A magnetic covalent organic framework aerogel for efficient recovery of lithium ions in water

Abstract

The application relates to the field of aerogels, and particularly discloses a magnetic covalent organic framework aerogel for efficiently recycling lithium ions in water; a preparation method comprises the following steps: S1: taking amine precursors, aldehyde precursors, N-methyl-2-pyrrolidone, mesitylene, water and isoquinoline, mixing, ultrasonic treatment, heating for 5 days, filtering and collecting precipitated solid, washing, drying, and obtaining covalent organic frameworks; S2: adding cotton pulp into a water solution containing NaOH and urea at-12 DEG C to obtain a cellulose solution; adding the covalent organic frameworks into the cellulose solution at-12 DEG C, uniformly mixing through rapid stirring, continuously treating at 45-60 DEG C for 3-6 hours, obtaining a solid hydrogel, and freeze-drying to obtain covalent organic framework@cellulose aerogels; and S3: immersing the covalent organic framework@cellulose aerogels into a magnetic suspension solution for 0.5-1 hours, and freeze-drying to obtain magnetic covalent organic framework aerogels.

Description

Technical Field

[0001] This invention relates to the field of aerogels, and specifically discloses a magnetic covalent organic framework aerogel for efficiently recovering lithium ions from water. Background Technology

[0002] In recent years, with the rapid development of electric vehicles, electronic products, and energy storage systems, the demand for energy metals (especially lithium) in the new energy sector has grown exponentially. Therefore, there is an urgent need to develop new methods to increase lithium production and capacity. Lithium-containing oilfield wastewater, electronic waste wastewater, and seawater, which contain considerable lithium reserves (10–1000 mg / L), are considered important alternative sources of lithium and have great recycling value. However, there are still certain challenges in the technology and research for the efficient recovery of lithium from these waste resources.

[0003] Currently, lithium ions (Li) can be directly recovered and extracted from water. + The techniques for recovering Li from water include adsorption, ion exchange, electrodialysis, and solvent extraction. Among these, adsorption is simple to operate, low in cost, and produces no secondary pollution, making it a popular method for recovering Li from water. + One of the best methods. Currently, there are existing methods for recycling Li. + The main adsorbents used are aluminum salt adsorbents and ion sieve adsorbents (manganese-based, titanium-based, etc.), but they still suffer from problems such as low adsorption capacity and easy collapse of the adsorbent core structure. Therefore, it is necessary to develop new and advanced adsorbents for Li in water. + To achieve efficient recycling.

[0004] Covalent organic frameworks (COFs) are novel, highly cross-linked porous organic polymers containing periodically extended and covalently bonded network structures. They possess characteristics such as high crystallinity, large specific surface area, low density, and strong robustness, attracting widespread attention in adsorption, catalysis, sensing, and energy storage. Existing COFs contain lithium-philic groups, such as imines, β-ketoamines, olefins, and boron-oxyhexacyclic linked COFs, where ordered one-dimensional channels are favorable for Lithium absorption. + Diffusion to lithium-philic groups, thereby effectively recovering Li + However, some shortcomings still exist: (1) Powdered COFs are prone to agglomeration during adsorption, leading to a decrease in the exposed specific lithium-loving groups and specific surface area; (2) Due to the presence of a large number of interfering salt ions (such as Mg) in lithium-containing water bodies. 2+ Na + K + and Ca 2+ ), especially Mg 2+ With Li + The physicochemical properties of these two types of COFs are very similar, but most of the COFs developed so far are for Li + / Mg 2+ The separation efficiency is poor, which limits its practical application. (3) The original COFs adsorb Li in the solution+ It is difficult to recycle and has poor reusability.

[0005] Therefore, a method for studying Li + Good adsorption effect, Li + / Mg 2+ The covalent organic framework, which has good separation efficiency, is easy to recover, and has good reusability, is of great significance. Summary of the Invention

[0006] The purpose of this invention is to provide a magnetic covalent organic framework aerogel for efficiently recovering lithium ions from water, so as to solve the problems mentioned in the background art.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a magnetic covalent organic framework aerogel for efficient recovery of lithium ions in water, comprising the following raw materials: covalent organic framework@cellulose aerogel (COFs@cellulose aerogel) and magnetic suspension; wherein the covalent organic framework@cellulose aerogel is prepared by doping covalent organic frameworks (COFs) into a cellulose solution.

[0008] Preferably, the preparation of covalent organic framework@cellulose aerogel includes the following steps: S1: Preparation of cellulose solution: cotton linter pulp is added to an aqueous solution containing NaOH and urea at -12℃ to obtain a cellulose solution;

[0009] S2: Add the covalent organic framework to a cellulose solution at -12℃, stir rapidly until uniformly mixed, and then maintain the mixture at 45-60℃ for 3-6 hours to obtain a solid hydrogel. Freeze-dry the hydrogel to obtain a covalent organic framework@cellulose aerogel.

[0010] Preferably, the covalent organic framework@cellulose aerogel comprises the following raw materials, by mass parts: 2-3 parts short cotton linters, 97-98 parts aqueous solution containing NaOH and urea, and 0.02 parts covalent organic framework; wherein the aqueous solution containing NaOH and urea contains 7 wt% NaOH, 12 wt% urea, and the remainder is water.

[0011] Preferably, the covalent organic framework includes an aldehyde precursor and an amine precursor.

[0012] Preferably, the aldehyde precursor is 2,5-bis(2-methoxyethoxy)-p-phenylenedialdehyde; and the amine precursor is hexa(p-anilino)hexaazatrinaphthalene.

[0013] Preferably, the preparation of the covalent organic framework includes the following steps: S1: Synthesis of amine precursor: 4,5-dibromophenyl-1,2-diamine, hexaoxane octahydrate, and acetic acid are mixed and heated under reflux for 2 days to obtain mixture A. Mixture A is poured into ice water, and sodium carbonate aqueous solution is slowly added. The solid is filtered, washed, and dried to obtain an intermediate. The intermediate, Pd(PPh3)4, K2CO3, pinacol ester of 4-aminophenylboronic acid, DMF, and water are mixed and heated to 145-155°C for 2 days. After the reaction is completed, mixture B is obtained. Mixture B is poured into ice water, filtered, and washed to obtain the amine precursor.

[0014] S2: Synthesis of covalent organic framework: Take hexa(p-anilino)hexaazatrinaphthalene, 2,5-bis(2-methoxyethoxy)p-phenylenedialdehyde, N-methyl-2-pyrrolidone, mesitylene, water, and isoquinoline, mix them, sonicate them, and heat them at 180-220℃ for 5 days. Filter and collect the precipitate solid, wash it, and dry it to obtain the covalent organic framework.

[0015] Preferably, the intermediate comprises the following raw materials in parts by weight: 8-12 parts of 4,5-dibromophenyl-1,2-diamine, 3-5 parts of hexaoxane octahydrate, 180-220 parts of acetic acid, 100 parts of ice water, and 100 parts of sodium carbonate aqueous solution; the amine precursor comprises the following raw materials in parts by weight: 5-7 parts of the intermediate, 0.5-1 part of Pd(PPh3)4, 2-4 parts of K2CO3, and 12-16 parts of 4-aminophenylboronic acid. The covalent organic framework comprises the following raw materials, by mass: 0.008-0.02 parts hexa(p-aniline)hexaazatrinaphthalene, 0.008-0.018 parts 2,5-bis(2-methoxyethoxy)p-phenylenedialdehyde, 0.5-1 part N-methyl-2-pyrrolidone, 0.5-1 part mesitylene, 0.2-0.5 parts water, and 0.4-1 part isoquinoline.

[0016] Preferably, the sodium carbonate aqueous solution has a mass concentration of 10%.

[0017] The above-mentioned method for preparing a magnetic covalent organic framework aerogel for efficient recovery of lithium ions in water is characterized by the following steps: immersing a covalent organic framework@cellulose aerogel in a magnetic suspension for 1 hour, followed by freeze-drying to obtain the magnetic covalent organic framework aerogel.

[0018] Preferably, the magnetic suspension comprises an Fe3O4 suspension, which is prepared by dispersing Fe3O4 in water and sonicating for 30 minutes to obtain the magnetic suspension.

[0019] Preferably, the magnetic covalent organic framework aerogel comprises the following raw materials, by mass parts: 10-15 parts Fe3O4 suspension and 0.5 parts covalent organic framework@cellulose aerogel.

[0020] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) The present invention uses the long-chain aldehyde precursor 2,5-bis(2-methoxyethoxy)-terephthalaldehyde and a self-made amine precursor to prepare COFs. The pore structure is small and the pore crowding degree is high, which can make Li + Pass, but put Mg 2+ Excluding it from the channel effectively improves Li + / Mg 2+ Separation efficiency, thereby efficiently recovering Li from water + Furthermore, Li enters the channel + It can effectively bind with the quinoline group of amine precursors in COFs, thus enabling more efficient recovery of Li from water. + ;

[0021] (2) In order to solve the problem that COFs are prone to agglomeration during the adsorption process, which leads to the exposure of specific lithium-loving groups and a decrease in surface area, the present invention further adds COFs to cellulose solution to obtain covalent organic framework@cellulose aerogel, thereby overcoming the above problem of COFs agglomeration.

[0022] (3) The covalent organic framework@cellulose aerogel is impregnated in a magnetic suspension to make it magnetic, which is beneficial for recycling and improves reusability. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0024] Figure 1 This is a structural diagram of the amine precursor described in this invention;

[0025] Figure 2 This is a scanning electron microscope image of a magnetic covalent organic framework aerogel;

[0026] Figure 3 This is a diagram showing the N2 adsorption-desorption process of magnetic covalent organic framework aerogels. Detailed Implementation

[0027] The following are preferred embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. For those skilled in the art, all other embodiments obtained by those skilled in the art without creative effort without departing from the principles of the embodiments of the present invention are within the scope of protection of the present invention.

[0028] Unless otherwise specified, all the following quantities are parts by weight.

[0029] Example 1: S1: Synthesis of amine precursor (hexa(p-anilino)hexaazatrinaphthalene): 10 parts of 4,5-dibromophenyl-1,2-diamine, 4 parts of hexaoxane octahydrate, and 200 parts of acetic acid were mixed and heated under reflux for 2 days to obtain mixture A. Mixture A was poured into 100 parts of ice water, and 100 parts of sodium carbonate aqueous solution were slowly added. The solid was filtered and washed 3 times with DMF and 3 times with acetone. The solid was dried to obtain an intermediate. 6 parts of the intermediate, 0.5 parts of Pd(PPh3)4, 3 parts of K2CO3, 15 parts of pinacol 4-aminophenylboronic acid, 250 parts of DMF, and 50 parts of water were mixed and heated to 150°C for 2 days to obtain mixture B. The mixture was poured into ice water, filtered, and washed successively with water, methanol, and tetrahydrofuran to obtain the amine precursor.

[0030] S2: 0.0124 parts of amine precursor and 0.0113 parts of 2,5-bis(2-methoxyethoxy)-p-phenylenedialdehyde were added to 1 part of N-methyl-2-pyrrolidone, 1 part of mesitylene, 0.4 parts of water and 0.8 parts of isoquinoline. The mixture was sonicated for 8 minutes, heated at 220°C for 5 days, filtered and the precipitated solid was collected. The solid was washed three times with tetrahydrofuran, dimethylformamide and N-methyl-2-pyrrolidone, respectively, and dried at 160°C for 24 hours to obtain COFs.

[0031] S3: Add 2 parts of cotton linter pulp to 98 parts of an aqueous solution containing NaOH and urea at -12℃ to obtain a cellulose solution; add 0.02 parts of COFs to the cellulose solution at -12℃, stir rapidly until uniformly mixed, and then keep at 60℃ for 3 hours to obtain a solid hydrogel. After freeze-drying at -80℃ for 24 hours, COFs@cellulose aerogel is obtained.

[0032] S4: Immerse 0.5 parts of COFs@cellulose aerogel in 13 parts of magnetic suspension (including 0.03 parts of Fe3O4) for 30 minutes, remove and freeze-dry at -80℃ for 24 hours to obtain magnetic covalent organic framework aerogel.

[0033] Example 2: S1: Synthesis of amine precursor (hexa(p-anilino)hexaazatrinaphthalene): 10 parts of 4,5-dibromophenyl-1,2-diamine, 4 parts of hexaoxane octahydrate, and 200 parts of acetic acid were mixed and heated under reflux for 2 days to obtain mixture A. Mixture A was poured into 100 parts of ice water, and 100 parts of sodium carbonate aqueous solution were slowly added. The solid was filtered and washed 3 times with DMF and 3 times with acetone. The solid was dried to obtain an intermediate. 6 parts of the intermediate, 0.5 parts of Pd(PPh3)4, 3 parts of K2CO3, 15 parts of pinacol 4-aminophenylboronic acid, 250 parts of DMF, and 50 parts of water were mixed and heated to 150°C for 2 days to obtain mixture B. The mixture was poured into ice water, filtered, and washed successively with water, methanol, and tetrahydrofuran to obtain the amine precursor.

[0034] S2: 0.0093 parts of amine precursor and 0.00845 parts of 2,5-bis(2-methoxyethoxy)-terephthalaldehyde were added to 0.5 parts of N-methyl-2-pyrrolidone, 0.5 parts of mesitylene, 0.2 parts of water, and 0.4 parts of isoquinoline. The mixture was sonicated for 6 minutes, heated at 200°C for 5 days, filtered, and the precipitated solid was collected. The solid was washed three times with tetrahydrofuran, dimethylformamide, and N-methyl-2-pyrrolidone, respectively, and dried at 150°C for 24 hours to obtain COFs.

[0035] S3: Add 2 parts of cotton linter pulp to 98 parts of an aqueous solution containing NaOH and urea at -12℃ to obtain a cellulose solution; add 0.02 parts of COFs to the cellulose solution at -12℃, stir rapidly until uniformly mixed, and then keep at 50℃ for 5 hours to obtain a solid hydrogel. After freeze-drying at -80℃ for 24 hours, COFs@cellulose aerogel is obtained.

[0036] S4: Immerse 0.5 parts of COFs@cellulose aerogel in 13 parts of magnetic suspension (including 0.04 parts of Fe3O4) for 45 minutes, remove and freeze-dry at -80℃ for 24 hours to obtain magnetic covalent organic framework aerogel.

[0037] Example 3: S1: Synthesis of amine precursor (hexa(p-anilino)hexaazatrinaphthalene): 10 parts of 4,5-dibromophenyl-1,2-diamine, 4 parts of hexaoxane octahydrate, and 200 parts of acetic acid were mixed and heated under reflux for 2 days to obtain mixture A. Mixture A was poured into 100 parts of ice water, and 100 parts of sodium carbonate aqueous solution were slowly added. The solid was filtered and washed 3 times with DMF and 3 times with acetone. The solid was dried to obtain an intermediate. 6 parts of the intermediate, 0.5 parts of Pd(PPh3)4, 3 parts of K2CO3, 15 parts of pinacol 4-aminophenylboronic acid, 250 parts of DMF, and 50 parts of water were mixed and heated to 150°C for 2 days to obtain mixture B. The mixture was poured into ice water, filtered, and washed successively with water, methanol, and tetrahydrofuran to obtain the amine precursor.

[0038] S2: 0.0186 parts of amine precursor and 0.0169 parts of 2,5-bis(2-methoxyethoxy)-p-phenylenedialdehyde were added to 1 part of N-methyl-2-pyrrolidone, 1 part of mesitylene, 0.4 parts of water and 0.8 parts of isoquinoline. The mixture was sonicated for 10 minutes, heated at 200°C for 5 days, filtered and the precipitated solid was collected. The solid was washed three times with tetrahydrofuran, dimethylformamide and N-methyl-2-pyrrolidone, respectively, and dried at 150°C for 24 hours to obtain COFs.

[0039] S3: Add 3 parts of cotton linter pulp to 97 parts of an aqueous solution containing NaOH and urea at -12℃ to obtain a cellulose solution; add 0.02 parts of COFs to the cellulose solution at -12℃, stir rapidly until uniformly mixed, and then keep at 45℃ for 6 hours to obtain a solid hydrogel. After freeze-drying at -80℃ for 24 hours, COFs@cellulose aerogel is obtained.

[0040] S4: Impregnate 0.5 parts of COFs@cellulose aerogel in 13 parts of magnetic suspension (including 0.05 parts of Fe3O4) for 60 minutes, remove and freeze-dry at -80℃ for 24 hours to obtain magnetic covalent organic framework aerogel.

[0041] Comparative Example 1: The difference from Example 3 is that the synthesis of COFs@cellulose aerogel and magnetic covalent organic framework aerogel is not carried out. Instead, the original COFs:S1:amine precursor (hexa(p-aniline)hexaazatrinaphthalene) is synthesized directly: 10 parts of 4,5-dibromophenyl-1,2-diamine, 4 parts of hexaoxane octahydrate, and 200 parts of acetic acid are mixed and heated under reflux for 2 days to obtain mixture A. Mixture A is then poured into 100 parts of ice water and slowly... Add 100 parts of sodium carbonate aqueous solution, filter to obtain solid, wash 3 times with DMF, wash 3 times with acetone, and dry to obtain intermediate; mix 6 parts of intermediate, 0.5 parts of Pd(PPh3)4, 3 parts of K2CO3, 15 parts of 4-aminophenylboronic acid pinacol ester, 250 parts of DMF, and 50 parts of water, heat to 150℃ for 2 days to obtain mixture B, pour the mixture into ice water, filter, and wash successively with water, methanol, and tetrahydrofuran to obtain amine precursor;

[0042] S2: 0.0186 parts of amine precursor and 0.0169 parts of 2,5-bis(2-methoxyethoxy)-p-phenylenedialdehyde were added to 1 part of N-methyl-2-pyrrolidone, 1 part of mesitylene, 0.4 parts of water and 0.8 parts of isoquinoline. The mixture was sonicated for 10 minutes, heated at 200°C for 5 days, filtered and the precipitated solid was collected. The solid was washed three times with tetrahydrofuran, dimethylformamide and N-methyl-2-pyrrolidone, respectively, and dried at 150°C for 24 hours to obtain COFs.

[0043] Comparative Example 2: The difference from Example 3 is that the synthesis of magnetic covalent organic framework aerogel was omitted, and COFs@cellulose aerogel was used directly: S1: Synthesis of amine precursor (hexa(p-aniline)hexaazatrinaphthalene): 10 parts of 4,5-dibromophenyl-1,2-diamine, 4 parts of hexaoxane octahydrate and 200 parts of acetic acid were mixed and heated under reflux for 2 days to obtain mixture A. Mixture A was poured into 100 parts of ice water and 100 parts of sodium carbonate aqueous solution were slowly added. The solid was filtered and washed 3 times with DMF and 3 times with acetone. The solid was dried to obtain an intermediate. 6 parts of the intermediate, 0.5 parts of Pd(PPh3)4, 3 parts of K2CO3, 15 parts of pinacol 4-aminophenylboronic acid, 250 parts of DMF and 50 parts of water were mixed and heated to 150°C for 2 days to obtain mixture B. The mixture was poured into ice water, filtered, and washed successively with water, methanol and tetrahydrofuran to obtain the amine precursor.

[0044] S2: 0.0186 parts of amine precursor and 0.0169 parts of 2,5-bis(2-methoxyethoxy)-p-phenylenedialdehyde were added to 1 part of N-methyl-2-pyrrolidone, 1 part of mesitylene, 0.4 parts of water and 0.8 parts of isoquinoline. The mixture was sonicated for 10 minutes, heated at 200°C for 5 days, filtered and the precipitated solid was collected. The solid was washed three times with tetrahydrofuran, dimethylformamide and N-methyl-2-pyrrolidone, respectively, and dried at 150°C for 24 hours to obtain COFs.

[0045] S3: Add 3 parts of cotton linter pulp to 97 parts of an aqueous solution containing NaOH and urea at -12℃ to obtain a cellulose solution; add 0.02 parts of COFs to the cellulose solution at -12℃, stir rapidly until uniformly mixed, and then keep at 45℃ for 6 hours to obtain a solid hydrogel. After freeze-drying at -80℃ for 24 hours, COFs@cellulose aerogel is obtained.

[0046] Comparative Example 3: The difference from Example 3 is that 2,5-dihydroxyterephthalaldehyde and an amine precursor were used to prepare COFs: S1: Synthesis of amine precursor (hexa(p-aniline)hexaazatrinaphthalene): 10 parts of 4,5-dibromophenyl-1,2-diamine, 4 parts of hexaoxane octahydrate and 200 parts of acetic acid were mixed and heated under reflux for 2 days to obtain mixture A. Mixture A was poured into 100 parts of ice water and 100 parts of sodium carbonate aqueous solution were slowly added. The solid was filtered and washed 3 times with DMF and 3 times with acetone, and dried to obtain an intermediate. 6 parts of the intermediate, 0.5 parts of Pd(PPh3)4, 3 parts of K2CO3, 15 parts of pinacol 4-aminophenylboronic acid, 250 parts of DMF and 50 parts of water were mixed and heated to 150°C for 2 days to obtain mixture B. The mixture was poured into ice water, filtered, and washed successively with water, methanol and tetrahydrofuran to obtain the amine precursor.

[0047] S2: 0.0186 parts of amine precursor and 0.00997 parts of 2,5-dihydroxyterephthalaldehyde were added to 1 part of N-methyl-2-pyrrolidone, 1 part of mesitylene, 0.4 parts of water and 0.8 parts of isoquinoline. The mixture was sonicated for 5 minutes, heated at 240°C for 3 days, filtered and the precipitated solid was collected. The solid was washed three times with tetrahydrofuran, dimethylformamide and N-methyl-2-pyrrolidone, respectively, and dried at 100°C for 24 hours to obtain COFs.

[0048] S3: Add 3 parts of cotton linter pulp to 97 parts of an aqueous solution containing NaOH and urea at -12℃ to obtain a cellulose solution; add 0.02 parts of COFs to the cellulose solution at -12℃, stir rapidly until uniformly mixed, and then keep at 45℃ for 6 hours to obtain a solid hydrogel. After freeze-drying at -80℃ for 24 hours, COFs@cellulose aerogel is obtained.

[0049] S4: Impregnate 0.5 parts of COFs@cellulose aerogel in 13 parts of magnetic suspension (including 0.05 parts of Fe3O4) for 60 minutes, remove and freeze-dry at -80℃ for 24 hours to obtain magnetic covalent organic framework aerogel.

[0050] Experiment 1: 100 mg of the magnetic covalent organic framework aerogel prepared in Examples 1-3, the COFs prepared in Comparative Example 1, the COFs@cellulose aerogel prepared in Comparative Example 2, and the magnetic covalent organic framework aerogel prepared in Comparative Example 3 were used as samples for the following experiments: (1) Li + Adsorption capacity determination: 50 mL of LiCl solution with a concentration of 200 mg / L was prepared. + Solution, add sample, adsorption time is 12 hours, Li + The adsorption capacity (Q, mg / g) is calculated according to the formula Q = (C0 - C) / ( ... e )×V / m, where C0 and C e Li in the solution before and after adsorption, respectively + Concentration (mg / L); V and m represent solution volume (L) and sample mass (g), respectively;

[0051] (2)Li + / Mg 2+ Separation coefficient determination: 50 mL of LiCl and MgCl2 was prepared. + (200mg / L), Mg 2+ A (200 mg / L) binary mixed solution was added to the sample, and the adsorption time was 12 hours. Li + / Mg 2+ Separation coefficient S = (C0 - C e ) / (C 01 -C e1 ), where C0 and Ce Li in the solution before and after adsorption, respectively + Concentration (mg / L); C 01 and C e1 Mg in the solution before and after adsorption, respectively. 2+ Concentration (mg / L);

[0052] (3) Reusability test: Adsorption: 50 mL of LiCl solution with a concentration of 200 mg / L was prepared. + Solution, add sample, adsorption time is 12 hours; separation and washing: after adsorption, separate the sample with a magnet, then wash with water for 12 hours, and add 200 mg / L Li again. + In solution, Li + (200 mg / L) and Mg 2+ Adsorption was performed in a (200 mg / L) binary mixed solution; after repeating the adsorption, separation, and washing process 7 times, Li was calculated. + Adsorption capacity, Li + / Mg 2+ Separation coefficient; the test results are shown in the table below:

[0053]

[0054]

[0055] Conclusion: The magnetic covalent organic framework aerogels prepared in Examples 1-3 exhibit good adhesion to Li in water. + It has a high adsorption capacity for Li, and at the same time, it has a high adsorption capacity for Li + / Mg 2+ The separation effect is excellent, with separation coefficients all above 117. Even after 7 repeated uses, it still retains 83.1–89.2 mg / g of Li. + Adsorption capacity and Li 111-116 + / Mg2 + The separation coefficient shows that it has excellent performance in recovering lithium from water and is reusable.

[0056] Experiment 2: The magnetic covalent organic framework aerogel prepared in Example 3 was subjected to the following experiments: (1) Surface morphology determination: its surface morphology was obtained by field emission scanning electron microscopy; first, the conductive adhesive was attached to the sample stage, then the sample was evenly dispersed and spread on the conductive adhesive, it was installed in the vacuum chamber and vacuumed, the accelerating voltage was set to 5kV, and its morphological characteristics were observed. The test results are as follows. Figure 2 ;

[0057] (2) Specific surface area determination: The N2 adsorption-desorption curves at 77K were determined using a specific surface area pore size distribution analyzer. Before measurement, the surface was degassed at 120℃ for 12 hours. The specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method. The test results are as follows: Figure 3 ;

[0058] Conclusion: The magnetic covalent organic framework aerogel prepared in Example 3 possesses abundant 3D porous structure and a large specific surface area, which is beneficial for Li in water. + Full adsorption and recovery;

[0059] Comparative Example 1 sample was a COF (carbon ionomer) sample. The original COFs readily aggregated in water, leading to a decrease in exposed specific lithium-loving groups and surface area, thus reducing their affinity for Lithium in water. + Adsorption performance and Li + / Mg 2+ The separation performance and reusability were greatly reduced; the sample in Comparative Example 2 was a COFs@cellulose aerogel, which was not impregnated with a magnetic suspension, resulting in a significant reduction in reusability. After being reused 7 times, only 53.4 mg / g of Li remained. + Adsorption capacity and 108 Li + / Mg 2+ The separation coefficient and the reduction in adsorption capacity were 40.3%. Comparative Example 3 used 2,5-dihydroxyterephthalaldehyde and an amine precursor to prepare COFs, which had lower pore crowding. COFs with lower pore crowding could not effectively separate Li. + / Mg 2+ Li + / Mg 2+ The separation coefficient is only 21, which is insufficient for Li in water. + The adsorption capacity was 81.1 mg / g, and after being reused 7 times, it only had 75.5 mg / g of Li. + Adsorption capacity and 15 Li + / Mg2 + Separation coefficient; Based on the above data and experiments, we can draw the following conclusions: The magnetic covalent organic framework aerogel prepared in this invention exhibits excellent lithium recovery performance from water, and Li... + / Mg 2+ With strong separation performance and high reusability, it is very practical in the field of new energy recycling.

[0060] Unless otherwise specified, the experimental methods used in the above embodiments are conventional methods; the raw materials used are commercially available unless otherwise specified, and the sources of the raw materials are as follows: 4,5-dibromophenyl-1,2-diamine (CAS: 49764-63-8); hexaoxane octahydrate (CAS: 527-31-1); acetic acid (CAS: 64-19-7); sodium carbonate (CAS: 497-19-8); DMF (CAS: 68-12-2); acetone (CAS: 67-64-1); Pd(PPh3)4 (CAS: 14221-01-3); K2CO3 (CAS: 584-08-7); pinacol ester of 4-aminophenylboronic acid (CAS: 214 360-73-3); Methanol (CAS: 67-56-1); Tetrahydrofuran (CAS: 109-99-9); 2,5-Bis(2-methoxyethoxy)-terephthalaldehyde (CAS: 2053247-15-5); N-Methyl-2-pyrrolidone (CAS: 872-50-4); Trimethylbenzene (CAS: 108-67-8); Isoquinoline (CAS: 119-65-3); Dimethylformamide (CAS: 68-12-2); Cotton linter pulp (M5+ Hubei Jinhanjiang Refined Cotton Co., Ltd.); NaOH (CAS: 1310-73-2); Urea (CAS: 57-13-6); Fe3O4 (CAS: 1317-61-9).

[0061] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the spirit and principles of the present invention and within the technical scope disclosed in this application should be included within the scope of protection of this application. Where there is no conflict, the embodiments and features described in the embodiments of this application can be combined with each other. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A magnetic covalent organic framework aerogel for efficient recovery of lithium ions from water, characterized in that: The preparation of the magnetic covalent organic framework aerogel includes the following steps: S1: Add cotton linter pulp to an aqueous solution containing NaOH and urea at -12℃ to obtain a cellulose solution; add a covalent organic framework to the cellulose solution at -12℃, stir rapidly until uniformly mixed, and then maintain at 45-60℃ for 3-6 hours to obtain a solid hydrogel. Freeze-dry to obtain a covalent organic framework@cellulose aerogel. S2: The covalent organic framework@cellulose aerogel was impregnated in a magnetic suspension for 0.5-1 h and then freeze-dried to obtain a magnetic covalent organic framework aerogel. The preparation of the covalent organic framework includes the following steps: taking an amine precursor, an aldehyde precursor, N-methyl-2-pyrrolidone, mesitylene, water, and isoquinoline, mixing them, sonicating them, heating them at 180-220°C for 5-6 days, filtering and collecting the precipitated solid, washing them, drying them, and obtaining the covalent organic framework. The aldehyde precursor is 2,5-bis(2-methoxyethoxy)-p-phenylenedialdehyde; the amine precursor is hexa(p-anilino)hexaazatrinaphthalene; The preparation of the amine precursor hexa(p-anilino)hexaazatrinaphthalene includes the following steps: 4,5-dibromophenyl-1,2-diamine, hexaoxane octahydrate, and acetic acid are mixed and heated under reflux for 2 days to obtain mixture A. Mixture A is poured into ice water, and sodium carbonate aqueous solution is slowly added. The solid is filtered, washed, and dried to obtain an intermediate. The intermediate, Pd(PPh3)4, K2CO3, pinacol ester of 4-aminophenylboronic acid, DMF, and water are mixed and heated to 145-155°C for 2 days. After the reaction is complete, mixture B is obtained. Mixture B is poured into ice water, filtered, and washed to obtain the amine precursor.

2. The magnetic covalent organic framework aerogel for efficient recovery of lithium ions in water according to claim 1, characterized in that: The intermediate comprises the following raw materials, by mass parts: 8-12 parts of 4,5-dibromophenyl-1,2-diamine, 3-5 parts of hexaoxane octahydrate, 180-220 parts of acetic acid, 100 parts of ice water, and 100 parts of sodium carbonate aqueous solution; the amine precursor comprises the following raw materials, by mass parts: 5-7 parts of the intermediate, 0.5-1 parts of Pd(PPh3)4, 2-4 parts of K2CO3, 12-16 parts of pinacol 4-aminophenylboronic acid, 200-300 parts of DMF, and 20-60 parts of water.

3. The magnetic covalent organic framework aerogel for efficient lithium ion recovery from water according to claim 1, characterized in that: The covalent organic framework@cellulose aerogel comprises the following raw materials, by mass parts: 2-3 parts cotton linter pulp, 97-98 parts aqueous solution containing NaOH and urea, and 0.02 parts covalent organic framework; wherein the aqueous solution containing NaOH and urea contains 5-10 wt% NaOH, 10-15 wt% urea, and the remainder is water.

4. The magnetic covalent organic framework aerogel for efficient recovery of lithium ions in water according to claim 1, characterized in that: The covalent organic framework comprises the following raw materials, in parts by mass: 0.008–0.02 parts amine precursor, 0.008–0.018 parts aldehyde precursor, 0.5–1 part N-methyl-2-pyrrolidone, 0.5–1 part mesitylene, 0.2–0.5 parts water, and 0.4–1 part isoquinoline.

5. The method for preparing a magnetic covalent organic framework aerogel for efficient lithium ion recovery from water according to claim 1, characterized in that: The magnetic covalent organic framework aerogel comprises the following raw materials, by mass: 10-15 parts magnetic suspension and 0.5 parts covalent organic framework@cellulose aerogel.

6. The method for preparing a magnetic covalent organic framework aerogel for efficient lithium ion recovery from water according to claim 5, characterized in that: The magnetic suspension includes an Fe3O4 suspension.

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