ANDERSON-TYPE POLYOXOMETALATE AND PREPARATION METHOD THEREFOR

Abstract

Provided is an Anderson-type polyoxometalate including titanium (Ti) as a heteroatom in the center of the Anderson-type polyoxometalate. A method for preparing an Anderson-type polyoxometalate includes mixing a titanium precursor and a tungsten precursor to prepare a mixture, sealing the mixture in a container and heating to form a hydrothermal synthetic solution, and cooling the hydrothermal synthetic solution and then adding a solute to form an Anderson-type polyoxometalate.

Claims

1. An Anderson-type polyoxometalate comprising: titanium as a heteroatom at a center of the Anderson-type polyoxometalate.

2. The Anderson-type polyoxometalate of claim 1, wherein: the heteroatom positioned at the center is Ti/WO.sub.6 having an octahedral geometry and six WO.sub.6 octahedrons around the heteroatom have edge-sharing of oxygen atoms.

3. The Anderson-type polyoxometalate of claim 2, wherein: the Anderson-type polyoxometalate is planar and has a zero-dimension framework structure.

4. The Anderson-type polyoxometalate of claim 1, wherein: the Anderson-type polyoxometalate includes titanium and tungsten, and a molar ratio of a titanium precursor deriving the titanium and a tungsten precursor deriving the tungsten is 0.5:6 to 2.5:6.

5. An Anderson-type polyoxometalate represented by the following Chemical Formula 1:
K.sub.6Na.sub.2Ti.sub.1aW.sub.6+aO.sub.24.Math.12H.sub.2O (0<a<0.2).[Chemical Formula 1]

6. The Anderson-type polyoxometalate of claim 5, wherein: Ti.sup.4+ and W.sup.4+ show occupancy at a ratio of (1a) to a in a hetero-site of the Anderson-type polyoxometalate.

7. A method for preparing an Anderson-type polyoxometalate, the method comprising: mixing a titanium precursor and a tungsten precursor to prepare a mixture, sealing the mixture in a container and heating to form a hydrothermal synthetic solution, and cooling the hydrothermal synthetic solution and then adding a solute to form an Anderson-type polyoxometalate.

8. The method for preparing an Anderson-type polyoxometalate of claim 7, wherein: the hydrothermal synthesis is carried out at 20 C. to 500 C. for 1 day to 3 days.

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

10. The method for preparing an Anderson-type polyoxometalate of claim 7, further comprising: Washing the formed Anderson-type polyoxometalate with a washing solution, carrying out centrifugation, and then drying to obtain Anderson-type polyoxometalate powder.

11. The method for preparing an Anderson-type polyoxometalate of claim 7, further comprising: filtering the formed Anderson-type polyoxometalate to obtain an Anderson-type polyoxometalate single crystal.

12. A method for preparing an Anderson-type polyoxometalate, the method comprising: mixing titanium oxysulfate and sodium tungstate to prepare a mixture, sealing the mixture in a container and heating to form a hydrothermal synthetic solution, and cooling the hydrothermal synthetic solution and then adding potassium chloride to form an Anderson-type polyoxometalate.

Description

DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a drawing which schematically shows a Ti/WO.sub.6 octahedron, six WO.sub.6 octahedrons, and a Ti/WO.sub.6 octahedron and six WO.sub.6 octahedrons connected through edge-sharing, according to an exemplary embodiment.

[0016] FIG. 2 is a drawing which shows a framework of Anderson-type K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.24.Math.12H.sub.2O according to an exemplary embodiment to an ab plane.

[0017] FIG. 3 is a drawing which shows a framework of Anderson-type K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.24.Math.12H.sub.2O according to an exemplary embodiment to an ac plane.

[0018] FIG. 4 is a drawing which schematically shows a process of synthesizing Anderson-type K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.24.Math.12H.sub.2O according to an exemplary embodiment.

[0019] FIG. 5 is a graph which shows results of P-XRD (Powder X-Ray Diffraction) pattern depending on a composition ratio of TiOSO.sub.4.Math.xH.sub.2SO.sub.4.Math.yH.sub.2O and Na.sub.2WO.sub.4.Math.2H.sub.2O for synthesizing Anderson-type K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.24.Math.12H.sub.2O according to an exemplary embodiment.

[0020] FIG. 6 is a graph which shows powder XRD of Anderson-type K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.24.Math.12H.sub.2O according to an exemplary embodiment.

[0021] FIG. 7 is a graph which shows comparison of powder XRD of Anderson-type K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.24.Math.12H.sub.2O and conventional K.sub.6Na.sub.2PtW.sub.6O.sub.24.Math.12H.sub.2O according to an exemplary embodiment.

MODE FOR INVENTION

[0022] Exemplary embodiments of the present disclosure will be described in detail so that a person with ordinary skill in the art to which the present disclosure pertains may easily carry out the exemplary embodiments, with reference to the accompanying drawings. The present disclosure may be implemented in various different forms and is not limited to the exemplary embodiments described herein. In the drawings, parts which are not relevant to the description have been omitted for clearly describing the present disclosure, and the same reference numerals are used for same or similar components throughout the specification. In addition, for well-known technologies, the specific description thereof will be omitted.

[0023] Throughout the specification, when a part comprises any component, unless particularly described to the contrary, it will be understood to imply the further inclusion of other components but not the exclusion of other components.

[0024] Then, an Anderson-type polyoxometalate and a method for preparing the same according to an exemplary embodiment will be described in detail.

[0025] The Anderson-type polyoxometalate according to an exemplary embodiment includes titanium (Ti) as a heteroatom in the center of the Anderson-type polyoxometalate.

[0026] Referring to FIG. 1, in the Anderson-type polyoxometalate, the heteroatom positioned at the center is Ti/WO.sub.6 having an octahedral geometry, and six WO.sub.6 octahedrons have edge-sharing of oxygen atoms.

[0027] Referring to FIGS. 2 and 3, the structure of the Anderson-type polyoxometalate is planar on the whole and has a zero-dimensional framework.

[0028] The Anderson-type polyoxometalate has a rhombohedral structure with space group R-3m (No. 166) and D.sub.3d symmetry.

[0029] The Anderson-type polyoxometalate includes titanium and tungsten, the titanium is derived from a titanium precursor, and the tungsten is derived from a tungsten precursor.

[0030] For example, the titanium precursor includes titanium oxysulfate, titanium disulfate, titanium chloride, titanium isopropoxide, and the like. The tungsten precursor includes tungstate. For example, the tungstate includes sodium tungstate, potassium tungstate, and the like.

[0031] A mixing molar ratio of the titanium precursor and the tungsten precursor may be 0.5:6 to 2.5:6. When the molar ratio is lower than 0.5:6, a synthesis reaction is possible, but compound phases having other crystal structures coexist, so that the synthesis yield of a pure Anderson-type polyoxometalate compound may drop significantly. When the molar ratio is higher than 2.5:6, other compound phases are produced, or powder is not formed.

[0032] The Anderson-type polyoxometalate according to an exemplary embodiment may be represented by the following Chemical Formula 1:

K.sub.6Na.sub.2Ti.sub.1aW.sub.6+aO.sub.24.Math.12H.sub.2O (0<a<0.2).[Chemical Formula 1]

[0033] In the hetero-site of the Anderson-type polyoxometalate, Ti.sup.4+ and W.sup.4+ show occupancy at a ratio of (1a) to a.

[0034] The method for preparing an Anderson-type polyoxometalate according to an exemplary embodiment includes: mixing a titanium precursor and a tungstate precursor to prepare a mixture; sealing the mixture in a container and heating to form a hydrothermal synthetic solution; and cooling the hydrothermal synthetic solution and then adding a solute to form an Anderson-type polyoxometalate in a powder form.

[0035] The preparing of a mixture includes mixing a titanium precursor and a tungstate precursor.

[0036] For example, in the mixing of a titanium precursor and a tungstate precursor with water or acetonitrile to prepare a mixture, compounds described above may be used as the titanium precursor and the tungstate precursor.

[0037] For example, the titanium precursor includes titanium oxysulfate, titanium disulfate, titanium chloride, titanium isopropoxide, and the like. The tungsten precursor includes a tungstate. For example, the tungstate includes sodium tungstate, potassium tungstate, and the like.

[0038] In addition, a mixing molar ratio of the titanium precursor and the tungsten precursor may be 0.5:6 to 2.5:6. When the mixing molar ratio is lower than 0.5:6, a synthesis reaction is possible, but compound phases having other crystal structures coexist, so that a synthesis yield of a pure Anderson-type polyoxometalate compound may drop significantly. When the mixing molar ratio is higher than 2.5:6, other compound phases are produced, or powder is not formed.

[0039] The forming of a hydrothermal synthetic solution includes sealing the mixture described above in a container and then heating.

[0040] In the sealing of the mixture in the container and heating to form a hydrothermal synthetic solution, hydrothermal synthesis may be carried out at about 20 C. to about 500 C. for about 1 day to about 3 days. When the synthesis temperature is lower than 20 C. and a synthesis period is less than 1 day, crystallinity may be greatly deteriorated and a synthesis yield may be significantly low. Even when the synthesis temperature is higher than 500 C. and the synthesis period is less than 1 day, crystallinity may be greatly deteriorated and a synthesis yield may be significantly low The forming of an Anderson-type polyoxometalate includes cooling and then filtering a hydrothermal synthetic solution. For example, by filtering the cooled hydrothermal synthetic solution, by-products may be removed from the cooled hydrothermal synthetic solution and only a pure Anderson-type polyoxometalate solution may be collected.

[0041] The forming of an Anderson-type polyoxometalate includes adding a solute to the pure Anderson-type polyoxometalate solution to recover the Anderson-type polyoxometalate in a powder state.

[0042] For example, the solute which is added after cooling the pure Anderson-type polyoxometalate solution obtained by the hydrothermal synthesis includes potassium chloride, potassium nitrate, potassium sulfate, potassium carbonate, and the like which are precursors including potassium. In addition, the solute may be used at 0.8 mol to 1.2 mol compared with the tungsten precursor, and when the solute is used at less than 0.8 mol, the synthesis yield may decrease, and when the solute is used at more than 1.2 mol, the solute is separated and removed in a washing process, but reagents may be wasted.

[0043] In addition, after the solute is added, stirring may be performed for about 0.5 days to about 1.5 days, and when a stirring time is shorter than 0.5 days, unreacted substances may remain, so that the synthesis yield may decrease, and when the stirring time is longer than 1.5 days, a process time may be wasted unnecessarily.

[0044] The method for preparing an Anderson-type polyoxometalate according to an exemplary embodiment may include washing the formed Anderson-type polyoxometalate with a washing solution, carrying out centrifugation, and then drying to obtain Anderson-type polyoxometalate powder. For example, the washing solution includes basic solutions such as sodium hydroxide and potassium hydroxide.

[0045] The method for preparing an Anderson-type polyoxometalate according to an exemplary embodiment may include filtering the formed Anderson-type polyoxometalate to obtain an Anderson-type polyoxometalate single crystal.

[0046] Hereinafter, the present disclosure will be described in more detail with the examples, but the following examples only illustrate the present disclosure and the present disclosure is not limited to the following examples.

Example 1

[0047] Referring to FIG. 4, Anderson-type K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.24.Math.12H.sub.2O is synthesized using a hydrothermal reaction. TiOSO.sub.4-xH.sub.2SO.sub.4.Math.yH.sub.2O (0.1599 g, 5.79104 mol), Na.sub.2WO.sub.4.Math.2H.sub.2O (0.8814 g, 2.67103 mol), and 10 mL of deionized water are mixed, the mixture is added to a 23 mL Teflon cup, which is then placed in a stainless steel autoclave. Next, the autoclave is sealed, heated at 230 C. for 2 days, and then cooled to room temperature. After the cooling, the autoclave is opened, filtration is performed to remove by-products, and a filtrate is collected. An excessive amount of KCl (2.5 g, 3.3510.sup.2 mol) is added to the filtrate and stirring is performed for 1 day.

[0048] A product formed in a cloudy form is washed with a NaOH solution (0.01 M), centrifuged, and then dried to obtain K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.24.Math.12H.sub.2O in a powder form. Additionally, in order to grow it into a single crystal, the product produced in a cloudy form is filtered before adding the NaOH solution, the filtrate is allowed to stand at room temperature to perform preparation.

Example 2

[0049] In order to confirm a range of compositions which may be synthesized, the experiment is carried out while changing a composition ratio. Experiment conditions are described in the following Table 1, and the experiment is carried out in the same manner as in Example 1 described above, except for the composition ratio. As synthesis results, whether the synthesis is successful or not is confirmed by powder XRD. Referring to FIG. 5, from the P-XRD results, synthesis is possible in a range of a ratio of TiOSO.sub.4-xH.sub.2SO.sub.4.Math.yH.sub.2O and Na.sub.2WO.sub.4.Math.2H.sub.2O from 1:6 to 2:6. However, when the amount of TiOSO.sub.4-xH.sub.2SO.sub.4.Math.yH.sub.2O increases, synthesis of other phases is confirmed. For example, when the ratio of TiOSO.sub.4-xH.sub.2SO.sub.4.Math.yH.sub.2O and Na.sub.2WO.sub.4.Math.2H.sub.2O is 3:6, powder is formed but synthesized in other phases, and when the ratio of TiOSO.sub.4-xH.sub.2SO.sub.4.Math.yH.sub.2O and Na.sub.2WO.sub.4.Math.2H.sub.2O is 1:1, the powder itself is not formed. In addition, when the amount of TiOSO.sub.4.Math.xH.sub.2SO.sub.4.Math.yH.sub.2O decreases, the synthesis yield of a pure Anderson-type polyoxometalate decreases. For example, when the ratio of TiOSO.sub.4.Math.xH.sub.2SO.sub.4.Math.yH.sub.2O and Na.sub.2WO.sub.4.Math.2H.sub.2O is 0.4:6, synthesis is possible, but compound phases having other crystal structures coexist, so that the synthesis yield of a pure K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.24.Math.12H.sub.2O compound significantly decreases.

TABLE-US-00001 TABLE 1 Ratio Synthesis No. TiOSO.sub.4xH.sub.2SO.sub.4yH.sub.2O Na.sub.2WO.sub.42H.sub.2O (Ti:W) H.sub.2O results 1 0.0492 g 0.8814 g 0.4:6 10 mL (1.78 10.sup.4 mol) (2.67 10.sup.3 mol) 2 0.1229 g 0.8814 g 1:6 10 mL (4.45 10.sup.4 mol) (2.67 10.sup.3 mol) 3 0.1599 g 0.8814 g 1.3:6 10 mL (5.79 10.sup.4 mol) (2.67 10.sup.3 mol) 4 0.2458 g 0.8814 g 2:6 10 mL (8.90 10.sup.4 mol) (2.67 10.sup.3 mol) 5 0.3687 g 0.8814 g 3:6 10 mL (1.34 10.sup.3 mol) (2.67 10.sup.3 mol) 6 0.1229 g 0.1469 g 1:1 10 mL (4.45 10.sup.4 mol) (4.45 10.sup.4 mol)

[0050] Referring to FIGS. 1 to 3, K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.24.Math.12H.sub.2O has a Rhombohedral structure with space group R-3m (No. 166) and D3d symmetry. Upon review of the crystal structure in detail, there is a heteroatom Ti/WO.sub.6 having octahedral geometry at the center, and six WO.sub.6 octahedrons around the heteroatom Ti/WO.sub.6 form a skeleton with edge-sharing of oxygen atoms. FIG. 2 shows a framework in an ab plane, and FIG. 3 shows a framework in an ac plane. K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.24.Math.12H.sub.2O is confirmed to be planar and have a zero-dimension framework structure, the same as general Anderson-type POM. Generally, an M/X ratio is 6, but the K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.24.Math.12H.sub.2O according to an exemplary embodiment did not have only Ti.sup.4+ at a hetero-site but showed occupancy of Ti.sup.4+ and W.sup.4+ at about 92% to 8% at the hetero-site. The crystal data of K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.24.Math.12H.sub.2O is shown in the following Table 2.

TABLE-US-00002 TABLE 2 Empirical formula K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.2412H.sub.2O Formula weight 2042.78 Crystal system Trigonal Space group R -3 m Z 3 a () 13.1000 10 b () 13.1000 10 c () 18.3313 14 V .sup.3 2724.4 5 Temperature (K) 173 2 .sub.calcd (g cm.sup.3) 3.735 mm.sup.1 20.189 R (F).sup.a 0.0120 R.sub.w (F.sup.2.sub.o).sup.b 0.0404

[0051] In Table 2, R(F) and R.sub.w (F.sup.2.sub.o) are calculated by the following Equations 1 and 2.

[00001]$\begin{array}{cc}R\left(F\right)=.Math..Math..Math.F_o.Math.-.Math.F_c.Math..Math./.Math..Math.F_o.Math.& \left[\mathrm{Equation}1\right]\end{array}$$\begin{array}{cc}{R}_w\left(F_0^2\right)={\left[.Math.{w\left(F_o^2-F_c^2\right)}^2/.Math.{w\left(F_o^2\right)}^2\right]}^{1/2}& \left[\mathrm{Equation}2\right]\end{array}$

[0052] Referring to FIG. 6, the powder XRD pattern of K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.24.Math.12H.sub.2O which is actually synthesized in Example 1 and the powder XRD pattern simulated based on the refined structure from single crystal XRD are compared, and it is represented that the two patterns match each other.

[0053] Referring to FIG. 7, K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.24.Math.12H.sub.2O which is actually synthesized in Example 1 and K.sub.6Na.sub.2PtW.sub.6O.sub.24.Math.12H.sub.2O which is conventional Anderson-type POM are compared. The K.sub.6Na.sub.2Ti.sub.0.92W.sub.6.08O.sub.24.Math.12H.sub.2O which is actually synthesized showed a structurally very similar pattern to K.sub.6Na.sub.2PtW.sub.6O.sub.24.Math.12H.sub.2O (space group R-3m (No. 166)). However, since the elements forming the heteroatom positioned at the center are Ti and Pt, respectively, which are different, the powder pattern shifts to the right on the whole due to a difference in a bond distance between X and O in XO.sub.6. The TiO bond distance is about 1.970 , and a PtO bond distance is about 2.013 . Accordingly, the lattice parameter of Ti-POM (a=b=13.1000 , c=18.1333 ) is smaller than that of the Pt-POM (a=b=13.1376 , c=18.3504 ).

[0054] In order to confirm that Ti is clearly contained in the Anderson-type polyoxometalate synthesized in Example 1 and also confirm the composition ratio, 10 mg of a synthesized powder sample is completely dissolved in 10 mL of a 0.01 M HCl solution, and the composition ratio is confirmed with Inductively coupled plasma-optical emission spectroscopy (ICP-OES). The results are represented in the following Table 3, and the composition ratio calculated from SC-XRD and the stoichiometric value (W/Ti 6.6) of the experimental value match each other.

TABLE-US-00003 TABLE 3 Atomic ratio (basis Ti) Calculated composition Experimental composition Element (SC-XRD) (ICP-OES) K 6.5 6.7 Na 2.2 2.4 Ti 1 1 W 6.6 6.6

[0055] Hereinabove, the preferred exemplary embodiments of the present disclosure have been described in detail, but the scope of rights for the present disclosure is not limited thereto, and various modifications and improved forms by a person skilled in the art using the basic concept of the present disclosure defined in the following claims also belong to the scope of rights for the present disclosure.