oxide on the surface of the support layer, the method further includes a step of preparing the dispersion of graphene oxide, the step including: dispersing graphene oxide in a dispersing agent, and adding a layer expanding stabilizer to form a dispersion liquid precursor; and adding an alkali solution into the dispersion liquid precursor to enable the pH value of the dispersion liquid precursor to reach 7-9, so as to obtain the required dispersion liquid of the graphene oxide.
Preferably, the mass concentration of the graphene oxide in the dispersion liquid of the graphene oxide is
0.1～5mg/ml。
Preferably, the dispersant includes any one of ultrapure water, ethanol, and N-methylpyrrolidone.
Preferably, the layer expanding stabilizer comprises any one of sodium deoxycholate, sodium dodecyl benzene sulfonate and sodium polystyrene sulfonate, and the mass percentage of the layer expanding stabilizer in the dispersion liquid of the graphene oxide is 0.1-5%.
Preferably, before the step of forming the composite membrane by compositing the dispersion liquid of graphene oxide on the surface of the support layer, the method further includes a step of treating the flat ultrafiltration membrane of the support layer, the step including: putting the flat ultrafiltration membrane into an aqueous solution of an adhesive, soaking and then airing; wherein in the aqueous solution of the adhesive, the mass percent of the adhesive is 1-10%.
Preferably, after the step of forming a composite membrane by compositing the dispersion of graphene oxide on the surface of the support layer and before the step of performing coordination ion strengthening on the composite membrane to obtain the desired reverse osmosis membrane, the method further includes a step of performing thermal reduction treatment on the composite membrane, and the step includes: and (3) heating the composite film at the temperature of 60-80 ℃ in vacuum for 30-45 min, and then cooling to room temperature.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic representation of a reverse osmosis membrane in an embodiment of the present invention;
FIG. 2 is a surface electron microscope image of a functional layer of a reverse osmosis membrane in an embodiment of the present invention;
FIG. 3 is a sectional electron microscope image of a reverse osmosis membrane according to an embodiment of the present invention;
FIG. 4 is a flow chart of a method of preparing a reverse osmosis membrane in an embodiment of the present invention.
Reference numerals:
1-functional layer, 2-support layer.
Detailed Description
As described in the background art, the reverse osmosis membrane made of materials such as cellulose acetate, linear polyamide and aromatic polyamide has the problem of low water yield in water treatment, and has poor solvation effect of the materials in the preparation process, can not be prepared by a solution method, needs interfacial polymerization, and has complex reaction and high defect rate; because the reverse osmosis process has high operation pressure and the material is easy to compact, the problems of low water yield, membrane blockage and the like are caused, and a novel functional layer material is needed to be explored.
Graphene Oxide (GO) is a derivative of Graphene, and is generally prepared by an improved Hummers method, and the structure of the GO is considered that a large number of oxygen-containing functional groups (such as hydroxyl, carboxyl, epoxy, carbonyl and the like) are embedded on the surface and the edge of Graphene, and the GO is similar to the structure of aquaporins, has good hydrophilicity and ion recognition functions, and has high specific surface area and high reactivity, so that Graphene Oxide is an ideal separation membrane material.
Based on the current situation, the embodiment of the invention provides a reverse osmosis membrane and a preparation method thereof, which aim to solve the problem of low water yield in the water treatment process. Referring to fig. 1 and 3, the reverse osmosis membrane includes: the supporting layer 2, the supporting layer 2 comprises a flat ultrafiltration membrane; a functional layer 1 formed on a support layer 2, the functional layer 1 comprising stacked overlapping graphene oxide sheets. In a section electron microscope image of the reverse osmosis membrane shown in fig. 3, the upper right part is a section of the support layer 2, the middle part is a section of the functional layer 1 from the upper left to the lower right along a diagonal of the image, and the lower left part is a surface of the functional layer 1.
In the reverse osmosis membrane provided by the embodiment of the invention, graphene oxide has good hydrophilicity and an ion recognition function, the functional layer 1 adopts the stacked and overlapped graphene oxide to form a layered film, so that a selective two-dimensional nano channel can be formed between graphene oxide sheet layers, and a high-speed transmission channel is provided for water molecules, thereby realizing high-efficiency water treatment and increasing the water yield in the water treatment process. Meanwhile, the two-dimensional nanochannel formed by the stacked and overlapped graphene oxide can prevent macromolecules from passing through, and the support layer 2 with the flat ultrafiltration membrane can also separate solute molecules with small and medium apertures in water, so that the separation performance of the reverse osmosis membrane is greatly improved under the combined action of the functional layer 1 and the support layer 2. In addition, the graphene oxide interlayer has strong hydrogen bonds, so that the graphene oxide interlayer has good mechanical properties and high mechanical strength, can continuously run under high operating pressure, and also has good cleaning resistance.
The functional layer 1 is formed by stacking and overlapping graphene oxide with a sheet structure, so that the flatness of stacking and the tightness of overlapping have great influence on the separation performance of the functional layer 1, and the main factors determining the flatness and tightness are the basic sheet size of the graphene oxide and the processing method. The size of the sheet diameter of the graphene oxide sheet has a large influence on the stability of the stacked functional layer 1, the sheet diameter is too small, and the graphene oxide sheet is poor in lap joint and easy to fall off; the sheet diameter is too large, and graphene oxide in the dispersion liquid is easy to agglomerate and precipitate in the preparation process, so that the selection of the graphene oxide sheet with a proper size is very important for forming the reverse osmosis membrane with good performance. Illustratively, the sheet diameter of the graphene oxide sheet can be 8-20 μm, or the sheet diameter of the graphene oxide sheet can also be 8-10 μm, 8-15 μm, 10-15 μm, 12-17 μm, 15-20 μm and the like, and the number of layers of the graphene oxide sheet can be 2-10, or the graphene oxide sheet with the number of layers of 2-5, 5-10, 2-8, 8-10, 4-7 or 6-9 can also be selected.
The thickness of the functional layer 1 formed by stacking and overlapping the graphene oxide sheets may be in the range of 0.1 to 0.5 μm, and may be, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, or the like.
In some embodiments, the surface pore size of the selected flat ultrafiltration membrane can be 0.1-1 μm.
In some embodiments, the functional layer 1 and the support layer 2 may be bonded by an adhesive, and the adhesive may include any one or more of polyethylene glycol, polyvinylpyrrolidone, and polyvinyl alcohol, that is, one of the adhesives described above may be used, or a mixture of two or more of the adhesives described above may be used as the adhesive.
Referring to fig. 4, an embodiment of the present invention further provides a method for preparing a reverse osmosis membrane, which is used for preparing the reverse osmosis membrane, and the method for preparing the reverse osmosis membrane comprises: compounding the dispersion liquid of the graphene oxide on the surface of a support layer 2 to form a composite membrane, wherein the support layer comprises a flat ultrafiltration membrane; and (3) performing coordination ion reinforcement on the composite membrane to obtain the required reverse osmosis membrane.
After graphene oxide is stacked to form a film, the stability of the film structure in a water phase is poor, and the stacked structure is easily decomposed and re-dispersed in a solvent, so that the separation performance of the graphene oxide is lost. According to the preparation method of the reverse osmosis membrane provided by the embodiment of the invention, the functional layer 1 is further reinforced by utilizing chemical crosslinking through the coordination ion reinforcement of the composite membrane, so that the prepared reverse osmosis membrane has higher stability and firmness. The beneficial effects of the reverse osmosis membrane prepared by the preparation method of the reverse osmosis membrane provided by the embodiment of the invention are the same as those of the reverse osmosis membrane provided by the embodiment of the invention, and are not repeated herein.
Referring to fig. 4, in some embodiments, before the step of combining the dispersion of graphene oxide on the surface of the support layer 2 to form the composite film, a step of preparing the dispersion of graphene oxide is further included, and the step includes: s11, dispersing graphene oxide in a dispersing agent, and adding a layer expanding stabilizing agent to form a dispersion liquid precursor; and S12, adding an alkali solution, such as ammonia water, a strong sodium oxide solution and the like, into the dispersion liquid precursor to enable the pH value of the dispersion liquid precursor to reach 7-9, and obtaining the required dispersion liquid of the graphene oxide.
In some embodiments, the mass concentration of the graphene oxide in the prepared dispersion liquid of the graphene oxide is 0.1-5 mg/ml, and for example, may be 0.1mg/ml, 5mg/ml, 2.5mg/ml, 1mg/ml, 2mg/ml, 3mg/ml, 4mg/ml, and the like.
The graphene oxide can be dispersed in various reagents, but the dispersion state of the graphene oxide sheets in the reagents directly affects the performance of the functional layer 1, so that an appropriate dispersant needs to be selected to improve the dispersion effect of the graphene oxide. Illustratively, any one of water, ethanol, and N-methylpyrrolidone may be selected as the dispersant to improve the dispersion effect of the graphene oxide. In the actual operation process, the dispersion effect of the graphene oxide is better by stirring and ultrasonic processing the solution.
Because the graphene oxide is easy to agglomerate, the retention rate is reduced, and therefore, in some embodiments, a small amount of a layer expanding stabilizer can be added into the dispersion liquid of the graphene oxide, so that the graphene oxide is smoothly lapped, the water flux is increased, the stability of the dispersion liquid is facilitated, and the difficulty in preparation and processing is reduced. The layer expanding stabilizer can be any one of sodium deoxycholate, sodium dodecyl benzene sulfonate and sodium polystyrene sulfonate, and the mass percentage of the layer expanding stabilizer in the dispersion liquid of the graphene oxide can be 0.1-5%.
Referring to fig. 4, in some embodiments, before the step of compounding the dispersion of graphene oxide on the surface of the support layer 2 to form the composite membrane, a step of treating the flat ultrafiltration membrane of the support layer 2 is further included, where the step includes: s2, the flat ultrafiltration membrane is put into the aqueous solution of the adhesive, soaked and dried. The mass percentage of the adhesive in the aqueous solution of the adhesive is 1 to 10%, and may be, for example, 1%, 3%, 5%, 6%, 8%, 10%, or the like. The adhesive can be one or more selected from polyethylene glycol, polyvinylpyrrolidone and polyvinyl alcohol.
In some embodiments, the flat plate ultrafiltration membrane of support layer 2 may be a polysulfone or polyethersulfone material. Because the surface tension of the dispersion liquid of the graphene oxide is different from that of a flat ultrafiltration membrane (polysulfone/polyethersulfone membrane) of the support layer 2, if the dispersion liquid of the graphene oxide is directly compounded on the support layer 2, the dispersion liquid may be in a fog drop shape on the surface of the support layer 2 and cannot form a membrane, so the support layer 2 needs to be treated, amphiphilic substances such as polyethylene glycol, polyvinylpyrrolidone and polyvinyl alcohol are used as adhesives to modify the surface of the support layer 2, the surface roughness of the support layer 2 is improved, the surface tension of the support layer 2 is closer to that of the dispersion liquid of the graphene oxide, the lipophilic group of the adhesives is microscopically combined with the support layer 2, and the hydrophilic group can be combined with the graphene oxide subsequently compounded on the surface of the support layer 2, so that the support layer 2 and the functional layer 1 are firmly adhered together. Therefore, the pretreatment of the support layer 2 is beneficial to the spreading of the graphene oxide on the surface of the support layer 2 and the firm bonding of the graphene oxide and the support layer.
Referring to fig. 4, in some embodiments, the step of compounding the dispersion of graphene oxide on the surface of the support layer 2 to form the composite film includes: s3, spraying the dispersion of graphene oxide on the surface of the support layer 2. In actual operation, a spraying method can be adopted to prepare the graphene oxide composite film, a spray gun is used as a spraying tool, graphene oxide sheets are stacked and continuously formed into a film by means of spraying pressure, the pressure of the spraying tool and the surface tension of the supporting layer 2 influence the structure of the composite film, illustratively, the spraying pressure is 0.1-0.5 MPa, the spraying effect is good, and the spraying pressure can be 0.1MPa, 0.5MPa, 0.25MPa, 0.3MPa and the like. The spraying time can be 1-10 s, for example, 1s, 10s, 5s, 2s, 3s, 6s, 7s or 8 s. The longer the spraying time, the higher the dispersion concentration of the graphene oxide, and the thicker the thickness of the functional layer formed.
Referring to fig. 4, in some embodiments, after the step of forming the composite membrane by compositing the dispersion of graphene oxide on the surface of the support layer 2, and before the step of performing coordination ion strengthening on the composite membrane to obtain the desired reverse osmosis membrane, the method further includes a step of performing thermal reduction treatment on the composite membrane, where the step includes: s4, heating the composite film in vacuum at 60-80 ℃ for 30-45 min, and then cooling to room temperature. Since the graphene oxide has a hydrophilic group, the formed functional layer 1 is applied in a water environment, the graphene oxide is easy to float and separate, and after the thermal reduction step, the stability of the graphene oxide can be increased, and the function of reinforcing the functional layer 1 is achieved.
Although the preliminarily prepared graphene oxide composite membrane has a separation function, the graphene oxide membrane is easy to cause structural collapse of the functional layer 1 along with water loss due to the fact that the graphene oxide membrane contains a large number of hydrophilic groups and runs in a long-term water environment, and the functional layer 1 is easy to peel off due to the fact that amphiphilic substances such as adhesives and the like are lost along with water, so that the formed composite membrane can be further reinforced. Referring to fig. 4, in some embodiments, the step of subjecting the composite membrane to complex ion strengthening to obtain the desired reverse osmosis membrane comprises: s51, placing the composite membrane into a reaction solution to carry out a coordination ion strengthening reaction; the reaction solution comprises a coordination ion aqueous solution and ethanol with the same volume as the coordination ion aqueous solution; and S52, performing shower on the composite membrane by using ethanol, and standing the composite membrane for a certain time to obtain the required reverse osmosis membrane.
In some embodiments, the complex ion aqueous solution may include any one or more of a calcium chloride solution, a magnesium chloride solution, and an aluminum chloride solution, that is, one of the complex ion aqueous solutions described above may be selected, or a mixture containing two or more of the complex ion aqueous solutions described above may be selected as the complex ion aqueous solution. The mass percentage of the solute in the complex ion aqueous solution is 3 to 10%, and for example, the mass percentage of the solute may be 3%, 10%, 6%, 7%, 5%, or the like.
In practical operation, the complex ion strengthening reaction can be performed at room temperature, and the reaction time can be 1-4 hours. After the reaction time is reached, the composite membrane can be taken out, the ethanol is used for showering the composite membrane, and redundant reactive ions are washed away, so that the reaction is stopped.
The graphene oxide is characterized in that a large number of oxygen-containing groups including hydroxyl and epoxy groups are introduced on a flaky basal plane, and carboxyl and carbonyl groups are distributed at the edge part of a graphene oxide sheet layer. Through coordination ion strengthening reaction, divalent metal ions (such as calcium ions, magnesium ions and aluminum ions) can be utilized to bond the edges of two graphene oxide sheets, so that the effect of chemical crosslinking strengthening is achieved. Meanwhile, the chemical crosslinking strengthening effect can be achieved for hydroxyl groups of the graphene oxide flaky base surface and hydroxyl groups of amphiphilic substances such as the adhesive on the surface of the support layer 2, so that the volume crosslinking of the functional layer 1 is realized, and the firmness of the functional layer is improved. As shown in fig. 2, the "wrinkles" indicate that the graphene oxide has been successfully attached to the surface of the support layer 2, forming a stable and robust functional layer 1.
Several examples of reverse osmosis membranes prepared using the method of the present invention are given below to facilitate a better understanding of the present invention by those skilled in the art.
Example 1
In the process of preparing the dispersion liquid of the graphene oxide, graphene oxide sheets with the sheet diameter of 8-10 microns and the number of layers of 2-5 are dispersed in ultrapure water, the mass concentration of the graphene oxide is 1mg/ml, the solution is magnetically stirred for 5min and ultrasonically dispersed for 30min, 1ml of sodium deoxycholate aqueous solution with the mass fraction of 1% is added, and the mixture is uniformly mixed to form a dispersion liquid precursor. And standing the dispersion liquid precursor for 1h, adding ammonia water with the concentration of 25% to adjust the pH value of the dispersion liquid precursor to 8.5, and stabilizing the solution for 30min to obtain the required dispersion liquid of the graphene oxide.
In the process of treating the support layer 2, a polysulfone flat ultrafiltration membrane with the pore diameter of 0.1 μm is selected as the support layer 2, and the flat ultrafiltration membrane is soaked in a polyvinyl alcohol aqueous solution with the mass concentration of 5% for two hours, taken out, placed for 24 hours and dried.
And spraying the dispersion liquid of the graphene oxide on the surface of the support layer 2 by using a spray gun to form the composite membrane, wherein the spraying pressure is 0.2MPa, and the spraying time is 5 s.
In the process of carrying out thermal reduction post-treatment on the composite film, the sprayed composite film is put into a vacuum oven for heat treatment for 30min at the temperature of 80 ℃, and then is put into room temperature.
In the process of strengthening the complex membrane by coordination ions, preparing a calcium chloride aqueous solution with the mass concentration of 5%, adding ethanol with the same volume as the calcium chloride aqueous solution, immersing the complex membrane after thermal reduction treatment into a mixed solution of the ethanol and the calcium chloride solution, reacting for 1h, taking out the complex membrane, repeatedly leaching with the ethanol, and standing for 24h after leaching to obtain the reverse osmosis membrane to be prepared, wherein the thickness of the functional layer 1 of the reverse osmosis membrane is 0.2 mu m.
Example 2
In the process of preparing the graphene oxide dispersion liquid, graphene oxide sheets with the sheet diameter of 15-20 microns and the number of layers of 5-8 are dispersed in N-methyl pyrrolidone, the mass concentration of the graphene oxide is 1mg/ml, the solution is magnetically stirred for 5min and ultrasonically dispersed for 30min, 2ml of sodium deoxycholate aqueous solution with the mass fraction of 1% is added, and the mixture is uniformly mixed to form a dispersion liquid precursor. And standing the dispersion liquid precursor for 1h, adding ammonia water with the concentration of 25% to adjust the pH value of the dispersion liquid precursor to 8.5, and stabilizing the solution for 30min to obtain the required dispersion liquid of the graphene oxide.
In the process of treating the support layer 2, a polysulfone flat ultrafiltration membrane with the pore diameter of 0.1 μm is selected as the support layer 2, and the flat ultrafiltration membrane is soaked in a polyvinyl alcohol aqueous solution with the mass concentration of 5% for two hours, taken out, placed for 24 hours and dried.
And spraying the dispersion liquid of the graphene oxide on the surface of the support layer 2 by using a spray gun to form the composite membrane, wherein the spraying pressure is 0.4MPa, and the spraying time is 8 s.
And in the process of carrying out thermal reduction post-treatment on the composite film, putting the sprayed composite film into a vacuum oven for heat treatment at 80 ℃ for 45min, and then putting the composite film to room temperature.
In the process of strengthening the complex membrane by coordination ions, preparing a calcium chloride aqueous solution with the mass concentration of 5%, adding ethanol with the same volume as the calcium chloride aqueous solution, immersing the complex membrane after thermal reduction treatment into a mixed solution of the ethanol and the calcium chloride solution, reacting for 1h, taking out the complex membrane, repeatedly leaching with the ethanol, and standing for 24h after leaching to obtain the reverse osmosis membrane to be prepared, wherein the thickness of the functional layer 1 of the reverse osmosis membrane is 0.25 mu m.
Example 3
In the process of preparing the graphene oxide dispersion liquid, graphene oxide sheets with the sheet diameter of 15-20 microns and the number of layers of 8-10 are dispersed in ethanol, the mass concentration of the graphene oxide is 5mg/ml, the solution is magnetically stirred for 5min and ultrasonically dispersed for 20min, 2ml of sodium deoxycholate aqueous solution with the mass fraction of 3% is added, and the mixture is uniformly mixed to form a dispersion liquid precursor. And standing the dispersion liquid precursor for 1h, adding ammonia water with the concentration of 25% to adjust the pH value of the dispersion liquid precursor to 8.5, and stabilizing the solution for 30min to obtain the required dispersion liquid of the graphene oxide.
In the process of treating the supporting layer 2, a polyethersulfone flat ultrafiltration membrane with the aperture of 0.1 mu m is selected as the supporting layer 2, and the flat ultrafiltration membrane is soaked in a polyvinyl alcohol aqueous solution with the mass concentration of 5% for two hours, taken out and placed for 24 hours to be dried.
And spraying the dispersion liquid of the graphene oxide on the surface of the support layer 2 by using a spray gun to form the composite film, wherein the spraying pressure is 0.2MPa, and the spraying time is 3 s.
And in the process of carrying out thermal reduction post-treatment on the composite film, putting the sprayed composite film into a vacuum oven for heat treatment at 80 ℃ for 45min, and then putting the composite film to room temperature.
Preparing a magnesium chloride aqueous solution with the mass concentration of 10% in the process of strengthening the complex membrane by coordination ions, adding ethanol with the same volume as the magnesium chloride aqueous solution into the calcium chloride aqueous solution, immersing the complex membrane after thermal reduction treatment into a mixed solution of the ethanol and the calcium chloride solution, reacting for 1h, taking out the complex membrane, repeatedly leaching with the ethanol, and standing for 24h after leaching to obtain the reverse osmosis membrane to be prepared, wherein the thickness of a functional layer 1 of the reverse osmosis membrane is 0.5 mu m.
Example 4
In the process of preparing the dispersion liquid of the graphene oxide, graphene oxide sheets with the sheet diameter of 8-10 microns and the number of layers of 4-6 are dispersed in ultrapure water, the mass concentration of the graphene oxide is 3mg/ml, the solution is magnetically stirred for 5min and ultrasonically dispersed for 30min, 1ml of sodium deoxycholate aqueous solution with the mass fraction of 1% is added, and the mixture is uniformly mixed to form a dispersion liquid precursor. And standing the dispersion liquid precursor for 1h, adding ammonia water with the concentration of 25% to adjust the pH value of the dispersion liquid precursor to 7, and stabilizing the solution for 30min to obtain the required dispersion liquid of the graphene oxide.
In the process of treating the support layer 2, a polysulfone flat ultrafiltration membrane with the pore diameter of 0.1 μm is selected as the support layer 2, and the flat ultrafiltration membrane is soaked in a polyethylene glycol aqueous solution with the mass concentration of 5% for two hours, taken out, placed for 24 hours and dried.
And spraying the dispersion liquid of the graphene oxide on the surface of the support layer 2 by using a spray gun to form the composite membrane, wherein the spraying pressure is 0.2MPa, and the spraying time is 2 s.
In the process of carrying out thermal reduction post-treatment on the composite film, the sprayed composite film is put into a vacuum oven for heat treatment for 30min at the temperature of 80 ℃, and then is put into room temperature.
In the process of strengthening the complex membrane by coordination ions, preparing a calcium chloride aqueous solution with the mass concentration of 5%, adding ethanol with the same volume as the calcium chloride aqueous solution, immersing the complex membrane after thermal reduction treatment into a mixed solution of the ethanol and the calcium chloride solution, reacting for 1h, taking out the complex membrane, repeatedly leaching with the ethanol, and standing for 24h after leaching to obtain the reverse osmosis membrane to be prepared, wherein the thickness of the functional layer 1 of the reverse osmosis membrane is 0.3 mu m.
Example 5
In the process of preparing the dispersion liquid of the graphene oxide, the graphene oxide sheets with the sheet diameter of 8-10 microns and the number of layers of 5-10 are dispersed in ultrapure water, the mass concentration of the graphene oxide is 3mg/ml, the solution is magnetically stirred for 5min and ultrasonically dispersed for 30min, 2ml of sodium dodecyl benzene sulfonate aqueous solution with the mass fraction of 1% is added, and the mixture is uniformly mixed to form a dispersion liquid precursor. And standing the dispersion liquid precursor for 1h, adding ammonia water with the concentration of 25% to adjust the pH value of the dispersion liquid precursor to 9, and stabilizing the solution for 30min to obtain the required dispersion liquid of the graphene oxide.
In the process of treating the support layer 2, a polysulfone flat ultrafiltration membrane with the pore diameter of 0.1 μm is selected as the support layer 2, and the flat ultrafiltration membrane is soaked in a polyvinyl alcohol aqueous solution with the mass concentration of 5% for two hours, taken out, placed for 24 hours and dried.
And spraying the dispersion liquid of the graphene oxide on the surface of the support layer 2 by using a spray gun to form the composite film, wherein the spraying pressure is 0.3MPa, and the spraying time is 9 s.
In the process of carrying out thermal reduction post-treatment on the composite film, the sprayed composite film is put into a vacuum oven for heat treatment for 30min at the temperature of 80 ℃, and then is put into room temperature.
In the process of strengthening the complex membrane by coordination ions, preparing a calcium chloride aqueous solution with the mass concentration of 5%, adding ethanol with the same volume as the calcium chloride aqueous solution, immersing the complex membrane after thermal reduction treatment into a mixed solution of the ethanol and the calcium chloride solution, reacting for 1h, taking out the complex membrane, repeatedly leaching with the ethanol, and standing for 24h after leaching to obtain the reverse osmosis membrane to be prepared, wherein the thickness of the functional layer 1 of the reverse osmosis membrane is 0.5 mu m.
Example 6
In the process of preparing the dispersion liquid of the graphene oxide, the graphene oxide sheets with the sheet diameter of 10-15 microns and the layer number of 2-10 are dispersed in ultrapure water, the mass concentration of the graphene oxide is 0.1mg/ml, the solution is magnetically stirred for 5min and ultrasonically dispersed for 30min, 3ml of sodium polystyrene sulfonate aqueous solution with the mass fraction of 0.1% is added, and the mixture is uniformly mixed to form a dispersion liquid precursor. And standing the dispersion liquid precursor for 1h, adding ammonia water with the concentration of 25% to adjust the pH value of the dispersion liquid precursor to 8, and stabilizing the solution for 30min to obtain the required dispersion liquid of the graphene oxide.
In the process of treating the support layer 2, a polyethersulfone flat ultrafiltration membrane with the pore diameter of 0.5 mu m is selected as the support layer 2, and the flat ultrafiltration membrane is soaked in a polyvinylpyrrolidone aqueous solution with the mass concentration of 1% for two hours, taken out, placed for 24 hours and dried.
And spraying the dispersion liquid of the graphene oxide on the surface of the support layer 2 by using a spray gun to form the composite film, wherein the spraying pressure is 0.1MPa, and the spraying time is 10 s.
In the process of carrying out thermal reduction post-treatment on the composite film, the sprayed composite film is put into a vacuum oven for heat treatment for 40min at 60 ℃, and then is put into room temperature.
In the process of strengthening the complex membrane by coordination ions, preparing an aluminum chloride aqueous solution with the mass concentration of 3%, adding ethanol with the same volume as the calcium chloride aqueous solution into the calcium chloride aqueous solution, immersing the complex membrane after thermal reduction treatment into a mixed solution of the ethanol and the calcium chloride solution, reacting for 4 hours, taking out the complex membrane, repeatedly leaching with the ethanol, and standing for 24 hours after leaching to obtain the reverse osmosis membrane to be prepared, wherein the thickness of the functional layer 1 of the reverse osmosis membrane is 0.2 mu m.
Example 7
In the process of preparing the graphene oxide dispersion liquid, graphene oxide sheets with the sheet diameter of 10-15 microns and the number of layers of 3-7 are dispersed in ethanol, the mass concentration of the graphene oxide is 2.5mg/ml, the solution is magnetically stirred for 5min and ultrasonically dispersed for 30min, 1ml of sodium deoxycholate aqueous solution with the mass fraction of 5% is added, and the mixture is uniformly mixed to form a dispersion liquid precursor. And standing the dispersion liquid precursor for 1h, adding ammonia water with the concentration of 25% to adjust the pH value of the dispersion liquid precursor to 8, and stabilizing the solution for 30min to obtain the required dispersion liquid of the graphene oxide.
In the process of treating the support layer 2, a polyethersulfone flat ultrafiltration membrane with the aperture of 1 mu m is selected as the support layer 2, and the flat ultrafiltration membrane is soaked in a polyvinylpyrrolidone aqueous solution with the mass concentration of 10% for two hours, then taken out, placed for 24 hours and dried.
And spraying the dispersion liquid of the graphene oxide on the surface of the support layer 2 by using a spray gun to form the composite membrane, wherein the spraying pressure is 0.5MPa, and the spraying time is 1 s.
In the process of carrying out thermal reduction post-treatment on the composite film, the sprayed composite film is placed in a vacuum oven for heat treatment at 70 ℃ for 35min, and then the composite film is placed at room temperature.
In the process of strengthening the complex membrane by coordination ions, preparing an aluminum chloride aqueous solution with the mass concentration of 7%, adding ethanol with the same volume as the calcium chloride aqueous solution into the calcium chloride aqueous solution, immersing the complex membrane after thermal reduction treatment into a mixed solution of the ethanol and the calcium chloride solution, reacting for 2.5 hours, taking out the complex membrane, repeatedly leaching with the ethanol, and standing for 24 hours after leaching to obtain the reverse osmosis membrane to be prepared, wherein the thickness of the functional layer 1 of the reverse osmosis membrane is 0.2 mu m.
The reverse osmosis membrane prepared in the above example was subjected to a performance test using a general dead-end cup-shaped reverse osmosis membrane evaluation device under 25 ℃, a test pressure of 2MPa, and a test solution of 1000ppm (parts per million concentration) aqueous NaCl solution, and sampling was performed after the reverse osmosis membrane was stably operated for 30 min. The specific testing process is referred to the prior art and is not described herein. The test results are shown in table 1.
TABLE 1
| Example numbering | Salt rejection (%) | Water flux (L/M)2/H) |
| 1 | 95 | 165 |
| 2 | 97 | 157 |
| 3 | 99 | 104 |
| 4 | 97.8 | 125 |
| 5 | 97.5 | 115 |
| 6 | 95 | 170 |
| 7 | 97 | 145 |
The dead end test performance of the commercial reverse osmosis membrane at present is about 95-97% of desalination rate, and the water flux is 35-50L/M2Comparing test result data in the embodiment of the invention, the reverse osmosis membrane prepared by the method has obvious advantage of improving water flux.
For the above example, a pressure swing test experiment is also performed, the experimental conditions are similar to the conditions for testing the performance of the reverse osmosis membrane, except that the test pressure is changed, that is, the performance of the reverse osmosis membrane under different pressures is respectively tested, and the test result shows that the reverse osmosis membrane provided by the embodiment of the invention has good pressure resistance. Since the test results of the respective examples have the same trend, the test results of the reverse osmosis membrane prepared in example 3 are listed as reference, and are shown in table 2.
TABLE 2
| Test pressure (MPa) | Salt rejection (%) | Water flux (L/M)2/H) |
| 1.5 | 97 | 97 |
| 2 | 99 | 104 |
| 3 | 99 | 120 |
| 5 | 99 | 119 |
As can be seen from table 2, with the gradual increase of the test pressure, the salt rejection rate and the water flux of the reverse osmosis membrane of the embodiment of the present invention both increase, and the reverse osmosis membrane does not have the phenomenon of functional layer densification caused by high pressure, and also does not have the phenomenon of reduced water production, functional layer failure, or sharp decline of salt rejection rate, which indicates that the reverse osmosis membrane of the embodiment of the present invention can withstand high operating pressure, and has good pressure resistance.
The reverse osmosis membrane prepared by the preparation method provided by the embodiment of the invention has good desalination rate and higher water flux, can continuously run under higher operation pressure, has good cleaning resistance, is simple in preparation method and long in membrane life cycle, is beneficial to large-scale production and wide application, and is suitable for the fields of ultrapure water preparation, seawater desalination and the like.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (16)
1. A reverse osmosis membrane, comprising:
a support layer comprising a flat ultrafiltration membrane;
a functional layer formed on the support layer, the functional layer comprising stacked overlapping graphene oxide sheets.
2. The reverse osmosis membrane according to claim 1, wherein the graphene oxide sheets have a sheet diameter of 8 to 20 μm and a number of layers of 2 to 10.
3. The reverse osmosis membrane according to claim 1, wherein the functional layer has a thickness of 0.1 to 0.5 μm.
4. The reverse osmosis membrane according to claim 1, wherein the surface pore size of the flat ultrafiltration membrane is 0.1-1 μm.
5. The reverse osmosis membrane of claim 1, wherein the functional layer is bonded to the support layer by an adhesive comprising any one or more of polyethylene glycol, polyvinylpyrrolidone, and polyvinyl alcohol.
6. A method for producing a reverse osmosis membrane, which is used for producing the reverse osmosis membrane according to any one of claims 1 to 5, comprising:
compounding the dispersion liquid of the graphene oxide on the surface of the supporting layer to form a composite film; the support layer comprises a flat ultrafiltration membrane;
and (3) performing coordination ion reinforcement on the composite membrane to obtain the required reverse osmosis membrane.
7. The method for preparing a reverse osmosis membrane according to claim 6, wherein the step of forming a composite membrane by compositing the dispersion of graphene oxide on the surface of the support layer comprises: spraying the dispersion of graphene oxide onto the surface of the support layer;
wherein the spraying pressure is 0.1-0.5 MPa, and the spraying time is 1-10 s.
8. The method of preparing a reverse osmosis membrane according to claim 6, wherein the step of subjecting the composite membrane to complex ion strengthening to obtain the desired reverse osmosis membrane comprises:
putting the composite membrane into a reaction solution to carry out a coordination ion strengthening reaction; the reaction solution comprises a coordination ion aqueous solution and ethanol with the same volume as the coordination ion aqueous solution;
and (3) showering the composite membrane by using ethanol, and standing the composite membrane for a certain time to obtain the required reverse osmosis membrane.
9. The preparation method of a reverse osmosis membrane according to claim 8, characterized in that the complex ion aqueous solution comprises one or more of a calcium chloride solution, a magnesium chloride solution and an aluminum chloride solution, and the mass percentage of solute in the complex ion aqueous solution is 3-10%.
10. The method for producing a reverse osmosis membrane according to claim 8, wherein the time for the complex ion strengthening reaction is 1 to 4 hours.
11. The method for preparing a reverse osmosis membrane according to claim 6, further comprising a step of preparing the dispersion liquid of graphene oxide before the step of forming the composite membrane by compositing the dispersion liquid of graphene oxide on the surface of the support layer, wherein the step of preparing the dispersion liquid of graphene oxide comprises:
dispersing graphene oxide in a dispersing agent, and adding a layer expanding stabilizer to form a dispersion liquid precursor;
and adding an alkali solution into the dispersion liquid precursor to enable the pH value of the dispersion liquid precursor to reach 7-9, so as to obtain the required dispersion liquid of the graphene oxide.
12. The method for preparing a reverse osmosis membrane according to claim 11, wherein the mass concentration of graphene oxide in the graphene oxide dispersion liquid is 0.1-5 mg/ml.
13. A method of manufacturing a reverse osmosis membrane according to claim 11, wherein the dispersant comprises any one of ultrapure water, ethanol, and N-methylpyrrolidone.
14. The preparation method of a reverse osmosis membrane according to claim 11, wherein the layer-expanding stabilizer comprises any one of sodium deoxycholate, sodium dodecylbenzenesulfonate and sodium polystyrene sulfonate, and the mass percentage of the layer-expanding stabilizer in the graphene oxide dispersion is 0.1-5%.
15. The method for preparing a reverse osmosis membrane according to claim 6, further comprising a step of treating the flat ultrafiltration membrane of the support layer before the step of forming the composite membrane by compositing the dispersion of graphene oxide on the surface of the support layer, wherein the step comprises: putting the flat ultrafiltration membrane into an aqueous solution of an adhesive, soaking and then airing; wherein in the aqueous solution of the adhesive, the mass percent of the adhesive is 1-10%.
16. The method for preparing a reverse osmosis membrane according to claim 6, further comprising a step of performing thermal reduction treatment on the composite membrane after the step of forming the composite membrane by compositing the dispersion of graphene oxide on the surface of the support layer and before the step of performing coordinated ion strengthening on the composite membrane to obtain the desired reverse osmosis membrane, wherein the step of performing thermal reduction treatment on the composite membrane comprises: and (3) heating the composite film at the temperature of 60-80 ℃ in vacuum for 30-45 min, and then cooling to room temperature.
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