KR101490776B1

KR101490776B1 - Manufacturing methods of carbon quantum dots using emulsion

Info

Publication number: KR101490776B1
Application number: KR20130068946A
Authority: KR
Inventors: 이시우; 권우성
Original assignee: 포항공과대학교 산학협력단
Priority date: 2013-06-17
Filing date: 2013-06-17
Publication date: 2015-02-06
Also published as: KR20140146695A

Abstract

The present invention relates to a method for mass-producing carbon quantum dots of uniform size using an emulsion, and an organic light emitting device, a solar cell, and a photocatalyst manufactured using the method.
The method for producing a carbon quantum dot according to the present invention is characterized in carbonizing the carbon source by dispersing a carbon source using a surfactant containing a functional group capable of bonding to a carbon quantum dots and heating the carbon source.
The carbon quantum dot manufacturing method according to the present invention can mass-produce and simplify the process using an emulsion, and exhibits excellent reaction yield. The carbon quantum dot manufacturing method according to the present invention can arbitrarily control the size of the carbon quantum dots. The carbon quantum dot manufacturing method according to the present invention can produce carbon quantum dots having a uniform size and a good quantum yield. The carbon quantum dot manufacturing method according to the present invention can produce carbon quantum dots suitable for organic light emitting devices, solar cells, and photocatalytic applications.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for producing carbon quantum dots using an emulsion,

The present invention relates to a method for mass-producing carbon quantum dots of uniform size using an emulsion, and an organic light emitting device, a solar cell, and a photocatalyst manufactured using the method.

Since 1993, Bawendi and colleagues at MIT have synthesized cadmium (Cd) -based semiconductor nanoparticles, research has been conducted on the properties and applications of various types of semiconductor nanoparticles.

In 1996, Professor Alivisatos of UC Berkeley identified the fact that the bandgap can be controlled by controlling the size of semiconductor nanoparticles. Particles with such characteristics are called quantum dots.

In 2005, the first quantum dot solar cell was announced using two kinds of quantum dots having different band intervals. Since then, it has been applied to various solar cell fields such as organic solar cell and dye sensitized solar cell in addition to pure quantum dot solar cell.

In general, quantum dots exhibit excellent optical, electrical properties and durability, but they are disadvantageous in that they require toxic and costly heavy metal raw materials and high temperature synthesis processes. Therefore, studies are being conducted to synthesize existing quantum dots in a safe and cheap material. Recently, carbon dots (carbon dots) synthesized by various methods have been attracting much attention.

The carbon quantum dots were discovered by Professor Scrivens' team at the University of South Carolina in 2004 when they synthesized carbon nanotubes. Currently, electrophoresis, laser ablation, thermal oxidation, electrooxidation, and pyrolysis are widely used . Carbon QDs have recently become widely used in life sciences because they can be easily synthesized at low temperatures based on cheap and nontoxic organic matter.

However, it is difficult to control the band gap, the quantum yield is low, and the internal chemical structure and optical characteristic development process are unclear.

As a method for solving such a problem, Korean Patent Application No. 2012- 0062170 discloses a method of manufacturing carbon quantum dots by heating a dispersed droplet containing a carbon source, but a problem that the manufacturing method is relatively complicated and the efficiency is low .

Accordingly, there is a continuing need for a new method for easily forming a droplet containing a carbon source and maintaining droplet stability during carbonization of the carbon source.

A problem to be solved by the present invention is to provide a new method for manufacturing carbon quantum dots in large quantities through a simple manufacturing process.

Another object of the present invention is to provide a method for producing carbon quantum dots having a high reaction yield by preventing aggregation of carbon quantum dots during the manufacturing process.

A further object of the present invention is to provide a method for producing carbon quantum dots of uniform size by arbitrarily controlling the size of the carbon quantum dots.

Another object of the present invention is to provide a method for producing carbon quantum dots having a high quantum yield.

Another object of the present invention is to provide a method of using a carbon quantum dot for an organic light emitting device, a solar cell, and a photocatalyst.

In order to solve the above problems, a method for producing carbon quantum dots by heating an emulsion containing a carbon source to carbonize the carbon source, characterized in that the emulsion is dispersed with a surfactant comprising a functional group capable of bonding to a carbon quantum dots .

In the present invention, the 'carbon quantum dot' means a quantum dot having carbon as a main component. Here, the 'main component' means that the weight or number of carbon atoms is the maximum in the constituent components of the quantum dots. More precisely, it means that the carbon content in the carbon quantum dots is at least 50 wt%, more precisely at least 55 wt%, most precisely at least 60 wt%.

In one embodiment of the present invention, the carbon quantum dots may be particles having a nanometer-sized carbon core and an amide group, a carbonyl group or the like formed on the surface of the carbon core, and the carbon core may include SP2 and SP3 bonds Carbon core.

In the present invention, the 'carbon source' means a compound that is carbonized by heating. In one embodiment of the present invention, the carbon source may be composed of a compound such as a monosaccharide, a polysaccharide, an organic acid, a carboxylic acid, a glycolic acid, or a water-soluble polymer, and is preferably citric acid. In the practice of the present invention, the citric acid is carbonized by intermolecular condensation through heating to form carbon quantum dots.

In the present invention, an emulsion containing a carbon source means a droplet containing a carbon source or a carbon source dispersed in a liquid dispersion medium by a surfactant. The emulsion may be an emulsion of a polar solvent such as water surrounded by a surface stabilizer molecule in a non-polar solvent such as a hydrocarbon. Since the size of the emulsion can be determined by the ratio of the volume of water and the surface stabilizer, the volume of droplets can be controlled by changing the volume ratio of water and surfactant. In a preferred embodiment of the invention, the size of the emulsion may be a microemulsion in micrometers in diameter, preferably in the range of 10 nm to 1,000 microns.

In the present invention, the nonpolar solvent may include hydrocarbons having 1 to 25 carbon atoms, for example, octadecene. The polar solvent may be water, acetone, methanol or the like, Can be used.

In the practice of the present invention, the emulsion containing the carbon source may be a state in which the droplet in which the carbon source is dissolved is dispersed by the surfactant, and preferably a micrometer-sized droplet in which the water- Dispersed in a nonpolar dispersion medium.

Although the surfactant according to the present invention is not limited in theory, it is stabilized with a droplet containing a carbon source to form an emulsion, and a functional group capable of binding to the carbon quantum dots is bonded to the carbon quantum dots formed by the heating of the carbon source to stabilize the carbon quantum dots do.

In the present invention, the surfactant comprising a functional group capable of binding to the quantum dots is a surfactant containing a functional group capable of binding to the carbon quantum dots, for example, an amine group, a carboxyl group, a thiol group, , More preferably 16 to 20, and has a primary amine group at the terminal. In a preferred embodiment of the present invention, the surfactant may be oleylamine, oleic acid, decanol or the like.

In the present invention, the heating is for heating the carbon source by carbonizing it, preferably by heating at a temperature higher than the boiling point of the droplet containing the carbon source to evaporate the droplet. In the practice of the present invention, when water is used as the polar solvent, the heating is preferably performed at a temperature of 100 ° C or higher, preferably 100 to 300 ° C.

In the practice of the present invention, the concentration range of the surfactant may range from 0.1 vol% to 99 vol%, and the heating time for carbonization may range from 30 minutes to 6 hours.

In one aspect, the present invention provides a method of forming an emulsion containing a carbon source stabilized with a surfactant comprising a functional group capable of bonding to a carbon QD point, and heating the carbon nanotube to carbonize the carbon source.

In one embodiment of the present invention, the carbon quantum dots may be carbon quantum dots including a nitrogen component so as to improve the characteristics of white light in an organic light emitting device, particularly an LED, and may include a surfactant containing an amine group Nitrogen-containing surfactants. The carbon quantum dots can be applied to organic light emitting devices by mixing with polymers such as acrylate, ester, carbonate, styrene and the like which are excellent in transparency and thermal stability. Examples of the carbon quantum dots include poly (methyl methacrylate) (PMMA) Can be mixed and used.

In another embodiment of the present invention, the carbon quantum dots may be mixed with a semiconductive polymer to form a thin film for use in a solar cell. The polymer may be a thiophene polymer having excellent charge mobility. For example, poly (3-hexylthiophene) may be used.

In another embodiment of the present invention, the carbon quantum dots are mixed with a metal oxide nanostructure for use in a photocatalyst to form a core-shell structure. The metal oxide nanostructure has a size of 2 to 200 nm and a band gap of 3.0 to 6.0 eV. For example, zinc oxide or titanium oxide nanoparticles can be used.

The carbon quantum dot manufacturing method according to the present invention can mass-produce and simplify the process using an emulsion, and exhibits excellent reaction yield. The carbon quantum dot manufacturing method according to the present invention can arbitrarily control the size of the carbon quantum dots. The carbon quantum dot manufacturing method according to the present invention can produce carbon quantum dots having a uniform size and a good quantum yield. The carbon quantum dot manufacturing method according to the present invention can produce carbon quantum dots suitable for organic light emitting devices, solar cells, and photocatalytic applications.

1 is a schematic view showing a reaction apparatus according to the present invention.
Fig. 2 is a schematic view showing the synthesis of carbon quantum dots in an emulsion, wherein (a) emulsion formation, (b) condensation polymerization, (c) carbonization and surface stabilization by oleylamine.
Fig. 3 is a TEM photograph (a, b) and a distribution histogram (c) of two types of carbon quantum dots of different sizes. (d, e, f, g) high-resolution TEM images with a scale bar of 5 nm.
Fig. 4 shows the absorption and emission spectra of two kinds of carbon quantum dots having different sizes.
5 is an FT-IR graph of (a) the reactant (citric acid), (b) the intermediate formulation, and (c) the carbon quantum dots.
6 (a) is a conceptual view and (b) is an actual driving state of an organic light emitting device using carbon quantum dots.
7 is a conceptual diagram of a solar cell using carbon quantum dots.
8 (a) is a conceptual view and (b) is an actual view of a photocatalyst using carbon quantum dots.

The present invention will be described in detail with reference to the following examples. The following examples are described in detail in order to illustrate the invention and should not be construed as limiting the scope of the invention.

Example

Carbon quantum dot synthesis

Example 1. Carbon quantum dot production using oleylamine and citric acid

As shown in FIG. 1, 3 mL of oleylamine and 7 mL of octadecane were added to a 100 mL round flask and stirred for 5 minutes to prepare a colorless transparent surfactant solution. Separately, 1 g of citric acid was added to 1 ml of water in a separate flask and stirred for about 10 minutes to prepare a colorless transparent reactant solution, which was added to the surfactant solution and stirred to form an emulsion.

When the emulsion was formed by stirring for 30 minutes, a gas pipe (gas inlet and gas outlet) was installed, and the solution was heated using a heating plate while flowing argon through a gas pipe. And heated at 250 ° C for 2 hours to form dark brown carbon quantum dots. Several drops of methanol were added to the synthesized carbon quantum dot solution, and the carbon quantum dots in the solution were precipitated by centrifugation. The precipitated carbon quantum dots were dissolved in octane and centrifuged again for 3 times to remove other reactants except the carbon quantum dots. The prepared carbon quantum dots were precipitated, washed and separated, and TEM photographs were taken to measure the diameter of the carbon quantum dots. The carbon quantum dots of 1.2 nm diameter were identified and the yield was 30%.

Example 2. Control of Carbon Quantum Dot Size by Change in Oleylamine Content

1 mL of oleylamine and 9 mL of octadecane were added to a 100 mL round flask and stirred for about 5 minutes to prepare a colorless transparent surfactant solution. Separately, 1 g of citric acid was added to 1 ml of water in a separate flask and stirred for about 10 minutes to prepare a colorless transparent reactant solution, which was added to the surfactant solution and stirred to form an emulsion.

When the emulsion was formed by stirring for 30 minutes, a gas pipe (gas inlet and gas outlet) was installed, and the solution was heated using a heating plate while flowing argon through a gas pipe. And heated at 250 ° C for 2 hours to form dark brown carbon quantum dots. Several drops of methanol were added to the synthesized carbon quantum dot solution, and the carbon quantum dots in the solution were precipitated by centrifugation. The precipitated carbon quantum dots were dissolved in octane and centrifuged again for 3 times to remove other reactants except the carbon quantum dots. The prepared carbon quantum dots were precipitated, washed and separated, and TEM photographs were taken to measure the diameter of the carbon quantum dots. 2.5 nm diameter carbon quantum dots were identified and the yield was 30%.

Carbon Quantum Point Analysis

A. Transmission Electron Microscopy (TEM) analysis

A small amount of a solution of the purified carbon nanotubes in toluene (5 mg mL ^-1 ) was coated on a TEM grid, and the internal structure of the carbon quantum dots was analyzed using a TEM apparatus. As a result, the lattice structure of the carbon was partially confirmed, and the change of the size of the carbon quantum dots according to the size of the micelle changed by the volume of the added surface stabilizer was confirmed (FIG. 3).

N. UV-Vis absorbance and luminescence analysis

The UV-Vis absorbance and the luminescence of the purified carbon nanotubes were dissolved in toluene (5 mg mL ^-1 ) in a transparent cuvette. The absorbance peaks and excitation wavelengths near 300 nm The wavelength dependence of the emission peak was observed. The change in absorbance and luminescence according to the size was also confirmed (Fig. 4).

Production of devices

A. Organic Light Emitting Device Fabrication

A solution (50 wt%) of poly (methyl methacrylate) dissolved in anisole was added to a solution (5 mg / mL) of the purified carbon nanotubes in Example 1 in toluene and stirred for 10 minutes to obtain a carbon quantum dot / Polymer complex solution was prepared. The carbon quantum dot / polymer complex solution was dropped on a flat glass plate and dried at room temperature for about 24 hours to prepare a carbon quantum dot polymer membrane. The carbon quantum dot polymer film was assembled with a light emitting device emitting light with a wavelength of 400 nm to generate white light (FIG. 6).

N. Production of solar cell (carbon quantum dot electron receiver)

A poly (3-hexylthiophene) was added to a solution (5 mg / mL) of purified carbon nanotubes in chloroform in Example 1 and stirred for about 10 minutes to prepare a carbon quantum dot / polymer composite solution. Several tens to several hundreds of microliters of the carbon quantum dot / polymer complex solution were dropped on the transparent electrode and dried at 50 to 100 ° C to form a bulk heterojunction. A bulk heterojunction solar cell was fabricated by depositing a metal electrode on the bulk heterojunction (Figure 7).

C. Production of solar cell (carbon quantum dot electron donor)

A certain amount of aminobenzoic acid was added to a solution (5 mg / mL) of purified carbon nanotubes in isopropyl alcohol in Example 1 and stirred for about 10 minutes to introduce carboxylic acid onto the surface of the carbon quantum dots. The metal oxide electrode was immersed in the solution for 24 hours to form a chemical bond between the carbon quantum dot and the metal oxide electrode. The electrolyte and the counter electrode were assembled to the metal oxide electrode to produce a solar cell. (Fig. 7)

D. Photocatalyst production

A predetermined amount of zinc oxide nanoparticles was added to a solution (1 mg / mL) of purified carbon nanotubes in isopropyl alcohol in Example 1, and the mixture was stirred at 50 to 100 ° C for about 24 hours to form a carbon quantum dot / Solution. The carbon quantum dot / metal oxide complex solution is centrifuged to precipitate the carbon quantum dot / metal oxide complex in the solution. The carbon quantum dot / metal oxide composite was dried at room temperature for about 24 hours to prepare a photocatalyst. (Fig. 8)

Claims

A method for producing carbon quantum dots by forming an emulsion in which a carbon source is dispersed by using a surfactant containing a functional group capable of binding to a carbon quantum dots and heating the carbon source to be carbonized.

The method of claim 1, wherein the surfactant comprises at least one functional group selected from the group consisting of an amine group, a carboxyl group, an alcohol group, and a thiol group.

The carbon quantum dot manufacturing method according to claim 1 or 2, wherein the functional group is a primary amine.

The method of claim 1 or 2, wherein the surfactant is at least one selected from the group consisting of oleylamine and primary amines having 6 to 20 carbon atoms.

The method of claim 1 or 2, wherein the emulsion is a dispersion of a droplet containing a carbon source in a dispersion medium.

6. The method of claim 5, wherein the emulsion is dispersed in a dispersion medium of an oil phase, wherein water containing a hydrophilic carbon source is dispersed.

The carbon quantum dot manufacturing method according to claim 1, wherein the carbon source is a monosaccharide, a polysaccharide, an organic acid, a carboxylic acid, a glycolic acid, or a water-soluble polymer.

8. The method of claim 7, wherein the carbon source is polymerized and carbonized.

The method of claim 1, wherein the emulsion is a microemulsion.

The method of claim 1, wherein the heating is performed in an inert gas atmosphere.

The carbon quantum dot manufacturing method according to claim 1, wherein the heating is performed at a temperature in the range of 100 to 300 占 폚.

The method of claim 1, further comprising precipitating and separating the carbon quantum dots.

A method for producing a carbon quantum dots by forming an emulsion in which a droplet containing a carbon source is dispersed by using a surfactant containing a functional group capable of binding to a carbon quantum dots, heating the carbon source to be carbonized, and separating the emulsion.

14. An organic light emitting device comprising a transparent polymer comprising a carbon quantum dot according to claim 13.

A solar cell comprising a semiconductive polymer comprising a carbon quantum dot according to claim 13.

13. A solar cell using the carbon quantum dot / metal oxide composite, wherein the carbon quantum dot according to claim 13 is bonded to a metal oxide.

A photocatalyst characterized in that the carbon quantum dots according to claim 13 are combined with a metal oxide complex.