Preparation and application of cationic imidazole-fused covalent organic frameworks

Abstract

The application provides a preparation method and application of a cationic imidazole-fused covalent organic framework material. Based on a self-locking ring-forming reaction of o-phenylenediamine and aldehyde groups, the imidazole-fused covalent organic framework material is successfully synthesized under acid catalysis, and the material is in-situ functionalized and modified through "in-situ dissociation-recombination", and a cationic imidazole-fused covalent organic framework material is prepared. The material has excellent removal effect on Cr(IV), can selectively adsorb Cr(IV) under the interference of oxygen-containing acid radicals, and the adsorption capacity can reach 150mg·g ‑1 .

Description

Technical Field

[0001] This invention relates to the preparation of a cationic imidazole fused covalent organic framework material and its application as an adsorbent to remove Cr(VI) from the environment, belonging to the field of functional organic porous materials technology. Background Technology

[0002] With the rapid development of industry and agriculture, wastewater discharged from various industrial activities has caused serious harm to the environment. The large-scale discharge of heavy metal ions, in particular, seriously endangers human health and the ecological environment. Chromium ions are widely used in metal processing, electroplating, and fertilizer industries, and are discharged into the aquatic environment through industrial wastewater. Chromium exists in aqueous solutions mainly in the forms of trivalent (Cr(III)) and hexavalent (Cr(VI)) ions. Both ions pose a serious threat to human health, with Cr(VI) being more toxic than Cr(III). It is carcinogenic, teratogenic, and toxic; Cr(VI) accumulation in the human body can lead to various cancers, such as lung cancer, laryngeal cancer, bladder cancer, kidney cancer, and thyroid cancer. Therefore, developing novel, efficient, and environmentally friendly adsorption materials is crucial for the removal of Cr(VI).

[0003] Covalent organic frameworks (COFs) are highly ordered porous organic materials composed of organic monomers linked by covalent bonds. Their structure is entirely composed of light elements (H, B, C, N, and O). As an emerging functional material, COFs possess advantages such as large specific surface area, high porosity, high crystallinity, tunable pore size, and ease of functionalization. They have enormous application prospects in fields such as gas adsorption, pollutant removal, catalysis, and energy storage. Currently, traditional COF materials mainly fall into three categories: BO, CC, and CN. Although reversible covalent bonds endow COFs with many excellent properties, these COFs still have defects under certain conditions, such as hydrolysis under acidic conditions and structural instability. Therefore, this invention, based on the self-locking cyclization reaction of o-phenylenediamine and aldehyde groups, successfully synthesized imidazole-fused covalent organic framework materials under acid catalysis. Furthermore, the materials were in-situ functionalized through an "in-situ dissociation-recombination" process to prepare cationic imidazole-fused covalent valuable framework materials. The stability of COF is improved by transforming the reversible linkages in traditional COF into irreversible heterocyclic linkages, so that it can be used for the removal of Cr(VI) in the environment. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing cationic imidazole fused covalent organic framework materials to improve the stability of COF.

[0005] Another object of the present invention is to provide the application of this cationic imidazole fused covalent organic framework material as an adsorbent for the adsorption and removal of Cr(VI) in the environment.

[0006] I. Preparation of cationic imidazole fused covalent organic framework materials

[0007] 1) First, 1,2,4,5-phenyltetramine tetrahydrochloride, 1,3,5-trialdehydebenzene and 1,3-dimethylimidazolium bromide are added to the reaction tube in sequence and mixed evenly. Then, mesitylene, 1,4-dioxane and N-methyl-2-pyrrolidone are added to the above reaction tube in sequence and sonicated to form a uniform dispersion system.

[0008] The molar ratio of 1,2,4,5-phenyltetramine tetrahydrochloride, 1,3,5-tricarboxyphenyl and 1,3-dimethylimidazolium bromide is (1.1~1.7):1:1; 1,3-dimethylimidazolium bromide is preferred as an inducer for cationic COFs; the volume ratio of mesitylene, 1,4-dioxane and N-methyl-2-pyrrolidone is (2~2.5):1:1, with N-methyl-2-pyrrolidone serving as both a reaction solvent and a reaction raw material;

[0009] The molar ratio of 1,3-dimethylimidazolium bromide to N-methyl-2-pyrrolidone is 1:(700~850).

[0010] 2) Vacuum the dispersion system from step 1), then introduce N2 into the system, repeat 3-5 times, and then seal the system; transfer the system to a muffle furnace, heat to 120℃, react at a constant temperature for 60-72 hours, then cool to room temperature for 6 hours to end the reaction;

[0011] 3) Remove the system after the reaction in step 2) from the muffle furnace, centrifuge, wash with anhydrous ethanol, and vacuum dry the product at 75~85℃ to obtain the crude product.

[0012] 4) The crude product obtained in step 3) is subjected to Soxhlet extraction, and then vacuum dried at 60~70℃ for 10~15h to obtain cationic imidazole fused covalent organic framework material.

[0013] Synthetic Mechanism: The cationic imidazole-fused covalent organic framework material was prepared in four steps using 1,2,4,5-phenyltetramine tetrahydrochloride and 1,3,5-trialdehydebenzene as starting materials in a mixture of mesitylene, 1,4-dioxane, and N-methyl-2-pyrrolidone, via a phenyltetramine tetrahydrochloride dissociation reaction, a self-locking cyclization reaction, an NMP-catalyzed ring-opening reaction, and an electrophilic substitution-rearrangement reaction. The reaction steps are as follows:

[0014]

[0015] II. Structural Characterization of Cationic Imidazole Fused Covalent Organic Framework Materials

[0016] Fourier transform infrared spectrum as follows Figure 1 As shown, 3345.82cm can be seen. -1 3228.57cm -1 The absorption peak at 1618.68 cm⁻¹ is attributed to the -NH stretching vibration in the imidazole ring of the material; -1 A new peak appears at 2960.61 cm⁻¹, which is caused by the -C=N stretching vibration in the newly formed imidazole ring. -1 2856.40 cm -1 The peak appearing at this point is attributed to the -CH stretching vibration of the alkyl group, which confirms that N-methyl-2-pyrrolidone participated in the post-modification of COF as a reactant, indicating the successful synthesis of cationic imidazole fused COF.

[0017] Thermogravimetric analysis diagram as follows Figure 2 As shown, the material maintains structural stability up to 200°C and only begins to lose weight after 200°C, indicating that the material has good thermal stability.

[0018] Scanning electron microscope image as follows Figure 3 As shown, the material exhibits an elongated coral shape, with a length of approximately 400nm-500nm and a width of approximately 100nm-150nm, and these elongated corals are stacked in layers.

[0019] Transmission electron microscope image as follows Figure 4 As shown, the material exhibits a clear elongated coral shape, consistent with the scanning electron microscope (SEM) results. It also displays a hollow structure, which is due to the porous structure formed during the COF forming process.

[0020] III. Performance Evaluation of Cationic Imidazole Fused Covalent Organic Framework Materials

[0021] 1. Adsorption of hexavalent chromium ions

[0022] 1) Preparation of hexavalent chromium ion solution: Dissolve K2Cr2O7 in distilled water to prepare a Cr(VI) stock solution with a concentration of 1000 mg / L. Dilute with an appropriate amount of distilled water to prepare a working solution with a concentration of 50 mg / L. Adjust the pH of the solution to 2 with HCl and NaOH.

[0023] 2) Hexavalent chromium ion adsorption process: Take 30 mL of Cr(VI) solution with pH 2 and a concentration of 50 mg / L and mix it with 12 mg of the material. Shake the mixture on a shaker for 5 min to reach adsorption saturation. Then, centrifuge to separate the adsorbent, take the supernatant, and measure the concentration of residual Cr(VI) in the supernatant at 540 nm using the 1,5-diphenylcarbazide method with a UV-Vis spectrophotometer.

[0024] The UV spectra of the material before and after Cr(VI) adsorption are as follows: Figure 5 As shown in the figure, under the above adsorption conditions, the absorbance of the 50 mg / L Cr(VI) solution was 1.1433 before adsorption, and 0.1684 after adsorption. It can be seen that the absorbance values ​​before and after adsorption differ significantly, indicating that almost all chromium ions are adsorbed, demonstrating that the material has a highly efficient adsorption capacity for hexavalent chromium ions.

[0025] Adsorption mechanism: Under acidic conditions (pH=2~6), the main species form of chromium is dichromate (Cr2O7). 2− ) and dichromate (HCrO4) − They are abbreviated as A. 2- and HA - Cationic imidazole fused covalent organic framework materials are abbreviated as R. + Cl - It is related to A 2- and HA - The adsorption mechanism between them is as follows:

[0026] 2R + Cl - + A 2- →2R + A 2- + 2Cl -

[0027] R + Cl - + HA - →R + A 2- + Cl -

[0028] That is, Cr2O7 2− HCrO4 − With -NH2Me + R is caused by strong electrostatic interaction forces. + Cl - Cl in - With Cr2O7 2− and HCrO4 − Ion exchange forms more stable ion pairs.

[0029]

[0030] 2. Adsorption selectivity

[0031] 1) Preparation of mixed solutions of different metal cations and Cr(VI): Dissolve 61.89 mg of anhydrous MgSO4, 54.98 mg of ZnSO4•7H2O, 55.98 mg of NiSO4•6H2O, 31.39 mg of anhydrous CuSO4 and 35.4 mg of K2Cr2O7 in distilled water to prepare a mixed solution of multiple metal ions with a concentration of 50 mg / L.

[0032] 2) Preparation of mixed solutions of different anions and Cr(VI): Dissolve 5 mg of NaCl, 5 mg of Na2SO4, 5 mg of NaHCO3, 5 mg of Na2CO3, 5 mg of NaNO3 and 35.35 mg of K2Cr2O7 in distilled water to prepare a mixed solution of different anions with a concentration of 50 mg / L.

[0033] 3) Adsorption process: Take 30 mL of a mixed solution with a pH of 2 and a concentration of 50 mg / L and mix it with 12 mg of the material. Shake the mixture on a shaker for 5 min to reach adsorption saturation. Then, centrifuge to separate the adsorbent, take the supernatant, and use a UV-Vis spectrophotometer to measure the concentration of residual Cr(VI) in the supernatant at 540 nm using the 1,5-diphenylcarbazide method.

[0034] Adsorption diagrams of hexavalent chromium ions in the presence of different metal cations are shown below. Figure 6 Under the above adsorption conditions, when different metal cations coexist with Cr(VI), the material still exhibits excellent adsorption selectivity for Cr(VI), with very little adsorption for other metal ions, and the adsorption is almost unaffected by other metal ions.

[0035] Adsorption diagrams of hexavalent chromium ions in the presence of different anions are shown below. Figure 7 Under the above adsorption conditions, when different anions coexist with Cr(VI), the adsorption of Cr(VI) by the material is hardly affected by other anions, and its removal rate can still reach more than 80%.

[0036] The above experiments demonstrate that the material has excellent selectivity and can achieve efficient adsorption of Cr(VI) under complex conditions, indicating that the material has broad application prospects for adsorbing Cr(VI) in complex environments.

[0037] The present invention has the following advantages over the prior art:

[0038] 1. This invention is the first to synthesize a cationic imidazole fused covalent organic framework material using a one-pot solvothermal method, without the need for post-modification reactions;

[0039] 2. The cationic imidazole fused covalent organic framework material synthesized in this invention uses 1,2,4,5-phenyltetramine hydrochloride and 1,3,5-trialdehydebenzene as reaction raw materials, which are simple, readily available, and reasonably priced.

[0040] 3. In this invention, 1,3-dimethylimidazolium bromide is selected as a stabilizer and inducer to ensure the stability of the cationic imidazolium fused covalent framework material; the selected solvent N-methyl-2-pyrrolidone can be used as both a reaction solvent and a post-modification raw material.

[0041] 4. The cationic imidazole fused covalent organic framework material synthesized in this invention can be directly used to remove Cr(VI) from acidic solutions with a pH of 1 to 3, with a removal rate of over 95%. Attached Figure Description

[0042] Figure 1 This is the Fourier transform infrared spectrum of the material in the embodiment of the present invention.

[0043] Figure 2 This is a thermogravimetric analysis diagram of the material in an embodiment of the present invention.

[0044] Figure 3 These are scanning electron microscope images of the materials in the embodiments of the present invention.

[0045] Figure 4 This is a transmission electron microscope image of the material in an embodiment of the present invention.

[0046] Figure 5 This is the ultraviolet spectrum of the material before and after adsorption of hexavalent chromium ions in the embodiments of the present invention.

[0047] Figure 6 This is an adsorption diagram of hexavalent chromium ions in the presence of different metal cations in the embodiments of the present invention.

[0048] Figure 7 This is an adsorption diagram of hexavalent chromium ions in the presence of different anions in the embodiments of the present invention. Detailed Implementation

[0049] The present invention will be further explained and described below with reference to specific embodiments. Example

[0050] 1) 150.4 mg (0.53 mM) of 1,2,4,5-phenyltetramine tetrahydrochloride, 56.6 mg (0.35 mM) of 1,3,5-trialdehydebenzene, and 23.5 mg (0.35 mM) of 1,3-dimethylimidazolium bromide were added sequentially to a 100 mL reaction tube. Then, 10 mL of mesitylene, 5 mL of 1,4-dioxane, and 5 mL of N-methyl-2-pyrrolidone were measured with a graduated cylinder and added sequentially to the above 100 mL reaction tube. The mixture was then sonicated for 30 s to obtain a uniformly dispersed system.

[0051] 2) After vacuuming and purging with nitrogen three times, the reaction system was sealed and placed in a muffle furnace. The reaction temperature was increased from 25°C to 120°C over 30 minutes and then maintained at 120°C for 72 hours. After the reaction was completed, the temperature was cooled from 120°C to room temperature over 6 hours.

[0052] 3) Remove the reaction system from the muffle furnace, centrifuge at 11000 r / min for 8 min, wash the product 5 times with anhydrous ethanol, and then vacuum dry the product at 80℃ for 12 h to obtain the crude product.

[0053] 4) The dried crude product was further extracted with acetone solvent at 90°C for 120 h using a Soxhlet extractor, and then vacuum dried at 70°C for 12 h. Finally, cationic imidazole fused COF was obtained.

[0054] Structural characterization and performance evaluation are described above.

Claims

1. A method for preparing a cationic imidazole fused covalent organic framework material, characterized in that, Includes the following steps: 1) First, 1,2,4,5-phenyltetramine tetrahydrochloride, 1,3,5-trialdehydebenzene and 1,3-dimethylimidazolium bromide are added to the reaction tube in sequence and mixed evenly. Then, mesitylene, 1,4-dioxane and N-methyl-2-pyrrolidone are added to the above reaction tube in sequence and sonicated to form a uniform dispersion system. 2) Vacuum the dispersion system from step 1), then introduce N2 into the system, repeat 3-5 times, and then seal the system; transfer the system to a muffle furnace, heat to 120℃, react at a constant temperature for 60-72 hours, then cool to room temperature for 6 hours to end the reaction; 3) Remove the system after the reaction in step 2) from the muffle furnace, centrifuge, wash with anhydrous ethanol, and vacuum dry the product at 75~85℃ to obtain the crude product. 4) The crude product obtained in step 3) is subjected to Soxhlet extraction, and then vacuum dried at 60~70℃ for 10~15h to obtain cationic imidazole fused covalent organic framework material.

2. The method for preparing a cationic imidazole fused covalent organic framework material as described in claim 1, characterized in that, The molar ratio of 1,2,4,5-phenyltetramine tetrahydrochloride, 1,3,5-tricarboxymethylbenzene and 1,3-dimethylimidazolium bromide is (1.1~1.7):1:

1.

3. The method for preparing a cationic imidazole fused covalent organic framework material as described in claim 1, characterized in that, The volume ratio of the mesitylene, 1,4-dioxane and N-methyl-2-pyrrolidone is (2~2.5):1:

1.

4. The method for preparing a cationic imidazole fused covalent organic framework material as described in claim 1, characterized in that, The molar ratio of 1,3-dimethylimidazolium bromide to N-methyl-2-pyrrolidone is 1:(700~850).

5. The application of a cationic imidazole fused covalent organic framework material prepared by the method described in claim 1 as an adsorbent for the adsorption and removal of Cr(VI) from a solution.

6. The application of the cationic imidazole fused covalent organic framework material as described in claim 5 as an adsorbent for the adsorption and removal of Cr(VI) from solution, characterized in that, Includes the following steps: 1) Preparation of hexavalent chromium ion solution: Dissolve K2Cr2O7 in distilled water to prepare a Cr(VI) stock solution with a concentration of 1000 mg / L, and dilute with an appropriate amount of distilled water to prepare a working solution with a concentration of 50 mg / L; adjust the pH of the solution to 2-6 with HCl and NaOH. 2) Hexavalent chromium ion adsorption process: Take 30 mL of Cr(VI) solution with pH 2~6 and concentration of 50 mg / L and mix it with 12 mg of material. Shake on a shaker for 5 min to reach adsorption saturation. Then, centrifuge to separate the adsorbent, take the supernatant, and use a UV-Vis spectrophotometer to measure the concentration of residual Cr(VI) in the supernatant at 540 nm using the 1,5-diphenylcarbazide method.

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