CN115716915A - Preparation method and application of polyimide covalent organic framework - Google Patents

Abstract

The invention discloses a preparation method and application of a polyimide covalent organic framework, belonging to the technical field of environmental protection. In the present invention, 5,5', 5'-(1,3,5-triazine-2,4,6-triyl) tris(pyridine-2-amine) and pyromellitic dianhydride are reacted through imide Preparation of polyimide covalent organic framework; the polyimide covalent organic framework uses C4N imide five-membered ring as the connecting unit, and there are a large number of pyridine nitrogen functional groups around the five-membered ring, which can be used for efficient adsorption and reduction of uranium Acyl ions, and has good adsorption selectivity for uranyl ions in rare earth tailings waste liquid. The polyimide covalent organic framework prepared by the invention has the advantages of simple preparation method, high crystallinity, regular pore structure, fast adsorption rate and good selectivity for uranyl ions, and can be used as an efficient adsorption reducing agent for uranyl ions.

Description

Preparation method and application of a polyimide covalent organic framework

technical field

The invention belongs to the technical field of environmental protection, and in particular relates to a preparation method and application of a polyimide covalent organic framework.

Background technique

The development and utilization of rare earth resources has greatly promoted economic and social development, but the improper disposal of rare earth tailings waste liquid has led to the problem of radioactive uranium pollution. Uranium is radioactive and chemically toxic, posing a threat to ecosystems and human health. Therefore, the development of new and efficient uranium adsorbents is crucial for the sustainable development of the rare earth industry. Covalent organic frameworks (COFs) are promising adsorbents due to their high crystallinity, regular channel structure, and high chemical hydrolytic stability. Currently, Schiff base COFs, sp ² c COFs and polyarylether COFs have been used for the adsorption of uranyl ions (UO ₂ ²⁺ ). Schiff base COFs are connected by highly reversible imine bonds, which have poor stability and affect their practical performance (W.-R.Cui, F.-F.Li, R.-H.Xu, C.-R. Zhang, X.-R. Chen, R.-H. Yan, R.-P. Liang, J.-D. Qiu, Regenerable covalent organic frameworks for photo-enhanced uranium adsorption from seawater, Angew. Chem. Int. Ed. 59 (2020) 17684-17690.). sp ² c COFs and polyarylether COFs are connected by irreversible carbon-carbon double bonds and ether bonds, respectively, and have good stability in practical applications (W.-R. Cui, C.-R. Zhang, W. Jiang, F.-F.Li, R.-P.Liang, J.Liu, J.-D.Qiu, Regenerable and stable sp ² carbon-conjugated covalent organic frameworks for selective detection and extraction of uranium, Nat.Commun.11(2020 )436.; X.Guan, H.Li, Y.Ma, M.Xue, Q.Fang, Y.Yan, V.Valtchev, S.Qiu, Chemically stable polyarylether-based covalent organic frameworks, Nature Chem.11(2019 ) 587-594.). Recently, the construction of polyimide COFs (termed PI-COFs) via an irreversible imide condensation reaction has attracted attention. Due to its excellent thermal stability, chemical stability, radiation resistance and outstanding mechanical properties, PI-COF is of great significance in applications (Q. Fang, Z. Zhuang, S. Gu, RB Kaspar, J. Zheng, J . Wang, S. Qiu, Y. Yan, Designed synthesis of large-pore crystalline polyimide covalent organic frameworks, Nat. Commun.5(2014) 4503.). In addition, rational design of targeted UO ₂ ²⁺ nanotrap is a powerful means to prepare novel highly efficient UO ₂ ²⁺ adsorbents (ASIvanov, BFParker, Z. Zhang, B. Aguila, Q. Sun, S. Ma, S. Jansone- Popova, J. Arnold, RT Mayes, S. Dai, VS Bryantsev, L. Rao, I. Popovs, Siderophore-inspired chelator hijacks uranium from aqueous medium, Nat. Commun. 10 (2019) 819). However, the development of PI-COF is still in its infancy, and its application in radionuclide extraction and removal has not yet been seen, and the design of highly selective UO ₂ ²⁺ nano-trap is still a difficulty in the field of radionuclide removal.

Contents of the invention

The object of the present invention is to provide a preparation method and application of a polyimide covalent organic framework. The present invention uses nitrogen-rich monomer 5,5',5'-(1,3,5-triazine-2,4,6-triyl)tris(pyridin-2-amine) (TTPA) and pyromellitic acid A novel polyimide covalent organic framework, PI-COF-6, was prepared by imide reaction between dianhydrides (PMDA). A large number of pyridine nitrogen functional groups in the nitrogen-rich monomer TTPA not only improve the affinity of PI-COF-6 for UO ₂ ²⁺ , but also the pyridine nitrogen in TTPA is compatible with the tertiary amine nitrogen and carbonyl oxygen in the five-membered ring of C4N imide. Synergistically, a new type of UO ₂ ²⁺ capture nano-trap (NNO) was constructed, which made PI-COF-6 have excellent adsorption selectivity and reduction ability for UO ₂ ²⁺ , which can be used to treat UO ₂ ² in rare earth tailings waste liquid ⁺ efficient adsorption. The polyimide covalent organic framework prepared by the method of the invention has the characteristics of simple preparation method, high crystallinity, regular pore structure, fast adsorption rate and good selectivity for UO ₂ ²⁺ , and has good application prospects.

To achieve the above object, the present invention specifically adopts the following technical solutions:

The invention provides a method for preparing a polyimide covalent organic framework, comprising the following steps:

1) Using 5,5',5'-(1,3,5-triazine-2,4,6-triyl) tri(pyridin-2-amine) and pyromellitic dianhydride as reaction raw materials, and then Adding N-methyl-2-pyrrolidone and 1,3,5-mesitylene, ultrasonically treating the mixture, adding isoquinoline to obtain a reaction mixture;

2) Degas the container containing the reaction mixture through a freeze-thaw cycle, heat it at 160-240°C for 3-7 days after sealing the flame, cool and filter to collect the precipitate, wash and dry to obtain a polyimide covalent organic framework .

Further, step 1) described 5,5',5'-(1,3,5-triazine-2,4,6-triyl)tris(pyridin-2-amine) and pyromellitic dianhydride The ratio of the amount of substance is (0.1-1):1.

Further, the volume ratio of N-methyl-2-pyrrolidone, 1,3,5-mesitylene and isoquinoline in step 1) is (5-15):(5-15):1.

The present invention also provides the application of the polyimide covalent organic framework obtained by the above preparation method in adsorbing uranyl ions.

Further, the polyimide covalent organic framework can selectively adsorb and remove uranyl ions in the presence of various interfering ions; the interfering ions include Y ³⁺ , Sc ³⁺ , La ³⁺ , Ce ³⁺ , Pr ³⁺ , Nd ³⁺ , Sm ³⁺ , Eu ³⁺ , Gd ³⁺ , Tb ³⁺ , ^{Dy 3+} , Ho ³⁺ , Er 3+ , Tm ³⁺ , Yb ³⁺ , Lu ³⁺ , Co ²⁺ , Mg ²⁺ , Al ³⁺ , Fe ³⁺ , Ca ²⁺ , Na ⁺ , Zn ²⁺ , Cu ²⁺ , Ni ²⁺ , Pb ²⁺ , Sr ²⁺ and K ⁺ .

Further, the polyimide covalent organic framework can reduce U(VI) to U(IV) during the process of adsorbing uranyl ions.

Compared with prior art, the beneficial effect of the present invention is:

(1) The present invention adopts a one-step method to synthesize polyimide covalent organic framework, the preparation method is simple, the crystallinity is high, the pore structure is regular, and it can be used for adsorbing UO ₂ ²⁺ without post-treatment.

(2) The polyimide covalent organic framework with the C4N imide five-membered ring as the linking unit prepared by the present invention contains a large amount of pyridine nitrogen functional groups around the imide five-membered ring, which improves UO ₂ ²⁺ affinity.

(3) The polyimide covalent organic framework prepared by the present invention constructs NNO nano-trap as the UO ₂ ²⁺ adsorption group, replacing the traditional amidoxime functional group, which is beneficial to the sustainable development of the ecological environment.

(4) The polyimide covalent organic framework prepared by the present invention has excellent adsorption selectivity for UO ₂ ^{2 +} under the coexistence condition of various interfering metal ions.

(5) The polyimide covalent organic framework prepared by the present invention can also reduce U(VI) to U(IV) during the process of adsorbing UO ₂ ²⁺ , which is beneficial to the solidification of uranium.

(6) The polyimide covalent organic framework prepared by the present invention realizes the rapid and selective adsorption of UO ₂ ²⁺ in rare earth tailings waste liquid, is an efficient adsorbent and remover of UO ₂ ²⁺ , and has good Application prospects.

Description of drawings

Figure 1 is a schematic diagram of the preparation process of polyimide covalent organic framework PI-COF-6.

Figure 2 is the experimental test PXRD pattern and AA stacking structure simulation PXRD pattern of PI-COF-6.

Fig. 3 is the infrared spectrogram of PMDA, TTPA and PI-COF-6.

Figure 4 is the adsorption isotherm diagram of PI-COF-6 on UO ₂ ²⁺ .

Fig. 5 is the adsorption kinetic diagram of PI-COF-6 on UO ₂ ²⁺ .

Figure 6 is the adsorption selectivity diagram of PI-COF-6 for UO ₂ ²⁺ in rare earth tailings waste liquid.

Figure 7 is the high-resolution XPS diagram of U 4f after PI-COF-6 adsorbed UO ₂ ²⁺ .

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with embodiments. Those who do not indicate the specific conditions in the examples are carried out according to the conventional conditions or the conditions suggested by the manufacturer. The reagents or instruments used were not indicated by the manufacturer, and they were all conventional products that could be purchased from the market.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field of the invention. The terms used in the description of the present invention are only for the purpose of describing specific embodiments, and are not used to limit the present invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Example 1: Preparation and Characterization of Polyimide Covalent Organic Framework

5,5',5'-(1,3,5-triazine-2,4,6-triyl)tris(pyridin-2-amine) (TTPA, 35.7mg), pyromellitic dianhydride ( PMDA, 32.7mg), N-methyl-2-pyrrolidone (0.50mL) and 1,3,5-mesitylene (0.50mL) were loaded into a 15mL Pyrex tube, sonicated for 10 minutes, and then added iso quinoline (0.05mL) to obtain the reaction mixture; after the Pyrex tube containing the reaction mixture was degassed through three freezing pump-thaw cycles, the flame was sealed and heated in an oven at 200°C for 5 days, and after cooling Filter, wash the obtained brick red solid product with anhydrous tetrahydrofuran (THF) several times, collect the solid, and dry it in vacuum at 80°C for 12 hours to obtain the polyimide covalent Organic Framework (PI-COF-6).

Figure 1 is a schematic diagram of the preparation process of polyimide covalent organic framework PI-COF-6.

The crystal structure of polyimide covalent organic framework PI-COF-6 was characterized by powder X-ray diffraction (PXRD). Figure 2 is the experimental test PXRD pattern of PI-COF-6 and the PXRD pattern of AA stacking structure simulation. It can be seen from Figure 2 that the 2θ of PI-COF-6 has a strong diffraction peak of the (110) crystal plane at 2.93°, and (200), (220) and ( 310) diffraction peaks of the crystal plane, the PXRD pattern measured by the experiment of PI-COF-6 matches the PXRD pattern simulated by the AA stacking structure, indicating that the polyimide covalent organic framework PI-COF-6 prepared by the method of the present invention high crystallinity.

Fig. 3 is the infrared spectrogram of PMDA, TTPA and PI-COF-6. It can be seen from Figure 3 that, compared with the infrared spectra of PMDA and TTPA, new absorption bands appear in the infrared spectra of PI-COF-6 at 1777cm ^-1 , 1721cm ^-1 and 1367cm ^-1 , corresponding to the The C=O asymmetric vibration and symmetric vibration in the amine ring as well as the CNC stretching vibration indicate that the polyimide covalent organic framework linked by imide five-membered rings has been successfully prepared in the present invention.

The porosity of polyimide covalent organic framework PI-COF-6 was measured by _N2 adsorption-desorption experiment, combined with non-localized density functional theory (NLDFT) calculation, it can be known that PI-COF-6 has a regular pore size distribution .

The characterization results of PXRD, infrared spectroscopy and _N2 adsorption-desorption experiments prove that the present invention has successfully prepared polyimide covalent organic framework PI with high crystallinity, regular pore structure and C4N imide five-membered ring as the connecting unit. -COF-6.

Example 2: Adsorption and removal of UO ₂ ²⁺ by PI-COF-6

(1) The effect of the initial concentration of UO ₂ ²⁺ on the adsorption of UO ₂ ²⁺ on PI-COF-6 was studied.

Add 5mg of polyimide covalent organic framework PI-COF-6 to 25mL aqueous solution containing different concentrations of UO ₂ ²⁺ (20-300mg/L), shake for 12 hours with a constant temperature oscillator, filter through 0.22μm microporous For membrane filtration, the content of UO ₂ ²⁺ in the filtrate was measured by inductively coupled plasma mass spectrometry, and the adsorption capacity of PI-COF-6 for UO ₂ ²⁺ was calculated. Figure 4 is the adsorption isotherm diagram of PI-COF-6 on UO ₂ ²⁺ . It can be seen from Figure 4 that due to the large driving force of the concentration gradient at the solid-liquid interface, the adsorption capacity of PI-COF-6 for UO ₂ ²⁺ increases with the increase of UO ₂ ²⁺ concentration until it reaches equilibrium. It conforms to the Langmuir model, indicating that PI-COF-6 is a single-layer adsorption for UO ₂ ²⁺ , and the maximum adsorption capacity for UO ₂ ²⁺ is 424.5mg/g.

(2) The effect of adsorption time on the adsorption of UO ₂ ²⁺ on PI-COF-6 was studied.

Add 5mg of polyimide covalent organic framework PI-COF-6 into 250mL aqueous solution containing 30mg/L UO ₂ ²⁺ , stir for different time, take samples, filter with 0.22μm microporous membrane, and use inductively coupled plasma The content of UO ₂ ^{2 +} in the filtrate was measured by mass spectrometry, and the adsorption capacity of PI-COF-6 for UO ₂ ²⁺ was calculated. Fig. 5 is the adsorption kinetic diagram of PI-COF-6 on UO ₂ ²⁺ . It can be seen from Figure 5 that the adsorption kinetics of PI-COF-6 to UO ₂ ²⁺ is fast, the adsorption capacity increases rapidly within 40 minutes, and reaches saturated adsorption in 60 minutes, indicating that the adsorption of PI-COF-6 on UO ₂ ²⁺ efficient. This is because the PI-COF-6 prepared in the present invention uses the C4N imide five-membered ring as the connecting unit, and contains a large number of pyridine nitrogen functional groups around the imide five-membered ring, which improves the affinity for UO ₂ ²⁺ . At the same time, the regular pore size distribution in the polyimide covalent organic framework PI-COF-6 facilitates the exposure of the binding sites and promotes the diffusion and mass transfer of UO ₂ ²⁺ .

Example 3: Adsorption selectivity and application of PI-COF-6 to UO ₂ ²⁺

The coexistence of metal ions (Y ³⁺ , Sc ³⁺ , La ³⁺ , Ce ³⁺ , Pr ³⁺ , Nd ³⁺ , Sm ³⁺ , Eu ³⁺ , Gd ³⁺ , Tb ³⁺ , Dy ³⁺ , Ho ^{3 +} , Er ³⁺ , Tm ³⁺ , Yb ³⁺ , Lu ³⁺ , Co ²⁺ , Mg ²⁺ , Al ³⁺ , Fe ³⁺ , Ca ²⁺ , Na ⁺ , Zn ²⁺ , Cu ²⁺ , Ni ²⁺ , Pb ²⁺ , Sr ²⁺ and K ⁺ ) on the selectivity of UO ₂ ²⁺ adsorption on PI-COF-6. Add 3 mg of PI-COF-6 to 30 mL of rare earth tailings waste liquid, stir for 12 h, filter with a 0.22 μm microporous membrane, and use inductively coupled plasma mass spectrometry to measure the content of UO ₂ ²⁺ and other metal ions in the filtrate, Calculate the removal efficiency of PI-COF-6 for UO ₂ ²⁺ and other metal ions. Figure 6 is the adsorption selectivity diagram of PI-COF-6 for UO ₂ ²⁺ in rare earth tailings waste liquid. It can be seen from Figure 6 that in the presence of mixed metal ions, the removal rate of PI-COF-6 for UO ₂ ²⁺ is still as high as 96.5%, while for other metal ions including lanthanide metal elements, transition metal elements and main group metal elements The removal rates were all lower than 4%, indicating that PI-COF-6 had good selectivity for UO ₂ ²⁺ adsorption. The coordination of PI-COF-6 to UO ₂ ²⁺ mainly relies on the NNO nanotrap constructed by the synergistic action of the pyridine nitrogen in the nitrogen-rich monomer TTPA, the tertiary amine nitrogen on the C4N imide and the carbonyl oxygen. PI-COF-6 selectively chelates UO ₂ ²⁺ through NNO nano-trap, which makes PI-COF-6 have excellent adsorption selectivity for UO ₂ ²⁺ .

The change of valence state of uranium after PI-COF-6 adsorbed UO ₂ ²⁺ was characterized by X-ray photoelectron spectroscopy (XPS). Figure 7 is the high-resolution XPS diagram of U 4f after PI-COF-6 adsorbed UO ₂ ²⁺ . It can be seen from Figure 7 that U(VI) and U(IV) exist in PI-COF-6 after adsorption of UO ₂ ²⁺ , indicating that the covalent organic framework of polyimide PI-COF-6 is effective in the adsorption of UO ₂ ²⁺ In the process, U(VI) can also be reduced to U(IV), which is beneficial to the solidification of radioactive pollutant uranium.

The above-described embodiments only express several preferred embodiments of the present invention, and the descriptions thereof are more specific and detailed, but are not intended to limit the present invention. It should be pointed out that for those skilled in the art, the present invention can also have various changes and modifications, and any modifications, equivalent replacements, improvements, etc. within the concept and principles of the present invention should be included in the within the protection scope of the present invention.

Claims (6)

1. a preparation method of polyimide covalent organic framework, is characterized in that, comprises the following steps: 1) Using 5,5',5'-(1,3,5-triazine-2,4,6-triyl) tri(pyridin-2-amine) and pyromellitic dianhydride as reaction raw materials, and then Adding N-methyl-2-pyrrolidone and 1,3,5-mesitylene, ultrasonically treating the mixture, adding isoquinoline to obtain a reaction mixture; 2) Degas the container containing the reaction mixture through a freeze-thaw cycle, heat it at 160-240°C for 3-7 days after sealing the flame, cool and filter to collect the precipitate, wash and dry to obtain a polyimide covalent organic framework . 2. The preparation method of a polyimide covalent organic framework according to claim 1, characterized in that 5,5',5'-(1,3,5-triazine-2 , 4,6-triyl)tris(pyridin-2-amine) and pyromellitic dianhydride in a mass ratio of (0.1-1):1. 3. the preparation method of a kind of polyimide covalent organic frame according to claim 1, is characterized in that, step 1) described N-methyl-2-pyrrolidone, 1,3,5-mesitylene and The volume ratio of isoquinoline is (5-15):(5-15):1. 4. The application of the polyimide covalent organic framework obtained by the preparation method described in any one of claims 1-3 in adsorbing uranyl ions. 5. according to the application of the polyimide covalent organic framework in the adsorption of uranyl ions according to claim 4, it is characterized in that, the polyimide covalent organic framework can be selected under the condition that multiple interfering ions exist The various interfering ions include Y ³⁺ , Sc ³⁺ , La ³⁺ , Ce ³⁺ , Pr ³⁺ , Nd ³⁺ , Sm ³⁺ , Eu ³⁺ , Gd ³⁺ , Tb ³⁺ , Dy ³⁺ , Ho ³⁺ , Er ³⁺ , ^{Tm 3+} , Yb ³⁺ , Lu ³⁺ , Co ²⁺ , Mg ²⁺ , Al ³⁺ , Fe ³⁺ , Ca ²⁺ , Na ⁺ , Zn ²⁺ , Cu ²⁺ , Ni ²⁺ , Pb ²⁺ , Sr ²⁺ and K ⁺ . 6. according to the application of the polyimide covalent organic framework in the adsorption of uranyl ions according to claim 4, it is characterized in that, in the process of adsorbing uranyl ions, the polyimide covalent organic framework can U(VI) reverts to U(IV).

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