KR20140025709A - A method for preparing bismuth telluride nanotubes and bismuth telluride nanotubes with high aspect ratio - Google Patents

Abstract

The present invention relates to a method for manufacturing bismuth telluride (Bi2Te3) nanotubes and bismuth telluride (Bi2Te3) nanotubes having enhanced thermoelectric properties manufactured by the same, including: a first phase, in which a solvent including one among tri-octylphosphineoxide (TOPO), sodium dodecyl-benzene-sulfonate (SDBS), and cetyl-trimethyl-ammonium-bromide, and a capping agent chosen from one among Polyvinylpyrrolidone (PVP), polyvinylalcohol, and sodium dodecyl-benzene-sulfonate, is dissolved with telluride oxide (TeO2), and added with a reducing agent, in order to manufacture tellurium nanowire; a second phase, in which a solution of bismuth precursor is mixed with the tellurium nanowire of the first phase, and added with an reducing agent, in order to manufacture a mixture solution; and a third phase, in which the mixture solution of the second phase is heat-treated, in order to manufacture the bismuth telluride (Bi2Te3) nanotubes.

Description

[0001] The present invention relates to a bismuth telluride nanotube and a bismuth telluride nanotube having a large aspect ratio, and to a bismuth telluride nanotube having a high aspect ratio,

The present invention relates to a bismuth telluride (Bi ₂ Te ₃₎ The method of the nanotube and thus the thermal properties prepared according improved bismuth telluride (Bi ₂ Te ₃₎ nanotubes.

Thermoelectric power generation using thermoelectric energy can generate electricity from any kind of heat source and cold source on the earth, and it is generated from natural energy such as solar heat and geothermal power, internal combustion engine, reactor, incinerator and various industrial equipments And waste heat energy such as industrial waste heat can be directly recycled as electric energy. In addition, unlike conventional power generation systems, there is no need for a mechanical drive unit, so there is no noise or vibration, and it has a long lifetime, high reliability, and easy operation and management.

Thermoelectric materials, which are used to convert thermal energy directly to electrical energy or vice versa, are materials in which heat is generated due to the movement of electric charge due to temperature difference, or a heat or cooling phenomenon occurs at both ends of the material joint when electric current is shed. The thermoelectric phenomenon has been studied since early 1900 and has been studied to obtain a conversion efficiency of about 4% for the loffe of the former Soviet Union, and currently has a conversion efficiency of about 10% or more. The thermoelectric phenomenon is caused by a seebeck effect that obtains an electromotive force using a temperature difference between both ends, a Peltier effect in which heat is generated at both ends due to electromotive force, a Thomson effect in which an electromotive force is generated due to a temperature difference on a conductor, ) Effects. By using such a thermoelectric material, it is possible to develop a thermoelectric element that can directly convert heat energy and electric energy into each other.

The thermoelectric energy conversion efficiency is summarized by the so-called merit formula of thermoelectric performance index (ZT), and can generally be expressed by the following equation (1).

&Quot; (1) "

(Where ZT is the thermoelectric performance index,? Is the Seebeck constant,? Is the electrical conductivity, K is the thermal conductivity, and T is the absolute temperature).

As can be seen from the above formula (1), in order to produce a thermoelectric material having a good thermoelectric efficiency, the electrical conductivity (σ) and the Seebeck constant ( α) is large, while the thermal conductivity (K) is low. However, since electrical conductivity (σ) and thermal conductivity (K) are dependent on each other, increasing the electrical conductivity (σ) increases the thermal conductivity (K) at the same time and limits the improvement of thermoelectric properties. ) Was almost never achieved. However, Professor Dresselhaus of the University of MIT in 1993 suggested that thermoelectric performance could be improved by fabricating thermoelectric materials with low-dimensional nanostructures of quantum dots and superlattices (Prior Art 1) With the development, many related scientists got attention. Therefore, in order to improve the thermoelectric efficiency of the thermoelectric material, by controlling the movement of the electrons and the phonon through the structural change and control of the nanomaterial, the electric conductivity is reduced to a smaller extent as compared with the decrease in the thermal conductivity, . ≪ / RTI >

Bismuth telluride (Bi ₂ Te ₃ ) is known as a material exhibiting the highest thermoelectric performance index at room temperature. It is a layered compound having a rhombohedral crystal structure and has a structure of -Te (1) -Bi-Te (2) -Bi -Te (1) - in this order. In this structure, the Te (1) -Te (1) bond has a weak van der Waals bond, the Te-Bi (1) bond forms a mixed bond of covalent bond and ionic bond, Is a covalent bond. It is known that the Te (1) -Te (1) bond, which is the weakest bond among the above bonds, has an easily broken anisotropy due to mechanical susceptibility, a large aspect ratio, have.

Researches for preparing bismuth telluride (Bi ₂ Te ₃ ) have been made variously, and generally are divided into a solvothermal synthesis method and a hydrothermal synthesis method. In addition, bismuth telluride (Bi ₂ Te ₃ ) shows a difference in thermoelectric performance depending on the shape, and a nanotube having a one-dimensional structure has the best thermoelectric performance and is known to be suitable as a thermoelectric material. When bismuth telluride (Bi ₂ Te ₃ ) is prepared by the solvent thermo-synthetic method, it has a merit that one-dimensional nanotubes can be relatively easily produced, but it is difficult to mass-produce nanotubes and thus it is difficult to apply industrially. In addition, in the case of the hydrothermal synthesis method, amorphous particles having a three-dimensional structure are generated in most cases, which makes it difficult to obtain one-dimensional nanotubes.

As a conventional technique, Korean Patent Laid-Open No. 10-2011-0058046 provides a method for producing Bi ₂ Te ₃ nanotubes. Specifically, a process for preparing a bismuth-containing solution by mixing a bismuth (Bi) compound with a mixed solution containing an aqueous alkali solution, a reducing agent and a surfactant; And a step of forming a Bi ₂ Te ₃ nanotube by hydrothermal reaction at a temperature of 80 ° C to 200 ° C by adding a tellurium (Te) nanowire into the bismuth (Bi) containing solution; The present invention provides a method for producing Bi ₂ Te ₃ nanotubes.

This method has a merit in that the manufacturing process is simple and the manufacturing cost can be greatly reduced and the mass production is easy, compared with the conventional solvent thermo-synthesis method and hydrothermal synthesis method using the tellurium precursor, but the nanostructure capable of improving thermoelectric properties There is a problem in that there is a limit in manufacturing.

Also, Korean Patent Laid-Open No. 10-2010-0138171 discloses a method for producing various types of bismuth telluride nanostructures by hydrothermal synthesis and a bismuth telluride nanostructure produced thereby. Specifically, a step of dissolving a mixture of tellurium (Te) powder and bismuth chloride (BiCl ₃ ) in distilled water to separately prepare and mix the respective aqueous solutions; Heat-treating the mixed solution; And provides a method for producing the heat-treated by cooling the mixed solution of bismuth telluride (Bi ₂ Te ₃₎ different types of bismuth including the step of synthesizing a nanostructure telluride (Bi ₂ Te ₃₎ nanostructures.

The method can produce nanoparticles, nanocapsules, nanowires, and nanotubes having a single crystal structure as a nanostructure by changing the heat treatment temperature or heating rate during hydrothermal synthesis, thereby obtaining a high thermoelectric performance index value, It is possible to increase the yield and length of nanowires and nanotubes. However, it is necessary to precisely control the temperature of nanostructures in order to produce desired nanostructures. Otherwise, nanostructures of various shapes may be mixed There is a problem.

Accordingly, the inventors of the present invention conducted studies to manufacture thermoelectric materials having improved thermoelectric properties while solving the conventional problems, and found that when trioctylphosphine oxide (TOPO) and polyvinylpyrrolidone (PVP) were mixed as a capping agent (Bi ₂ Te ₃ ) nanotubes having improved thermoelectric properties when they are used in the production of a bismuth telluride (Bi ₂ Te ₃ ) nanotube.

<Prior Art 1> L.D. Hicks and M.S. Dresselhaus, &quot; Effect of Quantumwell Structures on the Thermoelectric Figure of Merit, &quot; Physical Review B, Vol. 47, 1993, p. L.D.

Hicks and MS Dresselhaus, &quot; Thermoelectric Figure of a One-dimensional Conductor, &quot; Physical Review B, Vol. 47, 1993, p.

It is an object of the present invention to provide a method for producing bismuth telluride (Bi ₂ Te ₃ ) nanotubes.

It is also an object of the present invention to provide a bismuth telluride (Bi ₂ Te ₃ ) nanotube having improved thermoelectric properties produced by the above method.

Furthermore, it is an object of the present invention to provide a thermoelectric device including the bismuth telluride (Bi ₂ Te ₃ ) nanotube.

According to an aspect of the present invention,

Trioctylphosphine oxide (TOPO), sodium triphosphate (Na ₃ PO ₄ .12H ₂ O), sodium dodecyl-benzene-sulfonate (SDBS), and cetyltrimethylammonium bromide cetyl-trimethyl-ammonium-bromide), polyvinylpyrrolidone (PVP), polyvinylalcohol, and sodium dodecyl-benzene-sulfonate A step of dissolving tellurium oxide (TeO ₂ ) in a solvent containing a capping agent consisting of one species selected from the group consisting of: (1) preparing a tellurium nanowire by adding a reducing agent;

Mixing the bismuth precursor solution with the tellurium nanowire of step 1 and adding a reducing agent to prepare a mixed solution (step 2); And

Heat treating the mixed solution of step 2 to prepare a bismuth telluride (Bi ₂ Te ₃ ) nanotube (step 3);

(Bi ₂ Te ₃ ) nanotubes comprising the bismuth telluride (Bi ₂ Te ₃ ) nanotube.

The present invention also provides a bismuth telluride (Bi ₂ Te ₃ ) nanotube produced according to the above method.

Further, the present invention provides a thermoelectric device including the bismuth telluride (Bi ₂ Te ₃ ) nanotube.

The method for producing bismuth telluride (Bi ₂ Te ₃ ) nanotubes according to the present invention is a method for producing a bismuth telluride (Bi ₂ Te ₃ ) nanotube according to the present invention by mixing two kinds of capping agents, Nanotubes can be manufactured, and the nanotubes have a structure that simultaneously satisfies high electrical conductivity and low thermal conductivity. The prepared nanotubes have improved thermoelectric properties and can be used as thermoelectric materials such as thermoelectric semiconductors.

FIG. 1 (a) is a photograph of a bismuth telluride (Bi ₂ Te ₃ ) nanotube prepared in Example 1 of the present invention by a Field Emission Scanning Electron Microscope (FE-SEM) (b) is a photograph of a bismuth telluride (Bi ₂ Te ₃ ) nanotube prepared in Example 2 of the present invention by a field emission scanning electron microscope, and (c) (Bi ₂ Te ₃ ) nanotube with a field emission scanning electron microscope.
FIG. 2 (a) is a photograph of a bismuth telluride (Bi ₂ Te ₃ ) nanotube prepared in Example 1 of the present invention by high resolution transmission electron microscopy (HR-TEM) (b) is a photograph of the bismuth telluride (Bi ₂ Te ₃ ) nanotube prepared in Example 2 of the present invention by a high-resolution transmission electron microscope, and (c) is a photograph of the bismuth telluride (Bi ₂ Te ₃ ) nanotube with a high-resolution transmission electron microscope.
FIG. 3 (a) is a photograph of a tellurium (Te) nanotube prepared in Comparative Example 1 taken by a field emission scanning electron microscope (FE-SEM) (Te) nanotubes prepared in Example 1 were photographed by a field emission scanning electron microscope.
4 (a) is a photograph of a bismuth telluride (Bi ₂ Te ₃ ) nanotube prepared in Comparative Example 3 by a field emission scanning electron microscope (FE-SEM) Is a photograph of a bismuth telluride (Bi ₂ Te ₃ ) nanotube prepared in Comparative Example 4, which was photographed by a field emission scanning electron microscope.
FIG. 5 (a) is a photograph of a bismuth telluride (Bi ₂ Te ₃ ) nanotube prepared in Comparative Example 3 by high resolution transmission electron microscopy (HR-TEM) And a bismuth telluride (Bi ₂ Te ₃ ) nanotube prepared in Comparative Example 4 was photographed with a high-resolution transmission electron microscope.
6 (a) is a photograph of a tellurium nanowire prepared in Example 5 taken at a scanning electron microscope (SEM) at a magnification of 20,000, and FIG. 6 (b) is a photograph of a tellurium nanowire prepared in Comparative Example 6 (C) is a photograph of the tellurium nanowire prepared in Comparative Example 7, taken with a scanning electron microscope.
FIG. 7 is a graph of X-ray diffraction (XRD) of bismuth telluride (Bi ₂ Te ₃ ) nanotubes prepared in Examples 1 to 3 of the present invention.
8 is a graph of X-ray diffraction (XRD) of tellurium (Te) nanotubes prepared in Comparative Example 1 and Comparative Example 2. FIG.
9 is a graph of X-ray diffraction (XRD) of bismuth telluride (Bi ₂ Te ₃ ) nanotubes prepared in Comparative Example 3 and Comparative Example 4 of the present invention.

The present invention provides a method for producing bismuth telluride (Bi ₂ Te ₃ ) nanotubes.

Hereinafter, the present invention will be described in detail.

The present invention

Trioctylphosphine oxide (TOPO), sodium triphosphate (Na ₃ PO ₄ .12H ₂ O), sodium dodecyl-benzene-sulfonate (SDBS), and cetyltrimethylammonium bromide cetyl-trimethyl-ammonium-bromide), polyvinylpyrrolidone (PVP), polyvinylalcohol, and sodium dodecyl-benzene-sulfonate A step of dissolving tellurium oxide (TeO ₂ ) in a solvent containing a capping agent consisting of one species selected from the group consisting of: (1) preparing a tellurium nanowire by adding a reducing agent;

Mixing the bismuth precursor solution with the tellurium nanowire of step 1 and adding a reducing agent to prepare a mixed solution (step 2); And

Heat treating the mixed solution of step 2 to prepare a bismuth telluride (Bi ₂ Te ₃ ) nanotube (step 3);

Mixing the bismuth precursor solution with the tellurium nanowire of step 1 and adding a reducing agent to prepare a mixed solution (step 2); And

Heat treating the mixed solution of step 2 to prepare a bismuth telluride (Bi ₂ Te ₃ ) nanotube (step 3);

(Bi ₂ Te ₃ ) nanotubes comprising the bismuth telluride (Bi ₂ Te ₃ ) nanotube.

Hereinafter, a method for producing the bismuth telluride (Bi ₂ Te ₃ ) nanotube according to the present invention will be described in more detail step by step.

In the present invention, the step 1 may be performed by using trioctylphosphine oxide (TOPO), sodium triphosphate (Na ₃ PO ₄ .12H ₂ O), sodium dodecyl-benzene- polyvinylpyrrolidone (PVP), polyvinyl alcohol, and ethylenediaminetetraacetic acid (hereinafter, referred to as &quot; polyvinylpyrrolidone &quot;) and one selected from the group consisting of cetyltrimethylammonium bromide, sulfonate, SDBS and cetyl- (TeO ₂ ) is dissolved in a solvent containing a capping agent composed of one kind selected from the group consisting of sodium dodecyl-benzene-sulfonate, and a reducing agent is added to prepare a tellurium nanowire .

In step 1, trioctylphosphine oxide (TOPO), sodium triphosphate (Na ₃ PO ₄ .12H ₂ O), sodium dodecyl-benzene-sulfonate (SDBS) And polyvinylpyrrolidone (PVP), polyvinyl alcohol, and sodium dodecyl-benzene (hereinafter, referred to as &quot; polyvinylpyrrolidone &quot;) and one selected from the group consisting of cetyltrimethylammonium bromide -sulfonate) is preferably mixed with a capping agent in a weight% ratio of 98: 2 to 94: 6.

If mixed trioctylphosphine oxide (TOPO), sodium triphosphate (Na ₃ PO ₄ .12H ₂ O), sodium dodecyl-benzene-sulfonate (SDBS) and cetyltrimethyl Polyvinylpyrrolidone (PVP), polyvinylalcohol, and sodium dodecyl-benzene-ammonium bromide, which are selected from the group consisting of cetyl-trimethyl-ammonium- sulfonate) is less than 98 wt%: 2 wt%, trioctylphosphine oxide (TOPO), sodium triphosphate (Na ₃ PO ₄ .12H ₂ O ), Sodium dodecyl-benzene-sulfonate (SDBS), and cetyl-trimethyl-ammonium-bromide are used singly, and the diameter and shape on (PVP), polyvinylalcohol and sodium dodecyl-acetoacetate when the weight ratio of 94% by weight to 6% by weight is exceeded when the weight ratio of the polyvinylpyrrolidone (PVP) benzene-sulfonate), there is no difference in shape and diameter between the particles and 6 wt% of one selected from the group consisting of water, ethanol, benzene-sulfonate, and the like. In this case, the powder produced at this time has a problem of difficulty in filtration and drying, have.

In the present invention, the trioctylphosphine oxide (TOPO), sodium triphosphate (Na ₃ PO ₄ .12H ₂ O), sodium dodecyl-benzene-sulfonate (SDBS) And polyvinylpyrrolidone (PVP), polyvinyl alcohol, and sodium dodecyl-benzene (hereinafter, referred to as &quot; polyvinylpyrrolidone &quot;) and one selected from the group consisting of cetyltrimethylammonium bromide -sulfonate) is used as a capping agent to change the growth rate and internal structure of the nanostructure. More specifically, the trioctylphosphine oxide (TOPO) prevents not only the agglomeration of the tellurium (Te) precursor in the solvent but also the formation of a hollow round bar nanotube having a diameter of 100 nm or more . The above-mentioned polyvinylpyrrolidone (PVP) serves to produce particles of nanoribblet shape having a rectangular cross section with a diameter of 30 nm or less. Accordingly, in the present invention, the structure of nanotubes can be controlled by mixing two types of structure-forming agents, namely trioctylphosphine oxide (TOPO) and polyvinylpyrrolidone (PVP), and as a result, Can be improved.

Also, one kind selected from the group consisting of polyvinylpyrrolidone (PVP), polyvinylalcohol and sodium dodecyl-benzene-sulfonate has a weight average molecular weight (Mw) of 35,000 to 45,000 Is preferably used. If the weight average molecular weight of the polyvinylpyrrolidone (PVP) is less than 35000, the bismuth telluride (Bi ₂ Te ₃ ) nanotube to be produced can obtain ultrafine nanoparticles, but the shape and boundary of the particles locally It is difficult to have a complete one-dimensional structure as a whole, and when it is more than 45000, when the same weight is added, it has a relatively small number of molecules, resulting in post-synthesis nucleated and grown tellurium nanoparticles (Bi ₂ Te ₃ ) nanotubes that are not uniformly uniform due to contact and agglomeration of the nanoparticles in the solution are promoted.

The solvent that can be used in step 1 is preferably oleylamine. The oleylamine functions as a solvent and serves as a reducing agent for reducing some metal ions without adding a reducing agent at high temperature. In Example 1 of the present invention, tellurium oxide (TeO ₂ ) is dissolved in oleylamine. Tellurium oxide (TeO ₂ ) is ionized in oleylamine to form tellurium ions Te ^{4 +} ) state.

The viscosity of the solution can be controlled by adding an alkalizing agent to the solvent. In the first embodiment of the present invention, sodium hydroxide (NaOH) is used as an example, but the present invention is not limited thereto.

In addition, the tellurium oxide (TeO ₂ ) of the step 1 in the present invention is preferably included in the range of 7 wt% to 8 wt% with respect to the total weight of the solvent containing the capping agent. If the content of the capping agent is less than 7% by weight based on the total weight of the solvent containing the capping agent, the molar ratio of bismuth to tellurium varies, which makes it difficult to produce a complete bismuth telluride (Bi ₂ Te ₃ ) crystal nanotube If it exceeds 8 wt%, there is a problem that too much tellurium crystals are excessively aggregated and it is difficult to obtain a perfect one-dimensional nano structure.

The dissolution of the tellurium (Te) precursor in the step 1 is preferably carried out at 100 ° C to 130 ° C, more preferably at 120 ° C. The oxidation Tel when dissolution is less than the temperature 100 ℃ of tellurium (TeO ₂₎ oxide tellurium (TeO ₂₎ is sufficient and may cause insoluble problems, and it is not possible to control the reaction rate, if it exceeds 130 ℃ reducing agent added Previously, reduction may occur firstly due to the reducing action of the oleylamine, which is a solvent, to cause problems in controlling the tellurium structure.

In step 1, a tellurium (Te) nanowire can be prepared by adding a reducing agent to a mixed solution in which a capping agent, tellurium oxide (TeO ₂ ) and an alkaline agent are dissolved. The reducing agent in step 1 is preferably hydrazine monohydrate (N ₂ H ₄ .H ₂ O) or sodium borohydride (NaBH ₄ ), more preferably hydrazine monohydrate (N ₂ H ₄ .H ₂ O ) Is used. Sodium borohydride (NaBH ₄ ) is a more potent reducing agent than hydrazine monohydrate (N ₂ H ₄ .H ₂ O), which breaks down the tellurium, which is characteristic of crystal structure in the c-axis direction, and is typically amorphous, Tellurium (? -Te).

At this time, the tellurium (Te) nanowire of step 1 is preferably prepared by reacting at 140 to 160 ° C for 20 to 30 minutes, more preferably at 160 ° C for 20 minutes.

If the preparation of the tellurium (Te) nanotubes is carried out at a temperature of less than 140 ° C., a long reaction time is required because the minimum thermodynamic energy required for the reaction is not supplied, and the unreacted tellurium (Te ⁴⁺ ) Ion and tellurium (Te) metal may be present in a mixed state. When the reaction is carried out at a temperature higher than 180 ° C., the reaction proceeds rapidly, and the nanotube structure may be unstably formed . When the reaction time of the tellurium (Te) nanotube is less than 20 minutes, the tellurium is not sufficiently reduced, and a product in which a tellurium (Te) nanotube and a tellurium ion (Te ⁴⁺ ) are mixed can be obtained , And if it exceeds 30 minutes, the crystallinity of tellurium (Te) may decrease.

When a reducing agent is added to the mixed solution, the reduction reaction of tellurium ions (Te ^{4 +} ) dissolved in the solvent proceeds to produce a tellurium (Te) nanotube.

Next, the step 2 is a step of mixing a bismuth (Bi) precursor solution with the tellurium (Te) nanotubes of the step 1 and adding a reducing agent to prepare a mixed solution.

In step 2, the bismuth (Bi) precursor solution is preferably prepared by dissolving bismuth chloride (BiCl ₃ ) in oleylamine. Bismuth (Bi) used in the present invention simultaneously exhibits Seebeck efficiency and low thermal conductivity in a one-dimensional nanostructure, and exhibits improved thermoelectric properties.

The reducing agent to be added after mixing the bismuth (Bi) precursor solution with the tellurium nanotubes of the step 1 in the step 2 is the hydrazine monohydrate (N ₂ H ₄ .H ₂ O) or It is preferable to use sodium borohydride (NaBH ₄ ), more preferably hydrazine monohydrate (N ₂ H ₄ .H ₂ O). When the bismuth (Bi) reduced from the bismuth ion (Bi ³⁺ ) is attached to the surface of the tellurium (Te) nanowire, the reducing agent used in the step 2 diffuses in different directions at the interface between the two metals Bismuth telluride (Bi ₂ Te ₃ ) nanowire crystal is formed. More specifically, when a solution containing a bismuth (Bi) precursor is dissolved in a reactor containing a previously obtained tellurium (Te) nanowire and then a reducing agent is added, bismuth ions (Bi ^{3 +} ) are immediately reduced to bismuth atoms At the same time, bismuth telluride (Bi ₂ Te ₃ ) nanotube crystals start to be generated by mutual diffusion of bismuth atoms and tellurium atoms on the surface of the tellurium nanotubes.

Next, in the present invention, the step 3 is a step of preparing a bismuth telluride (Bi ₂ Te ₃ ) nanotube by heat-treating the mixed solution of the step 2.

At this time, the heat treatment is preferably performed at a temperature of 150 to 160 DEG C for 60 to 80 minutes, more preferably at 160 DEG C for 60 minutes. If the heat treatment is carried out at a temperature of less than 150 ° C, a long reaction time is required, and bismuth (Bi) or tellurium (Te) which has not reacted is mixed with bismuth telluride (Bi ₂ Te ₃ ) Problems may arise and the diffusion rate of reduced bismuth (Bi) atoms is faster than the diffusion rate of tellurium (Te) atoms when performed at a temperature higher than 160 DEG C, so that the nanotubes have a weak mechanical strength in the c- Resulting in a problem that the bismuth telluride nanotube grows in a short and uneven shape due to local breakage.

When the heat treatment time is less than 60 minutes, a product containing a mixture of tellurium (Te) and bismuth telluride (Bi ₂ Te ₃ ) nanotubes can be obtained. When the annealing time is longer than 80 minutes, bismuth telluride (Bi ₂ Te ₃ ) The crystal density of the nanotubes may decrease.

The resultant bismuth telluride (Bi ₂ Te ₃ ) nanotube crystal grows to form a bismuth telluride (Bi ₂ Te ₃ ) nano-scale structure having a small diameter and a pore structure therein A tube is produced.

The produced bismuth telluride (Bi ₂ Te ₃ ) nanotube has a void space inside and has a reduced thermal conductivity property, and has a one-dimensional structure, thereby increasing the electron movement by the quantum confinement effect, thereby maintaining a high electric conductivity value have. Due to the above characteristics, the thermoelectric performance index indicating the thermoelectric characteristics of the thermoelectric material can be increased and the thermoelectric material can be usefully used.

The present invention also provides a bismuth telluride (Bi ₂ Te ₃ ) nanotube produced according to the above-described production method.

The nanotubes produced according to the above method are produced as bismuth telluride (Bi ₂ Te ₃ ) nanotubes having a diameter of about 50 nm or less and a pore structure as a one-dimensional nanostructure. The nanotubes have a one-dimensional structure and a small diameter so that the quantum confinement effect can be expressed and the electrons can be restricted to move along the axis to form a two-dimensional quantum structure or a three-dimensional bulk material Have a higher electrical conductivity. In addition, a phonon, which serves as a heat transferring material, is scattered inside the one-dimensional structure to have a vacant space to have a low thermal conductivity. As a result, bismuth telluride (Bi ₂ Te ₃ ) Nanotubes.

The present invention also provides a thermoelectric device including the bismuth telluride (Bi ₂ Te ₃ ) nanotube. Specifically, when a thermoelectric device is manufactured using the nanotubes produced in the present invention, it is possible to improve the thermoelectric performance index to improve the efficiency and cost of the device, and the thermoelectric device can be used not only as a thermoelectric generator, It can be used for the development of various sensors.

Hereinafter, the present invention will be described in detail by way of examples. However, the following examples are illustrative of the present invention, and the present invention is not limited by the following examples.

Example 1 Production of Bismuth Telluride (Bi ₂ Te ₃ ) Nanotube 1

50 mL of ethylene glycol (purchased from Samchun Pure Chemical Co., Ltd., purity: 99.5%), 0.8 g sodium hydroxide (purchased from Jin chemical pharmaceutical co., Ltd., purity: 99% in a 300 mL flask ), 5 g of trioctylphosphine oxide (TOPO, purchased from Aldrich, purity: 90%), and 0.1 g of polyvinylpyrrolidone (PVP, purchased from Aldrich, molecular weight: 40000) were added and heated up to 120 ° C. The solution was dissolved and 0.479 g of tellurium oxide (TeO ₂ , Purchased from Aldrich, purity: 99% or more). After warming the temperature to 160 ℃ and hydrazine monohydrate in 0.3 mL as a reducing agent _{(N 2 H 4 · H 2} O, point of purchase: Aldrich, purity: 64% to 65%) by 20 minutes of reaction after addition of tellurium (Te ) Nanotubes were prepared.

To a 20 mL Erlenmeyer flask was added 0.631 g of bismuth chloride (BiCl ₃ , purchased from Aldrich, purity: 98% or more) to 10 mL of ethylene glycol (purchased from Samchun Pure Chemical Co., Ltd., purity: 99.5%) To prepare a bismuth precursor solution. The prepared bismuth precursor solution was mixed with a tellurium nanotube-made flask, and then 5 mL of hydrazine monohydrate (N ₂ H ₄ .H ₂ O, purchased from Aldrich, purity: 64 to 65%) was added , by reacting for 60 minutes at 160 ℃ to prepare a bismuth telluride (Bi ₂ Te ₃₎ nanotubes.

The prepared bismuth telluride (Bi ₂ Te ₃ ) nanotube was filtered, washed with ethanol, and dried at 70 ° C to 80 ° C to complete the production of bismuth telluride (Bi ₂ Te ₃ ) nanotubes.

Example 2: Preparation of bismuth telluride (Bi ₂ Te ₃ ) nanotube 2

Bismuth telluride (Bi ₂ Te ₃ ) nanotubes were prepared in the same manner as in Example 1, except that 0.2 g of polyvinylpyrrolidone was used.

&Lt; Example 3 > Preparation of bismuth telluride (Bi ₂ Te ₃ ) nanotube 3

Bismuth telluride (Bi ₂ Te ₃ ) nanotubes were prepared in the same manner as in Example 1, except that 0.3 g of polyvinylpyrrolidone was used.

COMPARATIVE EXAMPLE 1 Preparation of Tellurium (Te) Nanotube Added with Trioctylphosphine Oxide

In a 300 mL flask, 50 mL of ethylene glycol (purchased from Samchun Pure Chemical Co., Ltd., purity: 99.5%) and 0.8 g of sodium hydroxide (purchased from Jin chemical pharmaceutical co., Ltd., purity: 99% ) And 5 g of trioctylphosphine oxide (TOPO, purchased from Aldrich, purity: 90%) were charged, the temperature of the solution was raised to 120 ° C to dissolve the solution, and 0.479 g of tellurium oxide (TeO ₂ , Purchased from Aldrich, purity: 99% or more). After warming the temperature to 160 ℃ and hydrazine monohydrate in 0.3 mL as a reducing agent _{(N 2 H 4 · H 2} O, point of purchase: Aldrich, purity: 64% to 65%) by 20 minutes of reaction after addition of tellurium (Te ) Nanotubes were prepared.

The prepared tellurium nanotubes were filtered, washed with ethanol, and dried at 70 ° C to 80 ° C to complete the preparation of the tellurium nanotubes.

&Lt; Comparative Example 2 > Preparation of tellurium (Te) nanotubes to which polyvinylpyrrolidone was added

In a 300 mL flask, 50 mL of ethylene glycol (purchased from Samchun Pure Chemical Co., Ltd., purity: 99.5%) and 0.8 g of sodium hydroxide (purchased from Jin chemical pharmaceutical co., Ltd., purity: 99% ) And 0.3 g of polyvinylpyrrolidone (PVP, purchased from Aldrich, molecular weight: 40000) were charged and the solution was heated to 120 ° C to dissolve the solution, and 0.479 g of tellurium oxide (TeO ₂ , Purchased from Aldrich, purity: 99% or more). After warming the temperature to 160 ℃ and hydrazine monohydrate in 0.3 mL as a reducing agent _{(N 2 H 4 · H 2} O, point of purchase: Aldrich, purity: 64% to 65%) by 20 minutes of reaction after addition of tellurium (Te ) Nanotubes were prepared.

The prepared tellurium nanotubes were filtered, washed with ethanol, and dried at 70 ° C to 80 ° C to complete the preparation of the tellurium nanotubes.

&Lt; Comparative Example 3 > Preparation of bismuth telluride (Bi ₂ Te ₃ ) nanotubes to which trioctylphosphine oxide was added

In a 300 mL flask, 50 mL of ethylene glycol (purchased from Samchun Pure Chemical Co., Ltd., purity: 99.5%) and 0.8 g of sodium hydroxide (purchased from Jin chemical pharmaceutical co., Ltd., purity: 99% ) And 5 g of trioctylphosphine oxide (TOPO, purchased from Aldrich, purity: 90%) were charged, the temperature of the solution was raised to 120 ° C to dissolve the solution, and 0.479 g of tellurium oxide (TeO ₂ , Purchased from Aldrich, purity: 99% or more). After warming the temperature to 160 ℃ and hydrazine monohydrate in 0.3 mL as a reducing agent _{(N 2 H 4 · H 2} O, point of purchase: Aldrich, purity: 64% to 65%) by 20 minutes of reaction after addition of tellurium (Te ) Nanotubes were prepared.

Dissolve 0.631 g of bismuth chloride (BiCl ₃ , purchased from Aldrich, purity: 98% or more) in 10 mL of ethylene glycol (purchased from Samchun Pure Chemical Co., Ltd., purity: 99.5%) into a 20 mL Erlenmeyer flask To prepare a bismuth precursor solution. The prepared bismuth precursor solution was mixed with a tellurium nanotube-made flask, and then 5 mL of hydrazine monohydrate (N ₂ H ₄ .H ₂ O, purchased from Aldrich, purity: 64-65% Lt; 0 &gt; C for 60 minutes to prepare bismuth telluride (Bi ₂ Te ₃ ) nanotubes.

The prepared bismuth telluride (Bi ₂ Te ₃ ) nanotube was filtered, washed with ethanol, and dried at 70 ° C to 80 ° C to complete the production of bismuth telluride (Bi ₂ Te ₃ ) nanotubes.

&Lt; Comparative Example 4 > Preparation of bismuth telluride (Bi ₂ Te ₃ ) nanotubes to which polyvinylpyrrolidone was added

In a 300 mL flask, 50 mL of ethylene glycol (purchased from Samchun Pure Chemical Co., Ltd., purity: 99.5%) and 0.8 g of sodium hydroxide (purchased from Jin chemical pharmaceutical co., Ltd., purity: 99% ) And 0.3 g of polyvinylpyrrolidone (PVP, purchased from Aldrich, molecular weight: 40000) were charged and the solution was heated to 120 ° C to dissolve the solution, and 0.479 g of tellurium oxide (TeO ₂ , Purchased from Aldrich, purity: 99% or more). After warming the temperature to 160 ℃ and hydrazine monohydrate in 0.3 mL as a reducing agent _{(N 2 H 4 · H 2} O, point of purchase: Aldrich, purity: 64% to 65%) by 20 minutes of reaction after addition of tellurium (Te ) Nanotubes were prepared.

Dissolve 0.631 g of bismuth chloride (BiCl ₃ , purchased from Aldrich, purity: 98% or more) in 10 mL of ethylene glycol (purchased from Samchun Pure Chemical Co., Ltd., purity: 99.5%) into a 20 mL Erlenmeyer flask To prepare a bismuth precursor solution. The prepared bismuth precursor solution was mixed with a tellurium nanotube-made flask, and then 5 mL of hydrazine monohydrate (N ₂ H ₄ .H ₂ O, purchased from Aldrich, purity: 64-65% Lt; 0 &gt; C for 60 minutes to prepare bismuth telluride (Bi ₂ Te ₃ ) nanotubes.

The prepared bismuth telluride (Bi ₂ Te ₃ ) nanotube was filtered, washed with ethanol, and dried at 70 ° C to 80 ° C to complete the production of bismuth telluride (Bi ₂ Te ₃ ) nanotubes.

&Lt; Comparative Example 5 > Preparation of tellurium (Te) nanowire 3

To a 300 mL flask was added 50 mL of oleylamine (purchased from Samchum Pure Chemical Co., Ltd., purity: 99.5%) and 0.8 g of sodium hydroxide (purchased from Jin chemical pharmacurtical co., Ltd., purity: 99 , 5 g of trioctylphosphine oxide (TOPO, purchased from Aldrich, purity of 90%) and 0.3 g of polyvinylpyrrolidone (PVP, purchased from Aldrich, molecular weight of 40000). Thereafter, the temperature was raised to 160 ° C and 0.3 mL of hydrazine monohydrate (N ₂ H ₄ .H ₂ O, purchased from Aldrich, purity: 64% to 65%) was added as a reducing agent, Wire.

The prepared tellurium nanowire was filtered, washed with ethanol and dried at a temperature of 70 ° C to 80 ° C to prepare a tellurium nanowire.

&Lt; Comparative Example 6 > Preparation of tellurium (Te) nanowire 4

A tellurium (Te) nanowire was prepared in the same manner as in Comparative Example 5, except that 5 g of sodium dodecylbenzenesulfonate was used in place of 5 g of trioctylphosphine oxide in Comparative Example 5.

&Lt; Comparative Example 7 > Preparation of tellurium (Te) nanowire 5

In Comparative Example 5, a tellurium (Te) nanowire was produced in the same manner as in Comparative Example 5, except that 5 g of polyoxyethylene lauryl ether was used instead of 5 g of trioctylphosphine oxide.

Types of capping agent to be mixed



Manufactured
Nano structure

Trioctylphosphine
Oxide
(g)

Polyvinyl
Pyrrolidone
(g)
Sodium dodecylbenzene
Sulfonate
(g)
Polyoxy
Ethylene
Lauryl Ether
(g)
Example 1

5
0.1
-
-
Bismuth telluride nanotubes
Example 2

5
0.2
-
-
Bismuth telluride nanotubes
Example 3

5
0.3
-
-

Bismuth telluride nanotubes
Comparative Example 1

5
-
-
-
Tellurium nanowire
Comparative Example 2

-
0.3
-
-
Tellurium nanowire
Comparative Example 3

5
-
-
-
Bismuth telluride nanotubes
Comparative Example 4

-
0.3
-
-
Bismuth telluride nanowire
Comparative Example 5
5

0.3
-
-
Tellurium nanowire
Comparative Example 6
5

-
0.3
-
Tellurium nanowire
Comparative Example 7
5

-
-
0.3
Tellurium nanowire

Experimental Example 1: Morphology and microstructure analysis of a tellurium (Te) nanotube and a bismuth telluride (Bi ₂ Te ₃ ) nanotube

The morphology and microstructure of the tellurium (Te) nanowires and bismuth telluride (Bi ₂ Te ₃ ) nanotubes and nanowires prepared in Examples 1 to 3 and Comparative Examples 5 to 7 were compared with those of the field emission scanning electron microscope (manufacturer: Philips, model name: XL-30S FEG) and high-resolution transmission electron microscope to (manufacturer:: FEI, Model Tecnai G ²⁾ to record 1, 2, 3, 4, 5 and 6, Respectively.

FIG. 1 is a photograph of a bismuth telluride (Bi ₂ Te ₃ ) nanotube prepared in Examples 1, 2 and 3 of the present invention by field emission scanning electron microscopy.

As shown in FIGS. 1 (a), 1 (b) and 1 (c), by using trioctylphosphine oxide and polyvinylpyrrolidone as a capping agent, a bismuth tellurite It was confirmed that the nanotubes were produced. As the amount of polyvinylpyrrolidone was increased, it was observed that the diameter of the bismuth telluride nanotubes produced decreased. When the amount of polyvinylpyrrolidone was more than 0.3 g, it was confirmed that it had a form similar to that of the bismuth telluride nanotube of Comparative Example 4 prepared by using 0.3 g of polyvinylpyrrolidone alone, When the amount of the lauridone was less than 0.1 g, it was confirmed that the bismuth telluride nanotube of Comparative Example 3 had a shape similar to that of the bismuth telluride nanotube prepared using only 5 g of trioctylphosphine oxide.

FIG. 2 is a photograph of a bismuth telluride (Bi ₂ Te ₃ ) nanotube prepared in Examples 1, 2 and 3 of the present invention by a high-resolution transmission electron microscope. The bismuth telluride The microstructure of the rid nanotubes was more accurately observed. More specifically, it can be confirmed that (c) prepared in Example 3 has a hollow space with a reduced diameter in comparison with (a) and (b) prepared in Examples 1 and 2.

The shape change of the nanostructure according to the capping agent can be confirmed also in the comparative example in which the nanotubes were separately prepared using the respective capping agents. FIG. 3 is a photograph of a tellurium nanotube prepared in Comparative Example 1 and Comparative Example 2 of the present invention by a field emission scanning electron microscope, FIG. 4 is a photograph of the bismuth tellurium prepared in Comparative Example 3 and Comparative Example 4 of the present invention This is a photomicrograph of a ridged nanotube by field emission scanning electron microscope. As shown in FIG. 3A and FIG. 4A, when the capping agent is trioctylphosphine oxide, the nanostructure has a diameter of 130 nm to 160 nm, and when the capping agent is polyvinylpyrrolidone, It was confirmed that the diameter of the structure was 25 nm to 40 nm as shown in FIGS. 3 (b) and 4 (b).

The difference in internal structure was also observed clearly by manufacturing the nanotubes separately using the respective capping agents. 5 (a) and 5 (b), when only trioctylphosphine oxide is added as a capping agent, a hollow nanostructure having a large diameter and a hollow interior is produced. When only polyvinylpyrrolidone is used, It was confirmed that a thin nano structure was produced.

1 to 5, the role of trioctylphosphine oxide and polyvinylpyrrolidone as a capping agent can be confirmed. By using a capping agent, it is possible to manufacture a nanotube having a small diameter and a hollow space .

The shape of the tellurium nanostructure used as a template of the bismuth telluride of the present invention has a considerable influence on the determination of the shape of the final produced bis-bistuluride. In addition to trioctylphosphinothiad in polyvinylpolybdon, Type capping agent were mixed at appropriate ratios to observe differences in shape depending on the type of the capping agent through the change in the shape of the tellurium nanowires prepared in Comparative Examples 5 to 7 of the present invention. As shown in FIG. 6 (a), when trioctylphosphine oxide was used together with polyvinylpolybdon, a 1-dimensional nanowire having a diameter of 50 nm or less and a very large aspect ratio And as shown in FIG. 6 (b), when sodium dodecylbenzenesulfonate was used together with polyvinylpolybdone, there was considerable agglomeration between nanowires produced, and the diameter of the nanowires was also about 200 nm This is big. Also, when sodium dodecylbenzenesulfonate was used together with polyvinylpolybdone as shown in FIG. 6 (c), it was observed that the nanobelts of three-dimensional structure were much larger than those of one-dimensional nanowires. Therefore, it is preferable to use polyvinylpolybdon and trioctylphosphine oxide as a tellurium template for manufacturing a bismuth telluride nanotube having a small diameter.

<Experimental Example 2> Crystal structure analysis of a tellurium (Te) nanotube and a bismuth telluride (Bi ₂ Te ₃ ) nanotube

(Te) nanotubes and bismuth telluride (Bi ₂ Te ₃ ) nanotubes prepared in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 The crystal structure was analyzed by X-ray diffraction using an X-ray automatic diffractometer (manufacturer: Rigaku, model name: D / max-2200V) using a Cu - Kα line as a light source and shown in FIGS. 7, 8 and 9 .

FIG. 7 is a graph of X-ray diffraction analysis of bismuth telluride nanotubes prepared in Examples 1, 2 and 3 of the present invention, and FIG. 8 is a graph showing X-ray diffraction patterns of the tellurium nano- FIG. 9 is an X-ray diffraction analysis graph of the bismuth telluride nanotubes and nanowires prepared in Comparative Example 3 and Comparative Example 4. FIG.

As can be seen from FIG. 7, it was confirmed that the X-ray diffraction intensity and the half-value width were different depending on the amount of trioctylphosphine oxide and polyvinylpyrrolidone as the capping agent, and the amount of polyvinylpyrrolidone The bismuth telluride nanotubes prepared according to the present invention have a tendency to increase the half-width due to the increase of the fine particle size. The crystal structure of the nanostructure according to the above-described capping agent can be confirmed also in the comparative example in which the nanotubes were produced separately using the respective capping agents. In particular, in the graph of FIG. 9, the nanotubes prepared in Comparative Example 3 exhibited a diffraction intensity of 4,878 and a half-width of 0.263 in the vicinity of 27 degrees, whereas the nanotubes prepared in Comparative Example 4 had a diffraction intensity of 1,800 and a half-width of 0.413 The diffraction intensity was decreased and the half-value width was increased. The reason was as described above because of the fine particle size of the produced nanotubes.

7, 8, and 9, it was confirmed that when polyvinylpyrrolidone was added as a capping agent, a nanotube having a fine crystal structure was produced.

Claims (10)

Trioctylphosphineoxide (TOPO), trisodium phosphate (Na ₃ PO ₄ 12H ₂ O), sodium dodecyl-benzene-sulfonate (SDBS) and cetyltrimethylammonium bromide ( 1 type selected from the group consisting of cetyl-trimethyl-ammonium-bromide and polyvinylpyrrolidone (PVP), polyvinylalcohol and ethylenediaminotetraacetic acid salt (sodium dodecyl-benzene-sulfonate) Preparing tellurium nanowires by dissolving tellurium oxide (TeO ₂ ) in a solvent including a capping agent selected from the group consisting of 1 and adding a reducing agent (step 1);
Mixing the bismuth precursor solution with the tellurium nanowire of step 1 and adding a reducing agent to prepare a mixed solution (step 2); And
Heat treating the mixed solution of step 2 to prepare a bismuth telluride (Bi ₂ Te ₃ ) nanotube (step 3);
Mixing the bismuth precursor solution with the tellurium nanowire of step 1 and adding a reducing agent to prepare a mixed solution (step 2); And
Heat treating the mixed solution of step 2 to prepare a bismuth telluride (Bi ₂ Te ₃ ) nanotube (step 3);
Bismuth telluride (Bi ₂ Te ₃ ) comprising a nanotube manufacturing method.
The method of claim 1, wherein tri-octylphosphineoxide (TOPO), trisodium phosphate (Na ₃ PO ₄ 12H ₂ O), sodium dodecyl-benzene- sulfonate (SDBS) and cetyltrimethylammonium bromide (cetyl-trimethyl-ammonium-bromide) selected from the group consisting of 1 polyvinylpyrrolidone (PVP), polyvinyl alcohol (polyvinylalcohol) and ethylenediaminotetraacetic acid Method for producing bismuth telluride (Bi ₂ Te ₃ ) nanotubes, characterized in that the mixture is selected from the group consisting of salt (sodium dodecyl-benzene-sulfonate) in a weight% ratio of 98: 2 ~ 94: 6 .
2. The method according to claim 1, wherein the one selected from the group consisting of polyvinylpyrrolidone (PVP), polyvinylalcohol and sodium dodecyl-benzene-sulfonate has a weight- (Bi ₂ Te ₃ ) nanotubes having a weight average molecular weight of 45,000.
2. The bismuth telluride (Bi ₂ Te ₃ ) film according to claim 1, wherein the tellurium oxide (TeO ₂ ) in the step 1 is contained in a range of 7 to 8 wt% based on the total weight of the solvent containing the capping agent. Method of manufacturing nanotubes.
2. The bismuth telluride (Bi ₂ Te ₃ ) according to claim 1, wherein the reducing agent in steps 1 and 2 is hydrazine monohydrate (N ₂ H ₄ .H ₂ O) or sodium borohydride (NaBH ₄ ) Method of manufacturing nanotubes.
The method according to claim 1, wherein the tellurium nanowire of step 1 is prepared by reacting at a temperature of 100 ° C. to 130 ° C. for 20 minutes to 30 minutes to prepare a bismuth telluride (Bi ₂ Te ₃ ) nanotube Way.
The method of claim 1, wherein the Bi precursor solution of step 2 is a process for producing a bismuth telluride, characterized in that for preparing the mixture to dissolve the bismuth precursor in the oleyl amine (Bi ₂ Te ₃₎ nanotubes.
The method of claim 1 wherein the production of the third step of the heat treatment is bismuth telluride, characterized in that is carried out at a temperature of 150 ℃ to 160 ℃ for 60 minutes to 90 minutes (Bi ₂ Te ₃₎ nanotubes.
Bismuth telluride (Bi ₂ Te ₃ ) nanotubes prepared according to claim 1.
A thermoelectric device comprising the bismuth telluride (Bi ₂ Te ₃ ) nanotube of claim 13.

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