A uranium peroxo cluster with a core-shell structure and its preparation method and application

Abstract

The present invention relates to a uranium peroxide cluster with a core-shell structure and a preparation method and application thereof, wherein the crystal structure of the uranium peroxide cluster is a core-shell cluster structure; the core of the uranium peroxide cluster is formed by connecting 36 uranium polyhedra in a co-edge manner; the shell of the uranium peroxide cluster is composed of 6 uranium pentamers, each of which is composed of 5 uranium polyhedra and 5 oxalate ligands, and the 5 uranium polyhedra are connected in a co-edge manner to form a five-membered ring structure, and the negative charge of the uranium peroxide cluster is neutralized by potassium ions. The method of the present invention adopts oxalate with strong coordination ability with uranyl ions as ligands, selects potassium ions as counter ions, and prepares a uranium peroxide cluster with novel structure and properties by regulating the amount of reaction reagents, which is expected to be applied and promoted in nuclear fuel cycles.

Description

Technical Field

[0001] The invention relates to the technical field of polymetallic oxygen clusters and preparation thereof, and in particular to a uranium peroxo cluster with a core-shell structure and a preparation method and application thereof. Background Art

[0002] Polyoxometalates are a type of multinuclear aggregates formed by metal ions and oxygen. They have diverse nanostructures and are widely used in catalysis, optoelectronic materials, biomedicine, nuclear fuel cycles, and other fields. Research on polyoxometalates is mostly focused on clusters formed by the condensation of oxygen-containing acid radicals of high oxidation state ions of transition metals such as W, Mo, and V. However, actinide elements such as U, Th, and Pu have certain radioactivity and require certain qualifications for experimental sites and staff, so there are not many studies on actinide clusters. Only the research teams of Peter Burns and May Nyman in the United States and Thierry Loiseau in France have carried out some work.

[0003] At present, Professor Burns first synthesized the first uranium peroxy cluster in 2005 by reacting uranyl ions with hydrogen peroxide under alkaline conditions (Angew. Chem. Int. Ed. 2005, 44 (14), 2135-2139). The structure of the uranium peroxy cluster is composed of uranyl ions connected with peroxide and hydroxide. In the solution, it is in the form of giant anions with a size of about 2nm, which is much larger than common inorganic ions. Therefore, uranium in uranium ore, spent fuel, uranium-containing waste and other materials can be converted into uranium clusters, and then the uranium can be separated by using the size or weight difference between it and other components in the solution, and a uranium separation technology based on clusters can be developed.

[0004] Considering the application of this new uranium separation technology in the nuclear fuel cycle, especially in the reprocessing of spent fuel, researchers have carried out a series of work on the preparation and property research of uranium peroxide clusters in the past decade, and successfully synthesized dozens of uranium peroxide clusters (Dalton Trans. 2018, 47 (17), 5916-5927). However, most of these clusters have similar nanocage structures and their properties are also very similar. Therefore, it is necessary to explore new synthesis ideas to synthesize uranium peroxide clusters with different topological structures and properties, so as to provide more material options for the development of uranium separation technology based on uranium clusters. Summary of the invention

[0005] In order to solve the problem that the currently reported uranium peroxo clusters have a single structure and similar properties, the purpose of the present invention is to provide a uranium peroxo cluster with a core-shell structure and a preparation method and application thereof. The method of the present invention uses oxalate with strong coordination ability with uranyl ions as a ligand, selects potassium ions as counter ions, and explores a synthesis method of a new uranium peroxo cluster by regulating the concentration and dosage of the reaction reagents, the pH value of the reaction solution and other conditions, and prepares a uranium peroxo cluster with a novel structure and properties.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] A uranium peroxide cluster with a core-shell structure, wherein the crystal structure of the uranium peroxide cluster is a core-shell cluster structure;

[0008] The core of the uranium peroxo cluster is composed of 36 uranium polyhedrons connected by sharing edges;

[0009] The shell of the uranium peroxo cluster is composed of 6 uranium pentamers, each of which is composed of 5 uranium polyhedrons and 5 oxalate ligands, and the 5 uranium polyhedrons are connected by sharing edges to form a five-membered ring structure.

[0010] The negative charge of the uranium peroxo cluster is neutralized by potassium ions.

[0011] Furthermore, the uranium polyhedron in the core of the uranium peroxide cluster is a hexagonal bipyramidal polyhedron formed by the coordination of uranyl ions and 6 oxygen atoms from peroxide and / or hydroxide; the uranium polyhedrons in the cores of adjacent uranium peroxide clusters are connected by sharing edges to form a five-membered ring structure or a six-membered ring structure of uranium;

[0012] The uranium polyhedron in the shell of the uranium peroxo cluster is a hexagonal bipyramidal polyhedron formed by the coordination of uranyl ions and six oxygen atoms from peroxide and oxalate; the uranium polyhedrons in the shell of adjacent uranium peroxo clusters are connected by sharing edges to form a five-membered ring structure of uranium.

[0013] Furthermore, the six uranium pentamers are distributed at both ends of the core, and each of the uranium pentamers corresponds one-to-one to the five-membered ring structure in the core and is located directly above the five-membered ring structure in the core;

[0014] Each of the uranium pentamers is connected to the five-membered ring structure in the core through six potassium ions; and the six potassium ions are distributed between the uranium pentamer and the five-membered ring structure of the core, and one of the potassium ions is located at the center of the other five potassium ions;

[0015] One potassium ion is connected to the oxygen atoms of five uranyl ions in the uranium pentamer and the oxygen atoms of five peroxides in the five-membered ring structure in the core respectively;

[0016] The remaining five potassium ions correspond one by one to the positions of the five peroxide radicals of the five-membered ring structure in the core, and are connected to the adjacent uranyl ions and oxygen atoms of the peroxide radicals, respectively.

[0017] Furthermore, the uranyl ion in the core has two coordination modes, namely coordination mode I and coordination mode II;

[0018] The coordination mode I is that each uranyl ion is coordinated with three peroxide radicals respectively;

[0019] The coordination mode II is that each uranyl ion is coordinated with two peroxides and two hydroxides respectively;

[0020] The 24 uranyl ions distributed at both ends of the core adopt coordination mode I to form a hexagonal bipyramid polyhedron; and the 12 uranyl ions distributed in the middle of the core adopt coordination mode II to form a hexagonal bipyramid polyhedron.

[0021] Furthermore, the uranyl ions in each of the uranium pentamers adopt coordination mode III to form a hexagonal bipyramidal polyhedron; the coordination mode III is that each uranyl ion is coordinated with two peroxides and one oxalate.

[0022] Furthermore, the uranium peroxide cluster forms yellow block crystals after crystallization. The uranium peroxide cluster crystals crystallize in the monoclinic system with a space group of C 2 / c. The unit cell parameters are α=90°, β=90.87°, γ=90°;

[0023] The present invention also provides a method for preparing a uranium peroxo cluster having a core-shell structure, comprising the following steps:

[0024] Under stirring, a hydrogen peroxide solution, an alkali solution, a potassium oxalate solution and an iodic acid solution are added to a solution containing uranyl ions, mixed evenly, and then naturally evaporated at room temperature to obtain crystals of uranium peroxide clusters with a core-shell structure.

[0025] Furthermore, the solution containing uranyl ions is a uranyl nitrate solution; and the alkaline solution is a potassium hydroxide solution or a lithium hydroxide solution.

[0026] Furthermore, the concentration of the uranyl nitrate solution is 0.5 mol / L; the concentration of the hydrogen peroxide solution is 30% (wt.); the concentration of the alkaline solution is 2.4-4 mol / L; the concentration of the potassium oxalate solution is 1 mol / L; the concentration of the iodic acid solution is 0.5 mol / L;

[0027] The volume ratio of the solution containing uranyl ions, the hydrogen peroxide solution, the alkaline solution, the potassium oxalate solution and the iodic acid solution is 100:100:100-150:100-200:175-600.

[0028] Furthermore, the pH of the solution after uniform mixing is 5-7.

[0029] The invention also provides an application of a uranium peroxide cluster with a core-shell structure in a nuclear fuel cycle.

[0030] Beneficial effects of the present invention:

[0031] 1. The uranium peroxide cluster of the present invention is a core-shell cluster, in which the "core" is composed of 36 uranium polyhedrons connected together, so it is named U 36 The "shell" is composed of six identical uranium pentamers containing oxalate, each of which contains five uranium polyhedra and five oxalate ligands, so it is named U5-Oxa; accordingly, the core-shell cluster is named U 36 ·6U5-Oxa.

[0032] 2. The “core” U of the uranium peroxo cluster of the present invention 36 Both the uranium pentamer U5-Oxa on the "shell" are negatively charged, and their charges are neutralized by potassium ions distributed near their structures.

[0033] 3. The method of the present invention uses oxalate ions with strong coordination ability with uranyl ions as ligands, selects potassium ions as counter ions, and explores a new synthesis method of uranium peroxy clusters by regulating the amount of reaction reagents, the pH value of the reaction solution and other conditions, and prepares a uranium peroxy cluster with novel structure and properties. 36 ·6U5-Oxa is expected to be widely used in nuclear fuel cycle.

[0034] 4. The method of the present invention is helpful to synthesize more similar uranium peroxide clusters, providing more technical support for spent fuel reprocessing. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is the cluster compound U in the embodiment of the present invention 36 The structure of 6U5-Oxa presented in polyhedral mode (a), the structure of the "core" of the cluster (b), and the structure of a uranium pentamer in the "shell" of the cluster (c). In the figure, yellow: hexagonal bipyramidal polyhedron of uranium; blue: K; red: O; black: C.

[0036] Figure 2 is the cluster compound U in the embodiment of the present invention 36·6U5-Oxa framework diagram. In the diagram, each vertex represents a uranium atom.

[0037] Figure 3 (a) and (b) are clusters U observed from two different angles. 36 ·6U5-Oxa structure diagram.

[0038] In the figure, in order to show the U5-Oxa and U 36 The connection between them is shown in Figure 1. Only one pentamer and the potassium ion associated with it are retained, and no oxygen and carbon atoms are visible. In the figure, yellow: hexagonal bipyramidal polyhedron of uranium; blue: K; red: O; black: C. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0040] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0041] Unless otherwise specified, the experimental methods described in the following examples are all conventional methods; the reagents and materials described are all commercially available unless otherwise specified.

[0042] Example 1

[0043] A method for preparing a uranium peroxo cluster having a core-shell structure comprises the following steps:

[0044] S1. Prepare 0.5 mol / L uranyl nitrate solution, 30% (wt.) hydrogen peroxide solution, 2.4 mol / L lithium hydroxide solution, 1 mol / L potassium oxalate solution, and 0.5 mol / L iodic acid solution.

[0045] S2. In a 5mL glass reaction bottle, add 100μL of 0.5mol / L uranyl nitrate solution, 100μL of 30% (wt.) hydrogen peroxide solution, 100μL of 2.4mol / L lithium hydroxide solution, 200μL of 1mol / L potassium oxalate solution and 200μL of 0.5mol / L iodic acid solution in sequence under stirring; wherein, each time a solution is added, ensure that the solution in the glass reaction bottle is mixed evenly before adding the next solution. At this time, the pH of the mixed solution is between 5 and 7.

[0046] S3. Cover the mouth of the glass reaction bottle with a polytetrafluoroethylene membrane and poke 5-6 small holes in the membrane to allow the solution to evaporate slowly at room temperature. After 3-4 weeks, yellow block crystals will precipitate in the bottle, which is the uranium peroxide cluster U with a core-shell structure. 36 ·Crystals of 6U5-Oxa.

[0047] S4. The crystal was tested at 150 K using a single crystal X-ray diffractometer. Based on the collected data, the unit cell parameters of the crystal were calculated using APEX3 software (see Table 1), and the structure of the crystal was analyzed (see Figure 1 to Figure 3 ).

[0048] Table 1 Uranium peroxoclusters U 36 Crystallographic parameters of 6U5-Oxa

[0049]

[0050]

[0051] like Figure 1 As shown, uranium peroxide cluster U 36 ·6U5-Oxa's "core" U 36 The uranyl ions in the uranyl ion have two coordination modes: the 24 uranyl ions distributed at both ends have the same coordination mode, in which each uranyl ion is coordinated with three peroxides, forming a hexagonal bipyramidal polyhedron; the 12 uranyl ions in the middle have the same coordination mode, in which each uranyl ion is coordinated with two peroxides and two hydroxides, forming a hexagonal bipyramidal polyhedron. These 36 uranyl polyhedrons are connected by sharing edges to form the U 36 cage-like structure.

[0052] Uranium peroxycluster U 36 There are six uranium pentamers in the "shell" of 6U5-Oxa. In each uranium pentamer, the coordination mode of the uranyl ion is the same, all of which are coordinated with two oxygen atoms on two peroxides and one oxalate, forming a hexagonal bipyramidal polyhedron of uranium. These five uranium polyhedrons are also connected by sharing edges to form the five-membered ring structure of U5-Oxa.

[0053] U 36 and U5-Oxa are both negatively charged, and their charges are neutralized by potassium ions distributed near their structures.

[0054] In order to observe the uranium peroxide cluster U 36 The positional relationship between the "core" and "shell" in 6U5-Oxa. We only retained the uranium atoms and connected the adjacent uranium atoms to draw a framework diagram of the cluster, as shown in Figure 2 As shown. Figure 2 It can be found that six uranium pentamers are distributed in U36 Both ends of the pentamer are located at U 36 Above the five-membered ring structure.

[0055] In order to clearly show the uranium pentamer U5-Oxa and U 36 In terms of the connection mode of the five-membered ring structure, we only retained one pentamer and the potassium ion associated with it, and gave the structure diagrams observed from two different angles, such as Figure 3 As shown. Figure 3 It can be found that U 36 There is a potassium ion directly below the five-membered ring structure, and this potassium ion is connected to the five uranyl oxygens in the five-membered ring structure. 36 There are six potassium ions between the five-membered ring structure, one of which is located between U5-oxa and U 36 The remaining five potassium ions are distributed in the middle of the uranium pentamer U5-oxa and the nuclear U 36 The positional distribution of potassium ions and the connection mode with uranyl oxygen and peroxide indicate that potassium ions have an important effect on the core-shell cluster U 36 ·The formation of 6U5-Oxa plays an important role.

[0056] Example 2

[0057] A method for preparing a uranium peroxo cluster having a core-shell structure comprises the following steps:

[0058] S1. Prepare 0.5 mol / L uranyl nitrate solution, 30% (wt.) hydrogen peroxide solution, 2.4 mol / L lithium hydroxide solution, 1 mol / L potassium oxalate solution, and 0.5 mol / L iodic acid solution.

[0059] S2. In a 5mL glass reaction bottle, add 100μL of 0.5mol / L uranyl nitrate solution, 100μL of 30% (wt.) hydrogen peroxide solution, 100μL of 2.4mol / L lithium hydroxide solution, 200μL of 1mol / L potassium oxalate solution and 175μL of 0.5mol / L iodic acid solution in sequence under stirring; wherein, each time a solution is added, ensure that the solution in the glass reaction bottle is mixed evenly before adding the next solution. At this time, the pH of the mixed solution is between 5 and 7.

[0060] S3. Cover the mouth of the glass reaction bottle with a polytetrafluoroethylene membrane and poke 5-6 small holes in the membrane to allow the solution to evaporate slowly at room temperature. After 3-4 weeks, yellow block crystals will precipitate in the bottle, which is the uranium peroxide cluster U with a core-shell structure. 36 ·Crystals of 6U5-Oxa.

[0061] S4. Use a single crystal X-ray diffractometer to test the crystal at a low temperature of 150 K. Based on the collected data, the structure of the crystal is analyzed.

[0062] Uranium peroxy cluster U prepared in the embodiment of the present invention 36 The crystal structure of 6U5-Oxa is a core-shell cluster structure; in this uranium peroxide cluster U 36 In the crystal structure of 6U5-Oxa, the uranium polyhedron refers to a hexagonal bipyramidal polyhedron formed by the coordination of uranyl ions with six oxygen atoms from peroxide, hydroxide or oxalate. Adjacent uranium polyhedrons are connected by sharing edges to form a five-membered ring structure or a six-membered ring structure of uranium.

[0063] Among them, the uranium peroxide cluster U 36 ·6U5-Oxa's core U 36 It is composed of 36 uranium polyhedrons connected by sharing edges, forming U 36 Cage-like structure; "core" U 36 The uranyl ions in the structure have two coordination modes: the 24 uranyl ions distributed at both ends have the same coordination mode, in which each uranyl ion is coordinated with three peroxides to form a hexagonal bipyramidal polyhedron; the 12 uranyl ions in the middle have the same coordination mode, in which each uranyl ion is coordinated with two peroxides and two hydroxides to form a hexagonal bipyramidal polyhedron.

[0064] The uranium peroxo cluster U 36 The "shell" of 6U5-Oxa is composed of six uranium pentamers U5-Oxa, each of which is composed of five uranium polyhedrons and five oxalate ligands, and the five uranium polyhedrons are connected by sharing edges to form a five-membered ring structure. In each uranium pentamer, the coordination mode of the uranyl ion is the same, all of which are coordinated with two oxygen atoms on two peroxides and one oxalate, forming a hexagonal bipyramidal polyhedron of uranium.

[0065] U 36 and U5-Oxa are both negatively charged, and their charges are neutralized by potassium ions distributed near their structures.

[0066] The uranium peroxo cluster U 36 In the crystal structure of 6U5-Oxa, six uranium pentamers U5-Oxa are distributed in the nucleus U 36 Both ends of the pentamer are connected to the core U 36 The five-membered ring structure in the core U corresponds to each other. 36 Just above the five-membered ring structure in;

[0067] Core U 36There is a potassium ion just below the five-membered ring structure, and each uranium pentamer U5-Oxa is connected to the nucleus U via six potassium ions. 36 Specifically, one of the potassium ions is located between the five-membered ring structure of the uranium pentamer U5-oxa and the core U 36 The potassium ion is located in the middle of the five-membered ring structure, and the five uranyl oxygen atoms and the nuclear U of the uranium pentamer U5-Oxa are 36 The remaining five potassium ions are distributed between the uranium pentamer U5-oxa and the nuclear U 36 The positional distribution of potassium ions and the connection mode with uranyl oxygen and peroxide indicate that potassium ions have an important effect on the core-shell cluster U 36 ·6U5-Oxa plays an important role in the formation of uranium peroxide clusters. 36 The crystal structure of 6U5-Oxa is the same as that of Example 1, and they belong to the same crystal structure.

[0068] Example 3

[0069] A method for preparing a uranium peroxo cluster having a core-shell structure comprises the following steps:

[0070] S1. Prepare 0.5 mol / L uranyl nitrate solution, 30% (wt.) hydrogen peroxide solution, 4 mol / L potassium hydroxide solution, 1 mol / L potassium oxalate solution, and 0.5 mol / L iodic acid solution.

[0071] S2. In a 5mL glass reaction bottle, add 100μL of 0.5mol / L uranyl nitrate solution, 100μL of 30% (wt.) hydrogen peroxide solution, 150μL of 4mol / L potassium hydroxide solution, 100μL of 1mol / L potassium oxalate solution and 600μL of 0.5mol / L iodic acid solution in sequence under stirring; wherein, each time a solution is added, ensure that the solution in the glass reaction bottle is mixed evenly before adding the next solution. At this time, the pH of the mixed solution is between 5 and 7.

[0072] S3. Cover the mouth of the glass reaction bottle with a polytetrafluoroethylene membrane and poke 5-6 small holes in the membrane to allow the solution to evaporate slowly at room temperature. After 3-4 weeks, yellow block crystals will precipitate in the bottle, which is the uranium peroxide cluster U with a core-shell structure. 36 ·Crystals of 6U5-Oxa.

[0073] S4. Use a single crystal X-ray diffractometer to test the crystal at a low temperature of 150 K. Based on the collected data, the structure of the crystal is analyzed.

[0074] Uranium peroxy cluster U prepared in the embodiment of the present invention 36 The crystal structure of 6U5-Oxa is a core-shell cluster structure; in this uranium peroxide cluster U 36 In the crystal structure of 6U5-Oxa, the uranium polyhedron refers to a hexagonal bipyramidal polyhedron formed by the coordination of uranyl ions with six oxygen atoms from peroxide, hydroxide or oxalate. Adjacent uranium polyhedrons are connected by sharing edges to form a five-membered ring structure or a six-membered ring structure of uranium.

[0075] Among them, the uranium peroxide cluster U 36 ·6U5-Oxa's core U 36 It is composed of 36 uranium polyhedrons connected by sharing edges, forming U 36 Cage-like structure; "core" U 36 The uranyl ions in the structure have two coordination modes: the 24 uranyl ions distributed at both ends have the same coordination mode, in which each uranyl ion is coordinated with three peroxides to form a hexagonal bipyramidal polyhedron; the 12 uranyl ions in the middle have the same coordination mode, in which each uranyl ion is coordinated with two peroxides and two hydroxides to form a hexagonal bipyramidal polyhedron.

[0076] The uranium peroxo cluster U 36 The "shell" of 6U5-Oxa is composed of six uranium pentamers U5-Oxa, each of which is composed of five uranium polyhedrons and five oxalate ligands, and the five uranium polyhedrons are connected by sharing edges to form a five-membered ring structure. In each uranium pentamer, the coordination mode of the uranyl ion is the same, all of which are coordinated with two oxygen atoms on two peroxides and one oxalate, forming a hexagonal bipyramidal polyhedron of uranium.

[0077] U 36 and U5-Oxa are both negatively charged, and their charges are neutralized by potassium ions distributed near their structures.

[0078] The uranium peroxo cluster U 36 In the crystal structure of 6U5-Oxa, six uranium pentamers U5-Oxa are distributed in the nucleus U 36 Both ends of the pentamer are connected to the core U 36 The five-membered ring structure in the core U corresponds to each other. 36 Just above the five-membered ring structure in;

[0079] Core U 36 There is a potassium ion just below the five-membered ring structure, and each uranium pentamer U5-Oxa is connected to the nucleus U via six potassium ions. 36Specifically, one of the potassium ions is located between the five-membered ring structure of the uranium pentamer U5-oxa and the core U 36 The potassium ion is located in the middle of the five-membered ring structure, and the five uranyl oxygen atoms and the nuclear U of the uranium pentamer U5-Oxa are 36 The remaining five potassium ions are distributed between the uranium pentamer U5-oxa and the nuclear U 36 The positional distribution of potassium ions and the connection mode with uranyl oxygen and peroxide indicate that potassium ions have an important effect on the core-shell cluster U 36 ·6U5-Oxa plays an important role in the formation of uranium peroxide clusters. 36 The crystal structure of 6U5-Oxa is the same as that of Example 1, and they belong to the same crystal structure.

[0080] Example 4

[0081] A method for preparing a uranium peroxo cluster having a core-shell structure comprises the following steps:

[0082] S1. Prepare 0.5 mol / L uranyl nitrate solution, 30% (wt.) hydrogen peroxide solution, 4 mol / L potassium hydroxide solution, 1 mol / L potassium oxalate solution, and 0.5 mol / L iodic acid solution.

[0083] S2. In a 5mL glass reaction bottle, add 100μL of 0.5mol / L uranyl nitrate solution, 100μL of 30% (wt.) hydrogen peroxide solution, 150μL of 4mol / L potassium hydroxide solution, 150μL of 1mol / L potassium oxalate solution and 300μL of 0.5mol / L iodic acid solution in sequence under stirring; wherein, each time a solution is added, ensure that the solution in the glass reaction bottle is mixed evenly before adding the next solution. At this time, the pH of the mixed solution is between 5 and 7.

[0084] S3. Cover the mouth of the glass reaction bottle with a polytetrafluoroethylene membrane and poke 5-6 small holes in the membrane to allow the solution to evaporate slowly at room temperature. After 3-4 weeks, yellow block crystals will precipitate in the bottle, which is the uranium peroxide cluster U with a core-shell structure. 36 ·Crystals of 6U5-Oxa.

[0085] S4. Use a single crystal X-ray diffractometer to test the crystal at a low temperature of 150 K. Based on the collected data, the structure of the crystal is analyzed.

[0086] Uranium peroxy cluster U prepared in the embodiment of the present invention 36 The crystal structure of 6U5-Oxa is a core-shell cluster structure; in this uranium peroxide cluster U36 In the crystal structure of 6U5-Oxa, the uranium polyhedron refers to a hexagonal bipyramidal polyhedron formed by the coordination of uranyl ions with six oxygen atoms from peroxide, hydroxide or oxalate. Adjacent uranium polyhedrons are connected by sharing edges to form a five-membered ring structure or a six-membered ring structure of uranium.

[0087] Among them, the uranium peroxide cluster U 36 ·6U5-Oxa's core U 36 It is composed of 36 uranium polyhedrons connected by sharing edges, forming U 36 Cage-like structure; "core" U 36 The uranyl ions in the structure have two coordination modes: the 24 uranyl ions distributed at both ends have the same coordination mode, in which each uranyl ion is coordinated with three peroxides to form a hexagonal bipyramidal polyhedron; the 12 uranyl ions in the middle have the same coordination mode, in which each uranyl ion is coordinated with two peroxides and two hydroxides to form a hexagonal bipyramidal polyhedron.

[0088] The uranium peroxo cluster U 36 The "shell" of 6U5-Oxa is composed of six uranium pentamers U5-Oxa, each of which is composed of five uranium polyhedrons and five oxalate ligands, and the five uranium polyhedrons are connected by sharing edges to form a five-membered ring structure. In each uranium pentamer, the coordination mode of the uranyl ion is the same, all of which are coordinated with two oxygen atoms on two peroxides and one oxalate, forming a hexagonal bipyramidal polyhedron of uranium.

[0089] U 36 and U5-Oxa are both negatively charged, and their charges are neutralized by potassium ions distributed near their structures.

[0090] The uranium peroxo cluster U 36 In the crystal structure of 6U5-Oxa, six uranium pentamers U5-Oxa are distributed in the nucleus U 36 Both ends of the pentamer are connected to the core U 36 The five-membered ring structure in the core U corresponds to each other. 36 Just above the five-membered ring structure in;

[0091] Core U 36 There is a potassium ion just below the five-membered ring structure, and each uranium pentamer U5-Oxa is connected to the nucleus U via six potassium ions. 36 Specifically, one of the potassium ions is located between the five-membered ring structure of the uranium pentamer U5-oxa and the core U 36 The potassium ion is located in the middle of the five-membered ring structure, and the five uranyl oxygen atoms and the nuclear U of the uranium pentamer U5-Oxa are36 The remaining five potassium ions are distributed between the uranium pentamer U5-oxa and the nuclear U 36 The positional distribution of potassium ions and the connection mode with uranyl oxygen and peroxide indicate that potassium ions have an important effect on the core-shell cluster U 36 ·6U5-Oxa plays an important role in the formation of uranium peroxide clusters. 36 The crystal structure of 6U5-Oxa is the same as that of Example 1, and they belong to the same crystal structure.

[0092] Example 5

[0093] A method for preparing a uranium peroxo cluster having a core-shell structure comprises the following steps:

[0094] S1. Prepare 0.5 mol / L uranyl nitrate solution, 30% (wt.) hydrogen peroxide solution, 2.4 mol / L lithium hydroxide solution, 1 mol / L potassium oxalate solution, and 0.5 mol / L iodic acid solution.

[0095] S2. In a 5mL glass reaction bottle, add 100μL of 0.5mol / L uranyl nitrate solution, 100μL of 30% (wt.) hydrogen peroxide solution, 120μL of 2.4mol / L potassium hydroxide solution, 200μL of 0.5mol / L iodic acid solution and 160μL of 1mol / L potassium oxalate solution in sequence under stirring; wherein, each time a solution is added, ensure that the solution in the glass reaction bottle is mixed evenly before adding the next solution. At this time, the pH of the mixed solution is between 5 and 7.

[0096] S3. Cover the mouth of the glass reaction bottle with a polytetrafluoroethylene membrane and poke 5-6 small holes in the membrane to allow the solution to evaporate slowly at room temperature. After 3-4 weeks, yellow block crystals will precipitate in the bottle, which is the uranium peroxide cluster U with a core-shell structure. 36 ·Crystals of 6U5-Oxa.

[0097] S4. Use a single crystal X-ray diffractometer to test the crystal at a low temperature of 150 K. Based on the collected data, the structure of the crystal is analyzed.

[0098] Uranium peroxy cluster U prepared in the embodiment of the present invention 36 The crystal structure of 6U5-Oxa is a core-shell cluster structure; in this uranium peroxide cluster U 36In the crystal structure of 6U5-Oxa, the uranium polyhedron refers to a hexagonal bipyramidal polyhedron formed by the coordination of uranyl ions with six oxygen atoms from peroxide, hydroxide or oxalate. Adjacent uranium polyhedrons are connected by sharing edges to form a five-membered ring structure or a six-membered ring structure of uranium.

[0099] Among them, the uranium peroxide cluster U 36 ·6U5-Oxa's core U 36 It is composed of 36 uranium polyhedrons connected by sharing edges, forming U 36 Cage-like structure; "core" U 36 The uranyl ions in the structure have two coordination modes: the 24 uranyl ions distributed at both ends have the same coordination mode, in which each uranyl ion is coordinated with three peroxides to form a hexagonal bipyramidal polyhedron; the 12 uranyl ions in the middle have the same coordination mode, in which each uranyl ion is coordinated with two peroxides and two hydroxides to form a hexagonal bipyramidal polyhedron.

[0100] The uranium peroxo cluster U 36 The "shell" of 6U5-Oxa is composed of six uranium pentamers U5-Oxa, each of which is composed of five uranium polyhedrons and five oxalate ligands, and the five uranium polyhedrons are connected by sharing edges to form a five-membered ring structure. In each uranium pentamer, the coordination mode of the uranyl ion is the same, all of which are coordinated with two oxygen atoms on two peroxides and one oxalate, forming a hexagonal bipyramidal polyhedron of uranium.

[0101] U 36 and U5-Oxa are both negatively charged, and their charges are neutralized by potassium ions distributed near their structures.

[0102] The uranium peroxo cluster U 36 In the crystal structure of 6U5-Oxa, six uranium pentamers U5-Oxa are distributed in the nucleus U 36 Both ends of the pentamer are connected to the core U 36 The five-membered ring structure in the core U corresponds to each other. 36 Just above the five-membered ring structure in;

[0103] Core U 36 There is a potassium ion just below the five-membered ring structure, and each uranium pentamer U5-Oxa is connected to the nucleus U via six potassium ions. 36 Specifically, one of the potassium ions is located between the five-membered ring structure of the uranium pentamer U5-oxa and the core U 36 The potassium ion is located in the middle of the five-membered ring structure, and the five uranyl oxygen atoms and the nuclear U of the uranium pentamer U5-Oxa are 36The remaining five potassium ions are distributed between the uranium pentamer U5-oxa and the nuclear U 36 The positional distribution of potassium ions and the connection mode with uranyl oxygen and peroxide indicate that potassium ions have an important effect on the core-shell cluster U 36 · The formation of 6U5-Oxa plays an important role. 36 The crystal structure of 6U5-Oxa is the same as that of Example 1, and they belong to the same crystal structure.

[0104] Comparative Example 1

[0105] A method for preparing uranium peroxo clusters comprises the following steps:

[0106] S1. Prepare 0.5 mol / L uranyl nitrate solution, 30% (wt.) hydrogen peroxide solution, 2.4 mol / L lithium hydroxide solution, 1 mol / L potassium oxalate solution, and 0.5 mol / L iodic acid solution.

[0107] S2. In a 5mL glass reaction bottle, add 100μL of 0.5mol / L uranyl nitrate solution, 100μL of 2.4mol / L lithium hydroxide solution, 100μL of 30% (wt.) hydrogen peroxide solution, 200μL of 1mol / L potassium oxalate solution and 200μL of 0.5mol / L iodic acid solution in sequence under stirring; wherein, each time a solution is added, ensure that the solution in the glass reaction bottle is mixed evenly before adding the next solution. At this time, the pH of the mixed solution is between 5 and 7.

[0108] S3. Cover the mouth of the glass reaction bottle with a polytetrafluoroethylene membrane and poke 5-6 small holes on the membrane to allow the solution to evaporate slowly at room temperature.

[0109] Comparative Example 2

[0110] A method for preparing uranium peroxo clusters comprises the following steps:

[0111] S1. Prepare 0.5 mol / L uranyl nitrate solution, 30% (wt.) hydrogen peroxide solution, 2.4 mol / L lithium hydroxide solution, 1 mol / L potassium oxalate solution, and 0.5 mol / L iodic acid solution.

[0112] S2. In a 5mL glass reaction bottle, add 100μL of 2.4mol / L lithium hydroxide solution, 100μL of 0.5mol / L uranyl nitrate solution, 100μL of 30% (wt.) hydrogen peroxide solution, 200μL of 1mol / L potassium oxalate solution and 200μL of 0.5mol / L iodic acid solution in sequence under stirring; wherein, each time a solution is added, ensure that the solution in the glass reaction bottle is mixed evenly before adding the next solution. At this time, the pH of the mixed solution is between 5 and 7.

[0113] S3. Cover the mouth of the glass reaction bottle with a polytetrafluoroethylene membrane and poke 5-6 small holes on the membrane to allow the solution to evaporate slowly at room temperature.

[0114] Comparative Example 3

[0115] A method for preparing uranium peroxo clusters comprises the following steps:

[0116] S1. Prepare 0.5 mol / L uranyl nitrate solution, 30% (wt.) hydrogen peroxide solution, 2.4 mol / L lithium hydroxide solution, 1 mol / L potassium oxalate solution, and 0.5 mol / L iodic acid solution.

[0117] S2. In a 5mL glass reaction bottle, add 100μL of 0.5mol / L uranyl nitrate solution, 200μL of 1mol / L potassium oxalate solution, 100μL of 2.4mol / L lithium hydroxide solution, 100μL of 30% (wt.) hydrogen peroxide solution and 200μL of 0.5mol / L iodic acid solution in sequence under stirring; wherein, each time a solution is added, ensure that the solution in the glass reaction bottle is mixed evenly before adding the next solution. At this time, the pH of the mixed solution is between 5 and 7.

[0118] S3. Cover the mouth of the glass reaction bottle with a polytetrafluoroethylene membrane and poke 5-6 small holes on the membrane to allow the solution to evaporate slowly at room temperature.

[0119] Comparative Example 4

[0120] A method for preparing uranium peroxo clusters comprises the following steps:

[0121] S1. Prepare 0.5 mol / L uranyl nitrate solution, 30% (wt.) hydrogen peroxide solution, 2.4 mol / L lithium hydroxide solution, 1 mol / L potassium oxalate solution, and 0.5 mol / L iodic acid solution.

[0122] S2. In a 5mL glass reaction bottle, add 100μL of 0.5mol / L uranyl nitrate solution, 200μL of 1mol / L potassium oxalate solution, 200μL of 0.5mol / L iodic acid solution, 100μL of 2.4mol / L lithium hydroxide solution and 100μL of 30% (wt.) hydrogen peroxide solution in sequence under stirring; wherein, each time a solution is added, ensure that the solution in the glass reaction bottle is mixed evenly before adding the next solution. At this time, the pH of the mixed solution is between 5 and 7.

[0123] S3. Cover the mouth of the glass reaction bottle with a polytetrafluoroethylene membrane and poke 5-6 small holes on the membrane to allow the solution to evaporate slowly at room temperature.

[0124] In order to study the effect of the order of adding different raw materials on the crystal structure, we conducted a series of comparative tests. Comparative Examples 1 to 4 prepared uranium peroxy cluster crystals by changing the order of adding raw materials. However, when comparing the crystal structures prepared in Comparative Examples 1 to 4 with the crystal structures of Examples 1 and 5, we found that the change in the order of adding raw materials would affect the crystal structure, so that the crystals of the obtained uranium peroxy cluster products were different. We found during the experiment that the order of the first three solutions could not be changed, that is, the order of adding the first three solutions was uranyl nitrate solution, hydrogen peroxide solution, and lithium hydroxide solution; while the order of the last two solutions (potassium oxalate solution and iodic acid solution) could be exchanged.

[0125] Comparative Example 5

[0126] A method for preparing uranium peroxo clusters comprises the following steps:

[0127] S1. Prepare 0.5 mol / L uranyl nitrate solution, 30% (wt.) hydrogen peroxide solution, 2.4 mol / L lithium hydroxide solution, 1 mol / L potassium oxalate solution, and 0.5 mol / L iodic acid solution.

[0128] S2. In a 5mL glass reaction bottle, add 100μL of 0.5mol / L uranyl nitrate solution, 270μL of 2.4mol / L lithium hydroxide solution, 100μL of 30% (wt.) hydrogen peroxide solution, 200μL of 1mol / L potassium oxalate solution and 200μL of 0.5mol / L iodic acid solution in sequence under stirring; wherein, each time a solution is added, ensure that the solution in the glass reaction bottle is mixed evenly before adding the next solution. At this time, the pH of the mixed solution is greater than 7.0.

[0129] S3. Cover the mouth of the glass reaction bottle with a polytetrafluoroethylene membrane and poke 5-6 small holes on the membrane to allow the solution to evaporate slowly at room temperature.

[0130] Comparative Example 6

[0131] A method for preparing uranium peroxo clusters comprises the following steps:

[0132] S1. Prepare 0.5 mol / L uranyl nitrate solution, 30% (wt.) hydrogen peroxide solution, 2.4 mol / L lithium hydroxide solution, 1 mol / L potassium oxalate solution, and 0.5 mol / L iodic acid solution.

[0133] S2. In a 5mL glass reaction bottle, add 100μL of 0.5mol / L uranyl nitrate solution, 320μL of 2.4mol / L lithium hydroxide solution, 100μL of 30% (wt.) hydrogen peroxide solution, 200μL of 1mol / L potassium oxalate solution and 200μL of 0.5mol / L iodic acid solution in sequence under stirring; wherein, each time a solution is added, ensure that the solution in the glass reaction bottle is mixed evenly before adding the next solution. At this time, the pH of the mixed solution is greater than 7.

[0134] S3. Cover the mouth of the glass reaction bottle with a polytetrafluoroethylene membrane and poke 5-6 small holes on the membrane to allow the solution to evaporate slowly at room temperature.

[0135] In order to study the effect of different pH on the crystal structure, we conducted a series of comparative tests. Comparative Examples 5 to 6 prepared the crystals of uranium peroxy clusters by changing the pH of the final mixed solution. However, when the crystal structures prepared in Comparative Examples 5 to 6 were compared with the crystal structures of Example 1, it was found that when the pH was greater than 7, the resulting cluster compound was different from the crystal structure of the uranium peroxy cluster of Example 1 of the present invention. It is speculated that the crystal structure of the uranium peroxy cluster will also be affected in a peracid environment (pH <5). It can be seen that the pH of the mixed solution will also affect the crystal structure of the uranium peroxy cluster. Therefore, the preferred pH environment of the mixed solution is 5 to 7.

[0136] In summary, Examples 1 to 5 of the present invention use oxalate with strong coordination ability with uranyl ions as ligands, select potassium ions as counter ions, and explore the synthesis method of a new uranium peroxy cluster by regulating the amount of reaction reagents, the pH value of the reaction solution and other conditions, and prepare a uranium peroxy cluster with novel structure and properties. The successful preparation of the uranium peroxy cluster enriches the types, structures and properties of uranium peroxy clusters, and also enriches the crystal chemistry of uranium, which is expected to be applied to spent fuel reprocessing, uranium mining and metallurgy, catalysis and materials.

[0137] Application Example 1

[0138] The uranium peroxide cluster of Example 1 is used in spent fuel reprocessing.

[0139] The molecular weight and size of the uranium peroxide clusters prepared in Example 1 are much larger than those of conventional inorganic ions. Therefore, the uranium in uranium ore, nuclear waste, spent fuel and other materials can be converted into the uranium peroxide clusters in the embodiments of the present invention using the method provided in the embodiments of the present invention, and then the uranium can be separated out by using the size difference between the uranium peroxide clusters and other components, so as to develop uranium separation technology based on uranium clusters. Below we will take the separation process of uranium in simulated spent fuel as an example for specific explanation. Simulated spent fuel is a sample prepared according to the chemical composition of spent fuel, which has a chemical composition similar to that of spent fuel but has a relatively low radioactivity. The specific separation process includes the following steps:

[0140] S1. Prepare 0.5 mol / L uranyl nitrate solution, 30% (wt.) hydrogen peroxide solution, 2.4 mol / L lithium hydroxide solution, 1 mol / L potassium oxalate solution, and 0.5 mol / L iodic acid solution.

[0141] S2. Place an appropriate amount of simulated spent fuel in a 5mL glass reaction bottle, and add 30% (wt.) hydrogen peroxide solution, 2.4mol / L lithium hydroxide solution, 1mol / L potassium oxalate solution and 0.5mol / L iodic acid solution in sequence under stirring; the volume ratio of hydrogen peroxide solution, lithium hydroxide solution, potassium oxalate solution and iodic acid solution is 100:100:200:200. Each time a solution is added, ensure that the solution in the glass reaction bottle is mixed evenly before adding the next solution. At this time, the pH of the mixed solution is between 5 and 7.

[0142] The UO2 in the treated spent fuel is dissolved into uranyl ions under the action of hydrogen peroxide, and the concentration of the dissolved uranyl ions is controlled at 0.5 mol / L. Uranyl ions coordinate with peroxide, hydroxide, and oxalate to form uranium peroxide clusters in the form of giant anions; the negative charge of the uranium peroxide clusters is neutralized by potassium ions.

[0143] Pu, some minor actinides and fission products are present in the reaction solution as Pu 4+ 、MoO4 2- , Cs + The insoluble actinide products and fission products are separated and stored as high-level solid waste.

[0144] S3. Utilizing the different migration directions or speeds between uranium cluster ions and Pu, minor actinides and fission product ions in gel electrophoresis, uranium is extracted in the form of clusters, while Pu, minor actinides and fission products are stored as high-level liquid waste;

[0145] In the gel electrophoresis system, the gel is agar, the buffer is NaOH-Na2CO3 solution, and the reaction solution separated in S2 is slowly added. A voltage of 100V is applied between the two electrodes, and the cations in the solution move to the cathode. Since the precipitation rate of impurity anions is slower than that of uranium cluster anions, the uranium cluster solution is first precipitated from the anode. Repeat the above operation many times to achieve the separation of uranium clusters.

[0146] The analysis of the small angle X-ray scattering test shows that nano-scale uranium clusters exist in the solution after S2 is dissolved and the solution after S3 is treated, as well as in each experimental process. The crystals formed by the separated uranium clusters are subjected to X-ray single crystal diffraction, and it is found that they have the same crystallographic parameters as Table 1, indicating that the clusters in the embodiment of the present invention can indeed be obtained by using the spent fuel as the post-processing raw material according to the methods in S1 to S3, and the clusters are feasible for use in the uranium separation technology for spent fuel post-processing.

[0147] S4. Add 1 volume of 0.1 mol / L dilute nitric acid and two volumes of 30% hydrogen peroxide to the separated uranium cluster solution, control the solution pH at about 1, and convert the uranium peroxide cluster into uranium ore (UO2)O2(H2O)4 precipitate. A small amount of fission product ions adsorbed on the surface of the uranium peroxide cluster remain in the solution, filter, separate the uranium ore precipitate, and store the filtrate properly. Compared with the uranium content in the original spent fuel, the uranium recovery efficiency can reach 96%.

[0148] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A uranium peroxide cluster having a core-shell structure, characterized in that: The crystal structure of the uranium peroxo cluster is a core-shell cluster structure; The core of the uranium peroxo cluster is composed of 36 uranium polyhedrons connected by sharing edges; The shell of the uranium peroxo cluster is composed of 6 uranium pentamers, each of which is composed of 5 uranium polyhedrons and 5 oxalate ligands, and the 5 uranium polyhedrons are connected by sharing edges to form a five-membered ring structure. The negative charge of the uranium peroxo cluster is neutralized by potassium ions.

2. The uranium peroxo cluster having a core-shell structure according to claim 1, characterized in that The uranium polyhedron in the core of the uranium peroxo cluster is a hexagonal bipyramidal polyhedron formed by the coordination of uranyl ions and six oxygen atoms from peroxides and / or hydroxides; the uranium polyhedrons in the cores of adjacent uranium peroxo clusters are connected by sharing edges to form a five-membered ring structure or a six-membered ring structure of uranium; The uranium polyhedron in the shell of the uranium peroxo cluster is a hexagonal bipyramidal polyhedron formed by the coordination of uranyl ions and six oxygen atoms from peroxide and oxalate; the uranium polyhedrons in the shell of adjacent uranium peroxo clusters are connected by sharing edges to form a five-membered ring structure of uranium.

3. The uranium peroxo cluster having a core-shell structure according to claim 2, characterized in that: The six uranium pentamers are distributed at both ends of the core, and each of the uranium pentamers corresponds one-to-one to a five-membered ring structure in the core and is located directly above the five-membered ring structure in the core; Each of the uranium pentamers is connected to the five-membered ring structure in the core through six potassium ions; and the six potassium ions are distributed between the uranium pentamer and the five-membered ring structure of the core, and one of the potassium ions is located at the center of the other five potassium ions; One potassium ion is connected to the oxygen atoms of five uranyl ions in the uranium pentamer and the oxygen atoms of five peroxides in the five-membered ring structure in the core respectively; The remaining five potassium ions correspond one by one to the positions of the five peroxide radicals of the five-membered ring structure in the core, and are connected to the adjacent uranyl ions and oxygen atoms of the peroxide radicals, respectively.

4. The uranium peroxo cluster having a core-shell structure according to claim 2, characterized in that The uranyl ion in the core has two coordination modes, namely coordination mode I and coordination mode II; The coordination mode I is that each uranyl ion is coordinated with three peroxide radicals respectively; The coordination mode II is that each uranyl ion is coordinated with two peroxides and two hydroxides respectively; The 24 uranyl ions distributed at both ends of the core adopt coordination mode I to form a hexagonal bipyramidal polyhedron; the 12 uranyl ions distributed in the middle of the core adopt coordination mode II to form a hexagonal bipyramidal polyhedron; The uranyl ions in each of the uranium pentamers adopt coordination mode III to form a hexagonal bipyramidal polyhedron; the coordination mode III is that each uranyl ion is coordinated with two peroxides and one oxalate.

5. The uranium peroxo cluster having a core-shell structure according to claim 1, characterized in that The uranium peroxide cluster forms yellow block crystals after crystallization. The uranium peroxide cluster crystals are crystallized in the monoclinic system with a space group of C 2 / c. The unit cell parameters are α=90°, β=90.87°, γ=90°; 6. A method for preparing the uranium peroxo cluster having a core-shell structure according to claim 1, comprising the following steps: Under stirring, a hydrogen peroxide solution, an alkali solution, a potassium oxalate solution and an iodic acid solution are sequentially added to a solution containing uranyl ions, and the pH value of the solution after uniform mixing is 5-7; the solution evaporates naturally at room temperature to obtain a crystal of a uranium peroxide cluster with a core-shell structure.

7. The method for preparing a uranium peroxo cluster having a core-shell structure according to claim 6, characterized in that: The solution containing uranyl ions is a uranyl nitrate solution; and the alkaline solution is a potassium hydroxide solution or a lithium hydroxide solution.

8. The method for preparing a uranium peroxo cluster having a core-shell structure according to claim 7, characterized in that: The concentration of the uranyl nitrate solution is 0.5 mol / L; the concentration of the hydrogen peroxide solution is 30 wt%; the concentration of the alkaline solution is 2.4-4 mol / L; the concentration of the potassium oxalate solution is 1 mol / L; the concentration of the iodic acid solution is 0.5 mol / L; The volume ratio of the solution containing uranyl ions, the hydrogen peroxide solution, the alkaline solution, the potassium oxalate solution and the iodic acid solution is 100:100:100-150:100-200:175-600.

9. Use of the uranium peroxo cluster with a core-shell structure according to claim 1 in a nuclear fuel cycle.

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