Janus nanofiltration membrane, method for preparing the same and use thereof

Abstract

This invention relates to the field of nanofiltration membrane technology, and discloses a Janus nanofiltration membrane, its preparation method, and its applications. The preparation method includes the following steps: S1, a composite membrane is formed by free interface polymerization of an aqueous monomer solution and an oil monomer solution on the surface of a base membrane; S2, a polyethyleneimine solution is sprayed onto the surface of the composite membrane and cured by heating to obtain the Janus nanofiltration membrane; wherein, the aqueous monomer solution comprises aminated γ-cyclodextrin; and the oil monomer solution comprises terephthaloyl chloride. The positive and negatively charged Janus nanofiltration membrane prepared by this method constructs abundant low-resistance ultra-short transport channels, exhibiting excellent magnesium-lithium separation and permeability.

Description

Technical Field

[0001] This invention relates to the field of nanofiltration membrane technology, and in particular to a Janus nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] Nanofiltration is a membrane technology between ultrafiltration and reverse osmosis, exhibiting high rejection rates for divalent ions and soluble organic molecules with molecular weights above 200 Da. However, due to the typically monovalent surface charge of nanofiltration membranes, selectivity for monovalent / divalent counterions is often low. Therefore, Janus nanofiltration membranes (a relatively new concept in membrane technology referring to separation membranes with asymmetric structures or properties) have emerged. However, they still face challenges such as high mass transfer resistance, resulting in inefficient lithium separation and extraction from brine. Furthermore, the "trade-off" effect between selectivity and permeate flux makes it difficult for nanofiltration membranes to achieve breakthroughs in efficient magnesium-lithium separation and flux improvement.

[0003] Therefore, in order to overcome the limitations of existing nanofiltration membranes and improve the efficiency and flux of lithium extraction from salt lakes, it is particularly urgent to develop a novel method for preparing Janus nanofiltration membranes. Summary of the Invention

[0004] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the first aspect of the present invention proposes a method for preparing a Janus nanofiltration membrane. The Janus nanofiltration membrane prepared by this method constructs a low-resistance ultra-short transport channel, exhibits excellent magnesium-lithium separation and permeability, and reduces the trade-off effect between separation and permeability.

[0005] A second aspect of the present invention also provides a Janus nanofiltration membrane.

[0006] A third aspect of the present invention also provides an application of the Janus nanofiltration membrane.

[0007] A method for preparing a Janus nanofiltration membrane according to a first aspect embodiment of the present invention includes the following steps:

[0008] S1. A composite membrane is formed by free interfacial polymerization of aqueous monomer solution and oil-phase monomer solution on the surface of the base membrane.

[0009] S2. Spray a polyethyleneimine solution onto the surface of the composite membrane and heat to cure it to obtain the Janus nanofiltration membrane.

[0010] The aqueous monomer solution comprises amino-modified γ-cyclodextrin; the oil monomer solution comprises terephthaloyl chloride.

[0011] The method for preparing the Janus nanofiltration membrane according to embodiments of the present invention has at least the following beneficial effects:

[0012] This invention uses aminated γ-cyclodextrin as an aqueous monomer and terephthaloyl chloride as an oil monomer to carry out a free interface polymerization reaction on the surface of the base membrane. Then, the surface of the composite membrane is sprayed with polyethyleneimine solution. The resulting positive and negative charged Janus nanofiltration membrane constructs abundant low-resistance ultra-short transport channels, exhibiting excellent magnesium-lithium separation and permeability, and reducing the trade-off effect between separation and permeability.

[0013] Furthermore, this is because amino-modified γ-cyclodextrin reacts more readily with terephthaloyl chloride, causing most of the cyclodextrin cavities to be vertically arranged and distributed within the membrane, constructing abundant low-resistance ultra-short transport channels and an ultra-thin polyamide layer, and the cavities of γ-CDA also facilitate secondary separation of magnesium and lithium.

[0014] Furthermore, the polyethyleneimine solution reacts with unreacted terephthaloyl chloride, causing the membrane surface to become positively charged. Due to the electrostatic repulsion effect, this facilitates the separation of magnesium and lithium.

[0015] According to some embodiments of the present invention, the concentration of the aqueous monomer solution is 0.2 wt.% to 0.5 wt.%. Thus, within the above range, magnesium-lithium separation and permeability are increased.

[0016] According to some embodiments of the present invention, in step S1, the free interface polymerization reaction takes 1 to 5 minutes.

[0017] According to some embodiments of the present invention, in step S1, the free interface polymerization reaction takes 1 to 2 minutes. Therefore, good permeation flux and magnesium-lithium separation properties are achieved within this range.

[0018] According to some embodiments of the present invention, the concentration of the oil phase monomer solution is 0.05 wt.% to 1 wt.%.

[0019] According to some embodiments of the present invention, the concentration of the oil phase monomer solution is 0.05 wt.% to 0.1 wt.%. This increases both the membrane's separability and permeability.

[0020] According to some embodiments of the present invention, in step S2, the spraying time is 1 second to 5 seconds.

[0021] According to some embodiments of the present invention, the concentration of the polyethyleneimine solution is 0.05 wt.% to 0.25 wt.%.

[0022] According to some embodiments of the present invention, the temperature of the aqueous monomer solution is 10°C to 30°C.

[0023] According to some embodiments of the present invention, the temperature of the aqueous monomer solution is 10°C to 20°C. This increases the diffusion rate of the cyclodextrin monomer into the oil phase, and the membrane structure gradually becomes more complete. The membrane's permeation flux and separation factor reach their maximum.

[0024] Furthermore, when the temperature is above 20°C, the diffusion rate of cyclodextrin monomers continues to increase, and the hydroxyl groups on the cyclodextrin may also react with TPC, resulting in a decrease in the regularity of the cyclodextrin arrangement and an increase in film thickness.

[0025] According to some embodiments of the present invention, the temperature for heat curing is 50°C to 70°C.

[0026] According to some embodiments of the present invention, the aminated modified γ-cyclodextrin is prepared by the following method:

[0027] The γ-cyclodextrin, N,N'-carbonyldiimidazole and organic solvent are mixed, and then ethylenediamine is added to continue the mixing reaction to obtain the final product.

[0028] According to some embodiments of the present invention, the material of the base film is selected from at least one of polyethersulfone, sulfonated polysulfone, polyvinylidene fluoride, or polyacrylonitrile.

[0029] A Janus nanofiltration membrane according to a second aspect of the present invention is prepared by the preparation method described in the first aspect of the present invention. Thus, the Janus nanofiltration membrane of the present invention constructs abundant low-resistance ultra-short transport channels, exhibiting excellent magnesium-lithium separation and permeability, and reducing the trade-off effect between separation and permeability.

[0030] According to some embodiments of the present invention, the thickness of the Janus nanofiltration membrane is 20 nm to 50 nm.

[0031] A third aspect of the present invention provides a Janus nanofiltration membrane as described above; or the application of a Janus nanofiltration membrane prepared by the preparation method described above in seawater desalination and lithium extraction from salt lakes.

[0032] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0033] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0034] Figure 1 These are scanning electron microscope (FESEM) and transmission electron microscope (TEM) images of the surface of the Janus nanofiltration membrane prepared in Example 1 of this invention.

[0035] Figure 2 These are pore size distribution diagrams of the Janus nanofiltration membrane prepared in Example 1 and the nanofiltration membrane prepared in Comparative Example 1.

[0036] Figure 3 This is a surface potential diagram of the back and front sides of the Janus nanofiltration membrane obtained in Example 1 of the present invention. Detailed Implementation

[0037] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0038] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0039] Some of the raw materials used in this embodiment of the invention are as follows:

[0040] Aminated γ-cyclodextrin was prepared by the following method:

[0041] First, 5.20 g of γ-cyclodextrin (γ-CD) and 5.71 g of N,N'-carbonyldiimidazole (CDI) were weighed and dissolved in dimethyl sulfoxide (DMSO) solution. The solution was stirred at room temperature for 12 h under argon protection. Then, 53.6 mL of ethylenediamine (EDA) was added, and stirring continued for another 12 h. The solution was then concentrated to 40–50 mL using vacuum rotary evaporation. 500 mL of acetone was added, and the mixture was stirred and allowed to stand to precipitate. This process was repeated three times to precipitate the product. Finally, a small amount of deionized water was added, and the mixture was freeze-dried to obtain dry, pure, amino-modified γ-cyclodextrin (named γ-CDA).

[0042] Terephthaloyl chloride, polyethyleneimine, and polyethersulfone-based films are all commercially available products.

[0043] Example 1

[0044] This example provides a Janus nanofiltration membrane, the preparation method of which is as follows:

[0045] Prepare an aqueous monomer solution with a γ-CDA mass concentration of 0.25 wt.% and control the temperature of the γ-CDA aqueous monomer solution at 15℃.

[0046] Preparation of the oil phase monomer solution: Dissolve terephthaloyl chloride in n-hexane, with a concentration of 0.1 wt.%.

[0047] S1. Place the metal sieve with the polysulfone (PES) base film attached into a flat-bottomed glass tank, then add the γ-CDA aqueous monomer solution, ensuring that the liquid level is 0.5 cm above the PES base film plane. Then add the TPC oil phase monomer solution dropwise until it is 0.3 cm above the interface. Perform a free interface polymerization reaction for 2 min, and then slowly remove the metal mesh at a certain tilt angle.

[0048] S2. Spray a PEI aqueous solution with a mass concentration of 0.1% wt% onto the membrane surface using an atomizer for 4 seconds. Place the membrane in an oven and heat it at 60°C to cure it. The Janus nanofiltration membrane can then be removed and stored in deionized water for later use.

[0049] Example 2

[0050] This example provides a Janus nanofiltration membrane, whose preparation method and component dosage are basically the same as in Example 1, except that: the aqueous monomer solution is prepared with a γ-CDA mass concentration of 0.2 wt.%.

[0051] Example 3

[0052] This example provides a Janus nanofiltration membrane, whose preparation method and component dosage are basically the same as in Example 1, except that: the aqueous monomer solution is prepared with a γ-CDA mass concentration of 0.5 wt.%.

[0053] Example 4

[0054] This example provides a Janus nanofiltration membrane, whose preparation method and component dosage are basically the same as in Example 1, except that: the aqueous monomer solution is prepared with a γ-CDA mass concentration of 0.1 wt.%.

[0055] Example 5

[0056] This example provides a Janus nanofiltration membrane, whose preparation method and component dosage are basically the same as in Example 1, except that: the aqueous monomer solution is prepared with a γ-CDA mass concentration of 0.7 wt.%.

[0057] Example 6

[0058] This example provides a Janus nanofiltration membrane, whose preparation method and component dosage are basically the same as in Example 1, except that the temperature of the aqueous monomer solution is 10°C.

[0059] Example 7

[0060] This example provides a Janus nanofiltration membrane, whose preparation method and component dosage are basically the same as in Example 1, except that the temperature of the aqueous monomer solution is 20°C.

[0061] Example 8

[0062] This example provides a Janus nanofiltration membrane, whose preparation method and component dosage are basically the same as in Example 1, except that the temperature of the aqueous monomer solution is 30°C.

[0063] Comparative Example 1

[0064] This example provides a nanofiltration membrane, whose preparation method and component dosage are basically the same as in Example 1, except that the step of spraying polyethyleneimine solution is omitted.

[0065] Comparative Example 2

[0066] This example provides a nanofiltration membrane, the preparation method and component dosage of which are basically the same as in Example 1, except that pyromellitic methyl chloride is used instead of terephthaloyl chloride.

[0067] Performance testing

[0068] The Janus nanofiltration membrane prepared in Example 1 of this invention was subjected to FESEM analysis, wherein... Figure 1 a is a TEM image of the Janus nanofiltration membrane surface; Figure 1 b is a SEM cross-sectional view of the Janus nanofiltration membrane. Figure 1 As can be seen, uniform small protrusions appeared on the surface of the Janus film in Example 1, with a thickness of about 29 nm.

[0069] Furthermore, the nanofiltration membranes of Example 1 and Comparative Example 1 of the present invention were subjected to pore size testing, and the results are as follows: Figure 2 As shown, the membrane pore size of Comparative Example 1 is mainly concentrated at around 0.78 nm and the distribution is relatively concentrated; while the pore size of the Janus nanofiltration membrane of Example 1 of this application is mainly concentrated at around 0.72 nm, which is more conducive to magnesium-lithium separation.

[0070] Furthermore, the Janus nanofiltration membrane prepared in Example 1 of this invention was subjected to surface charge testing (sur-PASS solid surface zeta potential meter was used to measure the membrane surface charge), and the results are as follows. Figure 3 As shown, in the feed solution at pH 6.35, the potential on the back side is -16.6 mV, while the potential on the front side is 4.5 mV, indicating a significant change in the surface potential of the back / front membrane. This demonstrates the formation of Janus nanofiltration membranes with both positive and negative charges.

[0071] Furthermore, the permeate flux and separation factor S of the nanofiltration membranes prepared in the embodiments and comparative examples of the present invention were measured. Li,Mg Analysis of the separation performance of nanofiltration membranes:

[0072] (1) The formula for calculating the infiltration flux is as follows:

[0073]

[0074] Where F is the membrane permeability at a given pressure, in L·m -2 ·h -1 ·bar -1 V is the volume of the permeate solution, A is the effective area of ​​the membrane, and p is the filtration pressure.

[0075] The equation for solute repulsion rate (R) (retention) is as follows:

[0076]

[0077] Among them, C p and C f These represent the concentrations in the permeate solution and the feed solution, respectively.

[0078] Separation factor S, representing separation performance Li,Mg Calculated by the following formula:

[0079]

[0080] Among them, C Li,p and C Li,f Li in the permeate and feed solution, respectively + The concentration of C. Mg,p and C Mg,f Mg in the permeate and feed solution, respectively 2+ The concentration.

[0081] The effective test area of ​​the membrane is 12.56 cm². 2 The test temperature was 25℃, the filtration pressure was 1.5 bar, and the membrane surface flow rate was 10 L·h. -1 To more closely resemble the application, the feed solution simulated salt lake brine with a magnesium-to-lithium mass ratio of 30 and a concentration of 2000 ppm. During testing, the nanofiltration membrane was first pre-pressed at 2 bar for 0.5 h to allow it to stabilize. Samples were taken every 0.5 h, and the permeate volume was recorded. To avoid errors, each sample was tested at least three times. The results are shown in Table 1.

[0082] Table 1. Separation performance of nanofiltration membranes prepared in the examples and comparative examples.

[0083]

[0084]

[0085] As shown in Table 1, the PES / γ-CDA-TPC / PEI nanofiltration membrane prepared according to the embodiment of the present invention exhibits the highest magnesium-lithium separation performance and permeation flux. Li,Mg The permeation flux reached 22.5 and 6.5 L·m, respectively. -2 ·h -1·bar -1 This invention utilizes the fact that amino groups react more readily with TPC than hydroxyl groups, and employs low-temperature induction to induce a vertically aligned distribution of most cyclodextrin cavities within the membrane, constructing abundant and precise sieving channels. This allows for secondary separation of magnesium and lithium within the γ-CDA cavities. Simultaneously, a nano-sprayed PEI aqueous solution is applied to the membrane surface. The high positive potential of the membrane surface, due to electrostatic interactions, further facilitates magnesium and lithium separation, resulting in an ultrathin functional layer that shortens the mass transfer path and reduces the mass transfer resistance of water and ions. Therefore, this nanofiltration membrane demonstrates broad application prospects in seawater desalination and lithium extraction from salt lakes.

[0086] Comparative Example 2 used pyromellitic methyl methacrylate (PMMC) instead of terephthaloyl chloride. However, PMMC could not react with the aminated γ-cyclodextrin to achieve directional alignment, resulting in inaccurate and ineffective separation within the cavity, high water channel resistance, and a long transport path, thus leading to low permeability and separation performance.

[0087] The present invention has been described in detail above with reference to the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing a Janus nanofiltration membrane, characterized in that, Includes the following steps: S1. A composite membrane is formed by free interfacial polymerization of aqueous monomer solution and oil-phase monomer solution on the surface of the base membrane. S2. Spray a polyethyleneimine solution onto the surface of the composite membrane and heat to cure it to obtain the Janus nanofiltration membrane. The aqueous monomer solution comprises amino-modified γ-cyclodextrin; the oil monomer solution comprises terephthaloyl chloride. The concentration of the aqueous monomer solution is 0.2 wt.% to 0.5 wt.%; the concentration of the oil phase monomer solution is 0.05 wt.% to 1 wt.%. The amination-modified γ-cyclodextrin was prepared by the following method: The γ-cyclodextrin, N,N'-carbonyldiimidazole and organic solvent are mixed, and then ethylenediamine is added to continue the mixing reaction to obtain the final product.

2. The method for preparing the Janus nanofiltration membrane according to claim 1, characterized in that, In step S1, the free interface polymerization reaction takes 1 to 5 minutes.

3. The method for preparing the Janus nanofiltration membrane according to claim 1, characterized in that, In step S2, the spraying time is 1 to 5 seconds.

4. The method for preparing the Janus nanofiltration membrane according to claim 1, characterized in that, The temperature of the aqueous monomer solution is 10℃~30℃.

5. A Janus nanofiltration membrane, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 4.

6. The Janus nanofiltration membrane according to claim 5, characterized in that, The thickness of the Janus nanofiltration membrane is 20 nm to 50 nm.

7. The application of the Janus nanofiltration membrane according to claim 5 or 6 in seawater desalination or lithium extraction from salt lakes.

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