JP6103524B2 - Perovskite nanosheets based on homologous series layered perovskite oxide and uses thereof - Google Patents

Description

  The present invention relates to perovskite nanosheets and uses thereof. More particularly, the present invention relates to perovskite nanosheets based on homologous series layered perovskite oxide and uses thereof.

It has been found that some layered perovskite oxides typified by KCa ₂ Nb ₃ O ₁₀ can be exfoliated by a soft chemical treatment. Research on the properties of nanosheets obtained by single-layer peeling in this way is active. Development of nanosheets having high dielectric properties and photocatalytic properties is demanded.

  As described above, an object of the present invention is to provide a nanosheet based on a homologous series layered perovskite oxide and its use.

The perovskite nanosheet according to the present invention contains two or more types of octahedral blocks, thereby solving the above-mentioned problems.
The two or more types of octahedral blocks may be a combination of at least an MO ₆ octahedral block (M is Nb and / or Ta) and a TiO ₆ octahedral block.
The perovskite nanosheet may be represented by A _n-1 M ₃ Ti _n-3 O _{3n + 1} ^— (n ≧ 4, A is an element selected from the group consisting of Mg, Ca, Sr, and Ba). .
The A may be Ca and / or Sr.
n may be n ≦ 6.
The perovskite nanosheet may be separated from K [A _n-1 M ₃ Ti _n-3 O _{3n + 1} ] by a single layer.
In the perovskite nanosheet, ATiO ₃ and A ₂ M ₃ O ₁₀ may undergo a solid phase reaction.
The dielectric material according to the present invention comprises the perovskite nanosheet.
The photocatalytic material according to the present invention comprises the perovskite nanosheet.

The perovskite nanosheet according to the present invention includes two or more octahedral blocks. By allowing two or more types of octahedral blocks to coexist, polarization ability is improved and material design is facilitated. The perovskite nanosheet according to the present invention preferably comprises a combination of MO ₆ octahedral block (M is Nb and / or Ta) and TiO ₆ octahedral block as two or more types of octahedral blocks. Thereby, dielectric properties and photocatalytic properties can be improved. Such perovskite nanosheets are preferred for dielectric materials and photocatalytic materials.

Schematic showing an exemplary perovskite nanosheet according to the present invention. Flowchart illustrating an exemplary method for producing perovskite nanosheets of the present invention The figure which shows typically the exemplary manufacturing method of the perovskite nanosheet of this invention Shows a SEM images of the _{K [A n-1 M 3} Ti n-3 O 3n + 1] of Example 2, 3, 6 and 7 Shows the XRD pattern of _KCa 2 _Nb 3 _{O 10} and Example 2 of _KCa 3 _Nb 3 _{TiO 13} of Comparative Example 1 Shows the XRD pattern of _KCa 4 _Nb 3 _Ti 2 _{O 16} of _KCa 3 _Nb 3 _{TiO 13} and Example 3 Example 2 It shows an XRD pattern of _KCa 5 _Nb 3 _Ti 3 _{O 19} of Example 4 Shows the XRD pattern of _KSr 4 _Nb 3 _Ti 2 _{O 16} of _KSr 3 _Nb 3 _{TiO 13} and Example 7 Example 6 It shows the XRD pattern of _KCa 3 _Nb 3 _{TiO 13} and its hydrogen ion exchanger of Example 2 Shows the XRD pattern of _KCa 4 _Nb 3 _Ti 2 _{O 16} and its hydrogen ion exchanger of Example 3 It shows the XRD pattern of _KSr 3 _Nb 3 _{TiO 13} and its hydrogen ion exchanger of Example 6 Shows the XRD pattern of _KSr 4 _Nb 3 _Ti 2 _{O 16} and its hydrogen ion exchanger of Example 7 The figure which shows the behavior of the TG / DTA measurement of the hydrogen ion exchanger of Example 2. The figure which shows nanosheet formation of each hydrogen ion exchanger of Example 2, 3, 6 and 7 _Ca 3 _Nb 3 _{TiO 13} Example 2 ^- _Ca nanosheets and Example _{3 4 Nb 3 Ti 2 O 16} - shows an AFM image of nanosheets

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same number is attached | subjected to the same element and the description is abbreviate | omitted.

  The inventors of the present application have designed materials to develop nanosheets with improved various properties. As a result, it was found that it is effective to encapsulate two or more octahedral blocks in the perovskite nanosheet. Since two or more types of octahedral blocks coexist, polarization ability is improved. Furthermore, since the selection of the types of two or more octahedral blocks and the ratio of combinations can be artificially designed, material design such as composition and thickness of the perovskite nanosheet is easy.

The two or more octahedral blocks are preferably a combination of MO ₆ octahedral blocks (M is Nb and / or Ta) and TiO ₆ octahedral blocks. When the perovskite nanosheet includes the TiO ₆ octahedral block, the dielectric property and the photocatalytic property can be improved.

  FIG. 1 is a schematic diagram illustrating an exemplary perovskite nanosheet according to the present invention.

1A to 1C show perovskite nanosheets 100 of various thicknesses. In FIG. 1, the octahedral layer 110 comprises two or more types of octahedral blocks 120, preferably MO ₆ octahedral blocks of various ratios (M is Nb and / or Ta) and TiO ₆ octahedral. Composed of a combination of blocks. The perovskite nanosheet 100 includes a predetermined number of octahedral layers 110 due to cations 130. The cation 130 is an alkaline earth metal element ion selected from the group consisting of Mg, Ca, Sr and Ba.

When the perovskite nanosheet 100 according to the present invention is composed of a combination of MO ₆ octahedral block (M is Nb and / or Ta) and TiO ₆ octahedral block, the general formula A _n-1 M ₃ Ti _n-3 O _{3n + 1} ^- it may be represented by.

  Here, n is an integer of 4 or more, and there is no upper limit, but it is preferably 6 or less, more preferably 5 or less, for ease of production. If n is 4 or 5, it can be produced in a single phase with good yield. 1A to 1C schematically show perovskite nanosheets 100 in which n is 4, 5, and 6, respectively. As n increases, the thickness of the nanosheet can be increased and controlled in units of 0.4 nm to 0.5 nm. According to the present invention, it is possible to precisely control the composition and structure simply by changing n. Nanosheets thus precisely controlled can be used as functional building blocks and seed layers. In addition, since the dielectric constant improves as n increases, n can be appropriately selected to exhibit desired dielectric characteristics.

  A is an alkaline earth metal element selected from the group consisting of Mg, Ca, Sr and Ba, and is the cation 130 described above. A is preferably Ca and / or Sr. If A is Ca and / or Sr, the crystal structure is stable and a single phase can be produced. M is Nb and / or Ta. If M is Nb, since the polarization ability is high, it is advantageous because it exhibits higher dielectric properties than Ta.

The perovskite nanosheet 100 according to the present invention can be represented by the general formula described above, and is produced by a solid-phase reaction between ATiO ₃ and A ₂ M ₃ O _10, and A ₂ M ₃ O ₁₀ and ATiO _3. It can be designed easily by changing the molar ratio. That is, for example, a perovskite slab represented by SrTiO ₃ or the like is incorporated in a perovskite nanosheet represented by Ca ₂ M ₃ O ₁₀ or the like.

  Next, an exemplary manufacturing method of such a perovskite nanosheet will be described.

FIG. 2 is a flowchart showing an exemplary method for producing the perovskite nanosheet of the present invention.
FIG. 3 is a diagram schematically showing an exemplary method for producing the perovskite nanosheet of the present invention.

Step S210: The homologous series layered perovskite oxide 300 is acid-treated using an acid aqueous solution to generate a hydrogen ion exchanger 310. The homologous series layered perovskite oxide 300 is represented by the general formula K [A _n-1 M ₃ Ti _n-3 O _{3n + 1} ]. Here, n is an integer of 4 or more, and there is no upper limit, but it is preferably 6 or less, more preferably 5 or less, for ease of production. When n is 4 or 5, a perovskite nanosheet described later can be produced in a single phase with a high yield. Since n corresponds to the number of octahedrons in the thickness direction, the larger the n, the thicker the nanosheet that can be obtained. A is an alkaline earth metal element selected from the group consisting of Mg, Ca, Sr and Ba, and is the cation 130 described above. A is preferably Ca and / or Sr. If A is Ca and / or Sr, the crystal structure is stable and a single phase can be produced. M is Nb and / or Ta.

  As the acid aqueous solution, an inorganic acid or an organic acid can be used, but it is usually selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, acetic acid and carbonic acid.

When the homologous series layered perovskite oxide 300 is acid-treated with an acid aqueous solution, K ions are replaced with hydrogen ions or oxonium ions, and a hydrogen ion exchanger 310 is generated. Its composition is represented by the general formula H [A _n-1 M ₃ Ti _n-3 O _{3n + 1} ] .mH ₂ O (m = 0-2).

  As for the acid treatment conditions, the regulation of the acid aqueous solution is 0.1 or more, and the reaction is performed at room temperature (10 ° C. to 30 ° C.) for 1 to 7 days. When the regulation of the acid aqueous solution is smaller than 0.1 regulation, ion exchange does not proceed sufficiently, and the peeling reaction described later may be difficult to occur.

Step S220: The hydrogen ion exchanger 310 is reacted with a basic substance, and the hydrogen ion exchanger 310 is separated into a single layer. The basic substance is a substance that functions to exfoliate the layered structure of the hydrogen ion exchanger 310 obtained in step S220, and specifically includes tetrabutyl ammonium ion (TBA ⁺ ), tetrapropyl ammonium ion, tetraethyl An aqueous solution containing ammonium ions, tetramethylammonium ions, n-propylamine, n-ethylamine and ethanolamine. Among these, an aqueous solution of TBA ⁺ is desirable from the viewpoint of yield.

  The molar ratio between the protons in the hydrogen ion exchanger 310 and the basic substance is preferably in the range of 0.5-10. If the molar ratio is less than 0.5 or exceeds 10, peeling may not proceed sufficiently.

  In the peeling reaction, the hydrogen ion exchanger 310 and the basic substance may be simply mixed at room temperature, but may be shaken in addition to the mixing. Thereby, since peeling is accelerated, the yield is improved. The peeling reaction can be obtained at a yield of 100% by shaking for several days (for example, 4 days) or more. As peeling progresses, it becomes a milky white solution, so the reaction may be stopped by visual inspection.

  In this way, a colloidal solution in which the perovskite nanosheet 100 according to the present invention is dispersed, from which the hydrogen ion exchanger 310 (that is, the homologous series layered perovskite oxide 300) has been peeled, can be obtained. According to the method of the present invention, the homologous series layered perovskite oxide 300 may be simply acid-treated and stripped, so that a dedicated apparatus is unnecessary. Therefore, manufacturing is simple and suitable for mass production.

  In addition, by applying a colloid solution containing the perovskite nanosheet of the present invention thus obtained to an arbitrary base material such as a glass substrate, a silicon substrate, a metal substrate, a plastic substrate, a dielectric material, a photocatalytic material, A seed layer can be manufactured. Any method through a liquid phase process can be applied to the substrate, but preferably a group consisting of an alternating adsorption method, a Langmuir-Blodget (LB) method, a spin coating method, a drop method and a dip coating method. The method selected from is adopted.

The present invention will now be described in detail using specific examples, but it should be noted that the present invention is not limited to these examples. The examples consist of combinations of various ratios of MO ₆ octahedral blocks (M is Nb) and TiO ₆ octahedral blocks, with the general formula A _n-1 M ₃ Ti _n-3 O _{3n + 1} ⁻ (n = 4 A perovskite nanosheet represented by ˜6, A = Ca or Sr) was produced.

[Comparative Example 1]
In Comparative Example 1, the general formula _{A n-1 M 3 Ti n} -3 O 3n + 1 - in, n = 3, A = perovskite nano represented by Ca sheet _Ca 2 _Nb 3 _{O 10} ^- was prepared. Prior to the production of the perovskite nanosheet, KCa ₂ Nb ₃ O ₁₀ was produced as a layered perovskite oxide.

Mixing K ₂ CO ₃ (Rare Metallic Co., Ltd., purity of 99.99%) and, CaCO ₃ (Rare Metallic Co., Ltd., purity of 99.99%) and, _Nb 2 _{O 5} (Rare Metallic Co., Ltd., 99.99% purity) and・ Crushed. Here, the mixing molar ratio of K ₂ CO ₃ , CaCO ₃ and Nb ₂ O ₅ was 1.1: 4: 3.

Next, the pulverized raw material mixture was transferred to a platinum crucible and baked in an electric furnace. Specifically, the temperature is raised from room temperature to 900 ° C., held at 900 ° C. for 1 hour, taken out from the electric furnace, pulverized and mixed in a mortar, and then heated from 900 ° C. to 1200 ° C. Baked for 12 hours. The obtained compound was subjected to powder XRD measurement to confirm that it was a layered compound KCa ₂ Nb ₃ O ₁₀ single phase. The results are shown in FIG.

Next, perovskite nanosheets Ca ₂ Nb ₃ O ₁₀ ⁻ were synthesized using the obtained layered compound KCa ₂ Nb ₃ O ₁₀ .

The layered compound KCa ₂ Nb ₃ O ₁₀ was acid-treated using an aqueous nitric acid solution (13.5 N, manufactured by Wako Pure Chemical Industries, special grade) as an aqueous acid solution to produce a hydrogen ion exchanger. An aqueous nitric acid solution was prepared using ultrapure water (> 18 MΩcm) so as to be 5N.

Specifically, KCa ₂ Nb ₃ O ₁₀ (5 g) and nitric acid aqueous solution (200 mL) were stirred using a stirrer in a 500 mL beaker and reacted for 72 hours. After completion of the reaction, the product was filtered with ultrapure water and air-dried in air to obtain a hydrogen ion exchanger.

Next, 0.4 g of hydrogen ion exchanger and 100 mL of tetrabutylammonium hydroxide aqueous solution (TBAOHaq.) As a basic substance (10%, manufactured by Wako Pure Chemical Industries, special grade) are reacted to peel off the hydrogen ion exchanger, Ca ₂ Nb ₃ O ₁₀ ^- nanosheets was obtained dispersed colloidal solution.

The specific reaction is TBAOHaq. The molar ratio of TBA ⁺ in the hydrogen ion exchanger to H ⁺ in the hydrogen ion exchanger was adjusted to 1: 1. Put ultrapure water in a 200 mL Erlenmeyer flask, and then add TBAOHaq. 3.8 mL was added to make a total volume of 100 mL. To this solution, 0.4 g of a hydrogen ion exchanger was added and shaken with a shaker at 180 rpm for 4 days. It was confirmed that the solution in the Erlenmeyer flask became a milky white solution and the hydrogen ion exchanger was peeled off.

  The colloidal solution was applied to a quartz glass substrate and a silicon substrate subjected to hydrophilization treatment using an alternate adsorption method, and dielectric properties and photocatalytic properties were measured. The results will be described later.

[Example 2]
In Example 2, the general formula _{A n-1 M 3 Ti n} -3 O 3n + 1 - in, n = 4, A = perovskite nano represented by Ca sheet _Ca 3 _Nb 3 _{TiO 13} ^- was prepared. Prior to the production of the perovskite nanosheet, a homologous series KCa ₃ Nb ₃ TiO ₁₃ was produced as a layered perovskite oxide.

First, CaTiO ₃ was synthesized by the same procedure as in Comparative Example 1. Specifically, CaCO ₃ (rare metallic, purity 99.99%) and TiO ₂ (rare metallic, purity 99.99%) were mixed and pulverized at a molar ratio of 1: 1 to obtain KCa ₂ Nb. Firing was performed under the same conditions as ₃ O ₁₀ . The obtained compound was subjected to powder XRD measurement and confirmed to be a CaTiO ₃ single phase.

Next, CaTiO ₃ and KCa ₂ Nb ₃ O ₁₀ synthesized in Comparative Example 1 were mixed and pulverized at a molar ratio of 1: 1, and then fired. Specifically, the mixture was transferred to a platinum crucible, heated from room temperature to 1200 to 1300 ° C. in an electric furnace, and fired for 72 to 150 hours. The fired product was observed with a scanning electron microscope (SEM). Powder XRD measurement was performed on the fired product, and it was confirmed that it was a homologous series compound KCa ₃ Nb ₃ TiO ₁₃ . Further, the lattice constant was calculated from the obtained XRD pattern. These results are shown in FIGS.

Perovskite nanosheets Ca ₃ Nb ₃ TiO ₁₃ ⁻ were synthesized using the obtained layered compound KCa ₃ Nb ₃ TiO ₁₃ .

The layered compound KCa ₃ Nb ₃ TiO ₁₃ was acid-treated using an aqueous nitric acid solution (13.5 N, manufactured by Wako Pure Chemical Industries, special grade) as an aqueous acid solution to produce a hydrogen ion exchanger (FIGS. 2 and 3). Step S210). An aqueous nitric acid solution was prepared using ultrapure water (> 18 MΩcm) so as to be 5N.

Specifically, KCa ₃ Nb ₃ TiO ₁₃ (5 g) and an aqueous nitric acid solution (200 mL) were stirred with a stirrer in a 500 mL beaker and reacted for 1 to 7 days. After completion of the reaction, the product was filtered with ultrapure water and air-dried in air. It was confirmed by powder XRD measurement, differential thermogravimetric analysis (TG / DTA) and chemical analysis that the obtained substance was a hydrogen ion exchanger. Furthermore, the lattice constant was calculated from the obtained XRD pattern. These results are shown in FIGS. 9 and 13 and Table 3.

Next, 0.4 g of hydrogen ion exchanger and 100 mL of tetrabutylammonium hydroxide aqueous solution (TBAOHaq.) As a basic substance (10%, manufactured by Wako Pure Chemical Industries, special grade) are reacted to peel off the hydrogen ion exchanger, Ca ₃ Nb ₃ TiO ₁₃ ^- nanosheets was obtained dispersed colloidal solution (step S220 of FIG. 2 and FIG. 3).

The specific reaction is TBAOHaq. The molar ratio of TBA ⁺ in the hydrogen ion exchanger to H ⁺ in the hydrogen ion exchanger was adjusted to 1: 1. Put ultrapure water in a 200 mL Erlenmeyer flask, and then add TBAOHaq. 5.4 mL was added to make a constant volume of 100 mL. To this solution, 0.4 g of a hydrogen ion exchanger was added and shaken with a shaker at 180 rpm for 10 days. It was confirmed that the solution in the Erlenmeyer flask became a milky white solution and the hydrogen ion exchanger was completely peeled off. The observation results are shown in FIG.

  The diluted colloidal solution was dried on a quartz glass substrate, and the shape was observed with an atomic force microscope (AFM). The results are shown in FIG. In addition, a colloidal solution was applied to the quartz glass substrate and silicon substrate that had been subjected to a hydrophilic treatment by an alternating adsorption method, and dielectric properties and photocatalytic properties were measured.

[Example 3]
In Example 3, the general formula _{A n-1 M 3 Ti n} -3 O 3n + 1 - in, n = 5, A = perovskite nano represented by Ca sheet _{Ca 4 Nb 3 Ti 2 O 16} - was prepared.

First, prior to the production of the perovskite nanosheet, a homologous series KCa ₄ Nb ₃ Ti ₂ O ₁₆ was produced as a layered perovskite oxide. The production procedure is the same as that of Example 2 except that CaTiO ₃ and KCa ₃ Nb ₃ TiO ₁₃ synthesized in Example 2 are used as raw materials and mixed at a molar ratio of 1: 1. The fired product was observed with a scanning electron microscope (SEM). Powder XRD measurement was performed on the fired product to confirm that it was a homologous series compound KCa ₄ Nb ₃ Ti ₂ O ₁₆ , and a lattice constant was calculated. These results are shown in FIGS. 4 and 6 and Table 2.

Perovskite nanosheets Ca ₄ Nb ₃ Ti ₂ O ₁₆ ⁻ were synthesized using the obtained layered compound KCa ₄ Nb ₃ Ti ₂ O ₁₆ . The synthesis procedure was the same as in Example 2. The results of powder XRD measurement and lattice constant calculation for the hydrogen ion exchanger are shown in FIG. 10 and Table 3. _{Ca 4 Nb 3 Ti 2 O 16} - nanosheets were observed dispersed colloidal solution. The results are shown in FIG.

  The colloidal solution was applied to a quartz glass substrate and a silicon substrate subjected to a hydrophilic treatment by using an alternate adsorption method, and shape observation, dielectric properties and photocatalytic properties using AFM were measured. The results are shown in FIG.

[Example 4]
In Example 4, the general formula _{A n-1 M 3 Ti n} -3 O 3n + 1 - in, n = 6, perovskite nano represented by A = Ca sheet _{Ca 5 Nb 3 Ti 3 O 19} - was prepared.

First, prior to the production of the perovskite nanosheet, a homologous series compound KCa ₅ Nb ₃ Ti ₃ O ₁₉ was produced as a layered perovskite oxide. The production procedure is the same as in Example 2 except that CaTiO ₃ synthesized in Example 2 and KCa ₄ Nb ₃ Ti ₂ O ₁₆ synthesized in Example 3 were used as raw materials and mixed at a molar ratio of 1: 1. It is the same. The obtained fired product was subjected to powder XRD measurement, and confirmed to be a homologous series compound KCa ₅ Nb ₃ Ti ₃ O ₁₉ . The results are shown in FIG. The fired product was observed with a scanning electron microscope (SEM).

Perovskite nanosheets Ca ₄ Nb ₃ Ti ₂ O ₁₆ ⁻ were synthesized using the obtained layered compound KCa ₄ Nb ₃ Ti ₂ O ₁₆ . The synthesis procedure was the same as in Example 2. _{Ca 4 Nb 3 Ti 2 O 16} - where nanosheets were observed dispersed colloidal solution was milky white.

  The colloidal solution was applied to a quartz glass substrate and a silicon substrate subjected to hydrophilization treatment using an alternate adsorption method, and dielectric properties and photocatalytic properties were measured.

[Comparative Example 5]
In Comparative Example 5, the general formula _{A n-1 M 3 Ti n} -3 O 3n + 1 - in, n = 3, perovskite nano represented by A = Sr sheet _Sr 2 _Nb 3 _{TiO 10} ^- was prepared.

Prior to the production of the perovskite nanosheet, KSr ₂ Nb ₃ O ₁₀ was produced as a layered perovskite oxide. The synthesis procedure was the same as in Comparative Example 1 except that SrCO ₃ (rare metallic, purity 99.99%) was used instead of CaCO ₃ . The obtained layered compound was subjected to powder XRD measurement to confirm that it was KSr ₂ Nb ₃ O ₁₀ , and the lattice constant was calculated. The results are shown in Table 2.

A perovskite nanosheet Sr ₂ Nb ₃ O ₁₀ ⁻ was synthesized using the obtained layered compound KSr ₂ Nb ₃ O ₁₀ . The synthesis procedure was the same as in Example 2. Sr ₂ Nb ₃ O ₁₃ ^- where nanosheets were observed dispersed colloidal solution was milky white.

  The colloidal solution was applied to a quartz glass substrate and a silicon substrate subjected to hydrophilization treatment using an alternate adsorption method, and dielectric properties and photocatalytic properties were measured.

[Example 6]
In Example 6, perovskite nanosheets Sr ₃ Nb ₃ TiO ₁₃ ⁻ represented by general formula A _n-1 M ₃ Ti _n-3 O _{3n + 1} ⁻ where n = 4 and A = Sr were produced.

First, prior to the production of the perovskite nanosheet, a homologous series compound KSr ₃ Nb ₃ TiO ₁₃ was produced as a layered perovskite oxide. The production procedure is the same as that of Example 2 except that SrTiO ₃ and KSr ₂ Nb ₃ O ₁₀ synthesized in Comparative Example 5 are used as raw materials and these are mixed at a molar ratio of 1: 1. The fired product was observed with a scanning electron microscope (SEM). Powder XRD measurement was performed on the fired product to confirm that it was a homologous series compound KSr ₃ Nb ₃ TiO ₁₃ , and a lattice constant was calculated. These results are shown in FIGS. 4 and 8 and Table 2.

In addition, SrTiO ₃ used for the raw material is a mixture of SrCO ₃ (rare metallic, purity 99.99%) and TiO ₂ (rare metallic, purity 99.99%) in a molar ratio of 1: 1. The powder was synthesized by pulverizing and firing under the same conditions as in KCa ₂ Nb ₃ O _{10 of} Comparative Example 1.

A perovskite nanosheet Sr ₃ Nb ₃ TiO ₁₃ ⁻ was synthesized using the obtained layered compound KSr ₃ Nb ₃ TiO ₁₃ . The synthesis procedure was the same as in Example 2. FIG. 11 and Table 3 show the results of the powder XRD measurement and the calculation of the lattice constant of the hydrogen ion exchanger. Sr ₃ Nb ₃ TiO ₁₃ ^- nanosheets were observed dispersed colloidal solution. The results are shown in FIG.

  The colloidal solution was applied to a quartz glass substrate and a silicon substrate subjected to hydrophilization treatment using an alternate adsorption method, and dielectric properties and photocatalytic properties were measured.

[Example 7]
In Example 7, the general formula _{A n-1 M 3 Ti n} -3 O 3n + 1 - in, n = 5, A = perovskite nano represented by Sr seat _{Sr 4 Nb 3 Ti 2 O 16} - was prepared.

First, prior to the production of the perovskite nanosheet, a homologous series compound KSr ₄ Nb ₃ Ti ₂ O ₁₆ was produced as a layered perovskite oxide. The production procedure is the same as that of Example 2 except that SrTiO ₃ and KSr ₃ Nb ₃ TiO ₁₃ synthesized in Example 6 were mixed at a molar ratio of 1: 1. The fired product was observed with a scanning electron microscope (SEM). Powder XRD measurement was performed on the fired product, and it was confirmed that it was a homologous series compound KSr ₄ Nb ₃ Ti ₂ O ₁₆ , and a lattice constant was calculated. These results are shown in FIGS. 4 and 8 and Table 2.

Obtained layered compound _KSr 4 with _Nb 3 _Ti 2 _{O 16} perovskite nanosheets _{Sr 4 Nb 3 Ti 2 O 16} - was synthesized. The synthesis procedure was the same as in Example 2. FIG. 12 and Table 3 show the results of the powder XRD measurement and the calculation of the lattice constant of the hydrogen ion exchanger. _{Sr 4 Nb 3 Ti 2 O 16} - nanosheets were observed dispersed colloidal solution. The results are shown in FIG.

  The colloidal solution was applied to a quartz glass substrate and a silicon substrate subjected to hydrophilization treatment using an alternate adsorption method, and dielectric properties and photocatalytic properties were measured.

  The experimental conditions of the above examples and comparative examples are summarized in Table 1 for simplicity.

FIG. 4 is a diagram showing an SEM image of each K [A _n-1 M ₃ Ti _n-3 O _{3n + 1} ] in Examples 2, 3, 6 and 7.

4 (A) to 4 (D) respectively show KCa ₃ Nb ₃ TiO ₁₃ of Example 2, KCa ₄ Nb ₃ Ti ₂ O ₁₆ of Example ₃ , KSr ₃ Nb ₃ TiO _{13 of} Example 6, and It shows an SEM image of _KSr 4 _Nb 3 _Ti 2 _{O 16} of example 7. According to FIG. 4, all of the obtained compounds were aggregates of plate crystals having a lateral size of about 5 μm and a thickness of about 1 μm. Although not shown, KCa ₅ Nb ₃ Ti ₃ O _{19 of} Example 4 was a similar assembly.

FIG. 5 is a diagram showing XRD patterns of KCa ₂ Nb ₃ O _{10 of} Comparative Example 1 and KCa ₃ Nb ₃ TiO ₁₃ of Example 2.

From FIG. 5, it was found that KCa ₃ Nb ₃ TiO ₁₃ can be obtained in a single phase when the firing time exceeds 96 hours when the firing temperature is 1240 ° C.

6 is a diagram showing XRD patterns of KCa ₃ Nb ₃ TiO _{13 of} Example 2 and KCa ₄ Nb ₃ Ti ₂ O ₁₆ of Example 3. FIG.
7 is a view showing an XRD pattern of KCa ₅ Nb ₃ Ti ₃ O _{19 in} Example 4. FIG.
FIG. 8 is a diagram showing XRD patterns of KSr ₃ Nb ₃ TiO _{13 of} Example 6 and KSr ₄ Nb ₃ Ti ₂ O ₁₆ of Example 7.

According to FIG. 6, it was found that KCa ₃ Nb ₃ TiO _{13 of} Example 2 and KCa ₄ Nb ₃ Ti ₂ O _{16 of} Example 3 were obtained in a single phase. According to FIG. 8, it was found that KSr ₃ Nb ₃ TiO _{13 of} Example 6 and KSr ₄ Nb ₃ Ti ₂ O _{16 of} Example 7 were obtained in a single phase. On the other hand, according to FIG. 7, it was confirmed that KCa ₅ Nb ₃ Ti ₃ O ₁₉ of Example ₄ was obtained as a mixture with KCa ₄ Nb ₃ Ti ₂ O _{16 of} Example 3.

  Furthermore, according to FIGS. 6-8, all peaks of the XRD pattern were indexed to the orthorhombic lattice. From these, the lattice constant was calculated.

Regardless of the type of alkaline earth metal element A and the number of n, the a-axis length and b-axis length reflecting the periodic structure in the host layer were almost constant. On the other hand, the interlayer distance corresponding to half of the c-axis length was found to increase by about 0.8 nm as n increased by 1. This increment corresponds to the height of the MO ₆ octahedron (octahedral layer 110 in FIG. 1) and has a homologous structure consisting of a combination of NbO ₆ octahedron and TiO ₆ octahedron. The oxide is a homologous series layered perovskite oxide.

FIG. 9 is a diagram showing XRD patterns of KCa ₃ Nb ₃ TiO _{13 of} Example 2 and its hydrogen ion exchanger.
10 is a diagram showing an XRD pattern of KCa ₄ Nb ₃ Ti ₂ O ₁₆ and its hydrogen ion exchanger of Example 3. FIG.
FIG. 11 is a diagram showing XRD patterns of KSr ₃ Nb ₃ TiO ₁₃ and the hydrogen ion exchanger of Example 6.
12 is a diagram showing an XRD pattern of KSr ₄ Nb ₃ Ti ₂ O ₁₆ and its hydrogen ion exchanger of Example 7. FIG.

9 to 12, it is shown that the K ⁺ ions between the layers are replaced with hydrogen ions while maintaining the layered structure by performing the acid treatment. All peaks in the XRD pattern after acid treatment were indexed to the tetragonal lattice. From these, the lattice constant was calculated.

  As before the acid treatment, the a-axis length and the b-axis length were almost constant regardless of the type of alkaline earth metal element A and the number of n. On the other hand, the interlayer distance corresponding to half the c-axis length was found to increase by about 0.4 nm as n increased by 1. This suggests that the perovskite nanosheet of the present invention can be controlled in units of about 0.4 nm (0.4 nm to 0.5 nm) in thickness.

  FIG. 13 is a diagram showing the behavior of TG / DTA measurement of the hydrogen ion exchanger of Example 2.

According to FIG. 13, it was found that two-stage dehydration occurred by 300 ° C., and the total amount was about 5%. In addition, according to the chemical analysis results, it was confirmed that the content of other elements did not change although the K ⁺ ion content decreased to 4% or less after the acid treatment. This also indicates that K ⁺ ions were replaced with hydrogen ions, and H [Ca ₃ Nb ₃ TiO ₁₃ ] · 1.4H ₂ O was obtained. Similarly, in other examples, hydrogen ion exchangers represented by H [A _n-1 M ₃ Ti _n-3 O _{3n + 1} ] · mH ₂ O (m = 0 to 2) were obtained.

  FIG. 14 is a diagram showing nanosheet formation of the hydrogen ion exchangers of Examples 2, 3, 6, and 7.

  In any case, it was found that when a basic substance was reacted with a hydrogen ion exchanger, a colloidal solution suspended in white was formed.

15, _Ca 3 _Nb 3 _{TiO 13} Example 2 ^- shows the AFM image of nanosheets ^{_{- Ca 4 Nb 3 Ti 2 O}} 16 nanosheets and Example 3.

According to FIG. 15 (A), the thickness of _{2.87 ± 0.03nm Ca 3 Nb 3 TiO} 13 - nanosheets, according to FIG. 15 (B), the thickness of 3.42 ± 0.01nm _Ca 4 Nb ₃ Ti ₂ O ₁₆ ^- nanosheets was obtained. From this, it was shown that a nanosheet represented by the general formula A _n-1 M ₃ Ti _n-3 O _{3n + 1} ⁻ (n ≧ 4) was obtained based on the homologous series layered perovskite oxide.

  When the dielectric properties of the nanosheets synthesized in the examples and comparative examples were measured, it was confirmed that the dielectric constant was improved by introducing Ti. In particular, it was found that the nanosheet having a larger number of n has a higher dielectric constant. In addition, it was found that when the nanosheet formed by poly (diallyldimethylammonium chloride) (PDDA) as a cationic polymer was irradiated with ultraviolet rays, the layer spacing decreased. From this, it was confirmed that it has a photocatalytic property for decomposing substances present between the layers.

The perovskite nanosheet according to the present invention can exhibit properties superior to existing nanosheets by encapsulating two or more octahedral blocks. In particular, the perovskite nanosheet is a combination of MO ₆ octahedral block (M is Nb and / or Ta) and TiO ₆ octahedral block, with the general formula An _n-1 M ₃ Ti _n-3 O _{3n + 1} ⁻ When expressed, it is excellent in dielectric properties and photocatalytic properties, and therefore preferred for dielectric materials and photocatalytic materials. Moreover, since the thickness of the perovskite nanosheet of the present invention can be controlled in units of 0.4 nm to 0.5 nm, it is advantageous as a functional building block.

100 perovskite nanosheet 110 octahedral layer 120 octahedral block 130 cation

Claims (5)

A perovskite nano sheet containing therein two or more octahedral block,
The two or more types of octahedral blocks are a combination of at least an MO ₆ octahedral block (M is Nb and / or Ta) and a TiO ₆ octahedral block,
A _n-1 M ₃ Ti _n-3 O _{3n + 1} ⁻ (n is an integer satisfying 4 ≦ n ≦ 6, and A is an element selected from the group consisting of Mg, Ca, Sr and Ba). Perovskite nanosheet represented . The perovskite nanosheet according to claim 1, wherein A is Ca and / or Sr. The perovskite nanosheet according to claim 1, wherein the perovskite nanosheet is peeled from K [A _n-1 M ₃ Ti _n-3 O _{3n + 1} ]. A dielectric material comprising the perovskite nanosheet according to any one of claims 1 to 3 . A photocatalytic material comprising the perovskite nanosheet according to any one of claims 1 to 3 .