Zirconium-substituted arsenotungstic acid macrocyclic material, preparation method thereof and application thereof in iodine adsorption

Abstract

The present invention relates to two cases of internally ligand-regulated Zr-substituted macrocyclic arsenotungstates with the chemical formula [N(CH 3 ) 4 36 H 12 [NaZr 3 (μ 3 -O)(lac)(H 2 O) 4 (B-α-AsW 9 O 33 ) 2 6 ·196H 2 O (1) (lac = lactic acid) and [N(CH 3 ) 4 36 H 18 [NaZr 3 (μ 3 -O)(C 2 O 4 )(H 2 O) 4 (B-α-AsW 9 O 33 ) 2 6 ·203H 2 O (2). The differences between Compounds 1 and 2 mainly lie in the ligands, with the former coordinated by lactic acid and the latter by oxalic acid. In addition, Compounds 1 and 2 have similar structures, each consisting of six alkali metal-linked organic-inorganic hybrid arsenotungstates and both presenting a significant ring shape with a cavity of approximately 11 Å in size. The experimental results of iodine adsorption show that Compound 1 has good iodine adsorption performance. After 48 h, its iodine adsorption reaches equilibrium with a removal efficiency of 78.3%, while the adsorption performance of 2 is poor. This indicates that the internal ligand plays an important role in regulating the iodine adsorption behavior, providing new research ideas for the synthesis of other new polyoxometalate-based iodine adsorbents that are economical, efficient, and environmentally friendly.​​​​

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of polyacid-based iodine adsorption materials, and specifically relates to two zirconium-substituted arsenic tungstate macrocyclic materials, preparation methods and applications thereof in iodine adsorption, and explores their adsorption performance for radioactive hazardous substance iodine, and achieves regulation of improving the iodine adsorption performance of polyacid-based compounds by adjusting the type of ligands, which can be applied to environmental fields such as removal and treatment of radioactive iodine. Background Art

[0002] With the increasing demand for energy around the world, there is an urgent need to explore clean and safe energy to reduce greenhouse gas emissions and solve energy security issues. Based on this, it is very important to use nuclear energy correctly and rationally because it has ultra-high energy density and low carbon emissions. However, in the process of using nuclear energy, some nuclear waste, especially radioactive substances including iodine, will inevitably be discharged. Therefore, how to dispose of radioactive waste in a timely and effective manner is of great significance to environmental protection and human health. In recent years, effective iodine capture has attracted widespread attention in the research community. Generally, there are many methods to eliminate radioactive iodine, among which the adsorption method is considered to be a better choice due to its good recovery performance and the absence of secondary pollution, and is increasingly favored by scientific researchers. Therefore, finding a new type of iodine adsorbent that is economical, efficient and environmentally friendly has gradually become a research hotspot.

[0003] Generally, most adsorbents are composed of metal-organic frameworks (MOFs), and adsorbents based on polyoxometalates (POMs) are rarely reported. POMs are a class of well-defined polyoxoanionic metal clusters with oxygen-rich surfaces, which have a wide range of applications in magnetism, electrochemistry, catalysis, medicine, and optical materials. In particular, vacant polyoxometalates possess a large number of exposed nucleophilic oxygen atom sites to serve as multidentate inorganic ligands to coordinate with transition metal (TM) elements, thus forming a rich variety of polyoxometalates-based compounds. Therefore, it is feasible to construct novel TM-substituted compounds using various vacant POMs precursors as secondary building blocks. Although TM-substituted POM-based compounds have been widely studied, the research on TM-constructed cyclic molecular structures is still limited. Cyclic molecules are a class of compounds with pores that are formed by self-driven assembly of metal nodes and organic linkers in solution. They have attracted a lot of attention due to their unique structures, such as discrete molecular solids, closed cyclic spaces, and well-defined sizes. For example, their applications in catalysis and their size differences allow them to be used to separate some gas mixtures and adsorb some harmful substances. Therefore, cyclic POM-based adsorbents are an area that needs to be expanded and studied urgently.

[0004] The present invention focuses on the problem of removal and treatment of radioactive iodine and develops a polyacid-based iodine adsorbent with excellent adsorption capacity.

[0005] Under conventional aqueous solution conditions, the precursor As 2 W 19 , and the organic ligand are both prone to coordinate and assemble with Zr to form a macrocyclic structure. The main difference between Compounds 1 and 2 lies in the different organic ligands. It can be verified by experiments that Compound 1 has good iodine adsorption performance. After 48 h, its iodine adsorption reaches equilibrium and the removal efficiency is 78.3%, while the adsorption performance of Compound 2 is poor, indicating that the internal ligand plays an important role in regulating the iodine adsorption behavior. It should be noted that Compound 1 represents the first polyoxometalate-based iodine adsorbent with great application prospects, providing new research ideas for the synthesis of other new polyoxometalate-based iodine adsorption materials that are economical, efficient, and environmentally friendly. Summary of the Invention

[0006] The purpose of the present invention is to overcome the defects of the prior art and provide a zirconium-substituted arsenotungstic acid macrocyclic material, which is an efficient polyoxometalate-based iodine adsorption material. The iodine adsorption capacity thereof has been deeply studied and evaluated to effectively regulate the performance of the polyoxometalate-based iodine adsorbent using different ligands, laying a foundation for the preparation of high-performance polyoxometalate-based iodine adsorption materials and realizing their practical applications.

[0007] The present invention also provides a preparation method and application of the above zirconium-substituted arsenotungstic acid macrocyclic material.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] The zirconium-substituted arsenotungstic acid macrocyclic material is two polyoxometalate compounds containing Zr. The molecular formula of the zirconium-substituted arsenotungstic acid macrocyclic material is [N(CH 3 ) 4 ) 36 H 12 [NaZr 3 (μ 3 -O)(lac)(H 2 O) 4 (B-α-AsW 9 O 33 ) 2 ) 6 ·196H 2 O (Compound 1) and / or [N(CH 3 ) 4 ) 36 H 18 [NaZr 3 (μ 3 -O)(C 2 O 4 )(H 2 O) 4 (B-α-AsW9 O 33 ) 2 6 ·203H 2 O, (Compound 2) where lac = lactic acid.

[0010] The preparation method of the above zirconium-substituted arsenotungstic acid macrocyclic material, when the molecular formula is [N(CH 3 ) 4 36 H 12 [NaZr 3 (μ 3 -O)(lac)(H 2 O) 4 (B-α-AsW 9 O 33 ) 2 6 ·196H 2 O (Compound 1), the preparation steps are as follows:

[0011] 1) Dissolve ZrOCl 2 ·8H 2 O, Na 2 SO 4 in water, then add lactic acid, stir and mix evenly to obtain solution A;

[0012] 2) Add the precursor K 14 [As 2 W 19 O 67 (H 2 O)] to solution A, dropwise add alkali solution to adjust the pH to 2 - 3 to obtain solution B;

[0013] 3) Heat solution B at 80 - 100 °C for 1 - 3 hours, then add tetramethylammonium chloride (TMACl) and stir for 20 - 50 min to obtain solution C;

[0014] 4) Cool and filter solution C, evaporate at room temperature, and colorless block crystals can be obtained after about one week, thus obtaining.

[0015] Furthermore, step 1) is specifically: Dissolve 0.3 - 0.4 g of ZrOCl 2 ·8H 2 O and 0.05 - 0.09 g of Na 2 SO 4 in 8 - 15 mL of water, then add 0.2 - 0.6 mL of lactic acid, stir and mix evenly to obtain solution A.

[0016] Specifically, in step 2), the precursor K 14 [As​​​2 W 19 O 67 (H 2 O)] is added in an amount of 1.0 - 1.2 g. The lye can be an aqueous NaOH solution. The concentration of NaOH can be 2 mol / L for adjusting the pH of the solution. Preferably, the pH is adjusted to 2.5.

[0017] Furthermore, in step 3), the addition amount of tetramethylammonium chloride (TMACl) is 0.3 - 0.6 g.

[0018] For the above preparation method of the zirconium-substituted arsenotungstic acid macrocyclic material, when the molecular formula is [N(CH 3 ) 4 36 H 18 [NaZr 3 (μ 3 -O)(C 2 O 4 )(H 2 O) 4 (B-α-AsW 9 O 33 ) 2 6 ·203H 2 O (Compound 2), the preparation steps are as follows:

[0019] 1) Dissolve ZrOCl 2 ·8H 2 O in water, then add oxalic acid, and stir and mix evenly to obtain solution D;

[0020] 2) Add the precursor K 14 [As 2 W 19 O 67 (H 2 O)] (abbreviated as As 2 W 19 ) dropwise to solution D, and adjust the pH to 3 - 4 with lye to obtain solution E;

[0021] 3) Heat solution E at 80 - 100 °C for 1 - 3 hours, then add tetramethylammonium chloride (TMACl) and stir for 20 - 50 min to obtain solution F;

[0022] 4) Solution F is cooled, filtered, and evaporated at room temperature. Colorless block crystals can be obtained after about one week, thus obtaining the product.

[0023] Furthermore, step 1) is specifically: Dissolve 0.3 - 0.4 g of ZrOCl 2 ·8H 2 ​​O is dissolved in 15 - 25 mL of water, and then 0.2 - 0.4 g of oxalic acid is added. After stirring and mixing evenly, solution D is obtained.

[0024] Specifically, in step 2), the precursor K 14 [As 2 W 19 O 67 (H 2 O)] is added in an amount of 1.0 - 1.2 g. The alkali solution can be an aqueous NaOH solution. The concentration of NaOH can be 2 mol / L for adjusting the pH of the solution. Preferably, the pH is adjusted to 3.5.

[0025] Furthermore, in step 3), the addition amount of tetramethylammonium chloride (TMACl) is 0.3 - 0.6 g.

[0026] The present invention provides two examples of Zr - substituted macrocyclic arsenotungstates regulated by internal ligands prepared by the above - mentioned preparation method.

[0027] The present invention also provides the application of the above - mentioned zirconium - substituted arsenotungstic acid macrocyclic material as an iodine adsorbent in iodine adsorption, as well as the internal ligand regulation strategy of the polyoxometalate - based iodine adsorption material.

[0028] Two compounds of the present invention are a polyoxometalate - based iodine adsorption material. Its synthesis is to dissolve ZrOCl 2 ·8H 2 O in water, then add oxalic acid / lactic acid ligands. After the solution is mixed evenly, add the precursor K 14 [As 2 W 19 O 67 (H 2 O)]. Finally, two novel Zr - substituted POM - based macrocyclic materials are obtained under conventional aqueous solution conditions. The difference between compound 1 and compound 2 is mainly the difference in ligands. The former coordinates with lactic acid while the latter coordinates with oxalic acid. In addition, compound 1 and compound 2 have similar structures, which are respectively composed of six alkali - metal - linked organic - inorganic hybrid arsenotungstates and both show a significant ring shape with a cavity of about 11 Å in size. The experimental results of iodine adsorption show that compound 1 has good iodine adsorption performance. After 48 h, its iodine adsorption reaches equilibrium and the removal efficiency is 78.3%, while the adsorption performance of compound 2 is poor, indicating that the internal ligand plays an important role in regulating the iodine adsorption behavior. The present invention improves the iodine adsorption performance of the polyoxometalate - based material by adjusting the type of ligand. Among them, compound 1 represents the first polyoxometalate - based iodine adsorbent with great application prospects, providing a new research idea for the synthesis of other economical, efficient and environmentally friendly novel polyoxometalate - based iodine adsorbents. The ligands used in the present invention can be directly purchased or prepared according to the methods in the existing literature.

[0029] The polyoxometalate-based iodine adsorption material of the present invention, namely two examples of Zr-containing magnetic complexes, both use As 2 W 19 as the secondary building unit. This vacant polyoxometalate structure has a large number of exposed nucleophilic oxygen atom sites to serve as polydentate inorganic ligands, coordinating with transition metal Zr to form a closed macrocyclic polyoxometalate compound. The main difference between Compound 1 and Compound 2 lies in the ligands. The former coordinates with lactic acid while the latter coordinates with oxalic acid. Moreover, there are some methyl groups in the cavity of Compound 1, while there are no methyl groups in the cavity of Compound 2. These structural differences make Compound 1 have good iodine adsorption performance. After 48 h, its iodine adsorption reaches equilibrium and the removal efficiency is 78.3%, while the adsorption performance of Compound 2 is poor. The above results also indicate that the internal ligand plays an important role in regulating the iodine adsorption behavior.

[0030] The present invention provides a preparation method for the above two examples of polyoxometalate-based iodine adsorption materials and a method for regulating iodine adsorption performance. It is found that: the structures of Compound 1 and Compound 2 are roughly the same, crystallizing in the same trigonal system, and are respectively composed of six alkali metal-linked organic-inorganic hybrid arsenotungstates, both showing a significant ring shape with a cavity of about 11 Å in size. However, they exhibit significantly different iodine adsorption behaviors: Compound 1 has excellent iodine adsorption performance. After 8 h of treatment, the removal efficiency is 41.3%. After 12 h, the iodine removal efficiency reaches 51.6%. After 48 h, the iodine adsorption of Compound 1 almost reaches equilibrium, and the removal efficiency reaches 78.3%. While the adsorption performance of Compound 2 is poor, and the iodine concentration in the solution changes little after treatment. In addition, it can be clearly observed that the color of the solution changes from dark purple to light purple, and the color of the crystal changes from colorless to dark yellow, which means that iodine has been successfully adsorbed on Compound 1 to form I 2 @1 complex. Therefore, in a similar coordination environment, the performance of polyoxometalate-based iodine adsorption materials can be regulated by changing the ligands.

[0031] The polyoxometalate-based iodine adsorption material of the present invention is synthesized by the conventional solution evaporation method. The organic ligand, metal salt, and polyoxometalate precursor are mixed in a certain order to obtain a single crystal sample of the compound. Compared with some existing iodine adsorption materials, the present invention has the following beneficial effects and advantages:

[0032] 1) The present invention uses single crystal X-ray diffraction technology to accurately determine the molecular structures of two examples of polyoxometalate-based adsorption materials;

[0033] 2) The present invention adopts a solution evaporation self-assembly strategy, reacting under normal temperature and pressure, and the experimental operation is safe, green and environmentally friendly;

[0034] 3) The present invention explores the influence of internal ligands on the iodine adsorption performance of polyoxometalate compounds by adjusting organic ligands;

[0035] 4) The present invention effectively regulates the iodine adsorption behavior of Zr-substituted polyoxometalate macrocyclic materials, providing an experimental basis and theoretical reference for obtaining high-performance polyoxometalate-based iodine adsorption materials;

[0036] 5) Compared with existing iodine adsorption materials, compound 1 in the present invention exhibits excellent iodine adsorption performance and can be used as the first polyoxometalate-based iodine adsorbent, having potential practical applications in environmental fields such as the removal and treatment of radioactive iodine. Description of the Drawings

[0037] Figure 1 In (a) and (b), the synthetic routes for obtaining compounds 1 and 2 by changing the types of ligands, lactic acid and oxalic acid, respectively; (c) is compound 1, and (d) is compound 2;

[0038] Figure 2 In, (a) As 2 W 19 O 67 (H 2 )] 14- Polyhedron schematic diagram of the unit; (b) [Zr 3 Na(μ 3 -O)(lac)(H 2 ) 4 ) 10+ Polyhedron representation diagram of the unit; (c) [NaZr 3 (μ 3 -O)(lac)(H 2 ) 4 (B-α-AsW 9 O 33 ) 2 ) 6 48- Polyhedron and ball-and-stick schematic diagrams of; (d) Simplified structure diagram of compound 1; (e) [NaZr 3 (μ 3 -O)(lac)(H 2 ) 4 ) 6 48- Ball-and-stick schematic diagram of; (f) [Zr 3 Na(μ 3 -O)(lac)(H 2 ) 4 ) 10+ Ball-and-stick schematic diagram of the unit; (g) Distance between three Zr atoms;

[0039] Figure 3 Arrangement diagram of compound 1 along the c-axis;

[0040] Figure 4 In (a), ball-and-stick schematic diagram of the polyanion in Compound 1; (b), ball-and-stick schematic diagram of the polyanion in Compound 2; (c-d) [Zr 3 Na(μ 3 -O)(lac)(H 2 O) 4 6 60+ and [Zr 3 Na(μ 3 -O)(C 2 O 4 )(H 2 O) 4 6 54+ ball-and-stick schematic diagrams; (e-f) ball-and-stick schematic diagrams of lactic acid and oxalic acid;

[0041] Figure 5 In, (a) UV-visible spectra of the process of Compound 1 adsorbing iodine in 1 mmol / L cyclohexane solution over time; (b) UV-visible spectra of the process of Compound 2 adsorbing iodine in 1 mmol / L cyclohexane iodine solution over time; (c) adsorption kinetics graph of Compound 1 for iodine in 1 mmol / L cyclohexane iodine solution; (d) iodine removal efficiency in 1 mmol / L cyclohexane solution when 600 mg of Compound Sample 1 is added;

[0042] Figure 6 are the TGA curves of Compound 1 (a) and 2 (b);

[0043] Figure 7 are the IR graphs of Compound 1 (a) and 2 (b) during the heating process;

[0044] Figure 8 is the graph of the change in the color of the iodine solution over time after being treated with Compound 1;

[0045] Figure 9 In, (a) infrared spectra of Sample 1 before and after iodine adsorption; (b) PXRD graph of Compound 1;

[0046] Figure 10 is the XPS spectrum of the 3d of iodine after iodine adsorption;

[0047] Figure 11 is the UV-visible spectrum of iodine release in methanol solution. Specific Embodiments

[0048] The technical solutions of the present invention will be further introduced in detail below in conjunction with embodiments, but the protection scope of the present invention is not limited thereto.

[0049] ​​In the following examples, unless otherwise specified, the raw materials used are ordinary commercially available products that can be directly purchased or can be prepared by conventional methods in the art. For example, the precursor K 14 [As 2 W 19 O 67 (H 2 O)] can be prepared by referring to existing publicly available literature, so it will not be elaborated in this application. Room temperature refers to 25 ± 5 °C.

[0050] Example 1

[0051] Preparation method of polyoxometalate-based iodine adsorption material [N(CH 3 ) 4 36 H 12 [NaZr 3 (μ 3 -O)(lac)(H 2 O) 4 (B-α-AsW 9 O 33 ) 2 6 ·196H 2 O (Compound 1), which includes the following steps, and the specific synthesis route is as Figure 1 shown:

[0052] 1) Dissolve 0.32 g of ZrOCl 2 ·8H 2 O and 0.07 g of sodium sulfate Na 2 SO 4 in 10.00 mL of water, then add 0.40 mL of lactic acid, and mix and stir for about 10 min to obtain solution A;

[0053] 2) Add 1.06 g of the precursor K 14 [As 2 W 19 O 67 (H 2 O)] to solution A, and then gradually add 2.00 mol / L aqueous NaOH solution to adjust the pH to 2.50 to obtain solution B;

[0054] 3) Heat solution B at 90 °C for about 2 hours, then add 0.44 g of tetramethylammonium chloride (TMACl) and stir for about 30 min to obtain solution C;

[0055] 4) Cool, filter solution C, and evaporate it at room temperature. Colorless block crystals can be obtained after about one week, thus obtaining it.

[0056] Example 2 ​​

[0057] Polyanionic iodine adsorption material [N(CH 3 ) 4 36 H 18 [NaZr 3 (μ 3 -O)(C 2 O 4 )(H 2 O) 4 (B-α-AsW 9 O 33 ) 2 6 ·203H 2 O (Compound 2) and the preparation method thereof includes the following steps, and the specific synthesis route is as Figure 1 shown:

[0058] 1) Dissolve 0.32 g of ZrOCl 2 ·8H 2 O in 20 mL of water, then add 0.26 g of oxalic acid, mix and stir for about 10 min to obtain solution A;

[0059] 2) Add 1.06 g of the precursor K 14 [As 2 W 19 O 67 (H 2 O)] to solution A, and then gradually add 2.00 mol / L aqueous NaOH solution to adjust the pH to 3.50 to obtain solution B;

[0060] 3) Heat solution B at 90 °C for about 2 hours, then add 0.44 g of tetramethylammonium chloride (TMACl) and stir for about 30 min to obtain solution C;

[0061] 4) Cool, filter solution C, and evaporate it at room temperature. Colorless block crystals can be obtained after about one week, thus obtaining.

[0062] Compound structure identification

[0063] In the present invention, a Bruker Smart Apex II CDD type X-ray diffractometer is used, and the incident light source is selected as graphite monochromatized Mo-Kα ray ( λ = 0.071073 nm). At room temperature, through ω - φ ​​The crystal diffraction data of Compound 1 prepared in Example 1 and Compound 2 prepared in Example 2 were collected in the scanning mode. The unit cell parameters were obtained through the Smart program package, and the above data were reduced and corrected for the Lp factor using the SAINT software. Absorption correction was performed on the SADABS program. The structures of Compounds 1 and 2 were initially solved and refined using the Olex2 software program, and all non-hydrogen atoms were refined anisotropically.

[0064] The unit cell parameters of Compound 1 are as follows: trigonal system, R-3 space group, unit cell parameters a = 58.1452(11) Å, b = 58.1452(11) Å, c = 21.6531(4), α = 90.00, β = 90.00(2), γ = 120.00, V = 63398(3) Å 3 , Z = 3, R 1 = 0.0596, wR 2 = 0.1475.

[0065] The unit cell parameters of Compound 2 are as follows: trigonal system, R-3 space group, unit cell parameters a = 57.8637(10) Å, b = 57.8637(10) Å, c = 21.4214(4) Å, α = 90.00, β = 90.00, γ = 120.00, V = 62114(2) Å 3 , Z = 3, R 1 = 0.0512, wR 2 = 0.1210.

[0066] In view of the similar structures of Compounds 1 and 2, only Compound 1 is taken as an example for a detailed analysis of its structure.

[0067] As Figure 2 (a-g) shows, the framework of Compound 1 is composed of six organic-inorganic hybrid dimers [NaZr 3 (μ 3 -O)(lac)(H 2 O) 4 (B-α-AsW 9 O 33 ) 2 ) 8- units and 36 [N(CH 3 ) 4 )+ A cation and 12 H atoms + and 196 lattice water molecules. All these building units will spontaneously coordinate and assemble into a ring-shaped complex with a size of 11 Å. The polyoxoanion framework of Compound 1 is composed of six [NaZr 3 (μ 3 -O)(lac)(H 2 O) 4 (B-α-AsW 9 O 33 ) 2 8- dimer units. The dimer unit is composed of two three-vacancy Keggin-type [B-α-AsW 9 O 33 9- fragments and one [Zr 3 Na(μ 3 -O)(lac)(H 2 O) 4 10+ ({Zr3}) group. The {Zr3} structure is composed of three Zr ions modified by lactate, which are connected by μ 3 -O. In addition, three Zr atoms, one Na + and one lactate ligand coordinated with the Zr3 atoms are in a plane ( Figure 2 f), and the three Zr atoms also show an isosceles triangle arrangement order ( Figure 2 g). Interestingly, there are a large number of such six-membered rings in space, and there are a large number of organic amine cations between them. Through the electrostatic interaction between these cations and the six-membered rings, these rings are connected together (see Figure 3 ). It should be noted that there are a large number of hydrogen atoms inside the rings, allowing them to adsorb substances that can form hydrogen bonds with them, so they have excellent adsorption properties.

[0068] Figure 4 gives the structural comparison and ball-and-stick model diagrams of Compounds 1 and 2. According to Figure 4 , it can be seen that the overall configuration of Compound 2 is similar to that of 1, and the conformation of Compound 2 is roughly the same as that of Compound 1. However, there are also some differences between them. Compound 2 is modified by oxalic acid, while Compound 1 is modified by lactate. In addition, there are some methyl groups in the cavity of Compound 1, while there are no methyl groups in the cavity of Compound 2 ( Figure 4 c and d). This subtle difference may cause these two compounds to exhibit different adsorption properties.

[0069] Iodine adsorption test

[0070] ​​​Single crystal samples of Compound 1 and Compound 2 were collected separately and subjected to iodine adsorption tests under normal temperature and pressure. Considering the advantages of solution adsorption and the good solubility of iodine in cyclohexane, the solution adsorption method was selected to adsorb iodine in the organic solvent cyclohexane.

[0071] The specific iodine adsorption experiment is as follows: At room temperature, 0.6 g of the sample (Compound 1 or 2) was immersed in 5 mL of an iodine-cyclohexane solution with a concentration of 1 mmol / L, and the change in the iodine content in the supernatant was monitored using a UV-visible spectrophotometer. After each measurement, the supernatant was redistributed back into its respective vial to maintain a constant volume. The maximum wavelength of iodine (λmax = 521 nm) was selected to calculate the iodine content, and the absorbance value of the original solution was normalized to 100%. The iodine removal rate (R) was calculated using the following formula:

[0072] R = (C 0 – C t ) / C 0 × 100% (where C 0 and C t represent the initial concentration and the concentration at time t, respectively). The pseudo-second-order kinetic model was used to fit the iodine adsorption kinetics, and the formula used was as follows:

[0073] t / q t = 1 / h + t / q e

[0074] (q t , q e represent the adsorption capacity at a certain time t or equilibrium time, h is the initial adsorption rate, h = kq e 2 , and k is the rate constant). The fitting of the adsorption isotherm is as follows: 0.6 g of the solid sample was added to 5 mL of solutions with different iodine concentrations, and the Langmuir and Freundlich models were used to interpret the experimental data. The linear equation of the Langmuir isotherm model is expressed as follows:

[0075]

[0076] (q m is the maximum adsorption capacity (mg / g) corresponding exactly to monolayer coverage, k L is a constant indirectly related to the adsorption capacity and adsorption energy (L / mg), which characterizes the affinity between the adsorbate and the adsorbent.)After that, by plotting C e / q e versus C e and q m , linearized data can be obtained, and k L can be calculated from the slope and intercept.

[0077] The iodine adsorption kinetics of Compounds 1 and 2 are as follows Figure 5 As shown in a and b, Compound 1 has excellent iodine adsorption performance, while the performance of Compound 2 for iodine is not obvious. Figure 5 It shows that after treating with Compound 1 for 8 h, the removal efficiency is 41.3%. After 12 h, the iodine removal efficiency reaches 51.6%. After 48 h, the adsorption of iodine almost reaches equilibrium, and the removal efficiency reaches 78.3%. After treating for 120 h, the removal efficiency even approaches 90%. While the adsorption performance of Compound 2 is poor. After 120 h, the change in the concentration of iodine after treatment is not significant. Finally, the iodine removal efficiency of Compound 2 only reaches 13%. Generally, the carboxyl group is an electron-withdrawing group, and the methyl group is an electron-donating group. Iodine is prone to form polyiodide ions such as I 3- , I 5- etc. This indicates that the weak adsorption performance in Compound 2 may be attributed to the methyl group in the cavity, which will form -CH 3 ···I interaction, while there is no methyl group in the cavity of Compound 1. This tiny difference causes a huge change in the iodine adsorption performance. Therefore, this invention mainly studies and explores the adsorption performance of Compound 1. The obvious absorption of iodine by Compound 1 in the experiment is reflected by the change in the color of the solution and the crystal. The color of the solution changes from dark purple to light purple ( Figure 8 ), and at the same time, the color of the crystal changes from colorless to dark yellow compound, which means that iodine is efficiently and successfully adsorbed on Compound 1 to form I 2 @1 complex. In addition, we also explored the contact time in the iodine adsorption process in cyclohexane solution. The kinetic study shows that the pseudo-second-order rate equation can well fit the experimental data, and the R 2 value > 0.99 ( Figure 5 in c).

[0078] TG-DSC analysis was carried out on Compounds 1 and 2 to determine the number of lattice water molecules in the formula. As Figure 6 shown in a, the first weight loss rate of Compound 1 is 11.07% (calculated value is 11.27%), which occurs in the temperature range of 25 - 294 °C, and this is due to the release of 196 lattice water molecules. As Figure 6 shown in b, the first weight loss rate of Compound 2 is 11.22% (calculated value is 10.99%), which occurs in the temperature range of 25 - 294 °C, and this is due to the release of 203 lattice water molecules. In addition, the IR spectra of Compounds 1 and 2 were also measured during the heating process. As Figure 7 shown, the measurement results corroborate with the thermogravimetric analysis, indicating that Compounds 1 and 2 have good stability within 50 - 300 °C.

[0079] To prove the iodine adsorption effect of Compound 1, I 2@1 and the infrared spectrum of Compound 1 ( Figure 9 in a), it is easy to find that I 2 the fingerprint region of @1 is the same as that of Compound 1, manifested in I 2 the four characteristic peaks of ν (W-Ot), ν (W-Ob), ν (As-O) and ν (W-Oc) of the POM skeleton in the infrared spectrum of @1 are consistent with the infrared spectrum of fresh Compound 1, indicating that the absorption structure is stable during the absorption process, that is, the structure of Compound 1 remains unchanged after iodine adsorption. To further prove the above results, PXRD experiments were also carried out ( Figure 9 in b), and its I 2 @1 peaks are almost the same as those of fresh Sample 1. Correspondingly, it shows that the framework of Compound 1 still remains in contact with iodine after the iodine adsorption ends. To further verify the presence of iodine, the appearance of characteristic peaks in XPS proves the presence of adsorbed iodine in the sample (see Figure 10 ). All of the above studies indicate that the adsorption of iodine by 1 can be attributed to the intermolecular interaction force and the high porosity of 1.

[0080] The absorbent cycle repeatability is of great significance in practical applications. It should be noted that the iodine adsorption of Compound Sample 1 is reversible. Considering the cost and reusability of the synthetic material, methanol was used as the elution solvent to study the iodine release of the iodine-loaded Sample I 2 @1 in fresh methanol, and the corresponding iodine content was determined by a UV-visible spectrophotometer. It is easy to find that once the iodine-containing sample of I 2 @1 is immersed in the methanol solution, the methanol solution immediately deepens from colorless to yellow, clearly showing the desorption of the guest molecules from the iodine-containing sample. As can be seen from Figure 11 the peaks appearing at 290 and 358 nm can be attributed to the absorption of polyiodide anions. At room temperature, the iodine released in the methanol solution can be monitored by a UV-visible spectrophotometer. It was found that the iodine release rate is relatively fast. In particular, the color of the crystal changes from dark yellow to colorless, while the color of methanol changes from colorless to yellow. All of the above phenomena indicate that Compound 1 can be recycled and has potential practical application value in the field of iodine adsorption.

Claims

1. A preparation method of a zirconium-substituted arsenotungstic acid macrocyclic material, characterized in that, the preparation steps are as follows: 1) Dissolve ZrOCl 2 ·8H 2 O, Na 2 SO 4 in water, then add lactic acid, stir and mix evenly to obtain solution A; 2) Add the precursor K to solution A 14 [As 2 W 19 O 67 (H 2 O)], adjust the pH to 2 - 3 to obtain solution B; 3) Heat solution B at 80 - 100 °C for 1 - 3 hours, then add tetramethylammonium chloride and stir for 20 - 50 min to obtain solution C; 4) Cool and filter solution C, and evaporate it at room temperature to obtain colorless block crystals, thus obtaining the product.

2. The preparation method of the zirconium-substituted arsenotungstic acid macrocyclic material according to claim 1, characterized in that, Step 1) Specifically: Dissolve 0.3 - 0.4 g of ZrOCl 2 ·8H 2 O and 0.05 - 0.09 g of Na 2 SO 4 in 8 - 15 mL of water, then add 0.2 - 0.6 mL of lactic acid, and stir and mix evenly to obtain Solution A.

3. The preparation method of the zirconium-substituted arsenotungstic acid macrocyclic material according to claim 2, characterized in that, In step 2), the addition amount of K 14 [As 2 W 19 O 67 (H 2 O)] is 1.0 - 1.2 g.

4. The preparation method of the zirconium-substituted arsenotungstic acid macrocyclic material according to claim 3, characterized in that, in step 3), the addition amount of tetramethylammonium chloride is 0.3 - 0.6 g.

5. Application of the zirconium-substituted arsenotungstic acid macrocyclic material prepared by the preparation method according to any one of claims 1 to 4 as an iodine adsorbent in iodine adsorption.

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