Synthesis method of covalent organic framework adsorbent constructed based on diketone macromolecules

Abstract

The invention relates to a synthesis method of a covalent organic framework adsorbent constructed based on diketone macromolecules. The problems that an existing lithium adsorbent is low in adsorption capacity and insufficient in selectivity are solved. The method disclosed by the invention comprises the following steps: S1, stirring hydrazine hydrate and diethyl malonate under the condition of normal temperature and no solvent to prepare malonyl hydrazine; s2, enabling sym-tribenzaldehyde and malonyl hydrazine to react under the protection of nitrogen to prepare a COF adsorbent material; the covalent organic framework adsorbent material constructed on the basis of the diketone macromolecules synthesized by the method disclosed by the invention not only has relatively high selectivity and adsorption capacity on lithium ions, but also shows rapid adsorption kinetics, adsorption equilibrium can be achieved after adsorption is carried out for 65 minutes, and the adsorption capacity reaches 36.32 mg / g. And the selectivity coefficients alpha of Li (I) / K (I) and Li (I) / Na (II) respectively reach 85.46 and 69.68.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium adsorbents, and particularly to a synthesis method of a covalent organic framework adsorbent constructed based on diketone polymers. Background Art

[0002] With the reduction of traditional energy resources and the continuous improvement of environmental protection awareness, the demand for replacing traditional energy vehicles with electric vehicles has become increasingly urgent; among many battery technology options, lithium-ion batteries are regarded as the preferred energy storage solution in the field of electric vehicles due to their high energy storage capacity and good cycle life, and thus have been widely used; currently, the lithium batteries used in electric vehicles will have their performance degraded to 80% of that of a new battery after about 800 full charge and discharge cycles, thus approaching the retirement stage, and the annual retirement volume of lithium batteries in China is increasing year by year. Therefore, the resource treatment of retired lithium batteries is an effective way to alleviate the problem of traditional energy consumption; Among many lithium extraction technologies, the adsorption method is not only applicable to high Na / Li ratio salt lake brines, but also has the advantages of simple operation, environmental friendliness and low cost, and is recognized as the best method for extracting lithium from salt lake brines; currently, two major types of adsorbents are widely used in the field of lithium extraction: inorganic and organic, and they selectively extract lithium ions through coordination effects and ion sieves; however, there are few reports on the preparation of covalent organic framework adsorbents that combine the two effects; as a new type of porous material, covalent organic frameworks have great application prospects in the adsorption field due to their controllable structure, large specific surface area and high chemical stability; however, it is difficult to achieve good separation effects by simply using COF materials for size screening of metal ions; there are many literatures recording that the hydroxyl or carbonyl groups in β-diketone compounds can form stable chelate structures with lithium ions, so as to achieve targeted adsorption of metal lithium ions; In view of this, the present invention proposes a new type of adsorbent, which combines the characteristics of large specific surface area and high chemical stability of covalent organic frameworks and the + characteristics of strong affinity for Li, aiming to solve the limitations encountered by single-effect adsorbents in treating complex industrial wastewater, and at the same time provide an economical, efficient and environmentally friendly lithium extraction solution. Summary of the Invention

[0003] Aiming at the limitations of the current technology, the present invention aims to propose an innovative synthesis route of a covalent organic framework adsorbent constructed by diketone polymers to overcome the technical problems such as insufficient selectivity, limited adsorption capacity, high cost and cumbersome preparation process caused by single effects of existing lithium adsorbents.

[0004] The object of the present invention is achieved through the following technical solutions: A covalent organic framework adsorbent material constructed based on diketone polymers, which has the following chemical structural formula: The preparation method of the above-mentioned covalent organic framework adsorbent material constructed based on diketone polymers includes the following steps: S1. Add diethyl malonate and hydrazine hydrate into a round-bottom flask, stir and react under solvent-free conditions. After the reaction is completed, perform suction filtration. The obtained precipitate is vacuum dried to obtain malonyl hydrazide; S2. Add malonyl hydrazide into pure water and ultrasonicate to obtain a transparent and homogeneous solution A. Add 1,3,5-benzenetricarbaldehyde into dimethylformamide and ultrasonicate to obtain a transparent and homogeneous solution B. Mix the obtained solution A and solution B to obtain solution C. Transfer the mixed solution to a Schlenk tube, add trifluoroacetic acid as a catalyst for the Schiff base reaction into the Schlenk tube, stir evenly, perform freeze-thaw cycle treatment until all the air in the flask is replaced with nitrogen, and then place the sealed Schlenk tube in an oil bath for reaction. After the reaction is completed, cool to room temperature, perform suction filtration, and the obtained precipitate is vacuum dried to obtain a covalent organic framework adsorbent material containing diketone polymers.

[0005] Preferably, the dosage ratio of diethyl malonate to hydrazine hydrate in S1 is 1 moL: 2 moL.

[0006] Preferably, perform multiple suction filtrations with methanol in S1.

[0007] Preferably, the temperature of the stirring reaction in S1 is 25 °C, and the reaction time is 30 min; the temperature of the vacuum drying is 40 °C, and the time is 6-12 h.

[0008] Preferably, the dosage ratio of malonyl hydrazide to pure water in S2 is 250 mg: 1.5 mL - 3 mL.

[0009] Preferably, the dosage ratio of 1,3,5-benzenetricarbaldehyde to dimethylformamide in S3 is 200 mg: 1.5 mL - 3 mL.

[0010] Preferably, the molar ratio of 1,3,5-benzenetricarbaldehyde to malonyl hydrazide in S2 is 2 moL: 3 - 4 moL.

[0011] Preferably, the ultrasonic power in S2 is 200 W, and the ultrasonic time is 15 - 30 min.

[0012] Preferably, the dosage ratio of 1,3,5-benzenetricarbaldehyde to trifluoroacetic acid in S2 is 200 mg: 2 - 3 μL.

[0013] Preferably, perform 3 freeze-thaw cycle treatments in S2.

[0014] Preferably, in S2, multiple suction filtrations are carried out using ethanol and pure water.

[0015] Preferably, the temperature of the heating and stirring reaction in S2 is 120 °C, and the reaction time is 72 - 96 h; the temperature of the vacuum drying is 40 °C, and the time is 6 - 12 h.

[0016] The beneficial effects of the present invention are as follows: (1) The covalent organic framework adsorbent constructed based on diketone polymers prepared by the method of the present invention has the advantages that due to its highly ordered pore structure and adjustable pore size, the covalent organic framework can effectively promote the transport of ions; and the material has abundant β-diketone groups, which can provide more adsorption sites for firmly binding with lithium ions and can form a stable chelate structure with lithium ions; through the combination of the coordination effect and the ion sieving effect, the selective extraction of lithium ions is realized. (2) The present invention synthesizes a covalent organic framework adsorbent constructed based on diketone polymers, which has simple operation, low cost, high synthesis efficiency, and high selectivity and adsorption capacity for lithium ions; it is verified that the adsorption capacity of this material for lithium ions in water can reach up to 36.32 mg / g at most, and for lithium ions in lithium-containing wastewater containing a large amount of monovalent and multivalent competing ions coexisting, the adsorption of lithium ions is far superior to the adsorption of sodium, potassium, cobalt, manganese and other ions. Description of the Drawings

[0017] Figure 1 It is the synthesis route diagram of the covalent organic framework adsorbent material constructed based on diketone polymers in Example 1 of the present invention; Figure 2 It is the infrared spectrum diagram of malonyl hydrazide in Example 1 of the present invention; Figure 3 It is the 1H NMR spectrum diagram of malonyl hydrazide in Example 1 of the present invention; Figure 4 It is the infrared spectrum diagram of the covalent organic framework adsorbent material constructed based on diketone polymers in Example 1 of the present invention; Figure 5 It is the TGA thermogravimetric curve diagram of the covalent organic framework adsorbent material constructed based on diketone polymers in Example 1 of the present invention; Figure 6 It is the kinetic adsorption curve diagram of the covalent organic framework adsorbent material constructed based on diketone polymers in Example 1 of the present invention; Figure 7 It is the isothermal adsorption curve diagram of the covalent organic framework adsorbent material constructed based on diketone polymers in Example 1 of the present invention; Figure 8 It is the selective adsorption ability of the covalent organic framework adsorbent material constructed based on diketone polymers in Example 1 of the present invention for lithium ions in a monovalent metal mixed solution. Figure 9 For the covalent organic framework adsorbent material constructed based on diketone polymer in Example 1 of the present invention, the selective adsorption ability of lithium ions in a divalent metal mixed solution; Figure 10 It is a comparison chart of the selective adsorption ability of lithium ions of the covalent organic framework adsorbent material constructed based on diketone polymer in Example 1 of the present invention in a monovalent and divalent metal mixed solution. Specific embodiments

[0018] The present invention will be further described below with reference to the drawings and embodiments: Example 1: A preparation method of a covalent organic framework adsorbent constructed based on diketone polymer is carried out according to the following steps: S1. Diethyl malonate and hydrazine hydrate are added into a round-bottom flask, and stirred and reacted under solvent-free conditions. After the reaction is completed, the product is separated and purified by column chromatography, and malonyl hydrazide is obtained after purification; In this example, the molar ratio of diethyl malonate to hydrazine hydrate is 1 moL: 2 moL; S2. Prepare a covalent organic framework adsorbent material constructed based on diketone polymer, including the following steps: Malonyl hydrazide is added to pure water and ultrasonicated to obtain a transparent and uniform solution A. Melamine trialdehyde is added to dimethylformamide and ultrasonicated to obtain a transparent and uniform solution B. The obtained solution A and solution B are mixed to obtain solution C. The mixed solution is transferred to a schlenk tube, and trifluoroacetic acid is added to the schlenk tube as a catalyst for the Schiff base reaction, and stirred evenly. After freeze-thaw cycle treatment until all the air in the bottle is replaced with nitrogen, then the sealed schlenk tube is placed in an oil bath for reaction. After the reaction is completed, it is cooled to room temperature and filtered by suction. The obtained precipitate is vacuum dried to obtain a covalent organic framework adsorbent material containing diketone polymer; In this example, the dosage ratio of malonyl hydrazide to pure water is 250 mg: 1.5 mL to 3 mL; In this example, the dosage ratio of melamine trialdehyde to dimethylformamide is 200 mg: 1.5 mL to 3 mL; In this example, the molar ratio of melamine trialdehyde to malonyl hydrazide is 2 moL: 3 to 4 moL; In this example, the dosage ratio of melamine trialdehyde to trifluoroacetic acid is 200 mg: 2 to 3 μL; Example 2: In step S2, the dosage ratio of malonyl hydrazide to pure water is 250 mg: 1.5 mL; or the dosage ratio of malonyl hydrazide to pure water is 250 mg: 2 mL; or the dosage ratio of malonyl hydrazide to pure water is 250 mg: 3 mL; other steps are the same as those in Example 1.

[0019] Example 3: The dosage ratio of mellitene aldehyde and dimethylformamide described in step S2 is 200 mg: 1.5 mL; or the dosage ratio of mellitene aldehyde and dimethylformamide is 200 mg: 2 mL; or the dosage ratio of mellitene aldehyde and dimethylformamide is 200 mg: 3 mL; other steps are the same as those in Examples 1-2.

[0020] Example 4: The molar ratio of mellitene aldehyde and malonyl hydrazide described in step S2 is 2 moL: 3 moL; or the molar ratio of mellitene aldehyde and malonyl hydrazide is 2 moL: 3.5 moL; or the molar ratio of mellitene aldehyde and malonyl hydrazide is 2 moL: 4 moL; other steps are the same as those in Examples 1-3.

[0021] Example 5: The dosage ratio of mellitene aldehyde and trifluoroacetic acid described in step S2 is 200 mg: 2 μL; or the dosage ratio of mellitene aldehyde and trifluoroacetic acid is 200 mg: 3 μL; other steps are the same as those in Examples 1-4.

[0022] The covalent organic framework adsorbent material based on diketone polymer is prepared according to the methods of Examples 1-5. The specific steps are as follows: S1. Add 0.64 g of diethyl malonate and 0.4 g of hydrazine hydrate into a round-bottom flask, stir and react under solvent-free conditions. After the reaction is completed, filter with sodium methoxide. The obtained precipitate is vacuum-dried to obtain malonyl hydrazide. S2. Add 245 mg of malonyl hydrazide into 1.5 mL of pure water and ultrasonicate to obtain a transparent and uniform solution A. Add 200 mg of mellitene aldehyde into 3 mL of dimethylformamide and ultrasonicate to obtain a transparent and uniform solution B. Mix the obtained solution A and solution B to obtain solution C. Transfer the mixed solution to a schlenk tube, add 3 μL of trifluoroacetic acid as a catalyst for the Schiff base reaction into the schlenk tube, stir evenly, perform 3 freeze-thaw cycles until the inside of the flask is vacuum, then place the sealed schlenk tube in an oil bath at 120 °C for reaction. After the reaction is completed, cool to room temperature, filter with pure water and ethanol. The obtained precipitate is vacuum-dried to obtain the covalent organic framework adsorbent material based on diketone polymer.

[0023] Figure 2 and Figure 3 are the nuclear magnetic resonance hydrogen spectrum and infrared spectrum of malonyl hydrazide prepared in Example 1 respectively, and the results prove the successful preparation of malonyl hydrazide.

[0024] Figure 4 is the infrared spectrum of the covalent organic framework adsorbent material based on diketone polymer prepared in Example 1, 3295.3 cm -1 , 1658 cm -1and 1561 cm -1 The characteristic peaks at this position indicate the stretching vibrations of N-H, C=O, and C=N, suggesting the successful preparation of the covalent organic framework adsorbent material based on diketone polymers.

[0025] Figure 5 Figure is the TGA thermogravimetric curve of the covalent organic framework adsorbent material based on diketone polymers prepared in Example 1, indicating that the adsorbent starts to pyrolyze at 200 °C, and nearly 40% of the material remains undecomposed when heated to 700 °C, demonstrating good thermal stability.

[0026] The kinetic adsorption experiment 1 of the lithium-ion aqueous solution was carried out using the covalent organic framework adsorbent material based on diketone polymers prepared in Example 1: (1) First, prepare an aqueous lithium nitrate solution with an initial concentration of 500 mg / L. Take 100 mL of the lithium-containing solution and place it in a 250 mL beaker.

[0027] (2) Then, accurately weigh 100 mg of the covalent organic framework adsorbent material based on diketone polymers and put it into the beaker of the lithium-ion aqueous solution with a concentration of 500 mg / L.

[0028] (3) Use a magnetic stirring device, set the rotation speed to 500 revolutions per minute, and carry out stirring treatment for 180 minutes in an environment with a constant temperature of 25 °C. At the 0th, 1st, 3rd, 5th, 10th, 30th, 45th, 60th, 90th, 120th, and 180th minutes during the stirring process, respectively, extract 1 mL of the suspension sample from the reaction beaker. These samples need to be filtered through a polyethersulfone membrane with a pore size of 0.45 μL and appropriately diluted for subsequent analysis. Subsequently, use an atomic absorption spectrometer to accurately measure the concentration of lithium ions in each sample; Figure 6 Figure is the kinetic adsorption curve of the covalent organic framework adsorbent material based on diketone polymers prepared in Example 1. This adsorbent material shows a rapid adsorption rate. Within the first 20 minutes, its adsorption capacity reaches 25.5 mg / g, which is equivalent to 75.1% of the adsorption capacity at equilibrium (31.32 mg / g). By 60 minutes, it reaches the adsorption saturation state. In the actual kinetic adsorption process, the data is more in line with the description of the pseudo-second-order kinetic model, revealing that the main adsorption mechanism of the adsorbent for lithium ions is chemical adsorption.

[0029] The adsorption test experiment 2 of the lithium-ion aqueous solution was carried out using the covalent organic framework adsorbent material synthesized in Example 1 based on diketone polymers: (1) Prepare lithium nitrate aqueous solutions with lithium element concentrations of 10 mg / L, 30 mg / L, 50 mg / L, 80 mg / L, 100 mg / L, 150 mg / L, 200 mg / L, 250 mg / L, 300 mg / L, and 400 mg / L respectively; take 20 mL of each of these concentration solutions and place them in 10 conical flasks with a specification of 50 mL; (2) Weigh 10 portions of 20 mg of the covalent organic framework adsorbent material prepared based on diketone polymers, and separately add the weighed materials into the conical flasks containing lithium ion aqueous solutions with different concentrations. Place them in a constant temperature oscillator for adsorption experiments, and set the parameters as temperature 25 °C, rotation speed 180 rpm, and continuous oscillation for 24 h; (3) Take the ion solutions in the conical flasks before and after adsorption, and use an atomic absorption spectrometer (AAS) to measure the lithium ion concentration in the solution; Figure 7 The isothermal adsorption curve of the covalent organic framework adsorbent material prepared for Example 1 based on diketone polymers shows a high adsorption capacity of the adsorbent material for lithium ions. The adsorption capacity can reach 36.32 mg / g, and the fitting results of the Langmuir and Freundlich models show that the actual material isothermal adsorption process is more in line with the Langmuir adsorption model, indicating that the adsorption process of the adsorbent for lithium ions is mainly monolayer adsorption.

[0030] Use the covalent organic framework adsorbent material based on diketone polymers prepared by emulsion polymerization in Example 1 to explore its adsorption selectivity for lithium ions in a mixed solution containing multiple monovalent metals. The specific test steps are as follows: (1) Prepare a mixed aqueous solution containing 50 mMol / L of lithium ions, 50 mMol / L of sodium ions, and 50 mMol / L of potassium ions, with a volume of 20 mL; place it in a conical flask with a specification of 50 mL; (2) Weigh 20 mg of the covalent organic framework adsorbent material prepared based on diketone polymers in Example 1, and add it into a mixed aqueous solution containing 50 mMol / L of lithium ions, 50 mMol / L of cobalt ions, and 50 mMol / L of manganese ions. Place it in a constant temperature oscillator for adsorption experiments, and set the parameters as temperature 25 °C, rotation speed 180 rpm, and continuous oscillation for 24 h; (3) Take the ion solutions in the conical flasks before and after adsorption, and use inductively coupled plasma mass spectrometry (ICP-MS) technology to measure the concentrations of lithium ions, potassium ions, and sodium ions in the solution; Using the covalent organic framework adsorbent material based on diketone polymer prepared by emulsion polymerization in Example 1, its adsorption selectivity for lithium ions in a mixed solution containing various monovalent metals was explored. The specific test steps are as follows: (1) Prepare a mixed aqueous solution containing 50 mMol / L of lithium ions, 50 mMol / L of cobalt ions, 50 mMol / L of copper ions, 50 mMol / L of nickel ions, and 50 mMol / L of manganese ions, with a volume of 20 mL; place it in a conical flask with a specification of 50 mL; (2) Weigh 20 mg of the covalent organic framework adsorbent material based on diketone polymer in Example 1, put it into a mixed aqueous solution containing 50 mMol / L of lithium ions, 50 mMol / L of cobalt ions, 50 mMol / L of copper ions, 50 mMol / L of nickel ions, and 50 mMol / L of manganese ions, and place it in a constant temperature oscillator for an adsorption experiment. Set the parameters as temperature 25°C, rotation speed 180 rpm, and continuous oscillation for 24 h; (3) Take the ion solutions before and after adsorption in the conical flask, and use inductively coupled plasma mass spectrometry (ICP-MS) technology to measure the concentrations of lithium ions, cobalt ions, copper ions, nickel ions, and manganese ions in the solution; Figure 8 and Figure 9 The selective adsorption ability of the covalent organic framework adsorbent material based on diketone polymer for lithium ions in a mixed solution of monovalent metals and a mixed solution of divalent metals. It can be seen that the covalent organic framework adsorbent material based on diketone polymer can separate lithium ions from a mixed solution containing sodium ions, potassium ions, cobalt ions, copper ions, and manganese ions, indicating that the adsorbent material can excellently complete the separation and recovery of lithium ions whether in a mixed solution of monovalent metals or in a mixed solution of divalent metals.

[0031] Those skilled in the art should recognize that the present invention is not limited within the framework of the above specific embodiments. The content of the above embodiments and their descriptions is only used to explain the core concept of the present invention. Without departing from the basic principles and scope of the present invention, the present invention allows various forms of variations and optimizations, and these variations and optimizations also belong to the scope of protection requested by the present invention. The protection boundary of the present invention is clearly defined by the appended claims and their equivalent forms.

Claims

1. A method for synthesizing a covalent organic framework adsorbent based on diketone polymer, characterized in that: Includes the following step: S1. Add diethyl malonate and hydrazine hydrate into a round-bottom flask, stir and react in the absence of solvent, and filter after the reaction. The obtained precipitate is vacuum dried to obtain malonyl hydrazide; S2. Add malonic acid hydrazide to pure water and perform ultrasound to obtain a transparent uniform solution A. Add isopropylbenzaldehyde to dimethylformamide and perform ultrasound to obtain a transparent uniform solution B. The obtained solution A and solution B are mixed to obtain a solution C. The mixed solution is transferred to a schlenk tube. Trifluoroacetic acid is added to the schlenk tube as a catalyst for Schiff base reaction. The mixture is stirred evenly. The mixture is subjected to freeze-thaw cycle treatment until all the air in the bottle is replaced by nitrogen. The sealed schlenk tube is placed in an oil bath for reaction. After the reaction is completed, the mixture is cooled to room temperature and filtered. The precipitated material is vacuum dried to obtain a covalent organic framework adsorbent material containing diketone polymer.

2. The method for synthesizing a covalent organic framework adsorbent based on diketone polymer according to claim 1, characterized in that The molar ratio of diethyl malonate to hydrazine hydrate described in step S1 is 1 mol:2 mol.

3. The method for synthesizing a covalent organic framework adsorbent based on diketone polymer according to claim 1, characterized in that The reaction time in step S1 is 30 min.

4. The method for synthesizing a covalent organic framework adsorbent material containing a diketone polymer according to claim 1, characterized in that The reaction temperature in step S1 is 25°C.

5. The method for synthesizing a covalent organic framework adsorbent material containing a diketone polymer according to claim 1, characterized in that The method of step S1 is to use methanol for suction filtration.

6. The method for synthesizing a covalent organic framework adsorbent material containing a diketone polymer according to claim 1, characterized in that The step S1 is vacuum dried at 40-45° C. for 24 h.

7. The method for synthesizing a covalent organic framework adsorbent material containing a diketone polymer according to claim 1, characterized in that The molar ratio of trimesaldehyde to malonic acid hydrazide described in step S2 is 2 mol:3-4 mol.

8. The method for synthesizing a covalent organic framework adsorbent based on diketone polymer according to claim 1, characterized in that The reaction time described in step S2 is 72 h.

9. The method for synthesizing a covalent organic framework adsorbent material containing a diketone polymer according to claim 1, characterized in that The reaction temperature in step S2 is 120°C.

10. The method for synthesizing a covalent organic framework adsorbent material containing a diketone polymer according to claim 1, characterized in that The step S2 is to use pure water and ethanol for suction filtration.

11. The method for synthesizing a covalent organic framework adsorbent material containing a diketone polymer according to claim 1, characterized in that The step S2 is vacuum dried at 40-45° C. for 24 h.

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