Anderson-type polyoxometalates and methods for producing the same

Abstract

Anderson-type polyoxometalates containing titanium (Ti) as a central heteroatom are provided. A method for producing the Anderson-type polyoxometalates includes the steps of mixing a titanium precursor and a tungsten precursor to prepare a mixture, sealing the mixture in a container and then heating it to form a hydrothermal synthesis solution, and cooling the hydrothermal synthesis solution and then adding a solute to form the Anderson-type polyoxometalate.

Description

[Technical Field]

[0001] The present invention provides Anderson-type polyoxometalates and methods for producing the same. [Background technology]

[0002] Polyoxometalates (POMs) are metal oxide clusters composed of oxygen and early transition metals with high oxidation states, such as Mo, W, V, Nb, and Ta. Because the abundant oxygen atoms on the surface of polyoxometalates can donate electrons to electron acceptors, they are considered soft bases. However, the metal ions constituting the polyoxometalate skeleton have unfilled orbitals, so they can also be considered Lewis acids capable of accepting electrons. Therefore, polyoxometalates can function as either Lewis acids or Lewis bases depending on the conditions. Furthermore, polyoxometalates are known as electron reservoirs because they possess inherent redox properties, characterized by both strong electron-holding and electron-releasing capabilities. Furthermore, because polyoxometalates not only possess a variety of structures and sizes, but also allow for artificial modeling by substituting the elements that make up the polyoxometalates, they have applications in various fields such as catalysis, nanoscience, medicine, and optics.

[0003] Among polyoxometalates, Anderson-type polyoxometalates have the general formula [H y (XO6)M6O 18 ] n-(y = 0 - 6, n = 2 - 8, M = addenda atom, X = hetero atom). It is an Anderson-type polyoxometalate in which a hetero atom exists as XO6 with an octahedral geometry at its center, and six MO6 octahedra are edge-sharing around it to form a structure. The structure of the Anderson-type polyoxometalate is different from other types of polyoxometalates, such as the Keggin-type [XM 12 O 40 n- , the Dawson-type [XM 18 O 62 n- . Thus, the properties of the Anderson-type polyoxometalate are also different from those of other types of polyoxometalates.

[0004] Also, the Anderson-type polyoxometalate has two terminal oxygen atoms for each addenda atom. Such an Anderson-type polyoxometalate has high reactivity and various coordination modes, so it can be combined with hybrid substances with various functions and utilized as an ideal inorganic building block that can be modified.

[0005] ​​Anderson-type polyoxometalates can have their properties changed by varying the heteroatom. The redox properties of Anderson-type polyoxometalates strongly depend on the heteroatom and pH, and various materials such as CoMo6, IrW6, CrMo6, TeW6, etc. have been studied in relation to this. Also, the magnetic properties of Anderson-type polyoxometalates are brought about by the presence or absence of heteroatom symmetry. In addition, according to DFT (density functional theory) calculations, the HOMO-LUMO energy gap is determined by the heteroatom at the center of the polyoxometalate. Since such a HOMO-LUMO energy gap has a great influence on photocatalytic performance, research on comparing the photocatalytic performance while changing the heteroatom at the center of the polyoxometalate has been actively carried out.

[0006] When polyoxometalates contain heteroatoms, the size of the ionic radius is an important factor. The sizes of the ionic radii that have been successfully synthesized so far are approximately 67 - 88 pm in the XMo6 system and approximately 67 - 83 pm in the XW6 system. From the perspective of the size of the ionic radius, Ti 4+ (75 pm) fully belongs to the theoretically accessible range. Also, Ti 4+ has an ionic radius very similar to that of W 6+ (74 pm), and the most common coordination number is also the same, which is 6. It is known as the element that can be most easily substituted with polytungstate. Nevertheless, there has been no reported case of successful synthesis of Anderson-type polyoxometalates containing titanium as a heteroatom so far.

[0007] Prior art includes U.S. Patent Publication No. 2006-0108563, which discloses "Luminescent compounds," U.S. Patent Publication No. 2019-0352320, which discloses "Single-side modified beta-anderson-type heteropolymolybdate organic derivatives," and Amir Blazevic et al., which discloses "The Anderson-Evans polyoxometalate: From inorganic building blocks via hybrid organic-inorganic structures to tomorrows "Bio-POM" (Amir Blazevic, Annette Rompel, Coordination Chemistry Reviews 307(2016)42-64). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] U.S. Patent Application Publication No. 2006-0108563 [Patent Document 2] U.S. Patent Application Publication No. 2019-0352320 [Non-patent literature]

[0009] [Non-Patent Document 1] Amir Blazevicet.al “The Anderson-Evans polyoxometalate:From inorganic building blocks via hybrid organic-inorganic structures to tomorrows “Bio-POM”” (Amir Blazevic,Annette Rompel,Coordination Chemistry Reviews 307(2016)42-64) [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] One embodiment provides a novel Anderson-type polyoxometalate containing titanium as a central metal atom, and a method for producing the same.

[0011] Embodiments of the present invention can be used to achieve other problems not specifically mentioned above. [Means for solving the problem]

[0012] In one embodiment, the Anderson-type polyoxometalate contains a heteroatom of titanium (Ti) at its center.

[0013] An Anderson-type polyoxometalate according to one example is represented by the following chemical formula 1. Chemical formula 1: K6Na2Ti 1-a W 6+a O 24 ·12H2O(0 <a<0.2)

[0014] A method for producing Anderson-type polyoxometalate according to one embodiment includes the steps of: mixing a titanium precursor and a tungsten precursor to prepare a mixture; sealing the mixture in a container and heating it to form a hydrothermal synthesis solution; cooling the hydrothermal synthesis solution and then adding a solute to form Anderson-type polyoxometalate; and filtering the Anderson-type polyoxometalate.

[0015] A method for producing Anderson-type polyoxometalate according to one embodiment includes the steps of: mixing titanium oxysulfate and sodium tungstate to prepare a mixture; sealing the mixture in a container and heating it to form a hydrothermal synthesis solution; cooling the hydrothermal synthesis solution and then adding potassium chloride to form Anderson-type polyoxometalate; and filtering the Anderson-type polyoxometalate. [Effects of the Invention]

[0016] Among various transition metals such as Mo, W, V, Nb, and Ta, it is already known among experts in this field that the synthesis of Anderson-type polyoxometalates using titanium has not yet been successful. Therefore, the novel Anderson-type polyoxometalate containing titanium as the central metal atom, as described in one example, is a new material that can be utilized in various fields such as catalysis, nanoscience, medicine, and optics. [Brief explanation of the drawing]

[0017] [Figure 1] This diagram schematically shows a Ti / WO68-sided polyhedron and six WO68-sided polyhedra according to one embodiment, and a Ti / WO68-sided polyhedron and six WO68-sided polyhedra connected via edge-sharing. [Figure 2] This is a drawing showing the Anderson-type framework of K6Na2Ti0.92W6.08O24·12H2O according to one embodiment, relative to the ab plane. [Figure 3] This is a drawing showing the Anderson-type framework of K6Na2Ti0.92W6.08O24·12H2O according to one embodiment, relative to the ac plane. [Figure 4] This diagram schematically shows the process of synthesizing Anderson-type K6Na2Ti0.92W6.08O24·12H2O according to one embodiment. [Figure 5]This graph shows the P-XRD pattern results for the synthesis of Anderson-type K6Na2Ti0.92W6.08O24·12H2O according to one example, based on the composition ratio of TiOSO4·xH2SO4·yH2O and Na2WO4·2H2O. [Figure 6] This graph shows the powder XRD of Anderson-type K6Na2Ti0.92W6.08O24·12H2O according to one example. [Figure 7] This graph shows a comparison of powder XRD results between Anderson-type K6Na2Ti0.92W6.08O24·12H2O from one example and conventional K6Na2PtW6O24·12H2O. [Modes for carrying out the invention]

[0018] With reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those with ordinary skill in the art to which the invention pertains can easily implement them. The present invention can be implemented in a variety of different forms and is not limited to the embodiments described herein. In order to clearly illustrate the present invention in the drawings, parts not relevant to the description have been omitted, and the same reference numerals have been used throughout the specification for identical or similar components. Furthermore, in the case of widely known prior art, specific descriptions thereof have been omitted.

[0019] Throughout the specification, when a part "includes" a component, unless otherwise stated, it means that it may include other components rather than excluding them.

[0020] Next, an Anderson-type polyoxymetalate and its manufacturing method according to one embodiment will be described in detail.

[0021] In one embodiment, the Anderson-type polyoxometalate contains titanium (Ti) as a heterogeneous atom at its center.

[0022] Referring to Figure 1, in the Anderson-type polyoxometalate, the central heterogeneous atom is Ti / WO6 with octahedral geometry, and six WO6 octahedra around the heterogeneous atom share edges with the oxygen atom.

[0023] Referring to Figures 2 and 3, the structure of Anderson polyoxometalates is generally planar and has a zero-dimensional framework.

[0024] Anderson polyoxometalates are of type D, which is the Rhombohedral space group R-3m (No. 166). 3d It is formed with a symmetrical structure.

[0025] Anderson-type polyoxometalates contain titanium and tungsten, with the titanium derived from a titanium precursor and the tungsten from a tungsten precursor.

[0026] For example, titanium precursors include titanium oxysulfate, titanium disulfate, titanium chloride, and titanium isopropoxide. Tungsten precursors include tungstates. For example, tungstates include sodium tungstate and potassium tungstate.

[0027] The molar ratio of the titanium precursor to the tungsten precursor may be between 0.5:6 and 2.5:6. If the ratio is less than 0.5:6, synthesis is possible, but compound phases with different crystalline structures may coexist, potentially significantly reducing the yield of the pure Anderson-type polyoxometalate compound. If the ratio is greater than 2.5:6, other compound phases may be formed, or no powder may be formed.

[0028] An Anderson-type polyoxometalate according to one example is represented by the following chemical formula 1. Chemical formula 1: K6Na2Ti 1-a W 6+a O 24 ·12H2O(0 <a<0.2)

[0029] In the heterosite of Anderson polyoxometalates, Ti 4+ and W 4+ The occupancy is shown in a ratio of (1-a) to a.

[0030] A method for producing Anderson-type polyoxometalate according to one embodiment includes the steps of: mixing a titanium precursor and a tungstic acid precursor to prepare a mixture; sealing the mixture in a container and heating it to form a hydrothermal synthesis solution; and cooling the hydrothermal synthesis solution and then adding a solute to form a powdered Anderson-type polyoxometalate.

[0031] The step of preparing the mixture includes mixing the titanium precursor and the tungstic acid precursor.

[0032] For example, in the step of preparing a mixture by mixing a titanium precursor and a tungstic acid precursor with water or acetonitryl, the titanium precursor and tungstic acid precursor can be any of the aforementioned compounds. For example, titanium precursors include titanium oxysulfate, titanium disulfate, titanium chloride, and titanium isopropoxide. Tungsten precursors include tungstates. For example, tungstates include sodium tungstate and potassium tungstate.

[0033] Furthermore, the molar ratio of the titanium precursor to the tungsten precursor may be between 0.5:6 and 2.5:6. If the ratio is less than 0.5:6, synthesis is possible, but compound phases with different crystalline structures may coexist, potentially significantly reducing the yield of the pure Anderson-type polyoxometalate compound. If the ratio is greater than 2.5:6, other compound phases may form, or no powder may be formed.

[0034] The step of forming a hydrothermal synthesis solution involves sealing the aforementioned mixture in a container and then heating it.

[0035] In the step of sealing the mixture in a container and heating it to form a hydrothermal synthesis solution, hydrothermal synthesis can be carried out at approximately 20°C to 500°C for approximately 1 to 3 days. If the synthesis temperature is lower than 20°C and the synthesis period is less than 1 day, crystallinity may decrease significantly, and the synthesis yield may decrease significantly. Similarly, if the synthesis temperature is higher than 500°C and the synthesis period is less than 1 day, crystallinity may decrease significantly, and the synthesis yield may decrease significantly.

[0036] The step of forming Anderson-type polyoxometalate includes cooling the hydrothermal synthesis solution and then filtering it. For example, by filtering the cooled hydrothermal synthesis solution, by-products can be removed from the cooled hydrothermal synthesis solution, and only the pure Anderson-type polyoxometalate solution can be collected.

[0037] The step of forming Anderson-type polyoxometalate includes adding a solute to a pure Anderson-type polyoxometalate solution and recovering it in powder form.

[0038] For example, the solute added after cooling a pure Anderson-type polyoxometalate solution obtained by hydrothermal synthesis can be potassium-containing precursors such as potassium chloride, potassium nitrate, potassium sulfate, or potassium carbonate. The solute can be used in amounts of 0.8 to 1.2 moles relative to the tungsten precursor. If used in amounts less than 0.8 moles, the synthesis yield will decrease, and if used in amounts greater than 1.2 moles, the solute will be separated and removed during the washing process, but this may result in wasted reagent.

[0039] Furthermore, after adding the solute, the mixture can be stirred for approximately 0.5 to 1.5 days. If the stirring time is shorter than 0.5 days, unreacted material may remain, potentially reducing the synthesis yield. If the stirring time is longer than 1.5 days, process time may be unnecessarily wasted.

[0040] A method for producing Anderson-type polyoxometalate according to one embodiment may include the steps of washing the formed Anderson-type polyoxometalate with a washing solution, centrifuging it, drying it, and obtaining Anderson-type polyoxometalate powder. For example, the washing solution may be a basic solution such as sodium hydroxide or potassium hydroxide.

[0041] A method for producing Anderson-type polyoxometalate according to one embodiment may include the step of filtering the formed Anderson-type polyoxometalate to obtain Anderson-type polyoxometalate single crystals.

[0042] The present invention will be described in more detail below with reference to examples, but the following examples are examples of the present invention and the present invention is not limited to the following examples. [Examples]

[0043] (Example 1) Referring to Figure 4, the Anderson type K6Na2Ti is produced using a hydrothermal reaction. 0.92 W 6.08 O 24 Synthesize 12H2O. TiOSO4·xH2SO4·yH2O (0.1599g, 5.79x10) -4 (mol) and Na2WO4·2H2O(0.8814g, 2.67x10) -3 Mix the mol of KCl with 10 mL of deionized water, place the mixture in a 23 mL Teflon cup, and then place it in a stainless steel autoclave. Next, seal the autoclave and heat at 230°C for 2 days, then cool to room temperature. After cooling, open the autoclave, filter to remove by-products, and collect the filtrate. Add excess KCl (2.5 g, 3.35 x 10) to the filtrate. -2 Add (mol) and stir for 1 day. Wash the turbid product with NaOH solution (0.01M), centrifuge, and dry to obtain the powdered K6Na2Ti 0.92 W 6.08 O 24 • Obtain 12H2O. Furthermore, before adding the NaOH solution to grow the single crystal, filter the turbid product and leave the filtrate at room temperature for one day to complete the process.

[0044] (Example 2) To confirm the range of synthesizable compositions, experiments are conducted while varying the ratio of the compositions. The experimental conditions are described in Table 1 below, and the experiment is conducted in the same manner as in Example 1 described above, except for the composition ratio. The success or failure of the synthesis is confirmed by powder XRD. Referring to Figure 5, the P-XRD results show that synthesis is possible in the range of ratios of TiOSO4·xH2SO4·yH2O to Na2WO4·2H2O from 1:6 to 2:6. However, when the amount of TiOSO4·xH2SO4·yH2O increases, it is confirmed that it is synthesized in other phases. For example, when the ratio of TiOSO4·xH2SO4·yH2O to Na2WO4·2H2O is 3:6, powder is formed, but it is synthesized in a different phase, and when the ratio of TiOSO4·xH2SO4·yH2O to Na2WO4·2H2O is 1:1, no powder is formed at all. Furthermore, as the amount of TiOSO4·xH2SO4·yH2O decreases, the synthesis yield of pure Anderson-type polyoxometalates decreases. For example, when the ratio of TiOSO4·xH2SO4·yH2O to Na2WO4·2H2O is 0.4:6, synthesis is possible, but compound phases with different crystal structures coexist, resulting in the synthesis of pure K6Na2Ti 0.92 W 6.08 O 24 • The synthesis yield of 12H2O compounds decreases significantly. [Table 1]

[0045] Referring to Figures 1 to 3, K6Na2Ti 0.92 W 6.08 O 24 ·12H2O is a D type Rhombohedral space group R-3m (No. 166). 3d It is formed with a symmetrical structure. Looking at the crystal structure in detail, there is a heterogeneous Ti / WO6 atom with octahedral geometry at the center, and six WO6 octahedra around it form a framework by sharing edges with oxygen atoms. Figure 2 shows the framework in the ab plane, and Figure 3 shows the framework in the ac plane. K6Na2Ti0.92 W 6.08 O 24 ·12H2O is confirmed to be planar, similar to typical Anderson-type POMs, and possesses a zero-dimension framework structure. Generally, the M / X ratio is 6, but in one example, K6Na2Ti 0.92 W 6.08 O 24 In the case of 12H2O, all of the heterosites are Ti 4+ It's not just that, Ti 4+ and W 4+ K6Na2Ti shows approximately 92% to 8% occupancy at the site. 0.92 W 6.08 O 24 The crystal data for 12H2O is shown in Table 2 below. [Table 2]

[0046] Table 2 shows R(F) and Rw(F 2 o ) is calculated by the following formulas 1 and 2. [Formula 1] R(F) = Σ||Fo| - |Fc|| / Σ|Fo| [Formula 2] Rw(F 2 o )=[Σw(F 2 o -F 2 c ) 2 / Σw(F 2 o ) 2 ] 1 / 2

[0047] Referring to Figure 6, the K6Na2Ti actually synthesized in Example 1 0.92 W 6.08 O 24The powder XRD pattern of 12H2O and the simulated powder XRD pattern based on a structure refined from single-crystal XRD are compared, and it can be seen that the two patterns are identical.

[0048] Referring to Figure 7, the K6Na2Ti actually synthesized in Example 1 0.92 W 6.08 O 24 • 12H2O and the conventional Anderson-type POM K6Na2PtW6O 24 • 12H2O is compared. The actually synthesized K6Na2Ti 0.92 W 6.08 O 24 ·12H2O is K6Na2PtW6O 24 It exhibits a structurally very similar pattern to 12H2O (space group R-3m (No. 166)). However, because the elements constituting the heterogeneous atoms located at the center are different (Ti and Pt), the difference in bond distance between XO atoms within XO6 causes the powder pattern to shift to the right overall. The bond distance between Ti and O is approximately 1.970 Å, and the bond distance between Pt and O is approximately 2.013 Å. Consequently, the lattice parameters are also smaller for Ti-POM (a=b=13.1000 Å, c=18.1333 Å) compared to Pt-POM (a=b=13.1376 Å, c=18.3504 Å).

[0049] To confirm that the Anderson-type polyoxometalate synthesized in Example 1 clearly contains Ti, and to determine its composition ratio, 10 mg of the synthesized powder sample was completely dissolved in 10 mL of 0.01 M HCl solution, and the composition ratio was confirmed by ICP-OES (Inductively coupled plasma-optical emission spectroscopy). The results are shown in Table 3 below, and the composition ratio calculated from SC-XRD and the experimental stoichiometric value (W / Ti~6.6) are in agreement. [Table 3]

[0050] Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art that utilize the basic concepts of the present invention as defined in the following claims also fall within the scope of the present invention.

Claims

1. It contains titanium (Ti) as a heteroatom at its center. An Anderson-type polyoxometalate represented by the following chemical formula 1. Chemical formula 1: K 6 Na 2 Ti 1-a W 6+a O 24 ・12H 2 O (0<a<0.2)

2. The aforementioned heterogeneous atom located at the center has an octahedral geometry (Ti / WO). ６ And there are six WO around the aforementioned heterogeneous atoms ６ The Anderson-type polyoxometalate according to claim 1, wherein the octahedrons share oxygen atoms by edge-sharing.

3. The Anderson-type polyoxometalate according to claim 2, having a structure in which a central Ti / WO 68-hedron and six surrounding WO 68-hedrons are arranged on the same plane, and these form an isolated 0-dimensional cluster in the crystal.

4. The Anderson-type polyoxometalate according to claim 1, wherein the Anderson-type polyoxometalate contains titanium and tungsten, and the molar ratio of the titanium precursor derived from the titanium to the tungsten precursor derived from the tungsten is 0.5:6 to 2.5:

6.

5. At the heterosite of the Anderson-type polyoxometalate, Ti ４＋ and W ４＋ The Anderson-type polyoxometalate according to claim 1, wherein the occupancy is in a ratio of (1-a) to a.

6. The steps include: mixing a titanium precursor and a tungsten precursor to prepare a mixture; The steps include sealing the mixture in a container and then heating it to form a hydrothermal synthesis solution, and A method for producing Anderson-type polyoxometalate, comprising the step of cooling the hydrothermal synthesis solution and then adding a solute to form Anderson-type polyoxometalate.

7. The method for producing Anderson-type polyoxometalate according to claim 6, wherein the hydrothermal synthesis is carried out at 20°C to 500°C for 1 to 3 days.

8. The method for producing Anderson-type polyoxometalate according to claim 6, wherein the mixed molar ratio of the titanium precursor and the tungsten precursor is 0.5:6 to 2.5:

6.

9. The method for producing Anderson-type polyoxometalate according to claim 6, further comprising the steps of washing the formed Anderson-type polyoxometalate with a washing solution, centrifuging it, and drying it to obtain Anderson-type polyoxometalate powder.

10. The method for producing Anderson-type polyoxometalate according to claim 6, further comprising the step of filtering the formed Anderson-type polyoxometalate to obtain Anderson-type polyoxometalate single crystals.

11. The step of preparing a mixture by mixing titanium oxysulfate and sodium tungstate, The steps include sealing the mixture in a container and then heating it to form a hydrothermal synthesis solution, and A method for producing Anderson-type polyoxometalate, comprising the step of cooling the hydrothermal synthesis solution and then adding potassium chloride to form Anderson-type polyoxometalate.

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