KR20100138171A - Preparation method of bismuth telluride nanostructures having various morphology by hydrothermal synthesis and bismuth telluride nanostructures - Google Patents

Abstract

PURPOSE: A producing method of a bismuth telluride nanostructure, and the bismuth telluride nanostructure are provided to obtain the high thermoelectric performance value. CONSTITUTION: A producing method of a bismuth telluride nanostructure with various shapes comprises the following steps: melting bismuth chloride and tellurium powder to distilled water, separately, and mixing; heat-processing the mixed solution; and synthesizing the bismuth telluride nanostructure with the solution. The bismuth telluride nanostructure is formed in a shape selected from the group consisting of a nanoparticle, a nanocapsule, a nanowire, and a nanotube.

Description

Preparation method of bismuth telluride nanostructures having various morphology by hydrothermal synthesis and bismuth telluride nanostructures

The present invention relates to various types of bismuth telluride (Bi ₂ Te ₃₎ method of manufacturing a nano-structure and hence the variety of bismuth telluride (Bi ₂ Te ₃₎ nano-structure made by using the hydrothermal method.

A thermoelectric material is a material that generates heat or cools at both ends of a material junction when an electric field is formed or a current flows due to the movement of charges due to temperature difference. Thermoelectric phenomena began in the early 1900s, and research has been carried out to ensure that the former Soviet Union loffe achieves about 4% conversion efficiency. These thermoelectrics can be classified into the Seebeck effect of obtaining electromotive force by using the temperature difference between both ends, the Peltier effect of generating heat or cooling at both ends by electromotive force, and the Tomson effect of generating electromotive force by the temperature difference between conductors. By using such thermoelectric materials, thermoelectric devices capable of directly converting thermal energy and electrical energy can be developed. In order to protect the environment, the development of various cooling systems using thermoelectric materials that can be cooled without using refrigerant and thermoelectric power generation using waste heat are emerging as promising fields.

The properties of the thermoelectric material are summarized by the formula of so-called merit (Z), and can be generally represented by ZT as shown in Equation 1 below.

[Equation 1]

ZT = S ² σT / k

In Equation 1, S is a Seebeck coefficient, σ is an electrical conductivity, T is an absolute temperature, and k is a thermal conductivity. As can be seen in Equation 1, the thermoelectric performance index (ZT) should be large to obtain a thermoelectric material having excellent thermoelectric efficiency. Therefore, in order to manufacture a thermoelectric material having excellent thermoelectric efficiency, the electrical conductivity and the Seebeck coefficient should be large while the thermal conductivity should be low.

To date, thermoelectric devices have a low conversion efficiency (ZT <1) due to the correlation between Seebeck coefficient, electrical conductivity, and thermal conductivity, which determine the ZT in bulk materials. . In 1993, Dresselhaus of MIT University proposed theoretically that thermoelectric materials could be improved by manufacturing low-temperature nanostructures with quantum dots and superlattices (LD Hicks and MS Dresselhaus, “Effect of Quantumwell Structures on”). the Thermoelectric Figure of Merit, ”Physical Review B, Vol. 47, 1993, p. 12767; LD Hicks and MS Dresselhaus,“ Thermoelectric Figure of Merit of a One-dimensional Conductor, ”Physical Review B, Vol. 47, 1993, p.16631). As nanotechnology advances, nanomaterials can independently control Seebeck coefficient, electrical conductivity, and thermal conductivity, so that they can expect more than 30% of the thermoelectric performance index (ZT> 3), which is the efficiency of current energy conversion systems. It has been predicted.

Bimetallic bismuth (Bi) has several unique transport properties due to asymmetric anisotropic fermi surfaces, long mean free paths (I), and small effective mass (m *). Due to this active research is being conducted. In addition, bismuth has excellent thermoelectric properties, and in particular, in the one-dimensional nanowires, unlike the bulk type, bismuth exhibits both Seebeck efficiency and low thermal conductivity, thereby exhibiting excellent thermoelectric properties.

In particular, Bi _x Te _{1 -x} , an alloy of bismuth and tellurium, has a large mass and has a small spring constant due to the covalent bond between bismuth and tellurium with a van der Waals bond and tellurium, thereby reducing thermal conductivity. As a result, it is possible to increase the performance index (ZT) indicating the thermoelectric characteristics of the thermoelectric material, which is currently used as a thermoelectric material. In addition, by manufacturing the Bi _x Te _{1 -x} alloy as a thermoelectric nanostructure, it is possible to control the electron energy level density, and matching the shape and peak position of the electron energy level density function to the Fermi level affects the thermoelectric effect. The note will be able to adjust the Seebeck coefficient. In addition, the quantum confinement effect can increase the electronic motion to maintain a high electrical conductivity to overcome the limitations of the bulk thermoelectric material and obtain a relatively large thermoelectric performance index.

However, most of the bismuth telluride thermoelectrics to date are either polycrystalline nanowires or rod-based structures. Bismuth telluride is known to exhibit anisotropy with high electrical conductivity and thermal conductivity depending on the crystal direction due to its structural characteristics, and it is expected that anisotropy of electrical conductivity and thermal conductivity will be greater in the nano domain.

Therefore, the present inventors are studying to develop a bismuth telluride thermoelectric element having a high thermoelectric performance index, and the single crystal structure as a nanostructure by changing the heat treatment temperature or the temperature increase rate in the process of manufacturing the non-sumutal tellurium thermoelectric element using the hydrothermal synthesis method. It was found that the nanoparticles, nanocapsules, nanowires and nanotubes of the present invention was completed.

It is an object of the present invention to provide a method for preparing bismuth telluride (Bi ₂ Te ₃ ) nanostructures of various forms using hydrothermal synthesis.

Another object of the present invention to provide a bismuth telluride (Bi ₂ Te ₃ ) nanostructures of various forms prepared by the above method.

In order to achieve the above object, the present invention dissolves tellurium (Te) powder and bismuth chloride (BiCl ₃ ) in distilled water to prepare each of the aqueous solution separately, and then mixed through a heat treatment and cooling step of various forms of bismuth telluride (Bi ₂ Te ₃ ) Provides a method for producing a nanostructure.

The present invention also provides bismuth telluride (Bi ₂ Te ₃ ) nanostructures of various forms prepared according to the above method.

According to the present invention, it is possible to produce a single crystal nanoparticles, nanocapsules, nanowires and nanotubes as nanostructures by changing the heat treatment temperature or the rate of temperature increase during hydrothermal synthesis, it is possible to obtain a high thermoelectric performance index value, By varying the cooling rate conditions it is possible to increase the yield and length of the nanowires and nanotubes, which can be usefully used in industries that require such thermoelectric materials.

The present invention comprises the steps of dissolving tellurium (Te) powder and bismuth chloride (BiCl ₃ ) in distilled water to prepare each aqueous solution separately and mixing (step 1); Heat-treating the mixed solution prepared in step 1 (step 2); And cooling bismuth telluride (Bi ₂ Te ₃ ) nanostructures by cooling the mixed solution heat-treated in step 2 (step 3), using various forms of bismuth telluride (Bi ₂ Te ₃₎ using a hydrothermal synthesis method. ) Provides a method for producing a nanostructure.

Hereinafter, the manufacturing method according to the present invention will be described in more detail step by step.

First, step 1 according to the present invention is a step of preparing and mixing respective aqueous solutions by dissolving tellurium (Te) powder and bismuth chloride (BiCl ₃ ) in distilled water.

The tellurium (Te) powder may be dissolved in an aqueous sodium hydroxide solution containing sodium borohydride to prepare an aqueous solution containing tellurium ions. In addition, the bismuth chloride (BiCl ₃ ) may be dissolved in an aqueous solution containing EDTA to prepare an aqueous solution containing bismuth ions. The tellurium (Te) aqueous solution and the bismuth chloride (BiCl ₃ ) aqueous solution are preferably mixed into a high pressure steam sterilizer and sealed.

Next, step 2 is a step of heat-treating the mixed solution prepared in step 1. At this time, it is preferable to perform the stirring process at the same time.

In the production method according to the present invention, nanostructures of various forms can be obtained according to the conditions of the heat treatment temperature, the temperature increase rate, the stirring rate. Among the above conditions, the heat treatment temperature and the temperature increase rate condition play an important role in determining the shape of the nanostructure. Specifically, it is as follows.

The heat treatment temperature may be performed in the range of 90 ° C to 155 ° C, but preferably may be performed in a temperature range of 90 ° C to 120 ° C and 130 ° C to 155 ° C. Appropriate temperature increase rate conditions for the temperature range can be obtained to obtain the desired nanostructure.

First, the heat treatment is carried out at 90 ℃ to 120 ℃, if the temperature increase rate is adjusted to the range of 100 ℃ / hour to 20 ℃ / hour can be obtained nanoparticles or nanocapsules. At this time, by further subdividing the heat treatment section can be obtained nanoparticles or nanocapsules alone. Specifically, when the heat treatment is carried out at 90 ° C or more and 100 ° C or less, the nanoparticles may be obtained, and when performed at 100 ° C or more and 120 ° C or less, nanocapsules may be obtained.

Next, the heat treatment is carried out at 130 ℃ to 155 ℃, if the temperature increase rate is adjusted to the range of 3 ℃ / hour to 1.8 ℃ / hour to obtain a nanowire or nanotubes. At this time, by further subdividing the heat treatment section can be obtained nanowires or nanotubes alone. Specifically, nanowires may be obtained when the heat treatment is performed at 130 ° C. or more and 140 ° C. or less, and nanotubes may be obtained when the heat treatment is performed at 140 ° C. or more and 155 ° C. or less.

Next, step 3 is a step of synthesizing bismuth telluride (Bi ₂ Te ₃ ) nanostructures of various forms by cooling the heat-treated mixed solution obtained in step 2. In the case of preparing nanoparticles and nanocapsules according to the present invention, no special cooling conditions are required. On the other hand, when manufacturing nanowires and nanotubes according to the present invention can be increased by adjusting the cooling conditions and the yield and length of the nanowires and nanotubes. Specifically, it is preferable to adjust the cooling conditions within the cooling rate range of 3 ℃ / hour to 1 ℃ / hour.

Thereafter, the step of drying the nanostructure may be additionally performed, and the drying is preferably performed at 50 ° C. to 60 ° C. for at least 12 hours using an oven or a vacuum oven.

In addition, the present invention provides various forms of bismuth telluride (Bi ₂ Te ₃ ) nanostructures prepared according to the above method.

Various forms of bismuth telluride (Bi ₂ Te ₃ ) nanostructures prepared according to the present invention can obtain a desired form of bismuth telluride (Bi ₂ Te ₃ ) nanostructures by varying the heat treatment temperature or the rate of temperature increase and cooling. By varying the rate conditions, the yield and length of the nanowires and nanotubes can be increased.

Looking at the results of morphological changes of bismuth telluride (Bi ₂ Te ₃ ) nanostructures prepared by varying the heat treatment temperature according to the present invention, nanoparticles, nanocapsules, nanowires and nanocrystals of single crystal structure according to the heat treatment temperature conditions It can be seen that a nanostructure having a desired shape can be obtained by changing the shape of the nanostructure, such as a tube (see Experimental Example 1).

In addition, looking at the results of morphological changes of the bismuth telluride (Bi ₂ Te ₃ ) nanostructures prepared by varying the temperature increase rate during heat treatment according to the present invention, according to the temperature increase rate conditions, nanoparticles, nanocapsules, nanowires And it can be seen that the nanostructure of the desired form can be obtained by changing the shape of the nanostructure, such as nanotubes (see Experimental Example 2).

In addition, looking at the results of morphological changes of the bismuth telluride (Bi ₂ Te ₃ ) nanostructures prepared by varying the cooling rate according to the present invention, the yield and length of the nanowires and nanotubes increase depending on the cooling rate conditions It can be seen that it can be made (see Experimental Example 3).

Accordingly, the bismuth telluride (Bi ₂ Te ₃ ) nanostructures of the present invention can prepare nanoparticles, nanocapsules, nanowires, and nanotubes having a single crystal structure as nanostructures by changing the heat treatment temperature or the rate of temperature increase during hydrothermal synthesis. As a result, high thermoelectric performance index values can be obtained, and yields and lengths of nanowires and nanotubes can be increased by changing cooling rate conditions, which can be usefully used in industrial fields requiring such thermoelectric materials.

Hereinafter, the present invention will be described in detail through Examples and Experimental Examples. However, the following examples are merely to illustrate the present invention, but the content of the present invention is not limited by the following examples.

< Example  1> Bismuth Telluride ( Bi ₂ Te ₃ ) Preparation of Nanoparticles

Distilled water to 500 ㎖ 20 mmol BiCl ₃ and mix with 0.2 mmol EDTA BiCl ₃ An aqueous solution was prepared. Te aqueous solution was prepared by mixing 30 mmol Te powder (5N purity), 0.3 mmol sodium hydroxide, and 0.3 mmol sodium borohydride in 500 mL distilled water. After mixing the BiCl ₃ aqueous solution and Te aqueous solution, the mixture was placed in a high-pressure steam sterilizer and sealed, and then heat-treated to 100 ° C. At this time, the temperature increase rate was 2 ℃ / hour, and stirred at 400 rpm. After cooling, the bismuth telluride (Bi ₂ Te ₃ ) nanoparticles were prepared by drying in an oven or vacuum oven at 50 ° C. for at least 12 hours.

< Example  2> Bismuth Telluride ( Bi ₂ Te ₃ ) Preparation of Nanocapsules

Bismuth telluride (Bi ₂ Te ₃ ) nanocapsules were prepared in the same manner as in Example 1 except that the heat treatment was performed at 120 ° C.

< Example  3> Bismuth Telluride Bi ₂ Te ₃ ) Nanowire  Produce

Bismuth telluride (Bi ₂ Te ₃ ) nanowires were prepared in the same manner as in Example 1, except that the heat treatment was performed at 140 ° C.

< Example  4> Bismuth Telluride ( Bi ₂ Te ₃ ) Preparation of Nanotubes

Bismuth telluride (Bi ₂ Te ₃ ) nanotubes were prepared in the same manner as in Example 1, except that the heat treatment was performed at 155 ° C.

< Experimental Example  1> Bismuth telluride according to the heat treatment temperature ( Bi ₂ Te ₃ Morphological Changes of Nanostructures

The following experiment was performed to investigate the morphological changes of bismuth telluride (Bi ₂ Te ₃ ) nanostructures according to the heat treatment temperature.

Heat treatment conditions of the nanostructures of Examples 1 to 4 are shown in FIG. 1, X-ray diffraction analysis results are shown in FIG. 2, and high resolution transmission electron microscope (HR TEM) images are shown in FIG. 3. More specifically, the high-resolution transmission electron microscope (HR TEM) image of Example 1 is shown in (a) of 3, and the high-resolution transmission electron microscope (HR TEM) image of Example 2 is shown in (b) of 3 The high resolution transmission electron microscope (HR TEM) image of Example 3 is shown in (c) of 3, and the high resolution transmission electron microscope (HR TEM) image of Example 4 is shown in (d) of 3. .

As can be seen in Figure 2, it can be observed that the nanostructures of Examples 1 to 4 are all single crystals.

As can be seen in (a) of FIG. 3, bismuth telluride (Bi ₂ Te ₃ ) nanoparticles can be observed. In addition, as can be seen in Figure 3 (b), bismuth telluride (Bi ₂ Te ₃ ) nanocapsules can be observed. In addition, as can be seen in Figure 3 (c), bismuth telluride (Bi ₂ Te ₃ ) nanowires can be observed. Furthermore, as can be seen in FIG. 3 (d), bismuth telluride (Bi ₂ Te ₃ ) nanotubes can be observed.

Through this, it can be seen that the nanostructure of the desired shape can be obtained by changing the shape of the nanostructure, such as nanoparticles, nanocapsules, nanowires and nanotubes of the single crystal structure according to the heat treatment temperature conditions.

< Experimental Example  2> during heat treatment Elevated temperature  Bismuth Telluride Depending On Speed Bi ₂ Te ₃ Morphological Changes of Nanostructures

The following experiment was performed to investigate the morphological changes of bismuth telluride (Bi ₂ Te ₃ ) nanostructures according to the temperature increase rate during the heat treatment.

The temperature increase rate was performed as shown in Table 1 below, and the obtained nanostructures are shown in Table 1 below.

Heat treatment temperature (℃) Temperature rise rate (℃ / hour) Nano Structure 100 100 Nanoparticles 20 Nanoparticle + (nanocapsule) 120 100 Nanoparticle + (nanocapsule) 20 Nano Capsule 140
3 Nanowire 1.8 Nanowire + (nanotube) 155 3 Nanowire + (nanotube) 1.8 Nanowire + Nanotube

Referring to Table 1, when the heat treatment is performed at 100 ℃ nanoparticles are produced in the range of 100 ℃ / hour to 20 ℃ / hour, when performing the heat treatment at 120 ℃ 100 ℃ / hour to 20 ℃ It can be seen that the nanocapsules are produced in the range of / hour. In addition, when the heat treatment is performed at 140 ℃ nanowires are generated in the range of 3 ℃ / hour to 1.8 ℃ / hour, when performing the heat treatment at 155 ℃ in the range of 3 ℃ / hour to 1.8 ℃ / hour It can be seen that the nanotubes are produced.

Through this, it can be seen that the nanostructure of the desired shape can be obtained by changing the shape of the nanostructures, such as nanoparticles, nanocapsules, nanowires and nanotubes according to the temperature increase rate conditions.

< Experimental Example  3> according to the cooling rate Bismuth Telluride ( Bi ₂ Te ₃ Morphological Changes of Nanostructures

The following experiment was performed to investigate the morphological changes of bismuth telluride (Bi ₂ Te ₃ ) nanostructures with cooling rate.

The heat treatment temperature of 155 ℃, the temperature increase rate of 2 ℃ / hour, the cooling rate conditions of Table 2 were carried out as follows, the yield and length of the obtained nanostructures are shown in Table 2 below.

Cooling rate (℃ / hour) yield(%) Length (㎛) 100 Nanoparticles 100 0.2-1 Nano Capsule 0 - Nanowire 0 - Nanotube 0 - 50 Nanoparticles 100 0.1-1 Nano Capsule 0 - Nanowire 0 - Nanotube 0 - 3 Nanoparticles 15 0.5-2 Nano Capsule 20 0.5-1 Nanowire 50 1-3 Nanotube 15 0.5-1 One Nanoparticles 10 0.5-2 Nano Capsule 15 0.5-1 Nanowire 45 4-6 Nanotube 30 1-3

Referring to Table 2, it can be seen that the yield and the length of the nanostructure does not change significantly in the cooling rate section of 100 ℃ / hour to 50 ℃ / hour. In addition, the yield of nanotubes increased by 15% in the cooling rate section of 3 ℃ / hour to 1 ℃ / hour, the length is increased from 0.1-1 ㎛ to 1-3 ㎛, nanowire length is 1-3 ㎛ It can be seen that the length is 4-6 μm.

Through this, it can be seen that the yield and length of the nanowires and nanotubes can be increased according to the cooling rate conditions.

1 is a graph showing heat treatment conditions according to the present invention;

2 is an X-ray diffraction analysis of bismuth telluride (Bi ₂ Te ₃ ) nanostructures produced according to the heat treatment temperature according to the present invention;

3 is a high-resolution transmission electron microscope (HR TEM) image of bismuth telluride (Bi ₂ Te ₃ ) nanostructures produced according to the heat treatment temperature according to the present invention ((a) nanoparticles, (b) nanocapsules, (c)). ) Nanowires, (d) nanotubes).

Claims (11)

Dissolving tellurium (Te) powder and bismuth chloride (BiCl ₃ ) in distilled water to prepare and mix each aqueous solution separately (step 1); Heat-treating the mixed solution prepared in step 1 (step 2); And Method for producing a bismuth telluride (Bi ₂ Te ₃ ) nanostructures of various forms comprising the step (step 3) of cooling the mixed solution heat-treated in step 2 to synthesize a bismuth telluride (Bi2Te3) nanostructure. The method of claim 1, wherein the bismuth telluride (Bi ₂ Te ₃ ) nanostructure of the present invention is characterized in that simultaneously performing a stirring process during the heat treatment of step 2. According to claim 2, wherein the temperature during the heat treatment is 90 ℃ to 120 ℃, the temperature increase rate is 100 ℃ / hour to 20 ℃ / hour of various forms, characterized in that the nano-particles or nanocapsules are produced as a nanostructure Method for preparing bismuth telluride (Bi ₂ Te ₃ ) nanostructures. The method of claim 3 wherein the method of producing a variety of bismuth telluride (Bi ₂ Te ₃₎ nano-structure in which the heat treatment temperature characterized in that the nanoparticles are produced as a nanostructure or less than 90 ℃ 100 ℃. The method of claim 3, wherein the bismuth telluride (Bi ₂ Te ₃ ) nanostructure of the present invention is characterized in that the nanocapsules are produced as nanostructures when the temperature is greater than 100 ° C. and less than 120 ° C. during the heat treatment. According to claim 2, wherein the temperature during the heat treatment is 130 ℃ to 155 ℃, the temperature increase rate is 3 ℃ / hour to 1.8 ℃ / hour of various forms, characterized in that the nanowires or nanotubes are produced as a nanostructure Method for preparing bismuth telluride (Bi ₂ Te ₃ ) nanostructures. The method of manufacturing different types of bismuth telluride (Bi ₂ Te ₃₎ nanostructures, characterized in that the heat treatment temperature at which the nanowires are produced as nano-structures or less than 130 ℃ 140 ℃ to claim 6. According to claim 6, Bismuth telluride (Bi ₂ Te ₃ ) of the nanostructures manufacturing method characterized in that the nanotube is produced as a nanostructure when the temperature during the heat treatment is more than 140 ℃ 155 ℃ or less. The bismuth of various forms according to claim 6, wherein the resulting nanowires or nanotubes are cooled at a cooling rate of 3 ° C / hour to 1 ° C / hour to increase the yield and length of the nanowires or nanotubes. Method of preparing telluride (Bi ₂ Te ₃ ) nanostructures. Bismuth telluride (Bi ₂ Te ₃ ) nanostructures of various forms prepared according to the method of claim 1. The bismuth telluride of claim 10, wherein the bismuth telluride (Bi ₂ Te ₃ ) nanostructure is any one selected from the group consisting of nanoparticles, nanocapsules, nanowires, and nanotubes. Bi ₂ Te ₃ ) nanostructures.

Images