Two-dimensional COF-based separation membrane, preparation method and metal ion separation method

Abstract

The invention discloses a two-dimensional COF-based separation membrane, a preparation method and a metal ion separation method. A COF sheet adopted in the method has a good layered structure and has a good crystal form. Through mixing with graphene oxide (rGO) and a polyanion material, the interlamellar spacing and surface potential of COF are changed, and then the separation membrane is obtained through an interfacial polymerization method. The preparation method is simple in process, convenient to operate, mild in condition, low in cost and easy to implement, and the prepared membrane has good mass transfer rate and selectivity for monovalent metal ions.

Description

Technical Field

[0001] The present invention belongs to the field of two-dimensional COF, and in particular relates to a preparation method and application of an anionic COF interlayer potential. Background Art

[0002] In today's world, the rational use of resources and environmental protection have become two major challenges facing the world. Especially in the field of water resource management, efficient and precise water treatment technology is crucial to alleviating the water crisis and preventing water pollution. As an energy-saving and environmentally friendly separation method, membrane separation technology is widely used in many fields such as seawater desalination, wastewater treatment, and pure water preparation. However, faced with complex and changing separation tasks, traditional membrane materials often find it difficult to simultaneously meet the requirements of high flux and high selectivity. Especially in the field of ion separation, how to achieve highly selective retention and efficient transfer of specific ions has become a difficult problem that needs to be overcome.

[0003] In recent years, two-dimensional covalent organic frameworks (2D COFs), an emerging class of porous materials, have demonstrated unprecedented potential in separation science due to their unique two-dimensional sheet-like structure, well-organized nanopores, rich chemical functional groups, and exceptional stability. Unlike three-dimensional COFs, 2D COFs possess a more open pore system, facilitating rapid diffusion of substances. Furthermore, their planar structure imparts greater crystallinity and mechanical strength, making them more suitable for the preparation of high-performance separation membranes.

[0004] Interfacial polymerization, a mature membrane fabrication strategy, can construct a dense and continuous separation layer by initiating an in-situ polymerization reaction at the interface between two phases. It has been successfully applied to the synthesis of various polymer membranes. The ingenious integration of interfacial polymerization with 2D COFs not only fully leverages the unique advantages of 2D COFs but also effectively addresses their practical limitations, such as insufficient mechanical strength.

[0005] On the other hand, in the process of extracting lithium from salt lakes, K in brine + The existence of Li + The purity of separation is affected, and the conventional brine method has the problem of low removal, and the adsorption method also has the problem of low separation efficiency and large adsorbent consumption. When the nanofiltration method is used, there is also the problem of nanofiltration membrane for K + He Li + The problem of low separation coefficient. In particular, the surface electronegativity of the nanofiltration membrane will make the membrane surface + and K + The charge effect causes the two to pass through at the same time, which in turn affects the separation.

[0006] Conventional methods for preparing COF materials include solvothermal synthesis, microwave heating, and ionothermal synthesis. These methods often suffer from issues such as poor two-dimensional ordering of the resulting COF particles and difficulty in exfoliation. Solvothermal synthesis typically produces powders (see Coordination Chemistry Reviews 514(2024)215873). Summary of the Invention

[0007] One of the technical problems solved by the present invention is that the existence of negative charge on the surface of COF membrane leads to low separation effect on mixed metal ion solutions; the present invention provides a preparation method and application of changing the interlayer potential of anionic COF. The COF separation membrane obtained by this method has low negative charge, can have good mass transfer effect and separation ability for monovalent metal ions, and has good separation effect on monovalent metal ions.

[0008] A two-dimensional COF-based separation membrane comprises a base membrane and a selective separation layer on the surface of the base membrane. The selective separation layer mainly contains a polymer, including a two-dimensional COF nanosheet material, and also contains reduced graphene oxide (rGO) and / or a polyanion material. The two-dimensional COF nanosheet is anionic, and the separation membrane has a zeta potential value lower than that of the two-dimensional COF nanosheet.

[0009] The two-dimensional COF nanosheet has a zeta potential value of -80mV to -20mV; the zeta potential value of the separation membrane is -40mV to -5mV.

[0010] The COF nanosheet material is selected from one of boric acid, triazine, imine, phenylhydrazone, polyimide, phthalocyanine or porphyrin.

[0011] The loading amount of 2D COF nanosheets on the surface of the separation membrane is 5-20 mg / cm 2 .

[0012] The imine COF nanosheet has the following structure:

[0013]

[0014] The polymer is polyamide; the polyanion material refers to one or more of polystyrene sulfonate, polyacrylate, polyvinyl alcohol sulfonate, and polynitrile salt; the material of the base membrane is one or more of polyethersulfone, polypropylene, polyester, polyamide, polyurethane, polyvinylidene fluoride, and polyimide.

[0015] The method for preparing the above-mentioned two-dimensional COF-based separation membrane comprises the following steps:

[0016] Step 1, preparing an aqueous solution containing two-dimensional COF nanosheets, aqueous monomers, and reduced graphene oxide (rGO) and / or polyanion materials;

[0017] Step 2: After applying the aqueous solution to the surface of the base membrane, the oil phase solution containing the oil phase monomer is brought into contact with the base membrane to cause an interfacial polymerization reaction to obtain a separation membrane.

[0018] The aqueous phase monomer is one of an amine monomer and a piperazine monomer, and the oil phase monomer is an acyl chloride monomer.

[0019] In the aqueous solution, the weight ratio of the two-dimensional COF nanosheets, the aqueous monomer, the reduced graphene oxide, and the polyanion material is (4-20): (2-10): (0.00-0.08): (0.05-0.15).

[0020] In step 2, the aqueous solution is applied by filtering, soaking, or coating, and the aqueous solution has been subjected to ultrasonic dispersion treatment; the contact time between the oil phase monomer and the base film is 5-10 minutes, and the contact method is soaking.

[0021] A method for separating metal ions comprises contacting a solution containing metal ions with a two-dimensional COF-based separation membrane so that the metal ions are retained or permeated; the solution containing metal ions is pressurized or not pressurized.

[0022] The solution containing metal ions contains K + He Li + , so that K + Relative to Li + More through the membrane.

[0023] The second technical problem addressed by this invention is the low two-dimensional order and difficulty in exfoliating COF nanosheets obtained when traditional solvothermal methods are used to prepare COF materials. This invention provides a method for the controlled preparation of COF nanosheets based on a three-phase interface method. The COF sheets obtained by this method have a well-defined layered structure and exhibit a favorable crystal form as determined by XRD.

[0024] A method for preparing COF two-dimensional nanosheets comprises the following steps:

[0025] In a reaction vessel, the lower oil phase solution and the aqueous phase solution are added successively, so that the aqueous phase solution is at the top, and then the upper oil phase solution is slowly added and reacted to obtain a reaction solution containing COF material;

[0026] The upper oil phase solution and the lower oil phase solution respectively contain a first monomer and a second monomer that can form a covalent bond and obtain a COF material.

[0027] The COF material is selected from one of boric acid, triazine, imine, phenylhydrazone, polyimide, phthalocyanine or porphyrin.

[0028] The COF material is an imine material, and the first monomer and the second monomer are an amine-containing monomer and an aldehyde-containing monomer respectively; the aqueous phase solution is an acid aqueous solution.

[0029] The concentration of the first monomer in the upper oil phase solution is 1-20×10 -3 mmol / mL, the concentration of the second monomer in the lower oil phase solution is 0.5-15×10 -3 mmol / mL; the acid concentration of the aqueous solution is 1-6M.

[0030] The volume ratio of the upper oil phase solution, the water phase solution and the lower oil phase solution is 30-60:10-30:50-100.

[0031] The volume of the upper oil phase solution added per minute is 1-5% of the total volume of the lower oil phase.

[0032] The reaction time is 5-50h, and the reaction temperature is 1-50°C.

[0033] The COF two-dimensional nanosheets obtained by the above method are used to prepare metal ion separation membranes.

[0034] Beneficial effects

[0035] 1. The COF of the present invention is a two-dimensional porous material with a large number of surface lattices, which has excellent mass transfer and separation capabilities for monovalent metal ions. 2. The preparation method of the separation membrane of the present invention is simple, easy to operate, mild, low-cost, and easy to implement. The separation membrane produced has strong selective adsorption, strong anti-interference ability, good stability, fast adsorption rate, and easy separation, and is suitable for monovalent metal ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 IR spectra of rGO-TPPA-PSSNA prepared in Example 1 of the present invention and a comparative sample.

[0037] Figure 2 This is a TEM image of the COF prepared in Example 1 of the present invention.

[0038] Figure 3 These are SEM images of rGO-TPPA-PSSNA prepared in Example 1 of the present invention and a comparative sample.

[0039] Figure 4 2. Potential diagrams of rGO-TPPA-PSSNA prepared in Example 1 and a comparative sample.

[0040] Figure 5 This is a diagram showing the separation of monovalent metal ions by rGO-TPPA-PSSNA prepared in Example 1 of the present invention and a comparative sample.

[0041] Figure 6 TEM image of the COF prepared in comparative experiment 2.

[0042] Figure 7 1 is the XRD pattern of COF and rGO prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0043] Example 1

[0044] 1. The preparation method of rGO-TPPA-PSSNA (TPPA is the abbreviation of COF) is:

[0045] (1) COF nanosheets were prepared by the three-phase interface method. During the preparation process, the lower layer solution and the acetic acid aqueous solution were poured into a 150 mL high-necked beaker in turn, and the upper layer solution was sucked into a 50 mL disposable syringe, which was placed vertically on the beaker and added dropwise using a microinjection pump. The dropwise addition speed was 0.2 mm / min-1.1 mm / min. More specifically, the upper oil phase was 2,5-diaminobenzenesulfonic acid (0.15 mmol) dissolved in N,N-dimethylformamide (50 mL), and the lower oil phase was 1,3,5-triformaldehyde benzyltriol (0.1 mmol) dissolved in dichloromethane (80 mL). In the middle aqueous phase, 20 mL of 3 M acetic acid aqueous solution was added dropwise using a microfluidic control method (1.1 mm / min). The total dropwise addition time was about 70 min, and negatively charged COF nanosheets were obtained after 3 days.

[0046] (2) The COF nanosheets (0.8 mg / ml, 10 mL) prepared in (1) were mixed with rGO (1 mg / mL 4 mL) and PSSNA (polystyrene sulfonate, 1 wt% 5 mL), diluted to 200 mL, and 2 wt% 5 mL p-phenylenediamine solution was added. Ultrasonication was performed for 30 min, and rGO-TPPA-PSSNA membrane was prepared by vacuum filtration. The base membrane used was a polyacrylonitrile ultrafiltration membrane with a MWCO of 1 million and a diameter of about 3.5 cm. The prepared membrane was soaked in a hexane solution of triacyl chloride (0.2 wt%) for 10 min for curing, and then dried in an oven at 60°C for 10 min.

[0047] Comparative Experiment 1

[0048] There were 5 blank control groups in total, which differed from Example 1 in that PAANA and TPPA were not added to blank control group 1, TPPA was not added to blank control group 2, PAANA and rGO were not added to blank control group 3, rGO was not added to blank control group 4, and PAANA was not added to blank control group 5.

[0049] Comparative Experiment 2

[0050] Compared with the process of preparing COF nanosheets in Example 1, the dripping speed of the upper oil phase solution was not regulated. The characterization and comparison results of the obtained COF nanosheets are Figure 6 Transmission electron microscopy (TEM) images show that the morphology of TPPA nanosheets has undergone a significant transformation after microfluidic modification, with their average size expanding to approximately 8.5 microns in length and 3.5 microns in width, a significant improvement compared to the 1.7 microns in length and 4.2 microns in width of the uncontrolled material. Furthermore, the lattice structure has become denser, and the overall regularity has been significantly improved, demonstrating the positive effect of microfluidic technology on the quality of COF nanosheets when controlling the third phase flow rate.

[0051] The rGO-TPPA-PSSNA prepared in Example 1 of the present invention and the blank control group were characterized and analyzed.

[0052] 1. After Fourier transform infrared spectroscopy test, the results are as follows Figure 1 shown.

[0053] Figure 1 IR spectra of rGO-TPPA-PSSNA and the control group prepared in Example 1 of the present invention.

[0054] From the infrared spectra, we can see that the peaks and peak shapes of rGO-TPPA-PSSNA and the control group are basically the same. The rGO membrane contains -OH, while the others do not. The membrane containing TPPA has a peak at 800-1400 cm -1 It has the characteristic peak of -SO3H.

[0055] 2. After the transmission electron microscope test, the COF layer has a very good lattice. The test results are as follows Figure 2 shown.

[0056] 3. Figure 3 These are SEM images of rGO-TPPA-PSSNA prepared in Example 1 of the present invention and the control group.

[0057] It can be seen from the SEM image that the surface distribution of rGO-TPPA-PSSNA prepared in Example 1 of the present invention is relatively uniform.

[0058] 4. Figure 42. Potential diagram of rGO-TPPA-PSSNA prepared in Example 1 of the present invention and the control group.

[0059] It can be seen from the potential diagram that the potential of the rGO-TPPA-PSSNA prepared in Example 1 of the present invention increases with the addition of PSSNA. By comparing the TPPA membrane with the rGO-TPPA membrane, it can also be seen that the addition of rGO also helps to improve its potential, and the synergy of PSSNA and rGO can more effectively reduce its negative charge.

[0060] 5. The specific application is as follows: the rGO-TPPA-PSSNA membrane is placed in a U-shaped cell, with deionized water and a 0.1 mol mixed solution of KCl and LiCl on both sides, and freely diffused at 25°C for 24 hours. Figure 5 This is a separation performance diagram of rGO-TPPA-PSSNA prepared in Example 1 of the present invention and the control group.

[0061] 6. After the transmission electron microscope test, the COF without controlling the speed is that the layer does not have a good lattice. The test results are as follows Figure 6 shown.

[0062] From the separation performance, it can be seen that the performance of the rGO-TPPA-PSSNA prepared in Example 1 of the present invention increases with the addition of PSSNA, and the separation degree can be improved by 40% compared with the TPPA membrane.

Claims

1. A two-dimensional COF-based separation membrane, characterized in that The invention comprises a base membrane and a selective separation layer on the surface of the base membrane. The selective separation layer mainly contains a polymer, including a two-dimensional COF nanosheet material, and also contains reduced graphene oxide (rGO) and / or a polyanion material. The two-dimensional COF nanosheet is anionic, and the separation membrane has a zeta potential value lower than that of the two-dimensional COF nanosheet.

2. The two-dimensional COF-based separation membrane according to claim 1, characterized in that The two-dimensional COF nanosheet has a zeta potential value of -80mV to -20mV; the zeta potential value of the separation membrane is -40mV to -5mV.

3. The two-dimensional COF-based separation membrane according to claim 1, characterized in that The COF nanosheet material is selected from one of boric acid, triazine, imine, phenylhydrazone, polyimide, phthalocyanine or porphyrin; the loading amount of the two-dimensional COF nanosheet material on the surface of the separation membrane is 5-20 mg / cm 2 .

4. The two-dimensional COF-based separation membrane according to claim 1, characterized in that The imine COF nanosheet has the following structure:

5. The two-dimensional COF-based separation membrane according to claim 1, characterized in that The polymer is polyamide; the polyanion material refers to one or more of polystyrene sulfonate, polyacrylate, polyvinyl alcohol sulfonate, and polynitrile salt; the material of the base membrane is one or more of polyethersulfone, polypropylene, polyester, polyamide, polyurethane, polyvinylidene fluoride, and polyimide; the separation membrane is used to separate inorganic salt ions and organic matter.

6. The method for preparing a two-dimensional COF-based separation membrane according to claim 1, characterized in that: The steps include: Step 1, preparing an aqueous solution containing two-dimensional COF nanosheets, aqueous monomers, and reduced graphene oxide (rGO) and / or polyanion materials; Step 2: After applying the aqueous solution to the surface of the base membrane, the oil phase solution containing the oil phase monomer is brought into contact with the base membrane to cause an interfacial polymerization reaction to obtain a separation membrane.

7. The preparation method according to claim 6, characterized in that The aqueous phase monomer is one of an amine monomer and a piperazine monomer, and the oil phase monomer is an acyl chloride monomer.

8. The preparation method according to claim 6, characterized in that In the aqueous solution, the weight ratio of the two-dimensional COF nanosheets, aqueous monomers, reduced graphene oxide, and polyanion materials is (4-20): (2-10): (0.00-0.08): (0.05-0.15)。 9. The preparation method according to claim 6, characterized in that In step 2, the aqueous solution is applied by filtering, soaking, or coating, and the aqueous solution has been subjected to ultrasonic dispersion treatment; the contact time between the oil phase monomer and the base film is 5-10 minutes, and the contact method is soaking.

10. A method for separating metal ions, comprising contacting a solution containing metal ions with the two-dimensional COF-based separation membrane of claim 1, so that the metal ions are retained or permeated; wherein the solution containing metal ions contains K + He Li + , so that K + Relative to Li + More permeates the membrane layer; the solution containing metal ions is under pressure or not under pressure.

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