Anderson-type polyoxometalate and method 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] Provided are Anderson-type polyoxometalates and a method for producing the same.

Background Art

[0002] Polyoxometalates (POMs) are metal oxide clusters composed of early transition metals with high oxidation states, such as Mo, W, V, Nb, Ta, etc., and oxygen. In polyoxometalates, since the abundant oxygen atoms on the surface can donate electrons to an electron acceptor, polyoxometalates are regarded as soft bases. However, since the metal ions constituting the polyoxometalate skeleton have unfilled orbitals, they are also regarded as Lewis acids that can accept electrons. Therefore, polyoxometalates play the role of Lewis acids or Lewis bases depending on the conditions. In addition, polyoxometalates are known as electron reservoirs because they have unique redox properties of the ability to hold strong electrons and the ability to release electrons. Furthermore, since polyoxometalates have various structures and sizes and can be artificially modeled by replacing the elements constituting polyoxometalates, polyoxometalates are applied in various fields such as catalysts, nanoscience, medicine, and optics.

[0003] Among polyoxometalates, Anderson-type polyoxometalates have the general formula [H y (XO 6 )M 6 O 18 n- ​(where y = 0 - 6, n = 2 - 8, M = addenda atom, X = hetero atom). It is an Anderson-type polyoxometalate, in which the hetero atom is in an octahedral geometry at the center as XO 6 and six MO 6 octahedra are formed with edge-sharing 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- and the Dawson-type [XM 18 O 62 n- , which also makes the properties of the Anderson-type polyoxometalate different from 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] The properties of the Anderson-type polyoxometalate can change with the change of the hetero atom. The redox properties of the Anderson-type polyoxometalate strongly depend on the hetero atom and pH. In this regard, CoMo 6 , IrW 6 , CrMo 6 , TeW 6 ​​Various materials such as these are being studied. Also, the magnetic properties of Anderson-type polyoxometalates are brought about by the presence or absence of hetero atom symmetry. Additionally, according to DFT (density functional theory) calculations, the HOMO-LUMO energy gap is determined by the hetero atom at the center of the polyoxometalate. Since such a HOMO-LUMO energy gap has a great influence on photocatalytic performance, research is actively being conducted to compare the photocatalytic performance while changing the hetero atom at the center of the polyoxometalate.

[0006] When polyoxometalates contain hetero atoms, the size of the ionic radius is an important factor. The size of the ionic radius that has been successfully synthesized so far is about 67 - 88 pm in the XMo 6 system and about 67 - 83 pm in the XW 6 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+ is very similar to W 6+ (74 pm) in terms of its ionic radius, 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, no case of successfully synthesizing Anderson-type polyoxometalates containing titanium as a hetero element has been reported so far.

[0007] As prior art documents, U.S. Patent Application Publication No. 2006-0108563 discloses "Luminescent compounds", U.S. Patent Application Publication No. 2019-0352320 discloses "Single-side modified beta-anderson-type heteropolymolybdate organic derivatives", and Amir Blazevic et al. disclose "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

Patent Document 2

Non-Patent Documents

[0009]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

[0011] In order to achieve other problems not specifically mentioned in addition to the above problems, embodiments according to the present invention can be used.

Means for Solving the Problems

[0012] The Anderson-type polyoxometalate according to one embodiment contains titanium (Ti) as a heteroatom at the center.

[0013] The Anderson-type polyoxometalate according to one embodiment is 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)

[0014] The method for producing an Anderson-type polyoxometalate according to one embodiment includes the steps of mixing a titanium precursor and a tungsten precursor to prepare a mixture, heating the mixture in a sealed container to form a hydrothermal synthesis solution, adding a solute after cooling the hydrothermal synthesis solution to form an Anderson-type polyoxometalate, and filtering the Anderson-type polyoxometalate.

[0015] The manufacturing method of Anderson-type polyoxometalate according to one embodiment includes the steps of mixing titanium oxysulfate and sodium tungstate to prepare a mixture, heating the mixture sealed in a container to form a hydrothermal synthesis solution, adding potassium chloride after cooling the hydrothermal synthesis solution 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, regarding Ti, it is already known among experts in this field that no one has yet succeeded in synthesizing Anderson-type polyoxometalate substances. Therefore, the new Anderson-type polyoxometalate containing titanium as the central metal atom according to one embodiment is a new substance and can be utilized in various fields such as catalysts, nanoscience, medicine, and optics.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode 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 having ordinary knowledge in the technical field to which the present invention pertains can easily implement them. The present invention can be implemented in various different forms and is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts not related to the explanation are omitted, and the same reference numerals are used for the same or similar components throughout the specification. Also, in the case of well-known publicly known technologies, their specific explanations are omitted.

[0019] Throughout the specification, when a part "includes" a certain component, it means that other components can be further included without excluding other components unless otherwise stated to the contrary.

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

[0021] The Anderson-type polyoxymetallate according to an embodiment contains titanium (Ti) as a heteroatom at the center.

[0022] Referring to Fig. 1, for the Anderson-type polyoxometalate, the heteroatom located at the center has an octahedral geometry of Ti / WO 6 and six WO 6 octahedra share oxygen atoms at the edges around the heteroatom.

[0023] Referring to Figs. 2 and 3, the structure of the Anderson-type polyoxometalate is overall planar and has a zero-dimensional framework structure.

[0024] The Anderson-type polyoxometalate contains titanium and tungsten. Titanium is derived from a titanium precursor, and tungsten is derived from a tungsten precursor. 3d It is formed in a structure with a rhombohedral space group R-3m (No. 166) type of D

[0025] symmetry.

[0026] For example, the titanium precursors include titanium oxysulfate, titanium disulfate, titanium chloride, titanium isopropoxide, etc. The tungsten precursor is tungstate. For example, tungstates include sodium tungstate, potassium tungstate, etc.

[0027] The mixing molar ratio of the titanium precursor and the tungsten precursor may be from 0.5:6 to 2.5:6. When it is less than 0.5:6, synthesis is possible, but compound phases with different crystal structures coexist, and the synthesis yield of the pure Anderson-type polyoxometalate compound may significantly decrease. When it is greater than 2.5:6, other compound phases are generated or no powder is formed.

[0028] The Anderson-type polyoxometalate according to one embodiment is 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)

[0029] At the hetero-site of the Anderson-type polyoxometalate, Ti 4+ and W 4+ show occupancy in a ratio of (1 - a) to a.

[0030] The method for producing an Anderson-type polyoxometalate according to one embodiment includes the steps of mixing a titanium precursor and a tungstic acid precursor to prepare a mixture, heating the mixture sealed in a container to form a hydrothermal synthesis solution, and after cooling the hydrothermal synthesis solution, adding a solute to form a powdery Anderson-type polyoxometalate.

[0031] The step of preparing the mixture includes mixing a titanium precursor and a 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 acetonitrile, the aforementioned compounds can be used as the titanium precursor and the tungstic acid precursor. For example, the titanium precursor can be titanium oxysulfate, titanium disulfate, titanium chloride, titanium isopropoxide, etc. The tungsten precursor is tungstate. For example, tungstates include sodium tungstate, potassium tungstate, etc.

[0033] Also, the mixing molar ratio of the titanium precursor and the tungsten precursor may be 0.5:6 to 2.5:6. When it is smaller than 0.5:6, synthesis is possible, but compound phases with different crystal structures coexist, and the synthesis yield of the pure Anderson-type polyoxometalate compound may significantly decrease. When it is larger than 2.5:6, other compound phases are formed or no powder is formed.

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

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

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

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

[0038] For example, solutes added after cooling the pure Anderson-type polyoxometalate solution obtained by hydrothermal synthesis include potassium-containing precursors such as potassium chloride, potassium nitrate, potassium sulfate, and potassium carbonate. Also, the solute can be used in an amount of 0.8 mol to 1.2 mol relative to the tungsten precursor. When used in an amount less than 0.8 mol, the synthesis yield decreases. When used in an amount greater than 1.2 mol, the solute is separated and removed during the washing process, but the reagent may be wasted.

[0039] Also, after adding the solute, it can be stirred for about 0.5 days to about 1.5 days. If the stirring time is shorter than 0.5 days, unreacted substances may remain, so the synthesis yield may decrease. If it is longer than 1.5 days, the process time may be unnecessarily wasted.

[0040] The method for producing an Anderson-type polyoxometalate according to one embodiment can include the step of washing the formed Anderson-type polyoxometalate with a washing solution, centrifuging it, and then drying it to obtain Anderson-type polyoxometalate powder. For example, the washing solution includes basic solutions such as sodium hydroxide and potassium hydroxide.

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

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

Example

[0043] (Example 1) Referring to Figure 4, using a hydrothermal reaction, Anderson-type K 6 Na 2 Ti 0.92 W 6.08 O 24 ·12H 2 O is synthesized. TiOSO 4 ·xH 2 SO 4 ·yH 2 O (0.1599 g, 5.79x10 -4 mol) and Na 2 WO 4 ·2H 2 O (0.8814 g, 2.67x10 -3 mol) and 10 mL of deionized water are mixed, and the mixture is placed in a 23 mL Teflon cup and then put into a stainless steel autoclave. Next, the autoclave is sealed and heated at 230 °C for 2 days, and then cooled to room temperature. After cooling, the autoclave is opened, filtered to remove by-products, and the filtrate is collected. Excess KCl (2.5 g, 3.35x10 -2 mol) is added to the filtrate and stirred for 1 day. The turbid product is washed with NaOH solution (0.01 M), centrifuged, and then dried to obtain powdery K 6 Na 2 Ti 0.92 W 6.08 O 24 ·12H 2 O. Further, before adding the NaOH solution to grow into single crystals, the turbid product is filtered, and the filtrate is left at room temperature for 1 day for production.

[0044] (Example 2) To confirm the range of composable compositions, experiments are conducted while changing the composition ratios. The experimental conditions are described in Table 1 below, and except for the composition ratios, the experiments are conducted in the same manner as in Example 1 described above. The synthesis results are confirmed for the success or failure of synthesis by Powder XRD. Referring to Figure 5, from the P-XRD results, TiOSO 4 ·xH 2 SO 4 ·yH 2 O and Na 2 WO 4 ·2H 2 O can be synthesized in the range where the ratio is from 1:6 to 2:6. However, when the amount of TiOSO 4 ·xH 2 SO 4 ·yH 2 O increases, it is confirmed that synthesis occurs in other phases. For example, when the ratio of TiOSO 4 ·xH 2 SO 4 ·yH 2 O and Na 2 WO 4 ·2H 2 O is 3:6, a powder is formed, but it is synthesized into a different phase. When the ratio of TiOSO 4 ·xH 2 SO 4 ·yH 2 O and Na 2 WO 4 ·2H 2 O is 1:1, the powder itself is not formed. Also, when the amount of TiOSO 4 ·xH 2 SO 4 ·yH 2 O decreases, the synthesis yield of pure Anderson-type polyoxometalate decreases. For example, when the ratio of TiOSO 4 ·xH 2 SO 4 ·yH 2 O and Na 2 WO 4 ·2H 2 O is 0.4:6, synthesis is possible, but compound phases with different crystal structures coexist, and pure K 6 Na 2 Ti 0.92 W 6.08 O24 ·12H 2 The synthesis yield of the O compound decreases significantly. [Table 1]

[0045] Referring to FIGS. 1 to 3, K 6 Na 2 Ti 0.92 W 6.08 O 24 ·12H 2 O forms a structure with a rhombohedral space group R-3m (No. 166) type of D 3d symmetry. Looking closely at the crystal structure, there are heteroatoms Ti / WO with an octahedral geometry at the center, and six WO 6 octahedra form a framework by sharing oxygen atoms at the edges around it. FIG. 2 shows the framework in the ab plane, and FIG. 3 shows the framework in the ac plane. K 6 8 octahedra share oxygen atoms at the edges to form a framework. FIG. 2 shows the framework in the ab plane, and FIG. 3 shows the framework in the ac plane. K 6 Na 2 Ti 0.92 W 6.08 O 24 ·12H 2 O is planar, similar to a general Anderson-type POM, and is confirmed to have a zero-dimension framework structure. Generally, the M / X ratio is 6, but in one example of K 6 Na 2 Ti 0.92 W 6.08 O 24 ·12H 2 O, not only all Ti 4+ is present at the hetero-site, but Ti 4+ and W 4+ show an occupancy of about 92% to 8% at the site. K 6 Na 2 Ti 0.92 W 6.08 O 24 ·12H2 The crystal data of O are shown in Table 2 below.

Table 2

[0046] In Table 2, R(F) and Rw(F 2 o ) are 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 powder XRD pattern of K 6 Na 2 Ti 0.92 W 6.08 O 24 ·12H 2 O actually synthesized in Example 1 is compared with the powder XRD pattern simulated based on the structure refined from single crystal XRD, and it can be seen that the two patterns match each other.

[0048] Referring to Figure 7, K 6 Na 2 Ti 0.92 W 6.08 O 24 ·12H 2 O actually synthesized in Example 1 is compared with the conventional Anderson-type POM of K 6 Na 2 PtW 6 O 24 ·12H 2 O. K 6 Na 2 ​Ti 0.92 W 6.08 O 24 ·12H 2 O is K 6 Na 2 PtW 6 O 24 ·12H 2 O (space group R-3m (No.166)) shows a pattern that is very similar structurally. However, since the elements constituting the heteroatoms located at the center are Ti and Pt respectively, due to the difference in the bond distance between X-O in XO 6 the powder pattern is shifted to the right as a whole. The bond length of Ti-O is about 1.970 Å, and the bond length of Pt-O is about 2.013 Å. As a result, the lattice parameter is 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 Ti is clearly contained in the Anderson-type polyoxometalate synthesized in Example 1 and to confirm its composition ratio, 10 mg of the synthesized powder sample was completely dissolved in 10 mL of 0.01 M HCl solution, and then the composition ratio was confirmed by ICP-OES (Inductively coupled plasma-optical emission spectroscopy). The results are shown in Table 3 below, and the stoichiometric values (W / Ti ~ 6.6) of the composition ratio calculated from SC-XRD and the experimental values match each other.

Table 3

[0050] As described above, the preferred embodiments of the present invention have been described in detail. However, the scope of the rights of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concepts of the present invention defined in the following claims also belong to the scope of the rights of the present invention.

Claims

1. An Anderson-type polyoxometalate containing titanium (Ti) as a heteroatom at the center.

2.

3. The heteroatom located at the center has a Ti / WO with an octahedral geometry ６ and six WO are around the heteroatom ６ The Anderson-type polyoxometalate according to claim 1, wherein the octahedra share oxygen atoms at edges The Anderson-type polyoxometalate according to claim 2, which is planar and has a zero-dimensional framework structure.

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 and the tungsten precursor derived from the tungsten is 0.5:6 to 2.5:

6.

5. An Anderson-type polyoxometalate represented by the following Chemical Formula 1.

6. Chemical formula 1: K ６ Na ２ Ti １－ａ W ６＋ａ O ２４ ・12H ２ O (0 < a < 0.2)

7. In the hetero-site of the Anderson-type polyoxometalate, Ti ４＋ and W ４＋ show occupancy in a ratio of (1 - a) to a, the Anderson-type polyoxometalate according to claim 5. A step of mixing a titanium precursor and a tungsten precursor to prepare a mixture. A step of heating the mixture after sealing it in a container to form a hydrothermal synthesis solution. A method for producing an Anderson-type polyoxometalate, comprising a step of adding a solute after cooling the hydrothermal synthesis solution to form an Anderson-type polyoxometalate.

8. The method for producing an Anderson-type polyoxometalate according to claim 7, wherein the hydrothermal synthesis is performed at 20°C to 500°C for 1 day to 3 days.

9. The method for producing an Anderson-type polyoxometalate according to claim 7, wherein the mixing molar ratio of the titanium precursor and the tungsten precursor is 0.5:6 to 2.5:

6.

10. The method for producing an Anderson-type polyoxometalate according to claim 7, further comprising a step of washing the formed Anderson-type polyoxometalate with a washing solution, centrifuging, and then drying to obtain Anderson-type polyoxometalate powder.

11. The method for producing an Anderson-type polyoxometalate according to claim 7, further comprising a step of filtering the formed Anderson-type polyoxometalate to obtain Anderson-type polyoxometalate single crystals.

12. A step of mixing titanium oxy sulfate and sodium tungstate to prepare a mixture. ​ After sealing the mixture in a container, heating it to form a hydrothermal synthesis solution, and After cooling the hydrothermal synthesis solution, adding potassium chloride to form an Anderson-type polyoxometalate. A method for producing an Anderson-type polyoxometalate, comprising these steps.

Images