KR101415080B1 - Mesoporous layer-by-layer nanohybrids, preparing method of the same, and photocatalyst containing the same - Google Patents

Abstract

Layered double hydroxide (LDH) nanosheet having surface charges opposite to each other and self-assembled metal oxide nanosheets, and mesopores formed between the self-assembled nanosheets , A method for producing the mesoporous layered nanohybrid, and a photocatalyst comprising the mesoporous layered nanohybrid.

Description

MESOPOROUS LAYER-BY-LAYER NANOHYBRIDS, PREPARATION METHOD OF THE SAME, AND PHOTOCATALYST CONTAINING THE SAME [0002] The present invention relates to a mesoporous layered nanohybrid,

The present invention relates to a mesoporous layered nanohybrid comprising a layered double hydroxide and a layered metal oxide, a process for producing the same, and a photocatalyst comprising the same.

Solar energy is one of the promising renewable energy sources and can replace fossil fuels and meet the growing global demand for sustainable energy. One of the most effective approaches to harvesting the solar energy is the mineral oil production of H ₂ and O ₂ molecules by semiconductor photocatalysts. Despite the large amount of research, most of the inorganic photocatalysts that have been developed so far have been found to be highly visible due to their large band gap energy, low light stability, and inadequate band locations for the reduction of protons and the oxidation of oxide ions. splitting.

In order to overcome the drawbacks of these materials, attempts have been made to hybridize the two types of photocatalysts. In one example, a CdS-TiO ₂ hybrid system can harvest visible light using a narrow bandgap CdS component and the photo-generated electrons in CdS migrate into a broad bandgap TiO ₂ component. Such electron transfer leads to reduction of electron-hole recombination and improvement of photocatalytic activity of CdS.

As well as hybridization, the formation of nanostructures can provide an alternative way to enhance the photocatalytic activity of semiconductor materials. Many low-dimensional nanostructured semiconductor materials have been designed and studied as photocatalysts for the production of H ₂ or O ₂ gases. Research interest in nanostructured semiconductors has expanded into 2D nanostructured inorganic solids.

As an inorganic analogue to graphene, some exfoliated laminated metal oxide nanosheets are applicable as photocatalysts for photo-oxidation of organic contaminant molecules and for the optical generation of H ₂ gas. Compared with laminated metal oxides, laminated metal hydroxides such as layered double hydroxides or LDH (layered double hydroxides) have not been studied as photocatalysts yet.

A recent report on the high photocatalytic activity of Zn-Cr-LDH materials has raised interest in the application of LDH phases as photocatalysts. Considering the high photocatalytic efficiency and high quantum yield of the Zn-Cr-LDH compound for visible light-induced O ₂ generation, the material serves as a useful stepping stone for the study of new efficient photocatalysts. In addition, the difficulty in mineral oil production of O ₂ molecules requiring the involvement of four electrons increases the effectiveness of the LDH material as a useful photocatalyst. By hybridization with other semiconductors, it is expected that the photocatalytic activity on the Zn-Cr-LDH phase will be further increased through an increase in the lifetime of electrons and holes.

On the other hand, the improvement of chemical stability is very important in expanding the application field on the LDH. Layered nanohybrid composed of two types of nanosheets is electrostatically-induced self-assembly because the delaminated nanosheets of LDH and deposited titanium oxide possess opposite layer charge. . ≪ / RTI > Although various types of hybrid photocatalysts comprising low-dimensional nanostructured materials have been reported, the inventors have reported on the synthesis of heterolayered visible light-activated photocatalysts comprising two directly inorganic hybrid 2D nanosheets .

The present invention relates to a mesoporous layered nanohybrid having improved chemical stability as a mesoporous layered nanohybrid formed by self-assembly by electrostatic attraction between inorganic 2D nanosheets, a method for producing the mesoporous layered nanohybrid, And a photocatalyst comprising the mesophosphor layer nanohybrid.

However, the problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

One aspect of the present invention is a method of fabricating a mesoporous layer-by-layer (hereinafter referred to as " mesoporous layer-by-layer ") layer formed by self-assembly of a metal oxide nanosheet and a layered double hydroxide Nanohybrid) can be provided.

Another aspect of the present invention relates to a process for preparing a mesoporous layered nanohybrid according to the present invention, comprising laminating metal layered double hydroxide nanosized and metal oxide nanosheets having opposite surface charges by electrostatic induction-self-assembly Method can be provided.

Another aspect of the present invention provides a photocatalyst comprising the mesoporous layered nanohybrid according to the present invention.

The mesoporous layered nanohybrid according to the present invention formed by the self-assembly of layered double hydroxides (LDH) nanosheets and metal oxide nanosheets having surface charges opposite to each other has excellent chemical stability, And has high photocatalytic activity against O ₂ production through decomposition. The mesoporous layered nanohybrid according to the present invention shows strong absorption of visible light and significantly reduced photoluminescence signals showing effective electron coupling between the two structured 2D (two dimensional) nanosheets. Self-assembly between the 2D inorganic nanosheets induces the formation of a highly porous laminate structure, the porosity being controllable by altering the ratio of laminated metal layered double hydroxide nanosheets to metal oxide nanosheets.

The mesoporous layered nanohybrid according to the present invention has excellent photocatalytic activity as compared with pure metal layered double hydroxides, and has excellent activity as a photocatalyst for oxygen generation through water decomposition under visible light irradiation.

In the present application, it is believed that the layered alignment between the inorganic 2D nanosheets is highly effective in enhancing the photocatalytic activity of the component semiconductors as well as in synthesizing new porous LDH-based hybrid materials with improved chemical stability Can be clearly demonstrated.

Figure 1 is a schematic diagram of a ZCT nanohybrid of (a) ZCT-1, (b) ZCT-2, and (c) ZCT-3 according to one embodiment of the present invention, (d) the pure Zn- ) In the data (ac), circles and squares represent the in-plane Bragg reflection of the exfoliated titanium oxide nanosheets and Zn-Cr-LDH nanosheets, respectively.
FIG. 2 is a photograph of (a) Thin-film phenomenon image of a colloidal dispersion of a peeled Zn-Cr-LDH nanosheet according to an embodiment of the present invention and (b) a zeta potential curve and a c) HR-TEM image and (d) SAED pattern.
Figure 3 shows an HR-TEM cross-sectional image of (a) a ZCT-1 nanohybrid according to one embodiment of the present application and (b) an enlarged image and structural model thereof.
4 is an FE-SEM image of (a) ZCT-1, (b) ZCT-2, and (c) ZCT-3, respectively, according to one embodiment of the present application.
5 is an FE-SEM image (center) of an EDS element map and (a) ZCT-1, (b) ZCT-2, and (c) ZCT-3 according to one embodiment of the present application.
FIG. 6 is a graph showing the results of (a) ZCT-1, (b) ZCT-2, (c) Ti K-edge (left), Cr K- Zn-Cr-LDH / Zn-Cr-LDH, (e) anatase TiO ₂ / Cr ₂ O ₃ / ZnO (ZnO) , and is compared with (f) the reference spectrum of the rutile TiO ₂ / CrO _3.
Figure 7 shows the pore size distribution curves of (a) N ₂ adsorption-desorption isotherms according to one embodiment of the present application and (b) ZCT-1 (circle), ZCT-2 (triangle), and ZCT- to be.
FIG. 8 is a graph showing the results of a comparison between the ZCT-1 (solid line), ZCT-2 (dotted line), ZCT-3 (dot-dash line), pure Zn- ) (Plotted as a Kubelka-Munk function of the reflectivity R).
FIG. 9 is a graph showing the results of (A) ZCT-1 (solid line), ZCT-2 (dotted line), ZCT-3 (dot- (Triangle) of the deposited titanium oxide (B), and (B) a schematic model of the band structure of the ZCT nanohybrid and electron transfer of the transferred electrons.
10 is a graph showing the results of spectroscopic analysis of O ₂ (a), (b) ZCT-2 and (c) ZCT- (D) pure Zn-Cr-LDH and (e) stacked cesium titanate (10 mmol AgNO ₃ is used as the electron scavenger) ); (B) A graph showing the time-dependent change of zinc concentration dissolved from ZCT-1 nanohybrid (square) and pure Zn-Cr-LDH (circle) (right).

Hereinafter, embodiments and examples of the present invention will be described in detail with reference to the accompanying drawings, so that those skilled in the art can easily carry out the present invention.

It should be understood, however, that the present invention may be embodied in many different forms and is not limited to the embodiments and examples described herein. In the drawings, the same reference numbers are used throughout the specification to refer to the same or like parts.

Throughout this specification, when an element is referred to as "including " an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise. The terms "about "," substantially ", etc. used to the extent that they are used throughout the specification are intended to be taken to mean the approximation of the manufacturing and material tolerances inherent in the stated sense, Accurate or absolute numbers are used to help prevent unauthorized exploitation by unauthorized intruders of the referenced disclosure. The word " step (or step) "or" step "used to the extent that it is used throughout the specification does not mean" step for.

The expression "nanosheet" herein means a state in which a metal layered double hydroxide having a layered structure or a metal oxide having a laminated structure is dispersed in a solvent in a single layer state

The term "mesoporous layer-like nanohybrid" as used herein refers to a two-dimensional or three-dimensional porous structure having mesopores formed by layering of metal layered double hydroxide nanosheets and metal oxide nanosheets through self- ≪ / RTI >

The term "house-of-card form" as used herein means an average of 0.1 to 1,000 nm, or 0.1 to 500 nm, or 0.1 to 100 nm, Means a three-dimensional structure having a structure having a mesopore ranging from 1 to 50 nm.

One aspect of the present invention relates to a method of fabricating a nanostructure, which is formed by self-assembling a metal layered double hydroxide (LDH) nanosheet and a metal oxide nanosheet having mutually opposite surface charges, Wherein the mesoporous layered nanocomposite comprises a mesoporous mesoporous nanohybrid.

In one embodiment, the metal layered double hydroxide nanosheet may comprise, but is not limited to, a metal layered double hydroxide represented by the following general formula 1:

[Formula 1]

[M ^II _(1-x) M ^III _x (OH) ₂ ] [A ^{n -} ] _{x /} n .zH ₂ O;

In the general formula 1,

M < ^{II >} is a +2 valent metal cation,

M ^III is a +3 metal cation,

A ^{n -} is an anion selected from the group consisting of hydroxide ions (OH ^- ), nitrate ions (NO ₃ ^- ), PO ₄ ^{3 -} , HPO ₄ ^{2 -} , H ₂ PO ₄ ^-

0 < x < 1,

z is a number of from 0.1 to 15;

The metal layered double hydroxide has a layered structure composed of metal ions of +2 and +3, where +2 is substituted for the metal ion and part of the metal ion is substituted for the +3 -valent ion, so that the metal double hydroxide is positively charged. Therefore, the negative ions (A ^{n -} ) are stabilized in the space between the layers in order to maintain the charge of the whole material as neutral. Such a layered metal double hydroxide can be generally synthesized by a precipitation reaction in an aqueous solution or a precipitation-ion exchange reaction.

In one embodiment, the M ^II is ^{Ca 2 +, Mg 2 +,} Zn 2 +, Ni 2 +, Mn 2 +, Co 2 +, Fe 2 +, Cu 2 + , and selected from the group consisting of a combination of above, comprising a metal cation M ^III comprises a metal cation selected from the group consisting of ^{Fe 3 +, Al 3 +,} Cr 3 +, Mn 3 +, Ga 3 +, Co 3 +, Ni 3 + , and combinations thereof , But is not limited thereto.

In one embodiment, the metal oxide nanosheet may include, but is not limited to, a metal oxide semiconductor. For example, the metal oxide semiconductor may be at least one selected from the group consisting of Ti, Ni, Cu, Zr, Sr, Zn, In, Yr, La, V, Mo, W, Sn, Nb, Mg, Al, Y, Sc, And oxides of metals selected from the group consisting of combinations thereof, but the present invention is not limited thereto.

In one embodiment, the metal layered double hydroxide nanosheet is a metal layered double hydroxide (Zn-Cr-LDH) in which M ^II is Zn ^{2 +} in the general formula 1 and M ^III is Cr ^{3 +} ), And the metal oxide nanosheet may include, but not limited to, a titanium oxide nanosheet having a surface negative charge.

In one embodiment, the mesoporous layered nanohybrid of the present invention can enhance visible light responsiveness, specific surface area, and chemical stability by adjusting band gaps by hybridizing two semiconductor compounds having different band gaps.

On the basis of adjusting the band gap by hybridizing a metal layered double hydroxide nanosheet having a smaller band gap to a metal oxide nanosheet having a wide band gap. That is, by combining the two materials, covalent bonds are formed through heat treatment under appropriate conditions to induce impurity levels in the bandgap to impart visible light responsiveness. For example, in the case of hybridization with Zn-Cr-LDH sol particles having a small bandgap with titanium oxide and visible light response, these hybridized compounds have a lower band gap energy and a lower valence band Holes are generated in the valence band due to the electron transfer from the valence band to the conduction band of these sol particles upon irradiation with visible light. These holes can easily migrate to the valence band of titanium oxide with higher energy. Therefore, the hybridized compound can minimize the recombination reaction of electrons and holes, and thus can be more effectively used for decomposing water or organic matter. In addition, transition metal nanosol particles stabilized in the interlayer are expected to greatly improve the chemical stability of the particles themselves, and furthermore, these materials have a crosslinked structure with porosity, thereby exhibiting superior water decomposition and organic decomposition characteristics do.

In one embodiment, the metal layered double hydroxide nanosheets can be used without particular limitation as long as the metal layered double hydroxide nanosheets include metal layered double hydroxides capable of absorbing visible light. For example, 1, < / RTI > and the metal layered double hydroxide represented by < RTI ID = 0.0 > 1, < / RTI >

In one embodiment, the titanium oxide nanosheets have a layered structure and include, for example, Cs _y Ti _{2 -y / 4} O ₄ , K ₂ Ti ₂ O ₅ , Na ₂ Ti ₃ O ₇ , CsTi ₅ O _{12, KTiNbO 5, CsTi 2 NbO} 7, KTi 3 NbO 9, K 3 Ti 5 NbO 14 and but may be to include those selected from the group consisting of, without being limited thereto. When CsyTi _{2 -y / 4} O ₄ is used as the titanium oxide, the value of y is an important factor for determining whether the layered structure can maintain charge balance with cesium ions, and y is preferably in the range of 0.67 to 0.73 , and when y is 0.67, it is more preferable to keep the layered structure and more preferable.

In one embodiment, the metal layered double hydroxide nanosheets having opposite surface charges and the metal oxide nanosheets are hybridized to each other through self-assembly by electrostatic induction, so that they are layered to form a porous two-dimensional layer structure or card- but is not limited to, a three-dimensional layer structure of a house-of-card form. In the case of the card collection structure, the mesopores may be formed in an average of 0.1 to 1,000 nm, 0.1 to 500 nm, 0.1 to 100 nm, or 1 to 50 nm mesopores in the structure inner space, but the present invention is not limited thereto .

In one embodiment, the molar ratio of the metal layered double hydroxide to the metal oxide nanosheets may be 1: 0.1 to 100, but is not limited thereto. For example, the molar ratio of the metal layered double hydroxide to the metal oxide nanosheets may be 1: 0.1 to 100, or 1: 0.1 to 50, or 1: 0.1 to 30, or 1: 0.1 to 20, 10, but is not limited thereto. In one embodiment, the molar ratio of the metal layered double hydroxide to the metal oxide nanosheets can be selected, for example, from the sum of the charge of the metal oxide nanosheets, such as Zn-Cr-LDH and the metal layered double hydroxide nanosheets and titanium oxide But is not limited to, adjusting the layered re-layer of the nanosheet based on the balance (1: 0.91), area balance (1: 1.46) and / or intermediate composition (1: 1.16).

Another aspect of the present invention provides a photocatalyst comprising the mesoporous layered nanohybrid according to the present invention.

In one embodiment, the photocatalyst may be one that absorbs visible light, but is not limited thereto.

In another embodiment, the photocatalyst may have catalytic activity for water decomposition under visible light irradiation, but is not limited thereto.

The photocatalyst can be used to generate hydrogen gas through decomposition of water or to decompose organic matters causing environmental pollution. The photocatalyst is chemically stable, has a large specific surface area, and has photocatalytic activity and visible light activity.

In one embodiment herein, the layered alignment of positively charged Zn-Cr-LDH 2D nanosheets and the negatively charged laminated titanium oxide 2D nanosheets have excellent photocatalytic activity towards visible light-induced O ₂ production And a mesoporous hetero-laminated ZCT (Zn-Cr-LDH) nanohybrid having improved chemical stability can be produced. The heterogeneous stacked nanohybrid thus obtained has a visible light harvesting ability and a high porous structure, which can be attributed to electron coupling between the component nano-sheet and the stacked-card stack of layers, respectively. As a result of the protection of the LDH lattice by the deposited titanium oxide, the chemical stability of the Zn-Cr-LDH is significantly improved. Regardless of the chemical composition, the ZCT (Zn-Cr-LDH) nanohybrid exhibits highly effective photocatalytic activity against O ₂ production under visible light superior to that of pure Zn-Cr-LDH and deposited titanium oxide. The alignment of the heterogeneous stacked materials is critical in optimizing the visible light-induced photocatalytic activity of the component nanosheets. Such well-aligned heterogeneous layer structures can be fabricated by hybridization between two oppositely charged nanosheets with a charge-balanced composition.

Considering that the pure Zn-Cr-LDH phase is one of the most efficient visible light photocatalysts, the ZCT (Zn-Cr-LDH) nanohybrid according to one embodiment of the present invention, which has a further improved photocatalytic activity, ₂ It is useful as the best photocatalyst material applicable to the production.

In the present invention, hybridization between cationic and anionic inorganic 2D nanosheets can be usefully applied in developing highly efficient visible light active photocatalysts with improved chemical stability.

Another aspect of the present invention can provide a method for producing the mesoporous layered nanohybrid according to the present invention.

The process for preparing the mesoporous layered nanohybrid according to the present invention may comprise:

Preparing a first nanosheet dispersion containing a metal layered double hydroxide nanosheet having surface charge;

Preparing a second nanosheet dispersion containing a metal oxide nanosheet having a surface charge opposite to that of the metal layered double hydroxide nanosheet;

 The first nanosheet dispersion and the second nanosheet dispersion are mixed to form the mesoporous layered nanohybrid by self-assembling the metal layered double hydroxide nanosheets and the metal oxide nanosheets.

In one embodiment, the first nanosheet dispersion may include, but is not limited to, a metal layered double hydroxide nanosheet capable of absorbing visible light. For example, the first nanosheet dispersion may include, but is not limited to, a metal layered double hydroxide represented by the following general formula 1:

[Formula 1]

[M ^II _(1-x) M ^III _x (OH) ₂ ] [A ^{n -} ] _{x /} n .zH ₂ O;

In the general formula 1,

M < ^{II >} is a +2 valent metal cation,

M ^III is a +3 metal cation,

A ^{n -} is an anion selected from the group consisting of hydroxide ions (OH ^- ), nitrate ions (NO ₃ ^- ), PO ₄ ^{3 -} , HPO ₄ ^{2 -} , H ₂ PO ₄ ^-

0 < x < 1,

z is a number of from 0.1 to 15;

In one embodiment, the M ^II in the formula 1 is ^{Ca 2 +, Mg 2 +,} Zn 2 +, Ni 2+, Mn 2 +, Co 2 +, Fe 2 +, Cu 2 + , and combinations comprises a metal cation selected from the group consisting of a combination, wherein M ^III is ^{Fe 3 +, Al 3 +,} Cr 3 +, Mn 3 +, Ga 3 +, Co 3 +, Ni 3 + and combinations thereof But are not limited to, those selected from the group consisting of:

The metal layered double hydroxide has a layered structure composed of metal ions of +2 and +3, where +2 is substituted for the metal ion and part of the metal ion is substituted for the +3 -valent ion, so that the metal double hydroxide is positively charged. Therefore, the negative ions (A ^{n -} ) are stabilized in the space between the layers in order to maintain the charge of the whole material as neutral. Such a layered metal double hydroxide can be generally synthesized by a precipitation reaction in an aqueous solution or a precipitation-ion exchange reaction.

For example, the metal layered double hydroxide represented by the general formula 1 may be prepared by: i) coprecipitating an M ^II metal precursor and an M ^III metal precursor in a polar solvent to obtain a compound represented by the general formula [M ^II _(1-x) M ^III _x (OH ) ₂ ] [A ⁿ ] _{x /} n zH ₂ O; And ii) reacting the layered metal double hydroxide salt with at least one solvent selected from the group consisting of 1-butanol, 1-hexanol, 1-octanol, 1-decanol, CCl ₄ , xylene and HCONH ₂ In the form of a layered metal double hydroxide having a surface charge.

The coprecipitation step is usually carried out by adding a +2 valent metal salt such as calcium nitrate (Ca (NO ₃ ) ₂ .4H ₂ O) and a +3 valent metal salt such as iron nitrate (Fe (NO ₃ ) ₃ .9H ₂ O) Dissolved in distilled water and adjusted to a pH of 12 ± 0.2 and then stirred at room temperature for 6 hours to 7 days, preferably 1 day to 4 days, to form a layered structure Thereby forming a metal double hydroxide. The remaining unreacted elements can be removed by centrifugation, washing and drying.

The metal layered double hydroxide represented by the general formula (1) can be prepared by reacting the layered metal double hydroxide salt with 1-butanol, 1-hexanol, 1-octanol, 1-decanol, CCl ₄ , xylene and HCONH ₂ (Exfoliation) in the form of a layered metal double hydroxide having a cationic surface charge by reacting with at least one solvent selected from the group consisting of formamide, and formamide. The solvent is not limited as long as it can dissolve the layered metal double oxysulfate. However, the solvent is not limited as long as it can dissolve the layered metal double oxysulfate, but it is preferably composed of 1-butanol, 1-hexanol, 1-octanol, 1-decanol, CCl ₄ , xylene and HCONH ₂ At least one selected from the group can be effectively stripped, and among them, formamide is most preferable.

In one embodiment, the second nanosheet dispersion may comprise, but is not limited to, a metal oxide nanosheet containing a metal oxide semiconductor. For example, the metal oxide semiconductor may be at least one selected from the group consisting of Ti, Ni, Cu, Zr, Sr, Zn, In, Yr, La, V, Mo, W, Sn, Nb, Mg, Al, Y, Sc, And oxides of metals selected from the group consisting of combinations thereof, but the present invention is not limited thereto.

In one embodiment, the metal layered double hydroxide nanosheet is a metal layered double hydroxide (Zn-Cr-LDH) in which M ^II is Zn ^{2 +} in the general formula 1 and M ^III is Cr ^{3 +} ), And the metal oxide nanosheet may include, but not limited to, a titanium oxide nanosheet having a surface negative charge.

In one embodiment, the titanium oxide nanosheets can be formed by peeling from a laminated titanate having a layered structure, but are not limited thereto. For example, the titanium oxide nanosheets may include Cs _y Ti _{2 -y / 4} O ₄ , K ₂ Ti ₂ O ₅ , Na ₂ Ti ₃ O ₇ , CsTi ₅ O ₁₂ , KTiNbO ₅ , CsTi ₂ NbO ₇ , KTi ₃ NbO ₉ , or K ₃ Ti ₅ NbO ₁₄ And then peeling off the laminated titanate. For example, when using CsyTi _{2 -y / 4} O ₄ , the value of y is an important factor that determines whether the layered structure can maintain charge balance with cesium ions, y is preferably in the range of 0.67 to 0.73 , and when y is 0.67, it is more preferable to keep the layered structure and more preferable.

 In the manufacturing method according to the present invention, the first nanosheet dispersion and the second nanosheet dispersion are mixed to self-assemble the metal layered double hydroxide nanosheets and the metal oxide nanosheets to form a mesoporous layered nanohybrid . For example, the metal layered double hydroxide nanosheets having opposite surface charges and the metal oxide nanosheets are hybridized with each other through self-assembly by electrostatic induction and re-deposited to form a porous two-dimensional layer structure or a card house shape but not limited to, a mesoporous layer-like nanohybrid having a three-dimensional layer structure of -of-card form. In the case of the card collection structure, the mesopores may be formed in an average of 0.1 to 1,000 nm, 0.1 to 500 nm, 0.1 to 100 nm, or 1 to 50 nm mesopores in the structure inner space, but the present invention is not limited thereto .

In one embodiment, the molar ratio of the metal layered double hydroxide to the metal oxide nanosheets may be 1: 0.1 to 100, but is not limited thereto. For example, the molar ratio of the metal layered double hydroxide to the metal oxide nanosheets may be 1: 0.1 to 100, or 1: 0.1 to 50, or 1: 0.1 to 30, or 1: 0.1 to 20, 10, but is not limited thereto. In one embodiment, the molar ratio of the metal layered double hydroxide to the metal oxide nanosheets can be selected, for example, from the sum of the charge of the metal oxide nanosheets, such as Zn-Cr-LDH and the metal layered double hydroxide nanosheets and titanium oxide But is not limited to, adjusting the layered re-layer of the nanosheet based on the balance (1: 0.91), area balance (1: 1.46) and / or intermediate composition (1: 1.16).

Hereinafter, the present invention will be described in detail with reference to embodiments and drawings. However, the present invention is not limited to these embodiments and drawings.

[ Example ]

<Manufacturing>

The stacked cesium titanate, Cs _{0 .67 1 .83} Ti _0.17 O ₄ And the protonated derivative thereof, H _{0 .67} Ti _{1 .83 0.17} H ₂ O, wherein vacancy is represented, can be obtained by a conventional solid state reaction And subsequent 1 M HCl treatment. As reported previously (Sasaki, T .; Watanabe, M. J. Am . Chem . Soc . 1998, 120 , 4682-4689), the delamination of the laminated titanate is attributed to the formation of tetrabutyl Was achieved by intercalation of tetrabutylammonium (TBA) cations. The aqueous dispersion of the exfoliated titanium oxide nanosheets was freeze-dried for 6 days and redispersed in formamide. Specifically, the stacked cesium titanate, Cs _0.67 Ti _{1.83 0.17} O _4, was prepared using cesium carbonate (Cs ₂ CO ₃ ) and titanium dioxide (TiO ₂ ). Cesium carbonate and titanium dioxide were mixed well in accordance with the chemical amount, mixed and stirred for about 1 hour at the same time, and then heat-treated in air at 750 ° C for 24 hours. For optimized synthesis, the heat-treated compound was re-finely mixed and the specimens were prepared and heat-treated for 24 hours at 800 ° C in air. As a result, the solid, yet rectangular political (orthorhombic) is Les Croix feed site (lepidocrocite) form of _{Cs 0 .67 Ti 1 .83 0.17 O} 4 having a layered structure was formed. Manufacturing the Cs _{0 .67} Ti _{1 .83 0.17} O ion-H0 _{0 .67} Ti _{1 .83 0.17} O exchange of protons (H +) by the acid treatment _{4 4} · H ₂ O was prepared. First, 100 ml of a 1 M hydrochloric acid aqueous solution per 1 g of Cs _0.67 Ti _{1.83 0.17} O ₄ was added and stirred vigorously. At this time, the solution was repeated five times while changing the fresh acid solution every day for 3 days. The acid-treated powder was collected using a centrifugal separator and dried in an oven at 60 ° C to remove moisture. The dried to ensure that the X- ray diffractometry _{Cs 0 .67 Ti 1 .83 0.17 O} 4 instead of Cs ions are ion-exchanged with protons ^{_{(H +) H0 0 .67 Ti}} 1 .83 0.17 O 4 · H 2 O Was formed. The production of _{H0 0 .67 Ti 1 .83 0.17 O} 4 · H 2 O to prepare a titanium oxide having a negative charge separation by cation treatment. First, the _{H0 0 .67 Ti 1 .83 0.17 O} 4 · H 2 O between the samples in order to finely peel the following, titanium oxide, _{H0 0 .67 Ti 1 .83 0.17 O} 4 · H 2 O per 0.4g sample of distilled water 100 ml was added and the bulky cation TBA · OH (Tetrabutylammonium hydroxide) was added to a molar ratio of 3: 1 with H _{0 0 .67} Ti _{1 .83 0.17} O ₄ .H ₂ O sample. The mixed solution was then vigorously stirred for 10 days. H0 _0.67 Ti _{1.83 0.17} O _{4 .H 2} O, which was not ion-exchanged with cations, was separated by centrifuge (10,000 rpm, 10 min) and the supernatant was collected separately. At this time, the supernatant is cloudy, and titanium oxide having a negative charge in a colloidal solution state is obtained through this process.

Nitrate form of pure Zn-Cr-LDH can be prepared by the method described previously (Prevot, V .; Forano, C .; Besse, JP Inorg . Chem . 1998, 37 , 4293-4301) Zn ^{2 +} precursor and Cr ^{3 +} precursor were prepared by direct coprecipitation in a polar solvent such as water. The exfoliation of the Zn-Cr-LDH was carried out by vigorous stirring of LDH sample (1 g L ^-1 ) in formamide under N ₂ bubbling to avoid carbonate contamination.

The heterolayered ZCT nanohybrid was synthesized by mixing the formamide dispersion of Zn-Cr-LDH and the laminated titanium oxide nanosheets in an N ₂ atmosphere at room temperature under constant stirring. The repositioned ZCT nanohybrid was recovered by centrifugation at 6,000 rpm, rinsed with formamide and absolute ethanol, and finally vacuum dried at 65 ° C for 24 hours. The molar ratio of Zn-Cr-LDH to the deposited titanium oxide was adjusted by adjusting the layered layer of the nanosheet based on charge balance (1: 0.91), area balance (1: 1.46) and intermediate composition (1: .

[ Experimental Example ]

<Characteristic Analysis>

The crystal structures of the Zn-Cr-LDH and ZCT nanohybrids were measured by powder X-ray diffraction (XRD) using Ni-filtered Cu Kα radiation with a Rigaku diffractometer.

The chemical composition of the composite of this example was analyzed by Inductively Coupled Plasma (ICP) (Shimazu ICPS-5000) and CHN Elementary Analyzer (CE-instruments-EA-1110). High Resolution Transmission Electron Microscopy (HRTEM) / Selected Area-Electron Diffraction (SAED) analysis (HR-TEM / SAED) analysis was performed using a JEOL (JEM 2100F) microscope at 200 kV voltage .

The nanohybrid sample embedded in the epoxy resin was cut by an ultramicrotome for HR-TEM observation. In addition, their surface morphology and elemental distribution were studied by field emission-scanning electron microscopy (FE-SEM, Jeol JSM-6700F) with energy dispersive spectrometry (EDS).

The X-ray absorption near edge structure (XANES) analysis was performed in the Pohang accelerator laboratory (PAL) at Beamline 7C in Korea. The Ti K-edge, Cr K-edge, and Zn K-edge XANES data were collected at room temperature in a transmission mode using a gas ionization detector. All spectra were calibrated by simultaneously measuring the spectra of Ti, Cr, or Zn metal foil.

The N ₂ adsorption-desorption isotherm was measured at liquid nitrogen temperature with a gas sorption analyzer (ASAP 2020). Prior to measurement, the sample was degassed at 150 &lt; ⁰ &gt; C for 12 hours in a vacuum of less than 10 &lt; ^-3 &gt; Torr.

Diffuse reflective UV-vis spectra were obtained with a Sinco S-4100 spectrometer equipped with a 60 mm diameter integrator using BaSO ₄ as a reference.

The photoluminescence (PL) spectrum was measured with a Perkin-Elmer LS55 fluorescence spectrometer.

To determine the band structure of the Zn-Cr-LDH material, a CV curve of IVIUM STAT (Ivium Technologies, USA) was recorded using a conventional three electrode cell. Pt mesh and Ag / AgCl electrodes (+0.198 V vs. NHE) were used as reference and auxiliary electrodes, respectively. A working electrode was prepared by adhering a uniform layer of material on a glassy carbon electrode with the aid of a nafion adhesive. The electrodes were immersed in an aqueous solution of 0.1 M NaClO ₄ as an electrolyte under a nitrogen atmosphere.

For measurement of oxygen production through a photocatalyst, 10 mg of the nanohybrid powder was dispersed in a Pyrex reaction cell in 20 ml of water using a magnetic stirrer, and then 0.01 M AgNO ₃ was added as a sacrificial reagent . The head space of the reactor was sealed with an air stopping silicon stopper and the photocatalyst dispersion was completely degassed using argon gas for 0.5 hour. A 450 W Xe arc lamp (Newport) was used as the light source. Light was passed through a 10 cm IR water filter and a cut-off filter (visible light illumination (λ> 420 nm) and then aimed at the reactor.

The light intensity of the oxygen generating reaction was uniform up to 8 x 8 inches, and a Si solar cell (Mono-SiCKG filter; Certificate No. C-ISE 269) was used up to about 1.5 SIL radiation Respectively. During the O ₂ production process, the reactor and the entire assembly were maintained in an Ar-flow environment. The amount of O ₂ produced was measured after every hour by injecting 100 μl of the reactor headspace gas into on-line gas chromatography (GC, Shimadzu GC-2014).

The chemical stability of Zn-Cr-LDH hybridized with laminated titanium oxide was investigated by monitoring the leaching of zinc ions in a buffer solution with pH = 2 compared to the bare Zn-Cr-LDH . After 0.5 to 7 hours of reaction, the concentration of the zinc ions in the supernatant was examined by ICP analysis.

<Synthesis and exfoliation of Zn-Cr-LDH>

1 shows a powder XRD pattern of a Zn-Cr-LDH (ZCT) nanohybrid, pure Zn-Cr-LDH, and protonated stacked titanium oxide according to one embodiment of the present application. The pure Zn-Cr-LDH material exhibits well-developed Bragg reflections that can be indexed with a hexagonal stacked LDH structure with R-3m rhombohedral symmetry.

According to a least-squares fitting analysis, the lattice parameter is determined as a = 0.308 and c = 0.890 nm, which is in good agreement with the lattice parameter on the nitrate-inserted LDH. Clearly · 0.6H ₂ O ^- wherein CHNS elemental analysis and ICP spectroscopy carbonate of the material-free compositions (carbonate-free composition), _{i.e., Zn 0 .69 Cr 0 .31 (} OH) 2 · 0.31NO 3 Prove it. Like other LDH compounds, the Zn-Cr-LDH material can be stripped into individual monolayers through dispersion of the powder sample in a formamide solvent, which forms a cloudy dispersion. The resulting colloidal dispersion of the Zn-Cr-LDH nanosheets with a light pinkish purple color is stable for several weeks at room temperature.

As shown in Fig. 2A, the formation of a colloidal dispersion of the peeled Zn-Cr-LDH nanosheets was evidenced by observations of the apparent Tyndall phenomenon. The zeta potential measurement clearly demonstrates the positively charged state of the peeled Zn-Cr-LDH nanosheets, as shown in FIG. 2B. HR-TEM confirmed the formation of very thin nanosheets (FIG. 2C). The maintenance of the in-plane structure on the LDH after the exfoliation is evidenced by SAED in Fig. 2d, a clear hexagonal diffraction pattern being evident. The measured in-plane lattice parameter (0.302 nm) corresponds significantly to the a -axis lattice parameter ( a = 0.308 nm) measured from the powder XRD analysis.

<Powder XRD and HR-TEM analysis for ZCT nanohybrid>

Three types of the ZCT nanohybrid were synthesized by self-assembly between the oppositely charged nanosheets of Zn-Cr-LDH and the deposited titanium oxide with a stacked titanium oxide / Zn-Cr-LDH ratio of 0.91, 1.16 and 1.46 (The obtained nanohybrids are represented as ZCT-1, ZCT-2, and ZCT-3).

The final ratios of 0.91 and 1.46 correspond to compositions calculated on the basis of charge balance and area balance between two nanosheets, respectively. As shown in Figure 1, all of the ZCT nanohybrids show (001) reflections with equal spacing in the low 2 &amp;thetas; The formation of layered ordered structures for all reactant ratios employed in this example strongly suggests the flexibility of the chemical composition in the hybrid material. According to the least-squares fitting analysis, the prepared ZCT nanohybrid has an extended interlayer spacing of ~ 1.22-1.31 nm which is in good agreement with the thickness sum (~ 1.2 nm) of the laminated titanium oxide nanosheets and Zn-Cr- and basal spacing. This agreement provides strong evidence for stratified stratification of the two types of nanosheets. Among the nanohybrids, the ZCT-1 nanohybrid synthesized in a charge-balanced composition exhibits strongest and sharpest (001) reflections showing excellent c-axis alignment in this compound. This discovery highlights the importance of charge balance in the formation of a well-aligned heterogeneous stacked material composed of two oppositely charged nanosheets. Such an increase in randomness in such a stacked structure can be attributed to incorporation of charge compensating speci fi cs.

Based on the Scherrer calculation using the full-width-at-half-maximum (FWHM) of the (001) reflection, the thickness of each crystal along the c-axis is measured as ~ 50-80 Å . Judging from the interlayer spacing (~ 12-13 Å) of the prepared nanohybrid, the thickness obtained corresponds to ~4-7 layers of interlayered LDH / laminated titanium oxide superlattice.

Also, as can be clearly seen from FIG. 1, all of the ZCT nanohybrids also exhibited multiple XRD peaks in the high 2 theta area, corresponding to the in-plane Bragg reflection of the hexagonal Zn-Cr-LDH structure ) Corresponds to the in-plane Bragg reflection of an orthorhombic stacked titanium oxide (shown as a circle). Observation of this plane-internal reflection clearly shows the maintenance of the inherent in-plane structure of each constituent nanosheet after hybridization. In addition, a broad diffraction hump appears at 2θ = 30-40 °, which is due to the disordered lamination structure of the nanosheets.

Formation of the interlayered heterostructured structure of the Zn-Cr-LDH nanosheets and the laminated titanium oxide nanosheets was confirmed by HR-TEM analysis. As shown in FIG. 3, the HR-TEM cross-sectional image of the ZCT-1 nanohybrid exhibits a parallel-aligned dark line with two different spacings. A grating line with a smaller spacing of ~ 0.5 nm corresponds to the Zn-Cr-LDH layer, while another line with a larger spacing of ~ 0.7 nm is interpreted as the titanium oxide layer. The observed interlayer spacing of the nanohybrid (~1.2 nm) agrees well with the c-axis lattice parameter measured from the XRD analysis. The slight deformation of the laminated lattice is shown in the image of FIG. 3 above and as a result of the tension caused by the use of a superfine cutter, this suggests the flexibility of the interlayered superlattice structure.

<FE-SEM and EDS / element mapping analysis for ZCT nanohybrid>

The morphology of the ZCT nanohybrid was monitored by FE-SEM analysis as shown in Fig. The porous cardboard laminate of sheet-like crystals, which is common to all nanohybrids and strongly suggests the high porosity of such materials.

To confirm hybridization between Zn-Cr-LDH and laminated titanium oxide, the spatial distribution of metal and oxygen elements in the ZCT nanohybrid was investigated by EDS and elemental mapping analysis. As shown in FIG. 5, the zinc, chromium, titanium, and oxygen elements are uniformly distributed throughout the entirety of the hybrid material, which clearly demonstrates uniform mixing of the two types of nanosheets without any spatial separation. do.

<XANES spectroscopy for ZCT nanohybrid>

In the ZCT nanohybrid, the oxidation state and local symmetry of titanium, chromium, and zinc ions were investigated by XANES analysis.

The left graph of FIG. 6 is the Ti K-edge XANES spectrum of the protonated laminated titanium oxide with ZCT nanohybrid, anatase TiO ₂ , rutile TiO ₂ , and lepidocrocite structures. All of these materials represent three pre-edge peaks (denoted as P ₁ , P ₂ , P ₃ ) corresponding to a quadruple-permissive 1 s → 3d transition. The full spectral characteristics of these pre-edge peaks provide a sensitive measure of the local crystal structure of the titanium ions.

All of the above ZCT nanohybrids exhibit typical pre-edge characteristics of titanium oxides stacked in a lepidocrocite-structure, which can be clearly distinguished from those of the anatase and rutile TiO ₂ . In the main-edge region, there are three spectral features (denoted as A, B, and C) that are assigned as dipole-allowed 1s to 4p transitions. As with the pre-edge property, the main-edge spectrum of the ZCT nanohybrid is similar to the main-edge spectrum of the lepidocrocite-type stacked titanium oxide, but in rutile and anatase TiO ₂ phase, Are not similar. The observed spectral similarity between the nanohybrid and the protonated laminated titanium oxide clearly demonstrates the retention of the lepidocrocite-structured titanium oxide lattice after the hybridization with the LDH nanosheet.

The Cr K-edge XANES spectrum for the ZCT nanohybrid is compared to several reference spectra in the center graph of FIG. All of the ZCT nanohybrid and the pure Zn-Cr-LDH are compared with the reference CrO ₃ compound exhibiting a very strong free-edge peak P, and only the free-edge peak P corresponding to the dipole-inhibited 1s → 3d transition It shows weak strength for. This indicates the stabilization of Cr ^{3 +} ions in an octahedral symmetry in the nanohybrid material.

There is close similarity in overall spectral characteristics and edge positions between the ZCT nanohybrid and pure Zn-Cr-LDH, which strongly suggests retention of the LDH lattice after hybridization. The Zn K-edge XANES spectrum for the ZnO nanohybrid is shown on the right side of FIG. 6 along with the spectrum for pure Zn-Cr-LDH and bulk ZnO. The edge positions of the pure Zn-Cr-LDH and ZCT nanohybrid are similar to those of the reference ZnO, which shows the divalent oxidation state of Zn ions in these materials.

Compared to the reference ZnO, all of the ZCT nanohybrids exhibit the XANES property that is not well decomposed in the energy region of 9660-9670 eV. These spectral characteristics are similar to those of the pure Zn-Cr-LDH compound and confirm the retention of the Zn-Cr-LDH lattice after the hybridization. Cr K-edge and Zn K-edge XANES analysis, the experimental results clearly show negligible changes in the crystal structure and electronic structure of the Zn-Cr-LDH component after hybridization with the deposited titanium oxide.

<N ₂ adsorption-desorption isotherms analysis for ZCT nanohybrid>

The surface area and pore structure of the ZCT nanohybrid was studied by N ₂ adsorption-desorption isotherm measurements.

As shown in FIG. 7, all of the ZCT nanohybrids show a clear hysteresis at pp ₀ ^-1 > 0.45 and negligible N ₂ adsorption at pp ₀ ^-1 <0.4, and most of the porosity Quot; is understood to be derived from the mesopore formed by lamination of card-shaped forms of nanosheets.

The results are in agreement with the FE-SEM (Fig. 4) results. The isotherms of all the nano hybrids can be classified as Brunauer-Deming-Deaming-Teller BDDT, type IV, which is a characteristic of mesoporous materials with high adsorption energy. A clear hysteresis loop with a steep adsorption branch and an inclined desorption branch at pp ₀ ^-1 = 0.45 was observed for the ZCT-1 nanohybrid, which corresponds to type H2 by the IUPAC classification. The combination of such Type IV isotherms and Type H2 hysteresis indicates the presence of well-aligned pores with narrow and wide areas and connected channels.

In contrast, the other nanohybrids (ZCT-2 and ZCT-3) exhibit a type H3 hysteresis curve showing a steep adsorption branch and an inclined desorption branch in the high pp ₀ ^-1 region. The type of isotherm and hysteresis reflects an open slit-shaped capillary with a parallel wall or a capillary with a very wide body and a narrow and short neck, which is a slit- Are often observed for the agglomeration of plate-like particles. The observed hysteresis behavior indicates that both the ZCT-2 and ZCT-3 nanohybrids have more open and less ordered pore structures than the ZCT-1 nanohybrid.

According to one analysis fitting one the BET equation as the basis, the surface area of the nano-hybrid are respectively 67, 86, and 104 m ² g with respect to the ZCT-1, ZCT-2, and ZCT-3 ^samples is calculated to be ^1, which is Is larger than the surface area of pure cesium titanate and Zn-Cr-LDH (~ 1 m ² g ^-1 ).

The observed dependence of the surface area according to the composition can be understood as follows: ZCT-1 sample synthesized with the charge-balance ratio forms a well-aligned heterogeneous layer between the LDH and the titanium oxide nanosheet . Other nanohydrides with the reactant fraction deviating from the charge-balance composition have a more porous and open structure due to the charge mismatch between the two nanosheets compared to the ZCT-1.

The pore size of the nanohybrid was analyzed based on the Barrett-Joyner-Halenda (BJH) method. As shown in Fig. 7, all of the above-mentioned nanohybrids commonly have a mesopore with an average diameter of 3.3-3.9 nm.

In view of the pore size and interlayer spacing of the nanohybrid, the observed mesopores should be derived from the laminate structure of the nanohybrid crystals.

<Diffuse reflection UV-vis and PL spectroscopy of ZCT nanohybrid and determination of band structure>

The electronic structure and optical static characteristics of the ZCT nanohybrid were measured by diffuse reflection UV-vis spectroscopy. As shown in Fig. 8, the pure Zn-Cr-LDH material exhibits two strong absorption peaks at 2.2 and 3.0 eV corresponding to the dd transition of trivalent chromium ions. As a result of hybridization with Zn-Cr-LDH, the resulting nanohybrid materials commonly exhibit strong absorption of visible radiation with two absorption characteristics in common, and this results in the laminated titanium oxide and the Zn-Cr-LDH nano Exhibit effective electron coupling between sheets. The strong absorption of the observed visible light suggests the potential functionality of the ZCT nanohybrid as a visible light active photocatalyst.

Changes in the PL signal due to the hybridization were monitored for electron transfer observations between Zn-Cr-LDH and deposited titanium oxide. As shown on the left side of FIG. 9, the PL signal of the pure Zn-Cr-LDH was significantly weakened after hybridization with the laminated tinate, indicating a remarkable reduction in electron-hole recombination. In addition, the observed PL intensities of all the ZCT nanohybrids were much weaker than the PL intensities of the purely deposited titanium oxides, confirming the reduction of electron-hole recombination due to hybridization. This phenomenon is caused by electron transfer between Zn-Cr-LDH and deposited titanium oxide, which leads to spatial separation of electrons and holes. The reduction of the resultant electron-hole re-ply is certainly advantageous for the improvement of the photocatalytic activity.

To understand the electron transition between Zn-Cr-LDH and deposited titanium oxide, the band structure of Zn-Cr-LDH was measured from the results of electrochemical CV measurement and UV-vis spectroscopy. The lowest unfilled interband state position resulting in the first absorption peak at ~2.2 eV in the UV-vis spectrum of Zn-Cr-LDH is the on-set potential of the reduction peak in the CV data on-set potential.

9, the Zn-Cr-LDH has an absorption peak at ~ 3.0 eV in the UV-vis spectrum as in the case of the conduction band (CB), as compared with the CB of the laminated titanium oxide component A higher position is shown for the corresponding upper interband state. The photo-generated electrons in the Zn-Cr-LDH can be transferred into the CB of the deposited titanium oxide, which leads to spatial separation of electrons and holes. The resulting decrease in electron-hole recombination causes an observed decrease in PL intensity after the hybridization.

<Photocatalytic activity test for ZCT nanohybrid>

The photocatalytic activity of the ZCT nanohybrid was studied by monitoring time-dependent O ₂ production under visible light irradiation (?> 420 nm). To clearly demonstrate the effect of activation on the photocatalytic activity, the O ₂ product by the pure Zn-Cr-LDH and the deposited titanium oxide was also investigated.

As shown in the left side of FIG. 10, the pure Zn-Cr-LDH is a visible light-induced O ₂ Production, which is consistent with recent reports on this phase. Conversely, the deposited titanium oxide is photocatalytically inert under given conditions because of its wide bandgap nature.

After hybridization with the laminated titanium oxide, the high photocatalytic activity of the Zn-Cr-LDH material was significantly improved over the applied ratio of the deposited titanium oxide / Zn-Cr-LDH. Although the hybridization with the deposited titanium oxide reduces the content of the Zn-Cr-LDH phase in the final product, the O ₂ of the ZCT-1 nanohybrid The rate of formation (1.18 mmol h ^-1 g ^-1 ) was almost the same as the O ₂ of pure Zn-Cr-LDH (0.67 mmol h ^-1 g ^-1 ). Due to the considerable difference between the experimental conditions adopted in this and the previous literature, it is difficult to directly compare the activity of other efficient photocatalysts so far reported with the photocatalytic activity of the ZCT nanohybrid. However, a pure Zn-Cr-LDH phases visible light-induced O ₂ as viewed in consideration of the fact that one of the most effective photocatalyst for the production, also the nanohybrid the ZCT is a mineral oil having an improved photocatalytic activity O ₂ Can be regarded as a highly efficient visible light photocatalyst for production.

The improvement in photocatalytic activity observed after the hybridization can be attributed to the electron coupling and the expansion of the surface area between the two semiconducting nanosheets. As evidenced by the results of PL and band structure measurements (Fig. 9), the electron coupling between the deposited titanium oxide and the Zn-Cr-LDH leads to spatial separation of the light-induced holes and electrons, Leading to a reduction in hole recombination.

Further, the surface increase due to the hybridization may further contribute to enhancement of photocatalytic activity through provision of more reaction sites. Among the Nanohae briides, the ZCT-1 nanohybrid with smaller surface area has greater photocatalytic activity than the other nanohybrid. Moreover, such higher performance of the material can be attributed to the higher content of Zn-Cr-LDH nanosheets, as well as the more ordered hybrid structure, which makes it easier to transport holes to the reaction site and effective electron- Results.

<Chemical stability test for ZCT nanohybrid>

The effect of hybridization using the deposited titanium oxide on the chemical stability of the Zn-Cr-LDH can be evaluated by comparing the ZCT-1 nanohybrid and the pure Zn-Cr-LDH in an acidic medium, Lt; RTI ID = 0.0 &gt; time-dependent &lt; / RTI &gt; dissolution of the ions.

For the stability test, 0.019 g of Zn-Cr-LDH was reacted with 20 mL of an acidic buffer solution having pH = 2, while 0.03 g of the ZCT nanohybrid containing the same amount of Zn ions was used. Compared to the original pure Zn-Cr-LDH showing significant leaching of Zn ions, the ZCT-1 nanohybrid exhibits less dissolution of Zn ions. Due to the presence of surface-exposed Zn-Cr-LDH, the ZCT nanohybrid exhibits a remarkable elution of Zn ions at an early stage of the stability test. As the reaction process progresses, however, the elution of Zn ions from the ZCT nanohybrid is significantly reduced, which results in a greater solubility difference between the nanohybrid and the pure LDH material. The results provide strong evidence for a significant improvement in the chemical stability of the Zn-Cr-LDH due to the protection of the highly stable titanium oxide layer. Considering that the weak stability of the Zn-Cr-LDH phase inhibits the use of these photocatalytic materials in the acidic medium, the formation of the hetero-laminated nanohybrid with the deposited titanium oxide is very useful for extending the application field of the LDH material Method can be provided.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the present invention is not limited to the disclosed exemplary embodiments and the exemplary embodiments, but may be modified in various forms. It is evident that many variations are possible by the possessors.

Claims (20)

Layered double hydroxide (LDH) nanosheet having a surface charge opposite to that of the metal oxide nanosheet,
Wherein the metal layered double hydroxide nanosheet comprises a metal layered double hydroxide represented by the following general formula 1,
And a mesopore formed between the self-assembled nanosheets.
Mesoporous layered nanohybrid:
[Formula 1]
[M ^II _(1-x) M ^III _x (OH) ₂ ] [A ^n- ] _{x / n} .zH ₂ O;
In the general formula 1,
M &lt; ^{II &gt;} is a +2 valent metal cation,
M ^III is a +3 metal cation,
A ^n- is an anion selected from the group consisting of hydroxide ion (OH ^- ), nitrate ion (NO ₃ ^- ), PO ₄ ^3- , HPO ₄ ^2- , H ₂ PO ₄ ^-
0 &lt; x &lt; 1,
z is a number of from 0.1 to 15;
delete The method according to claim 1,
^Wherein M ^II comprises a metal cation selected from the group consisting of Ca ²⁺ , Mg ²⁺ , Zn ²⁺ , Ni ²⁺ , Mn ²⁺ , Co ²⁺ , Fe ²⁺ , Cu ²⁺ , ^Wherein M ^III comprises a metal cation selected from the group consisting of Fe ³⁺ , Al ³⁺ , Cr ³⁺ , Mn ³⁺ , Ga ³⁺ , Co ³⁺ , Ni ³⁺ and combinations thereof. Layered nanohybrid.
The method according to claim 1,
Wherein the metal oxide of the metal oxide nanosheet comprises a metal oxide semiconductor.
5. The method of claim 4,
The metal oxide semiconductor may be at least one selected from the group consisting of Ti, Ni, Cu, Zr, Sr, Zn, In, Yr, La, V, Mo, W, Sn, Nb, Mg, Al, Y, Sc, Sm, Pd, Ga, Wherein the metal nanoparticles comprise an oxide of a metal selected from the group consisting of metal nanoparticles.
The method according to claim 1,
The metal layered double hydroxide has the nanosheets in the general formula 1 wherein M ^II is Zn ²⁺ and M ^III comprises the Cr ³⁺ is a metal layered double hydroxide having a surface positive charge (Zn-Cr-LDH), the Wherein the metal oxide nanosheet comprises a titanium oxide nanosheet having a surface negative charge.
The method according to claim 1,
Wherein the metal layered double hydroxide nanosheets absorb visible light.
The method according to claim 1,
Wherein the mesoporous layered nanohybrid has a structure of a porous two-dimensional layer structure or a house-of-card form.
The method according to claim 1,
Wherein the mesoporous layered nanohybrid has improved chemical stability.
The method according to claim 1,
Wherein the molar ratio of the metal layered double hydroxide to the metal oxide nanosheets is 1: 0.1 to 100. The mesoporous layered nanohybrid according to claim 1,
A photocatalyst comprising a mesoporous layered nanohybrid according to any one of claims 1 to 10.
12. The method of claim 11,
Wherein the photocatalyst absorbs visible light.
12. The method of claim 11,
Wherein the photocatalyst has catalytic activity for water decomposition under visible light irradiation.
Preparing a first nanosheet dispersion containing a metal layered double hydroxide nanosheet having surface charge;
Preparing a second nanosheet dispersion containing a metal oxide nanosheet having a surface charge opposite to that of the metal layered double hydroxide nanosheet;
And the mesoporous layered nanohybrid is formed by mixing the first nanosheet dispersion and the second nanosheet dispersion to self-assemble the metal layered double hydroxide nanosheets and the metal oxide nanosheets
/ RTI &gt;
Wherein the metal layered double hydroxide nanosheet comprises a metal layered double hydroxide represented by the following general formula 1:
Method for producing mesoporous layered nanohybrid:
[Formula 1]
[M ^II _(1-x) M ^III _x (OH) ₂ ] [A ^n- ] _{x / n} .zH ₂ O;
In the general formula 1,
M &lt; ^{II &gt;} is a +2 valent metal cation,
M ^III is a +3 metal cation,
A ^n- is an anion selected from the group consisting of hydroxide ion (OH ^- ), nitrate ion (NO ₃ ^- ), PO ₄ ^3- , HPO ₄ ^2- , H ₂ PO ₄ ^-
0 &lt; x &lt; 1,
z is a number of from 0.1 to 15;
delete 15. The method of claim 14,
^Wherein M ^II comprises a metal cation selected from the group consisting of Ca ²⁺ , Mg ²⁺ , Zn ²⁺ , Ni ²⁺ , Mn ²⁺ , Co ²⁺ , Fe ²⁺ , Cu ²⁺ , ^Wherein M ^III comprises a metal cation selected from the group consisting of Fe ³⁺ , Al ³⁺ , Cr ³⁺ , Mn ³⁺ , Ga ³⁺ , Co ³⁺ , Ni ³⁺ and combinations thereof. A method for producing a layered nanohybrid.
15. The method of claim 14,
Wherein the metal oxide of the metal oxide nanosheet comprises a metal oxide semiconductor. &Lt; RTI ID = 0.0 &gt; 21. &lt; / RTI &gt;
18. The method of claim 17,
The metal oxide semiconductor may be at least one selected from the group consisting of Ti, Ni, Cu, Zr, Sr, Zn, In, Yr, La, V, Mo, W, Sn, Nb, Mg, Al, Y, Sc, Sm, Pd, Ga, And a metal oxide selected from the group consisting of a metal oxide and a metal oxide.
15. The method of claim 14,
The metal layered double hydroxide has the nanosheets in the general formula 1 wherein M ^II is Zn ²⁺ and M ^III comprises the Cr ³⁺ is a metal layered double hydroxide having a surface positive charge (Zn-Cr-LDH), the Wherein the metal oxide nanosheet comprises a titanium oxide nanosheet having a surface negative charge.
15. The method of claim 14,
Wherein the molar ratio of the metal layered double hydroxide to the metal oxide nanosheets is 1: 0.1 to 10.

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