KR101703124B1 - Method for Preparation of Zn-Al Layered Double Hydroxide Nanosheets - Google Patents

Abstract

The present invention relates to a manufacturing method of a Zn-Al layered double hydroxide nanosheet which is simple, economical, environmentally friendly, and easily applicable to mass production and, more specifically, relates to a manufacturing method of a Zn-Al layered double hydroxide nanosheet of a chemical formula of [Zn_(1-x)Al_x (OH)_2]^(x+)CO_3^(2-)_(x/2n)H_2O comprising: (A) a step of forming a ZnO (AZO) thin film on which aluminum is doped on a board; and (B) a step of dipping the AZO thin film into a carbonated water.

Description

[0001] The present invention relates to a Zn-Al layered double hydroxide nanosheets,

The present invention relates to a method for producing a Zn-Al layered double hydroxide nanosheet which is simple, economical, environmentally friendly and easy to apply to mass production.

A layered double hydroxide (hereinafter referred to as "LDH") is a layered material having an unusual structure in which an anion layer which balances a charge is interposed between cationic layers and a weakly bonded structure, and has the general formula [M ²⁺ _{1 ^{-x M 3+ x (OH) 2}} ] can be represented by _{^{x + (x n-) x /}} n · yH 2 O. Since the anions interposed between layers can be easily replaced by ion exchange, not only anions from organic anions such as Cl ^- , CO ₃ ^2- , organic anions such as benzoates and succinates, but also complex substances such as DNA, Can be achieved.

LDH is easy to control the composition and has not only anion exchange ability but also high adsorption power, biocompatibility and stability. These unique properties are utilized in a wide range of fields such as catalysts, ion exchangers, adsorbents, ceramic precursors, drug carriers, electrodes, films, optical storage elements, separating agents, and synthesis of organic-inorganic nano blends. As a specific example, it is possible to use a drug as a drug delivery material by intercalating a drug into a layered double hydroxide, thereby preparing a sustained-release preparation that slows the release rate of the drug in the body, Can be used.

So far various methods have been suggested for the production of LDH (Nalawade et al.). The most widely used method of producing LDH is hydrothermal method or co-precipitation method. The hydrothermal method involves dissolving nitrate, acetate or hydrochloride of divalent metal and trivalent metal in water and reacting with heat and pressure for several hours to several days. The reaction conditions are vigorous and it takes a long time to react. The coprecipitation method uses an alkaline substance such as NH ₄ OH, NaOH or KOH instead of relaxing the reaction conditions of heat and pressure in the hydrothermal method. Although the reaction temperature and pressure are lower than that of the hydrothermal method, it is still required to be heat-treated at 60 to 80 ° C for several hours to several days, and the manufacturing process is complex such that the metal salt mixture is added dropwise for several hours. Recently, Wang et al. Reported that Mg-Al LDH was grown at room temperature on Al sheet using MgCl ₂ solution and NaOH. However, since the reaction time is 18 hours and the acidic MgCl ₂ solution and the strong basic salt solution are used, there remains a problem that a weak substrate can not be used for acid or base.

On the other hand, the rapidly increasing concentration of carbon dioxide in the atmosphere is becoming one of the most important environmental problems. Emissions of carbon dioxide from combustion of coal, oil, and natural gas are expected to increase further as economic growth and industry developments progress. Therefore, a technology capable of capturing and removing carbon dioxide from a carbon dioxide emission source and reducing the emission of carbon dioxide is very important. In addition, many researchers have reported using the emitted carbon dioxide for electrochemical reactions, plasma, and photocatalytic synthesis.

Narawade et al., J. Sci. Ind. Res. 68, 267-272 (2009). Wang et al., Sci. Rep. 4, 6606-6613 (2014).

It is an object of the present invention to provide a method of manufacturing an LDH nanosheet in a short period of time by a simple process under mild conditions in order to overcome the problems of the prior art as described above.

Another object of the present invention is to provide a process for producing an environmentally friendly LDH nanosheet that does not cause environmental problems because chemical substances are not used or discharged.

According to an aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: (A) forming a ZnO thin film (AZO thin film) doped with aluminum (Al) on a substrate; Formula of _{[Zn 1-x Al x (} OH) 2] x + (CO 3 2-) x / 2 · nH 2 O comprising the; and (B) immersing the AZO thin film on soda (LDH) nanosheet having a Zn-Al layered double hydroxide (LDH) nanosheet.

Where x is greater than 0 and less than 1, and n is a positive number.

In the present invention, "carbonated water" refers to "water in which carbon dioxide is dissolved" and means that carbonic acid-derived CO ₃ ^2- is present in water as a simple source of charge balance anions. Even if DI water or distilled water is left in the air, the carbon dioxide in the air dissolves in water, and carbonic acid-derived CO ₃ ^2- is present in the water even if the process does not include the step of separately dissolving carbon dioxide in water. In the present invention, carbonic acid water having a concentration of CO ₃ ^2- sufficient to dissolve carbon dioxide in the air is sufficient. Thus, although it is described as "carbonated water ", it is possible to produce Zn-Al LDH nanosheets simply by immersing the AZO thin film in water placed in the air, unless the reaction is carried out in the presence of nitrogen or helium gas will be. It is, of course, also possible to use carbonic acid water separately dissolved by adding carbon dioxide to water.

The substrate is only for AZO thin film formation and does not affect the growth of Zn-Al LDH nanosheet, so that it is not affected by the material or shape if it can form AZO thin film. That is, any of a polymer resin, glass, and metal may be used. In the following example, an upper AZO thin film of an AZO / Au / AZO / PET (or glass) substrate, which is generally used as an electrode, However, it is only intended to directly apply the manufactured nanosheets to the device without forming a separate electrode, but it is also possible to form the AZO thin film on the polymer resin or glass and immerse the nanosheet in carbonated water, .

The AZO thin film may be formed by any conventionally known method. The present invention relates to a method of producing an AZO thin film by itself, in which the AZO thin film produces Zn-Al LDH nanosheets in water (carbonated water) in which carbon dioxide is dissolved, and the production method of the AZO thin film is widely known It will be easy for those skilled in the art to form the AZO thin film by a suitable method based on the prior art. Therefore, detailed description of the AZO thin film manufacturing method is omitted.

At this time, the doping amount of Al in the AZO thin film is preferably 3 to 20 at%. When the doping amount of Al is less than 3 at% or more than 20 at%, the growth of the LDH nanosheet is not smooth.

The thickness of the AZO thin film is preferably 30 to 100 nm. Since the Zn-Al nanosheets are produced from AZO thin films, if the thickness of the AZO thin films is too thin, the supply of Al for generating nanosheets may be insufficient and growth of the nanosheets may be restricted. Thickness of the AZO thin film is greater than 100 nm is not a problem for growth of the nanosheet. However, even if the thickness of the AZO thin film is increased, the thickness of the remaining AZO thin film is increased only after the LDH nanosheet is formed. The thickness of the AZO thin film may be about 100 nm if the growth of the LDH nanosheet is considered, not the additional benefit of thickening the thin film.

In the production method of the Zn-Al LDH nanosheet of the present invention, the charge balance anion is derived from carbon dioxide, that is, carbon dioxide dissolved in water. The solubility of carbon dioxide is inversely proportional to the temperature of water. Therefore, if the water temperature is too high, the concentration of CO ₃ ^{2- in} the water becomes low, which is not good for Zn-Al LDH nanosheet growth. According to the result of the growth test of the nanosheet according to the temperature, the temperature of the carbonated water in the step (B) is preferably 1 to 35 ° C, and no nanosheets are observed at 40 ° C (data not shown). This is probably due to the lower concentration of CO ₃ ^2- dissolved in the carbonated water as the temperature increases. Most preferably, considering the economics of the process The AZO thin film is immersed at room temperature without any additional cooling or elevated temperature.

The growth time of the Zn-Al LDH nanosheet according to the present invention is very fast. In the following examples, Zn-Al LDH nanosheets were grown five minutes after the AZO thin film was immersed in carbonated water. The growth rate of the Zn-Al LDH nanosheets was estimated from the pH change with the immersion time, It can be seen that a nanosheet is formed. As the Zn-Al LDH nanosheets grew, the thickness of the nanosheets gradually increased, the density of the nanosheets increased, and the size of the nanosheet particles increased. After a certain period of time, there was no significant change in thickness or density.

The Zn-Al LDH nanosheets produced by the present invention have a chemical formula of [Zn _1-x Al _x (OH) ₂ ] ^{x +} (CO ₃ ^2- ) _{x / 2} .nH ₂ O. Where x is greater than 0 and less than 1, and n is a positive number. In particular, the ZnO-Al LDH nanosheets prepared under the same conditions were Zn ₆ Al ₂ (OH) ₁₆ (where x = 0.25 and n = 0.5) were prepared by immersing the 10AZO thin film in water for 2 hours CO ₃₎ was confirmed that having the formula ^2- · 4H ₂ O. The LDH nanowire can be used as a precursor for the preparation of an LDH containing other anions as a charge balancing anion by the ion exchange method since the charge balance anions can be easily exchanged due to their characteristics. Examples of other anions include inorganic anions, biological materials such as DNA, organic materials such as drugs, nanoparticles modified with anion groups, and quantum dots, but the present invention is not limited thereto. Since modification of LDH by exchange of charge balanced anion has been variously introduced in the prior art, detailed description is omitted in the present invention (ex, Nalawade et al., Zhaoping Liu et al., J. Am. Chem. Soc. -7880, 2006).

The Zn-Al LDH nanosheets produced by the method of the present invention can be used on its own or as separate Zn-Al LDH nanosheets separated from the substrate.

The method may further include a step of heat-treating the Zn-Al LDH nanosheet produced by the step (B) after the step (B). The heat treatment can be performed in a state in which the Zn-Al LDH nanosheets are grown on the substrate, or in a state where the nanostructures are peeled off the substrate. The heat treatment temperature is preferably 100 to 150 ° C. According to the heat treatment, water present between the LDH layers appears to be removed, and the crystallinity of the nanosheet is further improved to have a single crystallinity. If the temperature is too low, the effect of removing water or increasing the crystallinity due to the heat treatment is not sufficient, and if the heat treatment is too high, the structure of the LDH may be broken.

As described above, according to the present invention, LDH nanosheets can be produced in a short time by simply dipping AZO thin film in water, so that LDH can be produced economically, which can be applied to various fields but has a complicated manufacturing process and limited application This makes it possible to further extend the application field of LDH.

Further, the LDH production method of the present invention is meaningful as an environmentally friendly method because it uses not only the use of chemicals or pollutants but also the carbon dioxide in the air, which is an important problem in the environmental field.

In addition, the LDH nanosheets produced by the present invention can be easily used as a precursor of LDH having various charge balance anions since the charge balance anions can be easily replaced by anion exchange.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a SEM surface image photograph showing the effect of Al doping on the formation of nanosheets.
Figure 2 is an SEM surface image photograph showing the effect of immersion time on the production of nanosheets.
Fig. 3 is a SEM image showing the effect of the formation of LDH nanosheets due to the increase in the thickness of the upper AZO thin film.
4 is an image photograph and a graph showing TEM and EDS analysis results for analyzing the components of the nanosheet.
5 is an X-ray diffraction spectrum of a Zn-Al LDH nanosheet.
6 shows FT-IR spectra of AZO thin films and Zn-Al LDH nanosheets.
7 is a graph showing the pH change of the saliva index due to the formation of Zn-Al LDH.
FIG. 8 is a photograph showing the results of TEM and EDS analysis showing the crystallinity of Zn-Al LDH nanosheets before and after heat treatment. FIG.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the drawings and the embodiments are only illustrative of the contents and scope of the technical idea of the present invention, and the technical scope of the present invention is not limited or changed. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the technical idea of the present invention based on these examples.

[Example]

Example 1: Growth of Zn-Al LDH nanosheet

The PET or glass substrate was cleaned and the surface was removed using nitrogen gas. AZO thin films were deposited at room temperature using rf sputtering method. The ZnO target doped with 3 ~ 30 at% Al was sintered at 1500 ℃ using a ceramic process (purity 99.99%) when AZO target (2 inch diameter) was deposited. The rf power applied to the target was maintained at 100 W, the working pressure was maintained at 0.13 Pa, the deposition rate was about 1 nm / min, and a sputtering gas of 10 sccm (standard cc / min) was used. The thickness of AZO thin film was controlled by deposition time.

The Au thin film was deposited in-situ on AZO thin film using dc sputtering method at room temperature to a thickness of 10 nm. The dc power applied to the target was 20 W, the working pressure was 0.39 Pa, the deposition rate was about 15 nm / min, and the sputtering gas was 10 sccm (standard cc / min) of Ar gas was used.

Then, the AZO thin film was deposited on the Au thin film layer under the same conditions as the formation of the AZO thin film to complete the AZO / Ag / AZO multilayer thin film.

The AZO / Au / AZO multilayer thin film prepared by the above method was immersed in DI water which was allowed to stand at room temperature (23 ° C) for 1 hour for 30 minutes to 3 hours to allow the LDH nanosheet to grow.

Example 2: Analysis of Zn-Al LDH nanosheets

1) Analysis of nanosheet growth by Al doping amount

AZO (60 nm) / Au (10 nm) / AZO (30 nm) / PET substrate prepared using a ZnO target doped with 3 to 30 at% of Al was left in the atmosphere for about 1 hour by the method of Example 1 DI water for 2 hours and then the surface was observed using a scanning electron microscope (SEM). FIG. 1 is a surface image of a substrate according to an amount of Al doping, and FIGS. 3A to 3E are surface images of AZO thin films doped with 0, 3, 10, 20 and 30% Al, respectively. It was confirmed that the nanosheets were grown on the surface by the DI water treatment in the 3AZO to 20AZO thin film (Fig. 1 (B) to (D)). The thickness of the nanosheet was approximately 800 to 900 nm regardless of the doping amount of Al. On the other hand, no nanosheet was formed in ZnO thin film (A) and 30AZO thin film (E).

2) Analysis of nanosheet growth with immersion time

The growth of the nanosheets was observed by SEM while changing the time for immersing 10 AZO (60 nm) / Au (10 nm) / 10 AZO (30 nm) / PET substrate in DI water to 5 minutes to 180 minutes, .

From FIG. 2, the nanosheets were already grown only after immersion for 5 minutes. After that, the nanosheets were gradually thickened as the nanosheets grew. However, after 90 minutes of immersion, the density, thickness and height did not change much. Unless otherwise noted, the following examples were analyzed using nanosheets grown by immersing 10 AzO (60 nm) / Au (10 nm) / 10 AzO (30 nm) / PET substrate for 2 hours.

3) Analysis of growth of nanosheet by thickness of AZO thin film

The change in height of the nanosheets was observed according to the thickness of the substrate by immersing the substrate in DI water for 2 hours using a 10AZO (90nm) / Au (10nm) / 10AZO (30nm) / PET substrate.

FIG. 3 is a SEM image of an LDH nanosheet formed by an upper AZO thin film of 90 nm. It was observed that the upper AZO thin film was thicker than the LDH nanosheet prepared by the upper AZO thin film of 60 nm, but the height of the nanosheet itself was increased I did.

4) Analysis of composition and crystallinity of nanosheet

The nanosheets were separated from the substrate and analyzed by TEM and Energy Dispersive Spectroscopy (EDS) to identify the constituents of the nanosheets. The separated nanosheets were divided into two areas (area 2) between nanosheet (area 1), nanosheet and AZO thin film, and EDS analysis was performed. FIG. 4 is an image and a graph showing the results of TEM and EDS analysis, and Table 1 shows the content ratio (at.%) Of each element by EDS analysis.

From the above analysis results, it was confirmed that the nanosheet had a composition of Zn ₆ Al ₂ (OH) ₁₆ (CO ₃ ^2- ) .4H ₂ O. On the other hand, only a small amount (~ 0.6 at%) of Al was detected in the interface region (area 2) compared to the Zn content. This suggests that the Al contained in the AZO thin film is continuously used in the growth of the Zn-Al LDH nanosheet to lower the Al concentration at the interface.

Crystallization was confirmed by X-ray spectroscopy of the nanosheet separated from the AZO thin film. The X-ray diffraction spectrum of FIG. 5 shows a crystalline form with polycrystalline properties. The composition of this nanosheet corresponds to XRD JCPDS number 38-0486.

The presence of CO ₃ ^2- as an anion component of the present nanosheet can be confirmed by FT-IR spectroscopy. Fig. 6 is an FT-IR spectrum of the AZO thin film after immersing the nanosheet in water before and after immersion in water. In the nanosheet grown by immersing the AZO thin film in water, a sharp peak of 1358 cm ^-1 , which is not observed in the AZO thin film, is observed, which corresponds to the vibration absorption peak of CO ₃ ^2- .

Since no separate reagent for the supply of CO ₃ ^2- was used, it was assumed that the carbon dioxide dissolved in the water served as the source of CO ₃ ^2- . Because the carbon dioxide in the air is dissolved in water to produce carbonic acid (H ₂ CO ₃ ), the freshly purified DI water changes to acidic over time. If the carbon dioxide dissolved in the water is a source of CO ₃ ^2- , the concentration of carbonic acid present in the water will decrease due to the growth of the nanosheets, so that the pH will increase. By measuring the pH of the DI water during the nanosheet growth process It was confirmed that the source of CO ₃ ^2- is carbon dioxide in the air.

First, metal ions in water were detected by ICP (inductively coupled plasma) in order to exclude the possibility that the pH of the water changes due to the elution of metal ions by immersing the thin film in water. In the case of 3AZO thin film and 10AZO thin film, since the Zn ion was detected when the thin film was immersed in water for 1 day, the pH change was measured using 20AZO thin film in which Zn ion was not detected. FIG. 7 is a graph showing the results of pH measured over time while repeatedly immersing 3 20AZO thin films of 1 x 1 cm 2 area in 15 mL of DI water.

The DI water (pH = 7.0) decreased the pH to 5.70 due to the dissolution of carbon dioxide in the air. When the 20AZO thin film specimen was immersed in it, the pH gradually increased to 6.74 in 3 hours. This seems to be due to the use of CO ₃ ^2- in the solution for the preparation of nanosheets. When the AZO specimen was removed after 3 hours, the pH was decreased again by the dissolution of carbon dioxide. When the 20AZO thin film specimen was immersed again, the pH increased to 6.85 again.

This means that CO ₃ ^2- , an anion of LDH nanosheets, is derived from carbon dioxide in the air, which is dissolved in water.

Example 3: Heat treatment of Zn-Al LDH nanosheets

Zn-Al LDH nanosheets. The Zn-Al LDH nanosheets prepared in Example 1 were heat-treated at 150 ° C for 1 hour in an oxygen atmosphere and specimens were prepared by a focused ion beam (FIB) process, and cross-sections were observed with a transmission electron microscope. 8 (a) is an image showing the nano-beam diffraction pattern and the EDS analysis result of the nanosheet prepared in Example 1. The constituent components Al, Zn, O, and C are evenly distributed along the nanosheet, Show that you have sex. On the other hand, it can be seen that the nanosheet after heat treatment for 1 hour has single crystallinity from the nano-beam diffraction pattern (b-1) (Fig. 8 (b)). The crystals grow in the [001] direction and the inter-lattice spacing is 0.26 nm from the high resolution (HR) TEM image (b-2). In order to clarify the crystallinity of the heat treated nanosheet, ZnO crystals and crystal characteristics were compared. (b-3) is a nano-beam diffraction pattern of ZnO nanocrystals showing a rhombohedral structure with a {100} inter-lattice spacing of 0.28 nm. Based on the crystallinity of ZnO, the axis of each side of the LDH has a rhombohedral structure (b-4) slightly longer than the ZnO crystal.

Claims (10)

(A) forming a ZnO thin film (AZO thin film) doped with Al on a substrate; And
(B) immersing the AZO thin film in carbonated water;
(LDH) nanosheet having the formula of Zn _1-x Al _x (OH) ₂ (CO ₃ ) _{x / 2} ^{2 -} nH ₂ O.
Where x is greater than 0 and less than 1, and n is a positive number.
The method according to claim 1,
Wherein the doping amount of Al in the AZO thin film is 3 to 20 at%.
The method according to claim 1,
Wherein the thickness of the AZO thin film is 30 to 100 nm.
The method according to claim 1,
Wherein the temperature of the carbonated water in step (B) is 1 to 35 占 폚.
The method according to claim 1,
Wherein the immersing in the carbonated water in the step (B) is performed for 1 minute to 3 hours.
The method according to claim 1,
The Zn-Al LDH nanosheets is x = 0.25 and n = 0.5 _{in, Zn 6 Al 2 (OH)} 16 (CO 3) 2- · 4H 2 O in the Zn-Al LDH nanosheets, characterized in that having the formula Gt;
The method according to claim 1,
(C) peeling the Zn-Al LDH nanosheet produced by the step (B) from the substrate;
Wherein the Zn-Al LDH nanosheets are formed on the substrate.
8. The method according to any one of claims 1 to 7,
(D) heat-treating the Zn-Al LDH nanosheet prepared in the step (B) and subsequent to the step (B);
Wherein the Zn-Al LDH nanosheets are formed on the substrate.
9. The method of claim 8,
Wherein the heat treatment is performed at 100 to 150 ° C.
9. The method of claim 8,
Wherein the Zn-Al LDH nanosheet after the heat treatment has monocrystalline properties.

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