Conjugated organic polymer material, preparation method thereof and application of conjugated organic polymer material in efficient photocatalysis of uranium extraction from seawater without additional sacrificial agent

Abstract

The invention discloses a conjugated organic polymer material which is obtained by carrying out Knoevenagel condensation reaction on 2, 2 '-(benzo [c] [1, 2, 5] thiadiazole-4, 7-diyl bis (4, 1-phenylene)) diacetonitrile and 5, 5', 5 ''-(benzene-1, 3, 5-triyl) tripyridylaldehyde and carrying out ammoximation. The material disclosed by the invention has high uranium extraction efficiency and excellent uranium extraction capacity under the condition of not additionally adding a sacrificial agent, and shows high selectivity to competitive ions and good cycling stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new materials for extracting uranium from seawater, and particularly relates to a conjugated organic polymer material, a preparation method thereof and application of the conjugated organic polymer material in efficient photocatalytic extraction of uranium from seawater without an external sacrificial agent. BACKGROUND

[0002] Due to the growing energy demand, nuclear energy has become one of the important pillars of the transition to a sustainable energy system, with zero carbon emissions and high load capacity. However, the sustainable supply of uranium, as a basic resource of the nuclear industry, faces major challenges. These challenges include the depletion of land-based uranium ore reserves and the environmental hazards caused by the exploitation of land-based uranium ore. Therefore, the exploration and utilization of unconventional uranium resources are becoming increasingly important. It is estimated that there are about 4.5 billion tons of uranium in the world's seawater, which is about 1,000 times the amount of land-based uranium reserves, making it a huge but underdeveloped uranium resource. However, the ultra-low concentration of uranium and the complex seawater matrix pose great challenges to the extraction of uranium. In the study of uranium extraction from seawater, adsorption and photocatalysis are considered to be the two most promising methods. Among them, the adsorption method has achieved kilogram-level uranium extraction in field tests. However, this method is often limited by low uranium extraction capacity and slow extraction rate. In contrast, the photocatalytic method has the advantages of large extraction capacity and fast rate, and is a highly feasible alternative method for seawater uranium extraction. Therefore, in recent years, a large number of photocatalysts have been developed, some of which have achieved the function of seawater uranium extraction. However, since photocatalytic uranium extraction mainly relies on the generation of photo-generated electrons, superoxide radicals (·O2 − ) and hydrogen peroxide (H2O2) to convert soluble uranium elements into insoluble uranium to achieve enrichment, due to the separation of electrons and holes under light, the remaining holes must rely on the consumption of an external sacrificial agent (such as alcohol or organic amine) to inhibit electron-hole recombination and maintain photocatalytic activity. However, considering the huge volume of seawater and the extremely low concentration of uranium, the external sacrificial agent is not feasible in actual marine uranium extraction. Therefore, the application of the photocatalytic method in the field of seawater uranium extraction has been limited to a certain extent.

[0003] Conjugated organic polymers (COPs) are composed of π-conjugated building blocks linked by covalent bonds. Due to the highly conjugated structure, the electrons in COPs can be efficiently transported in the conjugated system, thus endowing them with excellent photoelectrochemical properties. In addition, the structural tunability of COPs makes them an ideal platform for the design and construction of multifunctional photocatalysts. However, there are few reports on the application of COPs in seawater uranium extraction, and there is still a lack of design strategies for efficient COP-based photocatalysts. Therefore, it is necessary to develop a conjugated organic polymer material and its preparation method and efficient photocatalytic seawater uranium extraction application without external sacrificial agent, to solve the problems that the existing photocatalytic uranium extraction material is seriously dependent on external sacrificial agent and cannot be practically applied in large-scale marine environment; the high carrier recombination rate leads to low photocatalytic efficiency; the selective binding ability of uranyl ions is insufficient, and the anti-interference performance is poor. SUMMARY

[0004] Therefore, the present application provides a conjugated organic polymer material, which solves the problems of low uranium extraction efficiency and dependence on external sacrificial agent of the existing photocatalytic uranium extraction material.

[0005] In one aspect, the present application provides a conjugated organic polymer material, which is obtained by Knoevenagel condensation reaction of a compound containing a benzothiadiazole unit and a compound containing a pyridine monomer and then ammonoximation.

[0006] Preferably, the compound containing a benzothiadiazole unit is 2,2'-(benzo[c][1,2,5]thiadiazole-4,7-diylbis(4,1-phenylene))diacetonitrile, and the compound containing a pyridine monomer is 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarboxaldehyde.

[0007] Preferably, the molar ratio of 2,2'-(benzo[c][1,2,5]thiadiazole-4,7-diylbis(4,1-phenylene))diacetonitrile and 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarboxaldehyde is 3:2.

[0008] In another aspect, the present application provides a preparation method of a conjugated organic polymer material, which comprises dispersing 2,2'-(benzo[c][1,2,5]thiadiazole-4,7-diylbis(4,1-phenylene))diacetonitrile and 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarboxaldehyde in a solution containing 1,2-dichlorobenzene and n-butanol, mixing uniformly, adding tetrabutylammonium hydroxide and water, ultrasonic mixing again, degassing after freezing, vacuumizing, thawing and circulating, vacuum sealing, heating under high temperature conditions to complete the reaction, cooling to room temperature, and then obtaining the product after filtration, washing and drying; adding hydroxylamine hydrochloride and triethylamine to the product for stirring reaction, and then washing and drying to obtain the amine oxime group functionalized conjugated organic polymer material.

[0009] Preferably, the volume ratio of 1,2-dichlorobenzene and n-butanol is 1:9.

[0010] Another aspect of the present application provides a use of a conjugated organic polymer material in the preparation of a high-efficiency photocatalytic seawater uranium extraction material. Preferably, the photocatalysis is carried out without the addition of an external sacrificial agent.

[0011] A conjugated organic polymer material provided by the present application is used, in which benzothiadiazole and pyridine units are sequentially introduced into the conjugated organic polymer (COP) skeleton. Based on the material, not only a suitable energy band structure is obtained, but also the intramolecular donor-acceptor interaction is enhanced and the charge separation is promoted. H2O is used as a hole sacrificial agent, and no additional sacrificial agent is needed. On the other hand, by adsorbing and pre-activating dissolved oxygen, the generation of ·O2 − is enhanced, thereby improving the reaction efficiency. Further, the material of the present application has a high uranium extraction efficiency and an excellent uranium extraction capacity under the condition of no external sacrificial agent. In natural seawater, an excellent uranium extraction capacity of up to 19.80 mg g −1 is achieved in only 7 days, and high selectivity to competitive ions and good cycle stability are exhibited. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 The synthesis process and chemical structure of Example 1 BB-COP-AO, Comparative Example 1 TT-COP-AO and Comparative Example 2 BT-COP-AO are shown in the figure;

[0013] Figure 2 The infrared spectra of Example 1 BB-COP-AO, Comparative Example 1 TT-COP-AO and Comparative Example 2 BT-COP-AO are shown in the figure;

[0014] Figure 3 The solid-state 13 CCP / MAS NMR spectra of Example 1 BB-COP-AO, Comparative Example 1 TT-COP-AO and Comparative Example 2 BT-COP-AO are shown in the figure;

[0015] Figure 4 The scanning electron micrographs of Example 1 BB-COP-AO, Comparative Example 1 TT-COP-AO and Comparative Example 2 BT-COP-AO are shown in the figure;

[0016] Figure 5 The uranium extraction performance results of Example 1 BB-COP-AO, Comparative Example 1 TT-COP-AO and Comparative Example 2 BT-COP-AO are shown in the figure;

[0017] Figure 6 The uranium recovery results of Example 1 BB-COP-AO in different pH solutions (under dark and light conditions) are shown in the figure;

[0018] Figure 7 The kinetic test results of Example 1 BB-COP-AO photocatalytic uranium extraction in different concentrations of uranium solution;

[0019] Figure 8 The influence of competitive metal ions on the performance of Example 1 BB-COP-AO photocatalytic uranium recovery;

[0020] Figure 9 The reusability test results of Example 1 BB-COP-AO photocatalytic uranium recovery;

[0021] Figure 10 The uranium extraction performance of Example 1 BB-COP-AO in natural seawater under dark and light conditions;

[0022] Figure 11 The uranium extraction performance of different coexisting ions in natural seawater under light conditions. DETAILED DESCRIPTION

[0023] The principles and characteristics of the present application are described below in conjunction with the accompanying drawings, and the examples are only used to explain the present application and are not intended to limit the scope of the present application.

[0024] All chemical reagents and raw materials were purchased from commercial suppliers and used directly without further purification. [1,1':4',1''-Triphenyl]-4,4''-diacetonitrile (TPH-2CN), 2,2'-(benzo[c][1,2,5]thiadiazole-4,7-diylbis(4,1-phenylene))diacetonitrile (BTD-2CN), 5'-(4-formylphenyl)-[1,1':3',1''-triphenyl]-4,4''-dicarbaldehyde (TFPB), and 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarbaldehyde (BTPA) were purchased from Jilin Zhongke Research Technology Co., Ltd. n-Butanol (n-BuOH) and 1,2-dichlorobenzene (o-DCB) were purchased from Aldrich Reagent Co., Ltd. Tetrabutylammonium hydroxide (TBAH), hydroxylamine hydrochloride (NH2OH·HCl), and triethylamine were purchased from Macklin Reagent Co., Ltd. N,N-dimethylformamide (DMF), tetrahydrofuran (THF), and anhydrous ethanol (EtOH) were purchased from Xilong Scientific Co., Ltd.

[0025] Example 1: A preparation method of a conjugated organic polymer material (BB-COP-AO), comprising the following steps:

[0026] (1) Synthesis of BB-COP-CN

[0027] BTD-2CN (21.99 mg, 0.06 mmol) and BTPA (15.74 mg, 0.04 mmol) were uniformly dispersed in a mixed solution of o-DCB / n-BuOH (0.2 mL / 1.8 mL). The dispersion was placed in a 10 mL ampoule and sonicated for 5 min. Then 0.2 mL TBAH (1.0 M in methanol) and 0.1 mL deionized water were added and sonicated for another 5 min. After the ampoule was degassed by three freeze-pump-thaw cycles, it was flame-sealed under vacuum and heated at 120 °C for 3 days. After the reaction was completed, the mixture was cooled to room temperature, and the resulting precipitate was collected by suction filtration and washed with DMF, deionized water, and THF. The product was further purified by Soxhlet extraction (methanol and THF) and dried at 80 °C under vacuum for 12 h to obtain BB-COP-CN (yield 75.21%).

[0028] (2) Synthesis of BB-COP-AO

[0029] The 0.2 g BB-COP-CN was ultrasonically dispersed in 40 mL of anhydrous ethanol for 20 min. Then 1.0 g of hydroxylamine hydrochloride (NH2OH-HCl) and 5 mL of triethylamine were added and the reaction was stirred at 85 °C for 24 h. After the reaction was completed, the product was collected by suction filtration and washed with ethanol, deionized water, and methanol several times. The final solid was dried at 70 °C under vacuum for 24 h to obtain oxime-functionalized BB-COP-AO.

[0030] Comparative Example One: A method of preparing a conjugated organic polymeric material (TT-COP-AO) comprising the following steps:

[0031] (1) Synthesis of TT-COP-CN

[0032] TPH-2CN (12.33 mg, 0.06 mmol) and TFPB (15.62 mg, 0.04 mmol) were uniformly dispersed in a solution of o-DCB / n-BuOH (0.4 mL / 1.6 mL). The dispersion was placed in a 10 mL ampoule and sonicated for 5 min. Then 0.2 mL TBAH (1.0 M in methanol) and 0.1 mL deionized water were added and sonicated for another 5 min. After the ampoule was degassed by three freeze-pump-thaw cycles, it was flame-sealed under vacuum and heated at 120 °C for 3 days. After the reaction was completed, the mixture was cooled to room temperature, and the resulting precipitate was collected by suction filtration and washed with DMF, deionized water, and THF. The product was further purified by Soxhlet extraction (methanol and THF) and dried at 80 °C under vacuum for 12 h to obtain yellowish TT-COP-CN (22.71 mg, yield 81.26%).

[0033] (2) TT-COP-AO synthesis

[0034] TT-COP-CN (0.2 g, 0.06 mmol) was ultrasonically dispersed in 40 mL of absolute ethanol for 20 min. Then, 1.0 g of hydroxylamine hydrochloride (NH2OH HCI) and 5 mL of triethylamine were added and the reaction was stirred at 85 °C for 24 h. After completion of the reaction, the product was collected by suction filtration and washed thoroughly with ethanol, deionized water, and methanol. The final solid was dried at 70 °C under vacuum for 24 h to obtain oxime-functionalized TT-COP-AO.

[0035] Comparative Example Two: A method of preparing a conjugated organic polymeric material (BT-COP-AO) comprising the steps of:

[0036] (1) BT-COP-CN synthesis

[0037] BTD-2CN (21.99 mg, 0.06 mmol) and TFPB (15.62 mg, 0.04 mmol) were uniformly dispersed in a solution of n-BuOH (2 mL). The dispersion was placed in a 10 mL ampoule and ultrasonicated for 5 min. Then, 0.2 mL of TBAH (1.0 M in methanol) and 0.1 mL of deionized water were added and ultrasonicated again for 5 min. The ampoule was degassed by three freeze- vacuum-thaw cycles, flame-sealed under vacuum, and heated at 120 °C for 3 days. After completion of the reaction, the mixture was cooled to room temperature and the resulting precipitate was collected by suction filtration and washed sequentially with DMF, deionized water, and THF. The product was further purified by Soxhlet extraction (methanol and THF) and dried at 80 °C under vacuum for 12 h to obtain light yellow BT-COP-CN (yield 78.63%).

[0038] (2) BT-COP-AO synthesis

[0039] TT-COP-CN (0.2 g, 0.06 mmol) was ultrasonically dispersed in 40 mL of absolute ethanol for 20 min. Then, 1.0 g of hydroxylamine hydrochloride (NH2OH HCI) and 5 mL of triethylamine were added and the reaction was stirred at 85 °C for 24 h. After completion of the reaction, the product was collected by suction filtration and washed thoroughly with ethanol, deionized water, and methanol. The final solid was dried at 70 °C under vacuum for 24 h to obtain oxime-functionalized TT-COP-AO.

[0040] As Figure 1As shown, three conjugated organic polymer materials (COPs) were synthesized using the Knoevenagel condensation reaction: BB-COP-AO (Example 1), TT-COP-AO (Comparative Example 1), and BT-COP-AO (Comparative Example 2). Their monomer pairings were 2,2'-(benzo[c][1,2,5]thiadiazole-4,7-dimethylbis(4,1-phenylene))diacetonitrile (BTD-2CN) and 5,5',5''-(benzene-1,3,5-triyl)tripyridinecarboxaldehyde (BTPA), respectively. 1,1':4',1''-triphenyl]-4,4''-diacetonitrile (TPH-2CN) and 5'-(4-formylphenyl)-[1,1':3',1''-triphenyl]-4,4''-dicarboxaldehyde (TFPB), 2,2'-(benzo[c][1,2,5]thiadiazole-4,7-dimethylbis(4,1-phenylene))diacetonitrile (BTD-2CN) and 5'-(4-formylphenyl)-[1,1':3',1''-triphenyl]-4,4''-dicarboxaldehyde (TFPB).

[0041] (1) Fourier transform infrared spectroscopy (FT-IR) was used to characterize BB-COP-AO of Example 1, TT-COP-AO of Comparative Example 1, and BT-COP-AO of Comparative Example 2, as follows: Figure 2 The results showed that approximately 1740 cm in the monomer -1 The C=O stretching vibration peak of the aldehyde group disappears in the synthesized conjugated organic polymer materials COPs, proving that the monomer underwent a Knoevenagel condensation reaction. Furthermore, the cyano group has a peak at approximately 2248 cm⁻¹ in the monomer. -1 The C≡N stretching vibration peak shifted to approximately 2215 cm⁻¹ after polymerization. -1 This indicates that the chemical environment of the cyano group has changed. After oxime modification, the characteristic C≡N peak disappears, and the peak reappears at approximately 1631 cm⁻¹. -1 and 1263 cm -1 New absorption peaks appeared at [location], corresponding to the C=N and C–N stretching vibrations of the amidoxime group, respectively. This confirms the successful conversion of the cyano group to the amidoxime group. (Example: ...) Figure 3 solid state 13 C-cross polarization / magic angle rotation nuclear magnetic resonance (C-cross polarization / magic angle rotation nuclear magnetic resonance) 13 The C CP / MAS NMR results further confirmed the occurrence of the Knoevenagel condensation reaction and the presence of the amylopyridine oxime group, indicating the successful preparation of the aminooxime-modified conjugated organic polymer material COPs.

[0042] (2) The BB-COP-AO of Example 1, the TT-COP-AO of Comparative Example 1, and the BT-COP-AO of Comparative Example 2 were tested using a scanning electron microscope (SEM), such as... Figure 4The results show that the original TT-COP-CN, BT-COP-CN and BB-COP-CN all exhibit nanofiber morphology, and after modification by oximation, TT-COP-AO, BT-COP-AO and BB-COP-AO maintain the overall morphology and do not show obvious structural degradation.

[0043] Example three: The application of the conjugated organic polymer material prepared by the application to high-efficiency photocatalytic seawater uranium extraction without external sacrificial agent.

[0044] (1) Study the photocatalytic uranium extraction performance of TT-COP-AO, BT-COP-AO and BB-COP-AO,

[0045] A 300 W xenon lamp was used as a simulated sunlight source (light intensity 1 kW m -2 ), and a dark condition experiment was used as a control. The experiment was carried out in a jacketed quartz beaker reactor, and the reaction temperature was maintained at 23±2°C through a water cooling system. The uranium extraction solution was prepared by dissolving UO2(NO3)2·6H2O in deionized water, and the pH value of the solution was adjusted by HNO3 and NaHCO3.

[0046] During the extraction process, 2 mL was taken at regular time intervals and filtered through a 0.22 μm microporous filter. The uranium concentration in the solution was determined by inductively coupled plasma mass spectrometry (ICP-MS) and Arsenazo-III spectrophotometry with a detection wavelength of 652 nm. According to the change in uranium concentration, the real-time uranium extraction capacity (q t , mg / g) of the photocatalyst was calculated according to formula (1):

[0047] (1)

[0048] Where V (L) is the solution volume, m (g) is the photocatalyst mass, C0 and C t (mg / L) are the initial and t-time uranium concentrations, respectively. When the uranium extraction reaches equilibrium, the corresponding extraction capacity and concentration are denoted as q e and C e , respectively.

[0049] The results are shown in Figure 5 , and the uranium equilibrium adsorption capacities of the three COPs during the 3 h dark adsorption process are similar, verifying the binding ability of the amidoxime groups in the COPs to uranyl ions. Under light conditions, the uranium extraction performance of the three COPs is significantly improved, highlighting their photocatalytic function. Among them, BB-COP-AO shows the fastest uranium extraction rate, proving the success of the optimization strategy.

[0050] Table 1 Uranium extraction performance of conjugated organic polymer materials constructed from different monomers

[0051] Item / material BB-COP-AO BT-COP-AO TT-COP-AO Uranium extraction rate 43.09 mg g -1 h -1 ]]> 34.47 mg g -1 h -1 ]]> 30.93 mg g -1 h -1 ]]> Equilibrium uranium extraction capacity 775.54 mg g -1 ]] 758.42 mg g -1 ]]> 742.20 mg g -1 ]]>

[0052] (2) The effect of solution pH on the photocatalytic uranium extraction by BB-COP-AO was studied. The results are shown in Figure 6 and Figure 7 . The analysis of uranium extraction behavior under different pH conditions showed that the uranium extraction efficiency of BB-COP-AO reached the highest at pH 6. Under this condition, the uranium extraction capacity was as high as 2390.26 mg g -1 within 16 h when the initial uranium concentration was 64 ppm, which indicated that the BB-COP-AO of the present application had excellent uranium extraction performance without the addition of a sacrificial agent.

[0053] (3) The effect of competitive metal ions on the photocatalytic uranium extraction by BB-COP-AO was studied, as shown in Figure 8 . The results showed that even when the concentration of individual competitive ions (including Na + , K + , Cu 2+ , Zn 2+ , Fe 3+ , Co 2+ , Ba 2+ , Pb 2+ , Ni 2+ , Sr 2+ and V (V)) was 10 times that of uranium, the uranium recovery rate could still be over 90%, which showed the excellent anti-interference ability of BB-COP-AO and indicated that BB-COP-AO had high selectivity.

[0054] (4) The recycling performance of BB-COP-AO for photocatalytic uranium extraction was studied. The results are shown in Figure 9 . After six cycles of use, BB-COP-AO still maintained 82% of the initial recovery efficiency, which showed good reusability.

[0055] (5) The uranium extraction behavior of BB-COP-AO in natural seawater was studied. As shown in Figure 10 , the uranium adsorption capacity of BB-COP-AO was 4.70 mg g -1 in the dark, but increased significantly to 19.80 mg g -1 under light, which was equivalent to an increase of 4.21 times, indicating that light had a significant promoting effect on uranium extraction. Under light conditions, the uranium extraction capacity of BB-COP-AO in natural seawater was higher than that of most existing photocatalysts, which showed good application potential. As shown in Figure 11 , BB-COP-AO showed excellent selectivity to coexisting metal elements (including Fe, Cu, Mn, Zn, Al, Cr, Ni and V).

[0056] In summary, the conjugated organic polymer material provided by the present application introduces benzothiadiazole and pyridine units into the conjugated organic polymer (COP) skeleton in sequence, optimizes the energy band structure, enhances the intramolecular donor-acceptor interaction and promotes charge separation, and thus has excellent photocatalytic properties. On the other hand, the material provided by the present application can achieve an excellent uranium extraction capacity of up to 19.80 mg g -1 in natural seawater in only 7 days without an external sacrificial agent, and exhibits high selectivity to competitive ions and good cycle stability.

[0057] The above merely describes preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A conjugated organic polymer material, characterized in that, The material is obtained by Knoevenagel condensation of a compound containing a benzothiadiazole unit and a compound containing a pyridine monomer followed by ammonium oximeation.

2. The conjugated organic polymer material according to claim 1, characterized in that, The compound containing the benzothiadiazole unit is 2,2'-(benzo[c][1,2,5]thiadiazole-4,7-dimethylbis(4,1-phenylene))diacetonitrile, and the compound containing the pyridine monomer is 5,5',5''-(benzene-1,3,5-trimethyl)tripyridinecarboxaldehyde.

3. The conjugated organic polymer material according to claim 1, characterized in that, The molar ratio of 2,2'-(benzo[c][1,2,5]thiadiazole-4,7-dimethylbis(4,1-phenylene))diacetonitrile and 5,5',5''-(benzene-1,3,5-trimethyl)tripyridinecarboxaldehyde is 3:

2.

4. A method for preparing a conjugated organic polymer material according to any one of claims 1-3, characterized in that, 2,2'-(benzo[c][1,2,5]thiadiazole-4,7-dimethylbis(4,1-phenylene))diacetonitrile and 5,5',5''-(benzene-1,3,5-trimethyl)tripyridinecarboxaldehyde were dispersed in a solution containing 1,2-dichlorobenzene and n-butanol and mixed thoroughly. Tetrabutylammonium hydroxide and water were added, and the mixture was ultrasonically mixed again. After freezing, vacuuming, melting, and degassing, the mixture was vacuum-sealed. After the reaction was completed under high temperature conditions, the mixture was cooled to room temperature, filtered, washed, and dried to obtain the product. Hydroxylamine hydrochloride and triethylamine were added to the product and stirred to react. After washing and drying, a conjugated organic polymer material with a methylamine oxime group functionalized was obtained.

5. The method for preparing a conjugated organic polymer material according to claim 4, characterized in that, The volume ratio of 1,2-dichlorobenzene to n-butanol is 1:

9.

6. The application of the conjugated organic polymer material according to any one of claims 1-3 in the preparation of highly efficient photocatalytic seawater uranium extraction materials.

7. The application according to claim 6, characterized in that, Photocatalysis was carried out without the addition of any sacrificial agent.

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