Eu3+ ion doped nitrogen-rich covalent organic frameworks, preparation method and application thereof
By designing a nitrogen-rich covalent organic framework containing europium ions, the problem of limited functionality and low efficiency of COFs materials in tetracycline detection and removal was solved, achieving a "two-in-one" effect of high-sensitivity fluorescence sensing and high-efficiency photocatalysis, which is suitable for environmental monitoring and industrial water treatment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHANGCHUN UNIV OF SCI & TECH
- Filing Date
- 2026-03-16
- Publication Date
- 2026-06-12
Smart Images
Figure CN122188144A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of functional polymer materials technology, specifically relating to a nitrogen-rich covalent organic framework containing europium ions, its preparation method, and its application. Background Technology
[0002] Tetracycline, a broad-spectrum antibiotic, is widely used in medicine, aquaculture, and animal husbandry due to its significant inhibitory effect on both Gram-positive and Gram-negative bacteria and its low cost. However, its overuse has triggered a public health crisis, leading to increased bacterial resistance and a heightened risk of water pollution. Therefore, developing a material capable of rapidly and sensitively detecting and efficiently removing tetracycline is not only an urgent need to ensure public health and safety but also plays a crucial role in achieving sustainable ecological development.
[0003] In current tetracycline detection technologies, fluorescence detection has become a research hotspot due to its advantages such as high sensitivity, ease of operation, and low cost. Europium ion fluorescent sensing materials are particularly prominent in fluorescence detection methods. The unique characteristics of europium ions, such as long-wavelength emission, narrow emission band, and long excited-state lifetime, enable efficient detection of tetracycline. However, europium ions as fluorescent materials often face two important problems: poor stability of the matrix coordinated with europium ions during detection; and the ability of solvent molecules (such as water) to coordinate with unsaturated europium(III) ions, enhancing the non-radiative quenching effect, leading to decreased fluorescence or even quenching of europium(III) complexes when detecting tetracycline. Therefore, developing new matrices with robust structures and abundant coordination sites to ensure the stability of europium ions during use and reduce fluorescence quenching, thereby improving the sensitivity of tetracycline detection, is of great significance. In tetracycline removal technologies, photocatalysis technology shows great application potential due to its environmental friendliness, energy efficiency, and sustainability. Photocatalysis technology is inseparable from photocatalysts. Traditional inorganic photocatalysts (such as TiO2) have a wide band gap, can only absorb ultraviolet light, and have a high recombination rate of photogenerated carriers, resulting in limited utilization of sunlight. While organic photosensitive molecules (such as porphyrins) have broad-spectrum absorption characteristics and high light absorption coefficients, they have problems such as difficulty in recycling and easy secondary pollution. These are also important problems faced by photocatalysts.
[0004] Covalent organic frameworks (COFs), as a class of crystalline porous cross-linked polymers, possess excellent chemical stability, tunable framework structure, and ordered pore arrangement, and have been widely used in sensing, catalysis, drug delivery, energy storage, and separation. However, existing COF materials still suffer from the following limitations in tetracycline detection and removal: functional limitation—traditional COF materials only possess a single function of detection or catalysis, making it impossible to simultaneously achieve highly sensitive fluorescence sensing and efficient photocatalytic degradation of tetracycline in the same material system; insufficient selectivity and sensitivity—the selectivity and anti-interference ability for tetracycline are poor, making them susceptible to interference from other organic compounds, resulting in a high detection limit and narrow detection range; and the tendency for photogenerated carrier recombination to occur during photocatalysis, leading to a decline in catalytic efficiency. These limitations make it difficult to meet the integrated environmental governance requirements of "detection-removal".
[0005] To address the aforementioned challenges, this invention innovatively designs and synthesizes a europium-ion-containing nitrogen-rich COF material (TAPP-TNBTA-COF@Eu) from a structural design perspective, solving the problems and achieving a dual function of fluorescence detection and photocatalytic degradation of tetracycline. This material exhibits high-sensitivity fluorescence sensing and efficient photocatalytic capability, demonstrating significant application value in environmental monitoring and industrial water treatment. Summary of the Invention
[0006] The purpose of this invention is to provide a europium-containing nitrogen-rich covalent organic framework with dual functions of fluorescence detection and photocatalysis, its preparation method, and its applications. This europium-containing nitrogen-rich covalent organic framework, through the precise action of strong chelating coordination sites and the structural advantages of an extended π-conjugated system, achieves trace detection, rapid response, and high selectivity for tetracyclines. It also possesses excellent photocatalytic activity, stability, and reusability, providing a promising solution for the efficient monitoring and removal of tetracycline pollutants in the environment.
[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention designs and develops a nitrogen-rich covalent organic framework containing europium ions, characterized in that its structural formula is shown in (I): (I).
[0008] Another aspect of the present invention provides a method for preparing the above-mentioned europium ion-containing nitrogen-rich covalent organic framework, comprising the following steps: ① Under nitrogen protection (or in a closed, oxygen-free environment), 5,10,15,20-tetra(4-aminophenyl)porphyrin and 1,4,7,10-tetra(4-nitrobenzyl)-1,4,7,10-tetraazacyclododecane are mixed in a molar ratio of 1:1 to 1:1.5, dissolved in a solvent (N,N-dimethylformamide or N,N-dimethylacetamide), ultrasonically dispersed, and then a small amount of potassium hydroxide catalyst is added. ② Slowly heat the mixed solution from step ① to 120~150 ℃ and stir and heat for 48~72 hours; ③ Cool the mixed solution from step ② to room temperature, add deionized water for precipitation, filter, and wash the filtrate 3-5 times in sequence with dichloromethane, ethyl acetate, and tetrahydrofuran. Filter under vacuum and dry the filtrate under vacuum to obtain a nitrogen-rich covalent organic framework. ④ Mix the nitrogen-rich covalent organic framework obtained in step ③ with europium nitrate hexahydrate at a mass ratio of 1:(1~10), disperse in acetonitrile, stir and heat to 60 °C, and maintain for 12~24 hours; ⑤ Cool the mixed solution from step ④ to room temperature, filter it, and wash the product by centrifugation with acetonitrile and dichloromethane 3-5 times in sequence. After vacuum drying, obtain a nitrogen-rich covalent organic framework containing europium ions.
[0009] In the above preparation method, preferably, the reaction atmosphere is nitrogen protection.
[0010] In the above preparation method, preferably, the molar ratio of 5,10,15,20-tetra(4-aminophenyl)porphyrin and 1,4,7,10-tetra(4-nitrobenzyl)-1,4,7,10-tetraazacyclododecane is 1:1.
[0011] In the above preparation method, preferably, the solvent is N,N-dimethylformamide.
[0012] In the above preparation method, preferably, the mass ratio of nitrogen-rich covalent organic framework to europium nitrate hexahydrate is 1:6.7.
[0013] This invention also provides an application of a europium-containing nitrogen-rich covalent organic framework, which can be used as a fluorescence sensing material and a photocatalyst for fluorescence detection and photocatalytic degradation of tetracycline.
[0014] The technical advantages of this invention are as follows: This invention employs a sophisticated structural design, first synthesizing a covalent organic framework with nitrogen-rich multiple coordination sites, and then coordinating and anchoring europium ions to the covalent organic framework. This structural design supports its dual applications. The abundant nitrogen atoms in the framework provide strong chelating coordination sites for europium ions, enabling rapid response and high selectivity for trace detection of tetracycline. On the other hand, the cross-linked framework, the extended π-conjugated system, and the europium ion doping allow for the modulation of the material's band structure, promoting the separation and transfer of photogenerated carriers, thereby generating reactive oxygen species to degrade tetracycline. This also improves the material's chemical stability and photocatalytic activity, solving problems such as low solar energy utilization, difficulty in separation and recovery, and easy secondary pollution associated with small-molecule photocatalysts, aligning with the concept of green and environmentally friendly sustainable development.
[0015] Compared with existing technologies, the europium-containing nitrogen-rich covalent organic framework of this invention possesses dual functionalities of fluorescence sensing and photocatalysis. It can serve as an "on-off" fluorescent sensing material, exhibiting excellent sensitivity (detection limit as low as 0.061 nM), rapid response (only 20 s), and interference-free selectivity (interfering factors: metal ions, amino acids, antibiotics, etc.) in tetracycline detection. Furthermore, the europium-containing nitrogen-rich covalent organic framework can also achieve photocatalytic oxidative degradation of tetracycline (20 mg / L), achieving a degradation rate of 83% within 60 minutes, and exhibits good reusability. In addition, the fluorescence sensing properties of this europium-containing nitrogen-rich covalent organic framework can be used to monitor the photocatalytic degradation process of tetracycline. Attached Figure Description
[0016] Figure 1 Synthetic route of nitrogen-rich covalent organic frameworks containing europium ions.
[0017] Figure 2 Infrared spectrum of the europium-containing nitrogen-rich covalent organic framework prepared in Example 1.
[0018] Figure 3 Solid-state carbon NMR spectrum of the europium-containing nitrogen-rich covalent organic framework prepared in Example 1.
[0019] Figure 4 Europium-containing nitrogen-rich covalent organic frameworks were used as fluorescence sensing materials. (a) The fluorescence spectrum of tetracycline was detected. (b) The linear relationship between fluorescence intensity and tetracycline concentration was shown.
[0020] Figure 5 The degradation rate curve of tetracycline by using europium-ion-functionalized nitrogen-rich covalent organic frameworks as photocatalysts. Detailed Implementation
[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation steps, but the present invention is not limited to the following examples.
[0022] This invention provides a method for preparing a europium-rich nitrogen covalent organic framework, specifically comprising the following steps: ① Under nitrogen protection (or in a closed, oxygen-free environment), 5,10,15,20-tetra(4-aminophenyl)porphyrin and 1,4,7,10-tetra(4-nitrobenzyl)-1,4,7,10-tetraazacyclododecane are mixed in a molar ratio of 1:(1~1.5), dissolved in a solvent (N,N-dimethylformamide or N,N-dimethylacetamide), ultrasonically dispersed, and then a small amount of potassium hydroxide catalyst is added; ② Slowly heat the mixed solution from step ① to 120~150 ℃ and stir and heat for 48~72 hours; ③ Cool the mixed solution from step ② to room temperature, add deionized water for precipitation, filter, and wash the filtrate 3-5 times in sequence with dichloromethane, ethyl acetate, and tetrahydrofuran. Filter under vacuum and dry the filtrate under vacuum to obtain a nitrogen-rich covalent organic framework. ④ Mix the nitrogen-rich covalent organic framework obtained in step ③ with europium nitrate hexahydrate at a mass ratio of 1:(1~10), disperse in acetonitrile, stir and heat to 60 °C, and maintain for 12~24 h; ⑤ Cool the mixed solution from step ④ to room temperature, filter it, and wash the product by centrifugation with acetonitrile and dichloromethane 3-5 times in sequence. After vacuum drying, obtain a nitrogen-rich covalent organic framework containing europium ions.
[0023] In the above preparation method, preferably, the molar ratio of 5,10,15,20-tetra(4-aminophenyl)porphyrin and 1,4,7,10-tetra(4-nitrobenzyl)-1,4,7,10-tetraazacyclododecane is 1:1.
[0024] In the above preparation method, preferably, the solvent is N,N-dimethylformamide.
[0025] In the above preparation method, preferably, the mass ratio of nitrogen-rich covalent organic framework to europium nitrate hexahydrate is 1:6.7.
[0026] The present invention will be further described below with reference to embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions.
[0027] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.
[0028] Example 1: Under nitrogen protection, 5,10,15,20-tetra(4-aminophenyl)porphyrin and 1,4,7,10-tetra(4-nitrobenzyl)-1,4,7,10-tetraazacyclododecane were mixed in a flask at a molar ratio of 1:1, and then N,N-dimethylformamide was added. After ultrasonic dispersion and dissolution, a small amount of potassium hydroxide was added. The mixture was slowly heated to 150 °C and stirred for 48 hours. The mixture was cooled to room temperature, precipitated with deionized water, filtered, and the filtrate was washed three times successively with dichloromethane, ethyl acetate, and tetrahydrofuran. The filtrate was then vacuum dried to obtain a nitrogen-rich covalent organic framework. The obtained nitrogen-rich covalent organic framework and europium nitrate hexahydrate were mixed at a mass ratio of 1:6.7, dispersed in acetonitrile, and stirred and heated to 60 °C for 24 hours. Hours; the mixed solution was cooled to room temperature, filtered, and the product was washed three times by centrifugation with acetonitrile and dichloromethane in sequence. After vacuum drying, a nitrogen-rich covalent organic framework containing europium ions was obtained.
[0029] Figure 1 The image shows the infrared spectrum of the europium-containing nitrogen-rich covalent organic framework obtained in Example 1 of this invention. It can be observed from the image that the 1,4,7,10-tetra(4-nitrobenzyl)-1,4,7,10-tetraaza-heterocyclic unit in the infrared spectrum of the nitrogen-rich covalent organic framework is located at 1618 and 1515 cm⁻¹. -1 The characteristic vibrational peaks of -NO2 and the 5,10,15,20-tetra(4-aminophenyl)porphyrin units in the 3450-3370 cm⁻¹ range. -1 The -NH2 absorption peaks at all locations disappeared, and a peak appeared at 1410 cm⁻¹. -1 The discovery of new stretching vibration peaks at the N=N bond provides preliminary confirmation of the successful synthesis of a nitrogen-rich covalent organic framework. A comparison of the spectra with those of other nitrogen-rich covalent organic frameworks reveals that the vibrational peak of the CN bond in the heterocyclic form of the europium-containing nitrogen-rich covalent organic framework changes from 1346 cm⁻¹. -1 Displaced to 1385 cm -1 This result indicates that europium ions coordinate with nitrogen-rich covalent organic frameworks.
[0030] Figure 2 The solid-state carbon NMR spectrum of the europium-containing nitrogen-rich covalent organic framework obtained in Example 1 of this invention shows that the signal peaks at chemical shifts of 49, 119, 131, and 150 ppm are attributed to characteristic carbon atoms of the macrocyclic structure in the 1,4,7,10-tetra(4-nitrobenzyl)-1,4,7,10-tetraaza-heterocyclic ring and the 5,10,15,20-tetra(4-aminophenyl)porphyrin unit, respectively. The signal peak at chemical shift ~162 ppm corresponds to the carbon atom in the -CN=NC- linkage, further confirming the formation of azo bonds in the europium-containing nitrogen-rich covalent organic framework.
[0031] Based on the above characterization results, it can be seen that the preparation method provided by the present invention can effectively prepare the europium ion-containing nitrogen-rich covalent organic framework.
[0032] Example 2: Under nitrogen protection, 5,10,15,20-tetra(4-aminophenyl)porphyrin and 1,4,7,10-tetra(4-nitrobenzyl)-1,4,7,10-tetraazacyclododecane were mixed in a molar ratio of 1:1 and placed in a flask. N,N-dimethylacetamide was added as solvent, and the mixture was ultrasonically dissolved and dispersed. A small amount of potassium hydroxide was then added. The mixture was slowly heated to 150 °C and stirred for 72 hours. The mixture was cooled to room temperature, precipitated with deionized water, filtered, and the filtrate was washed three times successively with dichloromethane, ethyl acetate, and tetrahydrofuran. The filtrate was then vacuum dried to obtain a nitrogen-rich covalent organic framework. The obtained nitrogen-rich covalent organic framework and europium nitrate hexahydrate were mixed in a mass ratio of 1:6.7 and dispersed in acetonitrile. The mixture was stirred and heated to 60 °C and maintained for 24 hours. The mixture was cooled to room temperature and filtered. The product was washed three times by centrifugation with acetonitrile and dichloromethane, and then dried under vacuum to obtain a nitrogen-rich covalent organic framework containing europium ions.
[0033] Example 3: 5,10,15,20-tetra(4-aminophenyl)porphyrin and 1,4,7,10-tetra(4-nitrobenzyl)-1,4,7,10-tetraazacyclododecane were mixed in a molar ratio of 1:1 and placed in an ampoule. Then, N,N-dimethylformamide was added as a solvent, and after ultrasonic dispersion, a small amount of potassium hydroxide catalyst was added. Ampoules containing the above mixture were placed in a liquid nitrogen bath and frozen. The mixture was degassed three times using a freeze-thaw cycle. The ampoules were then sealed with a flame, and the temperature was slowly raised to 150 °C. The mixture was stirred and heated for 72 hours. The solution was cooled to room temperature, and deionized water was added for precipitation. After filtration, the filtrate was washed three times successively with dichloromethane, ethyl acetate, and tetrahydrofuran. The filtrate was then vacuum dried to obtain a nitrogen-rich covalent organic framework. The obtained nitrogen-rich covalent organic framework and europium nitrate hexahydrate were mixed at a mass ratio of 1:6.7 and dispersed in acetonitrile. The mixture was stirred and heated to 60 °C and maintained for 24 hours. The solution was cooled to room temperature, filtered, and the product was washed three times successively by centrifugation with acetonitrile and dichloromethane. After vacuum drying, a nitrogen-rich covalent organic framework containing europium ions was obtained.
[0034] Experimental Example 1: Fluorescence detection of tetracycline; The procedure for testing the europium-ion-containing nitrogen-rich covalent organic framework for tetracycline fluorescence detection prepared in Example 1 is as follows: 20 mg of TAPP-TNBTA-COF@Eu was dispersed in 20 mL of water or methanol and sonicated for 30 minutes to ensure uniform dispersion. 100 μL of this dispersion was then added sequentially to tetracycline solutions of different concentrations and transferred to quartz cuvettes. The fluorescence color and intensity changes of TAPP-TNBTA-COF@Eu at 617 nm were monitored using 375 nm excitation. To investigate the selectivity and anti-interference ability of TAPP-TNBTA-COF@Eu as a tetracycline fluorescence sensor, various potential interfering substances were used to replace tetracycline in the experiment.
[0035] like Figure 4 As shown in (a), a nitrogen-rich covalent organic framework containing europium ions was used as a fluorescent sensing material to detect tetracycline. At an excitation wavelength of 375 nm, no interaction with Eu was observed in the pure TAPP-TNBTA-COF@Eu dispersion. 3+ Obvious ion-related fluorescence was observed. Interestingly, when tetracycline was added to the detection system containing TAPP-TNBTA-COF@Eu, the fluorescence of the solution immediately and clearly turned purple-red. A distinct new emission peak at 617 nm appeared in the emission spectrum of TAPP-TNBTA-COF@Eu. The peak at 617 nm is attributed to Eu. 3+ Ions and tetracycline to Eu 3+ Highly sensitive energy transfer of ions. The above results demonstrate that TAPP-TNBTA-COF@Eu can achieve real-time detection with rapid response and extremely high sensitivity. Figure 4 As shown in (b), TAPP-TNBTA-COF@Eu exhibits an ultra-low detection limit and high sensitivity for tetracycline, with a detection limit of 0.061 nM, which is superior to most reported COFs fluorescent detection materials.
[0036] Experimental Example 2: Photocatalytic Degradation of Tetracycline; The process of photocatalytic degradation of tetracycline using the europium-ion-containing nitrogen-rich covalent organic framework TAPP-TNBTA-COF@Eu prepared in Example 1 is as follows: First, 5 mg of TAPP-TNBTA-COF@Eu was added to a prepared tetracycline aqueous solution (20 mg / L, 10 mL). The mixture was stirred in the dark to allow the catalyst to reach adsorption and desorption equilibrium. After 30 min, the xenon lamp light source (PLS-SXE300 from Beijing PLS-SXE300 Technology Co., Ltd., with a 400 nm short-wavelength cutoff filter) was turned on to begin the photocatalytic degradation of tetracycline. Every 15 min, the supernatant was drawn into a quartz cuvette using a syringe. The absorbance change at the maximum absorption peak of tetracycline in the solution was measured by ultraviolet-visible absorption spectroscopy (UV-Vis). The change in tetracycline concentration was then analyzed, and the tetracycline degradation rate was calculated.
[0037] like Figure 5 The figure shows the degradation rate curve of tetracycline under illumination using the europium-ion-containing nitrogen-rich covalent organic framework TAPP-TNBTA-COF@Eu as a photocatalyst. As can be seen from the figure, tetracycline underwent significant photodegradation with increasing illumination time, reaching a degradation rate of 83% after 60 minutes.
[0038] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.
[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.
Claims
1. A nitrogen-rich covalent organic framework containing europium ions, characterized in that, Its structural formula is shown in (I): (I).
2. The nitrogen-rich covalent organic framework according to claim 1, characterized in that, Its structural formula is shown in (II): (II).
3. The nitrogen-rich covalent organic framework according to claims 1 and 2, characterized in that, The material is prepared by polymerization of the following monomers: 5,10,15,20-tetra(4-aminophenyl)porphyrin and 1,4,7,10-tetra(4-nitrobenzyl)-1,4,7,10-tetraazacyclododecane.
4. The europium-containing nitrogen-rich covalent organic framework according to claim 1, characterized in that, The preparation method of the material includes the following steps: ① Under nitrogen protection (or in a closed, oxygen-free environment), 5,10,15,20-tetra(4-aminophenyl)porphyrin and 1,4,7,10-tetra(4-nitrobenzyl)-1,4,7,10-tetraazacyclododecane are mixed in a molar ratio of 1:(1~1.5), dissolved in a solvent (N,N-dimethylformamide or N,N-dimethylacetamide), ultrasonically dispersed, and then a small amount of potassium hydroxide catalyst is added. ② Slowly heat the mixed solution from step ① to 120~150 ℃ and stir and heat for 48~72 hours; ③ Cool the mixed solution from step ② to room temperature, add deionized water for precipitation, filter, and wash the filtrate 3-5 times in sequence with dichloromethane, ethyl acetate, and tetrahydrofuran. Filter under vacuum and dry the filtrate under vacuum to obtain a nitrogen-rich covalent organic framework. ④ Mix the nitrogen-rich covalent organic framework obtained in step ③ with europium nitrate hexahydrate at a mass ratio of 1:(1~10), disperse in acetonitrile, stir and heat to 60 ℃, and maintain for 12~24 hours; ⑤ Cool the mixed solution from step ④ to room temperature, filter it, and wash the product by centrifugation with acetonitrile and dichloromethane 3 to 5 times in sequence. Dry it under vacuum at 50 to 70 °C for 12 to 24 hours to obtain a nitrogen-rich covalent organic framework containing europium ions.
5. The europium-containing ion-functionalized nitrogen-rich covalent organic framework according to claim 1, characterized in that, The application areas of this material include: utilizing its fluorescence sensing properties to achieve highly selective detection of tetracycline; and utilizing its photocatalytic generation of reactive oxygen species to achieve efficient removal of tetracycline. Application scenarios include, but are not limited to, environmental monitoring (tetracycline residue analysis in water / soil), food safety (tetracycline detection in animal-derived foods), and pollution control (tetracycline wastewater treatment).