A novel ionic bipyridyl-based COF material, a preparation method and application thereof

Abstract

The application relates to the field of adsorption separation, in particular to a novel ion type bipyridyl group COF material and a preparation method and application thereof. The preparation method comprises the following steps: mixing 2,2',6,6'-tetramethyl-4,4'-bipyridine, 2,2'-bipyridine-5,5'-diformaldehyde, sodium hydroxide, trimethylbenzene and methanol to carry out reaction 1, and COF-CQWU-2 is obtained; the COF-CQWU-2 is placed in a mixed solution of iodomethane and chloroform to carry out reaction 2, and the novel ion type bipyridyl group COF material is obtained. The application successfully designs and prepares a novel ion type bipyridyl group COF material I@COF-CQWU-2 for removing perfluorinated compounds in water, the COF material has the advantages of simple preparation method, high adsorption capacity and recyclability, and the target of selectively adsorbing perfluorinated compounds from water is achieved.

Description

Technical Field

[0001] This invention relates to the field of adsorption separation, and in particular to a novel ionic bipyridine-based COF material, its preparation method, and its applications. Background Technology

[0002] Perfluoroalkyl compounds (PFAS) are a class of synthetic organic compounds with extremely strong chemical stability, thermal stability, and hydrophobic and oleophobic properties. They are widely used in industries such as fire-fighting foam, non-stick cookware coatings, waterproof fabrics, electroplating, and papermaking. Due to the presence of high-energy CF bonds in their molecules, PFAS are extremely difficult to degrade in the natural environment, exhibiting environmental persistence, bioaccumulation, and potential biotoxicity (such as hepatotoxicity, immunotoxicity, endocrine disruption, and carcinogenicity). They have been listed as emerging persistent organic pollutants globally by the United Nations Environment Programme.

[0003] In recent years, PFAS have been frequently detected in water bodies (surface water, groundwater, and drinking water) worldwide, with the pollution range continuously expanding, seriously threatening ecological security and human health. Traditional water treatment technologies, such as ion exchange, membrane separation, and advanced oxidation, have significant shortcomings in treating PFAS, while adsorption is recognized as the most promising method due to its simple operation, low cost, and good selectivity. However, existing adsorption materials still suffer from problems such as high cost, poor anti-interference ability, or poor adsorbent regeneration capacity, making it difficult to simultaneously achieve broad-spectrum and efficient removal, highly selective adsorption, stable regeneration and recycling, and low-energy, low-cost engineering applications for both long and short-chain PFAS. Therefore, developing novel, efficient, highly selective, stable, and recyclable PFAS removal materials is an urgent need and a research hotspot in the field of water environment management. Summary of the Invention

[0004] Based on the above, this invention provides a novel ionic bipyridyl-based COF material, its preparation method, and its applications. The novel ionic bipyridyl-based COF material (I@COF-CQWU-2) of this invention possesses advantages such as high specific surface area and porosity, excellent chemical stability, and recyclability. The prepared I@COF-CQWU-2 adsorbent not only has advantages such as chemical stability, simple synthesis route, mild reaction conditions, and simple adsorption process, but also exhibits high adsorption performance and regeneration performance for perfluorinated compounds.

[0005] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is a method for preparing a novel ionic bipyridyl COF material, comprising the following steps: Step 1: Mix 2,2',6,6'-tetramethyl-4,4'-bipyridine (TMBP), 2,2'-bipyridine-5,5'-dicarboxaldehyde (BPD), sodium hydroxide, thiomethylbenzene, and methanol to react 1 to obtain COF-CQWU-2; Step 2: The COF-CQWU-2 is placed in a mixed solution of iodomethane (CH3I) and chloroform to undergo reaction 2, thereby obtaining the novel ionic bipyridyl COF material (I@COF-CQWU-2).

[0006] The second technical solution of the present invention is a novel ionic bipyridyl COF material prepared by the above-mentioned preparation method.

[0007] The third technical solution of this invention is the application of the above-mentioned novel ionic bipyridyl COF material in the adsorption of perfluoroalkyl compounds.

[0008] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention successfully designed and prepared a novel ionic bipyridine-based COF material I@COF-CQWU-2 for removing perfluorinated compounds from water. This COF material has the advantages of simple preparation method, high adsorption capacity and recyclability, and achieves the goal of selectively adsorbing perfluorinated compounds from water. (2) The novel ionic bipyridine-based COF material I@COF-CQWU-2 prepared in this invention has a layered structure, which is beneficial for dispersion and adsorption; (3) I@COF-CQWU-2 has excellent chemical stability and is suitable for perfluorinated compound adsorption experiments at different pH values. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This is a SEM schematic diagram of I@COF-CQWU-2 in Embodiment 1 of the present invention; Figure 2 This is a TEM schematic diagram of I@COF-CQWU-2 in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the BET operation of I@COF-CQWU-2 in Embodiment 1 of the present invention; Figure 4 This is an FT-IR schematic diagram of I@COF-CQWU-2 in Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the adsorption isotherm performance of I@COF-CQWU-2 for perfluorooctanoic acid in Example 1 of the present invention; Figure 6 This is a schematic diagram of the adsorption kinetics of perfluorooctanoic acid by I@COF-CQWU-2 in Example 1 of the present invention; Figure 7 This is a test graph of the adsorption cycle performance of I@COF-CQWU-2 for perfluorooctanoic acid in Example 1 of the present invention; Figure 8 This is a schematic diagram of the adsorption performance of I@COF-CQWU-2 on perfluorooctanoic acid at different pH values ​​in Example 1 of the present invention; Figure 9 This is a schematic diagram of the adsorption performance of I@COF-CQWU-2 on perfluorooctanoic acid in the presence of other anions in Example 1 of the present invention. Detailed Implementation

[0011] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0012] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0013] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0014] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0015] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0016] Unless otherwise specified, "room temperature" in this invention refers to 15~30℃.

[0017] Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers composed of small organic molecule monomers linked by covalent bonds. Compared to traditional adsorbent materials (activated carbon, resins) and other porous materials (MOFs), COFs offer unique advantages in water treatment, including precisely tunable structure, high specific surface area and porosity, excellent chemical stability, and material functionalization. This invention is based on the bipyridine structure, which possesses strong coordination ability and ionization properties. Furthermore, through a nucleophilic substitution reaction, bipyridine is converted into a positively charged pyridinium salt (bipyridine cation), transforming the original COF material into a cationic COF material. Therefore, the resulting cationic COF material, due to its high-density positive charge within the framework, can efficiently adsorb negatively charged PFAS anions in water through strong electrostatic interactions. Theoretically, it can simultaneously achieve broad-spectrum, highly selective, and high-capacity adsorption of both long and short-chain PFAS. Therefore, this invention prepares a novel ionic bipyridyl COF material for removing perfluorinated compounds from water, which has the advantages of high adsorption capacity, high adsorption rate and recyclability for PFAS adsorption.

[0018] The first aspect of this invention provides a method for preparing a novel ionic bipyridyl COF material, comprising the following steps: Step 1: Mix 2,2',6,6'-tetramethyl-4,4'-bipyridine (TMBP), 2,2'-bipyridine-5,5'-dicarboxaldehyde (BPD), sodium hydroxide, thiomethylbenzene, and methanol to react 1 to obtain COF-CQWU-2; Step 2: The COF-CQWU-2 is placed in a mixed solution of iodomethane (CH3I) and chloroform to undergo reaction 2, thereby obtaining the novel ionic bipyridyl COF material (I@COF-CQWU-2).

[0019] In a preferred embodiment of the present invention, in step 1, the ratio of the amount of 2,2',6,6'-tetramethyl-4,4'-bipyridine to 2,2'-bipyridine-5,5'-dicarboxaldehyde, sodium hydroxide, trimethylbenzene and methanol is (0.4~0.8) mmol : (0.8~1.6) mmol : (175~350) mg : (20~40) ml : (30~40) ml.

[0020] In this invention, 2,2',6,6'-tetramethyl-4,4'-bipyridine (TMBP) and 2,2'-bipyridine-5,5'-dicarboxaldehyde (BPD) are used as ligands, sodium hydroxide is used as a catalyst, and thallium and methanol are used as solvents. I@COF-CQWU-2 can be synthesized by selecting TMBP and BPD as ligands. If other ligands such as 2,2',6,6'-tetramethyl-4,4'-biphenyl are used, I@COF-CQWU-2 of this invention cannot be prepared due to the insufficient activity of 2,2',6,6'-tetramethyl-4,4'-biphenyl.

[0021] In this invention, if the ligand ratio is too high or too low, or the amount of sodium hydroxide is too low, the target I@COF-CQWU-2 cannot be synthesized. If the ratio of trimethylbenzene to methanol is unbalanced, the yield of target I@COF-CQWU-2 will be too low. Therefore, this invention preferably limits the proportion of raw materials in step 1 to the above-mentioned parameter range.

[0022] In a preferred embodiment of the present invention, in step 1, the temperature of reaction 1 is 100~200℃, and the reaction time is 1~7 days. Preferably, the temperature of reaction 1 is 120~180℃, and the reaction time is 2~4 days.

[0023] In this invention, if the reaction temperature is too low, the target I@COF-CQWU-2 cannot be synthesized; if the reaction time is too short, the yield of the target I@COF-CQWU-2 will be too low.

[0024] In a preferred embodiment of the present invention, in step 2, the ratio of the amount of COF-CQWU-2 to the amount of iodomethane and chloroform is 50 mg: (1~20) mmol: (1~20) ml.

[0025] In this invention, if the amounts of iodomethane and chloroform are too small, the yield of target I@COF-CQWU-2 will be too low. Therefore, this invention limits the ratio of COF-CQWU-2 to iodomethane and chloroform to the range of parameters mentioned above.

[0026] In a preferred embodiment of the present invention, in step 2, reaction 2 is carried out at room temperature for 1 to 5 days, and stirring is performed during the reaction. The purpose of stirring is to uniformly disperse the reactants in the solution. The present invention does not impose a particular limitation on the stirring speed, and a stirring speed commonly used by those skilled in the art is adopted.

[0027] In a preferred embodiment of the present invention, after reaction 1 is completed, a washing and drying step is further included; after reaction 2 is completed, a washing and drying step is further included.

[0028] The solvent used for washing in step 1 and / or step 2 is selected from one or more of DMF, THF, water, ethanol and chloroform.

[0029] A second aspect of the present invention provides a novel ionic bipyridyl COF material prepared using the above-described preparation method.

[0030] The third aspect of this invention provides the application of the novel ionic bipyridyl COF material described above in the adsorption of perfluoroalkyl compounds.

[0031] In a preferred embodiment of the present invention, the perfluoroalkyl compound includes perfluorooctanoic acid.

[0032] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0033] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0034] Example 1: Preparation of I@COF-CQWU-2 Step 1: In a 100 ml reaction vessel, 2,2',6,6'-tetramethyl-4,4'-bipyridine (TMBP) (0.4 mmol, 84.9 mg), 2,2'-bipyridine-5,5'-dicarboxaldehyde (BPD) (0.8 mmol, 169.8 mg), sodium hydroxide (175 mg), trimethylbenzene (30 ml), and methanol (30 ml) were placed into the reaction vessel and sonicated until dissolved. The reaction system was then reacted in an oven at 180°C for 4 days. After the reaction was completed, the mixture was cooled and centrifuged. It was washed 3 times with DMF, 3 times with THF, 3 times with water, and 3 times with ethanol. It was then vacuum dried at 100°C for 12 hours to obtain a milky white COF-CQWU-2. Step 2: Place the above COF-CQWU-2 (50 mg) into a 20 ml glass bottle, then add a mixed solution of CH3I (1 mmol, 141.3 mg) and chloroform (10 ml), stir for 2 days, take it out, wash it 3 times with chloroform, then wash it 3 times with ethanol, and dry it under vacuum at 100°C for 12 hours to obtain milky white I@COF-CQWU-2.

[0035] Figure 1 This is a SEM schematic diagram of I@COF-CQWU-2 in Embodiment 1 of the present invention; by Figure 1 It can be seen that the SEM image of I@COF-CQWU-2 shows a distinct multi-layered spherical structure.

[0036] Figure 2 This is a TEM schematic diagram of I@COF-CQWU-2 in Embodiment 1 of the present invention; by Figure 1 It can be seen that the TEM image of I@COF-CQWU-2 also shows a two-dimensional layered morphological structure.

[0037] Figure 3 This is a schematic diagram of the BET operation of I@COF-CQWU-2 in Embodiment 1 of the present invention; by Figure 1 As can be seen from the BET plot, I@COF-CQWU-2 has a high specific surface area.

[0038] Figure 4 This is an FT-IR schematic diagram of I@COF-CQWU-2 in Embodiment 1 of the present invention; by Figure 1 The presence of the vinyl peak in I@COF-CQWU-2 indicates that I@COF-CQWU-2 was successfully synthesized.

[0039] Example 2 The only difference from Example 1 is that in step 1, the amount of thiol added is 40 ml and the amount of methanol added is 40 ml; the rest of the steps and parameters are the same as in Example 1.

[0040] Example 3 The only difference from Example 1 is that in step 1, the amount of thiol added is 20 ml and the amount of methanol added is 40 ml; the rest of the steps and parameters are the same as in Example 1.

[0041] Example 4 The only difference from Example 1 is that in step 1, the amount of TMBP added is 0.8 mmol; the rest of the steps and parameters are the same as in Example 1.

[0042] Example 5 The only difference from Example 1 is that in step 1, the amount of TMBP added is 0.8 mmol and the amount of BPD added is 1.6 mmol; the other steps and parameters are the same as in Example 1.

[0043] Example 6 The only difference from Example 1 is that in step 1, the amount of sodium hydroxide added is 350 mg; the rest of the steps and parameters are the same as in Example 1.

[0044] Example 7 The only difference from Example 1 is that in step 1, the reaction temperature in the oven is 120°C; the rest of the steps and parameters are the same as in Example 1.

[0045] Example 8 The only difference from Example 1 is that in step 1, the reaction time in the oven is 2 days; the rest of the steps and parameters are the same as in Example 1.

[0046] Example 9 The only difference from Example 1 is that in step 2, the amount of CH3I added is 2 mmol; the rest of the steps and parameters are the same as in Example 1.

[0047] Example 10 The only difference from Example 1 is that in step 2, the amount of chloroform added is 20 ml; the rest of the steps and parameters are the same as in Example 1.

[0048] Example 11 The only difference from Example 1 is that in step 2, COF-CQWU-2 (50 mg) was placed in a 20 ml glass bottle, and then a mixed solution of CH3I (1 mmol, 141.3 mg) and chloroform (10 ml) was added and stirred for 1 day before being taken out; the remaining steps and parameters are the same as in Example 1.

[0049] Example 12: Adsorption performance test of I@COF-CQWU-2 for perfluorooctanoic acid Before the experiment, the I@COF-CQWU-2 sample from Example 1 was pre-degassed by vacuum drying at 100℃ for 12 hours to fully activate the sample (10 mg). The activated sample was then transferred to an aqueous solution of perfluorooctanoic acid (PFOA) at a given concentration in a vial. The adsorption performance of the I@COF-CQWU-2 solution was recorded by liquid chromatography at 298 K. Specifically, 10 mg of I@COF-CQWU-2 was mixed with 20 ml of PFOA solution (pH=5) at a concentration of 50-1500 ppm and stirred at a constant temperature of 298 K for 48 h to obtain the adsorption isotherm of PFOA; 10 mg of I@COF-CQWU-2 was mixed with 10 ml of PFOA solution (pH=5) at a concentration of 100 ppm and stirred at a constant temperature of 298 K for 5-480 min to obtain the adsorption kinetics of PFOA. The adsorption capacity of perfluorooctanoic acid on I@COF-CQWU-2 was calculated using a mass measurement method.

[0050] The adsorption isotherm experiment of perfluorooctanoic acid (PFOA) showed that I@COF-CQWU-2 in Example 1 had a high adsorption capacity for PFOA, with a saturation adsorption capacity of 2.82 g / g (e.g., perfluorooctanoic acid adsorption isotherm experiment). Figure 5 (As shown in Table 1); Through adsorption kinetics experiments of perfluorooctanoic acid (PFOA), it can be concluded that I@COF-CQWU-2 in Example 1 has a high adsorption rate for PFOA, and equilibrium is reached in about 30 minutes (as shown in Table 1). Figure 6(As shown). This invention not only develops a novel ionic bipyridyl COF material, but also exhibits excellent adsorption performance for perfluorooctanoic acid.

[0051] Example 13: Cyclic performance test of regenerated I@COF-CQWU-2 for perfluorooctanoic acid adsorption After performing perfluorooctanoic acid (PFOA) adsorption experiments on I@COF-CQWU-2 from Example 1, 100 mg of the PFOA-adsorbed I@COF-CQWU-2 (denoted as PFOA-I@COF-CQWU-2) was stirred in 100 ml of methanol at room temperature for 12 hours. The mixture was then washed three times each with deionized water and ethanol, filtered, and dried under vacuum at 100°C for 12 hours. The desorbed I@COF-CQWU-2 material was then reused in PFOA adsorption experiments, with at least six cycles.

[0052] After six cycles of adsorption in perfluorooctanoic acid, I@COF-CQWU-2 still maintains more than 99% of its original maximum adsorption capacity (e.g., ...). Figure 7 (As shown).

[0053] Table 1. Adsorption capacity of I@COF-CQWU-2 in perfluorooctanoic acid solution in Examples 1-8

[0054] Example 14: Adsorption performance test of I@COF-CQWU-2 for perfluorooctanoic acid at different pH values I@COF-CQWU-2 from Example 1 was used to conduct adsorption tests on perfluorooctanoic acid (PFOA) at different pH values. First, PFOA solutions with an initial concentration of 100 ppm were prepared. The pH value of the PFOA solution was adjusted using dilute hydrochloric acid and sodium hydroxide. The pH values ​​of the PFOA solutions were set to 1, 3, 5, 7, 9, 11, and 13. 10 mg of I@COF-CQWU-2 was mixed with 10 ml of PFOA solutions with different pH values ​​and a concentration of 100 ppm and stirred at a constant temperature of 298 K for 480 min. The adsorption performance of I@COF-CQWU-2 on PFOA solutions at different pH values ​​was recorded by liquid chromatography.

[0055] In Example 1, I@COF-CQWU-2 exhibited the best adsorption performance for perfluorooctanoic acid (PFOA) solution at pH 5. As the solution pH increased from 1 to 5, the surface charge of I@COF-CQWU-2 gradually increased, leading to a continuous improvement in its electrostatic adsorption capacity for PFOA. The adsorption capacity reached its maximum saturation at pH 5. Further increasing the pH to neutral and alkaline conditions weakened the positive charge of I@COF-CQWU-2, which gradually converted to a negative charge, highlighting electrostatic repulsion and resulting in a continuous decrease in adsorption capacity (e.g., ...). Figure 8 (As shown).

[0056] Example 15: Adsorption performance test of I@COF-CQWU-2 for perfluorooctanoic acid in the presence of different metal ions The adsorption of perfluorooctanoic acid (PFOA) by I@COF-CQWU-2 from Example 1 was investigated under different anion conditions. First, a PFOA solution with an initial concentration of 100 ppm (pH=5) was prepared. Different anions were used to adjust the types of interfering anions in the PFOA solution, with the concentration also set to 100 ppm. The interfering metal ions were Cl... - NO3 - SO4 2- CO3 2- F - 10 mg of I@COF-CQWU-2 was mixed with 10 ml of perfluorooctanoic acid (PFOA) solution with different anions and a concentration of 100 ppm. The mixture was stirred at a constant temperature of 298 K for 480 min. The adsorption performance of I@COF-CQWU-2 on PFOA solution was recorded by liquid chromatography under the presence of different anions.

[0057] In Example 1, the adsorption capacity of I@COF-CQWU-2 for perfluorooctanoic acid (PFOA) solution remained above 99% of the initial adsorption capacity even in the presence of different anions. This indicates that in common aquatic anion coexistence systems, inorganic anions have almost no competitive inhibitory effect on the adsorption of PFOA by I@COF-CQWU-2 (e.g., ...). Figure 9 (As shown).

[0058] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a novel ionic bipyridyl COF material, characterized in that, Includes the following steps: Step 1: Mix 2,2',6,6'-tetramethyl-4,4'-bipyridine, 2,2'-bipyridine-5,5'-dicarboxaldehyde, sodium hydroxide, thiomethylbenzene, and methanol to react 1 to obtain COF-CQWU-2; Step 2: The COF-CQWU-2 is placed in a mixed solution of iodomethane and chloroform to undergo reaction 2, thereby obtaining the novel ionic bipyridyl COF material.

2. The preparation method according to claim 1, characterized in that, In step 1, the ratio of the amount of 2,2',6,6'-tetramethyl-4,4'-bipyridine to 2,2'-bipyridine-5,5'-dicarboxaldehyde, sodium hydroxide, trimethylbenzene and methanol is (0.4~0.8) mmol : (0.8~1.6) mmol : (175~350) mg : (20~40) ml : (30~40) ml.

3. The preparation method according to claim 1, characterized in that, In step 1, the temperature of reaction 1 is 100~200℃, and the reaction time is 1~7 days.

4. The preparation method according to claim 1, characterized in that, In step 2, the ratio of COF-CQWU-2 to iodomethane and chloroform is 50 mg: (1~20) mmol: (1~20) ml.

5. The preparation method according to claim 1, characterized in that, In step 2, reaction 2 is carried out at room temperature for 1 to 5 days, and stirring is performed during the reaction.

6. The preparation method according to claim 1, characterized in that, The reaction 1 is followed by a washing and drying step; the reaction 2 is followed by a washing and drying step.

7. A novel ionic bipyridyl COF material prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the novel ionic bipyridyl COF material as described in claim 7 in the adsorption of perfluoroalkyl compounds.

9. The application according to claim 8, characterized in that, The perfluoroalkyl compounds include perfluorooctanoic acid.

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