A photoresponsive covalent organic framework material and its preparation method and application

Abstract

The present invention relates to the technical field of nuclear pollutant treatment, and discloses a light-responsive covalent organic framework material, a preparation method thereof, and an application thereof. The present invention prepares a covalent organic framework material COFs having a porous structure by using metallized aldehyde porphyrin and 1,4-phenylenediacetonitrile as a matrix, thereby achieving its strong adsorption capacity. Furthermore, amidoxime groups are introduced into the COFs material through a specific chemical reaction, thereby improving the affinity and selectivity for uranyl and other uranium ions. At the same time, by using the porphyrin group as the covalent organic framework matrix of the COFs material, a catalytic ability is formed to reduce photocatalytically dissolved U(VI) to insoluble U(IV). That is, by combining the dual functions of photocatalysis and adsorption, the light-responsive covalent organic framework material can release active sites based on catalytic conditions, thereby improving the ability to enrich U(VI) and increase the capacity for uranium adsorption.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear pollutant treatment, and in particular to a light-responsive covalent organic framework material and a preparation method and application thereof. Background Art

[0002] Uranium, a key resource for nuclear energy, plays a vital role in the nuclear fuel cycle and related industries. However, global uranium resources are unevenly distributed, and the cost and environmental pressure of terrestrial uranium mining are increasing. Therefore, the extraction of uranium from sources such as low-concentration uranium-containing wastewater and seawater has become a hot topic of research. Uranium contamination in industrial wastewater, in particular, poses a threat to the ecological environment and human health and also results in a waste of resources. The development of efficient, economical, and environmentally friendly uranium extraction technologies is crucial for resource recovery and environmental governance.

[0003] Currently, the main methods for treating uranium-containing wastewater include chemical precipitation, solvent extraction, ion exchange, and adsorption. Adsorption has become the mainstream technology due to its low cost, ease of operation, and environmental friendliness. In recent years, with the advancement of materials science, a variety of adsorbent materials, such as nanomaterials, metal-organic frameworks, and covalent organic frameworks, have been applied to uranium extraction research. However, adsorption also presents some challenges. While these adsorbents have enhanced their selectivity and adsorption capacity for uranium through functional design, they still face several technical bottlenecks. Adsorption is limited in its effectiveness for treating low-concentration uranium solutions below 50 ppm, making it difficult to further increase uranium capture. The slow kinetic performance of most adsorbents limits their application in dynamic wastewater treatment. The selectivity of existing adsorbents for uranium is interfered with by other competing ions, resulting in low uranium extraction efficiency, particularly in complex aquatic environments.

[0004] For example, patent application publication number CN115894830A discloses the preparation and application of an adsorption-photocatalytic covalent organic framework material. The adsorption-synergistic photocatalytic organic covalent material disclosed in this patent constructs a system that integrates adsorption and photocatalysis. This material simultaneously adsorbs uranium (U(VI)) and catalyzes the reduction of dissolved uranium U(VI) to insoluble uranium (U(IV)), thereby releasing new active sites to capture more uranium. Although the organic covalent material provided by this patent can improve the ability to extract uranium from wastewater to a certain extent, the uranium extraction capacity of this material is limited by the release of uranium U(VI) from the active sites, that is, the catalytic efficiency of photogenerated electrons, and still suffers from the problem of low uranium adsorption capacity and efficiency. Summary of the Invention

[0005] Existing materials have low capacity and efficiency for uranium adsorption. In order to solve the above technical problems, the present invention provides a photoresponsive covalent organic framework material, its preparation method and application. The present invention prepares a covalent organic framework material COFs with a porous structure by using metallized aldehyde porphyrin and 1,4-phenylenediacetonitrile as a matrix to achieve its strong adsorption capacity, and introduces amidoxime groups into the COFs material through a specific chemical reaction to improve the affinity and selectivity for uranyl and other uranium ions. At the same time, by using porphyrin groups as the covalent organic framework matrix of the COFs material, a catalytic ability is formed to reduce photocatalytically dissolved U(VI) to insoluble U(IV). That is, combining the dual functions of photocatalysis and adsorption, the photoresponsive covalent organic framework material can release active sites based on catalytic conditions, thereby improving the ability to enrich U(VI) and increase the capacity for uranium adsorption.

[0006] The specific technical solutions of the present invention are:

[0007] In a first aspect, the present invention provides a method for preparing a photoresponsive covalent organic framework material, comprising the following steps:

[0008] Step S1: reacting aldehyde porphyrin with a metal salt to obtain a metallated aldehyde porphyrin;

[0009] Step S2: condensing the metallated aldehyde porphyrin with 1,4-benzenediacetonitrile to obtain a metalloporphyrin covalent organic framework;

[0010] Step S3: subjecting the metalloporphyrin covalent organic framework to an amidoximation reaction to obtain a photoresponsive covalent organic framework material.

[0011] The method of the present invention prepares a covalent organic framework material COFs with a porous structure by using metallated aldehyde porphyrin and 1,4-phenylenediacetonitrile as a matrix. The covalent organic framework material has a large adsorption capacity, and introduces amidoxime groups into the COFs material through a specific chemical reaction to improve the affinity and selectivity for uranyl and other uranium ions. At the same time, by using the porphyrin group as the covalent organic framework matrix of the COFs material, a catalytic ability is formed to reduce photocatalytically dissolved U(VI) to insoluble U(IV). That is, the dual functions of photocatalysis and adsorption are combined, so that the light-responsive covalent organic framework material can release active sites based on catalytic conditions, thereby enhancing the ability to enrich U(VI) and increase the uranium adsorption capacity.

[0012] As a preferred embodiment of the above preparation method, in step S1, the aldehyde porphyrin is a porphyrin derivative having an aldehyde group.

[0013] As a preferred embodiment of the above preparation method, in step S1, the metal salt is a copper salt and / or a nickel salt.

[0014] Metallization of aldehyde-based porphyrins allows the interaction of the copper (Cu) or nickel (Ni) metal's d-orbital with the porphyrin ring's π-electron system, effectively promoting charge carrier separation and enhancing the material's photocatalytic activity. Furthermore, copper- or nickel-metallized porphyrins enhance their catalytic adsorption capacity in the dark. Therefore, the metal salt is preferably a copper salt and / or a nickel salt.

[0015] In addition, copper and nickel have strong affinity in porphyrin coordination chemistry and can promote the stabilization of metal ions through coordination. The metallated porphyrin complex has unique advantages in applications such as catalysis.

[0016] As a preferred embodiment of the above preparation method, in step S1, the reaction is carried out under an inert gas atmosphere at a reaction temperature of 100-130°C.

[0017] The metallation of aldehyde porphyrins is carried out at high temperatures of 100-130°C, protected by an inert gas atmosphere. This temperature promotes the coordination reaction between the metal ion and the porphyrin ring, ensuring efficient and effective reaction. The inert atmosphere effectively prevents oxygen interference and oxidation reactions, ensuring the purity of the reaction and the stability of the metallated product.

[0018] As a preferred embodiment of the above preparation method, in step S2, the condensation reaction is carried out in the presence of a solvent and a catalyst, the solvent is 1,2-dichlorobenzene, and the catalyst is a basic catalyst.

[0019] The high boiling point of 1,2-dichlorobenzene helps to provide a stable reaction environment at higher temperatures, dissolve the reactants, promote uniform contact between molecules, and avoid the occurrence of side reactions.

[0020] Base catalysts can significantly improve the efficiency of the Knoevenagel condensation reaction and prevent side reactions, thereby ensuring high purity and high yield of the target product. DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) is a preferred base catalyst.

[0021] As a preferred embodiment of the above preparation method, in step S3, the metalloporphyrin covalent organic framework is subjected to amidoximation reaction with hydroxylamine.

[0022] As a preferred embodiment of the above preparation method, in step S3, the temperature of the amidoximation reaction is 80-100° C., and the reaction time is 20-30 hours.

[0023] The amidoximation reaction of the metalloporphyrin covalent organic framework of the present invention requires a relatively high temperature of 80-100°C to achieve amidoximation modification of the metalloporphyrin covalent organic framework. The temperature cannot be too high, otherwise it will damage the framework material structure and cause reaction completeness problems. The temperature cannot be too low, otherwise the efficiency of the target reaction will be reduced and side reactions will increase.

[0024] As a preferred embodiment of the above preparation method, in step S3, the catalyst for the amidoximation reaction is triethylamine.

[0025] Using triethylamine as a catalyst in the reaction provides a suitable alkaline environment for the amidoximation reaction, helping hydroxylamine to exert its nucleophilicity and accelerate the conversion of aldehyde groups to amidoxime groups. The alkaline conditions of triethylamine can prevent excessive alkalinity from damaging the COF structure while ensuring the high efficiency and selectivity of the reaction.

[0026] In a second aspect, the present invention provides a photoresponsive covalent organic framework material.

[0027] In a third aspect, the present invention provides the use of the photoresponsive covalent organic framework material prepared by the above preparation method in uranium extraction.

[0028] Compared with the prior art, the present invention has the following technical effects:

[0029] (1) The photoresponsive covalent organic framework material provided by the present invention has a porous structure of COFs and has a large adsorption capacity. The amidoxime group is introduced into the COFs material through a specific chemical reaction to improve the affinity and selectivity for uranyl and other uranium ions. At the same time, by using the porphyrin group as the covalent organic framework matrix of the COFs material, the catalytic ability of photocatalytically reducing dissolved U(VI) to insoluble U(IV) is formed. That is, the dual functions of photocatalysis and adsorption are combined, so that the photoresponsive covalent organic framework material can release active sites based on catalytic conditions, thereby improving the ability to enrich U(VI) and increase the uranium adsorption capacity.

[0030] (2) The photoresponsive covalent organic framework material provided by the present invention realizes the regulation of the photocatalytic performance of the photoresponsive covalent organic framework material by copper metal and nickel metal, so that the material expands the catalytic conditions for the reduction of U(VI) to insoluble U(IV), and can also realize the reduction catalysis of U(VI) under dark conditions. That is, the reduction catalytic ability of copper metal and nickel metal on the photoresponsive covalent organic framework material to U(VI) is effectively improved, thereby greatly improving the uranium adsorption capacity of the photoresponsive covalent organic framework material. Compared with the existing adsorption-photocatalytic system, the organic framework material is less affected by the limitation of photogenerated carriers.

[0031] (3) The light-responsive covalent organic framework material provided by the present invention can maintain good adsorption performance in multiple cycles and can remove adsorbed uranium ions through a simple washing step. It has good regeneration and long-term stability, reduces the generation of waste, and conforms to the concept of green environmental protection. In addition, the adsorption light-responsive metalloporphyrin COF material provided by the present invention is not only suitable for the treatment of low-concentration uranium-containing wastewater, but can also be extended to the extraction and utilization of uranium in seawater, and has important application value and market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a reaction flow chart of Example 1 of the present invention;

[0033] Figure 2 The H-NMR spectrum and C-NMR spectrum of aldehyde porphyrin;

[0034] Figure 3 The H-NMR spectrum and C-NMR spectrum of metallized nickel porphyrin;

[0035] Figure 4 This is a reaction flow chart of Example 2 of the present invention;

[0036] Figure 5 X-ray diffraction patterns of Ni-Por-COF and Cu-Por-COF;

[0037] Figure 6 The transient photocurrent diagram and Mott-Schottky curve diagram of Por-COF, Ni-Por-COF and Cu-Por-COF, among which the left figure is the transient photocurrent diagram and the right figure is the Mott-Schottky curve diagram;

[0038] Figure 7 The graph shows the results of the uranium extraction capacity test of Por-COF, Ni-Por-COF and Cu-Por-COF under dark and light conditions;

[0039] Figure 8 This is a schematic diagram of the application of the photoresponsive covalent organic framework material provided by the present invention in the treatment of low-concentration uranium-containing wastewater. DETAILED DESCRIPTION

[0040] The present invention provides a method for preparing a photoresponsive covalent organic framework material, comprising the following steps:

[0041] Step S1: reacting aldehyde porphyrin with a metal salt to obtain a metallated aldehyde porphyrin;

[0042] Step S2: condensing the metallated aldehyde porphyrin with 1,4-benzenediacetonitrile to obtain a metalloporphyrin covalent organic framework;

[0043] Step S3: subjecting the metalloporphyrin covalent organic framework to an amidoximation reaction to obtain a photoresponsive covalent organic framework material.

[0044] The present invention prepares a covalent organic framework material COFs with a porous structure by using metallated aldehyde porphyrin and 1,4-phenylenediacetonitrile as a matrix. The covalent organic framework material has a large adsorption capacity, and introduces amidoxime groups into the COFs material through a specific chemical reaction, thereby improving the affinity and selectivity for uranyl and other uranium ions. At the same time, by using the porphyrin group as the covalent organic framework matrix of the COFs material, a catalytic ability is formed to reduce photocatalytically dissolved U(VI) to insoluble U(IV). That is, by combining the dual functions of photocatalysis and adsorption, the light-responsive covalent organic framework material can release active sites based on catalytic conditions, thereby improving the ability to enrich U(VI) and increase the uranium adsorption capacity.

[0045] As a preferred embodiment of the above preparation method, in step S1, the aldehyde porphyrin is a porphyrin derivative having an aldehyde group.

[0046] Specifically, the aldehyde porphyrin can be prepared by following steps one to three:

[0047] Step 1: Dissolve neopentyl glycol, p-phthalaldehyde and p-toluenesulfonic acid monohydrate in toluene, and then reflux under stirring and N2 atmosphere; then purify by column chromatography using an ethyl acetate / petroleum ether mixed solvent to obtain a white product.

[0048] Step 2: Under N2 atmosphere, add the white product of step 1 and pyrrole to dry dichloromethane, then add trifluoroacetic acid and stir to mix; then add tetrachlorobenzoquinone, and stir the reaction mixture (protected from light) under N2 atmosphere at room temperature; after the reaction is completed, rotary evaporation and purification by dichloromethane column chromatography to obtain a purple product.

[0049] Step 3: Dissolve the purple product from step 2 in chloroform, then add TFA and stir the reaction at room temperature for a period of time. Use a saturated K2CO3 solution to adjust the pH value of the mixture to 4.5-5.5 and stir the reaction. Wash the crude product with water and then separate it. Take the organic phase and dry it with anhydrous Na2SO4, rotary evaporate it, wash it with methanol and filter it to obtain a dark purple aldehyde porphyrin.

[0050] As a preferred embodiment of the above preparation method, in step S1, the metal salt is a copper salt and / or a nickel salt.

[0051] Metallization of aldehyde-based porphyrins allows the interaction of the copper (Cu) or nickel (Ni) metal's d-orbital with the porphyrin ring's π-electron system, effectively promoting charge carrier separation and enhancing the material's photocatalytic activity. Furthermore, copper- or nickel-metallized porphyrins enhance their catalytic adsorption capacity in the dark. Therefore, the metal salt is preferably a copper salt and / or a nickel salt.

[0052] In addition, copper and nickel have strong affinity in porphyrin coordination chemistry and can promote the stabilization of metal ions through coordination. The metallated porphyrin complex has unique advantages in applications such as catalysis.

[0053] As a preferred embodiment of the above preparation method, in step S1, the reaction is carried out under an inert gas atmosphere at a reaction temperature of 100-130°C.

[0054] The metallation of aldehyde porphyrins is carried out at high temperatures of 100-130°C, protected by an inert gas atmosphere. This temperature promotes the coordination reaction between the metal ion and the porphyrin ring, ensuring efficient and effective reaction. The inert atmosphere effectively prevents oxygen interference and oxidation reactions, ensuring the purity of the reaction and the stability of the metallated product.

[0055] As a preferred embodiment of the above preparation method, in step S2, the condensation reaction is carried out in the presence of a solvent and a catalyst, the solvent is 1,2-dichlorobenzene, and the catalyst is a basic catalyst.

[0056] The high boiling point of 1,2-dichlorobenzene helps to provide a stable reaction environment at higher temperatures, dissolve the reactants, promote uniform contact between molecules, and avoid the occurrence of side reactions.

[0057] Base catalysts can significantly improve the efficiency of the Knoevenagel condensation reaction and prevent side reactions, thereby ensuring high purity and high yield of the target product. DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) is a preferred base catalyst.

[0058] As a preferred embodiment of the above preparation method, in step S3, the metalloporphyrin covalent organic framework is subjected to amidoximation reaction with hydroxylamine.

[0059] As a preferred embodiment of the above preparation method, in step S3, the temperature of the amidoximation reaction is 80-100° C., and the reaction time is 20-30 hours.

[0060] The amidoximation reaction of the metalloporphyrin covalent organic framework of the present invention requires a relatively high temperature of 80-100°C to achieve amidoximation modification of the metalloporphyrin covalent organic framework. The temperature cannot be too high, otherwise it will damage the framework material structure and cause reaction completeness problems. The temperature cannot be too low, otherwise the efficiency of the target reaction will be reduced and side reactions will increase.

[0061] As a preferred embodiment of the above preparation method, in step S3, the catalyst for the amidoximation reaction is triethylamine.

[0062] Using triethylamine as a catalyst in the reaction provides a suitable alkaline environment for the amidoximation reaction, helping hydroxylamine to exert its nucleophilicity and accelerate the conversion of aldehyde groups to amidoxime groups. The alkaline conditions of triethylamine can prevent excessive alkalinity from damaging the COF structure while ensuring the high efficiency and selectivity of the reaction.

[0063] The present invention will be further described below with reference to the following embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only a portion of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0064] Example 1

[0065] This embodiment provides a photoresponsive covalent organic framework material, and its preparation process is as follows: Figure 1 As shown, prepare according to the following steps 1 to 4:

[0066] Step 1: Preparation of aldehyde porphyrin

[0067] Neopentyl glycol (8.5 g, 82 mmol), p-phthalaldehyde (10.9 g, 82 mmol) and p-toluenesulfonic acid monohydrate (TsOH, 50 mg, 0.3 mmol) were dissolved in 100 mL of toluene in a round-bottom flask (volume 250 mL), and then refluxed for 23 h under stirring and N2 atmosphere. The reaction was monitored by thin layer chromatography (TLC); then purified by column chromatography with ethyl acetate / petroleum ether (v / v, 1 / 10) to obtain a white product. Under N₂ atmosphere, the white product (6.74 g, 30.6 mmol) and pyrrole (2.8 mL) were added to dry dichloromethane (720 mL). Trifluoroacetic acid (TFA, 1.9 mL) was then added and stirred for 60 min. Next, tetrachlorobenzoquinone (3.92 g, 15.9 mmol) was added. Stirring was carried out at room temperature under N₂ atmosphere in the dark for 14 h, with the reaction monitored by TLC. Triethylamine (1 mL) was then added dropwise to quench the reaction, and the mixture was stirred for 30 min. The mixture was then rotary evaporated and purified by dichloromethane column chromatography to obtain a purple product. Step 3: The purple product from Step 2 (378 mg, 0.35 mmol) was dissolved in chloroform (CHCl₃, 40 mL). After adding TFA (18 mL), the resulting solution was stirred at room temperature overnight, with TLC monitoring. The pH of the mixture was adjusted to 5.0 using a saturated solution of K2CO3 and stirred for 4 hours. The crude product was then washed with water and separated. The organic phase was dried over anhydrous Na2SO4 and rotary evaporated. The resulting product was washed with methanol, filtered, and dried to obtain a dark purple solid, which was the aldehyde porphyrin, denoted as Por-CHO.

[0068] The prepared Por-CHO was subjected to NMR testing, and the results are shown in Figure 2 , where a and b are the H-NMR spectrum and C-NMR spectrum of Por-CHO, respectively.

[0069] Step 2: Preparation of nickel metallated aldehyde porphyrin

[0070] Por-CHO (200 mg, 0.276 mmol) obtained in Step 1 was mixed with nickel acetate (Ni(CH3COO)2, 137.4 mg, 0.55 mmol) and DMF (40 mL). The mixture was stirred at 120°C under a nitrogen atmosphere for 4 h. After cooling to room temperature, 160 mL of deionized water was added to precipitate a solid. The solid was collected by filtration, washed with methanol, and dried under vacuum to obtain a deep red product, the nickel-metallated aldehyde porphyrin, designated Ni-Por.

[0071] The prepared Ni-Por was subjected to NMR test, and the results are shown in Figure 3 , where a and b are the H NMR spectrum and C NMR spectrum of Ni-Por respectively. 1In the H NMR spectrum, typical proton signals related to the porphyrin ring structure, as well as characteristic peaks of the aldehyde group (-CHO) and the metallated porphyrin center, can be observed; 13 The C NMR spectrum further provides carbon spectrum information of the porphyrin ring, showing the characteristic peaks of the carbon of the aldehyde group and the metal-coordinated carbon in the metallated porphyrin. These data indicate that the aldehyde porphyrin reacts with the metal ion Ni 2+ The coordination was successful and the synthesis of metallated porphyrins was efficient.

[0072] Step 3: Preparation of Metalloporphyrin Covalent Organic Framework

[0073] In an ampoule, the metallated aldehyde porphyrin obtained in step 2 (69.72 mg, 0.096 mmol), 1,4-phenylenediacetonitrile (PDAN, 30 mg, 0.192 mmol), 1,2-dichlorobenzene (4 mL) and a 5 M DBU solution (1,8-diazabicycloundec-7-ene aqueous solution, 0.4 mL) were added. The mixture was ultrasonicated for 5 min, freeze-thawed three times, sealed under a butane flame vacuum, and heated at 80 ° C for 3 days. The product was washed with dichloromethane, extracted with tetrahydrofuran and dichloromethane for two days, and dried under vacuum at 80 ° C for 12 h to obtain a metalloporphyrin covalent organic framework.

[0074] Step 4: Amidoximation of Metalloporphyrin Covalent Organic Framework

[0075] Disperse 0.2 g of the metalloporphyrin covalent organic framework obtained in step 3 in 20 mL of anhydrous ethanol and sonicate for 10 minutes. Add hydroxylamine hydrochloride (NH₂OH·HCl, 0.5 g) and triethylamine (N(CH₂CH₃), 3 mL). Stir at 85°C for 24 hours, then filter. Wash the solid sequentially with water, ethanol, and methanol. Dry under vacuum at 60°C for 12 hours to obtain the amidoximated metalloporphyrin covalent organic framework (Ni-Por-COF).

[0076] Example 2

[0077] This embodiment provides an amidoximated metalloporphyrin covalent organic framework material, denoted as Cu-Por-COF.

[0078] The preparation in this example differs from that in Example 1 only in that, in Step 2, 0.55 mmol of CuCl2 dihydrate (94 mg) is reacted with 0.276 mmol of Por-CHO to prepare the metallated aldehyde porphyrin. The remaining steps are identical to those in Example 1, including the same molar ratios used in the reactions.

[0079] The preparation flow chart of this embodiment is as follows Figure 4 shown.

[0080] Example 3

[0081] This embodiment provides an amidoximated metalloporphyrin covalent organic framework material, denoted as Co-Por-COF.

[0082] The preparation of this example differs from that of Example 1 only in that, in Step 2, 0.55 mmol of CoCl2 is reacted with 0.276 mmol of Por-CHO to prepare the metallated aldehyde porphyrin. The remaining steps are identical to those of Example 1, and the molar ratios of the reactions involved are the same as those of Example 1.

[0083] Performance Characterization

[0084] (1) X-ray diffraction (XRD) was used to characterize the crystal structures of the amidoximated metalloporphyrin covalent organic frameworks synthesized in Example 1 and Example 2. Figure 5 .

[0085] Figure 5 XRD patterns of amidoximated Ni-porphyrin covalent organic framework (Ni-Por-COF) and amidoximated Cu-porphyrin covalent organic framework (Cu-Por-COF) are presented. The XRD patterns reveal distinct crystalline structures and clear diffraction peaks for Ni-Por-COF and Cu-Por-COF, indicating highly ordered structures and good crystalline quality. Comparing the different metallated porphyrin frameworks, the XRD patterns reveal that the diffraction peak positions and intensities for amidoximated Ni-Por-COF and Cu-Por-COF are essentially identical, indicating similar crystal structures. However, Ni-Por-COF exhibits higher diffraction peak intensity, indicating better crystallinity and order.

[0086] (2) The Por-COF, Ni-Por-COF synthesized in Example 1 and the Cu-Por-COF synthesized in Example 2 were subjected to photocurrent test and Mott-Schottky analysis. The results are shown in Figure 6 The left figure shows the transient photocurrent response results, and the right figure shows the Mott-Schottky curve test results. Transient photocurrent testing assesses the material's photogenerated electron and charge transport capabilities by applying light to the surface of different materials and measuring their current response. Mott-Schottky analysis can provide information about the material's carrier concentration, band structure, and semiconductor type.

[0087] Figure 6The left figure shows the transient photocurrent responses of Por-COF, Ni-Por-COF, and Cu-Por-COF. The results show that Ni-Por-COF exhibits the highest transient photocurrent under illumination, indicating its strongest ability to generate and separate photogenerated electrons. In contrast, the transient photocurrents of Cu-Por-COF and Por-COF are lower, suggesting that Ni-Por-COF may exhibit better performance in photocatalytic applications. This phenomenon is related to the strong charge separation and photocatalytic ability of the Ni metallated porphyrin center.

[0088] Figure 6 The figure on the right shows the Mott-Schottky plots of Por-COF, Ni-Por-COF, and Cu-Por-COF. The results show that all materials exhibit typical Mott-Schottky curves, demonstrating their semiconductor properties. In particular, the Mott-Schottky plot of Ni-Por-COF reveals a high electron concentration and low electron migration resistance, indicating that Ni-Por-COF possesses superior electron conduction properties during photoelectrocatalysis. This provides strong support for the application of Ni-Por-COF and Cu-Por-COF in photocatalysis.

[0089] The characterization of steps (1) and (2) shows that the aldehyde porphyrin Por-COF and the metallated porphyrin (Ni-Por-COF and Cu-Por-COF) are successfully synthesized, and the metallated porphyrin covalent organic framework has a good crystal structure, high crystallinity and order. The metallated porphyrin covalent organic framework material of the present invention, especially Ni-Por-COF, has good photoelectric properties and structural stability.

[0090] (3) The Por-COF and Ni-Por-COF synthesized in Example 1, the Cu-Por-COF synthesized in Example 2, and the Co-Por-COF synthesized in Example 3 were used to conduct uranium extraction performance experiments from uranium-containing wastewater.

[0091] Experimental materials and methods: Experimental materials: A standard uranium solution with an initial uranium concentration of 20 ppm, and adsorption materials Por-COF, Ni-Por-COF, Cu-Por-COF, and Co-Por-COF were used; Experimental conditions: The adsorption performance of the above-mentioned adsorption materials for uranium (U(VI)) was measured under different lighting conditions, where the lighting conditions were divided into two conditions: "dark conditions (no light) and light conditions (simulated sunlight, light source intensity of 100 mW / cm²)", and the experimental temperature was maintained at room temperature (25 ℃); Operation steps: 10 mg of Por-COF, Ni-Por-COF, Cu-Por-COF or Co-Por-COF was added to a solution containing 20 ppm uranium, and the adsorption experiment was carried out. The experiment was stirred continuously for 12 hours under dark conditions and for 20 hours under light conditions. Samples were taken regularly to analyze the changes in uranium concentration in the solution, and the amount of uranium adsorbed was recorded. The maximum adsorption capacity q of Por-COF, Ni-Por-COF, Cu-Por-COF, and Co-Por-COF max See Table 1. The adsorption amount of uranium at different times for Por-COF, Ni-Por-COF, and Cu-Por-COF is shown in Table 1. Figure 7 , Table 1 and Figure 7 In the figure, Dark refers to dark conditions, and Light refers to light conditions.

[0092] Table 1

[0093] Adsorption materials Maximum adsorption capacity (Dark) Maximum adsorption capacity (Light) Por-COF 74.9 mg / g 114.7 mg / g Ni-Por-COF 219.0 mg / g 335.8 mg / g Cu-Por-COF 208.3 mg / g 291.7 mg / g Co-Por-COF 136.4 mg / g 152.5 mg / g

[0094] As shown in Table 1, Por-COF has a low uranium adsorption capacity even under illumination, while Co-Por-COF has a moderate uranium adsorption capacity. The catalytic ability of Co-Por-COF is not significantly improved under dark conditions. However, both Cu-Por-COF and Ni-Por-COF exhibit high adsorption capacities, with Ni-Por-COF reaching a maximum adsorption capacity of 335.8 mg / g. This indicates that metallization of aldehyde-based porphyrins with copper (Cu) or nickel (Ni) is highly effective. This may be due to the interaction between the outer electron orbitals of the copper or nickel metal and the π-electron system of the porphyrin ring. The interaction between the d orbitals of the copper or nickel metal and the π-electron system of the porphyrin ring can effectively promote the separation of charge carriers and enhance the photocatalytic activity of the material. Furthermore, copper- or nickel-metallized porphyrins can enhance their catalytic adsorption capacity under dark conditions. Therefore, the metallization of aldehyde-based porphyrins with copper and nickel metal salts is preferred.

[0095] Figure 7 The adsorption amount of uranium at different times of Por-COF, Ni-Por-COF and Cu-Por-COF is shown. Figure 7It can be seen that Ni-Por-COF and Cu-Por-COF both reached adsorption equilibrium within 20 hours, indicating that the process has rapid adsorption kinetics. Specifically, the adsorption amount increases with time and tends to be stable, showing a good dynamic response. Figure 7 The adsorption behavior of Por-COF, Ni-Por-COF, and Cu-Por-COF was confirmed to conform to the pseudo-second-order kinetic equation. This pseudo-second-order kinetic model indicates that uranium adsorption is not solely physical adsorption but also involves chemical reactions or other interactions. Adsorption isotherm analysis showed that the adsorption behavior of all materials conformed to the Langmuir isotherm model, further demonstrating that uranium adsorption occurs at a monolayer level and that the adsorption sites are uniform.

[0096] and by Figure 7 It can be seen that the adsorption of uranium under light conditions is excellent. Analysis of the reasons for this phenomenon can be attributed to the photocatalytic effect. Under light, the photogenerated electrons interact with the metal d orbitals of the metallized porphyrin and the porphyrin ring π electron system, effectively promoting the separation and transfer of electrons, thereby enhancing the photocatalytic reduction of U(VI) to insoluble U(IV). In addition, the electron reduction under light not only promotes the conversion of uranium but also releases additional active sites, further improving the adsorption capacity.

[0097] The uranium extraction performance experiment in step (3) can predict the application prospects of Ni-Por-COF and Cu-Por-COF in extracting uranium from low-concentration uranium-containing wastewater, especially in the fields of nuclear wastewater treatment, mining wastewater recycling and seawater uranium extraction. Taking Ni-Por-COF as an example, Figure 8 A schematic diagram showing the application of Ni-Por-COF in low-concentration uranium-containing wastewater. The treatment steps are as follows:

[0098] Wastewater pretreatment: Uranium-containing wastewater (20 ppm) is first filtered or settled to remove some impurities in order to improve the efficiency of the subsequent adsorption process.

[0099] Adsorption process: The pretreated wastewater is mixed with the Ni-Por-COF material and reacted under light conditions. The synergistic effect of adsorption and photocatalysis of the adsorption light-responsive covalent organic framework is utilized to quickly extract uranium ions from the wastewater.

[0100] Uranium extraction: After a period of reaction, the Ni-Por-COF material that has adsorbed uranium is recovered by filtration, and the adsorbed uranium is removed by washing, finally obtaining uranium-containing material and treated wastewater.

[0101] Uranium recovery and material regeneration: Uranium can be recovered through simple elution or solvent treatment, and the Ni-Por-COF material can be regenerated and reused for the next round of wastewater treatment.

[0102] Unless otherwise specified, the raw materials and equipment used in the present invention are commonly used in the art; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0103] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a photoresponsive covalent organic framework material, characterized in that: The following steps are involved: Step S1: reacting aldehyde porphyrin with a metal salt to obtain a metallated aldehyde porphyrin; the metal salt is a copper salt and / or a nickel salt; Step S2: condensing the metallated aldehyde porphyrin with 1,4-benzenediacetonitrile to obtain a metalloporphyrin covalent organic framework; the condensation reaction is carried out in the presence of a solvent and a catalyst, wherein the solvent is 1,2-dichlorobenzene and the catalyst is a basic catalyst; Step S3: subjecting the metalloporphyrin covalent organic framework to an amidoximation reaction to obtain a photoresponsive covalent organic framework material.

2. The preparation method according to claim 1, wherein: In step S1, the aldehyde porphyrin is a porphyrin derivative having an aldehyde group.

3. The preparation method according to claim 1 or 2, wherein: In step S1, the reaction is carried out under an inert gas atmosphere at a reaction temperature of 100-130°C.

4. The preparation method according to claim 1, wherein: In step S3, the metalloporphyrin covalent organic framework is reacted with hydroxylamine to undergo amidoximation reaction.

5. The preparation method according to claim 4, wherein: In step S3, the temperature of the amidoximation reaction is 80-100° C., and the reaction time is 20-30 hours.

6. The preparation method according to claim 4, wherein: In step S3, the catalyst for the amidoximation reaction is triethylamine.

7. A photoresponsive covalent organic framework material prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the photoresponsive covalent organic framework material prepared by the preparation method according to any one of claims 1 to 6 in uranium extraction.

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