Preparation method of ordered mesoporous MOFs with hollow structure and application thereof in uranium extraction

Abstract

The present application relates to a kind of ordered mesoporous MOFs of hollow structure preparation method and its application of extracting uranium, the present application is by accurately regulating the kind and content of organic ligand in reaction system, the molar ratio of terephthalic acid and amino terephthalic acid is controlled at 92:8, can be quickly synthesized in one step with hollow structure ordered mesoporous MOFs while amino functionalization, method is simple, operability is strong. Verified by experiment, the ordered mesoporous MOFs with hollow structure of the present application has excellent anti-interference ability, shows high selectivity adsorption to uranium, provides new ideas and selection for seawater uranium extraction.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nuclear engineering, and particularly relates to a novel material of hollow-structured ordered mesoporous MOFs and a simple synthesis preparation method thereof, and application of the material in adsorption and extraction of a key radionuclide uranium in seawater. BACKGROUND

[0002] With the continuous rise of global energy demand and the increasingly stringent carbon emission constraints, nuclear energy as a new clean energy has become increasingly prominent. However, the land deposits of uranium, as an irreplaceable nuclear fuel, are not only extremely unevenly distributed, but also face the dilemma of soaring mining costs. In contrast, the total amount of marine uranium resources is 4.5 billion tons (in the form of [UO2(CO3)3] 4- ], which can theoretically meet the energy needs of mankind for a thousand years. This makes seawater uranium extraction a major strategic issue. The materials currently used for seawater uranium extraction, including carbon nitride and covalent organic frameworks, have various problems such as poor stability, weak adsorption capacity, and poor selectivity, and there is an urgent need to develop new adsorbents.

[0003] Metal-Organic Frameworks (MOFs) as a new generation of seawater uranium extraction functional materials, with their unique structure controllability, ultra-high specific surface area, and precise adjustable pore chemical environment, have shown significant advantages in seawater uranium adsorption. The periodic self-assembly characteristics allow the precise control of pore size distribution, surface functional group type (such as amino, mercapto, etc.), and topological structure (such as ZIF-8, UiO-66 series) through molecular-level design of metal cluster nodes and organic ligands, thereby establishing a high-efficiency ion recognition and selective capture mechanism. However, traditional MOFs materials face multiple technical challenges in actual marine environments: first, the micropore-dominated structure (pore size < 2 nm) leads to blocked mass transfer path and limited diffusion of uranyl ions, resulting in lagging adsorption rate; second, the coordination-saturated metal nodes result in insufficient exposure of effective active sites, leading to a significant gap between the adsorption capacity and the theoretical value; third, the presence of interfering competitive ions (such as V 5+ , etc.), biological fouling (such as E. coli, etc.) and other constraints in complex marine environments severely weaken the actual application performance of the material. To solve the problem of low mass transfer efficiency caused by the microporous structure of MOFs, Huitao Fan et al. successfully prepared OM-Ce-MOF with ordered mesoporous structure by using Pluronic F127 as a soft template, cerium nitrate ammonia as a metal source, and terephthalic acid as an organic ligand. However, its adsorption capacity and adsorption rate have only been slightly improved in actual applications.

[0004] In summary, it is necessary to invent a new material with more excellent uranium adsorption effect. SUMMARY

[0005] The application aims to solve the technical problem that the existing metal organic framework material is not ideal for uranium adsorption effect, and provides a technical solution of optimizing MOFs structure and modifying functional groups, so that a new MOFs material is prepared through a simple step, and a more ideal seawater uranium extraction effect is achieved.

[0006] The strategy of the application team to optimize MOFs is to construct an ordered mesoporous structure and modify functional groups. Considering that amino groups can specifically bind to uranyl ions to improve material selectivity, it is initially conceived to perform amino functionalization on the basis of an ordered mesoporous structure. Direct synthesis method is tried, that is, other components (acetic acid, sodium perchlorate monohydrate, Pluronic F127, cerium nitrate ammonia) in the reaction system remain unchanged, and part of terephthalic acid is replaced with amino terephthalic acid to directly synthesize amino functionalized OM-Ce-MOF. During the test, when the material synthesized in one of the tests was characterized by transmission electron microscopy, we were shocked to find that the material surprisingly formed a hollow structure while having an ordered mesoporous structure and amino functionalization, so it was named H-OM-Ce-MOF-NH2. After the material is used for uranium extraction experiments, it is found that its adsorption performance and adsorption rate are greatly improved compared with microporous Ce-MOF and OM-Ce-MOF, which is because the coexistence of hollow structure and ordered mesoporous structure greatly improves the utilization rate of active sites of the material, and the amino functionalization further improves the number of active sites. Through further systematic investigation and arrangement, the complete technical solution of the application is formed, as follows:

[0007] The first aspect of the application is to provide a rapid preparation method of hollow ordered mesoporous MOFs, which is unique in that the structure of the material is controlled by adjusting the type and content of the organic ligand, and the whole reaction process has only one step:

[0008] After the acetic acid, sodium perchlorate monohydrate, Pluronic F127, cerium nitrate ammonia, terephthalic acid and amino terephthalic acid are added to the deionized water and uniformly mixed, they are reacted at 55-65 DEG C for 24-28 min, centrifuged, washed and dried to obtain the product;

[0009] The molar ratio of the terephthalic acid and the amino terephthalic acid is 92:8.

[0010] Further, the reaction time is 25 min.

[0011] Further, the molar ratio of the sodium perchlorate monohydrate, Pluronic F127, cerium nitrate ammonia, terephthalic acid and amino terephthalic acid is 300-400:0.7-0.9:90-110:92:8.

[0012] Further, the molar ratio of sodium perchlorate monohydrate, Pluronic F127, cerium nitrate, terephthalic acid and amino terephthalic acid is 356:0.79:100:92:8.

[0013] Further, the volume ratio of deionized water and acetic acid is 18-25:1; preferably, the volume ratio of deionized water and acetic acid is 20:1.

[0014] Further, the mass-volume ratio of Pluronic F127 and the deionized water is 100 mg:5-10 mL; preferably, the mass-volume ratio of Pluronic F127 and the deionized water is 100 mg:6 mL.

[0015] Further, the washing is sequentially washing with distilled water and DMF.

[0016] Further, after the centrifugal washing, the obtained solid material is soaked in ethanol at 55-65℃ for 1-3 days to remove the Pluronic F127 template, and the ethanol needs to be replaced at least 4 times a day during the soaking.

[0017] Further, the drying is placed in a vacuum drying oven at 60-80℃, and the drying time is 12-24 h.

[0018] The second aspect of the present application is to provide the ordered mesoporous MOFs of the hollow structure obtained by the above method.

[0019] The third aspect of the present application is to provide the application of the obtained ordered mesoporous MOFs of the hollow structure in the extraction of radionuclide uranium in seawater.

[0020] Further, the method comprises the following steps:

[0021] (1) Taking a solution containing radionuclide uranium, adding the ordered mesoporous MOFs of the hollow structure as an adsorbent, adjusting the pH, and performing adsorption;

[0022] (2) Shaking the obtained material in step (1) in a constant temperature oscillator, and then centrifuging for further separation.

[0023] In further, the shaking time in step (2) is 12 h.

[0024] The beneficial effects produced by the above technical solutions are:

[0025] (1) The reaction process of the present application only uses one step to prepare the three-in-one MOFs integrated with ordered mesoporous structure, hollow structure and amino functionalization, and the operation is simple, no harmful substances are produced, the stability is strong, storage is easy, and the present application has the feasibility of commercial production.

[0026] (2) The multifunctional MOFs obtained in the present application are a new type of adsorbent, and experiments have verified that the multifunctional MOFs have high adsorption capacity, fast adsorption rate and excellent selectivity in the field of seawater uranium removal. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The structure schematic diagram and transmission electron microscope image of the MOFs described in the test investigation example 1 of the present application under different reaction times are shown in the following figure;

[0028] Figure 2 The structure schematic diagram, transmission electron microscope image and corresponding adsorption kinetics of the synthesized material of the MOFs described in the test investigation example 2 of the present application under different amino terephthalic acid ratios are shown in the following figure;

[0029] Wherein: a is the structure schematic diagram of different amino terephthalic acid molar ratios; b1 is the transmission electron microscope image of the amino terephthalic acid molar ratio of 1%; b2 is the adsorption curve of the amino terephthalic acid molar ratio of 1%; c1 is the transmission electron microscope image of the amino terephthalic acid molar ratio of 3%; c2 is the adsorption curve of the amino terephthalic acid molar ratio of 3%; d1 is the transmission electron microscope image of the amino terephthalic acid molar ratio of 5%; d2 is the adsorption curve of the amino terephthalic acid molar ratio of 5%; e1 is the transmission electron microscope image of the amino terephthalic acid molar ratio of 8%; e2 is the adsorption curve of the amino terephthalic acid molar ratio of 8%; f1 is the transmission electron microscope image of the amino terephthalic acid molar ratio of 10%; and f2 is the adsorption curve of the amino terephthalic acid molar ratio of 10%;

[0030] Figure 3 The N2 adsorption and desorption curve graphs of H-OM-Ce-MOF-NH2, OM-Ce-MOF and microporous Ce-MOF described in the structure characterization test example 1 of the present application are shown in the following figure;

[0031] Figure 4 The infrared spectrograms of H-OM-Ce-MOF-NH2, OM-Ce-MOF and microporous Ce-MOF described in the structure characterization test example 1 of the present application are shown in the following figure;

[0032] Figure 5 The adsorption isotherm graphs of H-OM-Ce-MOF-NH2, OM-Ce-MOF and microporous Ce-MOF described in the effect investigation example 2 of the present application are shown in the following figure. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present application clearer, the following clearly and completely describes the present application with specific examples and drawings.

[0034] The experimental methods in the following examples and comparative examples are all conventional methods unless otherwise specified; the experimental materials used are all purchased from conventional biochemical reagent manufacturers unless otherwise specified.

[0035] Example 1

[0036] Preparation of hollow-structured ordered mesoporous MOFs (H-OM-Ce-MOF-NH2):

[0037] 0.36 mL of acetic acid, 600 mg of sodium perchlorate monohydrate, 120 mg of Pluronic F127, 658 mg of cerium nitrate, 183.27 mg of terephthalic acid and 17.38 mg of amino terephthalic acid (molar ratio of 92:8) were added to 9 mL of deionized water, mixed uniformly and reacted at 60°C for 25 min. The synthesized material was collected by centrifugation and washed with 36 mL of distilled water and DMF for 3 times respectively. After centrifugation, the obtained material was soaked in 60 mL of anhydrous ethanol at 60°C for two days to remove the F127 template, and the anhydrous ethanol was replaced every 6 hours during the soaking. After the anhydrous ethanol soaking was completed, the obtained material was placed in a 65°C vacuum drying oven, and the drying time was 12 h to obtain H-OM-Ce-MOF-NH2.

[0038] Example 2

[0039] Preparation of hollow-structured ordered mesoporous MOFs (H-OM-Ce-MOF-NH2):

[0040] 0.40 mL of acetic acid, 674.16 mg of sodium perchlorate monohydrate, 136.71 mg of Pluronic F127, 723.80 mg of cerium nitrate, 183.27 mg of terephthalic acid and 17.38 mg of amino terephthalic acid (molar ratio of 92:8) were added to 9 mL of deionized water, mixed uniformly and reacted at 60°C for 25 min. The synthesized material was collected by centrifugation and washed with 36 mL of distilled water and DMF for 3 times respectively. After centrifugation, the obtained material was soaked in 60 mL of anhydrous ethanol at 60°C for two days to remove the F127 template, and the anhydrous ethanol was replaced every 6 hours during the soaking. After the anhydrous ethanol soaking was completed, the obtained material was placed in a 65°C vacuum drying oven, and the drying time was 12 h to obtain H-OM-Ce-MOF-NH2.

[0041] Example 3

[0042] Preparation of hollow-structured ordered mesoporous MOFs (H-OM-Ce-MOF-NH2):

[0043] 0.35 mL acetic acid, 507.6 mg sodium perchlorate monohydrate, 106 mg Pluronic F127, 591.9 mg cerium ammonium nitrate, 183.27 mg terephthalic acid and 17.38 mg amino terephthalic acid (molar ratio of 92:8) were added to 9 mL of deionized water and mixed uniformly, and then reacted at 60°C for 25 min. The synthesized material was collected by centrifugation and washed with 36 mL of distilled water and DMF for 3 times, respectively. After centrifugation, the obtained material was soaked in 60 mL of anhydrous ethanol at 60°C for two days to remove the F127 template, and the anhydrous ethanol was replaced every 6 hours. After the anhydrous ethanol soaking was completed, the obtained material was placed in a 65°C vacuum drying oven, and the drying time was 12 h, to obtain H-OM-Ce-MOF-NH2.

[0044] Test Investigation Example 1

[0045] This test investigates the structure of MOFs materials prepared under different reaction times:

[0046] 0.36 mL acetic acid, 600 mg sodium perchlorate monohydrate, 120 mg Pluronic F127, 658 mg cerium ammonium nitrate, 183.27 mg terephthalic acid and 17.38 mg amino terephthalic acid (molar ratio of 92:8) were added to 9 mL of deionized water and mixed uniformly, and then reacted at 60°C for 15, 20, 35 and 50 min, respectively. The synthesized material was collected by centrifugation and washed with 36 mL of distilled water and DMF for 3 times, respectively. After centrifugation, the obtained material was soaked in 60 mL of anhydrous ethanol at 60°C for two days to remove the F127 template, and the anhydrous ethanol was replaced every 6 hours. After the anhydrous ethanol soaking was completed, the obtained material was placed in a 65°C vacuum drying oven, and the drying time was 12 h,

[0047] The MOFs obtained under different reaction times were analyzed by transmission electron microscopy, and the structure schematic diagram and transmission electron microscopy images are shown in Figure 1 By controlling the reaction time of the material synthesis (15-50 min), the formation and decomposition mechanism of the hollow structure of H-OM-Ce-MOF-NH2 was revealed. The material experienced five stages of morphological evolution: in the initial stage (15 min), a dense solid nanosphere was formed Figure 1 a,b); in the core-shell structure formation period (20 min), an obvious core-shell interface appeared Figure 1 c,d); in the hollowing stage (25 min), dispersed hollow spheres were formed by self-template sacrificial etching Figure 1 e,f); in the structure instability period (35 min), the surface of the spheres was observed to collapse inward Figure 1 g,h); and in the final stage (50 min), the material structure completely collapsed Figure 1i,j). This process is guided by the Kirkendall effect and Oswald ripening. Under initial supersaturation conditions, Ce 4+ forms a solid nanosphere. With the reaction proceeding, the asymmetric diffusion between the core region (high surface energy Ce 4+ enrichment region) and the shell layer (organic ligand stabilization region) leads to the vacancy enrichment at the interface (Kirkendall effect). Acetic acid selectively dissolves the core region as an etchant, while the shell layer forms a stable layer through enhanced Ce-O-C coordination bonds and π-π stacking. Oswald ripening promotes the directional migration of small grains to large grains, accelerating the formation of hollow structures. When the reaction time exceeds a certain value (35 min), excessive hydrolysis of the ligand leads to a decrease in the cross-linking degree of the shell layer, and the complete removal of the F127 template causes the mesoporous structure to lose support. At this time, the stress imbalance inside the shell layer leads to the collapse of the surface to the inside. After the reaction time reaches 50 min, the complete decomposition of the coordination framework leads to the complete collapse of the material.

[0048] Test Investigation Example 2:

[0049] This test investigates the preparation of MOFs materials with different molar ratios of terephthalic acid and 2-amino terephthalic acid:

[0050] 0.36 mL of acetic acid, 600 mg of sodium perchlorate monohydrate, 120 mg of Pluronic F127, and 658 mg of cerium nitrate ammonium were added to 197.21 mg of terephthalic acid and 2.17 mg of amino terephthalic acid (molar ratio 99:1), 193.22 mg of terephthalic acid and 6.52 mg of amino terephthalic acid (molar ratio 97:3), 189.24 mg of terephthalic acid and 10.86 mg of amino terephthalic acid (molar ratio 95:5), 183.27 mg of terephthalic acid and 17.38 mg of amino terephthalic acid (molar ratio 92:8), and 179.28 mg of terephthalic acid and 21.72 mg of amino terephthalic acid (molar ratio 90:10) in 9 mL of deionized water, mixed uniformly, and reacted at 60°C for 25 min. The synthesized material was centrifuged and washed with 36 mL of distilled water and DMF for 3 times. After centrifugation, the obtained material was soaked in 50 mL of ethanol at 60°C for two days to remove the F127 template, and the anhydrous ethanol was replaced every 6 hours during the soaking period. After the anhydrous ethanol soaking was completed, the obtained material was placed in a 65°C vacuum drying oven, and the drying time was 12 h.

[0051] The MOFs synthesized with different ratios of terephthalic acid and amino terephthalic acid were analyzed by transmission electron microscopy, and the structural schematic diagram and transmission electron microscopy images are as follows: Figure 2As shown, when the BDC-NH2 content is low (1-3%), the material exhibits a solid spherical structure with a diameter of 550 to 450 nm. This is attributed to homogeneous nucleation and isotropic growth under equilibrium coordination, i.e., the BDC-dominated symmetric coordination mode promotes the uniform aggregation of metal clusters. As the BDC-NH2 content increases to 5-10%, the material morphology undergoes a significant change, forming a hollow spherical structure with a diameter of 400 to 200 nm, and the particle size decreases with increasing amino content. This structural change is caused by the combined effect of three factors. First, the carboxylic acid-amino bifunctional groups of BDC-NH2 interact with Ce... 4+ It can form a strong coordination network and build a stable rigid shell, while the reduced BDC ratio weakens the coordination crosslinking density of the core region, leading to increased thermodynamic instability in the core region; secondly, Ce 4+ The outward diffusion rate of ions is significantly higher than the inward migration rate of ligands, resulting in a concentration gradient at the core-shell interface, which triggers vacancy aggregation. Finally, the increased BDC-NH2 content increases the nucleation density, leading to a reduction in the size of the primary grains. The smaller grains migrate to the surface of the larger particles through a dissolution and redeposition process, ultimately forming a hollow structure with a dense and uniform shell.

[0052] This experiment demonstrates that a precise transformation from a solid to a hollow structure can be achieved by simply adjusting the ratio of the two ligands, providing a new approach for morphology engineering of MOFs. Experiments showed that the adsorption performance peaked at a BDC-NH2 content of 8% (BDC / BDC-NH2 = 92:8), while decreasing at higher amino densities (10%). The optimal performance of this material stems from its balanced pore-ligand synergistic effect, where mesopores facilitate rapid diffusion of uranyl ions, a moderate -NH2 density provides sufficient active sites, and steric hindrance is minimal. The hollow structure maximizes the accessible surface area while maintaining structural integrity. Furthermore, partial ligand substitution introduces coordinatingly unsaturated Ce sites, enhancing the binding with uranyl ions. However, excessive amino content (10%) leads to overcrowded -NH2 groups clogging the pores, reducing the utilization of active sites and consequently decreasing adsorption efficiency.

[0053] This study confirms that a BDC / BDC-NH2 ratio of 92:8 can achieve the optimal balance between mass transfer efficiency and coordination strength, providing a new strategy for designing highly selective radionuclide adsorbents.

[0054] Comparative Example 1

[0055] Preparation of MOFs with ordered mesoporous structures without hollow structures (OM-Ce-MOF):

[0056] 0.36 mL of acetic acid, 600 mg of sodium perchlorate monohydrate, 120 mg of Planck F127, 658 mg of cerium ammonium nitrate, and 199.2 mg of terephthalic acid were added to 9 mL of deionized water and mixed thoroughly. The mixture was then reacted at 60 °C for 25 min. The synthesized material was collected by centrifugation and washed three times each with 36 mL of distilled water and DMF. After centrifugation, the obtained material was soaked in 60 mL of ethanol at 60 °C for two days to remove the F127 template, with the ethanol being replaced every 6 hours during this period. After soaking in anhydrous ethanol, the obtained material was placed in a vacuum drying oven at 65 °C for 12 h.

[0057] Comparative Example 2

[0058] Preparation of Ce-MOFs with only microporous structures:

[0059] 35.4 mg of terephthalic acid was dissolved in a mixture of 1.2 mL DMF and 400 μL of cerium ammonium nitrate solution (0.5333 M), followed by the addition of 1 mL formic acid as a conditioner. The mixture was transferred to a 10 mL glass bottle, sealed, and stirred at 100 °C for 15 min. After the reaction was complete, the pale yellow precipitate was collected by centrifugation and washed three times with DMF and acetone to remove unreacted substances. Finally, the obtained material was placed in a vacuum drying oven at 60 °C for 12 h.

[0060] Structural Characterization Test Example 1

[0061] (1) N2 adsorption-desorption tests were conducted on H-OM-Ce-MOF-NH2 prepared in Example 1, OM-Ce-MOF prepared in Comparative Example 1, and microporous Ce-MOF prepared in Comparative Example 2. The N2 adsorption-desorption curves are shown in the figure below. Figure 3 As shown, H-OM-Ce-MOF-NH2 and OM-Ce-MOF exhibit type IV isotherms, while Ce-MOF exhibits type I isotherms, and this is further confirmed by the pore size distribution diagram ( Figure 2 It can also be seen that H-OM-Ce-MOF-NH2 and OM-Ce-MOF both have mesoporous structures, while Ce-MOF only has microporous structures, which confirms the successful construction of mesoporous structures.

[0062] (2) Infrared spectroscopy was performed on the H-OM-Ce-MOF-NH2 prepared in Example 1, the OM-Ce-MOF prepared in Comparative Example 1, and the microporous Ce-MOF prepared in Comparative Example 2 using an infrared spectrometer. The results are as follows: Figure 4 As shown, except for 1654cm -1 Ce at the location 4+ -Characteristic peaks of carboxylic acid coordination and 1550 / 1390 cm⁻¹ -1 asymmetric / symmetric COO at the location -In addition to the peaks of stretching vibration, H-OM-Ce-MOF-NH2 has a new peak at 3200 cm⁻ 1

[0063] Effect evaluation example 1

[0064] The H-OM-Ce-MOF-NH2 prepared in Example 1, the OM-Ce-MOF prepared in Comparative Example 1 and the microporous Ce-MOF prepared in Comparative Example 2 were used to adsorb uranyl carbonate solution at 25°C in the dark, and the specific steps were as follows:

[0065] (1) 0.1 g / L of the adsorbent was added to 10 mg / L of uranyl carbonate solution with pH of 8.3, and the reaction was carried out at 25°C.

[0066] (2) The supernatant was taken by a sampler at 3, 5, 10, 15, 20, 30, 40 and 55 min, respectively, and was filtered and measured for absorbance, and the residual uranium concentration was calculated by a standard curve.

[0067] (3) The equilibrium concentration and the adsorption amount of the material for uranyl carbonate were calculated according to the initial concentration and the measured residual concentration.

[0068] (4) The adsorption time and adsorption amount curve was drawn, and the adsorption process of the adsorbent was inferred by quasi-first-order kinetics and quasi-second-order kinetics.

[0069] The results showed that H-OM-Ce-MOF-NH2 could reach reaction equilibrium in 30 min, and the adsorption amount reached 76.4 mg / g, and the adsorption rate was faster than that of OM-Ce-MOF and Ce-MOF. By comparing the correlation coefficients of quasi-first-order kinetics and quasi-second-order kinetics, the adsorption process was more consistent with the second-order kinetics, and it could be determined that the adsorption process of H-OM-Ce-MOF-NH2 belonged to physical and chemical adsorption.

[0070] The quasi-first-order kinetics and quasi-second-order kinetics models were used to fit the kinetic curves of the material to describe the removal behavior of the material, and the specific formulas were shown as formula 1 and formula 2:

[0071] ln( q e - q t ) = ln q e - K 1 t (1)

[0072] (2)​

[0073] wherein K 1 - the pseudo-first order adsorption constant (min −1 ) ;

[0074] K 2 - the pseudo-second order adsorption constant (g·(mg·min −1 ) ;

[0075] q t - the adsorption amount (mg·g −1 ) at the reaction time of t ;

[0076] q e - the adsorption amount (mg·g −1 ) at the reaction equilibrium.

[0077] Example 2

[0078] The H-OM-Ce-MOF prepared in Example 1, the OM-Ce-MOF prepared in Comparative Example 1 and the microporous Ce-MOF prepared in Comparative Example 2 were used to adsorb uranyl carbonate solutions with different concentrations at 25°C, and the specific steps were as follows:

[0079] (1) 0.1 g / L of the above materials were respectively added into 10, 20, 30, 40, 50, 60, 70 and 80 mg / L uranyl carbonate solutions (pH 8.3) in turn, and placed in a shaking bed overnight.

[0080] (2) After the reaction was completed, the supernatant was centrifuged, and the absorbance was measured. The residual uranium concentration was calculated by a standard curve.

[0081] (3) The equilibrium concentration and the adsorption amount of the material to uranyl carbonate were calculated according to the initial concentration and the measured residual concentration.

[0082] (4) The equilibrium concentration and the adsorption amount were plotted, and the fitting degree was compared by fitting the Langmuir and Freundlich isothermal adsorption models to determine the adsorption type.

[0083] The adsorption isotherm is as follows: Figure 5As shown, the results show that the maximum extraction amount of H-OM-Ce-MOF-NH2 calculated by the Langmuir model is 95.5 mg / g, which is much higher than that of OM-Ce-MOF (64.4 mg / g) and microporous Ce-MOF (46.9 mg / g). The correlation coefficients of the two models (0.985 < 0.907) show that the adsorption process is more consistent with the Langmuir model, that is, monolayer adsorption.

[0084] The adsorption isotherms of the material were simulated by Langmuir and Freundlich models. The specific formulas are shown in formula 3 and formula 4:

[0085] (3)

[0086] ln q e = ln K F +ln C e (4)

[0087] In the formula q e - the adsorption amount of pollutants at the reaction equilibrium (mg·g −1 ) ;

[0088] q max - the maximum theoretical adsorption amount of U(VI) (mg·g −1 ) ;

[0089] C e - the concentration of pollutants at the reaction equilibrium (mg·L −1 ) ;

[0090] K L - Langmuir model coefficient parameter (L·mg −1 ) ;

[0091] K F - Freundlich model coefficient parameter (mg 1−n ·L n ·g −1 ).

[0092] Effect observation example 3

[0093] The effect of H-OM-Ce-MOF-NH2 prepared in Example 1 on adsorbing uranyl carbonate solution under different background ion conditions at 25°C was detected, and the specific steps were as follows:

[0094] (1) Take 0.1 g / L of multi-functional uranium extraction material into 10 mg / L of uranyl carbonate solution with pH=8.3, and then add 0.01M of background ion solution (i.e. KNO3, Ca(NO3)2, Co(NO3)2, Cu(NO3)2, Mg(NO3)2, Sr(NO3)2, Zn(NO3)2, NaVO3, Na2SO4) in sequence, and shake in a shaker overnight.

[0095] (2) After the reaction is completed, the supernatant is obtained by centrifugation, and the absorbance is measured, and the residual uranium concentration is calculated by a standard curve.

[0096] (3) The equilibrium concentration and the adsorption amount of the material on uranyl carbonate are calculated according to the initial concentration and the measured residual concentration.

[0097] (4) The adsorption amounts with and without adding different background ions are compared, and the influence of different ions on the adsorption capacity of the material is summarized.

[0098] The results show that divalent cations exhibit stronger interference, because the coulomb force of active sites increases with the increase of ion valence. It is worth noting that VO3 - show obvious inhibition due to the priority coordination with -NH2 groups. Despite these interferences, H-OM-Ce-MOF-NH2 still maintains excellent selectivity.

[0099] Effect investigation example 4

[0100] The effect of H-OM-Ce-MOF-NH2 prepared in detection example 1 on adsorbing uranyl carbonate solution under different NaCl concentrations at 25°C is detected, and the specific steps are as follows:

[0101] (1) Different concentrations of NaCl (0.1 / 0.2 / 0.3 / 0.4 / 0.5 / 0.6 / 0.7 / 0.8 mol / L) are taken and mixed with uranyl carbonate to prepare a uniform solution, and stirred to ensure that the solution has no precipitate.

[0102] (2) Take 0.1 g / L of H-OM-Ce-MOF-NH2 into 10 mg / L of the above solution with pH=8.3, and shake in a shaker overnight.

[0103] (3) After the reaction is completed, the supernatant is obtained by centrifugation, and the absorbance is measured, and the residual uranium concentration is calculated by a standard curve.

[0104] (4) A column chart of NaCl concentration and adsorption amount is drawn, and the influence of NaCl on the extraction efficiency of the material is judged by comparing the adsorption amount.

[0105] The results show that the extraction efficiency of the material gradually decreases with the increase of the concentration of NaCl, but still can maintain a high extraction efficiency.

[0106] Application example

[0107] Actual seawater standard addition adsorption capacity determination:

[0108] (1) The actual seawater sample was taken from the southeast sea area of Xingcheng City, Huludao City, Liaoning Province, and was used to dissolve uranyl nitrate ions to configure a stock solution.

[0109] (2) 0.1 g / L of the material was added into 10, 20, 30, 40, 50, 60, 70 and 80 mg / L of the prepared solution, respectively, and was placed in a shaking bed for 2 days.

[0110] (3) After the reaction was completed, the supernatant was taken by centrifugation, and the absorbance was measured, and the residual uranium concentration was calculated by a standard curve.

[0111] (4) The equilibrium concentration and the adsorption capacity of the material to the seawater with standard addition were calculated according to the initial concentration and the measured residual concentration.

[0112] The calculated adsorption capacity is 13.92 mg·g −1 The hollow structure ordered mesoporous MOFs obtained by the method can be applied to the field of uranium extraction from seawater.

[0113] Although the present application is described in detail with reference to the foregoing embodiments, those skilled in the art can modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for rapid preparation of ordered mesoporous MOFs of hollow structure, characterized in that, The preparation method comprises: The acetic acid, sodium perchlorate monohydrate, Pluronic F127, cerium nitrate, terephthalic acid and amino terephthalic acid are added into deionized water, mixed uniformly, and then reacted at 55-65℃ for 24-28 min, centrifuged, washed and dried to obtain the product. The molar ratio of the terephthalic acid and the amino terephthalic acid is 92:

8.

2. The method for rapid preparation of hollow structured ordered mesoporous MOFs according to claim 1, characterized in that, The molar ratio of the sodium perchlorate monohydrate, Pluronic F127, cerium nitrate, terephthalic acid and amino terephthalic acid is 300-400:0.7-0.9:90-110:92:

8.

3. The method for rapid preparation of hollow structured ordered mesoporous MOFs according to claim 2, characterized in that, The molar ratio of the sodium perchlorate monohydrate, Pluronic F127, cerium nitrate, terephthalic acid and amino terephthalic acid is 356:0.79:100:92:

8.

4. The process for rapid preparation of hollow structured ordered mesoporous MOFs as claimed in claim 1 wherein, The volume ratio of the deionized water and the acetic acid is 18-25:1; the mass-volume ratio of the Pluronic F127 and the deionized water is 100 mg:5-10 mL.

5. The method for rapid preparation of hollow structured ordered mesoporous MOFs according to claim 1, characterized in that, The washing is sequentially carried out with distilled water and DMF.

6. The process for rapid preparation of hollow structured ordered mesoporous MOFs as claimed in claim-1 wherein, After the centrifugal washing, the obtained solid material is soaked in ethanol at 55-65℃ for 1-3 days to remove the Pluronic F127 template, and the ethanol needs to be replaced at least 4 times a day.

7. The process for rapid preparation of hollow structured ordered mesoporous MOFs as claimed in claim-1 wherein, The drying is carried out in a vacuum drying oven at 60-80℃ for 12-24 h.

8. An ordered mesoporous MOFs with hollow structure obtained by the preparation method of any one of claims 1-7.

9. Application of the ordered mesoporous MOFs with hollow structure of claim 8 in the removal of radionuclide uranium in seawater.

10. Use according to claim 9, characterized in that, The method comprises the following steps: (1) taking a solution containing radionuclide uranium, adding the ordered mesoporous MOFs with hollow structure as an adsorbent, adjusting pH, and performing adsorption; (2) oscillating the product obtained in step (1) in a constant temperature oscillator, and then centrifugally separating.

11. Use according to claim 10, characterized in that, In step (1), the pH is 8.25-8.35, and the adsorption temperature is 25℃; the initial concentration of the radionuclide uranium solution is 10-80 mg / L, and the mass concentration of the adsorbent is 0.1 g / L; in step (2), the oscillation time is 12 h.

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